JP2018133207A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery which is high in adhesion between a sealing part and metal foil and low in contact resistance between a restraining member and the metal foil.SOLUTION: A secondary battery 1 comprises an electrode assembly 11, and restraining members 12 abutting against ends of the electrode assembly 11 in a lamination direction thereof. The electrode assembly 11 has: terminating electrodes 3 disposed at both ends in the lamination direction; and a bipolar electrode 4 disposed between the terminating electrodes 3. The terminating electrodes 3 each have: first metal foil 31 having a flat surface-side face 311 abutting against the restraining member 12 and a backside face 312 larger, in surface roughness, than the surface-side face 311; and an active material layer 32 provided on the backside face 312. The bipolar electrode 4 has: second metal foil 41 in which the surface roughness of at least one of a surface-side face 411 and a backside face 412 is larger than the roughness of the surface-side face of the first metal foil 31; and an active material layer 42 provided on each of the surface-side face 411 and backside face 412 of the second metal foil 41.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a secondary battery.

  A secondary battery such as a nickel-metal hydride storage battery or a lithium secondary battery has an electrode assembly in which a plurality of electrodes are stacked via a separator, and a restraining member that compresses the electrode assembly in the stacking direction. As an electrode assembly, one having a termination electrode disposed at each end in the stacking direction and a bipolar electrode disposed between the termination electrodes is known.

  The bipolar electrode in this type of electrode assembly has a metal foil and an active material layer provided on both surfaces of the metal foil. The termination electrode has a metal foil that contacts the restraining member and an active material layer provided on one surface of the metal foil. The restraining member is electrically connected to the electrode assembly via the termination electrode, and is configured as a terminal that supplies power to the outside of the secondary battery.

  An electrolyte is held between adjacent electrodes in the electrode assembly. If this electrolyte leaks out of the electrode assembly or comes into contact with the outside air, the battery performance may be deteriorated. Therefore, a seal portion for suppressing leakage of electrolyte and entry of outside air may be provided at the peripheral portion of the metal foil.

  When providing a seal part at the peripheral part of the metal foil, it is possible to improve the adhesion with the seal part by roughening the surface of the metal foil, and to more effectively suppress the leakage of electrolyte and the entry of outside air. it can. For example, Patent Document 1 discloses an example of a bipolar electrode having a metal foil in which fine irregularities are formed on the surface on the side where the positive electrode active material layer is provided.

JP 2010-257893 A

  As described above, in the electrode assembly having the termination electrode and the bipolar electrode, the restraining member is in contact with the metal foil of each termination electrode. Therefore, when the surface of the metal foil is roughened, the contact area between the metal foil and the restraining member is narrowed, which may increase the contact resistance. As a result, there is a risk of increasing the internal resistance of the secondary battery.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a secondary battery having high adhesion between a seal portion and a metal foil and low contact resistance between the restraining member and the metal foil.

One aspect of the present invention is an electrode assembly including a plurality of electrodes stacked via a separator;
A constraining member that contacts each end in the stacking direction of the electrode assembly and is electrically connected to the electrode assembly;
The electrode assembly is
A first metal foil having a flat front side that abuts on each of the restraining members, a back side having a rougher surface roughness than the front side, and an active material provided on the back side of the first metal foil A termination electrode having a layer;
A second metal foil having a surface roughness of at least one of the front side surface and the back side surface that is rougher than the front side surface of the first metal foil, and actives provided on the front side surface and the back side surface of the second metal foil, respectively. A bipolar electrode having a material layer and disposed between the termination electrodes,
The separator interposed between the active material layers in the adjacent electrodes;
The secondary battery has a sealing portion that covers the peripheral portions of the first metal foil and the second metal foil and has a seal portion interposed between the metal foils in the adjacent electrodes.

  The secondary battery has an electrode assembly including a plurality of electrodes stacked with separators interposed therebetween. Further, at each end in the stacking direction of the electrode assembly, a first metal foil having a flat front side surface, a back side surface having a rougher surface roughness than the front side surface, and a back side of the first metal foil A termination electrode having an active material layer provided on the surface is disposed. The front side surface of the first metal foil is in contact with the restraining member. In the secondary battery, the contact surface between the first metal foil and the restraining member can be sufficiently widened by bringing the flat front side surface of the first metal foil into contact with the restraining member. As a result, an increase in contact resistance between the restraining member and the first metal foil can be suppressed, and consequently an increase in internal resistance of the secondary battery can be suppressed.

  Moreover, the surface roughness of the back side surface of the first metal foil in the termination electrode is rougher than that of the front side surface. Furthermore, the surface roughness of at least one surface of the second metal foil in the bipolar electrode is rougher than that of the front side surface of the first metal foil. That is, the back side surface of the first metal foil and at least one side of the second metal foil are roughened so that the surface roughness is rougher than the front side surface of the first metal foil. And the peripheral part of 1st metal foil and 2nd metal foil is coat | covered with the seal | sticker part, and the seal | sticker part is interposed between metal foils in an adjacent electrode.

