Research on Calculation Method of Internal Resistance of Lithium Battery Based on Capacity Increment Curve

Lithium-ion batteries are the most widely used and reliable power source for electric vehicles. With the development of electric vehicles, the safety performance, energy density, life and reliability of lithium-ion batteries have been continuously improved. However, as the battery ages, the battery performance is degraded, the internal resistance of the battery increases, and the internal resistance of the battery is closely related to the instantaneous charge and discharge capacity of the battery. In addition, in the battery packs connected in series, the battery resistance distribution is closely related to the consistency of the battery pack. In this paper, the lithium iron phosphate battery capacity increment curve (IC curve) was used as the analysis tool and the IC curve obtained by SOC-OCV was selected as the reference curve and the IC curves of the same batch in the battery pack are selected and compared with the reference curve. The voltage difference of the characteristic peaks and the current difference are used to reflect the internal resistance of each monomer. value. On this basis, a mathematical model was established, and the internal resistance of other cells is calculated one by using the characteristic points of I peak and II peak of IC curve obtained by SOC-OCV, so as to reflect the aging consistency of battery package. The actual capacity calculated from the SOC-OCV curve was compared and found to be consistent with the battery aging trend characterized by capacity, which shows that the method can quickly determined the internal resistance of each single cell of the battery pack, and can be applied in the normal charging process of the battery pack. In addition, the resistance values of all the single cells in the battery pack can be obtained in real time. The calculation and control of the battery resistance value is in the same charge state of the battery, the error is small, so it has a certain practical value for the safety diagnosis and early warning of the battery pack.