JP2008047400A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery causing no internal-short circuit even if shock such as a drop test is applied. <P>SOLUTION: In the nonaqueous electrolyte secondary battery housing a battery element formed by winding or stacking a positive electrode and a negative electrode through a separator in an outer packaging member made of a laminate material, a polymer support made of thermoplastic resin having a melting point or a gel melting point lower than that of the separator, such as polyvinylidene fluoride is arranged on the surface of the separator, the interface between the electrode and the separator is heat sealed through the polymer support, at least one side of the separator is projected 0.3 mm or more from the electrode end, and the ends of the projected separators are heat sealed with the thermoplastic resin of the polymer support. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery that can prevent an internal short circuit due to a drop test.

2. Description of the Related Art In recent years, portable electronic devices such as notebook personal computers, camera-integrated VTRs (Videotape Recorders) or mobile phones have appeared one after another, and their size and weight have been reduced. Along with this, secondary batteries have been spotlighted as portable power sources that are portable, and active research is being conducted to obtain higher energy density.
Under such circumstances, lithium ion secondary batteries using non-aqueous electrolytes are proposed as secondary batteries having higher energy density than aqueous electrolyte secondary batteries such as lead secondary batteries or nickel cadmium secondary batteries. And practical use has begun.

In a lithium ion secondary battery, conventionally, a liquid electrolyte (electrolytic solution) in which a lithium salt is dissolved in a non-aqueous solvent has been used as a substance that controls ion conduction. Therefore, in order to prevent liquid leakage, it is necessary to use a metal container as an exterior member and strictly ensure the airtightness inside the battery.
However, when a metal container is used for the exterior member, a thin and large area sheet type battery, a thin and small area card type battery, and a battery with a flexible and more flexible shape are produced. It was extremely difficult to do.

On the other hand, in polymer batteries that use laminate outer packaging materials, the mechanical strength of the outer packaging materials is lower than when metal can outer packaging materials are used. There was a problem that it was easy to do.
As a countermeasure against such a problem, for example, it has been proposed to improve by forming a separator in a bag shape by thermally welding all or part of the separator protruding from the positive and negative electrodes (Patent Document 1). To 3).

In addition to this, it has been proposed to prevent a short circuit between both electrodes due to impact by applying a resin to the protruding portion of the separator to increase the strength of the separator (see Patent Document 4).
JP 2006-66311 A Japanese Patent Laid-Open No. 06-36801 JP 09-213377 A JP 2000-149997 A

  However, the method described in the cited document 4 in which the strength is increased by applying a resin to the protruding portion of the separator is not necessarily effective, and in the method using the thermal welding described in Patent Documents 1 to 3, the separator is In addition to reducing productivity due to the need for a heat-welding process, the separator around the electrode has a bag shape, so it takes time to impregnate after injecting the electrolyte. There was a problem.

  The present invention has been made to solve the above-mentioned problems in the prior art, and the object of the present invention is to provide a non-aqueous electrolyte that does not cause an internal short circuit even when an impact such as a drop test is applied. The next battery is to provide.

  As a result of intensive studies to achieve the above object, the present inventors formed a polymer support made of a thermoplastic resin having a melting point or gel melting point lower than that of the separator on the surface of the separator, and The inventors have found that the above object can be achieved by thermally fusing the protruding portions from the extreme portion with the thermoplastic resin of the polymer support, and have completed the present invention.

  That is, the nonaqueous electrolyte secondary battery of the present invention is a nonaqueous electrolyte secondary battery in which a battery element in which a positive electrode and a negative electrode are wound or laminated via a separator is housed in an exterior member made of a laminate material. A polymer support made of a thermoplastic resin having a melting point lower than the melting point of the separator or a gel melting point is disposed on one side or both sides of the separator, and the interface between the positive electrode and / or the negative electrode and the separator through the polymer support. And at least one side of the separator protrudes 0.3 mm or more from the negative electrode end and the positive electrode end, and the ends of the protruded separator are heated by the thermoplastic resin constituting the polymer support. It is characterized by being fused.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery of the present invention, the thermoplastic resin constituting the polymer support is a polymer containing a polyvinylidene fluoride structure in the skeleton.

