Flat-shaped battery

Abstract

To provide a flat-shaped battery capable of effectively collecting power while using an annular collector with a simple shape.SOLUTION: A flat-shaped battery 1 comprises: an outer can 2 having a bottom part 21; an outer can 3 having a flat surface part 31; an electrode body 4; and two annular collector bodies 5. Each of the two annular collector bodies 5 is arranged to between the bottom part 21 and the electrode body 4, and between a flat surface part 31 and the electrode body 4. One part of the two annular collector bodies 5 is embedded into the electrode body 4 to a thickness direction. Also, each annular collector body 5 includes: an outer diameter D2 of 40% to 85% against a diameter D1 of the electrode body 4 and an inner diameter D3 of 30% to 75% in a plan view. Thus, by appropriately setting a relation of the diameter D1 of the electrode body 4, the outer diameter D2 and the inner diameter D3 of each annular collector body 5, power can be effectively connected even in the case of using an annular collector with a simple shape.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a flat battery containing an electrode assembly. [Background technology]

[0002] In general, a flat battery has a structure in which an electrode assembly having a negative electrode, a positive electrode, and a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte are housed inside a case consisting of an outer can and a sealing can. In such a flat battery, a current collector made of a thin metal plate is disposed between the outer can and the electrode assembly, or between the sealing can and the electrode assembly.

[0003] Japanese Patent Laid-Open Publication No. 2004-186073 (Patent Document 1) discloses a flat non-aqueous electrolyte secondary battery. The flat non-aqueous electrolyte secondary battery has an electrode group inside a positive electrode case and a metal thin plate between the positive electrode case or the negative electrode case and the electrode group. The metal thin plate has a through hole in the thickness direction and has a porosity of 10% to 60%. The metal thin plate has, for example, a diamond-shaped mesh shape. This reduces and stabilizes the internal resistance of the flat non-aqueous electrolyte secondary battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-186073 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the flat nonaqueous electrolyte secondary battery of Patent Document 1, the thin metal plate having a diamond-shaped mesh shape may generate burrs at the corners of the mesh when it is processed into the mesh shape. If the thin metal plate having such burrs is disposed inside the positive and negative electrodes of the flat nonaqueous electrolyte secondary battery, the burrs may fall off and get into the inside of the electrode group, causing a micro-short circuit, which may result in an abnormal voltage drop.

[0006] An object of the present disclosure is to provide a flat battery that can effectively collect current while using a current collector of a simple shape that does not produce burrs during processing. [Means for solving the problem]

[0007] In order to solve the above problems, the present disclosure is configured as follows. That is, the flat battery according to the present disclosure may include an exterior can having a bottom, a seal can having a flat surface, an electrode body accommodated between the exterior can and the seal can, and an annular current collector disposed either between the bottom and the electrode body or between the flat surface and the electrode body. A portion of the annular current collector may be embedded in the main surface of the electrode body in the thickness direction of the annular current collector. The annular current collector may have an outer diameter that is 40% to 85% and an inner diameter that is 30% to 75% of the diameter of the main surface of the electrode body in which the portion of the annular current collector is embedded, in a plan view. Effect of the Invention

[0008] According to the flat battery of the present disclosure, current can be collected effectively using a current collector with a simple shape. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a flat battery according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the annular current collector shown in FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of the annular current collector shown in FIG. [Figure 4] FIG. 4 is a plan view of the electrode body and the annular current collector shown in FIG. [Diagram 5] FIG. 5 is a plan view of the annular current collector shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view showing a flat battery according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The inventors have considered forming the current collector into a simple annular shape, i.e., a ring shape, in order to suppress burrs that occur during processing of the current collector. However, a simple annular current collector has a smaller current collection area than a current collector having a diamond-shaped mesh shape, etc., and therefore a lower current collection efficiency. As a result of intensive research, the inventors have found that current can be effectively collected by embedding a part of the annular current collector in the electrode body and appropriately setting the relationship between the diameter of the electrode body in a plan view and the outer diameter and inner diameter of the annular current collector. Based on this knowledge, the inventors have completed the present invention.

