Electrode structure, electrode body, secondary battery

Abstract

To provide an electrode structure that achieves both a reduction in ion transport distance and the securing of ion transport paths, an electrode body with high energy density, and a secondary battery. [Solution] The electrode body comprises current collectors 41, 51 and composite material layers 42, 52 formed on the current collectors 41, 51 and containing an active material. The composite material layers 42, 52 have a plurality of holes 7 formed along the thickness direction of the composite material layers 42, 52 from the first surface 42a, 52a, which is the surface opposite to the current collectors 41, 51. The electrode structure has such that the cross-sectional area of ​​the holes 7 perpendicular to the thickness direction becomes smaller from the first surface 42a, 52a toward the current collectors 41, 51.

Description

Technical Field

[0001] The present invention relates to an electrode structure, an electrode body, and a secondary battery.

Background Art

[0002] In recent years, batteries such as lithium-ion secondary batteries have been suitably used as power sources for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). It is known that the volumetric energy density and rate performance of a secondary battery vary depending on the electrode structure of the electrode body (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a secondary battery including an electrode structure in which a composite layer (an electrode portion in Patent Document 1) having two layers is provided between a separator (an electrolyte layer in Patent Document 1) and a current collector. By making the porosity of the layer on the current collector side of the composite layer lower than the porosity of the layer on the separator side, an increase in the capacity and an increase in the output of the secondary battery are achieved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The volumetric energy density of a secondary battery can be improved by securing ion migration paths and shortening ion migration distances. Securing ion migration paths is achieved by increasing the porosity of the composite layer, but this increases the amount of active material in the composite layer. Similarly, shortening ion migration distances is achieved by reducing the porosity of the composite layer, but this reduces energy loss due to diffusion resistance. Thus, there is a trade-off between securing ion migration paths and shortening ion migration distances. For this reason, even when multiple layers with different porosities are provided in the composite layer, as in Patent Document 1, the electrode layer closer to the separator restricts the ease of ion movement toward the electrode layer further from the separator, making it difficult to improve energy density by increasing the thickness of the composite layer.

[0006] This invention has been made in view of the above circumstances, and aims to provide an electrode structure that achieves both a reduction in ion transport distance and securing an ion transport path, an electrode body with high energy density, and a secondary battery. [Means for solving the problem]

[0007] The characteristic configuration of the electrode structure according to the present invention for achieving the above objective is as follows: Current collector and, The current collector comprises a composite layer containing an active material formed on the current collector, The asphalt mixture layer has a plurality of holes formed along the thickness direction of the asphalt mixture layer from the first surface, which is the surface opposite to the current collector, The cross-sectional area of ​​the hole, perpendicular to the thickness direction, is smaller as it moves from the first surface toward the current collector.

[0008] According to the above characteristic configuration, the pores formed in the asphalt layer serve as ion migration paths, making it easier for ions to move to areas far from the first surface, thus enabling effective utilization of the entire asphalt layer. Furthermore, the pores ensure ion migration paths from the first surface to the current collector in the asphalt layer, thereby improving the asphalt density on the first surface side of the electrode layer. This makes it possible to achieve both shortening the ion migration distance and securing ion migration paths, which were previously in a trade-off relationship when increasing energy density, thus increasing the overall energy density of the electrode structure compared to conventional designs. In particular, by increasing the cross-sectional area of ​​the pores on the first surface side, a large number of ions can move more easily, improving high-rate charge and discharge performance.

[0009] Further characteristic features of the electrode structure according to the present invention are: The aforementioned composite layer has a region on the current collector side that has a larger void ratio than the first surface side.

[0010] According to the above-described configuration, in addition to the pores, there is a region with a high porosity on the current collector side. This allows ions to move more easily in the region with a high porosity, and ensures a more reliable ion movement path from the first surface side to the current collector side. As a result, the density of the composite material on the first surface side of the electrode layer can also be improved. This allows for effective utilization of the entire composite material layer and increases the energy density of the entire electrode structure.

[0011] Further characteristic features of the electrode structure according to the present invention are: The point is that the aforementioned region does not have the aforementioned holes formed therein.

[0012] According to the above characteristic configuration, it becomes possible to increase the amount of active material in the electrode structure.

[0013] Further characteristic features of the electrode structure according to the present invention are: The distance between the centers of adjacent holes is less than or equal to twice the thickness of the composite layer.

