Abstract
Polycrystalline LiNixCoyMn1-x-yO2 (NCM) cathodes are promising candidates for next-generation lithium-ion batteries owing to their high specific capacity, but their structural instability during cycling leads to significant capacity degradation; given that surface coatings have proven effective in mitigating this issue, clarifying the underlying mechanisms of their crack-suppression effects on NCM particles is critical. To address this need, a electrochemo-mechanical model was developed in this study to simulate the influence of coatings on crack evolution in NCM particles: specifically, the Voronoi algorithm was employed to generate randomly distributed primary particle structures, with a perfectly bonded coating applied to the NCM particle surface, and cohesive elements were introduced at the interfaces between primary particles to simulate crack initiation and propagation-processes that were quantified via measurements of crack area and length. Through systematic investigations into the effects of coating thickness and modulus on crack evolution under varying charge rates (C-rates), three key findings were obtained: (1) coatings can completely suppress crack propagation when charge rates are below a critical threshold; (2) at high charge rates, the effectiveness of crack suppression is jointly determined by both coating thickness and modulus; (3) an excessively high coating modulus induces interfacial stress concentration, which may in turn cause fracture of the coating itself. Collectively, these results provide theoretical insights into the mechanisms of coating-mediated crack suppression and offer valuable guidance for the rational design of coatings as well as the optimization of electrode structures, ultimately contributing to enhanced structural stability of lithium-ion batteries.
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