A lithium battery thermal management system using a composite phase change material and liquid cooling

Abstract

The present invention relates to a composite phase change material-liquid cooling combined lithium battery thermal management system, belonging to the field of battery thermal management technology, the system includes a composite phase change material device, a liquid cooling device, an electrode heating plate, a temperature detection device and a control terminal, the battery is placed inside the composite phase change material device, the temperature detection device collects the temperature data of the battery, two electrode heating plates are respectively arranged on both sides of the composite phase change material device, the liquid cooling circulation pipeline in the liquid cooling device is evenly laid inside the composite phase change material device, and the control terminal controls the opening or closing of the liquid cooling device and the power on and off of the electrode heating plate according to the temperature data and the control strategy. The present invention stores heat and energy through the composite phase change material device, absorbs the heat emitted by the battery in time, and through the synergistic effect of the liquid cooling device and the electrode heating plate, reduces the energy consumption of the electric vehicle, improves the battery discharge capacity, and prolongs the service life of the battery pack, which is energy-saving and environmentally friendly, safe and reliable, and easy to use.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery thermal management, and in particular relates to a composite phase change material-liquid cooling combined lithium battery thermal management system. Background Art

[0002] Lithium batteries have the advantages of high energy density, long life cycle and low self-discharge rate. They are an indispensable energy storage and utilization solution in contemporary society and are widely used in new energy vehicles, energy storage power stations, etc. With the increasing demand for battery energy and power by terminals, the performance degradation and safety issues caused by heat during battery charging and discharging are becoming increasingly prominent. A series of electrochemical reactions occur during battery operation to generate heat, which leads to excessively high temperatures or uneven distribution, which will cause performance degradation and even thermal runaway. On the contrary, for example, under cold working conditions in northern my country, too low battery operating temperature will also reduce the discharge performance of the battery, and the discharge capacity will drop significantly. It is generally believed that the acceptable temperature range of lithium batteries is between -20 and 50°C, the optimal range is 15 to 35°C, and the temperature difference of the battery module should be controlled within 5°C. In order to improve battery performance, ensure life, and ensure thermal safety, there is an urgent need for a battery thermal management system with high efficiency and a wide thermal management temperature range.

[0003] At present, the mainstream technical routes for battery thermal management are air cooling, liquid cooling and phase change material (PCM) cooling. Air cooling is to use air to manage the battery thermally. It has the advantages of simple structure and low cost, but its heat dissipation efficiency is low and cannot meet the heat dissipation requirements of the battery pack under high power, high rate and high power operation. Liquid cooling is a method of heat dissipation by contacting the battery module with a high thermal conductivity liquid. Compared with air cooling, liquid cooling has high heat dissipation efficiency, but it also has the problem of excessive weight causing the energy density of the whole package to decrease, and continuous operation consumes too much energy, which reduces the cruising range of electric vehicles and other vehicles. Phase change material thermal management technology uses the principle of absorbing heat when the working fluid undergoes phase change to manage the battery thermally. It has the advantages of high reliability and simple structural design. Although pure solid-liquid phase change materials have the advantages of high latent heat, stable phase change temperature and chemical properties, they are easily leaked due to the mutual conversion of solid and liquid during the phase change process, and have high requirements for the quality of the package shell and low thermal conductivity, resulting in many limitations in practical applications.

[0004] Therefore, it is necessary to provide a lithium battery thermal management system that can effectively control the temperature of the battery cells and achieve efficient and energy-saving operation. Summary of the invention

[0005] In view of the problems existing in the background technology, the present invention provides a lithium battery thermal management system combining composite phase change material and liquid cooling. The system uses the phase change of composite phase change material to absorb heat and natural cooling at night or when not in operation to alleviate the energy consumption of long-term liquid cooling of power batteries or energy storage power stations. On the other hand, in the cold environment in the north, the phase change material can also store the heat generated by the battery when working, which can delay the drop in battery temperature when the car is parked, maintain the battery temperature in the optimal working range, and achieve energy saving.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A composite phase change material-liquid cooling combined lithium battery thermal management system, the system comprising a composite phase change material device, a liquid cooling device, an electrode heating plate, a temperature detection device and a control terminal;

