Cation-disordered rocksalt cathode for anode-free zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (ZIBs) suffer from sustained capacity loss at the zinc metal anode due to side reactions with the electrolyte, even under idle conditions. The concept of an anode-free ZIB would address this degradation by eliminating the metal anode source. A key requirement for such systems is a cathode that contains zinc in its pristine state and supports initial charging. Here, we report the synthesis and characterization of cation-disordered rocksalt (DRX) ZnMnO₂, a new cathode material suitable for anode-free ZIBs. ZnMnO₂ meets the essential criteria for anode-free operation of natively containing Zn in the pristine state, enabling an initial charge, as well as offering high initial charge capacity (312.8 mAh g⁻¹), and discharge voltage (1.36 V). We show that the dominant energy storage mechanism involves Mn dissolution and redeposition, with a smaller contribution arising from reversible Zn intercalation into a spinel phase that forms in situ during cycling. We further demonstrate the versatility of DRX cathodes by extending the concept to ZnFeO₂. These findings establish DRX materials as a promising platform for the development of cathodes suitable for anode-free ZIBs.