Method for manufacturing electrode plates for secondary batteries, and electrode plates

Abstract

The present invention provides a method for manufacturing electrode plates for secondary batteries that can fully obtain the effects of dielectric materials, and also provides electrode plates. [Solution] In the first step of the electrode plate manufacturing method, based on the measurement results of the pore distribution in the electrode plate composite, volume peaks of different sizes of pores are determined, and the size range of the first dielectric 23 with large particle size is set from the size of the large pores in which the volume peak appears, and the size range of the second dielectric 24 with small pore size is set from the size of the small pores in which the volume peak appears. In the second step of the electrode plate manufacturing method, based on the evaluation results of a secondary battery having an electrode plate 8 containing the first dielectric 23 and the second dielectric 24 whose size ranges were set in the first step, the mixing ratio of the first dielectric 23 and the second dielectric 24, and the ratio of the dielectric 22 to the total weight of the electrode plate composite are set.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an electrode plate of a secondary battery and an electrode plate.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, an electrode (an electrode of a secondary battery) provided with an active material-containing layer is well-known. In the case of Patent Document 1, in a lithium-ion secondary battery, a dielectric (ferroelectric particles) is contained in the active material-containing layer. Since the ferroelectric particles have a high relative permittivity, they have an effect of alleviating the bias of charges due to concentration polarization. When the bias of charges is alleviated on the surface of the active material particles, solvation and desolvation of lithium ions are likely to occur. Therefore, an electrode having ferroelectric particles is excellent in input / output characteristics and low-temperature characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in order to sufficiently obtain the effect when a dielectric is contained in the active material-containing layer, it was necessary to optimize the dielectric to be contained. An object of the present disclosure is to provide a method for manufacturing an electrode plate of a secondary battery and an electrode plate that can sufficiently obtain the effect of a dielectric.

Means for Solving the Problems

[0005] A method for manufacturing an electrode plate for a secondary battery that solves the above problem is a method comprising an electrode plate having an composite material manufactured by kneading an active material that causes an electrical reaction and an additive containing at least a dielectric, comprising: a first step of determining the volume peaks of each size of the pores based on the measurement results of the pore distribution of the composite material, setting a range for the size of a first dielectric with a large particle size from the size of the large pores in which the volume peak appears, and setting a range for the size of a second dielectric from the size of the small pores in which the volume peak appears; and a second step of setting the mixing ratio of the first dielectric and the second dielectric, and the ratio of the dielectric to the total weight of the composite material, based on the evaluation results of the secondary battery having the electrode plate containing the first dielectric and the second dielectric whose size ranges were set in the first step.

[0006] The electrode plate that solves the above problem has a configuration having an composite material manufactured by kneading an active material that causes an electrical reaction in a battery and an additive that includes at least a dielectric, wherein the composite material is the composite material for the negative electrode plate, and the dielectric has a first dielectric with a large particle size determined from the size of the large pores that appear when the distribution of pores in the composite material is measured and a volume peak appears, and a second dielectric with a small particle size determined from the size of the small pores that appear when the distribution of pores in the composite material is measured and a volume peak appears, wherein the size range of the first dielectric is 1 μm to 3 μm, and the size range of the second dielectric is 0.1 μm to 0.3 μm, and the mixing ratio of the first dielectric and the second dielectric is set to a ratio in which the sum of both values ​​is 100%, with the range of the first dielectric being 50 to 80% and the range of the second dielectric being 20 to 50%, and the ratio of the dielectric to the total weight of the composite material is set to a range of 0.5 wt% to 1.5 wt%. [Effects of the Invention]

[0007] This disclosure provides an electrode plate having a dielectric material in which the effects of the dielectric material can be fully obtained. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view of a secondary battery according to one embodiment. [Figure 2] This is a diagram showing the configuration of the electrode assembly. [Figure 3] This is a model diagram of the negative electrode active material of the negative electrode plate. [Figure 4] This graph shows the distribution of pore sizes in the negative electrode plate. [Figure 5] This table summarizes the amount of dielectric material, the proportion of small particle sizes, the proportion of large particle sizes, and the resistance reduction rate for each sample. [Figure 6] This graph shows the distribution of each sample, with dielectric quantity and resistance reduction rate as indicators. [Modes for carrying out the invention]

[0009] An embodiment of this disclosure is described below. This disclosure is not limited to these examples, and all modifications are made within the meaning and scope of equivalence to the claims. For illustrative purposes, the drawings may exaggerate or simplify some parts of the configuration, and the dimensional proportions of the parts may differ from those of the actual parts. The lower limit of a numerical range may be either "greater than or equal to" or "greater than," and the upper limit of a numerical range may be either "less than or equal to," "less than," or "smaller than."