  According to the present invention, since the protruding portions from both electrode end portions of the separator are heat-sealed by the thermoplastic resin, even if an impact such as a drop test is applied, non-water does not cause an internal short circuit. An electrolyte secondary battery can be provided.

  Next, the nonaqueous electrolyte secondary battery of the present invention will be described in detail. In the present specification, “%” represents mass percentage unless otherwise specified.

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

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 positive electrode terminal 11 and the negative electrode terminal 12 to prevent intrusion of outside air. The adhesion film 31 is made of a material having adhesion to the positive electrode terminal 11 and the negative electrode terminal 12. For example, when the positive electrode terminal 11 and the negative 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 or 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 (direct) Chain low density polyethylene), PET / PE / Al / PET / LDPE (low density polyethylene), and PET / Ny / Al / LDPE / CPP.

  FIG. 2 is a cross-sectional view taken along the line II of the battery element 20 shown in FIG. In the figure, a battery element 20 is wound with a positive electrode 21 and a negative electrode 22 facing each other with a polymer support layer (described later) 23 holding a non-aqueous electrolyte and a separator 24 interposed therebetween. The outermost peripheral part is protected by the protective tape 25.

Here, FIG. 3 is an exploded perspective view showing a laminated battery using a laminate material as another embodiment of the nonaqueous electrolyte secondary battery of the present invention. In addition, the same code | symbol is attached | subjected to the substantially same member as the winding type secondary battery mentioned above, and the description is abbreviate | omitted.
As shown in the figure, this stacked battery is substantially the same as the wound battery shown in FIG. 1 except that it includes a stacked battery element 20 ′ instead of the wound battery element 20 described above. It has a configuration.

In the laminated battery element 20 ′, a sheet-like positive electrode and a negative electrode are positioned to face each other with a polymer support layer holding a non-aqueous electrolyte as described above and a separator, for example, a negative electrode sheet, It has a laminated structure in which a polymer support layer, a separator, a polymer support layer, and a positive electrode sheet are laminated in this order.
In the embodiment shown in FIG. 3, the laminated battery element 20 ′ is obtained by alternately stacking sheet-like negative electrodes (negative electrode sheets) and sheet-like positive electrodes (positive electrode sheets) via separators. Furthermore, a polymer support layer is disposed between the positive electrode sheet and the separator and between the negative electrode sheet and the separator.
Since it has substantially the same configuration as the wound battery shown in FIG. 1 except for this point, the non-aqueous electrolyte secondary battery of the present invention will be described below by taking the wound battery again as an example. To continue.

As shown in FIG. 2, the positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is coated on both surfaces or one surface of a positive electrode current collector 21A having a pair of opposed surfaces. The positive electrode current collector 21 </ b> A has a portion exposed without being covered with the positive electrode active material layer 21 </ b> B at one end portion in the longitudinal direction, and the positive electrode terminal 11 is attached to the exposed portion.
The positive electrode current collector 21A is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

The positive electrode active material layer 21B includes one or more positive electrode materials capable of occluding and releasing lithium ions as a positive electrode active material, and a conductive material and a binder as necessary. May be included.
Examples of the positive electrode material capable of inserting and extracting lithium include sulfur (S), iron disulfide (FeS ₂ ), titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium diselenide. lithium (NbSe _2), vanadium oxide _{(V 2 O} 5), chalcogenides containing no lithium, such as titanium dioxide (TiO ₂₎ and manganese dioxide (MnO ₂₎ (especially layered compound and the spinel-type compound), containing lithium Examples thereof include conductive compounds such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

  Among these, lithium-containing compounds are preferable because some compounds can obtain a high voltage and a high energy density. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, and a phosphate compound containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, cobalt is particularly preferred. (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), titanium (Ti) or any mixture thereof. The inclusion is preferred.

