CN116068447A - Method for predicting calendar aging and cyclic aging of lithium ion battery - Google Patents
Method for predicting calendar aging and cyclic aging of lithium ion battery Download PDFInfo
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Abstract
The application provides a method for predicting calendar aging and cyclic aging of a lithium ion battery, the method comprises the following steps: establishing an electrochemical model of the lithium battery; establishing a total heat collection model, constructing a one-dimensional electrochemical-thermal coupling model, and inputting battery model parameters; introducing a solid electrolyte interface growth aging side reaction and an active substance loss aging side reaction on the basis of an electrochemical-thermal coupling model, and adding aging parameters into the model; dividing grids of the one-dimensional electrochemical model and grids of the one-dimensional thermal model respectively; setting initial and stop conditions of an electrochemical-thermal coupling model of a coupling aging mechanism, setting working conditions, calculating, obtaining results of calendar aging and cyclic aging of the battery, and carrying out post-treatment analysis. According to the method, the design, the structure and the working condition of the battery are simulated through the electrothermal coupling model, capacity attenuation caused by different aging mechanisms in calendar and cyclic aging is obtained, and guidance is provided for the design and the application of the battery.
Description
Technical Field
The application relates to the technical field of lithium batteries, in particular to a method for predicting calendar aging and cyclic aging of a lithium ion battery based on an electrothermal coupling model.
Background
Along with the development of new energy technology and electronic technology, lithium ion batteries are widely applied to the aspects of new energy automobiles, energy storage, electronic products and the like. However, in practical application scenarios, capacity loss of the battery occurs due to aging, resulting in degradation of performance thereof. Batteries are not always operating under a constant operating condition, for example, electric vehicles, home electric vehicles have been stationary for up to about 90% of the time, and batteries experience calendar aging; and 10% of the time is in operation, the battery can be aged circularly during operation, and capacity loss of the battery can occur under both working conditions. Under complex operation conditions, the battery management system predicts the battery capacity, so that the user experience is affected and even the safety problem can occur. The service life and the safety of lithium batteries are main problems in the development trend of new energy sources, and a battery model capable of predicting calendar aging and cyclic aging is needed to be established.
The current model capable of predicting the aging of the lithium ion battery is not comprehensive enough, lacks comprehensive analysis on calendar aging and cyclic aging, and lacks coupling to various side reactions in the aging process of the battery. This will result in a significant error in the prediction of the battery's aging parameters after changing the battery's operating conditions.
Disclosure of Invention
The application provides a battery model construction method for predicting calendar aging and cyclic aging of a lithium ion battery under the condition of not changing battery aging parameters. Based on a battery aging mechanism causing calendar aging and cyclic aging of the battery, a reference electrochemical-thermal coupling mechanism model is fused, a battery model capable of predicting calendar aging and cyclic aging of the lithium battery is established, a battery calendar aging result and a cyclic aging result are calculated, battery capacity attenuation caused by different aging factors is decomposed, and a model foundation is provided for aging research and management of the lithium ion battery.
The application provides a method for predicting calendar aging and cyclic aging of a lithium ion battery, which comprises the following steps: (1) establishing an electrochemical model of a lithium ion battery; (2) Establishing a total heat collection model, simplifying the cell structure of the lithium ion battery, reserving key factors in the heat propagation process, coupling the electrochemical model, constructing a one-dimensional electrochemical-thermal coupling model, and inputting battery model parameters; (3) Adding an aging mechanism on the basis of the electrochemical-thermal coupling model, introducing a solid electrolyte interface growth aging side reaction and an active substance loss aging side reaction, and adding an aging parameter in the electrochemical-thermal coupling model; (4) Dividing the grids of the electrochemical model and the grids of the thermal model respectively; (5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model coupled with solid electrolyte interface growth and active material loss aging mechanisms, setting working conditions, calculating, obtaining battery calendar aging and cycle aging results, and carrying out post-treatment analysis.
In some embodiments of the present application, the step (3) of adding an aging mechanism comprises: and adding an aging mechanism of solid electrolyte interface growth and an active material loss aging mechanism in a negative electrode calculation domain in the electrochemical model.
In some embodiments of the present application, the solid electrolyte interface growth is a kinetically-diffusion-limited behavior, and the aging cause of active material loss is diffusion-induced stress of the lithium battery.
In some embodiments of the present application, the step (5) further includes: setting application conditions of the battery model.
In some embodiments of the present application, the initial conditions of the electrochemical-thermal coupling model are: the initial charge state is 1, the initial voltage is 4.2V, and the electrolyte concentration is 1000mol/m 3 The method comprises the steps of carrying out a first treatment on the surface of the The stopping conditions of the electrochemical-thermal coupling model are as follows: the time was 300 days and the cut-off voltage was 2.8V.
