Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery (10) comprises an electrode body (14) in which a strip-shaped positive electrode sheet (11) and a strip-shaped negative electrode sheet (12) are wound in a spiral shape along the longitudinal direction of the electrode sheets with a separator (13) interposed therebetween. The positive electrode sheet (11) has a positive electrode core body (11A) and a positive electrode mixture layer (11B) that is formed on the surface of the positive electrode core body (11A). In a longitudinally intermediate portion of the positive electrode sheet (11), a rectangular exposed portion (11C) in which the positive electrode core body (11A) is exposed is formed in a portion that is in contact with only one end out of both ends in the short-side direction of the electrode sheet. The exposed portion (11C) and a portion of the positive electrode mixture layer (11B) that is adjacent to the outer edge portion of the exposed portion (11C) are covered by a tape (30), and the corner portion of the tape (30) on the other end side in the short-side direction of the electrode plate is chamfered.

Description

Nonaqueous electrolyte secondary battery

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

[0002] Known examples of non-aqueous electrolyte secondary batteries include lithium ion batteries. A non-aqueous electrolyte secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween. The positive electrode plate includes a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core.

[0003] For example, in the nonaqueous electrolyte secondary battery disclosed in Patent Document 1, a rectangular exposed portion is formed in a portion of the positive electrode plate that contacts only one of both ends in the short side direction of the plate, where the positive electrode core is exposed, and a positive electrode tab for current collection is joined to the exposed portion, and the exposed portion is covered with tape.

[0004] Japanese Patent Application Laid-Open No. 2004-311282

[0005] In the nonaqueous electrolyte secondary battery of Patent Document 1, tape is applied to the exposed portion and the positive electrode mixture layer surrounding the exposed portion. During charging and discharging of the battery, the portion of the positive electrode mixture layer where the tape is applied is subjected to tensile stress from the tape as the positive electrode plate expands or contracts. In particular, tensile stress is concentrated in the portion of the positive electrode mixture layer where the corner of the tape is applied, which may cause peeling or cracking of the positive electrode mixture layer. This may result in a deterioration in the battery characteristics of the nonaqueous electrolyte secondary battery.

[0006] Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte secondary battery that can prevent tensile stress from being locally concentrated on the mixture layer due to the tape as the electrode plate expands or contracts.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure is a nonaqueous electrolyte secondary battery including an electrode assembly in which a strip-shaped first electrode plate and a strip-shaped second electrode plate are spirally wound with a separator interposed between them along the longitudinal direction of the electrode plates, the first electrode plate having a first core and a first mixture layer formed on the surface of the first core, a rectangular first core exposed portion where the first core is exposed is formed in a portion of the middle part of the first electrode plate in the longitudinal direction of the electrode plate that contacts only one of both ends in the transverse direction of the electrode plate, the first core exposed portion and a portion of the first mixture layer adjacent to the outer edge of the first core exposed portion are covered with tape, and the corner of the tape on the other side in the transverse direction of the electrode plate is chamfered.

[0008] According to the nonaqueous electrolyte secondary battery of the present disclosure, it is possible to prevent the tensile stress from being locally concentrated by the tape due to the expansion or contraction of the electrode plate.

[0009] 1 is a cross-sectional view taken along the axial direction of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; 2 is a schematic development view of a positive electrode plate to which a tape is attached according to an embodiment of the present invention; 3 is a schematic development view of a positive electrode plate to which a tape is attached according to another embodiment of the present invention;

[0010] An example of an embodiment of the present disclosure will be described in detail below. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present disclosure, and can be appropriately changed according to the application, purpose, specifications, etc.

[0011] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery 10 as an example of an embodiment will be described with reference to FIG.

[0012] The nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), an outer can 15, and a sealing body 16. The wound electrode assembly 14 includes a strip-shaped positive electrode plate 11 as a first electrode plate, a strip-shaped negative electrode plate 12 as a second electrode plate, and a strip-shaped separator 13, with the positive electrode plate 11 and the negative electrode plate 12 being spirally wound with the separator 13 interposed therebetween. The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel polymer or the like.

[0013] In the following, each component may be described using the axial direction (arrow α in FIG. 1) and the radial direction (arrow β in FIG. 1). One axial side of the electrode body 14 may be referred to as the "upper" side, and the other axial side may be referred to as the "lower" side.

[0014] The positive electrode plate 11 serving as the first electrode plate has a strip-shaped positive electrode core 11A and a positive electrode tab 19 joined to the positive electrode core 11A (see FIG. 2 ). The positive electrode tab 19 is a conductive member for electrically connecting the positive electrode core 11A and a positive electrode terminal, and extends from the upper end of the positive electrode core 11A of the electrode body 14 to one axial side (upward). The positive electrode tab 19 is provided, for example, in approximately the center of the electrode body 14 in the radial direction. The positive electrode tab 19 is a strip-shaped conductive member. The material of the positive electrode tab 19 is not particularly limited. The positive electrode tab 19 is preferably made of a metal containing aluminum as a main component. Furthermore, the positive electrode plate 11 has a positive electrode mixture layer 11B formed on each of the inner winding surface (inner radial surface) and the outer winding surface (outer radial surface) of the positive electrode core 11A (see FIG. 2 ).

