Secondary battery and method for manufacturing a secondary battery

Abstract

To easily and reliably transport electrode plates in a manufacturing process of a nickel-hydrogen storage cell.SOLUTION: A nickel-hydrogen storage cell 1 comprises a cathode plate 2. The cathode plate comprises a cathode current collector 21, which is made of a rectangular plate-shaped porous metal, and a cathode mixture layer 22, which contains a cathode active material and is filled into the cathode current collector. There is a filling density difference such that the density of the cathode mixture layer 22 filled into the cathode current collector 21 gradually decreases from a dense surface 22c to a sparse surface 22a. When the cathode plate 2 is divided into three equal parts of a first layer L1, a second layer L2 and a third layer L3 in the direction of thickness from the sparse surface 22a, the first layer and the third layer each have a filling density difference of the active material from 2% to 10% inclusive relative to the second layer L2.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] This invention relates to a secondary battery and a method for manufacturing the same, and more specifically, to a secondary battery and a method for manufacturing the same that can facilitate the adsorption of electrode plates during manufacturing. [Background technology]

[0002] Electric vehicles (including hybrid vehicles, etc.) equipped with electric motors drive the motors using electricity stored in secondary batteries. Among such secondary batteries, alkaline secondary batteries, such as nickel-metal hydride batteries, are widely used in vehicles because they are safe and capable of high-current charging and discharging.

[0003] In the manufacturing process of such secondary batteries, when coating the composite layer containing the active material onto the current collector, a certain height may occur at the edges of the composite layer. Using such electrodes may affect the productivity and performance of the secondary battery.

[0004] Therefore, the invention disclosed in Patent Document 1 proposes a secondary battery having a wave-shaped portion at the widthwise end of the composite material layer of the current collector in at least one of the positive electrode and the negative electrode. In this invention, the generation of protrusions in the composite material layer is suppressed during the process of coating the composite material layer onto the current collector. As a result, the active material is uniformly filled into the current collector, and an electrode plate is manufactured in which the filling density in the thickness direction and the unevenness of the coating edges in the long side direction are uniform on both the front and back sides. Here, "filling density" refers to the weight ratio of the active material (e.g., positive electrode active material) to the paste to be coated (e.g., positive electrode composite material paste). As a result, it was possible to obtain a secondary battery, a method for manufacturing a secondary battery, and an electrode with stable performance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-063881 [Overview of the project] [Problems that the invention aims to solve]

[0006] In electrode plates manufactured using a conventional double-sided coating method as described in Patent Document 1, the composite material layer is uniformly formed on the current collector, and the packing density in the thickness direction and the unevenness of the coating edges in the long side direction can be made uniform on both the front and back sides.

[0007] However, there is a problem when transporting electrode plates, which are stacked in multiple layers in the thickness direction during the manufacturing process, by vacuum suction. With conventional electrode plates, the composite layer is permeable, so if the suction force is weak, the vacuum level may not be sufficiently high, and the electrode plates may fall off during transport. On the other hand, if the suction force is too strong, not only the target electrode plate but also the electrode plate underneath it may be transported.

[0008] The problem that the present invention's secondary battery and its manufacturing method aim to solve is to facilitate and ensure the transport of electrode plates. [Means for solving the problem]

[0009] To solve the above problems, the secondary battery of the present invention comprises a positive electrode plate having a positive electrode current collector made of a plate-shaped porous metal and a positive electrode composite layer containing positive electrode active material and filled in the positive electrode current collector, a negative electrode plate, and a separator, characterized in that the packing density of the positive electrode active material on the dense side surface, which is one end in the thickness direction of the positive electrode composite layer, is greater than the packing density of the positive electrode active material on the rough side surface, which is the other end, relative to the positive electrode current collector.

[0010] It is desirable that the packing density difference is configured such that the packing density of the positive electrode active material gradually decreases from the dense surface to the rough surface. Furthermore, it is desirable that the packing density difference be between 4% and 20%. In addition, when the positive electrode plate is divided into three equal layers in the thickness direction, it is desirable that there be a packing density difference of 2% or more and 10% or less between the dense surface layer and the rough surface layer relative to the central layer.

[0011] It is desirable that the width ΔW of the irregularities at the edge of the positive electrode composite layer in the short-side direction on the dense surface is greater than ΔW on the rough surface. It is also desirable that the relationship between the width ΔW of the irregularities at the edge of the positive electrode composite layer in the short-side direction on the dense surface and the standard coating width Ws in the short-side direction be ΔW / Ws ≥ 0.016.

[0012] This can be suitably implemented in a secondary battery in which the positive electrode current collector is composed of a foam made of nickel or a nickel alloy. Furthermore, the present invention relates to a method for manufacturing a secondary battery comprising a positive electrode plate having a positive electrode current collector made of a plate-shaped porous metal and a positive electrode composite layer containing positive electrode active material filled in the positive electrode current collector, a negative electrode plate, and a separator, wherein the positive electrode composite layer of the positive electrode plate has a difference in packing density with respect to the thickness direction of the positive electrode current collector, and the method for manufacturing a nickel-metal hydride storage battery comprises a coating step of coating one surface of the positive electrode current collector with a positive electrode composite paste containing a solvent for forming the positive electrode composite layer, wherein the coating step is characterized in that the positive electrode composite paste does not fall off the positive electrode current collector due to gravity, and the packing density of the positive electrode active material in the positive electrode composite paste is adjusted so that the lower part is higher than the upper part due to gravity.

[0013] It is desirable that the relationship between the unevenness width ΔW at the edge of the positive electrode composite layer in the short-side direction on the surface opposite to the coated side and the standard coating width Ws in the short-side direction be adjusted so that ΔW / Ws ≥ 0.016. The adjustment can be made by controlling the viscosity of the positive electrode composite paste.

[0014] In the coating process, the viscosity of the positive electrode composite paste is such that the shear rate is 10 [s] -1 When this occurs, it is desirable to set the pressure between 200 mPa·s and 1000 mPa·s. The process may include a transport step in which the uppermost positive electrode plate, on which multiple positive electrode plates are stacked and placed, is adsorbed from above by a vacuum adsorption device and transported. In this transport step, the positive electrode plate is placed such that its upper surface becomes a rough side surface where the packing density of the positive electrode active material in the positive electrode composite layer is low, and the rough side surface can be adsorbed from above by the vacuum adsorption device and transported. [Effect of the Invention]

[0015] According to the secondary battery and its manufacturing method of the present invention, there is an effect that the electrode plate can be transported easily and surely. [Brief Description of the Drawings]

[0016] [Figure 1] It is a perspective view showing the external appearance structure of the nickel-hydrogen storage battery of the present embodiment. [Figure 2] It is a perspective view including a partial cross-sectional structure of a part of the battery module of the nickel-hydrogen storage battery of the present embodiment. [Figure 3] It is a cross-sectional view of the electrode group provided in the nickel-hydrogen storage battery of the present embodiment. [Figure 4] It is a flowchart showing the manufacturing process of the nickel-hydrogen storage battery of the present embodiment. [Figure 5] It is a flowchart showing the manufacturing process of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment. [Figure 6] It is a schematic diagram showing a cross-section in the width direction W of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment. [Figure 7] It is a schematic diagram showing the rough-side surface of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment. [Figure 8] It is a schematic diagram showing the dense-side surface of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment. [Figure 9] It is a schematic diagram showing the state during the conveyance of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment. [Figure 10] It is a schematic diagram showing the filling density of the positive electrode active material in the positive electrode mixture layer of the positive electrode plate of the nickel-hydrogen storage battery of the present embodiment and the state during liquid injection. [Figure 11] It is a comparison table of an example of the composition of a conventional positive electrode mixture paste and an example of the composition of the positive electrode mixture paste of the present embodiment. [Figure 12] It is a perspective view showing an example of the coating device in the present embodiment. [Figure 13](a) A perspective view showing the coating process in this embodiment. (b) An enlarged cross-sectional view of the position where the die nozzle applies the positive electrode composite paste to the positive electrode current collector. [Figure 14] (a) is a plan view showing the positional relationship between the nickel substrate, the first support part, and the second support part. (b) is a cross-sectional view showing the nickel substrate supported by the first support part and the second support part before the paste is applied. (c) is an enlarged cross-sectional view of (b). [Figure 15] This is a schematic diagram showing the surface (coated side) of the positive electrode plate of a conventional nickel-metal hydride battery. [Figure 16] This is a schematic diagram showing the back surface of the positive electrode plate of a conventional nickel-metal hydride battery. [Figure 17] This is a schematic diagram showing the state of the positive electrode plate of a conventional nickel-metal hydride battery during transport. [Figure 18] This is a schematic diagram showing the packing density of the positive electrode active material in the positive electrode composite layer of the positive electrode plate of a conventional nickel-metal hydride battery and its state when injected. [Modes for carrying out the invention]

[0017] The secondary battery and its manufacturing method of the present invention will be described below with reference to Figures 1 to 14, using one embodiment of the nickel-metal hydride storage battery and its manufacturing method. (Configuration of this embodiment) <Outline of this embodiment> The nickel-metal hydride battery 1 of this embodiment comprises a positive electrode plate 2 having a positive electrode current collector 21 and a positive electrode composite layer 22 (see Figure 6), a negative electrode plate 3, and a separator 4, as shown in Figure 3. The positive electrode current collector 21 is made of a porous metal such as foamed nickel or foamed nickel alloy in the shape of a rectangular plate. In the coating process during manufacturing (Figure 5: S13), a positive electrode composite paste 25 containing positive electrode active material is filled into this porous positive electrode current collector 21 to form the positive electrode composite layer 22.

[0018] In this coating process (S13), the viscosity V [mPa·s] of the positive electrode mixture paste 25 is adjusted, and the positive electrode mixture paste 25 is discharged from above by the die nozzle 81, penetrating into the pores between the bones of the porous positive electrode current collector 21 due to gravity. On the other hand, the positive electrode mixture paste 25 penetrating from the upper surface 21j of the positive electrode current collector 21 will not flow down from the lower surface 21k of the positive electrode current collector 21 as long as it has a constant viscosity V [mPa·s], etc. Surface tension acts on the positive electrode mixture paste 25, and as it penetrates below the coating width Wp from above, the lower end becomes narrower than the standard coating width Ws. Furthermore, at the end 22d in the width direction W, surface tension and wettability with the three-dimensional mesh-like bones influence the formation of irregularities at the end 22d in the width direction W.

[0019] Furthermore, if the viscosity is a predetermined V [mPa·s], the packing density Df [%] of the positive electrode active material gradually increases as the particles of the positive electrode active material dispersed in the positive electrode composite paste 25 settle due to gravity and move downwards towards the positive electrode current collector 21.

[0020] <Main functions of this embodiment> As described above, the resulting positive electrode composite layer 22 varies depending on the configuration of the positive electrode current collector 21, the composition of the positive electrode composite paste 25, the particle size of the positive electrode active material, etc. Also, temperature [°C], viscosity [mPa·s], shear rate [s] -1 The wettability with the positive electrode current collector 21, the discharge amount from the coating machine 8, and the discharge speed also affect the result. In other words, in order to form the target positive electrode composite layer 22, it is necessary to meet these conditions.

[0021] Therefore, in this embodiment, the viscosity [mPa·s], which has a significant influence on the formation of the positive electrode composite layer 22, is adjusted using the gradient of the packing density Df [%] of the positive electrode active material within the positive electrode composite layer 22 as an indicator. At the same time, while adjusting the viscosity [mPa·s], which has a significant influence on the formation of the positive electrode composite layer 22, the relationship ΔW / Ws between the width of the irregularities at the edge of the positive electrode composite layer 22 in the width direction W on the dense side surface 22c and the standard coating width Ws in the short side direction is adjusted using this as an indicator.

[0022] Thus, although complex factors are intertwined, the inventors have found that by adjusting the viscosity V [mPa·s] of the positive electrode mixture paste 25, it is possible to manufacture a positive electrode plate 2 having a gradient of the packing density Df [%] of the positive electrode active material within the desired positive electrode mixture layer 22. Similarly, they have also found that by adjusting the viscosity V [mPa·s] of the positive electrode mixture paste 25, it is possible to manufacture a positive electrode plate having a desired relationship ΔW / Ws.

[0023] In other words, the key point of this embodiment is that the positive electrode plate 2 is manufactured by adjusting the viscosity V [mPa·s] of the positive electrode composite paste 25, etc., using the packing density Df [%], the unevenness width ΔW, and the desired relationship ΔW / Ws as indicators. This improves the transportability of the positive electrode plate 2 and reduces its internal resistance (DC-IR).

[0024] In this embodiment, the viscosity V [mPa·s] of the positive electrode composite paste 25 is adjusted to form a positive electrode composite layer 22 having a packing density Df [%], unevenness width ΔW, and a desired relationship ΔW / Ws. However, any method that can achieve the desired packing density Df [%], unevenness width ΔW, and desired relationship ΔW / Ws is acceptable. For example, the configuration of the positive electrode current collector 21 can be used. Specifically, the desired packing density Df [%], unevenness width ΔW, and desired relationship ΔW / Ws can be achieved by changing the size, shape, material, etc., of the mesh structure of the positive electrode current collector 21. In addition, other methods include the composition of the positive electrode composite paste 25, the particle size of the positive electrode active material, the temperature [°C], and the shear rate [s]. -1 The desired packing density Df[%], surface width ΔW, and desired relationship ΔW / Ws may be achieved by changing the discharge amount and discharge speed from the coating machine 8. Of course, the desired packing density Df[%], surface width ΔW, and desired relationship ΔW / Ws may also be achieved by combining these.

[0025] <Main effects of this embodiment> The nickel-metal hydride battery 1 of this embodiment has the following main effects due to its configuration. When transporting electrode plates by vacuum adsorption during the manufacturing process of the nickel-metal hydride battery 1, the degree of vacuum for adsorption is easily increased by the dense surface 22c, and the negative pressure is blocked by the dense surface 22c, so other positive electrode plates 2 stacked below are not attracted. As a result, the transportability of the positive electrode plates 2 in the manufacturing method of the nickel-metal hydride battery 1 can be improved, thereby increasing production efficiency.

[0026] In the manufacturing process of the nickel-metal hydride battery 1, when the electrolyte 5 is injected, the electrolyte 5 can penetrate efficiently on the rough surface 22a. On the other hand, increasing the packing density Df of the positive electrode active material on the dense surface 22c reduces air permeability, which leads to poor penetration of the electrolyte 5. However, in this embodiment, on the long side, the unevenness width ΔW in the short side direction (width direction W) of the end 22d is large, which increases the total length of the end 22d, making it easier for the electrolyte 5 to penetrate from there. In addition, by narrowing the standard coating width Ws, the electrolyte 5 can also penetrate more easily from the end of the positive electrode current collector 21. As a result, the absorption of the electrolyte 5 is improved for the positive electrode plate 2 as a whole, and the internal resistance (DC-IR) can be reduced.

[0027] The nickel-metal hydride battery 1 of this embodiment and its manufacturing method will be described in detail below. <Configuration of Nickel-Metal Hydride Battery 1> Figure 1 is a perspective view showing the external structure of the nickel-metal hydride battery 1 of this embodiment.

[0028] <Battery Module> As shown in Figure 1, the nickel-metal hydride battery 1 is configured as a battery module equipped with multiple battery cells 12. The nickel-metal hydride battery 1 is a sealed battery with a rectangular plate-like exterior. It comprises a battery case 13 that forms an integrated battery case capable of housing multiple (in this case, six) battery cells 12, and a lid 14 that seals the opening of the battery case 13. The battery case 13 houses six battery cells 12 that are electrically connected in series. The power of these battery cells 12 is taken from the positive electrode connection terminal 13a and the negative electrode connection terminal 13b provided on the battery case 13.

[0029] <Internal structure of nickel-metal hydride battery> Figure 2 is a partial perspective view of the battery module of the nickel-metal hydride battery 1, including its cross-sectional structure. As shown in Figure 2, the battery case 13 and lid 14 are made of polypropylene (PP) and polyphenylene ether (PPE), which are resin materials resistant to alkaline electrolytes. Inside the battery case 13, partition walls 18 are formed to separate multiple battery cells 12, and the portion separated by these partition walls 18 becomes a battery case 15 for each battery cell 12. Inside the battery case 15, an electrode group 6 is housed along with an alkaline electrolyte 5, which is an aqueous electrolyte mainly composed of potassium hydroxide (KOH).

[0030] A through-hole 17 is formed in the upper part of the partition wall 18, which is used to connect each battery cell 12. Two connecting protrusions, one protruding from the upper part of the positive electrode current collector plate 27 and the other protruding from the upper part of the negative electrode current collector plate 37, are welded together through the through-hole 17 by spot welding or the like. This electrically connects the electrode groups 6 of adjacent battery cells 12 in series. Of the through-holes 17, the through-holes 17 located on the outside of each of the battery cells 12 at both ends are fitted with a positive electrode connection terminal 13a or a negative electrode connection terminal 13b (see Figure 1) above the longitudinal end of the battery case 13. The positive electrode connection terminal 13a is welded to the connecting protrusion of the positive electrode current collector plate 27. The negative electrode connection terminal 13b is welded to the connecting protrusion of the negative electrode current collector plate 37. The total output of the series-connected electrode group 6, i.e., the multiple battery cells 12, is taken out from the positive electrode connection terminal 13a and the negative electrode connection terminal 13b.

