CN109613056B - Method for evaluating fire hazard risk of lithium ion battery - Google Patents

Method for evaluating fire hazard risk of lithium ion battery Download PDF

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CN109613056B
CN109613056B CN201811399532.1A CN201811399532A CN109613056B CN 109613056 B CN109613056 B CN 109613056B CN 201811399532 A CN201811399532 A CN 201811399532A CN 109613056 B CN109613056 B CN 109613056B
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lithium ion
ion battery
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CN109613056A (en
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李伟峰
王贺武
欧阳明高
张亚军
李成
卢兰光
李建秋
杜玖玉
韩雪冰
冯旭宁
苏岭
周安健
金国庆
杨辉前
刘波
张友群
万明春
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Tsinghua University
Chongqing Changan New Energy Automobile Technology Co Ltd
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Chongqing Changan New Energy Automobile Technology Co Ltd
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    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
    • G01N25/22—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/50—Investigating or analyzing materials by the use of thermal means by investigating flash-point; by investigating explosibility
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Abstract

The application relates to a method for evaluating fire hazard risk of a lithium ion battery. The method for evaluating the fire risk of the lithium ion battery provided by the embodiment of the application can effectively calculate and evaluate the fire risk level of the lithium ion battery. The method for evaluating the fire hazard of the lithium ion battery can definitely obtain the safety state of the lithium ion battery under the current state. When the fire hazard of the lithium ion battery is high, the lithium ion battery can be selected not to be applied to engineering. The fire hazard level of the lithium ion battery obtained by the method is beneficial to solving the problem of safety judgment of the lithium ion battery and is beneficial to large-scale commercial application of battery type selection and power supply industries.

Description

Method for evaluating fire hazard risk of lithium ion battery
Technical Field
The application relates to the technical field of power batteries, in particular to a method for evaluating fire hazard risk of a lithium ion battery.
Background
In recent years, the market share of electric vehicles has steadily increased. Lithium ion batteries have excellent performances such as high voltage, high specific energy, long cycle life, no environmental pollution, and the like, and are highly concerned by the electric automobile industry. However, lithium ion batteries are prone to eruption. The lithium ion battery can generate combustible mixed gas in the process of eruption. The combustible mixture accumulates inside the lithium ion battery. And after the internal pressure of the lithium ion battery reaches a certain pressure limit, the safety valve is opened, and the combustible mixed gas is released to the external environment along with the eruption of the lithium ion battery. In the process of spraying the lithium ion battery, the surface temperature of the lithium ion battery can reach about 1000 ℃ at most. In the process of lithium ion battery eruption, sparks are often accompanied. Because the high-temperature surface of the lithium ion battery and the temperature of the spark are far higher than the ignition temperature of the eruption, once the eruption is sprayed in the air and contacts with oxygen, the ignition phenomenon is easy to occur, and a fire disaster is caused. Fire and explosion accidents caused by thermal runaway of the lithium ion battery are frequently reported, so that the safety problem of the lithium ion battery becomes one of the main factors for preventing the lithium ion battery from being applied to large-scale commercialization in the power supply industry. Because the lithium ion battery fire involves the combustion of gas, liquid and solid and is electrified, the fire safety of the lithium ion battery cannot be evaluated in the traditional technical scheme.
Disclosure of Invention
Therefore, it is necessary to provide a method for evaluating the fire risk of a lithium ion battery, aiming at the problems that the lithium ion battery is involved in the combustion of gas, liquid and solid, and is charged, and the fire risk of the lithium ion battery cannot be evaluated by the conventional technical scheme.
A method for evaluating the fire risk of a lithium ion battery comprises the following steps:
s100, acquiring performance parameters of the lithium ion battery to be tested, wherein the performance parameters comprise one or more of thermal runaway temperature, electrolyte spontaneous combustion point or flash point, ignition limit index of a gas spray, time from thermal runaway to ignition of the battery, peak value of combustion heat release rate of the battery, combustion heat release quantity of the battery, explosion hazard index of a gaseous spray of the battery and concentration peak value of the gas spray;
s200, calculating the possibility coefficient of the lithium ion battery to be tested in the fire and the hazard coefficient of the lithium ion battery to be tested in the fire according to the performance parameters;
s300, calculating a risk coefficient of the lithium ion battery to be tested when the lithium ion battery to be tested is in fire through multiplying a possibility coefficient by a possibility weight factor, adding a hazard coefficient by a hazard weight factor, wherein the sum of the possibility weight factor and the hazard weight factor is equal to 1;
and S400, evaluating the fire risk level of the lithium ion battery to be tested according to the risk coefficient.
In one embodiment, the probability factor is equal to the thermal runaway probability factor multiplied by the thermal runaway probability weight factor, plus the electrolyte ignition probability factor multiplied by the electrolyte ignition probability weight factor, plus the gas spray ignition probability factor multiplied by the gas spray ignition probability weight factor;
wherein a sum of the thermal runaway probability weighting factor, the electrolyte ignition probability weighting factor, and the gas spray ignition probability weighting factor is 1.
In one embodiment, the coefficient of thermal runaway probability C(thermal runaway, to be tested)Calculated from the following equation:
Figure BDA0001876010330000021
wherein, T(thermal runaway, reference)As a reference for the temperature at which thermal runaway of the cell occurs, T(thermal runaway, to be tested)And the temperature is the temperature of the lithium ion battery to be tested when thermal runaway occurs.
In one embodiment, the electrolyte ignition probability coefficient C(electrolyte on fire, to be tested)Calculated from the following equation:
Figure BDA0001876010330000031
wherein, T(electrolyte, reference)For reference to the self-ignition or flash-point temperature, T, of the electrolyte occurring in the cell(electrolyte, to be tested)The self-ignition point temperature or the flash point temperature of the electrolyte of the lithium ion battery to be tested.
In one embodiment, the gas eruption firing probability coefficient C(gas eruption ignited, to be tested)Calculated from the following equation:
Figure BDA0001876010330000032
Figure BDA0001876010330000033
UFL(gaseous hairspray, to be tested)An upper limit of ignition, LFL, of the lithium ion battery gaseous propellant to be tested(gaseous hairspray, to be tested)Is the lower limit of ignition of the gaseous spray of the lithium ion battery to be tested, H(gaseous hairspray, to be tested)Is the ignition limit index, H, of the gaseous spray of the lithium ion battery to be tested(gaseous hairspray, reference)Is referred to as the ignition limit index of the battery's gaseous emissions.
In one embodiment, the hazard coefficient is equal to the thermal hazard coefficient multiplied by a thermal hazard weighting factor, plus the explosion hazard coefficient multiplied by an explosion hazard weighting factor, plus the toxic gas hazard coefficient multiplied by a toxic gas hazard weighting factor;
wherein the sum of the thermal hazard weighting factor, the explosion hazard weighting factor, and the toxic gas hazard weighting factor is 1.
In one embodiment, the thermal hazard coefficient C(thermal hazard, to be tested)Calculated from the following equation:
C(thermal hazard)，To be tested)＝FIT×C(IT，To be tested)+FPHRR×C(PHRR，To be tested)+FQ×C(Q，To be tested)
Figure BDA0001876010330000041
Figure BDA0001876010330000042
Figure BDA0001876010330000043
Wherein, ITTo be testedThe PHRR is the time from the occurrence of thermal runaway to the beginning of ignition of the lithium ion battery to be testedTo be testedIs the combustion heat release rate peak value, Q, of the lithium ion battery to be testedTo be testedThe heat release of the lithium ion battery to be tested is obtained;
ITreference toFor reference to the time from the occurrence of thermal runaway to the onset of fire, PHRR, of a batteryReference toFor reference to the peak combustion heat release rate, Q, of the cellReference toIs the heat release of the reference cell;
FITis a weight factor of the ignition time of the lithium ion battery to be tested, FPHRRIs the weight factor, F, of the combustion heat release rate peak value of the lithium ion battery to be testedQIs a weight factor of the heat release of the lithium ion battery to be tested, C(IT, to be tested)Is the hazard coefficient of the ignition time of the lithium ion battery to be tested, C(PHRR, to be tested)Is the harmfulness coefficient of the combustion heat release of the lithium ion battery to be tested, C(Q, to be tested)The hazard coefficient of the heat release of the lithium ion battery to be tested is obtained;
the sum of the weighting factor of the ignition time, the weighting factor of the combustion heat release rate peak and the weighting factor of the heat release amount is 1.
In one embodiment, the detonation hazard coefficient C(explosive hazard, to be tested)Calculated from the following equation:
Figure BDA0001876010330000044
Figure BDA0001876010330000045
wherein, Kg isTo be testedIs the explosion hazard index of the lithium ion battery gaseous eruption to be tested, V is the constant volume combustion bomb volume of the lithium ion battery to be tested,
Figure BDA0001876010330000051
and the maximum pressure rise rate of the lithium ion battery to be tested in the constant volume combustion bomb is determined.
In one embodiment, the toxic gas hazard coefficient(toxic gas hazard, to be tested)Calculated from the following equation:
C(toxic gas hazards)，To be tested)＝F(CO，To be tested)×C(CO，To be tested)+F(HF，To be tested)×C(HF，To be tested)
Figure BDA0001876010330000052
Figure BDA0001876010330000053
Wherein the content of the first and second substances,
Figure BDA0001876010330000054
releasing a concentration peak value of hydrofluoric acid for the lithium ion battery to be tested,
Figure BDA0001876010330000055
releasing a carbon monoxide concentration peak value for the lithium ion battery to be tested,
Figure BDA0001876010330000056
to reference the peak concentration of hydrofluoric acid released by the cell,
Figure BDA0001876010330000057
peak concentration of carbon monoxide released for the reference cell;
F(CO, to be tested)A weight factor, F, for the release of carbon monoxide by the lithium ion battery to be tested(HF, to be tested)A weight factor, C, for releasing hydrofluoric acid for the lithium ion battery to be tested(CO, to be tested)A hazard coefficient, C, for the release of carbon monoxide by the lithium ion battery to be tested(HF, to be tested)And releasing the harmfulness coefficient of hydrofluoric acid for the lithium ion battery to be tested.
