Science and technology
How to improve the low temperature performance of lithium iron phosphate batteries?
For lithium iron phosphate batteries, Waterma has done a more detailed study on the factors affecting its low-temperature characteristics: one is the influence of the positive electrode. The lithium iron phosphate positive electrode itself has relatively poor electronic conductivity, and it is more prone to polarization and reduce capacity Play; the second negative electrode, the negative electrode is important for low-temperature charging, because it will affect safety issues; the third is the electrolyte, which may increase the viscosity at low temperatures and increase the lithium ion migration resistance; The four are binders, which now have a relatively large impact on the low-temperature performance of the battery.
Waterma's whole idea is to improve the low-temperature performance of lithium iron phosphate batteries from four pieces of positive electrode, negative electrode, electro-hydraulic and binder.
As for the positive electrode, it is now nano-sized, and its particle size, electrical resistance, and the axis length of the AB plane will affect the low-temperature characteristics of the entire battery. Lithium iron phosphate was prepared through three processes. From the perspective of our overall preparation conditions, different lithium iron phosphate processes are nanometerized and coated. From the perspective of the axial length of the AB surface, the increase in the axial length of the AB surface makes the lithium The ion migration channel will become larger, which will help improve the battery rate performance. Different processes have different effects on the positive electrode. The low-temperature discharge characteristics of batteries made of lithium iron phosphate with a particle size of 100 to 200 nanometers are better, and 94% can be released at -20 degrees. That is, the nanometerization of the particle size shortens the migration path. It also improves the performance of low-temperature discharge, because the discharge of lithium iron phosphate is mainly related to the positive electrode.
Considering the charging characteristics of the negative electrode, Rao Mumin believes that low-temperature charging of lithium-ion batteries is mainly due to the negative electrode effect, including the particle size and the change in the distance between the negative electrodes. Three different artificial graphites are selected as the negative electrode to study the different layer spacing and particle The influence of diameter on low temperature characteristics. From the perspective of the three materials, in terms of impedance, the bulk resistance and ion migration resistance of granular graphite with a large interlayer spacing are relatively small.
For the electrolyte, the electrolyte freezes at -20 degrees and -30 degrees, the viscosity increases, and the formation performance deteriorates. The electrolyte comes from three aspects: solvent, lithium salt, and additives. Rao Mumin said that through experiments, we found that the low-temperature effect of solvents on lithium iron phosphate batteries ranges from more than 70% to more than 90%, with more than a dozen points of impact; secondly, different lithium salts have certain characteristics of low-temperature charge and discharge. influences. Based on the fixed solvent system and lithium salt, low-temperature additives can increase the discharge capacity from 85% to 90%. That is to say, in the entire electrolyte system, solvents, lithium salts and additives are all effective for our power lithium batteries. The characteristics have a certain influence, including other material systems are equally applicable.
In terms of adhesives, Rao Mumin said that there are three types, two types of dots and one type of linear ones. In the case of charging and discharging at -20 degrees, after the two dots have been cycled for more than 70 to 80, the entire pole piece has the current status of adhesive failure, and the linear adhesive will not have this problem. In the whole system, from the improvement of the positive electrode, negative electrode, electrolyte to the binder, we have done a relatively good result in the lithium iron phosphate battery cell. One is the charging characteristics, -20, -30,- The 0.5C charging constant current ratio at 40 degrees can reach 62.9%, and the discharge at -20 degrees can release 94%. This is some of the characteristics of the rate and cycle.