JPH11162436A - Thin secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin secondary battery capable of easily releasing gas to the outside and preventing a burst when gas is generated and the internal pressure rises at the time of an overcharge. SOLUTION: In this battery, a thin power generating element 5 having a positive electrode 7, a separator and a negative electrode 9 is stored in an exterior material 4 made of a laminated film laminated with at least a thermal fusion resin film 1, a metal foil 2 and a rigid resin film 3 in this order from the interior side so that external terminals 13, 17 electrically connected to the positive electrode 7 and the negative electrode 9 respectively are extended from the opening edge section of the exterior material 4. The thermal fusion resin film 1 is heat-fused at the opening edge section to seal the power generating element 5 in the exterior material 4. A notch section 18 is provided on the metal foil 2 of the exterior material 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin secondary battery, and more particularly, to a thin secondary battery provided with a gas release mechanism.

[0002]

2. Description of the Related Art In recent years, a thin secondary battery having a thickness of about 0.5 mm, such as a polymer lithium ion secondary battery, has attracted attention as a power source for cordless devices such as portable personal computers, which emphasize small size and light weight. It is being actively developed.

[0003] Important element technologies for putting the thin secondary battery into practical use include selection of active materials for a positive electrode and a negative electrode, a technology for constructing a battery, and a technology for sealing a thin power generation element pond with an exterior material. Can be When the sealing property of the thin power generating element by the exterior material is reduced, not only does the electrolyte constituting the power generating element volatilize and leak to reduce the battery reaction, but also moisture easily enters from the outside to reduce the performance. Invite.

[0004] For this reason, the conventional thin secondary battery includes a thin power generating element having a positive electrode, a separator, and a negative electrode in an exterior material having a heat-fusible resin film disposed on an inner surface thereof. The external power source connected to the current collector is housed so as to extend from an opening edge of the exterior material, and the heat-fusible resin films are heat-sealed to each other at the opening edge, thereby forming the power generation element. Is sealed in the exterior material. The exterior material is, for example, a laminated film in which a heat-fusible resin film, a barrier film such as an aluminum foil, and a rigid resin film such as a polyethylene terephthalate film are laminated at least in this order.

However, when gas is generated inside the thin secondary battery due to overcharging or the like, the internal pressure increases. For this reason, the laminated film as the exterior material expands and eventually bursts. When a thin secondary battery ruptures, its contents (especially electrolyte) are scattered, and if it is directly mounted on the device, the device will be damaged, and if it is a battery pack, the case will be damaged. Cause damage.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent gas from being easily escaping to the outside when gas is generated due to overcharge or the like and the internal pressure is increased, thereby preventing the gas from exploding. It is an object of the present invention to provide a thin secondary battery capable of performing the following.

[0007]

SUMMARY OF THE INVENTION A thin secondary battery according to the present invention has an outer package made of a laminated film in which a heat-fusible resin film, a metal foil and a rigid resin film are laminated at least in this order from the inner surface side. A thin type power generating element having a positive electrode, a separator and a negative electrode is housed in a material such that external terminals electrically connected to the positive and negative electrodes respectively extend from an opening edge of the exterior material, and the opening edge In the thin secondary battery in which the heat-fusible resin films are heat-sealed to each other and the power generation element is sealed in the exterior material, the cut portion is provided in the metal foil of the exterior material. It is a feature.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thin secondary battery according to the present invention, for example, a thin polymer electrolyte secondary battery will be described in detail with reference to the drawings. 1 is a perspective view showing a thin polymer electrolyte secondary battery according to the present invention, FIG. 2 is an exploded perspective view of the secondary battery shown in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is a sectional view taken along line IV-IV in FIG. A thin power generation element 5 is housed in an exterior material 4 composed of a laminated film in which a heat-fusible resin film 1, a metal foil 2, and a rigid resin film 3 are laminated at least in this order from the inner surface side. A sealing portion 6 in which the heat-fusible resin films 1 on the inner surface of the material 4 are heat-sealed to each other, for example, on three sides.
The power generating element 5 is sealed by a, 6b and 6c.
As shown in FIG. 3, the power generating element 5 has a structure in which a positive electrode 7, a polymer electrolyte layer 8 serving as a separator, and a negative electrode 9 are laminated in this order.

