JP2002198099A - Sheet-like lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary sheet cell which permits conducting an impregnating operation of an electrolyte into a laminate structure in production of the cell in a short period of time, does not have an unnecessary space between individual sheet electrodes in the laminate structure, said sheet electrodes being brought into uniformly close contact with respective separators or solid-state electrolyte layers, and exhibits excellent cell performance. SOLUTION: A tape 5 is wound around an outer periphery of a laminate structure (power generation element) 3 containing a plurality of units with a positive sheet electrode 1 and a negative sheet electrode 2 laminated on each other through a separator or solid-state electrolyte layer 4 to band and fix a plurality of sheet electrodes forming the laminate structure 3, and a plurality of through-holes 51 are distributedly provided in portions of the tape, which cover side faces 3B-1, 3B-2 of the laminate structure 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sheet-shaped lithium secondary battery.

[0002]

2. Description of the Related Art A lithium secondary battery having a large discharge capacity has been spotlighted as a battery for electronic equipment such as a portable telephone and a personal computer. Conventionally, as the lithium secondary battery, a three-dimensional battery such as a columnar or box-shaped battery has been mainly used. However, recently, attention has been paid to a sheet-shaped lithium secondary battery in view of a space factor and a light weight.

[0003] The advantage of a sheet-shaped lithium secondary battery is that it is thinner than a three-dimensional battery, so that the heat dissipation is good and the degree of heat trapped in the battery is low. Even if an overcurrent flows or a penetrating scratch occurs due to a nail or the like, an explosion accident due to burning of lithium inside the battery is unlikely to occur, which is extremely safe.

In general, in order to increase the battery capacity of a sheet-shaped lithium secondary battery, a laminated structure including a plurality of units in which a positive electrode sheet electrode and a negative electrode sheet electrode are stacked via a separator or a solid electrolyte layer is formed. This is used for the power generation element to increase the effective reaction area of the battery.

However, when the power generating element is formed in such a laminated structure, floating occurs between the sheet electrodes in the laminated structure (a state in which a gap is formed between the sheet electrodes), and the internal resistance of the battery increases. , Battery performance (especially rate characteristics, low temperature characteristics,
Cycle characteristics). Therefore, in order to prevent this, usually, an adhesive tape is wound around the outer periphery of such a laminated structure to bind and fix a plurality of sheet electrodes constituting the laminated structure.

[0006] In the binding with the adhesive tape, substantially the whole of the laminated structure (the current collecting terminals of the laminated structure protrude) so that the whole of each sheet electrode is in uniform contact with the separator or the solid electrolyte layer. The adhesive tape is wound around the entire surface (excluding the surface and the surface opposite thereto).
Therefore, when the electrolytic solution is impregnated into the laminated structure (the separator or the solid electrolyte layer is impregnated with the electrolytic solution), the electrolytic solution hardly permeates (flows) into the laminated structure, and as a result, the time required for the process , The productivity of the battery may decrease, or the electrolyte solution may not sufficiently penetrate (impregnate) every corner of the laminated structure, resulting in a decrease in battery performance.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to impregnate an electrolytic solution into every corner of a laminated structure in a short time at the time of impregnation of the electrolytic solution into a laminated structure at the time of manufacturing a battery. Provided is a sheet-shaped lithium secondary battery that can be formed, has no unnecessary gaps between each sheet electrode in the laminated structure, and each sheet electrode uniformly adheres to a separator or a solid electrolyte layer, and exhibits excellent battery performance. The purpose is to:

[0008]

The present invention has the following features to achieve the above object. (1) A laminated structure including a plurality of units in which a positive electrode sheet electrode and a negative electrode sheet electrode are stacked with a separator or a solid electrolyte layer interposed therebetween is used as a power generation element, and a tape is wound around the outer periphery of the laminated structure to form the laminated structure. A sheet-like lithium secondary battery in which a plurality of sheet electrodes to be configured are bound and fixed with a tape, and the surfaces of two sheet electrodes positioned at the outermost sides of the stacked structure are referred to as main surfaces of the stacked structure. A sheet-like lithium secondary battery, wherein a plurality of through-holes are dispersedly provided in a portion of the tape covering the side surface of the laminated structure, wherein a surface on which the end surfaces of the sheet electrodes are gathered is referred to as a side surface of the laminated structure. battery. (2) The positive electrode sheet electrode and the negative electrode sheet electrode are substantially rectangular sheets, the laminated structure has a substantially rectangular parallelepiped outer shape, and the tape is formed on both main surfaces and a pair of opposed side surfaces of the laminated structure. Wound, the area of the winding area of the tape,
The lithium ion secondary battery according to the above (1), wherein the total area of both main surfaces and a pair of opposed side surfaces of the laminated structure is 30% or more. (3) The diameter of each of the plurality of through holes is set in the range of 0.1 to 8 mm, and the distance between each two adjacent holes is 0.05 to
(1) or (2) above, which is set in the range of 8 mm
The sheet-shaped lithium secondary battery according to the above. (4) The above-mentioned (1) to (3) in which a solid electrolyte layer mainly composed of a salt, a compatible solvent, and a fluoropolymer having vinylidene fluoride as a main unit is interposed between the positive electrode sheet electrode and the negative electrode electrode. The sheet-shaped lithium secondary battery according to any one of the above. (5) The fluoropolymer of the solid electrolyte layer has a density of 0.60
The sheet-shaped lithium secondary battery according to the above (4), which is a porous body of 1.30 g / cm ³ .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically. The sheet-shaped lithium secondary battery according to the present invention includes, as a power generation element, a stacked structure including a plurality of units in which a positive electrode sheet electrode and a negative electrode sheet electrode are stacked with a separator or a solid electrolyte layer interposed therebetween. A plurality of sheet electrodes constituting a laminated structure are bound and fixed by winding a tape around the tape, and a plurality of through holes are formed in a portion of the tape covering at least a side surface of the laminated structure (ie, a surface on which end surfaces of the plurality of sheet electrodes are gathered). Are provided in a distributed manner. In general, the binding tape is preferably an adhesive tape, but may be a tape having no adhesive layer. In the case of a tape having no adhesive layer, after the tape is wound, the tape is fixed with a required adhesive or a stopper. The specific example described below is a preferred example using an adhesive tape.

