JP7853768B2 - Slurry composition for manufacturing solid-state batteries and method for manufacturing all-solid-state batteries - Google Patents

Description

This invention relates to a slurry composition for manufacturing solid-state batteries and a method for manufacturing all-solid-state batteries.

Lithium-ion batteries are widely used as power sources for many electronic devices due to their high energy density and excellent charge-discharge cycle characteristics. However, lithium-ion batteries contain flammable organic solvents, leading to frequent accidents such as leakage and explosions. Therefore, in recent years, all-solid-state lithium-ion batteries (hereinafter also referred to as "all-solid-state batteries") using inorganic solid electrolytes have been investigated. The manufacturing of all-solid-state batteries employs a wet process, where a slurry composition of inorganic electrolyte and binder resin dispersed in an organic solvent is coated and dried to create inorganic powder sheets of uniform thickness. These sheets are then stacked to form a battery, and the binder resin is removed by firing. While the binder resin is necessary for controlling thickness during coating and for lamination of the sheets, it must be removed by firing because its presence in the laminate creates electrical resistance, negatively impacting battery performance. For this reason, acrylic resins, which have particularly excellent degreasing properties, and polyvinyl acetal resins, which offer excellent dispersibility of inorganic powders and sheet strength, are used as binder resins.

Furthermore, in recent years, interfacial resistance between the electrolyte and the active material has become a problem in achieving high performance in all-solid-state batteries. To solve this problem, for example, Patent Document 1 discloses the use of an active material having a resistance layer formation suppression coating layer that suppresses the formation of high-resistance regions.
Furthermore, Patent Document 2 discloses that, in order to reduce interfacial resistance, oxide particles having a neutralization product on part or all of the surface of oxide particles containing an alkaline compound are used.
Furthermore, Patent Document 3 discloses a solid electrolyte slurry in which garnet-type solid electrolyte particles and compound particles containing lithium and boron are dispersed in a dispersion medium as a dispersed phase.

Japanese Patent Publication No. 2009-266728 Patent No. 5825455 Japanese Patent Publication No. 2021-51912

However, in Patent Document 1, since the active material is coated with a compound containing an alkali metal, when a slurry composition is formed, the slurry becomes strongly alkaline, which causes the binder resin to gel.
Furthermore, while Patent Document 2 describes a surface treatment in which oxide particles are coated with a neutralization product, even with this method, the resulting slurry exhibits strong alkalinity, leading to the problem of gelation of the binder resin.
Furthermore, Patent Document 3 states that in order to suppress the decomposition of lithium and boron-containing compounds by moisture, the amount of water in the organic solvent used as the dispersion medium must be reduced to 0.007% by mass or less, which requires the entire production facility to be kept in an extremely dry state, resulting in significant costs for the production equipment. Therefore, there is a need for a slurry that can be manufactured more easily.

The present invention aims to provide a slurry composition for manufacturing solid-state batteries that can suppress gelation of the slurry even when it contains alkali metal-containing inorganic powders, exhibits excellent sinterability, and enables the production of low-residue inorganic powder sheets, thereby enabling the manufacture of high-performance all-solid-state batteries. Furthermore, the invention aims to provide a method for manufacturing all-solid-state batteries using this slurry composition.

The present invention relates to a slurry composition for manufacturing solid batteries, comprising an organic solvent, a binder resin, and an inorganic powder containing an alkali metal, wherein the organic solvent is at least one selected from the group consisting of aromatic compounds, aliphatic hydrocarbons, and alicyclic hydrocarbons, and the binder resin is at least one selected from the group consisting of polystyrene resins and polypropylene resins.
The present invention will be described in detail below.

The inventors have discovered that by combining a specific organic solvent and binder resin, gelation of the binder resin can be suppressed even in a composition containing inorganic powders including alkali metals. Furthermore, they have found that by using such a slurry composition, it is possible to produce inorganic powder sheets with excellent sinterability, enabling the manufacture of high-performance all-solid-state batteries, thus completing the present invention.

<Binder resin>
The slurry composition for manufacturing solid batteries of the present invention contains a binder resin.
The above-mentioned binder resin is at least one selected from the group consisting of polystyrene resins and polypropylene resins.
Polystyrene and polypropylene resins contain numerous branched structures in their main carbon chains, and decomposition begins at these branches in high-temperature environments above 300°C. Therefore, they can be decomposed at relatively low temperatures in an air atmosphere compared to polyethylene and other materials that do not have branching.
On the other hand, while acrylic resins and polyvinyl acetal resins also have a branched structure in their main chain, the ester groups and acetal groups containing oxygen are undesirable because they quickly saponify in an alkaline environment.
Polystyrene and polypropylene resins are stable even in alkaline environments and do not have hydrolytic functional groups. Therefore, slurries made from these resins do not gel or undergo rapid viscosity changes even when they contain inorganic powders containing alkali metals, and inorganic powder sheets can be manufactured by coating them.

