A lithium ion battery thermal runaway element flow analysis method

Abstract

The application discloses a lithium ion battery thermal runaway element flow analysis method and relates to the field of batteries; the method comprises the following steps: firstly, determining the content of each element in the battery component material before the battery loses control; secondly, carrying out a thermal runaway experiment and testing the real-time components and content of the electrolyte spouted in the thermal runaway process; thirdly, after the battery loses control, collecting the gas generated in the thermal runaway process and carrying out qualitative and quantitative analysis by means of gas chromatography to determine the components and content of the gas generated in the thermal runaway process; fourthly, respectively analyzing the physicochemical properties of the residues and the spouted particulate matters after the battery loses control to determine the composition of the compounds and the content of the elements; and fifthly, carrying out element conservation calculation based on Hess law, establishing the chemical reaction equation of the endothermic and exothermic reactions in the thermal runaway process of the lithium ion battery, and obtaining the variation law of the key elements in the thermal runaway reaction process of different inducements to compare and analyze the element flow characteristics in the thermal runaway triggered by different inducements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a lithium ion battery thermal runaway element flow analysis method. BACKGROUND

[0002] Lithium ion power battery has the advantages of high energy density, low discharge rate and long service life, etc., and is one of the core components of new energy vehicles and electrochemical energy storage systems. However, lithium ion battery is relatively active, and is prone to thermal runaway under mechanical abuse, electrical abuse, thermal abuse, and electrochemical abuse, etc., which shows as smoking, spewing, burning and explosion. Lithium ion battery thermal runaway accidents not only cause serious economic losses and personal injuries to the vehicle owner and passengers, but also lead to "safety anxiety" of consumers on electric vehicles, and hinder the large-scale promotion and application of electrochemical energy storage.

[0003] Carrying out lithium ion battery thermal runaway accident investigation can clarify the causes of lithium ion battery thermal runaway from the nature, trace the occurrence and development process, and then optimize and upgrade the battery materials and structural assembly based on the accident causes to reduce the probability of accidents. At present, lithium ion battery thermal runaway accident investigation is mostly based on video analysis, macroscopic deformation trace change rule, charge and discharge data, etc. to carry out accident tracing, and the core of the investigation is also to find the first battery that triggers thermal runaway in the battery system; there is a lack of methods for deep tracing of lithium ion battery thermal runaway causes from the mechanism. SUMMARY

[0004] The purpose of the present application is to provide a lithium ion battery thermal runaway element flow analysis method to solve the above-mentioned problems existing in the prior art, which can trace the occurrence and development time sequence of lithium ion battery thermal runaway, analyze the causes of thermal runaway from the mechanism, and further provide support for improving the safety of lithium ion battery and enriching the lithium ion battery accident investigation method.

[0005] To achieve the above-mentioned purpose, the present application provides the following scheme:

[0006] The present application provides a lithium ion battery thermal runaway element flow analysis method, comprising the following steps:

[0007] Step one, determining the content of each element of the battery component material before the lithium ion battery loses control;

[0008] Step two, carrying out a thermal runaway experiment of the battery in a closed container, and connecting a Fourier Transform infrared spectroscopy (FTIR) at the gas outlet end to test the real-time composition and content of the electrolyte during the thermal runaway process;

[0009] Step three, carry out repetitive lithium-ion battery runaway experiment, trigger lithium-ion battery runaway with different incentives, calculate battery thermal runaway gas production according to the pressure change of the sealed container, collect thermal runaway gas to carry out gas chromatography qualitative and quantitative analysis, determine the composition and content of thermal runaway gas;

[0010] Step four, collect and weigh the spewing particulate matter and the remaining matter after thermal runaway, and analyze the physicochemical properties of the remaining matter and the spewing particulate matter respectively to determine the composition and content of the compounds.

