Suppressing Bulk Strain and Surface O₂ Release in Li-Rich Cathodes by Just Tuning the Li Content

Layered oxides represent a prominent class of cathodes employed in lithium-ion batteries. The structural degradation of layered cathodes causes capacity decay during cycling, which is generally induced by anisotropic lattice strain in the bulk of cathode particle and oxygen release at the surface. However, particularly in lithium-rich layered oxides (LLOs) that undergo intense oxygen redox reactions, the challenge of simultaneously addressing bulk and surface issues through a singular modification technique remains arduous. Here a thin (1-nm) and coherent spinel-like phase is constructed on the surface of LLOs particle to suppress bulk strain and surface O₂ release by just adjusting the amount of lithium source during synthesis. The spinel-like phase hinders the surface O₂ release by accommodating O₂ inside the surface layer, while the trapped O₂ in the bulk impedes strain evolution by ≈70% at high voltages compared with unmodified LLOs. Consequently, the enhanced structural stability leads to an improved capacity retention of 97.6% and a high Coulombic efficiency of ≈99.5% after 100 cycles at 0.1°C. These findings provide profound mechanistic insights into the functioning of surface structure and offer guidance for synthesizing high-capacity cathodes with superior cyclability.