JP2020024783A - Flexible battery - Google Patents

Abstract

To provide a flexible battery which suppresses creasing and positive electrode damage in a film exterior package body against repetition of bending of the battery.SOLUTION: The present invention relates to a flexible battery including a sheet-like electrode group 103 comprising: a positive electrode, a negative electrode and an electrolyte layer interposed between the positive electrode and the negative electrode; and a film exterior package body 108 in which the electrode group 103 is sealed and accommodated. The positive electrode comprises a positive electrode collector formed from a metal sheet, the film exterior package body 108 comprises a gas barrier layer formed from a metal layer, and a 0.2% yield strength of the positive electrode collector is equal to or higher than a 0.2% yield strength of the gas barrier layer.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a flexible battery provided with a flexible film package.

  In recent years, flexible power sources for small devices such as mobile phones, voice recording and playback devices, wristwatches, video and still image capture devices, liquid crystal displays, calculators, IC cards, temperature sensors, hearing aids, pressure-sensitive buzzers, and biological sticking devices A battery is used. A flexible battery includes a sheet-like electrode group and a film package housing the same. The film package has a gas barrier layer for preventing the outside air component from entering the inside of the battery.

  Patent Literature 1 discloses the thickness of an electrode group and the thickness of a thin battery from the upper and lower surfaces of the electronic device so that the electrode group is not broken or damaged when a flexible electronic device having a thin battery mounted therein is erroneously stepped on. It proposes to control the distance up to. Further, it has been proposed that the bending durability of the current collector be maintained by setting the tensile strength of the positive electrode current collector and the negative electrode current collector to 100 to 1200 MPa and the longitudinal elastic modulus to 7 to 220 GPa.

Patent Document 2 discloses that an aluminum foil having a 0.2% proof stress of 58 to 121 N / mm ² when a tensile test in a direction parallel to a rolling direction is performed as a metal layer constituting a battery packaging material. Has been proposed. It is stated that this allows the metal layer to appropriately follow the shape of the mold during molding, thereby suppressing the occurrence of pinholes and cracks.

JP 2013-161691 A International Publication No. 2013-183511

  When the thin battery is bent, wrinkles crossing the bending direction may be generated near the center of the outer package. The curvature tends to be large near the center of the bent thin battery outer package and the electrode group, and the stress from both sides to the center concentrates on the inside where the center is concave, and the stress from the center to both sides on the outside where the center is convex. Is easy to concentrate. If wrinkles occur in the exterior body in such a portion, cracks or disconnections may occur in the components of the electrode group due to the influence. Even when a current collector having a tensile strength and a longitudinal elastic modulus as in Patent Document 1 is used, a positive electrode having relatively low durability against bending is easily damaged.

  When a packaging material that easily follows the deformation is used as in Patent Literature 2, most of the stress when the battery is bent concentrates on the electrode group. Therefore, if the battery is repeatedly bent, the positive electrode is more likely to be damaged.

  One aspect of the present invention includes a positive electrode, a negative electrode, and a sheet-like electrode group including an electrolyte layer interposed between the positive electrode and the negative electrode, and a film package hermetically containing the electrode group, The positive electrode includes a positive electrode current collector formed of a metal sheet, the film package includes a gas barrier layer formed of a metal layer, and the 0.2% proof stress of the positive electrode current collector is determined by the gas barrier. A flexible battery having a 0.2% proof stress of the layer or more.

  In the flexible battery according to the present invention, generation of wrinkles and damage to the positive electrode of the film package can be suppressed.

It is sectional drawing of the laminated structure of the film exterior body which concerns on one Embodiment of this invention. FIG. 1 is a plan view of a flexible battery according to one embodiment of the present invention, with a portion cut away. FIG. 3 is a cross-sectional view of the flexible battery shown in FIG.

The flexible battery according to the present embodiment includes a sheet-like electrode group including a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode, and a film package that hermetically accommodates the electrode group. The positive electrode includes a positive electrode current collector formed of a metal sheet, and the film package includes a gas barrier layer formed of a metal layer. The 0.2% proof stress (σ _0.2PC ) of the positive electrode current collector is greater than or _{equal to} the 0.2% proof stress (σ _0.2GB ) of the gas barrier layer (σ _0.2PC ≧ σ _0.2GB ). Thereby, when the flexible battery is bent, the film package including the outer gas barrier layer expands and contracts preferentially, and the stress applied to the electrode group is reduced. Therefore, wrinkles are less likely to be generated on the film exterior body, and disconnection of the positive electrode is suppressed.

The ratio between the 0.2% proof stress (σ _0.2PC ) of the positive electrode current collector and the 0.2% proof stress (σ _0.2GB ) of the gas barrier layer: σ _0.2PC / σ _0.2GB may be 1 or more. Is preferably 1.2 or more and 3.0 or less. When σ _0.2PC and σ _0.2GB satisfy the above ratio, preferential expansion and contraction of the film package is promoted, and sufficient flexibility of the electrode group including the positive electrode is easily ensured.

