Electrode plate and power storage device

Abstract

This electrode plate 11 comprises a belt-like current collector 34, and an electrode active material layer 36 provided on the surface of the current collector 34. The current collector 34 has an exposed part 38 in which the electrode active material layer 36 is not provided. The exposed part 38 includes: an outer contour part 40 overlapping with an edge part in a short direction A of the current collector 34; an inner contour part 42 located closer to a center side of the current collector 34 than the outer contour part 40 in the short direction A; and a pair of connection contour parts 44a, 44b arranged in a longitudinal direction B of the current collector 34 and connecting the outer contour part 40 and the inner contour part 42. At least one of the connection contour parts 44a, 44b has, in at least a part thereof, an inclined part 46 extending diagonally with respect to the short direction A.

Description

Electrode Plate and Power Storage Device

[0001] The present disclosure relates to an electrode plate and a power storage device.

[0002] There is a strong demand for increased capacity in power storage devices such as secondary batteries. In response to such demands, for example, in Patent Document 1, a secondary battery is described in which a bare portion where no positive electrode active material layer is provided, that is, an exposed portion of the positive electrode current collector, is provided on the positive electrode current collector, and a positive electrode lead is welded to this exposed portion. Thus, by welding the lead to the exposed portion of the current collector, the area of the electrode active material layer can be increased, and the capacity of the power storage device can be increased.

[0003] Japanese Patent Application Laid-Open No. 2003-68271

[0004] As a result of intensive studies on an electrode plate having an exposed portion of a current collector, the present inventor has found that providing the exposed portion can cause a rapid fluctuation in the load on the manufacturing equipment for the electrode plate, leading to a deterioration in the quality of the electrode plate.

[0005] The present disclosure has been made in view of such circumstances, and one of its objectives is to provide a technology for improving the quality of an electrode plate.

[0006] One aspect of the present disclosure is an electrode plate. This electrode plate includes a strip-shaped current collector and an electrode active material layer provided on the surface of the current collector. The current collector has an exposed portion where no electrode active material layer is provided. The exposed portion has an outer contour portion that overlaps with the edge portion in the short side direction of the current collector, an inner contour portion that is located on the center side of the current collector from the outer contour portion in the short side direction, and a pair of connection contour portions that are arranged in the longitudinal direction of the current collector and connect the outer contour portion and the inner contour portion. At least one of the connection contour portions has at least a part of an inclined portion that extends obliquely with respect to the short side direction.

[0007] Another aspect of the present disclosure is a power storage device. This power storage device includes the electrode plate of the above aspect.

[0008] Any combination of the above components, as well as those obtained by converting the expression of the present disclosure among methods, devices, systems, etc., are also effective as aspects of the present disclosure.

[0009] According to the present disclosure, the quality of the electrode plate can be improved.

[0010] This is a cross-sectional view of an energy storage device according to an embodiment. This is a perspective view of the electrode group. This is a schematic diagram of the region of the electrode plate including the exposed portion. This is a schematic diagram of the region of the electrode plate including the exposed portion according to Modification 1. This is a schematic diagram of the region of the electrode plate including the exposed portion according to Modification 2.

[0011] The present disclosure will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the present disclosure. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. Furthermore, where terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. In addition, some components that are not important for explaining the embodiments are omitted in each drawing.

[0012] Figure 1 is a cross-sectional view of an energy storage device 1 according to an embodiment. Figure 2 is a perspective view of the electrode group 2. Note that the current collector 34 is not shown in Figures 1 and 2. The energy storage device 1 is, for example, a rechargeable secondary battery such as a lithium-ion battery, a nickel-metal hydride battery, or a nickel-cadmium battery, or a capacitor such as an electric double-layer capacitor. The energy storage device 1 includes an electrode group 2, a first insulating plate 4, a second insulating plate 6, and an outer casing 8.

