The contradiction between global energy supply-demand dynamics and the need for environmentally sustainable development urgently requires systematic solutions. Among novel energy storage technologies, electrochemical storage exhibits unique advantages in renewable energy grid integration, smart grid frequency regulation, and electric transportation due to its flexible configuration, fast system response, and environmental friendliness. Lithium-ion batteries (LIBs), despite their significant commercial success in consumer electronics and new energy vehicles owing to high energy density, face challenges in large-scale energy storage applications, particularly in remote areas for wind-solar-storage integration, due to factors like uneven distribution and price volatility of lithium resources. Sodium-ion batteries (SIBs), developed based on the advantages of high sodium abundance, low raw material cost, and intrinsic safety characteristics, share a homologous “rocking-chair” working principle with LIBs. Theoretical calculations show that SIBs using hard carbon anodes paired with layered oxide cathode materials can achieve energy densities above 140 Wh/kg and maintain 80% capacity retention at -40°C. Therefore, SIBs show application potential in distributed energy storage and specific electric vehicle scenarios, gradually transitioning from the laboratory to industrialization, with clear competitive advantages in cost-sensitive markets.
Both LIBs and SIBs face safety issues during operation. Although SIBs possess higher intrinsic thermal stability (thermal runaway trigger temperature is 50-80°C higher than LIBs), the substantial heat generated during charge/discharge cycles can cause battery temperature to rise. High temperatures accelerate internal chemical reactions, affecting performance and lifespan. Massive electrolyte decomposition and separator shrinkage/rupture can trigger thermal runaway, leading to serious accidents like fire or explosion. Effective thermal management technology is therefore crucial for the performance release and safe operation of Li/Na-ion batteries. Liquid cooling technology, with its high heat dissipation efficiency and excellent temperature uniformity, has become a key research focus in battery thermal management systems (BTMS).
The coolant is a key component of liquid cooling technology, and its performance directly affects the heat dissipation effect and safety of the cooling system. This review explores the classification and working principles of liquid cooling technology, analyzes the heat storage mechanism, basic characteristics of coolants, and their application in various liquid cooling technologies. It focuses on discussing recent research progress in cold plate, immersion, and spray liquid cooling technologies, and finally provides an outlook on the development of liquid cooling technology. The aim is to offer a reference for the research, development, and technical application of liquid coolants in battery cooling, promoting the further development and application of Li/Na-ion batteries in the energy storage field.
1. Introduction to Liquid Cooling Technology
Air cooling is the earliest used battery thermal management technology, utilizing air flow based on natural or forced convection heat transfer principles. It offers advantages like simple structure and low cost. However, due to air’s low thermal conductivity, battery temperature is significantly influenced by factors like airflow channels, resulting in poor temperature uniformity within a battery pack. It is generally suitable for battery packs in low heat generation scenarios. Liquids possess higher specific heat capacity and superior thermal conductivity compared to air. Liquid cooling technology, which uses liquid as the cooling medium, offers better heat dissipation efficiency and temperature uniformity, enabling thermal management for battery packs in high heat generation scenarios, garnering significant attention in recent years.
1.1 Types and Working Principles of Liquid Cooling Technology
Liquid cooling technology primarily includes three categories: cold plate, immersion, and spray cooling. Cold plate liquid cooling technology belongs to indirect cooling (battery-cold plate-coolant). It employs a cold plate with integrated internal flow channels in contact with the battery surface. A coolant, commonly a mixture of ethylene glycol and water, circulates within the cold plate channels to carry away the heat generated by the battery. Advantages include simple structure, high safety, easy maintenance, and compatibility with existing battery pack designs. Disadvantages include significant space occupation and poor temperature uniformity due to large contact thermal resistance.
Immersion liquid cooling technology is a direct cooling method. The battery pack is directly immersed in an insulating coolant, enabling direct heat exchange between the coolant and the battery to rapidly remove the generated heat. Its advantages are high heat dissipation efficiency and excellent temperature uniformity. The drawbacks are the high cost of high-performance coolants and the risk of coolant leakage.
Spray cooling technology can be applied in both direct and indirect cooling modes. Spray nozzles are typically arranged above or on the sides of the battery module, spraying coolant directly onto the heat-generating battery pack for cooling. The coolant is then collected via drainage plates and recirculated. Compared to cold plate and immersion cooling, spray cooling offers advantages like lower coolant volume requirement and higher flexibility. However, it faces challenges such as difficulty in achieving system compactness, complex liquid management, and high requirements for nozzle design.
1.2 Heat Transfer Mechanism of Coolants in Liquid Cooling Technology
When a material absorbs heat, its temperature increases or it undergoes a phase change. The absorbed heat is stored in two forms: sensible heat (temperature rise) and latent heat (phase change at constant temperature), with latent heat storage capacity being much higher than sensible heat. Solid-liquid phase change materials, with advantages like high latent heat, small volume change, low supercooling, stable chemical properties, and low cost, are commonly used in phase change material cooling systems and are also a common thermal management method for Li/Na-ion batteries. Utilizing the heat absorption characteristics of materials, liquid cooling technology primarily uses liquids in the temperature rise phase and the liquid-gas phase change phase as coolants to absorb heat and lower battery pack temperature.
