Lithium ion battery low temperature wake-up system and method in extremely cold climate

Abstract

The application provides a lithium ion battery low-temperature awakening system and method in extremely cold weather, and relates to the technical field of lithium battery low-temperature thermal management. The system comprises a pilot battery, a battery pack, a heating film, a MOSFET tube, a temperature sensor, a first relay, a second relay, a signal acquisition unit, a current sensor and a heating control unit. The system can make the battery pack heat up without relying on an external power supply in a low-temperature condition, so that the good working temperature of the battery is reached, the battery in a low-temperature "sleeping" state is awakened, the performance of the battery is activated, and the problems of poor low-temperature performance and difficult application of the battery are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery low-temperature thermal management, and particularly relates to a lithium ion battery low-temperature awakening system and method in extremely cold weather. BACKGROUND

[0002] The rapid development of new energy vehicles has driven the rapid development of the battery industry. Lithium ion batteries are widely used in new energy vehicles, energy storage systems, mobile electronic devices and the like due to a series of advantages such as high energy density, high power, high efficiency and long cycle life. However, the working characteristics of lithium ion power batteries are greatly affected by temperature, especially in extremely cold weather. Low-temperature environments can cause the capacity of the battery to decrease, reduce the working power, and shorten the cycle life, which has a negative impact on new energy vehicles and poses a safety hazard. This shortcoming limits the promotion and use of new energy vehicles in northern China, especially in extremely cold weather regions such as the northeast and northwest.

[0003] In order to solve the above problems, improving and developing various low-temperature resistant battery materials can fundamentally overcome this problem. However, the current level of technology development is difficult to achieve breakthroughs and commercialization of new battery materials in the short term. Therefore, the most convenient and effective solution is to approach from the perspective of battery management, explore efficient battery low-temperature heating technology, and establish a lithium ion power battery low-temperature heating system.

[0004] The commonly used low-temperature heating method can be divided into two categories: internal heating and external heating. External heating uses an external heat source, such as fluid heating, which uses thermal convection or thermal conduction to raise the temperature of the battery. However, its main disadvantage is slow heating rate and low energy utilization rate. Internal heating is a method that uses current flowing through the internal resistance of the battery to generate heat, including direct current heating, alternating current heating and pulse heating. Both internal and external heating have advantages and disadvantages, so researchers have combined the advantages and disadvantages of the two types of heating and proposed a composite heating method. However, the terminal voltage of the battery will decrease as the SOC and ambient temperature decrease during heating. When the battery itself is in a low power state, it is easy to be lower than the lower cut-off voltage in low temperature, which causes great damage to the battery. To avoid this situation, the initial temperature during heating needs to be improved, and pre-warming heating is needed before heating. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a lithium ion battery low-temperature awakening system and method in extremely cold weather, which is suitable for outdoor power sources, electric vehicles and energy storage systems.

[0006] In one aspect, a lithium-ion battery low-temperature wake-up system in an extremely cold climate includes a pilot battery, a battery pack, a heating film, a MOSFET tube, a temperature sensor, a first relay, a second relay, a signal acquisition unit, a current sensor, and a heating control unit.

[0007] The drain of the MOSFET tube is connected to the positive electrode of the pilot battery through a heating bypass, the source of the MOSFET tube is connected to the negative electrode of the pilot battery through another heating bypass, and the gate of the MOSFET tube is connected to the signal output end of the heating control unit.

[0008] The heating control unit sends a PWM signal to control the MOSFET tube module to perform the actions of connection and disconnection according to the set duty ratio and switching frequency. When the pilot battery reaches the maximum available capacity, heating of the pilot battery is stopped, and the heating control unit controls the first relay to be turned on to realize external heating of the battery pack.

[0009] The battery pack is composed of N battery monomers in series, and the heating film has N-1 pieces. Each piece of the heating film is clamped between two battery monomers and is attached to the largest surface of the battery monomers. The heating film and the battery monomers are evenly coated with thermal conductive silicone grease.

