CN114996932A - Modeling method of lithium ion battery overcharge thermal runaway model - Google Patents

Abstract

The invention discloses a modeling method of a lithium ion battery overcharge thermal runaway model, which comprises the following steps: acquiring a preset ambient temperature, a preset current multiplying power, a modeling structure and geometric size parameters of a first lithium ion battery; carrying out overcharge thermal runaway test on the first lithium ion battery to obtain voltage curves and temperature curves of the first lithium ion battery at different moments under an overcharge working condition; establishing an electrochemical quasi-two-dimensional model, a lumped thermal model and a total thermal abuse model of the first lithium ion battery, coupling the electrochemical quasi-two-dimensional model, the lumped thermal model and the total thermal abuse model, and calibrating the initial overcharge thermal runaway model by using voltage curves and temperature curves of the first lithium ion battery at different moments to obtain a final overcharge thermal runaway model of the electrochemical-thermal abuse coupling of the first lithium ion battery. The invention can more accurately simulate the overcharge thermal runaway behavior of the lithium ion battery and obtain the change rule of voltage and temperature in the overcharge thermal runaway process.

Description

A modeling method for lithium-ion battery overcharge thermal runaway model

technical field

The invention belongs to the technical field of lithium ion batteries, and more particularly, relates to a modeling method of a lithium ion battery overcharge thermal runaway model and a lithium ion battery.

Background technique

Lithium-ion batteries are widely used in pure electric vehicles and hybrid vehicles due to their high energy density, good power performance, and long service life. However, with the widespread application of lithium-ion batteries, their safety issues are particularly important. In recent years, thermal runaway accidents of the battery system of electric vehicles have emerged in an endless stream, especially the thermal runaway risk of high-capacity power batteries under abuse conditions will greatly increase.

Overcharging is a very easy form of abuse. It means that the battery continues to be charged with current after reaching the charging cut-off voltage. This extremely dangerous high nuclear power state is extremely dangerous and even causes the battery to explode. During the overcharging process, a series of side reactions occur inside the battery. These side reactions release a lot of heat, causing the battery temperature to rise rapidly, eventually triggering the thermal runaway of the battery. The thermal runaway process is usually accompanied by the occurrence of fire, explosion and other phenomena, which brings great adverse effects on personal safety. However, there is no relevant research on the thermal runaway of the battery due to the release of a large amount of heat by the side reaction.

Therefore, it is expected to invent a modeling method for the thermal runaway model of lithium-ion battery overcharge, which can fill the gap in the research on the thermal runaway of the battery caused by the heat released by the side reaction in the existing technology. Using a quasi-two-dimensional electrochemical model and considering internal changes There are many side reaction mechanisms to study the blank of the overcharge thermal runaway model.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a modeling method for the thermal runaway model of lithium ion battery overcharge, so as to fill the gap in the research on battery thermal runaway caused by the heat released by the side reaction in the prior art, using a quasi-two-dimensional electrochemical model and considering More side reaction mechanisms inside the gaps in the overcharge thermal runaway model.

In order to achieve the above purpose, the present invention provides a modeling method for a lithium-ion battery overcharge thermal runaway model, including:

Step 1: obtain the preset ambient temperature, preset current rate, modeling structure and geometric size parameters of the first lithium-ion battery;

Step 2: Perform an overcharge thermal runaway test on the first lithium-ion battery according to the preset ambient temperature and the preset current rate, and obtain the voltage of the first lithium-ion battery at different times under the overcharge condition curve and temperature curve;

Step 3: Establish an electrochemical quasi-two-dimensional model, a lumped thermal model, and a lumped thermal abuse model of the first lithium-ion battery, and based on the modeling structure and geometric size parameters of the first lithium-ion battery, coupling the electrochemical quasi-two-dimensional model, the lumped thermal model, and the lumped thermal abuse model to obtain an initial overcharge thermal runaway model of the first lithium-ion battery coupled electrochemical-thermal-thermal abuse;

Step 4: Use the voltage curve and temperature curve of the first lithium-ion battery at different times to calibrate the initial overcharge thermal runaway model to obtain the final electrochemical-thermal-thermal abuse coupling of the first lithium-ion battery. Overcharge thermal runaway model.

Optionally, the modeling method further includes performing the following steps after the step 2:

Step 2': Obtain a second lithium ion battery with the same specification and model as the first lithium ion battery, and obtain a relationship curve between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions and the second lithium ion battery The relationship between the negative electrode voltage of the battery and the stoichiometric number of lithium ions.

Optionally, the step 2' includes:

Step 21: Obtain the second lithium-ion battery with the same specification and model as the first lithium-ion battery;

Step 22: adjusting the second lithium ion battery to a zero electric state, and disassembling the second lithium ion battery, to obtain the positive pole piece and the negative pole piece of the second lithium ion battery;

Step 23: making the positive electrode pieces into a preset number of positive button batteries, and making the negative electrode pieces into the preset number of negative button batteries;

Step 24: Select one of the positive button batteries and one of the negative button batteries that meet the preset conditions from the preset number of the positive button batteries and the negative button batteries. The positive button battery and the negative button battery are subjected to an overcharge test, and the relationship curve between the positive voltage of the second lithium ion battery and the stoichiometric number of lithium ions and the negative voltage of the second lithium ion battery and the lithium ion chemistry are obtained. The relationship curve of the measurement number.

Optionally, the electrochemical quasi-two-dimensional model is established by the following steps:

establishing an initial electrochemical quasi-two-dimensional model of the first lithium-ion battery;

The relationship curve between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions and the relationship curve between the negative electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions are imported into the initial electrochemical quasi-two-dimensional In the model, the electrochemical quasi-two-dimensional model is obtained.

Optionally, the initial electrochemical quasi-two-dimensional model is established by the following steps:

Two dimensions are set, one dimension is the spherical coordinate system established along the radius direction of the positive and negative electrode active material particles of the first lithium ion battery, and the other dimension is established along the thickness direction of the current collector, pole piece, and separator of the battery x coordinate system, wherein, the positive and negative active material particles of the first lithium ion battery are materials that participate in redox reactions in the electrodes;

Based on the material conservation law and Fick's law, the lithium ion solid phase concentration and the lithium ion liquid phase concentration of the first lithium ion battery are calculated, and based on the lithium ion solid phase concentration and the lithium ion liquid phase concentration, a The lithium ion concentration field of the solid-liquid two-phase of the first lithium ion battery;

Based on Ohm's law under the condition of charge conservation, the lithium ion solid-phase potential of the first lithium ion battery is calculated, and based on Ohm's law and the concentrated solution theory, the lithium ion liquid phase potential of the first lithium ion battery is calculated, and establishing a solid-liquid two-phase potential distribution of the first lithium ion battery based on the lithium ion solid phase potential and the lithium ion liquid phase potential;

Based on the Butler-Volmer equation of the delithiation/intercalation reaction on the surface of the electrode active material particles, the local charge current density of the first lithium ion battery is calculated, and based on the local charge current density, the first lithium ion battery is established. Electrode electrochemical reaction equation;

Based on the set two dimensions, the lithium ion concentration field, the potential distribution of the solid-liquid two-phase phase, and the electrode electrochemical reaction equation, the initial electrochemical quasi-two-dimensional model is established.

Optionally, the lumped thermal model is established by the following steps:

respectively calculating the reversible heat, polarization heat, Joule heat and heat dissipated to the environment by the first lithium-ion battery during overcharging;

Based on the reversible heat, the polarization heat, the Joule heat, and the heat dissipated into the environment by the battery, a battery heat conservation equation is obtained;

Based on the battery heat conservation equation, the lumped heat model is established.

Optionally, the lumped heat abuse model is established by the following steps:

Calculate the reactant content of each side reaction and the heat generated by each side reaction in the overcharge thermal runaway process of the first lithium-ion battery respectively;

The lumped heat abuse model is established based on the reactant content of each of the side reactions and the heat generated by each of the side reactions.

Optionally, the side reactions include SEI film decomposition reaction, negative electrode material decomposition reaction, positive electrode material decomposition reaction, diaphragm material decomposition, electrolyte oxidative decomposition and reaction of lithium precipitated on the negative electrode surface and electrolyte.

Optionally, the coupling of the electrochemical quasi-two-dimensional model, the lumped thermal model and the lumped thermal abuse model comprises:

Applying the electrochemical quasi-two-dimensional model to calculate and obtain the heat source and lithium deposition current of the first lithium-ion battery, applying the lumped thermal model to calculate the temperature of the first lithium-ion battery, and applying the lumped The heat abuse model calculates the heat source of each of the side reactions and the reactant content of each of the side reactions of the first lithium-ion battery;

The heat source and lithium evolution current of the first lithium-ion battery calculated by the electrochemical quasi-two-dimensional model, the temperature calculated by the lumped thermal model, and each of the side reactions calculated by the lumped heat abuse model The heat source and the reactant content of each of the side reactions are bidirectionally coupled to obtain an overcharge thermal runaway model of the electrochemical-thermal-thermal abuse coupling of the first lithium-ion battery.

Optionally, the geometric dimension parameters include height parameters, width parameters and thickness parameters of the first lithium-ion battery.

The beneficial effects of the present invention are:

The modeling method of the lithium ion battery overcharge thermal runaway model of the present invention takes into account that the current state and the internal electrochemical reaction process of the battery change with the change of the overcharge degree during the overcharge process of the battery. The two-dimensional model, the lumped thermal model and the lumped thermal abuse model are coupled with each other, which can more accurately simulate the overcharge thermal runaway behavior of lithium-ion batteries, and obtain the variation law of voltage and temperature during the overcharge thermal runaway process. Security provides instructive directions.

Other features and advantages of the present invention will be described in detail in the detailed description that follows.

Description of drawings

The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of the exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the exemplary embodiments of the present invention. same parts.

FIG. 1 shows a flowchart of a method for modeling a lithium-ion battery overcharge thermal runaway model according to an embodiment of the present invention.

2 shows a schematic diagram of a first lithium-ion battery electrochemical-thermal-thermal abuse coupled initial overcharge thermal runaway model of a method for modeling a lithium-ion battery overcharge thermal runaway model according to an embodiment of the present invention .

3 shows a schematic diagram of the relationship between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions in a method for modeling a lithium ion battery overcharge thermal runaway model according to an embodiment of the present invention.

4 shows a schematic diagram of the relationship between the negative electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions in a method for modeling a lithium ion battery overcharge thermal runaway model according to an embodiment of the present invention.

FIG. 5 shows a comparison diagram between the results of simulation calculation and the experimental results using a modeling method for an overcharge thermal runaway model of a lithium ion battery according to an embodiment of the present invention.

FIG. 6 shows a schematic diagram of the result of simulation calculation by applying a modeling method of a lithium-ion battery overcharge thermal runaway model according to an embodiment of the present invention.

