JP2008071732A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery superior in liquid leakage resistance and cycle characteristics. <P>SOLUTION: This is the nonaqueous electrolyte secondary battery equipped with a positive electrode, a negative electrode, a nonaqueous electrolytic solution, a separator arranged between the both electrodes, and an outer sheath member made of a laminated film to house these. A polymer support is interposed between the positive electrode and/or the negative electrode, and the separator. There exists the nonaqueous electrolytic solution of 0.14 to 0.35 g per a battery capacity 1 cm<SP>3</SP>in this battery, a nonaqueous solvent constituting the nonaqueous electrolytic solution contains cyclic carbonate of weight ratio of 20 to 50% and low viscosity nonaqueous solvent of 50 to 80%, and as the low viscosity nonaqueous solvent, a chain-like carbonate having a boiling point of 130°C or more is desirably used. <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 having liquid leakage resistance and excellent cycle characteristics.

In recent years, many portable electronic devices such as camera-integrated VTRs (videotape recorders), mobile phones, and portable computers have appeared, and their size and weight have been reduced. Accordingly, the development of batteries, particularly secondary batteries, has been actively promoted as portable power sources for electronic devices. Among these, lithium ion secondary batteries are attracting attention as being capable of realizing a high energy density.
In recent years, the use of laminate films, etc., in place of aluminum and iron metal battery cans, which are battery exterior materials, has further promoted further reduction in size, weight and thickness of batteries. .

On the other hand, in order to increase the energy density, it is necessary to fill a larger amount of an active material that acts on the charge / discharge reaction, and accordingly, a sufficient amount of electrolyte solution for moving lithium ions between the positive and negative electrodes is also present. I need it. If the amount of the electrolytic solution is not sufficient, and the electrolytic solution does not completely fill the periphery of the active material, the portion not in contact with the electrolytic solution does not react and a sufficient battery capacity cannot be obtained.
Furthermore, since the electrolyte between the positive and negative electrodes is consumed as charging and discharging repeats, the battery discharge capacity gradually decreases before the positive and negative electrode active materials deteriorate, and cycle characteristics due to insufficient electrolyte There are also problems such as lowering of the internal temperature and occurrence of internal short circuits.

In order to solve such a problem, in a battery using a metal battery can, it has been proposed that the cycle characteristics can be improved by controlling the volume of the non-aqueous electrolyte with respect to the discharge capacity (for example, patents). Reference 1).
Japanese Patent Laid-Open No. 2-148576

However, in the non-aqueous electrolyte secondary battery using the laminate film as described above, it is difficult to say that the above problem has been sufficiently solved.
That is, when the laminate film is damaged, it is more easily broken than a strong metal can, and liquid leakage from the ruptured portion is likely to occur. Therefore, when the amount of the electrolytic solution is increased in order to improve the cycle characteristics, there is a problem that the liquid easily leaks.

  The present invention has been made to solve the above-described problems in the prior art, and an object of the present invention is to provide a nonaqueous electrolyte secondary battery excellent in leakage resistance and cycle characteristics.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by applying a non-aqueous solvent having a predetermined component configuration to the non-aqueous electrolyte. The invention has been completed.

That is, the non-aqueous electrolyte secondary battery of the present invention includes a non-aqueous electrolyte including a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator disposed between the two electrodes, and an exterior member made of a laminate film that accommodates these. In the electrolyte secondary battery, a polymer support is interposed between at least one of the positive electrode and the negative electrode and the separator, and the polymer support is in close contact with at least one of the positive electrode and the negative electrode and the separator. The nonaqueous solvent constituting the aqueous electrolyte contains 20 to 50% cyclic carbonate and 50 to 80% low-viscosity nonaqueous solvent in a mass ratio, and the nonaqueous electrolyte secondary battery includes The non-aqueous electrolyte present is 0.14 to 0.35 g per 1 cm ³ of the volume of the non-aqueous electrolyte secondary battery.

