Electrochemical Storage of Ammonium Versus Metal Ions in Bimetallic Hydroxide for Sustainable Aqueous Batteries

Abstract Aqueous batteries with high safety and cost efficiency usually employ metallic cations as charge carriers. Recently, ammonium (NH₄⁺) ion batteries using the nonmetal NH₄⁺ as a charge carrier exhibit distinct electrochemical features from conventional aqueous batteries. Herein, the electrochemical performances of a bimetallic hydroxide material are systematically studied with different charge carriers in the electrolytes, including NH₄⁺, as well as the conventional monovalent metallic cations K⁺ and Na⁺, respectively. Electrochemical results indicate that the charge storage process using NH₄⁺ as the working ions exhibits a higher discharge plateau, smaller electrochemical polarization, and larger discharge capacity than that using conventional metallic charge carriers. Experimental characterizations and theoretical calculations suggest that the strong interaction between NH₄⁺ and the electrode material, as well as the low NH₄⁺‐ion diffusion barrier lead to these superior electrochemical features. The assembled NH₄⁺‐ion battery exhibits a good energy density of 123 Wh kg_{(cathode+anode)}⁻¹ at the power density of 480 W kg_{(cathode+anode)}⁻¹. These fundamental findings are important for developing good safety, low‐cost, and high‐energy aqueous batteries with sustainable NH₄⁺ charge carriers.