Correlation between grain boundary coating and chemomechanics in Ni-rich layered Li cathodes

Ni-rich NCM, which has high discharge capacity, is attracting worldwide attention as a cathode material for lithium–ion batteries. However, during cycling, anisotropic lattice variation occurs and the structure becomes unstable, which causes problems in both electrochemical performance and stability. Herein, grain boundary Li₃PO₄ coating was applied via drop-wise coating to suppress the microcracks occurring between primary powder particles during cycling. A study combining experiments and calculations was conducted to allow systematic and deep understanding of the grain boundary coating mechanism between primary particles. As a result of the experiment, Ni-rich Ni_0.88Co_0.08Mn_0.04O₂ coated with grain boundary Li₃PO₄ coating (PC88_P1) showed better electrochemical performance than uncoated Ni-rich Ni_0.88Co_0.08Mn_0.04O₂ (PC88). In addition, SEM−EDS confirmed that the phosphate material was present both on the surface of the bulk particles, and inside the cross-section of the treated PC88_P1, resulting in the suppression of intergranular microcracks. This was theoretically elucidated by the intriguing “suspension bridge” concept using first principles calculations. Our systematic understanding of grain boundary Li₃PO₄ coating provides insight into facile strategies that apply to advanced cathodes for the LIB with long-term cycling stability.