In some embodiments of the present application, the condition parameters of the working condition in step (5) are: the initial temperature is 25 ℃, 45 ℃, 60 ℃, 10 ℃ and the charge states are 0.5 and 0.9 respectively, and the parameters of the working conditions are combined.
In some embodiments of the present application, the condition parameters of the operating condition of the electrochemical-thermal coupling model are: the initial temperature is 25 ℃ and 45 ℃, the charge-discharge current multiplying power is 1/3C and 1C respectively, the average lithium battery charge states are 0.3, 0.5 and 0.8 respectively, and the discharge depths are 0.4 and 0.8 respectively.
In some embodiments of the present application, the lithium ion batteries have a negative electrode diffusion coefficient of 2.5X10, respectively -14 m 2 /s、5×10 -14 m 2 /s、1×10 -13 m 2 S; the thickness of the negative electrode is 24.35 multiplied by 10 respectively -6 m、48.7×10 -6 m、97.4×10 -6 m。
In some embodiments of the present application, the operating conditions of the electrochemical-thermal coupling model include a charge-discharge operating condition that takes a charge-rest-discharge-rest period, and the time taken for the battery to charge and discharge is equal to the rest time.
According to the method for predicting the calendar and the cyclic aging of the lithium battery based on the electrothermal coupling model, the electrochemical-thermal coupling model capable of predicting the calendar aging and the cyclic aging is constructed, and the characteristic mutual influence relation of electrochemical-thermal-stress-SEI inside the battery during the calendar aging and the cyclic aging is clearly understood; the electrochemical-thermal coupling model constructed by the method can be used for predicting aging attenuation of the battery under the standing or circulating working condition, and solves the problems related to electrochemical-thermal-stress of the battery under the standing or circulating working condition; the voltage, current, temperature and heat generation quantity of the battery can be calculated, and the heat generation space property and time-varying property caused by the concentration distribution of reactants and the current density distribution inside the battery core are reflected; the aging behaviors of the battery under different working conditions are analyzed, and the decomposition of capacity attenuation of different aging factors can be realized; and providing an optimization direction for battery design by using a multi-field coupling model result of the lithium battery, and providing theoretical basis and data support for management and optimization design of the lithium battery.
Drawings
The following figures describe in detail exemplary embodiments disclosed in the present application. Wherein like reference numerals refer to like structure throughout the several views of the drawings. Those of ordinary skill in the art will understand that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of the present application, other embodiments may equally well accomplish the intent of the invention in this application. It should be understood that the drawings are not to scale.
Wherein:
FIG. 1 is a flow chart of a method of predicting calendar aging and cyclic aging of a lithium ion battery according to the present application;
FIG. 2 is a graph comparing calendar aging simulation and experimental data of the present application;
FIG. 3 is a graph comparing the cyclic aging simulation and experimental data of the present application;
FIG. 4 is a graph showing the capacity fade caused by SEI growth at different solid phase diffusion coefficients according to the present application;
FIG. 5 is a graph showing capacity fade due to active material loss at different solid phase diffusion coefficients according to the present application;
fig. 6 is a graph of the capacity fade caused by SEI growth at different electrode thicknesses in the present application;
FIG. 7 is a graph showing capacity fade due to active material loss at different electrode thicknesses according to the present application;
FIG. 8 is a graph showing the capacity fade caused by SEI growth under the blend conditions of the present application;
fig. 9 is a graph showing the capacity fade caused by active material loss under the mixing regime of the present application.
Detailed Description
The following description provides specific applications and requirements to enable any person skilled in the art to make and use the teachings of the present application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the application. Thus, the present application is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims.
The following describes the technical scheme of the present application in detail with reference to examples and drawings. The method for predicting calendar aging and cyclic aging of the lithium ion battery comprises the following steps:
1) Establishing an electrochemical model of the lithium ion battery; 2) Establishing a total heat collection model, moderately simplifying the real structure of the battery core, reserving key factors in the heat propagation process, coupling an electrochemical model, constructing a one-dimensional electrochemical-thermal coupling model, and inputting parameters of a battery model; 3) Adding an aging mechanism on the basis of an electrochemical-thermal coupling model, introducing a Solid Electrolyte Interface (SEI) growth aging side reaction and an active material Loss (LAM) aging side reaction, and adding aging parameters into the model; 4) Dividing grids of the one-dimensional electrochemical model and grids of the one-dimensional thermal model respectively; 5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model coupling SEI growth and active material loss aging mechanisms, setting working conditions, calculating, obtaining results of battery calendar aging and cycle aging, and carrying out post-treatment analysis.
