Cylindrical secondary battery

Abstract

The present invention is characterized by being provided with an electrode body (11) in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, at least one electrode tab (15) connected to the electrode body (11), a terminal plate (30) disposed on the upper side of the electrode body (11) and in contact with the electrode tab (15), and a bottomed cylindrical outer can (20) for accommodating the electrode body (11), and by being further provided with a pressing part (40) for pressing the electrode tab (15) onto the terminal plate (30).

Description

Cylindrical secondary battery

[0001] The present disclosure relates to a cylindrical secondary battery.

[0002] A cylindrical battery generally includes a wound electrode body, a bottomed cylindrical outer can that houses the electrode body, and a sealing body that closes the opening of the outer can. Patent Document 1 discloses a cylindrical battery having a current collector plate to which an electrode tab extending from an electrode constituting the electrode body is welded inside the outer can.

[0003] International Publication No. 2023 / 281973

[0004] When joining an electrode tab to a current collector plate by welding as in Patent Document 1, a poor joint of the electrode tab may occur due to a welding defect or the like. In particular, in a cylindrical secondary battery having a plurality of electrode tabs, the above problem becomes more prominent. From the viewpoint of ensuring the reliability and productivity of the cylindrical secondary battery, it is necessary to suppress a poor joint of the electrode tab.

[0005] A cylindrical secondary battery according to one aspect of the present disclosure includes an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, at least one or more electrode tabs connected to the electrode body, a terminal plate disposed above the electrode body and in contact with the electrode tab, and a bottomed cylindrical outer can that houses the electrode body, and further includes a biasing portion that biases the electrode tab against the terminal plate.

[0006] According to the cylindrical secondary battery according to one aspect of the present disclosure, a poor joint of the electrode tab can be suppressed. As a result, a cylindrical secondary battery excellent in reliability and productivity can be provided.

[0007] It is an axial cross-sectional view of a cylindrical secondary battery which is an example of an embodiment. It is an enlarged view of part A in FIG. 1.

[0008] A cylindrical secondary battery 10 which is an example of an embodiment will be described while referring to FIG. 1. FIG. 1 is an axial cross-sectional view of the cylindrical secondary battery 10.

[0009] As shown in Figure 1, the cylindrical secondary battery 10 comprises an electrode body 11, a non-aqueous electrolyte (not shown), and an outer casing 20 that houses the electrode body 11 and the non-aqueous electrolyte. The outer casing 20 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening 24 of the outer casing 20 is sealed by a sealing body 12. Hereafter, the side of the cylindrical secondary battery 10 with the sealing body 12 in the axial direction (up and down direction) will be referred to as "up," and the side of the outer casing 20 with the bottom 21 in the axial direction will be referred to as "down."

[0010] The electrode body 11 has a positive electrode, a negative electrode, and a separator (none of which are shown), and has a structure in which the positive electrode and the negative electrode are wound in a spiral shape with the separator in between. The positive electrode, the negative electrode, and the separator are all elongated strips, and are alternately stacked in the radial direction of the electrode body 11 by being wound in a spiral shape. The negative electrode is formed to be slightly larger than the positive electrode in order to prevent lithium deposition. That is, the negative electrode is formed to be longer than the positive electrode in both the longitudinal and width directions (short direction). The separator is formed to be at least slightly larger than the positive electrode, and two separators are arranged so as to sandwich the positive electrode. The cylindrical secondary battery 10 also includes insulating plates 13 and 14 arranged above and below the electrode body 11, respectively.

[0011] The positive electrode comprises a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core can be made of a metal foil that is stable in the positive electrode potential range, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core, excluding the exposed portion of the positive electrode core to which the positive electrode tab 15 is welded. The positive electrode can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to form the positive electrode mixture layer on both sides of the positive electrode core.

[0012] The positive electrode composite layer contains particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal elements constituting the lithium metal composite oxide are, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0013] Examples of conductive agents included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0014] The negative electrode comprises a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be made of a metal foil that is stable in the negative electrode potential range, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion of the negative electrode core to which the negative electrode tab 16 is welded. The negative electrode can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core, drying the coating, and then compressing it to form the negative electrode mixture layer on both sides of the negative electrode core.

