JP7540186B2 - Conductive composition for thermochemical battery electrodes - Google Patents

Description

The present invention relates to a conductive composition for thermochemical battery electrodes.

Thermochemical batteries generate electricity by using chemical reactions (such as oxidation-reduction reactions) caused by thermal energy in the presence of a heat source (Non-Patent Document 1), or they can be used as batteries in places where there is no heat source after generating electricity (charging) by using chemical reactions caused by thermal energy (Non-Patent Document 2).
The former is capable of generating electricity semi-permanently and continuously, and the latter can also be used repeatedly by repeatedly placing and maintaining it in a place with a heat source (high temperature) and a place without a heat source (low temperature). Thermochemical batteries basically consist of two electrodes, a positive electrode and a negative electrode or an anode and a cathode, and an electrolyte between them, and there are mainly two operating modes. In the first mode, when there is a temperature difference between the two electrodes, a carrier concentration difference occurs in the electrolyte due to the difference in the speed of the chemical reaction, generating a potential difference (called the one-cell type).
In the latter case, the electrolyte is separated by a separator, and when the entire structure including both electrodes is heated, electricity is generated (charged) due to the difference in chemical reactions on the left and right sides of the separator, and in low temperature locations, a reverse reaction occurs, generating a potential difference (this is called the two-cell type). In either case, a reaction between ions and electrons is required at the electrode interface in contact with the electrolyte, so electrodes are required.
Known electrodes for conventional thermochemical batteries include those using metals, particularly precious metals such as platinum, which have high catalytic activity (Non-Patent Document 3), and those using conductive polymers such as poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (hereinafter sometimes abbreviated as PEDOT/PSS) (Patent Document 1).

International Publication No. 2018/079325

“Seebeck coefficients in ionic liquids prospects for thermo-electrochemical cells”, T.J.Abraham, et al., Chem. Commun., 47, (2011) pp.6260-6262. “Charging-free electrochemical system for harvesting Low-grade thermal energy”, Y.ang, et al., PNAS, 111(48), (2014), pp.17011-17016. “Review of Thermally Regenerative Electrochemical Systems”, H.L.Chum and R.A.Osteryoung, Synopsis and Summary, vol.1, Solar Energy Research Institute, (1980) pp.1-53.

When using the materials described in the background art, precious metals such as platinum have problems with processability, and conductive polymers such as PEDOT/PSS have problems with durability and corrosion. Therefore, the problem that the present invention aims to solve is to provide a conductive composition for thermochemical battery electrodes with excellent conductivity that leads to low cost, high output, and high durability of thermochemical batteries.

The present inventors have conducted extensive research to solve the above problems, and have arrived at the present invention. That is, the present invention relates to a conductive composition for thermochemical battery electrodes, which comprises a material (A) having a condensed polycyclic hexagonal network surface and a binder resin (B), and which contains carbon and hetero elements as constituent elements of the condensed polycyclic hexagonal network surface, and in which the main component of the constituent elements is carbon.

The present invention also relates to the conductive composition for thermochemical battery electrodes, which contains a nitrogen element as a hetero element.

The present invention also relates to the above conductive composition for thermochemical battery electrodes, in which the proportion of surface terminal nitrogen atoms calculated by the formula N x (N 1 + N 2 ) is 0.5 to 25%, where N is the molar ratio of nitrogen atoms to all atoms on the surface of the material (A) having a condensed polycyclic hexagonal mesh surface, as measured by X-ray photoelectron spectroscopy (XPS), and N ₁ and N ₂ are the proportions of N1 _type nitrogen atoms and _N2 type nitrogen atoms to the total amount of nitrogen atoms on the surface of the material (A) having a condensed polycyclic hexagonal mesh surface, respectively.

The present invention also relates to the conductive composition for thermochemical battery electrodes, which further contains a base metal element as a constituent element.

The present invention also relates to the conductive composition for thermochemical battery electrodes, in which the base metal element contains Co and/or Fe.

The present invention also relates to the above-mentioned conductive composition for a thermochemical battery electrode, in which, when the molar ratios of carbon atoms and nitrogen atoms to all constituent atoms are _R and _R , respectively, the ratio of _R to _R is 1 to 40%.

The present invention also relates to the above-mentioned conductive composition for a thermochemical battery electrode, in which, when the molar ratios of carbon atoms, nitrogen atoms and base metal atoms to all constituent atoms are R _C , R _N and R _M , respectively, the ratio of R _N to R _C is 1 to 40%, and the ratio of R _M to R _C is 0.01 to 20%.

The present invention also relates to the above conductive composition for a thermochemical cell electrode, wherein the material (A) having a condensed polycyclic hexagonal network surface has a BET specific surface area (BET _N2 ) with nitrogen as the adsorbed species of 50 to 1200 m ² /g.

The present invention also relates to the conductive composition for thermochemical battery electrodes, in which, in an X-ray diffraction pattern obtained using CuKα radiation from the material (A) having a condensed polycyclic hexagonal network surface, the diffraction angle (2θ) has a peak in the range of 24 to 27°, and the half-width of the peak is 8° or less.

The present invention also relates to the conductive composition for thermochemical battery electrodes, which further contains a solvent.

By making the carbon material in the conductive composition for thermochemical battery electrodes a carbon material doped with a hetero element, the active sites for redox reactions are increased, leading to improved processability, higher output, and higher durability of the thermochemical battery, and the conductive composition for thermochemical battery electrodes with excellent conductivity is provided.

The present invention will be described in detail below. In this specification, the "material (A) having a condensed polycyclic hexagonal network surface" may be simply referred to as the "material (A)". Furthermore, the "conductive composition for thermochemical battery electrodes" may be simply referred to as the "conductive composition". Furthermore, the "resin" may be simply referred to as the "polymer".

