JP2013218824A - Square secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a square secondary battery in which cycle characteristics can be improved by reducing flexure of an electrode group with a simple structure.SOLUTION: A square secondary battery 1 has an electrode group 20 in which electrode plates 40, 30 are wound around a flat shaft core 10. The shaft core 10 has a substrate 11 composed of a synthetic resin material, and a stiffening member 80 composed of a material having a rigidity higher than that of the substrate 11, and extending in the winding width direction orthogonal, respectively, to the winding axis direction and the flat thickness direction of the electrode group 20 along the substrate 11.

Description

  The present invention relates to a prismatic secondary battery used for in-vehicle applications, for example.

  In recent years, lithium ion secondary batteries with high energy density have been developed as power sources for electric vehicles and the like. It is known that in a lithium ion secondary battery, when an active material layer of an electrode plate expands due to charging and deflection occurs in an electrode group in which the electrode plate is wound, deterioration of cycle characteristics occurs. As a countermeasure, a technique for loosening the winding state of the electrode plate when winding the electrode plate to form a flat electrode group is disclosed (Patent Document 1).

JP 2006-164956

  The technique disclosed in Patent Document 1 is complicated in operation, and it is difficult to stably provide a gap between the electrode plates. When the electrode group has a flat shaft core made of synthetic resin, the active material layer of the electrode plate expands due to charging, and when heated and heated to a high temperature, the shaft core deforms and increases the deflection of the electrode group. There was a risk of causing it.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a prismatic secondary battery that reduces deflection of an electrode group and improves cycle characteristics with a simple structure. is there.

  The prismatic secondary battery of the present invention that solves the above problems is a prismatic secondary battery having an electrode group in which an electrode plate is wound around a flat shaft core, and the shaft core includes a substrate made of a synthetic resin material. A stiffening member made of a material having higher rigidity than the base body and extending along the base body and extending in the winding width direction perpendicular to the winding axis direction and the flat thickness direction of the shaft core, respectively. It is a feature.

  According to the prismatic secondary battery of the present invention, the rigidity in the winding width direction of the shaft core can be improved by the stiffening member. Therefore, the deformation of the shaft core can be suppressed, the deflection of the electrode group can be reduced, and the cycle characteristics can be improved. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is an external perspective view of a prismatic secondary battery according to a first embodiment. The disassembled perspective view of the square secondary battery concerning 1st Embodiment. The perspective view which shows the electrode group of the square secondary battery concerning 1st Embodiment. The top view which shows the axial center of the square secondary battery concerning 1st Embodiment. The figure which expands and shows the principal part of the axial center of the square secondary battery concerning 1st Embodiment in a cross section. Sectional drawing of the electrode group of the square secondary battery concerning 1st Embodiment. The top view which shows the axial center of the square secondary battery concerning 2nd Embodiment. The perspective view which expands and shows the principal part of the electrode group concerning 2nd Embodiment. The top view which shows the axial center of the square secondary battery concerning 3rd Embodiment.

[First Embodiment]
Hereinafter, the present embodiment will be described in detail with reference to the drawings by taking a case of a square lithium ion secondary battery as an example.

  FIG. 1 is an external perspective view of a prismatic secondary battery according to the present embodiment, and FIG. 2 is an exploded perspective view of the prismatic secondary battery according to the present embodiment.

  The prismatic secondary battery 1 is a prismatic lithium ion secondary battery, and has a configuration in which an electrode group 20 that is a power generation element is accommodated in a battery container 78. The battery container 78 sealed with the battery lid 75 is referred to as a battery outer container. In this battery exterior container, a pair of wide side surfaces PW, a pair of narrow side surfaces PN, a bottom surface PB, and a battery lid 75 constitute a rectangular parallelepiped flat rectangular container.

  The battery cover 75 is provided with a gas discharge valve 77. When the pressure in the battery container rises, the gas discharge valve 77 is opened to discharge gas from the inside, and the pressure in the battery container is reduced. The battery lid 75 is provided with a liquid injection port 76 for injecting an electrolytic solution into the battery container 78. The liquid injection port 76 is sealed by a liquid injection plug 79 after the electrolytic solution is injected. The liquid injection plug 79 is welded to the battery lid 75. The electrolyte is, for example, 1 mol / L of lithium hexafluorophosphate in a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1. Use the dissolved one.

