Triggering Mixed Cationic‐Anionic Redox in Cu_2‐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 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 ≈0.4 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 (Sen2−/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 ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

Electrochemical Characterization of Salt-in-Water and Water-in-Salt Zinc Sulfate and Zinc Acetate Electrolytes

“…The lower amounts of water molecules and changes in the state of water molecules lead to the anodic shift of the oxygen evolution onset potential. Start of polarization on the cathodic side is mainly caused by zinc deposition and hydrogen evolution, and anodic peaks for hydrogen oxidation and zinc stripping are observed in some cases in −0.5-(−0.6) V. 41 For 1 m and 1.4 m Zn(OAc) 2 and 1 m and 3 m ZnSO 4 , the high H 2 O/Zn 2+ ratio ensures a sufficient number of free water molecules on the electrode surface, so the hydrogen evolution onset potential is less affected. Table I summarizes the acquired ESW of the different electrolytes.…”

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage

“…The galvanostatic charge and discharge (GCD) and galvanostatic intermittent titration technique (GITT) tests were conducted with LANHE CT2001A (Wuhan Land Electronic Co., Ltd.) battery testing systems. For the GITT test, the current density of 200 mA g –1 was applied for 120 s, and the relaxation time was 120 s. The diffusion coefficient was calculated by the following equation: , where τ refers to the duration of current pulse, L represents the Cu 2+ diffusion length, Δ E s and Δ E t are the steady-state voltage changes caused by the current pulse and the direct change of voltage ( V ) before relaxation, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out on a CHI 760E (Chenhua Instrument Company, Shanghai, China) electrochemical workstation.…”

Advanced cathodes for aqueous Zn batteries beyond Zn2+ intercalation

“…Based on this working principle, other Cu + -based cathodes, including Cu 2 S, Cu 2 O and Cu 2 Se, broaden cathode options for ZBs. 101 Although these monovalent Cu-based cathodes are stable in aqueous media, they exhibit the significant drawbacks of low reversible capacity (<300 mA h g −1 ) and limited cycling stability, limiting wider application. Additionally, the discharge plateau is low at <0.9 V, resulting in a low energy density output in practical application.…”