  The gas barrier layer is a layer having a gas barrier property, and the gas barrier property is a property of preventing an outside air component (particularly, moisture) from entering the inside of the battery.

  Here, the 0.2% proof stress of each of the positive electrode current collector and the gas barrier layer is measured by a tensile test based on JIS Z 2241 (2011).

Even in the case where the metal sheet or the metal layer has anisotropy in tensile strength, in at least one direction parallel to the plane direction of the flexible battery, the positive electrode current collector and the gas barrier layer in a stacked state have a difference of σ _0.2PC ≧ σ _If you satisfy the relationship of _0.2GB , you can get a reasonable effect. However, it is preferable that the relationship of σ _0.2PC ≧ σ _0.2GB is satisfied in all directions parallel to the plane direction of the flexible battery.

  Examples of the metal sheet or metal layer having anisotropy in tensile strength include a rolled metal foil. In the case of rolled metal foil, the 0.2% proof stress in the rolling direction is maximized, and the 0.2% proof stress in the direction perpendicular to the rolling direction is minimized.

From the viewpoint of simplifying the manufacturing process, it is preferable that the directions of the positive electrode current collector and the gas barrier layer can be arbitrarily set. Further, it is preferable that wrinkles of the film package and damage to the positive electrode can be suppressed regardless of the direction in which the flexible battery is bent. Therefore, when a metal sheet or a metal layer having anisotropic tensile strength is used, the minimum 0.2% proof stress of the metal sheet forming the positive electrode current collector and the maximum 0.2% proof stress of the metal layer forming the gas barrier layer are obtained. Most preferably, the 0.2% proof stress satisfies σ _0.2PC ≧ σ 0.2 _GB .

  The 0.2% proof stress of the metal sheet or metal layer can be controlled by the manufacturing conditions. For example, a metal sheet or metal layer having a desired 0.2% proof stress can be obtained by appropriately adjusting the annealing conditions for homogenization and the rolling conditions for a rolled metal foil. When the metal sheet or the metal layer is formed of an alloy, the 0.2% proof stress can be controlled by the alloy composition.

  The metal sheet forming the positive electrode current collector is preferably a stainless steel foil, an aluminum foil, or an aluminum alloy foil that is stable at the positive electrode potential. The content of elements other than aluminum in the aluminum alloy is preferably 5% by mass or less. The metal sheet forming the positive electrode current collector may be a rolled metal foil, a vapor-deposited film, or another metal sheet.

  The metal layer forming the gas barrier layer is preferably an aluminum foil or an aluminum alloy foil because it is easy to manufacture by vapor deposition, molding, and rolling. As the aluminum alloy, it is preferable to use an alloy in which the content of elements other than aluminum is 5% by mass or less, as in the case of the positive electrode current collector. The metal layer forming the gas barrier layer is preferably a rolled metal foil. This makes it easy to ensure high gas barrier properties of the gas barrier layer, and further facilitates enhancing the durability of the gas barrier layer.

  Elements forming the positive electrode current collector or the gas barrier layer include, in addition to aluminum, iron (Fe), titanium (Ti), nickel (Ni), cobalt (Co), manganese (Mn), zinc (Zn), and lead. (Pb), vanadium (V), platinum (Pt), gold (Au), silver (Ag), copper (Cu), palladium (Pd), gallium (Ga), and the like. Examples of the semimetal include phosphorus (P), silicon (Si), germanium (Ge), boron (B), and antimony (Sb). The metal sheet or the metal layer may contain only one of these, or two or more thereof.

  The 0.2% proof stress of the gas barrier layer is preferably 200 MPa or less, more preferably 180 MPa or less. Further, the 0.2% proof stress of the gas barrier layer is preferably 50 MPa or more. Thereby, the elasticity of the gas barrier layer becomes better, and when the flexible battery is bent, wrinkles of the film outer package become less likely to occur. The stress applied to the electrode group is also easily reduced.

  On the other hand, the 0.2% proof stress of the positive electrode current collector is preferably 300 MPa or less, and more preferably 250 MPa or less. Further, the 0.2% proof stress of the positive electrode current collector is preferably 50 MPa or more. Thereby, the balance between the strength and the flexibility of the positive electrode current collector becomes better.

The ratio of the thickness T _GB of the gas barrier layer to the thickness T _PC of the positive electrode current collector: T _GB / T _PC is preferably 0.3 or more and 1.7 or less, and more preferably 0.5 or more and 1.5 or less. Is more preferable, and 0.7 or more and 1.3 or less are still more preferable. Within such a range, the gas barrier layer does not become too thin with respect to the positive electrode current collector, and in addition to exhibiting excellent durability of the gas barrier layer, the gas barrier layer also has good elasticity. Therefore, the stress applied to the electrode group is easily alleviated.