The positive electrode 7 is made of a current collector 1 made of aluminum.
0 has a structure in which the positive electrode layer 11 is supported on both surfaces. The current collector 11 has a terminal portion 12 made of strip-shaped aluminum foil.
An external positive electrode lead 13 made of aluminum is connected to the terminal portion 12 by ultrasonic welding. The external lead 13 extends outside from the sealing portion 6b of the exterior material 4.

The negative electrode 9 has a structure in which a negative electrode layer 15 is supported on both surfaces of a current collector 14 made of copper. The current collector 14
Has a terminal portion 16 made of a strip-shaped copper foil.
6 is connected to an external negative electrode lead 17 by ultrasonic welding or the like. The external lead 17 extends outside from the sealing portion 6b of the exterior material 4.

A notch, for example, a linear notch 18
Is provided on the metal foil 2 of the exterior material 4 corresponding to the surface of the power generation element 5. Such a thin polymer electrolyte secondary battery is manufactured, for example, by the following method. First, as shown in FIG. 2, a linear cut portion 18 is formed in a predetermined portion of a metal foil by, for example, a cutter or the like, and the metal foil is heat-sealed to a heat-fusible resin film. Subsequently, a rigid resin film is adhered to the metal foil by dry lamination to produce a band-like laminated film 19. Subsequently, the thin film power generating element 5 to which the external terminals 13 and 17 of the positive and negative electrodes are attached is a part of the laminated film 19 where the cut portion 18 is not formed at the boundary of the bending line 20 located at the center part parallel to the short side. The external terminal 13,
17 is placed so as to extend from the short-side end face of the laminated film 19, and then the laminated film 19 is bent so as to wrap the power generation element 5 at the bending line 20. Thereafter, the three sides excluding the bent portion are heat-sealed to seal the power generation element 5, thereby producing the secondary battery shown in FIG.

The package 4, the positive electrode 7, the negative electrode 9 and the electrolyte layer 8 have the following configuration. 1) Exterior Material 4 The exterior material 4 is a laminated film in which a heat-fusible resin film 1, a metal foil 2, and a rigid resin film 3 are laminated at least in this order from the sealing surface side.

As the heat-fusible resin, for example, polyethylene (PE), ionomer, ethylene vinyl acetate (EVA) and the like can be used. As the metal foil, for example, an Al foil or a Ni foil can be used.

As the rigid resin, for example, polyethylene terephthalate (PET), nylon or the like can be used. Specifically, a laminated film of PE / Al foil / PET laminated from the sealing surface side to the outer surface;
Laminated film of PE / Al foil / nylon; Laminated film of ionomer / Ni foil / PET; EVA / Al foil / P
An ET laminated film; an ionomer / Al foil / PET laminated film or the like can be used. Here, the film other than PE, ionomer, and EVA on the sealing surface has moisture resistance, air resistance, and chemical resistance.

The exterior material is formed by bending the laminated film so that the heat-fusible resin film is located on the inner surface (sealing surface), and heat-sealing the end parallel to the bending line to produce a tubular material. An external terminal electrically connected to the positive electrode of the thin power generating element extends from one opening, and an external terminal electrically connected to the negative electrode extends from the other opening. And the power generating element may be sealed by heat sealing the two openings.

2) Positive Electrode 7 The positive electrode 7 has a structure in which a positive electrode layer 11 containing an active material, a non-aqueous electrolyte and a polymer holding the electrolyte is supported on both surfaces of a current collector 10 made of aluminum.

