Method for evaluating activity of electrode

Abstract

The problem to be solved by the present invention is to provide a method capable of accurately evaluating the activity of an electrode including an active material that absorbs and desorbs a charge transfer medium, such as an active material for a lithium ion battery. In order to solve the problem, this method for evaluating the activity of an electrode, which includes an active material, evaluates the activity of the electrode on the basis of the specific capacitance and specific surface area of an active material film comprising the active material monomer, and the specific capacitance of the electrode.

Description

Technical Field

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

[0002] In recent years, in order to ensure that more people can obtain affordable, reliable, sustainable and advanced energy, research and development related to secondary batteries that contribute to energy efficiency has been underway. Secondary batteries are highly anticipated as an alternative to existing fossil fuels, especially the development of vehicle-mounted batteries has been gaining increasing popularity in recent years. The characteristics required for vehicle-mounted batteries are various. Among them, reducing the resistance of each component inside the battery, which is directly related to performance or cost, is important, and various material developments are being carried out. In addition, while these material developments are being carried out, evaluation methods for battery performance when constructing a battery from each component have also been explored. For example, a method for evaluating the active surface area of an electrode for a fuel cell using an electrochemical method has been explored (Patent Documents 1 and 2). As an index for the cracking of lithium nickel manganese cobalt oxide (NMC) particles used as the positive electrode of a lithium ion secondary battery, a method for monitoring the electrochemical capacity using an electrochemical impedance method has been explored (Non-Patent Document 1).

[0003] [Prior Art Documents]

[0004] (Patent Documents)

[0005] Patent Document 1: Japanese Patent Laid-Open No. 2011-228131

[0006] Patent Document 2: Japanese Patent Laid-Open No. 2004-220786

[0007] (Non-Patent Documents)

[0008] 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

[0009] [Problems to be Solved by the Invention]

[0010] In secondary batteries, one of the problems is to improve electro-chemical properties such as output characteristics. In order to improve the electro-chemical properties of secondary batteries, it is desirable to develop a method for evaluating electrode activity. However, the electrodes used in lithium-ion secondary batteries are mixtures including electrode active materials, binders, and conductive aids. Further, in the case of non-aqueous solvent batteries, the electrodes are inserted into the battery in a state where they are impregnated with a liquid electrolyte. In addition, in the case of all-solid-state batteries, a solid electrolyte is sometimes added to the electrodes. Thus, the contact interface between the active material and the electrolyte in the electrode is complex and spatially extended over the entire surface of the electrode. Therefore, it is difficult to extract the interface between the active material and the electrolyte in the electrode, and thus it is difficult to evaluate electrode activity.

[0011] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a method capable of accurately evaluating the activity of an electrode including an active material that absorbs and desorbs a charge transfer medium such as an active material for a lithium-ion battery. And, further, it is advantageous for improving energy efficiency.

[0012] [Technical Means for Solving the Problems]

[0013] The present inventors have found that by measuring the specific capacitance and specific surface area of an active material film composed of active material monomers used in an electrode to be evaluated, and using the data of the active material film and the specific capacitance of the electrode to be evaluated, the activity of the electrode to be evaluated can be accurately evaluated, thereby completing the present invention. Therefore, the present invention provides the following method.

[0014] (1) A method for evaluating the activity of an electrode for evaluating the activity of an electrode including an active material, and evaluating the activity of the electrode based on the specific capacitance and specific surface area of an active material film composed of the aforementioned active material monomers, and the specific capacitance of the aforementioned electrode.

[0015] According to the method for evaluating the activity of an electrode according to (1), the activity of the electrode is evaluated based on the specific capacitance and specific surface area of an active material film composed of active material monomers, and the specific capacitance of the aforementioned electrode. Therefore, the activity of the electrode to be evaluated can be accurately evaluated.

[0016] (2) The method for evaluating the activity of an electrode according to (1), wherein the activity of the aforementioned electrode is evaluated using the specific surface area of electrode activity (m 2 / g) calculated according to the following formula (I):

[0017] Specific surface area of electrode activity (m 2 / g)=a×x + b (I)

[0018] In formula (I), a is the slope of the calibration curve of the specific capacitance and the specific surface area of the aforementioned active material film, b is the specific surface area of the aforementioned electrode when the surface roughness Ra of the aforementioned electrode is zero, and x is the specific capacitance of the aforementioned electrode.

