Battery pack safety evaluation method and system

Abstract

The invention discloses a battery pack safety evaluation method and system, belongs to the technical field of battery packs, solves the problem that complete safety evaluation of a battery pack is lacked in the new energy battery pack industry, constructs a battery safety function list based on a macroscopic battery pack safety target and a design principle, divides working conditions based on the actual battery pack accident occurrence probability, and improves the safety of the battery pack. Safety criteria under different working conditions are formulated, the identified battery pack phenomena are further graded according to the divided working conditions, phenomenon lists of the battery pack under different working conditions are formed, safety analysis is carried out on the phenomena of the battery pack under different working conditions one by one, comparison with the safety criteria is carried out, and evaluation of the accident consequence of the battery pack is output. The research and development design of the battery pack is guided, it is ensured that the design of the battery pack can be stably operated under the normal working condition, risks and damage can be reduced to the maximum extent when accidents happen, and therefore the overall safety and reliability of the electric automobile are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery packs and relates to a battery pack safety evaluation method and system. Background Art

[0002] With the development of society and the progress of technology, the number of new energy vehicles is also increasing. Among them, the power battery, as the core component of electric vehicles, its safety and reliability are particularly important. The power battery pack has a wide range of applications and can be used as the driving power source for vehicles such as electric vehicles, electric trucks, and electric mining vehicles. However, during use, various accidents may occur, which are likely to lead to safety accidents such as thermal runaway of the battery, thus endangering the safety of passengers.

[0003] For example, the invention patent with the application publication number CN116227831A discloses a charging operation safety evaluation and action method, which not only summarizes the failure causes of typical charging safety accidents but also provides a theoretical basis for the subsequent research on electric vehicle charging safety assessment. However, the battery pack safety evaluation indicators involve various working conditions, and the division principles for different working conditions also need to be deeply considered and studied. In the technical field of battery packs, there is no related technology that can guide the safe development of battery packs, nor is there a related method that can list battery pack accidents and conduct systematic safety analysis and evaluation. Therefore, there is an urgent need to design a battery pack safety evaluation method that can guide the safe development of battery packs to solve the problem of the lack of a complete safety evaluation of battery packs in the new energy battery pack industry. Summary of the Invention

[0004] The technical solution of the present invention is used to solve the problem of the lack of a complete safety evaluation of battery packs in the new energy battery pack industry.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] A battery pack safety evaluation method includes the following steps:

[0007] S1. Based on the battery pack safety objectives, construct safety design principles;

[0008] S2. Construct a battery pack safety function list;

[0009] S3. Divide the working conditions based on the probability of battery pack accidents and formulate safety criteria for different working conditions;

[0010] S4. Based on the safety function list, sort out the battery pack accident list;

[0011] S5. Classify the identified battery pack phenomena according to the divided working conditions to form a phenomenon list of the battery pack under different working conditions;

[0012] S6. Conduct a safety analysis on each phenomenon of the battery pack under different working conditions one by one;

[0013] S7. According to the safety criteria under different working conditions, determine whether the consequences of each accident meet the requirements. If not, improve the design again and conduct a safety analysis on this accident again until the safety criteria under this working condition are met. Repeat this process until all accidents under all working conditions meet the safety criteria corresponding to their respective working conditions;

[0014] S8. Output a safety evaluation report.

[0015] Furthermore, the specific safety design principles described in S1 are as follows:

[0016] S11. When the mass of hydrogen, carbon monoxide, methane, fluorocarbon, hydrofluoric acid, and benzene gas released by the battery pack under accident conditions is less than or equal to 0.01% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack, it is considered that the battery pack meets the first safety design principle;

[0017] S12. When the probability of thermal runaway and open fire of a single battery cell in the battery pack is between 0.1% and 1%, the probability of thermal runaway and open fire of two or more battery cells in the battery pack simultaneously is less than 0.1%, and the probability of battery pack explosion is less than 0.01% of the total mass, it is considered that the battery pack meets the second safety design principle;

[0018] S13. When the battery pack meets both the first safety design principle and the second safety design principle simultaneously, it meets the battery pack safety goal.

[0019] Furthermore, the battery pack safety function list described in S2 includes that the battery cells do not undergo thermal runaway, do not leak liquid, and the integrity of the airtightness of the battery pack outer casing.

[0020] Furthermore, the working conditions described in S3 include normal operation events, abnormal transient events, rare accidents, extreme accidents, and over - design accidents;

[0021] The annual occurrence probability of the normal operation time is between 10% and 100%, the annual occurrence probability of abnormal transient events is between 1% and 10%, the annual occurrence probability of rare accidents is between 0.1% and 1%, the annual occurrence probability of extreme accidents is between 0.01% and 0.1%, and the annual occurrence probability of over - design accidents is less than 0.01% of the total mass.

