JP2020061270A - Bipolar electrode and alkali storage battery - Google Patents

Abstract

To provide a bipolar electrode and an alkaline storage battery capable of promptly discharging a gas generated from a positive electrode active material layer to the outside of the positive electrode active material layer and replenishing the inside of the positive electrode active material layer with an electrolytic solution.SOLUTION: A bipolar electrode 1 includes a metal foil 2, a positive electrode active material layer 3 provided on one surface of the metal foil 2, and a negative electrode active material layer 4 provided on the other surface of the metal foil 2. The positive electrode active material layer 3 includes a flow channel groove 32 having an open end 321 opened to a side end surface 31, and a reserve groove 33 that is branched from the flow channel groove 32 and has a closed end 331 that is not open to the side end surface 31.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bipolar electrode and an alkaline storage battery.

  BACKGROUND OF THE INVENTION Alkaline storage batteries such as nickel-hydrogen storage batteries are used as batteries for vehicles such as forklifts, hybrid vehicles, and electric vehicles. This type of alkaline storage battery has an electrode assembly in which a plurality of positive electrodes and negative electrodes are laminated with a separator interposed therebetween. The electrode incorporated in the electrode assembly, a metal foil as a current collector, a positive electrode active material layer formed on one surface of the metal foil, a negative electrode active material layer formed on the other surface, Bipolar electrodes with may be used.

  In recent years, as the load capacity of a motor or the like connected to an alkaline storage battery increases, it is required to further increase the power density and energy density of the alkaline storage battery. In order to satisfy this requirement, the areas of the positive electrode active material layer and the negative electrode active material layer in the bipolar electrode tend to be wider. However, when the area of these active material layers becomes large, it becomes difficult for the electrolytic solution to permeate into the inside of the active material layer in the process of manufacturing the alkaline storage battery.

  Therefore, various techniques have been proposed in order to easily permeate the electrolytic solution into the inside of the active material layer. For example, in Patent Document 1, although it is an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery instead of an alkaline storage battery, one edge portion extending in the longitudinal direction of the electrode plate is formed on the surface of the active material layer. There is described an electrode with a groove extending from to the other edge.

JP 2004-207253 A

  Unlike a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, an alkaline storage battery may generate a gas derived from an electrolytic solution from a positive electrode active material layer during charging. In order to improve the efficiency of the electrode reaction in the positive electrode active material layer, the gas generated from the positive electrode active material layer is quickly discharged to the outside of the positive electrode active material layer, and the electrolytic solution is discharged from the outside to the inside of the positive electrode active material layer. It is desirable to supply and replenish the positive electrode active material layer with the electrolytic solution.

  However, when the groove as in Patent Document 1 is formed on the surface of the positive electrode active material layer, the gas generated from the positive electrode active material layer tends to collect in the groove. The gas collected inside the groove moves toward the outside of the positive electrode active material layer. This facilitates the formation of a flow toward the outside of the positive electrode active material layer inside the groove. When such a flow is formed inside the groove, it is necessary to move the electrolytic solution against the flow in order to supply the electrolytic solution existing outside the positive electrode active material layer into the positive electrode active material layer. is there.

  Therefore, when the groove as in Patent Document 1 is formed on the surface of the positive electrode active material layer, the supply of the electrolytic solution from the outside to the inside of the positive electrode active material layer is likely to be delayed. If the supply of the electrolytic solution is delayed, a region where the electrolytic solution is locally depleted may be formed in the positive electrode active material layer in some cases, which may lead to an increase in the internal resistance of the alkaline storage battery.

  The present invention has been made in view of such a background, and quickly discharges the gas generated from the positive electrode active material layer to the outside of the positive electrode active material layer, and quickly replenishes the electrolyte solution inside the positive electrode active material layer. It is intended to provide a bipolar electrode that can be used and an alkaline storage battery including the bipolar electrode.

One embodiment of the present invention, a metal foil,
A positive electrode active material layer provided on one surface of the metal foil,
A negative electrode active material layer provided on the other surface of the metal foil,
The positive electrode active material layer,
A channel groove having a plurality of open ends that are open to the side end surface,
And a reserve groove having a closed end that does not open to the side end surface and that branches from the flow path groove.

  The positive electrode active material layer of the bipolar electrode has two kinds of grooves: a flow groove having a plurality of open ends and a reserve groove branched from the flow groove and having a closed end. The plurality of open ends of the flow channel are arranged on the side end surface of the positive electrode active material layer, that is, the surface that is the edge in a plan view as seen from the thickness direction of the positive electrode active material layer. Therefore, the flow path groove can discharge the electrolytic solution or gas inside the groove from the opening end to the outside of the groove. On the other hand, since the closed end of the reserve groove is not opened to the side end surface of the positive electrode active material layer, it is difficult to discharge the electrolytic solution or gas inside the groove from the closed end to the outside of the groove. Therefore, the flow resistance of the electrolytic solution or gas flowing inside the reserve groove is higher than the flow resistance of the electrolytic solution or gas flowing inside the flow path groove.