[0014] According to the above characteristic configuration, ions are easily induced into the holes, and the holes easily function as the movement path of the ions. Therefore, it is easy to increase the energy density and output performance.

[0015] A further characteristic configuration of the electrode structure according to the present invention is that the shape formed by connecting the centers of the three holes that are closest to each other is an equilateral triangle.

[0016] According to the above characteristic configuration, since the holes are provided at equal intervals, ions are easily induced into the holes, and the holes easily function as the movement path of the ions. Therefore, it is easy to increase the energy density and output performance.

[0017] A further characteristic configuration of the electrode structure according to the present invention is that the cross-sectional shape perpendicular to the thickness direction of the hole is a hexagon.

[0018] According to the above characteristic configuration, since the ratio of the cross-sectional area of the hole to the volume of the hole is high, ions are easily induced into the hole, and the hole easily functions as the movement path of the ions. Therefore, it is easy to increase the energy density and output performance.

[0019] A characteristic configuration of the electrode body according to the present invention is an electrode body provided with the above-described electrode structure, the positive electrode current collector and the negative electrode current collector as the current collectors, the positive electrode composite layer and the negative electrode composite layer as the composite layers, and a separator disposed between the positive electrode composite layer and the negative electrode composite layer, where at least one of the positive electrode current collector and the positive electrode composite layer and the negative electrode current collector and the negative electrode composite layer has the electrode structure.

[0020] According to the above characteristic configuration, the energy density can be increased more than before. When the positive electrode side has the electrode structure, the discharge performance can be improved, and when the negative electrode side has the electrode structure, the charging performance can be improved.

[0021] The characteristic configuration of the secondary battery according to the present invention lies in including the above-described electrode body.

[0022] According to the above characteristic configuration, a secondary battery with high energy density and high output can be obtained. Also, since the heat generation amount can be reduced by reducing the ion diffusion resistance, it is possible to improve the life and safety of the secondary battery. When an electrode body with an electrode structure is used on the positive electrode side, the discharge performance can be improved, and when an electrode body with an electrode structure is used on the negative electrode side, the charging performance can be improved.

Effects of the Invention

[0023] As described above, according to the electrode structure, electrode body, and secondary battery according to the present invention, it is possible to achieve both shortening the ion movement distance and securing the ion movement path, and to increase the energy density.

Brief Description of the Drawings

[0024] [Figure 1] It is an exploded perspective view of the secondary battery. [Figure 2] It is a perspective view showing an electrode body with a part thereof unfolded. [Figure 3] It is a diagram showing the electrode structure. [Figure 4] It is a diagram showing a part of the first surface of the positive electrode composite layer in plan view. [Figure 5] It is a diagram showing the electrode structure according to the second embodiment. [Figure 6] It is a diagram showing the electrode structure according to another embodiment. [Figure 7] It is a diagram showing a part of the first surface of the positive electrode composite layer in plan view according to another embodiment.

Modes for Carrying Out the Invention

[0025] Hereinafter, the battery according to the embodiment of the present invention will be described with reference to the drawings. In the following, a lithium-ion secondary battery will be described as an example. Also, in the following, for the sake of clarity, each description and each drawing are appropriately simplified.

[0026] [First Embodiment] [Overview of secondary battery 1] Figure 1 is an exploded perspective view of a secondary battery 1 equipped with an electrode body 20. As shown in Figure 1, the secondary battery 1 includes a battery case 10 consisting of a case body 11 and a sealing plate 12, battery terminals PS and NS consisting of metal external terminals 25 and 26 and current collector terminals 30 and 31, and an electrode body 20. The secondary battery 1 is a sealed type secondary battery in which the electrode body 20 and current collector terminals 30 and 31 are housed inside the case body 11, the opening of the case body 11 is sealed with the sealing plate 12, and then an electrolyte is injected into the inside of the case body 11.

[0027] [Configuration of battery case 10] As shown in Figure 1, the battery case 10 consists of a case body 11 with a roughly rectangular parallelepiped shape and an open top, and a sealing plate 12 that seals the opening of the case body 11. In this embodiment, both the case body 11 and the sealing plate 12 are made of aluminum, but are not limited to this. Various metals and alloys can be appropriately selected for the case body 11 and the sealing plate 12 depending on the type and application of the battery.

[0028] In this embodiment, the sealing plate 12 has a shape corresponding to the shape of the opening of the case body 11 and is configured to seal the opening of the case body 11.