  The battery lid 75 is provided with an external terminal 73 on the positive electrode side and an external terminal 71 on the negative electrode side. A positive connection plate 74 is connected to the positive external terminal 73, and a negative connection plate 72 is connected to the negative external terminal 71. The electrode group 20 is connected to the positive-side connection plate 74 and the negative-side connection plate 72 to form a subassembly of the battery lid 75. The subassembly of the battery lid 75 is covered with an insulating sheet 90 and inserted into the battery container 78.

  The battery container 78 and the battery lid 75 are both made of an aluminum alloy. The positive side connecting plate 74 and the external terminal 73 are made of an aluminum alloy, and the negative side connecting plate 72 and the external terminal 71 are made of a copper alloy. Electric power is supplied to the external load via the external terminals 73 and 71, or external generated power is charged to the electrode group 20 via the external terminals 73 and 71.

FIG. 3 is a perspective view showing an electrode group of the prismatic secondary battery according to the present embodiment.
The electrode group 20 is configured by winding a negative electrode plate 30 and a positive electrode plate 40, which are electrode plates, around an axial core 10 having a flat plate shape, and has a flat shape with a cross section of an ellipse. . The electrode group 20 is wound in a flat shape in the order of the negative electrode plate 30, the separator 60, the positive electrode plate 40, and the separator 60 after winding the separator 60 around the shaft core 10. The electrode plate that is the outermost periphery of the electrode group 20 is the negative electrode plate 30, and the separator 60 is wound around the outer side thereof. The separator 60 is interposed between the positive electrode plate 40 and the negative electrode plate 30 and has a role of insulating between the two.

  The positive electrode plate 40 has a positive electrode mixture layer 41 on both surfaces of the positive electrode metal foil. The negative electrode plate 30 has a negative electrode mixture layer 31 on both surfaces of the negative electrode metal foil. The negative electrode mixture layer 31 is set to be larger in the winding axis direction than the positive electrode mixture layer 41, and the positive electrode mixture layer 41 and the negative electrode mixture layer 31 are overlapped with each other with the separator 60 interposed therebetween. In this state, the positive electrode mixture layer 41 is always sandwiched between the negative electrode mixture layers 31 and is configured to fall within the range of the negative electrode mixture layer 31 in the winding axis direction.

  The positive electrode plate 40 and the negative electrode plate 30 are arranged such that a positive electrode current collector 42 where the positive electrode metal foil is exposed and a negative electrode current collector 32 where the negative electrode metal foil is exposed are spaced apart on one side and the other side in the winding axis direction. It is wound so that. The positive electrode current collector 42 and the negative electrode current collector 32 are bundled at the planar portion of the electrode group 20 and connected to the connection plates 74 and 72 by welding or the like. In the present embodiment, the positive electrode current collector 42 is bundled in two in the thickness direction (Z direction) of the electrode group 20 at the flat portion at one end in the winding axis direction of the electrode group 20 ( For example, see FIG. 8), and joined to a pair of connecting plates 74 divided into two on the positive electrode side by ultrasonic welding. Similarly, the negative electrode current collector 32 is bundled in two in the thickness direction (Z direction) of the electrode group 20 at the plane part on the other side in the winding axis direction of the electrode group 20. Are joined to each of the pair of connecting plates 72 by ultrasonic welding. Although the separator 60 is wider than the negative electrode mixture layer 31 in the width direction, the separator 60 is wound at a position where the metal foil surface is exposed at the positive electrode current collector 42 and the negative electrode current collector 32. It will not be a hindrance.