  According to the present invention, a non-aqueous electrolyte secondary battery excellent in leakage resistance and cycle characteristics is provided because a predetermined polymer support is disposed and a non-aqueous solvent having a predetermined component configuration is used for the electrolyte. 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.
In the upper figure, this secondary battery 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-like 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 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 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 shows another embodiment of the non-aqueous electrolyte secondary battery of the present invention. That is, FIG. 3 is an exploded perspective view showing another embodiment of the non-aqueous electrolyte secondary battery according to the present invention and showing a laminated battery using a laminate material. 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 battery has the same configuration as the wound battery shown in FIG. 1 except that it includes a laminated battery element 20 ′ instead of the wound battery element 20 described above.

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 inserting and extracting 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.

Next, the polymer support layer 23 has ionic conductivity and can hold a non-aqueous electrolyte. In the embodiment shown in FIG. 2, the polymer support layer 23 adheres or adheres to the separator 24, but does not adhere to the separator and the electrode as in the separator 24 and the positive electrode 21 and the separator 24 and the negative electrode 22. It may be adhered, or may not be adhered or adhered to the separator, and may be adhered or adhered only to either one or both of the positive electrode 21 and the negative electrode 22.
Here, “adhesion” means that the polymer support layer 23 and the separator 24, the positive electrode 21, and the negative electrode 22 are in contact with each other to the extent that they do not move relative to each other unless a predetermined force is applied. .

  The polymer support layer 23 and the separator 24, or the polymer support layer 23 and the positive electrode or the negative electrode are in close contact or bonded to each other, so that the polymer support layer 23 holds the non-aqueous electrolyte and has a gel-like shape. In a state where the nonaqueous electrolyte layer is formed, the positive electrode 21 or the negative electrode 22 and the separator 24 are bonded via the nonaqueous electrolyte layer. The degree of adhesion is preferably such that, for example, the peel strength between the exposed portion of the positive electrode 21 and the negative electrode 22 where the active material layer is not provided and the current collector is exposed and the separator is 5 mN / mm or more. . The peel strength is measured between 6 seconds and 25 seconds after the current collector is placed on a support stand, pulled in a 180 ° direction at a speed of 10 cm / min, and the current collector is peeled off from the separator. , The average force required to peel.

  By such close contact or adhesion, in the nonaqueous electrolyte secondary battery of the present invention, it is possible to reduce excess nonaqueous electrolyte solution that is not substantially involved in the battery reaction, and the nonaqueous electrolyte solution is efficiently disposed around the electrode active material. Well supplied. Therefore, the non-aqueous electrolyte secondary battery of the present invention exhibits excellent cycle characteristics even when the amount of the non-aqueous electrolyte is smaller than that of the conventional one. Excellent liquidity.

The polymer support constituting the polymer support layer is not particularly limited as long as it retains the non-aqueous electrolyte and exhibits ionic conductivity, but the copolymerization amount of acrylonitrile is 50% or more. 80% or more of acrylonitrile polymer, aromatic polyamide, acrylonitrile / butadiene copolymer, acrylic polymer comprising acrylate or methacrylate homopolymer or copolymer, acrylamide polymer, vinylidene fluoride, etc. Examples thereof include a polymer, 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 from these polymers, acrylonitrile and vinyl carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylic Copolymerization of sulfonic acid, hydroxyalkylene glycol (meth) acrylate, alkoxyalkylene glycol (meth) acrylate, vinyl chloride, vinylidene chloride, vinyl acetate, various (meth) acrylates, preferably at a ratio of 50% or less, particularly 20% or less. It is also possible to use.
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 are preferable. Specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer A combination (PVdF-HFP) and a polyvinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene copolymer (PVdF-HEP-CTFE) can be mentioned.

  The separator 24 has a high ion permeability and a predetermined mechanical strength, such as a porous film made of a polyolefin-based synthetic resin such as polypropylene or 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 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.