[0029] [Battery terminal configuration PS, NS] In this embodiment, the secondary battery 1 is equipped with a positive external terminal 25 and a negative external terminal 26 as external terminals, and a positive current collector terminal 30 and a negative current collector terminal 31 as current collector terminals. The positive battery terminal PS is composed of the positive external terminal 25 and the positive current collector terminal 30, and the negative battery terminal NS is composed of the negative external terminal 26 and the negative current collector terminal 31. In this embodiment, the positive external terminal 25 and the positive current collector terminal 30 are made of aluminum, and the negative external terminal 26 and the negative current collector terminal 31 are made of copper, but the materials of these terminals are not particularly limited, and various metals and alloys with good conductivity can be used.

[0030] Furthermore, in this embodiment, the secondary battery 1 includes a positive electrode insulating member (not shown), a negative electrode insulating member (not shown), a positive electrode gasket 32, and a negative electrode gasket 33, all of which are made of insulating material. In this embodiment, PFA resin is used as the insulating material, but the invention is not limited to this.

[0031] The positive electrode current collector terminal 30 has a positive electrode current collector portion 30a extending downward from the back surface of a flat surface (not shown). The negative electrode current collector terminal 31 has a negative electrode current collector portion 31a extending downward from the back surface of a flat surface (not shown). The tip of the positive electrode current collector portion 30a is joined to a positive electrode terminal joint portion 21, which will be described later, and the tip of the negative electrode current collector portion 31a is joined to a negative electrode terminal joint portion 22, which will be described later.

[0032] Although a detailed explanation will be omitted, in the secondary battery 1 of this embodiment, the positive electrode external terminal 25 and the negative electrode external terminal 26 are insulated from the sealing plate 12 by a positive electrode gasket 32 ​​and a negative electrode gasket 33, respectively, and the positive electrode current collector terminal 30 and the negative electrode current collector terminal 31 are insulated from the sealing plate 12 by a positive electrode insulating member and a negative electrode insulating member, respectively.

[0033] [Configuration of electrode body 20] The electrode body 20 is composed of a positive electrode 4, a negative electrode 5, a separator 6, etc. The electrode body 20 may be a laminate formed by stacking the positive electrode 4 and the negative electrode 5 with the separator 6 in between, or it may be a wound body formed by stacking long strip-shaped positive electrode 4 and negative electrode 5 with the same strip-shaped separator 6 in between, winding them up, and compressing them into a flat shape. The electrode body 20 according to this embodiment is a wound body as shown in Figure 2, for example. A positive electrode terminal joint portion 21 to which the positive electrode current collector terminal 30 is joined is formed on one end of the electrode body 20 in the winding axis direction, and a negative electrode terminal joint portion 22 to which the negative electrode current collector terminal 31 is joined is formed on the other end.

[0034] In this embodiment, the electrode body 20 is housed inside the case body 11 in a position where its thickness and longitudinal directions are parallel to the horizontal direction, while covered with an insulating film. Furthermore, the electrode body 20 and the case body 11 are insulated from each other by an insulating film (not shown).

[0035] As shown in Figures 2 and 3, the positive electrode 4 of the electrode body 20 is a strip-shaped electrode having a positive electrode current collector 41 (an example of a current collector) and a positive electrode composite layer 42 (an example of a composite layer) formed on both sides of the positive electrode current collector 41. The positive electrode current collector 41 is, for example, aluminum foil. An unpainted portion 43 is formed on one end of the positive electrode current collector 41 in the longitudinal direction, where the positive electrode composite layer 42 is not formed. In the secondary battery 1 of this embodiment, the portion of the electrode body 20 consisting of the unpainted portion 43 is used as the positive electrode terminal junction 21.

[0036] The negative electrode 5 of the electrode body 20 is a strip-shaped electrode having a negative electrode current collector 51 (an example of a current collector) and a negative electrode composite layer 52 (an example of a composite layer) formed on both sides of the negative electrode current collector 51. The negative electrode current collector 51 is, for example, copper foil. An unpainted portion 53 is formed on the other longitudinal end of the negative electrode current collector 51, which is located on the opposite side of one longitudinal end of the positive electrode current collector 41, where the negative electrode composite layer 52 is not formed. In the secondary battery 1 of this embodiment, the portion of the electrode body 20 consisting of the unpainted portion 53 is used as the negative electrode terminal joint 22, similar to the positive electrode terminal joint 21.

