JP2001057208A - Thermosetting cathode paste not including diluent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode-paste-compounded material which has such suitable viscosity and elasticity that the cathode paste can be applied to a current collector even without the existence of diluent or volatile application solvent. SOLUTION: This cathode paste includes an active material comprising oxide containing transition metal having a particle diameter distribution ranging 1 to 15 μm, electrolyte solvent, and one or more types of thermosetting monomers. This cathode paste also includes a transition metal oxide active material with a specific surface area ranging 0.25 to 2.00 m2/g, electrolyte solvent, and one or more types of thermosetting monomers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diluent-free thermosetting cathode paste for a battery, and more particularly to, in particular,
The present invention relates to a diluent-free thermosetting cathode paste having viscoelasticity that enables the cathode paste to be applied on a current collector even in the absence of a diluent or a volatile application solvent. The present invention particularly relates to a cathode paste used for producing a cathode for a lithium ion battery.

[0002]

2. Description of the Related Art Lithium ion secondary batteries which can be used in various fields are known. In general, lithium ion batteries are particularly preferably used compared to other rechargeable batteries such as nickel cadmium and nickel metal hydride batteries because of their excellent light weight, energy density and overall efficiency.

[0003] Conventional thermosetting cathode paste formulations include an active material such as a transition metal oxide, an electrolyte solvent, one or more polymerizable monomers, and a diluent or coating solvent. The reason for using a diluent is that conventional cathode paste formulations have a high viscosity and elasticity, and if no diluent is used, uniform application on the current collector becomes extremely difficult and / or This is because it becomes practically impossible. The diluent reduces the viscosity and elasticity of the cathode paste, and enables uniform application of the cathode paste on the current collector.

[0004] Although cathode paste formulations using diluents have been researched and developed, the use of diluents is problematic for several reasons. First, the cost of forming the cathode paste formulation is substantially reduced because the diluent usage typically requires a diluent concentration of greater than 30% by weight based on the total cathode paste formulation. To increase. Second, after mixing the cathode paste, the diluent needs to be removed. This diluent removal is usually performed by a heating vacuum stripping method. Removal of diluents or coating solvents increases manufacturing time and therefore manufacturing costs. Third, there is the problem of discarding or recycling the collected diluent, further increasing the costs associated with battery manufacture. Fourth, after stripping off the diluent, the resulting "dry" cathode paste formulation becomes very porous, requiring the addition of steps such as compression and medium to high calendering. After the calendering treatment, stress remains in the cathode paste, which adversely affects the adhesion to the current collector. In addition, this residual stress promotes curling which is undesirable for the cathode paste, thus further complicating the battery manufacturing process. These disadvantages limit, inter alia, the range of formulation and thickness of the cathode paste applied to the current collector.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cathode paste formulation having a suitable viscosity and elasticity which allows the cathode paste to be applied on a current collector in the absence of a diluent or a volatile coating solvent. It is to provide.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have solved the above problems by setting the particle size distribution and the specific surface area of the transition metal oxide active material to specific ranges. They found what they could do and completed the present invention.

The present invention has been completed based on the above findings, and a first gist of the present invention is to provide an active material comprising an oxide containing a transition metal having a particle size distribution in the range of 1 to 15 μm, and an electrolyte solvent. And a diluent-free thermosetting cathode paste for a battery having at least one thermosetting monomer.

[0008] A second aspect of the present invention is to provide 0.25 m ² / g.
Present in a diluent-free thermosetting cathode paste for batteries comprising a transition metal oxide active material having a specific surface area in the range of 2.00 m ² / g, an electrolyte solvent and one or more thermosetting monomers. .

A third gist of the present invention is that the concentration of the active material is
The cathode paste according to the first or second aspect, which is 70% by weight or more based on the cathode paste.

A fourth aspect of the present invention resides in the cathode paste according to any one of the first to third aspects, wherein the active material comprises one or more lithium transition metal oxides.

A fifth aspect of the present invention resides in the cathode paste according to any one of the first to fourth aspects, further comprising a carbonaceous material.

