JP7125043B2 - Sulfur cathode and lithium sulfur solid state battery - Google Patents

Description

The present invention relates to sulfur cathodes and lithium-sulfur solid-state batteries.

2. Description of the Related Art In recent years, electronic devices, communication devices, and the like are rapidly becoming portable and cordless. As a power source for these electronic devices and communication devices, secondary batteries with high energy density and excellent load characteristics are in demand, and the use of lithium secondary batteries with high voltage, high energy density and excellent cycle characteristics is expanding. is doing.
On the other hand, the popularization of electric vehicles and the promotion of the use of natural energy require batteries with even higher energy densities. Therefore, it is desired to develop a new lithium secondary battery to replace the lithium ion secondary battery in which a lithium composite oxide such as LiCoO ₂ is used as a constituent material of the positive electrode.

Sulfur has an extremely high theoretical capacity density of 1672 mAh / g, and a lithium-sulfur battery that uses sulfur as a positive electrode constituent material has the potential to achieve the highest theoretical energy density among batteries. ing. Therefore, research and development of lithium-sulfur batteries have been actively carried out.

When an organic electrolyte is used as the electrolyte for a lithium-sulfur battery, sulfur molecules and reaction intermediates (e.g., lithium polysulfide, etc.) dissolve and diffuse into the organic electrolyte during charging and discharging. Therefore, there is a problem that self-discharge and deterioration of the negative electrode are induced, and the battery performance is deteriorated.
Therefore, in order to solve such problems, a method of modifying the electrolyte by adding an acid such as hydrochloric acid or nitric acid to the electrolyte (see Patent Document 1), Ketjenblack as a constituent material of the positive electrode A method using a composite containing sulfur nanoparticles (see Patent Document 2) and the like have been proposed.

JP 2013-114920 A JP 2012-204332 A

However, in the methods disclosed in Patent Documents 1 and 2, since the electrolyte itself is in a liquid state, the dissolution of sulfur molecules and reaction intermediates in the electrolyte cannot be completely suppressed, and sufficient effects cannot be obtained. There was a problem that there was no
A method of using a solid electrolyte is available as a method of solving the problem when using such an electrolytic solution. However, lithium-sulfur solid-state batteries with solid electrolytes have not yet been fully explored technically and have significant room for improvement.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel lithium-sulfur solid-state battery.

In order to solve the above problems, the present invention employs the following configuration.
[1]. A conductive sheet having a large number of voids, the voids being open to the outside of the conductive sheet, and the conductive sheet containing sulfur, a conductive aid, a binder and ions in the voids. containing a liquid, wherein the ionic liquid is one or more solvated ionic liquids selected from the group consisting of glyme-lithium salt complexes, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoro methanesulfonyl)imide, 1-butylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium bis(trifluoromethanesulfonyl)imide, tributyldodecylphosphonium bis (trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, butyltrimethylammonium bis(trifluoromethyl) and one or more ionic compounds selected from the group consisting of trimethylhexylammonium bis(trifluoromethanesulfonyl)imide and trimethylhexylammonium bis(trifluoromethanesulfonyl)imide.
[2]. [1], wherein the mass ratio of [mixed amount (mass) of the solvated ionic liquid]:[mixed amount (mass) of the ionic compound] in the ionic liquid is 99:1 to 80:20; A sulfur cathode as described.
[3]. The sulfur positive electrode according to [1] or [2], wherein in the sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet is 30% by mass or less.

[4]. The solvated ionic liquids include triglyme-lithium bis(fluorosulfonyl)imide complex, tetraglyme-lithium bis(fluorosulfonyl)imide complex, triglyme-lithium bis(trifluoromethanesulfonyl)imide complex, and tetraglyme-lithium bis(trifluoro The sulfur positive electrode according to any one of [1] to [3], which is one or more selected from the group consisting of romethanesulfonyl)imide complexes.
[5]. The sulfur positive electrode according to any one of [1] to [4], wherein the constituent material of the conductive sheet is carbon, copper, aluminum, titanium, nickel or stainless steel.
[6]. A lithium-sulfur solid-state battery comprising the sulfur positive electrode according to any one of [1] to [5], a negative electrode made of lithium, and a solid electrolyte.

SUMMARY OF THE INVENTION In accordance with the present invention, a novel lithium-sulfur solid-state battery is provided.

4 is a graph showing measurement results of internal resistance of the battery cell of Example 1. FIG. 5 is a graph showing measurement results of internal resistance of a battery cell of Reference Example 1. FIG. 5 is a graph showing measurement results of internal resistance of a battery cell of Reference Example 2. FIG. 4 is a graph showing measurement results of internal resistance of a battery cell of Reference Example 3. FIG. 4 is a graph showing measurement results of internal resistance of a battery cell of Reference Example 4. FIG. 10 is a graph showing the measurement results of the internal resistance of the battery cell of Reference Example 5. FIG. 10 is a graph showing the measurement results of the internal resistance of the battery cell of Reference Example 6. FIG. 4 is a graph showing the results of a charge/discharge test for the battery cell of Comparative Example 1. FIG.

<<Sulfur positive electrode>>
A sulfur positive electrode according to one embodiment of the present invention includes a conductive sheet having a large number of voids, the voids opening to the outside of the conductive sheet, and the conductive sheet having the voids Part contains sulfur, a conductive aid, a binder and an ionic liquid, and the ionic liquid is one or more solvated ionic liquids selected from the group consisting of glyme-lithium salt complexes, and 1-ethyl -3-methylimidazolium bis (trifluoromethanesulfonyl) imide (this specification may be abbreviated as "EMITFSI"), 1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (this specification In the book, it may be abbreviated as "BMITFSI"), 1-methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide (herein, it may be abbreviated as "P13TFSI"), 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (herein sometimes abbreviated as "P14TFSI"), 1-butylpyridinium bis (trifluoromethylsulfonyl) imide, 1- Butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium bis(trifluoromethanesulfonyl)imide, tributyldodecylphosphonium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoro methylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and trimethylhexylammonium bis(trifluoromethanesulfonyl)imide It is a mixture of one or two or more ionic compounds (hereinafter sometimes abbreviated as "essential ionic compound").

