How to heat up lithium-ion batteries in low temperature environments

When the ambient temperature is lower than minus 20°C, it will be very difficult to charge the lithium-ion battery. The problem of battery charging at low temperatures can be solved by heating the lithium-ion battery. There are many external heating methods for lithium-ion batteries. The difficulty of the law is to control the thermal balance of the entire battery pack; low temperature has a great influence on lithium-ion batteries. Too low temperature will cause the performance of the lithium-ion battery to decrease and even lose its working ability. In order to meet the requirements of lithium-ion batteries working in low-temperature environments, the batteries must be heated. At present, the heating methods of low-temperature batteries are as follows: External heating of lithium-ion batteries The external heating method is the most widely used heating mode. The battery is heated by an external heat source. The important feature is its simple structure. But the external heating efficiency is very low, so more power consumption, but it is also prone to temperature gradients in the battery, which leads to inconsistent internal battery failures and affects the service life of lithium-ion batteries. (1) Preheating the liquid Liquid has a higher thermal conductivity and heat capacity than air, so it conducts heat more effectively, but in contrast, the liquid preheating system is more complicated. According to whether the battery is in contact with the heat-conducting liquid during heating, liquid heating can be divided into two categories: 1) non-contact heating; 2) immersion heating. The structure of a typical liquid preheating system is shown in the figure below. Currently, non-contact liquid preheating systems have been applied to electric vehicles. For example, Volt uses a 360V heater to heat the liquid and then transfer it to the battery. (2) The air preheating air temperature control system is simple in structure and low in cost, and has been widely used in the field of electric vehicles. As shown in the figure below, the basic working principle of the air conditioning temperature control system is to heat the outside air through the heating system, and then enter the battery pack under the use of a fan to heat the battery. Air preheating is generally used, and the heating rate can reach 0.5-3°C/min. The speed and temperature of the airflow will affect the air preheating effect. Relevant studies have shown that the effect of increasing the air velocity is more obvious than the effect of increasing the air temperature. At the same time, increasing the air temperature will also cause a more obvious temperature gradient inside the battery, which will adversely affect the battery life. It has been used in Honda's Insight and Toyota's Prius, but it still has many shortcomings, such as noise and efficiency. (3) Preheating of phase change materials Air preheating and liquid preheating require more complicated structures inside the battery, such as pipes, pumps, heaters, etc., which will increase the cost and design difficulty of the battery pack. Battery pack preheating and phase change materials provide a simpler method. This method is important to achieve the purpose of battery heating and cooling through the heat released or absorbed by the phase change material during the phase change process, but the heat of the phase change material The conductivity is generally low, which is not conducive to rapid heat transfer to the battery. In order to solve this problem, people have proposed the connection method of carbon nanotubes and metal framework, but the current method is still in the laboratory stage and has not yet been applied. Electric heater preheating In addition to the above preheating methods, we can also preheat the battery through electric heaters. Electric heaters are divided into: 1) Peltier effect heater; 2) electric heating plate; 3) electric heating cover; 4 ) Electric movie. Peltier effect heater The heater uses the Peltier effect of the semiconductor to form a hot surface and a cold surface on two surfaces, respectively. By controlling the direction of the current, the position of the hot and cold sides can be controlled to achieve the purpose of cooling or heating the battery, and the temperature can be controlled by controlling the amplitude of the current. In this way, a heating rate of 0.6-1°C/min can be achieved, and the energy consumed by the preheating battery accounts for about 2.5% of the total battery energy. Heater preheating In the heating method of electric heating plates, the electric heating plates are generally placed on the top or bottom of the battery, and the heat generated by the electric heating plates is directly transferred to the battery. The electric heater is generally made of positive temperature coefficient material (PTC). As the temperature increases, the resistance increases, so as to achieve the purpose of automatic temperature control. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete.