本项工作的意义在于，从理论和结构设计两方面，对不同电极结构的力学表现做了深入研究，为解决高能量密度电极材料在充放电过程中由结构断裂和疲劳问题引起的严重的容量衰减和寿命低等问题提供了重要的指导作用。

    Lithium ion secondary batteries have become ubiquitous power sources for mobile applications, and have been used widely for power energy industries. It is the need for high density energy storage devices that prompts to the lithium ions battery with high capacity and long life. Thus, high charge capacity anode materials, like Si and Sn, have attracted great interests in recent years. However, lithiation and de-lithiation in anode materials with high capacity inevitably result in huge volume expansion and contraction, lead to high internal stresses and, thus, poor cycle life of high capacity anode batteries. Therefore the analysis of electrode material’s stress evolution during charging and discharging, and the improvement of electrode structure’s mechanical properties by electrode structure’s optimization have important engineering and scientific significance.

    There are complex strongly coupled interaction between electrochemical and mechanical process, the analytical solutions of the deformation and stress are difficult to obtain for the complex nonlinear coupling relation. Here by taking the equivalence of volume expansion (or shrinkage) as continuous insertion (or distraction) of infinitesimal dislocations, we supply a framework to solve the stress field of a cylinder with arbitrary insertion (distraction) profile of materials along the radial direction. Under the assumptions that the deformation is small and elastic, we supply analytical solutions of stress fields to several typical volume expansion or shrinkage profiles.

    Different from the traditional electrode materials, there are large irreversible deformation for electrode materials with high capacity during charging and discharging, so it is necessary to develop high performance numerical calculation method for simulating the changes of electrodes during charging and discharging. Here we developed a robust electrochemical-mechanical coupled numerical procedure to simulate electrode structures’ diffusive process, large elastic-plastic deformation and stress evolution. With the numerical results of thin film electrode structure, we analyze on examining the validity of the Stoney equation for in-situ stress measurements, identifying how the constitutive behavior of electrode materials and film-substrate interfacial properties affect the measured stress-capacity curves of electrodes, and establishing the relationship of electrode material parameters with the characteristics of stress-capacity curves.

    In fact, the working performance of lithium ion batteries has been restricted by serious structural damage which is caused by high stress status, hence, we simulated the stress evolution for several kinds of electrode structures during charging and discharging, based on reasonable assumption on the electrochemical-mechanical coupling constitutive relationship and the reliable experimental data. We designed porous electrode media with gradient distributed pores and validated its improvement on electrode structure’s stress status.

    This thesis is focused on the mechanical behavior of electrode materials in the view of electrochemical-mechanical coupling theory and structure design, and aims at providing direction to improve the electrochemical behavior influenced by fracture and fatigue problem on mechanical properties during charging and discharging.