Early warning method for battery thermal runaway and new energy automobile

Abstract

The invention discloses a battery thermal runaway early warning method and a new energy automobile, and belongs to the technical field of new energy automobile batteries, and the method comprises the steps: recording the maximum voltage and the minimum voltage of a battery cell through a battery management system (BMS) when the new energy automobile is fully charged each time, the capacity difference of each time is calculated according to the highest voltage and the lowest voltage of the battery cell recorded each time, the leakage current of the battery cell is calculated through the two adjacent capacity differences, and the average voltage of the battery cell with the lowest voltage in the battery pack in the time interval of two adjacent full charging is calculated; the short-circuit resistance of the lowest-voltage battery cell in the battery pack in the time interval of two adjacent full charging is calculated, when the two adjacent short-circuit resistances are calculated, a battery management system (BMS) judges whether battery thermal runaway early warning needs to be carried out or not according to related conditions, and if the related conditions are judged to be met, the battery thermal runaway early warning is carried out. According to the invention, early warning can be carried out before thermal runaway of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicle batteries, and in particular, relates to a battery thermal runaway early warning method and a new energy vehicle. Background Art

[0002] Battery safety is crucial in new energy vehicles. As the core component of new energy vehicles, batteries are not only related to the vehicle's power performance, but also directly related to the life safety of drivers and passengers. Once the battery has safety problems such as thermal runaway and short circuit, it may cause fire or even explosion, with disastrous consequences. Therefore, ensuring battery safety is the premise and foundation for the development of new energy vehicles.

[0003] Currently, new energy vehicles can only sound an alarm when battery thermal runaway has occurred, and cannot provide early warning. The current monitoring and alarm methods for battery thermal runaway in new energy vehicles mainly rely on the monitoring of the sudden drop in battery voltage and the temperature of the associated battery cells, or the monitoring of the smoke concentration in the battery pack through smoke sensors. However, these methods have obvious limitations, because they can usually only sound an alarm when a fault has occurred. When the battery voltage suddenly drops or the battery cell temperature rises abnormally, or the smoke sensor can only sound an alarm after smoke is generated, although the alarm system can be triggered, the time window left for the driver and passengers to take countermeasures is often very short, which can easily cause property damage and casualties.

[0004] Patent CN117465222B discloses a power battery fault warning method and a fault warning system. The power battery fault warning method is applied to the cloud, including: obtaining the cell detection data of the target vehicle power battery and the rated parameters of the power battery, and performing a first fault judgment; based on the first fault judgment result, obtaining load status information; and performing a small current over-discharge fault judgment according to the load status information to generate a warning result.

[0005] However, the technology disclosed in the above patent cannot provide early warning before thermal runaway of the battery occurs. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a battery thermal runaway early warning method and a new energy vehicle in view of the deficiencies in the prior art, so as to achieve the purpose of being able to provide an early warning before the battery thermal runaway occurs.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The present invention provides a battery thermal runaway early warning method, the method comprising the following steps:

[0009] S1: Charging the new energy vehicle for the first time;

[0010] S2: Continuously collect the voltage of the battery cell through the battery management system (BMS);

[0011] S3: When the new energy vehicle is fully charged for the first time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the first capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 1 ;

[0012] S4: Charging the new energy vehicle for the second time;

[0013] S5: Continuously collect the voltage of the battery cell through the battery management system (BMS);

[0014] S6: When the new energy vehicle is fully charged for the second time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the second capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 2 ;

[0015] S7: The battery management system (BMS) performs the following operations according to the first time interval T: 1 , the first capacity difference C 1 and the second capacity difference C 2 Calculate the leakage current I of the battery cell 1 ;

[0016] S8: The battery management system (BMS) calculates the first time interval T 1 The average voltage U of the lowest voltage cell in the battery pack 1 ;

[0017] S9: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack 1 ;

[0018] S10: Charging the new energy vehicle for the third time;

[0019] S11: Continuously collect the voltage of the battery cell through the battery management system (BMS);

[0020] S12: When the new energy vehicle is fully charged for the third time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the third capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 3 ;

