JPH11204088A - Sheet battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery maintaining high air tightness with improved energy efficiency per unit volume by thermally fusing and sealing an opening of a cylindrical enclosure member storing power generating elements. SOLUTION: In this battery, a belt-shaped positive electrode external terminal 2 and a belt-shaped negative electrode external terminal 3 are stored in a cylindrical enclosure member 2 having a gas barrier property, extending from the cylindrical enclosure member 1. The cylindrical enclosure member 1 is cylindrically shaped by a multi-layered film having a first thermal fusion resin film, a metal thin film, a second thermal fusion resin film, and a resin film laminated in order being pasted so that the first thermal fusion film is positioned on an inner face. At an opening of the cylindrical enclosure member, the first thermal fusion resin film is thermally fused with each other, and is fused. In the positive electrode, a positive electrode layer containing a positive electrode active substance, a non-aqueous electrolyte solution and a polymer holding this electrolyte solution is carried by a porous power collector. In the negative electrode, a negative electrode layer containing a negative electrode active substance, a non-aqueous electrolyte solution, and a polymer holding this electrolyte solution is carried by a porous power collector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet type battery having a structure in which a power generating element is housed in a film.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a non-aqueous electrolyte secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As such a secondary battery, a negative electrode using lithium or a lithium alloy as an active material, and a suspension containing an oxide, sulfide, or selenide as an active material, such as molybdenum, vanadium, titanium, or niobium, were applied. A lithium secondary battery including a positive electrode made of a current collector and a non-aqueous electrolyte is known.

In recent years, a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, such as coke, graphite, carbon fiber, a resin fired body, and pyrolytic gas phase carbon, has been used as a negative electrode. The development and commercialization of lithium ion secondary batteries using lithium and lithium manganese oxide-containing batteries are being actively pursued.

[0004] Initially, these non-aqueous electrolyte secondary batteries were mainly in the form of coins or cylinders. However, with the diversification of applications, these non-aqueous electrolyte secondary batteries have forms with excellent volume efficiency, such as rectangular and oval. The demand for things is growing. In addition, for the purpose of further reducing the weight and size, it has been studied to change the container for housing the power generation element from a conventional metal outer can to a film material.

As the film material, a metal foil such as an aluminum foil is disposed at the center so that gas such as water vapor and oxygen is not exchanged inside and outside of the film, and the metal foil such as polyethylene terephthalate is used as the outermost layer. Generally, a multilayer film (laminate film) provided with a resin layer for protecting against mechanical impact and a heat-fusible resin layer such as an ionomer as the innermost layer is generally used. To seal a battery using the multilayer film, first, a content to be a power generating element is disposed between two multilayer films so that the power generating element and the innermost layer are in contact with each other. This is performed by heat-pressing the sides and bonding the innermost layers at the periphery of the film. By sealing the power generation element with the film material in this manner, the battery can be made thinner and lighter.

In a battery having a structure sealed with a film material as described above, in order to make the battery hermeticity comparable to that using a conventional metal outer can, the area of the fused portion is increased to some extent. There is a need.

[0007]

However, when the fused portion is widened, the outer shape of the battery is increased by the size of the fused portion, so that the battery capacity is low for the size and the energy efficiency per unit volume is low. There is a problem that it becomes lower. An object of the present invention is to provide a sheet-type battery with improved energy efficiency per unit volume while maintaining high airtightness.

[0008]

A sheet-type battery according to the present invention has a structure in which a power generating element is housed in a cylindrical exterior material, and an opening of the cylindrical exterior material is sealed by heat sealing. It is characterized by having.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a sheet-type battery (for example, a sheet-type polymer secondary battery) according to the present invention will be described with reference to FIGS. FIG. 1 is a plan view showing a sheet-type battery according to the present invention, FIG. 2 is a perspective view showing the battery of FIG. 1, and FIG.
FIG. 4 is a partial cross-sectional view showing a cylindrical exterior material used in the battery of FIG.
FIG. 2 is a sectional view showing the battery of FIG. 1.

As shown in FIGS. 1 and 2, a sheet-like power generating element comprises a band-shaped positive external terminal 2 and a band-shaped negative external terminal 3 inside a cylindrical external material 1 having gas barrier properties. It is stored to extend from. The cylindrical exterior member 1 has a first heat-sealing resin film, a first heat-sealing resin film, a metal thin film, a second heat-sealing resin film, and a multilayer film in which a resin film is laminated in this order. It is made of one that is laminated and positioned in a tubular shape.
The opening of the cylindrical exterior material 1 is sealed by heat-sealing the first heat-sealing resin films to each other.

