Evaluation device for positive electrode slurry for all-solid-state batteries

Abstract

To accurately evaluate the coating state of a solid electrolyte on a positive electrode active material in a positive electrode slurry for an all-solid-state battery.SOLUTION: An evaluation device 1 for a positive electrode slurry for an all-solid-state battery includes a flow path 2 through which positive electrode slurry flows and a measurement unit 3 that measures the AC impedance of the positive electrode slurry, the measurement unit 3 includes a first channel unit that measures the AC impedance at a first predetermined frequency and a second channel unit that measures the AC impedance at a second predetermined frequency, and the measurement unit 3 includes an evaluation unit that evaluates the quality of the coating state of the solid electrolyte on the positive electrode active material on the basis of parameters on the imaginary axis of the AC impedance and parameters on the real axis of the AC impedance, which are measured by the first channel unit and the second channel unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an evaluation device for positive electrode slurry for an all-solid-state battery that accurately evaluates the quality of a positive electrode slurry containing an active material, a solid electrolyte, a conductive additive, a binder material, etc. for an all-solid-state battery in a slurry state. [Background technology]

[0002] In the production of electrode slurries for use in liquid electrolyte lithium-ion batteries and all-solid-state lithium-ion batteries, the quality of the electrode slurries is generally controlled by rheological evaluation such as viscosity. A known method for controlling the quality of electrode slurries is, for example, to sample electrode slurries immediately after production and measure the AC impedance of the electrode slurries to determine whether the electrode slurries are good or bad. Furthermore, a method for evaluating the quality of positive electrode slurries for all-solid-state lithium-ion batteries includes, for example, evaluating the coating state of a coating material on an electrode active material.

[0003] Patent Document 1 describes a method for producing a paste containing an active material, a solid electrolyte, and a conductive additive, which includes a measurement step of measuring the AC impedance of the paste corresponding to a predetermined measurement frequency band, a composition ratio determination step of determining whether or not the composition ratio of the paste is outside a predetermined range based on the width in the real part direction of an arc portion corresponding to the predetermined frequency band in a locus drawn by the measured AC impedance on a complex impedance plane, and a removal step of removing paste whose composition ratio is determined to be outside the predetermined range.

[0004] Patent Document 2 describes a paste evaluation method for evaluating a paste to be applied to the electrode surface of a battery, which uses a container having a rotation mechanism and a measurement unit that measures the AC impedance of the paste, and describes that the paste contained in the container is rotated by the rotation mechanism while the measurement unit measures the AC impedance of the paste, and that the measurement unit has a pair of application electrode plates arranged in parallel to apply an AC voltage to the paste, and that the measured values ​​of the AC impedance for one or more rotations by the rotation mechanism are averaged to correct measurement errors arising from errors in the parallelism of the pair of application electrode plates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-222651 [Patent Document 2] Patent No. 5505318 Summary of the Invention [Problem to be solved by the invention]

[0006] Compared to liquid electrolyte lithium-ion batteries, cathode slurries for all-solid-state batteries use more materials and contain a composite element between the active material and the solid electrolyte, and it is believed that the composite (coating state) of the solid electrolyte on the cathode active material contributes greatly to battery performance. However, no specific method has been found to evaluate the coating state of the solid electrolyte on the cathode active material in a slurry state, making it difficult to accurately evaluate the coating state.

[0007] In order to solve the above problems, the present application aims to accurately evaluate the coating state of a solid electrolyte on a positive electrode active material in a positive electrode slurry for an all-solid-state battery, thereby contributing to stabilization of battery performance, improvement of quality control in the manufacturing process, and ultimately to energy efficiency. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides the following means. [1] An evaluation device for a positive electrode slurry for an all-solid-state battery, which evaluates a coating state of a positive electrode slurry in which at least a positive electrode active material and a solid electrolyte are mixed and dispersed, comprising: a flow path through which the positive electrode slurry flows; a measurement unit that is provided in the flow path and that measures the AC impedance of the positive electrode slurry, the measurement unit has a first channel unit that measures the AC impedance at a first predetermined frequency and a second channel unit that measures the AC impedance at a second predetermined frequency, the measurement unit has an evaluation unit that evaluates the quality of a coating state of the solid electrolyte on the positive electrode active material based on a parameter on an imaginary axis of the AC impedance and a parameter on a real axis of the AC impedance measured by the first channel unit and the second channel unit.

