Evaluation method for positive electrode paste for all-solid-state battery

Abstract

The purpose of the present invention is to accurately evaluate the state of coverage of a solid electrolyte in a positive electrode active material in a positive electrode slurry for an all-solid-state battery. This evaluation method for a positive electrode slurry for an all-solid-state battery comprises: a measurement step for sealing a positive electrode slurry for an all-solid-state battery, in which a positive electrode active material, a solid electrolyte, a conductive assistant, and a binder material are kneaded and dispersed, in a measurement container having electrodes provided at both ends thereof, and measuring AC impedance; a frequency region determination step for determining a frequency region on the basis of the measurement data of the AC impedance; and an evaluation step for evaluating the quality of the state of coverage of the solid electrolyte in the positive electrode active material on the basis of the determined parameter of the imaginary axis of the AC impedance in the frequency region and the determined parameter of the real axis of the AC impedance in the frequency region.

Description

Technical Field

[0001] This application claims priority based on Japanese Patent Application No. 2023-094676 filed on June 8, 2023, the contents of which are incorporated herein.

[0002] The present invention relates to a method for accurately evaluating the quality of a positive electrode slurry containing an active material, a solid electrolyte, a conductive auxiliary agent, a binder material, etc. for an all-solid-state battery in a slurry state. Background Art

[0003] In the manufacture of electrode slurries for liquid electrolyte lithium-ion batteries and all-solid-state lithium-ion batteries, the quality of the electrode slurries is generally managed by evaluating rheology such as viscosity. In addition, the following techniques are known: as a quality management method for electrode slurries, for example, the electrode slurry just after manufacture is extracted to measure the AC impedance of the electrode slurry, thereby determining the quality of the electrode slurry. Moreover, as an evaluation method for the quality of the positive electrode slurry of an all-solid-state lithium-ion battery, for example, a method for evaluating the covering state of the covering material in the electrode active material can be cited.

[0004] Japanese Patent Gazette No. 2015-222651 describes the following: In a method for manufacturing a paste including an active material, a solid electrolyte and a conductive aid, the method comprises: a measuring step of measuring the AC impedance of the paste corresponding to a specified measurement frequency band; a composition ratio determination step of determining whether the composition ratio of the paste is outside a specified range based on the width in the direction of the real part of the arc portion corresponding to the specified frequency band in a trajectory of the measured AC impedance drawn on a complex impedance plane; and a removal step of removing the paste whose composition ratio is determined to be outside the specified range.

[0005] The following is described in Japanese Patent Gazette No. 5505318: In a paste evaluation method for evaluating a paste applied to the surface of a battery electrode, a container having a rotating mechanism and a measuring unit for measuring the AC impedance of the paste are used. The paste contained in the container is rotated by the rotating mechanism, and the AC impedance of the paste is measured by the measuring unit. The measuring unit has a pair of applying electrode plates arranged in parallel for applying an AC voltage to the paste. The measured values ​​of the AC impedance for more than one rotation by the rotating mechanism are averaged to correct the measurement error caused by the parallelism error of the pair of applying electrode plates. Summary of the invention

[0006] As for the positive electrode slurry for all-solid-state batteries, the materials used are increased for the slurry used for liquid electrolyte lithium-ion batteries, and the composite elements of active materials and solid electrolytes are included. The composite (covering state) of the solid electrolyte in the positive electrode active material contributes greatly to the battery performance. However, in the slurry state, no specific method for evaluating the covering state of the solid electrolyte in the positive electrode active material has been found, and it is difficult to evaluate the covering state with good accuracy.

[0007] In order to solve the above problems, the present application aims to accurately evaluate the coverage state of the solid electrolyte in the positive electrode active material in the positive electrode slurry for all-solid-state batteries, which helps to stabilize battery performance, improve quality management in the manufacturing process, and even improve energy efficiency.

