JP2009224221A - Nonaqueous electrolyte secondary battery and negative electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with a gel electrolyte that improves cycle characteristics. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a positive electrode, negative electrode and gel electrolyte. The negative electrode contains a negative electrode mixture containing a binding agent, and the binding agent contains polyvinylidene fluoride and polyvinyl pyrrolidone and a mass ratio of polyvinylidene fluoride and polyvinyl pyrrolidone is 99.9:0.1 to 70:30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte secondary battery and a negative electrode containing polyvinylidene fluoride and vinylpyrrolidone as a negative electrode binder.

  In recent years, many portable electronic devices such as a camera-integrated VTR (video tape recorder), a digital camera, a mobile phone, a portable information terminal, and a notebook computer have appeared, and their size and weight have been reduced. As a portable power source for these electronic devices, research and development for improving the energy density of batteries, particularly secondary batteries, are being actively promoted. Among them, a lithium ion secondary battery is widely put into practical use because a large energy density can be obtained as compared with a lead battery or a nickel cadmium battery which is a conventional aqueous electrolyte secondary battery.

Here, various additives have been studied in order to improve battery characteristics. For example, polyvinylidene fluoride is used as a binder for the negative electrode (see Patent Documents 1 to 3). This is for binding the active material layer and the current collector.
JP 2004-79370 A JP 2004-146253 A JP 2003-249212 A

However, the above prior art has room for improvement in improving the cycle characteristics.
The present invention has been made in view of the above problems, and an object thereof is to improve cycle characteristics in a nonaqueous electrolyte secondary battery provided with a gel electrolyte.

As a result of intensive investigations to achieve the above object, the present inventors have increased the affinity between the negative electrode and the gel electrolyte by including polyvinylidene fluoride and vinylpyrrolidone as the negative electrode binder. The present inventors have found that the object can be achieved and have completed the present invention.
That is, the present invention relates to the following nonaqueous electrolyte secondary battery and negative electrode.
[1] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a gel-like non-aqueous electrolyte,
The negative electrode contains a negative electrode mixture containing a binder,
The non-aqueous electrolyte, wherein the binder contains polyvinylidene fluoride and polyvinyl pyrrolidone, and the mass ratio of polyvinylidene fluoride and polyvinyl pyrrolidone is 99.9: 0.1 to 70:30. Secondary battery.
[2] A negative electrode mixture containing a binder is contained, the binder contains polyvinylidene fluoride and polyvinylpyrrolidone, and the mass ratio of polyvinylidene fluoride and polyvinylpyrrolidone is 99.9: 0. 1 to 70:30, The negative electrode characterized by the above-mentioned.

  According to the present invention, the affinity between the negative electrode and the gel electrolyte is increased, and as a result, the cycle characteristics can be improved.

Hereinafter, embodiments of the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an exploded perspective view showing an example of a laminated secondary battery as an embodiment of the nonaqueous electrolyte secondary battery of the present invention. As shown in the figure, this secondary battery is configured by enclosing a battery element 20 to which a negative electrode terminal 11 and a positive electrode terminal 12 are attached inside a film-shaped exterior member 30. The negative electrode terminal 11 and the positive electrode terminal 12 are led out from the inside of the exterior member 30 to the outside, for example, in the same direction. The negative electrode terminal 11 and the positive electrode terminal 12 are each made of a metal material such as aluminum (Al), copper (Cu), nickel (Ni), or stainless steel (SUS).

  The exterior member 30 is configured by a rectangular laminate film in which, for example, a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 30 is arrange | positioned so that the polyethylene film side and the battery element 20 may oppose, for example, and each outer edge part is mutually joined by melt | fusion or the adhesive agent. An adhesion film 31 is inserted between the exterior member 30 and the negative electrode terminal 11 and the positive electrode terminal 12 to prevent the outside air from entering. The adhesion film 31 is made of a material having adhesion to the negative electrode terminal 11 and the positive electrode terminal 12. For example, when the negative electrode terminal 11 and the positive electrode terminal 12 are made of the metal materials described above, polyethylene, polypropylene, modified It is preferably composed of a polyolefin resin such as polyethylene and modified polypropylene.

  In addition, the exterior member 30 may be configured by another structure, for example, a laminate film having no metal material, a polymer film such as polypropylene, or a metal film, instead of the above-described laminate film. Here, the general structure of an exterior member can be represented by the laminated structure of an exterior layer / metal foil / sealant layer (however, the exterior layer and the sealant layer may be composed of a plurality of layers), and the above. In this example, the nylon film corresponds to the exterior layer, the aluminum foil corresponds to the metal foil, and the polyethylene film corresponds to the sealant layer. In addition, as metal foil, it is sufficient if it functions as a moisture-permeable barrier film, and not only aluminum foil but also stainless steel foil, nickel foil and plated iron foil can be used, but it is thin and lightweight. Thus, an aluminum foil excellent in workability can be suitably used.

  The structures that can be used as the exterior member are listed in the form of (exterior layer / metal foil / sealant layer): Ny (nylon) / Al (aluminum) / CPP (unstretched polypropylene), PET (polyethylene terephthalate) / Al / CPP, PET / Al / PET / CPP, PET / Ny / Al / CPP, PET / Ny / Al / Ny / CPP, PET / Ny / Al / Ny / PE (polyethylene), Ny / PE / Al / LLDPE (directly) Chain low density polyethylene), PET / PE / Al / PET / LDPE (low density polyethylene), and PET / Ny / Al / LDPE / CPP.

  FIG. 2 is a schematic cross-sectional view taken along the line II-II of the battery element 20 shown in FIG. In the figure, a battery element 20 is formed by winding a negative electrode 21 and a positive electrode 22 facing each other with a non-aqueous electrolyte layer 23 and a separator 24 made of a gel-like non-aqueous electrolyte, The outermost periphery is protected by a protective tape 25.

[Negative electrode]
Here, the negative electrode 21 has a structure in which, for example, a negative electrode mixture layer 21B is provided on both surfaces or one surface of a negative electrode current collector 21A having a pair of opposed surfaces. The negative electrode current collector 21A has an exposed portion where the negative electrode mixture layer 21B is not provided at one end in the longitudinal direction, and the negative electrode terminal 11 is attached to the exposed portion. The negative electrode current collector 21A is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

The negative electrode mixture layer 21B includes, as a negative electrode active material, one or more of negative electrode materials capable of occluding and releasing lithium ions and metallic lithium, and polyvinylidene fluoride as a binder. And vinylpyrrolidone, and may contain a conductive agent as necessary. Further, the surface density of the negative electrode mixture layer 21B is preferably 5 mg / cm ² or more, more preferably 10 mg / cm ² or more, on both sides. By setting the surface density within such a range, the cycle improvement effect of the present invention can be easily obtained.

Examples of the anode material capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, natural graphite, artificial graphite, pyrolytic carbons, cokes, glassy carbons, organic high Examples thereof include carbon materials such as molecular compound fired bodies, carbon fibers, and activated carbon. Moreover, it is preferable that the specific surface area of a carbon material is 0.3-2 m < ² > / g from a viewpoint of negative electrode mixture slurry stability. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as phenol resin or furan resin at an appropriate temperature, and partly non-graphitizable carbon or graphitizable carbon. Some are classified as: Examples of the polymer material include polyacetylene and polypyrrole. These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density.
Further, non-graphitizable carbon is preferable because excellent characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically, those having a charge / discharge potential close to that of lithium metal are preferable because a high energy density of the battery can be easily realized.

Examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and including at least one of a metal element and a metalloid element as a constituent element. . This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable because a high energy density can be obtained and excellent cycle characteristics can be obtained.
This negative electrode material may be a single element or an alloy or a compound of a metal element or a metalloid element, or may have at least a part of one or more of these phases. In the present invention, the alloy includes an alloy containing one or more metal elements and one or more metalloid elements in addition to an alloy composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of metal elements or metalloid elements constituting the negative electrode material include magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), and germanium (Ge). ), Tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) ) And platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or metalloid element as a constituent element in the short-period type periodic table is preferable, and at least one of silicon (Si) and tin (Sn) is particularly preferable. It is included as an element. This is because silicon (Si) and tin (Sn) have a large ability to occlude and release lithium (Li), and a high energy density can be obtained.

