Electrode for electrochemical battery and battery using the same

Abstract

To provide an electrode for an electrochemical battery that has improved electrochemical activity and reduced IR drop, and an electrochemical battery using the same.SOLUTION: An electrode for an electrochemical battery is an electrode having a large number of fine recess portions formed in a depth direction from a surface thereof. An aspect ratio H / D which is a ratio of a depth H from the electrode surface to the bottom of the recess portion to an opening diameter D of the recess portion is greater than 0.35, the depth H from the electrode surface to the bottom of the recess portion is not less than 60 μm and not more than the thickness of the electrode, and the cavity of the recess portion is filled with a porous carbon material. There is also provided an electrochemical battery using the electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrode for an electrochemical cell and an electrochemical cell using the same. [Background technology]

[0002] Magnesium is an element that is more abundant and less unevenly distributed than lithium, so research, development, and commercialization of various magnesium batteries using magnesium metal as the anode have been progressing, and magnesium primary batteries have already been commercialized as emergency power sources and backup power sources. Secondary batteries that can be reused by repeated charging and discharging are now essential in various fields, and research and development of magnesium secondary batteries that use magnesium metal as the anode, which is abundant, inexpensive, and highly safe, is being conducted.

[0003] Problems with magnesium metal (hereinafter, the group consisting of pure magnesium and magnesium alloys will be referred to as magnesium metal) used for the negative electrode of magnesium batteries have been the ease with which a passive film forms on the magnesium metal surface and the low electrochemical activity of the (0001) plane formed parallel to the rolled surface of rolled magnesium material (see, for example, Non-Patent Document 1).

[0004] To solve this problem, Patent Document 1 reports an electrode material and a manufacturing method thereof, characterized in that the main reaction surface of the electrode material for electrochemical devices is inclined relative to the (0001) plane by devising a method for adjusting the chemical components and a manufacturing process. Patent Document 2 also reports an electrode material for electrochemical devices that uses a magnesium alloy containing additive elements such as Cu, with the aim of providing an electrochemically active magnesium alloy electrode material for electrochemical devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7344487 [Patent Document 2] International Publication No. 2020 / 013328 [Non-patent literature]

[0006] [Non-Patent Document 1] Kazumasa Yamazaki, "Development of negative electrode materials for magnesium alloy secondary batteries", Light Metals, 2022, Vol. 72, No. 3, pp. 92-98 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional rolled magnesium metal materials, the low electrochemical activity of the rolled surface formed parallel to the rolling direction and the formation of a passivation film on the magnesium metal surface tend to result in a significant IR drop (IR loss), the voltage drop immediately after discharge, when used as the negative electrode of a magnesium secondary battery. This increased IR drop causes problems such as a decrease in the discharge voltage of the secondary battery and deterioration of battery performance, including charge-discharge cycle characteristics. For this reason, it has been difficult to improve the performance of magnesium secondary batteries using conventional rolled magnesium metal materials, which are widely available and readily available. These low electrochemical activity of the surface of rolled magnesium metal materials and the tendency for a passivation film to form on the magnesium metal surface are issues not only for magnesium secondary batteries, but also for all magnesium batteries that use magnesium metal as an electrode, such as magnesium primary batteries, magnesium fuel cells, and magnesium-air batteries.

[0008] The phenomenon described above, in which an electrochemically inactive layer is formed on the electrode surface and battery characteristics deteriorate due to an increase in IR drop, etc., is not limited to magnesium-based metal electrodes, but is a problem in all electrochemical batteries that use other metal electrodes, metal alloy electrodes, metal oxide electrodes, ceramic electrodes, etc.

[0009] The present disclosure has been made in consideration of these problems, and aims to provide an electrode for an electrochemical battery, and a battery using the electrode, in which the surface of the electrode has a large number of fine recesses formed in the depth direction, thereby improving electrochemical activity through an electrode surface shape effect that affects the local diffusivity and concentration difference of chemical species in the electrolyte, and the IR drop is reduced by filling these recesses in the depth direction with a porous carbon material to cover the active surface. [Means for solving the problem]

[0010] The electrochemical activity of a metal electrode, in terms of electrochemical redox reactions, refers to the ease with which cations are generated through metal ionization. The formation of a passive film on the metal surface is one of the factors that hinders this. From the perspective of metal corrosion, this phenomenon translates into the fact that the more electrochemically active a metal is, the more susceptible it is to corrosion. Therefore, improving the electrochemical activity of a metal can be achieved by creating a metal surface that is more susceptible to corrosion. Pitting corrosion is a known corrosion phenomenon on metal surfaces. This occurs because of differences in the local diffusivity and concentration of oxygen and ionic species between the metal surface and recesses, which creates a local potential difference that promotes metal ionization and accelerates corrosion. This mechanism is due to the electrode surface shape effect.

[0011] In view of the above points, the present disclosure has reached the idea that by providing a large number of recesses with minute openings on the metal surface that function similarly to pitting corrosion pits in order to promote ionization of the metal, the electrochemical activity of the electrode can be improved by the electrode surface shape effect.

[0012] The above-mentioned technique involves forming recesses with a three-dimensional structure on a previously flat electrode surface, and utilizing the differences in local diffusivity and local concentration of oxygen and ionic species, etc., caused by the electrode surface shape effect. Because this technique is not dependent on chemical components or chemical composition, it can be applied not only to magnesium-based metal electrodes, but also to general electrodes for electrochemical batteries, such as other metal electrodes, metal alloy electrodes, metal oxide electrodes, and ceramic electrodes.

[0013] This electrochemical activation technique, which involves providing a metal surface with numerous recesses having minute openings that function similarly to corrosion pits and promote metal ionization, is based on the electrode surface shape effect, which affects the local diffusivity and concentration differences of chemical species in the electrolyte, and is not limited by the chemical composition, crystalline structure, orientation, etc. of the electrode material. Therefore, when the metal species of the electrode material is a magnesium-based metal, the electrode material of the present disclosure may be at least one selected from the group consisting of pure magnesium and magnesium alloys. Furthermore, the shape of the recesses in a planar view of the metal surface is not particularly limited, and examples include curved shapes such as circles and ellipses, and shapes with curves of different sizes distributed in a sea-island pattern.