[0022] Furthermore, the specific safety criteria described in S3 are as follows:

[0023] S31. When the battery pack accident is a normal operation event, the battery pack operates at its rated state and does not cause any accidents;

[0024] S32. When the battery pack accident is an abnormal transient event, it may cause the battery pack to be protected from power, but it will not cause the release of harmful substances such as mercury, chromium, and lead;

[0025] S33. When the battery pack accident is a rare accident, in order to prevent harmful consequences, mitigation measures or equipment need to be put into operation to make the mass of hydrogen, carbon monoxide, methane, fluorinated carbon, hydrofluoric acid, and benzene gas released from the battery pack less than or equal to 0.001% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack;

[0026] S34. When the battery pack accident is an extreme accident, it may cause the release of a large amount of harmful substances such as mercury, chromium, and lead. The design must be considered to make the mass of hydrogen, carbon monoxide, methane, fluorinated carbon, hydrofluoric acid, and benzene gas released from the battery pack less than or equal to 0.01% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack;

[0027] S35. When the battery pack accident is a beyond-design accident, the probability of this accident occurring is extremely low and it is not considered in the design.

[0028] Further, the list of battery pack accidents described in S4 is specifically as follows:

[0029] S41. Accidents of abnormal charge and discharge rate, and the accidents of abnormal charge and discharge rate include excessive continuous charging power, excessive continuous discharging power, excessive pulsed discharging power, and excessive pulsed charging power;

[0030] S42. Accidents of abnormal temperature, and the accidents of abnormal temperature include too high ambient temperature, too low ambient temperature, too fast temperature rise rate, short circuit, and continuous heating;

[0031] S43. Accidents of abnormal integrity of the battery pack housing, and the accidents of abnormal integrity of the battery pack housing include mechanical shock, bottom ball impact, collision, extrusion, immersion in water, scraping the bottom, and fire.

[0032] Further, the list of phenomena of the battery pack under different working conditions described in S5 is specifically as follows:

[0033] S51. When the battery pack accident is a normal operation event, the battery pack phenomena include power on, power off, rated rate discharging, rated rate charging, rated rate pulsed discharging, and rated rate pulsed charging;

[0034] S52. When the battery pack accident is an abnormal transient event, the battery pack phenomena include continuous overcurrent charging, continuous overcurrent power generation, overcurrent pulsed charging, overcurrent pulsed discharging, too high ambient temperature, and too low ambient temperature;

[0035] S53. When the battery pack accident is a rare accident, the battery pack phenomena include the decline in the cooling capacity of the water-cooling system caused by the damage of the cooling unit, the decline in the cooling capacity of the water-cooling system caused by the power failure of the water pump, the increase in the inlet temperature of the water-cooling system, the decrease in the flow rate of the water-cooling system, the broken shaft of the water pump, continuous heating, and the too-fast temperature rise rate.

[0036] S54. When the battery pack accident is an extreme accident, the battery pack phenomena include the decline in the cooling capacity of the water-cooling system caused by the stuck shaft of the water pump, thermal runaway caused by too large charge and discharge rates, collision, short circuit, mechanical shock, bottom ball impact, extrusion, immersion in water, scraping the bottom, and fire.

[0037] S55. When the battery pack accident is an over-design accident, the battery pack phenomena include the decline in the cooling capacity of the water-cooling system caused by the stuck shaft of the water pump, and the failure of the power-off protection of the protection system.

[0038] Further, the specific safety analysis of each phenomenon of the battery pack under different working conditions described in S6 is as follows:

[0039] S61. Analyze the cause of the phenomenon.

[0040] S62. Describe the overall process of the phenomenon.

[0041] S63. Describe the input conditions for the safety analysis, and the input conditions include set parameters and simplified assumptions.

[0042] S64. Evaluate the results of the safety analysis, and the results include cell short circuit, thermal runaway, analysis of the battery pack pressure relief rate, evaluation of the battery pack combustion and explosion.

[0043] The present invention also provides a battery pack safety evaluation system, including a safety principle module, a safety checklist module, a safety criterion module, an accident checklist module, a phenomenon checklist module, a safety analysis module, a loop traversal module, and a safety report module.

[0044] The safety principle module is used to construct safety design principles based on the battery pack safety objectives.

[0045] The safety checklist module is used to construct a battery pack safety function checklist.

[0046] The safety criterion module is used to divide working conditions based on the probability of battery pack accidents and formulate safety criteria under different working conditions.

[0047] The accident checklist module is used to sort out the battery pack accident checklist based on the safety function checklist.