  As an alloy of tin (Sn), for example, as a second constituent element other than tin (Sn), silicon (Si), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr) The thing containing at least 1 sort is mentioned. As an alloy of silicon (Si), for example, as a second constituent element other than silicon (Si), tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and chromium (Cr). The thing containing 1 type is mentioned.

  Examples of the compound of tin (Sn) or the compound of silicon (Si) include those containing oxygen (O) or carbon (C). In addition to tin (Sn) or silicon (Si), the above-described compounds Two constituent elements may be included.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as MnO ₂ , V ₂ O ₅ , and V ₆ O ₁₃ , sulfides such as NiS and MoS, and lithium nitrides such as LiN ₃ , and polymer materials include polyacetylene, Examples include polyaniline and polypyrrole.

  As materials capable of alloying lithium, various kinds of metals can be used, such as tin (Sn), cobalt (Co), indium (In), aluminum (Al), silicon (Si), and these. Often alloys are used. When metallic lithium is used, the powder may be formed into a coating film with a binder.

  The negative electrode binder in the present invention contains polyvinylidene fluoride and vinylpyrrolidone. Furthermore, the mass ratio of polyvinylidene fluoride and vinylpyrrolidone is 99.9: 0.1 to 70:30, preferably 99: 1 to 70:30. If the mass ratio of polyvinylidene fluoride and vinylpyrrolidone is within the above range, the stability of the negative electrode mixture slurry can be obtained. For example, polyvinylidene fluoride having an intrinsic viscosity of 1.5 to 10.0 dl / g is preferably used, but is not limited thereto.

  The total content of polyvinylidene fluoride and vinylpyrrolidone is preferably 2 to 6.5% by mass, more preferably 2.5 to 5% by mass based on the total content of the negative electrode mixture. By setting the total content of polyvinylidene fluoride and vinylpyrrolidone within the above range, good cycle characteristics can be obtained. As the binder, in addition to polyvinylidene fluoride and vinylpyrrolidone, polyacrylonitrile or the like may be mixed and used.

  As the conductive agent, for example, a carbon material such as carbon black or graphite is used.

[Positive electrode]
On the other hand, like the negative electrode 21, the positive electrode 22 has a structure in which, for example, both surfaces or one surface of a positive electrode current collector 22A having a pair of opposed surfaces are coated with a positive electrode mixture layer 22B. The positive electrode current collector 22A has a portion that is exposed without being covered with the positive electrode mixture layer 22B at one end portion in the longitudinal direction, and the positive electrode terminal 12 is attached to the exposed portion. The positive electrode current collector 22A is made of a metal foil such as an aluminum foil.

  The positive electrode mixture layer 22B includes, for example, a positive electrode material capable of inserting and extracting lithium ions as a positive electrode active material, and may include a conductive agent and a binder as necessary. Here, the positive electrode active material, the conductive agent, and the binder need only be uniformly dispersed, and the mixing ratio is not limited.

As a positive electrode material capable of occluding and releasing lithium used as a positive electrode active material, for example, lithium oxide, lithium phosphorous oxide, lithium sulfide, or an intercalation compound containing lithium is used depending on the type of the target battery. Lithium-containing compounds are suitable, and two or more of these may be mixed and used. In order to increase the energy density, a lithium-containing compound containing lithium, a transition metal element, and oxygen (O) is preferable. Among them, as the transition metal element, cobalt (Co), nickel (Ni), manganese (Mn), and iron It is more preferable if it contains at least one of the group consisting of (Fe). As such a lithium-containing compound, for example, a lithium composite oxide having a layered rock salt structure shown in Formula (1), a lithium composite oxide having a spinel structure shown in Formula (2), and a formula Examples thereof include lithium composite phosphates having the olivine type structure shown in (3). Specifically, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _0.33 Ni _0.33 Mn _0.33 There are O ₂ , LiFePO ₄ and the like.

