It's cold, how to improve the low temperature performance of lithium iron phosphate battery pack? It is almost October now, and the temperature has begun to drop slowly, which is a test for the low temperature performance of lithium iron phosphate battery pack. As we all know, the high temperature performance of lithium battery pack is very excellent, the heat peak can reach 350 ~ 500℃, high temperature (60℃) can still release 100% capacity. But the low temperature is worse than other battery systems, so how to improve its low temperature performance?
Lithium iron phosphate battery
Lithium iron phosphate battery refers to lithium ion battery which uses lithium iron phosphate as cathode material. The cathode materials of lithium ion batteries mainly include lithium cobalt acid, lithium manganese acid, lithium nickel acid, ternary materials, lithium iron phosphate and so on. Among them, lithium iron phosphate is the cathode material used in most lithium ion batteries. The demand for lithium iron phosphate battery packs is increasing rapidly, and improving the low temperature performance of lithium battery becomes the key.
What are the factors affecting the low temperature performance of lithium iron phosphate battery pack?
For the lithium iron phosphate battery pack, the experts in the energy storage electric industry have made a detailed study on the influencing factors of its low temperature characteristics. The reasons are as follows:
1. Production environment: lithium iron phosphate battery pack is a high-tech product with numerous chemical raw materials and complex processes. Its production environment has high requirements for temperature, humidity and dust, etc. If not controlled in place, the battery quality will fluctuate.
2, poor conductivity, slow diffusion rate of lithium ion. When charging and discharging at high rate, the actual specific capacity is low, which is a difficult problem to restrict the development of lithium iron phosphate industry. The reason why lithium iron phosphate has not been widely used so late is a major problem.
3, the influence of material, lithium iron phosphate anode itself electronic conductivity is relatively poor, in addition, it is easy to produce polarization, reduce the capacity of play; The negative part is mainly low temperature charging, because it will affect the safety issues; For the electrolyte, the viscosity and the migration impedance of lithium ions may increase at low temperature. The fourth is the binder, which has a relatively large impact on the low temperature performance of the battery.
How to improve the low temperature performance of lithium iron phosphate battery pack?
We improve the low temperature performance of lithium iron phosphate battery pack from the positive electrode, negative electrode, electro-hydraulic and binder.
In terms of the positive electrode, it is now nano, its particle size, electrical resistance, AB plane axis grow small three aspects will affect the low temperature characteristics of the whole battery. Different processes also have different effects on the positive electrode. The low-temperature discharge characteristics of batteries made of lithium iron phosphate with particle size of 100 to 200 nanoparticles are better, and 94% can be released at -20 degrees. That is to say, the nano-size of lithium iron phosphate shortens the migration path and improves the performance of low-temperature discharge, because lithium iron phosphate discharge is mainly related to the positive electrode.
Considering the charging characteristics from the negative electrode, the low temperature charging of lithium battery is mainly influenced by the negative electrode, including the particle size and the change of the distance between the negative electrode. Three different artificial graphite were selected as the negative electrode to study the influence of different layer spacing and particle size on the low temperature characteristics. From the point of view of the three materials, the bulk impedance and ion migration impedance of granular graphite with large layer spacing are smaller in terms of impedance.
In terms of charging, lithium battery packs have little problem in low temperature discharge in winter, mainly for low temperature charging. Because in terms of cross-flow ratio, 1C or 0.5C cross-flow ratio is very critical, and it takes a long time to reach constant pressure. By improving the comparison of three different kinds of graphite, it is found that one of them has a relatively large improvement in the constant current ratio of -20 degree charging, from 40% to more than 70%, the increase of layer spacing, and the reduction of particle size.
Electrolyte this piece, at -20 degrees, -30 degrees electrolyte icing, viscosity increases, formation performance deterioration. Electrolyte from three aspects: solvent, lithium salt, additive. The influence of solvent on low temperature of lithium iron phosphate battery pack is from 70% to 90%, there are more than ten points of influence; Secondly, different lithium salts have certain influence on the charging and discharging characteristics of low temperature. We have fixed the solvent system and lithium based, low temperature additives can increase the discharge capacity from 85% to 90%, that is to say, the entire electrolyte system, the solvent, lithium and additives have a certain impact on the low temperature characteristics of our power battery, including other material systems."
In terms of binder, in the case of 20 degrees of charge and discharge, two kinds of point about 70 to 80 cycles, the whole pole piece is the current situation of binder failure, and the use of linear binder will not exist this problem. On the whole system, from the positive and negative, electrolyte to the improvement of the binder, the lithium iron phosphate battery monomer do good effect, one is the charging characteristics, 20, 30, and 40 degrees temperature 0.5 C constant current charging ratio can reach 62.9%, 94% - 20 degrees temperature lowering electricity can release, this is ratio with some characteristics of the cycle.
