Slurry for power storage device negative electrodes, negative electrode for power storage devices, and power storage device

Abstract

The present invention provides a slurry for power storage device negative electrodes which has excellent adhesion and which makes it possible to produce a negative electrode for power storage devices that exhibits good charging / discharging durability characteristics.　A slurry for power storage device negative electrodes according to the present invention comprises: a negative electrode active material (A) obtained by pyrolyzing a rubber raw material containing sulfur, separating solid matter and dry distillation gas, separating the solid matter into metal and carbonized material, and heat-treating the carbonized material; at least one polymer (B) selected from the group consisting of conjugated diene based polymers, acrylic based polymers, acrylonitrile based polymers, polyurethanes, polyimides, and polyamidimides; and a liquid medium (C).

Description

Slurry for negative electrode of power storage device, negative electrode for power storage device, and power storage device

[0001] The present invention relates to a slurry for an electricity storage device negative electrode, an electricity storage device negative electrode formed by applying the slurry to a current collector and drying the slurry, and an electricity storage device including the electricity storage device negative electrode.

[0002] In recent years, there has been a demand for high-voltage, high-energy-density power storage devices as power sources for electronic devices. Lithium-ion batteries and lithium-ion capacitors are expected to be such power storage devices.

[0003] On the other hand, lithium, the main constituent element of the positive electrode active material in lithium-ion secondary batteries, is facing bottlenecks to mass production and large-scale production due to factors such as the rising price of lithium due to the expanding demand for lithium-ion secondary batteries and limited lithium reserves.

[0004] For this reason, research is being conducted on sodium batteries that use sodium, which is an abundant and low-cost resource, instead of lithium, and secondary batteries that do not require lithium or transition metal elements (see, for example, Patent Documents 1 to 4).

[0005] JP 2013-203565 A JP 2014-229452 A JP 2012-206925 A Japanese Patent No. 7246789 A

[0006] In the sodium batteries disclosed in Patent Documents 1 to 3 and the secondary battery disclosed in Patent Document 4, there has been a demand for further improvement in battery performance such as charge / discharge durability by improving adhesion at the negative electrode.

[0007] Some aspects of the present invention provide a slurry for an electricity storage device negative electrode that can produce an electricity storage device negative electrode that has excellent adhesion and exhibits good charge / discharge durability characteristics.

[0008] It has been empirically demonstrated that the bonding ability between active materials, the adhesion ability between the active material and the current collector, and the resistance to powder shedding are almost proportional to the performance, and therefore, in this specification, these are collectively referred to as "adhesion."

[0009] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized as any of the following aspects.

[0010] One embodiment of the slurry for an electric storage device negative electrode according to the present invention comprises: a negative electrode active material (A) obtained by thermally decomposing a sulfur-containing rubber raw material to separate it into a solid and a dry distillation gas, sorting the solid into a metal and a carbide, and heat-treating the carbide; a polymer (B) that is at least one selected from the group consisting of a conjugated diene-based polymer, an acrylic-based polymer, an acrylonitrile-based polymer, a polyurethane, a polyimide, and a polyamideimide; and a liquid medium (C).

[0011] In one embodiment of the slurry for a negative electrode of an electricity storage device, the rubber raw material may be derived from tires.

[0012] In any of the above embodiments of the slurry for an electricity storage device negative electrode, a thickener (E) may be further contained.

[0013] One aspect of the negative electrode for an electricity storage device according to the present invention includes a current collector and an active material layer formed by applying the slurry for an electricity storage device negative electrode according to any one of the above aspects to the surface of the current collector and drying the applied slurry.

[0014] An aspect of the electricity storage device according to the present invention includes the electricity storage device negative electrode of the above aspect.

[0015] In one embodiment of the electricity storage device, the device may have an electrolyte solution containing a sodium salt or a potassium salt.

[0016] The slurry for an electric storage device negative electrode according to the present invention can produce an electric storage device negative electrode that has excellent adhesion and exhibits good charge-discharge durability. Furthermore, the negative electrode active material contained in the slurry for an electric storage device negative electrode according to the present invention is produced by recycling a sulfur-containing rubber raw material, which is expected to reduce costs and environmental impact, and ultimately contribute to the mass production and upsizing of electric storage devices.

[0017] Preferred embodiments of the present invention will be described in detail below. It should be understood that the present invention is not limited to the embodiments described below, but also includes various modifications that are implemented within the scope of the present invention.

[0018] In this specification, a numerical range described as "X to Y" is interpreted as including the numerical value X as the lower limit and the numerical value Y as the upper limit.

[0019] In this specification, "(meth)acrylic acid" refers to "acrylic acid" or "methacrylic acid".

[0020] 1. Slurry for Electricity Storage Device Negative Electrode A slurry for an electricity storage device negative electrode according to one embodiment of the present invention contains a negative electrode active material (A), a polymer (B), and a liquid medium (C). The negative electrode active material (A) is obtained by pyrolyzing a sulfur-containing rubber raw material to separate it into a solid and a dry distillation gas, sorting the solid into a metal and a carbide, and heat-treating the carbide. The polymer (B) is at least one selected from the group consisting of a conjugated diene polymer, an acrylic polymer, an acrylonitrile polymer, a polyurethane, a polyimide, and a polyamideimide.

[0021] The slurry for an electric storage device negative electrode according to this embodiment can be used as a material for producing an electric storage device negative electrode (negative electrode active material layer) that has excellent adhesion and good charge / discharge durability. Hereinafter, components that can be contained in the slurry for an electric storage device negative electrode according to this embodiment and a production method thereof will be described in detail.