FIGS. 1 to 3 show a sheet-like lithium secondary battery according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of a laminated structure (power generation element). FIG. FIG. 3 is an enlarged cross-sectional view of a main part showing a state of lamination of the negative electrode sheet electrodes, and FIG. 3 is a schematic perspective view of a state in which an adhesive tape is wound around the laminated structure.

As shown in FIGS. 1 and 2, a laminated structure 3 as a power generation element has a structure including a plurality of units in which a rectangular positive electrode sheet electrode 1 and a negative electrode sheet electrode 2 are stacked with a separator or a solid electrolyte layer 4 interposed therebetween. It is a body, and its outer shape is a substantially rectangular parallelepiped.

Positive electrode sheet 1 constituting laminated structure 3
And the negative electrode sheet electrode 2, as shown in FIG.
An active material composition layer (a positive electrode active material composition layer 6, a negative electrode active material composition layer 7) obtained by mixing at least an active material and a binder, and further mixing a conductive material as necessary, is used as a sheet-like current collector 8, The active material composition layers (the positive electrode active material composition layer 6 and the negative electrode active material composition layer 7) face the separator or the solid electrolyte layer 4, respectively.
Each sheet electrode (positive sheet electrode 1, negative sheet electrode 2)
The current collectors 8 and 9 are provided with an unformed portion (not shown) of the active material composition layer, and a lead (not shown) is attached thereto by, for example, welding or the like. 1, the end of each lead is connected to the positive collector terminal 10;
The ends of the leads of the plurality of negative electrode sheet electrodes 2 are connected to the negative electrode current collecting terminals 11.

The surfaces 2a 'and 2a of the two outermost sheet electrodes (negative electrode electrodes 2a and 2b) of the laminated structure 3
As shown in FIG. 3, b ′ is referred to as a main surface of the laminated structure, and an aggregated surface of the end faces of the plurality of sheet electrodes (the positive electrode electrode 1 and the negative electrode electrode 2) is referred to as a side surface of the laminated structure. The adhesive tape 5 is wound around substantially the entire area of both the main surfaces 3A-1 and 3A-2 of the structure 3 and a pair of opposed side surfaces 3B-1 and 3B-2 of the laminated structure to form a plurality of sheets. The electrodes (the positive electrode sheet electrode 1 and the negative electrode sheet electrode 2) are bound and fixed, and a plurality of through holes are formed in a portion of the adhesive tape 5 covering a pair of opposed side surfaces 3B-1 and 3B-2. 51 are provided separately.

In the sheet-shaped lithium secondary battery, the laminated structure 3 on which the adhesive tape 5 is wound is impregnated with an electrolytic solution (each separator or solid electrolyte layer (its polymer substrate) 4 is impregnated with the electrolytic solution). The laminated structure 3 impregnated with the electrolytic solution is accommodated in a sheet-like exterior material (not shown), and the positive current collecting terminal 10 and the negative current collecting terminal 11
It is manufactured by sealing the exterior material in a state where the respective ends are pulled out of the exterior material. Note that the laminated structure that has not been subjected to the electrolytic solution impregnation treatment may be accommodated in an exterior material together with the electrolytic solution, and the electrolytic solution may permeate the laminated structure in the exterior material.

FIG. 4 shows a laminated structure in which a plurality of sheet electrodes are bound and fixed by winding an adhesive tape in a conventional sheet-shaped lithium secondary battery, and the same reference numerals as those in FIGS. I have. In the conventional sheet-shaped lithium secondary battery, as shown in this figure, both main surfaces 3A-1 and 3A-2 of the laminated structure 3 and a pair of opposing side surfaces 3B-1 and 3B-2 are provided over substantially the entire area. Of the side surfaces around which the adhesive tape 5 is wound and which serves as the electrolyte inflow region of the laminated structure 3, the side surfaces 3C-1 protruding from the current collecting terminals 10 and 11 and the side surface 3C-2 opposed thereto become open. , A set of opposing sides 3B different from the set of opposing sides
-1, 3B-2 are almost entirely covered with the adhesive tape. That is, the side surface 3 of the laminated structure 3 is substantially
B-1 and 3B-2 cannot be used as the inflow region of the electrolytic solution.

