Thermal management method for lithium ion battery pack of pure electric vehicle at low temperature

Abstract

The invention relates to a thermal management method for a lithium ion battery pack of a pure electric vehicle at low temperature, which comprises the following steps: starting the battery pack at low temperature, dividing each battery pack in the battery pack into a battery pack A and a battery pack B, vacuumizing a cavity between the battery pack A and an outer layer of a cavity, a heating device is arranged in the battery pack B; after the battery pack is started, the control system monitors the temperature of the battery pack B, if a heating condition is met, the control system controls the battery pack A to supply power to the heating device, and if the temperature of the battery pack B reaches a starting condition, the control system controls the battery pack A to stop supplying power to the heating device, otherwise, the control system stops supplying power to the heating device. And the battery pack B and the battery pack A directly start to supply power to the pure electric vehicle. Compared with the prior art, the method has the advantages that all the single batteries in the battery pack can overcome the limitation of low-temperature conditions, reach proper temperature and start to work as soon as possible, and the like.

Description

Technical Field

[0001] The present invention relates to the field of thermal management of batteries for pure electric vehicles, and in particular to a thermal management method for a lithium-ion battery pack for pure electric vehicles at low temperatures. Background Art

[0002] With the rapid development of economy and society, people's demand for energy is increasing, especially in the application of transportation sector. In response to the growing energy demand and promoting the sustainable energy development in the future, transportation electrification is a promising technology. In the past two decades, various electric vehicles have been developed and deployed. As the energy source of electric vehicles, the power battery system provides driving power for the whole vehicle. It can be called the blood of electric vehicles. Its performance directly affects the performance of the whole vehicle. Lithium-ion power batteries have excellent power output characteristics, low self-discharge rate, high safety and reliability, and long service life. They can meet the requirements of driving range and power performance of electric vehicles and have been widely used in the field of electric vehicles. However, the performance of lithium-ion batteries will be severely damaged in cold climates, especially in temperatures below zero, where its charging and discharging performance will be greatly attenuated, thus affecting the power performance and use cost of the whole vehicle. Therefore, improving the low-temperature performance of lithium-ion batteries is of great significance to improving the performance and life of power batteries, increasing the driving range and operation safety of the whole vehicle.

[0003] Thermal management has been proven to be an effective measure to improve the low-temperature performance of power batteries. The goal of thermal management of battery packs at low temperatures is to restore the energy and power capabilities of lithium-ion batteries. However, the preheating process in cold climates usually results in additional energy consumption for electric vehicles, which makes it more difficult to heat the battery from low temperatures than to cool it from high temperatures. Battery pack heating methods include two categories: internal heating and external heating. Internal heating usually uses the high battery impedance at low temperatures to generate a large amount of electrochemical heat inside the battery when current is applied. The heat generated by the electrochemical process can directly heat the battery's electrodes and electrolyte. This internal heating method is short-lived, but there is a risk of damaging battery performance, and it is rarely used in vehicle systems today. External heating strategies usually energize the heating element outside the battery cell to generate heat, and then the heat is transferred to the battery cell by convection or conduction to heat the battery to a pre-specified temperature value. However, when the heating element in the external heating strategy is powered by an external power source, such as a charging pile, the heating location is very limited; and if the battery cell itself is used as a power source to power the heating element, the battery cell itself still needs to start working at a low temperature, which will affect the performance of the battery cell. Due to the "barrel effect", the battery cell with the worst performance determines the overall performance of the battery pack, so the attenuation of the performance of the battery cell will limit the overall performance of the battery pack. Summary of the invention

[0004] The purpose of the present invention is to provide a thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperatures in order to ensure that all single cells in the battery pack can overcome the limitations of low temperature conditions, reach a suitable temperature and start working as soon as possible. This method can avoid the dilemma of electric vehicles being unable to start at extremely low temperatures, and can extend the service life of the battery pack, reduce costs and improve economic benefits.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature, the method comprising the following steps:

[0007] The battery pack is started at low temperature, wherein each battery group in the battery pack is divided into a battery group A and a battery group B, wherein the battery group A is located at the periphery of the battery pack, and the battery group B is the battery group other than the battery group A in the battery pack, wherein the battery group A is provided with an outer cavity layer, the cavity between the battery group A and the outer cavity layer is evacuated, and a heating device is provided in the battery group B;

[0008] After starting the battery pack, the control system monitors the temperature of battery group B. If the heating conditions are met, the control system controls battery group A to supply power to the heating device. After the temperature of battery group B reaches the starting conditions, the control system controls battery group A to stop supplying power to the heating device, and battery groups B and A start to supply power to the pure electric vehicle. If the heating conditions are not met, battery groups B and A start to supply power to the pure electric vehicle directly.

[0009] Furthermore, the group A battery pack includes single cells, a conventional outer shell of the group A battery pack is provided on the outside of the single cells, a cavity outer layer is provided on the outside of the group A battery pack, the inside of the cavity between the conventional outer shell of the battery pack and the cavity outer layer is evacuated, a shell support is provided between the conventional outer shell of the group A battery pack and the cavity outer layer, a vacuum pipeline interface is provided on the cavity outer layer, a negative pole wiring port of the group A and a positive pole wiring port of the group A are provided on the conventional outer shell of the group A battery pack and the cavity outer layer, and a shock-absorbing pad is provided on one side of the single cells of the group A.

[0010] Furthermore, a control system and group B single cells are provided inside the group B battery pack, a group B battery pack conventional shell is provided outside the group B single cells, a group B positive electrode connection port is provided on the conventional shell of the group B battery pack, and a heating element is provided between every two group B single cells.

[0011] Furthermore, the control system includes a temperature sensor, a relay and a thermostat, the thermostat is connected to the heating element via the relay, and the relay is connected to the negative electrode wiring port of group A and the positive electrode wiring port of group A.

[0012] Furthermore, the control system monitors the temperature of the battery pack of group B. If the heating condition is met, the specific steps of the control system controlling the battery pack of group A to supply power to the heating device are:

[0013] The temperature sensor obtains the temperature of the group B battery pack and sends it to the thermostat. If the thermostat determines that the temperature of the group B battery pack is lower than the first threshold temperature and meets the heating conditions, the thermostat controls the relay to close, and the group A negative terminal and the group A positive terminal of the group A battery pack are connected to the heating element, and the group A battery pack supplies power to the heating device.

[0014] Furthermore, after the temperature of the battery pack of group B reaches the starting condition, the specific steps of the control system controlling the battery pack of group A to stop supplying power to the heating device are:

[0015] The temperature sensor obtains the temperature of the group B battery pack and sends it to the thermostat. If the thermostat determines that the temperature of the group B battery pack is higher than the second threshold temperature, the start condition is met, and the thermostat controls the relay to disconnect, and the group A negative terminal and the group A positive terminal of the group A battery pack are disconnected from the heating element, and the group A battery pack stops supplying power to the heating device.

[0016] Furthermore, the temperature controller is a snap-type temperature control switch, and the relay is an electromagnetic relay.

[0017] Furthermore, the heating element is a metal film or a heating plate.

[0018] Furthermore, the battery pack A is arranged at the cooling medium inlet of the cooling system of the battery pack.

[0019] Furthermore, the connection between the outer layer of the cavity and the vacuum pipeline interface, as well as the negative electrode wiring port of group A and the positive electrode wiring port of group A are sealed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention installs a battery group A provided with a cavity as an outer cover on the side of a battery group B that needs to be heated. When the electric vehicle is started at low temperature, the battery group A provided with a vacuum insulation cover is used as a power source to power a heating device of the battery group B. The temperature of the battery group B in the battery pack is monitored by a control system, and the start and stop of the heating device are controlled. When each battery in the battery pack reaches a suitable temperature, it starts to work and the electric vehicle starts, thereby solving the problems of insufficient safety of internal heating and long preheating time, and alleviating the dependence of the heating element on an external power source (charging pile) during external heating, and eliminating the disadvantage that the performance of some battery cells in the battery pack is attenuated when the external heating is powered by a heat source at an extremely low temperature, ensuring that after the pure electric vehicle is parked for a long time in a low temperature environment in winter, all batteries in the battery pack can quickly reach a suitable working temperature and start working, thereby shortening the vehicle start time and promoting the popularization and application of pure electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the positions of the battery packs in the battery pack of the present invention;

[0023] Figure 2 It is a schematic diagram of the appearance of each battery group (only the conventional outer shell) in the battery pack;

[0024] Figure 3 It is a front cross-sectional schematic diagram of a battery pack of group A (a vacuum cover is provided outside a conventional housing);

[0025] Figure 4 It is a top view cross-sectional schematic diagram of a group B battery pack (only a conventional outer shell with a heating device arranged inside);

[0026] Figure 5 This is a test result chart of the thermal insulation performance of the vacuum layer of group A battery pack.