  The film package preferably includes a gas barrier layer, a seal layer laminated on one surface of the gas barrier layer, and a protective layer laminated on the other surface of the gas barrier layer. Thereby, the durability and handleability of the film package are improved.

  It is preferable that the volume ratio of the gas barrier layer in the film package is 33% or less. As a result, the film exterior body has improved strength, durability, and airtightness, and further has improved elasticity. From the viewpoint of achieving both excellent elasticity and excellent gas barrier properties, the volume ratio of the gas barrier layer in the film package is more preferably 15% or more and 30% or less. Within the above range, the sealing layer and the protective layer are not too thick with respect to the gas barrier layer, and the battery is easily thinned.

  The protective layer preferably contains at least one selected from the group consisting of polyolefin, polyamide and polyester. Thereby, the chemical resistance of the film package is improved. Among them, the protective layer is preferably formed of polyethylene. The use of polyethylene significantly improves the flexibility of the film package. However, the protective layer may contain additives other than polyethylene. The content of polyethylene in the protective layer may be 50% by mass or more.

  Since the seal layer comes into contact with the power generation element (eg, electrolyte) of the battery, a high degree of chemical resistance is required. Therefore, the seal layer preferably contains polyolefin. When the seal layer contains polyolefin, the bonding of the film exterior body by the thermal welding of the seal layer becomes easy. By using polyethylene among the polyolefins, the flexibility of the film package is further significantly improved.

  The type of polyethylene forming the protective layer and the seal layer is not particularly limited, and high-pressure low-density polyethylene (LDPE), linear short-chain branched polyethylene (LLDPE), medium-low pressure high-density polyethylene (HDPE), metallocene catalyst Linear short-chain branched polyethylene (LLDPE) or the like can be used. Among them, it is preferable to use HDPE as the protective layer because of its excellent strength. Further, it is preferable to use LDPE as the seal layer in terms of excellent sealing properties.

The thickness T _OU of the protective layer is preferably larger than the thickness T _GB of the gas barrier layer. By setting T _OU > T _GB , breakage of the gas barrier layer is significantly suppressed, and the elasticity of the film package is easily improved. At this time, by setting the ratio of thickness: T _OU / T _GB to 1.1 to 3.0, the elasticity of the film exterior body is significantly improved.

It is preferable that the thickness T _IN of the sealing layer is larger than the thickness T _GB of the gas barrier layer. By setting T _IN > T _GB , breakage of the gas barrier layer is more remarkably suppressed, and the elasticity of the film package is easily improved. At this time, by setting the thickness ratio: T _IN / T _GB to 1.1 to 3.0, the elasticity of the film outer package is further remarkably improved.

The thickness T _GB of the gas barrier layer is preferably from 5 μm to 200 μm, more preferably from 5 μm to 30 μm, even more preferably from 5 μm to 20 μm. When the content is within the above range, the gas barrier layer can easily achieve both excellent gas barrier properties and durability, and can easily ensure excellent stretchability of the film package.

The film package may further include a metal oxide layer formed on at least one surface of the gas barrier layer. The metal oxide layer can impart chemical resistance (for example, acid resistance) to the gas barrier layer. Metals constituting the metal oxide layer include chromium (Cr), aluminum (Al), silicon (Si), magnesium (Mg), cerium (Ce), titanium (Ti), molybdenum (Mo), and tungsten (W). , Zirconium (Zr) and the like. However, from the viewpoint of securing the flexibility of the film package, the thickness of the metal oxide layer is preferably less than 20% of the thickness T _GB of the gas barrier layer, and more preferably less than 10%.

  Strongly acidic substances may be generated inside the non-aqueous electrolyte battery. Therefore, a chromium oxide (chromate) layer having high acid resistance is preferable as the metal oxide layer.

  The flexible battery according to the present embodiment may be a primary battery or a secondary battery. Further, the flexible battery may be a non-aqueous electrolyte battery or an aqueous electrolyte battery.

  The sheet-like electrode group is a sheet-like laminate in which a sheet-like positive electrode, a negative electrode, and an electrolyte layer are respectively laminated. Such a laminate can be formed thin. Therefore, the total thickness of the electrode group and the film package can be set to, for example, 2 mm or less, and can be set to 1 mm or less. Thereby, a flexible battery having high flexibility can be provided.

  The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector. The positive electrode may be a single-sided electrode having a positive electrode active material layer formed on one surface of the positive electrode current collector, or may be a double-sided electrode having a positive electrode active material layer formed on both surfaces of the positive electrode current collector. .

  Similarly, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on a surface of the negative electrode current collector. The negative electrode may be a single-sided electrode having a negative electrode active material layer formed on one surface of the negative electrode current collector, or may be a double-sided electrode having a negative electrode active material layer formed on both surfaces of the negative electrode current collector. .