[0008] The composite phase change material device comprises a shell and a composite phase change material with heat storage and energy storage properties filling the shell, the shell is provided with a plurality of battery installation holes, a battery pack of lithium batteries passes through the battery installation holes and is placed inside the composite phase change material, the composite phase change material is coated on the outside of each battery, the two electrode heating plates are in close contact with the two sides of the composite phase change material device respectively, and the two electrode heating plates are respectively connected to the voltage output end of the control terminal through a conductive component;

[0009] The liquid cooling device comprises a liquid cooling box, a liquid cooling circulation pipeline, a control valve, a circulation pump and a refrigeration component. The liquid cooling circulation pipeline is evenly laid inside the composite phase change material device. The liquid inlet and liquid outlet of the liquid cooling circulation pipeline are respectively connected to the liquid cooling box. The liquid cooling circulation pipeline is provided with a control valve for controlling the opening or closing of the liquid cooling circulation pipeline, a circulation pump for driving the flow of liquid in the liquid cooling circulation pipeline and a refrigeration component for cooling the liquid in the liquid cooling circulation pipeline. The control valve is connected to the control terminal.

[0010] The temperature detection device is arranged on the surface of the battery, collects the temperature data of the battery in real time and feeds it back to the control terminal, and the control terminal executes the following control strategy:

[0011] Step 1: Read the temperature data of the battery at the current moment collected by the temperature detection device;

[0012] Step 2: Determine whether the temperature data is lower than a predetermined low temperature threshold. If so, control the electrode heating plate to be powered on to heat the composite phase change material device, and at the same time control the control valve to open, control the circulation pump to start, drive the liquid in the liquid cooling circulation pipeline to flow, so that the temperature of the phase change material is evenly increased to ensure balanced temperature rise of the battery, and then execute step 4; if not, execute step 3;

[0013] Step 3: Determine whether the temperature data is higher than a predetermined high temperature threshold. If so, control the refrigeration component to start, cool the liquid in the liquid cooling circulation pipe, and then execute step 5; if not, return to step 1 and re-read the temperature data of the battery collected by the temperature detection device at the next moment;

[0014] Step 4: re-read the temperature data of the battery collected by the temperature detection device at the next moment, and determine whether the temperature data is higher than a predetermined low temperature threshold. If so, control the electrode heating plate to be powered off, and control the control valve and the circulation pump to be turned off, and then return to step 1; if not, return to step 2;

[0015] Step 5: Re-read the temperature data of the battery collected by the temperature detection device at the next moment, and determine whether the temperature data is lower than a predetermined high temperature threshold. If so, control the refrigeration component to shut down, and then return to step 1; if not, return to step 3.

[0016] Beneficial effects of the present invention:

[0017] The present invention uses a composite phase change material device to store heat and energy, absorbs the heat emitted by the battery in a timely manner, and through the synergistic effect of the liquid cooling system and the electrode heating system, can reduce the energy consumption of the entire tram, increase the battery discharge capacity, and extend the service life of the battery pack;

[0018] The present invention complies with the national energy conservation and emission reduction policy, has a series of advantages such as energy conservation and environmental protection, heat storage, light weight, safety and reliability, and easy use, and can be vigorously promoted and implemented in battery thermal management systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the lithium battery thermal management system using a composite phase change material-liquid cooling system according to the present invention;

[0020] Figure 2 Schematic diagram of battery position distribution in a composite phase change material device;

[0021] Figure 3 A schematic diagram of the arrangement position of the temperature detection device on a single battery;

[0022] Figure 4 A control strategy flow chart for the control terminal;

[0023] Figure 5 Another flow chart of the control strategy for the control terminal.

[0024] Explanation of the accompanying drawings: 1. Composite phase change material device; 2. Electrode heating plate; 3. Temperature detection device; 4. Control terminal; 5. Battery; 6. Conductive component; 7. Liquid cooling box; 8. Liquid cooling circulation pipeline; 9. Control valve. DETAILED DESCRIPTION

[0025] The composite phase change material-liquid cooling combined lithium battery thermal management system of the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] See also Figure 1-Figure 5 The embodiment of the present invention provides a lithium battery thermal management system using a composite phase change material and liquid cooling. The system realizes temperature control and efficient energy-saving operation of battery cells by combining composite phase change materials, liquid cooling technology and electrode heating technology. Specifically, the lithium battery thermal management system includes a composite phase change material device 1, a liquid cooling device, an electrode heating plate 2, a temperature detection device 3 and a control terminal 4.

