What causes capacity degradation in lithium-ion batteries?
1. Misuse of lithium-ion batteries
Lithium-ion batteries show no significant capacity loss when the State of Charge (SOC) is below 120%. However, when the SOC exceeds 120%, lithium deposition begins at the negative electrode. Furthermore, the formation of a thicker SEI film increases impedance and leads to the loss of active lithium. Continued overcharging can cause thermal runaway in lithium-ion batteries. At excessively high SOCs, the electrolyte decomposition rate accelerates, resulting in a thick deposition layer on the graphite negative electrode, where the lithium contained within this layer precipitates.
In addition, high-rate charging and discharging can also cause capacity loss in lithium-ion batteries. This is because the positive and negative electrodes will shrink and expand in volume during the charging and discharging process. The larger the charging and discharging current, the more violent the shrinkage and expansion, and the greater the stress. As a result, the particles of the positive and negative electrodes are more likely to break or peel off from the current collector during rapid volume changes, leading to accelerated cycle decay.
2. Temperature factor
It's worth mentioning the impact of the operating environment and conditions on the capacity of lithium-ion batteries. Temperature is definitely one of the key factors affecting the lifespan of lithium-ion batteries. Excessively high or low temperatures can reduce the content of active lithium ions, damage the electrode material structure, and cause metal ions to dissolve, resulting in severe capacity decay.
The standard operating temperature for lithium-ion batteries is -20℃ to 60℃. However, the performance of lithium-ion batteries generally decreases below 0℃, and their discharge capacity also decreases accordingly. Therefore, the optimal operating temperature for lithium-ion batteries is typically 0~40℃. Lithium-ion batteries with special environmental requirements have different temperature ranges, and some can even operate normally in environments exceeding 100 degrees Celsius.
