Causes of performance of lithium battery in winter

　　Author ：Iflowpower – Portable Power Station Supplier

Since entering the market, lithium-ion batteries has been widely used in their advantages of their long life, large specific capacity, no memory effect. Low temperature in lithium ion battery is low, severe attenuation, poor cycle magnification, and obvious lithium phenomenon, and deinterlaxing lithium imbalance. However, as the application is continuously expanding, the restriction of low temperature performance of lithium-ion batteries is increasing.

According to reports, the discharge capacity of the lithium ion battery is only about 31.5% at room temperature at -20 ° C. The conventional lithium ion battery operating temperature is between -20 to + 55 ° C.

However, in the fields of aerospace, special, electric vehicles, etc., the battery can be required to work normally at -40 ° C. Therefore, it is of great significance to improve the low temperature properties of lithium ion batteries.

In factors constrained lithium-ion batteries, the viscosity of the electrolyte is increased, even partially solidified, resulting in a low temperature of the lithium ion battery, resulting in a decrease in the conductivity of the lithium ion battery. The compatibility between the electrolyte and the negative electrode and the diaphragm is deteriorated in a low temperature environment. The negative electrode of the lithium ion battery under low temperature environments was severely precipitated, and the precipitated metal lithium was reacted with an electrolyte, and the product deposition results in a solid state electrolyte interface (SEI) thickness increase.

 Lithium ion batteries decrease in the internal diffusion system in the active substance under low temperature environment, and the charge transfer impedance (RCT) is significantly increased. Discussion on the determinant of low temperature performance of lithium-ion batteries: The electrolyte has an important effect on the low temperature performance of lithium ion batteries, the composition and materialization properties of the electrolyte have an important impact on battery low temperature. The problem in the battery low temperature is: the viscosity of the electrolyte will be large, the ion conduction speed is slow, resulting in the electron migration speed of the external circuit, so the battery has severely polarized, and the charge and discharge capacity has a sharp decrease.

Especially when low-temperature charging, lithium ions can easily form lithium delegra in the surface of the negative electrode, resulting in failure of the battery. The low temperature performance of the electrolyte is closely related to the size of the electrolyte itself, and the transmission ion of the electrical conductivity is fast, and more capacity can be exhibited at low temperatures. The more lithium salts in the electrolyte, the more the number of migration is, the higher the conductivity.

The speed of electrical conductivity, the faster the ion conductivity, the smaller the polarization, the better the performance of the battery at low temperature. Therefore, higher conductivity is a necessary condition for achieving good low temperature performance of lithium ion batteries. The electrolyte electrical conductivity is related to the compositional composition of the electrolyte, and the viscosity of the solvent is to improve the pathway of the electrolyte electrical conductivity.

The fluidity of solvent is good at a low temperature of the solvent is the guarantee of ion transport, and the solid electrolyte membrane formed by the electrolyte in the low temperature electrolyte is also a key to affecting lithium ion conductance, and RSEI is the main impedance of a lithium ion battery in a low temperature environment. Expert 2: Limiting the main factor in low temperature performance of lithium ion batteries is a sharp increase in LI + diffusion impedance at low temperatures, but not the SEI film. Low Temperature Characteristics of Lithium Ion Battery Positive Materials - 1 - Low Temperature Characteristics of Layered Structure Positive Materials The layered structure has both a one-dimensional lithium-ion diffusion channel that is unparalleled, and has a three-dimensional channel structure stability, which is the first commercial lithium ion battery positive material.

Its representative substances include LiiCoO2, Li (CO1-XNIX) O2 and Li (Ni, Co, Mn) O2. Xie Xiaohua et al. Takes LiCoo2 / MCMB as research objects, tested its low temperature charging characteristics.

 The results show that as the temperature decreases, the discharge platform drops from 3.762V (0 ° C) to 3.207V (-30 ° C); its battery total capacity is also reduced from 78.

98mA · h (0 ° C) to 68.55mA · h (-30 ° C). - 2 - low temperature characteristics of spinel structure positive material Spinel structure LiMn2O4 positive material, due to the excellent cost, non-toxic advantages due to the co element However, the Mn valence gear is multi-change and the JAHN-Teller effect of Mn3 +, resulting in problems such as structural unstable and reversible differences.

 Peng Zhengshun, indicating that the electrochemical performance of LiMn2O4 positive electrode materials is large, and the RCT is used as an example: the RCT of LIMN2O4 synthesized by high temperature solid phase is significantly higher than the sol gel method, and this phenomenon is in lithium ion The diffusion coefficient is also reflected. The reason is mainly due to the fact that different synthetic methods have a great effect on product crystallinity and morphology. - 3 - low temperature characteristics of positive electrode material of phosphate system LIFEPO4 has become the main body of the current power battery positive material due to its excellent volume stability and safety, and the ternary material.