  Thus, the roughened surface in each metal foil and a seal part can be made to contact by covering the peripheral part of each metal foil with a seal part. As a result, the adhesion between the seal portion and each metal foil can be improved. Further, by improving the adhesiveness between the seal portion and each metal foil, it is possible to suppress leakage of the electrolyte to the outside of the electrode assembly and entry of outside air to the inside of the electrode assembly.

3 is a cross-sectional view showing the main parts of a secondary battery in Example 1. FIG. FIG. 2 is an enlarged view of the vicinity of a terminal electrode of the electrode assembly in FIG. 1. It is explanatory drawing of the operation | work which compresses the laminated body of an electrode and a separator in Example 1. FIG. 6 is a partial cross-sectional view showing a main part of a bipolar electrode in Example 2. FIG. FIG. 5 is an enlarged view of the vicinity of the front side surface of the second metal foil in FIG. 4. It is explanatory drawing of the evaluation method of contact resistance in an experiment example.

  In the secondary battery, the electrode assembly includes two terminal electrodes and one or more bipolar electrodes. These electrodes are arranged so that the polarities of the active material layers facing each other through the separator are different from each other. That is, in the electrode assembly, the positive electrode active material layer and the negative electrode active material layer are electrically connected in series. As a separator, a well-known separator for secondary batteries, such as a porous membrane and a nonwoven fabric, can be used.

  Each termination electrode has a first metal foil as a current collector and an active material layer provided on the back side surface of the first metal foil. As 1st metal foil, well-known metal foil can be used as a collector for secondary batteries, such as copper foil, copper alloy foil, aluminum foil, aluminum alloy foil, stainless steel foil, nickel foil, for example. . Moreover, the metal foil which gave plating processing, such as copper plating and nickel plating, to the metal foil mentioned above can also be used as a 1st metal foil. The thickness of the first metal foil can be appropriately set within a range of 5 to 100 μm, for example.

  Of the two termination electrodes arranged at both ends of the electrode assembly, at least one termination electrode may have a first metal foil that is thicker than the second metal foil. In preparing the termination electrode, the active material layer is usually applied on the first metal foil, and then the active material layer is adhered to the first metal foil, and the active material layer is reduced in porosity. The material layer is pressed.

  At this time, when the pressing is performed while the terminal electrode is conveyed by a roll press machine or the like, a tensile stress in a direction parallel to the conveying direction is generated in the active material layer after the pressing. However, since the termination electrode has the active material layer only on the back side surface, the termination electrode may be warped by the tensile stress generated by the active material layer. Such warpage of the terminal electrode is not preferable because it causes deterioration of workability in the assembly work of the electrode assembly. On the other hand, the rigidity of the first metal foil can be further improved by making the thickness of the first metal foil thicker than that of the second metal foil as described above. As a result, it is possible to suppress warping of the terminal electrode after pressing and to avoid deterioration of workability in the assembly work of the electrode assembly.

  From the viewpoint of more reliably avoiding warping of the termination electrode after pressing, the first termination electrode of at least one of the two termination electrodes has a thickness that is 1.5 times or more that of the second metal foil. It is preferable to have a metal foil.

  The front side surface of the first metal foil is flat, and the back side surface is rougher than the front side surface. In order to produce such a first metal foil, for example, one surface of a metal foil with flat surfaces may be subjected to a surface treatment to roughen the surface. As the surface treatment for roughening the metal foil, for example, a known surface treatment such as a chemical treatment such as etching treatment or plating treatment, a physical treatment such as sputtering, or a mechanical treatment such as polishing treatment is applied. be able to.

  The arithmetic average roughness Ra of the front side surface in the first metal foil can be 0.50 μm or less. The arithmetic average roughness Ra is a value obtained by a measuring method based on JIS B0601: 2013 using a stylus type surface roughness measuring instrument.

  On the other hand, the surface roughness of the back side surface of the first metal foil is rougher than that of the front side surface. Thereby, the adhesiveness of a 1st metal foil and the seal | sticker part provided in the peripheral part can be improved. Furthermore, in this case, it is possible to improve the adhesion between the first metal foil and the active material layer provided on the back side surface thereof, and to suppress the peeling and dropping of the active material layer from the metal foil.

  From the viewpoint of enhancing the above-described effects, the arithmetic average roughness Ra of the back side surface of the first metal foil is preferably 1 μm or more. However, if the value of the arithmetic average roughness Ra on the back side surface is excessively increased, the contact resistance between the first metal foil and the active material layer may increase, and the strength of the first metal foil may decrease. is there. From the viewpoint of avoiding these problems, the arithmetic mean roughness Ra of the back side surface of the first metal foil is preferably 2 μm or less.

