Pre-lithium quantity prediction method of silicon-based negative electrode, preparation method of silicon-based negative electrode and solid-state battery

Abstract

The invention relates to the technical field of batteries, and provides a pre-lithium quantity prediction method of a silicon-based negative electrode, a preparation method of the silicon-based negative electrode and a solid-state battery, and the pre-lithium quantity prediction method comprises the following steps: providing a silicon-based negative electrode material, and testing to obtain a lithium intercalation corresponding relation between the lithium intercalation quantity of the silicon-based negative electrode material and a lithium ion diffusion coefficient; and determining the discharge rate lambda of the silicon-based negative electrode in the working state, calculating the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction in the working state, and calculating the minimum pre-lithiation amount of the silicon-based negative electrode in combination with the lithium intercalation corresponding relation. The pre-lithiation amount of the silicon-based negative electrode is obtained through calculation, and the method is simple, high in accuracy and good in universality.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for predicting the amount of lithium in advance of a silicon-based negative electrode, a method for preparing a silicon-based negative electrode, and a solid-state battery. Background Art

[0002] Silicon-based negative electrodes have the advantages of high specific capacity, low cost, low risk of lithium precipitation, and good interface compatibility. However, due to the semiconductor properties of silicon, its electronic conductivity (about 10 -3 S / m) and the lithium ion diffusion coefficient (10 -14 ~10 -13 cm 2 / s) are relatively low, which easily leads to increased overpotential and increased lithium residue, severely limiting the rate performance of solid-state silicon-based negative electrodes. In traditional technology, the electronic conductivity and lithium ion diffusion coefficient of silicon-based negative electrodes can be improved by pre-lithiation of silicon-based negative electrodes to form lithium-silicon alloys. However, how to determine the pre-lithiation amount of silicon-based negative electrodes has become an urgent problem that needs to be solved. Summary of the invention

[0003] Based on this, an embodiment of the present application provides a method for predicting the pre-lithium amount of a silicon-based negative electrode with a simple method and high accuracy, a method for preparing a silicon-based negative electrode, and a solid-state battery.

[0004] In a first aspect, the present application provides a method for predicting the pre-lithium amount of a silicon-based negative electrode, the method for predicting the pre-lithium amount of a silicon-based negative electrode comprising:

[0005] Providing a silicon-based negative electrode material, and testing to obtain a lithium insertion correspondence relationship between a lithium insertion amount and a lithium ion diffusion coefficient of the silicon-based negative electrode material;

[0006] The discharge rate λ of the silicon-based negative electrode under working condition is determined, the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction under working condition is calculated, and the minimum pre-lithium amount of the silicon-based negative electrode is calculated in combination with the lithium insertion correspondence.

[0007] In some embodiments, the lithium insertion correspondence is obtained by testing using a constant current intermittent titration method.

[0008] In some embodiments, the method for calculating the minimum pre-lithium amount of the silicon-based negative electrode includes:

[0009] The maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte is calculated according to the discharge rate λ of the silicon-based negative electrode in the working state, mol / m 2 ·s;

[0010] Using Fick's second law, a partial differential equation for the diffusion process of lithium ions in the silicon-based negative electrode material in the diffusion direction is established;

[0011] ;

[0012] Wherein, C refers to the lithium ion concentration in the silicon-based negative electrode material, mol / m 3 ; t refers to the diffusion time, s; x refers to the diffusion distance in the diffusion direction, m; D s refers to the lithium ion diffusion coefficient;

[0013] Determine the boundary conditions and solve the partial differential equation in combination with the lithium insertion correspondence to obtain the minimum pre-lithium amount C0 / C of the silicon-based negative electrode. max ; Wherein, C0 refers to the initial lithium ion concentration of the silicon-based negative electrode material after pre-lithiation, mol / m 3 ; C max Refers to the maximum lithium ion concentration that can be accommodated in the silicon-based negative electrode material, mol / m 3 .