[0027] The composite phase change material device 1 includes a shell and a composite phase change material filling the shell, and the composite phase change material has the characteristics of heat storage and energy storage, that is, it can absorb heat and store it in itself under high temperature environment. A plurality of battery mounting holes are provided on the shell, and the number of battery mounting holes is determined according to the number of batteries in the installed battery pack. The battery pack of lithium batteries is placed in the shell after passing through the corresponding battery mounting holes and is located inside the composite phase change material. The composite phase change material is coated on the outside of each battery, so as to better absorb the heat generated when the battery is working.

[0028] The present invention utilizes the electrothermal conversion characteristics of composite phase change materials and adopts electrode heating to increase the ambient temperature of the battery. Specifically, an electrode heating plate 2 is provided on both sides of the composite phase change material device 1, and the electrode heating plate 2 is in close contact with the surface of the composite phase change material device 1. The two electrode heating plates 2 are respectively connected to the voltage output end of the control terminal 4 through the conductive component 6, and the control terminal 4 controls the power on or off of the two electrode heating plates 2. The conductive component 6 can be implemented by existing conductive wires, etc. Further, to ensure safety, the control terminal 4 triggers the composite phase change material through a low voltage. For example, the voltage output end of the control terminal 4 outputs a low voltage of 1 to 2.4V to the two electrode heating plates 2 through the conductive component 6, thereby realizing the heating of the composite phase change material device 1. At low temperatures, an unheated battery or a car battery pack can be used to power the control terminal 4, providing a low voltage value of 1 to 2.4V. When the composite phase change material device 1 is thicker, in order to improve the heating efficiency, multiple electrode heating plates 2 can be set on both sides of the composite phase change material device 1, and the multiple electrode heating plates 2 are respectively connected to the voltage output end of the control terminal 4 through their own conductive components 6, and the control terminal 4 controls the power on and off of all electrode heating plates 2 at the same time.

[0029] The composite phase change material in the present invention is composed of a phase change material and a framework material, wherein the framework material is generally selected from porous materials with good thermochemical stability and high specific surface area, including metal organic framework materials (Metal organic Framework, MOF), carbon nanotubes or covalent organic framework materials (Covalent Organic Framework, COFs), etc., and the phase change material can be selected from alkanes, polyethylene glycol (PEG), paraffin (PW), lauric acid (LA), stearic acid (SA) and other materials with good stability, high latent heat, easy to obtain and low cost. The above phase change materials and framework materials can be selected and combined according to actual needs, and will not be repeated here.

[0030] Furthermore, when preparing the composite phase change material, a physical co-impregnation method is used. First, 50wt% to 70wt% of the phase change material is heated to the melting temperature by a water bath or other method, and then 10wt% to 20wt% of MOFs materials, such as MIL-101 (Cr), Al-fum, etc., and 5wt% to 10wt% of expanded graphite, 1wt% to 20wt% of a cross-linking agent such as polyvinyl pyrrolidone (PVP) and 1wt% to 5wt% of carbon nanotubes are added to the melted phase change material in sequence. The mixed solution is stirred for 10 to 60 minutes, and then the mixed solution is taken out and formed in a mold. After forming, it is placed in a vacuum drying oven for vacuum drying for 24 hours. The composite phase change material prepared by the above method is black, has certain mechanical properties, does not deform under normal pressure, has certain elasticity, has a high load (up to about 70wt%), a thermal conductivity of 2 to 10W / m·K, a phase change enthalpy of 120 to 150J / g, a phase change temperature of 30 to 40°C, and the electrode plate heats up quickly after heating. The phase change material can improve the leakage problem after being compounded with the nanoframe material. Due to the strong interaction, the phase change material is adsorbed in the frame material during the entire phase change process, with a load of up to 70wt%, and no obvious leakage occurs when heated at 80°C. After the composite is modified by adding expanded graphite and carbon nanotubes, the thermal conductivity can be improved. Compared with the original thermal conductivity (about 0.5W / m·K), it is increased to more than 2W / m·K. The added PVP cross-linking agent and carbon nanotubes also improve the mechanical properties, so that the composite phase change material has compressive properties. The composite phase change material using the above composition and preparation method can be better applied to battery thermal management. After being prepared into a composite phase change material, the composite phase change material is encapsulated in a shell. Whether it is cooled or heated, even heated to 80 degrees Celsius, the composite phase change material will not leak and will not appear in liquid state.

