Development of a lifetime prediction model for lithium thionyl chloride batteries based on an accelerated degradation test

Battery life prediction is critical for lithium/thionyl chloride cells with a long storage life. The objective of this study was to develop models for rapidly estimating the storage life of Li/SOCl2 cells using the semiempirical approach. An accelerated degradation test involving numerous cells stored at various temperatures (room temperature or RT, 40, 50, 60, and 70 °C) was conducted to investigate the effect of the storage time and temperature on capacity degradation. The degradation law can be summarized on the basis of the test data for constructing the semiempirical equation; this law demonstrates that the residual capacity of aging cells exponentially changes with the storage time and temperature. The degradation data are also used for parameterization with the multiple nonlinear curve fitting method based on the universal global optimization algorithm. According to the simulation and comparison between the experimental data and prediction curve, the fitting prediction curve accurately fits the experimental data. This finding indicates that the semiempirical model is useful because of its satisfactory ability to approximate the measured data. In addition, characteristic values of the battery, including the storage life under various storage conditions, average self-discharge rate, and acceleration factor, can be calculated on the basis of the mathematical model.