[0048] The phenomenon checklist module is used to classify the identified battery pack phenomena according to the divided working conditions to form a phenomenon checklist of the battery pack under different working conditions.

[0049] The safety analysis module is used to conduct safety analysis on each phenomenon of the battery pack under different working conditions one by one;

[0050] The loop traversal module is used to determine whether the consequences of each accident meet the requirements according to the safety criteria under different working conditions. If not, the design is improved again, and the accident is re - analyzed for safety until the safety criteria under this working condition are met. The loop continues until the accidents under all working conditions meet the safety criteria corresponding to their respective working conditions;

[0051] The safety report module is used to output a safety evaluation report.

[0052] The advantages of the present invention are as follows:

[0053] Based on the macroscopic battery pack safety objectives and design principles, the present invention constructs a battery safety function list, divides working conditions based on the actual probability of battery pack accidents, formulates safety criteria for different working conditions, further classifies the identified battery pack phenomena according to the divided working conditions to form a list of phenomena of the battery pack under different working conditions, conducts safety analysis on each phenomenon of the battery pack under different working conditions one by one, compares with the safety criteria, and outputs an evaluation of the consequences of battery pack accidents. Each link is closely linked to form a complete evaluation system with theoretical and practical guiding significance, guiding the research and development design of the battery pack, solving the problem of the lack of a complete safety evaluation of the battery pack in the new energy battery pack industry, ensuring that the design of the battery pack can not only operate stably under normal working conditions, but also minimize risks and damages to the greatest extent in case of accidents, thereby improving the overall safety and reliability of electric vehicles. Description of the Drawings

[0054] Figure 1 is a flowchart of a battery pack safety evaluation method according to Embodiment 1 of the present invention;

[0055] Figure 2(a) is a schematic diagram of a battery pack simulation model based on CAE simulation according to Embodiment 1 of the present invention;

[0056] Figure 2(b) is a schematic diagram of setting safety analysis input conditions for the battery pack extrusion working condition according to Embodiment 1 of the present invention;

[0057] Figure 2(c) is a schematic diagram of the distance between the battery cell and the box before extrusion according to Embodiment 1 of the present invention;

[0058] Figure 2(d) is a schematic diagram of the force - induced deformation of the box after extrusion according to Embodiment 1 of the present invention;

[0059] Figure 2(e) is a schematic diagram of the distance between the battery cell and the box after extrusion according to Embodiment 1 of the present invention. Detailed Embodiments

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0061] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0062] Embodiment 1

[0063] As Figure 1 shown, specifically, a battery pack safety evaluation method is disclosed, including,

[0064] S1. Based on the battery pack safety objectives, construct safety design principles;

[0065] In this embodiment, the battery pack safety objective is to ensure that drivers, passengers, surrounding residents, and the environment are protected from the hazards caused by harmful substances through safety design protection measures, keep the hazards caused by harmful substances released from the battery pack at a low level, and reduce the probability of serious accidents with serious radioactive consequences caused by harmful substances.

[0066] Further, the safety design principles are specifically as follows:

[0067] S11. When the mass of hydrogen, carbon monoxide, methane, fluorocarbon, hydrofluoric acid, and benzene gas released under the accident conditions of the battery pack is less than or equal to 0.01% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack, it is considered that the battery pack meets the first safety design principle.

[0068] S12. When the probability of thermal runaway and open fire of a single battery cell in the battery pack is between 0.1% and 1%, the probability of simultaneous thermal runaway and open fire of two or more battery cells in the battery pack is less than 0.1%, and the probability of battery pack explosion is less than 0.01% of the total mass, it is considered that the battery pack meets the second safety design principle.

[0069] S13. When the battery pack simultaneously meets the first safety design principle and the second safety design principle, it meets the battery pack safety objective.

[0070] S2. Construct a battery pack safety function list;

[0071] In this embodiment, the construction of the safety function list focuses on preventing the leakage of harmful substances from the battery cells and the integrity of the battery pack housing. The battery pack safety function list includes no thermal runaway of the battery cells, no leakage of the battery cells, and the integrity of the airtightness of the battery pack housing.

[0072] In this embodiment, the safety function list is shown in Table 1 below:

[0073] Table 1 Battery Pack Safety Function List

[0074]

[0075]

[0076] In this embodiment, the specific meaning that the battery cells in the safety function list do not undergo thermal runaway is to prevent thermal runaway of the battery cells during the design of battery pack thermal management. During safety evaluation, whether the battery cells undergo thermal runaway needs to be taken as a consequence evaluation item. For example, the risk of thermal runaway caused by excessive temperature due to the failure of the cooling system;

[0077] The specific meaning that the battery cells do not leak is to prevent the damage to the integrity of the battery cell housing caused by the failure of the internal structure of the battery pack during the design of the battery pack structure, which may lead to risks such as leakage and release of radioactive substances. During safety evaluation, whether the battery cells leak needs to be taken as a consequence evaluation item. For example, whether the battery pack is affected by a crushing accident, resulting in the internal structure piercing the battery cell housing and causing a leakage risk.

