Secondary battery and method of manufacturing the same

Abstract

To improve an impregnation of an electrolyte of a positive electrode plate of a nickel hydride accumulator battery.SOLUTION: A nickel hydride accumulator battery comprises: a positive electrode plate 2 including a positive electrode collector made of a plate-like porous metals, and a positive electrode bonding layer containing a positive electrode active material and filled with the positive electrode collector; a negative electrode plate; and a separator. A plurality of concave parts 22e is provided onto a front surface of a positive electrode bonding layer 22 filled with the positive electrode plate, and a roughness part 22g having a roughness state as compared with the other filling part in a filling density of an active material of a part of a thickness direction just under a concave part 22e. Thus, by improving a wet property of an electrolyte 5 as a whole of the positive electrode plate 2, a secure of a battery capacitance and an improvement of an inner resistance (DC-IR) can be achieved.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a secondary battery and a method for manufacturing the secondary battery, and more particularly to a secondary battery and a method for manufacturing the secondary battery in which the penetration of an electrolyte into electrode plates during manufacturing is improved. [Background technology]

[0002] Electric vehicles (including hybrid vehicles) equipped with electric motors use power stored in secondary batteries to drive the motors. Among such secondary batteries, nickel-metal hydride batteries, for example, are widely used in vehicles because they are safe and capable of charging and discharging large currents.

[0003] For such secondary batteries, electrodes with thicker films for higher capacity and improved load characteristics are desired. In such secondary battery electrodes, it is necessary to effectively promote exchange between the active material and the electrolyte in order to utilize the active material of the electrode. For example, adding a fluorine-based binder to form an active material composite layer can bind the active material and form a stable active material composite layer. However, while fluorine-based binders have the advantage of a high binding rate, they also have the problem of segregating the binder on the electrode plate surface when the electrode plate is dried after coating, making it difficult for the electrolyte to penetrate the electrode.

[0004] Therefore, the invention disclosed in Patent Document 1 discloses the following electrode for a non-aqueous secondary battery. This invention discloses a non-aqueous secondary battery electrode having a specific average pore size, a mixture of an electrode active material, a thermoplastic binder, and a plasticizer, and a mixture of the electrode active material and the thermoplastic binder. 3 sec -1 Under a shear rate of 10 or more, the shear viscosity of the mixture is 1The electrode is extruded onto a metal substrate at a pressure of 0.1 MPa or less using an extruder. This method produces an electrode for a nonaqueous secondary battery having a specific average pore size by replacing the plasticizer with an electrolyte solution through extrusion molding. This method produces an electrode for a nonaqueous secondary battery, consisting of at least an electrode active material and a thermoplastic binder, with pores of 0.01 μm to 10 μm in size that allow the electrolyte solution to penetrate the electrode, and the average pore size dav is 0.1≦dav≦1 μm.

[0005] In such an electrode plate, the presence of pores allows for improved penetration of the electrolyte. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-348710 Summary of the Invention [Problem to be solved by the invention]

[0007] However, even if the pores allow the electrolyte to penetrate more easily, the active material is packed uniformly, so the electrolyte does not penetrate sufficiently from the surface of the electrode plate. In this application, the "amount of positive electrode active material per unit volume of the positive electrode plate" is referred to as the "packing density." The problem to be solved by the secondary battery and the method for manufacturing the secondary battery of the present invention is to improve the permeation of the electrolyte into the electrode plate. [Means for solving the problem]

[0008] In order to solve the above problems, the secondary battery of the present invention includes a positive electrode plate having a positive electrode current collector made of a plate-like porous metal, and a positive electrode composite layer containing a positive electrode active material and filled into the positive electrode current collector; a negative electrode plate; and a separator, wherein a plurality of recesses are provided on the surface of the positive electrode composite layer filled into the positive electrode plate, and the filling density of the active material in the inner portions of the recesses in the thickness direction is coarser than in other filled portions.

[0009] The packing density of the active material in the inner part of the recess in the thickness direction is preferably 5% or more lower than that of the other packed parts. The opening area of ​​the recess is 500 μm 2 ] or more, 90000[μm 2 ] or less, and the depth of the recess is 50 [μm] or more, and is a depth that does not penetrate the positive electrode mixture layer.

[0010] The plurality of recesses are formed on the surface of the positive electrode mixture layer, and each recess has a surface area of ​​100 mm 2 It is desirable to have at least one such facility per [location]. The average opening diameter of the pores of the positive electrode current collector is 300 [μm] or more and 600 [μm] or less, and the basis weight of the positive electrode mixture layer filled in the positive electrode current collector is 200 [g / m 2 ] or more, 400[g / m 2 ] or less is desirable.

[0011] Furthermore, the present invention provides a method for producing a secondary battery, which includes a positive electrode plate having a positive electrode current collector made of a plate-like porous metal and 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, wherein a plurality of recesses are formed on the surface of the positive electrode composite layer filled in the positive electrode plate, and the filling density of the active material in the inner portions of the recesses in the thickness direction is lower than that of other filled portions, the method being characterized in that the viscosity of a positive electrode composite paste forming the positive electrode composite layer is adjusted to be equal to or greater than 50 [mPa s] and equal to or less than 2000 [mPa s], and the method further includes a coating step of coating the positive electrode composite paste on the positive electrode current collector by single-sided coating, and a pressing step of compressing the positive electrode plate in the thickness direction so as to leave the recesses formed in the coating step.

[0012] The viscosity of the positive electrode mixture paste is preferably adjusted to 200 [mPa·s] or more and 1000 [mPa·s] or less. The average opening diameter of the pores of the positive electrode current collector is 300 [μm] or more and 600 [μm] or less, and the basis weight of the positive electrode mixture layer filled in the positive electrode current collector is 200 [g / m2 ] or more, 400[g / m 2 It is desirable to apply the positive electrode mixture paste so that the thickness is as follows:

[0013] The positive electrode mixture paste preferably contains carboxymethyl cellulose and sodium alginate. [Effects of the Invention]

