Model-based battery thermal runaway early warning system and method

Abstract

The invention provides a model-based battery thermal runaway early warning system and method, and the method comprises the following steps: S1, building an electrochemical-thermal and electrochemical-expansive force coupling model, and obtaining a temperature change curve, a temperature rise rate curve, a voltage curve and an expansive force curve of a battery under different working conditions; s2, establishing a thermal runaway-expansive force coupling model, and obtaining a time-temperature curve, a time-temperature rise rate curve, a time-expansive force curve and a time-expansive force change rate curve of the battery in a thermal runaway stage; s3, determining a multistage safety threshold Xt of the battery according to the curves obtained in the step S1 and the step S2; and S4, carrying out battery thermal runaway early warning according to the battery working safety threshold Xt in the step S3. According to the invention, the accuracy and timeliness of lithium ion battery thermal runaway early warning can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery thermal runaway warning technology, and in particular to a battery thermal runaway warning system and method based on a model. Background Art

[0002] In recent years, with the rise of new energy vehicles and energy storage industries, lithium-ion batteries have become ideal power devices for power systems due to their long life, high energy density, and low self-discharge rate. Countries around the world are actively developing high-energy-density batteries and installing them on new energy electric vehicles. However, energy density and safety are mutually constrained. At present, there are still many problems in the use of new energy electric vehicles, mainly including battery thermal safety, vehicle charging and battery replacement safety, electromagnetic radiation safety, battery mechanical safety, and vehicle wading safety. In new energy vehicle accidents, battery combustion and explosion are the main causes. Battery combustion and explosion are mainly caused by excessive temperature, which leads to thermal runaway of the battery. Since the operating conditions of lithium-ion batteries are extremely complex, and thermal runaway cannot be avoided from the battery mechanism in a short period of time, it is very important to carry out thermal runaway warning of lithium-ion batteries and take safety measures in advance.

[0003] There are currently a variety of early warning methods for thermal runaway of lithium-ion batteries, including monitoring voltage, temperature, gas production and other signals to predict the occurrence of thermal runaway in advance. However, these single signals still have problems such as misjudgment, susceptibility to interference, untimely alarm, and high monitoring costs. Therefore, it is necessary to further seek an accurate and timely early warning signal to avoid the occurrence of thermal runaway as much as possible, and to establish a multi-signal set of early warning systems and methods to achieve early thermal runaway warning of lithium-ion batteries. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a model-based battery thermal runaway warning system and method to improve the accuracy and timeliness of thermal runaway warning of lithium-ion batteries.

[0005] Note that the description of these objectives does not prevent the existence of other objectives. One embodiment of the present invention does not need to achieve all of the above objectives. Objectives other than the above objectives can be extracted from the description of the specification, drawings, and claims.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A battery thermal runaway early warning method based on a model comprises the following steps:

[0008] Step S1, establishing an electrochemical-thermal and electrochemical-expansion force coupling model to obtain a temperature change curve, a temperature rise rate curve, a voltage curve and an expansion force curve of a battery under different working conditions;

[0009] Step S2, establishing a thermal runaway-expansion force coupling model, and obtaining a time-temperature curve, a time-temperature rise rate curve, a time-expansion force curve, and a time-expansion force change rate curve of the battery in the thermal runaway stage;

[0010] Step S3: Determine the battery multi-level safety threshold X according to the curves obtained in step S1 and step S2. t ;

[0011] Step S4: According to the battery operation safety threshold X in step S3 t Provide battery thermal runaway warning.

[0012] In the above scheme, step S1 specifically includes the following steps:

[0013] The electrochemical-thermal and electrochemical-expansion force coupling model includes an electrochemical model, a thermal model and an expansion force model. The electrochemical parameters under safe operating conditions are calculated according to the electrochemical model to obtain the total heat generation rate q and the solid-phase lithium ion concentration c1 under safe operating conditions. Then, the total heat generation rate q under safe operating conditions is used as the input of the thermal model, and the solid-phase lithium ion concentration c1 is used as the input of the expansion force model, so as to obtain the distribution of the average temperature T of the entire region and the average pressure F on the battery surface; the regional average temperature T calculated by the thermal model is input into the electrochemical model in subsequent time steps to update the parameters of the electrochemical model, and the cycle is repeated in sequence, and the solid-phase lithium ion concentration c1 is also continuously updated accordingly; in subsequent time steps, heat and temperature values ​​are transferred back and forth between the electrochemical model and the thermal model, and the changes in the expansion force model are obtained through the solid-phase lithium ion concentration c1 continuously updated by the electrochemical model, so as to obtain the battery temperature change curve, temperature rise rate curve, voltage and expansion force curve based on coupling.

[0014] In the above scheme, the boundary conditions and operation equations in the electrochemical model are as follows:

[0015] Conservation of mass:

[0016] Solid mass conservation equation:

[0017] Where c1 is the solid phase lithium ion concentration; D1 is the solid phase diffusion coefficient of lithium ions; r is the radius of the solid spherical particle, and t is the calculation time of the model;

[0018] The boundary conditions are as follows:

[0019]

[0020] In the formula, j Li is the lithium ion flow density at the solid-liquid interface; R is the radius of the solid active particle;

[0021] Liquid mass conservation equation:

[0022] Where ε2 is the liquid volume fraction; is the effective diffusion coefficient of lithium ions in liquid phase; c2 is the concentration of lithium ions in liquid phase; is the initial ion transfer number; F const is the Faraday constant;

[0023] The boundary conditions are as follows:

[0024]

[0025] In the formula, x is the thickness direction of the plate, It is the junction between the leftmost end of the positive electrode and the negative electrode current collector. It is the junction between the rightmost end of the negative electrode and the positive electrode current collector;

[0026] Conservation of Charge:

[0027] Solid phase charge conservation equation:

[0028] Where φ1 is the solid phase potential; σ eff is the effective diffusion conductivity of the solid phase;

[0029] The boundary conditions are as follows:

[0030]

[0031] In the formula, φ cc is the collector potential, σ cc is the current collector conductivity; I tot is the charge and discharge current of the lithium-ion battery; n0 is the number of positive / negative electrode units, It is the junction between the rightmost end of the positive electrode and the diaphragm. It is the junction between the rightmost end of the diaphragm and the negative electrode;

[0032] Liquid phase charge conservation equation:

[0033] In the formula, k eff is the effective ionic conductivity of the liquid phase; φ2 is the liquid phase potential; f is the activity coefficient of the electrolyte; R is the molar gas constant; T is the average temperature of the battery area;

[0034] The boundary conditions are as follows:

[0035]

[0036] Electrode Kinetics:

[0037] According to the Butler-Volmer equation, the relationship between the lithium ion flow density on the particle surface and the overpotential is as follows:

[0038]

[0039] in:

[0040] a v =N(4πR 2 )=3ε2 / R

[0041]

[0042] In the formula, ɑ v is the specific surface area of ​​the reaction; i0 is the exchange current density; α ɑ is the anode transfer coefficient, α c is the cathode transfer coefficient; η is the surface overpotential; N is the number of active materials per unit volume; K is the reaction rate constant; ε2 is the solid phase volume fraction; c 1,max is the maximum lithium ion concentration of solid phase active particles, c 1,surf is the lithium ion concentration on the surface of solid active particles;

[0043] The surface overpotential η of a lithium-ion battery is the deviation between the electrode potential and the equilibrium potential, expressed as follows:

[0044] η=(φ1-φ2-U SEI )-E eq

[0045] Where U SEI is the pressure loss caused by the solid electrolyte interface (SEI) membrane; E eq is the open circuit potential of the electrode material.