As the non-aqueous solvent constituting the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, those containing 20 to 50% cyclic carbonate and 50 to 80% low-viscosity non-aqueous solvent are used.
Here, the low-viscosity non-aqueous solvent is preferably a chain carbonate having a boiling point of 130 ° C. or less.

As the cyclic carbonate, ethylene carbonate, propylene carbonate, and the like can be suitably used. However, the cyclic carbonate is not limited thereto, butylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolan-2-one (fluoro Ethylene carbonate), 4-chloro-1,3-dioxolan-2-one (chloroethylene carbonate), trifluoromethylethylene carbonate, and the like. These may be used alone or in any combination of two or more thereof. Can be used.
As described above, these cyclic carbonates are mixed and used in a mass ratio of 20 to 50%, preferably 25 to 40%, as described above, but when the amount of cyclic carbonate is less than 20%, The proportion of the low-viscosity non-aqueous solvent described later increases relatively, and the degree of dissociation of lithium ions decreases, thereby decreasing the conductivity of the electrolytic solution. This is because the ratio of the water solvent is relatively decreased, the viscosity is increased, and the conductivity of the electrolytic solution is decreased.

On the other hand, as the low-viscosity non-aqueous solvent, diethyl carbonate and ethyl methyl carbonate can be preferably used, but besides this, chain carbonates such as dimethyl carbonate and methyl propyl carbonate, methyl acetate, ethyl acetate, propionic acid Chain carboxylic acid esters such as methyl, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate, chain amides such as N, N-dimethylacetamide, methyl N, N-diethylcarbamate, N , N-diethylcarbamate and other chain esters, and 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran, 1,3-dioxolane and other ethers. 2 types or more of It may be mixed in.
These low-viscosity non-aqueous solvents are mixed and used in a mass ratio of 50 to 80%, preferably 60 to 75% as described above.

As the low-viscosity non-aqueous solvent, it is desirable to use a chain carbonate having a boiling point of 130 ° C. or lower, which can improve the conductivity of the non-aqueous electrolyte. Examples of such chain carbonates include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.
In addition, when the boiling point of the chain carbonate as the low-viscosity non-aqueous solvent exceeds 130 ° C., there is a possibility that a disadvantage that the operating temperature range of the battery is narrowed may occur.
By using such a non-aqueous electrolyte, the polymer support can be satisfactorily swelled with a small amount of non-aqueous electrolyte, and further compatibility between high battery conductivity and prevention of battery swelling is achieved. Can be achieved.

Moreover, it is more preferable that the non-aqueous electrolyte contains a cyclic carbonate derivative having a halogen atom as the cyclic carbonate, since the cycle characteristics are improved.
Examples of such cyclic carbonate derivatives include 4-fluoro-1,3-dioxolan-2-one and 4-chloro-1,3-dioxolan-2-one as described above. Can be used alone or in combination. The total content is preferably about 0.5 to 2%, and if the content is low, the effect of improving the cycle characteristics cannot be sufficiently obtained. Conversely, if the content is too high, the swelling during high-temperature storage increases. There is a tendency to end up. (★ Please correct)

The electrolyte salt contained in the non-aqueous electrolyte is not particularly limited as long as it dissolves or disperses in the non-aqueous solvent to generate ions, and lithium hexafluorophosphate (LiPF ₆ ) can be preferably used. Needless to say, the present invention is not limited to this.
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) imide Lithium salts of perfluoroalkanesulfonic acid derivatives such as (LiN (C ₂ F ₅ SO ₂ ) ₂ ) and lithium tris (trifluoromethanesulfone) methide (LiC (CF ₃ SO ₂ ) ₃ ) can also be used. Singly or in combination of two or more It is also possible to use it.

  In addition, it is preferable that content of such electrolyte salt shall be 5-25%. If it is less than 5%, sufficient conductivity may not be obtained, and if it exceeds 25%, the viscosity may increase excessively.

