JP7058525B2 - Electrodes for lithium-ion batteries - Google Patents

Description

The present invention relates to an electrode for a lithium ion battery and a method for manufacturing an electrode for a lithium ion battery.

In recent years, there has been an urgent need to reduce carbon dioxide emissions in order to protect the environment. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of secondary batteries for driving motors, which hold the key to their practical application, is earnest. It is done. As a secondary battery, a lithium ion battery that can achieve high energy density and high output density is attracting attention.

Patent Document 1 discloses a general method for manufacturing an electrode for a lithium ion battery. That is, it is a method in which a powdered active material, an electrode mixture containing a binder, and water or an organic solvent are mixed to form a mixture slurry, which is applied to a current collector on a sheet and dried. ..
Patent Document 1 describes as a problem in the above method that the powder material is significantly settled in the mixture slurry and it is difficult to maintain a uniform state.

Patent Document 1 proposes a method of preventing the powder material from settling by increasing the viscosity of the mixture slurry, and discloses that a thixotropy-imparting agent is used as a means of increasing the viscosity. Examples of the thixotropy-imparting agent include polyethylene oxide, fatty acid amide, fatty acid glyceride, and smectite.

Japanese Unexamined Patent Publication No. 2001-266855

The present inventors are studying a method for manufacturing an electrode different from a general method for manufacturing an electrode for a lithium ion battery as described in Patent Document 1.
This method is a method of applying an electrolytic solution slurry containing an electrode active material and an electrolytic solution to a current collector to prepare an electrode without drying, which is a simpler step as compared with the method described in Patent Document 1. The electrode can be manufactured with. Further, in this method, since the binder is not contained in the electrode, the ratio of the electrode active material can be increased, and the energy density of the electrode can be increased.

The present inventors have been studying preparing an electrolytic solution slurry containing an electrode active material and an electrolytic solution as described above and applying it to a current collector. As a result, a conventional method is used for an electrolytic solution slurry. It was found that the sedimentation of the electrode active material could not be prevented.
The present inventors presume that the effect of preventing sedimentation by the thixotropic agent as described in Patent Document 1 is not exhibited in the presence of a lithium salt as an electrolyte contained in the electrolytic solution.

The present invention has been made in view of the above problems, and is an electrode for a lithium ion battery and an electrode having a composition suitable for producing an electrode using an electrolytic solution slurry by preventing sedimentation of the electrode active material. It is an object of the present invention to provide a method for manufacturing an electrode for a lithium ion battery using an electrolytic solution slurry in which sedimentation of an active material is prevented.

The present inventors have arrived at the present invention as a result of diligent studies to solve the above problems.
That is, the present invention contains an electrode active material, an electrolytic solution containing a lithium salt as an electrolyte, and the compounds of the following (a) and / or (b), and is the sum of the compounds of the above (a) and (b). An electrode for a lithium ion battery characterized by having a weight of 0.1 to 2% by weight based on the electrode active material; an electrode active material, an electrolytic solution containing a lithium salt as an electrolyte, the following (a) and /. Alternatively, an electrolytic solution slurry containing the compound of (b) and having a total weight of the compounds of (a) and (b) of 0.1 to 2% by weight with respect to the electrode active material is applied to the current collector. The present invention relates to a method for manufacturing an electrode for a lithium ion battery, which comprises a step of construction.
(A) Cellulose acetate propionate (b) The number of repetitions of polyethylene glycol or its monoalkyl ether (meth) acrylate (b1) having an oxyethylene unit repetition number of 8 to 14 and the number of repetitions of oxyethylene unit are A copolymer containing polyethylene glycol (2 to 4) or (meth) acrylate (b2) of a monoalkyl ether thereof as an essential constituent monomer.

The electrode for a lithium ion battery of the present invention contains the compound of (a) and / or (b), and the total weight of the compounds of (a) and (b) is 0.1 with respect to the electrode active material. ~ 2% by weight. The compounds (a) and (b) can prevent the electrode active material from settling even in the presence of a lithium salt as an electrolyte. Therefore, the electrode for a lithium ion battery having such a composition is an electrode for a lithium ion battery having a composition suitable for producing an electrode using an electrolytic solution slurry by preventing the electrode active material from settling.
Further, in the method for producing an electrode for a lithium ion battery of the present invention, the compound of the above (a) and / or (b) is contained, and the total weight of the compounds of the above (a) and the above (b) is used as the electrode active material. On the other hand, an electrolytic solution slurry having an amount of 0.1 to 2% by weight is used. Since this electrolyte slurry does not cause the problem of sedimentation of the electrode active material even in the presence of a lithium salt as an electrolyte, it has excellent stability over time, and stabilizes the quality of the electrolyte slurry to form a current collector. It becomes possible to paint. Therefore, the thickness and characteristics of the electrode obtained after coating the electrolytic solution slurry are stable, and the quality of the electrode can be improved.

Hereinafter, the present invention will be described in detail.
The electrode for a lithium ion battery of the present invention is characterized by containing an electrode active material, an electrolytic solution containing a lithium salt as an electrolyte, and the following compounds (a) and / or (b).
(A) Cellulose acetate propionate (b) The number of repetitions of polyethylene glycol or its monoalkyl ether (meth) acrylate (b1) having an oxyethylene unit repetition number of 8 to 14 and the number of repetitions of oxyethylene unit are A copolymer containing polyethylene glycol (2 to 4) or (meth) acrylate (b2) of a monoalkyl ether thereof as an essential constituent monomer.

The electrode active material may be a positive electrode active material or a negative electrode active material. When the electrode active material is a positive electrode active material, the electrode for a lithium ion battery becomes a positive electrode, and when the electrode active material is a negative electrode active material, the electrode for a lithium ion battery becomes a negative electrode.

