WO2017155012A1

WO2017155012A1 - Solid-state battery positive electrode material, production method for solid-state battery positive electrode material, all-solid-state lithium-sulfur battery using solid-state battery positive electrode material, and production method for all-solid-state lithium-sulfur battery using solid-state battery positive electrode material

Info

Publication number: WO2017155012A1
Application number: PCT/JP2017/009359
Authority: WO
Inventors: 日出夫道畑; 聖志金村
Original assignee: 東京電力ホールディングス株式会社; 公立大学法人首都大学東京
Priority date: 2016-03-11
Filing date: 2017-03-09
Publication date: 2017-09-14

Abstract

[Problem] To provide: a positive electrode material for producing a lithium-sulfur solid-state battery that does not experience degradation of battery performance from charging/discharging cycling, does not present the fire risk of liquid electrolytes, and thereby makes battery performance compatible with safety; an all-solid-state lithium-sulfur battery that uses the positive electrode material; and a production method. [Solution] A lithium-sulfur solid-state battery positive electrode material that contains: sulfur; a conductive material; a binder; and an ionic liquid or a solvate ionic liquid. An all-solid-state lithium-sulfur battery that includes: a positive electrode that comprises the positive electrode material; a negative electrode; and an oxide solid electrolyte. The positive electrode material is manufactured by means of a method wherein a slurry obtained by adding an organic solvent to the sulfur, the conductive material, the binder, and the ionic liquid or solvate ionic liquid is applied to one surface of an oxide solid electrolyte formation body and dried to remove the organic solvent. Said method makes it possible to manufacture a positive electrode material that is adhered to a solid electrolyte and to reduce interface resistance between a positive electrode and a solid electrolyte and improve battery function.

Description

POSITIVE MATERIAL FOR SOLID BATTERY AND METHOD FOR MANUFACTURING THE SAME

The present invention relates to a positive electrode material for a solid battery and a manufacturing method thereof, and an all-solid lithium-sulfur battery using the positive electrode material for a solid battery and a manufacturing method thereof.

In recent years, portable and cordless electronic devices such as AV devices and personal computers and communication devices have been rapidly developed. Secondary batteries with high energy density and excellent load characteristics are demanded as power sources for these electronic and communication devices, and the use of lithium secondary batteries with high voltage, high energy density and excellent cycle characteristics has expanded. ing.

However, in the conventional lithium secondary battery, an electrolyte is generally used as an electrolyte, and the organic solvent constituting these electrolytes is flammable and there is a risk of ignition, so there is a problem in safety.

Since a so-called solid battery using a solid electrolyte as an electrolyte does not use a flammable electrolyte, it is highly safe and may have a theoretically high energy density. Research is being carried out at many universities and companies.

However, in a solid battery, not only the electrode but also the electrolyte is solid. Therefore, the contact portion at the interface between the particles constituting the electrode and the particles constituting the electrolyte is reduced, and lithium ions are compared with the case where an electrolyte is used as the electrolyte. And movement of electrons becomes difficult. As a result of the increase in interface resistance, battery characteristics such as energy density tend to be low.

As a method of suppressing the interface resistance between the solid electrolyte and the electrode, a method in which an interface layer composed of a mixture of the electrolyte particles and the electrode particles is sandwiched between the electrolyte and the electrodes, or the surfaces of the electrolyte particles and the electrode particles are coated with a conductive film. Although methods have been studied, interface resistance has not been significantly reduced.

On the other hand, since sulfur has a very high theoretical capacity density of 1675 mAh / g and is expected as a battery material having a high energy density, a lithium sulfur battery using sulfur as a positive electrode active material and lithium metal as a negative electrode. Is under consideration.

However, even in the case of a lithium-sulfur battery, when a solid electrolyte is used as the electrolyte, as described above, the energy density of the battery is not so high as expected due to the interface resistance generated at the interface between the electrolyte and the electrode. There is a problem.

In addition, when an electrolyte containing an organic solvent is used, in addition to the risk of fire, reaction intermediates (such as lithium polysulfide) produced by the reaction of sulfur molecules and lithium ions with sulfur during charge and discharge Dissolves in the electrolyte solution and diffuses to cause self-discharge and deterioration of the negative electrode. By using an ionic liquid as the electrolyte, the risk of fire can be avoided, but since it is impossible to prevent the sulfur molecules and polysulfide ions from dissolving, the battery performance may also deteriorate.

In Patent Document 1, as a method for manufacturing a battery electrode, a method of forming an active material layer by heating a mixture containing an electrode active material and an ambient temperature molten salt and applying a reduced pressure paste to a current collector. Has been proposed. Room temperature molten salt is composed of cation components such as imidazolium cations such as ethylmethylimidazolium tetrafluoroborate, ammonium cations such as diethylmethylpropylammonium trifluoromethanesulfonylimide, pyridinium cations such as ethylpyridinium tetrafluoroborate, and boron tetrafluoride. Anion (BF ₄ ⁻ ), phosphorus hexafluoride anion (PF ₆ ⁻ ), trifluorosulfonyl anion ((CF ₃ SO ₂ ) ₂ N ⁻ ), bis (trifluorosulfonyl) imide anion ((C ₂ F ₅ SO ₂ ) A combination with an anionic component such as ₂ N ⁻ ). A powder of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium manganese oxide or the like is mixed as a positive electrode active material in a liquid electrolyte obtained by adding a supporting salt (lithium salt) to this room temperature molten salt. ing.

