Flat-type battery

Abstract

To provide a flat battery that can increase battery capacity.SOLUTION: The flat battery includes: an outer can; a sealing can 3 that has a flat portion 3a; and a stacked electrode body. The stacked electrode body is formed of a positive electrode 20 housed in a bag-shaped separator and a negative electrode, which are stacked. A main surface of the positive electrode 20 has an area of 70% or larger with respect to an area of an inner surface of the flat portion 3a of the sealing can 3. Thereby, an area of the main surface of the positive electrode 20 becomes relatively large, and the battery capacity of the flat battery can be increased.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a flat battery containing a laminated electrode body.

Background Art

[0002] Generally, a flat battery has a structure in which an electrode body having a negative electrode, a positive electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte are housed inside a case composed of an exterior can and a sealing can. Among such flat batteries, a laminated flat battery in which a plurality of negative electrodes and positive electrodes are alternately laminated is known. Some laminated flat batteries have a positive electrode housed in a bag-shaped separator.

[0003] Japanese Unexamined Patent Application Publication No. 2011-9118 (Patent Document 1) discloses a coin-shaped secondary battery that can reliably discharge air remaining in a bag-shaped separator and suppress peeling between upper and lower films forming the separator. The coin-shaped secondary battery includes a positive electrode housed in a circular bag-shaped separator. The positive electrode has a substantially circular shape in plan view, and is shaped such that the position where the positive electrode lead is connected and the opposing position are linearly cut off. The separator housing the positive electrode is formed in a bag shape by adhering the peripheral edges of two films to each other along the outer periphery of the positive electrode. Non-adhesive portions for discharging air in the internal space of the separator are provided in a dispersed manner at the peripheral edge of the bag-shaped separator.

[0004] International Publication No. 2018 / 124152 (Patent Document 2) discloses a coin-shaped battery in which a positive electrode and a separator are integrated. The coin-shaped battery has separators disposed on both sides of the positive electrode, and a part of the peripheral edges of both separators is welded by heat pressing to form a joint portion at a part of the peripheral edges of the two separators, thereby integrating the positive electrode and the separator.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] As the performance of electronic devices and other equipment that use flat-type batteries as power sources improves, there is a growing demand for higher battery capacity in these batteries. However, there is still room to further increase the battery capacity of the coin-type secondary battery described in Patent Document 1 and the coin-type battery described in Patent Document 2.

[0007] Therefore, the objective of this disclosure is to provide a flat-type battery that can increase battery capacity. [Means for solving the problem]

[0008] To solve the above problems, this disclosure is configured as follows. Specifically, the flat-type battery according to this disclosure may comprise an outer casing, a sealing casing having a flat surface, and a laminated electrode body housed between the outer casing and the sealing casing. The laminated electrode body may be formed by laminating a positive electrode housed in a bag-shaped separator and a negative electrode. The main surface of the positive electrode may have an area of ​​70% or more of the area of ​​the inner surface of the flat surface.

[0009] Flat-type batteries may have an outer diameter of 15 mm or less.

[0010] The main surface of the positive electrode may have an area of ​​90% or less of the area of ​​the inner surface of the flat portion. [Effects of the Invention]

[0011] The flat-shaped battery of this disclosure makes it possible to increase the battery capacity. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing a flat-type battery according to this disclosure. [Figure 2] Figure 2 is an enlarged cross-sectional view of the flattened battery shown in Figure 1. [Figure 3] Figure 3 is a plan view showing the shape of the positive electrode of the flat-type battery shown in Figure 1. [Figure 4] Figure 4 is a plan view showing the flat surface and positive electrode of the sealed can shown in Figure 1. [Figure 5] Figure 5 is a plan view showing the positive electrode of this disclosure superimposed on the positive electrode of the prior art. [Figure 6] Figure 6 is a plan view showing the positive electrode and separator of the conventional technology. [Modes for carrying out the invention]

[0013] The flat-type battery 1 and the laminated electrode body 10 related to this disclosure will be described in detail below using Figures 1 to 5. First, as shown in Figure 1, the flat-type battery 1 has an outer casing 2, a sealing casing 3, a gasket 4, and a laminated electrode body 10. The outer casing 2, the sealing casing 3, and the gasket 4 are the case of the flat-type battery 1. The laminated electrode body 10 is housed in the case. The flat-type battery 1 has an outer diameter D of 15 mm or less. The outer diameter D of the flat-type battery 1 will be described in detail later.

