Water-air composite cooling device and cooling method for lithium battery pack

Abstract

The invention provides a water-air composite cooling device and a cooling method for a lithium battery pack, relates to the technical field of lithium battery thermal management, and solves the technical problems of low air cooling thermal conductivity, insufficient cooling capacity, high water cooling cost, complex structure and difficulty in adapting to different working conditions caused by limitation of a single cooling mode of an existing lithium battery. According to the technical scheme, an air cooling unit achieves basic heat dissipation through an air duct and a draught fan; the water cooling unit achieves efficient heat dissipation through a water channel, a water pump and a temperature control assembly, and the temperature of cooling liquid can be adjusted. The temperature monitoring control unit adopts a PT100 thermal resistor to collect temperature signals, and regulates and controls operation parameters of the air cooling unit and the water cooling unit through an intelligent switch; the intelligent optimization unit constructs a flow field and temperature field model based on computational fluid mechanics, optimizes structural parameters and the flow velocity of a cooling medium in combination with a neural network algorithm, and realizes self-adaptive adjustment of a cooling strategy; the heat dissipation efficiency and stability are improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium battery thermal management technology, specifically to a water-air composite cooling device and cooling method for lithium battery packs. Background Technology

[0002] Lithium-ion batteries, as a leading technology, have distinguished themselves among numerous electrochemical energy storage technologies such as lead-acid batteries, flow batteries, and supercapacitors due to their high energy density and long cycle life, and are widely used in various fields. However, the flammable electrolyte and electrode materials inside lithium-ion batteries pose a risk of thermal runaway and fire under abusive conditions. Especially in the pursuit of high energy density and low cost, the thermal stability of battery materials has decreased, and safety hazards have become increasingly prominent.

[0003] Studies have found that the higher the state of charge of a battery, the greater the heat, temperature, mass loss, and gas production during thermal runaway, and the shorter the internal thermal runaway propagation time. When the heating power increases, the thermal runaway trigger time, the pressure relief valve opening time, and the interval between the two are all shortened. Moreover, the heating power has a significant impact on the internal thermal runaway propagation characteristics of the battery, and the internal propagation time increases with the increase of heating power.

[0004] Currently, thermal management systems are classified into four categories based on the heat transfer medium: air cooling, liquid cooling, heat pipe cooling, and phase change material cooling. Research on air cooling systems mainly focuses on airflow velocity, channel design, and battery distribution; however, due to their low thermal conductivity, their cooling capacity is limited and cannot meet the heat dissipation requirements of large, sealed power battery packs. Liquid cooling systems offer good heat dissipation and are suitable for battery packs with high heat generation. For example, using curved pipe walls to ensure full contact with the cylindrical surface of the battery can significantly improve heat transfer efficiency. However, this system is costly, heavy, and structurally complex. Heat pipe cooling and phase change material cooling also have their advantages and disadvantages, and related research is still ongoing. Currently, with the continuous expansion of lithium-ion battery applications, the requirements for heat dissipation systems are becoming increasingly stringent. The pursuit of high energy density and high power density makes battery heat generation more prominent, and traditional single cooling methods are no longer sufficient. There is an urgent need to develop more efficient and intelligent cooling systems to overcome existing technological limitations. Summary of the Invention

[0005] Therefore, this invention solves the technical problems of low thermal conductivity and insufficient cooling capacity of air cooling and high cost and complex structure of water cooling in the existing single cooling methods, making it difficult to adapt to different working conditions. The lithium battery pack water-air hybrid cooling device and cooling method provided by this invention adopts a water-air coupling mode, combining the advantages of both, and can adapt to complex working conditions. This invention achieves controllable water temperature through PT100 thermal resistors and intelligent switches, accurately ensuring the battery operating temperature, and combines CFD and BPNN optimization to quickly select the best parameters, reduce trial and error costs, improve heat dissipation efficiency and stability, and reduce energy consumption. For the heat dissipation problem of lithium-ion batteries, an intelligent composite cooling system integrating air cooling and water cooling with controllable water temperature is designed. With the help of CFD and BPNN to optimize the air and water channel layout and parameters, a monitoring and control system is built with PT100 thermal resistors and intelligent switches to accurately regulate the water temperature. The heat generation law is explored through experiments and simulations to verify the effectiveness of the system, so as to overcome the heat dissipation limitations, improve the heat dissipation effect and stability of the battery pack, and promote the practical application of the technology.

