Revisiting the Initial Irreversible Capacity Loss of Lini0.6co0.2mn0.2o2 Cathode Material Batteries

Abstract

Layered LiNi0.6Co0.2Mn0.2O2 (NCM622) attracts widespread attention primarily due to its potential for high energy density and moderate thermal stability. However, the low initial coulombic efficiency (ICE) of the material limits the maximum utilization of their capacity. The capacity loss in the first cycle occurs under 4.0V and keep almost constant are considered as common characteristics for NCM-based materials. A clear cognition on the initial capacity loss may light the way to improve the practical reversible capacity of NCM622 at 4.0V. Conducting operando X-ray diffraction during galvanostatic charge/discharge cycling at different temperature (25°C, 45°C and 60°C) and different current (0.1C, 0.01C, 1C=120 mA g-1) in the voltage range of 2.7-4.0V, we find that only 8% of the measured initial irreversible capacity loss is associated with parasitic reactions that form cathode/electrolyte interface, and that the dominant contributors include the slow Li+ diffusion kinetics (~46% contribution) and irreversible O3/H1-3 phase transition (~46% contribution). This semi-quantitative study provides new insight on initial capacity loss, guiding further targeted modification and fully utilization of NCM622.

Keywords: LiNi0.6Co0.2Mn0.2O2, initial irreversible capacity loss, Li+ diffusion kinetics, structural change, lithium-ion battery.