Examples of the active material include various oxides (eg, lithium manganese composite oxide such as LiMn ₂ O ₄ );
Manganese dioxide, for example, a lithium-containing nickel oxide such as LiNiO ₂ , for example, a lithium-containing cobalt oxide such as LiCoO ₂ , a lithium-containing nickel cobalt oxide, and an amorphous vanadium pentoxide containing lithium.
And chalcogen compounds (for example, titanium disulfide, molybdenum disulfide, and the like). 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 (Li
PF ₆ ), lithium borotetrafluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (C
F 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 holding the nonaqueous electrolyte include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative, and a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP). Can be. 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 layer may contain 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.

As the current collector, for example, expanded metal made of aluminum, mesh made of aluminum, punched metal made of aluminum, or the like can be used. The positive electrode may have a structure in which a positive electrode layer is supported on one surface of a current collector.

3) Negative Electrode 9 The negative electrode 9 has a structure in which a negative electrode layer 15 containing an active material, a non-aqueous electrolyte and a polymer holding the electrolyte is supported on both surfaces of a current collector 14 made of copper.

Examples of the 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 electrolyte and the polymer, those similar to those described for the positive electrode described above are used. The negative electrode layer 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.

As the current collector, for example, copper expanded metal, copper mesh, copper punched metal and the like can be used. The negative electrode may have a structure in which a positive electrode layer is supported on one surface of a current collector.

4) Polymer Electrolyte Layer 8 This electrolyte layer 8 contains a non-aqueous electrolyte and a polymer holding the electrolyte. As the non-aqueous electrolyte and the polymer, the same ones as described for the positive electrode described above are used.

The electrolyte layer may contain an inorganic filler such as SiO ₂ powder in order to improve the compressive strength. The power generating element is not limited to one layer, and may be housed in the exterior material in two or more layers.

The cut portion provided in the metal foil of the exterior material is not limited to a linear shape but may be a cross shape. The position of the cut portion is not limited to the position corresponding to the surface of the power generating element 5,
As shown in FIG. 5, the cut portion 18 may be provided in the metal foil of the seal portion (for example, 6a).

In order to increase the volumetric energy density of the thin secondary battery, the external terminals 10, 14 shown in FIG. 1 or FIG. 5 are bent toward the surfaces of the parallel seal portions 3a, 3c except for the seal portion 3b extending therefrom. May be fixed.

According to the present invention described above, for example, a linear cut 18 is provided in the metal foil 2 of the exterior material 4 in which the thin power generating element 5 is housed, so that the power generating element 5 is overcharged or the like. Even if gas is generated and the internal pressure rises,
The gas can escape before the cutout 18 of the metal foil 2 of the exterior material 4 is broken and the entire exterior material 4 ruptures.

That is, when gas is generated inside the exterior material 4 and the exterior material 4 expands, the expansion force concentrates on the cut portion 18 of the metal foil 2 in which the mechanical strength of the exterior material 4 is reduced. As a result, when the exterior material 4 further expands, the cut portion 18 of the metal foil 2 opens outward, and finally the heat-sealing film 1 on the upper and lower surfaces of the metal foil 2 and the rigid resin film 3 are broken. As shown in FIG. 6, a hole 21 is opened in the exterior material 4, and gas can escape from the hole 21.

On the other hand, as shown in FIG. 5, by providing the cut portion 18 in the metal foil portion located at the sealing portion 6a of the exterior material 4, gas is generated due to overcharging or the like, and
Expands, a force is exerted to peel off in the vicinity of the seal portions 6a to 6c, and the force concentrates on the cut portion 18 of the metal foil. The heat-sealing film 1 and the rigid resin film 3 on the lower surface are broken, and a hole is opened in the exterior material 4, so that gas can escape from the hole.

