Current collector and nickel-zinc battery

Abstract

To provide a current collector capable of increasing capacity density.SOLUTION: The current collector is made of a metallic material. The current collector includes a first main surface and a second main surface, which are end faces in the thickness direction of the current collector. The first main surface has a plurality of first recesses recessed from the first main surface side toward the second main surface side. The plurality of first recesses are arranged at intervals in plan view. In plan view, the area of the bottom surface of each of the plurality of first recesses is at least 30% and 70% or less of the apparent area of each of the plurality of first recesses.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a current collector and a nickel-zinc battery. [Background technology]

[0002] For example, International Publication No. 2021 / 161900 (Patent Document 1) describes a nickel-zinc battery. The nickel-zinc battery described in Patent Document 1 has a resin plate (spacer), a current collector, and a separator.

[0003] The spacer has a first main surface and a second main surface which are end faces in the thickness direction of the spacer. A plurality of openings are formed in the spacer. The openings penetrate the spacer in the thickness direction. A current collector is disposed on the first main surface. A separator is disposed on the second main surface. An electrolyte is filled in the space defined by the openings, the current collector, and the separator, and an active material portion is disposed on the current collector. The active material portion contains zinc as an active material. The current collector and the active material portion constitute the negative electrode of the nickel-zinc battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 161900 Summary of the Invention [Problem to be solved by the invention]

[0005] In the nickel-zinc battery described in Patent Document 1, the movement of zinc in the direction along the first main surface (second main surface) is restricted by a spacer. Therefore, in the nickel-zinc battery described in Patent Document 1, the phenomenon (shape change) in which zinc segregates to the center of the negative electrode due to repeated charge and discharge is suppressed. Furthermore, in the nickel-zinc battery of Patent Document 1, the growth of zinc dendrites (needle-shaped crystals) due to shape change is suppressed, and the dendrites are also suppressed from breaking through the separator.

[0006] However, in the nickel-zinc battery described in Patent Document 1, the electrode group becomes thicker due to the spacer interposed between the current collector and the separator, which reduces the capacity density of the battery.

[0007] The present disclosure has been made in view of the above-mentioned problems of the conventional art. More specifically, the present disclosure provides a current collector that can increase the capacity density of a battery. [Means for solving the problem]

[0008] The current collector of the present disclosure is made of a metal material. The current collector has a first main surface and a second main surface, which are end surfaces in the thickness direction of the current collector. The first main surface has a plurality of first recesses recessed from the first main surface side toward the second main surface side. The plurality of first recesses are arranged at intervals in a plan view. In a plan view, the area of ​​the bottom surface of each of the plurality of first recesses is 30 percent to 70 percent of the apparent area of ​​each of the plurality of first recesses. [Effects of the Invention]

[0009] The current collector of the present disclosure can increase the capacity density. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view of a current collector 10. As shown in FIG. [Figure 2] FIG. 2 is a bottom view of the current collector 10. As shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view of a nickel-zinc battery 100 using the current collector 10. [Figure 5] FIG. 5 is a diagram showing the manufacturing process of the current collector 10. [Figure 6] FIG. 6 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity for Samples 1 to 3, Sample 6, and Sample 7. [Figure 7] FIG. 7 is a cross-sectional view of a nickel-zinc battery 100 using the current collector 10A. [Figure 8] FIG. 8 is a plan view of current collector 10B. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0012] (1) A current collector according to the embodiment is made of a metal material. The current collector has a first main surface and a second main surface, which are end surfaces in the thickness direction of the current collector. The first main surface has a plurality of first recesses recessed from the first main surface side toward the second main surface side. The first recesses are arranged at intervals in a plan view. In a plan view, the area of ​​the bottom surface of each of the first recesses is 30 to 70 percent of the apparent area of ​​each of the first recesses. The current collector described in (1) above can increase the capacity density of a battery.

[0013] (2) In the current collector described in (1) above, the second main surface may have a plurality of second recesses recessed from the second main surface side toward the first main surface side. Each of the plurality of second recesses may be arranged adjacent to each of the plurality of first recesses in a plan view. In a plan view, the area of ​​the bottom surface of each of the plurality of second recesses may be 30 percent to 70 percent of the apparent area of ​​each of the plurality of second recesses. The current collector described in (2) above can further increase the capacity density of the battery.