[0014] The surface inside the recesses exposed by creating recesses in the depth direction of the electrode is highly electrochemically active, and is therefore prone to forming electrochemically inactive layers such as passivation films, which can easily cause IR drop.The researchers developed an electrode for electrochemical batteries that reduces IR drop by filling the recesses in the depth direction of the electrode with a porous carbon material and allowing the electrochemical reaction of the electrode to occur through the voids in the porous carbon layer.

[0015] The porous carbon material to be filled in the recesses in the depth direction of the electrode surface is not particularly limited, and examples thereof include porous carbon fine powder such as graphite fine powder, carbon black, graphene, activated carbon, MXene, carbon nanotubes, or mixtures thereof, and those obtained by dispersing these in a binder made of resin, etc. In addition to the porous carbon material, a porous layer made of fine particles that does not interfere with the electrochemical reaction of the electrode can also be used by filling the recesses in the depth direction of the electrode surface.

[0016] The electrochemical battery electrode according to the present disclosure is an electrode having a large number of minute recesses formed in the depth direction from the surface, and is characterized in that the aspect ratio H / D, which is the ratio of the depth H from the electrode surface to the bottom of the recesses to the opening diameter D of the recesses, is greater than 0.35. Here, the depth H represents the average depth of the recesses, and the opening diameter D represents the equivalent diameter.

[0017] The electrode for an electrochemical cell according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, and the depth H from the electrode surface to the bottom of the recess is 60 μm or more and equal to or less than the thickness of the electrode.

[0018] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, and the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys.

[0019] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, the depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, and the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys.

[0020] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, and the voids of the numerous recesses provided on the surface of the electrode are filled with a porous carbon material.

[0021] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, the depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, and the voids of the recesses, which are numerous and provided on the surface of the electrode, are filled with the porous carbon material.

[0022] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys, and the voids of the numerous recesses provided on the surface of the electrode are filled with the porous carbon material.

[0023] The electrode for an electrochemical battery according to the present disclosure is characterized in that the aspect ratio H / D is greater than 0.35, the depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys, and the voids of the recesses, which are numerous and provided on the surface of the electrode, are filled with the porous carbon material.

[0024] The electrochemical cell according to the present disclosure is characterized by using the above-described electrode for an electrochemical cell. [Effects of the Invention]

[0025] According to one aspect of the present disclosure, it is possible to provide an electrode for an electrochemical battery, which has improved electrochemical activity compared to conventional electrodes for electrochemical batteries, and furthermore, by forming a hybrid electrode with a porous carbon layer, reduces IR drop, and an electrochemical battery using the same. The structure of the electrode for an electrochemical battery according to the present disclosure is not limited to magnesium-based metal electrodes, but can be applied to general electrodes for electrochemical batteries, such as other metal electrodes, metal alloy electrodes, metal oxide electrodes, and ceramic electrodes. [Brief explanation of the drawings]

[0026] [Figure 1] 1A is a schematic plan view, FIG. 1B is an enlarged plan view, and FIG. 1C is a cross-sectional view of an electrode for an electrochemical battery according to a first embodiment, the electrode having a large number of recesses formed in the depth direction from the surface. [Figure 2] 10A and 10B are a plan view and a cross-sectional view, respectively, schematically illustrating an electrode for an electrochemical cell in which voids in recesses according to a second embodiment are filled with a porous carbon material. [Figure 3]4 is a diagram showing the relationship between the etching time, the recess depth H, the opening diameter D, and the aspect ratio H / D in forming the magnesium metal electrode according to the first embodiment. FIG. [Figure 4] 10 is a table showing the etching time for forming recesses for each sample, the presence or absence of a recess pattern, and the presence or absence of a porous carbon layer. [Figure 5] 10A and 10B are a plan view and a cross-sectional view, respectively, schematically illustrating a magnesium secondary battery according to a third embodiment. [Figure 6] FIG. 10 is a diagram showing charge / discharge curves of magnesium secondary batteries when (a) electrode A according to Comparative Example 1, (b) electrode B according to Embodiment 3, and (c) electrode C are used as negative electrodes. [Figure 7] 10 is a diagram showing charge / discharge curves of magnesium secondary batteries in the case where (a) electrode D, (b) electrode E, and (c) electrode F according to embodiment 3 are used as negative electrodes. FIG. [Figure 8] FIG. 10 is a diagram showing charge / discharge curves of a magnesium secondary battery when electrode G according to Comparative Example 2 is used as the negative electrode. [Figure 9] FIG. 10 is a diagram showing charge / discharge curves of a magnesium secondary battery when (a) Electrode H and (b) Electrode I according to Embodiment 4 are used as negative electrodes. [Figure 10] FIG. 11 is a diagram showing the relationship between the aspect ratio H / D and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge, according to the third embodiment. [Figure 11] FIG. 11 is a diagram showing the relationship between the cross-section / planar ratio and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge, according to the third embodiment. [Figure 12] FIG. 10 is a diagram showing the relationship between etching time in forming various magnesium metal electrodes according to the third and fourth embodiments and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge. [Figure 13]This is a table showing the maximum voltage change ΔV0 immediately after switching from charge to discharge and the voltage difference ΔV10 between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge, regarding the charge and discharge characteristics of magnesium secondary batteries using various magnesium metal electrodes as the negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the embodiments described below, identical or common parts are denoted by the same reference numerals, and their description will not be repeated. For ease of understanding, the scale of each part in the drawings may differ from the actual scale. Directions such as parallel, right angle, orthogonal, horizontal, vertical, up / down, left / right, and terms such as identical and equal are permitted to be deviated to the extent that they do not impair the functions and effects of the embodiments. The X-axis, Y-axis, and Z-axis directions represent directions parallel to the X-axis, Y-axis, and Z-axis, respectively. The X-axis, Y-axis, and Z-axis directions are perpendicular to each other.

