Method for evaluating activity of electrode

Abstract

To provide a method for precisely evaluating the activity of an electrode containing active material that stores and releases a charge transfer medium such as an active material for a lithium ion battery.SOLUTION: A method for evaluating the activity of an electrode containing active material includes evaluating the activity of the electrode, on the basis of the specific capacitance and the specific area of an active material film consisting of the active material alone and the specific capacitance of the electrode.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the activity of an electrode. [Background technology]

[0002] In recent years, research and development into secondary batteries, which contribute to energy efficiency and ensure access to affordable, reliable, sustainable, and advanced energy for more people, has been underway. Secondary batteries are expected to replace traditional fossil fuels as an energy source, and the development of batteries for automotive applications has been particularly enthusiastic in recent years. Among the various characteristics required for automotive batteries, reducing the resistance of each internal component of the battery is particularly important, as it directly affects performance and cost. To address this, various materials have been developed. In parallel with this material development, methods for evaluating the performance of batteries constructed from these components are also being investigated. For example, electrochemical methods for evaluating the active surface area of fuel cell electrodes have been investigated (Patent Documents 1 and 2). A method for monitoring the electrochemical capacity using electrochemical impedance spectroscopy has been investigated as an indicator of particle cracking in nickel-rich lithium nickel manganese cobalt oxide (NMC) cathodes for lithium-ion secondary batteries (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-228131 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-220786 [Non-patent literature]

[0004] [Non-Patent Document 1] Stefan Oswald, Daniel Pritzl, Morten Wetjen, Hubert A. Gasteiger, “Novel Method for Monitoring the Electrochemical Capacitance by In Situ Impedance Spectroscopy as Indicator for Particle Cracking of Nickel-Rich NCMs: Part I. Theory and Validation,” Journal of The Electrochemical Society, 167, 100511 (2020) Summary of the Invention [Problem to be solved by the invention]

[0005] One of the challenges facing secondary batteries is improving their electrical characteristics, such as output power. To improve the electrical characteristics of secondary batteries, the development of a method for evaluating electrode activity is desirable. However, the electrodes used in lithium-ion secondary batteries are mixtures containing electrode active materials, binders, and conductive additives. Furthermore, in nonaqueous-solvent batteries, the electrodes are incorporated into the battery in a state impregnated with a liquid electrolyte. In all-solid-state batteries, a solid electrolyte may be added to the electrode. Thus, the contact interface between the active material and electrolyte in the electrode is complex and spatially widespread across the entire surface of the electrode. Therefore, it is not easy to extract the interface between the active material and electrolyte in the electrode, making it difficult to evaluate the electrode activity.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a method for accurately evaluating the activity of an electrode containing an active material that absorbs and releases a charge transfer medium, such as an active material for a lithium ion battery, which will ultimately contribute to improving energy efficiency. [Means for solving the problem]

[0007] The present inventors have found that by measuring the specific capacitance and specific surface area of an active material film made of a single active material used in an electrode to be evaluated and using the data on the active material film and the specific capacitance of the electrode to be evaluated, it is possible to accurately evaluate the activity of the electrode to be evaluated, and have completed the present invention. Accordingly, the present invention provides the following method.

[0008] (1) A method for evaluating the activity of an electrode containing an active material, the method comprising: evaluating the activity of the electrode based on the specific capacitance and specific surface area of an active material film made of the active material alone and the specific capacitance of the electrode.

[0009] According to the electrode activity evaluation method (1), the activity of the electrode is evaluated based on the specific capacitance and specific surface area of the active material film made of a single active material and the specific capacitance of the electrode, so that the activity of the electrode to be evaluated can be evaluated with high accuracy.

[0010] (2) The activity of the electrode was evaluated based on the electrode active specific surface area (m 2 The method for evaluating the activity of an electrode according to (1), wherein the activity is evaluated by measuring the concentration of the electrode in the electrode. Electrode active specific surface area (m 2 / g)=a×x+b (I) In formula (I), a is the slope of the calibration curve of the specific capacitance and specific surface area of the active material film, b is the specific surface area of the electrode when the surface roughness Ra of the electrode is set to zero, and x is the specific capacitance of the electrode.