  Due to such a difference in flow resistance, the bipolar electrode can collect the gas generated from the positive electrode active material layer in the flow channel having a relatively low flow resistance. Then, a flow from the inside of the positive electrode active material layer to the outside can be created inside the channel groove, and the gas collected in the channel groove can be moved toward the outside of the positive electrode active material layer. As a result, the flow path groove can quickly discharge the gas generated during charging to the outside of the positive electrode active material layer.

  On the other hand, since the reserve groove has a higher flow resistance than the flow path groove, a flow toward the outside of the positive electrode active material layer is unlikely to occur inside the groove. Therefore, the reserve groove can hold the electrolytic solution inside the groove. Further, the reserve groove, when the electrolytic solution in the positive electrode active material layer is reduced by the electrode reaction, quickly supplies the electrolytic solution held inside the groove to the positive electrode active material layer, and the electrolytic solution in the positive electrode active material layer is electrolyzed. The liquid can be replenished. As a result, exhaustion of the electrolyte solution in the positive electrode active material layer can be suppressed, and the internal resistance of the alkaline storage battery can be reduced.

  As described above, according to the bipolar electrode of the above aspect, the gas generated from the positive electrode active material layer is quickly discharged to the outside of the positive electrode active material layer, and the electrolyte solution is quickly replenished inside the positive electrode active material layer. can do.

5 is a plan view of the bipolar electrode in Example 1 viewed from the positive electrode active material layer side. FIG. FIG. 2 is a partial sectional view taken along the line II-II of FIG. 1. 5 is a plan view of a bipolar electrode in which a reserve groove is branched from all flow channel grooves in Example 2, as viewed from the positive electrode active material layer side. FIG. FIG. 7 is a perspective view of an alkaline storage battery including a bipolar electrode in Example 3. FIG. 6 is a partially enlarged plan view of the alkaline storage battery in Example 3 viewed from the liquid injection port side. 6 is a sectional view taken along the line VI-VI of FIG. FIG. 7 is a sectional view taken along the line VII-VII of FIG. 6.

  The flow path groove in the bipolar electrode has a groove shape that is recessed from the surroundings, and connects the open ends provided on the side end surface of the positive electrode active material layer. That is, the flow channel is a part of the groove provided in the positive electrode active material layer that serves as a path connecting one opening end and the other opening end.

  The width of the flow channel can be appropriately set within a range of 0.5 to 10 mm, for example. Moreover, the depth of the flow channel is not particularly limited. For example, the depth of the channel groove may be the same as the thickness of the positive electrode active material layer, or may be shallower than the thickness of the positive electrode active material layer.

  The arrangement of the flow channel can take various forms. For example, the flow channel may have a linear shape or a curved shape in a plan view as seen from the thickness direction of the bipolar electrode.

  For example, the flow path groove may have a linear portion that extends linearly from the opening end. In this case, it is possible to further reduce the flow resistance of the electrolytic solution and the gas flowing in the straight portion. As a result, the gas generated from the positive electrode active material layer can be more quickly discharged to the outside of the positive electrode active material layer, and the retention of the gas in the positive electrode active material layer can be more effectively reduced.

  When the positive electrode active material layer has a rectangular shape in a plan view when viewed from the thickness direction of the bipolar electrode, the straight line portion extends in a direction parallel to any side of the positive electrode active material layer in the plan view. May be. When the linear portion is arranged in this manner, the metal foil is cut between the active material layers after the positive electrode active material layer and the negative electrode active material layer are intermittently formed on the strip-shaped metal foil, a so-called roll-to-roll method is used. The bipolar electrode can be manufactured by adopting it. Therefore, the bipolar electrode can be manufactured more efficiently.

  The flow path groove may have a plurality of straight line portions and an intersecting portion intersecting the plurality of straight line portions. In this case, the gas generated from the positive electrode active material layer can be collected also in the intersection. Then, the gas in the intersecting portion can be quickly discharged to the outside of the positive electrode active material layer via the straight portion. As a result, the retention of gas in the positive electrode active material layer can be reduced more effectively.

  Further, in this case, the electrolytic solution held in the reserve groove can be supplied to the positive electrode active material layer through both the straight line portion and the crossing portion. Thereby, the electrolyte solution can be replenished to a wider range of the positive electrode active material layer.

  The width of the intersecting portion can be appropriately set within a range of 0.5 to 10 mm, for example. In addition, the depth of the intersection is not particularly limited. For example, the depth of the intersecting portion may be the same as the thickness of the positive electrode active material layer, or may be shallower than the thickness of the positive electrode active material layer. In addition, the depth of the intersecting portion may be the same as or different from the depth of the flow channel and the depth of the reserve groove.