In one embodiment, the step S400 of evaluating the fire risk level of the lithium ion battery according to the risk factor includes:
comparing the calculated risk coefficient with a fire hazard reference coefficient of a reference battery;
if the difference between the risk coefficient and the reference coefficient is less than or equal to 30%, the fire risk of the lithium ion battery to be tested is grade C, which represents safety;
if the difference between the risk coefficient and the reference coefficient is more than 30% and less than or equal to 70%, the fire risk of the lithium ion battery to be tested is B-level, which represents general risk;
and if the difference between the risk coefficient and the reference coefficient is more than 70%, the fire risk of the lithium ion battery to be tested is A grade, which represents a serious risk.
The application relates to a method for evaluating fire hazard risk of a lithium ion battery. The method for evaluating the fire risk of the lithium ion battery provided by the embodiment of the application can effectively calculate and evaluate the fire risk level of the lithium ion battery. The method for evaluating the fire hazard of the lithium ion battery can definitely obtain the safety state of the lithium ion battery under the current state. When the fire hazard of the lithium ion battery is high, the lithium ion battery can be selected not to be applied to engineering. The fire hazard level of the lithium ion battery obtained by the method is beneficial to solving the problem of safety judgment of the lithium ion battery and is beneficial to large-scale commercial application of battery type selection and power supply industries.
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Fig. 1 is a flowchart of a method for evaluating a fire risk of a lithium ion battery according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more clearly understood, the method for evaluating the fire risk of a lithium ion battery according to the present application is described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The application provides a method for evaluating the fire hazard of a lithium ion battery, which evaluates the fire hazard of the lithium ion battery by adopting a fire hazard coefficient and evaluates the fire hazard from two aspects of the possibility of the fire hazard and the hazard after the fire hazard occurs.
The risk of lithium ion batteries is assessed by three main performance parameters: thermal runaway trigger temperature, electrolyte flash point, and gassing firing limit index.
The thermal runaway trigger temperature is the temperature when the lithium ion battery starts to generate thermal runaway, and is the result of the comprehensive action of a series of thermal runaway trigger conditions such as the decomposition of an SEI film, the consumption of reaction lithium, the collapse of a diaphragm and the like caused by different abuse modes (thermal abuse, mechanical abuse, electrical abuse and the like), so the parameter can be used for representing the difficulty degree of the lithium ion battery in generating the thermal runaway. When the lithium ion battery is out of control thermally, gas such as H can be separated out after the interaction of the internal materials of the battery2、CO2、CO、CH4And the like.
The flash point of the electrolyte is a safety index for storing, transporting and using the electrolyte in the lithium ion battery, and is also an index for the volatility of the combustible liquid. Flammable liquid with low flash point, high volatility, easy ignition and poor safety. When the pressure in the battery exceeds a certain limit value, the gas in the battery can be released to the outside through a battery safety valve or through breaking a battery plastic film. The electrolyte can be ignited, burned and even exploded when contacting with air at high temperature.
The ignition limit index of the gaseous eruption is an index of the difficulty degree of ignition, combustion and even explosion of the gas generated by the lithium ion battery. The higher the ignition limit index, the more easily the combustible gas will catch fire, burn or even explode.
The thermal runaway trigger temperature, the electrolyte flash point and the gaseous propellant ignition limit index are all indexes used for evaluating the fire possibility of the lithium ion battery, and the thermal runaway trigger temperature, the electrolyte flash point and the gaseous propellant ignition limit index are used as evaluation indexes for evaluating the fire possibility of the lithium ion battery in the application.
Referring to fig. 1, in one embodiment, a method for evaluating a fire risk of a lithium ion battery is provided, which includes the following steps:
and S100, acquiring the performance parameters of the lithium ion battery to be tested. The performance parameters include one or more of a thermal runaway temperature, an electrolyte auto-ignition or flash point, a flammability limit index of the gas spray, a time from onset of thermal runaway to onset of ignition of the battery, a peak combustion heat release rate of the battery, a combustion heat release of the battery, an explosion hazard index of the battery's gaseous spray, and a peak gas spray concentration.
In this step, the performance parameters include, but are not limited to, one or more of the above various parameters. The lithium ion battery to be tested can be one of a lithium ion battery monomer, a lithium ion battery module or a lithium ion battery pack.
S200, calculating the possibility coefficient of the lithium ion battery to be tested in the fire and the hazard coefficient of the lithium ion battery to be tested in the fire according to the performance parameters.
In this step, the lithium ion battery fire risk is considered to include the possibility of fire occurrence and the hazard of fire occurrence. In another embodiment, the lithium ion battery fire risk may also include other factors.
And S300, calculating the risk coefficient of the lithium ion battery to be tested for fire through the combination of the possibility coefficient multiplied by the possibility weight factor and the hazard coefficient multiplied by the hazard weight factor, wherein the sum of the possibility weight factor and the hazard weight factor is equal to 1.
In this step, the possibility weight factor and the hazard weight factor are set when the lithium ion battery fire risk is calculated, and the lithium ion battery fire risk level can be clearly analyzed through different weight proportions. In particular, the sum of the likelihood weight factor and the hazard weight factor is equal to 1. For example, the likelihood weight factor may be set equal to the hazard weight factor equal to 0.5. The likelihood weight factor may also be set equal to 0.6 and the hazard weight factor equal to 0.4. And obtaining different risk coefficients of the lithium ion battery to be tested according to different weight proportions.
