JP7204408B2 - Bipolar electrodes and alkaline storage batteries - Google Patents

Description

The present invention relates to bipolar electrodes and alkaline storage batteries.

Alkaline storage batteries such as nickel-metal hydride storage batteries are used, for example, 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 stacked with separators interposed therebetween. The electrode incorporated in the electrode assembly includes a metal foil as a current collector, a positive electrode active material layer formed on one side of the metal foil, a negative electrode active material layer formed on the other side, Bipolar electrodes with a are sometimes used.

In recent years, with the increase in the load capacity of motors and the like connected to alkaline storage batteries, it is required to further increase the power density and energy density of alkaline storage batteries. In order to meet such requirements, there is a tendency for the area of the positive electrode active material layer and the negative electrode active material layer in the bipolar electrode to become wider. However, when the area of these active material layers increases, it becomes difficult for the electrolytic solution to permeate into the active material layers during the manufacturing process of the alkaline storage battery.

Therefore, various techniques have been proposed to allow the electrolytic solution to easily permeate into the active material layer. For example, Patent Document 1 describes an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery rather than an alkaline storage battery, but one end edge portion extending in the longitudinal direction of the electrode plate on the surface of the active material layer Electrodes are described with grooves extending from the edge to the other edge.

Japanese Patent Application Laid-Open No. 2004-207253

Unlike non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, alkaline storage batteries sometimes generate gas derived from the electrolyte solution from the 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 rapidly discharged to the outside of the positive electrode active material layer, and the electrolytic solution is introduced 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 electrolyte.

However, when grooves are formed on the surface of the positive electrode active material layer as in Patent Document 1, gas generated from the positive electrode active material layer tends to gather in the grooves. The gas collected inside the groove moves toward the outside of the positive electrode active material layer. This facilitates 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 to the inside of the positive electrode active material layer. be.

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

The present invention has been made in view of this background, and rapidly 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 inside the positive electrode active material layer. It is an object of the present invention to provide a bipolar electrode capable of

One aspect of the present invention is a metal foil,
a positive electrode active material layer provided on one surface of the metal foil;
and a negative electrode active material layer provided on the other surface of the metal foil,
The positive electrode active material layer is
It has a rectangular shape in a plan view viewed from the thickness direction of the bipolar electrode,
a channel groove having a plurality of open ends opened on the side end surface of the positive electrode active material layer ;
a reserve groove branched from the flow channel and having a closed end not open on the side end surface ;
When the length of the reserve groove is L1, and the distance from the flow channel connecting to the reserve groove to the side end face of the positive electrode active material layer closest to the closed end of the reserve groove is L2, L2 The bipolar electrode has a ratio L1/L2 of L1 to 0.7 or more and less than 1 .

The positive electrode active material layer of the bipolar electrode has two types of grooves: a channel groove having a plurality of open ends and a reserve groove branching from the channel groove and having a closed end. The plurality of open ends of the channel grooves are arranged on the side end surfaces of the positive electrode active material layer, that is, on the surfaces that become edges in plan view in the thickness direction of the positive electrode active material layer. Therefore, the flow channel groove can discharge the electrolytic solution and gas inside the groove to the outside of the groove from the open end. On the other hand, since the closed end of the reserve groove is not open to the side end surface of the positive electrode active material layer, it is difficult to discharge the electrolyte and gas inside the groove from the closed end to the outside of the groove. Therefore, the flow resistance of the electrolytic solution and gas flowing inside the reserve groove is higher than the flow resistance of the electrolytic solution and gas flowing inside the flow channel 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 channel groove with 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 channel 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 channel groove, a flow toward the outside of the positive electrode active material layer is less likely to occur inside the groove. Therefore, the reserve groove can retain the electrolytic solution inside the groove. In addition, when the electrolyte in the positive electrode active material layer decreases due to the electrode reaction, the reserve groove quickly supplies the electrolyte held inside the groove to the positive electrode active material layer, and the electrolytic solution is generated in the positive electrode active material layer. Liquid can be replenished. As a result, depletion 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 rapidly discharged to the outside of the positive electrode active material layer, and the electrolyte is quickly replenished inside the positive electrode active material layer. can do.