[0010] The positive electrode of the pilot battery is connected to one end of the first relay, the negative electrode of the pilot battery is connected to one end of the heating film, the other end of the heating film is connected to the other end of the first relay, and the heating film and the pilot battery are controlled to be turned on through the first relay. The optimal switching temperature is obtained by using the existing NSGA_II algorithm and the TOPSIS method. When the temperature of the battery pack reaches the optimal switching temperature, the heating control unit controls the first relay to be turned off and the second relay to be turned on.

[0011] The heating film and the battery pack are controlled to be turned on through the second relay. The positive electrode of the battery pack is connected to one end of the second relay, the negative electrode of the battery pack is connected to one end of the heating film, and the other end of the heating film is connected to the other end of the second relay. The genetic algorithm is used to optimize the heating cutoff temperature. The temperature of the power battery pack when it reaches the maximum available capacity is the temperature at which heating is stopped.

[0012] The temperature sensor is attached to the surface of each battery monomer in the pilot battery and the battery pack to measure the temperature data of the battery monomers and send them to the signal acquisition unit.

[0013] The current sensor is placed in the loop between the battery pack and the heating film to measure the current data of the lithium-ion battery low-temperature wake-up system and send them to the signal acquisition unit. The signal acquisition unit is connected to the positive and negative ends of the battery pack to acquire the battery voltage and is connected to the heating control unit, the temperature sensor, and the current sensor to acquire the temperature data, the voltage data, and the current data and send them to the heating control unit.

[0014] In another aspect, a method for low-temperature wake-up of a lithium-ion battery in an extremely cold climate, based on the aforementioned low-temperature wake-up system for a lithium-ion battery in an extremely cold climate, comprises the following steps:

[0015] Step 1: Initialize the duty cycle and control frequency of the MOSFET tube, and initialize the heating temperature threshold T L and the pilot battery heating stop temperature threshold T H1 ;

[0016] Step 2: Monitor the battery temperature value in real time through the temperature sensor. If the temperature value is lower than the heating temperature threshold T L , execute step 3, otherwise, execute step 6;

[0017] Step 3: Control the corresponding MOSFET tube of the pilot battery to close and conduct through the heating control unit, and control the duration of a single pulse flowing through the pilot battery ≤ 0.1s. Turn off the MOSFET tube when the pulse discharge of the pilot battery ends, and the static duration Δt;

[0018] Step 4: Use the temperature sensor to record the temperature value of the pilot battery, and judge whether the temperature value of the pilot battery is higher than the pilot battery heating stop temperature threshold T H1 . If yes, execute step 5, otherwise, execute step 3;

[0019] Step 5: Stop heating the pilot battery, and control the MOSFET tube to turn off through the heating control unit;

[0020] Step 6: Control the first relay to close through the heating control unit, and the pilot battery and the heating film form a conduction loop. The current flows through the heating film to generate heat, which is conducted to the battery pack;

[0021] Step 7: Use the temperature sensor to record the temperature value of each battery cell in the battery pack, and the heating control unit calculates the average temperature of the battery pack. Judge whether the battery pack external heating stop temperature T H2 is reached. If yes, execute step 8, otherwise, execute step 6;

[0022] Step 8: Control the first relay to turn off through the heating control unit, and the pilot battery and the heating film loop are disconnected;

[0023] Step 9: Control the second relay to close through the heating control unit, and the battery pack and the heating film form a conduction loop in series. The current flows through the heating film to generate heat, which heats each battery cell in the battery pack from the outside. The internal resistance of each battery cell generates ohmic heat, realizing composite heating of the battery cells in the battery pack;

[0024] Step 10: record the temperature value of each battery monomer in the battery pack by using the temperature sensor, the heating control unit calculates the average temperature of the battery pack, and judges whether the battery pack composite heating stop temperature T is reached H3 , if yes, step 11 is executed;

[0025] Step 11: the second relay is controlled to be turned off by the heating control unit, the series connection of the battery pack and the heating film loop is disconnected, and the heating is stopped.

