Why can't lithium batteries be charged at low temperature?
The reason is simple, 99% of cylindrical power lithium-ion batteries are not allowed, because of lithium extraction problems. Lithium anode analysis is the important factor to the lithium ion battery safety accident frequency, lead to lithium lithium ion battery cathode analysis of many factors, such as across the redundancy design is insufficient, battery charging at low temperature, the charging current is too large factors can lead to negative analysis such as lithium, lithium anode analysis not only leads to lithium ion battery can use less of lithium resources, capacity drops, will form in the cathode of lithium dendrite, lithium dendrite with the growth cycle of lithium ion battery, will eventually through the diaphragm, is caused by negative short circuit. Therefore, how to avoid negative anode separation is the key problem to be considered in the design of High security lithium ion batterys.
Low temperature is one of the important factors induce lithium lithium ion battery analysis, under the condition of low temperature intercalated-li dynamics condition of the cathode, anode of specific capacity is reduced, in a larger rechargeable lithium electricity down easily in the cathode surface coating, lithium dendrite, even so it is necessary for lithium ion battery cathode under low temperature characteristics and mechanism of the formation of lithium to do detailed research. From university of technology in Munich Christian von Lu ̈ ders and others through means such as static voltage and neutron diffraction for business 18650 lithium ion battery under - 2 ℃ analysis the characteristics and mechanism of lithium was studied, research shows that in the case of charging ratio more than 2 C/can significantly increase the number of lithium analysis, for example, in C / 2 cases, the cathode surface plating lithium accounted for the entire charge about 5.5% of the total capacity, under 1 C rate, has reached 9%. It is also found that the rate of lithium ion embedding into graphite structure depends on the number of lithium deposits, and the static voltage is closely related to the number of lithium deposits. Experiment Christian von Lu ̈ ders USES 18650 batteries, are extremely NCM111 material, negative extremely graphite material. Under the C / 20 multiplier at -2℃, the battery is limited by the diffusion conditions of electrolyte and the kinetic conditions of active substances at positive and negative electrodes, and can only produce about 87% of the capacity at 25℃, or 1687.21mAh. The following table shows the battery charging capacity at -2℃ with different multipliers. From the data, we can notice that with the increase of charging current, the temperature of the battery in the charging process gradually increases, which has a certain impact on the accuracy of measuring the low temperature performance of the battery. However, due to the thermal conductivity of the 18650 battery, this phenomenon is difficult to avoid.