Sustainable Aqueous Batteries Based on Bipolar Dissociation of Aluminum Hydroxyacetate Electrolyte

Rechargeable aqueous batteries are potential systems for large-scale energy storage due to their high safety and low cost. However, developing aqueous batteries with high sustainability, affordability, and reversibility is urgent and challenging. Here we report an amphoteric aluminum hydroxyacetate (AlAc(OH)₂) electrolyte with the ability of bipolar ionization of H⁺ and OH^-, which facilitates the redox reactions at both the anthraquinone (AQ) anode and nickel hydroxide (Ni(OH)₂) cathode. The bipolar ionization ability of the AlAc(OH)₂(H₂O)₃ solvation structure results from the strong polarization ability of Al³⁺ and OH^-. The H⁺/OH^- dissociation ability with a dissociation constant of 5.0/3.0 is stronger than that of water (14.0), which boosts the simultaneous stable redox reactions of electrodes. Specifically, H⁺ uptake prevents the AQ anode from the formation of an ionic bond, suppressing the electrode dissolution, whereas OH^- provides the local alkaline environment for the stable conversion reaction of the Ni(OH)₂ cathode. The AQ anode in the designed AQ||Ni(OH)₂ battery delivers a discharge capacity of 243.9 mAh g^-1 and a capacity retention of 78.2% after 300 cycles with high reversibility. Moreover, a pouch cell with a discharge capacity of 0.90 Ah was assembled, exhibiting an energy density of 44.7 Wh kg^-1 based on the total mass of the battery. This work significantly widens the types of aqueous batteries and represents a design philosophy of bipolar electrolytes and distinct electrochemical reactions with H⁺ and OH^-.