  The back side surface of the first metal foil may have a number of protrusions protruding from the first metal foil. In this case, when a seal part or an active material layer is provided on the back side surface, a state in which a part of the seal part or the active material layer enters between the protrusions can be easily realized. As a result, the adhesiveness between the first metal foil and the seal portion and the adhesiveness between the first metal foil and the active material layer can be further improved.

  A large number of protrusions may be arranged regularly or irregularly. For example, you may protrude in the thickness direction of metal foil, and you may protrude in the direction slightly inclined from the thickness direction. Further, the height and thickness of the protrusions or the interval between adjacent protrusions may or may not be constant. Furthermore, the protrusion may be connected to the adjacent protrusion through a convex portion formed on the side peripheral surface thereof.

  Each protrusion preferably has irregularities formed randomly on its side peripheral surface. In this case, by applying the active material layer on the back side surface and then pressing the active material layer, the active material layer is deformed along the unevenness to hold the active material layer more firmly on the protrusions. Can do. As a result, the active material layer and the metal foil can be more firmly bonded, and the active material layer can be more effectively suppressed from peeling off or falling off.

  The protrusion may have a height of 1 to 15 μm and a width of 1 to 5 μm in the cross section in the thickness direction of the first metal foil. In this case, a state in which a part of the active material layer enters between the protrusions can be more easily realized. As a result, the active material layer and the metal foil can be more firmly bonded, and the active material layer can be more effectively suppressed from peeling off or falling off.

  It is preferable that the protrusion has a protruding portion protruding to the side between the base portion and the distal end portion in the thickness direction of the metal foil. Examples of the protruding portion include a convex portion formed on the side peripheral surface of the protrusion, and a tip portion of the protrusion protruding in a direction slightly inclined from the thickness direction of the metal foil.

  In the case where the protrusion has a protruding portion, the space between the protruding portion and the base portion is recessed inside the protruding portion. Therefore, for example, by applying the active material layer on the back side surface and then pressing the active material layer, a part of the active material layer is bitten into the depressed portion, and the active material layer is held more firmly on the protrusion. can do. As a result, the active material layer and the metal foil can be more firmly bonded, and the active material layer can be more effectively suppressed from peeling off or falling off.

  In the case where the back side surface has a large number of protrusions as described above, it is possible to obtain the value of the arithmetic average roughness Ra itself by measurement using a stylus type surface roughness measuring instrument based on JIS B0601: 2013. However, in this case, since it is difficult to obtain an accurate roughness curve, an accurate arithmetic mean roughness Ra value on the front side cannot be obtained even if the above-described measurement is performed. The measured value of the arithmetic average roughness Ra of the back side surface obtained by measurement using a stylus type surface roughness measuring instrument is a measured value for a virtual surface in which the tips of many protrusions are smoothly connected. Conceivable.

  The measured value of the arithmetic average roughness Ra of the back side surface having a large number of protrusions is preferably 1.0 to 2.0 μm. In this case, a state in which a part of the seal portion or the active material layer enters between the protrusions can be more easily realized. As a result, the adhesiveness between the first metal foil and the seal portion and the adhesiveness between the first metal foil and the active material layer can be further improved. From the viewpoint of obtaining the above-described effects more reliably, it is more preferable to set the measured value of the arithmetic average roughness Ra to 1.25 to 1.75 μm.

  An active material layer is provided on the back side surface of the first metal foil. The active material layer usually includes an active material and a binder. Examples of the active material include lithium ion secondary battery active materials such as lithium cobaltate, spinel type lithium manganate, lithium nickelate, graphite, and hard carbon, and nickel hydride storage batteries such as nickel hydroxide and hydrogen storage alloys. An active material can be employed. Moreover, the active material layer may contain well-known additives, such as a conductive support agent, as needed.

The bipolar electrode is disposed between the two termination electrodes, and has a second metal foil as a current collector, and an active material layer provided on each of the front side surface and the back side surface of the second metal foil. ing.
As the second metal foil, for example, a metal foil known as a secondary battery current collector such as a copper foil, a copper alloy foil, an aluminum foil, an aluminum alloy foil, a stainless steel foil, or a nickel foil can be used. . Moreover, the metal foil which gave plating processing, such as copper plating and nickel plating, to the metal foil mentioned above can also be used as 2nd metal foil. The thickness of the second metal foil can be appropriately set within a range of 5 to 100 μm, for example.

  The surface roughness of at least one of the front side surface and the back side surface of the second metal foil is rougher than that of the front side surface of the first metal foil. In order to produce such a second metal foil, for example, surface treatment may be performed on at least one surface of a metal foil having flat surfaces to roughen the surface. As the surface treatment for roughening the metal foil, a well-known surface treatment can be applied as in the case of the first metal layer. In the following, a surface having a surface roughness that is rougher than the front side surface of the first metal foil in the second metal foil may be referred to as a “roughened surface” for convenience.

