JP7793326B2 - Electrodes housed in a pouch-shaped separator, laminated electrode body, and flat battery - Google Patents

Description

This disclosure relates to a stacked flat battery formed by alternately stacking multiple positive and negative electrodes, including one of the positive and negative electrodes housed in the internal space of the flat battery, a separator housing one of the electrodes, a stacked electrode assembly in which one electrode and the other of the positive and negative electrodes are alternately stacked, and a flat battery housing the stacked electrode assembly.

Generally, flat batteries are constructed by housing an electrode assembly having a negative electrode, a positive electrode, and a separator placed between the positive and negative electrodes, as well as a non-aqueous electrolyte, inside a case consisting of an outer can and a sealed can. Among such flat batteries, a stacked flat battery in which multiple negative electrodes and positive electrodes are alternately stacked is known. Some stacked flat batteries have a positive electrode housed in a pouch-shaped separator.

JP 2011-9118 A (Patent Document 1) discloses a coin-type secondary battery that reliably discharges air remaining in a pouch-shaped separator and prevents peeling between the upper and lower films that form the separator. The coin-type secondary battery includes a positive electrode housed in a circular, pouch-shaped separator. The positive electrode is approximately circular in plan view, with a linear cutout at the position where the positive electrode lead is connected and at the opposite position. The separator housing the positive electrode is formed into a pouch-like shape by bonding the peripheral edges of two films together along the periphery of the positive electrode. The peripheral edge of the pouch-shaped separator further includes dispersed non-adhesive sections for discharging air from the separator's internal space.

International Publication No. 2018/124152 (Patent Document 2) discloses a coin-type battery in which the positive electrode and separator are integrated. In this coin-type battery, a separator is placed on each side of the positive electrode, and portions of the peripheries of both separators are welded together using a hot press to form a joint at the peripheries of the two separators, thereby integrating the positive electrode and separator.

JP 2011-9118 A International Publication No. 2018/124152

As electronic devices and other devices that use flat batteries as their power source become more powerful, there is a demand for higher battery capacity. However, the coin-type secondary battery of Patent Document 1 and the coin-type battery of Patent Document 2 still have room for improvement in battery capacity.

Therefore, the objective of this disclosure is to provide an electrode that can increase battery capacity.

In order to solve the above problems, the present disclosure is configured as follows. That is, the electrode according to the present disclosure may be either a positive electrode or a negative electrode housed in the internal space of a flat battery. The electrode may have a substantially rectangular shape in plan view, with the four corners chamfered into an arc shape. The electrode may have arc portions at the four chamfered corners and straight portions located between each of the arc portions at the four corners.

The ratio of the length of the short side to the length of the long side of the approximately rectangular shape may be 1.12 to 1.25 when the length of the short side is 1.

The length of the straight line portion formed on the short side of the approximately rectangular shape may be 15 to 50% of the length of the short side of the approximately rectangular shape.

The separator according to the present disclosure may be a bag-shaped separator that houses an electrode. The separator may have a first film disposed on one main surface of the electrode and a second film disposed on the other main surface of the electrode. The peripheral edge of the first film may include a fixing portion that is fixed to the peripheral edge of the second film radially outward of the straight portion of the electrode when the electrode is housed in the separator.

The laminated electrode assembly according to the present disclosure may be formed by alternately stacking multiple electrodes housed in separators and either positive or negative electrodes.

The flat battery according to the present disclosure may house a laminated electrode body in the internal space of a case.

The electrodes, laminated electrode assembly, and flat battery disclosed herein can increase the battery capacity of flat batteries. The separator disclosed herein can sufficiently secure the peripheral edge of the separator to prevent the electrodes from protruding from the inside of the separator, and can accommodate electrodes that can be made to have a high capacity, thereby increasing the battery capacity of flat batteries.

FIG. 1 is a schematic diagram showing a flat battery according to the present disclosure. FIG. 2 is an enlarged cross-sectional view of the flat battery shown in FIG. FIG. 3 is a plan view showing the shape of the positive electrode of the flat battery shown in FIG. FIG. 4 is a plan view showing the positive electrode and separator of the flat battery shown in FIG. FIG. 5 is a plan view showing a state in which the positive electrode of the present disclosure and a positive electrode of the prior art are superimposed. FIG. 6 is a plan view showing a positive electrode and a separator according to the prior art.

