A method for quickly judging the effect of parallel electrical connection on thermal diffusion of battery pack system

Abstract

The present invention discloses a method for quickly judging the thermal diffusion effect of a parallel electrical connection on a battery pack system, comprising the following steps: S1. Measuring the maximum discharge energy E of the battery in the state of SOC = 100% max and the energy Q released during thermal runaway; S2. Measuring the energy Q released during the thermal runaway state of the battery under different state of charge, XSoC that is, detecting E XSOC and Q XSOC when SOC = X; S3. The total energy released by each battery under different state of charge is E XSoC +Q XSoC . Comparing the magnitudes of E XSoC +Q XSoC and Q. If E XSoC +Q XSoC ≥Q, the thermal diffusion of the parallel battery pack is relatively fast, and the thermal runaway occurring after the parallel battery pack discharges will promote the occurrence of thermal diffusion; if E XSoC +Q XSoC <Q, the thermal diffusion of the parallel battery pack is relatively slow. In this case, the thermal runaway occurring after the parallel battery pack discharges will delay the occurrence of thermal diffusion. The present invention can quickly obtain the influence of the parallel electrical connection on the thermal diffusion process of the battery pack and the system, providing technical support for a safer battery pack design, especially the electrical connection design.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery detection, and in particular is a method for quickly judging the effect of parallel electrical connection on the thermal diffusion of a battery pack system. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage fields, but safety accidents caused by battery thermal runaway and thermal diffusion occur frequently, becoming an important problem that needs to be solved in the current application of lithium-ion batteries.

[0003] Regarding the research on the mechanism of thermal runaway and thermal diffusion of lithium-ion batteries, Feng Xuning, Wang Qingsong and others have systematically studied the mechanism of thermal runaway of lithium-ion batteries, including the process of occurrence and development of thermal runaway, thermal runaway temperature and heat generation characteristics, thermal runaway reaction mechanism, etc., thus clearly indicating the boundary of thermal runaway of battery cells, which greatly promotes the understanding of battery safety and the improvement of battery safety technology. On the other hand, there is also continuous progress in battery system integration technology, through the study of thermal insulation materials, flame retardant materials, pressure-resistant materials, etc., the heat propagation of battery thermal runaway is effectively blocked, thereby cutting off the thermal diffusion behavior of the battery; there are also studies that quickly guide the heat released by battery thermal runaway, thereby reducing its heating effect on other battery cells, avoiding or delaying the critical conditions for other battery cells to reach thermal runaway to block or delay the occurrence of thermal diffusion.

[0004] Most of these studies study the thermal runaway and thermal diffusion of batteries from a thermal perspective. At the battery system level, most batteries need to be connected in series and parallel to achieve the required voltage and energy requirements. When one or more batteries in such a combination of batteries experience thermal runaway, it is usually accompanied by a short circuit in the thermal runaway battery, which will cause a discharge effect on other parallel batteries. Such effects often affect the severity of thermal runaway and thermal diffusion. Since such a discharge effect has an impact on thermal runaway and thermal diffusion, optimizing the design of electrical connections by systematically studying this influence mechanism will likely help us further improve the safety of batteries and improve their ability to block thermal diffusion. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quickly judging the effect of parallel electrical connection on the thermal diffusion of a battery pack system in response to the problems described in the background technology. By testing and analyzing the basic energy of the battery, the influence of parallel electrical connection on the thermal diffusion process of the battery pack and the system can be quickly obtained, providing technical support for safer battery pack design, especially electrical connection design.

[0006] A method for quickly determining the effect of parallel electrical connection on thermal diffusion of a battery system comprises the following steps:

[0007] S1. Test the maximum discharge energy E of the battery at SOC = 100% max and the energy Q released by thermal runaway;

[0008] S2. Test the energy Q released by the battery in thermal runaway state at different states of charge XSoC , that is, when SOC=X, side E XSOC and Q XSOC ;

[0009] S3. The total energy released by each battery at different states of charge is E XSoC +Q XSoC , compare E XSoC +Q XSoC and the size of Q, if E XSoC +Q XSoC ≥Q, the heat diffusion of the parallel battery pack is faster, and the thermal runaway of the parallel battery pack after discharge will promote the occurrence of heat diffusion; if E XSoC +Q XSoC <Q, the heat diffusion of the parallel battery pack is slower. In this case, thermal runaway of the parallel battery pack after discharge will delay the occurrence of heat diffusion.

