JP2009054354A - Nonaqueous electrolytic solution composition, and nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic solution composition used as a non-aqueous electrolytic solution which can improve initial charge and discharge efficiency and exhibits excellent charge and discharge cycle characteristics and is reduced in expansion under high-temperature environment, and to provide a non-aqueous electrolytic solution battery. <P>SOLUTION: The non-aqueous electrolytic solution secondary battery is provided with a positive electrode and a negative electrode as well as a non-aqueous electrolytic solution, and contains at least one kind of 0.01-0.2 mol/kg selected from alkaline metal ions other than lithium ion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte composition and a non-aqueous electrolyte secondary battery that are used as a non-aqueous electrolyte that has a high initial charge / discharge rate and excellent cycle characteristics and has reduced expansion under a high-temperature environment.

  In recent years, many portable electronic devices such as a camera-integrated VTR, a digital still camera, a mobile phone, a personal digital assistant, and a notebook computer have appeared, and their size and weight have been reduced. As portable power sources for these electronic devices, research and development for improving the energy density of batteries, particularly secondary batteries, are being actively promoted. Among them, a lithium ion secondary battery that uses carbon as a negative electrode active material, a lithium-transition metal composite oxide as a positive electrode active material, and a carbonate ester mixture as an electrolyte is a lead battery that is a conventional non-aqueous electrolyte secondary battery, Since a large energy density can be obtained compared to a nickel cadmium battery, it is widely put into practical use. In particular, a laminated battery using an aluminum laminated film for the exterior has a high energy density because it is lightweight. In the laminate battery, since the deformation of the laminate battery can be suppressed by swelling the electrolyte in the polymer, the laminate polymer battery is also widely used.

  On the other hand, the laminate battery has a problem that it easily expands in a high temperature environment. This is presumably because the carbonic acid ester in the electrolyte solution decomposes by reacting with the electrode in a high-temperature environment to generate gas. Such a phenomenon becomes a problem particularly in a thin battery such as a laminated battery. Therefore, dimethyl carbonate or ethyl methyl carbonate or diethyl carbonate, which has a high viscosity but is difficult to swell, has been used as an electrolyte solvent. Also, in recent years, the battery active material has been thickly coated to increase the capacity of the battery, but the electrolyte containing ethyl methyl carbonate or diethyl carbonate having a large viscosity is difficult to impregnate the electrode, When charging / discharging was repeated, there was a problem that the electrolytic solution was decomposed and metallic lithium was deposited on the negative electrode, resulting in a decrease in discharge capacity.

In view of this, it has been proposed to add a fluoroethylene carbonate to the electrolytic solution to suppress a decrease in the discharge capacity retention rate during the charge / discharge cycle (Patent Document 1).
However, when fluoroethylene carbonate is used, there is a problem that the battery tends to expand under a high temperature environment.

Also, by adding metal ions to the non-aqueous electrolyte and precipitating as a metal on the surface of the negative electrode during charging, or carrying a metal such as Pb on the negative electrode surface, the reactivity of the negative electrode active part with the non-aqueous electrolyte can be increased. It is disclosed to reduce (Patent Document 2).
However, there is a problem that the resistance increases because the metal always covers the surface of the negative electrode.

JP 2005-38722 A JP-A-8-171936

  Therefore, the present invention has been made in view of such problems, and can be used as a non-aqueous electrolyte that can improve initial charge and discharge efficiency and can suppress expansion during high temperature storage while exhibiting good charge and discharge cycle characteristics. It aims at providing the nonaqueous electrolyte composition and nonaqueous electrolyte battery which are used.

The inventors have improved the initial charge / discharge efficiency by adding a second metal ion having a larger ion radius than the first metal ion contained in the non-aqueous electrolyte composition at the highest concentration. The present invention has been completed by finding that it has good charge / discharge cycle characteristics.
That is, the present invention provides the following non-aqueous electrolyte composition and non-aqueous electrolyte secondary battery.
[1] A first metal ion contained in the highest concentration and a second metal ion having an ion radius larger than the first metal ion, the second metal ion being 0.01 A non-aqueous electrolyte composition characterized by containing ~ 0.2 mol / kg.
[2] A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte together with a positive electrode and a negative electrode,
The non-aqueous electrolyte solution includes a metal ion that is an electrode reactant, and 0.01 to 0.2 mol / kg of at least one selected from metal ions having a larger ion radius than the metal ion that is the electrode reactant. A non-aqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery of the present invention comprises, as an electrolyte, a first metal ion contained in the highest concentration and a second metal ion having a larger ion radius than the first metal ion. By using the contained non-aqueous electrolyte composition, the second metal precipitates faster than the first metal during charging. As a result, the deposition of the first metal can be suppressed, and the decomposition of the organic solvent used in the electrolytic solution can be suppressed. Thereby, the initial charge / discharge efficiency can be improved, and the expansion during high temperature storage can be suppressed while exhibiting good charge / discharge cycle characteristics.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following mode.

