Winter lithium-ion battery capacity will become unfarest, why is the lithium ion battery "fear" low temperature?

　　Author ：Iflowpower – Portable Power Station Supplier

Since entering the market, lithium-ion batteries have obtained a wide range of applications with its advantages of long life, large specific capacity, no memory effect. Low temperature of lithium-ion battery is low, severe attenuation, poor cycle magnification performance, obvious lithium phenomenon, deinterlaxing lithium imbalance, etc. However, with the continuous expansion of the application, the restriction of low temperature performance of lithium-ion batteries is more obvious.

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

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

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

● Lithium ion battery under low temperature environment is lowered, and the charge transfer impedance (RCT) is significantly increased. Discussion on low temperature performance factors affecting lithium ion batteries ● Expert perspective 1: Electrolyne solution has an important impact 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 performance. The problem in the battery low temperature is: the viscosity of the electrolyte will become large, the ion conduction speed is slow, resulting in the electron migration speed of the external circuit, so the battery is severely polarized, and the charge and discharge capacity has a sharp decrease.

Especially when low-temperature charging, lithium ions can easily form lithium delegranes on 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 own conductivity, the transmission ion of the electrical conductivity is fast, and more capacity can be exerted at low temperatures. The more lithium salts in the electrolyte, the more the number of migrations, the higher the conductivity.

High 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 electrical conductivity of the electrolyte is related to the composition of the electrolyte, and the viscosity of the solvent is to improve the pathway of 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 the lithium ion conduction, and the RSEI is the main impedance of the lithium ion battery in a low temperature environment. ● Expert opinion 2: Limited lithium-ion battery low temperature performance is a sharp increase in LI + diffusion impedance under low temperature, but not SEI film. Low temperature characteristics of the positive electrode material of the lithium ion battery ● 1, the low temperature characteristic layer structure of the layered structure positive electrode material has both a one-dimensional lithium ion diffusion channel, and has the structural stability of the three-dimensional channel, which is the earliest commercial commercial.

Lithium ion battery positive material. Its representative substances include LiCoO2, Li (CO1-XNIX) O2 and Li (Ni, Co, Mn) O2, etc. Xie Xiaohua, etc.

use LiCoo2 / MCMB as research objects, testing its low temperature charge 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, the low temperature characteristic of the positive material of the spinel structure spinel structure LiMn2O4 positive material, because there is no Co element, there is a low cost, non-toxic advantages. However, the Mn valence gear 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 Implanted on diffusion coefficients.

The reason is mainly due to different synthetic methods for the crystallinity and morphology of product. ● 3, the low temperature characteristics of the phosphate system positive electrode material LIFEPO4 is the main body of the current power battery positive material due to excellent volume stability and safety, with 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 delivering 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 interests.

The study found that LIMNPO4 has high potentials (4.1V), no pollution, low price, large specific capacity (170mAh / g), etc. However, due to the lower ion conductivity of LIMNPO4 than LiFePO4, it is often used to replace Mn to form a LiMn0.

8Fe0.2PO4 solid solution in the actual use of the FE portion. The low temperature characteristics of the negative electrode material of the lithium-ion battery are more serious relative to the positive electrode material, and the low temperature deterioration of the lithium ion battery is more severe, mainly three reasons: ● Low temperature high magnification charge and discharge, battery polarization is severe, negative surface metal Lithium is largely deposited, and the reaction product of metal lithium and the electrolyte generally does not have electrical conductivity; Affected by the low temperature;.

The study of low temperature electrolytic solutions undertakes the effect of transferring Li + in a lithium ion battery, and its ionic conductivity and SEI film formation performance have significant effect on battery low temperature performance. It is determined that the low temperature electrolytic solution is very particular, there are three main indicators: ionic conductivity, electrochemical windows, and electrode reactivity. The level of these three indicators is largely dependent on its compositional materials: 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 performance of the battery. ● EC-based electrolyte low temperature characteristics compared to chain carbonate, the cyclic carbonate structure is close, strong, has high melting point and viscosity. However, the large polarity of the annular structure makes it often have 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 point of small molecule solvent. ● Lithium salt is an important composition of electrolyte. The lithium salt can not only improve the ionic conductivity of the solution, but 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 line. This is because, the lithium ion concentration in the solvent depends on the dissociation of the lithium salt in the solvent and the strength of the association.

