Thermal Management Research and Development for Lithium Battery Energy Storage - Air Cooling VS Liquid Cooling VS Direct Cooling VS Immersion Cooling

 

In lithium battery energy storage systems, thermal management plays a crucial role in ensuring the performance, lifespan, and safety of the batteries. With the continuous development of energy storage technologies, various cooling methods have emerged, among which air cooling, liquid cooling, direct cooling, and immersion cooling have garnered significant attention. This article will delve into these four cooling methods, comparing their respective advantages and disadvantages, to provide a reference for selecting the appropriate cooling solution in lithium battery energy storage system design.

 

 

Air Cooling - The Economical and Practical Basic Choice

Working Principle

Air cooling is a relatively basic and common cooling method. Its principle involves using the flow of air to dissipate the heat generated by the batteries during charging and discharging. Typically, cooling fans are installed in the battery system to promote air circulation, which carries away the heat from the battery surface, thereby achieving the purpose of cooling. For example, in some small-scale energy storage devices, fans draw in external cold air, which passes through the battery modules and then the hot air is expelled outside the device, forming a simple cooling cycle.

 

Advantages Highlighted

• Low Cost: The composition of an air cooling system is relatively simple, with main components being fans and air ducts, without the need for a complex cooling medium circulation system. This results in lower initial equipment procurement costs and installation costs. For projects with limited budgets, air cooling is an economical and practical choice.

• Simple Structure: The system structure is not complex and is easy to understand and design. In terms of space layout, it does not require a large amount of space for the arrangement of cooling pipes and other facilities, allowing more space to be reserved for core components such as battery modules, facilitating the overall integration of the device.

• Easy Maintenance: If a fault occurs, troubleshooting and repairing an air cooling system is relatively straightforward. With fewer main components, technicians can quickly pinpoint the problem. For instance, if a fan fails, simply replacing the fan can resolve the issue, reducing the difficulty and time cost of maintenance.

 

Disadvantages Analysis

• Low Heat Dissipation Efficiency: Air has a relatively low specific heat capacity, which means its ability to absorb heat is limited. When batteries are charged and discharged at high power, generating a large amount of heat, the air cooling system may not be able to remove the heat in time, leading to an increase in battery temperature and affecting battery performance.

• High Environmental Sensitivity: External environmental temperature and humidity have a significant impact on air cooling effectiveness. In hot summer weather, the ambient air temperature is already high, and when it enters the battery system, the cooling effect is greatly reduced. In humid environments, moisture in the air may pose potential hazards such as corrosion to the batteries.

• Poor Temperature Uniformity: In large battery packs, it is difficult for air flow to ensure uniform cooling for each battery module. Areas close to the fans or air ducts dissipate heat well, while areas farther away may experience insufficient cooling, resulting in significant temperature differences within the battery pack, affecting the consistency and overall lifespan of the batteries.

 

Applicable Scenarios

Air cooling is suitable for small-scale, low-power energy storage projects, such as home energy storage systems and backup power supplies for small data centers. In these scenarios, the heat generation of the batteries is relatively low, and the cost is more sensitive. Air cooling systems can meet the basic cooling needs at a lower cost. Additionally, in scenarios where cooling requirements are not high, installation space is limited, and simple maintenance is desired, air cooling can also play to its strengths.

 

Liquid Cooling - The Efficient and Stable Advanced Choice

 

 

Working Principle

Liquid cooling systems primarily use liquid as a heat conduction medium, relying on the circulation of the liquid to remove the heat generated by the batteries. In lithium battery energy storage systems, liquid cooling pipes are typically arranged near the battery modules. The coolant (such as water, ethylene glycol solution, etc.) circulates driven by a pump. When the batteries generate heat, the heat is transferred to the closely contacting liquid cooling pipes. The coolant absorbs the heat, its temperature rises, and it then flows to the heat exchanger, where the heat is released to the external environment. The cooled coolant returns to the battery modules, repeating the cycle to achieve continuous cooling.

Advantages Elaborated

• High Heat Dissipation Efficiency: Liquids have much higher specific heat capacity and thermal conductivity than air, enabling them to absorb and transfer more heat. For example, water has a specific heat capacity about four times that of air and a thermal conductivity about 25 times that of air. This allows liquid cooling systems to remove a large amount of heat in a short period, ensuring that the batteries maintain an appropriate temperature even during high-power charging and discharging.