[0011] (Configuration 1) A flat battery according to an embodiment of the present disclosure may include an exterior can having a bottom, a seal can having a flat surface, an electrode assembly housed between the exterior can and the seal can, and an annular current collector disposed either between the bottom and the electrode assembly or between the flat surface and the electrode assembly. A portion of the annular current collector may be embedded in the main surface of the electrode assembly in the thickness direction of the annular current collector. The annular current collector may have an outer diameter that is 40% to 85% and an inner diameter that is 30% to 75% of the diameter of the main surface of the electrode assembly in which the annular current collector is embedded, in a plan view.

[0012] In this way, by embedding a portion of the simply shaped annular current collector in the electrode body and appropriately setting the inner and outer diameters of the annular current collector relative to the diameter of the electrode body in a plan view, current can be collected effectively.

[0013] (Configuration 2) In the flat battery of Configuration 1, the annular current collector may have an opening ratio of 65% or more, which can suppress the generation of burrs during processing of the annular current collector and can collect current more effectively.

[0014] (Configuration 3) In the flat battery of the configuration 1 or 2, the annular current collector may be embedded in the main surface of the electrode body to a depth of 50 μm or more, thereby enabling more effective current collection.

[0015] (First embodiment) Hereinafter, the flat battery 1 according to the first embodiment of the present disclosure will be specifically described with reference to Figures 1 and 2. Note that the same or corresponding components in the figures are given the same reference numerals and the same description will not be repeated. Note that, in order to make the description easier to understand, the drawings referred to below show the configuration in a simplified or schematic manner, and some components are omitted.

[0016] As shown in Fig. 1, the flat battery 1 has an outer can 2, a sealing can 3, an electrode body 4, an annular current collector 5, and a gasket 6. The outer can 2, the sealing can 3, and the gasket 6 form the case of the flat battery 1. The electrode body 4 and the annular current collector 5 are housed in the case. In this first embodiment, the flat battery 1 is a lithium ion secondary battery.

[0017] The outer can 2 has a bottom 21 that is circular in plan view, and a cylindrical peripheral wall 22 that is formed continuously from the outer periphery of the bottom 21. The peripheral wall 22 is provided so as to extend substantially perpendicular to the bottom 21 in a vertical cross-sectional view. The outer can 2 is made of a metal material such as stainless steel, nickel, or iron.

[0018] The sealing can 3 has a flat portion 31 that is circular in plan view, and a cylindrical peripheral wall portion 32 that is formed continuously from the outer periphery of the flat portion 31. The opening of the sealing can 3 faces the opening of the outer can 2. The sealing can 3 is made of a metal material such as stainless steel.

[0019] The exterior can 2 and the sealing can 3 accommodate the electrode body 4, a non-aqueous electrolyte (not shown), and an annular current collector 5, and then the exterior can 2 and the sealing can 3 are crimped together with a gasket 6 interposed between the peripheral wall 22 of the exterior can 2 and the peripheral wall 32 of the sealing can 3. That is, the exterior can 2 and the sealing can 3 are arranged so that their openings face each other, the peripheral wall 32 of the sealing can 3 is inserted inside the peripheral wall 22 of the exterior can 2, and then the exterior can 2 and the sealing can 3 are crimped together with the gasket 6 interposed between the peripheral wall 22 and the peripheral wall 32. In this manner, an internal space for accommodating the electrode body 4 is formed in the flat battery 1.

