Decoupling the thermal and non-thermal effects of discharge C-rate on the capacity fade of lithium-ion batteries

In battery-powered electronic devices, an increase in the discharge C-rate is expected when using functions that require more power. Temperature rise is the thermal effect of discharge C-rate due to ohmic heating, causing lithium-ion batteries to degrade faster. There are also non-thermal effects, such as increased mechanical stress on electrode particles and structure. How much each of the thermal and non-thermal effects contributes to the capacity fade is valuable for understanding the discharge C-rate-related degradation mechanisms in lithium-ion batteries. This paper decouples the thermal and non-thermal effects of discharge C-rate on the capacity fade of lithium-ion batteries. Pouch cells are subject to continuous charge-discharge cycling under six testing conditions. Two stress factors are investigated: discharge C-rate (0.5C, 1.75C, and 3C) and temperature control (constant battery surface temperature at 45 °C and constant ambient temperature at 45 °C). The capacity degradation mechanisms associated with thermal and non-thermal effects of discharge C-rate is revealed using cycling data, impedance measurement, incremental capacity analysis, and scanning electron microscopy/energy dispersive X-ray spectroscopy analysis. A capacity fade model is developed as the function of discharge C-rate and cycle numbers. The contributions of the thermal and non-thermal effects at different discharge C-rates on the capacity loss are quantified.