[0028] The electrochemical battery electrode according to the present disclosure has a structure in which numerous recesses are provided on the electrode surface to improve the electrochemical activity of the electrode, and further, the highly electrochemically active recesses are filled with a porous carbon material, so that the electrochemical reaction of the electrode occurs through the pores in the porous carbon layer. The characteristics of such an electrochemical battery electrode structure when applied to a magnesium metal electrode are shown below in an embodiment in which the electrode is used as the negative electrode of a non-liquid electrolyte magnesium secondary battery. However, the batteries to which the effects obtained by the electrochemical battery electrode structure according to the present disclosure can be applied are not limited to this, and the electrode can also be applied to magnesium batteries using magnesium metal as an electrode, such as magnesium ion batteries, magnesium-halogen secondary batteries, magnesium primary batteries, magnesium fuel cells, and magnesium-air batteries, as well as batteries using other metal electrodes, metal alloy electrodes, metal oxide electrodes, ceramic electrodes, etc.

[0029] Next, the case where the structure of the electrochemical battery electrode of the present disclosure is applied to a magnesium metal electrode and used in a non-liquid electrolyte magnesium secondary battery (magnesium iodine secondary battery) will be described in detail below.

[0030] [Embodiment 1] FIG. 1 shows (a) a plan view, (b) an enlarged plan view, and (c) a cross-sectional view, each showing a schematic shape of an electrode 10 according to a first embodiment of the present disclosure. The electrode 10 has a structure in which numerous substantially cylindrical recesses 21 are provided in the depth direction of the electrode surface 20. In the plan view of FIG. 1(b), the openings of the numerous substantially cylindrical recesses 21 are shown as approximately circular, and the recesses 21 are arranged in a hexagonal close-packed structure with six recesses 21 arranged around one central recess 21. However, the recess arrangement is not limited to this. In the cross-sectional view of FIG. 1(c), symbol H denotes the depth of the recesses 21, symbol D denotes the opening diameter of the recesses 21, symbol R denotes the center-to-center spacing of the recesses 21, and symbol T denotes the thickness of the electrode. There are no particular limitations on the thickness T of the electrode.

[0031] In the schematic diagram of Figure 1, the bottom of the recess 21 is flat (Figure 1c), but the bottom of the recess 21 actually formed by etching is not completely flat but has a curved surface. Furthermore, the shape of the recess 21 actually formed by etching in a plan view (Figure 1b) will deviate from a perfect circle even if etching is performed using a mask with a perfect circular through-hole. Therefore, the depth H here represents the average depth of the recess, and the opening diameter D represents the equivalent diameter.

[0032] The roughly cylindrical recess as shown in FIG. 1 is formed by forming a through hole in the resin film by laser ablation of the electrode having the resin film on the surface thereof, and then etching through the through hole.

[0033] The method for forming recesses in the electrode is not limited to the above, and may be, for example, an etching method using a pattern formed by photolithography using a resist, an etching method using a sea-island structure pattern formed by spray coating a resin, or an etching method using a print pattern formed by a printing method. Alternatively, a method of directly drawing recesses by ablation using a laser without using etching, or a method of directly drawing recesses by ablation using a laser and then dissolving and removing oxides on the electrode surface using etching in combination, may also be used. For etching, not only solution etching but also dry etching may be used. Mechanical processing methods such as milling, drilling, and punching may also be used. Furthermore, a method of forming recesses by pressing, or a method of combining etching with mechanical dents or indentations may also be used.

[0034] The resin film used was a polyimide tape, which has high water resistance and etching resistance, attached to the electrode. However, the present invention is not limited to this, and other resin adhesive tapes can also be used, such as polyester tape, vinyl chloride tape, polypropylene tape, cellophane tape, and fluororesin tape. Alternatively, instead of using resin adhesive tape, a resin can be directly coated on the electrode. Examples of such resins include styrene-based resins such as polystyrene and polyvinyltoluene; styrene-based copolymers such as styrene-acrylic acid ester copolymers, styrene-methacrylic acid ester copolymers, styrene-acrylonitrile copolymers, styrene-vinyl methyl ether copolymers, and styrene-vinyl ethyl ether copolymers; polyvinyl chloride, phenolic resins, acrylic resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane resins, polyamide resins, epoxy resins, and polypropylene resins.

[0035] When the electrode material is magnesium metal, an aqueous citric acid solution was used as the etching solution, but the citric acid solution is not particularly limited, and examples include acid baths of inorganic acids such as phosphoric acid, sulfuric acid, and nitric acid, acid baths based on organic acids such as malic acid, and weak alkaline baths based on sodium pyrophosphate. Furthermore, since bubbles are generated during solution etching and cover the electrode surface, inhibiting the uniformity and etching rate of the etching, an ultrasonic bath was used, but the use of an ultrasonic bath is not particularly limited, and methods such as uniform stirring of the etching solution can also be used.

[0036] A pulsed laser can be suitably used for laser ablation of resin films, and a through-hole pattern was formed in a resin film attached to a magnesium metal surface by focused irradiation and scanning of ns (nanosecond) pulsed laser (532 nm). A CW (continuous wave) laser can also be used to form the through-hole pattern in the resin film, but in that case, it is necessary to peel off and remove the laser-carbonized parts of the resin film by focused irradiation of the CW laser light.

[0037] Figure 3 shows the relationship between etching time and the depth H of the recesses, the opening diameter D, and the aspect ratio H / D when a magnesium metal plate (0.2 mm thick) bearing a polyimide tape on its surface, with 100 μm diameter, approximately circular through-holes arranged in a hexagonal close-packed structure as shown in Figure 1(b), was etched in a 2.5 wt% citric acid solution under ultrasonic irradiation. Here, depth H refers to the average depth of the recesses, and opening diameter D refers to the equivalent diameter. The depth H at 0 min of etching is 16.0 μm because laser ablation of the magnesium metal surface occurred simultaneously with the formation of the through-holes by laser ablation of the polyimide tape attached to the magnesium metal surface. As shown in Figure 3(a), the etching depth H increased almost linearly up to 3 min of etching time, but then gradually increased with subsequent etching times. This is due to the reduced diffusion of the etching solution and bubbles generated during etching within the fine, approximately cylindrical recesses as the depth H of the recesses increases.