[0014] The outer casing 2 comprises a circular bottom portion 2a in plan view and a cylindrical peripheral wall portion 2b that is continuously formed from the outer circumference of the bottom portion 2a. In a longitudinal cross-sectional view, the peripheral wall portion 2b is provided to extend substantially perpendicular to the bottom portion 2a. The outer casing 2 is made of a metal material such as stainless steel, nickel, or iron.

[0015] The sealed can 3 comprises a circular flat portion 3a and a cylindrical peripheral wall portion 3b that is continuously formed from the outer circumference of the flat portion 3a. The opening of the sealed can 3 faces the opening of the outer can 2. The sealed can 3 is made of a metal material such as stainless steel.

[0016] The gasket 4 is formed of a moisture low-permeability resin such as a polypropylene resin, a polyphenylene sulfide resin, or a PFA resin. The gasket 4 is formed in a cylindrical shape along the inner peripheral surface of the peripheral wall portion 2b of the outer can 2 and is disposed between the peripheral wall portion 2b of the outer can 2 and the peripheral wall portion 3b of the sealed can 3. The gasket 4 is not particularly limited as long as it can insulate the outer can 2 and the sealed can 3. For example, in addition to polyolefin resins such as polypropylene (PP), it can be composed of resins such as polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), or fluorine resins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA). In particular, in addition to PP, polyphenylene sulfide resins or fluorine resins such as PFA resins are preferably used in terms of moisture permeability and heat resistance.

[0017] After the outer can 2 and the sealed can 3 accommodate the laminated electrode body 10 and a non-aqueous electrolyte (not shown), they are caulked through the gasket 4 between the peripheral wall portion 2b of the outer can 2 and the peripheral wall portion 3b of the sealed can 3. That is, the outer can 2 and the sealed can 3 are caulked through the gasket 13 between the peripheral wall portion 2b and the peripheral wall portion 3b after opposing the openings of the outer can 2 and the sealed can 3 to each other and inserting the peripheral wall portion 3b of the sealed can 3 inside the peripheral wall portion 2b of the outer can 2. In this way, an internal space of the flat battery 1 for accommodating the laminated electrode body 10 is formed.

[0018] The laminated electrode body 10 is an electrode body in which a plurality of positive electrodes (electrodes) 20 and negative electrodes 30 are laminated alternately. The positive electrode 20 is housed in a bag-shaped separator 40. The number of laminations of the positive electrode 20 and the negative electrode 30 is determined by the desired battery capacity. Therefore, these numbers of laminations are not limited to those shown in the figure. Among the plurality of negative electrodes 30, the negative electrode 30 closest to the inner surface of the bottom 2a of the outer can 2 and the negative electrode 30 closest to the inner surface of the flat portion 3a of the sealing can 3 each have a negative electrode active material layer 32 provided only on one surface of the negative electrode current collector 31, and the negative electrode 30 closest to the inner surface of the flat portion 3a of the sealing can 3 has its negative electrode current collector 31 in contact with the flat portion 3a. Also, an insulating sheet 50 is provided between the negative electrode 30 closest to the inner surface of the bottom 2a of the outer can 2 and the bottom 2a of the outer can 2. The insulating sheet 50 insulates the negative electrode 30 closest to the inner surface of the bottom 2a of the outer can 2 and the bottom 2a of the outer can 2.