  By making the surface roughness of at least one of the front side surface or the back side surface of the second metal foil rougher than the flat front side surface of the first metal foil, the second metal foil and the seal portion provided on the peripheral portion thereof Adhesiveness can be improved. Furthermore, in this case, the adhesion between the second metal foil and the active material layer provided on the roughened surface of the second metal foil is improved, and the active material layer is peeled off from the second metal foil. Dropping can also be suppressed.

  From the viewpoint of enhancing the above-described effects, the arithmetic average roughness Ra of the roughened surface of the second metal foil is preferably 1 μm or more. However, if the value of the arithmetic average roughness Ra of the roughened surface becomes excessively large, the contact resistance between the second metal foil and the active material layer may increase, and the strength of the second metal foil may decrease. There is. From the viewpoint of avoiding these problems, the arithmetic mean roughness Ra of the roughened surface of the second metal foil is preferably 2 μm or less.

  The second metal foil has a flat front side surface and a back side surface having a rougher surface roughness than the front side surface, and the active material provided on the back side surface of the second metal foil includes the second metal foil. It is preferable that the adhesiveness with respect to a flat surface is low compared with the said active material provided in the front side surface of metal foil. That is, it is preferable to provide an active material layer with relatively high adhesion on the flat surface of the second metal foil, and to provide an active material layer with relatively low adhesion on the roughened surface.

  In this case, since the surface roughness of the back side surface is rougher than that of the front side surface, the adhesion with the active material layer provided on the back side surface can be sufficiently improved. Therefore, peeling and dropping of the active material layer from the second metal foil can be suppressed. In addition, since the active material layer having relatively high adhesiveness is provided on the front side surface, the front side surface of the metal foil and the active material layer provided on the front side surface without roughening the surface roughness Can be sufficiently improved. Therefore, peeling and dropping of the active material layer from the second metal foil can be suppressed.

  Thus, by selecting the combination of the surface shape of the second metal foil and the active material layer as described above, the active material layer that has relatively low adhesion to a flat surface and is likely to peel or fall off, and the flat surface Necessary and sufficient adhesiveness can be easily obtained for both the active material layer that has relatively high adhesion to the surface and is unlikely to peel off or fall off.

  Furthermore, by making the front side surface a flat surface, the thickness of the entire metal foil can be reduced compared to the case where both the front side surface and the back side surface are roughened, and consequently the thickness of the entire bipolar electrode is reduced. Can be thinned. Then, by incorporating such a bipolar electrode into the electrode assembly, the dimensions of the electrode assembly in the stacking direction, and hence the dimensions of the secondary battery can be easily reduced.

  Further, as described above, since the second metal foil can easily obtain necessary and sufficient adhesiveness to suppress the peeling and dropping of each active material layer, the amount of binder in each active material layer is increased. There is no need to do. Therefore, the second metal foil can further reduce the electric resistance with each active material layer, and can further reduce the internal resistance of the secondary battery.

  The roughened surface of the second metal foil may have a number of protrusions protruding from the second metal foil. In this case, when a seal part or an active material layer is provided on the roughened surface, a state in which a part of the seal part or the active material layer enters between the protrusions can be easily realized. As a result, the adhesion between the second metal foil and the seal portion and the adhesion between the second metal foil and the active material layer can be further improved.

  When providing a protrusion on the roughened surface of the second metal foil, the protrusion may have the same configuration as the protrusion provided on the first metal foil. The effect in this case is the same as the effect by the protrusion of the first metal foil described above.

  An active material layer is provided on each of the front side surface and the back side surface of the second metal foil. The active material layer provided on the front side surface has a polarity different from that of the active material layer provided on the back side surface. The active material layer usually includes an active material and a binder. Examples of the active material include lithium ion secondary battery active materials such as lithium cobaltate, spinel type lithium manganate, lithium nickelate, graphite, and hard carbon, and nickel hydride storage batteries such as nickel hydroxide and hydrogen storage alloys. An active material can be employed. Moreover, the active material layer may contain well-known additives, such as a conductive support agent, as needed.

  A restraining member is disposed at each end in the stacking direction of the electrode assembly. The restraining member is in contact with the front side surface of the first metal foil in the terminal electrode, and is electrically connected to the electrode assembly via the first metal foil. As the restraining member, for example, a member made of a metal such as aluminum, an aluminum alloy, or stainless steel can be employed.

  Moreover, the peripheral part of each metal foil in an electrode assembly is coat | covered with the seal | sticker part. A seal portion is interposed between adjacent metal foils. As the seal portion, for example, a material that can be welded by heating such as polyethylene, polypropylene, polyamide, polyphenylene ether, polyphenylene sulfide, or the like can be used.

