含缺陷锂电池硅负极材料断裂行为的原位观测与失效机理研究

锂电池硅负极材料具有比容量高、放电平台低、资源丰富、环境友好等优点，应用前景广阔。然而，由于制备或首次充放电过程中不可避免产生微孔洞、微裂纹等缺陷，在循环充放电时，裂纹的起裂、扩展等断裂问题变得尤为突出，造成电池可逆容量急剧衰减。传统单一的电化学或力学理论方法不能很好解决脱嵌锂过程中缺陷/扩散/变形强耦合问题。本项目拟（1）解决电化学氛围力学加载、原位电化学池、高精度光学观测和精确预制脆性硅缺陷等技术难题，研制含缺陷硅负极材料裂纹起裂、扩展原位观测实验平台；（2）提出裂纹扩散边界条件，发展考虑离子扩散反应动力学的非线性断裂准则，揭示缺陷/扩散/变形耦合作用机理；（3）获得电化学环境下硅负极材料裂纹扩展Paris公式，提出基于裂纹扩展长度的容量衰减模型，揭示裂纹扩展对使用寿命影响机理。期望在原位实验和理论建模方面获得原创性成果，为锂电池硅负极材料的设计、制备和寿命预测提供指导。

Silicon anodes are promising materials for lithium-ion batteries due to their enhanced safety，low cost and high-energy capacity. However, the commercial use of silicon anodes has been hindered by their large volume change (up to 300%) during lithium insertion and extraction which often leads to pulverization of the active alloy particles and the unstable solid-electrolyte interphase (SEI) films. Therefore, it is very important to research the fracture mechanics of the silicon anodes under the electro-chemo-mechanical coupled effect. This project will (1) set up an experimental platform based on loading system, high resolution light microscopes, in-suit half-cell and charge-discharge system for observing the initiation and growth of cracks on silicon anodes with pre-cracks or voids. The challenges of this part are the productions of anodes contain pre-cracks and the design of in-suit half-cell which should meet the both the optic and electrochemical demands; (2) propose the different diffusion boundary conditions of lithium ion. Then, the nonlinear fracture model which consider the full diffusion-deformation coupling will be established using the experimental and simulation methods. The model will try to explain the competition mechanisms between the brittle to ductile transition and diffusion induced softening effect near the crack tip; (3) establish the Paris law of the silicon based on the observation of the fatigue crack propagation under different electrochemical conditions. The safe region of silicon anodes will be mapped for different factors including electrochemical conditions, geometrical features of electrodes and interplay between cracks and new SEI films. This project is expected to gain original achievements in electro-chemo-mechanical fracture theory and in-suit experimental results which will provide profitable guidance for the design, manufacture and life prediction for lithium-ion batteries with silicon anodes.