JP6771292B2 - Manufacturing method of current collector for flexible secondary battery, electrode for flexible secondary battery, electrode laminated assembly for flexible secondary battery, flexible secondary battery and electrode for flexible secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a current collector for a flexible secondary battery, an electrode for a flexible secondary battery, an electrode laminated assembly for a flexible secondary battery, a flexible secondary battery, and an electrode for a flexible secondary battery.

In recent years, as information devices have become more sophisticated, higher performance, smaller size, and higher energy density of secondary batteries have been required. In particular, non-aqueous electrolyte secondary batteries using a non-aqueous electrolyte solution such as lithium ion secondary batteries can increase the battery voltage and can increase the energy density. Is being actively carried out. Among them, a non-aqueous electrolyte secondary battery in which a laminate is used as an exterior material and an electrode laminate (an electrode and a separator are sequentially laminated) and an electrolytic solution are stored therein has a high degree of freedom in shape. It is attracting attention because it can be made thinner.

Among such non-aqueous electrolyte secondary batteries, the flexible secondary battery that can be repeatedly bent or wound can follow the shape of the information device and is deformed according to the deformation of the shape of the information device. Since it is possible, development is being actively carried out.

However, when the flexible secondary battery including the conventional electrode laminate is bent or wound, a deviation (perimeter difference) in the plane direction occurs between each layer of the electrode laminate.

In order to maintain the positional relationship between the layers of the electrode laminate when the flexible secondary battery is bent or wound, one end of the electrode laminate is fixed and the other end is movable. The next battery is proposed in Patent Document 1.

U.S. Patent Application Publication No. 2014/0079979

However, when the flexible secondary battery is repeatedly bent or wound, the surfaces of the positive electrode and the negative electrode of the electrode laminate are repeatedly displaced, and the generated frictional force causes partial peeling between the positive electrode or the negative electrode and the separator. It ends up. In such a case, a region in which charging / discharging cannot be performed occurs in the flexible secondary battery, and the performance of the flexible secondary battery deteriorates. The flexible secondary battery proposed in Patent Document 1 can maintain the positional relationship in the plane direction between the layers of the electrode laminate, but the performance of the flexible secondary battery due to the occurrence of the above-mentioned deviation is Deterioration cannot be prevented.

Further, in the electrode laminate, it is necessary to absorb the lithium ions emitted from the positive electrode at the time of charging at the opposite negative electrode. Lithium ions absorbed by the negative electrode can return to the opposite positive electrode at the time of discharge. However, if the lithium ions emitted from the positive electrode during charging cannot be absorbed by the negative electrode, metallic lithium may precipitate. Precipitation of metallic lithium can lead to defects in the secondary battery such as short-circuit defects. Therefore, the conventional electrode laminate is configured so that the area of the main surface of the negative electrode facing the positive electrode is larger than that of the main surface of the facing positive electrode, and the lithium ions emitted from the positive electrode can be absorbed by the negative electrode. ..

However, in the flexible secondary battery, the positional relationship between the positive electrode and the negative electrode cannot be kept constant because the positive electrode and the negative electrode are displaced by the difference in peripheral length at the end of the electrode when bent or wound. That is, a part of the positive electrode cannot face the negative electrode at the electrode end, that is, it may protrude from the negative electrode end. In such a case, problems such as precipitation of metallic lithium and a decrease in the amount of discharge due to the absence of the positive electrode facing the negative electrode may occur.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a new and improved method capable of preventing deterioration of performance when a flexible secondary battery is repeatedly bent or wound. It is an object of the present invention to provide a method for manufacturing a flexible secondary battery current collector, a flexible secondary battery electrode, a flexible secondary battery electrode laminated assembly, a flexible secondary battery, and a flexible secondary battery electrode.

In order to solve the above problems, according to a certain viewpoint of the present invention, a sheet-shaped first current collector and a sheet-shaped current collector at least partially connected to the first current collector so as to be electrically connected to the first current collector. A flexible current collector having a second current collector, and the first current collector and the second current collector are arranged adjacent to each other via a buffer layer or so as to be in contact with each other. A current collector for the secondary battery is provided.

From this viewpoint, it is possible to prevent deterioration of performance when the flexible secondary battery is repeatedly bent or wound.

Here, the buffer layer may include a resin film.

From this viewpoint, it is possible to prevent deterioration of performance when the flexible secondary battery is repeatedly bent or wound.

Further, the resin film may contain a fluororesin or a polyolefin resin.

From this viewpoint, it is possible to prevent deterioration of performance when the flexible secondary battery is repeatedly bent or wound.

Further, the buffer layer may include a liquid layer.

From this viewpoint, it is possible to prevent deterioration of performance when the flexible secondary battery is repeatedly bent or wound.

According to another aspect of the present invention, at least a part of the first electrode active material layer and the sheet-shaped first current collector supporting the first electrode active material layer on one main surface. A sheet-shaped second current collector connected so as to be conductive with the first current collector, and a main surface of the second current collector on the side opposite to the main surface of the first current collector side. It has a second electrode active material layer supported on a surface, and the first current collector and the second current collector are arranged so as to be adjacent to each other via a buffer layer or in contact with each other. Flexible secondary battery electrodes are provided.

From this point of view, it is possible to provide a flexible secondary battery capable of preventing deterioration of performance when repeatedly bent or wound.

According to another aspect of the present invention, there is provided an electrode laminated assembly for a flexible secondary battery including the electrode for the flexible secondary battery.

From this point of view, it is possible to provide a flexible secondary battery capable of preventing deterioration of performance when repeatedly bent or wound.

According to another aspect of the present invention, a step of forming an electrode active material layer on one main surface of the first sheet-shaped current collector, and the first current collector and the second sheet-shaped current collector. The other main surface of the first current collector is opposed to the main surface of the second current collector so that the current collectors are adjacent to each other via a buffer layer or in contact with each other. Provided is a method for manufacturing an electrode for a flexible secondary battery, which comprises a step of connecting a current collector and the second current collector.

From this point of view, it is possible to manufacture a flexible secondary battery capable of preventing deterioration of performance when repeatedly bent or wound.

According to another aspect of the present invention, a sheet-shaped first current collector and a sheet-shaped second current collector connected so that at least a part thereof is electrically connected to the first current collector. A flexible secondary battery current collector is prepared, wherein the first current collector and the second current collector are arranged so as to be adjacent to each other via a buffer layer or in contact with each other. A method for manufacturing an electrode for a flexible secondary battery, which comprises a step of forming an electrode active material layer on a main surface of the first current collector opposite to the side of the second current collector. Is provided.

From this point of view, it is possible to manufacture a flexible secondary battery capable of preventing deterioration of performance when repeatedly bent or wound.

As described above, according to the present invention, it is possible to provide a flexible secondary battery capable of preventing deterioration of performance when repeatedly bent or wound.

