A binder composition used for making an electrode for a lithium-ion secondary battery, which comprises polymer particles dispersed in an organic medium having a boiling point of 80-350xc2x0 C. at normal pressure. The polymer (1) comprises structural units derived from a monoethylenically unsaturated carboxylic acid ester monomer, and at least one kind of structural units selected from (b) structural units derived from a monoethylenically unsaturated carboxylic acid monomer and (c) structural units derived from a conjugated diene monomer; (2) has a ratio of (a)/[(b)+(c)] of 99/1xe2x88x9260/40 by weight; (3) has a total content of (a), (b) plus (c) of at least 80 wt. % based on the total structural units; and (4) is substantially free from structural units of a monoethylenically aromatic hydrocarbon monomer. A lithium-ion secondary battery having an electrode made with the binder exhibits a large service capacity and enhanced charge-discharge characteristics at a high temperature.

This invention relates to a binder composition for an electrode of a lithium ion secondary battery, and utilization of the binder.
In recent years, portable electronic appliances such as a notebook-sized personal computer, a portable telephone and a personal digital assistant have spread wide. Among secondary batteries used as a power source of the portable electronic appliances, lithium ion secondary batteries are widely used.
Requirements for rendering portable electronic appliances small in size, thin in thickness, light in weight and high in performance are becoming severe. Thus the same requirements are also becoming severe for lithium ion secondary batteries (hereinafter abbreviated to xe2x80x9cbatteriesxe2x80x9d when appropriate). In addition, requirement for cost reduction is eagerly desired.
As a binder for an electrode of a lithium ion secondary battery, polyvinylidene fluoride (hereinafter abbreviated to xe2x80x9cPVDFxe2x80x9d) is widely used. However, secondary batteries having desired performances are difficult to fabricate with PVDF, because it is presumed that PVDF has a poor binding power.
Now various binders are being suited for providing secondary batteries having high performances. Polymers having structural units derived from a polar group-having monomer such as an ethylenically unsaturated carboxylic acid ester monomer attract widespread attention because these polymers give high adhesion between an active material and a collector. For example, polymer binders having structural units derived from an ethylenic hydrocarbon monomer was proposed, which include a copolymer of an ethylenically unsaturated carboxylic acid ester monomer, an ethylenic hydrocarbon monomer and an ethylenically unsaturated dicarboxylic acid anhydride monomer, which copolymer contains at least 40% by weight of structural units derived from the ethylenic hydrocarbon monomer (Japanese Unexamined Patent Publication [hereinafter abbreviated to xe2x80x9cJP-Axe2x80x9d] No. H6-223833), and a copolymer of an ethylenically unsaturated carboxylic acid ester monomer, an ethylenic hydrocarbon monomer and an ethylenically unsaturated dicarboxylic acid (or ester) monomer, which copolymer contains at least 40% by weight of structural units derived from the ethylenic hydrocarbon monomer (JP-A H6-325766). Further, a copolymer of at least one acrylic acid ester or methacrylic acid ester monomer, an acrylonitrile monomer and a vinyl monomer having an acid ingredient (JP-A H8-287915) and a methyl methacrylate-butadiene copolymer rubber (JP-A H4-255670) were proposed. A secondary battery having a positive electrode or negative electrode made by using these copolymer binders, exhibits good battery performances, especially good characteristics at repetition of charge-discharge cycles and a larger capacity. This is because these copolymer binders exhibits stronger force for binding an active material to each other and to a collector, than that obtained with PVDF binder. The amount of the binders can be reduced and thus the weight of a secondary battery can be reduced, as compared with the case where PVDF binder is used. Further, these copolymer binders are relatively inexpensive and thus the fabrication cost of a battery can be reduced. Thus, these copolymers are expected to be good binders.
With spread and development of portable electronic appliances, they are occasionally used and stored under various conditions, especially at a high temperature of 50xc2x0 C. or higher. A lithium ion secondary battery with an electrode made using the conventional PVDF binder exhibits good characteristics at repetition of charge-discharge cycles at room temperature of 20 to 25xc2x0 C., but poor characteristics at repetition of charge-discharge cycles at a high temperature of 50xc2x0 C. or higher. Thus, researches are being made for improving materials used for a battery, a method for fabricating a battery and structure of a battery to obtaining good characteristics of a battery at a high temperature, but satisfactory results have not been obtained. There is still an increasing need for improvement of a binder used for an electrode.
The present inventors found that a secondary battery having an electrode made by using the above-specified copolymer binders instead of the PVDF binder exhibits good characteristics at repetition of charge-discharge cycles at room temperature, but the characteristics at repetition of charge-discharge cycles are still reduced at a high temperature of 50xc2x0 C. or higher, which is prominent with copolymer binders containing structural units derived from an ethylenic hydrocarbon monomer or having a salient amount of a nitrile group.
A binder composition in the form of a polymer dispersion which comprises a polymer having a gel content of at least 50% as calculated as a toluene insoluble matter, and an organic dispersion medium having a boiling point of at least 80xc2x0 C. at normal pressure, has been proposed in WO 98/14519. This binder composition in a polymer dispersion form exhibits an enhanced strong force for binding an active material to each other and to a collector, and a battery with an electrode made by using the binder composition exhibits good characteristic at repetition of charge-discharge cycles, as compared with a binder composition in the form of a polymer solution in an organic solvent.
Further researches of the present inventors have revealed that a secondary battery having an electrode made by using a binder composition, specifically described in WO 98/14519, exhibits good characteristics at repetition of charge-discharge cycles at room temperature, but the characteristics at repetition of charge-discharge cycles are reduced at a high temperature of 50xc2x0 C. or higher. It is presumed that the reduction of the characteristics at repetition of charge-discharge cycles at a high temperature is due to the fact that the specific binder composition contains structural units derived from an aromatic hydrocarbon monomer.
As extensive researches of a lithium ion secondary battery exhibiting good characteristics at repetition of charge-discharge cycles at a high temperature, the present inventors have found that, when a polymer binder comprising a dispersion of a specific polymer dispersed in a specific organic liquid dispersion is used for the preparation of an electrode, a secondary battery with the electrode exhibits enhanced characteristics at repetition of charge-discharge cycles at a high temperature. The present invention has been completed on the basis of this finding.
Thus, in a first aspect of the present invention, there is provided a binder composition for an electrode of a lithium ion secondary battery, which comprises particles of a polymer and an organic liquid dispersion medium having a boiling point in the range of 80xc2x0 C. to 350xc2x0 C. at normal pressure; the polymer particles being dispersed in the organic liquid dispersion medium, and said polymer comprising:
(a) structural units derived from a monoethylenically unsaturated carboxylic acid ester monomer, and
at least one kind of structural units selected from (b) structural units derived from a monoethylenically unsaturated carboxylic acid monomer, and (c) structural units derived from a conjugated diene monomer;
the ratio of structural units (a)/[structural units (b) plus structural units (c)] being in the range of 99/1 to 60/40 by weight, provided that the sum of structural units (a), structural units (b) and structural units (c) is 100;
the sum of structural units (a), structural units (b) and structural units (c) being at least 80% by weight based on the weight of the total structural units of the polymer; and
said polymer being substantially free from structural units derived from a monoethylenically aromatic hydrocarbon monomer.
In a second aspect of the present invention there is provided a slurry for an electrode of a lithium ion secondary battery (which slurry is hereinafter referred to as xe2x80x9cslurryxe2x80x9d when appropriate), which comprises the above-mentioned binder composition and an active material.
In a third aspect of the present invention there is provided an electrode of a lithium ion secondary battery, which is made by using the above-mentioned slurry.
In a fourth aspect of the present invention there is provided a lithium ion secondary battery, which is fabricated by using the above-mentioned electrode.
The invention will be described in detail.
1. Binder Composition
The binder composition of the present invention is a dispersion of particles of a specific polymer in an organic liquid dispersion medium having a boiling point in the range of 80xc2x0 C. to 350xc2x0 C. at normal pressure. The amount of the polymer particles in the binder composition is usually in the range of 0.2 to 80% by weight, preferably 0.5 to 70% by weight, and more preferably 0.5 to 60% by weight, based on the weight of the binder composition.
Polymer Particles
The polymer particles used in the present invention comprise (a) structural units derived from a monoethylenically unsaturated carboxylic acid ester monomer (hereinafter abbreviated to as xe2x80x9cstructural units (a)xe2x80x9d when appropriate), and (b) structural units derived from a monoethylenically unsaturated carboxylic acid monomer (hereinafter abbreviated to as xe2x80x9cstructural units (b)xe2x80x9d when appropriate) and/or (c) structural units derived from a conjugated diene monomer (hereinafter abbreviated to as xe2x80x9cstructural units (c)xe2x80x9d when appropriate), and is substantially free from structural units derived from a monoethylenically aromatic hydrocarbon monomer, the sum of structural units (a), structural units (b) and structural units (c) being at least 80% by weight based on the weight of the total structural units of the polymer.