[0010] (Secondary battery 1) As shown in Figure 1, the secondary battery 1 is composed of multiple cells 2 combined together. The inside of the cell 2 case 3 is a battery case filled with a non-aqueous electrolyte. Inside the case 3 is an electrode body 4 in which positive and negative electrodes are stacked. The cell 2 has a positive electrode external terminal 5 and a negative electrode external terminal 6 that are electrically connected to the electrode body 4. The secondary battery 1 is a lithium-ion secondary battery that uses lithium ions as the ions that move between the positive and negative electrodes.

[0011] (Electrode body 4) As shown in Figure 2, the electrode body 4 comprises positive and negative electrode plates 8 and a separator 9 that insulates the electrode plates 8. The electrode plate 8 has a positive electrode plate 10, which is the positive electrode plate 8, and a negative electrode plate 11, which is the negative electrode plate 8. Each of the separator 9, the positive electrode plate 10, and the negative electrode plate 11 is formed in a strip shape, and the positive electrode plate 10 and the negative electrode plate 11, which are stacked and partitioned by two separators 9, are wound around an axis L1 that extends in the width direction of the strip (the Y-axis direction in Figure 2) to form a wound body.

[0012] (electrode plate 8) As shown in Figure 2, the electrode plate 8 comprises a current collector 13, which is the base material of the electrode plate 8, and a composite material 14 applied to the current collector 13. The composite material 14 comprises an active material that causes an electrical reaction and additives added to the active material. The electrode plate 8 is formed by coating both sides of the current collector 13 with a paste made by kneading the active material and additives, and then drying the electrode plate 4 after coating, thereby forming a layer of active material on the current collector 13.

[0013] The positive electrode plate 10 comprises a positive electrode current collector 15 and a positive electrode composite material 16 (positive electrode active material, positive electrode additives). The positive electrode current collector 15 is, for example, made of aluminum. Aluminum can be, for example, aluminum foil or aluminum alloy foil. The positive electrode active material can be, for example, a ternary (NMC) lithium-containing composite oxide containing nickel, manganese, and cobalt, or a lithium-containing composite oxide containing nickel, cobalt, and aluminum (NCA). The positive electrode additive includes, for example, a positive electrode solvent, a positive electrode conductive agent, and a positive electrode binder. The positive electrode solvent can be, for example, a non-aqueous solvent such as an NMP (N-methyl-2-pyrrolidone) solution. The positive electrode conductive agent may be, for example, carbon fibers such as carbon nanotubes (CNT) or carbon nanofibers (CNF), or carbon black such as graphite, acetylene black (AB), or Ketjen black.

[0014] The negative electrode plate 11 comprises a negative electrode current collector 17 and a negative electrode mixture 18 (negative electrode active material, negative electrode additives). The negative electrode current collector 17 is made of, for example, copper or copper foil. The negative electrode active material is made of, for example, a powdered carbon material such as graphite. The negative electrode additives include, for example, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode solvent is, for example, water. The negative electrode thickener is, for example, a polymer system that is insoluble in organic solvents and dissolves in water to exhibit viscosity. The polymer system is, for example, a cellulose derivative such as carboxymethylcellulose (CMC) or methylcellulose (MC).

[0015] For the positive electrode binder and the negative electrode binder, for example, polymer materials that disperse in water are used. Examples of polymer materials include vinyl acetate copolymer, styrene-butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), and rubbers such as gum arabic. Examples of polymer materials include fluorine-based resins such as polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE).