  The arrangement of the intersections can take various forms. For example, the intersecting portion may have a linear shape or a curved shape in a plan view as seen from the thickness direction of the bipolar electrode.

  The intersecting portion is preferably linear. In this case, the flow resistance of the electrolytic solution and gas flowing in the intersection can be further reduced. As a result, the gas generated from the positive electrode active material layer can be more quickly discharged to the outside of the positive electrode active material layer, and the retention of the gas in the positive electrode active material layer can be more effectively reduced.

  The intersecting portion is preferably extended in a direction perpendicular to the extending direction of the straight portion. In this case, it is possible to suppress an increase in the occupied area of the intersecting portion in a plan view as seen from the thickness direction of the bipolar electrode. As a result, it is possible to more quickly discharge the gas generated from the positive electrode active material layer to the outside of the positive electrode active material layer while suppressing the decrease in the capacity of the bipolar electrode.

  The flow channel may have a plurality of intersecting portions that are arranged at intervals. In this case, it is preferable that the interval between the adjacent intersecting portions is 0.9 to 1.1 times the interval between the adjacent linear portions. In this case, it is possible to dispose the straight line portions and the intersecting portions, which are the flow paths of the electrolytic solution and the gas, in the positive electrode active material layer without any bias. Therefore, the gas generated from the positive electrode active material layer can be easily collected in the flow channel groove, and the retention of the gas in the positive electrode active material layer can be more effectively reduced. Furthermore, by arranging the straight line portion and the intersecting portion in the positive electrode active material layer without unevenness, it is possible to supplement the electrolyte solution to a wider range of the positive electrode active material layer.

  The reserve groove in the positive electrode active material layer has a groove shape that is recessed from the surroundings and branches from the flow path groove. Further, the reserve groove has a closed end that is not open on the side end surface of the positive electrode active material layer. In other words, the reserve groove is a dead end at the branch point of the flow path groove, and is out of the path connecting the one opening end and the other opening end.

  The shape of the reserve groove can take various forms. For example, the width of the reserve groove can be appropriately set within the range of 0.5 to 10 mm. Moreover, the depth of the reserve groove is not particularly limited. For example, the depth of the reserve groove may be the same as the thickness of the positive electrode active material layer, or may be shallower than the thickness of the positive electrode active material layer. Further, the depth of the reserve groove may be the same as or different from the depth of the flow path groove.

  The reserve groove may have a linear shape or a curved shape in a plan view when viewed from the thickness direction of the bipolar electrode.

  The reserve groove preferably has a linear shape extending in a direction orthogonal to the flow path groove. In this case, when a flow from the inside of the positive electrode active material layer to the outside occurs inside the flow channel, it is possible to make it difficult for the electrolytic solution inside the reserve groove to be caught in the flow inside the flow channel. it can. Thereby, the outflow of the electrolytic solution from the reserve groove to the flow path groove can be more effectively suppressed, and the amount of the electrolytic solution retained inside the reserve groove can be increased. As a result, exhaustion of the electrolyte solution in the positive electrode active material layer can be suppressed more effectively.

  The positive electrode active material layer may have a plurality of reserve grooves arranged along the straight line portion of the flow path groove. In this case, the interval between adjacent reserve grooves is preferably 5 to 10 times the width of the reserve grooves. In this case, the reserve grooves can be arranged evenly along the flow paths of the electrolytic solution and gas in the flow path grooves, and the electrolytic solution can be replenished to a wider range of the positive electrode active material layer. As a result, exhaustion of the electrolyte solution in the positive electrode active material layer can be suppressed more effectively.

  The negative electrode active material layer of the bipolar electrode may or may not have a negative electrode groove in the shape of a groove recessed from the periphery. When the negative electrode groove is provided in the negative electrode active material layer, the position of the negative electrode groove is preferably on the back surface of the groove provided in the positive electrode active material layer. The negative electrode active material layer can absorb the gas generated from the positive electrode active material layer during charging of the alkaline storage battery, and can further return the gas to the electrolytic solution by an electrode reaction. By providing the negative electrode groove in the negative electrode active material layer, the surface area of the negative electrode active material layer can be increased. As a result, the amount of gas absorbed in the negative electrode active material layer can be increased.

The alkaline storage battery including the bipolar electrode may have the following configuration, for example. That is, the alkaline storage battery has an electrode assembly in which a plurality of electrodes are stacked with a separator interposed therebetween, and a case that covers a side circumferential surface of the electrode assembly.
The electrode assembly has, as an electrode, the bipolar electrode of the above aspect.
The case has a liquid injection wall portion having a liquid injection port for injecting an electrolytic solution into the electrode assembly.
Then, a part of the plurality of open ends of the flow channel is arranged at a position facing the liquid injection wall portion.

