As a lithium iron phosphate battery that has long been widely used, many parts have been retired or are close to retirement. The in-depth analysis of the lithium iron phosphate battery after deep cycle has important guiding significance for effectively improving the battery performance in the future.

　　1. The inconsistency of the polarization internal resistance of lithium batteries makes the voltage of some individual batteries change drastically during the charging and discharging process, which leads to drastic changes in the voltage of the entire battery pack.

　　2. The inconsistency of the voltage of the single cells in the battery pack reduces the energy released by the overall lithium iron phosphate battery pack.

　　3. Due to the exothermic and endothermic processes during battery operation, the battery temperature will change continuously. When the external charging and discharging conditions are inappropriate, the battery will overheat, which will cause performance degradation and safety hazards.

　　4. Capacity is the most serious factor in discreteness. Inconsistent capacity mainly causes performance problems in two aspects. First, some lithium iron phosphate batteries will be in a state of overcharge and over-discharge, resulting in a serious decrease in cycle life. The second is that the low-capacity single battery ends work early, which affects the energy of other single cells in the entire battery pack cannot be fully released, which causes the life of the entire lithium iron phosphate battery pack to decay.

　　5. The performance of the electrolyte significantly affects the specific capacity, life, rate charge and discharge performance, operating temperature range and safety performance of lithium-ion batteries.

　　6. Temperature is definitely one of the key factors affecting the life of lithium iron phosphate batteries. Too high or too low temperatures will reduce the active lithium-ion content, thereby reducing the life of the lithium battery.