[0031] The liquid cooling device includes a liquid cooling box 7, a liquid cooling circulation pipeline 8, a control valve 9, a circulation pump and a refrigeration component, wherein the liquid inlet end and the liquid outlet end of the liquid cooling circulation pipeline 8 are respectively connected to the liquid cooling box 7, and the middle section of the liquid cooling circulation pipeline 8 is completely or partially evenly laid inside the composite phase change material device 1, that is, evenly laid inside the composite phase change material. Optionally, the liquid cooling circulation pipeline 8 is evenly laid in layers in the horizontal and vertical directions inside the composite phase change material, for example, it is laid in 2 to 3 layers in the vertical direction and 6 to 10 layers in the horizontal direction to better achieve heat exchange. At the same time, the liquid cooling circulation pipeline 8 is provided with a control valve 9, a circulation pump and a refrigeration component respectively connected to the control terminal 4, wherein the control valve 9 can be a throttle valve, which is connected to the liquid cooling circulation pipeline 8 and has the function of controlling whether the pipeline is opened and closed. The liquid cooling circulation pipeline 8 can be opened or closed under the control of the control terminal 4, and the circulation pump is used to drive the liquid flow in the liquid cooling circulation pipeline 8 under the control of the control terminal 4, and the refrigeration component is used to refrigerate the liquid in the liquid cooling circulation pipeline 8 under the control of the control terminal 4. The liquid cooling box 7, liquid cooling circulation pipeline 8, control valve 9, circulation pump and refrigeration assembly in the present invention can be implemented by using components in the existing liquid cooling system, which will not be described in detail here.

[0032] The temperature detection device 3 is arranged on the surface of the battery 5, and is used to collect the temperature data of the battery 5 in real time and feed the temperature data back to the control terminal 4. The temperature detection device 3 can be a thermocouple or a temperature sensor, which is arranged on the surface of the battery 5 to collect the temperature of the battery. The temperature detection device 3 can be set to one or more. When the temperature detection device 3 is set to more than one, each temperature detection device 3 is respectively arranged on the surface of the corresponding battery 5, collects the temperature data of the corresponding battery 5 and uploads it to the control terminal 4. It should be noted that in order to more clearly show the relationship between the temperature detection device 3 and the control terminal 4, Figure 1 The temperature detection device 3 is shown separately.

[0033] Furthermore, a temperature detection device 3 is also provided on the battery pack shell package. The temperature detection device 3 collects the temperature data of the battery pack shell package in real time and feeds it back to the control terminal 4. The control terminal 4 records and stores the temperature data of the battery pack shell package. The temperature data of the battery pack shell package can be used for early warning of the battery thermal management system or subsequent data tracing, etc.

[0034] The present invention detects the temperature of the battery pack and the temperature of the composite phase change material device 1 in real time through the temperature detection device 3, uploads the temperature data to the control terminal 4, and selects whether to turn on the liquid cooling device or the electrode heating system by the command of the control terminal 4. The function of the control terminal 4 is mainly to determine whether the corresponding device works and how to work through the information returned by each device, and plays a role in coordinating the whole and ensuring the safety of the whole system. The control terminal 4 can be implemented by a microprocessor, a computer, etc.

[0035] The control terminal 4 specifically implements the following control strategy:

[0036] Step 1: Read the temperature data of the battery 5 at the current moment collected by the temperature detection device 3;

[0037] Step 2: Determine whether the temperature data is lower than a predetermined low temperature threshold value, the value range of the predetermined low temperature threshold value is -20°C to 15°C. If so, control the electrode heating plate 2 to be energized to heat the composite phase change material device 1, and at the same time control the control valve 9 to open, control the circulation pump to start, drive the liquid in the liquid cooling circulation pipeline 8 to flow, so that the temperature of the composite phase change material device is uniformly increased, and ensure that the battery 5 is uniformly heated, and then execute step 4; if not, execute step 3;