[0014] In the secondary battery and the method for manufacturing the secondary battery of the present invention, the permeation of the electrolyte into the electrode plate can be improved. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view showing the external structure of a battery module of a nickel-metal hydride storage battery according to an embodiment of the present invention. [Figure 2] 1 is a perspective view including a partial cross-sectional structure of a portion of a battery module of a nickel-metal hydride storage battery according to an embodiment of the present invention. [Figure 3] 2 is a cross-sectional view of an electrode group provided in the nickel-metal hydride storage battery of the present embodiment. FIG. [Figure 4] 3 is a flowchart showing a manufacturing process of the nickel-metal hydride storage battery of the present embodiment. [Figure 5] 3 is a flowchart showing a manufacturing process of a positive electrode plate of the nickel-metal hydride storage battery according to the present embodiment. [Figure 6] 1 is a schematic diagram showing the coated surface of a positive electrode plate of a nickel-metal hydride storage battery according to an embodiment of the present invention. [Figure 7] 2 is a schematic diagram showing the surface opposite to the coated side of the positive electrode plate of the nickel-metal hydride storage battery of the present embodiment. FIG. [Figure 8] 1 is a schematic diagram showing a cross section in the width direction of a positive electrode plate of a nickel-metal hydride storage battery according to an embodiment of the present invention. [Figure 9] FIG. 2 is a schematic diagram showing the relationship between a positive electrode current collector and a coated positive electrode composite paste. [Figure 10]1A is a schematic diagram showing an enlarged view of a part of a widthwise cross section of a positive electrode plate of a nickel-metal hydride storage battery according to this embodiment after a coating process and before a shaping and pressing process, and FIG. 1B is a schematic diagram showing an enlarged view of a part of a widthwise cross section of a positive electrode plate of a nickel-metal hydride storage battery according to this embodiment after a shaping and pressing process. [Figure 11] 1 is an SEM photograph of a cross section of a positive electrode plate of an example. [Figure 12] 1 is an SEM photograph of a cross section of a positive electrode plate of a comparative example. [Figure 13] 10 is an SEM photograph of a cross section of a positive electrode plate of another comparative example. [Figure 14] 1 is a comparison table showing an example of the composition of a conventional positive electrode composite paste and an example of the composition of a positive electrode composite paste of the present embodiment. [Figure 15] FIG. 1 is a perspective view showing an example of a coating device according to an embodiment of the present invention. [Figure 16] 1A is a perspective view showing a coating step in the present embodiment, and FIG. 1B is a cross-sectional view showing an enlarged view of a position where a die nozzle applies a positive electrode composite paste to a positive electrode current collector. [Figure 17] (a) is a plan view showing the positional relationship between the nickel base material, the first supporting part, and the second supporting part, (b) is a cross-sectional view showing the state in which the nickel base material is supported by the first supporting part and the second supporting part before the paste is applied, and (c) is an enlarged cross-sectional view of (b). [Figure 18] FIG. 1 is a schematic diagram showing the coated surface of a positive electrode plate of a conventional nickel-metal hydride storage battery. [Figure 19] FIG. 1 is a schematic diagram showing the surface opposite to the coated side of a positive electrode plate of a conventional nickel-metal hydride storage battery. [Figure 20] 1 is a schematic diagram showing a cross section in the width direction of a positive electrode plate of a conventional nickel-metal hydride storage battery. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the secondary battery and the method for manufacturing the secondary battery of the present invention will be described using one embodiment of a nickel-metal hydride storage battery and a method for manufacturing the same with reference to FIGS. (Configuration of this embodiment) <Outline of this embodiment> As disclosed in Patent Document 1, a mixture of an electrode active material, a thermoplastic binder, and a plasticizer is extruded onto a metal substrate using an extruder. This process replaces the plasticizer with an electrolyte solution, producing an electrode for a nonaqueous secondary battery with a specific average pore size. However, the present inventors have developed a battery with low internal resistance (DC-IR) that not only has pores but also has a structure that allows the electrolyte solution 5 to easily penetrate.

[0017] Fig. 1 is a perspective view showing the external structure of a battery module of a nickel-metal hydride storage battery 1 of this embodiment. Fig. 2 is a perspective view including a partial cross-sectional structure of a part of the battery module of the nickel-metal hydride storage battery 1 of this embodiment. Fig. 3 is a cross-sectional view of an electrode group 6 provided in the nickel-metal hydride storage battery 1 of this embodiment.

[0018] 3, the nickel-metal hydride storage battery 1 of this embodiment includes a positive electrode plate 2 having a porous metal positive electrode current collector 21 made of plate-shaped foamed nickel and a positive electrode composite layer 22 containing a positive electrode active material and filled into the positive electrode current collector 21. A large number of positive electrode plates 2 and negative electrode plates 3 are stacked with separators 4 interposed therebetween to form an electrode group 6.

[0019] Fig. 18 is a schematic diagram showing the surface of the coated side of a positive electrode plate of a conventional nickel-metal hydride storage battery. Fig. 19 is a schematic diagram showing the surface opposite the coated side of a positive electrode plate of a conventional nickel-metal hydride storage battery. Fig. 20 is a schematic diagram showing a cross section in the width direction of a positive electrode plate of a conventional nickel-metal hydride storage battery. Conventionally, as shown in Figs. 18 to 20, positive electrode composite layer 22 has been formed with a generally uniform filling density of positive electrode active material, and its surface has been flat.

[0020] The average opening diameter O of the positive electrode current collector 21 of this embodiment is set to 300 μm or more and 600 μm or less. Here, the "average opening diameter O" is the median diameter (d50) measured by mercury intrusion porosimetry.

[0021] A positive electrode mixture paste 25 containing carboxymethyl cellulose (CMC) and sodium alginate is applied to the positive electrode current collector 21 to form a positive electrode mixture layer 22. The viscosity of the positive electrode mixture paste 25 is adjusted to 50 [mPa·s] or more and 2000 [mPa·s] or less, preferably 200 [mPa·s] or more and 1000 [mPa·s] or less, and the positive electrode mixture paste 25 is applied to the positive electrode current collector 21 by single-sided coating. At this time, the basis weight of the positive electrode mixture layer 22 filled into the positive electrode current collector 21 is 200 [g / m 2 ] or more, 400[g / m 2 ] is as follows.

[0022] Fig. 6 is a schematic diagram showing the coated surface 22a of the positive electrode plate 2 of the nickel-metal hydride storage battery 1 of this embodiment. Fig. 7 is a schematic diagram showing the surface 22c opposite to the coated side of the positive electrode plate 2 of the nickel-metal hydride storage battery 1 of this embodiment. Fig. 8 is a schematic diagram showing a cross section in the width direction W of the positive electrode plate 2 of the nickel-metal hydride storage battery 1 of this embodiment.

[0023] By carrying out the coating step (S13, see FIG. 5) under the above-described conditions, the surface area of ​​the coating side surface 22a of the positive electrode composite layer 22 filled in the positive electrode plate 2 is 100 [mm 2 One or more recesses 22e can be formed around the area .

[0024] The recess 22e has an opening area of ​​500 μm 2 ] or more, 90000[μm 2 ] or less, more preferably 2500 [μm 2 ] or less, and the depth of recess 22e is 50 [μm] or more, and is set to a depth that does not penetrate positive electrode mixture layer 22.

[0025] Furthermore, by compressing positive electrode composite layer 22 in the shaping and pressing step (S15), the packing density of the active material in the portion inside recess 22e in the thickness direction can be made 5% or more, more desirably 10% lower than that in the other packed portions of positive electrode composite layer 22. Moreover, this value is preferably 20% or less.

[0026] <Principle of this embodiment> FIG. 9 is a schematic diagram showing the relationship between positive electrode current collector 21 and positive electrode composite paste 25 applied thereto.

[0027] <Formation of recess 22e> The positive electrode current collector 21 of this embodiment is a porous body made of foamed nickel. The positive electrode current collector 21 has a skeletal structure 21n and pores 21o formed by the skeletal structure 21n. The pores 21o vary in size. For example, the opening diameter O of the pore 21o shown on the left side of FIG. 9 is O1, and the opening diameter O of the pore 21o shown on the right side is O2.

[0028] A positive electrode composite paste 25 with an adjusted viscosity V is applied to the positive electrode current collector 21. The positive electrode composite paste 25 then adheres to the ribs 21n and is retained between the ribs 21n due to the surface tension. A meniscus is formed depending on the magnitude of the surface tension. The formation of this meniscus also varies depending on the wettability of the positive electrode composite paste 25 and the ribs 21n. If the meniscus is smaller than a predetermined size, such as the opening diameter O2, the positive electrode composite paste 25 can be retained between the ribs 21n at the opening. On the other hand, if the opening diameter O is larger than the predetermined size, such as the opening diameter O1, the positive electrode composite paste 25 cannot be retained between the ribs 21n around the opening.

[0029] In this way, recesses 22e are formed in positive electrode composite material layer 22 at locations where opening diameter O is equal to or larger than a predetermined size. In the manufacturing method of the nickel-metal hydride storage battery 1 of this embodiment, when the positive electrode composite paste 25 is applied to the positive electrode current collector 21, the viscosity V [mPa·s] of the positive electrode composite paste 25 is adjusted to a relatively low value so that the recesses 22e are formed. That is, the viscosity V [mPa·s] is adjusted as a premise so that the applied positive electrode composite paste 25 does not fall downward from the positive electrode current collector 21 due to gravity. Within this range, the positive electrode composite paste 25 forms the recesses 22e due to surface tension in places where the opening area of ​​the positive electrode current collector 21 is relatively large. Note that the conditions for forming the recesses 22e include, in addition to the viscosity V [mPa·s], the configuration of the pores 21o of the positive electrode current collector, differences in wettability, the size and properties of the positive electrode active material particles and binder contained in the positive electrode composite layer, and the basis weight [g / m 2 ] and various other conditions.

[0030] For example, basis weight [g / m 2 The relationship between the average opening diameter O of the holes 21o of the positive electrode current collector 21 and the surface area of ​​the positive electrode current collector 21 is important. 2 ], and the average opening diameter O is suitably 300 to 600 [μm].

[0031] In other words, the basis weight is 400 [g / m 2 If the average opening diameter O is greater than or equal to 300 μm, the positive electrode composite paste 25 will be excessive on the surface of the positive electrode current collector 21, and the recesses 22 e will not be formed. If the average opening diameter O is less than 300 μm, the positive electrode composite paste 25 will not penetrate well into the positive electrode current collector 21, and the recesses 22 e will not be formed easily. In addition, the coating width Wp will be narrowed, making it difficult to control the coating position.

[0032] On the other hand, the basis weight is 200 [g / m 2 If the average opening diameter O is less than 600 μm, the amount of positive electrode composite paste 25 on the surface of positive electrode current collector 21 will be insufficient, and recesses 22 e will not be formed. If the average opening diameter O is 600 μm or more, the positive electrode composite paste will not remain within positive electrode current collector 21 during coating. In particular, in single-sided coating, the positive electrode composite paste may drip to the back surface, making it impossible to ensure the specified weight.

[0033] In this way, the basis weight [g / m 2When the surface area 22a of the coating layer 22, the average opening diameter O [μm], and the viscosity V [mPa·s] are appropriate, the recesses 22e are formed against gravity by surface tension not only on the surface 22a of the coating side but also on the surface 22c of the opposite side to the coating side. In other words, it is desirable that the recesses 22e are formed not only on the surface 22a of the coating side but also on the surface 22c of the opposite side to the coating side.

[0034] In this embodiment, by adjusting these factors while feeding back the state of formation of the recesses 22e, it is possible to stably form the desired recesses 22e. Based on these assumptions, adjusting the viscosity V [mPa·s] is the easiest and most practical method to implement on the manufacturing floor.

[0035] <Compression in the shaping and pressing process (S15)> Fig. 10(a) is a schematic diagram showing an enlarged view of a part of a cross section in the width direction W of the positive electrode plate 2 of the nickel-metal hydride storage battery 1 of this embodiment after the coating step (S13) and before the shaping and pressing step (S15). Fig. 10(b) is a schematic diagram showing an enlarged view of a part of a cross section in the width direction W of the positive electrode plate 2 of the nickel-metal hydride storage battery 1 of this embodiment after the shaping and pressing step (S15).

[0036] After forming the predetermined recesses 22e by the method described above, the portions other than the recesses 22e are compressed and crushed from the state shown in Fig. 10(a) in the molding and pressing step (S15). This forms dense portions 22h where the packing density of the positive electrode active material is high other than the recesses 22e, as shown in Fig. 10(b). In particular, compressed portions 22i where the packing density of the positive electrode active material is high are formed near the surface 22a on the coating side.

[0037] On the other hand, recesses 22e are not substantially affected by compression, and therefore, the portion of positive electrode mixture layer 22 inside recesses 22e in the thickness direction becomes sparse portion 22g where the positive electrode active material has a relatively low packing density.

[0038] <Major Effects of This Embodiment> 8, the positive electrode plate 2 of this embodiment has such a configuration, and therefore the packing density of the positive electrode active material in the portion inside the recess 22e in the thickness direction is low, and the electrolyte solution 5 easily penetrates into the positive electrode composite layer 22 through the highly breathable rough portion 22g. Note that although the recess 22e on the coated side surface 22a has been described, similar recesses 22e are also formed on the surface 22c opposite the coated side. In this case, too, the rough portion 22g is present in the portion inside the recess 22e in the thickness direction.

[0039] On the other hand, since the packing density of the positive electrode active material in the entire positive electrode mixture layer 22 is not reduced, the content of the positive electrode active material in the entire positive electrode mixture layer 22 is not reduced, and the battery capacity can be ensured. In this way, by improving the wettability of the electrolyte 5 over the entire positive electrode plate 2, it is possible to ensure battery capacity and improve the internal resistance (DC-IR).

[0040] The nickel-metal hydride storage battery 1 of this embodiment and its manufacturing method will be described in detail below. <Configuration of nickel-metal hydride battery 1> FIG. 1 is a perspective view showing the external structure of a nickel-metal hydride storage battery 1 according to this embodiment.

[0041] <Battery module> As shown in FIG. 1, the nickel-metal hydride battery 1 is configured as a battery module including multiple battery cells 12. The nickel-metal hydride battery 1 is a sealed battery with a rectangular plate-like appearance. It includes a battery case 13 that forms an integrated battery container capable of accommodating multiple (six in this case) battery cells 12, and a lid 14 that seals the opening of the battery case 13. The battery case 13 accommodates six battery cells 12 that are electrically connected in series. Power from these battery cells 12 is extracted from a positive electrode connection terminal 13a and a negative electrode connection terminal 13b provided on the battery case 13.

[0042] <Internal structure of nickel-metal hydride storage battery> Fig. 2 is a partial perspective view, including a cross-sectional structure, of a battery module of a nickel-metal hydride storage battery 1. As shown in Fig. 2, the battery case 13 and the lid 14 are made of polypropylene (PP) and polyphenylene ether (PPE), which are resin materials resistant to alkaline electrolyte. Inside the battery case 13, partition walls 18 are formed to separate the multiple battery cells 12, and the areas separated by these partition walls 18 become battery cases 15 for each battery cell 12. Inside the battery cases 15 thus separated, an electrode group 6 is housed together with an alkaline electrolyte solution 5, which is an aqueous electrolyte containing potassium hydroxide (KOH) as the main component.

[0043] Through holes 17 used to connect the battery cells 12 are formed in the upper part of the partition wall 18. Two connection protrusions, one protruding from the upper part of the positive current collector plate 27 and the other protruding from the upper part of the negative current collector plate 37, are welded to each other through the through holes 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 outer sides 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 FIG. 1 ) above the longitudinal end of the battery case 13. The positive electrode connection terminal 13a is welded to the connection protrusion of the positive current collector plate 27. The negative electrode connection terminal 13b is welded to the connection protrusion of the negative current collector plate 37. The total output of the electrode group 6 thus connected in series, that is, the plurality of battery cells 12, is taken out from the positive electrode connection terminal 13a and the negative electrode connection terminal 13b.

[0044] <Electrode group 6> Fig. 3 is a cross-sectional view of an electrode group 6 provided in the nickel-metal hydride storage battery 1 of this embodiment. As shown in Fig. 3, the electrode group 6 is configured by stacking rectangular positive electrode plates 2 and negative electrode plates 3 with separators 4 interposed therebetween. In this case, the direction in which the positive electrode plates 2, negative electrode plates 3, and separators 4 are stacked is the thickness direction D.

[0045] The positive electrode plate 2 and the negative electrode plate 3 of the electrode group 6 have lead portions that protrude from opposite sides in the surface direction of the electrode plate. A positive electrode current collector plate 27 is joined to the side edge of the lead portion 211 of the positive electrode plate 2 (see FIGS. 6 and 7) by spot welding or the like. Furthermore, 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.

[0046] <Configuration of positive electrode plate 2> 6 to 10, the configuration of the positive electrode plate 2 will be described. The positive electrode plate 2 has a positive electrode current collector 21 and a positive electrode mixture layer 22 filled in the positive electrode current collector 21. The positive electrode mixture layer 22 has a positive electrode active material and additives (conductive material, binder, thickener, etc.).

[0047] <Positive electrode current collector 21> As shown in FIGS. 6 to 8, the positive electrode current collector 21 is formed in the shape of a rectangular plate made of a nickel foam, which is a three-dimensional porous metal body that serves as a substrate.