The polystyrene resin may be a copolymer of styrene and other monomers, but a styrene homopolymer is preferred.
Examples of styrene homopolymers include general-purpose polystyrene (GPPS) having an atactic structure and syndiotactic polystyrene having a syndiotactic structure.
Furthermore, examples of copolymers of styrene with other monomers include high-impact polystyrene (HIPS), styrene-butadiene copolymer, styrene-(meth)acrylic acid copolymer, styrene-acrylonitrile copolymer (SAN), and acrylonitrile-butadiene-styrene copolymer (ABS).
Among these, GPPS is preferable because it does not contain any other resin components. Furthermore, while GPPS comes in injection-molded and extruded grades, the extruded grade is preferred. Injection-molded grades are designed with a branched structure to reduce entanglement of branched chains. Using a linear grade with fewer branches improves the handling of the inorganic powder sheet.

Specifically, the polystyrene resins used include XC-315 (manufactured by DIC Corporation), CR-3500 (manufactured by DIC Corporation), and NormalFlow (manufactured by Toyo Engineering Corporation).

The above-mentioned polypropylene resin may be a copolymer of propylene and other monomers, but a propylene homopolymer is preferred.
Other monomers copolymerizable with propylene include, for example, α-olefins such as butene-1 and hexene-1. The polymerization form is not particularly limited and may be a random copolymer, a block copolymer, or the like.

Specifically, the polypropylene resins mentioned above can be Novatec MA3H (manufactured by Nippon Polypropylene Co., Ltd.), Novatec EA9 (manufactured by Nippon Polypropylene Co., Ltd.), Novatec FY4 (manufactured by Nippon Polypropylene Co., Ltd.), etc.

The binder resin can be an ethylene-modified or carboxylic acid-modified polystyrene resin or a polypropylene resin, as long as the sinterability does not deteriorate.
By modifying the inorganic powder with ethylene, the affinity with plasticizers is increased, improving the windability and break elongation of the inorganic powder sheet. Furthermore, by modifying it with carboxylic acid, the dispersibility of the inorganic powder can be improved.
The introduction rate of the modified structure in the binder resin is preferably 0 mol% or more, more preferably 0.1 mol% or more, even more preferably 0.5% or more, preferably 10 mol% or less, more preferably 8 mol% or less, and even more preferably 5 mol% or less.
If the introduction rate of the modified structure in the binder resin is within the above range, sinterability can be sufficiently maintained.

The above binder resin preferably has a melt flow index (MFR value) of 10 g/10 min or less according to ISO-1133.
The MFR value is preferably 8 g/10 min or less, more preferably 6 g/10 min or less, and even more preferably 4 g/10 min or less. The lower limit is not particularly limited, but for example, it is 0 g/10 min or more.
If the above MFR value is below the above upper limit, the strength of the resulting inorganic powder sheet can be sufficiently increased, resulting in excellent handling properties and the ability to produce thinner inorganic powder sheets.

The binder resin content in the slurry composition for solid-state battery manufacturing of the present invention is preferably 1% by weight or more, more preferably 2% by weight or more, even more preferably 4% by weight or more, preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less.

<Soluble Organic Solvents>
The slurry composition for manufacturing solid-state batteries of the present invention contains an organic solvent.
The above organic solvent is at least one selected from the group consisting of aromatic compounds, aliphatic hydrocarbons, and alicyclic hydrocarbons.
It is preferable that the inorganic powder sheet contains the above-mentioned organic solvent, as this provides excellent coating properties, drying properties, and dispersibility of the inorganic powder when the inorganic powder sheet is manufactured.

Examples of the above aromatic compounds include aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, methylbenzylxylene, alkylbenzenes such as 1,4-dimethyl-2-(1-phenylethyl)benzene and ethylbenzene, aromatic alcohols such as phenol, benzyl alcohol and cresol, and aromatic ketones such as acetophenone.
Examples of the aliphatic hydrocarbons mentioned above include hexane, n-heptane, isopentane, n-octane, n-nonane, n-decane, and other olefinic solvents such as normal paraffins, isoparaffins, α-olefins, and isobutylene derivatives. Aromatic compounds include aromatic hydrocarbons and aromatic alcohols.
Examples of the above-mentioned alicyclic hydrocarbons include limonene, dipentene, terpinene, nethol, synene, orange flavor, terpinolene, phellandrene, mentadiene, terebene, dihydrocymene, mothlene, isoterpinene, critomene, cautusin, cajeptene, oilimene, pinene, turpentine, menthane, pinan, terpene, cyclohexane, alkylcyclohexane such as methylcyclohexane, and others.
Among these, toluene, benzyl alcohol, methylcyclohexane, xylene, ethylbenzene, and isoparaffin are preferred.
These organic solvents may be used individually or in combination of two or more.