[0026] The beneficial effects generated by the above technical scheme are as follows:

[0027] The present application provides a kind of lithium ion battery low temperature wake-up system and method under extremely cold climate, the reduction of environmental temperature, the reduction of battery initial SOC and the reduction of heating film resistance will cause the end voltage drop when heating.When the end voltage is lower than the lower cut-off voltage of battery, it will cause damage to the battery, in this case, the battery pack cannot be self-heated, which can easily lead to the battery cannot be used normally at low temperature, causing the emergence of "car nest" phenomenon.The heating system established, since the "pilot battery + heating film" scheme is adopted, the pilot battery discharges the heating film, the temperature of the heating film rises, and the temperature of the battery pack is raised by heat conduction, and the battery pack is pre-warmed at low temperature, which increases the initial temperature of the battery pack when self-heating, and the low temperature performance of the main power battery pack is recovered, and the internal pressure during self-heating is reduced, so that the end voltage during heating is improved, to avoid being lower than the lower cut-off voltage, which can overcome the shortcomings of ineffective heating at low temperature and low SOC.At the same time, the present application includes a heating boundary surface, i.e., in a certain heating film resistance and any SOC, when using the pilot battery to wake up and heat, the lowest wake-up temperature can be calculated by using the curve, which provides a reference for the switching time of heating mode.Effectively solve the problems of low temperature capacity decline, performance decline and inability to heat under severe cold conditions of electric vehicles. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is the structure diagram of lithium battery pack low temperature low power wake-up heating system in the specific embodiment of the present application;

[0029] Figure 2 It is the structure diagram of pilot battery pulse self-heating system in the specific embodiment of the present application;

[0030] Figure 3 It is the structure diagram of pilot battery wake-up battery pack heating system in the specific embodiment of the present application;

[0031] Figure 4 It is the structure diagram of lithium battery pack composite heating system in the specific embodiment of the present application;

[0032] Figure 5 It is the heating boundary surface diagram in the specific embodiment of the present application;

[0033] Figure 6 The flow chart of the low-temperature and low-power wake-up heating method of the lithium battery pack in the specific embodiment of the present application;

[0034] Figure 7 The invalid heating schematic diagram when the wake-up is not used in the specific embodiment of the present application;

[0035] Figure 8 The heating process in the specific embodiment of the present application;

[0036] In the figure, 1 is a first battery monomer, 2 is a second battery monomer, 3 is a third battery monomer, 4 is a fourth battery monomer, 5 is a fifth battery monomer, 6 is a sixth battery monomer, 7 is a first heating film, 8 is a second heating film, 9 is a third heating film, 10 is a fourth heating film, 11 is a fifth heating film, 12 is a first relay, 13 is a second relay, 14 is a MOSFET tube, 15 is a pilot battery, 16 is a current sensor, 17 is a voltage sensor, 18 is a signal acquisition unit, 19 is a first temperature sensor, 20 is a second temperature sensor, 21 is a third temperature sensor, 22 is a fourth temperature sensor, 23 is a fifth temperature sensor, 24 is a sixth temperature sensor, 25 is a heating control unit, and 26 is a seventh temperature sensor. DETAILED DESCRIPTION

[0037] The specific embodiment of the present application will be further described in detail below in combination with the drawings and examples. The following examples are used to illustrate the present application but not to limit the scope of the present application.

[0038] In one aspect, a low-temperature wake-up system for lithium ion batteries in extremely cold climates includes a pilot battery, a battery pack, a heating film, a MOSFET tube, a temperature sensor, a first relay, a second relay, a signal acquisition unit, a current sensor, and a heating control unit, as shown in the figure. Figure 1

[0039] The drain of the MOSFET tube is connected to the anode of the pilot battery through a heating bypass, the source of the MOSFET tube is connected to the cathode of the pilot battery through another heating bypass, and the gate of the MOSFET tube is connected to the signal output end of the heating control unit.