[0011] Step five, calculate the mass of each element in the electrolyte vapor, mixed gas, remaining matter and particulate matter after thermal runaway, establish the chemical reaction equation of endothermic and exothermic reactions in the process of lithium-ion battery thermal runaway according to Hess's law, compare and analyze the valence change rules of main elements in the battery under different incentives, establish the linkage and traceability relationship between element flow and thermal runaway incentives, and establish the reaction timing, key element valence change and element flow rule database of lithium battery thermal runaway under different incentives.

[0012] Optionally, step one includes battery component quantitative analysis, the lithium-ion battery is disassembled, the positive material, negative material and separator inside the battery are separated, the weight of the positive material, the weight of the negative material, the weight of the separator, the weight of the aluminum foil, the weight of the copper foil and the mass of the electrolyte are calculated, and the mass of each element before the lithium-ion battery runaway is calculated according to the weight and element composition of the lithium-ion battery component material. The composition of the lithium-ion battery electrolyte is determined, the lithium-ion battery is heated in a constant temperature sealed environment at 130℃ until the mass of the battery does not change, at this time the electrolyte with a boiling point lower than 130℃ in the lithium-ion battery has been completely evaporated, the electrolyte is collected using a dropper to carry out GC-MS analysis to determine the composition and content of the electrolyte, and finally the mass of each element in the electrolyte is determined according to the proportion of the elements.

[0013] Optionally, step two includes qualitative and quantitative analysis of the electrolyte during the lithium battery runaway process. The battery is subjected to thermal runaway triggering experiment in a sealed pressure vessel, FTIR is connected at the exhaust outlet of the thermal runaway gas to detect the composition and content of the electrolyte generated during the initial spewing of the thermal runaway process in real time, and finally the mass of different elements in the electrolyte vapor generated during the spewing process is determined.

[0014] Optionally, step three includes carrying out repetitive lithium-ion battery thermal runaway triggering experiment, placing the lithium-ion battery in a constant volume pressure vessel, triggering the lithium-ion battery thermal runaway with any method (consistent with the real-time collection and determination method of the electrolyte), recording the pressure and temperature changes in the pressure vessel during the thermal runaway process, calculating the total gas production during the thermal runaway according to the ideal gas state equation. When the temperature in the cavity of the constant volume pressure vessel decreases to room temperature, the gas is collected using a gas collection bag, and the collected gas is subjected to gas chromatography qualitative and quantitative analysis.

[0015] Optionally, step four comprises cutting the residual shell of the out-of-control lithium ion battery, collecting the positive and negative electrode materials from different parts, then immersing the materials in ethylmethyl carbonate (EMC) solvent for 24 hours, taking out the materials, drying and placing in a crucible for grinding, filtering the ground positive and negative electrode materials using a filter screen and placing in a sealed bottle, finally testing the sample by inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), determining the sensitive elements and valence change rules of the battery component materials under the three physicochemical analysis methods according to the test results, and the sensitive elements are elements that are more sensitive to the physicochemical property analysis method; collecting the eruption particulate matter after the out-of-control, taking the same cleaning, drying and grinding treatment on the eruption particulate matter, then carrying out a series of physicochemical property analysis on it, and based on the above experimental steps, the characteristic relationship between the thermal runaway inducement, the thermal runaway process and the compound and element valence change after the out-of-control is established through element conservation calculation.

[0016] The present application has the following technical effects relative to the prior art:

[0017] Based on Hess's law, the present application analyzes the element flow change rule in the thermal runaway process of the lithium ion battery, which can help the accident investigators to trace back the time sequence of the occurrence and development of the lithium ion battery thermal runaway based on the key valence change elements, analyze the thermal runaway reason from the mechanism, and further provide support for improving the safety of the lithium ion battery and enriching the lithium ion battery accident investigation method. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0019] Figure 1 It is a flowchart of the lithium ion battery thermal runaway element flow analysis method of the present application; DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0021] The present application aims to provide a lithium ion battery thermal runaway element flow analysis method to solve the problems existing in the prior art, trace the occurrence and development time sequence of lithium ion battery thermal runaway, analyze the thermal runaway causes from the mechanism, and further provide support for improving the safety of lithium ion batteries and enriching the lithium ion battery accident investigation method.

