Effects of Cobalt Deficiency on Nickel-Rich Layered LiNi _0.8 Co _0.1 Mn _0.1 O ₂ Positive Electrode Materials for Lithium-Ion Batteries

The role of cobalt deficiency on the crystal structure, surface chemistry, and electrochemical performance of Ni-rich layered LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) positive electrode materials was experimentally studied possibly for the first time. We synthesized pristine and cobalt-deficient NCM811 samples by solid-state reaction. Using a variety of characterization techniques and electrochemical measurements, we show that cobalt nonstoichiometry can suppress Ni ²⁺ /Li ⁺ cation mixing, but can simultaneously promote the formation of oxygen vacancies, leading to rapid capacity fade and inferior rate capability compared to pristine NCM811. This study provides new insights into the effects of cobalt deficiency on the cation mixing and electrochemical performance of a Ni-rich layered NCM compound.