JP2005129234A - Secondary battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery which can improve reliability against an impact from the outside with an outer package structure using a laminated film, and to provide its manufacturing method. <P>SOLUTION: In this secondary battery wherein a power generating element is sealed using a three-layer structure laminated film 4 formed by laminating high polymer layers on both surfaces of metal foil 6, the size of the metal foil is set to be smaller than the size of the polymer layer. As a result, since the metal film 6 does not exist at the periphery of the laminated film 4, even when an excess length is cut off after the periphery is sealed by heat welding, the metal foil 6 is not exposed at the end face formed by cutting off the excess length, substantially eliminating failures caused by the contact of the metal foil 6 with terminals, etc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a secondary battery having a structure in which a power generation element is sealed with a laminate film.

  With the development and popularization of portable information devices such as mobile phones, notebook personal computers, and video cameras in recent years, the demand for secondary batteries that are small, lightweight, and have high energy density has greatly increased. Considering higher performance. As such a secondary battery, a lithium ion secondary battery is particularly attracting attention because of its high performance.

  The general structure of a lithium ion secondary battery is that a positive electrode active material layer made of a positive electrode active material powder such as lithium-cobalt composite oxide, a conductive powder, and a binder is formed on the surface of a positive electrode current collector made of aluminum foil. A negative electrode formed by forming a negative electrode active material layer made of a positive electrode, a carbon-based negative electrode active material powder, and a binder on the surface of a negative electrode current collector made of copper foil, with a separator made of a porous film interposed therebetween It is repeatedly impregnated with an electrolytic solution.

  And in order to increase the capacity as a secondary battery, a laminated element in which a plurality of pairs of positive and negative electrodes are laminated, a winding element in which a positive electrode and a negative electrode formed in a strip shape are wound, etc. are used. Since the electrolytic solution is also used, such an element is enclosed in a metal case so that the electrolytic solution does not leak to the outside. Therefore, in order to further reduce the size and weight of a secondary battery represented by a lithium ion secondary battery, it is necessary to replace the electrolyte with a polymer electrolyte or use an exterior material other than a metal case. Become.

  In order to make the exterior material thinner and lighter, it is most convenient to use a polymer film. However, since a polymer film cannot completely prevent permeation of moisture and a low molecular weight organic solvent, a laminate film made of a metal foil such as aluminum and a polymer film is used.

  In a laminated film used for such applications, a polymer film having a relatively high mechanical strength is attached as a protective layer on one surface of a metal foil, and a heat-fusing property is provided on the opposite surface. It generally has a three-layer structure with a plastic polymer film attached thereto.

  2A and 2B are diagrams showing an example of a conventional secondary battery using a laminate film having a three-layer structure as an exterior. FIG. 2A is a perspective view and FIG. 2B is an enlarged view of a cut end surface of the laminate film. FIG. In FIG. 2, 8 is a power generation element, 9 is a positive electrode terminal, 10 is a negative electrode terminal, 11 is a laminate film, 12 is a heat fusion layer, 13 is a metal foil, and 14 is a protective layer.

  In order to form such an exterior structure, the power generation element 8 is sandwiched between the laminate films 11 in a state where the heat fusion layer 12 is opposed to the heat fusion layer 12 from above and below in the figure, and the heat fusion layer 12 is formed on the surface of the power generation element 8. After forming the laminate film 11 so as to be in close contact with each other, the heat fusion layer 12 at the peripheral portion of the power generation element 8 is joined and integrated using a hot press or the like. And the peripheral part of the laminate film 11 is cut | disconnected so that the said integral part of fixed length may be ensured.

  As a problem of such an exterior structure, there is contact between the metal foil 13 constituting the laminate film 11 and a terminal. That is, as shown in FIG. 2 (b), a portion where the metal foil 13 is exposed to the outside is formed on the cut end surface of the laminate film 11, and this causes a defect by coming into contact with a terminal or a protection circuit. .

  As a technique for coping with this, Patent Document 1 discloses a power generation element including a positive electrode and a negative electrode that occlude and release lithium ions, and a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode, and the positive electrode. A positive electrode lead connected to the negative electrode, a negative electrode lead connected to the negative electrode, and a laminate in which the power generation element is housed so that ends of the positive electrode lead and the negative electrode lead extend outward and sealed by heat fusion The laminate film includes an outer layer formed from an insulating resin, and a layer facing the power generation element is formed from a heat-fusible resin, and a metal layer is formed on the heat-fusible resin layer. Is disclosed, and a lithium secondary battery is disclosed in which the metal layer does not exist in a portion of the fused portion that contacts the positive electrode lead and the negative electrode lead.

  That is, by removing the metal foil in the vicinity of the cut end surface of the laminate film at the portion where the positive and negative leads are drawn, short-circuit failure due to contact between the metal foil and the positive and negative leads is suppressed. However, since the portion where the metal foil is removed is limited to the vicinity of the positive and negative electrode leads, the secondary battery is subjected to an external impact, and as a countermeasure when the positive or negative electrode lead is displaced, There is room for improvement.