Such lithium-containing compounds are typically represented by the following general formula (1) or (2)
Li _x M ^I O ₂ (1)
Li _y M ^II PO ₄ (2)
(In the formula, M ^I and M ^II represent one or more transition metal elements, and the values of x and y vary depending on the charge / discharge state of the battery, but usually 0.05 ≦ x ≦ 1.10, 0.05 ≦ y ≦ 1.10), and the compound of the formula (1) generally has a layered structure, and the compound of the formula (2) generally has an olivine structure.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), lithium nickel cobalt composite oxide ( _Examples include Li _x Ni _1-z Co _z O ₂ (0 <z <1), lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure.
Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound having a olivine structure (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-v Mn _v PO ₄ (v < 1)).
In these composite oxides, for the purpose of stabilizing the structure, a transition metal is partially substituted with Al, Mg or other transition metal elements or included in the crystal grain boundary, and a part of oxygen is fluorine. The thing substituted by etc. can also be mentioned. Further, at least a part of the surface of the positive electrode active material may be coated with another positive electrode active material. Moreover, you may use a positive electrode active material in mixture of multiple types.

On the other hand, similarly to the positive electrode 21, the negative electrode 22 has a structure in which a negative electrode active material layer 22B is provided on both surfaces or one surface of a negative electrode current collector 22A having a pair of opposed surfaces, for example. The negative electrode current collector 22A has an exposed portion without being provided with the negative electrode active material layer 22B at one end in the longitudinal direction, and the negative electrode terminal 12 is attached to the exposed portion.
The anode current collector 22A is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

The negative electrode active material layer 22B includes one or more of a negative electrode material capable of occluding and releasing lithium ions and metallic lithium as a negative electrode active material, and a conductive material and a binder as necessary. An adhesive may be included.
Examples of the negative electrode material capable of inserting and extracting lithium include a carbon material, a metal oxide, and a polymer compound. Examples of carbon materials include non-graphitizable carbon materials, artificial graphite materials, and graphite-based materials. More specifically, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound firing Body, carbon fiber, activated carbon and carbon black.
Among these, coke includes pitch coke, needle coke and petroleum coke, and the organic polymer compound fired body is carbonized by firing a polymer material such as phenol resin or furan resin at an appropriate temperature. Say things. In addition, examples of the metal oxide include iron oxide, ruthenium oxide, and molybdenum oxide, and examples of the polymer compound include polyacetylene and polypyrrole.

Further, examples of the negative electrode material capable of inserting and extracting lithium include a material containing as a constituent element at least one of a metal element and a metalloid element capable of forming an alloy with lithium. The negative electrode material may be a single element, alloy or 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, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. Some of the structures include a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of these.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), Examples include gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr), and yttrium (Y).
Among them, a group 14 metal element or metalloid element in the long-period type periodic table is preferable, and silicon or tin is particularly preferable. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

As an alloy of tin, for example, as a second constituent element other than tin, silicon, magnesium (Mg), nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony And at least one selected from the group consisting of chromium (Cr).
As an alloy of silicon, for example, as a second constituent element other than silicon, tin, magnesium, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium can be used. The thing containing at least 1 sort (s) of them is mentioned.

  Examples of the tin compound or the silicon compound include those containing oxygen (O) or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

  The separator 24 is a porous film made of a polyolefin-based synthetic resin such as polypropylene (melting point: around 165 ° C.) or polyethylene (melting point: around 135 ° C.), or a porous material made of an inorganic material such as a ceramic nonwoven fabric. The membrane may be made of an insulating thin film having a high ion permeability and a predetermined mechanical strength, and a structure in which two or more kinds of porous membranes are laminated may be used. In particular, those containing a polyolefin-based porous membrane are suitable because they have excellent separability between the positive electrode 21 and the negative electrode 22 and can further reduce internal short-circuiting and open circuit voltage reduction.

In the nonaqueous electrolyte secondary battery of the present invention, the polymer support 23 is disposed between at least one of the positive electrode 22 and the negative electrode 21 and the separator 24. The polymer support layer 23 is made of a thermoplastic resin having a melting point or gel melting point lower than that of the separator 24, has ion conductivity, and can hold a nonaqueous electrolytic solution.
In the embodiment shown in FIG. 2 and FIG. 4 to be described later, the polymer support layer 23 is disposed on both surfaces of the separator 24, that is, between the separator 24 and the positive electrode 22, and between the separator 24 and the negative electrode 21. Although it is heat-sealed to the interface, it is not always necessary to dispose it on both sides of the separator 24. It is disposed only on the interface between the separator 24 and the positive electrode 22 or only on the interface between the separator 24 and the negative electrode 21 and is heat-sealed. Also good.