[0021] S13: The battery management system (BMS) performs the following operations according to the second time interval T 2 , the second capacity difference C 2 and the third capacity difference C 3 Calculate the leakage current I of the battery cell 2 ;

[0022] S14: The battery management system (BMS) calculates the second time interval T 2 The average voltage U of the lowest voltage cell in the battery pack 2 ;

[0023] S15: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack 2 ;

[0024] S16: The battery management system (BMS) determines whether the first condition, the second condition and the third condition are all satisfied. If yes, the process proceeds to S17; if not, the process proceeds to S18;

[0025] S17: The battery management system (BMS) performs a battery thermal runaway warning, and after the warning is completed, it enters S26;

[0026] S18: charging the new energy vehicle for the N+1th time;

[0027] S19: Continuously collect the voltage of the battery cell through the battery management system (BMS);

[0028] S20: When the new energy vehicle is fully charged for the N+1th time, the battery management system (BMS) records the highest and lowest voltages of the battery cells, and calculates the N+1th capacity difference C based on the recorded highest and lowest voltages of the battery cells. N+1 ;

[0029] S21: The battery management system (BMS) performs the following operations according to the Nth time interval T: N 、Nth capacity difference C N and the N+1 capacity difference C N+1 Calculate the leakage current I of the battery cell N ;

[0030] S22: The battery management system (BMS) calculates the Nth time interval T N The average voltage U of the lowest voltage cell in the battery pack N ;

[0031] S23: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack N ;

[0032] S24: The battery management system (BMS) determines whether the first condition, the second condition and the fourth condition are all satisfied. If so, the process proceeds to S17; if not, the process proceeds to S25;

[0033] S25: Take N=N+1;

[0034] S26: Enter S18.

[0035] Furthermore, N is a positive integer greater than 2, and N starts from 3.

[0036] Furthermore, I 1 =(C 2 -C 1 ) / T 1 , I 2 =(C 3 -C 2 ) / T 2 , I N =(C N+1 -C N ) / T N , where T 1 is the first time interval, T 2 is the second time interval, T N is the Nth time interval, C 1 is the first capacity difference, C 2 is the second capacity difference, C 3 is the third capacity difference, C N is the Nth capacity difference, C N+1 is the N+1th capacity difference, I 1 is the first time interval T 1 Leakage current of the inner cell, I 2 is the second time interval T 2 Leakage current of the inner cell, I N is the Nth time interval T N Leakage current of the internal battery.

[0037] Furthermore, R 1 =U 1 / I 1 , R 2 =U 2 / I 2 , R N =U N / I N , where I 1 is the first time interval T 1 Leakage current of the inner cell, I 2 is the second time interval T 2 Leakage current of the inner cell, I N is the Nth time interval T N Leakage current of the inner cell, U 1 is the first time interval T 1 The average voltage of the lowest voltage cell in the battery pack, U 2 is the first time interval T 2 The average voltage of the lowest voltage cell in the battery pack, U N is the Nth time interval T N The average voltage of the lowest voltage cell in the battery pack, R 1 is the first time interval T1 The short-circuit resistance of the lowest voltage cell in the battery pack, R 2 is the second time interval T 2 The short-circuit resistance of the lowest voltage cell in the battery pack, R N is the Nth time interval T N The short-circuit resistance of the lowest voltage cell in the battery pack.

[0038] Furthermore, the first time interval T 1 is the time difference between the first full charge of the new energy vehicle and the second full charge of the new energy vehicle. The second time interval T 2 is the time difference between the second time the new energy vehicle is fully charged and the third time the new energy vehicle is fully charged. The Nth time interval T N It is the time difference between the Nth time the new energy vehicle is fully charged and the N+1th time the new energy vehicle is fully charged.

[0039] Furthermore, the first condition is that the state of charge (SOC) of the battery is greater than a preset threshold.

[0040] Furthermore, the second condition is that the voltage steep drop speed of the lowest voltage battery cell in the battery pack is greater than a preset voltage steep drop speed and lasts for a time greater than a preset time.

[0041] Furthermore, the third condition is |R 2 -R 1 | / R 1 The value of is greater than 0.5.