[0027] Description of reference numerals:

[0028] Cavity outer layer-1, vacuum pipe interface-2, shell support-3, group A battery pack conventional shell-4, shock absorbing pad-5, group A single battery-6, group A negative electrode wiring port-7, group A positive electrode wiring port-8; temperature sensor-9, relay-10, heating element-11, group B single battery-12, group B battery pack conventional shell-13, group B positive electrode wiring port-14, thermostat-15. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0030] The present invention proposes a thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature. The method comprises: dividing each battery group in the battery pack into two groups, selecting three battery groups at the outer position of the battery pack as group A, and the remaining battery groups as group B; designing a suitable vacuum cavity as an outer cover for the battery group A; equipping the battery group B with a heating device; creating a vacuum-sealed environment inside the cavity by vacuuming, so as to insulate the residual heat of the battery group A after the battery group A finishes working; when the electric vehicle is started at low temperature, the battery group A provided with the vacuum insulation cover is used as a power source to power the heating device of the battery group B; monitoring the temperature of the battery group B in the battery pack through a control system, and controlling the start and stop of the heating device, and starting the battery group B when the batteries in the battery pack reach a suitable temperature, and the electric vehicle starts.

[0031] The method comprises the following steps:

[0032] A battery pack is started at low temperature, wherein each battery group in the battery pack is divided into an A battery group and a B battery group, wherein the A battery group is located at the periphery of the battery pack, and the B battery group is the battery group other than the A battery group in the battery pack, wherein the A battery group is provided with a cavity outer layer (1) on the outside, the cavity between the A battery group and the cavity outer layer (1) is evacuated, and a heating device is provided inside the B battery group;

[0033] After starting the battery pack, the control system monitors the temperature of battery group B. If the heating conditions are met, the control system controls battery group A to supply power to the heating device. After the temperature of battery group B reaches the starting conditions, the control system controls battery group A to stop supplying power to the heating device, and battery groups B and A start to supply power to the pure electric vehicle. If the heating conditions are not met, battery groups B and A start to supply power to the pure electric vehicle directly.

[0034] In the above steps, the group A battery pack includes a single cell 6, the outside of the group A single cell 6 is provided with a group A battery pack conventional outer shell 4, the outside of the group A battery pack is provided with a cavity outer layer 1, the inside of the cavity between the battery pack conventional outer shell 4 and the cavity outer layer 1 is evacuated, a shell support 3 is provided between the group A battery pack conventional outer shell 4 and the cavity outer layer 1, the cavity outer layer 1 is provided with a vacuum pipeline interface 2, the group A battery pack conventional outer shell 4 and the cavity outer layer 1 are provided with a group A negative pole wiring port 7 and a group A positive pole wiring port 8, and a shock-absorbing pad 5 is provided on one side of the group A single cell 6.

[0035] A control system and group B single cells 12 are provided inside the group B battery pack, a group B battery pack conventional housing 13 is provided outside the group B single cells 12, a group B positive electrode connection port 14 is provided on the group B battery pack conventional housing 13, and a heating element 11 is provided between every two group B single cells 12.

[0036] The control system includes a temperature sensor 9 , a relay 10 and a thermostat 15 . The thermostat 15 is connected to the heating element 11 via the relay 10 . The relay 10 is connected to the negative electrode connection port 7 of the group A and the positive electrode connection port 8 of the group A.

[0037] The control system monitors the temperature of the battery pack of group B. If the heating condition is met, the control system controls the battery pack of group A to supply power to the heating device. The specific steps are as follows:

[0038] The temperature sensor 9 obtains the temperature of the group B battery pack and sends it to the thermostat 15. If the thermostat 15 determines that the temperature of the group B battery pack is lower than the first threshold temperature and meets the heating condition, the thermostat 15 controls the relay 10 to close, and the group A negative terminal 7 and the group A positive terminal 8 of the group A battery pack are connected to the heating element 11, and the group A battery pack supplies power to the heating device.

