JP2000156242A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery which is easy to connect to the outside, and excellent in strength and of which airtightness and volume capacity are never deteriorated by extracting a lead formed of metal foil outside from a thermally fused part of a battery case, and by applying an insulation treatment between the lead formed of metal foil and the end face of a metal film layer constituting the battery case. SOLUTION: This secondary battery is composed by storing it in a case formed of a layered film comprising a thermally-fusible high-polymer film layer and a metal film layer 5b. An insulation treatment is applied between metal foil extracted as a lead toward the outside from the thermally-fused part of the case and the end face of the metal film layer 5b of the case. In the insulation treatment, the insulation treatment is performed not only to the end face of the metal film layer 5b but also to the end faces of all the layers of the layered film layer. The insulation treatment for the end face of the metal film layer 5b may be performed to any metal films before and after the formation of the layered film. An insulating paint or various kinds of high-polymer materials can be used as insulating materials A1 and A2 used in the insulation treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a thin lithium secondary battery using a gel electrolyte or a solid electrolyte.

[0002]

2. Description of the Related Art A conventional liquid lithium secondary battery, that is, a battery composed of a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte mainly composed of a lithium salt and a non-aqueous solvent, is a conventional type. It has a structure in which the laminated body of the positive electrode, the separator, and the negative electrode thus taken is housed in a metal can. Usually, the positive electrode is electrically connected to the metal can by a lead such as a nickel wire, so that the metal can forms a positive electrode of the battery. Further, the negative electrode is connected to the metal portion provided on the lid portion of the metal can insulated from the positive electrode by a lead, so that the metal portion forms a negative electrode of the battery. That is, in a conventional liquid lithium secondary battery, a metal can as a container forms an external terminal.

[0003] In recent years, since there is a possibility that the thickness of the positive electrode and the negative electrode can be further reduced as compared with the above-mentioned liquid type battery, a positive electrode and a negative electrode are laminated in a flat plate with an electrolyte layer interposed therebetween. Attention has been focused on a lithium secondary battery housed in a case made of a laminated film having good airtightness (particularly gas barrier properties) including a layer and a metal film layer. However, in order to realize a thin battery, it is necessary to develop a lead (and also an external terminal) for extracting electric power to the outside. However, a lead for a non-liquid secondary battery that does not use a metal can is still insufficient. No proposals have been made.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flat and thin lithium secondary battery using an electrolyte layer having no problem such as liquid leakage. Another object of the present invention is to provide a lithium secondary battery provided with a lead that is easily connected to the outside such as a charge / discharge control circuit, has excellent strength, and does not impair airtightness and volume capacity.

[0005]

As a result of intensive studies, the present inventor has found that in the case of a laminated film including a heat-fusible polymer film layer and a metal film layer, a specific means is used as a lead. It has been found that the above object can be easily achieved if the metal foil is provided skillfully.

The present invention has been completed based on the above findings. The gist of the present invention is that a positive electrode and a negative electrode are laminated in a flat plate with an electrolyte layer interposed therebetween, and a heat-fusible polymer film layer and a metal film are formed. A lithium secondary battery housed in a case made of a laminated film including a layer, comprising a metal foil as a lead taken out from a heat-sealed portion of the case, and an end face of the metal foil and the metal film layer And an insulating means is provided between the lithium secondary battery and the battery.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, for convenience of description, a unit battery element including a positive electrode, a negative electrode, and an electrolyte layer in the lithium secondary battery of the present invention will be described.

[0008] The lithium secondary battery of the present invention is basically the same as a conventionally known battery, and is configured by laminating a positive electrode and a negative electrode via an electrolyte layer. The positive electrode and / or the negative electrode are formed on a current collector as an active material-containing layer capable of inserting and extracting lithium ions. Then, any one of the above electrodes (usually a negative electrode) can be made of a metal itself such as a lithium foil.

As the current collector, a metal foil such as an aluminum foil or a copper foil is usually used, and its thickness is appropriately selected.
Usually, it is 1 to 50 μm, preferably 1 to 30 μm. If the thickness of the current collector is too thin, the mechanical strength will be weak,
If it becomes a problem in production and is too thick, the capacity of the battery as a whole decreases. The current collector is preferably used after being subjected to a roughening treatment in advance in order to increase the adhesive strength of the active material-containing layer. As a roughening method, a mechanical polishing method, an electrolytic polishing method,
Chemical polishing method and the like can be mentioned. In the mechanical polishing method, a polishing cloth paper having abrasive particles fixed thereon, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like is used.
Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and the conductivity of the active material-containing layer.

A positive electrode active material capable of inserting and extracting lithium ions is roughly classified into an inorganic compound and an organic compound.

As the positive electrode active material composed of an inorganic compound,
Transition metal oxides, composite oxides of lithium and transition metals,
Transition metal sulfide and the like. As the above transition metal, Fe, Co, Ni, Mn and the like are used. Specific examples of the inorganic compound used for the positive electrode active material include Mn
Transition metal oxides such as O, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ ; composite oxides of lithium and transition metals such as lithium nickelate, lithium cobaltate and lithium manganate; TiS
₂ , transition metal sulfides such as FeS and MoS ₂ .
These compounds may be partially elementally substituted in order to improve their properties.

As the positive electrode active material composed of an organic compound,
For example, polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts and the like can be mentioned.

[0013] The positive electrode active material may be a mixture of the above-mentioned inorganic compound and organic compound. The particle size of the positive electrode active material is appropriately selected in consideration of other components of the battery, but is usually 1 to 30 μm, preferably 1 to 30 μm, from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics. It is 10 μm.

Examples of the negative electrode active material capable of inserting and extracting lithium ions include carbon-based active materials such as graphite and coke. Such carbon-based active materials include metals, metal salts,
It can also be used in the form of a mixture with an oxide or a coating. Examples of the negative electrode active material include oxides and sulfates such as silicon, tin, zinc, manganese, iron, and nickel, lithium metal, Li-Al, Li-Bi-Cd, and Li-Sn.
Lithium alloys such as -Cd, lithium transition metal nitrides, silicon and the like can also be used. The particle size of the negative electrode active material is appropriately selected in consideration of other components of the battery, but is usually 1 to 50 μm, preferably 1 to 50 μm, from the viewpoint of improving battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics. Is 15-30μ
m.

In order to bind the active material on the current collector, a binder may be used for the positive electrode and the negative electrode. Examples of the binder include inorganic compounds such as silicate and glass, and various resins.

Examples of the binder resin include alkane-based polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, polyvinylpyridine and the like. Poly
Polymers having a ring such as N-vinylpyrrolidone, acrylics such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, etc. Polymers, fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; and polyvinyl chloride And halogen-containing polymers such as polyvinylidene chloride, and conductive polymers such as polyaniline. Further, a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer or the like of the above-mentioned polymers can be used. The molecular weight of these resins is usually 10,000 to 300
0000, preferably 100,000 to 1,000,000
It is said. If the molecular weight is too low, the strength of the coating film will decrease, and if it is too high, the viscosity will increase and it will be difficult to form an electrode.

[0017] The electrode may optionally contain additives exhibiting various functions such as a conductive material and a reinforcing material. The conductive material is not particularly limited as long as it is capable of imparting conductivity by being mixed in an appropriate amount with the active material, and usually includes acetylene black, carbon black, carbon powder such as graphite, and various metal fibers and foils. . In addition, to increase the stability and life of the battery, trifluoropropylene carbonate, vinylene carbonate,
1,6-Dioxaspiro [4,4] nonane-2,7-dione, 12-crown
-4-ether and the like can be used. Further, as the reinforcing material, various inorganic and organic fillers such as spherical, plate-like, rod-like, and fiber-like fillers can be used.

As a method of forming the electrodes, for example, (1)
An active material, an electrolytic solution, a coating for an electrode containing a polymer and / or a precursor thereof are prepared, and this is applied on a current collector,
A method of performing a heat treatment or the like as needed, and (2) a method of impregnating the voids with the electrolyte component after forming the active material layer having the voids may be mentioned.

In the above method (2), the active material layer having voids is preferably formed, for example, by applying an electrode coating material containing an active material, a binder and a solvent on a current collector and drying. You can do it. In this case, the compounding amount of the binder with respect to 100 parts by weight of the active material is usually 0.1.
It is 1 to 30 parts by weight, preferably 1 to 20 parts by weight.
If the blending amount of the binder is too small, the strength of the electrode decreases, and if too large, the void amount in the active material-containing layer decreases, and it becomes difficult to impregnate an electrolyte for forming a gel electrolyte described below. . The type of solvent used for preparing the electrode coating material is not particularly limited as long as it is inert to the active material and can dissolve the binder, and may be any of inorganic and organic solvents. One example of a suitable solvent is N
-Methylpyrrolidone. In addition, a ball mill, a sand mill, a twin-screw kneader, or the like is used for preparing the electrode coating material.

The active material layer having voids can also be formed by a method in which a mixture of an active material and a binder is softened by heating and is pressed or sprayed onto a current collector. Also in this case, the blending amount of the binder with respect to 100 parts by weight of the active material is in the above range. Further, a method of baking only the active material on the current collector can be adopted.

