The high internal temperature is caused by heat generation inside the LIBs, which happens at high current state, including operations with fast charging rate and fast discharging rate. The high temperature effects will also lead to the performance degradation of the batteries, including the loss of capacity and power. Generally, the loss of lithium and the reduction of active materials under high temperature will result in the loss of the capacity, while the increase of internal resistance is responsible for the loss of power. If the temperature is out of control, thermal runaway will be triggered, which may lead to self- ignition and even explosion in some cases.
Proper management of the operating temperature of LIBs is thus critical to the performance and safe operation of the batteries.