[0014] (3) In the current collector according to (1) or (2) above, the planar shape of each of the plurality of first recesses may be polygonal.

[0015] (4) In the current collector described in (2) above, the planar shape of each of the plurality of second recesses may be polygonal.

[0016] (5) In the current collector according to (3) or (4), the corners of the polygon may be rounded. The current collector according to (5) can improve the processability of the first recesses.

[0017] (6) In the current collector according to (3) or (4), the polygon may have four or more corners. The current collector according to (6) can improve the processability of the first recesses.

[0018] (7) In the current collector according to (3) or (4), the polygon may be a rectangle or a square. According to the current collector according to (7), the first recesses can be densely arranged.

[0019] (8) In the current collector according to (3) or (4), the polygon may be a regular hexagon. According to the current collector according to (8), the first recesses can be densely arranged and the rigidity of the current collector can be increased.

[0020] (9) In the current collector according to any one of (1) to (8), the metal material may have a tin content of 97.00 mass percent or more. The current collector according to (9) can suppress the generation of hydrogen and the generation of zinc dendrites.

[0021] (10) In the current collector according to any one of (1) to (9), the thickness of the current collector may be 10 μm or more. According to the current collector according to (10), even if the current collector is made of a soft material, the rigidity of the current collector can be ensured.

[0022] (11) In the current collector according to any one of (1) to (10), the depth of each of the plurality of first recesses may be 2.5 times or less the thickness of the current collector. The current collector according to (11) can improve the processability of the first recesses.

[0023] (12) In the current collector according to any one of (2) to (11), the depth of each of the second recesses may be 2.5 times or less the thickness of the current collector. The current collector according to (12) can improve the processability of the second recesses.

[0024] (13) The current collector according to any one of (1) to (12) above may further include an insulating layer. The insulating layer may be disposed on the first main surface between at least two adjacent first recesses. The current collector according to (13) above can suppress the generation of zinc dendrites near the separator.

[0025] (14) The current collector according to any one of (1) to (13) above may further include an insulating layer. The insulating layer may be disposed on the second main surface between at least two adjacent second recesses. The current collector according to (14) above can suppress the generation of zinc dendrites near the separator.

[0026] (15) The current collector according to any one of (1) to (14) above may be used for a nickel-zinc battery.

[0027] (16) A nickel-zinc battery according to the embodiment may include the current collector according to any one of (1) to (15) above.

[0028] [Details of the embodiments of the present disclosure] Next, details of embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated.

[0029] (First embodiment) The current collector according to the first embodiment will be described. The current collector according to the first embodiment is designated as current collector 10.

[0030] <Configuration of current collector 10> The configuration of the current collector 10 will be described below. FIG. 1 is a plan view of the current collector 10. FIG. 2 is a bottom view of the current collector 10. FIG. 2 shows the current collector 10 as seen from the opposite side to that of FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. As shown in FIGS. 1 to 3, the current collector 10 has a first main surface 10a and a second main surface 10b. The thickness direction of the current collector 10 is defined as a thickness direction DR1. The first main surface 10a and the second main surface 10b are end surfaces of the current collector 10 in the thickness direction DR1. The second main surface 10b is the surface opposite to the first main surface 10a.

[0031] The first main surface 10a has a plurality of first recesses 11. The first main surface 10a is recessed at the first recesses 11 from the first main surface 10a side toward the second main surface 10b side. In FIG. 1, which shows a plan view of the current collector 10, the first recesses 11 represented by solid lines are recessed relative to the paper surface, and the second recesses 12 represented by dashed lines are protruding relative to the paper surface. In FIG. 2, which shows a bottom view of the current collector 10, the first recesses 11 represented by dashed lines are protruding relative to the paper surface, and the second recesses 12 represented by solid lines are recessed relative to the paper surface. The planar shapes of the first recesses 11 and the second recesses 12 are, for example, polygonal. The planar shape of the first recesses 11 is, for example, square. 1 and 2, the planar shape of the first recess 11 and the planar shape of the second recess 12 are square, but the planar shape of the first recess 11 and the planar shape of the second recess 12 may be rectangular or may be a polygon other than a quadrangle, such as an equilateral triangle or a regular hexagon. Note that the term "polygon" does not mean a polygon in the strict mathematical sense. In other words, even if the corners are rounded, it is included in the term "polygon."