Based on whether the coolant undergoes a liquid-gas phase change during the heat dissipation process, immersion liquid cooling can be divided into single-phase and two-phase immersion cooling. These two systems differ in working principle, application scenarios, etc. A comparison is shown in the table below:
| Cooling Technology | Working Principle / Coolant State | Technical Characteristics |
|---|---|---|
| Single-phase Immersion | Based on sensible heat transfer of liquid medium; coolant remains liquid. | Thermodynamically stable; good medium adaptability; high potential for energy efficiency optimization. |
| Two-phase Immersion | Based on latent heat of phase change; coolant undergoes “liquid-vapor-liquid” cycle. | Higher heat transfer efficiency; better temperature uniformity; good low-temperature applicability. |
The working principle of single-phase immersion cooling systems is based on sensible heat transfer of the liquid medium. Batteries immersed in a high-boiling-point coolant cause the local coolant temperature to rise when they generate heat. Forced convection is used to transport the locally heated coolant to a heat exchanger for cooling, after which it is recirculated around the batteries. Repeating this process lowers the battery pack temperature. Single-phase immersion cooling is characterized by: 1) Thermodynamic stability. The cooling medium remains liquid throughout, avoiding instabilities caused by phase change. 2) Good medium adaptability. Coolants with different viscosities and dielectric strengths can be selected based on operational requirements. 3) High potential for energy efficiency optimization. Utilizing temperature differences for zero-power heat dissipation in low-heat or low-temperature environments improves system energy efficiency ratio. However, this technology has clear limitations. Heat dissipation efficiency dominated by sensible heat transfer is lower than with two-phase coolants. In high-temperature conditions, flow rate needs to be increased to meet heat dissipation demands, increasing the proportion of pump power consumption.
The working principle of two-phase immersion cooling technology is based on the latent heat of liquid phase change. Batteries are immersed in a low-boiling-point insulating coolant. The coolant absorbs heat and reaches its boiling point, undergoing a liquid-to-vapor transition. During this process, the coolant absorbs a large amount of latent heat, rapidly carrying away the battery’s generated heat for efficient cooling. The vaporized coolant is condensed in a condenser back into liquid, returning to the battery surroundings to complete the cycle. Two-phase immersion cooling offers the following advantages: 1) Higher heat transfer efficiency. The convective heat transfer coefficient of two-phase coolant is more than twice that of single-phase coolant. 2) Better temperature uniformity. The temperature remains stable during the phase change process, resulting in better battery temperature uniformity. 3) Good low-temperature adaptability. Two-phase coolants have lower boiling points, allowing the thermal management system to operate within a lower temperature range, which helps improve battery performance and lifespan. However, two-phase immersion cooling also faces challenges. The phase change process imposes high requirements on system sealing; coolant leakage and volatilization pose safety risks. The design and control of the liquid cooling system are relatively complex, requiring precise control of parameters like coolant flow rate, temperature, and pressure to ensure stable operation. The high cost of low-boiling-point fluorinated liquids makes large-scale use in energy storage systems difficult.
2. Key Performance Requirements for Coolants in Liquid Cooling Technology
The heat dissipation effect, system reliability, and economic viability of liquid cooling technology highly depend on the physical and chemical properties of the coolant. The coolant must meet stringent requirements in terms of thermodynamics, electrochemistry, and material compatibility while also balancing environmental friendliness and cost. In recent years, with the promotion of high-energy-density batteries in the energy storage field, coolant system optimization and the development of new fluids have become hot research topics in liquid cooling technology.
2.1 Thermal Performance Requirements
The thermal performance of the coolant is key to affecting battery heat dissipation efficiency, mainly including parameters such as specific heat capacity, thermal conductivity, and kinematic viscosity. These parameters are interrelated and collectively determine the heat dissipation effect of the coolant in the battery thermal management system. Specific thermal performance requirements are as follows:
- High Specific Heat Capacity: Specific heat capacity directly affects the amount of heat absorbed per unit mass of coolant per unit temperature rise. A coolant with high specific heat capacity experiences a smaller self-temperature increase when absorbing the same amount of heat, allowing it to more effectively carry away the heat generated by the battery. This is beneficial for maintaining temperature stability during high-rate charge/discharge. Water-based coolants have a specific heat capacity of about 4.2 kJ/(kg·K), much higher than oil-based liquids.
- High Thermal Conductivity: Thermal conductivity is a physical quantity measuring the heat conduction capability of the coolant, reflecting the efficiency of heat transfer within the coolant. Higher thermal conductivity facilitates faster heat transfer and is a key indicator for achieving battery temperature uniformity. The thermal conductivity of water is about 0.6 W/(m·K), better than most oils.
