CN114859232A - Method and device for quantitatively evaluating thermal runaway dangerousness of lithium batteries in different charge states - Google Patents

Abstract

The invention provides a method and a device for quantitatively evaluating the thermal runaway risk of lithium batteries with different states of charge. Flame characteristic diameter, heat release rate, oxygen concentration, temperature of combustion products in exhaust duct, concentration of toxic and asphyxiating gases. Based on the heat release rate evaluation formula and the toxic gas or asphyxiating gas evaluation model, an evaluation set is established to evaluate the thermal hazard index, dimensionless flame heat release rate, toxic gas hazard index or asphyxiating gas hazard index caused by thermal runaway of lithium batteries. The entropy method is used to determine the weight coefficient of each risk index, and a quantitative evaluation formula for battery risk is constructed to obtain the battery risk under different states of charge. The invention solves the technical problems of lack of quantitative assessment and incomplete risk assessment.

Description

Quantitative assessment method and device for thermal runaway risk of lithium batteries with different states of charge

technical field

The invention relates to the field of quantitative assessment of the risk of thermal runaway of energy storage batteries, and more particularly to a method and device for quantitative assessment of the risk of thermal runaway of lithium batteries with different states of charge.

Background technique

Under the dual pressures of energy shortage and ecological environment deterioration, electrochemical energy storage systems with lithium-ion batteries as the main storage medium have developed rapidly. As the core component of electrochemical energy storage systems, lithium batteries are prone to thermal runaway under abuse conditions such as thermal, electrical, and mechanical damage due to their high energy density and flammable and explosive material systems. Due to the large number of lithium batteries, large installed capacity and poor heat dissipation conditions in the energy storage system, once the huge heat released by a single battery thermal runaway will cause a chain thermal runaway of the entire battery module, which will lead to a fire in the module and even the entire energy storage system. , so it is necessary to evaluate the risk of thermal runaway leading to combustion in the case of thermal abuse of lithium batteries.

The existing invention patent with the application number of CN202111109557.5, "A Gradient Boosting Tree-Based Lithium-ion Battery Fault Diagnosis Method", includes the following steps: acquiring historical fault data of lithium-ion batteries and uploading them to a database platform, processing and screening the data Obtain battery characteristic value parameters or key values to form a data set, divide the data set into a training set and a test set, and bring the selected training set and prediction indicators into the gradient boosting tree model for training, and through iterative optimization, the gradient boosting tree model After convergence, the gradient boosting tree model is output; the battery eigenvalue parameters or key values during the operation of the lithium-ion battery are collected, and the trained gradient boosting tree model is input to diagnose the fault of the lithium-ion battery. It can be seen from the description of the existing patent that the existing patent provides early warning of safety accidents such as thermal runaway of lithium batteries by constructing and training a gradient boosting tree model. Qualitative early warning is given for failures such as runaway, and it is impossible to quantitatively assess the danger of lithium batteries.

The existing invention patent with the application number of CN201911311757.1 "A battery management system and method with an early warning function of lithium battery failure" includes: a main controller and a gas concentration detection module connected to the main controller. The gas concentration detection The module includes one or more gas detection units built in the battery box, each gas detection unit includes a gas sensor and a data processing subunit, and the data processing subunit collects various gas concentration data through different types of gas sensors respectively, The collected data is transmitted to the main controller, and the main controller judges the failure level of the battery according to the comprehensive analysis of the received data of various gas concentrations and their proportions in the gas production of the battery. The beneficial effects of the invention are as follows: a combination of multiple gas sensors is used to detect the gas generated by the battery failure, and the concentration and composition ratio of the detected gas are analyzed, and comprehensive calculation is performed to accurately determine the battery failure level. Although the existing patent collects various gas concentration data through sensors, the existing patent only uses the gas concentration data as a fault warning input parameter, and does not evaluate the toxic gas concentration and the hazards of asphyxiating gas released by the lithium battery during combustion. The existing patent is significantly different from the technical solution of the present application, and at the same time, it is impossible to evaluate the toxic gas concentration and the hazard of asphyxiating gas released by the lithium battery during combustion.

As can be seen from the aforementioned existing patents, the existing researches on assessing the risk of thermal runaway combustion of lithium batteries mainly have the following deficiencies:

(1) When a lithium battery is thermally runaway and ignited under thermal abuse, most of the existing evaluation methods evaluate the hazard of lithium battery combustion from a qualitative point of view, and there is a lack of methods or means to quantitatively evaluate the risk of lithium battery.

(2) When assessing the risk of thermal runaway of lithium batteries, the existing methods pay more attention to the thermal hazard of lithium battery combustion, ignoring the toxic gas concentration and suffocating gas released by lithium batteries during combustion, that is, dangerous The hazard assessment method cannot fully reflect the hazard of lithium battery combustion.

To sum up, the existing technology lacks quantitative assessment and the technical problems of incomplete risk assessment.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is how to solve the technical problems of lack of quantitative assessment and incomplete risk assessment in the prior art.

The present invention adopts the following technical solutions to solve the above-mentioned technical problems: a quantitative assessment method for the thermal runaway risk of lithium batteries with different states of charge includes:

S1. Obtain lithium battery samples with no less than a preset number of overcharged SOCs and a preset number of normal charged SOCs;

S2, according to the state of charge of the lithium battery sample, establish the index set U of different states of charge;

S3. Carry out thermal abuse thermal runaway ignition experiments of SOC lithium batteries with different states of charge, obtain characteristic parameters of thermal runaway ignition risk assessment, and divide the characteristic parameters into thermal hazard characteristic parameters and toxic and harmful gas hazard characteristics parameters and asphyxiating gas hazard characteristic parameters;

S4, according to the preset toxic and harmful or suffocating gas evaluation model, the dimensionless flame release rate is obtained, and the toxic gas index FEC, asphyxiating gas index FED and dimensionless gas index FEC, asphyxiating gas index FED and dimensionless ignited by lithium batteries of different states of charge are quantitatively evaluated according to the characteristic parameters The flame release rate Q ^* is used to establish the evaluation set V of the ignition of lithium batteries with different states of charge;

S5. According to the index set U and the evaluation set V of the lithium battery samples with different states of charge, a sample matrix S is established, and the sample matrix S is standardized to obtain a standardized matrix X;

S6, utilize the entropy value method to sequentially determine the weight coefficients of the dimensionless flame release rate Q ^* , the toxic gas index FEC index and the asphyxiating gas index FED index according to the standardized matrix X as ω ₁ , ω ₂ and ω ₃ ;

S7. Construct a risk relationship of the thermal runaway of lithium batteries according to the weight coefficient, so as to evaluate the risk of ignition of lithium batteries in different states of charge.