The flat battery 1 and stacked electrode assembly 10 according to the present disclosure will be described in detail below with reference to Figures 1 to 5. First, as shown in Figure 1, the flat battery 1 has an outer can 2, a sealing can 3, a gasket 4, and a stacked electrode assembly 10. The outer can 2, the sealing can 3, and the gasket 4 form the case of the flat battery 1. The stacked electrode assembly 10 is housed in the case.

The outer can 2 has a bottom 2a that is circular in plan view and a cylindrical peripheral wall 2b that is formed continuously from the outer periphery of the bottom 2a. The peripheral wall 2b extends approximately perpendicular to the bottom 2a in a vertical cross-sectional view. The outer can 2 is made of a metal material such as stainless steel, nickel, or iron.

The sealing can 3 has a circular flat surface 3a and a cylindrical peripheral wall 3b that is formed continuously from the outer periphery of the flat surface 3a. 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.

The gasket 4 is made of a resin with low moisture permeability, such as polypropylene resin, polyphenylene sulfide resin, or PFA resin. The gasket 4 is formed in a cylindrical shape that conforms to the inner surface of the peripheral wall 2b of the outer can 2 and is positioned between the peripheral wall 2b of the outer can 2 and the peripheral wall 3b of the sealed can 3. The gasket 4 is not particularly limited as long as it can insulate the outer can 2 from the sealed can 3. For example, it can be made of a polyolefin resin such as polypropylene (PP), as well as resins such as polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), or a fluororesin such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA). In particular, in addition to PP, fluororesins such as polyphenylene sulfide resin or PFA resin are preferably used due to their moisture permeability and heat resistance.

After the laminated electrode assembly 10 and non-aqueous electrolyte (not shown) are housed in the outer can 2 and the sealing can 3, they are crimped together with a gasket 4 between the peripheral wall 2b of the outer can 2 and the peripheral wall 3b of the sealing can 3. That is, the openings of the outer can 2 and the sealing can 3 are aligned to face each other, the peripheral wall 3b of the sealing can 3 is inserted inside the peripheral wall 2b of the outer can 2, and then the peripheral wall 2b and the peripheral wall 3b are crimped together with a gasket 13 between them. In this way, an internal space for the flat battery 1 is formed to house the laminated electrode assembly 10.

The laminated electrode assembly 10 is an electrode assembly in which multiple positive electrodes (electrodes) 20 and negative electrodes 30 are alternately stacked. The positive electrodes 20 are housed in pouch-shaped separators 40. The number of stacked positive electrodes 20 and negative electrodes 30 is determined by the desired battery capacity. Therefore, the number of stacked electrodes is not limited to that shown in the figure. Of the multiple 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 sealed can 3 each have a negative electrode active material layer 32 provided on only one surface of the negative electrode current collector 31. The negative electrode 30 closest to the inner surface of the flat portion 3a of the sealed can 3 has its negative electrode current collector 31 in contact with the flat portion 3a. 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, which is closest to the inner surface of the bottom 2a of the outer can 2, from the bottom 2a of the outer can 2.

The flat battery 1 also contains a positive electrode lead 20a and a negative electrode lead 30a within its internal space. The positive electrode lead 20a extends continuously from the peripheral edge of the positive electrode current collector 21 of each positive electrode 20 (see FIG. 2, which will be described later). Each positive electrode lead 20a electrically connects the corresponding positive electrode 20 to the bottom 2a of the outer can 2. The negative electrode lead 30a extends continuously from the peripheral edge of the negative electrode current collector 31 of each negative electrode 30 (see FIG. 2, which will be described later). Each negative electrode lead 30a connects the corresponding negative electrode 30 to 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.

As shown in FIG. 2, each positive electrode 20 has a positive electrode current collector 21 and positive electrode active material layers 22 disposed on both sides of the positive electrode current collector 21. The positive electrode current collector 21 is, for example, a metal foil such as aluminum foil. The positive electrode active material layer 22 is, for example, a compression-molded layer of a positive electrode active material such as lithium cobalt oxide, a binder, a conductive additive, etc.

