Suppressing Cu-based cathode dissolution in rechargeable aqueous zinc batteries with equilibrium principles

Abstract

Cathode materials with conversion reaction would offer higher theoretical capacities than intercalation-type materials. Copper-based materials can undergo two electron transfers from the redox couples of Cu2+/Cu+ and Cu+/Cu, which at the same time provides desirable redox potentials as cathode materials for aqueous zinc batteries. However, most Cu2+ components are soluble in water, leading to the continuous loss of active material and capacity decay upon cycling. Herein, we prevent Cu2+ dissolution with fundamental equilibrium principles. The CuO cathode experiences rapid capacity decay within few cycles in conventional zinc electrolytes upon the formation of soluble charged products. The dissolution equilibrium is effectively shifted to the left by increasing the concentration of the associated anion TFSI- in the electrolyte of 21 m LiTFSI + 1 m Zn(TFSI)2, and Cu2+ is confined in the cathode in the forms of Cu(TFSI)2 and CuO. A stable capacity retention of 91.2% realized after 300 cycles, and the stable evolution of differential capacity curves furthermore demonstrates the well-preserved energy storage process. A good capacity of 180 mAh g−1 is achieved at 100 mA g−1. This work provides a feasible strategy to suppress active material dissolution and highlights the potential utilization of copper-based conversion cathode materials for aqueous zinc batteries.