The power battery is an important part of the electric vehicle, and its performance directly restricts the power, safety and economy of the vehicle. The energy density of the power battery determines the mileage of the electric vehicle, the power density determines the maximum gradient and the maximum speed, the cycle life and cost affect the cost of the vehicle and the economy of use, and the electric/thermal safety and environmental adaptability of the power battery determine the electric vehicle. The key factor of vehicle safety and environmental adaptability.
Lithium-ion batteries are an upgraded version of nickel-metal hydride batteries. They have high energy density (about 250 W h/kg) and power density (about 1500 W/kg), and have strong advantages in terms of cruising range and service life. It is the focus of current research and development and industrialization.
Lithium-ion battery system is an electrochemical power source with complex flow and heat transfer process. Temperature is the key factor affecting its performance, which is mainly reflected in three aspects: (1) The increase in temperature will aggravate the decline of battery capacity. Cause thermal runaway; (2) If the temperature is too low, the power and capacity of the battery will decrease significantly, and the charge and discharge efficiency will decrease; (3) The temperature difference between different batteries in the battery pack will lead to inconsistencies in the internal resistance and capacity of the cells and uneven speed Aging, forming a short board in the performance and life of the entire battery system.
Therefore, the working performance of the power battery is largely affected by temperature. It is necessary to design a reasonable thermal management system structure and develop an advanced thermal management control strategy to make the power battery work within a suitable temperature range and effectively control the temperature difference between cells. , thereby improving the performance of the power battery.
This paper first introduces the heat generation mechanism of lithium-ion batteries and the influence of temperature on their performance, explains the importance of thermal management of battery packs and the design requirements of thermal management systems; Research on battery thermal management of heat pipe technology; finally, the key issues and research prospects to be solved in the research of battery thermal management based on heat pipe technology are proposed.
01 Lithium-ion battery heat generation characteristics and thermal management requirements
The essence of the charging and discharging process of lithium-ion batteries is ion migration and chemical reaction. Li+ is intercalated and extracted in layered carbon materials and metal oxides, as shown in Figure 1. Under normal working conditions, the sources of battery heat include ohmic heat, electrochemical reaction heat, and polarization heat. As the temperature rises, a series of exothermic chemical reactions occur inside the battery, including electrolyte decomposition, negative electrode thermal decomposition, reaction between negative electrode and electrolyte, SEI film decomposition reaction, etc. Excessive temperature may lead to thermal runaway. The reactions that take place inside the battery are shown in Figure 2.
Figure 1 Schematic diagram of ion movement during charging and discharging of lithium-ion batteries
Figure 2 Electrochemical reactions inside Li-ion batteries at different temperatures
Temperature causes changes in electrochemical performance, which affects battery performance and life. As the temperature rises, the electrochemical reaction rate increases, which intensifies the battery capacity attenuation; the low temperature environment will also cause battery performance attenuation, the migration ability of lithium ions in the electrode active material is weakened, and the charge and discharge capacity drops rapidly.
In addition, too high or too low temperature will accelerate battery aging and affect battery life. Especially in the case of high-rate charging and discharging, the impact of temperature on battery life is more significant. Studies have shown that the capacity loss of Sony 18650 lithium batteries is 30% after 800 cycles at 25°C, and nearly 60% after 800 cycles at 50°C. Too high or too low storage temperature will also cause lithium battery capacity decay and accelerate aging.
Vehicle battery systems are usually composed of hundreds or thousands of battery cells, and battery packs face more severe thermal problems. Affected by factors such as heat transfer structure, series-parallel connection mode, and operating conditions, the temperature of each single battery in the battery pack shows strong inconsistency during operation, which leads to inconsistency in internal resistance, capacity attenuation, and depth of discharge of the battery, which in turn leads to the overall Battery pack usable capacity and life decay (Figure 3).
Figure 3 Effect of temperature difference on available capacity of battery pack
In fact, the consistency of cell temperature is an important parameter to determine the utilization rate of cell life, which in turn affects the life of the battery pack (equation (1)). Therefore, it is particularly important to ensure the consistency of cell temperature.
Battery pack life = battery life x battery life utilization rate (1)
To sum up, it is of great significance to control the temperature of the power battery pack and reduce the temperature difference between the single cells to improve the performance of the battery pack. At present, it is believed that the optimal operating temperature range of lithium batteries is 25~40°C, and the temperature difference between cells is less than 5°C. Most of the current thermal management technologies aim at the above-mentioned temperature and temperature difference, and design the structure and control method of the thermal management system to ensure the working efficiency and service life of the power battery pack.
