Simultaneous surface modification method for 0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries: Acid treatment and LiCoPO4 coating

Li-rich layered cathode materials have been considered the most promising candidates for large-scale Li-ion batteries due to their low cost and high reversible capacity. However, these materials have many drawbacks that hinder commercialization, such as low initial efficiency and cyclability at elevated temperatures. To overcome these barriers, we propose an efficient and effective surface modification method, in which chemical activation (acid treatment) and LiCoPO4 coating were carried out simultaneously. During the synthesis, the lithium ions were extracted from the lattice, leading to improved Columbic efficiency, and these ions were used for the formation of LiCoPO4. The Ni and Co doped spinel phase was formed at the surface of the host material, which gives rise to the facile pathway for lithium ions. The LiCoPO4 and highly doped spinel on the surface acted as double protection layers that effectively prevented side reactions on the surface at 60 °C. Moreover, the transition metal migration of the modified cathode was weakened, due to the presence of the spinel structure at the surface. Consequently, the newly developed Li-rich cathode material exhibited a high 1st efficiency of 94%, improved capacity retention of 82% during 100 cycles at 60 °C, and superior rate capability of 62% at 12C (1C = 200 mA/g) rate at 24 °C. In addition, the thermal stability of the modified cathode was significantly improved as compared to that of a bare counterpart at 4.6 V, showing a 60% decrease in the total heat generation.