Experiment and simulation method for lithium ion battery lithium precipitation aging speed

Abstract

The invention discloses an experiment and simulation method for lithium ion battery lithium precipitation aging speed. The method comprises the following steps: establishing a lithium battery electrochemical model; establishing a lumped heat model, and constructing a one-dimensional electrochemical-thermal coupling model; introducing a solid electrolyte interface growth aging side reaction and a lithium precipitation aging side reaction on the basis of the electrochemical-thermal coupling model, and adding aging parameters into the model; initial conditions and stop conditions of the electrochemical-thermal coupling model coupled with the solid electrolyte interface growth and lithium precipitation aging mechanism are set, working conditions are set and calculated, and an aging result is obtained and subjected to post-processing analysis. Lithium precipitation quantitative detection analysis is carried out by using an ICP-OES experiment, and the ratio of lithium precipitation to capacity loss in the capacity loss is determined, so that the aging speeds of different aging mechanisms are determined. According to the method, the attenuation speeds of different aging mechanisms are obtained through a method of combining a model and an experiment, and guidance is provided for management and use of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to an experimental and simulation method for the lithium deposition aging rate of a lithium-ion battery. Background Art

[0002] With the rapid development of new energy technology and electronic technology, lithium-ion batteries are widely used in many fields such as new energy vehicles. During use, their capacity will inevitably decay, and their lifespan will be affected by various factors, mainly the growth of the SEI film and lithium deposition. In the presence of multiple aging mechanisms, determining the decay rate of different aging mechanisms is a key issue and is of great significance for battery management and use. At present, there is an urgent need to establish a model that can determine the battery aging rate.

[0003] Currently, the lithium-ion battery aging model is not comprehensive enough and lacks a comprehensive analysis of the aging rates of SEI and lithium deposition, which may lead to large errors in the prediction results after changing the battery operating conditions. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide an experimental and simulation method for the lithium deposition aging rate of a lithium-ion battery. Based on the electrochemical-thermal coupling mechanism model, the SEI growth and lithium deposition side reactions are coupled; combined with the lithium deposition quantitative experiment, a battery model for the lithium deposition aging rate of a lithium-ion battery is established, the battery cycle aging results are calculated, and the battery capacity decay caused by different aging factors is decomposed, providing a model basis for the aging research and management of lithium-ion batteries.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] An experimental and simulation method for the lithium deposition aging rate of a lithium-ion battery, comprising: (1) establishing an electrochemical model of the lithium-ion battery; (2) establishing a lumped thermal model, simplifying the cell structure of the lithium-ion battery, retaining the key factors in the heat propagation process, coupling the electrochemical model, constructing an electrochemical-thermal coupling model, and inputting battery model parameters; (3) adding an aging mechanism to the electrochemical-thermal coupling model, introducing the solid electrolyte interface growth aging side reaction and the lithium deposition aging side reaction, and adding aging parameters to the electrochemical-thermal coupling model; (4) setting the initial conditions and stop conditions of the electrochemical-thermal coupling model coupled with the solid electrolyte interface growth and lithium deposition aging mechanisms, setting the working conditions and performing calculations, obtaining the aging results and performing post-processing analysis; (5) performing a lithium deposition quantitative detection experiment to determine the proportion of lithium deposition in the capacity loss, and further establishing the aging rates of different aging mechanisms.

[0007] The aging mechanism added in step (3) includes: adding an aging mechanism for the growth of the solid electrolyte interphase and a lithium plating aging mechanism in the negative electrode calculation domain of the electrochemical model.

[0008] The aging incentives for the growth of the solid electrolyte interphase and lithium plating are behaviors simultaneously restricted by kinetics and diffusion.

[0009] The condition parameters of the working conditions of the electrochemical-thermal coupling model are: the initial temperatures are -5°C, 5°C, and 25°C respectively, and the charge-discharge current rates are 0.5C, 1C, 2C, and 3C respectively.

[0010] The initial conditions of the electrochemical-thermal coupling model are: the initial state of charge is 1, the initial voltage is 3.65V, and the electrolyte concentration is 1000 mo1 / m 3 ; The stop condition of the electrochemical-thermal coupling model is: the cut-off voltage is 2.5V and the number of cycles is 20.

[0011] The working conditions of the electrochemical-thermal coupling model include charge-discharge working conditions. The charge-discharge working conditions take charge - rest - discharge - rest as a cycle, and the time used for battery charge and discharge is equal to the rest time.