[0046] In the above scheme, the thermal model expression equation is as follows:

[0047]

[0048] Where q = q re +q o h m +q act +q exc h

[0049] Where ρ is the density of active material; C p is the specific heat capacity of the active material; T is the average temperature of the battery area; λ represents the thermal conductivity; q is the total heat generation rate, which includes the reaction heat q re , Ohm heat q ohm , polarization heat q act And the heat dissipation rate q exch ;

[0050] in:

[0051]

[0052] In the formula, j Li is the lithium ion flow density at the solid-liquid interface; σ eff is the effective diffusion conductivity of the solid phase; is the solid phase potential; k eff is the effective ionic conductivity of the liquid phase; is the liquid phase potential; is the initial ion transfer number; f is the electrolyte activity coefficient; R is the molar gas constant; c2 is the liquid phase lithium ion concentration; is the temperature variation coefficient; h is the convective heat transfer coefficient; U eq is the open circuit voltage of the battery; T am is the external ambient temperature.

[0053] In the above scheme, the expansion force model expression equation under normal conditions is as follows:

[0054]

[0055] Where ΔV is the change volume, v0 is the initial volume, and f vol is the material strain function, c1 is the solid phase lithium ion concentration;

[0056] The expansion force model expression equation under normal conditions is the relationship between the volume change of the macroscopic electrode material and the lithium ion concentration, and the particle diffusion stress constitutive equation caused by the embedding and detachment of lithium ions from the active particles is as follows:

[0057]

[0058] In the formula, σ ij is the stress component, ε ij is the strain component, v is Poisson's ratio, E is the elastic modulus, δ ij is the Dirac function, when i≠j its value is 0, when i=j its value is 1, σ kk is the diagonal element of the stress component, c1(r) is the solid lithium ion concentration with respect to the radius of the solid particles, and the active particles are spherical particles, belonging to spherical coordinates, so they are divided into tangential strain and radial strain;

[0059]

[0060] In the formula, ε θ is the tangential strain, ε r is the radial strain, σ θ is the tangential stress, σ r is the radial stress;

[0061] As a quasi-static mechanical equilibrium system, the electrode particles follow the stress equilibrium equation as follows:

[0062]

[0063] Where r is the radius of the solid spherical particle;

[0064] Von Mises stress is used to represent the average pressure F on the battery surface in a safe state:

[0065]

[0066] In the formula, σ v-m is the Von Mises stress, σ p1 is the first principal stress, σ p2 is the second principal stress, σ p3 is the third principal stress.

[0067] In the above scheme, the step S2 determines the total heat generation rate Q1 of thermal runaway and the amount of internal gas generated n according to the side reaction rate in the thermal runaway-expansion force coupling model, so as to calculate and obtain the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, and time-expansion force change rate curve of the thermal runaway stage, which specifically includes the following steps:

[0068] The expression equation of the thermal runaway-expansion force coupling model is as follows:

[0069] Heat balance equation: Q1=Q sei +Q neg +Q pos +Q ele

[0070] Where: ρ is the battery density; C p is the specific heat capacity of the battery; T is the average temperature of the battery area; λ represents the thermal conductivity; Q1 is the total heat generation rate; the total heat generation rate includes the SEI film decomposition heat Q sei , heat of reaction between negative electrode and electrolyte Q neg , heat of reaction between positive electrode and electrolyte Q pos And the electrolyte decomposition reaction heat Q ele ;

[0071] The heat of reaction equations are as follows:

[0072] SEI film decomposition reaction:

[0073]

[0074] Q QR2 =H QR2 W QR2 R QR2

[0075]

[0076] Negative electrode and electrolyte reaction:

[0077]

[0078] Q dRg =H dRg W dRg R dRg

[0079]

[0080] Positive electrode and electrolyte reaction:

[0081]

[0082] Q m.Q =H m.Q W m.Q R m.Q

[0083]

[0084] Electrolyte decomposition reaction:

[0085]

[0086] Q R / R =H R / R W R / R R R / R

[0087]

[0088] In the formula, Q sei is the heat generation rate of SEI film decomposition reaction, Q neg is the normalized concentration of the reactant between the negative electrode and the electrolyte, Q pos is the heat generation rate of the reaction between the positive electrode and the electrolyte, Q R / R is the heat generation rate of the electrolyte decomposition reaction, A sei is the pre-factor of SEI film decomposition reaction, A neg A is the pre-factor for the reaction between the negative electrode and the electrolyte. pos A is the pre-factor for the reaction between the positive electrode and the electrolyte. ele is the pre-factor of the electrolyte decomposition reaction, R sei is the reaction rate of SEI film decomposition reaction, R neg is the reaction rate of the negative electrode and the electrolyte, R pos is the reaction rate of the positive electrode and the electrolyte, R eleis the reaction rate of the electrolyte decomposition reaction, Ea sei is the activation energy of SEI film decomposition reaction, Ea neg is the activation energy of the reaction between the negative electrode and the electrolyte, Ea pos is the activation energy of the reaction between the positive electrode and the electrolyte, Ea ele is the activation energy of the electrolyte decomposition reaction, H sei is the heat generation rate of SEI film decomposition reaction, H neg is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the positive electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H ele is the decomposition heat generation rate of the electrolyte decomposition reaction, W sei is the amount of SEI film decomposition reaction substances, W neg is the amount of the negative electrode and electrolyte reaction substances, W pos is the amount of the reacting substance between the positive electrode and the electrolyte, W ele is the amount of electrolyte decomposition reaction substances, R const is the ideal gas constant;

[0089] The internal gas generation amount n is calculated by calculating the internal gas generation rate R d The real-time gas generation is obtained by integrating the gas and performing subsequent expansion force calculations.