[0031] <Electrode group 6> Figure 3 is a cross-sectional view of the electrode group 6 provided in the nickel-metal hydride battery 1 of this embodiment. As shown in Figure 3, the electrode group 6 is constructed by stacking rectangular positive electrode plates 2 and negative electrode plates 3 with a separator 4 in between. In this case, the direction in which the positive electrode plate 2, negative electrode plate 3 and separator 4 are stacked is the thickness direction D.

[0032] The positive electrode plate 2 and negative electrode plate 3 of the electrode group 6 are provided with lead portions that protrude from opposite sides of the electrode plates in the planar direction. A positive electrode current collector plate 27 is joined to the side edge of the lead portion 21l (see Figures 6 and 7) of the positive electrode plate 2 by spot welding or the like. Similarly, a negative electrode current collector plate 37 is joined to the side edge of the lead portion (not shown) of the negative electrode plate 3 by spot welding or the like.

[0033] <Configuration of positive electrode plate 2> Figure 6 is a schematic diagram showing a cross-section in the width direction W of the positive electrode plate 2 of the nickel-metal hydride battery 1 of this embodiment. The positive electrode plate 2 has a positive electrode current collector 21 and a positive electrode composite material layer 22 filled in the positive electrode current collector 21. The positive electrode composite material layer 22 has a positive electrode active material and additives (conductive material, binder, thickener, etc.).

[0034] <Positive electrode current collector 21> The positive electrode current collector 21 is formed in the shape of a rectangular plate from a nickel foam, which is a three-dimensional porous metal substrate. The periphery of the positive electrode current collector 21 is compressed and has a higher density, and functions as a frame that maintains the shape of the positive electrode current collector 21. In addition, because the porous structure of the periphery is crushed and the air permeability is reduced, the absorption of the electrolyte 5 from the surface is worse compared to the central part. The positive electrode current collector 21 has the function of a carrier that supports the positive electrode composite layer 22 in the space formed by its three-dimensional mesh-like structure, and the function of a current collector that collects current from the positive electrode active material in the positive electrode composite layer 22.

[0035] The positive electrode current collector 21 uses foamed nickel, which is a type of foamed metal. Foamed nickel has numerous pores inside and can be easily compressed. The method for manufacturing foamed nickel is not particularly limited, but for example, it can be manufactured by applying nickel plating to the surface of a foamed urethane skeleton and then burning off the foamed urethane.

[0036] Figure 7 is a schematic diagram showing the rough side surface 22a of the positive electrode plate of the nickel-metal hydride battery of this embodiment. As shown in Figures 6 and 7, the lead portion 21l is formed by welding a metal material such as iron to the center of one of the long sides of the rectangular positive electrode current collector 21 in the length direction L. This lead portion 21l is provided in the center of the thickness direction D of the positive electrode current collector 21.

[0037] The lead portion 21l is formed by welding a metal member, such as iron, to a frame portion that is compressed and has high density and strength on one of the long sides of the positive electrode current collector 21. A connection surface is formed on one surface of this metal member. The lead portion 21l is connected to the positive electrode connection terminal 13a of the adjacent battery cell 12 by a connection projection that protrudes from its upper part.

[0038] Furthermore, in this embodiment, it is desirable that the thickness of the positive electrode current collector 21 before the coating process (S13) be 0.5 mm or more and 1.0 mm or less. It is desirable to use foamed nickel with an average pore size of 300 μm or more and 600 μm or less. Also, the basis weight should be 200 g / m².2 ] or more, 400[g / m 2 It is desirable to use the following:

[0039] <Positive electrode composite paste 25> The positive electrode composite paste 25, which forms the positive electrode composite layer 22, contains positive electrode active material particles mainly composed of nickel hydroxide, a conductive material made of cobalt (Co), a thickener, a binder, and a solvent such as water.

[0040] Figure 11 is a comparison table showing an example of the composition of a conventional cathode composite paste and an example of the composition of the cathode composite paste 25 of this embodiment. As shown in Figure 11, the composition (wt%) of the positive electrode composite paste 25 of this embodiment, excluding the solvent water, is preferably as follows: Nickel hydroxide as the positive electrode active material is preferably 85 wt% to 95 wt%. Cobalt (Co) as the conductive material is preferably 5 wt% to 10 wt%. Zinc oxide is preferably 0.5 wt% to 1.5 wt% for adjusting the potential. Yttrium oxide is preferably 0.5 wt% to 1.5 wt%. Carboxymethylcellulose (CMC) as a thickener is preferably 0.01 wt% to 0.2 wt%. Sodium alginate is preferably 0.01 wt% to 0.2 wt% as a thickener. Furthermore, a fluorine-based binder is preferred in an amount of 0.05 (wt%) or more and 0.3 (wt%) or less.

[0041] While "fluorine-based binders" exhibit desirable performance as binders, they have the problem of segregation on the electrode surface during drying. In this embodiment, this problem is solved, making it possible to use fluorine-based binders. Details will be described later.

[0042] The positive electrode composite paste 25 of this embodiment is made by forming a paste from a positive electrode active material, conductive material, binder, thickener, etc., with a solvent such as water. The viscosity V [mPa·s] is adjusted by the solvent and thickener, and in this embodiment, it is 50 [mPa·s] or more and 2000 [mPa·s] or less. More preferably, it is 200 [mPa·s] or more and 1000 [mPa·s], and is adjusted to, for example, 500 [mPa·s]. The value of the viscosity V [mPa·s] is such that the shear rate is 10 [s -1 This shows the value in the case of ].

[0043] <Features of the positive electrode composite paste 25 of this embodiment> As shown in Figure 11, conventional cathode composite pastes do not contain sodium alginate as a thickening agent. Therefore, the viscosity [mPa·s] is not adjusted. Furthermore, they differ in that they do not contain polyvinylidene fluoride (PVDF), a fluorine-based binder. As a result, the binding strength is low.

[0044] <Cathode active material> Examples of positive electrode active materials include particulate materials mainly composed of nickel oxides such as nickel hydroxide and nickel oxyhydroxide.

[0045] <Conductive material> The conductive material is a metal or a metallic compound, such as cobalt compounds including metallic cobalt (Co), cobalt monoxide (CoO), or cobalt oxyhydroxide (CoOOH), which coat the surface of a nickel oxide. Cobalt oxyhydroxide, which has high conductivity, is preferred because it forms a conductive network within the positive electrode, thereby increasing the utilization rate of the positive electrode.

[0046] <Thickening agent> Examples of thickening agents include glucose-based substances such as xanthan gum, and acrylic-based substances such as sodium acrylate.

[0047] <Binding agent> The material contains a fluorine-based binder. Examples of fluorine-based binders include organic solvent-based polyvinylidene fluoride (PVDF) and aqueous dispersants. While fluorine-based binders have good binding properties, they tend to segregate on the surface of the positive electrode composite layer 22. In this embodiment, even if such segregation occurs, the structure facilitates the penetration of the electrolyte 5 into the positive electrode composite layer 22. Therefore, in this embodiment, even fluorine-based binders that tend to segregate can be effectively utilized.

[0048] Furthermore, other examples of binding agents include latex-based materials such as Rubron (a registered trademark of Daikin Industries, Ltd.) and polyethylene oxide (PEO). <Solvent> In this embodiment, water (H2O) is used as the solvent. The solvent, along with the thickener, is used to adjust the viscosity of the positive electrode composite paste 25. The amount added is adjusted while taking into account the packing density Df of the positive electrode active material, the unevenness width ΔW, and the relationship ΔW / Ws.

[0049] <Positive electrode composite layer 22> The positive electrode composite paste 25 described above is applied to the positive electrode current collector 21, and after drying and shaping press, the positive electrode composite layer 22 is formed. Further details will be described later.