Here, a description will be given of the structure of the cylindrical exterior member 1 where the ends of the multilayer film are bonded to each other. As shown in FIG. 3, one end of the multilayer film has a first heat-sealing resin film 4a, a metal thin film 5a, a second heat-sealing resin film 6a from the lower surface to the upper surface.
A resin film 7a is laminated in this order, and the upper surface of the first heat-sealing resin film 4a and the metal thin film 5a
Are cut out stepwise so that the upper surface of the is exposed. The other end of the multilayer film is formed from a lower surface side to an upper surface side with a first heat-sealing resin film 4b, a metal thin film 5b,
The second heat-sealing resin film 6b and the resin film 7b are laminated in this order, and are cut out stepwise so that the lower surface of the metal thin film 5b and the lower surface of the second heat-sealing resin film 6b are exposed. Has been. The first heat-fusion resin films at one end and the other end and the second heat-fusion resin films at the one end and the other end are bonded by heat fusion. The metal thin film 5b at the other end is placed on the upper surface of the first heat-fused resin film 4a at one end.
Are bonded by heat fusion, and a second heat fusion resin film 6b at the other end is bonded to the upper surface of the metal thin film 5a at one end by heat fusion. By bonding the end portions of the multilayer film to each other in this manner, a cylindrical exterior material having gas barrier properties is formed.

Next, a description will be given of the sheet-like power generation element housed in the tubular exterior member 1. Fig. 4
As shown in FIG. 1, a negative electrode 10 having a structure in which a negative electrode layer 8 is supported on both surfaces of a porous current collector 9 is provided. Two positive electrodes 11
Are arranged on both surfaces of the negative electrode 10. Each positive electrode 11
Has a structure in which the positive electrode layer 12 is supported on both surfaces of the porous current collector 13. The solid electrolyte layer 14 is interposed between the positive electrode 11 and the negative electrode 10. The current collector 13 of each of the positive electrodes 11 has a band-shaped positive terminal 15 at a portion located on the back side in FIG. Further, the current collector 9 of the negative electrode 10 is positioned so as not to overlap the positive electrode terminal 15 (for example, FIG.
(A portion located on the near side of the above) has a strip-shaped negative electrode terminal 16. The two positive terminals 15 are connected to the external positive terminal 2. On the other hand, the negative terminal 16 is connected to the external negative terminal 3.

As the positive electrode, the negative electrode, the electrolyte layer and the multilayer film of the sheet-type battery, for example, those described below can be used. (Positive Electrode) The positive electrode is formed from a positive electrode layer containing a positive electrode active material, a non-aqueous electrolyte, and a polymer holding the electrolyte supported on a porous current collector.

Examples of the positive electrode active material include various oxides (eg, lithium-manganese composite oxide such as LiMn ₂ O ₄ , manganese dioxide, lithium-containing nickel oxide such as LiNiO _2, and lithium-containing cobalt oxide such as LiCoO ₂ , for example). Oxide, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide and the like, and chalcogen compounds (for example, titanium disulfide and molybdenum disulfide). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent,
Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DE
C), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (TH
F) and 2-methyltetrahydrofuran. The non-aqueous solvents may be used alone or as a mixture of two or more.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN
(CF ₃ SO ₃ ) ₂ ].

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l. Examples of the polymer having the property of retaining a non-aqueous electrolyte include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative, a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), and the like. Can be used. The copolymerization ratio of the HFP depends on the method of synthesizing the copolymer, but is usually at most about 20% by weight.

The positive electrode may include a conductive material from the viewpoint of improving conductivity. Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like.

The porous current collector and the terminal portion can be formed of, for example, an aluminum expanded metal, an aluminum mesh, an aluminum punched metal, or the like.

The positive electrode lead as the external positive electrode terminal can be formed, for example, from an aluminum foil. (Negative Electrode) The negative electrode is formed of a negative electrode active material, a non-aqueous electrolyte, and a negative electrode layer containing a polymer holding the electrolyte supported on a porous current collector.

Examples of the negative electrode active material include carbonaceous materials that occlude and release lithium ions. Such carbonaceous materials include, for example, those obtained by firing organic polymer compounds (eg, phenolic resin, polyacrylonitrile, cellulose, etc.), those obtained by firing coke and mesophase pitch, and those made by artificial graphite. And carbonaceous materials represented by natural graphite and the like. Among them, 500
It is preferable to use a carbonaceous material obtained by calcining the mesophase pitch at a temperature of from ℃ to 3,000 ℃ under normal pressure or reduced pressure.

As the non-aqueous electrolytic solution and the polymer having the property of retaining the non-aqueous electrolytic solution, those similar to those described for the positive electrode described above are used. The negative electrode is allowed to contain conductive materials such as artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, nickel powder, and polyphenylene derivatives, and fillers such as olefin polymers and carbon fibers.

