CN104008293B - Suppress the method for designing of power battery module thermal runaway extension - Google Patents

Abstract

The present invention provides a design scheme for suppressing thermal runaway expansion of a power battery module, including: conducting a heating thermal runaway experiment in an adiabatic environment for a first power battery unit; establishing a first mathematical model for the heating thermal runaway experiment results Model; carry out a certain thermal runaway trigger experiment for a second power battery cell; establish a second mathematical model for the experimental results of the thermal runaway trigger experiment; according to the first mathematical model and the second mathematical model, establish a thermal runaway The third mathematical model of runaway expansion; carry out thermal runaway expansion experiments, and use the experimental results of thermal runaway expansion to verify the third mathematical model; reduce the power of the secondary extended battery in the third mathematical model, and obtain the ability to suppress thermal runaway through simulation calculations The discharge capacity of the expanded sub-section extended battery; experimental verification is performed on the discharge capacity of each sub-section extended battery, and a design scheme for suppressing thermal runaway expansion of the power battery module is obtained.

Description

Design method to suppress thermal runaway expansion of power battery module

technical field

The invention belongs to the field of batteries, and relates to a design method for suppressing thermal runaway expansion of a power battery module.

Background technique

Under the dual pressure of energy crisis and environmental pollution, the electrification of automobile power system has become one of the important symbols of automobile development. At present, the power battery system of new energy vehicles mostly uses power batteries with high energy density, such as lithium-ion power batteries. However, occasional safety accidents make the lithium-ion power battery system questioned.

Power battery system accidents are generally caused by thermal runaway of the power battery. Power battery thermal runaway refers to the process of instantaneously converting chemical energy into heat energy due to the internal materials of the power battery at a certain temperature. The power battery system usually includes multiple single power batteries connected in series and parallel. After some battery cells experience thermal runaway, the heat energy released violently will spread to the surrounding batteries, causing the surrounding batteries to continue to be thermally runaway due to high temperature heating. This process in which the surrounding batteries are affected by the existing thermal runaway and then thermal runaway occurs is called the expansion process of thermal runaway. The expansion of thermal runaway is very dangerous, which means that after the local thermal runaway of the power battery system occurs, the entire system will experience thermal runaway due to the expansion of thermal runaway. Preventing the occurrence of thermal runaway expansion in the power battery system and limiting thermal runaway to local areas will greatly improve the safety performance of the power battery system and ensure the safety of people's lives and property.

However, the current design scheme for suppressing the thermal runaway expansion of the power battery module is only through trial and error, and a large number of experiments are carried out to determine the design parameters. This method is time-consuming and labor-intensive, and the accuracy is not high. It will be of great significance if a scheme with high efficiency and high precision can be designed to suppress the thermal runaway expansion of the power battery module.

Contents of the invention

In view of this, it is indeed necessary to provide a design method with high efficiency and high precision to suppress thermal runaway expansion of the power battery module.

The invention provides a design method for suppressing thermal runaway expansion of a power battery module, which includes the following steps:

S1: Conduct a heating thermal runaway experiment on a first power battery cell in an adiabatic environment, and record the temperature T(t) of the first power battery cell at different times;

S2: Establish a first mathematical model T(t) _I of the first power battery cell during the heating thermal runaway experiment, use T(t) to calibrate the first mathematical model T(t) _I , the first mathematical model T(t) I A mathematical model T(t) _I is the temperature of the first power battery cell at a certain time t under heating thermal runaway conditions;

S3: Provide a second power battery unit, the second power battery unit is the same as the first power battery unit, conduct a thermal runaway trigger test on the second power battery unit, and record the second power The temperature T'(t) of the battery cell at different times;

S4: Establish a second mathematical model T(t) _II of the second power battery cell during the thermal runaway triggering experiment, and use T′(t) to calibrate the second mathematical model T(t) _II , The second mathematical model T(t) _II is the temperature of the second power battery cell at a certain moment t during the thermal runaway triggering experiment;

S5: Conduct a heating thermal runaway expansion experiment on a first power battery module, the first power battery module includes at least two battery cells, the battery cells are connected to the first power battery cell and the second power battery cell The same, and the thermal runaway trigger form in the first power battery module is the same as the thermal runaway trigger form of the second power battery cell, record the temperature T"(t) of the first power battery module at different times;

S6: Obtain a third mathematical model T(t) of the power battery module during the heating thermal runaway expansion experiment process through the first mathematical model T(t) _I and the second mathematical model T(t) _{II III} , using T″(t) to calibrate the third mathematical model T(t) _III , the third mathematical model T(t) _III is the temperature of the first power battery module during a heating thermal runaway expansion experiment. temperature at time t;

S7: Define the battery cell triggered by thermal runaway in the first power battery module as the first trigger battery, define the battery cells other than the first trigger battery as the second extended battery, and reduce the third mathematical model T (t) _III , the power of each sub-section extended battery in the third mathematical model T(t) _III is simulated to obtain the power of each sub-section extended battery that can suppress the thermal runaway expansion of the first power battery module Discharge capacity;

S8: Select a second power battery module, the second power battery module is the same as the first power module, after reducing the power of the second extended battery in the second power battery module, power the second power battery Module conducts thermal runaway expansion experiment, the thermal runaway trigger form in the second power battery module is the same as the thermal runaway trigger form of the first power battery module, using the experimental results of the second power battery module thermal runaway expansion experiment The discharge capacity of each sub-section extended battery is verified experimentally, the design parameters of the discharge capacity of each sub-section extended battery capable of suppressing the expansion of thermal runaway are determined, and a design method for suppressing the expansion of thermal runaway of the power battery module is obtained.

The design method for suppressing the thermal runaway expansion of the power battery module provided by the present invention is to establish a mathematical model of the thermal runaway expansion process of the power battery module, and use the mathematical model to perform simulation calculations to obtain the parameters of the discharge capacity of each sub-section extended battery , and carry out experimental verification on the parameters of the discharge capacity. After the thermal runaway trigger of the battery cells triggered in the first section is triggered, the extended battery cells in the second section are quickly discharged according to the parameters of the discharge capacity, so as to suppress heat. The purpose of uncontrolled expansion. This design scheme can greatly shorten the experimental time, improve efficiency, and effectively save research and development costs. In addition, the design method is verified by experiments with high accuracy.

Description of drawings

Fig. 1 is a comparison chart of the calculation results and the experimental results of the first mathematical model in the embodiment of the present invention.

Fig. 2 is a comparison chart of the calculation results and the experimental results of the second mathematical model in the embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a power battery module provided in an embodiment of the present invention.

FIG. 4 is a comparison chart of calculation results and experimental results of a battery cell obtained through a third mathematical model in an embodiment of the present invention.

Fig. 5 is a comparison chart of the calculation results and the experimental results of the battery pole obtained through the third mathematical model in the embodiment of the present invention.

FIG. 6 is a simulation calculation result of expansion of thermal runaway after reducing the power of the secondary extended battery in the embodiment of the present invention.

FIG. 7 is an experimental result when the state of charge of the second to sixth battery cells is 75% in the embodiment of the present invention.

FIG. 8 is an experimental result when the state of charge of the second to sixth battery cells is 50% in the embodiment of the present invention.

FIG. 9 is a structural block diagram of a battery module design method for suppressing expansion of thermal runaway through discharge according to an embodiment of the present invention.

Description of main component symbols

Ternary lithium ion power battery 100

battery cell 10

Positive pole 11

Negative pole 12

Metal connection piece 20

metal clamp 30

Insulation 40

Lancet 50

The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

An embodiment of the present invention provides a method for quantitatively analyzing heat transfer during thermal runaway expansion of a power battery module, which includes the following steps:

S1: Conduct a heating thermal runaway experiment on a first power battery cell in an adiabatic environment, and record the temperature T(t) of the first power battery cell at different times;

S2: Establish a first mathematical model T(t) _I of the first power battery cell during the heating thermal runaway experiment, use T(t) to calibrate the first mathematical model T(t) _I , the first mathematical model T(t) I A mathematical model T(t) _I is the temperature of the first power battery cell at a certain time t under heating thermal runaway conditions;

S3: Provide a second power battery unit, the second power battery unit is the same as the first power battery unit, conduct a thermal runaway trigger test on the second power battery unit, and record the second power The temperature T'(t) of the battery cell at different times;

S4: Establish a second mathematical model T(t) _II of the second power battery cell during the thermal runaway triggering experiment, and use T′(t) to calibrate the second mathematical model T(t) _II , The second mathematical model T(t) _II is the temperature of the second power battery cell at a certain moment t during the thermal runaway triggering experiment;

S5: Conduct a heating thermal runaway expansion experiment on a first power battery module, the first power battery module includes at least two battery cells, the battery cells are connected to the first power battery cell and the second power battery cell The same, and the thermal runaway trigger form in the first power battery module is the same as the thermal runaway trigger form of the second power battery cell, record the temperature T"(t) of the first power battery module at different times;

S6: Obtain a third mathematical model T(t) of the power battery module during the heating thermal runaway expansion experiment process through the first mathematical model T(t) _I and the second mathematical model T(t) _{II III} , using T″(t) to calibrate the third mathematical model T(t) _III , the third mathematical model T(t) _III is the temperature of the first power battery module during a heating thermal runaway expansion experiment. temperature at time t;

S7: Define the battery cell triggered by thermal runaway in the first power battery module as the first trigger battery, define the battery cells other than the first trigger battery as the second extended battery, and reduce the third mathematical model T (t) _III , the power of each sub-section extended battery in the third mathematical model T(t) _III is simulated to obtain the power of each sub-section extended battery that can suppress the thermal runaway expansion of the first power battery module Discharge capacity;

S8: Select a second power battery module, the second power battery module is the same as the first power module, after reducing the power of the second extended battery in the second power battery module, power the second power battery Module conducts thermal runaway expansion experiment, the thermal runaway trigger form in the second power battery module is the same as the thermal runaway trigger form of the first power battery module, using the experimental results of the second power battery module thermal runaway expansion experiment The discharge capacity of each sub-section extended battery is verified experimentally, the design parameters of the discharge capacity of each sub-section extended battery capable of suppressing the expansion of thermal runaway are determined, and a design method for suppressing the expansion of thermal runaway of the power battery module is obtained.

In step S1, the first power battery unit may be a lithium-ion power battery unit. Performing a thermal runaway test on the first power battery unit in an adiabatic environment is conducive to accurately obtaining the heat released and absorbed by the first power battery unit during the thermal runaway process. In this embodiment, an adiabatic acceleration calorimeter is used to conduct a thermal runaway test on the first power battery unit, and the first power battery unit is a ternary lithium-ion power battery.

The first mathematical model T(t) _I of the first power battery unit during the heating thermal runaway experiment can be obtained by using the chemical reaction kinetic equation and Ohm's law.

For the first power battery unit, the establishment of the first mathematical model T(t) _I may include the following steps:

S21: Obtain the calculation formula of the sum Q _I (t) of the heat generation power generated by the internal chemical reaction of the first power battery cell;

S22: Establish the first power battery cell according to Q _I (t) calculation formula;

S23: According to A calculation formula for T(t) _I of the first power battery unit is established.

In step S21, the expression of described Q _I (t) is:

Q1( _t )=Qr(t)+ _{Qe (} t) (1).

Wherein, Q _r (t) represents the heat generation power of the chemical reaction of the material inside the first power battery cell, and Q _e (t) represents the electric power released by the short circuit in the first power battery cell.

The expression of said Q _r (t) is:

Q _r (t) = Q _SEI + Q _anode + Q _separator + Q _cathode + Q _electrolyte + Q _PVDF (2).

Among them, Q _SEI represents the heat generation power of the SEI film decomposition reaction; _{Q anode} represents the heat generation power of the reaction between the negative electrode and the _electrolyte ; Q _separator represents the heat absorption power of the diaphragm decomposition; Decomposition heat generation power; Q _PVDF represents the heat generation power of the adhesive decomposition reaction. The Q _SEI , Q _anode , Q _separator , Q _cathode , Q _electrolyte and Q _PVDF can all be described in the form of Arrhenius formula. For example, the calculation formula of Q _SEI is:

Among them, H _SEI represents the total energy that can be released by the decomposition reaction of the SEI film, and the unit is J, which can be selected according to the existing literature; c _SEI (t) represents the normalized concentration of the SEI film, that is, c _SEI (0 )=1, when the reaction terminates, c _SEI (∞)=0, c _SEI (t) is a variable that changes with time during the simulation process; A _SEI represents the frequency factor of the SEI membrane reaction, and the unit is s ^{- 1} ; E _{a, SEI} is the activation energy of chemical reaction, the unit is J/mol, can choose according to existing literature; R is ideal gas constant, R=8.314J/(mol K); T _i (t) is battery The temperature of the monomer at time t. It can be understood that the expressions of Q _anode , Q _separator , Q _cathode , Q _electrolyte and Q _PVDF are obtained by modifying the subscript of the Q _SEI expression accordingly.

According to the chemical reaction kinetic equation and the law of energy conservation, the calculation formula of the first power battery unit Q _e (t) is:

For the first power battery cell, when the internal temperature T _i (t) of the battery at time t is less than or equal to the melting temperature T _onset of the internal diaphragm of the first power battery cell, only a micro-short circuit occurs inside the first power battery cell , and the corresponding reaction heat generation power is Q _short (t). In the expression of Q _short (t), A _short is the rate factor of the weak short circuit, and b is the exponent term of the short circuit. When the internal temperature T _i (t) of the battery at time t is greater than the melting temperature T _onset of the internal diaphragm of the first power battery cell, a large-scale internal short circuit will occur inside the first power battery cell, and the corresponding heat generation power is Where ΔH represents the total energy released by the short circuit, Δt represents the average reaction time, which determines the speed of the reaction, Represents the energy of a weak short circuit that has occurred.

The calculation formula of Q _I (t) can be obtained by substituting the calculation formulas of Q _r (t) and Q _e (t) into Q _I (t)=Q _r (t)+Q _e (t).

In step S22, according to the law of energy conservation, the first power battery unit satisfies the formula during the thermal runaway process:

Wherein, M is the mass of the first power battery unit in kg; C _p is the specific heat capacity of the first power battery unit in J/(kg·K). Bring the calculation formula of Q _I (t) into the formula (5) to get calculation formula.

In step S23, the temperature of the first power battery cell at a certain moment t under the heating thermal runaway condition, that is, the first mathematical model T(t) _I satisfies the formula:

T(0) _I is a known quantity. according to The calculation formula and the formula (6) can get the calculation formula of the first mathematical model T(t) _I .

The step of using T(t) to calibrate the first mathematical model T(t) _I includes: for Qr( _t ), selecting a set of A _SEI and E _{a, SEI} , A _anode and E a according to existing literature _{a, anode} , A _separator and E _{a, separator} , A _cathode and E _{a, cathode} , A _electrolyte and E _{a, electrolyte} , and the value of A _{a, PVDF} and E _{a, PVDF} ; for Q _e (t), according to the actual A set of values for A _short , b, Δt, and ΔH was selected empirically. Utilize described first mathematical model T (t) ₁ to carry out simulation calculation and obtain the temperature of described first power battery cell at different moments, if the temperature obtained through described simulation calculation and the experimental result T (t) in step S1 If the difference is large, adjust A _SEI and E _{a, SEI} , A _anode and E _{a, anode} , A _separator and E _{a, separator} , A _cathode and E _{a, cathode} , A _electrolyte and E _{a, electrolyte} within a certain range, The values of A _{a, PVDF} and E _{a, PVDF} and A _short , b, Δt and ΔH, each adjustment adopts the first mathematical model T(t) _I to carry out a simulation calculation until the simulation calculation result is close to the experimental result .

In this embodiment, the calibrated A _SEI and E _{a, SEI} , A _anode and E _{a, anode} , A _separator and E _{a, separator} , A _cathode and E _{a, cathode} , A _electrolyte and E _{a, electrolyte} , A _{a , PVDF} and E _{a, see Table 1 for the values of PVDF} and A _short , b, Δt and ΔH. Since the ternary lithium ion power battery is used in this embodiment, the positive electrode of the ternary material has two different chemical reactions, so the values of A _cathode , E _{a , cathode} , and H _cathode in Table 1 have two values. The groups are A _{cathode, 1} , E _{a, cathode, 1} , H _{cathode, 1} , A _{cathode, 2} , E _{a, cathode, 2} , H _{cathode, 2} .

Table 1

symbol preferred value symbol preferred value A _SEI 1.667×10 ¹⁵ (s ^-1 ) A _{cathode, 2} 1.077×10 ¹² (s ^-1 ) E. _{a, SEI} 1.3508×10 ⁵ (J·mol ^-1 ) E _{a, cathode, 2} 1.5888×10 ⁵ (J·mol ^-1 ) H _SEI 2.5849×10 ⁴ (J) H _{cathode, 2} 1.5046×10 ⁴ (J) A _{a node} 2.5×10 ¹³ (s ^-1 ) A _Electrolyte 5.14×10 ²⁵ (s ^-1 ) E. _{a, a node} 1.3508×10 ⁵ (J·mol ^-1 ) E. _{a,electrolyte} 2.74×10 ⁵ (J·mol ^-1 ) h _{a node} 1.72394×10 ⁵ (J) h _Electrolyte 3.078×10 ⁴ (J) A _separator 1.5×10 ⁶¹ (s ^-1 ) A _PVDF 1.917×10 ²⁵ (s ^-1 ) E. _{a, separator} 5×10 ⁵ (J·mol ^-1 ) E. _{a, PVDF} 2.86×10 ⁵ (J·mol ^-1 ) h _separator -3.895×10 ³ (J) H _PVDF 3.621×10 ⁴ (J) A _{cathode, 1} 1.75×10 ⁹ (s ^-1 ) A _short 1.048×10 ^-8 (s ^-1 ) E _{a, cathode, 1} 1.1495×10 ⁵ (J·mol ^-1 ) b 39.279 H _{cathode, 1} 1.3792×10 ⁴ (J) Δt 4(s) ΔH 385000(J)

It can be understood that for the first power battery unit, reasonable simplification of the first mathematical model T(t) _I may be further included. In the process of simplifying the first mathematical model T(t) _I , it should be ensured that the simulation calculation results of the first mathematical model T(t) _I are similar to the experimental results, that is, the accuracy of the simulation calculation of the first mathematical model T(t) _I should be guaranteed . Since in the first power battery cell, when the battery internal temperature T _i (t) at time t is less than or equal to the melting temperature T _onset of the internal diaphragm of the first power battery cell, only the internal temperature of the first power battery cell Micro-short circuit, the energy generated by this micro-short circuit is small and can be ignored. So in the first mathematical model T(t) _I of heating thermal runaway, step S21 may further include simplifying _Qe (t) as:

Please refer to FIG. 1 , in this embodiment, using the first mathematical model T(t) _I , the simulation calculation result of the first power battery unit is compared with the experimental result T(t), which has better accuracy.

In step S3, a thermal runaway triggering experiment is performed on the second power battery unit, the form of the trigger is not limited, as long as it can be guaranteed that the thermal runaway trigger can cause the second power battery unit to release enough heat , so that the adjacent battery cells have enough temperature rise and thermal runaway occurs. Preferably, the triggering form of thermal runaway is acupuncture triggering, overcharging triggering or heating triggering. When acupuncture is used as the thermal runaway trigger, the diameter of the puncture needle is preferably 5-8 mm, and the puncture speed is preferably 10-30 mm/s. In this embodiment, a thermal runaway triggering experiment is performed on the second power battery unit by acupuncture, the diameter of the needle 50 is 8 mm, and the puncture speed is 10 mm/s.

In step S4, the establishment of the second mathematical model T (t) _II further includes the following steps:

S41: Establish a calculation formula for the heat generation power Q _II (t) of the second power battery unit during the thermal runaway triggering process;

S42: According to Q _II (t), it is obtained that calculation formula;

S43: According to Get the calculation formula of T(t) _II .

In step S41, the calculation formula of said Q _II (t) is:

Q _II (t) = Q _r (t) + Q _{e_in} (t) - Q _h (t) (8).

Among them, Q _r (t) is the reaction heat power released by the thermochemical reaction of the second power battery unit during the thermal trigger experiment; Q _{e_in} (t) is the heat power released instantaneously by the internal short circuit; Q _h (t) is the Describe the heat dissipation power of the second power battery unit. Since the second power battery cell is exactly the same as the first power battery cell, the calculation formula of Q _r (t) in formula (8) is the same as the Q _r (t) of the first power battery cell The calculation formula of t) is the same, that is, Q _r (t) in formula (8) can be calculated according to formulas (2) and (3) in step S21. In this embodiment, for the second power battery unit, A _SEI and E _a,SEI after calibration, A _anode and E _a,anode , A _separator and E _a,separator , A _cathode and E _a,cathode , The values of A _electrolyte and E _{a, electrolyte} , A _{a, PVDF} and E _{a, PVDF} and A _short , b, Δt and ΔH are the same as those in the first power battery unit, please refer to Table 1.

Draw according to the variant form of chemical reaction kinetic equation, the calculation formula of described Q _{e_in} (t) is:

Among them, ΔH represents the sum of the electric energy released due to the short circuit during the short-circuit process triggered by the thermal runaway of the second power battery cell. For a specific battery cell, ΔH is a known quantity; ∫Q _{e_in} (t)dt represents the The electrical energy that has been released at time t; v represents the reaction rate in exponential form.

The calculation formula of said Q _h (t) is:

Q _h (t) = h _II ·A _II ·(T(t) _II -T _amb (t)) (10).

Among them, h _II represents the heat transfer coefficient of the second power battery unit to the environment, the unit is W/(m ² ·K); A _II represents the surface heat dissipation area of the second power battery unit, the unit is m ² ; T( t) _II represents the temperature of the simulation model of the second power battery unit, the unit is K; T _amb (t) represents the temperature of the surrounding environment, the unit is K.

In step S42, according to the law of energy conservation, the second power battery unit satisfies the formula during the thermal runaway triggering process:

Wherein, M is the mass of the second power battery unit in kg; C _p is the specific heat capacity of the second power battery unit in J/(kg.K). Bring the calculation formula of Q _II (t) into the formula (11) to get calculation formula.

In step S43, the temperature of the second power battery cell at a certain moment t under the trigger condition of thermal runaway, that is, the second mathematical model T(t) _II satisfies the formula:

T(0) _II is the temperature before the thermal runaway of the second power battery unit is triggered, which is a known quantity. According to step S42 The calculation formula and the formula (12) can get the calculation formula of the second mathematical model T(t) _II .

The step of using T'(t) to calibrate the second mathematical model T(t) _II includes: selecting a group of ΔH, v, h _II according to empirical values, and using the second mathematical model T(t) _II to simulate Calculate the temperature of the second power battery cell at different times, if the temperature calculated by the simulation of the second mathematical model T(t) _II differs greatly from the experimental result T'(t) in step S3, then in Adjust the values of ΔH, v, and h _II within a certain range, and use the second mathematical model T(t) _II to perform a simulation calculation every time the value of ΔH, v, and h _II is adjusted, until the result of the simulation calculation is consistent with the experimental result T′( t) until close. In this embodiment, after calibration, ΔH=385000J, v=0.001, h _II =2W/(m ² ·K).

Please refer to FIG. 2 , it can be seen from the figure that the calculation result of the second power battery unit through the second mathematical model T(t) _II has better accuracy than the experimental result T′(t).

It can be understood that reasonable simplification of the second mathematical model T(t) _II may be further included. Because the second mathematical model T(t) _II includes some secondary factors that have less influence in the calculation of the thermal runaway expansion model. Approximating or ignoring these less influential secondary factors can improve the simulation calculation speed of the thermal runaway extended model. In the process of simplifying the second mathematical model T (t) _II , it should be ensured that the simulation calculation results of the second mathematical model T (t) _II are similar to the experimental results, that is, the accuracy of the simulation calculation of the second mathematical model T (t) _II should be guaranteed . Since there is an exponential form in the calculation formula of said Q _{e_in} (t), the calculation speed is relatively slow, so, under the condition of ensuring the simulation calculation accuracy, the equation can be: Simplifies to a linear equation:

In step S6, at least two battery cells in the first power battery module may be connected in series or in parallel. Please refer to FIG. 3 , in this embodiment, the first power battery module is a 25Ah ternary lithium-ion power battery 100 with a shell, and the ternary lithium-ion power battery 100 includes six battery cells 10, a plurality of The metal connection piece 20 , a plurality of metal clamps 30 and a plurality of heat insulation layers 40 . Each battery cell 10 includes a positive pole 11 and a negative pole 12 . The metal connecting piece 20 is used to connect six battery cells 10 in series; the metal clamp 30 is used to clamp the battery cells 10 ; the heat insulating layer 40 is used to isolate the battery cells 10 with 30 metal clamps.

Using the lumped parameter method, each battery cell and the pole of each battery cell are regarded as nodes with a single mass, a single heat capacity and a single temperature. Each node has its own mass M _i , heat capacity C _pi and temperature T _i .

Define the battery cell that is subjected to the thermal runaway triggering experiment in the first power battery module as the first trigger battery, and define the battery cells other than the first trigger battery in the first power battery module as the second extended battery . The obtaining of the third mathematical model T _i (t) _III may further include the following steps:

S61: respectively establish the energy change rate Q _i calculation formulas of the trigger battery of the first section, the extended battery of the second section, the battery pole, and the fixture under the condition of heating thermal runaway expansion;

S62: According to Q _i , respectively establish the conditions of the first trigger battery, the second extended battery, the battery pole and the fixture under the condition of heating thermal runaway expansion calculation formula;

S63: According to The calculation formulas of T _i (t) _III of the first trigger battery, the second extended battery, the battery pole and the fixture under the condition of heating thermal runaway expansion are respectively established.

In step S61, according to the law of energy conservation, under the condition of heating thermal runaway expansion, the calculation formula of the energy change rate Q _i of the first trigger battery, the second extension battery, the battery pole and the fixture can be expressed as:

Q _i (t) = Q _sheng (t) - Q _san (t) (14).

Among them, Q _san (t) represents heat dissipation power; Q _sheng (t) represents heat generation power. For the first trigger cell Q _sheng (t)=Q _I (t)=Q _r (t)+Q _{e_in} (t), -Q _san (t)=-∑Q _ij (t)-Q _ih (t); For the sub-section extended battery, Q _sheng (t)=Q _II (t)=Q _r (t)+Q _e (t), -Q _san (t)=-∑Q _ij (t)-Q _ih (t) ; Since poles and fixtures are pure metal materials, no chemical reaction will occur, so for poles and fixtures, Q _sheng (t)=0, -Q _san (t)=-∑Q _ij (t)-Q _ih (t). Among them, Q _ij represents the heat dissipation power from node i to node j; Q _ih (t) represents the heat dissipation power from node i to the surrounding environment.

For the power battery module, the calculation formula of Q _i is specifically:

The thermal resistance method is used to establish the heat transfer model between nodes. According to the Fourier heat conduction formula, the calculation formula of the heat dissipation power Q _ij for heat transfer from node i to node j is:

Q _ij (t)=A _ij ·(T _i (t) _III -T _j (t) _III )/R _ij (16).

Among them, A _ij (t) represents the effective heat transfer area between node i and node j, the unit is m ² ; R _ij (t) represents the thermal resistance of heat transfer between node i and node j, the unit is (m ² ·K)/W; T _i (t) _III represents the temperature of node i at time t, and T _j (t) _III represents the temperature of node j at time t.

According to the Fourier heat conduction formula, the calculation formula of the heat dissipation power Q _ih (t) for node i to dissipate heat to the surrounding environment is:

Q _ih (t)＝A _ih ·(T _i (t) _III -T _h (t))/R _ih (17)

Wherein, the A _ih (t) represents the equivalent area of the node i for heat dissipation to the environment, and the unit is m ² ; the equivalent thermal resistance of R _ih (t) to the heat dissipation of the environment, the unit is (m ² ·K)/W; T _i (t) _III is the temperature of node i at time t, and T _h (t) represents the ambient temperature at time t.

In the formula (15), the expression of the short-circuit energy Q _e (t) of the extended battery in the second section is:

in, is the temperature calculated by interpolation, the Satisfies the formula:

Among them, α is the weight factor in the calculation process, 0<α<0.5. Preferably, α=0.23; T _i-1 (t) is the model calculation temperature of the i-1th battery cell, T _i (t) is the model calculation temperature of the i-th battery cell, i=2,3 , 4, 5 or 6.

In step S62, according to the law of conservation of energy:

It can be obtained respectively that the triggering battery of the first section, the extended battery of the second section, and the battery pole and the fixture are heated under the condition of thermal runaway expansion. calculation formula.

In step S63, under the condition of heating thermal runaway expansion, T _i (t) _III of the trigger battery of the first section, the extended battery of the second section, and the battery pole and the clamp satisfy the formula:

Wherein, T(0) _III is a known quantity. Will Introducing formula (21) to obtain the third mathematical model T(t) _III of the trigger battery of the first section, the extended battery of the second section, and the battery pole and fixture under the condition of heating thermal runaway expansion.

The use of T"(t) to calibrate the third mathematical model T(t) _III may include: selecting a set of values of R _ij and A _ij according to existing literature, using the third mathematical model T( t) _III performs simulation calculation to obtain the temperature of each node of the power battery module at different times, if it is quite different from the experimental result T″(t) in step S5, then adjust the values of R _ij and A _ij within a certain range, every Adjust once and use the third mathematical model T(t) _III to perform a simulation calculation until the simulation calculation result is close to the experimental result.

The first trigger battery in the first power battery module is defined as the first battery cell, the battery cell adjacent to the first battery cell is the second battery cell, and the battery cell adjacent to the second battery cell is The adjacent battery cell is the third battery cell, and so on. In this embodiment, please refer to Table 2 for a set of preferred results of the calibrated values of R _ij and A _ii .

Table 2

Please refer to Figure 4-5, it can be seen from the figure that the first trigger battery and its positive and negative electrode columns and the second extended battery and its positive and negative electrode columns calculated by the third mathematical model in this embodiment are heated Compared with the experimental results, the temperature at different times during the runaway expansion process has smaller errors, which shows that the third mathematical model T(t) _III has better precision. It can also be seen from Figure 5 that the time difference between the thermal runaway of the first battery cell and the second battery cell is about 480s, and the core temperature of the second battery cell reaches 110°C before thermal runaway occurs.

In step S7, after reducing the power of the secondary extended battery in the third mathematical model, the instantaneous electric power release value Q _e of the secondary extended battery satisfies the formula:

It can be understood that formula (22) can be further simplified as:

Among them, _Tonset represents the melting temperature of the internal diaphragm of the extended battery in the second section, that is, the thermal runaway temperature; ΔH represents the total electric energy released by the short circuit; Represents the energy of the weak short circuit that has occurred; Δt represents the duration of the large-scale internal short circuit when the temperature reaches the thermal runaway temperature point; K _SOC represents the percentage of the total power of the secondary extended battery after discharge to the initial total power of the secondary extended battery .

During the entire thermal runaway expansion process, the sum ΔH of the electric energy release of all sub-section extended battery cells should satisfy the formula:

ΔH＝∫Q _e dt......(24)

In the process of simulation calculation, for the triggering battery of the first section, K _SOC is equal to 100%; for each extended battery of the second section, K _SOC is less than 100%, and the K _SOC of each extended battery of the second section is equal. In this embodiment, for the second battery cell to the sixth battery cell, several sets of different K _SOCs are set for simulation calculation, wherein, in each set of data, the second battery cell to the sixth battery cell The K _SOC of the monomers are all equal. Please refer to Table 3 for details:

table 3

Please refer to FIG. 6 . It can be seen from the figure that in the simulation calculation, when the K _SOC is between 50% and 100%, thermal runaway will occur in the second battery cell. When the K _SOC is 80% to 100%, thermal runaway expansion will occur in the third battery cell, and when the K _SOC of the second battery cell is 75% or below, the third battery cell will not Expansion of thermal runaway occurs; indicating that the design parameter of the discharge capacity of the secondary extended battery is the boundary value K _SOC-B ≈75% of the electric quantity of the secondary extended battery. In the simulation calculation, when the power of the second battery cell to the sixth battery cell is lower than the boundary value K _SOC-B , the expansion of thermal runaway inside the power battery module can be effectively suppressed.

In step S8, experimental verification is performed on the discharge capacity of each sub-section extended battery. Specifically, select a second power battery module, the second power battery module is the same as the first power module, and select multiple sets of experiments near the power boundary value K _SOC-B of the sub-section extended battery obtained in the simulation calculation Parameters, discharge the power of the second extension battery in the second power battery module according to K _SOC-B , conduct a thermal runaway expansion experiment on the second power battery module, and the thermal runaway in the second power battery module triggers The form is the same as that of the thermal runaway triggering form of the first power battery module, and the experimental results of the thermal runaway expansion experiment of the second power battery module are used to verify the discharge capacity of each sub-section extended battery, and the experimental verification is carried out Obtain the boundary value K _SOC-B of the next extended battery in the actual situation.

In this embodiment, experiments were carried out by selecting K _SOC as 75% and 50% respectively. The specific design situation is shown in Table 4:

Table 4

Please refer to Figure 7. It can be seen from the figure that when the K _SOC of the extended battery in the second section is 75%, the time difference between the thermal runaway of the first battery cell and the second battery cell is about 680s, which is the same as that in Figure 5 Compared with the time difference between the thermal runaway of the first battery cell and the second battery cell when the secondary extended battery is not discharged, which is about 480s, the delay of the thermal runaway of the second battery cell is longer. This increase in time delay caused the core temperature of the second battery cell to reach 220°C before thermal runaway occurred in the experiment, much higher than the 110°C in Figure 5. It can also be seen from the figure that when the thermal runaway of the second battery cell occurs, the maximum temperature reaches 928°C, which leads to the sequential thermal runaway of the third battery cell to the sixth battery cell. This may be because the thermal stability of the power battery module in this embodiment changes drastically when the state of charge is around 75%. The result of Fig. 7 shows that although K _SOC-B = 75% in the simulation calculation, in the actual process, K _SOC-B should be less than 75%.

Please refer to Fig. 8. It can be seen from the figure that when the K _SOC of the extended battery in the second section is 50%, after the first battery cell is triggered by acupuncture, the temperature of the second battery cell rises slowly, and the maximum The temperature reached 263°C. No thermal runaway occurred in the second battery cell to the sixth battery cell. It can be understood that the lack of thermal runaway of the second battery cell has a certain relationship with the rise of the thermal runaway temperature point T _onset of the power battery module in this embodiment when the state of charge is 50%. The experimental results in Fig. 8 show that in the actual process, K _SOC-B is greater than 50%.

Through experimental verification, it can be concluded that in this embodiment, the discharge capacity of the sub-section extended battery cell has a boundary value K _SOC-B , 50%<K _SOC-B <75%.

According to the experimental verification results, the design parameters of the discharge capacity of the battery cells capable of suppressing the expansion of thermal runaway are determined. Specifically, after the thermal runaway of the first battery cell occurs, within the time limit for the thermal runaway to extend to the second battery cell, the second to sixth battery cells in the power battery module are discharged as soon as possible to The power is less than or equal to K _SOC-B . In this embodiment, when K _SOC =100%, the thermal runaway interval between the first battery cell and the second battery cell is 481s, and the thermal runaway interval between the second battery cell and the third battery cell is 481s. The thermal runaway interval between the third battery cell and the fourth battery cell is 156s, the thermal runaway interval between the fourth battery cell and the fifth battery cell is 157s, and the fifth battery cell and The thermal runaway interval of the sixth battery cell is 137s. The average time interval of thermal runaway expansion between adjacent battery cells can be selected as any value from 137s to 161s. In this embodiment, the average time interval of thermal runaway expansion between adjacent battery cells is selected as 160s. In order to suppress the expansion of thermal runaway, the power of adjacent battery cells should be reduced to 50% or less than 50% of the initial power as soon as possible within 160s. According to the formula: discharge current I=(C _e ×3600×K _SOC )/(nΔt), the minimum discharge current at which the second battery cell to the sixth battery cell does not continue to expand thermal runaway can be obtained. Among them, C _e represents the initial power of the first trigger battery in the power battery module, in AH; Δt represents the average time interval of thermal runaway expansion between adjacent battery cells, in s; n represents the number of average time intervals. In this embodiment, C _e =25AH; Δt=160s; for the second battery cell, n=1; for the third battery cell, n=2; for the fourth battery cell, n=3; The fifth battery cell, n=4; for the sixth battery cell, n=5, K _SOC is less than 50%, it can be obtained through calculation that the second battery cell to the sixth battery cell do not continue The minimum discharge currents for thermal runaway expansion are I ₂ =281A; I ₃ =141A. I ₄ =94A; I ₅ =70A; I ₆ =56A.

Please refer to FIG. 9 . In this embodiment, a schematic diagram of a battery module design method for suppressing expansion of thermal runaway is provided. In addition to powering the power device 60 , the ternary lithium-ion power battery needs to supply power to the power device 60 . In order to suppress possible expansion of thermal runaway, each cell of the ternary lithium-ion power battery is connected to a safety discharge device through a circuit. In order to prevent thermal runaway expansion of the third adjacent battery, the safety discharge device should enable any battery to be quickly discharged to 50% state of charge at a current of 141A.

In addition, those skilled in the art can also make other changes within the spirit of the present invention, and these changes made according to the spirit of the present invention should be included in the scope of protection claimed by the present invention.

Claims (10)

