Since its introduction to the market, lithium-ion batteries have gained widespread applications due to their long lifespan, high specific energy, and lack of memory effect. However, using lithium-ion batteries at low temperatures poses several challenges such as reduced capacity, severe degradation, poor cycling performance, pronounced lithium plating, and imbalanced lithium stripping.

As the application areas continue to expand, the limitations imposed by poor low-temperature performance of lithium-ion batteries become more apparent.

According to reports, at -20°C, the discharge capacity of a lithium-ion battery is only about 31.5% of that at room temperature. Traditional lithium-ion batteries typically operate within a temperature range of -20°C to +55°C. However, many industries require batteries that can operate normally at -40°C. Therefore improving the low-temperature properties of lithium-ion batteries is significantly meaningful in facilitating wider applications.

Factors affecting the low temperature performance of lithium-ion batteries

• In low temperature environments, the viscosity of the electrolyte increases, and even some parts solidify, leading to a decrease in the conductivity of lithium-ion batteries.
• In low temperature environments, the compatibility between the electrolyte and negative electrode as well as separator deteriorates.
• In low temperature environments, lithium deposition on the negative electrode is severe in lithium-ion batteries, and the reaction between deposited metallic lithium and electrolyte leads to increased thickness of Solid Electrolyte Interphase (SEI) resulting from product deposition.
• In low temperature environments, diffusion within active materials inside lithium-ion batteries decreases significantly. As a result, charge transfer resistance (Rct) increases noticeably.

Discussion on Factors Affecting the Low-Temperature Performance of Lithium-Ion Batteries

Expert viewpoint: The influence of electrolyte on the low temperature performance of lithium-ion batteries is significant. The composition and physicochemical properties of the electrolyte have an important impact on the low temperature performance of the battery.

The problems faced by batteries during cycling at low temperatures are as follows: the viscosity of the electrolyte increases, leading to slower ion conduction, which causes a mismatch in electron migration speed in the external circuit. As a result, severe polarization occurs in the battery, and there is a sharp decrease in charge-discharge capacity. Especially during low-temperature charging, lithium ions easily form dendrites on the surface of the negative electrode, leading to battery failure.

The low temperature performance of electrolytes is closely related to their own conductivity. Electrolytes with higher conductivity allow for faster ion transport and can deliver more capacity at low temperatures. The more dissociated lithium salts are in electrolytes, the greater number of migrating ions and therefore higher conductivity they exhibit.

Higher conductivity leads to faster ion conduction rates and less polarization, resulting in better performance at low temperatures. Therefore, having higher conductivity is a necessary condition for achieving good cold weather performance in lithium-ion batteries.

The electrical conductivity of an electrolyte depends on its composition. Reducing solvent viscosity is one way to improve electrolyte conductance. Good flowability of solvents at lower temperatures ensures smooth ion transport. Additionally, solid-state electrolyte films formed on negative electrodes play a key role in influencing lithium ion conduction at lower temperatures while RSEI (Residue Solid Electrolye Interphase) acts as major impedance point for Lithium-ion Batteries under Low-Temperature Conditions

Expert 2: The main factors to limit the low temperature performance of lithium -ion batteries are the sharply increased LI+diffusion impedance at low temperature, not a SEI film.

Low -temperature characteristics of lithium ion battery positive materials

The low temperature characteristics of layer -shaped structure positive electrode materials

The layered structure has the unparalleled percentage performance of the one -dimensional lithium ion diffusion channel, but also the structural stability of the three -dimensional channel. It is the earliest commercial lithium -ion battery positive material. Its representative substances include LICOO2, Li (CO1-XNIX) O2 and Li (Ni, Co, Mn) O2.

Xie Xiaohua and others tested their low -temperature charging discharge special with LICOO2/MCMB as the research object.

The results showed that as the temperature decreased, its discharge platform dropped from 3.762V (0 ° C) to 3.207V (–30 ° C); its total battery capacity was also sharply reduced from 78.98ma · H (0 ° C) to 68.55ma · H · H (–30 ° C).

The low -temperature characteristics of the orthopedic material of the spinel structure

Speedstone structure Limn2O4 positive electrode material, because it does not contain CO elements, has the advantage of low cost and non -toxicity.

However, MN-priced and MN3 +’s Jahn-Teller effects have caused the component to have problems such as unstable structure and reversibility.

Peng Zhengshun and others pointed out that different preparation methods have a great impact on the electrochemical properties of Limn2O4 positive electrode materials. Taking RCT as an example: The RCT of LIMN2O4 synthesized by high -temperature solid -phase method is significantly higher than that of the solution gel method, and this phenomenon is lithium ion in lithium ion The diffusion coefficient is also reflected. The reason is mainly because different synthetic methods have a greater impact on the crystallization and appearance of the product.