[0019] According to the method for evaluating the activity of the electrode in (2), the activity of the electrode is evaluated using the specific surface area of the electrode activity calculated according to formula (I). Therefore, the activity of the electrode to be evaluated can be evaluated more accurately.

[0020] (3) According to the method for evaluating the activity of the electrode described in (1) or (2), wherein the capacitance of the aforementioned active material film is measured by an electrochemical impedance method, and the obtained capacitance is divided by the mass of the aforementioned active material film, thereby calculating the specific capacitance of the aforementioned active material film.

[0021] According to the method for evaluating the activity of the electrode in (3), the specific capacitance of the active material film can be accurately measured. Therefore, the activity of the electrode to be evaluated can be evaluated more accurately.

[0022] (4) According to the method for evaluating the activity of the electrode described in any one of (1) to (3), wherein the surface area of the aforementioned active material film is measured by a surface probe microscope method, and the obtained surface area is divided by the mass of the aforementioned active material film, thereby calculating the specific surface area of the aforementioned active material film.

[0023] According to the method for evaluating the activity of the electrode in (4), the specific surface area of the active material film can be accurately measured. Therefore, the activity of the electrode to be evaluated can be evaluated more accurately.

[0024] (5) According to the method for evaluating the activity of the electrode described in any one of (1) to (4), wherein the aforementioned electrode is used in a battery using a liquid electrolyte.

[0025] According to the method for evaluating the activity of the electrode in (5), the activity of the electrode used in a battery using a liquid electrolyte can be evaluated.

[0026] (6) According to the method for evaluating the activity of the electrode described in (5), wherein the capacitance of the aforementioned electrode is measured by an electrochemical impedance method in a state where the liquid electrolyte used in the battery using the aforementioned electrode is in contact with the aforementioned electrode, and the obtained capacitance is divided by the mass of the active material in the aforementioned electrode, thereby calculating the specific capacitance of the aforementioned electrode.

[0027] According to the method for evaluating the activity of the electrode in (6), the specific capacitance of the electrode is measured in a state close to the battery using a liquid electrolyte. Therefore, the activity of the electrode in the battery using a liquid electrolyte can be evaluated more accurately.

[0028] (7) The method for evaluating the activity of an electrode according to any one of (1) to (4), wherein the electrode is used in a battery using a solid electrolyte.

[0029] The method for evaluating the activity of an electrode according to (7) can evaluate the activity of an electrode for an all-solid-state battery using a solid electrolyte.

[0030] (8) The method for evaluating the activity of an electrode according to (7), wherein, in a state where the solid electrolyte used in the battery using the electrode is in contact with the electrode, the capacitance of the electrode is measured by an electrochemical impedance method, and the obtained capacitance is divided by the mass of the active material in the electrode, thereby calculating the specific capacitance of the electrode.

[0031] According to the method for evaluating the activity of an electrode according to (8), the specific capacitance of the electrode is measured in a state close to a solid secondary battery using a solid electrolyte, and therefore, the activity of the electrode in the solid secondary battery can be evaluated more accurately.

[0032] (Effects of the Invention)

[0033] According to the present invention, a method capable of accurately evaluating the activity of an electrode including an active material that absorbs and desorbs a charge transfer medium such as an active material for a lithium ion battery can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a chart showing a calibration curve of the specific capacitance and specific surface area of the positive electrode active material film produced in Example 1. DETAILED DESCRIPTION

[0035] Hereinafter, an embodiment of the method for evaluating the activity of an electrode of the present invention will be described.

[0036] The method for evaluating the activity of an electrode in the present embodiment is used to evaluate the activity of an electrode including an active material.

[0037] The electrode to be evaluated can be used, for example, in a battery using a solid electrolyte or in a battery using a liquid electrolyte. The battery can be, for example, a lithium battery using lithium as a charge transfer medium. The active material can be a positive electrode active material or a negative electrode active material.