It is a top view which shows the appearance of the flexible secondary battery which concerns on 1st Embodiment of this invention. FIG. 5 is a cross-sectional view taken along the line xx'of the flexible secondary battery shown in FIG. It is a vertical partial enlarged sectional view of the flexible secondary battery shown in FIG. It is a partially enlarged sectional view of the flexible secondary battery which concerns on the modification of 1st Embodiment. It is a vertical sectional view of the flexible secondary battery which concerns on 2nd Embodiment of this invention. It is a vertical partial enlarged sectional view of the flexible secondary battery shown in FIG. It is a schematic diagram which shows the outline of the measurement experiment of the dynamic friction force between current collectors.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

[1. Flexible rechargeable battery]
<First Embodiment>
The configuration of the flexible secondary battery 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a plan view showing the appearance of the flexible secondary battery 1 according to the first embodiment of the present invention, and FIG. 2 is a sectional view taken along line xx'of the flexible secondary battery 1 shown in FIG. Is a partially enlarged cross-sectional view of the flexible secondary battery 1 shown in FIG. 1 in the vertical direction.

The flexible secondary battery 1 shown in FIGS. 1 to 3 is a non-aqueous electrolyte secondary battery having a sheet shape as a whole and having flexibility. The flexible secondary battery 1 can be repeatedly bent or wound due to its overall shape and flexibility.

As shown in FIGS. 1 and 2, the flexible secondary battery 1 includes negative electrodes 10A, 10B, 10C, a positive electrode 30, a separator 50, a negative electrode terminal 70, a positive electrode terminal 80, and an electrolytic solution (not shown). And an exterior material (not shown). Further, the negative electrodes 10A, 10B, 10C, the positive electrode 30, and the separator 50 are laminated bodies in which the negative electrodes 10A, 10B, 10C, and the positive electrode 30 are alternately laminated via the separator 50 (electrode laminated assembly for flexible secondary battery). ) Is formed.

In the illustrated embodiment, the flexible secondary battery 1 is composed of three negative electrodes 10A, 10B, 10C and two positive electrodes 30, but the flexible secondary battery according to the present invention is not limited thereto. In the flexible secondary battery according to the present invention, the number of positive electrodes and negative electrodes can be appropriately selected according to the required capacity, voltage and degree of flexibility. Further, in the flexible secondary battery 1, the end faces of the laminated body thereof are formed by the negative electrodes 10A and 10C, but the flexible secondary battery according to the present invention is not limited to this. In the flexible secondary battery according to the present invention, either the positive electrode or the negative electrode may be arranged at the end of the laminate. Further, one of the end faces of the laminated body may be composed of a positive electrode and the other may be composed of a negative electrode.

(Construction of negative electrode)
The negative electrodes 10A, 10B, and 10C each include a negative electrode current collector (negative electrode current collector) 11, a negative electrode active material layer 13 formed on both sides of the negative electrode current collector 11, and a negative electrode current collector tab 15. More specifically, in the negative electrodes 10A and 10C forming the end faces of the laminated body of the flexible secondary battery 1, only one main surface of the negative electrode current collector 11 faces the positive electrode 30, so that the negative electrode current collector 11 is the same. The negative electrode active material layer 13 is arranged only on the main surface. On the other hand, in the negative electrode 10B sandwiched between the two positive electrodes 30, since both main surfaces of the negative electrode current collector 11 face the positive electrode 30, the negative electrode active material layer 13 is arranged on both main surfaces of the negative electrode current collector 11. ing.

The negative electrode current collector 11 is a foil formed of a conductor. The negative electrode current collector 11 may be any conductor, and is made of, for example, copper, stainless steel, nickel-plated steel, or the like.

The negative electrode active material layer 13 may be any material as long as it is used as the negative electrode active material layer 13 of the lithium ion secondary battery. For example, the negative electrode active material layer 13 may contain a negative electrode active material and may further contain a binder. The negative electrode active material is, for example, graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si) or tin (Sn), or an oxide thereof. Mixtures of fine particles of graphite and graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, titanium oxide (TiO _x ) compounds such as Li ₄ Ti ₅ O ₁₂ can be used. .. The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, for example, metallic lithium or the like can be used as the negative electrode active material.

The binder is not particularly limited, and any binder used for the negative electrode active material layer of the conventional lithium ion secondary battery can be used. For example, polyvinylidene fluoride polymer, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) polymer, vinylidene fluoride-perfluorovinyl ether polymer, vinylidene fluoride-tetrafluoroethylene (Vinylidene fluoride-tetrafluoroethylene) tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, ethylenepropylenediene ternary copolymer, styrene butadiene rubber (styrene-butadiene rubber) rubber Polymeryl-butadiene rubber, fluororubber, polyvinylidene acetate, polymethylmethacrylate, polyethylene (polymethylene), nitrocellulose, cellulose, etc.

The negative electrode current collector tab 15 is arranged at one end in the longitudinal direction of the negative electrode current collector 11. The negative electrode current collector tab 15 is formed by extending a part of the negative electrode current collector 11, and is made of the same material as the negative electrode current collector 11. The negative electrode current collecting tab 15 is welded together with the other negative electrode current collecting tabs 15 in the vicinity of the end opposite to the negative electrode current collecting portion 11 to form the negative electrode terminal 70.

The negative electrode current collector tab 15 may be made of a conductive material different from that of the negative electrode current collector 11. Further, the negative electrode current collecting tab 15 may be configured as a separate member from the negative electrode current collecting unit 11, and may be connected by welding or the like, for example.

The negative electrodes 10A, 10B, and 10C described above preferably have a smaller area than the separator 50 when viewed in a plan view. More specifically, the negative electrodes 10A, 10B, and 10C preferably have a smaller length and width than the separator 50 when viewed in a plan view. This makes it possible to prevent a short circuit between the negative electrodes 10A, 10B, 10C and the positive electrode 30.
The manufacturing method of the negative electrodes 10A, 10B and 10C will be described later.

(Construction of positive electrode)
The positive electrode 30 has a positive electrode current collector (current collector for a flexible secondary battery) 31, a positive electrode active material layer 33, and a positive electrode current collector tab 35, respectively.

FIG. 3 shows the layer structure of the positive electrode 30. As shown in the figure, the positive electrode current collector 31 and the positive electrode active material layer 33 are in the form of a sheet. Further, the positive electrode active material layer 33 is arranged on the main surface of the positive electrode current collector 31 facing the negative electrodes 10A, 10B or 10C. That is, the positive electrode active material layer 33 is arranged on both main surfaces of the positive electrode current collector 31.

As shown in FIG. 3, the positive electrode current collector 31 is arranged between the two sheet-shaped current collectors (first and second current collectors, current collector sheets) 311 and the current collector 311. It has a buffer layer 313. By arranging the two current collectors 311 adjacent to each other via the buffer layer 313, the two current collectors 311 can move to each other in a direction parallel to the main surface (planar direction). As a result, when the flexible secondary battery 1 is bent or wound, the two current collectors 311 can be preferentially displaced. Therefore, when the flexible secondary battery 1 is bent or wound, the stress caused by the difference in peripheral length at other parts of the laminated body of the flexible secondary battery 1 can be relaxed. Therefore, between the positive electrode current collector 31 and the positive electrode active material layer 33, between the negative electrode current collector 11 and the negative electrode active material layer 13, and between the positive electrode active material layer 33 or the negative electrode active material layer 13 and the separator 50. Peeling is prevented.