Example 1
Examples of the secondary battery will be described with reference to the drawings. As shown in FIG. 1, the secondary battery 1 is in contact with an electrode assembly 11 including a plurality of electrodes 3 and 4 stacked via a separator 2, and each end of the electrode assembly 11 in the stacking direction. And a restraining member 12 electrically connected to the electrode assembly 11. As shown in FIG. 2, the electrode assembly 11 includes termination electrodes 3 (3p, 3n) disposed at both ends in the stacking direction, bipolar electrodes 4 disposed between the termination electrodes 3, and adjacent electrodes. The separator 2 interposed between the active material layers 32 and 42 in 3 and 4 and the peripheral portions 313 and 413 of the first metal foil 31 and the second metal foil 41 are covered, and the metal in the adjacent electrodes 3 and 4 It has the seal | sticker part 5 interposed between foil 31,41.

  The termination electrode 3 includes a first metal foil 31 having a flat front side surface 311 in contact with each restraining member 12, a back side surface 312 having a rougher surface roughness than the front side surface 311, and a back side of the first metal foil 31. And an active material layer 32 provided on the surface 312. The bipolar electrode 4 includes a second metal foil 41 having a surface roughness of at least one of the front side surface 411 and the back side surface 412 that is rougher than the front side surface of the first metal foil 31, and the front side surface 411 of the second metal foil 41 and And an active material layer 42 provided on each of the back side surfaces 412.

  As shown in FIG. 1, the electrode assembly 11 of this example includes a first termination electrode 3p disposed at one end in the stacking direction, a second termination electrode 3n disposed at the other end, and these termination electrodes. A plurality of bipolar electrodes 4 disposed between 3p and 3n. The termination electrodes 3p and 3n and the bipolar electrode 4 are laminated via a separator 2 made of a nonwoven fabric of polyolefin resin. The separator 2 is impregnated with an electrolyte.

  As shown in FIGS. 1 and 2, the first termination electrode 3 p includes a first metal foil 31 having a flat front side surface 311 and a back side surface 312 having a surface roughness rougher than that of the front side surface 311, 1 having a positive electrode active material layer 32p provided on the back side surface 312 of the metal foil 31. As shown in FIG. 1, the second termination electrode 3 n includes a first metal foil 31 and a negative electrode active material layer 32 n provided on the back side surface 312 of the first metal foil 31.

  The first metal foil 31 in this example is a metal foil having a thickness of 20 μm. Further, the arithmetic average roughness Ra of the front side surface 311 of the first metal foil 31 is 0.50 μm or less, and the arithmetic average roughness Ra of the back side surface 312 is larger than 0.50 μm. The first metal foil 31 of this example can be produced by, for example, subjecting one surface of a metal foil having flat surfaces to a surface treatment such as a polishing treatment and roughening the surface.

  As shown in FIGS. 1 and 2, the bipolar electrode 4 includes a second metal foil 41 whose surface roughness of both the front side surface 411 and the back side surface 412 is rougher than that of the front side surface 311 of the first metal foil 31, and the second metal foil 41. The negative electrode active material layer 42 n provided on the front side surface 411 of the metal foil 41 and the positive electrode active material layer 42 p provided on the back side surface 412 of the second metal foil 41 are provided.

  The second metal foil 41 in this example is a metal foil having a thickness of 10 μm. Further, the arithmetic average roughness Ra of the front side surface 411 and the back side surface 412 of the second metal foil 41 is larger than 0.50 μm. The second metal foil 41 of this example can be produced by, for example, subjecting both surfaces of a metal foil with flat surfaces to a surface treatment such as a polishing treatment and roughening the surface.

  As shown in FIG. 1, the peripheral portions 313 and 413 of the first metal foil 31 and the second metal foil 41 are covered with the seal portion 5. Further, the seal portion 5 is interposed between the metal foils 31 and 41 in the adjacent electrodes 3 and 4. The seal portion 5 of this example is in direct contact with the peripheral portions 313 and 413 of the first metal foil 31 and the second metal foil 41, and the inner seal portion 51 and the inner seal portion interposed between the adjacent electrodes 3 and 4 51 and an outer seal portion 52 that covers the front side surface 311 of the peripheral edge portion 313 of the first metal foil 31 in the terminal electrode 3. The inner seal portion 51 is made of polyphenylene ether, and the outer seal portion 52 is made of polypropylene.

  In addition, metal restraining members 12 are disposed at both ends of the electrode assembly 11 in the stacking direction. The restraining member 12 is held in contact with the flat front side surface 311 of the first metal foil 31 in each terminal electrode 3.

