基于SEI膜演化动力学和理化性质研究高电位正极材料LiNi0.5Mn1.5O4表面改性作用机理

Surface modification of high-potential LiNi0.5Mn1.5O4 (LNMO) spinel is one of effective method to improve its cycling performance and rate capability. Electrode/electrolyte interfacial layer, or called solid/electrolyte interphase layer (SEI layer), formed during the decomposition of electrolyte, plays a key role in the electrochemical performance of cathodes. Starting with a comparison on electrochemical oxidation behaviors of electrolyte by various metal oxide and graphene electrodes, the mechanism for the improvement on the performance after surface modification by several typical metal oxides and graphene will be studied in depth especially based on the kinetics of forming and stripping SEI layer and physicochemical characteristics of SEI layer. The inherent relationship between chemical properties of modification layers and electrochemical performance of corresponding surface-modified LNMO will be investigated. Electrochemical quartz crystal microbalance (EQCM) is used to quantitatively investigate the kinetics, and synchrotron radiation spectroscopy is applied to preciously characterize the composition and distribution along depth of the SEI layer..The results of this study can lay a scientific material foundation for the application of LNMO and other 5V class cathodes in new generation advanced Li-ion battery with both high specific energy and specific power, and supply theoretical foundation for the design of surface modification of LNMO and other cathodes.

对高压正极材料LiNi0.5Mn1.5O4尖晶石（LNMO）进行表面包覆改性，是提高其充放电循环稳定性和倍率性能的有效方法之一。鉴于电解液氧化分解所生成的电极/电解液界面膜层(SEI膜)是影响正极材料电化学性能的关键，本项目以多种金属氧化物和石墨烯电极对电解液电化学氧化行为的比较为研究切入点，从表面改性对LNMO表面SEI膜演化动力学及其理化性质影响的角度，研究几种典型金属氧化物和石墨烯改性的作用机理，分析改性层材料化学性质与表面改性LNMO电化学性能之间的内在联系规律。将采用电化学石英微晶天平技术（EQCM），实现SEI膜演化动力学的定量研究；使用同步辐射光谱学技术精确表征SEI膜的成分及沿厚度的分布状态。.研究结果将为以LNMO为代表的高电位正极材料在新一代先进锂离子电池中的应用奠定材料科学基础，还为LNMO和其他正极材料表面改性的设计提供理论依据。

对高压正极材料 LiNi0.5Mn1.5O4尖晶石（LNMO）进行表面包覆改性，是提高其充放电循环稳定性和倍率性能的有效方法之一。鉴于电解液氧化分解所生成的电极/电解液界面膜层(SEI 膜)是影响正极材料电化学性能的关键，本项目从表面改性对LNMO 表面SEI 膜演化动力学及其理化性质影响的角度，研究RuO2、Al2O3两种典型金属氧化物表面改性和石墨烯改性的作用机理，分析改性层材料化学性质与表面改性LNMO 电化学性能之间的内在联系规律。重要研究结果如下：（1）采用溶胶凝胶法成功制得表面改性材料均匀分布且含量可控的RuO2、Al2O3表面改性LNMO，首次提出采用电泳沉积的方法制得石墨烯表面改性LNMO整体电极，首次提出采用添加RuO2-炭黑复合纳米颗粒改性LNMO电极；（2）RuO2能够持续消耗F自由基，这是RuO2改性促使阻抗稳定的SEI膜形成进而提高循环性能的原因，而Al2O3不能持续消耗F自由基，因而其改性未能提高循环性能；（3）150oC处理RuO2含量为5 wt%的改性LNMO，其RuO2改性层呈现连续形貌和部分晶化，此时具有最优倍率性能，20C放电比容量达到47 mAh/g；（4）LNMO电极表面电泳沉积胺基化石墨烯能够有效提高电极循环性能，原因在于胺基基团能消耗电解液中的H+离子，减少LNMO离子溶出；（5）同步辐射X射线吸收谱研究发现SEI膜参与反应所导致的充电态LNMO的表面富锂现象和表面区域的氧失去电子的现象。