[0038] Figure 3(b) shows the relationship between etching time and recess opening diameter D, with D increasing as etching time increases. Figure 3(c) shows the relationship between etching time and the aspect ratio H / D, which is the ratio of recess depth H to opening diameter D, with the aspect ratio H / D increasing as etching time increases. Anisotropy was observed in the solution etching of magnesium metal.

[0039] [Embodiment 2] FIG. 2 shows (a) a plan view and (b) a cross-sectional view of an electrochemical battery electrode in which the voids of numerous recesses 21 formed on the electrode surface are filled with a porous carbon material 22. In the case of a metal-based electrode, if the internal crystal planes of the recesses 21 formed on the surface are exposed, the electrode is susceptible to the formation of electrochemically inactive layers such as passivation films, resulting in a large IR drop. The IR drop was reduced by filling the recesses 21 on the electrode surface with a porous carbon material 22. The electrochemical reaction of the electrode occurs through the voids in the porous carbon layer 22. In the schematic diagram of FIG. 2, the bottoms of the recesses 21 are flat (FIG. 2b). However, the bottoms of the recesses 21 actually formed by etching are not completely flat but have a curved surface. Furthermore, the planar shape of the recesses 21 actually formed by etching (FIG. 2a) will deviate from a perfect circle even if etching is performed using a mask with circular through-holes.

[0040] 4 is a table showing the etching time for forming recesses, the presence or absence of a recess pattern, and the presence or absence of a porous carbon layer for each sample. Carbon conductive paint and multilayer graphene were used as porous carbon materials.

[0041] [Embodiment 3] Various electrode samples shown in Figure 4 were used as negative electrodes in non-liquid electrolyte magnesium secondary batteries (magnesium iodine secondary batteries), and their characteristics were evaluated. Figure 5 shows (a) a plan view and (b) a cross-sectional view, each of which is a schematic representation of the structure of a non-liquid electrolyte magnesium secondary battery. The non-liquid electrolyte magnesium secondary battery consists of a half-cell including a negative electrode 10 and a first non-liquid electrolyte layer 30, and a half-cell including a positive carbon electrode 11 and a second non-liquid electrolyte layer 31. The second non-liquid electrolyte layer 31 contains ionic species different from those of the first non-liquid electrolyte layer 30. Electrodes A, B, C, D, E, F, G, H, and I shown in Figure 4 were used as negative electrodes, and a carbon electrode prepared by applying a carbon conductive paint to a porous microfiber cloth was used as the positive electrode. The first non-liquid electrolyte 30 was prepared by dispersing potassium iodide in polyvinyl alcohol (PVA), and the second non-liquid electrolyte 31 was prepared by dispersing lithium chloride in polyvinyl alcohol (PVA). The electrode / non-liquid electrolyte layer junction area is 1 cm 2 It was decided.

[0042] Figure 6 shows the charge-discharge curves of magnesium secondary batteries using Electrode A (Comparative Example 1), Electrode B, and Electrode C as the negative electrode. Electrode A, the comparative example, is a sample in which the surface of rolled magnesium metal was simply degreased with ethanol without any etching treatment. In its charge-discharge curve (Figure 6a), a sharp spike-like voltage drop was observed immediately after switching from charge to discharge, and in addition, voltage fluctuations occurred during charge and discharge.

[0043] Electrode B (etching time 1 minute, Figure 6b) and electrode C (etching time 2 minutes, Figure 6c), which have recesses, showed an improvement in the voltage fluctuation behavior during charge and discharge observed with electrode A. However, there was no improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge, or in the voltage difference between charge and discharge in the subsequent time period.

[0044] Figure 7 shows the charge-discharge curves of magnesium secondary batteries using electrodes D, E, and F as anodes. Electrode D (etching time: 3 min, Figure 7a) with recesses showed no improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge, but the voltage difference between charge and discharge was reduced after that time. Electrodes E (etching time: 5 min, Figure 7b) and F (etching time: 7 min, Figure 7c), which had longer etching times, showed even more significant improvements in the voltage difference between charge and discharge. This is because the depth H and aspect ratio H / D of the recesses increased with increasing etching time, as shown in Figure 3, which significantly enhanced the electrode surface shape effect and improved the electrochemical activity of the magnesium metal electrode.

[0045] The depth H of the recesses of electrodes B, C, D, E, and F shown in Figure 3 is 33.9 μm, 48.3 μm, 60.7 μm, 73.4 μm, and 80.5 μm, respectively, and in order to improve the electrochemical activity of the magnesium metal electrode, the depth H of the recesses needs to be 60 μm or more. Here, the depth H represents the average depth of the recesses.

[0046] Figure 8 shows the charge / discharge curves of a magnesium secondary battery using electrode G (Comparative Example 2) as the negative electrode. Electrode G, a comparative example, is a sample in which the rolled surface of magnesium metal was uniformly etched for 10 minutes without providing a resin film mask with through holes on the magnesium metal surface. The magnesium metal surface after etching is flat and roughly parallel to the original rolled surface. The charge / discharge curve showed little improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge, and in the voltage difference between charge and discharge.

[0047] FIG. 10 shows the relationship between the aspect ratio H / D, which is the ratio of the recess depth H to the opening diameter D, and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge. In Figure 10, ΔV10 decreases critically in the region exceeding the aspect ratio of electrode C (region where the aspect ratio H / D is greater than 0.35). In contrast, in the region where the aspect ratio H / D is 0.35 or less, there is almost no decrease in ΔV10 with increasing aspect ratio H / D. This indicates that in order for the depressions formed on the electrode surface to function like pits that promote metal ionization and improve electrochemical activity, the aspect ratio H / D must be greater than 0.35. When the aspect ratio H / D is small, there is little difference in diffusion and concentration between the electrode surface and the depressions, so it is thought that the electrode surface shape effect due to the formation of depressions is unlikely to occur.