However, in the lithium ion secondary battery described in Patent Document 1, a room-temperature molten salt electrolyte is impregnated into a layered structure in which a positive electrode active material layer and a negative electrode active material layer face each other with a separator interposed therebetween. A coin-type lithium ion secondary battery is manufactured. Therefore, it is not an all-solid-type lithium secondary battery using a solid electrolyte as an electrolyte.

JP 2004-022294 A

The object of the present invention is to reduce the interfacial resistance between the solid electrolyte and the electrode, thereby solving the problems derived from the solid electrolyte, and to obtain a lithium-sulfur solid battery having both safety and battery performance. A positive electrode material, an all-solid-state lithium-sulfur battery using the positive electrode material, and a method for producing the same are provided.

In order to solve the above problems, the present inventors have conducted intensive studies. As a result, by including an ionic liquid or a solvated ionic liquid in the positive electrode material for a lithium-sulfur solid battery, it becomes possible to reduce the interface resistance between the solid electrolyte and the electrode, and the charge / discharge capacity of the lithium-sulfur solid battery I got new knowledge that improved.
In addition, a positive electrode slurry containing sulfur, a carbon material, a binder (binder) and an ionic liquid or a solvated ionic liquid is applied to a predetermined position of the solid electrolyte molded body and dried to remove the solvent to obtain a positive electrode material. The new knowledge that a solid electrolyte and a positive electrode material can be closely_contact | adhered by forming was acquired.

That is, the present invention is as follows.

(1) A positive electrode material for a lithium-sulfur solid battery, comprising sulfur, a conductive material, a binder, and an ionic liquid or a solvated ionic liquid.
(2) The positive electrode material for a lithium-sulfur solid battery according to (1), wherein the ionic liquid contains a lithium salt.
(3) The positive electrode material for a lithium-sulfur solid battery according to (1), wherein the solvated ionic liquid comprises a lithium salt and glyme.
(4) The lithium salt is at least one selected from lithium-bis (fluorosulfonyl) imide and lithium-bis (trifluoromethanesulfonyl) imide, and the glyme is at least one selected from triglyme and tetraglyme. The positive electrode material for a lithium-sulfur solid battery according to (3) above.
(5) The positive electrode material for a lithium-sulfur solid battery according to any one of (1) to (4), wherein the conductive material is conductive carbon black.
(6) The positive electrode material for a lithium-sulfur solid battery according to any one of (1) to (5), wherein the binder is polyvinylidene fluoride.
(7) The ratio of each component in the positive electrode material is 45-60 mass%, 20-35 mass%, 0.1-10 mass% for sulfur, conductive material, binder and ionic liquid or solvated ionic liquid, respectively. The positive electrode material for a lithium-sulfur solid battery according to any one of (1) to (6), which is 10 to 20% by mass.

(8) A method for producing a positive electrode material for a lithium-sulfur solid battery containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid,
A step of applying a masking tape on one side of the oxide-based solid electrolyte molded body, leaving a portion for forming a positive electrode;
Applying a positive electrode slurry containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid to a portion of the oxide-based solid electrolyte molded body forming the positive electrode, and uniformly spreading the step;
After the positive electrode slurry is vacuum dried and solidified, the masking tape is removed and a positive electrode is formed on the oxide-based solid electrolyte formed body; and
The manufacturing method of the positive electrode material for lithium sulfur solid batteries characterized by including.
(9) The positive electrode slurry according to (8), wherein sulfur and a conductive material are pulverized and mixed, and then a binder solution and an ionic liquid or a solvated ionic liquid are added and further a solvent is added to form a slurry. A method for producing a positive electrode material for a lithium-sulfur solid battery.
(10) Nonvolatile content of the positive electrode slurry excluding the solvent is sulfur: 45 to 60% by mass, conductive material: 20 to 35% by mass, binder: 0.1 to 10% by mass, ionic liquid or solvated ionic liquid: The method for producing a positive electrode material for a lithium-sulfur solid battery according to (8) or (9), comprising 10 to 20% by mass.
(11) The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of (8) to (10), wherein the ionic liquid contains a lithium salt.
(12) The solvated ionic liquid comprising at least one selected from lithium-bis (fluorosulfonyl) imide and lithium-bis (trifluoromethanesulfonyl) imide, and at least one selected from triglyme and tetraglyme. (8) The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of (10) to (10).
(13) The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of (8) to (12), wherein the conductive material is conductive carbon black.
(14) The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of (8) to (13), wherein the binder is polyvinylidene fluoride.
(15) The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of (8) to (14), wherein the oxide-based solid electrolyte comprises a lithium-lanthanum-zirconium composite oxide.

(16) having a positive electrode made of the positive electrode material according to any one of (1) to (7), a negative electrode containing lithium metal, and a layer of an oxide-based solid electrolyte interposed between the positive electrode and the negative electrode All solid lithium sulfur battery.
(17) The all solid lithium-sulfur battery according to (16), wherein the oxide-based solid electrolyte is a lithium-lanthanum-zirconium composite oxide.
(18) The all-solid-state lithium-sulfur battery according to (17), wherein the lithium-lanthanum-zirconium composite oxide is a composite oxide further containing one or more elements selected from aluminum, tantalum, niobium and bismuth.
(19) The all-solid-state lithium-sulfur battery according to any one of (16) to (18), wherein the operating temperature is 110 ° C. or lower.
(20) A positive electrode made of a positive electrode material for a lithium-sulfur solid battery produced by the method according to any one of (8) to (15), a negative electrode containing lithium metal, and interposed between the positive electrode and the negative electrode An all-solid-state lithium-sulfur battery having an oxide-based solid electrolyte layer.
(21) An automobile equipped with the all-solid-state lithium-sulfur battery according to any one of (16) to (20).
(22) A power storage system in which power is supplied from the all-solid-state lithium-sulfur battery according to any one of (16) to (20) to a power network, or power is supplied to the all-solid-state lithium-sulfur battery from the power network.
(23) A step of bonding a negative electrode metal to one surface of the oxide-based solid electrolyte molded body and heat-treating the negative electrode metal;
Applying a masking tape to the surface opposite to the surface on which the negative electrode of the oxide-based solid electrolyte formed body is formed, leaving a portion for forming the positive electrode;
Applying a positive electrode slurry containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid to a portion of the oxide-based solid electrolyte molded body forming the positive electrode, and uniformly spreading the step;
After the positive electrode slurry is vacuum dried and solidified, the masking tape is removed and a positive electrode is formed on the oxide-based solid electrolyte formed body; and
A method for producing a lithium-sulfur solid state battery comprising:

The positive electrode material for a lithium-sulfur solid battery of the present invention contains a liquid but non-volatile, non-combustible ionic liquid or solvated ionic liquid. Further, according to the method for producing a positive electrode material for a lithium-sulfur solid battery of the present invention, since the positive electrode material is formed in close contact with the surface of the solid electrolyte, a liquid ionic liquid or solvent is present at the interface between the solid electrolyte and the positive electrode. As a result of the presence of the ionic liquid, the contact area between the solid electrolyte and the positive electrode can be increased. And since the ionic liquid or solvated ionic liquid has lithium ion conductivity, the interfacial resistance between the solid electrolyte and the positive electrode is reduced, and it is possible to obtain a lithium-sulfur solid battery with little performance degradation even after repeated charge / discharge cycles It becomes.

In addition, since the electrolyte layer becomes a solid electrolyte, it is possible to prevent a decrease in battery performance due to the dissolution and diffusion of sulfur and polysulfides in the electrolytic solution, and the operating temperature is 110 ° C. or less, so there is also a risk of fire It is possible to provide a safe and all-solid lithium-sulfur battery.

3 is a graph showing the results of a charge / discharge cycle test (1 to 3 cycles) of a coin-type battery using a positive electrode material of the present invention containing an ionic liquid or a solvated ionic liquid. 6 is a graph showing the results of a charge / discharge cycle test (4 to 6 cycles) of a coin-type battery using the positive electrode material of the present invention containing an ionic liquid or a solvated ionic liquid. It is a graph which shows the result of the charging / discharging cycle test of the coin-type battery using the positive electrode material of the comparative example which does not contain an ionic liquid or a solvated ionic liquid.

The positive electrode material for a lithium-sulfur solid battery of the present invention must contain an ionic liquid or a solvated ionic liquid. Basically, a binder such as sulfur, a conductive material, or polyvinylidene fluoride, and an ionic liquid or solvate. Consists of ionic liquids.

The ionic liquid or solvated ionic liquid used in the present invention is liquid when it is about 150 ° C. or lower, and is a non-volatile, non-flammable liquid having ionic conductivity.

Examples of ionic liquids include 1-ethyl-3-methylimidazolium-bis (trifluorosulfonyl) imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, trimethylpropylammonium-bistrifluoromethylsulfonylimide, ethylpyridinium Examples thereof include tetrafluoroborate. An ionic liquid may be used independently and may be used in combination of 2 or more type.

In the ionic liquid, as a supporting salt, lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium trifluoromethylsulfonate (Li (CF ₃ SO ₃ )), lithium-bis ( Trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ), lithium-bis (pentafluoroethanesulfonyl) imide (LiN (C ₂ F ₅ SO ₂ ) ₂ ), lithium hexafluorophosphate (LiPF ₆ ), etc. These known lithium salts can be mixed and used. A supporting salt may be used independently and may be used in combination of 2 or more type.

The mixing ratio (molar ratio) between the ionic liquid and the supporting salt is preferably 1: 0.1 to 2, and more preferably 1: 0.8 to 1.2. Particularly preferred is 1: 1.

The solvated ionic liquid is a mixture of lithium salt and glyme. Different combinations of lithium salt and glyme produce products having different thermal decomposition temperatures. It is preferable to select a solvated ionic liquid that does not thermally decompose at about 100 ° C.

Examples of the lithium salt include lithium-bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ ), lithium-bis (trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ), lithium-bis (penta Fluoroethanesulfonyl) imide LiN (C ₂ F ₅ SO ₂ ) ₂ ) and the like. A lithium salt may be used independently and may be used in combination of 2 or more type.

As the glyme, both ends may be the same alkyl group or different alkyl groups, for example, triglyme such as triethylene glycol dimethyl ether, triethylene glycol diethyl ether, trimethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, Examples include tetraglyme such as tetraethylene glycol diethyl ether and tetraethylene glycol methyl ethyl ether. The alkyl group may be substituted with fluorine. Among these lithium salts, lithium-bis (fluorosulfonyl) imide and lithium-bis (trifluoromethanesulfonyl) imide are preferable. A glyme may be used independently and may be used in combination of 2 or more type.

Of the above ionic liquids or solvated ionic liquids, solvated ionic liquids are preferred because they are excellent in lithium ion conductivity and are difficult to elute sulfur and polysulfides. , LiFSI) and triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether are preferred.

The mixing ratio (molar ratio) of lithium salt and glyme is preferably lithium salt: glyme = 40: 60 to 60:40, and more preferably 45:55 to 55:45. Particularly preferred is 50:50.