[0011] According to the electrode activity evaluation method (2), the activity of the electrode is evaluated using the electrode active specific surface area calculated by the formula (I), so that the activity of the electrode to be evaluated can be evaluated with higher accuracy.

[0012] (3) The method for evaluating the activity of an electrode according to (1) or (2), wherein the specific capacitance of the active material film is calculated by measuring the capacitance of the active material film by an electrochemical impedance method and dividing the obtained capacitance by the mass of the active material film.

[0013] According to the method for evaluating the activity of an electrode (3), it is possible to measure the specific capacitance of the active material film with high accuracy, and therefore the activity of the electrode to be evaluated can be evaluated with even higher accuracy.

[0014] (4) The method for evaluating the activity of an electrode according to any one of (1) to (3), wherein the specific surface area of the active material film is calculated by measuring the surface area of the active material film by a surface probe microscope and dividing the obtained surface area by the mass of the active material film.

[0015] According to the method for evaluating the activity of an electrode in (4), it is possible to measure the specific surface area of the active material film with high accuracy, and therefore the activity of the electrode to be evaluated can be evaluated with even higher accuracy.

[0016] (5) The method for evaluating the activity of an electrode according to any one of (1) to (4), wherein the electrode is for a battery using a liquid electrolyte.

[0017] According to the method for evaluating the activity of an electrode (5), the activity of an electrode for a battery using a liquid electrolyte can be evaluated.

[0018] (6) The method for evaluating the activity of an electrode according to (5), wherein the specific capacitance of the electrode is calculated by measuring the capacitance of the electrode by an electrochemical impedance method while the electrode is in contact with a liquid electrolyte used in a battery using the electrode, and dividing the obtained capacitance by the mass of the active material in the electrode.

[0019] According to the electrode activity evaluation method (6), the specific capacitance of the electrode is measured under conditions similar to those of a battery using a liquid electrolyte, so that the activity of the electrode in a battery using a liquid electrolyte can be evaluated with even greater accuracy.

[0020] (7) The method for evaluating the activity of an electrode according to any one of (1) to (4), wherein the electrode is for a battery using a solid electrolyte.

[0021] According to the method for evaluating the activity of an electrode (7), the activity of an electrode for an all-solid-state battery using a solid electrolyte can be evaluated.

[0022] (8) The method for evaluating the activity of an electrode according to (7), wherein the specific capacitance of the electrode is calculated by measuring the capacitance of the electrode by an electrochemical impedance method while the electrode is in contact with the solid electrolyte used in a battery using the electrode, and dividing the obtained capacitance by the mass of the active material in the electrode.

[0023] According to the electrode activity evaluation method (8), the specific capacitance of the electrode is measured under conditions similar to those of a solid secondary battery using a solid electrolyte, so that the activity of the electrode in the solid secondary battery can be evaluated more accurately. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a method capable of accurately evaluating the activity of an electrode containing an active material that absorbs and releases a charge transfer medium, such as an active material for a lithium ion battery. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a graph showing calibration curves of the specific capacitance and specific surface area of the positive electrode active material thin film produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, one embodiment of the method for evaluating electrode activity of the present invention will be described. The method for evaluating the activity of an electrode according to this embodiment is a method for evaluating the activity of an electrode containing an active material. The electrode to be evaluated may be for a battery using, for example, a solid electrolyte or a liquid electrolyte. The battery may be, for example, a lithium battery using lithium as a charge transfer medium. The active material may be a positive electrode active material or a negative electrode active material.

[0027] In the electrode activity evaluation method of this embodiment, the activity of the electrode to be evaluated is evaluated based on the specific capacitance and specific surface area of an active material film made of a single active material used in the electrode to be evaluated, and the specific capacitance of the electrode to be evaluated.