[0048] In addition to the above, in the case of metal-based electrodes, the formation of numerous recesses with minute openings extending from the surface to the depth direction may also be a factor in improving the electrochemical activity of the electrode by increasing the exposure of the internal cross-section. Therefore, the cross-section / plane ratio, calculated from the ratio of the cross-sectional area of ​​the recesses to the area of ​​the electrode surface parallel to the rolled surface, was calculated and its relationship with ΔV10, the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge, was calculated and shown in Figure 11. In calculating the cross-sectional area of ​​the recesses to the depth direction, the recesses were assumed to be cylindrical. If the improvement in the electrochemical activity of the electrode was due to the activity of the metal crystal planes exposed at the recesses, a proportional relationship should be observed between the cross-section / plane ratio and ΔV10, but this was not observed in Figure 11. Although ΔV10 decreases critically in the region with a larger cross-section / plane ratio than that of electrode C (region with an aspect ratio H / D greater than 0.35), in the region with a cross-section / plane ratio less than that of electrode C (region with an aspect ratio H / D less than 0.35), almost no change in ΔV10 was observed with increasing cross-section / plane ratio.

[0049] The above results suggest that the improvement in electrochemical activity caused by forming numerous micro-pits on an electrode is primarily due to the electrode surface shape effect, where the micro-pits on the electrode surface act as pits to promote metal ionization. This indicates that the electrochemical activity of the electrode surface can be improved by the electrode surface shape effect, which is not limited to the orientation of magnesium crystal planes such as the (0001) plane, the type of added elements, or their chemical composition, but rather by the local diffusivity and concentration difference of chemical species in the electrolyte.

[0050] [Embodiment 4] Regarding the sharp spike-like voltage drop immediately after switching from charge to discharge, no significant improvement was observed with an increase in the recess depth H. This phenomenon of voltage dropping immediately after discharge is related to IR drop (IR loss) caused by an increase in the overvoltage of the electrochemical reaction, and one possible cause is the influence of the formation of an electrochemically inactive layer such as a passivation film.

[0051] Figure 9 shows the charge-discharge curves for electrodes H and I, in which the recesses in the depth direction of a magnesium metal electrode (etched for 5 minutes under the same conditions as electrode E) were filled with a porous carbon material. The electrode structure, in which magnesium metal and porous carbon material are hybridized, completely eliminated the sharp spike-like voltage drop that occurs immediately after switching from charge to discharge. Furthermore, the porous carbon layer maintains the electrochemical activity of the recesses, significantly reducing the voltage difference between charge and discharge.

[0052] 12 shows the relationship between the etching time in the formation of various magnesium metal electrodes and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge. In a comparison of a series of samples (electrodes B, C, D, E, and F) etched in a 2.5 wt% citric acid solution using a polyimide tape with approximately circular through-holes of 100 μm diameter as a mask, the change in ΔV10 was small up to 2 minutes of etching, but a decrease in ΔV10 was observed from around 3 minutes of etching (recess depth H = 60.7 μm).

[0053] Figure 12 also shows the ΔV10 value for electrode G, where the rolled surface of magnesium metal was uniformly etched for 10 minutes. When the rolled surface was uniformly etched, no depressions were formed to improve the electrochemical activity of the magnesium metal electrode, and little effect in reducing ΔV10 was observed.

[0054] Figure 12 also shows the ΔV10 values ​​for electrodes H and I, in which the recesses in the depth direction of the magnesium metal electrode were filled with porous carbon material. The electrode structure, in which magnesium metal and porous carbon material are hybridized, significantly reduced ΔV10.

[0055] 13 is a table showing the charge-discharge characteristics of magnesium secondary batteries using various magnesium metal electrodes as the negative electrode, showing the maximum voltage change ΔV0 immediately after switching from charge to discharge and the voltage difference ΔV10 between the charge voltage and discharge voltage 10 minutes after switching from charge to discharge. ΔV10 for electrode D, which had a recess depth H of 60 μm or more (etching time 3 minutes, recess depth H = 60.7 μm), was 0.368 V, a smaller value than the ΔV10 value of 0.385 V for electrode G, in which the rolled surface of magnesium metal was uniformly etched for 10 minutes.

[0056] In Figure 13, electrode H, which has a hybrid structure of magnesium metal and porous carbon material (carbon conductive paint film), completely eliminates the sharp spike-like voltage drop immediately after switching from charge to discharge, and furthermore, ΔV10 was reduced to approximately one-tenth. The reason why electrode H, which uses a carbon conductive paint film as the porous carbon material, has improved characteristics compared to electrode I, which uses multilayer graphene as the porous carbon material, is due to the difference in uniformity of the porous carbon layer that covers the recesses of the magnesium metal electrode; a porous carbon layer that more uniformly covers the recesses can reduce the IR drop. [Specific example] Next, specific examples and comparative examples of the embodiments of the present disclosure will be described. The present disclosure is not limited to these specific examples. The materials and devices used in the specific examples are as follows.

[0057] [material] (1) Magnesium plate (magnesium alloy AZ31 rolled material): manufactured by AS ONE; thickness approximately 0.2 mm, 150 x 300 mm. (2) Potassium iodide: manufactured by Futaba Chemical Co., Ltd. (3) Lithium chloride: manufactured by Merck. (4) Polyvinyl alcohol (PVA) solution: ELMER'S; PVA 14% or more, aqueous solution. (5) Crosslinking agent for PVA: ELMER'S; sodium bicarbonate 1% or more, aqueous solution. (6) Glycerin: manufactured by Hayashi Pure Chemical Industries. (7) Water-soluble carbon conductive paint: Polycarm WCP-EG163CG manufactured by Plus Coat Co., Ltd., surface resistivity 28.2 Ω / □ (when film thickness is 25 μm), resin binder component acrylic, diluent component alcohol / water-based, carbon fine particles graphite and carbon black. (8) Multilayer graphene powder: multilayer graphene; manufactured by Beijing Dingshen Special Ceramics Manufacture Co., Ltd., 6 to 10 layer graphene powder, specific surface area: 100 to 300 m 2 / g. (9) Purified water: Manufactured by Kenei Pharmaceutical Co., Ltd. (10) Absolute ethanol: Manufactured by Matsumotokiyoshi Holdings; 99.5%. (11) Microfiber cloth: Made by Etsumi; Clean Cloth Plus, material: acrylic + polyester. Thickness: approximately 0.1 mm. (12) Polyimide tape: manufactured by Doyeemei; width 30 mm, thickness approximately 0.05 mm. (13) Polypropylene (PP) sheet: manufactured by Sunnote Co., Ltd.; thickness approximately 0.05 mm. (14) Citric acid: manufactured by Kiyo Shochugiku Co., Ltd.; citric acid (anhydrous) 99.5% or more.

