Method for Extracting Thermal Runaway Debris of Power Battery of New Energy Vehicle and Judging Cause

Abstract

The present invention discloses a method for extracting the thermal runaway wreckage of a power battery for a new energy vehicle and judging the cause, mainly including steps of investigation and sampling, wreckage extraction, analysis of the structure of the wreckage current collector, analysis of the crystal structure of the powder of the wreckage material, and analysis of the carbon components of the material. This method systematically combines the on-site investigation of new energy vehicle fire accidents with laboratory analysis and detection technologies, provides technical support for the analysis and detection of the power battery wreckage in fire accident investigations, effectively improves the current new energy vehicle fire accident investigation system, and facilitates relevant accident investigators to conduct new energy vehicle fire accident investigations and effectively judge the cause of the accident.

Description

Technical Field

[0001] The present invention relates to battery thermal runaway judgment technology, and particularly to a method for extracting the debris of a power battery in thermal runaway of a new energy vehicle and judging the cause thereof. Background Art

[0002] From 2020 to 2023, the penetration rate of new energy vehicles in China has soared from 5.4% to 31.6%. This trend is expected to continue to grow in 2024, approaching a penetration rate of 40%. However, fire accidents of new energy vehicles have occurred frequently in recent years. According to the statistical data of the emergency management department, the self-ignition rate increased by 32% in the first quarter of 2023, and on average, 8 new energy vehicles caught fire every day.

[0003] The importance of investigating fire accidents of new energy vehicles is self-evident. With the improvement of environmental awareness and the progress of technology, new energy vehicles have become an important development direction of the automotive industry. However, as one of the potential safety risks of new energy vehicles, once a fire occurs, it not only endangers the lives of passengers but also may cause significant property losses and affect the public's confidence in new energy vehicles. Thoroughly investigating fire accidents of new energy vehicles can accurately locate the cause of the accident, whether it is due to battery technology defects, charging facility problems, improper use, or external collisions, etc. This is crucial for subsequent technological improvements, the formulation of safety standards, and the improvement of regulatory policies. Therefore, strengthening the investigation of fire accidents of new energy vehicles is the cornerstone for ensuring public safety and promoting the sustainable development of the new energy vehicle industry.

[0004] The power battery of new energy vehicles is complex and precise, mainly composed of multiple battery modules, a thermal management system, a battery management system, an electrical system, and structural components, etc. Among them, the battery cell is the basic energy storage unit of the power battery, which is composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode often uses transition metal oxides such as cobalt, nickel, manganese, and iron, and the negative electrode is graphite. The electrolyte is responsible for ion conduction and can be liquid or solid. The battery module is formed by connecting multiple battery cells in series or in parallel above to achieve the required voltage and capacity. The module also includes conductive connectors, plastic frames, cooling systems, etc. For different battery cells in the power battery that have experienced the same fire accident, the causes of their thermal runaway may vary. The first ignited battery cell may be self-ignited due to external abnormal effects. Other battery cells around it will experience thermal runaway due to the high-temperature heat conducted from it or an open flame. However, currently, the main method for investigating the power battery wreckage in new energy vehicle fire accident investigations is on-site visual observation. For example, after disassembling the battery accident module, observe whether there are signs such as mutual extrusion deformation, pole piece arching between the single-cell top cover, side plate, and battery cells, and whether there are signs such as arc melting through the single-cell shell to speculate on the cause of the accident. There is still a lack of more effective technologies for extracting the thermal runaway wreckage of new energy vehicle power batteries and judging the cause. The methods for sampling the internal materials of the power battery wreckage after a fire accident and subsequent analysis technical means need to be improved urgently. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a method for extracting the thermal runaway wreckage of new energy vehicle power batteries and judging the cause, which can effectively determine the cause of thermal runaway of the corresponding power battery cell, and provide technical support for the effective determination of the cause of new energy vehicle fire accidents.

[0006] To achieve the above purpose, the technical solution of the present invention is:

[0007] A method for extracting the thermal runaway wreckage of new energy vehicle power batteries and judging the cause, the method includes:

[0008] An investigation and sampling step to obtain battery pole pieces after a fire accident;

[0009] A wreckage extraction step, which conducts separation and extraction of wreckage substances on the battery pole pieces obtained in the investigation and sampling step to separate the wreckage of the battery pole pieces that have experienced a fire accident according to different main material components, and obtain battery pole piece wreckage with different particle sizes.

[0010] a step of analyzing the structure of the residual current collector, screening out the battery pole piece debris that meets a first particle size value from the battery pole piece debris of different particle sizes, wherein the battery pole piece debris that meets the first particle size value is a copper current collector, treating the copper current collector, observing the structure of the treated copper current collector with a metallographic microscope, and analyzing the metallographic microstructure of the copper foil to analyze the cause of the thermal runaway accident;

[0011] The step of analyzing the crystal structure of the powder of the debris material is to select the battery pole pieces that meet the second particle size value from the battery pole pieces of different particle sizes to carry out X-ray powder diffraction test, and analyze the conditions that have caused thermal runaway based on the test spectrum;

[0012] The material carbon component analysis step is to select the battery pole piece debris that meets the third particle size value from the battery pole piece debris of different particle sizes for Raman spectroscopy analysis, and analyze and infer the thermal runaway conditions that have occurred based on the Raman spectrum.

[0013] Optionally, the survey sampling step includes:

[0014] Remove the power battery pack that has experienced the fire accident from the vehicle, cut off the electrical connection lines, and then disassemble the battery pack;

[0015] Observe the burned area, remove the most severely burned module, dismantle the module casing, and take out the internal battery cells;

[0016] Observe the deformation characteristics of the entire battery cell group inside the module, and remove the battery cell that is most severely squeezed and deformed in the module or the battery cell that is initially determined to be the trigger point through fire trace analysis at the accident site;

[0017] Remove the single body shell, take out the pole piece at the location with severe burning inside, and if the burning situation is not much different, take out the pole piece in the area with the most serious extrusion and deformation; if the accident power battery has been extinguished with fire water, first remove the particulate matter remaining on the pole piece, and then take out the pole piece at the location with severe burning inside.

[0018] Optionally, the battery pole pieces obtained in the investigation and sampling step are subjected to material separation and extraction of the debris, so as to separate the battery pole piece debris that has experienced the fire accident according to different main material components to obtain battery pole piece debris of different particle sizes, including:

[0019] Soak the battery pole pieces after the fire accident in a 30℃~35℃, 50%~70% concentration ethanol solution, and adjust the solution pH value to 6.0±0.5 with acetic acid; after soaking for 2~3 hours, filter, and rinse with anhydrous ethanol and ionized water alternately for no less than 3 times until the filtrate pH value is about 7.0;

[0020] The battery pole piece after the above treatment is transferred to a vacuum oven and dried at 50°C to 80°C and a relative vacuum degree of 0.06 to 0.09 MPa for 24 hours to ensure that the pole piece debris is completely dried;

[0021] The dried block-shaped battery pole pieces are transferred into a planetary ball mill, agate grinding beads are placed in the mill, and the powder and flake-like loose pole piece debris samples are obtained at a speed of 100 r / min to 150 r / min for 1 to 2 hours. Then, a vertical multi-layer screening method is used to screen the loosely dispersed pole piece debris from top to bottom in the order of 20 mesh, 30 mesh, 50 mesh, 60 mesh or 80 mesh, and the loosely dispersed pole piece debris are separated according to the particle size of ≥0.9 mm, 0.9 mm to 0.6 mm, 0.6 mm to 0.355 mm, 0.355 to 0.3 mm or 0.3 to 0.2 mm.

[0022] Optionally, the processing of the copper current collector includes:

[0023] The black positive / negative electrode materials remaining on the surface of the copper current collector are wiped off, and then transferred to anhydrous ethanol, and the remaining black substances on the surface of the copper current collector are cleaned by ultrasonic dispersion. The cleaned copper current collector is moved to a vacuum oven for drying; the surface of the dried copper current collector is polished.

[0024] Optionally, the analysis of the cause of the thermal runaway accident by metallographic microstructure analysis of the copper foil includes:

[0025] If circular black spots are found on the copper foil through observation, it is caused by a high current breakdown process; if the area of ​​the circular black spots is smaller than the preset value and appears densely, it is judged that thermal runaway caused by overcharging has occurred there;

[0026] If there are small dendrites or equiaxed crystals in a location in the copper foil, and large equiaxed crystals are scattered around other locations, it means that this location has experienced the highest temperature during the thermal runaway process and is also the location where the temperature drops the earliest and the drop rate is the fastest. Therefore, it is judged that this location is the initiation site of the local internal short circuit.