On the other hand, in the sheet-shaped lithium secondary battery of the present invention, as shown in FIG. 3, of the adhesive tape 5 wound around the laminated structure 3, the side surface 3B-
1, 3B-2, a plurality of through holes 5
1 are distributed, so that substantially all of the sides (ie, a set of opposing sides 3 on one side) of the laminated structure are provided.
C-1, 3C-2 and a pair of opposite side surfaces 3B-1 and 3B-2) on the other side serve as an inflow region of the electrolytic solution and extend to every corner in the laminated structure 3 (each separator or solid electrolyte layer). (Every corner of No. 4) The electrolyte can be permeated (impregnated) in a short time.

In the present invention, the pressure-sensitive adhesive tape is wound around the surface to be wound of the laminated structure so that the tightening force of the pressure-sensitive adhesive tape sufficiently acts on a plurality of sheet electrodes constituting the laminated structure. Preferably, the area is as large as possible. For example, the positive electrode sheet electrode 1 and the negative electrode sheet electrode 2 of FIG.
In the case of the laminated structure 3 having a substantially rectangular parallelepiped outer shape, both main surfaces 3A of the laminated structure 3 to which the adhesive tape is to be wound are provided.
-1, 3A-2 and a set of opposing sides 3B-1, 3
With respect to B-2, the area of the wrapping area 5A of the adhesive tape is preferably 30% or more, more preferably 50% or more, based on the total area of these surfaces.

Although FIG. 3 shows one large-area wrapping area 5A made of a wide adhesive tape, for example, a plurality of small-area wrapping areas are formed with a narrow-width adhesive tape, and a plurality of wrapping areas are formed. The total area of the region is the above 30 with respect to the total area of the surface to be wound.
% (Preferably 50% or more).

In the present invention, the diameter (pitch) of each through-hole and the interval (pitch) between two adjacent holes among a plurality of through-holes provided in a dispersed manner at a portion covering the side surface of the laminated structure of the adhesive tape are individual holes. Is set in consideration of the ease of passage of the electrolyte solution, the permeability of the electrolyte solution to the side of the laminated structure, the strength of the tape, and the like. The diameter of each through hole is preferably in the range of 0.1 to 8 mm, A range of 5 to 5 mm is particularly preferred. The interval (pitch) between two adjacent holes is preferably in the range of 0.05 to 8 mm, and particularly preferably in the range of 0.1 to 5 mm. That is, by setting the hole diameter of each through-hole and the interval (pitch) between two adjacent holes in the above-described preferable range, the electrolyte solution can quickly pass through each through-hole and be viewed from the side of the laminated structure. It can uniformly penetrate into the inside and can sufficiently suppress the occurrence of tape breakage during the winding operation of the adhesive tape and / or after the winding of the adhesive tape. In addition, "the interval (pitch) between two adjacent holes" is the interval between the nearest parts of the periphery of two adjacent holes.

The proportion of the through hole in the portion of the adhesive tape covering the side surface of the laminated structure (the ratio of the total opening area of the plurality of through holes to the area of the portion of the adhesive tape covering the side surface of the laminated structure) is 30. It is preferably from 70% to 70%, particularly preferably from 40% to 60%. If the proportion of the through-holes exceeds this range and the proportion of the through-holes increases, there is a concern about the problem of tape breakage.If the proportion of the through-holes decreases, the penetration rate of the electrolyte into the laminated structure may not be sufficiently improved. is there.

In the present invention, the shape of the through hole provided in the adhesive tape is not particularly limited. For example, in addition to a circle as shown in FIG. 3, a polygon such as an ellipse and a quadrangle may be used. The above-mentioned `` hole diameter '' of the through hole is a diameter when the through hole is circular, and assumes a circular hole having an area equal to the opening area when the through hole has a shape other than the circle. It is the diameter of the circular hole at the time of performing.

The through holes may be formed before the adhesive tape is wound around the laminated structure, or may be formed after the adhesive tape is wound around the laminated structure. When forming a through hole in the adhesive tape before winding the adhesive tape on the laminated structure, the through hole is located on the side surface of the laminated structure in consideration of the size of the laminated structure, elongation at the time of winding the tape, and the like. The through hole is formed as described above, or the through hole is formed in the entire adhesive tape to be wound. When forming a through-hole in the entire adhesive tape to be wound, there is no need to adjust the formation position of the through-hole.However, since the through-hole is formed in the entire adhesive tape to be wound, the adhesive tape can be used during or after the winding operation. There is a concern that the adhesive tape may break or decrease in adhesive strength over time after winding. Therefore, when the through-hole is formed in the entire adhesive tape to be wound, the type of the adhesive tape, the ratio of the through-hole in the entire adhesive tape, and the like are determined in consideration of such points.

In the sheet lithium secondary battery of the present invention,
The size of one sheet electrode is appropriately selected according to the battery design, and is usually selected from the range of 10 to 100 cm ² . Also, the number of units in which the positive electrode sheet electrode and the negative electrode sheet electrode in the laminated structure are laminated via the separator or the solid electrolyte layer is appropriately selected according to the battery design, and is usually selected from the range of 2 to 20. . In the example of FIG. 3, the two outermost sheet electrodes are both negative electrode sheets, but one of the two sheet electrodes is a positive electrode electrode and the other is a negative electrode sheet. Needless to say, it differs depending on the battery design, such as the case of the electrodes or the case where both are the positive electrode sheets.