By the term xe2x80x9cmonoethylenically aromatic hydrocarbon monomerxe2x80x9d used herein, we mean a monoethylenically unsaturated hydrocarbon monomer having an aromatic ring. As specific examples of the monoethylenically aromatic hydrocarbon monomer, there can be mentioned styrene, o-, m- and p-methylstyrene, 2,4-dimethylstyrene, o-, m- and p-ethylstyrene, and vinyl naphthalene. By the phrase xe2x80x9csubstantially free from structural units derived from a monoethylenically aromatic hydrocarbon monomerxe2x80x9d used herein, we mean that the amount of structural units derived from a monoethylenically aromatic hydrocarbon monomer is not larger than 5% by weight, preferably not larger than 2% by weight, and most preferably not larger than 1% by weight, based on the weight of the total structural units of polymer.
The ratio of structural units (a)/[structural units (b) plus structural units (c)] in the polymer particles used in the present invention is in the range of 99/1 to 60/40 by weight, preferably 99/1 to 65/35 by weight, and more preferably 98/2 to 70/30 by weight, provided that the sum of structural units (a), structural units (b) and structural units (c) is 100. The sum of structural units (a), structural units (b) and structural units (c) is at least 80% by weight, preferably at least 90% by weight based on the weight of the total structural units of polymer. When the structural units of the polymer satisfy the above-mentioned requirements, good battery performance is manifested even at a high temperature.
Further, the polymer is preferably substantially free from structural units derived from a nitrile group-containing monomer in view of stabilized characteristics at repetition of charge-discharge cycles at a high temperature. By the phrase xe2x80x9csubstantially free from structural units derived from a nitrile group-containing monomerxe2x80x9d used herein we mean that the amount of the structural units is similar to the above-described amount of a monoethylenically aromatic hydrocarbon monomer. The nitrile group-containing monomer includes, for example, nitrile group-containing monoethylenically unsaturated monomers such as acrylonitrile and methacrylonitrile.
The monoethylenically unsaturated carboxylic acid ester monomer giving structural units (a) includes, for example, monoethylenically unsaturated monocarboxylic acid ester monomers having an alkyl group or a substituted alkyl group in the alcohol residue, such as an acrylic acid ester, a methacrylic acid ester and a crotonic acid ester. As specific examples of the monoethylenically unsaturated monocarboxylic acid alkyl or substituted alkyl ester monomers, there can be mentioned acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydrocypropyl acrylate and lauryl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxypropyl methacrylate and lauryl methacrylate; crotonic acid esters such as methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexyl crotonate, 2-ethylhexyl crotonate and hydroxypropyl crotonate; amino group-containing methacrylic acid esters such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate. Acrylic acid esters and methacrylic acid esters, which have a substituted alkyl group with a substituent such as a phosphoric acid residue, a sulfonic acid residue or a boric acid residue, in the alcohol residue can also be mentioned. Of these monoethylenically unsaturated monocarboxylic acid ester monomers, acrylic acid esters and methacrylic acid esters, which have an alkyl group with 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms can be mentioned as especially preferable examples.
The monoethylenically unsaturated carboxylic acid monomer giving structural units (b) includes, for example, unsaturated monocarboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid and isocrotonic acid; and unsaturated dicarboxylic acid monomers such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid and itaconic acid, and their acid anhydrides. Of these, monoethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable.
The conjugated diene monomer giving structural units (c) includes, for example, 1,3-butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene and 1,3-heptadiene.
The above-mentioned monoethylenically unsaturated carboxylic acid ester monomers, monoethylenically unsaturated carboxylic acid monomers and conjugated diene monomers may be used either alone or as a combination of at least two thereof.
The polymer particles used in the present invention may comprise either structural units (b) or structural units (c), or both of structural units (b) and structural units (c). Preferably the polymers particles comprises both of structural units (b) and structural units (c) in a proportion of 1/99 to 99/1 by weight, more preferably 10/90 to 90/10 by weight and especially preferably 30/70 to 80/20 by weight, because of enhanced bonding properties.
Of the above-mentioned polymer particles, especially preferable are polymer particles comprising (d) structural units derived from a polyfunctional ethylenically unsaturated monomer [which structural units are hereinafter abbreviated to xe2x80x9cstructural units (d)xe2x80x9d], in addition to structural units (a), structural units (b) and structural units (c). The polyfunctional ethylenically unsaturated monomer giving structural units (d) includes crosslinking monomers, for example, divinyl compounds such as divinylbenzene; dimethacrylic acid esters such as diethylene glycol dimethacrylate and ethylene glycol dimethacrylate; trimethacrylic acid esters such as trimethylolpropane trimethacrylate; diacrylic acid esters such as polyethylene glycol diacrylate and 1,3-butylene glycol diacrylate; triacrylic acid esters such as trimethylolpropane triacrylate. The amount of structural units (d) in the polymer particles is not larger than 20% by weight, preferably not larger than 15% by weight and more preferably not larger than 10% by weight, based on the weight of the total structural units. Especially when structural units (d) are contained in this amount and of at least 0.1% by weight, preferably at least 0.5% by weight and more preferably at least 1% by weight, stabilized characteristics at repetition of charge-discharge cycles at a high temperature can be obtained.
The polymer particles may further comprise structural units derived from other monoethylenically unsaturated compound, in addition to the above-mentioned structural units. The amount of such structural units is not larger than 15% by weight, preferably not larger than 10% by weight and more preferably not larger than 5% by weight, based on the weight of the total structural units.
Specific examples of the copolymers constituting the polymer particles used in the present invention will be recited below. These copolymers may be either uncrosslinked or crosslinked. However, the copolymers are preferably crosslinked polymers in view of good resistance to an electrolyte solution.
a 2-ethylhexyl acrylate/acrylic acid copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid copolymer, a butyl acrylate/acrylic acid copolymer, a 2-ethylhexyl methacrylate/acrylic acid copolymer, a 2-ethylhexyl acrylate/acrylic acid/ethylene glycol dimethacrylate copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/acrylic acid copolymer, a diethylaminoethyl acrylate/acrylic acid copolymer, a methoxypolyethylene glycol monomethacrylate/acrylic acid copolymer, a 2-ethylhexyl crotonate/acrylic acid copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/acrylic acid copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid/polyethylene glycol diacrylate copolymer, a butyl acrylate/acrylic acid/divinylbenzene copolymer, a 2-ethylhexyl acrylate/acrylic acid/methacrylic acid copolymer, a 2-ethylhexyl acrylate/acrylic acid/maleic acid copolymer, a 2-ethylhexyl acrylate/itaconic acid copolymer, a 2-ethylhexyl methacrylate/acrylic acid/methacylic acid copolymer, a 2-ethylhexyl methacylate/acrylic acid/maleic acid copolymer, a 2-ethylhexyl methacrylate/itaconic acid copolymer, a 2-ethylhexyl acrylate/methacrylic acid copolymer, a 2-ethylhexyl acrylate/hexyl methacrylate/methacrylic acid copolymer, a butyl acrylate/methacrylic acid copolymer, a 2-ethylhexyl acrylate/methacrylic acid/ethylene glycol dimethacrylate copolymer, a 2-ethylhexyl methacrylate/hydroxypropyl acrylate/acrylic acid copolymer, a diethylaminoethyl acrylate/methacrylic acid copolymer, a methoxypolyethylene glycol monomethacrylate/methacrylic acid copolymer, a 2-ethylhexyl crotonate/methacrylic acid copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/methacrylic acid copolymer, a 2-ethylhexyl methacrylate/ethyl acrylate/methacrylic acid/polyethylene glycol diacrylate copolymer, a butyl acrylate/methacrylic acid/divinylbenzene copolymer, a 2-ethylhexyl acrylate/crotonic acid copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/crotonic acid copolymer, a butyl acrylate/crotonic acid copolymer, a 2-ethylhexyl methacrylate/crotonic acid copolymer, a 2-ethylhexyl acrylate/crotonic acid/ethylene glycol dimethacrylate copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/crotonic acid copolymer, a diethylaminoethyl acrylate/crotonic acid copolymer, a methoxypolyethylene glycol monomethacrylate/crotonic acid copolymer, a 2-ethylhexyl crotonate/crotonic acid copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/crotonic acid copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/crotonic acid/polyethylene glycol diacrylate copolymer, a butyl acrylate/crotonic acid/trimethylolpropane triacrylate copolymer, a 2-ethylhexyl acrylate/ maleic acid copolymer, a 2-ethylhexyl acrylate/ethyl methacrylate/maleic acid copolymer, a butyl acrylate/maleic acid copolymer, a 2-ethylhexyl acrylate/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/1,3-butadiene copolymer, a butyl acrylate/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/1,3-butadiene/ethylene glycol dimethacrylate copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/1,3-butadiene copolymer, a diethylaminoethyl acrylate/1,3-butadiene copolymer, a methoxypropylethylene glycol monomethacrylate/1,3-butadiene copolymer, a 2-ethylhexyl crotonate/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/1,3-butadiene/polyethylene glycol diacrylate copolymer, a butyl acrylate/1,3-butadiene/divinylbenzene copolymer, a 2-ethylhexyl acrylate/1,3-butadiene/methacrylic acid copolymer, a 2-ethylhexyl acrylate/1,3-butadiene/maleic acid copolymer, a 2-ethylhexyl methacrylate/acrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/1,3-butadiene/maleic acid copolymer, a 2-ethylhexyl acrylate/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl methacrylate/isoprene copolymer, a butyl acrylate/isoprene copolymer, a 2-ethylhexyl acrylate/isoprene/ethylene glycol dimethacrylate copolymer, a 2-ethylhexyl, methacrylate/hydroxypropyl acrylate/isoprene copolymer, a diethylaminoethyl acrylate/isoprene copolymer, a methoxypolyethylene glycol monomethacrylate/isoprene copolymer, a 2-ethylhexyl crotonate/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/isoprene copolymer, a 2-ethylhexyl methacrylate/ethyl acrylate/isoprene/polyethylene glycol diacrylate copolymer, a butyl acrylate/isoprene/divinylbenzene copolymer, a 2-ethylhexyl acrylate/acrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid/1,3-butadiene copolymer, a butyl acrylate/acrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/isoprene copolymer, a 2-ethylhexyl acrylate/acrylic acid/ethylene glycol methacrylate/isoprene copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/acrylic