[0008] [1] A method for evaluating a positive electrode slurry for an all-solid-state battery, wherein:

[0009] The evaluation method of the positive electrode slurry for the all-solid-state battery has the following characteristics:

[0010] The measuring step is to seal the positive electrode slurry for the all-solid-state battery obtained by mixing and dispersing the positive electrode active material, the solid electrolyte, the conductive auxiliary agent and the binder material into a measuring container with electrodes provided at both ends, and measure the AC impedance;

[0011] a frequency region determining step of determining a frequency region based on the measured data of the AC impedance; and

[0012] The evaluation step evaluates the quality of the coating state of the solid electrolyte in the positive electrode active material based on the determined parameters of the imaginary axis of the AC impedance in the frequency region and the determined parameters of the real axis of the AC impedance in the frequency region.

[0013] The evaluation method of the positive electrode slurry for an all-solid-state battery of the present invention can accurately evaluate the coverage state of the solid electrolyte in the positive electrode active material based on the parameters of the imaginary axis of the AC impedance in a specific frequency region and the parameters of the real axis of the AC impedance in a specific frequency region according to the measured AC impedance of the positive electrode slurry for an all-solid-state battery.

[0014] [2] The method for evaluating a positive electrode slurry for an all-solid-state battery according to [1], wherein the parameter of the imaginary axis of the AC impedance is the imaginary component (Zim) of the AC impedance of the positive electrode slurry for an all-solid-state battery or the polarization charge (Cp) derived from the imaginary component (Zim) of the AC impedance.

[0015] The evaluation method of the positive electrode slurry for an all-solid-state battery of the present invention uses the imaginary component (Zim) of the AC impedance or the polarization charge (Cp) derived from the imaginary component (Zim) of the AC impedance as a parameter of the imaginary axis of the AC impedance, thereby being able to accurately evaluate the coverage state of the solid electrolyte in the positive electrode active material.

[0016] [3] The method for evaluating a positive electrode slurry for an all-solid-state battery according to [1] or [2], wherein the parameter of the real axis of the AC impedance is a real component (Zre) of the AC impedance of the positive electrode slurry for an all-solid-state battery.

[0017] The method for evaluating the positive electrode slurry for an all-solid-state battery of the present invention uses the real component (Zre) of the AC impedance of the positive electrode slurry for an all-solid-state battery as a parameter of the real axis of the AC impedance, and therefore can accurately evaluate the dispersion state of the positive electrode slurry.

[0018] [4] The method for evaluating a positive electrode slurry for an all-solid-state battery according to any one of [1] to [3], wherein in the frequency region determining step, the AC impedance of the positive electrode slurry for an all-solid-state battery is divided into two or more frequency regions for evaluation.

[0019] The method for evaluating the positive electrode slurry for an all-solid-state battery of the present invention evaluates the AC impedance of the positive electrode slurry for an all-solid-state battery in two or more frequency regions, and thus can accurately evaluate the coverage state of the solid electrolyte in the positive electrode active material.

[0020] [5] An evaluation method for a positive electrode slurry for an all-solid-state battery according to any one of [1] to [4], wherein, in the frequency region determination step, the polarization charge (Cp) derived from the imaginary component (Zim) of the AC impedance and the real component (Zre) of the AC impedance obtained in different frequency regions are evaluated separately or in combination to evaluate the quality.

[0021] The evaluation method of the positive electrode slurry for an all-solid-state battery of the present invention divides the AC impedance of the positive electrode slurry for an all-solid-state battery into two or more frequency regions, and combines the parameters of the AC impedance imaginary axis and the parameters of the AC impedance real axis for evaluation, thereby being able to more accurately evaluate the coverage state of the solid electrolyte in the positive electrode active material.

[0022] According to the aspect of the present invention, in the positive electrode slurry for an all-solid-state battery, the coverage state of the solid electrolyte in the positive electrode active material can be evaluated with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flowchart showing a method for evaluating the positive electrode slurry for an all-solid-state battery according to the present embodiment.