<Material (A) Having Condensed Polycyclic Hexagonal Network Surface>
The material (A) having a condensed polycyclic hexagonal mesh surface refers to a material in which the atoms constituting the hexagonal mesh surface are covalently bonded to each other. The elements (constituent elements) constituting the hexagonal mesh surface are mainly carbon elements, and also contain other hetero elements (N, B, P, etc.). In addition, the constituent elements may contain base metal elements. The base metal elements referred to here are metal elements other than noble metal elements (Ru, Rh, Pd, Ag, Os, Ir, Pt, Au) among transition metal elements, and the base metal elements preferably contain one or more selected from the group consisting of Co, Fe, Ni, Mn, Cu, Ti, Vo, Cr, Zn and Sn, and more preferably contain Co and/or Fe.

The material (A) in the present invention is preferably one having a large specific surface area and high electronic conductivity. Since the redox reaction occurs on the surface of the electrode, the larger the specific surface area, the more reaction sites there are between the electrolyte ions, protons, and electrons, which leads to improved battery output. In addition, the higher the conductivity, the more electrons necessary for the redox reaction in the electrode can be supplied to the reaction sites, which leads to an increase in current, which is preferable. In addition, the more heteroatoms, especially nitrogen, are present on the surface of the material, the more active sites there are on the surface, which is preferable, and it is even more preferable that N is a terminal nitrogen, mainly an N1-type nitrogen atom, as described below.

In the material (A) in the present invention, when the molar ratios of carbon atoms and nitrogen atoms to all constituent atoms are R _C and R _N , respectively, the ratio of R _N to R _C is preferably 1 to 40%.

In the material (A) of the present invention, when the molar ratios of carbon atoms, nitrogen atoms and base metal atoms to all constituent atoms are R _C , R _N and R _M , respectively, it is preferable that the ratio of R _N to R _C is 1 to 40%, and the ratio of R _M to R _C is 0.01 to 20%.

When the element ratio of nitrogen atoms and base metal atoms to carbon atoms is within the above range, it is expected that the number and quality of active sites will be improved by the base metal elements acting effectively as electrodes for thermochemical batteries during the active site formation stage, such as by promoting carbon crystallization, developing pores, and generating edges.

In addition, when the molar ratio of nitrogen atoms to all atoms on the surface of material (A) measured by X-ray photoelectron spectroscopy (XPS) is N, and the proportions of N1 type nitrogen atoms and N2 type nitrogen atoms to the total amount of nitrogen atoms on the surface of material (A) are N ₁ and N ₂ , respectively, the proportion of surface terminal nitrogen atoms calculated by the formula N×(N ₁ +N ₂ ) is preferably 0.5 to 25%, more preferably 1 to 18%.

For example, in the case of material (A) in which the molar ratio N of nitrogen atoms to all elements on the surface of material (A) is 0.1, the proportion N of the amount of N1-type nitrogen atoms to the total amount of nitrogen on the surface of material (A) determined by peak separation of the _N1s spectrum of XPS is 30%, and the proportion _N of the amount of N2-type nitrogen atoms is 20%, the proportion of surface terminal nitrogen is 5% according to the following calculation formula.
{N×(N ₁ +N ₂ )}=0.1×(30%+20%)=5%

As shown in the structural formula below, when the heteroatom in the material (A) is a nitrogen atom, the nitrogen atom exists in various states to replace the carbon element in the carbon hexagonal mesh plane. In the present invention, the N1 type nitrogen atom has a binding energy of 398.5±0.5 eV for the N1s electron and has a structure similar to pyridine. The N2 type nitrogen atom has a binding energy of 400±0.5 eV for the N1s electron and has a structure similar to pyrrole. These are called pyridine N and pyrrole N, respectively, and in the present invention, these are collectively referred to as terminal nitrogen. When these peaks overlap, the peaks are separated by fitting by optimizing each peak component as a Gaussian function with the peak intensity, peak position, and full width at half maximum as parameters. Here, since it is difficult to separate the peaks of those with a pyridone-like structure, for convenience, it is considered that they may be included in the terminal nitrogen. Nitrogen atoms other than those mentioned above are classified as N3 type nitrogen atoms (quaternary ones that are mainly present inside a carbon ring and are bonded to three carbon atoms) and N4 type nitrogen atoms (those that are oxidized and have a different element such as oxygen bonded to them).

The terminal nitrogen has an unshared electron pair, and it has been reported that the terminal nitrogen affects the electronic state of the surrounding carbon, and the adjacent carbon atom acts as an active site, and also works favorably for the formation of a base metal-N4 structure in which a nitrogen atom is coordinated to a base metal. Therefore, it is believed that there is a large amount of terminal nitrogen on the surface of a highly active catalyst, and the surface terminal nitrogen ratio is an index that indicates the amount of terminal nitrogen present on the surface.

The material (A) in the present invention preferably has a BET specific surface area (BET _N2 ) with nitrogen as the adsorbed species of 50 to 1200 ^m2 /g. If the BET _N2 is in the above range, it is preferable because it can increase the reaction field where the reaction occurs. It is more preferable to have a BET N2 of 100 to 1000 ^m2 /g.

In the present invention, the specific surface area refers to the surface area per unit mass of a sample, and can be determined by a gas ( _N2 or _H2O ) adsorption method. The BET method is used as the analytical method, and the BET specific surface area can be calculated by determining the monomolecular adsorption amount from the intercept and gradient of a straight line obtained by plotting the relative pressure (P (adsorption equilibrium pressure)/P0 (saturated vapor pressure) = 0.05 to 0.3) versus the amount of gas adsorption.