[0037] The positive electrode composite layer 42 and the negative electrode composite layer 52 contain the active material of the positive electrode 4 or the negative electrode 5. The active material can be any known compound that can be used for the positive electrode 4 or the negative electrode 5. The composite layers 42 and 52 may also contain additives such as conductive additives and binders.

[0038] The separator 6 is positioned to insulate the positive electrode composite layer 42 of the positive electrode 4 from the negative electrode composite layer 52 of the negative electrode 5. In this embodiment, the separator 6, negative electrode 5, separator 6, and positive electrode 4 are stacked in this order, and in a view in the stacking direction, the positive electrode composite layer 42 and the negative electrode composite layer 52 overlap with the separator 6. The separator 6 can be made of an insulating material that allows ions to pass through (for example, a porous insulating resin material).

[0039] [Electrode structure] The volumetric energy density of secondary battery 1 can be improved by securing ion migration paths and shortening ion migration distances. Securing ion migration paths can be achieved by increasing the porosity of the composite material layers 42 and 52, but this increases the amount of active material in the composite material layers 42 and 52. Similarly, shortening ion migration distances can be achieved by reducing the porosity of the composite material layers 42 and 52, but this reduction in porosity leads to energy loss due to diffusion resistance. Thus, there is a trade-off between securing ion migration paths and shortening ion migration distances, making it difficult to effectively improve energy density simply by increasing or decreasing porosity.

[0040] Therefore, in order to overcome the trade-off relationship described above, the electrode body 20 according to this embodiment has an electrode structure as shown in Figure 3. Specifically, the positive electrode composite layer 42 according to this embodiment has a plurality of holes 7 formed along the thickness direction of the positive electrode composite layer 42 (the vertical direction of the paper in Figure 3) from the first surface 42a, which is the surface opposite to the positive electrode current collector 41. Similarly, the negative electrode composite layer 52 also has a plurality of holes 7 formed along the thickness direction of the negative electrode composite layer 52 from the first surface 52a, which is the surface opposite to the negative electrode current collector 51. The holes 7,7 of the composite layers 42,52 are filled with an electrolyte such as lithium hexafluoride phosphate (LiPF6). As a result, the holes 7,7 become a movement path for ions such as lithium ions, and ions can move through the composite layers 42,52 by passing through the holes 7,7.

[0041] By using the pores 7 as ion movement paths, energy loss due to ion diffusion resistance in the composite layers 42 and 52 is suppressed, and ions can move more easily from the negative electrode current collector 51 to the positive electrode current collector 41. This increases the effective energy density of the secondary battery 1 and improves its output. Furthermore, since it is not necessary to increase the porosity of the composite layers 42 and 52 to secure ion movement paths, the amount of active material can be increased, and the capacity of the secondary battery 1 can be increased. Therefore, by having pores 7 in the composite layers 42 and 52, it is possible to achieve both shortening the ion movement distance and securing ion movement paths, which were previously in a trade-off relationship when increasing energy density, and thus increase the energy density of the secondary battery 1 compared to conventional batteries.

[0042] The holes 7,7 may penetrate the asphalt layers 42,52 if openings are formed in the first surfaces 42a,52a of the asphalt layers 42,52, or they may be formed only partway through the asphalt layers 42,52, as shown in Figure 3. The dimensions of the holes 7,7 in the thickness direction of the asphalt layers 42,52 are not particularly limited. If the holes 7,7 penetrate the asphalt layers 42,52, ions can easily move toward the positive electrode current collector 41, and if the holes 7,7 are formed only partway through the asphalt layers 42,52, the amount of active material in the asphalt layers 42,52 can be increased.

[0043] Figure 4 shows a portion of the first surface 42a of the positive electrode composite layer 42 in a plan view. As shown in Figure 4, the cross-sectional shape of the holes 7 perpendicular to the thickness direction (parallel to the first surface 42a) in the positive electrode composite layer 42 is circular. The negative electrode composite layer 52 is not shown in the illustration, but similar to the positive electrode composite layer 42, the cross-sectional shape of the holes 7 perpendicular to the thickness direction is also circular. The opening diameter of the holes 7 on the first surfaces 42a and 52a should be greater than 0 μm and less than or equal to 30 μm.