[0013] Electrode group 2 is, for example, cylindrical, and has a wound structure in which a strip-shaped first electrode plate 10 and a strip-shaped second electrode plate 12 are stacked with a strip-shaped separator 14 in between, and wound in a spiral shape. Therefore, the first electrode plate 10, the second electrode plate 12 and the separator 14 are stacked alternately in the radial direction Y of electrode group 2. In electrode group 2, the longitudinal direction of each electrode plate and separator 14 is the winding direction Z, and the short direction of each electrode plate and separator 14, in other words, the width direction, is the axial direction X. In this embodiment, the first electrode plate 10 is the positive electrode plate and the second electrode plate 12 is the negative electrode plate. However, the first electrode plate 10 may be the negative electrode plate and the second electrode plate 12 may be the positive electrode plate. Furthermore, in the following, when the polarity of the electrode plates is not distinguished, the first electrode plate 10 and the second electrode plate 12 will be collectively referred to as electrode plate 11. The separator 14 is composed of a microporous film having ion permeability and insulating properties, such as polypropylene or polyethylene.

[0014] A first lead 16 is attached to the first electrode plate 10. A second lead 18 is attached to the second electrode plate 12. Each lead is attached to the current collector 34 (see Figure 3, etc.) of each electrode plate 11 by welding or the like. The first lead 16 protrudes from one end of the electrode group 2 in the axial direction X. The second lead 18 protrudes from the other end of the electrode group 2 in the axial direction X. In this embodiment, one lead is attached to each electrode, but multiple leads may be attached to each electrode. Also, the attachment positions of the leads on each electrode are not limited to those illustrated in Figure 2. The structure of the electrode plate 11 will be described in detail later.

[0015] The first insulating plate 4 and the second insulating plate 6 are arranged so as to sandwich the electrode group 2 in the axial direction X. The electrode group 2, the first insulating plate 4, and the second insulating plate 6 are housed together with the electrolyte (not shown) in an outer container 8. The outer container 8 is a bottomed cylindrical metal container. The first insulating plate 4 is positioned on the opening side of the outer container 8. The second insulating plate 6 is positioned on the bottom side of the outer container 8. A sealing body 20 is fitted into the opening of the outer container 8. A gasket 22 is provided between the outer container 8 and the sealing body 20. This seals the electrode group 2, the first insulating plate 4, the second insulating plate 6, and the electrolyte inside the outer container 8.

[0016] The sealing body 20 includes a filter 24, a lower valve body 26, an upper valve body 28, an insulating member 30, and a cap 32. Each component of the sealing body 20 has, for example, a disc shape or a ring shape. In addition, each component except the insulating member 30 is electrically connected to one another. The filter 24 has an opening 24a and covers the opening of the outer can 8. The lower valve body 26 and the upper valve body 28 cover the opening of the outer can 8 and close the opening 24a. The lower valve body 26 and the upper valve body 28 are connected at their respective central portions, with the insulating member 30 interposed between their respective peripheral portions. When the internal pressure of the outer can 8 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 26 may rupture. As a result, the upper valve body 28 bulges towards the cap 32 and separates from the lower valve body 26. Consequently, the electrical connection between the lower valve body 26 and the upper valve body 28 is interrupted. A cap 32 is placed over the outside of the upper valve body 28.

[0017] The first lead 16 extends towards the sealing body 20 through a through hole in the first insulating plate 4. The second lead 18 extends towards the bottom of the outer can 8, passing outside the second insulating plate 6. The first lead 16 is connected to the filter 24 by welding or the like. The cap 32 is electrically connected to the filter 24 to form the first electrode terminal. The second lead 18 is connected to the bottom of the outer can 8 by welding or the like. Therefore, the outer can 8 forms the second electrode terminal.

[0018] Next, the structure of the electrode plate 11 will be described in detail. Figure 3 is a schematic diagram of the region of the electrode plate 11 including the exposed portion 38. The electrode plate 11 comprises a current collector 34 and an electrode active material layer 36. The current collector 34 is made of a strip-shaped metal foil, and the electrode active material layer 36 is provided on the surface of the current collector 34. As an example, the electrode active material layer 36 is laminated on both main surfaces of the current collector 34.

