Layered Li-rich oxides have attracted much attention because of higher capacity than that of traditional layered oxides (more than 250 mAh g⁻¹). However, the intrinsic issues of Li-rich cathode materials suffer from lattice oxygen loss, poor rate capability, voltage fade, and limited cycle life. To tackle these problems, the Li-rich cathode containing intergrown layer and spinel phases was proposed, and this heterostructure material meets the requirements of high energy and stable surface with a fast Li⁺ diffusion channel. Herein, we review the recent progress and in-depth understanding about heterostructure including microstructure and morphology, performance of advancement and degradation mechanisms, and modification strategies. Special attention is given to the high-performance energy mechanism as follows: (a) spinel phase and oxygen vacancy jointly enhance the lattice structure and prevent the irreversible oxygen release, (b) higher capacity is achieved by promotion of activation of Li2MnO3 phase and control of the activation rate to realize stable long-term cyclability, and (c) spinel phase provides the 3D interconnected Li⁺ diffusion channels and protects the surface region from side reactions. The other issue that aroused interest is the undesirable changes of phase transition and degradation mechanisms as follows: (a) the key reconstruction process is to produce a “good” spinel to maintain the surface and interior structure stability. (b) It is significant to figure out the structure degradation and phase transition mechanism in the cycled heterostructure. This review aims to provide inspiration and opportunities for the design of high-energy-density cathode materials, thereby bridging the gap between laboratory research and practical battery applications.

Layered Ni-rich materials for lithium-ion batteries exhibit high discharge capacities but degraded cyclability at the same time. The limited cycling stability originates from many aspects. One of the critical factors is the intrinsic insulating residual lithium compounds and the rock-salt (NiO) phase on the surface of particles. In this work, LiNi_0.8Co_0.1Mn_0.1O₂ material is etched with a trace amount of boric acid and used as a model to demonstrate the influences of weak acid treatment on the surface phase regulations. After the etching process, the pH of the material is reduced from 12.08 to 11.82, along with a lower cation mixing degree and promoting electrochemical performances. Corresponding measurements demonstrate that weak acids such as H₃BO₃ can also etch the NiO phase on the surface to adjust the surface of the particles to a pure layered structure. This process improves the lithium-ion diffusion and electron transport in the interface between material and electrolyte, consequently leading to better cycling performance and rate capability. This study provides a novel strategy and comprehensive understanding of acid modification and surface phase regulation process of Ni-rich cathode materials for lithium-ion batteries.