[0019] In the internal space of the flat battery 1, a positive electrode lead 20a and a negative electrode lead 30a are further housed. The positive electrode lead 20a extends continuously from the peripheral end portion of the positive electrode current collector 21 of each positive electrode 20 shown in FIG. 2 described later. Each positive electrode lead 20a electrically connects the corresponding positive electrode 20 and the bottom 2a of the outer can 2. The negative electrode lead 30a extends continuously from the peripheral end portion of the negative electrode current collector 31 of each negative electrode 30 shown in FIG. 2 described later. Each negative electrode lead 30a connects the corresponding negative electrode 30 and the flat portion 3a of the sealing can 3. Therefore, the outer can 2 functions as a positive electrode can, and the sealing can 3 functions as a negative electrode can.

[0020] As shown in FIG. 2, each positive electrode 20 has a positive electrode current collector 21 and a positive electrode active material layer 22 disposed on both surfaces of the positive electrode current collector 21. The positive electrode current collector 21 is, for example, a metal foil such as an aluminum foil. The positive electrode active material layer 22 is, for example, a layer formed by compression molding a positive electrode active material such as lithium cobaltate, a binder, a conductive auxiliary agent, and the like.

[0021] Each negative electrode 30 has a negative electrode current collector 31 and a negative electrode active material layer 32 disposed on both sides or one side of the negative electrode current collector 31. The negative electrode current collector 31 is, for example, a metal foil such as copper foil. The negative electrode active material layer 32 is, for example, a layer formed by compression molding a negative electrode active material such as graphite with a binder and a conductive additive.

[0022] The positive electrode current collector 21 is electrically connected to the outer casing 2 via the positive electrode lead 20a. The end of the positive electrode lead 20a closest to the positive electrode current collector 21 is covered by a bag-shaped separator 40. The portion of the positive electrode lead 20a covered by the separator 40 is bent toward the bottom 2a of the outer casing 2. The ends of multiple positive electrode leads 20a closest to the outer casing 2 are bundled together and connected to the outer casing 2.

[0023] Each of the bag-shaped separators 40 is, for example, a microporous film made of polyethylene with excellent insulating properties. This allows the separators 40 to permeate lithium ions. Details of the separators 40 (films 40a and 40b) will be described later.

[0024] As shown in Figure 3, the positive pole 20, in plan view, has a shape in which the four corners of a roughly rectangular shape, indicated by a dashed line in the figure, are beveled in an arc shape, and has arc sections 23a, 23b, 23c, and 23d, and straight sections 24a, 24b, 24c, and 24d. The arc sections 23a, 23b, 23c, and 23d are formed along the circumference of a circle having center C, that is, along the circumference of the same circle. The straight section 24a is formed between arc sections 23a and 23b. The straight section 24b is formed between arc sections 23b and 23c. The straight section 24c is formed between arc sections 23c and 23d. The straight section 24d is formed between arc sections 23a and 23d. In other words, each straight section is formed between adjacent arc sections. The circle with center C is a concentric circle with a smaller diameter than the circle traced by the outer edge of the flat portion 3a of the circular sealing can 3 described above. That is, center C is located on the cylindrical axis of the flat-shaped battery 1. This ensures that the positive electrode 20 is properly housed in the internal space of the flat-shaped battery 1. Furthermore, center C is located closer to the straight portion 24d side (left side in the figure) where the positive electrode lead 20a is located than the intersection of the diagonals of the roughly rectangular shape described above (not shown). That is, the straight portion 24d where the positive electrode lead 20a is located is longer than its opposite straight portion 24b. This ensures that, as shown in Figure 1 or 2, when the positive electrode 20 housed in the separator 40 is housed in the internal space of the flat-shaped battery 1, space can be secured to accommodate the positive electrode lead 20a.

[0025] The roughly rectangular shape in the figure has a short side α and a long side β. The positive electrode lead 20a is connected to the positive electrode current collector 21, which is a straight section 24d formed on the long side β. The short side α has a length L1. The long side β has a length L2. The ratio of length L1 to length L2 is preferably 1.12 to 1.25 when length L1 is 1. More preferably, this ratio is 1.15 to 1.21 when length L1 is 1. This makes it possible to maximize the area of ​​the positive electrode 20 in plan view, which has a roughly rectangular shape with the four corners beveled in an arc shape, while securing space for housing the positive electrode lead 20a and the negative electrode lead 30a, as well as space for providing the fixing portion 41 of the separator 40 described later, within the limited internal space of the flat-type battery 1. As a result, the capacity of the flat-type battery 1 can be increased.