02 Common thermal management methods
Battery thermal management includes high temperature heat dissipation and low temperature heating. Common battery heat dissipation methods include battery heat dissipation technologies based on gas (air), liquid, solid phase change material (phase change material, PCM) and heat pipes. The low-temperature heating methods of the battery module mainly include external heating based on fluid or positive temperature coefficient (PTC) and internal heating based on the heat generated by the battery itself.
2.1 Battery cooling technology
Application of air mainly includes forced convection and natural cooling. The researchers studied the heat transfer characteristics of the battery pack through the design of the cooling air duct structure, the design of the battery arrangement, and the optimization of the ventilation control strategy, and proposed measures to enhance heat transfer and improve temperature uniformity. Due to the advantages of low cost, simple system structure, and easy maintenance, the air-cooled system is applied to some models with short cruising range and high cost performance. For example, Nissan LEAF uses a passive battery thermal management system to dissipate heat for its lithium-ion pouch battery pack. , In addition, Toyota Prius, Kia Soul EV, SAIC Roewe MARVELX also use air cooling. However, for large-scale lithium-ion battery packs, air cooling cannot meet the heat dissipation requirements due to the large thermal load of the battery and the long relaxation time of heat conduction. Especially in high-temperature environments, the heat transfer efficiency of air-cooled thermal management technology is low, and the inconsistency is large, which makes it difficult to meet the thermal management requirements.
Due to the low convective heat transfer coefficient of air, the use of liquid instead of air has become an inevitable means of enhancing heat transfer. Research usually arranges liquid cooling plates at the bottom of the battery pack or between the cells for heat dissipation. At present, most of the research on liquid cooling system is focused on the design of cooling channels: by increasing the number of cooling liquid channels, improving the structure of cooling channels, arranging fins in channels, and designing connected combined cold plates to improve heat dissipation and temperature uniformity. In recent years, research on the use of new refrigerants as heat management coolants is also common, such as the use of liquid metals, nano-metal fluids, etc. to achieve enhanced heat dissipation.
At present, different car companies have different application methods for liquid cooling and heat dissipation. The Tesla liquid cooling system uses a mixed coolant of water and ethylene glycol with a mass ratio of 1:1, and arranges the cooling pipes in the 18650 battery stack in a meandering manner. Heat dissipation for each cell; the Chevrolet Volt pouch battery module also uses liquid cooling to dissipate heat. As shown in Figure 4, every two pouch cells constitute a unit, and an aluminum plate with a liquid-cooled flow channel is arranged on the Between the two cells, a parallel flow channel design is adopted to realize large-area cooling of each cell. In addition, there is a battery heat dissipation method based on the principle of liquid phase change, that is, the air-conditioning system evaporator is installed at the bottom of the battery system, and the heat generated by the battery is taken away by refrigerant evaporation, also known as direct cooling. Typical applications are BMW i3 series. Liquid cooling and heat management is a relatively common method in current engineering applications, but the system is more complicated, the mass is larger, and there is a possibility of leakage.
Figure 4 Volt battery cooling system and cold plate structure
Battery thermal management based on solid-liquid phase change materials is another current research focus. The principle is to use PCM phase change to absorb heat to reduce battery temperature. PCM can effectively ensure the temperature uniformity of the battery pack, but the thermal conductivity of the material is poor, so current research mainly focuses on the preparation of PCM materials and improving their thermal conductivity. In addition, the heavy weight of PCM reduces the energy density of the battery pack. The above reasons limit the application of phase change materials in the thermal management of power batteries.
2.2 Battery heating technology
The charge and discharge performance of lithium-ion batteries is significantly reduced in low temperature environments. Therefore, it is necessary to preheat the batteries to improve their performance. The current heating technology is mainly divided into two categories: internal heating and external heating.
Internal heating refers to the heating method of the battery through its internal resistance to generate heat, including external AC heating, mutual pulse charging and discharging heating between batteries, and battery self-discharging heating. In addition, Wang et al. designed a three-electrode battery, adding nickel electrodes and achieving rapid heating start of the fast battery through electrode switching.
External heating mainly includes air heating method and liquid heating method. The former uses electric heating wire to heat the air and then heat the battery, the temperature is uniform but the energy consumption is high. The latter heats the battery pack by heating the liquid in the flow channel, which has a more complex structure and a slower temperature rise. In addition to the above-mentioned heating method based on convection, PTC or low-power heating film can also be used to directly heat the battery surface, which will have a certain impact on battery heat dissipation. In addition, there is also a method of thermal management of the battery using the principle of heat absorption/release of PCM.