[0040] The heating control unit sends a PWM signal according to the pre-written heating program to control the MOSFET tube module to perform the joint and disconnection actions according to the set duty ratio and switching frequency, so that the pilot battery performs self-discharge in the form of pulsed large current to realize internal heat generation, the temperature rises rapidly, and the low-temperature wake-up of the pilot battery is realized. When the pilot battery reaches the maximum available capacity, the heating of the pilot battery is stopped, and the heating control unit controls the first relay to be turned on to realize the external heating of the battery pack.​

[0041] The battery pack is composed of N battery monomers in series, and the heating film has N-1 pieces, each of which is clamped between two monomer batteries and attached to the largest surface of the battery monomer. The heating film and the battery monomer are evenly coated with thermal conductive silicone grease.

[0042] The positive electrode of the pilot battery is connected to one end of the first relay, the negative electrode of the pilot battery is connected to one end of the heating film, and the other end of the heating film is connected to the other end of the first relay. The heating film and the pilot battery are controlled to be conductive through the first relay, forming a "pilot battery + heating film" direct current heating loop. In this embodiment, considering the temperature rise rate and energy utilization rate, the initial temperature, initial SOC, maximum allowable current value, and battery lower cutoff voltage are input into the thermocouple combination model and the available SOC model. The optimal switching temperature is obtained by the existing NSGA_II algorithm and the TOPSIS method. When the battery pack temperature reaches the optimal switching temperature, the heating control unit controls the first relay to be closed and the second relay to be opened.

[0043] The heating film and the battery pack are controlled to be conductive through the second relay. The positive electrode of the battery pack is connected to one end of the second relay, the negative electrode of the battery pack is connected to one end of the heating film, and the other end of the heating film is connected to the other end of the second relay, forming a "heating film" direct current heating loop. The genetic algorithm is used to optimize the heating cutoff temperature, and the temperature at which the power battery pack reaches the maximum available capacity is the stopping heating temperature.

[0044] The temperature sensor is attached to the surface of each battery monomer in the pilot battery and the battery pack, measures the temperature data of the battery monomer, and sends it to the signal acquisition unit.

[0045] The current sensor is placed in the loop between the battery pack and the heating film, measures the current data of the lithium ion battery low-temperature wake-up system, and sends it to the signal acquisition unit. The signal acquisition unit is connected to the positive and negative terminals of the battery pack to acquire the battery voltage, and is connected to the heating control unit, the temperature sensor, and the current sensor, respectively, to acquire the temperature data, the voltage data, and the current data and send them to the heating control unit.

[0046] A lithium battery pack low-temperature wake-up heating system in this embodiment, as shown in Figure 1 and Figure 4 The negative electrode of the first battery monomer 1 is connected to the positive electrode of the second battery monomer 2, and the negative electrode of the second battery monomer 2 and the positive electrode of the third battery monomer 3 are connected. The other battery monomers are connected in the same way, forming a battery pack. As shown in Figure 1 、 Figure 3 and Figure 4As shown, the first contact of the first heating film 7 is connected to the positive pole of the first battery monomer 1, the second contact of the first heating film 7 is connected to the first contact of the second heating film 8, the second contact of the second heating film 8 is connected to the first contact of the third heating film 9, and the other heating films are connected in the same way, such as the fourth heating film 10 in the figure. In this embodiment, the second contact of the last fifth heating film 11 is connected to the negative pole of the sixth battery monomer, forming a heating loop. Figure 1 and Figure 2 As shown, the drain of the MOSFET tube 14 is connected to the positive pole of the pilot battery 15 through the heating bypass, and the source of the MOSFET tube 14 is connected to the negative pole of the pilot battery 15 through the heating bypass. The MOSFET tube is connected to the heating control unit 25, and the heating control unit 25 is used to control the opening and closing of the MOSFET tube and the first relay 12 and the second relay 13 according to the temperature data, voltage data and current data sent by the signal acquisition unit 18; as Figure 1 、 Figure 3 and Figure 4 As shown, the first temperature sensor 19, the second temperature sensor 20, the third temperature sensor 21, the fourth temperature sensor 22, the fifth temperature sensor 23, the sixth temperature sensor 24 and the seventh temperature sensor 26 are respectively attached to the surface of the first battery monomer 1, the second battery monomer 2, the third battery monomer 3, the fourth battery monomer 4, the fifth battery monomer 5, the sixth battery monomer 6 and the pilot battery 15, for measuring the temperature data of the battery monomer and sending to the signal acquisition unit 18; the signal acquisition unit 18 is connected to the pilot battery and the positive and negative ends of the battery pack to acquire the battery voltage, and is respectively connected to the heating control unit 25, each temperature sensor, voltage sensor 17 and current sensor 16, for acquiring temperature data, voltage data and current data and sending to the heating control unit 25.