[0014] In some embodiments, the differential equation satisfies the following boundary conditions:

[0015] (1) , indicating that there is no lithium ion flux at the diffusion center of the silicon-based negative electrode material;

[0016] (2) , indicating that the lithium ion flux at the contact interface between the silicon-based negative electrode material and the solid electrolyte is the diffusion flux required to meet the discharge rate λ requirement;

[0017] (3) , indicating that the lithium ion concentration at the contact interface between the silicon-based negative electrode material and the solid electrolyte is equal to 0 at the discharge cut-off time;

[0018] (4) , indicating that the amount of remaining lithium ions in the silicon-based negative electrode material at the end of discharge is equal to the initial pre-lithium amount;

[0019] Among them, D s (C / C max ) refers to the lithium insertion correspondence; Λ s Refers to the longest diffusion distance of lithium ions in the silicon-based negative electrode material, m.

[0020] In some embodiments, the silicon-based negative electrode contains a solid electrolyte. s is 0.95 to 1.05 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte, sIt is 0.95 to 1.05 times the thickness of the silicon-based negative electrode.

[0021] In some embodiments, the method for calculating the maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte includes:

[0022] ;

[0023] Among them, L s is the equivalent diffusion distance of lithium ions in the silicon-based negative electrode material, m.

[0024] In some embodiments, the silicon-based negative electrode contains a solid electrolyte, L s is 0.30 to 0.35 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte, L s It is 0.95 to 1.05 times the thickness of the silicon-based negative electrode.

[0025] In a second aspect, the present application provides a method for preparing a silicon-based negative electrode, the method for preparing a silicon-based negative electrode comprising:

[0026] The method for predicting the pre-lithium amount of the silicon-based negative electrode as described in the first aspect is used to calculate the minimum pre-lithium amount, and a pre-lithium layer is formed according to the minimum pre-lithium amount;

[0027] The pre-lithium layer and the negative electrode active layer containing the silicon-based negative electrode material are stacked to obtain a silicon-based negative electrode.

[0028] In some embodiments, the method for preparing the silicon-based negative electrode comprises:

[0029] providing a pre-lithium layer;

[0030] A negative electrode slurry containing a silicon-based negative electrode material, a binder and a solvent is prepared, and the negative electrode slurry is coated on the surface of the pre-lithium layer to form a negative electrode active layer, thereby preparing the silicon-based negative electrode.

[0031] Optionally, the solvent includes at least one of toluene, xylene, butyl butyrate, isobutyl isobutyrate and n-heptane.

[0032] Optionally, the pre-lithium layer comprises lithium foil.

[0033] In a third aspect, the present application provides a solid-state battery, comprising a silicon-based negative electrode prepared by the method for preparing a silicon-based negative electrode as described in the second aspect.

[0034] Compared with the traditional technology, this application has at least the following beneficial effects:

[0035] The present application utilizes the lithium insertion correspondence between the lithium insertion amount of the silicon-based negative electrode material and the lithium ion diffusion coefficient, and thus calculates the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction under the working state according to the discharge rate of the silicon-based negative electrode under the working state. Since the lithium ion concentration distribution state at the discharge cut-off moment is determined by the corresponding lithium ion diffusion coefficient, the pre-lithium amount required for the silicon-based negative electrode is obtained. The present application predicts the pre-lithium amount by the working parameters of the silicon-based negative electrode. Compared with the traditional technology of preparing multiple silicon-based negative electrodes with different pre-lithium amounts for testing, it has the characteristics of simple method, strong versatility and accurate results. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A method for predicting the pre-lithium amount of a silicon-based negative electrode is provided in a specific embodiment of the present application.

[0037] Figure 2 This is a lithium insertion correspondence diagram between the lithium ion diffusion coefficient and the lithium insertion amount of the silicon material in Example 1 of the present application.