Based on the heat release rate evaluation formula and the toxic gas or asphyxiating gas evaluation model, the present invention evaluates the thermal risk index dimensionless flame heat release rate Q ^* , the toxic gas risk index FEC or the asphyxiating gas risk index of the thermal runaway of the lithium battery. FED, establishes the evaluation set V of thermal runaway ignition of lithium batteries with different states of charge. The entropy method is used to determine the weight coefficients of thermal hazard, toxic gas irritant and asphyxiating gas hazard, and a quantitative evaluation formula for battery risk is constructed, which realizes the quantitative evaluation of the risk of thermal runaway of energy storage batteries.

In a more specific technical solution, the step S2 includes:

S11. Select lithium batteries of the same specification;

S12. Use a battery charge-discharge cycle tester to discharge the lithium battery to different states of charge in a constant current discharge mode, and obtain a preset normal number of normal state-of-charge lithium batteries and a preset number of overcharge states of charge lithium battery.

In a more specific technical solution, the step S3 includes:

S21. Obtain the difference SOC data of the lithium battery in the normal state of charge and the lithium battery in the overcharge state;

S22. Construct the indicator set U of the state of charge of the lithium battery according to the difference SOC data.

In a more specific technical solution, the step S4 includes:

S31, performing a thermal runaway ignition test and a thermal abuse ignition test on the lithium battery samples with different states of charge on the lithium battery thermal abuse thermal runaway ignition risk platform;

S32, carrying out no less than 2 combustion experiments on the lithium battery samples in each state of charge;

S33. Obtain the characteristic flame diameter D of the lithium battery sample in the second stable combustion state, the differential pressure Δp of the combustion product in the exhaust duct, the temperature _Te of the combustion product, the oxygen concentration X _O2 , the toxic gas concentration and suffocation gas concentration;

S34, the characteristic diameter D of the flame, the differential pressure Δp of the combustion product in the exhaust duct, the temperature _Te of the combustion product, the oxygen concentration X _O2 , the toxic gas concentration and the asphyxiating gas The concentration is averaged as the characteristic parameter;

S35, pretreatment of the thermal abuse thermal runaway quantitative evaluation parameter of the lithium battery sample;

S36 , obtaining and classifying the lithium battery thermal abuse igniting evaluation parameters to obtain the thermal hazard characteristic parameter, the toxic and harmful gas hazard characteristic parameter, and the asphyxiating gas hazard characteristic parameter.

The invention utilizes the lithium battery thermal abuse ignition test platform to sequentially carry out the overcharge state and normal state of charge lithium battery thermal abuse ignition experiments, and obtains the required average value of the quantitative evaluation parameters of the lithium battery ignition risk. The data collected by the abuse ignition test platform is used to quantify the parameters related to thermal abuse ignition, and to more comprehensively evaluate the safety of lithium batteries under specific temperature conditions.

In a more specific technical solution, the step S41 includes:

S43, according to described poisonous and harmful gas evaluation parameter, obtain described poisonous gas index FEC with following logical processing:

表示每种气体的浓度，F是对逃生人员造成威胁的气体临界浓度。, where,

Indicates the concentration of each gas, and F is the critical concentration of the gas that poses a threat to escaping personnel.

S44, according to the characteristic parameter of the asphyxiant gas danger, obtain the asphyxiating gas index FED with the following logic processing, namely:

表示气体的浓度，V表示气体分子的频率因子，Δt表示时间持续时间，即(t₂-t₁0；In the formula,

represents the concentration of the gas, V represents the frequency factor of the gas molecules, Δt represents the time duration, namely (t ₂ -t ₁ 0;

S45, according to the toxic gas index FEC, the asphyxiating gas index FED and the dimensionless flame release rate Q ^* , sequentially calculate the characteristic parameter values corresponding to the lithium battery samples under each state of charge, and construct The evaluation set V={Q ^* , FEC, FED} for the ignition of lithium batteries with different states of charge SOC.

The quantitative assessment of the flammability hazard of the lithium battery in the present invention is a comprehensive quantitative assessment of its thermal hazard, toxic gas hazard and suffocating gas hazard. Characterization of heat release rate due to thermal runaway of lithium battery; toxic gases HF, SO ₂ , NO _X can be quantitatively characterized by FEC of effective concentration percentage of toxic gases; asphyxiating gases CO and CO ₂ can be characterized by FED of effective dose percentage. The present invention quantifies the flammability hazard of the lithium battery to a specific value through the aforementioned three types of indices, so as to comprehensively evaluate the flammability hazard of the lithium battery.

In a more specific technical solution, the step S41 includes:

S411. Process the mass fraction of oxygen X _O2 , the differential pressure _Δp , and the temperature Te of combustion products in the exhaust pipe with the following logic to obtain the flame heat release rate

以得到所述无量纲火焰释放速率：S412. Process the thermal hazard characteristic parameter and the flame heat release rate with the following logic

To obtain the dimensionless flame release rate:

为火焰的热释放速率。where D is the characteristic diameter of the flame,

is the heat release rate of the flame.

In a more specific technical solution, the step S6 includes:

S61, according to the index set U and the index set V, establish the sample matrix S with the following logic:

In the formula, s _ij is the actual value of the ith lithium battery sample about the index j, 1≤i≤15, 1≤j≤3;

S62, standardize the sample matrix S with the following logic to obtain the standard matrix X:

In the formula,

In a more specific technical solution, the step S7 includes:

S71. Determine the weight y _ij of the ith lithium battery sample with respect to the index j with the following logic:

S72, according to the weight y _ij , determine the entropy value of the j-th evaluation index with the following logic:

In the formula, e _j represents the entropy value of the jth evaluation index;

S73. According to the weight y _ij and the entropy value of the evaluation index j, use the following logic to estimate the weight coefficient ω _j of the j-th evaluation index:

In a more specific technical solution, in the step S8, the following logic is used to construct the lithium battery thermal abuse thermal runaway ignition risk relationship data according to the weight coefficient: H=ω ₁ ·x ₁₁ +ω ₂ ·x ₁₂ + ω ₃ ·x ₁₃ .