  When the electrolytic solution is injected into the case in the process of manufacturing the alkaline storage battery having such a configuration, the electrolytic solution first enters the gap between the injection wall portion and the positive electrode active material layer. Next, the electrolytic solution enters the channel groove from the open end provided at the position facing the injection wall portion. The electrolytic solution that has entered the flow channel penetrates into the positive electrode active material layer while moving inside the flow channel. This allows the electrolyte solution to quickly permeate the entire positive electrode active material layer.

(Example 1)
Examples of the bipolar electrode and the alkaline storage battery will be described with reference to FIGS. As shown in FIG. 1, the bipolar electrode 1 includes a metal foil 2, a positive electrode active material layer 3 provided on one surface of the metal foil 2, and a negative electrode active material layer provided on the other surface of the metal foil 2. And the material layer 4. The positive electrode active material layer 3 has a flow path groove 32 having a plurality of open ends 321 open to the side end surface 31, and a reserve groove having a closed end 331 branched from the flow path groove 32 and not open to the side end surface 31. 33, and. Hereinafter, the structure of the bipolar electrode 1 of this example will be described in detail.

  The metal foil 2 of the bipolar electrode 1 has a rectangular shape. The dimensions of the metal foil 2 can be appropriately set, for example, within a range of 150 to 300 mm in length and 300 to 600 mm in width. As the metal foil 2, for example, nickel foil, nickel-plated stainless steel foil, steel foil, or the like can be used. The metal foil 2 of this example is a nickel foil having a length of 250 mm and a width of 450 mm.

  The positive electrode active material layer 3 is provided on one surface of the metal foil 2. The positive electrode active material layer 3 contains nickel hydroxide as a positive electrode active material, an acrylic resin emulsion as a binder, and carboxymethyl cellulose.

  The positive electrode active material layer 3 of this example is a rectangular parallelepiped having a length of 204 mm, a width of 400 mm, and a thickness of 110 μm, and has a rectangular shape when seen in a plan view from the thickness direction of the bipolar electrode 1. The positive electrode active material layer 3 has four side end faces 31 (311 and 312) which are the edges of the positive electrode active material layer 3 in a plan view as seen from the thickness direction of the bipolar electrode 1. In the following, for convenience, the two side end faces 31 that are the short sides of the positive electrode active material layer 3 in a plan view viewed from the thickness direction are referred to as first side end faces 311 and the two side end faces that are the long sides are referred to. 31 is referred to as the second side end surface 312. Further, the positive electrode active material layer 3 is arranged in the center of the metal foil 2 in a plan view as seen from the thickness direction of the bipolar electrode 1. The size of the positive electrode active material layer 3 can be appropriately set, for example, in the range of 100 to 250 mm in length, 200 to 500 mm in width, and 80 to 140 μm in thickness.

  The positive electrode active material layer 3 has a channel groove 32 and a reserve groove 33 branched from the channel groove 32. The flow path groove 32 and the reserve groove 33 are groove-shaped recessed from the surroundings. The flow path groove 32 of the present example has a plurality of straight line portions 322 linearly extended from the opening end 321 and an intersection portion 323 intersecting these straight line portions 322. The straight line portions 322 and the intersecting portions 323 are arranged in a grid pattern.

  More specifically, the linear portions 322 of this example have a linear shape extending in a direction parallel to the long side of the positive electrode active material layer 3 (that is, a horizontal direction), and are spaced from each other in the vertical direction. It is arranged with a gap. In addition, the linear portion 322 is each of the first side end surface 311 of the positive electrode active material layer 3, that is, two surfaces corresponding to the short sides of the positive electrode active material layer 3 in a plan view viewed from the thickness direction of the bipolar electrode 1. It has an open end 321 that is open at. The width of the straight line portion 322 in this example is 4 mm. The interval between the straight line portions 322 is eight times the width of the straight line portions 322.

  The intersecting portions 323 have a linear shape extending in a direction perpendicular to the extending direction of the linear portions 322 (that is, the vertical direction), and are arranged in the lateral direction with a space therebetween. Each intersection 323 intersects with all the straight portions 322. The width of the intersecting portion 323 in this example is 4 mm. The interval between the adjacent intersecting portions 323 is 1.0 times the interval between the adjacent linear portions 322.

  The reserve groove 33 of this example is branched from the outermost linear portion 322a of the plurality of linear portions 322. The reserve grooves 33 are linear and extend outward in the vertical direction, and are arranged in the horizontal direction at intervals from each other. Further, the reserve groove 33 and the intersecting portion 323 of this example are arranged on the same straight line.