Layered _{rock-salt: Li p Mn (1-p} -q-r) Ni q M1 r] O (2-y1) F z1 (1)
In formula (1), M1 is cobalt (Co), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper It represents at least one selected from the group consisting of (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). p, q, r, y1 and z1 are 0 <p ≦ 0.2, 0.1 ≦ q ≦ 0.8, 0 ≦ r ≦ 0.5, −0.1 ≦ y1 ≦ 0.2, 0 ≦ It is a value within the range of z1 ≦ 0.1.

_{Spinel: Li a Mn 2-b M4} b O c F d (2)
In the formula (2), M4 represents at least one selected from the group consisting of cobalt, nickel, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium, and tungsten. To express. a, b, c and d are values within the ranges of a ≧ 0.9, 0 ≦ b ≦ 0.6, 3.7 ≦ c ≦ 4.1, and 0 ≦ d ≦ 0.1.

Olivine type: Li _a M5PO ₄ (3)
In Formula (3), M5 is at least one selected from the group consisting of cobalt, manganese, iron, nickel, magnesium, aluminum, boron, titanium, vanadium, niobium, copper, zinc, molybdenum, calcium, strontium, tungsten, and zirconium. Represents a species. It is a value satisfying a ≧ 0.9.

In addition to these, examples of the positive electrode material capable of inserting and extracting lithium include inorganic compounds such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS that do not contain lithium.

  In addition, as the conductive agent, for example, carbon materials such as carbon black and graphite are used. Furthermore, as the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene trifluoride, or the like is used.

[Nonaqueous electrolyte layer]
The nonaqueous electrolyte layer 23 is formed of a gel-like nonaqueous electrolyte. The gel-like nonaqueous electrolyte is formed by gelling a nonaqueous electrolyte with a matrix polymer. The gel-like nonaqueous electrolyte is configured such that a nonaqueous electrolyte is impregnated or held in a matrix polymer. By such swelling, gelation or non-fluidization of the matrix polymer, it is possible to effectively suppress leakage of the nonaqueous electrolyte in the obtained battery. As the non-aqueous electrolyte, those generally used for lithium ion secondary batteries can be used. As such a nonaqueous electrolytic solution, a solution obtained by dissolving an electrolyte salt in a nonaqueous solvent can be used.

  Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used as the nonaqueous solvent, and it is preferable to use one of ethylene carbonate and propylene carbonate, in particular, a mixture of both. This is because the cycle characteristics can be improved.

  As the non-aqueous solvent, in addition to these cyclic carbonates, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate. This is because high ionic conductivity can be obtained.

  The non-aqueous solvent preferably further contains 2,4-difluoroanisole or vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can improve cycle characteristics. Therefore, it is preferable to use a mixture of these because the discharge capacity and cycle characteristics can be improved.

  In addition to these, examples of the non-aqueous solvent include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl- 1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N , N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide and trimethyl phosphate.

  A compound in which at least a part of hydrogen in these nonaqueous solvents is substituted with a halogen such as fluorine may improve the reversibility of the electrode reaction depending on the type of electrode to be combined. is there.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently and 2 or more types may be mixed and used for it. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₃ , LiClO ₄ , LiNO ₃ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , difluoro [oxolato-O, O ′] lithium borate, lithium bisoxalate borate, LiBr, Examples include LiCl and LiI. The concentration for dissolving the lithium salt is preferably in the range of 0.4 mol / kg to 2.0 mol / kg with respect to the non-aqueous solvent. From the viewpoint of oxidation stability, it is desirable to use LiPF ₆ or LiBF ₄ . Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

The gel-like nonaqueous electrolyte is prepared by gelling the above-described nonaqueous electrolyte with a matrix polymer. The matrix polymer is not particularly limited as long as it is compatible with a nonaqueous electrolytic solution obtained by dissolving the electrolyte salt in the nonaqueous solvent and can be gelled. Moreover, the preferable content in the nonaqueous electrolyte of a matrix polymer is 5-30 mass%. As the matrix polymer, a polymer containing at least vinylidene fluoride as a monomer is preferable. Specifically, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, vinylidene fluoride, hexafluoropropylene, and monochloro Examples thereof include a copolymer of trifluoroethylene and a copolymer of vinylidene fluoride, hexafluoropropylene, and monomethylmaleic acid ester, and in particular, from the viewpoint of redox stability, vinylidene fluoride and hexafluoropropylene. And a copolymer are preferred. A copolymer in which hexafluoropropylene is introduced into polyvinylidene fluoride or vinylidene fluoride at a ratio of 75% or less can be used. Such polymers have a number average molecular weight in the range of 5.0 × 10 ^{5 to} 7.0 × 10 ⁵ (500,000 to 700,000) or a weight average molecular weight of 2.1 × 10 ^{5 to} 3. It is in the range of 1 × 10 ⁵ (210,000-310,000), and the intrinsic viscosity is in the range of 1.7 (dl / g) to 2.1 (dl / g). Such a polymer may be used individually by 1 type, and may mix and use 2 or more types.