The low temperature resistance of the iron phosphate is mainly because the material itself is the insulator, the electron conductivity is low, the lithium ion diffusion is poor, so that the internal resistance of the battery increases, the polarization is high, the battery charge and discharge is blocked, so low temperature Performance is not ideal. Valley Yidi, etc., when studying the charge and discharge behavior of LifePO4 at low temperatures, the Kulen efficiency is 64% at 96% and -20 ° C at 55 ° C to 0 ° C, and the discharge voltage is from 55 ° C 3.

11V. 2.62V of delivery to -20 ° C.

 XING et al, discovery, after the addition of nanocarbon conductive agents, the electrochemical properties of LiFePO4 decreased, and the low temperature performance is improved; the discharge voltage of LiFePO4 after modification 3.40 V fell to 3.09V at -25 ° C, the decrease was only 9.

12%; and its battery efficiency was 57.3%, higher than 53.4% ​​of the non-nanocarbon electrical agent at -25 ° C.

 Recently, LIMNPO4 has attracted people's interested interest. The study found that LIMNPO4 has the advantages of high potential (4.1V), no pollution, low price, large specific capacity (170mAh / g).

However, since the LIMNPO4 is lower than LiFePO4 lower ionic conductivity, it is often used in the actual substitution of Mn to form a LiMn0.8Fe0.2PO4 solid solution.

 The low temperature characteristics of the lithium-ion battery negative electrode material are more serious relative to the positive electrode material, and the low temperature deterioration of the lithium ion battery negative electrode material is more serious, mainly the following three reasons: The battery is extremely polarized when the low temperature high magnification is charged and discharge, and the negative surface metal lithium is deposited, and the reaction product of the metal lithium and the electrolyte generally does not have electrical conductivity; From the thermodynamic angle, the electrolyte contains a large amount of C-O, C-N isolaty, and can react with the negative electrode material, and the formed SEI film is more susceptible to the low temperature; The carbon negative electrode is difficult to lithium lithium under low temperature, and there is a charge and discharge asymmetry. The study electrolyte electrolyte electrolyte electrolyte in a lithium ion battery has a significant effect on the ionic conductivity and SEI film formation properties to the battery low temperature performance. It is judged that the low temperature electrolyte is extremely very detro, there are three main indicators: ionic conductivity, electrochemical windows, and electrode reactivity.

The level of these three indicators is largely dependent on its compositional material: solvent, electrolyte (lithium salt), additive. Therefore, the study of the low temperature performance of each part of the electrolyte, is of great significance for understanding and improving the low temperature energy of the battery. The EC-based electrolyte low temperature characteristics compared to chain carbonate, the cyclic carbonate structure is tight, high, has a high melting point and viscosity.

However, the large polarity brought by the annular structure often has a large dielectric constant. EC solvent has a large dielectric constant, high ion conductivity, perfect film formation performance, effectively prevents the solvent molecule from being co-inserted, so that it is an indispensable position, so that mostly low temperature electrolytic solution systems are large, and then mixed Low melting small molecule solvent. Lithium salt is an important composition of electrolyte.

The lithium salt can not only improve the ionic conductivity of the solution in the electrolyte, and can also reduce the diffusion distance of Li + in the solution. In general, the larger the Li + concentration in the solution, the greater the ion conductivity. However, the concentration of the lithium ion concentration in the electrolyte is not linearly correlated, but is a parabolic.

This is because the concentration of lithium ion concentration in the solvent depends on the dissolution of the lithium salt in the solvent and the strength of the association. The study of low temperature electrolyte except for the battery composed of the actual operation, the performance of the battery can also have a large impact on the performance of the battery. Preparation Process.

YaquB et al. Research on electrode load and coating thickness on low temperature performance of lini0.6co0.

2 mn0.2O2 / graphite battery, in terms of capacity retention ratio, the smaller the electrode load, the thinner coating layer, the better the low temperature performance . Charge and discharge state.

Petzl et al., The effect of low temperature charge and battery cycle life, found that when the discharge depth is large, a large capacity loss is caused, and the cycle life is lowered. Other factors.

The surface area of ​​the electrode, the aperture, the electrode density, the wettability of the electrode and the electrolyte, and the like, which affect the low temperature performance of the lithium ion battery. In addition, the impact of defects in materials and processes on battery low temperature performance can not be ignored. Summary To ensure the low temperature performance of the lithium-ion battery, you need to do the following: Form a thin and dense SEI film; Ensure that Li + has a large diffusion coefficient in active substance; The electrolyte has a high ionic conductivity at a low temperature.

 In addition, the study can also take a different approach to another type of lithium-ion battery - full solid lithium ion battery. Compared to conventional lithium-ion batteries, all solid-state lithium ion batteries, especially full solid thin film lithium ion batteries, are expected to completely solve the capacity attenuation problem and cycle safety issues used under low temperatures.