[0032] When the planar shape of the first recess 11 is square, the length of one side of the first recess 11 in plan view is defined as length L1. When the planar shape of the second recess 12 is square, the length of one side of the second recess 12 in plan view is defined as length L2. Lengths L1 and L2 are, for example, 1500 μm or less. Lengths L1 and L2 are preferably 1000 μm or less, and more preferably 500 μm or less.

[0033] The multiple first recesses 11 are arranged at intervals in a plan view. More specifically, the multiple first recesses 11 are arranged, for example, in a checkerboard grid in a plan view. The row and column directions of this grid are defined as a row direction DR2 and a column direction DR3, respectively. The row direction DR2 and the column direction DR3 are perpendicular to the thickness direction DR1. Note that "plan view" refers to the case where the current collector 10 is viewed along the thickness direction DR1. When the multiple first recesses 11 are arranged in a checkerboard grid in a plan view, the first recesses 11 are arranged at equal intervals in the row direction DR2 and the column direction DR3.

[0034] In a plan view, the area of ​​the bottom surface of the first recess 11 is 30 percent to 70 percent of the apparent area of ​​the first recess 11. The depth of the first recess 11 is defined as depth D1. Depth D1 is the distance in the thickness direction DR1 between the portion of the first main surface 10a where no first recess 11 is formed (i.e., the portion of the first main surface 10a between two adjacent first recesses 11) and the bottom surface of the first recess 11. The thickness of the current collector 10 is defined as thickness T. Depth D1 is, for example, 2.5 times or less the thickness T. Depth D1 is preferably 2.2 times or less the thickness T.

[0035] The second recesses 12 are arranged at intervals in a plan view. More specifically, the second recesses 12 are arranged, for example, in a checkerboard grid in a plan view. The row direction and column direction of this grid are aligned along the row direction DR2 and the column direction DR3, respectively. The second recesses 12 are adjacent to the first recesses 11 in a plan view, and the first recesses 11 are adjacent to the second recesses 12 in a plan view. From another perspective, the first recesses 11 and the second recesses 12 are alternately aligned along the row direction DR2 in a plan view, and alternately aligned along the column direction DR3 in a plan view.

[0036] In a plan view, the area of ​​the bottom surface of the second recess 12 is 30 percent to 70 percent of the apparent area of ​​the second recess 12. The depth of the second recess 12 is defined as depth D2. Depth D2 is the distance in the thickness direction DR1 between the portion of the second main surface 10b where no second recess 12 is formed (i.e., the portion of the second main surface 10b between two adjacent second recesses 12) and the bottom surface of the second recess 12. Depth D2 is, for example, 2.5 times or less the thickness T. Depth D2 is preferably 2.2 times or less the thickness T.

[0037] The current collector 10 is made of a metal material. The tin content in the metal material constituting the current collector 10 is, for example, 97.00 mass percent or more. The tin content in the metal material constituting the current collector 10 is preferably 99.90 mass percent or more. The tin content in the metal material constituting the current collector 10 is, for example, 99.99 mass percent or less. However, the metal material constituting the current collector 10 is not limited to this. The metal material constituting the current collector 10 may have, for example, copper foil and a tin layer disposed on the surface of the copper foil.

[0038] Fig. 4 is a cross-sectional view of a nickel-zinc battery 100 using the current collector 10. As shown in Fig. 4, the nickel-zinc battery 100 has the current collector 10, an active material layer 20, a positive electrode 30, and a separator 40. The current collector 10 and the active material layer 20 form the negative electrode 50 of the nickel-zinc battery 100. Although not shown, the positive electrode 30 is electrically connected to the negative electrode 50.

[0039] The active material layer 20 is disposed on the bottom surface of the first recess 11 and on the bottom surface of the second recess 12. The active material layer 20 disposed on the bottom surface of the first recess 11 also contacts the side surface of the first recess 11, and the active material layer 20 disposed on the bottom surface of the second recess 12 also contacts the side surface of the second recess 12. The active material layer 20 contains zinc (more specifically, zinc oxide) as a negative electrode active material. The active material layer 20 is porous.

