Understanding the mechanism of capacity increase during early cycling of commercial NMC/graphite lithium-ion batteries

A capacity increase is often observed in the early stage of Li-ion battery cycling. This study explores the phenomena involved in the capacity increase from the full cell, electrodes, and materials perspective through a combination of non-destructive diagnostic methods in a full cell and post-mortem analysis in a coin cell. The results show an increase of 1% initial capacity for the battery aged at 100% depth of discharge (DOD) and 45 degrees C. Furthermore, large DODs or high temperatures accelerate the capacity increase. From the incremental capacity and differential voltage (IC-DV) analysis, we concluded that the increased capacity in a full cell originates from the graphite anode. Furthermore, graphite/Li coin cells show an increased capacity for larger DODs and a decreased capacity for lower DODs, thus in agreement with the full cell results. Post-mortem analysis results show that a larger DOD enlarges the graphite d -space and separates the graphite layer structure, facilitating the Li+ diffusion, hence increasing the battery capacity.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. This is an open access article under the CC BY license (http://creati-vecommons.org/licenses/by/4.0/).

Automated summary

This study investigates the capacity increase observed in the early stage of Li-ion battery cycling. The results show that the increased capacity mainly originates from the graphite anode, and larger depth of discharge and high temperatures accelerate this capacity increase.