  By such heat fusion, in the non-aqueous electrolyte secondary battery of the present invention, it is possible to reduce excess non-aqueous electrolyte that does not substantially participate in the battery reaction, and the non-aqueous electrolyte is an electrode active material. It will be supplied efficiently to the surroundings, and even if the amount of non-aqueous electrolyte is smaller than the conventional one, excellent cycle characteristics will be demonstrated, and by reducing the amount of non-aqueous electrolyte to be used, leakage resistance Even better.

  4 shows a cross section parallel to the winding direction of the wound battery element 20 shown in FIG. 1, that is, a sectional view taken along the line II-II (the laminated battery element 20 ′ shown in FIG. 3). In the non-aqueous electrolyte secondary battery of the present invention, the end of the separator 24 has a predetermined length from the ends of the positive electrode 21 and the negative electrode 22 in the non-aqueous electrolyte secondary battery of the present invention. It arrange | positions so that only E may protrude.

In this manner, by projecting the end of the separator 24 from the ends of the positive electrode 21 and the negative electrode 22, the separator 24 protrudes when the separator 24 and the electrodes 21 and 22 are heat-sealed in the battery manufacturing process. Since the end portions are simultaneously heat-sealed by the thermoplastic resin of the polymer support layer 23, there is no internal short circuit even by a drop test without newly establishing a process or increasing the number of steps. A water electrolyte secondary battery can be obtained.
The protruding length E of the separator 24 is required to be 0.3 mm or more from the viewpoint of causing the above-described heat fusion, but this heat fusion is further ensured. If the protruding length is too large, the volume loss of the portion becomes large, so it is desirable to control it within the range of 0.5 to 1.0 mm.

  The thermoplastic resin constituting the polymer support layer 23 is not particularly limited as long as it retains the non-aqueous electrolyte and exhibits ionic conductivity and has a lower melting point or gel melting point than the separator 24. Although not limited thereto, the copolymerization amount of acrylonitrile is 50% or more, in particular 80% or more, and consists of a homopolymer or copolymer of acrylonitrile-based polymer, aromatic polyamide, acrylonitrile / butadiene copolymer, acrylate or methacrylate. Examples thereof include acrylic polymers, acrylamide polymers, fluorine-containing polymers such as vinylidene fluoride, polysulfone, and polyallylsulfone. In particular, a polymer having an acrylonitrile copolymerization amount of 50% or more has a CN group in its side chain, so that a polymer gel electrolyte having a high dielectric constant and high ion conductivity can be produced.

In order to improve the support of non-aqueous electrolytes for these polymers and the ionic conductivity of polymer gel electrolytes composed of these polymers, acrylonitrile and vinyl carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, Methacrylsulfonic acid, hydroxyalkylene glycol (meth) acrylate, alkoxyalkylene glycol (meth) acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, various (meth) acrylates, etc. are preferably used at a ratio of 50% or less, particularly 20% or less. A polymerized product can also be used.
In addition, since the aromatic polyamide is a high heat-resistant polymer, it is a preferable high-molecular polymer when a polymer gel electrolyte that requires high heat resistance such as an automobile battery is required. Further, a polymer having a crosslinked structure obtained by copolymerizing butadiene or the like can also be used.

  In particular, a polymer containing vinylidene fluoride as a constituent component, that is, a homopolymer, a copolymer and a multi-component copolymer can be preferably used. Specifically, polyvinylidene fluoride (PVdF, melting point: 60 to 100) ° C), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP, melting point: 60-100 ° C), and polyvinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer (PVdF-HFP-CTFE), etc. Can be mentioned.

Any non-aqueous electrolyte may be used as long as it contains an electrolyte salt and a non-aqueous solvent.
Here, as the electrolyte salt, any electrolyte salt may be used as long as it dissolves or disperses in a nonaqueous solvent described later, and lithium hexafluorophosphate (LiPF ₆ ) can be suitably used. Needless to say, it is not limited.

That is, lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF _6), lithium perchlorate (LiClO _4), four lithium aluminum chloride acid ( Inorganic lithium salts such as LiAlCl ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), lithium bis (pentafluoromethanesulfone) methide (LiN (C ₂ F ₅ SO ₂ ) ₂ ) and lithium salts of perfluoroalkanesulfonic acid derivatives such as lithium tris (trifluoromethanesulfone) methide (LiC (CF ₃ SO ₂ ) ₃ ) can also be used. These can be used alone or in combination of two or more. It is also possible to use them together.