[0040] The positive electrode 30 includes a metal porous body made of, for example, nickel or a nickel alloy, and a positive electrode active material filled inside the metal porous body. The positive electrode active material contains nickel (more specifically, nickel hydroxide). The separator 40 is made of a material that is permeable to hydroxide ions. The separator 40 is sandwiched between the positive electrode 30 and the negative electrode 50.

[0041] Although not shown, the positive electrode 30 and the negative electrode 50 are filled with an electrolyte. In the negative electrode 50, the electrolyte is filled in the space defined by the first recess 11 and the separator 40 and in the space defined by the second recess 12 and the separator 40. The electrolyte is an aqueous solution containing dissolved zinc and hydroxide ions. The electrolyte is, for example, an aqueous potassium hydroxide solution containing dissolved zinc oxide.

[0042] During charging, hydroxide ions react at the positive electrode 30, releasing electrons and producing oxygen and water. During charging, electrons released from the positive electrode 30 and supplied to the current collector 10 react with zinc oxide in the active material layer 20, hydroxide ions in the electrolyte, and water in the electrolyte at the negative electrode 50, producing zinc. During discharging, the opposite reaction occurs, and current flows from the positive electrode 30 to the negative electrode 50.

[0043] <Method of manufacturing current collector 10> A method for producing the current collector 10 will be described below. 5 is a manufacturing process diagram of the current collector 10. As shown in FIG. 5, the manufacturing method of the current collector 10 includes a preparation step S1 and an embossing step S2. In the preparation step S1, a sheet member is prepared. The sheet member is made of the same metal material as the current collector 10.

[0044] In the embossing step S2, the sheet member is embossed to form the sheet member into the current collector 10. The sheet member is embossed using, for example, an electric heating embosser.

[0045] <Effects of current collector 10> The effects of the current collector 10 will be described below. In the current collector 10, a plurality of first recesses 11 are formed on the first main surface 10a, and a plurality of second recesses 12 are formed on the second main surface 10b. In a plan view, the area of ​​the bottom surface of each first recess 11 is small, at 30 to 70 percent of the apparent area of ​​each first recess 11, and the area of ​​the bottom surface of each second recess 12 is small, at 30 to 70 percent of the apparent area of ​​each second recess 12. As a result, in a nickel-zinc battery using the current collector 10, the movement of zinc from one first recess 11 to another first recess 11 and from one second recess 12 to another second recess 12 are restricted. Therefore, shape change due to zinc segregation in the center of the negative electrode of a nickel-zinc battery 100 using the current collector 10 and the growth of zinc dendrites resulting from the shape change are suppressed.

[0046] In a nickel-zinc battery using the current collector 10, it is not necessary to interpose a spacer between the current collector 10 and the separator 40 to suppress the movement of zinc. Therefore, in a nickel-zinc battery using the current collector 10, the thickness of the electrode group is reduced, thereby increasing the capacity density.

[0047] When the tin content of the metal material constituting the current collector 10 is 97.00 mass percent or more, hydrogen generation and zinc dendrite formation in the negative electrode 50 can be suppressed. When the thickness T is 10 μm or more, the rigidity of the current collector 10 can be ensured even if the current collector 10 is made of a soft material such as a metal material with a tin content of 97.00 mass percent or more. The depth D1 (depth D2) depends on the thickness T before processing, and the greater the depth D1 (depth D2), the more the active material can be increased, thereby increasing the battery capacity. From this perspective, the thickness T is preferably 10 μm or more and 2000 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0048] When the depth D1 is 2.5 times or less the thickness T (when the depth D2 is 2.5 times or less the thickness T), processability in the embossing step S2 can be ensured. When the planar shape of the first recesses 11 (second recesses 12) is rectangular (square, oblong), equilateral triangular, or regular hexagonal, the first recesses 11 (second recesses 12) can be arranged more densely than when the planar shape of the first recesses 11 (second recesses 12) is, for example, circular. When the planar shape of the first recesses 11 (second recesses 12) is a regular hexagon, the current collector 10 has a honeycomb structure, and therefore the rigidity of the current collector 10 can be ensured. When the planar shape of the first recesses 11 (second recesses 12) has four or more corners, the interior angles of the polygon become large, and processability in the embossing step S2 can be ensured.

