JP2000294202A - Thin battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin battery capable of being thinned while using a metallic case superior in mechanical strength as exterior material. SOLUTION: In a thin battery comprising a box-shaped metallic case 1, a generating element accommodated in the case 1, and a metallic cover body 7, mounted on an opening of the case, the case has a structure that a projected area of a bottom surface is larger than a projected area of each side surface. An opening end of the case 1 is outwardly folded, and the cover body is fixed to the folded part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin battery having an improved container.

[0002]

2. Description of the Related Art In recent years, portable information devices such as portable telephones and portable personal computers have become widespread, and there has been a demand for lighter and thinner secondary batteries.

In a lithium ion secondary battery, which is an example of a secondary battery, a separator is interposed between a metal container and a positive electrode and a negative electrode which are contained in the container and contain an active material for absorbing and releasing lithium ions. An electrode group having a structure, and a non-aqueous electrolyte accommodated in the container are provided. As shown in FIG. 7, as the container 21, a container having a bottomed rectangular cylindrical shape is known. Such a container is formed of, for example, an aluminum alloy.

In order to reduce the thickness of a lithium ion secondary battery using such a container, it is necessary to reduce the width of the container perpendicular to the longitudinal direction. Since the container is formed by drawing, the width perpendicular to the longitudinal direction is set to, for example, 5
If the thickness is reduced to not more than mm, there is a problem that the container is cracked during drawing.

[0005] A thin secondary battery in which a power generation element is housed in a laminated film having a multilayer structure composed of a resin layer and a metal layer is also known. According to such a secondary battery,
The thickness of the battery can be reduced to 5 mm or less. However, this thin secondary battery causes inconveniences such as the laminate film swelling and deforming when gas is generated from the power generation element due to, for example, overcharging, and the electronic device is damaged or cannot enter the electronic device. In addition, there is a problem that handling at the time of manufacturing is difficult due to low shape reproducibility and stability.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin battery which can be made thin while using a metal container having excellent mechanical strength as an exterior material.

[0007]

According to the present invention, there is provided a thin-type container having a box-shaped metal container, a power generation element housed in the container, and a metal lid disposed at an opening of the container. In the battery, the container has a structure in which the projected area of the bottom surface is larger than the projected area of each side surface.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first thin battery (for example, a thin lithium ion secondary battery) according to the present invention will be described with reference to FIGS.

FIG. 1 is a perspective view showing an example of a thin battery according to the present invention, and FIG. 2 is a cross-sectional view of the thin battery of FIG. 1 taken along the line AA.

A metal container 1 having a box-shaped structure in which the projected area of the bottom surface is larger than the projected area of each side surface has an open end bent outward and a bent portion 2. Electrode group 3
Is manufactured by spirally winding the positive electrode 4 and the negative electrode 5 therebetween with the separator 6 interposed therebetween, and then crushing the flat shape. The electrode group may be manufactured by stacking a plurality of strip-shaped electrode units in which a separator is interposed between a positive electrode and a negative electrode. The electrode group 3 is accommodated in the container 1 such that the lamination direction is parallel to the longitudinal direction of the container 1. The non-aqueous electrolyte is contained in the container 1. A lid 7 made of a metal rectangular plate having two rectangular openings is fixed to the bent portion 2 of the container 1 by welding or an adhesive having non-aqueous electrolyte resistance and environmental resistance such as temperature. I have. The prismatic positive electrode terminal 8 is fixed to one opening of the lid 7 with a hermetic seal 9 with upper and lower end surfaces protruding from the lid 7. The prismatic negative electrode terminal 10 is fixed to the other opening of the lid 7 with a hermetic seal 11 with upper and lower end surfaces protruding from the lid 7. The positive electrode 4 and the positive electrode terminal 8 are electrically connected by a lead (not shown). The negative electrode 5 and the negative terminal 10 are
They are electrically connected by leads (not shown).

Hereinafter, the container 1, the positive electrode 4, the negative electrode 5, the separator 6, and the non-aqueous electrolyte will be described.

1) Container 1 This container 1 is box-shaped, the projected area of the bottom surface is larger than the projected area of each side surface, and the opening end is bent outward.