In a more specific technical solution, a quantitative assessment device for thermal runaway risk of lithium batteries with different states of charge includes:

The overcharged SOC sample module is used to obtain not less than a preset number of overcharged SOCs and a preset number of lithium battery samples under normal charged SOCs;

an indicator set module for establishing indicator sets U of different states of charge according to the state of charge of the lithium battery sample, and the indicator set module is connected to the lithium battery thermal abuse thermal runaway ignition experiment platform;

The characteristic parameter module is used to carry out thermal abuse thermal runaway ignition experiments of SOC lithium batteries with different states of charge, obtain characteristic parameters of thermal runaway ignition risk assessment, and divide the characteristic parameters into thermal risk characteristic parameters, toxic and harmful gas hazard characteristic parameters and asphyxiating gas hazard characteristic parameters, the characteristic parameter module is connected to the indicator set module;

The evaluation set module is used to quantitatively evaluate the toxic gas index FEC and asphyxiating gas index FED of lithium batteries with different states of charge according to the preset toxic and harmful or asphyxiating gas evaluation model and the dimensionless flame release rate according to the characteristic parameters. and the dimensionless flame release rate Q ^* to establish an evaluation set V of the ignition of lithium batteries with different states of charge, and the evaluation set module is connected with the characteristic parameter module;

The standardized matrix module is used to establish a sample matrix S according to the index set U and the evaluation set V of the lithium battery samples with different states of charge, and standardize the sample matrix S to obtain a standardized matrix X, the standardized The matrix module is connected with the evaluation set module;

A weighting module is used to sequentially determine the weighting coefficient of the dimensionless flame release rate Q ^* , the toxic gas index FEC index and the asphyxiating gas index FED index according to the standardized matrix X by using the entropy method as ω ₁ , ω ₂ and ω ₃ , the weight module is connected with the normalization matrix module;

The risk assessment module is used to construct the risk relationship of thermal runaway and thermal runaway of lithium batteries according to the weight coefficient, so as to evaluate the risk of ignition of lithium batteries in different states of charge, the risk assessment module and the weight module connect.

Compared with the prior art, the present invention has the following advantages: based on the heat release rate evaluation formula and the toxic gas or suffocating gas evaluation model, the present invention evaluates the thermal hazard index dimensionless flame heat release rate Q ^* , the toxic gas or suffocating gas caused by the thermal runaway of the lithium battery. The gas hazard index FEC or the asphyxiating gas hazard index FED is used to establish the evaluation set V of thermal runaway ignition of lithium batteries with different states of charge. The entropy method is used to determine the weight coefficients of thermal hazard, toxic gas irritant and asphyxiating gas hazard, and a quantitative evaluation formula for battery risk is constructed, which realizes the quantitative evaluation of the risk of thermal runaway of energy storage batteries.

The invention sequentially carries out the thermal abuse ignition test of the lithium battery in the overcharged state of charge and the normal state of charge, obtains the average value of the required quantitative evaluation parameters of the ignition risk of the lithium battery, and collects the data according to the lithium battery thermal abuse ignition test platform. , to quantify the related parameters of thermal abuse and ignition, and to more comprehensively evaluate the safety of lithium batteries under specific temperature conditions.

The quantitative assessment of the flammability hazard of the lithium battery in the present invention is a comprehensive quantitative assessment of its thermal hazard, toxic gas hazard and suffocating gas hazard. Characterization of heat release rate due to thermal runaway of lithium battery; toxic gases HF, SO ₂ , NO _X can be quantitatively characterized by FEC of effective concentration percentage of toxic gases; asphyxiating gases CO and CO ₂ can be characterized by FED of effective dose percentage. The present invention quantifies the flammability hazard of the lithium battery to a specific value through the aforementioned three types of indices, so as to comprehensively evaluate the flammability hazard of the lithium battery. The invention solves the technical problems of lack of quantitative assessment and incomplete risk assessment in the prior art.

Description of drawings

1 is a schematic flowchart of a quantitative assessment method for thermal runaway risk of lithium batteries with different states of charge according to Embodiment 2 of the present invention;

FIG. 2 is a schematic diagram of the composition of the device for quantitative assessment of the risk of thermal runaway ignition of a lithium battery according to Embodiment 3 of the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the present invention. examples, but not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

The invention discloses a method for quantitatively evaluating the risk of ignition caused by thermal abuse of lithium batteries in different states of charge, which is applied to the field of quantitative evaluation of the risk of ignition caused by thermal runaway of energy storage batteries. This method is used for the problem that the existing technical means cannot solve the problem of quantitative assessment of the risk of ignition caused by thermal abuse of lithium batteries with different states of charge SOC (State Of Charge). The flammability hazard of lithium battery thermal abuse involves the hazard of combustion heat, the hazard of toxic gas and the hazard of suffocating gas. The existing assessment methods for the hazard of lithium batteries only involve one of the above three hazards, and cannot comprehensively and quantitatively assess the hazard of lithium batteries for energy storage. Through the battery cycle test system, discharge to different states of charge in constant current discharge mode, namely 100% SOC, 80% SOC, 60% SOC, 50% SOC, 30% SOC, 10% SOC, 0% SOC, a total of 7 normal State of charge and 8 overcharge states of charge (125% SOC, 150% SOC, 175% SOC, 200% SOC, 225% SOC, 250% SOC, 275% SOC, 300% SOC) to construct different states of charge Lithium battery indicator set U. The thermal abuse ignition experiments of SOC lithium batteries with different states of charge were carried out in turn, and the differential pressure Δ, flame characteristic diameter D, heat release rate, oxygen O ₂ concentration, and smoke exhaust duct combustion during the second stable stage of thermal abuse ignition of lithium batteries were obtained. Product temperature _Te , toxic gas (HF, SO2, _NOx ) concentration and asphyxiating gas (CO, _{CO2 )} concentration. Based on the evaluation formula of heat release rate and the evaluation model of toxic gas or asphyxiating gas, the thermal hazard index, dimensionless flame heat release rate Q ^* , toxic gas hazard index FEC or asphyxiating gas hazard index FED, caused by thermal runaway of lithium battery, are evaluated. The thermal runaway ignition evaluation set V of lithium batteries with different states of charge is established. The entropy method is used to determine the weight coefficient ω _j of thermal hazard, toxic gas irritant and asphyxiating gas hazard, and a quantitative evaluation formula of battery hazard H=ω ₁ ·x ₁₁ +ω ₂ ·x ₁₂ +ω ₃ ·x ₁₃ is constructed , including flammable heat hazard index, toxic gas or suffocating gas hazard index, and obtain the battery hazard H under different states of charge.