[0009] By dividing the channel into a first channel section corresponding to a first predetermined frequency and a second channel section corresponding to a second predetermined frequency and measuring the AC impedance for each channel section, the measurement time can be shortened compared to when measuring the AC impedance while changing the frequency of the channel section, the amount of positive electrode slurry that is subject to quality judgment can be reduced, and erroneous judgments can be suppressed.

[0010] [2] The flow path has a first measurement area that is a measurement area of ​​the first channel section and a second measurement area that is a measurement area of ​​the second channel section, The device for evaluating a positive electrode slurry for an all-solid-state battery according to [1], wherein the first measurement area and the second measurement area are defined adjacent to each other in an extension direction of the flow channel.

[0011] The channel is divided into a first channel section corresponding to a first predetermined frequency and a second channel section corresponding to a second predetermined frequency, and a measurement area is provided for each channel section. By dividing the measurement areas adjacent to each other in the direction of extension of the flow path (the direction in which the positive electrode slurry flows), the same slurry can be measured using multiple channels, making it possible to inspect all positive electrode slurries.

[0012] [3] The measurement unit has a third channel unit that measures the AC impedance at a third predetermined frequency, the flow path has a third measurement region that is a measurement region of the third channel portion, The device for evaluating a positive electrode slurry for an all-solid-state battery according to [2], wherein the first measurement area, the second measurement area, and the third measurement area are defined adjacent to each other in an extension direction of the flow channel.

[0013] By providing a third channel section corresponding to a third predetermined frequency in addition to the first channel section corresponding to the first predetermined frequency and the second channel section corresponding to the second predetermined frequency, the AC impedance of the positive electrode slurry can be measured more accurately.

[0014] [4] The first predetermined frequency corresponds to a second arc of a Nyquist diagram drawn based on an imaginary axis parameter of the AC impedance measured by the first channel unit and a real axis parameter of the AC impedance measured by the second channel unit; The device for evaluating a positive electrode slurry for an all-solid-state battery according to any one of [1] to [3], wherein the second predetermined frequency corresponds to a third arc of a Nyquist diagram drawn based on a parameter on an imaginary axis of the AC impedance measured by the first channel unit and the parameter on a real axis of the AC impedance measured by the second channel unit.

[0015] By distinguishing between the second arc corresponding to the first predetermined frequency and the third arc corresponding to the second predetermined frequency in the Nyquist diagram, information obtained from the measurement results of the AC impedance of the positive electrode slurry can be analyzed more accurately.

[0016] [5] The device for evaluating a positive electrode slurry for an all-solid-state battery according to [3], wherein the third predetermined frequency corresponds to a first arc of a Nyquist diagram drawn based on a parameter on an imaginary axis of the AC impedance measured by the third channel unit and a parameter on a real axis of the AC impedance.

[0017] In the Nyquist diagram, by distinguishing the first arc corresponding to the third predetermined frequency from the second arc corresponding to the first predetermined frequency and the third arc corresponding to the second predetermined frequency, information obtained from the measurement results of the AC impedance of the positive electrode slurry can be analyzed more accurately.

[0018] [6] The evaluation device for evaluating a positive electrode slurry for an all-solid-state battery according to [1], wherein the evaluation unit evaluates the quality of the coating state based on a polarization charge amount derived from a real component of the AC impedance measured by the first channel unit and an imaginary component of the AC impedance measured by the second channel unit.

[0019] The amount of solid content can be estimated from the amount of polarization charge derived from the imaginary component of AC impedance.

[0020] [7] The flow path has a temperature adjustment unit upstream of the measurement unit, [1] The apparatus for evaluating a positive electrode slurry for an all-solid-state battery according to [1], further comprising: a control unit that adjusts the temperature of the positive electrode slurry by the temperature adjustment unit so that the temperature of the positive electrode slurry is within a predetermined range.