1 is a plan view of a bipolar electrode viewed from the positive electrode active material layer side in Example 1. FIG. FIG. 2 is a partial cross-sectional view taken along line II-II of FIG. 1; FIG. 10 is a plan view of a bipolar electrode in which reserve grooves are branched from all the channel grooves in Example 2, viewed from the positive electrode active material layer side. 10 is a perspective view of an alkaline storage battery with bipolar electrodes in Example 3. FIG. FIG. 11 is a partially enlarged plan view of the alkaline storage battery in Example 3 as viewed from the liquid inlet side; FIG. 6 is a sectional view taken along the line VI-VI of FIG. 5; FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 6;

The channel 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 faces of the positive electrode active material layer. That is, the channel groove is a portion of the groove provided in the positive electrode active material layer, which serves as a path connecting one open end and the other open end.

The width of the channel groove can be appropriately set within a range of, for example, 0.5 to 10 mm. Also, the depth of the channel groove 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.

Arrangement of flow channels can take various forms. For example, the channel groove may have a linear shape or a curved shape in a plan view viewed from the thickness direction of the bipolar electrode.

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

When the positive electrode active material layer has a rectangular shape in plan view in the thickness direction of the bipolar electrode, the linear portion extends in a direction parallel to one side of the positive electrode active material layer in plan view. may be In the case of arranging the straight portions in this way, a so-called roll-to-roll method is adopted in which the metal foil is cut between the active material layers after intermittently forming the positive electrode active material layer and the negative electrode active material layer on the strip-shaped metal foil. can be employed to fabricate the bipolar electrode. Therefore, bipolar electrodes can be produced more efficiently.

The channel groove may have a plurality of straight portions and crossing portions that intersect the plurality of straight portions. In this case, the gas generated from the positive electrode active material layer can also be collected in the intersection. Then, the gas in the intersecting portion can be rapidly discharged to the outside of the positive electrode active material layer through the straight portion. As a result, it is possible to more effectively reduce gas retention in the positive electrode active material layer.

Furthermore, 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 portion and the intersection portion. Thereby, the electrolytic solution can be replenished in a wider range of the positive electrode active material layer.

The width of the crossing portion can be appropriately set within a range of, for example, 0.5 to 10 mm. Also, the depth of the intersection is not particularly limited. For example, the depth of the intersection 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. Also, the depth of the crossing portion may be the same as or different from the depth of the channel groove or the reserve groove.

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

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

It is preferable that the intersecting portion extends in a direction perpendicular to the extending direction of the straight portion. In this case, it is possible to suppress an increase in the area occupied by the crossing portion in plan view in the thickness direction of the bipolar electrodes. 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 while suppressing the decrease in the capacity of the bipolar electrode.

The flow channel may have a plurality of spaced intersections. In this case, the interval between adjacent intersections is preferably 0.9 to 1.1 times the interval between adjacent straight portions. In this case, the straight portions and crossing portions serving as flow paths for the electrolytic solution and gas can be evenly arranged in the positive electrode active material layer. Therefore, the gas generated from the positive electrode active material layer can be more easily collected inside the channel groove, and the retention of the gas in the positive electrode active material layer can be reduced more effectively. Furthermore, by arranging the linear portions and the crossing portions evenly within the positive electrode active material layer, it is possible to replenish the electrolytic solution in 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 channel groove. In addition, 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 has a dead end at the end branched from the channel groove, and is out of the path connecting one open end and the other open 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. Also, 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. Also, the depth of the reserve groove may be the same as or different from the depth of the channel groove.