[0050] <Negative electrode plate 3> The negative electrode plate 3 includes a plate-shaped negative electrode current collector 31 made of rectangular perforated metal or the like. The negative electrode current collector 31 is both a mechanical substrate and a current collector that collects current from the negative electrode active material. It also includes a hydrogen storage alloy (MH) coated on the negative electrode current collector 31. The type of hydrogen storage alloy is not particularly limited, but for example, it may be an alloy of mischmetal, which is a mixture of rare earth elements, and nickel, or a part of the alloy in which metals such as aluminum, cobalt, or manganese are replaced. The negative electrode plate 3 is coated with a negative electrode composite paste. The negative electrode composite paste is made by adding a thickening agent such as carbon black and a binder such as styrene-butadiene copolymer to a hydrogen storage alloy and processing it into a negative electrode composite paste. The negative electrode plate 3 is manufactured by filling the negative electrode composite paste into the negative electrode current collector 31, which is made of a core material such as perforated metal, and then drying, rolling, and cutting it.

[0051] <Separator 4> Separator 4 is made of a nonwoven fabric of an olefin resin such as polypropylene, or, if necessary, this fabric has been treated with a hydrophilic treatment such as sulfonation.

[0052] These positive electrode plate 2, negative electrode plate 3, and separator 4 are used to manufacture a battery module. <Electrolyte 5> The electrolyte 5 is held within the separator 4 and conducts ions between the positive electrode plate 2 and the negative electrode plate 3. The electrolyte 5 is, for example, an alkaline aqueous solution with potassium hydroxide (KOH) as the main solute component.

[0053] <Manufacturing process for nickel-metal hydride battery 1> Figure 4 is a flowchart showing the manufacturing process of the nickel-metal hydride battery 1 of this embodiment. Next, the manufacturing method of the nickel-metal hydride battery 1 of this embodiment, which has the configuration described above, will be explained with reference to Figure 4. The manufacturing process of the nickel-metal hydride battery 1 consists of a source process (S1), an electrode group manufacturing process (S2), an electrode group assembly process (S3), a liquid injection process (S4), a sealing process (S5), and an inspection process (S6).

[0054] In the source process (S1), the battery elements, namely the positive electrode plate 2, the negative electrode plate 3, and the separator 4, are manufactured. In the electrode group manufacturing process (S2), the positive electrode plate 2, the negative electrode plate 3, and the separator 4 manufactured in the source process (S1) are stacked, and the positive electrode current collector plate 27 and the negative electrode current collector plate 37 are welded to manufacture the electrode group 6 as shown in Figure 3. In the electrode group assembly process (S3), the electrode group 6 manufactured in the electrode group manufacturing process (S2) is housed in each of the battery cases 15 of the integrated battery case 13, as shown in Figure 2. The electrode groups 6 housed in each of the battery cases 15 are then electrically connected by welding or other means, and the positive electrode connection terminal 13a and the negative electrode connection terminal 13b (see Figure 1) are attached. In the electrolyte injection process (S4), electrolyte 5 is injected into each of the battery cases 15 of the battery case 13. In the sealing process (S5), the lid 14 is attached to the battery case 13, which has been filled with electrolyte in the electrolyte filling process (S4), and sealed. This completes the assembly of the nickel-metal hydride battery 1, which is the battery module of this embodiment. In the inspection process (S6), the assembled nickel-metal hydride battery 1 undergoes initial charging, aging, internal resistance (DC-IR) testing, OCV testing, self-discharge testing, etc. Only those that pass these tests become the nickel-metal hydride battery module 1 as a product.

[0055] <Manufacturing process for positive electrode plate 2> Figure 5 is a flowchart showing the manufacturing process of the positive electrode plate of the nickel-metal hydride battery according to this embodiment. Next, the manufacturing process of the positive electrode plate 2 will be described in detail with reference to Figure 5. This manufacturing process of the positive electrode plate 2 is a part of the source process (S1) of the nickel-metal hydride battery 1.

[0056] The manufacturing process for the positive electrode plate consists of the positive electrode current collector manufacturing process (S11), the positive electrode composite paste manufacturing process (S12), the coating process (S13), the drying process (S15), and the shaping and pressing process (S16).

[0057] <Positive electrode current collector manufacturing process (S11)> First, the positive electrode current collector manufacturing process (S11) is the process of manufacturing the positive electrode current collector 21. First, a positive electrode current collector 21 of a predetermined size is cut from a long sheet of foamed nickel by a cutting process. Next, the peripheral portion of the positive electrode current collector 21, which has been shaped to a predetermined thickness, is compressed in a shaping and pressing process to shape it to a predetermined length and width. The shaped peripheral portion of the positive electrode current collector 21 is compressed and crushed, increasing its density. This increased density increases its mechanical strength, allowing it to maintain its shape as the frame of the positive electrode current collector 21. Furthermore, this compression and crushing of the peripheral portion crushes the spaces in the porous foamed nickel, reducing its permeability and making it difficult for the electrolyte 5 to be absorbed.

[0058] A lead portion 21l, as shown in Figures 6 and 7, is welded to the center of one of the longer sides of the periphery of the positive electrode current collector 21. <Cathode composite paste manufacturing process (S12)> In the positive electrode composite paste manufacturing process (S12), the positive electrode composite paste 25 described above is manufactured. The positive electrode composite paste 25 is made by mixing positive electrode active material particles, conductive material, binder, thickener, etc. with a solvent to form a paste with a predetermined viscosity V [mPa·s].

[0059] <Coating process (S13)> In the coating process (S13), the positive electrode composite paste 25 manufactured in the positive electrode composite paste manufacturing process (S12) is coated onto the positive electrode current collector 21 manufactured in the positive electrode current collector manufacturing process (S11).

[0060] Figure 12 is a perspective view showing an example of a coating apparatus in this embodiment. Figure 13(a) is a perspective view showing the coating process in this embodiment. <Coating machine 8> As shown in Figure 12, the coating machine 8 for applying the positive electrode composite paste 25 to the positive electrode current collector 21 comprises a die nozzle 81 for applying the positive electrode composite paste 25 to the positive electrode current collector 21, a support member 85, and a stage 86.

[0061] <Die nozzle 81> The die nozzle 81 comprises a die 82 and a nozzle 83. The die 82 stores the positive electrode mixture paste 25 supplied from a supply unit (not shown), such as a tank, through a supply pipe at high pressure. The nozzle 83 has a discharge port at its tip facing the upper surface of the positive electrode current collector 21 (in this embodiment, the surface on the rough side surface 22a of the positive electrode mixture layer 22). The discharge port is spaced apart from the upper surface 21j with a predetermined clearance. The nozzle 83 extends in the second direction Y (the width and traverse W of the positive electrode current collector 21), and its discharge port is partitioned to correspond to the coating areas 21a to 21d, discharging the positive electrode mixture paste 25 onto the upper surface 21j of the coating areas 21a to 21d. The positive electrode mixture paste 25 discharged from the discharge port flows down to the upper surface 21j.

[0062] The die nozzle 81 is equipped with a pressing roller 84 in the area of ​​the nozzle 83 that is not coated with the positive electrode mixture paste 25 when dispensing the positive electrode mixture paste 25 onto the upper surface 21j of the positive electrode current collector 21. The pressing roller 84 contacts the upper surface 21j just before the nozzle 83 applies the positive electrode mixture paste 25 to the upper surface 21j, pressing the positive electrode current collector 21 toward the support member 85. As a result, the pressing roller 84 removes the waviness of the positive electrode current collector 21 and maintains a constant distance between the nozzle 83 and the upper surface 21j.

[0063] <Support member 85> The support member 85 supports the coating area 21a to 21d from the lower surface 21k side until the positive electrode composite paste 25 is applied to the upper surface 21j of the positive electrode current collector 21 by the nozzle 83.

[0064] Figure 14(a) is a plan view showing the positional relationship between the nickel substrate, the first support, and the second support. Figure 14(b) is a cross-sectional view showing the nickel substrate supported by the first and second support before the paste is applied. Figure 14(c) is an enlarged cross-sectional view of (b).

[0065] As shown in Figures 14(a) to (c), the support member 85 comprises a first support portion 85a, an insertion portion 85b, and a connecting portion 85c. The first support portion 85a supports each of the coating areas 21a to 21d by contacting them from the lower surface 21k side. The insertion portion 85b is provided between adjacent first support portions 85a. The connecting portion 85c (see Figure 13(a)) connects the first support portions 85a that are separated from each other by the insertion portion 85b in the second direction Y (see Figure 12). The support member 85 has a comb-like shape overall.

[0066] <First support part 85a> Four first support parts 85a are provided, corresponding to the coating areas 21a to 21d. Each first support part 85a extends in the first direction X and is spaced parallel to each other. In each first support part 85a, the support surface that supports the coating areas 21a to 21d is preferably a flat surface that can provide stable support and is easily slidable against the lower surface 21k of the coating areas 21a to 21d. This makes it easier for the first support part 85a to dislodge from below the coating areas 21a to 21d.