[0015] The negative electrode composite layer generally contains a carbon material that reversibly intercepts and releases lithium ions as the negative electrode active material. Suitable examples of carbon materials include natural graphite such as flake graphite, lumpy graphite, and clay graphite, as well as artificial graphite such as lumpy artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). In addition, a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element may be used as the negative electrode active material. Among these, composite materials containing Si are preferred.

[0016] A preferred example of a composite material containing Si is SiO ２ Examples include materials in which Si nanoparticles are dispersed in a phase or a silicate phase such as lithium silicate, or materials in which Si nanoparticles are dispersed in an amorphous carbon phase. A conductive layer, such as a carbon film, is formed on the particle surface of the composite material.

[0017] The binder in the negative electrode mixture layer may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0018] A porous sheet having ion permeability and insulating properties is used as the separator. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include polyethylene, polyolefins such as polypropylene, and cellulose. The separator may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator. A filler layer containing an inorganic filler may be formed at the interface between the separator and at least one of the positive and negative electrodes.

[0019] In the example shown in Figure 1, a positive electrode tab 15 is connected to the positive electrode, and a negative electrode tab 16 is connected to the end of the winding of the negative electrode. The positive electrode tab 15 extends towards the sealing body 12 through a through-hole in the insulating plate 13. The positive electrode tab 15 abuts against the lower surface of the terminal plate 30 that constitutes the sealing body 12, and is electrically connected to the sealing body 12, making the sealing body 12 the positive electrode terminal. Figure 1 illustrates the case where four positive electrode tabs 15 are led out from the positive electrode. Note that there may be only one positive electrode tab 15. The negative electrode tab 16 extends towards the bottom 21 of the outer casing 20 through the outside of the insulating plate 14. The negative electrode tab 16 is connected to the inner surface of the bottom 21 of the metal outer casing 20 by welding or the like, making the outer casing 20 the negative electrode terminal. Note that the current collection method is not limited to the above configuration. For example, the negative electrode and the outer casing 20 may be electrically connected by providing a negative electrode core exposed portion at the lower end of the negative electrode, and connecting the negative electrode core exposed portion to a current collector that electrically connects to the outer casing 20, or by welding to the bottom 21 of the outer casing 20.

[0020] The non-aqueous electrolyte contained in the outer container 20 is lithium ion conductive. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0021] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted compounds (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include lithium salts such as LiPF6.

[0022] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0023] The outer casing 20 is a bottomed cylindrical metal container with an open top. The outer casing 20 has a bottom 21 and side portions 22 that form the sides of the cylindrical secondary battery 10. The side portions 22 are the parts of the outer casing 20 excluding the bottom 21 and include grooved portions 23 and openings 24, which will be described later.

[0024] The grooved portion 23 is a part of the side surface 22 that is recessed radially inward, and is provided in an annular shape along the circumferential direction of the outer can 20. The grooved portion 23 supports the sealing body 12 on its upper surface. The grooved portion 23 can be formed, for example, by spinning a part of the side surface 22 radially inward to create an annular recess toward the radially inward side.

[0025] The opening 24 is the region of the side portion 22 above the grooved portion 23, and forms the opening of the outer can 20. The opening 24 is bent radially inward when the sealing body 12 is crimped and fixed to the outer can 20. As a result, the opening 24 forms an opening side portion 25 that forms part of the side of the cylindrical secondary battery 10 and covers the outer circumferential surface of the gasket 27, and a crimped portion 26 that forms part of the upper surface of the cylindrical secondary battery 10 and extends radially inward.