- Wide Operating Temperature Range: The melting and boiling points of the coolant directly affect the usable range of the liquid cooling technology. A low melting point prevents the coolant from solidifying at low temperatures, making it unusable. A high boiling point avoids coolant boiling at high temperatures. For example, ethylene glycol-water solutions can have boiling points of 105–130°C, meeting the heat dissipation needs of high-heat-generation scenarios.
- Low Kinematic Viscosity: Kinematic viscosity significantly impacts the fluidity and heat dissipation effect of the coolant. Low-viscosity coolant flows with less resistance, making it easier to reduce circulation pump energy consumption and achieve rapid heat transport. High-viscosity coolant flows with difficulty, easily forming local hot spots, unable to utilize the coolant’s heat dissipation function, resulting in higher maximum temperatures and larger battery temperature differences.
The combined effect of these properties can be evaluated using a heat transfer effectiveness parameter. A simplified figure of merit (FOM) for coolant thermal performance in forced convection can be expressed as:
$$ FOM_{th} = \frac{k \cdot c_p}{\nu} $$
where \(k\) is thermal conductivity, \(c_p\) is specific heat capacity, and \(\nu\) is kinematic viscosity. A higher FOM indicates better overall thermal performance for a given pumping power.
2.2 Chemical Stability and Material Compatibility
Stable chemical properties and material compatibility are basic characteristics of a coolant. A stable coolant should avoid decomposition, oxidation, or reactions with other substances that produce impurities, corrosive substances, or performance degradation, ensuring long-term stable system operation. The stability of the coolant is related to its composition; for example, fluorinated liquids have strong chemical bonds, giving them significantly higher chemical stability than hydrocarbon-based coolants. Additionally, high temperature, high pressure, and high humidity environments can easily cause chemical changes in the coolant.
Based on the structure of the battery thermal management system and the usage scenarios of the coolant, the coolant must not only be non-corrosive to metals (copper, aluminum, steel, etc.), rubber seals, plastic pipes, etc., but also resistant to high-temperature oxidation and UV degradation, avoiding the generation of acidic substances or precipitates.
2.3 Safety and Environmental Friendliness
The coolant must be non-toxic, non-hazardous, non-flammable or have a high flash point, and be biodegradable. During production, use, and disposal, the coolant’s negative impact on the environment should be minimized. For example, the volatility and toxicity of fluorocarbon coolants adversely affect the ecological environment and human health. Some coolants containing heavy metals can cause damage to water and soil if leaked, making them unsuitable for use in battery management systems. Being non-flammable and having a high flash point reduces fire risk. For instance, fluorinated liquids have flash points above 200°C, while mineral oil’s flash point is about 150°C, requiring attention to safety in high-temperature use scenarios. The biodegradability of the coolant is a core indicator of its environmental friendliness. In the event of an accidental leak, a rapidly biodegradable coolant can greatly reduce the pollution burden on soil and water bodies. It also simplifies the disposal process at the end of the coolant’s life, reducing costs.
2.4 Electrical Insulation
Electrical insulation is a key performance indicator for immersion liquid cooling technology, playing an important role in ensuring normal battery operation and system safety. Electrical insulation is primarily measured by resistivity and dielectric constant. Higher material resistivity indicates better electrical insulation, and the dielectric constant should be within a suitable range. Since voltage differences exist across battery terminals during charge/discharge, and the coolant is in direct contact with electrical components, poor electrical insulation of the coolant can lead to serious problems like battery self-discharge and short circuits, potentially causing fire, explosion, and other safety accidents. To ensure the insulation performance of the coolant, the purity and impurity content of raw materials must be strictly controlled during the coolant’s R&D and production process, as metal ions and moisture can significantly degrade the coolant’s electrical insulation performance. The requirement can be expressed as needing a high volume resistivity \(\rho_v\):
$$ \rho_v > 10^{12} \ \Omega \cdot cm $$
and a relatively low dielectric constant \(\epsilon_r\) to minimize capacitive coupling.
2.5 Other Practical Requirements
In addition to the above characteristics, the coolant must meet a series of key practical requirements in actual applications, such as easy maintenance, long service life, good defoaming properties, low cost, and easy availability. These requirements collectively determine its market acceptance and lifecycle cost. Easy maintenance means the cooling system does not require frequent, complex maintenance operations, reducing system maintenance costs. Long service life is a key indicator for reducing coolant cost by extending the replacement cycle. Bubble generation can affect coolant circulation and heat transfer efficiency; defoamers can be added to suppress foam formation or quickly eliminate it. Reasonable cost and easy availability are the cornerstones for promoting the large-scale application of coolants, requiring a stable supply chain and market competitiveness.
