Suppressing Bulk Strain and Surface O 2 Release in Li-rich Cathodes by Just Tuning the Li Content.

Layered oxides represent a prominent class of cathode materials extensively employed in lithium-ion batteries. The structural degradation of layered cathodes causes the capacity decay during battery cycling, which is generally induced by anisotropic lattice strain in the bulk of the cathode particle and undesirable 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 we construct a thin (1-nm) and coherent spinel-like phase on the surface of LLOs particle (Li x Mn 0.54 Ni 0.13 Co 0.13 O 2 ) to suppress bulk strain and surface O 2 release by just adjusting the amount of lithium source during synthesis. The spinel-like phase hinders the surface O 2 release by accommodating O 2 inside the surface layer, while the trapped O 2 in the bulk lattice impedes strain evolution by about 70% at high voltages compared with unmodified LLOs cathodes. Consequently, the enhanced structural stability in bulk and surface leads to a significantly improved capacity retention of 97.6% and a high Coulombic efficiency of about 99.5% after 100 cycles at a rate of 0.1 C. Our findings provide profound mechanistic insights into the functioning of surface structure and offer guidance for synthesizing high-capacity cathodes with superior cyclability. This article is protected by copyright. All rights reserved.