Proton Donation and Surface Armor Effects of Aluminum Ion Additive Enabling Long‐Life and High‐Voltage Aqueous Proton Batteries

Abstract Aqueous proton batteries (APBs) have been regarded as promising candidates for large‐scale energy storage owing to their environmental friendliness and intrinsic safety. However, the commonly‐used strong acid electrolytes in APBs often lead to dissolution and corrosion of the electrodes. To address these challenges, a new mildly acidic CH 3 COONa electrolyte with Al 2 (SO 4 ) 3 addition is proposed for stable APBs. The Al 3 ⁺ additive in APBs plays a dual role of both proton donors to continuously sustain proton supply for working electrodes and the formation of cathode‐electrolyte interphases (CEI) on the cathode surface to prevent the dissolution and structural collapse of electroactive materials. The Co–Ni double hydroxide (CoNiDH) material exhibits a proton‐dominated charge storage mechanism in the hybrid electrolyte with a high discharge capacity of 230 mAh g −1 with excellent rate capability. Additionally, an APB assembled with the hybrid electrolyte achieves a high cell voltage of 2.2 V, an impressive energy density of 94.7 Wh kg −1 , and a prolonged cycling life of over 8500 cycles, outperforming most reported APBs. This mild electrolyte design is highly expected to broaden the range of electrode materials suitable for APBs, providing new opportunities for the development of high‐performance aqueous batteries.