Since their introduction, lithium-ion batteries have been widely used due to their advantages such as long lifespan, high specific capacity, and lack of recall effects. However, lithium-ion batteries suffer from problems such as low capacity, severe degradation, poor cycle ratio, significant lithium disconnection, and lithium disconnection imbalance when used at low temperatures. Furthermore, with the continuous expansion of application areas, the low-quality constraints caused by the low-temperature performance of lithium-ion batteries are becoming increasingly apparent.
It has been reported that the discharge capacity of lithium-ion batteries at -20°C is only about 31.5% of that at room temperature. Traditional lithium-ion batteries operate between -20°C and +55°C. However, in specialized aerospace, special applications, and electric vehicles, batteries must operate normally at -40°C. Therefore, improving the low-temperature performance of lithium-ion batteries is of great significance.
Factors limiting the low-temperature performance of lithium-ion batteries
At low temperatures, the viscosity of the electrolyte increases, and some may even solidify, leading to a decrease in the conductivity of lithium-ion batteries.
At low temperatures, the compatibility between the electrolyte and the negative electrode and the diaphragm deteriorates.
At low temperatures, lithium-ion batteries experience severe deposition at the negative electrode. The lithium ions deposited from the metallic lithium react with the electrolyte, and the accumulation of these products leads to an increase in the thickness of the solid electrolyte interface (SEI).
At low temperatures, the charge transfer impedance (Rct) of lithium-ion batteries increases significantly as the dispersion system in the active material decreases.
Why does the capacity of lithium-ion batteries decrease in winter?
Discussion of the decisive factors affecting the low-temperature performance of lithium-ion batteries
Expert Opinion 1: Electrolyte has the greatest impact on the low-temperature performance of lithium-ion batteries. The composition and physicochemical properties of the electrolyte significantly affect the low-temperature performance of the battery. At low temperatures, the battery cycle faces the following problems: increased electrolyte viscosity and slower ion conduction speed lead to a mismatch in the electron removal rate of the external circuit, resulting in severe battery polarization and a sharp decline in charge and discharge capacity. Especially during low-temperature charging, lithium ions can form lithium dendrites on the surface of the negative electrode, leading to battery failure.
The low-temperature performance of an electrolyte is closely related to its conductivity. Electrolytes with high conductivity exhibit fast ion transport, allowing them to perform at greater capacities at low temperatures. The more lithium ions dissociate in the electrolyte, the higher the lithium ion removal rate, and the higher the lithium ion conductivity. Higher conductivity results in faster ion conduction, less polarization, and better low-temperature battery performance. Therefore, high conductivity is a necessary condition for achieving good low-temperature performance in lithium-ion batteries.
The conductivity of an electrolyte is related to its composition. Reducing solvent viscosity is one way to improve electrolyte conductivity. Excellent solvent fluidity at low temperatures is crucial for ensuring ion transport and the formation of a negative electrode in a solid electrolyte membrane at low temperatures. Resi is also an important impedance factor for lithium-ion batteries in low-temperature environments.
Expert 2: The key factor limiting the low-temperature performance of lithium-ion batteries is the sharp increase in lithium-ion dispersion impedance at low temperatures, rather than SEI.