[0027] If there are colorful ring patterns in the copper foil, it is the trace left by the initial flame burning, which means that there has been thermal runaway caused by open flames.

[0028] If the copper foil shows an overall uniform color change, it is judged that the area has been heated and overheated, causing thermal runaway.

[0029] Optionally, the screening out of battery pole piece debris meeting the second particle size value and conducting X-ray powder diffraction testing includes:

[0030] Screen out the battery electrode powder residues on a 30-mesh or 50-mesh test sieve and conduct X-ray powder diffraction tests. When testing, the scanning angle range should at least cover 20° to 43°.

[0031] Optionally, analyzing the conditions that triggered thermal runaway based on the test pattern includes:

[0032] If the relative intensities of the newly added peaks in the range of 21° to 24° are close, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of increasing first and then decreasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall trend of decreasing first and then increasing, it is determined that thermal runaway caused by overcharging occurred at this location;

[0033] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall trend of increasing first and then decreasing, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of decreasing first and then increasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall close trend, it is determined that thermal runaway caused by local internal short circuit occurred at this location;

[0034] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall decreasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks in the range of 33° to 35° are close, and the relative intensities of the newly added peaks in the range of 38° to 43° are close, it is determined that thermal runaway caused by fire occurred at this location;

[0035] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall trend of increasing first and then decreasing, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of decreasing first and then increasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall decreasing trend, it is determined that thermal runaway caused by overheating occurred at this location.

[0036] Optionally, screening out the battery electrode residues that meet the third particle size value and conducting Raman spectroscopy analysis includes:

[0037] Screen out the battery electrode powder residues on a 60-mesh or 80-mesh test sieve and conduct Raman spectroscopy analysis. At 1350 ± 10 cm in the Raman spectrum -1 and at 1580 ± 10 cm -1The carbon Raman active peaks that appear nearby are the objects of analysis and research, corresponding to the amorphous carbon D peak and the graphitized carbon G peak respectively. The conditions that triggered thermal runaway that occurred there are analyzed and inferred based on the relative intensity ratio of the G peak to the D peak.

[0038] Optionally, the analysis and inference of the conditions that triggered thermal runaway that occurred there based on the relative intensity ratio of the G peak to the D peak includes:

[0039] If the relative intensity ratio of the G peak to the D peak is between 1 and 2, it is determined that thermal runaway caused by local internal short circuit occurred there;

[0040] If the relative intensity ratio of the G peak to the D peak is between 3 and 5, it is determined that thermal runaway caused by overheating occurred there;

[0041] If the relative intensity ratio of the G peak to the D peak is between 6 and 9, it is determined that thermal runaway caused by overcharging occurred there;

[0042] If the relative intensity ratio of the G peak to the D peak is greater than 10, it is determined that thermal runaway caused by fire occurred there.

[0043] Optionally, the vertical multi-layer screening method refers to vertically stacking a series of standard sieves with different pore sizes or different mesh numbers in descending order of pore size or increasing order of mesh number from top to bottom for screening.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) The method and system for extracting the thermal runaway wreckage of new energy vehicle power batteries and judging the cause provided by the present invention systematically combines the on-site investigation of new energy vehicle fire accidents with laboratory analysis and detection technologies, provides technical support for the analysis and detection of power battery wreckage in fire accident investigations, effectively improves the current new energy vehicle fire accident investigation system, and facilitates relevant accident investigators to carry out new energy vehicle fire accident investigations and effectively judge the cause of the accident.

[0046] (2) The method for extracting the thermal runaway wreckage of new energy vehicle power batteries and judging the cause provided by the present invention invents a power battery wreckage extraction technology. Through battery disassembly, monomer selection, wreckage pole piece sampling, impurity removal, alcohol solution soaking to remove fire extinguishing liquid method, ball milling and powdering, and vertical multi-layer screening method, the pole piece wreckage of the battery that has experienced a fire accident can be effectively separated according to different main material components, solving the problem that it is difficult to extract materials for analysis and research in a targeted manner after the pole pieces of the battery are sintered after a fire accident. It is applicable to the investigation of various fire accidents caused by thermal runaway of lithium-ion battery systems, and has the characteristics of easy operation, high efficiency, and strong applicability.

[0047] (3) Most of the existing methods for determining the ignition point of power batteries in new energy vehicles are to first look at the battery operation data recorded by the vehicle, including checking the battery charging current, the maximum and minimum temperatures, the maximum and minimum voltages, and the change in insulation resistance of the battery cells. Based on the characteristics of these data, it is predicted which conditions caused the problem. Then, the battery is disassembled on-site. After removing the battery pack, the structure of the battery cells is observed, and the battery cell that is squeezed is judged as the ignition point. The method for extracting the thermal runaway wreckage of power batteries in new energy vehicles and determining the cause provided by the present invention is based on the residual copper current collector metallographic analysis technology, the material crystal structure analysis technology, and the material carbon composition analysis technology, and clarifies the image features or parameter thresholds for different triggering methods. It is of great significance for improving the effectiveness of investigating the causes of new energy vehicle fire accidents and studying the occurrence laws of new energy vehicle fires. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flowchart of the method for extracting the thermal runaway wreckage of power batteries in new energy vehicles and determining the cause provided by the embodiment of the present invention;

[0049] Figure 2 It is a photo of the sampling situation in Application Example 1 of the present invention, including the single-cell sampling situation diagram (a) and the electrode sampling situation diagram (b).

[0050] Figure 3 It is a schematic diagram of the vertical multi-layer screening method in Application Example 1 of the present invention (a), a photo of the substance separated and extracted by a 20-mesh standard sieve (b1), a scanning electron microscope image of its material (b2), and an energy spectrum diagram of its material elements (b3), a photo of the substance separated and extracted by a 50-mesh standard sieve (c1), a scanning electron microscope image of its material (c2), and an energy spectrum diagram of its material elements (c3), a photo of the substance separated and extracted by an 80-mesh standard sieve (d1), a scanning electron microscope image of its material (d2), and an energy spectrum diagram of its material elements (d3).

[0051] Figure 4 It is a metallurgical microscope image of the current collector wreckage in Application Example 1 of the present invention, including the metallurgical microstructure of the electrode current collector at the sampling position (a) and the metallurgical microstructure of the current collector at the comparison position (b).

[0052] Figure 5 It is an X-ray powder diffraction pattern of the battery wreckage material in Application Example 1 of the present invention (a), an X-ray powder diffraction pattern of the normal battery cathode material (b), an X-ray powder diffraction pattern of the normal battery anode material (c), and an X-ray powder diffraction pattern of copper (d).

[0053] Figure 6 It is a Raman spectrum diagram of the battery wreckage in Application Example 1 of the present invention.

[0054] Figure 7 It is a photo of the sampling situation in Application Example 2 of the present invention, including the single - body sampling situation diagram (a) and the electrode sampling situation diagram (b).

[0055] Figure 8 It is a photo of the substance extracted and separated by a 20 - mesh standard sieve (a1), a scanning electron microscope image of its material (a2), and an energy - dispersive X - ray spectroscopy map of its material (a3) after sieving by the vertical multi - layer sieving method in Application Example 2 of the present invention, a photo of the substance extracted and separated by a 50 - mesh standard sieve (b1), a scanning electron microscope image of its material (b2), and an energy - dispersive X - ray spectroscopy map of its material (b3), and a photo of the substance extracted and separated by an 80 - mesh standard sieve (c1), a scanning electron microscope image of its material (c2), and an energy - dispersive X - ray spectroscopy map of its material (c3).

[0056] Figure 9 It is a metallurgical microscope image of the current collector debris in Application Example 2 of the present invention.

[0057] Figure 10 It is an X - ray powder diffraction pattern of the battery debris material in Application Example 2 of the present invention.

[0058] Figure 11 It is a Raman spectrum of the battery debris in Application Example 2 of the present invention.

[0059] Figure 12 It is a photo of the sampling situation in Application Example 3 of the present invention, including the single - body sampling situation diagram (a) and the electrode sampling situation diagram (b).