[0044] As shown in Figures 3 and 4, the cross-sectional area of ​​the hole 7 perpendicular to the thickness direction is formed to decrease from the first surfaces 42a, 52a toward the current collectors 41, 51. The shape of the hole 7 according to this embodiment is a frustum of a cone. The cross-sectional area of ​​the hole 7 on the current collector side 41, 51 is not particularly limited as long as it is smaller than the cross-sectional area of ​​the hole 7 on the first surfaces 42a, 52a, but the ratio of the cross-sectional area of ​​the hole 7 on the first surfaces 42a, 52a to the cross-sectional area of ​​the hole 7 on the current collector side 41, 51 should be greater than 0 and less than or equal to 0.9. Note that as long as the cross-sectional area of ​​the hole 7 perpendicular to the thickness direction is formed to decrease from the first surfaces 42a, 52a toward the current collectors 41, 51, the hole 7 does not have to be a frustum of a cone, but may be a cone, a polygonal pyramid, or a frustum of a polygonal pyramid.

[0045] In the electrode body 20, the amount of ion movement is greatest near the separator 6. Therefore, if the cross-sectional area perpendicular to the thickness direction of the hole 7 is larger on the side of the first surface 42a, 52a, i.e., the side of the separator 6, than on the side of the current collector 41, 51, then a large number of ions can easily move through the hole 7 near the separator 6. This increases the amount of ion movement, making it possible to improve high-rate charge and discharge performance.

[0046] If the resistance to movement of ions in the path through the pores 7 is smaller than the resistance to movement of ions in the path through the composite layers 42 and 52, the ions will choose the path through the pores 7. Since the resistance to movement is determined by multiplying the resistance coefficient in that region by the distance traveled, the smaller the distance d between the centers of the two adjacent pores 7, 7, the easier it is for ions in the composite layers 42 and 52 to be guided to the pores 7, 7, and the easier it is for the pores 7 to function as an ion movement path. The distance d between the centers of adjacent pores 7, 7 should be less than or equal to twice the thickness t of the composite layers 42 and 52, taking into account the balance between the volume of the pores 7 and the volume of the composite layers 42 and 52 between the adjacent pores 7, 7 (see Figures 3 and 4). If the distance d between the centers of adjacent pores 7, 7 is less than or equal to twice the thickness t of the composite layers 42 and 52, the pores 7 can easily function as an ion movement path, and the energy density can be improved. The optimal distance d between the centers of the holes 7,7 varies depending on the thickness of the positive electrode 4 and negative electrode 5, as well as the target rate performance, energy density, diffusion coefficient, and other physical properties. Therefore, it is preferable to determine the optimal value through optimization calculations according to the target physical properties.

[0047] The arrangement of the multiple pores 7 in the composite layers 42 and 52 is not particularly limited, but it is preferable that they be arranged such that the shape formed by connecting the centers of the n closest adjacent pores 7 is a regular n-gon (where n is an integer of 3 or more). By providing the pores 7 at equal intervals in this way, ions are more easily guided into the pores 7, and the pores 7 function more easily as ion migration paths. In this embodiment, the pores 7 are arranged such that the shape formed by connecting the centers of the three closest adjacent pores 7 is an equilateral triangle. Therefore, among the ions present in the composite layers 42 and 52, ions located inside the hexagonal region A shown by the dashed line in Figure 4, centered on the pore 7, are easily guided to the pore 7 located at the center of region A. Region A is the range in which the distance between an ion located inside region A and the pore 7 located at its center is less than or equal to the distance between that ion and other pores 7 adjacent to that pore 7. In other words, region A indicates the range in which the pore 7 located at the center of region A affects the ions located inside region A. Therefore, ions located outside one region A and in other regions A adjacent to one region A are less likely to be guided from the other regions A to the pore 7 located at the center of one region A, and more likely to be guided to the pore 7 located at the center of the other regions A. In this way, ion movement across regions A is unlikely to occur, and the dashed line in Figure 4 indicates the boundary line that ions cannot cross. In this embodiment, region A is assumed to be hexagonal, but it is preferable to use a shape corresponding to the shape formed by connecting the centers of the n closest adjacent pores 7.

[0048] The porosity of the composite material layers 42 and 52, including the pores 7, should be equal to or less than the porosity of the composite material layer without the pores 7. If the porosity of the composite material layers 42 and 52, including the pores 7, is equal to the porosity of the composite material layer without the pores 7, then the porosity of the composite material layers 42 and 52 excluding the pores 7 will be lower than the porosity of the composite material layer without the pores 7. This ensures that the pores 7 provide a path for ion movement and maintains the amount of active material in the composite material layers 42 and 52, making it possible to increase the energy density while suppressing a decrease in the capacity of the secondary battery 1.

