Method for manufacturing negative electrode for zinc secondary battery

Abstract

To provide a manufacturing method for a negative electrode for a zinc battery, which can have excellent life performance.SOLUTION: A manufacturing method for a negative electrode for a zinc battery including a negative electrode current collector 21, a first negative electrode material layer provided on one surface 21a of the negative electrode current collector, and a second negative electrode material layer provided on the other surface 21b of the negative electrode current collector 21 includes a negative electrode material layer forming step of forming the first negative electrode material layer and the second negative electrode material layer in such a way that the negative electrode current collector 21 is transmitted between a first wall surface 51 and a second wall surface 52 while negative electrode material pastes 23a, 23b on both surfaces are brought into contact with the first wall surface 51 and the second wall surface 52 facing each other with the negative electrode material pastes 23a, 23b adhering to both surfaces of the negative electrode current collector 21. In the negative electrode material layer forming step, a ratio of a distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 to a distance D1 between the first wall surface 51 and the one surface 21a of the negative electrode current collector 21 is 0.7 to 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing a negative electrode for a zinc battery, and a negative electrode for a zinc battery. [Background technology]

[0002] Known zinc batteries include nickel-zinc batteries, air-zinc batteries, and silver-zinc batteries. For example, nickel-zinc batteries are aqueous batteries that use an aqueous electrolyte such as an aqueous potassium hydroxide solution, and are therefore highly safe. The combination of zinc electrodes and nickel electrodes is known to produce a high electromotive force for an aqueous battery. Furthermore, nickel-zinc batteries have excellent input / output performance and low cost, and therefore their applicability to industrial applications (e.g., backup power sources) and automotive applications (e.g., hybrid vehicles) is being considered.

[0003] The charge and discharge reactions of a nickel-zinc battery proceed, for example, according to the following formula (discharge reaction: rightward, charge reaction: leftward). (Positive electrode)2NiOOH+2H2O+2e - → 2Ni(OH)2+2OH - (Negative electrode) Zn+2OH - → Zn(OH)2+2e -

[0004] As shown in the above formula, zinc hydroxide (Zn(OH)2) is produced in zinc batteries by the discharge reaction. Zinc hydroxide is soluble in the electrolyte, and when zinc hydroxide dissolves in the electrolyte, it turns into zinc tetrahydroxide ions ([Zn(OH)4]2 -) diffuses into the electrolyte. As a result, the morphology (deformation) of the negative electrode progresses and the distribution of the charging current becomes uneven, causing zinc to precipitate locally on the negative electrode, resulting in the formation of dendrites (branched crystals). In conventional zinc batteries, when dendrites grow due to repeated charging and discharging, they may penetrate the separator, causing a short circuit. Therefore, various attempts have been made to prevent such short circuits caused by dendrites and improve battery life. For example, Patent Document 1 below discloses a technology for preventing short circuits caused by dendrites by interposing a nickel-plated nonwoven fabric between electrodes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 58-126665 Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, further improvements in the life performance of zinc batteries are required.

[0007] An object of one aspect of the present invention is to provide a method for producing a zinc battery anode that can provide excellent life performance, and a zinc battery anode. [Means for solving the problem]

[0008] One aspect of the present invention provides a method for manufacturing a zinc battery anode including a negative electrode current collector, a first negative electrode material layer provided on one side of the negative electrode current collector, and a second negative electrode material layer provided on the other side of the negative electrode current collector, the method comprising: a negative electrode material paste adhered to both sides of the negative electrode current collector; passing the negative electrode current collector between the first and second wall surfaces while bringing the negative electrode material paste into contact with the opposing first and second wall surfaces to form the first and second negative electrode material layers; and in the negative electrode material layer forming step, the ratio of the distance between the first wall surface and one side of the negative electrode current collector to the distance between the second wall surface and the other side of the negative electrode current collector is 0.7 to 1. Zinc batteries using a zinc battery anode obtained by this manufacturing method have excellent life performance.

[0009] In one aspect, the above ratio may be less than one.

[0010] In one aspect, the difference between the distance between the first wall surface and one surface of the negative electrode current collector and the distance between the second wall surface and the other surface of the negative electrode current collector is preferably 0.03 mm or less.

[0011] Another aspect of the present invention provides a zinc battery anode comprising a negative electrode current collector, a first negative electrode material layer provided on one side of the negative electrode current collector, and a second negative electrode material layer provided on the other side of the negative electrode current collector, wherein the ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer is 0.7 to 1. A zinc battery using this zinc battery anode has excellent life performance.

[0012] In another aspect, the ratio may be less than one.