[0060] Figure 13 It is a photo of the substance extracted and separated by a 20 - mesh standard sieve (a1), a scanning electron microscope image of its material (a2), and an energy - dispersive X - ray spectroscopy map of its material (a3) after sieving by the vertical multi - layer sieving method in Application Example 3 of the present invention, a photo of the substance extracted and separated by a 50 - mesh standard sieve (b1), a scanning electron microscope image of its material (b2), and an energy - dispersive X - ray spectroscopy map of its material (b3), and a photo of the substance extracted and separated by an 80 - mesh standard sieve (c1), a scanning electron microscope image of its material (c2), and an energy - dispersive X - ray spectroscopy map of its material (c3).

[0061] Figure 14 It is a metallurgical microscope image of the current collector debris in Application Example 3 of the present invention.

[0062] Figure 15 It is an X - ray powder diffraction pattern of the battery debris material in Application Example 3 of the present invention.

[0063] Figure 16 It is a Raman spectrum of the battery debris in Application Example 3 of the present invention.

[0064] Figure 17 It is a photo of the sampling situation in Application Example 4 of the present invention.

[0065] Figure 18 These are the photos of the substances (a1) extracted by separating through a 20-mesh standard sieve after screening using the vertical multi-layer screening method in Application Example 4 of the present invention, the scanning electron microscope images (a2) of their materials, and the energy dispersive spectroscopy diagrams (a3) of their materials; the photos of the substances (b1) extracted by separating through a 50-mesh standard sieve, the scanning electron microscope images (b2) of their materials, and the energy dispersive spectroscopy diagrams (b3) of their materials; the photos of the substances (c1) extracted by separating through an 80-mesh standard sieve, the scanning electron microscope images (c2) of their materials, and the energy dispersive spectroscopy diagrams (c3) of their materials.

[0066] Figure 19 These are the metallographic microscope images of the current collector debris in Application Example 4 of the present invention.

[0067] Figure 20 These are the X-ray powder diffraction spectra of the battery debris materials in Application Example 4 of the present invention.

[0068] Figure 21 These are the Raman spectra of the battery debris in Application Example 4 of the present invention. Detailed implementation manners

[0069] Example:

[0070] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and examples.

[0071] Refer to Figure 1 As shown, the method for extracting and determining the cause of thermal runaway debris of a new energy vehicle power battery provided in this embodiment mainly includes the following steps:

[0072] The investigation and sampling step to obtain the battery electrode sheets after a fire accident, specifically including:

[0073] Remove the power battery pack that has experienced a fire accident from the vehicle. After cutting off the electrical connection lines at various places, disassemble the battery pack. Observe the fire area, take out the most severely burned module, remove the module housing, and take out the internal battery cells; observe the deformation characteristics of the entire group of battery cells inside the module, and take out the battery cell with the most severe extrusion deformation in the module or the battery cell at the initial ignition point preliminarily determined through fire trace analysis at the accident site; remove the cell housing. If the accident power battery has been extinguished by fire-fighting water and there are often hard foam particles remaining on the electrode sheet, first use tools to remove the above-mentioned particulate matter. The hard foam particles are obvious white, yellow, yellowish-white, brown or other colored foam particles, salt particles or other types of crystalline substances remaining from the fire-fighting water on the electrode sheet. The tools used can be tweezers, pliers, clips, brushes and other tools that can remove hard foam particles, etc. If there is no fire-fighting water extinguishing, this step can be skipped; take out the electrode sheet at the severely burned position inside, and take out the electrode sheet in the most severely extruded and deformed area when the burn conditions are not very different. The amount taken can be determined according to the actual situation. The area of the taken electrode sheet is not less than 2 cm 2 , and the thickness is not less than 3 mm. When sampling the electrode sheet remains of the power battery cell, multiple areas can also be selected for sampling analysis according to the fire situation. The power battery is mainly a lithium-ion battery

[0074] Debris extraction steps: Carry out debris material separation and extraction on the battery electrode sheets obtained in the investigation and sampling steps to separate the battery electrode sheet remains that have experienced a fire accident according to different main material components, and obtain battery electrode sheet remains with different particle sizes, specifically including:

[0075] Carry out debris material separation and extraction on the battery electrode sheets obtained from the accident site investigation and sampling in the investigation and sampling steps in the laboratory. Due to the fire process, the separator has melted away, the positive aluminum current collector has melted out, and various organic substances have carbonized. At this time, the electrode sheet often presents a sintered block shape. Use the alcohol solution immersion method to remove the remaining fire-fighting liquid substances, surfactants and oil stains, etc. That is, immerse the processed electrode sheet in an ethanol solution with a temperature of 30°C to 35°C and a concentration of 50% to 70%, and adjust the pH value of the solution to 6.0 ± 0.5 with acetic acid to remove the remaining fire-fighting liquid substances, surfactants and oil stains, etc.; after soaking for 2 to 3 hours, filter, and then alternately rinse with anhydrous ethanol and ionized water no less than 3 times until the pH value of the filtrate is about 7.0. In this step, the purpose of filtration is to remove the remaining fire-fighting liquid to avoid affecting subsequent analysis. If there is no fire-fighting water extinguishing, filtration can be omitted, and directly alternately rinse with anhydrous ethanol and ionized water no less than 3 times, and then operate according to the subsequent steps

[0076] Transfer the above-treated electrode to a vacuum oven and dry it at 50℃~80℃ and 0.06~0.09Mpa relative vacuum for 24 hours to ensure that the electrode debris is completely dried. Transfer the above-dried block electrode to a planetary ball mill, put in agate grinding beads, and grind and disperse at a speed of 100r / min~150r / min for 1~2 hours to obtain a loose electrode debris sample with coexistence of powder and flakes. Of course, you can also put the dried block electrode into a mortar and use manual grinding and dispersion to obtain a loose electrode debris sample with coexistence of powder and flakes.

[0077] Then, a vertical multi-layer screening method is used to screen from top to bottom with mesh sizes of 20, 30, 50, 60 or 80, and the loosely dispersed pole piece debris is separated according to the particle size into ≥0.9mm, 0.9mm-0.6mm or 0.6mm-0.355mm, 0.355-0.3mm or 0.3-0.2mm for subsequent testing and analysis. The above-mentioned different particle size distribution areas correspond to different main components. The size diameter ≥0.9mm is mainly sheet-like current collector materials. The materials less than 0.9mm are mainly black powders of positive electrode materials, negative electrode materials and carbonized materials. Since the positive electrode materials are transition metal oxides such as cobalt, nickel, manganese, and iron, they are often sintered into larger blocks after experiencing a fire. Therefore, the carbonized materials collected in the two particle size intervals of 0.9mm-0.6mm and 0.6mm-0.355mm often contain higher positive electrode material components. After the fire, the binder between the negative electrode graphite materials is completely carbonized, and the combined effects of heat, force and gas during the fire cause the graphite particles to pulverize and disperse. Therefore, the materials obtained in the particle size range of 0.355-0.3mm and 0.3-0.2mm contain more carbon. Next, the different materials screened out according to the particle size are tested and analyzed in turn. It should be noted that the "vertical multi-layer screening method" refers to a series of standard sieves with different apertures or different mesh numbers stacked vertically from top to bottom in the order of decreasing aperture or increasing mesh number for screening. The number, aperture or mesh number of the standard sieves used can be adjusted according to actual needs. The "positive electrode material" refers to the positive electrode material commonly used in power ion batteries, including nickel cobalt manganese oxide lithium positive electrode material, lithium iron phosphate positive electrode material, etc. The "negative electrode material" refers to the negative electrode material commonly used in power ion batteries, including graphite materials, etc.

[0078] Thus, in this step, the battery wreckage of power batteries is extracted. Through battery disassembly, monomer selection, sampling of wreckage pole pieces, impurity removal, the method of removing fire extinguishing liquid by soaking in alcohol solution, ball milling pulverization, and vertical multi-layer screening, the pole piece wreckage of the battery that has experienced a fire accident can be effectively separated according to different main material components, solving the problem that it is difficult to extract materials for analysis and research specifically after the pole pieces of the battery are sintered after a fire accident. It is applicable to the investigation of various fire accidents caused by thermal runaway in the lithium-ion battery system, and has the characteristics of easy operation, high efficiency, and strong applicability.