[0078] The integrity of the airtightness of the battery pack housing specifically means to ensure the structural strength and airtightness of the battery pack housing during the design of the battery pack. During safety evaluation, it is necessary to consider whether the battery pack housing maintains airtight integrity in the event of an accident. For example, the damage to the housing integrity caused by a stone impact accident.

[0079] S3. Divide the working conditions based on the occurrence probability of battery pack accidents, and formulate safety criteria for different working conditions;

[0080] In this embodiment, the occurrence of accidents is divided into different working conditions based on the size of the occurrence probability of battery pack accidents. For the risks that may be caused by each working condition, specific safety requirements adapted to different working conditions are formulated.

[0081] Furthermore, the working conditions include normal operation events, abnormal transient events, rare accidents, extreme accidents, and over-design accidents; the annual occurrence probability of normal operation time is between 10% and 100%, the annual occurrence probability of abnormal transient events is between 1% and 10%, the annual occurrence probability of rare accidents is between 0.1% and 1%, the annual occurrence probability of extreme accidents is between 0.01% and 0.1% of the total mass, and the annual occurrence probability of over-design accidents is less than 0.01% of the total mass, as shown in Table 2 below:

[0082] Table 2 Different Working Conditions of Battery Pack Accidents

[0083] Operating Condition Classification Operating Condition Name Annual Occurrence Probability Operating Condition 1 Normal Operation Event In the range of 10% - 100% Operating Condition 2 Abnormal Transient Event In the range of 1% - 10% Operating Condition 3 Rare Accident In the range of 0.1% - 1% Operating Condition 4 Extreme Accident In the range of 0.01% - 0.1% of the total mass Operating Condition 5 Accident Beyond Design Annual Occurrence Frequency < 0.01% of the total mass

[0084] Furthermore, the safety criteria are specifically as follows:

[0085] S31. When the battery pack accident is a normal operation event, the battery pack operates at the rated state and will not cause any accidents;

[0086] S32. When the battery pack accident is an abnormal transient event, it may cause the battery pack to be protected and powered off, but will not cause the release of harmful substances such as mercury, chromium, and lead;

[0087] S33. When the battery pack accident is a rare accident, in order to prevent harmful consequences, mitigation measures or equipment need to be put into operation so that the mass of hydrogen, carbon monoxide, methane, fluorinated carbon, hydrofluoric acid, and benzene gas released from the battery pack is less than or equal to 0.001% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack;

[0088] S34. When the battery pack accident is an extreme accident, it may cause the release of a large amount of harmful substances such as mercury, chromium, and lead. The design must be considered so that the mass of hydrogen, carbon monoxide, methane, fluorinated carbon, hydrofluoric acid, and benzene gas released from the battery pack is less than or equal to 0.01% of the total mass of the corresponding harmful gases generated after thermal runaway of all the battery cells in the battery pack;

[0089] S35. When the battery pack accident is a beyond-design accident, the probability of this accident occurring is extremely low and is not considered in the design.

[0090] In this embodiment, the safety criteria are shown in Table 3 below:

[0091] Table 3 Safety Criteria for Different Operating Conditions of Battery Pack Accidents

[0092]

[0093] S4. Based on the safety function list, sort out the battery pack accident list;

[0094] In this embodiment, based on the specific design scheme and safety function list of the battery pack, combined with the operation mode of the battery pack, a battery pack accident list including all-range basic events of battery pack accident conditions is formed.

[0095] Furthermore, the battery pack accident list is specifically as follows:

[0096] S41. Charging and discharging rate abnormal accidents, and the charging and discharging rate abnormal accidents include excessive continuous charging power, excessive continuous discharging power, excessive pulsed discharging power, and excessive pulsed charging power;

[0097] S42. Temperature abnormal accidents, and the temperature abnormal accidents include too high ambient temperature, too low ambient temperature, too fast temperature rise rate, short circuit, and continuous heating;

[0098] S43. Battery pack housing integrity abnormal accidents, where the battery pack housing integrity abnormal accidents include mechanical shock, bottom ball impact, collision, extrusion, immersion in water, scraping the bottom, and fire.

