An experimental device and method for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control

Abstract

The invention discloses a lithium battery thermal runaway flame propagation characteristic under the influence of multiple parameters and its prevention and control experimental device and method, which belongs to the field of lithium battery safety protection, and includes a bracket and a visual pressure container; the upper and lower ends of the visual pressure container are respectively fixed with an upper end cover flange and a lower end cover flange; a prevention and control suppression system is installed on the upper end cover flange, and the prevention and control suppression system includes a plurality of visual pipe sections stacked in sequence, and the upper end of the visual pipe section is connected to the external environment; a porous fire-blocking component is installed between two adjacent visual pipe sections; a through hole is opened on the upper end cover flange, and the interior of the visual pressure container is connected to the interior of the visual pipe section; and also includes a battery bearing system, a pressure acquisition system, an image acquisition system and a microscopic flow field acquisition system, a synchronous controller, a program control and data acquisition system, a thermal runaway trigger system, a product analysis test system and a temperature acquisition system. The device and method can conduct thermal runaway research on battery packs and single lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery safety protection, and specifically relates to a lithium battery thermal runaway flame propagation characteristic under the influence of multiple parameters and its prevention and control suppression experimental device and method. Background Art

[0002] As a storage medium with high energy voltage, lithium battery has become one of the important electrochemical energy storage media with its excellent comprehensive performance. The special chemical composition, structure and energy storage characteristics of lithium battery make it very easy to cause thermal runaway fire and even explosion under abuse conditions such as overcharging, overheating and mechanical damage. Therefore, it is of great significance to control the flame propagation characteristics of thermal runaway of lithium battery and take effective protective measures to prevent lithium battery fire accidents.

[0003] The solid electrolyte interface film (SEI) is a solid electrolyte interface film formed at the negative electrode during the first charge and discharge process of a lithium battery. When the temperature of the lithium battery reaches 80~120°C, the metastable components of the SEI film begin to decompose. After the SEI film decomposes, the lithium embedded in the negative electrode loses protection and comes into direct contact with the electrolyte, causing it to react exothermically with the electrolyte. During this period, the battery's self-heat generation rate is greater than the heat dissipation rate, causing the internal temperature to continue to rise. When the temperature reaches the melting point of the diaphragm (130~170°C), the diaphragm begins to melt and collapse, and the positive and negative electrodes of the battery are in direct contact, resulting in a short circuit in the battery, generating a large amount of heat, and further increasing the battery temperature. When the temperature exceeds 150 °C, the positive electrode material of the battery reaches the pyrolysis temperature and begins to decompose, producing a large amount of combustible gas and oxygen. When the internal pressure of the battery reaches the threshold of the safety valve, the combustible gas sprays out to form a jet-like flame.

[0004] The current focus of lithium battery thermal runaway fire protection is mainly on adding fire extinguishing agents, and there is a lack of research on the role of porous fire-blocking components in inhibiting the spread of lithium battery thermal runaway flames.

[0005] The current research on the suppression of thermal runaway fires of lithium batteries mainly focuses on single batteries. In life, battery packs composed of single batteries are the main application form of lithium batteries. Due to their high energy density, the fire hazard is higher after thermal runaway occurs. Therefore, it is difficult to form a complete theoretical guidance for the existing research on the suppression of thermal runaway fires of lithium batteries. Summary of the invention

[0006] The present invention provides a lithium battery thermal runaway flame propagation characteristic under the influence of multiple parameters and its prevention and control suppression experimental device and method, which are used to solve the above-mentioned defects.

[0007] The invention discloses a multi-parameter-influenced lithium battery thermal runaway flame propagation characteristic and prevention and control suppression experimental device, comprising a bracket, wherein a visual pressure container is provided on the upper surface of the bracket; an upper end cover flange and a lower end cover flange are respectively fixed to the upper end and the lower end of the visual pressure container; the lower end of the visual pressure container is mounted on the bracket through the lower end cover flange, and the lower end of the visual pressure container is kept sealed;

[0008] A control and suppression system is installed on the upper surface of the upper end cover flange, and the control and suppression system includes a plurality of visualization pipe sections stacked in sequence, and the side walls of the visualization pipe sections can be seen through; each visualization pipe section is connected; the upper end of the visualization pipe section at the upper end is connected to the external environment; a porous fire-blocking component is installed between two adjacent visualization pipe sections;

[0009] A through hole is provided on the upper end cover flange, and the interior of the visualized pressure container is connected with the interior of the visualized pipe section at the lower end through the through hole;

[0010] It also includes a battery carrying system for limiting the lithium battery in the through-hole position and sealing the through-hole with the lithium battery; it also includes a pressure acquisition system for acquiring pressure data in each visualization pipeline; it also includes an image acquisition system and a microscopic flow field acquisition system for acquiring flame images and microscopic flow field images in each visualization pipeline respectively; it also includes a synchronization controller, a program control and data acquisition system for controlling and receiving the acquired data; it also includes a thermal runaway trigger system for causing thermal runaway of the lithium battery; it also includes a product analysis test system for acquiring gas components in each visualization pipeline; it also includes a temperature acquisition system for acquiring temperature data in each visualization pipeline.

[0011] Furthermore, the battery carrying system includes:

[0012] The sealing end cap has two types, which are used to limit the position of a single lithium battery and a battery pack composed of multiple lithium batteries. The sealing end cap of the battery pack is type A, and the sealing end cap of the single lithium battery is type B. Type A includes: a jacket, It is in the shape of a circular ring, inserted in the through hole, and coincides with the axis of the through hole, so as to ensure that the outer wall of the outer sleeve and the inner wall of the through hole are sealed; the earring is sleeved on the outer sleeve and fixedly connected to the outer sleeve, and the lower surface of the earring is in contact with the upper surface of the upper end cover flange; the horizontal plate is fixed on the inner wall of the outer sleeve, and the edge of the horizontal plate fits the inner wall of the outer sleeve to ensure that the outer wall of the horizontal plate and the inner wall of the outer sleeve are sealed; each positive pole of the battery pack passes through the horizontal plate, and a hole for each positive pole of the battery pack to pass through is opened on the horizontal plate; the clamping ring is fixed on the inner wall of the outer sleeve and sleeved on the battery pack, so that the battery pack can be assembled on the selection A and the selection A and the battery pack can be integrated; the selection B has no clamping ring, and the number of holes on the horizontal plate of the selection B is only one, and the other structures of the selection B are the same as those of the selection A;

[0013] A sealing flange is installed on the lower surface of the bracket;

[0014] A long hole passing through the lower surface of the visualized pressure vessel, the surface of the bracket, and the surface of the sealing flange;

[0015] The pressing component is used to support the lower end of the battery pack or the single lithium battery, and can make the upper end of the battery pack or the single lithium battery closely attached to and sealed with the sealing end cover.

[0016] The two types of sealing end caps can limit the single lithium battery and the battery pack respectively. When it is necessary to study the impact of different numbers of lithium batteries on thermal runaway, the two types of sealing end caps can be adapted to the corresponding lithium batteries.

[0017] Further, the pressing component comprises:

[0018] The adjustable screw has an axis that coincides with the axis of the long hole and is rotatably connected to the long hole, and the outer wall of the adjustable screw is sealed with the inner wall of the long hole;

[0019] The movable rod has a lower end sleeved on the upper end of the adjustable screw rod, and the movable rod is threadedly connected to the adjustable screw rod;

[0020] The stop plate is fixed to the upper end of the movable rod; the upper surface of the stop plate is concave downward to form a limiting groove, and the stop plate can be sleeved on the lower end of the battery pack or the single lithium battery through the limiting groove;

[0021] The placement edge is fixed on the inner wall of the visual pressure container;

[0022] A support plate is installed on the upper surface of the placement edge; the movable rod passes through the support plate, and a through hole is provided on the support plate for the movable rod to pass through;

[0023] The limiting long rod is fixed on the lower surface of the abutment plate. The axis of the limiting long rod is arranged vertically. The limiting long rod passes through the supporting plate. The limiting long rod, the abutment plate and the movable rod can slide along the axis direction of the limiting long rod as a whole.

[0024] Furthermore, the thermal runaway trigger system includes:

[0025] Two arc-shaped electric heaters are installed on the upper surface of the support plate and are located inside the visible pressure container; when observed along the radial direction of the movable rod, the two arc-shaped electric heaters are symmetrically arranged with respect to the axis of the movable rod; the battery can be heated to thermal runaway; each arc-shaped electric heater includes a plurality of heating rods arranged from top to bottom; the heating position can be changed by turning on or off the plurality of heating rods respectively;

[0026] The variable frequency power regulator and the voltage-stabilized power supply are electrically connected to the two arc-shaped electric heaters through a wire, and can energize the two arc-shaped electric heaters and make them work; the variable frequency power regulator is used to adjust the heating power of the arc-shaped electric heaters.