[0038] Step 3: Determine whether the temperature data is higher than a predetermined high temperature threshold value, the predetermined high temperature threshold value ranges from 35°C to 50°C. If so, control the refrigeration component to start, refrigerate the liquid in the liquid cooling circulation pipe 8, and then execute step 5; if not, return to step 1 and re-read the temperature data of the battery 5 collected by the temperature detection device 3 at the next moment;

[0039] Step 4: re-read the temperature data of the battery 5 collected by the temperature detection device 3 at the next moment, and determine whether the temperature data is higher than the predetermined low temperature threshold. If so, the electrode heating plate 2 is powered off, and the control valve 9 and the circulation pump are closed, and then the process returns to step 1; if not, the process returns to step 2;

[0040] Step 5: Re-read the temperature data of the battery 5 collected by the temperature detection device 3 at the next moment, and determine whether the temperature data is lower than the predetermined high temperature threshold. If so, control the refrigeration component to shut down, and then return to step 1; if not, return to step 3.

[0041] When there are multiple temperature detection devices 3, the control terminal 4 reads the temperature data of the battery at the current moment collected by each temperature detection device 3 and calculates the temperature average value, and then applies the temperature average value as the temperature data of the battery at the current moment to steps 2 to 5.

[0042] Furthermore, the control strategy of the control terminal 4 also takes into account the temperature change of the composite phase change material device 1. Specifically, a temperature detection device 3 connected to the control terminal 4 is also provided on the composite phase change material device 1, and the temperature detection device 3 collects the temperature data of the composite phase change material device 1 in real time and uploads the temperature data to the control terminal 4. The control strategy of the control terminal 4 also includes the following steps:

[0043] Step 6: When the temperature data of the battery is within the predetermined range, determine whether the temperature of the composite phase change material device 1 gradually rises. If so, execute step 7; if not, end this round of control or return to step 1; wherein the predetermined range refers to the temperature range from a predetermined low temperature threshold to a predetermined high temperature threshold, for example, the predetermined range is -20°C to 50°C or 15°C to 35°C, etc.;

[0044] Step 7: Determine whether the temperature of the composite phase change material device 1 fluctuates within a small range or exceeds the temperature threshold for multiple consecutive moments. If so, execute step 8; if not, end this round of control or return to step 1;

[0045] Step 8: Determine whether the temperature of the battery 5 is gradually rising. If so, control the refrigeration component to start; if not, end this round of control or return to step 1.

[0046] During the running of the electric vehicle, the battery continues to discharge and the temperature rises. At this time, the liquid cooling device is not used for cooling. Instead, the composite phase change material device 1 is used to absorb heat. When the limit of the composite phase change material device 1 is exceeded or the suitable temperature of the battery is exceeded, the liquid cooling device is used for thermal management to lower the battery temperature so that it can work in an environment with suitable temperature, thereby increasing the battery life.

[0047] When the tram is running in a cold environment, the operating temperature of the tram power battery is far below its optimal operating temperature range (15-35°C). At this time, the electrode heating plate 2 is used to conduct the composite phase change material device 1 to increase the battery temperature, so that the battery temperature works in the optimal temperature range, thereby increasing the battery discharge capacity and improving the tram mileage. While the electrode is heated, the liquid in the liquid cooling circulation pipeline 8 will also absorb heat and heat up. At this time, the circulation of the liquid in the pipeline can be controlled to evenly accelerate the battery heating speed. At the same time, the excess heat is used to heat the vehicle body, reduce the use of the air conditioning system, and save energy.

[0048] Specifically, in a high temperature environment, when the battery is working, heat will be generated. At this time, the control terminal 4 chooses to use the composite phase change material device 1 to work, absorb the heat generated by the battery and store it in itself. In the short-term operation of the car, the temperature of the battery can be completely controlled within a suitable range by relying on this device. Due to the characteristics of the composite phase change material, the temperature of the composite phase change material device 1 will not change much. At this time, the temperature detection device 3 is used to monitor in real time and feedback the temperature data to the control terminal 4. When the temperature of the composite phase change material device 1 continues to rise (that is, the energy storage capacity of the composite phase change material reaches a certain limit) or the temperature of the battery exceeds the optimal temperature of the battery operation, the control terminal 4 controls the start of the liquid cooling device to cool the battery. At this time, it has entered another state. The participation of the liquid cooling device is not only to cool the composite phase change material but also to ensure the safety of the entire system. When the battery stops working, the liquid cooling device is turned off to allow the composite phase change material to cool naturally over time. In this way, the whole process consumes less energy than the traditional system that only uses liquid cooling for cooling, and is more environmentally friendly.