[0022] 1.1. Components 1.1.1. Negative Electrode Active Material (A) The slurry for an electricity storage device negative electrode according to this embodiment contains a negative electrode active material (A) obtained by thermally decomposing a sulfur-containing rubber raw material to separate it into a solid and a dry distillation gas, sorting the solid into a metal and a carbide, and heat-treating the carbide.

[0023] Examples of sulfur-containing rubber raw materials that can be used include various rubber products containing sulfur and silicon, such as tires, which are discarded after use, and waste products containing sulfur and silicon as the main component, which are generated as defective products or surplus materials during the manufacturing process and discarded.

[0024] First, the raw rubbers are pyrolyzed using a pyrolysis furnace. This separates the rubbers into solid matter and gaseous dry distillation gas. The solid matter separated from the rubbers by pyrolysis is then sorted using a sorting machine. This separates the solid matter into metals and carbides. The metals separated from the solid matter can be recycled as a metal resource.

[0025] On the other hand, the carbonized material separated from the solid matter can be pulverized and recycled as the negative electrode active material (A) of the battery.

[0026] The content of the negative electrode active material (A) in the negative electrode active material layer is not particularly limited, but is preferably 80 to 95 mass %.

[0027] 1.1.2. Polymer (B) The slurry for an electricity storage device negative electrode according to this embodiment contains a polymer (B). The polymer (B) is at least one selected from the group consisting of a conjugated diene polymer, an acrylic polymer, an acrylonitrile polymer, a polyurethane, a polyimide, and a polyamideimide. These polymers (B) may be used alone or in combination of two or more. These polymers (B) may be commercially available polymers or may be manufactured.

[0028] The content of the polymer (B) in the slurry for the negative electrode of an electricity storage device according to this embodiment is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, even more preferably 3 to 12 parts by mass, and particularly preferably 5 to 10 parts by mass, relative to 100 parts by mass of the negative electrode active material (A). When the content of the polymer (B) is within the above range, the dispersibility of the negative electrode active material (A) in the slurry is good, and the coating properties of the slurry are also excellent.

[0029] 1.1.3. Liquid Medium (C) The slurry for an electricity storage device negative electrode according to this embodiment contains a liquid medium (C). The liquid medium (C) is not particularly limited, but may be an aliphatic hydrocarbon such as hexane, heptane, octane, decane, or dodecane; an alicyclic hydrocarbon such as cyclohexane, cycloheptane, cyclooctane, or cyclodecane; an aromatic hydrocarbon such as toluene, xylene, mesitylene, naphthalene, or tetralin; a ketone such as methylhexyl ketone, dipropyl ketone, or diisobutyl ketone; an ester such as butyl acetate, butyl butyrate, or methyl butanoate; an ether such as dibutyl ether, tetrahydrofuran, or anisole; (mono-, di-, tri-, or poly)ethylene glycol monomethyl ether; Examples of the liquid medium (C) that can be used include glycol ethers such as (tri- or poly)ethylene glycol dimethyl ether and ethylene glycol phenyl ether; lactams such as β-lactam, γ-lactam, δ-lactam, N-methyl-2-pyrrolidone and 2-pyrrolidone; lactones such as α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone and ε-caprolactone; amides such as N-methylacetamide, dimethylacetamide, N-methylformamide and dimethylformamide; and aliphatic sulfoxides such as dimethyl sulfoxide and di-n-butyl sulfoxide. These liquid media (C) can be used alone or in combination of two or more.

[0030] The content of the liquid medium (C) in the slurry for an electric storage device negative electrode according to this embodiment is preferably 100 to 10,000 parts by mass, more preferably 500 to 2,000 parts by mass, per 100 parts by mass of the polymer component. When the content of the liquid medium (C) is equal to or greater than the lower limit, the mixing of the polymer component and the negative electrode active material is improved when preparing the slurry for an electric storage device negative electrode. On the other hand, when the content of the liquid medium (C) is equal to or less than the upper limit, the coating properties of the slurry for an electric storage device negative electrode are improved when producing a negative electrode active material layer, and concentration gradients of the polymer component and the negative electrode active material are less likely to occur during the drying process after coating. Here, the polymer component includes the polymer (B) and the thickener (E) described below.

[0031] 1.1.4 Other Additives The slurry for an electricity storage device negative electrode according to this embodiment may contain additives other than the components described above, as needed. Examples of such additives include a conductive additive (D), a thickener (E), a pH adjuster, and a corrosion inhibitor.

[0032] <Conductive Aid (D)> A conductive aid (D) may be further added to the slurry for the negative electrode of an electricity storage device according to this embodiment for the purpose of imparting conductivity.

[0033] Specific examples of the conductive additive (D) include carbon such as carbon nanotubes, carbon nanofibers, acetylene black, ketjen black, furnace black, graphite, fullerene, carbon nanohorns, activated carbon, graphite, and carbon fibers. Among these, at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, acetylene black, ketjen black, and furnace black can be preferably used.

[0034] Examples of carbon nanotubes include single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT). Carbon nanotubes may be composed of only carbon, or may have a structure partially substituted with other elements or chemically modified, or may be a composite with a metal (e.g., gold, silver, copper, aluminum, nickel, cobalt, titanium, platinum, etc.).

[0035] The content of the conductive additive (D) is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 8 parts by mass, and particularly preferably 0.03 to 6 parts by mass, relative to 100 parts by mass of the total solid content of the slurry for the negative electrode of an electricity storage device.

[0036] <Thickener (E)> The slurry for an electricity storage device negative electrode according to this embodiment may contain a thickener (E). By containing the thickener (E), it may be possible to further improve the coatability of the slurry and the charge / discharge characteristics of the obtained electricity storage device.