Each negative electrode 30 has a negative electrode current collector 31 and a negative electrode active material layer 32 disposed on one or both sides 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, a binder, a conductive additive, etc.

The positive electrode current collector 21 is electrically connected to the outer can 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 pouch-shaped separator 40. The positive electrode lead 20a is bent toward the bottom 2a of the outer can 2 at the location where it is covered by the separator 40. The ends of the multiple positive electrode leads 20a closest to the outer can 2 are bundled together and connected to the outer can 2.

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

As shown in FIG. 3 , in a plan view, the positive electrode 20 has a generally rectangular shape, indicated by the dashed-dotted lines in the figure, with the four corners chamfered into an arc shape, and includes arc portions 23a, 23b, 23c, and 23d, as well as linear portions 24a, 24b, 24c, and 24d. Arc portions 23a, 23b, 23c, and 23d are formed along the circumference of a circle having a center C, i.e., along the circumference of the same circle. Linear portion 24a is formed between arc portions 23a and 23b. Linear portion 24b is formed between arc portions 23b and 23c. Linear portion 24c is formed between arc portions 23c and 23d. Linear portion 24d is formed between arc portions 23a and 23d. In other words, each linear portion is formed between adjacent arc portions. The circle with center C is a concentric circle with a smaller diameter than the circle formed by the outer periphery of the flat portion 3a of the circular sealing can 3. In other words, center C is positioned on the cylindrical axis of the cylindrical flat battery 1. This allows the positive electrode 20 to be properly accommodated within the internal space of the flat battery 1. Furthermore, center C is positioned closer to the linear portion 24d (left side in the figure) on which the positive electrode lead 20a is located than the intersection (not shown) of the diagonals of the approximately rectangular shape. In other words, linear portion 24d on which the positive electrode lead 20a is located is longer than the opposing linear portion 24b. This ensures that, when the positive electrode 20 housed in the separator 40 is accommodated within the internal space of the flat battery 1, as shown in Figures 1 and 2, sufficient space is available to accommodate the positive electrode lead 20a.

The approximate rectangle 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 at the straight portion 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 maximizes the area in plan view of the positive electrode 20, which has an approximate rectangular shape with four arc-chamfered corners, while still providing space to accommodate the positive electrode lead 20a and negative electrode lead 30a and the fixing portion 41 of the separator 40 (described below) within the limited internal space of the flat battery 1. As a result, the capacity of the flat battery 1 can be increased.

As shown in FIG. 4, the positive electrode 20 is housed in a pouch-shaped separator 40. As shown in FIG. 2, the separator 40 has a film 40a arranged on one main surface (upper side in the figure) of the positive electrode 20 and a film 40b arranged 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 end of the positive electrode lead 20a connected to the positive electrode 20 on the positive electrode 20 side. The films 40a and 40b are, for example, microporous polyethylene films. The method for housing the positive electrode 20 in the separator 40 is as follows. First, the films 40a and 40b are prepared. The positive electrode 20 is placed between the films 40a and 40b. Finally, a portion of the peripheral edge of the film 40a and the peripheral edge of the film 40b facing the portion of the peripheral edge of the film 40a are fixed together by hot pressing. In this way, the separator 40 is formed into a bag shape and houses the positive electrode 20.

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 a non-fixed portion 42 that is not fixed. In other words, separator 40 has a fixed portion 41 and a non-fixed portion 42 on its peripheral edge. More specifically, fixed portion 41 is formed and positioned radially outward from linear portions 24a, 24b, 24c, and 24d shown in FIG. 3, and non-fixed portion 42 is formed and positioned radially outward from arc portions 23a, 23b, 23c, and 23d. Furthermore, fixed portion 41, located radially outward from linear portion 24d, is formed to follow both side edges of positive electrode lead 20a. The outer peripheral edge of the fixed portion 41, located radially outward from the linear portions 24a and 24c, is formed by an arc that follows the periphery of the flat portion 3a of the sealing can 3 and a straight line that follows the linear portions 24a and 24c. Therefore, the planar shape of the fixed portion 41, located radially outward from the linear portions 24a and 24c, is fan-shaped. In this way, the fixed portion 41 prevents the positive electrode 20 from protruding from the inside of the bag-shaped separator 40. Furthermore, the non-fixed portion 42 allows air remaining inside the bag-shaped separator 40 to be discharged. The method for fixing the peripheral portion of the separator 40 is not limited to welding by hot pressing, and may also be adhesion using an adhesive or the like, and is not particularly limited.

