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

• DOI: 10.1016/j.jechem.2022.07.005
• Publication Date: 2022-07-12T02:09:22Z
• Authors: Jia Guo; Yaqi Li; Jinhao Meng; Kjeld Pedersen; Leonid Gurevich; Daniel-Ioan Stroe
• Keywords: Capacity increasing; Lithium-ion battery; 0202 electrical engineering, electronic engineering, information engineering; 02 engineering and technology; Full cell; Coin cell; 7. Clean energy; Graphite anode

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 °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.