Detailed ways

Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

A method for modeling a lithium-ion battery overcharge thermal runaway model according to the present invention includes:

Step 1: obtain the preset ambient temperature, preset current rate, modeling structure and geometric size parameters of the first lithium-ion battery;

Step 2: performing an overcharge thermal runaway test on the first lithium-ion battery according to a preset ambient temperature and a preset current rate, to obtain voltage curves and temperature curves of the first lithium-ion battery at different times under an overcharge condition;

Step 3: Establish an electrochemical quasi-two-dimensional model, a lumped thermal model and a lumped thermal abuse model of the first lithium-ion battery, and based on the modeling structure and geometric parameters of the first lithium-ion battery, the electrochemical quasi-two-dimensional The model, the lumped thermal model and the lumped thermal abuse model are coupled to obtain the initial overcharge thermal runaway model of the electrochemical-thermal-thermal abuse coupling of the first lithium-ion battery;

Step 4: Use the voltage curve and temperature curve of the first lithium-ion battery at different times to calibrate the initial overcharge thermal runaway model, and obtain the final overcharge thermal runaway model of the first lithium-ion battery coupled with electrochemical-thermal-thermal abuse.

Specifically, the modeling method of the lithium-ion battery overcharge thermal runaway model of the present invention takes into account that the current state and the internal electrochemical reaction process of the battery change with the change of the overcharge degree during the overcharge process of the battery. The electrochemical quasi-two-dimensional model, the lumped heat model and the lumped heat abuse model are coupled with each other, which can more accurately simulate the thermal runaway behavior of lithium-ion batteries, and obtain the variation law of voltage and temperature during the thermal runaway process of overcharge, as Provide guiding directions for improving the safety of batteries.

Further, on the basis of the classical quasi-two-dimensional (P2D) electrochemical model of lithium-ion batteries, the present invention introduces a lumped heat abuse model and a lumped parameter thermal model of thermal runaway side reactions under the condition of battery overcharge, which are respectively used Simulate the change degree of the side reaction of the battery during the overcharge process and the temperature change of the battery itself during the thermal runaway process. A model composed of charge conservation and material conservation; the electrochemical kinetics uses the Butler-Volmer equation to calculate local charge transfer to describe the intercalation and deintercalation process of lithium ions on the surface of battery electrode active material particles; the charge conservation is determined by following Ohm's law. The solid phase potential distribution in the positive and negative active materials and the liquid phase potential distribution in the lithium ion transport process following the concentrated solution theory; The material conservation of the solid-liquid two-phase lithium ion concentration field in the spherical coordinate system; the side reactions in the overcharge thermal runaway process considered by the lumped heat abuse model include: SEI film decomposition reaction, anode material decomposition reaction, cathode material decomposition reaction , the decomposition reaction of the diaphragm material, the oxidative decomposition of the electrolyte, and the reaction between the lithium precipitated on the surface of the negative electrode and the electrolyte. The lumped parameter thermal model includes two parts of heat generation and heat dissipation of the battery. The heat generation of the battery includes three parts: reversible heat, polarization heat and Joule heat. The heat dissipation of the battery includes radiation and convection.

In one example, the modeling method further includes performing the following steps after step 2:

Step 2': Obtain a second lithium ion battery with the same specification and model as the first lithium ion battery, and obtain a relationship curve between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions and the negative electrode voltage of the second lithium ion battery and lithium ion battery. A plot of the stoichiometric number of ions.

In one example, step 2' includes:

Step 21: Obtain a second lithium-ion battery with the same specification and model as the first lithium-ion battery;

Step 22: adjusting the second lithium ion battery to a zero electric state, and disassembling the second lithium ion battery, to obtain the positive pole piece and the negative pole piece of the second lithium ion battery;

Step 23: making the positive pole pieces into a preset number of positive button batteries, and making the negative pole pieces into a preset number of negative button batteries;

Step 24: Select a positive button battery and a negative button battery that meet the preset conditions from the preset number of positive button batteries and negative button batteries, and perform an overcharge test on the selected positive button battery and negative button battery respectively. , to obtain a relationship curve between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions and a relationship curve between the negative electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions.

Specifically, a second lithium ion battery is provided, the model of the second lithium ion battery is the same as that of the first lithium ion battery, the second lithium ion battery is disassembled, and each preferred lithium ion battery including the positive and negative electrodes of the second lithium ion battery is prepared respectively. Six button batteries, two positive and negative button batteries with relatively good consistency were selected from the six button batteries, and the two button batteries were overcharged to obtain the positive voltage and lithium ion chemical during the overcharging process. The number of counts and the relationship between the negative electrode voltage and the stoichiometric number of lithium ions.

Further, the way of obtaining the positive electrode and the negative electrode is as follows: making a positive and negative button battery in a glove box; the positive electrode of the positive button battery is the positive electrode material of the second lithium ion battery, and the negative electrode is metal lithium; The positive electrode of the negative button battery is the negative electrode material of the second lithium ion battery, and the negative electrode is metal lithium.

In one example, an electrochemical quasi-2D model is built by the following steps:

establishing the initial electrochemical quasi-2D model of the first lithium-ion battery;

The relationship between the positive electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions and the relationship curve of the negative electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions are imported into the initial electrochemical quasi-two-dimensional model, and the electrochemical results are obtained. Quasi-2D model.

In one example, an initial electrochemical quasi-2D model is built by the following steps:

Set two dimensions, one dimension is the spherical coordinate system established along the radial direction of the positive and negative active material particles of the first lithium ion battery, and the other dimension is the x coordinate established along the thickness direction of the current collector, pole piece, and separator of the battery system, wherein the positive and negative active material particles of the first lithium ion battery are materials that participate in redox reactions in the electrodes;

Based on the material conservation law and Fick's law, the lithium ion solid phase concentration and lithium ion liquid phase concentration of the first lithium ion battery are calculated, and based on the lithium ion solid phase concentration and lithium ion liquid phase concentration, the first lithium ion battery solid state Lithium ion concentration field in the liquid and two phases;

Based on Ohm's law under the condition of charge conservation, the lithium-ion solid-phase potential of the first lithium-ion battery was calculated, and based on Ohm's law and concentrated solution theory, the lithium-ion liquid-phase potential of the first lithium-ion battery was calculated, and based on the lithium-ion battery Solid-phase potential and lithium-ion liquid-phase potential to establish the solid-liquid two-phase potential distribution of the first lithium-ion battery;

Based on the Butler-Volmer equation of the delithiation/intercalation reaction on the surface of the electrode active material particles, the local charge current density of the first lithium ion battery is calculated, and based on the local charge current density, the electrode electrochemical reaction equation of the first lithium ion battery is established;

Based on the set two dimensions, lithium ion concentration field, solid-liquid two-phase potential distribution and electrode electrochemical reaction equation, an initial electrochemical quasi-two-dimensional model is established.