[Separator]
The separator 24 has a high ion permeability and a predetermined mechanical strength, such as a porous film made of a polyolefin-based organic resin such as polypropylene and polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. It is good also as a structure which laminated | stacked these 2 or more types of porous films. In particular, those containing a polyolefin-based porous membrane are preferable because they have excellent separability between the negative electrode 21 and the positive electrode 22 and can further reduce internal short circuit and open circuit voltage drop.

Next, an example of the manufacturing method of the nonaqueous electrolyte secondary battery mentioned above is demonstrated.
The laminate type secondary battery can be manufactured as follows. First, the negative electrode 21 is produced. For example, when a particulate negative electrode active material is used, a negative electrode mixture is prepared by mixing the negative electrode active material, the above-described binder, and a conductive agent as necessary, and dispersing N-methyl-2-pyrrolidone or the like A negative electrode mixture slurry is prepared by dispersing in a medium. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 21A, dried, and compression molded to form the negative electrode mixture layer 21B.

  Moreover, the positive electrode 22 is produced. For example, when a particulate positive electrode active material is used, a positive electrode mixture is prepared by mixing the positive electrode active material and, if necessary, a conductive agent and a binder, and a dispersion medium such as N-methyl-2-pyrrolidone. To produce a positive electrode mixture slurry. Thereafter, the positive electrode mixture slurry is applied to the positive electrode current collector 22A, dried, and compression molded to form the positive electrode mixture layer 22B.

  Next, the negative electrode terminal 11 is attached to the negative electrode 21, and the positive electrode terminal 12 is attached to the positive electrode 22. At this time, you may stick the protective tape 25 on the collector of the welding part of the negative electrode terminal 11 or the positive electrode terminal 12, and its back surface, or the boundary part of a mixture application part and an electrical power collector exposure part.

  Next, the nonaqueous electrolyte layer 23 is formed on one side or both sides of the obtained negative electrode 21. For example, an electrolyte salt such as lithium hexafluorophosphate, a nonaqueous solvent such as ethylene carbonate and propylene carbonate, and a matrix polymer such as polyvinylidene fluoride are mixed and dissolved in a diluent solvent such as dimethyl carbonate and (DMC). A sol-like nonaqueous electrolyte is prepared. The sol-like non-aqueous electrolyte is applied to the negative electrode 21 and the diluting solvent is volatilized to form a non-aqueous electrolyte layer 23 made of a gel-like non-aqueous electrolyte.

  Furthermore, the nonaqueous electrolyte layer 23 is formed on one side or both sides of the obtained positive electrode 22. For example, the electrolyte salt such as lithium hexafluorophosphate described above, a nonaqueous solvent such as ethylene carbonate and propylene carbonate, and a matrix polymer such as polyvinylidene fluoride are mixed with a diluting solvent such as dimethyl carbonate (DMC). Dissolve to produce a sol-like non-aqueous electrolyte. This sol-like non-aqueous electrolyte is applied to the positive electrode 22 and the diluting solvent is volatilized to form a non-aqueous electrolyte layer 23 made of a gel-like non-aqueous electrolyte.

  Thereafter, the separator 24, the positive electrode 22 with the non-aqueous electrolyte layer 23 formed thereon, the separator 24 and the negative electrode 21 with the non-aqueous electrolyte layer 23 formed thereon are sequentially stacked and wound, and the protective tape 25 is adhered to the outermost peripheral portion. Element 20 is formed. Further, the battery element 20 is packaged with an exterior member 30 to complete the laminate type secondary battery shown in FIGS.

