三维预留孔容碳/纳米硅复合锂电负极材料的结构设计与性能研究

The unmanageable volumetric expansion of Si upon Li+ insertion results in drastic and fast capacity fading, dampening the prospect of exploiting the high capacity Si possesses for lithium ion batteries. To solve this issue, we design a new kind of nano Si-C anode materials with three-dimensional presetting porous structure. The material includes highly conductive carbon as the structural support as well as the component to facilitate effective charge transport. Nano-scale Si particles can be homogeneously distributed in the carbon in such a way that three-dimensional presetting porous structure with a large amount of void spaces can be prepared. The three-dimensional presetting pores can be used as buffered spaces during charge/discharge and offer two distinct advantages, to guarantee the dispersion of Si particles and to prevent the destruction of carbon matrix, resulting in the superior cyclic performance. In this project, comprehensive methods of surface modification of nano Si, encapsulation of SiO2 template and co-pyrolysis of organic carbon are employed for the preparation of materials. The formation mechanism of the three-dimensional presetting pores and the influence of reaction conditions on the performance of the compound electrodes will be studied, and then the optimum techniques of nano Si-C anode materials can be obtained. The transmission of Li+ in the novel electrodes and its energy storage mechanism will be also researched, and eventually a theoretical model describing the dynamic behavior of the novel Si-C electrode will be presented. The research work in this project will put forward on theoretical basis of the design and application of new lithium ion batteries with large capacity, high power and long cycle life.

硅在锂嵌入时的巨大体积变化限制了其在锂离子电池中的实际应用，为解决该问题，项目提出了一种具有三维预留孔容结构的锂离子电池用碳/硅复合负极材料。该复合负极以具有高导电率和稳定结构的碳材料作为基体，分散地容纳高容量纳米硅，在每一颗或几颗纳米硅周围预留有合适的三维膨胀空间，使硅的膨胀与收缩均发生在自身周围的小区域内，这样既保证了硅颗粒在碳基体中的独立分散性，又可防止硅的膨胀应力破坏碳基体，从而得到结构稳定的电极。项目将结合表面修饰技术、二氧化硅模板包覆技术和有机碳共热解技术来制备该复合负极；重点研究三维预留孔容形成的反应机理与动力学，揭示合成条件对材料理化性能的影响规律，找到具有高容量与优异循环性能复合负极的制备工艺；研究锂离子在电极中的传输行为与规律，阐明其储能机理，建立该新型负极在锂离子电池体系中的工作模型。项目的研究，可为设计高容量、高功率及长寿命新型锂离子电池奠定理论基础与实践指导。

为解决锂离子电池用高容量硅负极存在的在充放电过程中由于体积膨胀而结构坍塌，进而引起活性物质失效的问题，本项目提出一种具有三维预留孔结构的硅碳复合负极材料。项目综合利用纳米硅表面修饰技术、二氧化硅模板包覆技术和有机碳共热解技术成功制备了该复合负极材料。重点研究了纳米Si修饰、Si@SiO2核壳结构、Si@SiO2/C三层核壳结构与Si/C预留孔结构等关键形成步骤。通过研究合成条件对负极材料理化性能的影响，得到了优化的工艺条件，建立了预留孔结构硅碳负极材料的脱嵌锂力学模型。此外，项目还利用预留孔空间的设计思路制备了三维结构石墨烯以及其他同类型高容量电极材料，并研究其在锂离子电池中的应用。实验结果证明了碳基体中的预留孔结构由于具有高效的导电网络和稳定的结构，且可以很好地容纳充放电过程中的体积膨胀，对硅、锡、硫等高容量锂电电极材料具有优良的改善作用，可以得到容量高、循环稳定、大倍率性能良好的复合电极材料。