[0024] Figure 2 This is a diagram showing an example of a Nyquist plot as a result of measuring the AC impedance of a positive electrode slurry for an all-solid-state battery.

[0025] Figure 3 This is a graph showing the relationship between the load intensity and the polarization charge amount (Cp) in the solid electrolyte coating step of the active material for an all-solid-state battery in Example 1.

[0026] Figure 4 This is a diagram showing the relationship between the load intensity and the real component (Zre) in the solid electrolyte coating step of the active material for an all-solid-state battery in Example 1. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described in detail.

[0028] [Evaluation method for positive electrode slurry for all-solid-state batteries]

[0029] The evaluation method of the positive electrode slurry for an all-solid-state battery involved in the embodiment of the present invention comprises: a measuring step, in which the positive electrode slurry for an all-solid-state battery obtained by kneading and dispersing a positive electrode active material, a solid electrolyte, a conductive auxiliary agent and a binder material is sealed in a measuring container with electrodes provided at both ends, and the AC impedance is measured; a frequency region determination step, in which the frequency region is determined according to the measurement data of the AC impedance; and an evaluation step, in which the quality of the coverage state of the solid electrolyte in the positive electrode active material is evaluated based on the parameters of the AC impedance imaginary axis determined in the frequency region and the parameters of the AC impedance real axis determined in the frequency region.

[0030] The evaluation method of the positive electrode slurry for all-solid-state batteries according to the present embodiment may include a step of preparing the positive electrode slurry for all-solid-state batteries to be evaluated by the evaluation method of the positive electrode slurry for all-solid-state batteries according to the present embodiment.

[0031] Figure 1 This is a flowchart showing a method for evaluating the positive electrode slurry for an all-solid-state battery according to the present embodiment.

[0032] "Preparation process"

[0033] In the evaluation method of the positive electrode slurry for all-solid-state batteries of the present embodiment, the preparation step ( Figure 1 Evaluation of the positive electrode slurry for all-solid-state batteries prepared in S1) shown.

[0034] The positive electrode slurry for an all-solid-state battery that is the subject of quality control by the evaluation method for the positive electrode slurry for an all-solid-state battery of the present embodiment contains a positive electrode active material, a solid electrolyte, a conductive auxiliary agent, and a binder material.

[0035] As the positive electrode active material, there is no particular limitation as long as it is a material that can reversibly release and absorb lithium ions and can transport electrons, and known positive electrode active materials that can be applied to the positive electrode of an all-solid-state lithium ion battery can be used. For example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), solid solution oxide (Li2MnO3-LiMO2 (M=Co, Ni, etc.)), lithium-manganese-nickel-cobalt oxide (LiNi x Mn y Co z O2, x+y+z=1), composite oxides such as olivine lithium phosphorus oxide (LiFePO4); conductive polymers such as polyaniline and polypyrrole; sulfides such as Li2S, CuS, Li-Cu-S compounds, TiS2, FeS, MoS2, Li-Mo-S compounds; mixtures of sulfur and carbon; etc. The positive electrode active material can be composed of one of the above materials alone, or it can be composed of two or more of the above materials.

[0036] As a solid electrolyte, there is no particular restriction as long as there is lithium ion conductivity and insulation, and generally speaking, materials for all-solid-state lithium ion batteries can be used. For example, sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, inorganic solid electrolytes such as lithium salts, solid electrolytes of polymer systems such as polyethylene oxide, and gel-based solid electrolytes containing lithium salts and ionic liquids with lithium ion conductivity can be cited. Among them, from the viewpoint of high electrical conductivity of lithium ions, structural formability based on pressure, and good interface bonding, sulfide solid electrolyte materials are preferably used.

[0037] The form of the solid electrolyte material is not particularly limited, and an example thereof is a particle form.