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

It is preferable that the reserve groove has a linear shape extending in a direction orthogonal to the channel 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 involved in the flow inside the flow channel. can. Thereby, the outflow of the electrolytic solution from the reserve groove to the channel groove can be more effectively suppressed, and the amount of the electrolytic solution held inside the reserve groove can be increased. As a result, depletion of the electrolytic 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 linear portion of the channel groove. In this case, the interval between adjacent reserve grooves is preferably 5 to 10 times the width of the reserve groove. In this case, the reserve grooves can be evenly arranged along the flow paths of the electrolyte and gas in the channel grooves, and the electrolyte can be replenished in a wider range of the positive electrode active material layer. As a result, depletion of the electrolytic 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 that is recessed from its surroundings. 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 rear surface of the groove provided in the positive electrode active material layer. The negative electrode active material layer can absorb gas generated from the positive electrode active material layer during charging of the alkaline storage battery, and can return the gas to the electrolytic solution through electrode reaction. By providing the negative electrode grooves 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 provided with the bipolar electrodes may have, for example, the following configuration. That is, an alkaline storage battery has an electrode assembly in which a plurality of electrodes are stacked with separators interposed therebetween, and a case that covers the side peripheral surface of the electrode assembly.
The electrode assembly has the bipolar electrode of the above aspect as an electrode.
The case has an injection wall portion with an injection port for injecting electrolyte into the electrode assembly.
A part of the plurality of open ends of the channel groove is arranged at a position facing the liquid injection wall.

When the electrolytic solution is injected into the case during the manufacturing process of 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 an open end provided at a position facing the injection wall. The electrolytic solution that has entered the channel grooves penetrates into the positive electrode active material layer while moving inside the channel grooves. Thereby, the electrolytic solution can be rapidly permeated into the entire positive electrode active material layer.

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

Metal foil 2 of bipolar electrode 1 has a rectangular shape. The dimensions of the metal foil 2 can be appropriately set within a range of, for example, 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 with a length of 250 mm and a width of 450 mm.

A 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, and acrylic resin emulsion and carboxymethyl cellulose as binders.

The cathode active material layer 3 of this example has a rectangular parallelepiped shape with a length of 204 mm, a width of 400 mm, and a thickness of 110 μm. The positive electrode active material layer 3 has four side end faces 31 (311, 312) that serve as edges of the positive electrode active material layer 3 in plan view in the thickness direction of the bipolar electrode 1 . In the following, for convenience, the two side end faces 31 that become the short sides of the positive electrode active material layer 3 in plan view in the thickness direction are referred to as first side end faces 311, and the two side end faces that become the long sides are referred to as first side end faces 311. 31 is called a second side end face 312 . Moreover, the positive electrode active material layer 3 is arranged in the center of the metal foil 2 in plan view in the thickness direction of the bipolar electrode 1 . The dimensions of the positive electrode active material layer 3 can be appropriately set, for example, within the ranges 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 channel groove 32 and the reserve groove 33 are recessed from the surroundings. The channel groove 32 of this example has a plurality of linear portions 322 extending linearly from an open end 321 and intersecting portions 323 that intersect these linear portions 322 . The straight portions 322 and the crossing 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 sides of the positive electrode active material layer 3 (that is, in the horizontal direction), and are spaced apart from each other in the vertical direction. are placed apart. In addition, the straight portions 322 correspond to the first side end surfaces 311 of the positive electrode active material layer 3, that is, the two surfaces corresponding to the short sides of the positive electrode active material layer 3 in plan view in the thickness direction of the bipolar electrode 1. It has an open end 321 open to the outside. The width of the straight portion 322 in this example is 4 mm. Also, the interval between the straight portions 322 is eight times the width of the straight portions 322 .

The intersecting portions 323 have straight lines extending in a direction perpendicular to the extending direction of the straight portions 322 (that is, in the vertical direction), and are spaced apart from each other in the horizontal direction. Each intersection 323 intersects with all straight portions 322 . The width of the intersection 323 in this example is 4 mm. Also, the interval between adjacent intersection portions 323 is 1.0 times the interval between adjacent linear portions 322 .

The reserve groove 33 of this example branches off from the outermost linear portion 322 a of the plurality of linear portions 322 . The reserve grooves 33 are linear and extend outward in the vertical direction, and are arranged side by side in the horizontal direction at intervals. 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 face 31 at the tip in the extending direction. In other words, the reserve groove 33 has a dead end at the end branched from the straight portion 322a. The width of the reserve grooves 33 in this example is 4 mm, and the interval between the reserve grooves 33 is eight times the width of the reserve grooves 33 . In addition, as shown in FIG. 2, the length L1 of the reserve groove 33 varies 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. 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.