In the present invention, the pressure-sensitive adhesive tape 5 preferably has excellent electrical insulation properties and has resistance to heat generation of the power generating element and an electrolytic solution, and is preferably a vinyl chloride resin, a polyester resin, a polyolefin resin, cotton, or a fluorine resin. It is preferable that a tape base made of a polyimide resin or the like, a rubber-based adhesive, an acrylic-based adhesive, a pressure-sensitive adhesive layer formed of a silicone-based adhesive or the like is formed, particularly preferably a tape base made of polypropylene, an acrylic-based An adhesive layer is formed by an adhesive. The thickness of the substrate is 5 to 100 μm
The thickness of the pressure-sensitive adhesive is preferably 10 to 50 μm.

In the present invention, as the positive electrode active material used for the positive electrode sheet electrode, a known positive electrode active material for a lithium secondary battery can be used, but a Li-transition metal composite oxide is preferable, and a Li-Co composite oxide is particularly preferable. Object, Li-M
at least one compound selected from n-composite oxides and Li-Ni complex oxides;
i-Co composite oxide.

Examples of the conductive material used together with the positive electrode active material include natural and artificial graphites such as fibrous graphite, flaky graphite, and spherical graphite, and conductive carbon materials that have been widely used in the art. Black or the like can be used. The amount of the conductive material to be used is preferably 1% by weight to 10% by weight, more preferably 3% by weight to 7% by weight, per 100 parts by weight of the total amount of the positive electrode active material, the binder and the conductive material.

As the binder used together with the positive electrode active material, for example, polytetrafluoroethylene,
Suitable examples include polyvinylidene fluoride, polyethylene, and ethylene-propylene-diene-based polymers. The amount of the binder used is a positive electrode active material,
Per 100 parts by weight of the total amount of binder and conductive material,
Preferably it is 1% to 7% by weight, more preferably 2% to 5% by weight.

Examples of the current collector for the positive electrode include a foil and an expanded metal formed of a conductive metal such as aluminum, an aluminum alloy, and titanium, and these may have holes.

Graphitized carbon is preferably used as the negative electrode active material used for the negative electrode sheet electrode. Examples of such graphitized carbon include various natural graphites and artificial graphites, for example, graphites such as fibrous graphite, flaky graphite, and spherical graphite. Further, as the binder used together with the negative electrode active material, as in the conventional case, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, ethylene-propylene-diene-based polymer and the like are preferably mentioned, and among them, polyvinylidene fluoride is particularly preferred. Is preferred. The amount of the negative electrode active material used is preferably about 2 to 20 parts by weight per 100 parts by weight of the total amount of the negative electrode active material and the binder.

As the current collector for the negative electrode, copper, nickel,
Examples include foils and expanded metals made of silver, stainless steel, and the like, and these may have holes formed therein.

In the case of a battery of a type in which a separator is interposed between a positive electrode sheet electrode and a negative electrode sheet electrode, a known separator for a lithium secondary battery can be used without any limitation. Preferably, a polyolefin porous separator is particularly preferred. The polyolefin (porous) separator may be a single layer of a polyethylene layer or a polypropylene layer, or may be a composite separator in which a polyethylene layer and a polypropylene layer are laminated. The laminated structure of the composite separator is not particularly limited, and a polyethylene layer / polypropylene layer,
Polyethylene layer / polypropylene layer / polyethylene layer,
Various laminated structures such as a polypropylene layer / polyethylene layer / polypropylene layer can be used.

The thickness of the separator is generally 5
To 100 μm, particularly preferably 10 to 30 μm
m. Here, the thickness of the separator is a thickness in a state where the separator is interposed between the positive electrode and the negative electrode (in a state where the battery is actually assembled), and is equal to a separation distance between the positive electrode and the negative electrode.

When a battery (polymer battery) of a type in which a solid electrolyte layer is interposed between a positive electrode sheet electrode and a negative electrode sheet electrode, a known solid electrolyte layer for a lithium secondary battery is used as the solid electrolyte layer. Although it can be used without limitation, a solid electrolyte layer prepared so that a polymer substrate is impregnated with an electrolyte solution (lithium salt (electrolyte) + compatible solvent) to be gelled and itself exhibit ion conductivity. Among them, polymer substrates include polyethylene oxide, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl chloride, polyvinylidene carbonate,
It is particularly preferable to use a fluoropolymer having vinylidene fluoride as a main unit (including polyvinylidene fluoride), and use a fluoropolymer having vinylidene fluoride as a main unit from the viewpoint of battery rate characteristics, low-temperature characteristics, and the like. Particularly preferred are the following. In addition, if a solid electrolyte layer is used, better adhesion to a sheet electrode can be obtained due to gelation as compared with a separator.

The fluoropolymer having vinylidene fluoride as a main unit includes a homopolymer of vinylidene fluoride (polyvinylidene fluoride (PVdF)),
Alternatively, it means a copolymer of vinylidene fluoride and another vinyl monomer having a fluorine atom, and these may be used alone or in combination. Vinyl monomers having a fluorine atom other than the above vinylidene fluoride include hexafluoropropylene (HF
P), chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE) and the like. Also,
The form of the copolymer may be any of a random form and a block form. In the case of a copolymer, the proportion of (units) of vinylidene fluoride is preferably at least 70 mol%, particularly preferably at least 75 mol%.