[0026] As described above, the sealing body 12 is positioned above the electrode body 11 and closes the opening 24 of the outer casing 20. In this embodiment, the sealing body 12 is made of a single terminal plate 30, and the positive electrode tab 15 is in contact with the lower surface of the terminal plate 30. In other words, the terminal plate 30 that the positive electrode tab 15 is in contact with functions as the sealing body 12 and forms the top surface of the cylindrical secondary battery 10. By making the sealing body 12 of a single terminal plate 30, the volume occupied by the sealing body 12 within the battery can be reduced. As a result, the volume of the electrode body 11 can be increased, making it easier to improve the battery capacity. The terminal plate 30 is crimped and fixed to the opening 24 of the outer casing 20 via a gasket 27. Furthermore, as will be described in more detail later, a leaf spring 40 is provided on the lower surface of the terminal plate 30 as a biasing part that biases the positive electrode tab 15 to press against the terminal plate 30.

[0027] The gasket 27 is a flexible insulating member that electrically isolates the sealing body 12, which is the positive terminal, from the outer can 20, which is the negative terminal, while ensuring airtightness inside the outer can 20 when compressed. The material of the gasket 27 is not particularly limited as long as it is a compressible insulating material, and for example, polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyamide (PA), etc. can be used.

[0028] In this embodiment, the gasket 27 has an outer peripheral portion 27A that clamps the terminal plate 30, and a recess 27B provided radially inward of the outer peripheral portion 27A and recessed downward relative to the outer peripheral portion 27A. A through hole 27C is provided in the radial center of the recess 27B, through which the positive electrode tab 15 passes. The size of the through hole 27C can be appropriately set according to the number and shape of the positive electrode tab 15. The diameter of the through hole 27C is, for example, 20% or more and 60% or less of the outer diameter of the gasket 27.

[0029] Next, with further reference to Figure 2, the terminal plate 30 and the leaf spring 40 that constitute the sealing body 12 will be described in detail. Figure 2 is an enlarged view of part A in Figure 1.

[0030] As shown in Figures 1 and 2, the terminal plate 30 is crimped and fixed to the opening 24 of the outer container 20 via a gasket 27, thereby sealing the opening 24 of the outer container 20. The terminal plate 30 is a circular metal member when viewed from above. The constituent material of the terminal plate 30 is not particularly limited as long as it is a material that does not leach out during normal use, but examples of suitable constituent materials include aluminum or an aluminum alloy.

[0031] A protrusion 31 is provided in the center of the terminal board 30, projecting outwards from the battery. The protrusion 31 has a circular shape when viewed from above. The diameter of the protrusion 31 is not particularly limited, but for example, it is 25% or more and 60% or less of the diameter of the terminal board 30. The height of the protrusion 31 is not particularly limited, but for example, it is 0.5 mm or more and 5.0 mm or less. The upper surface of the terminal board 30 may be flat throughout.

[0032] The positive electrode tab 15 is in contact with the area around the protrusion 31 on the lower surface of the terminal plate 30. More specifically, the positive electrode tab 15 extends upward from the electrode body 11 and is bent radially outward. Near the tip of the positive electrode tab 15, it is pressed against the lower surface of the terminal plate 30 by a leaf spring 40, which will be described later.

[0033] In the examples shown in Figures 1 and 2, four positive electrode tabs 15 are led out from the electrode body 11. Each of the four positive electrode tabs 15 is bent radially outward and arranged to be stacked at their respective ends.

[0034] The positive electrode tab 15 is a strip-shaped conductive member, made of a metal, for example, primarily composed of aluminum. The width and thickness of the positive electrode tab 15 vary depending on the size and capacity of the battery, but an example of the width of the positive electrode tab 15 is 2 mm or more and 15 mm or less. An example of the thickness of the positive electrode tab 15 is 0.03 mm or more and 0.15 mm or less. Multiple positive electrode tabs 15 may have different widths and thicknesses, but in this embodiment, all positive electrode tabs 15 have substantially the same width and thickness.

[0035] As shown in Figures 1 and 2, a leaf spring 40 is provided on the lower surface of the terminal plate 30 to bias the positive electrode tabs 15 against the terminal plate 30. The leaf spring 40 is positioned in the space formed by the recess 27B of the gasket 27. The radially outer portion of the leaf spring 40 is joined to the lower surface of the terminal plate 30 by welding or the like. Preferably, the leaf spring 40 is electrically connected to the terminal plate 30. The radially inner portion of the leaf spring 40 presses the four stacked positive electrode tabs 15 against the terminal plate 30.