1. A design method for suppressing power battery module thermal runaway expansion, comprising the following steps: S1: Conduct a heating thermal runaway experiment on a first power battery cell in an adiabatic environment, and record the temperature T(t) of the first power battery cell at different times; S2: Establish a first mathematical model T(t) _I of the first power battery cell during the heating thermal runaway experiment, use T(t) to calibrate the first mathematical model T(t) _I , the first mathematical model T(t) I A mathematical model T(t) _I is the temperature of the first power battery cell at a certain time t under heating thermal runaway conditions; S3: Provide a second power battery unit, the second power battery unit is the same as the first power battery unit, conduct a thermal runaway trigger test on the second power battery unit, and record the second power The temperature T'(t) of the battery cell at different times; S4: Establish a second mathematical model T(t) _II of the second power battery cell during the thermal runaway triggering experiment, and use T′(t) to calibrate the second mathematical model T(t) _II , The second mathematical model T(t) _II is the temperature of the second power battery cell at a certain moment t during the thermal runaway triggering experiment; S5: Conduct a heating thermal runaway expansion experiment on a first power battery module, the first power battery module includes at least two battery cells, the battery cells are connected to the first power battery cell and the second power battery cell The same, and the thermal runaway trigger form in the first power battery module is the same as the thermal runaway trigger form of the second power battery cell, record the temperature T"(t) of the first power battery module at different times; _S6 : Obtain a third mathematical model _T ( t) _III , using T″(t) to calibrate the third mathematical model T(t) _III , the third mathematical model T(t) _III is the thermal runaway expansion experiment of the first power battery module during heating the temperature at a certain time t; S7: Define the battery cell triggered by thermal runaway in the first power battery module as the first trigger battery, define the battery cells other than the first trigger battery as the second extended battery, and reduce the third mathematical model T (t) _III , the power of each sub-section extended battery in the third mathematical model T(t) _III is simulated to obtain the power of each sub-section extended battery that can suppress the thermal runaway expansion of the first power battery module Discharge capacity; S8: Select a second power battery module, the second power battery module is the same as the first power battery module, after reducing the power of the second extended battery in the second power battery module, The thermal runaway extension experiment is carried out on the battery module, the thermal runaway trigger form in the second power battery module is the same as that of the first power battery module, and the experimental results of the thermal runaway extension experiment of the second power battery module are used Perform experimental verification on the discharge capacity of each sub-section extended battery, determine the design parameters of the discharge capacity of each sub-section extended battery that can suppress the expansion of thermal runaway, and obtain a design method for suppressing the expansion of thermal runaway of the power battery module. 2. The design method for suppressing power battery module thermal runaway expansion according to claim 1, wherein the establishment of the first mathematical model T (t) _I further comprises the following steps: S21: Obtain the calculation formula of the sum Q _I (t) of the heat generation power generated by the internal chemical reaction of the first power battery cell, said Q _I (t)=Q _r (t)+Q _e (t), Q _r (t) represents the heat generation power of the chemical reaction of the internal material of the first power battery cell, and Q _e (t) represents the electric power released by the short circuit in the battery; S22: According to Q _I (t), establish the the calculation formula for ; and S23: According to Establish the formula for calculating the T(t) _I of the battery cell that is triggered in the first section. 3. The design method for suppressing thermal runaway expansion of a power battery module according to claim 2, wherein the formula for calculating Qr( _t ) is: Q _r (t)＝Q _SEI +Q _anode +Q _separator +Q _cathode +Q _electrolyte +Q _PVDF , Among them, Q _SEI represents the heat generated by the SEI film decomposition reaction; _{Q anode} represents the heat generated by the reaction between the negative electrode and the _electrolyte ; Q _separator represents the heat absorbed by the decomposition of the diaphragm; Heat; Q _PVDF represents the heat generated by the decomposition reaction of the adhesive, and the calculation formula of the Q _SEI is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; dc</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; I</span>}}}{{\mathrm{<span\; class="notranslate">\; RT</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$ Among them, H _SEI represents the total energy that can be released by the decomposition reaction of the SEI film, and the unit is J; c _SEI (t) represents the normalized concentration of the SEI film; A _SEI represents the frequency factor of the SEI film reaction, and the unit is s ^-1 ; E _{a, SEI} is the activation energy of the chemical reaction, the unit is J/mol; R is the ideal gas constant; T _i (t) is the temperature of the battery cell at time t, the Q _anode , Q _separator , g _cathode , the calculation formulas of Q _electrolyte and Q _PVDF are obtained by modifying the subscripts of the Q _SEI calculation formula to anode, separator, cathode, electrolyte or PVDF respectively. 4. The design method for suppressing thermal runaway expansion of a power battery module according to claim 2, wherein the formula for calculating Q _e (t) is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 273</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; ,</span>& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>\\ \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ,</span>$ Among them, A _short is the rate factor of the weak short circuit, b is the exponential term of the short circuit, ΔH represents the total energy released by the short circuit, Δt represents the average reaction time, Represents the energy of the weak short circuit that has occurred, Q _short (t) represents the heat generation power of the reaction, T _i (t) represents the internal temperature of the first power battery cell at time t; T _onset represents the first power battery The melting temperature of the internal diaphragm of the cell; T represents the temperature of the first power battery cell at different times; T _short represents the temperature at which a weak short circuit occurs in the first power battery cell. 5. The design method for suppressing thermal runaway expansion of power battery modules according to claim 4, characterized in that, the is further simplified to 6. The design method for suppressing thermal runaway expansion of a power battery module according to claim 1, wherein the establishment of the second mathematical model T(t) _II comprises the following steps: S41: Establish a calculation formula for the heat generation power Q _II (t) of the second power battery unit during the thermal runaway triggering process, the Q _II (t)=Q _r (t)+Q _{e_in} (t)-Q _h (t), Q _r (t) is the reaction heat power released by the thermochemical reaction of the second power battery cell during the thermal trigger experiment, Q _{e_in} (t) is the thermal power released instantaneously by the internal short circuit, Q _h (t) Power for dissipating heat from the second power battery unit; S42: According to Q _II (t), it is obtained that the calculation formula for ; and S43: According to Get the calculation formula of T(t)II. 7. The design method for suppressing thermal runaway expansion of a power battery module according to claim 6, wherein the calculation formula of the Q _r (t) is the same as the calculation formula of Q _r (t) in the first power battery unit the same formula; Among them, ΔH represents the sum of the electric energy released due to the short circuit during the short-circuit process triggered by the thermal runaway of the second power battery unit, ΔH is a known quantity, and ∫Q _{e_in} (t)dt represents the electric energy that has been released when the time is t Electric energy, v represents the reaction rate in exponential form; the Q _h (t) = h _II · A _II · (T (t) _II -T _amb (t)), wherein, h _II represents the second power battery monomer pair The heat transfer coefficient of the environment, the unit is W/(m ² ·K), A _II represents the surface heat dissipation area of the second power battery cell, the unit is m ² , T(t) _II represents the simulation of the second power battery cell Model temperature, the unit is K, _Tamb (t) represents the temperature of the surrounding environment, the unit is K. 8. The design method for suppressing thermal runaway expansion of power battery modules according to claim 7, characterized in that, the can be further simplified to 9. The design method for suppressing the thermal runaway expansion of the power battery module according to claim 1, wherein the battery cell in the first power battery module that is subjected to the thermal runaway triggering experiment is defined as the first trigger battery, and the In the first power battery module, other battery cells other than the first trigger battery are defined as the second extended battery, and the first power battery module further includes a plurality of metal connecting pieces, a plurality of metal clamps and a plurality of heat insulation layers , the establishment of the third mathematical model T (t) _III may include the following steps: S61: respectively establish the energy change rate Q _i (t) calculation formula of the trigger battery of the first section, the extended battery of the second section, the battery pole and the fixture under the condition of heating thermal runaway extension, the Among them, Q _ij represents the heat dissipation power from node i to node j; Q _ih (t) represents the heat dissipation power from node i to the surrounding environment, Q _san (t) represents the heat dissipation power; Q _sheng (t) represents the generation Thermal power, Q _{e_in} (t) is the thermal power released instantly by the internal short circuit of the trigger battery in the first cell, Q _e (t) represents the short-circuit energy of the extended battery in the second cell, and Q _r (t) is the trigger battery in the first cell or the extended battery in the second cell The reaction heat power released by the thermochemical reaction; S62: According to Q _i (t), respectively establish the conditions of the first trigger battery, the second extended battery, the battery pole and the fixture under the condition of heating thermal runaway expansion the calculation formula for ; and S63: According to The calculation formulas of T _i (t) _III of the first trigger battery, the second extended battery, the battery pole and the fixture under the condition of heating thermal runaway expansion are respectively established. 10. The design method for suppressing thermal runaway expansion of a power battery module according to claim 1, characterized in that, after reducing the power of each sub-section extended battery in the third mathematical model T(t) _III , the sub-section extended battery The expression of the electric power Q _e (t) released during thermal runaway is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>\\ \frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; C</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ,</span>$ Among them, K _SOC represents the percentage of the total power of the secondary extended battery after discharge to the initial total electric power of the secondary extended battery, Δt represents the duration of a large-scale internal short circuit when the temperature reaches the thermal runaway temperature point, _Tonset represents the secondary extended battery The melting temperature of the internal diaphragm of the battery, that is, the thermal runaway temperature, ΔH represents the total electric energy released by the short circuit; Represents the energy of the weak short circuit that has occurred, T _short represents the temperature of the weak short circuit of the secondary extended battery, T represents the temperature of the secondary extended battery at different times, T _i (t) represents the secondary extended battery at time t internal temperature of the battery.