Fig. 4.

a The rate capability of Na symmetric batteries with different electrolytes. b Charge–discharge curves of the double layer capacitor. c EIS of symmetric cells after different cycles at − 20 °C. d Voltage–time curve of a Na symmetric cell. e Cycling performance of the Na-CO₂ batteries with ether-[C₄C₁im][BF₄] electrolyte from − 20 to 25 °C. f dQ/dV curves and g full discharge–charge curves of Li-CO₂ batteries. h Median voltage and voltage gap of Li-CO₂ battery with CoPc across a wide-temperature range. i Rate performance working at − 20 and 60 °C