The sulfur positive electrode of this embodiment is suitable as a positive electrode for a lithium sulfur solid state battery.

<Conductive sheet>
The voids hold components other than the conductive sheet of the sulfur positive electrode, that is, sulfur, a conductive aid, a binder, and an ionic liquid, and the conductive sheet can function as a positive electrode current collector.
In addition, the voids are open to the outside of the conductive sheet, and by adding the above-mentioned components such as sulfur to the conductive sheet later, it is possible to retain these components. ing.

The shape of the voids in the conductive sheet is not particularly limited as long as the above conditions are satisfied.
For example, a void may be connected to one or more other voids, or may be independent without being connected to other voids.
In addition, both the connected voids and the unconnected voids may penetrate from one surface of the conductive sheet to the other surface on the opposite side, or may not penetrate. It may be a dead end inside the sex sheet.
Both the connected voids and the unconnected voids may reach the same surface again from one surface of the conductive sheet via the inside of the conductive sheet.

The form of the conductive sheet includes, for example, a porous body; a woven fabric, a non-woven fabric, or the like in which fibrous materials are entangled with each other.

The constituent material of the conductive sheet may be conductive, but preferably has no reactivity with sulfur.
More specifically, examples of the constituent material of the conductive sheet include carbon, metals (single metals, alloys), and the like.
Among them, preferred constituent materials of the conductive sheet include constituent materials of the positive electrode current collector, more specifically, carbon, copper, aluminum, titanium, nickel, stainless steel, and the like.

The constituent materials of the conductive sheet may be of one type or two or more types, and when two or more types are used, the combination and ratio thereof can be arbitrarily selected according to the purpose.

Preferred conductive sheets include, for example, carbon felt and carbon cloth.

The thickness of the conductive sheet is not particularly limited, and may be appropriately set according to the purpose of the battery to be applied. Generally, the thickness of the conductive sheet is preferably 100-30000 μm, more preferably 200-1000 μm.

<Conductivity aid>
The conductive aid may be a known one, and specific examples thereof include graphite; carbon black such as ketjen black and acetylene black; carbon nanotube; graphene; fullerene and the like.
The conductive aid contained in the sulfur positive electrode may be of one type or two or more types, and when two or more types are used, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode, the ratio of the total content of sulfur and conductive aid to the total content of sulfur, conductive aid, binder and ionic liquid is not particularly limited, but is preferably 65 to 85% by mass, and 70 More preferably, it is up to 80% by mass. When the ratio of the total content is equal to or higher than the lower limit, the charge/discharge characteristics of the battery are further improved. When the ratio of the total content is equal to or less than the upper limit, the effect of using components other than sulfur and the conductive aid can be obtained more remarkably.

In the sulfur positive electrode, the mass ratio of [sulfur content (parts by mass)]:[conductivity aid content (parts by mass)] is not particularly limited, but is preferably 30:70 to 70:30, It is more preferably 45:55 to 65:35. The higher the sulfur content ratio, the better the charge/discharge characteristics of the battery, and the higher the conductive aid content ratio, the better the conductivity of the sulfur positive electrode.

In the sulfur positive electrode, sulfur and the conductive aid may form a composite.
For example, a sulfur-carbon composite can be obtained by mixing sulfur and a carbon-containing material (eg, Ketjenblack, etc.) and firing the mixture. Such a composite is also suitable as a component contained in the sulfur positive electrode.

<Binder>
The binder may be a known one, and specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-propylene hexafluoride copolymer (PVDF-HFP), polyacrylic acid (PAA), Polylithium acrylate (PAALi), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), carboxymethylcellulose (CMC), polyacrylonitrile (PAN), polyimide (PI) etc.
The binder contained in the sulfur positive electrode may be of one type or two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode, the ratio of the content of the binder to the total content of sulfur, conductive aid, binder and ionic liquid is not particularly limited, but is preferably 2 to 15% by mass, and 6 to 10% by mass. It is more preferable to have When the content ratio is equal to or higher than the lower limit, the structure of the sulfur positive electrode can be more stably maintained. When the content ratio is equal to or less than the upper limit, the charge/discharge characteristics of the battery are further improved.

<Ionic liquid>
The ionic liquid is a component for easily moving lithium ions in a battery such as a lithium-sulfur solid-state battery described later. Since the sulfur positive electrode contains the ionic liquid, although the contact area between the sulfur positive electrode and the solid electrolyte is small, the ionic liquid moves lithium ions between the sulfur positive electrode and the solid electrolyte. Therefore, the solid-state battery using the sulfur positive electrode has a small interfacial resistance value at the interface of the sulfur positive electrode and has excellent battery characteristics in spite of not using an electrolytic solution.

The sulfur positive electrode contains, as an ionic liquid, one or more solvated ionic liquids selected from the group consisting of glyme-lithium salt complexes, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ( EMITFSI), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI), 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13TFSI), 1-butyl-1- methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P14TFSI), 1-butylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium bis ( trifluoromethanesulfonyl)imide, tributyldodecylphosphonium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide one or more ionic compounds (essential ionic compounds) selected from the group consisting of imide, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and trimethylhexylammonium bis(trifluoromethanesulfonyl)imide; contains a mixture of
In this way, the sulfur positive electrode contains an ionic liquid in a specific range of combinations of one or more solvated ionic liquids and one or more of the essential ionic compounds. A solid battery using a positive electrode has a remarkably small interfacial resistance value at the sulfur positive electrode interface, and has particularly excellent battery characteristics.

[Solvated ionic liquid (glyme-lithium salt complex)]
Examples of the lithium salt in the glyme-lithium salt complex include lithium bis(fluorosulfonyl)imide (LiN(SO ₂ F) ₂ , herein sometimes abbreviated as “LiFSI”), lithium bis ( trifluoromethanesulfonyl)imide (LiN(SO ₂ CF ₃ ) ₂ , sometimes abbreviated as “LiTFSI” in this specification), and the like.