[0026] As shown in Figure 4, the positive electrode 20 is housed in a bag-shaped separator 40. As shown in Figure 2, the separator 40 has a film 40a positioned on one main surface (upper side in the figure) of the positive electrode 20 and a film 40b positioned on the other main surface (lower side in the figure) of the positive electrode 20. The radial size of each of the films 40a and 40b is slightly larger than the positive electrode 20 and the positive electrode 20 side end of the positive electrode lead 20a connected to the positive electrode 20. Films 40a and 40b are, for example, microporous films made of polyethylene. The method for housing the positive electrode 20 in the separator 40 is as follows: First, prepare films 40a and 40b. The positive electrode 20 is placed between films 40a and 40b. Finally, a portion of the peripheral edge of film 40a and the peripheral edge of film 40b facing the portion of the peripheral edge of film 40a are fixed together by heating and pressing. In this way, the separator 40 is formed in a bag shape and houses the positive electrode 20.

[0027] The peripheral edge of film 40a includes a fixed portion 41 that is partially fixed to the peripheral edge of the opposing film 40b, and an unfixed portion 42 that is not fixed. In other words, the separator 40 has a fixed portion 41 and an unfixed portion 42 at its peripheral edge. More specifically, the fixed portion 41 is formed to be located radially outward from the straight portions 24a, 24b, 24c, and 24d shown in Figure 3, and the unfixed portion 42 is formed to be located radially outward from the arc portions 23a, 23b, 23c, and 23d. Furthermore, the fixed portion 41 located radially outward from the straight portion 24d is also formed to follow both sides of the positive electrode lead 20a. The outer peripheral end of the fixing portion 41, located radially outward from the straight portions 24a and 24c, is formed by an arc along the periphery of the flat portion 3a of the sealing can 3 and a straight line along the straight portions 24a and 24c. Therefore, the plan view shape of the fixing portion 41 located radially outward from the straight portions 24a and 24c is sector-shaped. In this way, the fixing portion 41 prevents the positive electrode 20 from protruding from the inside of the bag-shaped separator 40. The non-fixed portion 42 allows residual air and other substances inside the bag-shaped separator 40 to be discharged. Note that the method of fixing the peripheral portion of the separator 40 is not limited to welding by heat pressing, but may also be bonded with an adhesive, and is not particularly limited.

[0028] The dashed line in Figure 4 indicates the outer peripheral edge on the inner surface of the flat portion 3a of the sealing can 3. In plan view, the radius of the arc portion of the peripheral edge of the separator 40 is smaller than or equal to the radius of the circle traced by the outer peripheral edge on the inner surface of the flat portion 3a of the sealing can 3. This allows the positive electrode 20 housed in the separator 40 to be properly housed in the internal space of the flat battery 1. Furthermore, by providing the straight portions 24b and 24d, predetermined spaces are formed between the laminated electrode body 10 shown in Figure 1 and the peripheral wall portion 3b of the sealing can 3. The negative electrode lead 30a is housed in the space facing the straight portion 24b. The positive electrode lead 20a, which is bent toward the bottom 2a of the outer casing 2, is housed in the space facing the straight portion 24d.