[0048] The positive electrode current collector 21 is made of foamed nickel, which is a type of foam metal. Foamed nickel has many pores inside and can be easily compressed. There are no particular restrictions on the method for producing foamed nickel; for example, foamed nickel can be produced by plating the skeleton surface of foamed urethane with nickel and then burning the foamed urethane.

[0049] As shown in FIG. 9, the positive electrode current collector 21 manufactured in this manner has a three-dimensional network bone portion 21n. A large number of holes 21o are formed in the gaps between the three-dimensional network bone portion 21n. The holes 21o are interconnected. The sizes of the holes 21o vary. For example, the opening diameter O of the hole 21o shown on the left side of FIG. 9 is a diameter O1, and the opening diameter O of the hole 21o shown on the right side is a diameter O2. This opening diameter O is measured, for example, by mercury intrusion porosimetry.

[0050] Because of this structure, positive electrode current collector 21 is easily crushed by compression. The peripheral portion of positive electrode current collector 21 is crushed, increasing its density and strength, and functions as a frame that maintains the shape of positive electrode current collector 21. Furthermore, the porous structure of the peripheral portion is crushed, reducing its breathability, so that the absorption of electrolyte solution 5 from the surface is poorer than in the central portion. Positive electrode current collector 21 functions as a carrier that supports positive electrode mixture layer 22 in the space formed by its three-dimensional network-like framework, and as a current collector that collects current from the positive electrode active material in positive electrode mixture layer 22.

[0051] 6 and 7, the lead portion 21l is formed by welding a metal material such as an iron material to the center of one long side of the rectangular positive electrode current collector 21 in the length direction L. The lead portion 21l is provided in the center of the thickness direction D of the positive electrode current collector 21.

[0052] The lead portion 21l is formed by welding a metal member such as an iron material to a frame portion that is compressed along one long side of the positive electrode current collector 21 to increase its density and strength. 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 via a connection protrusion protruding from its upper portion.

[0053] In this embodiment, the thickness of the positive electrode current collector 21 before the coating step (S13) is preferably 0.5 mm or more and 1.0 mm or less. The foamed nickel to be used preferably has an average pore size of 300 μm or more and 600 μm or less.

[0054] <Positive electrode mixture paste 25> Positive electrode mixture paste 25 that becomes positive electrode mixture layer 22 contains positive electrode active material particles mainly composed of nickel hydroxide, a conductive material made of cobalt (Co), a thickener, a binder, etc., and a solvent such as water.

[0055] FIG. 14 is a comparison table showing an example of the composition of a conventional positive electrode composite paste and an example of the composition of positive electrode composite paste 25 of this embodiment. As shown in FIG. 14 , the composition (wt%) of the positive electrode composite paste 25 of this embodiment, excluding the water solvent, is as follows: nickel hydroxide as the positive electrode active material is preferably 85 (wt%) or more and 95 (wt%) or less; cobalt (Co) as the conductive material is preferably 5 (wt%) or more and 10 (wt%) or less; zinc oxide for potential adjustment is preferably 0.5 (wt%) or more and 1.5 (wt%) or less; yttrium oxide is preferably 0.5 (wt%) or more and 1.5 (wt%) or less; carboxymethyl cellulose (CMC) as the thickener is preferably 0.01 (wt%) or more and 0.2 (wt%) or less; and sodium alginate as the thickener is preferably 0.01 (wt%) or more and 0.2 (wt%) or less. As the binder, it is desirable that the fluorine-based binder be present in an amount of 0.05 (wt%) or more and 0.3 (wt%) or less.

[0056] Here, a "fluorine-based binder" exhibits favorable performance as a binder, but has the problem of segregation on the electrode plate surface during drying. In this embodiment, this problem is solved by promoting the penetration of the electrolyte solution 5 from the recesses 22e, making it possible to use a fluorine-based binder. This will be described in more detail later.

[0057] The positive electrode composite paste 25 of this embodiment is prepared by mixing a positive electrode active material, a conductive material, a binder, a thickener, and the like in a solvent such as water to form a paste. The viscosity V [mPa·s] is adjusted by the solvent and thickener. The value is calculated at a shear rate of 10 [s -1 The viscosity V [mPa·s] is preferably 50 [mPa·s] or more and 2000 [mPa·s] or less, and more preferably 200 [mPa·s] or more and 1000 [mPa·s] or less. In this embodiment, it is adjusted to, for example, 500 [mPa·s].

[0058] <Features of the Positive Electrode Composite Paste 25 of the Present Embodiment> As shown in Figure 11, the conventional cathode composite paste does not contain sodium alginate as a thickener. This means that the viscosity [mPa·s] is not adjusted. It also differs in that it does not contain polyvinylidene fluoride (PVDF), a fluorine-based binder. This results in a lower binding strength.

[0059] <Cathode active material> The positive electrode active material may be a particulate material containing nickel oxide, such as nickel hydroxide or nickel oxyhydroxide, as a main component.

[0060] <Conductive material> The conductive material is a metal or a metal compound, such as metallic cobalt (Co), cobalt monoxide (CoO), or a cobalt oxyhydroxide (CoOOH), which coats the surface of the nickel oxide. Cobalt oxyhydroxide, which has high conductivity, is preferred because it forms a conductive network within the positive electrode and increases the utilization rate of the positive electrode.

[0061] <Thickener> Suitable thickeners include carboxymethyl cellulose (CMC) and sodium alginate. Other examples include glucose-based thickeners such as xanthan gum and acrylic thickeners such as sodium acrylate. In particular, in the positive electrode composite paste 25 of this embodiment, sodium alginate plays an important role in forming the recesses 22e.

[0062] <Binding material> The binder contains a fluorine-based binder. Examples of the fluorine-based binder include organic solvent-based polyvinylidene fluoride (PVDF) and aqueous dispersions. Fluorine-based binders have good binding properties, but tend to segregate on the surface of positive electrode mixture layer 22. This embodiment is configured to facilitate penetration of electrolyte solution 5 into positive electrode mixture layer 22 even when such segregation occurs. Therefore, this embodiment can effectively utilize fluorine-based binders that tend to segregate.

[0063] Further examples of binders include latex-based binders such as Lubron (a registered trademark of Daikin Industries, Ltd.) and polyethylene oxide (PEO). <Solvent> In this embodiment, water (H2O) is used as the solvent. The solvent, together with a thickener, is used to adjust the viscosity of positive electrode composite paste 25. The amount of the solvent added is adjusted taking into consideration the formation of recesses 22e.

[0064] <Positive electrode composite layer 22> The above-described positive electrode composite paste 25 is applied to positive electrode current collector 21 in a coating step (S13), and then passes through a drying step (S14) and a shaping and pressing step (S15) to form positive electrode composite layer 22. Details will be described later.

[0065] <Negative electrode plate 3> The negative electrode plate 3 includes a rectangular plate-shaped negative electrode current collector 31 made of punched metal or the like. The negative electrode current collector 31 functions as both a mechanical substrate and a current collector that collects current from the negative electrode active material. A hydrogen storage alloy (MH) is also coated on the negative electrode current collector 31. The type of hydrogen storage alloy is not particularly limited, but examples include an alloy of nickel and misch metal, a mixture of rare earth elements, or an alloy in which part of the alloy is replaced with a metal such as aluminum, cobalt, or manganese. The negative electrode plate 3 is coated with a negative electrode composite paste. The negative electrode composite paste is prepared by adding a thickener such as carbon black and a binder such as a styrene-butadiene copolymer to the 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 punched metal, followed by drying, rolling, and cutting.

[0066] <Separator 4> The separator 4 is a nonwoven fabric of an olefin resin such as polypropylene, or a nonwoven fabric that has been subjected to hydrophilic treatment such as sulfonation as required.

[0067] The positive electrode plate 2, the negative electrode plate 3 and the separator 4 are used to manufacture a battery module. <Electrolyte 5> The electrolyte 5 is held in 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 containing potassium hydroxide (KOH) as a solute.

