Triggering Mixed Cationic-Anionic Redox in Cu_2-xSe Cathodes via Tailored Charge-Carrier for High Energy Density Aqueous Zn Batteries

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 Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn-Cu2-xSe 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 Cu2-xSe (vs Zn2+/Zn, working voltage from approximate to 0.4 to approximate to 1.2 V) but also activates the anionic redox centers of Cu2-xSe (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-)/Se2-) 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 Cu2-xSe cathode), which is approximate to 8.4 times higher than that of conventional Zn-Cu2-xSe batteries, representing an advanced development toward energetic AZBs.