And S400, evaluating the fire risk level of the lithium ion battery according to the risk coefficient.
In this step, the level of the fire risk of the lithium ion battery may be evaluated based on the risk factor. The fire hazard level of the lithium ion battery can be referred to guide the large-scale commercial application of the lithium ion battery type selection and the power supply industry.
In the embodiment, the evaluation of the fire risk level of the lithium ion battery is realized through the steps. The lithium ion battery fire hazard refers to the hazard caused by fire. The application combines the influence of thermal hazard, explosion hazard and toxic gas hazard on the fire hazard of the lithium ion battery. The hazard coefficient is adopted to represent the fire hazard of the lithium ion battery, and the hazard caused by the lithium ion battery after the fire happens can be clearly evaluated. In this embodiment, the method for evaluating the fire risk of the lithium ion battery can effectively calculate and evaluate the fire risk level of the lithium ion battery. The method for evaluating the fire risk of the lithium ion battery can definitely give the fire risk level of the lithium ion battery and provide a certain basis for the type selection of the lithium ion battery.
The risk coefficient in step S300 may be represented in the form of formula (1):
C(hazardous, to be tested)＝Possibility of×C(possibility, to be tested)+Harmfulness of×C(hazard, to be tested)Formula (1)
Wherein, C(hazardous, to be tested)Representing the risk coefficient of the lithium ion battery to be tested in fire. C(possibility, to be tested)Representing the possibility coefficient of fire of the lithium ion battery to be tested. C(possibility, to be tested)Representing the hazard coefficient of the lithium ion battery to be tested in fire. Said FPossibility ofAnd said FHarmfulness ofRepresents a weight factor, and FPossibility of+FHarmfulness of＝1。
FPossibility ofAnd FHarmfulness ofThe two weight factors can be selected from factor analysis method, correlation coefficient method, expert ranking method, RSR method, Delphi method, arithmetic mean number combination weighting method, continuous multiplication accumulation combination weighting method, fuzzy mathematic judgment method, priority chart method and the like. When the weight factor can not be determined due to lack of related data, an empirical method can be adopted, and F can be set in the applicationPossibility of＝FHarmfulness of0.5. Of course, it can also be set to FPossibility of＝0.6，FHarmfulness of＝0.4。FPossibility of＝0.55，FHarmfulness of＝0.45。FPossibility of＝0.45，FHarmfulness of＝0.55。FPossibility of＝0.4，FHarmfulness of＝0.6。FPossibility of＝0.3，FHarmfulness of＝0.7。
In one embodiment, the probability coefficient is calculated primarily from the three aspects of the occurrence of thermal runaway, ignition of the electrolyte, and ignition of the gaseous propellant. The specific calculation may be that the probability coefficient equals the thermal runaway probability coefficient multiplied by a thermal runaway probability weight factor, plus the electrolyte ignition probability coefficient multiplied by an electrolyte ignition probability weight factor, plus the gas spray ignition probability coefficient multiplied by a gas spray ignition probability weight factor. Can be calculated using the following formula (2):
the probability coefficient C(possibility, to be tested)Calculated from equation (2):
C(possibility, to be tested)＝
F thermal runaway XC (thermal runaway, test) + F electrolyte ignition XC (electrolyte ignition, test) + F gas spray ignition XC (gas spray ignition, test) formula (2)
Wherein, FThermal runawayIs the weight factor of thermal runaway of the lithium ion battery to be tested, C(thermal runaway, to be tested)Is the thermal runaway probability coefficient, F, of the lithium ion battery to be testedElectrolyte solution ignitionA weight factor C for ignition of the lithium ion battery electrolyte to be tested(electrolyte on fire, to be tested)Is the ignition possibility coefficient of the electrolyte of the lithium ion battery to be tested, FGas eruption firingA weight factor, C, for the ignition of the gas eruption of the lithium ion battery to be tested(gas eruption on fire, waitTest)And the thermal runaway possibility coefficient of the ignition of the lithium ion battery gas eruption to be tested.
In this step, wherein FThermal runaway+FElectrolyte solution ignition+FIgnition of gaseous eruptionThe weighting factor can be determined by a factor analysis method, a correlation coefficient method, an expert ranking method, an RSR method, a Delphi method, an arithmetic mean combined weighting method, a multiplication-accumulation combined weighting method, a fuzzy mathematical judgment method, a sequence chart method and the like. When the weight factor cannot be determined due to lack of relevant data, an empirical method may be adopted, and F may be set in this embodimentThermal runaway＝FElectrolyte solution ignition＝FIgnition of gaseous eruption1/3. F can also be setThermal runaway＝0.3，FElectrolyte solution ignition,0.3，FIgnition of gaseous eruption＝0.4。
In one embodiment, the coefficient of thermal runaway probability C(thermal runaway, to be tested)Calculated from equation (3):
Figure BDA0001876010330000101
wherein, T(thermal runaway, to be tested)The temperature of the lithium ion battery to be tested when thermal runaway occurs can be tested through an accelerated adiabatic calorimeter experiment. In this embodiment, a method for calculating the thermal runaway probability coefficient is provided, which may be used to calculate, by combining with a thermal runaway temperature of a reference battery, a temperature at which thermal runaway of the lithium ion battery to be tested occurs and the thermal runaway probability coefficient of the lithium ion battery to be tested. The calculation method provided in the embodiment enables the calculated thermal runaway probability coefficient to be more accurate.