Further, when the flexible secondary battery 1 is bent or wound, the two current collectors 311 are preferentially displaced, so that the positions of the layers of the laminated body except between the two current collectors 311 are located. It is hard to slip off. For example, the displacement between the positive electrode active material layer 33 supported on the current collector 311 and the adjacent separator 50 and the negative electrode active material layer 13 adjacent to the separator 50 is prevented. As a result, the positive electrode 30 can more reliably face the negative electrode 10A, 10B or 10C even in the vicinity of the end portion thereof, and the positive electrode 30 is not located on the opposite side of the negative electrode 10A, 10B or 10C due to the precipitation of metallic lithium. This prevents problems such as a decrease in the amount of discharge.

As a result of the above, the flexible secondary battery 1 is prevented from deteriorating in performance when it is repeatedly bent or wound.

The current collector 311 is a sheet member composed of a conductor. The material constituting the current collector 311 is not particularly limited, and may be, for example, aluminum, stainless steel, nickel-plated steel, or the like.

The thickness of the current collector 311 is not particularly limited, but can be, for example, 1 to 100 μm, preferably 9 to 30 μm. As a result, the durability against friction caused by the displacement from the buffer layer 313 can be made high, and the positive electrode 30 can be made relatively thin.

The arithmetic mean surface roughness Ra on the side of the current collectors 311 facing each other is not particularly limited, but is, for example, 0.01 to 10 μm, preferably 0.1 to 1 μm based on JIS B 0601. It can be 5 μm. As a result, the current collectors 311 can move in the plane direction with each other with a relatively small stress, and the stress caused by the difference in peripheral length at other parts in the laminated body of the flexible secondary battery 1 can be further relaxed.

The coefficient of dynamic friction between the current collectors 311 (via the buffer layer 313) is not particularly limited, but can be, for example, 0.7 or less, preferably 0.01 to 0.6. As a result, the current collectors 311 can move in the plane direction with each other with a relatively small stress.

The coefficient of dynamic friction between the current collectors 311 (via the buffer layer 313) is larger than the coefficient of dynamic friction between the separator 50 and the negative electrodes 10A to 10C described later and / or the coefficient of dynamic friction between the separator 50 and the positive electrode 30. Small is preferable. More specifically, the coefficient of kinetic friction between the current collectors 311 (via the buffer layer 313) is the coefficient of kinetic friction between the separator 50 and the negative electrodes 10A to 10C described later and / or the separator 50 and the positive electrode 30. It is preferable that the coefficient of kinetic friction between them is, for example, 0.01 or more, preferably 0.05 or more, and more preferably 0.10 or more. As a result, the current collectors 311 can move preferentially in the plane direction, and as a result, the stress and the displacement of the positional relationship due to the difference in peripheral length in other parts of the laminated body of the flexible secondary battery 1 are further alleviated. can do.

A part of each current collector 311 is extended at one end (one end in the longitudinal direction in the drawing) to form a positive electrode current collector tab 35. The adjacent positive electrode current collecting tabs 35 are electrically connected at the positive electrode terminals 80 described later. As a result, the adjacent current collectors 311 are electrically connected to each other.

The buffer layer 313 is a layer arranged between the current collectors 311. The buffer layer 313 is interposed between the two current collectors 311 to reduce the frictional force when the current collectors 311 move in the plane direction. As a result, the current collectors 311 can move in the plane direction with each other with a relatively small stress, and the stress caused by the difference in peripheral length at other parts in the laminated body of the flexible secondary battery 1 can be further relaxed.

The buffer layer 313 is not particularly limited as long as it assists the movement of the current collectors 311 in the plane direction, and is, for example, a gel layer composed of a resin film or a gel or a liquid layer composed of a liquid. be able to.

The resin film is a film composed of a resin that is insoluble in the electrolytic solution. Such a resin film is not particularly limited as long as it is insoluble in the electrolytic solution, but is a flexible elastomer or rubber sheet such as silicone rubber, butyl rubber, fluororubber, nitrile rubber, acrylic rubber, polyurethane, and perfluoro rubber. In addition, polytetrafluoroethylene (polytetrafluoroethylene (PTFE) film, perfluoroalkoxy resin (tetrafluoroethylene perfluororo alkyl vinyl copolymer, PFA) film, perfluoroethylene propene copolymer (perfluoropolymer) fluoropolymer (perfluoroethylene) And a polyolefin resin film such as a polyethylene film, a polypropylene film, and a polybutylene film.

Among the above-mentioned resin films, the fluororesin film and the polyolefin resin film are preferable, and the PTFE film, the PFA film and the polyethylene film are more preferable. Such a film is a smooth film having excellent smoothness, and can sufficiently reduce the frictional force when the current collectors 311 move in the plane direction.

The thickness of the resin film is not particularly limited, but can be, for example, 0.1 to 200 μm, preferably 1 to 50 μm.

The arithmetic mean surface roughness Ra on the side of the resin film facing the current collector 311 is not particularly limited, but is, for example, 0.01 to 5 μm, preferably 0.01 to 1 μm, based on JIS B 0601. be able to. As a result, the frictional force when the current collectors 311 move in the plane direction can be sufficiently reduced.

The gel contained in the gel layer is not particularly limited as long as it can form a gel, and is composed of, for example, a gel-like polymer and an electrolytic solution. Examples of such polymers include fluoropolymers, and more specifically, polyvinylidene fluoride (PVDF), vinylidene fluoride (VDF) and hexafluoropropylene (HFP). Examples thereof include the copolymer of the above. If the mass ratio of HFP to VDF is too large, the fluoropolymer will dissolve in the electrolytic solution. Therefore, the mass ratio of VDF to HFP should be such that the fluoropolymer does not dissolve in the non-aqueous electrolytic solution. It may be adjusted. Other examples of fluoropolymers include copolymer P (VDF-TFE) of vinylidene fluoride and tetrafluoroethylene, and copolymer P (VDF-) of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene. TFE-HFP) and the like.

Examples of the liquid layer include silicone fluids such as silicone oil, silicone grease, silicon oxide and silicone emulsions, various electrically insulating fluids such as paraffin chloride, amine oil, glycerin, petrolatum and fluorine oil, and electrolytic solutions. Be done. Among the above, the electrolytic solution is preferable. Such an electrolytic solution is not particularly limited, and examples thereof include an electrolytic solution described later. In this case, the electrolytic solution may be the same as or different from the electrolytic solution used in the flexible secondary battery 1, but it is preferably the same.

The positive electrode current collector tab 35 is arranged at one longitudinal end of the current collector 311. The positive electrode current collector tab 35 is formed by extending a part of the current collector 311 and is made of the same material as the current collector 311. The positive electrode current collector tab 35 is welded together with other positive electrode current collector tabs 35 near the end opposite to the current collector 311 to form the positive electrode terminal 80.

The positive electrode current collector tab 35 may be made of a conductive material different from that of the current collector 311. Further, the positive electrode current collector tab 35 may be configured as a separate member from the current collector 311 and may be connected by welding or the like, for example.

