Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) includes: an electrode body (14) in which a first electrode (11) having first electrode mixture layers formed on both surfaces of a band-shaped first electrode core body and a second electrode (12) having second electrode mixture layers formed on both surfaces of a band-shaped second electrode core body are wound with a separator (13) interposed therebetween; and a cylindrical outer can (15) that accommodates the electrode body (14). A core member (50) extending in a winding axis direction (α) is disposed on the inner side of the innermost periphery of the electrode body (14). In the electrode body (14), in a state before the core member (50) is disposed, an internal surface pressure difference is generated between both end portions in the winding axis direction (α). The core member (50) has a structure asymmetric in the winding axis direction (α) so as to reduce the internal surface pressure difference between both end portions of the electrode body (14) in the winding axis direction (α).

Description

Non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventionally, a non-aqueous electrolyte secondary battery including an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an exterior can containing the electrode body and an electrolyte has been known. In recent years, higher input / output of secondary batteries used in electric vehicles and the like has been demanded. For this purpose, in a non-aqueous electrolyte secondary battery, as in the configuration described in Patent Document 1, four current collecting leads (current collecting tabs) are joined to four core body exposed surfaces (uncoated portions of the positive electrode) where the mixture of the positive electrode is peeled off, and it is considered to improve battery characteristics.

[0003] Japanese Patent Application Laid-Open No. 2000-243376

[0004] By the way, in the negative electrode of the electrode body of a non-aqueous electrolyte secondary battery, the portion facing the uncoated portion of the positive electrode does not expand during charge and discharge. Therefore, in the electrode body, at the portion where the uncoated portion of the positive electrode and the winding axis direction corresponding to the positive electrode width direction coincide, the internal surface pressure becomes small, and an internal gap is likely to occur. An increase in the internal gap of the electrode body causes Li to precipitate on the negative electrode, which is not desirable.

[0005] On the other hand, in the configuration described in Patent Document 1, on the side opposite to the uncoated portion of the positive electrode in the winding axis direction of the electrode body, the internal surface pressure is higher than that on the uncoated portion side of the positive electrode. As a result, an internal surface pressure difference occurs between both ends in the winding axis direction of the electrode body. In this case, as the number of charge / discharge cycles of the secondary battery increases, the internal surface pressure difference becomes larger. In order to reduce this internal gap, it is conceivable to dispose a core member inside the innermost circumference of the electrode body. In this case, however, the tightening force on the side opposite to the uncoated portion of the positive electrode in the winding axis direction of the electrode body may become excessive. Therefore, deformation that causes a voltage drop may occur in the inner peripheral side portion of the electrode body. In addition, as the electrode body expands due to charge and discharge of the secondary battery and the internal surface pressure difference becomes even larger, the above-mentioned disadvantages are more likely to occur.

[0006] The above describes a case where an uncoated portion of the positive electrode is provided only in a part of the winding axis direction, resulting in an internal surface pressure difference between the two ends of the electrode body in the winding axis direction. However, in the unfolded state of the negative electrode, an uncoated portion of the negative electrode is provided over the entire longitudinal direction of one end in the width direction of the negative electrode, where the negative electrode mixture layer is not formed on the surface of the negative electrode core body. In this case as well, an internal surface pressure difference is generated between the two ends of the electrode body in the winding axis direction, which may cause the same problems as described above.

[0007] The purpose of this disclosure is to suppress the occurrence of internal gaps in the electrode body and to suppress deformation that causes a voltage drop in the inner circumference portion of the electrode body in a non-aqueous electrolyte secondary battery.

[0008] The non-aqueous electrolyte secondary battery according to this disclosure comprises an electrode body in which a first electrode having a first electrode mixture layer formed on both sides of a strip-shaped first electrode core and a second electrode having a second electrode mixture layer formed on both sides of a strip-shaped second electrode core are wound together with a separator in between, and a cylindrical outer container housing the electrode body, wherein a core member extending in the winding axis direction is arranged inside the innermost circumference of the electrode body, and an internal surface pressure difference occurs between the two ends of the electrode body in the winding axis direction before the core member is placed, and the core member has an asymmetrical structure in the winding axis direction to reduce the internal surface pressure difference between the two ends of the electrode body in the winding axis direction.

[0009] In the non-aqueous electrolyte secondary battery according to this disclosure, an internal surface pressure difference is generated between the two ends in the winding axis direction of the electrode body before the core member is placed therein, and the core member is placed inside the innermost circumference of the electrode body. The core member has an asymmetric shape in the winding axis direction to reduce the internal surface pressure difference between the two ends in the winding axis direction of the electrode body. This suppresses the generation of internal gaps in the electrode body and suppresses deformation that causes a voltage drop in the inner circumference portion of the electrode body.

[0010] This is a cross-sectional view along the axial direction of a non-aqueous electrolyte secondary battery of an embodiment. This is a perspective view of the electrode body constituting the non-aqueous electrolyte secondary battery of an embodiment. This is an exploded view of the positive electrode in an embodiment. This is an exploded view of the negative electrode in an embodiment. This is a side view of the core member in an embodiment. This is a perspective view of the core member constituting another embodiment. This is a cross-sectional view of the core member constituting another embodiment. This is a side view of the core member constituting another embodiment. This is a cross-sectional view along the axial direction of a non-aqueous electrolyte secondary battery of another embodiment. This is a perspective view of the electrode body shown in Figure 9. This is an exploded view of the outer winding surface of the negative electrode constituting the electrode body shown in Figure 10. This is a perspective view of the electrode body constituting a non-aqueous electrolyte secondary battery of another embodiment. This is an exploded view of the positive electrode constituting the electrode body shown in Figure 12. This is a cross-sectional view of the core member constituting a non-aqueous electrolyte secondary battery of another embodiment.