  The secondary battery 1 of this example can be manufactured by the following procedures, for example. First, the termination electrode 3 and the plurality of bipolar electrodes 4 described above are prepared. Next, the inner seal portion 51 is provided on the back side surface 312 of the peripheral edge portion 313 of the first metal foil 31 in the first terminal electrode 3p and on the back side surface 412 of the peripheral edge portion 413 of the second metal foil 41 in the bipolar electrode 4. Deploy.

  Next, as shown in FIG. 3, the electrodes 3, 4 and the separator 2 are alternately stacked so that the active material layers 32, 42 of the electrodes 3, 4 face each other with the separator 2 interposed therebetween, and the stacked body 110. Assemble. In this laminate 110, the negative electrode active material layer 42n of the bipolar electrode 4 faces the first termination electrode 3p side in the lamination direction of the laminate 110, and the positive electrode active material layer 41a faces the second termination electrode 3n side in the lamination direction. It is suitable.

  Thereafter, while compressing the laminated body 110 in the laminating direction as indicated by an arrow 111, the inner seal portion 51 is heated, and the inner seal portion 51 is surrounded by the peripheral portions 313 of the metal foils 31 and 41 in the adjacent electrodes 3 and 4; 413 to be welded. After the inner seal portion 51 is cooled and solidified, the outer surface of the inner seal portion 51 is further covered with the outer seal portion 52. Thus, the electrode assembly 11 can be obtained. And after making the restraint member 12 contact | abut to each termination | terminus electrode 3, the secondary battery 1 can be obtained by inject | pouring electrolyte solution into the inner side seal part 52 from the injection hole which is not shown in figure.

  Next, the effect of the secondary battery 1 of this example is demonstrated. Since the restraining member 12 in the secondary battery 1 of this example is in contact with the flat front side surface 311 of the first metal foil 31, the contact area between the first metal foil 31 and the restraining member 12 should be sufficiently widened. Can do. As a result, an increase in the contact resistance between the restraining member 12 and the first metal foil 31 can be suppressed, and consequently an increase in the internal resistance of the secondary battery 1 can be suppressed.

  Further, the back side surface 312 of the first metal foil 31 and the both sides 411 and 412 of the second metal foil 41 are roughened so that the surface roughness is rougher than that of the front side surface 311 of the first metal foil 31. And the peripheral parts 313 and 413 of the 1st metal foil 31 and the 2nd metal foil 41 are coat | covered with the seal part 5, and the seal part 5 is between the metal foils 31 and 41 in the adjacent electrodes 3 and 4 between. Intervene.

  Thus, by covering the peripheral edge portions 313 and 413 of the metal foils 31 and 41 with the seal portion 5, the roughened surfaces of the metal foils 31 and 41 and the seal portion 5 can be brought into contact with each other. . As a result, the adhesiveness between the seal portion 5 and the metal foils 31 and 41 can be improved. Further, by improving the adhesion between the seal portion 5 and each of the metal foils 31 and 41, it is possible to suppress leakage of electrolyte to the outside of the electrode assembly 11 and entry of outside air to the inside of the electrode assembly 11. Can do.

  In addition, the two termination electrodes 3 disposed at both ends of the electrode assembly 11 in the stacking direction have the first metal foil 31 that is thicker than the second metal foil 41. Furthermore, the thickness of the first metal foil 31 is 1.5 times or more the thickness of the second metal foil 41. Therefore, it is possible to suppress warping of the termination electrode 3 after the active material layer 32 is pressed in the process of manufacturing the termination electrode 3. Thereby, it is possible to avoid deterioration in workability in the assembly work of the electrode assembly 11.

(Example 2)
This example is an example of the secondary battery 102 using a metal foil having a flat front surface 431 and a large number of protrusions 433 on the back surface 432 as the second metal foil 43. Of the reference numerals used in and after the present embodiment, the same reference numerals as those used in the above-described embodiments represent the same constituent elements as those in the above-described embodiments unless otherwise specified.

  The secondary battery 102 of this example is configured as a nickel metal hydride storage battery. Specifically, the first metal foil 31 in the first terminal electrode 3p is a nickel foil. Moreover, the positive electrode active material layer 32p contains spherical particles of nickel hydroxide as a positive electrode active material and a binder. The first metal foil 31 in the second terminal electrode 3n is a nickel foil, and the negative electrode active material layer 32n contains amorphous particles of a hydrogen storage alloy as a negative electrode active material and a binder.

  As shown in FIGS. 4 and 5, the bipolar electrode 402 of this example includes a second metal foil 43, a negative electrode active material layer 42 n provided on the front side surface 431 of the second metal foil 43, and a second metal foil. 43, and a positive electrode active material layer 42p provided on the back side surface 432 of 43. The front side surface 431 of the second metal foil 43 is flat, and the back side surface 432 has a large number of protrusions 433.

