Methods for improving low-temperature performance of lithium-ion batteries(2)



The conductivity and film-forming impedance of the electrolyte have an important impact on the low-temperature performance of lithium-ion batteries.

For low-temperature electrolytes, the electrolyte solvent system, lithium salts and additives should be comprehensively optimized. For electrolyte solvents, solvent systems with low melting point, low viscosity and high dielectric constant should be selected, and linear carboxylic ester solvents have excellent low temperature performance, but they have a great impact on cycling performance, so they need to be blended with cyclic carbonates with high dielectric constants such as EC and PC. For lithium salts and additives, the migration rate of lithium ions is mainly improved by reducing the film-forming impedance. In addition, increasing the concentration of lithium salt at low temperature can improve the conductivity of the electrolyte and improve the low-temperature performance.

(3)Anode material

Selecting the appropriate anode material is the key factor to improve the low-temperature performance of the battery, and the low-temperature performance is mainly optimized by means of anode surface treatment, surface coating, doping to increase the layer spacing, and controlling the particle size.

4. Conclusion

To sum up, the low-temperature performance of lithium-ion batteries is the key factor restricting the application of lithium batteries, and how to improve the low-temperature performance of lithium batteries is still a hot spot and difficult point in current research.

The reaction process of the battery system mainly includes four steps: Li transport in the electrolyte, crossing the electrolyte/electrode interface membrane, charge transfer, and Li diffusion in the active substance body. At low temperature, the rate of each step decreases, resulting in an increase in the impedance of each step, which leads to the aggravation of electrode polarization, resulting in the reduction of low-temperature discharge capacity and the negative electrode lithium separation.

To improve the low-temperature performance of lithium batteries, the influence of comprehensive factors such as cathode, anode, and electrolyte in the battery should be comprehensively considered, and the conductivity of the electrolyte should be improved by optimizing the composition of electrolyte solvent, additives and lithium salts, and the film-forming impedance should be reduced. The positive and negative electrode materials were modified by doping, coating, and small granulation to optimize the material structure and reduce the interfacial impedance and the diffusion impedance of Li in the active substance body. Through the optimization of the battery system as a whole, the polarization of the lithium battery at low temperature is reduced, and the low temperature performance of the battery is further improved.