Calculation method of heat production in thermal runaway process of electrochemical energy storage battery

Abstract

The invention discloses a method for calculating heat production in a thermal runaway process of an electrochemical energy storage battery, and belongs to the field of battery safety. Comprising the following steps: selecting an electrochemical energy storage battery with a certain electric quantity, measuring the residual heat of thermal runaway residual substances of the battery, disassembling a new battery, calculating the reaction heat among components of the battery, calculating the heat of combustion gas by combining the combustion condition of the battery, and finally introducing revision parameters to calculate the heat production of the thermal runaway process of the battery. According to the method, the heat released in the thermal runaway process of the electrochemical energy storage battery is calculated in an indirect mode, the difficulty that the heat release amount in the thermal runaway process of the energy storage battery cannot be directly measured is overcome, the accuracy is high, and the practicability is high.

Description

Technical Field

[0001] The present invention belongs to the field of battery safety, and in particular relates to a method for calculating heat generation during thermal runaway of an electrochemical energy storage battery. Background Art

[0002] At present, electrochemical energy storage batteries have been proven to be very important energy storage devices. They are widely used in the field of energy storage because of their advantages such as high energy density, high power density, and long cycle life. However, electrochemical energy storage batteries, such as lithium-ion batteries and sodium-ion batteries, will inevitably experience thermal runaway under the conditions of overcharging, short circuiting, extrusion, puncture, overheating, and other abuses. Thermal runaway of batteries is usually manifested as an uncontrollable and rapid rise in temperature. The heat generation rate of the chemical reaction inside the battery is much higher than the heat dissipation rate, and may be accompanied by combustion and explosion. At present, the research on thermal runaway of lithium-ion batteries is very mature. It can not only clearly explain the reaction conditions of each stage of thermal runaway of lithium-ion batteries, but also clearly divide the gas components of thermal runaway of batteries. However, battery thermal runaway is complex and changeable. In the process of thermal runaway, the battery will inevitably experience combustion or explosion. The danger of battery thermal runaway is not constant under different conditions, so the thermal danger of batteries is always difficult to determine.

[0003] During the thermal runaway of the battery, as the temperature continues to rise, the electrolyte itself can not only gasify and decompose, but also react with the active substances inside the battery to generate combustible gases such as methane, ethane and carbon monoxide. The various gases released by the chemical reactions of these electrolytes mix with the vaporized electrolyte vapor, causing serious harm. However, in some environments, when the battery itself experiences thermal runaway, the combustible gas will not be ignited because the temperature itself is not high or there is no open flame. In order to minimize the harm caused by battery combustion, it is necessary to have a clear understanding of the energy that can be generated by electrochemical energy storage batteries during thermal runaway (combustion or non-combustion). Therefore, there is an urgent need to develop an energy analysis method for energy storage batteries during thermal runaway to provide a theoretical basis for the subsequent design of electrochemical energy storage battery safety protection structures. In view of this situation, the present invention aims at the above-mentioned problems and establishes a method for calculating the heat generated during the thermal runaway process of electrochemical energy storage batteries. Summary of the invention

[0004] The objectives of this technical invention are achieved through the following technical solutions:

[0005] A method for calculating the heat generated during thermal runaway of an electrochemical energy storage battery comprises the following steps:

[0006] (1) Select a certain type of electrochemical energy storage battery (lithium-ion battery, sodium-ion battery, etc.), measure the heat release of thermal runaway, select the overheating mode as the thermal runaway trigger condition, and select a conventional closed explosion tank as the experimental device. The ambient atmosphere is inert gas;

[0007] (2) Thermocouples attached to the battery surface are used to detect the battery surface temperature and record the highest temperature T that the battery can reach during the battery thermal runaway test. max and the accumulated gas production data (composition and proportion); after the battery thermal runaway ends, the battery is disassembled and the remaining materials are weighed, with a mass of m 1 After uniform mixing, take part of the remaining material sample and heat it for differential scanning calorimetry (DSC) test (temperature condition is higher than T max 20-50℃ rounded to make the reaction fully proceed and reduce the error), calculate the energy released, and thus calculate the mass m 1 The total heat of the remaining material in the battery thermal runaway is Q 1 ; Select the battery without thermal runaway test under the same power state and disassemble it in the vacuum glove box, and weigh the mass of the positive electrode mixture (including binder, conductive agent, etc.), negative electrode mixture, separator and electrolyte respectively. c 、m a 、m s and m e ;