[0011] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc., are examples to facilitate understanding of the present invention and can be appropriately modified to suit the specifications of the non-aqueous electrolyte secondary battery. Furthermore, the term "abbreviated" below is used to include, for example, cases where they are exactly the same, as well as cases where they can be considered substantially the same. Moreover, when multiple embodiments and modifications are included below, it is intended from the outset that their characteristic parts may be appropriately combined and used.

[0012] Figure 1 is a cross-sectional view along the axial direction of the non-aqueous electrolyte secondary battery 10 of the embodiment. Figure 2 is a perspective view of the electrode body 14 constituting the non-aqueous electrolyte secondary battery 10. Figure 3 is an exploded view of the positive electrode 11. Figure 4 is an exploded view of the negative electrode 12. Figure 5 is a side view of the core member 50.

[0013] As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), an outer casing 15, and a sealing body 16. The wound electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and as shown in Figure 2, the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The positive electrode 11 corresponds to the first electrode, and the negative electrode 12 corresponds to the second electrode. Hereafter, one side of the electrode body 14 in the winding axis direction α may be referred to as "upper," and the other side in the winding axis direction α may be referred to as "lower." The outer casing 15 is a bottomed cylindrical shape that houses the electrode body 14 and the electrolyte. Hereafter, the non-aqueous electrolyte secondary battery 10 will be referred to as secondary battery 10.

[0014] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The secondary battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0015] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the input characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0016] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0017] As shown in Figures 2 and 3, the positive electrode 11 is electrically connected to a plurality of (four in the illustrated example) elongated plate-shaped positive electrode tabs 20, which serve as the first current collector. Each positive electrode tab 20 is a conductive member for electrically connecting the positive electrode core 30 (Figure 3), which constitutes the positive electrode 11, to the positive electrode terminal, and extends from the upper end of the positive electrode core 30 in one direction (upward) in the winding axis direction α of the electrode body 14.

[0018] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to suppress lithium deposition, and is longer than the positive electrode 11 in both the longitudinal and widthwise (short-side) directions. The two separators 13 are also formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separators 13 protrude upward above the positive electrode 11 and the negative electrode 12, while the negative electrode 12 protrudes downward above the positive electrode 11 and the separators 13.

[0019] As shown in Figure 4, the negative electrode 12 has two uncoated negative electrode portions 41a and 41b, which are exposed core portions of the negative electrode core body 40 where the negative electrode mixture layer 42 is not provided, at one end and the other end of the longitudinal direction X2 in the deployed state. The negative electrode core body 40 corresponds to the second electrode core body. The negative electrode mixture layer 42 corresponds to the second electrode mixture layer. Each uncoated negative electrode portion 41a and 41b is provided so as to extend in the width direction over the entire width direction Y2 of the deployed state of the negative electrode 12. Two elongated plate-shaped negative electrode tabs 21a and 21b are joined to the two uncoated negative electrode portions 41a and 41b, respectively. Each negative electrode tab 21a and 21b corresponds to the second current collector portion. Each negative electrode tab 21a, 21b is a conductive member for electrically connecting the negative electrode core 40 to the bottom of the outer casing 15, which is the negative electrode terminal as the second electrode terminal, and extends from the lower end of the negative electrode core 40 in the other direction (downward) in the winding axis direction α of the electrode body 14.

[0020] Referring to Figure 3, the positive electrode 11 has a strip-shaped positive electrode core 30 and positive electrode mixture layers 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 corresponds to the first electrode core. The positive electrode mixture layers 32 correspond to the first electrode mixture layer. For the positive electrode core 30, for example, a metal foil such as aluminum, or a film with the metal arranged on its surface, can be used. A preferred positive electrode core 30 is a metal foil mainly composed of aluminum or an aluminum alloy. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm.

[0021] The positive electrode mixture layer 32 preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode core 30, followed by drying and rolling.

[0022] Examples of positive electrode active materials include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. While lithium-containing transition metal oxides are not particularly limited, they generally have the formula Li １＋ｘ MO ２ It is preferable that the composite oxide is represented by the formula (wherein -0.2 < x ≤ 0.2, and M includes at least one of Ni, Co, Mn, and Al).

[0023] Examples of the conductive agents mentioned above include acetylene black (AB), carbon black (CB) such as Ketjenblack, and carbon materials such as graphite. Examples of the binders mentioned above include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. These may be used individually or in combination of two or more types.

[0024] As shown in Figure 3, in the unfolded state of the positive electrode 11, at multiple positions in the longitudinal direction X1 (four positions in the example of Figure 3), there are four uncoated positive electrode portions 31, which are core exposed portions where the surface of the metal constituting the positive electrode core 30 is exposed, only at one end in the width direction Y1 on the sealing body 16 side. The width direction Y1 of the positive electrode 11 coincides with the winding axis direction α in the wound state (Figure 1). The uncoated positive electrode portions 31 are the portions to which the positive electrode tab 20 is joined, and are portions on the surface of the positive electrode core 30 where the positive electrode mixture layer has not been formed. Preferably, the uncoated positive electrode portions 31 are formed in positions that overlap when viewed in the thickness direction on both sides of the positive electrode 11, and the positive electrode tab 20 is joined to only one side, but the uncoated positive electrode portions may also be formed on only one side of the positive electrode 11. In Figure 3, the positive electrode mixture layer 32 is shown as a sandy area. The four positive electrode tabs 20 are joined to the four uncoated positive electrode portions 31, for example, by ultrasonic welding. The positive electrode tabs 20 are covered with insulating tape (not shown), thereby preventing short circuits between the positive electrode 11 and the negative electrode 12.

