富勒烯构建动力锂离子电池复合SEI膜及其性能研究

Currently, the main obstacles for commercialization of power Li-ion batteries come from safety, capacity, cyclic life et al. Solid electrolyte interface (SEI) takes a critical influence on the performance of Li-ion batteries, and also acts as the key point to solve above-mentioned problems. The systemic study on SEI film is one of the effective ways to solve the embarrassment faced by power lithium battery. For example, the first reaction is the decomposition of SEI film at the beginning of the thermal runaway of batteries. To obtain a high-performance SEI film now are focused on the fields of surface modification to anode materials or selecting more suitable lithium salts, solvents, additives et al. Fullerenes show a unique geometry and electronic structure, and have been used in many commercialized products such as cosmetic, cues of golf. Fullerene-coated Silicon anodes exhibit an excellent electrochemical performance, especially the cyclic property. Thus this project propose to build a composite SEI film with a polymerized fullerene film as its backbone, and then systematically study the relationship between the component, structure of SEI film and the performances of battery. Thermo-induced or electro-induced polymerizing a layer of fullerene film or fullerene/polymer film was coated on the surface of anode materials, such as graphite and silicon. The composition and structure of polymerized fullerene film and composite SEI film will be examined with infrared, Raman, NMR and other similar spectra. And DSC, TGA and AFM and other equipments would be used to study the thermal stability and mechanical properties of the composite SEI film. Toward the future application of composite SEI film and developing the theory of interfacial Li-ion activity, we should study (1) the effects of polymerized fullerene film and composite SEI film on battery performances in safety, cyclic life, storage, etc; (2) the effects of these two films on the electrochemical activities of anode surface; and (3) the possible mechanism of Li-ion transference through these two films.

固体电解质界面膜(SEI膜)对锂电池的性能有着至关重要的影响，对其深入的研究也是解决动力锂电池所面临诸多难题的有效途径之一。目前SEI膜的研究主要集中在材料表面的改性和寻找更好的锂盐、溶剂、添加剂等领域。富勒烯分子具有独特的几何、电子结构，用它包覆的电极材料表现出优异的电化学性能，因此本课题拟以富勒烯聚合物为骨架构建复合的SEI膜，并系统的研究其组成、结构与性能之间的关系：采用热聚合、电化学聚合等方式在碳基、硅基两类负极材料表面聚合一层富勒烯聚合物膜或富勒烯/高分子的共聚膜，借助红外、拉曼、核磁、阻抗等手段检测聚合膜和复合SEI膜的组成和结构，借助DSC、TGA、AFM等设备研究其热稳定性和机械性能，找出富勒烯聚合膜、复合SEI膜对电池安全、循环、存储等性能的影响，探索复合SEI膜对电极界面电化学行为的影响以及锂离子的传输机制，丰富锂电池界面研究理论，为复合SEI膜的应用提供理论支持。

锂离子电池的固体电解质界面膜(SEI)结构复杂，但对电池的性能有着举足轻重的影响。通过构建人工组分，进而研究SEI膜的形成机理，对理解SEI膜有很大帮助。我们借助于富勒烯这一直径约为0.7nm的笼状分子，在电极材料表面构筑一层富勒烯分子，然后在充放电过程中形成富勒烯复合的SEI膜。这种复合结构的SEI膜在强度和热稳定性方面优于原生的SEI膜。这种优越性具体表现在电化学方面的性能提高。由于其结构稳定，对材料保护充分，因而使得材料的充放电循环稳定性得到了大幅度的提高：(一)在Pt基底材料上实现了富勒烯的聚合，聚合薄膜的厚度大约在12μm左右，薄膜是由微米级的富勒烯聚合颗粒组成。颗粒之间有缝隙，有利于实现构建人工复合SEI膜。(二) 对隔膜材料进行表面处理，然后修饰离子导电聚合物，发现这种修饰后的隔膜对LiFePO4和富锂锰基正极材料的放电容量及循环性能均有较大幅度的提高。EIS分析结果说明修饰层对SEI膜的形成和性质有帮助。(三)采用双功能模版剂制备高容量和高首次效率的富锂锰层状氧化物：放电比容量高达308 mAh/g并且首次库仑效率达到85%。然后对富锂锰基正极材料进行富勒烯C60的修饰，使得材料的容量衰减得到充分的抑制，循环性能得到大幅度的提高。相关研究成果发表在ACS Applied Materials & Interfaces、Journal of Power Sources等SCI一区杂志上，并在第十八届全国电化学会议上对研究成果作口头报告。