[0029] The relationship between the ratio of length L1 and length L2 described above can also be explained from the following point of view. Referring to Figures 3 and 4, if the length L3 of the straight section 24a or 24c formed on the short side α is shortened, that is, if the radius of the circle containing the arc sections 23a, 23b, 23c and 23d is kept constant and the length L2 of the long side β becomes longer than the length L1 of the short side α, the area of ​​the positive electrode 20 in plan view will increase, but the radial width (vertical width shown in Figure 4) of the fixing sections 41, 41 located radially outward from the straight sections 24a and 24c will decrease, and the fixing of the peripheral edge of the separator 40 may become insufficient. As a result, the positive electrode 20 may be exposed outward from the separator 40 due to poor fixing, causing a short circuit. On the other hand, as the length L3 of the straight portion 24a or 24c formed on the short side α increases, that is, as the ratio of the length L1 of the short side α to the length L2 of the long side β approaches 1:1 while keeping the radius of the circle containing the arc portions 23a, 23b, 23c, and 23d constant, the area of ​​the positive pole 20 in plan view decreases, but the radial width of the fixing portions 41, 41 located radially outward from the straight portions 24a and 24c increases, allowing the peripheral edge of the separator 40 to be sufficiently fixed. From this viewpoint, the length L3 of the straight portion 24a or 24c formed on the short side α should be 15% or more, preferably 20% or more, and more preferably 25% or more, of the length L1 of the short side α. Also, the length L3 of the straight portion 24a or 24c formed on the short side α should be 50% or less, preferably 45% or less, and more preferably 40% or less, of the length L1 of the short side α. Alternatively, the ratio of length L1 to length L2 should be such that when length L1 is 1, length L2 is between 1.12 and 1.25. More preferably, this ratio should be such that when length L1 is 1, length L2 is between 1.15 and 1.21.

[0030] Furthermore, from the viewpoint of housing the positive electrode lead 20a and the negative electrode lead 30a within the internal space of the flat-shaped battery 1, the lengths of the straight sections 24b and 24d formed on the long side β should be longer than the widths of the negative electrode lead 30a and the positive electrode lead 20a, respectively. However, if the positive electrode lead 20a and the negative electrode lead 30a can be housed within the internal space of the flat-shaped battery 1, it is desirable that the space in which the negative electrode lead 30a and the positive electrode lead 20a are housed be as small as possible. For this reason, it is preferable that the lengths of the straight sections 24b and 24d formed on the long side β be as short as possible relative to the length L2 of the long side β.

[0031] As described above, the positive electrode (electrode) 20 according to this disclosure has a plan view shape in which the four corners of a roughly rectangular shape are beveled in an arc shape, thereby maximizing the area of ​​the positive electrode 20 in plan view and increasing the battery capacity of the flat battery 1. Furthermore, by positioning the fixing portion 41 of the separator 40 radially outward of the straight portions 24a, 24b, 24c, and 24d of the positive electrode 20, the peripheral portion of the film 40a and the peripheral portion of the film 40b can be sufficiently fixed, preventing the positive electrode 20 from protruding from inside the bag-shaped separator 40, while accommodating the positive electrode 20 with its maximized area in plan view, thereby increasing the battery capacity of the flat battery 1. Moreover, by housing the laminated electrode body 10 including this positive electrode (electrode) 20 in the flat battery 1, the battery capacity of the flat battery 1 can be increased. The positive electrode 20 is housed in a bag-shaped separator 40 having a fixing portion 41. Therefore, the stacked electrode body 10 and the flat-shaped battery 1 prevent the positive electrode 20 from protruding from inside the bag-shaped separator 40.