As the positive electrode active material, the positive electrode active material is a composite oxide of lithium and a transition metal {composite oxide having one transition metal element (LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO ₂ , LiMn ₂ O ₄ , etc.). ), Composite oxides with two transition metal elements (eg LiFeMnO ₄ , LiNi _1-x Co _x O ₂ , LiMn _{1-y Coy} O ₂ , LiNi _1/3 Co _1/3 Al _1/3 O ₂ ) And LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) and composite oxides containing three or more transition metal elements [eg LiM _{a M'b} M'c O ₂ (M, _M'and M''Is a different transition metal element and satisfies a + b + c = 1. For example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ )] etc.}, Lithium-containing transition metal phosphate (eg LiFePO ₄ , LiCoPO). ₄ , LiMnPO ₄ and LiNiPO ₄ ), transition metal oxides (eg MnO ₂ and V ₂ O ₅ ), transition metal sulfides (eg MoS ₂ and TiS ₂ ) and conductive polymers (eg polyaniline, polypyrrole, polythiophene, polyacetylene). , Poly-p-phenylene and polyvinylcarbazole) and the like, and two or more thereof may be used in combination.
The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is replaced with another transition metal.

As the negative electrode active material, the negative electrode active material includes carbon-based materials [for example, graphite, refractory carbon, amorphous carbon, resin fired body (for example, phenol resin, furan resin, etc. fired and carbonized), cokes, etc. (For example, pitch coke, needle coke, petroleum coke, etc.), silicon carbide, carbon fiber, etc.], conductive polymers (for example, polyacetylene and polypyrrole, etc.), silicon-based compounds (silicon, silicon oxide (SiOx), Si—C composites, etc.) , Si—Al alloys, Si—Li alloys, Si—Ni alloys, Si—Fe alloys, Si—Ti alloys, Si—Mn alloys, Si—Cu alloys and Si—Sn alloys), metals (tin, aluminum, zirconium and Titanium, etc.), metal oxides (titanium oxides, lithium-titanium oxides, silicon oxides, etc.) and metal alloys (eg, Li-Sn alloys, Li-Al alloys, Li-Al-Mn alloys, etc.), etc. Examples thereof include a mixture with a carbon-based material.
The Si—C composite includes silicon particles, silicon oxide particles whose surface is coated with carbon and / or silicon carbide, and the like.
Among the negative electrode active materials, those that do not contain lithium or lithium ions inside may be pre-doped with a part or all of the active materials containing lithium or lithium ions in advance.

The electrode active material may be the electrode active material itself, and is a coated electrode active material coated with an electrode coating layer containing a polymer compound in which a part or all of the surface of the electrode active material is a coating resin. Although it may be present, it is preferably a coated electrode active material.
When the surface of the electrode active material is coated with the electrode coating layer, it becomes easy to keep the distance between the electrode active materials constant, and it becomes easy to maintain the conductive path, which is preferable.

The electrode coating layer contains a polymer compound which is a coating resin. Further, if necessary, a conductive auxiliary agent described later may be further contained.
In the coated electrode active material, a part or all of the surface of the electrode active material is coated with an electrode coating layer containing a polymer compound, but in the electrode active material molded body, for example, a coated electrode. Even if the active materials come into contact with each other, the electrode coating layers do not irreversibly adhere to each other on the contact surface due to the coating resin.

Examples of the polymer compound constituting the electrode coating layer include thermoplastic resins and thermosetting resins, and examples thereof include the lithium ion battery active material coating resin described in International Publication No. 2015/005117.

The electrode coating layer preferably further contains a conductive auxiliary agent.
The conductive auxiliary agent is selected from materials having conductivity, and specifically, carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.)], PAN-based carbon. Carbon fibers such as fibers and pitch-based carbon fibers, carbon nanofibers, carbon nanotubes, and metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.] can be used.
These conductive auxiliaries may be used alone or in combination of two or more. Moreover, you may use these alloys or metal oxides. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and mixtures thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is more preferable. Further, as these conductive aids, a conductive material (a metal one among the above-mentioned conductive materials) may be coated around a particle-based ceramic material or a resin material by plating or the like. Polypropylene resin kneaded with graphene is also preferable as a conductive auxiliary agent.

The average particle size of the conductive auxiliary agent is not particularly limited, but is preferably 0.01 to 10 μm, preferably 0.02 to 5 μm, from the viewpoint of the electrical characteristics of the electrode for the lithium ion battery. It is more preferably 0.03 to 1 μm, and even more preferably 0.03 to 1 μm. In the present specification, the particle diameter of the conductive auxiliary agent means the maximum distance L among the distances between arbitrary two points on the contour line of the particles formed by the conductive auxiliary agent. As the value of the "average particle size of the conductive auxiliary agent", the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of is adopted.

The shape (form) of the conductive auxiliary agent is not limited to the particle form, and may be a form other than the particle form, and may be, for example, a fibrous conductive auxiliary agent.
As the fibrous conductive aid, the surface of a conductive fiber formed by uniformly dispersing a metal having good conductivity or graphite in a synthetic fiber, a metal fiber obtained by fiberizing a metal such as stainless steel, or an organic fiber can be used. Examples thereof include conductive fibers coated with metal, conductive fibers in which the surface of an organic substance is coated with a resin containing a conductive substance, and the like.
The average fiber diameter of the fibrous conductive aid is preferably 0.1 to 20 μm.

When a coated electrode active material is used as the electrode active material, for example, a polymer solution containing a polymer compound is applied over 1 to 90 minutes in a state where the electrode active material is placed in a universal mixer and stirred at 30 to 50 rpm. The coated electrode is mixed by dropping and mixing, and if necessary, a conductive auxiliary agent is mixed, the temperature is raised to 50 to 200 ° C. with stirring, the pressure is reduced to 0.007 to 0.04 MPa, and then the temperature is maintained for 10 to 150 minutes. Active material can be obtained.

As the electrolytic solution containing a lithium salt as an electrolyte, an electrolytic solution containing an electrolyte and a non-aqueous solvent used in the production of a lithium ion battery can be used.