The boiling point of the above organic solvent is preferably 100°C or higher, more preferably 110°C or higher, preferably 240°C or lower, more preferably 220°C or lower, even more preferably 200°C or lower, and even more preferably 190°C or lower.
If the boiling point is above the lower limit, evaporation will not occur too quickly, further improving handling. If the boiling point is below the upper limit, the residue of organic solvents on the inorganic powder sheet can be reduced, improving the sheet strength and further enhancing printability.

The content of the above-mentioned organic solvent in the slurry composition for solid-state battery manufacturing of the present invention is preferably 20% by weight or more, more preferably 30% by weight or more, even more preferably 40% by weight or more, preferably 70% by weight or less, and more preferably 60% by weight or less.

The slurry composition for manufacturing solid-state batteries of the present invention may contain other solvents, such as aliphatic alcohols, in addition to the organic solvents mentioned above.

The content of the organic solvent in the slurry composition for solid-state battery manufacturing of the present invention is not particularly limited, but a preferred lower limit is 10% by weight and a preferred upper limit is 60% by weight. Within this range, coating properties and the dispersibility of inorganic powders can be improved.

<Inorganic powder>
The slurry composition for manufacturing solid batteries of the present invention contains inorganic powder.
The above inorganic powder contains alkali metals.
By including the above-mentioned inorganic powder, the characteristics of the resulting battery can be significantly enhanced.
The alkali metals mentioned above are lithium, sodium, potassium, rubidium, cesium, and francium, with lithium being preferred.

Examples of inorganic powders containing the alkali metals mentioned above include _sulfide materials such as _Li₂S - _P₂S₅ , _{Li₂S -} GeS₂, Li₂S- _{GeS₂ - P₂S₅} , _Li₂S - _SiS₂ , _{Li₂S - B₂S₃} , _{and Li₃PO₄ - P₂S₅ .} Furthermore, materials obtained by adding lithium halides to the above-mentioned sulfide materials (e.g., LiI _{-Li₂S-P₂S₅ , LiCl} -LiI- _Li₂S - _P₂S₅ , LiBr-LiI- _Li₂S - _P₂S₅ , LiI- _Li₂S - _SiS₂ , LiI- _Li₂S - _{B₂S₃ , etc.} ) are also mentioned. Among these, sulfide-based inorganic powders of _Li₂S - _{P₂S₅ -} based materials are preferred because _they do not contain expensive rare earth elements and have high ionic conductivity.
Furthermore, in order to design batteries with a large capacity, it is preferable to use an active material consisting of an alkali metal oxide containing Li. Specifically, examples include lithium _lanthanum zirconium-containing composite oxides ( _LLZ series) such as _{Li₂₀La₃Zr₂O₁₂} , Al _- doped LLZO, lithium lanthanum titanium-containing composite oxides (LLT series), Al-doped LLT series, lithium phosphate series, and other composite oxide materials. Other examples include lithium cobalt oxide, lithium nickel oxide, lithium-nickel-cobalt-aluminum oxide, lithium-nickel-manganese-cobalt oxide, and lithium-manganese-nickel compounds.

The inorganic powder described above may be coated with a lithium metal compound.
The lithium metal compound used for coating is not particularly limited and includes, for example, lithium niobate, lithium titanate, lithium silicate, lithium borosilicate, lithium boric acid, lithium phosphoric acid, lithium phosphorous acid, and lithium phosphorous acid.

The inorganic powder content in the slurry composition for solid-state battery manufacturing of the present invention is not particularly limited, but a preferred lower limit is 10% by weight, a more preferred lower limit is 20% by weight, an even more preferred lower limit is 30% by weight, a preferred upper limit is 90% by weight, a more preferred upper limit is 80% by weight, an even more preferred upper limit is 70% by weight, an even more preferred upper limit is 60% by weight, and a particularly preferred upper limit is 50% by weight. By setting the content above the lower limit, sufficient viscosity and excellent coating properties can be achieved, while by setting the content below the upper limit, excellent dispersibility of the inorganic powder can be achieved.

<Other>
The slurry composition for manufacturing solid batteries of the present invention may further contain a plasticizer.
Examples of the plasticizers mentioned above include 1,3-di-tert-butyltoluene, α-methylstyrene dimer, low molecular weight polyolefin wax, and liquid polyolefin. Aromatic plasticizers such as dioctyl phthalate and dibutyl phthalate can also be used.

The boiling point of the plasticizer is preferably 240°C or higher and less than 390°C. A boiling point of 240°C or higher facilitates evaporation during the drying process, preventing residue in the molded article. A boiling point below 390°C prevents the generation of residual carbon. Note that the boiling point refers to the boiling point at atmospheric pressure.

The content of the plasticizer in the slurry composition for solid-state battery manufacturing of the present invention is not particularly limited, but a preferred lower limit is 0.1% by weight, a more preferred lower limit is 0.5% by weight, a preferred upper limit is 3.0% by weight, and a more preferred upper limit is 2.0% by weight. By keeping the content within these ranges, the amount of plasticizer residue after firing can be reduced.