  The nonaqueous electrolyte secondary battery may be manufactured as follows. For example, instead of wrapping the completed battery element with an exterior member, a matrix polymer monomer or polymer is applied on the negative electrode 21 and the positive electrode 22 or on the separator 24 and wound to produce a wound electrode body. Alternatively, the non-aqueous electrolyte layer 23 may be formed by injecting the non-aqueous electrolyte described above after being housed in the exterior member 30. However, it is preferable to polymerize the monomer inside the exterior member 30 because the bondability between the nonaqueous electrolyte layer 23 and the separator 24 is improved and the internal resistance can be lowered. In addition, it is preferable to inject a non-aqueous electrolyte into the exterior member 30 to form a gel-like non-aqueous electrolyte because it can be easily manufactured with fewer steps.

  In the secondary battery described above, when charged, lithium ions are released from the positive electrode mixture layer 22 </ b> B and inserted into the negative electrode mixture layer 21 </ b> B through the nonaqueous electrolyte layer 23. When discharge is performed, lithium ions are released from the negative electrode mixture layer 21 </ b> B and inserted into the positive electrode mixture layer 22 </ b> B through the nonaqueous electrolyte layer 23.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Specifically, operations as described in the following examples were performed to produce a laminate type secondary battery as shown in FIGS. 1 and 2, and the performance was evaluated.

(Example 1-1)
<Production of negative electrode>
First, 99% by mass of artificial graphite having a specific surface area of 0.7 m ² / g as a negative electrode active material, 0.999% by mass of polyvinylidene fluoride (PVDF) as a binder, and 0.001% by mass of vinylpyrrolidone (PVP). %, And N-methyl-2-pyrrolidone (NMP) was added to obtain a negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry was uniformly applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and compression-molded by a roll press to form a negative electrode mixture layer (double-side surface density: 20 mg / cm ² , binder content: 1% by mass) was formed and cut into a width of 52 mm to produce a negative electrode. Thereafter, a negative electrode terminal made of nickel was attached to the negative electrode.

<Preparation of positive electrode>
Next, 96 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 1 part by mass of ketjen black as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder are uniformly mixed, NMP was added to obtain a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and compression-molded with a roll press machine. : 40 mg / cm ² ) was formed and cut into a width of 50 mm to produce a positive electrode. Thereafter, a positive electrode terminal made of aluminum was attached to the positive electrode.

<Preparation of nonaqueous electrolyte>
1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a non-aqueous solvent obtained by mixing at a ratio of ethylene carbonate (EC): propylene carbonate (PC) = 1: 1 (mass ratio). It was made to melt | dissolve to kg and the electrolyte solution was produced. Using a copolymer of polyvinylidene fluoride: hexafluoropropylene = 94: 6 (mass ratio) as a matrix polymer for forming the gel, mixing at a ratio of matrix polymer: electrolyte = 10: 90 (mass ratio), A sol-like nonaqueous electrolyte was prepared using dimethyl carbonate as a solvent. The obtained sol-like nonaqueous electrolyte was uniformly applied to both surfaces of the obtained negative electrode and positive electrode, and the solvent was volatilized to form a gel-like nonaqueous electrolyte layer on the negative electrode and positive electrode.

<Production of battery>
The negative electrode and the positive electrode on which the gel-like nonaqueous electrolyte layer is formed are laminated through a separator made of porous polyethylene having a thickness of 10 μm, and wound to produce a battery element, which is formed by an aluminum laminate film as an exterior member. The non-aqueous electrolyte secondary battery was obtained by packaging. The following evaluation was performed on the obtained secondary battery, and the results are shown in Table 1.

<Battery evaluation>
Negative electrode mixture slurry stability:
After stirring the negative electrode mixture slurry, a sample in which sedimentation of the binder was not visually recognized after standing for 30 minutes was evaluated as “◯”, and a sample in which sedimentation was visually confirmed was determined as “x”.
Cycle characterization:
The ratio (%) of the discharge capacity when charging the battery for 3 hours at 1 C with 4.2 V as the upper limit and repeating constant current discharge with 3 C as the lower limit at 1 C was used as an evaluation index.
Tensile strength:
A tape was applied to the surface of the active material of the sample in which the active material was applied on the current collector foil (tape size 1.5 mm × 100 mm). One side of the tape was fixed to a tensile tester and pulled at a constant speed (5 mm / s), and the strength at that time was measured. The average strength was calculated and taken as the peel strength.