[0022] In order to make the above-mentioned purposes, characteristics and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0023] As shown in Figure 1 The present application provides a lithium ion battery thermal runaway element flow analysis method, which is based on the element conservation before and after the thermal runaway of the lithium ion battery. The thermal runaway element flow analysis process includes thermal runaway electrolyte eruption, thermal runaway gas production element distribution, thermal runaway particle emission element distribution, thermal runaway residue element distribution, and key element valence change rule analysis, etc. Finally, an element flow diagram is drawn according to the above analysis to analyze the nature mechanism of the accident. The method includes the following steps:

[0024] Step one, determine the content of each element of the unrunaway battery sample before the thermal runaway of the lithium ion battery by means of battery disassembly, separation, constant temperature heating, etc., including positive electrode material mass determination, negative electrode material mass determination, electrolyte mass determination, separator mass determination, conductive agent, binder mass determination, and C, H, O, Ni, Co, Mn, Al, Cu element mass calculation in the battery sample;

[0025] Step two, carry out adiabatic thermal runaway test experiment of the battery in a closed space, connect Fourier Transform infrared spectroscopy (FTIR) at the gas outlet to test the real-time composition and content of the electrolyte produced in the initial spurt during the thermal runaway process. Here, the composition and content of the electrolyte are mainly determined;

[0026] Step three, carry out repeated lithium ion battery thermal runaway gas production experiment, calculate the battery thermal runaway gas production according to the pressure change of the closed container, collect the thermal runaway gas to carry out qualitative and quantitative analysis by gas chromatography, and determine the composition and content of the thermal runaway gas;

[0027] Step four, using ICP-MS, XRD, XPS respectively on the remaining material and the eruption of particulate matter after the runaway, to determine the content of the compound and the content of the elements. Under different thermal runaway inducements, lithium-ion battery thermal runaway changes from the initial state to carbonized residue, ejected particulate matter, electrolyte and flammable gas mixture, accompanied by energy absorption and release;

[0028] Step five, according to Hess law to carry out thermodynamic calculation, establish the chemical reaction equation of lithium ion in the process of thermal runaway endothermic, exothermic reaction, and determine the reaction normalized heat of generation of compounds, analyze the compound reaction path under different inducements and different thermal runaway severity, determine the key variable elements, determine the relationship between the key variable elements and the thermal runaway inducement, analyze the relationship between the release law of different inducements and the generated products in the process of element conservation, and establish the database of reaction product change law of different inducement thermal runaway.

[0029] Specifically, step one includes battery component quantitative analysis. First, the test lithium-ion battery is disassembled, and the positive electrode material, negative electrode material and separator inside the battery are separated. The separator is cleaned using EMC to remove the lithium salt on the surface of the separator, then dried and weighed to determine the weight of the separator. Subsequently, the negative electrode material is soaked in deionized water to obtain clean copper foil and weigh it. The total mass of the negative electrode sheet is subtracted from the weight of the copper foil to obtain the weight of the negative electrode material. The positive electrode material is soaked using EMC, then a puncher is used to cut positive electrode material of uniform size, and a small knife is used to scrape the positive electrode material. Then the weight of the aluminum foil is weighed, and the weight of the full battery positive electrode material and aluminum foil is obtained by mapping the weight of the cut circular aluminum foil to the full battery. Finally, the total mass of the battery is subtracted from the known component weight to obtain the mass of the electrolyte. According to the weight and element composition of the battery component material, the mass of each element before battery runaway is calculated.

[0030] Step two includes the determination of lithium-ion battery electrolyte components. The organic solvents commonly used in lithium-ion batteries include cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). When the temperature inside the battery exceeds 80°C, the low-boiling-point electrolyte inside the lithium-ion battery will become vapor and diffuse out of the battery. To accurately determine the content and components of the electrolyte inside the lithium-ion battery, the battery can be placed in a constant-temperature sealed environment at 130°C and heated until the battery mass no longer changes. At this point, it can be considered that the electrolyte with a boiling point below 130°C inside the battery has been completely evaporated. The electrolyte is collected using a dropper and subjected to GC-MS analysis to determine the components and content of the electrolyte. Finally, the mass of each element in the electrolyte is determined based on the proportion of elements.