The low temperature characteristics of the positive pole material of the phosphate system

Lifepo4 has become the main body of current power battery positive materials due to excellent volume stability and safety, together with ternary materials. The low temperature of lithium iron phosphate is mainly due to its material itself is an insulator, with low electronic conductivity, poor lithium ion diffusion, poor conductivity at low temperature, which increases the internal resistance of the battery. Performance is not ideal.

Gu Yijie and others found that when the charging and discharge behavior of LIFEPO4 was found at low temperature, it was found that its Kuron efficiency dropped from 100%of 55 ° C to 96%and 64%at 96%and -20 ° C; Sumid to 2.62V when -20 ° C.

Xing et al. Using nano -carbon to modify LIFEPO4, it is found that after adding nano -carbon conductive agents, the electrochemical performance of LIFEPO4 reduces the sensitivity of temperature and improves low temperature performance. V’s 3.09V when it dropped to -25 ° C, the decrease was only 9.12%; and the battery efficiency was 57.3%at the time of -25 ° C, which was higher than 53.4%without nano -carbon conducted.

Recently, Limnpo4 has attracted a lot of interest. Studies have found that LimnPO4 has the advantages of high potential (4.1V), pollution -free, low price, and larger capacity (170mAh/g). However, due to the lower ionic conductivity than LIFEPO4 than LIFEPO4, the FE part is often used to replace the MN to form LIMN0.8FE0.2PO4 solid solution.

Low -temperature characteristics of lithium ion battery negative materials

Compared to the positive electrode material, the low temperature deterioration of the negative electrode material of the lithium -ion battery is more serious, mainly in the following three reasons:

• During the low temperature and large multiplier, the battery polarization is severe, the negative surface metal lithium is deposited in large quantities, and the reaction product of the metal lithium and the electrolytic solution generally does not have conductivity;
• From the perspective of thermodynamics, the electrolyte contains a large number of polar groups such as C -O, C -N, which can react with the negative electrode material.
• The carbon negative electrode is difficult to embed lithium at low temperature, and there is an asymmetry of charging and discharge.

Research on low temperature electrolyte

The electrolyte in the lithium ion battery has the role of conveying LI+, and its ionic conductivity and SEI film performance have significantly impact on the low temperature performance of the battery. Determine low -temperature electrolytes and disadvantages. There are three main indicators: ionic conductivity, electrochemical windows and electrode reaction activity.

The level of these three indicators depends to a large extent on its components: solvents, electrolytes (lithium salt), additives. Therefore, the research of the low temperature performance of each part of the electrolyte is of great significance for understanding and improving the low temperature performance of the battery.

• Compared with the chain -shaped carbonate, EC -based electrolyte low -temperature characteristics are closely structured and strong, and have high melting points and viscosity. However, the large polarity brought by the ring structure makes it often have a large dielectric constant. EC solvents’ large agencies, high ion conductivity, and excellent film performance, effectively prevent the insertion of solvents molecules, so that they have an indispensable position. Low melting point small molecule solvents.
• Lithium salt is an important component of electrolyte. In the electrolyte, lithium salt can not only improve the ion conductivity of the solution, but also reduce the diffusion distance in the solution in the solution. Generally speaking, the greater the LI+concentration in the solution, the greater its ionic conductivity. However, the lithium ion concentration in the electrolyte is not linearly related to the concentration of lithium salt, but is parabolic. This is because the lithium ion concentration in the solvent depends on the dissolution of the lithium salt in the solvent and the strength of the connection effect.

In addition to the battery composition itself, the process factors in actual operation will also have a great impact on the performance of the battery.

• Preparation Process
  Yaqub et al. Research the effects of electrode load and coating thickness on Lini0.6CO0.2MN0.2O2 /Graphite battery at low temperature performance. It is found that the smaller the electrode load, the thinner the coating layer, and the better the low temperature performance, the better the low temperature performance. Essence
• Charging and discharge state
  PETZL and others have studied the effects of low -temperature charging state on battery cycle life. It is found that when the discharge depth is large, it will cause a large capacity loss and reduce the cycle life.
• Other factors
  The surface area, pores, electrode density, electrode and electrolytes of the electrode, and the moisture and diaphragm of the electrode are all affecting the low temperature performance of lithium -ion batteries. In addition, the impact of the defects of materials and crafts on the low temperature performance of the battery cannot be ignored.

Summarize

In order to ensure the low temperature performance of the lithium -ion battery, the following points need to be done:

Form a thin and dense SEI film;

Ensure that Li+ has a large diffusion coefficient in active substances;

The electrolyte has a high ion conductivity at low temperature.

In addition, in the study, you can also set a different approach to invest in another type of lithium -ion battery -a full solid lithium ion battery. Compared with conventional lithium -ion batteries, all -solid lithium -ion batteries, especially all -solid -film lithium -ion batteries, are expected to completely solve the problem of capacity attenuation and cycle safety of batteries at low temperature.

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