[0090] Internal gas generation rate R d The formula is as follows:

[0091]

[0092] In the formula, A n is the gas generation forward factor, E n is the activation energy of gas generation, n is the amount of internal gas generated;

[0093] The expansion force under thermal runaway is expressed as follows:

[0094] Internal pressure changes

[0095] Using the Attoine equation to obtain the internal electrolyte vapor pressure

[0096] In the formula, p n Indicates the internal pressure, R const is the ideal gas constant, T is the average temperature of the battery area, V void is the void volume in the sealed cell, p dmc is the electrolyte vapor pressure;

[0097] The effect of temperature on expansion force is described by the following formula:

[0098] ε th =α*(T)*(TT ref )

[0099] F h =ε th *E

[0100] In the formula, ε th is the thermal strain, α is the thermal expansion coefficient, T is the average temperature of the battery area, T ref is the initial reference temperature, F h is the thermal expansion pressure, E is the elastic modulus;

[0101] Finally, the average expansion force P of the battery surface is calculated all =p n +p dmc , F all =P all S+F h ,

[0102] Where P all is the total pressure, S is the large surface area of ​​the battery, F all It is the expansion force under thermal runaway state, that is, the average pressure F on the battery surface during thermal runaway.

[0103] In the above scheme, the battery operating safety threshold X in step S3 t It includes the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate, and specifically includes the following steps:

[0104] Through the electrochemical-thermal and electrochemical-expansion force coupling model established in step S1, the relationship between the battery temperature, voltage, and expansion force changes and the peak value under safe working conditions are studied to obtain the battery threshold evaluation indicators under normal conditions, namely, the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt; through the thermal runaway-expansion force coupling model established in step S2, the battery temperature, temperature rise rate, expansion force, and expansion force change rate under thermal runaway conditions are studied to obtain early thermal runaway indicators, including the starting temperature T2 generated by battery self-heating, the battery spray valve temperature T3, the expansion force safety peak threshold F1, the expansion force danger peak F2, and the battery temperature rise rate soaring node;

[0105] The battery safety temperature peak T1 and the normal expansion force change rate dF / dt are calibrated as the safety threshold X1, indicating the occurrence of abnormal conditions. The starting temperature T2 generated by the battery self-heating and the expansion force safety peak threshold F1 are calibrated as the safety threshold X2, indicating that the battery enters the early stage of irreversible thermal runaway. The battery valve temperature T3 and the pressure danger peak F2 are calibrated as the safety threshold X3, indicating that the battery is about to enter the thermal runaway outbreak period. The battery temperature rise rate increases exponentially as the safety threshold X4, indicating that the battery has entered thermal runaway.

[0106] In the above scheme, step S4 specifically includes the following steps:

[0107] The battery operating safety threshold X determined in step S3 t Predict the time required for the battery to reach the initial safety threshold, adjust the threshold parameter settings according to the prediction results, adjust the safety warning time, determine the safety level of the battery, and formulate a safety strategy to achieve safety warning for the battery;

[0108] The battery multi-level safety threshold X determined in step S3 t Provide battery thermal runaway warning, specifically:

[0109] When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased;

[0110] When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again;

[0111] When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance;

[0112] When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

[0113] A system for implementing the model-based battery thermal runaway early warning method, comprising a data acquisition module, a threshold setting module and a safety early warning module;

[0114] The data acquisition module is used to obtain characteristic parameters of batteries in the battery pack;

[0115] The threshold setting module is used to establish an electrochemical-thermal and electrochemical-expansion force coupling model, obtain the temperature change curve, temperature rise rate curve, voltage curve and expansion force curve of the battery under different working conditions, establish a thermal runaway-expansion force coupling model, obtain the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, time-expansion force change rate curve of the battery in the thermal runaway stage, and determine the battery multi-level safety threshold X according to the obtained curves t ;

[0116] The safety warning module is used to provide a thermal runaway warning based on the collected data according to the working safety threshold Xt set by the threshold setting module.

[0117] In the above scheme, the data acquisition module includes a sensor, which is connected to the out-of-control warning module; the sensor includes a voltage sensor, a temperature sensor and a pressure sensor; the voltage sensor is used to collect the battery voltage in real time, the temperature sensor is used to collect the battery center temperature in real time, and the pressure sensor is used to collect the average pressure F on the battery surface;

[0118] The threshold setting module obtains the working safety threshold value X set by the curve according to the model t Including the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate;

[0119] The safety warning module takes specific measures to warn and alarm:

[0120] When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased;

[0121] When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again;

[0122] When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance;

[0123] When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

[0124] Compared with the prior art, the present invention has the following beneficial effects:

[0125] The present invention can determine the safety threshold of the battery state by predicting the battery system parameters under the battery safety condition and the dangerous thermal runaway condition, thereby realizing the real-time update of the battery state. The warning threshold increases the expansion force pressure value on the basis of the temperature, realizes the multi-signal collection warning, avoids the warning false alarm, ensures the accuracy of the warning, and the expansion force pressure value changes ahead of the temperature value, which can realize the early warning of thermal runaway, thereby increasing the thermal runaway processing time, improving the accuracy and timeliness of the thermal runaway warning of lithium-ion batteries, and reducing the occurrence and loss of lithium-ion battery accidents.

[0126] Note that the description of these effects does not prevent the existence of other effects. One embodiment of the present invention does not necessarily have all of the above effects. Effects other than the above can be clearly seen and extracted from the description of the specification, drawings, claims, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Figure 1 It is a flow chart of a model-based battery thermal runaway early warning method according to an embodiment of the present invention;

[0128] Figure 2 It is a schematic diagram comparing a temperature prediction curve diagram and a measured curve diagram of an early warning method according to an embodiment of the present invention;

[0129] Figure 3 It is a schematic diagram comparing the expansion force prediction curve and the measured curve of the early warning method according to one embodiment of the present invention. DETAILED DESCRIPTION

[0130] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0131] Figure 1 A battery thermal runaway early warning method based on a model according to an embodiment of the present invention comprises the following steps:

[0132] Step S1, establishing an electrochemical-thermal and electrochemical-expansion force coupling model to obtain a temperature change curve, a temperature rise rate curve, a voltage curve and an expansion force curve of a battery under different working conditions;

[0133] Step S2, establishing a thermal runaway-expansion force coupling model, and obtaining a time-temperature curve, a time-temperature rise rate curve, a time-expansion force curve, and a time-expansion force change rate curve of the battery in the thermal runaway stage;

[0134] Step S3: Determine the battery multi-level safety threshold X according to the curves obtained in step S1 and step S2. t ;

[0135] Step S4: According to the battery operation safety threshold X in step S3 t Provide battery thermal runaway warning.