As described above, the nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention contains an electrolyte salt in a nonaqueous solvent having a predetermined component structure. Is preferably in the range of 0.14 to 0.35 g, more preferably 0.22 to 0.32 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 desired battery performance cannot be obtained, and if it exceeds 0.35 g, the leakage resistance deteriorates.

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, the polymer support layer 23 is formed on the separator 24. As a method of forming the polymer support layer 23 on the separator 24, a method of applying a solution containing the polymer support to the surface of the separator 24 and removing the solvent, and a separately formed polymer support layer are used. A technique of closely fixing to the surface of the separator 24 is exemplified.
As a method of applying a solution containing a polymer support to the surface of the separator 24, a method of immersing the separator in a solution containing a polymer support, a method of supplying and applying by a T-die extrusion method, a spray method, a roll coater, a knife A technique of applying the solution to the surface of the substrate with a coater or the like can be mentioned.
Examples of the solvent removal treatment method for removing the solvent include a method for drying and removing, a method for extracting and removing the solvent by immersing it in a poor solvent for the polymer support, and a method for drying and removing the poor solvent, or a combination thereof. Can be used.
As a method of closely fixing the separately formed polymer support layer to the surface of the separator 24, it is possible to adhere using an adhesive, but in this case, the type of electrolyte used (acid, alkali, organic solvent, etc.) ), It is necessary to select an adhesive appropriately and to prevent clogging.
Moreover, as a method of closely attaching the polymer support layer formed on the separator, heat fusion at a temperature equal to or higher than the gel transition point can be mentioned. In particular, heat fusion while applying pressure such as hot roll compression is preferable.

  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.

(Example 1-1)
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. At that time, the ratio of the capacity of the positive electrode to the capacity of the negative electrode was set to 1.5. Subsequently, the negative electrode terminal 12 was attached to the negative electrode 22.

Polyvinylidene fluoride was used as the polymer compound used for the polymer support layer 23. The polymer solution dissolved in N-methyl-2-pyrrolidone solution so as to be 15 parts by mass was applied to both sides of a separator 24 made of a microporous polyethylene film having a thickness of 20 μm 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 nonaqueous electrolyte is injected into the exterior member 30 containing the battery element 20 so that the weight of the electrolyte in the cell is 1.85 g, and the remaining one side of the exterior member 30 is thermally melted under reduced pressure. Wear and seal.
As the electrolytic solution, ethylene carbonate (EC) and propylene carbonate (PC), which are cyclic carbonates, and diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), which are chain carbonates, are used. These are EC: PC: A solution in which lithium hexafluorophosphate was dissolved at a rate of 1.2 mol / L in a solvent mixed at a mass ratio of DEC: EMC = 20: 10: 40: 30 was used. The boiling points of diethyl carbonate and ethyl methyl carbonate are 127 ° C. and 108 ° C., respectively.

Thereafter, the obtained sealed body was sandwiched between steel plates and heated at 70 ° C. for 3 minutes, whereby the separator 24 was bonded to the positive electrode 21 and the negative electrode 22 via the polymer support layer 23.
As described above, a nonaqueous electrolyte secondary battery having a cell size of 4 × 35 × 50 mm (7 cm ³ ) as shown in FIGS. 1 and 2 was obtained.
(Example 1-2)
Except that the nonaqueous solvent ratio of the electrolytic solution was EC: DEC = 20: 80, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 1-3)
Except that the nonaqueous solvent ratio of the electrolytic solution was EC: DEC = 30: 70, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 1-4)
The non-aqueous electrolyte secondary battery of this example was repeated by repeating the same operation as in Example 1-1 except that the non-aqueous solvent ratio of the electrolytic solution was EC: PC: DEC: EMC = 30: 10: 40: 20. Got.