[0008] (3) Based on the composition and proportion of the gas produced during thermal runaway of the battery recorded in step (2), the mass of the gas produced is equivalent to the mass of the electrolyte volatilized itself, which is m' e (This is directly related to the duration of thermal runaway heating), and then the mass of the electrolyte that reacts with the internal materials of the battery is calculated to be approximately m e -m' e。 The electrolyte in step (2) is divided into two equal parts, each with a mass of 0.5 m e Take a portion of the electrolyte sample from one portion and mix it with an appropriate amount of the positive electrode mixture obtained by disassembling step (2) and then perform a DCS test, wherein the mass ratio of the positive electrode mixture to the electrolyte is 2:1 (the test temperature is the same as the DCS test temperature in (2)). After sufficient reaction, calculate the heat release value, and then calculate the mass 0.5m e The electrolyte and m e The total heat obtained when the positive electrode mixture mass is disassembled in step (2) is Q c ; Do the same experiment and calculate the other mass 0.5m e The electrolyte content and m e The total heat obtained when the negative electrode mixture mass is disassembled in step (2) is reacted is Q a ; Then the remaining mass is m c- m e The positive electrode mixture and the remaining mass are m a- m e The negative electrode mixture is mixed and DSC test is performed to obtain a heat of Q 2(The test temperature is the same as the DCS test temperature in (2)); Finally, the mass obtained by disassembling step (2) is m s The diaphragm is tested individually for a total heat of Q s (The test temperature is the same as (2) DCS test temperature); therefore, the heat released by the battery when thermal runaway occurs in a nitrogen environment is:

[0009] Q=Q c +Q a +Q s +Q 2 -Q 1

[0010] (4) However, when the battery is in thermal runaway in an external air environment, combustion may occur. The content of each component of the battery gas production increases relative to the content of the component in step (2), and the total heat released will change significantly. The battery is tested for thermal runaway by using the same test method as step (1), i.e., overheating method and closed explosion tank, but the test environment is changed from nitrogen to air, and the thermal runaway gas production data (including components and content) in the air environment are collected. The difference in the content of each component of the battery thermal runaway gas production under two different environments (the battery thermal runaway gas production under two different environments is basically the same) can be approximately regarded as the amount of gas consumed by combustion (N in the air). 2 and O 2 The proportion reaches 99%, and the impact on gas production can be ignored). Due to the different safety of different electrochemical energy storage batteries, some batteries will not burn even if thermal runaway occurs in an air environment. However, there may be other open flames in actual applications. For this type of battery, the heat release under combustion needs to be manually ignited during the thermal runaway of the battery (place an ignition device 15-30cm away from the battery safety valve port);

[0011] In the above steps, the main components of the gas produced by thermal runaway of the battery under nitrogen and air conditions include electrolyte vapor (dimethyl carbonate DMC, ethylene carbonate EC, propylene carbonate PC, etc.), H 2 , CO, CH 4 , C 2 H 4 The combustion enthalpies of these gases are H 2 :-286kJ / mol, CH 4 :-890kJ / mol, C 2 H 6 :-1560kJ / mol, CO:-283kJ / mol, DMC:-1450kJ / mol, EC:-1200kJ / mol, PC:-1800kJ / mol. Through the combustion reaction of these gases with oxygen, it can be known that the heat released by the combustion of gases in the thermal runaway gas production of the battery is Q'.

[0012] (5) Theoretically, the gas can be completely burned under air conditions, but in reality, part of the gas diffuses directly into the air, so the heat generated by actual combustion is less than the heat generated by theoretical complete combustion; then the heat released by the battery in the case of thermal runaway under air conditions is

[0013] Q 总 =x·Q+y·Q'

[0014] x, y are correction coefficients, where 1<x<2 (when the battery is burning, the reaction of each component will be more intense due to the higher temperature), 0<y<1 (the difference in the gas production data of the battery thermal runaway under two different environments will not lead to complete combustion. Due to the diffusion of the gas itself, a part of the combustible gas will diffuse into the air without burning).