The slurry composition for manufacturing solid-state batteries of the present invention may further contain sintering aids such as organic peroxides.
Examples of the above-mentioned organic peroxides include 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane.
The above organic peroxide preferably has a half-life temperature of 150°C or higher over 10 hours.

The slurry composition for manufacturing solid batteries of the present invention may further contain additives such as surfactants.
The above-mentioned surfactants are not particularly limited and include, for example, cationic surfactants, anionic surfactants, and nonionic surfactants.
The above nonionic surfactant is not particularly limited, but it is preferable that it is a nonionic surfactant with an HLB value of 10 or more and 20 or less. Here, the HLB value is used as an indicator of the hydrophilicity and lipophilicity of a surfactant, and several calculation methods have been proposed. For example, for ester-based surfactants, the saponification value is S, the acid value of the fatty acid constituting the surfactant is A, and the HLB value is defined as 20 (1-S/A). Specifically, nonionic surfactants having polyethylene oxide obtained by adding alkylene ether to a fatty acid chain are preferred, and specifically, for example, polyoxyethylene lauryl ether and polyoxyethylene cetyl ether are preferably used. Although the above nonionic surfactant has good thermal decomposition properties, if it is added in large quantities, the thermal decomposition properties of the slurry composition for solid battery manufacturing may decrease, so the preferred upper limit of the content is 5% by weight.

The pH of the slurry composition for manufacturing solid batteries according to the present invention is preferably 11 or higher.
A pH of 11 or higher can significantly improve the performance of the resulting battery.
The above pH can be confirmed, for example, by using pH test paper.

The viscosity of the slurry composition for manufacturing solid batteries of the present invention is not particularly limited, but when measured at 20°C using a B-type viscometer with a probe rotation speed of 5 rpm, the preferred lower limit of viscosity is 0.1 Pa·s and the preferred upper limit is 100 Pa·s.
By setting the viscosity to 0.1 Pa·s or higher, the inorganic powder sheet obtained after coating by die-coating printing or the like can maintain a predetermined shape. Furthermore, by setting the viscosity to 100 Pa·s or lower, problems such as the die coating marks not disappearing can be prevented, resulting in excellent printability.

The method for preparing the slurry composition for solid-state battery manufacturing of the present invention is not particularly limited, and conventionally known stirring methods can be used. Specifically, examples include stirring the binder resin, the inorganic powder, the organic solvent, and other components such as plasticizers added as needed using a three-roll stirrer, high-speed stirrer, etc.

An inorganic powder sheet can be manufactured by coating the slurry composition for solid-state battery manufacturing of the present invention onto a support film that has been treated with a single-sided release agent, drying the organic solvent, and forming it into a sheet.
The inorganic powder sheet described above preferably has a thickness of 1 to 20 μm.

Examples of methods for producing the inorganic powder sheet include forming a uniform coating on a support film using a coating method such as a roll coater, die coater, squeeze coater, or curtain coater, based on the slurry composition for solid-state battery manufacturing of the present invention.

The support film used in manufacturing the above-mentioned inorganic powder sheet is preferably a resin film that is heat-resistant, solvent-resistant, and flexible. The flexibility of the support film allows the slurry composition for solid-state battery manufacturing to be applied to its surface using a roll coater, blade coater, etc., and the resulting inorganic powder sheet-forming film can be stored and supplied in a rolled state.

Examples of resins used to form the support film include polyethylene terephthalate, polyester, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, polyfluoroethylene and other fluororesins, nylon, cellulose, and the like.
The thickness of the support film is preferably, for example, 20 to 100 μm.
Furthermore, it is preferable that the surface of the support film be treated with a release agent, which facilitates the peeling operation of the support film during the transfer process.

An inorganic powder sheet can be manufactured by coating and drying the slurry composition for solid-state battery manufacturing of the present invention. Furthermore, an all-solid-state battery can be manufactured by firing the inorganic powder sheet. In addition, a multilayer ceramic capacitor can be manufactured by using the slurry composition for solid-state battery manufacturing and the inorganic powder sheet of the present invention as a dielectric green sheet and electrode paste, respectively.

A method for manufacturing the above-mentioned all-solid-state battery includes the steps of: forming an electrode active material layer slurry containing an electrode active material and an electrode active material layer binder to produce an electrode active material sheet; laminating the electrode active material sheet and the inorganic powder sheet of the present invention to produce a laminate; and firing the laminate.

The electrode active material is not particularly limited and examples include glass powder, ceramic powder, phosphor nanoparticles, silicon oxide, metal nanoparticles, etc.