The positive electrode material of the present invention uses sulfur as an active material. However, since sulfur itself has a problem of poor electrical conductivity, it is necessary to use a conductive material in combination. Examples of the conductive material include carbon blacks such as acetylene black, ketjen black, channel black, and furnace black, graphites such as natural graphite such as flake graphite and artificial graphite, conductive fibers such as carbon fiber and metal fiber, Metal powders such as copper and silver, organic conductive materials such as polyphenylene compounds, carbon nanotubes, and the like can be used.

Among the conductive materials, carbon blacks are preferable because they are porous and exhibit an effect as a binder by incorporating sulfur, an ionic liquid or a solvated ionic liquid into the pores. Conductive carbon black having a hollow shell structure such as is preferable.

The conductive carbon black preferably has a BET specific surface area by a nitrogen gas adsorption method of 500 m ² / g or more, more preferably 750 m ² / g or more, and still more preferably 1000 m ² / g or more.

Furthermore, it is preferable to use a binder in combination with the positive electrode material of the present invention. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene copolymer, and vinylidene fluoride. -Perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), propylene-tetrafluoroethylene copolymer, polyvinyl Pyrrolidone, polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), etc. But are lower, polyvinylidene fluoride is preferably used. These binders may be used alone or in combination of two or more.

The method for adding these binders is not particularly limited. For example, it can be used as a powder, or can be used as a solution dissolved in an organic solvent or an emulsion using water as a solvent. As the organic solvent, N-methyl-2-pyrrolidone is preferable.

The content of sulfur in the positive electrode material of the present invention composed of sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid is preferably 45 to 60% by mass, more preferably 50 to 55% by mass. is there. If sulfur is 45 mass% or more, it becomes possible to ensure a high theoretical energy density as a battery. On the other hand, if the sulfur is 60% by mass or less, it is possible to sufficiently ensure the content of a conductive material, an ionic liquid, or a solvated ionic liquid, so that necessary conductivity can be imparted to the positive electrode material, The interface resistance between the positive electrode material and the solid electrolyte can be reduced.

The content of the conductive material is preferably 20 to 35% by mass, more preferably 20 to 30% by mass. When the conductive material is 20% by mass or more, sufficient conductivity can be imparted to the positive electrode. On the other hand, if the conductive material is 35% by mass or less, the content of sulfur, ionic liquid or solvated ionic liquid can be sufficiently ensured, so that the energy density of the battery can be improved, and the positive electrode material and The interface resistance between the solid electrolytes can be reduced.

The content of the binder is preferably 0.1 to 10% by mass, more preferably 5 to 10% by mass, and still more preferably 7 to 9% by mass. When the binder is 0.1% by mass or more, the retention of sulfur or ionic liquid or solvated ionic liquid in the pores of the conductive material such as ketjen black and the fixing of the conductive material to the solid electrolyte are more effectively enhanced. be able to. On the other hand, if it is 10 mass% or less, the fall of the electroconductivity of the positive electrode material derived from the binder itself being an insulator can be avoided. *

The content of the ionic liquid or solvated ionic liquid is preferably 10 to 20% by mass, more preferably 12 to 18% by mass. When the ionic liquid or solvated ionic liquid is 10% by mass or more, the interface resistance between the positive electrode material and the solid electrolyte can be effectively reduced. On the other hand, if it is 20% by mass or less, it is possible to avoid the uneconomical use of waste even though the effect of reducing the interface resistance is no longer improved.

Next, a method for producing the positive electrode material of the present invention will be described.

The method for producing a positive electrode material of the present invention aims to reduce the interfacial resistance between the positive electrode material and the solid electrolyte by forming the positive electrode material so as to be as close as possible to the surface of the solid electrolyte.

As the solid electrolyte, known lithium composite oxides and lithium-containing sulfides can be used in lithium ion batteries, but lithium-containing sulfides may react with moisture and oxygen in the atmosphere to generate toxic gases. Therefore, an oxide-based solid electrolyte is preferable, and it is more preferable to use a lithium composite oxide.

Examples of the lithium composite oxide include lithium-lanthanum-zirconium composite oxide, lithium-lanthanum-titanium composite oxide, lithium-niobium composite oxide, lithium-niobium-zirconium composite oxide, and lithium-lanthanum-zirconium-tantalum. Examples of the composite oxide include lithium-lanthanum-zirconium composite oxide (hereinafter referred to as “LLZ”). A well-known method can be used for the manufacturing method of LLZ. LLZ is a composite oxide composed of lithium, lanthanum and zirconium whose basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ , and, if necessary, one or more selected from aluminum, tantalum, niobium and bismuth. It may contain an element.

Since the shape and size of the solid electrolyte forming the positive electrode material differ depending on the shape and size of the battery to be finally assembled, the positive electrode material of the present invention is exemplified by the case where a coin-type battery is assembled using LLZ as the solid electrolyte. The details of the all-solid-state lithium-sulfur battery using the same, and the production method thereof will be described.

As the oxide-based solid electrolyte molded body, for example, an LLZ molded body having a diameter of about 12 mm and a thickness of about 0.5 mm can be used. The LLZ molded body can be produced by a known method, and for example, a method disclosed in JP-A-2015-146299 can be used.

That is, a stoichiometric amount of a lanthanum compound powder and a zirconium compound powder are mixed while being pulverized, formed into a predetermined shape with a press, and then fired in an electric furnace, preferably at 1300 to 1700 ° C. A zirconium oxide compact is obtained. This molded body preferably has a porosity of 75% or more, more preferably 80 to 90%. When the porosity is 75% or more, the lithium compound is easily impregnated. On the other hand, if the porosity is 90% or less, the strength of the molded product can be maintained. The porosity is a value calculated from the total pore volume (cm ³ / g) according to the mercury intrusion method (based on JIS R 1655) and the apparent density (g / cm ³ ) measured by the Archimedes method. The porosity can be adjusted by the firing temperature or the like.