acid/1,3-butadiene copolymer, a diethylaminoethyl acrylate/acrylic acid/1,3-butadiene copolymer, a methoxypolyethylene glycol monomethacrylate/acrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl crotonate/acrylic acid/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/acrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid/polyethylene glycol diacrylate/1,3-butadiene copolymer, a butyl acrylate/acrylic acid/divinylbenzene/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/acrylic acid/methacrylic acid/isoprene copolymer, a 2-ethylhexyl acrylate/acrylic acid/maleic acid/isoprene copolymer, a 2-ethylhexyl acrylate/itaconic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/methacrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/maleic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/itaconic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl methacrylate/methacrylic acid/isoprene copolymer, a butyl acrylate/methacrylic acid/isoprene copolymer, a 2-ethylhexyl acrylate/methacrylic acid/ethylene glycol dimethacrylate/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/hydroxypropyl acrylate/acrylic acid/1,3-butadiene copolymer, a diethylaminoethyl acrylate/methacrylic acid/isoprene copolymer, a methoxypolyethylene glycol monomethacrylate/methacrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl crotonate/methacrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/methacrylic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/ethyl acrylate/methacrylic acid/polyethylene glycol diacrylate/1,3-butadiene copolymer, a butyl acrylate/methacrylic acid/divinylbenzene/isoprene copolymer, a 2-ethylhexyl acrylate/crotonic acid/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/crotonic acid/1,3-butadiene copolymer, a butyl acrylate/crotonic acid/1,3-butadiene copolymer, a 2-ethylhexyl methacrylate/crotonic acid/isoprene copolymer, a 2-ethylhexyl acrylate/crotonic acid/ethylene glycol dimethacrylate/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/crotonic acid/isoprene copolymer, a diethylaminoethyl acrylate/crotonic acid/1,3-butadiene copolymer, a methoxypolyethylene glycol monomethacrylate/crotonic acid/isoprene copolymer, a 2-ethylhexyl crotonate/crotonic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/crotonic acid/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/crotonic acid/polyethylene glycol diacrylate/1,3-butadiene copolymer, a butyl acrylate/crotonic acid/trimethylolpropane triacrylate/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl methacrylate/maleic acid/1,3-butadiene copolymer, a butyl acrylate/maleic acid/1,3-butadiene copolymer, a 2-ethylhexyl acrylate/itaconic acid/isoprene copolymer, a 2-ethylhexyl acrylate/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/ethyl methacrylate/1,3-pentadiene copolymer, a butyl acrylate/isoprene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/1,3-pentadiene copolymer, a 2-ethylhexyl methacrylate/ethyl acrylate/1,3-pentadiene/polyethylene glycol diacrylate, a butyl acrylate/1,3-pentadiene/divinylbenzene copolymer, a 2-ethylhexyl acrylate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid/1,3-pentadiene copolymer, a butyl acrylate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/acrylic acid/ethylene glycol dimethacrylate/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/hydroxypropyl acrylate/acrylic acid/1,3-pentadiene copolymer, a diethylaminoethyl acrylate/acrylic acid/1,3-pentadiene copolymer, a methoxypolyethylene glycol monomethacrylate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl crotonate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/ethyl crotonate/acrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/ethyl acrylate/acrylic acid/polyethylene glycol diacrylate/1,3-butadiene/1,3-pentadiene copolymer, a butyl acrylate/acrylic acid/divinylbenzene/1,3-butadiene/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/acrylic acid/methacrylic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/acrylic acid/maleic acid/1,3-pentadiene copolymer, a 2-ethylhexyl acrylate/itaconic acid/1,3-pentadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/methacrylic acid/1,3-butadiene/1,3-pentadiene copolymer, a 2-ethylhexyl methacrylate/acrylic acid/maleic acid/1,3-pentadiene copolymer, and a 2-ethylhexyl methacrylate/itaconic acid/isoprene/1,3-pentadiene copolymer.
The binder composition of the present invention is a liquid dispersion of the above-mentioned polymer in the form of particles, dispersed in a specific organic liquid dispersion medium. The method for preparing the liquid dispersion is not particularly limited, but, in view of enhanced production efficiency, preferable is a method wherein a latex comprising polymer particles dispersed in an aqueous medium is prepared by a conventional procedure, and thereafter, water contained in the latex is substituted with an organic liquid dispersion medium. The manner in which water is substituted with an organic liquid dispersion medium, includes those in which a latex having incorporated therein an organic liquid dispersion medium is subjected to a distillation method, a fractional filtration method, or a method of phase reversal of dispersion medium, to remove water. Preferably water is removed to an extent such that the residual water is not larger than 3% by weight, preferably not larger than 1% by weight, and more preferably not larger than 0.5% by weight, to attain an excellent effect of enhancing the initial battery capacity. The mechanism therefor is not clearly elucidated, but, it is presumed that water remaining in a slurry used for preparation of an electrode for battery tends to retard drying of a coating of the slurry formed on a collector at the step of preparation of the electrode.
The procedure for preparing latex of the polymer is not particularly limited, and includes an emulsion polymerization procedure and a suspension polymerization procedure. For example, a latex, i.e., an aqueous dispersion of polymer particles in water, can be prepared by a method described in Jikken Kagaku Kouza, Vol. 28, edited by Nihon Kagakukai [Japanese Chemical Society] and published by Maruzen K.K.), namely, a method wherein a closed vessel provided with a stirrer and a heating means is charged with an initiator, monomers, water, a dispersing agent, an emulsifying agent, a crosslinking agent and other additives to prepare a monomer charge having a predetermined composition; the monomer charge is stirred whereby the monomers are emulsified or dispersed in water; and the temperature is elevated while the monomer charge is stirred, to initiated a polymerization. Alternatively, the binder composition of the present invention can be directly produced by a dispersion polymerization method using an organic liquid dispersion medium.
The emulsifier and the dispersing agent can be chosen from those which are conventionally used in an emulsion polymerization method, a suspension polymerization method and a dispersion polymerization method. As specific examples of the emulsifier and the dispersing agent, there can be mentioned benzenesulfonate salts such as sodium dodecylbenzenesulfonate and sodium dodecyl-phenyl-ether-sulfonate; alkylsulfate salts such as sodium laurylsulfate, sodium tetradodecylsulfate and a formaldehyde condensate of sodium alkylnaphthalenesulfonate; sulfosuccinate salts such as sodium dioctylsulfosuccinate and sodium dihexylsulfosuccinate; fatty acid salts such as sodium laurate; ethoxysulfate salts such as sodium polyoxyethylene-lauryl-ether-sulfate and sodium polyoxyethylene-nonyl-phenyl-ether-sulfate; alkanesulfonate salts; sodium alkyl-ether-phosphate ester; and nonionic emulsifiers such as polyoxyethylene nonyl phenyl ether, polyoxyethylene sorbitan lauryl ester and polyoxyethylene-polyoxypropylene block copolymer. These emulsifiers and dispersing agents can be used either alone or as a combination of at least two thereof. The amount of the emulsifier and the dispersing agent can be freely chosen, but is usually in the range of about 0.01 to 10 parts by weight based on 100 parts by weight of the total monomers. Depending upon the polymerization conditions, the polymerization can be conducted without the dispersing agent.
Additives such as a molecular weight modifier can be used. As specific examples of the molecular weight modifier, there can be mentioned mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan and n-octyl mercaptan; and halogenated hydrocarbons such as carbon tetrachloride and carbon tetrabromide. These molecular weight modifiers can be added to the polymerization system before or during the polymerization. The amount of the molecular weight modifier is usually in the range of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the monomers.
The polymerization initiator is chosen from those which are used in ordinary emulsion polymerization, dispersion polymerization and suspension polymerization. The polymerization initiator includes, for example, persulfate salts such as potassium persulfate and ammonium persulfate; hydrogen peroxide; and organic peroxide such as benzoyl peroxide and cumene hydroperoxide. These initiators may be used either alone, or as a redox polymerization initiator which is a combination thereof with a reducing agent such as sodium acid sulfate, sodium thiosulfate and ascorbic acid.
The polymerization initiator further includes, for example, azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 4,4xe2x80x2-azobis(4-cyanopentanoic acid; and amidine compounds such as 2,2xe2x80x2-azobis(2-aminodipropane)dihydrochloride, 2,2xe2x80x2-azobis(N,N-dimethyleneisobutylamidine) and 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutylamidine) dihydrochloride. These initiators may be used either alone, or as a combination of at least two thereof.
The amount of the polymerization initiator is in the range of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on the total weight of the monomers.
The polymerization temperature and the polymerization time can be appropriately chosen depending upon the particular procedure for polymerization and the kind of polymerization initiator, but, are usually in the range of about 30 to 200xc2x0 C. and about 0.5 to 30 hours, respectively. A polymerization aid such as an amine can be used.
To a latex produced by the above-mentioned polymerization procedures, a basic aqueous solution can be added to adjust the pH value of 5 to 10, preferably 5 to 9. The basic aqueous solution is an aqueous solution of a base, for example, a hydroxide of an alkali metal such as Li, Na, K, Rb or Cs; ammonia; an inorganic ammonium compound such as NH4Cl; an organic amine compound such as ethanolamine or diethylamine. Of these bases, an alkali metal hydroxide is preferable because a bonding force (peel strength) between a collector and an active material can be enhanced.
The pH value is measured under the following conditions.
(i) Apparatus: HM-12P available from Toa Dempa Kogyo K.K.
(ii) Measurement temperature: 25xc2x0 C.
(iii) Amount of liquid tested: 100 ml