[0038] Figure 3 This is a comparison chart of the test results of the solid-state batteries in Example 1 of the present application and Comparative Example 1. DETAILED DESCRIPTION

[0039] Below in conjunction with the embodiments and examples, the present application is further described in detail. These embodiments and examples are only used to illustrate the present application and are not used to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the understanding of the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms, and is not limited to the embodiments and examples described herein. Those skilled in the art can make various changes or modifications without violating the connotation of the present application, and the equivalent form obtained also falls within the protection scope of the present application. In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0041] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0042] In this application, the terms "first", "second", etc. in "the first aspect", "the second aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0043] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0044] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for a broad range of quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0045] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0046] In traditional technology, silicon-based negative electrodes with different pre-lithium amounts are prepared, and the minimum pre-lithium amount of the silicon-based negative electrode is confirmed through multiple tests, screening and repeated attempts. In addition, new experiments need to be carried out for different silicon-based negative electrodes or silicon-based negative electrodes in different working states. This method is not only complex, but also costly.

[0047] The first aspect of the present application provides a method for predicting the pre-lithium amount of a silicon-based negative electrode, such as Figure 1As shown, the method for predicting the pre-lithium amount of the silicon-based negative electrode includes:

[0048] Providing a silicon-based negative electrode material, and testing to obtain a lithium insertion correspondence relationship between a lithium insertion amount and a lithium ion diffusion coefficient of the silicon-based negative electrode material;

[0049] The discharge rate λ of the silicon-based negative electrode under working condition is determined, the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction under working condition is calculated, and the minimum pre-lithium amount of the silicon-based negative electrode is calculated in combination with the lithium insertion correspondence.

[0050] The present application found that compared with carbon negative electrode materials, the amount of lithium embedded in silicon-based negative electrode materials and the lithium ion diffusion coefficient show a monotonically increasing relationship. Therefore, the present application utilizes the lithium embedding correspondence between the amount of lithium embedded in silicon-based negative electrode materials and the lithium ion diffusion coefficient, and thus calculates the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction under the working state according to the discharge rate of the silicon-based negative electrode under the working state. Since the lithium ion concentration distribution state at the discharge cut-off time is determined by the corresponding lithium ion diffusion coefficient, the pre-lithium amount required for the silicon-based negative electrode is obtained. The present application predicts the pre-lithium amount by the working parameters of the silicon-based negative electrode. Compared with the traditional technology of preparing multiple silicon-based negative electrodes with different pre-lithium amounts for testing, it has the characteristics of simple method, strong versatility and accurate results.

[0051] In some embodiments, the lithium insertion correspondence is obtained by constant current intermittent titration. It is understandable that in the lithium insertion correspondence of silicon-based negative electrode materials, the amount of lithium insertion and the lithium ion diffusion coefficient are material properties, which are not affected by parameters such as current pulse intensity, pulse time and recovery time during the constant current intermittent titration test. However, it will be affected by the temperature during the test, so it is necessary to test at the actual working temperature of the silicon-based negative electrode.

[0052] In some embodiments, the method for calculating the minimum pre-lithium amount of the silicon-based negative electrode includes:

[0053] The maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte is calculated according to the discharge rate λ of the silicon-based negative electrode in the working state, mol / m 2 ·s;

[0054] Using Fick's second law, a partial differential equation for the diffusion process of lithium ions in the silicon-based negative electrode material in the diffusion direction is established;

[0055] ;

[0056] Wherein, C refers to the lithium ion concentration in the silicon-based negative electrode material, mol / m 3; t refers to the diffusion time, s; x refers to the diffusion distance in the diffusion direction, m; D s refers to the lithium ion diffusion coefficient;

[0057] Determine the boundary conditions and solve the partial differential equation in combination with the lithium insertion correspondence to obtain the minimum pre-lithium amount C0 / C of the silicon-based negative electrode. max ; Wherein, C0 refers to the initial lithium ion concentration of the silicon-based negative electrode material after pre-lithiation, mol / m 3 ; C max Refers to the maximum lithium ion concentration that can be accommodated in the silicon-based negative electrode material, mol / m 3 .

[0058] In this application, Fick's second law is used to obtain the partial differential equation of the diffusion process of lithium ions in silicon-based negative electrode materials, and the lithium insertion correspondence is further combined with the boundary conditions to calculate the minimum pre-lithium amount of the silicon-based negative electrode.