[0099] In this embodiment, the battery pack accident list is as shown in Table 4 below:

[0100] Table 4 Battery Pack Accident List

[0101]

[0102] S5. Classify the identified battery pack phenomena according to the divided working conditions to form a list of phenomena of the battery pack under different working conditions;

[0103] In this embodiment, based on step S3, the occurrence of battery pack accidents is divided into different working conditions according to the occurrence probability of battery pack accidents, combined with step S4 to sort out the battery pack accident list, and the identified battery pack phenomena are classified to form a list of phenomena of the battery pack under different working conditions;

[0104] Further, the list of phenomena of the battery pack under different working conditions is specifically as follows:

[0105] S51. When the battery pack accident is a normal operation event, the battery pack phenomena include power on, power off, rated rate discharge, rated rate charge, rated rate pulse discharge, and rated rate pulse charge;

[0106] S52. When the battery pack accident is an abnormal transient event, the battery pack phenomena include continuous charging overcurrent, continuous power generation overcurrent, pulse charging overcurrent, pulse discharge overcurrent, too high ambient temperature, and too low ambient temperature;

[0107] S53. When the battery pack accident is a rare accident, the battery pack phenomena include a decrease in the cooling capacity of the water cooling system caused by the damage of the cooling unit, a decrease in the cooling capacity of the water cooling system caused by the power failure of the water pump, an increase in the inlet temperature of the water cooling system, a decrease in the flow rate of the water cooling system, a broken shaft of the water pump, continuous heating, and too fast temperature rise rate;

[0108] S54. When the battery pack accident is an extreme accident, the battery pack phenomena include a decrease in the cooling capacity of the water cooling system caused by the stuck shaft of the water pump, thermal runaway caused by too large charge and discharge rate, collision, short circuit, mechanical shock, bottom ball impact, extrusion, immersion in water, scraping the bottom, and fire;

[0109] S55. When the battery pack accident is an over-design accident, the battery pack phenomena include a decrease in the cooling capacity of the water cooling system caused by the stuck shaft of the water pump, and the failure of the power-off protection of the protection system.

[0110] In this embodiment, the list of phenomena of the battery pack under different working conditions is as shown in Table 5 below:

[0111] Table 5 List of phenomena of the battery pack under different working conditions

[0112]

[0113]

[0114] S6. Conduct a safety analysis on each phenomenon of the battery pack under different working conditions one by one;

[0115] Furthermore, the safety analysis includes experimental analysis and simulation analysis;

[0116] In this embodiment, taking the case where there is a battery pack extrusion phenomenon when the battery pack accident is an extreme accident (working condition 4) as an example, a safety analysis is carried out on the battery pack extrusion phenomenon through CAE simulation or experimental means to evaluate the integrity of the battery pack housing and whether the internal part causes short - circuit of the battery cells, and by analogy, the safety analysis of all the phenomenon lists is carried out.

[0117] Furthermore, the specific process of conducting a safety analysis on each phenomenon of the battery pack under different working conditions one by one is as follows:

[0118] S61. Analyze the cause of the phenomenon;

[0119] In this embodiment, taking the battery pack composed of cylindrical battery cells as an example, when there is a battery pack extrusion phenomenon, the deformation amount of the battery pack housing, the short - circuit condition of the internal electrical circuit and the thermal runaway of the battery cells under extreme accident working conditions are evaluated through CAE simulation. Finally, the number of thermally runaway battery cells and the dose of harmful substances released by the thermally runaway battery cells are evaluated. The main sources of the battery pack extrusion working condition can be summarized as the following aspects:

[0120] I. Extrusion in traffic accidents; When an electric vehicle has a collision accident, especially when the battery pack's ability to resist external extrusion is insufficient, the battery pack will be extruded by the vehicle structure, and the extrusion will occur in side collisions, bottom collisions or front collisions.

[0121] II. Vehicle rollover; When an electric vehicle rolls over, the battery pack will also be extruded. Since the battery pack is usually installed at the bottom of the electric vehicle, the rollover accident will cause the battery pack to be extruded by the ground or other obstacles.

[0122] III. Human error operation; During the installation, maintenance or accident - site rescue of the battery pack, incorrect operations will lead to inappropriate extrusion of the battery pack, such as incorrect handling or processing will cause the battery pack to be subjected to excessive external force.

[0123] IV. Natural disasters; When natural disasters (such as earthquakes) occur, the collapse of buildings or vehicles will also cause extrusion to the battery pack.

[0124] S62. Description of the overall process of the phenomenon;

[0125] In this embodiment, by describing the overall process of the phenomena of the battery pack under different working conditions, it is possible to comprehensively understand the gradual development and evolution process of the battery pack under the corresponding working conditions, providing the necessary background and logical framework for subsequent safety analysis, so as to design protective measures and emergency response plans in a targeted manner.