[0067] The tip opposite to the connecting portion 85c that connects each first support portion 85a is located at least below the press roller 84. This allows each first support portion 85a to work in cooperation with the press roller 84 to firmly grip the positive electrode current collector 21. More preferably, the tip of the first support portion 85a may also be long enough to be located below the nozzle 83. That is, the first support portion 85a may be configured to contact and support the lower surface 21k of the coating area 21a to 21d until the positive electrode mixture paste 25 penetrates from the upper surface 21j to the lower surface 21k of the positive electrode current collector 21. This allows the first support portion 85a to support the lower surface 21k of the coating area 21a to 21d until just before it comes into contact with the penetrating positive electrode mixture paste 25.

[0068] <Insertion section 85b> The insertion portion 85b, located between adjacent first support portions 85a, is a slit that penetrates in the thickness direction D, extends in the first direction X, and has an open end below the nozzle 83.

[0069] <Second support part 85d> As shown in Figure 14(c), the support member 85 is a member positioned between the die nozzle 81 and the stage 86. The insertion portion 85b of this support member 85 is through which the second support portion 85d provided on the stage 86 is inserted, so that the second support portion 85d can support the lower surface 21k of the uncoated areas 21e to 21i of the positive electrode current collector 21. That is, the width of each insertion portion 85b (the distance between adjacent first support portions 85a) is, for example, a width through which the second support portion 85d can be inserted, and is slightly wider than the width of the second support portion 85d.

[0070] The die nozzle 81 and the support member 85 are connected via a connecting mechanism (not shown) that includes a connecting member, and move synchronously in the direction of movement indicated by the arrow, which is one of the first directions X relative to the positive electrode current collector 21. In other words, the positive electrode current collector 21 and the stage 86 do not move, while the die nozzle 81 and the support member 85 move in the direction of movement indicated by the arrow relative to the positive electrode current collector 21 and the stage 86.

[0071] <Stage 86> Stage 86 is configured such that a support member 85 and a die nozzle 81 synchronized with the support member 85 are movable in a first direction X. Stage 86 is provided with a second support portion 85d on the support surface of the support member 85. The second support portion 85d is inserted through the insertion portion 85b of the support member 85 and supports the lower surface 21k of the positive electrode current collector 21 with its tip surface. For example, the second support portion 85d has a length corresponding to the first direction X of the positive electrode current collector 21 on which it is placed (the length of the uncoated areas 21e to 21i in the first direction X). In the second support portion 85d, the support surface that supports the uncoated areas 21e to 21i is preferably a flat surface that is less slippery with respect to the lower surface 21k of the uncoated areas 21e to 21i. This prevents the positive electrode current collector 21 from being dragged along and moving in the same direction as the movement of the support member 85 indicated by the arrow.

[0072] Specifically, before the positive electrode composite paste 25 is applied to the upper surface 21j of the positive electrode current collector 21, the lower surfaces 21k of the applied areas 21a to 21d are supported by the first support part 85a, and the lower surfaces 21k of the unapplied areas 21e to 21i are supported by the second support part 85d. Then, the die nozzle 81 and the support member 85 move in the direction indicated by the arrows relative to the positive electrode current collector 21 and the stage 86. As a result, in the portion of the positive electrode current collector 21 to which the positive electrode composite paste 25 has been applied, only the lower surfaces 21k of the unapplied areas 21e to 21i are supported by the second support part 85d. The space between the lower surfaces 21k of the applied areas 21a to 21d and the stage 86 becomes a gap when the first support part 85a is removed, preventing the positive electrode composite paste 25 that has penetrated to the lower surface 21k of the positive electrode current collector 21 from coming into contact with the stage 86. Furthermore, by inserting the second support portion 85d into the insertion portion 85b, the second support portion 85d also functions as a guide rail for the support member 85 that moves relative to the stage 86, and the insertion portion 85b also functions as a guide groove into which the guide rail is inserted. Note that the guiding mechanism for the support member 85 relative to the stage 86 can also be provided in addition to the insertion portion 85b.

[0073] When the positive electrode composite paste 25 is applied to the upper surface 21j of the positive electrode current collector 21, the support member 85 moves relative to the positive electrode current collector 21 in the direction indicated by the arrow. Therefore, the positive electrode current collector 21 may be dragged and moved by the movement of the support member 85 in the direction indicated by the arrow. To address this, the second support portion 85d is equipped with a holding means to hold the positive electrode current collector 21 so that it does not move in the direction indicated by the arrow. The holding means is a vacuum suction pad or a magnetic suction pad that holds the positive electrode current collector 21 on the second support portion 85d.

[0074] <Coating Procedure> Figure 13(b) is an enlarged cross-sectional view showing the position where the die nozzle 81 applies the positive electrode composite paste 25 to the positive electrode current collector 21. The coating process (S13) is carried out using the coating machine 8 described above. The coating procedure will be explained with reference to Figure 13.

[0075] As shown in Figures 13(a) and 13(b), the die nozzle 81 and the support member 85 move synchronously and sequentially in the direction indicated by the arrows. As a result, the first support portion 85a of the support member 85 retracts sequentially from below the upper surface 21j of the coating area 21a to 21d, and thereafter, the positive electrode composite paste 25 penetrates from the upper surface 21j to the lower surface 21k. This prevents contact between the positive electrode composite paste 25 on the lower surface 21k and the first support portion 85a. In other words, after the positive electrode composite paste 25 is applied, only the uncoated area 21e to 21i of the positive electrode current collector 21 is supported by the second support portion 85d of the stage 86.

[0076] The positive electrode current collector 21 is coated with the positive electrode composite paste 25 through the process described above. <Positive electrode composite paste 25 in coating process (S13)> In the coating process (S13), as described above, the die nozzle 81 applies the positive electrode composite paste 25 to the positive electrode current collector 21.

[0077] As shown in Figure 13(b), when the positive electrode composite paste 25 is discharged from the upper surface 21j of the positive electrode current collector 21, the positive electrode composite paste 25 is coated on the upper surface 21j of the positive electrode current collector 21 with a coating width Wp, as shown in Figures 6 and 7. The coated positive electrode composite paste 25 penetrates into the interior of the positive electrode current collector 21. At this time, due to its viscosity V [mPa·s], surface tension, and wettability, the width W of the positive electrode composite paste 25 gradually decreases as it penetrates downwards due to gravity from the coating width Wp, as shown in Figure 6. Then, at the lower surface 21k, it is adjusted to have a standard coating width Ws.

[0078] As shown in Figure 7, the coated positive electrode composite paste 25 is applied to a coating width Wp. However, the end 22d in the width direction W does not form a straight line along the length direction L, but rather has a wavy, random unevenness in the width direction W. This is caused by the skeletal structure of the positive electrode current collector 21 and the unevenness of the positive electrode composite paste 25 absorbed therein. The average width of this unevenness is denoted as the unevenness width ΔW. Here, the coating width Wp and the reference coating width Ws are the trajectories of the straight line obtained by averaging such unevenness width ΔW.

[0079] Next, Figure 8 is a schematic diagram showing the dense surface 22c of the positive electrode composite layer 22 of the positive electrode plate 2 of the nickel-metal hydride battery 1 of this embodiment. As shown in Figure 6, the width of the positive electrode composite paste 25, which is coated and penetrates the positive electrode current collector 21, narrows by the time it reaches the bottom surface 21k. Therefore, on the dense surface 22c shown in Figure 8, the width of the positive electrode composite layer 22 is the standard coating width Ws. Also, as the positive electrode composite paste 25 penetrates the interior 22b of the positive electrode current collector 21, the irregularities at its edges expand. Therefore, on the dense surface 22c shown in Figure 8, the irregularity width ΔW of the edge 22d of the positive electrode composite layer 22 in the width direction W is larger than that of the rough surface 22a. If the length of the curved edge 22d of the dense surface 22c is straightened out, the length of the edge 22d of the dense surface 22c is longer than that of the rough surface 22a due to the greater curvature. Furthermore, because the width of the unevenness ΔW is large, there are parts where the structural frame of the porous positive electrode current collector 21 is exposed.

[0080] In this embodiment, the unevenness width ΔW of the end portion 22d of the positive electrode composite layer 22 in the short-side direction (width direction W) on the dense-side surface 22c is adjusted to be larger than the unevenness width ΔW on the rough-side surface 22a.