(Example 1-5)
Except that the nonaqueous solvent ratio of the electrolyte was EC: DEC = 40: 60, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 1-6)
The non-aqueous electrolyte secondary battery of this example was repeated by repeating the same operation as in Example 1-1 except that the non-aqueous solvent ratio of the electrolytic solution was EC: PC: DEC: EMC = 40: 10: 30: 20. Got.

(Example 1-7)
Except that the nonaqueous solvent ratio of the electrolytic solution was EC: DEC = 50: 50, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Comparative Example 1-1)
A nonaqueous electrolyte secondary battery of this example was obtained by repeating the same operation as in Example 1-1 except that the nonaqueous solvent ratio of the electrolytic solution was EC: DEC: EMC = 15: 60: 25.

(Comparative Example 1-2)
The non-aqueous electrolyte secondary battery of this example was repeated by repeating the same operation as in Example 1-1 except that the non-aqueous solvent ratio of the electrolytic solution was EC: PC: DEC: EMC = 5: 5: 60: 30. Got.

(Comparative Example 1-3)
The non-aqueous electrolyte secondary battery of this example was repeated by repeating the same operation as in Example 1-1 except that the non-aqueous solvent ratio of the electrolytic solution was EC: PC: DEC: EMC = 50: 5: 30: 15. Got.

(Comparative Example 1-4)
The same operation as in Example 1-1 was repeated except that the non-aqueous solvent ratio of the electrolytic solution was EC: PC: DEC = 30: 25: 45, to obtain a non-aqueous electrolyte secondary battery of this example.

(Discharge capacity evaluation)
For each of the secondary batteries of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-4 obtained as described above, a constant current and constant voltage charge of 200 mA was performed at 23 ° C. to an upper limit of 4.2 V for 7 hours. Then, a constant current discharge of 200 mA was performed to a final voltage of 2.5 V, and the initial discharge capacity was obtained.
After that, each secondary battery was charged / discharged at 23 ° C. with 500 mA constant current and constant voltage charge up to an upper limit of 4.2 V for 2 hours, followed by 500 mA constant current discharge to a final voltage of 2.5 V. The capacity maintenance rate at the 300th cycle was determined by setting the discharge capacity at the first cycle in a 500 mA discharge as 100%. Table 1 shows the initial discharge capacity and the capacity maintenance rate at the 300th cycle.

(Measurement of electrolyte weight)
Moreover, about the secondary battery obtained by the said Example and comparative example, the electrolyte solution weight in a cell was measured.
That is, for the secondary battery after obtaining the initial discharge capacity, after measuring the battery weight, the electrode body was taken out, the electrode body was decomposed into a positive electrode, a negative electrode, and a separator, and then the positive electrode, the negative electrode, the separator, and the exterior member were dimethyl carbonate. After being immersed in the solution for 2 days, it was filtered and vacuum-dried for 3 days, and the weight of the electrolyte was determined by subtracting the weight after vacuum drying from the initial weight. The results are shown in Table 1.

As shown in Table 1, the secondary batteries of Examples 1 to 7 had excellent cycle characteristics, whereas the secondary batteries of Comparative Examples 1-1 to 1-4 had poor cycle characteristics. This is because in the batteries of Comparative Examples 1-1 to 1-4, the solvent composition range was 20% to 50% cyclic carbonate, and 50% to 80% low-viscosity non-aqueous solvent. It seems that the adhesion between the electrode and the separator is not sufficient, and the cycle characteristics are deteriorated.
That is, the polymer support layer 23 holding the non-aqueous electrolyte is interposed between the positive electrode 21 and the separator 24 and between the negative electrode 22 and the separator 24, and the non-aqueous electrolyte has a solvent of 20% or more as 50% or more. It was found that the cycle characteristics were excellent when a cyclic carbonate of 50% or less and a low-viscosity non-aqueous solvent of 50% or more and 80% or less were contained.

(Example 2-1)
Example 1 except that the polymer support layer 23 of the separator 24 was formed only on one side, and the wound battery element 20 was produced so that the surface on which the polymer support layer 23 was formed faced the negative electrode 22. -1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 2-2)
Example 1 except that the polymer support layer 23 of the separator 24 was formed only on one side, and the wound battery element 20 was produced so that the surface on which the polymer support layer 23 was formed faced the positive electrode 21. -1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 2-3)
Except that the nonaqueous electrolyte was injected so that the weight of the electrolyte in the cell was 1.01 g, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 2-4)
Except that the nonaqueous electrolyte was injected so that the weight of the electrolyte in the cell was 2.45 g, the same operation as in Example 1-1 was repeated to obtain the nonaqueous electrolyte secondary battery of this example.

(Comparative Example 2-1)
Except that the non-aqueous electrolyte was injected so that the weight of the electrolyte in the cell was 0.93 g, the same operation as in Example 1-1 was repeated to obtain a non-aqueous electrolyte secondary battery of this example.

(Comparative Example 2-2)
Except that the nonaqueous electrolyte was injected so that the weight of the electrolyte in the cell was 2.57 g, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Comparative Example 2-3)
The same procedure as in Example 1-1 was repeated except that the nonaqueous electrolyte was injected so that the cell capacity was 9.0 cm ³ and the weight of the electrolyte in the cell was 1.17 g. A non-aqueous electrolyte secondary battery was obtained.

(Comparative Example 2-4)
This example was repeated except that the nonaqueous electrolyte was injected so that the cell capacity was 6.0 cm ³ and the weight of the electrolyte in the cell was 2.34 g. A non-aqueous electrolyte secondary battery was obtained.

(Discharge capacity evaluation and electrolyte weight measurement)
About each secondary battery of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-4 obtained as described above, the initial discharge capacity and the capacity at the 300th cycle are the same as in Example 1-1. While measuring the maintenance factor, the electrolyte weight was measured. These results are shown in Table 2 together with the results of Example 1-1.

(Leakage test)
A liquid leakage test was performed on each secondary battery obtained in the above Examples and Comparative Examples and the secondary battery in Example 1.
First, 10 cells of each of these secondary batteries were produced, a hole with a diameter of 0.5 mm was formed in the exterior member 30A, and pressed with a pressure of 5 MPa, thereby obtaining the number of batteries in which the electrolyte solution leaked. The results are also shown in Table 2.

As can be seen from Table 2, the secondary batteries of Examples 1-1, 2-1 to 2-4 have excellent cycle characteristics and no leakage was confirmed, whereas Comparative Example 2 The cycle characteristics of the secondary batteries of −1 and 2-3 were poor, and the number of leak cells was large in the batteries of Comparative Examples 2-2 and 2-4. This is because, in the batteries of Comparative Examples 2-1 and 2-3, the cycle characteristics deteriorated because the electrolyte solution was insufficient, and in the batteries of Comparative Examples 2-2 and 2-4, excess electrolyte solution was generated, resulting in leakage. It is considered that the number of cells was large.
That is, a polymer support 23 supporting a non-aqueous electrolyte is interposed between the positive electrode 21 and / or the negative electrode 22 and the separator 24, and the amount of the non-aqueous electrolyte present in the battery is 1 cm in battery volume. If it was 0.14g-0.35g per ^3, it turned out that cycling characteristics are excellent and it has liquid-proof property.

(Example 3-1)
As a polymer compound for forming the polymer support layer 23, a copolymer obtained by copolymerizing 91 parts by mass of vinylidene fluoride, 4 parts by mass of hexafluoropropylene, and 5 parts by mass of chlorotrifluoroethylene was used. Except for the above, the same operation as in Example 1-1 was repeated to obtain a nonaqueous electrolyte secondary battery of this example.