[0126] In this embodiment, when there is a battery pack extrusion phenomenon in the battery pack, a three-dimensional coordinate system is established based on the battery pack structure. The battery pack accident will cause the XYZ directions of the battery pack to be extruded and deformed. If the deformation of the battery pack is serious, components such as the internal structure, electrical, and thermal management of the battery pack will be damaged, further leading to serious consequences such as internal short circuit and thermal runaway of the battery cells. By establishing a three-dimensional coordinate system of the battery pack structure and describing the overall process of the battery pack under different working conditions, it can provide the necessary input conditions for subsequent safety analysis.

[0127] S63. Description of the input conditions for safety analysis, where the input conditions include set parameters and simplified assumptions;

[0128] In this embodiment, a battery pack simulation model is constructed based on CAE simulation as shown in Fig. 2(a). The battery pack extrusion working condition complies with the "Safety Requirements for Power Batteries for Electric Vehicles" (GB 38031-2020). The extrusion direction is set to the X direction as shown in Fig. 2(b). The form of the extrusion plate is set to a semi-cylinder with a radius of 75 mm, and the length of the semi-cylinder is greater than the size of the battery cell to be extruded. The extrusion speed is set to 1 mm / s, and the extrusion stop condition is: when the deformation amount of the battery pack reaches 15% or the extrusion force reaches 100 kN or the extrusion force reaches 1000 times the weight of the experimental object, stop the extrusion.

[0129] S64. Evaluation of the results of safety analysis, where the results include analysis of battery cell short circuit, thermal runaway, battery pack pressure relief rate, and evaluation of battery pack combustion and explosion.

[0130] In this embodiment, the distance between the battery cells and the box of the battery pack before extrusion is 95.5 mm as shown in Fig. 2(c); when the semi-cylindrical extrusion plate moves 9.7 mm towards the box direction, the extrusion force reaches 100 kN, and the extrusion working condition meets the stop condition requirement to stop the extrusion. The force on the box reaches 695 Mpa, mainly located in the extrusion area, and the box has been torn and deformed. After extrusion, the front end of the box moves 10 mm inward as shown in Fig. 2(d); at this time, the distance between the battery cells and the box is shortened to 84.8 mm as shown in Fig. 2(e). Based on this working condition and input conditions, the extrusion plate does not squeeze the battery cells, and there is no risk of liquid leakage, short circuit, thermal runaway, combustion, or explosion.

[0131] S7. Determine whether the consequences of each accident meet the requirements according to the safety criteria under different working conditions. If not, improve the design again and re - conduct the safety analysis of this accident until the safety criteria under this working condition are met. Repeat this process until the accidents under all working conditions meet the corresponding safety criteria of their respective working conditions;

[0132] In this embodiment, taking the example that there is a battery pack extrusion phenomenon when the battery pack accident is an extreme accident (working condition 4), before making the battery pack sample, the integrity of the battery pack housing under the collision condition and whether internal short - circuit of the battery cells is caused can be evaluated through CAE simulation to ensure that the simulation results meet the safety criteria under extreme accidents (working condition 4);

[0133] After the physical sample is made, conduct a physical collision test to ensure that the test consequences also meet the safety criteria under extreme accidents (working condition 4). And so on, determine the consequences of all accidents and the safety criteria under the corresponding working conditions. If not, improve the design again and re - conduct the safety analysis of this accident until the safety criteria under this working condition are met.

[0134] Specifically, taking the CAE simulation results of the extrusion working condition in step S6 as an example, under this extrusion working condition, the box body is deformed, but the deformed box body does not squeeze the battery cells and does not cause thermal runaway of the battery cells. Therefore, no harmful gases caused by thermal runaway are generated inside the battery pack, meeting the safety criteria requirements under extreme accident working conditions (the mercury and its compounds released by the battery pack do not exceed 0.0005% of the total mass, cadmium and its compounds do not exceed 0.002% of the total mass, and lead and its compounds do not exceed 0.01% of the total mass). Therefore, the consequences of the battery pack under the extrusion accident in this design are acceptable, and then check whether the safety analysis results of the next accident meet the safety criteria corresponding to this working condition. Repeat this process until the accidents under all working conditions are traversed.

[0135] S8. Output a safety evaluation report.

[0136] Furthermore, when all accidents under all working conditions are traversed and meet the corresponding safety criteria, output a battery pack safety analysis report, give a battery pack safety evaluation conclusion, and output a complete safety evaluation report in the form of text, pictures, and tables with the above results.