In the X-ray diffraction (XRD) diagram obtained using CuKα radiation as an X-ray source, the material (A) in the present invention preferably has a peak at a diffraction angle (2θ) of 24.0 to 27.0°, and the half-width of the peak is 8° or less.

In an X-ray diffraction diagram obtained using CuKα radiation, it is preferable to have a diffraction peak originating from the (002) plane of carbon within the range of 24 to 27°. The position of the diffraction peak originating from the (002) plane of carbon changes within the above range depending on the distance between the hexagonal mesh planes, but the higher the peak position is on the higher angle side, the closer the hexagonal mesh planes are, meaning that the structural regularity is high. Also, the sharper the shape of the peak, the smaller the half-width of the peak, but the larger the crystallite size, indicating that the crystal structure is developed.

The smaller the half-width of the peak, the higher the crystallinity and electrical conductivity. Higher electrical conductivity is preferable because it can supply the electrons required for the oxygen reduction reaction in the electrode to the reaction field, leading to an increase in current. The half-width is preferably 8° or less, and more preferably 1° or less.

The content of material (A) is preferably 40 to 99 mass% of 100 mass% solids of the conductive composition, more preferably 60 to 96 mass%, even more preferably 70 to 92 mass%, and particularly preferably 75 to 85 mass%. When the content of material (A) is 40 to 99 mass%, the conductive network of the electrode formed by the conductive composition is well formed, and high durability due to high adhesion can be achieved.

<Binder Resin (B)>
First, the binder resin (B) will be described.
The binder resin may include one or more selected from the group consisting of polyurethane resin, polyamide resin, acrylonitrile resin, acrylic resin, butadiene resin, polyvinyl butyral resin, polyolefin resin, polyester resin, polystyrene resin, ethylene-vinyl acetate copolymer resin, epoxy resin, polyvinylidene fluoride resin, and silicone resin. In particular, polyurethane resin, polyamide resin, and polyester resin are preferred. However, the binder resin is not limited to these resins. The binder resin may be used alone or in combination of two or more.
The binder resin can also be a curable resin, which undergoes a curing (crosslinking) reaction after the binder resin is supported on the substrate.
In other words, the binder resin may be selected to be self-curing or may be combined with a curing agent, which will be described later, so that the conductive composition can be printed or coated on a substrate and then cured (crosslinked).

As the binder resin, a polyurethane resin is preferred from the viewpoints of volume resistivity, adhesion to the substrate, and durability. When the conductive composition is printed or coated on the substrate and then (hot) pressed, the resin softens and flows in the thickness direction while roughly maintaining the planar pattern shape of the conductive circuit at the time of printing/coating. This reduces voids and increases contact between the materials (A), so that a decrease in the volume resistivity of the resulting conductive circuit can be expected. Therefore, a binder resin that moderately softens and flows when (hot) pressed is preferred.

From the viewpoint of coatability and handling, the weight average molecular weight of the binder resin is preferably in the range of 1,000 to 200,000. From the viewpoint of adhesion, the glass transition temperature is preferably -40°C to 200°C. From the viewpoint of film durability, the acid value or hydroxyl value that acts as a crosslinking point during curing is preferably 5.0 mgKOH/g or more, whichever is higher, and more preferably 5.0 mgKOH/g or more and 50 mgKOH/g or more.

<Polyurethane resin>
The method for synthesizing the polyurethane resin is not particularly limited, but examples thereof include a method for producing the polyurethane resin by reacting a polyol compound (a) with a diisocyanate (b).

As the polyol compound (a), polyether polyols, polyester polyols, polycarbonate polyols, and other low molecular weight diols, which are generally known as polyol components constituting polyurethane resins, can be used.

Examples of polyether polyols include polymers or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, and the like.
Examples of polyester polyols include low molecular weight diols such as saturated and/or unsaturated hydrocarbon diols, including ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, hexanediol, octanediol, 1,4-butylenediol, diethylene glycol, triethylene glycol, dipropylene glycol, and dimer diol, and n-butyl glycidyl ether. Examples of such polyester polyols include polyester polyols obtained by dehydration condensation of alkyl glycidyl ethers such as alkyl glycidyl ether and 2-ethylhexyl glycidyl ether, monocarboxylic acid glycidyl esters such as versatic acid glycidyl ester, and dicarboxylic acids such as adipic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, or their anhydrides, and polyester polyols obtained by ring-opening polymerization of cyclic ester compounds.

Examples of polycarbonate polyols include 1) reaction products of diols or bisphenols with carbonate esters, and 2) reaction products of diols or bisphenols with phosgene in the presence of an alkali. Examples of carbonate esters include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, and the like. Examples of diols include the low molecular weight diols listed above. Examples of bisphenols include bisphenol A, bisphenol F, and bisphenols with alkylene oxides such as ethylene oxide and propylene oxide added to bisphenols.

The number average molecular weight (Mn) of the polyol compound is appropriately determined taking into consideration the solubility of the polyurethane resin when producing the conductive composition, the durability of the conductive circuit formed, the adhesive strength to the substrate, and the like, but is usually preferably in the range of 580 to 8,000, more preferably 1,000 to 5,000.
The above polyol compounds may be used alone or in combination of two or more kinds.

Examples of the diisocyanate compound (b) include aromatic diisocyanates, aliphatic diisocyanates, alicyclic isocyanates, and mixtures thereof. Examples of aromatic diisocyanates include 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-benzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, and xylylene diisocyanate.

Examples of the aliphatic diisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.
Examples of the alicyclic diisocyanate include cyclohexane-1,4-diisocyanate, isophorone diisocyanate, norbornane diisocyanate methyl, bis(4-isocyanate cyclohexyl)methane, 1,3-bis(isocyanate methyl)cyclohexane, and methylcyclohexane diisocyanate.

