From coating to doping: Effect of post-annealing temperature on the alumina coating of LiNi0.5Mn1.5O4 cathode material

Spinel LiNi0.5Mn1.5O4 is considered as one of the most promising cathode materials due to high working voltage and high energy density. However, the fast capacity degradation, mainly induced by the instability of electrode/electrolyte interface and bulk structure, heavily prevents its commercial application. To alleviate above two issues, LiNi0.5Mn1.5O4 material was first coated with Al(OH)3 via double hydrolysis reactions between NaAlO2 and AlCl3·6H2O, where the corrosion of LiNi0.5Mn1.5O4 material is avoided by controlling the feeding sequence, and the uniform coating of Al(OH)3 on particle surface is achieved by controlling the feeding rate. The Al(OH)3-coated LiNi0.5Mn1.5O4 material was post-annealed at different temperatures, and the effects of different post-annealing temperatures on the structure, morphology and electrochemical performance of LiNi0.5Mn1.5O4 material were systematically investigated. It is found that the LiNi0.5Mn1.5O4 material after post-annealing treatment at 600 ​°C exhibits the optimal rate and cycling performances, which can be mainly attributed to the synergistic effect of Al2O3 surface coating and doping. The uniform and thin Al2O3 coating layer can avoid the direct contact of electrode with electrolyte, capture corrosive HF and increase oxygen vacancy on particle surface, while Al3+ doping can eliminate LixNi1-xO impurity phase, reduce Mn3+ content, strengthen the spinel structure and make Li+ ions diffusion easier, thus leading to the simultaneous improvement of interfacial and structural stability of LiNi0.5Mn1.5O4 material.