Example 2

As shown in FIG. 1 , the present embodiment discloses a quantitative assessment method for the risk of thermal abuse of lithium batteries with different states of charge, including:

S1. Obtain not less than a preset number of overcharged SOC and a preset number of lithium battery samples under normal charge SOC; in this embodiment, lithium battery samples with different states of charge are obtained. Select lithium-ion batteries of the same capacity produced by the same supplier, discharge them to different states of charge in constant current discharge mode through a battery charge-discharge cycle tester, and obtain 100% SOC, 80% SOC, 60% SOC, 50% SOC, 30% SOC, 10% SOC, 0% SOC, a total of 7 normal state of charge lithium batteries and 8 overcharged lithium batteries (125% SOC, 150% SOC, 175% SOC, 200% SOC, 225 %SOC, 250%SOC, 275%SOC, 300%SOC). In this embodiment, the battery charge and discharge cycle tester can charge the battery to the target state of charge SOC under constant current, constant voltage and constant power charge and discharge conditions, and can monitor and record the voltage, Important parameters such as current, capacity and temperature. In this embodiment, the lithium battery with 100% SOC is charged with constant current through the battery cycle system to obtain 8 different states of charge in the overcharge mode, namely 125% SOC, 150% SOC, 175% SOC, 200% SOC , 225% SOC, 250% SOC, 275% SOC, 300% SOC; 100% SOC lithium battery is obtained through the constant current discharge mode of the battery cycle system to obtain lithium batteries with 7 different states of charge under normal conditions, that is, 100% SOC, 80% SOC, 60% SOC, 50% SOC, 30% SOC, 10% SOC, 0% SOC. Five groups of lithium batteries are prepared for each state of charge, which is convenient for repeatable experiments on thermal runaway ignition of lithium batteries.

S2. According to the state of charge of the lithium battery sample, establish an index set U of different states of charge, in this embodiment, construct an index set U={SOC _300% , SOC ₂₇₅ including 15 kinds of state of charge of lithium batteries _% , SOC _250% , SOC _225% , SOC _200% , SOC _175% , SOC _150% , SOC _125% , SOC _100% , SOC _80% , SOC _60% , SOC _50% , SOC _30% , SOC _10% , SOC _0% }.

In this embodiment, the state of charge SOC of the battery refers to the ratio of the remaining capacity of the battery to the capacity of the battery, that is, SOC=Q _r /Q _I . Among them, Q _r refers to the current remaining capacity of the battery, and Q _I refers to the battery capacity when the battery is discharged with a constant current I to the cut-off voltage. It is generally believed that the state of charge of the battery is 100 when the battery is first discharged to the cut-off voltage of the battery at I current through a charge-discharge cycle tester, and then charged to the cut-off voltage by a constant current and constant voltage method until the current is lower than 1.0A. %SOC.

S3. Carry out thermal abuse thermal runaway ignition experiments of SOC lithium batteries with different states of charge, obtain characteristic parameters of thermal runaway ignition risk assessment, and divide the characteristic parameters into thermal hazard characteristic parameters and toxic and harmful gas hazard characteristics parameters and asphyxiating gas hazard characteristic parameters; in this embodiment, the quantitative evaluation parameters for thermal runaway caused by thermal abuse of lithium batteries are obtained. The thermal runaway ignition experiment of lithium batteries with different states of charge selected in step 2 was carried out on the platform of thermal abuse and thermal runaway ignition risk of lithium batteries with different states of charge. The lithium battery combustion experiment for each state of charge was repeated three times to obtain the characteristic diameter D of the flame under the second stable combustion state of the lithium battery, the differential pressure Δp of the combustion products in the exhaust duct, the temperature _Te of the combustion products, and the oxygen concentration X The concentration of _O2 , toxic gas (HF, SO2, _NOx ) and asphyxiating gas (carbon monoxide CO, carbon _{dioxide CO2} ), the characteristic parameters of the above-mentioned quantitative assessment of the combustion hazard of lithium batteries are the average values after three repeated experiments. In this embodiment, the second stable stage of the combustion process of the lithium battery is divided based on the entire flame shape of the thermal runaway combustion of the lithium battery. The entire thermal runaway combustion process of lithium batteries can be divided into the first stable combustion stage, the jet spark stage, the second stable combustion stage and the flame decay stage. Lithium battery thermal runaway combustion In the second stable combustion stage, the flame height, flame area and flame heat release rate all reach the maximum value. Selecting the characteristic width of the flame at this stage as the characteristic flame diameter is more representative and can better reflect Thermal hazards of thermal runaway combustion of lithium batteries.

Quantitative evaluation parameters for thermal runaway ignition caused by thermal abuse of pretreated lithium batteries. Step 3 After obtaining the evaluation parameters of thermal abuse of lithium batteries, they are divided into three categories, namely thermal hazard, toxic gas hazard and asphyxiating gas hazard.

即：S4. According to the preset toxic and harmful or asphyxiating gas evaluation model and the dimensionless flame release rate, quantitatively evaluate the toxic gas index FEC, the asphyxiating gas index FED and the dimensionless flame ignited by lithium batteries with different states of charge according to the characteristic parameters The release rate Q ^* is used to establish the evaluation set V of the ignition of lithium batteries with different states of charge; in this embodiment, for the thermal hazard, a dimensionless flame release rate is established, in order to be related to the effective concentration percentage of toxic gases FEC, asphyxiating gas The effective dose percentage FED evaluation index type is the same, and the dimensionless heat release rate Q ^* expression of the ignition flame of lithium battery is constructed, involving the flame diameter D and the flame heat release rate

which is:

是锂电池热失控致燃的热释放速率，ρ₀是空气的密度，c_p是空气比热容，T₀环境初始温度，g是重力加速度，D是燃烧稳定第二阶段的火焰特征直径，这里火焰热释放速率

为：In the formula,

is the heat release rate due to thermal runaway of the lithium battery, _ρ0 is the density of air, _cp is the specific heat capacity of air, _T0 is the initial ambient temperature, g is the acceleration of gravity, D is the characteristic flame diameter of the second stage of combustion stabilization, where the flame heat release rate

for:

是锂电池燃烧的热释放速率，Δh_c/r₀为消耗单位质量的氧气所消耗的能量，取一常数13.1kJ/g，C是孔板流量计校准常数，Δp是差压传感器测得的燃烧产物差压数值，T_e为排烟管道内燃烧产物的温度，

是某时刻t下气体分析仪测得得氧气浓度，

是初始时刻气体分析仪测得得氧气浓度。在本实施例中，Servomex 4100气体分析仪，可在线精确测量氧气O2、一氧化碳CO、二氧化碳CO₂的浓度数据，配置多个测量模块，可同时测四路样气的浓度数据，测得的排烟管道内的氧气浓度数据X _O2、排烟管道内燃烧产物的温度T_e和微差压传感器测得的差压Δp共同来评估计算锂电池热失控致燃的热释放速率

