钠离子电池硬碳负极表面固体电解质膜的形成机理和稳定性研究

Hard carbon is emerging as one of the most promising anodes for sodium-ion batteries, because of the high reversible capacity, low storage voltage and excellent cycling stability. It is critical for further improving electrochemical properties of hard carbon anodes that understanding the interface behavior of hard carbon anodes during cycling, and the correlation between the formation of a compact，ideally passivated, stable solid electrolyte interphase (SEI) and electrolyte components. Therefore, it is necessary to study basic problems involved with the SEI. In this project, we will investigate the formation mechanism and stability of the SEI on the hard carbon anodes, and the SEI formation processes of the hard carbon anodes with different surface characteristic, discuss how the hard carbon surface influences the SEI formation, thus providing the better guidance for the electrolyte optimization and hard carbon modification. Hard carbon membranes will be used as anodes in this project to avoid the effect to SEI formation from binder and conductive additive. Moreover, TGA/DSC-GC/MS techniques will be used to analysis thermostability of the SEI, and it also provides the ability to analysis thermal decomposition products that assist in defining SEI components.

无序性的硬碳材料由于具有高的可逆容量、低的钠储存电位和良好的循环稳定性等优点，被认为是最具有应用前景的钠离子电池负极材料。理解硬碳负极材料在电解液中的界面行为，进而理解硬碳材料表面形成致密、完整和稳定的固体电解质膜(SEI)与电解液成分的关系，是进一步提高硬碳材料性能的关键。本项目拟系统地研究钠离子电池中硬碳负极表面SEI膜的形成、反应机理、以及SEI膜的稳定性，探索硬碳电极表面特性对SEI膜的影响，为下一步电解液的组分优化、硬碳材料的形貌设计及表面改性研究提供思路和指导。为消除粘结剂和导电添加剂对SEI膜生长及成分分析的影响，提高结果可靠性及对硬碳材料表面SEI膜本征特性更清楚的认识，本项目中将直接采用硬碳膜作为负极进行SEI膜研究，同时将采用热重/差热-色谱/质谱联用系统，解析SEI膜热分解过程及分解产物，反推其成分，更加清楚地认识SEI膜的组分。

硬碳负极材料由于具有资源丰富、可逆容量高和良好的循环稳定性等优点，在钠离子电池中具有广泛的应用前景。工作过程中，硬碳负极和电解液界面会不可避免地生成固体电解质膜（SEI），而SEI对电池的电化学性能和安全性能等都具有重要影响。为避免粘结剂和导电添加剂对SEI生长和成分分析的影响，本项目直接采用硬碳膜作为研究电极，系统研究了SEI膜的形成过程和稳定性，获得了一些有意义的研究成果。钠离子电池中硬碳表面的SEI的成分主要包含PEO类低聚物、RCO3Na等有机物和Na2CO3、NaF、NaxPOyFz和NaxPFy等无机物。无机成分含量明显高于有机成分，靠近硬碳电极一侧以无机成分为主，而靠近电解液一侧主要是有机物。电解液的组分对SEI的形成过程和成分都有极其重要影响，20% DMC的添加，促进了更多Na2CO3等无机成分的生成。此外，硬碳的表面状态也会影响SEI的形成，相对低温碳化的硬碳具有更丰富的表面，且表面具有更多的缺陷和杂原子，这些都会促进SEI的生长。