Beyond Phase Selectivity in Conversion Copper Selenides Cathode through Activated Anionic Redox.

Crystalline phase with variable stoichiometry is a critical lever for controlling ion adsorption and storage mechanisms in battery electrodes. However, overreliance on deliberate phase selection significantly hinders access to most members of the anticipated electrode material family, limiting the utilization of capacity and high-potential redox couples. Herein, we demonstrate that the activated anionic redox can overcome the performance limitations arising from pristine crystalline-phase selectivity, and we validate the strategy in a series of zinc-storage copper selenides with variable stoichiometries (CuySe, y = 0.5-2). Using hexagonal CuSe as an example, we show that once the selenium anionic redox is activated, this most thermodynamically stable yet zincophobic phase achieves a hundred-fold increase in capacity from 4 mAh g-1 to 413 mAh g-1 and a doubled battery voltage. Combined structural and spectroscopic evidence during the in situ electrochemical process reveals that CuSe is reconstructed into the favored phase, interwoven with active selenium (Se0) via nucleophile-induced anionic redox, promoting deep and reversible multielectron conversions that transcend inherent capacity constraints. The anion-anchored phase with selenium redox enables the copper selenide family to operate as a stable, high-capacity cathode in zinc batteries for the first time, with a lifespan reaching 4000 cycles. We also confirm the robust applicability of this strategy to other nucleophilic additives, offering new avenues for revitalizing this long-dormant material family.