  FIG. 1 schematically shows a configuration of a laminated battery according to an embodiment of the present invention. This secondary battery is a so-called laminate film type, and has a wound electrode body 20 to which a positive electrode lead 21 and a negative electrode lead 22 are attached accommodated in a film-shaped exterior member 30.

  The positive electrode lead 21 and the negative electrode lead 22 are led out from the inside of the exterior member 30 to the outside, for example, in the same direction. The positive electrode lead 21 and the negative electrode lead 22 are made of, for example, a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 30 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 30 is disposed, for example, so that the polyethylene film side and the wound electrode body 20 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 31 is inserted between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22 to prevent intrusion of outside air. The adhesion film 31 is made of a material having adhesion to the positive electrode lead 21 and the negative electrode lead 22, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 30 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 2 shows a cross-sectional structure taken along line II of the spirally wound electrode body 20 shown in FIG. The wound electrode body 20 is obtained by laminating a positive electrode 23 and a negative electrode 24 via a separator 25 and an electrolyte layer 26 and winding them, and the outermost periphery is protected by a protective tape 27.

(Active material layer)
The positive electrode 23 has a structure in which a positive electrode active material layer 23B is provided on both surfaces of a positive electrode current collector 23A. The negative electrode 24 has a structure in which a negative electrode active material layer 24B is provided on both surfaces of a negative electrode current collector 24A, and the negative electrode active material layer 24B and the positive electrode active material layer 23B are arranged to face each other. In the non-aqueous electrolyte secondary battery of the present invention, the thickness of each of the positive electrode active material layer 23B and the negative electrode active material layer 24B per side is 40 μm or more, preferably 80 μm or less. More preferably, it is the range of 40 micrometers or more and 60 micrometers or less. By setting the thickness of the active material layer to 40 μm or more, it is possible to increase the capacity of the battery. Moreover, the discharge capacity maintenance factor when charging / discharging is repeated can be enlarged by setting it as 80 micrometers or less.

(Positive electrode)
The positive electrode current collector 23A is made of, for example, a metal material such as aluminum, nickel, or stainless steel. The positive electrode active material layer 24B includes, for example, any one or more of positive electrode materials capable of occluding and releasing lithium as a positive electrode active material, and a conductive agent such as a carbon material and polyvinylidene fluoride as necessary. It may contain a binder.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium cobaltate LiCoO ₂ , lithium nickelate LiNiO ₂ , and solid solutions thereof (Li (Ni _x Co _y Mn _z ) O ₂ )) (x, The values of y and z are 0 <x <1, 0 <y <1, 0 ≦ z <1, x + y + z = 1), manganese spinel (LiMn ₂ O ₄ ) and its solid solution (Li (Mn _2−v Ni _v ) O ₄ ) (value of v is 0 <v <2) and the like, and phosphate compounds having an olivine structure such as lithium iron phosphate (LiFePO ₄ ) are preferable. This is because a high energy density can be obtained. Examples of positive electrode materials capable of inserting and extracting lithium include oxides such as titanium oxide, vanadium oxide and manganese dioxide, disulfides such as iron disulfide, titanium disulfide and molybdenum sulfide, sulfur, And conductive polymers such as polyaniline and polythiophene.

(Negative electrode)
The negative electrode 24 has, for example, a structure in which a negative electrode active material layer 24B is provided on both surfaces of a negative electrode current collector 24A having a pair of opposed surfaces. The negative electrode current collector 24A is made of a metal material such as copper, nickel, and stainless steel, for example.

  The negative electrode active material layer 24B includes one or more negative electrode materials capable of occluding and releasing lithium as a negative electrode active material.

  Examples of the negative electrode material capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, and fired organic polymer compounds And carbon materials such as carbon fiber or activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body refers to a carbonized material obtained by firing a polymer material such as phenol resin or furan resin at an appropriate temperature, and in part, it is made of non-graphitizable carbon or graphitizable carbon. Some are classified. Examples of the polymer material include polyacetylene and polypyrrole. These carbon materials are preferable because the change in the crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent characteristics can be obtained. Furthermore, a battery having a low charge / discharge potential, specifically, a battery having a charge / discharge potential close to that of lithium metal is preferable because a high energy density of the battery can be easily realized.

  Further, as the negative electrode material, in addition to the carbon material shown above, a material containing an element that forms an alloy with lithium, such as silicon, tin, and a compound thereof, magnesium, aluminum, germanium, or the like may be used. Further, a material containing an element that forms a composite oxide with lithium, such as titanium, can be considered.