The porous current collector and the terminal portion can be formed of, for example, a copper expanded metal, a copper mesh, a copper punched metal, or the like. The negative electrode lead as an external negative electrode terminal can be formed from, for example, a copper foil.

(Gel Electrolyte Layer) This electrolyte layer contains a non-aqueous electrolyte and a polymer holding the electrolyte. As the non-aqueous electrolyte and the polymer having the property of retaining the non-aqueous electrolyte, those similar to those described for the positive electrode described above are used.

From the viewpoint of further improving the strength, the electrolyte layer may contain an inorganic filler such as silicon oxide powder. (Cylindrical exterior material) This cylindrical exterior material is formed by joining both ends of a multilayer film having a metal thin film and heat-sealing resin films disposed on both surfaces of the metal thin film with the metal thin film at one end and the other end. It is formed by aligning the heat-sealing resin film at the side end so as to overlap, and bonding the metal thin film at one end and the heat-sealing resin film at the other end by heat-sealing. The opening of the cylindrical exterior material is sealed by heat fusion. For this reason, it is necessary to arrange a heat-sealing resin on the inner surface of the cylindrical exterior material. The inner surface may be formed of the heat-sealing resin film, but may be formed of another heat-sealing resin film.

The metal thin film is formed of a metal having moisture resistance and air permeability. An example of such a metal is aluminum (Al). The heat sealing resin film can be formed from, for example, an ionomer or polyethylene.

It is preferable that the outer surface of the cylindrical exterior member is provided with a resin having impact resistance. As such a resin, for example, polyethylene terephthalate (PE
T), polyester and nylon.

As the multilayer film, specifically,
Polyethylene (P) laminated from the sealing surface side to the outer surface
E) / Al / PE / polyester multilayer film.

As described in detail above, the sheet-type battery according to the present invention has a structure in which the power generating element is housed in the cylindrical exterior material, and the opening of the cylindrical exterior material is sealed by heat sealing. Having. In such a battery, a power generation element is covered with an exterior film, and the number of openings to be sealed by heat sealing is reduced as compared with a conventional sheet-type battery in which the opening of the exterior film is sealed by heat fusion. Therefore, the outermost dimension (battery size) can be reduced. As a result, the battery can improve energy efficiency per unit volume while maintaining high airtightness.

Both ends of the multilayer film having the tubular exterior material and a metal thin film and a heat-sealing resin film disposed on both surfaces of the metal thin film are formed on one end and the other end on the other end. The heat-sealing resin film of the part is overlapped and formed by bonding the metal thin film and the heat-sealing resin film by heat-sealing, so that the sealing property of the power generation element by the exterior material is improved. Can be improved. In addition, since the adhesive is not used when bonding both ends of the multilayer film, a defect accompanying the use of the adhesive (for example, in a sheet-type polymer secondary battery, the adhesive dissolves in the non-aqueous electrolyte, Airtightness is impaired).

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings. (Example) <Preparation of Positive Electrode> First, a composition formula of LiMn ₂ was used as an active material.
A lithium manganese composite oxide represented by O ₄ , carbon black, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder, and dibutyl phthalate (DBP) as a plasticizer are mixed in acetone. Then, a paste was prepared. The obtained paste was applied on a polyethylene terephthalate film (PET film) to form a sheet, and a positive electrode sheet not impregnated with a non-aqueous electrolyte was prepared. A positive electrode not impregnated with a non-aqueous electrolyte was produced by heat-pressing the obtained positive electrode sheet on both surfaces of a current collector made of aluminum expanded metal and having a positive electrode terminal portion using a hot roll.

<Preparation of Negative Electrode> Mesophase pitch carbon fiber as an active material, VdF-HFP copolymer powder,
DBP was mixed with acetone to prepare a paste.
The obtained paste was applied on a PET film and formed into a sheet, thereby producing a negative electrode sheet not impregnated with an electrolyte solution. A negative electrode not impregnated with an electrolyte was prepared by heat-pressing the obtained negative electrode sheet on both surfaces of a current collector made of copper expanded metal and having a negative electrode terminal portion with a hot roll.

<Preparation of Solid Polymer Electrolyte Layer> Silicon oxide powder, VdF-HFP copolymer powder, and DBP were mixed in acetone to form a paste. The obtained paste was applied on a PET film, formed into a sheet, and an electrolyte layer not impregnated with the electrolyte was prepared.

<Preparation of Nonaqueous Electrolyte> LiPF ₆ as an electrolyte was dissolved in a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed to prepare a nonaqueous electrolyte.