  In addition, the content of such an electrolyte salt is preferably in the range of 0.1 mol to 3.0 mol, and more preferably in the range of 0.5 mol to 2.0 mol, with respect to 1 liter (l) of the solvent. This is because higher ion conductivity can be obtained within this range.

Examples of the non-aqueous solvent include various high dielectric constant solvents and low viscosity solvents.
As the high dielectric constant solvent, ethylene carbonate, propylene carbonate, and the like can be suitably used, but are not limited thereto, butylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolan-2-one Cyclic carbonates such as (fluoroethylene carbonate), 4-chloro-1,3-dioxolan-2-one (chloroethylene carbonate), and trifluoromethylethylene carbonate can be used.

  Further, as a high dielectric constant solvent, instead of or in combination with a cyclic carbonate, a lactone such as γ-butyrolactone and γ-valerolactone, a lactam such as N-methylpyrrolidone, and a cyclic carbamate such as N-methyloxazolidinone A sulfone compound such as tetramethylene sulfone can also be used.

  On the other hand, diethyl carbonate can be preferably used as the low-viscosity solvent, but besides this, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate Chain carboxylic acid esters such as ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate, chain amides such as N, N-dimethylacetamide, methyl N, N-diethylcarbamate and N, Chain carbamates such as ethyl N-diethylcarbamate and ethers such as 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran and 1,3-dioxolane can be used.

In addition, as a non-aqueous electrolyte used for the non-aqueous electrolyte secondary battery of the present invention, the above-mentioned high dielectric constant solvent and low-viscosity solvent may be used alone or in combination of two or more. However, those containing 20 to 50% cyclic carbonate and 50 to 80% low viscosity solvent (low viscosity non-aqueous solvent) are preferred, and those having a boiling point of 130 ° C. or less as the low viscosity solvent are particularly preferred Is desirable.
If the ratio between the cyclic carbonate and the low viscosity solvent deviates from the above range, the dielectric constant is low when the low viscosity solvent is too much, and conversely, the viscosity becomes low when the low viscosity solvent is too low, In either case, sufficient conductivity cannot be obtained, and good battery characteristics may not be obtained.

The filling amount of the non-aqueous electrolyte in the non-aqueous electrolyte secondary battery of the present invention is preferably in the range of 0.14 to 0.35 g per 1 cm ^{3 of} battery capacity.
That is, if the filling amount of the non-aqueous electrolyte is less than 0.14 g per unit capacity, the expected battery performance cannot be obtained, and if it exceeds 0.35 g, the leakage resistance tends to deteriorate.

Next, an example of a method for manufacturing the secondary battery described above will be described.
The laminate type secondary battery can be manufactured as follows.
First, the positive electrode 21 is produced. For example, when a particulate positive electrode active material is used, a positive electrode mixture is prepared by mixing a positive electrode active material and, if necessary, a conductive material and a binder, and a dispersion medium such as N-methyl-2-pyrrolidone. To produce a positive electrode mixture slurry.
Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded to form the positive electrode active material layer 21B.

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

Then, a polymer support layer 23 made of a thermoplastic resin is formed on the separator 24. As a method for forming a high-molecular support layer 23 on the separator 24, a technique for removing the solvent by applying a solution containing the thermoplastic resin constituting the polymeric support on the surface of the separator 24, and a separately formed A technique for closely fixing the polymer support layer to the surface of the separator 24 is exemplified.

As a method of applying the solution containing the thermoplastic resin to the surface of the separator 24, a method of immersing the separator in the resin-containing solution, a method of supplying and applying by a T-die extrusion method, a spray method, a roll coater, a knife coater, etc. The method of apply | coating a solution to the base-material surface by these, etc. are mentioned.
Desolvation treatment methods for removing the solvent include a method for drying and removing, a method for extracting and removing the solvent by dipping in a poor solvent for a thermoplastic resin, a method for drying and removing the poor solvent, or a combination of these methods, etc. Can be used.