[0036] The leaf spring 40 has, for example, a substantially rectangular shape when viewed from above. The leaf spring 40 has a width greater than the width of the positive electrode tab 15, and presses the positive electrode tab 15 against the terminal plate 30 across its entire width. The shape of the leaf spring 40 is not limited to the form shown in Figures 1 and 2, as long as it is possible to bias the positive electrode tab 15 to press against the terminal plate 30.

[0037] The constituent material of the leaf spring 40 is not particularly limited as long as it is a material that does not leach out during normal use, but a suitable example of a constituent material is aluminum or an aluminum alloy, similar to the terminal plate 30. Furthermore, when the terminal plate 30 and the leaf spring 40 are joined by welding, it is preferable that the terminal plate 30 and the leaf spring 40 be made of the same material from the viewpoint of ensuring joint strength.

[0038] In this embodiment, the positive electrode tab 15 is not welded to the lower surface of the terminal plate 30, but is pressed against the leaf spring 40, making it immovable relative to the terminal plate 30. As a result, welding defects in the positive electrode tab 15 cannot occur, and therefore, joining defects in the positive electrode tab 15 caused by welding defects do not occur.

[0039] As shown in Figure 2, the radial length (L) from the radial inner end of the contact area where the leaf spring 40 and the positive electrode tab 15 come into contact to the tip of the positive electrode tab 15 is preferably 2 mm or more, and more preferably 2.5 mm or more. By setting this length (L) to 2 mm or more, the positive electrode tab 15 is stably fixed and less likely to come off the terminal plate 30.

[0040] As described above, the cylindrical secondary battery 10 of this embodiment includes a terminal plate 30 positioned above the electrode body 11 and in contact with the positive electrode tab 15, and a leaf spring 40 as a biasing part that biases the positive electrode tab 15 to press against the terminal plate 30. This makes it difficult for the positive electrode tab 15 to come off the terminal plate 30, and prevents poor bonding of the positive electrode tab 15. Furthermore, since the positive electrode tab 15 can be fixed to the terminal plate 30 without welding the positive electrode tab 15 to the terminal plate 30, it is possible to prevent poor bonding of the positive electrode tab 15 caused by welding defects.

[0041] The above embodiments can be modified without altering the purpose of this disclosure. For example, in the above embodiments, the positive electrode tab 15 is not welded to the lower surface of the terminal plate 30, but it may be welded to the lower surface of the terminal plate 30. Even in this case, the positive electrode tab 15 is pressed against the terminal plate 30 by the leaf spring 40, making it difficult for the positive electrode tab 15 to come off the terminal plate 30.

[0042] Furthermore, in the above embodiment, a case in which a leaf spring 40 is used as the biasing part that biases the positive electrode tab 15 to press against the terminal plate 30 was described, but it is not limited to a leaf spring 40 as long as it is possible to bias the positive electrode tab 15 to press against the terminal plate 30. For example, a spring other than the leaf spring 40, such as a coil spring, may be used as the biasing part, either in place of or in addition to the leaf spring 40. However, from the viewpoint of making it difficult for the positive electrode tab 15 to come off the terminal plate 30, it is preferable to use a leaf spring 40 as the biasing part.

[0043] Furthermore, although the above embodiment described a case in which the cylindrical secondary battery 10 has one leaf spring 40, the number of leaf springs 40 can be appropriately changed depending on the number and arrangement of the positive electrode tabs 15. In other words, the cylindrical secondary battery 10 may have multiple leaf springs 40. When the cylindrical secondary battery 10 has multiple leaf springs 40, the multiple leaf springs 40 may be arranged, for example, at approximately equal angular intervals when viewed from above the cylindrical secondary battery 10.

