Why can't I charge a lithium battery at low temperature? Among all environmental factors, temperature has the greatest impact on the charge/discharge performance of the battery. The electrochemical reaction at the electrode/electrolyte interface is related to the ambient temperature, and the electrode/electrolyte interface is regarded as the heart of the battery. The viscosity of electrolyte decreases, conductivity decreases, and the activity of active material decreases at low temperature. What is the effect of charging lithium battery at low temperature?
Why can't charge lithium battery at low temperature
At present, lithium battery is the most used in electric vehicles, this kind of battery has high safety and long life of the single cell, but there is a fatal drawback: the performance in low temperature is slightly worse than other technical systems of batteries, low temperature on the positive and negative electrodes of lithium batteries, electrolyte and adhesive, etc. There are effects.
When the lithium battery is charged at low temperature, lithium ions may not be embedded in the graphite cathode, thus precipitating on the surface of the cathode to form lithium metal dendrites, this reaction will consume the lithium ions in the battery can be repeatedly charged and discharged, and significantly reduce the battery capacity, the precipitated lithium metal dendrites may also puncture the diaphragm, thus affecting the safety performance.
Try to avoid charging lithium batteries at low temperatures. When the battery must be charged at low temperatures, you need to select as much as possible a small current to charge the lithium-ion battery, and after charging the lithium-ion battery to be fully placed, and then to ensure that the negative electrode dendritic lithium metal can react with graphite, embedded in the graphite negative electrode from scratch.
The effect of charging lithium battery in low temperature environment
The lithium metal in the battery at low temperature will produce the deposition phenomenon, and no longer react chemically with the substance, thus occurring the internal short circuit of the battery. Because as the temperature decreases, the kinetic and thermodynamic properties of the graphite negative electrode progresses to become worse, the electrochemical polarization of the negative electrode increases significantly during charging, and the precipitated lithium metal tends to form lithium dendrites, penetrating the diaphragm and leading to a short circuit of the positive and negative electrodes.
The electrode reaction rate also decreases, assuming that the battery voltage remains constant, the discharge current decreases, and the power output of the battery also decreases. If the temperature rises, the opposite is true, that is, the battery power output will rise, the temperature also affects the electrolyte transfer rate temperature rise is accelerated, the transfer temperature drops, the transfer slows down, the lithium battery charge and discharge performance will also be affected.
The electrolyte used in lithium batteries as an organic liquid, will become viscous or even condensed at low temperatures, at this time, the conductive lithium salts in the activity is greatly restricted, in which case the charging efficiency is very low, which will lead to slow charging of lithium batteries at low temperatures, charging is not enough, discharge is also the case.
As the temperature decreases, the discharge performance of lithium batteries significantly decreases, the discharge platform is significantly reduced, the discharge capacity is significantly reduced; when the temperature drops to -30 ℃, the discharge capacity of the battery is 87.0% of the room temperature discharge capacity, the average voltage of the discharge than the room temperature is reduced by 0.598V, while the stored energy is only about 70% of the ordinary environment.
What are the factors affecting the low temperature performance of lithium batteries?
Lithium battery is mainly composed of positive electrode material, negative electrode material, diaphragm, electrolyte, in the low-temperature environment of the lithium battery exists in the discharge voltage platform decline, low discharge capacity, rapid capacity decay, poor multiplier performance and other characteristics. The main factors that limit the low-temperature performance of lithium batteries are as follows.
1, cathode material: the three-dimensional structure of the cathode material restricts the diffusion rate of lithium ions, and the effect is especially obvious at low temperatures.
2, electrolyte: electrolyte material and physical and chemical parameters have an important impact on the low-temperature performance of the battery, electrolyte viscosity increases, ion conduction rate slows down, and the external circuit electron migration rate does not match, the charge and discharge capacity appears to be sharply reduced. Especially in the case of low-temperature charging, lithium ions are easy to form lithium dendrites on the surface of the negative electrode, resulting in battery failure.
3, lithium ion diffusion rate: the low-temperature environment in the graphite cathode of lithium ion diffusion rate is reduced, the lithium battery charge migration impedance increases resulting in lithium ion in the graphite cathode diffusion rate is reduced is an important reason affecting the low-temperature performance of lithium-ion batteries.
4, SEI film: the low temperature environment of the lithium-ion battery anode SEI film thickening, SEI film impedance increases resulting in lithium ion conduction rate in the SEI film is reduced, and ultimately lithium-ion battery charging and discharging at low temperatures to form polarization reduces charging and discharging efficiency.
Factors affecting the low temperature performance of lithium batteries are battery production process, chemical system, aging system, etc. The low temperature cycle performance of lithium batteries can be improved by reducing internal resistance and low temperature polarization of lithium batteries. Low-temperature performance limits the application of lithium batteries in the field of electric vehicles, military and extreme environments, the development of lithium batteries with excellent low-temperature performance is an urgent need of the market.
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