  Although the configuration of the electrode group is not particularly limited, for example, the following configuration examples can be given. Note that the electrode group is not limited to the following configuration examples.

  (I) The first embodiment includes a minimum unit electrode group including a positive electrode that is a single-sided electrode and a negative electrode that is a single-sided electrode, and arranged so that the positive electrode active material layer and the negative electrode active material layer face each other. It is.

  (Ii) The second embodiment includes one positive electrode that is a double-sided electrode, and two negative electrodes that are one-sided electrodes arranged so as to sandwich the positive electrode, and the positive electrode active material layer and the negative electrode active material layer It is a group of electrodes arranged to face each other.

  (Iii) In the third embodiment, one positive electrode as a double-sided electrode, two negative electrodes as a double-sided electrode arranged so as to sandwich the positive electrode, and a single-sided electrode further disposed outside each negative electrode. This is an electrode group including two positive electrodes and arranged so that the positive electrode active material layer and the negative electrode active material layer face each other.

  (Iv) In the fourth embodiment, one positive electrode as a double-sided electrode, one negative electrode as a double-sided electrode, one negative electrode as a single-sided electrode disposed outside the positive electrode as a double-sided electrode, and a double-sided electrode And a positive electrode, which is a single-sided electrode disposed outside the negative electrode, and is a group of electrodes arranged so that the positive electrode active material layer and the negative electrode active material layer face each other.

In the thin sheet-like electrode group as described above, regardless of the arrangement of the positive electrode and the negative electrode, the effect of suppressing wrinkles of the film exterior body and damage to the positive electrode by _setting σ _0.2PC ≧ σ _{0.2 GB} is obtained. Can be. However, by arranging the positive electrode having relatively low bending resistance at the center of the electrode group as much as possible, the effect of suppressing the breakage of the positive electrode is further enhanced. Further, when the flexible battery is bent, it is preferable that negative electrodes having relatively excellent flexibility are disposed at both ends of the electrode group to which the tension is applied most or the curvature is smallest. That is, when the sheet-like electrode group includes a plurality of negative electrodes, it is preferable that a pair of negative electrodes is disposed at both ends of the electrode group. Further, it is preferable that a positive electrode is disposed at the center of the electrode group.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment.

FIG. 1 is a cross-sectional view showing a laminated structure of a film package according to an embodiment of the present invention.
The film package 10 includes a gas barrier layer 11 formed of a metal layer, a seal layer 12 laminated on one surface of the gas barrier layer 11, and a protective layer 13 laminated on the other surface of the gas barrier layer 11. I do.

  The film exterior body 10 has, for example, a gas barrier layer 11 formed on one surface of a seal layer 12 (protective layer 13) by a vapor phase method, and a surface of the gas barrier layer 11 that does not contact the seal layer 12 (protective layer 13). Is covered with a protective layer 13 (seal layer 12). The vapor phase method includes a vapor deposition method, a sputtering method, an ion plating method, and the like.

  The film package 10 may be formed using a metal foil prepared in advance (for example, a rolled metal foil) as a metal layer. In this case, for example, the film package 10 is formed by bonding the seal layer 12, the metal foil, and the protective layer 13. When forming a gas barrier layer of 5 μm or more or 10 μm or more, it is desirable to form the gas barrier layer 11 by bonding a metal foil to one surface of the seal layer 12 (protective layer 13). The bonding is performed, for example, by stacking a resin film serving as the seal layer 12 and / or a resin film serving as the protective layer 13 and a metal foil serving as the gas barrier layer 11, and applying pressure while heating both using a roller or the like. It can be done by:

  Note that the metal layer may be subjected to a chromate treatment to form a metal oxide layer adjacent to the gas barrier layer 11.

  The resin components forming the seal layer 12 and the protective layer 13 are not particularly limited, but include, for example, polyolefins such as polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); Polyamide (PA) such as polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 9T, and polyamide 66; polyurethane; polyethylene-vinyl acetate copolymer (EVA); or modified products thereof. Above all, the seal layer 12 preferably contains a polyolefin from the viewpoint of excellent flexibility and heat welding property, and preferably 50% by mass or more, more preferably 90% by mass or more of the seal layer 12 is polyethylene. The protective layer 13 preferably contains a polyolefin in terms of excellent flexibility and chemical resistance, and preferably 50% by mass or more, more preferably 90% by mass or more of the protective layer 13 is made of polyethylene.

  The thickness of the film package 10 is, for example, 25 μm to 400 μm, preferably 30 μm to 300 μm, more preferably 40 μm to 260 μm, and particularly preferably 50 μm to 200 μm. Thereby, it becomes easy to obtain an exterior body that is excellent in mechanical strength and gas barrier properties and that can achieve both flexibility and durability.