3. Types and Characteristics of Coolants
The selection of coolant is critical for the design of an efficient battery management system. The table below summarizes the primary categories of coolants used in liquid cooling for battery thermal management.
| Coolant Type | Key Characteristics | Typical Examples |
|---|---|---|
| Water-based Coolants | Low cost, easy preparation, non-flammable, but poor insulation and prone to deterioration. | Water, Water/Ethylene Glycol, Water/Propylene Glycol |
| Nanofluids | Good thermal conductivity, high thermal stability, but high cost and potentially poor flowability. | Al2O3/TiO2/SiO2 – H2O/Glycol suspensions |
| Hydrocarbons & Silicones | Low cost, high flash point, but high viscosity and density. | Mineral Oil, Synthetic Oil, Silicone Oil |
| Fluorocarbons | High thermal conductivity, low viscosity, non-flammable, but expensive, some are environmentally hazardous. | Hydrofluoroethers (HFE), Perfluorocarbons (PFC) |
| Boiling Liquids | Self-regulating, highly energy-efficient, but noisy and potentially corrosive. | Chlorofluorocarbons, Hydrofluoroethers |
| Liquid Metals | Very high thermal conductivity, good stability, but expensive and pose safety hazards. | Gallium alloys, Tin alloys |
3.1 Water-based Coolants
Deionized water has relatively high specific heat capacity [~4.2 kJ/(kg·K)] and thermal conductivity [~0.6 W/(m·K)] and is low cost. When used as a coolant in battery thermal management systems, it is often used as a base fluid with additives like antifreeze (e.g., ethylene glycol, propylene glycol), corrosion inhibitors, and surfactants. Adding ethylene glycol or propylene glycol effectively lowers the coolant’s freezing point, making it suitable for low-temperature environments, but the thermal conductivity of the coolant decreases as the proportion of glycol increases. Water-based coolants are commonly used in indirect contact liquid cooling thermal management systems, where components like cold plates are added between the battery and the coolant to absorb the heat generated by the battery, which is then carried away by the flowing water-based coolant. This is widely used in current commercial electric vehicles and energy storage fields.
3.2 Nanofluids
Nanofluids refer to new heat transfer media prepared by dispersing metal or non-metal nanoparticles into traditional heat exchange media like water, alcohol, and oil to form uniform, stable, and highly conductive suspensions. In the field of battery thermal management, nanoparticles such as Cu, Al, CuO, Al2O3, TiO2, SiO2, and CNTs are often added to water and alcohol mixtures to improve the thermal conductivity of the coolant. Studies have shown that the thermal conductivity of ethylene glycol/water mixtures decreases with an increasing percentage of ethylene glycol. However, for a specific mixture (e.g., 50:50), adding Al2O3 nanoparticles at volume fractions of 0.1%, 0.3%, and 0.5% increased thermal conductivity by approximately 2%, 4.2%, and 7.5%, respectively. Research on hybrid nanofluids found that their thermal conductivity is an increasing function of nanoparticle volume fraction. The enhancement in thermal conductivity \(k_{nf}\) relative to the base fluid \(k_{bf}\) can often be approximated by models like:
$$ \frac{k_{nf}}{k_{bf}} = 1 + a\phi $$
where \(\phi\) is the nanoparticle volume fraction and \(a\) is an empirical constant.
3.3 Hydrocarbons and Silicones
Hydrocarbon-based coolants have a long history of wide application in the industrial field and have garnered attention in immersion cooling systems for Li/Na-ion batteries. They mainly include natural mineral oils, synthetic oils, and silicone oils. Natural mineral oils are distilled from petroleum and undergo deep hydrogenation treatment, offering the advantage of low cost and are widely used in outdoor transformer cooling. However, natural mineral oils have some obvious disadvantages, such as oxidation and decomposition of hydrocarbon molecules during use, increasing acidity and generating contaminants, affecting the coolant’s thermal conductivity and fluidity, and reducing the service life of the battery thermal management system. Synthetic oils are artificially synthesized based on alkane or ester compounds, mainly including polyalphaolefins, gas-to-liquid synthetic oils, and synthetic esters. Compared to natural mineral oils, synthetic oils have lower impurity content, better oxidation resistance, thermal conductivity, and material compatibility, but they also share the issue of low flash points, posing safety risks of fire and explosion when used at higher temperatures. Silicone oils have higher flash points due to the presence of siloxane bonds in their structure, offering clear advantages in battery thermal management system applications. However, the flash point of silicone oil is positively correlated with viscosity; high flash point silicone oils have higher viscosity, resulting in poorer fluidity and affecting the heat dissipation performance of the corresponding thermal management system. Furthermore, silicone oils are prone to hydrolysis and precipitation in humid environments, increasing coolant viscosity and leading to decreased heat dissipation performance.