In the above scheme, in the step 1), the modeling theory of the electrochemical model is based on a P2D model proposed by Newman, and the ternary nickel cobalt lithium manganate (NCM)/graphite soft-pack battery with the rated capacity of 10Ah is taken as an object, the control equation is shown in table 1, and the symbols and the description are shown in table 2. The geometry is one-dimensional and is divided into a negative electrode, a diaphragm and a positive electrode. The positive and negative electrode portions each contain a particle dimension for calculating the lithium concentration distribution, stress, etc. in the particles.
The control equation of the thermal model in the step 2) is shown in table 1, and the symbols and the description are shown in table 2. The geometric structure of the thermal model is one-dimensional, the temperature and electrochemistry of the lithium ion battery are mutually influenced in the thickness direction of the battery, and the application range of the battery model is increased by introducing the thermal model.
Table 1 electrochemical and thermal model control equation
TABLE 2 sign illustration of electrochemical model and thermal model equation
In the step 3), an aging mechanism of SEI growth and an active material loss aging mechanism are added in a negative electrode calculation domain in an electrochemical model.
Further, SEI growth is a behavior limited by both kinetics-diffusion, the equilibrium potential of the SEI growth reaction is 0.4V, and the initial SEI film thickness is 5nm; the SEI growth is formulated as shown in Table 3, equation (9), to establish a function of the local current density and the SEI side reaction related parameters.
Further, the aging cause caused by the loss of the active material is the diffusion induced stress of the lithium battery, and the calculation equation of the diffusion induced stress is shown in the table 3 (15-16). The result of the loss of active material can be equivalent to the decrease in the volume fraction of the electrode containing active lithium, and the transient response control equation for the loss of active material is shown in table 3, equation (18). SEI growth and active loss aging model control equations are shown in Table 3, and symbols and descriptions are shown in Table 4.
Table 3SEI growth aging model and active loss aging model equation
Table 4 symbols and description
In the above scheme, in the step 4), after the electrochemical model is geometrically gridded, the information is as follows, 29 grid vertices, 28 grid cells, the cell length ratio is 0.956, and the grid length is 6.973 ×10-5m. After the geometric meshing of the thermal model, the information is as follows: 28 mesh vertices, 27 mesh cells, cell length ratio of 1.0, mesh length of 0.0085m.
In the above scheme, in the step 5), initial value parameters of an electrochemical-thermal coupling model of the fusion side reaction are set: initial state of charge, initial voltage, electrolyte concentration, initial temperature; the end condition parameters are: time, cutoff voltage; the working condition parameters are as follows: current multiplying power, average SOC, depth of discharge (DOD).
The method for predicting the aging of the lithium ion battery based on the electrochemical-thermal coupling model comprises the following steps:
(1) And establishing an electrochemical model of the lithium ion battery, and determining a one-dimensional geometric structure based on a P2D modeling theory, wherein the one-dimensional geometric structure comprises electrode dimensions and particle dimensions.
(2) The method comprises the steps of establishing a total heat collection model, moderately simplifying the real structure of a battery cell into a one-dimensional structure, coupling the one-dimensional structure with an electrochemical model, enabling a coupling mechanism of the electrochemical model and the thermal model to be an interface for heat generated by the electrochemical model to be used as a heat source to be supplied to the thermal model, enabling temperature to be used as a variable to be input to the electrochemical model, enabling heat-dependent parameters in the electrochemical model to be dynamically updated according to temperature input, constructing the one-dimensional electrochemical-thermal coupling model, and inputting battery model parameters.
(3) An aging mechanism is added on the basis of an electrochemical-thermal coupling model, an SEI growth aging side reaction and an active substance loss aging side reaction are introduced, the main reasons of calendar aging of the battery are SEI growth, the main reasons of cyclic aging include SEI growth and active substance loss, and aging parameters are added in the model. SEI growth is a behavior limited by dynamics and diffusion, the equilibrium potential of SEI growth reaction is 0.4V, and the initial SEI film thickness is 5nm; and analyzing the SEI growth in a formulated way, and substituting the SEI growth into a function analysis mode to analyze and calculate. The aging cause of the loss of the active material is diffusion induced stress of the lithium battery, and the result caused by the loss of the active material can be equivalent to the reduction of the volume fraction of the electrode containing active lithium, and the control equation is transient reaction.
(4) Dividing the grids of the one-dimensional electrochemical model and the one-dimensional thermal model respectively. The principle of balancing precision and calculation speed is followed, and a finer grid division mode is adopted.