[0015] The negative electrode plate 12 serving as the second electrode plate has a strip-shaped negative electrode core and a negative electrode tab 20 joined to the negative electrode core. The negative electrode tab 20 is a conductive member for electrically connecting the negative electrode core and an outer can 15 (described later) and extends from the lower end of the negative electrode core of the electrode body 14 to the other axial side (downward). The outer can 15 serves as a negative electrode terminal. The negative electrode tab 20 is provided, for example, on the inner winding portion (inner peripheral portion) of the electrode body 14. The negative electrode tab 20 is a strip-shaped conductive member. The material of the negative electrode tab 20 is not particularly limited. The negative electrode tab 20 is preferably made of a metal primarily containing nickel or copper, or a metal containing both nickel and copper. Furthermore, the negative electrode plate 12 has a negative electrode mixture layer formed on each of the inner winding surface (radially inner surface) and the outer winding surface (radially outer surface) of the negative electrode core.

[0016] Furthermore, the negative electrode core is exposed on the outermost surface of the electrode body 14 and is in contact with the inner surface of the cylindrical portion 15A of the outer can 15, and is electrically connected to the outer can 15. This electrical connection between the negative electrode plate 12 and the cylindrical portion 15A of the outer can 15 ensures even better current collection.

[0017] As described above, the electrode body 14 has a wound structure in which the positive electrode plate 11 and the negative electrode plate 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode plate 11, the negative electrode plate 12, and the separator 13 are all formed in a strip shape, and are wound spirally so as to be alternately stacked in the radial direction of the electrode body 14.

[0018] 1 , an outer can 15 and a sealing body 16 form a metal battery case that houses an electrode assembly 14 and a non-aqueous electrolyte. Insulating plates 17 and 18 are provided above and below the electrode assembly 14. A positive electrode tab 19 passes through a through-hole in the upper insulating plate 17, extends toward the sealing body 16, and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the non-aqueous electrolyte secondary battery 10, a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal.

[0019] The outer can 15 is a bottomed, cylindrical, metallic container having an opening. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure airtightness within the outer can 15. The outer can 15 has a grooved portion 21 formed, for example, by spinning the side surface from the outside to the inside in the radial direction. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its upper surface. The sealing body 16 seals the opening of the outer can 15.

[0020] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 breaks, and the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 breaks, and gas is released from the opening 26A of the cap 26.

[0021] [Positive Electrode Plate] A positive electrode plate 11 to which a tape 30 is attached as an example of an embodiment will be described with reference to FIG. 2 .

[0022] The positive electrode plate 11 has a strip-shaped positive electrode core 11A and a positive electrode mixture layer 11B formed on both surfaces of the positive electrode core 11A. Hereinafter, the positive electrode plate 11 may be described using the electrode plate longitudinal direction (arrow γ in the figure) and the electrode plate lateral direction (arrow δ in the figure). In this case, the electrode plate longitudinal direction (arrow γ in the figure) is the winding direction of the positive electrode plate 11, and the electrode plate lateral direction (arrow δ in the figure) is the axial direction.

[0023] The positive electrode substrate 11A may be, for example, a foil of a metal such as aluminum, or a film having such a metal disposed on its surface. A suitable positive electrode substrate 11A is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode substrate 11A is, for example, 10 μm to 30 μm.

[0024] The positive electrode mixture layer 11B preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode plate 11 is produced by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, the binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode substrate 11A, followed by drying and rolling.

[0025] Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal oxides are not particularly limited, but include those represented by the general formula Li １ + ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0026] Examples of the conductive agent include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder include fluorine-based resins 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 carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0027] An exposed portion 11C is formed as a rectangular positive electrode core exposed portion where the positive electrode core 11A is exposed in a portion that contacts only one of both ends of the positive electrode plate 11 in the short-side direction of the electrode plate. The exposed portion 11C is a portion to which the positive electrode tab 19 is joined, and is a portion where the surface of the positive electrode core 11A is not covered by the positive electrode mixture layer 11B. The exposed portions 11C are preferably formed on both sides of the positive electrode core 11A so as to overlap each other in the thickness direction. The length of the exposed portion 11C in the short-side direction of the electrode plate is preferably 5 to 50% of the length of the positive electrode plate 11 in the short-side direction of the electrode plate.

