JP2007335175A - Method of manufacturing coating composition for electrode mixture layer of nonaqueous electrolyte battery, electrode for nonaqueous electrolyte battery, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery capable of determining a suitable condition of a mixing step, and improving performance of a battery to be obtained, and to provide an electrode for the nonaqueous electrolyte battery and the nonaqueous electrolyte battery. <P>SOLUTION: In the method of manufacturing the coating composition for the electrode mixture layers of the nonaqueous electrolyte battery, at least an electrode active material, a conductive agent, and a binder are mixed, and then at least a solvent is added to a mixture composition for the electrode mixture layer to be obtained and dispersed. A zeta potential change rate (ζ<SB>1</SB>/ζ<SB>0</SB>× 100) defined by an absolute value (ζ<SB>0</SB>) of the zeta potential right after mixing and the absolute value (ζ<SB>1</SB>) of the zeta potential after the elapse of 24 to 27 hours after mixing is controlled to be 110% or less for a mixture composition for the electrode mixture layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery, an electrode for a nonaqueous electrolyte battery, and a nonaqueous electrolyte battery, and more specifically, a zeta of a kneaded composition for an electrode mixture layer. The present invention relates to a method for producing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery having a potential change rate set in a predetermined range, a nonaqueous electrolyte battery electrode and a nonaqueous electrolyte battery obtained using the same.

Unlike conventional non-aqueous secondary batteries that use lithium metal as a negative electrode, lithium ion secondary batteries prepare an electrode paint by dispersing an electrode active material in a solvent together with a binder and collect the paint. It is applied to a conductive substrate that also functions as a body, dried to form a coating-like mixture layer containing an active material, and a strip-like positive and negative electrode is produced.
The positive electrode paint contains a positive electrode active material, a binder, and a conductive agent. In such a method for preparing a positive electrode paint, a positive electrode paint is obtained through a kneading and dispersing process using a kneader of a type in which a stirring blade revolves while rotating in a kneading container (for example, see Patent Document 1). .
Among them, kneading is a step of kneading the positive electrode active material, the binder and the conductive agent at a high concentration. Thereby, the secondary particles of the powder are crushed and the powder is wetted with the solvent, so that the dispersion efficiency can be increased.
Since the solid content of the paint after dispersion is lowered to some extent, the dispersion state can be confirmed as a numerical value by a rheological measurement method.
JP-A-4-253157

However, since kneading is carried out at a high concentration, the viscosity is remarkably high. Therefore, it cannot be measured with a viscometer, and evaluation by a rheological method is difficult.
A conventional evaluation method in kneading is often judged by a torque current value applied to a stirring blade during kneading. However, this method cannot directly determine the paint state. Therefore, judgment of paint after kneading often relies on visual judgment.
Thus, since there was no index that can be judged numerically, it was not possible to elucidate suitable kneading conditions, and as a result, the causal relationship with the obtained battery performance was not fully elucidated.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to determine a suitable condition for the kneading step numerically and to improve the performance of the battery obtained. It is providing the manufacturing method of the coating composition for electrode mixture layers of an electrolyte battery, the electrode for nonaqueous electrolyte batteries obtained by this, and a nonaqueous electrolyte battery.

  As a result of intensive studies to achieve the above object, the present inventor has focused on the zeta potential and measured the zeta potential of the kneaded composition for the electrode mixture layer, and the zeta potential change when the zeta potential changes When the rate is set within a predetermined range, the discharge capacity maintenance rate of the obtained lithium ion secondary battery is improved, and the present invention has been completed.

That is, in the method for producing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery according to the present invention, at least an electrode active material, a conductive agent and a binder are kneaded, and then the obtained kneaded composition for an electrode mixture layer In the method for producing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery in which at least a solvent is added and dispersed in the product, the absolute value of the zeta potential immediately after kneading (ζ ₀ ) for the electrode mixture layer kneading composition The zeta potential change rate (ζ ₁ / ζ ₀ × 100) defined by the absolute value of the zeta potential (ζ ₁ ) after elapse of 24 to 27 hours after kneading is controlled to 110% or less.