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model coupling SEI growth and active material loss aging mechanisms, setting working conditions, calculating, obtaining results of battery calendar aging and cycle aging, and carrying out post-treatment analysis. Setting initial condition parameters: initial state of charge, initial voltage, electrolyte concentration, initial temperature; the end condition parameters are: time, cutoff voltage; the working condition parameters are as follows: current multiplying power, average SOC, depth of discharge.
(6) Setting a mixed working condition, circulating by taking charge-rest-discharge-rest as a cycle, wherein the charge-discharge time of the battery accounts for 50% of the total cycle time of the battery, and calculating to obtain an aging result of the battery.
Example 1:
(1) Establishing an electrochemical model of a lithium ion battery
And (3) equivalent the soft-packed battery into a negative electrode, a diaphragm and a positive electrode, drawing a one-dimensional geometric structure of the lithium battery, and building a pseudo two-dimensional electrochemical model of the lithium ion battery based on a lithium battery modeling control equation listed in table 1. The electrochemical model comprises three calculation domains, namely a positive electrode, a diaphragm and a negative electrode; four calculation points are included, negative electrode-negative current collector side, negative electrode-separator side, separator-positive electrode side, positive electrode-positive current collector side, respectively. The positive electrode and the negative electrode are homogenized porous electrodes. Setting boundary conditions of the negative current collector side, and selecting calculation points of the negative-negative current collector side; the electrochemical model was assigned the cell design parameters listed in table 5, and a one-dimensional cell electrochemical model was created.
(2) The thermal model adopts a total heat collection model, is coupled with an electrochemical model, and builds a one-dimensional electrochemical-thermal coupling model, and endows parameters to the battery model.
And adding a heat transfer model on the basis of the one-dimensional electrochemical model, wherein the thermal model comprises a calculation domain which is the thickness of the soft-packed battery and comprises two boundaries which are the upper side surface and the lower side surface of the soft-packed battery respectively. Selecting heat flux, setting heat transfer type as convection heat flux, and heat transfer coefficient as 25W/(m) 2 ·K)。
(3) And adding an aging mechanism on the basis of an electrochemical-thermal coupling model, and introducing SEI growth aging side reaction and active substance loss aging side reaction. And adding aging parameters to the model.
Adding SEI aging mechanism, adding ordinary differential equation in electrochemical model, adding table 3 Chinese (9) under distributed ordinary differential equation interface, adding equation 1 in electrochemical model, inputting table 3 Chinese (10), adding equation 2, inputting table 3 Chinese (11), adding equation 3, inputting table 3 Chinese (14), adding variable in electrochemical model, inputting table 3 Chinese (12-13), adding electrode reaction at negative electrode, inputting j SEI And (5) a relational expression.
Adding active substance loss mechanism, adding variable in electrochemical model, inputting into table 3 (15-17), adding ordinary differential equation, and adding table 3 (18) in distributed ordinary differential equation. Table 3 (20) is input to the variables of the negative electrode, and a constant negative electrode volume fraction is added to the model as a variable. Input in model parameters the parameters listed in table 6.
(4) Dividing the grids of the one-dimensional electrochemical model and the one-dimensional thermal model respectively.
The size of the dividing unit is selected to be finer, and the grids of the electrochemical model are divided, wherein the information is as follows, 29 grid vertexes, 28 grid units, the unit length ratio is 0.956, and the grid length is 6.973 multiplied by 10 -5 m. The mesh of the thermal model is partitioned as follows: 28 mesh vertices, 27 mesh cells, cell length ratio of 1.0, mesh length of 0.0085m.
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model for coupling SEI growth and active material loss aging mechanism, setting working conditions and calculating to obtain calendar aging and cycle aging results of the battery.
The initial value condition parameters of the electrochemical-thermal coupling model of the fusion side reaction are as follows: the initial charge state is 1, the initial voltage is 4.2V, and the electrolyte concentration is 1000mol/m 3 The method comprises the steps of carrying out a first treatment on the surface of the The end condition parameters are: the time is 300 days, and the cut-off voltage is 2.8V; the calendar working condition parameters are as follows: the initial temperature is 25 ℃, 45 ℃, 60 ℃, 10 ℃, and the states of charge are 0.5 and 0.9, and the parameters of the working conditions are combined. The parameters of the circulation working condition are as follows: the initial temperature is 25 ℃, 45 ℃, the charge-discharge current multiplying power is 1/3C, 1C, the average SOC is 0.3, 0.5, 0.8, the depth of discharge is 0.4, 0.8, and the parameters of the working conditions are combined.