[0013] In another aspect, the difference in thickness between the first negative electrode material layer and the second negative electrode material layer is preferably 0.03 mm or less. [Effects of the Invention]

[0014] According to one aspect of the present invention, it is possible to provide a method for manufacturing a zinc battery anode that can achieve excellent life performance, and a zinc battery anode. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a micrograph showing the cross-section of a conventional double-sided coated negative electrode, the cross-section of which changes with the number of battery cycles. [Figure 2] FIG. 1 is a schematic diagram showing an example of an apparatus used in a method for producing a zinc battery negative electrode according to an embodiment. [Figure 3] 3 is a schematic cross-sectional view showing a layer forming section in the apparatus shown in FIG. 2. [Figure 4] FIG. 2 is a plan view showing an example of a measurement point for the thickness of a negative electrode material layer. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. The sizes of the components in each figure are conceptual, and the relative size relationships between the components are not limited to those shown in each figure.

[0017] In this specification, a numerical range indicated with "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in a certain stage can be arbitrarily combined with the upper or lower limit of a numerical range in another stage. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. "A or B" may include either A or B, or may include both. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. In this specification, when multiple substances corresponding to each component are present in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified. Furthermore, in this specification, the term "layer" encompasses not only a structure that is formed over the entire surface when observed in a plan view, but also a structure that is formed only partially. Furthermore, in this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0018] The negative electrode obtained by the manufacturing method according to the following embodiment is a negative electrode (negative electrode for zinc battery) used in a zinc battery. Examples of zinc batteries (e.g., zinc secondary batteries) include nickel-zinc batteries, air-zinc batteries, and silver-zinc batteries. The basic structure of a zinc battery can be the same as that of a conventional zinc battery. The zinc battery in this specification may be either formed or unformed.

[0019] In one embodiment, a method for manufacturing a negative electrode for a zinc battery includes a negative electrode current collector, a first negative electrode material layer provided on one side of the negative electrode current collector, and a second negative electrode material layer provided on the other side of the negative electrode current collector, and includes a negative electrode material layer forming step of forming the first negative electrode material layer and the second negative electrode material layer by passing the negative electrode current collector between the first wall surface and the second wall surface while bringing the negative electrode material paste on both sides into contact with the first wall surface and the second wall surface facing each other, with the negative electrode material paste adhered to both sides of the negative electrode current collector, and in the negative electrode material layer forming step, the ratio of the distance between the first wall surface and one side of the negative electrode current collector to the distance between the second wall surface and the other side of the negative electrode current collector is 0.7 to 1.

[0020] Furthermore, one embodiment of the negative electrode for a zinc battery includes a negative electrode current collector, a first negative electrode material layer provided on one side of the negative electrode current collector, and a second negative electrode material layer provided on the other side of the negative electrode current collector, and the ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer is 0.7 to 1.

[0021] By using the zinc battery negative electrode according to these embodiments, it is possible to obtain excellent life performance in the zinc battery. The reason why such an effect is obtained is not clear, but the inventors speculate as follows.

[0022] In the negative electrode for zinc batteries (hereinafter simply referred to as the "negative electrode"), metallic zinc, which is the negative electrode active material, is converted into tetrahydroxide zincate ions ([Zn(OH)4]2 - ) and elutes as [Zn(OH)4]2 - is supersaturated in the electrolyte and precipitates as zinc oxide (ZnO) on the negative electrode layer. - The concentration of ZnO and the amount of ZnO deposited are thought to be affected by the thickness of the negative electrode material layer. When the negative electrode material layer is thick, [Zn(OH)4]2 -The concentration of ZnO increases, and therefore, when the negative electrode layer is thick, the amount of ZnO deposited on the negative electrode layer also increases. Since ZnO is slightly soluble in the electrolyte, the amount of ZnO deposited near the ZnO particles is [Zn(OH)4]2 - exists in a supersaturated state, which further promotes the precipitation of ZnO.

[0023] There are so-called double-coated negative electrodes, in which a negative electrode material layer is provided on each side of a current collector. As mentioned above, the amount of ZnO deposited increases as the thickness of the negative electrode material layer increases. Therefore, in a double-coated negative electrode, if there is a large difference in thickness between the negative electrode material layer on one side and the negative electrode material layer on the other side, an environment is created where ZnO is likely to be deposited unevenly on the surface of the thicker negative electrode material layer. Furthermore, it is thought that the difference in thickness between the front and back of the same negative electrode increases as the number of battery cycles increases.

[0024] FIG. 1 shows micrographs (scanning electron microscope, 200x magnification) of the cross section of a conventional double-coated negative electrode observed over the course of battery cycles. FIG. 1(a) shows the state of the negative electrode before use, with the number of cycles increasing in the order of FIGS. 1(b), 1(c), and 1(d). In the double-coated negative electrode 10 shown in FIG. 1(a), there is a difference in thickness between the first negative electrode material layer 12 provided on one side of the negative electrode current collector 11 and the second negative electrode material layer 13 provided on the other side of the negative electrode current collector 11. That is, the first negative electrode material layer 12 is thicker than the second negative electrode material layer 13. In this negative electrode 10, as shown in FIGS. 1(b) to 1(d), the difference in thickness between the first negative electrode material layer 12 and the second negative electrode material layer 13 increases over the course of battery cycles. This is thought to be because, for the reasons mentioned above, the thicker the negative electrode material layer is, the more unevenly ZnO is deposited.