[0012] The process of step (5) is as follows:

[0013] a) After the battery is cycled, disassemble it in a glove box, react the negative electrode with water, and obtain a liquid formed by the reaction of irreversible lithium on the negative electrode surface with water;

[0014] b) Use ICP-OES to detect the lithium element content in this liquid

[0015] c) In order to reduce the error caused by the residual electrolyte, use ICP-OES to detect the lithium element content of a fresh battery;

[0016] d) Subtract the lithium element content of the fresh battery from that of the cycled battery, then the lithium element content generated by lithium plating can be considered, and then converted into the capacity loss caused by lithium plating, and further adjust the capacity loss in the model to establish the aging rate of lithium plating in the model;

[0017] e) Subtract the capacity loss caused by lithium plating from the total capacity loss, and the remaining capacity loss can be attributed to that caused by the SEI film, so as to adjust the capacity loss of SEI growth in the model to establish the aging rate of SEI growth in the model.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] An electrochemical-thermal coupling model that can establish both the SEI growth rate and the lithium plating rate is constructed to clearly understand the mutual influence relationship of the electrochemical-thermal-SEI-lithium plating characteristics inside the battery; the electrochemical-thermal coupling model constructed by this method can predict the attenuation rate under different working conditions, solve the electrochemical-thermal-aging related problems of the battery under different working conditions, analyze the aging behavior of the battery under different working conditions, and decompose the capacity attenuation caused by different aging factors; by using the results of the multi-field coupling model of lithium batteries, an optimization direction is proposed for battery design and use, providing a theoretical basis and data support for the management and optimal design of lithium batteries. Brief Description of the Drawings

[0020] Figure 1 It is the experimental flow chart of the present invention;

[0021] Figure 2 It is the SEM image of the negative electrode plate after 20 cycles at 5°C;

[0022] Figure 3 It is the comparison chart of the capacity loss caused by lithium plating and the experiment after 20 cycles at 5°C;

[0023] Figure 4 It is the comparison chart of the total capacity loss simulation and the experiment after 20 cycles at 5°C;

[0024] Figure 5 It is the contribution chart of different aging mechanisms to the capacity loss after 20 cycles at 5°C;

[0025] Figure 6 It is the SEM image of the negative electrode plate after 20 cycles at -5°C;

[0026] Figure 7 It is the comparison chart of the capacity loss caused by lithium plating and the experiment after 20 cycles at -5°C;

[0027] Figure 8 It is the comparison chart of the total capacity loss simulation and the experiment after 20 cycles at -5°C;

[0028] Figure 9 It is the contribution chart of different aging mechanisms to the capacity loss after 20 cycles at -5°C;

[0029] Figure 10 It is the comparison chart of the battery simulation and the experiment at room temperature (25°C). Detailed Embodiments

[0030] Specific embodiments are given below in conjunction with the drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and do not limit the protection scope of this application.

[0031] The present invention provides an experimental and simulation method for the lithium deposition aging rate of a lithium-ion battery, comprising the following steps:

[0032] (1) Based on the P2D model proposed by Newman, taking a lithium iron phosphate (LFP) / graphite battery as the research object, an electrochemical model of the lithium-ion battery is established; the battery geometric structure is one-dimensional and is divided into a negative electrode, a separator, and a positive electrode;

[0033] Solid-phase diffusion equation:

[0034]

[0035] Liquid-phase diffusion equation:

[0036]

[0037] Solid-phase Ohm's law:

[0038]

[0039] Liquid-phase Ohm's law:

[0040]

[0041] Bulter-Volmer kinetic equation:

[0042]

[0043] In the formula, c s is the solid-phase lithium-ion concentration, c e is the liquid-phase lithium-ion concentration, is the liquid-phase effective diffusion coefficient, ρ is the battery cell density, D s is the solid-phase diffusion coefficient, a s is the specific surface area, r is the radius of the active particle, j r is the lithium-ion flux, λ is the thermal conductivity, ε e is the liquid-phase volume fraction, φ s is the solid-phase electric potential, φ e is the liquid-phase electric potential, i s is the solid-phase current density, is the transference number, is the solid-phase effective conductivity, κ eff is the liquid-phase effective conductivity, i 0 is the exchange current density, j r is the charge transfer current density;

[0044] (2) Establish a lumped thermal model, moderately simplify the actual structure of the battery cell while retaining the key factors in the heat propagation process, couple the electrochemical model, construct an electrochemical-thermal coupling model, and input the battery model parameters; the geometric structure of the thermal model is one-dimensional, along the thickness direction of the battery. The temperature and electrochemistry of the lithium-ion battery affect each other. Introducing the thermal model increases the applicable range of the battery model;