The above-mentioned glass powder is not particularly limited and includes, for example, glass powders such as bismuth oxide glass, silicate glass, lead glass, zinc glass, and boron glass, as well as glass powders of _{various silicon oxides such as CaO-Al₂O₃-SiO₂ systems , MgO} - _Al₂O₃ - _SiO₂ systems, and _LiO₂ - _{Al₂O₃ -SiO₂ systems} .
Furthermore, the glass powders mentioned above include: SnO- _B2O3 - _P2O5 - _Al2O3 mixture, _PbO - _{B2O3 -SiO2 mixture} , BaO-ZnO- _B2O3 - _SiO2 mixture, _ZnO - _Bi2O3 - _B2O3 - _SiO2 mixture, _Bi2O3 - _B2O3 - _BaO - _CuO mixture, _{Bi2O3 - ZnO} - _{B2O3 -Al2O3-SrO mixture, ZnO-Bi2O3-B2O3 mixture , Bi2O3 - SiO2 mixture , P2O5 - Na2O - CaO - BaO} - _{Al2O3 - B 2} O ₃ mixture, P ₂ O ₅ -SnO mixture, P ₂ O ₅ -SnO-B ₂ O ₃ mixture, P ₂ O ₅ -SnO-SiO ₂ mixture, CuO-P ₂ O ₅ -RO mixture, SiO ₂ -B ₂ O ₃ -ZnO-Na ₂ O-Li ₂ O-NaF-V ₂ O ₅ mixture, P ₂ O ₅ -ZnO-SnO-R ₂ O-RO mixture, B ₂ O ₃ -SiO ₂ -ZnO mixture, B ₂ O ₃ -SiO ₂ -Al ₂ O ₃ -ZrO ₂ mixture, SiO ₂ -B ₂ O ₃ -ZnO-R ₂ O-RO mixture, SiO ₂ -B ₂ O _{3 Al₂O₃} - _RO - _R₂O mixture, SrO-ZnO- _P₂O₅ mixture, SrO-ZnO- _P₂O₅ mixture, BaO-ZnO- _{B₂O₃ -SiO₂ mixture ,} etc., can also be used. Note that R is an element selected from the group consisting of Zn, Ba, Ca, Mg, Sr, Sn, Ni, Fe _, and Mn.
In particular, lead-free glass powders such _as PbO- _{B2O3 - SiO2} mixture glass powder, or lead-free BaO- _ZnO - _B2O3 - _SiO2 mixture or ZnO- _Bi2O3 - _{B2O3 - SiO2} mixture are preferred.

The above ceramic powders are not particularly limited and include, for example, alumina, ferrite, zirconia, zircon, barium zirconate, calcium zirconate, titanium oxide, barium titanate, strontium titanate, calcium titanate, magnesium titanate, zinc titanate, lanthanum titanate, neodymium titanate, lead zirconate titanate, alumina nitride, silicon nitride, boron nitride, boron carbide, barium stanate, calcium stanate, magnesium silicate, mullite, steatite, cordierite, forsterite, and the like.
In addition, ITO, FTO, niobium oxide, vanadium oxide, tungsten oxide, lanthanum strontium manganite, lanthanum strontium cobalt ferrite, yttrium-stabilized zirconia, gadolinium-doped ceria, nickel oxide, lanthanum chromite, and others can also be used.
The above-mentioned phosphorescent nanoparticles are not particularly limited, and for example, as phosphorescent materials, conventionally known blue phosphorescent materials, red phosphorescent materials, and green phosphorescent materials used for displays can be used. As blue phosphorescent materials, for example, MgAl ₁₀ O ₁₇ : Eu, Y ₂ SiO ₅ : Ce system, CaWO ₄ : Pb system, BaMgAl ₁₄ O ₂₃ : Eu system, BaMgAl ₁₆ O ₂₇ : Eu system, BaMg ₂ Al ₁₄ O ₂₃ : Eu system, BaMg ₂ Al ₁₄ O ₂₇ : Eu system, and ZnS: (Ag, Cd) system can be used. Examples of red phosphors used include _Y₂O₃ (Eu-based ₎ , _Y₂SiO₅ (Eu-based ₎ , _{Y₃Al₅O₁₂} ( _Eu -based ₎ , _Zn₃ ( _PO₄ ) _₂ (Mn-based), _YBO₃ (Eu-based), (Y,Gd) _BO₃ (Eu-based), _GdBO₃ (Eu-based), _ScBO₃ (Eu-based), and _LuBO₃ (Eu-based). Examples of green phosphors used include _Zn₂SiO₄ (Mn-based ₎ , _{BaAl₁₂O₁₇ (} Mn-based), _{SrAl₁₃O₁₇ (} Mn-based), _{CaAl₁₂O₁₇} (Mn-based), _YBO₃ (Tb-based ₎ , _{BaMgAl₁₄O₂₃ (} Mn-based), _LuBO₃ (Tb-based), _GdBO₃ (Tb-based), _ScBO₃ ( _Tb -based), and _{Sr₆Si₃O₃Cl₄} (Eu- _{based )} . Other types of compounds that can be used include ZnO (Zn-based), ZnS ((Cu,Al)-based) _, ZnS (Ag _- based), Y₂O₂S (Eu-based), ZnS (Zn-based), (Y _, Cd) _BO₃ (Eu-based), and _{BaMgAl₁₂O₂₃} (Eu-based).