[0025] In zinc batteries, hydroxide ions (OH), which are charge carriers, are transported between the opposing positive and negative electrodes via a separator such as a microporous membrane or nonwoven fabric. - As shown in Figure 1, if one of the negative electrode layers loses weight unevenly, smooth OH diffusion with the opposing positive electrode is prevented. -This is thought to inhibit the charge / discharge reaction because the exchange of charge and discharge is no longer possible.

[0026] More specifically, in the discharge reaction, OH diffused from the positive electrode - However, if the negative electrode layer facing the positive electrode is reduced in weight, the OH - The need for diffusion of OH to the active material in the negative electrode layer on the opposite side of the positive electrode through the negative electrode current collector such as punched metal increases. This increases the diffusion resistance, which is presumed to gradually impair the discharge capacity. In addition, the charge reaction is a reaction in the opposite direction to the discharge reaction, and OH is transferred from the negative electrode to the positive electrode. - Therefore, if the negative electrode material layer facing the positive electrode is reduced in weight, the charge capacity is impaired due to an increase in diffusion resistance, similar to the discharge reaction. If the charge capacity is impaired, it is thought that the decrease in discharge capacity will be further accelerated.

[0027] On the other hand, in the negative electrode obtained by the manufacturing method according to this embodiment, the difference in thickness between the first negative electrode material layer provided on one side of the negative electrode current collector and the second negative electrode material layer provided on the other side of the negative electrode current collector is small, so that it is possible to prevent ZnO from being deposited unevenly on one of the negative electrode material layers. - This allows for the transfer of charge and discharge, preventing the charge-discharge reaction from being inhibited. As a result, it is believed that the life performance of zinc batteries can be improved.

[0028] <Method of manufacturing anode for zinc battery> A method for manufacturing a negative electrode for a zinc battery according to one embodiment includes a negative electrode material layer forming step of forming a first negative electrode material layer and a second negative electrode material layer by passing the negative electrode current collector between the first wall surface and the second wall surface while bringing the negative electrode material paste adhered to both surfaces of the negative electrode current collector into contact with the first wall surface and the second wall surface facing each other.

[0029] The negative electrode current collector has, for example, a plate shape, a sheet shape, or the like. The negative electrode current collector may be a three-dimensional mesh-structured current collector composed of foam metal, expanded metal, punched metal, metal fiber felt, or the like. The negative electrode current collector is composed of a material having electrical conductivity and alkali resistance. Examples of such materials include materials that are stable even at the reaction potential of the negative electrode (materials with a redox potential higher than the reaction potential of the negative electrode, materials that form a protective coating such as an oxide coating on the substrate surface in an alkaline aqueous solution for stabilization, etc.). In addition, at the negative electrode, a decomposition reaction of the electrolyte proceeds as a side reaction, generating hydrogen. Materials with a high hydrogen overvoltage are preferred because they can suppress the progression of such side reactions. Specific examples of materials that constitute the negative electrode current collector include zinc, lead, tin, and metal materials plated with metals such as tin (copper, brass, steel, nickel, etc.).

[0030] The negative electrode material paste is a paste containing components that form the negative electrode layer. The negative electrode material paste may be, for example, a paste obtained by adding the components that form the negative electrode layer to a dispersion medium such as water and kneading them.

[0031] The negative electrode paste contains a negative electrode active material containing zinc. Examples of the negative electrode active material include metallic zinc, zinc oxide, zinc hydroxide, etc. For example, the negative electrode paste contains metallic zinc in a fully charged state, and zinc oxide and zinc hydroxide in an end-of-discharge state.

[0032] The amount of the negative electrode active material is preferably in the following range based on the total mass of the non-volatile content of the negative electrode paste (components excluding the dispersion medium from the negative electrode paste). From the viewpoint of easily achieving both excellent life performance and discharge performance, the amount of the negative electrode active material is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 75 mass% or more. From the viewpoint of easily achieving both excellent life performance and discharge performance, the amount of the negative electrode active material is preferably 95 mass% or less, more preferably 90 mass% or less, and even more preferably 85 mass% or less. From these viewpoints, the amount of the negative electrode active material is preferably 50 to 95 mass%.

[0033] The negative electrode paste may contain additives other than the negative electrode active material. Examples of additives include a binder and a conductive agent. Examples of binders include polytetrafluoroethylene, hydroxyethyl cellulose, polyethylene oxide, polyethylene, and polypropylene. The amount of the binder may be, for example, 0.5 to 10 parts by mass per 100 parts by mass of the negative electrode active material. Examples of conductive agents include indium compounds (indium oxide, etc.). The amount of conductive agent may be, for example, 1 to 20 parts by mass per 100 parts by mass of the negative electrode active material.