[0027] Furthermore, it also includes a battery heat flow control system, and the battery heat flow control system includes:

[0028] Four adhesive surface thermocouples; two of them are set as a group, for a total of two groups; the two groups of adhesive surface thermocouples are respectively attached to the side surfaces of two adjacent lithium batteries in the battery pack; or any one of the four adhesive surface thermocouples is attached to the side wall of a single lithium battery;

[0029] The two groups of adhesive surface thermocouples are respectively group A and group B, and the two adjacent lithium batteries are respectively lithium battery A and lithium battery B; then one of the two adhesive surface thermocouples of group A is attached to the middle position of the side of lithium battery A facing the arc electric heater, and the other is attached to the middle position of the side of lithium battery A not facing the arc electric heater; the meaning of facing is: observing from the axis of the movable rod, the adhesive surface thermocouple is not between the multiple single lithium batteries; the meaning of not facing is: observing from the axis of the movable rod, the adhesive surface thermocouple is between the multiple single lithium batteries;

[0030] One of the two adhesive surface thermocouples in group B is attached to the upper end of lithium battery B, and the other is attached to the lower end of lithium battery B. Both adhesive surface thermocouples in group B face the arc electric heater;

[0031] The heat flow data acquisition instrument is located outside the visual pressure container; it is electrically connected to all adhesive surface thermocouples through temperature data lines, and is used to collect temperature data of adhesive surface thermocouples and convert it into electrical signals for storage; it is also electrically connected to the positive and negative electrodes of the battery pack or single lithium battery through voltage data lines, and is used to monitor the voltage changes of the battery pack or single lithium battery and convert it into electrical signals for storage.

[0032] For single lithium batteries and battery packs, the adhesive surface thermocouples used are pasted in different positions, and the temperature data collected by the adhesive surface thermocouples are more objective and comprehensive.

[0033] Furthermore, the adjustable screw rod, movable rod and abutment plate are all hollow, and the temperature data line and the voltage data line pass through the adjustable screw rod, movable rod and abutment plate from the hollow positions of the adjustable screw rod, movable rod and abutment plate.

[0034] The arc electric heater can reduce the burning of the voltage data line and the temperature data line, thereby avoiding thermal damage to the voltage data line and the temperature data line.

[0035] Further, the gas supply system comprises:

[0036] The main air pipe is fixed on the outer wall of the visualized pressure container, one end of which is connected to the inside of the visualized pressure container and the other end is sealed;

[0037] Multiple branch air pipes, one end of which is respectively connected to the outer wall of the main air pipe and communicates with the main air pipe;

[0038] Multiple gas cylinder gas sources are arranged one by one corresponding to the gas distribution pipes, and are respectively connected to the end of the corresponding gas distribution pipe away from the main gas pipe. The internal gas can be filled into the visual pressure container through the gas distribution pipe and the main gas pipe respectively. Auxiliary valves are installed on the multiple gas distribution pipes respectively; and the main gas pipe is installed with a main valve.

[0039] Different types of gases can be filled into the visualized pressure vessel to study the effects of different types of gases on battery thermal runaway.

[0040] Furthermore, an exhaust pipe is installed on the outer side wall of the visualized pressure container, one end of the exhaust pipe is connected to the external environment of the visualized pressure container, and the other end is connected to the external environment of the visualized pressure container, and an exhaust valve is installed on the exhaust pipe;

[0041] A control main pipe is installed on the outer wall of the visualized pressure container, one end of the control main pipe is connected to the visualized pressure container, and the other end is sealed. An exhaust pipe and an air blowing pipe are installed on the outer wall of the control main pipe, one end of the exhaust pipe and the air blowing pipe are connected to the control main pipe, and the other ends are respectively connected to a vacuum pump and a compressor. A first valve is installed on the control main pipe; a second valve and a third valve are installed on the exhaust pipe and the air blowing pipe; a vacuum pressure gauge for monitoring the pressure in the visualized pressure container is installed on the control main pipe.

[0042] The pressure in the visualized pressure container can be adjusted to make the pressure in the visualized pressure container exceed or be lower than the atmospheric pressure, and the influence of different initial environmental pressures on the thermal runaway of lithium batteries can be studied. The experimental products in the visualized pressure container can also be purged out of the visualized pressure container through the exhaust pipe.

[0043] Furthermore, the voltage-stabilized power supply is also electrically connected to the lithium battery for charging the lithium battery to prevent electrical abuse of the lithium battery, which includes overcharging and external short circuit.

[0044] It can study the effect of lithium battery abuse on thermal runaway of lithium batteries.

[0045] An experimental method for thermal runaway flame propagation characteristics of lithium batteries under the influence of multiple parameters and its prevention and control inhibition includes the following steps:

[0046] S1: Assemble the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries and its prevention and control under the influence of multiple parameters;

[0047] S2: Close the exhaust valve, the main valve, multiple auxiliary valves, the first valve, the second valve and the third valve; turn off the vacuum pump and the compressor;

[0048] S3: Manually open the first valve, the second valve and the vacuum pump; the vacuum pump evacuates the interior of the visual pressure container;

[0049] When the pressure value of the vacuum pressure gauge reaches Q, the first valve, the second valve and the vacuum pump are manually closed; at this time, the vacuum in the pressure container is visualized;

[0050] S4: manually open the main valve and one or more of the auxiliary valves; fill one or more types of gas into the visual pressure container; when the pressure value of the vacuum pressure gauge reaches the standard atmospheric pressure, close the main valve and the auxiliary valves;

[0051] S5: Turn on all high-speed cameras, all schlieren instruments and high-frequency infrared thermal imagers in the image acquisition system and the microscopic flow field acquisition system through the synchronous control system, program control and data acquisition system;

[0052] Through the synchronous control system, program control and data acquisition system, the arc electric heater is turned on to heat the lithium battery until the lithium battery has thermal runaway;

[0053] S6: Through the synchronous control system, program control and data acquisition system, collect the pressure data of all high-frequency pressure sensors in the pressure acquisition system, the temperature data of all high-frequency temperature thermocouples in the temperature acquisition system, the temperature distribution and temperature rise process image data taken by the high-frequency infrared thermal imager in the image acquisition system, the discharge flame propagation characteristic image data taken by the high-speed camera in the image acquisition system, the microscopic flow field structure image data taken by the schlieren instrument in all microscopic flow field acquisition systems, the ion composition data in the product analysis test system, and the surface temperature data of the lithium battery in the heat flow data acquisition instrument and the voltage data during thermal runaway;

[0054] At this point, an experiment is completed and a set of data is obtained; after the experiment is over, the exhaust valve, the first valve, the third valve and the compressor are opened; ensuring that the experimental product of the visualized pressure container is purged out of the visualized pressure container from the exhaust pipe;

[0055] S7: dismantle the control and suppression system and reinstall the lithium battery, change the experimental conditions, repeat S1-S7, conduct multiple experiments, and collect multiple sets of data;

[0056] Experimental conditions include:

[0057] 1) In step S4, after the gas pressure inside the visualized pressure container reaches the standard atmospheric pressure, the first valve, the second valve and the vacuum pump are manually opened, and the gas in the visualized pressure container is extracted by the vacuum pump, so that the gas pressure inside the visualized pressure container in step S4 is lower than the normal pressure;

[0058] Alternatively, in step S4, after the air pressure inside the visualized pressure container reaches the standard atmospheric pressure, the first valve, the third valve and the compressor are manually opened, and air is filled into the visualized pressure container through the compressor, so that the air pressure inside the visualized pressure container in step S4 is higher than the normal pressure;

[0059] Able to explore the effects of different initial pressures inside the visual pressure vessel on the thermal runaway process of lithium batteries and the flame propagation characteristics of thermal runaway;

[0060] 2) In step S4, manually open the main valve and one or more of the auxiliary valves; change the type of liquid charged into the visual pressure container;

[0061] Able to explore the effects of different types of gases inside a visual pressure vessel on the thermal runaway process of lithium batteries and the flame propagation characteristics of thermal runaway;

[0062] 3) In step S1, the type, number of holes, thickness, installation position or effective area of ​​the two porous fire-blocking components are changed;

[0063] Able to explore the effect of porous fire-blocking components on the suppression of lithium battery jet flames when the lithium battery is in thermal runaway; able to determine the optimal porous fire-blocking components and installation locations;

[0064] 4) In step S5, the triggering condition of thermal runaway is changed, and the triggering condition includes changing the heating power and heating position of the arc electric heater by the variable frequency power regulator; and also includes charging the lithium battery with a regulated power supply to realize the situation of overcharging and abuse of the lithium battery; electrical abuse: overcharging, external short circuit;

[0065] 5) In step S7, the selection of single lithium battery or battery pack, the series and parallel connection of each single lithium battery in the resistor group, the state of charge SOC of the lithium battery, the positive electrode material of the lithium battery, the cycle aging degree of the lithium battery, and the mechanical damage degree of the lithium battery are changed;

[0066] Able to explore the influence of lithium battery status on its thermal runaway process and thermal runaway flame propagation characteristics;

[0067] S8: Analyze multiple sets of data. Beneficial Effects

[0068] The process of fluid flow state transformation, flow and heat transfer, shock wave attenuation, etc. when the released product explosion flame enters the two porous fire-blocking components is clarified. The quantitative relationship between the fire-blocking components and the thermal runaway flame propagation speed and shock wave pressure of lithium batteries under the influence of multiple parameters is established, and the optimization method of the fire-blocking components is proposed. The critical conditions and critical criteria of fire blocking are clarified, so as to effectively control the propagation of thermal runaway flames and prevent the battery pack from self-igniting or igniting other combustibles, providing theoretical basis and technical support for the development of lithium battery thermal runaway disaster protection theory and key protection technology research and development.