The container 1 is made of metal. Such a metal may be selected in consideration of strength, shape reproducibility / stability, corrosiveness and solvent resistance, for example, iron, stainless steel,
Titanium, aluminum, an aluminum alloy, iron having a surface plated with nickel, a clad metal, and the like can be given. Considering lightness, workability and economy,
Among them, aluminum or aluminum alloy is preferable.

The thickness of the container 1 is 0.2 to 0.5 mm
It is desirable to be within the range.

The width of the bent portion 2 is desirably as small as possible within a range in which the sealing property can be ensured in view of the volume energy density, and is desirably about 1 mm or less.

2) Positive Electrode 4 The positive electrode 4 contains an active material that stores and releases lithium ions.

The positive electrode 4 is prepared, for example, by kneading an active material for absorbing and releasing lithium ions, a conductive agent and a binder in the presence of an organic solvent to prepare a paste, and applying the paste to a current collector. After drying and drying, it is produced by pressing.

[0018] As the positive electrode active material, various oxides (e.g., lithium manganese composite oxides such as LiMn ₂ O _4, manganese dioxide, for example, lithium-containing nickel oxides such as LiNiO _2, for example, lithium-containing cobalt such as LiCoO ₂ Oxide, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide and the like, and chalcogen compounds (for example, titanium disulfide and molybdenum disulfide). The positive electrode active materials may be used alone or in combination of two or more. Among them, lithium manganese composite oxide,
It is preferable to use lithium-containing cobalt oxide and lithium-containing nickel oxide.

Examples of the conductive agent include carbon black.

Examples of the binder include polyvinylidene fluoride (PVdF).

Examples of the organic solvent include N-methyl 2-pyrrolidone (NWP).

As the current collector, for example, a metal foil such as an aluminum foil can be used.

3) Negative Electrode 5 The negative electrode 5 contains an active material that stores and releases lithium ions.

For the negative electrode 5, for example, a paste is prepared by kneading an active material that absorbs and releases lithium ions, a conductive agent and a binder in the presence of an organic solvent, and the paste is applied to a current collector. After drying and drying, it is produced by pressing.

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. The negative electrode active materials may be used alone or as a mixture of two or more. Among them, it is preferable to use a carbonaceous material obtained by firing the mesophase pitch at a temperature of 500 ° C. to 3000 ° C. in an inert gas atmosphere such as an argon gas or a nitrogen gas under normal pressure or reduced pressure.

Examples of the conductive agent, the binder and the organic solvent include the same ones as described for the positive electrode.

As the current collector, for example, a metal foil such as a copper foil can be used.

4) Separator 6 As the separator 6, for example, a porous film made of a synthetic resin such as a microporous polypropylene film can be used.

5) Non-aqueous electrolyte The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and dimethyl carbonate (D
MC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-
BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. 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), boric tetrafluoride lithium (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium salts such as lithium trifluoromethane sulfonate (LiCF ₃ SO ₃₎ may be mentioned. The electrolytes may be used alone or as a mixture of two or more.

According to the first thin battery of the present invention described in detail above, the metal container for storing the power generating element is box-shaped, and the projected area of the bottom surface is larger than the projected area of each side surface. In order to reduce the battery thickness to 5 mm or less, the height of the container is reduced instead of the width orthogonal to the longitudinal direction of the container. Therefore, it is possible to avoid the occurrence of cracks in the container during the deep drawing, so that the thickness of the battery can be reduced to 1 to 5 mm. By the way, if the open end of the container is not bent, the lid is placed on the open end of the container, and the boundary between the container and the lid is welded. There is a risk of poor welding. By bending the open end of the container outward as in the present invention and fixing the lower surface of the lid to the bent portion, the container can be formed without employing the method of welding the boundary between the container and the lid described above. Since the battery can be sealed, a thin battery with excellent airtightness can be realized.

The second thin battery according to the present invention (for example,
A thin lithium ion secondary battery will be described with reference to FIG.

FIG. 3 is a sectional view showing a thin battery according to the present invention. 1 to 1 in the first thin battery described above.
2 are given the same reference numerals.