[0025] The constituent material of the positive electrode tab 20 is not particularly limited. Preferably, the positive electrode tab 20 is made of a metal mainly composed of aluminum.

[0026] In Figure 3, the four uncoated positive electrode portions 31 are unevenly arranged along the longitudinal direction X1 of the positive electrode 11, but the multiple uncoated positive electrode portions 31 may be evenly arranged along the longitudinal direction X1.

[0027] Referring to Figure 4, the negative electrode 12 has a strip-shaped negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. In Figure 4, the negative electrode mixture layer 42 is shown as a sandy area. For the negative electrode core 40, for example, a metal foil such as copper, or a film with the metal arranged on the surface layer can be used. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm.

[0028] The negative electrode mixture layer 42 preferably contains a negative electrode active material and a binder. The negative electrode 12 is manufactured by, for example, applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and water to both sides of the negative electrode core, and then drying and rolling it.

[0029] The negative electrode active material is not particularly limited as long as it can reversibly intercept and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and composite oxides containing these can be used. The binder contained in the negative electrode active material layer is, for example, the same resin as in the case of the positive electrode 11. When preparing the negative electrode mixture slurry with an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid or its salts, polyvinyl alcohol, etc. can be used. These may be used individually or in combination of two or more.

[0030] A porous sheet having ion permeability and insulating properties is used for the separator 13 (Figure 2). Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably an olefin resin such as polyethylene or polypropylene. The thickness of the separator 13 is, for example, 10 μm to 50 μm. The separator 13 is becoming thinner as batteries increase in capacity and power output. The separator 13 has a melting point of, for example, 130°C to 180°C.

[0031] As shown in Figure 4, in the unfolded state of the negative electrode 12, both ends in the longitudinal direction X2 have uncoated negative electrode portions 41a and 41b where the negative electrode mixture layer is not formed over the entire width direction Y2. A negative electrode tab 21a, which is long in the width direction of the negative electrode 12, is joined to the uncoated negative electrode portion 41a provided at the winding start end of the negative electrode 12 at the overlapping portion with the negative electrode 12. A negative electrode tab 21b, which is long in the width direction of the negative electrode 12, is joined to the uncoated negative electrode portion 41b provided at the winding end end of the negative electrode 12 at the overlapping portion with the negative electrode 12. The negative electrode tab 21a joined to the starting end of the negative electrode 12 passes through a through hole in the insulating plate 29 located below the electrode body 14, then bends approximately perpendicular to the battery central axis and extends toward the opposite side with respect to the battery central axis. The negative electrode tab 21b, which is joined to the winding end of the negative electrode 12, passes outside the insulating plate 29 and is then bent so as to overlap the negative electrode tab 21a. The overlapping portions of each negative electrode tab 21a and 21b are joined to the inner surface of the bottom of the outer can 15. In this way, each negative electrode tab 21a and 21b is electrically connected to the outer can 15, which serves as the negative electrode terminal.

[0032] In the example shown in Figure 1, the battery case is composed of an outer casing 15 and a sealing body 16. The sealing body 16 is formed by stacking an upper metal terminal cap sealing plate 17 and a lower metal current collector plate 18 having a through hole 18a, with a metal plate 19 sandwiched between them in the vertical direction. The sealing plate 17 is hat-shaped with its center bulging upwards. The outer casing 15 has an annular grooved portion 15b formed by recessing the upper end of the cylindrical portion 15a radially inward along its entire circumference. The sealing body 16 is fitted inward through the opening at the upper end of the cylindrical portion 15a of the outer casing 15 via an insulating gasket 27, and while locked to the upper surface of the grooved portion 15b, the upper end of the cylindrical portion 15a is crimped radially inward. In this way, the sealing body 16 is crimped and fixed to the inside of the opening end of the outer casing 15 via the outer gasket 27.

[0033] An insulating plate 28 is provided on the upper side of the electrode body 14. Multiple positive electrode tabs 20 extend towards the sealing body 16 through through holes in the insulating plate 28, pass through through holes 18a in the current collector plate 18, and are joined between the current collector plate 18 and the metal plate 19. In the secondary battery 10, the sealing plate 17, which is electrically connected to the current collector plate 18 and the metal plate 19, becomes the positive electrode terminal, which is the first electrode terminal. As a result, multiple positive electrode tabs 20 are electrically connected to the sealing plate 17.

[0034] On the other hand, as described above, the negative electrode 12 is electrically connected to the outer casing 15, which is the negative electrode terminal, via two negative electrode tabs 21a and 21b, which are the second current collection section. As shown in Figure 4, the two negative electrode tabs 21a and 21b are connected to the unpainted negative electrode portions 41a and 41b of the negative electrode 12. Unlike the unpainted positive electrode portion 31 to which the positive electrode tab 20 is connected, the unpainted negative electrode portions 41a and 41b extend across the entire width of the negative electrode 12. The negative electrode tabs 21a and 21b are long in the width direction of the negative electrode 12 at the overlapping portion with the unpainted negative electrode portions 41a and 41b. For this reason, the current collection structure that electrically connects the positive electrode 11 and the positive electrode terminal and the current collection structure that electrically connects the negative electrode 12 and the negative electrode terminal are of different types. In this configuration, where the current collection structures of the positive electrode 11 and the negative electrode 12 are of different types, an internal surface pressure difference is likely to occur between the two ends of the electrode body 14 in the winding axial direction.