[0047] In this embodiment, a ternary lithium battery with 10Ah and nominal voltage 4.2V is used as the battery monomer, an IPT012N08N5 type MOSFET tube is used, and an STM32F103 series single-chip microcomputer with peripheral circuit is used as the control unit; a K-type thermocouple is used as the temperature sensor;

[0048] On the other hand, a lithium ion battery low temperature wake-up method in extremely cold climate, based on the foregoing lithium ion battery low temperature wake-up system in extremely cold climate, as Figure 6 shown, comprising the following steps:

[0049] Step 1: initialize the duty cycle of the MOSFET tube, the control frequency, and initialize the heating temperature threshold T L and the pilot battery heating stop temperature threshold T H1 .

[0050] The MOSFET tube duty cycle λ = 10% in this embodiment, control frequency f = 10Hz, initialization heating temperature threshold T L =-30℃ and heating stop temperature threshold T H1 =0℃;

[0051] Step 2: real-time monitoring of battery temperature value by temperature sensor, if the temperature value is lower than the heating temperature threshold T L , then step 3 is executed, otherwise, step 6 is executed;

[0052] In this embodiment, the battery temperature value is monitored in real time by the temperature sensor, and if the temperature value is lower than the heating temperature threshold T L , then step 3 is executed, otherwise, step 6 is executed;

[0053] Step 3: control the MOSFET tube corresponding to the pilot battery to close and conduct by the heating control unit, in order to reduce the influence of heating on the durability of the battery, control the duration of single pulse flowing through the pilot battery ≤0.1s, turn off the MOSFET tube when the pulse discharge of the pilot battery is over, and the static time Δt;

[0054] In this embodiment, the ratio of current duration and static time is controlled by the duty cycle of the corresponding MOSFET tube, and the battery current and heat generation rate are as follows:

[0055]

[0056] Q = I batt (t) 2 R0 (2)

[0057] Wherein, U batt (t) and I batt (t) are the open circuit voltage and current of the battery, R0 and R E are the internal resistance of the pilot battery and the external resistance of the heating bypass, T is the period, λ is the duty cycle; t is the heating time; Q is the battery heat generation rate;

[0058] Step 4: record the temperature value of the pilot battery by the temperature sensor, and judge whether the average temperature T m of the battery monomer at the current time is higher than the heating stop temperature threshold T H1 of the pilot battery, if yes, step 5 is executed, otherwise, return to step 3;

[0059] Step 5: stop heating the pilot battery, and control the MOSFET tube to be turned off by the heating control unit;

[0060] Step 6: control the first relay to close by the heating control unit, and the pilot battery and the heating film form a conduction loop, the current flows through the heating film to generate heat, which is conducted to the battery pack;

[0061] The MOSFET tube is closed in the embodiment, the heating control unit controls the first relay to close, and the pilot battery and the heating film circuit are turned on. The current flows through the heating film, the heating film generates heat, and the heat is conducted to the main battery pack through the heat-conducting silicone grease.

[0062] The battery current and the heating film heat generation rate are as follows:

[0063]

[0064] Q film = I(t) 2 R film (4)

[0065] wherein U batt (t) and I(t) are the open-circuit voltage and current of the battery, R0 and R film are the internal resistance of the pilot battery and the total resistance of the heating film, respectively, and Q film is the heat generation rate of the heating film.

[0066] Step 7: The temperature values of each battery cell in the battery pack are recorded by the temperature sensor, and the average temperature of the battery pack is calculated by the heating control unit to determine whether the external heating stop temperature T H2 of the battery pack is reached. If yes, step 8 is executed;

[0067] The temperature values of each battery cell in the battery pack are recorded by the temperature sensor, and the average temperature T m of the battery cell at the current time is calculated to determine whether it is greater than the heating stop temperature threshold T H2 . If yes, step 8 is executed; otherwise, step 6 is executed.