A sixth aspect of the present invention resides in the cathode paste according to any one of the first to sixth aspects, further comprising one or more thermal initiators.

[0013] A seventh aspect of the present invention resides in a cathode paste according to the sixth aspect, wherein the thermal initiator is a peroxide.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. Since the present invention is capable of various embodiments, the present invention is not limited to the following embodiments and descriptions.

The cathode paste for a battery of the present invention does not contain a diluent or a coating solvent, and can be coated on a current collector even in that state. Therefore, many problems associated with an electrode manufacturing technique using a diluent or a coating solvent are solved. The cathode paste formulation of the present invention comprises an active material comprising an oxide containing a transition metal, an electrolyte solvent, and one or more thermosetting monomers. The cathode paste formulation of the present invention is free of diluents or coating solvents, has a sufficiently low inherent viscosity and elasticity of the cathode paste, and can be prepared using a conventional extrusion die without using a diluent. Can be applied.

Examples of the active material include metal oxides such as transition metal oxides such as manganese oxide, vanadium oxide and titanium oxide, and lithium transition metal oxides such as lithium nickelate, lithium manganate and lithium cobaltate. And especially an oxide containing a transition metal.
Preferably, a lithium transition metal oxide is used. These oxides include those in which a predetermined site is replaced with another element as necessary. These active materials preferably have a particle size in the range of 1 to 15 μm, more preferably 1 to 12 μm.
μm. Further, it may have a specific surface area in the range of 0.25 to 2.00 m ² / g, preferably 0.25 to 1.5 m ² / g, more preferably 0.25 to 1.0 m ² / g. preferable. The most preferred embodiment is an active material having the above particle size range and the above specific surface area range.

Examples of the electrolyte solvent include LiPF ₆ , LiAsF ₆ or L 2 dissolved in propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), or the like.
Salts such as iBF ₄ are exemplified.

Suitable thermosetting monomers include acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxy Ethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetra Ethylene glycol diacrylate, polyethylene glycol Diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 2-
(2-ethoxyethoxy) ethyl acrylate (EEE
Acrylic monomers such as A) can be mentioned. Among them, acrylates, particularly alkylene oxide-modified acrylates are preferred. These monomers are easily polymerized, and the polymer obtained by the polymerization exhibits excellent properties as a binder for an electrode and a gelling agent for an electrolyte component. Specific product names include, for example, commercially available Photomer (Photomer) 4050 and / or Photomer (Photomer) 4158 (manufactured by Osaka Gas Co., Ltd.)
Japan) can be used.

Furthermore, the weight average molecular weight in the cathode paste is usually 10 ⁵ to 10 ⁶ , preferably about 300,00.
A polymer component such as polyethylene oxide (PEO), which is zero, can be introduced. Further, the anode formulation may be a succinic anhydride, 1,6-dioxaspiro [4.4], as disclosed in US Pat. No. 5,853,917, the entire contents of which are incorporated herein by reference. Nonan
Additives such as 2,7-dione and / or 1,4-dioxaspiro [4.5] decan-2-one can be included.

[0020] The cathode paste formulation optionally includes a commercially available Timrex® SFG-
6. Timrex SFG-10 and Timrex S
It may contain a carbonaceous material such as carbon black or graphite such as FG-15 (manufactured by Timcal, Switzerland) and MCMB10-28 (manufactured by Osaka Gas, Japan). Above all, MCMB10-28 in view of the fact that it has higher fluidity than other non-spherical carbonaceous sources and does not cause an increase in the viscosity and elasticity of the cathode paste.
And the like.

In preparing the blend, a thermal initiator may be added to the mixing vessel. As the thermal initiator, various ones capable of initiating polymerization of the monomer component by heat can be used, and typically, a peroxide and an azo compound can be used. In the present invention, a peroxide is preferably used. Examples of the peroxide include ketone peroxide, hydroperoxide, diacyl peroxide, dialkyl peroxide, peroxyketal, perester, percarbonate and the like. Among them, perester (peroxide ester) is preferable. Specific examples of the peroxide ester include t-butylperoxy-2-ethylhexanoate and t-butylperoxy-
3,5,5-trimethorhexanoate can be mentioned. As the properties of the thermal initiator, those which are in a liquid state in an environment where they are added and mixed are preferable from the viewpoint of easy mixing. Commercially available products include TRIGNOX-21 or T
RIGNOX-42S and the like are exemplified. The content of the thermal initiator is usually 0.001% by weight or more, preferably 0.01% by weight.
% By weight or more, more preferably 0.1% by weight or more,
Further, it is usually at most 20% by weight, preferably at most 10% by weight, more preferably at most 5% by weight.