Japanese Patent No. 3283213

  Accordingly, an object of the present invention is to provide a secondary battery having an exterior structure using a laminate film, which has improved reliability against external impacts and the like, and a manufacturing method thereof.

  This invention is made | formed as a result of examining the structure of the heat-fusion part of the laminate film which can solve the said subject, and the method for implement | achieving it.

  That is, the present invention relates to a secondary battery in which the power generation element is enclosed by a power generation element having a positive electrode, a negative electrode, and an electrolyte, and a laminate film having a metal foil and a polymer layer. The secondary battery is characterized in that the metal foil does not exist.

  Further, the present invention is characterized in that the laminate film has a protective layer made of a polymer on one surface of the metal foil, and a heat fusion layer made of a polymer on the opposite surface, Secondary battery.

  Further, the present invention uses a laminate film having a heat sealing layer made of a polymer, a metal foil and a protective layer made of a polymer, as a power generation element in which a positive electrode terminal and a negative electrode terminal are drawn out in a plate shape, The heat-sealing layer is sandwiched between the heat-generating layers, and the laminate film is formed so that the heat-sealing layer is in close contact with the surface of the power-generating element, and the heat-sealing layer at the peripheral edge of the power-generating element In the method of manufacturing a secondary battery in which the peripheral portion of the laminate film is cut so that the integrated portion of a certain length remains after the heat-pressing is performed to form the integrated portion, the peripheral edge of the metal foil Is made smaller than the heat-fusible layer and the protective layer, so that the metal foil is not exposed at the end face of the laminated film cut.

  In the secondary battery having the laminate film exterior of the present invention, since there is no exposed portion of the metal foil on the cut end surface of the laminate film, the contact between the metal foil and the terminal, as has been conventionally seen, Defects caused by can be extremely reduced.

  Further, since the metal foil is not present on the cut end face of the laminate film, the interface peeling of the joint surface of different materials does not occur, and the reliability in use over a long period of time can be improved. In general, most of the peeling occurs from the cut end face, so it can be said that the present invention contributes to prevention of peeling.

  FIG. 1 is a diagram showing an example of an embodiment of the present invention, FIG. 1 (a) is a perspective view showing an arrangement of a power generation element and a laminate film, and FIG. 1 (b) is an enlarged cross-sectional view of a cut end surface of the laminate film. FIG. In FIG. 1, 1 is a power generation element, 2 is a positive electrode terminal, 3 is a negative electrode terminal, 4 is a laminate film, 5 is a heat fusion layer, 6 is a metal foil, and 7 is a protective layer.

  In FIG. 1, for convenience of explanation, the laminate film 4 is shown in a state before the constituent materials are laminated, and the laminate film 4 disposed on the upper side in the drawing is omitted.

  As shown in FIG. 1, the laminate film 4 used in the present invention is laminated with a metal foil 6 having dimensions smaller than that of the protective layer 7 or the heat sealing layer 5 made of polymer. The metal foil 6 used for such a purpose is excellent in ductility and malleability and is required to be flexible. Specifically, aluminum or copper is used.

  Further, the heat-sealable layer 5 is required to have a certain level of mechanical strength at room temperature and to exhibit adhesiveness when softened at a high temperature. Is preferred. Specific examples include an ethylene-vinyl acetate copolymer and an ethylene-ethyl acrylate copolymer. A material excellent in adhesiveness selected from so-called ionomers can also be used.

  An ionomer is a copolymer of an olefin and acrylic acid or maleic acid treated with a metal compound. It has an ionic crosslinking structure and exhibits properties like a thermosetting polymer at room temperature. Suitable for such applications.

  Further, since the protective layer 7 is required to have mechanical strength, abrasion resistance, scratch resistance, and the like, a relatively hard polymer is used, specifically, polyethylene terephthalate, polypropylene, or the like can be used. . In addition, since these polymers have relatively poor adhesion, a two-layer film having a polymer layer constituting a heat-sealing layer and a polymer layer constituting a protective layer, obtained by two-layer extrusion molding By using this, the bonding strength of the heat-sealing surface can be increased.

  In addition, the conventional heat press method, the heat-fusion method using an ultrasonic wave, etc. can be used for heat fusion of the peripheral part of a laminate film as it is.

  Next, the present invention will be described in detail with specific examples.

  First, as a current collector, an aluminum foil having a thickness of 20 μm was prepared for the positive electrode and a copper foil having a thickness of 20 μm was prepared for the negative electrode, and each of them was cut to have a width of 40 mm and a length of 70 mm.

  Next, preparation of the positive electrode will be described. First, lithium carbonate and cobalt carbonate were mixed so that the molar ratio of lithium to cobalt was 1: 1, and baked in air at 900 ° C. for 5 hours. The fired body was pulverized using a mortar to obtain a fired powder having an average particle size of 6 μm. Further, the obtained fired powder and lithium carbonate powder were mixed so that the weight ratio was 95/5.