Further, the supply of the electrolytic solution component into the voids can be performed by a method in which an electrolytic solution for forming a gel electrolyte is applied to the surface of the active material layer having the voids and impregnated into the voids. Further, after the positive electrode and the negative electrode are laminated via the spacer, the electrolyte component may be impregnated from the side surface.
After the voids are impregnated with the electrolyte solution containing the polymer precursor, a polymerization process may be performed to gel the electrolyte solution. Alternatively, the electrolytic solution in which the polymer is dissolved at a high temperature may be cooled and gelled.

The gel electrolyte formed as described above is a substance mainly composed of an electrolytic solution and a gelling polymer, in which the electrolytic solution is held in a polymer network and the fluidity as a whole is significantly reduced. . In the case of such a gel electrolyte, properties such as ionic conductivity are similar to those of a normal electrolyte, but fluidity and volatility are significantly suppressed, and safety is enhanced.

The above electrolyte mainly comprises a lithium salt and a solvent. The type of the solvent is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specific examples of the solvent include ethylene carbonate, cyclic carbonates such as propylene carbonate, dimethyl carbonate,
Non-cyclic carbonates such as diethyl carbonate and ethyl methyl carbonate; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane; lactones such as γ-butyl lactone; sulfur compounds such as sulfolane; nitriles such as acetonitrile; Can be These can also be used as a mixture. Further, compounds in which a part of hydrogen atoms in these molecules are substituted with halogen or the like can also be used.

In the above, one selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.
Species or mixtures of two or more are preferred. The concentration of the lithium salt in the electrolyte is usually 0.5 to 2.5 mol / L.

In order to enhance the stability, performance and life of the battery, for example, trifluoropropylene carbonate, vinylene carbonate, 1,6-dioxaspiro [4,4] n
Additives such as onane-2,7-dione and 12-crown-4-ether may be added.

The above lithium salt includes a positive electrode active material and
Stable to negative electrode active material and positive for lithium ions
To perform an electrochemical reaction with a polar active material or a negative electrode active material
Use any non-aqueous substance that can move.
Can be. Specific examples of lithium salts include LiP
F₆, LiAsF₆, LiSbF₆, LiBF_Four, LiCl
O _Four, LiI, LiBr, LiCl, LiAlCl, L
iHF_Two, LiSCN, LiSO_ThreeCF_TwoEtc.
You. Among them, LiPF₆Or LiClO_FourIs preferred
is there.

When a gel electrolyte is used, (3) a method of cooling the polymer to room temperature by using an electrolyte containing a polymer that can be gelled by cooling in a heated state, 4) A method of polymerizing a monomer using an electrolytic solution containing the monomer is preferably used. According to such a method, an electrolytic solution similar to the above-mentioned electrolytic solution is held by the polymer, and the electrolyte becomes a gel.

The type of the polymer is not particularly limited as long as it forms a gel with the electrolytic solution and is stable as a battery material. However, since the electrolyte used for the lithium battery has polarity, a polymer having a certain degree of polarity is preferable. The molecular weight of the polymer is usually from 10,000 to
5,000,000, preferably 100,000 to 10,000
00 range. If the molecular weight is too low, it is difficult to form a gel, and if the molecular weight is too high, the viscosity is too high and handling becomes difficult.

In the above method (3), it is usually sufficient to apply the polymer-containing electrolytic solution to the surface of the active material layer and leave it for an appropriate time. However, the electrolyte is impregnated into the voids of the active material layer. Operations such as press-fitting and vacuum impregnation may be performed in order to increase the speed of the immersion. The gel electrolyte is preferably formed by completely filling the voids in the active material layer. However, even if a certain amount of voids remain, there is no significant problem in battery characteristics. In the case where voids are generated to the extent that battery characteristics deteriorate, it is preferable to adopt the above-described method of increasing the impregnation rate. On the other hand, in the method (4), since the viscosity of the monomer-containing electrolytic solution is low, it is easy to impregnate the voids in the active material layer with the electrolytic solution. Since the thickness of the active material layer is usually 1 mm or less, impregnation with the electrolytic solution is completed quickly. In any case, by applying a calender treatment to the coating film, the coating film can be compacted and the filling amount of the active material can be increased.

Specific examples of the polymer used in the above method (3) include polymers having a ring such as polyvinylpyridine, poly-N-vinylpyrrolidone, polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate. Acryl-based polymers such as polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, fluorine-based resins such as polyvinyl fluoride and polyvinylidene fluoride, polyacrylonitrile, polyvinylidene cyanide and the like Examples include CN group-containing polymers, polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol, and halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. In addition, a mixture of the above-mentioned polymers, a modified substance, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can also be used.