(Examples 1-2 to 1-4, Comparative Examples 1-1 to 1-4)
Respective secondary batteries were obtained in the same manner as Example 1-1 except that the blending ratio of PVdF and PVP in the negative electrode binder was changed as shown in Table 1. The evaluation results are shown in Table 1.

  From the results of Table 1, the secondary batteries of Examples 1-1 to 1-4 exhibited cycle characteristics superior to those of Comparative Example 1-1 in which only PVdF was used as a negative electrode binder, and the stability of the negative electrode mixture was stable. It was found that it was possible to ensure sex. Moreover, in Comparative Examples 1-2 to 1-4 in which the blending ratio of PVdF and PVP is outside the scope of the present invention, since the negative electrode mixture slurry could not be stably formed, a highly reliable capacity retention rate could not be measured. It was. Further, the peel strength was maximized in the case of Example 1-3 with PVDF: PVP = 90: 10, but in the range of 99: 1 to 70:30, peel strength almost similar to that of Example 1-3 was obtained. I was able to. On the other hand, in Comparative Examples 1-2 to 1-4, since the negative electrode mixture slurry could not be stably formed, the peel strength could not be measured. This is considered to be because when the blending ratio of PVP is high, the electrode becomes hard, and does not peel well during the peel test, and the active material layer may break, and stable measurement cannot be performed.

(Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1 except that the binder content of the negative electrode was 2% by mass. The evaluation results are shown in Table 2.

  From the results of Table 2, the secondary batteries of Examples 2-1 to 2-4 showed cycle characteristics and tensile strength characteristics superior to those of Comparative Example 2-1, in which only PVdF was used as the binder for the negative electrode. It was found that the stability of the mixture could be ensured. Moreover, in Comparative Examples 2-2 to 2-4 in which the blending ratio of PVdF and PVP was outside the scope of the present invention, the stability of the negative electrode mixture was poor, and the cycle characteristics and tensile strength characteristics could not be evaluated.

(Examples 3-1 to 3-4, Comparative examples 3-1 to 3-4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1 except that the binder content of the negative electrode was 3.5% by mass. The evaluation results are shown in Table 3.

  From the results of Table 3, the secondary batteries of Examples 3-1 to 3-4 showed cycle characteristics and tensile strength characteristics superior to those of Comparative Example 3-1, in which only PVdF was used as a negative electrode binder. It was found that the stability of the mixture could be ensured. Moreover, in Comparative Examples 3-2 to 3-4 in which the blending ratio of PVdF and PVP is outside the scope of the present invention, the stability of the negative electrode mixture was poor, and the cycle characteristics and the tensile strength characteristics could not be evaluated.

(Examples 4-1 to 4-4, Comparative Examples 4-1 to 4-4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1 except that the binder content of the negative electrode was changed to 5% by mass. The evaluation results are shown in Table 4.

  From the results of Table 4, the secondary batteries of Examples 4-1 to 4-4 showed cycle characteristics and tensile strength characteristics superior to those of Comparative Example 4-1, in which only PVdF was used as a binder for the negative electrode. It was found that the stability of the mixture could be ensured. Moreover, in Comparative Examples 4-2 to 4-4 in which the blending ratio of PVdF and PVP was outside the scope of the present invention, the stability of the negative electrode mixture was poor, and the cycle characteristics and tensile strength characteristics could not be evaluated.

(Examples 5-1 to 5-4, Comparative Examples 5-1 to 5-4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1 except that the binder content of the negative electrode was 6.5% by mass. The evaluation results are shown in Table 5.