The metal container 12 having a box-shaped structure in which the projected area of the bottom surface is larger than the projected area of each side surface has an open end bent inward and a bent portion 13. The electrode group 3 is produced by spirally winding the positive electrode 4 and the negative electrode 5 with a separator 6 interposed therebetween, and then crushing the spirally flat shape. The electrode group 3 is housed in the container 12 such that the laminating direction is parallel to the longitudinal direction of the container 12. The non-aqueous electrolyte is contained in the container 12. The lid 7 made of a metal rectangular plate having two rectangular openings is fixed to the bent portion 13 of the container 12 with an adhesive having non-aqueous electrolyte resistance and environmental resistance such as temperature. The prismatic positive electrode terminal 8 is fixed to one opening of the lid 7 with a hermetic seal 9 with upper and lower end surfaces protruding from the lid 7. A prismatic negative electrode terminal (not shown) is fixed to the other opening of the lid 7 with hermetic seals with upper and lower end surfaces protruding from the lid 7. The positive electrode 4 and the positive electrode terminal 8 are electrically connected by a lead (not shown). The negative electrode 5 and the negative electrode terminal are electrically connected by a lead (not shown).

The positive electrode 4, the negative electrode 5, the separator 6, and the non-aqueous electrolyte may be the same as those described in the first thin battery.

The container 12 is made of metal. Examples of such a metal include those similar to those described in the first thin battery.

The thickness of the container 12 is 0.2 to 0.5 m
m is desirable.

It is preferable that the width of the bent portion 13 be 2 mm or more and a size that does not impair the weight energy density. If the width is less than 2 mm, the hermeticity of the lid of the container may be reduced.

According to the second thin battery of the present invention described in detail above, the metal container for storing the power generating element is box-shaped, and the projected area of the bottom surface is larger than the projected area of each side surface. To reduce the battery thickness to 5 mm or less, the height of the container must be reduced. Therefore, it is possible to avoid the occurrence of cracks in the container during the deep drawing, so that the thickness of the battery can be reduced to 1 to 5 mm. Further, by bending the open end of the container inward and fixing the lower surface of the lid to the bent portion, the container can be sealed without employing a method of welding a boundary between the container and the lid. Therefore, a thin battery having excellent airtightness can be realized.

The third thin battery according to the present invention (for example,
The thin lithium ion secondary battery will be described with reference to FIG.

FIG. 4 is a sectional view showing a thin battery according to the present invention. 1 to 1 in the first thin battery described above.
2 are given the same reference numerals.

The electrode group 3 is housed in a metal container 14 having a box-shaped structure in which the projected area of the bottom surface is larger than the projected area of each side surface. The electrode group 3 includes a positive electrode 4 and a negative electrode 5
Is spirally wound through the separator 6 therebetween, and then crushed into a flat shape. The electrode group 3 is housed in the container 14 so that the laminating direction is parallel to the longitudinal direction of the container 14. The non-aqueous electrolyte is contained in the container 14. The lid 15 made of a metal rectangular plate whose periphery is bent downward has two rectangular openings. The lid 15 has a bent portion 16
Is fixed to the surface of the container 14 by welding or an adhesive having non-aqueous electrolyte resistance and environmental resistance such as temperature. The bent portion 16 is formed by, for example, bending or drawing. The prismatic positive electrode terminal 8 is fixed to one opening of the lid 15 with a hermetic seal 9 with upper and lower end surfaces protruding from the lid 15. A prismatic negative electrode terminal (not shown) is fixed to the other opening of the lid 15 with a hermetic seal with upper and lower end surfaces protruding from the lid 15. The positive electrode 4 and the positive electrode terminal 8 are electrically connected by a lead (not shown). The negative electrode 5 and the negative electrode terminal are electrically connected by a lead (not shown).

As the positive electrode 4, the negative electrode 5, the separator 6, and the non-aqueous electrolyte, those similar to those described in the first thin battery can be used.

The container 14 is made of metal. Examples of such a metal include those similar to those described in the first thin battery.

The thickness of the container 14 is 0.2 to 0.5 m
m is desirable.

The width of the bent portion 16 is 2 mm or more,
It is preferable to set the height within the range of the height of the container 14. This is due to the following reasons. If the width is less than 2 mm, the hermeticity of the lid of the container may be reduced.

According to the third thin battery of the present invention described in detail above, the metal container for storing the power generating element is box-shaped, and the projected area of the bottom surface is larger than the projected area of each side surface. To reduce the battery thickness to 5 mm or less, the height of the container must be reduced. Therefore, it is possible to avoid the occurrence of cracks in the container during the deep drawing, so that the thickness of the battery can be reduced to 1 to 5 mm. Further, the container can be hermetically sealed without bending the edge of the lid by fixing the bent portion to the side surface of the container by welding the boundary between the container and the lid. Thus, a thin battery having excellent airtightness can be realized.