[0137] Based on the macroscopic battery pack safety objectives and design principles, this embodiment constructs a battery safety function list, divides working conditions based on the actual probability of battery pack accidents, formulates safety criteria for different working conditions, further grades the identified battery pack phenomena according to the divided working conditions to form a phenomenon list of the battery pack under different working conditions, conducts safety analysis on each phenomenon of the battery pack under different working conditions one by one, compares with the safety criteria, outputs the evaluation of the battery pack accident consequences, and each link is closely linked to form a complete evaluation system with theoretical and practical guiding significance, guiding the research and development design of the battery pack, solving the problem of the lack of a complete safety evaluation of the battery pack in the new energy battery pack industry, ensuring that the design of the battery pack can not only operate stably under normal working conditions, but also minimize risks and damages to the greatest extent in case of accidents, thereby improving the overall safety and reliability of electric vehicles.

[0138] The present invention also provides a battery pack safety evaluation system, including a safety principle module, a safety list module, a safety criterion module, an accident list module, a phenomenon list module, a safety analysis module, a loop traversal module, and a safety report module;

[0139] The safety principle module is used to construct safety design principles based on the battery pack safety objectives;

[0140] The safety list module is used to construct a battery pack safety function list;

[0141] The safety criterion module is used to divide working conditions based on the probability of battery pack accidents and formulate safety criteria for different working conditions;

[0142] The accident list module is used to sort out the battery pack accident list based on the safety function list;

[0143] The phenomenon list module is used to grade the identified battery pack phenomena according to the divided working conditions to form a phenomenon list of the battery pack under different working conditions;

[0144] The safety analysis module is used to conduct safety analysis on each phenomenon of the battery pack under different working conditions one by one;

[0145] The loop traversal module is used to determine whether the consequences of each accident meet the requirements according to the safety criteria under different working conditions. If not, improve the design again and conduct safety analysis on this accident again until the safety criteria under this working condition are met, and loop until all accidents in all working conditions meet the corresponding safety criteria of this working condition;

[0146] The safety report module is used to output a safety evaluation report.

[0147] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery pack safety evaluation method, characterized in that: The following steps are involved: S1. Establish safety design principles based on battery pack safety goals; S2. Build a battery pack safety feature list; S3. Divide the working conditions based on the probability of battery pack accidents and formulate safety criteria under different working conditions; S4. Based on the safety function list, sort out the battery pack accident list; S5. Classify the identified battery pack phenomena according to the divided working conditions to form a list of battery pack phenomena under different working conditions; S6. Conduct safety analysis on each phenomenon of the battery pack under different working conditions; S7. Determine whether the consequence of each accident meets the requirements according to the safety criteria under different working conditions. If not, re-improve the design and re-analyze the accident until it meets the safety criteria under the working condition. Repeat until all accidents under all working conditions meet the safety criteria corresponding to the working condition. S8. Output safety evaluation report.

2. A battery pack safety evaluation method according to claim 1, characterized in that: The specific safety design principles described in S1 are: S11. When the mass of hydrogen, carbon monoxide, methane, carbon fluoride, hydrofluoric acid, and benzene released under the battery pack accident condition is less than or equal to 0.01% of the total mass of the corresponding harmful gases produced after thermal runaway of all cells in the battery pack, the battery pack is considered to meet the first safety design principle; S12: When the probability of thermal runaway and open fire in a single battery cell in the battery pack is between 0.1% and 1%, the probability of thermal runaway and open fire in two or more batteries in the battery pack is less than 0.1%, and the probability of battery pack explosion is less than 0.01% of the total mass, the battery pack is considered to meet the second safety design principle; S13. When the battery pack meets both the first safety design principle and the second safety design principle, it meets the battery pack safety goal.

3. A battery pack safety evaluation method according to claim 1, characterized in that: The battery pack safety feature list described in S2 includes the absence of thermal runaway of the battery cells, the absence of leakage of the battery cells, and the airtight integrity of the battery pack outer shell.

4. A battery pack safety evaluation method according to claim 1, characterized in that: The operating conditions described in S3 include normal operating events, abnormal transient events, rare accidents, extreme accidents and beyond-design accidents; The annual probability of normal operation time is between 10% and 100%, the annual probability of abnormal transient events is between 1% and 10%, the annual probability of rare accidents is between 0.1% and 1%, the annual probability of extreme accidents is between 0.01% and 0.1%, and the annual probability of beyond-design accidents is less than 0.01% of the total mass.

