Influence of annealing atmosphere on Li ₂ ZrO ₃ -coated LiNi _0.6 Co _0.2 Mn _0.2 O ₂ and its high-voltage cycling performance

Layered Ni-rich oxides have attracted much attention for the positive electrode in lithium-ion batteries due to their low cost and high capacity. However, they still suffer from poor cycling and rate performance, especially at high voltage. In this work, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ powders are surface-modified by a Li ₂ ZrO ₃ coating prepared under either dry air or oxygen. The effect of the coating atmosphere on the electrochemical properties of Li ₂ ZrO ₃ /LiNi _0.6 Co _0.2 Mn _0.2 O ₂ are systematically investigated by multiple structural characterization (synchrotron HRXRD, SEM, TEM, and XPS) and electroanalytical (EIS, SSCV, and GITT) techniques. The Li ₂ ZrO ₃ coating prepared in oxygen is largely amorphous. It not only provides surface protection against the electrolyte corrosion but also enables faster lithium-ion transport at the interfacial regions. Additionally, oxygen atmosphere facilitates Zr diffusion from the surface coating to the bulk of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , which stabilizes the crystal structure and enhances lithium-ion diffusion. Consequently, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ cathodes coated with Li ₂ ZrO ₃ in oxygen exhibit improved high-voltage cycling stability and high-rate performance.