[0010] In the above scheme, in step S1, the maximum discharge energy E of the battery is tested. max The method is as follows: connect the battery cell to the charging and discharging equipment, discharge it to the discharge cut-off voltage through constant current; let it stand for a period of time t0; then charge it to the charge cut-off voltage through constant current and then switch to constant voltage charging until the charging current drops to 0.05C; let it stand for a period of time t0; then discharge it to the discharge cut-off voltage through constant current, and use the amount of this discharge as the maximum discharge energy E of the battery. max .

[0011] In the above scheme, in step S2, the energy Q released by the battery in the thermal runaway state at different states of charge is tested. XSoC When testing the battery's specific heat capacity C p The detection method is as follows: using the adiabatic environment provided by the accelerated adiabatic calorimeter, the heating sheet provides constant power heating to the battery to the highest temperature T, and obtains a linear curve of battery temperature changing with time, and Cp is calculated by formula 1;

[0012] Where m is the battery weight and W is the heating amount;

[0013] When the temperature is lower than the maximum heating temperature T, the change of specific heat capacity with temperature is very small and can be ignored. The average value is taken as the specific heat capacity C of the battery. p ;

[0014] Then the SOC of the battery is adjusted to n%, and the method is: first fully charge the battery, that is, SOC = 100%, and then use 1C constant current discharge for 60*(1-n%)min, that is, the SOC of the battery can be adjusted to n%;

[0015] After adjusting the battery to the target SoC, weigh the battery mass m, and then place the battery in an accelerated adiabatic calorimeter for a battery thermal runaway test. Heat the battery with the accelerated adiabatic calorimeter and compare the battery temperature rise rate dT / dt with the battery's self-generated heat temperature rise rate limit onset. When the battery temperature rise rate dT / dt>onset, it indicates that a chain reaction occurs in the battery. The accelerated adiabatic calorimeter stops heating and enters an adiabatic state. The battery temperature is recorded as T1. The battery releases heat in the adiabatic state and the temperature continues to rise. When the battery temperature reaches T2, it will enter a thermal runaway state. The battery continues in a thermal runaway state and the temperature rises rapidly. The highest temperature T3 of the thermal runaway state is detected, and the energy Q released in the thermal runaway state of the battery is calculated. XSoC , the calculation formula is:

[0016] Q XSoC =C p m(T3-T1); T3 is the highest temperature and T1 is the self-heating temperature.

[0017] In the above scheme, there are five situations when the battery has thermal runaway:

[0018] C1. Energy released by battery thermal runaway Q XSoC Lower than the stored electrical energy E XSOC At the same time, even when the battery is in the state of SoC = 0%, thermal runaway will still release a certain amount of energy. The energy released by thermal runaway of the battery is Q XSoC The slope is less than the electric energy E XSOC The slope of release. In this case, when the battery undergoes thermal runaway after discharge, the total energy released is higher than the energy released by thermal runaway in its fully charged state, that is, E XSoC +Q XSoC ≥Q, in this case, thermal runaway of the parallel battery pack after discharge will promote the occurrence of thermal diffusion;

[0019] C2. Energy released by battery thermal runaway Q XSoC Equal to the stored electrical energy E XSOC At the same time, even when the battery is in the state of SoC=0%, thermal runaway will still release a certain amount of energy. Therefore, the slope of the energy released by the battery thermal runaway must be smaller than the slope of the electric energy release. In this case, when the battery thermal runaway occurs after discharge, the total energy released is higher than the energy released by the thermal runaway of its fully charged state. In this case, when the parallel battery pack thermal runaway occurs after discharge, it will promote the occurrence of heat diffusion.

[0020] C3. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , and the slope of energy released by thermal runaway of the battery is equal to the slope of electric energy released. In this case, when thermal runaway occurs after discharge, the total energy released is equal to the energy released by thermal runaway of the fully charged state. In this case, the parallel structure has no effect on the total energy released by thermal diffusion.