Examples of glyme in the glyme-lithium salt complex include triethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₃ OCH ₃ , triglyme), tetraethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₄ OCH ₃ , tetraglyme) and the like.

Examples of the glyme-lithium salt complex include a complex composed of one glyme molecule and one lithium salt molecule, but the glyme-lithium salt complex is not limited thereto.

The glyme-lithium salt complex is obtained, for example, by mixing a lithium salt and glyme such that the molar ratio of lithium salt (mol): glyme (mol) is preferably 10:90 to 90:10. can be made.

Preferred glyme-lithium salt complexes include, for example, triglyme-LiFSI complex, tetraglyme-LiFSI complex, triglyme-LiTFSI complex, tetraglyme-LiTFSI complex, and the like.
That is, the glyme-lithium salt complex (solvated ionic liquid) is one or more selected from the group consisting of triglyme-LiFSI complex, tetraglyme-LiFSI complex, triglyme-LiTFSI complex, and tetraglyme-LiTFSI complex. is preferably

The glyme-lithium salt complex is preferably obtained by mixing a lithium salt and glyme at a molar ratio of lithium salt (mol):glyme (mol) of 10:90 to 90:10. ):glyme (mol) is more preferably mixed at a molar ratio of 25:75 to 75:25, and the molar ratio of lithium salt (mol):glyme (mol) is 40:60 to 60:40. Those obtained by mixing as are particularly preferable. By using the glyme-lithium salt complex with such a mixed molar ratio, the interfacial resistance value at the sulfur positive electrode interface of the solid battery becomes smaller.

More preferred glyme-lithium salt complexes include, for example, those obtained by mixing LiFSI and triglyme at a molar ratio of LiFSI (mol): triglyme (mol) of 10:90 to 90:10; obtained by mixing glyme and LiFSI (mol): tetraglyme (mol) at a molar ratio of 10:90 to 90:10; obtained by mixing at a molar ratio of 10:90 to 90:10; and the like.

Further preferred glyme-lithium salt complexes include, for example, those obtained by mixing LiFSI and triglyme at a molar ratio of LiFSI (mol): triglyme (mol) of 25:75 to 75:25; obtained by mixing glyme and LiFSI (mol): tetraglyme (mol) at a molar ratio of 25:75 to 75:25; obtained by mixing at a molar ratio of 25:75 to 75:25; and the like.

Particularly preferred glyme-lithium salt complexes include, for example, those obtained by mixing LiFSI and triglyme at a molar ratio of LiFSI (mol): triglyme (mol) of 40:60 to 60:40; obtained by mixing glyme and LiFSI (mol): tetraglyme (mol) at a molar ratio of 40: 60 to 60: 40; obtained by mixing at a molar ratio of 40:60 to 60:40; and the like.

When two or more glyme-lithium salt complexes are contained in the sulfur positive electrode, the combination and ratio thereof can be arbitrarily selected depending on the purpose.

[Essential ionic compound]
The essential ionic compounds include EMITFSI, BMITFSI, P13TFSI, P14TFSI, 1-butylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium bis( trifluoromethanesulfonyl)imide, tributyldodecylphosphonium bis(trifluoromethanesulfonyl)imide, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide It is one or more selected from the group consisting of imide, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and trimethylhexylammonium bis(trifluoromethanesulfonyl)imide.
When two or more essential ionic compounds are contained in the sulfur positive electrode, their combination and ratio can be arbitrarily selected according to the purpose.

In the ionic liquid that is a mixture of the solvated ionic liquid (glyme-lithium salt complex) and the essential ionic compound, [mixed amount (mass) of solvated ionic liquid]: [Mixing of essential ionic compound amount (mass)] is preferably 99:1 to 80:20, more preferably 96:4 to 84:16, and particularly preferably 93:7 to 87:13. . When the mass ratio is within such a range, the interfacial resistance value at the sulfur positive electrode interface of the solid battery becomes smaller.

In the sulfur positive electrode, the ratio of the content of the ionic liquid to the total content of sulfur, conductive aid, binder and ionic liquid is not particularly limited, but is preferably 3 to 30% by mass, and 10 to 20% by mass. is more preferable. When the content ratio is equal to or higher than the lower limit value, the conductivity of the sulfur positive electrode is further improved. When the content ratio is equal to or less than the upper limit, the charge/discharge characteristics of the battery are further improved.

Preferably, the sulfur cathode contains anion moieties of the same type as the solvated ionic liquid (glyme-lithium salt complex) and the essential ionic compound. In other words, the anion part forming the solvated ionic liquid in the sulfur positive electrode and the anion part forming the essential ionic compound in the sulfur positive electrode are preferably of the same type. More specifically, both the anion part constituting the solvated ionic liquid in the sulfur positive electrode and the anion part constituting the essential ionic compound in the sulfur positive electrode are bis(trifluoromethanesulfonyl) It is preferably an imide anion (also referred to as "bis(trifluoromethylsulfonyl)imide anion").
By containing such a combination of ionic liquids, the charge/discharge characteristics of the battery are further improved.

[Other ingredients]
The sulfur positive electrode contains other components (excluding the solvent described later) in addition to sulfur, a conductive aid, a binder, and an ionic liquid as constituent components other than the conductive sheet within a range that does not impair the effects of the present invention. may contain.
The other components are not particularly limited and can be arbitrarily selected according to the purpose.
Examples of the other components include ionic liquids other than the essential ionic compound and the solvated ionic liquid (glyme-lithium salt complex) (herein, "other ionic liquids").
It should be noted that, in the present specification, the description of a mere "ionic liquid" refers to the "solvated ionic liquid (glyme-lithium salt complex)" and "essential ionic compound" described above, unless otherwise specified. or "a mixture of a solvated ionic liquid (glyme-lithium salt complex) and an essential ionic compound".

(other ionic liquids)
The other ionic liquid can be appropriately selected from known ones, for example.
However, other ionic liquids, for example, in a temperature range of less than 170° C., preferably have a lower sulfur solubility, and particularly preferably do not dissolve sulfur.

Other ionic liquids include, for example, ionic compounds that are liquid at a temperature of less than 170°C.