[0136] In step S1, the electrochemical-thermal and electrochemical-expansion force coupling model includes an electrochemical model, a thermal model and an expansion force model,

[0137] In step S1, the electrochemical-thermal coupling model and the electrochemical-expansion force coupling model are used to obtain the internal electrochemical parameters of the battery based on the quasi-two-dimensional (Pseudo-Two-Dimensional, P2D) electrochemical model of the lithium battery, and the thermal model and the expansion force model are input to realize the simulation of the battery temperature field and mechanical field. At the same time, the temperature field data is fed back to the electrochemical model to obtain the changes in the expansion force model, so as to realize data update and complete coupling. According to the electrochemical model, the electrochemical parameters under safe operating conditions are calculated to obtain the total heat generation rate q and the solid-phase lithium ion concentration c1 under safe operating conditions. Then, the total heat generation rate q under safe operating conditions is used as the input of the thermal model, and the solid-phase lithium ion concentration c1 is used as the input of the expansion force model, so as to obtain the average temperature T distribution of the entire region and the average pressure F on the battery surface; the regional average temperature T calculated by the thermal model is input into the electrochemical model in subsequent time steps to update the parameters of the electrochemical model, and the cycle is repeated in sequence, and the solid-phase lithium ion concentration c1 is also continuously updated; in subsequent time steps, heat and temperature values ​​are transferred back and forth between the electrochemical model and the thermal model, and the changes in the expansion force model are obtained through the solid-phase lithium ion concentration c1 continuously updated by the electrochemical model, and the battery temperature change curve, temperature rise rate curve, voltage and expansion force curve based on coupling are obtained.

[0138] The electrochemical model includes mass conservation, charge conservation, and electrode kinetic equations. The boundary conditions and operational equations in the electrochemical model are as follows:

[0139] Mass conservation includes the solid phase mass conservation equation and the liquid phase mass conservation equation:

[0140] Solid mass conservation equation:

[0141] Where c1 is the solid phase lithium ion concentration; D1 is the solid phase diffusion coefficient of lithium ions; r is the radius of the solid spherical particle, and t is the calculation time of the model;

[0142] The boundary conditions are as follows:

[0143]

[0144] In the formula, j Li is the lithium ion flow density at the solid-liquid interface; R is the radius of the solid active particle;

[0145] Liquid mass conservation equation:

[0146] Where ε2 is the liquid volume fraction; is the effective diffusion coefficient of lithium ions in liquid phase; c2 is the concentration of lithium ions in liquid phase; is the initial ion transfer number; F const is the Faraday constant;

[0147] The boundary conditions are as follows:

[0148]

[0149] In the formula, x is the thickness direction of the plate, It is the junction between the leftmost end of the positive electrode and the negative electrode current collector. It is the junction between the rightmost end of the negative electrode and the positive electrode current collector;

[0150] The charge conservation equation includes the solid phase charge conservation equation and the liquid phase charge conservation equation:

[0151] Solid phase charge conservation equation:

[0152] Where φ1 is the solid phase potential; σ eff is the effective diffusion conductivity of the solid phase;

[0153] The boundary conditions are as follows:

[0154]

[0155] In the formula, φ cc is the collector potential, σ cc is the current collector conductivity; I tot is the charge and discharge current of the lithium-ion battery; n0 is the number of positive / negative electrode units, It is the junction between the rightmost end of the positive electrode and the diaphragm. It is the junction between the rightmost end of the diaphragm and the negative electrode;

[0156] Liquid phase charge conservation equation:

[0157] In the formula, k eff is the effective ionic conductivity of the liquid phase; φ2 is the liquid phase potential; f is the activity coefficient of the electrolyte; R is the molar gas constant; T is the average temperature of the battery area;

[0158] The boundary conditions are as follows:

[0159]

[0160] Electrode Kinetics:

[0161] According to the Butler-Volmer equation, the relationship between the lithium ion flow density on the particle surface and the overpotential is as follows:

[0162]

[0163] in:

[0164] a v =N(4πR 2)=3ε2 / R

[0165]

[0166] In the formula, ɑ v is the specific surface area of ​​the reaction; i0 is the exchange current density; α ɑ is the anode transfer coefficient, α c is the cathode transfer coefficient; η is the surface overpotential; N is the number of active materials per unit volume; K is the reaction rate constant; ε2 is the solid phase volume fraction; c 1,max is the maximum lithium ion concentration of solid phase active particles, c 1,surf is the lithium ion concentration on the surface of solid active particles.

[0167] The surface overpotential η of a lithium-ion battery is the deviation between the electrode potential and the equilibrium potential, expressed as follows:

[0168] η=(φ1-φ2-U SEI )-E eq

[0169] Where U SEI is the pressure loss caused by the solid electrolyte interface (SEI) membrane; E eq is the open circuit potential of the electrode material;

[0170] The thermal model describes the relationship between battery heat generation, heat transfer, and heat dissipation. The expression equation is as follows:

[0171]

[0172] q=q re +q ohm +q act +q exch

[0173] Where ρ is the density of active material; C p is the specific heat capacity of the active material; T is the average temperature of the battery area; λ represents the thermal conductivity in each direction; q is the total heat generation rate; the total heat generation rate includes the reaction heat q re , Ohm heat q ohm , polarization heat q act And the heat dissipation rate q exch ;

[0174] in:

[0175]

[0176] In the formula, j Li is the lithium ion flow density at the solid-liquid interface; σ effis the effective diffusion conductivity of the solid phase; is the solid phase potential; k eff is the effective ionic conductivity of the liquid phase; is the liquid phase potential; is the initial ion transfer number; f is the electrolyte activity coefficient; R is the molar gas constant; c2 is the liquid phase lithium ion concentration; is the temperature variation coefficient; h is the convective heat transfer coefficient; U eq is the open circuit voltage of the battery; T am is the external ambient temperature.

[0177] The expansion force model under normal conditions predicts the change in battery expansion force caused by the volume change of the graphite negative electrode inside the battery. The specific expression equation is as follows:

[0178]

[0179] Where ΔV is the change volume, v0 is the initial volume, and f vol is the material strain function, c1 is the solid phase lithium ion concentration;

[0180] The expansion force model expression equation under normal conditions is the relationship between the volume change of the macroscopic electrode material and the lithium ion concentration, and the particle diffusion stress constitutive equation caused by the embedding and detachment of lithium ions from the active particles is as follows:

[0181]

[0182] In the formula, σ ij is the stress component, ε ij is the strain component, v is Poisson's ratio, E is the elastic modulus, δ ij is the Dirac function, when i≠j its value is 0, when i=j its value is 1, σ kk is the diagonal element of the stress component, c1(r) is the solid lithium ion concentration with respect to the solid particle radius. The active particles are spherical particles and belong to spherical coordinates, so they are divided into tangential strain and radial strain.