The above-mentioned metal nanoparticles are not particularly limited and include, for example, powders made of copper, nickel, palladium, platinum, gold, silver, aluminum, tungsten, or alloys thereof.
Furthermore, metals such as copper and iron, which have good adsorption properties with carboxyl groups, amino groups, amide groups, etc., and are easily oxidized, can also be suitably used. These metal powders may be used individually or in combination of two or more.
In addition to metal complexes, various types of carbon black, carbon nanotubes, etc., may also be used.

The electrode active material described above preferably contains lithium or titanium. Specifically, for example, low-melting-point glasses such as _LiO₂・_Al₂O₃・_{SiO₂ inorganic} glass, lithium-sulfur-based glasses such as _Li₂S - _MxSy (M=B, Si, Ge, P), lithium-cobalt composite oxides such as _LiCoO₂ , lithium- _manganese composite oxides such as _LiMnO₄ , lithium nickel composite oxides, lithium vanadium composite oxides, lithium zirconium composite oxides, lithium hafnium composite oxides, lithium silicate (Li _3.5 Si _0.5 P _{0.5 O₄} ), lithium titanium phosphate ( _LiTi₂ ( _PO₄ ) _₃ ), _lithium titanate ( _{Li₄Ti₅O₁₂} ), Li₄ _{/ 3Ti₅/ 3O₄} , lithium germanium phosphate ( _LiGe₂ ( _PO₄ ) _{₃ )} , _Li₂ -SiS-based glass, Li _{4 GeS4 - Li3PS4} glass, _LiSiO3 , _LiMn2O4 , _Li2S - _{P2S5 glass} /ceramics _{, Li2O} -SiO2, _Li2O - _V2O5 -SiO2, LiS- _SiS2 - _Li4SiO4 glass, ion-conductive oxides such _{as LiPON} , _lithium oxide compounds such as _Li2O - _P2O5 - _{B2O3 , Li2O - GeO2Ba , LixAlyTiZ ( PO4 ) 3 glass , LaxLiyTiOz glass , LixGeyPzO4 glass , Li7La3} Examples include _{Zr₂O₁₂ -} type glass, _{Li₂vSi₂wP₀SyClₙ - type} glass, lithium _niobium oxides such as _LiNbO₃ , lithium alumina compounds such as Li-β-alumina, _and lithium zinc oxides such as _Li₁₄Zn ( _GeO₄ ) _₄ .

As the binder for the electrode active material layer mentioned above, polystyrene resins, polypropylene resins, and (meth)acrylic resins can be used.

Methods for laminating the electrode active material sheet and the inorganic powder sheet of the present invention include methods such as heat pressing, thermal lamination, etc., after each sheet has been formed.

In the above firing process, the preferred lower limit of the heating temperature is 250°C, and the preferred upper limit is 600°C.

By the above manufacturing method, an all-solid-state battery can be obtained.
The above-mentioned all-solid-state battery preferably has a structure in which a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer are stacked.
A method for manufacturing an all-solid-state battery, comprising the steps of obtaining an inorganic powder sheet using the slurry composition for manufacturing solid-state batteries of the present invention, and firing the inorganic powder sheet at a temperature of 600°C or lower, is also one of the present inventions.

A method for manufacturing the above-mentioned multilayer ceramic capacitor includes the steps of printing a conductive paste onto the inorganic powder sheet, drying it to produce a dielectric sheet, and laminating the dielectric sheets.

The conductive paste described above contains conductive powder.
The material of the conductive powder described above is not particularly limited as long as it is a conductive material, and examples include nickel, palladium, platinum, gold, silver, copper, and alloys thereof. These conductive powders may be used individually or in combination of two or more types.

The method for printing the above conductive paste is not particularly limited and includes, for example, screen printing, die-coating, offset printing, gravure printing, and inkjet printing.

In the above-described method for manufacturing multilayer ceramic capacitors, a multilayer ceramic capacitor is obtained by stacking dielectric sheets printed with the conductive paste described above.

According to the present invention, even when the slurry contains inorganic powders including alkali metals, gelation of the slurry can be suppressed, and it also exhibits excellent sinterability, enabling the production of low-residue inorganic powder sheets and providing a slurry composition for manufacturing high-performance all-solid-state batteries. Furthermore, a method for manufacturing an all-solid-state battery using this slurry composition can be provided.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
In a separable flask equipped with a Liebig condenser, a temperature-adjustable oil bath, and a stirring blade, 100 parts by weight of polystyrene resin (polystyrene homopolymer, DIC Corporation, XC-315, MFR value 3.2 g/10 min) as a binder resin and 1000 parts by weight of toluene (boiling point 110°C) as an organic solvent were added. The oil bath was then heated to 80°C and stirred for 6 hours to dissolve the polystyrene resin.
A vacuum pump and solvent trap were set up, and the solution was treated with the vacuum pump for one hour to recover trace amounts of unreacted monomers and toluene containing water, thereby obtaining a polystyrene resin solution with a resin solids content of 12% by weight. The resin solids content was evaluated by the drying method.
33.3 parts by weight of the obtained polystyrene resin solution (4 parts by weight of resin) was weighed into a poly container for a high-speed stirrer, and organic solvents were added to achieve the formulation shown in Table 1. 1,3-di-tert-butyltoluene was added as a plasticizer, and the sealed container was rotated at high speed to uniformly mix the resin solution.
40 parts by weight of Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ, manufactured by Toyoshima Seisakusho Co., Ltd.) as a conductive inorganic powder was added to the obtained resin solution, and the inorganic powder was dispersed by rotating the container at high speed while it was sealed to prepare a slurry composition.

