Mechanical failure assessment of Lithium ion battery electrode under electrochemical-mechanical condition

Lithium ion battery appears to be the dominant energy source of electric vehicles and most portable electronic devices, due to its high energy density, low self-discharge rate as well as wide temperature range. However, its inherent operation mechanism that, Li-ion reversibly inserts into/extracts from battery electrode, would lead to the repeated swelling and shrinking of the host electrode material and the generation of diffusion-induced stress (DIS). The mechanical failure behaviours under diffusion-induced stress could influence the cyclic performance of electrode and battery. Hence, the structural integrity assessment of battery electrode upon electrochemical condition is vital for the development of this new energy source. This thesis presents the studies of diffusion-induced stress related mechanical failure analyses of Li-ion battery electrode. Firstly, the diffusion driven method and chemical potential driven method are developed and implemented by writing finite element subroutines. These methods make it available to use ABAQUS platform to effectively and efficiently conduct coupled diffusion-stress analysis. Secondly, with using the extended Finite Element Method (XFEM), the complete crack initiation, propagation and fracture process of electrode particle can be investigated, and the critical cracking failure boundaries are innovatively proposed for assessing the different crack status. Thirdly, with using the Linear Matching Method Framework (LMMF), knowledge has been extended on shakedown, reverse plasticity and ratcheting behaviours of battery electrode under electrochemical conditions. Furthermore, a fatigue damage evaluation method is innovatively proposed, which makes it available to assess the continuous mechanical degradation of oxide electrode material. With the proposed assessment method, the fatigue degradation trends of battery electrode configurations under different material levels are modeled. The research works in this thesis offer valuable insights into mechanical failure mechanisms of lithium ion battery electrode under electrochemical loads and provide theoretical information on the optimization of electrode material.Lithium ion battery appears to be the dominant energy source of electric vehicles and most portable electronic devices, due to its high energy density, low self-discharge rate as well as wide temperature range. However, its inherent operation mechanism that, Li-ion reversibly inserts into/extracts from battery electrode, would lead to the repeated swelling and shrinking of the host electrode material and the generation of diffusion-induced stress (DIS). The mechanical failure behaviours under diffusion-induced stress could influence the cyclic performance of electrode and battery. Hence, the structural integrity assessment of battery electrode upon electrochemical condition is vital for the development of this new energy source. This thesis presents the studies of diffusion-induced stress related mechanical failure analyses of Li-ion battery electrode. Firstly, the diffusion driven method and chemical potential driven method are developed and implemented by writing finite element subroutines. These methods make it available to use ABAQUS platform to effectively and efficiently conduct coupled diffusion-stress analysis. Secondly, with using the extended Finite Element Method (XFEM), the complete crack initiation, propagation and fracture process of electrode particle can be investigated, and the critical cracking failure boundaries are innovatively proposed for assessing the different crack status. Thirdly, with using the Linear Matching Method Framework (LMMF), knowledge has been extended on shakedown, reverse plasticity and ratcheting behaviours of battery electrode under electrochemical conditions. Furthermore, a fatigue damage evaluation method is innovatively proposed, which makes it available to assess the continuous mechanical degradation of oxide electrode material. With the proposed assessment method, the fatigue degradation trends of battery electrode configurations under different material levels are modeled. The research works in this thesis offer valuable insights into mechanical failure mechanisms of lithium ion battery electrode under electrochemical loads and provide theoretical information on the optimization of electrode material