[0079] The step of analyzing the structure of the wreckage current collector is to screen out the pole piece wreckage of the battery that meets the first particle size value. The pole piece wreckage that meets the first particle size value is a copper current collector. The copper current collector is processed, and the structure of the processed copper current collector is observed by a metallurgical microscope, and the cause analysis of the thermal runaway accident is carried out through the metallographic microstructure analysis of the copper foil. Specifically, it includes:

[0080] Take the pole piece wreckage on the 20-mesh test sieve in the wreckage extraction step for testing. The particle size of the pole piece wreckage here is ≥0.9 mm, mostly broken and flaky copper current collectors, and there are still a lot of black positive / negative electrode materials adhering to the copper current collector. Take the above current collector, first wipe the large black positive / negative electrode materials remaining on the surface with a soft brush. Then, transfer it to absolute ethanol and ultrasonically disperse and clean the remaining black substances on the surface of the copper foil for 1 h. Transfer the above-treated pole piece to a vacuum oven and dry it at 50 °C under a relative vacuum of 0.08 - 0.09 Mpa for 2 h to ensure that the current collector is completely dried. Finally, after polishing the surface of the copper foil with non-woven fabric, observe the structure with a metallurgical microscope, and carry out the cause analysis of the thermal runaway accident through the metallographic microstructure analysis of the copper foil. The analysis and judgment method is as follows:

[0081] If it is found through observation that there are circular black spots on the copper foil, it is caused by experiencing a high-current breakdown process. If the area of the above circular black spot pattern is small and appears densely, it is judged that thermal runaway caused by overcharging has occurred there. "Overcharging" includes the situation where the charging power of the power battery exceeds the rated capacity of the battery or the acceptable charging range and the voltage of the power battery continues to rise and exceeds the rated working voltage of the battery during charging.

[0082] If there are fine dendritic crystals or equiaxed crystal forms at a position in the copper foil, and large-grained equiaxed crystal forms are scattered at other positions around it, it indicates that the position has experienced the highest temperature during the thermal runaway process and is also the site where the temperature first drops and the dropping rate is the fastest. From this, it can be judged that this position is the site caused by local internal short circuit;

[0083] If a colorful circular pattern appears in the copper foil, it is a trace left after experiencing the initial flame burning, indicating that thermal runaway caused by an open fire occurred at that location. Among them, the "open fire" includes the open fire deliberately or accidentally ignited by the accident perpetrator, the fire of the automotive wiring harness, electrical appliances or interior trim, and the open fire generated by the prior thermal runaway of other battery cells.

[0084] If the copper foil shows a relatively uniform discoloration as a whole, such as turning red, reddish-brown or black as a whole, it is judged that thermal runaway occurred after overheating caused by heat. The "overheating caused by heat" includes the heat transfer of the target power battery cell by a non-open-fire high-temperature heat source, including an abnormally operating high-temperature vehicle, the first cell to experience thermal runaway, and the high-temperature heat source generated by high-voltage arcing.

[0085] Steps for analyzing the crystal structure of the debris material powder to screen out the battery electrode debris that meets the second particle size value for X-ray powder diffraction testing, and analyze the conditions for thermal runaway that occurred based on the test pattern, specifically including:

[0086] When a lithium-ion battery undergoes thermal runaway, a series of chemical reactions occur inside, generating a large amount of heat and gas, accompanied by the melting of the positive current collector and separator materials at high temperatures, and the decomposition of the positive electrode material and binder under the action of the electrolyte. After thermal runaway, various materials inside the battery debris are sintered and blended together, presenting a highly mixed crystal form. The crystal form characteristics of these materials can be used to identify the high-temperature thermal runaway process experienced by the materials. The positive electrode material changes from the original monodisperse particle structure to a sintered block structure. There will also be a situation where it is difficult to peel off the co-agglomerated graphite negative carbon material. During the detection of its crystal structure, if there is too much graphite phase, the ultra-high carbon X-ray diffraction peak will cover other new characteristic peaks related to the positive electrode material, seriously affecting the analysis of the test results. Therefore, in order to obtain more components of the positive electrode material for crystal structure analysis, it is necessary to conduct X-ray powder diffraction testing (XRD) on the powder debris on the 30-mesh or 50-mesh test sieve in (2). When testing, the scanning angle (2θ) range should at least cover 20° to 43°, and the specific scanning angle range can be selected according to the test needs. In the four angular ranges of 21° to 24°, 29° to 32°, 33° to 35°, and 38° to 43° on the XRD test pattern, multiple new characteristic peaks may be generated in each of these angular ranges. Based on the relative intensity characteristics of each group of these new series of diffraction peaks, analyze and infer the conditions for thermal runaway that occurred at that location. Taking the ternary positive electrode material system as an example, the analysis and judgment method is as follows:

[0087] If the relative intensities of the newly added peaks in the range of 21° to 24° are close, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of increasing first and then decreasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall trend of decreasing first and then increasing, it is determined that thermal runaway occurred due to overcharging at this location;

[0088] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall trend of increasing first and then decreasing, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of decreasing first and then increasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall close trend, it is determined that thermal runaway occurred due to local internal short circuit at this location; the "local internal short circuit" includes local micro - short circuit of the battery caused by foreign objects entering the power battery, partial piercing or complete piercing, including internal short circuit caused by the generation of lithium dendrites due to internal defects of the power battery, etc.

[0089] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall decreasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks in the range of 33° to 35° are close, and the relative intensities of the newly added peaks in the range of 38° to 43° are close, it is determined that thermal runaway occurred due to fire at this location;

[0090] If the relative intensities of the increasing peaks from the low angle to the high angle in the range of 21° to 24° show an overall trend of increasing first and then decreasing, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 29° to 32° show an overall increasing trend, the relative intensities of the newly added peaks from the low angle to the high angle in the range of 33° to 35° show an overall trend of decreasing first and then increasing, and the relative intensities of the newly added peaks from the low angle to the high angle in the range of 38° to 43° show an overall decreasing trend, it is determined that thermal runaway occurred due to overheating at this location.

[0091] It should be noted that for different battery material systems, the change characteristics of data can be established through the above - mentioned method, that is, the conditions for thermal runaway that occurred at this location are analyzed and inferred according to the high - low characteristics of the relative intensities of each group of newly added series of diffraction peaks.

[0092] The steps for analyzing the carbon components of the material are to screen the battery electrode sheet residues that meet the third particle size value for Raman spectroscopy analysis, and analyze and infer the conditions for thermal runaway that occurred according to the Raman spectrogram, specifically including:

[0093] The carbon components in the wreckage are mainly the graphite anode material and the carbonized products of other organic substances such as polymers and high polymers in the battery. Therefore, the carbon components experiencing different thermal runaway processes will exhibit different molecular structures. Take the powder wreckage on the 60-mesh or 80-mesh test sieve in (2) to carry out Raman spectroscopy analysis. Using the carbon Raman active peaks appearing near 1350±10 cm -1 and 1580±10 cm -1 as the analysis and research objects, they respectively correspond to the amorphous carbon (D peak) and the graphitized carbon (G peak). According to the relative ratio of the intensity of the G peak to the intensity of the D peak, analyze and infer the thermal runaway conditions that occurred there. The analysis and judgment method is as follows:

[0094] If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 1 and 2, it is judged that thermal runaway occurred there due to local internal short circuit;

[0095] If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 3 and 5, it is judged that thermal runaway occurred there due to overheating;

[0096] If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 6 and 9, it is judged that thermal runaway occurred there due to overcharging;

[0097] If the relative ratio of the intensity of the G peak to the intensity of the D peak is greater than 10, it is judged that thermal runaway occurred there due to fire;

[0098] In the actual process of thermal runaway initiation, it may be caused by the superposition of multiple factors. Then, the analysis results of different particle size materials can be comprehensively judged according to the above method.

