Research On The Application Of Segmented Match Method In Lithium Iron Phosphate Battery

New energy vehicles, especially electric vehicles, will become increasingly popula r due to the increasing environmental pollution and the shortage of oil and other non-renewable resources. The single battery could be used after combining with others to generate the hig h power and high capacity which the electric vehicle needs. There are still some differences between the combined batteries though the performance parameters of them are exactly similar. The difference s between the combined batteries will widen during the recycling use and eventually, which will lead to failure of the battery pack. Thus, it is necessary to sort out the battery of similar performance and combined them into a battery pack. Although single parameter separation method, multiple parameter separa tion method, charge and discharge curve separation method are applied more current ly, these methods cannot be applied to the electric car battery sorting, because the sorting basis of single parameter separation method is single, which result into more defects. Multiple parameter separation method takes more characteristics into consideration than single parameter separation method. Although its sorting advantage is obvious, it still has certain defects because it fails to focus the parameters change in t he process of battery working, and thus cannot present the essential differences among the batteries. The separation method which combined multiple parameters selecting with charge and discharge curves can reflect the dynamic characteristics of battery, this method is more complex, and it does not apply to the actual production well. Based on the existing cell sorting methods, this paper proposes a new battery sorting method.Therefore, in this work, we examined the charge and discharge characteristics of lithium iron phosphate battery HL- LFP- 100 Ah and HL- LFP- 50 Ah produced by lithium energy. By studying the relationship between the SOC and voltage, DC internal resistance, we have gradually summarized an effective model of selection methods: fragmen t screening with group method. T he method divided the battery SOC into three sections according to its interval segmentation: 0% ~ 20% SOC, 20% ~ 80% SOC, 80% ~ 100% SOC. Lithium battery in each SOC period has different features and exhibits a certain pattern in DC internal resistance and voltage. We have studied five parameters of the three SOC sections list below:1. Discharge the l ithium battery to the DC internal resistance of 20% SOC. The DC internal resistance test current was kept as 3 C;2. Discharging the lithium battery to the end. The end of the discharge current was kept as 1 C;3. Charging or discharging the l ithium battery to DC internal resistance or discharge platform of 50% SOC;4. Charging the lithium battery to DC internal resistance platform of 80% SOC. The DC internal resistance test current was kept as 3 C;5. Charging the lithium battery until the end of charging. The current should be kept as a constant in the whole process.The battery group selected by the above five parameters selec tion match method has a good consistency. Each battery of battery pack can perform well, and the performance and cycle life of the battery pack has a certain degree of improvement.