[0183]

[0184] In the formula, ε θ is the tangential strain, ε r is the radial strain, σ θ is the tangential stress, σ r is the radial stress;

[0185] As a quasi-static mechanical equilibrium system, the electrode particles follow the stress equilibrium equation as follows:

[0186]

[0187] Where r is the radius of the solid spherical particle;

[0188] Von Mises stress is used to represent the average pressure F on the battery surface in a safe state:

[0189]

[0190] In the formula, σ v-m is the Von Mises stress, σ p1 is the first principal stress, σ p2 is the second principal stress, σ p3 is the third principal stress.

[0191] After determining the expression equation of the model, identify and set the parameters required in the model. The parameters of the thermal model and the expansion force model are obtained by direct measurement, and the parameters required for the electrochemical model are obtained by table lookup, measurement, etc. The specific parameters are:

[0192] Battery parameters: geometric dimensions, density, specific heat capacity, thermal conductivity, Poisson's ratio, and elastic modulus.

[0193] Electrochemical model parameters: thickness of single-layer positive and negative electrode materials and separator, radius of positive and negative electrode particles, solid-liquid phase porosity, solid-liquid phase conductivity, solid-liquid phase diffusion coefficient, initial electrolyte concentration, positive and negative electrode equilibrium potential, maximum embeddable lithium ion concentration of positive and negative electrodes, positive and negative electrode reaction transfer coefficients, reference exchange current density, and solid electrolyte interface film resistance.

[0194] According to the electrochemical model, the electrochemical parameters under safe operating conditions are calculated to obtain the total heat generation rate q and the solid-phase lithium ion concentration c1 under safe operating conditions. Then the total heat generation rate q under safe operating conditions is used as the input of the thermal model, and the solid-phase lithium ion concentration c1 is used as the input of the expansion force model, so as to obtain the average temperature T distribution of the entire region and the average pressure F on the battery surface; the regional average temperature T calculated by the thermal model is input into the electrochemical model in subsequent time steps to update the parameters of the electrochemical model, and the cycle is repeated in sequence, and the solid-phase lithium ion concentration is continuously updated accordingly; in subsequent time steps, heat and temperature values ​​are transferred back and forth between the electrochemical model and the thermal model, and the changes in the expansion force model are obtained through the solid-phase lithium ion concentration continuously updated by the electrochemical model, forming a battery temperature change curve, temperature rise rate, voltage and expansion force curve based on coupling.

[0195] Step S2, determining the total heat generation rate Q1 of thermal runaway and the amount of internal gas generated n according to the side reaction rate in the thermal runaway-expansion force coupling model, and calculating the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, and time-expansion force change rate curve of the thermal runaway stage,

[0196] In step S2, the present invention establishes a thermal runaway-expansion force coupling model based on the battery side reaction mechanism through the Arrhenius formula, and uses the internal side reaction rate to connect the heat generation rate and the gas generation rate to obtain the temperature change and the expansion force change.

[0197] The expression equation of the thermal runaway-expansion force coupling model is as follows:

[0198] Heat balance equation: Q1=Q sei +Q neg +Q pos +Q ele

[0199] Where: ρ is the battery density; C p is the specific heat capacity of the battery; T is the average temperature of the battery area; λ represents the thermal conductivity; Q1 is the total heat generation rate; the total heat generation rate includes the SEI film decomposition heat Q sei , heat of reaction between negative electrode and electrolyte Q neg , heat of reaction between positive electrode and electrolyte Q pos And the electrolyte decomposition reaction heat Q ele ;

[0200] The heat of reaction equations are as follows:

[0201] SEI film decomposition reaction:

[0202]

[0203] Q QR2 =H QR2 W QR2 R QR2

[0204]

[0205] Negative electrode and electrolyte reaction:

[0206]

[0207] Q dRg =H dRg W dRg R dRg

[0208]

[0209] Positive electrode and electrolyte reaction:

[0210]

[0211] Q m.Q =H m.Q W m.Q Rm.Q

[0212]

[0213] Electrolyte decomposition reaction:

[0214]

[0215] Q R / R =H R / R W R / R R R / R

[0216]

[0217] In the formula, Q sei is the heat generation rate of SEI film decomposition reaction, Q neg is the normalized concentration of the reactant between the negative electrode and the electrolyte, Q pos is the heat generation rate of the reaction between the positive electrode and the electrolyte, Q R / R is the heat generation rate of the electrolyte decomposition reaction, A sei is the pre-factor of SEI film decomposition reaction, A neg A is the pre-factor for the reaction between the negative electrode and the electrolyte. pos A is the pre-factor for the reaction between the positive electrode and the electrolyte. ele is the pre-factor of the electrolyte decomposition reaction, R sei is the reaction rate of SEI film decomposition reaction, R neg is the reaction rate of the negative electrode and the electrolyte, R pos is the reaction rate of the positive electrode and the electrolyte, R ele is the reaction rate of the electrolyte decomposition reaction, Ea sei is the activation energy of SEI film decomposition reaction, Ea neg is the activation energy of the reaction between the negative electrode and the electrolyte, Ea pos is the activation energy of the reaction between the positive electrode and the electrolyte, Ea ele is the activation energy of the electrolyte decomposition reaction, H sei is the heat generation rate of SEI film decomposition reaction, H neg is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the positive electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H ele is the decomposition heat generation rate of the electrolyte decomposition reaction, W sei is the amount of SEI film decomposition reaction substances, W neg is the amount of the negative electrode and electrolyte reaction substances, W pos is the amount of the reacting substance between the positive electrode and the electrolyte, W ele is the amount of electrolyte decomposition reaction substances, Rconst is the ideal gas constant;

[0218] The internal gas generation amount n is calculated by calculating the internal gas generation rate R d The real-time gas generation is obtained by integrating the gas and performing subsequent expansion force calculations.

[0219] Internal gas generation rate R d The formula is as follows:

[0220]

[0221] In the formula, A n is the gas generation forward factor, E n is the activation energy of gas generation, n is the amount of internal gas generated;

[0222] The expansion force under thermal runaway is expressed as follows:

[0223] Internal pressure changes

[0224] Using the Attoine equation to obtain the internal electrolyte vapor pressure

[0225] In the formula, p n Indicates the internal pressure, R const is the ideal gas constant, T is the average temperature of the battery area, V void is the void volume in the sealed cell, p dmc is the electrolyte vapor pressure;

[0226] Since the thermal runaway temperature is too high, considering the thermal expansion effect of temperature on battery materials, the formula describing the influence of temperature on expansion force is as follows:

[0227] ε th =α*(T)*(TT ref )

[0228] F h =ε th *E,

[0229] In the formula, ε th is the thermal strain, α is the thermal expansion coefficient, T is the average temperature of the battery area, T ref is the initial reference temperature, F h is the thermal expansion pressure, E is the elastic modulus;

[0230] Finally, the average expansion force P of the battery surface is calculated all =p n +p dmc , F all =P all S+F h ,

[0231] Where P all is the total pressure, S is the large surface area of ​​the battery, F all It is the expansion force under thermal runaway state, that is, the average pressure F on the battery surface during thermal runaway.