[0039] After the temperature of the battery pack of group B reaches the starting condition, the specific steps for the control system to control the battery pack of group A to stop supplying power to the heating device are as follows:

[0040] The temperature sensor 9 obtains the temperature of the group B battery pack and sends it to the thermostat 15. If the thermostat 15 determines that the temperature of the group B battery pack is higher than the second threshold temperature, the start condition is met, and the thermostat 15 controls the relay 10 to disconnect, and the group A negative terminal 7 and the group A positive terminal 8 of the group A battery pack are disconnected from the heating element 11, and the group A battery pack stops supplying power to the heating device.

[0041] In the present invention, each battery group in the battery pack is divided into two groups. According to the requirements, several battery groups at the periphery of the battery pack are selected as group A, and the remaining battery groups are group B.

[0042] Design a suitable external cover for the battery pack A, such as selecting a cavity such as an aluminum alloy as the outer cover;

[0043] Provide heating device for group B battery pack;

[0044] A vacuum-sealed environment is created inside the cavity by evacuating the air, thereby isolating the residual heat of the A group of batteries after they finish working;

[0045] When the electric vehicle is started at low temperature, the battery pack A provided with the vacuum heat-insulating cover is used as a power source to supply power to the heating device of the battery pack B;

[0046] The control system monitors the temperature of group B batteries in the battery pack and controls the start and stop of the heating device. When each battery in the battery pack reaches a suitable temperature, it starts working and the electric car starts.

[0047] There are multiple battery groups in the battery pack, and the single cells in each battery group are soft-pack lithium-ion batteries. The outer position of the battery pack refers to the cooling medium inlet of the cooling system.

[0048] The outer layer of the cavity designed for group A battery pack is manufactured in different ways according to different materials, such as being made of welded aluminum alloy materials; the gap H between the cavity and the internal battery pack is: 5mm≤H≤50mm, separated by the shell support, and a shock-absorbing pad is laid on the bottom of the cavity.

[0049] The heat source of the heating device provided for the B-group battery pack is a metal film or a heating plate, and the metal film or the heating plate is attached to the largest side of each battery unit inside the B-group battery pack.

[0050] The way to create a vacuum-sealed environment inside the cavity is to design a vacuum pipeline to evacuate and seal the cavity gap through a vacuum pump, and there is no contact between the conventional outer shell of the internal group A battery pack and the edge of the outer cavity. The connection between the vacuum pipeline and the outer layer of the cavity and the positive and negative circuit interfaces of the group A battery pack are sealed, thereby insulating the residual heat of the group A battery at the end of work and keeping the battery warm.

[0051] When the car is started, the group A batteries kept warm by the vacuum cavity are used as a power source to supply power to the group B battery heating device to heat the group B batteries.

[0052] The control system includes a temperature detector, a thermostat and a relay; the temperature detector is connected to the battery pack, and the thermostat is connected to the heating device through a relay; when the temperature detected by the temperature sensor is lower than a first threshold temperature, the thermostat controls the heating device to start heating the B group battery, and when the temperature detected by the temperature sensor is higher than a second threshold temperature, the thermostat controls the heating device to stop heating, the battery pack starts working, and the car starts.

[0053] The cavity is of detachable design, the shell support is made of high temperature resistant heat insulating materials such as plastic, bakelite, rock wool, etc., and the shock absorbing pad is made of shock absorbing materials such as polyurethane foam.

[0054] The sealing treatment adopts detachable sealing methods such as ring plugs or sealing ring grooves, and vacuum silicone grease and vacuum mud are used for additional sealing at all interfaces.

[0055] The relay is an electromagnetic relay.