[0021] C4. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , the slope of the energy released by the battery thermal runaway is smaller than the slope of the electric energy released. In this case, when the battery thermally runs away after discharge, the total energy released is higher than the energy released by the thermal runaway of the fully charged state. In this case, when the parallel battery pack thermally runs away after discharge, it will promote the occurrence of heat diffusion;

[0022] C5. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , the slope of energy released by thermal runaway of the battery is greater than the slope of electrical energy release. In this case, when the battery undergoes thermal runaway after discharge, its total released energy is less than the energy released by thermal runaway in its fully charged state. In this case, when the parallel battery pack undergoes thermal runaway after discharge, the occurrence of thermal diffusion will be delayed.

[0023] The beneficial effects of the present invention are as follows: the method for quickly judging the effect of parallel electrical connection on the thermal diffusion of the battery pack system of the present invention can be used to determine the energy E released by the battery discharge. XSoC and the energy released by thermal runaway Q XSoC By comparing the thermal diffusion performance of the battery when it is connected in parallel with other batteries and thermal runaway occurs after discharge, when E XSoC +Q XSoC When E ≥ Q, the heat diffusion of the parallel battery pack is faster, and the thermal runaway of the parallel battery pack after discharge will promote the occurrence of heat diffusion; when E XSoC +Q XSoC When <Q, the heat diffusion of the parallel battery pack is slower. In this case, thermal runaway of the parallel battery pack after discharge will delay the occurrence of heat diffusion. This judgment method can quickly obtain the impact of parallel electrical connections on the heat diffusion process of the battery pack and the system, providing technical support for safer battery pack design, especially electrical connection design. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flowchart for testing the energy released by a battery in thermal runaway state.

[0025] Figure 2 This is the obtained battery thermal runaway curve.

[0026] Figure 3It is a curve diagram of the battery releasing electrical energy and the energy released due to thermal runaway in C1.

[0027] Figure 4 It is a curve diagram of the battery releasing electrical energy and thermal runaway energy in C2.

[0028] Figure 5 This is a curve diagram of battery electrical energy release and thermal runaway energy release in C3.

[0029] Figure 6 It is a curve diagram of battery electrical energy release and thermal runaway energy release in C4.

[0030] Figure 7 The graph shows the energy released by the battery and the energy released due to thermal runaway in C5.

[0031] Figure 8 This is a curve diagram of battery electrical energy release and thermal runaway energy release in Application Example 1.

[0032] Fig. 9 This is a curve diagram of battery electrical energy release and thermal runaway energy release in Application Example 2. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention is clearly and completely described below through embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for quickly determining the effect of parallel electrical connection on thermal diffusion of a battery system comprises the following steps:

[0036] S1. Test the maximum discharge energy E of the battery at SOC = 100% max and the energy Q released by thermal runaway;

[0037] Connect the battery cell to the charging and discharging equipment, discharge it to the discharge cut-off voltage with 1C constant current; let it stand for 30 minutes; then charge it to the charge cut-off voltage with 1C constant current and then switch to constant voltage charging until the charging current drops to 0.05C; let it stand for 30 minutes; then discharge it to the discharge cut-off voltage with 1C constant current, and use the amount of discharge as the maximum discharge energy E of the battery. max After the test, charge the battery with 1C constant current until the charging cut-off voltage is reached, then switch to constant voltage charging until the charging current drops to 0.05C. Let the battery sit for 30 minutes to complete the charging process in preparation for subsequent tests.

[0038] S2. Test the energy Q released by the battery in thermal runaway state at different states of charge XSoC , that is, when SOC=X, side E XSOC and Q XSOC , including the following methods:

[0039] First, test the specific heat capacity C of the battery. p The detection method is as follows: using the adiabatic environment provided by the accelerated adiabatic calorimeter, the heating sheet provides constant power heating to the battery to the highest temperature T, T can be set to 60°C, and a linear curve of battery temperature changing with time is obtained, and Cp is calculated by formula 1;

[0040] Where m is the weight of the battery, Cp is the specific heat capacity of the battery, and W is the energy consumed by heating;

[0041] Because when the temperature is less than the maximum heating temperature of 60°C, the change of specific heat capacity with temperature is very small and can be ignored, so the average value is taken as the specific heat capacity C of the battery. p .

[0042] Then adjust the SOC of the battery to n%. The method is as follows: first fully charge the battery. The method for fully charging the battery is the same as the above method. The constant current charging method can be used to charge the medium voltage and then switch to constant voltage charging. After fully charged, use 1C constant current discharge for 60*(1-n%)min to adjust the SOC of the battery to n%. In this method, it is usually necessary to adjust the battery to different SoC states, generally including 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%. The smaller the interval of SoC, the more accurate the result will be.

