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 K 0.41 MnO 2 ·0.5H 2 O (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 Zn 2+ 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.