[0068] <Nickel-metal hydride battery 1 manufacturing process> Fig. 4 is a flowchart showing the manufacturing process of the nickel-metal hydride storage battery 1 of this embodiment. Next, a manufacturing method of the nickel-metal hydride storage battery 1 of this embodiment configured as described above will be described with reference to Fig. 4. The manufacturing process of the nickel-metal hydride storage battery 1 comprises a source step (S1), an electrode group manufacturing step (S2), an electrode group assembling step (S3), a liquid injection step (S4), a sealing step (S5), and an inspection step (S6).

[0069] In the source step (S1), the positive electrode plate 2, negative electrode plate 3, and separator 4, which are battery elements, are each prepared. In the electrode assembly manufacturing step (S2), the positive electrode plate 2, negative electrode plate 3, and separator 4 manufactured in the source step (S1) are stacked, and a positive electrode current collector plate 27 and a negative electrode current collector plate 37 are welded to manufacture an electrode assembly 6 as shown in FIG. 3. In the electrode assembly assembling step (S3), the electrode assembly 6 manufactured in the electrode assembly manufacturing step (S2) is housed in each battery case 15 of a battery case 13, which is an integrated battery case, as shown in FIG. 2. Then, the electrode groups 6 housed in each battery case 15 are electrically connected by welding or the like, and a positive electrode connection terminal 13a and a negative electrode connection terminal 13b (see FIG. 1) are attached. In the liquid injection step (S4), the electrolyte 5 is injected into each battery case 15 of the battery case 13. In the sealing step (S5), the lid 14 is attached to the battery case 13 into which the liquid has been poured in the liquid pouring step (S4), and the battery case 13 is sealed. This completes the assembly of the nickel-metal hydride storage battery 1, which is the battery module of this embodiment. In the inspection step (S6), the nickel-metal hydride storage battery 1 thus assembled is subjected to initial charging, aging, internal resistance (DC-IR) inspection, OCV inspection, self-discharge inspection, etc. Only those batteries that pass these tests become the nickel-metal hydride storage battery 1 battery module as a product.

[0070] <Manufacturing process of positive electrode plate 2> Fig. 5 is a flowchart showing the manufacturing process of the positive electrode plate of the nickel-metal hydride storage battery of this embodiment. Next, the manufacturing process of the positive electrode plate 2 will be described in detail with reference to Fig. 5. This manufacturing process of the positive electrode plate 2 is a step that forms part of the source process (S1) of the nickel-metal hydride storage battery 1.

[0071] The manufacturing process of the positive electrode plate includes a positive electrode current collector manufacturing step (S11), a positive electrode composite paste manufacturing step (S12), a coating step (S13), a drying step (S14), a shaping and pressing step (S15), and a positive electrode composite paste 25 preparation step (S16).

[0072] <Positive electrode current collector manufacturing process (S11)> First, the positive electrode current collector manufacturing step (S11) is a step of manufacturing the positive electrode current collector 21. First, a positive electrode current collector 21 of a predetermined size is cut out from a long thin sheet of nickel foam in a cutting process. Next, the peripheral portion of the positive electrode current collector 21, which has been shaped to a predetermined thickness in a shaping and pressing process, is compressed to be shaped to a predetermined length and width. The peripheral portion of the shaped positive electrode current collector 21 is compressed and crushed to increase its density. As the density increases, the mechanical strength increases and the frame of the positive electrode current collector 21 maintains its shape. Furthermore, when this peripheral portion is compressed and crushed, the spaces in the porous nickel foam are crushed, reducing its breathability and making it difficult for the electrolyte 5 to be absorbed.

[0073] A lead portion 21l as shown in FIGS. 6 and 7 is welded to the center of one long side of the peripheral edge of this positive electrode current collector 21. <Positive electrode composite paste manufacturing process (S12)> In the positive electrode composite paste production step (S12), the above-described positive electrode composite paste 25 is produced. The positive electrode composite paste 25 is produced by mixing positive electrode active material particles, a conductive material, a binder, a thickener, and the like with a solvent, etc., to form a paste having a predetermined viscosity V [mPa s].

[0074] <Coating process (S13)> In the coating step (S13), positive electrode composite paste 25 produced in the positive electrode composite paste production step (S12) is applied to positive electrode current collector 21 produced in the positive electrode current collector production step (S11).

[0075] Fig. 15 is a perspective view showing an example of a coating device in this embodiment, and Fig. 16(a) is a perspective view showing a coating step in this embodiment. <Coating machine 8> As shown in FIG. 15, the coater 8 that applies the positive electrode composite paste 25 to the positive electrode current collector 21 includes a die nozzle 81 that applies the positive electrode composite paste 25 to the positive electrode current collector 21, a support member 85, and a stage 86.

[0076] <Die Nozzle 81> The die nozzle 81 includes a die 82 and a nozzle 83. The die 82 stores, at high pressure, the positive electrode composite paste 25 supplied from a supply unit (not shown) such as a tank through a supply pipe. The nozzle 83 has a discharge port at its tip that faces the upper surface of the positive electrode current collector 21 (in this embodiment, the surface on the side of the coarse side surface 22a of the positive electrode composite 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 transverse width W of the positive electrode current collector 21) and has discharge ports defined therein corresponding to the application regions 21a to 21d. The nozzle 83 discharges the positive electrode composite paste 25 onto the upper surfaces 21j of the application regions 21a to 21d. The positive electrode composite paste 25 discharged from the discharge port flows down until it reaches the upper surface 21j.

[0077] When the die nozzle 81 ejects the positive electrode composite paste 25 onto the upper surface 21j of the positive electrode current collector 21, the die nozzle 81 is provided with a pressure roller 84 in an area on the side of the nozzle 83 where the positive electrode composite paste 25 is not applied. The pressure roller 84 comes into contact with the upper surface 21j immediately before the nozzle 83 applies the positive electrode composite paste 25 to the upper surface 21j, and presses the positive electrode current collector 21 toward the support member 85. In this way, the pressure roller 84 removes any undulations in the positive electrode current collector 21, and keeps the distance between the nozzle 83 and the upper surface 21j constant.

[0078] <Support member 85> Support member 85 supports application regions 21a to 21d from the lower surface 21k side until positive electrode composite paste 25 is applied to upper surface 21j of positive electrode current collector 21 by nozzle 83.

[0079] Fig. 17(a) is a plan view showing the positional relationship between the nickel base material, the first support part, and the second support part. Fig. 17(b) is a cross-sectional view showing the nickel base material supported by the first support part and the second support part before the paste is applied. Fig. 17(c) is an enlarged cross-sectional view of (b).

[0080] As shown in FIGS. 17(a) to 17(c), the support member 85 includes first support portions 85a, insertion portions 85b, and connecting portions 85c. The first support portions 85a contact and support each of the application regions 21a to 21d from the lower surface 21k side. The insertion portions 85b are provided between adjacent first support portions 85a. The connecting portions 85c connect the first support portions 85a that are spaced apart from each other in the second direction Y by the insertion portions 85b (see FIG. 15). The support member 85 has an overall comb shape.

[0081] <First support part 85a> Four first support portions 85a are provided corresponding to the application regions 21a-21d, and each first support portion 85a extends in the first direction X and is spaced apart and parallel to one another. In each first support portion 85a, the support surface that supports the application regions 21a-21d may, for example, be configured as a flat surface that can provide stable support and that easily slides against the undersurfaces 21k of the application regions 21a-21d. This makes it easier for the first support portions 85a to come out from under the application regions 21a-21d.

[0082] The tip of each of the first support portions 85a opposite to the connecting portion 85c connecting the first support portions 85a is located at least below the pressure roller 84. This allows each of the first support portions 85a to firmly clamp the positive electrode current collector 21 in cooperation with the pressure roller 84. More preferably, the tip of each of the first support portions 85a may have a length that allows it to be located below the nozzle 83. That is, the first support portions 85a may be configured to contact and support the lower surfaces 21k of the application regions 21a to 21d until the positive electrode composite paste 25 permeates from the upper surface 21j to the lower surface 21k of the positive electrode current collector 21. This allows the first support portions 85a to support the lower surfaces 21k of the application regions 21a to 21d until they are immediately before coming into contact with the permeated positive electrode composite paste 25.