[0034] 2 is a schematic diagram showing an example of an apparatus used in the method for producing a zinc battery negative electrode according to this embodiment. The zinc battery negative electrode according to this embodiment can be produced, for example, using the apparatus shown in FIG.

[0035] In this manufacturing method, first, a roll-shaped negative electrode current collector 21 is unwound by an unwinding unit 30, and then the negative electrode current collector 21 is passed through a tank 40 containing a negative electrode material paste, thereby adhering the negative electrode material paste to the negative electrode current collector 21. In this manufacturing method, the roll-shaped negative electrode current collector 21 is unwound by the unwinding unit 30. Alternatively, a flat or sheet-shaped negative electrode current collector may be prepared and then introduced into the tank 40. Next, the negative electrode current collector is lifted up from the tank 40. The negative electrode material paste is adhered to both surfaces (one surface and the other surface of the negative electrode current collector 21) of the lifted negative electrode current collector 21. This results in a negative electrode current collector 22 having the negative electrode material paste adhered to both surfaces. In the negative electrode current collector 22 having the negative electrode material paste adhered to both surfaces, the negative electrode material paste may be adhered to a portion of one surface and the other surface of the negative electrode current collector 21, or may be adhered to the entire surface.

[0036] Next, the negative electrode current collector 22 with the negative electrode material paste attached to both sides thereof is passed through the layer forming section 50 .

[0037] 3 is a schematic cross-sectional view showing a layer forming unit 50 in the apparatus shown in FIG. 2. The layer forming unit 50 has a gap 53 formed by a first wall surface 51 and a second wall surface 52 facing each other. A negative electrode current collector 22 having negative electrode material paste applied to both sides thereof is passed through this gap 53 in the direction of the arrow. At this time, the negative electrode current collector 22 having negative electrode material paste applied to both sides thereof is passed through the gap 53 while the negative electrode material paste 23a applied to one side 21a of the negative electrode current collector 21 is in contact with the first wall surface 51 and the negative electrode material paste 23b applied to the other side 21b of the negative electrode current collector 21 is in contact with the second wall surface 52.

[0038] Immediately after being pulled out of the tank 40 (before passing through the layer forming unit 50), the negative electrode current collector 22 with the negative electrode material paste attached to both sides may have unevenness on the surface of the negative electrode material paste or unevenness in the amount of the attached negative electrode material paste, as shown in Fig. 3. By passing this negative electrode current collector 22 through the layer forming unit 50 while contacting the first wall surface 51 and the second wall surface 52 of the layer forming unit 50, the unevenness on the surfaces of the negative electrode material pastes 23a and 23b can be made uniform.

[0039] Furthermore, in the manufacturing method of this embodiment, the ratio (D2 / D1) of the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 to the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 is 0.7 to 1. This makes it possible to obtain a negative electrode in which the difference in thickness between the first negative electrode material layer finally formed on one surface 21a of the negative electrode current collector 21 and the second negative electrode material layer finally formed on the other surface 21b of the negative electrode current collector 21 is small. The distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 is longer than the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21, or is the same as the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21.

[0040] From the viewpoint of easily obtaining a zinc battery negative electrode having excellent life performance, the distance ratio (D2 / D1) is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 0.95 or more. The distance ratio (D2 / D1) is particularly preferably 1, but may be less than 1.

[0041] The ratio of the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 to the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 can be adjusted by adjusting the position in the gap 53 through which the negative electrode current collector 21 passes.

[0042] From the viewpoint of easily obtaining a zinc battery negative electrode having excellent life performance, the difference between the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the first wall surface 51 and the other surface 21b of the negative electrode current collector 21 is preferably 0.03 mm or less, more preferably 0.02 mm or less, and even more preferably 0.01 mm or less. It is particularly preferable that the difference between the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the first wall surface 51 and the other surface 21b of the negative electrode current collector 21 is 0, but it may be greater than 0.

[0043] From the viewpoint of ensuring a charge reserve (excess chargeable capacity on the negative electrode side), the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 are each preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.35 mm or more. From the viewpoint of ensuring an energy density, the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 are each preferably 0.5 mm or less, more preferably 0.45 mm or less, and even more preferably 0.4 mm or less.

[0044] The distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 can be adjusted, for example, by a gap adjuster 54 provided in the layer forming unit 50. The gap adjuster 54 can change the positions of the first wall surface 51 and the second wall surface 52 and adjust the size of the gap 53. As a result, the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 are also adjusted. The method for adjusting the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 is not limited to this.

[0045] 2, the negative electrode current collector 22 having the negative electrode material paste attached to both sides thereof after passing through the layer forming unit 50 is passed through a drying furnace 60. Examples of the drying furnace 60 include a reduced pressure drying furnace and a drying furnace equipped with an infrared heater.

