JPH11102682A - Thin secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid burst when overcharged and improve safety by forming a second degassing hole to communicate with a first degassing hole opening in an enclosing material in a support plate thermally fused on an enclosing material inside surface, and forming a safety valve mechanism by arranging an elastic valve body to block up the second degassing hole in its support plate and a third degassing hole in a cover to cover the elastic valve body. SOLUTION: A second degassing hole 15 to communicate with a first degassing hole 13 opening in an enclosing material 1 is formed in a support plate 14 thermally fused on an inside surface of the enclosing material 1. In the support plate 14, an elastic valve element 17 which blocks up the second degassing hole 15 and has a projection in the center, is arranged in a compressed condition between a cover 16 to surround the second degassing hole 15, a recessed part of the cover 16 and the support plate 14. A third degassing hole 18 is arranged in the cover 16, and when internal pressure increases since gas is generated in the enclosing material 1 by overcharge, the projection of the elastic valve element 17 is dislocated sideways. Therefore, the gas escapes from the third, the second and the first degassing holes 18, 15 and 13, and a burst is prevented, and it becomes safe.

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 safety valve 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.

Important elemental 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 generating element with an exterior material. . 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 terminals electrically connected to the housing are housed so as to extend from the 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. It has a structure 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 rechargeable battery ruptures, its contents (especially the electrolytic solution) splatter, damaging the device if it is directly mounted on the device, or deforming the case of a battery pack, and similarly mounting the device. 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 a gas is generated due to overcharge or the like and the internal pressure is increased, thereby preventing the gas from exploding. It is intended to provide a possible thin secondary battery.

[0007]

According to the present invention, there is provided a thin secondary battery comprising 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. An external terminal electrically connected to the negative electrode is accommodated 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 edge to generate the power. In a thin secondary battery in which elements are sealed in the exterior material, a safety valve mechanism is provided on the inner surface of the exterior material, and the safety valve mechanism includes a first gas vent hole opened in the exterior material, A support plate thermally fused to the inner surface of the exterior material; a second gas vent hole formed in the support plate so as to communicate with the first gas vent hole; and a second gas vent hole formed in the support plate. An elastic valve element disposed so as to close the gas vent hole; It is characterized in further comprising a cover that is fixed so as to cover the elastic valve body, and a third vent hole opened in the cover.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One example of a thin secondary battery (a thin polymer electrolyte secondary battery) according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a plan view showing a thin secondary battery according to the present invention, FIG. 2 is a perspective view showing a state where a fused portion along a longitudinal direction of the thin secondary battery according to the present invention is folded back,
3 is a sectional view showing a power generation element included in the secondary battery of FIGS. 1 and 2, FIG. 4 is a sectional view showing a main part of the secondary battery of FIGS. 1 and 2, and FIG. 5 is a safety valve mechanism of FIG. FIG.

As shown in FIG. 1, the thin power generating element is hermetically sealed in a state where a positive electrode lead 2 and a negative electrode lead 3 extend from the exterior material 1 in an exterior material 1. The exterior material 1 has a heat-fusible resin film disposed on the inner surface. The exterior material 1 is folded in two, and the films of the opening edge portion 4 are sealed by heat fusion. As shown in FIG. 2, in the thin secondary battery, two heat-sealed portions 4 along the longitudinal direction are folded on the upper surface in order to improve the volume energy density.

The thin power generating element of such a thin secondary battery has, for example, a structure as shown in FIG. That is, the thin power generating element has a structure in which a positive electrode layer 6 containing an active material is supported on both surfaces of a mesh current collector 5 and a structure in which a negative electrode layer 8 is supported on both surfaces of a mesh current collector 7. And a negative electrode having the same. Solid polymer electrolyte layer 9 as separator
Is disposed between the positive electrode layer 6 and the negative electrode layer 8. The positive electrode current collector 5 has a strip-shaped terminal portion 10 made of the same material as the current collector. On the other hand, the negative electrode current collector 7 has a strip-shaped terminal portion 11 made of the same material as the current collector.
At a position where it does not overlap with the positive electrode terminal portion 10. For example, a positive electrode lead 2 made of a band-shaped metal foil is connected to the positive electrode terminal section 10, and the positive electrode lead 2 and the positive electrode terminal section 10 constitute an external positive terminal. For example, the negative electrode lead 3 made of a strip-shaped metal foil is
1, the negative electrode lead 3 and the negative electrode terminal 11
Constitutes an external negative terminal.