The positive electrode active material layer 33 contains at least the positive electrode active material. The positive electrode active material is not particularly limited as long as it is a substance capable of reversibly storing and releasing lithium ions, and is, for example, lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, and nickel cobalt aluminum acid. Lithium (hereinafter sometimes referred to as "NCA"), lithium nickel cobalt manganate (hereinafter sometimes referred to as "NCM"), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur , Iron oxide, vanadium oxide and the like. These positive electrode active materials may be used alone or in combination of two or more.

Among the examples of the positive electrode active material mentioned above, the positive electrode active material is particularly preferably a lithium salt of a transition metal oxide having a layered rock salt type structure. The lithium salt of a transition metal oxide having such a layered rock-salt structure, for _{example, Li 1-x-y-} z Ni x Co y Al z O 2 (NCA) or _{Li 1-x-y-z} Ni lithium salt of _{x Co y Mn z O 2 (} NCM) (0 <x <1,0 <y <1,0 <z <1, and x + y + z <1) 3 -component transition metal oxide which is expressed by Can be mentioned.

Further, the positive electrode active material layer 33 may further contain a conductive agent and a binder.
The conductive agent is, for example, carbon black such as Ketjen black or acetylene black, natural graphite, artificial graphite, or the like, but is not particularly limited as long as it is for enhancing the conductivity of the positive electrode.

The binder binds the positive electrode active materials to each other and also binds the positive electrode active material to the current collector 311 of the positive electrode current collector 31. The type of the binder is not particularly limited, and any binder used for the positive electrode active material layer of the conventional lithium ion secondary battery can be used. The binder mentioned in the negative electrode active material layer 13 described above can be used.

The positive electrode 30 described above preferably has a smaller area than the separator 50 when viewed in a plan view. More specifically, it is preferable that the positive electrode 30 has a smaller length and width than the separator 50 when viewed in a plan view. This makes it possible to prevent a short circuit between the positive electrode 30 and the negative electrodes 10A, 10B, and 10C.

Further, it is preferable that the positive electrode 30 has a smaller area than the opposing negative electrodes 10A, 10B and / or 10C when viewed in a plan view. Specifically, the positive electrode 30 is preferably smaller in length and width than the opposing negative electrodes 10A, 10B and / or 10C when viewed in a plan view. More specifically, the positive electrode 30 is smaller in length and width than the opposing negative electrodes 10A, 10B and / or 10C, for example, 0.05 to 20 mm, preferably 1.0 to 10 mm, when viewed in a plan view. Is preferable. Lithium ions from the end of the positive electrode 30 tend to concentrate on the end faces of the negative electrodes 10A, 10B and / or 10C, but the area is smaller than that of the negative electrodes 10A, 10B and / or 10C to which the positive electrode 30 faces. This makes it possible to prevent concentration of lithium ions on the end faces of the negative electrodes 10A, 10B and / or 10C, and prevent precipitation of metallic lithium. As a result, it is possible to prevent problems of the flexible secondary battery 1 such as a short circuit.

Further, the distance between the current collector 311 of the positive electrode 30 and the current collector 311 of the positive electrode 30 adjacent to the positive electrode 30 (that is, the positive electrode active material layer 33, the two separators 50, and the negative electrode 10A, 10B or 10C). The total thickness) is not particularly limited, but can be, for example, 50 to 1000 μm, preferably 100 to 500 μm. By arranging the positive electrodes 30 having the multi-layered current collectors at predetermined intervals in this way, when the flexible secondary battery 1 is bent or wound, the stress on each member between the positive electrodes 30 is applied. Is fully relaxed.

The method for manufacturing the positive electrode 30 described above will be described later.

(Structure of separator)
The separator 50 is not particularly limited, and may be any as long as it is used as a separator for a lithium ion secondary battery. As the separator 50, it is preferable to use a porous membrane, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the resin constituting the separator 50 include a polyolefin resin typified by polyethylene, polypropylene, etc., a polyethylene terephthalate, a polybutylene terephthalate, and the like. Polyethylene resin, PVDF, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene ( terrafluoroethylene polymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetonee copolymer, vinylidene fluoride copolymer. -Ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene (Hexafluoropolypropylene) polymer, vinylidene fluoride-ethylene (ethylene) -tetrafluoroethylene (terrafluoropolyethylene) copolymer and the like can be mentioned.

Further, it is preferable that an adhesive layer is formed on both surfaces of the separator 50. The adhesive layer improves the adhesive force between each electrode and the separator 50, and is a porous body. The adhesive layer is not particularly limited as long as it is used for a non-aqueous electrolyte secondary battery. Preferred resins constituting the adhesive layer include polyvinylidene fluoride (PVDF) -based fluororesins. Examples of such a fluororesin include, in addition to PVDF, a copolymer of vinylidene fluoride (VDF) and another monomer (hexafluoropropylene (HFP), etc.).

The adhesive layer containing the fluororesin is formed on the surface of the separator 50 by, for example, the following first method or second method.

In the first method, a slurry is prepared by dissolving a fluororesin in an organic solvent such as NMP (N-methylpyrrolidone), dimethylacetamide, and acetone. Then, after applying this slurry to the separator 50, the fluororesin is phase-separated using a poor solvent such as water, methanol, or tripropylene glycol to form an adhesive layer in which the fluororesin is made porous. In the second method, a heated slurry is prepared by dissolving a fluororesin in a heated electrolytic solution using dimethyl carbonate, propylene carbonate, ethylene carbonate or the like as a solvent. Then, the coating layer is formed by applying this heated slurry to the separator 50. Then, by cooling the coating layer, the fluororesin is transferred to a gel (a porous film swollen with an electrolytic solution). That is, an adhesive layer is produced.

By forming such an adhesive layer on the surface of the separator 50, the displacement between the negative electrode 10A, 10B or 10C or the positive electrode 30 and the separator 50 can be more reliably eliminated. As a result, the two current collectors 311 in the positive electrode 30 are more likely to be displaced with priority, and the effect of the present invention can be obtained more remarkably.

However, in order to develop the adhesiveness of the adhesive layer, a so-called heat pressing step of pressing the electrode laminate at a constant pressure and temperature in the presence of an electrolytic solution is required. This heat press process is performed at a high temperature such that a sol-gel transition of the polymer occurs. As a result, the polymer in the adhesive layer enters the micropores of the electrode or separator (so-called anchor effect). In addition, the polymer in the adhesive layer interacts with the binder present on the electrode surface. By these actions, the adhesive force between the electrodes is developed. The conditions of the heat press are not particularly limited, but for example, the temperature is preferably 25 to 90 ° C. and the pressure is preferably 10 to 100 kgf / cm ² . If the temperature is less than 25 ° C., the adhesive force between the separator 50 and the negative electrodes 10A, 10B, 10C, and the positive electrode 30 may not be sufficient. If the temperature exceeds 90 ° C., the buffer layer may melt and adhere to the current collector foil. In addition, the electrolytic solution may boil and gas may be generated. If the pressure is less than 10 kgf / cm ² , the adhesive force between the separator 50 and the negative electrodes 10A, 10B, 10C, and the positive electrode 30 may not be sufficient. If the pressure exceeds 100 kgf / cm ² , the electrode laminate may be excessively compressed and the characteristics may be deteriorated.

