What is the reason why the lithium-ion battery cannot be charged at low temperature?

The working principle of lithium-ion batteries is mainly dependent on the movement of lithium between the positive electrode and the negative electrode to work. During the charging and discharging process, Li+ intercalates and deintercalates back and forth between the two electrodes: when recharging the battery, Li+ deintercalates from the positive electrode and inserts into the negative electrode through the electrolyte, and the negative electrode is in a lithium ion-rich state; the opposite is true during discharge. Due to the high activity of lithium-ion batteries, consistency is also a problem, so even if the products of the same batch, the same material, and the same process, the performance will be very different, and we cannot set a standard amount. Regarding lithium-ion batteries, whether it is a national standard or an enterprise standard, there are strict restrictions on the lower limit temperature of discharge: not less than -20°C. Regarding the charging temperature, not only will the minimum temperature be the same as the discharge, but it will even be clearly specified that it can only be charged at a low rate and cannot be fully charged at low temperatures (for example, it can only be charged at 0.2C at 0 to 15 degrees, and the upper limit voltage is 4.0. V). At present, the temperature range of general power lithium-ion batteries can be controlled between -20 degrees and -60 degrees. As long as it is within a controllable temperature range, charging will not be a safety issue. In addition, the current batteries are subject to low-temperature and high-temperature charge and discharge testing before they leave the factory or during customer review. Batteries that fail the test are not allowed to enter the market. At present, lithium-ion batteries are the most commonly used batteries in electric vehicles. This type of battery has high safety and long cell life, but it has a fatal disadvantage: its low temperature performance is slightly worse than that of other technical systems. The positive and negative electrodes, electrolyte, and adhesives of lithium-ion batteries all have an impact. When a lithium-ion battery is charged at low temperature, lithium may not have time to be embedded in the graphite negative electrode, which precipitates and forms metallic lithium ion dendrites on the surface of the negative electrode. This reaction will consume the lithium in the battery that can be repeatedly charged and discharged, and greatly reduce the battery capacity. The metal lithium ion dendrites may also pierce the diaphragm, thereby affecting safety performance. Try to prevent lithium-ion batteries from charging at low temperatures. When the battery must be charged at low temperature, it is necessary to choose a small current to charge the lithium-ion battery as much as possible, and to fully place the lithium-ion battery after charging, and then ensure that the metal lithium ions separated from the negative electrode can react with the graphite. Embedded in the graphite anode. The influence of low-temperature environmental charging of lithium-ion batteries At low temperatures, the metal lithium ions in the battery will deposit and no longer chemically react with the substance, resulting in a short circuit inside the battery. Because as the temperature decreases, the kinetic and thermodynamic properties of the graphite negative electrode become worse. During the charging process, the electrochemical polarization of the negative electrode is significantly increased, and the precipitated metal lithium ions are likely to form lithium ion dendrites, which can break through the diaphragm and cause The positive and negative poles are short-circuited. The reaction rate of the electrode also decreases. Assuming that the battery voltage remains constant and the discharge current decreases, the power output of the battery will also decrease. If the temperature rises, the opposite is true, that is, the battery output power will rise, and the temperature will also affect the transfer speed of the electrolyte. The temperature rise will speed up, the transfer temperature will drop, and the transfer will slow down, and the charge and discharge performance of the lithium ion battery will also be affected. As an organic liquid, the electrolyte used in lithium-ion batteries will become viscous or even condense at low temperatures. At this time, the activity of conductive lithium-ion salts in it is greatly restricted. In this case, the charging efficiency is very low, which will lead to lithium-ion batteries. Charging is slow at low temperatures, the charging is dissatisfied, and so is the discharging. As the temperature decreases, the discharge performance of lithium-ion batteries decreases significantly, the discharge platform is significantly reduced, and 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, and the average discharge voltage ratio At room temperature, it is reduced by 0.598V, and the stored energy is only about 70% of the normal environment. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What kind of power lithium-ion batteries need attention?