尖晶石锰酸锂正极在Water-in-salt电解液中的电化学性能

Electrochemical performance of spinel LiMn2O4 in Water-in-salt aqueous electrolyte

尖晶石型锰酸锂正极作为一种主流的水系锂电池正极材料被广泛用于水系锂离子电池,研究表明其电化学性能高度依赖于锰酸锂材料自身化学组分、颗粒尺寸、形貌和晶体结构等材料属性。本文针对性选取了LiMn2O4、铝掺杂LiAlxMn2-xO4、富锂Li1+xMn2-xO4三种典型的尖晶石型锰酸锂,通过一系列分析、表征手段研究循环前后其晶体结构、材料形貌以及化学组分的变化,探究在高盐浓度Water-in-salt电解液中3种材料电化学性能不同的原因。研究发现充放电时未经处理的尖晶石LiMn2O4因为严重的Mn溶解和Jahn-Teller效应产生了不可逆的相变和形貌变化,容量衰减严重,循环性能差;铝掺杂一定程度上抑制了尖晶石锰酸锂的Jahn-Teller畸变,但不能完全解决Mn溶解和晶格变形问题,也存在较严重的容量衰减;富锂Li1+xMn2-xO4可以有效抑制尖晶石锰酸锂在水系电解液中的Mn溶解和Jahn-Teller畸变,晶体结构稳定,综合电化学性能好,适合用于水系锂离子电池,提高其整体电化学性能。

Spinel LiMn2 O4 cathode is widely used in aqueous lithium-ion batteries whose electrochemical performance are highly dependent on its material properties including the chemical composition, particle size, morphology, crystal structure and so on. In this study, we objectively investigate three typical kinds of spinel LiMn2 O4: pure LiMn2 O4, LiAlxMn2-xO4, and Li1+xMn2-xO4 respectively in super-high concentrated aqueous electrolytes. The evolution of crystal structure, morphology and chemical composition with the cycles carefully investigate by a series of chemical analysis(ICP), crystal structure(XRD), morphology characterization(TEM, SEM) and multiple electrochemical methods(EIS, CV) whose influence on the electrochemical performances is discussed detailly. It is discovered that pure LiMn2 O4 is prone to Mn dissolution and Jahn-teller distortion resulting in the irreversible phase transitions and structure detraction thereby leading to severe capacity fading;the trace amount of Al3+doping in LiMn2 O4 enables to suppress the Jahn-Teller effect of Mn to a certain extent but cannot avoid completely Mn dissolution and lattice deformation whose cycling fading still exists evidently;compared with above-mentioned two kinds of cathodes,lithium-rich Li1+xMn2-xO4 presents much better electrochemical performance because the introduction of excessive Li in the crystal structure is favorable to effectively inhibit Mn dissolution and suppress JahnTeller distortion, thereby, it is suggested as an ideal cathode candidate for aqueous lithium ion battery.