In one embodiment, the electrolyte ignition probability coefficient C(electrolyte on fire, to be tested)Calculated from equation (4):
Figure BDA0001876010330000111
wherein, T(electrolyte, to be tested)Is a stand forThe self-ignition point temperature or the flash point temperature of the electrolyte of the lithium ion battery to be tested can be tested through a self-ignition point or flash point test experiment. In this embodiment, a method for calculating the ignition possibility coefficient of the electrolyte is provided, which can calculate the self-ignition point temperature or the flash point temperature of the electrolyte of the lithium ion battery to be tested and the ignition possibility coefficient of the electrolyte by combining the electrolyte ignition point of the reference battery. The calculation method provided in the embodiment enables the calculated ignition possibility coefficient of the electrolyte to be more accurate.
In one embodiment, the gas eruption firing probability coefficient C(gas eruption ignited, to be tested)Calculated from equations (5) and (6):
Figure BDA0001876010330000112
Figure BDA0001876010330000113
UFL(gaseous hairspray, to be tested)An upper ignition limit, LFL, for the lithium ion battery spray to be tested(gaseous hairspray, to be tested)Is the lower ignition limit, H, of the lithium ion battery spray to be tested(gaseous hairspray, to be tested)And the ignition limit index of the lithium ion battery eruption to be tested is shown. The upper ignition limit and the lower ignition limit of the lithium ion battery to be tested can be tested by an explosion analysis tester. In this embodiment, a method for calculating the ignition possibility coefficient of the gas eruption is provided, which can be used to calculate the ignition upper limit of the lithium ion battery eruption to be tested, the ignition lower limit of the lithium ion battery eruption to be tested, the ignition limit coefficient of the lithium ion battery eruption to be tested, and the ignition possibility coefficient of the gas eruption by combining the ignition limit coefficient of the gas eruption of a reference battery. The calculation method provided in the embodiment makes the calculated ignition possibility coefficient of the gas eruption object more accurate.
In the above embodiment, the hazard coefficient of the lithium ion battery to be testedThe method is mainly used for calculating heat hazard, explosion hazard and toxic gas hazard. In one embodiment, wherein FHeat hazard+FHazard of explosion+FToxic gas harmThe weighting factor can be determined by a factor analysis method, a correlation coefficient method, an expert ranking method, an RSR method, a Delphi method, an arithmetic mean combined weighting method, a multiplication-accumulation combined weighting method, a fuzzy mathematical judgment method, a sequence chart method and the like. When the weight factor cannot be determined due to lack of relevant data, an empirical method may be adopted, and F may be set in this embodimentHeat hazard＝FHazard of explosion＝FToxic gas harm＝1/3。FHeat hazard＝0.3，FHazard of explosion＝0.3，FToxic gas harm＝0.4。
In one embodiment, the hazard coefficient C(hazard, to be tested)Calculated from equation (7):
C(harmfulness of disease)，To be tested)
＝FHeat hazard×C(thermal hazard)，To be tested)+FHazard of explosion×C(explosion hazard)，To be tested)+FToxic gas harm
×C(toxic gas hazard, to be tested)Formula (7)
Wherein, FHeat hazardGenerating a thermal hazard weight factor, C, for the lithium ion battery to be tested(thermal hazard, to be tested)Is the thermal hazard coefficient of the lithium ion battery to be tested, FHazard of explosionIs the weight factor C of the lithium ion battery to be tested(explosion hazard, i to be tested)The explosion hazard coefficient, F, of the lithium ion battery to be testedToxic gas harmIs the weight factor of the generated toxic gas hazard of the lithium ion battery to be tested, C(toxic gas hazard, to be tested)And the toxic gas hazard coefficient of the lithium ion battery to be tested is obtained. The sum of the thermal hazard weighting factor, the explosion hazard weighting factor and the toxic gas hazard weighting factor is 1. In one embodiment FHeat hazard＝FHazard of explosion＝FToxic gas harm1/3, where F may also be setHeat hazard＝0.3，FHazard of explosion＝0.3，FToxic gas harm＝0.4。
In one embodiment, the thermal hazard coefficient C(thermal hazard, to be tested)Calculated from equation (8) to equation (11):
C(thermal hazard, to be tested)＝FIT×C(IT, to be tested)+FPHRR×C(PHRR, to be tested)+FQ×C(Q, to be tested)Formula (8)
Figure BDA0001876010330000131
Figure BDA0001876010330000132
Figure BDA0001876010330000133
Wherein IT (ignition time) is the time from the beginning of thermal runaway to the beginning of ignition of the battery, PHRR is the peak value of the combustion heat release rate of the battery, Q is the combustion heat release quantity of the battery, and FITAs a weighting factor for the ignition time, FPHRRWeighting factor, F, for the peak of the combustion heat release rate of the batteryQWeighting factor for the heat release of the combustion of the battery, C(IT, to be tested)Is the hazard coefficient of the ignition time of the lithium ion battery to be tested, C(PHRR, to be tested)Is the harmfulness coefficient of the combustion heat release of the lithium ion battery to be tested, C(Q, to be tested)And the harmfulness coefficient of the heat release of the lithium ion battery to be tested is obtained. In this embodiment, the shorter the ignition time IT is, the more hazardous IT is. The greater the exotherm peak PHRR, the greater the hazard. The more the exotherm Q, the more hazardous. In one embodiment, FIT+FPHRR+FQThe weighting factor can be determined by a factor analysis method, a correlation coefficient method, an expert ranking method, an RSR method, a Delphi method, an arithmetic mean combined weighting method, a multiplication-accumulation combined weighting method, a fuzzy mathematical judgment method, a sequence chart method and the like. When the weighting factor cannot be determined due to lack of correlation data, the method can be adoptedEmpirically, F can be set in this embodimentIT＝FPHRR＝FQF may also be provided 1/3IT＝0.3，FPHRR＝0.3，FQ＝0.4。