[0042] Furthermore, the fourth condition is |R N -R N-1 | / R N-1 The value of is greater than 0.5.

[0043] The present invention also provides a new energy vehicle, which uses the above-mentioned battery thermal runaway warning method to perform battery thermal runaway warning.

[0044] The battery thermal runaway early warning method of the present invention has the following advantages:

[0045] (1) The battery thermal runaway warning method of the present invention can provide a warning before the battery thermal runaway occurs, thereby gaining more time windows for users.

[0046] (2) Through the present invention, after the battery management system (BMS) determines that a battery thermal runaway warning is needed, the battery management system (BMS) will push the battery thermal runaway warning information to the enterprise platform and users to facilitate subsequent safety inspections of the battery, while also avoiding property losses and casualties.

[0047] (3) The present invention provides an early warning before thermal runaway of the battery occurs, thereby improving the safety of the entire vehicle.

[0048] (4) The battery management system (BMS) of the present invention combines multiple judgment conditions before issuing a battery thermal runaway warning, thereby better avoiding misjudgment and improving the accuracy of the warning before the battery thermal runaway occurs.

[0049] (5) The present invention can solve the problem of the early internal short circuit phenomenon not being obvious by detecting the leakage between two adjacent charging times of the new energy vehicle, and also supplement the mid- and late-stage detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] This specification includes the following drawings, which show the following contents:

[0051] Figure 1 It is a flow chart of a battery thermal runaway early warning method of the present invention. DETAILED DESCRIPTION

[0052] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention and facilitating their implementation.

[0053] Figure 1 The present invention is a flowchart of a battery thermal runaway early warning method, the method comprising the following steps:

[0054] S1: The first time to charge a new energy vehicle, corresponding to Figure 1 S1 in.

[0055] S2: The battery management system (BMS) continuously collects the voltage of the battery cell, which corresponds to Figure 1 Specifically, during the charging process of the new energy vehicle, the voltage of the battery cell is continuously collected through the battery management system (BMS), for example, the voltage of the battery cell can be collected once every 0.01 seconds.

[0056] S3: When the new energy vehicle is fully charged for the first time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the first capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 1 , that is, corresponding to Figure 1 Specifically, when the new energy vehicle is fully charged for the first time, the capacity difference between the highest voltage cell and the lowest voltage cell is calculated by the highest voltage and the lowest voltage among the voltages collected by the battery management system (BMS), and is recorded as the first capacity difference C 1 .

[0057] S4: The second time to charge the new energy vehicle, that is, Figure 1 S4 in.

[0058] S5: The battery management system (BMS) continuously collects the voltage of the battery cell, which corresponds to Figure 1 Specifically, during the charging process of the new energy vehicle, the voltage of the battery cell is continuously collected through the battery management system (BMS), for example, the voltage of the battery cell can be collected once every 0.01 seconds.

[0059] S6: When the new energy vehicle is fully charged for the second time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the second capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 2 , that is, corresponding to Figure 1 Specifically, when the new energy vehicle is fully charged for the second time, the capacity difference between the highest voltage cell and the lowest voltage cell is calculated by the highest voltage and the lowest voltage among the voltages collected by the battery management system (BMS), and is recorded as the second capacity difference C 2 .

[0060] S7: The battery management system (BMS) performs the following operations according to the first time interval T: 1 , the first capacity difference C 1 and the second capacity difference C 2 Calculate the leakage current I of the battery cell 1 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) is based on I 1 =(C 2 -C 1 ) / T 1 Calculate the leakage current I of the battery cell 1 , where T 1 is the first time interval, the first time interval T 1 It is not a fixed time value. The first time interval T 1 C is the time difference between the first full charge of a new energy vehicle and the second full charge of a new energy vehicle. This time difference is recorded by the battery management system (BMS). The specific value of this time difference depends on how long the owner takes to charge the new energy vehicle for the second time after the first full charge of the new energy vehicle. In addition, C 1 is the first capacity difference, C 2 is the second capacity difference, I 1 is the first time interval T 1 Leakage current of the internal battery.

