The significance of measuring self discharge rate

The significance of measuring self discharge rate
The self discharge rate, as an important performance indicator of lithium-ion batteries, has a significant impact on battery screening and assembly. Therefore, measuring the self discharge rate of lithium-ion batteries has far-reaching significance.

1. Prediction problem: For the same batch of battery cells, the materials and manufacturing controls are basically the same. When there are individual batteries with significantly larger white discharge, the reason is likely to be severe micro short circuits caused by impurities and burrs piercing the separator internally. Because the impact of micro short circuits on batteries is slow and irreversible. So, in the short term, the performance of such batteries will not differ much from normal batteries, but after long-term storage, as the irreversible reactions inside gradually deepen, the performance of the battery will be far lower than its factory performance and other normal battery performance. Therefore, in order to ensure the quality of the factory batteries, self discharging large batteries must be removed. Two pairs of batteries need to be assembled and assembled. Lithium batteries require good consistency, including capacity, voltage, internal resistance, and white discharge rate. The impact of the self discharge rate of a battery on a battery pack is mainly manifested as follows: once assembled into a module, due to the different self discharge rates of each individual lithium battery, the voltage will decrease to varying degrees during storage or cycling, and under series charging, the current received will be equal. Therefore, after each charge, overcharged or undercharged individual batteries may appear in the lithium battery module. As the number of charge and discharge cycles increases, the battery performance will gradually deteriorate, and the cycle life will significantly decrease compared to unassembled individual batteries. Therefore, battery assembly requires precise measurement and screening of the self discharge rate of lithium-ion batteries. 3 Battery SOC estimation corrected state of charge, also known as remaining charge, represents the ratio of the remaining capacity of a battery after a period of use or long-term storage to its fully charged capacity, commonly expressed as a percentage. The self discharge rate has important reference value for SOC estimation of lithium-ion batteries. By correcting the initial SOC value through self discharge current, the accuracy of SOC estimation can be improved. On the one hand, customers can estimate the product’s usable time or driving distance based on the remaining power; On the other hand, improving the SOC prediction accuracy of BMS can effectively prevent battery overcharging and overdischarging, thereby extending battery life.