In one embodiment, the explosion hazard coefficient C(explosive hazard, to be tested)Calculated from equations (12) and (13):
Figure BDA0001876010330000134
Figure BDA0001876010330000141
wherein Kg is an explosion hazard index, V is the volume of the constant volume bomb,
Figure BDA0001876010330000142
is the maximum pressure rise rate generated by the combustion of the battery gas eruption in the constant volume combustion bomb. In this embodiment, a method for calculating the explosion hazard coefficient is provided, which may be used to calculate the explosion hazard coefficient of the lithium ion battery to be tested when the lithium ion battery to be tested has explosion hazard by combining with an explosion hazard index of a reference battery. The calculation method provided in the embodiment enables the calculated explosion hazard coefficient to be more accurate.
In one embodiment, the toxic gas hazard coefficient(toxic gas hazard, to be tested)Calculated from equation (14) to equation (16):
C(toxic gas hazard, to be tested)＝F(CO, to be tested)×C(CO, to be tested)+F(HF, to be tested)×C(HF, to be tested)Formula (14)
Figure BDA0001876010330000143
Figure BDA0001876010330000144
Wherein Pc is the concentration peakThe value of the one or more of,
Figure BDA0001876010330000145
releasing a concentration peak value of hydrofluoric acid for the lithium ion battery to be tested,
Figure BDA0001876010330000146
and releasing a carbon monoxide concentration peak value for the lithium ion battery to be tested.
In this embodiment, F may be setCO+FHFThe weighting factor can be determined by a factor analysis method, a correlation coefficient method, an expert ranking method, an RSR method, a Delphi method, an arithmetic mean combined weighting method, a multiplication-accumulation combined weighting method, a fuzzy mathematical judgment method, a sequence chart method and the like. When the weighting factor cannot be determined due to lack of correlation data, an empirical approach may be used, and F may be set in one embodimentCO＝FHFIn another exemplary embodiment, F may also be provided equal to 0.5CO＝0.6，FHF＝0.4。
In one embodiment, in order to obtain an absolute value reflecting the fire risk of the battery, a reference battery may be set, and the result of the lithium ion battery to be tested and the result of the reference battery are normalized (i.e., scaled by a certain ratio) to obtain the absolute value, so that the fire hazard classification may be performed, and the value of any one evaluation parameter of the reference battery is 1. The reference battery-related performance parameters (e.g., electrolyte flash point, gassing firing limit index, peak heat release rate, etc.) may be an ideal and safer battery. In one embodiment, the step S400 of evaluating the fire risk level of the lithium ion battery according to the risk factor includes:
and S410, selecting a reference battery and acquiring the performance parameters of the reference battery.
S420, calculating a fire possibility coefficient and a fire hazard coefficient of the lithium ion battery to be tested, and further calculating a fire hazard coefficient;
s431, if the fire hazard coefficient is larger than or equal to 1.5, the fire hazard of the lithium ion battery to be tested is A level, which represents serious hazard;
s432, if the fire risk coefficient is more than or equal to 0.5 and less than 1.5, the fire risk of the lithium ion battery to be tested is class B, which represents a general risk;
and S433, if the fire risk coefficient is less than 0.5, the fire risk of the lithium ion battery to be tested is grade C, which represents safety.
In the present embodiment, a specific procedure for evaluating the fire risk level of the lithium ion battery based on the risk factor is provided. And combining the risk coefficient with the evaluation of the fire risk level of the lithium ion battery, so that the safety state of the lithium ion battery in the current state can be definitely obtained. And evaluating the fire hazard grade of the lithium ion battery according to the hazard coefficient, so that the problem of safety judgment of the lithium ion battery is solved, and large-scale commercial application of the power supply industry is facilitated.
In the above way, in the practical application process, the possibility of fire of the lithium ion battery and the hazard of the fire need to be judged and fed back in time. The possibility of fire in the lithium ion battery is closely related to the physical and chemical properties of the lithium ion battery. The lithium ion battery fire hazard assessment comprises two aspects: the likelihood of fire and the hazard of fire. The fire risk coefficient is used for representing the fire risk of the lithium ion battery. The heat hazard of the lithium ion battery is characterized by adopting the ignition time of the lithium ion battery, the peak value of the combustion heat release rate of the battery, the combustion heat release quantity of the battery and the like. The explosion hazard index of the gas eruption is used to characterize the explosion hazard of the lithium ion battery. And characterizing the hazard of the toxic gas of the lithium ion battery by adopting the battery gas eruption and the highest concentration of the toxic gas in the combustion emission of the battery. The method for evaluating the fire hazard of the lithium ion battery can definitely obtain the safety state of the lithium ion battery under the current state.