In the above method (4), suitable polymers produced by polymerization of monomers include, for example,
Polyester, polyamide, polycarbonate, polymer generated by polycondensation such as polyimide, polyurethane, polymer generated by polyaddition such as polyurea,
Polymers formed by addition polymerization, such as acrylic derivative polymers such as polymethyl methacrylate, and polyvinyl polymers such as polyvinyl acetate and polyvinyl chloride, etc. A polymer produced by addition polymerization that does not generate a product is preferable. In particular, a polymer produced by addition polymerization of a monomer containing a reactive unsaturated group has excellent productivity.

The reactive unsaturated group-containing monomers used in the above method (4) include acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, and ethoxyethyl acrylate. , Methoxyethyl acrylate,
Ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N diethylaminoethyl acrylate, N, N dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile , N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol Call dimethacrylate and the like.

The polymerization method of the above monomers includes heat,
A method using ultraviolet rays, an electron beam and the like can be mentioned, but a method using ultraviolet rays is preferable from the viewpoint of productivity. In this case, in order to make the reaction proceed effectively, a polymerization initiator that reacts with ultraviolet light may be added to the electrolytic solution. As the ultraviolet polymerization initiator, benzoin, benzyl, acetophenone,
Benzophenone, Michler's ketone, biacetyl, benzoyl peroxide and the like can be mentioned.

In the case of thermal polymerization, the structure of the gel can be controlled and the ionic conductivity and the like can be improved by changing the type and amount of the thermal polymerization initiator, the type and amount of the monomer, and the number of reactive groups in the monomer. Can be done. Further, since the whole reaction proceeds uniformly, a uniform gel is formed. In thermal polymerization, a polymerization initiator can be used for controlling the reaction. Examples of the thermal polymerization initiator include 1,1-di (tert-butylperoxy) -3,3,5-trimethylcyclohexane and 2,2-bis- [4,4-di (tert-butylperoxycyclohexyl) propane. ], 1,1
-Di (tert-butylperoxy) -cyclohexane, tert-butylperoxy-3,5,5-trimethylhexanonate, tert-butylperoxy-2
-Ethyl hexanonate, dibenzoyl peroxide and the like.

The proportion of the polymer in the gel electrolyte is usually 0.1 to 80% by weight, preferably 1 to 50% by weight. If the ratio of the polymer is too low, it becomes difficult to hold the electrolytic solution, causing a liquid leakage. If the ratio is too high, the ionic conductivity is lowered and the battery characteristics are deteriorated. The ratio of the polymer to the solvent is appropriately selected according to the molecular weight.
The content is 1 to 50% by weight, preferably 1 to 30% by weight.
If the proportion of the polymer is too small, the formation of a gel becomes difficult, the retention of the electrolytic solution is reduced, and the problems of flow and liquid leakage tend to occur. When the proportion of the polymer is too large, the viscosity becomes too high to make handling difficult, and the ionic conductivity tends to decrease due to a decrease in the concentration of the electrolytic solution, and battery characteristics such as rate characteristics tend to deteriorate.

When a solid electrolyte is used, for example, one obtained by removing the solvent in the above method (4) can be suitably used. That is, by polymerizing the monomer using a mixture of the monomer and the lithium salt, a solid electrolyte composed of the lithium salt and the polymer is obtained.

The electrolyte layer used in the present invention is composed of a gel electrolyte or a solid electrolyte as described above. The gel electrolyte or the solid electrolyte is used by being contained in a spacer such as a nonwoven fabric, a separator or a filter. May be.

In the present invention, the unit cell element is formed by laminating a positive electrode and a negative electrode in a plate shape with an electrolyte layer interposed therebetween. The term “flat” refers to a state in which the electrodes and the electrolyte layer are not wound up and are stacked flat. However, deformation such as gentle curvature is not a problem. Further, the positive electrode and the negative electrode may be formed on both surfaces of the current collector.

Next, the lithium secondary battery of the present invention will be described with reference to the accompanying drawings. 1 to 3 are explanatory views showing an assembly process of the lithium secondary battery of the present invention, and FIGS.
Is an explanatory view of another example of the lithium secondary battery of the present invention. FIGS. 9 to 13 are provided between the metal foil and the end face of the metal film layer of the case in the lithium secondary battery of the present invention. FIG. 4 is an explanatory view of an example of an insulating means.

The lithium secondary battery of the present invention is a lithium secondary battery housed in a case made of a laminated film including a heat-fusible polymer film layer and a metal film layer. A metal foil is provided as a lead which is taken out to the outside, and an insulating means is provided between the metal foil and an end face of the metal film layer. In a preferred aspect of the present invention, the metal foil as a lead taken out from the heat-sealed portion of the case is folded along the surface of the case and fixed on the heat-sealed portion to serve also as an external terminal. . In addition, a plurality of the unit battery elements housed in the case are stacked as necessary.

As the case, a case composed of a laminated film including a heat-fusible polymer film layer and a metal film layer is used. The laminated film is preferably, on the metal film layer, airtightness, solvent resistance, strength, printability,
It is formed by laminating a plurality of protective film layers having excellent wear resistance and the like as necessary.

As the material of the heat-fusible polymer film layer, polyethylene, polypropylene and modified products thereof are preferably used because they have excellent airtightness and solvent resistance. The thickness of the heat-fusible polymer film layer is not particularly limited, but is preferably from 10 to 100 μm. If it is too thin, the fusion will be insufficient and the airtightness will decrease. If it is too thick, the volume of the battery will increase and the energy capacity will decrease.

As the material of the metal film layer, any material can be used as long as it is a metal which can form a thin film and is chemically stable. The metal film layer can completely block permeation of water and oxygen from the outside, and significantly improves the safety and storage stability of the lithium secondary battery. Examples of the material of the metal include copper, iron, aluminum, and nickel. Aluminum is particularly preferred because it is lightweight.
The thickness of the metal film layer is usually in the range of 1 to 100 μm, preferably 10 to 50 μm. If the metal film layer is too thin, the barrier properties against water and the like are reduced, and if the metal film layer is too thick, the weight and volume are increased and the capacity of the battery is reduced.

As the material of the protective film layer, nylon, polyimide, metal, composite film of polymer and powder, and the like can be used. The thickness of the protective film layer is not particularly limited, but is preferably 10 to 100 μm. If the protective film layer is too thin, functions such as airtightness, solvent resistance, and strength cannot be sufficiently exhibited.If the protective film layer is too thick, the volume of the battery increases and the energy capacity increases, as in the case described above. Causes a decrease in

The above-mentioned laminated film wraps the unit cell element or its laminated body with the heat-fusible polymer film layer inside, and forms a case by heat-sealing the opening. As the wrapping method, two sheets may be used facing each other and four sides may be heat-sealed, or a part may be heat-sealed in advance. Alternatively, a method may be adopted in which a part is folded back to form a bag and only the opening is heat-sealed. The width of the heat-sealed portion is usually 1 to 10 mm, preferably 2 to 10 mm in order to secure a dead space (free space) formed on the upper portion. And such a relatively large width heat-sealed portion is
Not only is it effectively used as described above, but also an effect of compensating for a decrease in airtightness due to the presence of the metal foil in the heat-sealed portion is exerted.

In the lithium secondary battery of the present invention, a metal foil is used as a lead for extracting current from the case to the outside. The use of the metal foil is easier to bend and the like and is more airtight than a case where a circular conductor having a cross-sectional area of the same order is used. The thickness of the metal foil is usually in the range of 1 to 150 μm, but from the viewpoint of airtightness, strength, and retention of conductivity,
A range of 15 to 100 μm is preferred. In addition, the above thickness is also preferable in that the return, swelling, breakage, and the like of the folded portion hardly occur. Furthermore, 30-1
A thickness in the range of 00 μm is preferable in terms of increasing strength and providing an external terminal having excellent durability. On the other hand, the width of the metal foil is usually in the range of 1 to 20 mm, preferably 3 to 10 mm. If the width of the metal foil is too small, the electric resistance increases and the strength is reduced, so that problems such as cutting are likely to occur. If the width of the metal foil is too wide, the airtightness of the upper and lower surfaces of the metal foil decreases.

As the metal foil, any kind of metal foil can be used as long as it is stable in air and in a battery and has high electric conductivity. For example, foils of gold, silver, copper, aluminum, nickel, iron and the like can be used. Alloy foils can also be used to provide strength and chemical stability. Further, at the time of heat fusion, an intermediate layer may be provided and used in order to enhance the adhesion between the metal foil and the heat fusion layer. As the intermediate layer, a method of treating the surface of the metal foil with an organic substance, or a method in which a polymer containing a polar group and a copolymer polymer such as polyethylene or polypropylene can be used.

Further, the metal foil can be used by covering one side with an adhesive film. In this case, the foil is not cut when the metal foil is folded. Further, it is also possible to prevent the folded portion from being broken due to deterioration. Furthermore, if a double-sided adhesive film is used, fixing and reinforcement can be realized at the same time. Further, the remaining surface may be covered except for a portion used for electrical connection. Various tapes can be used as the adhesive film used at this time, and in particular, vinyl tape and polyimide tape are preferably used from the viewpoint of strength and electrical insulation.