[0028] The activity of the electrode to be evaluated is evaluated, for example, based on the electrode active specific surface area (m 2 / g). Electrode active specific surface area (m 2 / g)=a×x+b (I) In formula (I), a is the slope of the calibration curve of the specific capacitance and specific surface area of the active material film, b is the specific surface area obtained by dividing the surface area of the electrode when the surface roughness Ra of the electrode is set to zero by the mass of the active material contained in the electrode, and x is the specific capacitance of the electrode.

[0029] At the interface between an electrode and an electrolyte in a battery, two materials with different elastic moduli come into contact. Surface analysis of the electrode's surface roughness can determine the surface area of the electrode-electrolyte contact interface. However, in a typical battery, the electrode and electrolyte are in complex contact with each other over a wide area, making nondestructive surface analysis of the electrode's surface roughness difficult. Therefore, in this embodiment, the specific capacitance of the electrode being evaluated is correlated with the contact area at the interface between the electrode and the electrolyte using the above formula (I). Specifically, by substituting the specific capacitance of the electrode being evaluated for x in the above formula (I), the electrode active specific surface area, which indicates the contact area at the interface between the active material in the electrode being evaluated and the electrolyte, is calculated. Furthermore, since a in the above formula (I) is the slope obtained from a calibration curve of the specific capacitance and specific surface area of an active material film made of an active material film, it is not necessary to separately consider the capacitance values of individual materials, such as the active material, binder, and conductive additive, contained in a typical electrode. Therefore, by using the above formula (I), the electrode active specific surface area of the electrode to be evaluated can be quantitatively determined without considering the specific capacitance of anything other than the active material. In other words, the electrode active specific surface area, which is an index of the contact area at the interface between the active material and the electrolyte in the electrode to be evaluated, can be obtained from the specific capacitance value of the electrode to be evaluated.

[0030] The electrode active specific surface area can be obtained, for example, by a method including the following steps. (1) Active material film production process (2) A measurement step for measuring the specific surface area and specific capacitance of the active material film (3) A calculation step of calculating the slope of the calibration curve of the specific capacitance and specific surface area of the active material film (4) Measuring the specific capacitance of the electrode to be evaluated (5) A step of calculating the specific surface area of the electrode to be evaluated when the surface roughness Ra of the electrode to be evaluated is set to zero (6) Calculation step of calculating the electrode active specific surface area

[0031] In step (1), an active material film made of a single active material is prepared. The active material film can be formed on a conductive substrate. The active material film may be a thin film having a thickness of, for example, 20 nm to 1 μm.

[0032] The active material film may be produced by either a dry process or a wet process. Examples of dry processes that can be used include pulsed laser deposition (PLD) and RF sputtering. Examples of wet processes that can be used include applying an active material precursor solution to a substrate and firing the resulting coating film to produce an active material. Furthermore, if the active material used in the electrode to be evaluated has a coating layer on its surface, a coating layer may be formed on the surface of the active material film.

[0033] In step (1), three or more types of active material films with different surface roughness Ra may be prepared in order to prepare a calibration curve of the specific capacitance and specific surface area of the active material film in step (3) described below.

[0034] In step (2), the specific surface area and specific capacitance of the active material film obtained in step (1) are measured.

[0035] The specific surface area of the active material film can be obtained, for example, by measuring the surface area and mass of the active material film and dividing the obtained surface area by the mass of the active material film. The surface area of the active material film can be measured, for example, by surface probe microscopy. Here, a supplementary note on the specific surface area is provided. The specific surface area of the active material film described above is used when the elastic modulus of the active material film is equal to or greater than the elastic modulus of the solid electrolyte. In this case, the contact interface between the positive electrode and the solid electrolyte in the battery depends on the surface roughness of the positive electrode. On the other hand, the specific surface area of the solid electrolyte is used when the elastic modulus of the active material film is lower than the elastic modulus of the solid electrolyte. In this case, the contact interface between the positive electrode and the solid electrolyte in the battery depends on the surface roughness of the solid electrolyte. The specific surface area of the active material film can be obtained by measuring the surface area of the active material film and dividing it by the mass of the active material film. The specific surface area of the solid electrolyte can be obtained, for example, by measuring the surface area of the solid electrolyte film and dividing the obtained surface area of the solid electrolyte film by the mass of the active material film.