A pH meter is turned on and maintained as it is for about 30 minutes to be thereby stabilized. The area to be detected is washed with pure water at least three times, and wiped with clean sanitary cotton. Calibration of standard solution is conducted by single-point calibration. An electrode is dipped in a standard neutral phosphate salt solution having a pH value of 6.86, and then the solution is shaken two or three times to remove bubbles. The solution is left to stand for 10 minutes, and then, the measured value is read and then is calibrated. After the calibration, the electrode is washed with pure water at least three times and then wiped with sanitary clean cotton. Thereafter the electrode is dipped in the liquid to be tested, and shaken twice or three times to remove bubbles. The liquid is then left to stand for 10 minutes and reading of the pH value is made.
The organic liquid dispersion medium in which the above-mentioned polymer particles are dispersed has a boiling point in the range of 80 to 350xc2x0 C., preferably 100 to 300xc2x0 C. and more preferably 120 to 280xc2x0 C. at normal pressure. As specific examples of the organic liquid dispersion medium, there can be mentioned the following substances. Numeral within each parenthesis denotes a boiling point (unit: xc2x0 C.) at normal pressure as expressed by counting fractions of 0.5 and over as a whole number and disregarding the rest. When the boiling point falls within a certain range, it was confirmed that the lower limit is 80xc2x0 C. or higher, and the upper limit is denoted in parenthesis.
Hydrocarbons: heptane (98), n-octane (125), isooctane (117), n-nonane (150), decane (174), decaline (194), xcex1-pinene (156), xcex2-pinene (163), xcex4-pipene (161), 1-chlorooctane (182), 1,2-dichloroethane (83), chlorodecane (223), tetrachloroethylene (121), cyclohexane (81), cycloheptane (118), methylcyclopentane (101), chlorocyclohexane (144), cyclohexene (83), cycloheptene (115), benzene (80), toluene (111), o-xylene (144), m-xylene (139), p-xylene (138), styrene (145), chlorobenzene (132), o-chlorotoluene (159), m-chlorotoluene (162), p-chlorotoluene (162), ethylbenzene (136), propylbenzene (159), diisopropylbenzene (231), butylbenzene (183), isobutylbenzene (173), n-amylbenzene (202), and cumene (152);
Alcohols: 1-propanol (97), 2-propanol (82), 1-butanol (117), t-butanol (83), 1-pentanol (138), 2-pentanol (119), 3-pentanol (116), 1-hexanol (157), 2-hexanol (139), 3-hexanol (135), 1-octanol (195), 2-octanol (179), benzyl alcohol (205), 4-t-butylcatechol (285), cyclopentanol (141), glycerin (290);
Ketones: methyl ethyl ketone (80), 2-pentanone (102), 2-hexanone (127), 3-hexanone (125), cyclopentanone (131), cyclohexanone (156), cycloheptanone (180), 2,6-dimethyl-4-heptanone (168), and isophrone (215);
Ethers: propyl ether (91), butyl ether (142), isobutyl ether (123), n-amyl ether (188), isoamy ether (173), methyl n-amyl ether (100), ethyl butyl ether (92), ethyl isobutyl ether (81), ethyl n-amyl ether (120), ethyl isoamyl ether (112), phenetole (170), 1,3-dioxane (106) and 1,4-dioxane (101);
Esters: Propyl formate (82), butyl formate (107), pentyl formate (132), isopropyl acetate (89), n-propyl acetate (101), n-butyl acetate (126), s-butyl acetate (112), t-butyl acetate (98), methyl lactate (144), ethyl lactate (154), butyl lactate (187), methyl benzoate (200) and ethyl benzoate (213);
Amines: o-toluidine (200), m-toluidine (203), p-toluidine (200), N,N-dimethylaniline (194) and piperidine (105);
Amides: N,N-dimethylformamide (153), N-methylpyrrolidone (202) and N,N-dimethylacetamide (194);
Sulfur-containing compounds: diemthylsulfoxide (189);
Nitrile group-containing compounds: lactonitrile (184), ethylene cyanohydrin (220) and adiponitrile (295);
Oxygen-containing heterocyclic compounds: furfural (162);
Nitrogen-containing heterocyclic compounds: pyridine (116), pyrrole (130) and pyrrolidine (88);
Cellosolve acetates: ethylcellosolve acetate (192);
Glycols: ethylene glycol (198), diethylene glycol (186) and propylene glycol (188);
Ethylene glycol alkyl ethers: diethylene glycol monoethyl ether (195), diethylene glycol dimethyl ether (159), diethylene glycol monobutyl ether (230) and triethylene glycol dimethyl ether (222);
Lactones: xcex3-butyrolactone (206), xcex3-valerolactone (207) and xcex3-caprolactone (216); and
Lactams: xcex2-butyrolactam (245) and xcex4-valerolactam (256).
The polymer particles having structural units (a) and structural units (b) and/or (c), used in the present invention, may be either particles composed of one kind of polymer, or composite particles composed of two or more kinds of polymers, provided that the polymer particles are produced form a monomer composition satisfying the above requirements. More specifically the composite particles can be produced, for example, by a two-stage polymerization process wherein one or more kinds of monomers are polymerized by an ordinary procedure and subsequently other kind of monomer or monomers are added and polymerized by an ordinary procedure.
The composite particles have an odd-shaped structure which includes, for example, a core-shell type structure, an islands-in-sea type structure, a side-by-side type structure, a tumbler type structure, an octopus ocellus type structure and a raspberry type structure, which are called in the field of latexes and described in xe2x80x9cSetchaku (Adhesion)xe2x80x9d vol. 34, No. 1, p13-23, especially illustrated in FIG. 6 on page 17.
It is important that the polymer particles in the binder composition of the present invention are insoluble or only slightly soluble in an electrolyte solution. Thus, the polymer particles preferably have a gel content, as calculated as insoluble matter in an electrolyte solution, of 50% to 100% by weight, more preferably 60% to 100% by weight, and especially preferably 70% to 100% by weight. The gel content (hereinafter referred to as xe2x80x9cgel content G1xe2x80x9d) used herein means that as calculated as insoluble matter in an electrolyte solution, which is a one mole/liter solution of LiPF6 in a mixed liquid comprised of propylene carbonate/ethylene carbonate/diethyl carbonate/dimethyl carbonate/methylethyl carbonate at a ratio of 20/20/20/20/20 by volume at 20xc2x0 C.
The gel content G1 is determined as follows. A glass plate is coated with a polymer binder composition to form a filmy coating having a thickness of about 0.1 mm. The filmy coating is air-dried at 120xc2x0 C. for 24 hours and further vacuum-dried at 120xc2x0 C. for 2 hours. The dry film is weighed (weight: D1) and then is dipped in the above-mentioned electrolyte solution in an amount of 100 times by weight of the film at 70xc2x0 C. for 74 hours. Then, the dipped film is filtered through a wire mesh sieve with a 200 mesh size. The insoluble matter remaining on the sieve is vacuum-dried at 120xc2x0 C. for 24 hours and then weighed (weight: D2). The gel content G1 is calculated according to the equation:
Gel content G1(%)=(D2/D1)xc3x97100
It is also important that the polymer is present in the form of particles in the binder composition. The presence of the polymer particles can be confirmed by the transmission electron microscopy. Thus, the polymer particles preferably have a gel content, as calculated as insoluble matter in an organic liquid dispersion medium, of 50% to 100% by weight, more preferably 60% to 100% by weight, and especially preferably 70% to 100% by weight, in view of the characteristics at repetition of charge-discharge cycles at a high temperature of 60xc2x0 C., and initial service capacity at a high temperature of 60xc2x0 C. The gel content (hereinafter referred to as xe2x80x9cgel content G2xe2x80x9d) used herein means that as calculated as insoluble matter in the organic liquid dispersion medium contained in the polymer binder composition.
The gel content G2 is determined as follows. Weight D1 of the polymer film is measured by the same procedure as described in the above method of calculating gel content G1. The film is dipped in an organic liquid dispersion medium (the same as that used for the preparation of the binder composition) in an amount of 100 times by weight of the film at 30xc2x0 C. for 24 hours. Then, the dipped film is filtered through a wire mesh sieve with a 200 mesh size. The insoluble matter remaining on the sieve is vacuum-dried at 120xc2x0 C. for 24 hours and then weighed (weight: D3). The gel content G2 is calculated according to the equation:
Gel content G2 (%)=(D3/D1)xc3x97100
Additives such as a viscosity modifier and a fluidizing agent can be added in the binder composition of the present invention to improve coating fluid properties of a slurry for an electrode for a secondary battery, hereinafter described. As specific examples of the additives, there can be mentioned cellulosic polymeric materials such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose, and ammonium salts and alkali metal salts of these cellulosic polymeric materials; polyacrylic acid salts such as sodium polyacrylate; polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, a copolymer of acrylic acid or its salt with vinyl alcohol, a copolymer of maleic anhydride, maleic acid or fumaric acid with vinyl alcohol, modified polyvinyl alcohol, modified polyacrylic acid, polyethylene glycol, polycarboxylic acid, an ethylene-vinyl alcohol copolymer, a vinyl acetate polymer, and other water-soluble polymers. The amount of these additives can be appropriately chosen according to the need.
The binder composition of the present invention may contain polymers (hereinafter referred to as xe2x80x9cother polymersxe2x80x9d) other than the above-mentioned polymers, which may be either dissolved in the organic liquid medium, or dispersed in the form of particles. The amount of such other polymers is preferably not larger than 5 part by weight based on 1 part of the polymer particles.
(2) Slurry for Electrode for Secondary Battery
The slurry of the present invention is prepared by incorporating an active material and additives, which are described below, in the binder composition of the present invention.
Active Material
The active material is not particularly limited provided that it is used for ordinary lithium ion secondary batteries.
As specific examples of the active material for a negative electrode, there can be mentioned carbonaceous materials such as amorphous carbon, graphite, natural graphite, MCMB, and pitch carbon fiber, electrically conductive polymers such as polyacene, and composite metal oxides represented by the formula AxMyOz wherein A is an alkali metal or a transition metal, M is at least one transition metal selected from Co, Ni, Al, Sn and Mn, O is an oxygen atom, x, y and z represent numbers satisfying the formulae: 1.10xe2x89xa7xxe2x89xa70.05, 4.00xe2x89xa7yxe2x89xa70.85, and 5.00xe2x89xa7zxe2x89xa71.5, and other metal oxides.
The active material used for a positive electrode is not particularly limited provided that it is used for ordinary lithium ion secondary battery. As specific examples of the active material for a positive electrode, there can be mentioned metal sulfides and metal oxides such as TiS2, TiS3, amorphous MoS3, Cu2V2O3, amorphous V2O-P2O5, MoO3, V2O5 and V6O13; and lithium-containing composite metal oxides such as LiCoO2, LiNiO2, LiMnO2 and LiMn2O4. The active material for a positive electrode further includes organic compounds including electrically conductive polymers such as polyacetylene and poly-p-phenylene.