Therefore, when a gas is generated at the time of overcharging and the internal pressure rises, the gas is easily escaping to the outside due to the breakage of the exterior material near the cut portion of the metal foil, and the exterior material is ruptured. It is possible to provide a thin secondary battery capable of preventing the occurrence thereof. For this reason, it is possible to avoid scattering of the contents (especially, the electrolytic solution) due to the rupture of the exterior material, and to prevent damage to the device when directly mounted on the device.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) <Preparation of positive electrode> A copolymer of vinylidene fluoride-hexafluoropropylene (VdF-HFP) in acetone (trade name, manufactured by Elphatochem Co., Ltd .; KYNAR2801, copolymerization ratio [VdF: HFP] is 88:12) After dissolving the powder, the acetone solution was mixed with dibutyl phthalate (DB).
P) and a lithium-containing cobalt oxide (manufactured by Nippon Heavy Industries, Ltd.) having a composition formula of LiCoO ₂ as an active material were added to prepare a positive electrode paste. Subsequently, a positive electrode paste having the above composition was applied to a porous current collector made of an aluminum mesh using a knife coater, and dried with dry air, so that a positive electrode not impregnated with electrolyte on both surfaces of the porous current collector was applied. A positive electrode material on which a layer was formed was produced.

<Preparation of Negative Electrode> A vinylidene fluoride-hexafluoropropylene copolymer similar to that used for the positive electrode was dissolved in acetone to prepare an acetone solution. Then, dibutyl phthalate (D
After adding BP), a mesophase pitch-based carbon fiber (manufactured by Petka Corporation) was added as an active material and mixed to prepare a paste for a negative electrode. This negative electrode paste was applied to a porous current collector made of a copper mesh using a knife coater, and dried with dry air to form a negative electrode having an electrolyte-impregnated negative electrode layer formed on both surfaces of the porous current collector. The material was made.

<Preparation of Solid Polymer Electrolyte Layer> A copolymer of vinylidene fluoride-hexafluoropropylene similar to that used for the positive electrode was dissolved in acetone to prepare an acetone solution. After adding dibutyl phthalate (DBP), the mixture was mixed to prepare an electrolyte layer paste. After applying the paste on a smooth glass plate, dried in the same manner as the positive and negative electrodes,
By peeling off the glass plate, a solid polymer electrolyte material not impregnated with an electrolyte was prepared.

<Preparation of Non-Aqueous Electrolyte> LiPF ₆ as an electrolyte was mixed with ethylene carbonate (EC) and dimethyl carbonate (DMC) in a non-aqueous solvent in a volume ratio of 1: 1 at a concentration of 1 mol / mol. 1 to prepare a non-aqueous electrolyte.

The obtained positive electrode material, solid polymer electrolyte material and negative electrode material were stacked in this order,
And laminated by heating and pressing with a rigid roll heated to a thickness of 1.0 mm and an outer dimension of 40 mm × 60 mm. Subsequently, the laminate was immersed in methanol to elute DBP in the positive electrode material, the negative electrode material, and the polymer electrolyte material, and these members were used as a porous electrolyte-unimpregnated power generating element having a porous structure. Continued,
External terminals were respectively connected to the strip-shaped terminal portions of the positive and negative porous current collectors of the power generating element by ultrasonic welding or the like.

Next, an aluminum foil having a thickness of 10 μm and a width of 8 mm
Is cut by a cutter, this Al foil is thermally fused to an ionomer resin film having a thickness of 50 μm, and a PET film having a thickness of 12 μm is dry-laminated on the Al foil to have a thickness of 0.1 mm. 70m
A strip-shaped laminated film composed of three layers of mx 153 mm was prepared, and the electrolyte-impregnated power generating element to which the external terminals of the positive and negative electrodes were attached was mounted so that the external terminals extended from the short side of the laminated film. Thereafter, the laminated film was bent at the center thereof so as to surround the electrolyte-unimpregnated power generating element in parallel with its short side. Continued, width 10 excluding the bent part
mm were heat sealed on three sides. However, a part of one of the two sides excluding the side from which the external terminal extends was left as an unsealed portion. Thereafter, the non-aqueous electrolytic solution is injected into the inside through the unsealed portion, and the unsealed portion is again heat-sealed to form the thin power generating element 5 in the exterior material 4 made of the laminated film shown in FIG. Are sealed and housed. Except for an external terminal having a linear cutout 15 provided at a position of the Al foil of the exterior material 4 corresponding to the surface of the power generating element 4, the external dimensions are 100 mm × 75 mm, and the electric capacity is 100 mAh. Two thin polymer electrolyte secondary batteries were manufactured.