  The reserve groove 33 has a closed end 331 that is not open to the side end surface 31 at the tip in the extending direction. In other words, the reserve groove 33 is a dead end at the point branched from the straight line portion 322a. The width of the reserve groove 33 in this example is 4 mm, and the interval between the reserve grooves 33 is 8 times the width of the reserve groove 33. Further, as shown in FIG. 2, the length L1 of the reserve groove 33 is measured from the outermost linear portion 322a to the second side end surface 312 of the positive electrode active material layer 3, that is, the thickness direction of the bipolar electrode 1. Further, it is 7/8 times the distance L2 to the surface corresponding to the long side of the positive electrode active material layer 3 in plan view.

  The negative electrode active material layer 4 is provided on the other surface of the metal foil 2. The negative electrode active material layer 4 contains a hydrogen storage alloy as a negative electrode active material, an acrylic resin emulsion as a binder, and carboxymethyl cellulose.

  The negative electrode active material layer 4 of this example has a rectangular shape with a length of 210 mm and a width of 410 mm when viewed in a plan view from the thickness direction of the bipolar electrode 1. Further, the negative electrode active material layer 4 is arranged in the center of the metal foil 2 in a plan view as seen from the thickness direction of the bipolar electrode 1. The dimensions of the negative electrode active material layer 4 can be appropriately set, for example, in the range of 160 to 310 mm in length and 310 to 610 mm in width.

  The negative electrode active material layer 4 of this example has a negative electrode groove 41. The negative electrode groove 41 is in the shape of a groove depressed more than the surroundings. As shown in FIG. 2, the negative electrode groove 41 is a groove provided in the positive electrode active material layer 3 in the back surface of the flow channel groove 32 and the reserve groove 33, that is, in a plan view when the bipolar electrode 1 is viewed from the thickness direction. It is provided in a position that overlaps with.

  Next, the function and effect of the bipolar electrode 1 of this example will be described. The positive electrode active material layer 3 of the bipolar electrode 1 has a channel groove 32 and a reserve groove 33. The flow channel 32 has a plurality of open ends 321 on the first side end face 311 of the positive electrode active material layer 3, and the electrolyte or gas inside the flow channel 32 is discharged from the open end 321 to the outside of the groove. can do. On the other hand, the closed end 331 of the reserve groove 33 does not open on either the first side end surface 311 or the second side end surface 312 of the positive electrode active material layer 3, so that the inside of the groove is larger than the flow path groove 32. The flow resistance of the electrolyte and gas flowing through is high.

  Therefore, according to the bipolar electrode 1 of the present example, the gas generated from the positive electrode active material layer 3 can be collected in the flow channel groove 32 having a relatively low flow resistance. Then, a flow toward the outside of the positive electrode active material layer 3 can be created inside the flow channel 32, and the gas collected in the flow channel 32 can be moved toward the outside of the positive electrode active material layer 3. As a result, the channel groove 32 can quickly discharge the gas generated during charging to the outside of the positive electrode active material layer 3.

  On the other hand, since the reserve groove 33 has a higher flow resistance than the flow channel 32, a flow toward the outside of the positive electrode active material layer 3 is less likely to occur inside the groove. Therefore, the reserve groove 33 can hold the electrolytic solution inside the groove. In addition, the reserve groove 33 can quickly supply the electrolyte solution held in the groove to the positive electrode active material layer 3 when the electrolyte solution in the positive electrode active material layer 3 decreases due to an electrode reaction. As a result, depletion of the electrolytic solution in the positive electrode active material layer 3 can be suppressed, and the internal resistance of the alkaline storage battery can be reduced.

  As described above, according to the bipolar electrode 1, the gas generated from the positive electrode active material layer 3 is promptly discharged to the outside of the positive electrode active material layer 3, and the electrolyte solution is quickly replenished inside the positive electrode active material layer 3. can do.

  The positive electrode active material layer 3 of this example has a rectangular shape in a plan view when viewed from the thickness direction of the bipolar electrode 1, and the flow channel grooves 32 are parallel to the long sides of the positive electrode active material layer 3 in the plan view. Has been extended to. Therefore, the roll-to-roll method can be adopted for manufacturing the bipolar electrode 1 of this example. Then, by adopting the roll-to-roll method, the bipolar electrode 1 can be manufactured more efficiently.

  The flow path groove 32 has a plurality of straight line portions 322 and an intersecting portion 323 that intersects the plurality of straight line portions 322. Therefore, the gas generated from the positive electrode active material layer 3 can be collected also in the intersection 323. Then, the gas in the intersecting portion 323 can be quickly discharged to the outside of the positive electrode active material layer 3 via the straight portion 322. As a result, gas retention in the positive electrode active material layer 3 can be more effectively reduced.