[0049] [Method for manufacturing electrodes and secondary batteries] First, composite layers 42 and 52 are prepared by known methods. These composite layers 42 and 52 are obtained, for example, by applying a slurry containing active material and binder to current collectors 41 and 51, drying it, and then pressing it with a roller or the like. After that, holes 7 are formed in the composite layers 42 and 52 using a drill or laser. Then, the positive electrode 4 and negative electrode 5 are stacked via a separator 6, and these are wound up to obtain the electrode body 20 (see Figure 2). After sealing the electrode body 20 in the battery case 10, an electrolyte is injected into the inside of the case body 11, allowing the electrolyte to penetrate the holes 7 and form a secondary battery 1.

[0050] As described above, since the ion diffusion resistance of the electrode body 20 according to this embodiment is low, the amount of heat generated by the electrode body 20 can be reduced, which in turn allows for simplification of the restraining components for the electrode body 20 and an improvement in the lifespan of the electrode body 20. Furthermore, by reducing the amount of heat generated by the electrode body 20, the safety of the secondary battery 1 can be enhanced.

[0051] [Second Embodiment] The electrode body 20 according to the second embodiment will be described with reference to Figure 5. The positive electrode composite layer 42 of the electrode body 20 according to the second embodiment consists of two layers: a first region 421 formed on the first surface 42a side and a second region 422 formed on the positive electrode current collector 41 side. The second region 422 is a layer with a larger porosity than the first region 421 formed on the first surface 42a side. The first region 421 and the second region 422 are preferably formed of the same material except for the porosity. The other configurations are the same as in the first embodiment, so the same configurations as in the first embodiment will not be described.

[0052] As shown in Figure 5, the pores 7 are provided in both the first region 421 and the second region 422. Therefore, ions present in both the first region 421 and the second region 422 can move through the pores 7.

[0053] In this embodiment, since the porosity of the second region 422 is greater than that of the first region 421, the ion migration paths in the positive electrode composite layer 42, excluding the pores 7, are more easily secured in the second region 422 than in the first region 421. For this reason, the pores 7 are frustoconical with a smaller cross-sectional area as they approach the positive electrode current collector 41, and even if the volume of the pores 7 in the second region 422 is smaller than the volume of the pores 7 in the first region 421, it is easier to secure ion migration paths in the second region 422. As a result, the entire second region 422 can be effectively utilized, making it possible to increase the effective energy density of the secondary battery 1.

[0054] The holes 7 according to the second embodiment may be formed using a drill or laser after the positive electrode composite layer 42 having a first region 421 and a second region 422 has been formed.

[0055] [Another embodiment] [1] In the above embodiment, the hole 7 is a frustocone, but as long as the cross-sectional area perpendicular to the thickness direction of the hole 7 decreases from the first surfaces 42a, 52a toward the current collectors 41, 51, it is not limited to a form in which the cross-sectional area gradually decreases, and a part of the hole 7 may have a constant cross-sectional area in the thickness direction. An example of a hole 7 formed in the positive electrode composite layer 42 is shown in Figure 6. As shown in Figure 6, the hole 7 according to this embodiment has a frustocone portion 71 and a cylindrical portion 72 that extends from the surface of the frustocone portion 71 toward the positive electrode current collector 41 and has a constant area in the thickness direction. A frustocone portion is further provided on the positive electrode current collector 41 side of the cylindrical portion 72, the cross-sectional area of ​​which gradually decreases toward the positive electrode current collector 41. By enlarging the opening on the first surface 42a side of the positive electrode composite layer 42 of the pore portion 7, ions can move more easily through the pore portion 7, improving high-rate discharge performance. Furthermore, by forming a cylindrical portion 72 on the positive electrode current collector 41 side, the amount of active material in the positive electrode composite layer 42 on the positive electrode current collector 41 side can be increased, thereby increasing the capacity of the secondary battery 1. Pores 7 of a similar shape may also be formed in the negative electrode composite layer 52. The cylindrical portion 72 may be a frustoconical or conical shape with a smaller apex angle than the frustoconical portion 71.