[0019] In a typical lithium-ion secondary battery, the current collector 34 is made of aluminum foil or the like if it is the positive electrode, and copper foil or the like if it is the negative electrode. The electrode active material layer 36 can be formed by pressing an electrode active material sheet onto the surface of the current collector 34 if a dry electrode mixture is used. The electrode active material sheet is obtained by forming a sheet of dry electrode mixture containing materials such as electrode active material, binder, and conductive material. Alternatively, if a wet electrode mixture is used, the electrode active material layer 36 can be formed by applying a wet electrode mixture to the surface of the current collector 34, drying, and rolling. A wet electrode mixture is obtained by kneading materials such as electrode active material, binder, and conductive material in a dispersion medium and dispersing them uniformly. In a typical lithium-ion secondary battery, the electrode active material is lithium cobalt oxide or lithium iron phosphate for the positive electrode, and graphite for the negative electrode. The binders are polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), etc. The conductive agents are graphite, carbon black, acetylene black, etc.

[0020] The current collector 34 has an exposed portion 38 at the end in the short direction A of the current collector 34. The short direction A of the current collector 34 coincides with the short direction of the electrode plate 11. The exposed portion 38 is the part of the current collector 34 that is not covered by the electrode active material layer 36. The first lead 16 is connected to the exposed portion 38 of the current collector 34 of the first electrode plate 10 by welding or the like. The second lead 18 is connected to the exposed portion 38 of the current collector 34 of the second electrode plate 12 by welding or the like.

[0021] The exposed portion 38 has a convex shape in the short-side direction A toward the center of the current collector 34. Therefore, the exposed portion 38 has an outer contour portion 40, an inner contour portion 42, and a pair of connecting contour portions 44a and 44b. The outer contour portion 40 overlaps with the edge of the current collector 34 in the short-side direction A and extends in the longitudinal direction B of the current collector 34. The longitudinal direction B of the current collector 34 coincides with the longitudinal direction of the electrode plate 11. The outer contour portion 40 is formed by the edge of the current collector 34. The inner contour portion 42 is located closer to the center of the current collector 34 than the outer contour portion 40 in the short-side direction A of the current collector 34 and extends in the longitudinal direction B of the current collector 34.

[0022] The connecting contours 44a and 44b are arranged at a predetermined interval along the longitudinal direction B of the current collector 34 and extend approximately in the short direction A of the current collector 34, connecting the outer contour 40 and the inner contour 42. One end of the connecting contour 44a is connected to one end of the outer contour 40, and the other end is connected to one end of the inner contour 42. One end of the connecting contour 44b is connected to the other end of the outer contour 40, and the other end is connected to the other end of the inner contour 42.

[0023] Each of the connection contours 44a and 44b has at least a portion of an inclined portion 46 that extends obliquely with respect to the short-side direction A of the current collector 34. The electrode plate 11 having the exposed portion 38 can be formed, for example, as follows. That is, as an example, when the electrode active material layer 36 is composed of a dry electrode mixture, first the dry electrode mixture is formed into a sheet by roll molding or the like to obtain a long electrode mixture sheet. The electrode mixture sheet is conveyed downstream by a transport roll. Subsequently, a portion of the electrode mixture sheet being transported is cut off by a rotary die cutter or the like. The electrode mixture sheet from which a portion has been cut off is transported toward a pair of bonding rolls located downstream. As an example, two sets of transport rolls and rotary die cutters are provided, and two electrode mixture sheets are transported toward a pair of bonding rolls. At the same time as the transport of the electrode mixture sheet, the current collector 34 is also transported toward the pair of bonding rolls.