[0021] The control unit adjusts the temperature of the positive electrode slurry to be within a predetermined range, thereby reducing the effect on AC impedance of changes in viscosity of the positive electrode slurry caused by temperature changes, and enabling more accurate analysis of information obtained from the measurement results of the AC impedance of the positive electrode slurry. [Effects of the Invention]

[0022] According to the present invention, in a positive electrode slurry for an all-solid-state battery, the coating state of a positive electrode active material with a solid electrolyte can be evaluated with high accuracy. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing an evaluation device for a positive electrode slurry for an all-solid-state battery according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing a measurement unit constituting an evaluation device for a positive electrode slurry for an all-solid-state battery according to an embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing an equivalent circuit formed by a positive electrode slurry. [Figure 4] FIG. 2 is a diagram showing an example of a Nyquist diagram of AC impedance measurement of a positive electrode slurry, obtained by a measurement unit of the evaluation device for a positive electrode slurry for an all-solid-state battery according to an embodiment of the present invention. [Figure 5] FIG. 1 is a Nyquist diagram created based on the parameter (Zim) of the imaginary axis of AC impedance and the parameter (Zre) of the real component of AC impedance in the example. [Figure 6] FIG. 10 is a diagram showing the relationship between the parameter (Zre) of the real component of the AC impedance corresponding to the second arc and the solid content of the positive electrode slurry for the all-solid-state battery in the Examples. [Figure 7] FIG. 1 is a Nyquist diagram created based on the parameter (Zim) of the imaginary axis of AC impedance and the parameter (Zre) of the real component of AC impedance in the example. [Figure 8] FIG. 10 is a diagram showing the relationship between the polarization charge (Cp) derived from the parameter (Zim) of the AC impedance imaginary axis corresponding to the third arc and the solid content of the positive electrode slurry for an all-solid-state battery in the Examples. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0025] [Evaluation equipment for positive electrode slurry for all-solid-state batteries] Fig. 1 is a schematic diagram showing an evaluation device for a positive electrode slurry for an all-solid-state battery according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing a measurement unit constituting the evaluation device for a positive electrode slurry for an all-solid-state battery according to an embodiment of the present invention. Note that the drawings used in the following description may conveniently show characteristic portions enlarged to make the characteristics easier to understand, and the dimensional ratios of the respective components are not limited to those shown.

[0026] As shown in FIG. 1, an evaluation device 1 for an all-solid-state battery positive electrode slurry according to this embodiment (hereinafter sometimes abbreviated as "evaluation device") includes a flow path 2, a measurement unit 3, a kneading unit 4, a supply unit 5, a non-defective product recovery unit 6, and a defective product recovery unit 7. The evaluation device 1 may also include a viscosity measurement unit 8 and a temperature adjustment unit 9. The evaluation device 1 is a device that evaluates the coating state (the coating state of the positive electrode active material by the solid electrolyte) of an all-solid-state battery positive electrode slurry (hereinafter sometimes abbreviated as "positive electrode slurry") in which at least a positive electrode active material and a solid electrolyte are kneaded and dispersed.

[0027] Flow path 2 is a flow path through which the positive electrode slurry flows.

[0028] The measuring unit 3 is provided in the flow path 2 and measures the AC impedance of the positive electrode slurry flowing within the flow path 2.

[0029] 2, the measurement unit 3 has a first channel unit 11, a second channel unit 12, and an evaluation unit. The first channel unit 11 measures the AC impedance of the positive electrode slurry at a first predetermined frequency. The second channel unit 12 measures the AC impedance of the positive electrode slurry at a second predetermined frequency.

[0030] The evaluation unit evaluates the quality of the coating state of the solid electrolyte on the positive electrode active material contained in the positive electrode slurry based on the imaginary axis parameter of the AC impedance of the positive electrode slurry and the real axis parameter of the AC impedance of the positive electrode slurry measured by the first channel unit 11 and the second channel unit 12. In detail, the evaluation unit evaluates the quality of the coating state of the positive electrode slurry based on the polarization charge amount derived from the real component of the AC impedance of the positive electrode slurry measured by the first channel unit 11 and the imaginary component of the AC impedance of the positive electrode slurry measured by the second channel unit 12.

[0031] The flow path 2 has a first measurement region 11A that is the measurement region of the first channel section 11, and a second measurement region 12A that is the measurement region of the second channel section 12. The first measurement region 11A and the second measurement region 12A are defined adjacent to each other in this order in the extension direction of the flow path 2 (the direction in which the positive electrode slurry flows).

[0032] 2, the measurement unit 3 preferably has a third channel unit 13. The third channel unit 13 measures the AC impedance of the positive electrode slurry at a third predetermined frequency.

[0033] It is preferable that the evaluation unit evaluates the quality of the coating state of the solid electrolyte on the positive electrode active material contained in the positive electrode slurry based on the imaginary axis parameter of the AC impedance of the positive electrode slurry measured by the third channel unit 13 and the real axis parameter of the AC impedance of the positive electrode slurry.