The cation moiety constituting the other ionic liquid may be either an organic cation or an inorganic cation, but is preferably an organic cation.
The anion part constituting the other ionic liquid may be either an organic anion or an inorganic anion.

Among the cation moieties, organic cations include, for example, imidazolium cation, pyridinium cation, pyrrolidinium cation, phosphonium cation, and ammonium cation. , sulfonium cation, and the like.
However, the organic cation is not limited to these.

Among the anion moieties, organic anions include alkylsulfate anions such as methylsulfate anion (CH ₃ SO ₄ ⁻ ) and ethylsulfate anion (C ₂ H ₅ SO ₄ ⁻ );
Tosylate anion (CH ₃ C ₆ H ₄ SO ₃ ⁻ );
alkanesulfonate anions such as methanesulfonate anion (CH ₃ SO ₃ ⁻ ), ethanesulfonate anion (C ₂ H ₅ SO ₃ ⁻ ), butanesulfonate anion (C ₄ H ₉ SO ₃ ⁻ );
trifluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ), pentafluoroethanesulfonate anion (C ₂ F ₅ SO ₃ ⁻ ), heptafluoropropanesulfonate anion (C ₃ H ₇ SO ₃ ⁻ ), nonafluorobutanesulfonate anion (C ₄ perfluoroalkanesulfonate anions such as H ₉ SO ₃ ⁻ );
Bis(trifluoromethanesulfonyl)imide anion ((CF ₃ SO ₂ )N ⁻ ), bis(nonafluorobutanesulfonyl)imide anion ((C ₄ F ₉ SO ₂ )N ⁻ ), nonafluoro-N-[(trifluoromethane) sulfonyl]butanesulfonylimide anion ((CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ )N ⁻ ), N,N-hexafluoro-1,3-disulfonylimide anion (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ N ⁻ ) and other perfluoroalkanesulfonylimide anions;
Acetate anion (CH ₃ COO ⁻ );
hydrogen sulfate anion (HSO ₄ ⁻ ); and the like.
However, the organic anions are not limited to these.

Among the anion moieties, inorganic anions include, for example, bis(fluorosulfonyl)imide anion (N(SO ₂ F) ₂ ⁻ ); hexafluorophosphate anion (PF ₆ ⁻ ); tetrafluoroborate anion (BF ₄ ⁻ ). ; halide anions such as chloride ions (Cl ⁻ ), bromide ions (Br ⁻ ), iodide ions (I ⁻ ); tetrachloroaluminate anions (AlCl ₄ ⁻ ), thiocyanate anions (SCN ⁻ ), etc. is mentioned.
However, the inorganic anions are not limited to these.

Examples of the ionic compound, which is another ionic liquid, include those composed of a combination of any of the above cation moieties and any of the above anion moieties.
For example, other ionic liquids whose cation moiety is an imidazolium cation include 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium methanesulfonate. , 1-butyl-3-methylimidazolium methanesulfonate, 1,2,3-trimethylimidazolium methylsulfate, methylimidazolium chloride, methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-ethyl-3-methylimidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetra chloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-2,3-dimethylimidazolium ethylsulfate and the like.

The other components contained in the sulfur positive electrode may be of one type or two or more types, and when there are two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode, the content ratio of the other components to the total content of sulfur, conductive aid, binder and ionic liquid is not particularly limited, but is preferably 10% by mass or less, and 5% by mass or less. is more preferably 3% by mass or less, particularly preferably 1% by mass or less, and may be 0% by mass.

In the sulfur positive electrode, the ratio of the total mass of sulfur, conductive aid, binder and ionic liquid to the mass of the conductive sheet is preferably 10 to 50 mass%, more preferably 25 to 35 mass%. .

As described above, the sulfur positive electrode contains a combination of ionic liquids within a specific range, so that the amount of sulfur used in the sulfur positive electrode can be significantly reduced compared to conventional methods. As a result, it is possible to further improve the conductivity of the sulfur positive electrode.
For example, in the sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet is preferably 30% by mass or less, more preferably 20% by mass or less. When the mass ratio of sulfur is equal to or less than the upper limit, the conductivity of the sulfur positive electrode is further increased.

In the sulfur positive electrode, the lower limit of the mass ratio of sulfur to the mass of the conductive sheet is not particularly limited as long as the effects of the present invention are not impaired. For example, the mass ratio of sulfur is preferably 5% by mass or more, more preferably 10% by mass or more. When the mass ratio of sulfur is equal to or higher than the lower limit, the charge/discharge capacity of a solid battery using this sulfur positive electrode is increased.

<<Method for producing sulfur positive electrode>>
The sulfur positive electrode can be manufactured, for example, by a manufacturing method including a step of impregnating the conductive sheet with a positive electrode material containing sulfur, a conductive aid, a binder, and an ionic liquid.
The manufacturing method may further include other steps such as a step of drying the impregnated positive electrode material.

[Cathode material]
Preferable positive electrode materials include, for example, those containing sulfur, a conductive aid, a binder, an ionic liquid, a solvent, and, if necessary, the other components described above.

The solvent is a component for dissolving or dispersing each component such as sulfur described above and imparting appropriate fluidity to the positive electrode material.
In this specification, unless otherwise specified, any ionic liquid is not included in the solvent (all ionic liquids are not treated as solvents).

The solvent can be arbitrarily selected according to the type of each component such as sulfur described above, and organic solvents are preferred.
Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol and 2-propanol; amides such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF); ketones such as acetone. mentioned.
The solvent contained in the positive electrode material may be of one type or two or more types, and when two or more types are used, the combination and ratio thereof can be arbitrarily selected according to the purpose.
The content of the solvent in the positive electrode material is not particularly limited, and can be adjusted as appropriate according to the types of components other than the solvent.