The two-dot chain line in Figure 4 indicates the outer peripheral edge of 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 formed by the outer peripheral edge of 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 within the internal space of the flat battery 1. Furthermore, by providing the straight portions 24b and 24d, a predetermined space is formed between the laminated electrode body 10 shown in Figure 1 and the peripheral wall portion 3b of the sealing can 3. The space facing the straight portion 24b houses the negative electrode lead 30a. The space facing the straight portion 24d houses the positive electrode lead 20a bent toward the bottom 2a of the outer can 2.

The relationship between the ratio of length L1 and length L2 can also be explained from the following perspective. Referring to Figures 3 and 4, shortening the length L3 of the straight portion 24a or 24c formed on the short side α—that is, increasing the length L2 of the long side β relative to the length L1 of the short side α while maintaining a constant radius of the circle containing the arc portions 23a, 23b, 23c, and 23d—increases the area of the positive electrode 20 in a planar view. However, the radial width (vertical width as shown in Figure 4) of the fixing portions 41, 41 located radially outward of the straight portions 24a and 24c decreases, potentially resulting in insufficient fixing of the peripheral edge of the separator 40. As a result, the positive electrode 20 may be exposed outward from the separator 40 due to poor fixing, potentially 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, i.e., 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 maintaining a constant radius of the circle including the arc portions 23a, 23b, 23c, and 23d, the area of the positive electrode 20 in a planar view decreases, but the radial width of the fixing portions 41, 41 located radially outward of the straight portions 24a and 24c increases, allowing the peripheral portion of the separator 40 to be sufficiently fixed. From this perspective, the length L3 of the straight portion 24a or 24c formed on the short side α is preferably 15% or more, preferably 20% or more, and more preferably 25% or more of the length L1 of the short side α. Furthermore, the length L3 of the straight portion 24a or 24c formed on the short side α is preferably 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 1.12 to 1.25 when length L1 is 1. More preferably, the ratio should be 1.15 to 1.21 when length L1 is 1.

Furthermore, from the perspective of accommodating the positive electrode lead 20a and the negative electrode lead 30a within the internal space of the flat battery 1, the lengths of the straight portions 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, as long as the positive electrode lead 20a and the negative electrode lead 30a can be accommodated within the internal space of the flat battery 1, it is desirable that the space in which the negative electrode lead 30a and the positive electrode lead 20a are accommodated be as small as possible. Therefore, it is preferable that the lengths of the straight portions 24b and 24d formed on the long side β be as short as possible relative to the length L2 of the long side β.

As described above, the positive electrode (electrode) 20 according to the present disclosure has a generally rectangular shape with arc-shaped chamfered corners in plan view, 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 edge of the film 40a and the peripheral edge of the film 40b can be sufficiently fixed together. This prevents the positive electrode 20 from protruding from the inside of the pouch-shaped separator 40, while accommodating a positive electrode 20 with a maximized area in plan view, thereby increasing the battery capacity of the flat battery 1. Furthermore, by accommodating a laminated electrode body 10 including this positive electrode (electrode) 20 in a flat battery 1, the battery capacity of the flat battery 1 can be increased. The positive electrode 20 is housed in a pouch-shaped separator 40 having a fixing portion 41. Therefore, the stacked electrode body 10 and flat battery 1 can prevent the positive electrode 20 from protruding from the inside of the pouch-shaped separator 40.

In the above embodiment, the positive electrode 20 is housed in the separator 40, but the negative electrode (electrode) 30 may also be housed in the separator 40.

(Example)
The positive electrode 20 (Example) of the above-described embodiment and a positive electrode 120 (Comparative Example) housed in a bag-shaped separator 140 of the prior art that can be housed in the same internal space as the flat battery 1 of the above-described embodiment were prepared, and the difference in area between the positive electrode 20 and the positive electrode 120 was confirmed by overlapping them as shown in FIG. 5 .

