Water cointercalation for high-energy-density aqueous zinc-ion battery based potassium manganite cathode

Aqueous zinc-ion batteries (ZIBs) are gaining widespread attention owing to their intrinsic safety and low cost. However, it is still a challenge that finding robust cathode materials to build a high-energy-density aqueous ZIBs. Here, we synthesize a novel layered K0.41MnO2·0.5H2O (KMO) cathode material for aqueous ZIBs. The constructed Zn//KMO battery shows an ultrahigh discharge capacity of 425 mAh g−1 and a remarkable energy density of 503 Wh kg−1 at 175 mA g−1, as well as an good durability over 1500 cycles with no obvious capacity fading. A comprehensive study suggests that the water molecules can intercalate into layered KMO with H+ and Zn2+ ions during discharging process. The co-intercalating water not only facilitates ions insertion, but serves as pillars to stabilize the structure of KMO. This work demonstrates the mechanism about water cointercalation and provides a way for designing high-energy-density aqueous ZIBs. •The layered K0.41MnO2·0.5H2O is used as cathode for aqueous zinc-ion battery.•The Zn//K0.41MnO2·0.5H2O battery shows a remarkable energy density of 503 Wh kg−1.•The co-intercalation mechanism of water molecules, H+, and Zn2+ ions is confirmed.•Co-intercalating water can facilitate ions insertion and serve as pillars.