(Separator)
The separator 25 separates the positive electrode 23 and the negative electrode 24 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 25 is made of, for example, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of ceramic, and a plurality of these porous films are laminated. It may be a structure. For example, the separator 25 is impregnated with an electrolytic solution that is a liquid electrolyte.

(Nonaqueous electrolyte composition)
The non-aqueous electrolyte composition of the present invention (hereinafter sometimes referred to as electrolyte solution) includes a first metal ion contained in the highest concentration and a second ion radius larger than that of the first metal ion. The second metal ion is contained in an amount of 0.01 to 0.2 mol / kg. By making content of the 2nd metal ion in a non-aqueous electrolyte composition into this range, the viscosity of an electrolyte composition can be suppressed and it is preferable.
The first metal ion is an electrode reactant and can include an alkali metal ion, preferably a lithium ion.
When lithium salt is used as the electrolyte salt, the deposition of lithium is suppressed by adding ions having a larger ion radius than lithium ions (for example, alkali metal ions other than lithium metal) to the non-aqueous electrolyte composition. Discharge efficiency can be improved. Since lithium is deposited at the lowest voltage in organic solvents, other alkali metals are deposited earlier than lithium. As a result, another alkali metal precipitates instead of lithium. Since alkali metals other than lithium are less reactive with organic solvents than lithium, decomposition of organic solvents can be suppressed. That is, the initial charge and discharge efficiency can be improved by adding and dissolving an alkali metal salt other than lithium.

  The alkali metal ion concentration in the electrolytic solution composition can be measured by ion chromatography or the like.

The second metal is an ion having an ionic radius larger than that of the first metal ion, and is preferably an alkali metal ion other than lithium ion.
Examples of the alkali metal ion other than lithium ion include sodium ion, potassium ion, rubidium ion, cesium ion, and francium ion, preferably sodium ion, potassium ion, rubidium ion, and cesium ion, sodium ion and potassium ion Ions are more preferred.
As the atomic number of the alkali metal increases, the reactivity with the organic solvent decreases, but potassium ions are more preferable from the viewpoint of solubility and the like.
Further, sodium ion is more preferable from the viewpoint of ion radius close to lithium.
Since alkali metal has a small difference in deposition potential from lithium, the alkali metal deposited during charging can be dissolved again in the electrolytic solution composition during discharging, and this is considered to exhibit excellent cycle characteristics.

In the present invention, the alkali metal ion other than the lithium ion is preferably an alkali metal ion generated by adding an alkali metal salt other than the lithium salt to the electrolytic solution composition. By adding an alkali metal salt other than the lithium salt to the electrolytic solution composition and dissolving it, an alkali metal ion other than the lithium ion can be generated.
The alkali metal salt other than the lithium salt is preferably a strong acid salt, and more preferably a salt of an alkali metal other than a strong acid having a pKa of 1 or less, preferably 0 or less, and lithium.
Examples of the alkali metal salt other than lithium salt include hexafluorophosphate, hexafluoroarsenate, tetrafluoroborate, perchlorate, trifluoromethanesulfonate, and other alkali metals other than lithium. Bis (trifluoromethanesulfonyl) imide salt is preferable, and hexafluorophosphate is more preferable because of low reactivity.
More preferably, potassium hexafluorophosphate, potassium hexafluoroarsenate, potassium tetrafluoroborate, potassium perchlorate, potassium trifluoromethanesulfonate, potassium bis (trifluoromethanesulfonyl) imide, hexafluorophosphate Examples thereof include sodium, rubidium perchlorate, and cesium perchlorate, and potassium hexafluorophosphate is particularly preferable.

  Here, the pKa of the acid can be measured (calculated) by the hydrogen ion concentration of the aqueous acid solution.

  The present invention is not limited to the above compounds. That is, any alkali metal salt other than lithium can be used. In addition, alkali salts having an anion having a special action, such as tetraphenylborate described in JP 2000-340258 A, are excluded.

  Moreover, the nonaqueous electrolytic solution composition of the present invention includes, for example, a solvent and an electrolyte salt dissolved in the solvent.

(solvent)
The solvent used in the electrolytic solution composition is preferably a high dielectric constant solvent having a relative dielectric constant of 30 or more. This is because the number of lithium ions can be increased. The content of the high dielectric constant solvent in the electrolytic solution composition is preferably in the range of 15 to 50% by mass. It is because higher charging / discharging efficiency is obtained by setting it within this range.