[0020] The electrode body 4 is formed by alternately stacking a plurality of positive electrodes 41 and negative electrodes 42. The positive electrodes 41 are housed in a pouch-shaped separator 43. The number of stacked positive electrodes 41 and negative electrodes 42 is determined by the desired battery capacity. Therefore, the number of stacked layers is not limited to that shown in the figure. Among the plurality of negative electrodes 42, the negative electrode 42 closest to the inner surface of the bottom 21 of the outer can 2 and the negative electrode 42 closest to the inner surface of the flat surface portion 31 of the sealing can 3 each have a negative electrode active material layer provided only on one surface, and the negative electrode 42 closest to the inner surface of the flat surface portion 31 of the sealing can 3 is in contact with the flat surface portion 31. In addition, an insulating sheet 44 is provided between the negative electrode 42 closest to the inner surface of the bottom 21 of the outer can 2 and the bottom 21 of the outer can 2. The insulating sheet 44 insulates the negative electrode 42 closest to the inner surface of the bottom 21 of the outer can 2 from the bottom 21 of the outer can 2.

[0021] The flat battery 1 further contains a positive electrode lead 411 and a negative electrode lead 421 in its internal space. Although not shown in the figure, the positive electrode lead 411 and the negative electrode lead 421 are bundles of lead wires extending from the multiple positive electrodes 41 and the multiple negative electrodes 42, respectively.

[0022] The positive electrode leads 411 extend continuously from the peripheral end of each positive electrode 41. The multiple positive electrode leads 411 are bundled together and bent toward the bottom 21 of the outer can 2. The bundled positive electrode leads 411 are connected to the positive electrode current collector foil 412 disposed between the insulating sheet 44 and the annular current collector 5. In this manner, the positive electrode 41 is connected to the outer can 2 via the positive electrode lead 411 and the positive electrode current collector foil 412. Therefore, the outer can 2 functions as a positive electrode can. The positive electrode current collector foil 412 is a metal foil such as aluminum or an aluminum alloy.

[0023] The negative electrode lead 421 extends continuously from the peripheral end of each negative electrode 42. Each negative electrode lead 421 is connected to a negative electrode current collector foil 422 arranged between the annular current collector 5 and the negative electrode 42 closest to the flat surface portion 31 of the sealing can 3. In this manner, the negative electrode 42 is connected to the sealing can 3 via the negative electrode lead 421 and the negative electrode current collector foil 422. Therefore, the sealing can 3 functions as a negative electrode can. The negative electrode current collector foil 422 is a metal foil such as copper or nickel.

[0024] Each of the positive electrodes 41 includes a positive electrode active material layer. The positive electrode active material layer is, for example, a layer formed by compression molding a positive electrode active material such as lithium cobalt oxide, a binder, a conductive additive, etc. Each of the negative electrodes 42 includes a negative electrode active material layer. The negative electrode active material layer is, for example, a layer formed by compression molding a negative electrode active material such as graphite, a binder, a conductive additive, etc.

[0025] Each of the bag-shaped separators 43 is, for example, a microporous film made of polyethylene having excellent insulating properties, etc. This allows the separators 43 to be permeable to lithium ions.

[0026] The annular current collector 5 is disposed either between the bottom 21 of the outer can 2 and the electrode body 4, or between the flat surface 31 of the sealing can 3 and the electrode body 4. In this embodiment, the annular current collector 5 is disposed both between the bottom 21 of the outer can 2 and the electrode body 4, and between the flat surface 31 of the sealing can 3 and the electrode body 4. The annular current collector 5 is a ring body of a simple shape having an opening penetrating through the center in a plan view. In this way, since the annular current collector 5 has a simple annular shape, it is possible to suppress the generation of burrs when processing the annular current collector 5. This makes it possible to suppress abnormal voltage drops caused by burrs falling off.

[0027] As shown in FIG. 2, a part of the annular current collector 5 of the outer can 2 is embedded in the insulating sheet 44 via the positive electrode current collector foil 412 in the thickness direction of the annular current collector 5. That is, a part of the annular current collector 5 arranged between the bottom 21 of the outer can 2 and the electrode body 4 is embedded in the electrode body 4. Also, as shown in FIG. 3, a part of the annular current collector 5 arranged between the flat surface portion 31 of the sealing can 3 and the electrode body 4 is embedded in the negative electrode 42 closest to the flat surface portion 31 via the negative electrode current collector foil 422 in the thickness direction of the annular current collector 5. That is, a part of the annular current collector 5 arranged between the flat surface portion 31 of the sealing can 3 and the electrode body 4 is embedded in the electrode body 4. By embedding a part of the annular current collector 5 in the electrode body 4 in this way, the current collection area is increased. This allows for effective current collection. The depth d1 at which the annular current collector 5, arranged between the bottom 21 and the electrode body 4, is embedded in the electrode body 4, and the depth d2 at which the annular current collector 5, arranged between the planar portion 31 and the electrode body 4, is embedded in the electrode body 4 will be described later.