[0045] The energy conservation equation is:

[0046]

[0047] The heat transfer equation is:

[0048]

[0049] In the formula, C p is the specific heat capacity, h is the heat transfer coefficient, T surf is the surface temperature, and T amb is the ambient temperature;

[0050] (3) Add the aging mechanism to the electrochemical-thermal coupling model, introduce the side reactions of the growth and aging of the solid electrolyte interface (SEI) and the side reaction of lithium plating (LPL) aging, and add the aging mechanisms of SEI growth and lithium plating aging to the negative electrode calculation domain in the electrochemical model;

[0051] Furthermore, the growth of SEI is a behavior limited by both kinetics and diffusion. The equilibrium potential of the SEI growth reaction is 0.4V, and the initial SEI film thickness is 5nm; perform a formulaic analysis of the SEI growth, establish a function of the local current density and the relevant parameters of the SEI side reaction. The control equations of the SEI growth model include:

[0052] The calculation formula for the SEI reaction current density is:

[0053]

[0054] The EC mass conservation equation:

[0055]

[0056] The SEI mass conservation equation:

[0057]

[0058] The calculation formula for the SEI thickness is:

[0059]

[0060] The calculation formula for the SEI film group is:

[0061]

[0062] The calculation formula for porosity change caused by SEI growth is:

[0063]

[0064] In the formula, k 0,SEI is the SEI growth rate constant, D EC is the EC diffusion rate, U SEI is the SEI growth equilibrium potential, is the initial concentration of EC, is the concentration of EC on the graphite surface, δ film is the SEI film thickness, c SEI is the SEI molar concentration, M SEI is the molar mass of the SEI film, ρ SEI is the density of the SEI film, κ SEI is the SEI conductivity;

[0065] Furthermore, the aging cause caused by lithium deposition is the local negative electrode potential relative to Li / Li + When the value becomes negative, the graphite negative electrode will have a side reaction of metal lithium deposition; the control equations of the lithium deposition aging model include:

[0066] The calculation formula for the current density of lithium precipitation reaction is:

[0067]

[0068] Conservation equation of metallic lithium:

[0069]

[0070] SEI film and metallic lithium form a surface film:

[0071]

[0072] In the formula, i 0,lpl is the lithium exchange current density, c Li is the molar concentration of metallic lithium;

[0073] (4) setting the initial conditions and stop conditions of the electrochemical-thermal coupling model that couples the SEI growth and lithium precipitation aging mechanism, setting the operating conditions and performing calculations, obtaining the cycle aging results and performing post-processing analysis;

[0074] (5) Conducting quantitative lithium deposition detection experiments and performing analysis to determine the proportion of different aging mechanisms, and then determine the decay rates of different aging mechanisms;

[0075] a) After the battery cycle, the battery is disassembled in a glove box, and the negative electrode is reacted with water to obtain a liquid formed by the irreversible reaction of lithium and water on the negative electrode surface;

[0076] b) Detect the lithium element content of the liquid using ICP - OES;

[0077] c) To reduce the error caused by the residual electrolyte, detect the lithium element content of the fresh battery using ICP - OES;

[0078] d) Subtract the lithium element content of the fresh battery from that of the cycled battery, then the lithium element content generated by lithium plating can be considered, and further converted into the capacity loss caused by lithium plating, and then adjust the capacity loss in the model to establish the aging rate of lithium plating in the model;

[0079] e) Subtract the capacity loss caused by lithium plating from the total capacity loss, and the remaining capacity loss can be attributed to the SEI film. Then adjust the capacity loss caused by SEI growth in the model to establish the aging rate of SEI growth in the model.

[0080] Example 1

[0081] (1) Establish an electrochemical model of a lithium - ion battery; Equivalent the battery to a negative electrode, a separator and a positive electrode, draw the one - dimensional geometric structure of the lithium battery, and build a pseudo - two - dimensional electrochemical model of the lithium - ion battery based on the modeling control equations of the lithium battery;

[0082] (2) The thermal model adopts a lumped thermal model, which is coupled with the electrochemical model to construct an electrochemical - thermal coupling model, and assign parameters to the battery model;

[0083] (3) Add aging mechanisms to the electrochemical - thermal coupling model, introduce side reactions of SEI growth aging and lithium plating aging, and add aging parameters to the model;

[0084] (4) The working conditions adopted in the experiment: the temperature is 5°C, and the rates are 1C, 2C, and 3C;

[0085] (5) After the battery is cycled, disassemble it in a glove box and react with water to obtain a liquid formed by the reaction of irreversible lithium and water. Detect the lithium element content of the liquid using ICP - OES.