First, as shown in FIG. 1A, a positive electrode (1) and a negative electrode (2) are laminated in a plate shape via an electrolyte layer (3), and a unit battery as shown in FIG. Assemble the element (4). At this time, the positive electrode current collector (11) and the negative electrode current collector (2)
As 1), each of the lead joints (12) and (2)
It is preferable to use one cut so that 2) protrudes. The symbols (10) and (20) are respectively
1 shows a positive electrode active material layer and a negative electrode active material layer.

Next, as shown in FIG. 2, metal foils (13) and (23) are connected to the lead joints (12) and (22), respectively. As the metal foil, it is preferable to use an aluminum foil on the positive electrode side and a copper foil on the negative electrode side. Means for connecting the lead joint to the metal foil include heat fusion, ultrasonic fusion, soldering, riveting, and the like. In addition,
Each of the above metal foils may be integrated with an electrode,
Also, they may be connected via a lead wire or the like. When a plurality of unit battery elements are used by laminating as necessary, for example, each positive electrode-side metal foil and each negative electrode-side metal are united, and an assembly metal foil is attached to the tip of each unit. The metal foil is replaced with the metal foils (13) and (2).
It can be handled in the same way as 3).

Next, as shown in FIG. 3 (a), the unit battery element is housed in a case (5) made of a laminated film, and metal foils (13) and (23) as leads are heat-sealed to the case. Take it out from (51). In this state, as shown in FIG. 3B, a dead space (free space) is formed above the heat-sealed portion (51) due to a height difference from the electrode enclosing portion (52). In addition, the heat fusion part (51)
Although it is thin, it is rigid and has excellent strength. The airtightness of the case (5) is sufficiently ensured because the periphery of the metal foils (13) and (23) is adhered by fusion. Of course, since there is no battery element immediately below the heat-sealing portion, there is no problem in performing processing such as fusion. In addition,
FIG. 3B is a schematic cross-sectional view taken along the line AA of FIG.

In the present invention, the height difference (difference between the thickness) of the heat-sealed portion (51) of the case (5) and the electrode enclosing portion (52) is usually 0.1 mm or more. From the viewpoint of providing an installation space for external terminal reinforcing means or a protection circuit to be provided, preferably 1 to 5 mm, more preferably 2 to 4 mm
Range. If the height difference exceeds 5 mm, the total thickness of the battery becomes 5 mm or more, which is not preferable from the viewpoint of realizing a thin battery. Of course, if the above-mentioned height difference is too small, the effective utilization of the dead space (free space) formed above the heat-sealed portion (51) is impaired.

Next, as shown in FIGS. 4A and 4B, the metal foils (13) and (23) are folded back along the surface of the case and fixed on the heat-sealed portion (51). Use as In the case of the illustrated example, the metal foils (13) and (23) are folded back toward the case (5), and are folded again along the heat-sealed portion (51). Note that FIG. 4B is shown as a schematic cross section along the line AA in FIG. 4A.

The secondary battery shown in FIGS. 5A and 5B
A lithium secondary battery according to a preferred embodiment of the present invention, in which the lower surfaces of portions functioning as external terminals of the metal foils (13) and (23) are tightly fixed to the case (5). ing. As the fixing means, an adhesive, an adhesive tape, a double-sided tape, or the like can be used,
The illustrated example is an example of fixing with an adhesive (6).

According to the above aspect, the metal foils (13) and (23) have excellent mechanical strength on the entire surface and function well as external terminals. Connection to an external device can be made by soldering a conductive wire or the like. Further, since the heat-sealed portion (51) to which the metal foils (13) and (23) are fixed is rigid, a leaf spring-shaped metal terminal, a screw-shaped metal terminal, or the like is used for connection to an external device. You can do it. FIG.
(B) is shown as a schematic cross section along the line AA in FIG. 5 (a).

The secondary battery shown in FIGS. 6A and 6B
A lithium secondary battery according to a preferred embodiment of the present invention in which the folded portions of the metal foils (13) and (23) are reinforced. That is, each folded portion of the metal foils (13) and (23) has a structure in which the metal foil protrudes outside from the heat-sealed portion (51). Therefore, in order to prevent damage due to impact and short-circuit due to contact, it is preferable to reinforce and protect each folded portion of the metal foils (13) and (23). As the reinforcing means, a method of covering from outside with a tape (7) is preferable, as in the example shown in the figure. Metal foil on negative electrode side (23)
Is shown with the tape omitted to show the folded state. FIG. 6B is a schematic cross-sectional view taken along line AA of FIG. 6A.