[0036] The specific capacitance of an active material film can be measured as follows, for example, when the active material is a positive electrode active material. First, an active material film cell is prepared in which the active material film is used as the positive electrode, lithium or a lithium alloy is used as the negative electrode, and an electrolyte is disposed between the positive electrode and the negative electrode. Next, the capacitance of the positive electrode is measured. The specific capacitance is calculated by dividing the obtained capacitance by the mass of the active material film. The electrolyte of the active material film cell can be the same as the electrolyte of the battery in which the electrode to be evaluated is used. Electrochemical impedance analysis can be used to measure the capacitance.

[0037] In step (3), a calibration curve is created using the specific surface area and specific capacitance of the active material film obtained in step (2). The calibration curve has the specific capacitance on the horizontal axis and the specific surface area on the vertical axis. An approximation equation (linear regression equation) for the obtained calibration curve is found, and the slope of the obtained approximation equation is obtained.

[0038] In step (4), the specific capacitance of the electrode to be evaluated is measured. For example, when the electrode to be evaluated is a positive electrode, the specific capacitance of the electrode to be evaluated can be measured as follows. First, an electrode cell to be evaluated is prepared, in which the electrode to be evaluated is used as the positive electrode, lithium or a lithium alloy is used as the negative electrode, and an electrolyte is disposed between the positive and negative electrodes. Next, the capacitance of the electrode to be evaluated is measured. The specific capacitance is then calculated by dividing the obtained capacitance by the mass of the active material in the electrode to be evaluated. The electrolyte in the electrode cell to be evaluated can be the same as the electrolyte in the active material film cell. The electrochemical impedance method can be used to measure the capacitance.

[0039] In step (5), the specific surface area of the electrode to be evaluated is calculated when the surface roughness Ra of the electrode to be evaluated is set to 0. Specifically, the specific surface area is calculated by dividing the geometric surface area of the electrode to be evaluated by the content of the active material in the electrode to be evaluated.

[0040] In step (6), the slope of the calibration curve of the specific capacitance and specific surface area of the active material film obtained in step (3) is defined as a, and the specific surface area of the electrode to be evaluated obtained in step (5) is defined as b. The specific capacitance of the electrode to be evaluated obtained in step (4) is substituted for x in the following formula (I) to obtain the active specific surface area of the electrode. Electrode active specific surface area (m 2 / g)=a×x+b (I)

[0041] The electrode active specific surface area is an index of the contact area at the interface between the active material and electrolyte in the electrode being evaluated. Therefore, a large electrode active specific surface area means that the contact area at the interface between the active material and electrolyte is large, making it easier for the electrode reaction of the active material to occur. Therefore, an electrode with a large electrode active specific surface area has improved output characteristics.

[0042] According to the electrode activity evaluation method of the present embodiment configured as described above, the activity of the electrode is evaluated based on the specific capacitance and specific surface area of the active material film made of a single active material and the specific capacitance of the electrode being measured, so that the activity of the electrode being evaluated can be evaluated with high accuracy. Furthermore, according to the electrode activity evaluation method of the present embodiment, the activity of the electrode being evaluated can be evaluated with high accuracy by evaluating the activity of the electrode using the electrode activity specific surface area calculated by formula (I). According to the electrode activity evaluation method of the present embodiment, the activity of either an electrode for a solid electrolyte battery or an electrode for a battery using a liquid electrolyte can be evaluated.

[0043] According to the electrode activity evaluation method of this embodiment, the capacitance of the active material film is measured by electrochemical impedance spectroscopy, and the specific capacitance is calculated by dividing the obtained capacitance by the mass of the active material film, thereby enabling accurate measurement of the specific capacitance of the active material film, and thereby enabling more accurate evaluation of the activity of the electrode to be evaluated. Also, according to the electrode activity evaluation method of this embodiment, the specific surface area of the active material film is measured by surface probe microscopy, and the specific surface area is calculated by dividing the obtained surface area by the mass of the active material film, thereby enabling accurate measurement of the specific surface area of the active material film, and thereby enabling more accurate evaluation of the activity of the electrode to be evaluated.