Examples of the high dielectric constant solvent include carbonates having carbon-carbon multiple bonds such as vinylene carbonate, ethylene carbonate, propylene carbonate, butylene carbonate and vinyl ethylene carbonate, lactones such as γ-butyrolactone and γ-valerolactone, N- Examples include lactams such as methyl-2-pyrrolidone, cyclic carbamates such as N-methyl-2-oxazolidinone, and sulfone compounds such as tetramethylene sulfone.
Among these, a carbonic acid ester having a carbon-carbon multiple bond is preferable, and a carbonic acid ester having a carbon-carbon double bond such as ethylene carbonate and vinylene carbonate is more preferable.
The content of the carbonic acid ester having a carbon-carbon multiple bond in the electrolytic solution composition is preferably in the range of 0.1% by mass to 2% by mass. Moreover, the said high dielectric constant solvent may be used individually by 1 type, and may mix and use multiple types.

The solvent used in the electrolytic solution composition is preferably used by mixing a low-viscosity solvent having a viscosity of 1 mPa · s or less with the above-mentioned high dielectric constant solvent. This is because high ion conductivity can be obtained. The ratio (mass ratio) of the low-viscosity solvent to the high-dielectric-constant solvent is preferably in the range of high-dielectric-constant solvent: low-viscosity solvent = 2: 8 to 5: 5. It is because a higher effect can be obtained by setting it within this range.
Examples of the low viscosity solvent include chain carbonate esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and trimethyl. Chain carboxylic acid esters such as methyl acetate and ethyl trimethylacetate, chain amides such as N, N-dimethylacetamide, chain carbamic acid esters such as methyl N, N-diethylcarbamate and ethyl N, N-diethylcarbamate And ethers such as 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran, and 1,3-dioxolane, and preferably ethyl methyl carbonate. These low-viscosity solvents may be used alone or in combination of two or more.

Moreover, the non-aqueous electrolyte composition of the present invention may contain a halogenated carbonate.
This is because a good film can be formed on the negative electrode 22 and the decomposition reaction of the electrolytic solution can be suppressed. By containing the chloroethylene carbonates in the electrolytic solution composition, expansion under a high temperature environment can be reduced while maintaining good charge / discharge cycle characteristics. Chloroethylene carbonate is decomposed by charging and reacts with lithium ions in the electrolytic solution to form a lithium chloride film on the negative electrode surface. Since this film suppresses decomposition of the solvent in the electrolytic solution, generation of gas is suppressed. As a result, it is considered that the expansion of the battery is reduced.

  Examples of halogenated carbonates include fluorinated ethylene carbonates such as 4-fluoro-1,3-dioxolan-2-one (fluoroethylene carbonate) represented by the following formula (1), 4-methyl-5-fluoro-1 , 3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one, etc., trifluoropropylene carbonate represented by the following formula (2), 4-trifluoromethyl- 1,3-dioxolan-2-one and trifluoromethylene carbonate such as ethylene trifluoromethylene carbonate, and 4-chloro-1,3-dioxolan-2-one (chloroethylene carbonate) represented by the following formula (3) A chlorinated ethylene carbonate is mentioned. The content of the halogenated carbonate in the electrolytic solution composition is preferably in the range of 0.1% by mass to 2% by mass. In addition, the halogenated carbonate may be used alone or in combination of two or more.

  The content of the halogenated carbonate in the electrolytic solution composition is preferably 0.1% by mass or more and less than 5% by mass, more preferably 0.2 to 3% by mass, based on the solvent. The amount of 0.2% by mass or more is preferable because a sufficient film can be formed. Moreover, when 5 mass% or more is added, it becomes difficult to reduce expansion particularly in a laminate type battery.

(Electrolyte salt)
As the electrolyte salt, e.g., lithium hexafluorophosphate (LiPF _6), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF ₆₎ , Inorganic lithium salts such as lithium perchlorate (LiClO ₄ ) and lithium tetrachloroaluminate (LiAlCl ₄ ), and lithium trifluoromethanesulfonate (CF ₃ SO ₃ Li), lithium bis (trifluoromethanesulfone) imide [(CF ₃ SO ₂ ) ₂ NLi], lithium bis (pentafluoroethanesulfone) imide [(C ₂ F ₅ SO ₂ ) ₂ NLi] and lithium tris (trifluoromethanesulfone) methide [(CF ₃ SO ₂ ) ₃ CLi] Of perfluoroalkanesulfonic acid derivatives Lithium salts. One electrolyte salt may be used alone, or a plurality of electrolyte salts may be mixed and used.

(Polymer compound)
The battery of the present invention may be in the form of a gel by containing a polymer compound that swells with the electrolyte and serves as a holding body that holds the electrolyte. This is because by including a polymer compound that swells with the electrolytic solution composition, high ionic conductivity can be obtained, excellent charge / discharge efficiency can be obtained, and battery leakage can be prevented. When a polymer compound is added to the electrolytic solution composition, the content of the polymeric compound in the electrolytic solution composition is preferably in the range of 0.1% by mass to 2% by mass. When a polymer compound such as polyvinylidene fluoride is applied on both sides of the separator, the mass ratio of the electrolyte composition to the polymer compound is preferably in the range of 50: 1 to 10: 1. It is because higher charging / discharging efficiency is obtained by setting it within this range.