Figure 5 Schematic diagram of the working principle of the heat pipe
The use of heat pipes as heat transfer elements for high-temperature heat dissipation/low-temperature heating of batteries is a new thermal management method. The heat pipe is an efficient heat exchange element based on the principle of gas-liquid phase change, and its working principle is shown in Figure 5. The liquid working medium evaporates and vaporizes at the heating end, flows to the other end driven by the pressure difference, and condenses and releases heat in the condensation section. The liquid working medium returns to the evaporation section along the porous material through capillary force, which has the advantages of high heat transfer efficiency and good temperature uniformity. .
Figure 6 Schematic diagram of performance comparison of thermal management systems based on air cooling, liquid cooling and heat pipes
Heat pipes have been widely used in energy and chemical industry, aerospace, electronic power and other fields. In the field of battery thermal management, heat pipes have strong advantages in terms of heat dissipation/heating rate and battery pack temperature uniformity (Figure 6). In terms of high-temperature heat dissipation, compared with forced air cooling, the method of heat conduction through heat pipes and then air-cooled heat exchange can reduce the battery temperature by more than 20°C (20 Ah square battery, 5C discharge); in terms of low-temperature heating, batteries based on heat pipe heat conduction The heating rate is 1.5 times higher than that of PTC direct heating. Especially under high current charging and discharging conditions, the heat pipe exhibits more superior heat transfer performance and temperature uniformity. The application of heat pipes helps to realize the research and development of future high-performance battery packs, and has received extensive attention in recent years.
03 Research on battery thermal management based on heat pipe technology
FIG. 7 is a schematic diagram of a typical battery thermal management system using heat pipes as heat transfer components. The heat generated during the charging and discharging process of each cell is directly (or through a heat-conducting medium such as an aluminum plate) transferred to the heat pipe arranged on the side or bottom of the cell, and then the heat is taken away by the heat dissipation system at the cold end of the heat pipe. It can be seen from the figure that the main factors affecting the heat transfer performance of the system include three aspects: (1) The operating conditions and heat production of the power battery, that is, the influence of the working conditions of the heat source on the performance of the thermal management system; (2) The heat transfer characteristics of the heat pipe, mainly It involves the influence of the internal structure design of the heat pipe and its arrangement in the power battery pack on the heat dissipation performance of the system; (3) The heat dissipation at the cold end of the heat pipe mainly includes two forms of direct air cooling and water cooling for secondary heat exchange. In addition, at low temperatures, the heat pipe needs to be locally heated by PTC or electric heating film, and then transferred to the battery in the form of heat conduction. This part of the research involves heating system design and heating strategy research.
Figure 7 Schematic diagram of battery thermal management system based on heat pipe
3.1 Research on battery operating conditions and its impact on system heat transfer
The operating condition of the system determines the heat generation characteristics of the battery and is a key factor affecting the heat transfer of the system. Before the temperature of the battery rises to the start-up temperature of the heat pipe, the heat pipe transfers heat in the form of heat conduction through the shell. When the temperature rises to the start-up temperature, the working medium in the tube starts to absorb heat by using the latent heat of phase change, thereby increasing its thermal conductivity, and gradually making the battery temperature gradually increase. more stable.
Studies have shown that the time required for the battery to reach a stable temperature from the initial discharge under constant rate discharge is about 400-2000s, which is related to factors such as the battery discharge rate and the heat dissipation conditions of the cold end of the heat pipe. The heat production rate of the battery increases non-linearly with the discharge rate. The heat production rate of a 10 Ah square battery at 3, 5 and 8C rates is about 10.5, 25.4, and 54.4 W, respectively. The change of heat source conditions leads to different thermal resistances of the heat pipes and achieves stability. The temperature distribution is also different. In addition, the greater the amount of heat transfer at the cold end, the shorter the time required for the heat pipe to stabilize and the lower the stable temperature.
The operating environment of electric vehicles is complex and changeable, and they are faced with acceleration, landslides, sudden braking and other situations at any time. The thermal characteristics of power batteries are quite different from those in steady-state conditions. Figure 8 shows the difference in battery temperature and temperature difference variation law under stable and unsteady operating conditions. Tran et al. used time-varying heating power to simulate the driving conditions of vehicles, compared the temperature fluctuation of the heating module under the two conditions of fin air cooling and fin air cooling based on heat pipes, and showed that the battery temperature using heat pipe coupled fin air cooling However, during the change process, the change trend of temperature and heat flux is not consistent. Affected by thermal inertia, the heat production rate drops suddenly while the temperature continues to rise and then falls.
