Study On Internal Resistance Of Lifepo₄ Battery

The electronic conductivity and lithium ion diffusion coefficient of lithium iron phosphate?LiFePO4?materials are low due to the characteristics of its crystal structure,which results in the high internal resistance of the LiFePO₄ battery.Therefore,the study on internal resistance of the LiFePO4 battery is necessary.In this article,it was discussed from two aspects:LiFePO₄ materials and production technology of the battery.The effect of active material morphology,graphene,conductive agent and binders on the resistance characteristics of LiFePO₄ battery were investigated by resistance test,EIS etc.Through the test of battery capacity,rate,cycle and processing performance,the effect of resistance on performance of the battery was analyzed and the feasibility of the methods to improve the resistance of LiFePO₄ battery was discussed.LiFePO₄ with different morphologies and its battery were studied.The physical properties of LiFePO₄ materials were analyzed by XRD,SEM and particle size measurement etc.The internal resistance,EIS,rate and processing performance were measured.The relationship between the morphology of LiFePO₄ and the internal resistance of LiFePO₄ battery was investigated.The feasibility of the method to improve internal resistance by morphology of LiFePO₄ was discussed.The results show that,compared with non spherical LiFePO₄ material,spherical LiFePO₄ material has better physical properties,whose 14500 battery has lower charge transfer resistance and diffusion impedance,the internal resistance of spherical LiFePO₄ battery is only 50.6 m?,reduced by 17.4 m?and the battery has excellent processing performance and rate performance.It has a high feasibility of the method to improve internal resistance of the battery by spherical LiFePO₄.The battery was prepared using graphene coated LiFePO₄ as cathode active material.The internal resistance and electrochemical properties of the battery were measured.The effect of graphene on the resistance characteristics of LiFePO4 battery was investigated.The results show that the graphene coated LiFePO₄ battery has low internal resistance and good rate performance,the lithium ion diffusion resistance of which has been greatly improved.At the same time,the graphene coating enhances the stability of the structure of LiFePO₄material.Therefore,graphene coated LiFePO₄ battery shows excellent cycle performance.The effect of conductive agents on the resistance characteristics of LiFePO₄ battery was investigated.The results show that with the increase of the content of conductive agent,the internal resistance of LiFePO₄ battery decreases gradually,the charge transfer resistance of which is reduced,the cell rate performance is enhanced.When the content of Super-P is3%,the capacity retention rate of the battery at 10 C can reach 70.7%.However,the more the content of conductive agent,the worse the dispersion of the slurry,the higher the demand for the pulp environment,which leads to the poor processing performance of the battery.The effect of binders on the resistance characteristics of LiFePO₄ battery was investigated.The discharge capacity and safety performance of the battery were analyzed.The feasibility of process improvement was considered synthetically.The results show that the effect of binders on the internal resistance of the battery is significant.The binders influence internal resistance of LiFePO₄ battery by affecting cathode resistivity,compaction density and charge transfer resistance.Water binders have advantages of low cost and environmental protection.However,the cathode using water binders is difficult to dry completely.Residual water reacts with electrolyte,which decreases discharge capacity of batteries using LA133 and CMC/SBR as binders.Electrolysis of water produces gas,which causes the flatulence of the battery and decline of the safety performance.