[0056] The purpose is to provide a thermal management method for lithium-ion battery packs of pure electric vehicles at low temperatures, which is used to solve the problems of insufficient safety of internal heating and long preheating time, and to alleviate the dependence of heating elements on external power sources (charging piles) during external heating, and to eliminate the disadvantage that some cells in the battery pack work at extremely low temperatures to power the heat source during external heating, causing the performance of the cells to decay, so as to ensure that after the pure electric vehicle is parked for a long time in a low temperature environment in winter, all batteries in its battery pack can quickly reach a suitable operating temperature (the batteries in group B still need to be preheated because they have no vacuum insulation) and start working, shortening the car start time and promoting the popularization and application of pure electric vehicles. The present invention designs an effective thermal management method to ensure that all single cells in the battery pack can overcome the limitations of low temperature conditions, reach a suitable temperature and start working as soon as possible, which can avoid the dilemma of electric vehicles being unable to start at extremely low temperatures, and can extend the service life of the battery pack, reduce costs, and improve economic benefits.

[0057] Take part of the battery pack of a pure electric vehicle battery pack, and design a simple and detachable vacuum cavity as a cover for it. When used at low temperatures, this part of the battery pack is pre-installed with a cover to insulate the large amount of waste heat after the battery pack is finished working, so that it is at a suitable temperature. The insulated battery pack (group A) can start working at this suitable temperature at any time; when the car starts at low temperatures, the group A batteries start working, and power the preheating device of the remaining battery pack (group B batteries) to generate heat to heat the group B batteries to a suitable working temperature; all battery packs in the battery pack can start working at a suitable temperature, avoiding the low-temperature start of any battery in the battery pack. The cover can be removed at high temperatures in summer, which is conducive to good heat dissipation of the battery pack and ensures the economical, efficient and safe operation of pure electric vehicles. The design of the present invention helps to promote the popularization and application of pure electric vehicles in cold areas, and has important practical application significance.

[0058] Figure 1 It is a schematic diagram of the location of each battery group in the battery pack; Figure 2 It is a schematic diagram of the appearance of each battery group (only the conventional outer shell) in the battery pack; Figure 3 It is a front cross-sectional schematic diagram of a battery pack of group A (a vacuum cover is provided outside a conventional housing); Figure 4 It is a top view cross-sectional schematic diagram of a group B battery pack (only a conventional outer shell with a heating device arranged inside); Figure 5 This is a test result chart of the thermal insulation performance of the vacuum layer of group A battery pack. Figure 1 Among them, the marked ones are 3 group A battery packs, and the rest are group B battery packs; Figure 2 In the diagram, “+” is the positive terminal of the battery pack, and “-” is the negative terminal of the battery pack.

[0059] In some embodiments, there are 36 battery packs in the battery pack, and the single cells in each battery pack are all soft-pack lithium-ion batteries. The selected group A battery pack has 3 battery packs, which are located outside the battery pack, and the remaining battery packs are group B battery packs. The position of the group A battery pack is the inlet of the cooling medium of the cooling system, because the temperature of each battery pack inside the battery pack continues to rise after the battery pack works normally, and the temperature of the group A battery pack with a special design rises faster, and the cooling system needs to circulate to take away the heat emitted by the battery pack. The cooling medium has the lowest temperature at the inlet, so it can effectively take away the heat of the group A battery pack to avoid the group A battery pack being unable to meet the heat dissipation requirements under high temperature.

[0060] In some embodiments, the outer layer of the cavity designed for the battery pack of group A is made of acrylic material, with a shell support and a battery pack in the cavity separated by a gap of 50 mm, and a shock-absorbing pad is laid at the bottom of the cavity. The outer layer of the cavity is formed by splicing, bonding, and assembling acrylic sheets of designed size, and adopts a detachable design, leaving one side of the cavity open, so that the outer layer of the cavity can be removed in the hot summer season to ensure a good heat dissipation effect of the battery pack of group A; the shell support is made of high temperature resistant insulation materials such as plastic, bakelite, rock wool, etc.; the shock-absorbing pad is made of materials such as polyurethane foam, which can prevent the battery pack of group A from being damaged by contact and friction with the outer layer of the vacuum cavity, and the shock-absorbing pad has both filling and heat insulation functions.

[0061] In some embodiments, the heating device of the B battery pack is a metal film made of pure aluminum or other materials. After the metal film is connected to the circuit, it acts as a heating element to generate heat. After its own temperature rises, it can heat the battery with a lower temperature, so that the battery temperature rises. In order to enhance the heating effect and shorten the heating time, the metal film is preferably attached to the largest side of each battery cell inside the B battery pack.

