JP2008016378A - Anode for nonaqueous electrolyte secondary battery, and the nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode for a nonaqueous electrolyte secondary battery in which the increase in the resistance in the cathode resulting from capacity expansion can be suppressed, and to provide the nonaqueous electrolyte secondary battery that uses this. <P>SOLUTION: The cathode for the nonaqueous electrolyte battery is equipped with a metal foil that functions as the cathode current collector, and the cathode mixture layer formed on one face or both faces of the metal foil that contains the cathode active material and conductive agent in which lithium ion can be stored and released. In the cathode mixture layer, the difference between the conductive agent amount (atomic number) in the vicinity of the metal foil and the conductive agent amount (atomic number) at its surface is 20.0% or lower; while the content of the conductive agent is 0.5% to 10%. The nonaqueous electrolyte secondary battery is equipped with the cathode for the nonaqueous electrolyte secondary battery, the anode for the nonaqueous electrolyte secondary battery that contains the anode active material in which lithium ion can be stored and released, the nonaqueous electrolyte, a separator, and the exterior member that houses these. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery, and more specifically, a positive electrode for a nonaqueous electrolyte secondary battery in which a conductive agent amount in a positive electrode mixture layer is set within a predetermined range, And a lithium ion non-aqueous electrolyte secondary battery using the same.

  In recent years, many portable electronic devices such as a camera-integrated VTR (video tape recorder), a video camera, a digital still camera, a mobile phone, a portable information terminal, 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 increasing the capacity of batteries, particularly secondary batteries, are being actively promoted. Among them, lithium ion non-aqueous electrolyte secondary batteries are widely put into practical use because they have a higher energy density than lead batteries and nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries (patents) Reference 1).

  Generally, in a lithium ion non-aqueous electrolyte secondary battery, a positive electrode containing lithium cobaltate / lithium nickelate / spinel type lithium manganate composite oxide as a positive electrode active material and a lithium ion as a negative electrode active material are occluded. And a negative electrode containing a detachable carbon-based material or the like. In addition, a nonaqueous electrolyte containing an electrolytic solution in which a lithium salt is dissolved as a solute in an organic solvent is used. The lithium ion non-aqueous electrolyte secondary battery is charged and discharged by inserting and extracting lithium ions between the positive and negative electrodes via the non-aqueous electrolyte.

In such a lithium ion non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are formed by forming an electrode mixture layer on a current collector, and this electrode mixture layer is generally composed of an electrode active material, a conductive agent, and the like. It is comprised from a binder and the additive added suitably.
And as a manufacturing method of such a positive electrode and a negative electrode, the materials of the positive electrode and the negative electrode as described above are respectively added to a solvent at once to prepare a mixed solution, and this mixed solution is prepared for each of the positive electrode and the negative electrode. The method of apply | coating on a collector (for example, aluminum foil, copper foil, etc., respectively) and drying is mentioned.
Various proposals have been made for such an electrode structure (see Patent Documents 2 and 3).
JP-A-4-332479 JP-A-9-265976 JP 2004-95538 A

By the way, especially in a high capacity lithium ion secondary battery, since the area density of a positive electrode and a negative electrode increases, the resistance in the electrode mixture layer formed on a collector becomes high.
Then, in the positive electrode and the negative electrode, the potential difference between the vicinity of the current collector of the electrode mixture layer and the surface becomes large. Therefore, when a lithium ion secondary battery is manufactured using such an electrode, for example, the internal Impedance also increases.
In addition, by increasing the thickness of the electrode mixture layer, the impregnating ability of the electrolyte solution decreases, so that the ability to occlude and release lithium ions in the electrode active material decreases near the current collector, affecting various characteristics. There is also concern about the effect.

  This invention is made | formed in view of the subject which such a prior art has, The place made into the objective used the positive electrode for nonaqueous electrolyte secondary batteries which can suppress the resistance increase in a positive electrode, and this The object is to provide a non-aqueous electrolyte secondary battery.

  The present inventor made extensive studies to achieve the above object, and as a result, the content of the conductive agent in the positive electrode mixture layer was set within a predetermined range, and the amount of the conductive agent in the vicinity of the metal foil and the surface of the positive electrode mixture layer. The inventors have found that the above object can be achieved by setting the difference in (number of atoms) within a predetermined range, and have completed the present invention.

  That is, the positive electrode for a non-aqueous electrolyte secondary battery of the present invention includes a metal foil functioning as a positive electrode current collector, a positive electrode active material and a conductive agent that are formed on one or both surfaces of the metal foil and can occlude and release lithium ions. A positive electrode layer for a non-aqueous electrolyte secondary battery, wherein the positive electrode mixture layer includes a conductive agent amount (number of atoms) in the vicinity of the metal foil and a conductive agent amount on the surface thereof. The difference from (number of atoms) is 20.0% or less, and the content of the conductive agent is 0.5 to 10%.

  Further, a preferred embodiment of the positive electrode for a non-aqueous electrolyte secondary battery of the present invention is an aluminum foil that functions as a positive electrode current collector, and is formed on one or both surfaces of the aluminum foil, and can occlude and release lithium ions. A positive electrode mixture layer containing a positive electrode active material which is a composite oxide containing a transition metal element and a conductive agent, and the positive electrode mixture layer includes the metal The difference between the amount of conductive agent (number of atoms) in the vicinity of the foil and the amount of conductive agent (number of atoms) on the surface thereof is 20.0% or less, and the content of the conductive agent is 0.5 to 10%. It is characterized by.

  Furthermore, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery containing a negative electrode active material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery comprising a separator and an exterior member that accommodates the separator, wherein the positive electrode for a non-aqueous electrolyte secondary battery includes a metal foil that functions as a positive electrode current collector, and the metal foil A positive electrode mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions and a conductive agent, formed on one or both surfaces, and the positive electrode mixture layer has a conductive agent amount (number of atoms) in the vicinity of the metal foil; ) And the amount of conductive agent (number of atoms) on the surface thereof is 20.0% or less, and the content of the conductive agent is 0.5 to 10%.

 According to the present invention, the content of the conductive agent in the positive electrode mixture layer is set to a predetermined range, and the difference in the amount (number of atoms) of the conductive agent in the vicinity of the metal foil and the surface of the electrode mixture layer is set to the predetermined range. Therefore, it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery that can suppress an increase in resistance at the positive electrode due to an increase in capacity, and a non-aqueous electrolyte secondary battery using the same.

  Hereinafter, the positive electrode for a non-aqueous electrolyte secondary battery of the present invention will be described in detail. In the present specification and claims, “%” for concentration, content, etc. represents mass percentage unless otherwise specified.

As described above, the positive electrode for a nonaqueous electrolyte secondary battery of the present invention includes a metal foil that functions as a positive electrode current collector, and a positive electrode active material that is formed on one or both surfaces of the metal foil and that can occlude and release lithium ions. A positive electrode for a non-aqueous electrolyte secondary battery comprising a positive electrode mixture layer containing a conductive agent, wherein the positive electrode mixture layer includes a conductive agent amount (number of atoms) in the vicinity of the metal foil and a surface portion thereof. The difference from the amount of conductive agent (number of atoms) is 20.0% or less, and the content of the conductive agent is 0.5 to 10%, and is suitably used for lithium ion non-aqueous electrolyte secondary batteries. It is done.
When such a positive electrode mixture layer is formed on the positive electrode current collector, it is possible to suppress an increase in resistance in the positive electrode accompanying an increase in capacity.

Here, the vicinity and surface of the metal foil of the positive electrode mixture layer will be described with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating the vicinity of the metal foil and the position of the surface of the positive electrode mixture layer. FIG. 4A is a cross-sectional view showing an example of the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, and FIG. 4B shows a metal obtained by bending the positive electrode of FIG. It is sectional drawing which shows the state which excluded some foils.
As shown in the figure, the positive electrode 21 for the non-aqueous electrolyte secondary battery includes a positive electrode current collector (metal foil) 21A, and a positive electrode active material and a conductive agent that are formed on both surfaces and can occlude and release lithium ions. And a positive electrode mixture layer 21 </ b> B containing
And the site | part corresponding to the positive electrode surface in the positive mix layer 21B is the surface a of the positive mix layer 21B (refer the figure (a) and (b)), and the side close | similar to metal foil in the positive mix layer 21B In other words, the surface of the positive electrode mixture layer that appears when the metal foil is removed by bending or the like from the positive electrode mixture layer is the vicinity of the metal foil b of the positive electrode mixture layer (see FIG. 5B).

In the present invention, the difference between the amount of conductive agent (number of atoms) in the vicinity of the metal and the amount of conductive agent (number of atoms) on the surface is required to be 20.0% or less as described above.
If this difference exceeds 20.0%, the potential difference between the vicinity of the metal and the surface becomes large, so that it is not possible to suppress an increase in resistance in the positive electrode due to the increase in capacity. Furthermore, from the viewpoint that the increase in resistance in the positive electrode accompanying the increase in capacity can be further suppressed, the difference is preferably 15.0% or less, and particularly preferably no difference.
In addition, when measuring / calculating the difference in the amount of conductive agent (number of atoms), for example, it is measured by SEM / EDX (scanning electron microscope and energy dispersive spectroscopic analyzer), and from the larger value of the number of atoms. What is necessary is just to subtract a small value.

Moreover, in this invention, it is required that content of the electrically conductive agent of a positive mix layer is 0.5 to 10%, and it is preferable that it is 0.5 to 7.0%.
If the content of the conductive agent is less than 0.5%, the conductivity of the positive electrode is significantly reduced. Further, when the content of the conductive agent exceeds 10%, surface resistance and the like are improved, but not only a high viscosity control process is required at the time of producing the positive electrode, but also the yield is remarkably lowered.

Examples of the positive electrode active material capable of inserting and extracting lithium ions 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)
[M ^I and M ^{II in} Formulas (1) and (2) 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. 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 (LiCoO ₂ ), lithium manganese composite oxide (LiMnO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), and the like. solid solution _{(Li (Ni x Co y Mn} z) O 2) of a lithium-nickel-cobalt composite oxide _{(LiNi 1-z Co z O} 2 (z <1)), lithium manganese composite oxide having a spinel structure (LiMn ₂ O ₄ ) and solid solutions thereof (Li (Mn _2−x Ni _y ) O ₄ ) and the like.
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)).

Examples of the conductive agent include carbon such as acetylene black, graphite, and ketjen black.
Furthermore, examples of the binder added as necessary include polyvinylidene fluoride, polyvinyl pyridine, and polytetrafluoroethylene.

Moreover, as metal foil which functions as a positive electrode electrical power collector, aluminum foil, nickel foil, or stainless steel foil can be used conveniently.
Furthermore, although the thickness of metal foil is 10-20 micrometers normally, it is not limited to this.

Next, the nonaqueous electrolyte secondary battery of the present invention will be described in detail.
As described above, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery containing a negative electrode active material capable of occluding and releasing lithium ions, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery comprising an electrolyte, a separator, and an exterior member that accommodates the separator, wherein the positive electrode for a non-aqueous electrolyte secondary battery includes a metal foil that functions as a positive electrode current collector, and the metal foil And a positive electrode mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions and a conductive agent. The positive electrode mixture layer has a conductive agent amount (atomic atoms in the vicinity of the metal foil). Number) and the amount of the conductive agent (number of atoms) on the surface thereof is 20.0% or less, and the content of the conductive agent is 0.5 to 10%.
In such a non-aqueous electrolyte secondary battery, the increase in resistance in the positive electrode and further in the battery due to the increase in capacity is suppressed.

FIG. 2 is an exploded perspective view showing an example of a laminated battery as an embodiment of the nonaqueous electrolyte secondary battery of the present invention.
As shown in the figure, the secondary battery is configured by enclosing a battery element 20 to which a positive electrode terminal 11 and a negative electrode terminal 12 are attached in a film-shaped exterior member 30. 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.

  As the exterior member, usable configurations 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. 3 is a cross-sectional view taken along the line II of the battery element 20 shown in FIG. In the figure, a battery element 20 is formed by winding a positive electrode 21 and a negative electrode 22 facing each other with a non-aqueous electrolyte layer 23 and a separator 24 made of a non-aqueous electrolyte, and the outermost peripheral portion. Is protected by a protective tape 25.

Here, the positive electrode 21 has a structure in which a positive electrode mixture layer 21B is coated on both surfaces or one surface of a positive electrode current collector 21A having a pair of opposed surfaces, and the nonaqueous electrolyte secondary of the present invention described above. It is a positive electrode for batteries.
The positive electrode current collector 21A has a portion that is exposed without being covered with the positive electrode mixture layer 21B at one end portion in the longitudinal direction, and the positive electrode terminal 11 is attached to the exposed portion.

On the other hand, the negative electrode 22 has a structure in which, for example, a negative electrode mixture layer 22B is provided on both surfaces or one surface of a negative electrode current collector 22A having a pair of opposed surfaces, similarly to the positive electrode 21. The negative electrode current collector 22A has an exposed portion without being provided with the negative electrode mixture layer 22B at one end portion 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.

Here, the negative electrode mixture layer 22B includes one or more of a negative electrode material capable of occluding and releasing lithium ions and metallic lithium as a negative electrode active material, and conductive as necessary. An agent and a binder may be included.
Examples of the negative electrode active material that can occlude and release lithium ions include carbon materials, metal oxides, and polymer compounds. 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 active material capable of occluding and releasing lithium include a material containing at least one of a metal element and a metalloid element capable of forming an alloy with lithium as a constituent element. This negative electrode active material may be a single element or an alloy or a compound of a metal element or a metalloid element, or may have at least a part of one or more of these phases.
In the present invention, 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 a metal element or metalloid element include tin (Sn), lead (Pb), magnesium (Mg), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony ( Sb), bismuth (Bi), 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, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony and chromium ( And those containing at least one member of the group consisting of 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.

  Furthermore, the negative electrode active material as described above may be an element that forms a composite oxide with lithium, such as titanium. Of course, metallic lithium may be precipitated and dissolved, and magnesium and aluminum other than lithium may be precipitated and dissolved.

  The nonaqueous electrolyte may be either a liquid electrolyte or a solid electrolyte. For example, as the nonaqueous electrolyte, one containing a nonaqueous solvent and an electrolyte salt can be used. Examples of such a non-aqueous solvent include various high dielectric constant solvents and low viscosity solvents.

  As the high dielectric constant solvent, propylene carbonate or the like can be preferably used, but is not limited thereto, and ethylene carbonate, butylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolane-2-one Cyclic carbonates such as (fluoroethylene carbonate), 4-chloro-1,3-dioxolan-2-one (chloroethylene carbonate), and trifluoromethylethylene carbonate can be used.

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

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

In the non-aqueous electrolyte, the high dielectric constant solvent and the low viscosity solvent described above can be used alone or in combination of two or more.
Moreover, it is preferable that content of the above-mentioned non-aqueous solvent shall be 70 to 90%. If it is less than 70%, the viscosity may increase excessively, and if it exceeds 90%, sufficient conductivity may not be obtained.

Further, as the electrolyte salt, any electrolyte salt may be used as long as it dissolves or disperses in the above non-aqueous solvent to generate ions, and lithium hexafluorophosphate (LiPF ₆ ) can be preferably used, but is not limited thereto. It goes without saying that it is not done.
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 (pentafluoroethanesulfone) methide Lithium salts of perfluoroalkanesulfonic acid derivatives such as (LiC (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 10 to 30%. If it is less than 10%, sufficient conductivity may not be obtained, and if it exceeds 30%, the viscosity may increase excessively.

Furthermore, it is possible to add a predetermined polymer compound and swell the polymer compound with a non-aqueous electrolyte so that the non-aqueous electrolyte is impregnated or held in the polymer compound.
Due to the swelling, gelation or non-fluidization of such a polymer compound, it is possible to effectively suppress leakage of the nonaqueous electrolyte in the obtained battery.
Examples of such a polymer compound include polyvinyl formal, polyacrylic acid ester, and polyvinylidene fluoride.
Moreover, it is preferable that content of a high molecular compound shall be 0.1 to 5%. If it is less than 0.1%, gelation is difficult, and if it exceeds 5%, fluidity may decrease.

  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.

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 (this is the positive electrode for a non-aqueous electrolyte secondary battery of the present invention described above). For example, when a particulate positive electrode active material is used, a positive electrode mixture is prepared by mixing the positive electrode active material, a conductive agent, and a binder as necessary, and a dispersion medium such as N-methyl-2-pyrrolidone. To produce a positive electrode mixture slurry.
Next, this positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded to form the positive electrode mixture 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 the negative electrode active material and, if necessary, a conductive agent 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 mixture layer 22B.

  Next, after attaching the positive electrode terminal 11 to the positive electrode 21 and attaching the negative electrode terminal 12 to the negative electrode 22, the separator 24, the positive electrode 21, the separator 24, and the negative electrode 22 are sequentially stacked and wound, and the protective tape 25 is attached to the outermost peripheral portion. A wound electrode body is formed by bonding. Further, the wound electrode body is sandwiched between the exterior members 30, and the outer peripheral edge except one side is heat-sealed to form a bag shape.

Thereafter, a nonaqueous electrolyte containing an electrolyte salt such as lithium hexafluorophosphate (LiPF ₆ ) described above and a nonaqueous solvent such as propylene carbonate is prepared, and the inside of the wound electrode body is opened from the opening of the exterior member 30. The opening of the exterior member 30 is heat-sealed and sealed. Thereby, the nonaqueous electrolyte layer 23 is formed, and the secondary battery shown in FIGS. 2 and 3 is completed.

In addition, you may manufacture this secondary battery as follows.
For example, instead of injecting the nonaqueous electrolyte after producing the wound electrode body, the nonaqueous electrolyte is applied on the positive electrode 21 and the negative electrode 22, or after applying the nonaqueous electrolyte to the separator 24, and enclosed in the exterior member 30. You may make it do.
When a polymer-type non-aqueous electrolyte secondary battery having a gel-like non-aqueous electrolyte is produced, a monomer of a polymer compound such as polyvinylidene fluoride described above on the positive electrode 21 and the negative electrode 22 or the separator 24. The gel-like non-aqueous electrolyte may be formed by injecting the non-aqueous electrolyte after being coated and wound and housed in the exterior member 30. However, it is preferable to polymerize the monomer inside the exterior member 30 because the bondability between the nonaqueous electrolyte and the separator 24 is improved and the internal resistance can be lowered. In addition, it is preferable to inject a nonaqueous electrolyte into the exterior member 30 to form a gel-like nonaqueous electrolyte because it can be easily manufactured with fewer steps.

In the secondary battery described above, when charged, lithium ions are released from the positive electrode mixture layer 21 </ b> B and inserted into the negative electrode mixture layer 22 </ b> B through the nonaqueous electrolyte layer 23. When discharging is performed, lithium ions are released from the negative electrode mixture layer 22 </ b> B and inserted into the positive electrode mixture layer 21 </ b> B through the nonaqueous electrolyte layer 23.
Here, the positive electrode mixture layer constituting the positive electrode contains a positive electrode active material capable of inserting and extracting lithium ions and a conductive agent. The difference between the amount of conductive agent (number of atoms) in the vicinity of the metal foil and the amount of conductive agent (number of atoms) on the surface is 20.0% or less, and the content of the conductive agent is 0.5 to 10%. It is. Such a positive electrode can suppress an increase in resistance in the positive electrode due to an increase in capacity. Therefore, in this secondary battery, the increase in resistance in the battery due to the increase in capacity is suppressed.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
Specifically, the operations described in the following examples were performed to produce a laminate type battery as shown in FIGS. 2 and 3, and its performance was evaluated.

(Example 1-1)
<Preparation of positive electrode>
First, 95 parts by weight of lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 0.5 parts by weight of ketjen black as a conductive agent, and 4.5% of polyvinylidene fluoride (PVdF) as a binder. Then, N-methyl-2-pyrrolidone (NMP) was added, and the mixture was stirred and dispersed with a mixer to obtain a positive electrode mixture slurry.
Next, the obtained positive electrode mixture slurry was directly and evenly applied on both sides of an aluminum (Al) foil having a thickness of 20 μm, and then the organic solvent in the slurry was dried with a drier and rolled with a roll press. A positive electrode (thickness: 150 μm) was prepared, and a positive electrode terminal was further attached. The difference in the amount of conductive agent (number of atoms) between the vicinity of the Al foil and the surface of the positive electrode mixture layer in this positive electrode was 3.0% (n = 3 average). Table 1 shows the specifications of the positive electrode.

In addition, EDX conditions at the time of measuring the amount of conductive agents (number of atoms) in the vicinity of the Al foil of the positive electrode mixture layer and the surface with SEM / EDX are: acceleration voltage: 15 kV, take-out angle: 33.0 °, measurement time: 120 seconds, analysis elements: carbon (C), oxygen (O), fluorine (F), phosphorus (P), cobalt (Co).
When measuring the amount of conductive agent (number of atoms) in the vicinity of the Al foil, the positive electrode was immersed in liquid nitrogen and bent, and the Al foil was removed as shown in FIG. The same applies to the following examples and comparative examples.

<Production of negative electrode>
First, 95 parts by weight of natural graphite as a negative electrode active material and 5 parts by weight of PVdF as a binder were kneaded, and NMP was added and dispersed to obtain a negative electrode mixture slurry. Next, the obtained negative electrode mixture slurry was directly and evenly applied on both sides of a 15 μm thick copper (Cu) foil, and then the organic solvent content in the slurry was dried with a dryer and rolled with a roll press. A negative electrode (thickness: 140 μm) was prepared, and a negative electrode terminal was further attached.

<Preparation of nonaqueous electrolyte>
Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of propylene carbonate and diethyl carbonate, PVdF was added thereto, and heated and dissolved in an oven to prepare a gel-like nonaqueous electrolyte solution.

<Production of laminated battery>
A bag which is an example of an exterior member made of an aluminum laminate film, in which a gel-like nonaqueous electrolyte solution is applied to the positive electrode and the negative electrode, laminated and wound through a separator made of a microporous polyethylene film having a thickness of 20 μm Then, the bag was heat-sealed to obtain a laminate type secondary battery of this example.

(Example 1-2 to Example 1-4)
Except for adjusting the mixer stirring time (dispersion time) in the production of the positive electrode, the same operation as in Example 1-1 was repeated to obtain the positive electrode having the specifications shown in Table 1, and the laminated secondary battery of each example. Got.

(Comparative Example 1-1 and Comparative Example 1-2)
Except for adjusting the mixer stirring time (dispersion time) in the production of the positive electrode, the same operation as in Example 1-1 was repeated to obtain the positive electrode having the specifications shown in Table 1, and the laminated secondary battery of each example. Got.

(Example 2-1)
In the production of the positive electrode, 92.5 parts by weight of lithium-cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material, 3 parts by weight of ketjen black as the conductive agent, and polyvinylidene fluoride (PVdF) as the binder. The same procedure as in Example 1-1 was repeated except that 4.5 parts by weight were kneaded, NMP was added, and the mixture was stirred and dispersed in a mixer to obtain a positive electrode mixture slurry. An example laminate type secondary battery was obtained.
In addition, the difference between the Al foil vicinity and the surface conductive agent amount (number of atoms) of the positive electrode mixture layer in this positive electrode was 2.4% (n = 3 average). Table 2 shows the specifications of the positive electrode.

(Example 2-2 and Example 2-3)
Except for adjusting the mixer stirring time (dispersion time) in the production of the positive electrode, the same operation as in Example 2-1 was repeated to obtain the positive electrode having the specifications shown in Table 2, and the laminated secondary battery of each example. Got.

(Comparative Example 2-1 to Comparative Example 2-3)
Except for adjusting the mixer stirring time (dispersion time) in the production of the positive electrode, the same operation as in Example 2-1 was repeated to obtain the positive electrode having the specifications shown in Table 2, and the laminated secondary battery of each example. Got.

(Example 3-1)
In the production of the positive electrode, 88.5 parts by weight of lithium-cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material, 7 parts by weight of ketjen black as the conductive agent, and polyvinylidene fluoride (PVdF) as the binder. The same procedure as in Example 1-1 was repeated except that 4.5 parts by weight were kneaded, NMP was added, and the mixture was stirred and dispersed in a mixer to obtain a positive electrode mixture slurry. An example laminate type secondary battery was obtained.
The difference in the amount of conductive agent (number of atoms) between the vicinity of the Al foil and the surface of the positive electrode mixture layer in this positive electrode was 2.6% (n = 3 average). Table 3 shows the specifications of the positive electrode.

(Example 3-2 to Example 3-5)
Except for adjusting the mixer stirring time (dispersion time) in the production of the positive electrode, the same operation as in Example 3-1 was repeated to obtain the positive electrode having the specifications shown in Table 3, and the laminated secondary battery of each example. Got.

(Comparative Example 3-1)
Except that the mixer stirring time (dispersion time) was adjusted in the production of the positive electrode, the same operation as in Example 3-1 was repeated to obtain the positive electrode having the specifications shown in Table 3, and the laminate type secondary battery of this example Got.

(Example 4-1)
In the production of the positive electrode, 85.5 parts by weight of lithium-cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material, 10 parts by weight of ketjen black as the conductive agent, and polyvinylidene fluoride (PVdF) as the binder. The same procedure as in Example 1-1 was repeated except that 4.5 parts by weight were kneaded, NMP was added, and the mixture was stirred and dispersed in a mixer to obtain a positive electrode mixture slurry. An example laminate type secondary battery was obtained.
Note that the difference in the amount of conductive agent (number of atoms) between the vicinity of the Al foil and the surface of the positive electrode mixture layer in this positive electrode was 1.9% (n = 3 average). Table 4 shows the specifications of the positive electrode.

(Example 4-2 to Example 4-4)
In the production of the positive electrode, except that the mixer stirring time (dispersion time) was adjusted, the same operation as in Example 4-1 was repeated to obtain the positive electrode having the specifications shown in Table 4, and the laminated secondary battery of each example. Got.

(Comparative Example 4-1 and Comparative Example 4-2)
In the production of the positive electrode, except that the mixer stirring time (dispersion time) was adjusted, the same operation as in Example 4-1 was repeated to obtain the positive electrode having the specifications shown in Table 4, and the laminated secondary battery of each example. Got.

[Performance evaluation]
Twenty laminated secondary batteries of each example were produced, and various battery performances measured under the following conditions were compared. The obtained result is shown to Tables 1-4 with the specification of the positive electrode of each example. Furthermore, the results of Tables 1 to 4 are shown in the graphs of FIGS.

(AC resistance)
The AC resistance (200 kHz) immediately after the production of the laminate type secondary battery was measured.

(First discharge capacity)
After charging at constant current and constant voltage at 0.2 C to 4.2 V (amount of current fully charged in 5 hours), the capacity of discharging 1 C to 3.0 V was measured after an open time.

(Load characteristics)
The retention of the 3C discharge capacity was measured and calculated based on the 0.2C discharge capacity.

(Cycle characteristics)
Each charge and discharge was 1 C, and the retention at 3 V cut-off was measured and calculated.

As shown in Tables 1-4 and FIGS. 4-7, the content of the conductive agent in the positive electrode mixture layer is 0.5% (Tables 1 and 4), 3% (Tables 2 and 5), 7% ( Table 3 and FIG. 6) In any of 10% (Table 4 and FIG. 7), the difference between the amount of conductive agent (number of atoms) in the vicinity of the metal foil and the amount of conductive agent (number of atoms) on the surface is 20%. If it does not exceed the range, sufficient initial discharge capacity, load characteristics, and cycle characteristics can be exhibited while maintaining low AC resistance.
In particular, when the content of the conductive agent in the positive electrode mixture layer is 10%, the difference in the conductive agent amount and each performance of the battery correspond significantly, and the difference is large even if the difference in the conductive agent amount exceeds 20%. As this happens, the increase in AC resistance and the decrease in the initial discharge capacity become significant.
As described above, the examples included in the scope of the present invention use the positive electrode that can suppress the increase in resistance in the positive electrode due to the increase in capacity, compared with the corresponding comparative examples. Increase in resistance is suppressed.
In addition, the initial discharge capacity, load characteristics, and cycle characteristics are excellent.

