Relieving the Reaction Heterogeneity at the Subparticle Scale in Ni-Rich Cathode Materials with Boosted Cyclability.

ABSTRACT

Ni-rich layered LiNi0.8Co0.1Mn0.1O2 (NCM811), as a highly suitable candidate for commercialized cathode materials, inevitably suffers from reaction inhomogeneity during electrochemical processes owing to the polycrystalline aggregate particle morphology, especially at high voltages. With the cycles proceeding, intergranular microcracks induced by an anisotropic volume change emerge and accumulate, leading to contact loss of the internal grains. Subsequently, a decrease in accelerated diffusion kinetics and internal Li+ deactivation take place, which further deteriorate the reaction heterogeneity between the surface and bulk phases within polycrystalline subparticles, ultimately leading to rapid capacity failure. To deal with these issues, a microstructural tailored NCM811 with a suitable subparticle size and ordered primary grain arrangement is employed as an alternative cathode. Owing to the optimized microstructure, reaction homogeneity has been significantly promoted, which causes enhanced electrochemical properties with long-term cycling. It is revealed that the mechanically strengthened microstructure contributes to maintaining contact between the surface and bulk phases, resulting in a reversible H2-H3 phase transition and superior Li+ kinetics upon cycling. This microstructural engineering route based on the rational electrode architecture can boost reaction homogeneity and provide guidance for the design of advanced cathode materials.