[0038] In the method for evaluating the activity of an electrode in the present embodiment, the activity of the electrode to be evaluated is evaluated based on the specific capacitance and specific surface area of the active material film composed of the active material monomers used in the electrode to be evaluated and the specific capacitance of the electrode to be evaluated.

[0039] The evaluation of the activity of the electrode to be evaluated can be performed, for example, using the electrode activity specific surface area (m2 by / g):

[0040] Electrode active specific surface area (m 2 / g) = a × x + b (I)

[0041] 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 zero by the mass of the active material contained in the electrode, and x is the specific capacitance of the electrode.

[0042] In the interface between the electrode and the electrolyte in the battery, two materials with different elastic moduli are in contact. According to the surface analysis of the surface roughness of the electrode, the surface area of the contact interface between the electrode and the electrolyte can be obtained. However, in a general battery, the electrode and the electrolyte are spatially expanded and complexly in contact, so it is difficult to perform non-destructive surface analysis of the surface roughness of the electrode. Therefore, in the present embodiment, according to the above formula (I), the specific capacitance of the electrode to be evaluated is correlated with the contact area at the interface between the electrode to be evaluated and the electrolyte. That is, by substituting the specific capacitance of the electrode to be evaluated into x in the above (I), the electrode active specific surface area is calculated, and the electrode active specific surface area is an index of the contact area at the interface between the active material and the electrolyte in the electrode to be evaluated. In addition, a in the above formula (I) is the slope obtained from the calibration curve of the specific capacitance and specific surface area of the active material film composed of the active material, so there is no need to separately consider the capacitance values of various materials such as the active material, binder, and conductive additive contained in the ordinary electrode. Therefore, by using the above formula (I), the electrode active specific surface area of the electrode to be evaluated can be quantitatively grasped without considering the specific capacitance other than the active material. That is to say, based on the specific capacitance value of the electrode to be evaluated, the electrode active specific surface area can be obtained, and the electrode active specific surface area is an index of the contact area at the interface between the active material and the electrolyte in the electrode to be evaluated.

[0043] The electrode active specific surface area can be obtained, for example, by a method including the following steps.

[0044] (1) Production process of the active material film

[0045] (2) Measurement process of measuring the specific surface area and specific capacitance of the active material film

[0046] (3) Calculation process of calculating the slope of the calibration curve of the specific capacitance and specific surface area of the active material film

[0047] (4) Measurement process of measuring the specific capacitance of the electrode to be evaluated

[0048] Step of calculating the specific surface area of the evaluation object electrode when the surface roughness Ra of the evaluation object electrode is zero

[0049] Step of calculating the electrode active specific surface area

[0050] In the step (1), an active material film composed of active material monomers is fabricated.

[0051] The active material film can be formed on a conductive substrate. The active material film is, for example, a thin film having a thickness in the range of 20 nm or more and 1 μm or less.

[0052] The method for fabricating the active material film can be a dry process or a wet process. As the dry process, a pulse laser deposition method (Pulse Laser Deposition, PLD method), a radio frequency (RF) sputtering method can be used. As the wet process, the following method can be used, that is, an active material precursor solution is coated on a substrate, and the obtained coated film is fired to generate an active material. In addition, when the active material used in the evaluation object electrode has a coating layer on the surface, a coating layer can also be formed on the surface of the active material film.

[0053] Since in the step (3) described below, a calibration curve of the specific capacitance and the specific surface area of the active material film is fabricated, in the step (1), three or more active material films having different surface roughnesses Ra can be fabricated.

[0054] In the step (2), the specific surface area and the specific capacitance of the active material film obtained in the step (1) are measured.

[0055] The specific surface area of the active material film can be obtained, for example, by measuring the surface area and the mass of the active material film and dividing the obtained surface area of the active material film by the mass of the active material film. The measurement of the surface area of the active material film can use, for example, a surface probe microscopy method.

[0056] Here, the specific surface area is supplemented. The specific surface area of the aforementioned active material film is used when the elastic modulus of the active material film is equal to or greater than the elastic modulus of the solid electrolyte. This is because, 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 less than the elastic modulus of the solid electrolyte. This is because, 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.