  As shown in FIG. 4, the front side surface 431 of the second metal foil 43 is a flat surface having no protrusions. The arithmetic average roughness Ra of the front side surface 431 is 0.5 μm. On the front side surface 431, a positive electrode active material layer 42p including spherical particles 421p of nickel hydroxide as a positive electrode active material and a binder is provided. In FIG. 4 and FIG. 5, the binder is not shown for convenience.

  A number of protrusions 433 provided on the back side surface 432 protrude from the second metal foil 43 randomly. Further, as shown in FIG. 5, the protrusion 433 has irregularities formed randomly on the side peripheral surface thereof. The height h of the protrusion in the cross section in the thickness direction of the second metal foil 43 is in the range of 1 to 15 μm. Further, the width w of the protrusion 433 in the cross section is in the range of 1 to 5 μm.

  Many of the protrusions 433 have a protruding portion 436 protruding to the side between the base portion 434 and the distal end portion 435 in the thickness direction of the second metal foil 43. As shown in FIG. 5, as the protruding portion 436, the protruding portion 437 formed on the side peripheral surface of the protrusion 433, or the tip portion of the protrusion 433 protruding in a direction slightly inclined from the thickness direction of the second metal foil 43. There is 435a.

  As shown in FIGS. 4 and 5, since there are many protrusions 433 on the back side surface 432 of the second metal foil 43, it is not possible to obtain an accurate arithmetic average roughness Ra value as described above. However, the measured value of the arithmetic average roughness Ra obtained by measurement using a stylus type surface roughness measuring instrument is 1.5 μm. On the back side surface 432, a negative electrode active material layer 42n including amorphous particles 421n of a hydrogen storage alloy as a negative electrode active material and a binder is provided. Others are the same as in the first embodiment.

  The bipolar electrode 402 of this example includes a second metal foil 43 including a flat front side surface 431 and a back side surface 432 having a surface roughness rougher than that of the front side surface 431. When the secondary battery 102 is configured as a nickel hydride storage battery as in this example, the positive electrode active material layer 42p including the spherical particles 421p as the positive electrode active material is the negative electrode active material layer including the amorphous particles 421n as the negative electrode active material. Adhesiveness to flat surfaces is lower than 42n.

  That is, in the bipolar electrode 402 of this example, the negative active material layer 42n having a relatively high adhesiveness is provided on the flat front side surface 431, and the adhesiveness is relatively low on the back side surface 432 having a rough surface roughness. A positive electrode active material layer 42p is provided. Therefore, both of the positive electrode active material layer 42p that has relatively low adhesion to a flat surface and easily peels and drops, and the negative electrode active material layer 42n that has relatively high adhesion to a flat surface and does not easily peel and drop off. Necessary and sufficient adhesion can be easily obtained.

  Furthermore, by making the front side surface 431 flat, it is possible to reduce the thickness of the entire metal foil as compared with the case where both the front side surface 431 and the back side surface 432 are roughened surfaces. The overall thickness can be reduced. By incorporating such a bipolar electrode 402 into the electrode assembly 11, the dimensions of the electrode assembly 11 in the stacking direction, and thus the dimensions of the secondary battery 102 can be easily reduced.

  Further, as described above, the second metal foil 43 can easily obtain necessary and sufficient adhesiveness to suppress the peeling and dropping of each active material layer 42, so that the binder in each active material layer 42 can be obtained. There is no need to increase the amount. Therefore, by using the second metal foil 43, the electric resistance of each active material layer 42 and the second metal foil 43 can be further reduced, and as a result, the internal resistance of the secondary battery 102 can be further reduced. .

  Further, the back side surface 432 of the second metal foil 43 has a large number of protrusions 322 protruding from the second metal foil 43. Therefore, when the seal portion 5 and the active material layer 42 are provided on the back side surface 432, a state in which a part of the seal portion 5 and the active material layer 42 enters between the protrusions 433 can be easily realized. As a result, the adhesiveness between the second metal foil 43 and the seal portion 5 and the adhesiveness between the second metal foil 43 and the active material layer 42 can be further improved. In addition, the secondary battery 102 of this example can achieve the same effects as those of the first embodiment.

(Experimental example)
In this example, the contact resistance between the first metal foil 31 of the termination electrode 3 and the restraining member 12 is measured. In this example, metal foils (test materials 1 to 4) having the thickness and arithmetic average roughness Ra shown in Table 1 were prepared. Among these test materials, the test material 1 and the test material 3 are test materials simulating the flat front side surface 311 of the first metal foil 31. The test material 2 and the test material 4 are test materials that simulate the back side surface 312 of the first metal foil 31, that is, the surface subjected to the roughening treatment. In Table 1, the value of thickness converted from the mass of each test material using the values of density and area of each test material is shown.

  In this example, a mating material simulating the restraining member 12 was prepared separately from these test materials. Specifically, a metal foil having a thickness of 50 μm was used as the counterpart material.