  Further, by providing the intersecting portion 323, the electrolytic solution held in the reserve groove 33 can be supplied to the positive electrode active material layer 3 through both the straight portion 322 and the intersecting portion 323. As a result, the electrolyte solution can be replenished to a wider range of the positive electrode active material layer 3.

  The intersecting portion 323 extends in a direction perpendicular to the extending direction of the straight portion 322. Therefore, it is possible to suppress an increase in the area occupied by the intersecting portion 323 in a plan view when viewed from the thickness direction of the bipolar electrode 1. As a result, the gas generated from the positive electrode active material layer 3 can be more quickly discharged to the outside of the positive electrode active material layer 3 while suppressing the decrease in the capacity of the bipolar electrode 1.

  The flow path groove 32 has a plurality of intersecting portions 323 arranged at intervals from each other, and the interval between the adjacent intersecting portions 323 is 0.9 to 1 ... of the interval between the adjacent linear portions 322. It is 1 time. Therefore, the straight line portion 322 and the crossing portion 323, which serve as the flow paths of the electrolytic solution and the gas, can be uniformly arranged in the positive electrode active material layer 3. Therefore, the gas generated from the positive electrode active material layer 3 can be easily collected inside the flow channel groove 32, and the retention of the gas in the positive electrode active material layer 3 can be more effectively reduced. Furthermore, by arranging the straight line portion 322 and the crossing portion 323 in the positive electrode active material layer 3 without any bias, it is possible to supplement the electrolyte solution to a wider range of the positive electrode active material layer 3.

  The reserve groove 33 of this example extends in a direction parallel to the short side of the positive electrode active material layer 3, that is, in a direction orthogonal to the flow channel groove 32. Therefore, when the flow toward the outside of the positive electrode active material layer 3 occurs in the flow channel 32, the electrolytic solution in the reserve groove 33 can be prevented from being easily caught in the flow in the flow channel 32. Thereby, the outflow of the electrolytic solution from the reserve groove 33 to the flow path groove 32 can be more effectively suppressed, and the amount of the electrolytic solution held in the reserve groove 33 can be increased. As a result, depletion of the electrolytic solution in the positive electrode active material layer 3 can be suppressed more effectively.

  The positive electrode active material layer 3 has a plurality of reserve grooves 33 arranged at intervals in the direction along the straight line portion 322. The interval between the adjacent reserve grooves 33 is 5 to 10 times the width of the reserve grooves 33. As a result, the reserve grooves 33 can be evenly arranged along the flow paths of the electrolytic solution or gas in the flow path grooves 32, and the electrolytic solution can be replenished to a wider range of the positive electrode active material layer 3. As a result, depletion of the electrolytic solution in the positive electrode active material layer 3 can be suppressed more effectively.

  The negative electrode active material layer 4 of the bipolar electrode 1 has a negative electrode groove 41 arranged on the back surface of the flow channel 32 and the reserve groove 33. Therefore, the surface area of the negative electrode active material layer 4 can be increased, and the amount of gas absorbed in the negative electrode active material layer 4 can be increased.

(Example 2)
The bipolar electrode 102 of this example has a positive electrode active material layer 302 including a plurality of flow channel grooves 34 and a reserve groove 35 branched from each flow channel groove 34. In addition, among the reference numerals used in the present example and subsequent ones, the same reference numerals as those used in the already-explained examples indicate the same components and the like as those in the already-explained examples unless otherwise specified.

  As shown in FIG. 3, the bipolar electrode 102 of this example has a plurality of flow channel grooves 34 each having a linear portion 342 having a linear shape extending in the lateral direction. The plurality of flow channel grooves 34 are arranged side by side in the longitudinal direction at intervals. Further, each flow path groove 34 has an opening end 341 at each of two first side end faces 311 in the positive electrode active material layer 302.

  Each flow path groove 34 has a plurality of reserve grooves 35 extending on both sides in the width direction. The reserve groove 35 has a linear shape extending in the vertical direction. The closed end 351 of the reserve groove 35 extending from each flow path groove 34 is separated from the closed end 351 of the reserve groove 35 extending from the flow path groove 34 adjacent to the flow path groove 34. The interval between the reserve grooves 35 adjacent in the lateral direction is 5 to 10 times the width of the reserve groove 35. Others are the same as the first embodiment.

  By providing the reserve groove 35 in each flow path groove 34 as in this example, it is possible to retain a larger amount of the electrolytic solution in the reserve groove 35. This makes it more difficult for the electrolyte to be depleted, and more effectively suppresses an increase in the internal resistance of the alkaline storage battery. In addition, the bipolar electrode 102 of the present example can achieve the same operational effect as that of the first embodiment except for the operational effect of the intersection 323. In this example, all the flow channels 34 have no crossing portion, but the flow channel 32 having the crossing portion 323 and the flow channel having no crossing portion are provided in the positive electrode active material layer 3. Both the road groove 34 may be provided.