[0069] Change the structural parameters of porous fire-blocking components (fire-blocking method, number of layers, mesh size, type, effective area, etc.) to study the factors affecting fire prevention and control and their mechanism of action;

[0070] In-depth research on the influence of the structural parameters of fire-blocking components on the blocking of runaway products by fire-blocking components, establish the influence of the structural parameters of fire-blocking components on the suppression of lithium battery jet flames, and establish a quantitative relationship between multiple factors affecting the fire-blocking characteristic parameters, determine the optimal structure of the fire-blocking components and their combined installation method, and achieve effective prevention and control of thermal runaway flames of lithium-ion batteries;

[0071] It can realize the comprehensive correlation analysis of the flame propagation characteristics and characteristic parameters (combustible gas composition, flame temperature, pressure and its pressure rise rate, flame morphology transformation, etc.) during the thermal runaway of lithium-ion batteries, and clarify the transient evolution process of the discharge flame and flow field under the coupling of multiple physical fields such as temperature field, velocity field, pressure field, density field, etc. when the thermal runaway of lithium-ion batteries is triggered, which makes up for the lack of research on the evolution and propagation laws of the dangerous characteristics of thermal runaway of lithium-ion batteries. At the same time, it deeply analyzes the intermittent development process and laws of the thermal runaway jet flame of lithium-ion batteries, reveals its re-ignition and weakening mechanism, and provides technical guidance for the safety protection of lithium batteries.

[0072] It can realize the research on the flame characteristics of thermal runaway fire of lithium-ion batteries and the influence law and mechanism of fire protection, and the research on the flame dynamic characteristics of lithium batteries under multi-parameter conditions and their influence mechanism.

[0073] The use of porous fire-blocking components to prevent and control the spread of thermal runaway flames in lithium batteries, combined with different thermal runaway triggering methods such as external heat sources and overcharging, can enable research on the flame propagation process and its prevention and control performance under different working conditions as well as its influencing factors and mechanisms, which can deeply reveal the mechanism of fire-blocking prevention and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a schematic diagram of the overall structure of the device;

[0075] Figure 2 It is a structural diagram of the visual pipe segment;

[0076] Figure 3It is a schematic diagram of the structure when the sealing gland is connected to the battery pack;

[0077] Figure 4 It is a schematic diagram of the structure when the sealing gland is connected to a single lithium battery;

[0078] Figure 5 This is a front view of the adhesive surface thermocouple connected to the battery pack;

[0079] Figure 6 It is a top view of the adhesive surface thermocouple connected to the battery pack;

[0080] Figure 7 It is a structural schematic diagram of the pressing component;

[0081] Figure 8 This is a schematic diagram of the development process of the jet flame morphology of the thermal runaway of 18650 lithium-ion battery;

[0082] Fig. 9 This is the image of the fourth jet flame process of the thermal runaway flame;

[0083] Fig.10 is the temperature curve of each point in the fourth jet flame; Fig.10 (a) is the temperature curve diagram of the first temperature collection point; Fig.10 (b) is the temperature curve diagram of the 5th temperature collection point; Fig.10 (c) is the temperature curve diagram of the 9th temperature collection point; Fig.10 (d) is the temperature curve diagram of the 13th temperature collection point.

[0084] Fig.11 This is a schematic diagram of the battery temperature and voltage changing over time.

[0085] 1. Bracket; 2. Visual pressure vessel; 3. Upper end cover flange; 4. Lower end cover flange; 5. Visual window; 6. Exhaust pipe; 7. Exhaust valve; 8. Control main pipe; 9. Exhaust pipe; 10. Blowing pipe; 11. First valve; 12. Vacuum pump; 13. Compressor; 14. Second valve; 15. Third valve; 16. Visual pipe section; 17. Porous fire-blocking component; 18. Through hole; 19. First window; 20. Second window; 21. Third window; 22. Sealing gland; 23. Jacket; 24. Earring; 25. Horizontal plate; 26. Clamp; 27. Sealing flange; 28. Placement edge; 29. ​​Support plate; 30. Wire hole; 31. Long hole; 32, adjustable screw; 33, movable rod; 34, stop plate; 35, limit long rod; 36, arc electric heater; 37, variable frequency power regulator; 38, voltage-stabilized power supply; 39, gas cylinder gas source; 40, main gas pipe; 41, gas distribution pipe; 42, main valve; 43, auxiliary valve; 451, light source; 452, focusing lens; 453, reflector; 454, second high-speed camera; 46, high-frequency pressure sensor; 47, high-frequency temperature thermocouple; 48, high-speed infrared thermal imager; 49, adhesive surface thermocouple; 50, heat flow data acquisition instrument; 51, temperature data line; 52, voltage data line; 53, ion detector; 54, vacuum pressure gauge. DETAILED DESCRIPTION

[0086] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of 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.

[0087] See Figure 1 Embodiment 1: A multi-parameter lithium battery thermal runaway flame propagation characteristics and its prevention and control suppression experimental device, including a visual pressure bearing system, a prevention and control suppression system, a battery bearing system, a thermal runaway trigger system, a gas supply system, an image acquisition system, a microscopic flow field acquisition system, a pressure acquisition system, a temperature acquisition system, a battery heat flow control system, a product analysis and testing system, a synchronous control system, and a program control and data acquisition system.

[0088] Among them, the visual pressure system includes:

[0089] Bracket 1; made of stainless steel;

[0090] Visual pressure container 2, in this embodiment, the visual pressure container 2 is in the shape of a hollow cube; it is placed on the upper surface of the bracket 1; the upper end and lower end of the outer wall of the visual pressure container 2 are respectively fixed with an upper end cover flange 3 and a lower end cover flange 4, and the lower end cover flange 4 is connected to the bracket 1 by bolts. The bracket 1 serves to support and fix the visual pressure container 2 and can seal the lower end of the visual pressure container 2. A visual window 5 is installed on the side of the visual pressure container 2, and the battery surface temperature and its morphological changes during the heating process of the lithium battery in the visual pressure container 2 can be observed through the visual window 5.

[0091] The exhaust pipe 6 is installed on the outer wall of the visualized pressure container 2, one end of which is connected to the inside of the visualized pressure container 2, and the other end of which is connected to the external environment of the visualized pressure container 2. The exhaust pipe 6 is installed with an exhaust valve 7 for opening and closing the exhaust pipe 6. The exhaust pipe 6 is used to achieve the purpose of gas replacement between the inside and outside of the visualized pressure container 2. The valves mentioned in the previous and later parts of this application are all ball valves.

[0092] The control main pipe 8 is installed on the outer wall of the visualization pressure container 2, one end of which is connected to the visualization pressure container 2, and the other end is sealed. The gas in the visualization pressure container 2 can be extracted out of the visualization pressure container 2 through the control main pipe 8 to change the internal pressure of the visualization pressure container 2; the gas can also be blown into the visualization pressure container 2 through the control main pipe 8 to achieve the purpose of blowing away the experimental product or changing the internal pressure of the visualization pressure container 2.

[0093] Specifically, an exhaust pipe 9 and an air blowing pipe 10 are connected to the side wall of the control main pipe 8, respectively, and the exhaust pipe 9 and the air blowing pipe 10 can be connected to the control main pipe 8 respectively. A vacuum pressure gauge 54 is installed on the control main pipe 8 to monitor the internal pressure of the visual pressure container 2. A first valve 11 is also installed on the control main pipe 8. The first valve 11 is located between the vacuum pressure gauge 54 and the outer wall of the visual pressure container 2. The first valve 11 is used to open and close the control main pipe 8 and can also protect the vacuum pressure gauge 54. A vacuum pump 12 is connected to the end of the exhaust pipe 9 away from the control main pipe 8; a compressor 13 is connected to the end of the air blowing pipe 10 away from the control main pipe 8; a second valve 14 and a third valve 15 are installed on the exhaust pipe 9 and the air blowing pipe 10 respectively.

[0094] Close the exhaust valve 7, open the vacuum pump 12, the first valve 11 and the second valve 14, the vacuum pump 12 can extract the gas inside the visualization pressure container 2 out of the visualization pressure container 2, and reduce the pressure in the visualization pressure container 2. Close the exhaust valve 7, open the compressor 13, the first valve 11 and the third valve 15, the compressor 13 can fill the outside gas into the visualization pressure container 2, and increase the pressure in the visualization pressure container 2. Open the exhaust valve 7, open the compressor 13, the first valve 11 and the third valve 15, the compressor 13 can fill the outside gas into the visualization pressure container 2 and discharge it from the exhaust pipe 6, so as to achieve the purpose of purging the experimental products inside the visualization pressure container 2.

[0095] See Figure 2 , the prevention and control suppression system includes:

[0096] Three visualization pipe sections 16 are stacked in sequence. The three visualization pipe sections 16 have different shapes. Assuming that the center lines of the three visualization pipe sections 16 are all arranged vertically and overlap, the three visualization pipe sections 16 can be interconnected.

[0097] Assume that three visualization pipe segments 16 are visualization pipe segment A, visualization pipe segment B and visualization pipe segment C from top to bottom, and two adjacent visualization pipe segments 16 are connected by flanges.

[0098] Among them, the visualization pipe section C is fixed to the upper surface of the upper end cover flange 3 by flanges and bolts. A porous fire-blocking component 17 is provided between two adjacent visualization pipe sections 16, and the porous fire-blocking component 17 is fixed between two adjacent visualization pipe sections 16 by compression. The porous fire-blocking component 17 adopts a porous structure. In this embodiment, only the porous fire-blocking component 17 is provided between the visualization pipe section A and the visualization pipe section B, and between the visualization pipe section B and the visualization pipe section C; the porous fire-blocking component 17 between the visualization pipe section A and the visualization pipe section B is set as the first porous fire-blocking component; the porous fire-blocking component 17 between the visualization pipe section B and the visualization pipe section C is set as the second porous fire-blocking component.