(Examples 2-6, Comparative Examples 1, 3-4)
A slurry composition was obtained in the same manner as in Example 1, except that the type and formulation of the binder resin, organic solvent, and plasticizer were changed as shown in Table 1.
The following organic solvents, binder resins, and plasticizers were used.
<Soluble Organic Solvents>
Benzyl alcohol (boiling point 205°C)
Ethylcyclohexane (boiling point 160°C)
Xylene (boiling point 139°C)
Ethylbenzene (boiling point 136°C)
Liquid paraffin NAS-3 (boiling point 195°C), butyl acetate manufactured by NOF Corporation (boiling point 126°C)
<Binder resin>
CR-3500: Polystyrene homopolymer, manufactured by DIC Corporation. NormalFlow: Polystyrene homopolymer, manufactured by Toyo Engineering Corporation. Novatec FY4: Polypropylene homopolymer, manufactured by Nippon Polypropylene Co., Ltd. Novatec EA9: Polypropylene homopolymer, manufactured by Nippon Polypropylene Co., Ltd. Novatec MA3H: Polypropylene homopolymer, manufactured by Nippon Polypropylene Co., Ltd. Esrec BM-S: Polyvinyl acetal resin, manufactured by Sekisui Chemical Co., Ltd. HighFlow: Polystyrene homopolymer, manufactured by Toyo Engineering Corporation. <Plasticizer>
α-Methylstyrene dimer octyl phthalate Excellex 07500: Liquid polyolefin, manufactured by Mitsui Chemicals; Unitol P-801: Hydroxyl-modified polyolefin, manufactured by Mitsui Chemicals; Lucant HC-40: Ethylene-α-olefin copolymer, manufactured by Mitsui Chemicals; Dibutyl phthalate, manufactured by Mitsui Chemicals.

(Comparative Example 2)
In a separable flask equipped with a cooling tube, a temperature-adjustable oil bath, a nitrogen inlet tube, and a stirring blade, 100 parts by weight of methyl methacrylate (MMA) as a monomer and 100 parts by weight of butyl acetate as an organic solvent were added. The oil bath was set to 80°C, and Perloyl L (manufactured by NOF Corporation) was added as a polymerization initiator to polymerize the monomer. When the resin solids content was evaluated using the drying method, it was confirmed that the monomer had polymerized to almost 100%. After dilution with the addition of 600 parts by weight of butyl acetate, the butyl acetate containing trace amounts of unreacted monomer and water was recovered in the same manner as in Example 1 to obtain a resin solution with a resin solids content of 15% by weight.
Forty parts by weight (6 parts by weight) of the resin solution were weighed into a poly container for a high-speed stirrer, and organic solvents were added to achieve the formulation shown in Table 1. Dibutyl phthalate was added as a plasticizer, and the sealed container was rotated at high speed to uniformly mix the resin solution.
40 parts by weight of Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ, manufactured by Toyoshima Seisakusho Co., Ltd.) as a conductive inorganic powder was added to the obtained resin solution, and the inorganic powder was dispersed by rotating the container at high speed while it was sealed to prepare a slurry composition.

<Evaluation>
The binder resins used in the examples and comparative examples, and the slurry compositions obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 1 and 2.

(1) MFR value: MFR was measured in accordance with ISO 1133. Note that ISO 1133 specifies measurement conditions depending on the type of resin, and the measurement was performed under the following conditions.
Polystyrene resin: Temperature 200°C, load 5 kg
Polypropylene resin: Temperature 230°C, load 16 kg
Polyvinyl acetal resin: Temperature 150°C, load 5 kg
Polymethyl methacrylate: Temperature 230°C, load 3.8 kg

(2) pH of the slurry composition
The obtained slurry composition was applied to pH test paper (manufactured by Advantec Co., Ltd.) using a dropper, and the pH of the slurry composition was measured from the degree of color change and evaluated according to the following criteria. A low pH indicates a low amount of alkali metal in the slurry composition, suggesting inferior battery performance.
○: The slurry composition was strongly alkaline, with a pH of 11 or higher.
×: The pH was less than 11, and the slurry composition was not strongly alkaline.

