Aqueous proton battery stably operates in mild electrolyte and low-temperature conditions

Abstract

The electrode based on the conversion reaction of Mn²⁺/MnO₂ is regarded as a promising cathode for aqueous proton batteries (APBs) due to its high redox potential and cost-effectiveness, but it needs a strongly acidic medium to trigger this redox reaction. Herein, a mild perchlorate-based electrolyte without strong acid addition (3.5 M Mn(ClO₄)₂) is proposed to improve the deposition/dissolution efficiency of Mn²⁺/MnO₂. Comprehensive analyses confirm that the ClO₄⁻ anion not only ensures the fast and stable deposition of Mn²⁺ by regulating the solvation energy of Mn²⁺ but also accelerates the dissolution of MnO₂ by improving the degree of freedom of water molecules. Hence, the novel aqueous proton battery with a carbon felt (CF) cathode, polyaniline anode and 3.5 M Mn(ClO₄)₂ electrolyte exhibits a lifetime of 500 cycles with an 81.6% capacity retention rate and excellent rate capability of up to 100C (18 A g⁻¹). Surprisingly, this system operates well even at low-temperature conditions because of the anti-freezing electrolyte with a −122 °C freezing point. High discharge capacities of 112 mA h g⁻¹ and 52.9 mA h g⁻¹ are obtained at −50 °C and −70 °C, respectively.