As the electrolyte, those used in known electrolytic solutions and the like can be used, and preferred ones are lithium salt-based electrolytes of inorganic acids such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiClO ₄ . A sulfonylimide-based electrolyte having a fluorine atom such as LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ and other fluorine atoms. Examples thereof include a sulfonylmethide-based electrolyte having.

As the non-aqueous solvent used for the electrolytic solution, an aprotic solvent can be preferably used. The aprotic solvent is a solvent that does not have a hydrogen ion-donating group (a group having a dissociative hydrogen atom, for example, an amino group, a hydroxyl group, and a thio group).
As the aprotonic solvent, a lactone compound, a cyclic or chain carbonate ester, a chain carboxylic acid ester, a cyclic or chain ether, a phosphoric acid ester, a nitrile compound, an amide compound, a sulfone and the like, and a mixture thereof are preferably used. It is possible, and more preferably, a non-aqueous solvent used in a known non-aqueous electrolytic solution can be used.

Examples of the lactone compound include a 5-membered ring lactone compound (γ-butyrolactone, γ-valerolactone and the like), a 6-membered ring lactone compound (δ-valerolactone and the like) and the like.

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate and the like.
Examples of the chain carbonate ester include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate and the like.

Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate and the like.
Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,4-dioxane and the like.
Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

Examples of the phosphoric acid ester include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, and tri (trichloromethyl) phosphate. Tri (trifluoroethyl) phosphate, Tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2- Examples thereof include dioxaphosphoran-2-one and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.
Examples of the nitrile compound include acetonitrile and the like. Examples of the amide compound include N, N-dimethylformamide (hereinafter, also referred to as DMF) and the like. Examples of the sulfone include chain sulfones such as dimethyl sulfone and diethyl sulfone, and cyclic sulfones such as sulfolane.
One kind of aprotic solvent may be used alone, or two or more kinds may be used in combination.

The non-aqueous solvent preferably contains ethylene carbonate, and the non-aqueous solvent is more preferably a mixed solvent of ethylene carbonate and propylene carbonate or a mixed solvent of ethylene carbonate and diethyl carbonate.

The concentration of the above-mentioned electrolyte contained in the electrolytic solution is preferably 0.3 to 3 M from the viewpoint of battery characteristics at low temperature and the like.

The electrode for a lithium ion battery of the present invention contains the following compounds (a) and / or (b).
(A) Cellulosic acetate propionate (b) The number of repetitions of polyethylene glycol or its monoalkyl ether (meth) acrylate (b1) having an number of repetitions of oxyethylene units of 8 to 14 and the number of repetitions of oxyethylene units are A copolymer containing (meth) acrylate (b2) of polyethylene glycol or a monoalkyl ether thereof, which is any one of 2 to 4, as an essential constituent monomer. Hereinafter, the compound of (a) is compounded (a) in the present specification. ) And (b) are also referred to as compound (b).

(A) Cellulose Acetate Propionate Cellulose acetate propionate is obtained by substituting at least a part of the hydroxyl groups of cellulose with an acetyl group and a propionyl group, and is described in a known method, for example, JP-A-2017-200009. It can be manufactured by the method described.
As the cellulose acetate propionate, a commercially available product can be used, for example, "CAP-482-20" (acetyl group content = 2.5% by weight, propionyl group content = 46% by weight, number average molecular weight: 75). 000), "CAP-504-0.2" (acetyl group content = 0.6% by weight, propionyl group content = 42.5% by weight, number average molecular weight: 15,000), "CAP-504-" 0.5 "(acetyl group content = 2.5% by weight, propionyl group content = 45.0% by weight, number average molecular weight: 25,000) (all manufactured by Eastman Chemical Japan Co., Ltd., trade name) And so on.

(B) The (meth) acrylate (b1) of polyethylene glycol or a monoalkyl ether thereof having an oxyethylene unit repetition number of 8 to 14 and an oxyethylene unit repetition number of any of 2 to 4. Polymer containing polyethylene glycol or (meth) acrylate (b2) of its monoalkyl ether as an essential constituent monomer This copolymer is a polymer of (meth) acrylic acid and a side chain consisting of a polyoxyethylene skeleton. Coweight of (b1) which is a (meth) acrylate having a long PEO chain and (b2) which is a (meth) acrylate having a short PEO chain and has a structure in which (hereinafter referred to as PEO chain) is bonded. It is a coalescence.
The binding mode of (b1) and (b2) may be block or random, but is preferably random binding. That is, (b) is preferably a random copolymer of (b1) and (b2).

When the PEO chain of (b1) is a monoalkyl ether having an oxyethylene unit repetition number of 8 to 14, the number of carbon atoms of the alkyl group of the monoalkyl ether is 1 to 4. Is preferable.

Examples of (b1) include polyethylene glycol (meth) acrylate, methoxy-polyethylene glycol (meth) acrylate, ethoxy-polyethylene glycol (meth) acrylate, propoxy-polyethylene glycol (meth) acrylate, butoxy-polyethylene glycol (meth) acrylate, and the like ( In each case, the number of repetitions of the oxyethylene unit is 8 to 14).
Polyethylene glycol having 8 to 14 repetitions of the oxyethylene unit constituting (b1) is commercially available under trade names such as PEG400 and PEG600, and (b1) is the same as the above-mentioned commercially available polyethylene glycol (meth). ) Ester with acrylic acid [also referred to as (meth) acrylate] can be used, and the following commercially available (meth) acrylate can be used.
(B1) can be obtained by esterifying the above polyethylene glycol or an alkyl ether thereof with (meth) acrylic acid by a known method, and is a commercially available (meth) acrylate that can be used as (b1). Blemmer series (manufactured by Nichiyu Co., Ltd., Blemmer PME-400, AME-400, PE-350, AE-400, etc., Brenmer is a registered trademark of Nichiyu Co., Ltd.) and light acrylate series (manufactured by Kyoeisha Chemical Co., Ltd.) , Light acrylate 130A, etc., Light acrylate is a registered trademark of Kyoeisha Chemical Co., Ltd.), AM-130G [manufactured by Shin-Nakamura Chemical Co., Ltd.] and the like can be used.