[0059] In some embodiments, the differential equation satisfies the following boundary conditions:

[0060] (1) , indicating that there is no lithium ion flux at the diffusion center of the silicon-based negative electrode material;

[0061] (2) , indicating that the lithium ion flux at the contact interface between the silicon-based negative electrode material and the solid electrolyte is the diffusion flux required to meet the discharge rate λ requirement;

[0062] (3) , indicating that the lithium ion concentration at the contact interface between the silicon-based negative electrode material and the solid electrolyte is equal to 0 at the discharge cut-off time;

[0063] (4) , indicating that the amount of remaining lithium ions in the silicon-based negative electrode material at the end of discharge is equal to the initial pre-lithium amount.

[0064] Among them, D s (C / C max ) refers to the lithium insertion correspondence; Λ s Refers to the longest diffusion distance of lithium ions in the silicon-based negative electrode material, m.

[0065] It is understandable that the present application does not limit the method for solving the above partial differential equation, and the solution can be obtained by finite element simulation.

[0066] In some embodiments, the silicon-based negative electrode contains a solid electrolyte. s is 0.95 to 1.05 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte,s It is 0.95 to 1.05 times the thickness of the silicon-based negative electrode. It can be understood that when the silicon-based negative electrode contains a solid electrolyte, the length of the contact interface between the largest particle in the silicon-based negative electrode material and the solid electrolyte in the silicon-based negative electrode from the center of the particle is the longest diffusion distance of lithium ions in the silicon-based negative electrode material. Therefore, Λ s Approximately the maximum particle radius in the silicon-based negative electrode material. When the silicon-based negative electrode does not contain a solid electrolyte, the length of the contact interface between the silicon-based negative electrode and the solid electrolyte layer and the negative electrode current collector is the longest diffusion distance of lithium ions in the silicon-based negative electrode material. Therefore, Λ s Approximately the thickness of the silicon-based negative electrode.

[0067] In some embodiments, the method for calculating the maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte includes:

[0068] ;

[0069] Among them, L s is the equivalent diffusion distance of lithium ions in the silicon-based negative electrode material, m.

[0070] In some embodiments, the silicon-based negative electrode contains a solid electrolyte, L s is 0.30 to 0.35 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte, L s It is 0.95 to 1.05 times the thickness of the silicon-based negative electrode. It can be understood that when the silicon-based negative electrode contains a solid electrolyte, the distance from the center of the largest particle in the silicon-based negative electrode material to the contact interface of the solid electrolyte in the negative electrode is one-third of the length of the particle, which is the equivalent diffusion distance of lithium ions in the silicon-based negative electrode material. Therefore, L s It is approximately one-third of the maximum particle radius in the silicon-based negative electrode material. When the silicon-based negative electrode does not contain a solid electrolyte, the length of the contact interface between the silicon-based negative electrode and the solid electrolyte layer and the negative electrode current collector is the equivalent diffusion distance of lithium ions in the silicon-based negative electrode material. Therefore, L s Approximately the thickness of the silicon-based negative electrode.

[0071] In some embodiments, the thickness of the silicon-based negative electrode is 5 μm to 50 μm.

[0072] In some embodiments, the average volume particle size Dv50 of the silicon-based negative electrode material is 0.1 μm to 10 μm.

[0073] Exemplarily, a method for predicting the pre-lithium amount of the above-mentioned silicon-based negative electrode is provided, comprising the following steps:

[0074] Providing silicon-based negative electrode materials, and using a constant current intermittent titration method to test the lithium insertion correspondence between the lithium insertion amount of the silicon-based negative electrode materials and the lithium ion diffusion coefficient;

[0075] According to the discharge rate λ of the silicon-based negative electrode in the working state, the maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte is calculated;

[0076] ;

[0077] Using Fick's second law, a partial differential equation for the diffusion process of lithium ions in the silicon-based negative electrode material in the diffusion direction is established;

[0078] ;

[0079] The following boundary conditions are met:

[0080] (1) ;

[0081] (2) ;

[0082] (3) ;

[0083] (4) ;

[0084] The partial differential equation is solved in combination with the lithium insertion correspondence relationship to obtain the minimum pre-lithium amount C0 / C of the silicon-based negative electrode. max .