[0037] Examples of the thickener (E) include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the above-mentioned cellulose compounds or the above-mentioned poly(meth)acrylic acid; modified polyvinyl alcohol, polyethylene oxide; polyvinylpyrrolidone, polycarboxylic acid, oxidized starch, starch phosphate, casein, various modified starches, chitin, and chitosan derivatives. Among these, cellulose-based polymers are preferred.

[0038] Commercially available thickeners (E) include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0039] When the slurry for an electric storage device negative electrode according to this embodiment contains a thickener (E), the content of the thickener (E) is preferably 5% by mass or less, and more preferably 0.1 to 3% by mass, relative to 100% by mass of the total polymer components. Here, the polymer components include the polymer (B) and the thickener (E), etc.

[0040] <pH Adjuster> A pH adjuster may be further added to the slurry for the negative electrode of the electricity storage device according to this embodiment, depending on the type of active material, for the purpose of suppressing corrosion of the current collector.

[0041] Examples of pH adjusters include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred.

[0042] <Corrosion Inhibitor> A corrosion inhibitor may be further added to the slurry for the negative electrode of the electricity storage device according to this embodiment, depending on the type of active material, for the purpose of suppressing corrosion of the current collector.

[0043] Examples of the corrosion inhibitor include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, potassium molybdate, etc. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0044] 1.2. Manufacturing Method of Slurry for Electrical Storage Device Negative Electrode The slurry for an electrical storage device negative electrode according to this embodiment may be manufactured by any method as long as it contains the above-described components. From the viewpoint of manufacturing a slurry having better dispersibility and stability more efficiently and inexpensively, it is preferable to manufacture the slurry by adding and dissolving the polymer (B) in the liquid medium (C), then adding the negative electrode active material (A) and any optional additional components used as needed, and mixing them.

[0045] As a mixing and stirring means for producing a slurry for an electric storage device negative electrode, it is necessary to select a mixer that can stir the active material particles to an extent that no agglomerates remain in the slurry, and necessary and sufficient dispersion conditions. The degree of dispersion can be measured using a particle gauge, but it is preferable to mix and disperse the active material particles so that no agglomerates larger than 100 μm remain. Examples of mixers that meet these conditions include ball mills, bead mills, sand mills, defoamers, pigment dispersers, crushers, ultrasonic dispersers, homogenizers, planetary mixers, and Hobart mixers.

[0046] It is preferable that at least a part of the preparation of the slurry for the negative electrode of the electric storage device (the operation of mixing each component) is carried out under reduced pressure. This can prevent the formation of bubbles in the obtained negative electrode active material layer. The degree of reduced pressure is 5.0 × 10 absolute pressure. ３ ~5.0 x 10 ５ It is preferable to set it to about Pa.

[0047] 2. Negative Electrode for Electricity Storage Device According to one embodiment of the present invention, the negative electrode for an electricity storage device includes a current collector and an active material layer formed by applying the above-described slurry for an electricity storage device negative electrode to the surface of the current collector and drying the slurry. Such a negative electrode for an electricity storage device can be produced by applying the above-described slurry for an electricity storage device negative electrode to the surface of a current collector such as a metal foil to form a coating film, and then drying the coating film to form a negative electrode active material layer. The negative electrode for an electricity storage device produced in this manner comprises a negative electrode active material layer containing the above-described negative electrode active material (A), polymer (B), and optional components added as needed, bound to the surface of the current collector. Therefore, a negative electrode for an electricity storage device having excellent adhesion and exhibiting good charge / discharge durability can be produced.

[0048] The current collector is not particularly limited as long as it is made of a conductive material. Metal current collectors such as iron, copper, aluminum, nickel, and stainless steel are commonly used, but the effects of the slurry for the negative electrode of an electricity storage device described above are most pronounced when copper is used. The shape and thickness of the current collector are not particularly limited, but a sheet-like current collector with a thickness of about 0.001 to 0.5 mm is preferred.

[0049] There are no particular limitations on the method for applying the slurry for the negative electrode of an electric storage device to a current collector. Application can be performed by any suitable method, such as a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, an immersion method, or a brush coating method. The amount of the slurry for the negative electrode of an electric storage device is also not particularly limited. However, it is preferably an amount that results in a thickness of the negative electrode active material layer formed after removing the liquid medium (C) of 0.005 to 5 mm, more preferably 0.01 to 2 mm. By ensuring that the thickness of the negative electrode active material layer is within the above range, the electrolyte can be effectively impregnated into the negative electrode active material layer. As a result, metal ions can be easily exchanged between the negative electrode active material in the negative electrode active material layer and the electrolyte during charge and discharge, which is preferable because it can further reduce electrode resistance. Furthermore, when the thickness of the negative electrode active material layer is within the above range, even when the electrode is processed by folding, rolling, or the like, the negative electrode active material layer does not peel off from the current collector, has good adhesion, and is therefore preferred in that a highly flexible negative electrode for an electricity storage device can be easily obtained.

[0050] The method for drying and removing the liquid medium (C) from the coating film after application is not particularly limited, and examples thereof include drying with warm air, hot air, or low-humidity air; vacuum drying; and drying by irradiation with (far) infrared rays, electron beams, etc. The drying speed can be appropriately set so that the liquid medium can be removed as quickly as possible within a speed range that does not cause cracks in the negative electrode active material layer due to stress concentration or peeling of the negative electrode active material layer from the current collector.