Further, when the PEO chain of (b2) is a monoalkyl ether having an oxyethylene unit repetition number of 2 to 4, the number of carbon atoms of the alkyl group of the monoalkyl ether is 1 to 4. Is preferable.

Examples of (b2) include polyethylene glycol (meth) acrylate, methoxy-polyethylene glycol (meth) acrylate, ethoxy-polyethylene glycol (meth) acrylate, propoxy-polyethylene glycol (meth) acrylate, butoxy-polyethylene glycol (meth) acrylate, and the like ( In each case, the number of repetitions of the oxyethylene unit is 2 to 4).
Polyethylene glycol having 2 to 4 repetitions of the oxyethylene unit constituting (b2) is commercially available under trade names such as diethylene glycol and PEG200, and (b2) is the same as the above-mentioned commercially available polyethylene glycol (meth). ) Ester with acrylic acid [also referred to as (meth) acrylate (2)] can be used, and the following commercially available (meth) acrylate can be used.
(B2) can be obtained by esterifying the above polyethylene glycol or an alkyl ether thereof with (meth) acrylic acid by a known method, and is a commercially available (meth) acrylate that can be used as (b2). Blemmer series (manufactured by NOF Corporation, Blemmer PME-200, Brenmer is a registered trademark of NOF Corporation) and light acrylate series (manufactured by Kyoeisha Chemical Co., Ltd., light acrylate MTG-A, EC-A, light acrylate) Is a registered trademark of Kyoeisha Chemical Co., Ltd.) and the like can be used.

The compound (b) is a copolymer containing (b1) and (b2) as essential constituent monomers, and a monomer composition containing (b1) and (b2) is known as a polymerization method (bulk). It is obtained by polymerization by polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc. (see JP-A-2018-006340, etc.).
The total weight ratio of (b1) and (b2) contained in (b) is preferably 50 to 100% by weight based on the total weight of the monomers constituting (b).
The ratio of (b1) to (b2) in the monomer constituting the compound (b) is preferably (b1) :( b2) = 95: 5 to 50:50 in terms of molar ratio, and 90: 10 to 60:40 is more preferable.

Only one kind of compound (a) and compound (b) may be used, or a plurality of kinds may be used. Further, the compound (a) and the compound (b) may be used in combination.

In the electrode for a lithium ion battery, the total weight of the compounds (a) and (b) is 0.1 to 2% by weight with respect to the electrode active material.
When the total weight of the compounds (a) and (b) is less than 0.1% by weight with respect to the electrode active material, the electrode active material precipitates when the electrode for a lithium ion battery is manufactured by the method described later. Cannot be prevented. Further, if the total weight of the compounds (a) and (b) exceeds 2% by weight with respect to the electrode active material, the capacity of the electrode cannot be secured.

The electrode for a lithium ion battery may contain a conductive material in addition to the above-mentioned conductive auxiliary agent which may be contained in the coating layer. It is preferable to include a conductive material because it is easy to maintain a conductive path between active materials.
As the conductive material, the same materials as those exemplified as the conductive auxiliary agent contained in the coating layer can be used, and the preferred ones are also the same.

The electrode for a lithium ion battery of the present invention has an electrode active material layer, and the electrode active material layer is made of a non-bonded body of the above electrode active material and a mixture containing the compounds (a) and / or (b). Is preferable.
The non-binding body means that the electrode active materials are not irreversibly fixed to each other by a binder (also referred to as a binder).
In other words, it means that the electrode active material layer does not contain a binder.
Known binders for lithium ion batteries such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene and styrene-butadiene copolymers. Can be mentioned.
Since the electrode active material layer in a conventional lithium ion battery is manufactured by applying a slurry in which an electrode active material and a binder are dispersed in a solvent to the surface of a current collector or the like, and heating and drying the electrode active material layer. The electrode active material layer is in a state of being hardened by a binder. At this time, the electrode active materials are fixed to each other by the binder, and the positions of the electrode active materials are fixed. When the electrode active material layer is hardened by the binder, excessive stress is applied to the electrode active material due to expansion and contraction during charging and discharging, and the electrode active material is liable to self-destruct.
Furthermore, since the electrode active material layer is fixed to the surface of the current collector by the binder, cracks occur in the electrode active material layer solidified by the binder due to expansion and contraction during charging and discharging of the electrode active material. Alternatively, the electrode active material layer may peel off or fall off from the surface of the current collector.

In the case of a non-bonded body of the above mixture in which the electrode active material is a coated electrode active material, even if the coated electrode active materials are in contact with each other in the electrode active material layer, the coated resin compositions are contacted with each other on the contact surface. However, the bonding is temporary and can be loosened without destroying the coated electrode active materials. Therefore, the coated electrode active materials are irreversibly bonded to each other by the coating resin composition. It is not fixed. Therefore, the electrode active material layer including the non-bonded body of the mixture containing the coated electrode active material is not one in which the coated electrode active materials are bound to each other.

The electrode active material layer is composed of a non-bonded body of the electrode active material and a mixture containing the compounds of (a) and / or (b), and the present invention is due to the fact that the electrode active material layer further contains an electrolytic solution. It becomes an electrode for a lithium ion battery.

The thickness of the electrode active material layer of the electrode for the lithium ion battery is preferably 150 μm or more, more preferably 200 μm or more, and further preferably 400 μm or more. Further, it is preferably 2000 μm or less.
When the thickness of the electrode active material layer is thick, the proportion of the electrode active material layer in the battery becomes high when the laminated battery is used, and the battery can be made into a battery having a high energy density.

Further, the electrode for a lithium ion battery of the present invention may be an electrode in which an electrode active material layer is formed on a current collector.

Examples of the material constituting the positive electrode current collector as the current collector include copper, aluminum, titanium, stainless steel, nickel, calcined carbon, a conductive polymer, and conductive glass. Further, as the positive electrode current collector, a resin current collector composed of a conductive agent and a resin may be used.