[0028] As shown in FIG. 4, the annular current collector 5 has an outer diameter D2 of 40% to 85% of the diameter D1 of the electrode body 4 in a plan view, and an inner diameter D3 of 30% to 75%. The diameter D1 of the electrode body 4 in a plan view is the diameter of the main surface of the electrode body 4. That is, in the annular current collector 5 arranged between the bottom 21 and the electrode body 4, the diameter D1 of the electrode body 4 is the diameter of one main surface of the electrode body 4 facing the bottom 21. In the annular current collector 5 arranged between the flat portion 31 and the electrode body 4, the diameter D1 of the electrode body 4 is the diameter of the other main surface of the electrode body 4 corresponding to the flat portion 31. This allows for effective current collection. From the viewpoint of effective current collection, the outer diameter D2 is preferably 40% or more, preferably 45% or more, more preferably 50% or more, and 85% or less, preferably 80% or less, more preferably 75% or less, of the diameter D1 of the electrode body 4. The inner diameter D3 is 30% or more, preferably 35% or more, more preferably 40% or more, and 75% or less, preferably 70% or less, more preferably 65% ​​or less, of the diameter D1 of the electrode body 4. In the plan view shown in Fig. 4, the electrode body 4 has a circular shape with a linear cutout in order to accommodate the positive electrode lead 411 and the negative electrode lead 421 (see Fig. 1) in the case. The diameter D1 of the electrode body 4 can be said to be the diameter of the circular shape.

[0029] In this way, with the flat battery 1, a portion of the annular current collector 5 is embedded in the electrode body 4, and the relationship between the diameter D1 of the electrode body in a planar view, and the outer diameter D2 and inner diameter D3 of the annular current collector 5 is appropriately set, thereby making it possible to effectively collect current while using a simply shaped annular current collector 5.

[0030] As shown in FIG. 5, the annular current collector 5 has an opening 51 penetrating in the thickness direction. The annular current collector 5 has an opening ratio of 65% or more in a plan view. This allows the annular current collector 5 to more effectively collect current while suppressing the generation of burrs during processing. From the viewpoint of suppressing the generation of burrs during processing of the annular current collector 5, the opening ratio is preferably 65% ​​or more, preferably 70% or more, and more preferably 75% or more, and from the viewpoint of the annular current collector 5 having a certain width and more effectively collecting current, the opening ratio is preferably 90% or less, preferably 85% or less, and more preferably 80% or less. The aperture ratio R is calculated by the following formula: R = A1 / (A1+A2) x 100 In the formula, A1 represents the opening area of ​​the opening 51 in a plan view, and A2 represents the area of ​​the annular current collector 5 in a plan view.

[0031] As shown in FIG. 2, the annular current collector 5 arranged on the bottom 21 side of the outer can 2 has a depth d1 where a part of it is embedded in the electrode body 4 (positive electrode current collector foil 412 and insulating sheet 44). The depth d1 is 50 μm or more. This allows the annular current collector 5 to collect current more effectively. From the viewpoint of effective current collection, the depth d1 is preferably 50 μm or more, more preferably 55 μm or more, and more preferably 60 μm or more. The upper limit of the depth d1 is not particularly limited, but may be determined so that a part of the annular current collector 5 protrudes from one main surface of the electrode body 4 according to the thickness of the annular current collector 5. For example, the depth d1 is preferably 80 μm or less.

