Study on Fatigue Damage and Cycle Life of Cathode Particles in Lithium‐Ion Batteries Based on Representative Volume Element

ABSTRACT Cyclic diffusion‐induced stress due to the diffusion of lithium ions gives rise to fatigue in the active material of lithium‐ion battery electrodes along with the repeated thermal and mechanical loads, which tends to decrease battery capacity and shorten life. Therefore, this paper comprehensively investigates the fatigue behavior of LiNi x Mn y Co z O 2 cathode active particles under cyclic multiload conditions by establishing a multiparticle representative volume element (RVE) model. With the linear matching method (LMM), the reverse plasticity limits of particles with varying numbers but the same volume fraction are calibrated. Additionally, the plastic strain range of cathode active particles is calculated by Direct Steady Cycle Analysis (DSCA), where the influences of different load combinations on fatigue failure are evaluated. A semianalytical model is derived to predict the fatigue damage of active particles under complex multiple loads. Moreover, by utilizing the unified procedure for fatigue and ratchet analysis (UPFRA) with material fatigue parameters, a series of constant fatigue life boundaries is established, and the impacts of working temperature and target structural life on these boundaries are investigated. This research also reveals that the fatigue life of active particles is significantly extended with the particle radius below the critical threshold.