[0085] In one embodiment of the present application, a device for predicting the pre-lithium amount of a silicon-based negative electrode is provided, which adopts the above-mentioned method for predicting the pre-lithium amount, including:

[0086] A detection module, used to detect the lithium insertion correspondence between the lithium insertion amount of the silicon-based negative electrode material and the lithium ion diffusion concentration;

[0087] Input module, input and determine the working parameters of silicon-based negative electrode, including discharge rate, etc.;

[0088] The calculation module is used to calculate the minimum pre-lithium amount of the silicon-based negative electrode according to the input data of the input module and the corresponding relationship between the lithium insertion of the detection module.

[0089] The second aspect of the present application provides a method for preparing a silicon-based negative electrode, the method for preparing a silicon-based negative electrode comprising:

[0090] The method for predicting the pre-lithium amount of the silicon-based negative electrode as described in the first aspect is used to calculate the minimum pre-lithium amount, and a pre-lithium layer is formed according to the minimum pre-lithium amount;

[0091] The pre-lithium layer and the negative electrode active layer containing the silicon-based negative electrode material are stacked to obtain a silicon-based negative electrode.

[0092] It is understandable that the pre-lithium amount in the present application is the lithium content contained in a unit silicon-based negative electrode. Therefore, the mass of the pre-lithium material in the pre-lithium layer can be determined according to the size of the silicon-based negative electrode.

[0093] In some embodiments, the method for preparing the silicon-based negative electrode comprises:

[0094] Providing the pre-lithium layer;

[0095] A negative electrode slurry containing a silicon-based negative electrode material, a binder and a solvent is prepared, and the negative electrode slurry is coated on the surface of the pre-lithium layer to form a negative electrode active layer, thereby preparing the silicon-based negative electrode.

[0096] Furthermore, after the silicon-based negative electrode is pressed and chemically treated, the pre-lithium layer is integrated into the silicon-based negative electrode to form a lithium-silicon alloy in the silicon-based negative electrode.

[0097] In some embodiments, when preparing a silicon-based negative electrode, a pre-lithium layer is formed on the negative electrode current collector, and then the negative electrode slurry is coated on the pre-lithium layer. Thus, the pre-lithium layer is disposed between the silicon-based negative electrode and the current collector, which can avoid the pre-lithium layer from contacting with the solid electrolyte layer to cause side reactions and affect the pre-lithium effect.

[0098] Optionally, the solvent includes at least one of toluene, xylene, butyl butyrate, isobutyl isobutyrate and n-heptane. The present application adopts the above-mentioned solvent with lower polarity to prepare the negative electrode slurry, and the negative electrode slurry can be directly coated on the surface of the pre-lithium layer to avoid the side reaction between the solvent with higher polarity and the lithium in the pre-lithium layer, which affects the pre-lithium effect.

[0099] Optionally, the pre-lithium layer comprises lithium foil.

[0100] In some embodiments, the silicon-based negative electrode material includes at least one of silicon, silicon oxide, and silicon carbon.

[0101] In some embodiments, the binder includes polyvinylidene fluoride (PVDF).

[0102] In some embodiments, the negative electrode current collector comprises copper foil.

[0103] A third aspect of the present application provides a solid-state battery, comprising a silicon-based negative electrode prepared by the method for preparing a silicon-based negative electrode as described in the second aspect.

[0104] In some embodiments, the silicon-based negative electrode solid-state battery includes a positive electrode and a silicon-based negative electrode alternately stacked, and also includes a solid electrolyte layer located between the positive electrode and the silicon-based negative electrode. It is understandable that it also includes a positive electrode current collector and a negative electrode current collector, the positive electrode current collector is arranged on the positive electrode, and the negative electrode current collector is arranged on the silicon-based negative electrode.

[0105] In some embodiments, the thickness of the positive electrode is 20 μm to 200 μm.

[0106] In some embodiments, the solid electrolyte layer has a thickness of 20 μm to 600 μm.

[0107] Furthermore, the present application also provides an electrical device, comprising the above-mentioned solid-state battery of the present application.

[0108] The above-mentioned electrical devices may include any equipment or devices that use secondary batteries as driving sources, such as mobile phones, laptop computers, electric vehicles, ships, satellites, energy storage devices, smart home appliances, etc., but are not limited thereto.