[0032] As mentioned above, the dashed line in Figure 4 indicates the outer peripheral edge of the inner surface of the flat portion 3a of the sealed can 3. The inner surface of the flat portion 3a is formed in a planar shape. On the other hand, the main surface of the positive electrode 20, in other words, the main surface of the positive electrode active material layer 22 as shown in Figure 2, is formed in a planar shape. In the illustration, the main surface of the positive electrode 20 is the upper surface of the positive electrode 20. That is, the main surface of the positive electrode 20 is the surface facing the inner surface of the flat portion 3a. In the limited internal space of the flat-shaped battery 1, increasing the area of ​​the main surface of the positive electrode 20 contributes to increasing the battery capacity. However, it is not easy to increase the area of ​​the main surface of the positive electrode 20 housed in the bag-shaped separator 40. The main surface of the positive electrode 20 has an area of ​​70% or more of the area of ​​the inner surface of the flat portion 3a. That is, by making the positive electrode 20 the shape described above, the area of ​​the main surface of the positive electrode 20 can be made 70% or more of the area of ​​the inner surface of the flat portion 3a. This allows the area of ​​the main surface of the positive electrode 20 to be relatively larger, thereby increasing the battery capacity. As shown in Figure 1 or Figure 2, when the flat-type battery 1 has multiple positive electrodes 20, it is sufficient that the area of ​​the main surface of any one of the positive electrodes 20 is 70% or more of the area of ​​the inner surface of the flat portion 3a. However, since each of the multiple positive electrodes 20 usually has the same main surface shape and area as the others, and from the viewpoint of providing a gap between the positive electrode 20 and the peripheral wall portion 3b of the sealing can 3, it is preferable to determine the area of ​​the main surface of the multiple positive electrodes 20 based on the positive electrode 20 closest to the flat portion 3a of the sealing can 3. Therefore, the area of ​​the main surface of the positive electrode 20 can also be defined as the area of ​​the main surface of the multiple positive electrodes 20 that is closest to the flat portion 3a of the sealing can 3. Furthermore, the main surface of the positive electrode 20 has an area of ​​90% or less of the area of ​​the inner surface of the flat portion 3a. If the surface area of ​​the main surface of the positive electrode 20 becomes too large, it becomes difficult to secure sufficient space between the laminated electrode body 10 and the sealing can 3, making it difficult to accommodate the laminated electrode body 10 in the internal space of the outer can 2 and the sealing can 3.

[0033] As described above, the flat-type battery 1 has an outer diameter D of 15 mm or less (see Figure 1). In this embodiment, the outer diameter D of the flat-type battery 1 can also be said to be the outer diameter of the outer casing 2. In a relatively small flat-type battery 1, the width of the gap between the positive electrode 20 and the peripheral wall portion 3b of the sealing casing 3 is relatively larger compared to a relatively large flat-type battery 1. That is, in a relatively small flat-type battery 1, it is not easy to relatively increase the area of ​​the main surface of the positive electrode 20. With the flat-type battery 1, even a relatively small flat-type battery 1 with an outer diameter D of 15 mm or less can have the area of ​​the main surface of the positive electrode 20 be 70% or more of the area of ​​the inner surface of the flat portion 3a, thereby increasing the battery capacity. Furthermore, in the flat-type battery 1, the smaller the outer diameter D becomes, the more difficult it becomes to relatively increase the area of ​​the main surface of the positive electrode 20. According to the flat-type battery 1, even with relatively small flat-type batteries having an outer diameter D of 12 mm or less, 11 mm or less, 10 mm or less, 9 mm or less, 8 mm or less, and 7 mm or less, the area of ​​the main surface of the positive electrode 20 can be made 70% or more of the area of ​​the inner surface of the flat portion 3a, thereby increasing the battery capacity.

[0034] In the above-described embodiment, the positive electrode 20 is housed in the separator 40, but the negative electrode 30 may also be housed in the separator 40. In that case, the flat-type battery 1 can have the main surface area of ​​the negative electrode 30 be 70% or more of the inner surface area of ​​the flat portion 3a of the sealing can 3. [Examples]

[0035] (Examples) A positive electrode 20 (example) of the above-described embodiment and a positive electrode 120 (comparative example) housed in a conventional bag-shaped separator 140 that can be accommodated in the same internal space as the flat-shaped battery 1 of the above-described embodiment were prepared, and as shown in Figure 5, the difference in their respective areas was confirmed by overlapping the positive electrode 20 and the positive electrode 120.

[0036] As shown in Figure 6, the comparative positive electrode 120 differs from the positive electrode 20 in that both short sides of the roughly rectangular shape are cut out in an arc shape. The bag-shaped separator 140 has a fixing portion 141 along the periphery of the positive electrode 120 and the positive electrode side of the positive electrode lead 120a. The separator 140 is formed in a bag shape by the fixing portion 141 that fixes its periphery, similar to the separator 40 of the embodiment. The separator 140 also has a non-fixing portion 142 in a part of the arc shape. Thus, the comparative separator 140 has a fixing portion 141 with a predetermined width formed around the positive electrode 120. Therefore, the radius of the arc-shaped cut-out portion of the positive electrode 120 is smaller than that of the positive electrode 20 of the embodiment. Furthermore, if the shape of the positive electrode 120 in plan view is simply a larger, similar shape, the area of ​​the positive electrode 120 can be increased, but the radial width of the fixing portion 141 will decrease accordingly, which may lead to the problem that the peripheral edge of the separator 140 cannot be sufficiently fixed.

