Tuning the Li/Ni Disorder of the NMC811 Cathode by Thermally Driven Competition between Lattice Ordering and Structure Decomposition

Ni-rich layered LiNi x Mn y Co z O2 (NMC) cathodes for lithium-ion batteries are receiving a lot of attention owing to their promising large capacity, whereas the high content of Ni results in several issues including poor thermal stability and serious Li/Ni disorder. Although a little degree of the Li/Ni disorder may be beneficial for the structural stability of NMC cathodes and even migration of Li ions, a high degree of the Li/Ni disorder certainly deteriorates their electrochemical performances. Therefore, tuning the Li/Ni disorder is of great interest in the development of safer NMC cathodes with larger accessible capacity. Post-synthesis annealing is a facile and low-cost way to manipulate lattice defects, yet has not been utilized to optimize the Ni-rich NMC cathodes. In this work, we report that post-synthesis annealing can induce the competition between lattice ordering and structure decomposition. The thermal annealing promoted that lattice ordering would prevail until the decomposition of oxygen lattice. Once the annealing temperature reaches the critical temperature to form oxygen vacancies, Ni ions can easily migrate into the Li slab. The Li/Ni disorder can be facilely tuned through post-synthesis annealing to optimize the electrochemical performances of NMC cathodes.