Because temperatures that are too high or too low will directly affect the service life and performance of power lithium-ion batteries, and may lead to safety issues in the battery system, and the long-term uneven distribution of the temperature field in the battery box will cause various battery modules, units Due to the imbalance of performance between bodies, a battery thermal management system is necessary for electric vehicle power lithium-ion battery systems. Reliable and efficient thermal management systems are of great significance for the reliable and safe use of electric vehicles.

　　The battery pack thermal management system has the following five important functions:

　　①Accurate measurement and monitoring of battery temperature.

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

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　　② Effective heat dissipation and ventilation when the battery pack temperature is too high.

　　③Rapid heating under low temperature conditions.

　　④ Effective ventilation when harmful gases appear.

　　⑤ Ensure the average distribution of the battery pack temperature field.

　　Basic methods of heat transfer in batteries

　　There are three main ways of heat transfer in the battery: heat conduction, convection heat transfer and radiation heat transfer.

　　The heat exchanged between the battery and the environment is also carried out through three methods: radiation, conduction and convection. Thermal radiation mainly occurs on the battery surface and is related to the properties of the battery surface material.

　　Heat conduction refers to the heat transfer that occurs when a substance is in direct contact with an object. The electrodes, electrolytes, current collectors, etc. inside the battery are all heat conduction media. Taking the battery as a whole, the temperature of the interface layer between the battery and the environment and the environmental heat conduction properties determine the heat conduction in the environment.

　　Thermal convection refers to the exchange of heat on the battery surface through the flow of environmental media (generally fluid), which is also proportional to the temperature difference.

　　Regarding the interior of a single cell, thermal radiation and thermal convection have little impact, and heat transfer is mainly determined by thermal conduction. The amount of heat absorbed by the battery itself is related to the specific heat capacity of its material. The greater the specific heat capacity, the more heat dissipation, and the smaller the temperature rise of the battery. If the heat dissipation is greater than or equal to the heat present, the battery temperature will not rise. If the heat dissipation is less than the generated heat, heat will accumulate in the battery body and the battery temperature will rise.

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