[0049] <Example> Samples 1 to 7 are nickel-zinc battery samples. In Samples 1 to 7, the negative electrode current collector was made of tin foil. The tin content of the tin foil was 99.90 mass percent. In Samples 1 to 3, first recesses 11 and second recesses 12, each with a square planar shape, were formed on the negative electrode current collector. In Samples 4 to 7, the first recesses 11 and second recesses 12 were not formed on the negative electrode current collector. In Samples 1 to 3, the depth D1, depth D2, length L1, length L2, bottom area of ​​the first recesses 11, and bottom area of ​​the second recesses 12 were changed on the negative electrode current collector. In Samples 4 to 7, the thickness T of the negative electrode current collector was changed. Details of the negative electrode current collectors for Samples 1 to 7 are shown in Table 1.

[0050] [Table 1]

[0051] The active material slurry used in the negative electrodes of Samples 1 to 7 had a dried composition of 90 mass percent zinc oxide, 5 mass percent AB (acetylene black), 0.5 mass percent CMC (granulated binder), 1.5 mass percent PTFE (polytetrafluoroethylene), and 3 mass percent SBR (styrene butadiene rubber). The fixed content in the active material slurry was 60 mass percent.

[0052] In the preparation of the negative electrodes of Samples 1 to 7, first, a current collector shown in Table 1 was prepared. Second, the active material slurry was applied to one main surface of the current collector using a doctor blade. Third, the active material slurry was dried using hot air at 100°C. Excess active material slurry was removed with a brush. Fourth, a nickel lead was joined to the current collector by welding.

[0053] The positive electrodes of Samples 1 to 7 were made of nickel porous metal bodies (nickel porous bodies) filled with active material slurry. The composition of the active material slurry after drying was 90 mass percent nickel hydroxide, 7 mass percent cobalt hydroxide, 0.3 mass percent CMC, and 2.7 mass percent SBR. The fixed content in the active material slurry was 78 mass percent.

[0054] In the preparation of the positive electrodes of Samples 1 to 7, first, the thickness was 1.2 mm and the metal amount was 300 g / m 2 A nickel porous body was prepared. Second, the thickness was adjusted by roll pressing, and the active material slurry was filled into the nickel porous body. Third, the active material slurry was dried with hot air at 100°C. Fourth, the nickel porous body was roll pressed to densify it. Fifth, a nickel lead was welded to the nickel porous body. Details of the negative and positive electrodes of Samples 1 to 7 are shown in Table 2.

[0055] [Table 2]

[0056] In Samples 1 to 7, an anion conductive membrane with a thickness of 150 μm was interposed between the positive and negative electrodes as a separator to form an electrode assembly. This electrode assembly was placed in a polypropylene bag, and the bag was fixed by sandwiching it between acrylic plates from the outside. A 1 mol / L potassium hydroxide aqueous solution in which zinc oxide was saturated was used as the electrolyte. The electrolyte was supplied into the bag until the electrode assembly was completely immersed, and the electrode assembly was impregnated under reduced pressure.

[0057] In Samples 6 and 7, a 0.5 mm thick polyethylene sheet was interposed between the negative electrode and the separator as a spacer. Multiple openings were formed in the polyethylene sheet. The openings penetrated the polyethylene sheet in the thickness direction. The diameter of the openings was 100 μm, and the pitch between two adjacent openings was 200 μm. Details of Samples 1 to 7 are shown in Table 3. The capacity density of the nickel-zinc batteries shown in Table 3 was calculated by dividing the capacity of the positive electrode by (electrode area × thickness of the electrode group).

[0058] [Table 3]

[0059] The thickness of the negative electrode of Sample 6 was similar to that of Sample 1. The thickness of the negative electrode of Sample 7 was similar to that of Samples 2 and 3. However, the capacity density of Sample 6 was smaller than that of Sample 1, and the capacity density of Sample 7 was smaller than that of Samples 2 and 3. From this comparison, it was confirmed that when current collector 10 is used as the negative electrode current collector, the thickness of the electrode group is smaller than when a separator having openings formed between the negative electrode current collector and the separator is disposed, and the capacity density of the nickel-zinc battery is improved.