A 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, and an acrylic resin emulsion and carboxymethyl cellulose as binders.

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 in plan view in the thickness direction of the bipolar electrode 1 . In addition, the negative electrode active material layer 4 is arranged in the center of the metal foil 2 in plan view in the thickness direction of the bipolar electrode 1 . The dimensions of the negative electrode active material layer 4 can be appropriately set within a range of, for example, 160 to 310 mm in length and 310 to 610 mm in width.

The negative electrode active material layer 4 of this example has negative electrode grooves 41 . The negative electrode groove 41 has a groove shape that is recessed from its surroundings. Further, as shown in FIG. 2, the negative electrode groove 41 is a groove provided in the positive electrode active material layer 3 when viewed from the back side of the channel groove 32 and the reserve groove 33, that is, when the bipolar electrode 1 is viewed from the thickness direction. It is located in a position overlapping with the

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

Therefore, according to the bipolar electrode 1 of this example, the gas generated from the positive electrode active material layer 3 can be collected in the channel groove 32 with relatively low flow resistance. Then, a flow toward the outside of the positive electrode active material layer 3 is created inside the channel groove 32 , and the gas collected in the channel groove 32 can be moved toward the outside of the positive electrode active material layer 3 . As a result, the flow channel 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 channel groove 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. Further, the reserve groove 33 can quickly supply the electrolyte retained in the groove to the positive electrode active material layer 3 when the electrolyte in the positive electrode active material layer 3 decreases due to the 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 rapidly discharged to the outside of the positive electrode active material layer 3, and the inside of the positive electrode active material layer 3 is quickly replenished with the electrolyte. can do.

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

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

Moreover, by providing the intersections 323 , the electrolytic solution held in the reserve grooves 33 can be supplied to the positive electrode active material layer 3 through both the straight portions 322 and the intersections 323 . Thereby, the electrolytic solution can be replenished in 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 plan view in the thickness direction of the bipolar electrode 1 . As a result, the gas generated from the positive electrode active material layer 3 can be discharged to the outside of the positive electrode active material layer 3 more quickly while suppressing the decrease in the capacity of the bipolar electrode 1 .

The channel groove 32 has a plurality of intersecting portions 323 spaced apart from each other. 1x. Therefore, the straight portions 322 and the crossing portions 323 serving as flow paths for the electrolytic solution and gas can be evenly arranged in the positive electrode active material layer 3 . Therefore, the gas generated from the positive electrode active material layer 3 can be more easily gathered inside the flow channel 32, and the retention of the gas in the positive electrode active material layer 3 can be reduced more effectively. Furthermore, by arranging the straight portions 322 and the intersection portions 323 evenly within the positive electrode active material layer 3 , it is possible to replenish the electrolytic solution in a wider range of the positive electrode active material layer 3 .

The reserve grooves 33 of this example extend in a direction parallel to the short sides of the positive electrode active material layer 3 , that is, in a direction orthogonal to the channel grooves 32 . Therefore, when a flow toward the outside of the positive electrode active material layer 3 occurs in the channel groove 32 , the electrolytic solution in the reserve groove 33 can be made less likely to be involved in the flow in the channel groove 32 . As a result, the electrolyte can be more effectively prevented from flowing out of the reserve grooves 33 into the channel grooves 32, and the amount of electrolyte retained in the reserve grooves 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 portion 322 . The interval between 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 circulation paths of the electrolyte and the gas in the channel grooves 32 , and the electrolyte can be replenished in 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 channel groove 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 by 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 having a plurality of channel grooves 34 and reserve grooves 35 branched from each channel groove 34 . It should be noted that, of the reference numerals used in the present and subsequent examples, the same reference numerals as those used in the previous examples denote the same components and the like as those in the previous examples unless otherwise specified.

As shown in FIG. 3, the bipolar electrode 102 of this example has a plurality of channel grooves 34 having linear portions 342 extending in the horizontal direction. The plurality of channel grooves 34 are arranged in a line at intervals in the longitudinal direction. Each channel groove 34 has an open end 341 on each of the two first side end surfaces 311 of the positive electrode active material layer 302 .