[0044] In the electrode activity evaluation method of this embodiment, if the electrode to be evaluated is for a battery using a liquid electrolyte, the specific capacitance of the electrode to be evaluated in the battery can be evaluated with greater accuracy by measuring the capacitance of the electrode to be evaluated in contact with the liquid electrolyte by electrochemical impedance spectroscopy and dividing the obtained capacitance by the mass of the active material in the electrode to be evaluated. In the electrode activity evaluation method of this embodiment, if the electrode to be evaluated is for a solid secondary battery using a solid electrolyte, the specific capacitance of the electrode to be evaluated in the battery can be evaluated with greater accuracy by measuring the capacitance of the electrode to be evaluated in contact with the solid electrolyte by electrochemical impedance spectroscopy and dividing the obtained capacitance by the mass of the active material in the electrode to be evaluated. [Example]

[0045] The present invention will be described below based on examples, but the present invention should not be construed as being limited to these examples.

[0046] [Example 1] LiNbO3 coated NMC (composition: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The activity of the electrode containing O2 () as the positive electrode active material was evaluated as follows.

[0047] <Preparation of thin film of positive electrode active material> A Si single crystal substrate (10 mm long x 10 mm wide) with a Pt current collecting layer sputter-deposited over the entire surface was prepared as a current collecting substrate. First, a LiNi target was placed on one side of the current collecting substrate. 1 / 3 Co 1 / 3 Mn 1 / 3 An NMC thin film (9mm long x 9mm wide x 75nm thick) was deposited by pulsed laser deposition (PLD) using a sintered body of O2 (NMC). The deposition conditions for the NMC thin film were as follows: oxygen gas pressure in the chamber shown in Table 1, temperature 650°C, holding time 50 minutes, Nd-YAG laser (wavelength 266nm), output 200mW, oscillation frequency 10Hz.

[0048] Next, a LiNbO3 coating layer (9 mm long x 9 mm wide x several nm thick) was formed on the NMC film by PLD using a LiNbO3 sintered body as the target. The LiNbO3 coating layer was formed under the same conditions as the NMC thin film except that the temperature was 400°C and the holding time was 15 minutes. In this way, thin films of positive electrode active material Nos. 1 to 3 shown in Table 1 were obtained.

[0049] [Table 1]

[0050] <Measurement of specific surface area and specific capacitance of thin film of positive electrode active material> The specific surface area and specific capacitance of the positive electrode active material thin films of Sample Nos. 1 to 3 were measured as follows. The results are shown in Table 2.

[0051] (Method for measuring specific surface area) The surface roughness Ra value of the thin film of positive electrode active material was measured using a surface probe microscope in tapping mode. The surface area of the thin film of positive electrode active material was calculated from the obtained surface roughness Ra value. In addition, the weight of the current collecting substrate on which the thin film of positive electrode active material was formed was measured using a precision balance, and the weight of the thin film of positive electrode active material was calculated by subtracting the weight of the current collecting substrate, which had been measured previously. The specific surface area was obtained by dividing the surface area by the weight of the positive electrode active material film.

[0052] (Method for measuring specific capacitance) A thin film positive electrode active material cell was fabricated as follows. The current collecting substrate on which the thin film of the positive electrode active material was formed was placed. Next, a cylindrical container with an opening of 16 mm in diameter was attached to the pressure shaft, and then an argyrodite-based sulfide (composition: Li 5.5 PS 4.5 Cl 1.5 250 mg of powder of argyrodite-based sulfide was placed in the cylindrical container. Another pressure shaft was inserted into the other end of the cylindrical container, and the molding pressure shown in Table 2 was applied to the argyrodite-based sulfide powder using the pressure shaft. This formed a sulfide-based solid electrolyte layer composed of the argyrodite-based sulfide powder on the thin cathode active material film. The pressure shaft inserted later was then removed, and a lithium-indium foil (Li-In foil) was placed on the removed pressure shaft. The pressure shaft with the Li-In foil then was reinserted, and a molding pressure of 115 MPa was applied using the pressure shaft. In this way, a thin cathode active material cell was fabricated, in which the current collecting substrate with the thin cathode active material film formed served as the positive electrode, the Li-In foil served as the negative electrode, and a sulfide-based solid electrolyte layer was placed between the positive and negative electrodes.

