锂离子电池三元正极核-壳结构的电化学-力学模拟

Electrochemical-mechanical Simulation of Ternary Cathode Materials with Core-shell Structure for Lithium-ion Batteries

利用有限元模拟技术构建了电化学-力学耦合的三维多物理场锂离子电池模型,进而获得了核-壳正极在放电过程中Li+浓度、应变和应力的分布与演变情况,并研究了放电结束时不同放电倍率、壳厚度和核粒径对应变和应力的影响.结果表明,颗粒中心及核-壳界面处的应力在放电初期迅速达到最大值,然后随着Li+扩散过程的进行,应力逐渐减小.另外,黏结剂和相邻颗粒对电极应力分布有显著影响.减小放电速率和核粒径以及增加壳厚度能够降低电极中的应力.研究结果可为核-壳正极结构的设计与优化以及锂离子电池放电策略提供参考.

Ternary cathode material LiNixCoyMnzO_(2)(NCM)with a core-shell structure is one of the key materials for the development of lithium-ion batteries with high specific capacity and long term cycle stability.However,stress-induced mechanical failure is one of the main factors that would lead to the capacity decay of such types of electrode materials.In order to better understand the stress distribution and evolution in the core-shell structural cathode during the electrochemical reaction process,a three-dimensional multiphysics lithium-ion battery model for electrochemistry-mechanics coupling was constructed in this paper.The distribution and evolution of Li+concentration,strain and stress in the core-shell cathode during the discharge process were first obtained through the model,and then the effects of various discharge rates,shell thicknesses,and core radiuses on the strain-stress at the end of the discharge were investigated.The results show that stresses at the centre of the particle and the core-shell interface rapidly reach their maximum at the beginning of the discharge,and then undergo a gradual decreasing process with the prolonged diffusion process of Li+.The binder and neighboring particles have significant effects on the stress distribution in this cathode.Decreasing the discharge rate and core radius,as well as increasing the shell thickness,can reduce the stress in the cathode.The obtained conclusions can provide a reference for the design and optimization of core-shell cathode structures as well as discharge strategies for lithium-ion batteries.