A Novel Measurement Method for the Self-Discharge of Lithium-Ion Cells Employing an Equivalent Resistance Model

Self-discharge is an important indicator to evaluate the quality of lithium-ion cells. This paper proposes a novel method to quickly measure the self-discharge of lithium-ion cells. A self-discharge equivalent model is developed for analyzing self-discharge measurement requirements. The load capacitance in the model is obtained by using the characteristic curve of open circuit voltage and state of charge. Based on the relationship between the weak current and time of the cell in the charging state, the self-discharge resistance is quickly determined. The corresponding measurement process is introduced. The first experiment preliminarily verifies the plausibility of the load capacitance measurement method proposed in this paper. The second experiment uses this new method to investigate the self-discharge dependence of state-of-charge and further analyzes the influence of load capacitance accuracy on measurement. In order to verify the efficiency and accuracy of the new method, a comparison experiment is conducted by three typical methods and the new method. The results show that this new method is useful; the difference between the results is acceptable while the required measurement time is shortened to less than 6 h.