(3) Gelation of the slurry composition The polyethylene container for the high-speed stirrer containing the obtained slurry composition was opened in a room adjusted to a dew point of -30°C, and the slurry was stirred with a spatula to check the gelation state and evaluated according to the following criteria.
○: The slurry was fluid, and no solidified material was observed.
△: The slurry was fluid but solidified within one hour.
×: The slurry had already gelled when the container was opened.

(4) Printability of Slurry Compositions For slurry compositions that showed fluidity in "(3) Gelation of Slurry Compositions", an inorganic powder sheet was prepared by coating it with an applicator onto a Teflon® sheet fixed on a glass plate in a dry room with a dew point of -30°C, drying it in a forced-air oven set to 120°C for 30 minutes, and evaluating it according to the following criteria. If the printability is excellent, a uniform sheet can be prepared, and it can be said that a high-performance all-solid-state battery can be prepared.
○: A sheet with a smooth and dense coating surface was produced.
△: Problems such as smudging, bleed, and blurring were observed.
×: It did not exhibit fluidity and could not be printed. Or, it had poor fluidity and could not be coated with a uniform thickness.

(5) Handling properties of inorganic powder sheets The Teflon® sheet was peeled off from the inorganic powder sheet obtained in "(4) Printability of slurry composition," and the inorganic powder sheet was placed on a ceramic plate for firing using tweezers. The condition of the sheet was visually checked and evaluated according to the following criteria. If the handling properties are excellent, it is easier to manufacture electrodes and thus easier to manufacture batteries.
○: No cracks or fractures were observed in the test specimen.
△: Although some cracks were observed, the sheet shape was maintained, and it was possible to conduct the firing test.
×: The slurry did not exhibit fluidity, making it impossible to produce an inorganic powder sheet. Alternatively, the sheet broke into small pieces and became pulverized.

(6) Sinterability of Inorganic Powder Sheets In "(5) Handling of Inorganic Powder Sheets", inorganic powder sheets placed on ceramic plates were fired in an electric furnace. The firing conditions were degreasing at 600°C for 30 minutes, followed by firing at 1000°C for 5 hours. The cross-section of the sheet after firing was observed with an electron microscope and evaluated according to the following criteria. If the sinterability is high, it can be said that a uniform sheet with few impurities can be produced, and a higher performance all-solid-state battery can be produced.
○: A dense inorganic powder sintered body was obtained, free from voids and calcination residue (soot).
△: Some firing residue (soot) was observed.
×: Inorganic powder sheets could not be fabricated. Alternatively, voids or cavities due to calcination residue (soot) were observed in some places.

In Comparative Examples 1 and 2, gelation and rapid thickening occurred, making it impossible to produce good sheets. In Comparative Example 3, while no decrease in fluidity due to gelation was observed, the printed and dried sheets cracked finely and could not maintain their sheet shape. Furthermore, in Comparative Example 4, although no decrease in fluidity due to gelation was observed, applicator marks remained during printing, repulsion occurred in the film, and voids and air pockets formed after sintering. Using these slurry compositions, it was not possible to densely laminate sheets, making it impossible to produce high-performance all-solid-state batteries. On the other hand, in Examples 1 to 6, even when containing large amounts of alkali metals, gelation of the slurry compositions was suppressed, and printability was good. Although some cracking was observed in some areas, there were no voids or soot after sintering, and dense sheets were produced. Using such slurry compositions, it is possible to densely laminate sheets and produce higher-performance all-solid-state batteries.

According to the present invention, even when the slurry contains inorganic powders including alkali metals, gelation of the slurry can be suppressed, and it also exhibits excellent sinterability, enabling the production of low-residue inorganic powder sheets and providing a slurry composition for manufacturing high-performance all-solid-state batteries. Furthermore, a method for manufacturing an all-solid-state battery using this slurry composition can be provided.

Claims (4)

A slurry composition for producing an all-solid-state battery , wherein the binder resin is removed by firing an inorganic powder sheet, which has been coated onto a support film that has been treated with a single-sided release agent, at a degreasing temperature of 600°C or lower .
It contains an organic solvent, a binder resin, and an inorganic powder containing an alkali metal.
The organic solvent is at least one selected from the group consisting of aromatic compounds, aliphatic hydrocarbons, and alicyclic hydrocarbons.
The binder resin is at least one selected from the group consisting of styrene homopolymers and propylene homopolymers.
A slurry composition for manufacturing solid batteries, wherein the MFR value of the binder resin is 10 g/10 min or less. A slurry composition for manufacturing solid-state batteries according to claim 1, wherein the pH is 11 or higher. The slurry composition for manufacturing solid-state batteries according to claim 1 or 2, wherein the inorganic powder contains lithium. A method for manufacturing an all-solid-state battery, comprising the steps of: obtaining an inorganic powder sheet using a slurry composition for manufacturing solid-state batteries according to any one of claims 1 to 3; and firing the inorganic powder sheet at a temperature of 600°C or lower.