As a Ni-MH Battery Pack Supplier, to share with you, the mainstream ways to
improve the ion diffusion performance of cathode materials at low temperatures
1. The method of surface coating the active material body with a material with excellent conductivity improves the electrical conductivity of the interface of the positive electrode material, reduces the interface impedance, and at the same time reduces the side reaction of the positive electrode material and the electrolyte and stabilizes the material structure.
The cyclic voltammetry and AC impedance method were used to study the low-temperature performance of carbon-coated LiFepO4. It was found that the discharge capacity gradually decreased as the temperature decreased, and the capacity at -20°C was only 33% of the normal temperature capacity. The author believes that as the temperature decreases, the charge transfer impedance and the Weber impedance of the battery gradually increase, and the difference between the redox potential in the CV curve increases, which indicates that the diffusion of lithium ions in the material is slowed at low temperatures, and the Faraday of the battery The weakening of the reaction kinetic rate causes a significant increase in polarization.
A composite cathode material coated with fast ion conductor coated nickel-cobalt-manganese lithium was designed and synthesized. The composite material showed excellent low-temperature performance and rate performance, and maintained a reversible capacity of 127.7mAhg-1 at -20°C, far superior 86.4mAhg-1 for lithium nickel cobalt manganate material. By introducing a fast ion conductor with excellent ionic conductivity to effectively improve the Li+ diffusion rate, it provides a new idea for improving the low temperature performance of lithium ion batteries.
2. Bulk doping the material body with Mn, Al, Cr, Mg, F and other elements, adding a layer spacing of the material to increase the diffusion rate of Li+ in the body, reduce the diffusion resistance of Li+, and thus improve the low temperature performance of the battery .
Compared with the original LiFepO4, the carbon-coated LiFepO4 cathode material prepared by Mn doping has a certain degree of polarization reduction at different temperatures, which significantly improves the electrochemical performance of the material at low temperatures. Al doping of LiNi0.5Co0.2Mn0.3O2 material found that Al increased the interlayer distance of the material, reduced the diffusion resistance of lithium ions in the material, and greatly increased the gram capacity at low temperature.
The phase transition of the lithium iron phosphate cathode material from the lithium iron phosphate phase to the iron phosphate phase during the charging process is slower than the phase transition from the iron phosphate phase to the lithium iron phosphate phase during the discharge process, and Cr doping can promote the discharge process from the iron phosphate phase The phase transition to the lithium iron phosphate phase improves the rate performance and low temperature performance of LiFepO4.
3. Reduce the material particle size 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.
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