And (3) checking that the model parameters are correctly set, calculating after the physical field coupling is correct, and processing and analyzing the data after the calculation is completed.
Fig. 2 shows calendar aging of the battery while it is resting at different temperatures and different SOC states. The built model has the capability of predicting calendar aging of the lithium battery at different temperatures and under different shelving SOC working conditions, and has certain precision. FIG. 2 shows the cyclic aging of the battery at different temperatures, different average SOCs, different DODs, and different rates of change conditions, with the ability to predict cyclic aging of the battery under different conditions.
Example 2:
(1) Establishing an electrochemical model of a lithium ion battery
And (3) equivalent the soft-packed battery into a negative electrode, a diaphragm and a positive electrode, drawing a one-dimensional geometric structure of the lithium battery, and building a pseudo two-dimensional electrochemical model of the lithium ion battery based on a lithium battery modeling control equation listed in table 1. The electrochemical model comprises three calculation domains, namely a positive electrode, a diaphragm and a negative electrode; four calculation points are included, negative electrode-negative current collector side, negative electrode-separator side, separator-positive electrode side, positive electrode-positive current collector side, respectively. The positive electrode and the negative electrode are homogenized porous electrodes. Setting boundary conditions of the negative current collector side, and selecting calculation points of the negative-negative current collector side; the electrochemical model was assigned the cell design parameters listed in table 5, and a one-dimensional cell electrochemical model was created.
(2) The thermal model adopts a total heat collection model, is coupled with an electrochemical model, and builds a one-dimensional electrochemical-thermal coupling model, and endows parameters to the battery model.
And adding a heat transfer model on the basis of the one-dimensional electrochemical model, wherein the thermal model comprises a calculation domain which is the thickness of the soft-packed battery and comprises two boundaries which are the upper side surface and the lower side surface of the soft-packed battery respectively. Selecting heat flux, setting heat transfer type as convection heat flux, and heat transfer coefficient as 25W/(m) 2 ·K)。
(3) And adding an aging mechanism on the basis of an electrochemical-thermal coupling model, and introducing SEI growth aging side reaction and active substance loss aging side reaction. And adding aging parameters to the model.
Adding an SEI aging mechanism, adding a normal differential equation in an electrochemical model, adding a formula (9) in a table 3 under a distributed normal differential equation interface, adding a formula (1) in the electrochemical model, inputting a formula (10) in the table 3, adding a formula (2), inputting a formula (11) in the table 3, adding a formula (3), inputting a formula (14) in the table 3, adding a variable in the electrochemical model, and inputting a formula (12-13) in the table 3. Adding electrode reaction at the negative electrode, input j SEI And (5) a relational expression.
Adding active substance loss mechanism, adding variable in electrochemical model, inputting into table 3 (15-17), adding ordinary differential equation, and adding table 3 (18) in distributed ordinary differential equation. Table 3 (20) is input to the variables of the negative electrode, and a constant negative electrode volume fraction is added to the model as a variable. The parameters listed in table 6 are input into the model parameters.
(4) Dividing the grids of the one-dimensional electrochemical model and the one-dimensional thermal model respectively.
The size of the dividing unit is selected to be finer, and the grids of the electrochemical model are divided, wherein the information is as follows, 29 grid vertexes, 28 grid units, the unit length ratio is 0.956, and the grid length is 6.973 multiplied by 10 -5 m. The mesh of the thermal model is partitioned as follows: 28 mesh vertices, 27 mesh cells, cell length ratio of 1.0, mesh length of 0.0085m.
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model for coupling SEI growth and active material loss aging mechanism, setting working conditions and calculating to obtain calendar aging and cycle aging results of the battery.
The initial value condition parameters of the electrochemical-thermal coupling model of the fusion side reaction are as follows: initial charge state of 0.1, electrolyte concentration of 1000mol/m 3 The end condition parameters are: the time is 300 days, and the cut-off voltage is 2.8V; the working condition parameters are as follows: the temperature is 25 ℃, the charge-discharge current multiplying power is 1/3C, the average SOC is 0.3, the depth of discharge is 0.4, and the negative electrode diffusion coefficient is 2.5X10 -14 m 2 /s、5×10 -14 m 2 /s、1×10 -13 m 2 And/s, carrying out parameter combination on the working conditions.
And (3) checking that the model parameters are correctly set, clicking for calculation after the physical field coupling is correct, and processing and analyzing the data after the calculation is completed.
As can be seen from fig. 4, changing the solid-phase diffusion coefficient of the anode has no obvious effect on the growth of the SEI; as can be seen from fig. 5, the larger the solid phase diffusion coefficient of the negative electrode, the smaller the capacity loss due to the loss of the active material.