<Polyamide resin>
As the binder resin, polyamide resin is preferable from the viewpoints of volume resistivity, adhesion to the substrate, and durability. The volume resistivity is good because the resin content is easy to flow during (hot) pressing.
The polyamide resin used in the present invention is a general term for polymers having amide bonds obtained by various reactions, such as the polycondensation of dibasic acids and diamines, the polycondensation of aminocarboxylic acids, or the ring-opening polymerization of lactams, and is a broad concept that includes various modified polyamides, as well as those produced from partially hydrogenated reaction products, those produced by partial copolymerization of other monomers, and those mixed with other substances such as various additives.

The polyamide resin used in the present invention is not particularly limited as long as the above conditions are satisfied, but dimer acid modified polyamide resin obtained by condensation polymerization of dibasic acid mainly composed of dimer acid and polyamines is preferred. As the dimer acid used in producing dimer acid modified polyamide resin, dimer acid obtained by polymerizing natural monobasic unsaturated fatty acids contained in tall oil fatty acid, soybean oil fatty acid, etc. is widely used industrially. Commercially available products of the dimer acid include Haridimer 200, 300 (manufactured by Harima Chemicals), Versadigm 228, 216, Empol 1018, 1019, 1061, 1062 (manufactured by Cognis), etc. Furthermore, hydrogenated dimer acid can also be used, and commercially available products of hydrogenated dimer acid include Pripol 1009 (manufactured by Croda Japan Co., Ltd.) and Empol 1008 (manufactured by Cognis).

In addition to the above dimer acids, various dicarboxylic acids can be used as dibasic acids. Specific examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid (anhydride), maleic acid (anhydride), glutaric acid, adipic acid, vimelic acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 1,3- or 1,4-cyclohexanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, and 1,16-hexadecanedicarboxylic acid.

<Polyester Resin>
As the binder resin, a polyester resin is preferred from the viewpoints of volume resistivity and adhesion to the substrate, and the volume resistivity is favorable because the resin content is easily fluidized during (hot) pressing.
The polyester resin is a polymer composed of polyvalent carboxylic acid and polyhydric alcohol as monomers. Known polyester resins can be used. Examples of polyvalent carboxylic acid components constituting the polyester resin include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, unsaturated dicarboxylic acids, and trivalent or higher carboxylic acids, and one or more of these can be selected and used. On the other hand, examples of polyhydric alcohol components constituting the polyester resin include aliphatic glycols, ether glycols, and trivalent or higher polyalcohols, and one or more of these can be selected and used. Commercially available polyester resins include Vylon (manufactured by Toyobo Co., Ltd., "Vylon" is a registered trademark), Polyester (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., "Polyester" is a registered trademark), and Teslac (manufactured by Hitachi Chemical Polymer Co., Ltd., "Teslac" is a registered trademark).

When using an aqueous liquid medium, a binder resin, generally known as an aqueous emulsion, can also be used. An aqueous emulsion is one in which the binder resin is not dissolved in water but is dispersed in the form of fine particles.

The emulsion used is not particularly limited, but examples include (meth)acrylic emulsions, nitrile emulsions, urethane emulsions, diene emulsions (such as SBR (styrene butadiene rubber)), and fluorine-based emulsions (such as PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene)).

<Conductive composition for thermochemical battery electrode>
The conductive composition for a thermochemical battery electrode contains a material (A) and a binder resin (B), and the entire surface of the material (A) is not covered with the binder resin (B) so that active sites can be exposed. Therefore, the reactive sites can function effectively in the target oxidation-reduction reaction.

The conductive composition for thermochemical battery electrodes may contain a solvent or dispersant as necessary. The ratio of the material (A) and the solvent to the binder resin (B) and the dispersant is not particularly limited and may be appropriately selected within a wide range. The appropriate viscosity of the conductive composition for thermochemical battery electrodes depends on the coating method of the conductive composition for thermochemical battery electrodes, but is generally preferably 10 mPa·s or more and 30,000 mPa·s or less.

<Solvent>
Next, the solvent will be described. When the material (A) in the conductive composition and the binder resin (B) are mixed uniformly, a solvent can be appropriately used. Examples of such a solvent include an organic solvent and water.
The organic solvent may be an appropriate one depending on the composition of the conductive composition from among alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol methyl ether, diethylene glycol methyl ether, etc., ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc., ethers such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc., hydrocarbons such as hexane, heptane, octane, etc., aromatics such as benzene, toluene, xylene, cumene, etc., esters such as ethyl acetate, butyl acetate, etc. Two or more kinds of solvents may be used.
When a printing/coating method such as screen printing is employed that requires the conductive composition to have a certain level of viscosity, the viscosity of the organic solvent at 25° C. is preferably 30 mPa·s to 75,000 mPa·s. Within the above range, both high conductivity and dispersibility suitable for coating can be achieved.
Examples of the high-viscosity solvent include terpineol, dihydroterpineol, 2,4-diethyl-1,5-pentanediol, 1,3-butylene glycol, and isobornylcyclohexanol. Two or more of the high-viscosity solvents mentioned here may be used, and they may also be used in combination with a low-viscosity solvent having a viscosity of less than 30 mPa·s at 25° C., such as methyl ethyl ketone, toluene, and isopropyl alcohol.