  Next, the positive electrode terminal 11 is attached to the positive electrode 21 and the negative electrode terminal 12 is attached to the negative electrode 22, and then the separator 24 with the polymer support layer 23, the positive electrode 21, the same separator 24, and the negative electrode 22 are sequentially laminated and wound. Rotate and adhere the protective tape 25 to the outermost periphery to form a wound electrode body. Further, the wound electrode body is sandwiched between the exterior members 30 (30A and 30B), and the outer peripheral edge except one side is heat-sealed to form a bag shape.

Thereafter, an electrolyte salt such as lithium hexafluorophosphate and a non-aqueous electrolyte solution containing a non-aqueous solvent such as ethylene carbonate are prepared, and injected into the wound electrode body from the opening of the exterior member 30, The opening of the exterior member 30 is heat-sealed and sealed. Thereby, the non-aqueous electrolyte is held on the polymer support layer 23, and the secondary battery shown in FIGS. 1 and 2 is completed.
In this way, after the polymer support layer is formed and stored, the electrolyte is swollen to form an electrolyte. In this method, the precursor and solvent that are the raw materials for forming the polymer support are removed in advance, and the electrolyte is almost completely removed from the electrolyte. It is possible not to leave it, and the polymer support forming step can be well controlled. Therefore, the separator, the positive electrode, the negative electrode, and the polymer support can be adhered to each other.

  In the secondary battery described above, when charged, lithium ions are released from the positive electrode active material layer 21 </ b> B and occluded in the negative electrode active material layer 22 </ b> B through the non-aqueous electrolyte held in the polymer support layer 23. Is done. When discharging is performed, lithium ions are released from the negative electrode active material layer 22B, and are inserted in the positive electrode active material layer 21B through the polymer support layer 23 and the nonaqueous electrolytic solution.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples with reference to the drawings, but the present invention is not limited to these examples.

First, cobalt carbonate (CoCO ₃ ) is mixed at a ratio of 1 mol with respect to 0.5 mol of lithium carbonate (Li ₂ CO ₃ ), and baked at 900 ° C. for 5 hours in the air, whereby a lithium cobalt composite as a positive electrode active material. An oxide (LiCoO ₂ ) was obtained.
Next, 85 parts by mass of the obtained lithium cobalt composite oxide, 5 parts by mass of graphite as a conductive agent, and 10 parts by mass of polyvinylidene fluoride as a binder were prepared to prepare a positive electrode mixture. Was dispersed in N-methyl-2-pyrrolidone as a dispersion medium to obtain a positive electrode mixture slurry. Subsequently, this positive electrode mixture slurry is uniformly applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm, dried, and then compression molded by a roll press to form a positive electrode active material layer 21B. A positive electrode 21 was produced. After that, the positive electrode terminal 11 was attached to the positive electrode 21.

On the other hand, a pulverized graphite powder is prepared as a negative electrode active material, and 90 parts by mass of the graphite powder and 10 parts by mass of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture, which is further dispersed in a dispersion medium. Was dispersed in N-methyl-2-pyrrolidone as a negative electrode mixture slurry.
Next, the negative electrode mixture slurry was uniformly applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm, dried, and then compression-molded with a roll press to form a negative electrode active material layer 22B. A negative electrode 22 was produced. Subsequently, the negative electrode terminal 12 was attached to the negative electrode 22.

Further, as the thermoplastic resin constituting the polymer support layer 23, the following various types of polyvinylidene fluoride (PVdF) polymers were used. Both surfaces of the separator 24 made of a microporous polyethylene film (melting point: 135 ° C.) having a thickness of 20 μm were dissolved in the N-methyl-2-pyrrolidone solution so as to be 15 parts by mass. ) Using a coating apparatus.
The polyethylene film coated with the polymer solution was immersed in deionized water, and then dried to prepare a polymer support layer 23 having a thickness of 5 μm on a separator 24 made of polyethylene film.

By making the positive electrode 21 and the negative electrode 22 produced as described above closely contact each other through the separator 24 on which the polymer support layer 23 is formed, the positive electrode 21 and the negative electrode 22 are wound in the longitudinal direction, and a protective tape 25 is applied to the outermost periphery. A wound battery element 20 was produced.
Further, the produced battery element 20 was sandwiched between the exterior members 30A and 30B, and the three sides were heat-sealed. As the exterior member 30 (30A, 30B), a moisture-proof aluminum laminate film in which a 25 μm thick nylon film, a 40 μm thick aluminum foil, and a 30 μm thick polypropylene film are laminated in order from the outermost layer was used.

