Electrochemically Activated Cu_2–xTe as an Ultraflat Discharge Plateau, Low Reaction Potential, and Stable Anode Material for Aqueous Zn-Ion Half and Full Batteries

The utilization of Zn anodes to build aqueous Zn–metal batteries has captured extensive attention in the domain of energy storage, but this task faces scientific challenges, such as Zn dendrites and unsatisfactory stripping/plating efficiency as well as gas evolution. Herein, cation-deficient Cu_2–xTe (Cu_1.81Te) is proposed as an attractive intercalated anode material for aqueous Zn-ion batteries. It delivers an ultraflat discharge plateau of 0.2 V (vs Zn²⁺/Zn) and a capacity of 158 mAh g⁻¹, of which 86% capacity is contributed from the discharge plateau at 0.2 V. Moreover, it shows superior cyclability with 100% capacity retention over 2000 cycles at 2.5 C (1 C = 242 mA g⁻¹). Experimental characterization reveals that it undergoes sequential insertion and conversion mechanism: Zn²⁺ is first inserted into the Cu_2-xTe which is further converted into Cu and ZnTe. Theoretical calculations demonstrate that the crystal defects in Cu_2–xTe can manipulate the electronic structure to enhance reactivity and simultaneously reduce diffusion barriers. Moreover, an aqueous “rocking-chair” Cu_2–xTe//Na₃V₂(PO₄)₃Zn-ion full battery is demonstrated. It delivers an energy density of 58 Wh kg⁻¹ with a voltage output of 0.98 V, and keeps 92% capacity retention after 1000 cycles. This research provides an ultralow discharge plateau and stable anode material for aqueous Zn-ion batteries.