Each channel groove 34 has a plurality of reserve grooves 35 extending on both sides in its 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 groove 34 is spaced apart from the closed end 351 of the reserve groove 35 extending from the flow groove 34 adjacent to that flow groove 34 . The interval between reserve grooves 35 adjacent in the lateral direction is 5 to 10 times the width of the reserve grooves 35 . Others are the same as the first embodiment.

By providing the reserve groove 35 in each channel groove 34 as in this example, a larger amount of electrolytic solution can be held in the reserve groove 35 . As a result, depletion of the electrolytic solution is less likely to occur, and an increase in the internal resistance of the alkaline storage battery can be more effectively suppressed. In addition, the bipolar electrode 102 of this example can achieve the same effects as those of the first embodiment, except for the effects of the intersections 323 . In this example, none of the channel grooves 34 have any intersections. Both the groove 34 and the 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 includes an electrode assembly 11 in which a plurality of electrodes 1 and 103 are stacked with separators 111 interposed therebetween, and a side peripheral surface 110 of the electrode assembly 11. Case 6 and . 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 an injection wall portion 61 having an 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 ( 321 a and 321 b ) of the channel groove 32 in the bipolar electrode 1 , an open end 321 a , is arranged at a position facing the injection wall portion 61 . In addition, 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. A square tube-shaped case 6 is arranged on the side peripheral surface of the alkaline storage battery 5 . The case 6 has an injection wall portion 61 having an injection port 611 and a side wall portion 62 that covers the side peripheral surface 110 of the electrode assembly 11 together with the injection wall portion 61 . As shown in FIGS. 5 to 7, the injection port 611 is closed by a plug 612 for preventing electrolyte leakage.

As shown in FIGS. 6 and 7, an electrode assembly 11 is housed in the cylinder of the case 6 . A sealing material 63 is interposed between the electrode assembly 11 and the case 6 to seal the gap therebetween. Specifically, the sealing material 63 is provided on the peripheral edge portion of the metal foil 2 of the bipolar electrode 1 and the terminating electrode 103 which will be described later. Further, as shown in FIGS. 5 and 6 , a through hole 631 is provided at a position of the sealing member 63 facing the injection port 611 . The liquid injection port 611 and the electrode assembly 11 communicate with each other via a through hole 631 .

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

As shown in FIG. 7, the bipolar electrode 1 and the terminating electrode 103 of this example are configured so that one open end 321a of the open ends 321 (321a, 321b) of each linear portion 322 faces the injection wall portion 61. are placed.

The bipolar electrode 1 and the terminating 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. A 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 is formed 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 . These single cells C are electrically connected in series via a metal foil 2 as a current collector.

Also, the metal foil 2 of the terminal electrode 103 in the electrode assembly 11 is exposed through openings 64 provided on the top and bottom surfaces 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 with the channel grooves 32 and the reserve grooves 33 . Therefore, the gas generated from the positive electrode active material layer 3 can be rapidly discharged to the outside of the positive electrode active material layer 3, and the inside of the positive electrode active material layer 3 can be quickly replenished with the electrolytic solution. As a result, the internal resistance of alkaline storage battery 5 can be reduced.

In addition, the open end 321 a of the channel groove 32 in the alkaline storage battery 5 of this 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 manufacturing process of the alkaline storage battery 5, the electrolytic solution is allowed to enter the channel groove 32 from the opening end 321a provided at a position facing the injection wall portion 61. can be done. Then, the electrolytic solution that has entered the channel groove 32 permeates into the positive electrode active material layer 3 while moving toward the other open end 321b, thereby allowing the electrolytic solution to quickly permeate 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 varied. In this example, a bipolar electrode 1 (specimens 1 and 2) having the same configuration as that of 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 test samples 1 and 2, test sample 3 without reserve groove 33 and closed end 331 of reserve groove 33 were opened to second side end surface 312 of positive electrode active material layer 3. A test body 4 was produced. Table 1 shows the length L1 (mm) of the reserve groove 33 and the length from the outermost channel groove 32a of the plurality of channel grooves 32 to the second side end face 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 of .