[0028] [Tape] The exposed portion 11C is covered with tape 30. The tape 30 is attached to the positive electrode mixture layer 11B around the exposed portion 11C so that the tape 30 covers the entire exposed portion 11C. In other words, the portion of the positive electrode mixture layer 11B adjacent to the outer edge of the exposed portion 11C is covered by the tape 30 along with the exposed portion 11C. When the tape 30 is attached to the exposed portion 11C to which the positive electrode tab 19 is joined, the tape 30 covers part of the positive electrode tab 19. The tape 30 protects the exposed portion 11C and prevents a short circuit of the negative electrode plate 12 facing the exposed portion 11C.

[0029] The tape 30 is an adhesive tape having a base layer and an adhesive layer formed on one surface of the base layer. A heat-resistant layer containing inorganic particles such as metal oxide may be provided between the base layer and the adhesive layer. The base layer may be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate).

[0030] The adhesive layer is provided to attach the tape 30 to the surface of the positive electrode plate 11. The adhesive layer may contain at least one of a rubber-based polymer and an acrylic-based polymer. The adhesive layer may further contain, for example, a silicone-based polymer.

[0031] The tape 30 is formed in a substantially rectangular shape. The corners of the tape 30 on the other end side in the electrode plate short-side direction are chamfered to form inclined portions 30A. Here, chamfering means removing the vertices of right-angled corners of the rectangular tape, and means, for example, forming the corners in a straight line oblique to the electrode plate short-side direction or in a curved line convex toward the outside of the tape 30. Note that even if the corners of the tape 30 are chamfered, the tape 30 still covers the positive electrode mixture layer 11B adjacent to the outer edge of the exposed portion 11C.

[0032] At the other end of the tape 30 in the electrode plate short-side direction, the tape 30 is chamfered so that at least a right-angled corner is not formed. As a result, even when the portion of the positive electrode mixture layer 11B to which the tape 30 is attached is pulled due to expansion or contraction of the positive electrode plate 11, tensile stress does not locally concentrate at the corner of the portion of the positive electrode mixture layer 11B to which the tape 30 is attached, and peeling or cracking of the positive electrode mixture layer 11B can be prevented. Note that the inclination angle of the inclined portion 30A with respect to the electrode plate short-side direction is approximately 45° in this embodiment. However, the inclination angle of the inclined portion 30A in the present disclosure is not particularly limited.

[0033] Another embodiment of the tape 40 will be described with reference to Fig. 3. In the following description of the tape 40, only the configurations that differ from the above-described tape 30 will be described, and the description of the configurations that are the same as those of the tape 30 will be omitted.

[0034] The tape 40 is formed in a substantially rectangular shape. The corners of the other end of the tape 40 in the electrode plate short-side direction are chamfered to form a curved portion 40A. Even if the corners of the tape 40 are chamfered, the positive electrode mixture layer 11B adjacent to the outer edge of the exposed portion 11C is covered by the tape 30. The other end of the tape 40 in the electrode plate short-side direction is chamfered in a curved shape, so that no right-angled corners are formed. As a result, even if the portion of the positive electrode mixture layer 11B to which the tape 40 is attached is pulled due to expansion and contraction of the positive electrode plate 11, there is no location where tensile stress concentrates on the outer periphery of the portion of the positive electrode mixture layer 11B to which the tape 40 is attached, and peeling or cracking of the positive electrode mixture layer 11B can be prevented.

[0035] It should be noted that the present disclosure is not limited to the above-described embodiment and its variations, and various modifications and improvements are possible within the scope of the claims of the present application. For example, a rectangular negative electrode core exposed portion in which the negative electrode core is exposed may be formed in a portion of the negative electrode plate that contacts only one end in the short side direction of the plate, tape may be attached to the negative electrode core exposed portion, and the corner of the tape on the other side in the short side direction of the plate may be chamfered.

[0036] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode plate (first electrode plate), 11A positive electrode core (first electrode core), 11B positive electrode mixture layer (first electrode mixture layer), 11C exposed portion (first electrode core exposed portion), 12 negative electrode plate (second electrode plate), 13 separator, 14 electrode body, 15 outer can, 15A cylindrical portion, 16 sealing body, 17 insulating plate, 18 insulating plate, 19 positive electrode tab, 20 negative electrode tab, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26A opening, 27 gasket, 30 tape, 30A inclined portion, 40 tape, 40A curved portion

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a band-shaped first electrode plate and a band-shaped second electrode plate are spirally wound along the longitudinal direction of the electrodes with a separator interposed therebetween, wherein the first electrode plate has a first core and a first mixture layer formed on the surface of the first core, a rectangular first core exposed portion where the first core is exposed is formed in a portion of the intermediate portion of the first electrode plate in the longitudinal direction of the electrodes that contacts only one of both ends in the transverse direction of the electrodes, the first core exposed portion and a portion of the first mixture layer adjacent to the outer edge of the first core exposed portion are covered with tape, and a corner of the tape on the other end side in the transverse direction of the electrodes is chamfered.

2. A non-aqueous electrolyte secondary battery as defined in claim 1, wherein the corners of the tape are chamfered in an outwardly convex curve.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the first electrode plate is a positive electrode plate.