Specifically, a spherical coordinate system is established with the center of the positive and negative active material particles of the lithium ion battery as the origin, and the positive and negative active material particles of the lithium ion battery are the materials participating in the redox reaction in the electrode; according to the material conservation, the battery solid-liquid two-phase is established In the lithium ion concentration field, the solid phase lithium ion concentration follows Fick's second law, and the liquid phase lithium ion concentration change includes the lithium ion diffusion caused by the concentration gradient, and the lithium ion migration under the action of the liquid phase electric field; according to the charge conservation condition The solid-liquid two-phase potential distribution of the battery is established according to Ohm's law and concentrated solution theory under the following conditions; the battery solid-liquid two-phase electrochemical kinetic equation is established according to the Butler-Volmer equation of the de/lithium intercalation reaction on the surface of the electrode active material particles, which is also called the electrode electric field. chemical reaction equation.

In one example, a lumped thermal model is built with the following steps:

Calculate the reversible heat, polarization heat, Joule heat and heat dissipated from the battery to the environment during the overcharge process of the first lithium-ion battery, respectively;

Based on the reversible heat, polarization heat, Joule heat and the heat dissipated from the battery to the environment, the battery heat conservation equation is obtained;

Based on the battery heat conservation equation, a lumped heat model is established.

In one example, a lumped heat abuse model is built with the following steps:

Calculate the reactant content of each side reaction and the heat generated by each side reaction in the overcharge thermal runaway process of the first lithium-ion battery respectively;

Based on the reactant content of each side reaction and the heat generated by each side reaction, a lumped heat abuse model is established.

In one example, the side reactions include SEI film decomposition reaction, negative electrode material decomposition reaction, positive electrode material decomposition reaction, separator material decomposition, electrolyte oxidative decomposition, and reaction of lithium precipitated on the negative electrode surface with the electrolyte.

Specifically, in practical applications, preferably, the side reaction is at least one of the SEI film decomposition reaction, the negative electrode material decomposition reaction, the positive electrode material decomposition reaction, the diaphragm material decomposition, the oxidative decomposition of the electrolyte solution, and the reaction between the lithium precipitated on the surface of the negative electrode and the electrolyte solution. one.

In one example, coupling an electrochemical quasi-2D model, a lumped heat model, and a lumped heat abuse model includes:

The heat source and lithium-evolution current of the first lithium-ion battery are calculated using the electrochemical quasi-two-dimensional model, the temperature of the first lithium-ion battery is calculated using the lumped thermal model, and the first lithium-ion battery is calculated using the lumped heat abuse model. The heat source of each side reaction and the reactant content of each side reaction;

The heat source and lithium evolution current of the first lithium-ion battery calculated by the electrochemical quasi-2D model, the temperature calculated by the lumped thermal model, and the heat source of each side reaction and the reactant of each side reaction calculated by the lumped heat abuse model The content is bidirectionally coupled, and the overcharge thermal runaway model of the electrochemical-thermal-thermal abuse coupling of the first lithium-ion battery is obtained.

Specifically, the modeling method of the present invention considers that the current state of the battery and the internal electrochemical reaction process change with the degree of overcharge during the overcharge process; In the above, the control equation for the heat generation of the battery side reaction is introduced to represent the heat generated by the side reaction heat generation of the battery during the thermal runaway process; then the lumped thermal model is used to simulate the temperature change of the battery during the overcharge process; Simulation calculation can quantitatively analyze the progress of each side reaction in the process of thermal runaway of lithium-ion battery overcharge, and at the same time predict the temperature and voltage changes of lithium-ion battery in the process of thermal runaway of overcharge, so as to monitor the safety state of the battery during the overcharge process. and provide guidance on reducing the risk of thermal runaway.

In one example, the geometric parameter includes a height parameter, a width parameter, and a thickness parameter of the first lithium-ion battery.

Example 1

As shown in Figure 1, a modeling method of a lithium-ion battery overcharge thermal runaway model includes:

Step 1: obtain the preset ambient temperature, preset current rate, modeling structure and geometric size parameters of the first lithium-ion battery;

Step 2: performing an overcharge thermal runaway test on the first lithium-ion battery according to a preset ambient temperature and a preset current rate, to obtain voltage curves and temperature curves of the first lithium-ion battery at different times under an overcharge condition;

Step 3: Establish an electrochemical quasi-two-dimensional model, a lumped thermal model and a lumped thermal abuse model of the first lithium-ion battery, and based on the modeling structure and geometric parameters of the first lithium-ion battery, the electrochemical quasi-two-dimensional The model, the lumped thermal model and the lumped thermal abuse model are coupled to obtain the initial overcharge thermal runaway model of the electrochemical-thermal-thermal abuse coupling of the first lithium-ion battery;

Step 4: Use the voltage curve and temperature curve of the first lithium-ion battery at different times to calibrate the initial overcharge thermal runaway model, and obtain the final overcharge thermal runaway model of the first lithium-ion battery coupled with electrochemical-thermal-thermal abuse.