A heat-resistant filler may be added to the adhesive layer in order to improve the heat resistance of the flexible secondary battery 1. The heat-resistant filler is, for example, ceramic particles, and more specifically, metal oxide particles. Examples of the metal oxide particles include fine particles of alumina, boehmite, titania, zirconia, magnesia, zinc oxide, aluminum hydroxide, magnesium hydroxide and the like.

(Composition of electrolyte)
In the present embodiment, the electrolytic solution is a non-aqueous electrolyte solution, which is a solution in which the electrolyte is dissolved in an organic solvent. The electrolytic solution exists so as to fill the gaps between the members packaged in the exterior material. In particular, the electrolytic solution is impregnated in the separator 50 and enables the movement of lithium ions between the negative electrode 10A, 10B or 10C and the positive electrode 30.

The electrolyte is not particularly limited, and for example, in this embodiment, a lithium salt can be used. Examples of the lithium _{salt, LiClO 4, LiBF 4, LiAsF} 6, LiPF 6, LiPF 6-x (C n F 2n + 1) x ( where, 1 <x <6, n = 1 or 2), LiSCN, LiBr, Inorganic ions containing one of lithium (Li), sodium (Na) or potassium (K) such as LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, etc. Salt, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClo ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃₎ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClo ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate (benzoate), (C ₂ H ₅ ) ₄ N-phthalate (phtalate), lithium stearyl sulfonate (stearyl sulphonic acid lithium), lithium octyl sulfonate (octyl sulphonic acid), lithium dodecylbenzene sulfonate (dodecy) Examples thereof include organic ion salts such as bentene sulphonic acid), and these ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte solution used in the conventional lithium secondary battery, and is not particularly limited. In this embodiment, a non-aqueous electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.8 to 1.5 mol / L can be used.

Examples of the organic solvent include propylene carbonate (propylene carbonate), ethylene carbonate (ethylene carbonate), butylene carbonate (ethylene carbonate), chloroethylene carbonate (chloroethylene carbonate), vinylene carbonate (vinylene carbonate) and the like. ) Classes; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate (dimethyl carbonone), diethyl carbonate (diethyl carbonate), ethyl methyl carbonate (ether methyl carbonate) and the like. Classes; chain esters such as methyl formate, methyl acetate, methyl butyric acid methyl, ethyl acetate, ether rotate, etc .; tetrahydrofuran (Terahydro) Derivatives thereof; 1,3-dioxane (dioxane), 1,4-dioxane (dioxane), 1,2-dimethoxyethane (dimethoxyether), 1,4-dibutoxiethane, methyl diglyme, etc. Ethers; nitriles such as acetonitrile, benzonitrile, benzonitile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or Examples of the derivative and the like alone or a mixture of two or more thereof can be mentioned, but the present invention is not limited thereto. The electrolytic solution is impregnated in the separator 50.

(Composition of exterior material)
The composition of the exterior material is not particularly limited, and any material applicable to a non-aqueous electrolyte secondary battery can be suitably used in the present embodiment. For example, the exterior material may be a laminate such as an aluminum laminate. When the exterior material is laminated, it is difficult for the exterior material to suppress the shape change of the electrode laminate.

In the flexible secondary battery 1 described above, the positive electrode current collector 31 of the positive electrode 30 is multi-layered and is configured to include a plurality of current collectors 311. The current collectors 311 are configured to be movable with each other. ing. As a result, when the flexible secondary battery 1 is bent or wound, the two current collectors 311 can be preferentially displaced. Therefore, when the flexible secondary battery 1 is bent or wound, the stress caused by the difference in peripheral length at other parts of the laminated body of the flexible secondary battery 1 can be relaxed. Therefore, between the positive electrode current collector 31 and the positive electrode active material layer 33, between the negative electrode current collector 11 and the negative electrode active material layer 13, which will be described later, and between the positive electrode active material layer 33 or the negative electrode active material layer 13 and the separator 50. Peeling between them is prevented.

Further, in the flexible secondary battery 1, the two current collectors 311 are preferentially displaced when bent or wound, so that between the layers of the laminated body except between the two current collectors 311. The position is hard to shift. The positive electrode 30 can more reliably face the negative electrode 10A, 10B or 10C even in the vicinity of its end, and discharge due to precipitation of metallic lithium or the absence of the positive electrode 30 facing the negative electrodes 10A, 10B and 10C. Problems such as volume reduction are prevented.

As a result of the above, the flexible secondary battery 1 is prevented from deteriorating in performance when it is repeatedly bent or wound.

<Modification example>
The first embodiment of the present invention has been described above. Hereinafter, some modifications of the first embodiment of the present invention will be described. In addition, each modification described below may be applied alone to the first embodiment of the present invention, or may be applied in combination to the first embodiment of the present invention. Further, each modification may be applied in place of the configuration described in the first embodiment of the present invention, or may be additionally applied to the configuration described in the first embodiment of the present invention. May be good.

First, as a modification of the above-described first embodiment, for example, a flexible secondary battery 1A having a configuration as shown in FIG. 4 can be mentioned. FIG. 4 is a partially enlarged cross-sectional view of the flexible secondary battery 1A according to the modified example of the first embodiment. The flexible secondary battery 1A shown in FIG. 4 has a different configuration of the positive electrode current collector 31A from the flexible secondary battery 1. The positive electrode current collector 31A does not have a buffer layer and is adjacent to each other so that the current collectors 311 are in contact with each other. Even in such a case, the current collectors 311 can move to each other. Therefore, the flexible secondary battery 1A can also have the same effect as the flexible secondary battery 1 described above.

As another modification, there is a flexible secondary battery in which a buffer layer is partially arranged between the current collectors 311 and the current collectors 311 are in contact with each other in the other portion. Such a flexible secondary battery can also exhibit the same effect as the flexible secondary battery 1 described above.

Further, as another modification, there is a flexible secondary battery in which a plurality of buffer layers are arranged between the current collectors 311. The plurality of buffer layers may be, for example, one in which a plurality of resin films are arranged, or one in which a resin film and a liquid layer or a gel layer are arranged. In particular, when a plurality of layers, for example, two resin films are arranged, the frictional force when the current collectors 311 move in the plane direction can be sufficiently reduced.

Further, as another modification, a resin layer as a resin film may be formed on the main surface of at least one current collector 311 facing the adjacent current collector 311. That is, one of the current collectors 311 and the resin film may be adhered to each other. Further, when inserting a plurality of layers of resin films, the two current collectors 311 may be adhered to adjacent resin films.

<Second embodiment>
The first embodiment and modification of the present invention have been described above. Next, a second embodiment of the present invention will be described. In the flexible secondary battery according to the second embodiment, the negative electrode has a negative electrode current collector having a plurality of current collectors instead of the positive electrode. Hereinafter, the differences from the first embodiment described above will be mainly described, and the description of the same parts will be omitted.

FIG. 5 is a vertical sectional view of the flexible secondary battery 1B according to the second embodiment of the present invention, and FIG. 6 is an enlarged vertical sectional view of the flexible secondary battery 1B shown in FIG.

In the flexible secondary battery 1B shown in FIG. 5, the positive electrode 30A has a positive electrode current collecting unit 31A, a positive electrode active material layer 33, and a positive electrode current collecting tab 35. The positive electrode current collector 31B is a single-layer current collector.