  Next, an example of a flexible battery including the above-mentioned film package will be described. FIG. 2 is a plan view of the flexible battery according to the present embodiment in which a part of a film exterior body is cut away. FIG. 3 is a cross-sectional view of the flexible battery taken along line III-III.

  The flexible battery 100 includes an electrode group 103, an electrolyte (not shown), and a film package 108 that stores these. The electrode group 103 includes a pair of first electrodes 110 located outside, a second electrode 120 disposed therebetween, and a separator 107 interposed between the first electrode 110 and the second electrode 120. Have. The first electrode 110 includes a first current collector 111 and a first active material layer 112 attached to one surface thereof. The second electrode 120 includes a second current collector 121 and a second active material layer 122 attached to both surfaces thereof. The pair of first electrodes 110 are arranged with the second electrode 120 interposed therebetween such that the first active material layer 112 and the second active material layer 122 face each other with the separator 107 interposed therebetween.

  A first tab 114 cut out of the same conductive sheet material as the first current collector 111 extends from one side of the first current collector 111. The first tabs 114 of the pair of first electrodes 110 overlap with each other and are electrically connected, for example, by welding. Thereby, the collection tab 114A is formed. The first lead 113 is connected to the collecting tab 114A, and the first lead 113 is drawn out of the film package 108.

  Similarly, a second tab 124 cut from the same conductive sheet as the second current collector 121 extends from one side of the second current collector 121. The second lead 123 is connected to the second tab 124, and the second lead 123 is drawn out of the film package 108.

  The ends of the first lead 113 and the second lead 123 led out of the film package 108 function as positive or negative external terminals or external terminals, respectively. It is desirable to interpose a sealing material 130 between the film exterior body 108 and each lead in order to enhance the sealing performance. As the sealant 130, a thermoplastic resin can be used.

  In the illustrated example, the electrode group is generally shown as a rectangle, but the shape of the electrode group is not limited to this. However, from the viewpoint of productivity of the thin battery, a rectangle or a substantially rectangle is preferable. When the electrode group is rectangular or substantially rectangular, the ratio of the long side to the short side is, for example, long side: short side = 1: 1 to 8: 1. The number and structure of the positive electrode and the negative electrode included in the electrode group are not particularly limited.

  The method for manufacturing the flexible battery 100 is not particularly limited, but for example, it can be manufactured by the following procedure. First, a band-shaped film exterior body 108 is prepared, the band-shaped film exterior body 108 is folded into two with the sealing layer inside, and both ends of the band-shaped film exterior body 108 are overlapped and welded to form a tubular shape. . Next, after the electrode group is inserted from one opening of the cylindrical film package 108, the opening is closed by heat welding. At this time, the ends of the first lead 113 and the second lead 123 are led out from one opening of the tubular film package 108, and the sealing material 130 is interposed between the opening end and each lead. As a result, the film package 108 has an envelope shape or a bag shape. Next, the electrolyte is injected from the remaining opening of the envelope-shaped film package 108, and then the remaining opening is closed by heat welding in a reduced-pressure atmosphere. Thereby, the flexible battery is completed.

  Next, an example in which the flexible battery is a lithium ion secondary battery will be described with respect to main members and electrolytes constituting an electrode group.

(Negative electrode)
The negative electrode has a negative electrode current collector as a first or second current collector, and a negative electrode active material layer as a first or second active material layer. A metal film, a metal foil, or the like is used for the negative electrode current collector. The material of the negative electrode current collector is preferably at least one selected from the group consisting of copper, nickel, titanium, alloys thereof, and stainless steel. The thickness of the negative electrode current collector is preferably, for example, 5 to 30 μm.

  The negative electrode active material layer contains a negative electrode active material and, if necessary, a binder and a conductive agent. The negative electrode active material layer may be a deposited film formed by a gas phase method (for example, vapor deposition). Examples of the negative electrode active material include Li metal, a metal or an alloy that electrochemically reacts with Li, a carbon material (eg, graphite), a silicon alloy, and a silicon oxide. The thickness of the negative electrode active material layer is preferably, for example, 1 to 300 μm.

(Positive electrode)
The positive electrode has a positive electrode current collector as a first or second current collector and a positive electrode active material layer as a first or second active material layer. As the positive electrode current collector, a metal film, a metal foil (stainless steel foil, aluminum foil, or aluminum alloy foil) or the like is used.

The positive electrode active material layer contains a positive electrode active material and a binder, and optionally contains a conductive agent. The positive electrode active material is not particularly limited, but a lithium-containing composite oxide such as LiCoO ₂ or LiNiO ₂ can be used. The thickness of the positive electrode active material layer is preferably, for example, 1 to 300 μm.