[0051] Furthermore, it is preferable to further press the coating film after removing the liquid medium (C) to increase the density of the negative electrode active material layer. Examples of pressing methods include die pressing and roll pressing. The pressing conditions should be appropriately set depending on the type of pressing equipment used and the desired density of the negative electrode active material layer. These conditions can be easily set by those skilled in the art through a few preliminary experiments. For example, in the case of roll pressing, the linear pressure of the roll press machine can be set to 0.1 to 10 t / cm, preferably 0.5 to 5 t / cm, and the roll temperature can be set to 20 to 100°C, and the feed rate of the coating film after removing the liquid medium (C) (roll rotation speed) can be set to 1 to 80 m / min, preferably 5 to 50 m / min.

[0052] 3. Electricity Storage Device An electricity storage device according to one embodiment of the present invention includes the above-described electricity storage device negative electrode. The electricity storage device according to this embodiment contains, in addition to the above-described electricity storage device negative electrode, a electricity storage device positive electrode, and an electrolyte solution, and can be manufactured according to a conventional method using components such as a separator. Specific manufacturing methods include, for example, stacking the negative electrode and positive electrode with a separator interposed between them, rolling or folding the stack according to the battery shape, and then placing the stack in a battery container, injecting the electrolyte solution into the battery container, and sealing the container. The battery can have any suitable shape, such as a coin shape, a cylindrical shape, a rectangular shape, or a laminate shape.

[0053] The electricity storage device according to this embodiment includes the above-described electricity storage device negative electrode, electricity storage device positive electrode, and electrolyte, and the electricity storage device negative electrode is formed using the above-described electricity storage device negative electrode slurry. In the electricity storage device negative electrode and electricity storage device according to this embodiment, known secondary battery components can be used for components other than those described above.

[0054] The positive electrode for the power storage device used in the power storage device according to this embodiment has a current collector and a positive electrode active material layer formed on the surface of the current collector. The positive electrode active material layer is typically formed of a positive electrode mixture containing a positive electrode active material and a binder.

[0055] The positive electrode active material is preferably a positive electrode active material containing at least one sulfur-containing compound selected from the group consisting of sulfur-containing compounds represented by the following general formula (1) and sulfur-containing compounds represented by the following general formula (2):

[0056] M ｘ S ｙ O ｚ (1) In formula (1), M is sodium (Na) or potassium (K). x represents the proportion of M and is in the range of more than 0 and not more than 3. y represents the proportion of sulfur (S) and is in the range of 1 to 8. z represents the proportion of oxygen (O) and is in the range of 1 to 8. In formula (1), x, y, and z each may not be an integer (i.e., a decimal). In other words, the sulfur-containing compound represented by general formula (1) may also be a non-stoichiometric oxide. In formula (1), when x, y, and z are within the above ranges, the positive electrode active material can provide a positive electrode capable of repeated charge and discharge. The values ​​of x, y, and z can be adjusted by controlling the amount of raw materials used, production conditions, etc.

[0057] M ｘ H.S. ｙ O ｚ (2) In formula (2), M is sodium (Na) or potassium (K). x represents the proportion of M and is in the range of more than 0 to 3. y represents the proportion of sulfur (S) and is in the range of more than 0 to 8. z represents the proportion of oxygen (O) and is in the range of 1 to 8. In formula (2), x, y, and z each may not be an integer (i.e., a decimal). In other words, the sulfur-containing compound represented by general formula (2) may also be a non-stoichiometric oxide. In formula (2), when x, y, and z are within the above ranges, the positive electrode active material can provide a positive electrode capable of repeated charge and discharge. The values ​​of x, y, and z can be adjusted by controlling the amount of raw materials used, production conditions, etc.

[0058] Hereinafter, when there is no need to distinguish between the sulfur-containing compound represented by general formula (1) and the sulfur-containing compound represented by general formula (2), they will be collectively referred to as "specific sulfur-containing compounds."

[0059] Suitable examples of the specific sulfur-containing compound include sulfur-containing compounds in which M is Na in the above general formula (1) or (2). ２ SO ３ , NaHSO ３ , Na ２ SO ４ , NaHSO ４ , Na ２ SO ５ , Na ２ SO ８ , Na ２ S ２ O ３ , Na ２ S ２ O ４ , Na ２ S ２ O ５ , Na ２ S ２ O ６ , Na ２ S ２ O ７ and Na ２ S ２ O ８ Among these, sodium thiosulfate (Na ２ S ２ O ３ ) is particularly preferred.

[0060] Other preferred examples of the specific sulfur-containing compound include sulfur-containing compounds represented by the general formula (1) or (2) in which M is K. Such specific sulfur-containing compounds include K ２ SO ３ , K.H.S.O. ３ , K. ２ SO ４ , K.H.S.O. ４ , K. ２ SO ５ , K. ２ SO ８ , K. ２ S ２ O ３ , K. ２ S ２ O ４ , K. ２ S ２ O ５ , K. ２ S２ O ６ , K. ２ S ２ O ７ and K. ２ S ２ O ８ Among these, potassium thiosulfate (K ２ S ２ O ３ ) is particularly preferred.

[0061] The specific sulfur-containing compound is not limited to a crystalline form, but may be amorphous or a mixture of crystalline and amorphous forms. The specific sulfur-containing compound may be either a non-hydrate or a hydrate.

[0062] The positive electrode active material may contain one kind of the specific sulfur-containing compound alone or two or more kinds of the specific sulfur-containing compound.

[0063] The positive electrode active material may consist solely of the specific sulfur-containing compound, but may also contain other components, such as carbides, as long as the effects of the present invention are not impaired.

[0064] Here, the term "carbide" refers to a carbonized carbon-containing raw material (organic material), and may contain only carbon (C), but may also contain elements other than carbon as long as the object of the present invention is not impaired. Examples of elements other than carbon include nitrogen (N), sulfur (S), oxygen (O), and metal elements such as iron (Fe), but are not limited as long as the object of the present invention is not impaired.