[0086] To reduce the error caused by the residual electrolyte, it is necessary to subtract the lithium element content of the fresh battery from that of the cycled battery. Then the lithium element content generated by lithium plating can be considered, and further converted into the capacity loss caused by lithium plating, and then adjust the capacity loss in the model to establish the aging rate of lithium plating in the model;

[0087] Then, subtract the capacity loss caused by lithium plating from the total capacity loss, and the remaining capacity loss can be attributed to the SEI film. Then adjust the capacity loss caused by SEI in the model to establish the aging rate of SEI growth in the model.

[0088] Figure 2 SEM images at different rates after disassembling after 20 cycles at 5°C. As the rate increases, the pore blockage becomes more severe and more lithium is precipitated. Figure 3 Comparison chart of simulation and experiment of capacity loss caused by lithium precipitation in the battery after 20 cycles at 5°C, and the lithium precipitation rate of the model is determined. Figure 4 Comparison chart of simulation and experiment of total capacity loss after 20 cycles at 5°C. Figure 5 Shows the capacity loss caused by SEI and lithium precipitation under different working conditions after 20 cycles at 5°C. The capacity loss is split, and the SEI growth rate of the model is established.

[0089] Example 2

[0090] (1) Establish an electrochemical model of a lithium-ion battery

[0091] The battery is equivalent to a negative electrode, a separator and a positive electrode. Draw a one-dimensional geometric structure of the lithium battery. Based on the modeling control equation of the lithium battery, build a pseudo-two-dimensional electrochemical model of the lithium-ion battery;

[0092] (2) The thermal model adopts a lumped thermal model, which is coupled with the electrochemical model to construct a one-dimensional electrochemical-thermal coupling model, and assign parameters to the battery model;

[0093] (3) Add an aging mechanism to the electrochemical-thermal coupling model, introduce the SEI growth aging side reaction and the lithium precipitation aging side reaction. And add aging parameters to the model;

[0094] (4) The working conditions adopted in the experiment: the temperature is -5°C, and the rates are 1C and 2C;

[0095] (5) After cycling, disassemble in a glove box and react with water to obtain a liquid formed by the reaction of irreversible lithium and water. Use ICP-OES to detect the lithium element content in the liquid.

[0096] In order to reduce the error caused by the residual electrolyte, the lithium element content of the fresh battery needs to be subtracted from the cycled battery, then it can be considered as the lithium element content generated by lithium precipitation, and then converted into the capacity loss caused by lithium precipitation, and then adjust the capacity loss in the model to establish the aging rate of lithium precipitation in the model.

[0097] Then, subtract the capacity loss caused by lithium precipitation from the total capacity loss to obtain the remaining capacity loss attributable to the SEI film, and then adjust the capacity loss caused by SEI in the model to establish the aging rate of SEI growth in the model.

[0098] Figure 6 SEM images at different rates after disassembling after 20 cycles at -5°C. As the rate increases, the pore blockage becomes more severe and more lithium is precipitated.Figure 7 The simulation and experimental comparison chart of the capacity loss caused by lithium plating in the battery after 20 cycles at -5°C, which determines the lithium plating rate of the model. Figure 8 The simulation and experimental comparison chart of the total capacity loss after 20 cycles at -5°C. Figure 9 It shows the capacity losses caused by SEI and lithium plating respectively under different working conditions after 20 cycles at -5°C. The capacity loss is split to determine the SEI growth rate of the model.

[0099] Example 3

[0100] (1) Establish an electrochemical model of a lithium-ion battery

[0101] Equivalent the battery into a negative electrode, a separator and a positive electrode, draw the one-dimensional geometric structure of the lithium battery, and build a pseudo-two-dimensional electrochemical model of the lithium-ion battery based on the modeling control equation of the lithium battery;

[0102] (2) The thermal model adopts a lumped thermal model, which is coupled with the electrochemical model to construct a one-dimensional electrochemical-thermal coupling model and assign battery model parameters;

[0103] (3) Add an aging mechanism to the electrochemical-thermal coupling model, introduce the SEI growth aging side reaction and the lithium plating aging side reaction. And add aging parameters to the model;

[0104] (4) The working conditions adopted in the experiment: the temperature is 25°C, and the rates are 0.5C, 1C, 2C;

[0105] (5) Use the experimental data under different working conditions to verify the accuracy of the established lithium plating aging rate.