[0083] <Insertion portion 85b> The insertion portion 85b located between the adjacent first support portions 85a is a slit penetrating in the thickness direction D, extends in the first direction X, and has an open end below the nozzle 83.

[0084] <Second support part 85d> 17(c), the support member 85 is a member disposed between the die nozzle 81 and the stage 86. The insertion portions 85b of the support member 85 are configured so that second support portions 85d provided on the stage 86 are inserted therethrough, and the second support portions 85d can support the lower surfaces 21k of the non-coated regions 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 that allows the second support portions 85d to be inserted therethrough and is slightly wider than the width of the second support portions 85d.

[0085] Die nozzle 81 and support member 85 are connected via a connecting mechanism (not shown) including a connecting member or the like, and move synchronously in the movement direction indicated by the arrow, which is one of first directions X, relative to positive electrode current collector 21. In other words, positive electrode current collector 21 and stage 86 do not move, and die nozzle 81 and support member 85 move in the movement direction indicated by the arrow relative to positive electrode current collector 21 and stage 86.

[0086] <Stage 86> The stage 86 is arranged so that the support member 85 and the die nozzle 81 synchronized with the support member 85 are movable in the first direction X. The stage 86 includes a second support portion 85d on the support surface of the support member 85. The second support portion 85d is inserted into the insertion portion 85b of the support member 85, and supports the lower surface 21k of the positive electrode current collector 21 at its tip surface. As an example, the second support portion 85d has a length corresponding to the first direction X of the positive electrode current collector 21 to be placed thereon (the length of the non-coated regions 21e-21i in the first direction X). As an example, the support surface of the second support portion 85d that supports the non-coated regions 21e-21i may be configured as a flat surface that is not slippery relative to the lower surface 21k of the non-coated regions 21e-21i. This prevents the positive electrode current collector 21 from being dragged in the movement direction indicated by the arrow of the support member 85 and moving in the same direction.

[0087] 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 application regions 21a to 21d are supported by the first support portion 85a, and the lower surfaces 21k of the non-application regions 21e to 21i are supported by the second support portion 85d. The die nozzle 81 and the support member 85 then move in the direction indicated by the arrow 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 where the positive electrode composite paste 25 has been applied, only the lower surfaces 21k of the non-application regions 21e to 21i are supported by the second support portion 85d. The removal of the first support portion 85a creates a gap between the lower surfaces 21k of the application regions 21a to 21d and the stage 86, preventing the positive electrode composite paste 25, which has permeated to the lower surface 21k of the positive electrode current collector 21, from contacting the stage 86. Therefore, recesses 22e are also formed in a non-contact manner on surface 22c of positive electrode composite layer 22 opposite the coated side.

[0088] 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 guide mechanism for the support member 85 relative to the stage 86 can also be provided in a location other than the insertion portion 85b and the insertion portion 85b.

[0089] 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 in the direction indicated by the arrow relative to the positive electrode current collector 21. Therefore, there is a risk that the positive electrode current collector 21 will be dragged and moved by the movement of the support member 85 in the direction indicated by the arrow. Therefore, the second support portion 85d is provided with a holding means that holds 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, and holds the positive electrode current collector 21 on the second support portion 85d.

[0090] <Coating procedure> Fig. 16(b) is an enlarged cross-sectional view of the position where die nozzle 81 applies positive electrode composite paste 25 to positive electrode current collector 21. The coating step (S13) is carried out using coater 8 as described above. The coating procedure will be described with reference to Figs. 16(a) and 16(b).

[0091] As shown in FIGS. 16(a) and 16(b), the die nozzle 81 and the support member 85 move synchronously in the direction indicated by the arrows. As a result, the first support portion 85a of the support member 85 is sequentially retracted from below the upper surface 21j of each of the application regions 21a to 21d. After this, the positive electrode composite paste 25 permeates from the upper surface 21j to the lower surface 21k. This prevents the positive electrode composite paste 25 on the lower surface 21k from contacting the first support portion 85a. That is, after the positive electrode composite paste 25 is applied, only the non-application regions 21e to 21i of the positive electrode current collector 21 are supported by the second support portion 85d of the stage 86.

[0092] Positive electrode current collector 21 is coated with positive electrode composite paste 25 through the above-described steps. <Positive electrode composite paste 25 in coating process (S13)> In the coating step (S13), as described above, die nozzle 81 applies positive electrode composite paste 25 to positive electrode current collector 21. At this time, the amount of positive electrode composite paste 25 discharged is set to 200 [g / m 2 ] or more, 400[g / m 2 ] and the setting value will be adjusted within the range below.

[0093] 16(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 with a coating width Wp on the upper surface 21j of the positive electrode current collector 21, as shown in FIGS. 6 and 7. The coated positive electrode composite paste 25 permeates into the positive electrode current collector 21. At this time, due to the viscosity V [mPa s], surface tension, and wettability of the positive electrode composite paste 25, the width in the width direction W gradually decreases as the positive electrode composite paste 25 permeates downward from the coating width Wp due to gravity.

[0094] As shown in FIG. 6, the coated positive electrode composite paste 25 is applied to a coating width Wp. At this time, the end 22d in the width direction W is not a straight line along the length direction L, but rather has random, wavy irregularities 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 the irregularities at this time is defined as the irregularity width ΔW. Here, the coating width Wp and the reference coating width Ws are the locus of a straight line averaging such irregularity width ΔW.

[0095] <Recess 22e> 6, recesses 22e are randomly formed on the entire surface 22a of the coating side of positive electrode composite layer 22. The recesses 22e are formed on the surface 22a of the coating side of positive electrode composite layer 22 within a surface area of ​​100 mm 2 ] and produce it in at least one location per

[0096] The opening area of ​​each recess 22e is 500 μm 2 ] or more, 90000[μm 2Preferably, the thickness is 2500 [μm] or less. 2 ] is as follows. That is, the opening diameter O is manufactured to be approximately 22 μm or more and 300 μm or less, and more preferably 50 μm or less.

[0097] 10, recesses 22e have a depth Dh of 50 μm or more, provided that the depth does not penetrate positive electrode composite material layer 22. 7 is a schematic diagram showing surface 22c opposite to the coated side of positive electrode composite layer 22 of positive electrode plate 2 of nickel-metal hydride storage battery 1 of this embodiment. As shown in Fig. 7, recesses 22e are formed on surface 22c opposite to the coated side due to the surface tension of positive electrode composite paste 25, similar to surface 22a on the coated side.

[0098] <Drying process (S14)> In the drying step (S14), the positive electrode composite paste 25 applied to the positive electrode current collector 21 in the application step (S13) is dried by, for example, hot air, cold air, infrared radiation, or the like to evaporate the solvent and harden the positive electrode composite paste 25, thereby forming the positive electrode composite layer 22.

[0099] <Shaping and pressing process (S15)> In the shaping and pressing step (S15), after the positive electrode composite paste 25 has been hardened in the drying step (S14) to form the positive electrode composite layer 22, the positive electrode plate 2 is pressed to a predetermined thickness by a roller press (not shown) and its surface shape is adjusted. This corresponds to the pressing step of the present invention.