[0034] The flow path 2 has a third measurement region 13A, which is the measurement region of the third channel portion 13. The first measurement region 11A, the second measurement region 12A, and the third measurement region 13A are defined adjacent to each other in this order in the direction in which the flow path 2 extends (the direction in which the positive electrode slurry flows).

[0035] The kneading unit 4 kneads the materials for the positive electrode slurry, such as the positive electrode active material, solid electrolyte, binder, and solvent, supplied from the supply unit 5. As the kneading unit 4, for example, a planetary rotation / revolution mixer can be used.

[0036] The non-defective product recovery unit 6 recovers the positive electrode slurry that has been determined to be non-defective by the evaluation in the measuring unit 3.

[0037] The defective product collecting section 7 collects the positive electrode slurry that has been determined to be defective by the evaluation in the measuring section 3.

[0038] Viscosity measuring unit 8 is provided in flow path 2 and measures the viscosity of the positive electrode slurry flowing within flow path 2.

[0039] Temperature adjusting unit 9 is provided in flow path 2 and adjusts the temperature of the positive electrode slurry flowing within flow path 2.

[0040] The evaluation device 1 preferably has a control unit that adjusts the temperature of the positive electrode slurry flowing in the flow channel 2 using a temperature adjustment unit 9 so that the temperature of the positive electrode slurry is within a predetermined range.

[0041] A method for evaluating the positive electrode slurry using the evaluation device 1 of this embodiment will be described.

[0042] In the kneading section 4, the materials for the positive electrode slurry, such as the positive electrode active material, solid electrolyte, binder, and solvent, supplied from the supply section 5, are kneaded to prepare the positive electrode slurry.

[0043] Here, the positive electrode slurry will be described. The positive electrode slurry contains a positive electrode active material, a solid electrolyte, a conductive additive, and a binder material.

[0044] The positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions and transport electrons, and known positive electrode active materials applicable to the positive electrode of all-solid-state lithium ion batteries 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-type lithium phosphate (LiFePO4); conductive polymers such as polyaniline and polypyrrole; sulfides such as Li2S, CuS, Li-Cu-S compounds, TiS2, FeS, MoS2, and Li-Mo-S compounds; mixtures of sulfur and carbon; etc. The positive electrode active material may be composed of one kind of the above materials alone, or may be composed of two or more kinds.

[0045] The solid electrolyte is not particularly limited as long as it has lithium ion conductivity and insulating properties, and materials generally used in all-solid-state lithium ion batteries can be used. Examples include inorganic solid electrolytes such as sulfide solid electrolyte materials, oxide solid electrolyte materials, halide solid electrolytes, and lithium-containing salts, polymer-based solid electrolytes such as polyethylene oxide, and gel-based solid electrolytes containing lithium-containing salts and lithium ion-conducting ionic liquids. Among these, sulfide solid electrolyte materials are preferred from the viewpoints of high lithium ion conductivity, structural formability by pressing, and interfacial bonding. The form of the solid electrolyte material is not particularly limited, and examples thereof include particulate forms.

[0046] The positive electrode slurry may contain a conductive additive to improve the conductivity of the positive electrode. Examples of the conductive additive include carbon blacks such as acetylene black and Ketjen black; carbon fibers; vapor-grown carbon fibers; graphite powder; and carbon nanotubes. The conductive additive may be composed of one or more of the above materials.

[0047] The positive electrode slurry may contain a solvent in order to adjust the viscosity.

[0048] The positive electrode slurry is considered to form an equivalent circuit shown in Figure 3. In Figure 3, R1 / C1 indicates ionic polarization, R2 / C2 indicates orientation polarization, and R3 / C3 indicates interface polarization. Here, the equivalent circuit of the positive electrode slurry will be described. We prepared a slurry containing only the positive electrode active material in a solvent, a slurry containing the positive electrode active material and a solid electrolyte in a solvent, and a slurry containing the positive electrode active material and a binder. We measured the natural frequencies of each slurry, resulting in the Nyquist diagram shown in Figure 4. The slurry containing only the positive electrode active material exhibits a low natural frequency; the slurry containing a binder exhibits a medium-frequency natural frequency; and the slurry containing a solid electrolyte exhibits a high-frequency natural frequency. These frequencies correspond to the first, second, and third arcs of the Nyquist diagram. From the above, we infer that the high-frequency measurement frequency of the first arc indicates ionic polarization of the mixture of the positive electrode active material, binder, and solid electrolyte; the medium-frequency measurement frequency of the second arc indicates orientation polarization between the positive electrode active material and the binder; and the low-frequency measurement frequency of the third arc indicates interfacial polarization between the positive electrode active materials.

