Design scheme for the heat dissipation structure of lithium battery packs

First, analysis of heat dissipation goals and requirements

Temperature control range: The operating temperature of lithium battery packs usually needs to be controlled between 20℃ and 45℃. Exceeding 45℃ will lead to accelerated capacity decline of the battery, shortened lifespan, and may even cause thermal runaway.

Temperature uniformity: The temperature difference between each individual battery within the battery pack should be controlled within 5℃ to avoid inconsistent performance due to local overheating.

Heat dissipation efficiency: In scenarios of high-power discharge or fast charging, the heat dissipation system needs to quickly dissipate heat to prevent the battery temperature from rising sharply.

Second, selection of heat dissipation structure type

Natural heat dissipation

Principle: Heat dissipation is achieved through the natural convection between the battery pack's casing and the outside air.

Applicable scenarios: It is suitable for low-power and small-capacity lithium battery packs, such as batteries for small portable devices.

Features: Simple structure, low cost, but limited heat dissipation efficiency, and it is difficult to meet the heat dissipation requirements in high-temperature environments or high-power operation.

Air-cooled heat dissipation

Principle: Utilize a fan to force air flow, accelerating the heat exchange between the battery pack and the outside air.

Applicable scenarios: It is suitable for medium-power and medium-capacity lithium battery packs, such as those for electric bicycles and some electric vehicles.

Features: The heat dissipation efficiency is higher than natural heat dissipation, the structure is relatively simple, and the cost is moderate. However, the fan will produce noise, and the heat dissipation effect will be affected in high-temperature or dusty environments.

Liquid cooling heat dissipation

Principle: The heat generated by the battery is carried away by the coolant circulating in the pipes inside the battery pack.

Applicable scenarios: It is suitable for high-power and large-capacity lithium battery packs, such as batteries for high-end electric vehicles and energy storage systems.

Features: High heat dissipation efficiency, good temperature uniformity, but complex structure, high cost, and requires additional coolant circulation systems and sealing measures.

Heat dissipation of phase change materials

Principle: By utilizing phase change materials to absorb or release a large amount of heat during the phase change process, the temperature regulation of the battery pack is achieved.

Applicable scenarios: It is suitable for lithium battery packs with high requirements for temperature control and limited space, such as some small electronic device batteries.

Features: The heat dissipation process is smooth with small temperature fluctuations. However, the number of phase transitions of phase change materials is limited, and their performance will decline after long-term use. Moreover, the cost is relatively high.

Third, key points of heat dissipation structure design

Battery layout optimization

Individual battery arrangement: A compact and regular arrangement is adopted to reduce the gap between batteries and improve space utilization. For example, arranging the batteries in a rectangular array can make the temperature distribution inside the battery pack more uniform.

Battery spacing setting: According to the heat generation and heat dissipation method of the batteries, set the spacing between batteries reasonably. For air-cooled heat dissipation, the battery spacing is generally no less than 5mm. For liquid cooling heat dissipation, the battery spacing can be appropriately reduced to increase the energy density of the battery pack.

Heat dissipation channel design

Air-cooled channel: In the air-cooled heat dissipation structure, a well-designed air duct ensures that air can flow smoothly through the battery pack. The cross-sectional shape and size of the air duct should be optimized based on the performance of the fan and the heat dissipation requirements of the battery pack. Generally, rectangular or circular air ducts are adopted.

Liquid cooling pipeline layout: In the liquid cooling heat dissipation structure, the liquid cooling pipelines should be evenly distributed inside the battery pack and fully contact the battery surface. The layout of the pipes can adopt serpentine, parallel and other forms to improve the flow efficiency of the coolant and the uniformity of heat dissipation.

Selection of heat dissipation materials

Thermal conductive materials: High thermal conductive materials such as thermal conductive silicone and thermal conductive gaskets are used between the battery and the heat dissipation structure to enhance the heat conduction efficiency. The thermal conductivity of thermal conductive materials should not be less than 1W/(m·K).

Heat dissipation shell material: Select shell materials with good heat dissipation performance, such as aluminum alloy, copper alloy, etc. These materials not only have good thermal conductivity but also are relatively light in weight, which is conducive to improving the energy density of the battery pack.

Temperature monitoring and control

Temperature sensor layout: Temperature sensors are placed at key positions inside the battery pack to monitor the temperature changes of the battery in real time. The number and placement of temperature sensors should be determined based on the size of the battery pack and the heat dissipation requirements. Generally, one temperature sensor is set for each battery cell or every few battery cells.

Control strategy formulation: Based on the feedback signal from the temperature sensor, formulate a reasonable control strategy. When the battery temperature exceeds the set threshold, the cooling system is activated. When the battery temperature drops below the set threshold, reduce the power of the cooling system or stop its operation to achieve energy conservation and precise temperature control.

Fourth, examples of heat dissipation structure design in different application scenarios

Electric vehicle battery pack

Liquid cooling is the main method: Due to the large power and high capacity of electric vehicle battery packs, liquid cooling is usually adopted for heat dissipation. The coolant circulates in the pipes inside the battery pack, taking away the heat generated by the battery and dissipating it into the outside air through the radiator.

Optimize the air duct design: Design a reasonable air duct on the battery pack casing, combined with fans to force air flow, and assist the liquid cooling heat dissipation system for heat dissipation to improve the heat dissipation efficiency.

Battery pack of energy storage system

Combination of air cooling and liquid cooling: For battery packs in large-scale energy storage systems, a heat dissipation method that combines air cooling and liquid cooling can be adopted. Air ducts are set inside the battery pack for initial heat dissipation through fans. For areas with high heat generation, liquid cooling is adopted for focused heat dissipation.

Phase change material assistance: Phase change materials are filled inside the battery pack. When the battery temperature rises, the phase change materials absorb heat and undergo phase change, playing a role in temperature regulation and reducing temperature fluctuations.

Batteries for small electronic devices

Combination of natural heat dissipation and phase change materials: For small electronic device batteries, due to limited space, a heat dissipation method combining natural heat dissipation and phase change materials can be adopted. Wrap a layer of phase change material around the battery. By taking advantage of the heat absorption property of the phase change material, the temperature rise rate of the battery can be slowed down, and at the same time, natural heat dissipation can be achieved through the device casing and the outside air.