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The low-temperature performance of lithium-ion batteries is one of the key factors that restrict the widespread use of lithium batteries. How to improve the low-temperature performance of lithium batteries is still a hot and difficult point of current research.
The battery system reaction process mainly includes four steps: Li+ transport in the electrolyte, crossing the electrolyte/electrode interface membrane, charge transfer, and Li+ diffusion in the active material body. At low temperatures, the rate of each step decreases, which causes the impedance of each step to increase, which leads to aggravation of electrode polarization, and causes problems such as a decrease in low- temperature discharge capacity and lithium precipitation in the negative electrode. The poor low-temperature performance of lithium-ion batteries is mainly due to the following three factors:
1. At low temperatures, the viscosity of the electrolyte increases, and the conductivity decreases;
2. The electrolyte/electrode interface membrane impedance and charge transfer impedance increase;
3. The migration rate of lithium ions in the active material body is reduced. As a result, the electrode polarization is increased at low temperatures and the charge and discharge capacity is reduced.
To improve the low temperature performance of lithium batteries, the influence of the positive electrode, negative electrode, electrolyte and other comprehensive factors in the battery should be comprehensively considered. The conductivity of the electrolyte should be improved by optimizing the composition of electrolyte solvent, additives and lithium salt, while reducing the film-forming resistance; The electrode material undergoes modification treatments such as doping, coating, and granulation to optimize the material structure and reduce the interface resistance and the diffusion resistance of Li+ in the active material body. Through the overall optimization of the battery system, the polarization of the lithium battery at low temperatures is reduced, and the low temperature performance of the battery is further improved.
The mainstream ways to improve the ion diffusion performance of cathode materials at low temperatures are as follows: First, use materials with excellent conductivity to coat the active material body to improve the conductivity of the cathode material interface, reduce the interface impedance, and reduce the positive electrode material and The side reaction of the electrolyte stabilizes the material structure. The second is to do bulk- doping of the material body with Mn, Al, Cr, Mg, F and other elements to increase the layer spacing of the material to increase the diffusion rate of Li+ in the body, reduce the diffusion resistance of Li+, and increase the low temperature of the battery. performance. The third is to reduce the particle size of the material and shorten the Li+ migration path. It should be pointed out that this method will increase the specific surface area of the material and increase the side reaction with the electrolyte.
As an important part of the lithium ion battery, the electrolyte not only determines the migration rate of Li+ in the liquid phase, but also participates in the formation of the SEI film, which plays a key role in the performance of the SEI film. At low temperatures, the viscosity of the electrolyte increases, the conductivity decreases, the impedance of the SEI film increases, and the compatibility with the positive and negative materials deteriorates, which greatly deteriorates the energy density and cycle performance of the battery. At present, there are two ways to improve the low-temperature performance of the electrolyte: one is to improve the low-temperature conductivity of the electrolyte by optimizing the composition of the solvent and using new electrolyte salts; the second is to use new additives to improve the properties of the SEI membrane, so that It is conducive to Li+ conduction at low temperatures.
Dongguan Power Long Battery Technology Co., Ltd. (PLB) specializes in the R&D and manufacturing of 26650 cylindrical lithium- ion batteries. PLB effectively improves the low-temperature performance of the battery through in-depth research on the low-temperature mechanism of lithium ion, and optimizes and improves materials that affect the low-temperature performance of the battery. So that 26650 lithium iron phosphate can meet application scenarios or projects with low temperature requirements.