Temperature is indeed an important factor affecting the internal resistance of lithium-ion batteries, and its core mechanism lies in the regulation of temperature on the internal electrochemical process of the battery. Specifically, temperature changes change the internal resistance of the battery primarily by affecting the electrochemical reaction rate at the electrode/electrolyte interface and the physical properties of the electrolyte

‌Electrochemical reaction rate: The rate of electrochemical reaction inside the battery is highly sensitive to temperature. According to the principle of chemical kinetics, increasing temperature increases the thermal motion of ions and molecules, increasing the collision frequency of reactants, thereby speeding up the charge transfer reaction rate and reducing charge transfer impedance (a key internal resistance component). Conversely, in low-temperature environments, the reaction rate slows down significantly, resulting in a sharp increase in charge transfer impedance, which is a major factor limiting battery performance

‌Electrolyte conductivity: The ionic conductivity of the electrolyte increases with temperature, which reduces the bulk impedance of the battery. At low temperatures, the viscosity of the electrolyte increases, the conductivity decreases, and the migration of ions is blocked, further increasing the internal resistance

‌SEI membrane properties: The stability and resistance of the solid electrolyte interface (SEI) film on the anode surface are also affected by temperature. High temperature may accelerate the decomposition of electrolyte, resulting in thickening or structural changes in the SEI film and increasing the interfacial resistance. Low temperatures may make SEI films brittle, affecting their conductivity

‌Combined impact: At extreme low temperatures (such as below -20°C), the increase of charge transfer impedance far exceeds that of bulk phase impedance and SEI film impedance, becoming the dominant part of the total internal resistance of the battery, resulting in a sharp drop in battery output power and low charging efficiency At high temperatures, while reduced internal resistance is beneficial for power output, it accelerates side reactions (e.g., electrolyte oxidation, attenuation of positive and negative electrode materials) that can harm battery life in the long run

Therefore, temperature has a complex and far-reaching impact on the internal resistance of lithium-ion batteries by regulating electrochemical reaction kinetics and electrolyte transport characteristics, which is the fundamental reason why battery management systems need precise thermal management