The charging process prior to NMR experiments was achieved by constant-potential hold. The cell voltage was held at 0 V for 1 hour before being held at a desired voltage for at least another 1 hour. The electronic charge was calculated via the integral of the current vs. time data. Following charging, the Swagelok cell was then transferred into the N2-filled glovebox and disassembled as quickly as possible (typically within 5 minutes). The positive and negative electrodes were then packed into separate 2.5 mm rotors for solid-state NMR experiments. Excess electrolyte was removed using a small amount of tissue paper, to ensure stable spinning of the sample during the NMR measurements.