Figure 8. Schematic diagram of battery temperature change under vehicle conditions. (a) Stable condition; (b) Unsteady condition
The above research discussed the impact of unstable working conditions on the battery and the reliability of the heat pipe from the monomer level. The dynamic heat transfer characteristics of the battery group are quite different from those of the single battery, especially the thermal management structure has a more obvious influence on the temperature difference in the battery group.
The temperature rise and temperature distribution of the battery pack are closely related to the dynamic heat transfer process of the thermal management system. The current research is still in the heat transfer effect verification stage. How to combine the operating conditions of the battery pack to formulate an effective real-time control strategy for the thermal management system to achieve high efficiency. , Low-energy battery thermal management is a problem that needs to be further solved.
3.2 Heat transfer characteristics analysis and design research of heat pipe
3.2.1 Design and optimization of heat pipe based on power battery
Heat pipe design is an important factor affecting heat transfer performance. Its heat transfer effect is closely related to factors such as channel size, liquid-absorbing core structure, and liquid filling rate. Reasonable heat pipe design is very important to improve battery thermal management efficiency. Due to the particularity of power battery heat generation, many scholars have conducted research on the design of heat pipes for batteries. Jang et al. studied the effect of different working fluids on the heat transfer performance of loop-type gravity heat pipes. When the battery calorific value is 50 W, using acetone as the working fluid can control the average temperature of the battery below 45°C, which is better than using water as the working fluid. Quality cooling effect. Putra et al. found that the heat dissipation effect of the working fluid is closely related to the heat generation rate of the battery. According to the heat generated by different heat sources, different working fluids can be used to maximize the efficiency of the heat pipe. When the heat production rate of the battery is greater than 1.61 W/cm2, ethanol is used as the working fluid the highest heat transfer efficiency. Chi et al studied the effect of the liquid filling rate on the heat transfer of the pulsating heat pipe, and found that the optimal liquid filling rate of the heat pipe increases with the increase of the heat production rate of the battery. Therefore, it is necessary to select the appropriate type of working fluid and liquid filling rate according to the heat source conditions to achieve the best heat transfer effect.
Most of the current research studies and optimizes the heat transfer characteristics of heat pipes used in power batteries from the level of working fluid (type of working fluid, liquid filling rate), and there are also a few literatures that improve the performance of heat pipes from the perspective of structure. Swanepoel designed a battery thermal management system based on pulsating heat pipes, analyzed the influence of medium and pipe width on the heat transfer performance of heat pipes, and found that when the working fluid in the heat pipe is ammonia water, the width of the heat pipe must be less than 2.5 mm to ensure its performance in battery thermal management. The start-up and heat dissipation efficiency in.
Different types of heat pipes are used in the existing thermal management research of power batteries, such as gravity heat pipes, sintered heat pipes, pulsating heat pipes, flat-plate loop heat pipes, flat-plate micro-heat pipes, etc., and there is no unified selection or design method. From the structural point of view, flat-plate heat pipes show superiority in power battery thermal management systems, and are expected to become the first choice for power battery thermal management. However, there are currently few researches on the design of flat heat pipes.
3.2.2 Heat pipe layout scheme design
The layout of the battery thermal management system is another key factor affecting the thermal conductivity of the heat pipe. Tran et al. compared the thermal conductivity of heat pipes when placed horizontally and vertically. Applying a 38 W heat source to simulate the heat generation of the battery pack, the temperature at the evaporation end of the heat pipe reaches 61°C when it is arranged horizontally, and only 51°C when it is arranged vertically. Rao Zhonghao also obtained a similar rule by using pulsating heat pipes to conduct experiments. He built a battery thermal management experimental test platform as shown in Figure 9. The experiment shows that under the same heat generation power, the temperature rise of the battery surface is small when the battery is placed vertically, and the local temperature difference Smaller than when placed horizontally.
Figure 9 Schematic diagram of the pulsating heat pipe battery cooling system
In addition, the tilt angle of the device also affects the heat transfer. When the heat pipe is installed horizontally, the temperature difference on the battery surface is greatly affected by the inclination angle; when the heat pipe is installed vertically, the dual effects of gravity and capillary force reduce the heat transfer resistance of the heat pipe, and the slope of the road has little effect on the local temperature difference.
