Dry Battery.Introduction to the design of thermal management system for power lithium iron phosphate battery pack

　　Introduction to the design of thermal management system for power lithium iron phosphate battery pack

　　Introduction to the design of thermal management system for power lithium iron phosphate battery pack. If the lithium iron phosphate battery pack operates at excessively high temperatures for a long time, its lifespan will be seriously affected. If the temperature is too high, lithium batteries are at risk of damage and thermal runaway. Once the protective film begins to dissolve, the self-generated heat process outside of operation begins, and the battery enters the thermal runaway preparation stage.

　　Design of thermal management system for power lithium iron phosphate battery pack

　　The thermal management system adjusts the operating temperature of the lithium battery pack by applying heating or heat dissipation to the lithium iron phosphate battery pack system, and tries to keep the temperature environment in the most suitable range for the lithium battery to maximize the capacity of the battery pack and delay Battery age.

　　There are three main forms of thermal management systems. Air medium thermal management system, liquid medium thermal management system, phase change material thermal management system.

　　Power batteries are the energy source of electric vehicles. During the charging and discharging process, the battery itself will generate a certain amount of heat, causing the temperature to rise. The temperature rise will affect many working characteristics parameters of the battery, such as internal resistance, voltage, SOC, and available capacity. , charge and discharge efficiency and battery life.

　　The thermal effect of the battery will affect the performance and cycle life of the vehicle. Therefore, good thermal management is very important for the performance and life of the lithium battery pack and the mileage of the vehicle.

　　The main functions of the thermal management system

　　1) Heat dissipation

　　Effectively dissipate heat when the lithium iron phosphate battery temperature is high to prevent thermal runaway accidents;

　　2) Preheat

　　Preheat when the battery temperature is low to increase the battery temperature to ensure charging and discharging performance and safety at low temperatures;

　　3) Temperature balance

　　Reduce the temperature difference within the power lithium battery pack, inhibit the formation of local hot zones, and prevent the battery from decaying too quickly at high temperature locations to increase the overall life of the battery pack.

　　The necessity of thermal management of power lithium battery packs

　　1. Generation of battery heat

　　Due to the existence of battery impedance, during the battery charging and discharging process, current passes through the battery, causing heat to be generated inside the battery. In addition, the electrochemical reaction inside the battery will also generate a certain amount of heat.

　　2. The impact of rising temperature on battery life

　　The increase in temperature has an impact on the life of the power lithium battery pack.

　　Temperature has a great impact on battery life. For the same battery cell, when the ambient temperature is 23°C, the remaining capacity of the battery is 80% after 6238 days. However, when the battery is exposed to an environment of 55°C, the remaining capacity of the battery has reached 80% after 272 days. When the temperature rises by 32°C, the calendar life of the battery core decreases by more than 95%. Therefore, temperature has a great impact on the life of lithium battery packs. The higher the temperature, the more serious the decline in battery life.

　　Research shows that the optimal operating temperature of lithium batteries is 0°C-40°C. When the temperature inside the lithium iron phosphate battery pack for electric vehicles falls outside this range due to the influence of the external environment, the service life of the electric vehicle battery will decrease. The capacity will be reduced. At the same time, when the temperature is too high, the lithium battery may undergo "thermal runaway", resulting in serious thermal runaway events such as battery pack smoke, fire or even explosion, threatening the lives of vehicle drivers and passengers.

　　Therefore, when the temperature of the external environment is lower than 0°C, currently high-end electric vehicles generally adopt the practice of preheating lithium batteries before starting. When the external environment and the temperature inside the battery pack are too high, special cooling equipment is mainly used to assist the battery pack in cooling. In short, in order to ensure the performance, safety and life of the power battery, the thermal management system in the lithium battery pack of electric vehicles is also one of the key technologies of electric vehicles.

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