[0062] In some embodiments, the method of creating a vacuum environment inside the cavity is to design a vacuum pipeline to evacuate and seal the cavity gap through a vacuum pump, and the conventional outer shell of the group A battery pack inside the cavity has no contact with the outer edge of the cavity, wherein the built-in cavity support can prevent the pressure difference from causing the cavity to deform; the connection between the vacuum pipeline and the outer layer of the cavity and the positive and negative circuit interfaces of the group A battery pack all adopt detachable sealing methods such as ring plugs or sealing ring grooves, and vacuum silicone grease and vacuum mud are used for additional sealing at all interfaces. The use of a double sealing step is conducive to maintaining a good vacuum inside the cavity in a low temperature environment, and is convenient for removing the outer layer of the cavity in a high temperature environment in summer. Because the vacuum layer has an excellent thermal insulation effect, the set vacuum layer can effectively retain the residual heat of the internal group A battery pack, reduce the heat transfer between the internal battery pack and the external low temperature environment, and prevent its temperature from dropping below the temperature required for battery operation.

[0063] In some embodiments, when the car starts, the group A battery pack that is insulated by the vacuum cavity starts working first, and serves as a power source to power the group B battery pack preheating device in the battery pack. When the pure electric vehicle stops for a long time in a low-temperature environment after finishing working, the temperature of the group A battery pack can be maintained above zero for a long time because the vacuum cavity is set as the outer cover. Since the group B battery pack uses a conventional battery pack shell, its temperature will drop to the outdoor low temperature level. In order to avoid the situation where the service life of lithium-ion batteries is severely shortened when working at low temperatures, the group A battery pack with a suitable temperature is used as a power source to power the group B battery pack heating device, and heat is generated to heat the group B battery pack to a suitable temperature before starting to work.

[0064] In some embodiments, the temperature of the battery pack is monitored by a control system, and heating stops when the set value is reached, and the battery pack starts to work and start the electric vehicle. The control system includes a temperature sensor, a thermostat and a relay; the thermostat is a sudden jump temperature control switch, and the relay is an electromagnetic relay. In actual use, by setting a control system, the temperature sensor is connected to the B group battery pack, and the thermostat is connected to the heating device through a relay to facilitate simple control of the heating device. When the temperature detected by the temperature sensor is less than the first threshold temperature, the thermostat controls the heating device to heat the B group battery; when the temperature detected by the temperature sensor is higher than the second threshold temperature, the heating device stops heating, and the battery pack starts to work and start the car. The first threshold and the second threshold can be pre-set according to the actual working environment of the battery pack.

[0065] The actual performance test is as follows:

[0066] In order to better demonstrate the feasibility of the above technical solution, the following will experimentally verify the above technical solution in combination with the drawings in the specification and the performance test data to highlight its actual effect. It should be noted that the present invention reasonably distributes the battery packs in the battery pack, and for the first time proposes the idea of ​​using a vacuum layer to insulate the residual heat of the battery pack, that is, the group A battery pack design in the present invention; and the solution of heating the battery by heating a heating device such as a heating metal film or a heating plate is not the first time proposed by the present invention, it is a very mature heating strategy, that is, the group B battery pack design in the present invention. The technical solution in the present invention is to combine the two designs in order to provide a complete battery pack thermal management solution. In the performance test step, only the group A battery pack design proposed for the first time in the present invention will be verified.

[0067] The vacuum insulation layer is used to test the residual heat of the A-group battery pack in a cold environment (-20°C):

[0068] The acrylic sheets of designed size are spliced, bonded and assembled into a closed box. Two terminals are attached to one side of the box to connect the positive and negative poles of the battery pack. A vacuum pipeline is added to the other side to connect to the vacuum pump. The box adopts a side-opening door design, and sealing ring grooves are affixed around the door. Vacuum silicone grease and vacuum mud are used to make additional sealing treatments at all interfaces.

[0069] The low temperature environment is simulated by using a circulating water bath. Coils made of PVC hoses are wrapped around the sides of the outside of the acrylic box. The coils fit tightly against the surface of the box, and coolant is passed through the hoses.