As shown in FIG. 4, the return-type safety valve mechanism 12 is disposed on the inner surface of the exterior material 1 so as to face a space surrounded by external positive and negative terminals in the exterior material 1.
By forming the safety valve mechanism 12 at a position that does not face the power generating element and each external terminal in the exterior material, a short circuit between the safety valve mechanism and the positive and negative external terminals or the power generating element can be prevented. As shown in FIGS. 4 and 5, the safety valve mechanism 12 includes a first vent hole 13 opened in the exterior material 1, and a rectangular support plate 14 thermally fused to the inner surface of the exterior material 1. (For example, a metal such as SUS 304), a second gas vent hole 15 formed in the support plate 14 so as to communicate with the first gas vent hole 13, and a second gas vent hole 15 formed in the support plate 14. Second vent hole 1
5, a dish-shaped cover 16 (for example,
SUS 304), and a cylindrical elastic valve having a projection at the center and disposed between the recess of the cover 16 and the support plate 14 so as to close the second gas vent hole 15. It has a body 17 and one third gas vent hole 18 formed in a portion of the cover 16 connected from the concave portion to the edge. The elastic valve element 17 is disposed between the cover 16 and the support plate 14 in a compressed state.

In such a thin secondary battery,
When gas is generated in the exterior material 1 due to overcharging or the like and the internal pressure increases, the elastic valve body 17 is pressurized through the third gas vent hole 18, and the protrusion of the elastic valve body 17 becomes gas. The protrusions are pushed and deformed, and the protrusions are shifted laterally, so that a gap is generated between the elastic valve body 17 and the second gas vent hole 15. As a result, the gas in the exterior material 1 escapes to the outside through the third gas vent hole 18, the second gas vent hole 15, and the first gas vent hole 13, thereby preventing rupture. be able to.

It is preferable that the elastic valve is made of, for example, an elastic material having resistance to dissolution in an organic solvent.
Specifically, a fluorine-based elastomer (for example, Du P
perfluoroelastomer whose product name is KALREZ manufactured by Ont Corporation), silicone rubber, and the like.

It is preferable that the exterior material is formed of a multilayer film having a heat-fusible resin disposed on a sealing surface and a metal thin film such as aluminum (Al) interposed therebetween. Specifically, polyethylene (PE) / polyethylene terephthalate (PE) laminated from the sealing surface side to the outer surface
T) / Al foil / PET multilayer film; PE / Nylon / Al foil / PET multilayer film; Ionomer / Ni
A multilayer film of foil / PE / PET; a multilayer film of ethylene vinyl acetate (EVA) / PE / Al foil / PET; a multilayer film of ionomer / PET / Al foil / PET can be used. Here, P on the sealing surface side
Films other than E, ionomer, and EVA have moisture resistance, air resistance, and chemical resistance.

As the positive electrode, the negative electrode, and the electrolyte layer of the thin secondary battery, for example, those described below can be used. (Positive Electrode) This positive electrode is formed of a positive electrode layer containing a positive electrode active material, a non-aqueous electrolyte, and a polymer for holding the electrolyte, supported on a 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 preferably 0.2 mol / l to 2 mol / l. Examples of the polymer for holding the nonaqueous electrolyte include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative,
A copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) or 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 net-like current collector and the net-like terminal portion can be made of, for example, aluminum expanded metal, aluminum mesh, aluminum punched metal, or the like. The current collector and the terminal of the positive electrode may be formed of, for example, a metal foil such as an aluminum foil.

The positive electrode lead can be made of, for example, aluminum, nickel, or the like. The positive electrode may include a conductive material from the viewpoint of improving conductivity. As the conductive material, for example, artificial graphite,
Carbon black (eg, acetylene black),
Nickel powder and the like can be mentioned.

(Negative Electrode) The negative electrode is formed of a current collector in which a negative electrode layer containing a negative electrode active material, a non-aqueous electrolyte, and a polymer for holding the electrolyte is supported on a current collector.

Examples of the negative electrode active material include a carbonaceous material that stores and releases 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 net-like current collector and the net-like terminal portion can be formed of, for example, a copper expanded metal, a copper mesh, a copper punched metal, or the like. The current collector and the terminal of the negative electrode may be formed of a metal foil such as a copper foil.

