Near-Equilibrium Control of LiTiO Nanoscale Layer Coated on LiNiCoMnO Cathode Materials for Enhanced Electrochemical Performance.

Ni-rich layered metal oxide of LiNiCoMnO is a promising cathode material for next-generation lithium ion batteries because of its capability to deliver a high capacity; however, intrinsic problems, especially the side reactions between Ni ions and the electrolyte, adversely affect its electrochemical and thermal stability. Surface coating by a protective and Li-conducting LiTiO layer is a strategic approach to remit those problems. The normal deposition strategies depend on the hydrolysis of titanium alkoxides, making it difficult to control the reaction equilibrium. Herein we report a near-equilibrium deposition tactic to achieve a uniform LiTiO nanoscale layer coated on the surface of LiNiCoMnO microspheres to improve electrochemical performance and thermal stability. With pH modulation and BO scavenger in the (NH)TiF precursor solution, the ion product for the coating layer is controlled to be slightly bigger than its solubility product. The hydrolysis reaction chemistry can thus be manipulated at a near-equilibrium condition. Within the critical pH range of 4.8-5.2, a uniform coating layer of LiTiO with the thickness of about 4 nm can be successfully deposited on the surface of the LiNiCoMnO cathode material, which greatly enhances its capacity retention to 93.5% after 200 cycles at 0.5 C. The appropriate LiTiO coating can increase the mobility of Li ions and suppress the side reactions between electrolytes and cathode materials, which further makes the modified cathode display the higher peak temperature in differential scanning calorimetry analysis and capacity enhancement at 60 °C, which are related to safety concerns.