The ratio of the sulfur content to the total content of components other than the solvent in the positive electrode material is the sulfur content relative to the total content of sulfur, conductive aid, binder, ionic liquid and other components in the sulfur positive electrode. It is the same as the proportion of quantity. This is the same for conductive aids, binders, ionic liquids and other components other than sulfur.
Therefore, the ratio of the total content of sulfur and the conductive aid to the total content of components other than the solvent in the positive electrode material is the total amount of sulfur, the conductive aid, the binder, the ionic liquid and the other components in the sulfur positive electrode. It is the same as the ratio of the total content of sulfur and conductive aid to the content.

A positive electrode material is obtained by blending each component such as the above-described sulfur.
There are no particular restrictions on the order of addition of each component when blending, and two or more components may be added at the same time.
When using a solvent, the solvent is mixed with any component other than the solvent (that is, any component of the above sulfur, conductive aid, binder, ionic liquid and other components), and this component is It may be used by diluting in advance, or may be used by mixing the solvent with any of the components other than the above-mentioned solvent without diluting them in advance.

The method of mixing each component at the time of blending is not particularly limited, and known methods include a method of mixing by rotating a stirring rod, a stirrer, or a stirring blade; a method of mixing using a mixer; a method of mixing by applying ultrasonic waves. method can be selected as appropriate.
The temperature and time during the addition and mixing of each component are not particularly limited as long as each component does not deteriorate. Generally, the temperature during mixing is preferably 15 to 30°C.

The composition obtained by adding and mixing each component may be used as it is as a positive electrode material, or the obtained composition may be subjected to some operation such as removing part of the added solvent by distillation or the like. may be used as a positive electrode material.

The impregnation of the conductive sheet with the positive electrode material can be performed, for example, by coating the conductive sheet with the positive electrode material in a liquid state, by immersing the conductive sheet in the positive electrode material in a liquid state, or the like.
Although the temperature of the positive electrode material impregnated into the conductive sheet is not particularly limited, it can be, for example, 15 to 30.degree. However, this is an example.

Drying of the positive electrode material can be performed under normal pressure or reduced pressure by a known method. For example, it is preferably dried under conditions of 70 to 90° C. for 8 to 24 hours, but the drying conditions are not limited thereto.

<<Lithium sulfur solid state battery>>
A lithium-sulfur solid-state battery according to an embodiment of the present invention includes the sulfur positive electrode, a negative electrode made of lithium, and a solid electrolyte.
The lithium-sulfur solid-state battery of the present embodiment can have the same configuration as a known lithium-sulfur solid-state battery, except that it includes the sulfur positive electrode described above.

Since the lithium-sulfur solid-state battery of the present embodiment includes the sulfur positive electrode described above, it can achieve a sufficient charge/discharge capacity and has excellent battery characteristics.

<Sulfur positive electrode>
The sulfur positive electrode in the lithium-sulfur solid-state battery of this embodiment has been described above.

<Negative Electrode>
The negative electrode in the lithium-sulfur solid-state battery of the present embodiment is made of lithium (is a lithium negative electrode), and a known lithium negative electrode can be used.

The thickness of the negative electrode is not particularly limited, and may be appropriately set according to the purpose of the battery to which it is applied. Generally, the thickness of the negative electrode is preferably 10-2000 μm, more preferably 100-1000 μm.

<Solid electrolyte>
The constituent material of the solid electrolyte is not particularly limited, and may be any of a crystalline material, an amorphous material and a glass material.
More specifically, the constituent material of the solid electrolyte includes, for example, a material containing no sulfide and containing an oxide (hereinafter sometimes referred to as an "oxide-based material"), at least a sulfide. well-known materials such as those containing (sometimes referred to as “sulfide-based material” in this specification).

_Examples of the oxide-based material _{include Li7La3Zr2O12} ( _LLZ ), _{Li2.9PO3.3N0.46 ( LIPON ) , La0.51Li0.34TiO2.94 , Li1.3Al0.3Ti1.7 ( PO4 ) 3 , 50Li4SiO4.50Li3BO3 , Li3.6Si0.6P0.4O4 , Li1.07Al0 _ _ _ .69} Ti _1.46 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and the like.
Examples of the oxide-based material include those obtained by adding (doping) elements such as aluminum, tantalum, niobium, and bismuth to composite oxides such as Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ). be done. Here, only one element or two or more elements may be added, and when two or more elements are added, the combination and ratio thereof can be arbitrarily selected according to the purpose.

Examples of the _{sulfide -} based material _{include Li10GeP2S12 ( LGPS} ), _{Li3.25Ge0.25P0.75S4 , 30Li2S.26B2S3.44LiI} , _{63Li2S . 36SiS2.1Li3PO4 , 57Li2S.38SiS2.5Li4SiO4 , 70Li2S.30P2S5 ( LISPS ) , 50Li2S.50GeS2 , Li7P3S11 , Li3.25 _ _} P _0.95 S ₄ and the like.

The constituent materials of the solid electrolyte may be of one type or two or more types, and when there are two or more types, their combination and ratio can be arbitrarily selected according to the purpose.

The constituent material of the solid electrolyte is preferably the above-described oxide-based material because it has high stability in the air and can produce a highly dense solid electrolyte.

The thickness of the solid electrolyte is not particularly limited, and may be appropriately set according to the purpose of the battery to which it is applied. Generally, the thickness of the solid electrolyte is preferably 10-1000 μm, more preferably 50-500 μm.

<<Method for producing lithium-sulfur solid-state battery>>
The lithium-sulfur solid-state battery can be manufactured in the same manner as a known lithium-sulfur solid-state battery, except that the sulfur positive electrode is used. That is, the lithium-sulfur solid-state battery of the present embodiment can be manufactured by laminating the sulfur positive electrode, the solid electrolyte and the negative electrode in this order in the thickness direction.

The lithium-sulfur solid-state battery of the present embodiment is preferably kept under temperature conditions of 100° C. or less. By doing so, vaporization of the ionic liquid can be suppressed, and the lithium-sulfur solid state battery exhibits better battery characteristics.

The lithium-sulfur solid-state battery of the present embodiment has excellent battery characteristics as described above and is highly safe. Taking advantage of these features, the lithium-sulfur solid-state battery is suitable for use as, for example, household power sources; emergency power sources; and power sources for airplanes, electric vehicles, and the like.