[0032] The depth d1 at which the annular current collector 5 is embedded can be measured as follows. The flat battery 1 is assembled and the first charge and discharge are performed. After that, the flat battery 1 is disassembled and the annular current collector 5 is removed from the electrode body 4. At that time, a groove-shaped recess is formed on the main surface of the electrode body 4 as a trace of the removal of the annular current collector 5. Then, the recess is observed using a one-shot 3D shape measuring machine (manufactured by Keyence Corporation, VR series model number VR3100), and the opening surface, i.e., the distance from the virtual line connecting the opening ends to the bottom of the recess in the vertical direction is measured. The distance measured in this way can be the depth d1.

[0033] 3, the annular current collector 5 arranged on the flat portion 31 side of the sealing can 3 has a depth d2 where a part of it is embedded in the electrode body 4 (the negative electrode current collector foil 422 and the negative electrode 42). The depth d2 and the method for measuring the depth d2 are similar to those for the depth d1 described above, and therefore a detailed description thereof will be omitted.

[0034] The gasket 6 is made of a resin with low moisture permeability, such as polypropylene resin, polyphenylene sulfide resin, or PFA resin. The gasket 6 is formed in a cylindrical shape along the inner peripheral surface of the peripheral wall 22 of the outer can 2, and is disposed between the peripheral wall 22 of the outer can 2 and the peripheral wall 32 of the sealed can 3. The gasket 6 is not particularly limited as long as it can insulate the outer can 2 and the sealed can 3, but may be made of, for example, a polyolefin resin such as polypropylene (PP), a resin such as polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyether sulfone (PES), polyphenylene sulfide (PPS), or polyether ether ketone (PEEK), or a fluororesin such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA). In particular, in addition to PP, a fluororesin such as polyphenylene sulfide resin or PFA resin is preferably used from the viewpoints of moisture permeability and heat resistance.

[0035] Next, the flat battery 1 of the second embodiment will be specifically described with reference to Fig. 6. Note that a description of the same configuration as the flat battery 1 of the first embodiment will be omitted, and basically, the configuration different from the flat battery 1 of the first embodiment will be specifically described. The flat battery 1 of the second embodiment is an all-solid-state secondary battery.

[0036] The flat battery 1 has an electrode assembly 4 housed between an exterior can 2 and a sealing can 3 .

[0037] The electrode body 4 has a positive electrode 41 arranged on the exterior can 2 side, a negative electrode 42 arranged on the sealing can 3 side, and an isolation layer (solid electrolyte layer) 45 arranged between the positive electrode 41 and the negative electrode 42. That is, the electrode body 4 is formed by laminating a layer of the positive electrode 41, a layer of the negative electrode 42, and the isolation layer 45.

[0038] The positive electrode 41 is a positive electrode pellet formed into a cylindrical shape from a positive electrode mixture containing lithium cobalt oxide, a sulfide-based solid electrolyte, and graphene as a conductive additive in a mass ratio of 65:30:5 as a positive electrode active material. The positive electrode active material of the positive electrode 41 is not particularly limited as long as it can function as a positive electrode layer, and may be, for example, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese composite oxide, olivine-type composite oxide, or an appropriate mixture of these.

[0039] The negative electrode 42 is made of LTO (Li4Ti5O 12 The negative electrode pellet is a negative electrode mixture containing lithium carbide (lithium titanate), a sulfide-based solid electrolyte, and graphene in a weight ratio of 50:40:10, which is formed into a cylindrical shape. The negative electrode active material of the negative electrode 42 is not particularly limited as long as it can function as a negative electrode layer, and may be, for example, metallic lithium, a lithium alloy, a carbon material such as graphite or low-crystalline carbon, an oxide such as SiO, or an appropriate mixture of these. Other constituent materials and their ratios are also not particularly limited.

