A high-rate and ultrastable anode for lithium ion capacitors produced by modifying hard carbon with both surface oxidation and intercalation

Due to the difference of energy storage mechanisms between the anode and cathode materials, the power density or rate performance of a lithium-ion capacitor is greatly limited by its anode material. Hard carbon is a promising anode material for lithium ion capacitors, and its modification is an important way to improve the electrochemical performance of lithium-ion capacitors. A commercial hard carbon from Kuraray Inc was modified by oxidation followed by intercalation with ZnCl₂ (ZnCl₂―OHC). The reversible capacity of a half-cell prepared using this material was 257.4 mAh·g⁻¹ at 0.05 A·g⁻¹, which is obviously higher than the unmodified one (172.5 mAh·g⁻¹). The capacity retention of a full cell prepared using ZnCl₂―OHC as the anode and activated carbon as the cathode reached 43.3% when the current density increased from 0.1 to 10 A·g⁻¹, which is more than twice that of the untreated hard carbon. After 5 000 charge-discharge cycles at 1 A·g⁻¹, the capacity retention of the full cell was about 98.4%. The modification of hard carbon by surface oxidation and intercalation is therefore a promising way to improve its anode performance for lithium ion capacitors.