Fading Mechanism Analysis of NCM Lithium-Ion Battery Under Different Degrees of Overcharge

Abstract

Power batteries are always misused and abused due to the fault or failure of battery management system (BMS), resulting the overcharge and over-discharge. In this study, NCM lithium-ion battery is used as the research object. Cyclic experiments of different overcharge degrees under voltage and capacity as cut-off conditions are performed, respectively. The evolution of the basic performance parameters under different conditions are observed. As the overcharge deepens, it will lead to accelerated degradation of capacity and deterioration of kinetic performance. In addition, overcharge with capacity has worse performance and is accompanied by a sharp rise in battery cut-off voltage. In-situ analysis method is used to describe the battery fading mechanism. The phase change reaction at 4.4V consumes the cathode material used for the normal charging process. The side reactions after charging to 4.7V generate a large amount of heat. Inventory lithium ions are lost and the electrode reaction uniformity is deteriorated as the cycle process. Ultimately, the battery has different tolerances under different overcharge strategies. Overcharge with capacity has faster decay rate, while overcharge with voltage has worse security