The present invention will be described in more detail below with reference to specific examples. However, the present invention is by no means limited to the examples shown below.

<<Manufacturing of Lithium Sulfur Solid State Battery>>
[Example 1]
<Production of sulfur cathode>
[Manufacturing of positive electrode material]
Ketjen black (1 part by mass) was added to pulverized sulfur (5 parts by mass) and mixed for 30 minutes, heat-treated at 150 ° C. for 6 hours, and then heat-treated at 250 ° C. for 5 hours to obtain sulfur and Ketjen. A black composite was obtained. As a result of thermogravimetric measurement of the obtained composite, the sulfur content was 51.2% by mass (the carbon content was 48.8% by mass). The resulting composite was vacuum dried at room temperature for 1 day. Then, in a glove box, this composite (1.313 parts by weight (of which sulfur is 0.673 parts by weight and Ketjenblack is 0.640 parts by weight)) is added to KF polymer (12% by weight of polyfluorinated An N-methylpyrrolidone solution containing vinylidene, manufactured by Kureha Corporation (1.217 parts by mass) was added. Then, while stirring the resulting mixture, N-methylpyrrolidone was added little by little to a total of 1028 parts by mass, and further, tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), to obtain a slurry-like positive electrode material. Here, the tetraglyme-LiTFSI complex is obtained by mixing LiTFSI and tetraglyme at a LiTFSI (mol):tetraglyme (mol) molar ratio of 50:50. In addition, the mass ratio of [amount of tetraglyme-LiTFSI complex used (mass)]:[amount of EMITFSI used (mass)] was 90:10.

[Production of sulfur cathode]
The positive electrode material obtained above was applied to a carbon cloth (mass: 0.00592 g, diameter: 8 mm, thickness: 250 μm, circular shape) to sufficiently impregnate the inside of the carbon cloth with the positive electrode material.
Next, the impregnated carbon cloth was dried at 80° C. for 12 hours to completely remove N-methylpyrrolidone and obtain a sulfur positive electrode (0.0076 g).

In the obtained sulfur positive electrode, sulfur, conductive aid (Ketjenblack), binder (polyvinylidene fluoride) and ionic liquid (tetraglyme-LiTFSI complex and EMITFSI with respect to the mass of the conductive sheet (carbon cloth) mixture) was 28.4% by weight.
In the obtained sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet (carbon cloth) was 11.4% by mass.

<Production of lithium-sulfur solid-state battery>
[Production of solid electrolyte]
Lanthanum hydroxide (purity 99.99%, Kojundo Chemical Laboratory Co., Ltd.) (40.38 g), lithium hydroxide (purity 98.0%, Kanto Chemical Co., Ltd.) (20.44 g) and zirconium oxide (Tosoh Corporation ) (17.47 g) were weighed and mixed while pulverizing in a ball mill for 2 hours. The obtained powder (73.10 g) was weighed, transferred to a ceramic container for firing, fired at 900 ° C. for 15 hours using an electric furnace, cooled at a temperature decrease rate of 5 ° C./min, and finally cooled to room temperature. to obtain a lithium-lanthanum-zirconium composite oxide.
The resulting composite oxide (54.67 g) and aluminum oxide (γ-alumina, purity 99.99%, manufactured by Kojundo Chemical Laboratory Co., Ltd.) (0.90 g) were weighed and ground in a ball mill for 2 hours. while mixing. A disk-shaped pellet having a diameter of 15 mm and a thickness of 1 mm was produced by molding the obtained mixture using a double-axis press.
Transfer the pellets (0.5 g) obtained above to a ceramic container for firing spread with mother powder (mixed powder of lanthanum hydroxide, lithium hydroxide, zirconium oxide and aluminum oxide), and cover the pellets with mother powder. , was fired using an electric furnace. Firing conditions were as follows. That is, the temperature was raised from room temperature to 1,200° C. at a temperature elevation rate of 5° C./min, maintained at 1,200° C. for 24 hours, cooled at a temperature drop rate of 5° C./min, and finally cooled to room temperature. Next, the mother powder adhering to the pellet was removed by polishing.
As described above, a pellet-shaped aluminum-doped lithium-lanthanum-zirconium composite oxide (Al-doped LLZ) compact (Li _6.25 Al _0.25 La ₃ Zr ₂ O ₁₂ , diameter 11 mm, A thickness of 0.5 mm and a mass of 0.26 g) were obtained.

[Production of lithium-sulfur solid-state battery]
Gold was sputtered onto the negative electrode side surface of the Al-doped LLZ compact obtained above. This is to eliminate as much as possible the influence of the battery characteristics caused by the negative electrode during evaluation, which will be described later, and to more accurately evaluate the battery characteristics of the sulfur positive electrode. By bringing the Al-doped LLZ molded body and the negative electrode into contact with each other with a gold sputtered layer interposed therebetween, they are reliably brought into contact with each other and the resistance is reduced.
On the other hand, the sulfur positive electrode obtained above was attached to the positive electrode side surface of the Al-doped LLZ molded body to obtain a laminate composed of the sulfur positive electrode and the solid electrolyte laminated.

Next, using a commercially available coin-shaped battery cell container, a ring-shaped gasket was fitted to the lower lid, and a stainless steel washer was placed on the lower lid. A disk-shaped negative electrode current collector made of stainless steel and having an outer diameter of 15 mm and a thickness of 0.3 mm was placed on the washer, and a lithium foil (diameter 8 mm, thickness 600 μm) was placed. Furthermore, by superimposing the above sputtered gold layer on the negative electrode, a laminate of the sulfur positive electrode and the solid electrolyte is placed on the negative electrode, and aluminum is placed on the sulfur positive electrode of the laminate as a positive electrode current collector. A foil (8 mm diameter, 20 μm thickness) was placed. Finally, the upper lid was closed to obtain a battery cell (lithium-sulfur solid state battery) for evaluation.

