A novel aqueous K 2 CO 3 electrolyte enables high performance of FeS anodes in Ni–Fe batteries at both room and elevated temperatures

Fe-based electrodes in conventional KOH electrolytes are prone to chemical corrosion and surface passivation, which cause progressive deterioration of active substances and a rapid decline in cycling stability. Herein, we propose a novel aqueous K₂CO₃ electrolyte that enables FeS to exhibit excellent electrochemical performance at both room and elevated temperatures when used as an anode material in Ni-Fe batteries. The FeS electrode in a 5.8 M K₂CO₃ electrolyte delivers specific capacities of 590.0 mAh g^-1 at 25 °C and 591.3 mAh g^-1 at 80 °C at a current density of 300 mA g^-1 and exhibits capacity retention rates of 99.47% and 99.88% after 300 cycles, respectively. Even at a high current density of 1 A g^-1, the FeS electrode exhibits reversible capacities as high as 540.4 and 564.7 mAh g^-1 at 25 and 80 °C, respectively.