Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

Abstract The further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually <1 V vs Zn 2+ /Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu 2‐x Se battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu 2‐x Se (vs Zn 2+ /Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu 2‐x Se (capacity release from 143.4 to 323.2 mAh g −1 at 0.4 A g −1 ). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Se n 2− /Se 2− ) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg −1 at 240 W kg −1 is implemented (calculated based on the mass of Cu 2‐x Se cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu 2‐x Se batteries, representing an advanced development toward energetic AZBs.