The cathode paste of the present invention is applied to a current collector, preferably made of aluminum foil. The thickness of the aluminum foil is usually 1 to 30 μm, preferably 1 to 20 μm.

The above description is merely illustrative, and various modifications can be made without departing from the spirit of the present invention.

Hereinafter, as an example of the above modifications, the configurations of the cathode paste for lithium ion batteries and the cathode preferably used in the present invention will be described.

Active material: The active material used in the cathode paste is as described above, but may contain other active materials. Other active materials include TiS ₂ , FeS,
Ti, Fe, Co, Ni, represented by MoS ₂ etc.
Sulfides of transition metals such as Mn can be mentioned. Further, polyaniline, polypyrrole, polyacene, a disulfide compound, and a polysulfide compound can be used in combination.

The amount of the active material to be used is generally 20% by weight or more, preferably 40% by weight or more, more preferably 60% by weight or more, and most preferably 70% by weight or more based on the whole cathode paste. In the cathode paste of the present invention, the amount of the active material can be made larger than usual.
However, it is not realistic that the content is too large, and the ion conductivity may deteriorate. Therefore, the content is usually 99% by weight or less, preferably 90% by weight or less.

Electrolyte solvent: The electrolyte solvent is a non-aqueous solvent in which a lithium salt as a supporting electrolyte is usually dissolved.

As the supporting electrolyte, any non-aqueous substance can be used as long as it is stable as an electrolyte and can transfer lithium ions to perform an electrochemical reaction with a positive electrode active material or a negative electrode active material. Can be. LiPF ₆ in particular, LiAsF _6, LiSb
F ₆ , LiBF ₄ , LiClO ₄ , LiI, LiBr, L
iCl, LiAlCl, LiHF ₂ , LiSCN, Li
Lithium salts such as SO ₃ CF ₂ are mentioned. Among them, LiPF ₆ and LiClO ₄ are particularly preferable.

The concentration of these supporting electrolytes is generally 0.1.
5 to 2.5 mol / L. The nonaqueous solvent in which these supporting electrolytes are dissolved is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, ethylene carbonate, cyclic carbonates such as propylene carbonate, dimethyl carbonate, diethyl carbonate, non-cyclic carbonates such as ethyl methyl carbonate,
Tetrahydrofuran, 2-methyltetrahydrofuran,
Examples include glymes such as dimethoxyethane, lactones such as γ-butyrolactone, sulfur compounds such as sulfolane, and nitriles such as acetonitrile. Also, one or a mixture of two or more of these can be used.

Among these, one or more solvents selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are particularly preferred. is there. In addition, those in which a part of hydrogen atoms in these molecules are substituted with halogen or the like can also be used.

The amount of the electrolyte solvent used is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more based on the whole cathode paste. If the amount is too small, the ion conductivity tends to decrease, but if the amount is too large, the overall capacity tends to decrease. Therefore, the amount is usually 70% by weight or less, preferably 50% by weight or less, more preferably 30% by weight or less. is there.