It should be noted that, in FIG.
Although the inner surface of the bent portion 16 is fixed to the surface of the container 14, it may be fixed to the inner surface of the container 14.

The lower end of the bent portion 16 of the lid 15 may be deformed in a wavy manner so that the container 14 and the lid 15 are engaged with each other.

Although the rectangular plate-like lid 7 is used in FIG. 2 described above, a lid 17 having a structure in which the vicinity of the center protrudes upward as shown in FIG. 5, for example, may be used. The inner surface of the lid 17 at the periphery of the projecting portion 18 is fixed to the bent portion 2 of the container 1. In FIG. 5, the same members as those in FIGS. 1 and 2 in the first thin battery described above are denoted by the same reference numerals. Also in FIG. 3, a lid having a structure in which the vicinity of the center protrudes upward can be used instead of the rectangular plate-shaped lid.

In FIGS. 1 and 2 described above, the positive and negative terminals are formed on the upper surface of the lid. However, for example, as shown in FIG. good. In FIG. 6, the same members as those in FIGS. 1 and 2 in the first thin battery described above are denoted by the same reference numerals. Also,
Only the positive terminal may be formed on the side surface of the container, and the container itself may be used as the negative terminal. Further, in FIGS. 2 to 4, the positive and negative terminals can be formed on the side of the container, or only the positive terminal can be formed on the side of the container, and the container itself can be used as the negative terminal.

In FIGS. 1 to 6 described above, an example in which the present invention is applied to a lithium ion secondary battery has been described. However, the present invention is applied to a primary battery such as an alkaline battery or an air battery, a nickel hydrogen secondary battery or a nickel cadmium secondary battery. The present invention can be similarly applied to an alkaline secondary battery and a polymer lithium secondary battery. Since a lighter and higher capacity battery can be obtained, it is preferable to apply the present invention to a lithium ion secondary battery and a polymer lithium secondary battery.

As the power generating element of the polymer lithium secondary battery, those described below can be used.

This power generation element stores and stores lithium ions.
A positive electrode having a structure in which a positive electrode layer containing an active material to be released, a non-aqueous electrolyte solution, and a polymer holding the electrolyte solution is supported on a positive electrode current collector; an active material to occlude and release lithium ions; A negative electrode having a structure in which a negative electrode layer containing a polymer holding the electrolytic solution is supported on a negative electrode current collector, a nonaqueous electrolytic solution disposed between the positive and negative electrodes, and an electrolyte layer containing a polymer holding the electrolytic solution And

(Positive Electrode) Examples of the positive electrode active material include those similar to those described in the aforementioned thin lithium ion secondary battery. 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 and the electrolyte, those similar to those described in the aforementioned thin lithium ion secondary battery can be used.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l.

The polymer desirably has a binding function in addition to the function of holding the non-aqueous electrolyte. Examples of such a polymer include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative, a polytetrafluoropropylene, a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), and a polyvinylidene fluoride ( PVdF) or the like can be used. The polymers may be used alone or in combination of two or more. Among them, a VdF-HFP copolymer is preferred.

The positive electrode 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. The conductive materials may be used alone or in combination of two or more.

As the positive electrode current collector, for example, a porous substrate such as a metal plate, a mesh, an expanded metal or a punched metal can be used. The current collector may be formed of aluminum or an aluminum alloy.

(Negative Electrode) Examples of the negative electrode active material include carbonaceous materials that occlude and release lithium ions. Examples of such a carbonaceous material include those similar to those described for the thin lithium ion secondary battery described above. Above all, in an inert gas atmosphere such as argon gas or nitrogen gas, 500 ° C. to 3000 ° C.
It is preferable to use a carbonaceous material obtained by firing the mesophase pitch at a temperature of ° C. under normal pressure or reduced pressure.

As the non-aqueous electrolyte, the same one as described for the positive electrode described above is used.

The polymer desirably has a binding function in addition to the function of holding the non-aqueous electrolyte. As such a polymer, the same type of polymer as that described for the above-described positive electrode can be used.
HFP copolymers are preferred.

As the negative electrode current collector, for example, a metal plate, a mesh, a porous substrate such as an expanded metal or a punched metal, or the like can be used. The current collector may be formed of copper or a copper alloy.