[0006] The present invention provides a water-air composite cooling device for lithium battery packs, comprising an air cooling unit, a water cooling unit, a temperature monitoring and control unit, and an intelligent optimization unit.

[0007] The air-cooling unit is an important component of the intelligent water-air hybrid cooling system, working in conjunction with the water-cooling unit. Its core principle is the strategically placed arrangement of multiple fans around the battery pack, utilizing the airflow generated by these fans to directly act on the surface of the lithium battery pack. The air-cooling unit is deeply integrated with the temperature monitoring and control unit, enabling coordinated regulation of fan speed and the number of fans operating based on the real-time temperature distribution of the battery pack. Under low load conditions (0.5C-1C charge / discharge), only 2-3 fans in the center and top of the battery pack are activated, maintaining a speed of 1000r / min-1500r / min to achieve energy-saving heat dissipation through low-power operation. Under medium load conditions (1C-1.5C charge / discharge), 70%-80% of the fans are activated, with the fan speed in high-heat areas increased to 1800r / min-2500r / min, and the fan speed in low-heat areas maintained at 1200r / min-1500r / min, balancing heat dissipation and energy consumption. Under high load conditions (1.5C-2C charge / discharge), all fans are activated at full capacity, with the fan speed in high-heat areas increased to 2500r / min-3500r / min, ensuring that a large amount of heat can be removed through high airflow intensity even without airflow channels, achieving efficient heat dissipation in conjunction with the water cooling unit.

[0008] Furthermore, the water-cooling unit is a core component of the intelligent water-air hybrid cooling system, working in conjunction with the air-cooling unit to achieve efficient heat dissipation. It includes a water pump, liquid-cooling pipes, an electric heater, and a coolant tank. The liquid-cooling pipes employ a multi-segment arc-shaped bending structure. Based on the diameter of the cylindrical battery cell (e.g., 18mm for an 18650 battery), the bending radius of the liquid-cooling pipes is designed to be 9mm-10mm, ensuring that the contact area between the inner surface of the liquid-cooling pipe and the cylindrical surface of the battery reaches 90%. Compared to the traditional single-bend structure, the contact area is increased by 20%-30%, significantly reducing thermal resistance. Simultaneously, tiny protrusions (0.5mm-1mm in diameter, 2mm-3mm spacing) are set on the inner wall surface where the liquid cooling pipe contacts the battery. These protrusions are manufactured using a precision mold forming process. Specifically, an electrical discharge machining (EDM) mold is first created, and the inner core surface of the mold is machined with recesses matching the protrusion dimensions. The mold material is Cr12MoV alloy, hardened to a hardness of HRC60-62. Then, the 304 stainless steel liquid cooling pipe is degreased (using an alkaline solution). The liquid cooling tube undergoes pretreatment including soaking in a degreasing agent at 50℃ for 15 minutes, pickling (soaking in a 5% hydrochloric acid solution at room temperature for 5 minutes), water washing, and drying. The pretreated tube is then fitted into the inner core of a molding die, and a hydraulic bulging process of 8-12 MPa is used, holding the pressure for 30-60 seconds. This causes the inner wall of the liquid cooling tube to conform to the mold recesses, forming a raised structure. Finally, residual impurities are removed by 5 MPa high-pressure water rinsing, and ultrasonic testing verifies the integrity of the raised structure and the absence of cracks in the tube. This enhances the turbulence effect of the coolant within the tube, improves the heat exchange efficiency between the coolant and the tube wall, and compensates for the heat dissipation shortcomings of air-cooled systems without ductwork under high-load conditions. The liquid cooling tube is equipped with an inlet and an outlet; the inlet connects to a water pump, and the outlet connects to a coolant tank. An electric heater heats the coolant, quickly and stably raising the coolant temperature to a suitable range when the battery is in a low-temperature environment or during initial startup, preheating the battery to improve performance and charge / discharge efficiency. This unit, in conjunction with the temperature monitoring and control unit, accurately measures the coolant temperature and converts it into an electrical signal, which is then transmitted to the control terminal. The control terminal compares the temperature with the preset optimal water temperature range and adjusts parameters such as the water pump flow rate and the electric heater power to achieve precise water temperature control. When the battery generates a high amount of heat, it works in conjunction with the air-cooling unit to efficiently remove a large amount of heat.

