A procedure for evaluating the soh of li-ion batteries from data during the constant voltage charge phase and the use of an ECM with internal resistance

Abstract

Lithium-ion batteries (LIBs) are present in virtually all sectors: communications, leisure, transportation, and even energy distribution. However, LIBs are affected by various ageing processes that cause a deterioration in their performance and can pose safety risks during operation. Therefore, it is vital to determine the State of Health (SOH) of the battery without affecting its regular operation. This paper presents a procedure for estimating and diagnosing the SOH of LIBs from data recorded during Constant Voltage (CV) phase charging. The developed method is based on specific battery parameters experimentally obtained and provides accurate results of the internal resistance and battery capacity. One of the advantages of the proposed procedure is that it can provide battery SOH results just from the value of only one measured point of current intensity during charging in the CV phase once some characteristic parameters of the battery are previously determined. Two NCA lithium batteries of different geometry (18650 and 26650) have been used in the diagnostics. The results of the proposed procedure have been validated experimentally, demonstrating high accuracy and fit. The proposed method can be implemented in a BMS to determine the SOH of the battery using the values of current intensity during a standard LIB charge.