[0065] The carbonized material can also be made porous, depending on the carbon-containing raw material and the firing conditions. The conditions for producing the carbonized material are determined appropriately in consideration of the type of carbon-containing raw material and the physical properties (crystallinity, porosity, etc.) of the desired carbonized material. Typically, the carbonized raw material is heated under a low oxygen partial pressure (for example, N ２ The carbonization treatment is carried out by heating the mixture in an inert gas atmosphere (such as a gas atmosphere) at a temperature of 500°C or higher and 2000°C or lower, for example.

[0066] The carbon-containing raw material used as the raw material for the carbonized material may be any material as long as it does not impair the object of the present invention, and examples thereof include biomass raw materials (for example, wood, bamboo, rice husks, etc.), various resin materials, and plastics such as rubber materials.

[0067] The positive electrode active material is preferably a composite of a specific sulfur-containing compound and a carbide (hereinafter simply referred to as a "composite"). Here, the composite does not simply mean a mixture of the specific sulfur-containing compound and the carbide, but a composite in which the specific sulfur-containing compound and the carbide are physically and / or chemically combined. The physical composite is a composite in which the specific sulfur-containing compound is physically held on the carbide, for example, a composite in which the specific sulfur-containing compound is supported on the carbide, a composite in which the specific sulfur-containing compound is adsorbed on the carbide, or a composite in which the specific sulfur-containing compound is precipitated on the carbide. The chemical composite is a composite in which the specific sulfur-containing compound and the carbide are chemically bonded, and can be produced, for example, by mixing the specific sulfur-containing compound or its precursor compound with the carbide and heat-treating it under an inert gas atmosphere.

[0068] In the composite of the specific sulfur-containing compound and the carbide, the specific sulfur-containing compound composited with the carbide may be in a solid, liquid, or mixed state of a solid and a liquid.

[0069] The use of a composite of a specific sulfur-containing compound and a carbide as a positive electrode active material improves battery performance. Although the reason for this is not entirely clear at this stage, it is presumed that one of the reasons is that the formation of a composite of a specific sulfur-containing compound and a carbide allows for smoother electron transfer between the carbide and the sulfur-containing compound compared to a mixture of the specific sulfur-containing compound and a carbide.

[0070] A suitable example of the carbon-containing raw material that serves as the raw material for the carbide in the composite is a tire. Tires are primarily made of rubber (e.g., natural rubber (NR), styrene-butadiene rubber (SBR), isoprene rubber (IR)), and contain various compounding agents and structural materials. Thus, a suitable example of the positive electrode active material (A) is a composite using a tire-derived carbide.

[0071] The content of the specific sulfur-containing compound in the positive electrode active material is, for example, 5 to 100% by mass, where the total mass of the positive electrode active material is 100% by mass.

[0072] The content of the positive electrode active material in the slurry for a positive electrode of an electric storage device is preferably 10 to 60 mass %, more preferably 20 to 55 mass %, and particularly preferably 25 to 50 mass %, when the total mass of the slurry for a positive electrode of an electric storage device is taken as 100 mass %. When the content of the positive electrode active material (A) is within the above range, the resistance of the battery is easily reduced, and the battery performance is further improved.

[0073] The binder may be the same as that usable in the slurry for the negative electrode of the electricity storage device, and therefore a description thereof will be omitted. The current collector may be made of a conductive material such as nickel, copper, or stainless steel (SUS). The current collector may be made of a foil, mesh, expanded grid (expanded metal), punched metal, or the like, similar to the current collector for the negative electrode of the electricity storage device.

[0074] The positive electrode active material layer can be formed on the current collector by the same method as that for forming the negative electrode active material layer on the current collector as described above.

[0075] <Electrolyte> The electrolyte used in the electricity storage device according to this embodiment may be liquid or gel-like, and may be selected from known electrolytes used in electricity storage devices that effectively exhibit the functions of a battery depending on the type of active material. The electrolyte is not particularly limited and may be in either liquid or solid form. Typically, a solution in which a sodium salt or potassium salt of an electrolyte salt is dissolved in an electrolyte solution (non-aqueous solvent) is used. The electrolyte contained in the electrolyte used in the electricity storage device according to this embodiment is not particularly limited, but the electrolyte disclosed in the examples is a suitable example.

[0076] The electrolyte salt may be any electrolyte salt commonly used in sodium secondary batteries or potassium secondary batteries. One type of electrolyte salt may be used, or two or more types may be used in combination.

[0077] As the electrolyte, electrolytes used in sodium secondary batteries or potassium secondary batteries can be used, and examples thereof include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; ethers such as 1,2-dimethoxyethane and 1,3-dimethoxypropane; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; phosphates such as tris(2,2,2-trifluoroethyl)phosphate; and the above organic solvents further having a fluorine substituent introduced therein.

[0078] 4. Examples The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are by mass unless otherwise specified.

[0079] 4.1. Production of Negative Electrode Active Material The negative electrode active material used was a waste tire-derived charcoal "Renesis A1" (manufactured by Renesis Corporation), produced as follows. First, waste tires were heated to 400°C for 2 hours in an inert atmosphere container, and the components within the waste tires were gasified and cooled to oil (approximately 55% total gasification and oilification), and the residue that was not gasified or oiled was collected. Next, the collected waste tire pyrolysis residue was further heat-treated and pulverized to an average particle size of 20 μm, and then magnetic material was completely removed using a 16,000 gauss electromagnetic separator to obtain "Renesis A1," a waste tire pyrolysis residue-derived charcoal.