[0035] Specifically, in a configuration like this example, where the positive electrode 11 has an uncoated positive electrode portion 31 (Figure 3) only at one end in the width direction Y1, the portion of the negative electrode 12 of the electrode body 14 facing the uncoated positive electrode portion 31 does not expand during charging and discharging. Therefore, if no other member is inserted inside the innermost circumference of the electrode body 14, and only a columnar space exists, a gap is generally likely to occur inside the electrode body 14 in the portion where the uncoated positive electrode portion 31 and the positive electrode 11 coincide in the winding axis direction α corresponding to the width direction Y1. In this case, the internal surface pressure in the electrode body 14 tends to be lower on the side of the uncoated positive electrode portion 31 in the winding axis direction α, and higher on the opposite side of the uncoated positive electrode portion 31 in the winding axis direction α. ​​As a result, an internal surface pressure difference occurs between the two ends of the electrode body 14 in the winding axis direction. As described above, a decrease in internal surface pressure and an increase in internal gap in a part of the electrode body 14 is undesirable because it causes Li to precipitate on the negative electrode 12.

[0036] On the other hand, if the clamping force on the electrode body 14 is excessive on the side opposite to the uncoated positive electrode portion 31 in the winding axis direction α, deformation that causes a voltage drop is likely to occur in the inner circumference portion of the electrode body 14. For this reason, it is necessary to prevent the clamping force inside the electrode body 14 from becoming excessive. In this embodiment, in order to prevent such problems, a core member 50 is arranged inside the innermost circumference of the electrode body 14, extending in the winding axis direction α and being asymmetrical in the winding axis direction α. ​​The core member 50 and its arrangement configuration will be described below with reference to Figures 1, 3, and 5.

[0037] Figure 5 is a side view of the core member 50. The core member 50 has a cylindrical large-diameter section 51 provided at the upper end, which is on the side of the uncoated positive electrode, and a cylindrical small-diameter section 52 connected to the large-diameter section 51 via an annular plate-shaped connecting section 53, extending in the winding axis direction α. ​​The large-diameter section 51 and the small-diameter section 52 share the same central axis. The outer diameter of the large-diameter section 51 is larger than the outer diameter of the small-diameter section 52.

[0038] On the other hand, in the electrode body 14, before the core member 50 is placed, the above-described internal surface pressure difference occurs between the two ends in the winding axis direction α. ​​Specifically, in the electrode body 14, before the core member 50 is placed, the internal surface pressure is lower at the upper end, which is one side in the winding axis direction α, than at the lower end, which is the other side. The core member 50 is placed inside the innermost circumference of the electrode body 14 such that the outer diameter of the large-diameter cylindrical portion 51 facing the upper end of the electrode body 14 is larger than the outer diameter of the small-diameter cylindrical portion 52 facing the lower end of the electrode body 14.

[0039] Furthermore, the large-diameter cylindrical portion 51 faces the inner circumferential surface of the portion of the electrode body 14 where the uncoated positive electrode portion 31 exists, in the winding axis direction α, while the small-diameter cylindrical portion 52 faces the inner circumferential surface of the electrode body 14 below the portion facing the large-diameter cylindrical portion 51. The large-diameter cylindrical portion 51 does not face the inner circumferential surface of the portion of the electrode body 14 where the uncoated positive electrode portion 31 does not exist, in the winding axis direction α. ​​The outer circumferential surface of the large-diameter cylindrical portion 51 is either in contact with the innermost circumferential surface of the separator 13 that constitutes the innermost circumference of the electrode body 14, or faces it with a small gap in between.

[0040] For example, when the electrode body 14 is wound, the core member 50 is inserted into the center of the electrode body 14, thereby being positioned inside the innermost circumference of the electrode body 14. For example, the entire assembly may be integrally formed from the same resin material. The core member 50 can also be formed from a metal such as iron.

[0041] Furthermore, the radial thickness of the large-diameter cylindrical portion 51 and the small-diameter cylindrical portion 52 of the core member 50 is the same. Therefore, with respect to the bending stiffness in any direction perpendicular to the winding axis direction α of the core member 50, the bending stiffness of the large-diameter cylindrical portion 51 facing the upper end of the electrode body 14 is higher than the bending stiffness of the small-diameter cylindrical portion 52 facing the lower end of the electrode body 14. In this case, "bending stiffness" is expressed as (Young's modulus of the core member 50) × (second moment of area of ​​the cross section of the core member 50 perpendicular to the axial direction). As a result, the core member 50 has an asymmetric structure in the winding axis direction α so as to reduce the difference in internal surface pressure between the two ends of the electrode body 14 in the winding axis direction α.

[0042] The axial length L1 (Fig. 5) of the large-diameter cylindrical portion 51 of the core member 50 is preferably the same as or slightly smaller than the length La (Fig. 3) of the uncoated positive electrode portion 31 in the winding axial direction α. The large-diameter cylindrical portion 51 of the core member 50 is not opposed to the portion of the positive electrode 11 where the positive electrode mixture layer 32 is formed below the uncoated positive electrode portion 31. This makes it easier to make the internal surface pressure difference of the electrode body 14 smaller. The overall axial length of the core member 50 is preferably substantially the same as or greater than the winding axial length of the opposed portions of the positive electrode 11 and the negative electrode 12 via the separator 13 in the electrode body 14.