[0031] Step three includes placing the battery in a constant-volume pressure vessel and triggering the battery thermal runaway in any way. The exhaust port is connected to the FTIR for real-time qualitative and quantitative analysis of the thermal runaway gas, and the elemental content of the initial electrolyte vapor during thermal runaway is determined. The same triggering method is used for thermal runaway gas production experiments, and the pressure and temperature changes in the pressure vessel during thermal runaway are recorded. According to the ideal gas state equation, the total gas production during thermal runaway is calculated. The gas in the tank is collected using a gas collection bag and placed in a gas chromatograph for analysis to determine the components and content of the thermal runaway gas. Finally, the mass of each element in the thermal runaway gas is calculated based on the composition of the elements in the gas. It should be noted that the gas chromatograph used for directional and quantitative analysis needs to be calibrated in advance with a standard curve for battery thermal runaway gas. During calibration, the carrier gas needs to be calibrated. The commonly used carrier gases for thermal runaway gas production include nitrogen, argon, and helium. Directional calibration of the carrier gas is mainly to reduce calculation errors. The configuration of the gas chromatograph standard gas can refer to the research results reported in the literature and be calibrated and corrected at multiple points.

[0032] Step four includes, the mass of the thermal runaway residue element. In the process of thermal runaway of lithium ion battery, electrolyte, flammable mixed gas, and spewing particulate matter will be released, especially the mass loss of prismatic battery after thermal runaway is often less than 50%. The shell of the residue after the thermal runaway of the battery is cut open, and the positive and negative electrode materials are collected from different parts (at least three points or more). Then the materials are soaked in EMC solvent for 24 hours, and after drying, the materials are placed in a crucible and ground. The ground positive and negative electrode materials are filtered through a filter screen and placed in a sealed bottle. Finally, the samples are tested by ICP-MS, XRD and XPS. According to the test results, the sensitive elements and valence change rules under the three kinds of physicochemical analysis methods are determined. The elements of the thermal runaway spewing particulate matter are determined. The thermal runaway test of the lithium ion battery is carried out in a closed clean space, and the spewing particulate matter after thermal runaway is collected. The spewing particulate matter is subjected to the same cleaning, drying and grinding treatment, and then a series of physicochemical property analysis is carried out, and the characteristic relationship between the thermal runaway process and the compound and element valence change after thermal runaway is established.

[0033] The thermal runaway process of lithium ion battery contains more than a dozen chemical reactions, and the thermal runaway reaction timing is very difficult to sort out. Especially after the thermal runaway accident of new energy vehicles and energy storage stations, it is very difficult to find out the cause of the accident from the most essential point. The current lithium ion battery accident investigation has the problems of difficult accident investigation and insufficient investigation depth. The present application provides a way to trace the cause of the lithium ion battery accident in depth. And on this basis, new thermal runaway cause investigation methods and technologies can be derived, such as comparing the physicochemical property analysis results under different trigger modes, refining the key feature rules, and establishing a feature database, which can help improve the efficiency of lithium ion battery accident investigation and solve the problem of difficult lithium ion battery accident investigation.

[0034] In the description of the present application, it should be noted that the terms "center", "top", "bottom", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] In the present application, specific examples are used to illustrate the principles and implementation modes of the present application. The above examples are only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In view of the above, the content of the specification should not be understood as limiting the present application.