[0057] For example, when the active material is a positive electrode active material, the specific capacitance of the active material film can be measured as follows. First, a single cell of the active material film battery is fabricated, where the single cell of the active material film battery has the active material film as the positive electrode, lithium or a lithium alloy as the negative electrode, and an electrolyte is disposed between the positive electrode and the negative electrode. Then, the capacitance of the positive electrode is measured. Then, the obtained capacitance is divided by the mass of the active material film to calculate the specific capacitance. The electrolyte of the single cell of the active material film battery can be the same as the electrolyte of the battery using the electrode to be evaluated. As a method for measuring the capacitance, an electrochemical impedance method can be used.

[0058] In the process of (3), the specific surface area and specific capacitance of the active material film obtained in the process of (2) are used to make a calibration curve. The calibration curve has the specific capacitance as the horizontal axis and the specific surface area as the vertical axis. The approximate equation (linear regression equation) of the obtained calibration curve is obtained, and thus the slope of the obtained approximate equation is obtained.

[0059] In the process of (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, a single cell of the electrode to be evaluated battery is fabricated, where the single cell of the electrode to be evaluated battery has the electrode to be evaluated as the positive electrode, lithium or a lithium alloy as the negative electrode, and an electrolyte is disposed between the positive electrode and the negative electrode. Then, the capacitance of the electrode to be evaluated is measured. Then, the obtained capacitance is divided by the mass of the active material in the electrode to be evaluated to calculate the specific capacitance. The electrolyte of the single cell of the electrode to be evaluated battery can be the same as the electrolyte of the single cell of the active material film battery. As a method for measuring the capacitance, an electrochemical impedance method can be used.

[0060] In the process of (5), calculate the specific surface area of the evaluation target electrode when the surface roughness Ra of the evaluation target electrode is zero. Specifically, the specific surface area is calculated by dividing the geometric surface area of the evaluation target electrode by the content of the active material in the evaluation target electrode.

[0061] In the process of (6), in the following formula (I), the slope of the calibration curve of the specific capacitance and the specific surface area of the active material film obtained in the process of (3) is set as a, the specific surface area of the evaluation target electrode obtained in the process of (5) is set as b, and the specific capacitance of the evaluation target electrode obtained in the process of (4) is substituted into x in the following formula (I) to obtain the electrode active specific surface area:

[0062] Electrode active specific surface area (m 2 / g) = a × x + b (I)

[0063] The electrode active specific surface area is an index of the contact area at the interface between the active material and the electrolyte in the evaluation target electrode.

[0064] Thus, a larger electrode active specific surface area means a larger contact area at the interface between the active material and the electrolyte, and the electrode reaction of the active material is likely to occur. Therefore, the output characteristics of the electrode with a larger electrode active specific surface area are improved.

[0065] According to the electrode activity evaluation method of the present embodiment configured as above, based on the specific capacitance and specific surface area of the active material film composed of active material monomers and the specific capacitance of the measurement target electrode, the activity of the electrode is evaluated. Therefore, the activity of the evaluation target electrode can be accurately evaluated. In addition, according to the electrode activity evaluation method of the present embodiment, by using the electrode active specific surface area calculated according to formula (I) to evaluate the activity of the electrode, the activity of the evaluation target electrode can be evaluated more accurately. According to the electrode activity evaluation method of the present embodiment, the activity of any one of the electrodes for a solid electrolyte battery and the electrodes for a battery using a liquid electrolyte can be evaluated.

[0066] According to the electrode activity evaluation method of the present embodiment, by using the electrochemical impedance method to measure the capacitance of the active material film and calculating by dividing the obtained capacitance by the mass of the active material film, the specific capacitance of the active material film can be accurately measured. Therefore, the activity of the evaluation target electrode can be evaluated more accurately. In addition, according to the electrode activity evaluation method of the present embodiment, by using the surface probe microscopy method to measure the surface area of the active material film, dividing the obtained surface area by the mass of the active material film to calculate the specific surface area of the active material film, the specific surface area of the active material film can be accurately measured. Therefore, the activity of the evaluation target electrode can be evaluated more accurately.