[0053] The capacitance of the thin film of the positive electrode active material of the obtained thin film cell of the positive electrode active material was measured as follows. First, the thin-film positive electrode active material cell was connected to a charge-discharge device. The thin-film cell was charged and discharged three times at a constant current (CC) of 1 μA over a voltage range of 2.08 V to 3.68 V. The capacity was measured at the third discharge cycle to calculate the C-rate. Next, the thin-film positive electrode active material cell was connected to a potentio-galvanostat with electrochemical impedance (EIS) measurement function. First, the cell was discharged to 2.08 V at a constant current (CC) of 0.1 C. At the point where the voltage reached 2.08 V, constant current-constant voltage (CC-CV) discharge was performed until the residual current fell below 0.01 C. After the thin-film positive electrode active material cell was left to stand for 3 hours, the capacitance of the thin-film positive electrode active material was measured by EIS. The EIS measurement conditions were a frequency range of 1 MHz to 10 mHz and an AC voltage amplitude of 10 mV. The thin-film positive electrode active material cell was placed in a thermostatic chamber and the EIS measurement was performed at 25°C.

[0054] The capacitance value was calculated based on the Z" value in the vicinity of 180 mHz obtained by EIS measurement, and the specific capacitance was obtained by dividing the value by the weight of the above-mentioned positive electrode active material thin film.

[0055] [Table 2]

[0056] <Calculation of the slope of the calibration curve for the specific capacitance and specific surface area of the thin film of positive electrode active material> A calibration curve was created with the specific capacitance shown in Table 2 on the horizontal axis and the specific surface area on the vertical axis. The resulting calibration curve is shown in Figure 1. The approximate equation (linear regression equation) for the resulting calibration curve was y = 0.5892x + 5.6247. This approximate equation shows that the specific capacitance and specific surface area of the positive electrode active material thin film correlate with each other, with a slope of 0.5892.

[0057] <Preparation of electrodes to be evaluated> A composite layer containing positive electrode active material powder (NMC coated with LiNbO3), argyrodite-based sulfide solid electrolyte powder, conductive additive (acetylene black), and binder (styrene butadiene rubber) in a mass ratio of 75:21:3:1 was formed on an aluminum current collector foil. The content of the positive electrode active material powder in the composite layer was 16 mg. The aluminum current collector foil with the composite layer obtained was punched out into a circular shape with a diameter of 10 mm to obtain an electrode to be evaluated.

[0058] <Measurement of the specific capacitance of the electrode to be evaluated> An electrode cell to be evaluated was prepared as follows. The electrode to be evaluated was inserted into a cylindrical container with a circular opening of 10 mm in diameter. Then, an argyrodite-based sulfide (composition: Li 5.5 PS 4.5 Cl 1.5 100 mg of argyrodite-based sulfide powder was placed in the cylindrical container. A pressure shaft was inserted into each of the openings on both sides of the container, and a molding pressure of 100 MPa was applied to the argyrodite-based sulfide powder. This formed a sulfide-based solid electrolyte layer composed of the argyrodite-based sulfide powder on the composite layer of the electrode to be evaluated. The pressure shaft on the sulfide-based solid electrolyte layer side was then removed, and a lithium-indium foil (Li-In foil) was placed on top of the sulfide-based solid electrolyte layer. The pressure shaft was then reinserted on top of the Li-In foil, and a molding pressure of 150 MPa was applied using the pressure shaft. In this way, an electrode cell to be evaluated was fabricated, with the electrode to be evaluated as the positive electrode, the Li-In foil as the negative electrode, and a sulfide-based solid electrolyte layer placed between the positive and negative electrodes.