• Precise Temperature Control: Liquid cooling systems can achieve precise temperature control of the batteries, effectively reducing temperature differences within the battery pack. By reasonably designing the layout of the liquid cooling pipes and the flow rate of the coolant, each battery module can receive uniform cooling, ensuring the consistency of the battery pack and extending the overall lifespan of the batteries.

• Strong Integrability: The pipes and components of liquid cooling systems can be flexibly designed and arranged according to the structure of the battery system, making it easy to integrate with battery modules. This is a significant advantage for energy storage projects with limited space and high integration requirements, enhancing the compactness and overall performance of the system.

• Adaptability to Complex Environments: Compared to air cooling, which is highly sensitive to environmental temperature and humidity, liquid cooling systems are less affected by external environmental factors. Even in harsh conditions such as high temperature and high humidity, they can still stably perform cooling functions, ensuring the normal operation of the energy storage system.

 

Disadvantages Analysis

• High Cost: The equipment cost of liquid cooling systems is relatively high, including components such as liquid cooling pipes, coolant, pumps, and heat exchangers. Their procurement and installation costs are much higher than those of air cooling systems. Moreover, the coolant requires regular replacement and maintenance, which also increases the operational costs.

• Complex System: The structure and operating principles of liquid cooling systems are relatively complex, involving multiple stages such as liquid circulation and heat exchange. They have higher requirements for system design, installation, and commissioning. In case of a fault, troubleshooting and repair are more challenging and require professional technicians and equipment.

• Leakage Risk: There is a possibility of coolant leakage. If leakage occurs, it will not only affect the cooling effect but may also cause corrosion and damage to the batteries and other equipment, and even lead to safety accidents. Therefore, strict sealing measures and regular inspection and maintenance are necessary to reduce the risk of leakage.

 

Applicable Scenarios

Liquid cooling is suitable for large-scale, high-power energy storage projects, such as grid-side energy storage stations and backup power supplies for large data centers. In these projects, the heat generation of the battery packs is enormous, and the requirements for heat dissipation efficiency and temperature control are extremely high. Liquid cooling systems can meet their strict cooling needs, ensuring the stable operation and long lifespan of the energy storage systems. For example, in some energy storage projects accompanying new energy power generation, to ensure the efficient and safe operation of the energy storage batteries under various working conditions, liquid cooling technology is widely applied.

 

Direct Cooling - The Emerging Innovative Choice

 

 

Working Principle

Direct cooling technology is a relatively novel cooling method that cools the batteries directly through the phase change process of the refrigerant. In the direct cooling system, the refrigerant absorbs the heat generated by the batteries in the evaporator, transitioning from a liquid to a gaseous state. This process absorbs a large amount of heat, thereby achieving efficient cooling of the batteries. The gaseous refrigerant is then compressed by the compressor into a high-temperature, high-pressure gas, which enters the condenser. In the condenser, it releases heat to the external environment and re-liquefies. It then passes through an expansion valve to reduce pressure and returns to the evaporator to continue the next cycle. In simple terms, it is similar to the refrigeration principle of an air conditioner, except that the cooling effect is directly applied to the batteries, making the batteries the "space to be cooled."

 

Advantages Highlighted

• Superior Heat Transfer Performance: Compared to air cooling and liquid cooling, direct cooling has higher heat transfer efficiency. The phase change latent heat of the refrigerant is large, allowing it to absorb a significant amount of heat during the phase change process and quickly reduce the battery temperature. For example, in some high-performance electric vehicle battery cooling, direct cooling technology can rapidly lower the battery temperature from a high-temperature state to an appropriate working temperature range in a short time, ensuring stable battery performance during high-load operation.

• Lower System Complexity: Direct cooling systems do not require the complex coolant circulation pipes and pumps found in liquid cooling systems. It directly introduces the refrigerant into the cooling plates in close contact with the batteries, reducing the number of components and making the system structure more compact. This not only facilitates system installation and maintenance but also reduces potential failure points due to numerous components.

• Significant Space Savings: Due to the relatively simple structure of direct cooling systems, which do not require the arrangement of a large number of pipes and circulation equipment, they occupy less space in battery energy storage systems. For applications with strict space requirements, such as space-limited distributed energy storage stations, direct cooling systems can better adapt, improve space utilization, and make the overall equipment layout more rational.