The secondary battery shown in FIGS. 7A and 7B
An example is shown in which a protection circuit (7) is installed in a dead space (free space) above a heat fusion part (51). Protection circuit (8)
Is provided as necessary when a secondary battery is connected to an external device. The protection circuit (8) in the illustrated example is soldered on its lower surface to an external terminal composed of the metal foils (13) and (23). Since the positions of the external terminals are stable, soldering can be easily performed by an automatic machine. The secondary battery can be used as it is incorporated in a computer or the like as it is. However, in many cases, the entire secondary battery is stored in an external case for ease of handling such as transportation and storage.

FIGS. 8A and 8B show the secondary battery housed in the outer case (9). The outer case (9) is often made of plastic and has a rectangular parallelepiped shape rather than a complicated shape in terms of productivity, cost, weight, and the like. The external case (9) is provided with respective fitting-type metal terminals (14) and (24), and is used as a battery pack. In the present invention, the lithium secondary battery is
A plurality of them can be housed in a package and used electrically connected in series or in parallel.

In the secondary battery of the present invention, an insulating means is provided between the metal foils (13) and (23) and the end face of the metal film layer of the case (5).
Specific examples of such insulating means include the means illustrated in FIGS. 9 to 13 described below. In addition, FIG.
The symbol (5a) in 11 is a heat-fusible polymer film layer,
(5b) indicates a metal film layer, (5c) indicates a protective film layer, and each of these figures is shown as a schematic cross section of the case (5) shown in FIG. 3 before the heat-sealed portion (51) is formed. ing.

FIG. 9 shows an example of insulating means on the end face of the metal film layer (5b) of the laminated film. In the figure, not only the end faces of the metal film layer (5b) but also the end faces of all the laminated films are insulated. The insulating treatment of the end face of the metal film layer (5b) may be performed on any of the metal films before and after the formation of the laminated film. As the insulating materials (A1) and (A2) used for the insulating treatment, an insulating paint, various polymers (particularly, heat-fusible polymers), and the like are used.

FIG. 10 shows a means for insulating the end face of the metal film layer (5b), as in FIG. 9, but the heat-fusible polymer, in particular, the one protruding from the heat-fusible polymer film layer (5a). 2 illustrates an insulating means on the end face of the metal film layer (5b) by a portion of the polymer. In the case of such an insulating means, there is no need to separately prepare an insulating material, and the formation of an insulator can be realized by controlling the conditions for forming a laminated film (laminating conditions), so that the productivity is excellent.

FIG. 11 shows an example of the insulating means on the premise that the metal foil (13) as a lead taken out from the heat-sealed portion of the case is folded along the case surface as shown in FIG. ing. In this case, the metal foil portion in contact with the end face of the metal film layer (5b) of the laminated film is insulated. As the insulating materials (B1) and (B2),
Insulating paints and various polymers (especially heat-fusible polymers) are used. However, by selecting an insulating material having high adhesion to the metal foils (13) and (23), the airtightness can be improved. It is planned.

FIGS. 12 and 13 show specific examples of the insulating means shown in FIG. The means shown in FIG. 12 is a means for laminating an insulating material (B1) for each of the metal foils (13) and (23). On the other hand, the means shown in FIG. 13 is a means for laminating a sheet-like insulating material (B1) common to the metal foils (13) and (23). 12 and 13
Shows only the insulating material (B1) located above the metal foils (13) and (23). Any of the above means has the effect of effectively preventing the intrusion of moisture and the like through the metal foil portion, but the common sheet-like insulating material (B
The means shown in FIG. 13 for laminating 1) has the advantage of being excellent in productivity.

The following Table 1 shows the results of evaluating the insulation properties of the end faces of various laminated films including metal film layers having different thicknesses. As an evaluation method, a laminated film was cut, then held vertically, and a metal rod 2 having a diameter of 2 mm was used.
A method was adopted in which a book was pressed orthogonally against a laminated film, and the resistance between metal bars was measured with an ohmmeter.

[0065]

[Table 1]

As shown in Table 1, a laminated film having a metal film layer sometimes exhibits electric conduction through its end face. However, the thicker the metal film layer, the higher the possibility of conduction, and from the viewpoint of moisture barrier properties. If the required thickness of the metal film layer is 10 μm or more, the possibility of conduction becomes particularly high.