[0059] The capacitance of the composite layer of the obtained electrode cell to be evaluated was measured in the same manner as the capacitance of the above-mentioned positive electrode active material thin film. The capacitance of the obtained composite layer was divided by the content of the positive electrode active material powder in the composite layer to calculate the specific capacitance of the positive electrode active material powder of the electrode cell to be evaluated. The obtained specific capacitance was 0.28 F / g.

[0060] <Calculation of the specific surface area of the positive electrode active material powder when the surface roughness Ra of the electrode to be evaluated is zero> The geometric surface area of the electrode to be evaluated was divided by the content of the positive electrode active material powder in the composite layer, and the value was calculated as the specific surface area of the positive electrode active material powder when the surface roughness Ra was zero. The specific surface area of the positive electrode active material powder when the obtained surface roughness Ra was zero was 0.005 m 2 / g.

[0061] <Calculation of the active specific surface area of the positive electrode active material powder of the electrode to be evaluated> The specific surface area (0.005 m) of the positive electrode active material powder when the surface roughness Ra is zero 2 / g) and the slope (0.5892) of the relationship between the specific capacitance and the specific surface area of the positive electrode active material thin film, the following formula (II) was obtained as the relational expression between the specific capacitance and the active specific surface area of the positive electrode active material powder of the electrode to be evaluated. y=0.5892x+0.005 (II)

[0062] The specific capacitance (0.28 F / g) of the positive electrode active material powder of the electrode to be evaluated was substituted for x in the above formula (II) to calculate the electrode active specific surface area y of the positive electrode active material powder of the electrode to be evaluated. As a result, the electrode active specific surface area y was found to be 0.17 m 2 / g.

Claims

1. 1. A method for evaluating the activity of an electrode comprising an active material, comprising: A method for evaluating the activity of an electrode, which evaluates the activity of the electrode based on the specific capacitance and specific surface area of an active material film made of the single active material and the specific capacitance of the electrode.

2. The activity of the electrode was evaluated based on the electrode active specific surface area (m ２ The method for evaluating the activity of an electrode according to claim 1, wherein the activity is evaluated by a method using a ion exchanger (IEX). Electrode active surface area (m ２ / g)=a×x+b・・・(I) In formula (I), a is the slope of the calibration curve of the specific capacitance and specific surface area of the active material film, b is the specific surface area of the electrode when the surface roughness Ra of the electrode is set to zero, and x is the specific capacitance of the electrode.

3. 3. The method for evaluating electrode activity according to claim 1, wherein the specific capacitance of the active material film is calculated by measuring the capacitance of the active material film by an electrochemical impedance method and dividing the obtained capacitance by the mass of the active material film.

4. 3. The method for evaluating electrode activity according to claim 1, wherein the specific surface area of the active material film is calculated by measuring the surface area of the active material film by a surface probe microscopy method and dividing the obtained surface area by the mass of the active material film.

5. 3. The method for evaluating electrode activity according to claim 1, wherein the electrode is for a battery using a liquid electrolyte.

6. 6. The method for evaluating electrode activity according to claim 5, wherein the specific capacitance of the electrode is calculated by measuring the capacitance of the electrode by an electrochemical impedance method while the electrode is in contact with a liquid electrolyte used in a battery using the electrode, and dividing the obtained capacitance by the mass of the active material in the electrode.

7. 3. The method for evaluating electrode activity according to claim 1, wherein the electrode is for a battery using a solid electrolyte.

8. 8. The method for evaluating electrode activity according to claim 7, wherein the specific capacitance of the electrode is calculated by measuring the capacitance of the electrode by an electrochemical impedance method in a state in which the electrode is in contact with the solid electrolyte used in a battery that uses the electrode, and dividing the obtained capacitance by the mass of the active material in the electrode.

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