[Reference example 1]
At the time of manufacturing the positive electrode material, the amount of the composite of sulfur and Ketjenblack used was replaced with 1.313 parts by mass to 1.068 parts by mass (of which 0.547 parts by mass of sulfur and Ketjenblack 0.521 parts by mass), and instead of adding tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), EMITFSI (0.179 parts by mass ) was added in the same manner as in Example 1 to produce a sulfur positive electrode and to produce a battery cell (lithium sulfur solid state battery) for evaluation.

[Reference example 2]
At the time of manufacturing the positive electrode material, the amount of the composite of sulfur and Ketjenblack used is replaced with 1.313 parts by mass to 1.144 parts by mass (of which 0.586 parts by mass of sulfur and Ketjenblack 0.558 parts by mass), and instead of adding tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), BMITFSI (0.192 parts by mass ) was added in the same manner as in Example 1 to produce a sulfur positive electrode and to produce a battery cell (lithium sulfur solid state battery) for evaluation.

[Reference example 3]
At the time of manufacturing the positive electrode material, the amount of the composite of sulfur and Ketjenblack used was changed to 1.221 parts by mass instead of 1.313 parts by mass (of which 0.625 parts by mass of sulfur and Ketjenblack 0.596 parts by mass), and instead of adding tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), P13TFSI (0.205 parts by mass) ) was added in the same manner as in Example 1 to produce a sulfur positive electrode and to produce a battery cell (lithium sulfur solid state battery) for evaluation.

[Reference Example 4]
At the time of manufacturing the positive electrode material, the amount of the composite of sulfur and Ketjenblack used was replaced with 1.313 parts by mass to 1.145 parts by mass (of which 0.586 parts by mass of sulfur and Ketjenblack 0.559 parts by mass), and instead of adding tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), P14TFSI (0.198 parts by mass ) was added in the same manner as in Example 1 to produce a sulfur positive electrode and to produce a battery cell (lithium sulfur solid state battery) for evaluation.

<<Evaluation of battery characteristics>>
[Test Example 1]
The internal resistance of the battery cells obtained in Example 1 and Reference Examples 1 to 4 was measured by the AC impedance method described below.
That is, the battery cells were placed in a constant temperature bath at 100° C., and AC impedance was measured in a frequency range of 3 MHz to 0.1 Hz. The measurement results at this time are shown in FIGS. 1 shows the measurement results of the battery cell of Example 1, FIG. 2 shows the measurement results of the battery cell of Reference Example 1, FIG. 3 shows the measurement results of the battery cell of Reference Example 2, and FIG. is the measurement result of the battery cell of Reference Example 3, and FIG. 5 is the measurement result of the battery cell of Reference Example 4. FIG.

The measurement results of the battery cell obtained in Example 1 shown in FIG. There is From this measurement result, it was found that the interfacial resistance value at the sulfur positive electrode interface in the battery cell of Example 1 was 400 Ω·cm.
It was confirmed that the battery cell obtained in Example 1 has the effect of reducing the interfacial resistance value at the sulfur positive electrode interface.

The measurement results of the battery cell obtained in Reference Example 1 shown in FIG. There is From this measurement result, it was found that the interfacial resistance value at the interface of the sulfur positive electrode in the battery cell of Reference Example 1 was 1400 Ω·cm.

The measurement results of the battery cells obtained in Reference Examples 2 to 4 shown in FIGS. There is a straight line part to consider. From these measurement results, the interfacial resistance value at the sulfur positive electrode interface was 2100 Ω cm for the battery cell of Reference Example 2, 1800 Ω cm for the battery cell of Reference Example 3, and 800 Ω cm for the battery cell of Reference Example 4.・It turned out to be cm.

In the battery cells obtained in Reference Examples 1 to 4, only the essential ionic compound is used as the ionic liquid, and such battery cells also have the effect of reducing the interfacial resistance value at the sulfur positive electrode interface. confirmed.
However, as is clear from the comparison between FIG. 1 and FIGS. 2 to 5, the battery cells obtained in Example 1 have a higher sulfur positive electrode interface than the battery cells obtained in Reference Examples 1 to 4. The interfacial resistance value was remarkably small, and the effect of reducing the interfacial resistance value was particularly excellent. As described above, it was confirmed that when the essential ionic compound and the solvated ionic liquid are used together in the positive electrode material, a remarkable effect of improving the battery characteristics can be obtained.
The battery cells obtained in Reference Examples 1 to 4 were expected to have improved battery characteristics by using a solvated ionic liquid in addition to the essential ionic compound in the positive electrode material.

<<Manufacturing of Lithium Sulfur Solid State Battery>>
[Reference Example 5]
In the production of the positive electrode material, sulfur (16.0 parts by mass) and graphite powder (KS4, 1.6 parts by mass) were used instead of the composite of sulfur and Ketjenblack (1.313 parts by mass). Instead of adding points, and tetraglyme-LiTFSI complex (0.198 parts by weight) and EMITFSI (0.022 parts by weight), only tetraglyme-LiTFSI complex (2.95 parts by weight) was added. A sulfur positive electrode was manufactured in the same manner as in Example 1, except that the above points were changed, and a battery cell (lithium sulfur solid state battery) for evaluation was manufactured.
In the obtained sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet (carbon cloth) was 270% by mass.

[Reference Example 6]
At the time of manufacturing the positive electrode material, the amount of the composite of sulfur and Ketjenblack used was replaced with 1.313 parts by mass to 5.671 parts by mass (of which sulfur is 2.908 parts by mass, Ketjenblack is 2.763 parts by mass), instead of adding the tetraglyme-LiTFSI complex (0.198 parts by mass) and EMITFSI (0.022 parts by mass), the tetraglyme-LiTFSI complex (0.022 parts by mass) was added. 95 parts by mass) was added, and the diameter of the carbon cloth was changed to 14 mm instead of 8 mm. Sulfur solid state battery) was manufactured.
In the obtained sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet (carbon cloth) was 15.1% by mass.

<<Evaluation of battery characteristics>>
[Test Example 2]
For the battery cells obtained in Reference Examples 5 and 6, the internal resistance was measured in the same manner as in Test Example 1 to obtain the interfacial resistance value at the sulfur positive electrode interface. The measurement results for the battery cell of Reference Example 5 are shown in FIG. 6, and the measurement results for the battery cell of Reference Example 6 are shown in FIG.