傅里叶变换红外光谱分析仪23，是基于对干涉后的红外光进行傅里叶变换的原理而开发的红外光谱仪，以便携或可移动的形式设计，可在高分辨率下测量低浓度的复杂混合气体。In the formula,

is the heat release rate of lithium battery combustion, Δh _c /r ₀ is the energy consumed by unit mass of oxygen, take a constant 13.1kJ/g, C is the calibration constant of the orifice flowmeter, and Δp is measured by the differential pressure sensor The differential pressure value of the combustion product, T _e is the temperature of the combustion product in the exhaust pipe,

is the oxygen concentration measured by the gas analyzer at a certain time t,

is the oxygen concentration measured by the gas analyzer at the initial moment. In this embodiment, the Servomex 4100 gas analyzer can accurately measure the concentration data of oxygen O2, carbon monoxide CO, and carbon dioxide _CO2 online. It is equipped with multiple measurement modules and can simultaneously measure the concentration data of four sample gases. The oxygen concentration data X _O2 in the flue gas duct, the temperature _Te of the combustion products in the flue gas duct and the differential pressure Δp measured by the differential pressure sensor are used to evaluate and calculate the heat release rate of the lithium battery caused by thermal runaway.

The Fourier Transform Infrared Spectrometer 23 is an infrared spectrometer developed based on the principle of Fourier transform of the infrared light after interference. It is designed in a portable or mobile form and can measure low concentrations of complex gas mixture.

For the evaluation parameters of toxic gases, establish the FEC quantitative evaluation parameters of the effective concentration percentage of toxic gases, namely:

表示每种气体的浓度，F是对逃生人员造成威胁的气体临界浓度，为一常数。In the formula,

Indicates the concentration of each gas, F is the critical concentration of gas that poses a threat to escape personnel, and is a constant.

The percent effective dose FED for asphyxiating gas is:

表示气体的浓度，V表示气体分子的频率因子，Δt表示时间持续时间，即(t₂-t₁)。In the formula,

represents the concentration of the gas, V represents the frequency factor of the gas molecules, and Δt represents the time duration, ie (t ₂ -t ₁ ).

According to the above three quantitative evaluation indicators, the characteristic parameter values corresponding to the lithium battery under each state of charge are calculated in turn, and an evaluation set V of the ignition risk of SOC lithium batteries with different states of charge is constructed, that is, the index set V={Q ^* , FEC, FED};

S5. According to the index set U and the evaluation set V of the lithium battery samples with different states of charge, a sample matrix S is established, and the sample matrix S is standardized to obtain a standardized matrix X; in this embodiment, quantitative Assess the hazard of thermal runaway from thermal abuse of lithium batteries.

(1) According to the index set U of SOC lithium batteries with different states of charge in step 2 and the evaluation index set V of lithium batteries in step 4, a sample matrix S is established. In this embodiment, the ignition risk of lithium batteries with different states of charge is established. Sample evaluation matrix: The present invention has 15 lithium batteries with different states of charge, and 3 evaluation indicators, that is, the sample matrix S is:

In the formula, s _ij is the actual value of the ith lithium battery sample about the index j, 1≤i≤15, 1≤j≤3, for example, s ₁₃ is the actual value of the first lithium battery sample about the index 3, that is, the load The percentage FED of the effective dose of asphyxiating gas produced by the thermal abuse of a lithium battery with an electrical state SOC of 300%.

(2) Standardize the sample matrix S: the dimensionless flame heat release rate Q ^* , the effective concentration percentage FEC of toxic gases and the effective dose percentage FED of asphyxiating gases have large differences in numerical order of magnitude of the evaluation indicators of the heat hazard caused by lithium batteries. Among them, the FEC index of the effective concentration percentage of toxic gases is one order of magnitude larger than the effective dose percentage FED of asphyxiating gases, so it is necessary to standardize the sample matrix S. According to domestic and foreign literature research, the dimensionless flame heat release rate Q ^* , the effective concentration percentage of toxic gases FEC and the effective dose percentage FED of asphyxiating gases are positively correlated with the state of charge of the battery, and the greater the above three indicators are, the greater the ignition risk of lithium batteries The greater the sex, the definition of a standardized matrix X is:

In the formula,

S6, utilize the entropy value method to sequentially determine the weight coefficients of the dimensionless flame release rate Q ^* , the toxic gas index FEC index and the asphyxiating gas index FED index according to the standardized matrix X as ω ₁ , ω ₂ and ω ₃ ; in this embodiment, (3) the determination of the weight of the evaluation index: after the sample matrix S is standardized into a standard matrix X, the weight y _ij of the i-th lithium battery sample with respect to the index j is defined as:

Further, the entropy value of the jth evaluation index is:

In the formula, e _j represents the entropy value of the jth evaluation index, k is a constant, k=1/ln15. According to the weight y _ij of the index j and its entropy value, the weight ω _j of the j-th evaluation index can be estimated as:

Determination of the ignition risk H of lithium batteries in different states of charge: According to the standard sample matrix X and the weight coefficient of the evaluation index, the ignition risk H of lithium batteries = ω ₁ · x ₁₁ +ω ₂ · x ₁₂ +ω ₃ · x ₁₃ , so far, the ignition risk H of the lithium battery under different states of charge can be obtained. The smaller the value is, the lower the risk of the lithium battery is.

S7. According to the weight coefficient, construct the risk relationship of thermal runaway of lithium battery due to thermal abuse, so as to evaluate the risk of ignition of lithium battery in different states of charge; According to the standard sample matrix X and the weight coefficient of the evaluation index, the ignition hazard H=ω ₁ ·x ₁₁ +ω ₂ ·x ₁₂ +ω ₃ ·x ₁₃ of the lithium battery can obtain different charges. Lithium battery in the state of ignition hazard H.