  From the results of Table 5, the secondary batteries of Examples 5-1 to 5-4 showed cycle characteristics and tensile strength characteristics superior to those of Comparative Example 5-1, in which only PVdF was used as the negative electrode binder. It was found that the stability of the mixture could be ensured. Moreover, in Comparative Examples 5-2 to 5-4 in which the blending ratio of PVdF and PVP was outside the scope of the present invention, the stability of the negative electrode mixture was poor, and the cycle characteristics and tensile strength characteristics could not be evaluated.

(Examples 6-1 to 6-4, Comparative Examples 6-1 to 6-4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1 except that the binder content of the negative electrode was 8 mass%. The evaluation results are shown in Table 6.

  From the results of Table 6, the secondary batteries of Examples 6-1 to 6-4 showed cycle characteristics and tensile strength characteristics superior to those of Comparative Example 6-1 in which only PVdF was used as the binder for the negative electrode. It was found that the stability of the mixture could be ensured. Moreover, in Comparative Examples 6-2 to 6-4 in which the blending ratio of PVdF and PVP is outside the scope of the present invention, the stability of the negative electrode mixture was poor, and the cycle characteristics and the tensile strength characteristics could not be evaluated.

  Moreover, from the results of Tables 1 to 6, when the binder content, that is, the content of polyvinylidene fluoride and vinylpyrrolidone was 1% by mass and 8% by mass, the cycle characteristics were deteriorated. From this, it was found that the total content of the polyvinylidene fluoride and vinylpyrrolidone negative electrode mixture is preferably 2 to 6.5% by mass.

(Examples 7-1 to 7-2, Comparative examples 7-1 to 7-2)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 4-3 except that the specific surface area of the artificial graphite as the negative electrode active material was changed as shown in Table 7. The evaluation results are shown in Table 7.

From the results of Table 7, it was found that when the specific surface area of graphite is 0.3 to ² m ² / g, the stability of the negative electrode mixture can be secured, and the cycle characteristics and the tensile strength characteristics can be maintained well.

(Comparative Examples 8-1 to 8-7)
As shown in Table 8, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 4-3 except that polyvinylidene fluoride and vinylpyrrolidone were added as the binder for the positive electrode. The evaluation results are shown in Table 8.

  From the results of Table 8, even when PVP was added to the positive electrode in the battery of Comparative Example 8-1 not including PVP as in Comparative Examples 8-2 to 8-7, no improvement in cycle characteristics was observed, rather Slightly decreased. This is presumably because, unlike the negative electrode active material, the positive electrode active material has a high affinity with the gel-like nonaqueous electrolyte, so that the affinity effect does not change even when PVP is added.

It is one Embodiment of the nonaqueous electrolyte secondary battery of this invention, Comprising: It is a disassembled perspective view which shows an example of a laminate type battery. It is typical sectional drawing along the II-II line of the battery element shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Negative electrode terminal, 12 ... Positive electrode terminal, 20 ... Battery element, 21 ... Negative electrode, 21A ... Negative electrode collector, 21B ... Negative electrode mixture layer, 22 ... Positive electrode, 22A ... Positive electrode collector, 22B ... Positive electrode mixture layer , 23 ... Gel-like non-aqueous electrolyte layer, 24 ... Separator, 25 ... Protective tape, 30 ... Exterior member, 31 ... Adhesive film

Claims (5)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a gel-like non-aqueous electrolyte,
The negative electrode contains a negative electrode mixture containing a binder,
The non-aqueous electrolyte, wherein the binder contains polyvinylidene fluoride and polyvinyl pyrrolidone, and the mass ratio of polyvinylidene fluoride and polyvinyl pyrrolidone is 99.9: 0.1 to 70:30. Secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte includes a polymer including at least vinylidene fluoride as a monomer.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a total content of the polyvinylidene fluoride and polyvinylpyrrolidone with respect to the negative electrode mixture is 2 to 6.5 mass%. ^2. The nonaqueous electrolyte secondary battery according to claim 1, comprising graphite having a specific surface area of 0.3 to ² m ² / g as an active material of the negative electrode.   A negative electrode mixture containing a binder, wherein the binder contains polyvinylidene fluoride and polyvinylpyrrolidone, and the mass ratio of polyvinylidene fluoride and polyvinylpyrrolidone is 99.9: 0.1 to 70 : A negative electrode characterized by being 30.

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