[0099] The following combines several application examples to further illustrate the method of the present invention:

[0100] Application Example 1:

[0101] Taking a thermal runaway accident of a power battery as an example, the extraction and analysis of the wreckage of the power battery monomer are as follows:

[0102] As Figure 2 shown, take out the battery monomer at the initial initiation point preliminarily determined by fire trace analysis at the accident site. From Figure 2 (a), it can be seen that the surface of the battery monomer is covered with residual hard foam-like particles of fire extinguishing liquid. After disassembling the monomer shell and cleaning the surface residue of the fire extinguishing liquid with tweezers and a brush, visually observe the deformation and extrusion direction of the internal monomer electrode of the battery. It can be seen that Figure 2 (b) the position indicated by the arrow is the position with the most severe extrusion deformation. Take a 3 cm area of the electrode at this position 2, with a thickness of 5 mm. It is soaked in a 70% ethanol solution, the pH value of the solution is adjusted to 6.5 with acetic acid, and it is placed in an incubator at 35°C for 2 h to remove residual substances of fire extinguishing liquid, surfactants, oil stains, etc. Filter, and rinse alternately with anhydrous ethanol and ionized water 3 times until the pH value of the filtrate is about 7.0. Transfer the above-treated electrode sheet to a vacuum oven and dry it at 80°C under a relative vacuum of 0.09 Mpa for 24 h. Transfer the dried block-shaped electrode sheet into a planetary ball mill, put in agate grinding beads, and grind and disperse at a rotation speed of 100 r / min for 1 hour to obtain a loose electrode sheet residue sample coexisting with powder and flakes.

[0103] Subsequently, the electrode sheet sample is screened by the vertical multi-layer screening method, and the mesh numbers are 20 mesh, 50 mesh, and 80 mesh in sequence from top to bottom ( Figure 3 (a)). As Figure 3 (b1) shows, yellow and black mixed residues are separated and extracted on the 20-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 3 (b2)), it can be seen that the microstructure of the residue separated and extracted on the 20-mesh standard sieve is mainly flaky structure; from its elemental energy spectrum detection chart (3(b3)), it can be seen that the main elements of the residue separated and extracted on the 20-mesh standard sieve are Cu. Based on the above, it is confirmed that the main component of the residue separated and extracted on the 20-mesh standard sieve is the copper current collector. As Figure 3 (c1) shows, black powder residues are separated and extracted on the 50-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 3 (c2)), it can be seen that the microstructure of the residue separated and extracted on the 50-mesh standard sieve is mainly spherical sintered blocks; from its elemental energy spectrum detection chart ( Figure 3 (c3)), it can be seen that the main elements of the residue separated and extracted on the 50-mesh standard sieve include Mn, Ni, Co, O, C, P. Based on the above, it is confirmed that the main component of the residue separated and extracted on the 50-mesh standard sieve is the residue of spherical cathode materials sintered together. As Figure 3 (d1) shows, black powder residues are separated and extracted on the 80-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 3 (d2)), it can be seen that the microstructure of the residue separated and extracted on the 80-mesh standard sieve is mainly dispersed block flakes; from its elemental energy spectrum detection chart ( Figure 3 (d3)), it can be seen that the main element of the residue separated and extracted on the 80-mesh standard sieve is C. Based on the above, it is confirmed that the main component of the residue separated and extracted on the 80-mesh standard sieve is pulverized and dispersed irregular flaky graphite anode material.

[0104] The sheet debris of the copper current collector on a 20-mesh test sieve was taken for testing. First, the large black residual materials on the surface were wiped off with a soft brush. Then, it was transferred into absolute ethanol, and the remaining black substances on the surface of the copper foil were ultrasonically dispersed and cleaned for 1 h. The above-treated electrode was transferred to a vacuum oven and dried at 50 °C under a relative vacuum of 0.09 Mpa for 2 h to ensure that the current collector was completely dried. After polishing the surface of the copper foil with non-woven fabric, the structure was observed with a metallurgical microscope. For comparative analysis, the debris of the current collector at a position 10 cm away from the sampling position of this electrode was also taken and observed after the same treatment operation. From Figure 4 (a), it can be seen that the current collector of the electrode at the extruded part shows fine dendritic crystals and equiaxed crystals as a whole, and a large amount of eutectic tissue of red cuprous oxide and black copper oxide is distributed along the grain boundaries. The current collector far from this part shows large-grained equiaxed crystals, and a small amount of eutectic tissue of red cuprous oxide and black copper oxide is distributed along the grain boundaries ( Figure 4 (b)).

[0105] The debris powder sample on a 50-mesh test sieve was taken for X-ray powder diffraction test (XRD), and the test angle (2θ) range was selected as 10° - 80°. As Figure 5 (a) shows, the diffraction peak positions of the XRD spectra of the three parallel experimental battery debris powder samples are consistent, indicating excellent operational parallelism of this method. Comparing with the XRD crystal pattern of the normal battery cathode material ( Figure 5 (b)), the XRD crystal pattern of the normal battery anode material ( Figure 5 (c)), and the XRD crystal pattern of the copper material ( Figure 5 (d)), it can be seen that the characteristic peaks near 36.8° and 44.5° in the XRD spectrum of the original battery cathode material still exist, but the diffraction peaks at 18.5°, 38.5°, 48.6° and 64.2° positions have disappeared, mainly because the cathode material decomposed or a new material system was formed due to the reaction between the cathode and the electrolyte during the fire, resulting in the change of the unit cell structure. The diffraction peak of graphite carbon corresponding to 26.6° in the XRD spectrum of the original battery anode material still exists, indicating the existence of a large amount of residual carbon in the battery debris after the fire process, and the diffraction intensity of this peak is the highest. The diffraction characteristic peaks at 43.0°, 50.1°, 73.8° in the XRD spectrum of copper still exist after the fire, but all show a certain degree of right shift, indicating that the unit cell size of the copper component becomes smaller after the thermal runaway process. Through observation, as Figure 5(a) In the marked sample XRD pattern after experiencing a thermal runaway fire process, in the range of 21° to 24°, the relative intensity of the newly emerging peaks from low angle to high angle generally shows a trend of first increasing and then decreasing. In the range of 29° to 32°, the relative intensity of the newly emerging peaks from low angle to high angle generally shows an increasing trend. In the range of 33° to 35°, the relative intensity of the newly emerging peaks from low angle to high angle generally shows a trend of first decreasing and then increasing. In the range of 38° to 43°, the relative intensity of the newly emerging peaks from low angle to high angle generally shows an approaching trend.

[0106] Powder residues on an 80-mesh test sieve were taken for Raman spectroscopy analysis. The laser wavelength used for Raman spectroscopy testing was 532 nm. As Figure 6 can be seen, the peak positions of the diffraction peaks in the Raman spectra of the carbon component characteristics of the battery residue powder samples tested in 3 parallel experiments are basically the same, indicating excellent operational parallelism of this method. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) in parallel sample 1 are located at 1355.8 cm -1 and 1585.0 cm -1 respectively. After baseline subtraction, the relative intensities of the peaks are 1563.4 and 2159.8 respectively. It can be calculated that the intensity ratio of the G peak to the D peak is 1.38. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) in parallel sample 2 are located at 1354.2 cm -1 and 1585.5 cm -1 respectively. After baseline subtraction, the relative intensities of the peaks are 1301.2 and 2038.3 respectively. It can be calculated that the intensity ratio of the G peak to the D peak is 1.56. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) in parallel sample 3 are located at 1356.0 cm -1 and 1585.2 cm -1 respectively. After baseline subtraction, the relative intensities of the peaks are 1234.3 and 1830.9 respectively. It can be calculated that the intensity ratio of the G peak to the D peak is 1.48. The relative intensity ratios of the G peak to the D peak obtained from the above 3 parallel tests are all between 1 and 2.

[0107] Based on the above test analysis results, the cause of the thermal runaway fire of this monomer is due to local internal short circuit.