(Electrolyte Layer) As the non-aqueous electrolyte, the same one as described in the above-mentioned positive electrode is used.

It is desirable that the polymer has a binding function in addition to the function of holding the non-aqueous electrolyte. As such a polymer, the same type of polymer as that described for the above-described positive electrode can be used.
HFP copolymers are preferred.

From the viewpoint of further improving the strength, an organic filler or an inorganic filler such as silicon oxide powder may be added to the electrolyte layer.

Note that a separator may be used instead of the electrolyte layer. Examples of the separator include a porous film made of a synthetic resin. Examples of the synthetic resin include polyolefins such as polypropylene and polyethylene. The synthetic resins may be used alone or as a mixture of two or more.

[0071]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Positive Electrode> A lithium cobalt composite oxide having a composition formula of LiCoO ₂ 90% by weight, carbon black 5% by weight, and polyvinylidene fluoride (PVdF) 5
% By weight was added to N-methyl 2-pyrrolidone (NMP) and kneaded to prepare a paste. The paste was applied to an aluminum foil by die coating so as to have a width of 50 mm, dried, and then roll-pressed to produce a positive electrode.

<Preparation of Negative Electrode> After the mesophase pitch-based carbon fiber was pulverized, a heat treatment was performed at 2800 ° C. to obtain a negative electrode active material. 90% by weight of the negative electrode active material, 5% by weight of carbon black, and polyvinylidene fluoride (P
VdF) and 5% by weight of N-methyl 2-pyrrolidone (NM
P) and kneaded to prepare a paste. The paste was applied to an aluminum foil by die coating so as to have a width of 52 mm, dried, and then roll-pressed to produce a negative electrode.

A separator made of a microporous polypropylene film having a width of 53 mm (trade name: Celgard 2400) is interposed between the positive electrode and the negative electrode, spirally wound, and then flattened. To prepare an electrode group.

On the other hand, ethylene carbonate (EC) and γ
-LiPF ₆ is used as an electrolyte in a non-aqueous solvent in which butyrolactone is mixed at a volume ratio of 1: 2, and the concentration thereof is 1 mo.
1 / l to prepare a non-aqueous electrolyte.

An aluminum plate having a thickness of 0.3 mm was drawn so as to have an inner size of 35 mm in width, 60 mm in length and 3 mm in height, and the opening end of the obtained container was turned outward. Folded and the thickness of 15 μm on the inner surface of the container
Nickel plating. The size of the opening of the obtained container is 35 mm in width and 60 mm in length. Also,
The width of the bent portion is 1 mm. In addition, a lid made of a metal rectangular plate having positive and negative terminals fixed to two rectangular openings by hermetic seal was prepared. The lid has a thickness of 0.3 mm. The lid is made of aluminum, and has a lower surface plated with nickel having a thickness of 15 μm.

After storing the electrode group in the container, a non-aqueous electrolyte having the above composition was injected. The lid is disposed on the bent portion of the container such that the surface of the lid plated with nickel is in contact with the container, and the lower edge of the lid is fixed to the bent portion of the container by laser welding. ~
A thin lithium ion secondary battery having the structure shown in FIG. 2 and having a thickness of 3.6 mm was assembled.

(Example 2) An aluminum plate having a thickness of 0.3 mm was subjected to drawing so as to have an inner size of 35 mm in width, 60 mm in length and 3 mm in height. The end was bent inward, and the inner surface of the container was plated with nickel having a thickness of 15 μm. The size of the opening of the obtained container is 35 mm in width and 60 mm in length. The width of the bent portion is 1 mm.

After the same electrode group as described in Example 1 was accommodated in the container, a non-aqueous electrolyte having the same composition as that described in Example 1 was injected. After applying an acid-modified polyolefin as an adhesive to the bent portion of the container, a lid similar to that described in Example 1 described above was arranged so that the nickel-plated surface was in contact with the container, The lower surface periphery of the lid was fixed to the bent portion of the container, and a thin lithium ion secondary battery having the structure shown in FIG. 3 described above and having a thickness of 3.6 mm was assembled.