Example 3
(1) Establishing an electrochemical model of a lithium ion battery
And (3) equivalent the soft-packed battery into a negative electrode, a diaphragm and a positive electrode, drawing a one-dimensional geometric structure of the lithium battery, and building a pseudo two-dimensional electrochemical model of the lithium ion battery based on a lithium battery modeling control equation listed in table 1. The electrochemical model comprises three calculation domains, namely a positive electrode, a diaphragm and a negative electrode; four calculation points are included, negative electrode-negative current collector side, negative electrode-separator side, separator-positive electrode side, positive electrode-positive current collector side, respectively. The positive electrode and the negative electrode are homogenized porous electrodes. Setting boundary conditions of the negative current collector side, and selecting calculation points of the negative-negative current collector side; the electrochemical model was assigned the cell design parameters listed in table 5, and a one-dimensional cell electrochemical model was created.
(2) The thermal model adopts a total heat collection model, is coupled with an electrochemical model, and builds a one-dimensional electrochemical-thermal coupling model, and endows parameters to the battery model.
Adding a heat transfer model based on a one-dimensional electrochemical model, wherein the thermal model comprises a calculation domain and is softThe thickness of the pack battery comprises two boundaries, namely an upper side surface and a lower side surface of the soft pack battery. Selecting heat flux, setting heat transfer type as convection heat flux, and heat transfer coefficient as 25W/(m) 2 ·K)。
(3) And adding an aging mechanism on the basis of an electrochemical-thermal coupling model, and introducing SEI growth aging side reaction and active substance loss aging side reaction. And adding aging parameters to the model.
Adding an SEI aging mechanism, adding a normal differential equation in an electrochemical model, adding a formula (9) in a table 3 under a distributed normal differential equation interface, adding a formula (1) in the electrochemical model, inputting a formula (10) in the table 3, adding a formula (2), inputting a formula (11) in the table 3, adding a formula (3), inputting a formula (14) in the table 3, adding a variable in the electrochemical model, and inputting a formula (12-13) in the table 3. Adding electrode reaction at the negative electrode, input j SEI And (5) a relational expression.
Adding active substance loss mechanism, adding variable in electrochemical model, inputting into table 3 (15-17), adding ordinary differential equation, and adding table 3 (18) in distributed ordinary differential equation. Table 3 (20) is input to the variables of the negative electrode, and a constant negative electrode volume fraction is added to the model as a variable. The parameters listed in table 6 are input into the model parameters.
(4) Dividing the grids of the one-dimensional electrochemical model and the one-dimensional thermal model respectively.
The size of the dividing unit is selected to be finer, and the grids of the electrochemical model are divided, wherein the information is as follows, 29 grid vertexes, 28 grid units, the unit length ratio is 0.956, and the grid length is 6.973 multiplied by 10 -5 m. The mesh of the thermal model is partitioned as follows: 28 mesh vertices, 27 mesh cells, cell length ratio of 1.0, mesh length of 0.0085m.
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model for coupling SEI growth and active material loss aging mechanism, setting working conditions and calculating to obtain calendar aging and cyclic aging results of the battery
The initial value condition parameters of the electrochemical-thermal coupling model of the fusion side reaction are as follows: initial charge state of 0.1, electrolysisMass concentration 1000mol/m 3 The end condition parameters are: the time is 300 days, and the cut-off voltage is 2.8V; the working condition parameters are as follows: the temperature is 25 ℃, the charge-discharge current multiplying power is 1/3C, the average SOC is 0.3, the depth of discharge is 0.4, and the thickness of the negative electrode is 24.35 multiplied by 10 -6 m、48.7×10 -6 m、97.4×10 -6 And m is respectively corresponding to 1/2 times of the electrode thickness, the normal electrode thickness and 2 times of the electrode thickness, and the parameters of the working conditions are combined.
And (3) checking that the model parameters are correctly set, clicking for calculation after the physical field coupling is correct, and processing and analyzing the data after the calculation is completed.
As can be seen from fig. 6, the larger the design thickness of the negative electrode, the larger the battery capacity degradation caused by the SEI growth; as can be seen from fig. 7, the larger the design thickness of the negative electrode, the larger the capacity loss due to the loss of the active material.