[0108] Application Example 2

[0109] Taking the sudden thermal runaway accident of a certain power battery during charging as an example, the extraction and analysis of the power battery monomer residue are as follows:

[0110] As Figure 7 shown, the battery monomer with the most serious burning damage was taken out. From Figure 7(a) The battery cell shell is severely damaged and the pole piece is blown out. It has not been exposed to firefighting fluid, so there are no residual hard foam particles of firefighting fluid on the surface. Since a large number of pole pieces have been blown out, it is impossible to remove the pole pieces according to the extrusion direction of the pole pieces. Therefore, the pole pieces with more serious burns are removed for analysis. The area of ​​the pole piece at this position is 5cm 2 , thickness 5mm. Then, rinse alternately with anhydrous ethanol and deionized water 3 times. Transfer the above-treated electrode to a vacuum oven and dry it at 70°C and 0.09Mpa relative vacuum for 24 hours. Transfer the above-dried block electrode to a planetary ball mill, put in agate grinding beads, and grind and disperse at a speed of 100r / min for 1 hour to obtain a loose electrode debris sample with coexistence of powder and flakes. The electrode samples were then screened by vertical multi-layer screening method, and the mesh sizes from top to bottom were 20 mesh, 50 mesh and 80 mesh. Figure 8 As shown in (a1), yellow and black mixed debris were separated and extracted on a 20-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 8 (a2)) shows that the microstructure of the debris separated and extracted on the 20-mesh standard sieve is mainly a flake structure; from its element spectrum detection diagram ( Figure 8 a3) It can be seen that the main element of the debris separated and extracted on the 20-mesh standard sieve is Cu. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 20-mesh standard sieve is the copper current collector. Figure 8 As shown in (b1), black powder residue was separated and extracted on a 50-mesh standard sieve; from its scanning electron microscope micrograph (Fig. Figure 8 (b2)) shows that the microstructure of the debris separated and extracted on the 50-mesh standard sieve is mainly spherical sintered blocks; from its element spectrum detection diagram ( Figure 8 (b3)) shows that the main elements of the debris separated and extracted on the 50-mesh standard sieve include Mn, Ni, Co, O, C, P and Al. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 50-mesh standard sieve is the debris of spherical positive electrode materials sintered together. Figure 8 As shown in (c1), black powder residue was separated and extracted on a 80-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 8 From the element spectrum detection diagram (8(c3)), it can be seen that the main element of the debris separated and extracted on the 80-mesh standard sieve is C. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 80-mesh standard sieve is powdered and dispersed irregular flake graphite negative electrode material.

[0111] Take the copper current collector sheet debris on a 20-mesh test sieve for testing. First, wipe the surface with a soft brush to remove the large pieces of black residual material. Then, transfer it into anhydrous ethanol and ultrasonically disperse and clean the remaining black substances on the copper foil surface for 1 h. Transfer the above-treated electrode sheet to a vacuum oven and dry it at 50 °C under a relative vacuum of 0.09 Mpa for 2 h to ensure that the current collector is completely dried. After polishing the copper foil surface with non-woven fabric, observe the structure with a metallurgical microscope. From Figure 9 It can be seen that dense circular black spots appear on the copper foil, which are caused by the high-current breakdown process.

[0112] Take the debris powder sample on a 50-mesh test sieve and conduct X-ray powder diffraction testing (XRD). The test angle (2θ) range is selected from 10° to 65°. As Figure 10 It can be seen that the diffraction peak positions of the XRD spectra of the battery debris powder samples in 3 parallel experiments are consistent, indicating excellent operational parallelism of this method. The diffraction peak corresponding to graphite carbon at the 26.5° position in the XRD spectrum indicates the existence of a large amount of residual carbon in the battery debris after experiencing the fire process, and the diffraction intensity of this peak is the highest. Through observation, as Figure 10 marked in, on the XRD pattern of the sample after experiencing the thermal runaway fire process, the relative intensities of the newly added peaks in the range of 21° - 24° are relatively weak and almost close. In the range of 29° - 32°, the relative intensities of the newly added peaks from the low angle to the high angle show an obvious increasing trend as a whole. In the range of 33° - 35°, the relative intensities of the newly added peaks from the low angle to the high angle are weak and show a trend of increasing first and then decreasing as a whole. In the range of 38° - 43°, the relative intensities of the newly added peaks from the low angle to the high angle are relatively strong and show an obvious trend of decreasing first and then increasing as a whole.

[0113] Take the powder debris on an 80-mesh test sieve for Raman spectroscopy analysis. The laser wavelength used for Raman spectroscopy testing is 532 nm. As Figure 11 It can be seen that the diffraction peak positions of the Raman spectra of the carbon component characteristics of the battery debris powder samples in 3 parallel experiments are basically the same, indicating excellent operational parallelism of this method. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) of parallel sample 1 are located at 1357.5 cm -1 and 1577.3 cm -1 , and the relative intensities of the peaks after baseline subtraction are 381.6 and 3336.1 respectively. It can be calculated that the intensity ratio of the G peak to the D peak is 8.74. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) of parallel sample 2 are located at 1362.4 cm -1 and 1578.6 cm -1After deducting the baseline, the relative intensities of the peaks are 527.6 and 4447.5, respectively. The calculated ratio of the intensity of the G peak to the intensity of the D peak is 8.43. The peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) of parallel sample 3 are located at 1351.5 cm -1 and 1578.7cm -1 , the relative intensities of the peaks after deducting the baseline were 256.3 and 1589.5 respectively, and the calculated ratio of the intensity of the G peak to the intensity of the D peak was 6.20. The relative ratios of the intensity of the G peak to the intensity of the D peak obtained in the above three parallel tests were all between 6 and 9.

[0114] Based on the above test analysis results, the thermal runaway fire in the monomer was caused by overcharging.

[0115] Application Example 3

[0116] Taking a power battery in a thermal runaway accident as an example, the extraction and analysis of the power battery monomer wreckage are as follows:

[0117] like Figure 12 As shown in the figure, remove the battery cells that are severely burned. Figure 12 (a) It can be seen that the battery cell shell has been completely burned and has not been exposed to fire-fighting fluid, so there are no residual hard foam particles of fire-fighting fluid on the surface. According to the situation, the overall burning of the cell is relatively uniform. The pole piece at the middle position is taken out as shown in 12 (b). The area of ​​the pole piece at this position is about 5cm 2 , thickness 3mm. Then, rinse alternately with anhydrous ethanol and deionized water 3 times. Transfer the above-treated electrode to a vacuum oven and dry it at 80°C and 0.09Mpa relative vacuum for 24 hours. Transfer the above-dried block electrode to a planetary ball mill, put in agate grinding beads, and grind and disperse at a speed of 150r / min for 1 hour to obtain a loose electrode debris sample with coexistence of powder and flakes. The electrode samples were then screened by vertical multi-layer screening method, and the mesh sizes from top to bottom were 20 mesh, 50 mesh and 80 mesh. As Figure 13 As shown in (a1), black flaky debris was separated and extracted on a 20-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 13 (a2)) shows that the microstructure of the debris separated and extracted on the 20-mesh standard sieve is mainly a flake structure; from the element spectrum detection Figure 13 (a3) It can be seen that the main element of the debris separated and extracted on the 20-mesh standard sieve is Cu. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 20-mesh standard sieve is copper current collector. Figure 13 As shown in (b1), black powder residue was separated and extracted on a 50-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 13As can be seen from (b2), the microstructure of the residue separated and extracted on the 50-mesh standard sieve is mainly spherical sintered blocks; as can be seen from its elemental energy spectrum detection chart (13(b3)), the main elements of the residue separated and extracted on the 50-mesh standard sieve include Mn, Ni, Co, O, C, P, and Al. Based on the above, it is confirmed that the main component of the residue separated and extracted on the 50-mesh standard sieve is the residue of spherical cathode materials sintered together. As Figure 13 As shown in (c1), black powder residue was separated and extracted on the 80-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 13 (c2)), it can be seen that the microstructure of the residue separated and extracted on the 80-mesh standard sieve is mainly dispersed blocky flakes; from its elemental energy spectrum detection chart (13(c3)), it can be seen that the main element of the residue separated and extracted on the 80-mesh standard sieve is C. Based on the above, it is confirmed that the main component of the residue separated and extracted on the 80-mesh standard sieve is pulverized and dispersed irregular flaky graphite anode material.

[0118] Take the sheet-like residue of the copper current collector on the 20-mesh test sieve for testing. First, wipe the surface with a soft brush to remove the large black residual material. Then, transfer it to anhydrous ethanol and ultrasonically disperse and clean the remaining black substances on the surface of the copper foil for 1 h. Transfer the above-treated electrode sheet to a vacuum oven and dry it at 50 °C under a relative vacuum of 0.09 Mpa for 2 h to ensure that the current collector is completely dried. After polishing the surface of the copper foil with non-woven fabric, observe the structure with a metallurgical microscope. From Figure 14 it can be seen that colorful circular patterns are found in the copper foil, which are the traces left by the initial open flame burning.