[0070] The battery pack is placed in a 45°C oven for 12 hours. After a long period of temperature adaptation, the overall temperature of the battery pack is at 45°C, simulating the battery pack temperature inside the battery pack after the electric vehicle has finished working.

[0071] When the water bath equipment displays the temperature reaches -20℃, put the preheated battery into the acrylic box, connect the wires of the temperature data acquisition device integrated with the battery pack to the positive and negative terminals on the box, add bakelite around the battery pack and the inner wall of the box for support, and a piece of foam at the bottom of the battery for shock absorption and support. Then close the side door of the box, start the vacuum pump, and create a vacuum environment in the 50mm thick gap between the acrylic box and the conventional outer shell of the battery pack to form a vacuum cavity. One end of the USB adapter used in conjunction with the temperature data monitoring device is connected to the terminal, and the other end is connected to the computer. At this time, the software starts to record the temperature data of the battery pack.

[0072] Comparative test:

[0073] The setting of vacuum layer and the setting of no vacuum layer are used as variables, and other variables are kept consistent, that is, no vacuum layer is set, the vacuum pump is not turned on, and the gap between the acrylic box and the conventional shell of the battery pack is an air layer. The temperature change of the battery pack of group A is tested. The comparative test steps are as follows:

[0074] The acrylic sheets of designed size are spliced, bonded and assembled into a closed box. Two terminals are attached to one side of the box to connect the positive and negative poles of the battery pack. A vacuum pipeline is added to the other side to connect to the vacuum pump. The box adopts a side-opening door design, and sealing ring grooves are affixed around the door. Vacuum silicone grease and vacuum mud are used to make additional sealing treatments at all interfaces.

[0075] The low temperature environment is simulated by using a circulating water bath. Coils made of PVC hoses are wrapped around the sides of the outside of the acrylic box. The coils fit tightly against the surface of the box, and coolant is passed through the hoses.

[0076] The battery pack is placed in a 45°C oven for 12 hours. After a long period of temperature adaptation, the overall temperature of the battery pack is at 45°C to simulate the temperature of the battery pack in the battery pack after the electric vehicle finishes working.

[0077] When the water bath equipment displays that the temperature reaches -20℃, put the battery into the acrylic box, connect the wires of the temperature data acquisition device integrated with the battery pack to the positive and negative terminals on the box, add bakelite around the battery pack and the inner wall of the box for support, and there is a piece of foam at the bottom of the battery for shock absorption and support. Then close the side door of the box, do not start the vacuum pump, at this time, the 50mm gap between the acrylic box and the conventional shell of the battery pack is an air layer. One end of the USB adapter used with the temperature data monitoring device is connected to the terminal, and the other end is connected to the computer. At this time, the software starts to record the temperature data of the battery pack.

[0078] like Figure 5 As shown in the figure, by setting a vacuum cavity outside the battery pack to create a 50mm thick vacuum layer, the initial temperature of the battery pack is 45°C, and after staying in a low temperature environment of -20°C for 12 hours, the temperature of the battery pack is 15.4°C, while the temperature of the battery pack without a vacuum insulation layer (comparison sample) is reduced to -5°C. This proves the superiority and operability of the vacuum insulation layer in the insulation of residual heat of the battery pack.

[0079] According to the technical solution of the present invention, the A battery pack is provided with a vacuum insulation layer, and the B battery pack is provided with a heating device. When the electric vehicle is parked for a long time in a low-temperature environment, the residual heat of the A battery pack is preserved, and its temperature is at a suitable working temperature, so it can directly start to provide energy for the heating device of the B battery pack, heat the B battery pack to a suitable working temperature, and ensure that all battery packs in the battery pack can be started at a suitable temperature to provide power for the vehicle. This can prevent any battery from working under low-temperature conditions, improve the capacity of the battery pack, and alleviate the mileage anxiety problem; at the same time, it gets rid of the dependence of the heating device in the traditional thermal management method on the external power supply (grid or charging pile), improves the flexibility of the use of electric vehicles, and has a very far-reaching practical engineering significance for the promotion of electric vehicles.