Example 3

As shown in Figure 2, the lithium battery thermal runaway ignition quantitative evaluation device includes a lithium battery thermal abuse thermal runaway ignition risk platform, which includes: a soft-pack lithium battery sample 1, an electric spark igniter 2, and a soft-pack lithium battery sample 1. The upper surface is placed flush. In this embodiment, the lithium battery used in the present invention adopts a 60Ah large-size cuboid soft-pack lithium iron phosphate battery or a ternary lithium ion battery. The battery capacity can also be larger than 60Ah or less than 60Ah. lithium battery. The spark igniter 2 releases the spark 3, which is used to ignite the flammable gas released by the thermal runaway of the soft pack battery, the heat shield 4, the lithium battery sample released by the soft pack lithium battery sample 1 that is placed in the thermal runaway. The lifting platform 5, the lithium battery The sample lifting platform 5 is used to lift the lithium battery sample to a suitable height. The soft-pack lithium battery sample 1 has a thermal runaway ignition combustion chamber 6. In order to facilitate the entry of air into the thermal runaway ignition combustion chamber 6, the supporting feet 10 are separated from the ground for a period of time. Distance, fume collection hood 7, used to collect toxic and harmful fumes released by thermal runaway combustion of lithium batteries, high temperature silicon carbon rods 8, radiated heat after power-on, providing heat required for thermal abuse, ventilation holes 9 to facilitate thermal runaway of lithium batteries The released combustion products enter the smoke exhaust duct 12 through the ventilation holes 9, and the thermal runaway causes the observation window 11 of the combustion chamber 6 to be used for the camera 13 to capture the characteristic parameters of the flame during the combustion process of the lithium battery, and the variable frequency fan 14 is used to collect soft-pack lithium The flue gas generated by the thermal runaway combustion of battery sample 1 is discharged through the exhaust pipe 12. When the thermal runaway ignition experiment of lithium batteries is carried out, the difference in battery capacity will lead to differences in the output of flue gas generated by the combustion of lithium batteries. According to the difference in capacity Adjust the power of the variable frequency fan in the exhaust duct to prevent the accumulation of toxic and harmful fumes in the combustion chamber, which leads to a high measurement error of the quantitative evaluation parameters of the ignition risk of lithium batteries. The differential pressure sensor probe 15, connected with the differential pressure sensor 19, is used to measure the differential pressure of the mixed gas of the thermal runaway combustion product of the lithium battery, the thermocouple 16, and the temperature acquisition module 20 (7018 module, convert the temperature signal into RS232 signal ), the data conversion module 21 (7520 module, the RS232 signal transmitted by the 7018 module is converted into an RS485 signal) is connected to measure the temperature _Te of the combustion product, the first gas sampling probe 17 is connected to the Servomex 4100 gas analyzer 22 , for measuring the concentration of oxygen O2, carbon monoxide CO, carbon dioxide CO2 in the exhaust pipe 12, the second gas sampling probe 18, connected with the Fourier transform infrared spectrometer 23, for measuring the concentration of toxic gases, control The terminal 24 is used to display, save and record the differential pressure measurement data, the temperature measurement data of the exhaust pipe, and the gas concentration data value. In this embodiment, the lithium battery thermal abuse thermal runaway ignition experimental platform consists of a thermal runaway ignition chamber, a fume collection hood, a radiation source, a fume exhaust pipe, a variable frequency fan, and a gas collection and analysis system. The thermal runaway ignition chamber is a non-closed cuboid, which is convenient for air to enter and exchange to provide the oxygen required for combustion. It is used for thermal runaway ignition experiments of lithium batteries with different states of charge and SOC under the action of radiation sources. The heat radiation source is composed of 18 silicon carbide rod heating elements of the same size and parallel to each other. The size of the radiation heating surface is 60cm×60cm. The size of the radiation intensity can be adjusted by the numerical control button. The fume collecting hood 7 can be determined according to the size of the research object, and is used to collect the fume released by the thermal runaway combustion of the lithium battery. The smoke exhaust duct 12 is used to discharge the flue gas released by the combustion chamber 6 caused by thermal runaway on the one hand, and on the other hand, by setting sampling holes and measuring holes on the exhaust duct 12, it is used to collect the difference of the thermal runaway combustion products of the lithium battery. pressure Δp, the concentration of toxic and asphyxiating gases in the mixed flue gas. The variable frequency fan 14 is connected to the end of the exhaust pipe 12 , and the rotating speed of the variable frequency fan 14 is adjusted according to the amount of flue gas to collect all the flue gas or combustion products released by the thermal runaway combustion of the lithium battery through the exhaust pipe 12 . The gas collection and analysis system, by placing the second gas sampling probe 18 on the sampling hole of the exhaust pipe, the collected gas is filtered, cooled and dried, and then connected to the gas analyzer for measuring toxic gases, asphyxiating gases and the concentration of oxygen. In the measurement holes provided on the exhaust pipe 12, a differential pressure sensor probe 15 and a thermocouple 16 probe are respectively placed to measure the differential pressure Δp and temperature _Te of the thermal runaway combustion products of lithium batteries with different states of charge. The sampling hole on the exhaust pipe 12 is used for placing the second gas sampling probe 18 for collecting the concentrations of oxygen O2, carbon dioxide CO2, carbon monoxide CO and toxic gases hydrogen fluoride HF and sulfur dioxide SO2. The second gas sampling probe 18 passes the collected gas to the gas analyzer after filtering, cooling and drying. In the present invention, the non-toxic gases oxygen O2, carbon dioxide CO2, and carbon monoxide CO2 are measured by a Servomex 4100 gas analyzer, and the concentrations of toxic gases such as hydrogen fluoride HF, sulfur dioxide SO2, etc. are measured by a Fourier transform infrared spectrometer 23.

In this embodiment, the lithium battery thermal abuse thermal runaway ignition risk platform designed by the present invention can obtain parameters such as the thermal runaway combustion flame characteristic parameters, thermal runaway release rate, toxic gas concentration, asphyxiating gas concentration and other parameters of the lithium battery. To quantitatively evaluate the hazard of thermal runaway ignition of lithium batteries with different states of charge. The lithium battery combustion test platform designed by the present invention is specifically as follows:

