Why will the lithium ion battery capacity be lowered in winter?

　　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.

However, in the fields of aerospace, special, electric vehicles, require the battery to work in -40 ° C. Therefore, it is of great significance to improve the low temperature properties of lithium ion batteries. Factors constrained lithium-ion batteries low temperature performance, the viscosity of the electrolyte increases, even partially solidified, resulting in a low-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 caused to a solid electrolyte interface (SEI) thickness. Lithium-ion batteries under low temperature environment reduce the internal diffusion system of the active substance, the charge transfer impedance (RCT) is significantly increased.

Exploration on the influence of the decisive factors affecting the 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 performance. The problem in the surface of the battery is: the viscosity of the electrolyte will become large, the ion conductivity 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 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 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 the key to affecting lithium ion conductance, and RSEI is an important impedance of a lithium ion battery in a low temperature environment.

Expert 2: Important factors in limiting low temperature performance of lithium ion batteries are low temperature, new Li + diffusion impedance, but not SEI film. 1, the low temperature characteristic laminated 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 first 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, its discharge platform is dropped from 3.

207V (0 ° C) (–30 ° C); its battery total capacity is also reduced by 78.98mAh (0 ° C) to 68.55mAh (–30 ° C).

2, the low temperature characteristics of the spine structure positive electrode material LIMN2O4 positive material, due to the excellent 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 important because different synthetic methods have a large number of crystallinity and morphology of product. 3. Lithium phosphate low temperature performance is important because its material itself is an insulator, low electron conductivity, poor conductivity in low temperature, so that the internal resistance of the battery increases, the polarization is high, and the battery charge and discharge is blocked.

Low temperature is not ideal. Gu Yighao, etc.–64% at 20 ° C; the discharge voltage is reduced from 3.

11V at 55 ° C to–2.62V at 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 dropped to–3.09V at 25 ° C, the decrease is only 9.12%; and it is–The battery efficiency was 57.

3% at 25 ° C, above 53.4% ​​of the non-nanocarbon electrical agent. 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 related to the positive electrode material, the low temperature deterioration of the lithium ion battery negative electrode material is more serious, and it is important to have the following three reasons: low temperature high magnification charge and discharge, battery polarization is severe, negative surface metal lithium A large deposition, 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 number of c–O, C–N and the like can be reacted with the negative electrode material, the formed SEI film is more susceptible to the low temperature; the carbon negative electrode is difficult to lithium at low temperature, and there is charge and discharge asymmetry.