The electrode for a non-aqueous electrolyte battery according to the present invention is a non-aqueous electrolyte battery formed by applying a coating composition for an electrode mixture layer containing an electrode active material, a conductive agent, a binder and a solvent to an electrode current collector and drying it. In the electrode for a water electrolyte battery, at least a solvent is added to the kneaded composition for an electrode mixture layer obtained by kneading at least the electrode active material, the conductive agent and the binder. The kneaded composition for an electrode mixture layer obtained by dispersing has an absolute value of zeta potential (ζ ₀ ) immediately after kneading and an absolute value of zeta potential (ζ ₁ after 24 to 27 hours after kneading). ) And the zeta potential change rate (ζ ₁ / ζ ₀ × 100) defined by:

Furthermore, the nonaqueous electrolyte battery of the present invention includes a positive electrode and a negative electrode, a nonaqueous electrolyte, a separator, and an exterior member that accommodates these, and an electrode mixture layer formed on the electrode current collector by the positive electrode and the negative electrode. In the non-aqueous electrolyte battery having the above, an electrode mixture layer coating composition is used for forming at least one of the positive electrode and negative electrode electrode mixture layers, and the electrode mixture layer coating composition is at least an electrode active material. The electrode mixture layer kneaded composition obtained by kneading the conductive agent and the binder is obtained by adding and dispersing at least a solvent. The zeta potential change rate (ζ ₁ / ζ ₀ × 100) defined by the absolute value of the zeta potential (ζ ₀ ) and the absolute value of the zeta potential (ζ ₁ ) after 24 to 27 hours after kneading is 110% or less. It is characterized by being.

  According to the present invention, since the zeta potential change rate when the zeta potential changes is set within a predetermined range, the suitable conditions for the kneading step can be judged numerically, and the performance of the obtained battery can be improved. The manufacturing method of the coating composition for electrode mixture layers of a water electrolyte battery, the electrode for nonaqueous electrolyte batteries obtained by this, and a nonaqueous electrolyte battery can be provided.

Hereinafter, the manufacturing method of the coating composition for electrode mixture layers of the nonaqueous electrolyte battery of the present invention will be described in detail. In the present specification, “%” represents mass percentage unless otherwise specified.
As described above, the method for producing a coating composition for an electrode mixture layer of a non-aqueous electrolyte battery according to the present invention comprises kneading at least an electrode active material, a conductive agent, and a binder to obtain a kneaded composition for an electrode mixture layer. Next, at least a solvent is added to the obtained kneaded composition for an electrode mixture layer and dispersed to obtain a coating composition for an electrode mixture layer.
In this production method, the kneaded composition for an electrode mixture layer has an absolute value of zeta potential (ζ ₀ ) immediately after kneading and an absolute value of zeta potential (ζ ₁ ) 24 to 27 hours after kneading. The zeta potential change rate (ζ ₁ / ζ ₀ × 100) defined by
The method for producing a coating composition for an electrode mixture layer, which undergoes a kneading step to obtain such a kneading composition for an electrode mixture layer, improves the performance of electrodes and batteries using the coating composition produced using the coating composition. Can be. For example, when applied to a lithium ion secondary battery, it is possible to improve the discharge capacity maintenance rate during repeated discharge.

Here, the “kneaded composition for an electrode mixture layer” is obtained by kneading an electrode active material, a conductive agent and a binder, and includes those containing some solvent.
The “electrode mixture layer coating composition” includes an electrode active material, a conductive agent, a binder and a solvent.

The usable electrode active material is not particularly limited as long as it can cause an electrode reaction, that is, a positive electrode reaction or a negative electrode reaction, and various kinds of materials can be exemplified. It will be described later.
Further, usable conductive agents are not particularly limited as long as the conductivity during use of the electrode can be maintained, and examples thereof include conventionally known graphite, carbon black, and carbon fiber (VGCF). be able to.
In addition, the usable binder is not particularly limited as long as it can maintain the shape maintaining property during the production or use of the electrode. For example, conventionally known polyvinyl pyrrolidone and polyvinylidene fluoride (PVdF) are known. Fluororesin such as styrene butadiene resin.
Furthermore, as a usable solvent, sufficient kneading and dispersion are required at the time of preparing the electrode mixture layer kneading composition and the electrode mixture layer coating composition, and sufficient at the time of electrode preparation. Although it will not specifically limit if it can be made to dry, For example, conventionally well-known N-methyl- 2-pyrrolidone (NMP) etc. can be mentioned.

