PW was prepared as a slurry containing PW powder (synthesised as described in section 2.1, ABET = 5.49 m 2 g -1 ), carbon black (Timcal Ensaco, 250 P) and carboxymethyl cellulose binder (CMC) dissolved in 1.5 g of deoxygenated DI H2O at a ratio of 85:10:5. GC was prepared in the same way, but with an 80:10:10 ratio and using GC powder (spherical powder, 2-13 µm, 99.95% trace metals basis, ABET = 1.49 m 2 g -1 , Sigma-Aldrich). While the HC slurry contained HC powder and CMC dissolved in 1.5 g water at a 95:5 ratio. All slurries were ball billed at 30 Hz for 1 h before being coated onto the current collectors using a doctor blade set to 200 µm, punched (PW/GC to Ø 13 mm and Ø 16 mm, HC to Ø 16 mm) and dried at 170°C for 20 hours. Subsequent Karl-Fisher titrations (Omnis, Metrohm) of the dried PW and HC electrodes showed there to be 6.28 ppm and 2.26 ppm H2O respectively (Shell temperature set to 250°C and 200°C for the PW and HC electrodes respectively). Active masses and resulting capacities of each electrode were calculated prior to each experiment using the electrode weight, active material ratio and theoretical capacity (150 mAh g -1 and 300 mAh g -1 for PW and HC respectively). The electrolyte, henceforth referred to as NP40, was prepared by dissolving dried NaPF6 salt (at 80°C for 12 hours under vacuum) in a mixture of molten ethylene carbonate (EC, >99%, Sigma-Aldrich) and diethylene carbonate (DEC, >99%, Sigma-Aldrich). The resulting electrolyte contained 3 ppm H2O as determined by Karl-Fisher titration. In the event a symmetrical cell was assembled, the counter electrode was either sodiated against PW (for HC|HC cells) or desodiated against HC (for the PW/GC|PW cells) in a custom cylindrical cell.