[0040] The separator layer (solid electrolyte layer) 45 contains a sulfide-based solid electrolyte. The separator layer 45 is formed into a cylindrical shape. The solid electrolyte contained in the positive electrode 41, the negative electrode 42, and the separator layer 45 is not particularly limited, but a sulfide-based solid electrolyte, particularly an argyrodite-type sulfide-based solid electrolyte, is preferably used in terms of ion conductivity. When using a sulfide-based solid electrolyte, it is preferable to coat the surface of the positive electrode active material with a lithium ion conductive material such as niobium oxide in order to prevent reaction with the positive electrode active material. The solid electrolyte contained in the separator layer 45, the positive electrode 41, and the negative electrode 42 may be a hydride-based solid electrolyte, an oxide-based solid electrolyte, or the like.

[0041] The annular current collector 5 is disposed either between the bottom 21 of the outer can 2 and the positive electrode 41 of the electrode assembly 4, or between the flat portion 31 of the sealing can 3 and the negative electrode 42 of the electrode assembly 4. In this embodiment, the annular current collector 5 is disposed both between the bottom 21 of the outer can 2 and the positive electrode 41 of the electrode assembly 4, and between the flat portion 31 of the sealing can 3 and the negative electrode 42 of the electrode assembly 4.

[0042] A portion of the annular current collector 5 arranged on the exterior can 2 side is embedded in the main surface of the positive electrode 41, i.e., one main surface of the electrode body 4 facing the bottom 21 of the exterior can 2. A portion of the annular current collector 5 arranged on the sealing can 3 side is embedded in the main surface of the negative electrode 42, i.e., the other main surface of the electrode body 4 facing the flat portion 31 of the sealing can 3. The depths d1 and d2 of the annular current collector 5 and the method for measuring the depths are the same as those of the flat battery 1 of the first embodiment described above.

[0043] Even in such an all-solid-state secondary battery, by disposing the annular current collector 5 either between the bottom 21 of the exterior can 2 and the positive electrode 41 of the electrode body 4, or between the flat portion 31 of the sealing can 3 and the negative electrode 42 of the electrode body 4, it is possible to effectively collect current while using a current collector with a simple shape.

[0044] In the flat battery 1 of the first and second embodiments, the positive electrode and the negative electrode may be interchanged, and in the flat battery 1 of the second embodiment, a bipolar flat battery 1 may be formed by connecting a plurality of electrode bodies 4 in series. In the flat battery 1 of the second embodiment, the isolating layer 45 may be replaced with a separator and an electrolyte solution may be accommodated in the case, so that the flat battery 1 can be a lithium ion secondary battery, a lithium ion capacitor, an electric double layer capacitor, or the like. In this case, the separator and the electrolyte solution are those that are normally used in lithium ion secondary batteries, lithium ion capacitors, electric double layer capacitors, or the like. In addition, the positive electrode 41 and the negative electrode 42 may be replaced with a mixture layer of a positive electrode and a negative electrode that are normally used in various flat batteries 1.

[0045] Furthermore, the present invention can contribute to achieving Goal 7 "Ensure access to affordable, reliable, sustainable and modern energy for all" and Goal 12 "Ensure sustainable consumption and production patterns" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0046] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. EXAMPLES

[0047] Flat batteries (outer diameter: 6.8 mm, height: 4.0 mm) of Examples 1 to 5 and Comparative Examples 1 to 5 having the electrode body 4 shown in Fig. 1 were fabricated, and the planar shape of the current collector contained in each flat battery was changed to evaluate the occurrence of cycle noise. In addition, the occurrence rate of burrs on the current collector was evaluated.