3.4 Fluorocarbons
Compared to hydrocarbons, fluorocarbons incorporate a large number of fluorine atoms, resulting in relatively weaker intermolecular forces, higher thermal conductivity, and lower viscosity. High thermal conductivity enables faster heat transfer, improving heat dissipation efficiency. Low viscosity facilitates coolant flow, reducing pump power requirements while enabling rapid coolant transport and improved heat exchange efficiency. The introduction of highly electronegative fluorine atoms strengthens carbon-fluorine bond energy, making the molecular structure more stable, with no flash point and non-flammable properties. Fluorocarbons are chemically inert, less likely to react with other substances, thus exhibiting good compatibility with other materials. Depending on their composition and structure, fluorocarbons can be classified into chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and hydrofluoroethers (HFEs). CFCs and HCFCs are recognized as prohibited refrigerants in the Montreal Protocol due to their destructive effect on the atmospheric environment, particularly the ozone layer. HFCs are widely used refrigerants in household refrigerators and air conditioners. Although they do not deplete the ozone layer, they exacerbate the greenhouse effect, and their use in immersion cooling technology is also subject to certain restrictions. PFCs include types like perfluoroalkanes, perfluoroamines, and perfluoropolyethers, with properties suitable for semiconductor equipment cooling scenarios in terms of boiling point and dielectric constant. However, their promotion is limited due to the greenhouse effect. HFEs are promising coolants for immersion cooling, with no ozone depletion potential, relatively low global warming potential, and high dielectric constant. They are already widely used in data center fields. As the price of fluorocarbon-based coolants decreases, they will gradually be applied in electric vehicles and battery energy storage.
3.5 Boiling Liquids
Boiling liquids utilize the absorption of a large amount of vaporization heat during the boiling process to achieve efficient cooling of batteries. Common boiling liquids mainly include chlorofluorocarbons, perfluorocarbons, and hydrofluoroethers. Compared to traditional cooling methods, boiling liquid cooling has obvious advantages. A novel SF33 fluid cooling (two-phase) immersion liquid cooling system was proposed, and its effect on battery pack performance was evaluated by assessing the cooling performance on 18650 batteries. Results showed that effective thermal homogenization and cooling of the battery can be achieved through heat exchange with the boiling medium. In the initial stage of battery heat generation, when the coolant temperature is below its boiling point, sensible heat absorption occurs. As the battery temperature slightly exceeds the boiling point, the surrounding fluid absorbs sensible heat through natural convection. When the battery temperature continues to rise, the coolant reaches partial boiling and eventually stabilizes in the full nucleate boiling stage.
3.6 Liquid Metals
Liquid metals generally refer to metals or alloys with melting points near room temperature, possessing excellent electrical and thermal conductivity and combining the properties of metals and fluids. Typical liquid metals include gallium-based alloys, bismuth-based alloys, and tin-based alloys. 3D numerical simulations of single-phase flow and conjugate heat transfer in microchannel heat sinks subjected to constant heat flux were conducted using different gallium alloys (EGaInSn, EGaIn, GaSn, and GaIn) and various substrate materials (copper alloy, aluminum, tungsten, and silicon). A comprehensive study of the effects on temperature distribution, pumping power, pressure drop, maximum heat flux, etc., was performed over a range of Reynolds numbers (300–1900). Among all considered coolants, EGaIn was found to most effectively reduce flow resistance. The thermal conductivity of the substrate material significantly affects the thermal resistance of the microchannel, with higher conductivity leading to lower thermal resistance. Furthermore, GaIn alloy, with higher thermal conductivity and specific heat compared to other gallium alloys, exhibited better thermal performance. A novel coolant, liquid metal, was proposed for the thermal management of battery packs. The cooling capability, pump power consumption, and module temperature uniformity of the liquid metal cooling system were evaluated through mathematical analysis and numerical simulation and compared with water cooling. Results indicated that under the same flow rate conditions, the liquid metal cooling system could achieve lower and more uniform module temperatures with less required pump power consumption.
4. Recent Research Progress in Liquid Cooling Technologies
Continued innovation in the battery management system is essential for safety and performance. Recent advancements focus on optimizing the cooling systems within the BMS.
4.1 Cold Plate Liquid Cooling
Cold plate liquid cooling is currently the most researched and widely used battery thermal management system. Recent research has mainly focused on various innovative designs and optimization strategies for cold plate liquid cooling thermal management systems of lithium-ion battery packs. These strategies primarily revolve around improving cooling efficiency, ensuring temperature uniformity, and enhancing the safety of the thermal management system. They mainly include optimizing coolant properties, innovative structural flow channel design, improving the thermal management system, and optimizing system-level flow distribution. Based on a finite element model, a ternary lithium battery pack was designed, and simulations were performed using a coolant composed of ethylene glycol (50%) and water (50%) mixed solution with the addition of graphene nanoplatelets (GNPs) at 0.001 vol% and 0.005 vol%. Single-layer, double-layer, and triple-layer system designs of the battery pack were simulated to optimize the heat dissipation effect and surface contact between the flowing coolant and the batteries. Compared to the ethylene glycol/water mixed coolant, the coolant with 0.001 and 0.005 vol% GNP additions reduced the battery pack temperature difference by approximately 12%~24% and 24%~29%, respectively. The improvement in the cooling system’s cooling capability was attributed to the high thermal conductivity and large surface area of GNPs.