The lithium battery thermal abuse thermal runaway ignition experimental platform consists of a thermal runaway combustion chamber 6, a fume hood 7, a radiation source, and a gas acquisition and analysis system. The pouch lithium battery samples 1 with different states of charge are placed on the lithium battery sample lifting platform 5 to adjust the level of the pouch lithium battery, so that the camera 13 can collect the characteristic diameter of the combustion flame of the pouch lithium battery sample 1. The pouch lithium battery sample 1 is in the thermal runaway igniting combustion chamber 6, and the radiation power is adjusted under the working conditions of the thermal radiation source until the lithium battery 1 expands. When the internal pressure of the battery body is too high, the expanded pouch lithium battery 1 will The positive and negative electrodes of the battery can see the release of flammable gas, and the released flammable gas undergoes a violent combustion chemical reaction under the ignition of the spark 3 of the igniter 2, resulting in a flame and toxic and harmful fumes. The flame generated by the thermal runaway combustion of the lithium battery is collected and analyzed by the camera 13 . When the variable frequency fan 14 is started, the flue gas mixture enters the fume collecting hood 7 through the ventilation hole 9 on the upper part of the radiation source, and then enters the fume exhaust duct 12. Four sampling holes are arranged in the fume exhaust duct 12, and the differential pressure sensor probes 15 and 12 are placed in sequence. The thermocouple 16, the first gas sampling probe 17 and the second gas sampling probe 18, the differential pressure sensor probe 15 is connected to the differential pressure sensor 19 to display the differential pressure of the gas mixture product, and the temperature signal collected by the thermocouple 16 passes through the The temperature acquisition module 20 is converted into an RS232 electrical signal, and then converted into an RS485 signal identifiable by a computer through the data conversion module 21. The mixed combustion gas products collected by the first gas sampling probe 17 and the second gas sampling probe 18 pass through the Servomex respectively. The 4100 gas analyzer 22, the Fourier transform infrared spectrum analyzer 23, and the control terminal 24 computer are used to display the above-measured concentrations of oxygen, O2, toxic gases and asphyxiating gases. The invention designs an experimental platform for thermal runaway ignition of lithium batteries with different states of charge, and sequentially conducts thermal abuse ignition experiments of lithium batteries in overcharged state and normal state of charge to obtain the required quantitative evaluation of the ignition risk of lithium batteries The average value of the parameters is divided into three categories according to the data collected by the lithium battery thermal abuse ignition test platform: lithium battery ignition heat hazard data, lithium battery ignition toxic gas HF, SO2, NOx hazard and lithium battery The hazard of battery-induced asphyxiating gases CO and CO2. The video of the combustion process of the lithium battery is collected by the camera and the characteristic diameter D of the flame obtained in the second stable combustion stage of the thermal runaway of the lithium battery is extracted. , and obtain (HF, SO2, NOX) concentration by Fourier transform infrared spectrum flue gas analyzer. In this embodiment, the lithium battery is ignited by thermal runaway, and the external excitation source used in the present invention is a thermal radiation source, and the thermal runaway of lithium batteries with different states of charge is triggered by adjusting the radiation intensity of the radiation source. Due to the increase of internal expansion pressure of the lithium battery with thermal runaway, the thermal runaway flammable gas generated inside usually escapes from the positive and negative terminals of the battery. A spark igniter is placed between the positive and negative terminals of the lithium battery. for igniting escaping flammable gases. An electric spark igniter, used to ignite the escaping combustible gas, is placed between the positive and negative terminals of the lithium battery and flush with the upper surface of the lithium battery.

In this embodiment, the danger of the heat hazard caused by thermal abuse of the lithium battery can be characterized by the flame diameter D and the release rate of the heat caused by the thermal runaway of the lithium battery; the toxic gases HF, SO ₂ and NO _X can be characterized by the effective concentration percentage FEC of the toxic gases To quantitatively characterize; asphyxiating gases CO, CO ₂ can be characterized by percent effective dose FED. In this embodiment, the flame diameter D is obtained through a camera during the thermal runaway combustion process of the lithium battery, and the combustion video of the lithium battery is obtained. According to the flame characteristics of the combustion video, the characteristic diameter is the width of the flame in the second stable stage of the lithium battery combustion process D.

To sum up, the present invention evaluates the thermal risk index dimensionless flame heat release rate Q ^* , the toxic gas risk index FEC or the asphyxiating gas of a lithium battery caused by thermal runaway based on the heat release rate evaluation formula and the toxic gas or asphyxiating gas evaluation model. The risk index FED is used to establish the evaluation set V of thermal runaway ignition of lithium batteries with different states of charge. The entropy method is used to determine the weight coefficients of thermal hazard, toxic gas irritant and asphyxiating gas hazard, and a quantitative evaluation formula for battery risk is constructed, which realizes the quantitative evaluation of the risk of thermal runaway of energy storage batteries.

The invention sequentially carries out the thermal abuse ignition test of the lithium battery in the overcharged state of charge and the normal state of charge, obtains the average value of the required quantitative evaluation parameters of the ignition risk of the lithium battery, and collects the data according to the lithium battery thermal abuse ignition test platform. , to quantify the related parameters of thermal abuse and ignition, and to more comprehensively evaluate the safety of lithium batteries under specific temperature conditions.

The quantitative assessment of the flammability hazard of the lithium battery in the present invention is a comprehensive quantitative assessment of its thermal hazard, toxic gas hazard and suffocating gas hazard. Characterization of heat release rate due to thermal runaway of lithium battery; toxic gases HF, SO ₂ , NO _X can be quantitatively characterized by FEC of effective concentration percentage of toxic gases; asphyxiating gases CO and CO ₂ can be characterized by FED of effective dose percentage. The present invention quantifies the flammability hazard of the lithium battery to a specific value through the aforementioned three types of indices, so as to comprehensively evaluate the flammability hazard of the lithium battery. The invention solves the technical problems of lack of quantitative assessment and incomplete risk assessment in the prior art.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The recorded technical solutions are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A method for quantitatively evaluating thermal runaway risks of lithium batteries with different charge states is characterized by comprising the following steps:

s1, obtaining lithium battery samples of which the number is not less than a preset number of overcharged SOC and a preset number of normal SOC;

s2, establishing index sets U of different charge states according to the charge states of the lithium battery samples;

s3, carrying out thermal abuse thermal runaway ignition experiments of SOC lithium batteries with different charge states, obtaining characteristic parameters for thermal runaway ignition risk assessment, and dividing the characteristic parameters into thermal risk characteristic parameters, toxic and harmful gas risk characteristic parameters and asphyxiating gas risk characteristic parameters;

s4, obtaining the dimensionless flame release rate according to the preset toxic harmful or asphyxiating gas evaluation model, and quantitatively evaluating the toxic gas index FEC, the asphyxiating gas index FED and the dimensionless flame release rate Q of the lithium batteries in different charge states according to the characteristic parameters ^* Establishing an evaluation set V of ignition of lithium batteries with different charge states;

s5, establishing a sample matrix S according to the index set U and the evaluation set V of the lithium battery samples with different charge states, and standardizing the sample matrix S to obtain a standardized matrix X;

s6, sequentially determining the dimensionless flame release rate Q according to the standardized matrix X by using an entropy method ^* The weight coefficients of the toxic gas index FEC index and the asphyxia gas index FED index are omega ₁ 、ω ₂ And ω ₃ ；

S7, constructing a lithium battery thermal abuse thermal runaway ignition risk degree relation according to the weight coefficient, and accordingly evaluating the ignition risk degrees of the lithium batteries in different charge states.

2. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S1 comprises:

s11, selecting lithium batteries with the same specification;

and S12, discharging the lithium batteries to different charge states in a constant current discharge mode by using a battery charge-discharge cycle tester, and acquiring a preset normal charge state lithium battery and a preset overcharge charge state lithium battery.

3. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S2 comprises:

s21, acquiring difference SOC data of the normal state of charge lithium battery and the overcharge state of charge lithium battery;

and S22, constructing the index set U of the state of charge of the lithium battery according to the difference SOC data.

4. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S3 comprises:

s31, performing a thermal runaway ignition experiment and a thermal abuse ignition experiment on the lithium battery sample with different charge states on the thermal abuse thermal runaway ignition danger platform of the lithium battery;

s32, carrying out combustion experiments for the lithium battery sample in each charge state for not less than 2 times;

s33, acquiring the flame characteristic diameter D of the lithium battery sample in the second stable combustion state, the differential pressure delta p of combustion products in the smoke exhaust pipeline and the temperature T of the combustion products _e Oxygen concentration X _O2 Toxic gas concentration and asphyxiant gas concentration;

s34, characterizing the flame diameter D,The differential pressure delta p of combustion products in the smoke exhaust pipeline and the temperature T of the combustion products _e The oxygen concentration X _O2 Averaging the toxic gas concentration and the asphyxia gas concentration to serve as the characteristic parameters;

s35, preprocessing the thermal abuse thermal runaway ignition quantitative evaluation parameters of the lithium battery sample;

s36, acquiring and classifying the thermal abuse ignition evaluation parameters of the lithium battery to obtain the thermal risk characteristic parameters, the toxic and harmful gas risk characteristic parameters and the asphyxiating gas risk characteristic parameters.

5. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S4 comprises:

s41, acquiring and processing oxygen data in the smoke exhaust pipeline according to preset logic to obtain the dimensionless flame release rate;

s42, according to the toxic and harmful gas evaluation parameters, obtaining the toxic gas index FEC through the following logic processing:

in the formula (I), the compound is shown in the specification,

which indicates the concentration of each gas, F is a critical concentration of the gas that poses a threat to evacuees.

S43, according to the suffocation gas danger characteristic parameter, obtaining the suffocation gas index FED by the following logic processing, namely:

in the formula (I), the compound is shown in the specification,

representing the concentration of the gas, V representing the frequency factor of the gas molecules, Δ t representing the time duration, i.e. (t) ₂ -t ₁ 0；

S44, FEC according to the toxic gas index, FED and Q ^* Sequentially calculating characteristic parameter values corresponding to the lithium battery samples in each state of charge, and constructing the evaluation set V-Q of lithium battery ignition in different states of charge SOC ^* ，FEC，FED}。

6. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 5, wherein the step S41 comprises:

s411, processing the mass fraction of oxygen in the smoke exhaust pipeline according to the following logic

Differential pressure Δ p, temperature T of combustion products _e To obtain the flame heat release rate

S412, processing the thermal hazard characteristic parameter and the flame heat release rate by the following logic

To obtain the dimensionless flame release rate:

wherein D is the characteristic diameter of the flame,

Is the heat release rate of the flame.

7. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S5 comprises:

s51, according to the index set U and the index set V, establishing the sample matrix S according to the following logic:

in the formula, s _ij I is more than or equal to 1 and less than or equal to 15, and j is more than or equal to 1 and less than or equal to 3 for the actual value of the index j of the ith lithium battery sample;

s52, processing the sample matrix S by the following logic standardization to obtain the standard matrix X:

in the formula (I), the compound is shown in the specification,

8. the method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein the step S6 comprises:

s61, determining the weight y of the ith lithium battery sample relative to the index j according to the logic _ij ：

S62, according to the weight y _ij Determining the jth evaluation index with the logicEntropy value:

in the formula, e _j Entropy representing a jth evaluation index;

s63, the weight y according to the evaluation index j _ij And the entropy value, the weight coefficient omega of the jth evaluation index is estimated by the following logic _j ：

9. The method for quantitatively evaluating the thermal runaway risk of lithium batteries with different charge states as claimed in claim 1, wherein in the step S7, the following logic is used to construct the thermal runaway ignition risk relationship data of lithium batteries according to the weight coefficients: h ═ ω ₁ ·x ₁₁ +ω ₂ ·x ₁₂ +ω ₃ ·x ₁₃ 。

10. The device for quantitatively evaluating the thermal runaway risks of the lithium batteries with different charge states is characterized by comprising the following components:

the overcharge SOC sample module is used for acquiring lithium battery samples which are not less than a preset number of overcharge SOCs and a preset number of normal SOCs;

the index set module is used for establishing index sets U with different charge states according to the charge states of the lithium battery samples, and the index set module is connected with the lithium battery thermal abuse thermal runaway ignition experiment platform;

the characteristic parameter module is used for carrying out thermal abuse thermal runaway ignition experiments on the lithium batteries with different charge states SOC to obtain characteristic parameters for thermal runaway ignition danger assessment, and dividing the characteristic parameters into thermal danger characteristic parameters, toxic and harmful gas danger characteristic parameters and asphyxiating gas danger characteristic parameters, and the characteristic parameter module is connected with the index set module;

the evaluation set module is used for quantitatively evaluating the toxic gas index FEC, the asphyxia gas index FED and the dimensionless flame release rate Q of the lithium batteries in different charge states according to the preset toxic harmful or asphyxia gas evaluation model and the dimensionless flame release rate ^* Establishing an evaluation set V of ignition of lithium batteries with different charge states, wherein the evaluation set module is connected with the characteristic parameter module;

the standardization matrix module is used for establishing a sample matrix S according to the index set U and the evaluation set V of the lithium battery samples with different charge states, standardizing the sample matrix S to obtain a standardization matrix X, and the standardization matrix module is connected with the evaluation set module;

a weight module for sequentially determining the dimensionless flame release rate Q according to the standardized matrix X by using an entropy method ^* The weight coefficients of the toxic gas index FEC index and the asphyxia gas index FED index are omega ₁ 、ω ₂ And ω ₃ The weight module is connected with the standardized matrix module;

and the risk degree evaluation module is used for constructing a lithium battery thermal abuse thermal runaway ignition risk degree relation according to the weight coefficient so as to evaluate the ignition risk degree of the lithium batteries with different charge states, and is connected with the weight module.

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