[0109] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0110] Example 1

[0111] (1) Pre-lithiation amount of silicon-based negative electrode

[0112] Silicon is provided as a silicon-based negative electrode material, and the lithium insertion correspondence between the lithium insertion amount and the lithium ion diffusion coefficient of the silicon-based negative electrode material is tested by constant current intermittent titration method. The constant current intermittent titration method includes:

[0113] At an ambient temperature of 45°C, the silicon-based negative electrode half-cell was lithium-intercalated for 10 minutes at a current rate of 0.1C, and then left for 2 hours. The above process was repeated until the cut-off voltage was reached. The lithium ion diffusion coefficient corresponding to different lithium insertion amounts was calculated using the voltage curve of the left-standing period, and the following was obtained: Figure 2 The lithium insertion correspondence diagram shown.

[0114] The discharge rate λ of the silicon-based negative electrode at 45°C is determined to be 2C, and the maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte is calculated;

[0115] ;

[0116] Among them, the C of silicon material max 311050mol / m3 The designed silicon-based negative electrode does not contain solid electrolyte, the thickness of the silicon-based negative electrode is 6μm, L s is 6μm.

[0117] Using Fick's second law, a partial differential equation for the diffusion process of lithium ions in the silicon-based negative electrode material in the diffusion direction is established;

[0118] ;

[0119] The following boundary conditions are met:

[0120] (1) ;

[0121] (2) ;

[0122] (3) ;

[0123] (4) ;

[0124] The designed silicon-based negative electrode does not contain a solid electrolyte, and the designed silicon-based negative electrode thickness is 6 μm. s is 6μm.

[0125] The partial differential equation is solved in combination with the lithium insertion correspondence relationship to obtain the minimum pre-lithium amount C0 / C of the silicon-based negative electrode. max =21%.

[0126] (2) Preparation of silicon-based negative electrode

[0127] Providing a lithium-copper composite strip comprising a 5 μm lithium foil and a 9 μm copper foil arranged in a stacked manner;

[0128] Silicon and PVDF were weighed in a mass ratio of 95:5, and zirconium beads and isobutyl isobutyrate solvent were added to prepare negative electrode slurry using a double planetary agitator; the negative electrode slurry was coated on the side of the lithium copper composite strip with lithium foil, and dried to obtain a silicon-based negative electrode with a thickness of 6 μm. Since the 6 μm silicon-based negative electrode contains 1.4 mg / cm 2 When silicon is fully lithiated to generate Li 15 The required lithium loading for Si4 is 1.3 mg / cm 2 , while 5μm lithium foil contains 0.27 mg / cm 2 of lithium loading, so the pre-lithium content of the silicon-based negative electrode is 21%.

[0129] (3) Solid-state batteries

[0130] Positive electrode preparation: The active material LiCoO2 (LCO), sulfide electrolyte Li6PS5Cl and vapor grown carbon fiber (VGCF) were weighed in a mass ratio of 70:25:5 and put into a mortar, and manually ground and mixed for 20 minutes to obtain a positive electrode powder.

[0131] A Si|Li6PS5Cl|LCO all-solid-state battery was assembled using a mold with a diameter of 10 mm. First, 85 mg of sulfide electrolyte Li6PS5Cl powder was weighed and added to the mold to be flattened, and then pressed at a pressure of 300 MPa for 2 minutes; then the cut silicon-based negative electrode was attached to the other side of the solid electrolyte layer and pressed at a pressure of 900 MPa for 10 minutes to promote the spontaneous lithiation reaction between lithium and silicon; then 21 mg of the above positive electrode powder was weighed and evenly flattened on one side of the solid electrolyte layer, and pressed at a pressure of 300 MPa for 2 minutes; finally, a stainless steel fixture was used to apply a pressure of 100 MPa to the mold battery for the next electrochemical test. All assembly processes were carried out in a glove box filled with argon gas, and the environmental requirements were water content <0.01 ppm and oxygen content <0.01 ppm.

