Extended Data Fig. 3: Cycling performance of Na/Cl₂ battery at different capacities.

a, Cycling performance of a Na/Cl₂ battery at 500 mAh g⁻¹ (150 mA g⁻¹). The battery was kept at open circuit in a discharged state for two weeks. We found that simply aging the battery in the discharged state for days could improve the battery’s cycle life, probably due to the slower formation of a more uniform SEI layer on the electrode. The loading of aCNS was about 4.5 mg cm⁻². b, Na/Cl₂ battery cycling at 1,200 mAh g⁻¹. The electrolyte was 4 M AlCl₃ in SOCl₂ + 1 wt% NaFSI + 1 wt% NaTFSI. c, Na/Cl₂ battery cycling at 1,200 mAh g⁻¹. The electrolyte was 4 M AlCl₃ in SOCl₂ + 2 wt% NaFSI + 2 wt% NaTFSI. Both of the batteries in b, c were first cycling at 500 mAh g⁻¹ (150 mA g⁻¹) for 15 cycles and the cycling capacity was gradually increased to 1,200 mAh g⁻¹ with 150 mA g⁻¹ and 100 mA g⁻¹ currents. The loading of both batteries was about 2.6 mg cm⁻². d, Cycling performance of Na/Cl₂ battery as the charging current increased from 0.3 C (150 mA g⁻¹) up to 3.9 C (1,950 mA/g⁻¹) with 0.3 C (150 mA g⁻¹) increased for every five cycles. The discharge current was kept at 0.3 C (150 mA g⁻¹). The loading of aCNS was about 3 mg cm². e, Cycling performance of Na/Cl₂ battery at 1,200 mAh g⁻¹ with charging current increased to 0.5 C (600 mA g⁻¹) and discharging current kept at 0.08 C (100 mA g⁻¹). Cycles 1–3: 0.0625 C (75 mA g⁻¹), cycles 4 and 5: 0.08 C (100 mA g⁻¹) for battery stabilization. The loading of the battery was about 3 mg cm⁻². f, Typical charge–discharge curves of Na/Cl₂ battery at 1,200 mAh g⁻¹. Black curve: 0.5 C (600 mA g⁻¹) charging, 0.08 C (100 mA g⁻¹) discharging. Red curve: 0.08 C (100 mA g⁻¹) charging and discharging. Only a slight increase in overpotential (about 182 mV at 0.08 C versus about 298 mV at 0.5 C) was observed. The loading of the battery was about 3 mg cm⁻².