  As the conductive agent contained in the active material layer, graphite, carbon black, or the like is used. The amount of the conductive agent is, for example, 0 to 20 parts by mass per 100 parts by mass of the active material. Fluororesin, acrylic resin, rubber particles, and the like are used as the binder contained in the active material layer. The amount of the binder is, for example, 0.5 to 15 parts by mass per 100 parts by mass of the active material.

(Separator)
As the separator, a resin microporous film or a nonwoven fabric is preferably used. As a material (resin) of the separator, polyolefin, polyamide, polyamideimide, or the like is preferable. The thickness of the separator is, for example, 8 to 30 μm.

(Electrolytes)
A non-aqueous electrolyte containing a lithium salt and a non-aqueous solvent in which the lithium salt is dissolved is preferable. Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , and imide salts. As the non-aqueous solvent, propylene carbonate, ethylene carbonate, cyclic carbonates such as butylene carbonate, diethyl carbonate, ethyl methyl carbonate, chain carbonates such as dimethyl carbonate, γ-butyrolactone, cyclic carboxylic acid esters such as γ-valerolactone And the like.

  It is preferable that at least a part of the nonaqueous electrolyte impregnated in the electrode group forms a gel electrolyte. The gel electrolyte includes, for example, a non-aqueous electrolyte and a resin that swells with the non-aqueous electrolyte. As the resin that swells with the nonaqueous electrolyte, a fluororesin containing a vinylidene fluoride unit is preferable. The fluororesin containing the vinylidene fluoride unit easily retains the non-aqueous electrolyte and easily gels.

  Hereinafter, the present invention will be described more specifically based on examples. However, the following examples do not limit the present invention.

<< Example 1 >>
In the following procedure, a thin battery having a pair of negative electrodes and a positive electrode sandwiched therebetween was manufactured.
(1) Preparation of Negative Electrode An 8 μm thick electrolytic copper foil was prepared as a negative electrode current collector. A negative electrode mixture slurry was applied to one surface of the electrolytic copper foil, dried, and then rolled to form a negative electrode active material layer, thereby obtaining a negative electrode sheet.

  The negative electrode mixture slurry contains 100 parts by mass of graphite (average particle size: 22 μm) as a negative electrode active material, 8 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP). It was prepared by mixing. The thickness of the negative electrode active material layer was 145 μm.

  A 23 mm × 55 mm size negative electrode having a 5 mm × 5 mm negative electrode tab was cut out from the negative electrode sheet, and the active material layer was peeled off from the negative electrode tab to expose the copper foil. Thereafter, a negative electrode lead made of copper was ultrasonically welded to the tip of the negative electrode tab.

(2) Preparation of Positive Electrode A rolled aluminum foil having a thickness of 15 μm was prepared as a positive electrode current collector. The 0.2% proof stress in the rolling direction of the rolled aluminum foil is 195 MPa. The positive electrode mixture slurry was applied to both surfaces of the aluminum foil, dried, and then rolled to form a positive electrode active material layer, thereby obtaining a positive electrode sheet.

The positive electrode mixture slurry includes 100 parts by mass of LiNi _0.8 Co _0.16 Al _0.04 O ₂ (average particle size: 20 μm) as a positive electrode active material, 0.75 parts by mass of acetylene black as a conductive agent, and polyfluoride as a binder. It was prepared by mixing 0.75 parts by mass of vinylidene and an appropriate amount of NMP. The thickness per side of the positive electrode active material layer was 80 μm.

  A 21 mm × 53 mm size positive electrode having a 5 mm × 5 mm tab was cut out from the positive electrode sheet, and the active material layer was peeled off from the positive electrode tab to expose the aluminum foil. Thereafter, a positive electrode lead made of aluminum was ultrasonically welded to the tip of the positive electrode tab.

(3) Non-aqueous electrolyte LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent (volume ratio: 20:30:50) of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), A non-aqueous electrolyte was prepared.

(4) Preparation of Film Outer Body Rolled aluminum foil (thickness: 15 μm) serving as a gas barrier layer (metal layer) is stacked on one surface of a polyethylene (PE) film serving as a sealing layer, and both are rolled while being heated. After forming a two-layer structure, a PE film serving as a protective layer was stacked on the rolled aluminum foil, and the whole was rolled to produce a film exterior body (thickness 75 μm) having a 30 μm-thick PE layer on both surfaces. . The 0.2% proof stress of the rolled aluminum foil in the rolling direction is 160 MPa.

(5) Assembly of flexible battery 5 parts by mass of polyvinylidene fluoride was dissolved in 100 parts by mass of the mixed solvent to prepare a polymer solution. The polymer solution was applied to both sides of a separator made of a microporous polyethylene film (9 μm in thickness) having a size of 23 mm × 59 mm, and then the solvent was evaporated to form a polyvinylidene fluoride film. The amount of the applied polyvinylidene fluoride was 15 g / m ² . Thereafter, a positive electrode was arranged between the pair of negative electrode active material layers with a separator interposed therebetween, to form an electrode group.