The lanthanum compound is not particularly limited. For example, lanthanum hydroxide, lanthanum oxide, lanthanum chloride, lanthanum nitrate, or the like can be used. Lanthanum hydroxide that generates less harmful gas during firing is preferable.

The zirconium compound is not particularly limited. For example, zirconium oxide, zirconium chloride, zirconium nitrate, zirconium acetate or the like can be used. Zirconium oxide, which generates little toxic gas during firing, is preferred.

Next, an aqueous solution in which a stoichiometric amount of a lithium compound is dissolved in the lanthanum-zirconium oxide molded body is added, and the pores of the molded body are impregnated with the lithium compound, and then, preferably, using a microwave firing furnace or the like. Is fired at 200 to 500 ° C., more preferably 300 to 450 ° C. There is an advantage that a dense LLZ sintered body can be obtained by using a microwave as a heating source. When hot air or infrared rays are used as a heating source, the lithium compound reacts at the heated portion, so that the reaction proceeds only on the surface of the molded body, and a dense molded body having a Li ₇ La ₃ Zr ₂ O ₁₂ structure is obtained. May be difficult. The microwave is irradiated with a microwave having a frequency of 1 to 300 GHz, usually 2.45 GHz. The microwave output is preferably adjusted in the range of 1.5 to 9.5 kW, and after reaching a predetermined firing temperature, the temperature is preferably maintained by controlling the microwave irradiation by PID control or the like.

The lithium compound impregnated in the molded body is preferably used so that the molar ratio of lithium, lanthanum, and zirconium is 7: 3: 2 according to the basic composition of LLZ.

The lithium compound is not particularly limited. For example, lithium hydroxide, lithium oxide, lithium chloride, lithium nitrate, lithium sulfate, lithium acetate, or the like can be used. Among them, lithium hydroxide (LiOH) or lithium oxide (Li ₂ O) that dissolves in water to become lithium hydroxide is preferable because of its high solubility in water and low generation of toxic gas during firing.

The method for impregnating the lanthanum-zirconium oxide compact with lithium is not particularly limited as long as it is a method capable of impregnating a stoichiometric amount of lithium. For example, the following methods can be mentioned.
(1) A lanthanum-zirconium oxide molded body is impregnated with a part of a solution obtained by dissolving a required amount of a lithium compound in a solvent, and then the molded body is dried to remove the solvent. Again, a part of the solution is impregnated into the molded body, and then dried to remove the solvent. Then, impregnation and drying are repeated until the prepared solution disappears.
(2) A lanthanum-zirconium oxide molded body is impregnated with a slurry in which a required amount of lithium hydroxide or the like is dispersed in a small amount of water. In this case, as the lithium hydroxide, it is preferable to use fine particles that can easily enter the pores (voids) of the molded body.
(3) A highly soluble Li salt (for example, LiCl) is dissolved in water to prepare a highly concentrated LiCl aqueous solution, and the lanthanum-zirconium oxide compact is impregnated with the aqueous solution.
(4) Powdered LiOH is added to the lanthanum-zirconium oxide compact and impregnated with LiOH by heat melting. In this case, the melting temperature is preferably equal to or higher than the melting point of LiOH (462 ° C.).

The shape and size of the lanthanum-zirconium oxide molded body and LLZ are not particularly limited. Depending on the structure of the battery, for example, it may be formed into a plate shape, a sheet shape, a cylindrical shape, or the like.

In the present invention, before forming the positive electrode material on the surface of the oxide-based solid electrolyte molded body, a thin gold film is formed by sputtering on the surface on the negative electrode side of the molded body, that is, the surface opposite to the surface on which the positive electrode material is formed. It is preferable to form it in advance. Thereafter, when assembling the battery cell, the gold thin film and the metal lithium as the negative electrode are bonded together, and preferably heated at 60 to 170 ° C., more preferably 100 to 140 ° C., so that the metal lithium and gold are alloyed, and the negative electrode And the interface resistance between the solid electrolyte can be reduced.

Practically, a method is preferred in which metal lithium such as a lithium foil is attached to the negative electrode side surface of the oxide-based solid electrolyte molded body without gold sputtering, and then the metal lithium is heated and pressed if necessary. . Thereby, the contact property (adhesion) between the negative electrode and the solid electrolyte is improved, and the interface resistance can be reduced.
In the above case, after forming the positive electrode on the oxide-based solid electrolyte molded body, it is preferable to perform heat treatment by attaching a lithium foil to the surface of the oxide-based solid electrolyte molded body on the side opposite to the positive electrode. Alternatively, after the lithium foil is attached to the oxide solid electrolyte and heat treatment is performed, the positive electrode can be formed on the surface opposite to the surface on which the lithium foil of the oxide solid electrolyte is attached. The heat treatment temperature is not particularly limited as long as the lithium foil is softened. The temperature is preferably 60 to 170 ° C, more preferably 100 to 140 ° C.

After sputtering gold on the negative electrode side of the solid electrolyte, a polyimide tape from which the positive electrode forming part has been cut out is attached to the opposite surface as a masking tape. In addition, the masking tape should just be a polymer which is insoluble in a slurry solvent, and does not melt | dissolve at the time of the vacuum drying mentioned later, and is not limited to a polyimide.