Thermosetting monomers: Thermosetting monomers are:
After application of the cathode paste, it becomes a polymer by polymerization treatment such as heating, and usually acts as a binder for the cathode or a gelling agent for the electrolytic solution. Therefore, there is no particular limitation as long as it is a substance capable of performing such an action. For example, by polymerization, polyethylene, polypropylene, poly-1,1
Alkane-based polymers such as dimethylethylene and hexafluoropropylene; unsaturated polymers such as polybutadiene and polyisoprene; polymers having a ring such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; polymethyl methacrylate Acrylic polymers such as poly (ethyl methacrylate), poly (butyl methacrylate), poly (methyl acrylate), poly (methyl acrylate), poly (ethyl acrylate), poly (acrylic acid), poly (methacrylic acid), and polyacrylamide; polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, etc. Fluorinated resins; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; polyvinyl chloride Conductive polymers such as polyaniline; halogen-containing polymers such as polyvinylidene chloride
Components that generate a vinyl-based polymer such as polyester, polyamide, polycarbonate, polyimide, polyurethane, polyurea, polyvinyl acetate, polyvinyl chloride, and polyvinylidene fluoride may be used. Preferably, the above-mentioned acrylic monomers, particularly acrylic esters, are used. Of course, more than one monomer can be present.

The amount of the thermosetting monomer used is usually 0.1% by weight or less, preferably 0.5% by weight or more, more preferably 1% by weight or more based on the whole cathode paste. However, if the content is too large, the ionic conductivity and capacity may be reduced. Therefore, the content is usually 20% by weight or less, preferably 10% by weight or less.

Additives: The cathode paste can contain various additives. Examples of the additive include a conductive material, a reinforcing material, and a film forming material. The conductive material is not particularly limited as long as it can impart conductivity by being mixed with an appropriate amount of the active material, but acetylene black, carbon black, carbon powder such as graphite, and various metal fibers and foils Can be mentioned. As the reinforcing material, various inorganic and organic spherical and fibrous fillers can be used. Further, the film-forming material refers to various additives used for forming a film that can be formed on the surface of the active material after forming the electrode and further after manufacturing the battery. acid,
In addition to 1,6-dioxaspiro [4,4] nonane-2,7-dione, 1,4-dioxaspiro [4,5] decane-2-one, and carbonates such as vinylene carbonate, trifluoropropylene carbonate, and catechol carbonate , Cyclic ethers such as 12-crown-4-ether, acid anhydrides such as glutaric anhydride, cyclic ketones such as cyclopentanone and cyclohexanone, sultones such as 1,3-propane sultone and 1,4-butane sultone; Examples thereof include sulfur-containing compounds including thiocarbonates and nitrogen-containing compounds including imides. The molecular weight of these additives is usually 1000 or less, preferably 500 or less,
More preferably, it is 300 or less. If the molecular weight is too large, the influence of the inhibiting factor on charge / discharge increases, and ion conduction may be inhibited, resulting in an adverse effect.

The amount of the above additives is usually 10% by weight or less, preferably 5% by weight, based on the whole cathode paste.
The following is assumed.

Polymer component: As described above, the cathode paste can contain a polymer component such as polyethylene oxide. If the amount of the polymer component is too large, the viscosity of the cathode paste may be so high that application without a diluent may be difficult. Therefore, the concentration is usually 10% by weight or less, particularly 5% by weight or less of the whole cathode paste. And On the other hand, the presence of the polymer component may improve the retention of the electrolyte component, the binding of the active material, and the binding to the current collector substrate. Such inorganic compounds, alkane-based polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, polyvinylpyridine and poly-N-vinylpyrrolidone Acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide; polyfluorinated Vinyl, polyfluoride Fluorinated resins such as nilidene and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing such as polyvinyl chloride and polyvinylidene chloride polymer;
A conductive polymer such as polyaniline can be used.

Structure and manufacturing method of cathode: The obtained cathode paste is usually extruded onto a current collector substrate, and then a monomer component is polymerized by heat treatment to form a cathode electrode.

Examples of the material of the current collector substrate include various metals such as copper, aluminum, nickel and stainless steel, and alloys thereof. Preferably, aluminum is used as the current collector substrate. If it is too thin, the mechanical strength tends to be weak, which is a problem in production. If it is too thick, the capacity of the battery as a whole decreases. It is preferable that the surface of the current collector substrate be subjected to a roughening treatment in advance, since the adhesive strength of the electrode material increases. Examples of the surface roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. Examples of the mechanical polishing method include a method of polishing the surface of the current collector with a polishing cloth paper having abrasive particles fixed thereon, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like. Further, an intermediate layer may be formed on the surface of the current collector to increase the adhesive strength and the conductivity. Further, the shape of the current collector substrate may be a plate shape other than the metal mesh.