The amount of an active material in the slurry for an electrode for a secondary battery is not particularly limited and is usually 1 to 1,000 times, preferably 2 to 500 times, more preferably 3 to 500 times and especially preferably 5 to 300 times, of the weight of the polymer particles (i.e., the solid content in the binder composition). When the amount of an active material is too small, an active material layer formed on a collector has a reduced activity and the electrode is liable to have poor performances. When the amount of an active material is too large, the adhesion of the active material to a collector becomes poor and the active material tends to be fallen from the collector. A liquid medium can be added to the slurry so that the concentration of an active material in the slurry be suitable for coating a collector with the slurry.
Additives
According to the need, additives such as a viscosity modifier and a fluidizing agent, which are hereinbefore mentioned as for the binder composition of the present invention, can be incorporated in the slurry. Further, electrically conductive materials including carbon such as graphite and active carbon, and a metal powder, can be incorporated in the slurry provided that the object of the invention can be achieved.
(3) Electrode for Lithium Ion Secondary Battery
The electrode of the present invention for a lithium ion secondary battery is made by coating a collector such as a metal foil with the above-mentioned slurry of the present invention, and drying the coating to fix an active material on the collector. The electrode may be either a positive electrode or a negative electrode.
The collector used is not particularly limited provided that it is composed of an electrically conductive material. The collector is usually composed of metal such as iron, copper, aluminum, nickel or stainless steel. The shape of the collector is also not particularly limited, and the collector is usually used in a sheet form having a thickness of about 0.001 mm to 0.5 mm.
The procedure of coating the collector with the slurry is not particularly limited. The collector can be coated with the above-mentioned slurry by a conventional coating procedure such as doctor-blade coating, dip coating, reverse-roll coating, direct-roll coating, gravure coating, extrusion coating and brush coating. The amount of the slurry applied is not particularly limited, and is usually such that the thickness of the dried coating formed on the collector has a thickness of about 0.005 mm to 5 mm, preferably about 0.1 mm to 2 mm. The procedure for drying an as-formed coating is not particularly limited, and includes, for example, warm-air drying, hot-air drying, low-humid-air drying, vacuum drying, infrared drying, far-infrared drying, electron radiation drying. The drying conditions should be chosen so that the liquid medium used is removed as soon as possible provided that occurrence of stress crack in the active material layer due to stress concentration, and separation of the active material layer from the collector can be avoided.
The electrode can be pressed, if desired, to enhance the density of the active material layer. The pressing can be carried out by a conventional procedure, such as a mold pressing and a roll pressing.
(4) Lithium Ion Secondary Battery
The lithium ion secondary battery of the present invention comprises the above-mentioned electrode and an electrolyte solution, and a separator and other elements according to the need. The lithium ion secondary battery is fabricated by a conventional procedure. For example, a positive electrode and a negative electrode are superposed with a separator interposed between the two electrodes, and the thus-formed assembly is wound or folded and then inserted into a vessel. An electrolyte solution is introduced into the vessel, and the vessel is sealed. The shape of the secondary battery is not particularly limited, and is, for example, coin-shape, button-shape, sheet-shape, cylindrical shape, rectangular shape and flat shape.
The electrolyte solution is selected from those which are conventionally used for a lithium ion secondary battery. A suitable electrolyte solution can be chosen depending upon the particular active material used so as to obtain the desired battery performances.
The electrolyte of the secondary battery includes known lithium salts. As specific examples of the electrolyte, there can be mentioned LiClO4, LiBF6, LiPF6, LiCF3, LiCF3CO2, LiAsF6, LiSbF6, LiB10Cl10, LiAlCl4, LiCl, LiBr, Li/B(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N and lithium salt of lower fatty acids.
The liquid medium used for dissolving the electrolyte is not particularly limited and includes conventional liquid mediums. As specific examples of the liquid medium, there can be mentioned carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate and diethyl carbonate; lactones such as xcex3-butyrolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxide such as dimethylsulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing compound such as acetonitrile and nitromethane; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate; inorganic acid esters such as phosphoric acid triesters and carbonic acid diesters including dipropyl carbonate; diglymes; triglymes; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; and sultones such as 1,3-propanesultone, 1,4-butanesultone and naphthasultone. These liquid mediums may be used either alone or as a mixed liquid comprised of at least two thereof.
The invention will now be described more specifically by the following working examples that by no means limit the scope of the invention.
In the working examples, parts and % are by weight unless otherwise specified.
Properties of electrodes and batteries were evaluated by the following methods.
(1) Bending of Electrode
An electrode is cut into a strip of 3 cm widthxc3x979 cm length. A stainless steel wire having a diameter of 1 mm is placed at the center of the strip (i.e., at a distance of 4.5 cm from the ends of the length) perpendicularly to the length of the strip. The strip is bent at an angle of 180xc2x0 along the stainless steel wire, and the state of a film coating on the electrode at the bent portion is observed. This bending test is conducted on ten electrode specimens. The evaluation results are expressed by the following two ratings.
Rating A: crack formation in a film coating and peeling thereof are not observed at all on ten specimens.
Rating B: at least one crack occurring in a film coating or peeling thereof is observed on at least one of ten specimens.
(2) Peel Strength of Electrode
A strip specimen is cut from an electrode in the same manner as in the banding test (1). A self-adhesive tape (xe2x80x9cCellotapexe2x80x9d available from Nichiban K.K., stipulated in JIS Z1522) is adhered to the strip specimen, and the strip specimen is fixed. The adhered strip is quickly peeled tape and a peel strength (g/cm) is measured. The measurement is conducted on 10 specimens and the results are expressed by the average value.
(3) Initial Service Capacity of Battery at High Temperature
Charge-discharge cycles of a battery is repeated at a high temperature in a manner described below. Initial service capacity is measured at the third cycle of the charge-discharge cycling test.
(4) Characteristics of Battery at Repetition of Charge-Discharge Cycles at High Temperature
A coin-shaped secondary battery specimen is fabricated by the method described below. A negative electrode test is conducted at a voltage from 0 V to 1.2 V by using a lithium metal positive electrode (Examples 1-4 and Comparative Examples 1 and 2), and a positive electrode test is conducted at a voltage from 3 V to 4.2 V by using a lithium metal negative electrode (Examples 5-8 and Comparative Examples 3 and 4), at a temperature of 65xc2x0 C. and at a constant current of 0.1 C. The retention of capacity at repetition of charge-discharge cycles is expressed by percentage of the ratio (A/B) of service capacity (A) (unit: mAh/g of active material) as measured at the 50th cycle to service capacity (B) (unit: mAh/g of active material) as measured at the third cycle. The larger the percentage of A/B, the smaller the capacity reduction at repetition of charge-discharge cycles.
Coin-shaped secondary battery is fabricated as follows. A positive electrode and a negative electrode, each having an active material layer formed by using a polymer binder for evaluation are prepared as follows. An aluminum foil collector having a thickness of 20 xcexcm is uniformly coated with an active material-containing slurry for positive electrode by a doctor blade. A copper foil collector having a thickness of 18 xcexcm is uniformly coated with an active material-containing slurry for negative electrode by a doctor blade. Each as-formed coating is dried at 120xc2x0 C. for 15 minutes in a drier, and further vacuum-dried under 5 mmHg at 120xc2x0 C. for 2 hours. The dried coated aluminum foil is preserved by a twin roll press so that the density of an active material is 3.2 g/cm3 to prepare a positive electrode having an active material layer. The dried coated copper foil is pressed by a twin roll press so that the density of an active material is 1.3 g/cm3 to prepare a negative electrode having an active material layer.
Each of the positive electrode and the negative electrode is cut into a circular shape having a diameter of 15 mm. A battery is fabricated by using the circular positive electrode or the circular negative electrode, a lithium metal counter electrode and a separator, which is sandwiched between the positive electrode or the negative electrode and the lithium metal counter electrode so that the active material layers of the two electrodes confront to each other. The separator is comprised of a circular porous polypropylene film having a diameter of 18 mm and a thickness of 25 xcexcm. An assembly of the two electrodes and the separator is placed in a coin-shaped outer casing having a diameter of 20 mm and a height of 1.8 mm and made of a stainless steel sheet having a thickness of 0.25 mm, so that the aluminum foil of the positive electrode or lithium metal is kept in contact with the casing bottom. An expanded metal part is placed on the copper foil of the negative electrode or on lithium metal of the counter electrode. A polypropylene packing is packed within the casing. An electrolyte solution, which is a solution of LiPF6 with a concentration of 1 mol/liter of a mixed liquid composed of propylene carbonate/ethylene carbonate/diethyl carbonate/dimethyl carbonate/methyl ethyl carbonate at a mixing ratio of 20/20/20/20/20 (volume ratio at 20xc2x0 C.), is injected into the casing so that no air remains within the casing. The thus-fabricated assembly is covered with a stainless steel cap having a thickness of 0.2 mm via the polypropylene packing. The assembly-packed casing is sealed whereby a coin-shaped battery having a diameter of 20 mm and a thickness of about 2 mm is obtained.