The shape and size of the positive electrode forming part of the masking tape is such that the LLZ surface of at least about 2 mm in width remains around the positive electrode so that the formed positive electrode does not protrude around the solid electrolyte and short circuit occurs. It is good to make it. For example, in the case of an LLZ molded body having a diameter of 12 mm, a polyimide tape having a circular positive electrode forming portion having a diameter of about 8 mm may be used as a masking tape.

Next, an appropriate amount of the positive electrode slurry is placed on the positive electrode forming portion of the polyimide tape, and is spread using a spatula or glass plate so that it is flattened, and then the solvent in the positive electrode slurry is removed by vacuum drying. Remove. After removing the solvent, the polyimide tape is peeled off and the positive electrode material in a state of being in close contact with the LLZ compact can be produced.

Since the thickness of the positive electrode slurry to be applied is the same as the thickness of the polyimide tape, the weight or thickness of the positive electrode material to be formed can be adjusted by changing the thickness of the polyimide tape to be used.

The conditions for vacuum drying are not particularly limited, but if the solvent in the positive electrode slurry is rapidly evaporated, the close adhesion of the positive electrode material to the surface of the LLZ compact may be hindered. The temperature is preferably about 70 to 90 ° C. The time is about 10 to 15 hours.

The positive electrode slurry can be prepared by a known method. A predetermined amount of sulfur and a predetermined amount of conductive material such as conductive carbon black are mixed while being pulverized, and then a predetermined amount of binder powder such as polyvinylidene fluoride. Alternatively, a solution and a predetermined amount of ionic liquid or solvated ionic liquid can be added, and the mixture can be slurried by gradually adding the solvent.

As the solvent, a known solvent for lithium ion batteries can be used. For example, amide solvents such as N-methyl-2-pyrrolidone and dimethylacetamide, amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine, ketone solvents such as methyl ethyl ketone, ester solvents such as acetate ester, tetrahydrofuran And ether solvents such as toluene, hydrocarbon solvents such as toluene, xylene, n-hexane and cyclohexane.

The amount of these solvents used is not particularly limited. If the positive electrode slurry has such a fluidity that it can be transferred to the positive electrode forming portion of the LLZ compact using a glass rod or the like, and an amount showing a viscosity that does not flow and spread after being transferred to the positive electrode forming portion is used. good.

Using a commercially available coin-type battery cell container or the like, a lithium foil as a negative electrode is placed on the lower lid of the cell container, and the LLZ molded body is aligned with the surface opposite to the positive electrode forming part with respect to the lithium foil. Is placed. Next, a battery cell is assembled by placing a metal foil such as a stainless steel foil or an aluminum foil as a positive electrode current collector on the positive electrode of the LLZ molded body, and a battery container is completed by covering the upper lid of the cell container.

In the all solid lithium-sulfur battery of the present invention, the solid electrolyte layer is interposed between the positive electrode and the negative electrode.
The negative electrode is not particularly limited as long as it contains a material that absorbs and releases lithium ions as a negative electrode active material. For example, a lithium metal such as a lithium foil, a lithium alloy that is an alloy of lithium and aluminum, silicon, tin, magnesium, or the like, a metal oxide that can occlude and release lithium ions, a metal sulfide, a carbon material, and the like can be given. Among them, lithium metal is preferable because it has a high theoretical capacity density, is easy to handle, and is easy to assemble a battery cell.
As the current collector, for example, a metal such as copper, aluminum, nickel, and stainless steel can be used. As the negative electrode current collector and the positive electrode current collector, stainless steel foil or aluminum foil is preferable because it is inexpensive.

The all-solid-state lithium-sulfur battery may have a separator in addition to the positive electrode material, the positive electrode current collector, the solid electrolyte, the negative electrode material, and the negative electrode current collector described above. The shape of the all-solid-state lithium-sulfur battery is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type.

In the all-solid-state lithium-sulfur battery of the present invention, since the positive electrode material contains an ionic liquid or a solvated ionic liquid and the ionic liquid or solvated ionic liquid has good lithium ion conductivity, the operating temperature is 110 ° C. or lower. is there. Since the operating temperature is 110 ° C. or lower, the ionic liquid and the solvated ionic liquid do not evaporate. Ionic liquids and solvated ionic liquids are nonflammable electrolytes and are not flammable. As described above, since the operating temperature is low, it is easy to keep the battery warm when not in use, and the charge / discharge efficiency as the final battery system is improved. The conventional sodium-sulfur battery has a high operating temperature, and the higher the operating temperature, the more heat energy is required to keep the battery warm, and the total efficiency decreases. There is very little danger and it is excellent in safety, and durability, battery safety and cycle safety are improved.

The use of the all solid lithium lithium battery of the present invention is not particularly limited. For example, it can be suitably used for hybrid vehicles, electric vehicles, power storage, and the like.
By storing power using the all-solid-state lithium-sulfur battery of the present invention, a power system is constructed in which power is supplied from the all-solid-state lithium-sulfur battery to the power grid. Or, in addition to thermal power generation, hydroelectric power generation, pumped-storage power generation, nuclear power generation, a power system that supplies power to the all-solid-state lithium-sulfur battery from a power network that uses natural energy power generation such as solar power generation and wind power generation as a power source. Built.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the following examples.

