新型锂离子电池锡基负极材料的失效机理及扩散应力调控

Metal tin anode has a high theoretical specific capacity and conductivity, which has the great potential to replace the graphite anode materials of Li-ion batteries. Unfortunately, during the battery charge/discharge process, the alloying reaction of Sn with lithium causes significant volume expansion and high internal stress, making the Sn electrode fracture, flaked from current collector and failure, and final resulting rapid decay of capacity. The project will systematically study the diffusion-induced stresses of Sn and Sn-based alloy SnM (M = Fe, Cu, Ni) anodes and their effects on the electrochemical performances of Li-ion batteries (such as specific capacity, cycle stability, etc.) from the experimental and theoretical aspects. Following, the failure mechanism of Sn anode will be revealed for determining the microstructures optimization criteria and preparation conditions of Sn-based alloys, which guides the microstructure design, preparation and theoretical analysis of Sn-based alloy anodes, thus achieving the tuning of diffusion-induced stress and improving the electrochemical performances of Sn-based alloy anodes.The content of this subject involves computational materials science, mechanics, electrochemistry, and physics, which intends to investigate the failure mechanism of Sn anode and then tune the diffusion-induced stress of Sn-based alloys. This project can provide a theoretical and experimental guidance for the development of Li-ion rechargeable batteries with high electrochmical performances.

锂离子电池金属锡负极具有高的理论比容量和导电率，是最有潜力取代石墨的锂离子电池负极材料之一。但是在电池的充放电过程中，锂离子的嵌入和脱出会导致锡发生巨大的体积变化，从而产生很大的扩散应力，使得电极材料发生粉化、剥落和失效，造成容量的快速衰减。本申请项目将从实验和理论两个方面系统地研究锡及锡基合金SnM(M = Fe, Cu, Ni)负极在充放电过程中的扩散应力及其对锂离子电池的比容量和循环稳定性等电化学性能的影响，揭示锡负极材料的失效机理，从而确定锡基合金负极微结构优化准则和制备工艺条件，并指导金属锡基合金负极的微结构设计、制备和理论分析，进而实现电极扩散应力的调控，改善金属锡基负极锂离子电池的性能。本项目结合计算材料学、力学、电化学和物理学，研究锡负极中扩散应力导致的电极失效机理，在此基础上进行锡基合金的扩散应力调控，为高性能锂离子电池的研制提供理论和技术指导。

本项目以具有重要应用潜力的金属锡及其合金(如SnNi)负极材料为研究对象，探索锡基负极在充放电过程中由于扩散诱发应力导致的电极失效破坏机理，在此基础实现锡基负极的扩散应力调控、从而获得具有优异电化学性能的锡基负极材料。我们发现：（1）简单的机械球磨能够显著地降低活性物质Sn颗粒的尺寸，但由于机械球磨不能获得活性相Sn均匀分散包覆的Sn/C复合材料，从而Sn负极的锂离子存储性能提高不是很理想（在0.2C电流密度下具有400 mA h g-1的稳定比容量）；（2）基于液相自组装的化学方法得到的锡纳米颗粒内嵌的Sn/C空心微球具有活性Sn颗粒尺寸小、分散均匀、碳包覆充分、比表面积大的优点，从而极大地提高了材料的循环稳定性和倍率性能（在0.25C, 0.5C, 1C, 2.5C和5C电流密度下的稳定比容量分别为600, 550, 480, 400, 380 mA h g-1）;（3）引入非活性相Ni构造纳米多孔结构的Sn-Ni合金空心框架结构能进一步提高材料的循环稳定性（在整个400次循环周期内，0.2C电流密度下的比容量稳定在700 mA h g-1），Ni非活性骨架能够有效缓解锂离子嵌入过程中引起的电极体积膨胀，同时其良好的电子导电性提高了材料的倍率性能，赋予了其快速充放电性能。本项目的顺利开展及其取得的研究成果为新型高性能锂离子电池负极材料的研发提供了理论和技术指导。