[0009] Furthermore, the temperature monitoring and control unit is a key component of the intelligent water-air composite cooling system for the lithium battery pack, consisting of a PT100 resistance temperature detector (RTD), intelligent switches, and control logic. The PT100 RTD, as a high-precision temperature sensor, is installed at critical locations within the battery pack, accurately measuring the temperature of the battery pack and coolant. It converts the temperature signal into a resistance signal, which is then conditioned into a standard electrical signal and transmitted to the control terminal. When determining high and low heat generation areas, the temperature values ​​collected by all RTDs are first processed using a moving average filter (window size of 5 data sets) to remove abnormal fluctuations. Then, the arithmetic mean of the temperatures at all measuring points on the battery pack is used. As a reference temperature, a temperature difference threshold ΔT of 3℃ is set (which can be adjusted according to battery type and application scenario). When the temperature at a certain measuring point... - When the value is greater than ΔT, the area where the measuring point is located is determined to be a high-heat area. - When the temperature exceeds ΔT, it is identified as a low-heat area, while the remaining areas are considered normal-heat areas. The intelligent switch compares the received temperature signal with a preset optimal temperature range. When the temperature is below the lower limit, it controls the electric heater to start heating; when it is above the upper limit, it regulates the cooling equipment to lower the water temperature; and when it is within the appropriate range, it maintains the current state. This achieves precise control of the water temperature and the operating parameters of the air-cooled and water-cooled units, ensuring that the battery operates at a suitable temperature.

[0010] Furthermore, the intelligent optimization unit is the core module for achieving efficient adaptation and performance maximization of the cooling system, completing the optimization process through deep collaboration between CFD and BPNN algorithms. The CFD simulation uses the standard k-ε turbulence model, with model constants set to... =0.09、 =1.44、 =1.92、 =1.0、 =1.3, a hybrid structured and unstructured mesh generation method was adopted. The mesh size for battery cells and liquid cooling pipe areas was 1mm, and the mesh size for other areas was 3mm-5mm. After mesh independence verification (the highest battery temperature deviation was ≤1% when the number of meshes was 1 million, 1.5 million, and 2 million respectively), the optimal mesh size was determined to be 1.5 million. The battery heat generation model adopted the Joule heating + reaction heat coupling model, and the heat generation rate formula was Q=I²R+ (I is the charging and discharging current, and R is the dynamic internal resistance of the battery, which varies with temperature and SOC and is obtained through experimental fitting.) The heat of chemical reaction is set at 5 W / m³. Boundary conditions are set as follows: ambient temperature 25℃ (adjustable within the range of 0℃-50℃), liquid cooling pipe inlet boundary as mass flow rate inlet, outlet as pressure outlet (atmospheric pressure), fan outlet as velocity boundary, and battery surface as coupled heat transfer boundary. Based on this, a three-dimensional simulation model of the lithium battery pack and cooling system is constructed to accurately simulate the thermal characteristics and fluid motion state under different operating conditions. Parameters such as battery charge / discharge rate (0.5C-2C) and ambient temperature (0℃-50℃) are input to analyze the internal heat generation law of the battery and the geometry of the liquid cooling pipe (bending radius 10-20mm). Parametric modeling was performed to simulate the flow resistance, pressure distribution, and temperature field diffusion process of the cooling medium (air velocity 2-5 m / s, water velocity 1-3 L / min), generating over 500 sets of structural parameters and heat dissipation effect correlation data. The BPNN model used 11 parameters as its basis, including the liquid cooling pipe bending radius (mm), liquid cooling pipe protrusion diameter (mm), protrusion spacing (mm), coolant velocity (L / min), fan speed (r / min), ambient temperature (°C), battery charge / discharge rate (C), battery internal resistance (mΩ), coolant specific heat capacity (J / (kg・K)), liquid cooling pipe wall thickness (mm), and number of fans. The parameters are used as the input layer, and the highest temperature of the battery pack (°C), the maximum temperature difference of the battery pack (°C), and the system energy consumption (W) are used as the output layer. Two hidden layers are set, with 20 nodes in the first layer and 10 nodes in the second layer. The activation functions are ReLU (hidden layer) and linear function (output layer). The learning rate is set to 0.001, the number of iterations is 1000, the batch size is 32, the regularization coefficient is 0.0001, the Adam optimizer is used, and the loss function is mean squared error (MSE). The training set, validation set, and test set are divided in a ratio of 7:2:1. Training is stopped when the loss function of the validation set converges and there is no decrease for 50 consecutive iterations. The final model error is controlled within 3%. After importing CFD simulation data into the BPNN model for training, a nonlinear mapping relationship of "structural parameters - operating parameters - heat dissipation effect" is formed. During the optimization phase, the BPNN model can quickly predict the performance of different parameter combinations, completing the optimization process that would take 3 days using traditional trial and error methods in just 8 hours. The optimal parameter combination (such as 8mm air duct width, 15mm liquid cooling pipe bending radius, and 1.2L / min water pump flow rate) is selected to achieve the optimization goals of improving heat dissipation efficiency and reducing energy consumption.