  In measuring the contact resistance, first, as shown in FIG. 6, the test material E and the counterpart material M were laminated so that a part of the test material E and a part of the counterpart material M overlapped. At this time, the dimension of the overlapping portion between the test material E and the counterpart material M was 30 mm in length and 30 mm in width. Next, the insulator 61 was arrange | positioned on the both sides of the lamination direction of the test material E and the other material M so that the overlap part of the test material E and the other material M might be covered. A holding plate 62 was disposed on each insulator 61, and an overlapping portion of the test material E and the counterpart material M was sandwiched between the two holding plates 62. In this state, the contact resistance between the test material E and the counterpart material M was measured three times. Table 1 shows the measurement results of each time and the average value of three times.

  As shown in Table 1, in the same thickness, the test specimens 1 and 3 having a small arithmetic average roughness Ra are in contact with the test specimens 2 and 4 having a larger arithmetic average roughness Ra than these test specimens. The resistance value has decreased. From these results, it can be easily understood that the contact resistance between the restraining member 12 and the first metal foil 3 can be reduced by bringing the restraining member 12 and the flat front side surface 311 of the first metal foil 3 into contact with each other.

  The mode of the secondary battery according to the present invention is not limited to the mode of the above-described examples and comparative examples, and the configuration can be changed as appropriate without departing from the spirit of the present invention. For example, in Example 1, although the example which used the metal foil by which the both surfaces 411 and 412 of the 2nd metal foil 41 were roughened was shown, either one of the front side surface 411 or the back side surface 412 is made into a flat surface. The other may be a roughened surface. In this case, in addition to the operational effects of the first embodiment, it is possible to obtain the operational effects of reducing the thickness of the second metal foil 41 and reducing the dimension of the secondary battery 1 in the stacking direction.

  Moreover, in Example 2, although the example which provided the processus | protrusion 433 in the back side surface 432 of the 2nd metal foil 43 was shown, the processus | protrusion 433 can also be provided in the front side surface 431 of the 2nd metal foil 43. FIG. However, in this case, there is a possibility that the effect of reducing the thickness of the second metal foil 43 obtained when the protrusion 433 is provided only on the back side surface 432 cannot be obtained sufficiently.

  Moreover, in Example 2, although the example using the same 1st metal foil 31 as Example 1 was shown, the processus | protrusion similar to the 2nd metal foil 43 is provided in the back side surface 312 of the 1st metal foil 31. Thus, the back side surface 312 may be roughened. In this case, the adhesiveness between the first metal foil 31 and the active material layer 32 can be further improved, and peeling and dropping of the active material layer 32 from the first metal foil 31 can be more effectively suppressed.

  Moreover, in Example 2, although the example which comprised the secondary battery 102 as a nickel hydride storage battery was shown, the secondary battery 102 may be a lithium ion secondary battery.

DESCRIPTION OF SYMBOLS 1,102 Secondary battery 11 Electrode assembly 12 Constraining member 2 Separator 3 Termination electrode 31 1st metal foil 311 Front side 312 Back side 313 Peripheral part 32 Active material layer 4, 402 Bipolar electrode 41, 43 2nd metal foil 411, 431 Front side surface 412, 432 Back side surface 413 Peripheral part 42 Active material layer 5, 51, 52 Seal part

Claims (5)

An electrode assembly comprising a plurality of electrodes stacked via a separator;
A constraining member that contacts each end in the stacking direction of the electrode assembly and is electrically connected to the electrode assembly;
The electrode assembly is
A first metal foil having a flat front side that abuts on each of the restraining members, a back side having a rougher surface roughness than the front side, and an active material provided on the back side of the first metal foil A termination electrode having a layer;
A second metal foil having a surface roughness of at least one of the front side surface and the back side surface that is rougher than the front side surface of the first metal foil, and actives provided on the front side surface and the back side surface of the second metal foil, respectively. A bipolar electrode having a material layer and disposed between the termination electrodes,
The separator interposed between the active material layers in the adjacent electrodes;
A secondary battery that covers peripheral edges of the first metal foil and the second metal foil and has a seal portion interposed between the metal foils in the adjacent electrodes.   2. The secondary battery according to claim 1, wherein at least one of the two termination electrodes includes the first metal foil having a thickness larger than that of the second metal foil.   3. The secondary battery according to claim 2, wherein at least one of the two termination electrodes includes the first metal foil having a thickness 1.5 times or more that of the second metal foil. .   The second metal foil has a flat front side and a back side whose surface roughness is rougher than the front side, and the active material provided on the back side of the second metal foil includes the above The secondary battery according to any one of claims 1 to 3, wherein adhesion to a flat surface is lower than that of the active material provided on the front side surface of the second metal foil.   The secondary battery of any one of Claims 1-4 which is a nickel hydride storage battery.

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