[0080] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature, characterized in that: The method comprises the following steps: A battery pack is started at low temperature, wherein each battery group in the battery pack is divided into an A battery group and a B battery group, wherein the A battery group is located at the periphery of the battery pack, and the B battery group is the battery group other than the A battery group in the battery pack, wherein the A battery group is provided with a cavity outer layer (1) on the outside, the cavity between the A battery group and the cavity outer layer (1) is evacuated, and a heating device is provided inside the B battery group; After starting the battery pack, the control system monitors the temperature of battery group B. If the heating conditions are met, the control system controls battery group A to supply power to the heating device. After the temperature of battery group B reaches the starting conditions, the control system controls battery group A to stop supplying power to the heating device, and battery groups B and A start to supply power to the pure electric vehicle. If the heating conditions are not met, battery groups B and A start to supply power to the pure electric vehicle directly.

2. The thermal management method of a lithium-ion battery pack for a pure electric vehicle at low temperature according to claim 1, characterized in that: The group A battery pack comprises a single cell (6); a group A battery pack conventional outer shell (4) is arranged outside the group A single cell (6); a cavity outer layer (1) is arranged outside the group A battery pack; the interior of the cavity between the group A battery pack conventional outer shell (4) and the cavity outer layer (1) is evacuated; a shell support (3) is arranged between the group A battery pack conventional outer shell (4) and the cavity outer layer (1); a vacuum pipeline interface (2) is arranged on the cavity outer layer (1); a group A negative electrode wiring port (7) and a group A positive electrode wiring port (8) are arranged on the group A battery pack conventional outer shell (4) and the cavity outer layer (1); and a shock absorbing pad (5) is arranged on one side of the group A single cell (6).

3. The thermal management method of a lithium-ion battery pack for a pure electric vehicle at low temperature according to claim 2, characterized in that: The B-group battery pack is provided with a control system and B-group single batteries (12) inside, a B-group battery pack conventional housing (13) outside the B-group single batteries (12), a B-group positive electrode connection port (14) is provided on the B-group battery pack conventional housing (13), and a heating element (11) is provided between every two B-group single batteries (12).

4. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 3, characterized in that: The control system comprises a temperature sensor (9), a relay (10) and a temperature controller (15); the temperature controller (15) is connected to the heating element (11) via the relay (10); and the relay (10) is connected to the negative electrode wiring port (7) of the group A and the positive electrode wiring port (8) of the group A.

5. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 4, characterized in that: The control system monitors the temperature of the battery pack of group B. If the heating condition is met, the control system controls the battery pack of group A to supply power to the heating device. The specific steps are as follows: The temperature sensor (9) obtains the temperature of the group B battery pack and sends it to the temperature controller (15). If the temperature controller (15) determines that the temperature of the group B battery pack is lower than a first threshold temperature and meets the heating condition, the temperature controller (15) controls the relay (10) to close, and the group A negative electrode connection port (7) and the group A positive electrode connection port (8) of the group A battery pack are connected to the heating element (11), and the group A battery pack supplies power to the heating device.

6. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 5, characterized in that: After the temperature of the battery pack of group B reaches the starting condition, the specific steps for the control system to control the battery pack of group A to stop supplying power to the heating device are as follows: The temperature sensor (9) obtains the temperature of the group B battery pack and sends it to the temperature controller (15). If the temperature controller (15) determines that the temperature of the group B battery pack is higher than the second threshold temperature, the start condition is met, and the temperature controller (15) controls the relay (10) to disconnect, and the group A negative electrode connection port (7) and the group A positive electrode connection port (8) of the group A battery pack are disconnected from the heating element (11), and the group A battery pack stops supplying power to the heating device.

7. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 4, characterized in that: The temperature controller (15) is a snap-action temperature control switch, and the relay (10) is an electromagnetic relay.

8. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 3, characterized in that: The heating element (11) is a metal film or a heating plate.

9. The thermal management method for a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 2, characterized in that: The battery pack A is arranged at the cooling medium inlet of the cooling system of the battery pack.

10. The thermal management method of a lithium-ion battery pack of a pure electric vehicle at low temperature according to claim 2, characterized in that: The connection between the cavity outer layer (1) and the vacuum pipeline interface (2) as well as the group A negative electrode connection port (7) and the group A positive electrode connection port (8) are sealed.

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