  Next, the rolling direction of the rolled aluminum foil of the film casing and the rolling direction of the rolled aluminum foil serving as the positive electrode current collector were placed on the tubular film casing (thickness: 75 μm) with the sealing layer inside. Were stored in the same direction. The positive electrode lead and the negative electrode lead were led out from one opening of the film package, each lead was surrounded by a thermoplastic resin serving as a sealing material, and the openings were sealed by heat welding.

  Next, a nonaqueous electrolyte was injected from the other opening, and the other opening was heat-sealed under a reduced pressure atmosphere of -650 mmHg. Thereafter, the battery was aged in a 45 ° C. environment, and the electrode group was impregnated with a non-aqueous electrolyte. Finally, the battery was pressed at 25 ° C. for 30 seconds at a pressure of 0.25 MPa to produce a 0.5 mm thick battery A1.

<< Example 2 >>
A flexible battery A2 was produced in the same manner as in Example 1, except that the positive electrode current collector was changed to a rolled aluminum foil having a thickness of 15 μm and a 0.2% proof stress in the rolling direction of 160 MPa.

<< Comparative Example 1 >>
A flexible battery B1 was produced in the same manner as in Example 1, except that the positive electrode current collector and the gas barrier layer were replaced.

<< Example 3 >>
The positive electrode current collector was changed to a rolled aluminum foil having a thickness of 15 μm and a 0.2% proof stress in the rolling direction of 210 MPa, and the gas barrier layer was changed to a rolled aluminum foil having a thickness of 15 μm and a 0.2% proof stress of 210 MPa in the rolling direction. A flexible battery A3 was produced in the same manner as in Example 1 except for the above.

<< Examples 4 to 9 >>
Example 1 Except that the thickness of the rolled aluminum foil serving as the gas barrier layer was changed to 3 μm (A4), 5 μm (A5), 10 μm (A6), 20 μm (A7), 25 μm (A8) or 27 μm (A9). In the same manner as in the above, flexible batteries A4 to A9 were produced.

<< Example 10 >>
A flexible battery A10 was produced in the same manner as in Example 1, except that the protective layer was changed to a polyamide (nylon (NY)) layer having a thickness of 30 μm.

<< Example 11 >>
A flexible battery A11 was produced in the same manner as in Example 1, except that the protective layer was changed to a PE layer having a thickness of 15 μm.

<< Example 12 >>
A flexible battery A12 was produced in the same manner as in Example 1, except that the protective layer was changed to a polypropylene (PP) layer having a thickness of 30 μm.

<< Example 13 >>
A flexible battery A13 was produced in the same manner as in Example 1, except that the sealing layer was changed to a PE layer having a thickness of 15 μm.

<< Example 14 >>
A flexible battery A14 was produced in the same manner as in Example 1, except that the arrangement of the positive electrode and the negative electrode was changed in the opposite manner. That is, the negative electrode was used as a double-sided electrode, the positive electrode was used as a single-sided electrode, and the negative electrode was arranged between the pair of positive electrode active material layers of the positive electrode with a separator interposed therebetween to form an electrode group.

[Evaluation]
(Initial battery capacity)
Under the environment of 25 ° C., the battery was charged and discharged as described below, and the initial capacity (C ₀ ) was obtained. However, the design capacity of the battery is 1 C (mAh).

(1) Constant current charging: 0.2 CmA (final voltage 4.2 V)
(2) Constant voltage charging: 4.2 V (final current 0.05 CmA)
(3) Constant current discharge: 0.5 CmA (final voltage 2.5 V)

(Capacity maintenance rate after bending test)
A pair of expandable and contractible fixing members were horizontally arranged to face each other, and the closed portions of both ends of the charged battery were fixed by heat welding with the fixing members. Then, in an environment of a humidity of 65% and 25 ° C., a jig having a curved portion having a curvature radius R of 20 mm is pressed against the battery, and the battery is bent along the curved portion, and then the jig is separated from the battery. The shape of the battery was restored. This operation was repeated 4000 times. Thereafter, the flexible battery was charged and discharged under the same conditions as described above, and the discharge capacity (C _x ) after the bending test was determined. From the obtained discharge capacity C _x and the initial capacitance C _0, the capacity retention ratio was obtained from the following equation.

Capacity retention rate after bending test (%) = (C _x / C ₀ ) × 100

  Ten batteries were manufactured for each of the examples and comparative examples, and the same test was performed for each of the batteries, and the average value of the capacity retention ratio was determined. Table 1 shows the results.

  As shown in Table 1, in each of the examples, the capacity retention rate was 90% or more, whereas in Comparative Example 1, the capacity retention rate was significantly reduced to 72%. This is because the 0.2% proof stress of the gas barrier layer is larger than that of the positive electrode current collector, so that the flexibility of the film package is relatively insufficient, and the film package is wrinkled. When the battery was disassembled and the electrode group was observed, cracks were found in the positive electrode current collector.