Binder composition for electrode for lithium-ion secondary battery and utilization thereof


A method of treating medical conditions with proteinase inhibitors of the formula: ##STR1## wherein B is H or an amino acid blocking group for the N-terminal amino acid nitrogen;. R.sub.1 is an optionally protected .alpha.-amino acid side chain such that P.sub.2 is the residue of an .alpha.-amino acid selected from the group consisting of phenylalanine (Phe), leucine (Leu), tyrosine (Tyr) and valine (Val), and substituted analogs thereof, particularly including Tyr(OMe); PA1 R.sub.2 is an optionally protected .alpha.-amino acid side chain such that P.sub.1 is the residue of an .alpha.-amino acid selected from the group consisting of alanine (Ala), arginine (Arg), aspartic acid (Asp), glutamic acid (Glu), histidine (His), homophenylalanine (HPhe), phenylalanine (Phe), ornithine (Orn), serine (Ser) and threonine (Thr), and substituted analogs thereof; PA1 X is a fluorine-free leaving group selected from the group consisting of phenoxy, substituted phenoxy and heterophenoxy; PA1 E and G are one or more atoms more electronegative than carbon; and PA1 D is hydrogen, methyl or a substituted methyl.

The present invention relates generally to peptidyl ketone inhibitors, and more particularly to peptidyl ketone inhibitors designed for the in vivo management of cysteine proteases, particularly cathepsin B and L, and their primitive enzymatic counterparts.
Cathepsins B and L are cysteinyl proteases involved in normal protein degradation. As such, they are generally located in the lysosomes of cells. When these enzymes are found extralysosomaly they have been implicated by use of synthetic substrate technology and by natural endogenous inhibitors as playing a causative role in a number of disease states such as rheumatoid arthritis, osteo arthritis, pneumocystis carinii, schistosomiasis, trypanosoma cruzi, trypanosoma brucei bruci, Crithidia fusiculata, malaria, periodontal disease, tumor metastasis, metachromatic leukodystrophy, muscular dystrophy, etc. In particular, a connection between cathepsin B-type enzymes and rheumatoid arthritis has been suggested in van Noorden and Everts, "Selective Inhibition of Cysteine Proteinases by Z-Phe-Ala-CH.sub.2 F Suppresses Digestion of Collagen by Fibroblasts and Osteoclasts," 178 Biochemical and Biophysical Research Communications 178; Rifkin, Vernillo, Kleekner, Auszmann, Rosenberg and Zimmerman, "Cathepsin B and L Activities in Isolated Osteoclasts," 179 Biochemical and Biophysical Research Communications 63; Grinde, "The Thiol Proteinase Inhibitors, Z-Phe-Phe-CHN.sub.2 and Z-Phe-Ala-CHN.sub.2, Inhibit Lysosomal Protein Degradation in Isolated Rat Hepatocytes," 757 Biochimica et Biophysica Acta 15; Mason, Bartholomew and Hardwick, "The Use of Benzyloxycarbonyl[.sup.125 I]iodotyrosylalanyldiazomethane as a Probe for Active Cysteine Proteinases in Human Tissues," 263 Biochem. J. 945; van Noorden, Smith and Rasnick, "Cysteine Proteinase Activity in Arthritic Rat Knee Joints and the Effects of a Selective Systemic Inhibitor, Z-Phe-Ala-CH.sub.2 F," 15 J. Rheumatol. 1525; and van Noorden, Vogels and Smith, "Localization and Cytophotometric Analysis of Cathepsin B Activity in Unfixed and Undecalified Cryostat Sections of Whole Rat Knee Joints," 37 J. Histochemistry and Cytochemistry 617. A connection between cathepsin B and osteo arthritis has been suggested in Delaisse, Eeckhout and Vaes, "In Vivo and In Vitro Evidence for the Involvement of Cysteine Proteinases in Bone Resorption," 125 Biochemical and Biophysical Research Communications 441; a connection between cathepsin B and pneumocystis carinii has been suggested in Hayes, Stubberfield, McBride and Wilson, "Alterations in Cysteine Proteinase Content of Rat Lung Associated with Development of Pneumocystis Carinii Infection," 59 Infection and Immunity 3581; a connection between cysteine proteinases and schistosomiasis has ben suggested in Cohen, Gregoret, Amiri, Aldape, Railey and McKerrow, "Arresting Tissue Invasion of a Parasite by Protease Inhibitors Chosen With the Aid of Computer Modeling." 30 Biochemistry 11221. A connection between cysteine proteinases and trypanosoma cruzi, trypanosoma brucei brucei and crithidia fasciculata has been suggested in Ashall, Harris, Roberts, Healy and Shaw, "Substrate Specificity and Inhibitor Sensitivity of a Trypanosomatid Alkaline Peptidase," 1035 Biochimica et Biophysica Acta 293, and/or in Ashall, Angliker and Shaw, "Lysis of Trypanosomes by Peptidyl Fluoromethyl Ketones," 170 Biochemical and Biophysical Research Communications 923. A connection between cysteine proteinases and malaria has been suggested in Rosenthal, Wollish, Palmer and Rasnick, "Antimalarial Effects of Peptide Inhibitors of a Plasmodium Falciparum Cysteine Proteinase," 88 J. Clin. Invest. 1467, and in Rosenthal, Lee and Smith, "Inhibition of a Plasmodium Vinckei Cysteine Proteinase Cures Murine Malaria," (in press). A connection between cathepsin B and tumor metathesis has been suggested in Smith, Rasnick, Burdick, Cho, Rose and Vahratian, "Visualization of Time-Dependent Inactivation of Human Tumor Cathepsin B Isozymes by a Peptidyl Fluoromethyl Ketone Using a Fluorescent Print Technique," 8 Anti-cancer Research 525. A connection between cathepsin B and cancer has been suggested in Gordon and Mourad, 2 Blood Coagulation and Fibrinolysis 735. A connection between cathepsin B and periodontal disease has been suggested in Cox, Cho, Eley and Smith, "A Simple, Combined Fluorogenic and Chromogenic Method for the Assay of Proteases in Gingival Crevicular Fluid," 25 J. Periodont. Res. 164; Uitto, Larjava, Heino and Sorsa, "A Protease of Bacteriodes Gingivalis Degrades Cell Surface and Matrix Glycoproteins of Cultured Gingival Fibroblasts and Induces Secretion of Collagenase and Plasminogen Activator," 57 Infection and Immunity 213; Kunimatsu, Yamamoto, Ichimaru, Kato and Kato, "Cathepsins B, H and L Activities in Gingival Crevicular Fluid From Chronic Adult Periodontitis Patients and Experimental Gingivitis Subjects," 25 J Periodont Res 69; Beighton, Radford and Naylor, "Protease Activity in Gingival Crevicular Fluid From Discrete Periodontal Sites in Humans With Periodontitis or Gingivitis"; 35 Archs oral Biol. 329; Cox and Eley, "Preliminary Studies on Cysteine and Serine Proteinase Activities in Inflamed Human Gingiva Using Different 7-Amino-4-Trifluoromethyl Courmarin Substrates and Protease Inhibitors," 32 Archs oral Biol. 599; and Eisenhauer, Hutchinson, Javed and McDonald, "Identification of a Cathepsin B-Like Protease in the Crevicular Fluid of Gingivitis Patients," 62 J Dent Res 917. A connection between cathepsin B and metachromatic leukodystrophy has been suggested in von Figura, Steckel, Conary Hasilik and Shaw, "Heterogeneity in Late-Onset Metachromatic Leukodystrophy. Effect of Inhibitors of Cysteine Proteinases," 39 Am J Hum Genet. 371; a connection between cathepsin B and muscular leukodystrophy has been suggested in Valentine, Winand, Pradhan, Moise, de Lahunta, Kornegay and Cooper, "Canine X-Linked Muscular Dystrophy as an Animal Model of Duchenne Muscular Dystrophy: A Review," 42 Am J Hum Genet 352; a connection between cathepsin B and rhinovirus has been suggested in Knott, Orr, Montgomery, Sullivan and Weston, "The Expression and Purification of Human Rhinovirus Protease 3C," 182 Eur. J. Biochem. 547; a connection between cathepsin B and kidney disease has been suggested in Baricos, O'Connor, Cortez, Wu and Shah, "The Cysteine Proteinase Inhibitor, E-64, Reduces Proteinuria in an Experimental Model of Glomerulonephritis," 155 Biochemical and Biophysical Research Communications 1318; and a connection between cathepsin B and multiple sclerosis has been suggested in Dahlman, Rutschmann, Kuehn and Reinauer, "Activation of the Multicatalytic Proteinase from Rat Skeletal Muscle by Fatty Acids or Sodium Dodecyl Sulphate," 228 Biochem. J. 171.
Although a number of cysteine proteinase inhibitors have been identified, most of these have drawbacks for in vivo use. In particular, drawbacks such as reversibility of inhibition, lack of specificity, and rapid clearance from the body have been associated with prior art inhibitors. The microbial products antipain and leupeptin, for example, are effective but reversible inhibitors of cysteine proteinase (McConnell et al., 33 J. Med. Chem. 86-93; Sutherland et al. 110 Biochem. Biophys. Res. Commun. 332-38), and also inhibit certain serine proteinases (Umezawa, 45 Meth. Enzymol. 678-95). The compound E64 and its synthetic analogues are more selective inhibitors (see, e.g., Barret et al., 201 Biochem. J. 189-98, and Grinde, 701 Biochem. Biophys. Acta. 328-33), but disappear too quickly from the circulation for in vivo use (Hashida et al. 91 J. Biochem. 1373-80).
The most promising type of cysteine proteinase inhibitors have an activated carbonyl with a suitable .alpha.-leaving group fused to a programmed peptide sequence that specifically directs the inhibitor to the active site of the targeted enzyme. Once inside the active site, the inhibitor carbonyl is attached by a cysteine thiolate anion to give the resulting hemiacetal. If the .alpha.-leaving group then breaks off, the bond between enzyme and inhibitor becomes permanent and the enzyme is irreversibly inactivated.
The usefulness of an inhibitor in inactivating a particular enzyme therefore depends not only on the "lock and key" fit of the peptide portion, but also on the reactivity of the bond holding the .alpha.-leaving group to the rest of the inhibitor. It is important that the leaving group be reactive only to the intramolecular displacement via a 1,2-migration of sulfur in the breakdown of the hemithioacetal intermediate.
Groundbreaking work regarding cysteine proteinase inhibitors having an activated carbonyl, a suitable .alpha.-leaving group and a peptide sequence effective to specifically direct the inhibitor to the active site of the targeted enzyme was disclosed in U.S. Pat. No. 4,518,528 to Rasnick, incorporated herein by reference. That patent established peptidyl fluoromethyl ketones to be unprecedented inhibitors of cysteine proteinase in selectivity and effectiveness. The fluoromethyl ketones described and synthesized by Rasnick included those of the formula: ##STR2## wherein R.sub.1 and R.sub.2 are independently selected from the group hydrogen, alkyl of 1-6 carbons, substituted alkyl of 1-6 carbons, aryl, and alkylaryl where the alkyl group is of 1-4 carbons; n is an integer from 1-4 inclusive; X is a peptide end-blocking group; and Y is an amino acid or peptide chain of from 1-6 amino acids.
Peptidylketone inhibitors using a phenol leaving group are similar to the peptidyl fluoroketones. As is known in the art, oxygen most closely approaches fluorine in size and electronegativity. Further, when oxygen is bonded to an aromatic ring these values of electronegativity become even closer due to the electron withdrawing effect of the sp2 carbons. The inductive effect of an .alpha.-ketophenol versus an .alpha.-ketofluoride when measured by the pKa of the .alpha.-hydrogen, appears comparable within experimental error.
Although the general association between various disease states and cysteine proteinase inhibitors is known, the prior art has not identified specific methods of treatment using specific inhibitors of the type first described by Rasnick. A need therefore exists for methods of treating various disease states characterized by extralysosomal cathepsin B and/or cathepsin L activity. The present invention addresses that need.

