Non-layer-transformed Mn3O4 cathode unlocks optimal aqueous magnesium-ion storage via synergizing amorphous ion channels and grain refinement

Aqueous rechargeable magnesium ion batteries (ARMBs) have obtained more attention due to the two electrons transfer nature, low cost and safety. However, the scarcity of cathode materials seriously hinders the development of ARMBs because of the unfavorable strong interaction between Mg2+ and cathode material. Herein, we choose a pre-treated spinel Mn3O4 cathode for aqueous Mg2+ storage. The pretreatment in Na2SO4 solution induces the grain refinement decorated with tortuous amorphous ion diffusion channels, facilitating the production of electrochemical reaction active sites and the diffusion of Mg2+, respectively, which achieve a (sub-)surface pseudocapacitance reaction between Mn (II) and Mn (III). As a result, the pre-treated Mn3O4 cathode exhibits a package of optimal performances, i.e., a capacity of 98.9 mAh g(-1) and a high capacity retention rate of 99.4% after 2000 cycles. To the best of our knowledge, our work not only provides a new reaction mechanism of spinel Mn3O4 in aqueous batteries system, but also affords a high cycle stability electrode material for rechargeable Mg2+ energy storage. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.