Specifically, Fig. 2 shows a schematic diagram of the electrochemical-thermal-thermal abuse coupling model of the battery of the present invention, which can be understood as a coupling mode involving three modules of electrochemistry, heat and thermal abuse in the model. The coupling relationship of the three parts includes During the overcharge process, the heat source calculated by the electrochemical quasi-2D model, the lithium evolution current and the temperature calculated by the lumped heat model, the side reaction heat source and the content of side reactants calculated by the lumped heat abuse model; among them, the electrochemical quasi-2D model It is based on the electrochemical kinetics, charge and material conservation equations of solid and electrolyte phases, and provides the heat generated by the electrochemical reaction of the battery during use; the lumped heat model is used to solve the heat transfer behavior of the battery. Coupling of thermal abuse models to describe the behavior of side-reaction changes during thermal runaway of a battery during overcharge. The model can quantitatively analyze the progress of each side reaction during the thermal runaway process of lithium-ion battery overcharge, and at the same time predict the temperature and voltage changes of lithium-ion battery during the thermal runaway process of lithium-ion battery overcharge. Provides guidance on reducing the risk of thermal runaway.

Further, step 4 is further described in detail as follows:

First, a spherical coordinate system is established with the center of the active material particles of the positive and negative electrodes of the battery as the origin. Both the positive and negative electrodes of the battery are considered to be the superposition of the solid phase of the active material and the liquid phase of the electrolyte. The electrochemical P2D model is composed of 5 equations , describe the material distribution of the solid phase in the r direction, the potential distribution of the solid phase in the x direction, the material distribution of the liquid phase in the x direction, the potential distribution of the liquid phase in the x direction, and the electrochemical reaction rate at the two-phase interface, the following Introduce these equations separately:

1. Material conservation, including liquid-phase material conservation and solid-phase material conservation, the present invention not only considers the diffusion caused by the concentration gradient, but also considers the convection caused by the fluid motion and the electromigration caused by the electric field; Each material is represented by volume fraction, and the diffusion process of lithium ions in it follows Fick's second law. The mass conservation equation of lithium ions through electrodes and electrolytes can be described by Fick's law.

The lithium ion concentration cs of the solid phase satisfies:

where _Ds is the diffusion coefficient of solid phase Li ⁺ and r is the spherical particle coordinate.

And the lithium ion concentration c _e of the liquid phase satisfies:

where ε _e is the volume fraction of the electrolyte, _De ^eff is the effective diffusion coefficient of Li ⁺ in the liquid phase, t ⁺ is the migration number of Li ⁺ , j(x, t) is the volume current density, and F is the Faraday constant.

2. Charge conservation, that is, the electron transport of lithium ions in the solid phase and the ion transport conservation in the liquid phase. These two transports follow Ohm's law and concentrated solution theory respectively. Among them, the theory of concentrated solution follows the law that the concentration changes with the reaction of mass flow.

The solid-phase potential φ _s satisfies:

where σ _s ^eff is the solid-phase effective conductivity.

The liquid potential φ _e satisfies:

The first term is determined by Ohm's law, the second term is determined by the effect of ion-concentrated solution, σ _e ^eff is the effective conductivity of the liquid phase, R is the ideal gas constant, T is the temperature, and f is the electrolyte activity coefficient.

3. Electrochemical kinetics is the process of intercalation and deintercalation of lithium ions on the ionic surface of the electrode active material. It is necessary to calculate the local charge transfer. The local charge transfer current density j(x, t) is determined by the Butler-Volmer equation to describe the solid-liquid interface. The electrochemical reaction rate at

where i ₀ is the exchange current density of lithium ion intercalation and deintercalation reactions, α _a and α _c are the transfer coefficients of the anode and cathode, respectively, η is the local reaction overpotential, and α _s is the reaction specific surface area.

where k is the reaction rate constant of lithium ion insertion and extraction, c _s,max is the maximum lithium insertion concentration of the active material, c _s,e (x,t) is the lithium ion concentration on the surface of the electrode active material particle, U(x, t) is the open circuit voltage of the electrode.

The lumped parameter thermal model is used to solve the temperature distribution of the battery during the thermal runaway process of overcharging. The heat sources considered in the present invention include: the entropy change heat Q _rev produced by the reversible electrochemical reaction, the irreversible electrochemical polarization heat Q _pol , The irreversible Joule-Ohm heat Q _Ohm , the heat Q _side generated by the thermal runaway side reaction, and the heat Q _short generated by the large-scale internal short circuit of the battery. First, the energy conservation equation satisfied by the total heat Q _tot generated by the battery:

Q _tot =Q _rev +Q _pol +Q _Ohm +Q _side +Q _short (9)

Where m is the battery mass, C _p is the specific heat capacity of the cell, V _cell is the volume of the cell, h is the convective heat transfer coefficient, A _suf is the surface area of the cell, and _Tamb is the ambient temperature.

Q _pol = jη (11)

The bidirectional coupling between the electrochemical P2D model and the lumped parameter thermal model is based on the heat generation equation of the P2D model and the temperature field of the lumped parameter thermal model. The detailed description refers to the temperature-related reaction equation and lumped thermal model in the electrochemical model. Reaction couplings related to heat generation in . Among them, some electrochemical parameters in the electrochemical model should be related to temperature. These parameters include positive and negative reaction rate constant k, solid-phase diffusion coefficient D _s , which can be corrected by Arrhenius formula respectively, and the unified parameter K can be used for temperature correction. describe. The parameters related to the electrolyte in the electrochemical P2D model, including liquid-phase diffusion coefficient, liquid-phase conductivity, liquid-phase activity coefficient, and liquid-phase transfer number, are derived from the import of external measured data. The measured data are temperature and 2D interpolation of concentrations. The unified expression of the Arrhenius formula is as follows:

Among them, K _ref is the reference value at the reference temperature, and E _a is the activation energy corresponding to this parameter. Temperature correction helps to accurately simulate the concentration of active substances, current density, heat source, etc. inside the battery. The open circuit voltage U _eq of the electrode is related to the temperature T and the state of charge SOC, according to the Taylor series expansion:

