Ni-Rich Cathode Active Materials Surface Degradation in Ambient Air with Stabilisation Treatment Proposal

Abstract

Ni-rich cathode active materials, such as NMC811 (Li[Ni0.8Mn0.1Co0.1]O2), are promising cathode materials due to their higher theoretical capacity of 200mAh/g, lower cobalt ratio, and overall decreased material expenses. However, the material undergoes a phase transition from layered ( ) through spinel ( ) to rock salt ( ) at high state of charge with oxygen release, and formation of rock salt structures on the surface with lithium carbonates and lithium hydroxides (Residual Lithium Compound (RLC)) while material is exposed to ambient air, all of which is followed by an increase in surface impedance and a decrease in final battery performance.Here, we explore the chemical and electrochemical evaluation of the Ni-rich cathode active material surfaces when exposed to ambient air for fourteen days (RH~40%). The combination of Fourier-transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy (EIS) will be investigated. These complementary non-destructive approaches will be utilised to characterise the decomposition of the original layered surface and formation of RLC. In addition, the research will be evaluated using STA, XRD, formation, diffusion coefficient, and cycle life in a half-cell using lithium-ion discs as counter electrodes. Furthermore, we show a technique for stabilising the material in air using Experimental ElectroRite®1 Additive provided by Lubrizol Ltd. which reduces the formation of the RLC and the corresponding surface phase changes, often attributed to the presence of Ni2+ ions. This work contributes to a greater understanding of the surface stabilisation through chemical treatment required and suggests routes to create stable water-based Ni-rich cathode inks.