[0232] After the thermal runaway-expansion force model is constructed, the parameters need to be determined, and the battery kinetic parameters are obtained through measurement and electrochemical experimental calibration. The specific thermal runaway model parameters are shown in Table 1:

[0233] Table 1 Thermal runaway model parameters

[0234]

[0235]

[0236] It is obtained by establishing a battery thermal runaway and expansion force coupling model, and the thermal runaway heat generation rate Q1 and the internal gas generation n are determined according to the side reaction rate in the model. The time-temperature curve, time-temperature rise rate curve, time-expansion force curve, and time-expansion force change rate curve of the thermal runaway stage are calculated.

[0237] Step S3: Determine the battery multi-level safety threshold X according to the above curve t ;

[0238] The battery operation safety threshold value X in step S3 t It includes the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate, and specifically includes the following steps:

[0239] Through the electrochemical-thermal and electrochemical-expansion force coupling model established in step S1, the relationship between the battery temperature, voltage, and expansion force changes and the peak value under safe working conditions are studied to obtain the battery threshold evaluation indicators under normal conditions, namely, the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt. Through the thermal runaway-expansion force coupling model established in step S2, the battery temperature, temperature rise rate, expansion force, and expansion force change rate under thermal runaway conditions are studied to obtain early thermal runaway indicators, including the starting temperature T2 generated by the battery self-heating (the evaluation standard is the heat generation rate ≥ 0.02°C / min), the battery spray valve temperature T3, the expansion force safety peak threshold F1, the expansion force dangerous peak F2, and the battery temperature rise rate soaring node (the evaluation standard is the heat generation rate ≥ 1°C / s);

[0240] The battery safety temperature peak T1 and the normal expansion force change rate dF / dt are calibrated as the safety threshold X1, which indicates the occurrence of abnormal conditions. The starting temperature T2 generated by the battery self-heating and the expansion force safety peak threshold F1 are calibrated as the safety threshold X2, which indicates that the battery has entered the early stage of irreversible thermal runaway. The battery valve temperature T3 and the pressure danger peak F2 are calibrated as the safety threshold X3, which indicates that the battery is about to enter the thermal runaway outbreak period. The battery temperature rise rate increases exponentially, which is calibrated as the safety threshold X4, which indicates that the battery has entered thermal runaway and there is a major risk to the vehicle.

[0241] Step S4: according to the battery working safety threshold X t Provide battery thermal runaway warning.

[0242] The battery operating safety threshold X determined in step S3 t Predict the time required for the battery to reach the initial safety threshold, adjust the threshold parameter settings according to the prediction results, adjust the safety warning time, determine the safety level of the battery, and formulate a safety strategy to achieve safety warning for the battery; compare the temperature force prediction results with the actual measurement results. Figure 2 As shown in Figure 2, the expansion force prediction results are compared with the actual measurement results. Figure 3 As shown, the error is small on the time scale, and the error between the temperature and expansion force in the vertical coordinate peak direction is less than 3%, which can provide accurate prediction results. In addition, the prediction results show that the expansion force warning is at least 60s ahead of the temperature warning, which improves the timeliness of thermal runaway warning for lithium-ion batteries. Then, according to the prediction results, the threshold parameter settings are adjusted, the safety warning time is adjusted, the safety level of the battery is determined, and a safety strategy is formulated to achieve safety warning for the battery.

[0243] The battery multi-level safety threshold X determined in step S3 t Provide battery thermal runaway warning, specifically:

[0244] When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased;

[0245] When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again;

[0246] When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance;

[0247] When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

[0248] A warning system for a battery thermal runaway warning method based on a model, comprising a data acquisition module, a threshold setting module and a safety warning module;

[0249] The data acquisition module is used to obtain characteristic parameters of batteries in the battery pack;

[0250] The threshold setting module is used to establish an electrochemical-thermal and electrochemical-expansion force coupling model, obtain the temperature change curve, temperature rise rate curve, voltage curve and expansion force curve of the battery under different working conditions, establish a thermal runaway-expansion force coupling model, obtain the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, time-expansion force change rate curve of the battery in the thermal runaway stage, and determine the battery multi-level safety threshold X according to the obtained curves t ;

[0251] The safety warning module is used to provide a thermal runaway warning based on the collected data according to the working safety threshold Xt set by the threshold setting module.

[0252] Preferably, the data acquisition module includes a sensor, which is connected to the out-of-control warning module; the sensor includes a voltage sensor, a temperature sensor and a pressure sensor; the voltage sensor is used to collect the battery voltage in real time, the temperature sensor is used to collect the battery center temperature in real time, and the pressure sensor is used to collect the average pressure F on the battery surface;

[0253] The threshold setting module obtains the working safety threshold value X set by the curve according to the model t Including the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate;

[0254] Preferably, the safety warning module takes specific measures to issue a warning alarm:

[0255] When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased;

[0256] When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again;

[0257] When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance;

[0258] When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

[0259] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

[0260] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0261] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A model-based battery thermal runaway early warning method, characterized in that: The following steps are involved: Step S1, establishing an electrochemical-thermal and electrochemical-expansion force coupling model to obtain a temperature change curve, a temperature rise rate curve, a voltage curve and an expansion force curve of the battery under different working conditions; Step S2, establishing a thermal runaway-expansion force coupling model, and obtaining a time-temperature curve, a time-temperature rise rate curve, a time-expansion force curve, and a time-expansion force change rate curve of the battery in the thermal runaway stage; Step S3: Determine the battery multi-level safety threshold X according to the curves obtained in step S1 and step S2. t ; Step S4: According to the battery operation safety threshold X in step S3 t Provide battery thermal runaway warning.

2. The model-based battery thermal runaway early warning method according to claim 1, characterized in that: The step S1 specifically includes the following steps: The electrochemical-thermal and electrochemical-expansion force coupling model includes an electrochemical model, a thermal model and an expansion force model. The electrochemical parameters under safe operating conditions are calculated according to the electrochemical model to obtain the total heat generation rate q and the solid-phase lithium ion concentration c1 under safe operating conditions. Then, the total heat generation rate q under safe operating conditions is used as the input of the thermal model, and the solid-phase lithium ion concentration c1 is used as the input of the expansion force model, so as to obtain the distribution of the average temperature T of the entire region and the average pressure F on the battery surface; the regional average temperature T calculated by the thermal model is input into the electrochemical model in subsequent time steps to update the parameters of the electrochemical model, and the cycle is repeated in sequence, and the solid-phase lithium ion concentration c1 is also continuously updated accordingly; in subsequent time steps, heat and temperature values ​​are transferred back and forth between the electrochemical model and the thermal model, and the changes in the expansion force model are obtained through the solid-phase lithium ion concentration c1 continuously updated by the electrochemical model, so as to obtain the battery temperature change curve, temperature rise rate curve, voltage and expansion force curve based on coupling.