The above studies all show that the heat dissipation and temperature uniformity effect of the vertical arrangement of the heat pipe is better than that of the horizontal arrangement. Wang et al. studied the influence of battery placement direction on the heat transfer effect of heat pipes under the vertical arrangement of heat pipes, and showed that the working fluid in the tube can quickly transfer the heat from the high temperature end (electrode) to the condensation end, and the electrode facing upward under the same heat production power The method can delay the temperature rise time.
In order to ensure the heat transfer performance of the heat pipe, the structural design of the battery thermal management system should fully consider the influence of the heat pipe arrangement on its thermal conductivity.
3.3 Heat dissipation structure design and heat transfer analysis of thermal management system
As a heat transfer component for battery thermal management, the heat pipe needs to quickly dissipate the heat while absorbing the heat generated by the battery to ensure its normal operation in the battery pack. Usually, the cold end of the heat pipe can adopt two ways of cooling: air cooling and water cooling. The former has a simple structure and is easy to implement, while the latter has a relatively complex structure, but it shows better performance when the heat dissipation demand is large.
3.3.1 Air-cooled heat dissipation at the cold end
Direct air cooling is the simplest heat dissipation method for the condensing section of the heat pipe. Ye et al. used forced air cooling at the cold end of the heat pipe to keep the battery (LiFePO4, 18 Ah) below 35°C under 1C discharge conditions. If the cold end was naturally cooled, the temperature at the end of discharge would be higher than 40°C. In order to strengthen the heat dissipation capacity of the heat pipe, methods such as increasing the number of fins at the cold end, improving the design of the fins at the cold end, increasing the flow rate of air cooling, and increasing the length of the condensation section can be used.
The number of heat pipes, the number of fins, and the spacing between fins also have an important impact on the heat dissipation effect. Arranging multiple heat pipes on the surface of a battery can enhance heat dissipation, but because the average heat transfer coefficient of the cold end along the airflow direction is getting lower and lower, the unevenness of the battery surface temperature is increased. The temperature uniformity of the battery surface can be improved by arranging the spoiler tube before the first heat pipe (Fig. 10(d)).
Fig.10 Design scheme of heat pipe condensing section. (a) Condensing end is bare pipe; (b) Fin spacing is 10 mm; (c) Fin spacing is 3 mm; (d) Cooling end has a virtual heat pipe
Many researchers use heat pipes and phase change materials to couple heat dissipation to improve battery surface temperature uniformity, attach PCM to the battery surface, heat pipes are embedded in PCM to take away heat, and cold ends use air cooling to dissipate heat. Figure 11 is a typical heat pipe- PCM is coupled with an air-cooled heat dissipation system. This structure can ensure that the maximum temperature difference of the battery pack is lower than 2°C after 2C discharge, and the cooling wind speed will affect the maximum temperature rise of the battery.
Figure 11 Prismatic battery heat pipe-PCM coupled thermal management system
Increasing the length of the condensation section is another effective way to improve the heat dissipation capacity of the heat pipe. However, increasing the length of the condensation section will lead to an increase in the temperature difference of the battery pack. There is an optimum value for the length of the condensation section.
3.3.2 Liquid cooling at the cold end
Due to the low specific heat capacity of air, the use of heat pipes and liquid cooling coupled to dissipate heat can make up for the lack of air cooling. According to the contact mode between the cold end of the heat pipe and the liquid flow channel, it can be divided into contact liquid cooling heat transfer and non-contact liquid cooling heat transfer. The contact liquid cooling system is shown in Figure 12. The cold end of the heat pipe is soaked in a water tank, and a certain flow rate of liquid is introduced into the interior. After half an hour of continuous discharge at 2C, the battery temperature does not exceed 42°C, which shows the heat dissipation effect of the heat pipe and liquid cooling coupling.
Fig.12 Schematic diagram of the contact liquid cooling heat exchange system at the cold end of the heat pipe
Zhao et al. used water spraying at the cold end to improve the heat dissipation efficiency of the battery. A flat micro-heat pipe was placed between every two batteries and water was sprayed on the surface at a certain frequency. The temperature rise of the battery was only 4°C under the continuous discharge condition of 2C. , The temperature difference under 3C discharge condition is less than 2.5°C.
