From：CTECHI GROUP Limited Release time：2019-10-09
Overview：Among all environmental factors, temperature has the greatest influence on the charge and discharge performance of the battery. The electrochemical reaction of the lithium battery at the electrode/electrolyte interface is related to the ambient temperature, and the electrode/electrolyte interface is regarded as the heart of the battery.
What effect does low temperature have on the performance of lithium batteries?
Among all environmental factors, temperature has the greatest influence on the charge and discharge performance of the battery. The electrochemical reaction of the lithium battery 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. The conductivity is lowered and the activity of the active material is also lowered. The concentration difference of the electrolyte is increased, the polarization is enhanced, and the charging is terminated early. More importantly, the diffusion rate of lithium ions in the carbon negative electrode will be slower. It is easy to have lithium precipitated. As the temperature drops, the reaction rate of the electrode also decreases. Assuming that the battery voltage remains constant, the discharge current is reduced and the power output of the battery is also reduced.
Effect of low temperature on lithium iron phosphate battery
At present, lithium iron phosphate battery is the most used battery in electric vehicles. This battery has high safety and long life, but lithium iron phosphate has a fatal disadvantage. The low temperature performance of lithium iron phosphate battery is better than other technical systems. The battery is slightly worse. The low temperature affects both the positive and negative electrodes of lithium iron phosphate, the electrolyte and the binder. For example, the lithium iron phosphate positive electrode itself has relatively poor electronic conductivity, and is prone to polarization in a low temperature environment, thereby reducing battery capacity; due to low temperature, the graphite lithium insertion rate is lowered, and it is easy to precipitate metallic lithium on the surface of the negative electrode, and if the charging time is insufficient When it is put into use, the metal lithium cannot be completely embedded in the graphite, and some metal lithium continues to exist on the surface of the negative electrode, which is likely to form lithium dendrites, which affects the safety of the battery. At low temperatures, the viscosity of the electrolyte increases, and the lithium ion migration resistance also follows. In addition, in the production process of lithium iron phosphate, the adhesive is also a very critical factor, and the low temperature also has a great influence on the performance of the adhesive.
Effect of low temperature on lithium titanate battery
The same is a lithium battery, lithium titanate battery has a low temperature performance. The lithium titanate anode material of the spinel structure has a lithium insertion potential of about 1.5 V, and does not form lithium dendrites, and the volume strain is less than 1% during charge and discharge. The nano-sized lithium titanate battery can be charged and discharged at a high current, and achieves low-temperature fast charging while ensuring durability and safety of the battery. For example, Yinlong New Energy, which specializes in lithium titanate batteries, has a normal charge and discharge capacity of -50-60 °C. Lithium titanate batteries have the advantage of materials, and they can still achieve fast charging at low temperatures. This kind of material is difficult to learn from other materials.
Preheating improves the low temperature performance of lithium batteries
In the face of the limited use of lithium batteries at low temperatures, the countermeasures that technicians have found are charging preheating. Although it is an expedient measure, it has obvious effects on improving the low temperature performance of lithium batteries.
The battery must be preheated before charging or using the lithium battery in a low temperature environment. The battery management system (BMS) of an electric vehicle has a battery heating method which can be roughly divided into external heating and internal heating. External heating methods include air heating, liquid heating, phase change material heating, and thermal resistance heater or heat pump heating. These heating methods are generally located in the battery pack or in a container of the thermal cycle medium. The internal heating method heats the battery, and the internal electrochemical material of the battery is excited by the alternating current, so that the battery itself generates heat.