Example 4
(1) Establishing an electrochemical model of a lithium ion battery
And (3) equivalent the soft-packed battery into a negative electrode, a diaphragm and a positive electrode, drawing a one-dimensional geometric structure of the lithium battery, and building a pseudo two-dimensional electrochemical model of the lithium ion battery based on a lithium battery modeling control equation listed in table 1. The electrochemical model comprises three calculation domains, namely a positive electrode, a diaphragm and a negative electrode; four calculation points are included, negative electrode-negative current collector side, negative electrode-separator side, separator-positive electrode side, positive electrode-positive current collector side, respectively. The positive electrode and the negative electrode are homogenized porous electrodes. Setting boundary conditions of the negative current collector side, and selecting calculation points of the negative-negative current collector side; the electrochemical model was assigned the cell design parameters listed in table 5, and a one-dimensional cell electrochemical model was created.
(2) The thermal model adopts a total heat collection model, is coupled with an electrochemical model, and builds a one-dimensional electrochemical-thermal coupling model, and endows parameters to the battery model.
And adding a heat transfer model on the basis of the one-dimensional electrochemical model, wherein the thermal model comprises a calculation domain which is the thickness of the soft-packed battery and comprises two boundaries which are the upper side surface and the lower side surface of the soft-packed battery respectively. Selecting heat flux, setting heat transfer type as convection heat flux, and heat transfer systemThe number is 25W/(m) 2 ·K)。
(3) And adding an aging mechanism on the basis of an electrochemical-thermal coupling model, and introducing SEI growth aging side reaction and active substance loss aging side reaction. And adding aging parameters to the model.
Adding an SEI aging mechanism, adding a normal differential equation in an electrochemical model, adding a formula (9) in a table 3 under a distributed normal differential equation interface, adding a formula (1) in the electrochemical model, inputting a formula (10) in the table 3, adding a formula (2), inputting a formula (11) in the table 3, adding a formula (3), inputting a formula (14) in the table 3, adding a variable in the electrochemical model, and inputting a formula (12-13) in the table 3. Adding electrode reaction at the negative electrode, input j SEI And (5) a relational expression.
Adding active substance loss mechanism, adding variable in electrochemical model, inputting into table 3 (15-17), adding ordinary differential equation, and adding table 3 (18) in distributed ordinary differential equation. Table 3 (20) is input to the variables of the negative electrode, and a constant negative electrode volume fraction is added to the model as a variable. The parameters listed in table 6 are input into the model parameters.
(4) Dividing the grids of the one-dimensional electrochemical model and the one-dimensional thermal model respectively.
The size of the dividing unit is selected to be finer, and the grids of the electrochemical model are divided, wherein the information is as follows, 29 grid vertexes, 28 grid units, the unit length ratio is 0.956, and the grid length is 6.973 multiplied by 10 -5 m. The mesh of the thermal model is partitioned as follows: 28 mesh vertices, 27 mesh cells, cell length ratio of 1.0, mesh length of 0.0085m.
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model for coupling SEI growth and active material loss aging mechanism, setting working conditions and calculating to obtain calendar aging and cyclic aging results of the battery
The initial value condition parameters of the electrochemical-thermal coupling model of the fusion side reaction are as follows: initial charge state of 0.1, electrolyte concentration of 1000mol/m 3 The end condition parameters are: the time is 300 days, and the cut-off voltage is 2.8V; the working condition parameters are as follows: the temperature is 25 ℃ and 45 ℃, and the charge and discharge are carried outThe current multiplying power is 1/3C, the average SOC is 0.5, the discharging depth is 0.8, the charging and discharging working conditions are set to be charging-placing-discharging-placing as a period, the time for charging and discharging the battery is equal to the placing time, namely, the cycle working condition and the calendar working condition respectively account for 50% of the total time, and the cycle is carried out. And carrying out parameter combination on the working conditions.
And (3) checking that the model parameters are correctly set, clicking for calculation after the physical field coupling is correct, and processing and analyzing the data after the calculation is completed.
As can be seen from fig. 8, the degradation caused by cycling the battery SEI at 50% duty cycle is slightly greater than cycling the battery at 100% duty cycle; as can be seen from fig. 9, the degradation caused by the loss of the battery active material at the cycle 50% duty cycle is smaller than that of the battery at the cycle 100% duty cycle.
Table 5 cell design parameters
Table 6SEI and LAM model aging parameters
a represents the parameter obtained from the literature
Compared with the prior art, the application has the advantages that: an electrothermal coupling model capable of predicting calendar aging and cyclic aging is built, and the characteristic mutual influence relation of electrochemical-thermal-stress-SEI inside the battery during calendar aging and cyclic aging is clearly understood; the electrothermal coupling model constructed by the method can be used for predicting aging attenuation of the battery under the standing or circulating working condition, and solves the problem of electrochemistry-heat-stress correlation of the battery under the standing or circulating working condition; the voltage, current, temperature and heat generation quantity of the battery can be calculated, and the heat generation space property and time-varying property caused by the concentration distribution of reactants and the current density distribution inside the battery core are reflected; the aging behaviors of the battery under different working conditions are analyzed, and the decomposition of capacity attenuation of different aging factors can be realized; and providing an optimization direction for battery design by using a multi-field coupling model result of the lithium battery, and providing theoretical basis and data support for management and optimization design of the lithium battery.
