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 Ni0.88Co0.08Mn0.04O2 coated with grain boundary Li3PO4 coating (PC88_P1) showed better electrochemical performance than uncoated Ni-rich Ni0.88Co0.08Mn0.04O2 (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.