The working electrodes were prepared using the active material, Super P (SP, MTI Corp.) and polyvinylidene difluoride (PVDF, MTI Corp) in a weight ratio of 80:10:10. The PVDF binder was dissolved in N-methyl-2-pyrrolidone (NMP, Sigma Aldrich) with a concentration of 0.04 g mL -1 . The active material and Super P were mixed in a mortar for 10 min. The PVDF solution was then added, and mixed for another 5 min to form a homogenous slurry, which was then cast onto carbon-coated Al foil (MTI Corp.) with a doctor blade at a thickness of 300 µm. All the above-mentioned steps were carried out in an argon-filled glove box (with H2O and O2 concentrations <0.1 ppm). The electrodes were dried on a hot plate and then punched into 12 mm diameter electrodes which were then dried in a Büchi at 120 °C for 12 h. 1 M NaClO4 dissolved in PC:FEC (propylene carbonate, fluoroethylene carbonate, Sigma Aldrich) with a volume ratio of 98:2 was used as the electrolyte and glass fiber (Whatman) as the separator. 2032-type coin cells were assembled in an argon-filled glove box with sodium metal (BASF Corp.) as the counter electrode. All cells were tested in the voltage range between 2.5 and 4.4 V (vs.