PACK thermal management system research: air cooling, liquid cooling, direct cooling

Air cooling is a heat dissipation method that uses low-temperature air as a medium and uses heat convection to reduce the temperature of the battery. It is divided into natural cooling and forced cooling (using fans, etc.). This technology uses natural wind or a fan to cool the battery with the car’s own evaporator. The system is simple in structure and easy to maintain. It was widely used in early electric passenger cars, such as Nissan Leaf, KIA Soul EV, etc., in current electric buses. , Electric logistics vehicles are also widely adopted.

The basic schematic diagram of air cooling is as follows:

Schematic diagram of air cooling principle

KIASoul EV wind Cold path

Liquid cooling

Liquid cooling technology transfers heat through liquid convection to take away the heat generated by the battery and lower the battery temperature. The liquid medium has a high heat transfer coefficient, large heat capacity, and fast cooling speed, which has a significant effect on reducing the maximum temperature and improving the consistency of the battery pack temperature field. At the same time, the volume of the thermal management system is relatively small. The form of liquid cooling system is more flexible: battery cells or modules can be immersed in liquid, cooling channels can be set between battery modules, or cooling plates can be used at the bottom of the battery. When the battery is in direct contact with liquid, the liquid must be insulated (such as mineral oil) to avoid short circuit. At the same time, the air-tightness requirements of the liquid cooling system are also higher. In addition, it is the mechanical strength, vibration resistance, and life requirements.

Liquid cooling is currently the preferred solution for many electric passenger cars. Typical domestic and foreign products such as BMWi3, TESLA, Volt, ZINORO, Geely Emgrand.

The basic principle diagram of liquid cooling is as follows:

Basic principle diagram of liquid cooling

VOLT's coolant is glycol solution , Each soft-packed cell is cooled on a large surface, parallel flow channels, compactness, and low cost.

GMVOLT cooling 2D diagram

GMVOLT 5 parallel cooling channels

Compared with the parallel flow channels of GM VOLT, TESLA's liquid cooling adopts serial flow channels, and the cold plate is installed in the battery gap. The structural design of this design is more difficult. At the same time, the serpentine cold plate has increased to a large extent. The pressure loss of the liquid cooling system.

2D schematic diagram of TESLA liquid cooling structure

3D schematic diagram of TESLA liquid cooling structure

TESLA liquid cooling structure entity diagram

Comparison of cooling methods between GMVOLT and TESLA

Direct cooling

Direct cooling It uses the huge heat storage capacity of phase change material (PCM). When PCM is used as a battery thermal management system, the battery pack is immersed in the PCM, and the PCM absorbs the heat released by the battery to reduce the temperature rapidly, and the heat changes in phase. The heat is stored in the PCM and released when it is charged or working in a very cold environment. The basic idea is as follows:

Basic principle diagram of direct cooling

Schematic diagram of direct cooling scheme

Currently, the cooling method through direct cooling is basically in electric passenger cars, the most typical one is BMW i3 (i3 has liquid cooling, direct cooling Two cooling schemes).

BMW i3 direct cooling structure

The advantage of direct cooling is;

(a). Cooling efficiency is higher than liquid cooling 3~4 times;

(b). It can better meet the needs of fast charging;

(c). Compact structure;

(d). Potential The cost is greatly reduced;

(e). Avoiding the flow of glycol solution inside the battery box

The promotion of lithium battery industry chain enterprises, lithium grid (li-b.cn) ) Contributions are welcome.