Source: Lithium Battery UPS • Author: lithium battery UPS

(Source: Lithium battery UPS)

Introduction to the low-temperature performance of lithium-ion batteries, the factors restricting the low-temperature performance of lithium-ion batteries. Since commercialization, lithium-ion batteries have been widely used for their advantages such as long life, large specific capacity, and no memory effect. In the past, more attention has been paid to the cycle life and safety of lithium-ion batteries. With the continuous expansion of application fields, lithium The restrictions brought by the low temperature performance of ion batteries are becoming more and more obvious.

With the rapid development of the application of lithium-ion batteries in the field of electric vehicles and military industry, the shortcomings of their low-temperature performance that cannot adapt to special low-temperature weather or extreme environments have become more apparent. Under low temperature conditions, the effective discharge capacity and effective discharge energy of lithium-ion batteries will be significantly reduced, and at the same time, it is almost not rechargeable in an environment below -10 ℃, which seriously restricts the application of lithium-ion batteries.

Among all environmental factors, temperature has the greatest impact on the batterys charge and discharge performance. The electrochemical reaction of the lithium battery at the electrode/electrolyte interface is related to the ambient temperature. At low temperatures, the viscosity of the electrolyte decreases, the conductivity decreases, and the activity of the active material also decreases, which will increase the concentration difference of the electrolyte, increase the polarization, and terminate the charging prematurely. More importantly, the diffusion rate of lithium ions in the carbon anode will be slower, the temperature will drop, and the reaction rate of the electrode will also decrease.

Lithium ion batteries work under low temperature conditions, the capacity of the battery drops sharply and the polarization is enhanced. Under low temperature conditions, lithium ions are difficult to insert into the negative electrode and are relatively easy to get out of the negative electrode, thus leading to a decrease in capacity and the discharge of the battery The change is related to the decrease in the conductivity of the electrolyte at low temperature, the decrease in the diffusion rate of lithium ions in the electrode, and the increase in impedance due to the formation of a new SEI film on the surface of the negative electrode due to the deposition of lithium metal during charging.

The battery must be preheated before charging or using it in a low temperature environment. The battery management system of the electric vehicle onboard battery can be divided into two types: external heating and internal heating. These heating methods are generally located in the battery pack, or set in the container of the thermal cycle medium. The internal heating method heats the battery, which is to excite the electrochemical substances inside the battery by alternating current, so that the battery itself generates heat.

Factors restricting the low-temperature performance of lithium-ion batteries: 1. The three-dimensional structure of the cathode material restricts the diffusion rate of lithium ions. Different cathode materials have different three-dimensional structures, and the effect is particularly obvious at low temperatures; 2. The electrolyte and the anode and separator at low temperatures. Compatibility becomes worse; the viscosity of the electrolyte increases, or even partially solidifies, resulting in low ionic conductivity; 3. The diffusion coefficient of lithium ions in the active material decreases at low temperatures, and the charge transfer resistance increases significantly; 4. Lithium under low temperature The thickness of the SEI film of the negative electrode of the ion battery is thickened, and the increase in the impedance of the SEI film leads to a reduction in the conduction rate of lithium ions in the SEI film; The thickness of the electrolyte interface increases.

In the face of the limited use of lithium batteries at low temperatures, the countermeasure is to charge and preheat. Although it is an expedient measure, it has a significant effect on improving the low temperature performance of lithium batteries. Compared with conventional lithium-ion batteries, all-solid-state lithium-ion batteries, especially all-solid-state thin-film lithium-ion batteries, are expected to completely solve the problem of capacity attenuation and cycle safety of batteries used at low temperatures.
       (Editor in charge: fqj)