[0046] The temperature inside the drying oven 60 may be, for example, 90° C. or more, 100° C. or more, or 110° C. or more, and may be 150° C. or less, 140° C. or less, or 130° C. or less. The time for passing through the drying oven 60 (drying time) may be, for example, 1 minute or more, 3 minutes or more, or 5 minutes or more, and may be 60 minutes or less, 30 minutes or less, or 20 minutes or less.

[0047] By passing through the drying furnace 60, the dispersion medium contained in the negative electrode material paste volatilizes, and a first negative electrode material layer is formed on one side of the negative electrode current collector 21, and a second negative electrode material layer is formed on the other side, thereby obtaining an unformed negative electrode 24. As shown in Fig. 2, the continuously produced negative electrodes 24 are cut to a predetermined size and can be used in the production of zinc batteries.

[0048] The method for manufacturing a zinc battery negative electrode according to the embodiment described above can be modified in various ways.

[0049] For example, in the method for manufacturing a negative electrode for a zinc battery, the method for applying the negative electrode material paste to the negative electrode current collector may be application using an applicator or the like. Alternatively, a negative electrode current collector to which the negative electrode material paste has already been applied may be prepared.

[0050] The layer forming section may include two separate members, and the negative electrode current collector with the negative electrode material paste attached thereto may be passed between the two separate members while the negative electrode material paste is brought into contact with the wall surfaces of each of the two separate members.

[0051] After the negative electrode current collector with the negative electrode material paste attached to both sides is passed through the layer forming section, pressing or the like may be performed as necessary, thereby obtaining a negative electrode with an increased density of the negative electrode material layer.

[0052] In the method for drying the negative electrode material paste, a drying furnace may not be used, and the negative electrode current collector on which the layer of negative electrode material paste has been formed may be left standing in a room temperature environment, for example.

[0053] In the above-described embodiment, an apparatus capable of manufacturing a negative electrode for a zinc battery through a series of steps as shown in FIG. 2 was used, but the step of attaching a negative electrode material paste to a negative electrode current collector, the step of passing the negative electrode material paste through a layer forming section, and the step of drying the negative electrode material paste may be performed in separate apparatuses.

[0054] <Anode for zinc batteries> A zinc battery negative electrode according to one embodiment comprises a first negative electrode material layer provided on one side of a negative electrode current collector and a second negative electrode material layer provided on the other side of the negative electrode current collector, and the ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer is 0.7 to 1. The zinc battery negative electrode may be either formed or unformed. An unformed zinc battery negative electrode can be obtained, for example, by the method for producing a zinc battery negative electrode described above.

[0055] The embodiment of the negative electrode current collector may be the same as the embodiment of the negative electrode current collector in the above-described method for producing a negative electrode for a zinc battery.

[0056] The negative electrode layer contains a negative electrode active material containing zinc. The form of the negative electrode active material may be the same as the negative electrode active material contained in the negative electrode material paste described above. In addition to the negative electrode active material, the negative electrode layer may also contain the above-mentioned additives.

[0057] In this specification, the "thickness of the negative electrode material layer" refers to the distance between one surface of the negative electrode current collector and the surface of the negative electrode material layer provided on that surface opposite the negative electrode current collector, and refers to the average value measured at nine locations on the negative electrode material layer. The nine measurement locations may be the upper left corner, upper center, upper right corner, left center, center, right center, lower left corner, lower center, and lower right center when viewed from the stacking direction of the negative electrode. FIG. 4 is a plan view showing an example of measurement locations for the thickness of the negative electrode material layer. As shown in FIG. 4, the thickness of the negative electrode material layer 25 provided on the negative electrode current collector 21 is measured at nine locations: the upper left corner a, upper center b, upper right corner c, left center d, center e, right center f, lower left corner g, lower center h, and lower right center i, and the average of these measurements can be used. The thickness at each location on the negative electrode can be measured using, for example, a micrometer.

[0058] The ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer (thickness of the second negative electrode material layer / thickness of the first negative electrode material layer) is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 0.95 or more, from the viewpoint of easily obtaining a zinc battery negative electrode with excellent life performance. The thickness ratio (thickness of the second negative electrode material layer / thickness of the first negative electrode material layer) is particularly preferably 1, but may be less than 1. The thickness of the first negative electrode material layer is thicker (larger) than the thickness of the second negative electrode material layer, or the same thickness as the second negative electrode material layer.

[0059] From the viewpoint of easily obtaining a zinc battery negative electrode having excellent life performance, the difference in thickness between the first negative electrode material layer and the second negative electrode material layer is preferably 0.03 mm or less, more preferably 0.02 mm or less, and even more preferably 0.01 mm or less. It is particularly preferable that the difference in thickness between the first negative electrode material layer and the second negative electrode material layer is 0, but it may be greater than 0.

[0060] The thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer are each preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.35 mm or more, from the viewpoint of ensuring charge reserve. The thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer are each preferably 0.6 mm or less, more preferably 0.5 mm or less, and even more preferably 0.4 mm or less, from the viewpoint of ensuring energy density. The thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer may correspond to the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 and the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21, respectively, in the above-mentioned manufacturing method.