[0106] Figure 10 The simulation and experimental comparison chart of the total capacity loss at 25°C, and it is observed that the fitting degree of the experimental and simulation data is good.

[0107] Table 1 Battery design parameters

[0108]

[0109]

[0110] Table 2 SEI and LAM model aging parameters

[0111]

[0112] Compared with the prior art, the advantages of the present application are as follows: By means of experiments, quantitative detection and analysis of lithium deposition are carried out to determine the proportion of lithium deposition in the capacity loss, and then the proportion in the model is adjusted, and then the aging rates of different aging mechanisms are established. By combining the model with experiments, the attenuation rates of different aging mechanisms are obtained, the electrochemistry-thermal-aging related problems of the battery under different working conditions are solved, the aging behavior of the battery under different working conditions can be analyzed, and the decomposition of capacity attenuation caused by different aging factors can be realized; Using the results of the multi-field coupling model of lithium batteries, an optimization direction is proposed for battery design and use, providing a theoretical basis and data support for the management and optimized design of lithium batteries.

[0113] What is not described in the present invention is applicable to the prior art.

Claims

1. An experimental and simulation method for the aging rate of lithium ion batteries, characterized in that: include: (1) Establish an electrochemical model for lithium-ion batteries; (2) establishing a lumped thermal model, simplifying the cell structure of the lithium-ion battery, retaining the key factors in the heat propagation process, coupling the electrochemical model, constructing an electrochemical-thermal coupling model, and inputting battery model parameters; (3) Adding aging mechanism to the electrochemical-thermal coupling model, introducing solid electrolyte interface growth aging side reaction and lithium precipitation aging side reaction, and adding aging parameters to the electrochemical-thermal coupling model; (4) setting the initial conditions and stop conditions of the electrochemical-thermal coupling model that couples the solid electrolyte interface growth and lithium precipitation aging mechanism, setting the operating conditions and performing calculations, obtaining the cycle aging results and performing post-processing analysis; (5) Conduct quantitative detection experiments on lithium plating to determine the proportion of lithium plating in capacity loss, and then establish the aging speed of different aging mechanisms in the model.

2. The experimental and simulation method for the aging speed of lithium ion battery according to claim 1, characterized in that: The step (3) of adding the aging mechanism comprises: adding the aging mechanism of solid electrolyte interface growth and the aging mechanism of lithium precipitation in the negative electrode calculation domain in the electrochemical model.

3. The experimental and simulation method for the aging speed of lithium ion battery according to claim 2, characterized in that: The solid electrolyte interface growth and lithium deposition are behaviors that are simultaneously limited by kinetics and diffusion.

4. The experimental and simulation method for the lithium ion battery aging rate according to claims 1 to 3, characterized in that: The step (4) also includes: setting application conditions of the battery model.

5. The experimental and simulation method for the lithium ion battery lithium deposition aging speed according to claim 1, characterized in that: The condition parameters of the electrochemical-thermal coupling model include: initial temperatures of -5°C, 5°C, and 25°C, respectively; charge and discharge current rates of 0.5C, 1C, 2C, and 3C, respectively; initial state of charge of 1, initial voltage of 3.65V, and electrolyte concentration of 1000mol / m 3 ; Stop conditions are: cut-off voltage is 2.5V, number of cycles is 20.

6. The experimental and simulation method for the lithium ion battery lithium deposition aging speed according to claim 1, characterized in that: The operating conditions of the electrochemical-thermal coupling model include charge-discharge operating conditions, which have a cycle of charge-rest-discharge-rest, and the time taken for battery charge and discharge is equal to the rest time.

7. The experimental and simulation method for the aging rate of lithium ion battery according to claim 1, characterized in that: The process of step (5) is as follows: a) After the battery cycle, it is disassembled in a glove box and reacted with water to obtain a liquid formed by the irreversible reaction of lithium and water on the negative electrode surface; b) using ICP-OES to detect the lithium content of the liquid; c) In order to reduce the error caused by residual electrolyte, the lithium content of fresh batteries was detected by ICP-OES; d) Subtracting the lithium content of the fresh battery from the cycled battery can be considered as the lithium content generated by lithium precipitation, which can then be converted into the capacity loss caused by lithium precipitation, and then the capacity loss in the model is adjusted to establish the aging rate of lithium precipitation in the model; e) Subtract the capacity loss caused by lithium plating from the total capacity loss to obtain the remaining capacity loss attributable to the SEI film, and then adjust the capacity loss of SEI growth in the model to establish the aging rate of SEI growth in the model.

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