[0100] As shown in FIG. 10(a), immediately after the coating step (S15), the packing density of the positive electrode active material in the positive electrode composite layer 22 is generally uniform. Then, in the drying step (S14), the fluorine-based binder segregates on the surface, increasing the packing density of the positive electrode active material across the entire surface. Then, in the shaping and pressing step (S15), the positive electrode plate 2 is compressed in the thickness direction D from the state shown in FIG. 10(a), and the overall thickness of the positive electrode plate 2 is crushed and reduced. At this time, as shown in FIG. 10(b), the compression width Dp is smaller than the depth Dh of the recesses 22e. Therefore, the portions other than the recesses 22e are compressed under the compressive force. On the other hand, the compressive force is hardly exerted on the bottoms 22f of the recesses 22e. As a result, the portions other than the recesses 22e and the portion directly below them to the surface 22c opposite the coating side are compressed to form a dense portion 22h with a relatively high packing density of the positive electrode active material. In particular, the surface 22a on the coated side that receives the direct compressive force and the portion close to the surface 22c opposite the coated side become compressed portions 22i that have a high packing density due to the segregation of the fluorine-based binder, as well as a high packing density of the positive electrode active material.

[0101] On the other hand, the area from directly below recess 22e to surface 22c opposite the coated side receives almost no compressive force, so the packing density of the positive electrode active material does not change, and rough portion 22g is formed, where the packing density of the positive electrode active material is relatively lower than that of the surrounding area. Note that although surface 22a on the coated side has been described in detail here, the inside of recess 22e in the thickness direction on surface 22c opposite the coated side also similarly becomes rough portion 22g, where the packing density of the positive electrode active material is relatively lower than that of the surrounding area.

[0102] <Preparation of Positive Electrode Composite Paste 25 (S16)> In the coating step (S13), as described above, recesses 22e are formed on the surface 22a on the coating side as a target. In the shaping and pressing step (S15), the portions other than the recesses 22e are compressed. Therefore, when the shaping and pressing step (S15) is completed, the number, size, depth, etc. of the recesses 22e of the completed positive electrode plate 2 are inspected and compared with the design values ​​to inspect whether the positive electrode composite layer 22 is properly configured. If the inspection result shows that the positive electrode composite layer 22 is not proper (S16: NO), the process returns to the positive electrode composite paste manufacturing step (S11) again. Then, the viscosity V [mPa·s] of the positive electrode composite paste 25 and other shear rates [s -1 If positive electrode mixture layer 22 is suitable (S16: YES), the product is completed.

[0103] The adjustment of the positive electrode composite paste 25 (S16) does not necessarily have to be performed all the time, but can be performed for each production lot whose composition changes, for example. This completes the manufacturing process for the positive electrode plate 2. After that, the process proceeds to the electrode assembly manufacturing process (S2), in which 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 the negative electrode current collector plate 37 are welded together to manufacture the electrode assembly 6.

[0104] (Experimental Example of the Present Embodiment) An example of the positive electrode plate 2 of this embodiment as described above will be explained in comparison with Comparative Examples 1 and 2, which were prepared under different conditions. The conditions for the examples were a positive electrode composite paste 25 having the composition shown in FIG.

[0105] <Positive electrode current collector 21> The positive electrode current collector 21 used was the same as in Example, Comparative Example 1, and Comparative Example 2. That is, it was made of foamed nickel, and the average inner diameter of the pores 21o was 450 μm (d50).

[0106] <Basis weight [g / m 2 ]> In addition, the coating weight is 315 [g / m 2 ] and the same value.

[0107] <Positive electrode mixture paste 25> Next, the positive electrode composite paste 25 is subjected to a shear rate of 10 [s -1 In Comparative Example 1, the same positive electrode composite paste 25 as in the Examples was used. On the other hand, in Comparative Example 2, the positive electrode composite paste 25 was applied at a shear rate of 10 [s -1 ], the viscosity was set to V = 2500 [mPa·s].

[0108] <Thickener> Regarding the thickener, carboxymethyl cellulose (CMC) and sodium alginate were added as thickeners in Examples, whereas in Comparative Example 1, only carboxymethyl cellulose (CMC) was used, and no sodium alginate was added.

[0109] In Comparative Example 2, carboxymethyl cellulose (CMC) and sodium alginate were added as thickeners, as in the Examples. The experiment was carried out under these conditions.

[0110] <Result> Fig. 11 is an SEM photograph of a cross section of the positive electrode plate 2 of Example. Fig. 12 is an SEM photograph of a cross section of the positive electrode plate 2 of Comparative Example 1. Fig. 13 is an SEM photograph of a cross section of the positive electrode plate 2 of Comparative Example 2.

[0111] In the example, the recesses 22e were clearly observed, whereas in the comparative examples 1 and 2, the recesses 22e were not formed. <Evaluation> In Comparative Example 1, which had the same viscosity V [mPa·s] as the Examples but did not contain "sodium alginate," no recesses 22e were formed. This revealed that "sodium alginate" plays an important role in the formation of recesses 22e.

[0112] Although "sodium alginate" was added, in Comparative Example 2 where the viscosity V [mPa·s] was set to 2500, the recesses 22e were not formed. It was found that the viscosity V [mPa·s] has an important effect on the formation of the recesses 22e. In other words, it was revealed that if the viscosity is too high, the recesses 22e cannot be formed.

[0113] The positive electrode current collector 21 has a smaller weight per unit area than conventional current collectors. Therefore, the weight per unit area is 315 g / m 2 It was found that the position before and after ] was appropriate. It was found that the average inner diameter of the holes 21o of the positive electrode current collector 21 is appropriate when it is about 450 μm (d50).

[0114] However, even with the same viscosity, the type of binder and other factors can have a significant effect on whether or not the recesses 22e are formed. Therefore, uniform conditions cannot be set, and a certain amount of trial and error is required. However, since adjusting the viscosity V [mPa·s] covers a wide range of differences in other conditions, it is fully possible for a person skilled in the art to set the conditions.

[0115] The present inventors have conducted many such experiments under different conditions and identified conditions suitable for forming the recesses 22e described above. (Action of this embodiment) The internal resistance (DC-IR) was measured and compared for an example of a nickel-metal hydride storage battery 1 having a positive electrode plate 2 with a recess 22e formed therein as shown in Figure 8 and a comparative example of a nickel-metal hydride storage battery 1 having a conventional positive electrode plate 2 without a recess 22e as shown in Figure 20.

[0116] The DC-IR measurement method involves charging the battery until the state of charge (SOC) reaches 50% of its capacity. After a 10-minute rest, the battery is discharged at 10A for 10 seconds. After a 1-minute rest, the battery is discharged at 50A for 10 seconds. The DC-IR is calculated from the slope of the plot of each current value versus the voltage at 10 seconds.

[0117] As a result, it was confirmed that the example using the positive electrode plate 2 of this embodiment had a DC-IR reduction of approximately 1% compared to the comparative example. (Effects of this embodiment) (1) In the nickel-metal hydride storage battery and the manufacturing method thereof according to the present embodiment, the penetration of the electrolyte 5 into the positive electrode plate 2 can be improved.

[0118] (2) As shown in FIG. 8, electrolyte 5 easily permeates into positive electrode composite layer 22 from coarse portion 22g, which has a low filling density of the positive electrode active material directly below recess 22e and is highly breathable. (3) On the other hand, since the packing density of the positive electrode active material in the entire positive electrode mixture layer 22 is not reduced, the content of the positive electrode active material in the entire positive electrode mixture layer 22 is not reduced, and the battery capacity can be ensured.

[0119] (4) By improving the wettability of the electrolyte 5 across the entire positive electrode plate 2, it is possible to ensure battery capacity and improve the internal resistance (DC-IR). (5) In the manufacture of such nickel-metal hydride storage batteries 1, even if the lot changes, the recesses 22e can be formed accurately by adjusting the viscosity V [mPa·s].

[0120] (6) The packing density of the active material in the portion directly below the recess 22e in the thickness direction is 20% or more lower than that in the other packed portions, so that the absorption of the electrolyte solution 5 can be effectively improved in the recess 22e.

[0121] (7) The opening area of ​​the recess 22e is set to 2500 [μm 2 ] or more, 90000[μm 2 ] or less, and the depth of recess 22e is 50 [μm] or more and is a depth that does not penetrate positive electrode mixture layer 22. Therefore, recess 22e can effectively improve absorption of electrolyte solution 5.

