Storage degradation mechanism of layered Ni-rich oxide cathode material LiNi0.8Co0.1Mn0.1O2

Abstract

With advantages such as high specific capacity and low cost, Ni-rich layered oxides are considered to be ideal cathode materials for power batteries. However, due to the high sensitivity of materials to air, structural degradation occurs during transportation and storage, resulting in the formation of an impurity layer. The degradation of the structure will weaken the comprehensive properties of Ni-rich cathode materials. The impurity layer will bring difficulties to the subsequent electrode manufacturing process, which seriously limits the practical application of Ni-rich materials. Therefore, it is particularly important to explore the storage decline mechanism of Ni-rich materials. Herein, the decay mechanism of structure and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 materials after storage at room temperature and high humidity and high-temperature and humidity were studied. It is found that the instability of Ni3+ leads to the appearance of NiO rock salt phase on the surface of the material, accompanied by the formation of reactive oxygen species. Lithium and reactive oxygen species in the material react with H2O and CO2 in the air to form surface residual lithium compounds. The formation of the inert NiO layer and residual lithium compounds hinders the diffusion kinetics of Li+, resulting in serious capacity loss. During the high-temperature storage process, the material forms thicker residual lithium compounds, which aggravates the decay process. After 28 days of high-temperature storage, a residual lithium compound layer of about 7 nm thickness was formed, which seriously hindered the transmission of Li+. This study is helpful to deeply understand the storage failure behavior of Ni-rich cathode materials and promote the large-scale industrial production and application of Ni-rich cathode materials.