Study on the NiO-like phase in Ni-rich cathode materials for lithium ion batteries

Ni-rich cathode materials have become the main research focus in the field of Li-ion batteries due to the urgent need for cathode materials with higher weight and volume energy density for application of Li-ion batteries in electric vehicles. However, the conditions for the preparation of these materials are harsh, they are unstable during storage in air, and problems like capacity fading and structure deterioration are hard to overcome. All these drawbacks are related to Li/Ni disorder and NiO-like phases, which cover the surface of Ni-rich cathode materials. In this article, the influence of NiO-like phases on the electrochemical properties of Ni-rich cathode materials during preparation, cycling, and storage in air is studied, and a formation mechanism for NiO-like phases is proposed. The results confirm that the amount of NiO-like phases, especially on the surface, must be reduced for the preparation of Ni-rich cathode materials with high performance.