  Examples of the polymer compound include ether-based polymer compounds such as polyvinyl formal represented by the following formula (4), polyethylene oxide and a crosslinked product containing polyethylene oxide, and ester-based polymers such as polymethacrylate represented by the following formula (5). Polymers of vinylidene fluoride such as molecular compounds, acrylate-based polymer compounds, polyvinylidene fluoride represented by the following formula (6), and copolymers of vinylidene fluoride and hexafluoropropylene are mentioned. A high molecular compound may be used individually by 1 type, and multiple types may be mixed and used for it. In particular, it is desirable to use a fluorine-based polymer compound such as polyvinylidene fluoride from the viewpoint of the effect of preventing swelling during high temperature storage.

In the above formulas (4) to (6), s, t, and u are each an integer of 100 to 10000, R is C _x H _{2x + 1} O _y (x is an integer of 1 to 8, y is 0 to 4) And y is x-1 or less).

(Production method)
For example, the secondary battery can be manufactured as follows.

  The positive electrode can be produced, for example, by the following method. First, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 23A and the solvent is dried. Then, the positive electrode active material layer 23B is formed by compression molding using a roll press or the like, and the positive electrode 23 is manufactured. At this time, the thickness of the positive electrode active material layer 23B is set to 40 μm or more.

  Moreover, a negative electrode can be produced by the following method, for example. First, after preparing a negative electrode mixture by mixing a negative electrode active material containing at least one of silicon and tin as constituent elements, a conductive agent, and a binder, the negative electrode mixture was mixed with N-methyl-2. -Disperse in a solvent such as pyrrolidone to obtain a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 24A, dried, and compression-molded to form a negative electrode active material layer 24B containing negative electrode active material particles made of the negative electrode active material described above. Get. At this time, the thickness of the negative electrode active material layer 24B is set to 40 μm or more.

  Next, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 23 and the negative electrode 24, and the mixed solvent is volatilized to form the electrolyte layer 26. Next, the positive electrode lead 21 is attached to the positive electrode current collector 23A, and the negative electrode lead 22 is attached to the negative electrode current collector 24A. Subsequently, the positive electrode 23 and the negative electrode 24 on which the electrolyte layer 26 is formed are laminated through a separator 25 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 27 is attached to the outermost peripheral portion. The wound electrode body 20 is formed by bonding. After that, for example, the wound electrode body 20 is sandwiched between the exterior members 30, and the outer edge portions of the exterior members 30 are in close contact with each other by thermal fusion or the like and sealed. At that time, an adhesion film 31 is inserted between the positive electrode lead 21 and the negative electrode lead 22 and the exterior member 30. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 23 and the negative electrode 24 are prepared as described above, and after the positive electrode lead 21 and the negative electrode lead 22 are attached to the positive electrode 23 and the negative electrode 24, the positive electrode 23 and the negative electrode 24 are stacked and wound via the separator 25. Rotate and adhere the protective tape 27 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 20. Next, the wound body is sandwiched between the exterior members 30, and the outer peripheral edge except for one side is heat-sealed to form a bag shape, and is stored inside the exterior member 30. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, and other materials such as a polymerization initiator or a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 30 is prepared. After the injection, the opening of the exterior member 30 is heat-sealed and sealed. After that, if necessary, heat is applied to polymerize the monomer to form a polymer compound, thereby forming the gel electrolyte layer 26 and assembling the secondary battery shown in FIGS.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 23 and inserted in the negative electrode 24 through the electrolytic solution. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 24 and inserted into the positive electrode 24 through the electrolytic solution.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the embodiment, and various modifications can be made. For example, in the above embodiment and the case where an electrolytic solution is used as the electrolyte, and the case where a gel electrolyte in which the electrolytic solution is held in a polymer compound is also described, other electrolytes are used. It may be. Other electrolytes include, for example, a mixture of an ion conductive inorganic compound such as ion conductive ceramics, ion conductive glass or ionic crystal and an electrolyte, or a mixture of another inorganic compound and an electrolyte. Or a mixture of these inorganic compounds and a gel electrolyte.

In the above embodiment, a battery using lithium as an electrode reactant has been described. However, another alkali metal such as sodium (Na) or potassium (K), or an alkaline earth metal such as magnesium or calcium (Ca). The present invention can also be applied to the case of using other light metals such as aluminum.
That is, even in such a battery, the main metal ion, that is, a metal ion larger than the metal ion contained in the highest concentration as the electrode reactant in the non-aqueous electrolyte composition, To contain.

  Further, in the above embodiment, the capacity of the negative electrode is a so-called lithium ion secondary battery represented by a capacity component due to insertion and extraction of lithium, or lithium metal is used for the negative electrode active material, and the capacity of the negative electrode is Although a so-called lithium metal secondary battery represented by a capacity component due to precipitation and dissolution has been described, the present invention makes the charge capacity of the negative electrode material capable of occluding and releasing lithium smaller than the charge capacity of the positive electrode. Thus, the present invention can be similarly applied to a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof. .

  Furthermore, in the above embodiment, the laminate type secondary battery has been specifically described, but it goes without saying that the present invention is not limited to the above shape. That is, the present invention can be applied to a cylindrical battery, a square battery, and the like. Further, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

<Example 1>
First, 94 parts by weight of lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 3 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride (PVdF) as a binder are homogeneous. After mixing, N-methylpyrrolidone was added to obtain a positive electrode mixture coating solution. Next, the obtained positive electrode mixture coating liquid was uniformly applied on both surfaces of a 20 μm thick aluminum foil and dried to form a positive electrode mixture layer of 20 mg / cm ² per side. This was cut into a shape having a width of 50 mm and a length of 300 mm to produce a positive electrode.
Next, 97 parts by weight of graphite as a negative electrode active material and 3 parts by weight of PVdF as a binder were homogeneously mixed, and N-methylpyrrolidone was added to obtain a negative electrode mixture coating solution. Next, the obtained negative electrode mixture coating solution was uniformly applied on both sides of a 15 μm thick copper foil serving as a negative electrode current collector and dried to form a negative electrode mixture layer of 10 mg / cm ² per side. This was cut into a shape having a width of 50 mm and a length of 300 mm to produce a negative electrode.
The electrolyte was prepared by mixing at a ratio (weight ratio) of ethylene carbonate / ethyl methyl carbonate / lithium hexafluorophosphate / potassium hexafluorophosphate = 34/51 / 13.4 / 1.6.
This positive electrode and negative electrode are laminated and wound through a separator made of a microporous polyethylene film having a thickness of 9 μm, and put into a bag made of an aluminum laminate film. After injecting 2 g of the electrolyte into the bag, the bag is heat-sealed to produce a laminated battery. The capacity of this battery is 700 mAh.
After charging this battery for 3 hours at 350 mA in a 23 ° C. environment with 4.2 V as the upper limit, the ratio of the discharge amount to the charge amount when constant current discharging was performed with 140 mA at 3 V as the lower limit was expressed as initial charge / discharge efficiency (%). It was shown in 1. In addition, after charging for 3 hours at 700 mA at 23 mA in a 23 ° C. environment for 3 hours and then discharging at a constant current of 700 mA at 3 V as a lower limit, the discharge capacity retention rate (%) was measured for 300 cycles. It was shown to.

<Examples 2 to 4>
A laminated battery was prepared in the same manner as in Example 1 except that the concentration of potassium hexafluorophosphate was changed to the concentration shown in Table 1, and the physical properties of the battery were evaluated.

<Example 5>
A laminate type battery was prepared in the same manner as in Example 1 except that 1% of fluoroethylene carbonate was added and the amount of ethylene carbonate was reduced by that amount, and the physical properties of the battery were evaluated.

<Example 6>
A laminate type battery was prepared in the same manner as in Example 5 except that the fluoroethylene carbonate was changed to chloroethylene carbonate, and the physical properties of the battery were evaluated.

<Example 7>
A laminate type battery was prepared in the same manner as in Example 1 except that 1% of vinylene carbonate was added and the amount of ethylene carbonate was reduced by that amount, and the physical properties of the battery were evaluated.

<Example 8>
A laminated battery was prepared in the same manner as in Example 7 except that vinylene carbonate was changed to vinyl ethylene carbonate, and the physical properties of the battery were evaluated.

<Example 9-13>
A laminate type battery was prepared in the same manner as in Example 1 except that the alkali metal salt was changed to the potassium salt shown in Table 1, and the physical properties of the battery were evaluated.

<Example 14-16>
A laminate type battery was prepared in the same manner as in Example 1 except that the alkali metal salt was changed to the salt shown in Table 1, and the physical properties of the battery were evaluated.

<Comparative Example 1>
A laminate type battery was prepared in the same manner as in Example 1 except that the alkali salt was not mixed, and the physical properties of the battery were evaluated.

<Comparative example 2>
A laminate type battery was prepared in the same manner as in Example 1 except that the amount of potassium hexafluorophosphate added was changed to 0.3 mol / kg, and the physical properties of the battery were evaluated.

<Comparative Example 3>
A laminate type battery was prepared in the same manner as in Example 1 except that the potassium hexafluorophosphate salt was changed to the potassium carbonate salt shown in Table 1, and the physical properties of the battery were evaluated.

FEC: Fluoroethylene carbonate
CEC: Chloroethylene carbonate
VC: Vinylene carbonate
VEC: Vinyl ethylene carbonate

As shown in Table 1, in Examples 1 to 16 in which an alkali metal salt was added to the electrolytic solution, the initial charge / discharge efficiency and the discharge capacity retention rate after 300 cycles were improved as compared with Comparative Example 1.
From the results of Examples 1 to 4 and Comparative Example 2, it can be said that the addition amount of the alkali metal salt other than the lithium salt is preferably 0.01 to 0.2 mol / Kg.
In Example 5 to which fluoroethylene carbonate was added and Example 6 to which chloroethylene carbonate was added, the initial charge efficiency was improved and the cycle characteristics were greatly improved.
In addition, Example 5 to which vinylene carbonate was added and Example 8 to which chloroethylene carbonate was added improved the initial charge efficiency and greatly improved the cycle characteristics as compared to Example 1.
It turns out that the lithium carbonate used for the comparative example 3 does not melt | dissolve and a metal ion cannot be contained in electrolyte solution.

<Example 17>
A laminate type battery was produced in the same manner as in Example 1 except that a separator having a thickness of 7 μm and a separator coated with 2 μm of polyvinylidene fluoride on both sides was used. After charging this battery for 3 hours at 350 mA in a 23 ° C. environment with 4.2 V as the upper limit, the ratio of the discharge amount to the charge amount when constant current discharging was performed with 140 mA at 3 V as the lower limit was expressed as initial charge / discharge efficiency (%). It was shown in 2. In addition, after charging for 3 hours at 700 mA at 23 mA in an environment of 23 ° C. for 3 hours and then discharging at a constant current of 700 mA at 3 V as a lower limit, the discharge capacity retention rate (%) was measured for 300 cycles. It was shown to.

<Examples 18 to 20>
A laminate type battery was prepared in the same manner as in Example 17 except that the concentration of potassium hexafluorophosphate was changed to the concentration shown in Table 2, and the physical properties of the battery were evaluated.

<Example 21>
A laminate type battery was prepared in the same manner as in Example 17 except that 1% of fluoroethylene carbonate was added and the amount of ethylene carbonate was reduced by that amount, and the physical properties of the battery were evaluated.

<Example 22>
A laminate type battery was prepared in the same manner as in Example 21 except that the fluoroethylene carbonate was changed to chloroethylene carbonate, and the physical properties of the battery were evaluated.

<Example 23>
A laminate type battery was prepared in the same manner as in Example 17 except that 1% of vinylene carbonate was added and the amount of ethylene carbonate was reduced by that amount, and the physical properties of the battery were evaluated.

<Example 24>
A laminated battery was prepared in the same manner as in Example 23 except that vinylene carbonate was changed to vinyl ethylene carbonate, and the physical properties of the battery were evaluated.

<Examples 25-29>
A laminated battery was prepared in the same manner as in Example 17 except that the alkali metal salt was changed to the potassium salt described in Table 2, and the physical properties of the battery were evaluated.

<Examples 30-32>
A laminated battery was prepared in the same manner as in Example 17 except that the alkali salt was changed to that shown in Table 2, and the physical properties of the battery were evaluated.

<Comparative example 4>
A laminate type battery was prepared in the same manner as in Example 17 except that the alkali salt was not mixed, and the physical properties of the battery were evaluated.

<Comparative Example 5>
A laminate type battery was prepared in the same manner as in Example 17 except that the amount of potassium hexafluorophosphate added was changed to 0.3 mol / kg, and the physical properties of the battery were evaluated.

<Comparative Example 6>
A laminate type battery was prepared in the same manner as in Example 17 except that potassium hexafluorophosphate was changed to the potassium carbonate salt shown in Table 1, and the physical properties of the battery were evaluated.

FEC: Fluoroethylene carbonate
CEC: Chloroethylene carbonate
VC: Vinylene carbonate
VEC: Vinyl ethylene carbonate

As shown in Table 2, Example 17 using a polymer compound (polyvinylidene fluoride) on both sides of the separator had an initial charge and discharge efficiency equivalent to that of Example 1 without using a polymer compound (polyvinylidene fluoride) and 300. The discharge capacity retention rate after cycling was shown.
Moreover, Examples 17-32 which added the alkali metal salt in electrolyte solution improved the first time charging / discharging efficiency and the discharge capacity maintenance factor after 300 cycles from the comparative example 4. FIG.
From the results of Examples 17 to 20 and Comparative Example 5, it can be said that the addition amount of the alkali metal salt other than the lithium salt is preferably 0.01 to 0.2 mol / Kg.
In Example 21 to which fluoroethylene carbonate was added and Example 22 to which chloroethylene carbonate was added, the initial charge efficiency was improved and the cycle characteristics were greatly improved.
In addition, Example 23 to which vinylene carbonate was added and Example 24 to which chloroethylene carbonate was added improved the initial charge efficiency and greatly improved cycle characteristics compared to Example 17.
It turns out that the lithium carbonate used for the comparative example 6 does not melt | dissolve and a metal ion cannot be contained in electrolyte solution.

