According to reports, the discharge capacity of lithium-ion batteries at -20°C is only 31.5% of room temperature. The operating temperature of traditional lithium-ion batteries is between -20 and +55°C. However, in the field of aerospace, industry and electric vehicles, batteries are required to work normally at -40°C. Therefore, improving the low-temperature performance of lithium-ion batteries is of vital importance.
Factors that limit the low-temperature performance of lithium-ion batteries
In a low-temperature environment, the viscosity of the electrolyte increases, or even partially solidifies, resulting in a decrease in the conductivity of the lithium-ion battery.
In a low temperature environment, the compatibility between the electrolyte, the negative electrode and the separator becomes poor.
In a low temperature environment, the negative electrode of a lithium ion battery is severely precipitated, and the precipitated metal lithium reacts with the electrolyte, and the product deposition causes the thickness of the solid electrolyte interface (SEI) to increase.
In a low-temperature environment, the diffusion system inside the active material of the lithium-ion battery is reduced, and the charge transfer resistance (Rct) is significantly increased.
Discussion on the decisive factors affecting the low-temperature performance of lithium-ion batteries
1: The electrolyte has the greatest impact on the low-temperature performance of lithium-ion batteries, and the composition and physical and chemical properties of the electrolyte have an important impact on the low-temperature performance of the battery. The problem faced by the battery cycle at low temperatures is: the viscosity of the electrolyte will increase and the ion conduction speed will slow down, resulting in a mismatch in the electron migration speed of the external circuit, so the battery will be severely polarized and the charge and discharge capacity will drop sharply. Especially when charging at low temperatures, lithium ions are likely to form lithium dendrites on the surface of the negative electrode, causing battery failure.
The low temperature performance of the electrolyte is closely related to the conductivity of the electrolyte itself. The high conductivity of the electrolyte can transport ions faster, and can exert greater capacity at low temperatures. The more the lithium salt in the electrolyte dissociates, the greater the number of migrations, and the higher the conductivity. The higher the conductivity, the faster the ion conductivity, the smaller the polarization, and the better the battery's performance at low temperatures. Therefore, higher electrical conductivity is a necessary condition for achieving good low-temperature performance of lithium-ion batteries.
The conductivity of the electrolyte is related to the composition of the electrolyte, and reducing the viscosity of the solvent is one of the ways to increase the conductivity of the electrolyte. Good solvent fluidity at low temperature is the guarantee of ion migration. The solid electrolyte membrane formed by the electrolyte on the negative electrode at low temperature is also the key to the conduction of lithium ions. RSEI is an important impedance of lithium for ion batteries in low temperature environments.
2: The important factor limiting the low-temperature performance of lithium-ion batteries is the rapid increase of Li+ diffusion resistance at low temperatures, not the SEI film.
As far as current technology is concerned, lithium-ion batteries can only be replaced with new ones if there is a problem, there is no technology on the market that can repair lithium-ion batteries!
In contrast, the repair technology of lead-acid batteries is much more mature, and a large part of the lead-acid batteries that are eliminated can be used after repair!