Examples of the material constituting the negative electrode current collector as the current collector include copper, aluminum, titanium, stainless steel, nickel, and metal materials such as nickel and alloys thereof. Of these, copper is preferable from the viewpoint of weight reduction, corrosion resistance, and high conductivity. The negative electrode current collector may be a current collector made of calcined carbon, a conductive polymer, conductive glass, or the like, or a resin current collector made of a conductive agent and a resin.

As the conductive agent constituting the resin current collector, the same as the conductive material which is an arbitrary component of the mixture can be preferably used for both the positive electrode current collector and the negative electrode current collector.
The resins constituting the resin collector include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), and polytetra. Fluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin and mixtures thereof, etc. Can be mentioned.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) or polycycloolefin (PCO) is preferable, and polyethylene (PE), polypropylene (PP) or polymethylpentene is more preferable. (PMP).

Subsequently, a method for manufacturing the electrode for a lithium ion battery of the present invention will be described.
In the method for producing an electrode for a lithium ion battery of the present invention, a current collector contains an electrode active material, an electrolytic solution containing a lithium salt as an electrolyte, and an electrolytic solution slurry containing the following compounds (a) and / or (b). It is characterized by including a step of coating.
(A) Cellulose acetate propionate (b) The number of repetitions of polyethylene glycol or its monoalkyl ether (meth) acrylate (b1) having an oxyethylene unit repetition number of 8 to 14 and the number of repetitions of oxyethylene unit are A copolymer containing polyethylene glycol (2 to 4) or (meth) acrylate (b2) of a monoalkyl ether thereof as an essential constituent monomer.

First, the electrode active material and the compound (a) and / or the compound (b) are prepared.
When a coated electrode active material is used as the electrode active material, the coated electrode active material is, for example, a polymer solution containing a polymer compound in a state where the electrode active material is placed in a universal mixer and stirred at 30 to 50 rpm. The mixture is added dropwise over ~ 90 minutes, and if necessary, a conductive additive is mixed, the temperature is raised to 50 to 200 ° C. with stirring, the pressure is reduced to 0.007 to 0.04 MPa, and then the mixture is held for 10 to 150 minutes. Can be obtained by
As the compound (a) and the compound (b), a commercially available product may be used, or a synthesized product may be used. As a method for synthesizing the compound (b), a method of polymerizing a monomer composition containing (b1) and (b2) by a known method, and a method of repeating poly (meth) acrylic acid with 8 oxyethylene units. Polyethylene glycol or monoalkyl thereof (preferably 1 to 4 carbon atoms) ether which is any of 14 to 14, and polyethylene glycol or monoalkyl thereof (preferably monoalkyl which has 2 to 4 repetitions of oxyethylene units). Carbon number 1 to 4) A method of esterifying ether by a known method or the like can be used.

In addition, an electrolyte and a non-aqueous solvent are mixed to prepare an electrolytic solution containing a lithium salt as an electrolyte.

Next, an electrolytic solution containing a lithium salt as an electrolyte, an electrode active material, and the compound (a) and / or the compound (b) are mixed to prepare an electrolytic solution slurry.
If necessary, the above-mentioned conductive material may be added to the electrolytic solution slurry.
Further, it is preferable that the electrolytic solution does not contain the above-mentioned binder.
The viscosity of the electrolytic solution slurry is preferably 10.0 to 7.0 Pa · s in the case of the positive electrode active material slurry. The viscosity of the negative electrode active material slurry is preferably 38 to 42 Pa · s. Within this range, the effect of preventing the precipitation of the electrode active material by the compound (a) and / or the compound (b) is more exerted, which is preferable.

The ratio of the electrode active material in the electrolytic solution slurry is preferably 40 to 70% by weight.

The ratio of the compound (a) and the compound (b) in the electrolytic solution slurry is 0.1 to 2% by weight, preferably 0.4 to 0.7% by weight, based on the total weight of the electrode active material. When the ratio of the compound (a) and the compound (b) in the electrolytic solution slurry is 0.4 to 0.7% by weight based on the total weight of the electrode active material, the compound (a) and / or the compound (b) This is preferable because the effect of preventing the precipitation of the electrode active material due to the above-mentioned effect is more exhibited.

Subsequently, the electrolytic solution slurry is applied to the current collector. The coating can be performed using any coating device such as a bar coater or a brush.
It is preferable to apply the electrolytic solution slurry to the current collector to form an electrode active material layer composed of the electrode active material and a non-bonded mixture containing the compound (a) and / or the compound (b). .. An electrode with a current collector can be obtained by applying an electrolytic solution slurry on the current collector.

The method for manufacturing an electrode for a lithium ion battery of the present invention is suitable for coating a large area of a coated surface.
The electrolytic solution slurry used in the method for manufacturing an electrode for a lithium ion battery of the present invention does not cause the problem of sedimentation of the electrode active material even in the presence of a lithium salt as an electrolyte, and is therefore excellent in stability over time. It is possible to stabilize the quality of the electrolyte slurry and apply it to the current collector. Therefore, even if the coating area is large and the coating time is long, it is possible to apply the coating uniformly. Then, the thickness and characteristics of the electrode obtained after coating the electrolytic solution slurry are stabilized, and the quality of the electrode can be improved.

After applying the electrolytic solution slurry on the current collector, filter paper or mesh is applied to the surface of the coated electrolytic solution slurry, and the mixture is absorbed by a vacuum pump to collect the mixture contained in the electrolytic solution slurry. It is possible to form an electrode active material layer that is fixed on the body and is loosely maintained in its shape so as not to flow.