On the other hand, the negative electrodes 10D, 10E, and 10F have a negative electrode current collector 11B, a negative electrode active material layer 13, and a negative electrode current collector tab 15. Further, as shown in FIG. 6, the negative electrode current collector 11B has two current collectors 111 and a buffer layer 113 arranged between them. The configuration of the current collector 111 can be the same as that of the current collector 111 described above, except for its constituent materials. Further, the structure of the buffer layer 113 can be the same as that of the buffer layer 313. The buffer layer 113 may be partially or completely omitted.

Even in the flexible secondary battery 1B as described above, when the flexible secondary battery 1B is bent or wound, the two current collectors 111 can be preferentially displaced. Therefore, the flexible secondary battery 1B can also exhibit the same effect as the flexible secondary battery 1 according to the first embodiment described above.

Further, in the present embodiment, it is possible to apply the same modification as the modification of the first embodiment described above.

[2. Flexible secondary battery manufacturing method]
<First Embodiment>
Next, the method for manufacturing the flexible secondary battery according to the first embodiment will be described by taking the above-described method for manufacturing the flexible secondary battery 1 as an example. Moreover, the manufacturing method of the electrode for a flexible secondary battery will also be described by taking the manufacturing method of the positive electrode 30 as an example.

The method for manufacturing the positive electrode 30 (method for manufacturing the electrode for a flexible secondary battery) according to the present embodiment is a positive electrode active material layer (electrode) on one main surface of a sheet-shaped current collector (first current collector) 311. The step of forming the active material layer) 33 (first step) and
Current collector (first current collector) 311 so that the current collector 311 and the sheet-shaped additional current collector (second current collector) 311 are adjacent to each other via the buffer layer 313 or in contact with each other. The other main surface of the current collector (second current collector) 311 is opposed to the main surface of the current collector (second current collector) 311 to connect the two current collectors 311 (second step).

First, the positive electrode active material layer 33 is formed on one main surface of the current collector 311 (first step). Specifically, first, the material of the positive electrode active material layer 33 is dispersed in an organic solvent or water to form a positive electrode mixture slurry, and the positive electrode mixture slurry is applied onto the current collector 311. As a result, a coating layer is formed. Then, the coating layer is dried. Then, the dried coating layer is rolled together with the positive electrode current collector 31. As a result, the positive electrode active material layer 33 is formed.

Next, the negative electrodes 10A to 10C are manufactured. The negative electrodes 10A to 10C are manufactured by, for example, the following method. First, a slurry is formed by dispersing a mixture of a negative electrode active material and a binder in a desired ratio in a solvent (for example, water, an organic solvent (for example, N-methyl-2-pyrrolidone), etc.). Next, the slurry is formed (for example, coated) on the negative electrode current collector 11 and dried to form the negative electrode active material layer 13. Further, the negative electrode active material layer 13 is compressed to a desired thickness by a compressor. As a result, the negative electrodes 10A to 10C are manufactured. Here, the thickness of the negative electrode active material layer 13 is not particularly limited as long as it is the thickness of the negative electrode active material layer 13 of the lithium ion secondary battery. Further, when metallic lithium is used as the negative electrode active material layer 13, the metallic lithium foil may be laminated on the negative electrode current collector 11. The negative electrode current collector tab 15 is cut so that the negative electrode current collector tab 15 is arranged on the extension of the negative electrode current collector 11 at the time of forming (cutting) the negative electrode current collector 11, thereby collecting the negative electrode. It is possible to obtain a negative electrode current collecting tab 15 formed integrally with the electric unit 11. In the negative electrode current collector 11 on the outer surface side of the negative electrodes 10A and 10C, the negative electrode active material layer 13 is omitted.

Next, the current collector 311 on which the positive electrode active material layer 33 is formed, the buffer layer 313, the negative electrodes 10A to 10C, and the separator 50 are laminated and adhered in a predetermined order to obtain an electrode laminated assembly for a flexible secondary battery. ..

Further, in this step, the current collector 311 on which the positive electrode active material layer 33 is formed and the sheet-shaped further current collector (second current collector) 311 are adjacent to each other via the buffer layer 313 or in contact with each other. As described above, the other main surface of the current collector (first current collector) 311 is opposed to the main surface of the current collector (second current collector) 311, and the two current collectors 311 are connected. Can be done (second step).

Specifically, the current collector 311 and the buffer layer 313, the negative electrodes 10A to 10C, and the separator 50 are laminated in a predetermined order to prepare an electrode laminate. In the present embodiment, at the time of stacking, the current collector 311 and the buffer layer 313 are laminated in the order of forming the positive electrode 30. That is, a buffer layer 313 is arranged between the two current collectors 311 and a positive electrode active material layer 33 is arranged on the main surface of the current collector 311 on the side opposite to the buffer layer 313. To do so. Further, the stacking order of the current collector 311 and the buffer layer 313 as the positive electrode 30, the negative electrodes 10A to 10C and the separator 50 is such that the plurality of positive electrodes 30 and the negative electrodes 10A to 10C to be formed alternate with each other via the separator 50. To be placed in. In the present embodiment, the negative electrode 10C, the separator 50, the positive electrode 30, the separator 50, the negative electrode 10B, the separator 50, the positive electrode 30, the separator 50, and the negative electrode 10A are laminated in this order from the bottom.

Then, as in the first embodiment, the electrode laminate is pressed in the direction perpendicular to the main surface of the obtained electrode laminate. Further, the negative electrode current collecting tabs 15 are welded to each other to form the negative electrode terminals 70, and the positive electrode current collecting tabs 35 are welded to each other to form the positive electrode terminals 80. In this way, the adjacent current collectors 311 are electrically connected to each other, and the positive electrode 30 is manufactured. As described above, a flexible secondary battery electrode laminated assembly in which the negative electrodes 10A to 10C, the positive electrode 30 and the separator 50 are laminated and adhered in a predetermined order is obtained.

At the time of stacking, the positive electrode current collecting tabs 35 of the positive electrode 30 are arranged at the same position, and the negative electrode current collecting tabs 15 of the plurality of negative electrodes 10A to 10C are arranged at the same position. Further, it is preferable that adhesive layers are formed in advance on both surfaces of the separator 50. As a result, an electrode laminate is produced.

Next, it is pressed in the direction perpendicular to the main surface of the obtained electrode laminate (heat press is performed if an adhesive layer is present). The conditions of the heat press are not particularly limited, but for example, the temperature is preferably 25 to 90 ° C. and the pressure is preferably 10 to 100 kgf / cm ² . Even without heating, the press pressure is preferably 10-100 kgf / cm ² .

Next, the negative electrode current collecting tabs 15 are welded to each other to form the negative electrode terminals 70, and the positive electrode current collecting tabs 35 are welded to each other to form the positive electrode terminals 80. As a result, a flexible secondary battery electrode laminated assembly in which the negative electrodes 10A to 10C, the positive electrode 30 and the separator 50 are laminated and adhered in a predetermined order is obtained.