[0049] In a low temperature environment, when the battery temperature is lower than the optimal temperature range, the battery discharge capacity will drop significantly. At this time, the composite phase change material is in a solid state, waiting to be triggered by the electrode. The temperature detection device 3 feeds back the real-time temperature of the battery to the control terminal 4. The control terminal 4 controls the electrode heating plate 2 to be turned on. The composite phase change material heats the battery in the form of electrothermal conversion, thereby increasing the battery discharge capacity. The composite phase change material can realize the continuous operation of the heating process, and because the composite phase change material evenly wraps the battery, the surface temperature of the battery will also be more uniform, reducing the temperature difference of the battery surface temperature. While the electrode heating plate 2 heats the composite phase change material, the liquid in the pipeline heats up synchronously. At this time, the refrigeration component is in a closed state. The control terminal 4 controls the circulation of the liquid in the liquid circulation pipeline by starting the circulation pump, which can speed up the rate of battery heating. At the same time, the excess heat can be used to heat the vehicle body to increase the temperature inside the vehicle, thereby reducing the use of the electric vehicle air conditioning system in a low temperature environment. In addition, since the battery itself will generate heat during the discharge process, when the battery temperature rises to the lower limit of the acceptable temperature range (-20°C), the control terminal 4 will stop the electrode heating plate 2 from conducting the composite phase change material device 1 and stop heating the battery. Thermal management of batteries in low temperature environments is urgently needed by modern thermal management equipment. Heating batteries by conducting composite phase change materials through the electrode heating plate 2 has shown great potential in battery thermal management.

[0050] The basic working principle of the present invention is: when the battery is at a high temperature, the composite phase change material changes its state by absorbing external energy. In the process of solid to liquid state, it absorbs a large amount of heat, which is divided into two states of sensible heat and latent heat to work together to absorb the heat emitted by the battery and reduce the use of the liquid cooling system. When the battery is at a low temperature, the electrode heating plate 2 turns on the composite phase change material device 1, heats the battery through electrothermal conversion, and increases the battery temperature.

[0051] The present invention is divided into two stages in the high-temperature working stage. The first stage is to use only the composite phase change material device 1 to act on the battery and absorb the heat emitted by the battery. The second stage is the synergistic effect of the liquid cooling device and the composite phase change material device 1, and the liquid cooling device is the dominant part. In this stage, there are two situations. One situation is that when the battery temperature is in a suitable range (i.e., a predetermined range), the heat emitted by the battery can no longer be effectively absorbed and stored by the composite phase change material device 1. At this time, the temperature of the composite phase change material device 1 gradually rises. At this time, the control terminal 4 turns on the liquid cooling device for timely cooling; the other situation is that when the composite phase change material device 1 is still capable of working, the temperature of the battery exceeds the suitable temperature range (i.e., a predetermined range). At this time, the temperature of the composite phase change material device 1 fluctuates in a small range, but the temperature of the battery pack gradually rises. At this time, the control terminal 4 promptly turns on the liquid cooling device to cool down and maintain the safety of the battery pack.

[0052] The present invention is also divided into two stages in the low-temperature working stage. The first stage is when the battery temperature is lower than the lower limit of the acceptable temperature range of the battery (for example, -20°C) (i.e., the predetermined low temperature threshold), the control terminal 4 controls the electrode heating plate 2 to conduct the composite phase change material device 1 with a low voltage, relying on the electrothermal conversion effect of the material to heat the battery, and heats the battery in the form of sensible heat. At the same time, the liquid in the liquid circulation pipeline heats up, the control terminal 4 controls the circulation pump to start, the circulation pump controls the circulation of the liquid to accelerate the battery heating rate, and uses the excess heat to heat the vehicle body, increase the temperature inside the vehicle, reduce the use of the air conditioning system to a certain extent, and save energy. When the battery operating temperature reaches the lower limit of the acceptable temperature range (i.e., the predetermined low temperature threshold), the control terminal 4 stops conducting the electrode heating plate 2, terminates the heating, and at the same time, the control terminal 4 controls the circulation pump to turn off and stop the circulation of the liquid. The second stage is to heat the battery by the characteristic that the battery releases heat during the discharge process, and the composite phase change material is in a solid state during the entire heating process. The discharge capacity of the battery in the normal temperature range is larger than that of the battery at low temperature, so this is also conducive to energy saving.