Next, other components will be described. If necessary, various additives such as ultraviolet absorbers, ultraviolet stabilizers, radical scavengers, fillers, thixotropy-imparting agents, antiaging agents, antioxidants, antistatic agents, flame retardants, thermal conductivity improvers, plasticizers, antisagging agents, antifouling agents, preservatives, bactericides, defoamers, leveling agents, antiblocking agents, thickeners, pigment dispersants, and silane coupling agents may be added to the conductive composition for thermochemical battery electrodes of the present invention, within the scope that does not impede the effects of the present invention.

<Dispersing machine/mixing machine>
As an apparatus that can be used when obtaining the conductive composition, a dispersing machine or a mixer that is generally used for dispersing pigments or the like can be used.
For example, mixers such as a Disper, a Homomixer, or a Planetary Mixer; homogenizers such as "Clearmix" manufactured by M Technique Co., Ltd. or "Filmix" manufactured by PRIMIX Co., Ltd.; media-type dispersers such as a paint conditioner (manufactured by Red Devil Co., Ltd.), a ball mill, a sand mill ("Dynomill" manufactured by Shinmaru Enterprises, etc.), an attritor, a pearl mill ("DCP Mill" manufactured by Eirich Co., Ltd., etc.), or a Coball mill; media-less dispersers such as a wet jet mill ("Genus PY" manufactured by Genus Co., Ltd., "Starburst" manufactured by Sugino Machine Ltd., "Nanomizer" manufactured by Nanomizer Co., Ltd., etc.), "Clear SS-5" manufactured by M Technique Co., Ltd., or "MICROS" manufactured by Nara Machine Co., Ltd.; or other roll mills, but are not limited thereto.

For example, when using a media-type disperser, it is preferable to use a disperser in which the agitator and vessel are made of ceramic or resin, or to use a disperser in which the metallic agitator and vessel surface is treated with tungsten carbide spraying or resin coating. As the media, it is preferable to use glass beads, or ceramic beads such as zirconia beads or alumina beads. Only one type of dispersing device may be used, or multiple types of devices may be used in combination.

<Electrodes>
When an electrode is produced using the conductive composition of the present invention, the conductive composition can be printed or formed into a free-standing film on one or both sides of a substrate such as paper or plastic, depending on the intended use, by a conventional printing method such as screen printing, rotary screen printing, flexographic printing, gravure printing, gravure offset printing, offset printing, letterpress printing, inkjet printing, or casting.

As the paper substrate, coated paper, uncoated paper, and various other processed papers such as synthetic paper, polyethylene coated paper, impregnated paper, water-resistant paper, insulating paper, and stretchable paper can be used. As the plastic substrate, substrates made of plastics such as polyester, polyethylene, polypropylene, cellophane, vinyl chloride, vinylidene chloride, polystyrene, vinyl alcohol, ethylene-vinyl alcohol, nylon, polyimide, and polycarbonate can be used. As the metal substrate, metal foils or alloy foils such as aluminum foil, copper foil, nickel foil, and stainless steel foil can be used.

The volume resistivity of an electrode manufactured using the conductive composition of the present invention is preferably less than 5×10 ⁻² Ω·cm. When the volume resistivity is less than 5×10 ⁻² Ω·cm, the electrode can be suitably used as an electrode for a thermochemical battery. Note that a lower volume resistivity is preferable because it can reduce the internal resistance in the thermochemical battery.

The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the scope of the invention. In the production examples, examples, and comparative examples, "parts" means "parts by mass," "%" means "% by mass," Mw means weight average molecular weight, and Tg means glass transition temperature.

Before explaining the examples, we will describe the manufacturing methods of the material (A) and binder resin (B) used in the examples.

The following measuring instruments were used to determine the element molar ratio (ratio of N1 type nitrogen atom amount to N2 type nitrogen atom amount), surface terminal nitrogen ratio, BET specific surface area, and X-ray diffraction angle peak position and peak half width shown in Table 1 for material (A). In addition, the presence of carbon atoms constituting the carbon hexagonal mesh plane and nitrogen atoms substituted for carbon atoms on the carbon hexagonal mesh plane was confirmed.
Surface terminal nitrogen: X-ray spectroscopic analysis (XPS) (Shimadzu/KRATOS AXIS-HS)
Measurement of BET specific surface area: Nitrogen adsorption measurement (Microtrack BELSORP-mini)
X-ray diffraction: fully automatic horizontal multipurpose X-ray diffraction device (Rigaku Corporation, Smartlab)
R _C , R _N , R _M : C H N elemental analysis (PerkinElmer 2400 type CHN elemental analysis device), ICP emission spectrometry (SPECTRO ARCO S FHS12 manufactured by SPECTRO)

The binder resin (B) was evaluated as follows.
<Method for measuring weight average molecular weight (Mw)>
The Mw was measured using a GPC (gel permeation chromatography) "HPC-8020" manufactured by Tosoh Corporation. The measurement was performed using tetrahydrofuran (THF) as the eluent and two "LF-604" columns (manufactured by Showa Denko K.K.: GPC column for rapid analysis: 6 mm ID x 150 mm size) connected in series, under conditions of a flow rate of 0.6 ml/min and a column temperature of 40°C, and the weight average molecular weight (Mw) was determined in terms of polystyrene with a known molecular weight.