In order to obtain the positive electrode plate 40, 10 parts by weight of flaky graphite as a conductive material and 10 parts by weight of polyvinylidene fluoride as a binder with respect to 100 parts by weight of lithium manganate (chemical formula LiMn ₂ O ₄ ) as a positive electrode active material. (Hereinafter referred to as PVDF) was added, and N-methylpyrrolidone (hereinafter referred to as NMP) was added as a dispersion solvent thereto and kneaded to prepare a positive electrode mixture. This positive electrode mixture was applied to both surfaces of an aluminum foil (positive metal foil) having a thickness of 20 μm, leaving a positive electrode current collector portion 42 as a plain positive electrode metal foil exposed portion, whereby a positive electrode mixture layer 41 was formed. Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode plate 40 having a thickness of 90 μm in the thickness of a positive electrode active material application portion that does not include an aluminum foil.

  In order to obtain the negative electrode plate 30, 10 parts by weight of PVDF as a binder is added to 100 parts by weight of amorphous carbon powder as a negative electrode active material, and NMP is added and kneaded as a dispersion solvent thereto. An agent was prepared. This negative electrode mixture was applied to both surfaces of a 10 μm-thick copper foil (negative electrode metal foil) leaving the negative electrode current collector portion 32 as the negative electrode metal foil exposed portion, thereby forming a negative electrode mixture layer 31. Thereafter, drying, pressing, and cutting were performed to obtain a negative electrode plate 30 having a negative electrode active material coating portion thickness of 70 μm that does not include a copper foil.

  In this embodiment, amorphous carbon is exemplified as the negative electrode active material. However, the present invention is not limited to this. Natural graphite capable of inserting and removing lithium ions, various artificial graphite materials, and coke are not limited thereto. A carbonaceous material or the like may be used, and the particle shape is not particularly limited to a scale shape, a spherical shape, a fiber shape, a lump shape, or the like. Further, in the present embodiment, an example in which PVDF is used as the binder is shown, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, Polymers such as nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof can be used.

FIG. 4 is a plan view showing the axis of the prismatic secondary battery according to the present embodiment.
The shaft core 10 has a flat plate shape corresponding to the flat shape of the electrode group 20. The shaft core 10 has a substantially rectangular shape in plan view, and its one end and the other end in the winding axis direction become narrower in the winding width direction as it moves outward in the winding axis direction. It is formed in a taper shape.

  A pair of shaft convex portions 10a projecting along the winding axis direction are provided at one end and the other end of the winding axis 10 of the shaft core 10 apart from each other in the winding width direction. Yes. When the positive electrode plate 40 or the like is wound around the shaft core 10, the shaft core convex portion 10a serves as a holding portion that is attached to a winding machine (not shown).

  On the outer periphery of the rectangular portion of the shaft core 10, a portion corresponding to the positive electrode mixture layer 41 of the positive electrode plate 40 and a portion corresponding to the negative electrode mixture layer 31 of the negative electrode plate 30 are wound. A portion corresponding to the positive electrode current collector 42 of the positive electrode plate 40 is wound on the outer periphery of the taper portion on the one side in the axial direction and the shaft core convex portion 10a, and the taper portion and the shaft core convex portion on the other side in the winding axis direction are wound. A portion corresponding to the negative electrode current collector 32 of the negative electrode plate 30 is wound around the outer periphery of 10a.

  The shaft core 10 is composed of a base body 11 made of a synthetic resin material such as polypropylene resin and a stiffening member 80 made of a material higher in rigidity than the base body 11 such as metal. The stiffening member 80 is made of, for example, a metal material such as aluminum or an aluminum alloy and copper / copper alloy or nickel / nickel alloy.

  The base body 11 has a basic shape for constituting the shaft core 10, and the stiffening member 80 is wound along the base body 11 in the winding axis direction (X direction) and the flat thickness direction (Z Extending in the winding width direction (Y direction) orthogonal to each direction.

  The stiffening member (first stiffening member) 80 is interposed at an intermediate position between one end of the base 11 in the winding axis direction and the other end, and one end of the base 11 in the winding width direction. And the other end. In the present embodiment, the base 11 is bisected in the winding axis direction by being interposed at the center position of the base 11 in the winding axis direction, and the base members 11A and 11B on one side and the other side in the winding axis direction are mutually connected. It is joined and integrated.

