关键词: 高电压镍锰酸锂, 正极/电解液界面, 本征性质, 固体电解质界面, 电解液氧化分解, 表面膜

Abstract:

To obtain high energy density, developing high-voltage cathode materials is an effective approach. The cathode/electrolyte interface stability is the key factor for the cycle performance and safety performance of high-voltage lithium ion batteries. It is, therefore, of significant importance to study the stability of cathode/electrolyte interface. However, many reports have shown that at the cathode/electrolyte interface the cathodes were prepared by coating the mixture of active materials with a conductive additive and a binder on an Al current collector. The introduction of additives will interfere the surface morphology and component analyses, resulting in difficulty to acquire the intrinsic information at the cathode/electrolyte interface. In this paper, the LiNi_0.5Mn_1.5O₄ (LNMO) film electrodes were prepared via sol-gel method without using conductive additive and binder. The surface morphology and the intrinsic property of LNMO electrode/electrolyte interface during the charge/discharge process were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Electrochemical impedance spectroscopy (EIS). The results demonstrated that both solvents and LiPF₆ salt degraded during the charge/discharge process. The degradation of LiPF₆ mainly happened at the high-voltage charge process and the intermediate POF₃ was unstable which continued to be reacted during the discharge process. The degraded residues deposit on the surface of LNMO cathode to form a surface film and the compositions of the surface film varied with voltages during the electrochemical process.

Key words: high-voltage LiNi_0.5Mn_1.5O₄ cathode material, cathode/electrolyte interface, intrinsic property, solid electrolyte interphase, oxidized decomposition of electrolyte, surface film