<Measurement of Acid Value>
Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 ml of a toluene/ethanol (volume ratio: toluene/ethanol = 2/1) mixture was added and dissolved. Phenolphthalein test solution was added as an indicator and the mixture was held for 30 seconds. After that, the solution was titrated with 0.1N alcoholic potassium hydroxide solution until it turned a light pink color. The acid value was calculated using the following formula (unit: mgKOH/g). Acid value (mgKOH/g) = (5.611 x a x F)/S
however,
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (ml)
F: Potency of 0.1N alcoholic potassium hydroxide solution

<Measurement of Hydroxyl Value>
Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 ml of a toluene/ethanol (volume ratio: toluene/ethanol = 2/1) mixture was added and dissolved. Exactly 5 ml of an acetylating agent (a solution of 25 g of acetic anhydride dissolved in pyridine to a volume of 100 ml) was then added and stirred for approximately 1 hour. Phenolphthalein test solution was added as an indicator and allowed to stand for 30 seconds. The solution was then titrated with 0.1 N alcoholic potassium hydroxide solution until it turned a light pink color.
The hydroxyl value was calculated according to the following formula (unit: mgKOH/g).
Hydroxyl value (mgKOH/g) = [{(b-a) x F x 28.05}/S] + D
however,
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (ml)
b: Amount of 0.1N alcoholic potassium hydroxide solution consumed in the blank experiment (ml)
F: Potency of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH/g)

<Method of measuring glass transition temperature>
The measurement was carried out using a "DSC-1" manufactured by Mettler Toledo Co., Ltd., raising the temperature from -80 to 150°C at a rate of 2°C/min.

<Production of Material (A) Having Condensed Polycyclic Hexagonal Network Plane>
[Production Example 1]
Graphene nanoplatelets xGnP-C-750 (manufactured by XGsciences) and iron phthalocyanine P-26 (manufactured by Sanyo Pigment Co., Ltd.) were weighed out to a mass ratio of 1/0.5 (graphene nanoplatelets/iron phthalocyanine) and dry-mixed to obtain a mixture. The mixture was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800°C for 2 hours to obtain material (A-1).

[Production Example 2]
Ketjen Black EC-600JD (manufactured by Lion Specialty Chemicals) and cobalt phthalocyanine (manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed out to a mass ratio of 1/0.5 (Ketjen Black/Cobalt phthalocyanine) and dry mixed to obtain a mixture. The mixture was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 700°C for 2 hours to obtain material (A-2).

[Production Example 3]
Carbon nanotubes VGCF-H (manufactured by Showa Denko K.K.) and iron phthalocyanine (manufactured by Sanyo Pigment Co., Ltd.) were weighed out to a mass ratio of 1/0.5 (carbon nanotubes/iron phthalocyanine) and dry-mixed to obtain a mixture. The mixture was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800°C for 2 hours to obtain material (A-3).

[Production Example 4]
Knobel MJ(4)150 (manufactured by Toyo Tanso Co., Ltd.) and iron phthalocyanine (manufactured by Sanyo Pigment Co., Ltd.) were weighed out to a mass ratio of 1/0.5 (Knobel/iron phthalocyanine) and dry-mixed to obtain a mixture. The mixture was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800°C for 2 hours to obtain material (A-4).

[Production Example 5]
Phenol resin (PSM-4326, manufactured by Gun-ei Chemical Industry Co., Ltd.) and iron phthalocyanine P-26 (manufactured by Sanyo Pigment Co., Ltd.) were weighed in a mass ratio of 3.3:1 and wet-mixed in acetone. The mixture was distilled under reduced pressure, then pulverized in a mortar to obtain a precursor. The precursor powder was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 600 ° C. for 2 hours to obtain a carbon sintered body (1). The carbon sintered body (1) was reslurried in concentrated hydrochloric acid, allowed to stand, and after the carbon sintered body (1) had precipitated, the supernatant was removed. The above operation was repeated until the color of the supernatant disappeared, and the mixture was filtered, washed with water, and dried, and then pulverized in a mortar, filled into an alumina crucible, and heat-treated in an electric furnace under an ammonia atmosphere at 800 ° C. for 1 hour to obtain a carbon sintered body (2). The carbon sintered body (2) was reslurried in concentrated hydrochloric acid, allowed to stand, and after the carbon sintered body had precipitated, the supernatant was removed. The above procedure was repeated until the color of the supernatant disappeared, and then the mixture was filtered, washed with water, dried, and pulverized in a mortar to obtain material (A-5).

[Production Example 6]
Polyvinylpyridine (PVP, manufactured by Aldrich) was dissolved in dimethylformamide, and iron chloride hexahydrate was added in a mass ratio of 2:1 to the PVP, followed by stirring at room temperature for 24 hours to obtain a polyvinylpyridine-iron complex. The polyvinylpyridine-iron complex was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800°C for 2 hours, and the resulting carbide was pulverized in a mortar to obtain material (A-6).

[Production Example 7]
Polyvinylpyridine (PVP, manufactured by Aldrich) was dissolved in dimethylformamide, and iron chloride hexahydrate was added in a mass ratio of 2:1 to PVP, and the mixture was stirred at room temperature for 24 hours to obtain a polyvinylpyridine-iron complex. The polyvinylpyridine and Ketjen Black (EC-600JD manufactured by Lion Corporation) were weighed in a mass ratio of 1:1 and dry-mixed in a mortar to obtain a precursor. The precursor powder was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800°C for 2 hours, and the obtained carbide was pulverized in a mortar to obtain material (A-7).

[Production Example 8]
Graphene nanoplatelets xGnP-C-750 (manufactured by XGsciences) were filled into an alumina crucible and heat-treated in an electric furnace under an ammonia nitrogen atmosphere at 1000° C. for 2 hours to obtain material (A-8).

[Production Example 9]
90 parts of ion-exchanged water, 0.2 parts of iron (II) chloride tetrahydrate, and 3.2 parts of copper phthalocyanine derivative SOLSPERSE12000 (manufactured by Lubrizol Japan) were weighed into a glass bottle to prepare a uniform aqueous solution, and then 6.6 parts of graphene nanoplatelets xGnP-C-750 (manufactured by XGsciences) were added, and zirconia beads were further added as media, and then dispersed with a paint shaker (Mitsuwa Tech Co., Ltd.: Scandex SK450) to obtain a precursor mixture paste. This precursor mixture paste was distilled under reduced pressure with a rotary evaporator, and the obtained solid was finely ground in a mortar to obtain a uniform precursor powder. The obtained precursor powder was filled into an alumina crucible and heat-treated in an electric furnace under a nitrogen atmosphere at 800 ° C. for 2 hours to obtain a material (A-9).