  Contrary to Comparative Example 1, in Example 1 in which the 0.2% proof stress of the positive electrode current collector was larger than that of the gas barrier layer, the film package expanded and contracted preferentially, and the stress applied to the electrode group was reduced. Therefore, wrinkles did not occur on the film exterior body, and the capacity retention ratio was maintained at 100%.

  The 0.2% proof stress of both the gas barrier layer and the positive electrode current collector was 160 MPa, and even in Example 2 in which there was no difference between them, a very good capacity retention rate was obtained.

  In Example 3, in which both the gas barrier layer and the positive electrode current collector had a 0.2% proof stress of 210 MPa, a good capacity retention ratio was obtained. However, since the absolute value of the 0.2% proof stress of the gas barrier layer exceeded 200 MPa, slight wrinkles were observed on the film exterior body, and the capacity retention ratio was slightly lowered.

The 0.2% proof stress of the gas barrier layer and the positive electrode current collector is the same as in Example 1, but in Examples 4 to 9 in which the thickness of the gas barrier layer was changed in the range of 3 to 27 μm, the capacity retention ratio was different. It was observed. From the results in Table 1, it can be understood that the thickness ratio T _GB / T _PC is preferably 0.3 to 1.7, and more preferably 0.5 to 1.5. In Example 4 in which the gas barrier layer was 3 μm, a slight crack was generated in the gas barrier layer. Further, in Example 9 in which the gas barrier layer was 27 μm, slight wrinkles were observed in the film package.

  In Examples 10 to 13 in which the configurations of the protective layer and the seal layer were changed, good capacity retention rates were obtained. However, the capacity retention ratio was slightly lower than that in Example 1 in which a sufficiently thick PE layer was used for both the protective layer and the seal layer. In Example 10 in which nylon (NY) was used for the protective layer and Example 12 in which PP was used for the seal layer, slight wrinkles were observed on the film package. Further, in Examples 11 and 13 in which the protective layer or the seal layer was thinner than the gas barrier layer, slight cracks occurred in the gas barrier layer.

  Also in Example 14 in which the positive electrode was disposed on both ends of the electrode group as a single-sided electrode, a good capacity retention ratio was obtained. However, the capacity retention ratio was slightly lower than that of Example 1 having the reverse arrangement. When the battery was disassembled and the electrode group was observed, a slight crack was found in the positive electrode current collector.

  The flexible battery according to the present invention is suitable for applications that may be greatly deformed, for example, as a power source for a small electronic device such as a biomedical device or a wearable portable terminal.

  10, 108: film package, 11: gas barrier layer, 12: seal layer, 13: protective layer, 100: flexible battery, 103: electrode group, 107: separator, 110: first electrode, 111: first current collector , 112: first active material layer, 113: first lead, 114: first tab, 120: second electrode, 121: second current collector, 122: second active material layer, 123: second lead, 124 : Second tab, 130: sealing material

Claims (8)

A positive electrode, a negative electrode and a sheet-like electrode group including an electrolyte layer interposed between the positive electrode and the negative electrode,
Including a film exterior body that hermetically stores the electrode group,
The positive electrode includes a positive electrode current collector formed of a metal sheet,
The film exterior body includes a gas barrier layer formed by a metal layer,
A flexible battery, wherein the 0.2% proof stress of the positive electrode current collector is not less than the 0.2% proof stress of the gas barrier layer.   The flexible battery according to claim 1, wherein the 0.2% proof stress of the gas barrier layer is 200 MPa or less. Ratio of the thickness T _{GB of the} gas barrier layer to the thickness T _PC of the positive electrode current collector:
The flexible battery according to claim 1, wherein T _GB / T _PC is 0.3 or more and 1.7 or less. The film exterior body,
The gas barrier layer,
A sealing layer laminated on one surface of the gas barrier layer,
A protective layer laminated on the other surface of the gas barrier layer,
4. The flexible battery according to claim 1, wherein a volume ratio of the gas barrier layer in the film package is 33% or less. 5. The flexible battery according to claim 4, wherein the thickness T _OU of the protective layer is larger than the thickness T _{GB of the} gas barrier layer, and is formed of polyethylene. The flexible battery according to claim 4, wherein the thickness T _IN of the seal layer is larger than the thickness T _{GB of the} gas barrier layer, and is formed of polyethylene. The flexible battery according to claim 1, wherein a thickness T _GB of the gas barrier layer is 5 μm or more and 200 μm or less. The sheet-shaped electrode group includes a plurality of the negative electrodes,
The flexible battery according to any one of claims 1 to 7, wherein a pair of the negative electrodes is disposed at both ends of the electrode group.

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