(Production Example 1)
33.9 g of lanthanum hydroxide (purity 99.9%, manufactured by Shin-Etsu Chemical Co., Ltd.) and 14.7 g of zirconium oxide (manufactured by Tosoh Corp.) were weighed and mixed while pulverizing with a ball mill for 1 hour. 0.26 g of the obtained powder was weighed, put into a die having a predetermined size, and molded by a single screw press machine to produce 10 plate-shaped compacts having a diameter of 13 mm and a thickness of 1 mm. The produced 10 plate-like molded bodies were each transferred to a firing ceramic container, fired at 1500 ° C. for 36 hours using an electric furnace, and then allowed to cool naturally to obtain a plate-like lanthanum-zirconium oxide molded body. .
Separately, 2.8 g of lithium hydroxide (manufactured by Kanto Kagaku) was dissolved in 30 ml of water to prepare a lithium aqueous solution, 1.0 ml of the prepared lithium aqueous solution was weighed, and a plate-like lanthanum-zirconium oxide was obtained. Was added to each of the firing ceramic containers.
Next, the ceramic container for firing is transferred to a microwave firing furnace, irradiated with microwaves and fired at a furnace temperature of 400 ° C. for 36 hours, and a plate-like lithium-lanthanum-zirconium composite oxide having a diameter of 12 mm and a thickness of about 0.5 mm. A molded body (LLZ molded body) was obtained.

Example 1
Using one of the plate-like LLZ compacts produced in Production Example 1, gold was sputtered on the negative electrode side, and then the positive electrode material was formed on the opposite side. The positive electrode material was formed as follows.

Make a masking tape by concentrically cutting the center part of polyimide tape (thickness 0.09mm) into a circle with a diameter of 8mm, and sticking it on the positive electrode side of the LLZ molded body. The circular part was used as a positive electrode forming part.

On the other hand, 1.00 g of sulfur was weighed in an agate mortar and ground. Next, 0.50 g of ketjen black (specific surface area 1270 m ² / g, manufactured by Lion Corporation, EC-600JD) was weighed and added, mixed for 30 minutes, dried at 155 ° C. for 6 hours, A mixture of ketjen black was obtained. 0.180 g of this was weighed into an agate mortar, carried into a glove box, 0.167 g of KF polymer (N-methyl-2-pyrrolidone solution containing 12% by mass of polyvinylidene fluoride, manufactured by Kureha), and [Li (G4)] [FSI] (a solution obtained by dissolving equimolar lithium-bis (fluorosulfonyl) imide (LiFSI) (manufactured by Kishida Chemical Co.) in tetraglyme (manufactured by Kishida Chemical Co.) was added. Then, N-methyl-2-pyrrolidone was added little by little using a micropipette and mixed to prepare a slurry. The total amount of N-methyl-2-pyrrolidone added was 1.0 ml.

Take the prepared slurry at the tip of a glass rod, apply it to the center of the positive electrode forming part of the LLZ compact, and reciprocate it two or three times while scraping the slurry on the end face of the slide glass. It was spread out evenly and evenly. Next, it was dried overnight at 80 ° C. using a vacuum dryer to completely remove N-methyl-2-pyrrolidone and the solvent N-methyl-2-pyrrolidone contained in the KF polymer, and then the masking tape was peeled off to form LLZ. A positive electrode material was produced on the body. The amount of the positive electrode material determined from the mass difference between the LLZ compacts before and after the formation of the positive electrode material was 0.00075 g.

(Example 2)
The following coin-type battery was assembled using the positive electrode material prepared in Example 1.
Using a commercially available coin-type battery cell container, fit a ring-shaped gasket on the lower lid, place a washer (material is stainless steel) on the lower lid, and a spacer (material stainless steel, outer diameter 15 mm, thickness) as a negative electrode current collector And a lithium foil (diameter 8 mm, thickness 600 μm) as a negative electrode was placed on the spacer, and then a LLZ molded body was placed so that the sputtered gold layer was superimposed on the lithium foil. Then, it heated at 120 degreeC and the lithium foil was stuck to the LLZ molded object. A stainless steel foil (diameter 8 mm, thickness 20 μm) was placed on the positive electrode material of the LLZ compact as a positive electrode current collector, and the upper lid was closed to assemble a battery cell.

The battery cell was stored at 100 ° C. for 12 hours, and then a charge / discharge test was performed. The conditions of the charge / discharge test were as follows: the voltage was 1.0 V to 3.5 V, 10 μA (1/30 C) up to 3 cycles, and 2 μA (1/150 c) after 4 cycles of charge and discharge up to 6 cycles. . The results up to 3 cycles are shown in FIG. 1, and the results of 4 to 6 cycles are shown in FIG.

(Comparative Example 1)
A positive electrode material was produced on the LLZ molded body in the same manner as in Example 1 except that [Li (G4)] [FSI] was not used.

(Comparative Example 2)
Using the positive electrode material of Comparative Example 1, a coin-type battery was assembled in the same manner as in Example 2, and a charge / discharge test was performed. The results are shown in FIG.

From FIG. 3, the coin type battery using the positive electrode material of the comparative example without adding [Li (G4)] [FSI] shows an initial discharge capacity of about 250 mAh / g, but the voltage at the initial discharge is not constant. It can be said that a stable discharge state is not shown because a flat discharge curve is not shown.

On the other hand, the coin-type battery using the positive electrode material of the present invention has a charge / discharge capacity of about 400 mAh / g, and does not add [Li (G4)] [FSI] to the positive electrode material. It can be seen that it has a larger capacity than the coin type battery.

As shown in FIGS. 1 and 2, the coin-type battery using the positive electrode material of the present invention exhibits a charge / discharge capacity of about 400 mAh / g up to the sixth cycle, and in any charge / discharge cycle, the voltage The charge / discharge plateau area | region which shows that it is a stable charging / discharging state is recognized without changing, and it turns out that it has favorable charging / discharging cycling characteristics. It can be said that the increase in the discharge capacity and the stability of the discharge potential are the effects of the solvated ionic liquid.