(Example 3-2)
The same operation as in Example 1-1 was repeated except that polymethylmethacrylic acid was used as the polymer compound for forming the polymer support layer 23, whereby a nonaqueous electrolyte secondary battery of this example was obtained.

(Example 3-3)
A non-aqueous electrolyte secondary battery of this example was obtained by repeating the same operation as in Example 1-1 except that polyvinyl formal was used as the polymer compound forming the polymer support layer 23.

(Example 3-4)
The same operation as in Example 1-1 was repeated except that styrene-butadiene rubber was used as the polymer compound for forming the polymer support layer 23, whereby a nonaqueous electrolyte secondary battery of this example was obtained.

(Discharge capacity evaluation)
For each of the secondary batteries of Examples 3-1 to 3-4 obtained as described above, the initial discharge capacity and the capacity retention ratio at the 300th cycle were measured in the same manner as in Example 1-1. These results are shown in Table 3 together with the results of Example 1-1 using polyvinylidene fluoride.

As shown in Table 3, the secondary batteries according to Examples 1-1 and 3-1 to 3-4 were excellent in cycle characteristics.
That is, it was found that cycle characteristics are excellent when a polymer containing polyvinylidene fluoride as a component, polymethacrylic acid, polyvinyl acetal, or styrene butadiene rubber is used as the polymer compound.

(Examples 4-1 to 4-7)
The non-aqueous solvent ratio of the electrolytic solution is EC: DEC = 30: 70, and 4-fluoro-1,3-dioxolan-2-one (FEC) and 4-chloro-1,3-dioxolane with respect to the electrolytic solution Except that 2-one (CEC) was added as shown in Table 4, the same operation as in Example 1-1 was repeated, and secondary batteries of these examples were respectively produced.
For the fabricated secondary batteries of Examples 4-1 to 4-7, the initial discharge capacity and the capacity retention rate were measured by the same method as in Example 1-1. These results are shown in Table 4 together with the results of Example 1-3.

As can be seen from Table 4, Examples 4-1 to 4- when the electrolyte contains at least one of 4-fluoro-1,3-dioxolan-2-one and 4-chloro-1,3-dioxolan-2-one Also in 4-7, it was confirmed that the cycle characteristics were excellent as in Example 1-3, and the capacity retention rate was superior to that in Example 1-1.
That is, it is more preferable to add one or both of 4-fluoro-1,3-dioxolan-2-one and 4-chloro-1,3-dioxolan-2-one to the electrolytic solution from the viewpoint of improving cycle characteristics. I understood.

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-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.

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, 24 ... separator, 25 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (9)

In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator disposed between the two electrodes, and an exterior member made of a laminate film that accommodates these, at least one of the positive electrode and the negative electrode The polymer support is interposed between the separator and the separator, the polymer support is in close contact with at least one of the positive electrode and the negative electrode and the separator, and the non-aqueous solvent constituting the non-aqueous electrolyte is a mass. The nonaqueous electrolyte solution containing 20 to 50% cyclic carbonate and 50 to 80% low-viscosity nonaqueous solvent in the nonaqueous electrolyte secondary battery is contained in the nonaqueous electrolyte solution. A non-aqueous electrolyte secondary battery, wherein the capacity is 0.14 to 0.35 g per 1 cm ³ of the volume of the secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the low-viscosity non-aqueous solvent is a chain carbonate having a boiling point of 130 ° C or lower.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer support contains a polymer containing polyvinylidene fluoride as a component.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the polymer support is polymethacrylic acid.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer support is polyvinyl acetal and / or a derivative thereof.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer support is styrene butadiene rubber.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the laminate film is made of aluminum and a resin.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte solution includes a cyclic carbonate derivative having a halogen atom.   The non-aqueous electrolyte contains at least one of 4-fluoro-1,3-dioxolan-2-one and 4-chloro-1,3-dioxolan-2-one as a cyclic carbonate derivative. Item 9. The nonaqueous electrolyte secondary battery according to Item 8.

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