The physical properties of the material (A) obtained in Production Examples 1 to 9 are shown in Table 1.

<Production of binder resin (B)>
[Production Example 10]
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 455.5 parts of a polyester polyol obtained from terephthalic acid, adipic acid, and 3-methyl-1,5-pentanediol ("Kuraray Polyol P-2011", Mn=2011, manufactured by Kuraray Co., Ltd.), 16.5 parts of dimethylolbutanoic acid, 105.2 parts of isophorone diisocyanate, and 140 parts of toluene, and reacted at 90°C for 3 hours under a nitrogen atmosphere, and 360 parts of toluene was added to this to obtain a urethane prepolymer solution having an isocyanate group. Next, 969.5 parts of the obtained urethane prepolymer solution having isocyanate groups was added to a mixture of 19.9 parts of isophorone diamine, 0.63 parts of di-n-butylamine, 294.5 parts of 2-propanol, and 335.5 parts of toluene, and the mixture was reacted at 50° C. for 3 hours and then at 70° C. for 2 hours. The mixture was diluted with 126 parts of toluene and 54 parts of 2-propanol, removed, and dried in a vacuum to obtain a polyurethane resin binder resin (B-1) having Mw=61,000, acid value=10 mgKOH/g, and a total equivalent of the amino groups in the polyamino compound and the reaction stopper relative to the free isocyanate groups at both ends of the urethane prepolymer of 0.98.

[Production Example 11]
In a four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, inlet tube, and thermometer, 156.2 g of Pripol 1009 as a polybasic acid compound, 5.5 g of 5-hydroxyisophthalic acid, 146.4 g of Priamine 1074 as a polyamine compound, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature was stabilized, the temperature was raised to 110°C, and after confirming the outflow of water, the temperature was raised to 120°C after 30 minutes, and then the dehydration reaction was continued while raising the temperature by 10°C every 30 minutes. When the temperature reached 230°C, the reaction was continued at that temperature for 3 hours, and the temperature was lowered for 1 hour under a vacuum of about 2 kPa. Finally, an antioxidant was added to obtain a polyamide resin binder resin (B-2) having a weight average molecular weight of 24,000, an acid value of 13.2 KOHmg/g, a hydroxyl value of 5.5 KOHmg/g, and a glass transition temperature of -32°C.

<Preparation of Conductive Composition for Thermochemical Battery Electrode>
[Example 1]
9.6 parts of material (A-1), 49.2 parts of water as an aqueous liquid medium, and 40 parts of an aqueous solution of carboxymethylcellulose (CMC) as a thickener (solid content 2%) were mixed in a mixer, and further dispersed in a sand mill. After that, 4 parts (solid content 50%) of an emulsion-type acrylic resin dispersion solution (manufactured by Toyochem Co., Ltd.: W-168) was added as a binder resin and mixed in a mixer to obtain a conductive composition (1) for a thermochemical battery electrode.
The obtained conductive composition for thermochemical battery electrodes (1) was poured into a Teflon (registered trademark) container, dried at 80°C for 1 hour, and then dried at 100°C for 3 hours to obtain a conductive film. At this time, the amount of the conductive composition was adjusted so that the film thickness after curing was 60 μm. The obtained conductive film was punched into a disk shape of φ16 mm to obtain an electrode.

<Assembling the coin cell battery>
A CR2032 coin-type battery was prepared in a glove box filled with an argon atmosphere using a SUS316 case, with a polypropylene separator between two of the electrodes obtained above, and an aqueous solution of 0.5M _K3 [Fe(CN) ₆ ]/ _K4 [Fe(CN) ₆ ] _.3H2O was injected as an electrolyte.

[Examples 2 to 9]
An electrode and a coin-type battery were obtained in the same manner as in Example 1, except that the material (A) and the binder resin were changed to the types and amounts shown in Table 2.

[Example 10]
12 parts of the material (A-1), 2.9 parts of the binder resin (B-1), and 29.5 parts of N-methylpyrrolidone as a solvent were mixed in a mixer and further dispersed in a sand mill to obtain a conductive composition for thermochemical battery electrodes (10). An electrode and a coin-type battery were produced from the obtained conductive composition for thermochemical battery electrodes (10) in the same manner as in Example 1.

[Examples 11 to 18]
An electrode and a coin-type battery were obtained in the same manner as in Example 10, except that the types and amounts of the material (A) and the binder resin were changed to those shown in Table 2.

<Comparative Example 1>
PEDOT/PSS solution Orgacon S315 (Agfa Chemicals Japan) was poured into a Teflon (registered trademark) container, dried at 80°C for 1 hour, and then dried at 150°C for 3 hours to obtain a conductive film. At this time, the amount of conductive composition was adjusted so that the film thickness after drying was 60 μm. The obtained conductive film was punched into a disk shape of φ16 mm to form an electrode. Furthermore, a coin-type battery was produced in the same manner as in Example 1.

The electrodes and coin-type batteries obtained using the above method were evaluated using the following methods. The results are shown in Table 2.