Inspired by maple leaf veins and streamlined shapes, a new bionic liquid cold plate was designed. To evaluate the cooling performance of the leaf-shaped channel, a validated battery model was used to simulate the thermal behavior of lithium-ion batteries during charging and discharging. Comparing the cooling performance of the leaf-shaped channel with straight, fishbone, and serpentine channels, it was found that under the same heat exchange area and boundary conditions, the leaf-shaped channel outperformed its counterparts in thermal management and energy efficiency and more effectively optimized the impact of battery tabs. During charging, the average battery temperature of the leaf-shaped channel was 0.4°C and 0.14°C lower than that of straight and fishbone channels, respectively. Further optimization of the leaf-shaped channel reduced the battery pack temperature difference and energy consumption by 11% and 13%, respectively, enhancing the practicality of manufacturing and applying the liquid cooling system. A new bionic vascular flow channel liquid cold plate was designed, inspired by human vascular structure. Compared with traditional V-shaped and serpentine channels, the novel design demonstrated significant advantages in heat dissipation performance. A new serpentine liquid cold plate structure was designed to improve the cooling performance of the liquid cold plate. Numerical simulation was used to study the effects of ethylene glycol (50%) solution coolant mass flow rate, inlet temperature, flow direction, and number of channels on the performance of the liquid cold plate under a 2C discharge rate. The cooling performance of the new serpentine cold plate was better than that of the traditional serpentine cold plate.
A cold plate-flame retardant plate-cold plate based battery indirect cooling system was proposed, combining the good cooling performance of the liquid cold plate with the fire resistance of flame-retardant materials to suppress the propagation of battery thermal runaway. The effects of three typical cooling channel structures and three typical flame-retardant materials (glass wool, aerogel, and polyimide foam) were investigated. Results showed that the CFCP-based cooling system could achieve better cooling performance. When the flow velocity was 0.05 m/s, it could effectively suppress heat transfer from a thermal runaway cell to adjacent cells. Furthermore, the aerogel-based cooling system and the cold plate with a 5-vertical-channel structure achieved the best cooling effect. A novel manifold microchannel heat sink coupling a manifold inlet/outlet structure, distributed jets, and micro pin-fins was proposed to achieve efficient heat dissipation. A Swiss-roll type battery thermal management system was designed, and the effects of system structural parameters, coolant inlet flow rate, coolant type, and inlet temperature on the battery heat dissipation performance were studied. Results showed that the coolant inlet flow rate was the main controlling factor for the heat dissipation performance of the battery module. After optimization, the maximum temperature and temperature difference of the Swiss-roll battery module were 300.4 K and 3.3 K, respectively. Compared to other researchers’ optimized serpentine channel BTMS, the Swiss-roll battery module’s maximum temperature and temperature difference were reduced by 1.2 K and 0.2 K, respectively. It was proposed to regulate the size of different orifice plates to change the pressure drop in tertiary pipes and design different flow branches by changing secondary pipe branches. These two methods made the flow field distribution in a single battery cluster uniform, thereby controlling the error within 10%. Changing the diameter of the secondary pipeline could make the flow distributed from the primary pipeline to each secondary pipeline uniform, achieving uniform flow distribution at the inlet of each battery module in the liquid cooling system.
4.2 Immersion Liquid Cooling
Immersion liquid cooling is nowadays one of the most promising battery thermal management technologies. Multiple studies, through comparison and simulation, consistently prove that immersion cooling significantly outperforms traditional air cooling in terms of cooling effect and stability/uniformity. Comparative studies were conducted on air cooling, HFE7100 static flow immersion cooling, forced flow immersion cooling, and immersion-coupled direct cooling. Results showed that compared to natural convection conditions, the maximum temperatures for static flow immersion cooling, forced flow immersion cooling, and immersion-coupled direct cooling were reduced by 4.23%, 5.70%, and 13.29%, respectively. The forced flow immersion cooling mode had the highest sensitivity to the flow parameters of the coolant. Regulating the flow velocity of the coolant could improve the coolant’s thermal conductivity and specific heat capacity, reducing the maximum temperature of the battery module.
Comparative studies investigated the effects of air cooling and a novel immersion cooling system on the cooling performance of an 18650 battery pack. It was found that the maximum temperature difference in the immersion-cooled battery pack was 1.5°C, much lower than that of air cooling (15°C). After 600 cycles, the capacity retention rate of the immersion-cooled battery pack increased by 3.3%. A three-dimensional model of a 60-cell immersion liquid-cooled battery pack was established. Simulation results showed that at a 2C discharge rate and a low flow rate of 0.2 L/min, the maximum temperature of the battery pack was 34.22°C, with no local abnormal overheating observed inside. As the coolant flow rate increased, the temperature uniformity within the battery pack improved significantly. It was suggested to maintain the flow rate above 0.5 L/min to ensure the battery temperature difference remains below 5°C.