The negative electrode lead can be formed of, for example, copper or nickel. In addition, the said negative electrode sheet is
It 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.

(Solid Polymer Electrolyte Layer) This electrolyte layer contains a non-aqueous electrolyte and a polymer for holding the electrolyte.

As the non-aqueous electrolyte and the polymer, the same ones as described for the positive electrode described above are used. From the viewpoint of further improving the strength, the electrolyte layer may include an inorganic filler such as silicon oxide powder.

As described above in detail, according to the thin secondary battery of the present invention, the safety valve mechanism is provided on the inner surface of the exterior material, and the safety valve mechanism is provided with the first opening formed in the exterior material.
A gas vent hole, a support plate thermally fused to the inner surface of the exterior material, a second gas vent hole formed in the support plate so as to communicate with the first gas vent hole, An elastic valve element disposed on the plate so as to close the second gas vent hole;
A cover fixed to the support plate so as to cover the elastic valve body; and a third gas vent hole opened in the cover. In such a secondary battery, when gas is generated in the exterior material due to overcharge or the like and the internal pressure increases, the elastic valve body is pressurized through the third gas vent hole, and the elastic valve body and the elastic valve body are pressurized. A gap is created between the second vent holes. As a result, the gas in the exterior material escapes to the outside through the third gas vent hole, the second gas vent hole, and the first gas vent hole, so that bursting can be prevented.

[0029]

Embodiments of 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.
Lithium manganese composite oxide represented by O ₄ , carbon black, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder, and dibutyl phthalate (DBP) A paste was prepared by mixing in dimethylformamide. 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, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder,
A plasticizer {dibutyl phthalate (DBP)} was mixed in NN-dimethylformamide to prepare a paste.
The obtained paste was applied on a polyethylene terephthalate film (PET film) and formed into a sheet to prepare a negative electrode sheet not impregnated with an electrolyte. 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, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder, and a plasticizer {dibutyl phthalate (DBP)} were mixed in acetone. Mix and make into a paste. The obtained paste was applied on a polyethylene terephthalate film (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 Laminated Electrode> Two positive electrodes, one negative electrode and two electrolyte layers were prepared. 2 above
One positive electrode and one negative electrode were alternately laminated with the electrolyte layer interposed therebetween, and these were heat-pressed with a rigid roll heated to 145 ° C. to produce a laminate. Five such laminates were produced. Each laminate was immersed in methanol, and the DBP in the laminate was extracted with methanol and removed. Each laminate is dried, and from these five laminates, the laminate thickness is 3.0 mm and the outer diameter is 52 × 78 m
m of laminated electrodes were produced. External positive terminals were formed by welding ten positive electrode terminal portions of the laminated electrode and a strip-shaped aluminum foil having a thickness of 0.05 mm as a positive electrode lead. Further, a strip-shaped copper foil having a thickness of 0.05 mm as a negative electrode lead was welded to the five negative electrode terminal portions of the laminated electrode to form external negative electrode terminals.

<Formation of Safety Valve Mechanism on Exterior Material> As the exterior material, a polyester film having a thickness of 12 μm, an aluminum foil having a thickness of 20 μm, a polyester film having a thickness of 12 μm, and a maleic anhydride modified with a thickness of 50 μm were used. A composite film in which a polypropylene film (heat-fusible resin film) was laminated in this order was prepared. A first gas vent hole having an inner diameter of 1 mm was formed in this film by punching from the heat-fusible resin film.

On the other hand, a return type safety valve having the structure described below was prepared. That is, the safety valve is a SUS 3 having a second vent hole having an inner diameter of 0.5 mm.
04 (5 mm long, 3 mm wide, 0.2 mm thick) and a SUS 304 dish-shaped fixed to the support plate so as to surround the second vent hole. Cover (depth of the recess is 0.65 mm and inner diameter of the recess is 1.8
mm, a thickness of 0.15 mm), a third vent hole having an inner diameter of 0.5 mm formed at a location leading from the recess of the cover to the edge, and a gap between the recess of the cover and the support plate. DuPo is disposed in a compressed state so as to close the second gas vent hole, and has a columnar shape having a protrusion at the top.
and an elastic valve made of perfluoroelastomer whose product name is KALREZ manufactured by nt. Next, the safety valve was arranged on the heat-fusible resin film side of the exterior material such that the second gas vent hole of the support plate and the first gas vent hole of the exterior material communicated with each other. Subsequently, a heating plate was applied from the polyester film side of the exterior material, and the safety valve was attached to the exterior material by heat sealing.