Fluoropolymers having vinylidene fluoride as a main unit include carboxyl groups (—COO).
H) a vinyl group having a functional group consisting of a sulfonic acid group (—SO ₂ OH), a carboxylic acid ester group (—COOR), an amide group (—CONH ₂ ), or a phosphoric acid group (—PO (OH) ₂ ). A polymer of a monomer may be grafted (the substituent R in the carboxylic acid ester group (—COOR) is a lower alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, and a butyl group). . When the fluoropolymer is formed into a polymer form in which a polymer containing such a functional group is grafted, the adhesion of the solid electrolyte layer to the sheet electrode is further improved, and the resistance between the electrodes is further reduced. Characteristics and low-temperature characteristics) are further improved. As the vinyl monomer having a functional group, a monomer composed of a compound having a carbon number of 4 or less excluding the functional group is preferable. Examples of the carboxyl group-containing monomer include those having one carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, vinyl acetic acid, and allyl acetic acid, and two carboxyl groups such as itaconic acid and maleic acid.
Those having more than one can also be used. As the sulfonic acid group-containing monomer, styrene sulfonic acid, vinyl sulfonic acid and the like are preferable. As the carboxylic acid ester group-containing monomer, methyl acrylate, butyl acrylate, and the like are preferable. Acrylamide and the like are preferable as the amide group-containing monomer. As the phosphate group-containing monomer, triphenyl phosphate, tricresyl phosphate, and the like are preferable. Most preferred of these are acrylic acid or methacrylic acid.

The grafting method is not particularly limited, but a radiation method is preferred. For example, the polymer chain substrate (the polymer to be grafted) and the graft monomer material coexist, and the radiation is continuously or intermittently irradiated, or more preferably, the radiation is applied to the polymer substrate before the coexistence of both. Preliminary irradiation. As the radiation, an electron beam, X-ray or γ-ray is used. Upon irradiation, the polymer substrate generates and activates free radicals.

The degree of grafting can be determined by several factors, but most importantly, the length of time the activated substrate is in contact with the graft monomer,
The extent of preactivation of the substrate by radiation, the extent to which the grafted monomeric material can penetrate the substrate, and the temperature at which the substrate and monomer are in contact. For example,
When the graft monomer is an acid, the degree of grafting can be observed by sampling the solution containing the monomer, titrating against the base, and measuring the residual monomer concentration. The degree of grafting is preferably from 2 to 20% of the final weight, particularly preferably from 3 to 12%.
%, Particularly preferably 5 to 10%. The grafting may be performed by a method of activating (generating free radicals) the polymer substrate by light irradiation or heat.

The fluoropolymer having vinylidene fluoride as a main unit preferably has a melt flow index at 1.0 ° C. or less of 1.0 g / 10 min at 230 ° C. and 10 kg, more preferably 0.2 to 0.7 g / 10 min. preferable. The melt flow index is
It is a value measured by the method described in standard ASTM D1238. When the melt flow index is 1.0 g / 10 min or less, the mechanical strength of the solid electrolyte layer is improved, and the ionic conductivity at room temperature is further improved.

Further, by using a porous body of a fluoropolymer having vinylidene fluoride as a main unit, the rate characteristics, low-temperature characteristics, and the like are further improved. The density of the porous body is preferably ^{0.60g / cm 3 ~1.30g / cm 3} , particularly preferably 0.70~1.00g / cm ^3. If the density of the porous body is less than 0.60 g / cm ³ , there is a concern that the mechanical strength is reduced, and that the porous structure becomes difficult to handle at the time of producing the laminated structure, and the density is 1.30 g / cm ^3.
If it is larger, it is difficult to obtain the desired effect of improving the rate characteristics and low-temperature characteristics.

The average pore diameter of the pores in the porous body is preferably 0.01 to 10 μm, particularly preferably 0.1 to 10 μm.
５5.0 μm. The “average pore diameter” was determined by taking out arbitrary 10 pores by SEM observation, calculating the average value of the pore diameters of these 10 pores, and determining the average pore diameter.

The lithium salt (electrolyte) constituting the electrolytic solution (lithium salt (electrolyte) + compatible solvent) used for the solid electrolyte layer is LiClO ₄ , LiBF ₄ , LiP
F ₆ , LiAsF ₆ , LiAlCl ₄ and Li (CF ₃
One or more selected from the group consisting of SO ₂ ) ₂ N is used. Examples of the compatible solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, , 3-dioxolan, 2-methyltetrahydrofuran, diethyl ether and the like, and any one or a mixture of two or more selected from these are used. When a mixed solvent is used, a mixture containing at least one selected from diethyl carbonate and ethyl methyl carbonate, and further containing ethylene carbonate, propylene carbonate, and dimethyl carbonate is particularly preferable. The mixing ratio of each component constituting such a mixture is at least one type selected from diethyl carbonate and ethyl methyl carbonate, from 25% by volume to 50% by volume.
% By volume, more preferably 30% by volume to 35% by volume. In ethylene carbonate, the mixing ratio is preferably 4% by volume to 20% by volume,
More preferably, it is 6% by volume to 18% by volume. In propylene carbonate, the mixing ratio is preferably from 3% by volume to 17% by volume, and more preferably from 5% by volume to 15% by volume. In dimethyl carbonate, the mixing ratio is preferably more than 40% by volume and 60% by volume or less, and more preferably 45% by volume to 55% by volume.

The lithium salt (electrolyte) concentration in the electrolyte is
It is preferably from 0.1 mol / L to 2 mol / L, particularly preferably from 0.5 mol / L to 1.5 mol / L. If the concentration of the salt (electrolyte) is such a preferable concentration, more preferable results can be obtained in terms of rate characteristics and low-temperature characteristics.