Cysteine protease inhibitors effective for in vivo use


Motion sickness is reduced for users of mechanical systems used to practice sports that comprise an immersive virtual reality device. In particular, the use of prediction and interpolation algorithms enable fluid movements to be displayed within the virtual environment.

Mechanical systems for practicing sports are systems allowing a user to practice a sporting activity indoors by generally simulating a real sporting activity on a controlled apparatus. It is possible to cite indoor bikes, cross-trainers, indoor rowing machines, treadmills and so on as examples of such systems. These systems are typically made up of the sports apparatus in itself which allows the user to make an effort. This is typically a bicycle, a rowing machine etc. This sports apparatus is coupled with an adjustable resistance which makes it possible to control the effort level which has to be provided by the user when using the sports apparatus. This resistance may assume a variety of forms, it may be, for example, a flywheel slowed down by friction or by an adjustable magnetic field or even oars immersed in water, the movement of which slows down the movement of the sports apparatus as is the case in certain indoor rowing machines.
Nowadays, the adjustment of the resistance is generally controlled by a computer controlling the activity. This control computer allows the display of different activity programs and the display of a human-machine interface making it possible to choose one's program and thus to act on the level of resistance. The functions of the control computer are complemented by functions for monitoring and establishing statistics on the activity sessions, monitoring the user's heart rate etc.
Virtual reality is a visual or auditive, immersive, interactive, computer-based simulation of real or imaginary environments. The purpose of virtual reality is to provide someone (or several people) with a sensory-motor and cognitive activity in an artificial world, created digitally, which may be imaginary, symbolic or a simulation of certain aspects of the real world.
Coupled with a mechanical system for practicing sports, virtual reality makes it possible to simulate the sporting activity in a virtual environment which can, for example, simulate an outdoor activity. Thus, the activity is made more entertaining and enjoyable than an activity in a fixed indoor environment.
Despite numerous possible applications, the use of virtual reality is not yet widespread and attempts to market a product based on virtual reality have been hampered by a recurring problem: motion sickness or cybersickness.
Motion sickness or cybersickness occurs when being exposed to a virtual environment brings about symptoms which are similar to the symptoms of travel sickness. This syndrome causes dizziness, headaches, feelings of disorientation, nausea etc. It can occur during the virtual experience, but equally when returning to reality and may last for several hours.
Motion sickness is different from travel sickness in that it can be caused by the visual perception of movements without an actual movement of the user being necessary. Motion sickness is the critical point limiting the launch of commercial applications based on virtual reality.

Method for generating multimedia data associated with a system for practicing sports


Power-fail safe compression and dynamic capacity for a storage device in a computer system is provided. Metadata stored with each logical block in non-volatile memory in the storage device ensures that the mapping table may be recovered and stored in volatile memory for use by the computer system after power is restored to the computer system. In addition, the metadata ensures that a list of free logical block addresses written to the storage device prior to shutting down the computer system to provide access to the additional capacity that is available in the storage device by storing compressed data in the storage device may also be recovered.

A computer system typically includes a volatile system memory, for example, a Dynamic Random Access Memory (DRAM) and a storage device that includes non-volatile memory. Storage devices that include non-volatile memory include a secure digital card, a multimedia card, a flash drive (for example, a Universal Serial Bus (USB) flash drive also known as a "USB thumb drive" or "USB memory stick" that includes non-volatile memory with an integrated USB interface), and a solid-state drive.
Volatile memory is memory whose state (and therefore the data stored in it) is indeterminate if power is interrupted to the device. Dynamic volatile memory requires refreshing the data stored in the device to maintain state.
Nonvolatile memory refers to memory whose state is determinate even if power is interrupted to the device. A logical block is the smallest addressable data unit for read and write commands to access data stored in the storage device. The address of the logical block is commonly referred to as a Logical Block Address (LBA).
Although the following Detailed Description will proceed with reference being made to illustrative embodiments of the claimed subject matter, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly, and be defined only as set forth in the accompanying claims.

Method and apparatus for power-fail safe compression and dynamic capacity for a storage device


A variable position target assembly for pinball machines comprises a target and shaft assembly mechanically linked to an opto-interrupter or other transducer. As the shaft assembly is linearly displaced incrementally, its movement causes the transducer to signal at each increment a main processing unit of the pinball game to assign a score or other award.

The present invention relates generally to pinball games, and more particularly to a target assembly for pinball games.
Pinball games, as commonly known, consist of an inclined playfield and a plurality of play features arranged on the playfield. A player uses flippers or similar means to direct a ball at playfield features such as targets or ramps in order to score points. A fixed number of points are typically assigned to each playfield feature, though the number of points may be changed through multipliers awarded as a result of other playfield activity.
Players select pinball machines based on several criteria, including the variety and originality of playfield features found on the machines. Another factor considered by players is the degree of skill necessary to maximize scored points or to strike particular targets. Thus, the success of a particular pinball game, or series of games, is dependent upon the inclusion of new and original playfield features in such games that challenge the players and stimulate interest in the machines.
Accordingly, it is an object of the present invention to provide a novel playfield feature in the form of a target having variable positions for achieving different point values, resulting in a game that is more challenging to players.
It is a further object of the invention to provide such a playfield feature include an optical device for transducing the target position into an electronic signal for communication with a processor, for awarding points based on target position.
These and other objects of the invention will become apparent to those skilled in the art.


A synchronous monitoring device and a method for radial and axial vibration of a shearer drum. The monitoring device includes a laser, a first optical fiber coupler, an optical isolator, a second optical fiber coupler, a third optical fiber coupler, an optical fiber collimator, a first photodetector, a second photodetector, a first signal processing module, and a second signal processing module which are disposed on a shearer ranging arm, as well as a reflective coating disposed on a shearer drum. By measuring a phase difference between original light and reflected light, axial vibration of the shearer drum is monitored, and by measuring an intensity difference between original light and reflected light, radial vibration of the shearer drum is monitored.

China is rich in coal resources. Coal is also a main energy source and raw material for consumption in China, and it will always dominates in energy sources in the current and future period. Therefore, whether the coal mining industry can develop healthily and steadily will directly affect further improvement and development of all walks of life in China.
The health state of a shearer, as one important mining equipment in underground coal mines, is directly related to efficient and safe mining of coal mines. Since the shearer operates all year round in high-dust concentration, high-impact load, high-temperature and high-pressure, and humid environment, the stability and reliability thereof will be affected by the harsh environment. Once a fault occurs, production halts will be caused in the entire fully-mechanized mining face, thereby leading to considerable economic damage. Therefore, the health state of the shearer must be monitored in real time.
A drum is a mechanism for coal cutting, coal dropping and coal loading directly on the shearer, and it is essential to ensure normal, safe and smooth operation of the drum in order to guarantee the efficiency of coal mining. As a typical rotating machine, the drum is prone to axial misalignment, structural fracture and other faults, and 80% of the faults can be reflected by vibration anomalies. Therefore, a vibration signal of the drum contains rich state information, so it is necessary to monitor the vibration signal of the shearer drum in real time without shutdown or disassembly, and the vibration signal is analyzed to determine the deterioration degree and fault nature of the shearer drum.
In current practical applications, the indirect method is generally adopted for vibration monitoring of the shearer drum, that is, a sensor and a monitoring system are mounted on a mechanical structure and a power device (such as a ranging arm) near the shearer drum and directly associated with the shearer drum, and an electrical vibration sensor and monitoring system are generally adopted. Researches show that synchronous monitoring of radial and axial vibration of the shearer drum is difficult to realize with such an indirect monitoring method in practical applications, and the monitoring process is easily interfered by a strong electromagnetic field in the fully-mechanized mining face, so that the monitoring sensitivity is low, and thus the health state of the shearer drum cannot be directly and accurately reflected.

Synchronous monitoring device and method for radial and axial vibration of shearer drum

CHINA UNIVERSITY OF MINING AND TECHNOLOGY

XUZHOU ZHONGMINE TRANSMISSION TRACK TECHNOLOGY CO., LTD


A write queue, for queuing a packet in a traffic manager coupled to a memory device, is selected from among a preemptable write queue configured to queue packets that are candidates for being retrieved from the traffic manager before the packets are written to the memory device and a non-preemptable write queue configured to queue packets that are not candidates for being retrieved from the traffic manager before the packets are written to the memory device. The packet is written to the selected write queue. A read request is generated for retrieving the packet from the memory device, and it is determined whether the packet is queued in the preemptable write queue. If the packet is queued in the preemptable write queue, the packet is extracted from the preemptable write queue for retrieving the packet from the traffic manager before the packet is written to the memory device.