[0056] [2] In the above embodiment, the hole 7 was assumed to be a frustocone, but as shown in Figure 7, it may also be a frustoconical pyramid with a hexagonal cross-sectional shape perpendicular to the thickness direction. If the cross-sectional shape of the hole 7 is hexagonal, the ratio of the cross-sectional area of ​​the hole 7 to the volume of the hole 7 becomes high when the shape formed by connecting the centers of the three most adjacent holes 7 is an equilateral triangle, so that ions are more easily guided into the hole 7 and the hole 7 can easily function as an ion migration path. The cross-sectional shape of the hole 7 may be determined according to the arrangement of the holes 7.

[0057] [3] In the second embodiment described above, the holes 7 are provided in both the first region 421 and the second region 422, but the holes 7 do not have to be provided in the second region 422. If the holes 7 are not provided in the second region 422, the amount of positive electrode active material in the second region 422 can be increased, and the capacity of the secondary battery 1 can be improved. Furthermore, the positive electrode composite layer 42 is not limited to a two-layer structure of the first region 421 and the second region 422, but may have multiple layers, as long as it has a structure in which the porosity increases from the first surface 42a toward the positive electrode current collector 41. The negative electrode composite layer 52 may also have a region on the negative electrode current collector 51 side that has a larger porosity than the first surface 52a side, similar to the positive electrode composite layer 42.

[0058] [4] In the above embodiment, the holes 7 of the positive electrode 4 and the negative electrode 5 are formed symmetrically with respect to the separator 6, but they may be asymmetrical. For example, the opening diameter of the hole 7 of the negative electrode 5 on the first surface 52a may be smaller than the opening diameter of the hole 7 of the positive electrode 4 on the first surface 42a. Also, the centers of the holes 7 formed in the positive electrode composite layer 42 and the centers of the holes 7 formed in the negative electrode composite layer 52 may or may not overlap when viewed in the stacking direction of the composite layers 42 and 52. However, from the viewpoint of shortening the ion migration path and reducing ion migration resistance between the positive electrode 4 and the negative electrode 5, it is preferable that the holes 7 formed in the positive electrode composite layer 42 and the holes 7 formed in the negative electrode composite layer 52 overlap when viewed in the stacking direction.

[0059] [5] In the above embodiment, an example was shown in which the holes 7 are formed in both the positive electrode composite layer 42 and the negative electrode composite layer 52, but the holes 7 may be formed in either one of them. When the holes 7 are formed only in the positive electrode composite layer 42, the discharge performance can be improved, and when the holes 7 are formed only in the negative electrode composite layer 52, the charging performance can be improved.

[0060] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Explanation of Symbols]

[0061] 1: Secondary battery 4: Positive electrode 5: Negative electrode 6: Separator 7: Hole 20: Electrode body 41: Positive electrode current collector (current collector) 42: Positive electrode composite material layer (compound material layer) 42a: Front page 51: Negative electrode current collector (current collector) 52: Negative electrode composite material layer (compound material layer) 52a: Front page d: Distance between centers t: thickness

Claims

1. Current collector and, The current collector comprises a composite layer containing an active material formed on the current collector, The asphalt mixture layer has a plurality of holes formed along the thickness direction of the asphalt mixture layer from the first surface, which is the surface opposite to the current collector, The electrode structure is such that the cross-sectional area of ​​the hole portion perpendicular to the thickness direction decreases as it moves from the first surface toward the current collector.

2. The electrode structure according to claim 1, wherein the composite layer has a region on the current collector side with a larger void ratio than the first surface side.

3. The electrode structure according to claim 2, wherein the aforementioned region is not formed with the aforementioned hole.

4. The electrode structure according to claim 1, wherein the distance between the centers of adjacent holes is less than or equal to twice the thickness of the composite layer.

5. The electrode structure according to claim 1, wherein the shape formed by connecting the centers of the three most adjacent holes is an equilateral triangle.

6. The electrode structure according to claim 1, wherein the cross-sectional shape of the hole portion perpendicular to the thickness direction is hexagonal.

7. An electrode body having the electrode structure described in any one of claims 1 to 6, The positive electrode current collector and the negative electrode current collector, as current collectors, The aforementioned composite material layers include a positive electrode composite material layer and a negative electrode composite material layer, A separator is disposed between the positive electrode composite layer and the negative electrode composite layer, An electrode body in which at least one of the positive electrode current collector and the positive electrode composite layer, and the negative electrode current collector and the negative electrode composite layer, has the electrode structure.

8. A secondary battery comprising the electrode body described in claim 7.

Images