(Example 3) An aluminum plate having a thickness of 0.3 mm was subjected to drawing so as to have an inner size of 35 mm in width, 60 mm in length and 3 mm in height, and then the inner surface of the obtained container. Was plated with nickel having a thickness of 15 μm. The size of the opening of the obtained container is 35 mm in width and 60 mm in length. In addition, a lid made of a metal rectangular plate whose peripheral edge was bent downward was prepared. The lid has two rectangular openings, and positive and negative terminals are fixed to these openings by hermetic seals. The lid has a thickness of 0.3 mm and a width of the bent portion of 2.5 mm. The lid is made of aluminum and has a lower surface plated with nickel having a thickness of 15 μm.

After the same electrode group as described in the first embodiment was accommodated in the container, a non-aqueous electrolyte having the same composition as that described in the first embodiment was injected. At the opening end of the container, the lid was disposed such that the surface subjected to nickel plating was in contact with the container, and the bent portion of the lid was fixed to the surface of the container by laser welding. A thin lithium ion secondary battery having the structure shown and having a thickness of 3.6 mm was assembled.

(Embodiment 4) An electrode group similar to that described in the first embodiment is housed in a container similar to that described in the third embodiment, and then described in the first embodiment. A non-aqueous electrolyte having the same composition as that of the above was injected. A lid similar to that described in the first embodiment is disposed at the open end of the container such that the nickel-plated surface is in contact with the container, and the lid is placed at the open end of the container. Then, a laser beam was applied to the boundary between the lid and the lid to perform welding, thereby assembling a thin lithium ion secondary battery having a thickness of 3.6 mm.

(Comparative Example 1) An aluminum plate having a thickness of 0.3 mm was formed with an opening having a size of 35 × 3 mm and a depth of 60 mm.
When it was drawn to a thickness of 0.2 mm, a crack was formed because it could not be drawn. Therefore, a thin lithium ion secondary battery could not be assembled.

Comparative Example 2 A laminate film mainly composed of a polypropylene film and an aluminum foil was prepared. A thin lithium ion secondary battery having a thickness of 3.6 mm was assembled by sealing the same electrode group and non-aqueous electrolyte solution as described in Example 1 by heat-sealing the laminate film.

The obtained secondary batteries of Examples 1 to 4 and Comparative Example 2 were subjected to a charge / discharge cycle of charging to 4.2 V at a constant current of 500 mA and then discharging to 3 V at a constant current of 500 mA. At this time, the capacity retention ratio at the 300th cycle relative to the discharge capacity at the first cycle was measured, and the results are shown in Table 1 below.

[0086]

[Table 1]

As is evident from Table 1, the secondary batteries of Examples 1 to 4 having a box-shaped metal container having a structure in which the projected area of the bottom surface is larger than the projected area of each side surface as the exterior material are as follows. It can be seen that the capacity maintenance ratio at the 300th cycle is high. On the other hand, in the secondary battery of Comparative Example 2 including the laminate film as the exterior material, the laminate film swelled by 3 mm due to the gas generated with the progress of the charge / discharge cycle, and could not be used midway.

[0088]

As described above in detail, according to the present invention, it is possible to provide a thin battery capable of preventing deformation of a container due to gas generation or the like and achieving a reduction in thickness.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a thin battery according to the present invention.

FIG. 2 is a sectional view of the thin battery of FIG. 1 taken along the line AA.

FIG. 3 is a sectional view showing another thin battery according to the present invention.

FIG. 4 is a sectional view showing still another thin battery according to the present invention.

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

FIG. 6 is a perspective view showing still another thin battery according to the present invention.

FIG. 7 is a perspective view showing a container used for a conventional prismatic lithium ion secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Bending part, 7 ... Lid, 8 ... Positive electrode terminal, 10 ... Negative electrode terminal.

Claims (5)

[Claims] 1. A thin battery comprising a box-shaped metal container, a power generation element housed in the container, and a metal lid disposed at an opening of the container, wherein the container has a bottom surface Characterized by having a structure in which the projected area is larger than the projected area of each side surface. 2. The thin battery according to claim 1, wherein an opening end of the container is bent outward, and the lid is fixed to the bent portion. 3. The thin battery according to claim 1, wherein an opening end of the container is bent inward, and the lid is fixed to the bent portion. 4. The thin battery according to claim 1, wherein a peripheral edge of the lid is bent downward, and the bent portion is fixed to a side surface of the container. 5. The thin battery according to claim 1, wherein the container and the lid are made of aluminum or an aluminum alloy.