<Battery thickness change>
Table 3 shows changes in battery thickness when the batteries of Example 17 and Comparative Example 4 were charged at 700 mA at 23 ° C. and 4.2 V as the upper limit for 3 hours and then stored at 90 ° C. for 4 hours.

  As is apparent from Table 3, blistering during high temperature storage can be suppressed by adding potassium hexafluorophosphate to the electrolytic solution.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above embodiments and can be variously modified.

It is a disassembled perspective view showing the structure of the nonaqueous electrolyte secondary battery which concerns on one embodiment of this invention. It is sectional drawing showing the structure along the II line of the winding electrode body shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Winding electrode body, 23 ... Positive electrode, 23A ... Positive electrode collector, 23B ... Positive electrode active material layer, 24 ... Negative electrode, 24A ... Negative electrode collector, 24B ... Negative electrode active material layer, 25 ... Separator, 21 ... Positive electrode Lead, 22 ... negative electrode lead, 26 ... electrolyte layer, 27 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (17)

  The first metal ion contained in the highest concentration and the second metal ion having an ionic radius larger than that of the first metal ion, the second metal ion being 0.01-0. A non-aqueous electrolyte composition containing 2 mol / kg.   The non-aqueous electrolyte composition according to claim 1, wherein the first metal ion is a lithium ion.   The non-aqueous electrolyte composition according to claim 2, wherein the second metal ion is at least one selected from sodium ions, potassium ions, rubidium ions, and cesium ions.   The non-aqueous electrolyte composition according to claim 2, wherein the second metal ion is at least one selected from sodium ions or potassium ions.   The second metal ion is a hexafluorophosphate, hexafluoroarsenate, tetrafluoroborate, perchlorate, trifluoromethanesulfonate, bis (trifluoro) of the second metal ion. The non-aqueous electrolyte composition according to claim 2, wherein the non-aqueous electrolyte composition is a metal ion generated by addition of (romethanesulfonyl) imide salt to the non-aqueous electrolyte composition.   The non-aqueous electrolyte composition according to claim 2, further comprising a halogenated carbonate.   The non-aqueous electrolyte composition according to claim 2, further comprising a carbonic acid ester having a carbon-carbon multiple bond. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte together with a positive electrode and a negative electrode,
The non-aqueous electrolyte solution includes a metal ion that is an electrode reactant, and 0.01 to 0.2 mol / kg of at least one selected from metal ions having a larger ion radius than the metal ion that is the electrode reactant. A non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 8, wherein the metal ions as the electrode reactant are lithium ions.   The nonaqueous electrolytic solution according to claim 9, wherein the metal ion having a larger ion radius than the metal ion that is the electrode reactant is at least one selected from sodium ion, potassium ion, rubidium ion, and cesium ion. Secondary battery.   The non-aqueous electrolyte secondary battery according to claim 9, wherein the metal ion having an ion radius larger than that of the metal ion that is the electrode reactant is at least one selected from sodium ions and potassium ions.   The alkali metal ion other than the lithium ion is a hexafluorophosphate, hexafluoroarsenate, tetrafluoroborate, perchlorate or trifluoromethanesulfonate of an alkali metal ion other than the lithium ion. The non-aqueous electrolyte secondary battery according to claim 9, which is an alkali metal ion generated by adding bis (trifluoromethanesulfonyl) imide salt to the non-aqueous electrolyte.   The non-aqueous electrolyte secondary battery according to claim 7, wherein the non-aqueous electrolyte further contains a halogenated carbonate.   The non-aqueous electrolyte secondary battery according to claim 9, wherein the non-aqueous electrolyte further contains a carbonate having a carbon-carbon multiple bond.   The non-aqueous electrolyte secondary battery according to claim 9, wherein the electrode body and the non-aqueous electrolyte are accommodated in an exterior member made of a laminate film.   The non-aqueous electrolyte secondary battery according to claim 9, comprising a polymer compound that swells with the non-aqueous electrolyte.   The non-aqueous electrolyte secondary battery according to claim 16, wherein the polymer compound is polyvinylidene fluoride.

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