[0067]

According to the lithium secondary battery of the present invention described above, the following specific effects can be obtained. That is, the case made of the laminated film used in the present invention is lightweight and does not become bulky because it comes into close contact with the battery. Therefore, a battery excellent in volume capacity and weight capacity can be obtained. In addition, since the metal film layer of the case retains remarkable airtightness, penetration of moisture from the outside is highly suppressed. Further, since the insulating means is provided between the metal foil and the end face of the metal film layer of the case, there is no possibility that the positive electrode and the negative electrode are short-circuited via the metal film layer.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an assembling process of a lithium secondary battery of the present invention.

FIG. 2 is an explanatory view showing an assembling step of the lithium secondary battery of the present invention.

FIG. 3 is an explanatory view showing an assembling process of the lithium secondary battery of the present invention.

FIG. 4 is an explanatory view of an example of the lithium secondary battery of the present invention.

FIG. 5 is an explanatory view of another example of the lithium secondary battery of the present invention.

FIG. 6 is an explanatory view of another example of the lithium secondary battery of the present invention.

FIG. 7 is an explanatory view of another example of the lithium secondary battery of the present invention.

FIG. 8 is an explanatory view of still another example of the lithium secondary battery of the present invention.

FIG. 9 is an explanatory view of an example of an insulating means provided between the metal foil and the end face of the metal film layer of the container in the lithium secondary battery of the present invention.

FIG. 10 is an explanatory view of another example of the insulating means provided between the metal foil and the end face of the metal film layer of the container in the lithium secondary battery of the present invention.

FIG. 11 is an explanatory view of still another example of the insulating means provided between the metal foil and the end face of the metal film layer of the container in the lithium secondary battery of the present invention.

FIG. 12 is an explanatory view of a specific example of the insulating means shown in FIG.

FIG. 13 is an explanatory view of another specific example of the insulating means shown in FIG. 11;

[Explanation of symbols]

 1: Positive electrode 10: Positive electrode active material layer 11: Positive electrode current collector 12: Positive electrode side lead joint 13: Positive electrode side metal foil 2: Negative electrode 20: Negative electrode active material layer 21: Negative electrode current collector 22: Negative electrode side lead joint 23: negative electrode side metal foil 3: electrolyte layer 4: unit battery element 5: case 5a: heat-fusible polymer film layer 5b: metal film layer 5c: protective film layer 51: heat-fused portion 52: electrode enclosing portion 6 : Adhesive 7: Tape 8: Protection circuit 9: External case 14: Positive side fitting type metal terminal 24: Negative side fitting type metal terminal A1, A2, B1, B2: Insulating material

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // H01M 10/40 H01M 10/40 Z F term (reference) 5H011 AA01 AA03 AA04 AA17 CC02 CC06 CC10 DD06 DD13 DD17 DD21 DD22 EE04 FF01 GG09 HH02 JJ25 JJ27 KK01 5H029 AJ03 AJ11 AJ15 AK03 AK16 AL01 AL02 AL07 AL12 AL18 AM03 AM04 AM05 AM07 AM16 BJ04 CJ02 CJ03 CJ05 CJ22 DJ02 DJ03 DJ05 DJ07 EJ01 EJ12 HJ04

Claims (9)

[Claims] 1. A lithium secondary battery in which a positive electrode and a negative electrode are laminated in a flat plate with an electrolyte layer interposed therebetween, and housed in a case comprising a laminated film including a heat-fusible polymer film layer and a metal film layer. And a metal foil as a lead taken out of the heat-sealed portion of the case to the outside, and insulating means is provided between the metal foil and an end face of the metal film layer. Next battery. 2. A metal foil as a lead taken out from the heat-sealed portion of the case to the outside is folded along the surface of the case and fixed on the heat-sealed portion to serve also as an external terminal. 4. The lithium secondary battery according to 1. 3. The lithium secondary battery according to claim 1, wherein the thickness of the metal film layer of the laminated film is 10 to 50 μm. 4. The lithium secondary battery according to claim 1, wherein a difference in thickness between the heat-sealed portion of the case and the electrode enclosing portion is 1 mm or more. 5. The lithium secondary battery according to claim 1, wherein a lower surface of a portion of the metal foil functioning as an external terminal is fixedly attached to the case. 6. The lithium secondary battery according to claim 1, wherein the folded portion of the metal foil is reinforced. 7. The lithium secondary battery according to claim 1, wherein the end face of the metal film layer of the laminated film is insulated. 8. The lithium secondary battery according to claim 1, which is insulated by a heat-fusible polymer. 9. A metal foil as a lead taken out from the heat-sealed portion of the case to the outside is folded along the surface of the case, and a metal foil portion in contact with an end face of the metal film layer of the laminated film is insulated. The lithium secondary battery according to claim 1.