[0067] In the method for evaluating the activity of an electrode according to this embodiment, when the electrode to be evaluated is used in a battery using a liquid electrolyte, by measuring the capacitance of the electrode to be evaluated using electrochemical impedance spectroscopy in a state of contact with the liquid electrolyte, and dividing the obtained capacitance by the mass of the active material in the electrode to be evaluated, the specific capacitance of the electrode to be evaluated is calculated, and the activity of the electrode to be evaluated in the battery can be evaluated more accurately. In the method for evaluating the activity of an electrode according to this embodiment, when the electrode to be evaluated is used in a solid secondary battery using a solid electrolyte, in a state of contact with the solid electrolyte, the capacitance of the electrode to be evaluated is measured using electrochemical impedance spectroscopy, and the obtained capacitance is divided by the mass of the active material in the electrode to be evaluated to calculate the specific capacitance of the electrode to be evaluated. Thus, the activity of the electrode to be evaluated in the battery can be evaluated more accurately.

[0068] [Examples]

[0069] Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the interpretation of these examples.

[0070] [Example 1]

[0071] The activity of the electrode to be evaluated was evaluated as follows. The electrode to be evaluated included NMC (composition: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2() as the positive electrode active material.

[0072] [Fabrication of positive electrode active material thin film]

[0073] A substrate on which a Pt current collector layer was sputter-deposited over the entire surface of a Si single crystal substrate (10 mm long × 10 mm wide) was prepared as the current collector substrate.

[0074] First, on one side of the above current collector substrate, using a pulsed laser deposition method (PLD method) with a sintered body of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NMC) as the target, a thin film of NMC (9 mm long × 9 mm wide × 75 nm thick) was fabricated. The film formation conditions for the NMC thin film were as follows: the oxygen pressure in the chamber was as shown in Table 1, the temperature was 650 °C, the holding time was 50 minutes, a Nd-YAG laser (wavelength 266 nm) was used, the output was 200 mW, and the oscillation frequency was 10 Hz.

[0075] Next, on the NMC film, a LiNbO3 coating (9 mm long × 9 mm wide × thickness: several nm) was formed using PLD with a LiNbO3 sintered body as the target. The film formation conditions for the LiNbO3 coating were a temperature of 400 °C and a holding time of 15 minutes. Other than that, the film formation conditions were the same as those for the NMC thin film.

[0076] In this way, the positive electrode active material films of sample numbers 1 to 3 shown in Table 1 were obtained.

[0077] [Table 1]

[0078] Sample number of the positive electrode active material film Oxygen pressure in the chamber (Pa) 1 10.5 2 9.99 3 10.1

[0079] <Measurement of Specific Surface Area and Specific Capacitance of Positive Electrode Active Material Film>

[0080] For the positive electrode active material films of sample numbers 1 to 3, the specific surface area and specific capacitance were measured in the following manner. The results are shown in Table 2.

[0081] (Measurement method of specific surface area)

[0082] The surface roughness Ra value of the positive electrode active material film was obtained in the tapping mode of the surface probe microscope. The surface area of the positive electrode active material film was calculated based on the obtained surface roughness Ra value. In addition, the weight of the current collector substrate formed with the positive electrode active material film was measured using an analytical balance, and the weight of the current collector substrate measured in advance was subtracted. Thus, the weight of the positive electrode active material film was calculated.

[0083] The specific surface area was obtained by dividing the above surface area by the film weight of the above positive electrode active material.

[0084] (Measurement method of specific capacitance)

[0085] The positive electrode active material film battery single cell was fabricated in the following manner.

[0086] The current collector substrate formed with the positive electrode active material film was arranged. Next, a cylindrical container with an opening of 16 mm in diameter was mounted on the pressure shaft. After that, 250 mg of argyrodite-type sulfide (composition: Li 5.5 PS 4.5 Cl 1.5Powder of ( ). Insert another pressing shaft from the other end of the cylindrical container, apply the molding pressure shown in Table 2 to the argyrodite-type sulfide powder using the pressing shaft, and form a sulfide-based solid electrolyte layer composed of the argyrodite-type sulfide powder on the positive electrode active material film. Then, pull out the pressing shaft inserted from the rear, place a lithium-indium foil (Li-In foil) on the pulled-out pressing shaft, and insert the pressing shaft with the Li-In foil again, and apply a molding pressure of 115 MPa using the pressing shaft. In this way, a single positive electrode active material film battery is fabricated, where the single positive electrode active material film battery has a current collector substrate with a formed positive electrode active material film as the positive electrode, a Li-In foil as the negative electrode, and a sulfide-based solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0087] Measure the capacitance of the positive electrode active material film of the obtained single positive electrode active material film battery in the following manner.

