Some factors affecting Li-ion batteries’ internal resistance

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One of the most revealing attributes of a Li-ion battery's health is its internal resistance. IR plays a vital role to make the best performance of the Li-ion batteries. The battery's IR is affected by various usage conditions like temperature, depth of discharge. Besides, the battery structure design, raw material performance, manufacturing processes also affect its IR.

Mainly talking about the usage conditions, the influence of temperature on Li-ion batteries' IR is obvious. The lower the temperature, the slower the ion transmission inside the battery, and the greater the battery's IR. The 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 electrolyte ionic conductivity. The change trend at low temperature is consistent with the change trend of electrolyte conductivity. Compared with the increase of bulk impedance and SEI film resistance at low temperatures, the charge reaction impedance increases more significantly with the decrease in temperature. Below -20°C, the charge reaction impedance accounts for almost 100% of the battery's total IR.

When the Li-ion battery is in different SOC, its IR is also different. Especially the DC internal resistance directly affects the power performance of the battery. The DC internal resistance of the Li-ion battery varies with the depth of discharge (DOD) of the battery. The IR is basically unchanged in the 10%~80% discharge interval. Generally, with deeper discharge depth, the battery's IR increases significantly. Besides, long-term improper storing the Li-ion battery will also cause the battery aging, and IR increasing.
 

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