Referring to tables 1 and 2, a reference cell and two lithium ion cells to be tested are provided. The table shows the performance parameters of the reference cell and the two lithium ion cells to be tested andand calculating the possibility coefficient, the hazard coefficient, the risk coefficient and the risk level. In a specific embodiment, FPossibility of＝FHarmfulness of0.5, the probability coefficient C of fire of the first lithium ion battery to be tested(possibility, to be tested)0.82, and the hazard coefficient C of the first lithium ion battery to be tested in fire(hazard, to be tested)0.47, the first lithium ion battery to be tested has the risk coefficient C of fire(hazardous, to be tested)Is 0.64. And if the fire risk coefficient (0.64) of the first lithium ion battery to be tested is more than or equal to 0.5 and less than 1.5, the fire risk of the first lithium ion battery to be tested is class B, which represents general risk.
In another specific embodiment, FPossibility of＝FHarmfulness of0.5, and the possibility coefficient C of fire occurrence of the second lithium ion battery to be tested(possibility, to be tested)1.71, and the hazard coefficient C of the second lithium ion battery to be tested in fire(hazard, to be tested)1.73, and the risk coefficient C of fire of the second lithium ion battery to be tested(hazardous, to be tested)Is 1.72. And (3) the fire risk coefficient (1.72) of the second lithium ion battery to be tested is greater than 1.5, so that the fire risk of the second lithium ion battery to be tested is A level, which represents a serious risk.
In the above embodiment, only a part of the performance parameters are selected for calculating the fire risk coefficient. The electrolyte flash point and the thermal runaway temperature are used for calculating a fire hazard coefficient, and the explosion hazard index and the HF concentration peak value are used for calculating the fire hazard coefficient. In another embodiment, more performance parameters can be selected to accurately calculate the fire risk coefficient of the lithium ion battery, and the worker is prompted to perform early warning.
Table 1: performance parameters of three cells
Figure BDA0001876010330000171
Table 2: coefficients of different types of three batteries and danger level
Coefficient of likelihood Coefficient of harmfulness Coefficient of risk Hazard class
Reference cell 1.00 1.00 1.00 —
First lithium ion battery to be tested 0.82 0.47 0.64 Class B
Second lithium ion battery to be tested 1.71 1.73 1.72 Class A
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (8)

1. A method for evaluating the fire risk of a lithium ion battery is characterized by comprising the following steps:
s100, acquiring performance parameters of the lithium ion battery to be tested, wherein the performance parameters comprise thermal runaway temperature, electrolyte spontaneous combustion point or flash point, ignition limit index of a gas eruption, time from thermal runaway to ignition start of the battery, combustion heat release rate peak value of the lithium ion battery, combustion heat release quantity of the lithium ion battery, explosion hazard index of a lithium ion battery gaseous eruption and gas eruption concentration peak value;
s200, calculating the possibility coefficient of the lithium ion battery to be tested in the fire and the hazard coefficient of the lithium ion battery to be tested in the fire according to the performance parameters;
s300, calculating a risk coefficient of the lithium ion battery to be tested when the lithium ion battery to be tested is in fire through multiplying a possibility coefficient by a possibility weight factor, adding a hazard coefficient by a hazard weight factor, wherein the sum of the possibility weight factor and the hazard weight factor is equal to 1;
the probability coefficient is equal to the thermal runaway probability coefficient multiplied by a thermal runaway probability weight factor, plus the electrolyte ignition probability coefficient multiplied by an electrolyte ignition probability weight factor, plus the gas spray ignition probability coefficient multiplied by a gas spray ignition probability weight factor;
wherein the sum of the thermal runaway potential weight factor, the electrolyte ignition potential weight factor, and the gas spray ignition potential weight factor is 1;
the hazard coefficient is equal to the thermal hazard coefficient multiplied by a thermal hazard weight factor, the explosion hazard coefficient multiplied by an explosion hazard weight factor, and the toxic gas hazard coefficient multiplied by a toxic gas hazard weight factor;
wherein the sum of the thermal hazard weighting factor, the explosion hazard weighting factor and the toxic gas hazard weighting factor is 1;
and S400, evaluating the fire risk level of the lithium ion battery to be tested according to the risk coefficient.
2. The method for evaluating the fire risk of a lithium ion battery according to claim 1, wherein the thermal runaway probability coefficient C is(thermal runaway, to be tested)Calculated from the following equation:
Figure FDA0002299866270000021
wherein, T(thermal runaway, reference)As a reference for the temperature at which thermal runaway of the cell occurs, T(thermal runaway, to be tested)And the temperature is the temperature of the lithium ion battery to be tested when thermal runaway occurs.
3. The method for evaluating the fire risk of a lithium ion battery according to claim 2, wherein the electrolyte ignition probability coefficient C is(electrolyte on fire, to be tested)Calculated from the following equation:
Figure FDA0002299866270000022
wherein, T(electrolyte, reference)Generating a self-ignition or flash point temperature of the electrolyte for reference cellsDegree, T(electrolyte, to be tested)The self-ignition point temperature or the flash point temperature of the electrolyte of the lithium ion battery to be tested.
