What are the effects of low temperature on the performance of lithium batteries?
Among all the environmental factors, temperature has the greatest impact on the charge and discharge performance of the battery. The electrochemical reaction of the lithium battery pack at the electrode/electrolyte interface is related to the ambient temperature, and the electrode/electrolyte interface is regarded as the heart of the battery. At low temperatures, the viscosity of the electrolyte decreases. As the conductivity decreases, the activity of the active material also decreases. The concentration difference of the electrolyte will become larger, the polarization will be enhanced, and the charging will be terminated early. More importantly, the diffusion rate of lithium ions in the carbon anode will be slower. Lithium is easily precipitated. As the temperature drops, the reaction rate of the electrode also drops. Assuming that the battery voltage remains constant and the discharge current decreases, the power output of the battery will also decrease.
The effect of low temperature on lithium iron phosphate batteries
Currently, lithium iron phosphate batteries are the most commonly used batteries in electric vehicles. This type of battery has high safety and a long lifespan. , But lithium iron phosphate has a fatal disadvantage. The low temperature performance of lithium iron phosphate batteries is slightly worse than that of batteries of other technical systems. Low temperature has an impact on the positive and negative electrodes, electrolyte and binder of lithium iron phosphate. For example, the lithium iron phosphate positive electrode itself has relatively poor electronic conductivity, and it is prone to polarization in low temperature environments, thereby reducing battery capacity; affected by low temperature, the speed of graphite lithium insertion is reduced, and metal lithium is likely to precipitate on the surface of the negative electrode. If it is left for insufficient time after charging When put into use, the metal lithium cannot be fully embedded in the graphite again. Part of the metal lithium continues to exist on the surface of the negative electrode, which is very likely to form lithium dendrites, which affects battery safety; at low temperatures, the viscosity of the electrolyte will increase, and the lithium ion migration resistance will also change. In addition, in the production process of lithium iron phosphate, the adhesive is also a very critical factor, and low temperature will also have a greater impact on the performance of the adhesive.
The influence of low temperature on lithium titanate battery
The same is a lithium battery, but the low temperature performance of lithium titanate battery is relatively excellent. The lithium titanate anode material with spinel structure has a lithium insertion potential of about 1.5V, does not form lithium dendrites, and the volumetric strain is less than 1% during charge and discharge. The nanometerized lithium titanate battery can be charged and discharged with high current, which realizes low-temperature fast charging while ensuring the durability and safety of the battery. For example, Yinlong New Energy, which focuses on lithium titanate batteries, has its products with normal charge and discharge capabilities at -50-60°C. Lithium titanate batteries have material advantages. They can still be charged quickly at low temperatures. This kind of willfulness is difficult to learn from batteries with other materials.
Pre-heating improves the low-temperature performance of lithium batteries
Faced with the limited use of lithium batteries at low temperatures, the response strategy found by technicians is charging pre-heating, although it is a stopgap measure , But it has a significant effect on improving the low temperature performance of lithium batteries.
Before charging or using the lithium battery pack in a low temperature environment, the battery must be preheated. The way that the battery management system (BMS) of the electric vehicle heats the battery can be roughly divided into two categories: external heating and internal heating. External heating methods include air heating, liquid heating, phase change material heating, and heat resistance heater or heat pump heating. These heating methods are generally located in the battery pack, or set in the container of the thermal cycle medium. The internal heating method heats the battery by exciting the electrochemical substances inside the battery through alternating current, so that the battery itself generates heat. P>
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