[0119] Take the powder sample of the residue on the 50-mesh test sieve and conduct X-ray powder diffraction test (XRD), and select the test angle (2θ) range of 10° to 70°. As Figure 15 it can be seen that the diffraction peak of graphite carbon corresponding to the position of 26.7° in the XRD spectrum indicates the existence of a large amount of residual carbon in the battery residue during the fire process, and the diffraction intensity of this peak is the highest. Through observation, as Figure 15 marked in, on the XRD pattern of the sample after the thermal runaway fire process, the relative intensity of the newly added peaks in the range of 21° to 24° shows a decreasing trend from low angle to high angle as a whole, the relative intensity of the newly added peaks in the range of 29° to 32° shows an increasing trend from low angle to high angle as a whole, the relative intensity of the newly added peaks in the range of 33° to 35° is close, and the relative intensity of the newly added peaks in the range of 38° to 43° is close.

[0120] Take the powder residue on the 80-mesh test sieve for Raman spectroscopy analysis. The laser wavelength used for Raman spectroscopy test is 532 nm. As Figure 16 it can be seen that the peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) on the Raman spectrum of the carbon component characteristics of the experimental battery residue powder sample are located at 1351.9 cm-1 and 1576.3cm -1 After deducting the baseline, the relative intensities of the peaks are 375.3 and 4709.7 respectively. The calculated intensity ratio of the G peak to the D peak is 12.55, and the relative intensity ratio is higher than 10.

[0121] Based on the above test analysis results, the thermal runaway fire in the monomer was caused by ignition of open flames.

[0122] Application Example 4

[0123] Taking a power battery in a thermal runaway accident as an example, the extraction and analysis of the power battery monomer wreckage are as follows:

[0124] like Figure 17 As shown in the figure, the battery cell with severe burn damage was taken out. It has not been exposed to fire-fighting liquid, so no residual hard foam particles of fire-fighting liquid are seen on the surface. Take out the pole piece at the location with severe burn damage that is squeezed inward (as shown in the marked box in the figure). The area of ​​the pole piece at this location is about 4cm 2 , thickness 3mm. Then, rinse alternately with anhydrous ethanol and deionized water 3 times. Transfer the above-treated electrode to a vacuum oven and dry it at 80°C and 0.09Mpa relative vacuum for 24 hours. Transfer the above-dried block electrode to a planetary ball mill, put in agate grinding beads, and grind and disperse at a speed of 100r / min for 1 hour to obtain a loose electrode debris sample with coexistence of powder and flakes. The electrode samples were then screened by vertical multi-layer screening method, and the mesh sizes from top to bottom were 20 mesh, 50 mesh and 80 mesh. Figure 18 As shown in (a1), black and yellow large flakes of debris were separated and extracted on a 20-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 18 (a2)) shows that the microstructure of the debris separated and extracted on the 20-mesh standard sieve is mainly a flake structure; from the element spectrum detection Figure 18 (a3) It can be seen that the main element of the debris separated and extracted on the 20-mesh standard sieve is Cu. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 20-mesh standard sieve is copper current collector. Figure 18 As shown in (b1), black powder residue was separated and extracted on a 50-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 18 (b2)) shows that the microstructure of the debris separated and extracted on the 50-mesh standard sieve is mainly spherical sintered blocks; from its element spectrum detection diagram (18 (b3)), it can be seen that the main elements of the debris separated and extracted on the 50-mesh standard sieve include Mn, Ni, Co, O, C, P and Al. Based on the above, it is confirmed that the main component of the debris separated and extracted on the 50-mesh standard sieve is the debris sintered together by spherical positive electrode materials. Figure 18(As shown in (c1), black powder residues were separated and extracted on an 80-mesh standard sieve; from its scanning electron microscope micrograph ( Figure 18 (c2)), it can be seen that the microstructure of the residues separated and extracted on the 80-mesh standard sieve is mainly dispersed blocky flakes; from its elemental energy spectrum detection graph ( Figure 18 (c3)), it can be seen that the main element of the residues separated and extracted on the 80-mesh standard sieve is C. Based on the above, it is confirmed that the main component of the residues separated and extracted on the 80-mesh standard sieve is pulverized and dispersed irregular flaky graphite anode material.

[0125] Take the copper current collector flaky residues on a 20-mesh test sieve for testing. First, wipe the surface with a soft brush to remove the large black residual materials. Then, transfer it into absolute ethanol and ultrasonically disperse and clean the remaining black substances on the surface of the copper foil for 1 h. Transfer the above-treated electrode sheet to a vacuum oven and dry it at 50 °C under a relative vacuum of 0.09 Mpa for 2 h to ensure that the current collector is completely dried. After polishing the surface of the copper foil with non-woven fabric, observe the structure with a metallurgical microscope. From Figure 19 it can be seen that the copper foil shows an overall uniform red color.

[0126] Take the residue powder sample on a 50-mesh test sieve and carry out X-ray powder diffraction test (XRD), and select the test angle (2θ) range of 10° - 65°. As Figure 20 it can be seen that the diffraction peak of graphite carbon corresponding to the position of 26.5° in the XRD spectrum indicates the existence of a large amount of residual carbon in the battery residues during the fire process, and the diffraction intensity of this peak is the highest. By observation, in the XRD pattern of the sample after experiencing the thermal runaway fire process, the relative intensity of the new peaks from low angle to high angle in the range of 21° - 24° shows a trend of first increasing and then decreasing as a whole, the relative intensity of the new peaks from low angle to high angle in the range of 29° - 32° shows an increasing trend as a whole, the relative intensity of the new peaks from low angle to high angle in the range of 33° - 35° shows a trend of first decreasing and then increasing as a whole, and the relative intensity of the new peaks from low angle to high angle in the range of 38° - 43° shows a decreasing trend as a whole.

[0127] Take the powder residues on an 80-mesh test sieve for Raman spectroscopy analysis, and the laser wavelength used for Raman spectroscopy test is 532 nm. As Figure 21 it can be seen that the peak positions of the amorphous carbon (D peak) and graphitized carbon (G peak) on the Raman spectrum of the carbon component characteristics of the experimental battery residue powder sample are located at 1354.1 cm -1 and 1578.9 cm -1 respectively. After subtracting the baseline, the relative intensities of the peaks are 814.3 and 2923.1 respectively. It can be calculated that the intensity ratio of the G peak to the D peak is 3.58, and the relative intensity ratio is between 3 and 5.

[0128] Based on the above test analysis results, the cause of the thermal runaway fire of this monomer is due to overheating triggering thermal runaway.

[0129] Combined with the above several application examples, the present invention has the following advantages and effects compared with the prior art:

[0130] (1) The method and system for extracting thermal runaway debris and determining the cause of new energy vehicle power batteries provided by the present invention systematically combines the on-site investigation of new energy vehicle fire accidents with laboratory analysis and detection technologies, provides technical support for the analysis and detection of power battery debris in fire accident investigations, effectively improves the current new energy vehicle fire accident investigation system, and facilitates relevant accident investigators to carry out new energy vehicle fire accident investigations and effectively judge the cause of the accident.

[0131] (2) The method for extracting thermal runaway debris and determining the cause of new energy vehicle power batteries provided by the present invention has invented a technology for extracting power battery debris. Through battery disassembly, monomer selection, sampling of debris pole pieces, impurity removal, the method of removing fire extinguishing liquid by soaking in alcohol solution, ball milling and vertical multi-layer screening, it can effectively separate the battery pole piece debris that has experienced a fire accident according to different main material components, solves the problem that it is difficult to extract materials for analysis and research targeted after the battery pole pieces are sintered after a fire accident, and is applicable to the investigation of various fire accidents caused by thermal runaway of lithium-ion battery systems, and has the characteristics of easy operation, high efficiency and strong applicability.

[0132] (3) The method for extracting thermal runaway debris and determining the cause of new energy vehicle power batteries provided by the present invention has invented the metallographic analysis technology based on the residual copper current collector, the material crystal structure analysis technology and the material carbon composition analysis technology, and has clarified the image features or parameter thresholds for different triggering mode determinations. It is of great significance for improving the effectiveness of new energy vehicle fire accident cause investigations and studying the occurrence laws of new energy vehicle fires.