[0043] After adjusting the battery to the target SoC, weigh the battery mass m, and then place the battery in an accelerated adiabatic calorimeter for a battery thermal runaway test. Heat the battery with the accelerated adiabatic calorimeter and compare the battery temperature rise rate dT / dt with the battery's self-generated heat temperature rise rate limit onset, which can be set to 0.02°C / min. When the battery temperature rise rate dT / dt>onset, it indicates that a chain reaction occurs in the battery, and the accelerated adiabatic calorimeter stops heating and enters an adiabatic state. The battery temperature is recorded as T1. The battery releases heat in the adiabatic state, and the temperature continues to rise. When the battery temperature reaches T2, it will enter a thermal runaway state. The battery continues in a thermal runaway state, and the temperature rises rapidly. The highest temperature T3 of the thermal runaway state is detected, and the energy Q released in the thermal runaway state of the battery is calculated. XSoC , the calculation formula is:

[0044] Q XSoC =Cp m(T3-T1); where T3 is the maximum temperature and T1 is the self-heating temperature.

[0045] During the heating process, if the battery temperature is greater than T F , and when dT / dt<onset, the battery starts to be cooled; T F Can be set to 350°C.

[0046] After entering the adiabatic state, if dT / dt is less than onset again, it means that the battery has not entered the thermal runaway state. Then it returns to the heating state and heats the battery until dT / dt>onset. Then it re-enters the adiabatic state and detects the highest temperature T3 of the battery thermal runaway state.

[0047] After the thermal runaway ends, the energy Q released by the battery in the thermal runaway state is calculated through the thermal runaway curve of the battery. XSoC , the calculation formula is:

[0048] Q XSoC =C p m(T3-T1).

[0049] S3. The energy released by thermal runaway of each single battery under full charge condition is represented by Q. For parallel modules, the energy released comes from the energy released by discharge E. XSoC and the energy released by thermal runaway Q XSoC , then the total energy released by each battery is E XSoC +Q XSoC , when E XSoC +Q XSoC When E ≥ Q, the heat diffusion of the parallel battery pack is faster, and the thermal runaway of the parallel battery pack after discharge will promote the occurrence of heat diffusion; when E XSoC +Q XSoC When <Q, the heat diffusion of the parallel battery pack is slow. In this case, the thermal runaway of the parallel battery pack after discharge will delay the occurrence of thermal diffusion. In the above scheme, there are five situations when the battery has thermal runaway:

[0050] C1. Energy released by battery thermal runaway Q XSoC Lower than the stored electrical energy E XSOC At the same time, even if the battery is in the state of SoC = 0%d, thermal runaway will still release a certain amount of energy. The energy released by thermal runaway of the battery is Q XSoC The slope is less than the electric energy E XSOC The slope of release. In this case, when the battery undergoes thermal runaway after discharge, the total energy released is higher than the energy released by thermal runaway in its fully charged state, that is, E XSoC +Q XSoC ≥Q, in this case, thermal runaway of the parallel battery pack after discharge will promote the occurrence of thermal diffusion;

[0051] C2. Energy released by battery thermal runaway Q XSoC Equal to the stored electrical energy E XSOC At the same time, even when the battery is in the state of SoC=0%, thermal runaway will still release a certain amount of energy. Therefore, the slope of the energy released by the battery thermal runaway must be smaller than the slope of the electric energy release. In this case, when the battery thermal runaway occurs after discharge, the total energy released is higher than the energy released by the thermal runaway of its fully charged state. In this case, when the parallel battery pack thermal runaway occurs after discharge, it will promote the occurrence of heat diffusion.

[0052] C3. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , and the slope of energy released by thermal runaway of the battery is equal to the slope of electric energy released. In this case, when thermal runaway occurs after discharge, the total energy released is equal to the energy released by thermal runaway of the fully charged state. In this case, the parallel structure has no effect on the total energy released by thermal diffusion.

[0053] C4. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , the slope of the energy released by the battery thermal runaway is smaller than the slope of the electric energy released. In this case, when the battery thermally runs away after discharge, the total energy released is higher than the energy released by the thermal runaway of the fully charged state. In this case, when the parallel battery pack thermally runs away after discharge, it will promote the occurrence of heat diffusion;

[0054] C5. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSOC , the slope of energy released by thermal runaway of the battery is greater than the slope of electrical energy release. In this case, when the battery undergoes thermal runaway after discharge, its total released energy is less than the energy released by thermal runaway in its fully charged state. In this case, when the parallel battery pack undergoes thermal runaway after discharge, the occurrence of thermal diffusion will be delayed.