[0061] S8: The battery management system (BMS) calculates the first time interval T 1 The average voltage U of the lowest voltage cell in the battery pack1 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) sets the first time interval T 1 The sum of the voltages of the lowest voltage cells in the battery pack collected within the first time interval T 1 The total number of times the internal battery management system (BMS) collects the voltage of the battery cell is compared to obtain the first time interval T 1 The average voltage U of the lowest voltage cell in the battery pack 1 .

[0062] S9: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack 1 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) is based on R 1 =U 1 / I 1 Calculate the short-circuit resistance R of the lowest voltage cell in the battery pack 1 , where I 1 is the first time interval T 1 Leakage current of the inner cell, U 1 is the first time interval T 1 The average voltage of the lowest voltage cell in the battery pack, R 1 is the first time interval T 1 The short-circuit resistance of the lowest voltage cell in the battery pack.

[0063] S10: The third time charging the new energy vehicle, corresponding to Figure 1 The S10 in.

[0064] S11: The battery management system (BMS) continuously collects the voltage of the battery cell, which corresponds to Figure 1 Specifically, during the charging process of the new energy vehicle, the voltage of the battery cell is continuously collected through the battery management system (BMS), for example, the voltage of the battery cell can be collected once every 0.01 seconds.

[0065] S12: When the new energy vehicle is fully charged for the third time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the third capacity difference C according to the recorded highest voltage and the lowest voltage of the battery cell. 3 , that is, corresponding to Figure 1 Specifically, when the new energy vehicle is fully charged for the third time, the capacity difference between the highest voltage cell and the lowest voltage cell is calculated by the highest voltage and the lowest voltage among the voltages collected by the battery management system (BMS), and is recorded as the third capacity difference C 3 .

[0066] S13: The battery management system (BMS) performs the following operations according to the second time interval T 2 , the second capacity difference C 2 and the third capacity difference C 3 Calculate the leakage current I of the battery cell 2 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) is configured according to I 2 =(C 3 -C 2 ) / T 2 Calculate the leakage current I of the battery cell 2 , where T 2 is the first time interval, the second time interval T 2 It is not a fixed time value. The second time interval T 2 C is the time difference between the second and third full charging of the new energy vehicle. This time difference is recorded by the battery management system (BMS). The specific value of this time difference depends on how long the owner takes to charge the new energy vehicle for the third time after the second full charging of the new energy vehicle. In addition, C 2 is the second capacity difference, C 3 is the third capacity difference, I 2 is the second time interval T 2 Leakage current of the internal battery.

[0067] S14: The battery management system (BMS) calculates the second time interval T 2 The average voltage U of the lowest voltage cell in the battery pack 2 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) sets the second time interval T 2 The sum of the voltages of the lowest voltage cells in the battery pack collected within the second time interval T 2 The total number of times the internal battery management system (BMS) collects the voltage of the battery cell is compared to obtain the second time interval T 2 The average voltage U of the lowest voltage cell in the battery pack 2 .

[0068] S15: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack 2 , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) is based on R 2 =U 2 / I 2 Calculate the short-circuit resistance R of the lowest voltage cell in the battery pack 2 , where I 2 is the second time interval T 2 Leakage current of the inner cell, U2 is the second time interval T 2 The average voltage of the lowest voltage cell in the battery pack, R 2 is the second time interval T 2 The short-circuit resistance of the lowest voltage cell in the battery pack.

[0069] S16: The battery management system (BMS) determines whether the first condition, the second condition and the third condition are all satisfied. If so, it proceeds to S17; if not, it proceeds to S18, corresponding to Figure 1 S16 in the above. The first condition is that the state of charge (SOC) of the battery is greater than a preset threshold value, the second condition is that the voltage drop rate of the lowest voltage cell in the battery pack is greater than a preset voltage drop rate and the duration is greater than a preset time, and the third condition is |R 2 -R 1 | / R 1 The value of is greater than 0.5.