[0058] [measurement] (15) Battery charging / discharging device: Hokuto Denko HJ1020mSD8. (16) Hot plate stirrer: AS ONE; CHPS-170DF. (17) Ultrasonic cleaner: manufactured by SND Co., Ltd.; US-350S, 50W. (18) Optical microscope: Olympus BX51M. (19) Automatic stage: Sigma Koki OSMS60-10ZF. (20) Automatic stage controller: Sigma Koki; Mark-204. (21) Nanosecond pulse laser: CNI; MPL-H-532, 532 nm, 30 μJ. (22) Galvanometer scanner: manufactured by MASTER LASER, f-θ lens focal length 100 mm, control software EzCAD manufactured by BJJCZ. (23) Data analysis software: WaveMetrics Igor Pro. [Example]

[0059] [Creating a magnesium metal electrode with many fine recesses] A magnesium plate (rolled, 0.2 mm thick) was cut to a size of 15 mm x 40 mm, and polyimide tape was attached to both the front and back sides. It was then placed under the f-theta lens of a galvanometer scanner and subjected to focused irradiation and scanning with a laser beam. The laser beam was scanned using EzCAD, a galvanometer scanner control software with CAD functionality, to create a pattern as shown in Figure 1. The polyimide through-holes for forming the recesses 21 were designed with an opening diameter D of 100 μm and a center-to-center spacing R of 231 μm, arranged in a hexagonal close-packed structure. The laser beam scanning for the through-hole formation involved scanning a group of circles, each 8 μm apart from the opening diameter D (100 μm), in a tree-ring pattern. The polyimide tape within the circle of opening diameter D (100 μm) was removed by laser ablation, forming through-holes in the polyimide tape. A large number of such through-holes were formed in a square area with a side length L of 10 mm (Figure 1a).

[0060] The magnesium metal, to which polyimide tape having 100 μm diameter through-holes arranged in a hexagonal close-packed structure was attached, was placed in a plastic container filled with 2.5% citric acid solution, which was then placed in an ultrasonic cleaner tank filled with water and subjected to ultrasonic treatment for a predetermined period of time. After ultrasonic treatment, the polyimide tape was peeled off from the magnesium metal surface, and the fine particle precipitates on the magnesium metal surface caused by ultrasonic treatment were wiped off with 2.5% citric acid solution and ethanol.

[0061] The shape and depth of the recesses formed in the magnesium metal were observed using an optical microscope. While changing the height of the optical microscope stage using an automatic stage and stage controller, the focal positions of the magnesium metal surface and the bottom of the recess were read from the display on the stage controller, and the difference between these positions was calculated to determine the recess depth H as the average value of multiple points. Figure 3 shows the change in recess depth H and opening diameter D with etching time. Here, depth H represents the average depth of the recesses, and opening diameter D represents the equivalent diameter. Depth H increased linearly up to 3 minutes of etching time, but then gradually increased with subsequent etching times. This is due to the decreased diffusion of the etching solution and air bubbles within the tiny, roughly cylindrical recesses as depth H increased. Figure 4 shows the etching time, the presence or absence of a recess pattern, and the presence or absence of a porous carbon layer for each magnesium metal electrode sample.

[0062] During the laser ablation process, ablation of the magnesium metal surface beneath the polyimide tape can also occur simultaneously. Furthermore, the laser-ablated areas are more oxidized than the unirradiated magnesium metal surface, resulting in a faster etching rate. Therefore, even without using a polyimide tape with through holes as a mask, etching with a citric acid solution or similar can selectively increase the depth H of the laser-irradiated depressions. However, because etching of the unirradiated magnesium metal surface also occurs simultaneously, the increase in the depth H of the depressions over time is more pronounced when a polyimide tape with through holes is used as a mask. [Example]

[0063] [Development of a magnesium battery electrode with a hybrid structure of magnesium metal and porous carbon material] An electrode for an electrochemical battery, in which the voids of the recesses are filled with a porous carbon material, as shown schematically in Figure 2, was prepared as follows. Electrode H was prepared by applying a water-soluble carbon conductive paint diluted with ethanol to the magnesium metal electrode with the numerous recesses described above. Multilayer graphene powder was then pressure-coated onto the magnesium metal electrode with the numerous recesses using a spatula. The multilayer graphene layer after pressure coating exhibited a silvery-white metallic luster. [Example]

[0064] [Creating a non-liquid electrolyte magnesium secondary battery] One embodiment of the non-liquid electrolyte magnesium secondary battery (magnesium iodine secondary battery) of the present disclosure is shown schematically in Figure 5. Details of its components and secondary battery assembly are described below. [Preparation of carbon electrodes] Polyimide tape was adhered to one side of a porous microfiber cloth, which was then cut into a rectangular shape (15 mm long x 40 mm wide), and copper tape 42 used as an electrode terminal was attached to one longitudinal end. A process of applying a water-soluble carbon conductive paint to the microfiber cloth and copper tape and drying was repeated three times to prepare a carbon electrode 11. The water-soluble carbon conductive paint penetrates into the porous structure of the microfiber cloth, resulting in an interpenetrating structure between the porous microfiber cloth and the carbon layer. The surface resistance after drying was approximately 6.71 Ω / □. In one embodiment of the secondary battery of the present disclosure, a current collector made of a metal material (not shown in the schematic diagram of the secondary battery in FIG. 5) may be provided on electrode 10 or carbon electrode 11.

[0065] [Preparation of first non-liquid electrolyte] 5 g of potassium iodide was added to 20 g of polyvinyl alcohol (PVA) solution (PVA 14% or more) and dissolved, and then 5 g of glycerin was added and stirred. 10 g of an aqueous solution of a crosslinker for PVA was added to this mixture to obtain a uniform electrolyte solution 1. This solution was applied and heated on a hot plate (60 to 80°C) to prepare an adhesive first non-liquid electrolyte layer 30.

