Mg secondary batteries are promising scalable secondary batteries for next-generation energy storage. However, Mg-storage cathode materials are greatly demanded to construct high-performance Mg batteries. Electrochemical conversion reaction provides plenty of cathode options, and strategy for cathode selection and performance optimization is of special significance. In this work, Ni_0.85Se with nanostructures of dispersive hexagonal nanosheets (D-Ni_0.85Se) and flower-like assembled nanosheets (F-Ni_0.85Se) is synthesized and investigated as Mg-storage cathodes. Compared with F-Ni_0.85Se, D-Ni_0.85Se delivers a higher specific capacity of 168 mAh g^‒1 at 50 mA g^‒1 as well as better rate performance, owing to its faster Mg²⁺ diffusion and lower resistance. D-Ni_0.85Se also exhibits a superior cycling stability over 500 cycles. An investigation on mechanism indicates an evolution of Ni_0.85Se towards NiSe with cycling, and the Mg-storage reaction occurs between NiSe and metallic Ni⁰. The present work demonstrates that advanced conversion-type Mg battery cathode materials could be constructed by soft selenide anions, and the electrochemical properties could be manipulated by rational material morphology optimization.

镁二次电池有望用于下一代储能的可扩展二次电池。但是，对于构造高性能的Mg电池非常需要Mg储存阴极材料。电化学转化反应提供了大量的阴极选择，并且阴极选择和性能优化的策略具有特殊的意义。在这项工作中，镍_0.85硒与色散六边形纳米片的纳米结构的（d-Ni系_0.85 SE）和花状纳米片组装（F-Ni系_0.85 Se）的合成和研究作为Mg的存储阴极。与F-镍相比_0.85硒，d-Ni系_0.85硒提供的168毫安g的较高的比容量^-1在50mA克^-1由于其更快的Mg ²⁺扩散和较低的电阻，因此具有更高的速率性能。D-Ni _0.85 Se在500个循环中也表现出优异的循环稳定性。机理研究表明，Ni _0.85 Se随着循环而向NiSe方向析出，并且在NiSe与金属Ni ⁰之间发生Mg储存反应。目前的工作表明，先进的转化型镁电池正极材料可以由软硒化物阴离子构成，电化学性能可以通过合理的材料形态优化来控制。