[0049] The positive electrode slurry material prepared in the kneading unit 4 is sent to the measurement unit 3. The positive electrode slurry sent to the measurement unit 3 is first placed between two electrodes 21 and 22 provided in the first channel unit 11. The measurement unit 3 applies an AC voltage or AC current between the two electrodes 21 and 22 to measure the AC impedance of the positive electrode slurry. The first channel unit 11 continuously changes a first predetermined frequency of the AC voltage or AC current used to measure the AC impedance of the positive electrode slurry, for example, from 1 kHz to 1 MHz. The first predetermined frequency corresponds to a second arc of a Nyquist diagram drawn based on the imaginary axis parameter of the AC impedance of the positive electrode slurry measured by the first channel unit 11 and the real axis parameter of the AC impedance of the positive electrode slurry.

[0050] Next, the positive electrode slurry is placed between two electrodes 23, 24 provided in the second channel section 12. The measurement section 3 applies an AC voltage or AC current between the two electrodes 23, 24 to measure the AC impedance of the positive electrode slurry. The second predetermined frequency of the AC voltage or AC current used to measure the AC impedance of the positive electrode slurry in the second channel section 12 is continuously changed, for example, from 5 Hz to 1 kHz. The second predetermined frequency corresponds to the third arc of a Nyquist diagram drawn based on the imaginary axis parameter of the AC impedance of the positive electrode slurry measured by the second channel section 12 and the real axis parameter of the AC impedance of the positive electrode slurry.

[0051] Next, the positive electrode slurry is placed between two electrodes 25, 26 provided in the third channel section 13. The measurement section 3 applies an AC voltage or an AC current between the two electrodes 25, 26 to measure the AC impedance of the positive electrode slurry. The second predetermined frequency of the AC voltage or the AC current used to measure the AC impedance of the positive electrode slurry in the third channel section 13 is set to, for example, 1 MHz. The third predetermined frequency corresponds to a first arc of a Nyquist diagram drawn based on the imaginary axis parameter of the AC impedance of the positive electrode slurry measured by the third channel section 13 and the real axis parameter of the AC impedance of the positive electrode slurry.

[0052] From the measurement data of AC impedance acquired by the measurement unit 3, an AC frequency range to be used for evaluating the coating state of the solid electrolyte on the positive electrode active material is identified. In the evaluation device 1 of this embodiment, the coating state of the positive electrode slurry can be accurately evaluated by using parameters on the imaginary axis of the AC impedance in a specific frequency range and parameters on the real axis of the AC impedance in a specific frequency range, among the AC impedance measurement data acquired by the measurement unit 3. The first predetermined frequency of the AC voltage or AC current used to measure the AC impedance of the positive electrode slurry in the first channel unit 11 is selected to be, for example, 1 kHz to 1 MHz. The second predetermined frequency of the AC voltage or AC current used to measure the AC impedance of the positive electrode slurry in the second channel unit 12 is selected to be, for example, 5 Hz to 1 kHz. The second predetermined frequency of the AC voltage or AC current used to measure the AC impedance of the positive electrode slurry in the third channel unit 13 is selected to be, for example, 1 MHz.

[0053] The parameter on the imaginary axis of the AC impedance of the positive electrode slurry 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. A method for specifying the frequency domain of the imaginary component (Zim) or the polarization charge (Cp) used to evaluate the coating state of the positive electrode slurry will be described. The imaginary component (Zim) of AC impedance or the polarization charge (Cp) derived from the imaginary component (Zim) of AC impedance in the AC frequency range from 5 Hz to 1 MHz changes most significantly depending on the type of positive electrode slurry being measured. The imaginary component (Zim) or the polarization charge (Cp) at the frequency at which the imaginary component (Zim) or the polarization charge (Cp) changes most significantly is defined as the imaginary axis parameter used to evaluate the coating state of the positive electrode slurry. The frequency at which this imaginary axis parameter changes most significantly varies depending on the material of the active material, and the frequency at which the imaginary axis parameter changes most significantly can be identified, for example, by evaluating samples in which the load strength when coating the positive electrode active material with the solid electrolyte is changed.

