Anion intercalation into graphite from a sodium-containing electrolyte

The stability of aluminum and nickel as a current collector was investigated at high potentials in the presence of 0.5 M NaPF6 or 0.1 M NaBF4 dissolved in EC:DEC (1:1 wt.-%). Cyclovoltammetry showed that nickel is unstable under experimental conditions, whereas aluminum is electrochemically stable and can be used as a current collector. The feasibility of sodium-based dual-ion cells was studied with self-prepared graphite electrodes in the presence of both electrolytes. The cells showed a fairly stable reversible specific capacity of 15 mAh/g for NaBF4 and 55 mAh/g for NaPF6.