The heat Q _side generated by the thermal runaway side reaction mainly comes from the lumped heat abuse model. The side reactions in the overcharge thermal runaway process considered in the present invention include: SEI film decomposition reaction, negative electrode material decomposition reaction, positive electrode material decomposition reaction, diaphragm The decomposition reaction, the oxidative decomposition of the electrolyte, and the reaction between the lithium precipitated on the surface of the negative electrode and the electrolyte. The expression of Q _side is shown in equation (15):

Q _side =Q _Li +Q _SEI +Q _an +Q _ca +Q _e +Q _sep (15)

where Q _Li is the heat production rate of the reaction between the lithium metal precipitated on the surface of the negative electrode and the electrolyte, Q _SEI is the heat production rate of the decomposition reaction of the SEI film, Q _an is the heat production rate of the decomposition reaction of the negative electrode material, and Q _ca is the decomposition reaction of the positive electrode material. The heat generation rate of , Q _e is the heat generation rate of the oxidative decomposition of the electrolyte, and Q _sep is the heat generation rate of the decomposition reaction of the diaphragm material.

The calculation formula of Q _Li is shown in formula (16), where H _Li is the energy released by the reaction of lithium metal per unit mass with the electrolyte, the unit is J/g, and R _Li is the rate of the reaction between lithium metal and the electrolyte, the unit is 1 /s. m _Li is the mass of lithium metal precipitated in a unit volume of cells, and the unit is kg/m^3.

Q _Li =H _Li *R _Li *m _Li (16)

where R _Li conforms to the Arrhenius formula, as shown in formula (17), where A _Li represents the frequency factor of the reaction between metal lithium and the electrolyte, in s ^-1 , and E _Li is the activation energy of the reaction, in J /mol, c _Li is the amount of the precipitated lithium substance, the unit is mol, c _e is the normalized concentration of the representative electrolyte, and k_Li is the proportionality coefficient of the lithium deposition reaction.

During the overcharging process, the amount of precipitated lithium metal follows the mass conservation equations shown in equations (18) and (19), where c _Li,0 is the initial amount of lithium metal.

i _Li is the lithium deposition current, which follows the Butler-Volmer equation, as shown in equation (20), where i ₀ is the lithium deposition exchange current, in A/m^2, and r _SEI is the SEI film internal resistance. The lithium evolution reaction occurs only when the surface potential of the negative electrode is lower than 0 V, that is, when _Van -I·r _SEI <0.

The calculation formula of Q _SEI is shown in formula (22), where H _SEI is the energy released by the total decomposition of the SEI film in the negative electrode per unit mass, in J/g, and R _SEI is the decomposition rate of the SEI film, in 1/s . m _an is the mass of the negative electrode material per unit volume, in kg/m^3.

Q _SEI = H _SEI · R _SEI · m _an (22)

R _SEI conforms to the Arrhenius formula, as shown in formula (23), where A _SEI represents the frequency factor of the SEI film decomposition reaction, in s ^-1 , E ^SEI is the activation energy of the reaction, in J/mol, c _SEI is the normalized concentration representing the SEI membrane.

The content of the SEI film follows the mass conservation equations shown in equations (24) and (25), where c _{SEI, 0} is the initial value of the normalized concentration of the SEI film, and the value ranges from 0 to 1. The reaction of lithium metal and electrolyte will generate a new SEI film, which has an influence on the content of the SEI film, and k _SEI is the influence coefficient. The decomposition of the SEI film will affect the SEI film impedance, as shown in formula (21), r _{SEI, 0} is the initial value of the impedance, k _{r, SEI} is the influence coefficient, the value range is 0-0.1.

The calculation formula of Q _an is shown in formula (26), where _Han is the energy released by the total decomposition of the negative electrode material per unit mass, in J/g, R _an is the decomposition rate of the negative electrode material, and m _an is the negative electrode of the battery cell per unit volume The mass of the material, in kg/m^3.

Q _an =H _an ·R _an ·man ₍ 26)

R _an is in accordance with the Arrhenius formula, as shown in formula (27), where A _an represents the frequency factor of the decomposition reaction of the negative electrode material, in s ^-1 , E _an is the activation energy of the reaction, in J/mol, c _an is the normalized concentration representing the negative electrode material. exp(c _SEI /c _{SEI, ref} ) characterizes the effect of SEI film thickness on the decomposition reaction of anode materials.

The content of the negative electrode material follows the mass conservation equations shown in equations (30) and (31), where can _{, 0} is the initial value of the normalized concentration of the negative electrode material.

The formula for calculating Q _ca is shown in formula (30), where H _ca is the energy released by the decomposition reaction of the positive electrode material per unit mass, in J/g, R _ca is the decomposition rate of the positive electrode material, and m _ca is the unit volume of the cell The mass of the positive electrode material, in kg/m^3.

Q _ca = H _ca · R _ca · m _ca (30)

R _ca conforms to the Arrhenius formula, as shown in formula (31), where A _ca is the frequency factor of the reaction in s ^-1 , E _ca is the activation energy of the reaction in J/mol, and c _ca is represents the normalized concentration of the cathode material.

The content of the positive electrode material follows the mass conservation equations shown in equations (32) and (33), where c_(ca, 0) is the initial value of the normalized concentration of the positive electrode material. The decomposition reaction of the electrolyte will consume part of the positive electrode material, and k _ca is the influence coefficient.

The calculation formula of Q _e is shown in formula (34), where He is the energy released by the oxidative decomposition of the electrolyte per unit mass, in J/g, _Re is the oxidative decomposition rate of the electrolyte _, and _me is the unit volume of the cell in the cell. The mass of the electrolyte, in kg/m^3.