[0099] The porous fire-blocking member 17 can be made of metal mesh, nickel foam and ceramic foam. The size of the porous fire-blocking member 17 is determined by the horizontal cross-sectional area of ​​the visualization pipe section 16 to ensure that the porous fire-blocking member 17 can completely cover the opening of the visualization pipe section 16.

[0100] See Figure 1 and Figure 2A through hole 18 is provided in the middle of the upper end cover flange 3, and the axis of the through hole 18 is arranged vertically. The three visualization pipe segments 16 as a whole can communicate with the interior of the visualization pressure container 2 through the through hole 18, and the upper end thereof is communicated with the external environment. The visualization pipe segment A, the visualization pipe segment B and the visualization pipe segment C are respectively provided with a first window 19, a second window 20 and a third window 21, which are used to observe the interior of the three visualization pipe segments 16.

[0101] See Figure 3 and Figure 4 , the battery carrying system includes:

[0102] The sealing gland 22 has two types of options, which are used to limit the position of a single lithium battery and a battery pack composed of multiple lithium batteries; multiple lithium batteries in the battery pack can be connected in parallel or in series. The two types of options of the sealing gland 22 are respectively: option A and option B. Figure 3 , Selection A is used to limit the battery pack composed of multiple lithium batteries, see Figure 4 , Type B is used to limit the position of single lithium battery.

[0103] Option A includes:

[0104] The outer sleeve 23 is annular and is inserted into the through hole 18 . The axis of the outer sleeve 23 coincides with the axis of the through hole 18 . The outer wall of the outer sleeve 23 is in contact with the inner wall of the through hole 18 and is sealed.

[0105] The earring 24 is in a circular shape and is sleeved on the outer sleeve 23. The earring 24 is located at the upper end of the outer sleeve 23 and is fixedly connected to the outer sleeve 23. The earring 24 is placed on the upper surface of the upper end cover flange 3, that is, the lower surface of the earring 24 abuts against the upper surface of the upper end cover flange 3; the lower surface of the flange at the lower end of the visualization pipe section C abuts against the upper surface of the earring 24, and the flange at the lower end of the visualization pipe section C is connected to the upper end cover flange 3 by bolts, so as to achieve the purpose of stably restricting the earring 24 on the upper end cover flange 3. In this embodiment, the earring 24 is also fixed to the upper end cover flange 3 by bolts.

[0106] The horizontal plate 25 is fixed on the inner wall of the outer shell 23, and the edge of the horizontal plate 25 is in close contact with the inner wall of the outer shell 23 to maintain a seal. The horizontal plate 25 is provided with a plurality of holes in the vertical direction, each of which is sleeved on the positive electrode of each lithium battery of the battery pack and clamps the lithium battery as a whole. In this embodiment, the horizontal plate 25 is provided with four holes, which can be sleeved on each positive electrode of the battery pack composed of four single lithium batteries.

[0107] The clamp ring 26 is fixed to the lower end of the inner wall of the outer sleeve 23 and is in a circular ring shape. The axis of the clamp ring 26 coincides with the axis of the outer sleeve 23. A limiting ring that cooperates with the clamp ring 26 is provided on the outer wall of the battery pack composed of four single lithium batteries. The battery pack can be assembled into a whole more firmly with the selection A by relying on the cooperation between the clamp ring 26 and the limiting ring.

[0108] See Figure 4 The difference between the selection B and the selection A is that the horizontal plate 25 of the selection B has only one hole and can only be mounted on the positive electrode of the single lithium battery. In addition, the selection B does not have a clamping ring 26, and there is no need to firmly limit the single lithium battery. Whether it is the selection A or the selection B, the horizontal plate 25 is sealed with the upper surface of the single lithium battery or the battery pack.

[0109] See Figure 1 , the battery carrying system also includes:

[0110] A sealing flange 27 is mounted on the lower surface of the bracket 1;

[0111] The placement edge 28 is horizontally arranged in the visualization pressure container 2 . The placement edge 28 is ring-shaped, and the outer wall of the placement edge 28 is fixedly connected to the inner wall of the visualization pressure container 2 .

[0112] The support plate 29 is horizontally placed on the upper surface of the placement edge 28, and is fixedly connected to the placement edge 28 by bolts. A through hole is provided in the middle of the support plate 29. Two wire holes 30 are also provided on the support plate 29 to prevent the support plate 29 from dividing the visualized pressure container 2 into two independent cavities.

[0113] The long hole 31 is arranged in the vertical direction and passes through the lower surface of the visual pressure container 2, the surface of the bracket 1 and the surface of the sealing flange 27;

[0114] See Figure 7 , a clamping component; the clamping component further comprises:

[0115] The adjustable screw rod 32 is hollow and penetrates the long hole 31. The axis of the adjustable screw rod 32 coincides with the axis of the long hole 31. The lower end of the adjustable screw rod 32 passes through the long hole 31. The lower end of the adjustable screw rod 32 is provided with a knob for a person to rotate the adjustable screw rod 32. The adjustable screw rod 32 is rotatably connected in the long hole 31. The adjustable screw rod 32 can rotate around the axis of the long hole 31. The adjustable screw rod 32 and the long hole 31 are sealed.

[0116] The movable rod 33 is hollow, and its lower end is sleeved on the adjustable screw rod 32, and the movable rod 33 is threadedly connected with the adjustable screw rod 32. The movable rod 33 is inserted into the through hole.

[0117] The plate 34 is hollow inside and fixed to the upper end of the movable rod 33. The upper surface of the plate 34 is concave downward to form a limiting groove. The plate 34 can be sleeved on the lower end of the single lithium battery or battery pack through the limiting groove. The upper surface of the plate 34 can abut the lower surface of the single lithium battery or battery pack. As the operator continuously rotates the adjustable screw 32, the plate 34 and the movable rod 33 continuously move upward as a whole, and the lower surface of the horizontal plate 25 and the upper surface of the plate 34 jointly press the single lithium battery or battery pack.

[0118] The limiting long rod 35 is fixed on the lower surface of the abutment plate 34 . The axis of the limiting long rod 35 is arranged vertically. The limiting long rod 35 passes through the support plate 29 . The limiting long rod 35 can slide relative to the support plate 29 along its axis direction.

[0119] When the operator turns the knob, the adjustable screw 32 also rotates because the movable rod 33 is threadedly connected to the adjustable screw 32. At the same time, the movable rod 33 is also restricted by the support plate 29 through the abutment plate 34 and the limiting long rod 35. Therefore, the movable rod 33 slides vertically under the action of the adjustable screw 32, that is, the movable rod 33, the abutment plate 34 and the limiting long rod 35 slide vertically as a whole.

[0120] See Figure 1 , the thermal runaway trigger system includes:

[0121] The two arc-shaped electric heaters 36 are both fixed on the upper surface of the support plate 29 and are located inside the visible pressure container; viewed along the radial direction of the movable rod 33, the two arc-shaped electric heaters 36 are symmetrically arranged with respect to the axis of the movable rod 33. The two arc-shaped electric heaters 36 are used to heat the above-mentioned single lithium battery or battery pack. Viewed from the axis of the movable rod 33, the shape of the two arc-shaped electric heaters 36 is an arc. The arc-shaped electric heater 36 includes a plurality of heating rods spaced from top to bottom, and the opening and closing of each heating rod can be controlled separately by the variable frequency power regulator 37 described below, thereby realizing the change of the heating position of the single lithium battery or battery pack.

[0122] The variable frequency power regulator 37 and the voltage-stabilized power supply 38 are electrically connected to the two arc-shaped electric heaters 36 through wires. Taking the connection of one of the arc-shaped electric heaters 36 as an example, the data line passes from the side wall of the visualized pressure vessel 2 to the inside of the visualized pressure vessel 2, and the data line is located below the support plate 29 at this time, and then the data line passes through the wire hole 30 to connect with one of the arc-shaped electric heaters 36, and finally, the data line passes from the side wall of the visualized pressure vessel 2 back to the voltage-stabilized power supply 38 to form a loop. The voltage-stabilized power supply 38 provides electrical energy for the operation of the arc-shaped electric heater 36, and the variable frequency power regulator 37 is used to regulate the heating power of the arc-shaped electric heater 36.

[0123] The voltage-stabilized power supply 38 is also electrically connected to the positive and negative electrodes of the single lithium battery or battery pack through wires to simulate thermal runaway of the single lithium battery or battery pack under electrical abuse.

[0124] The gas supply system includes:

[0125] Three gas cylinders 39, with Figure 1 From the perspective, from left to right, it contains high-pressure air, high-pressure carbon dioxide and high-pressure nitrogen respectively;

[0126] The main air pipe 40 is fixed on the outer wall of the visualized pressure container 2, one end of which is connected to the inside of the visualized pressure container 2 and the other end is sealed; the main air pipe 40 is connected to a main valve 42 for opening and closing the main air pipe 40;

[0127] The three gas distribution pipes 41 are respectively connected to the outer wall of the main gas pipe 40 and are all connected to the main gas pipe 40; the three gas cylinder gas sources 39 are respectively connected to one end of the corresponding gas distribution pipes 41 away from the main gas pipe 40. The three gas distribution pipes 41 are respectively connected to the auxiliary valves 43 for opening and closing the corresponding gas distribution pipes 41.