[0055] Application Example 1

[0056] A lithium-ion battery with a rated capacity of 25Ah was selected as the test object. The battery cell was connected to the charging and discharging equipment. 1) Discharged with a constant current of 25A to the discharge cut-off voltage; 2) Stand for 30 minutes; 3) Charged with a constant current of 25A to the charge cut-off voltage and then switched to constant voltage charging until the charging current dropped to 1.25A; 4) Stand for 30 minutes; 5) Discharged with a constant current of 25A to the discharge cut-off voltage; 6) Stand for 30 minutes; 7) Charged with a constant current of 25A to the charge cut-off voltage and then switched to constant voltage charging until the charging current dropped to 1.25A. The discharge energy in step 5) is taken as the maximum discharge energy of the battery, which is 297.18kJ.

[0057] 2. Thermal runaway energy release test of batteries at different states of charge

[0058] 1) Use accelerated adiabatic calorimeter (ARC) to test the specific heat capacity of the battery

[0059] In order to detect the heat generated by battery thermal runaway, it is necessary to measure the specific heat capacity Cp of the battery. At the same time, in order to provide the basic parameters of thermal characteristics for the thermal model, the specific heat capacity, an important thermodynamic parameter, is also required. The specific heat capacity test adopts the constant power heating test method. Using the adiabatic environment provided by the accelerated adiabatic calorimeter (ARC), the heating plate provides constant power heating to the battery to 60°C (if the temperature is higher, it is easy to damage the battery), and a linear curve of the battery temperature changing with time is obtained. Finally, Cp is calculated by formula (1) p .

[0060]

[0061] The maximum heating temperature in the specific heat capacity test is set within 60°C. Within this range, the specific heat capacity changes very little with temperature and can be ignored. The average value is taken as the specific heat capacity of the monomer, and its specific heat capacity is 1.2 kJ kg -1 K -1 .

[0062] 2) Adjust the battery SoC

[0063] When the battery SOC needs to be adjusted to n%, follow the method in “1. Battery maximum discharge energy test” to fully charge the battery, and then discharge it at a constant current of 25A for 60*(1-n%)min.

[0064] In the study, the battery SoC was adjusted to 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

[0065] 2) Use an accelerated adiabatic calorimeter to test the thermal runaway heat release of the battery

[0066] The battery was adjusted to the target SoC and weighed, with a weight of m = 0.6 kg, and then placed in the ARC for a battery thermal runaway test. The ARC provides a precisely controlled, insulated environment.

[0067] according to Figure 1 Battery thermal runaway test flow chart for battery thermal runaway test. Among them:

[0068] dT / dt: battery temperature rise rate; onset: self-heating temperature rise rate limit, set to 0.02℃ / min to determine whether self-heating occurs; T: battery surface temperature; T F : Maximum temperature, used to determine whether the test is finished, set to 350℃.

[0069] The measured thermal runaway release energy is as follows:

[0070]

[0071]

[0072] 3. Comparison of battery discharge energy and thermal runaway energy characteristics

[0073] After plotting the thermal runaway energy and discharge energy, Figure 8 As shown, it meets the situation of C2. The energy released by the battery thermal runaway is equal to the electric energy stored in it, and the slope of the battery thermal runaway energy release is less than the slope of the electric energy release. In this case, the battery thermal runaway occurs after discharge, and its total energy released is higher than the energy released by its fully charged thermal runaway. In this case, the parallel battery pack will promote the occurrence of thermal diffusion after thermal runaway occurs after discharge. It shows that parallel electrical connection will promote the occurrence of thermal diffusion.

[0074] Application Example 2

[0075] A lithium-ion battery with a rated capacity of 30Ah was selected as the test object. The battery cell was connected to the charging and discharging equipment. 1) Discharged with a constant current of 30A to the discharge cut-off voltage; 2) Stand for 30 minutes; 3) Charged with a constant current of 30A to the charge cut-off voltage and then switched to constant voltage charging until the charging current dropped to 1.5A; 4) Stand for 30 minutes; 5) Discharged with a constant current of 30A to the discharge cut-off voltage; 6) Stand for 30 minutes; 7) Charged with a constant current of 30A to the charge cut-off voltage and then switched to constant voltage charging until the charging current dropped to 1.5A. The discharge energy in step 5) is taken as the maximum discharge energy of the battery, which is 333.8kJ.