Claims

1. A method for analyzing the elemental flow during thermal runaway in lithium-ion batteries, characterized in that: Includes the following steps: Step 1: Determine the content of each element in the components of the lithium-ion battery before it runs away from control; Step 2: Conduct a thermal runaway experiment on the battery in a sealed container, and connect a Fourier transform infrared spectroscopy device at the gas outlet to test the real-time composition and content of the electrolyte during the thermal runaway process. Step 3: Different triggers are used to induce runaway of lithium-ion batteries. The amount of gas generated by thermal runaway is calculated based on the pressure change of the sealed container. The thermal runaway gas is collected and subjected to qualitative and quantitative analysis by gas chromatography to determine the components and contents of the thermal runaway gas. Step 4: Collect and weigh the ejected particles and the residue after the thermal runaway process. Conduct physicochemical property analysis on the residue and ejected particles to determine the composition of the compounds and the content of elements. Step 5: Calculate the mass of each element in the electrolyte vapor, mixed gas, residue, and ejected particulate matter after thermal runaway. Based on Hess's law, establish the chemical reaction equations for the endothermic and exothermic reactions of the lithium-ion battery during thermal runaway. Compare and analyze the valence variation patterns of the main elements inside the battery under different inducing factors, and establish the linkage and tracing relationship between element flow and thermal runaway inducing factors. Establish a database of the reaction timing, key element valence changes, and element flow patterns of lithium-ion batteries under different inducing factors.

2. The method for analyzing the elemental flow of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: Step one includes quantitative analysis of battery components. The lithium-ion battery is disassembled, and the positive electrode material, negative electrode material, and separator inside the battery are separated. The weight of the positive electrode material, negative electrode material, separator, aluminum foil, copper foil, and electrolyte are calculated respectively. Based on the weight and elemental composition of the lithium-ion battery components, the mass of each element before the lithium-ion battery runs away is calculated. Determining the elements in the electrolyte requires first identifying its composition and content. This is done by heating the lithium-ion battery in a constant-temperature, sealed environment at 130°C until the battery mass stops changing. At this point, all the electrolyte with a boiling point below 130°C inside the lithium-ion battery has evaporated. The electrolyte is then collected using a dropper and analyzed by gas chromatography-mass spectrometry (GC-MS) to determine its composition and content. Finally, the mass of each element in the electrolyte is determined based on the element ratios.

3. The method for analyzing the elemental flow of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: Step two includes determining the electrolyte composition during lithium-ion battery runaway. A thermal runaway triggering experiment is conducted on the battery in a sealed pressure vessel. Fourier transform infrared spectroscopy is connected to the runaway gas outlet to detect the electrolyte composition and content generated during the initial spray in real time. Finally, the mass of different elements in the electrolyte vapor generated during the spray process is determined.

4. The method for analyzing the elemental flow of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: Step three involves conducting repetitive lithium-ion battery thermal runaway triggering experiments. The lithium-ion battery is placed in a constant-volume pressure vessel, and thermal runaway is triggered using any method. The pressure and temperature changes inside the pressure vessel during the thermal runaway process are recorded, and the amount of gas generated during thermal runaway is calculated based on the ideal gas law. After the temperature of the cavity inside the constant-volume pressure vessel drops to room temperature, the gas is collected using a gas collection bag, and the collected gas is subjected to qualitative and quantitative analysis by gas chromatography.

5. The method for analyzing the elemental flow of thermal runaway in lithium-ion batteries according to claim 1, characterized in that: Step four includes cutting open the casing of the lithium-ion battery residue after the runaway, collecting positive and negative electrode materials from different parts, then immersing the materials in methyl methacrylate solvent for 24 hours, removing the materials, drying them, grinding them in a crucible, filtering the ground positive and negative electrode materials with a filter screen, and placing them in a sealed bottle. Finally, inductively coupled plasma mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy are performed on the samples. Based on the test results, the sensitive elements and valence change rules of the battery component materials under the three physicochemical analysis methods are determined. The so-called sensitive elements are those that are more sensitive to the physicochemical property analysis methods. The ejected particulate matter during the runaway process was collected and subjected to the same cleaning, drying, and grinding treatment. Subsequently, a series of physicochemical property analyses were conducted on the particulate matter. Through element conservation calculations, characteristic relationships between the thermal runaway inducing factors, the thermal runaway process, and the changes in the valence of compounds and elements after the runaway were established.

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