It should be understood that the term "and/or" as used in this embodiment includes any or all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present.
It should also be understood that the "high temperature resistant" performance, "corrosion resistant" performance, and the like used in this embodiment refer to the high temperature requirement that the high temperature resistant performance of the electrolyte and the battery cell and the soft package lithium battery needs to reach, and the requirement of the electrolyte on the corrosion speed of the aluminum plastic film or the high temperature resistant organic glue, which are recognized by those skilled in the soft package lithium battery field.
It will be further understood that the terms "comprises," "comprising," "includes" or "including," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Claims (9)
1. A method for predicting calendar aging and cyclic aging of a lithium ion battery, comprising:
(1) Establishing an electrochemical model of the lithium ion battery;
(2) Establishing a total heat collection model, simplifying the cell structure of the lithium ion battery, reserving key factors in the heat propagation process, coupling the electrochemical model, constructing a one-dimensional electrochemical-thermal coupling model, and inputting battery model parameters;
(3) Adding an aging mechanism on the basis of the electrochemical-thermal coupling model, introducing a solid electrolyte interface growth aging side reaction and an active substance loss aging side reaction, and adding an aging parameter in the electrochemical-thermal coupling model;
(4) Dividing the grids of the electrochemical model and the grids of the thermal model respectively;
(5) Setting initial conditions and stop conditions of an electrochemical-thermal coupling model coupled with solid electrolyte interface growth and active material loss aging mechanisms, setting working conditions, calculating, obtaining battery calendar aging and cycle aging results, and carrying out post-treatment analysis.
2. The method of predicting calendar aging and cyclic aging of a lithium ion battery of claim 1, wherein said step (3) adding an aging mechanism comprises: and adding an aging mechanism of solid electrolyte interface growth and an active material loss aging mechanism in a negative electrode calculation domain in the electrochemical model.
3. The method of predicting calendar aging and cyclic aging of a lithium ion battery of claim 2, wherein the solid electrolyte interface growth is a kinetically-diffusion limited behavior and the aging cause of active material loss is diffusion induced stress of the lithium battery.
4. The method of predicting calendar aging and cyclic aging of a lithium ion battery of claim 3, wherein step (5) further comprises: setting application conditions of the battery model.
5. The method of predicting calendar aging and cyclic aging of a lithium ion battery of claim 4, wherein the electrochemical-thermal coupling model has initial conditions of: the initial charge state is 1, the initial voltage is 4.2V, and the electrolyte concentration is 1000mol/m 3 The method comprises the steps of carrying out a first treatment on the surface of the The stopping conditions of the electrochemical-thermal coupling model are as follows: the time was 300 days and the cut-off voltage was 2.8V.
6. The method for predicting calendar aging and cyclic aging of a lithium ion battery of claim 4, wherein the condition parameters of the working condition in step (5) are: the initial temperature is 25 ℃, 45 ℃, 60 ℃, 10 ℃ and the charge states are 0.5 and 0.9 respectively, and the parameters of the working conditions are combined.
7. The method of predicting calendar aging and cyclic aging of a lithium ion battery of claim 4, wherein the operating condition parameters of the electrochemical-thermal coupling model are: the initial temperature is 25 ℃ and 45 ℃, the charge-discharge current multiplying power is 1/3C and 1C respectively, the average lithium battery charge states are 0.3, 0.5 and 0.8 respectively, and the discharge depths are 0.4 and 0.8 respectively.
8. The method for predicting calendar aging and cyclic aging of a lithium ion battery of claim 4, wherein the lithium ion battery has a negative electrode diffusion coefficient of 2.5 x 10, respectively -14 m 2 /s、5×10 -14 m 2 /s、1×10 -13 m 2 S; the thickness of the negative electrode is 24.35 multiplied by 10 respectively -6 m、48.7×10 -6 m、97.4×10 -6 m。
9. The method of predicting calendar aging and cyclic aging of a lithium-ion battery of claim 4, wherein the operating conditions of the electrochemical-thermal coupling model comprise charge-discharge operating conditions that take the same time as a rest time for battery charge-discharge with charge-rest-discharge-rest as a cycle.
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