[0081] Furthermore, the relationship between the unevenness width ΔW at the end 22d of the positive electrode composite layer 22 in the short-side direction of the dense surface 22c and the standard coating width Ws in the short-side direction is set to ΔW / Ws ≥ 0.016. The positive electrode plate 2 of this embodiment has the configuration described above. As a result, even if the penetration rate of the electrolyte 5 on the dense side surface 22c of the positive electrode composite layer 22 decreases, the electrolyte 5 can easily penetrate from the portion where the bones of the porous positive electrode current collector 21 are exposed to the end portion 22d of the positive electrode composite layer 22 in the width direction W.

[0082] <Packing density Df of positive electrode active material in positive electrode composite layer 2> As described above, when the positive electrode composite paste 25 is applied to the positive electrode current collector 21, gravity causes it to gradually penetrate the positive electrode current collector 21. At this time, in the positive electrode composite paste 25 with an appropriately adjusted viscosity V [mPa·s], the particles of the positive electrode active material have a density [g / cm³]. 3 Because the ] is relatively large, it settles faster than other materials. Therefore, the packing density Df[%] of the positive electrode active material is greater in the lower part of the applied positive electrode composite paste 25 than in the upper part. That is, the packing density Df[%] of the positive electrode active material at the dense side surface 22c, which is the lower end of the thickness direction D of the positive electrode composite layer 22 relative to the positive electrode current collector 21, has a packing density difference ΔDf that is greater than the packing density Df[%] of the positive electrode active material at the rough side surface 22a, which is the upper end.

[0083] The higher the packing density Df[%] of the positive electrode active material, the less easily the electrolyte 5 penetrates the positive electrode composite layer 22. Specifically, in this embodiment, the packing density difference ΔDf is preferably 4% or more and 20% or less.

[0084] Figure 10 is a schematic diagram showing the packing density Df of the positive electrode active material in the positive electrode composite layer 22 of the positive electrode plate 2 of the nickel-metal hydride battery 1 of this embodiment, and the state when the electrolyte 5 is injected. When the positive electrode plate 2 is divided into three equal layers in the thickness direction D, the packing density difference ΔDf of the positive electrode active material is averaged between the second layer L2 in the central portion and the third layer L3 on the dense side surface 22c and the first layer L1 on the rough side surface 22a, with respect to each other. This difference is between 2% and 10%. In this embodiment, the packing density difference ΔDf is 5% in each case.

[0085] <Preparation of positive electrode composite paste 25 (S14)> In the coating process (S13), as described above, the unevenness width ΔW of the edge 22d of the positive electrode composite layer 22 in the short-side direction on the target dense-side surface 22c, the standard coating width Ws in the short-side direction, and a predetermined relationship ΔW / Ws are defined. The target packing density difference ΔDf is also defined. Therefore, after the coating process (S13), the positive electrode composite layer 22 is inspected to ensure it is properly constructed. If the inspection reveals that the positive electrode composite layer 22 is not suitable (S14:NO), the process returns to the positive electrode composite paste manufacturing process (S11). Then, the viscosity V [mPa·s] of the positive electrode composite paste 25 and other shear rates [s -1 Adjust the following: If the positive electrode composite layer 22 is appropriate (S14: YES), proceed to the drying process (S15).

[0086] Furthermore, the adjustment of the positive electrode composite paste 25 (S14) does not necessarily have to be performed continuously; for example, it can be done for each production lot in which the composition changes. <Drying process (S15)> In the drying process (S15), the positive electrode composite paste 25 applied to the positive electrode current collector 21 in the coating process (S13) is dried by methods such as hot air, cold air, or infrared irradiation to evaporate the solvent and harden the positive electrode composite paste 25, thereby forming the positive electrode composite layer 22.

[0087] <Shaping and pressing process (S16)> In the drying process (S15), the positive electrode composite paste 25 is hardened to form the positive electrode composite layer 22. Then, the positive electrode plate 2 is pressed to a predetermined thickness using a roller press machine (not shown) and its surface shape is adjusted.

[0088] This completes the manufacturing process for the positive electrode plate 2. The process then proceeds to the electrode group manufacturing process (S2), where the negative electrode plate 3 and separator 4 manufactured in the source process (S1) are stacked, and the positive electrode current collector plate 27 and negative electrode current collector plate 37 are welded together to manufacture the electrode group 6.

[0089] (Operation of this embodiment) Next, the operation of the nickel-metal hydride battery 1 of this embodiment and its manufacturing method will be described. <Operation of positive electrode plate 2 during transport> Figure 17 is a schematic diagram showing the state of transporting the positive electrode plate 2 of a conventional nickel-metal hydride battery 1. Conventionally, the packing density Df of the positive electrode active material in the positive electrode composite layer 22 of the positive electrode plate 2 was uniform. The manufacturing process of the nickel-metal hydride battery 1 may include a transport step in which the uppermost positive electrode plate, which is stacked and placed on top of multiple positive electrode plates 2 as components, is transported by adsorption from above using the adsorption pad 91 of a vacuum adsorption device 9. At this time, since the packing density Df of the positive electrode active material in the positive electrode composite layer 22 is conventionally uniform, the degree of air permeability is also uniform. Therefore, if the vacuum level of the adsorption pad 91 is low, the negative pressure is insufficient, and the positive electrode plate 2 cannot be reliably transported. On the other hand, if the vacuum level of the adsorption pad 91 is increased in order to reliably transport the positive electrode plate 2, the negative pressure will extend not only to the uppermost positive electrode plate 2 being transported, but also to the other positive electrode plates 2 stacked below it. As a result, the negative pressure caused a problem in that it transported not only the uppermost positive electrode plate 2 that was being transported, but also the other positive electrode plates 2 stacked below it.

[0090] Therefore, in the nickel-metal hydride battery 1 of this embodiment, the packing density Df of the positive electrode active material on the dense surface 22c below the positive electrode composite layer 22 of the positive electrode plate 2 is greater than the packing density Df of the rough surface 22a above the positive electrode composite paste, resulting in a packing density difference ΔDf. Furthermore, the packing density Df is configured to gradually increase from the rough surface 22a to the dense surface 22c.

[0091] Specifically, as shown in Figure 9, the packing density difference ΔDf is calculated by dividing the positive electrode plate 2 equally into a first layer L1, a second layer L2, and a third layer from top to bottom along the thickness direction D. In this case, there is a packing density difference ΔDf of 2% to 10% between the third layer L3 on the dense side surface 22c and the first layer L1 on the rough side surface 22a, relative to the central second layer L2.

[0092] Therefore, as shown in Figure 9, in the positive electrode plate 2 transport process of the manufacturing process of nickel-metal hydride battery 1, the positive electrode plate 2 is placed so that its upper surface becomes the rough side surface, where the packing density Df of the positive electrode active material in the positive electrode composite layer 22 is low. Then, the rough side surface 22a is adsorbed from above and transported by the adsorption pad 91 of the vacuum adsorption device 9. As a result, the first layer L1 of the rough side surface 22a has good permeability, so negative pressure reaches the interior of the positive electrode composite layer 22. However, the third layer L3 of the dense side surface 22c has low permeability, so the negative pressure does not reach the other positive electrode plates 2 stacked below it. As a result, even if the vacuum level of the adsorption pad 91 is sufficiently high, only the positive electrode plates 2 stacked on top can be reliably transported. In this way, even if the positive electrode plate 2 is stacked so that its upper surface becomes the highly permeable rough side surface 22a, the positive electrode plate 2 can be transported easily and reliably.

[0093] In addition, depending on the manufacturing process, the dense surface 22c may be the upper surface. In this case as well, since the air permeability of the dense surface 22c is low, the positive electrode plate 2 can be reliably transported under high vacuum conditions by being adsorbed from above by the suction pad 91 of the vacuum suction device 9 on the rough surface 22a. Furthermore, because the air permeability of the dense surface 22c is low, the negative pressure of the suction pad 91 of the vacuum suction device 9 is blocked, and the negative pressure does not reach the other positive electrode plates 2 stacked below it. As a result, even if the vacuum level of the suction pad 91 is sufficiently high, only the positive electrode plates 2 stacked on top can be reliably transported.

[0094] <The effect of the osmotic solution 5> Figure 15 is a schematic diagram showing the surface (coated side) of the positive electrode composite layer 22 of the positive electrode plate 2 of a conventional nickel-metal hydride battery 1. Figure 16 is a schematic diagram showing the back surface of the positive electrode plate 2 of a conventional nickel-metal hydride battery 1. Figure 18 is a schematic diagram showing the packing density Df of the positive electrode active material in the positive electrode composite layer 22 of the positive electrode plate 2 of a conventional nickel-metal hydride battery 1 and its state when injected.