The operating temperature of the battery (especially at low temperatures)
For the purpose of preventing crystallization of the electrolytic solution at the same time, together with the above compatible solvent, tetraethylene glycol dimethyl ether,
It is preferable to use a plasticizer such as N-methyl-pyrrolidone (1-methyl-2-pyrrolidone), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether. The amount of the plasticizer used is 1 to the compatible solvent.
% By weight is preferred. By adding the plasticizer, crystallization of the electrolyte solution that has been impregnated (impregnated) into the fluoropolymer hardly occurs, and sufficient ion conductivity of the solid electrolyte layer can be secured.

The thickness of the solid electrolyte layer varies depending on the shape, size and the like of the sheet electrodes (positive sheet electrode and negative electrode sheet electrode), but generally the average thickness is 5 to 100 μm.
It is particularly preferably 8 to 50 μm, particularly preferably 10 to 30 μm. The thickness of the solid electrolyte layer referred to here is a state interposed between the positive electrode sheet electrode and the negative electrode sheet electrode (state in which the battery is actually assembled).
And is equal to the separation distance between the positive electrode electrode and the negative electrode electrode.

In the present invention, the method for forming the solid electrolyte layer is not particularly limited. For example, (a) a polymer substrate material is formed into a film by molding into a film by a known molding method such as extrusion molding, or a coating liquid (paste) is prepared by mixing the polymer substrate material and an appropriate solvent. Then, the coating liquid (paste) is applied to the surface of the release substrate using a suitable coater to form a coating film, and the coating film is heated, dried, and then peeled from the release substrate. A method in which the obtained film is immersed in an electrolytic solution (a solution in which a lithium salt is dissolved in a compatible solvent) to be gelled (including a case where the film is immersed in a solution together with a positive electrode and a negative electrode in a battery manufacturing process). (B) A lithium salt for an electrolyte and a compatible solvent are dissolved in an appropriate solvent, a material for a polymer substrate is further added, and the material for a polymer substrate is dissolved while heating, if necessary, to form a coating solution ( Paste) and peel it off A coating film is formed by applying an appropriate coater on the surface of the base material for coating, and the coating film is heated stepwise, heated and dried to evaporate the solvent, and the solid electrolyte layer is separated from the base material for peeling. How to peel off the
(C) forming a coating film directly on at least one surface of the positive electrode sheet electrode and / or the negative electrode by a coating liquid (paste) in which the above-mentioned lithium salt, the compatible solvent and the polymer substrate material are dissolved, and evaporating the solvent; To form a solid electrolyte layer.

In the above methods (a) to (c), if a foaming agent is further added to and mixed with the coating liquid (paste) to generate bubbles as the solvent evaporates, the polymer substrate is present in a porous body. A solid electrolyte layer can be obtained.

As the solvent in the methods (b) and (c), for example, tetrahydrofuran (THF),
Dimethylacetamide, dimethylformamide and the like are preferred.

As the foaming agent used when the polymer substrate is made into a porous body, any of a decomposable foaming agent, a gas foaming agent and a volatile foaming agent can be used. A gas foaming agent or a volatile foaming agent is preferable. As the gas foaming agent, nitrogen, carbon dioxide, propane, neopentane, methyl ether, methane difluoride methane, n-butane, isobutane and the like are preferable. Examples of the foaming agent include n-octanol, 1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2-pentanol, 3-pentanol, and 2-pentanol.
Methyl-2-butanol, 3-methyl-2-butanol and the like are preferred. In the above methods (b) and (c), a volatile foaming agent is preferred, among which n-octanol, 1-pentanol, 3-methyl-1-butanol and the like are particularly preferred, and n-octanol is particularly preferred. .

The density of the porous body when the polymer substrate is made into a porous body is adjusted by changing the amount of the foaming agent and various conditions at the time of production. For example, in the case of the method (a), the manufacturing conditions that greatly affect the density (expansion degree) other than the amount of the foaming agent include a molding temperature, a molding speed, and a molding pressure. In the case of the methods (b) and (c), the production conditions that greatly affect the density (expansion degree) other than the amount of the foaming agent include a coating speed, a drying temperature profile, a degree of exhaustion, and a molding speed. is there.

As an electrolyte used in a battery of a type in which a separator is interposed between sheet electrodes, an electrolyte (lithium salt (electrolyte) + compatible solvent) for impregnating the polymer substrate of the solid electrolyte layer is used. .

As the packaging material in the sheet-shaped lithium secondary battery of the present invention, a thermoplastic resin laminated metal sheet or a thermoplastic resin laminated foil having a thermoplastic resin laminate on one or both sides is preferable. The exterior material having such a thermoplastic resin laminate has a superior heat-sealing property by utilizing the thermoplastic resin laminate in terms of excellent anti-permeation properties against water and gas permeation and electric insulation. It is preferable because it can be sealed.