[0080] 4.2. Synthesis of Positive Electrode Active Material <Positive Electrode Active Material (P-1)> Positive electrode active material (P-1) was obtained according to Experimental Example 1 of JP 2023-98729 A. That is, 5.5 g (24.2% of the total raw materials) of waste tire-derived charcoal "Renesis A1 (product number)" (manufactured by Renesis Corporation) as a charcoal, 8.44 g of sodium percarbonate (37.2% of the total raw materials), 2.75 g of coal tar (12.1% of the total raw materials), and 6 g of sulfur (26.4% of the total raw materials) were kneaded in a stainless steel container and placed in a heating furnace, and nitrogen gas was introduced into the container to create an inert atmosphere. After 10 minutes, heating was started. The temperature was raised to 300 ° C in 50 minutes, and heating continued even after reaching 300 ° C., and stopped at 350 ° C. After that, the temperature dropped to 200 ° C., and the mixture was removed from the heating furnace and allowed to cool naturally. The synthesized product was taken out after the temperature inside the container became 50° C. or less. The weight of the synthesized product was 15.2 g. The synthesized product was pulverized in a mixer to obtain a positive electrode active material (P-1) consisting of powder with an average particle size of 20 μm.

[0081] <Positive Electrode Active Material (P-2)> Positive electrode active material (P-2) was obtained according to Experimental Example 4 of JP 2023-98729 A. That is, 10 g (20.5% of the total raw materials) of waste tire-derived charcoal "Renesis A1 (product number)" (manufactured by Renesis Corporation) as the charcoal, 25 g of potassium bicarbonate (51.2% of the total raw materials), 3.8 g of coal tar (7.8% of the total raw materials), 10 g of sulfur (20.5% of the total raw materials) total raw materials of 48.8 g were kneaded in a stainless steel container and placed in a heating furnace, and nitrogen gas was introduced into the container to create an inert atmosphere, and heating began 10 minutes later. The temperature was increased to 300 ° C in 50 minutes, and heating continued even after reaching 300 ° C, and stopped at 350 ° C. Thereafter, the temperature dropped to 200 ° C, and the product was removed from the heating furnace and allowed to cool naturally. The synthesized product was removed after the temperature inside the container reached 50 ° C or below. The weight of the synthesized product was 32.5 g, which was a yield of 67%. The synthesized product was pulverized in a mixer to obtain a positive electrode active material (P-2) made of powder with an average particle size of 20 μm.

[0082] 4.3. Synthesis of Polymer (B) <Synthesis of Conjugated Diene Polymer> An aqueous polymer dispersion was obtained by single-stage polymerization as shown below. A reactor was charged with 200 parts by mass of water, a monomer mixture consisting of 50 parts by mass of 1,3-butadiene, 35 parts by mass of styrene, 5 parts by mass of methacrylic acid, and 10 parts by mass of acrylonitrile, 0.5 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 1 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.02 parts by mass of cumene hydroperoxide, 0.01 parts by mass of ethylenediaminetetraacetic acid tetrasodium salt, 0.006 parts by mass of iron(II) sulfate heptahydrate, and 0.03 parts by mass of sodium formaldehyde sulfoxylate as polymerization initiators, and the mixture was polymerized at 15°C for 10 hours with stirring to obtain an aqueous polymer dispersion.

[0083] Next, the polymer aqueous dispersion was added dropwise to 3,000 parts by mass of a 0.5% aqueous calcium chloride solution. The resulting aggregates were washed with water. The resulting aggregates were added to N-methyl-2-pyrrolidone and stirred overnight to prepare a conjugated diene polymer solution in which the polymer was dissolved in N-methyl-2-pyrrolidone. The polymer content was adjusted to 8% by mass when the entire conjugated diene polymer solution was taken as 100% by mass.

[0084] <Synthesis of Acrylic Polymer> An aqueous polymer dispersion was obtained by single-stage polymerization as shown below. A reactor was charged with 500 parts by mass of water, a monomer mixture consisting of 1 part by mass of styrene, 5 parts by mass of acrylic acid, 64 parts by mass of 2-ethylhexyl acrylate, 25 parts by mass of acrylonitrile, and 5 parts by mass of isopropylidenemalononitrile, 1 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, and 0.3 parts by mass of potassium persulfate as a polymerization initiator, and the mixture was polymerized at a polymerization temperature of 75°C for 8 hours to obtain an aqueous polymer dispersion.

[0085] Next, the polymer aqueous dispersion was added dropwise to 3,000 parts by mass of a 0.5% aqueous calcium chloride solution. The resulting aggregates were washed with water. The resulting aggregates were added to N-methyl-2-pyrrolidone and stirred overnight to prepare an acrylic polymer solution in which the polymer was dissolved in N-methyl-2-pyrrolidone. The polymer content was adjusted to 8% by mass when the total acrylic polymer solution was taken as 100% by mass.

[0086] Synthesis of hydrogenated NBR (nitrile rubber) 240 parts by mass of water, 2.5 parts by mass of sodium alkylbenzenesulfonate, 20 parts by mass of acrylonitrile, 30 parts by mass of butyl acrylate, and 4.5 parts by mass of methacrylic acid were placed in an autoclave equipped with a stirrer in this order, and after the atmosphere inside the bottle was replaced with nitrogen, 45.5 parts by mass of butadiene was added under pressure, and 0.25 parts by mass of ammonium persulfate was added, followed by polymerization reaction at a reaction temperature of 40°C, to obtain a polymer comprising polymerization units having nitrile groups and conjugated diene monomer units. The iodine value was 280.