<Volume resistivity of electrode>
The volume resistivity of the electrode was determined by measuring it by the four-terminal method (JIS-K7194) using Loresta GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) The evaluation results are shown in Table 1.
◎◎: "Volume resistivity is less than 3.5×10 ^-3 Ω·cm (very excellent)"
◎〇: "Volume resistivity is 3.5×10 ^-3 Ω·cm or more and less than 4×10 ^-3 Ω·cm (very excellent)"
◎: "Volume resistivity is 4×10 ⁻³ Ωcm or more and less than 5×10 ⁻³ Ωcm (very good)"
○: "Volume resistivity is 5×10 ⁻³ Ω·cm or more and less than 1×10 ⁻² Ω·cm (good)"
○△: "Volume resistivity is 1×10 ^-2 Ω·cm or more and less than 5×10 ^-2 Ω·cm (within the usable range)"
△: "Volume resistivity is 5×10 ⁻² Ω·cm or more and less than 1×10 ⁻¹ Ω·cm (poor)"
×: "Volume resistivity is 1×10 ⁻¹ Ω·cm or more (very poor)"

<Electrode durability>
The resistance to moisture and heat was evaluated based on the rate of increase (rate of change) in the volume resistivity after the moisture and heat resistance test relative to the volume resistivity before the test. The evaluation method is as follows. The prepared electrode was placed in a small environmental tester (Espec Corporation: Model SH-661) and stored at a temperature of 60° C. and a relative humidity of 90% for 5000 hours to perform the moisture and heat resistance test, and then the volume resistivity was measured in the same manner as above.
◎: The increase in volume resistivity is less than 10% (very good)
◯: The increase in volume resistivity is 10% or more and less than 20% (good)
△: The increase in volume resistivity is 20% or more and less than 30% (within the range of use)
×: The increase in volume resistivity is 30% or more (very poor)

<Battery evaluation>
The output of the coin battery was measured using the coin battery. The coin battery was placed on a hot plate heated to 65°C indoors at 25°C, creating a temperature difference of 40°C above and below the coin battery. Next, a source meter was connected to the anode and cathode sides to measure the voltage and current values, and the output was calculated.
◎◎: Battery output is 15μW or more (very good)
◎: Battery output is 10 μW or more and less than 15 μW (good)
〇: Battery output is between 5μW and 10μW (within the operating range)
△: Battery output is less than 5 μW (defective)

The materials used in the examples are shown below.
<Binder Resin (B)>
B-1: Polyurethane resin (polyurethane resin obtained in Production Example 10)
B-2: Polyamide resin (polyamide resin obtained in Production Example 11)
B-3: Polyester resin Vylon GK130 (manufactured by Toyobo Co., Ltd.)
B-4: (meth)acrylic resin NeoCryl B-728 (manufactured by Kusumoto Chemicals Co., Ltd.)
B-5: Polyacrylonitrile resin Product No. 181315 (Sigma-Ald
Rich Co., Ltd.)

In Examples 1 to 18, the resistance value of the electrodes was low, and therefore high output as a thermochemical battery was confirmed. On the other hand, in Comparative Example 1, the resistance value was high, and therefore output as a thermochemical battery was low. In addition, while the durability of the electrodes was excellent in Examples 1 to 18, it was revealed that the durability of Comparative Example 1 was low, and therefore poor practicality as an electrode for a thermochemical battery was poor.

Claims (9)

The conductive composition for a thermochemical battery electrode comprises a material (A) having a condensed polycyclic hexagonal network surface and a binder resin (B), the conductive composition for a thermochemical battery electrode comprising a carbon element and a hetero element as constituent elements of the condensed polycyclic hexagonal network surface, the main component of the constituent elements being carbon element, and the hetero element being nitrogen element . The conductive composition for thermochemical battery electrodes according to claim 1, wherein the molar ratio of nitrogen atoms to all atoms on the surface of the material (A) having a condensed polycyclic hexagonal mesh surface measured by X-ray photoelectron spectroscopy (XPS) is N, and the proportion of N1 type nitrogen atoms and the proportion of N2 type nitrogen atoms to the total amount of nitrogen atoms on the surface of the material (A) having a condensed polycyclic hexagonal mesh surface are _N1 and _N2 , respectively, and the proportion of surface terminal nitrogen atoms calculated by the formula N x ( _N1 + _N2 ) is 0.5 to 25%. 3. The conductive composition for a thermochemical battery electrode according to claim 1, further comprising a base metal element as a constituent element. 4. The conductive composition for a thermochemical battery electrode according to claim 3 , wherein the base metal element comprises Co and/or Fe. The conductive composition for a thermochemical battery electrode according to any one of claims 1 to 4 , wherein the molar ratio of carbon atoms and the molar ratio of _nitrogen atoms to all constituent atoms are _R and _R , respectively, and the ratio of R to _R is 1 to 40%. The conductive composition for a thermochemical battery electrode according to any one of claims 3 to 5, wherein the molar ratio of carbon atoms, the molar ratio of nitrogen atoms and the molar ratio of base metal atoms to all constituent atoms are R _C , R _N and R _M , respectively, and the ratio of R _N to R _C is 1 to 40%, and the ratio of R _M to R _C is 0.01 to 20%. 7. The conductive composition for thermochemical battery electrodes according to claim 1, wherein the material (A) having a condensed polycyclic hexagonal network surface has a BET specific surface area (BET _N2 ) of 50 to 1200 m ² /g when nitrogen is the adsorbed species. 8. The conductive composition for a thermochemical battery electrode according to claim 1, wherein in an X-ray diffraction pattern obtained using CuKα radiation from the material (A) having a condensed polycyclic hexagonal network surface, the material (A) has a peak in the diffraction angle (2θ) range of 24 to 27 °, and the half-value width of the peak is 8° or less. The conductive composition for a thermochemical battery electrode according to any one of claims 1 to 8 , further comprising a solvent.