Since the lithium-ion battery entered the market, it has been widely used due to its advantages such as long life, large specific capacity and no memory effect. Low-temperature use of lithium-ion batteries has problems such as low capacity, serious attenuation, poor cycle rate performance, obvious lithium evolution, and unbalanced lithium deintercalation. However, with the continuous expansion of application areas, the restrictions brought by the low-temperature performance of lithium-ion batteries have become more and more obvious.
According to reports, the discharge capacity of lithium-ion batteries at -20°C is only about 31.5% of that at room temperature. The operating temperature of traditional lithium-ion batteries is between -20 and +60°C. However, in the fields of aerospace, military industry, and electric vehicles, batteries are required to work normally at -40°C. Therefore, improving the low-temperature properties of lithium-ion batteries is of great significance.
Factors restricting the low-temperature performance of lithium-ion batteries:
1. In a low temperature environment, the viscosity of the electrolyte increases, or even partially solidifies, resulting in a decrease in the conductivity of the lithium-ion battery.
2. The compatibility between the electrolyte, the negative electrode and the diaphragm becomes poor in a low temperature environment.
3. In low-temperature environments, lithium-ion battery negative electrodes are severely precipitated, and the precipitated metal lithium reacts with the electrolyte, and the product deposition causes the thickness of the solid electrolyte interface (SEI) to increase.
4. In a low temperature environment, the diffusion system of the lithium ion battery in the active material decreases, and the charge transfer resistance (Rct) increases significantly.
Discussion on the factors affecting the low-temperature performance of lithium-ion batteries:
Expert opinion 1: The electrolyte has the greatest impact on the low-temperature performance of lithium-ion batteries, and the composition and physical and chemical properties of the electrolyte have an important impact on the low-temperature performance of the battery. The problems faced by the battery cycle at low temperatures are: the viscosity of the electrolyte will increase, and the ion conduction speed will slow down, resulting in a mismatch in the electron migration speed of the external circuit. Therefore, the battery will be severely polarized and the charge and discharge capacity will drop sharply. Especially when charging at low temperature, lithium ions can easily form lithium dendrites on the surface of the negative electrode, causing the battery to fail.
The low temperature performance of the electrolyte is closely related to the conductivity of the electrolyte itself. The high conductivity of the electrolyte transports ions faster, and it can exert more capacity at low temperatures. The more the lithium salt in the electrolyte is dissociated, the greater the number of migration and the higher the conductivity. The higher the electrical conductivity, the faster the ion conductivity, the smaller the polarization, and the better the performance of the battery at low temperatures. Therefore, higher electrical conductivity is a necessary condition for achieving good low-temperature performance of lithium-ion batteries.
The conductivity of the electrolyte is related to the composition of the electrolyte, and reducing the viscosity of the solvent is one of the ways to improve the conductivity of the electrolyte. The good fluidity of the solvent at low temperature is the guarantee of ion transport, and the solid electrolyte membrane formed by the electrolyte on the negative electrode at low temperature is also the key to affecting lithium ion conduction, and RSEI is the main impedance of lithium ion batteries in low temperature environments.
Expert opinion 2: The main factor limiting the low-temperature performance of lithium-ion batteries is the sharply increased Li+ diffusion resistance at low temperatures, not the SEI film.
So, how to treat lithium batteries correctly in winter?
1. Do not use lithium batteries in low temperature environments
Temperature has a great influence on lithium batteries. The lower the temperature, the lower the activity of lithium batteries, which directly leads to a significant decrease in charge and discharge efficiency. Generally speaking, the operating temperature of lithium batteries is between -20 degrees and -60 degrees.
When the temperature is lower than 0℃, be careful not to charge outdoors, you can’t charge it even if you charge it, we can take the battery to charge indoors (note, be sure to stay away from flammable materials!!!), when the temperature is lower than -20 ℃, the battery will automatically enter the dormant state and cannot be used normally. Therefore, the north is especially the user in cold places.
If there is really no indoor charging condition, you should make full use of the residual heat when the battery is discharged, and charge it in the sun immediately after parking to increase the charging capacity and avoid lithium evolution.
2. Develop the habit of using and charging
In winter, when the battery power is too low, we must charge it in time and develop a good habit of charging as soon as it is used. Remember, never estimate the battery power in winter based on the normal battery life.
Lithium battery activity decreases in winter, which is very easy to cause overdischarge and overcharge, which will affect the service life of the battery and cause a burning accident in the worst case. Therefore, in winter, we must pay more attention to charging with shallow discharge and shallow charging. In particular, it should be pointed out that do not park the vehicle for a long time in the way of charging all the time to avoid overcharging.
3. Don‘t stay away when charging, remember not to charge for a long time
Don‘t leave the vehicle in a charging state for a long time for the sake of convenience, just pull it out when it is fully charged. In winter, the charging environment should not be lower than 0℃, and when charging, don‘t leave too far to prevent emergencies and deal with it in time.
4. Use a special charger for lithium batteries when charging
The market is flooded with a large number of inferior chargers. Using inferior chargers can damage the battery and even cause a fire. Don‘t be greedy to buy cheap products without guarantees, and don‘t use lead-acid battery chargers; if your charger cannot be used normally, stop using it immediately, and don‘t lose sight of it.
5. Pay attention to the battery life and replace it with a new one in time
Lithium batteries have a life span. Different specifications and models have different battery life. In addition to improper daily use, the battery life span varies from several months to three years. If the car is powered off or has an abnormally short battery life, please contact us in time Lithium battery maintenance personnel handle it.
6. Leave surplus electricity to survive the winter
In order to use the vehicle normally in the spring next year, if the battery is not used for a long time, remember to charge 50%-80% of the battery, and remove it from the vehicle for storage, and charge it regularly, about once a month. Note: The battery must be stored in a dry environment.
7. Place the battery correctly
Do not immerse the battery in water or make the battery damp; do not stack the battery more than 7 layers, or turn the battery upside down.