 

Disadvantages Shortcomings

• High Pressure and Sealing Requirements: Refrigerants typically operate under certain pressures, which poses high requirements for the system's pressure resistance and sealing performance. If a refrigerant leak occurs, it will not only lead to the loss of cooling effectiveness but may also cause serious harm to the batteries and the surrounding environment. For example, refrigerant leakage may trigger fire, explosion, and other safety accidents. Therefore, during the manufacturing and installation of direct cooling systems, high-quality sealing materials and strict sealing processes must be used, increasing the system's cost and manufacturing difficulty.

• Challenges in Temperature Uniformity: Although direct cooling systems can quickly cool the batteries, achieving uniform temperature throughout the battery pack is not easy. During the flow of the refrigerant, factors such as pipe layout and refrigerant distribution may cause differences in cooling effects on different parts of the batteries, resulting in localized overheating or undercooling. This can affect the consistency of the battery pack and shorten the overall lifespan of the batteries.

• Limited Heat Pump Mode: In scenarios where the batteries need to be heated, the heat pump mode of direct cooling systems has certain limitations. When the ambient temperature is too low, the physical properties of the refrigerant may change, leading to poor heating performance of the heat pump, which cannot meet the battery's warming requirements. Additional heating equipment is then required to assist, increasing the system's complexity and cost.

 

 

Applicable Scenarios

Direct cooling is suitable for specific energy storage scenarios with extremely high heat dissipation requirements, limited space, and relatively low cost sensitivity. For example, in high-performance electric vehicle battery thermal management, where the batteries generate a large amount of heat during rapid charging and discharging, and the vehicle's internal space is limited, direct cooling technology can well meet its heat dissipation needs while saving space. In some small-scale energy storage devices with extremely high energy density requirements, direct cooling can also leverage its advantages of efficient heat dissipation and compact structure to ensure stable battery operation.

 

Immersion Cooling - The Stable and Safe Design Choice

Working Principle

Immersion cooling, as a cutting-edge cooling method, completely submerges the batteries in a coolant with high thermal conductivity. The coolant directly contacts the battery surface and quickly absorbs the heat generated by the batteries during charging and discharging through heat conduction. The coolant, after absorbing the heat, is transported to the heat exchanger through a circulation system, where the heat is released to the external environment. The cooled coolant then returns to the battery area, forming a continuous cooling cycle. The entire process is akin to "immersing" the batteries in an efficient cooling "bath," ensuring that heat is promptly and effectively removed.

 

Outstanding Advantages

• Exceptional Cooling Performance: The coolant has full contact with the batteries, eliminating the thermal resistance caused by air gaps and significantly improving heat dissipation efficiency. Under high-power charging and discharging conditions, it can quickly control the battery temperature within a reasonable range, ensuring stable battery performance. For example, in some large-scale energy storage stations, battery systems using immersion cooling technology can maintain the battery temperature within an appropriate working range even during long-term, high-power charging and discharging, effectively avoiding performance degradation due to overheating.

• Excellent Temperature Uniformity: The coolant can evenly envelop all parts of the batteries, resulting in minimal temperature differences among different locations within the battery pack. This helps improve the consistency of the battery pack and extend the overall lifespan of the batteries. Taking electric vehicle batteries as an example, battery packs with good temperature uniformity have a more uniform rate of battery degradation over long-term use, better maintaining the overall performance of the battery pack and reducing the risk of battery pack replacement due to the decline in individual battery performance.

• Significantly Enhanced Safety: The coolant has good insulation properties and flame-retardant characteristics, effectively suppressing the occurrence and spread of battery thermal runaway. When a battery abnormally heats up, the coolant can quickly absorb the heat and lower the battery temperature, preventing serious accidents such as fires caused by thermal runaway. In energy storage scenarios with extremely high safety requirements, such as energy storage stations near residential areas or important facilities, the safety advantages of immersion cooling are particularly prominent, providing reliable safety protection for the surrounding environment and personnel.

• Perfect Integration of Temperature Control and Firefighting: Some immersion cooling systems use coolants with fire-extinguishing functions, achieving an organic combination of temperature control and firefighting. In the event of battery thermal runaway, the coolant can not only cool down promptly but also extinguish the fire quickly, effectively reducing the risk of accidents. This feature is of great application value in places with a higher risk of fire, such as backup power supply energy storage systems in data centers, greatly enhancing the overall safety of the system.

 

Disadvantages Considerations

• High Cost: Immersion cooling systems require special coolants and sealed containers, resulting in high equipment procurement costs. The cost of replacing and maintaining the coolant is also significant, leading to a substantial increase in overall operating costs. For projects with limited budgets, the high cost may become a major barrier to adopting immersion cooling technology.