[0016] The electrode plate 8 has an uncoated portion 19 formed in the current collector 13 where the composite material 14 is not applied. The uncoated portion 19 of the positive electrode plate 10 is electrically connected to the positive electrode external terminal 5. The uncoated portion 19 of the negative electrode plate 11 is electrically connected to the negative electrode external terminal 6. In this way, the electrode plate 8 is electrically connected to the positive electrode external terminal 5 and the negative electrode external terminal 6 via the uncoated portion 19 of the current collector 13.

[0017] (Arrangement of active material and dielectric 22 on the current collector 13) As shown in Fig. 3, each particle of the negative electrode active material (hereinafter referred to as the negative electrode active material particle 21) is laminated on the negative electrode current collector 17. The negative electrode active material particle 21 has a characteristic of "spheroidization" in which the active material particles are folded, for example, in the case of natural graphite. The spheroidization is formed such that the active material particles assume polygons (in Fig. 3, substantially rhomboid) having different areas with substantially the same center. Therefore, the negative electrode active material particle 21 using natural graphite or the like has a characteristic of having a gap between the layers of the folded and adjacent active material particles.

[0018] The negative electrode plate 11 has a dielectric 22 that exhibits an effect of relaxing the charge bias due to concentration polarization in the secondary battery 1. For the dielectric 22, for example, BaTiO3 (barium titanate) is used. The dielectric 22 includes a first dielectric 23 having a large particle size and a second dielectric 24 having a small particle size. The powder of the first dielectric 23 having a large particle size is often arranged, for example, between adjacent negative electrode active material particles 21 due to its size. The powder of the second dielectric 24 having a small particle size often enters the gaps inside the negative electrode active material particles 21 and is thus arranged inside the negative electrode active material due to its size.

[0019] (Conditions of the dielectric 22) The size range of the first dielectric 23 shown in Fig. 3 is preferably, for example, 1 μm to 3 μm. The size range of the second dielectric 24 is preferably, for example, 0.1 μm to 0.3 μm. The ratio of the dielectric 22 to the total weight of the composite material 14 (negative electrode composite material 18) is preferably set in the range of, for example, 0.5 wt% to 1.5 wt%.

[0020] The mixing ratio of the first dielectric 23 and the second dielectric 24 is set such that the range of the first dielectric 23 is 50 to 80% and the range of the second dielectric 24 is 20 to 50%, and the sum of both values is 100%. As an example, for example, when the first dielectric 23 is 80%, the second dielectric 24 is set to 20%, or when the first dielectric 23 is 50%, the second dielectric 24 is also set to 50%.

[0021] (Operation of the embodiment) Next, the method for manufacturing the electrode plates of the secondary battery 1 of this embodiment and the operation of the electrode plates 8 will be described.

[0022] (First step in electrode plate manufacturing: Selection of dielectric particle size 22) Figure 4 is a graph showing the pore size distribution of the negative electrode plate 11. In the graph of Figure 4, the horizontal axis represents pore size [μm] and the vertical axis represents differential pore volume [mL / g]. In this example, the pore distribution is measured using, for example, a mercury porosimeter. However, other methods may be used to measure the pore distribution, such as gas adsorption, mercury intrusion, small-angle X-ray scattering, or image processing.

[0023] As shown in the figure, two peaks appear in the differential pore volume. Specifically, one peak appears in the region with small pore diameters, and another peak appears in the region with large pore diameters. These two peaks are presumed to be, for example, a peak originating from inside the negative electrode active material particles 21 and a peak originating from between the negative electrode active material particles 21. Specifically, since the negative electrode active material has a spherical shape property, there are gaps inside the negative electrode active material particles 21, and it is thought that these gaps cause one peak in the region with small pore diameters. In addition, there are many gaps of a certain size between adjacent negative electrode active material particles 21, and it is thought that these gaps cause another peak in the region with large pore diameters. Therefore, when adding dielectric 22 to the composite material 14 of the electrode plate 8, adding dielectric 22 powder with a particle size corresponding to these peaks will make it easier for the dielectric 22 to adhere to the composite material 14.

[0024] Based on the above, the particle size of the dielectric 22 is selected based on these peaks. Specifically, when the negative electrode active material is natural graphite, the particle size of the larger dielectric 22, i.e., the particle size of the first dielectric 23, is set in the range of 1 μm to 3 μm, taking into account the gaps between adjacent negative electrode active material particles 21. Also, when the negative electrode active material is natural graphite, the particle size of the smaller dielectric 22, i.e., the particle size of the second dielectric 24, is set in the range of 0.1 μm to 0.3 μm or less, taking into account the gaps inside the negative electrode active material particles 21.