[0024] Then, with the current collector 34 positioned between the two electrode mixture sheets, the two electrode mixture sheets and the current collector 34 are passed between a pair of bonding rolls. As a result, the electrode mixture sheets are pressed onto the main surfaces on both sides of the current collector 34, forming the electrode plate 11. The current collector 34 is exposed in the portion of the electrode mixture sheet that has been cut away. This exposed portion becomes the exposed portion 38.

[0025] If the connection contours 44a and 44b of the exposed portion 38 are parallel to the short-side direction A of the current collector 34, then the blades in the rotary die cutter corresponding to the connection contours 44a and 44b will extend perpendicular to the transport direction of the electrode mixture sheet, in other words, parallel to the rotation axis of the rotary die cutter. In this case, the entire blade will be inserted into the electrode mixture sheet simultaneously. Therefore, a sudden and large load will be placed on the rotary die cutter when the blade is inserted, making it difficult to maintain high-precision cutting of the electrode mixture sheet.

[0026] Furthermore, when the connection contours 44a and 44b are parallel to the short-side direction A of the current collector 34, the pressure distribution on the electrode plate 11 from the laminating rolls changes abruptly as the connection contours 44a and 44b pass between the pair of laminating rolls. A rapid change in pressure distribution can lead to a rapid change in the magnitude of the pressure received. This can cause a deterioration in the quality of the electrode plate 11, such as the formation of wrinkles on the exposed portion 38. In addition, the electrode plate 11 may also be compressed by a pair of rolling rolls. In this case as well, the pressure distribution on the electrode plate 11 changes, which can cause a deterioration in the quality of the electrode plate 11. Note that when the electrode active material layer 36 is composed of a wet electrode mixture, it is unlikely that a rotary die cutter or laminating rolls will be used, but rolling rolls may be used. Therefore, the deterioration in the quality of the electrode plate 11 described above can occur.

[0027] In contrast, the connection contours 44a and 44b of this embodiment have inclined portions 46. The inclined portions 46 are tilted obliquely with respect to the short-side direction A of the current collector 34. Therefore, in the rotary die cutter, the blade corresponding to the inclined portion 46 extends obliquely with respect to the rotation axis of the rotary die cutter. In this case, the blade is gradually inserted into the electrode mixture sheet from the portion located upstream in the rotation direction of the rotary die cutter. Therefore, it is possible to suppress the sudden application of a large load to the rotary die cutter and to maintain high-precision cutting of the electrode mixture sheet. In addition, the inclined portions 46 can smooth out the change in pressure distribution that occurs when the connection contours 44a and 44b pass between a pair of laminating rolls or a pair of rolling rolls. Therefore, the quality of the electrode plate 11 can be improved.

[0028] The inclined portions 46 of the connecting contours 44a and 44b in this embodiment extend linearly across the entirety of each connecting contour 44a and 44b. This further suppresses abrupt changes in the load applied to the rotary die cutter and abrupt changes in the pressure distribution. In addition, the two inclined portions 46 are inclined to move closer to each other as you move from the outer contour 40 side towards the inner contour 42 side. This allows the outer contour 40 to be longer than the inner contour 42. As a result, the work of joining the lead to the exposed portion 38 can be made easier.

[0029] The inclination θ of the inclined portion 46 of the current collector 34 with respect to the short direction A is preferably 1° or more and 40° or less. By setting the inclination θ to 1° or more, the quality improvement effect of the electrode plate 11 described above can be more reliably achieved. Furthermore, by setting the inclination θ to 40° or less, interference between the leads and the electrode active material layer 36 in the vicinity of the inner contour portion 42 can be more easily suppressed.

[0030] The inclination θ of the inclined portion 46 may differ between the connecting contour portion 44a and the connecting contour portion 44b. The inclined portion 46 may extend in a curved shape in part or in whole. The inclined portion 46 of the connecting contour portion 44a and the inclined portion 46 of the connecting contour portion 44b may extend parallel to each other, or they may be inclined to move away from each other as they move from the outer contour portion 40 side toward the inner contour portion 42 side. It is preferable that both the connecting contour portion 44a and the connecting contour portion 44b have an inclined portion 46, but the above-mentioned effects can be achieved to a considerable extent if at least one of the connecting contour portions 44a and 44b has an inclined portion 46. It is preferable that the inclined portion 46 is provided at least on the first electrode plate 10, but the second electrode plate 12 may provide it instead of or in addition to the first electrode plate 10.