Using these bipolar electrodes 1, an alkaline storage battery 5 having the same configuration 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, the battery was discharged at a discharge rate of 1C, 2C, 5C or 10C for 5 seconds, and the voltage immediately after discharge was measured. Thereafter, the battery was charged for 5 seconds at the same charging rate as the discharging 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 taken as the internal resistance of the alkaline storage battery 5 . Table 1 shows the internal resistance value of the alkaline storage battery 5 using each test piece.

As shown in Table 1, when using the specimens 1 and 2 having the reserve groove 33 with the closed end 331, the specimen 3 without the reserve groove 33 and the reserve groove 33 are placed on the second side end surface 312. The internal resistance became smaller than that of the specimen 4 with openings.

From these results, the internal resistance of the alkaline storage battery 5 can be reduced by providing the channel groove 32 with the open end 321 and the reserve groove 33 with the closed end 331 in the positive electrode active material layer 3 of the bipolar electrode 1. It can be understood that it can be reduced. Moreover, it can be said that 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 embodiments of the bipolar electrode and alkaline storage battery according to the present invention are not limited to the embodiments and experimental examples described above, and can be appropriately modified within the scope of the present invention.

Reference Signs List 1, 102 Bipolar electrode 2 Metal foil 3 Positive electrode active material layer 31 Side end face 32, 34 Channel groove 321, 341 Open end 33, 35 Reserve groove 331, 351 Closed end

Claims (10)

metal foil;
a positive electrode active material layer provided on one surface of the metal foil;
and a negative electrode active material layer provided on the other surface of the metal foil,
The positive electrode active material layer is
It has a rectangular shape in a plan view viewed from the thickness direction of the bipolar electrode,
a channel groove having a plurality of open ends opened on the side end surface of the positive electrode active material layer;
a reserve groove branched from the flow channel and having a closed end not open on the side end surface;
When the length of the reserve groove is L1, and the distance from the flow channel connecting to the reserve groove to the side end face of the positive electrode active material layer closest to the closed end of the reserve groove is L2, L2 A bipolar electrode having a ratio L1/L2 of L1 to L1 of 0.7 or more and less than 1. The bipolar electrode according to claim 1, wherein the ratio L1/L2 of said L1 to said L2 is 0.8 or more and 0.95 or less. 3. The bipolar electrode according to claim 1, wherein said channel groove has a linear portion extending linearly from said opening end. 4. The bipolar electrode according to claim 3 , wherein said straight portion extends in a direction parallel to one side of said positive electrode active material layer in said plan view. The flow channel groove has a plurality of the linear portions spaced apart from each other, and the reserve groove is branched from the outermost linear portion among the plurality of the linear portions. 5. The bipolar electrode of claim 4, wherein The bipolar electrode according to any one of claims 3 to 5, wherein said reserve groove has a linear shape extending in a direction orthogonal to said linear portion. 6. The positive electrode active material layer has a plurality of reserve grooves arranged along the linear portion, and the interval between adjacent reserve grooves is 5 to 10 times the width of the reserve groove. The bipolar electrode described in . 8. The bipolar electrode according to any one of claims 3 to 7, wherein said channel groove has a plurality of said straight portions and crossing portions intersecting said plurality of said straight portions. The flow channel groove has a plurality of intersecting portions arranged at intervals, and the interval between the adjacent intersecting portions is 0.9 to 1.1 times the interval between the adjacent linear portions. 9. The bipolar electrode of claim 8, which is double. An alkaline storage battery comprising an electrode assembly in which a plurality of electrodes are stacked with separators interposed therebetween, and a case covering a side peripheral surface of the electrode assembly,
The electrode assembly has the bipolar electrode according to any one of claims 1 to 9 as the electrode,
The case has an injection wall portion having an injection port for injecting an electrolyte into the electrode assembly,
The alkaline storage battery, wherein a part of the plurality of open ends of the channel groove is arranged at a position facing the liquid injection wall.

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