[0038] From the viewpoint of improving the conductivity of the positive electrode, the positive electrode slurry for the all-solid-state battery may also contain a conductive aid. As the conductive aid, generally speaking, a conductive aid that can be used in an all-solid-state lithium-ion battery can be used. For example, carbon black such as acetylene black and Ketjen black; carbon fiber; gas-phase carbon fiber; graphite powder; carbon nanotubes and other carbon materials can be cited. The conductive aid may be composed of one of the above materials alone, or may be composed of two or more of the above materials.

[0039] The positive electrode slurry for an all-solid-state battery may contain a solvent from the viewpoint of adjusting the viscosity.

[0040] The positive electrode slurry for all-solid-state batteries can be prepared by mixing the positive electrode active material, solid electrolyte, conductive aid and binder material in a specified ratio, and kneading the mixture including the positive electrode active material, solid electrolyte, conductive aid and binder material with a mixer.

[0041] "Measurement process"

[0042] In the measurement process, the positive electrode slurry for the all-solid-state battery is arranged between two electrodes, and an AC voltage or an AC current is applied between the two electrodes to measure the AC impedance ( Figure 1 S2 shown).

[0043] In the evaluation method of the positive electrode slurry for all-solid-state batteries of the present embodiment, the frequency of the AC voltage or AC current used for measuring the AC impedance of the positive electrode slurry for all-solid-state batteries is continuously changed from 5 MHz to 1 Hz, for example.

[0044] Frequency region determination process

[0045] In the frequency region determining step, based on the AC impedance measurement data obtained in the measurement step, an AC frequency region ( Figure 1 S3 shown).

[0046] In the evaluation method of the coverage state of the solid electrolyte in the positive electrode active material of the present invention, the parameters of the imaginary axis of the AC impedance in a specific frequency region and the parameters of the real axis of the AC impedance in a specific frequency region in the AC impedance measurement data obtained in the measurement process are used, thereby being able to evaluate the coverage state with good accuracy. As the frequency region of the AC used for evaluating the coverage state, for example, 5kHz to 50kHz, 100Hz to 1kHz, 5Hz to 20Hz, etc. are selected.

[0047] The parameter of the imaginary axis of the AC impedance of the positive electrode slurry for all-solid-state batteries is preferably the imaginary component (Zim) of the AC impedance, or the polarization charge (Cp) derived from the imaginary component (Zim) of the AC impedance. The method for determining the frequency region of the imaginary component (Zim) or the polarization charge (Cp) used for the evaluation of the covering state is described. The imaginary component (Zim) or the polarization charge (Cp) derived from the imaginary component (Zim) of the AC impedance in the frequency region of 5Hz to 20Hz is selected as the imaginary axis parameter for the evaluation of the covering state. The frequency at which the imaginary axis parameter changes greatly varies according to the material of the active material, etc. For example, by evaluating the sample obtained by changing the load intensity of the solid electrolyte covering process of the active material for all-solid-state batteries with respect to the material, the frequency of the large change can be determined. In the case of the positive electrode slurry for an all-solid-state battery in the embodiment, the frequency at which the imaginary component (Zim) or the polarization charge (Cp) changes at the maximum amplitude is, for example, 10 Hz.

[0048] The parameter of the real axis of the AC impedance of the positive electrode slurry for all-solid-state batteries is preferably the real component (Zre) of the AC impedance of the positive electrode slurry for all-solid-state batteries. A method for determining the frequency region of the real component (Zre) used for evaluating the coverage state will be described.

[0049] The data of the AC impedance acquired in the measurement step are divided into a real number component (Zre) on the horizontal axis and an imaginary number component (Zim) on the vertical axis, and displayed on a complex plane (Nyquist plot). Figure 2 1 is a diagram showing an example of a Nyquist plot of the AC impedance measurement of the positive electrode slurry for an all-solid-state battery obtained by the measurement step. Figure 2 In this way, in the Nyquist plot of the positive electrode slurry for all-solid-state batteries, there are theoretically three arc parts. However, the first arc part in the real part direction is difficult to obtain with the measurement equipment currently used. Figure 2 In the embodiment, the frequency of the boundary between the second arc portion and the third arc portion in the real part direction from the low impedance side is set as the frequency of the real number component (Zre) used for evaluation of the coverage state.