Further, the "absolute value of the zeta potential immediately after the kneading (zeta _0)", after the kneading step completion, the absolute value of the zeta potential measured rapidly by a predetermined procedure (zeta _0).
Further, the “absolute value of zeta potential (ζ ₀ ) after the elapse of 24 to 27 hours after the kneading” means that it is allowed to stand for 24 to 27 hours (for example, 24 hours) after the kneading process, It is the absolute value (ζ ₁ ) of the zeta potential measured by the procedure.
In the production method of the present invention, for example, the kneaded composition for the electrode mixture layer may be collected, and the zeta potential change rate of one sample collected may be calculated. Further, the second and subsequent zeta potential measurements may be omitted by feeding back kneading and other processing conditions that can realize a predetermined zeta potential change rate as necessary.
The above “predetermined procedure” means that the sample after completion of the kneading step, or after the kneading step has been allowed to stand for a predetermined time (for example, 24 hours) is put into a solvent, stirred, and measured with a zeta electrometer. To do. For example, when using a zeta electrometer (manufactured by Microtech Nichion Co., Ltd., ZEECOM), 5 mg of a sample may be put into 200 mL of NMP and measured while stirring until the liquid color in the flask becomes uniform. However, the present invention is not necessarily limited to this.

In the kneaded composition for the electrode mixture layer, the zeta potential change rate (ζ ₁ / ζ ₀ × 100 defined by the absolute value of the zeta potential (ζ ₀ ) and the absolute value of the zeta potential (ζ ₁ ) described above. ) Needs to be 110% or less, preferably 100 to 110%, more preferably 100 to 105%.

Moreover, although it does not specifically limit in the manufacturing method of the coating composition for electrode mixture layers of the nonaqueous electrolyte battery of this invention, It is preferable to knead | mix for 70 to 90 minutes.
If the kneading time is less than 70 minutes, the kneading may not be sufficiently performed. If the kneading time exceeds 90 minutes, the electrode active material may break due to excessive kneading, resulting in a decrease in battery performance. there is a possibility.

Furthermore, in the method for producing the coating composition for the electrode mixture layer of the nonaqueous electrolyte battery of the present invention, although not particularly limited, the dispersion is preferably performed for 35 to 360 minutes, and is performed for 45 to 120 minutes. Is more preferable.
If the dispersion time is less than 35 minutes, the charge / discharge cycle characteristics may be deteriorated or the capacity may be lowered at low temperatures. If the dispersion time exceeds 360 minutes, safety due to cracking of the active material ( Heating).

Furthermore, in the method for producing a coating composition for an electrode mixture layer of a nonaqueous electrolyte battery according to the present invention, the thixotropy value of the resulting coating composition for an electrode mixture layer is 12, 000 Pa / s or less is preferable.
When the thixotropy value exceeds 12,000 Pa / s, the charge / discharge cycle characteristics may be deteriorated or the capacity may be lowered at low temperatures.
The “thixotropic value” may be measured, for example, from a hysteresis loop using a parallel disk viscometer (rheometer).

Next, the electrode for a nonaqueous electrolyte battery of the present invention will be described in detail.
As described above, the electrode for a non-aqueous electrolyte battery of the present invention is obtained by applying a coating composition for an electrode mixture layer containing an electrode active material, a conductive agent, a binder and a solvent to an electrode current collector and drying it. Become.
And this coating composition for electrode mixture layers knead | mixes at least an electrode active material, a electrically conductive agent, and a binder, and the absolute value ((zeta) ₀ ) of zeta potential immediately after kneading | mixing and 24-27 hours pass after kneading | mixing. give the absolute value (zeta ₁₎ and zeta potential change rate defined from _{(ζ 1 / ζ 0 × 100} ) is electrode mixture layer kneaded composition is not more than 110% of the zeta potential, then the resulting It is obtained by adding and dispersing at least a solvent to the kneaded composition for the electrode mixture layer.
Such an electrode can improve the performance of a battery obtained using the electrode. For example, when applied to a lithium ion secondary battery, it is possible to improve the discharge capacity maintenance rate during repeated discharge.