[0095] In a conventional nickel-metal hydride battery 1, as shown in Figure 4, the electrolyte 5 is injected into each battery case 15 shown in Figure 2 during the electrolyte injection process (S4). At this time, as shown in Figure 3, the electrolyte 5 permeates the electrode group 6. The electrolyte 5 first immerses the ends of the electrode group 6 in the width direction W, then permeates the separator 4 which has good permeability and allows the electrolyte 5 to easily permeate, and further permeates the surface of the stacked positive electrode plate 2 via the separator 4.

[0096] In the conventional technology, as shown in Figures 15 and 16, the packing density Df of the positive electrode active material in the positive electrode composite layer 22 is uniform. Also, since it is a double-sided coating, the coating width of the edges 22d of the positive electrode composite layer 22 in the short-side direction (width direction W) of both surfaces is equal. Furthermore, the unevenness width ΔW is small and equal. Therefore, the relationship ΔW / Wp of the reference coating width Ws in the short-side direction of one surface is equal to the relationship ΔW / Ws on the other surface.

[0097] In the positive electrode composite layer 22 of the nickel-metal hydride battery 1 of this embodiment, there is a packing density difference ΔDf between the packing density Df of the positive electrode active material on the rough side surface 22a of the upper surface (coated surface of the positive electrode composite paste 25) shown in Figure 7 and the dense side surface 22c of the lower surface shown in Figure 8. Furthermore, the coating process (S13) is single-sided coating. Therefore, when comparing the coating width Wp on the rough side surface 22a with the standard coating width Ws on the dense side surface 22c, the standard coating width Ws is narrower than the coating width Wp. In other words, the portion of the end of the positive electrode current collector 21 where the positive electrode composite layer 22 is not present is wider on the dense side surface 22c than on the rough side surface 22a.

[0098] Furthermore, the coating process (S13) is a single-sided coating. Therefore, by appropriately adjusting the viscosity V [mPa·s], the edges of the positive electrode composite paste 25 become significantly wavy before it penetrates the positive electrode current collector 21. As a result, the unevenness width ΔW of the edges 22d of the positive electrode composite layer 22 in the short-side direction (width direction W) on the dense-side surface 22c is adjusted to be greater than the unevenness width ΔW on the rough-side surface 22a. In addition, the relationship between the unevenness width ΔW of the edges 22d of the positive electrode composite layer 22 in the short-side direction on the dense-side surface 22c and the standard coating width Ws in the short-side direction is adjusted so that ΔW / Ws ≥ 0.016.

[0099] As a result, as shown in Figures 6 and 10, the point P1 on the rough surface 22a has a lower packing density Df of positive electrode active material than the conventional nickel-metal hydride battery 1, resulting in high air permeability and good penetration of the electrolyte 5. Furthermore, while the electrolyte 5 does not easily penetrate the peripheral portion of the positive electrode current collector 21, at point P2, which is the gap between the peripheral portion of the positive electrode current collector 21 and the end portion 22d of the rough surface 22a, the penetration of the electrolyte 5 is equivalent to that of the conventional nickel-metal hydride battery 1.

[0100] On the other hand, at point P3 on the dense surface 22c, the packing density Df of the positive electrode active material is higher than that of the conventional nickel-metal hydride battery 1, resulting in lower air permeability and less penetration of the electrolyte 5. However, at point P4, which is the gap between the peripheral edge of the positive electrode current collector 21 and the end 22d of the dense surface 22c, the portion of the end of the positive electrode current collector 21 where the positive electrode composite material layer 22 is absent is wider on the dense surface 22c than on the rough surface 22a. The relationship between the unevenness width ΔW and the standard coating width Ws in the short-side direction is adjusted so that ΔW / Ws ≥ 0.016, and the length of the end 22d is longer than in the conventional design.

[0101] As a result, the penetration rate of the electrolyte 5 in the nickel-metal hydride battery 1 of this embodiment is improved compared to conventional electrolytes 5, with the entire positive electrode plate 2 exhibiting improved penetration rate. As a result, the internal resistance (DC-IR) of the nickel-metal hydride battery 1 in this embodiment was reduced by approximately 1% compared to the internal resistance (DC-IR) of a conventional nickel-metal hydride battery 1.

[0102] (Effects of this embodiment) (1) In this embodiment, the nickel-metal hydride battery 1 has a relatively high packing density Df of the positive electrode active material near the dense side surface 22c of the positive electrode composite layer 22, resulting in low permeability and easy maintenance of negative pressure. Therefore, the positive electrode plate 2 can be easily and reliably transported by vacuum adsorption during the manufacturing process.

[0103] (2) In conventional positive electrode plates 2, the positive electrode composite layer 22 has high permeability, so if the suction force is small, the vacuum level may not be sufficiently high, and the positive electrode plate 2 may fall off during transport. On the other hand, if the suction force is too high, there is a problem that not only the target positive electrode plate 2 but also the positive electrode plate 2 below it will be transported. In the nickel-metal hydride battery 1 of this embodiment, the negative pressure downward can be blocked. Therefore, in the transport process described above, when transporting the uppermost positive electrode plate 2 of multiple positive electrode plates 2 stacked in the thickness direction D using the suction pad 91 of the vacuum suction device 9, only the uppermost positive electrode plate 2 can be reliably transported.

[0104] (3) After the coating process (S13), the manufacturing process proceeds with the rough surface 22a facing upwards. Even when the highly permeable rough surface 22a is facing upwards, the low permeability of the dense surface 22c on the bottom surface allows the suction pad 91 of the vacuum suction device 9 to maintain sufficient negative pressure and block negative pressure from moving downwards. Therefore, it is not necessary to invert the device each time to face the less permeable dense surface 22c upwards, and the negative pressure inside the suction pad 91 can be reliably maintained and the device transported in its current position.

[0105] (4) Furthermore, as described above, the packing density Df of the positive electrode active material near the dense surface 22c of the positive electrode composite layer 22 is relatively high, resulting in poor penetration of the electrolyte 5. However, the electrolyte 5 penetrates well from the rough surface 22a and the edges 22d of the dense surface 22c. Therefore, the penetration of the electrolyte 5 is actually good for the positive electrode plate 2 as a whole.

[0106] (5) Due to the good penetration of the electrolyte 5, the internal resistance (DC-IR) of the nickel-metal hydride battery 1 can be reduced by about 1% compared to conventional batteries. (6) In the manufacturing method of the nickel-metal hydride battery of this embodiment, the viscosity V [mPa·s] of the positive electrode composite paste 25 in the coating step (S13) is determined based on the packing density Df of the positive electrode active material. This makes it possible to form a positive electrode composite layer 22 having a desired packing density Df of the positive electrode active material.

[0107] (7) In addition, in the manufacturing method of nickel-metal hydride batteries of this embodiment, the viscosity V [mPa·s] of the positive electrode composite paste 25 in the coating process (S13) is determined based on the coated positive electrode composite layer 22. This makes it possible to control the desired coating width Wp in the width direction W, the reference coating width Ws, the width of irregularities ΔW at the edges of the positive electrode composite layer in the width direction W, and consequently the relationship between these ΔW / Ws.

[0108] (8) By controlling the coating width Wp and reference coating width Ws in the desired width direction W in this way, a portion without the positive electrode composite layer 22 can be created at the edge of the positive electrode plate 2, making it easier for the electrolyte 5 to penetrate. As a result, the internal resistance (DC-IR) of the nickel-metal hydride battery 1 can also be reduced compared to conventional batteries.

[0109] (9) Furthermore, by controlling the width ΔW of the irregularities at the end of the positive electrode composite layer in the desired width direction W, and by controlling the relationship between these ΔW / Ws, the length of the curve at the end 22d of the positive electrode composite layer 22 can be increased, making it easier for the electrolyte 5 to penetrate.

[0110] (10) Therefore, by controlling the viscosity V [mPa·s], the relationship between the unevenness width ΔW of the edge 22d of the positive electrode composite layer 22 in the short-side direction of the dense surface 22c and the reference coating width Ws in the short-side direction can be configured such that ΔW / Ws ≥ 0.016. As a result, the internal resistance (DC-IR) of the nickel-metal hydride battery 1 can also be reduced compared to conventional batteries.