A new battery thermal management system based on FS49 was proposed and tested for a liquid-cooled module of cylindrical lithium-ion batteries under fast charging conditions. The temperature responses of the battery module at 2C and 3C charging rates under forced air cooling and liquid immersion cooling were compared. Results showed that the liquid immersion cooling module’s peak temperature was 7.7°C and 19.6°C lower than that of forced air cooling at 2C and 3C charging rates, respectively, while the corresponding cooling energy consumption of liquid immersion cooling was only 14.41% and 40.37% of that of forced air cooling. Simultaneously, the battery pack under liquid immersion cooling had better temperature uniformity.
An immersion liquid-cooled battery cooling system with a fish-shaped hole flow-guiding structure was proposed, designed based on conformal mapping technology and bionic principles. Compared to the case without a flow guide, at a 3C discharge rate and a mass flow rate of 0.00273 kg/s, using a LIBCS with an ordinary flow guide reduced the maximum lithium-ion battery temperature by 5.3%, but increased pump power consumption by 81.4%. Using flow guides with circular holes and fish-shaped holes could reduce the maximum LIB temperature by 9.2% and 12.2%, respectively, while keeping the maximum temperature difference within 5°C. Furthermore, under the same operating conditions, the LIBCS using the fish-shaped hole flow guide reduced pump power consumption by 42.1% and 11.8% compared to the ordinary flow guide and the circular hole flow guide, respectively. At a mass flow rate of 0.00273 kg/s, the comprehensive performance factor of the LIBCS using the fish-shaped hole flow guide was 24%, 39.3%, and 7.3% higher than the cases without a flow guide, with an ordinary flow guide, and with a circular hole flow guide, respectively, indicating greater application value in practical engineering.
4.3 Spray Liquid Cooling
Spray liquid cooling technology has become an important research direction in battery thermal management due to its unique advantages of efficient heat dissipation and thermal runaway suppression. Research in this technology mainly focuses on two aspects: First, optimizing system design for conventional heat dissipation, including improving flow uniformity and cooling efficiency through nozzle structure, arrangement, nozzle parameters, and coolant properties, thereby significantly reducing the maximum temperature and temperature difference of the battery pack. Second, its excellent thermal safety protection capability; multiple studies have confirmed its effectiveness in cutting off the propagation path of battery thermal runaway.
Research progress in typical nozzle arrangements, system configurations, and more efficient system designs for spray cooling systems was summarized. Future development directions for spray cooling technology were proposed: achieving uniform flow distribution through nozzle structure design and arrangement, while also studying reasonable drainage solutions to avoid liquid accumulation and directional restrictions.
A single-phase spray technology was introduced to optimize the flow field and enhance thermal characteristics in battery thermal management systems. Computational fluid dynamics simulations were used to analyze key factors such as dielectric fluid type, nozzle diameter, spray angle, and nozzle position. It was concluded that thermal conductivity and viscosity were key for the coolant (Novec7500 performed better), and the optimal conditions for spray cooling were determined: nozzle diameter and spray angle of 0.47 mm and 88.16°, respectively. Under these conditions, the maximum temperature and temperature difference of the battery pack were 25.43°C and 3.41°C, respectively. Furthermore, this system reduced the maximum temperature and temperature difference of a 36-cell battery module by 27.28% and 69.39%, respectively.
Non-conductive liquid hydrofluoroether was combined with forced air flow. A three-dimensional transient heat transfer model for a cylindrical lithium-ion battery module was established using computational fluid dynamics software to study the effects of liquid spray rate and injector arrangement on the cooling performance of the battery module. Research results showed that compared to traditional air cooling, this technology effectively reduced the maximum temperature and temperature difference within the battery module. The optimized system required placing nozzles between the first and second rows of the battery module and maintaining a flow rate of 20 g/s, reducing the battery pack’s maximum temperature and temperature difference by approximately 6°C and 4°C, respectively.
R410A coolant was used to study the suppression effect of spray cooling on overheating propagation within a battery pack. Increasing the number of nozzles and initiating spraying earlier effectively reduced the average temperature of overheated batteries and suppressed the overheating decomposition reaction. Simultaneously, spray cooling effectively suppressed the thermal propagation of overheated batteries within the pack, preventing and delaying the occurrence of thermal runaway in the battery pack. The heat dissipation effect of spray cooling technology (using C6F12O coolant) on a 4×4 arranged 18650 cylindrical battery pack was studied. Results indicated that for a spray height of 6 cm and a flow rate of 2.05 g/s, the heat carried away by the liquid film accounted for about 30% of the total heat dissipation, while direct spray cooling accounted for about 70%, effectively cutting off the propagation of battery thermal runaway.