Then, a non-aqueous electrolyte is injected into the exterior member 30 that houses the battery element 20, and the remaining one side of the exterior member 30 is heat-sealed and sealed under reduced pressure, as shown in FIGS. Such a non-aqueous electrolyte secondary battery was obtained.
As the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) are used, and these are mixed in a mass ratio of EC: DEC = 3: 7 in a ratio of 1 mol / L hexafluorophosphoric acid. What dissolved lithium was used.

(Example 1)
A polymer support layer comprising a negative electrode 22 having a width of 46.0 mm and a positive electrode 21 having a width of 45.0 mm, and comprising a polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP, gel melting point: 65 ° C.) on both surfaces. These are wound through a separator 24 having a width of 47.0 mm with 23 and wrapped with an aluminum laminate film, and a nonaqueous electrolyte secondary having a thickness of 3.8 mm, a width of 34.0 mm, and a height of 50.0 mm. I assembled the battery.
Then, the separator 24 was heat-sealed to the positive electrode 21 and the negative electrode 22 through the polymer support layer 23 by heating at 70 ° C. for 3 minutes with the steel sheet sandwiched therebetween. As a result, the ends of the separator 24 protruding 0.5 mm (= E) from the negative electrode 22 are also heat-sealed simultaneously.

(Example 2)
As a thermoplastic resin, instead of PVdF-HFP copolymer, polyvinylidene fluoride (PVdF, gel melting point: 90 ° C.) was used, and the same operation as in Example 1 was performed except that the heat fusion temperature was set to 100 ° C. The nonaqueous electrolyte secondary battery of this example was obtained.

(Example 3)
The non-aqueous electrolyte of this example was repeated by repeating the same operation as in Example 1 except that a polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVdF-CTFE, gel melting point: 63 ° C.) was used as the thermoplastic resin. A secondary battery was obtained.

Example 4
The non-aqueous electrolyte secondary of this example was repeated by repeating the same operation as in Example 1 except that the polymer support layer 23 made of a PVdF-HFP copolymer was disposed only on the surface in contact with the negative electrode 22 in the separator 24. A battery was obtained.

(Comparative Example 1)
The same operation as in Example 1 was repeated except that the separator 24 made of a microporous polyethylene film was used as it was without forming the polymer support layer 23 made of a PVdF-HFP copolymer. A nonaqueous electrolyte secondary battery was obtained.

(Comparative Example 2)
The same operation as in Example 1 was repeated except that heat fusion by heating in a state sandwiched between steel plates was omitted, and a nonaqueous electrolyte secondary battery of this example was obtained.

(Drop test)
For each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 obtained as described above, each surface was dropped twice from the height of 1.9 m to the concrete floor surface, resulting in a total of 12 times. The number of internal short circuit occurrences was investigated. The results are shown in Table 1. The evaluation number was 20 in each example.

As a result of disassembling the battery, the whole protruding portion of the separator 24 was thermally fused with the thermoplastic resin in any of the cells of Examples 1 to 4, and the positive electrode 21 and the negative electrode 22 were wrapped in the bag of the separator 24 It was confirmed that
As is clear from the results in Table 1, when the protruding portion of the separator 24 is heat-sealed, no internal short circuit occurred even when any thermoplastic resin was used.

On the other hand, when there is no polymer support layer 23 made of a thermoplastic resin as in Comparative Example 1, an internal short circuit occurs, and there is a polymer support layer 23 as in Comparative Example 2. Even if the heat fusion is not performed, the occurrence rate is lowered, but the internal short circuit cannot be prevented.
Thus, it was confirmed that the internal short circuit at the time of a drop test was prevented by heat-seal | fusing the protrusion part of the separator 24. FIG.

Example 4
The same operation as in Example 1 was repeated except that the width of the separator 24 was set to 46.6 mm (projection length E = 0.3 mm) and the battery height was set to 49.6 mm. The next battery was obtained.

(Example 5)
The same operation as in Example 1 was repeated except that the width of the separator 24 was set to 48.0 mm (projection length E = 1.0 mm) and the battery height was set to 51.0 mm. The next battery was obtained.