The obtained exterior film was folded in two so that the heat-fusible resin film was located inside, and covered with the laminated electrode. In this coating, the tips of the positive electrode lead and the negative electrode lead protrude from an opening edge perpendicular to the longitudinal direction of the film, and a safety valve fixed to the inner surface of the outer film is surrounded by positive and negative external terminals in the outer film. It was carried out so as to face the separated space. Next, the edge of the opening from which the positive and negative electrode leads extend was heat-sealed with a width of 5 mm, and one of the remaining opening edges (opening edge along the longitudinal direction) was heat-sealed with a width of 5 mm. After the nonaqueous electrolyte having the above composition was injected from the other opening edge, the opening edge was thermally fused with a width of 5 mm to seal the laminated electrode in the exterior film and have a thickness of 3 mm. Thirty thin polymer electrolyte secondary batteries having a size of 0.5 mm and an outer diameter of 55 × 90 mm excluding the lead portion were manufactured.

Each of the obtained secondary batteries has a battery storage space of 57 × 92 × 4.2 mm and an outer dimension of 58 × 93 ×
The battery was housed in a 6.0 mm polypropylene case with external connection terminals to form a battery pack. (Comparative Example) Thirty thin polymer electrolyte secondary batteries were manufactured in the same manner as in the Example except that a safety valve was not provided on the inner surface of the exterior film. Each of the obtained secondary batteries was housed in a polypropylene case with external connection terminals similar to the example,
It was a pack type battery.

With respect to the battery packs of Examples and Comparative Examples,
Conducted overcharge test to charge for 3 hours at 2C, 15V,
Measure the number of valve operations and the thickness of the battery pack after the overcharge test,
The results are shown in Table 1 below.

Table 1 Thickness of pack after overcharge test (average of 30 pieces) Number of valve operations Example 6.0 mm 30 pieces Comparative example 8.6 mm No safety valve As is apparent from Table 1, the secondary battery of the example is clear. Indicates that the thickness of the pack is not deformed after overcharging, and the safety valve was activated immediately after the internal pressure was increased. On the other hand, it can be seen that, in the secondary battery of the comparative example, at the time of overcharging, the film expands to such an extent that the pack is deformed and then bursts.

[0040]

As described above in detail, according to the present invention, it is possible to provide a thin secondary battery in which rupture at the time of overcharge is avoided and safety is improved.

[Brief description of the drawings]

FIG. 1 is a plan view showing a thin secondary battery according to the present invention.

FIG. 2 is a perspective view showing a state in which a fused portion along a longitudinal direction of the thin secondary battery according to the present invention is folded back on the upper surface.

FIG. 3 is a cross-sectional view showing a power generation element included in the secondary batteries of FIGS. 1 and 2.

FIG. 4 is a sectional view showing a main part of the secondary battery of FIGS. 1 and 2;

FIG. 5 is a plan view showing the safety valve mechanism of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exterior material, 2 ... Positive electrode lead, 4 ... Fusion part, 10 ... Positive electrode terminal part, 12 ... Safety valve mechanism, 13 ... First gas vent hole, 14 ... Support plate, 15 ... Second gas vent hole, 16: cover, 17: elastic valve element, 18: third gas vent hole.

Claims (2)

[Claims] 1. A thin power generation 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, and external terminals electrically connected to the positive and negative electrodes, respectively. The thin secondary battery is housed so as to extend from an opening edge of the battery, and the heat-fusible resin films are heat-sealed to each other at the opening edge to seal the power generation element in the exterior material. A safety valve mechanism is provided on the inner surface of the exterior material, the safety valve mechanism includes a first gas vent hole opened in the exterior material, and a support plate thermally fused to the inner surface of the exterior material,
A second gas vent hole formed in the support plate so as to communicate with the first gas vent hole, and an elastic valve element disposed in the support plate so as to close the second gas vent hole; A cover fixed to the support plate so as to cover the elastic valve body,
And a third gas vent hole opened in the cover. 2. The thin secondary battery according to claim 1, wherein the safety valve mechanism is disposed at a position in the exterior material that does not face the power generation element and the external terminals.