[0011] The present invention also provides a cooling method for the above-mentioned cooling device, comprising the following steps:

[0012] S1: Determine the operating conditions of the lithium battery pack, namely low load, medium load and high load conditions;

[0013] S2: Under low load conditions, only the fans in the center and top of the lithium battery pack are activated, maintaining a speed of 1000r / min-1500r / min to achieve energy-saving heat dissipation through low-power operation; under medium load conditions, 70%-80% of the fans are activated, with the fan speed in high-heat areas increasing to 1800r / min-2500r / min and the fan speed in low-heat areas maintaining 1200r / min-1500r / min, balancing heat dissipation and energy consumption; under high load conditions, all fans are activated, with the fan speed in high-heat areas increasing to 2500r / min-3500r / min.

[0014] In step S1, the lithium battery pack's 0.5C-1C charge / discharge is considered a low-load condition, 1C-1.5C charge / discharge is a medium-load condition, and 1.5C-2C charge / discharge is a high-load condition. In step S2, the high and low heat generation areas are determined based on the thermal resistance, and the arithmetic mean of the temperatures at all measuring points is calculated. Set a temperature difference threshold ΔT of 3℃, when the temperature at a certain measuring point... - When the temperature reaches >ΔT, it is determined to be a high fever area. - When the temperature reaches >ΔT, it is determined to be a low-fever area.

[0015] The present invention has the following advantages over the prior art:

[0016] 1. The lithium battery pack water-air hybrid cooling device and cooling method provided by the present invention adopts a water-air coupling mode, which integrates the advantages of both and can adapt to complex working conditions; the water temperature is controllable through PT100 thermal resistor and intelligent switch, which accurately ensures the battery working temperature.

[0017] 2. The lithium battery pack water-air hybrid cooling device and method provided by this invention addresses the heat dissipation problem of lithium-ion batteries by designing an intelligent hybrid cooling system that integrates air cooling and water cooling with controllable water temperature. By optimizing the air and water channel layout and parameters using CFD and BPNN, and constructing a monitoring and control system using PT100 RTDs and intelligent switches, the system precisely regulates the water temperature. Through experiments and simulations, the heat generation law is explored, and the system's effectiveness is verified. This overcomes heat dissipation limitations, improves the heat dissipation effect and stability of the battery pack, and promotes the practical application of the technology. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1This is a schematic diagram of the overall structure of the present invention.

[0020] Explanation of reference numerals in the attached figures:

[0021] 1. Air-cooled unit; 1-1. Fan; 2. Water-cooled unit; 2-1. Water pump; 2-2. Liquid cooling pipe; 2-2-1. Liquid cooling pipe inlet; 2-2-2. Liquid cooling pipe outlet; 2-3. Electric heater; 2-4. Coolant tank; 3. Temperature monitoring and control unit; 3-1. Resistance temperature detector (RTD); 3-2. Smart switch; 4. Smart optimization unit; 5. Lithium battery pack. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] Figure 1 This is a schematic diagram of the overall structure of the water-air composite cooling device for the lithium battery pack provided in this embodiment, as shown below. Figure 1As shown, this includes: installing PT100 RTDs 3-1 at appropriate locations in the lithium battery pack 5 to ensure accurate monitoring of temperature changes in the battery pack 5. Special attention should be paid to ensuring the PT100 RTDs 3-1 are evenly distributed across different areas of the lithium battery pack 5, such as the surface, center, and edges, to comprehensively and accurately obtain the temperature of each part of the lithium battery pack 5, avoiding undetected overheating in certain areas. The liquid cooling pipes 2-2 of the water-cooling unit 2 are tightly attached to the surface of the lithium battery pack 5. The tiny protrusions on the inner wall of the liquid cooling pipes 2-2 have been processed using a precision mold forming process. This process first uses electrical discharge machining (EDM) to create a protrusion forming mold. The inner core surface of the mold is machined with a recessed structure matching the protrusion size. The mold material is Cr12MoV alloy, which is quenched to a hardness of HRC60-62. Then, 304 stainless steel liquid cooling pipes are degreased (using an alkaline degreaser, soaked at 50℃ for 15 minutes). The liquid cooling tube undergoes pretreatment including pickling (immersion in 5% hydrochloric acid solution at room temperature for 5 minutes), washing, and drying. The pretreated tube is then fitted into the inner core of the forming mold, and a hydraulic bulging process of 8-12 MPa is used, holding the pressure for 30-60 seconds to form a raised structure where the inner wall of the liquid cooling tube conforms to the mold recesses. Finally, residual impurities are removed by 5 MPa high-pressure water rinsing, and ultrasonic testing verifies the integrity of the raised structure and the absence of cracks in the tube. During bonding, an insulating and thermally conductive material is used to ensure efficient heat transfer at the bonding point. This material should have good corrosion resistance and high-temperature resistance to adapt to the operating environment of the lithium battery pack 5. The inlet 2-2-1 and outlet 2-2-2 of the liquid cooling tube 2-2 are connected to the corresponding interfaces of the water pump 2-1 and the coolant tank 2-4 via pipes to ensure smooth water flow. During the connection process, strict sealing treatment must be performed at the interfaces, using sealing rings or similar methods to prevent cooling water leakage. Fan 1-1 is connected to the smart switch 3-2 of the temperature monitoring and control unit 3 via a cable to achieve speed regulation. The smart switch 3-2 of the temperature monitoring and control unit 3 is installed in a location easily accessible for operation and signal reception, and is connected to the PT100 RTD 3-1, fan 1-1, water pump 2-1, and electric heater 2-3 via a data cable to ensure stable signal transmission. When installing the smart switch 3-2, its operating environment should be considered; avoid installing it in places with excessively high temperatures, high humidity, or strong electromagnetic interference to ensure its normal operation.

[0025] When lithium battery pack 5 starts generating heat, PT100 RTD 3-1 monitors the temperature of battery pack 5 in real time. During the monitoring process, the collected temperature values ​​are processed by moving average filtering (window size is 5 sets of data), and the arithmetic mean of the temperatures at all measuring points is calculated. A temperature difference threshold ΔT of 3℃ is set to determine high and low heat generation areas, and the processed temperature signal is fed back to the intelligent switch 3-2. When the temperature rises to the set threshold (e.g., 35℃), the intelligent switch 3-2 sends a command to start the water pump 2-1 and the fan 1-1, causing the coolant to flow out of the coolant tank 2-4, be pressurized by the water pump 2-1, and then flow into the inlet 2-2-1 of the liquid cooling pipe 2-2. After circulating in the pipe and absorbing the heat generated by the lithium battery pack 5, it flows out from the outlet 2-2-2 and back to the coolant tank 2-4. At the same time, the fan 1-1 starts, delivering airflow to assist in heat dissipation. The intelligent switch 3-2 adjusts the speed of the fan 1-1 and the flow rate of the water pump 2-1 according to the temperature change. If the temperature continues to rise, the intelligent switch 3-2 increases the speed of the fan 1-1 and the flow rate of the water pump 2-1 to enhance the cooling effect; conversely, if the temperature drops to a suitable range (e.g., 25-35℃), the speed of the fan 1-1 and the flow rate of the water pump 2-1 are reduced to reduce energy consumption. In low-temperature environments (such as below 10℃), when the PT100 RTD 3-1 detects that the battery temperature is too low, the smart switch 3-2 activates the electric heater 2-3 to heat the coolant. Once the temperature rises to a suitable range, the electric heater 2-3 is turned off to prevent the battery performance from being affected by low temperature.

[0026] Regular maintenance and inspections should be performed on all units of the system, including checking the accuracy of the PT100 RTD 3-1 (calibration can be performed by comparing with standard temperature measuring equipment); checking for blockages or leaks in the liquid cooling pipe 2-2 and tightening all connections; cleaning impurities from the coolant tank 2-4 to ensure the cleanliness of the coolant; and checking the operating status of the fan 1-1, water pump 2-1, and electric heater 2-3. If any abnormalities are found, they should be repaired or replaced promptly to ensure the long-term stable and efficient operation of the system, effectively cooling and protecting the lithium battery pack 5. During maintenance, each maintenance session should be recorded, including the maintenance time, maintenance content, problems found, and corrective measures, to facilitate long-term tracking and analysis of the system's operational status.