[0044] Also, in the above-described embodiment, the sealing body 12 is constituted by a single terminal plate 30, and the terminal plate 30 forms the top surface (upper surface) of the cylindrical secondary battery 10. However, the configuration of the sealing body 12 is not limited to this. For example, the sealing body 12 may further have a circular member on the upper side of the terminal plate 30, and the circular member may form the top surface of the cylindrical secondary battery 10. That is, a member with which the positive electrode tab 15 is not in contact may form the top surface of the cylindrical secondary battery 10. As described above, by constituting the sealing body 12 with a single terminal plate 30, the volume occupied by the sealing body 12 inside the battery can be reduced. As a result, the volume of the electrode body 11 can be increased, and it becomes easy to improve the battery capacity.

[0045] Also, in the above-described embodiment, the positive electrode tab 15 is in contact with the terminal plate 30. However, the negative electrode tab 16 may be in contact with the terminal plate 30. In that case, the leaf spring 40 biases the negative electrode tab 16 against the terminal plate 30, and the sealing body 12 functions as a negative electrode terminal. On the other hand, the positive electrode tab 15 extends, for example, through the outside of the insulating plate 14 to the bottom 21 side of the outer can 20 and is connected to the inner surface of the bottom 21 of the outer can 20 by welding or the like. As a result, the outer can 20 becomes the positive electrode terminal.

[0046] This disclosure is further illustrated by the following embodiments: Configuration 1: A cylindrical secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator between them; at least one electrode tab connected to the electrode body; a terminal plate disposed above the electrode body and in contact with the electrode tabs; and a bottomed cylindrical outer casing for housing the electrode body, further comprising a biasing part that biases the electrode tabs to press against the terminal plate. Configuration 2: The cylindrical secondary battery according to Configuration 1, wherein the biasing part includes a leaf spring. Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, wherein the radially outer portion of the biasing part is joined to the terminal plate. Configuration 4: The cylindrical secondary battery according to any one of Configurations 1 to 3, wherein the terminal plate forms the top surface of the cylindrical secondary battery. Configuration 5: The cylindrical secondary battery according to any one of Configurations 1 to 4, wherein the electrode tabs are not welded to the terminal plate. Configuration 6: A cylindrical secondary battery according to any one of Configurations 1 to 5, wherein the radial length from the radial inner end of the contact area where the biasing portion and the electrode body tab come into contact to the tip of the electrode tab is 2 mm or more. Configuration 7: A cylindrical secondary battery according to any one of Configurations 1 to 6, comprising a plurality of biasing portions, wherein the plurality of biasing portions are arranged at approximately equal angular intervals when viewed from above the cylindrical secondary battery.

[0047] 10 Cylindrical secondary battery (battery), 11 Electrode body, 12 Sealing body, 13, 14 Insulating plate, 15 Positive electrode tab (electrode tab), 16 Negative electrode tab, 20 Outer casing, 21 Bottom, 22 Side, 23 Grooved part, 24 Opening, 25 Side of opening, 26 Crimped part, 27 Gasket, 27A Outer circumference, 27B Recess, 27C Through hole, 30 Terminal plate, 31 Protrusion, 40 Leaf spring (biasing part).

Claims

1. A cylindrical secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator between them; at least one electrode tab connected to the electrode body; a terminal plate disposed above the electrode body and in contact with the electrode tab; and a bottomed cylindrical outer casing for housing the electrode body, further comprising a biasing part that biases the electrode tab to press against the terminal plate.

2. The cylindrical secondary battery according to claim 1, wherein the biasing portion includes a leaf spring.

3. The cylindrical secondary battery according to claim 1, wherein the radially outer portion of the biasing portion is joined to the terminal plate.

4. The cylindrical secondary battery according to claim 1, wherein the terminal plate forms the top surface of the cylindrical secondary battery.

5. The cylindrical secondary battery according to claim 1, wherein the electrode tab is not welded to the terminal plate.

6. The cylindrical secondary battery according to claim 1, wherein the radial length from the radial inner end of the contact area where the biasing portion and the electrode tab come into contact to the tip of the electrode tab is 2 mm or more.

7. The cylindrical secondary battery according to claim 1, comprising a plurality of biasing units, wherein the plurality of biasing units are arranged at substantially equal angular intervals when viewed from above the cylindrical secondary battery.

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