Improving electrochemical properties of LiNi0.8Mn0.1Co0.1O2 cathode materials for lithium ion batteries by controlling calcination gas atmosphere

Abstract

Layered lithium nickel manganese cobalt oxides (LiNixMnyCozO2, x + y + z = 1) with high Ni content (x ≥ 0.8), called as high Ni NMC, are one of the most promising cathode materials for lithium-ion batteries of electric vehicle (EV) application. High Ni NMC synthesis includes a calcination step under pure O2 atmosphere to minimize Li/Ni mixing in crystal structure, which highly influences the long term cyclability and C-rate capability of batteries. Herein, we demonstrate that the electrochemical properties of high Ni LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials for lithium ion batteries can be further improved by controlling the calcination atmosphere. Interestingly, the results showed that a slightly oxygen deficient calcination atmosphere (mixture of O2/Ar with 96/4 vol% ratio) is effective to provide a stable discharge capacity retention (89%) after 200 cycles, and high C-rate capability (>70% at 20C vs 1C), whereas NMC811 calcined under pure O2 suffers from an excessive oxidation of Ni and Co on the surface and an increase of residual lithium, leading to an increase of surface resistance, as a consequence, a fast capacity fade over cycling and lower C-rate capability. The finding of this study suggests that calcination atmosphere could play a key role in determining the electrochemical properties of high Ni cathode materials, and can also be interesting from the industrial point of view, since producing O2 with a small deficiency (e.g. Ar) needs less efforts in the purification than pure O2.