[0128] The image acquisition system includes:

[0129] Multiple high-speed cameras ( Figure 1 ), which are used to collect images of the flame morphology evolution and propagation characteristics after thermal runaway of the lithium battery in the corresponding visualization pipe section 16 through the first window 19, the second window 20 and the third window 21 respectively; and can also collect the ignition process and the flame morphology evolution and propagation characteristics after the external environment at the upper end of the visualization pipe section A releases gas.

[0130] The multiple high-speed cameras are electrically connected to the program control and data acquisition system through a synchronous controller, so as to control the startup of each high-speed camera.

[0131] The high-speed infrared thermal imager 48, with the lens facing the upper end of the visualization pipe A, is used to collect the temperature distribution and temperature rise process of the lithium battery main structure at different stages of the heating process, the thermal radiation propagation process of the thermal runaway flame, and the flame temperature distribution change law under the fire prevention and control conditions of the blocked components. The program control and data acquisition systems are connected through the synchronous controller.

[0132] The microscopic flow field acquisition system includes:

[0133] Multiple Schlieren instruments can respectively capture microscopic flow field images in the corresponding visualization pipe segment 16 through the first window 19, the second window 20 and the third window 21. The Schlieren instrument belongs to the prior art, and includes a light source 451, a focusing lens 452, two reflectors 453 and a second high-speed camera 454. The light emitted by the light source 451 shines on one of the reflectors 453, and the reflector 453 reflects the light to the other reflector 453, and finally, the light is captured by the second high-speed camera 454 through the focusing lens 452. The optical path between the two reflectors 453 in each Schlieren instrument can respectively pass through the corresponding first window 19, the second window 20 and the third window 21. The Schlieren instrument can also capture the microscopic flow field image of the external environment at the upper end of the visualization pipe segment A. Similarly, the optical path between the two reflectors 453 of the Schlieren instrument passes through the external environment at the upper end of the visualization pipe segment A.

[0134] See Figure 1 and Figure 2 , the pressure acquisition system includes:

[0135] The four high-frequency pressure sensors 46 are respectively denoted as high-frequency pressure sensor A, high-frequency pressure sensor B, high-frequency pressure sensor C and high-frequency pressure sensor D; the four high-frequency pressure sensors 46 are connected to the program control and data acquisition system through a synchronous controller.

[0136] Among them, the high-frequency pressure sensor A is installed on the side of the visualization pipe section C, and the height of the high-frequency pressure sensor A is lower than the second porous fire-blocking component; it is used to collect the pressure data changes before the flame and shock wave formed after the thermal runaway of the lithium battery reach the second porous fire-blocking component.

[0137] The high-frequency pressure sensor B is installed on the side of the visualization pipe section B. The height of the high-frequency pressure sensor B is lower than the first porous fire-blocking component but higher than the second porous fire-blocking component. It is used to collect the pressure data changes after the flame and shock wave formed after thermal runaway of the lithium battery passes through the second porous fire-blocking component and before reaching the first porous fire-blocking component.

[0138] The high-frequency pressure sensor C is installed on the side of the visualization pipe section A. The height of the high-frequency pressure sensor C is higher than the first porous fire-blocking component, but lower than the upper end of the visualization pipe section A. It is used to collect the pressure data changes after the thermal runaway flame of the lithium battery passes through the first porous fire-blocking component and the second porous fire-blocking component.

[0139] The high-frequency pressure sensor D is installed above the upper end of the visualization pipe section A to collect the pressure data changes after the flame of the lithium battery is released to the outside above the visualization pipe A after thermal runaway.

[0140] The temperature acquisition system includes:

[0141] The four high-frequency temperature thermocouples 47 are respectively denoted as high-frequency temperature thermocouple A, high-frequency temperature thermocouple B, high-frequency temperature thermocouple C and high-frequency temperature thermocouple D; all of them are connected to the program control and data acquisition system through a synchronous controller.

[0142] The high-frequency temperature thermocouple A, the high-frequency temperature thermocouple B, the high-frequency temperature thermocouple C and the high-frequency temperature thermocouple D are at the same height as the corresponding high-frequency pressure sensor A, the high-frequency pressure sensor B, the high-frequency pressure sensor C and the high-frequency pressure sensor D, and are installed near the corresponding high-frequency pressure sensor A, the high-frequency pressure sensor B, the high-frequency pressure sensor C and the high-frequency pressure sensor D.

[0143] The high-frequency temperature thermocouple A is used to collect temperature data changes before the flame and shock wave formed after the thermal runaway of the lithium battery reach the second porous fire-blocking component;

[0144] The high-frequency temperature thermocouple B is used to collect temperature data changes after the flame and shock wave formed after thermal runaway of the lithium battery pass through the second porous fire-blocking component and before reaching the first porous fire-blocking component.

[0145] The high-frequency temperature thermocouple C is used to collect temperature data changes after the thermal runaway flame of the lithium battery passes through the first porous fire-blocking component and the second porous fire-blocking component.

[0146] The high-frequency temperature thermocouple D is used to collect the temperature data changes after the flame of the lithium battery is released to the outside at the upper end of the visualization pipeline A after thermal runaway.

[0147] See Figure 5 and Figure 6 , the battery heat flow control system includes:

[0148] The four adhesive surface thermocouples 49 are respectively denoted as adhesive surface thermocouple A, adhesive surface thermocouple B, adhesive surface thermocouple C and adhesive surface thermocouple D; they are connected to the program control and data acquisition system through a synchronous controller.

[0149] For a battery pack consisting of four single lithium batteries, the adhesive surface thermocouple A, the adhesive surface thermocouple B, the adhesive surface thermocouple C and the adhesive surface thermocouple D are attached in the following manner:

[0150] First, two adjacent single lithium batteries in a battery pack consisting of four single lithium batteries are selected and recorded as lithium battery A and lithium battery B respectively;

[0151] Paste the adhesive surface thermocouple A on the middle of the side wall of the lithium battery A, and ensure that the adhesive surface thermocouple A faces the arc-shaped electric heater 36; the direction means: see Figure 5 From the top view, the adhesive surface thermocouple A is located between the four single lithium batteries of the battery pack.

[0152] The adhesive surface thermocouple B is attached to the middle of the side wall of the lithium battery A, and it is ensured that the adhesive surface thermocouple A is not facing the arc-shaped electric heater 36; the meaning of non-facing is: see Figure 5 , from a top view, the adhesive surface thermocouple B is located between the four single lithium batteries of the battery pack.

[0153] Paste the adhesive surface thermocouple C on the side wall of the lithium battery B near the positive electrode, and ensure that the adhesive surface thermocouple C faces the arc-shaped electric heater 36;

[0154] The adhesive surface thermocouple D is attached to one end of the side wall of the lithium battery B close to the negative electrode, and ensure that the adhesive surface thermocouple D faces the arc-shaped electric heater 36 .

[0155] For a single lithium battery, each adhesive surface thermocouple 49 is attached in the following manner:

[0156] First, any one of the adhesive surface thermocouples A, B, C and D is selected as the adhesive surface thermocouple 49; the other adhesive surface thermocouples 49 are not used.

[0157] Then, the adhesive surface thermocouple 49 is attached to the side of the single lithium battery. Because the side of a single lithium battery is facing the arc-shaped electric heater 36, the surface temperature of the single lithium battery can be collected by simply attaching the adhesive surface thermocouple 49 to the side of the single lithium battery.

[0158] See Figure 1 , a heat flow data acquisition instrument 50 is located outside the visual pressure vessel 2 and is electrically connected to each adhesive surface thermocouple 49 through a temperature data line 51. The temperature collected by each adhesive surface thermocouple 49 is recorded in the heat flow data acquisition instrument 50;

[0159] In addition, there is a voltage data line 52, one end of which is connected to the positive and negative electrodes of all lithium batteries respectively, and the other end is connected to the thermal flow data collector 50. It is used to collect the battery voltage change from the initial state before the experiment to the thermal runaway state.

[0160] The temperature data line 51 and the voltage data line 52 pass through the internal cavities of the adjustable screw 32, the movable rod 33 and the contact plate 34 in sequence, and finally pass through the upper end of the contact plate 34, and are respectively connected to the corresponding adhesive surface thermocouple 49 or lithium battery. Since most of the temperature data line 51 and the voltage data line 52 are located in the internal cavities of the adjustable screw 32, the movable rod 33 and the contact plate 34, the heating effect of the arc electric heater 36 on the temperature data line 51 and the voltage data line 52 can be reduced, and the temperature data line 51 and the voltage data line 52 can be prevented from being damaged by heat. At the same time, due to the internal cavities of the adjustable screw 32, the movable rod 33 and the contact plate 34, the temperature data line 51 and the voltage data line 52 are not affected by the rotation and movement of the adjustable screw 32, the movable rod 33 and the contact plate 34.

[0161] Product analysis and testing system includes:

[0162] four ion detectors 53, respectively denoted as ion detector A, ion detector B, ion detector C and ion detector D;

[0163] Ion detector A, ion detector B, ion detector C and ion detector D are respectively at the same height as the corresponding high-frequency temperature thermocouple A, high-frequency temperature thermocouple B, high-frequency temperature thermocouple C and high-frequency temperature thermocouple D. Among them, ion detector A, ion detector B, ion detector C are respectively installed on the side walls of visualization pipeline C, visualization pipeline B and visualization pipeline A; ion detector D is installed above the upper end of visualization pipeline A.