[0122] (8) The plurality of recesses 22e are formed on the surface 22a of the coating side of the positive electrode composite layer 22, and each recess has a surface area of ​​100 mm 2 Therefore, the absorption of the electrolyte 5 can be effectively improved in the recess 22e.

[0123] (9) The average opening diameter O of the holes 21o of the positive electrode current collector 21 is set to 300 μm or more and 600 μm or less. This allows the positive electrode composite paste 25 to easily penetrate, and the recesses 22e are easily formed.

[0124] (10) The basis weight of the positive electrode composite layer 22 filled in the positive electrode current collector 21 is 200 [g / m 2 ] or more, 400[g / m 2 Therefore, an appropriate amount of positive electrode composite paste 25 is filled into positive electrode current collector 21, and does not overflow upward or flow downward, which makes it easier to form recesses 22e.

[0125] (11) The recesses 22e are formed not only on the surface 22a on the coating side but also on the surface 22c on the opposite side to the coating side, so that the electrolyte 5 can be effectively absorbed in the recesses 22e.

[0126] (12) In the shaping and pressing step (S15), positive electrode plate 2 is compressed in thickness direction D so as to leave recesses 22e formed in coating step (S13), and therefore the packing density of the positive electrode active material in positive electrode composite layer 22 inside recesses 22e is not increased, thereby enabling recesses 22e to effectively absorb electrolyte solution 5.

[0127] (13) Positive electrode mixture paste 25 contains carboxymethyl cellulose and sodium alginate, which allows for appropriate adjustment of viscosity V [mPa·s]. In particular, sodium alginate facilitates the formation of recesses 22e.

[0128] (Another example) Regardless of the above embodiment, the present invention can be implemented as follows. In this embodiment, the formation of the recesses 22e was attempted mainly by adjusting the viscosity V [mPa·s]. However, the conditions for forming the recesses include not only the viscosity V [mPa·s] but also the structure of the hole 21o of the positive electrode current collector, the difference in wettability, the size and properties of the particles of the positive electrode active material contained in the positive electrode mixture layer, the binder, and the basis weight [g / m 2 ]. The recesses 22e may be formed under these conditions other than the viscosity V [mPa·s]. In other words, the viscosity V [mPa·s] is merely one means for forming the recesses 22e, and the present invention is not limited thereto.

[0129] Although the nickel-metal hydride storage battery 1 of this embodiment has been described as an example of a battery for driving a vehicle, the battery's uses are not limited thereto, and it can be used in aircraft, ships, and stationary applications. The drawings are schematic diagrams for explaining the nickel-metal hydride storage battery 1 of this embodiment, and the quantity and dimensional balance of the components may be exaggerated and may not be accurate.

[0130] 4 and 5 are merely examples, and steps may be added, deleted, swapped, or modified. For example, the order of the positive electrode current collector manufacturing step (S11) and the positive electrode composite paste manufacturing step (S12) does not matter.

[0131] The values ​​of the viscosity V [mPa s] of the positive electrode composite paste and the like are merely 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 these values ​​to suit the configuration of the nickel-metal hydride storage battery 1.

[0132] It goes without saying that the present invention can be implemented by those skilled in the art by adding, deleting or modifying its configuration without departing from the scope of the claims. [Explanation of symbols]

[0133] 1... Nickel-metal hydride battery 2...Positive electrode plate 3...Negative electrode plate 4...Separator 5...Electrolyte 6...Electrode group 8... Coating machine 12...Battery cell 13...Battery case (integrated battery case) 13a...Positive connection terminal 13b...Negative connection terminal 14...lid body 15...Battery container 16...Opening 17...Through hole 18...Bulkhead 21...Positive electrode current collector 21a to 21d...coating area 21e~21i...Non-coated area 21j…Top surface 21k…Bottom side 21l...Lead section 21m…Inner peripheral surface 21n…Bone part 21o…hole 22...Positive electrode mixture layer 22a...(coated side) surface 22b...(Positive electrode composite layer) interior 22c...(opposite side to the coated side) 22d...End portion in width direction W 22e...recess 22f…Bottom 22g…coarse part 22h…Secret area 22i...Compression section 25...Positive electrode mixture paste 25e…Top surface 25f…bottom surface 27...Positive current collector plate 31...Negative electrode current collector 37...Negative electrode current collector plate 81...Die nozzle 82...Die 83...Nozzle 84...Pressure roller 85...Support member 85a...first support part 85b...Passage part 85c...Connection part 85d…Second support part 86...Stage 91...Suction pad L: Length direction (coating direction) W: Width direction (short side direction) D: Thickness direction Dh...(recess) depth Dp...Compression width Wp: Coating width (on the coated surface) Ws: Coating width (on the surface opposite to the coated side) ΔW...unevenness width (of end 22d of the positive electrode composite material layer in the width direction W) V…Viscosity [mPa·s] O…Opening diameter [μm] O1…Opening diameter [μm] O2…Opening diameter [μm]

Claims

1. a positive electrode plate including a positive electrode current collector made of a plate-shaped porous metal and a positive electrode mixture layer containing a positive electrode active material and filled into the positive electrode current collector; A negative electrode plate; a separator; A plurality of recesses are provided on the surface of the positive electrode mixture layer filled in the positive electrode plate, A secondary battery characterized in that the amount of the positive electrode active material per unit volume of the positive electrode plate in the thickness-wise inner part of the recess is coarser than in other filled parts, the opening area of ​​the recess is 500 μm 2 or more and 90,000 μm 2 or less, and the depth of the recess is 50 μm or more and is a depth that does not penetrate the positive electrode composite layer.

2. 2. The secondary battery according to claim 1, wherein the amount of the positive electrode active material per unit volume of the positive electrode plate in the thickness direction inner portion of the recess is 5% or more less than that in other filled portions.

3. The plurality of recesses are formed on the surface of the positive electrode mixture layer, and each recess has a surface area of ​​100 mm ２ 3. The secondary battery according to claim 1, wherein the electrode is provided at one or more positions per one of the electrode layers.

4. The average opening diameter of the pores of the positive electrode current collector is 300 μm or more and 600 μm or less, and the basis weight of the positive electrode mixture layer filled in the positive electrode current collector is 200 g / m ２ ] or more, 400 [g / m ２ 4. The secondary battery according to claim 1, wherein the capacitance is 0.01 to 0.25 μm.

5. a positive electrode plate including a positive electrode current collector made of a plate-shaped porous metal and a positive electrode mixture layer containing a positive electrode active material and filled into the positive electrode current collector; A negative electrode plate; a separator; A plurality of recesses are provided on the surface of the positive electrode mixture layer filled in the positive electrode plate, a method for manufacturing a secondary battery in which an amount of the positive electrode active material per unit volume of the positive electrode plate in a portion inside the recess in a thickness direction is sparse compared to other filled portions, a coating step of coating the positive electrode composite paste onto the positive electrode current collector by single-side coating, the viscosity of the positive electrode composite paste being adjusted to 50 [mPa s] or more and 2000 [mPa s] or less; a pressing step of compressing the positive electrode plate in a thickness direction so as to leave the recess formed in the coating step.

6. 6. The method for manufacturing a secondary battery according to claim 5, wherein the viscosity of the positive electrode composite paste is adjusted to 200 mPa·s or more and 1000 mPa·s or less.

7. The average opening diameter of the pores of the positive electrode current collector is 300 μm or more and 600 μm or less, and the basis weight of the positive electrode mixture layer filled in the positive electrode current collector is 200 g / m ２ ] or more, 400 [g / m ２ 7. The method for manufacturing a secondary battery according to claim 5, wherein the positive electrode composite paste is applied so that the thickness of the positive electrode composite paste is equal to or less than 1 / 2 mm.

8. 8. The method for manufacturing a secondary battery according to claim 5, wherein the positive electrode composite paste contains carboxymethyl cellulose and sodium alginate.

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