[0071] S17: The battery management system (BMS) issues a battery thermal runaway warning. After the warning is completed, it enters S26, which corresponds to Figure 1 S17 in the figure. Specifically, the battery management system (BMS) pushes the warning information of battery thermal runaway to the enterprise platform and users so that the battery can be safely inspected and repaired later. That is, it can issue a warning before the battery thermal runaway occurs, thereby buying more time windows for users, avoiding property losses and casualties, and improving the safety of the entire vehicle. In addition, it can better avoid misjudgment and improve the accuracy of warning before the battery thermal runaway occurs.

[0072] S18: Charging the new energy vehicle for the N+1th time, corresponding to Figure 1 S18 in.

[0073] S19: The battery management system (BMS) continuously collects the voltage of the battery cell, which corresponds to Figure 1 S19 in the above. Specifically, during the charging process of the new energy vehicle, the voltage of the battery cell is continuously collected through the battery management system (BMS). For example, the voltage of the battery cell can be collected every 0.01 seconds.

[0074] S20: When the new energy vehicle is fully charged for the N+1th time, the battery management system (BMS) records the highest and lowest voltages of the battery cells, and calculates the N+1th capacity difference C based on the recorded highest and lowest voltages of the battery cells. N+1 , that is, corresponding to Figure 1 Specifically, when the new energy vehicle is fully charged for the N+1th time, the capacity difference between the highest voltage cell and the lowest voltage cell is calculated by the highest voltage and the lowest voltage among the voltages collected by the battery management system (BMS), and is recorded as the N+1th capacity difference CN+1 .

[0075] S21: The battery management system (BMS) performs the following operations according to the Nth time interval T: N 、Nth capacity difference C N and the N+1 capacity difference C N+1 Calculate the leakage current I of the battery cell N , that is, corresponding to Figure 1 Specifically,

[0076] Battery Management System (BMS) according to I N =(C N+1 -C N ) / T N Calculate the leakage current I of the battery cell N , where T N is the Nth time interval, the Nth time interval T N It is not a fixed time value. The Nth time interval T N C is the time difference between the Nth full charge of the new energy vehicle and the N+1th full charge of the new energy vehicle. The time difference is recorded by the battery management system (BMS). The specific value of the time difference depends on how long the owner has to wait for the N+1th charge of the new energy vehicle after the Nth full charge of the new energy vehicle. In addition, C N is the Nth capacity difference, C N+1 is the N+1th capacity difference, I N is the Nth time interval T N Leakage current of the internal battery.

[0077] S22: The battery management system (BMS) calculates the Nth time interval T N The average voltage U of the lowest voltage cell in the battery pack N , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) sets the Nth time interval T N The sum of the voltages of the lowest voltage cells in the battery pack collected during the Nth time interval T N The internal battery management system (BMS) collects the total number of times the voltage of the battery cell is compared to obtain the Nth time interval T N The average voltage U of the lowest voltage cell in the battery pack N .

[0078] S23: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack N , that is, corresponding to Figure 1 Specifically, the battery management system (BMS) is based on R N =U N / I NCalculate the short-circuit resistance R of the lowest voltage cell in the battery pack N , where I N is the Nth time interval T N Leakage current of the inner cell, U N is the Nth time interval T N The average voltage of the lowest voltage cell in the battery pack, R N is the Nth time interval T N The short-circuit resistance of the lowest voltage cell in the battery pack.

[0079] S24: The battery management system (BMS) determines whether the first condition, the second condition and the fourth condition are all satisfied. If so, it proceeds to S17; if not, it proceeds to S25, corresponding to Figure 1 S24 in the above. The first condition is that the state of charge (SOC) of the battery is greater than a preset threshold value, the second condition is that the voltage drop rate of the lowest voltage cell in the battery pack is greater than a preset voltage drop rate and the duration is greater than a preset time, and the fourth condition is |R N -R N-1 | / R N-1 The value of is greater than 0.5.

[0080] S25: Take N=N+1, that is, corresponding to Figure 1 Specifically, when N=N+1, the N+1th time of charging the new energy vehicle becomes the N+2th time of charging the new energy vehicle, and the same applies to other parameters with N.

[0081] S26: Enter S18, corresponding to Figure 1 S26 in.

[0082] In this specific implementation, N is a positive integer greater than 2, and N starts from 3.

[0083] In this specific implementation, the preset threshold is 15%, the preset voltage steep drop rate is 0.2 V / S, and the preset time is 1 second.

[0084] In addition, the present invention also provides a new energy vehicle, which uses the above-mentioned battery thermal runaway warning method to perform battery thermal runaway warning.

[0085] Functions and Effects of the Embodiments

[0086] The battery management system (BMS) determines whether the first, second and third conditions are all met. If so, the battery management system (BMS) pushes the warning information of battery thermal runaway to the enterprise platform and users so that the battery can be safely inspected and repaired later, that is, it can issue a warning before the battery thermal runaway occurs, thereby buying more time windows for users, avoiding property losses and casualties, and improving the safety of the entire vehicle; in addition, it can better avoid misjudgment and improve the accuracy of warning before the battery thermal runaway occurs. Among them, the first condition is that the battery's state of charge (SOC) is greater than the preset threshold, the second condition is that the voltage drop rate of the lowest voltage cell in the battery pack is greater than the preset voltage drop rate and the duration is greater than the preset time, and the third condition is |R 2 -R 1 | / R 1 The value of is greater than 0.5.

[0087] The battery management system (BMS) determines whether the first, second and fourth conditions are all met. If so, the battery management system (BMS) pushes the warning information of battery thermal runaway to the enterprise platform and users so that the battery can be safely inspected and repaired later, that is, it can issue a warning before the battery thermal runaway occurs, thereby buying more time windows for users, avoiding property losses and casualties, and improving the safety of the entire vehicle; in addition, it can better avoid misjudgment and improve the accuracy of warning before the battery thermal runaway occurs. Among them, the first condition is that the battery's state of charge (SOC) is greater than the preset threshold, the second condition is that the voltage drop rate of the lowest voltage cell in the battery pack is greater than the preset voltage drop rate and the duration is greater than the preset time, and the fourth condition is |R N -R N-1 | / R N-1 The value of is greater than 0.5.

[0088] In addition, the present invention can solve the problem of the early internal short circuit phenomenon not being obvious by detecting the leakage amount between two adjacent charging periods of the new energy vehicle, and also supplement the mid- and late-stage detection.

[0089] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A battery thermal runaway early warning method, characterized in that: The method comprises the following steps: S1: Charging a new energy vehicle for the first time; S2: Continuously collect the voltage of the battery cell through the battery management system (BMS); S3: When the new energy vehicle is fully charged for the first time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the first capacity difference C1 according to the recorded highest voltage and the lowest voltage of the battery cell; S4: Charging the new energy vehicle for the second time; S5: Continuously collect the voltage of the battery cell through the battery management system (BMS); S6: When the new energy vehicle is fully charged for the second time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the second capacity difference C2 according to the recorded highest voltage and the lowest voltage of the battery cell; S7: The battery management system (BMS) calculates the leakage current I1 of the battery cell according to the first time interval T1, the first capacity difference C1 and the second capacity difference C2; S8: The battery management system (BMS) calculates the average voltage U1 of the lowest voltage cell in the battery pack within the first time interval T1; S9: The battery management system (BMS) calculates the short-circuit resistance R1 of the lowest voltage cell in the battery pack; S10: Charging the new energy vehicle for the third time; S11: Continuously collect the voltage of the battery cell through the battery management system (BMS); S12: When the new energy vehicle is fully charged for the third time, the battery management system (BMS) records the highest voltage and the lowest voltage of the battery cell, and calculates the third capacity difference C3 according to the recorded highest voltage and the lowest voltage of the battery cell; S13: The battery management system (BMS) calculates the leakage current I2 of the battery cell according to the second time interval T2, the second capacity difference C2 and the third capacity difference C3; S14: The battery management system (BMS) calculates the average voltage U2 of the lowest voltage cell in the battery pack within the second time interval T2; S15: The battery management system (BMS) calculates the short-circuit resistance R2 of the lowest voltage cell in the battery pack; S16: The battery management system (BMS) determines whether the first condition, the second condition and the third condition are all satisfied. If yes, the process proceeds to S17; if not, the process proceeds to S18; S17: The battery management system (BMS) performs a battery thermal runaway warning, and after the warning is completed, it enters S26; S18: charging the new energy vehicle for the N+1th time; S19: Continuously collect the voltage of the battery cell through the battery management system (BMS); S20: When the new energy vehicle is fully charged for the N+1th time, the battery management system (BMS) records the highest and lowest voltages of the battery cells, and calculates the N+1th capacity difference C based on the recorded highest and lowest voltages of the battery cells. N+1 ; S21: The battery management system (BMS) performs the following operations according to the Nth time interval T: N 、Nth capacity difference C N and the N+1 capacity difference C N+1 Calculate the leakage current I of the battery cell N ; S22: The battery management system (BMS) calculates the Nth time interval T N The average voltage U of the lowest voltage cell in the battery pack N ; S23: The battery management system (BMS) calculates the short-circuit resistance R of the lowest voltage cell in the battery pack N ; S24: The battery management system (BMS) determines whether the first condition, the second condition and the fourth condition are all satisfied. If so, the process proceeds to S17; if not, the process proceeds to S25; S25: Take N=N+1; S26: Enter S18.