[0043] According to the secondary battery 10 described above, before the core member 50 is disposed in the electrode body 14, an internal surface pressure difference occurs between both ends in the winding axial direction α, and the core member 50 is disposed inside the innermost circumference of the electrode body 14. The core member 50 has a structure asymmetric in the winding axial direction α so as to reduce the internal surface pressure difference between both ends in the winding axial direction α of the electrode body 14. Thereby, the generation of the internal gap of the electrode body 14 can be suppressed, and the deformation that causes the voltage drop in the inner peripheral side portion of the electrode body 14 can be suppressed. Specifically, since the large-diameter cylindrical portion 51 and the small-diameter cylindrical portion 52 of the core member 50 face the upper end portion with a high surface pressure and the lower end portion with a low surface pressure of the electrode body 14, respectively, the internal surface pressure difference of the electrode body 14 before charge and discharge of the secondary battery 10 can be reduced. Also, even when the electrode body 14 expands due to charge and discharge of the secondary battery 10, the internal surface pressure difference of the electrode body 14 can be reduced. Thereby, generation of an internal gap due to a decrease in the surface pressure of the electrode body 14 can be suppressed both before and after charge and discharge, and deformation that causes a voltage drop in the inner peripheral side portion of the electrode body 14 due to an excessive surface pressure can be suppressed.

[0044] Further, in this example, with respect to the bending rigidity in an arbitrary direction orthogonal to the winding axis direction α of the core member 50, the bending rigidity of the portion facing the upper end portion of the electrode body 14 is higher than the bending rigidity of the portion facing the lower end portion. Thereby, when the electrode body 14 expands due to charge and discharge of the secondary battery 10, it is possible to suppress an increase in the surface pressure difference of the electrode body 14. Further, in the core member 50, since the outer diameter of the portion facing the upper end portion of the electrode body 14 is larger than the outer diameter of the portion facing the lower end portion, it is possible to more effectively suppress an increase in the surface pressure difference of the electrode body 14.

[0045] Note that a through hole may be formed in the central portion of the upper insulating plate 28 of the electrode body 14, and the core member may be disposed inside the electrode body 14 in a state where the upper end portion of the large-diameter cylindrical portion of the core member is press-fitted and fixed to the through hole.

[0046] FIG. 6 is a perspective view of a core member 50a constituting another example of the embodiment. The core member 50a in the configuration of this example is cylindrical with the same outer diameter from the upper end to the lower end. Further, a substantially rectangular notch 70 extending along the axial direction upward from the lower end is formed in a part of the circumferential direction of the core member 50a. The upper end of the notch 70 reaches a position near the lower side of the lower end edge of the first portion 72 which is the cylindrical portion of the core member 50a. Thereby, the second portion 73 continuous with the lower side of the first portion 72 of the core member 50a has the notch 70 in a part of the circumferential direction. Further, the radial thickness of the entire core member 50a is the same.

[0047] The first portion 72 faces the inner peripheral surface of the portion where the positive electrode non-coated portion 31 (FIG. 3) of the electrode body 14 (see FIG. 1) exists in the winding axis direction α, and the second portion 73 faces the inner peripheral surface of the lower portion of the electrode body 14 than the portion facing the first portion 72. The first portion 72 does not face the inner peripheral surface of the portion where the positive electrode non-coated portion 31 of the electrode body 14 does not exist in the winding axis direction α. Thereby, with respect to the bending rigidity in an arbitrary direction orthogonal to the winding axis direction α of the core member 50a, the bending rigidity of the first portion 72 facing the upper end portion of the electrode body 14 is higher than the bending rigidity of the second portion 73 facing the lower end portion of the electrode body fourteen.

[0048] The axial length L1a of the first portion 72 of the core member 50a is preferably the same as or slightly smaller than the length La (see Figure 3) of the uncoated positive electrode portion 31 in the winding axis direction α. ​​The first portion 72 of the core member 50a is not positioned opposite the portion of the positive electrode 11 (see Figure 3) where the positive electrode mixture layer 32 (see Figure 3) is formed below the uncoated positive electrode portion 31.

[0049] The configuration in this example also suppresses the occurrence of internal gaps in the electrode body 14 and suppresses deformation that causes voltage drop in the inner circumference portion of the electrode body 14. In this example, the other configurations and operations are the same as those in Figures 1 to 5.

[0050] Figure 7 is a cross-sectional view of a core member 50b that constitutes another embodiment. In this embodiment, the core member 50b is cylindrical in shape, with the same outer diameter from the upper end to the lower end. In this embodiment, the inner diameter of the first portion 72a provided at the upper end of the core member 50b is smaller than the inner diameter of the second portion 73a connected to the lower side of the first portion 72a. As a result, the radial thickness of the core member 50a is greater in the first portion 72a than in the second portion 73a.

[0051] The first portion 72a faces the inner circumferential surface of the portion of the electrode body 14 (see Figure 1) where the uncoated positive electrode portion 31 (Figure 3) exists, in the winding axis direction α, and the second portion 73a faces the inner circumferential surface of the electrode body 14 below the portion facing the first portion 72a. The first portion 72a does not face the inner circumferential surface of the portion of the electrode body 14 where the uncoated positive electrode portion 31 does not exist, in the winding axis direction α. ​​As a result, with respect to the bending rigidity of the core member 50b in any direction perpendicular to the winding axis direction α, the bending rigidity of the first portion 72a facing the upper end of the electrode body 14 is higher than the bending rigidity of the second portion 73a facing the lower end of the electrode body 14. In this example, the other configurations and operations are the same as those in Figures 1 to 5, or Figure 6.

