What are the influencing factors of the internal resistance of lithium iron phosphate batteries

The uniformity of the slurry dispersion during mixing affects whether the conductive agent can be evenly dispersed in the active material in close contact with it, which is related to the internal resistance of the lithium iron phosphate battery. By adding high-speed dispersion, the average dispersion of the slurry can be improved, and the internal resistance of the lithium iron phosphate battery is smaller. The addition of surfactants can improve the uniformity of the distribution of the conductive agent in the electrode, reduce the electrochemical polarization and increase the median discharge voltage. 2 Coating surface density is one of the key parameters in the design of lithium iron phosphate battery. When the capacity of lithium iron phosphate battery is pressed, the new pole piece surface density will inevitably reduce the total length of the current collector and the diaphragm, which is within the ohm of the lithium iron phosphate battery. The resistance will decrease accordingly, so within a certain range, the internal resistance of the lithium iron phosphate battery will decrease with the increase of the areal density. The migration and separation of solvent molecules during coating and drying is closely related to the temperature of the oven. It directly affects the distribution of the binder and conductive agent in the pole piece, and then affects the formation of the conductive grid inside the pole piece. Therefore, the coating and drying process Temperature is also an important process for optimizing the performance of lithium iron phosphate batteries. The lithium iron phosphate battery 3 is rolled to a certain extent, and the internal resistance of the lithium iron phosphate battery decreases with the increase of the compaction density. Because the compaction density increases, the distance between the raw material particles decreases, and the contact between the particles increases. , The more conductive bridges and channels, the lower the impedance of the lithium iron phosphate battery. The control of compaction density is mainly achieved by rolling thickness. Different rolling thickness has a greater impact on the internal resistance of the lithium iron phosphate battery. When the rolling thickness is large, the contact resistance between the active material and the current collector increases due to the failure of the active material to be rolled tightly, and the internal resistance of the lithium iron phosphate battery The resistance increases. Moreover, after the lithium iron phosphate battery is cycled, cracks appear on the surface of the positive electrode of the lithium iron phosphate battery with a larger thickness, which will further increase the contact resistance between the surface active material of the pole piece and the current collector. 4-pole piece turnaround time Different shelf time of the positive electrode has a greater impact on the internal resistance of the lithium iron phosphate battery. When the shelf time is short, it is affected by the effect of the carbon coating on the surface of the lithium iron phosphate and the use of the lithium iron phosphate. The internal resistance of the battery increases slowly; when it is left for a long time (more than 23h), the internal resistance of the lithium iron phosphate battery increases more clearly due to the combined effect of the reaction between lithium iron phosphate and water and the bonding purpose of the adhesive. Therefore, it is necessary to strictly control the turnaround time of pole pieces in actual processing. 5 The ionic conductivity of the injected electrolyte determines the internal resistance and rate characteristics of the lithium iron phosphate battery. The conductivity of the electrolyte is inversely proportional to the viscosity of the solvent, and is also affected by the concentration of lithium salt and the size of anions. In addition to the optimization study on the conductivity, the injection volume and the infiltration time after injection also directly affect the internal resistance of the lithium iron phosphate battery. Small injection volume or insufficient infiltration time will cause the internal resistance of the lithium iron phosphate battery to be too large. , Thereby affecting the capacity of lithium iron phosphate batteries. 1 Temperature The influence of temperature on the internal resistance is obvious. The lower the temperature, the slower the ion transmission inside the lithium iron phosphate battery, and the greater the internal resistance of the lithium iron phosphate battery. Lithium iron phosphate battery impedance can be divided into bulk impedance, SEI membrane impedance and charge transfer impedance. The bulk impedance and SEI membrane impedance are mainly affected by the electrolyte ion conductivity. The change trend at low temperature is consistent with the change trend of electrolyte conductivity. . Compared with the increase in bulk impedance and SEI film resistance at low temperatures, the increase in charge reaction resistance is more significant with the decrease in temperature. Below -20°C, the charge reaction resistance accounts for almost 100% of the total internal resistance of lithium iron phosphate batteries. 2SOC When the lithium iron phosphate battery is in different SOC, the internal resistance is different, especially the DC internal resistance directly affects the power performance of the lithium iron phosphate battery, and then reflects the lithium iron phosphate battery in the actual state. Battery performance: The DC internal resistance of the lithium iron phosphate battery is added with the increase of the depth of discharge DOD of the lithium iron phosphate battery. The internal resistance is basically the same in the 10% to 80% discharge interval, generally at a deeper depth of discharge The internal resistance increased significantly. 3 Storage As the storage time of lithium-ion lithium iron phosphate batteries increases, lithium iron phosphate batteries continue to age, and their internal resistance continues to increase. Different types of lithium iron phosphate batteries have different degrees of change in internal resistance. After a long period of storage from September to October, the internal resistance increase rate of LFP lithium iron phosphate batteries is higher than that of NCA and NCM lithium iron phosphate batteries. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.