Engineering Li⁺ Transport in Ni-Rich Layered Cathodes Toward Homogenization

Nickel-rich layered oxide (NRLO) cathodes (Ni≥80%) are promising for next-generation lithium-ion batteries with energy densities exceeding 300 Wh kg^-1, but suffer from rapid degradation under deep delithiation, including phase transitions, microcracking, and surface reconstruction. These failure modes are increasingly recognized to be coupled through heterogeneous Li⁺ transport across multiple length scales. Here we show that spatial variations in Li⁺ transport originate from atomic, structural, and interfacial factors and ultimately evolve into macroscopic chemo-mechanical degradation. On this basis, we introduce transport homogenization as a unifying design principle for regulating Li⁺ transport in NRLO cathodes. Within this framework, diverse material engineering strategies, including bulk structural design, interfacial transport engineering, and dynamic transport regulation, are interpreted from a common transport-centered perspective. We further summarize emerging characterization approaches for quantifying transport heterogeneity and discuss future opportunities for establishing predictive cross-scale design principles. Overall, this review establishes a transport-centered framework that unifies degradation in NRLO cathodes and provides a mechanistic basis for rational design of next-generation high-energy-density cathode materials.