This study uses electrochemical techniques to examine three cathode materials. It finds that increased lithium content boosts Anion Redox Reactions (ARRs), enhancing capacity but causing polarization. Activation of Li-rich materials triggers ARRs, raising resistance. Voltage drops are tied to ARRs in Li-rich materials. Adjusting voltage is key for harnessing extra capacity from ARRs. The research provides valuable insights for the design and use of Li-rich materials.

Abstract

Lithium-rich (Li-rich) manganese-based layered oxide materials are promising candidates for positive electrode materials due to their high energy density. However, challenges such as transition metal cation migration and irreversible anionic redox hinder their application. This study employs various electrochemical methods to systematically investigate three types of cathode materials: LiNi_0.6Mn_0.2Co_0.2O₂ (NCM622), Li_1.12Ni_0.39Mn_0.49O₂ (Li1.12), and Li_1.2Ni_0.2Mn_0.6O₂ (Li1.2). The findings indicate that an increase in lithium content leads to higher participation of anions in Anion Redox Reactions (ARRs), resulting in an augmented capacity. However, this also brings about significant polarization. The activation process of Li-rich materials triggers the ARRs mechanism, resulting in a sharp increase in resistance. Voltage drops during shelving and cycling are closely tied to the ARRs occurring at high potentials in Li-rich materials. To make the best use of the additional capacity associated with ARRs, it is essential to adjust the formation/cycling voltage in accordance with the characteristics of positive electrode materials with varying lithium contents. This study offers valuable insights for the design and utilization of Li-rich materials.