High Power and Energy Density Aqueous Proton Battery Operated at −90 °C

Abstract Freezing electrolyte and sluggish ionic migration kinetics limited the low‐temperature performance of rechargeable batteries. Here, an aqueous proton battery is developed, which achieves both high power density and energy density at the ultralow temperature conditions. Electrolyte including 2 m HBF 4 + 2 m Mn(BF 4 ) 2 is used for the ultralow freezing point of below − 160 ° C and high ionic conductivity of 0.21 mS cm −1 at − 70 ° C. Spectroscopic and nuclear magnetic resonance analysis demonstrate the introduction of BF 4 − anions efficiently break the hydrogen‐bond networks of original water molecules, resulting in ultralow freezing point. Based on H + uptake/removal reaction in alloxazine (ALO) anode and MnO 2 /Mn 2+ conversion in carbon felt cathode, the aqueous proton battery can operate regularly even at − 90 ° C and obtain a high specific discharge capacity of 85 mA h g −1 . Benefiting from the rapid diffusion of proton and the pseudocapacitive character of ALO electrolyte, this battery shows a high specific energy density of 110 Wh kg −1 at a specific power density of 1650 W kg −1 at − 60 ° C. This work presents a new way of developing low‐temperature batteries.