[0050] The second arc portion is an arc portion corresponding to a frequency range of 1 kHz to 1 MHz, and the third arc portion is an arc portion corresponding to a frequency range of 5 Hz to 1 kHz.

[0051] "Step for evaluating the coating state of the solid electrolyte in the positive electrode active material"

[0052] In the evaluation step of the coverage state of the solid electrolyte in the positive electrode active material (hereinafter referred to as the evaluation step), the coverage state of the solid electrolyte in the positive electrode active material is evaluated based on the parameters of the imaginary axis of the AC impedance and the parameters of the real axis of the AC impedance at the frequency determined by the frequency region determination step in the AC impedance measurement result of the positive electrode slurry for the all-solid-state battery obtained in the measurement step. Figure 1 S4 shown).

[0053] When the parameters of the imaginary axis of the AC impedance in the frequency region determined by the frequency region determination process satisfy the reference value set in advance according to the AC impedance measurement results of the all-solid-state battery positive electrode slurry (hereinafter referred to as the qualified slurry) with good coverage of the solid electrolyte in the positive electrode active material, and the parameters of the real axis of the AC impedance in the frequency region determined by the frequency region determination process satisfy the reference value set in advance according to the AC impedance measurement results of the qualified slurry, it is determined to be the all-solid-state battery positive electrode slurry with good coverage of the solid electrolyte in the positive electrode active material. As the reference value, for example, it is determined according to the AC impedance measurement results of the following slurry, and the slurry refers to the slurry that is determined to be a qualified slurry based on battery performance, the dispersion state of the slurry obtained by an analysis method such as a particle size distribution meter, and the coverage thickness of the solid electrolyte calculated by an analysis method such as an electron microscope. The upper limit and lower limit of the reference value are determined according to the type of positive electrode slurry for all-solid-state batteries.

[0054] When the parameters of the imaginary axis of the AC impedance in the frequency region determined by the frequency region determination process do not satisfy the reference values ​​pre-set according to the AC impedance measurement results of the qualified slurry, and / or the parameters of the real axis of the AC impedance in the frequency region determined by the frequency region determination process do not satisfy the reference values ​​pre-set according to the AC impedance measurement results of the qualified slurry, it is determined that the positive electrode slurry for an all-solid-state battery has a poor coverage state of the solid electrolyte in the positive electrode active material.

[0055] According to the evaluation method of the positive electrode slurry for all-solid-state batteries of the present embodiment, the AC impedance of the positive electrode slurry for all-solid-state batteries can be measured in a specific frequency region, and based on the obtained parameters of the imaginary axis of the AC impedance and the real axis of the AC impedance, the coverage state of the solid electrolyte in the positive electrode active material can be evaluated with good accuracy.

[0056] [Example]

[0057] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0058] [Example 1]

[0059] "Preparation of positive electrode slurry for all-solid-state batteries"

[0060] In order to change the coating state of the positive electrode active material, a composite material was prepared in advance in which the processing conditions in the solid electrolyte coating step were changed in four examples. The four examples were prepared under conditions ranging from low to high processing loads.

[0061] Thereafter, a positive electrode slurry for an all-solid-state battery was prepared as shown below.

[0062] The binder solution and the conductive auxiliary agent dispersion were stirred and mixed at 2000 rpm for 1 minute using a rotary and revolving stirrer (kneading device), thereby obtaining a mixture 1.

[0063] To the obtained mixture 1, zirconia balls with a diameter of 2 mm, positive electrode active material (the solid electrolyte has been covered, for example, positive electrode active material: solid electrolyte = 75:25 to 90:10 (mass ratio)), and solvent (butyl butyrate) are added, and the mixture is stirred and mixed at 2000 rpm for 1 minute to obtain a mixture 2.