3. The model-based battery thermal runaway early warning method according to claim 2, characterized in that: The boundary conditions and operation equations in the electrochemical model are as follows: Conservation of mass: Solid mass conservation equation: Where c1 is the solid phase lithium ion concentration; D1 is the solid phase diffusion coefficient of lithium ions; r is the radius of the solid spherical particle, and t is the calculation time of the model; The boundary conditions are as follows: In the formula, j Li is the lithium ion flow density at the solid-liquid interface; R is the radius of the solid active particle; Liquid mass conservation equation: Where ε2 is the liquid volume fraction; is the effective diffusion coefficient of lithium ions in liquid phase; c2 is the concentration of lithium ions in liquid phase; is the initial ion transfer number; F const is the Faraday constant; The boundary conditions are as follows: In the formula, x is the thickness direction of the plate, x = Th pos,cc The leftmost end of the positive electrode is at the junction with the negative electrode current collector, x = Th tot -Th neg,cc It is the junction between the rightmost end of the negative electrode and the positive electrode current collector; Conservation of Charge: Solid phase charge conservation equation: Where φ1 is the solid phase potential; σ eff is the effective diffusion conductivity of the solid phase; The boundary conditions are as follows: In the formula, φ cc is the collector potential, σ cc is the current collector conductivity; I tot is the charge and discharge current of the lithium-ion battery; n0 is the number of positive / negative electrode units, x = Th pos,cc +Th pos It is the junction between the rightmost end of the positive electrode and the diaphragm, x = Th pos,cc +Th pos +Th sep It is the junction between the rightmost end of the diaphragm and the negative electrode; Liquid phase charge conservation equation: In the formula, k eff is the effective ionic conductivity of the liquid phase; φ2 is the liquid phase potential; f is the activity coefficient of the electrolyte; R is the molar gas constant; T is the average temperature of the battery area; The boundary conditions are as follows: Electrode Kinetics: According to the Butler-Volmer equation, the relationship between the lithium ion flow density on the particle surface and the overpotential is as follows: in: a v =N(4πR 2 )=3ε2 / R In the formula, ɑ v is the specific surface area of ​​the reaction; i0 is the exchange current density; α ɑ is the anode transfer coefficient, α c is the cathode transfer coefficient; η is the surface overpotential; N is the number of active materials per unit volume; K is the reaction rate constant; ε2 is the solid phase volume fraction; c 1,max is the maximum lithium ion concentration of solid phase active particles, c 1,surf is the lithium ion concentration on the surface of solid active particles; The surface overpotential η of a lithium-ion battery is the deviation between the electrode potential and the equilibrium potential, expressed as follows: η=(φ1-φ2-U SEI )-E eq Where U SEI is the pressure loss caused by the solid electrolyte interface (SEI) membrane; E eq is the open circuit potential of the electrode material.

4. The model-based battery thermal runaway early warning method according to claim 2, characterized in that: The thermal model expression equation is as follows: where q = q re + q ohm + q act + q exch Where ρ is the density of active material; C p is the specific heat capacity of the active material; T is the average temperature of the battery area; λ represents the thermal conductivity; q is the total heat generation rate, which includes the reaction heat q re , Ohm heat q ohm , polarization heat q act And the heat dissipation rate q exch ; in: In the formula, j Li is the lithium ion flow density at the solid-liquid interface; σ eff is the effective diffusion conductivity of the solid phase; is the solid phase potential; k eff is the effective ionic conductivity of the liquid phase; is the liquid phase potential; is the initial ion transfer number; f is the electrolyte activity coefficient; R is the molar gas constant; c2 is the liquid phase lithium ion concentration; is the temperature variation coefficient; h is the convective heat transfer coefficient; U eq is the open circuit voltage of the battery; T am is the external ambient temperature.

5. The model-based battery thermal runaway early warning method according to claim 2, characterized in that: The expansion force model expression equation under normal conditions is as follows: Where ΔV is the change volume, v0 is the initial volume, and f vol is the material strain function, c1 is the solid phase lithium ion concentration; The expansion force model expression equation under normal conditions is the relationship between the volume change of the macroscopic electrode material and the lithium ion concentration, and the particle diffusion stress constitutive equation caused by the embedding and detachment of lithium ions from the active particles is as follows: In the formula, σ ij is the stress component, ε ij is the strain component, v is Poisson's ratio, E is the elastic modulus, δ ij is the Dirac function, when i≠j its value is 0, when i=j its value is 1, σ kk is the diagonal element of the stress component, c1(r) is the solid lithium ion concentration with respect to the radius of the solid particles, and the active particles are spherical particles, belonging to spherical coordinates, so they are divided into tangential strain and radial strain; In the formula, ε θ is the tangential strain, ε r is the radial strain, σ θ is the tangential stress, σ r is the radial stress; As a quasi-static mechanical equilibrium system, the electrode particles follow the stress equilibrium equation as follows: Where r is the radius of the solid spherical particle; Von Mises stress is used to represent the average pressure F on the battery surface in a safe state: In the formula, σ v-m is the Von Mises stress, σ p1 is the first principal stress, σ p2 is the second principal stress, σ p3 is the third principal stress.