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

  In the above embodiment, the negative electrode mixture layer containing the negative electrode active material capable of occluding and releasing lithium ions in the metal foil functioning as the negative electrode current collector as described above is formed as the negative electrode. However, the present invention is not limited to this. That is, it is not particularly limited as long as it contains a negative electrode active material capable of inserting and extracting lithium ions, and a negative electrode active material layer containing only the negative electrode active material is formed on a metal foil that functions as a current collector. Even those that do not include a metal foil that functions as a current collector can be used, and the present invention can be similarly applied to such batteries.

  Further, in the above embodiment, the case where the separator 24 made of a microporous polyethylene film is used has been described. However, when a gel-like non-aqueous electrolyte is applied, it can have a role as a separator. The present invention can be similarly applied to such a battery.

  In the above embodiment, the case where the film-shaped exterior member 30 is used has been described. However, the battery having other shapes such as a so-called cylindrical shape, square shape, coin shape, and button shape using a can as the exterior member. Similarly, the present invention can be applied. Furthermore, it is applicable not only to a secondary battery but also to a primary battery.

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

It is sectional drawing explaining the metal foil vicinity and surface position of a positive mix layer. It is one Embodiment of the nonaqueous electrolyte secondary battery of this invention, Comprising: It is a disassembled perspective view which shows an example of a laminate type battery. FIG. 3 is a cross-sectional view taken along line II of the battery element 20 shown in FIG. 2. It is a graph which shows the result of each example shown in Table 1. 3 is a graph showing the results of each example shown in Table 2. It is a graph which shows the result of each example shown in Table 3. It is a graph which shows the result of each example shown in Table 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Positive electrode terminal, 12 ... Negative electrode terminal, 20 ... Battery element, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode mixture layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode mixture layer , 23 ... Nonaqueous electrolyte layer, 24 ... Separator, 25 ... Protective tape, 30 ... Exterior member, 31 ... Adhesive film, a ... Surface of positive electrode mixture layer, b ... Near positive electrode current collector

Claims (3)

A non-aqueous electrolyte comprising a metal foil functioning as a positive electrode current collector and a positive electrode mixture layer formed on one or both surfaces of the metal foil and containing a positive electrode active material capable of inserting and extracting lithium ions and a conductive agent A positive electrode for a secondary battery,
In the positive electrode mixture layer, the difference between the conductive agent amount (number of atoms) in the vicinity of the metal foil and the conductive agent amount (number of atoms) on the surface thereof is 20.0% or less, and the content of the conductive agent is A positive electrode for a non-aqueous electrolyte secondary battery, characterized by being 0.5 to 10%.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal foil is an aluminum foil, and the positive electrode active material is a composite oxide containing lithium and a transition metal element. A positive electrode for a non-aqueous electrolyte secondary battery; a negative electrode for a non-aqueous electrolyte secondary battery containing a negative electrode active material capable of occluding and releasing lithium ions; a non-aqueous electrolyte; a separator; and an exterior member that accommodates these. A non-aqueous electrolyte secondary battery comprising:
The positive electrode for a non-aqueous electrolyte secondary battery includes a metal foil that functions as a positive electrode current collector, a positive electrode active material that is formed on one or both sides of the metal foil, and that can occlude and release lithium ions, and a conductive agent. A positive electrode mixture layer,
In the positive electrode mixture layer, the difference between the conductive agent amount (number of atoms) in the vicinity of the metal foil and the conductive agent amount (number of atoms) in the surface portion is 20.0% or less, and the content of the conductive agent Is a non-aqueous electrolyte secondary battery characterized by being 0.5 to 10%.

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