[0025] (Manufacturing of secondary battery 1 for performance evaluation) To evaluate the performance of the secondary battery 1, first, a secondary battery 1 containing a dielectric 22 having a selected particle size is manufactured. The manufacturing process of the secondary battery 1 includes, for example, in the following order: "mixing," "kneading," "coating," "drying," "pressing," "punching," "battery assembly," "liquid injection," and "cell assembly."

[0026] When manufacturing the negative electrode plate 11, first, in the compounding process, for example, a negative electrode active material, a negative electrode thickener, a negative electrode binder, and a dielectric 22 (dielectric powder) are compounded. In this example, the amount of negative electrode active material is 98 wt%, the amount of negative electrode thickener is 1 wt%, and the amount of negative electrode binder is 1 wt%. The dielectric 22 is compounded from a material with a large particle size in the range of 1 μm to 3 μm and a material with a small particle size in the range of 0.1 μm to 0.3 μm.

[0027] In the mixing process, the blended materials (negative electrode active material, negative electrode thickener, negative electrode binder, and dielectric 22) are mixed in a mixer to produce a paste-like negative electrode mixture 18. In the coating process, the paste-like negative electrode mixture 18 is coated onto the negative electrode current collector 17 of the negative electrode plate 11. In the drying process, the negative electrode mixture 18 coated onto the negative electrode current collector 17 is dried. It is preferable that the coating process and the drying process be carried out continuously.

[0028] In the pressing process, the negative electrode plate 11, which has a negative electrode current collector 17 on which the dried negative electrode composite material 18 is laminated, is pressed. This pressing process improves the adhesion strength between the negative electrode composite material 18 and the negative electrode current collector 17. In the punching process, the pressed negative electrode plate 11 is cut into the shape required for the battery component.

[0029] The manufacturing procedure for the positive electrode plate 10 is the same as that for the negative electrode plate 11, although the required materials are different. Therefore, the manufacturing of the positive electrode plate 10 will not be explained here. In the battery assembly process, the manufactured positive electrode plate 10 and negative electrode plate 11 are separated by a separator 9, and the electrode body 4, which is formed by winding this laminate, is housed inside the case 3 of the secondary battery 1. In the electrolyte injection process, electrolyte is injected into the case 3 in which the electrode body 4 is housed. Preferably, the electrolyte is one in which 1 mole of LiPF6 as a salt is dissolved in a solvent mixed with EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) in a volume ratio of 1:1:1. In the cell assembly process, the secondary battery 1 is completed by assembling each cell 2 manufactured in the above procedure.

[0030] (Second step in electrode plate manufacturing: Performance evaluation of secondary battery 1) Figures 5 and 6 show the performance evaluation results of secondary batteries 1 fabricated using dielectric 22 with selected particle sizes. In this example, the resistance reduction rate was evaluated for multiple samples (12 in this example) in which the amount of dielectric 22, the ratio of small particle sizes, and the ratio of large particle sizes were varied as part of the performance evaluation of secondary batteries 1. Figure 5 is a table summarizing the amount of dielectric 22, the ratio of small particle sizes, the ratio of large particle sizes, and the resistance reduction rate for each sample from "Number 1" to "Number 12". Figure 6 is a graph showing the distribution of each sample using the amount of dielectric 22 and the resistance reduction rate as indicators. In Figure 6, the number of each sample is indicated by a circled number.

[0031] As shown in Figure 6, there is a correlation between the amount of dielectric 22 and the improvement in the resistance reduction rate. In other words, when the amount of dielectric 22 (amount added) is within a predetermined range, an improvement in the resistance reduction rate can be expected. Specifically in this example, when the amount of dielectric 22 was 0.5 wt% to 1.5 wt%, an evaluation result was obtained showing an improvement in the resistance reduction rate of about 4%. Therefore, it is preferable to set the amount of dielectric 22 added to the electrode plate 8 to 0.5 wt% to 1.5 wt%.

[0032] As shown in Figure 5, focusing on each sample (sample numbers "4" to "9" in this example) with a dielectric 22 amount of 0.5 wt% to 1.5 wt%, the ratio of large to small particle sizes of dielectric 22 can be derived from the combination of "large particle size:small particle size = 50% to 80%:20% to 50%". Therefore, it is preferable to set the mixing ratio of the first dielectric 23 and the second dielectric 24 so that the range of the first dielectric 23 is 50 to 80% and the range of the second dielectric 24 is 20 to 50%, with the sum of both values ​​being 100%.

[0033] Incidentally, since the negative electrode active material has internal spaces, when setting the content of large and small particle sizes of dielectric 22, it is conceivable to determine the content using specific surface area as an indicator. The specific surface area inside the negative electrode active material is larger than that of the surface of the negative electrode active material. Therefore, if the ratio of large to small particle sizes of dielectric 22 is simply determined by specific surface area, the mixing ratio of large to small particle sizes will be about 30%:70%, resulting in too much dielectric 22 inside the negative electrode active material. As a result, the pores may become blocked, potentially increasing the resistance of the secondary battery 1. In contrast, in this example, the optimal combination of large and small particle sizes of dielectric 22 is derived by actually evaluating the battery, so the aforementioned concerns do not arise.

[0034] (Effects of the embodiment) According to the configuration of this embodiment, the following effects can be obtained. (1) The above embodiment is a method for manufacturing an electrode plate for a secondary battery 1, comprising an electrode plate 8 having an composite material 14 manufactured by kneading an active material that causes an electrical reaction with an additive containing at least a dielectric 22. The electrode plate manufacturing method of this example comprises a first step of determining the volume peaks of different sizes of pores based on the measurement results of the pore distribution of the composite material 14, setting the size range of the first dielectric 23 with a large particle size from the size of the large pores in which the volume peak appears, and setting the size range of the second dielectric 24 from the size of the small pores in which the volume peak appears. The electrode plate manufacturing method of this example comprises a second step of setting the mixing ratio of the first dielectric 23 and the second dielectric 24 and the ratio of the dielectric 22 to the total weight of the composite material 14, based on the evaluation results of the secondary battery 1 having an electrode plate 8 containing the first dielectric 23 and the second dielectric 24 whose size ranges were set in the first step.

[0035] With this configuration, in the first step, it is possible to select the optimal size for both the first dielectric 23 with large particle size and the second dielectric 24 with small particle size. This makes it easier for the dielectric 22 to adhere to the active material, thus allowing the full effect of the dielectric 22 to be obtained. Furthermore, in the second step, it is possible to set the mixing ratio of the first dielectric 23 and the second dielectric 24, and the ratio of the dielectric 22 to the total weight of the composite material 14, to optimal values. This makes it less likely for the inside of the active material to be blocked by the dielectric 22, thus allowing the full effect of the dielectric 22 to be obtained in this respect as well.

[0036] (2) The size range of the first dielectric 23 is 1 μm to 3 μm. The size range of the second dielectric 24 is 0.1 μm to 0.3 μm. With this configuration, the ranges of the first dielectric 23 and the second dielectric 24 are set to the optimal range using the measurement results of the pore distribution of the electrode plate 8 that have been actually measured, so that an electrode plate 8 with sufficiently high performance can be manufactured.

[0037] (3) The mixing ratio of the first dielectric 23 and the second dielectric 24 is set so that the sum of the two values ​​is 100%, with the first dielectric 23 in the range of 50-80% and the second dielectric 24 in the range of 20-50%. With this configuration, the mixing ratio of the first dielectric 23 and the second dielectric 24 is set to an optimal value based on the results of actually evaluating and confirming the performance of the secondary battery 1, so that an electrode plate 8 with sufficiently high performance can be manufactured.

[0038] (4) The ratio of dielectric material 22 to the total weight of composite material 14 is set in the range of 0.5 wt% to 1.5 wt%. With this configuration, the ratio of dielectric material 22 to the total weight of composite material 14 is set to an optimal value based on the results of actually evaluating and confirming the performance of the secondary battery 1, so that an electrode plate 8 with sufficiently high performance can be manufactured.