[0060] Samples 1 through 7 were activated prior to evaluation. First, they were charged to 1.9 V at 0.1 C, followed by three cycles of discharging to 1.5 V at 0.1 C. Second, they were charged to 1.9 V at 0.2 C, followed by three cycles of discharging to 1.5 V at 0.2 C. Third, they were charged to 1.9 V at 0.5 C, followed by three cycles of discharging to 1.5 V at 0.5 C.

[0061] In the first test, the discharge capacities of the negative electrodes of Samples 1 to 7 were compared. In the first test, the negative electrodes were charged at 0.5 C to 1.9 V in a constant temperature bath at 30°C. The cutoff voltage during CV was 5 hours or a current value of 10 mA. In the first test, the negative electrodes were discharged at 0.2 C, 0.5 C, and 1 C to 1.5 V. The results of the first test are shown in Table 4. The discharge capacities shown in Table 4 are the average values ​​of N=5.

[0062] [Table 4]

[0063] In Samples 4 and 5, a short circuit occurred between the positive and negative electrodes during the activation process, making it impossible to conduct the first test. This is thought to be because Samples 4 and 5 did not have a spacer between the negative electrode and the separator, which prevented zinc ion migration. This led to the growth of zinc dendrites in the negative electrode, causing a short circuit between the positive and negative electrodes. Samples 1 to 3 exhibited higher discharge capacities than Samples 6 and 7 at all discharge rates. This is thought to be because Samples 1 to 3 had a smaller electrode assembly thickness than Samples 6 and 7, which had spacers, thereby suppressing the increase in resistance due to the electrolyte.

[0064] In the second test, the cycle characteristics of the negative electrodes of Samples 1 to 3, Sample 6, and Sample 7 were evaluated. In the second test, charging and discharging were alternately repeated. Charging was performed in the same manner as in the first test. Discharging was performed at 0.5 C until the voltage reached 1.5 V. Figure 6 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity of Samples 1 to 3, Sample 6, and Sample 7. The values ​​shown in the graph in Figure 6 are average values ​​of N=5. As shown in Figure 6, Samples 1 to 3 showed the smallest decrease in discharge capacity with increasing number of charge / discharge cycles compared to Samples 6 and 7.

[0065] As described above, the results of the first and second tests confirmed that by using the current collector 10 as the negative electrode of a nickel-zinc battery, short circuits between the positive and negative electrodes can be suppressed and excellent cycle characteristics can be exhibited.

[0066] (Second embodiment) A current collector according to the second embodiment will be described. The current collector according to the second embodiment is designated as current collector 10A. Here, differences from current collector 10 will be mainly described, and overlapping descriptions will not be repeated.

[0067] <Configuration of current collector 10A> The configuration of the current collector 10A will be described below. Current collector 10A has a first main surface 10a and a second main surface 10b. In current collector 10A, first main surface 10a has a plurality of first recesses 11, and second main surface 10b has a plurality of second recesses 12. In these respects, the configuration of current collector 10A is common to the configuration of current collector 10.

[0068] FIG. 7 is a cross-sectional view of a nickel-zinc battery 100 using the current collector 10A. As shown in FIG. 7, the current collector 10A further includes an insulating layer 13 and an insulating layer 14. The insulating layer 13 is disposed on a portion of the first main surface 10a where the first recesses 11 are not formed (i.e., a portion of the first main surface 10a between two adjacent first recesses 11). The insulating layer 14 is disposed on a portion of the second main surface 10b where the second recesses 12 are not formed (i.e., a portion of the second main surface 10b between two adjacent second recesses 12). Although not shown, the insulating layer 13 may also be disposed on the side surfaces of the first recesses 11, and the insulating layer 14 may also be disposed on the side surfaces of the second recesses 12.

[0069] The constituent materials of insulating layer 13 and insulating layer 14 are electrically insulating. The constituent materials of insulating layer 13 and insulating layer 14 are, for example, resin materials mixed with inorganic filler. Specific examples of the inorganic materials include silica and alumina. Specific examples of the resin materials include acrylic and fluororesin. In these respects, the configuration of current collector 10A differs from the configuration of current collector 10. In a nickel-zinc battery 100 using current collector 10A, insulating layer 13 or insulating layer 14 is interposed between separator 40 and current collector 10A.

