Gas impurity in calcination atmosphere governing electrochemical properties of LiNi0.8Mn0.1Co0.1O2 cathode material for lithium ion batteries

In this work, we investigated the influence of gas impurity in oxygen as calcination gas on the electrochemical properties of high Ni LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials. Among investigated gas compositions, the oxygen mixed with a small amount of argon (96% O2, 4% Ar) shows the same level of Li/Ni cation mixing as 100% O2 sample, with not only a very stable discharge capacity retention (89% at 200 cycles) but also higher C-rate capability (67% at 20C) compared to other samples. Despite well suppressed Li/Ni cation mixing, 100% O2 sample suffers from an over-oxidation of Ni and Co of the surface, leading to an increase of surface resistance, as a consequence, a fast capacity fade over cycling with lower C-rate capability compared to the material calcined under 96% O2/4% Ar. This result demonstrates that calcination gas composition plays a key role in determining the electrochemical properties of high Ni cathode materials, not only in terms of Li/Ni cation mixing in the bulk structure, but also the oxidation properties of Ni, Co at the surface.