[0061] <Zinc battery> Hereinafter, a nickel-zinc battery will be described as an example of the zinc battery according to this embodiment. The nickel-zinc battery according to one embodiment includes, for example, a battery case, an electrolyte, and an electrode group (e.g., an electrode plate group). The electrode group and the electrolyte are housed in the battery case.

[0062] The electrode group is composed of, for example, a separator, and a positive electrode (such as a positive electrode plate) and a negative electrode (such as a negative electrode plate) facing each other with the separator interposed therebetween. In the electrode group, the positive electrodes and the negative electrodes are connected to each other, for example, by a strap. The negative electrode may be the zinc battery negative electrode according to the above-described embodiment.

[0063] The positive electrode may include, for example, a positive electrode current collector, a first positive electrode material layer provided on one side of the positive electrode current collector, and a second positive electrode material layer provided on the other side of the positive electrode current collector. The positive electrode may be either before or after chemical formation.

[0064] The positive electrode current collector has, for example, a plate shape, a sheet shape, or the like. The positive electrode current collector may be a three-dimensional mesh-structured current collector composed of foamed metal, expanded metal, punched metal, or metal fiber felt. The positive electrode current collector is composed of a material having electrical conductivity and alkali resistance. Examples of such materials include materials that are stable even at the reaction potential of the positive electrode (e.g., materials with a redox potential higher than the reaction potential of the positive electrode, materials that form a protective coating such as an oxide coating on the substrate surface in an alkaline aqueous solution to stabilize the positive electrode). In addition, at the positive electrode, a decomposition reaction of the electrolyte proceeds as a side reaction, generating oxygen gas. Materials with a high oxygen overvoltage are preferred because they can suppress the progression of such side reactions. Specific examples of materials for the positive electrode current collector include platinum; nickel (e.g., foamed nickel); and metal materials (e.g., copper, brass, steel) plated with a metal such as nickel. Among these, a positive electrode current collector composed of foamed nickel is preferably used. From the viewpoint of further improving the high rate discharge performance, it is preferable that at least the portion of the positive electrode current collector that supports the positive electrode material (positive electrode material support portion) is made of foamed nickel.

[0065] The positive electrode layer contains a positive electrode active material containing nickel. Examples of the positive electrode active material include nickel oxyhydroxide (NiOOH) and nickel hydroxide. The positive electrode layer contains, for example, nickel oxyhydroxide in a fully charged state and nickel hydroxide in an end-of-discharge state. The content of the positive electrode active material may be, for example, 50 to 95 mass% based on the total mass of the positive electrode layer.

[0066] The positive electrode layer may further contain other components as additives in addition to the positive electrode active material, such as a binder, a conductive agent, and an expansion inhibitor.

[0067] Examples of the binder include hydrophilic or hydrophobic polymers. Specifically, for example, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), sodium polyacrylate (SPA), and fluorine-based polymers (polytetrafluoroethylene (PTFE) and the like) can be used as the binder. The content of the binder is, for example, 0.01 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

[0068] Examples of the conductive agent include cobalt compounds (metallic cobalt, cobalt oxide, cobalt hydroxide, etc.) The content of the conductive agent is, for example, 1 to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0069] Examples of the expansion inhibitor include zinc oxide, etc. The content of the expansion inhibitor is, for example, 0.01 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0070] The separator may be, for example, a separator having a shape such as a flat plate or a sheet. Examples of the separator include a polyolefin-based microporous membrane, a nylon-based microporous membrane, an oxidation-resistant ion-exchange resin membrane, a cellophane-based recycled resin membrane, an inorganic-organic separator, and a polyolefin-based nonwoven fabric. The separator may be processed into a bag shape so as to accommodate the positive electrode and / or the negative electrode. In this case, the positive electrode and / or the negative electrode may be accommodated in the separator. One type of separator may be used alone, or two or more types may be used in combination.

[0071] The manufacturing method of the nickel-zinc battery described above includes a component manufacturing process for obtaining components of the zinc battery, and an assembly process for assembling the components to obtain the zinc battery. In the component manufacturing process, at least electrodes (positive and negative electrodes) are obtained. The manufacturing method of the negative electrode is the manufacturing method of the negative electrode for the zinc battery described above.

[0072] The positive electrode is made of a positive electrode material paste obtained by adding a dispersion medium (e.g., water) to the raw material of the positive electrode layer and kneading the mixture. Methods for obtaining the positive electrode include, for example, the same method as the above-mentioned method for producing a negative electrode for a zinc battery, and a method in which the positive electrode material paste is applied to or immersed in a positive electrode current collector and then dried.

[0073] In the assembly process, for example, the positive and negative electrodes obtained in the component manufacturing process are stacked alternately with separators interposed therebetween, and then the positive electrodes and negative electrodes are connected with straps to form an electrode group. Next, this electrode group is placed in a battery case, and a lid is attached to the top of the battery case to obtain an unformed zinc battery (nickel-zinc battery).