(Example 6)
The same operation as in Example 1 was repeated except that the width of the separator 24 was set to 50.0 mm (projection length E = 2.0 mm) and the battery height was set to 53.0 mm. The next battery was obtained.

(Comparative Example 3)
The non-aqueous electrolyte secondary battery of this example was repeated except that the width of the separator 24 was 46.0 mm (projection length E = 0 mm) and the battery height was 49.0 mm, and the same operation as in Example 1 was repeated. Got.

(Comparative Example 4)
The same operation as in Example 1 was repeated except that the width of the separator 24 was set to 46.4 mm (projection length E = 0.2 mm) and the battery height was set to 49.4 mm. The next battery was obtained.

(Drop test)
About each secondary battery of Examples 4-6 and Comparative Examples 3-4 obtained by the above, the same drop test was done. These results are shown in Table 2 together with the results of Example 1 above.

As a result of disassembling the battery, it was confirmed that when the length E of the protruding portion was 0.3 mm or more, the entire protruding portion was heat-sealed. It was not heat-sealed.
From the results shown in Table 2, no battery was internally short-circuited when the protrusion was 0.3 mm or more, but an internal short circuit occurred when the protrusion was 0.2 mm or less, and the protrusion length E was required to be 0.3 mm or more. I understood that.

  As described above, in the battery in which the positive and negative electrodes 21 and 22 and the separator 24 are heat-fused by the polymer support layer 23 made of the thermoplastic resin and the laminate member is used for the exterior member, the separator 24 is made of the positive and negative electrodes 21, The protrusions of the separator 24 protrude by 0.3 mm or more from the end of the member 22, and the protrusions of the separator 24 are simply heat-sealed by the thermoplastic resin of the polymer support layer 23 having a melting point or gel melting point lower than that of the separator 24. In spite of a simple battery manufacturing process, it is possible to manufacture a non-aqueous electrolyte secondary battery that does not internally short during a drop test.

As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.
For example, in the above-described embodiment, the case of including the battery element 20 in which the positive electrode 21 and the negative electrode 22 are stacked and wound has been described, but a flat battery element in which a pair of positive and negative electrodes are stacked, or a plurality of battery elements The present invention can also be applied to a case where a stacked battery element in which a positive electrode and a negative electrode are stacked is provided. Moreover, it is applicable not only to a secondary battery but also to a primary battery.

  Furthermore, as described above, the present invention relates to a battery using lithium as an electrode reactant, but the technical idea of the present invention is that other alkali metals such as sodium (Na) or potassium (K), magnesium ( The present invention can also be applied to the case of using an alkaline earth metal such as Mg) or calcium (Ca), or another light metal such as aluminum.

FIG. 2 is an exploded perspective view showing an example of a laminated battery, which is an embodiment of the nonaqueous secondary battery of the present invention. It is sectional drawing along the II line of the battery element shown in FIG. It is other embodiment of the nonaqueous electrolyte secondary battery of this invention, Comprising: It is a disassembled perspective view which shows the other example of a laminate type battery. FIG. 3 is a cross-sectional view taken along the line II-II of the battery element shown in FIG. 1 or along the line III-III or IV-IV of the battery element shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Positive electrode terminal, 12 ... Negative electrode terminal, 20 ... Winding battery element, 20 '... Laminated battery element, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector Electrical body, 22B ... negative electrode active material layer, 23 ... polymer support layer (thermoplastic resin), 24 ... separator, 25 ... protective tape, 30 ... exterior member, 31 ... adhesive film.

Claims (2)

In a non-aqueous electrolyte secondary battery in which a battery element in which a positive electrode and a negative electrode are wound or laminated via a separator is housed in an exterior member made of a laminate material,
A polymer support made of a thermoplastic resin having a melting point lower than the melting point of the separator or a gel melting point is disposed on one side or both sides of the separator, and the positive electrode and / or the negative electrode and the separator are interposed via the polymer support. The interface is thermally fused, and at least one side of the separator protrudes 0.3 mm or more from the negative electrode end and the positive electrode end, and the end portions of the protruded separator are formed by the thermoplastic resin constituting the polymer support. A non-aqueous electrolyte secondary battery characterized by being thermally fused.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thermoplastic resin constituting the polymer support is a polymer containing a polyvinylidene fluoride structure in the skeleton.

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