2. A battery thermal runaway early warning method as claimed in claim 1, characterized in that: The N is a positive integer greater than 2, and N starts from 3.

3. A battery thermal runaway early warning method as claimed in claim 2, characterized in that: I1 = (C2-C1) / T1, I2 = (C3-C2) / T2, I N =(C N+1 -C N ) / T N , where T1 is the first time interval, T2 is the second time interval, T N is the Nth time interval, C1 is the first capacity difference, C2 is the second capacity difference, C3 is the third capacity difference, C N is the Nth capacity difference, C N+1 is the N+1th capacity difference, I1 is the leakage current of the battery cell in the first time interval T1, I2 is the leakage current of the battery cell in the second time interval T2, I N is the Nth time interval T N Leakage current of the internal battery.

4. A battery thermal runaway early warning method as claimed in claim 3, characterized in that: R1=U1 / I1,R2=U2 / I2,R N =U N / I N , where I1 is the leakage current of the battery cell in the first time interval T1, I2 is the leakage current of the battery cell in the second time interval T2, and I N is the Nth time interval T N The leakage current of the inner cell, U1 is the average voltage of the lowest voltage cell in the battery pack in the first time interval T1, U2 is the average voltage of the lowest voltage cell in the battery pack in the first time interval T2, U N is the Nth time interval T N The average voltage of the lowest voltage cell in the battery pack, R1 is the short-circuit resistance of the lowest voltage cell in the battery pack in the first time interval T1, R2 is the short-circuit resistance of the lowest voltage cell in the battery pack in the second time interval T2, R N is the Nth time interval T N The short-circuit resistance of the lowest voltage cell in the battery pack.

5. A battery thermal runaway early warning method as claimed in claim 4, characterized in that: The first time interval T1 is the time difference between the first time the new energy vehicle is fully charged and the second time the new energy vehicle is fully charged, the second time interval T2 is the time difference between the second time the new energy vehicle is fully charged and the third time the new energy vehicle is fully charged, and the Nth time interval T N It is the time difference between the Nth time the new energy vehicle is fully charged and the N+1th time the new energy vehicle is fully charged.

6. The battery thermal runaway early warning method according to claim 1, characterized in that: The first condition is that the state of charge (SOC) of the battery is greater than a preset threshold.

7. The battery thermal runaway early warning method according to claim 1, characterized in that: The second condition is that the voltage steep drop speed of the lowest voltage cell in the battery pack is greater than a preset voltage steep drop speed and lasts for a time greater than a preset time.

8. The battery thermal runaway early warning method according to claim 1, characterized in that: The third condition is that the value of |R2-R1| / R1 is greater than 0.

5.

9. A battery thermal runaway early warning method as claimed in claim 2, characterized in that: The fourth condition is |R N -R N-1 | / R N-1 The value of is greater than 0.

5.

10. A new energy vehicle, characterized in that: The new energy vehicle uses the battery thermal runaway warning method as described in any one of claims 1 to 9 to provide battery thermal runaway warning.

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