[0070] <Effects of current collector 10A> The effects of the current collector 10A will be described below. If an electrochemical reaction occurs near separator 40 and zinc dendrites are generated, they will easily break through separator 40. In current collector 10A, as described above, insulating layer 13 is disposed on the portion of first main surface 10a between two adjacent first recesses 11, and insulating layer 14 is disposed on the portion of second main surface 10b between two adjacent second recesses 12.

[0071] Therefore, no electrochemical reaction occurs in the portion of the first main surface 10a between two adjacent first recesses 11 and in the portion of the second main surface 10b between two adjacent second recesses 12. As a result, in the nickel-zinc battery 100 using the current collector 10A, the generation of zinc dendrites near the separator 40 can be suppressed.

[0072] (Third embodiment) A current collector according to the third embodiment will be described. The current collector according to the third embodiment will be referred to as current collector 10B. Here, differences from current collector 10 will be mainly described, and overlapping descriptions will not be repeated.

[0073] 8 is a plan view of current collector 10B. Current collector 10B has a first main surface 10a and a second main surface 10b. In current collector 10A, first main surface 10a has a plurality of first recesses 11. In these respects, the configuration of current collector 10B is common to the configuration of current collector 10.

[0074] However, in current collector 10B, second main surface 10b does not have a plurality of second recesses 12. In this respect, the configuration of current collector 10B differs from the configuration of current collector 10. In nickel-zinc battery 100 using current collector 10B, there is also no need to interpose a spacer between current collector 10B and separator 40 to restrict the movement of zinc ions, so the thickness of the electrode assembly can be reduced and the capacity density is improved.

[0075] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims rather than the above embodiments, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0076] 10, 10A, 10B Current collector 10a First principal surface 10b Second principal surface 11 First recess 12 Second recess 13,14 Insulating layer 20 Active material layer 30 positive electrode 40 Separator 50 negative electrode 100 Nickel-Zinc Batteries D1, D2 depth DR1 thickness direction DR2 row direction DR3 column direction L1, L2 length S1 Preparation process S2 Embossing process T Thickness

Claims

1. A current collector made of a metal material, a first main surface and a second main surface which are end surfaces in a thickness direction of the current collector; the first main surface has a plurality of first recesses recessed from the first main surface side toward the second main surface side, the plurality of first recesses are arranged at intervals in a plan view, a current collector, wherein, in a plan view, the area of ​​a bottom surface of each of the plurality of first recesses is 30 percent to 70 percent of the apparent area of ​​each of the plurality of first recesses.

2. the second main surface has a plurality of second recesses recessed from the second main surface side toward the first main surface side, each of the second recesses is disposed adjacent to each of the first recesses in a plan view; The current collector according to claim 1 , wherein, in a plan view, the area of ​​the bottom surface of each of the plurality of second recesses is 30 percent to 70 percent of the apparent area of ​​each of the plurality of second recesses.

3. The current collector according to claim 1 , wherein the planar shape of each of the plurality of first recesses is a polygon.

4. The current collector according to claim 2 , wherein the planar shape of each of the plurality of second recesses is polygonal.

5. The current collector according to claim 3 or 4, wherein corners of the polygon are rounded.

6. The current collector according to claim 3 or 4, wherein the polygon has four or more corners.

7. The current collector according to claim 3 or 4, wherein the polygon is a rectangle or a square.

8. The current collector according to claim 3 or 4, wherein the polygon is a regular hexagon.

9. The current collector according to claim 1 or 2, wherein the metal material has a tin content of 97.00 mass percent or more.

10. 3. The current collector according to claim 1, wherein the current collector has a thickness of 10 μm or more.

11. 3. The current collector according to claim 1, wherein the depth of each of the plurality of first recesses is 2.5 times or less the thickness of the current collector.

12. The current collector according to claim 2 , wherein the depth of each of the plurality of second recesses is 2.5 times or less the thickness of the current collector.

13. Further comprising an insulating layer; The current collector according to claim 1 , wherein the insulating layer is disposed on the first main surface between at least two adjacent ones of the plurality of first recesses.

14. Further comprising an insulating layer; The current collector according to claim 2 , wherein the insulating layer is disposed on the second main surface between at least two adjacent ones of the plurality of second recesses.

15. The current collector according to claim 1 or 2, which is for a nickel-zinc battery.

16. A nickel-zinc battery comprising the current collector according to claim 1 or 2.

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