Improved Low‐Temperature Performance of Rocking‐Chair Sodium‐Ion Hybrid Capacitor by Mitigating the De‐Solvation Energy and Interphase Resistance

Abstract Hybrid capacitors, which bear the advantages of secondary batteries and supercapacitors, can deliver high power with a relatively fair amount of energy. However, its kinetic performance, especially at low temperatures, is strongly limited by the battery‐type electrode and electrolyte. In this work, Na‐ion, which has a lower solvation energy than Li‐ion, is chosen as the charge carrier to build the hybrid capacitor. A sodium‐ion hybrid capacitor is built with an activated carbon cathode and a pre‐sodiated hard carbon anode. To achieve a better kinetic performance, the de‐solvation energy and interphase resistance is decreased through replacing conventional carbonate electrolyte with a diethylene glycol dimethyl ether (DEGDME) based electrolyte. As a result, the sodium‐ion capacitor delivers an energy density of 42 Wh kg^–1 and a high power of 4565 W kg^–1 for 3000 cycles at 2.5 A g^–1. Furthermore, this capacitor could sustain an energy density of 36 Wh kg^–1 at the low temperature of −30 °C and maintain 70% of the capacity after 500 cycles. The strategies of reducing de‐solvation energy and optimizing the solid electrolyte interphase property offers a clear path for developing electrochemical energy storage devices at lower temperatures.