The study of low temperature electrolyte except that the battery is composed of itself, and the process factors in the actual operation will also have a significant impact on the performance of the battery. ● (1) Preparation Process YAQUB et al, the impact of electrode load and coating thickness on LINI0.6CO 0.

2 mn0.2O2 / graphite battery low temperature performance revealed that the smaller the electrode load is smaller, the less coating layer is thinner The better the low temperature performance. ● (2) Charge and discharge status Petzl et al, the impact of low-temperature charge-discharge status on battery cycle life found that when the depth of discharge can cause greater capacity loss, and reduce circulatory life.

(3) The surface area, the aperture, the electrode density, the wettability of the electrode and the electrolytic solution, and the like, which affect the low temperature performance of the lithium ion battery. In addition, the impact of the defects of materials and processes on low temperature performance of the battery can not be ignored. Therefore, in order to ensure the low temperature performance of the lithium-ion battery, it is necessary to do the following: ● (1) forming a thin and dense SEI film; ● (2) guarantees that Li + has a large diffusion coefficient in active substance; ● (3) ) The electrolyte has high ion conductivity at low temperatures.

In addition, the study can also take another approach, and the eye is turned to another kind 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, is expected to completely solve the capacity attenuation problem and cycle safety issues used in battery low temperatures. So how do you treat lithium batteries in winter? 1.

Do not use the lithium battery temperature in the low temperature environment for the effect of lithium battery, the lower the temperature of the lithium battery, the lower the activity of the lithium battery, which directly leads to a significant reduction in charge and discharge efficiency, which is generally, the work of lithium batteries Temperature is between -20 degrees -60 degrees. When the temperature is less than 0 ° C, be careful not to charge outdoors, you can charge it, we can take the battery in the room (note, stay away from flammable!!!), When the temperature is below -20 At ° C, the battery will automatically enter the sleep state and cannot be used normally. So the user of the north is especially cold.

There is no indoor charging condition. To make full use of the rest of the battery, immediately charge the sun after parking, to increase charging, and avoid lithium. 2, develop the accompanying habitual winter, when the battery is too low, we must make timely charging, develop a good habit of accompanying, remember, never follow the normal battery to return to the winter battery power.

Winter lithium battery activity declines, very easy to cause overcharge, lightly affect battery life, and trigger a combustion accident. Therefore, pay more attention to charging in a shallow-shallow manner in winter. Especially need to be pointed out, don't park the vehicle for a long time, avoid over charge.

3, do not stay away from remember not to charge for a long time, don't make it convenient, put the vehicle for a long time in the state of charge, and you can. When the charging environment in winter is less than 0 ° C, when charging, don't leave too far, to prevent emergencies, timely handling. 4.

When charging, use a lithium battery's special charger market full of inferior charger, using inferior chargers, can cause battery damage, and even cause fire. Don't buy low-priced non-guaranteed products, don't use lead-acid battery chargers; if your charger can't use it, stop using it, don't don't lose. 5, pay attention to battery life, timely change in new lithium battery life, different types of battery life, plus daily way of use, the life of the battery is not equal, if the car is powered down or endless Short, please contact lithium battery maintenance personnel to handle the lithium battery repair person during the short, please contact the lithium battery maintenance personnel.

6, there is a good electricity for the winter, in order to use the vehicle in the middle of the spring, if you don't have a battery long long, you will remember to charge 50% - 80% of the battery, and remove it from the car, and make regular charging, about one month Charge. Note: The battery is stored in a dry environment. 7.

Correctly place the battery Do not immerse the battery in water, or make the battery moist; do not stack more than 7 floors, or invert the battery direction, lithium.