Next, the battery of the present invention will be described in detail by taking a lithium ion secondary battery as an example.
FIG. 1 is an exploded perspective view showing an example of a laminated battery as an embodiment of a battery of the present invention, particularly a lithium ion secondary battery.
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-like 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 a laminated film having another structure, a polymer film such as polypropylene, a metal film, or the like instead of the above-described laminated film.
Here, the general structure of an exterior member can be represented by the laminated structure of an exterior layer / metal foil / sealant layer (however, the exterior layer and the sealant layer may be composed of a plurality of layers), and the above. In this example, the nylon film corresponds to the exterior layer, the aluminum foil corresponds to the metal foil, and the polyethylene film corresponds to the sealant layer.
In addition, as metal foil, it is sufficient if it functions as a moisture-permeable barrier film, and not only aluminum foil but also stainless steel foil, nickel foil and plated iron foil can be used, but it is thin and lightweight. Thus, an aluminum foil excellent in workability can be suitably used.

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

  FIG. 2 is a 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 nonaqueous electrolyte composition layer 23 and a separator 24 as an example of a nonaqueous electrolyte. The outermost peripheral part is protected by a protective tape 25. Further, at least one of the positive electrode 21 and the negative electrode 22 is composed of the electrode for a non-aqueous electrolyte battery of the present invention.

Here, the positive electrode 21 has, for example, 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. 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.
The positive electrode current collector 21A is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

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

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

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

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), and solid solutions thereof (Li (Ni _x Co _y Mn _{z) O} 2), 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 their solid solutions _{(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)).

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.

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

Furthermore, examples of the negative electrode material capable of inserting and extracting 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 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 metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), Examples include gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr), and yttrium (Y).
Among them, the 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.

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

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

The nonaqueous electrolyte composition layer 23 is, for example, a dispersion or solution of an electrolyte in a nonaqueous medium or a solid electrolyte. In addition to a nonaqueous electrolyte solution in which an electrolyte is dissolved in a nonaqueous solvent such as propylene carbonate, the electrolyte Is dissolved in a non-aqueous dispersion medium (polymer such as polyvinylidene fluoride) in a gel form and a solid electrolyte having lithium ion conductivity.
Such a non-aqueous electrolyte can be roughly classified into a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solution, a gel electrolyte obtained by dissolving an electrolyte in a non-aqueous dispersion medium that forms a gel, and a solid electrolyte.

Here, as an electrolyte dissolved in a non-aqueous solvent or dispersed in a gel-like non-aqueous dispersion medium, various lithium salts such as LiCl, LiBr, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ or LiB (C ₆ H ₅ ) ₄ and a mixture of these arbitrarily combined, etc. Of these, it is particularly preferable to use LiPF ₆ or LiBF ₄ .

As the non-aqueous solvent, as in the conventional non-aqueous lithium battery, an aprotic solvent such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, γ-butyrolactan, sulfolane, methylsulfolane, 1 , 2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate, Dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, propionitrile, acetonitrile, anisole, diethyl ether, acetate ester, butyrate ester and propionate ester Etc.
In particular, from the viewpoint of voltage stability, for example, cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate and diethyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, ethyl acetate and propion It is desirable to use chain esters such as methyl acid, ethers such as tetrahydrofuran and 1,2-dimethoxyethane, and the like.
Moreover, these non-aqueous solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

On the other hand, as the non-aqueous dispersion medium that forms a gel, various polymers can be used as long as they absorb the non-aqueous electrolyte and gel. For example, a fluorine polymer such as polyvinylidene fluoride or polyvinylidene fluoride-CO-hexafluoropropylene, an ether polymer such as polyethylene oxide or a crosslinked product thereof, or polyacrylonitrile can be used. In particular, it is desirable to use a fluorine-based polymer from the viewpoint of redox stability. The molecular weight of these polymers is suitably about 300,000 to 800,000.
The dispersion of the electrolyte in the polymer can be typically performed by dissolving a polymer such as polyvinylidene fluoride in a nonaqueous electrolytic solution in which the electrolyte is dissolved in a nonaqueous solvent, and making it into a sol.