[0133] The above embodiments are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it accordingly, and it should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the essence of the content of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for extracting thermal runaway debris from power batteries of new energy vehicles and determining the cause of the thermal runaway, characterized in that: The method comprises: Investigate sampling procedures to obtain battery electrodes after fire incidents; The debris extraction step is to separate and extract the debris materials of the battery pole pieces obtained in the investigation and sampling step, so as to separate the battery pole piece debris that has experienced the fire accident according to different main material components and obtain battery pole piece debris with different particle sizes. a step of analyzing the structure of the residual current collector, screening out the battery pole piece debris that meets a first particle size value from the battery pole piece debris of different particle sizes, wherein the battery pole piece debris that meets the first particle size value is a copper current collector, treating the copper current collector, observing the structure of the treated copper current collector with a metallographic microscope, and analyzing the metallographic microstructure of the copper foil to analyze the cause of the thermal runaway accident; The step of analyzing the crystal structure of the powder of the debris material is to select the battery pole pieces that meet the second particle size value from the battery pole pieces of different particle sizes to carry out X-ray powder diffraction test, and analyze the conditions that have caused thermal runaway based on the test spectrum; The material carbon component analysis step is to screen out the battery pole piece debris that meets the third particle size value from the battery pole piece debris of different particle sizes for Raman spectroscopy analysis, and analyze and infer the thermal runaway conditions that have occurred based on the Raman spectrum.

2. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 1, characterized in that: The survey sampling steps include: Remove the power battery pack that has experienced the fire accident from the vehicle, cut off the electrical connection lines, and then disassemble the battery pack; Observe the burned area, remove the most severely burned module, dismantle the module casing, and take out the internal battery cells; Observe the deformation characteristics of the entire battery cell group inside the module, and remove the battery cell that is most severely squeezed and deformed in the module or the battery cell that is initially determined to be the trigger point through fire trace analysis at the accident site; Remove the single body shell, take out the pole piece at the location with severe burning inside, and if the burning situation is not much different, take out the pole piece in the area with the most serious extrusion and deformation; if the accident power battery has been extinguished with fire water, first remove the particulate matter remaining on the pole piece, and then take out the pole piece at the location with severe burning inside.

3. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 1 or 2, characterized in that: The battery pole pieces obtained in the investigation and sampling step are subjected to separation and extraction of the debris materials, so as to separate the battery pole piece debris that has experienced the fire accident according to different main material components, and obtain battery pole piece debris with different particle sizes, including: Soak the battery pole pieces after the fire accident in a 30℃~35℃, 50%~70% concentration ethanol solution, and adjust the solution pH value to 6.0±0.5 with acetic acid; after soaking for 2~3 hours, filter, and rinse with anhydrous ethanol and ionized water alternately for no less than 3 times until the filtrate pH value is about 7.0; The battery pole piece after the above treatment is transferred to a vacuum oven and dried at 50°C to 80°C and a relative vacuum degree of 0.06 to 0.09 MPa for 24 hours to ensure that the pole piece debris is completely dried; The dried block-shaped battery pole pieces are transferred into a planetary ball mill, agate grinding beads are placed in the mill, and the powder and flake-like loose pole piece debris samples are obtained at a speed of 100 r / min to 150 r / min for 1 to 2 hours. Then, a vertical multi-layer screening method is used to screen the loosely dispersed pole piece debris from top to bottom in the order of 20 mesh, 30 mesh, 50 mesh, 60 mesh or 80 mesh, and the loosely dispersed pole piece debris are separated according to the particle size of ≥0.9 mm, 0.9 mm to 0.6 mm, 0.6 mm to 0.355 mm, 0.355 to 0.3 mm or 0.3 to 0.2 mm.

4. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 1, characterized in that: The processing of the copper current collector comprises: The black positive / negative electrode materials remaining on the surface of the copper current collector are wiped off, and then transferred to anhydrous ethanol, and the remaining black substances on the surface of the copper current collector are cleaned by ultrasonic dispersion. The cleaned copper current collector is moved to a vacuum oven for drying; the surface of the dried copper current collector is polished.

5. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 1, characterized in that: The cause analysis of thermal runaway accidents through metallographic microstructure analysis of copper foil includes: If circular black spots are found on the copper foil through observation, it is caused by a high current breakdown process; if the area of ​​the circular black spots is smaller than the preset value and appears densely, it is judged that thermal runaway caused by overcharging has occurred there; If there are small dendrites or equiaxed crystals in a location in the copper foil, and large equiaxed crystals are scattered around other locations, it means that this location has experienced the highest temperature during the thermal runaway process and is also the location where the temperature drops the earliest and the drop rate is the fastest. Therefore, it is judged that this location is the initiation site of the local internal short circuit. If there are colorful ring patterns in the copper foil, it is the trace left by the initial flame burning, which means that there has been thermal runaway caused by open flames. If the copper foil shows an overall uniform color change, it is judged that the area has been heated and overheated, causing thermal runaway.

6. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 3, characterized in that: The method of screening out battery pole piece debris that meets the second particle size value and conducting X-ray powder diffraction testing includes: The battery pole piece powder residues on the 30-mesh or 50-mesh test sieve are screened out for X-ray powder diffraction testing. The scanning angle range during the test must be at least 20° to 43°.

7. The method for extracting thermal runaway debris and determining the cause of the new energy vehicle power battery according to claim 6, characterized in that: The analysis of the thermal runaway conditions that have occurred based on the test map includes: If the relative intensity of the newly added peaks in the range of 21° to 24° is close, the relative intensity of the newly added peaks from low angle to high angle in the range of 29° to 32° shows an overall increasing trend, the relative intensity of the newly added peaks from low angle to high angle in the range of 33° to 35° shows an overall trend of first increasing and then decreasing, and the relative intensity of the newly added peaks from low angle to high angle in the range of 38° to 43° shows an overall trend of first decreasing and then increasing, it is judged that thermal runaway caused by overcharging has occurred; If the relative intensity of the newly added peaks from low angle to high angle in the range of 21° to 24° shows an overall trend of increasing first and then decreasing, the relative intensity of the newly added peaks from low angle to high angle in the range of 29° to 32° shows an overall trend of increasing, the relative intensity of the newly added peaks from low angle to high angle in the range of 33° to 35° shows an overall trend of decreasing first and then increasing, and the relative intensity of the newly added peaks from low angle to high angle in the range of 38° to 43° shows an overall trend of approaching, it is judged that thermal runaway caused by local internal short circuit has occurred; If the relative intensity of the newly added peaks from low angle to high angle in the range of 21° to 24° shows a decreasing trend as a whole, and the relative intensity of the newly added peaks from low angle to high angle in the range of 29° to 32° shows an increasing trend as a whole, and the relative intensity of the newly added peaks in the range of 33° to 35° is close, and the relative intensity of the newly added peaks in the range of 38° to 43° is close, it is judged that thermal runaway caused by fire has occurred; If the relative intensity of the newly added peaks from low angles to high angles in the range of 21° to 24° shows an overall trend of first increasing and then decreasing, the relative intensity of the newly added peaks from low angles to high angles in the range of 29° to 32° shows an overall trend of increasing, the relative intensity of the newly added peaks from low angles to high angles in the range of 33° to 35° shows an overall trend of first decreasing and then increasing, and the relative intensity of the newly added peaks from low angles to high angles in the range of 38° to 43° shows an overall trend of decreasing, it is judged that thermal runaway caused by overheating has occurred.

8. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 3, characterized in that: The method of screening out battery pole piece debris meeting the third particle size value and conducting Raman spectroscopy analysis includes: The battery pole powder residues on the 60-mesh or 80-mesh test sieve were screened out for Raman spectroscopy analysis. -1 and 1580±10cm -1 The carbon Raman active peaks that appear nearby are the objects of analysis and research, which correspond to the D peak of amorphous carbon structure and the G peak of graphitized carbon respectively. The relative ratio of the intensity of the G peak to the intensity of the D peak is used to analyze and infer the conditions that have caused thermal runaway.

9. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 8, characterized in that: The analysis and inference of the thermal runaway-inducing conditions that occurred at the location based on the relative ratio of the intensity of the G peak to the intensity of the D peak includes: If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 1 and 2, it is judged that thermal runaway caused by a local internal short circuit has occurred; If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 3 and 5, it is judged that thermal runaway caused by overheating has occurred; If the relative ratio of the intensity of the G peak to the intensity of the D peak is between 6 and 9, it is judged that thermal runaway caused by overcharging has occurred; If the relative ratio of the intensity of peak G to the intensity of peak D is greater than 10, it is judged that thermal runaway caused by fire has occurred.

10. The method for extracting thermal runaway debris and determining the cause of a new energy vehicle power battery according to claim 3, characterized in that: The vertical multi-layer screening method refers to stacking a series of standard sieves with different apertures or different mesh sizes vertically from top to bottom in the order of decreasing aperture or increasing mesh size for screening.

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