[0068] Step 8: The first relay is controlled to be closed by the heating control unit, and the pilot battery and the heating film circuit are disconnected;

[0069] Step 9: The second relay is controlled to be closed by the heating control unit, and the battery pack and the heating film form a conduction circuit, the current flows through the heating film to generate heat, and the battery pack is heated from the outside to the inside, and the internal resistance of each battery cell generates ohmic heat to realize composite heating of the battery cells in the battery pack;

[0070] In the embodiment, the heating control unit controls the first relay to close, and the heating film and the pilot battery circuit are disconnected. The second relay 13 is closed, and the battery pack and the heating film circuit are turned on. The current flows through the heating film, the heating film generates heat, and the battery is heated from the outside to the inside, and the internal resistance of the battery generates heat, and the battery is heated from the inside to the outside.

[0071] The battery current and the heating film heat generation rate are as follows:

[0072]

[0073] Q0 = Q1 + Q2 (6)

[0074] Q1 = I2(t) 2 R1 (7)

[0075] Q2 = I2(t) 2 R film (8)

[0076] wherein U1(t) and I2(t) are the open circuit voltage and current of the battery pack, R1 and R film are the total internal resistance of the battery pack and the total resistance of the heating film, respectively, Q0 is the total heat generation rate of the heating circuit, Q1 is the total heat generation rate of the battery pack internal resistance, and Q2 is the total heat generation rate of the heating film.

[0077] Step 10: record the temperature value of each battery cell in the battery pack using the temperature sensor, and the heating control unit calculates the average temperature of the battery pack to determine whether the battery pack composite heating stop temperature T H3 is reached, if so, step 11 is executed, otherwise step 9 is executed;

[0078] Step 11: control the second relay to turn off by the heating control unit, disconnect the series connection of the battery pack and the heating film circuit, and stop heating.

[0079] Stop heating, control all relays to turn off by the heating control unit.

[0080] Through the above heating steps, the battery pack is heated according to the heating scheme, and the heating control result is obtained. As shown in Figure 5 , it represents the minimum total resistance of the heating film allowed to be used to make the heating terminal voltage not lower than the lower limit value at a certain SOC and a certain temperature. Through the first step of pulse heating wake-up, in the "pilot battery + heating film" direct current heating process, Figure 7 is the current-voltage curve, the minimum heating voltage rises from 12.79V to 15.61V, and the average heating current rises from 6.92A to 9.25A, Figure 8 is the temperature rise curve, the temperature rise rate increases from 0.71℃ to 1.15℃ / min, an increase of 62.0%, solving the problem of ineffective heating of the battery pack at low temperature and low power; after the second step of "pilot battery + heating film" direct current heating, the battery pack temperature is heated from -20℃ to -10℃, at this time, the "heating film" is heated again, the minimum heating voltage rises from 7.7V to 12.8V, the average heating current flowing through the heating film rises from 17.00A to 28.88A, and the temperature rise rate increases from 12.1℃ / min to 17.8℃ / min, an increase of 46.6%.

[0081] The above description is merely that of the preferred embodiments of the present disclosure and a description of the technical principles of the present disclosure. It should be understood by those skilled in the art that the inventive scope of the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by the combinations of the above technical features or equivalent features without departing from the above inventive concept. For example, the technical solutions formed by the mutual replacement of the above features and the technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to) form the technical solutions.

Claims

1. A low temperature wake-up system for lithium-ion batteries in extreme cold climates, characterized in that, The battery group, heating film, MOSFET tube, temperature sensor, first relay, second relay, signal acquisition unit, current sensor and heating control unit are connected in series. The drain of the MOSFET tube is connected to the anode of the pilot battery through a heating bypass, the source of the MOSFET tube is connected to the cathode of the pilot battery through another heating bypass, and the gate of the MOSFET tube is connected to the signal output end of the heating control unit. The anode of the pilot battery is connected to one end of the first relay, the cathode of the pilot battery is connected to one end of the heating film, the other end of the heating film is connected to the other end of the first relay, and the heating film is controlled to be turned on through the first relay. The optimal switching temperature is obtained by using the existing NSGA_II algorithm and TOPSIS method. The battery group is controlled to be turned on through the second relay.