[0076] 2. Thermal runaway energy release test of batteries at different states of charge

[0077] 1) Use accelerated adiabatic calorimeter (ARC) to test the specific heat capacity of the battery

[0078] In order to detect the heat generated by battery thermal runaway, it is necessary to measure the specific heat capacity Cp of the battery. At the same time, in order to provide the basic parameters of thermal characteristics for the thermal model, the specific heat capacity, an important thermodynamic parameter, is also required. The specific heat capacity test adopts the constant power heating test method. Using the adiabatic environment provided by the accelerated adiabatic calorimeter (ARC), the heating plate provides constant power heating to the battery to 60°C (if the temperature is higher, it is easy to damage the battery), and a linear curve of the battery temperature changing with time is obtained. Finally, Cp is calculated by formula (1) p .

[0079]

[0080] The maximum heating temperature in the specific heat capacity test is set within 60°C. Within this range, the specific heat capacity changes very little with temperature and can be ignored. The average value is taken as the specific heat capacity of the monomer, and its specific heat capacity is 1.3 kJ kg -1 K -1 .

[0081] 3) Adjust the battery SoC

[0082] When the battery SOC needs to be adjusted to n%, follow the method in “1. Battery maximum discharge energy test” to fully charge the battery, and then discharge it at a constant current of 25A for 60*(1-n%)min.

[0083] In the study, the battery SoC was adjusted to 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

[0084] 2) Use an accelerated adiabatic calorimeter to test the thermal runaway heat release of the battery

[0085] The battery was adjusted to the target SoC and weighed, with a weight of m = 1.1 kg, and then placed in the ARC for a battery thermal runaway test. The ARC provides a precisely controlled, insulated environment.

[0086] according to Figure 1 Battery thermal runaway test flow chart for battery thermal runaway test. Among them:

[0087] dT / dt: battery temperature rise rate; onset: self-heating temperature rise rate limit, set to 0.02℃ / min to determine whether self-heating occurs; T: battery surface temperature; T F : Maximum temperature, used to determine whether the test is finished, set to 350℃.

[0088] The measured thermal runaway release energy is as follows:

[0089]

[0090]

[0091] 3. Comparison of battery discharge energy and thermal runaway energy characteristics

[0092] After plotting the thermal runaway energy and discharge energy, Fig. 9 As shown, it meets the situation of C5. The energy released by the battery thermal runaway is greater than the electric energy it stores, and the slope of the energy released by the battery thermal runaway is greater than the slope of the electric energy release. In this case, the battery thermal runaway occurs after discharge, and its total released energy is less than the energy released by its fully charged thermal runaway. In this case, the parallel battery pack thermal runaway after discharge will delay the occurrence of thermal diffusion.

[0093] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for quickly determining the effect of parallel electrical connection on the thermal diffusion of a battery system, characterized in that: The following steps are involved: S1, test the maximum discharge energy E of the battery at SoC=100% max and the energy Q released by thermal runaway; S2. Test the energy released by the battery in thermal runaway state at different states of charge. XSoC and Q XSoC , that is, when SoC=X, measure E XSoC and Q XSoC ; S3. The total energy released by each battery at different states of charge is E XSoC + Q XSoC ,Compare E XSoC + Q XSoC and the size of Q, if E XSoC + Q XSoC ≥Q, the heat diffusion of the parallel battery pack is faster, and the thermal runaway of the parallel battery pack after discharge will promote the occurrence of heat diffusion; if E XSoC + Q XSoC <Q, the heat diffusion of the parallel battery pack is slower. In this case, thermal runaway of the parallel battery pack after discharge will delay the occurrence of heat diffusion.

2. The method for quickly determining the effect of parallel electrical connection on the thermal diffusion of a battery system according to claim 1, characterized in that: In step S1, the maximum discharge energy E of the battery is tested. max The method is as follows: connect the battery cell to the charging and discharging equipment, discharge it to the discharge cut-off voltage through constant current; let it stand for a period of time t0; then charge it to the charge cut-off voltage through constant current and then switch to constant voltage charging until the charging current drops to 0.05C; let it stand for a period of time t0; then discharge it to the discharge cut-off voltage through constant current, and use the amount of this discharge as the maximum discharge energy E of the battery. max .