[0031] The embodiments of this disclosure have been described in detail above. The embodiments described above are merely examples of how to implement this disclosure. The content of the embodiments does not limit the technical scope of this disclosure, and many design changes, such as changes, additions, and deletions of components, are possible as long as they do not depart from the spirit of the invention as defined in the claims. A new embodiment with design changes will have the combined effects of both the embodiment and the variation. In the embodiments described above, the content in which such design changes are possible is emphasized with notations such as "of this embodiment" or "in this embodiment," but design changes are also permitted even if there are no such notations. Furthermore, any combination of components included in each embodiment is also valid as an embodiment of this disclosure. The hatching applied to the cross-section in the drawings does not limit the material of the object to which the hatching is applied.

[0032] The structure of the energy storage device 1 can be modified as appropriate. For example, the energy storage device 1 is not limited to a cylindrical battery, but may be a rectangular battery with a rectangular metal case, a laminated battery with a resin casing, etc. Furthermore, the following modifications can be made to the shape of the connection contours 44a and 44b.

[0033] (Modification 1) Figure 4 is a schematic diagram of the region of the electrode plate 11 including the exposed portion 38 according to Modification 1. In this modification, the inclined portion 46 extends linearly over a portion of the connecting contours 44a and 44b. This portion is continuous with the inner contour 42. Therefore, in the connecting contours 44a and 44b, the remaining portion continuous with the outer contour 40 extends parallel to the short-side direction A of the current collector 34. Also, the two inclined portions 46 are inclined to approach each other as you move from the outer contour 40 side towards the inner contour 42 side.

[0034] The inclination θ of the inclined portion 46 with respect to the short-side direction A of the current collector 34 is preferably 40° or more and 60° or less. Since the inclined portion 46 extends only to a part of the connecting contour portions 44a and 44b, the inclination angle can be made larger compared to the case where it extends over the entire connecting contour portions 44a and 44b. As in the embodiment, the inclination θ of the inclined portion 46 may be different for the connecting contour portion 44a and the connecting contour portion 44b. The two inclined portions 46 may extend parallel to each other, or they may be inclined to move away from each other as they move from the outer contour portion 40 side towards the inner contour portion 42 side. Also, only one of the connecting contour portion 44a and the connecting contour portion 44b may have an inclined portion 46.

[0035] (Modification 2) Figure 5 is a schematic diagram of the region of the electrode plate 11 including the exposed portion 38 according to Modification 2. The inclined portion 46 in this modification has a meandering shape and extends to at least a portion of the connecting contour portions 44a and 44b. That is, at least a portion of the connecting contour portions 44a and 44b has a shape in which portions that are inclined to approach each other and portions that are inclined to move away from each other are alternately arranged in the short-side direction A of the current collector 34 as you move from the outer contour portion 40 side to the inner contour portion 42 side. As an example, the inclined portion 46 shown in Figure 5 extends in a zigzag shape over the entirety of the connecting contour portions 44a and 44b.

[0036] The portions of the two inclined sections 46 that connect to the inner contour section 42 are inclined so that they approach each other as they move from the outer contour section 40 side towards the inner contour section 42 side. The inclination θ of these portions with respect to the short-side direction A of the current collector 34 is preferably 40° or more and 60° or less. The inclination θ of the portions excluding these can be set arbitrarily. The meandering shapes of the two inclined sections 46 may have different amplitudes, wavelengths, periods, etc. of meandering. The lines constituting the meandering shapes may be straight or curved. In addition, the amplitude, wavelength, period, etc. of meandering in each inclined section 46 may be uniform or random. Furthermore, the inclined sections 46 may extend only to a portion of the connecting contour sections 44a and 44b. Also, only one of the connecting contour section 44a and the connecting contour section 44b may have an inclined section 46.

