电池材料中活性金属相的流动扩散路径与累积应变的原位测试方法研究

在电池材料中，活性相金属如锂和镍的流动扩散引起的不可逆变形是造成电池性能退化主要原因之一，研究测试退化变形过程和变形机理具有重要科学意义。本项目研究这种活性相在运行状态下变形过程的原位测试方法和技术，结合三维扫描显微仪器，研制具有高温、氧化还原气氛和充放电性能动能的微型设备，组成原位测试系统；测试电池材料内部高温扩散变形过程、氧化还原循环和充放电循环下的微观结构的演化和化学反应-力学耦合作用机理下变形过程；主要解决，流动扩散Ni引起变形是发生在高温下还是在降温过程中、这种活性金属如何流动到电极材料表面,揭开我们新发现的“趋面效应”现象的由来；还有SEI膜是如何和活性金属锂发生相互作用并引起损伤断裂等电池性能退化机理；利用电池材料的化学反应扩散随动梯度层化耦合模型，建立燃料电池活性金属相变扩散及锂电池扩散沉积下SEI膜的变形破坏模型。

The diffusion flux of active materials alters during redox or repeated charge and discharge cycles of the battery, causing volumetric expansion and contraction promoting strains in electrode particles and changes in solid electrolyte interface(SEI), therefore, understanding cell degradation mechanisms in the microstructure scale is important to enhance the lifetime and reliability of the cell system. Based on the 3D X-ray computed tomography platform and digital volume correlation method, we develop the in situ technique and method to characterize the volume variation, evolution of the microstructure, coarsening, agglomeration and diffusion flux behavior of nickel particles, interreaction of lithium deposition with solid electrolyte interface and deformation of SEI and the induced strains. To solve the problems such as how the active materials diffusion and flux to surface of anode, irreversible strain development associated with SEI formation in composite graphite electrode and damage and degradation during cycles, accumulated strain in solid oxide fuel cell aroused at high temperature or at cooling down. On the other hand, coupled lithium dendrite growth, diffusion and SEI deformation, nickel flux and oxidation growth and irreversible damage strain are also investigated.