[0015] Further, the electrochemical energy storage battery in step (1) may be a lithium ion battery, a sodium ion battery, etc., and the battery may be in different power states, such as 100 SOC%, 80 SOC%, 30 SOC%, etc.

[0016] Advantages of the present invention:

[0017] (1) This method uses an indirect method to calculate the heat released during the thermal runaway process of the electrochemical energy storage battery, overcoming the difficulty of directly measuring the amount of heat released during the thermal runaway process of the energy storage battery;

[0018] (2) This method can not only calculate the calorific value of the two thermal runaway states of battery combustion and non-combustion, but also calculate the heat released by thermal runaway of electrochemical energy storage batteries of different specifications and systems, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the explosion tank test

[0020] Figure 2 This is a flow chart of a method for calculating the heat generated during thermal runaway of an electrochemical energy storage battery provided by the present invention.

[0021] Figure 3 The heat test data of the battery in the embodiment of the thermal runaway combustion in the large cone calorimeter DETAILED DESCRIPTION

[0022] The essential features and significant advantages of the present invention are further illustrated below in conjunction with the accompanying drawings and specific embodiments, but are not limited thereto.

[0023] Example

[0024] (1) Select 100SOC% 314Ah lithium iron phosphate energy storage battery (5.5kg); use overheating to trigger battery thermal runaway, and the maximum temperature of the battery under inert gas environment reaches 510℃. The gas components PC, EC, DMC volatile gas 0.12L, 0.08L, 0.3L; H 2 , CO, CH 4 , C 2 H 4 They are approximately 153L, 67L, 42L, and 38L respectively.

[0025] After the battery thermal runaway ended, the battery was disassembled and the remaining materials were weighed, with a mass of 3.6 kg. After uniform mixing, some samples were heated for DSC testing, and the energy released was calculated to obtain a residual heat of 103 kJ for the remaining materials in the battery thermal runaway.

[0026] (2) Battery components include positive electrode mixture, negative electrode mixture, electrolyte, separator and other materials. The mass proportion of each material is m after disassembling the battery in the glove box and weighing it. c 、m a 、m s and m e They are 1.95kg, 1.25kg, 0.8kg and 0.5kg respectively. Part of the electrolyte is soaked in the other three materials.

[0027] (3) Take part of the dried electrode material and mix it with the electrolyte (mass ratio is 2:1); dry the remaining electrode material and mix it with a sample and a part of the mass separator for DSC test, and the total heat of the reaction between the positive and negative electrode mixtures and the electrolyte is 1030kJ and 410kJ respectively. After the remaining positive and negative electrodes are mixed, take appropriate amount of samples and the separator for heat test, and the total heat of the reaction of the remaining positive and negative electrode materials and the total heat of the separator are 622kJ and 120kJ respectively. Therefore, the heat released by the thermal runaway of the battery under this environment is:

[0028] Q=1030kJ+410kJ+622kJ+120kJ-103kJ=2.1MJ

[0029] (4) The gas production results of thermal runaway test (ignition) in open environment are 0.03L, 0.05L, and 0.16L of volatile gas for PC, EC, and DMC; 2 , CO 2 , CO, CH 4 , C 2 H 4 They are approximately 88L, 200L, 32L, 15L, and 22L respectively. Combining (1), the heat released is 9.4MJ, so the heat released by thermal runaway of the battery under ignition is approximately:

[0030] Q总 =1.2·2.1+0.6·9.4=8.16MJ

[0031] (5) Figure 3 As shown in the test data of the large industrial cone calorimeter, the heat released by the thermal runaway combustion of the 314Ah battery is approximately 7MJ, but due to the large instrument environment, some heat loss was not detected. Combined with the test results of the heat loss of the cone calorimeter (about 10-15%), it shows that this method is feasible.