[0111] (Another example) The present invention can be implemented as follows, notwithstanding the above embodiments. ○ In this embodiment, the viscosity V of the positive electrode mixture paste 25 [mPa·s] is adjusted by adding water as a solvent or a thickener, thereby forming a positive electrode mixture layer 22 having a desired packing density Df [%], uneven width ΔW, and a desired relationship ΔW / Ws. However, it is not limited to the adjustment of the viscosity V [mPa·s], and any method can be used as long as it can achieve the desired packing density Df [%], uneven width ΔW, and desired relationship ΔW / Ws. The key is to adjust the packing density Df [%], uneven width ΔW, and relationship ΔW / Ws using means related to these, with the set packing density Df [%] and set relationship ΔW / Ws as indicators, as long as these can be adjusted.

[0112] ○ For this purpose, for example, the configuration of the positive electrode current collector 21 can be cited. Specifically, by changing the size, shape, material, etc. of the mesh structure of the positive electrode current collector 21, the desired packing density Df [%], uneven width ΔW, and desired relationship ΔW / Ws may be achieved.

[0113] ○ As another method, the composition of the positive electrode mixture paste 25 and the positive electrode active material may be changed. For example, by changing the type and diameter of the positive electrode active material in the positive electrode mixture paste 25, the sedimentation rate of the positive electrode active material particles can be controlled. Also, by adjusting the wettability (water repellency) between the positive electrode mixture paste 25 and the bone part of the positive electrode current collector 21, the spread and disturbance of the positive electrode mixture paste 25 can be adjusted.

[0114] ○ By changing the temperature of the positive electrode mixture paste 25 [°C], the viscosity can also be changed. Also, by controlling the shear rate [s -1 , the viscosity can be indirectly adjusted.

[0115] Also, by changing the discharge amount, discharge speed, discharge pressure, shape of the discharge port, discharge gap, etc. from the coater 8, the desired packing density Df [%], uneven width ΔW, and desired relationship ΔW / Ws may be achieved.

[0116] ○ Of course, a combination of these may be used to achieve the desired packing density Df [%], uneven width ΔW, and desired relationship ΔW / Ws. ○In this embodiment, multiple positive electrode plates 2 as components are stacked with the rough side surface 22a facing upwards, and the rough side surface 22a is adsorbed and transported by the suction pad 91. However, it is not limited to this, and the dense side surface 22c may be stacked on top, and the dense side surface 22c may be adsorbed and transported by the suction pad 91.

[0117] ○Although the nickel-metal hydride battery 1 of this embodiment has been described using a vehicle drive battery as an example, the battery's applications are not limited and can be used in aircraft, ships, and even for stationary applications. ○Some of the drawings are schematic diagrams illustrating the nickel-metal hydride battery 1 of this embodiment, and the quantities and dimensional balance of the components may not always be accurate, and some may be exaggerated.

[0118] ○The flowcharts shown in Figures 4 and 5 are illustrative examples, and the steps can be added, deleted, rearranged, or modified. For example, the order of the positive electrode current collector manufacturing process (S11) and the positive electrode composite paste manufacturing process (S12) does not matter.

[0119] The numerical values ​​such as the viscosity V [mPa·s] of the positive electrode composite paste are illustrative examples in the embodiments, and the present invention is not intended to be limited to these values ​​or ranges. Those skilled in the art can optimize them to suit the configuration of the nickel-metal hydride battery 1.

[0120] It goes without saying that the present invention can be implemented by those skilled in the art by adding, deleting, or modifying its configuration, as long as it does not deviate from the scope of the claims. [Explanation of Symbols]

[0121] 1… Nickel-metal hydride battery 2…Positive plate 3… Negative plate 4... Separator 5...Electrolyte 6...Electrode group 8…Coating machine 9...Vacuum suction device 12…Battery cell 13…Battery case (integrated battery case) 13a…Positive electrode connection terminal 13b…Negative electrode connection terminal 14…Cover body 15…Electrolytic cell 16…Opening 17…Through hole 18…Partition wall 21…Positive electrode current collector 21a~21d…Coating area 21e~21i…Non - coating area 21j…Upper surface 21k…Lower surface 21l…Lead part 22…Positive electrode composite layer 22a…Rough side surface 22b…(Inside of the positive electrode composite layer) 22c…Dense side surface 22d…End part in the width direction W 25…Positive electrode composite paste 25e…Upper surface 25f…Lower surface 26…Positive electrode active material 27…Positive electrode current collector plate 31…Negative electrode current collector 37…Negative electrode current collector plate 81…Nozzle 82…Die 83…Nozzle 84…Pressing roller 85…Supporting member 85a…First support part 85b…Insertion part 85c…Connection part 85d…Second support part 86…Stage 91…Adsorption pad L…Length direction (coating direction) W…Width direction (short side direction) D…Thickness direction Wp…Coating width Ws…Reference coating width (in the width direction W) ΔW…Uneven width (of the end part of the positive electrode composite layer in the width direction W) V…Viscosity [mPa·s] L1…First layer L2…Second layer L3…Third layer P1…Point P2... Points P3... Points P4... Points

Claims

1. A positive electrode plate having a positive electrode current collector made of a plate-shaped porous metal and a positive electrode composite layer containing a positive electrode active material and filled in the positive electrode current collector, The negative electrode plate and Equipped with a separator, For each of the positive electrode current collectors, the packing density of the positive electrode active material on the dense side surface, which is one end in the thickness direction of the positive electrode composite layer, is greater than the packing density of the positive electrode active material on the rough side surface, which is the other end. The standard coating width Ws on the dense side is formed to be narrower than the coating width Wp of the positive electrode composite layer on the rough side surface. A secondary battery characterized in that the average width of the irregularities at the edges of the positive electrode composite layer in the short-side direction on the dense side surface is greater than the ΔW on the rough side surface.

2. The secondary battery according to claim 1, characterized in that the packing density difference is configured such that the packing density of the positive electrode active material gradually decreases from the dense side surface to the rough side surface.

3. The secondary battery according to claim 1 or 2, characterized in that the difference in filling density is 4% or more and 20% or less.

4. The secondary battery according to any one of claims 1 to 3, characterized in that when the positive electrode plate is divided into three equal layers in the thickness direction, there is a difference in the packing density of the active material between the dense-side surface layer and the coarse-side surface layer, with respect to the central layer, of 2% or more and 10% or less, respectively.

5. The relationship between the width of the irregularities ΔW at the edge of the positive electrode composite layer in the short-side direction of the dense surface and the reference coating width Ws in the short-side direction is ΔW / Ws≧0.016 A secondary battery according to claim 1, wherein the following conditions are met.

6. The secondary battery according to any one of claims 1 to 5, characterized in that the positive electrode current collector is made of a foam made of nickel or a nickel alloy.

7. The positive electrode plate comprises a positive electrode current collector made of a rectangular plate-shaped porous metal, a positive electrode composite layer containing a positive electrode active material filled in the positive electrode current collector, a negative electrode plate, and a separator. A method for manufacturing a nickel-metal hydride battery, wherein the positive electrode composite layer of the positive electrode plate has a difference in packing density with respect to the thickness direction of the positive electrode current collector, The process includes a coating step of applying a positive electrode composite paste containing a solvent for forming a positive electrode composite layer to one surface of the positive electrode current collector, In the coating process described above, the positive electrode composite paste is adjusted so that it does not fall off the positive electrode current collector due to gravity, and so that the packing density of the positive electrode active material in the positive electrode composite paste is higher in the lower vertical section than in the upper vertical section due to gravity. The lower reference coating width Ws is formed to be narrower than the upper positive electrode composite layer coating width Wp. A method for manufacturing a secondary battery, characterized in that the relationship between the unevenness width ΔW, which is the average width of the unevenness at the edge of the positive electrode composite layer in the short-side direction on the surface opposite to the coated side, and the standard coating width Ws in the short-side direction is adjusted so that ΔW / Ws ≥ 0.

016.

8. The method for manufacturing a secondary battery according to claim 7, characterized in that the adjustment is made by the viscosity of the positive electrode composite paste.

9. In the aforementioned coating process, the viscosity of the positive electrode composite paste is such that the shear rate is 10 [s] －１ A method for manufacturing a secondary battery according to claim 7 or 8, characterized in that the pressure is 200 [mPa·s] or more and 1000 [mPa·s] or less when [condition].

10. A method for manufacturing a secondary battery according to any one of claims 7 to 9, characterized in that it includes a transport step of using a vacuum suction device to pick up and transport the uppermost positive electrode plate, which is vertically above on which a plurality of positive electrode plates are stacked and placed.

11. The method for manufacturing a secondary battery according to claim 10, characterized in that the transport step involves placing the positive electrode plate such that the upper surface of the positive electrode plate vertically above becomes a rough surface in which the packing density of the positive electrode active material in the positive electrode composite layer is low, and transporting the rough surface by adsorption from vertically above using the vacuum adsorption device.

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