[0037] (Modification 3) When the connecting contour portion 44a and the connecting contour portion 44b have inclined portions 46, the inclined portions 46 of the connecting contour portion 44a and the inclined portions 46 of the connecting contour portion 44b may have different shapes in each of the embodiment, modification 1 and modification 2. That is, for example, the inclined portion 46 of the connecting contour portion 44a may have the shape described in the embodiment, and the inclined portion 46 of the connecting contour portion 44b may have the shape described in modification 1.

[0038] The embodiments may be specified by the items described below. [Item 1] Electrode plates (10, 11, 12) comprising a strip-shaped current collector (34) and an electrode active material layer (36) provided on the surface of the current collector (34), wherein the current collector (34) has an exposed portion (38) on which the electrode active material layer (36) is not provided, and the exposed portion (38) has an outer contour portion (40) that overlaps with the edge of the current collector (34) in the short direction (A), an inner contour portion (42) that is located closer to the center of the current collector (34) than the outer contour portion (40) in the short direction (A), and a pair of connecting contour portions (44a, 44b) that are aligned in the longitudinal direction (B) of the current collector (34) and connect the outer contour portion (40) and the inner contour portion (42), and at least one of the connecting contour portions (44a, 44b) has at least a portion of an inclined portion (46) that extends obliquely with respect to the short direction (A). [Item 2] The electrode plates (10, 11, 12) of Item 1, wherein the inclined portion (46) extends over the entire length of the connecting contour portion (44a, 44b). [Item 3] The electrode plates (10, 11, 12) of Item 2, wherein each of the pair of connecting contour portions (44a, 44b) has an inclined portion (46), and the two inclined portions (46) are inclined to approach each other as they move from the outer contour portion (40) side toward the inner contour portion (42) side. [Item 4] The electrode plates (10, 11, 12) of Item 1, wherein the inclined portion (46) extends linearly over a portion of the connecting contour portion (44a, 44b) that is continuous with the inner contour portion (42). [Item 5] The electrode plates (10, 11, 12) of Item 1, wherein the inclined portion (46) has a meandering shape and extends over at least a portion of the connecting contour portion. [Item 6] An energy storage device (1) comprising any electrode plates (10, 11, 12) specified in items 1 through 5.

[0039] This disclosure can be used in electrode plates and energy storage devices.

[0040] 1 Energy storage device, 11 Electrode plate, 34 Current collector, 36 Electrode active material layer, 38 Exposed portion, 40 Outer contour portion, 42 Inner contour portion, 44a, 44b Connecting contour portions, 46 Inclined portion.

Claims

1. An electrode plate comprising a strip-shaped current collector and an electrode active material layer provided on the surface of the current collector, wherein the current collector has an exposed portion on which the electrode active material layer is not provided, the exposed portion having an outer contour portion that overlaps with the edge of the current collector in the short direction, an inner contour portion located on the center side of the current collector in the short direction from the outer contour portion, and a pair of connecting contour portions that are aligned in the longitudinal direction of the current collector and connect the outer contour portion and the inner contour portion, and at least one of the connecting contour portions has at least a portion of an inclined portion that extends obliquely with respect to the short direction.

2. The electrode plate according to claim 1, wherein the inclined portion extends over the entire length of the connecting contour portion.

3. The electrode plate according to claim 2, wherein each of the pair of connecting contours has the inclined portion, and the two inclined portions are inclined to approach each other as they move from the outer contour side toward the inner contour side.

4. The electrode plate according to claim 1, wherein the inclined portion extends linearly to a portion of the connecting contour that is continuous with the inner contour portion.

5. The electrode plate according to claim 1, wherein the inclined portion has a meandering shape and extends to at least a portion of the connecting contour.

6. An energy storage device comprising the electrode plate described in any one of claims 1 to 5.

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