[0064] A solid electrolyte and a solvent (butyl butyrate) were added to the obtained mixture 2, and the mixture was kneaded at 2000 rpm for 1 minute using a kneading device to obtain a mixture 3.

[0065] A diluting solvent (butyl butyrate) was added to the obtained mixture 3, and the mixture was stirred and mixed at 2000 rpm for 2 minutes, thereby obtaining a mixture 4.

[0066] Thereafter, a process of kneading while repeating dilution was performed.

[0067] "Impedance measurement: Imaginary component (Cp)"

[0068] The AC impedance of the positive electrode slurry for all-solid-state batteries obtained by changing the processing conditions was measured, and the polarization charge (Cp) derived from the parameter (Zim) of the imaginary axis of the AC impedance was calculated. The relationship between the load intensity conditions in the treatment of the covering process and the polarization charge (Cp) was investigated. The results are shown in Figure 3 In. According to Figure 3 The results show that the load intensity is proportional to the polarization charge (Cp), and the greater the load intensity, the smaller the polarization charge (Cp). This indicates that the greater the load intensity, the more the solid electrolyte covers the active material, thereby reducing the surface area exposed on the surface of the positive electrode active material, and the solid electrolyte is well covered as a particle.

[0069] "Impedance determination: Real component (Zre)"

[0070] The real component (Zre) of the AC impedance of the positive electrode slurry for all-solid-state batteries was calculated as a parameter of the real axis of the AC impedance obtained, and the relationship between the processing conditions of the positive electrode slurry for all-solid-state batteries and the real component (Zre) was investigated. The results are shown in Figure 4 In. According to Figure 4 The results shown show that the load intensity and the real number component (Zre) are proportional, and the greater the load intensity, the greater the real number component (Zre). In this regard, it is inferred from other verification results that there is no direct causal relationship between it and the coverage state of the solid electrolyte. However, the dispersion state is different in the all-solid slurry obtained by changing the processing conditions, and it is inferred that the difference in the dispersion state is shown. If the real axis parameter falls within the preset reference value, it can be judged as a state with a good dispersion state.

[0071] As mentioned above, although embodiment of this invention is described in detail, this invention is not limited to the said embodiment, Various deformation|transformation and change are possible within the range of the summary of this invention described in the range of claims.

Claims

1. A method for evaluating a positive electrode slurry for an all-solid-state battery, wherein: The evaluation method of the positive electrode slurry for the all-solid-state battery has the following characteristics: The measuring step is to seal the positive electrode slurry for the all-solid-state battery obtained by mixing and dispersing the positive electrode active material, the solid electrolyte, the conductive auxiliary agent and the binder material into a measuring container with electrodes provided at both ends, and measure the AC impedance; a frequency region determining step of determining the frequency region based on the measured data of the AC impedance; as well as The evaluation step evaluates the quality of the coating state of the solid electrolyte in the positive electrode active material based on the determined parameters of the imaginary axis of the AC impedance in the frequency region and the determined parameters of the real axis of the AC impedance in the frequency region.

2. The method for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein: The parameter of the imaginary axis of the AC impedance is the imaginary component (Zim) of the AC impedance of the positive electrode slurry for the all-solid-state battery or the polarization charge (Cp) derived from the imaginary component (Zim).

3. The method for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein: The parameter of the real axis of the AC impedance is the real component (Zre) of the AC impedance of the positive electrode slurry for an all-solid-state battery.

4. The method for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein: In the frequency region determining step, the AC impedance of the positive electrode slurry for an all-solid-state battery is divided into two or more frequency regions for evaluation.

5. The method for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein: In the frequency region determination step, the polarization charge amount (Cp) derived from the imaginary component (Zim) of the AC impedance and the real component (Zre) of the AC impedance obtained in different frequency regions are evaluated individually or in combination.

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