  FIG. 5 is an enlarged cross-sectional view of the main part of the shaft core of the prismatic secondary battery according to the present embodiment, and is a cross-sectional view taken along line AA in FIG. In FIG. 5, the cross section of the joint portion between the base members 11A and 11B and the stiffening member 80 is shown from one side in the winding width direction.

  As for the stiffening member 80, the fitting recessed part is formed in the joining end surface of the winding axial direction both sides, respectively. The base member 11 </ b> A, 11 </ b> B is formed with a fitting convex portion on a joint end face with the stiffening member 80. Then, the fitting convex portion of the base member 11A is fitted into one fitting concave portion of the stiffening member 80, and the fitting convex portion of the base member 11B is fitted into the other fitting concave portion of the stiffening member 80. Thus, the base members 11A and 11B are joined together to form the shaft core 10. The method of joining the base members 11A and 11B and the stiffening member 80 is not limited to the above, and various changes can be made. For example, the stiffening member 80 may be provided with a fitting protrusion, and the base member 11A, 11B may be provided with a fitting recess, or another known joining method may be employed.

  Next, the mechanism by which the shaft core is deformed by the expansion of the negative electrode mixture layer will be described with reference to FIG.

  In the electrode group 20, when the negative electrode mixture layer 31 expands due to charging, the planar portion of the electrode group 20 expands in the direction of arrow A, which is the wound thickness direction. Since the positive electrode plate 40 and the negative electrode plate 30 are made of a metal foil at the center, there is little deformation in the extending direction, and even if the flat portion of the electrode group 20 swells, the length of the outer periphery of the electrode group 20 hardly changes. . Therefore, the electrode group 20 is compressed in the arrow B direction which is the winding width direction.

  For example, when the shaft core is composed only of a synthetic resin, the shaft core may be deformed by a force compressing in the winding width direction, and is likely to be deformed particularly at high temperatures. When the shaft core is deformed, the parallelism between the positive electrode plate 40 and the negative electrode plate 30 of the electrode group 20 is disturbed, so that a so-called deflection state occurs, and a gap is generated between the electrode plates, leading to performance deterioration such as an increase in resistance.

  On the other hand, according to the present embodiment, the stiffening member 80 made of a material having higher rigidity than the base body 11 is provided so as to extend in the winding width direction along the base body 11. The rigidity in the winding width direction can be improved, and the rigidity can be prevented from decreasing even at high temperatures. Therefore, the force compressing in the winding width direction can be resisted, the deformation of the shaft core 10 can be suppressed, the deflection of the electrode group 20 can be reduced, and the battery performance deterioration due to the deflection can be prevented. And since it becomes possible to prevent the deformation | transformation of the shaft core 10 by high temperature and to control the expansion | swelling shape of the electrode group 20, the cycling characteristics at the time of high temperature can be improved.

  In the present embodiment, the case where the stiffening member 80 is provided at the center position in the winding axis direction of the base body 11 has been described as an example, but between the one end portion and the other end portion in the winding axis direction. As long as it is provided at an intermediate position, and may be provided at a position displaced in the winding axis direction from the center position. In the present embodiment, the case where the base 11 is divided into two in the winding axis direction and joined and integrated by the stiffening member 80 has been described as an example. However, the base 11 is not necessarily configured to be divided. For example, it is good also as a structure which formed the ditch | groove along the winding width direction in the plane part of the base | substrate 11, and fitted the stiffening member 80 in this ditch | groove.

[Second Embodiment]
Next, a second embodiment will be described.
FIG. 7 is a plan view showing the axis of the prismatic secondary battery according to the present embodiment, and FIG. 8 is an enlarged perspective view showing the main part of the electrode group according to the second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  What is characteristic in the present embodiment is that, in addition to the configuration of the first embodiment, a stiffening member (second stiffening member) 81 is provided at one end and the other end of the base 11 in the winding axis direction. It is to have established.

  The stiffening member 81 is inserted between a pair of axial protrusions 10a spaced apart in the winding width direction (Y direction), and attached in a state where both ends are in contact with the axial protrusions 10a. The stiffening member 81 is made of the same metal material as that of the stiffening member 80 made of a material having higher rigidity than that of the base 11, and has a substantially triangular prism shape as shown in FIG.