[0039] (5) The electrode plate 8 is the negative electrode plate 11. The active material is natural graphite. With this configuration, the size and amount of the dielectric 22 contained in the natural graphite, which is the active material of the negative electrode plate 11, can be optimized, so that a negative electrode plate 11 can be obtained in which the dielectric 22 can exert its full effect. Thus, a low-resistance negative electrode plate 11 can be manufactured.

[0040] (Other embodiments) This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0041] The negative electrode active material is not limited to natural graphite; any material that exhibits "spherical" particulate properties is acceptable. The dielectric 22 may be, for example, zirconium oxide (ZrO2), titanium oxide (TiO2), or aluminum oxide (Al2O3).

[0042] • For dielectric 22, it is preferable to use, for example, a ferroelectric material. The electrode plate 8 manufactured by the electrode plate manufacturing method in this example is not limited to a negative electrode plate 11, but may also be a positive electrode plate 10.

[0043] • Secondary battery 1 is not limited to lithium-ion secondary batteries; other types of batteries may also be used. The secondary battery 1 is not limited to being a sealed battery with a rectangular parallelepiped shape; it may also have a shape other than a rectangular parallelepiped, such as a cylindrical shape.

[0044] The secondary battery 1 is not limited to being installed in electric vehicles or hybrid vehicles, but may also be installed in vehicles such as gasoline vehicles and diesel vehicles. Furthermore, the secondary battery 1 may be used as a power source for mobile vehicles such as trains, ships, aircraft, and robots, or for electrical products such as information processing devices.

[0045] This disclosure is described in accordance with the embodiments, but is not limited to the structures of these embodiments and includes various modifications and variations within the equivalence range. This disclosure also includes various combinations and forms, as well as combinations and forms of one, more, or fewer of these elements. [Explanation of Symbols]

[0046] 1...Secondary battery, 8...Electrode plate, 11...Negative electrode plate, 14...Composite material, 22...Dielectric, 23...First dielectric, 24...Second dielectric.

Claims

1. A method for manufacturing an electrode plate for a secondary battery, comprising an electrode plate having an composite material produced by kneading an active material that causes an electrical reaction with an additive containing at least a dielectric, A first step involves determining the volume peaks of each size of the pores based on the measurement results of the pore distribution in the composite material, setting a range for the size of the first dielectric with a large particle size from the size of the large pores in which the volume peak appears, and setting a range for the size of the second dielectric from the size of the small pores in which the volume peak appears. A method for manufacturing an electrode plate for a secondary battery, comprising: a second step of setting the mixing ratio of the first dielectric and the second dielectric, and the ratio of the dielectric to the total weight of the composite material, based on the evaluation results of the secondary battery having the electrode plate containing the first dielectric and the second dielectric, whose size range was set in the first step.

2. The size range of the first dielectric is 1 μm to 3 μm. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the size range of the second dielectric is 0.1 μm to 0.3 μm.

3. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the mixing ratio of the first dielectric and the second dielectric is set such that the range of the first dielectric is 50 to 80% and the range of the second dielectric is 20 to 50%, and the sum of both values ​​is 100%.

4. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the ratio of the dielectric material to the total weight of the composite material is set in the range of 0.5 wt% to 1.5 wt%.

5. The electrode plate is a negative electrode plate, The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the active material is natural graphite.

6. An electrode plate having a composite material manufactured by kneading an active material that causes an electrical reaction in a battery with an additive containing at least a dielectric, The aforementioned composite material is a composite material for the negative electrode plate, The dielectric comprises a first dielectric with a large particle size determined by the size of the large pores that produce a volume peak when the pore distribution of the composite material is measured, and a second dielectric with a small particle size determined by the size of the small pores that produce a volume peak when the pore distribution of the composite material is measured. The size range of the first dielectric is 1 μm to 3 μm. The size range of the second dielectric is 0.1 μm to 0.3 μm. The mixing ratio of the first dielectric and the second dielectric is set such that the sum of the two values ​​is 100%, with the first dielectric in the range of 50-80% and the second dielectric in the range of 20-50%. An electrode plate in which the ratio of the dielectric material to the total weight of the composite material is set in the range of 0.5 wt% to 1.5 wt%.

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