[0088] First, connect the single positive electrode active material film battery to a charge-discharge device. Perform charge and discharge three times in a constant current (CC) of 1 μA within a voltage range of 2.08 V to 3.68 V for the thin film battery. Measure the capacity during the discharge in the third cycle and calculate the C rate. Then, connect the single positive electrode active material film battery to a potentiostat device with an electrochemical impedance spectroscopy (EIS) measurement function. First, discharge at a constant current (CC) of 0.1 C until 2.08 V, and at the moment of reaching 2.08 V, perform constant current - constant voltage (CC-CV) discharge until the remaining current is below 0.01 C. Then, leave the single positive electrode active material film battery stationary for 3 hours and measure the capacitance of the positive electrode active material film using the EIS method. The EIS measurement conditions are: frequency range: 1 MHz to 10 mHz, AC voltage amplitude: 10 mV. The EIS measurement is carried out by placing the single positive electrode active material film battery in a thermostatic bath and performing it at a temperature of 25°C.

[0089] Based on the Z” value near 180 mHz obtained by EIS measurement, calculate the capacitance value, divide it by the weight of the aforementioned positive electrode active material film, and obtain the specific capacitance.

[0090] [Table 2]

[0091] Sample number of the positive electrode active material film <![CDATA[Specific surface area (m 2 / g)]]> Molding pressure (MPa) Specific capacitance (F / g) 1 9.62 290 6.83 2 6.33 150 1.40 3 7.22 150 2.40

[0092] <Calculation of the slope of the calibration curve of the specific capacitance and specific surface area of the positive electrode active material film>

[0093] Prepare a calibration curve with the specific capacitance shown in Table 2 on the horizontal axis and the specific surface area on the vertical axis. The obtained calibration curve is shown in Figure 1 . The approximate equation (linear regression equation) of the obtained calibration curve is y = 0.5892x + 5.6247. From this approximate equation, it can be seen that the specific capacitance of the positive electrode active material film is related to the specific surface area with a slope of 0.5892.

[0094] <Fabrication of the electrode to be evaluated>

[0095] A composite material layer is formed on an aluminum current collector foil. The composite material layer contains positive electrode active material powder (NMC coated with LiNbO3), argyrodite-type sulfide solid electrolyte powder, conductive additive (acetylene black), and binder (styrene-butadiene rubber) in a mass ratio of 75:21:3:1. The content of the positive electrode active material powder in the composite material layer is 16 mg. The obtained aluminum current collector foil with the composite material layer is punched into a circle with a diameter of 10 mm to obtain the electrode to be evaluated.

[0096] <Measurement of the specific capacitance of the electrode to be evaluated>

[0097] The battery cell of the electrode to be evaluated is fabricated as follows.

[0098] In a cylindrical container having a circular opening with a diameter of 10 mm, the electrode to be evaluated is inserted and arranged. Then, 100 mg of argyrodite-type sulfide (composition: Li 5.5 PS 4.5 Cl 1.5 ) powder is added onto the composite material layer of the electrode to be evaluated. Pressing shafts are respectively inserted into the two openings on both sides of the cylindrical container, and a forming pressure of 100 MPa is applied to the argyrodite-type sulfide powder by the pressing shafts to form a sulfide-type solid electrolyte layer composed of argyrodite-type sulfide powder on the composite material layer of the electrode to be evaluated. Then, the pressing shaft on the sulfide-type solid electrolyte layer side is pulled out. After arranging a lithium-indium foil (Li-In foil) on the sulfide-type solid electrolyte layer, the pressing shaft is inserted again on the Li-In foil, and a forming pressure of 150 MPa is applied by the pressing shaft. In this way, the battery cell of the electrode to be evaluated is fabricated, where the battery cell of the electrode to be evaluated has the electrode to be evaluated as the positive electrode, the Li-In foil as the negative electrode, and a sulfide-type solid electrolyte layer is arranged between the positive electrode and the negative electrode.