Battery thermal runaway propagation characteristics were studied, and emergency spray technology with different cooling durations was applied at various stages of thermal runaway propagation. Results showed that continuous spraying effectively reduced the maximum battery temperature and delayed the spread of thermal runaway among multiple batteries. An innovative method of spray cooling to control thermal runaway in ternary lithium batteries was explored. The effects of two coolants (R134a, R227ea) and three different spray modes on emergency cooling efficiency were systematically studied. Results showed that coolant spray significantly reduced the temperature of the thermal runaway cell and had a noticeable thermal suppression effect on adjacent batteries. Furthermore, intermittent spraying with short intervals had better cooling performance than continuous spraying. When the inlet temperature of R134a coolant was 0°C and intermittent spraying was used, the battery temperature decreased at a relatively fast rate.
An emergency spray cooling method using coolant for the overheating stage of lithium-ion ternary batteries was proposed to prevent thermal runaway. A coupled computational model of lithium-ion battery overheating behavior and emergency spray cooling was established, and the spray cooling effects at four battery overheating stages were studied separately. Research results indicated that at the solid electrolyte interphase decomposition stage, applying a minimum spray pressure of 0.8 MPa could prevent the battery overheating decomposition reaction; at the anode-solvent reaction stage, increasing the maximum spray pressure to 2.4 MPa and the spray duration to 5.4 seconds could interrupt the overheating decomposition reaction; at the cathode-solvent reaction stage, increasing the number of nozzles from two to four could successfully prevent the reaction from continuing; at the electrolyte decomposition reaction stage, although refrigerant spray cooling could not stop the reaction, it could slow down the battery’s temperature rise rate and thermal runaway time, delaying the time for the battery to reach 160°C, 200°C, and 240°C by 10.4, 14.3, and 18.7 seconds, respectively.
5. Outlook and Future Perspectives
As the core of new energy storage technologies, the thermal safety of Li/Na-ion batteries is particularly critical in highly integrated, high-power-density scenarios. Liquid cooling technology, with its efficient heat dissipation capability and excellent temperature uniformity, has become a core solution to battery thermal management challenges. Based on the characteristics and related research progress of liquid cooling technologies: cold plate type offers simple structure and good adaptability but faces contact thermal resistance issues; immersion type provides high heat dissipation efficiency and good temperature uniformity but is limited by coolant cost and system sealing; spray type offers high flexibility but requires optimization of nozzle design and liquid flow distribution. The integration of advanced thermal management directly into the battery management system architecture is key for future development.
The coolant, as the core of liquid cooling technology, directly determines system energy efficiency. Its future development will revolve around the development of new coolant systems and multi-technology integration. In terms of high-performance coolant system development, for example, designing high-performance coolants through molecular structure design to improve thermal conductivity while reducing kinematic viscosity; optimizing coolant formulations, adding thermal conductivity enhancers and stabilizers to prevent the aggregation and deposition of conductive materials in the coolant; accelerating the development of environmentally friendly coolants, improving the biodegradability and environmental friendliness of coolants. In terms of integrating multiple cooling technologies, the combined design and development of hybrid cooling systems combining liquid cooling with air cooling, phase change material cooling, heat pipe cooling, etc., have significant value. Hierarchical thermal management strategies can reduce energy consumption, lower thermal resistance, and improve heat dissipation efficiency.
The mature experience of liquid cooling technology in lithium-ion batteries provides an important reference for its migration to sodium-ion batteries. Future development needs to focus on targeted innovation around the characteristics of sodium-ion batteries, focusing on the following directions: (1) Developing sodium-ion battery-compatible liquid cooling technology based on the electrode system, cell structure, and charge/discharge characteristics of sodium-ion batteries. (2) Matching the low-cost core advantage of sodium-ion batteries by developing low-cost, easily obtainable coolants, such as optimizing the insulation of water-based coolants, modifying the oxidation resistance and fluidity of hydrocarbon-based coolants, reducing the viscosity of high flash point silicone oils, and improving heat dissipation efficiency. (3) Combining the staged characteristics of sodium-ion battery heat generation to develop multi-technology integration and intelligent management strategies, such as developing staged flow control strategies to reduce pump consumption during low heat generation stages and increase flow during high heat stages to optimize energy efficiency; using three-dimensional simulation models to predict battery pack temperature distribution in real-time, dynamically adjusting coolant flow rate, velocity, and channel switching to avoid local overheating. In summary, the application of liquid cooling technology in sodium-ion batteries needs to focus on low cost and high compatibility as the core, promoting the safe and efficient application of sodium-ion batteries in large-scale energy storage fields through cross-technology integration and precise design, providing key support for the energy transition under the “dual carbon” goals.