(Example 2) The same structure as in Example 1 except that the cut portion (length 8 mm) was formed in the Al foil of the sealing portion of the exterior material, and the 100 thin polymer shown in FIG. An electrolyte secondary battery was manufactured.

(Comparative Example 1) 100 thin polymer electrolyte secondary batteries having the same dimensions and electric capacity as in Example 1 except that no cut portion was formed in the Al foil of the exterior material were manufactured.

The obtained secondary batteries of Examples 1 and 2 and Comparative Example 1 were prepared using an internal space of 72 mm × 77 mm × 4.0 m.
Each battery was housed in a polypropylene case having external connection terminals of 75 mm × 80 mm × 6.0 mm and external dimensions of 75 mm × 80 mm × 6.0 mm such that the external terminals of the positive and negative electrodes of each battery were connected to the external connection terminals to assemble a pack-type battery.

An overcharge test was performed on each of the pack-type batteries under the conditions of 1 C and 3 hours, and the amount of deformation of the battery pack case in the thickness direction was measured. The results are shown in Table 1 below. Table 1 Case deformation number Average deformation amount of deformed case Example 10-Example 20-Comparative example 1 100 2.4 mm As is clear from Table 1, the thin secondary batteries of Examples 1 and 2 are packed. When the batteries were used, no deformation of the case was observed. On the other hand, when the thin secondary battery of Comparative Example 1 was a pack-type battery, deformation was observed in 100 out of 100 batteries. In addition, when the pack type batteries of Examples 1 and 2 were disassembled and the thin polymer electrolyte secondary batteries inside the case were examined, all the secondary batteries were broken due to the smell of the cut portion of the Al foil of the exterior material. It was recognized that.

[0045]

As described in detail above, according to the present invention, when gas is generated at the time of overcharging and the internal pressure rises,
It is possible to provide a highly safe thin secondary battery capable of easily escaping the gas to the outside and preventing the gas from exploding.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a thin polymer electrolyte secondary battery according to the present invention.

FIG. 2 is an exploded perspective view of the secondary battery of FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG. 1;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1;

FIG. 5 is a perspective view showing another thin polymer electrolyte secondary battery according to the present invention.

FIG. 6 is a perspective view for explaining breakage of an exterior material when a gas is generated due to overcharge in the thin polymer electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heat-fusible resin film, 2 ... Metal foil, 3 ... Rigid resin film, 4 ... Exterior material, 5 ... Thin power generation element, 6a-6c ... Seal part, 7 ... Positive electrode, 8 ... Polymer electrolyte layer 9, 9 negative electrode, 13, 17 external terminal, 18 notch.

Claims (2)

[Claims] 1. A thin power generating element having a positive electrode, a separator, and a negative electrode in an exterior material composed of a laminated film in which a heat-fusible resin film, a metal foil, and a rigid resin film are laminated at least in this order from an inner surface side. External terminals electrically connected to the positive and negative electrodes, respectively, are housed so as to extend from an opening edge of the exterior material, and the heat-fusible resin films are thermally fused to each other at the opening edges. A thin secondary battery in which the power generating element is sealed in the exterior material, wherein the cut portion is provided in a metal foil of the exterior material. 2. The thin secondary battery according to claim 1, wherein the cut portion is provided in a metal foil located at a heat-sealed portion of the exterior material.