Q _e =H _e ·R _e · _me (34)

_Re conforms to the Arrhenius formula, as shown in formula (35), where A _e represents the frequency factor of the oxidative decomposition reaction of the electrolyte, in s ^-1 , and E _e is the activation energy of the reaction, in J/mol , c _e represents the normalized concentration of the electrolyte, α _e is the transfer constant, and _{Ve, ref} is the equilibrium potential of the electrolyte decomposition reaction. The oxidative decomposition of the electrolyte occurs only when the surface voltage of the positive electrode is greater than the equilibrium potential _Ve,ref , that is, when V _ca -V _e,ref >0.

During the overcharging process, the content of the electrolyte in the battery follows the mass conservation equations shown in equations (36) and (37), where c _e,0 is the initial value of the normalized concentration of the electrolyte. The consumption rate of the electrolyte is affected by three aspects: (1) its own oxidative decomposition rate R _e ; (2) the reaction rate _{ke, 1} · R _Li , _{ke, 1} of the metal lithium and the electrolyte is the influence coefficient; (3) The reaction rate _{ke, 2} ·R _an , _{ke, 2} of the negative electrode material and the electrolyte is an influence coefficient.

The calculation formula of Q _sep is shown in formula (38), where H _sep is the energy released by the decomposition of the diaphragm per unit mass, in J/g, R _sep is the decomposition rate of the diaphragm, m _sep is the mass of the diaphragm in the unit volume of the cell, The unit is kg/m^3.

Q _sep = H _sep · R _sep · m _sep (38)

R _sep conforms to the Arrhenius formula, as shown in Eq. (39), where A _sep represents the frequency factor of the membrane decomposition reaction in s ^-1 , E _sep is the activation energy of the reaction in J/mol, c _sep is the normalized concentration of the representative separator material.

The content of the diaphragm material follows the mass conservation equations shown in equations (40) and (41), where c _sep,0 is the initial value of the normalized concentration of the diaphragm material.

The formula for calculating Q _short is shown in Equation (42), where ΔH _short represents the total energy released by the short circuit, in J, Δt represents the average reaction time, which determines the reaction speed, and ∫ _Qshort (t)dt represents the energy that has occurred short circuit. The large-scale internal short circuit occurs only when the battery temperature T(t) is greater than the large-scale internal short circuit temperature T _short .

The specific effects of this embodiment are as follows:

Fig. 5 shows the comparison between the simulation calculation results of the first lithium-ion battery and the experimental results using the established mathematical model. In Fig. 5(a), the abscissa is the time, the ordinate is the full electric voltage, the dotted line represents the full electric voltage variation curve obtained by the experiment, and the solid line represents the full electric voltage obtained by the simulation calculation using the mathematical model established by the modeling method of the present invention. It can be seen from the electric voltage change curve that the solid line and the dotted line have a good degree of coincidence, indicating that the modeling method of the present invention can accurately simulate the change of the full electric voltage of the battery during the thermal runaway process of the battery overcharge; the horizontal line in Figure 5(b) The coordinate is the time, the ordinate is the negative voltage, the dotted line represents the negative voltage change curve obtained by the experiment, and the solid line represents the negative voltage change curve obtained by the simulation calculation using the mathematical model established by the modeling method of the present invention, and the solid line can be seen. The coincidence degree with the dotted line is good, indicating that the modeling method of the present invention can accurately simulate the change of the negative electrode voltage of the battery during the thermal runaway process of the battery overcharge. The results of Fig. 5(a) and (b) show that the mathematical model established by the modeling method of the present invention has better accuracy.

A positive and negative coin cell battery made of a second lithium ion battery of the same type as the first lithium ion battery is used to obtain the relationship curve between the positive and negative electrode voltage of the second lithium ion battery and the stoichiometric number of lithium ions, as shown in Figure 3 and shown in Figure 4. In Figure 3, the abscissa is the amount of lithium intercalation, and the ordinate is the positive electrode OCV. In Figure 4, the abscissa is the amount of lithium intercalation, and the ordinate is the negative electrode OCV. 6 is a simulation result obtained by overcharging at a rate of 2.5C under the condition that the cell is fully charged at 25°C and calculated by the modeling method of the present invention. The abscissa in Figure 6(a) is time, the ordinate on the left represents voltage, and the ordinate on the right represents temperature. It can be clearly seen from the figure that the highest overcharge voltage, The onset temperature and maximum temperature of thermal runaway and the moment when thermal runaway occurs. In Figure 6(b), the abscissa is the time, and the ordinate is the change in the content of each side reaction reactant in thermal runaway. From the figure, it can be seen that the progress of each side reaction change during the overcharge thermal runaway process. In Figure 6(c), the abscissa is the time, and the ordinate is the temperature rise rate. From the figure, we can see the change rule of the temperature rise rate of the cell in the process of overcharging and thermal runaway.

Various embodiments of the present invention have been described above, and the foregoing descriptions are exemplary, not exhaustive, and not limiting of the disclosed embodiments. Numerous modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims (10)

1. A modeling method of a lithium ion battery overcharge thermal runaway model is characterized by comprising the following steps:

step 1: acquiring a preset ambient temperature, a preset current multiplying power, a modeling structure and geometric size parameters of a first lithium ion battery;

step 2: carrying out overcharge thermal runaway test on the first lithium ion battery according to the preset environment temperature and the preset current multiplying power to obtain voltage curves and temperature curves of the first lithium ion battery at different moments under an overcharge working condition;

and step 3: establishing an electrochemical quasi-two-dimensional model, a lumped thermal model and a collective thermal abuse model of the first lithium ion battery, and coupling the electrochemical quasi-two-dimensional model, the lumped thermal model and the lumped thermal abuse model based on a modeling structure and geometric dimension parameters of the first lithium ion battery to obtain an initial overcharge thermal runaway model of the electrochemical-thermal abuse coupling of the first lithium ion battery;

and 4, step 4: and calibrating the initial overcharge thermal runaway model by using the voltage curve and the temperature curve of the first lithium ion battery at different moments to obtain a final overcharge thermal runaway model of the electrochemical-thermal abuse coupling of the first lithium ion battery.