6. The model-based battery thermal runaway early warning method according to claim 1, characterized in that: The step S2 determines the total heat generation rate Q1 of thermal runaway and the amount of internal gas generated n according to the side reaction rate in the thermal runaway-expansion force coupling model, and calculates the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, and time-expansion force change rate curve of the thermal runaway stage, which specifically includes the following steps: The expression equation of the thermal runaway-expansion force coupling model is as follows: Heat balance equation: Q1=Q sei +Q neg +Q pos +Q ele Where: ρ is the battery density; C p is the specific heat capacity of the battery; T is the average temperature of the battery area; λ represents the thermal conductivity; Q1 is the total heat generation rate; the total heat generation rate includes the SEI film decomposition heat Q sei , heat of reaction between negative electrode and electrolyte Q neg , heat of reaction between positive electrode and electrolyte Q pos and the electrolyte decomposition reaction heat Q ele ; The heat of reaction equations are as follows: SEI film decomposition reaction: Q sei =H sei W sei R sei Negative electrode and electrolyte reaction: Q neg =H neg W neg R neg Positive electrode and electrolyte reaction: Q pos =H pos W pos R pos Electrolyte decomposition reaction: Q ele =H ele W ele R ele In the formula, Q sei is the heat generation rate of SEI film decomposition reaction, Q neg is the normalized concentration of the reactant between the negative electrode and the electrolyte, Q pos is the heat generation rate of the reaction between the positive electrode and the electrolyte, Q ele is the heat generation rate of the electrolyte decomposition reaction, A sei is the pre-factor of SEI film decomposition reaction, A neg is the pre-factor for the reaction between the negative electrode and the electrolyte, A pos A is the pre-factor for the reaction between the positive electrode and the electrolyte. ele is the pre-factor of the electrolyte decomposition reaction, R sei is the reaction rate of SEI film decomposition reaction, R neg is the reaction rate of the negative electrode and the electrolyte, R pos is the reaction rate of the positive electrode and the electrolyte, R ele is the reaction rate of the electrolyte decomposition reaction, Ea sei is the activation energy of SEI film decomposition reaction, Ea neg is the activation energy of the reaction between the negative electrode and the electrolyte, Ea pos is the activation energy of the reaction between the positive electrode and the electrolyte, Ea ele is the activation energy of the electrolyte decomposition reaction, H sei is the heat generation rate of SEI film decomposition reaction, H neg is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the positive electrode and electrolyte reaction, H pos is the decomposition heat generation rate of the negative electrode and electrolyte reaction, H ele is the decomposition heat generation rate of the electrolyte decomposition reaction, W sei is the amount of SEI film decomposition reaction substances, W neg is the amount of the negative electrode and electrolyte reaction substances, W pos is the amount of the reacting substance between the positive electrode and the electrolyte, W ele is the amount of electrolyte decomposition reaction substances, R const is the ideal gas constant; The internal gas generation amount n is calculated by calculating the internal gas generation rate R n The real-time gas generation is obtained by integrating the gas and performing subsequent expansion force calculations. Internal gas generation rate R n The formula is as follows: In the formula, A n is the gas generation forward factor, E n is the activation energy of gas generation, n is the amount of internal gas generated; The expansion force under thermal runaway is expressed as follows: Internal pressure changes Using the Attoine equation to obtain the internal electrolyte vapor pressure In the formula, p n Indicates the internal pressure, R const is the ideal gas constant, T is the average temperature of the battery area, V void is the void volume in the sealed cell, p dmc is the electrolyte vapor pressure; The effect of temperature on expansion force is described by the following formula: e th =α*(T)*(TT ref ) F h =e th *E In the formula, ε th is the thermal strain, α is the thermal expansion coefficient, T is the average temperature of the battery area, T ref is the initial reference temperature, F h is the thermal expansion pressure, E is the elastic modulus; Finally, the average expansion force P of the battery surface is calculated all =p n +p dmc , F all =P all S+F h , Where P all is the total pressure, S is the large surface area of ​​the battery, F all It is the expansion force under thermal runaway state, that is, the average pressure F on the battery surface during thermal runaway.

7. The model-based battery thermal runaway early warning method according to claim 1, characterized in that: The battery operation safety threshold value X in step S3 t It includes the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate, and specifically includes the following steps: Through the electrochemical-thermal and electrochemical-expansion force coupling model established in step S1, the relationship between the battery temperature, voltage, and expansion force changes and the peak value under safe working conditions are studied to obtain the battery threshold evaluation indicators under normal conditions, namely, the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt; through the thermal runaway-expansion force coupling model established in step S2, the battery temperature, temperature rise rate, expansion force, and expansion force change rate under thermal runaway conditions are studied to obtain early thermal runaway indicators, including the starting temperature T2 generated by battery self-heating, the battery spray valve temperature T3, the expansion force safety peak threshold F1, the expansion force danger peak F2, and the battery temperature rise rate soaring node; The battery safety temperature peak T1 and the normal expansion force change rate dF / dt are calibrated as the safety threshold X1, indicating the occurrence of abnormal conditions. The starting temperature T2 generated by the battery self-heating and the expansion force safety peak threshold F1 are calibrated as the safety threshold X2, indicating that the battery enters the early stage of irreversible thermal runaway. The battery valve temperature T3 and the pressure danger peak F2 are calibrated as the safety threshold X3, indicating that the battery is about to enter the thermal runaway outbreak period. The battery temperature rise rate increases exponentially as the safety threshold X4, indicating that the battery has entered thermal runaway.

8. The model-based battery thermal runaway early warning method according to claim 1, characterized in that: The step S4 is based on the battery multi-level safety threshold X determined in step S3. t Carry out battery thermal runaway warning, specifically including the following steps: When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased; When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again; When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance; When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

9. A system for implementing the model-based battery thermal runaway early warning method according to any one of claims 1 to 8, characterized in that: It includes data acquisition module, threshold setting module and safety warning module; The data acquisition module is used to obtain characteristic parameters of batteries in the battery pack; The threshold setting module is used to establish an electrochemical-thermal and electrochemical-expansion force coupling model, obtain the temperature change curve, temperature rise rate curve, voltage curve and expansion force curve of the battery under different working conditions, establish a thermal runaway-expansion force coupling model, obtain the time-temperature curve, time-temperature rise rate curve, time-expansion force curve, time-expansion force change rate curve of the battery in the thermal runaway stage, and determine the battery multi-level safety threshold X according to the obtained curves t ; The safety warning module is used to provide a thermal runaway warning based on the collected data according to the working safety threshold Xt set by the threshold setting module.

10. The system of the model-based battery thermal runaway early warning method according to claim 9, characterized in that: The data acquisition module includes a sensor, which is connected to the out-of-control warning module; the sensor includes a voltage sensor, a temperature sensor and a pressure sensor; the voltage sensor is used to collect the battery voltage in real time, the temperature sensor is used to collect the battery center temperature in real time, and the pressure sensor is used to collect the average pressure F on the battery surface; The threshold setting module obtains the working safety threshold value X set by the curve according to the model t Including the safety threshold value X1 corresponding to the battery safety temperature peak value T1 and the normal expansion force change rate dF / dt, the safety threshold value X2 corresponding to the starting temperature T2 of the battery self-heating and the expansion force safety peak value threshold F1, the safety threshold value X3 corresponding to the battery spray valve temperature T3 and the expansion force dangerous peak value F2, and the safety threshold value X4 corresponding to the exponential growth of the battery temperature rise rate; The safety warning module takes specific measures to warn and alarm: When the battery status reaches the threshold value X1, the battery status is self-checked and the heat dissipation power of the battery thermal management in the relevant area is increased; When the battery status reaches the threshold value X2, the battery stops working and the heat dissipation power of the battery thermal management in the relevant area is increased again; When the battery status reaches the threshold value X3, the battery isolation device is activated, and the heat dissipation power of the battery thermal management in the relevant area is increased, and fire prevention measures are prepared in advance; When the battery temperature reaches the threshold value X4, it is determined that the battery has thermal runaway and fire-fighting measures are initiated.

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