An organic acid-alkali coordinately regulated liquid electrolyte enables stable cycling of high-voltage proton battery

Protons are seen as promising charge carriers in next-generation energy storage systems due to their extremely small ion radius, high natural abundance, and environment friendliness. However, the limited electrochemical window of aqueous electrolytes severely restricts the energy density of proton batteries and the option of electrode material. Herein, an organic acid-alkali coordinately regulated liquid electrolyte comprising of organic acid bis(trifluoromethane sulfonyl)imide (HTFSI), organic alkali 1-methyl-1,2,4-triazole (MTA) and organic solvent tetramethylene sulfone (TMS), noted as HTFSI-MTA-TMS, was investigated, and exhibited a stable electrochemical window over 4 V and good compatibility with inorganic electrodes. Benefiting from this, the oxide cathode (Ni0.6Co0.2Mn0.2)xOy-Nb was for the first time described to show a reversible proton storage ability, high reduction potential (0.72 V vs Ag/Ag+) and good cycling stability in this electrolyte. Consequently, the assembled (Ni0.6Co0.2Mn0.2)xOy-Nb//MoO3 button-type proton full battery exhibited a stable operating voltage window over 1.8 V, a clear discharge platform at 1.3 V, an initial discharge specific capacity of 120 mAh/g at 1 A/g, and a good long-term cycling stability (70 % capacity retention after 10,000 cycles). These findings demonstrate that the HTFSI-MTA-TMS electrolyte can endow proton batteries with distinctive high-voltage characteristics and favorable electrochemical stability, which will promote the research and development of high-voltage proton batteries.