If the current collector is a filter paper containing conductive fibers such as carbon fibers or a material that can permeate a liquid such as a metal mesh, the lower surface of the current collector (the surface on which the electrolytic solution slurry is not applied) is covered with filter paper. It is also possible to form an electrode active material layer by fixing the mixture contained in the electrolytic solution slurry on the current collector by applying liquid such as a mesh or a mesh and sucking the liquid with a vacuum pump.
Further, the liquid may be absorbed by placing a liquid absorbing material on the lower surface of the current collector. As the liquid-absorbent material, a liquid-absorbent cloth such as a towel, paper, a liquid-absorbent resin or the like can be used.
At this time, pressurization from the surface of the coated electrolytic solution slurry may also be performed. Even in this way, the mixture contained in the electrolytic solution slurry can be fixed on the current collector to form an electrode active material layer in which the shape is maintained loosely to the extent that it does not flow.

Further, the electrolytic solution slurry is coated on the current collector, the separator is placed on the surface of the coated electrolytic solution slurry, and the liquid is absorbed from the upper surface side of the separator, and the mixture is placed between the current collector and the separator. It may be fixed.

As the separator, an aramid separator (manufactured by Nippon Baileen Co., Ltd.), polyethylene, a microporous film made of polypropylene, a multilayer film of a porous polyethylene film and polypropylene, a non-woven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and Examples thereof include those having ceramic fine particles such as silica, alumina, and titania adhered to their surfaces.

The lithium ion battery using the electrode for a lithium ion battery of the present invention can be obtained by combining electrodes to be opposite electrodes, storing the electrode together with a separator in a cell container, injecting an electrolytic solution, and sealing the cell container.
Further, a positive electrode is formed on one surface of the current collector, and a negative electrode is formed on the other surface to prepare a bipolar electrode. The bipolar electrode is laminated with a separator and stored in a cell container to store an electrolytic solution. It can also be obtained by injecting and sealing the cell container.
Further, the electrode for the lithium ion battery of the present invention may be used for either the positive electrode or the negative electrode, and both the positive electrode and the negative electrode may be used as the electrode for the lithium ion battery of the present invention as the lithium ion battery.

Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples as long as it does not deviate from the gist of the present invention. Unless otherwise specified, parts mean parts by weight and% means parts by weight.

In order to evaluate the coatability of the electrolytic solution slurry, an electrolytic solution slurry was prepared and its settling time was evaluated.

[Production Example 1: Polyethylene glycol monoalkyl ether acrylate having 9 oxyethylene unit repeats and polyethylene glycol monoalkyl ether acrylate having 3 oxyethylene unit repeats (compound (compound (compound) b) 1)]
A 100 mL test tube container equipped with a stirrer, temperature sensor, nitrogen line, decompression line, and recirculation adapter in a personal synthesizer (Chemistation, manufactured by EYELA) with a polyethylene glycol monomethyl ether having a repetition rate of 9 in oxyethylene units. Ester with acrylic acid (manufactured by Kyoeisha Chemical Co., Ltd., light acrylate 130A) by 18 parts by weight, tri (ethylene glycol) monomethyl ether (repetition number of oxyethylene unit is 3) and ester of acrylic acid (Kyoeisha Chemical Co., Ltd.) A monomer mixture was prepared by adding 6 parts by weight of light acrylate MTG-A) and 23 parts by weight of propylene carbonate. Next, nitrogen was blown into the prepared monomer mixture for 1 minute while stirring at a stirring speed of 400 rpm, and then a depressurization operation was performed for 1 minute. This operation was repeated 5 times to perform nitrogen substitution. Then, the temperature of the monomer mixture was raised to 65 ° C., and an initiator mixture in which 0.02 parts by weight of 2,2'-azobis (2,4-dimethylvaleronitrile) was dissolved in 1 part by weight of propylene carbonate was added. Radical polymerization was carried out for 3 hours. Then, the same initiator mixture as above was added again, and the reaction was continued for another 2 hours to obtain a polymer solution having a resin concentration of 50% by weight. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 7800. The measurement conditions of GPC when measuring the weight average molecular weight of the polymer were as follows.
Measuring device: HLC-8120GPC (manufactured by Tosoh Corporation)
Eluent: Water / Methanol (1/1 volume ratio) KCl solution Standard substance: Polyethylene glycol Sample concentration: 0.5 mg / mL
Column stationary phase: (Used by connecting Tosoh TSK GL6000 PWXL, GL3000 PWXL, GL2500 PWXL)
Column temperature: 40 ° C

[Production Example 2: Polyethylene glycol monoalkyl ether acrylate having 13 oxyethylene unit repeats and polyethylene glycol monoalkyl ether acrylate having 2 oxyethylene unit repeats (compound (compound (compound) b) 2)]
In the synthesizer of Production Example 1, 23 parts by weight of an ester (AM-130G, manufactured by Shin-Nakamura Chemical Co., Ltd.) of polyethylene glycol monomethyl ether having 13 repetitions of oxyethylene units and acrylic acid, and diethylene glycol mono Add 1 part by weight of an ester of ethyl ether (the number of repetitions of oxyethylene unit is 2) and acrylic acid (light acrylate EC-A manufactured by Kyoeisha Chemical Co., Ltd.) and 23 parts by weight of propylene carbonate to prepare a monomer mixture. A polymer solution having a resin concentration of 50% by weight was obtained by the method described in Production Example 1 except for the preparation. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 8200.

[Production Example 3: Polyethylene glycol monoalkyl ether acrylate having 9 oxyethylene unit repeats and polyethylene glycol monoalkyl ether acrylate having 3 oxyethylene unit repeats (compound (compound (compound) b) 3)]
In the synthesizer of Production Example 1, 21.9 parts by weight of an ester (light acrylate 130A manufactured by Kyoeisha Chemical Co., Ltd.) of polyethylene glycol monomethyl ether having 9 repetitions of oxyethylene unit and acrylic acid was added to the bird (tri). Add 1.1 parts by weight of monomethyl ether (oxyethylene unit repeat number 3) and acrylic acid ester (light acrylate MTG-A manufactured by Kyoeisha Chemical Co., Ltd.) and 23 parts by weight of propylene carbonate. A polymer solution having a resin concentration of 50% by weight was obtained by the method described in Production Example 1 except that a monomer mixed solution was prepared. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 6400.