3. The method for quickly determining the effect of parallel electrical connection on the thermal diffusion of a battery system according to claim 1, characterized in that: In step S2, the energy released by the battery in the thermal runaway state at different states of charge is tested. Q XSoC When testing the specific heat capacity C of the battery, p The detection method is as follows: using the adiabatic environment provided by the accelerated adiabatic calorimeter, the heating sheet provides constant power heating to the battery to the highest temperature T, and obtains a linear curve of battery temperature changing with time, and Cp is calculated by formula 1; (1); where m is the battery weight and W is the heating amount; When the temperature is lower than the maximum heating temperature T, take the average value as the specific heat capacity of the battery. C p ; Then adjust the battery's SoC to n% by: first fully charge the battery, that is, SoC=100%, and then use 1C constant current discharge for 60*(1-n%)min, which can adjust the battery's SoC to n%; After adjusting the battery to the target SoC, weigh the battery mass m, and then place the battery in an accelerated adiabatic calorimeter for a battery thermal runaway test. Heat the battery with the accelerated adiabatic calorimeter and compare the battery temperature rise rate dT / dt with the battery's self-generated heat temperature rise rate limit onset. When the battery temperature rise rate dT / dt>onset, it indicates that a chain reaction occurs in the battery. The accelerated adiabatic calorimeter stops heating and enters an adiabatic state. The battery temperature is recorded as T1. The battery releases heat in the adiabatic state and the temperature continues to rise. When the battery temperature reaches T2, it will enter a thermal runaway state. The battery continues in a thermal runaway state and the temperature rises rapidly. The highest temperature T3 of the thermal runaway state is detected and the energy released in the thermal runaway state of the battery is calculated. Q XSoC , the calculation formula is: Q XSoC = C p m ( T 3- T 1); T3 is the highest temperature and T1 is the self-heating temperature.

4. The method for quickly judging the effect of parallel electrical connection on thermal diffusion of a battery system according to claim 1, characterized in that: There are five situations when the battery has thermal runaway: C1. Energy released by battery thermal runaway Q XSoC Lower than the stored electrical energy E XSoC At the same time, even when the battery is in the state of SoC=0%, the energy released by the battery thermal runaway is Q XSoC The slope is less than the electric energy E XSoC The slope of release. In this case, when the battery undergoes thermal runaway after discharge, the total energy released is higher than the energy released by thermal runaway in its fully charged state, that is, E XSoC + Q XSoC ≥Q, in this case, the thermal runaway of the parallel battery pack after discharge will promote the occurrence of thermal diffusion; C2. Energy released by battery thermal runaway Q XSoC Equal to the stored electrical energy E XSoC At the same time, even when the battery is in the state of SoC=0%, thermal runaway will still release a certain amount of energy. Therefore, the slope of energy released by thermal runaway of the battery must be smaller than the slope of electric energy release. In this case, when the battery has thermal runaway after discharge, the total energy released is higher than the energy released by thermal runaway in its fully charged state. In this case, thermal runaway of the parallel battery pack after discharge will promote the occurrence of heat diffusion. C3. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSoC , and the slope of energy released by thermal runaway of the battery is equal to the slope of electric energy released. In this case, when thermal runaway occurs after discharge, the total energy released is equal to the energy released by thermal runaway of the fully charged state. In this case, the parallel structure has no effect on the total energy released by thermal diffusion. C4. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSoC , the slope of the energy released by the battery thermal runaway is smaller than the slope of the electric energy released. In this case, when the battery thermally runs away after discharge, the total energy released is higher than the energy released by the thermal runaway of the fully charged state. In this case, when the parallel battery pack thermally runs away after discharge, it will promote the occurrence of heat diffusion; C5. Energy released by battery thermal runaway Q XSoC Greater than the stored electrical energy E XSoC , the slope of energy released by thermal runaway of the battery is greater than the slope of electrical energy release. In this case, when the battery undergoes thermal runaway after discharge, the total energy released is less than the energy released by thermal runaway in its fully charged state. In this case, when the parallel battery pack undergoes thermal runaway after discharge, the occurrence of thermal diffusion will be delayed.

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