[0164] Ion detector A is used to collect the ion products of high-temperature combustible gas ejected from the lithium battery safety valve after the lithium battery releases heat.

[0165] The ion detector B is used to collect the ion products of the high-temperature combustible gas after being suppressed by the second porous fire-blocking component;

[0166] The ion detector C is used to collect the high-temperature combustible gas and the ion products after being suppressed by the second porous fire-blocking component and the first porous fire-blocking component.

[0167] The ion detector D is used to collect the ion products of high-temperature combustible gas after being suppressed by the second porous fire-blocking component 17 and the first porous fire-blocking component and finally ejected from the upper end of the visualization pipeline.

[0168] The gas composition analyzer is electrically connected to each ion detector 53 and is used to convert the ion product signal detected by each ion detector 53 into an electrical signal and analyze and store it, and can analyze and store the gas composition and content.

[0169] Example 2: An experimental method for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control, comprising the following steps:

[0170] S1: Assemble the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries and its prevention and control under the influence of multiple parameters;

[0171] S2: Close the exhaust valve 7, the main valve 42, the plurality of auxiliary valves 43, the first valve 11, the second valve 14 and the third valve 15; close the vacuum pump 12 and the compressor 13;

[0172] S3: Manually open the first valve 11, the second valve 14 and the vacuum pump 12; the vacuum pump 12 evacuates the interior of the visual pressure container 2;

[0173] When the pressure value observed by the vacuum pressure gauge 54 reaches Q, it indicates that the visual pressure container 2 has been evacuated, and the first valve 11, the second valve 14 and the vacuum pump 12 are manually closed.

[0174] S4: Manually open the main valve 42 and one or more of the multiple auxiliary valves 43; fill the visual pressure container 2 with one or more types of gas; when the pressure value of the vacuum pressure gauge 54 observed by a person reaches normal pressure (standard atmospheric pressure), close the main valve 42 and the multiple auxiliary valves 43.

[0175] S5: Turn on all high-speed cameras, all schlieren instruments and high-frequency infrared thermal imagers through the synchronous control system, program control and data acquisition system;

[0176] Through the synchronous control system, program control and data acquisition system, the arc electric heater 36 is turned on to heat the lithium battery until the lithium battery has thermal runaway;

[0177] S6: Through the synchronous control system, program control and data acquisition system, the pressure data of all high-frequency pressure sensors 46, the temperature data of all high-frequency temperature thermocouples 47, the temperature distribution and temperature rise process image data taken by the high-frequency infrared thermal imager, the discharge flame propagation characteristic image data taken by all high-speed cameras, and the microscopic flow field structure image data taken by all schlieren instruments are collected; through the synchronous control system, program control and data acquisition system, in combination with the gas composition analyzer, the ion product data collected by all ion detectors 53 are collected; through the synchronous control system, program control and data acquisition system, in combination with the heat flow data acquisition instrument 50, the surface temperature data of all adhesive surface thermocouples 49 monitoring the lithium battery and the voltage data of the lithium battery during thermal runaway are collected.

[0178] At this time, an experiment is completed and a set of data is obtained; after the experiment, the exhaust valve 7, the first valve 11, the third valve 15 and the compressor 13 are opened; the experimental product of the visualized pressure container 2 is blown out of the visualized pressure container 2 through the line hole 30 and the exhaust pipe 6 in sequence;

[0179] S7: First, remove the visualization pipe section C together with the visualization pipe section A and the visualization pipe section B as a whole from the upper end cover flange 3;

[0180] Then remove the sealing gland 22 together with the lithium battery as a whole from the upper end cover flange 3, and take the whole out of the through hole 18, remove the adhesive surface thermocouple 49 from the lithium battery, and replace it with a single lithium battery or a battery pack consisting of four lithium batteries; form a sealing gland 22 adapted to the single lithium battery or battery pack, the single lithium battery or the battery pack consisting of four lithium batteries into a whole, re-paste the aforementioned adhesive surface thermocouple 49 on the whole, and then re-place the sealing gland 22, the single lithium battery or the battery pack and the adhesive surface thermocouple 49 into the through hole 18, and install the earring 24 on the upper end cover flange 3;

[0181] Then reinstall the visualization pipe section C together with the visualization pipe section A and the visualization pipe section B as a whole onto the upper end cover flange 3, and press the earring 24 of the sealing gland 22 onto the upper surface of the upper end cover flange 3 to ensure that the sealing gland 22 cannot move;

[0182] Then, the adjustable screw 32 is screwed to make the sealing gland 22 and the abutment plate 34 respectively press the upper and lower surfaces of the single lithium battery or the battery pack consisting of four lithium batteries to ensure that the single lithium battery or the battery pack consisting of four lithium batteries cannot move;

[0183] S8: Change the experimental conditions, repeat S1-S8, conduct multiple experiments, and collect multiple sets of data;

[0184] Experimental conditions include:

[0185] 1) In step S4, the first valve 11, the second valve 14 and the vacuum pump 12 are manually opened, and the gas in the visualized pressure container 2 is extracted by the vacuum pump 12, so that the gas pressure inside the visualized pressure container 2 in step S4 is lower than the normal pressure;

[0186] Alternatively, in step S4, the first valve 11, the third valve 15 and the compressor 13 are manually opened, and air is filled into the visualized pressure container 2 through the vacuum pump 12, so that the air pressure inside the visualized pressure container 2 in step S4 is higher than normal pressure;

[0187] It can explore the influence of different initial pressures inside the visualized pressure vessel 2 on the thermal runaway process of lithium batteries and the propagation characteristics of thermal runaway flames; clarify the transient evolution of the flame and flow field under the coupling of multiple physical fields such as temperature field, velocity field, pressure field, and density field when the thermal runaway of lithium batteries is triggered, which makes up for the lack of research on the evolution and propagation laws of the dangerous characteristics of thermal runaway of lithium-ion batteries. Among them, the velocity field refers to: the flame image taken by a high-speed camera, and the flame speed is calculated according to the scale. The density field refers to: the microscopic flow field of the flame observed by the Schlieren system.

[0188] 2) In step S4, manually open the main valve 42 and one or more of the auxiliary valves 43; change the type of liquid charged into the visual pressure container 2;

[0189] It can explore the influence of different types of gases inside the visual pressure vessel 2 on the thermal runaway process of lithium batteries and the flame propagation characteristics of thermal runaway;

[0190] 3) In step S1, the type, number of holes, thickness, installation position or effective area of ​​the two porous fire-blocking components 17 are changed; because the horizontal cross-sectional area of ​​each visualization pipe segment is different, and each porous fire-blocking component can close the visualization pipe segment at each position, the horizontal cross-sectional area of ​​the porous fire-blocking components at each position is different, and the effective area refers to the horizontal cross-sectional area of ​​the connection between each visualization pipe segment.

[0191] It is possible to explore the effect of the porous fire-blocking component 17 on the suppression effect of the lithium battery jet flame when the lithium battery is in thermal runaway; it is possible to determine the optimal porous fire-blocking component 17 and installation position;

[0192] 4) In step S5, the triggering conditions of thermal runaway are changed, and the triggering conditions include changing the heating power and heating position of the arc electric heater 36 through the variable frequency power regulator; and also include using the stabilized power supply 38 to charge the lithium battery to achieve the situation of overcharging and abuse of the lithium battery; electrical abuse: overcharging, external short circuit.

[0193] Able to explore the influence of flame propagation characteristics of lithium battery thermal runaway under different working conditions;

[0194] 5) In step S7, the selection of single lithium battery or battery pack, the series and parallel connection of each single lithium battery in the resistor group, the SOC (state of charge) of the lithium battery, the positive electrode material of the lithium battery, the cycle aging degree of the lithium battery, and the mechanical damage degree of the lithium battery are changed;

[0195] It can explore the influence of the state of lithium batteries on their thermal runaway process and thermal runaway flame propagation characteristics.

[0196] S9: Through a large amount of test data, the pressure data collected by the high-frequency pressure sensor 46, the temperature data of the discharge flame collected by the high-frequency temperature thermocouple 47, the temperature distribution and temperature rise change process image data taken by the high-frequency infrared thermal imager, the discharge flame propagation characteristic image data taken by the high-speed camera, the microscopic flow field structure image data taken by the schlieren instrument, the ion product data collected by the ion detector 53, and the voltage data and lithium battery surface temperature data during thermal runaway of the lithium battery in the heat flow data acquisition instrument 50 are analyzed.

[0197] The analysis results are as follows:

[0198] See Figure 8 ,

[0199] The thermal runaway flame is in the form of four consecutive jets of flame, such as Figure 8 This is the first jet flame process. At 640 milliseconds, a spark forms about 222 mm above the nozzle and ignites the first jet, and the flame spreads upward. At 747 milliseconds, another fireball appears about 72 mm above the nozzle. More high-temperature sparks are ejected from the battery shell, and the gas concentration is within the flammable critical value. The second fireball appears, spreads upward and mixes with the first fireball, and then the flame expands. With the occurrence of the second fireball, the take-off height of the jet flame will decrease. After that, the lift-off height increases, the flame height decreases, and the flame begins to shrink. Then, another fireball appears and mixes with the previous fireball, and then the flame shrinks, and so on and so forth until the first jet flame is extinguished at 1527 milliseconds.