(Example 3)
This example is an example of an alkaline storage battery 5 having a bipolar electrode 1. As shown in FIGS. 4 and 6, the alkaline storage battery 5 of this example covers the electrode assembly 11 in which a plurality of electrodes 1 and 103 are stacked with the separator 111 interposed therebetween, and the side peripheral surface 110 of the electrode assembly 11. And a case 6. As shown in FIGS. 6 and 7, the electrode assembly 11 has a bipolar electrode 1 as an electrode. As shown in FIG. 4, the case 6 has a liquid injection wall portion 61 having a liquid injection port 611 for injecting an electrolytic solution into the electrode assembly 11. As shown in FIG. 7, a part of the open ends 321 (321a, 321b) of the flow channel 32 in the bipolar electrode 1 is arranged at a position facing the liquid injection wall portion 61. In FIG. 6, the structure of the positive electrode active material layer 3 is simplified for convenience.

  The alkaline storage battery 5 of this example has a substantially rectangular parallelepiped shape as shown in FIG. On the side surface of the alkaline storage battery 5, a case 6 having a rectangular tube shape is arranged. The case 6 has a liquid injection wall portion 61 having a liquid injection port 611, and a side wall portion 62 that covers the liquid injection wall portion 61 and the side peripheral surface 110 of the electrode assembly 11. As shown in FIGS. 5 to 7, the liquid injection port 611 is closed by a plug 612 for preventing leakage of the electrolytic solution.

  As shown in FIGS. 6 and 7, the electrode assembly 11 is housed in the cylinder of the case 6. A sealant 63 for sealing the gap between the electrode assembly 11 and the case 6 is interposed. Specifically, the sealing material 63 is provided on the periphery of the metal foil 2 in the bipolar electrode 1 and the termination electrode 103 described later. Further, as shown in FIGS. 5 and 6, a through hole 631 is provided at a position facing the liquid injection port 611 in the sealing material 63. The liquid injection port 611 and the electrode assembly 11 communicate with each other through the through hole 631.

  As shown in FIG. 6, the electrode assembly 11 includes, as electrodes, the termination electrodes 103 (103p, 103n) disposed at both ends in the stacking direction and the bipolar electrode 1 disposed between the termination electrodes 103. Have Of the two termination electrodes 103, the first termination electrode 103p arranged at one end in the stacking direction has the same structure as the bipolar electrode 1 except that the negative electrode active material layer 4 is not provided. The second termination electrode 103n arranged at the other end in the stacking direction has the same configuration as the bipolar electrode 1 except that the positive electrode active material layer 3 is not provided.

  As shown in FIG. 7, in the bipolar electrode 1 and the termination electrode 103 of this example, one of the opening ends 321 (321a, 321b) of each linear portion 322 is arranged so that one opening end 321a faces the liquid injection wall portion 61. It is arranged.

  The bipolar electrode 1 and the termination electrode 103 are arranged such that the positive electrode active material layers 3 and the negative electrode active material layers 4 are alternately arranged in the stacking direction. Further, the separator 111 is interposed between the positive electrode active material layer 3 and the negative electrode active material layer 4. As a result, a single cell C in which the positive electrode active material layer 3 and the negative electrode active material layer 4 face each other with the separator 111 interposed between the metal foils 2 is formed. These unit cells C are electrically connected in series via the metal foil 2 as a current collector.

  Further, the metal foil 2 of the terminal electrode 103 in the electrode assembly 11 is exposed in the openings 64 provided on the top surface and the bottom surface of the case 6. The electrode assembly 11 of this example can be charged and discharged by connecting the metal foil 2 of the terminal electrode 103 to an external circuit. Although not shown in the drawing, a restraining member that restrains the electrode assembly 11 in the stacking direction is in contact with the metal foil 2 of the terminal electrode 103.

  The electrode assembly 11 in the alkaline storage battery 5 of this example has the electrodes 1 and 103p provided with the flow channel 32 and the reserve groove 33. Therefore, the gas generated from the positive electrode active material layer 3 can be quickly discharged to the outside of the positive electrode active material layer 3, and the electrolyte solution can be quickly replenished inside the positive electrode active material layer 3. As a result, the internal resistance of the alkaline storage battery 5 can be reduced.

  Further, the open end 321 a of the flow channel 32 in the alkaline storage battery 5 of the present example is arranged so as to face the liquid injection wall portion 61. Therefore, when the electrolytic solution is injected into the case 6 in the process of manufacturing the alkaline storage battery 5, the electrolytic solution is allowed to enter the flow channel groove 32 from the opening end 321a provided at a position facing the injection wall portion 61. You can Then, the electrolytic solution that has entered the flow channel 32 penetrates into the positive electrode active material layer 3 while moving toward the other open end 321b, so that the electrolytic solution quickly permeates the entire positive electrode active material layer 3. be able to.