(Manufacturing of flexible secondary batteries)
Next, the obtained flexible secondary battery electrode laminated assembly is inserted into an exterior body (for example, a laminated film) together with an electrolytic solution, and the exterior body is sealed to produce a flexible secondary battery 1. When sealing the exterior body, the negative electrode terminals 70 and the positive electrode terminals 80 formed by the negative electrode current collecting tab 15 and the positive electrode current collecting tab 35 are projected to the outside of the exterior body, respectively.

<Second embodiment>
Next, the method for manufacturing the flexible secondary battery according to the second embodiment will be described by taking the above-described method for manufacturing the flexible secondary battery 1 as an example. Moreover, the manufacturing method of the electrode for a flexible secondary battery will also be described by taking the manufacturing method of the positive electrode 30 as an example.

In the method for manufacturing a flexible secondary battery according to the present embodiment, mainly in the method for manufacturing the positive electrode 30, the point that the current collector 311 is overlapped before the formation of the positive electrode active material layer 33 is the method according to the first embodiment described above. Different from. That is, in the method for manufacturing a flexible secondary battery according to the present embodiment, the positive electrode 30 is manufactured before the electrode laminate is formed.

First, a sheet-shaped current collector (first current collector) 311 and a further sheet-shaped current collector (second current collector) connected so that at least a part thereof is electrically connected to the current collector 311. A positive current collector (current collector for a flexible secondary battery) 31 having a current collector 311 and having these current collectors 311 arranged so as to be adjacent to each other via a buffer layer 313 or in contact with each other is prepared. (First step).

Specifically, two metal foils serving as current collectors are laminated via a buffer layer 313 to form a laminated sheet, and the laminated sheet is wound up by a roll. Next, while taking out the laminated sheet from the roll, welding is performed at the portion to be formed of the positive electrode current collecting tab 35, and the laminated sheet is wound on the roll again.

Next, the positive electrode active material layer (electrode active material layer) 33 is formed on the main surface of at least one current collector 311 opposite to the other current collector 311 side (second step). The method for forming the positive electrode active material layer 33 can be the same as the method in the first embodiment described above. Further, since both sides of the laminated sheet are metal foils, the positive electrode active material layer 33 is formed on both sides of the laminated sheet. That is, the positive electrode active material layer 33 as the electrode active material layer is formed on the outer surface side of the two connected current collectors 311.

Next, the laminated sheet is cut into a predetermined shape to obtain a positive electrode 30.
Next, the negative electrodes 10A to 10C are manufactured in the same manner as in the first embodiment.

Next, the positive electrode 30, the negative electrodes 10A to 10C, and the separator 50 are laminated in a predetermined order to prepare an electrode laminate. Further, the stacking order of the positive electrode 30, the negative electrodes 10A to 10C and the separator 50 is such that the plurality of positive electrodes 30 and the negative electrodes 10A to 10C to be formed are alternately arranged via the separator 50. In the present embodiment, the negative electrode 10C, the separator 50, the positive electrode 30, the separator 50, the negative electrode 10B, the separator 50, the positive electrode 30, the separator 50, and the negative electrode 10A are laminated in this order from the bottom.

Then, as in the first embodiment, the electrode laminate is pressed in the direction perpendicular to the main surface of the obtained electrode laminate. Further, the negative electrode current collecting tabs 15 are welded to each other to form the negative electrode terminals 70, and the positive electrode current collecting tabs 35 are welded to each other to form the positive electrode terminals 80. As described above, a flexible secondary battery electrode laminated assembly in which the negative electrodes 10A to 10C, the positive electrode 30 and the separator 50 are laminated and adhered in a predetermined order is obtained.

Next, as in the first embodiment, the flexible secondary battery electrode laminated assembly is inserted into the exterior body (for example, a laminate film) together with the electrolytic solution, and the exterior body is sealed to produce the flexible secondary battery 1. To do.

Hereinafter, the secondary battery according to the present embodiment will be specifically described with reference to Examples and Comparative Examples. The examples shown below are merely examples, and the secondary battery according to the present embodiment is not limited to the following examples.

1. 1. Manufacturing and characterization of flexible secondary batteries [Example 1]
(Formation of positive electrode active material layer)
A positive electrode mixture slurry was prepared by dissolving and dispersing lithium cobalt oxide, acetylene black, and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone at a mass ratio of solid content of 98: 1: 1. Then, the positive electrode mixture slurry was applied to one side of an aluminum foil current collector having a thickness of 12 μm, and then dried. A positive electrode active material layer was formed by rolling the coated layer after drying. The total thickness of the aluminum foil current collector on which the positive electrode active material layer was formed was 80 μm. Then, an aluminum lead wire having a thickness of 80 μm was welded to the tip of the aluminum foil current collector in the length direction as a positive electrode current collector tab. The length and width of the aluminum foil current collector on which the positive electrode active material layer was formed were set to 50 mm and 25 mm, respectively.

(Preparation of negative electrode)
A negative electrode mixture slurry was prepared by dissolving and dispersing natural graphite, carboxymethyl cellulose, and SBR (styrene butadiene rubber) in an aqueous solvent at a mass ratio of solid content of 98: 1: 1. Next, this negative electrode mixture slurry was applied to one side of a copper foil current collector having a thickness of 8 μm, and then dried. A negative electrode active material layer was obtained by rolling the coated layer after drying. That is, a negative electrode was produced. The total thickness of the negative electrode was 85 μm. Then, the nickel lead wire was welded to the tip of the negative electrode as a negative electrode current collecting tab. The length and width of the negative electrode were set to 53 mm and 28 mm, respectively, in order to make them larger than the length and width of the positive electrode.

(Making a separator)
As a separator, a corona-treated porous polyethylene separator film having a thickness of 12 μm was prepared. The length and width of the separator were set to 56 mm and 30 mm, respectively, in order to make them larger than the negative electrode.

(Creation of polyethylene film)
A polyethylene film having a thickness of 100 μm was prepared as a lubricant (buffer layer) between the aluminum foil current collectors. The size of the polyethylene film was the same as that of the separator.

(Preparation of electrode laminate)
The negative electrode was installed with the coated surface facing up, and the separator was laminated on it. Next, the aluminum foil current collector was laminated so that the coated surface of the aluminum foil current collector on which the positive electrode active material layer was formed faced the negative electrode. Next, a polyethylene film was laminated on the uncoated surface of the aluminum foil current collector. Next, an aluminum foil current collector having a further positive electrode active material layer formed was prepared, and the aluminum foil current collector was laminated so that the non-coated surface side of the aluminum foil current collector faced the polyethylene film. A separator was laminated on it. The negative electrode was laminated on the negative electrode so that the coated surface side of the negative electrode faced the separator. As a result, an electrode laminate was formed. Further, two aluminum foil current collectors sandwiched the polyethylene film, and a positive electrode having positive electrode active material layers formed on both outer main surfaces was obtained.
(Battery production)
A battery was produced by sealing the electrode laminate with a laminate film composed of three layers of polypropylene / aluminum / nylon together with an electrolytic solution so that the two lead wires were exposed to the outside. As the electrolytic solution, a solvent obtained by dissolving 1 M of LiPF ₆ in a solvent in which ethylene carbonate / ethyl methyl carbonate was mixed at a ratio of 3: 7 (volume ratio) was used. A flexible secondary battery was produced by the above steps.

