does SOC and DOD affect the lifespan of lifepo4 battery?
Jul 28, 2022
Definition of state of charge (SOC) and depth of discharge (DOD) and their impact on lifespan of lifepo4 battery
1. State of Charge (SOC, State of Charge): In layman's terms, it is the ratio of the power stored in the battery (releasable capacity) to the maximum power that the battery can store. For example, if a battery with a maximum capacity of 100Ah(fully charged) is fully discharged to 50Ah, or fully charged to 50Ah after fully discharged, then the releasable capacity stored in the battery is 50Ah (regardless of energyloss), and its state of charge is equal to 50/100*100%=50%SOC. Image metaphor: a cup with a maximum of 500mL has only 200mL of water in it, and the state at this time is 200/500*100%=40%.
2. Depth of Discharge (DOD, Depth of Discharge): refers to the ratio of the capacity released by the battery discharged from one SOC to another SOC to the maximum discharge capacity of the battery. It is simply understood as the difference between the SOC at the beginning of discharge and the SOC at the end of discharge. For example, when a 100% SOC battery is fully discharged, the depth of discharge is 100% DOD. When a battery is discharged from 100% SOC to 50% SOC, the depth of discharge is 50% DOD. Similarly, when a battery is discharged from 80% SOC to 40% SOC,the depth of discharge is 40% DOD, and so on!
The number of cycles that the battery discharges from 100% SOC to 0% SOC. Simply put, it is the cycle at 100% DOD, also called deep cycle. We refer to cycles with depth of discharge below 100% DOD as "shallow charge and shallow discharge" cycles. The service life of the battery shows a significant upward trend as the depth of discharge DOD decreases, as shown in the figure below: a 12V30Ah battery cycles 500 times at 100% DOD, but exceeds 4000 cycles at 30% DOD.At the same time, from the curve, in the case of the same depth of discharge DOD, the number of cycles corresponding to different SOC intervals is also different. The performance is as follows: the cycle life of the low SOC range is better than that of the high SOC range, that is, the overcharge is usually said to cause more damage to the lithium-ion battery.