[0053] The use of composite phase change materials for heat and energy storage can reduce the use of liquid cooling systems, reduce the overall energy consumption of the vehicle, lower the battery temperature in high temperature environments, and prevent thermal runaway. The system is energy-saving, environmentally friendly, safe and reliable, green and pollution-free, lightweight, and can extend the service life of the battery.

[0054] In this embodiment, if the phase change material uses alkanes or polyethylene glycol (PEG), the heat storage density is about 200-300KJ / Kg. The heat emitted by the electric vehicle battery for one hour is about 4300KJ. When the temperature does not exceed the appropriate range of battery operation, only 15-22Kg of composite phase change material is needed to continuously cool the battery within 1 hour, and no liquid cooling system is required. Therefore, the composite phase change material device in the present invention is very suitable for the battery thermal management system of electric vehicles. For the use of an electrode heating plate to conduct the composite phase change material device to increase the battery temperature, the present invention conducted a battery thermal management experiment. In the experiment, MOFs / n-octadecane and the like were used to prepare a composite phase change material. The load rate of n-octadecane can reach 70wt%, and the latent heat value is about 140J / g. The experimental results show that under the working condition of -30℃, the composite phase change material device is triggered by a working voltage of 1.1V, and the temperature of the lithium-ion battery can be raised to the working temperature (-20℃) within one minute, which is highly efficient.

[0055] The present invention stores heat and energy through a composite phase change material device, absorbs the heat emitted by the battery in a timely manner, and through the synergistic effect of a liquid cooling system and an electrode heating system, can reduce the energy consumption of the entire tram, increase the battery discharge capacity, and extend the service life of the battery pack.

[0056] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A lithium battery thermal management system using a composite phase change material and liquid cooling, characterized in that: It comprises a composite phase change material device (1), a liquid cooling device, an electrode heating plate (2), a temperature detection device (3) and a control terminal (4); The composite phase change material device (1) comprises a shell and a composite phase change material having heat storage and energy storage properties filling the shell, the shell being provided with a plurality of battery installation holes, a battery pack of lithium batteries passing through the battery installation holes and then placed inside the composite phase change material, the composite phase change material coating the outside of each battery (5), the two electrode heating plates (2) respectively being in close contact with two sides of the composite phase change material device (1), and the two electrode heating plates (2) respectively being connected to the voltage output end of the control terminal (4) via a conductive component (6); The liquid cooling device comprises a liquid cooling box (7), a liquid cooling circulation pipe (8), a control valve (9), a circulation pump and a refrigeration component. The liquid cooling circulation pipe (8) is evenly laid inside the composite phase change material device (1). The liquid inlet and liquid outlet of the liquid cooling circulation pipe (8) are respectively connected to the liquid cooling box (7). The liquid cooling circulation pipe (8) is provided with a control valve (9) for controlling the opening or closing of the liquid cooling circulation pipe, a circulation pump for driving the flow of liquid in the liquid cooling circulation pipe (8) and a refrigeration component for cooling the liquid in the liquid cooling circulation pipe (8). The control valve (9) is connected to the control terminal (4). The temperature detection device (3) is arranged on the surface of the battery (5), collects temperature data of the battery (5) in real time and feeds it back to the control terminal (4), and the control terminal (4) executes the following control strategy: Step 1: reading the temperature data of the battery (5) at the current moment collected by the temperature detection device (3); Step 2: Determine whether the temperature data is lower than a predetermined low temperature threshold value. If so, control the electrode heating plate (2) to be powered on to heat the composite phase change material device (1), and at the same time control the control valve (9) to open, control the circulation pump to start, drive the liquid in the liquid cooling circulation pipe (8) to flow, so that the temperature of the composite phase change material device (1) is evenly increased, and the battery (5) is evenly heated, and then execute step 4; if not, execute step 3; Step 3: determining whether the temperature data is higher than a predetermined high temperature threshold value; if so, controlling the refrigeration component to start, cooling the liquid in the liquid cooling circulation pipe (8), and then executing step 5; if not, returning to step 1, and re-reading the temperature data of the battery (5) collected by the temperature detection device (3) at the next moment; Step 4: re-read the temperature data of the battery (5) collected by the temperature detection device (3) at the next moment, and determine whether the temperature data is higher than a predetermined low temperature threshold value; if so, control the electrode heating plate (2) to be powered off, and control the control valve (9) and the circulation pump to be turned off, and then return to step 1; if not, return to step 2; Step 5: Re-read the temperature data of the battery (5) collected by the temperature detection device (3) at the next moment, and determine whether the temperature data is lower than a predetermined high temperature threshold. If so, control the refrigeration component to be turned off, and then return to step 1; if not, return to step 3.

2. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 1, characterized in that: The composite phase change material device (1) is provided with a temperature detection device connected to the control terminal (4), and the control strategy further comprises the following steps: Step 6: When the temperature data of the battery (5) is within a predetermined range, determine whether the temperature of the composite phase change material device (1) is gradually rising. If so, execute step 7; if not, end this round of control; Step 7: determining whether the temperature of the composite phase change material device (1) fluctuates, if so, executing step 8; if not, ending this round of control; Step 8: Determine whether the temperature of the battery (5) is gradually rising. If so, control the refrigeration component to start; if not, end this round of control.

3. The composite phase change material-liquid cooling lithium battery thermal management system according to claim 1, characterized in that: The electrode heating plates (2) are arranged in plurality, and the plurality of electrode heating plates (2) are respectively connected to the voltage output end of the control terminal (4) via respective conductive components (6).

4. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 1 or 2, characterized in that: The voltage output end of the control terminal (4) outputs a low voltage of 1 to 2.4 V to the two electrode heating plates (2) through a conductive component (6).

5. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 1 or 2, characterized in that: The liquid cooling circulation pipelines (8) are evenly laid in layers in the horizontal and vertical directions inside the composite phase change material device (1).

6. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 1 or 2, characterized in that: The temperature detection devices (3) are arranged in plurality, and each of the temperature detection devices (3) is arranged on the surface of a corresponding battery (5); The control terminal (4) reads the temperature data of the battery at the current moment collected by each of the temperature detection devices (3) and obtains an average temperature value, and uses the average temperature value as the temperature data of the battery (5) at the current moment.

7. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 1 or 2, characterized in that: A temperature detection device (3) is provided on the battery pack outer shell package. The temperature detection device (3) collects temperature data of the battery pack outer shell package in real time and feeds it back to the control terminal (4). The control terminal (4) records and stores the temperature data of the battery pack outer shell package. The temperature detection device (3) adopts a thermocouple or a temperature sensor.

8. A lithium battery thermal management system using a composite phase change material and liquid cooling according to claim 1 or 2, characterized in that: The composite phase change material is composed of a phase change material and a framework material. The phase change material uses any one or more of alkanes, polyethylene glycol, paraffin, lauric acid, and stearic acid. The framework material uses any one or more of metal organic framework materials, covalent organic framework materials, and carbon nanotubes.

9. A composite phase change material-liquid cooling lithium battery thermal management system according to claim 8, characterized in that: The composite phase change material is prepared by a physical blending method, comprising the following steps: Taking 50wt% to 70wt% of the phase change material and heating it to the melting temperature; 10wt% to 20wt% of metal organic framework material, 5wt% to 10wt% of expanded graphite, 1wt% to 20wt% of polyvinyl pyrrolidone crosslinking agent and 1wt% to 5wt% of carbon nanotubes are sequentially added to the melted phase change material, stirred for 10 to 60 minutes, taken out and formed in a mold, and after forming, placed in a vacuum drying oven for vacuum drying for 24 hours.

10. A lithium battery thermal management system using a composite phase change material and liquid cooling according to claim 1 or 2, characterized in that: The predetermined low temperature threshold has a value range of -20°C to 15°C, and the predetermined high temperature threshold has a value range of 35°C to 50°C.

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