[0048] [Table 1]

[0049] (Cycle noise evaluation) In flat batteries that can effectively collect current, the discharge capacity tends to decrease gradually with repeated charge and discharge cycles. On the other hand, in flat batteries that cannot collect current stably, the discharge capacity increases and decreases drastically with repeated charge and discharge cycles. Therefore, when comparing the IC discharge capacity at the nth cycle with the IC discharge capacity at the n-1th cycle, if the IC discharge capacity at the nth cycle is decreased by 2% or more than the IC discharge capacity at the n-1th cycle, or if it is increased by 1% or more, the nth cycle is determined to be the point at which "noise" occurred. Since the discharge capacity also increases and decreases due to fluctuations in the environmental temperature, an increase of up to 1% and a decrease of up to 2% are considered to be within the normal allowable range. 500 charge and discharge cycles were repeated, and the rate at which "noise" occurred (cycle noise occurrence rate) was used to evaluate whether or not current was effectively collected. The evaluation method is as follows. Cycle noise occurrence rate 0%:A More than 0%, less than 20% :B More than 20%, less than 50%:C 50% or more :D

[0050] (burr occurrence rate) The appearance of 100 current collectors for each of the examples and comparative examples was observed, and the incidence rate of current collectors with burrs was determined.

[0051] (Evaluation Results) In Examples 1 to 5, the occurrence rate of cycle noise was 20% or less, and current collection was effective. In Examples 1 to 5, the current collector with burrs was 0%. In addition, when Examples 1 to 3 and Example 4 were compared, the occurrence rate of cycle noise was evaluated as "B" when the aperture ratio was below 65%. It is presumed that if the aperture ratio is 65% or more, current collection tends to be effective. In addition, when Examples 1 to 5 and Comparative Example 5 were compared, the ratio of the outer diameter to the diameter of the electrode body was greater than 85% and the ratio of the inner diameter to the diameter of the electrode body was greater than 75% in Comparative Example 5, but it is presumed that the aperture ratio should be 80% or less. In addition, when Examples 1 to 3 and Example 5 were compared, the occurrence rate of cycle noise was evaluated as "B" when the depths d1 and d2 at which the current collector was buried were less than 50 μm. Therefore, it is presumed that if the depths d1 and d2 were 50 μm or more, current collection tends to be effective.

[0052] In Comparative Example 1, the occurrence rate of cycle noise was rated as "B", but 1% of the current collectors had burrs.

[0053] In Comparative Examples 2 and 3, cycle noise was relatively high, current collection by the current collector was unstable, and burrs were present in 1% of the current collectors.

[0054] In Comparative Examples 4 and 5, a ring-shaped current collector was used, but when the ratio of the outer diameter to the diameter of the electrode body was outside the range of 40% to 85% and the ratio of the inner diameter to the diameter of the electrode body was outside the range of 35% to 75%, effective current collection was not possible.

[0055] In this way, by embedding a ring-shaped current collector having a simple shape in the electrode body and appropriately setting the ratio of the outer diameter and inner diameter to the diameter of the electrode body, effective current collection could be obtained.

[0056] The annular current collectors of Examples 1 to 5 were easy to embed in the electrode body. Therefore, the total thickness of the electrode body and the annular current collector embedded in the electrode body was reduced. In other words, the thickness of the electrode body could be increased accordingly, and it is presumed that the annular current collectors of Examples 1 to 5 contribute to improving the battery capacity of the flat battery 1. [Explanation of symbols]

[0057] 1 flat battery, 2 outer can, 3 sealing can, 4 electrode body, 5 annular current collector, 6 gasket, D1 diameter, D2 outer diameter, D3 inner diameter, d1 depth, d2 depth

Claims

1. an exterior can having a bottom; A sealing can having a flat surface portion; an electrode assembly accommodated between the exterior can and the sealing can; a ring-shaped current collector disposed either between the bottom portion and the electrode body or between the planar portion and the electrode body; a portion of the annular current collector is embedded in a main surface of the electrode assembly in a thickness direction of the annular current collector, The annular current collector has, in a plan view, an outer diameter that is 40% to 85% and an inner diameter that is 30% to 75% of the diameter of the main surface of the electrode body in which a portion of the annular current collector is embedded.

2. 2. The flat battery according to claim 1 , The annular current collector has an aperture ratio of 65% or more.

3. The flat battery according to claim 1 or 2, A flat battery, wherein the annular current collector is embedded in the main surface of the electrode body to a depth of 50 μm or more.

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