5. A battery pack safety evaluation method according to claim 4, characterized in that: The specific safety criteria described in S3 are: S31. When the battery pack accident is a normal operating event, the battery pack operates at the rated state and will not cause any accident; S32. When the battery pack accident is an abnormal transient event, it may cause the battery pack protection to shut down, but will not cause the release of harmful substances such as mercury, chromium, and lead; S33. When the battery pack accident is a rare accident, in order to prevent harmful consequences, mitigation measures or equipment need to be put into operation to make the mass of hydrogen, carbon monoxide, methane, carbon fluoride, hydrofluoric acid, and benzene released from the battery pack less than or equal to 0.001% of the total mass of the corresponding harmful gases generated after thermal runaway of all cells in the battery pack; S34. When the battery pack accident is an extreme accident, it may cause the release of a large amount of harmful substances such as mercury, chromium, and lead. The design must take this into consideration so that the mass of hydrogen, carbon monoxide, methane, carbon fluoride, hydrofluoric acid, and benzene released from the battery pack is less than or equal to 0.01% of the total mass of the corresponding harmful gases generated after thermal runaway of all the cells in the battery pack; S35. When the battery pack accident is an over-design accident, the probability of the accident occurring is extremely low and is not considered in the design.

6. A battery pack safety evaluation method according to claim 1, characterized in that: The battery pack accident list described in S4 is as follows: S41, abnormal charge and discharge rate accidents, including excessive continuous charging power, excessive continuous discharge power, excessive pulse discharge power and excessive pulse charging power; S42. Temperature abnormality accidents, including excessively high ambient temperature, excessively low ambient temperature, excessively fast temperature rise rate, short circuit and continuous heating; S43. Accidents related to abnormal integrity of battery pack shell, including mechanical impact, bottom ball hit, collision, extrusion, immersion in water, bottom scraping and fire.

7. A battery pack safety evaluation method according to claim 1, characterized in that: The specific list of phenomena of the battery pack under different working conditions described in S5 is as follows: S51. When the battery pack accident is a normal operation event, the battery pack phenomena include power-on, power-off, rated rate discharge, rated rate charge, rated rate pulse discharge and rated rate pulse charge; S52. When the battery pack accident is an abnormal transient event, the battery pack phenomena include continuous charging overcurrent, continuous power generation overcurrent, pulse charging overcurrent, pulse discharge overcurrent, excessively high ambient temperature, and excessively low ambient temperature; S53. When the battery pack accident is a rare accident, the battery pack phenomena include the decrease in cooling capacity of the water cooling system due to damage to the cooling unit, the decrease in cooling capacity of the water cooling system due to power failure of the water pump, the increase in the inlet temperature of the water cooling system, the decrease in the flow of the water cooling system, the broken shaft of the water pump, continuous heating and excessive temperature rise rate; S54. When the battery pack accident is an extreme accident, the battery pack phenomena include reduced cooling capacity of the water cooling system due to the water pump shaft jam, thermal runaway due to excessive charge and discharge rates, collision, short circuit, mechanical shock, bottom ball hit, extrusion, immersion, bottom scraping and fire; S55. When the battery pack accident is an over-design accident, the battery pack phenomena include the reduction of cooling capacity of the water cooling system due to the stuck shaft of the water pump and the failure of the power-off protection of the protection system.

8. A battery pack safety evaluation method according to claim 1, characterized in that: The safety analysis of each phenomenon of the battery pack under different working conditions described in S6 is as follows: S61. Analyze the causes of the phenomenon; S62. Description of the overall process of the phenomenon; S63. Description of input conditions for safety analysis, wherein the input conditions include setting parameters and simplifying assumptions; S64. Evaluate the results of the safety analysis, including battery cell short circuit, thermal runaway, battery pack pressure release rate analysis, battery pack combustion and explosion assessment.

9. A battery pack safety evaluation system, characterized in that: It includes safety principle module, safety checklist module, safety criterion module, accident checklist module, phenomenon checklist module, safety analysis module, loop traversal module and safety report module; The safety principle module is used to construct safety design principles based on battery pack safety goals; The safety list module is used to construct a battery pack safety function list; The safety criteria module is used to divide the working conditions based on the probability of battery pack accidents and formulate safety criteria under different working conditions; The accident list module is used to sort out the battery pack accident list based on the safety function list; The phenomenon list module is used to classify the identified battery pack phenomena according to the divided working conditions to form a phenomenon list of the battery pack under different working conditions; The safety analysis module is used to perform safety analysis on each phenomenon of the battery pack under different working conditions one by one; The loop traversal module is used to determine whether the consequence of each accident meets the requirements according to the safety criteria under different working conditions. If not, the design is improved and the accident is re-analyzed until the safety criteria under the working condition are met. The loop is repeated until all accidents under all working conditions meet the safety criteria corresponding to the working condition. The safety reporting module is used to output a safety evaluation report.

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