[0037] As shown in Figure 5, the positive pole 20 and the positive pole 120 are superimposed. The positive pole 20 is shown as a solid line, and the positive pole 120 is shown as a dashed line. As shown in Figure 5, it was found that, unlike the positive pole 120, even after subtracting the point having a straight section 24a, the radius of the arc section of the positive pole 20 can be increased, and the area in plan view can be larger than that of the positive pole 120.

[0038] Furthermore, a comparison was made between the positive electrode according to this disclosure, which is formed with a short side L1 length of 4.195 mm and a long side L2 length of 4.95 mm, and an arc radius of 2.575 mm, as shown in Figure 3, and a conventional positive electrode structure such as the positive electrode 120 described above, in which the entire short side is an arc shape, and the radius of the arc is changed to 2.5 mm so that the peripheral edge of the separator located radially outward can be fixed. The area of ​​the positive electrode active material layer of the conventional positive electrode structure in a plan view was 17.96 mm². 2 In contrast, the area of ​​the positive electrode active material layer of the positive electrode relating to this disclosure is 18.76 mm². 2 As a result, the positive electrode of this disclosure has a 4.5% larger area compared to the conventional structure, which in turn allowed for a higher battery capacity.

[0039] Furthermore, the positive electrode 20 of the embodiment and the positive electrode 120 of the comparative example were each housed in the same flat-type battery 1 as in the embodiment described above. The outer diameter D of the flat-type battery 1 (outer casing 2) was 6.77 mm, and the area of ​​the planar inner surface of the flat portion 3a of the sealing casing 3 of the flat-type battery 1 was 26.24 mm². As described above, the area of ​​the positive electrode 120 in plan view was 17.96 mm². 2 This amounted to 68.4% of the surface area of ​​the inner surface of the flat portion 3a. On the other hand, the surface area of ​​the main surface of the positive electrode 20 in a plan view was 18.76 mm². 2 This resulted in an area of ​​71.5% of the inner surface area of ​​the flat portion 3a. Thus, even with a relatively small flat battery 1 having an outer diameter D of 6.77 mm when housed in the same flat battery 1, the area of ​​the positive electrode 20 in a plan view was 70% or more of the effective area of ​​the flat portion 3a, making it possible to increase the battery capacity.

[0040] Although embodiments have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the disclosure. [Explanation of symbols]

[0041] 1 Flat-shaped battery, 2 Outer casing, 3 Sealing casing, 4 Gasket, 10 Laminated electrode body, 20 Positive electrode, 21 Positive electrode current collector, 22 Positive electrode active material layer, 23a~23d Arc section, 24a~24d Straight section, 20a Positive electrode lead, 30 Negative electrode, 31 Negative electrode current collector, 32 Negative electrode active material layer, 40 Arc section, 30 Negative electrode, 40 Separator, 41 Fixed section, 42 Non-fixed section, 50 Insulating sheet, α Short side, β Long side

Claims

1. The outer can and A sealed can having a flat surface, The system comprises a laminated electrode body housed between the outer can and the sealing can, The aforementioned laminated electrode body is formed by stacking a positive electrode housed in a bag-shaped separator and a negative electrode, The main surface of the positive electrode has an area of ​​70% or more of the area of ​​the inner surface of the flat portion. The positive electrode is a flat-shaped battery with a plan view shape that is roughly rectangular with the four corners beveled in an arc shape.

2. A flat-shaped battery according to claim 1, The flat-shaped battery is a flat-shaped battery having an outer diameter of 15 mm or less.

3. A flat-shaped battery according to claim 1 or 2, A flat-type battery in which the main surface of the positive electrode has an area of ​​90% or less of the area of ​​the inner surface of the flat portion.

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