Network devices, such as routers or switches, often include memory devices for buffering packets ready for transmission, for example to implement traffic management of different flows transmitted by the network devices, or merely to temporarily store packets when transmit ports are not immediately available for transmission. Memory controllers coupled to such memory devices typically include queues for queuing write requests for writing packets to the memory devices and read request queues for queuing read requests for reading packets from the memory devices. The memory controller implements a suitable scheduling scheme for providing access to the memory device such that write requests and read requests can be executed in some fair and/or efficient manner. Generally, writing packets to the memory device and reading packets from the memory device creates a load on a bus that connects the memory controller to the memory device.


A semiconductor memory device includes bit line pair precharge circuits for precharging bit lines in a memory cell array. The semiconductor memory device includes a number of memory cells each sharing a pair of bit lines, each bit line pair together with corresponding memory cells constituting the memory cell array. The memory device further includes a first bit line precharge circuit coupled to a first position along each bit line pair for precharging the respective bit lines under the control of a block selection signal and a write enable signal. A second bit line precharge circuit is connected at a second position along the bit line pair for precharging the respective bit line pair under the control of the write enable signal. A positional distance between the first position and the second position being such as to optimally reduce a bit line precharge time and a write recovery time associated with each bit line pair in the memory cell array.

1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to a circuit for precharging bit lines.
2. Description of the Related Art.
In highly integrated semiconductor memory devices, integrated circuits must necessarily be capable of high speed operation. However, memory cell sensing steps substantially reduce the highest speed operation of an integrated circuit.
In order to improve the overall speed of the bit line sensing steps during memory operations, a bit line precharge circuit is conventionally used to maintain a constant voltage level on bit lines at least during a stand-by mode of operation.
An external supply voltage VCC or VCC-.alpha. (where .alpha. is an arbitrary constant) is generally selected as the given constant voltage level determined in accordance with a particular memory's design characteristics so as to maximize the speed of a read operation (where each bit line in an associated pair of bit lines is complementarily biased in active read mode).
A bit line precharge circuit serves to precharge a bit line pair to the given constant voltage level. Such precharge voltage signals however adversely contribute in the creation of parasitic capacitances along the bit line circuit paths due to the general complexity thereof.
Researchers continue to seek ways to improve the current driving capacity of a bit line precharge circuit so as to provide more accurate memory cell readings by providing voltage levels along bit lines (i.e., supply voltage VCC or ground voltage VSS) which substantially correspond to bit line voltages after a write operation.
A conventional bit line precharge circuit 10 and interconnection thereof is illustrated in FIG. 1. A bit line precharge circuit is shown connected to one end of a bit line pair. The bit line precharge circuit 10 includes a first bit line set of precharge transistors P1 and P2 normally turned on and a second set of bit line precharge transistors P3 and P4 controlled by bit line precharge signal .PHI.PRE. This signal is generally derived from a word line enable buffer. Alternatively, bit line precharge signal .PHI.PRE may also be derived from a combination of an output of a word line enable buffer with the output from an address transition detector, the operation of which components is well understood in the art of semiconductor memory devices.
Signals of bit lines BL1 and BL1 are transferred through transfer transistors N1, P5, N2 and P6 to data lines DL1 and DL1 by column decoding signals Y1 and Y1 when memory cells M1, . . . , M1 are selected.
Supply voltage VCC is continuously provided to bit lines BL1 and BL1 regardless of the mode of operation as the first set of bit line precharge transistors P1 and P2 are normally turned on. This is necessary as it improves the switch to a memory cell read operation immediately after a write operation.
The second set of bit line precharge transistors P3 and P4 are enabled (turned on) in read mode to prevent overdriving already active precharge transistors P1 and P2. As a result, the speed of a read operation can be significantly improved as bit lines BL1 and BL1 can be precharged much faster up to supply voltage level Vcc following a write operation.
Conversely, precharge transistors P3 and P4 can be disabled (turned off) during a write mode/operation as sufficiently less current drive is necessary and adequately provided by active precharge transistors P1 and P2.
Bit line precharge circuit 10 is shown arranged at one end of the present chip configuration for a more convenient chip layout.
FIG. 2 shows a memory cell array layout of a chip including the precharge circuit interconnection in FIG. 1. As illustrated therein, first and second bit line precharge circuits 110 and 120 are arranged on the same side of a memory cell array 100.
Each of the second set of bit line precharge transistors P3 and P4 in the conventional bit line precharge circuit 10 of FIG. 1 is increased in size to enhance current driving capacity. In so doing, however, the load on line 11 which transmits bit line precharge signal .PHI.PRE is necessarily increased. As a result, read mode is delayed for a sufficient time until all the second set of bit line precharge transistors P3 and P4 are enabled immediately following a write operation.
This bit line precharge delay which results from the switch from an appropriate bit line voltage (i.e., supply voltage level Vcc or ground voltage level Vss) during a write operation to a constant voltage precharge level in preparation for a read operation, sufficiently degrades a memory device's maximum speed of operation.
In order to overcome the load problem discussed above, precharge circuit configurations have been proposed in which the size of a first set of bit line precharge transistors P1 and P2 is increased while the size of a second set of bit line precharge transistors P3 and P4 is decreased.
However, when such a configuration is implemented in a memory array layout as in FIG. 2, a bit line precharge time delay difference .tau. (where .tau.=R.multidot.C, and R and C denote bit line parasitic resistance and bit line parasitic capacitance, respectively) occurs during a read operation--immediately following a write operation--between memory cells M1 and Mi respectively arranged nearest to and farthest from bit line precharge circuit 10.
Furthermore, when all first and second bit line precharge transistors P1, P2, P3 and P4 are enabled for a read operation, a bit line current difference per unit time is present between memory cells M1 and Mi which serves to degrade a memory cell current sensing operation.

Semiconductor memory device with improved bit line precharged circuits


A holder for a hand held appliance has first and second hook members for supporting the handle and head of the appliance, respectively, and at least one cross bar for connecting the two hook members together such that the hook members project outwardly from a flat surface to which the holder is secured. The hook members and cross bar are formed separately and are releasably secured to one another prior to attachment to a flat surface.

The present invention relates generally to a holder or support for attachment to a wall, the holder being designed to hold a hand held electrical appliance such as a hair dryer or the like.
It is convenient to store hand held electrical appliances such as hair dryers, curling irons, shavers, and the like in places where they are readily accessible for use. In hotels, hair dryers are placed in wall mounted, shelf-like stands in bathrooms. One such stand is described in U.S. Pat. No. 5,590,475 of Andis, which describes a cradle like device having a first, arcuate seat for receiving the head of the hair dryer, a recess for receiving the handle of the hair dryer at the location of the on-off switch, and a lower end on which the lower end of the dryer is seated. The recess is designed to automatically move the switch into an off position when-the hair dryer is seated in the device.
Other holders or stands for hair dryers are described in U.S. Design Pat. No. 347,538 of Fleischer, U.S. Design Pat. No. 414,364 of Malcolm, Sr., and U.S. Design Pat. No. 335,935 of Rouail. All of these holders are generally formed in one piece which is mounted on a vertical wall surface, and are relatively bulky.
It is an object of the present invention to provide a new and improved holder for an electrical appliance such as a hair dryer.
According to the present invention, a holder for a hand held appliance having a handle portion and a head portion with an electrical lead connected to the handle portion is provided, which comprises a first hook member, a second hook member, and at least one cross bar for connecting the two hook members together such that the hook members project outwardly from a flat surface to which the holder is secured, the hook members and cross bar being formed separately and being releasably securable to one another prior to attachment to a flat surface.
In one embodiment of the invention, each hook member has a first, generally straight portion extending from one end, and a curved, hook portion at the other end, and the cross member is secured between the straight portions of the hook members. The cross member has at least one angled bend such that the straight portion of the second hook member is secured at an angle to the straight portion of the first hook member. There may be two spaced cross members secured between the hook members for added strength, each cross member having an equivalent angled bend in its length. The cross members may also have openings for receiving suitable fasteners for securing the assembled holder to a flat surface such as a wall or cabinet.
In an exemplary embodiment, the opposite ends of the cross members have first snap engaging formations and the straight portions of the hook members have corresponding, second snap engaging formations for releasable snap engagement with the first formations on the cross members. In one example, the first snap engaging formations comprise pins of reduced dimensions projecting from the ends of the cross members, while the second snap engaging formations comprise corresponding openings in the straight portions of the hook members. The openings may extend all the way through the hook members, such that they may be secured to the cross members in a first orientation in which each hook portion extends in a first direction transverse to the cross bars, or in a second orientation in which each hook portion is rotated through 180xc2x0 from the first orientation to extend in a second direction opposite to the first direction. Since the first hook member is intended to support the head portion of an appliance such as a hair dryer, and the second hook member is intended to support the handle portion, the ability to assemble the holder with the hook portions extending in opposite directions allows the holder to be modified for right or left handed users.
The holder in the exemplary embodiment is assembled from three or four parts which are designed to snap together. This allows the assembly to be stored and shipped with the parts separated and stored in a generally flat, compact package. The parts may be of molded plastic material, such that they are lightweight, inexpensive to manufacture, and can be made in various colors to match bathroom color schemes.
The hair dryer holder of this invention is easy to assemble and may be mounted on any convenient surface such as a wall, cupboard surface, or the like. The holder will keep the hair dryer secure against the wall where it is conveniently ready for use. The hair dryer is held flat against the wall and does not project outwardly any significant distance or cause any obstruction. It can be installed near the outlet used by the dryer, so that the dryer does not need to be unplugged after use.

Holder for hair dryer or other hand held appliance