[0052] Figure 8 is a side view of a core member 50c that constitutes another embodiment. In this embodiment, the core member 50c is cylindrical, having a first conical portion 75 provided at the upper end and whose outer circumferential surface is a conical surface inclined with respect to the axial direction, and a second cylindrical portion 76 connected to the lower side of the first portion 75. The outer diameter of the first portion 75 decreases from the upper end to the lower end. The outer diameter of the second portion 76 is the same as the outer diameter of the lower end of the first portion 75. The radial thickness of the core member 50c is approximately the same throughout the core member 50c.

[0053] The first portion 75 faces the inner circumferential surface of the portion of the electrode body 14 (see Figure 1) where the uncoated positive electrode portion 31 (Figure 3) exists, in the winding axis direction α, and the second portion 76 faces the inner circumferential surface of the electrode body 14 below the portion facing the first portion 75. The first portion 75 does not face the inner circumferential surface of the portion of the electrode body 14 where the uncoated positive electrode portion 31 does not exist, in the winding axis direction α. ​​As a result, with respect to the bending rigidity of the core member 50c in any direction perpendicular to the winding axis direction α, the bending rigidity of the first portion 75 facing the upper end of the electrode body 14 is higher than the bending rigidity of the second portion 76 facing the lower end of the electrode body 14. Also, in the core member 50c, the outer diameter of the portion facing the upper end of the electrode body 14 is larger than the outer diameter of the portion facing the lower end of the electrode body 14. In this example, the other configurations and operations are the same as those in Figures 1 to 5, or Figure 6.

[0054] Figure 9 is a cross-sectional view along the axial direction of a secondary battery 10a of another embodiment. Figure 10 is a perspective view of the electrode body 14a shown in Figure 9. Figure 11 is an unfolded view of the outer surface of the negative electrode 12a constituting the electrode body 14a.

[0055] In this example, the sealing body 16a of the secondary battery 10a is crimped and fixed to the inside of the opening end of the outer casing 15 via a gasket 27a on the outer circumference. An insulating plate 28 is provided on the upper side of the electrode body 14a. The positive electrode 11a constituting the electrode body 14a has six unpainted positive electrode portions (not shown) only at its upper end, and a positive electrode tab 20 connected to each unpainted positive electrode portion extends towards the sealing body 16a through a through hole in the insulating plate 28, passes through a through hole 60a in the current collector plate 60, and is joined by being sandwiched between the current collector plate 60 and the metal plate 61. In the secondary battery 10a, the sealing plate 17a, which is electrically connected to the current collector plate 60 and the metal plate 61, becomes the positive electrode terminal, which is the first electrode terminal.

[0056] In this example, the current collection structure of the negative electrode 12a includes a current collection plate 62 as a second current collection section, which is located on the lower side of the negative electrode 12a, on one side in the winding axis direction α, and is welded to the bottom of the outer casing 15, which is the second electrode terminal. Furthermore, in the unfolded state, the negative electrode 12a has a first uncoated negative electrode portion 41c at the lower end on one side in the width direction on the current collection plate 62 side, where the negative electrode mixture layer 42 is not formed on the surface of the negative electrode core body 40 over its entire length. Therefore, the lower end of the electrode body 14 in the winding axis direction α is composed of the first uncoated negative electrode portion 41c of the negative electrode 12a.

[0057] The first unpainted portion 41c of the negative electrode is joined to the current collector plate 62. Specifically, the first unpainted portion 41c of the negative electrode 12a is pressed against the upper surface of the current collector plate 62 on the lower side of the electrode body 14 and joined to it while tilted radially inward. As a result, the negative electrode 12a is electrically connected to the outer casing 15, which serves as the negative electrode terminal, via the current collector plate 62.

[0058] Furthermore, the negative electrode 12a extends beyond the winding end of the separator 13 towards the winding end. The winding end end of the outer surface of the negative electrode 12a has a second uncoated negative electrode portion 41d (Figure 11) that extends substantially over the entire width of the negative electrode 12a. The second uncoated negative electrode portion 41d exposed on the outer circumferential surface of the negative electrode 12 contacts the inner circumferential surface of the outer can 15 and is electrically connected.

[0059] In this example, the lower end of the negative electrode 12a is joined to the current collector plate 62 along its entire longitudinal direction in the electrode body 14a. Therefore, the internal surface pressure on the lower side of the electrode body 14a, opposite to the unpainted positive electrode portion 31 in the winding axis direction α, is even greater than that on the upper end, which is on the side of the unpainted positive electrode portion 31, compared to the configurations shown in Figures 1 to 4. For this reason, the difference in internal surface pressure between the two ends in the winding axis direction α tends to be larger before the core member 50, described later, is placed on the electrode body 14a. In this example, similar to the configurations in Figures 1 to 5, the core member 50 is placed on the innermost side of the electrode body 14a, asymmetrically oriented in the winding axis direction α. ​​As a result, in this example, the core member 50 significantly suppresses the occurrence of internal gaps in the electrode body 14a and suppresses deformation that causes voltage drop in the inner circumference portion of the electrode body 14a. In this example, the other configurations and operations are the same as those in Figures 1 to 5.

[0060] In addition, in the configuration of this example, any of the core members 50a, 50b, or 50c shown in Figures 6 to 8 can be used as the core member.