<Preparation of Unit Cell> Two positive electrodes, one negative electrode, and two electrolyte layers were prepared, and the positive electrode and the negative electrode were alternately laminated with the electrolyte layer interposed therebetween. These were heat-pressed with a heated rigid roll to produce a laminate. Such a laminate was immersed in methanol, and the DBP in the laminate was extracted with methanol, removed, and dried. Next, a positive electrode lead (made of strip-shaped aluminum foil) as an external positive electrode terminal is connected to the two positive electrode terminals, and a negative electrode lead (made of strip-shaped copper foil) as an external negative electrode terminal is connected to the negative electrode terminal. Thus, a sheet-like power generating element was obtained.

<Preparation of cylindrical exterior material> The first polyethylene film, Al foil, second polyethylene film and polyester film were laminated in this order to a thickness of 120 μm.
m was prepared. One end of the multilayer film was cut out stepwise so that the upper surface of the first polyethylene film and the upper surface of the Al foil were exposed as shown in FIG. Further, the other end was cut out stepwise so that the lower surface of the second polyethylene film and the lower surface of the Al foil were exposed as shown in FIG. Both ends of this multilayer film were overlapped so that the first polyethylene film was located on the inner surface, and formed into a cylindrical shape. At this time, the Al foil at the other end was laminated on the upper surface of the first polyethylene film at one end, and the second polyethylene film at the other end was laminated on the upper surface of the Al foil at one end. . In addition, the ends of the second polyethylene film and the polyester film were abutted. Then, by applying heat and pressure to the overlapped ends, the polyethylene films at both ends, the metal thin film at one end and the second polyethylene film at the other end, and the metal at the other end The thin film and the first polyethylene film at one end were bonded by heat fusion to obtain a cylindrical exterior material having gas barrier properties.

<Assembly of Battery> The power generating element was housed in the obtained cylindrical exterior material so that the positive and negative electrode leads extended from the exterior material. The opening from which the positive and negative electrode leads extended was sealed by heat-sealing the first polyethylene film on the inner surface. The power generating element was impregnated with the non-aqueous electrolyte by injecting the non-aqueous electrolyte having the above composition from the remaining openings. Next, the opening is sealed by heat-sealing the first polyethylene film on the inner surface, and has the structure shown in FIGS. 1 and 2 described above, has a thickness of 1.3 mm, and has an outer surface excluding the lead portion. A sheet-type polymer secondary battery having a diameter of 40 × 60 mm was manufactured. (Comparative Example) A power generating element was manufactured in the same manner as in the above-described embodiment. First, a multilayer film of the same type as
It was folded in two so that the polyethylene film was located. The power generating element was covered with the film so that the positive and negative electrode leads extended from the film. Subsequently, two of the three openings of the film were sealed by heat-sealing the first polyethylene film on the inner surface, and the same nonaqueous electrolyte as in the example was injected from the remaining openings. Then, the power generation element was impregnated with the electrolytic solution. Next, the opening was sealed by heat-sealing the first polyethylene film on the inner surface, and the thickness was 1.3 mm.
A sheet-type polymer secondary battery having an outer diameter of 50 × 60 mm excluding the lead portion was manufactured.

The occupied volumes of the obtained secondary batteries of the example and the comparative example were calculated, and based on the obtained volume values, a pack case having a minimum shape capable of accommodating the respective secondary batteries was produced. . The internal volume of the pack case in which the secondary battery of the example was stored was 3.12 cm ³ . On the other hand, the internal volume of the pack case accommodating the secondary battery of the comparative example was 3.90 cm ^3, which was 25% larger. This shows that the sheet-type polymer secondary battery of the example can reduce the occupied volume and can improve the volume energy density as compared with the sheet-type polymer secondary battery of the comparative example.

[0039]

As described above in detail, according to the present invention, it is possible to improve the energy efficiency per unit volume while maintaining high airtightness, and to provide a highly reliable sheet type battery. it can.

[Brief description of the drawings]

FIG. 1 is a plan view showing a sheet-type battery according to the present invention.

FIG. 2 is a perspective view showing the battery of FIG. 1;

FIG. 3 is a partial cross-sectional view showing a cylindrical exterior material used for the battery of FIG. 1;

FIG. 4 is a sectional view showing the battery of FIG. 1;

[Explanation of symbols]

 1 ... cylindrical exterior material, 2 ... positive electrode external terminal, 3 ... negative electrode external terminal.

Claims (2)

[Claims] 1. A sheet-type battery having a structure in which a power generating element is housed in a cylindrical exterior material, and an opening of the cylindrical exterior material is sealed by heat sealing. 2. The method according to claim 1, wherein the cylindrical exterior material includes a metal thin film and a heat-sealing resin film disposed on both sides of the metal thin film. 2. The sheet-shaped sheet according to claim 1, wherein the metal thin film and the heat-fusible resin film are adhered by heat-sealing, so that the heat-fusible resin film at the end of the sheet is overlapped. battery.