A novel method for constructing the relationships between state of charge and open-circuit voltage of lithium-ion battery under different temperatures with reduced test time

The equivalent circuit models (ECMs) have been extensively applied to estimate the state-of-charge (SOC) for lithium-ion batteries. And it is significant for ECMs to establish the relationship between the open-circuit voltage (OCV) and SOC. The accurate relationship is usually obtained from the incremental OCV (IO) test, which is time-consuming for each OCV test point. To overcome this shortcoming, a novel method for obtaining the relationship is proposed to save test time. Firstly, five OCV test points of the IO tests are used under different temperatures, and the OCV change trend along the SOC is acquired from the low-current OCV test at room temperature, from which the feature points are extracted by the Douglas-Peucker algorithm to express the OCV change trends. Finally, the OCV test points are connected by moving feature points twice to construct the SOC-OCV curves under different temperatures with fewer OCV test points. The SOC estimations of two different lithium-ion batteries are achieved based on the second-order RC ECM using the adaptive extended Kalman filter. The results indicate that the SOC estimations are more accurate in a wide temperature range compared to the traditional method while the time for OCV tests is reduced by at least 50%.