As shown in FIG. 6, the positive electrode 120 of the comparative example differs from the positive electrode 20 in that both short sides of the approximately rectangular shape are entirely cut out in an arc shape. The pouch-shaped separator 140 has a fixing portion 141 along the periphery of the positive electrode 120 and along the side of the positive electrode lead 120a on the positive electrode 120 side. Similar to the separator 40 of the embodiment, the separator 140 is formed in a pouch shape with the fixing portion 141 fixing its periphery. The separator 140 also has a non-fixed portion 142 in part of the arc shape. In this way, the separator 140 of the comparative example has a fixing portion 141 with a predetermined width formed around the periphery of the positive electrode 120. Therefore, the radius of the arc-shaped cutout portion of the positive electrode 120 is smaller than that of the positive electrode 20 of the example. If the shape of the positive electrode 120 in plan view were simply made larger and similar, the area of the positive electrode 120 could be increased, but the radial width of the fixing portion 141 would be reduced accordingly, which could result in the problem of not being able to sufficiently fix the peripheral edge of the separator 140.

As shown in Figure 5, the positive electrode 20 and the positive electrode 120 were overlapped. The positive electrode 20 is shown by a solid line, and the positive electrode 120 is shown by a dashed line. As shown in Figure 5, even if we take into account that the positive electrode 20, unlike the positive electrode 120, has a straight line portion 24a, it was found that the radius of the arc portion can be made larger and the area in a planar view can be made larger than that of the positive electrode 120.

Furthermore, a comparison was made between a positive electrode according to the present disclosure, which is formed so that the short side L1 shown in FIG. 3 has a length of 4.195 mm, the long side L2 has a length of 4.95 mm, and the radius of the arc portion is 2.575 mm, and a positive electrode of a conventional structure, such as the above-described positive electrode 120, in which the entire short side is arc-shaped and the radius of the arc portion is changed to 2.5 mm so that the peripheral portion of the separator located radially outward can be fixed. The area of the positive electrode active material layer in a plan view of the positive electrode of the conventional structure was 17.96 ^mm² , while the area of the positive electrode active material layer of the positive electrode according to the present disclosure was 18.76 ^mm² . The positive electrode of the present disclosure was able to increase the area by 4.5% compared to the conventional structure, thereby achieving a corresponding increase in battery capacity.

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

1: Flat battery, 2: Outer can, 3: Sealing can, 4: Gasket, 10: Laminated electrode assembly, 20: Positive electrode, 21: Positive electrode current collector, 22: Positive electrode active material layer, 23a-23d: Arc portions, 24a-24d: Straight portions, 20a: Positive electrode lead, 30: Negative electrode, 31: Negative electrode current collector, 32: Negative electrode active material layer, 40: Arc portion, 30: Negative electrode, 40: Separator, 41: Bonded portion, 42: Non-bonded portion, 50: Insulating sheet, α: Short side, β: Long side

Claims (4)

An electrode housed in a pouch-shaped separator,
One of a positive electrode and a negative electrode accommodated in an internal space of the flat battery that is circular in plan view;
a bag-shaped separator that houses the electrodes;
the electrode has a substantially rectangular shape in plan view, with four corners chamfered in an arc shape, and includes arc portions at the four corners that are chamfered in an arc shape, and linear portions located between each of the arc portions at the four corners;
Each of the four corner arc portions is formed along the circumference of a circle having the same center,
the separator has a first film disposed on one main surface of the electrode and a second film disposed on the other main surface of the electrode,
An electrode housed in a bag-shaped separator , wherein the peripheral edge of the first film has a fixing portion fixed to the peripheral edge of the second film radially outward of each straight portion of the electrode . An electrode housed in the pouch-shaped separator according to claim 1,
The electrode is housed in a pouch-shaped separator, wherein the ratio of the length of the short side to the length of the long side of the approximately rectangular shape is 1.12 to 1.25 when the length of the short side is 1. A laminated electrode body, comprising a plurality of electrodes, each of which is a positive electrode or a negative electrode housed in the pouch-shaped separator according to claim 1 , and a plurality of electrodes, each of which is a positive electrode or a negative electrode housed in the pouch-shaped separator according to claim 1, stacked alternately. A flat battery comprising the laminated electrode assembly according to claim 3 housed in the internal space of a case.