[0066] [Preparation of second non-liquid electrolyte] 2 g of lithium chloride and 2 g of purified water were added to 2.65 g of polyvinyl alcohol (PVA) solution (PVA 14% or more), and the mixture was stirred at 70°C for 5 hours to obtain a uniform electrolyte solution 2. This solution was applied and heated on a hot plate (60 to 80°C) to prepare an adhesive second non-liquid electrolyte layer 31.

[0067] [Assembling secondary battery cells] A rectangular opening measuring 10 mm long x 10 mm wide was made in polyimide tape (30 mm long x 40 mm wide) 41, and the tape was attached to a microfiber cloth (20 mm long x 30 mm wide). This was attached to a magnesium metal electrode (15 mm long x 40 mm wide) in a recessed portion, aligning the position of the opening, to form a separator 40. The electrolyte solution 1 was applied dropwise to the microfiber cloth portion above the recessed portion of the magnesium metal electrode 10, and the process of heating and drying on a hot plate (60 to 80°C) was repeated three times to form a sticky gel-like first non-liquid electrolyte layer 30 (approximately 0.6 mm thick).

[0068] The electrolyte solution 2 was applied dropwise to the carbon electrode 11, and then heated and dried on a hot plate (60 to 80°C), thereby forming a sticky gel-like second non-liquid electrolyte layer (thickness approximately 0.2 mm) 31 on the carbon electrode 11.

[0069] A non-liquid magnesium secondary battery cell (FIG. 5) was formed by bonding together a magnesium metal electrode 10 on which the first non-liquid electrolyte layer 30 was formed and a carbon electrode 11 on which the adhesive second non-liquid electrolyte layer 31 was formed on the surface. This was then covered and sealed with polyimide tape to form a secondary battery cell for measurement, but this part is not shown in FIG. 5. [Example]

[0070] [Charge / discharge curve measurement] Constant current (100μA), current density 100μ / cm 2Under these conditions, charging (10 minutes) and discharging (10 minutes) were repeated and the charge / discharge curve was measured.

[0071] [Comparative Example 1: Charge / Discharge Characteristics of Magnesium Metal Electrode Without Recesses] In the case of electrode A, a sample in which the surface of rolled magnesium metal was simply degreased with ethanol without any etching treatment, the charge-discharge curve (Figure 6a) showed a sharp spike-like voltage drop immediately after switching from charge to discharge, and in addition, voltage fluctuations occurred during charge and discharge.

[0072] Figure 6 shows the charge-discharge curves for magnesium metal electrode B (etching time 1 minute, Figure 6b) and electrode C (etching time 2 minutes, Figure 6c), both of which have numerous recesses formed using a mask of polyimide tape with roughly circular through-holes 100 μm in diameter. Compared to the charge-discharge curve for magnesium metal electrode A (Figure 6a), which does not have recesses, there is less voltage fluctuation during charge and discharge, suggesting an improvement. However, there is a sharp spike-like voltage drop immediately after switching from charge to discharge, and no significant improvement was observed in the voltage difference between charge and discharge.

[0073] Figure 7 shows the charge-discharge curves for electrodes D, E, and F used as negative electrodes in non-liquid magnesium secondary batteries. Electrode D (etching time: 3 minutes, Figure 7a) with the recessed portion did not show any improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge, but the voltage difference between charge and discharge was reduced after that time. Electrodes E (etching time: 5 minutes, Figure 7b) and F (etching time: 7 minutes, Figure 7c), which had been etched for a longer time, did not show any improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge, but the voltage difference between charge and discharge was clearly improved.

[0074] [Comparative Example 2: Charge / Discharge Characteristics of Magnesium Metal Electrode with Uniformly Etched Rolled Surface and No Recesses] Figure 8 shows the charge / discharge curves of a magnesium secondary battery using electrode G as the negative electrode. Electrode G is a sample in which the rolled surface of magnesium metal was uniformly etched for 10 minutes without providing a mask with through holes on the magnesium metal surface. The magnesium metal surface after etching is flat and roughly parallel to the original rolled surface. The charge / discharge curve did not show any improvement in the sharp spike-like voltage drop immediately after switching from charge to discharge. There was also little improvement in the voltage difference between charge and discharge.

[0075] Figure 9 shows the charge-discharge curves for electrodes H and I, in which the recesses in the depth direction of a magnesium metal electrode (etched for 5 minutes under the same conditions as electrode E) were filled with porous carbon material. The hybrid magnesium metal / porous carbon material electrode structure completely eliminated the sharp spike-like voltage drop immediately after switching from charge to discharge. The sharp spike-like voltage drop immediately after switching from charge to discharge is related to the IR drop (IR loss) caused by an increase in the overpotential of the electrochemical reaction. One cause of the increase in overpotential is the formation of an electrochemically inactive layer, such as a passivation film, on the magnesium metal surface. The hybrid magnesium metal / porous carbon material electrode structure allows the electrochemical reaction of the magnesium metal to occur through the pores in the porous carbon layer, thereby eliminating the sharp spike-like voltage drop immediately after switching from charge to discharge. Covering the recesses and surface of the magnesium metal electrode with porous carbon material was effective in reducing the IR drop.

[0076] Figure 10 shows the relationship between the aspect ratio H / D, which is the ratio of the recess depth H to the opening diameter D, and ΔV10, which is the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge. The curve shown in Figure 10 was obtained by curve fitting using a Gaussian function in data analysis software. Figure 10 shows that ΔV10 decreases critically in the region exceeding the aspect ratio of electrode C (region where the aspect ratio H is greater than 0.35). In contrast, in the region where the aspect ratio H / D is 0.35 or less, there is almost no decrease in ΔV10 with increasing aspect ratio H / D. When the aspect ratio H is 0.35 or less, there is little difference in diffusivity or local concentration between the electrode surface and the recesses, so the electrode surface shape effect due to the formation of recesses is unlikely to occur.

[0077] Figure 11 shows the relationship between the cross-section / flat ratio, calculated from the ratio of the cross-sectional area of ​​the recess in the depth direction to the area of ​​the electrode surface parallel to the rolled surface of the magnesium metal, and ΔV10, the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge. When calculating the cross-sectional area of ​​the recess in the depth direction, the recess was assumed to be cylindrical. The curve shown in Figure 11 was obtained by curve fitting using a Gaussian function in data analysis software. In Figure 11, ΔV10 did not change in proportion to the cross-section / flat ratio. In the case of electrode C, in the region below the cross-section / flat ratio (the region below 0.35 in terms of aspect ratio H / D), almost no change in ΔV10 was observed with increasing cross-section / flat ratio, despite the increased exposure of the cross-section in the depth direction of the recess.