[0200] See Fig. 9 ,

[0201] In the fourth jet flame process, the flame has the maximum height at 2101ms. At this moment, 15 points with the same intervals are selected from the infrared thermal image of the flame, such as Fig.10 Among them, the first point is near the flame root, and the temperature changes of the 1st, 5th, 9th and 13th points are shown in Figure 10.

[0202] Fig.10 of Fig.10 (a)- Fig.10 (d) The temperature changes and infrared images of the 1st, 5th, 9th and 13th temperature collection points. Fig.10 (a) It can be seen that the smoke image changes from orange to yellow in the range of 40 to 57 frames. The temperature of the fifth point starts to rise at 37 frames and reaches the first and second peaks at 43 and 61 frames. The change of smoke color is related to Fig.10(a) is the same. This reflects the occurrence of sparks and the increase in spark temperature. The temperature of the 9th and 13th points begins to increase at frames 61 and 65, and reaches the first peak at frames 69 and 74. It corresponds to the occurrence of the first jet fire and its spread, as shown in Fig.10 (c) and (d). After that, the temperature decreases and increases, and new temperature peaks appear continuously, representing the degradation and expansion of the jet flame. Fig.10 (ac) It can be seen that the temperatures of points 1, 5, and 9 reach their maximum values ​​after the first mixing of the two fireballs. However, the temperature of point 13 reaches its maximum value at the beginning of the first jet shot. The height of the fourth jet shot decreases with time. The flame front cannot reach points 9 and 13. The temperatures of points 9 and 13 are below 255 °C at frames 200 and 249. The temperature of point 1 is below 200 °C until the fire is extinguished.

[0203] See Fig.11 ,

[0204] Fig.11 The voltage change during the thermal runaway process of a 21700 battery with SOC100%. It is roughly divided into three stages: Stage I: The stage of slight voltage reduction. During the continuous heating of the battery, its surface temperature continues to rise, and the battery capacity decays under the influence of high temperature, which leads to a small decrease in voltage. Stage II: The stage of continuous voltage reduction. When the surface temperature of the battery rises to the self-heating starting temperature θ1, due to the melting of SEI on the surface of the battery's negative electrode material, the electrolyte and the negative electrode material contact and react with each other, and the heat released by the battery itself increases. The battery voltage continues to decrease in this process, from 4.18 V to about 3.8 V. Stage III: The voltage drops suddenly to zero.

Claims

1. An experimental device for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control, characterized in that: The invention comprises a bracket (1), wherein a visual pressure container (2) is provided on the upper surface of the bracket (1); an upper end cover flange (3) and a lower end cover flange (4) are respectively fixed to the upper end and the lower end of the visual pressure container (2); the lower end of the visual pressure container (2) is mounted on the bracket (1) via the lower end cover flange (4), and the lower end of the visual pressure container (2) is kept sealed; A control and suppression system is installed on the upper surface of the upper end cover flange (3), and the control and suppression system includes a plurality of visualization pipe sections (16) stacked in sequence, and the side walls of the visualization pipe sections (16) can be seen through; each visualization pipe section (16) is connected; the upper end of the visualization pipe section (16) at the upper end is connected to the external environment; and a porous fire-blocking component (17) is installed between two adjacent visualization pipe sections (16); A through hole (18) is provided on the upper end cover flange (3), and the interior of the visible pressure container (2) is connected to the interior of the visible pipe section (16) at the lower end through the through hole (18); It also includes a battery carrying system for limiting the lithium battery at the position of the through hole (18) and sealing the through hole (18) with the lithium battery; it also includes a pressure acquisition system for acquiring pressure data in each visualization pipeline; it also includes an image acquisition system and a microscopic flow field acquisition system for acquiring flame images and microscopic flow field images in each visualization pipeline respectively; it also includes a synchronous controller, a program control and data acquisition system for controlling and receiving the acquired data; it also includes a thermal runaway trigger system for causing the lithium battery to have thermal runaway; it also includes a product analysis test system for acquiring gas components in each visualization pipeline; it also includes a temperature acquisition system for acquiring temperature data in each visualization pipeline; Among them, the battery carrying system includes: The sealing end cover has two types, which are respectively used for limiting the position of a single lithium battery and a battery pack composed of multiple lithium batteries; the sealing end cover of the battery pack is type A, and the sealing end cover of the single lithium battery is type B; type A includes: a jacket (23) in a circular shape, which is inserted into the through hole (18) and coincides with the axis of the through hole (18) to ensure that the outer wall of the jacket (23) and the inner wall of the through hole (18) are sealed; an earring (24) is sleeved on the jacket (23) and fixedly connected to the jacket (23), and the lower surface of the earring (24) abuts against the upper surface of the upper end cover flange (3); a horizontal plate (25) is fixed to the inner wall of the jacket (23), and the edge of the horizontal plate (25) is in contact with the inner wall of the jacket (23) to ensure that the horizontal plate (2 5) The outer wall is sealed with the inner wall of the outer jacket (23); each positive electrode of the battery pack passes through the horizontal plate (25), and the horizontal plate (25) is provided with a hole for each positive electrode of the battery pack to pass through; a snap ring (26) is fixed on the inner wall of the outer jacket (23), and is sleeved on the battery pack, so that the battery pack can be assembled on the selected type A and the selected type A and the battery pack can form a whole; the selected type B does not have the snap ring (26), and the number of holes on the horizontal plate (25) of the selected type B is only one, and the other structures of the selected type B are the same as those of the selected type A; A sealing flange (27) is mounted on the lower surface of the bracket (1); A long hole (31) passes through the lower surface of the visible pressure container (2), the surface of the bracket (1) and the surface of the sealing flange (27); A pressing component is used to support the lower end of the battery pack or the single lithium battery, and to make the upper end of the battery pack or the single lithium battery closely attached to and sealed with the sealing end cover; Among them, the pressure acquisition system includes: Four high-frequency pressure sensors (46), respectively denoted as high-frequency pressure sensor A, high-frequency pressure sensor B, high-frequency pressure sensor C and high-frequency pressure sensor D; the four high-frequency pressure sensors 46 are connected to the program control and data acquisition system through a synchronous controller; High-frequency pressure sensor A, high-frequency pressure sensor B, and high-frequency pressure sensor C are installed on the inner wall of the visualized pressure container (2), and high-frequency pressure sensor D is installed above the upper end of the visualized pressure container (2); The image acquisition system includes: A plurality of high-speed cameras for collecting images of the flame morphology evolution and propagation characteristics of the lithium battery after thermal runaway in the corresponding visualization pressure container (2); High-speed infrared thermal imager, used to collect the temperature distribution and temperature change process of the lithium battery main structure at different stages of the heating process, the thermal radiation propagation process of the thermal runaway flame, and the flame temperature distribution change law under the conditions of fire prevention and control of the blocked components; Product analysis and testing system includes: Four ion detectors, respectively denoted as ion detector A, ion detector B, ion detector C and ion detector D; ion detector A, ion detector B, ion detector C are installed on the side wall of the visualization pressure container (2), and ion detector D is installed above the upper end of the visualization pipeline A; The temperature acquisition system includes: Four high-frequency temperature thermocouples are respectively recorded as high-frequency temperature thermocouple A, high-frequency temperature thermocouple B, high-frequency temperature thermocouple C and high-frequency temperature thermocouple D; high-frequency temperature thermocouple A, high-frequency temperature thermocouple B, high-frequency temperature thermocouple C and high-frequency temperature thermocouple D are at the same height as the corresponding high-frequency pressure sensor A, high-frequency pressure sensor B, high-frequency pressure sensor C and high-frequency pressure sensor D; The microscopic flow field acquisition system includes: A plurality of schlieren instruments, each of which comprises a light source, a focusing lens, two reflecting mirrors and a second high-speed camera, and is capable of taking a corresponding visual microscopic flow field image in the pressure container (2); The pressing components include: The adjustable screw (32) has an axis that coincides with the axis of the long hole (31) and is rotatably connected to the long hole (31), and a seal is maintained between the outer wall of the adjustable screw (32) and the inner wall of the long hole (31); A movable rod (33), the lower end of which is sleeved on the upper end of the adjustable screw rod (32), and the movable rod (33) is threadedly connected to the adjustable screw rod (32); The contact plate (34) is fixed to the upper end of the movable rod (33); the upper surface of the contact plate (34) is concave downward to form a limiting groove, and the contact plate (34) can be sleeved on the lower end of the battery pack or the single lithium battery through the limiting groove; A placement edge (28) is fixed on the inner wall of the visual pressure container (2); A support plate (29) is mounted on the upper surface of the placement edge (28); a movable rod (33) passes through the support plate (29), and a through hole is provided on the support plate (29) for the movable rod (33) to pass through; A limiting long rod (35) is fixed on the lower surface of the abutment plate (34), the axis of the limiting long rod (35) is arranged vertically, the limiting long rod (35) passes through the support plate (29), and the limiting long rod (35), the abutment plate (34), and the movable rod (33) can slide along the axis direction of the limiting long rod (35) as a whole; Among them, the thermal runaway trigger system includes: Two arc-shaped electric heaters are mounted on the upper surface of the support plate and are located inside the visible pressure container (2); when observed along the radial direction of the movable rod (33), the two arc-shaped electric heaters (36) are symmetrically arranged about the axis of the movable rod (33); the battery can be heated to thermal runaway; each arc-shaped electric heater includes a plurality of heating rods arranged from top to bottom; the heating position can be changed by turning on or off the plurality of heating rods; A variable frequency power regulator (37) and a voltage-stabilized power supply (38), wherein the voltage-stabilized power supply (38) is electrically connected to the two arc-shaped electric heaters (36) through a wire, and can energize the two arc-shaped electric heaters (36) and make them work; the variable frequency power regulator (37) is used to adjust the heating power of the arc-shaped electric heaters (36); Among them, the battery heat flow control system includes: Four adhesive surface thermocouples (49); two of them are set as a group, for a total of two groups; the two groups of adhesive surface thermocouples (49) are respectively attached to the side surfaces of two adjacent lithium batteries in the battery pack; or any one of the four adhesive surface thermocouples (49) is attached to the side wall of a single lithium battery; The two groups of adhesive surface thermocouples (49) are respectively group A and group B, and the two adjacent lithium batteries are respectively lithium battery A and lithium battery B; then one of the two adhesive surface thermocouples (49) of group A is adhered to the middle position of the side of lithium battery A facing the arc electric heater (36), and the other is adhered to the middle position of the side of lithium battery A not facing the arc electric heater (36); the meaning of facing is: when observed from the axis of the movable rod (33), the adhesive surface thermocouple (49) is not between the multiple single lithium batteries; the meaning of not facing is: when observed from the axis of the movable rod (33), the adhesive surface thermocouple (49) is between the multiple single lithium batteries; One of the two adhesive surface thermocouples (49) in group B is attached to the upper end of lithium battery B, and the other is attached to the lower end of lithium battery B. Both adhesive surface thermocouples (49) in group B face the arc-shaped electric heater (36); The heat flow data acquisition instrument (50) is located outside the visual pressure container (2); it is electrically connected to all the adhesive surface thermocouples (49) via a temperature data line (51) and is used to collect temperature data of the adhesive surface thermocouples (49) and convert it into electrical signals for storage; it is also electrically connected to the positive and negative electrodes of a battery pack or a single lithium battery via a voltage data line (52) and is used to monitor voltage changes of the battery pack or the single lithium battery and convert it into electrical signals for storage.