[0087] 400 mL (48 g total solids) of the polymer, adjusted to a total solids concentration of 12 wt%, was placed in a 1 L autoclave equipped with a stirrer, and nitrogen gas was passed through for 10 minutes to remove dissolved oxygen in the polymer. Then, 75 mg of palladium acetate was dissolved in 180 mL of water containing 4 times the molar amount of nitric acid relative to Pd as a hydrogenation catalyst and added. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50°C under pressure of 3 MPa with hydrogen gas, and hydrogenation reaction was carried out for 6 hours. At this time, the iodine value of the polymer was 35.

[0088] Next, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate was dissolved in 60 mL of water containing 4 times the molar amount of nitric acid relative to Pd as a hydrogenation catalyst and added. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50°C under a pressure of 3 MPa with hydrogen gas, and hydrogenation reaction was carried out for 6 hours.

[0089] Thereafter, the contents were returned to room temperature, the system was emptied into a nitrogen atmosphere, and the mixture was concentrated using an evaporator to a solids concentration of 40%, to obtain a polymer aqueous dispersion. The iodine value of the obtained polymer was 10. 320 parts by mass of N-methylpyrrolidone was added to 100 parts by mass of this polymer aqueous dispersion, and water was evaporated under reduced pressure to prepare a hydrogenated NBR solution in which the polymer was dissolved in N-methylpyrrolidone.

[0090] <Synthesis of Polyurethane> 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 by mass of a polyester polyol obtained from terephthalic acid, adipic acid, and 3-methyl-1,5-pentanediol ("Kuraray Polyol P-2011" manufactured by Kuraray Co., Ltd., Mn=2011), 16.5 parts by mass of dimethylolbutanoic acid, 105.2 parts by mass of isophorone diisocyanate, and 140 parts by mass of toluene, and the mixture was reacted at 90°C for 3 hours under a nitrogen atmosphere, and 360 parts by mass of toluene was added to obtain a urethane prepolymer solution having isocyanate groups. Next, 969.5 parts by mass of the obtained urethane prepolymer solution having isocyanate groups was added to a mixture of 19.9 parts by mass of isophorone diamine, 0.63 parts by mass of di-n-butylamine, 294.5 parts by mass of 2-propanol, and 335.5 parts by mass 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 by mass of toluene and 54 parts by mass of 2-propanol to obtain a polyurethane solution having Mw = 61,000, an acid value = 10 mgKOH / g, and a total equivalent of 0.98 of the amino groups in the polyamino compound and the reaction terminator relative to the free isocyanate groups at both ends of the urethane prepolymer.

[0091] <Synthesis of Polyimide> In a four-neck flask equipped with a condenser and a nitrogen gas inlet, 1.0 mol of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 0.95 mol of o-tolidine diisocyanate, and N-methyl-2-pyrrolidone (NMP) were mixed to a solids concentration of 20% by mass, and 0.01 mol of diazabicycloundecene was added as a catalyst, followed by stirring and reaction at 120°C for 4 hours to obtain a polyimide solution.

[0092] <Synthesis of Polyamideimide> In a flask equipped with a condenser, a nitrogen gas inlet tube, and a stirrer, 0.7 mol of trimellitic anhydride, 0.3 mol of 3,3',4,4'-benzophenonetetracarboxylic anhydride, 1 mol of naphthalene diisocyanate, and 0.01 mol of diazabicycloundecene were dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a solution with a monomer concentration of 15% by mass, and the reaction was carried out at 80°C for 3 hours to obtain a polyamideimide solution.

[0093] 4.4. Example 1 <Preparation of Negative Electrode> 1.5 g (92.71% of the total) of the negative electrode active material prepared above and 0.106 g (solid content equivalent, 6.55% of the total) of SBR (trade name "TRD 105A", manufactured by ENEOS Material Corporation) as a binder were dissolved in an aqueous solution containing 0.007 g of carboxymethyl cellulose (CMC) and 0.005 g of CNT (trade name "TUBALL") as a solvent. TM BATT H ２ The mixture was mixed (kneaded) with 1.2 g of "O.O. CMC" (manufactured by Kusumoto Chemicals Co., Ltd.) to obtain a negative electrode slurry.

[0094] The resulting negative electrode slurry was then applied to an aluminum sheet (thickness: 16 μm) that would serve as a negative electrode current collector, and dried at 70° C. for 3 hours to obtain a negative electrode sheet. A negative electrode having a diameter of 11.3 mm was then cut out from the resulting negative electrode sheet.

[0095] <Preparation of Positive Electrode> The positive electrode of Example 1 was prepared as follows: 0.8 g (74% of the total) of the positive electrode active material (P-1) obtained above and 0.2 g (19% of the total) of acetylene black as a conductive material were uniformly mixed (kneaded) with the acrylic polymer solution obtained above to a total weight of 0.076 g (7.01% of the total) in terms of solid content, thereby obtaining a positive electrode slurry of Example 1.

[0096] Next, the obtained positive electrode slurry was applied to an aluminum sheet (thickness: 16 μm) that would serve as a positive electrode current collector, and dried at 50° C. for 3 hours to obtain a positive electrode sheet. A piece of 15 mm diameter was cut out from the obtained positive electrode sheet to provide the positive electrode of Example 1.

[0097] <Preparation of Secondary Battery> The obtained positive electrode and negative electrode were combined with an electrolyte solution prepared by dissolving sodium bis(fluorosulfonyl)imide (NaFSI) as a sodium salt in tris(2,2,2-trifluoroethyl)phosphate (TFEP) to a concentration of 2 mol / L, and Celgard 2400 as a separator, to obtain a secondary battery of Example 1 (coin-type battery (cylindrical, outer diameter 20 mm / height 3.2 mm)).

