context: Numerous studies reported core–shell 3D-nanostructured Li-ion electrodes with active components such as Si, Sn, TiO2, Nb2O5, Co3O4 or iron oxides, mostly applicable as negative electrodes (anodes). On the other hand, nanostructured 3D positive electrodes (cathodes) based on active materials with a desirable high redox potential vs. Li+/Li (e.g. lithiated manganese oxides, V2O5 or LiCoO2 have been reported in comparatively fewer publications. For such cathodes, a big difficulty lies in inherent oxidation of the 3D current collector during the synthesis of high voltage cathode materials – the latter typically requiring temperatures above 700 °C. By lowering the synthesis temperature to 300 °C, Zhang et al. and Pikul et al. successfully demonstrated both core–shell cathodes and full 3D Li-ion microbatteries which employed lithiated manganese oxides coated on inverse nickel opal current collectors. Impressively, the devices were operational at C-rates above 1000 (where the rate of 1C corresponds to the current required for 1 hour of a complete charge or discharge). The same group also demonstrated other high-performance 3D cathodes, such as a carbon foam coated with dense LiCoO2 or inverted opals doubly-filled with V2O5 and Li2MnSiO4. Currently, however, the electrode design based on regular inverse opal current collectors is difficult to envision for large scale battery manufacturing, as the fabrication of these current collectors is time consuming (e.g. >24 h for a 20 μm-thick structure), involves difficult to handle colloidal templates and is limited to small surfaces (∼1 cm2). Importantly, the application of a current collector with yet a higher volumetric surface area may allow further reducing the thickness of the active material and gaining access to its full theoretical capacity.
answer: inverted opals doubly-filled with V2O5 and Li2MnSiO4