[0132] Comparative Example 1

[0133] (1) Preparation of silicon-based negative electrode

[0134] A plurality of lithium-copper composite strips are provided, including a copper foil with a thickness of 9 μm and a lithium foil arranged on the surface of the copper foil, wherein the thickness of the lithium foil in the lithium-copper composite strips is 1 μm (equivalent to a pre-lithium amount of 4%), 2 μm (equivalent to a pre-lithium amount of 8%), 3 μm (equivalent to a pre-lithium amount of 12%), 4 μm (equivalent to a pre-lithium amount of 16%), 5 μm (equivalent to a pre-lithium amount of 20%), 6 μm (equivalent to a pre-lithium amount of 24%) and 7 μm (equivalent to a pre-lithium amount of 28%).

[0135] Silicon and PVDF were weighed in a mass ratio of 95:5, zirconium beads and isobutyl isobutyrate solvent were added, and a negative electrode slurry was prepared using a double planetary stirrer; the negative electrode slurry was respectively coated on one side of the lithium copper composite tape with lithium foil, and dried to obtain a silicon-based negative electrode with a thickness of 6 μm.

[0136] (2) Solid-state batteries

[0137] The silicon-based negative electrode is assembled into a solid-state battery according to the method of Example 1. The solid-state battery with a pre-lithium amount of 4% is numbered D-1, the solid-state battery with a pre-lithium amount of 8% is numbered D-2, the solid-state battery with a pre-lithium amount of 12% is numbered D-3, the solid-state battery with a pre-lithium amount of 16% is numbered D-4, the solid-state battery with a pre-lithium amount of 20% is numbered D-5, the solid-state battery with a pre-lithium amount of 24% is numbered D-6, and the solid-state battery with a pre-lithium amount of 28% is numbered D-7.

[0138] The solid-state batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the testing method included:

[0139] The assembled solid-state battery was transferred to a constant temperature box with an ambient temperature of 45 degrees and left to stand for 24 hours. Then, the solid-state battery was subjected to rate charge and discharge tests using the Neware battery test system. The first cycle was charged and discharged at a rate of 0.05C to simulate the formation process of the solid-state battery before it was put into use, and to promote the continued lithiation reaction between the residual lithium foil and silicon. After that, it was cycled for 3 cycles at 0.1C, 0.2C, 0.5C, 1C, and 2C to obtain rate performance data. The test results are shown in the figure. Figure 3 shown.

[0140] It can be seen from the above embodiments and comparative examples that the minimum pre-lithium amount of the silicon-based negative electrode obtained through trial testing in Comparative Example 1 is 20%. It can be understood that a solid-state battery with a pre-lithium amount in the range of 16% to 24% can also be prepared to further determine the optimal pre-lithium amount. The pre-lithium amount calculated in this application is similar to the pre-lithium amount obtained by the test in Comparative Example 1. Therefore, this application utilizes the lithium insertion correspondence between the lithium insertion amount and the lithium ion diffusion coefficient of the silicon-based negative electrode material, so as to calculate the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction under the working state according to the discharge rate of the silicon-based negative electrode under the working state. Since the lithium ion concentration distribution state at the discharge cut-off time is determined by the corresponding lithium ion diffusion coefficient, the pre-lithium amount required for the silicon-based negative electrode is obtained. This application predicts the pre-lithium amount by the working parameters of the silicon-based negative electrode. Compared with the traditional technology of preparing multiple silicon-based negative electrodes with different pre-lithium amounts for testing, it has the characteristics of simple method, strong versatility and accurate results.

[0141] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0142] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for predicting the amount of lithium in a silicon-based negative electrode, characterized in that: The method for predicting the pre-lithium amount of the silicon-based negative electrode comprises: Providing a silicon-based negative electrode material, and testing to obtain a lithium insertion correspondence relationship between a lithium insertion amount and a lithium ion diffusion coefficient of the silicon-based negative electrode material; The discharge rate λ of the silicon-based negative electrode in the working state is determined, the lithium ion concentration distribution state of the silicon-based negative electrode material in the diffusion direction in the working state is calculated, and the minimum pre-lithium amount of the silicon-based negative electrode is calculated in combination with the lithium insertion correspondence.

2. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 1, characterized in that: The lithium insertion correspondence is obtained by testing using a constant current intermittent titration method.

3. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 1 or 2, characterized in that: The method for calculating the minimum pre-lithium amount of the silicon-based negative electrode includes: The maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte is calculated according to the discharge rate λ of the silicon-based negative electrode in the working state, mol / m 2 ·s; Using Fick's second law, a partial differential equation for the diffusion process of lithium ions in the silicon-based negative electrode material in the diffusion direction is established; ； Wherein, C refers to the lithium ion concentration in the silicon-based negative electrode material, mol / m 3 ; t refers to the discharge time, s; x refers to the diffusion distance in the diffusion direction, m; D s refers to the lithium ion diffusion coefficient; Determine the boundary conditions and solve the partial differential equation in combination with the lithium insertion correspondence to obtain the minimum pre-lithium amount C0 / C of the silicon-based negative electrode. max ; Wherein, C0 refers to the initial lithium ion concentration of the silicon-based negative electrode material after pre-lithiation, mol / m 3 ; C max Refers to the maximum lithium ion concentration that can be accommodated in the silicon-based negative electrode material, mol / m 3 .

4. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 3, characterized in that: The differential equation satisfies the following boundary conditions: (1) , indicating that there is no lithium ion flux at the diffusion center of the silicon-based negative electrode material; (2) , indicating that the lithium ion flux at the contact interface between the silicon-based negative electrode material and the solid electrolyte is the diffusion flux required to meet the discharge rate λ requirement; (3) , indicating that the lithium ion concentration at the contact interface between the silicon-based negative electrode material and the solid electrolyte is equal to 0 at the discharge cut-off time; (4) , indicating that the amount of remaining lithium ions in the silicon-based negative electrode material at the end of discharge is equal to the initial pre-lithium amount; Among them, D s (C / C max ) refers to the lithium insertion correspondence; Λ s Refers to the longest diffusion distance of lithium ions in the silicon-based negative electrode material, m.

5. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 4, characterized in that: The silicon-based negative electrode contains a solid electrolyte, s is 0.95 to 1.05 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte, s It is 0.95 to 1.05 times the thickness of the silicon-based negative electrode.

6. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 3, characterized in that: The method for calculating the maximum diffusion flux J0 at the contact interface between the silicon-based negative electrode material and the solid electrolyte includes: ； Among them, L s is the equivalent diffusion distance of lithium ions in the silicon-based negative electrode material, m.

7. The method for predicting the pre-lithium amount of a silicon-based negative electrode according to claim 6, characterized in that: The silicon-based negative electrode contains a solid electrolyte, L s is 0.30 to 0.35 times the maximum particle radius of the silicon-based negative electrode material in the silicon-based negative electrode; or, the silicon-based negative electrode does not contain a solid electrolyte, L s It is 0.95 to 1.05 times the thickness of the silicon-based negative electrode.

8. A method for preparing a silicon-based negative electrode, characterized in that: The method for preparing the silicon-based negative electrode comprises: The method for predicting the pre-lithium amount of a silicon-based negative electrode according to any one of claims 1 to 7 is used to calculate a minimum pre-lithium amount, and a pre-lithium layer is formed according to the minimum pre-lithium amount; The pre-lithium layer and the negative electrode active layer containing the silicon-based negative electrode material are stacked to obtain a silicon-based negative electrode.

9. The method for preparing a silicon-based negative electrode according to claim 8, characterized in that: The method for preparing the silicon-based negative electrode comprises: Providing the pre-lithium layer; Preparing a negative electrode slurry containing a silicon-based negative electrode material, a binder and a solvent, and coating the negative electrode slurry on the surface of the pre-lithium layer to form a negative electrode active layer, thereby preparing the silicon-based negative electrode; Optionally, the solvent includes at least one of toluene, xylene, butyl butyrate, isobutyl isobutyrate and n-heptane; Optionally, the pre-lithium layer comprises lithium foil.

10. A solid-state battery, characterized in that: The solid-state battery comprises a silicon-based negative electrode prepared by the method for preparing a silicon-based negative electrode according to any one of claims 8 to 9.

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