As a result, the interfacial resistance value at the interface of the sulfur positive electrode in the battery cell of Reference Example 5 was 3750 Ω·cm.
In the battery cell of Reference Example 6, the interfacial resistance value at the sulfur positive electrode interface was 2500 Ω·cm.

In Reference Example 6, compared to Reference Example 5, the type of conductive aid was changed to reduce the mass ratio of sulfur to the mass of the conductive sheet (carbon cloth), so that the Also, the interface resistance value could be reduced.
In Example 1, unlike the case of Reference Example 6, in addition to the solvated ionic liquid (tetraglyme-LiTFSI complex) as the ionic liquid, the essential ionic compound (EMITFSI) was also used. The interfacial resistance value could be significantly reduced more than in the case of .
In this way, by using the solvated ionic liquid and the essential ionic compound together in the production of the sulfur positive electrode, the mass ratio of sulfur to the mass of the conductive sheet can be significantly reduced, and the battery characteristics can be impaired. It was confirmed that the interfacial resistance value can be significantly reduced.

[Comparative Example 1]
Ketjenblack (0.50g) was added to pulverized sulfur (1.00g), mixed for 30 minutes, and heat-treated at 155°C for 6 hours to obtain a mixture of sulfur and Ketjenblack. Next, in the glove box, KF polymer (N-methylpyrrolidone solution containing 12% by mass of polyvinylidene fluoride, manufactured by Kureha Co., Ltd.) (0.167 g) was added to this mixture (0.180 g). While stirring the obtained mixture, N-methylpyrrolidone was added little by little to a total of 1.0 mL to obtain a slurry-like positive electrode material for comparison.

As a masking tape, a polyimide tape (thickness 0.09 mm) in a shape in which concentric circles with a diameter of 8 mm were hollowed out was used on the positive electrode side of the same Al-doped LLZ molded body (solid electrolyte) produced in Example 1. affixed to any surface. Next, the comparative positive electrode material obtained above was adhered to the central portion of the exposed surface serving as the positive electrode side (the region not masked with the masking tape of the surface serving as the positive electrode). Then, the slide glass is reciprocated two or three times so that the end face of the slide glass slides over the comparative positive electrode material, so that the comparative positive electrode material is evenly distributed over the entire exposed surface. Spread and apply.
Next, using a vacuum dryer, this coated Al-doped LLZ molded body was dried at 80° C. for a day and night to remove all N-methylpyrrolidone, and a sulfur positive electrode for comparison was deposited on the Al-doped LLZ molded body. formed.
Next, the masking tape was peeled off from the Al-doped LLZ compact to obtain a laminate for comparison in which a sulfur positive electrode and a solid electrolyte for comparison were laminated. The amount of sulfur positive electrode formed for comparison, which was obtained from the difference in mass of the Al-doped LLZ compact before and after forming the sulfur positive electrode, was 0.00075 g.

A battery cell (lithium-sulfur solid state battery) for comparison was obtained in the same manner as in Example 1, except that the laminate for comparison obtained above was used.

<<Evaluation of battery characteristics>>
[Test Example 3]
Regarding the battery cell obtained in Comparative Example 1, the battery characteristics of the sulfur positive electrode were evaluated by the method shown below.
That is, after storing the battery cells at 100° C. for 12 hours, a charge/discharge test was performed with a constant current of 10 μA and a voltage range of 1.0 to 3.5 V. FIG. 8 shows the test results of the battery cells at this time.

As a result, although the battery cell of Comparative Example 1 had an initial discharge capacity of about 250 mAh/g, the voltage during the initial discharge was not stable, the discharge curve was not flat, and the discharge state was not stable. Furthermore, the charge-discharge curve after this did not show a flat curve, and the capacity was less than 25 mAh/g. That is, the sulfur positive electrode of Comparative Example 1 had insufficient battery characteristics.
In the battery cell of Comparative Example 1, the sulfur positive electrode for comparison did not contain an ionic liquid, and the battery characteristics were clearly inferior to those of the battery cells of Example 1 and Reference Examples 1-6.

INDUSTRIAL APPLICABILITY The present invention can be used in the general field of lithium-sulfur solid state batteries.

Claims (6)

A sulfur positive electrode for a lithium-sulphur solid state battery with a solid electrolyte, comprising:
The sulfur positive electrode includes a conductive sheet having a large number of voids,
The void is open to the outside of the conductive sheet,
The conductive sheet contains sulfur, a conductive aid, a binder and an ionic liquid in the voids,
The ionic liquid is one or more solvated ionic liquids selected from the group consisting of glyme-lithium salt complexes, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-butyl -3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-butylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium bis(trifluoromethanesulfonyl)imide, tributyldodecylphosphonium bis(trifluoromethanesulfonyl) imide, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and trimethyl and one or more ionic compounds selected from the group consisting of hexylammonium bis(trifluoromethanesulfonyl)imide. The mass ratio of [mixed amount (mass) of the solvated ionic liquid]:[mixed amount (mass) of the ionic compound] in the ionic liquid is 99: 1 to 80: 20. A sulfur cathode as described. 3. The sulfur positive electrode according to claim 1, wherein the sulfur positive electrode has a mass ratio of 30% by mass or less with respect to the mass of the conductive sheet. The solvated ionic liquids include triglyme-lithium bis(fluorosulfonyl)imide complex, tetraglyme-lithium bis(fluorosulfonyl)imide complex, triglyme-lithium bis(trifluoromethanesulfonyl)imide complex, and tetraglyme-lithium bis(trifluoro The sulfur positive electrode according to any one of claims 1 to 3, which is one or more selected from the group consisting of romethanesulfonyl)imide complexes. The sulfur positive electrode according to any one of claims 1 to 4, wherein the constituent material of said conductive sheet is carbon, copper, aluminum, titanium, nickel or stainless steel. A lithium sulfur solid state battery comprising the sulfur positive electrode according to any one of claims 1 to 5, a negative electrode made of lithium, and a solid electrolyte.

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