2. According to the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control according to claim 1, it is characterized in that: The adjustable screw rod (32), movable rod (33) and abutment plate (34) are all hollow, and the temperature data line (51) and the voltage data line (52) pass through the adjustable screw rod (32), movable rod (33) and abutment plate (34) from the hollow positions of the adjustable screw rod (32), movable rod (33) and abutment plate (34).

3. According to the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control according to claim 2, it is characterized in that: It also includes an air supply system, which includes: A main air pipe (40) is fixed on the outer wall of the visualized pressure container (2), one end of which is connected to the interior of the visualized pressure container (2) and the other end of which is sealed; A plurality of branch air pipes (41), one end of each of which is connected to the outer wall of the main air pipe (40) and communicates with the main air pipe (40); A plurality of gas cylinder gas sources (39) are arranged one by one corresponding to the gas distribution pipes (41) and are respectively connected to one end of the corresponding gas distribution pipes (41) away from the main gas pipe (40), and can respectively fill the internal gas into the visual pressure container (2) through the gas distribution pipes (41) and the main gas pipe (40). Auxiliary valves (43) are respectively installed on the plurality of gas distribution pipes (41); and a main valve (42) is installed on the main gas pipe (40).

4. According to the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control according to claim 3, it is characterized in that: An exhaust pipe (6) is installed on the outer wall of the visualized pressure container (2), one end of the exhaust pipe (6) is connected to the external environment of the visualized pressure container (2), and the other end is connected to the external environment of the visualized pressure container (2), and an exhaust valve (7) is installed on the exhaust pipe (6); A control main pipe (8) is installed on the outer wall of the visual pressure container (2). One end of the control main pipe (8) is connected to the visual pressure container (2), and the other end is sealed. An exhaust pipe (9) and a blow pipe (10) are installed on the outer wall of the control main pipe (8). One end of the exhaust pipe (9) and the blow pipe (10) are connected to the control main pipe (8), and the other ends are connected to a vacuum pump (12) and a compressor (13) respectively. A first valve (11) is installed on the control main pipe (8); a second valve (14) and a third valve (15) are installed on the exhaust pipe (9) and the blow pipe (10); and a vacuum pressure gauge (54) for monitoring the pressure in the visual pressure container (2) is installed on the control main pipe (8).

5. According to the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries under the influence of multiple parameters and its prevention and control suppression according to claim 4, it is characterized in that: The voltage-stabilized power supply (38) is also electrically connected to the lithium battery and is used to charge the lithium battery to prevent electrical abuse of the lithium battery, which includes overcharging and external short circuit.

6. A method for testing the flame propagation characteristics of thermal runaway lithium batteries under the influence of multiple parameters and its prevention and control inhibition, based on the device for testing the flame propagation characteristics of thermal runaway lithium batteries under the influence of multiple parameters and its prevention and control inhibition according to claim 5, characterized in that: The following steps are involved: S1: Assemble the experimental device for the flame propagation characteristics of thermal runaway of lithium batteries and its prevention and control under the influence of multiple parameters; S2: Close the exhaust valve, the main valve, multiple auxiliary valves, the first valve, the second valve and the third valve; turn off the vacuum pump and the compressor; S3: Manually open the first valve, the second valve and the vacuum pump; the vacuum pump evacuates the interior of the visual pressure container; When the pressure value of the vacuum pressure gauge reaches Q, the first valve, the second valve and the vacuum pump are manually closed; at this time, the vacuum in the pressure container is visualized; S4: manually open the main valve and one or more of the auxiliary valves; fill one or more types of gas into the visual pressure container; when the pressure value of the vacuum pressure gauge reaches the standard atmospheric pressure, close the main valve and the auxiliary valves; S5: Turn on all high-speed cameras, all schlieren instruments and high-frequency infrared thermal imagers in the image acquisition system and the microscopic flow field acquisition system through the synchronous control system, program control and data acquisition system; Through the synchronous control system, program control and data acquisition system, the arc electric heater is turned on to heat the lithium battery until the lithium battery has thermal runaway; S6: Through the synchronous control system, program control and data acquisition system, collect the pressure data of all high-frequency pressure sensors in the pressure acquisition system, the temperature data of all high-frequency temperature thermocouples in the temperature acquisition system, the temperature distribution and temperature rise process image data taken by the high-frequency infrared thermal imager in the image acquisition system, the discharge flame propagation characteristic image data taken by the high-speed camera in the image acquisition system, the microscopic flow field structure image data taken by the schlieren instrument in all microscopic flow field acquisition systems, the ion composition data in the product analysis test system, and the surface temperature data of the lithium battery in the heat flow data acquisition instrument and the voltage data during thermal runaway; At this point, an experiment is completed and a set of data is obtained; after the experiment is over, the exhaust valve, the first valve, the third valve and the compressor are opened; ensuring that the experimental product of the visualized pressure container is purged out of the visualized pressure container from the exhaust pipe; S7: dismantle the control and suppression system and reinstall the lithium battery, change the experimental conditions, repeat S1-S7, conduct multiple experiments, and collect multiple sets of data; Experimental conditions include: 1) In step S4, after the gas pressure inside the visualized pressure container reaches the standard atmospheric pressure, the first valve, the second valve and the vacuum pump are manually opened, and the gas in the visualized pressure container is extracted by the vacuum pump, so that the gas pressure inside the visualized pressure container in step S4 is lower than the normal pressure; Alternatively, in step S4, after the air pressure inside the visualized pressure container reaches the standard atmospheric pressure, the first valve, the third valve and the compressor are manually opened, and air is filled into the visualized pressure container through the compressor, so that the air pressure inside the visualized pressure container in step S4 is higher than the normal pressure; Able to explore the effects of different initial pressures inside the visual pressure vessel on the thermal runaway process of lithium batteries and the flame propagation characteristics of thermal runaway; 2) In step S4, manually open the main valve and one or more of the auxiliary valves; change the type of liquid charged into the visual pressure container; Able to explore the effects of different types of gases inside a visual pressure vessel on the thermal runaway process of lithium batteries and the flame propagation characteristics of thermal runaway; In step S1, the type, number of holes, thickness, installation position or effective area of ​​two porous fire-blocking components are changed; the effective area refers to the horizontal cross-sectional area at each visualized pipe section; Able to explore the effect of porous fire-blocking components on the suppression of lithium battery jet flames when the lithium battery is in thermal runaway; able to determine the optimal porous fire-blocking components and installation locations; In step S5, the triggering condition of thermal runaway is changed, and the triggering condition includes changing the heating power and heating position of the arc electric heater by the variable frequency power regulator; and also includes charging the lithium battery by the stabilized power supply to realize the situation of overcharging and abuse of the lithium battery; electrical abuse: overcharging, external short circuit; 5) In step S7, the selection of single lithium battery or battery pack, the series and parallel connection of each single lithium battery in the resistor group, the state of charge SOC of the lithium battery, the positive electrode material of the lithium battery, the cycle aging degree of the lithium battery, and the mechanical damage degree of the lithium battery are changed; Able to explore the influence of lithium battery status on its thermal runaway process and thermal runaway flame propagation characteristics; S8: Analyze multiple sets of data.

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