The non-contact liquid cooling system usually arranges the heat pipes on the surface of the battery, and the heat is taken away through the contact of the liquid cooling flow channel with the cold end of the heat pipe. The cold end of the heat pipe is not directly immersed in the cooling liquid, so the safety is higher. Audi has designed a battery thermal management solution as shown in Figure 13. A copper plate is arranged between every two batteries, and four sintered heat pipes are embedded in the copper plate. Finally, the heat is transferred through the liquid cooling plate attached to the cold end of the heat pipe. take away. Under the condition of 400W battery heat generation power, the system can maintain the battery temperature below 50°C, which has a good cooling effect.
Figure 13 Heat dissipation design scheme of power battery heat pipe
Most of the current research uses the temperature rise and temperature difference of the battery as the evaluation index. However, the enhanced heat transfer will bring more energy consumption and weight increase of the system, and there are few design considerations from the system level. How to take into account the battery discharge characteristics, heat dissipation effect, system energy consumption and light weight and other indicators, and propose an efficient heat dissipation scheme for the thermal management system is the focus of future research on enhanced battery heat dissipation.
3.4 Research on battery heating using heat pipes
As mentioned above, the charging and discharging efficiency of lithium-ion batteries is greatly reduced in low-temperature environments. At present, research on low-temperature heating using heat pipes as heat transfer components has attracted widespread attention.
Ye et al. arranged micro-plate heat pipes on the surface of the battery, and heated the other end with a heating element (Figure 14). The time it took for the battery to heat up from -10, -20, -30°C to 0°C was 350, 780, and 1100s, respectively. , The temperature rise rate is 1.5 times that of the traditional bottom heating method. During the heating process, the temperature difference can be controlled below 3°C, much lower than the traditional heating method (9°C). Liang Jianan et al. found that increasing the heating power can increase the heating rate of the battery, but at the same time increase the temperature difference on the battery surface. Therefore, it is necessary to comprehensively consider the heating time and the temperature difference of the battery to determine the optimal heating strategy.
Figure 14 Schematic diagram of the heating structure of lithium-ion batteries based on heat pipes
Zou et al. designed a heat pipe-liquid coupling integrated thermal management system as shown in Figure 15, which can realize both low-temperature heating and high-temperature cooling of the battery. The refrigerant in the pipe is heated by the PTC, and then transfers the heat to the battery through the heat pipe. In the initial stage of heating, the temperature of the battery rises rapidly. As the temperature difference between the cold and hot ends of the heat pipe gradually decreases, the heat transfer capacity weakens, and the final heat transfer value approaches a constant value. After about 900 s, the battery temperature rises to 20°C .
Figure 15 Schematic diagram of heat pipe heating system
The current battery heating system based on heat pipes usually uses traditional heat pipes or microchannel heat pipes to arrange on the surface of the battery, and the other end uses hot water heating or PTC heating. Most of the research is in the experimental verification stage. The existing research results fully demonstrate the high efficiency of heat pipe heating. and temperature uniformity, further research should focus on low-temperature heating strategies.
04 Summary and Outlook
Temperature is a key factor affecting the performance of power batteries, and an efficient thermal management system is of great significance to electric vehicles. Heat pipes have strong heat transfer and temperature uniformity capabilities, and are an important research direction for future battery thermal management systems. Significant progress has been made in the use of heat pipes as battery cooling/heating elements. However, with the improvement of electric vehicles' requirements for thermal management systems, there are still several problems to be solved in the application of heat pipes:
(1) The temperature of the power battery is closely related to its dynamic heat production conditions. Further research should be combined with the actual vehicle conditions to formulate an effective real-time control strategy to achieve efficient and low-energy battery thermal management.
(2) In terms of heat transfer of heat pipes, since there are many factors that affect the heat transfer performance of heat pipes, it is necessary to comprehensively consider the internal structure design of heat pipes and their arrangement in the battery pack to optimize their heat transfer performance during use, especially for the flat plate type The heat transfer characteristic analysis and optimal design research of heat pipe is one of the key points of future research.
(3) In terms of heat pipe heat dissipation, most current system designs focus on reducing the temperature rise and temperature difference of the battery pack, and less consideration is given to system energy consumption and weight. Further heat pipe enhanced heat dissipation research should focus on system multi-objective optimization, comprehensive system thermal and electrical characteristics, system energy consumption and light weight and other indicators, and propose thermal management system heat dissipation solutions.
(4) In terms of heating research using heat pipes, most of the current research is in the stage of testing and verifying the effect. Further research on the heat transfer characteristics of heat pipes in different environments, especially the research on heating strategies in low temperature environments, is one of the key points of future research. one.
With the development of electric vehicles and the continuous advancement of power battery technology and heat pipe technology, heat pipes will be more widely used in battery thermal management.
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