[0027] Example 2

[0028] This embodiment provides a cooling method based on the above-described cooling device, including the following steps:

[0029] S1: Determine the operating conditions of lithium battery pack 5, namely low load, medium load and high load conditions;

[0030] S2: Under low load conditions, only the fans 1-1 in the center and top of the lithium battery pack 5 are activated, maintaining a speed of 1000r / min-1500r / min to achieve energy-saving heat dissipation through low-power operation; under medium load conditions, 70%-80% of the fans 1-1 are activated, with the speed of fans 1-1 in high-heat areas increased to 1800r / min-2500r / min, and the speed in low-heat areas maintained at 1200r / min-1500r / min, balancing heat dissipation and energy consumption; under high load conditions, all fans 1-1 are activated, with the speed in high-heat areas increased to 2500r / min-3500r / min.

[0031] In step S1, the 0.5C-1C charge-discharge of the lithium battery pack 5 is a low-load condition, the 1C-1.5C charge-discharge is a medium-load condition, and the 1.5C-2C charge-discharge is a high-load condition; in step S2, the high and low heat generation areas are determined based on the thermal resistance.

[0032] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A water-air composite cooling device for lithium battery packs, characterized in that, include: A base is provided on which a lithium battery pack (5) is mounted; an air-cooling unit (1) is provided around the lithium battery pack (5), and a water-cooling unit (2) is provided inside; the air-cooling unit (1) and the water-cooling unit (2) work together to cool the lithium battery pack (5).

2. The lithium battery pack water-air composite cooling device according to claim 1, characterized in that, The air-cooling unit (1) includes multiple fans (1-1) arranged around the lithium battery pack (5).

3. The lithium battery pack water-air composite cooling device according to claim 2, characterized in that, The water-cooling unit (2) includes a liquid cooling pipe (2-2), which is disposed between different lithium batteries in the lithium battery pack (5); the liquid cooling pipe (2-2) is provided with an inlet (2-2-1) and an outlet (2-2-2), the inlet (2-2-1) is connected to the outlet of the water pump (2-1), and the outlet (2-2-2) is connected to the coolant tank (2-4); the inlet of the water pump (2-1) is connected to the coolant tank (2-4).

4. The lithium battery pack water-air composite cooling device according to claim 3, characterized in that, An electric heater (2-3) is installed between the water pump (2-1) and the water inlet (2-2-1).

5. The lithium battery pack water-air composite cooling device according to claim 4, characterized in that, It also includes a temperature monitoring and control unit (3), which includes a thermal resistor (3-1) and a smart switch (3-2); multiple thermal resistors (3-1) are uniformly arranged on the surface of the lithium battery pack (5), and the smart switch (3-2) is connected to the thermal resistor (3-1), fan (1-1), water pump (2-1) and electric heater (2-3) via a data cable.

6. The lithium battery pack water-air composite cooling device according to claim 5, characterized in that, The liquid cooling tube (2-2) adopts a multi-segment arc-shaped bending structure and is attached to the surface of the lithium battery.

7. The lithium battery pack water-air composite cooling device according to claim 6, characterized in that, The inner wall surface of the liquid cooling tube (2-2) in contact with the lithium battery is provided with tiny protrusions.

8. The lithium battery pack water-air composite cooling device according to claim 7, characterized in that, It also includes an intelligent optimization unit (4), which is configured to optimize various parameters of the device through CFD and BPNN algorithms.

9. A method for water-air composite cooling of a lithium battery pack based on the water-air composite cooling device according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Determine the working conditions of the lithium battery pack (5), namely low load, medium load and high load conditions; S2: Under low load conditions, only the fans (1-1) in the center and top of the lithium battery pack (5) are started, and the speed is maintained at 1000r / min-1500r / min. Energy-saving heat dissipation is achieved through low power operation. Under medium load conditions, 70%-80% of the fans (1-1) are started, and the speed of the fans (1-1) in the high heat area is increased to 1800r / min-2500r / min, while the speed in the low heat area is maintained at 1200r / min-1500r / min, balancing the heat dissipation effect and energy consumption. Under high load conditions, all fans (1-1) are started in full, and the speed in the high heat area is increased to 2500r / min-3500r / min.

10. A water-air composite cooling method for a lithium battery pack according to claim 9, characterized in that, In step S1, the lithium battery pack (5) is in a low-load condition when charged and discharged at 0.5C-1C, in a medium-load condition when charged and discharged at 1C-1.5C, and in a high-load condition when charged and discharged at 1.5C-2C; in step S2, the high and low heat generation areas are determined based on the thermal resistance (3-1).

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