[0061] Figure 12 is a perspective view of the electrode body 14b constituting a secondary battery in another embodiment. Figure 13 is an exploded view of the positive electrode 11b constituting the electrode body 14b.

[0062] In this example, the positive electrode 11b of the electrode body 14b does not have an uncoated positive electrode portion formed only at its upper end. As shown in Figure 13, in the unfolded state, the positive electrode 11b has an uncoated positive electrode portion 31a formed in the middle of its longitudinal direction, extending over its entire width. A long positive electrode tab 20a is joined to the uncoated positive electrode portion 31a at the overlapping portion with the positive electrode portion 31a. The positive electrode tab 20a extends from the upper end of the electrode body 14b and is electrically connected to the sealing plate 17a, which is the positive electrode terminal. Therefore, unlike the above examples, the presence of the uncoated positive electrode portion 31a does not cause a surface pressure difference between the upper and lower ends of the electrode body 14b.

[0063] On the other hand, in this example, similar to the configurations in Figures 9 to 11, the negative electrode 12a has a first uncoated negative electrode portion 41c extending over its entire length at its lower end, and this first uncoated negative electrode portion 41c is joined to the current collector plate 62 joined to the bottom of the outer casing 15. As a result, the surface pressure at the lower end of the electrode body 14b is greater than the surface pressure at the upper end, creating a surface pressure difference between the two ends of the electrode body 14b in the winding axis direction. In this example as well, similar to the configurations in Figures 1 to 5, a core member 50 is arranged on the innermost side of the innermost circumference of the electrode body 14b, asymmetrically positioned in the winding axis direction.

[0064] On the other hand, in this example, no uncoated portion of the positive electrode 11b is formed only at the upper end. For this reason, when the overall axial length of the core member 50 is approximately the same as, or greater than, the winding axial length of the opposing portions of the positive electrode 11 and negative electrode 12 in the electrode body 14b via the separator 13, it is preferable that the winding axial length L1 of the large-diameter cylindrical portion 51 (see Figure 5) of the core member 50 be 1 / 2 or less of the overall axial length of the core member 50. More preferably, the winding axial length L1 of the large-diameter cylindrical portion 51 is 1 / 3 or more and 1 / 2 or less of the overall axial length of the core member 50. This makes it possible to suppress the occurrence of internal gaps in the electrode body 14b, and to suppress deformation that causes a voltage drop in the inner circumference portion of the electrode body 14b, even in this example. In this example, the other configurations and operations are the same as those in Figures 1 to 5.

[0065] Figure 14 is a cross-sectional view of a core member 50d constituting a secondary battery in another embodiment. In this example, the core member 50d is positioned on the innermost side of the innermost circumference of the electrode body 14b (see Figure 12) as a core member in the configuration shown in Figures 12 to 13.

[0066] The core member 50d is a conical cylinder in which the outer surface is a conical surface inclined with respect to the axial direction over the entire length of the winding axis direction α. ​​The outer diameter of the core member 50d decreases from the upper end to the lower end. The radial thickness of the core member 50d is approximately the same throughout the core member 50d. As a result, the bending rigidity of the core member 50d in any direction perpendicular to the winding axis direction α is higher in the portion facing the upper end of the electrode body 14b (see Figure 12) than in the portion facing the lower end of the electrode body 14. Even when using such a core member 50d, the occurrence of internal gaps in the electrode body 14b can be suppressed, and deformation that causes voltage drop in the inner circumference portion of the electrode body 14b can be suppressed, similar to the configurations in Figures 12 to 13.

[0067] Although not shown in the illustration, instead of the core member 50d shown in Figure 14, a core member can also be used in which three or more cylindrical sections with different outer diameters are connected in the winding axis direction via an annular plate-shaped connecting section, such that the outer diameter decreases in a step-like manner from the upper end to the lower end.

[0068] Furthermore, the above examples described the case where the material of the core member is the same throughout. On the other hand, by using different materials for the upper and lower ends of the core member, the bending stiffness in any direction perpendicular to the winding axis α of the core member may be such that the bending stiffness of the portion facing the upper end of the electrode body is higher than the bending stiffness of the portion facing the lower end of the electrode body.

[0069] Furthermore, while the above examples described cases where the internal surface pressure at the upper end of the electrode body is smaller than that at the lower end, a configuration in which the internal surface pressure at the lower end of the electrode body is smaller than that at the upper end is also possible. In this case, the vertical direction of the core member placed inside the innermost circumference of the electrode body is reversed from that in the above examples, according to the difference in the magnitude of the internal surface pressures. For example, in the above examples, the first electrode may be the negative electrode and the second electrode may be the positive electrode. Also, in the configurations shown in Figures 1 to 5, multiple unpainted negative electrode sections may be provided only at the lower end in the width direction of the unfolded negative electrode, a negative electrode tab may be joined to each unpainted negative electrode section, and each negative electrode tab may be joined to the bottom of the outer can. In this case, the positive electrode may have the same configuration as the positive electrode 11b shown in Figure 13. In this case, the internal surface pressure at the lower end of the electrode body is smaller than that at the upper end.

