Phase Engineering of Nonstoichiometric Cu_2-xSe as Anode for Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are receiving widespread attention due to their abundant resources, low material cost, and high safety. However, the susceptibility of Zn metal anodes to corrosion and hydrogen evolution limits their further practical applications. Replacing Zn metal with intercalation-type anode material and constructing rocking-chair-type batteries could be an effective way to significantly prolong the cycle life of AZIBs. Herein, we present copper selenide with different crystal phase structures through a facile redox reaction as an anode for AZIBs. By comparing and analyzing different copper selenide phases, it is found that the cubic Cu_2-xSe shows superior structural stability and highly reversible Zn²⁺ storage. Theoretical calculation results further demonstrate that the cubic Cu_2-xSe possesses an increased electrical conductivity, higher Zn²⁺ adsorption energy, and reduced diffusion barrier, thereby promoting the storage reversibility and (de)intercalation kinetics of the Zn²⁺ ion. Thus, the Cu_2-xSe anode delivers a long-term service life of over 15 000 cycles and impressive cumulative capacity. Furthermore, the full-cells assembled with the MnO₂/CNT cathode operate stably for over 1500 cycles at 6 mA cm^-2 at a negative/positive (N/P) capacity ratio of ∼1.53. This work provides a more ideal Zn-metal-free anode, which helps to push the practical applications of AZIBs.