  The electrode group 20 has a substantially triangular prism-shaped space formed by bundling a positive electrode current collector 42 and a negative electrode current collector 32 at one end and the other end in the winding axis direction. In addition, the stiffening member 81 is accommodated. The stiffening member 81 is formed with groove-like engaging recesses 81a at both ends, and is inserted between the pair of shaft protrusions 10a so as to engage with each of the shaft protrusions 10a. ing.

  According to the present embodiment, the stiffening member 81 is provided so as to extend in the winding width direction at one end and the other end in the winding axis direction of the base body 11. The rigidity in the winding width direction can be further improved as compared with the first embodiment, and the rigidity can be prevented from decreasing even at high temperatures.

[Third Embodiment]
Next, a third embodiment will be described.
FIG. 9 is a plan view showing the axis of the prismatic secondary battery according to the present embodiment. The same components as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  What is characteristic in the present embodiment is that a plurality of stiffening members 80 are provided in the configuration of the second embodiment. A plurality of stiffening members 80 are provided at predetermined intervals in the winding axis direction. In the present embodiment, the plurality of stiffening members 80 are provided at a central position in the winding axis direction of the base body 11 and at positions separated by a predetermined distance on both sides in the winding axis direction, and there are a total of three. Yes. The base body 11 includes four base body members 11A to 11D that are divided into four in the winding axis direction by three stiffening members 80, and are joined and integrated with each other by the stiffening member 80.

  According to the present embodiment, since the plurality of stiffening members 80 are provided at predetermined intervals in the winding axis direction, the rigidity in the winding width direction of the shaft core 10 is set to the first and second embodiments. The rigidity can be further improved, and the rigidity can be prevented from decreasing even at high temperatures.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Square secondary battery 10 Shaft core 10a Shaft core convex part 11 Base | substrate 11A, 11B Base member 20 Electrode group 30 Negative electrode plate 31 Negative electrode mixture layer 32 Negative electrode current collection part 40 Positive electrode plate 41 Positive electrode mixture layer 42 Positive electrode current collection part 60 Separator 71 Negative electrode external terminal 72 Negative electrode connection plate 73 Positive electrode external terminal 74 Positive electrode connection plate 75 Lid 76 Pouring port 77 Safety valve 78 Battery container 79 Pouring plug 80 Stiffening member (first stiffening member)
81 Stiffening member (second stiffening member)
81a Engaging recess

Claims (7)

A prismatic secondary battery having an electrode group in which an electrode plate is wound around a flat shaft core,
The shaft core is
A substrate made of a synthetic resin material;
A stiffening member made of a material having higher rigidity than the base, and extending in the winding width direction perpendicular to the winding axis direction and the flat thickness direction of the shaft core along the base;
A prismatic secondary battery comprising:   The stiffening member is interposed at an intermediate position between one end and the other end of the base in the winding axis direction, and extends between the one end and the other end of the base in the winding width direction. 2. The prismatic secondary battery according to claim 1, further comprising a first stiffening member extending.   3. The square two according to claim 1, wherein the stiffening member has a pair of second stiffening members respectively provided at one end and the other end in the winding axis direction of the base body. Next battery. The electrode group has a configuration in which both ends of the electrode plate in the winding axis direction are divided into two in the flat thickness direction and bundled,
4. The prismatic secondary battery according to claim 3, wherein the pair of second stiffening members are detachably engaged with one end and the other end of the base in the winding axis direction, respectively. . The base body has a pair of axial protrusions that protrude in the winding axis direction from the winding axis direction one end and the other end, respectively, apart from each other in the winding width direction.
The second stiffening member includes a pair of engaging recesses that engage with each of the shaft core protrusions by being inserted between a pair of shaft core protrusions protruding apart from each other in the winding width direction. The prismatic secondary battery according to claim 3, wherein the prismatic secondary battery is provided.   The prismatic secondary battery according to claim 2, wherein a plurality of the first stiffening members are provided at predetermined intervals in the winding axis direction.   The prismatic secondary battery according to claim 1, wherein the stiffening member is made of a metal material.

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