  The mixed powder, graphite as a conductive material, and polyvinylidene fluoride as a binder are weighed and mixed at a weight ratio of 91/6/3, dispersed in N-methyl-2-pyrrolidone, and positive electrode active The material layer forming paste was obtained. This paste was applied to both sides of the current collector so that the thickness after removing the solvent was 100 μm and dried to obtain a positive electrode.

  Next, production of the negative electrode will be described. A carbon material having an average particle diameter of 7 μm obtained by firing and pulverizing a phenol resin in an inert gas stream, and polyvinylidene fluoride as a binder are weighed and mixed so that the weight ratio is 90/10. -Dispersed in methyl-2-pyrrolidone to obtain a paste for forming a negative electrode active material layer. Thereafter, a negative electrode was obtained in the same manner as the positive electrode.

  Next, preparation of the electrolyte layer for impregnating the electrolytic solution will be described. A paste was prepared by weighing 33 wt% of silica powder, 23 wt% of vinylidene fluoride-hexafluoropropylene copolymer powder and 44 wt% of dibutyl phthalate, and diluting and mixing with acetone. The electrolyte layer was obtained by forming a film so that the thickness after drying was 100 μm.

  Next, two each of the positive electrode and the negative electrode were laminated with the electrolyte layer interposed therebetween, heated and pressurized with a hot press, and subsequently extracted with dibutyl phthalate. Subsequently, positive and negative terminals were attached, and an electrolytic solution in which tetraethylanium tetrafluoroborate was dissolved in propylene carbonate at a concentration of 1 mol / L was impregnated to obtain a power generating element.

  Next, the laminate film used for the exterior will be described. Here, a two-layer film made of an ionomer obtained by treating polyethylene terephthalate and an ethylene-methacrylic acid copolymer with a zinc compound was used as a protective layer. The total thickness of the protective layer is 18 μm, and the thickness of the ionomer layer is 3 μm.

  Further, an aluminum foil having a thickness of 20 μm was used as the metal foil, and the above-mentioned ionomer was used as the heat fusion layer. The size of these three layers is set so that the metal foil is smaller than the other layers as shown in FIG.

  The laminate film having such a structure was bent with the heat-sealing layer inside, and the terminals were arranged on the release side, and the power generation element was sandwiched between them. Thereafter, the laminate film was formed so that the heat-sealing layer was in close contact with the surface of the power generating element, and the heat-sealing layer at the peripheral edge of the power generating element was integrated using a heat press.

  Subsequently, the extra length portion of the integrated heat fusion layer was cut to obtain a secondary battery. When the vicinity of the cut end face was cut in a direction perpendicular to the end face and the cross section was observed, as shown in FIG. 1B, a portion where the aluminum foil was exposed to the outside was not recognized. This confirmed the effect of the present invention.

  In addition, although the said Example demonstrated the lithium ion secondary battery, it is applicable also to another secondary battery and the electrochemical cell which has the same structure.

The figure which shows an example of embodiment of this invention. Fig.1 (a) is a perspective view which shows arrangement | positioning of a power generation element and a laminate film. FIG.1 (b) is sectional drawing to which the cut end surface of the laminate film was expanded. The figure which shows the example of the conventional secondary battery which used the laminate film of 3 layer structure for the exterior. FIG. 2A is a perspective view. FIG.2 (b) is sectional drawing to which the cut end surface of the laminate film was expanded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,8 Power generation element 2,9 Positive electrode terminal 3,10 Negative electrode terminal 4,11 Laminate film 5,12 Thermal fusion layer 6,13 Metal foil 7,14 Protective layer

Claims (3)

  In a secondary battery in which the power generation element is sealed with a power generation element having a positive electrode, a negative electrode, and an electrolyte, and a laminate film having a metal foil and a polymer layer, the metal foil is not present on an end surface of the laminate film. A secondary battery characterized by that.   2. The laminate film according to claim 1, wherein the laminate film has a protective layer made of a polymer on one surface of the metal foil, and has a heat fusion layer made of a polymer on the opposite surface. Next battery.   A power generation element in which a positive electrode terminal and a negative electrode terminal are drawn out in a plate shape is formed by using a heat sealing layer made of a polymer, a laminate film having a protective layer made of a metal foil and a polymer, and The laminate film is formed so that the heat-sealing layer is in close contact with the surface of the power generation element so as to be opposed to each other, and the heat-sealing layer at the peripheral edge of the power generation element is integrally heated and pressed. In the method for manufacturing a secondary battery, in which the peripheral portion of the laminate film is cut so that the integrated portion having a certain length remains after the formation portion is formed. A method for manufacturing a secondary battery, wherein the metal foil is not exposed to an end face obtained by cutting the laminate film by making the layer smaller than the protective layer and the protective layer.

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