[0052]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples. Example 1 [Preparation of negative electrode sheet electrode] Fibrous graphite serving as a negative electrode active material and polyvinylidene fluoride serving as a binder were mixed with N
-Mixed in methylpyrrolidone to obtain a slurry of a negative electrode active material composition. In the negative electrode active material composition, the binder was 10% by weight. The slurry was applied on both sides of a 15 μm thick copper foil serving as a current collector for the negative electrode, dried and rolled to form a negative electrode active material layer. A nickel plate was welded to the negative electrode current collector to form a lead, and a rectangular negative electrode sheet electrode having the following dimensions was obtained. Size of sheet electrode: 5 cm × 3 cm Thickness of sheet electrode: 160 μm Similarly, a negative electrode sheet electrode of the same size having a negative electrode active material layer on only one side of a copper foil was produced.

[Preparation of Positive Electrode Sheet Electrode] LiCoO _{2 serving as} a positive electrode active material, polyvinylidene fluoride serving as a conductive material and a binder were mixed in N-methylpyrrolidone and uniformly dispersed to form a slurry. I got something. In the positive electrode active material composition, the conductive material was 5% by weight and the binder was 4% by weight. The slurry was applied on both sides of an aluminum plate as a current collector for the positive electrode, dried, and rolled to form a positive electrode active material layer. An aluminum plate was welded to the current collector for the positive electrode to form a lead, and a rectangular positive electrode sheet electrode having the following dimensions was obtained. Sheet electrode size: 4.0 cm × 2.8 cm Sheet electrode thickness: 150 μm

[Preparation of Porous Polyvinylidene Fluoride Film] A coating liquid was prepared by mixing polyvinylidene fluoride, dimethylformamide (DMF) and n-octanol, and the coating liquid was coated on a substrate (aluminum foil). After heating and drying the coating film, it was peeled off from the substrate to obtain a porous film having a density of 0.75 g / cm ³ and an average thickness of 25 μm. Then, this film is cut to a predetermined size,
A bag having a size capable of accommodating the single positive electrode sheet electrode was produced by using a hot press having a hot press fitting having a broken line shape.

[Assembly of laminated structure] A positive electrode sheet electrode (8 pieces) accommodated in a bag of a porous polyvinylidene fluoride film, a negative electrode sheet electrode (7 pieces having an active material layer on both surfaces, 2 with active material layer)
Are alternately stacked, and the lead of each positive electrode sheet electrode is Ni
The laminated structure was assembled by welding to a positive electrode current collecting terminal made of a plate and welding the lead of each negative electrode sheet electrode to a negative electrode current collecting terminal made of a Ni plate. Next, an adhesive tape having a width of 47 mm (tape substrate: a polypropylene film having a thickness of 50 μm, an adhesive layer: a silicone-based adhesive having a thickness of 20 μm) was prepared.
When wound around the above-mentioned laminated structure, a portion covering a side surface of the laminated structure (a set of opposed side surfaces different from the side surface from which the current collecting terminal protrudes and the opposite side surface) is formed by a plurality of circular portions. (A diameter of each hole was set to about 2.0 mm, and an interval between two adjacent holes was set to 1 mm). Then, the pressure-sensitive adhesive tape having the plurality of through-holes was actually wound around the laminated structure, and the plurality of sheet electrodes constituting the laminated structure were bound and fixed, as shown in FIG. The ratio of the through hole to the portion of the laminated structure where the adhesive tape is wound around the side surface of the laminated structure of the adhesive tape (the total opening area of the plurality of through holes with respect to the area of the portion covering the side surface of the laminated structure of the adhesive tape) Was 60%. Next, in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a ratio of 50% by volume: 50% by volume, a concentration of LiPF ₆ of 1.0 mol / L ( (Concentration after preparation) to form a solid electrolyte layer by gelling the porous polyvinylidene fluoride film. At this time, the time required for the solution of LiPF ₆ to penetrate all the corners of the porous polyvinylidene fluoride film in the laminated structure and to reach between all the positive electrode-negative sheet electrodes (ie, The time required to achieve a proper penetration state) was 5 minutes. Further, the thickness of the solid electrolyte layer formed between each sheet electrode was substantially the same within the range of 22 to 28 μm. The permeation (injection) time of the electrolyte solution was initially charged for a plurality of batteries manufactured by variously changing the permeation time (working time) of the electrolyte solution, and a normal capacity (maximum capacity) was obtained. This is the time for which the permeation time was the minimum of those obtained. The thickness of the solid electrolyte layer was measured with a micrometer.

[Assembly of a sheet-shaped lithium secondary battery] The laminated structure wound with the above-mentioned pressure-sensitive adhesive tape is sequentially laminated from the inner side with a laminated structure of a heat seal layer, an insulating layer having electrolytic solution resistance, an aluminum layer and an insulating layer. It is housed in an exterior material (bag shape) made of a laminated film, and the positive current collecting terminal and the negative current collecting terminal protrude from the opening,
The opening of the exterior material was heat-sealed and sealed to complete a sheet-shaped lithium secondary battery.

Comparative Example Example 1 was repeated except that no through-hole was formed in the adhesive tape.
In the same manner as in the above, a sheet-shaped lithium secondary battery was produced.
The time required for the solution of LiPF ₆ to penetrate all the corners of the porous polyvinylidene fluoride film in the laminated structure and to reach all the space between the positive electrode and the negative electrode was about 60 minutes. Met.

The following low-temperature characteristic test and rate characteristic test were performed on the batteries produced in the above Examples and Comparative Examples. As a result, the battery of the example and the battery of the comparative example exhibited the same battery performance. Example (low-temperature characteristic (discharge capacity change rate) 85%, rate characteristic 97%) Comparative example (low-temperature characteristic (discharge capacity change rate) 86%, rate characteristic 97%) It was confirmed that it was possible to obtain a high-performance sheet-shaped lithium secondary battery which was significantly shorter than in the past and had no unnecessary gaps between the sheet electrodes in the laminated structure, and was capable of being obtained.