[0054] The parameter on the real axis of the AC impedance of the positive electrode slurry is preferably the real component (Zre) of the AC impedance of the positive electrode slurry. A method for specifying the frequency domain of the real component (Zre) used to evaluate the coating state will be described below. The AC impedance data acquired by the measurement unit 3 is displayed on a complex plane (Nyquist plot) with the real component (Zre) on the horizontal axis and the imaginary component (Zim) on the vertical axis. FIG. 4 shows an example of a Nyquist diagram of the AC impedance measurement of the positive electrode slurry obtained by the measurement unit 3. As shown in FIG. 4, the Nyquist diagram of the positive electrode slurry theoretically has three arcs. In the Nyquist diagram shown in FIG. 4, the third arc corresponds to the second predetermined frequency (5 Hz to 1 kHz). The second arc corresponds to the first predetermined frequency (1 kHz to 1 MHz). The first arc corresponds to the third predetermined frequency (1 MHz).

[0055] The evaluation unit of the measurement unit 3 evaluates the quality of the coating state of the solid electrolyte on the positive electrode active material based on a parameter on the imaginary axis of the AC impedance and a parameter on the real axis of the AC impedance at the frequency specified by the measurement unit 3, among the AC impedance measurement results of the positive electrode slurry measured by the first channel unit 11 and the second channel unit 12 of the measurement unit 3. Furthermore, it is preferable that the evaluation unit of the measurement unit 3 evaluates the quality of the coating state of the solid electrolyte on the positive electrode active material based on a parameter on the imaginary axis of the AC impedance and a parameter on the real axis of the AC impedance at the frequency specified by the measurement unit 3, among the AC impedance measurement results of the positive electrode slurry measured by the third channel unit 13 of the measurement unit 3.

[0056] If the parameter on the imaginary axis of the AC impedance in the frequency range determined by the measurement unit 3 satisfies a reference value previously set based on the AC impedance measurement results of a positive electrode slurry (hereinafter referred to as a "good slurry") in which the positive electrode active material is well coated with the solid electrolyte, and if the parameter on the real axis of the AC impedance in the frequency range determined by the measurement unit 3 satisfies a reference value previously set based on the AC impedance measurement results of a good slurry, the positive electrode slurry is determined to have a good solid electrolyte coating state in the positive electrode active material. The reference value is determined from the AC impedance measurement results of a slurry determined to be a good slurry, based on, for example, battery performance, the dispersion state of the slurry determined using an analytical method such as a particle size distribution analyzer, and the solid electrolyte coating thickness calculated using an analytical method such as an electron microscope. The upper and lower limits of the reference value are determined depending on the type of positive electrode slurry.

[0057] If the parameter on the imaginary axis of the AC impedance in the frequency range identified by the measurement unit 3 does not satisfy a predetermined reference value based on the AC impedance measurement results of a good slurry, or if the parameter on the real axis of the AC impedance in the frequency range identified by the measurement unit 3 does not satisfy a predetermined reference value based on the AC impedance measurement results of a good slurry, the positive electrode slurry is determined to have a poor coating state of the solid electrolyte on the positive electrode active material.

[0058] According to the evaluation device for a positive electrode slurry for an all-solid-state battery of this embodiment, the AC impedance of the positive electrode slurry for an all-solid-state battery can be measured in a specific frequency range, and the coating state of the solid electrolyte on the positive electrode active material can be evaluated with high accuracy based on the parameters on the imaginary axis of the obtained AC impedance and the parameters on the real axis of the AC impedance.

[0059] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims. [Example]

[0060] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0061] [Example] "Preparation of cathode slurry for all-solid-state batteries" A positive electrode slurry for an all-solid-state battery was prepared as follows. The binder solution and the conductive additive dispersion were mixed by stirring at 2000 rpm for 1 minute using a planetary centrifugal mixer (kneading device), and mixture 1 was obtained. To the obtained mixture 1, zirconia balls with a diameter of 2 mm, a positive electrode active material (coated with a solid electrolyte, for example, positive electrode active material:solid electrolyte=75:25 to 90:10 (mass ratio)), and a solvent (butyl butyrate) were added, and the mixture was stirred and mixed at 2000 rpm for 1 minute to obtain a positive electrode slurry for an all-solid-state battery.