The thickness of the active material layer formed on the current collector is
It is usually at least 1 μm, preferably at least 10 μm. Also, usually 200 μm or less, preferably 150 μm
It is as follows. If it is too thin, it becomes difficult to ensure uniformity of the active material layer, and the capacity tends to decrease. On the other hand, if the thickness is too large, the rate characteristics tend to decrease.

A primer layer can be provided between the current collector substrate and the active material layer. As a result, the adhesiveness between the current collecting substrate and the active material layer can be further improved. The primer layer can be formed by applying a paint containing a conductive material, a binder, and a solvent on a current collecting substrate and then drying the paint.

As the conductive material used for the primer layer, various materials such as carbonaceous particles such as carbon black and graphite, metal powder, and conductive polymers can be used. The same binder and solvent as those used for the active material layer can be used for the primer layer. The thickness of the primer layer is usually 0.05 μm or more, preferably 0.1 μm or more.
μm or more, and usually 20 μm or less, preferably 1 μm or less.
0 μm or less. If it is too thin, it tends to be difficult to ensure uniformity of the primer layer. If the thickness is too large, the capacity rate characteristics of the battery tend to decrease.

[0042]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 First, the cathode paste components shown in the following table were charged into a mixing vessel equipped with a rotating sigma blade.

[0044]

[Table 1]

Next, an initiator solution (thermal initiator T-21:
1.0% by weight (25% by weight / PC: 75% by weight) was added to 100.2 parts by weight of the cathode paste prepared above. The photomer 4158 and T-2 used above were used.
1 is trimethylolpropane ethylene oxide-modified triacrylate and t-butylperoxy-
2-ethylhexanoate. In addition, LiCoO ₂
Has a particle size distribution in the range of 1 to 10 μm (median diameter 5 μm) and a specific surface area distribution of 0.5 m ² / g.

After charging the cathode paste and the thermal initiator into the mixing vessel, stirring was started under control and continued until the paste was sufficiently homogenized. The cathode paste is then filled into a conventional electrode coating device to test applicability, and the normal oil pressure (approximately 1,000
p. s. i. The cathode paste was applied to a 4 cm ² × 10 milliinch thick aluminum current collector using the following method. The cathode paste was then thermally cured in an oven using conventional techniques. The obtained cathode paste sufficiently adhered to the current collector without curling and without the need for additional steps such as calendering. According to this experiment, the cathode paste can be prepared without using a diluent, and the obtained cathode paste can be applied in the absence of a diluent, because it still shows sufficiently low viscosity and elasticity, It can be seen that this has solved the above-mentioned problems associated with the use of the diluent.

[0047]

According to the cathode paste of the present invention, by using a transition metal oxide having a specific particle size and / or specific surface area, the cathode paste can be formed on a current collector even in the absence of a diluent or a volatile coating solvent. Since it has suitable viscosity and elasticity so that it can be applied to a liquid, the problems associated with the use of a diluent are eliminated, and the industrial value of the present invention is high.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/62 H01M 4/62 Z 10/40 10/40 Z

Claims (7)

[Claims] 1. A diluent-free heat for a battery comprising an active material comprising an oxide containing a transition metal having a particle size distribution in the range of 1 to 15 μm, an electrolyte solvent, and one or more thermosetting monomers. Curable cathode paste. 2. A transition metal oxide active material having a specific surface area in the range of 0.25m ² /g~2.00m ² / g, the electrolyte and a solvent for a battery having a one or more thermosetting monomers Diluent-free thermosetting cathode paste. 3. The cathode paste according to claim 1, wherein the concentration of the active material is 70% by weight or more based on the cathode paste. 4. The cathode paste according to claim 1, wherein the active material comprises at least one lithium transition metal oxide. 5. The method according to claim 1, further comprising a carbonaceous material.
5. The cathode paste according to any one of 4. 6. The cathode paste according to claim 1, further comprising one or more thermal initiators. 7. The cathode paste according to claim 6, wherein the thermal initiator is a peroxide.