[Low temperature characteristic test] After charging the produced lithium ion secondary battery at room temperature, this was charged to -20.
It is left for 24 hours in an air atmosphere at ℃. The charge is 1
After a current was supplied at a constant current of C (600 mA) until the voltage reached 4.2 V, a current was supplied at a constant voltage of 4.2 V until the entire charging time reached 2.5 hours. Next, this-
0.5C (300mAh) /
Discharge is performed at a 2.5 V cutoff voltage, and a discharge capacity [mA · H] at that time is obtained. At room temperature (20 ° C.), charging and discharging are performed under the same conditions, and the discharge capacity [mA · H] is obtained. Furthermore, the discharge capacity at −20 ° C. was divided by the discharge capacity at room temperature to obtain a discharge capacity change rate.

[Rate Characteristic Test] At room temperature (20 ° C.)
2C discharge was performed, and the ratio of the discharge capacity to the total capacity was calculated. Note that 2C refers to a constant current of 1200 mA with respect to the discharge capacity (600 mA) of the lithium ion secondary battery.

[0061]

As is clear from the above description, according to the present invention, a laminated structure (a plurality of units in which a positive electrode sheet electrode and a negative electrode sheet electrode are stacked with a separator or a solid electrolyte layer interposed therebetween) as a power generating element is included. Although the tape is wrapped around the laminated structure and the plurality of sheet electrodes constituting the laminated structure are bound and fixed, it is possible to infiltrate the electrolytic solution to every corner of the laminated structure in a short time, There is no unnecessary gap between the sheet electrodes in the laminated structure (each sheet electrode uniformly adheres to the separator or the solid electrolyte layer), and sheet-like lithium exhibiting excellent battery characteristics, particularly, good low-temperature characteristics and rate characteristics. A secondary battery can be manufactured efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a laminated structure (power generation element) used for a sheet-shaped lithium secondary battery according to an example of the present invention.

FIG. 2 is an enlarged sectional view of a main part showing a state of lamination of a positive electrode sheet electrode and a negative electrode sheet electrode in the laminated structure of FIG.

FIG. 3 is a schematic perspective view showing a state in which an adhesive tape having a plurality of through holes is wound around the laminated structure of FIG. 1;

FIG. 4 is a schematic perspective view of a laminated structure in which a pressure-sensitive adhesive tape in a conventional sheet-shaped lithium secondary battery is wound.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 positive electrode sheet electrode 2 negative electrode sheet electrode 3 multilayer structure (power generation element) 3A-1, 3A-2 main surface of multilayer structure 3B-1, 3B-2, 3C-1, 3C-2 side surface of multilayer structure 4 Separator or solid electrolyte layer 5 Adhesive tape 51 Through hole

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tosho 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Shogo Tanno 4-3-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Wire (72) Inventor Mitsuhiro Marumoto 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Co., Ltd.Itami Works F-term (reference) 5H029 AJ02 AJ06 AK03 AL07 AM02 AM03 AM04 AM05 AM07 AM16 BJ04 BJ06 BJ12 CJ07 DJ14 DJ15 EJ12 HJ03 HJ06 HJ07 HJ08 HJ12

Claims (5)

[Claims] 1. A power generation element comprising a laminated structure including a plurality of units in which a positive electrode sheet electrode and a negative electrode sheet electrode are laminated with a separator or a solid electrolyte layer interposed therebetween, and a tape wound around an outer periphery of the laminated structure. A sheet-like lithium secondary battery in which a plurality of sheet electrodes constituting a body are bound and fixed with a tape, and the surfaces of two sheet electrodes located at the outermost sides of the stacked structure are referred to as main surfaces of the stacked structure. The sheet-like lithium, wherein a plurality of through-holes are dispersed and provided in a tape covering a side surface of the laminated structure, wherein a surface on which the end surfaces of the plurality of sheet electrodes are gathered is referred to as a side surface of the laminated structure. Rechargeable battery. 2. The method according to claim 1, wherein the positive electrode sheet electrode and the negative electrode sheet electrode are substantially rectangular sheets, the laminated structure has a substantially rectangular parallelepiped outer shape, and tapes are provided on both main surfaces of the laminated structure and a pair of opposed side surfaces. 2. The lithium ion secondary battery according to claim 1, wherein the area of the winding region of the tape is 30% or more of the total area of the pair of opposite side surfaces with the two main surfaces of the laminated structure. 3. The hole diameter of each of the plurality of through holes is 0.1-8.
3. The sheet-shaped lithium secondary battery according to claim 1, wherein the distance between the adjacent two holes is set in a range of 0.05 to 8 mm. 4. 4. Between the positive electrode sheet electrode and the negative electrode sheet electrode,
The sheet-shaped lithium secondary battery according to any one of claims 1 to 3, further comprising a solid electrolyte layer mainly composed of a salt, a compatible solvent, and a fluoropolymer having vinylidene fluoride as a main unit. 5. The sheet-shaped lithium secondary battery according to claim 4, wherein the fluoropolymer of the solid electrolyte layer is a porous body having a density of 0.60 to 1.30 g / cm ³ .