[0070] This disclosure will be further described by the following embodiments. Configuration 1: An electrode body in which a first electrode having a first electrode mixture layer formed on both sides of a strip-shaped first electrode core and a second electrode having a second electrode mixture layer formed on both sides of a strip-shaped second electrode core are wound together with a separator; and a cylindrical outer can housing the electrode body, wherein a core member extending in the winding axis direction is disposed inside the innermost circumference of the electrode body, and an internal surface pressure difference is generated between the two ends of the electrode body in the winding axis direction before the core member is disposed, and the core member has an asymmetric structure in the winding axis direction to reduce the internal surface pressure difference between the two ends of the electrode body in the winding axis direction. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein, before the core member is placed, the internal surface pressure of the electrode body is lower at one end in the winding axis direction than at the other end, and with respect to the bending stiffness of the core member in any direction perpendicular to the winding axis direction, the bending stiffness of the portion facing one end of the electrode body is higher than the bending stiffness of the portion facing the other end of the electrode body. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or Configuration 2, wherein, before the core member is placed, the internal surface pressure of the electrode body is lower at one end in the winding axis direction than at the other end, and in the core member, the outer diameter of the portion facing one end of the electrode body is larger than the outer diameter of the portion facing the other end of the electrode body. Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the first electrode is electrically connected to the first electrode terminal via a first current collector, the second electrode is electrically connected to the second electrode terminal via a second current collector, and the current collection structure that electrically connects the first electrode and the first electrode terminal is of a different type from the current collection structure that electrically connects the second electrode and the second electrode terminal.Configuration 5: The current collection structure of the first electrode comprises a plurality of elongated plate-shaped current collection tabs connected to the first electrode terminal as the first current collection section, and at multiple positions in the longitudinal direction when the first electrode is deployed, there are uncoated portions on the surface of the first electrode core where the first electrode mixture layer is not formed, on only one side in the width direction, and the current collection tabs are joined to each of the plurality of uncoated portions, the non-aqueous electrolyte secondary battery according to Configuration 4. Configuration 6: The current collection structure of the second electrode comprises a current collection plate arranged on one side in the winding axis direction of the second electrode and joined to the second electrode terminal as the second current collection section, and when the second electrode is deployed, there is an uncoated portion on one end in the width direction on the current collection plate side, extending over the entire length, where the surface of the second electrode core where the second electrode mixture layer is not formed, and the uncoated portion is joined to the current collection plate, the non-aqueous electrolyte secondary battery according to Configuration 4 or Configuration 5.

[0071] 10, 10a Non-aqueous electrolyte secondary battery, 11, 11a, 11b Positive electrode, 12, 12a Negative electrode, 13 Separator, 14, 14a, 14b Electrode body, 15 Outer can, 16 Sealing body, 17 Sealing plate, 18 Current collector plate, 19 Metal plate, 20, 20a Positive electrode tab, 21a, 21b Negative electrode tab, 27 Gasket, 28, 29 Insulating plate, 30 Positive electrode core, 31, 31a Uncoated positive electrode portion, 32 Positive electrode mixture layer, 40 Negative electrode core, 41a, 41b Uncoated negative electrode portion, 41c First uncoated negative electrode portion, 41d Second uncoated negative electrode portion, 42 Negative electrode mixture layer, 50, 50a, 50b, 50c, 50d Core member, 51 Large diameter cylindrical section, 52 Small diameter cylindrical section, 53 Connecting section, 60 Current collector plate, 61 Metal plate, 62 Current collector plate, 70 Notch, 72, 72a First section, 73, 73a Second section, 75 First section, 76 Second section.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body in which a first electrode having a first electrode mixture layer formed on both sides of a strip-shaped first electrode core and a second electrode having a second electrode mixture layer formed on both sides of a strip-shaped second electrode core, are wound together with a separator; and a cylindrical outer container for housing the electrode body, wherein a core member extending in the winding axis direction is disposed inside the innermost circumference of the electrode body, and an internal surface pressure difference occurs between the two ends of the electrode body in the winding axis direction before the core member is placed, and the core member has an asymmetrical structure in the winding axis direction to reduce the internal surface pressure difference between the two ends of the electrode body in the winding axis direction.

2. The internal surface pressure of the electrode body is lower at one end in the winding axis direction than at the other end, in the state before the core member is placed, and with respect to the bending stiffness of the core member in any direction perpendicular to the winding axis direction, the bending stiffness of the portion facing one end of the electrode body is higher than the bending stiffness of the portion facing the other end of the electrode body, as described in claim 1.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, before the core member is placed, the internal surface pressure of the electrode body is lower at one end in the winding axis direction than at the other end, and the outer diameter of the portion of the core member facing one end of the electrode body is larger than the outer diameter of the portion facing the other end of the electrode body.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first electrode is electrically connected to the first electrode terminal via a first current collector, the second electrode is electrically connected to the second electrode terminal via a second current collector, and the current collection structure for electrically connecting the first electrode and the first electrode terminal is of a different type from the current collection structure for electrically connecting the second electrode and the second electrode terminal.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the current collection structure of the first electrode comprises a plurality of elongated plate-shaped current collection tabs connected to the terminals of the first electrode as the first current collection section, and at multiple positions in the longitudinal direction of the deployed state of the first electrode, there are uncoated portions on the surface of the first electrode core body on only one side in the width direction where the first electrode mixture layer is not formed, and the current collection tabs are joined to each of the plurality of such uncoated portions.

6. The current collection structure of the second electrode comprises a current collection plate as the second current collection portion, which is arranged on one side of the second electrode in the winding axis direction and joined to the second electrode terminal, and in the unfolded state of the second electrode, one end on the width direction side of the current collection plate has an uncoated portion over the entire length direction on the surface of the second electrode core body in which the second electrode mixture layer is not formed, and the uncoated portion is joined to the current collection plate, the non-aqueous electrolyte secondary battery according to claim 4.

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