[0074] Next, the electrolyte is poured into the battery case of the unformed zinc battery and left for a certain period of time. Then, the battery is formed by charging under predetermined conditions to obtain a zinc battery (nickel-zinc battery). The formation conditions can be adjusted depending on the properties of the positive and negative electrode active materials.

[0075] The above describes an example of a nickel-zinc battery (e.g., a nickel-zinc secondary battery) in which the positive electrode is a nickel electrode, but the zinc battery may also be an air-zinc battery (e.g., an air-zinc secondary battery) in which the positive electrode is an air electrode, or a silver-zinc battery (e.g., a silver-zinc secondary battery) in which the positive electrode is a silver oxide electrode. [Example]

[0076] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

[0077] Example 1 <Preparation of negative electrodes for zinc batteries> A negative electrode paste was prepared by weighing and mixing predetermined amounts of zinc oxide, metallic zinc, bismuth oxide, hydroxyethyl cellulose, and ion-exchanged water, and stirring the resulting mixture. The mass ratio of nonvolatile components in the negative electrode paste was adjusted to "zinc oxide: metallic zinc: bismuth oxide: hydroxyethyl cellulose = 72:20.5:5:2.5." AV-15F (trade name) manufactured by Sumitomo Seika Chemicals Co., Ltd. was used as the hydroxyethyl cellulose. The moisture content of the negative electrode paste was adjusted to 20.5 mass% based on the total mass of the negative electrode paste.

[0078] A zinc-cooled battery negative electrode was manufactured using the apparatus shown in FIG. 2. A rolled negative electrode current collector (copper punched metal) was set in the unwinding section 30. The negative electrode current collector was passed through a tank 40 containing a negative electrode material paste, and the negative electrode material paste was attached to both sides of the negative electrode current collector. Next, the negative electrode current collector with the attached negative electrode material paste was passed through a layer forming section 50. The width of the gap 53 in the layer forming section 50 and the position through which the negative electrode current collector passed were adjusted so that the distance D1 between the first wall surface 51 and one side of the negative electrode current collector in the layer forming section 50 and the distance D2 between the second wall surface 52 and the other side of the negative electrode current collector were 0.4 mm. Next, the negative electrode current collector that had passed through the layer forming section 50 was passed through a drying furnace with an internal temperature of 110°C for 10 minutes to volatilize the water contained in the negative electrode material paste. The dried negative electrode was cut into a rectangular shape of 50 mm×60 mm to obtain an unformed negative electrode for a zinc battery according to Example 1.

[0079] The thicknesses of the first and second negative electrode material layers of the negative electrode according to Example 1 were measured. The thicknesses were measured using a micrometer (PMU150-25MX, manufactured by Mitutoyo Corporation) at nine locations in FIG. 4 , namely, when viewed from the stacking direction of the negative electrode, the upper left corner a, the upper central portion b, the upper right corner c, the left central portion d, the central portion e, the right central portion f, the lower left corner g, the lower central portion h, and the lower right central portion i. Table 1 shows the thickness at each location, the difference between the thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer, and the ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer (thickness of the second negative electrode material layer / thickness of the first negative electrode material layer).

[0080] <Building a zinc battery> A grid made of foamed nickel with a porosity of 95% was prepared and pressure-molded to obtain a positive electrode current collector. Next, predetermined amounts of cobalt-coated nickel hydroxide powder, metallic cobalt, cobalt hydroxide, yttrium oxide, carboxymethyl cellulose, polytetrafluoroethylene, and ion-exchanged water were weighed and mixed, and the mixture was stirred to prepare a positive electrode material paste. The mass ratio of the solids was adjusted to "nickel hydroxide: metallic cobalt: yttrium oxide: cobalt hydroxide: carboxymethyl cellulose: polytetrafluoroethylene = 88:10.3:1:0.3:0.3:0.1." The moisture content of the positive electrode material paste was adjusted to 27.5 mass% based on the total mass of the positive electrode material paste. Next, the positive electrode material paste was applied to both sides of the positive electrode current collector and dried at 80°C for 30 minutes. The resulting mixture was then pressure-molded using a roll press to obtain an unformed positive electrode having a positive electrode material layer.

[0081] The separator used was a microporous membrane (UP3355, product name, manufactured by Ube Industries, Ltd., air permeability: 440 s / 100 mL) and a nonwoven fabric (product name: VL-100, product name, air permeability: 0.3 s / 100 mL, manufactured by Nippon Kodoshi Kogyo Co., Ltd.). The microporous membrane was hydrophilized using the surfactant Triton-X100 (manufactured by Sigma-Aldrich Japan, LLC) before battery assembly. The hydrophilization was performed by immersing the microporous membrane in an aqueous solution containing 1% Triton-X100 by mass for 24 hours and then drying at room temperature for 1 hour. The air permeability of the microporous membrane is the value after hydrophilization. The microporous membrane was then cut to a specified size, folded in half, and processed into a bag shape by heat welding the sides. The nonwoven fabric was also cut to a specified size.

