Conversion electrochemistry of copper selenides for robust and energetic aqueous batteries

Abstract The development of highly safe and low‐cost aqueous batteries is of great significance in the background of carbon neutrality. However, the practical deployment of aqueous batteries has been plagued due to their relatively low capacity and poor cycling stability. Herein, we propose unique conversion electrochemistry of copper selenides for robust and energetic aqueous charge storage. In situ X‐ray diffraction and operando Raman techniques reveal a reversible transformation from CuSe to Cu₂Se through the intermediates of Cu₃Se₂ and Cu_1.8Se. Such a conversion process activates the redox carrier of Cu²⁺ ion and delivers a remarkable rate capability of 285 mAh g⁻¹ at 20 A g⁻¹ and electrochemical durability up to 30,000 cycles. Furthermore, Cu²⁺ and H⁺ coinsertion chemistry is proposed to facilitate the conversion process. As a proof‐of‐concept, a hybrid aqueous pouch cell coupling CuSe//Zn is capable of affording maximum energy and power densities of 190 Wh kg^–1 and 1366 W kg⁻¹, respectively.