4. The method for evaluating the fire risk of a lithium ion battery according to claim 2, wherein the coefficient of probability of ignition C of the gas eruption is(gas eruption ignited, to be tested)Calculated from the following equation:
Figure FDA0002299866270000023
Figure FDA0002299866270000024
UFL(gaseous hairspray, to be tested)An upper limit of ignition, LFL, of the lithium ion battery gaseous propellant to be tested(gaseous hairspray, to be tested)Is the lower limit of ignition of the gaseous spray of the lithium ion battery to be tested, H(gaseous hairspray, to be tested)Is the explosion risk of the gaseous eruptions of the lithium ion battery to be tested, H(gaseous hairspray, reference)Reference is made to the explosion risk of gaseous eruptions from batteries.
5. The method for evaluating the fire risk of a lithium ion battery according to claim 1, wherein the thermal hazard coefficient C is(thermal hazard, to be tested)Calculated from the following equation:
C(thermal hazard, to be tested)＝FIT×C(IT, to be tested)+FPHRR×C(PHRR, to be tested)+FQ×C(Q, to be tested)
Figure FDA0002299866270000031
Figure FDA0002299866270000032
Figure FDA0002299866270000033
Wherein, ITTo be testedPHRR is the time from thermal runaway to ignition start of the lithium ion battery to be testedTo be testedIs the combustion heat release rate peak value, Q, of the lithium ion battery to be testedTo be testedThe combustion heat release of the lithium ion battery to be tested is obtained;
ITreference toFor reference to the time from the occurrence of thermal runaway to the onset of fire, PHRR, of a batteryReference toFor reference to the peak combustion heat release rate, Q, of the cellReference toIs the combustion heat release of the reference cell;
FITis a weight factor of the ignition time of the lithium ion battery to be tested, FPHRRIs the weight factor, F, of the combustion heat release rate peak value of the lithium ion battery to be testedQIs a weight factor of the heat release of the lithium ion battery to be tested, C(IT, to be tested)Is the hazard coefficient of the ignition time of the lithium ion battery to be tested, C(PHRR, to be tested)Is the harmfulness coefficient of the combustion heat release of the lithium ion battery to be tested, C(Q, to be tested)The hazard coefficient of the combustion heat release of the lithium ion battery to be tested is obtained;
the sum of the weighting factor of the ignition time, the weighting factor of the combustion heat release rate peak and the weighting factor of the heat release amount is 1.
6. The method for evaluating the fire risk of a lithium ion battery according to claim 5, wherein the explosion hazard coefficient C is(explosive hazard, to be tested)Calculated from the following equation:
Figure FDA0002299866270000034
Figure FDA0002299866270000035
wherein, Kg to be testedIs the explosion hazard index of the lithium ion battery gaseous eruption to be tested, V is the volume of the constant volume combustion bomb of the lithium ion battery gaseous eruption to be tested,
Figure FDA0002299866270000041
the maximum pressure rise rate in the constant volume combustion bomb of the lithium ion battery gaseous eruption to be tested is obtained.
7. The method for evaluating the fire risk of a lithium ion battery according to claim 5, wherein the toxic gas hazard coefficient C is(toxic gas hazard, to be tested)Calculated from the following equation:
C(toxic gas hazard, to be tested)＝F(CO, to be tested)×C(CO, to be tested)+F(HF, to be tested)×C(HF, to be tested)
Figure FDA0002299866270000042
Figure FDA0002299866270000043
Wherein Pc(HF, to be tested)Releasing a peak concentration of hydrofluoric acid, Pc, for the lithium ion battery to be tested(co, to be tested)The concentration peak value, Pc, of carbon monoxide released by the lithium ion battery to be tested(HF, ref.)For reference to the peak concentration of hydrofluoric acid released by the cell, Pc(co, ref)Peak concentration of carbon monoxide released for the reference cell;
F(co, to be tested)A weight factor, F, for the release of carbon monoxide by the lithium ion battery to be tested(HF, to be tested)A weight factor, C, for releasing hydrofluoric acid for the lithium ion battery to be tested(co, to be tested)A hazard coefficient, C, for the release of carbon monoxide by the lithium ion battery to be tested(HF, to be tested)Is that it isAnd (3) testing the harmfulness coefficient of hydrofluoric acid released by the lithium ion battery to be tested.
8. The method for evaluating the fire risk of a lithium ion battery according to claim 1, wherein the step S400 of evaluating the level of the fire risk of a lithium ion battery based on the risk factor includes:
comparing the calculated risk coefficient with a fire hazard reference coefficient of a reference battery;
if the difference between the risk coefficient and the reference coefficient is less than or equal to 30%, the fire risk of the lithium ion battery to be tested is grade C, which represents safety;
if the difference between the risk coefficient and the reference coefficient is more than 30% and less than or equal to 70%, the fire risk of the lithium ion battery to be tested is B-level, which represents general risk;
and if the difference between the risk coefficient and the reference coefficient is more than 70%, the fire risk of the lithium ion battery to be tested is A grade, which represents a serious risk.
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