2. The low temperature wake-up system for lithium-ion batteries in extreme cold climate according to claim 1, characterized in that, The optimal heating cutoff temperature is optimized by using a genetic algorithm.

3. The low temperature wake-up system for lithium-ion batteries in extreme cold climate according to claim 1, characterized in that, The PWM signal is sent by the heating control unit to control the MOSFET tube module to perform the joint and disconnection action according to the set duty ratio and switching frequency.

4. The low temperature wake-up system for lithium-ion batteries in extreme cold climate of claim 1, wherein, When the pilot battery reaches the maximum available capacity, the heating of the pilot battery is stopped, and the first relay is turned on by the heating control unit to realize the external heating of the battery group.

5. The low temperature wake-up system for lithium-ion batteries in extreme cold climate according to claim 1, characterized in that, The battery group is composed of N battery monomers connected in series, and the heating film has N-1 pieces.

6. A method for low temperature wake-up of a lithium-ion battery in an extremely cold climate, implemented by a system for low temperature wake-up of a lithium-ion battery in an extremely cold climate according to claim 1, characterized in that, The temperature sensor is attached to the surface of each battery monomer in the pilot battery and the battery group to measure the temperature data of the battery monomer and send it to the signal acquisition unit. Step 1: Initialize MOSFET tube duty cycle, control frequency, initialize heating temperature threshold T L with the pilot battery heating stop temperature threshold T H1 ; Step 2: Real-time monitoring of battery temperature value by temperature sensor, if the temperature value is lower than the heating temperature threshold T L then Step 3 is executed, otherwise Step 6 is executed; The current sensor is placed in the loop between the battery group and the heating film to measure the current data of the lithium ion battery low-temperature wake-up system and send it to the signal acquisition unit. Step 4: record the temperature value of the pilot battery by using the temperature sensor, and determine whether the temperature value of the pilot battery is higher than the pilot battery heating stop temperature threshold T H1 , if yes, execute Step 5, otherwise execute Step 3; The signal acquisition unit is connected to the positive and negative terminals of the battery group to collect the battery voltage, and is connected to the heating control unit, temperature sensor and current sensor respectively to collect the temperature data, voltage data and current data and send them to the heating control unit. The steps include: Step 7: The temperature value of each battery cell in the battery pack is recorded by the temperature sensor, and the average temperature of the battery pack is calculated by the heating control unit to determine whether the battery pack external heating stop temperature T H2 is reached, and if so, step 8 is performed, otherwise, step 6 is performed; Step 3: The MOSFET tube corresponding to the pilot battery is turned on by the heating control unit, and the duration of the single pulse flowing through the pilot battery is controlled to be ≤0.1s. Step 5: The heating of the pilot battery is stopped, and the MOSFET tube is turned off by the heating control unit. Step 6: The first relay is turned on by the heating control unit, and the pilot battery and the heating film form a conduction loop. Step 8: The first relay is turned off by the heating control unit, and the pilot battery and the heating film loop are disconnected. Step 9: The second relay is controlled to be closed by the heating control unit, a conduction loop is formed by connecting the battery pack and the heating film in series, current flows through the heating film to generate heat, and each battery cell in the battery pack is heated from the outside to the inside, the internal resistance of each battery cell generates ohmic heat, and composite heating of the battery cells in the battery pack is realized. Step 10: The temperature sensor records the temperature value of each battery cell in the battery pack, and the heating control unit calculates the average temperature of the battery pack to determine whether the battery pack composite heating stop temperature T is reached, if so, step 11 is executed. H3 , if so, step 11 is executed. Step 11: The second relay is controlled to be turned off by the heating control unit, the circuit of the battery pack and the heating film is disconnected, and the heating is stopped.

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