[0099] The capacitance of the composite material layer of the obtained battery cell of the electrode to be evaluated is measured in the same manner as the capacitance of the aforementioned positive electrode active material film. The capacitance of the obtained composite material layer is divided by the content of the positive electrode active material powder in the composite material layer to calculate the specific capacitance of the positive electrode active material powder of the battery cell of the electrode to be evaluated. The obtained specific capacitance is 0.28 F / g.

[0100] <Calculation of the specific surface area of the positive electrode active material powder when the surface roughness Ra of the evaluation object electrode is zero>

[0101] Calculate the value obtained by dividing the geometric surface area of the evaluation object electrode by the content of the positive electrode active material powder in the composite material layer, and take it as the specific surface area of the positive electrode active material powder when the surface roughness Ra is zero. The obtained specific surface area of the positive electrode active material powder when the surface roughness Ra is zero is 0.005 m 2 / g.

[0102] <Calculation of the active specific surface area of the positive electrode active material powder of the evaluation object electrode>

[0103] Based on the specific surface area of the positive electrode active material powder (0.005 m 2 / g) when the above-mentioned surface roughness Ra is zero, and the slope (0.5892) of the specific capacitance and specific surface area of the above-mentioned positive electrode active material thin film, set the relationship formula between the specific capacitance and the active specific surface area of the positive electrode active material powder of the evaluation object electrode, and obtain the following formula (II):

[0104] y = 0.5892x + 0.005 (II).

[0105] Substitute the specific capacitance (0.28 F / g) of the positive electrode active material powder of the above-mentioned evaluation object electrode into x in the above formula (II), and calculate the electrode active specific surface area y of the positive electrode active material powder of the evaluation object electrode. As a result, the electrode active specific surface area y is 0.17 m 2 / g.

Claims

1. A method for evaluating the activity of an electrode, which is used to evaluate the activity of an electrode including an active material, and evaluates the activity of the aforementioned electrode based on the specific capacitance and specific surface area of the active material film composed of the aforementioned active material monomers, and the specific capacitance of the aforementioned electrode.

2. The method for evaluating the activity of the electrode according to claim 1, wherein, The activity of the aforementioned electrode is evaluated using the specific surface area of the electrode active material (m 2 / g) calculated according to the following formula (I): 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 aforementioned active material film, b is the specific surface area of the aforementioned electrode when the surface roughness Ra of the aforementioned electrode is zero, and x is the specific capacitance of the aforementioned electrode.

3. The method for evaluating the activity of the electrode according to claim 1 or 2, wherein, The capacitance of the aforementioned active material film is measured by an electrochemical impedance method, and the obtained capacitance is divided by the mass of the aforementioned active material film, whereby the specific capacitance of the aforementioned active material film is calculated.

4. The method for evaluating the activity of the electrode according to claim 1 or 2, wherein, The surface area of the aforementioned active material film is measured by a surface probe microscopy method, and the obtained surface area is divided by the mass of the aforementioned active material film, whereby the specific surface area of the aforementioned active material film is calculated.

5. The method for evaluating the activity of the electrode according to claim 1 or 2, wherein, The aforementioned electrode is used in a battery using a liquid electrolyte.

6. The method for evaluating the activity of the electrode according to claim 5, wherein, In a state where the liquid electrolyte used in the battery using the aforementioned electrode is in contact with the aforementioned electrode, the capacitance of the aforementioned electrode is measured by an electrochemical impedance method, and the obtained capacitance is divided by the mass of the active material in the aforementioned electrode, whereby the specific capacitance of the aforementioned electrode is calculated.

7. The method for evaluating the activity of the electrode according to claim 1 or 2, wherein The aforementioned electrode is used in a battery using a solid electrolyte.

8. The method for evaluating the activity of the electrode according to claim 7, wherein, In a state where the aforementioned solid electrolyte used in the battery using the aforementioned electrode is in contact with the aforementioned electrode, the capacitance of the aforementioned electrode is measured by an electrochemical impedance method, and the obtained capacitance is divided by the mass of the active material in the aforementioned electrode, whereby the specific capacitance of the aforementioned electrode is calculated.

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