What‘s the application factor affect the lithium ion energy storage battery internal resistance?
Internal resistance is an important parameter to measure lithium-ion energy storage battery performance and evaluate battery life, the larger the internal resistance, the worse the rate performance of the battery, and the faster it increases in storage and recycling. The internal resistance is related to the battery structure, battery material properties and manufacturing process, and changes with ambient temperature and state of charge. Therefore, the development of low internal resistance battery is the key to improving battery power performance, and grasping the change law of battery internal resistance is of great practical significance for battery life prediction.
With the use of lithium batteries, battery performance continues to decay, mainly manifested as capacity attenuation, internal resistance increase, power decrease, etc., the change of battery internal resistance is affected by temperature, depth of discharge and other use conditions.
The influence of temperature and temperature on the size of the internal resistance is obvious, the lower the temperature, the slower the ion transfer inside the battery, and the greater the internal resistance of the battery. Battery impedance can be divided into bulk phase impedance, SEI film impedance and charge transfer impedance, bulk phase impedance and SEI film impedance are mainly affected by the ion conductivity of the electrolyte, and the change trend at low temperature is consistent with the change trend of electrolyte conductivity. Compared with the increase of bulk phase impedance and SEI film resistance at low temperature, the charge reaction impedance increases more significantly with the decrease of temperature, and the proportion of charge reaction impedance to the total internal resistance of the battery below -20 °C reaches almost 100%.
SOC When the battery is in different SOC, its internal resistance size is not the same, especially the DC internal resistance directly affects the power performance of the battery, and then reflects the battery performance in the actual state: the DC internal resistance of lithium battery increases with the increase of battery discharge depth DOD, and the size of the internal resistance is basically unchanged in the discharge interval of 10%~80%, and the internal resistance increases significantly at a deeper discharge depth.
Storage With the increase of lithium-ion battery storage time, the battery continues to age, and its internal resistance continues to increase. Different types of lithium batteries have different degrees of internal resistance. After a long period of storage from September to October, the internal resistance increase rate of LFP cells is higher than that of NCA and NCM cells. The increase rate of internal resistance is related to storage time, storage temperature and storage SOC.
Whether the cycle is storage or circulation, the influence of temperature on the internal resistance of the battery is consistent, and the higher the cycle temperature, the greater the increase rate of internal resistance. The internal resistance of the battery is also affected by different cycle intervals, and the internal resistance of the battery accelerates with the increase of the charge and discharge depth, and the increase of the internal resistance is proportional to the strengthening of the charge and discharge depth. In addition to the effect of the charge and discharge depth in the cycle, the charge-to-charge voltage also has an effect: too low or too high the upper charge voltage will increase the interface impedance of the electrode, too low the upper voltage can not form a passivation film well, and too high the upper voltage will cause the electrolyte to oxidize and decompose on the surface of the LiFePO4 electrode to form a product with low conductivity.
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