Furthermore, as the solid electrolyte, any inorganic solid electrolyte or polymer solid electrolyte can be used as long as the material has lithium ion conductivity. Examples of inorganic solid electrolytes include crystalline solid electrolytes such as lithium nitride (Li ₃ N) and lithium iodide (LiI), LiI · Li ₂ S · P ₂ S ₆ glass, and LiI · Li ₂ S · B ₂ S. Examples thereof include amorphous solid electrolytes typified by lithium ion conductive glass such as _6- series glass. The polymer solid electrolyte is composed of an electrolyte salt and a polymer compound that dissolves the electrolyte salt. The polymer compound is an ether polymer such as polyethylene oxide or the same cross-linked product, a polymethacrylate ester system, an acrylate system, or the like. Alternatively, it can be used by being copolymerized and mixed in the molecule.

  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, a coating composition for an electrode mixture layer for a positive electrode is produced by the method for producing a coating composition for an electrode mixture layer as described above, using the rate of change in zeta potential as an index.
Next, the positive electrode mixture layer coating composition is applied to the positive electrode current collector 21A, dried, and compression-molded to form the positive electrode mixture layer 21B, thereby producing the positive electrode 21.

Moreover, the coating composition for electrode mixture layers for negative electrodes is produced by the method for producing a coating composition for electrode mixture layers as described above in the same manner as in the case of the positive electrode.
Next, this negative electrode mixture layer coating composition is applied to the negative electrode current collector 22A, dried, and compression molded to form the negative electrode mixture layer 22B, thereby producing the negative electrode 22.

  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, the non-aqueous electrolyte described above is prepared and injected into the wound electrode body from the opening of the exterior member 30, and the opening of the exterior member 30 is heat-sealed and sealed. Thereby, the nonaqueous electrolyte composition layer 23 is formed, and the secondary battery shown in FIGS. 1 and 2 is completed.

In addition, you may manufacture this secondary battery as follows.
For example, instead of injecting the nonaqueous electrolyte composition after producing the wound electrode body, the nonaqueous electrolyte composition is applied on the positive electrode 21 and the negative electrode 22 or the separator 24 and then wound, and the exterior member 30 is wound. You may make it enclose inside.

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 composition 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 composition layer 23.
Here, the electrode mixture layer in the electrode is excellent in the mixed state. Therefore, the battery performance of the secondary battery is not greatly deteriorated during charging and discharging, and the discharge capacity maintenance rate during repeated charging and discharging is improved.

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 cylindrical battery, and its performance was evaluated.

Example 1
Carbon black (bulk specific gravity: 22-35 g / L) (0.76 parts by mass) as a conductive agent was charged into a mixer (PVM-1600-2D Planetary Despa, manufactured by Asada Tekko Co., Ltd.), and then prepared in advance. An NMP solution of PVdF (concentration: 13%) (17.44 parts by mass) as a binder solution was charged, and then preliminary kneading (preliminary kneading time: 20 minutes) was performed.
After preliminary kneading, carbon black (apparent density: 0.09 to 0.13 g / cm ³ ) (0.76 parts by mass) as a conductive agent and lithium cobalt acid composite oxide (71.78 parts by mass) as an electrode active material. Part) and then kneading (kneading time: 90 minutes) to obtain a kneaded composition for an electrode mixture layer.
And when the zeta potential of the kneaded composition for electrode mixture layers immediately after kneading was measured with a zeta potentiometer (manufactured by Microtech Nichion Co., Ltd., ZEECOM), it was −160 mV at room temperature (temperature 23 ° C.). In addition, when the zeta potential of the kneaded composition for electrode mixture layers after one day (24 hours) after kneading was measured in the same manner, it was -162 mV at room temperature (temperature 23 ° C).
Therefore, the zeta potential change rate of the kneaded composition for the electrode mixture layer was 101.3%.
NMP (7.08 parts by mass) as a solvent was added to the obtained kneaded composition for electrode mixture layer and dispersed (dispersion time: 45 minutes) to obtain a coating composition for electrode mixture layer.
In addition, when the thixotropy value of the coating composition for electrode mixture layers was measured with a rheometer (manufactured by HAAKE), 10950 Pa / at 0-300 (1 / s), 60 s / 300-0 (1 / s), 60 s. s.

The obtained electrode mixture layer coating composition was uniformly applied on both sides of a 20 μm thick aluminum foil serving as a positive electrode current collector and dried to form a positive electrode mixture layer of 40 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, and a positive electrode terminal was further attached.
Next, 97 parts by mass of graphite as a negative electrode active material and 3 parts by mass of PVdF as a binder were homogeneously mixed, and NMP was added to obtain a coating composition for a negative electrode mixture layer. Next, the obtained negative electrode mixture layer coating composition 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 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 negative electrode, and a negative electrode terminal was further attached.

The positive electrode and the negative electrode and a separator made of a microporous polypropylene film having a thickness of 20 μm were prepared, and the negative electrode, the separator, the positive electrode, and the separator were laminated in this order and wound many times to produce a wound electrode body. After producing the wound electrode body, the wound electrode body is sandwiched between a pair of insulating plates, the negative electrode terminal is welded to the bottom of the battery can, the positive electrode terminal is welded to the protrusion of the safety valve mechanism, and nickel plated iron It was stored inside the battery can. Next, a non-aqueous electrolyte was injected into the battery can. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a ratio of 1 mol / l in a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1 was used. Thereafter, the battery lid was caulked to the battery can through the insulating sealing gasket, and the safety valve mechanism, the heat sensitive resistance element, and the battery lid were fixed to obtain the cylindrical battery of this example.

(Example 2)
Except for the kneading time of 70 minutes, the same operation as in Example 1 was repeated to obtain a cylindrical battery of this example.
In addition, the zeta potential change rate of the kneaded composition for the electrode mixture layer was 105.2%.
Moreover, the thixotropy value of the coating composition for electrode mixture layers was 11457 Pa / s.

(Comparative Example 1)
Except for the kneading time being 50 minutes, the same operation as in Example 1 was repeated to obtain a cylindrical battery of this example.
The zeta potential change rate of the electrode mixture layer kneaded composition was 120.5%.
Moreover, the thixotropy value of the coating composition for electrode mixture layers was 13263 Pa / s.

(Comparative Example 2)
Except for the kneading time being 30 minutes, the same operation as in Example 1 was repeated to obtain a cylindrical battery of this example.
The zeta potential change rate of the electrode mixture layer kneaded composition was 240.0%.
Moreover, the thixotropy value of the coating composition for electrode mixture layers was 18210 Pa / s.
Table 1 shows the specifications of the electrode mixture layer coating composition in each of the above examples.

[Performance evaluation]
The cylindrical battery of each example was charged for 2 hours at a maximum of 4.2 V at 23 mA in a 23 ° C. environment, then rested for 30 minutes, and repeatedly discharged until reaching 2.5 V at 2.2 mA. The subsequent discharge capacity was measured. The discharge capacity retention ratio after 500 cycles is calculated from the discharge capacity after 500 cycles and the discharge capacity after 1 cycle, and the obtained results are also shown in Table 1.

From Table 1, it was found that the longer the kneading time, the larger the absolute value of the zeta potential. In addition, a difference in dispersibility appeared in the thixotropy value due to a change in zeta potential.
The change in the zeta potential at each kneading time is because the particles are wetted by kneading and electrostatic repulsion appears as the zeta potential. Moreover, the capacity maintenance rate at the time of charging / discharging is favorable in order with the absolute value of a zeta battery. Furthermore, in Examples 1 and 2, a rapid decrease in capacity maintenance rate was confirmed.
When comparing the zeta potential change rate of the kneaded composition for electrode mixture layer immediately after kneading and after 1 day (24 hours), compared to Examples 1 and 2 included in the scope of the present invention, Comparative Examples 1 and 2 are significantly higher. This is presumably because the material did not get wet with the solvent during the kneading, so that the material became wet and the absolute value of the zeta potential increased with time.
From the above, at least an electrode active material, a conductive agent and a binder are kneaded to obtain a kneaded composition for an electrode mixture layer, and then at least a solvent is added to the obtained kneaded composition for an electrode mixture layer and dispersed. In the method for producing an electrode mixture layer coating composition, an electrode mixture layer coating composition is obtained by kneading the absolute value of the zeta potential (ζ _t0 ) immediately after kneading of the obtained electrode mixture layer kneading composition. The kneading step is defined by setting the zeta potential change rate (ζ _t1 / ζ _t0 × 100) defined from the absolute value of the zeta potential (ζ _t1 ) after 24 to 27 hours later to 110% or less. As a result, the performance of the obtained battery can be improved. For example, when applied to a lithium ion secondary battery, it is possible to improve the discharge capacity maintenance rate during repeated discharge.
Note that the absolute value of the zeta potential can vary depending on the material, the solvent, and the like, but if kneading is sufficient, the change over time is reduced regardless of the material and the solvent.
Moreover, the solid content concentration of the kneaded composition for the electrode mixture layer is usually 83% or more, and preferably 83 to 85%. Furthermore, the solid content concentration of the electrode mixture layer coating composition is usually 77% or less, preferably 74 to 77%.