[0062] "AC impedance measurement" The AC impedance of the positive electrode slurry for an all-solid-state battery was measured, and a Nyquist diagram was created based on the parameter of the imaginary axis of the AC impedance (Zim) and the parameter of the real component of the AC impedance (Zre). The results are shown in Figures 5 and 7. The area enclosed by a frame in Figure 5 represents the second arc of the Nyquist diagram. The area enclosed by a frame in Figure 7 represents the third arc of the Nyquist diagram. We also investigated the relationship between the parameter (Zre) of the real component of the AC impedance corresponding to the second arc and the solid content of the positive electrode slurry for solid-state batteries. The results are shown in Figure 6. From the results shown in Figure 6, it was found that the parameter (Zre) of the real component of the AC impedance increases as the solid content decreases. This is thought to be because as the solid content decreases, the amount of solvent between the positive electrode active material particles increases, making polarization more difficult. Furthermore, the polarization charge (Cp) derived from the parameter (Zim) of the imaginary axis of AC impedance corresponding to the third arc was calculated, and the relationship between the polarization charge (Cp) and the solid content of the positive electrode slurry for all-solid-state batteries was investigated. The results are shown in Figure 8. From the results shown in Figure 8, it can be assumed that as the solid content decreases, the mass of the positive electrode active material in the same volume decreases, and the interfacial polarization charge decreases. [Explanation of symbols]

[0063] 1. Evaluation equipment for cathode slurry for all-solid-state batteries 2 Flow path 3 Measuring part 4. Mixing section 5 Supply section 6. Good Product Collection Department 7. Defective Product Collection Department 8 Viscosity measuring section 9 Temperature adjustment section 11 Channel 1 12 Second channel section 13 Third Channel

Claims

1. An evaluation device for a positive electrode slurry for an all-solid-state battery, which evaluates a coating state of a positive electrode slurry in which at least a positive electrode active material and a solid electrolyte are mixed and dispersed, comprising: a flow path through which the positive electrode slurry flows; a measurement unit that is provided in the flow path and that measures the AC impedance of the positive electrode slurry, the measurement unit has a first channel unit that measures the AC impedance at a first predetermined frequency and a second channel unit that measures the AC impedance at a second predetermined frequency, the measurement unit has an evaluation unit that evaluates whether a coating state of the solid electrolyte on the positive electrode active material is good or bad, based on a parameter on an imaginary axis of the AC impedance and a parameter on a real axis of the AC impedance measured by the first channel unit and the second channel unit.

2. the flow path has a first measurement region that is a measurement region of the first channel portion and a second measurement region that is a measurement region of the second channel portion, The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1 , wherein the first measurement area and the second measurement area are defined adjacent to each other in an extension direction of the flow channel.

3. the measurement unit has a third channel unit that measures the AC impedance at a third predetermined frequency, the flow path has a third measurement region that is a measurement region of the third channel portion, The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 2 , wherein the first measurement area, the second measurement area, and the third measurement area are defined adjacent to each other in an extension direction of the flow channel.

4. the first predetermined frequency corresponds to a second arc of a Nyquist diagram drawn based on an imaginary axis parameter of the AC impedance measured by the first channel unit and a real axis parameter of the AC impedance measured by the second channel unit; 4. The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein the second predetermined frequency corresponds to a third arc of a Nyquist diagram drawn based on a parameter on an imaginary axis of the AC impedance measured by the first channel unit and the parameter on a real axis of the AC impedance measured by the second channel unit.

5. 4. The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 3, wherein the third predetermined frequency corresponds to a first arc of a Nyquist diagram drawn based on a parameter on an imaginary axis of the AC impedance measured by the third channel unit and a parameter on a real axis of the AC impedance.

6. 2. The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, wherein the evaluation unit evaluates whether the coating state is good or bad based on a polarization charge amount derived from a real component of the AC impedance measured by the first channel unit and an imaginary component of the AC impedance measured by the second channel unit.

7. the flow path has a viscosity measuring unit and a temperature adjusting unit upstream of the measuring unit, 2. The device for evaluating a positive electrode slurry for an all-solid-state battery according to claim 1, further comprising a control unit that adjusts a temperature of the positive electrode slurry by the temperature adjustment unit so that the viscosity of the positive electrode slurry in the flow path measured by the viscosity measurement unit falls within a predetermined range.

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