• Difficult Maintenance: Since the batteries are completely submerged in the coolant, special equipment and techniques are required for maintenance, making the process complex. If a battery fails, maintenance personnel need to first drain the coolant before inspecting and repairing the battery, increasing the time and labor costs of maintenance. Moreover, during maintenance, it is necessary to ensure that the coolant's recovery and disposal meet environmental protection requirements, further increasing the difficulty and complexity of maintenance.

• High Battery Sealing Requirements: To prevent coolant leakage from damaging the batteries, the batteries must have a very high level of sealing. This imposes strict requirements on battery manufacturing processes and quality control, increasing the production cost and manufacturing difficulty of batteries. If the battery sealing is poor, coolant leakage may cause battery short-circuiting, corrosion, and other issues, severely affecting battery performance and lifespan.

 

Applicable Scenarios

Immersion cooling is suitable for large-scale energy storage projects with extremely high safety and performance requirements, such as grid-side large energy storage stations and backup power supplies for important data centers. These scenarios have stringent reliability and safety requirements for energy storage systems, and immersion cooling can meet their strict cooling and safety needs. For example, in large-scale energy storage projects accompanying wind farms and photovoltaic power stations, to ensure the safe and stable operation of energy storage systems under various complex conditions, immersion cooling technology is widely applied, providing a strong guarantee for the efficient utilization of new energy.

 

Comparison and Summary of the Four Cooling Methods

Comprehensive Comparison

To more intuitively compare air cooling, liquid cooling, direct cooling, and immersion cooling, we have summarized them in the following table:

 

Cooling Method	Heat Dissipation Efficiency	Cost
Air Cooling	Low, due to the low specific heat capacity of air and limited heat transfer ability	Low, with main equipment being fans and air ducts
Liquid Cooling	High, with liquids having high specific heat capacity and thermal conductivity, resulting in strong cooling ability	High, including liquid cooling pipes, pumps, heat exchangers, etc., with high procurement and operational costs
Direct Cooling	Relatively high, with the large phase change latent heat of the refrigerant enabling rapid cooling	Relatively high, with high requirements for pressure resistance and sealing, increasing equipment costs
Immersion Cooling	Extremely high, with the coolant having full contact with the batteries, resulting in high cooling efficiency	Extremely high, with special coolants and sealed containers having high costs and significant operational expenses

 

Selection Suggestions

When selecting the cooling method for a lithium battery energy storage system, multiple factors need to be considered comprehensively. If the project has low power, a limited budget, and relatively low cooling requirements, such as small-scale home energy storage or low-power distributed energy storage, air cooling is an economical and practical choice.

For large-scale, high-power energy storage projects, such as grid-side energy storage stations and backup power supplies for large data centers, liquid cooling systems can meet their strict requirements for cooling efficiency and temperature control. Although the cost is relatively high, considering long-term operation and system stability, it is a more suitable choice.

In specific scenarios with extremely high heat dissipation requirements, limited space, and relatively low cost sensitivity, such as high-performance electric vehicle battery thermal management or small-scale high-energy-density energy storage devices, direct cooling technology can better ensure stable battery operation with its advantages of efficient heat dissipation and compact structure.

For large-scale energy storage projects with extremely high safety and performance requirements, such as energy storage stations near residential areas or important facilities and backup power supplies for large data centers, immersion cooling is undoubtedly the best choice. Despite the high cost and complex maintenance, its exceptional cooling performance and safety can provide a solid guarantee for the reliable operation of the energy storage system.

 

Conclusion

Air cooling, liquid cooling, direct cooling, and immersion cooling each have their own strengths in lithium battery energy storage systems. Air cooling is low-cost and simple in structure but has limited heat dissipation efficiency; liquid cooling is highly efficient in cooling and precise in temperature control but is costly and complex in system structure; direct cooling has superior heat transfer performance and space-saving advantages but faces challenges in pressure resistance, sealing, and temperature uniformity; immersion cooling offers exceptional cooling performance and high safety but has high costs and maintenance difficulties.

In the actual design of lithium battery energy storage systems, we need to take into account various factors such as the project's power requirements, budget constraints, space conditions, and safety requirements, and make a comprehensive assessment to select the most suitable cooling method. In the future, with the continuous development of battery technology and the growing demand for energy storage, it is believed that cooling technologies will also continue to innovate, providing a more solid guarantee for the efficient and safe operation of lithium battery energy storage systems and helping the new energy industry move towards a more brilliant future.