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, a case where a stacked battery element in which a plurality of positive electrodes and negative electrodes are stacked is described, but a flat battery element in which a pair of positive electrodes and negative electrodes are stacked, or a positive electrode and a negative electrode are provided. The present invention can also be applied to a case where battery elements stacked and wound are provided.
In the above-described embodiment, the battery having a so-called cylindrical shape using a film-shaped exterior member 30 or a can for the exterior member 30 has been described, but a so-called square shape using a can for the exterior member, The present invention can be similarly applied to batteries having other shapes such as a coin type and a button type. Furthermore, it is applicable not only to a secondary battery but also to a primary battery.

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

1 is an exploded perspective view showing an example of a laminated battery according to an embodiment of the battery of the present invention. It is sectional drawing along the II line of the battery element shown in FIG.

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 ... Non-aqueous electrolyte composition layer, 24 ... Separator, 25 ... Protective tape, 30 ... Exterior member, 31 ... Adhesion film

Claims (6)

A coating composition for an electrode mixture layer of a nonaqueous electrolyte battery in which at least an electrode active material, a conductive agent and a binder are kneaded, and then at least a solvent is added to and dispersed in the obtained kneaded composition for an electrode mixture layer. In the manufacturing method,
About the kneading composition for electrode mixture layers, the zeta potential change rate defined by the absolute value of the zeta potential immediately after kneading (ζ ₀ ) and the absolute value of the zeta potential after lapse of 24 to 27 hours (ζ ₁ ). (Ζ ₁ / ζ ₀ × 100) is controlled to 110% or less,
The manufacturing method of the coating composition for electrode mixture layers of a nonaqueous electrolyte battery characterized by the above-mentioned.   The said kneading | mixing is performed for 70 to 90 minutes, The manufacturing method of the coating composition for electrode mixture layers of Claim 1 characterized by the above-mentioned.   The said dispersion is performed for 35 to 360 minutes, The manufacturing method of the coating composition for electrode mixture layers of Claim 1 characterized by the above-mentioned.   The method for producing a coating composition for an electrode mixture layer according to claim 1, wherein the thixotropic value of the coating composition for the electrode mixture layer is 12,000 Pa / s or less. In the electrode for a non-aqueous electrolyte battery formed by applying a coating composition for an electrode mixture layer containing an electrode active material, a conductive agent, a binder, and a solvent to an electrode current collector and drying it,
The electrode mixture layer coating composition is obtained by adding and dispersing at least a solvent to the electrode mixture layer kneaded composition obtained by kneading at least the electrode active material, the conductive agent and the binder. Yes,
The kneading composition for the electrode mixture layer has a zeta potential change defined by the absolute value of the zeta potential immediately after kneading (ζ ₀ ) and the absolute value of the zeta potential after the lapse of 24 to 27 hours (ζ ₁ ). The rate (ζ ₁ / ζ ₀ × 100) is 110% or less. In a nonaqueous electrolyte battery comprising a positive electrode and a negative electrode, a nonaqueous electrolyte, a separator, and an exterior member that accommodates these, and having an electrode mixture layer formed on the electrode current collector by the positive electrode and the negative electrode,
The electrode mixture layer coating composition is used for forming the positive electrode and / or negative electrode mixture layer,
The electrode mixture layer coating composition is obtained by adding and dispersing at least a solvent to the electrode mixture layer kneaded composition obtained by kneading at least the electrode active material, the conductive agent and the binder. Yes,
The kneading composition for an electrode mixture layer has a zeta potential change rate defined by an absolute value of zeta potential immediately after kneading (ζ ₀ ) and an absolute value of zeta potential after lapse of 24 to 27 hours (ζ ₁ ). (Ζ ₁ / ζ ₀ × 100) is 110% or less.

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