(Experimental example)
This example is an example of evaluating the internal resistance during charging when the length of the reserve groove 33 is variously changed. In this example, a bipolar electrode 1 (test samples 1 and 2) having the same configuration as in Example 1 except that the length of the reserve groove 33 was changed to the value shown in Table 1 was produced. In addition, in this example, for comparison with the test bodies 1 and 2, the test body 3 having no reserve groove 33 and the closed end 331 of the reserve groove 33 are opened to the second side end surface 312 of the positive electrode active material layer 3. A test body 4 was produced. In addition, in Table 1, along with the length L1 (mm) of the reserve groove 33, from the outermost channel groove 32a of the plurality of channel grooves 32 to the second side end surface 312 of the positive electrode active material layer 3. The ratio L1 / L2 (times) of the length of the reserve groove 33 based on the distance L2 is described.

  Using these bipolar electrodes 1, an alkaline storage battery 5 having the same structure as in Example 3 was produced, and the internal resistance was measured by the following method. First, the alkaline storage battery 5 was charged to a capacity of 60% of the fully charged state at a temperature of 25 ° C. From this state, discharge was carried out for 5 seconds at a discharge rate of 1C, 2C, 5C or 10C, and the voltage immediately after discharge was measured. Then, the battery was charged for 5 seconds at the same charge rate as the discharge rate, and the voltage immediately after charging was measured. Then, a graph was created by plotting the voltage at each measurement point on the vertical axis and the current value on the horizontal axis. The value of the 5-second resistance calculated based on the slope of this graph was defined as the internal resistance of the alkaline storage battery 5. The value of the internal resistance of the alkaline storage battery 5 using each test body was as shown in Table 1.

  As shown in Table 1, when the test bodies 1 and 2 having the reserve groove 33 having the closed end 331 are used, the test body 3 not having the reserve groove 33 and the reserve groove 33 are provided on the second side end surface 312. The internal resistance was smaller than that of the opened test body 4.

  From these results, the internal resistance of the alkaline storage battery 5 is improved by providing the positive electrode active material layer 3 of the bipolar electrode 1 with the flow channel 32 having the open end 321 and the reserve groove 33 having the closed end 331. It can be understood that it can be reduced. Further, the numerical range of L1 / L2 is preferably 0.7 or more and less than 1, and more preferably 0.8 or more and 0.95 or less.

  The aspects of the bipolar electrode and the alkaline storage battery according to the present invention are not limited to the aspects of the examples and experimental examples described above, and the configurations can be appropriately changed within a range not impairing the gist of the present invention.

1, 102 Bipolar electrode 2 Metal foil 3 Positive electrode active material layer 31 Side end surface 32, 34 Flow path groove 321, 341 Open end 33, 35 Reserve groove 331, 351 Closed end

Claims (8)

Metal foil,
A positive electrode active material layer provided on one surface of the metal foil,
A negative electrode active material layer provided on the other surface of the metal foil,
The positive electrode active material layer,
A channel groove having a plurality of open ends that are open to the side end surface,
And a reserve groove having a closed end that is branched from the flow path groove and does not open to the side end surface.   The bipolar electrode according to claim 1, wherein the flow channel has a linear portion linearly extending from the opening end.   The positive electrode active material layer has a rectangular shape in a plan view when viewed from the thickness direction of the bipolar electrode, and the linear portion extends in a direction parallel to any side of the positive electrode active material layer in the plan view. The bipolar electrode according to claim 2, which is provided.   The bipolar electrode according to claim 2 or 3, wherein the reserve groove has a linear shape extending in a direction orthogonal to the linear portion.   The positive electrode active material layer has a plurality of the reserve grooves arranged along the straight line portion, and the interval between the adjacent reserve grooves is 5 to 10 times the width of the reserve groove. The bipolar electrode according to.   The bipolar electrode according to any one of claims 2 to 5, wherein the flow path groove has a plurality of the linear portions and an intersection portion that intersects the plurality of the linear portions.   The flow path groove has a plurality of intersecting portions arranged at intervals, and the distance between the adjacent intersecting portions is 0.9 to 1 of the distance between the adjacent straight portions. 7. The bipolar electrode according to claim 6, which is 1 time. An alkaline storage battery comprising: an electrode assembly in which a plurality of electrodes are laminated via a separator; and a case that covers a side circumferential surface of the electrode assembly,
The electrode assembly has the bipolar electrode according to any one of claims 1 to 7 as the electrode,
The case has a liquid injection wall portion provided with a liquid injection port for injecting an electrolytic solution into the electrode assembly,
The alkaline storage battery, wherein a part of the plurality of opening ends of the flow channel is arranged at a position facing the liquid injection wall portion.

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