What is currently there in low temperature lithium battery heating?

　　Author ：Iflowpower – Portable Power Station Supplier

External heating method is currently the most widely used heating method, tightly heating the battery through external heat sources, is a simpler feature, but the external heating efficiency is low, so that consumes more electrical energy, it is easy to The temperature gradient occurs inside the battery, resulting in inconsistent speed of the internal decline of the battery, affecting the life of the lithium ion battery. (1) Liquid preheat compared to air, liquid has a higher thermal conductivity and heat capacity, so the thermal conductivity is higher, but the complexity of the liquid preheating system is higher than the liquid preheating system. When the battery is in contact with the thermally conductive liquid, the liquid heating can be divided into two categories: 1) non-contact heating; 2) immersion heating.

A typical liquid preheating system structure is shown below. At present, the current non-contact liquid preheating system has been used above the electric vehicle. For example, Volt uses a 360V heater to heat it, and then transferred to the battery, Tussez La also uses liquid preheating mode for battery pack heating.

(2) The temperature control system for air is high in air, the cost is simple, and there is a low cost, and therefore widely used in electric vehicles, the basic working principle is shown in the figure below, and the outside air is first heating after heating the heat system. Enter the battery pack under the use of the fan, thus heating the battery. In general, air preheating can achieve a temperature rise rate of 0.

5-3 ¡ã C / min. The speed and temperature of the air flow affect the effect of air preheating effect, and the relevant research statement is more distinct to increase the gas flow rate than the improvement of the air temperature. At the same time, the air temperature may also occur more significant temperature gradient inside the battery, thereby negative impact on battery life.

At present, this preheating method has been used by Honda's Insight model and Toyota's Prius model, but this method still has many shortcomings, such as noise problems, efficiency issues, etc. (3) Preheating of phase-bearing materials, whether air preheating or liquid preheating, more complex structures, such as pipes, pumps, and heaters, etc., will increase the cost and design difficulty of battery packs.

The phase change material is a more simple method for the preheating of the battery pack. This method is to achieve the amount of heat released or absorbed by the phase change material in the phase change process, but the purpose of heat and cooling is achieved. The thermal conductivity of the phase change material is generally relatively low, which is not conducive to the speed of quickly transferring to the battery.

In order to solve this problem, people have proposed a method such as carbon nanotubes and metal frameworks, but currently in the laboratory Stage, I have not been actually used. (4) Electric heater preheating In addition to the above preheating mode, we can also preheat the battery through the electric heater, and the electric heater can be divided into: 1) Peltier effect heater; 2) electric heating sheet; 3) electric heating sleeve; 4) electric hot film. Peltier Effect Heater This heater is a hot surface and a cold surface to which the hot surface and the cold surface are respectively formed in both surfaces of the semiconductor, and the position of the cooling surface can be controlled by the direction of the control current, thereby achieving the purpose of cooling or heating of the battery, And the temperature is high, can be controlled by controlling the current velocity.

In this way, the temperature rise rate of 0.6-1 ¡ã C / min can be achieved, and the energy consumed by the preheated battery is about 2.5% of the battery energy.

The electric heat sheet is preheated in the heating method using the electric heating sheet, the electric heat sheet is typically placed on the top or low end of the battery, and the heat brush appearing in the electric heat sheet is transmitted to the battery, usually the electric heating sheet will use a positive temperature coefficient material ( PTC) to make. The research statement uses the PTC thermal sheet to heat the battery heating to significantly increase the discharge voltage at low temperature, and increase the capacity of the battery, at -38 ¡ã C, the battery can still release more than 90% or more capacity. This approach has been used in early electric cars, such as the I-MIEV and Nissan's Leaf models of Mitsubishi, have taken a long time for battery, while it will be in the battery.

There is a temperature gradient internally, which is not conducive to the lifting of battery life. The electrothermal sleeve is earlier by Cheryautomobile, which is made by thermal resistance. It is used to make a protective sleeve in the battery.

The temperature change of the battery pack is controlled by the BMS system of the battery pack, thereby controlling preheating for the battery. This method can warm up the battery pack in 10 minutes to the working temperature and maintain a good temperature average. The electrothermal film electrotherm film is generally made of a metal foil and the insulating material is made, and the surface of the battery is pasted during use.

The advantage of this heating method is the heating film relatively thin (1-2 mm), so the occupied battery space is relatively small. This method can achieve higher temperature temperature rate in the case of lower energy consumption compared to the preheating mode of the electrothermal coefficient material. Second, internal heating is compared to external heating, the internal heating has a faster heating speed and higher heating rate, so the internal heating method is preheated to the lithium ion battery and has received extensive attention, but the internal heating control mechanism phase More complicated, and some internal heating methods have some safety hazards.

The internal heating method can be divided into two categories: self-heating and current excitation, the following table is a comparison of some common internal heating methods. 1. Since the heating method can see the self-heating method to occupy an absolute advantage in the heating speed, this method is to put a Ni foil into the inside of the battery, then lead the pole column outside the battery, control through the external circuit control Battery heating.

Test declaration of this approach to heating the battery from -30 ¡ã C to 0 ¡ã C to 60 ¡ã C / min, and this process consumes 5.5% energy. In order to reduce the temperature gradient in the battery during the heating process, a plurality of Ni foil can be added inside the battery, and the research declares that two Ni foils are added inside the battery to increase the temperature rate of the battery from -20 ¡ã C to 0 ¡ã C to 96 ¡ã C.

/ min, the energy consumption is only 2.9%, while the heating rate under the same conditions can only reach 60 ¡ã C / min, and 4.1% electric energy is consumed.

Thus, the manner of the multi-chip sheet can not only achieve effective reduction of temperature gradient inside the battery, and can also effectively improve the heating speed of the battery. 2, external current excitation method can be divided into several ways to DC preheating method, AC preheating method and pulse preheat. 3.

QU et al. Study declared that in this manner in 18650, it can achieve a heating speed of 4.29 ¡ã C / min (8, 9.

5 and 11A discharge). However, in order to meet the requirements of rapid heating, this means uses a large current discharge. At this time, the polarization of the battery is large, so that the battery capacity declines are added, and the research declares that the battery may only be only in such a preheating mode.

There are 81 cycle life. 4 Decline of battery capacity, while the AC mode is faster than DC electric heating, and the efficiency is also higher. Research statement, by increasing the current of AC, reducing the efficiency of increasing the frequency of AC electri.