[0082] A single positive electrode and a single negative electrode were housed in a microporous membrane processed into a bag shape. The positive electrode housed in the microporous membrane bag, the negative electrode housed in the microporous membrane bag, and nonwoven fabric were then stacked, and the plates of the same polarity were connected with straps to form an electrode assembly (electrode plate assembly). The electrode assembly consisted of 11 positive electrodes and 12 negative electrodes, with one nonwoven fabric placed between each positive and negative electrode (between the microporous membrane on the positive electrode side and the microporous membrane on the negative electrode side). This electrode assembly was then placed in a battery case, a lid was attached to the top of the battery case, and the above-mentioned electrolyte was poured into the battery case to obtain an unformed nickel-zinc battery. The battery was then charged at 800 mA for 15 hours to produce a nickel-zinc battery with a nominal capacity of 8000 mAh.

[0083] (Comparative Example 1) <Preparing the negative electrode for zinc batteries> An unformed zinc-carbon battery negative electrode manufactured by a conventional method was prepared. This negative electrode was manufactured by the same process as in Example 1, in which negative electrode material paste was applied to both sides of the negative electrode current collector, and then the negative electrode current collector 22 with the negative electrode material paste applied to both sides was passed through a gap 53 while the applied negative electrode material pastes 23a and 23b were brought into contact with a first wall surface 51 or a second wall surface 52. However, the ratio of the distance D2 between the second wall surface 52 and the other surface 21b of the negative electrode current collector 21 to the distance D1 between the first wall surface 51 and one surface 21a of the negative electrode current collector 21 was not adjusted, and the negative electrode current collector was positioned so that it was near the center of the gap 53 as determined by visual inspection.

[0084] The thicknesses of the first and second negative electrode material layers were measured in the same manner as in Example 1. Table 1 shows the thickness at each location, the difference between the thickness of the first negative electrode material layer and the thickness of the second negative electrode material layer, and the ratio of the thickness of the second negative electrode material layer to the thickness of the first negative electrode material layer (thickness of the second negative electrode material layer / thickness of the first negative electrode material layer).

[0085] <Building a zinc battery> A nickel-zinc battery was fabricated in the same manner as in Example 1, except that the negative electrode in Example 1 was changed to the negative electrode according to Comparative Example 1 described above.

[0086] <Evaluation of life performance> A test was conducted in which the nickel-zinc battery was charged at 25°C, 8000 mA (1 C), and a constant voltage of 1.9 V until the current value decayed to 400 mA (0.05 C), and then discharged at a constant current of 8000 mA (1 C) until the battery voltage reached 1.1 V, with one cycle being defined as this. The test was terminated when the discharge capacity fell below 60% of the discharge capacity of the first cycle, and cycle life performance was evaluated based on the number of cycles performed until the test was completed. The number of cycles performed until the test was completed is shown in Table 1. As shown in Table 1, the nickel-zinc battery according to Example 1 had an increased number of cycles and was superior in life performance compared to the nickel-zinc battery according to Comparative Example 1.

[0087] [Table 1] [Explanation of symbols]

[0088] 21...negative electrode current collector, 21a...one side of negative electrode current collector, 21b...other side of negative electrode current collector, 50...layer forming portion, 51...first wall surface, 52...second wall surface, 23a, 23b...negative electrode material paste, 24...negative electrode (negative electrode for zinc battery).

Claims

1. A method for manufacturing a double-sided coated negative electrode for a zinc secondary battery, the negative electrode comprising: a negative electrode current collector; a first negative electrode material layer provided on one surface of the negative electrode current collector; and a second negative electrode material layer provided on the other surface of the negative electrode current collector, a negative electrode material layer forming step of passing the negative electrode current collector between the first wall surface and the second wall surface while bringing the negative electrode material paste on both surfaces into contact with a first wall surface and a second wall surface facing each other, with the negative electrode material paste attached to both surfaces of the negative electrode current collector, and then passing the negative electrode current collector through a drying furnace to form the first negative electrode material layer and the second negative electrode material layer; in the negative electrode material layer forming step, a ratio of a distance between the second wall surface and the other surface of the negative electrode current collector to a distance between the first wall surface and the one surface of the negative electrode current collector is 0.7 to 1; a difference between a distance between the first wall surface and the one surface of the negative electrode current collector and a distance between the second wall surface and the other surface of the negative electrode current collector is 0.03 mm or less; The method for producing a negative electrode for a zinc secondary battery, wherein the temperature in the drying oven is 90 to 150°C.

2. The method for producing a negative electrode for a zinc secondary battery according to claim 1 , wherein the ratio is less than 1.

3. 3. The method for producing a negative electrode for a zinc secondary battery according to claim 1, wherein the time for passing the negative electrode current collector through the drying oven is 1 to 60 minutes.

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