(Characteristic evaluation)
A charge / discharge test was conducted using the flexible secondary battery prepared as described above. In the charging / discharging of the first cycle, the charging condition was set to 0.2 C and the constant current constant voltage (CCCV) was set to 0.05 Cut off, and the discharge condition was set to 0.5 C and set to CC discharge and 2.8 Vcut off. Next, in the charge / discharge of the second cycle, the rated discharge amount was 0.5 C at the time of charging and 0.2 C at the time of discharge.

Then, for the bending durability test, the flexible secondary battery was wound around a plastic cylinder having a radius of 20 mm and stretched, and the winding and stretching actions were repeated 10 times. The sowing started from the tab side of the battery and finished in 60 seconds each time.

Then, the charge / discharge test was performed again. In the third cycle, the charging / discharging conditions were set to 0.5 C for charging and 0.2 C for discharging. Then, the discharge load test in the fourth cycle was performed with the current amount set to 0.5 C during charging and 1 C during discharging. Then, the capacity ratio of the third cycle and the fourth cycle was calculated when the charge / discharge capacity of the second cycle was set to 100%. The results are shown in Table 1.

[Comparative Example 1]
A positive electrode having a positive electrode active material layer coated on both sides was prepared. The thickness was 130 μm. The same treatment as in Example was carried out except that this positive electrode was replaced with a combination of two aluminum foil current collectors coated on one side with a polyethylene film of Example sandwiched between them.

Table 1 summarizes the evaluation results. As is clear from Table 1, at 1C discharge, the flexible secondary battery according to Example 1 was able to have a larger remaining capacity than the flexible secondary battery according to Comparative Example 1.

2. Measurement of dynamic friction coefficient Next, in order to confirm the effect of the flexible secondary battery according to the present invention, the following experiment was conducted. The following experiments were performed to obtain a tendency for the ease of movement of the two current collector sheets (current collectors) in the positive electrode in the plane direction.

First, two Al foils (20 x 6 cm) as current collecting sheets are prepared, Al foils are laminated as shown in FIG. 7, and a resin sheet or liquid as a buffer layer shown in Table 1 is inserted between the Al foils. Infused.

Next, as shown in FIG. 7, a 5 cm square 1 kg weight block was placed on the overlapping portion of the Al foil.
Next, the lower Al foil is fixed, and the upper Al foil is pulled in the longitudinal direction (in the direction of the arrow in the figure) along the surface of the lower Al foil, and a tensile tester (manufactured by Shimadzu Corporation, Autograph AGS-) is pulled. The dynamic friction force between the Al foils at this time was measured by X).

For comparison, the coefficient of dynamic friction between the electrode and the separator was measured. Specifically, a positive electrode (20 × 6 cm) and a separator (20 × 6 cm) were prepared and placed in place of the Al foil in FIG. The positive electrode was manufactured in the same manner as in Example 1 described above. Next, propylene carbonate was filled between the positive electrode and the separator in order to obtain the state inside the battery for convenience. A tensile test was carried out on the positive electrode-separator laminate thus obtained, and the coefficient of dynamic friction between the electrode and the separator was measured.

The dynamic friction coefficient was calculated from the obtained dynamic friction force and the weight of the weight block according to the following formula. The results are shown in Table 2.
F'= μ'N
In the equation, F'is the dynamic friction force, μ'is the dynamic friction coefficient, and N is the normal force (load by the weight block).

As shown in Table 2, a coefficient of dynamic friction lower than that of the reference example was obtained in each of the examples. This indicates that the current collector foils are preferentially displaced over the electrodes and separators. In particular, the results of Example 1 suggest that the multi-layered current collector can move so that the current collectors are sufficiently displaced from each other even if the buffer layer is omitted. In addition, the results of Examples 3 and 4 suggest that the current collectors can easily move to each other when the resin film is arranged. In particular, it was suggested that this tendency became remarkable when the number of resin films was increased.

Moreover, from the result of Reference Example 1, it was shown that the coefficient of dynamic friction between the positive electrode and the separator was relatively high. If the current collector foil is not multi-layered, the gap between them will be preferentially shifted. At this time, it is suggested that a large frictional force acts to cause peeling between the electrode and the separator.

From the above results, the current collector for a flexible secondary battery, the electrode for a flexible secondary battery, the laminated assembly for a flexible secondary battery, and the flexible secondary battery of the present invention have a plurality of current collectors against bending and winding. It was shown that the stress generated between each layer can be relieved by absorbing the difference in peripheral length by the current collector having a body. In addition, defects can be prevented by preventing the positional relationship between the positive electrode and the negative electrode at the end of the electrode from shifting. Therefore, according to the present invention, it is possible to prevent deterioration of performance when the flexible secondary battery is repeatedly bent or wound.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that anyone with ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

1,1A, 1B Flexible secondary battery 10A, 10B, 10C, 10D, 10E, 10F Negative electrode 11, 11A, 11B Negative electrode current collector 111 Current collector 113 Buffer layer 13 Negative electrode active material layer 15 Negative electrode current collector tab 30, 30A Positive electrode 31, 31A Positive electrode current collector 311 Current collector 313 Buffer layer 33 Positive electrode active material layer 35 Positive electrode current collector tab 50 Separator 70 Negative electrode terminal 80 Positive electrode terminal

Claims (7)

A sheet-shaped first current collector and
It has, at least a part of, a sheet-shaped second current collector connected so as to be conductive with the first current collector.
Wherein the first current collector and the second current collector is disposed in contact with adjacent via the buffer layer, the buffer layer comprises a liquid layer, the flexible rechargeable battery current collector. The buffer layer comprises an electrolyte, current collectors for flexible secondary battery according to claim 1. The first electrode active material layer and
A sheet-shaped first current collector that supports the first electrode active material layer on one main surface, and
A sheet-shaped second current collector connected so that at least a part thereof is electrically connected to the first current collector.
A second electrode active material layer supported on a main surface of the second current collector opposite to the main surface of the first current collector side,
Have,
Wherein the first current collector and the second current collector is disposed so as to contact adjacent via the buffer layer, the buffer layer comprises a liquid layer, the flexible rechargeable battery electrode. A flexible secondary battery electrode laminated assembly comprising the flexible secondary battery electrode according to claim 3 . A flexible secondary battery comprising the electrode for the flexible secondary battery according to claim 3 . A step of forming an electrode active material layer on one main surface of a sheet-shaped first current collector, and
The first as a current collector, body and the sheet-like second collector contacts next through the buffer layer, the first current collector other said major surface of the second current collector by the major surface facing, have a, a step of connecting said first collector and the second current collector,
A method for manufacturing an electrode for a flexible secondary battery , wherein the buffer layer includes a liquid layer . It has a sheet-shaped first current collector and a sheet-shaped second current collector whose at least a part is connected to the first current collector so as to be electrically connected to the first current collector. a step body and said second current collector is disposed so as to contact adjacent via the buffer layer, to prepare said buffer layer comprises a liquid layer, current collector for flexible rechargeable battery,
A method for manufacturing an electrode for a flexible secondary battery, which comprises a step of forming an electrode active material layer on a main surface of the first current collector opposite to the side of the second current collector.

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