[Production Example 4: Copolymer of a polyethylene glycol monoalkyl ether acrylate having 9 oxyethylene unit repetitions and a polyethylene glycol monoalkyl ether acrylate having 2 oxyethylene unit repetitions (compound (compound (compound) b) 4)]
In the synthesizer of Production Example 1, 21.9 parts by weight of an ester (light acrylate 130A manufactured by Kyoeisha Chemical Co., Ltd.) of a monomethyl ether of polyethylene glycol having 9 repetitions of oxyethylene units and acrylic acid was added to the diethylene glycol. Monomer by adding 1.1 parts by weight of an ester of monoethyl ether (repeated number of oxyethylene units is 2) and acrylic acid (light acrylate EC-A manufactured by Kyoeisha Chemical Co., Ltd.) and 23 parts by weight of propylene carbonate. A polymer solution having a resin concentration of 50% by weight was obtained by the method described in Production Example 1 except that a mixed solution was prepared. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 7100.

[Production Example 5: Polymer of monoalkyl ether acrylate of polyethylene glycol having 9 repetitions of oxyethylene unit and acrylate of monoalkyl ether of polyethylene glycol having 4 repetitions of oxyethylene unit (compound (compound (compound) b) 5)]
In the synthesizer of Production Example 1, 21.9 parts by weight of an ester of acrylic acid and a monomethyl ether of polyethylene glycol having 9 repetitions of oxyethylene unit (light acrylate 130A manufactured by Kyoeisha Chemical Co., Ltd.) was added to the diethylene glycol. A monomer mixture containing 1.1 parts by weight of an ester of monomethyl ether (4 repetitions of oxyethylene unit) and acrylic acid (Blemmer PME-200 manufactured by Nichiyu Co., Ltd.) and 23 parts by weight of propylene carbonate. A polymer solution having a resin concentration of 50% by weight was obtained by the method described in Production Example 1 except for the preparation of the above. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 6100.

[Production Example 6: An acrylate homopolymer of a monoalkyl ether of polyethylene glycol having 9 repetitions of oxyethylene units (Comparative Compound 4)]
In the synthesizer of Production Example 1, 23 parts by weight of an ester of polyethylene glycol monomethyl ether having 9 repetitions of oxyethylene unit and acrylic acid (light acrylate 130A manufactured by Kyoeisha Chemical Co., Ltd.) and 23 parts of propylene carbonate were added. A polymer solution having a resin concentration of 50% by weight was obtained by the method described in Production Example 1 except that the monomer mixture was prepared by adding parts by weight. The weight average molecular weight of the obtained polymer was measured by GPC and found to be 3600.

(Examples 1-1 to 1-10, Comparative Examples 1-1 to 1-6)
(Preparation of electrolyte slurry)
In each Example and Comparative Example, the following compounds were used as the compound (a), the compound (b) or the comparative compound to be compared.
Compound (a) 1: Cellulose acetate propionate: (CAP-482-20: manufactured by Eastman Chemical Japan Co., Ltd.)
Compound (a) 2: Cellulose acetate propionate: (CAP-482-0.5: manufactured by Eastman Chemical Japan Co., Ltd.)
Compound (b) 1: Copolymer produced in Production Example 1 (molar ratio is polyethylene glycol monoalkyl ether acrylate in which the number of repetitions in oxyethylene units is 9. Polyethylene in which the number of repetitions in oxyethylene units is 3. Glycol monoalkyl ether acrylate = 6: 4)
Compound (b) 2: Copolymer produced in Production Example 2 (molar ratio is polyethylene glycol monoalkyl ether acrylate in which the number of repetitions in oxyethylene units is 13. Polyethylene in which the number of repetitions in oxyethylene units is 2. Glycol monoalkyl ether acrylate = 9: 1)
Compound (b) 3: Copolymer produced in Production Example 3 (molar ratio is polyethylene glycol monoalkyl ether acrylate in which the number of repetitions in oxyethylene units is 9. Polyethylene in which the number of repetitions in oxyethylene units is 3. Glycol monoalkyl ether acrylate = 9: 1)
Compound (b) 4: Copolymer produced in Production Example 4 (molar ratio is polyethylene glycol monoalkyl ether acrylate in which the number of repetitions in oxyethylene units is 9. Polyethylene in which the number of repetitions in oxyethylene units is 2. Glycol monoalkyl ether acrylate = 9: 1)
Compound (b) 5: Copolymer produced in Production Example 5 (molar ratio is polyethylene glycol monoalkyl ether acrylate in which the number of repetitions in oxyethylene units is 9. Polyethylene in which the number of repetitions in oxyethylene units is 4. Glycol monoalkyl ether acrylate = 9: 1)
Comparative Compound 1: Polyvinylpyrrolidone (K-90: manufactured by Nippon Shokubai Co., Ltd.)
Comparative compound 2: Polyvinylpyrrolidone (K-30: manufactured by Nippon Shokubai Co., Ltd.)
Comparative compound 3: Carboxymethyl cellulose (CMC Daicel 1240: manufactured by Daicel FineChem Co., Ltd.)
Comparative Compound 4: An electrolytic solution containing LiPF ₆ at a concentration of 1 M as the copolymer electrolytic solution produced in Production Example 6 and using a mixed solvent of EC (ethylene carbonate) and PC (propylene carbonate) as a non-aqueous solvent. Prepared.
Using the addition amounts of these compounds shown in Table 1, the NCA-based positive electrode active material (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder: average particle diameter 5 μm) 64.5% by weight was used as the electrode active material. An electrolytic solution slurry was prepared by mixing 1.5% by weight of carbon nanotubes (VGCF: manufactured by Showa Denko KK) as a conductive auxiliary agent and the balance of the above electrolytic solution.

(Evaluation of sedimentation time)
After stirring and mixing this electrolyte slurry with a universal mixer, the slurry was transferred to several 100 mL sedimentation tubes (length 20 cm) and allowed to stand.
Sampling glass tube from the liquid level of the settling tube every 30 minutes from the start of standing to the 2nd hour, every 2 hours until the 12th hour over 2 hours, and every 12 hours after the 12th hour. About 5 g of the supernatant was gently sampled and weighed the slurry. Then, the sampled slurry was dried under reduced pressure at 80 ° C. to distill off the electrolytic solution, and the weight of the residue was weighed to determine the solid content concentration of the sampled slurry. The difference between the solid content concentration immediately after mixing (solid content concentration of the slurry at 0 hours after the start of standing) and the solid content concentration of the sampled slurry (decrease in solid content concentration) is relative to the solid content concentration immediately after mixing. The maximum value of the sampling time not exceeding 1% was evaluated as the settling resistance time.

It can be seen that the electrolytic solution slurry containing the compound (a) or the compound (b) in a predetermined amount can prevent the electrode active material from settling even in the presence of a lithium salt as an electrolyte.
Since this electrolyte slurry does not cause the problem of sedimentation of the electrode active material even in the presence of a lithium salt as an electrolyte, it has excellent stability over time, and stabilizes the quality of the electrolyte slurry to form a current collector. It becomes possible to paint. Therefore, the thickness and characteristics of the electrode obtained after coating the electrolytic solution slurry are stable, and the quality of the electrode can be improved.

(Examples 2-1 to 2-10, Comparative Examples 2-1 to 2-6)
(Formation of positive electrode active material layer)
An electrolytic solution slurry was prepared in the same manner as in Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-6 except that NCA having a conductive film on the surface was used as the electrode active material. .. Next, an electrolytic solution slurry was applied onto an aluminum foil having a thickness of 20 μm in a square frame of 50 mm × 50 mm so that the electrode basis weight was 12 mAh / cm ² using an applicator. After coating the electrolytic solution slurry, three non-woven fabrics of aramid having a thickness of 20 μm were covered and the electrodes were pressed at a pressure of 0.1 MPa to form a positive electrode active material layer.

(Making a lithium-ion battery)
Copper foil with terminals (5 mm x 3 cm) (3 cm x 3 cm, thickness 17 μm) (trade name "NC-WS lithium ion battery electrolytic copper foil for negative electrode" [Furukawa Denko]) and carbon coat with terminals (5 mm x 3 cm) Aluminum foil (3 cm x 3 cm, thickness 21 μm) with aluminum foil (3 cm x 3 cm, thickness 21 μm) is laminated in order in the same direction with the two terminals coming out, and two heat-sealing type aluminum laminated films (10 cm x 8 cm) (trade name "SPALF") are laminated. "[Made by Showa Denko]), and one side where the terminals are exposed was heat-sealed to produce a laminated cell.
The positive electrode active material layer formed in the previous section was peeled off from the aluminum foil and placed on the aluminum foil of the laminated cell. A separator (5 cm x 5 cm, thickness 23 μm, trade name "Cellguard 2500" [made by Cellguard] polypropylene) is placed on the positive electrode active material layer, and a 60 mm x 60 mm metallic lithium foil (trade name "rolling") is used as the negative electrode side electrode. "Lithium foil" [made by Honjo Metal]) was placed on the separator so that the positive electrode part was hidden. Next, two sides orthogonal to one side heat-sealed at the tip of the laminated cell were heat-sealed. Then, the laminated cell was sealed by heat-sealing the opening while evacuating the inside of the cell using a vacuum sealer to obtain a lithium ion battery.

(Measurement of battery characteristics)
Regarding the produced lithium ion batteries according to Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-6, the charge / discharge measuring device "HJ0501SM" [manufactured by Hokuto Denko Co., Ltd.] was used by the following method. A charge / discharge test was performed to determine the ratio of each discharge capacity (called Coulomb efficiency) to the charge capacity at the time of the first charge and the charge capacity in the third cycle. The results are shown in Table 2.
Under the condition of 45 ° C., the lithium ion battery for battery characteristic evaluation is charged to 4.2V with a current of 0.1C, and after a 10-minute rest, it is discharged to 2.6V with a current of 0.1C. The process was repeated 3 times with a 10 minute pause.

In the lithium ion batteries of Examples 2-1 to 2-10, it was found that the coulombic efficiency was large at the first time by adding a predetermined amount of the dispersant, and the coulombic efficiency exceeded 99.9% in the third cycle. rice field. Since the slurry is uniformly dispersed, the conductive path after coating can be formed well and the transfer of lithium ions is also advantageous, so that the Coulomb efficiency can be achieved to 99% or more at an early stage. Comparative Examples 2-2 to 2-4, which have a small function of preventing sedimentation, could not be evaluated by a battery because coating defects occurred due to sedimentation and aggregation of the slurry.

The electrode for a lithium ion battery of the present invention is particularly useful as an electrode for a bipolar secondary battery and a lithium ion secondary battery used for a mobile phone, a personal computer, a hybrid vehicle and an electric vehicle.

Claims (2)

Electrode active material and
An electrolytic solution containing a lithium salt as an electrolyte and
Including the following compounds (a) and / or (b)
An electrode for a lithium ion battery, wherein the total weight of the compounds (a) and (b) is 0.1 to 2% by weight with respect to the electrode active material.
(A) Cellulose acetate propionate (b) The number of repetitions of polyethylene glycol or its monoalkyl ether (meth) acrylate (b1) having an oxyethylene unit repetition number of 8 to 14 and the number of repetitions of oxyethylene unit are A copolymer containing polyethylene glycol (2 to 4) or (meth) acrylate (b2) of a monoalkyl ether thereof as an essential constituent monomer. The electrode for a lithium ion battery has an electrode active material layer and has an electrode active material layer.
The electrode for a lithium ion battery according to claim 1, wherein the electrode active material layer comprises a non-bonded body of the electrode active material and a mixture containing the compounds of (a) and / or (b).