2. The modeling method for the lithium ion battery overcharge thermal runaway model according to claim 1, further comprising performing the following steps after the step 2:

step 2': and acquiring a second lithium ion battery with the same specification and model as the first lithium ion battery, and acquiring a relation curve of the positive electrode voltage and the lithium ion stoichiometric number of the second lithium ion battery and a relation curve of the negative electrode voltage and the lithium ion stoichiometric number of the second lithium ion battery.

3. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 2,

the step 2' comprises the following steps:

step 21: acquiring the second lithium ion battery with the same specification and model as the first lithium ion battery;

step 22: adjusting the second lithium ion battery to a zero state, and disassembling the second lithium ion battery to obtain a positive pole piece and a negative pole piece of the second lithium ion battery;

step 23: manufacturing the positive pole pieces into a preset number of positive button batteries, and manufacturing the negative pole pieces into the preset number of negative button batteries;

step 24: and selecting one positive button cell and one negative button cell which meet preset conditions from the preset number of positive button cells and negative button cells, and respectively carrying out overcharge test on the selected positive button cell and the selected negative button cell to obtain a relation curve of the positive voltage and the lithium ion stoichiometric number of the second lithium ion battery and a relation curve of the negative voltage and the lithium ion stoichiometric number of the second lithium ion battery.

4. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 2,

establishing the electrochemical quasi-two-dimensional model by:

establishing an initial electrochemical quasi-two-dimensional model of the first lithium ion battery;

and importing the relation curve of the positive electrode voltage of the second lithium ion battery and the lithium ion stoichiometric number and the relation curve of the negative electrode voltage of the second lithium ion battery and the lithium ion stoichiometric number into the initial electrochemical quasi-two-dimensional model to obtain the electrochemical quasi-two-dimensional model.

5. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 4,

establishing the initial electrochemical quasi-two-dimensional model by:

setting two dimensions, wherein one dimension is a spherical coordinate system established along the radius direction of the positive and negative active material particles of the first lithium ion battery, and the other dimension is an x coordinate system established along the thickness direction of a current collector, a pole piece and a diaphragm of the battery, wherein the positive and negative active material particles of the first lithium ion battery are materials participating in oxidation-reduction reaction in the electrode;

calculating to obtain the lithium ion solid-phase concentration and the lithium ion liquid-phase concentration of the first lithium ion battery based on a material conservation law and a Fick law, and establishing a lithium ion concentration field of a solid-liquid two-phase of the first lithium ion battery based on the lithium ion solid-phase concentration and the lithium ion liquid-phase concentration;

calculating to obtain the lithium ion solid-phase potential of the first lithium ion battery based on the ohm law under the charge conservation condition, calculating to obtain the lithium ion liquid-phase potential of the first lithium ion battery based on the ohm law and the concentrated solution theory, and establishing the solid-liquid two-phase potential distribution of the first lithium ion battery based on the lithium ion solid-phase potential and the lithium ion liquid-phase potential;

calculating to obtain the local charge current density of the first lithium ion battery based on a Butler-Volmer equation of lithium removal/insertion reaction on the surface of electrode active material particles, and establishing an electrode electrochemical reaction equation of the first lithium ion battery based on the local charge current density;

and establishing the initial electrochemical quasi-two-dimensional model based on the two set dimensions, the lithium ion concentration field, the solid-liquid two-phase potential distribution and the electrode electrochemical reaction equation.

6. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 1,

establishing the lumped thermal model by:

respectively calculating reversible heat, polarization heat, joule heat and heat dissipated to the environment by the first lithium ion battery during the overcharge process;

obtaining a battery heat conservation equation based on the reversible heat, the polarization heat, the joule heat and the heat dissipated by the battery to the environment;

and establishing the lumped thermal model based on the battery heat conservation equation.

7. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 1,

establishing the collective thermal abuse model by:

respectively calculating the reactant content of each side reaction and the heat generated by each side reaction of the first lithium ion battery in the overcharge thermal runaway process;

establishing the collective thermal abuse model based on the reactant content of each of the side reactions and the amount of heat generated by each of the side reactions.

8. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 7,

the side reactions comprise SEI film decomposition reaction, negative electrode material decomposition reaction, positive electrode material decomposition reaction, diaphragm material decomposition, electrolyte oxidative decomposition and lithium precipitation on the surface of the negative electrode to react with the electrolyte.

9. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 1,

said coupling said electrochemical quasi-two-dimensional model, said lumped thermal model, and said lumped thermal abuse model comprises:

calculating by using the electrochemical quasi-two-dimensional model to obtain a heat source and a lithium analysis current of the first lithium ion battery, calculating by using the lumped thermal model to obtain the temperature of the first lithium ion battery, and calculating by using the lumped thermal abuse model to obtain a heat source of each side reaction of the first lithium ion battery and the reactant content of each side reaction;

and performing bidirectional coupling on the heat source and the lithium analysis current of the first lithium ion battery calculated by the electrochemical quasi-two-dimensional model, the temperature calculated by the lumped thermal model, and the heat source of each side reaction and the reactant content of each side reaction calculated by the lumped thermal abuse model to obtain an overcharge thermal runaway model of the electrochemical-thermal abuse coupling of the first lithium ion battery.

10. The modeling method of the lithium ion battery overcharge thermal runaway model according to claim 1,

the geometric parameters include a height parameter, a width parameter, and a thickness parameter of the first lithium ion battery.

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