Claims

1. A method for calculating the heat generated during thermal runaway of an electrochemical energy storage battery, characterized in that: The following steps are involved: (1) Select a certain type of electrochemical energy storage battery, measure the heat release of thermal runaway, select the overheating mode as the thermal runaway trigger condition, select a conventional closed explosion tank as the experimental device, and the ambient atmosphere is inert gas; (2) Thermocouples attached to the battery surface are used to detect the battery surface temperature and record the highest temperature T that the battery can reach during the battery thermal runaway test. max and the cumulative gas production data: composition and proportion; after the battery thermal runaway ends, the battery is disassembled and the remaining materials are weighed, with a mass of m1; after uniform mixing, some of the remaining material samples are heated for differential scanning calorimetry (DSC) testing, and the temperature condition is higher than T max The energy released is calculated by rounding the temperature from 20 to 50 °C, and the heat of the remaining material in the total battery thermal runaway is calculated as Q1, which is a mass of m1. Batteries that have not been tested for thermal runaway in the same state of charge are selected and disassembled in a vacuum glove box, and the masses of the positive electrode mixture (including binder, conductive agent, etc.), negative electrode mixture, separator and electrolyte are weighed as m, respectively. c 、m a 、m s and m e ; (3) Based on the composition and proportion of the gas produced during thermal runaway of the battery recorded in step (2), the mass of the gas produced is equivalent to the mass of the electrolyte volatilized itself, which is m' e , and then the mass of the electrolyte that reacts with the internal materials of the battery is calculated to be approximately m e -m' e。 The electrolyte in step (2) is divided into two equal parts, each with a mass of 0.5 m e Take a portion of the electrolyte sample from one portion and mix it with an appropriate amount of the positive electrode mixture obtained by disassembling step (2) and then perform a DCS test, wherein the mass ratio of the positive electrode mixture to the electrolyte is 2:

1. After sufficient reaction, calculate the heat release value, and then calculate the mass 0.5m e The electrolyte and m e The total heat obtained when the positive electrode mixture mass is disassembled in step (2) is Q c ; Do the same experiment and calculate the other mass 0.5m e The electrolyte content and m e The total heat obtained when the negative electrode mixture mass is disassembled in step (2) is reacted is Q a ; Then the remaining mass is m c- m e The positive electrode mixture and the remaining mass are m a- m e The negative electrode mixture is mixed and DSC test is performed to obtain a heat of Q2; finally, the mass obtained by disassembling step (2) is m s The diaphragm is tested individually for a total heat of Q s ; Therefore, the heat released by thermal runaway of the battery in a nitrogen environment is: Q=Q c +Q a +Q s +Q2-Q1 (4) However, when the battery is in thermal runaway in an external air environment, combustion may occur. The content of each component of the battery gas production increases relative to the content of the component in step (2), and the total heat released will change significantly. The battery is tested for thermal runaway by using the same test method as step (1), i.e., overheating method and closed explosion tank, but the test environment is changed from nitrogen to air, and the thermal runaway gas production data (including components and content) in the air environment are collected. The difference in the content of each component of the battery thermal runaway gas production under two different environments can be approximately regarded as the amount of gas consumed by combustion. Due to the different safety of different electrochemical energy storage batteries, some batteries will not burn even if they have thermal runaway in an air environment, but there may be other open flames in actual application. For such batteries, the heat release under combustion needs to be manually ignited during the thermal runaway of the battery, and an ignition device is placed 15-30 cm from the battery safety valve port. In the above steps, the main components of the gas produced by thermal runaway of the battery under nitrogen and air conditions include electrolyte vapor (dimethyl carbonate DMC, ethylene carbonate EC, propylene carbonate PC, etc.), H2, CO, CH4, C2H4, etc. The combustion enthalpies of these gases are respectively H2: -286kJ / mol, CH4: -890kJ / mol, C2H6: -1560kJ / mol, CO: -283kJ / mol, DMC: -1450kJ / mol, EC: -1200kJ / mol, PC: -1800kJ / mol. Through the combustion reaction of these gases with oxygen, it can be known that the heat released by the combustion of gases in the thermal runaway gas production of the battery is Q'; (5) Theoretically, the gas can be completely burned under air conditions, but in reality, part of the gas diffuses directly into the air, so the heat generated by actual combustion is less than the heat generated by theoretical complete combustion; then the heat released by the battery in the case of thermal runaway under air conditions is Q 总 =x·Q+y·Q' x, y are correction coefficients, where 1<x<2, 0<y<1.

2. The method according to claim 1, characterized in that The electrochemical energy storage battery in step (1) may be a lithium-ion battery, a sodium-ion battery, etc., and the battery may be in different states of charge, such as 100 SOC%, 80 SOC%, 30 SOC%, etc.

3. The method according to claim 1, characterized in that The test temperature during the DCS test in step (3) is the same as the DCS test temperature in step (2).

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