[0098] <Evaluation of Adhesion Strength> A knife was used to make 10 incisions in each direction, 2 mm apart, on the surface of the negative electrode for an electricity storage device obtained above, from the negative electrode active material layer to a depth reaching the current collector, creating a grid pattern. An 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Cellotape" (registered trademark), specified in JIS Z1522:2009) was attached to the incisions and immediately peeled off, and the degree of detachment of the negative electrode active material layer was evaluated by visual inspection. The evaluation criteria were as follows. The evaluation results are shown in Table 1 below. (Evaluation Criteria) 5 points: 0 negative electrode active material layers detached. 4 points: 1 to 5 negative electrode active material layers detached. 3 points: 6 to 20 negative electrode active material layers detached. 2 points: 21 to 40 negative electrode active material layers detached. 1 point: 41 or more negative electrode active material layers detached.

[0099] <Evaluation of Cycle Characteristics> The secondary batteries manufactured as described above were charged at a constant current (1.0 C) in a thermostatic chamber maintained at 25°C. When the voltage reached 2.5 V, charging was continued at a constant voltage (2.5 V). Charging was completed (cutoff) when the current reached 0.01 C. Discharging was then initiated at a constant current (1.0 C). Discharge was completed (cutoff) when the voltage reached 0.5 V, and the discharge capacity at the first cycle was calculated. This cycle was repeated 200 times. The capacity retention was calculated using the following formula (3) and evaluated according to the following criteria. The evaluation results are shown in Table 1 below. Capacity Retention (%) = (Discharge Capacity at 200th Cycle) / (Discharge Capacity at First Cycle) (3) (Evaluation Criteria) 5 points: Capacity retention of 95% or more. 4 points: Capacity retention of 90% or more but less than 95%. 3 points: Capacity retention of 85% or more but less than 90%.・2 points: Capacity retention rate is 80% or more but less than 85%. ・1 point: Capacity retention rate is 75% or more but less than 80%. ・0 point: Capacity retention rate is less than 75%.

[0100] 4.5. Examples 2 to 10 and Comparative Examples 1 and 2 Positive electrodes, negative electrodes, and secondary batteries were fabricated and evaluated in the same manner as in Example 1, except that the materials listed in Table 1 below were used.

[0101] 4.6. Evaluation Results Table 1 below shows the materials used in Examples 1 to 10 and Comparative Examples 1 and 2, as well as the evaluation results.

[0102]

[0103] The materials in Table 1 above represent the following compounds: <Positive electrode active material> Sodium thiosulfate: sodium thiosulfate pentahydrate (Na ２ S ２ O ３ ・5H ２O, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) Potassium thiosulfate: potassium thiosulfate anhydrous, manufactured by Kishida Chemical Co., Ltd. <Polymer> Acrylonitrile-based: Polyacrylonitrile (manufactured by Aldrich, Mw 150,000, atactic type) was added to N-methyl-2-pyrrolidone and mixed at room temperature to dissolve the polyacrylonitrile, preparing a polyacrylonitrile solution (10% by mass). PVA: trade name "20CLPAH", manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., polyvinyl alcohol. TRD105: trade name "TRD 105A", manufactured by ENEOS Materials Corporation, styrene butadiene rubber (SBR) <Electrolyte> Sodium: sodium bis(fluorosulfonyl)imide (NaFSI) was dissolved in tris(2,2,2-trifluoroethyl)phosphate (TFEP) to give a concentration of 2 mol / L. Potassium: potassium bis(fluorosulfonyl)imide (KFSI) dissolved in tris(2,2,2-trifluoroethyl)phosphate (TFEP) to give a concentration of 2 mol / L.

[0104] As is clear from Table 1 above, the slurries for negative electrodes of electricity storage devices according to the present invention shown in Examples 1 to 10 have higher adhesion strength and can produce negative electrodes for electricity storage devices with excellent cycle characteristics compared to Comparative Examples 1 and 2. The reason for this is presumed to be that the polymer (B) homogeneously disperses the negative electrode active material (A) in the slurry for negative electrodes of electricity storage devices, thereby improving the adhesion of the resulting negative electrodes. As a result, the cycle characteristics of the electricity storage devices are also presumed to be improved.

[0105] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially identical to the configurations described in the embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention also includes configurations that achieve the same effects or purposes as the configurations described in the above embodiments. Furthermore, the present invention also includes configurations in which publicly known technology is added to the configurations described in the above embodiments.

Claims

1. A slurry for an electric storage device negative electrode, comprising: a negative electrode active material (A) obtained by thermally decomposing a sulfur-containing rubber raw material to separate it into a solid and a dry distillation gas, separating the solid into a metal and a charcoal, and heat-treating the charcoal; a polymer (B) that is at least one selected from the group consisting of a conjugated diene polymer, an acrylic polymer, an acrylonitrile polymer, a polyurethane, a polyimide, and a polyamideimide; and a liquid medium (C).

2. The slurry for a negative electrode of an electricity storage device according to claim 1, wherein the rubber raw material is derived from tires.

3. The slurry for a negative electrode of an electricity storage device according to claim 1 or 2, further comprising a thickener (E).

4. A negative electrode for an electricity storage device, comprising a current collector and an active material layer formed by applying the slurry for a negative electrode of an electricity storage device according to claim 1 or 2 to the surface of the current collector and drying it.

5. An electricity storage device comprising the electricity storage device negative electrode according to claim 4.

6. The electricity storage device according to claim 5, which has an electrolyte solution containing a sodium salt or a potassium salt.

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