According to the present invention, it is possible to provide a lithium-sulfur solid state battery excellent in safety and cycle characteristics and having a high energy density because a decrease in battery performance due to repeated charge and discharge is suppressed.

Claims

A positive electrode material for a lithium-sulfur solid battery comprising sulfur, a conductive material, a binder, and an ionic liquid or a solvated ionic liquid.
The positive electrode material for a lithium-sulfur solid battery according to claim 1, wherein the ionic liquid contains a lithium salt.
The positive electrode material for a lithium-sulfur solid battery according to claim 1, wherein the solvated ionic liquid comprises a lithium salt and glyme.
4. The lithium salt is at least one selected from lithium-bis (fluorosulfonyl) imide and lithium-bis (trifluoromethanesulfonyl) imide, and the glyme is at least one selected from triglyme and tetraglyme. The positive electrode material for lithium-sulfur solid batteries described in 1.
The positive electrode material for a lithium-sulfur solid battery according to any one of claims 1 to 4, wherein the conductive material is conductive carbon black.
The positive electrode material for a lithium-sulfur solid battery according to any one of claims 1 to 5, wherein the binder is polyvinylidene fluoride.
The ratio of each component in the positive electrode material is 45 to 60 mass%, 20 to 35 mass%, 0.1 to 10 mass%, 10 to 10 mass% for sulfur, conductive material, binder and ionic liquid or solvated ionic liquid, respectively. The positive electrode material for a lithium-sulfur solid battery according to any one of claims 1 to 6, which is 20 mass%. *
A method for producing a positive electrode material for a lithium-sulfur solid battery containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid,
A step of applying a masking tape on one side of the oxide-based solid electrolyte molded body, leaving a portion for forming a positive electrode;
Applying a positive electrode slurry containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid to a portion of the oxide-based solid electrolyte molded body forming the positive electrode, and uniformly spreading the step;
After the positive electrode slurry is vacuum dried and solidified, the masking tape is removed and a positive electrode is formed on the oxide-based solid electrolyte formed body; and
The manufacturing method of the positive electrode material for lithium sulfur solid batteries characterized by including.
The lithium-sulfur solid battery according to claim 8, wherein the positive electrode slurry is obtained by pulverizing and mixing sulfur and a conductive material, and then adding a binder solution and an ionic liquid or a solvated ionic liquid, and further adding a solvent to form a slurry. Method for manufacturing positive electrode material.
Nonvolatile content of the positive electrode slurry excluding the solvent is sulfur: 45 to 60% by mass, conductive material: 20 to 35% by mass, binder: 0.1 to 10% by mass, ionic liquid or solvated ionic liquid: 10 to 20 The manufacturing method of the positive electrode material for lithium sulfur solid batteries of Claim 8 or 9 comprised by the mass%.
The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of claims 8 to 10, wherein the ionic liquid contains a lithium salt.
The solvated ionic liquid comprises at least one selected from lithium-bis (fluorosulfonyl) imide and lithium-bis (trifluoromethanesulfonyl) imide, and at least one selected from triglyme and tetraglyme. The manufacturing method of the positive electrode material for lithium sulfur solid batteries in any one of 10.
The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of claims 8 to 12, wherein the conductive material is conductive carbon black.
The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of claims 8 to 13, wherein the binder is polyvinylidene fluoride.
The method for producing a positive electrode material for a lithium-sulfur solid battery according to any one of claims 8 to 14, wherein the oxide-based solid electrolyte comprises a lithium-lanthanum-zirconium composite oxide.
An all-solid lithium-sulfur battery comprising a positive electrode comprising the positive electrode material according to any one of claims 1 to 7, a negative electrode containing lithium metal, and an oxide-based solid electrolyte layer interposed between the positive electrode and the negative electrode.
The all-solid-state lithium-sulfur battery according to claim 16, wherein the oxide-based solid electrolyte is a lithium-lanthanum-zirconium composite oxide.
The all-solid-state lithium-sulfur battery according to claim 17, wherein the lithium-lanthanum-zirconium composite oxide is a composite oxide further containing one or more elements selected from aluminum, tantalum, niobium and bismuth.
The all-solid-state lithium-sulfur battery according to any one of claims 16 to 18, wherein the operating temperature is 110 ° C or lower.
A positive electrode comprising a positive electrode material for a lithium-sulfur solid battery produced by the method according to any one of claims 8 to 15, a negative electrode containing lithium metal, and an oxide-based solid electrolyte interposed between the positive electrode and the negative electrode. And an all solid lithium sulfur battery.
An automobile equipped with the all-solid-state lithium-sulfur battery according to any one of claims 16 to 20.
21. A power storage system in which power is supplied from the all-solid-state lithium-sulfur battery according to claim 16 to a power network, or power is supplied to the all-solid-state lithium-sulfur battery from the power network.
Bonding a negative electrode metal to one side of the oxide-based solid electrolyte molded body and heat-treating;
Applying a masking tape to the surface opposite to the surface on which the negative electrode of the oxide-based solid electrolyte formed body is formed, leaving a portion for forming the positive electrode;
Applying a positive electrode slurry containing sulfur, a conductive material, a binder and an ionic liquid or a solvated ionic liquid to a portion of the oxide-based solid electrolyte molded body forming the positive electrode, and uniformly spreading the step;
After the positive electrode slurry is vacuum dried and solidified, the masking tape is removed and a positive electrode is formed on the oxide-based solid electrolyte formed body; and
A method for producing a lithium-sulfur solid state battery comprising: