An inverse-spinel Mg2MnO4 cathode for high-performance and flexible aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have gained extensive attention owing to low cost and high safety but their development has reached a bottleneck due to the limited number of suitable cathode materials available. Here, we report an inverse-spinel-structured Mg2MnO4 nanosheet cathode for AZIBs. Mn4+-rich Mg2MnO4 allows remarkable discharge capacity and structure stability. Thus, the Zn//Mg2MnO4 battery exhibits a high discharge capacity of 371.7 mA h g(-1) at 150 mA g(-1) and excellent long-cycle life over 500 and 2000 cycles with no obvious capacity fading at 1500 and 3000 mA g(-1), respectively. Moreover, the Mg2MnO4 electrode exhibits a Zn2+/H+ deintercalation/intercalation mechanism during the charging/discharging process, resulting in fast ion-transfer kinetics. In addition, copolymerized 2-acrylamido-2-methylpropane sulfonic acid-acrylamide (P-APSA) hydrogel electrolyte is utilized to fabricate a flexible Zn//P-APSA//Mg2MnO4 battery. Benefitting from the good compatibility and high adhesion between the P-APSA hydrogel and Zn anode, the battery exhibits impressive electrochemical performance. This work provides an option to design high-performance AZIBs for durable applications.