[0078] Figure 12 shows the relationship between etching time and ΔV10, the voltage difference between the charge voltage and the discharge voltage 10 minutes after switching from charge to discharge, in the formation of various magnesium metal electrodes. The change in ΔV10 was small up to 2 minutes of etching time, but a decrease in ΔV10 began to be observed around 3 minutes of etching time (electrode D, recess depth H = 60.7 μm). Furthermore, ΔV10 (0.368 V) for electrode D (etching time 3 minutes, recess depth H = 60.7 μm) was smaller than ΔV10 (0.385 V) for electrode G, in which the rolled surface of magnesium metal was uniformly etched for 10 minutes. To improve the electrochemical activity of the magnesium metal electrode, a recess depth H of 60 μm or more was required.

[0079] Electrode G, in which the rolled surface of magnesium metal was uniformly etched for 10 minutes, showed only a slight reduction in ΔV10. This is because when the rolled surface of magnesium metal is uniformly etched, no depressions that can cause the electrode surface shape effect are formed, making it difficult to improve the electrochemical activity of the magnesium metal electrode.

[0080] Figure 12 also shows the ΔV10 values ​​for Electrode H and Electrode I. The electrode structure, which combines magnesium metal and porous carbon material, significantly reduced and improved ΔV10.

[0081] Figure 13 shows the charge-discharge characteristics of magnesium secondary batteries using various magnesium metal electrodes as the negative electrode, including the maximum voltage change ΔV0 immediately after switching from charge to discharge and the voltage difference ΔV10 between the charge voltage and discharge voltage 10 minutes after switching from charge to discharge. Electrode H, which has an electrode structure in which magnesium metal and porous carbon material (carbon conductive paint film) are hybridized, completely eliminated the sharp spike-like voltage drop immediately after switching from charge to discharge, and was able to reduce ΔV10 to approximately one-tenth.

[0082] In Figure 13, electrode H, which uses a carbon conductive paint film as the porous carbon material, has better characteristics than electrode I, which uses graphene as the porous carbon material. This is due to the difference in the uniformity of the porous carbon layer that covers the recesses of the magnesium metal electrode, and shows that a porous carbon layer that covers the recesses more uniformly can reduce the IR drop.

[0083] Graphene is a two-dimensional layered material, and multilayer graphene is extremely thin, with 6 to 10 layers. However, the size of the graphene sheets in the two-dimensional plane direction is on the order of several micrometers square, making it a carbon material with a high aspect ratio. When multilayer graphene with such an anisotropic shape is pressure-bonded and coated, the graphene sheet planes are parallel to the magnesium metal surface, resulting in good coverage. However, it is difficult to fully fill the recesses formed in the depth direction from the surface with the graphene sheet planes. As a result, the values ​​of ΔV0 and ΔV10 for electrode I (multilayer graphene film) were larger than those for electrode H (carbon conductive paint film). [Industrial Applicability]

[0084] According to the present disclosure, an electrode for an electrochemical battery and an electrochemical battery using the same are provided, which have a large number of recesses with fine openings on the surface thereof, thereby improving electrochemical activity by the electrode surface shape effect that affects the local liquid diffusivity and concentration difference of chemical species in the electrolyte, and furthermore, by filling these recesses in the depth direction with a porous carbon material, thereby reducing IR drop, and can be suitably used as a power source for various electronic devices.

[0085] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible, such as combinations with or substitutions for part or all of other embodiments. [Explanation of symbols]

[0086] 10 electrodes 11 Carbon electrode 20 Electrode surface 21 Recess 22 Porous carbon layer 30 First non-liquid electrolyte layer 31 Second non-liquid electrolyte layer 40 Separator 41 Polyimide film 42 Copper tape 43 Electrode / non-liquid electrolyte layer junction area

Claims

1. An electrode having a large number of minute recesses formed in a depth direction from a surface thereof, wherein an aspect ratio H / D, which is a ratio of a depth H from the electrode surface to a bottom of the recesses and an opening diameter D of the recesses, is greater than 0.

35. Electrode for an electrochemical cell.

2. The depth H from the electrode surface to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode.

2. An electrode for an electrochemical cell according to claim 1.

3. The material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys.

2. An electrode for an electrochemical cell according to claim 1.

4. A depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, and the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys.

2. An electrode for an electrochemical cell according to claim 1.

5. The voids of the recesses provided on the surface of the electrode are filled with a porous carbon material.

2. An electrode for an electrochemical cell according to claim 1.

6. The depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, and the voids of the recesses provided in large numbers on the surface of the electrode are filled with the porous carbon material.

2. An electrode for an electrochemical cell according to claim 1.

7. The material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys, and the voids of the recesses provided in large numbers on the surface of the electrode are filled with the porous carbon material.

2. An electrode for an electrochemical cell according to claim 1.

8. a depth H from the surface of the electrode to the bottom of the recess is 60 μm or more and is equal to or less than the thickness of the electrode, the material of the electrode is at least one selected from the group consisting of pure magnesium and magnesium alloys, and the voids of the recesses provided in large numbers on the surface of the electrode are filled with the porous carbon material.

2. An electrode for an electrochemical cell according to claim 1.

9. Use of the electrode for electrochemical cells according to claim 1, 2, 3, 4, 5, 6, 7 or 8 An electrochemical battery comprising:

10. Use of the electrode for electrochemical cells according to claim 3, 4, 7 or 8 A magnesium battery.

11. Use of the electrode for electrochemical cells according to claim 3, 4, 7 or 8 A magnesium secondary battery.

12. A method for manufacturing a semiconductor device comprising the steps of: forming through holes in a resin film by laser ablation of an electrode having a surface thereof; and forming a large number of recesses in the electrode by etching through the through holes. A method for producing an electrode for an electrochemical cell comprising the steps of:

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