JP2015179615A - Positive electrode mixture and all-solid-state lithium sulfur battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode mixture which can be suitably used for a positive electrode mixture layer of an all-solid-state lithium sulfur battery having excellent charge or discharge capacity per a positive electrode mixture by making the most of the excellent physical properties of sulfur and also to provide the all-solid-state lithium sulfur battery equipped with the positive electrode mixture layer of the positive electrode mixture.SOLUTION: Disclosed is a positive electrode mixture which includes components of (I) phosphorus sulfide or a discharge product thereof, whose weight ratio of sulfide (P) is 0.15 to 0.55 and (II) a conductive material and which is used for a positive electrode mixture layer of an all-solid-state lithium sulfur battery.

Description

The present invention relates to a positive electrode mixture and an all solid-state lithium-sulfur battery.

Sulfur is known to have a very high theoretical capacity of about 1672 mAh / g, and lithium sulfur batteries using sulfur as a positive electrode active material have been actively studied.
Lithium-sulfur batteries are roughly classified into liquid lithium-sulfur batteries that use liquid electrolytes as electrolytes and all-solid-state lithium-sulfur batteries that use solid electrolytes.

In the liquid type lithium-sulfur battery, lithium polysulfide produced by the reaction between lithium ions and sulfur is dissolved in the electrolyte solution, which adversely affects the charge / discharge capacity and life of the battery.

On the other hand, the all-solid-state lithium-sulfur battery is suitable for maintaining the charge / discharge capacity of the battery and extending its life because there is no problem that lithium polysulfide dissolves into the electrolyte solution. In addition, attention has been focused on the excellent characteristics of all-solid-state lithium-sulfur batteries, such as the absence of flammable organic solvents, which ensures safety without the risk of liquid leakage or ignition, and the need for a separator. ing.
In the positive electrode mixture layer of the all-solid-state lithium-sulfur battery, among the reversible reactions represented by the following formula (1), a rightward reaction during discharge and a leftward reaction during charging proceed in a dominant manner.
S + 2Li ⁺ + 2e ⁻ ⇔ Li ₂ S (1)

However, in the all-solid-state lithium-sulfur battery, the negative electrode, the solid electrolyte layer, and the positive electrode mixture layer substantially contain no solvent, and the sulfur contained in the positive electrode mixture layer as the positive electrode active material is electrically insulating. Therefore, the electronic conductivity and lithium ion conductivity in the positive electrode mixture layer are very low. In particular, when sulfur is charged at a high ratio in the positive electrode mixture, there is a problem that the reactivity of the reaction shown in the above formula (1) is poor at the time of charge and discharge, and a sufficient charge and discharge capacity cannot be secured. .

Patent Document 1 proposes an electrode material containing sulfur, a conductive substance, and a solid electrolyte containing a lithium atom, a phosphorus atom, and a sulfur atom as an electrode material used for a positive electrode of an all-solid lithium battery. In this document, according to the electrode material described above, the battery performance of the all-solid lithium battery can be improved.

International Publication No. 2013/076955

However, in fact, the all-solid-state lithium battery electrode material described in Patent Document 1 is not practical when used at a low current that is impractical even if it is assumed to be used for a low power output of a smartphone or a personal computer. When using with a large current, it was difficult to ensure a sufficient charge / discharge capacity.
In other words, the all-solid-state lithium-sulfur battery equipped with the conventional positive electrode mixture layer still needs to be improved in charge and discharge capacity, realizing an all-solid-state lithium-sulfur battery that can withstand practical use at high currents. In doing so, there was a problem that the excellent physical properties of sulfur could not be fully utilized.

The present invention maximizes the excellent physical properties of sulfur and uses a positive electrode mixture that can be suitably used for a positive electrode mixture layer of an all-solid-state lithium-sulfur battery having an excellent charge / discharge capacity per positive electrode mixture. The purpose is to provide. Moreover, it aims at providing the all-solid-state lithium-sulfur battery provided with the positive electrode compound material layer containing the said positive electrode compound material.

The inventors of the present invention have studied various positive electrode composites used in all solid-state lithium-sulfur batteries. Instead of using phosphorous sulfide containing phosphorus at a predetermined weight ratio and / or its discharge product as a positive electrode active material and ion conductive material, an all-solid-state lithium-sulfur battery excellent in charge / discharge capacity can be obtained. Based on this finding, the present invention has been completed.

That is, the positive electrode mixture of the present invention relates to the following:
[1]
[I] Phosphorus sulfide and / or its discharge product, wherein the weight ratio of phosphorus (P) is 0.15 to 0.55, and
[II] A positive electrode mixture comprising a component of a conductive material and used for a positive electrode mixture layer of an all-solid-state lithium-sulfur battery;
[2]
Positive electrode components specific surface area of [II] is is 1000 m ² / g or more, [1];
[3]
The component [I] is P _x S _y (where x and y independently represent an integer giving a stoichiometric ratio) or a composite containing Li, S and P, [1] to [3] The positive electrode mixture according to any one of the above;
[4]
A composite containing Li, S and P contains at least Li ₂ S and S and P, or at least Li ₂ S and P _x S _y (where x and y are independently a stoichiometry). A positive electrode mixture of [3], which is obtained by mechanical milling treatment.
[5]
A composite containing Li, S and P is M _z S (where M represents Si, Ge, B or Al and Z represents an integer giving a stoichiometric ratio), phosphorus oxide, At least one selected from the group consisting of lithium oxide and lithium iodide is obtained by mechanical milling with Li ₂ S, S and P, or Li ₂ S and P _x S _y , [4] positive electrode composite;
[6]
The positive electrode composite material according to any one of [1] to [5], wherein the content of component [I] is 70% by weight or more of the total positive electrode composite material; and [7]
An all-solid-state lithium-sulfur battery comprising a positive electrode mixture layer, a solid electrolyte layer, a negative electrode, and a current collector including the positive electrode mixture according to any one of [1] to [6].

The positive electrode mixture of the present invention uses, as its positive electrode active material and ion conductive material, phosphorus sulfide containing phosphorus at a predetermined weight ratio and / or its discharge product, so that all-solid-state lithium-sulfur is obtained due to its insulating properties. As a result of eliminating the use of elemental sulfur as the positive electrode active material, which has hindered the improvement in battery performance, an all-solid-state lithium-sulfur battery excellent in charge / discharge capacity can be provided.
Such a positive electrode mixture and an all-solid-state lithium-sulfur battery using the positive electrode mixture can be used for, for example, an electric vehicle or a hybrid vehicle. Therefore, according to the present invention, it contributes to CO ₂ reduction. be able to.

<< Positive electrode mixture >>
First, the positive electrode mixture of the present invention will be described.
The positive electrode mixture of the present invention is a positive electrode mixture used for the positive electrode mixture layer of an all-solid-state lithium-sulfur battery,
[I] Phosphorus sulfide and / or its discharge product, wherein the weight ratio of phosphorus (P) is 0.15 to 0.55, and
[II] A component of a conductive material is included.

<Phosphorus sulfide and / or its discharge product [I]>
The phosphorus sulfide and / or its discharge product [I] is contained as a positive electrode active material / ion conductive material (solid electrolyte) in the positive electrode mixture of the present invention (hereinafter also referred to as component [I]). .
The phosphorus sulfide and / or its discharge product [I] is not particularly limited as long as the weight ratio of phosphorus is 0.15 to 0.55. Specific examples thereof include P _x S _y (here And x and y independently represent an integer giving a stoichiometric ratio), a composite containing Li, S and P, and the like.
These may be used alone or in combination of two or more.
By using such a material containing a specific amount of phosphorus as the positive electrode active material and ion conductive material, it is not necessary to use separate materials as the positive electrode active material and the ion conductive material. As a result of the substantial filling rate of the positive electrode active material occupying the composite material, the energy density per positive electrode can be improved.
On the other hand, in the phosphorus sulfide and / or its discharge product [I], when the weight ratio of phosphorus is less than 0.15 or exceeds 0.55, the energy density of the positive electrode active material itself decreases. The energy density per positive electrode may decrease, which is not preferable.

As the composite containing Li, S and P, a composite obtained by mechanical milling at least Li ₂ S, S and P (hereinafter simply referred to as a composite of Li ₂ S, S and P), , At least Li ₂ S and P _x S _y (where x and y independently represent an integer giving a stoichiometric ratio) and a composite obtained by mechanical milling (hereinafter simply referred to as Li ₂ S and a compound of P _x S _y are preferred.
This is because bonds can be easily rearranged by mechanical milling, and an amorphous ion conductive material can be obtained.

In the present invention, the “composite” is not simply a mixture of predetermined components, but mechanical, thermal, or chemical energy is added to a mixture of predetermined components, and A chemical reaction that has occurred in whole or in part.
In this specification, “composite” does not mean simply mixing predetermined components, but by adding mechanical, thermal, or chemical energy to a mixture of predetermined components. It causes chemical reaction to all or a part of the components.

When the phosphorus sulfide and / or its discharge product [I] is one of the composite of Li ₂ S, S and P and the composite of Li ₂ S and P _x S _y , In the composite, the molar ratio of Li ₂ S is not particularly limited as long as the content of phosphorus contained in the composite is 0.15 to 0.55 by weight.

As the mechanical milling process, a conventionally known method can be used. Specific examples thereof include, for example, a planetary ball mill and a rotation speed of 225 to 500 rpm and a revolution speed of 450 to 1000 rpm (rotation and reverse rotation). And a method of treating for 5 to 10 hours.
It can be confirmed by Raman spectroscopy whether Li ₂ S and P _x S _y are combined or Li ₂ S and P _x S _y are simply mixed. For example, in the case of a composite of Li ₂ S and P ₂ S ₅ , the 300 cm ⁻¹ peak derived from P ₂ S _5, which is the raw material used for the composite, disappears, or the main peak near 400 cm ^−1. Therefore, it can be confirmed that Li ₂ S and P ₂ S ₅ are combined.

Since the composite containing Li, S and P may be able to further improve the ionic conductivity, M _z S (where M is Si, Ge, B or Al, Z is , Each representing an integer giving a stoichiometric ratio), at least one selected from the group consisting of phosphorus oxide, lithium oxide and lithium iodide, Li ₂ S, S and P, or Li ₂ S and P _x with S _y may be those obtained by mechanical milling.

For the same reason, the composite containing Li, S, and P may further contain a lithium salt or lithium nitride.
Is not particularly restricted but includes lithium salt, for _{example, Li 3 PO 4, Li 4} SiO 4, LiBH 4 , and the like.
Although not particularly restricted but includes lithium nitride, for example, Li 3 _N and the like.

<Conductive material [II]>
The positive electrode mixture of the present invention contains a conductive material [II] as an electronic conductor (hereinafter also referred to as component [II]).
Although it does not specifically limit as said electrically conductive material [II], For example, activated carbon, furnace black, a carbon nanotube, graphene etc. are mentioned.
In these, since it is excellent in electroconductivity and BET specific surface area is large, activated carbon, a graphene, and furnace black are preferable, and activated carbon and furnace black which has a hollow shell structure are more preferable.

The furnace black having a hollow shell structure is a kind of conductive furnace black and has a hollow shell structure with a porosity of about 60 to 80%. Here, the “hollow shell structure” refers to a structure in which graphite crystals are thinly gathered to form an outer shell in the form of particles and have voids inside the outer shell. As furnace black which has the said hollow shell structure, ketjen black (made by Lion Corporation) etc. are mentioned, for example.

The BET specific surface area of the conductive material [II] used in the present invention is preferably 1000 m ² / g or more, more preferably 1800 m ² / g or more, and even more preferably 2500 m ² / g or more. .
When the BET specific surface area is less than 1000 m ² / g, the area of the reaction interface with the phosphorus sulfide and / or its discharge product [I] decreases, the reaction resistance increases, and the charge / discharge capacity decreases. There is.

In this specification, the BET specific surface area refers to the specific surface area determined by the Brenauer-Emmet-Telle (BET) method. Specifically, a conductive carbon sample is subjected to nitrogen gas at a liquid nitrogen temperature. The specific surface area determined using a nitrogen adsorption isotherm obtained by adsorption.
As a measuring device for obtaining the BET specific surface area, for example, an automatic specific surface area / pore distribution measuring device (BELSORP-mini II manufactured by Nippon Bell Co., Ltd.) can be used.

The specific surface area of the conductive material [II] is 1000 m ² / g or more, preferably 1800 m ² / g or more, because it can remarkably enjoy the effect of improving the charge / discharge capacity, and is preferably 2500 m ² / g. More preferably.
On the other hand, the preferable upper limit of the specific surface area of the conductive material [II] is 4000 m ² / g.

In the positive electrode mixture of the present invention, the content ratio (component [I]: component [II]) of each component of the phosphor sulfide and / or its discharge product [I] and the conductive material [II] on a weight basis is as follows: 70 to 95: 5 to 30 is preferable.
When the content ratio of the phosphorus sulfide and / or the discharge product [I] is smaller than the above range, the theoretical capacity per positive electrode mixture may be reduced, and a sufficient charge / discharge capacity may not be obtained. If it exceeds the range, the conductive material [II] responsible for electronic conduction may be insufficient, and the battery may not operate sufficiently.

The positive electrode mixture of the present invention may contain optional components such as a binder and a solvent as necessary.

<Binder>
Although it does not specifically limit as said binder, A thermoplastic resin, a thermosetting resin, etc. can be used, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, Tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer , Vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentaph Olefin copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl Examples include vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polymethacrylic acid, polysodium methacrylate, and polylithium methacrylate.
These binders may be used alone or in combination of two or more.

When the positive electrode mixture of the present invention is obtained by mixing the binder, the content thereof is not particularly limited, but is preferably 0.01 to 10% by weight in the positive electrode mixture.

<Solvent>
In the positive electrode mixture obtained by mixing the solvent, a positive electrode mixture layer can be easily produced. The solvent is removed by drying when the positive electrode mixture layer is produced.
The solvent is not particularly limited. For example, amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, Examples include amide solvents such as dimethylacetamide and 1-methyl-2-pyrrolidone, and hydrocarbon solvents such as toluene, xylene, n-hexane, and cyclohexane.
These solvents may be used alone or in combination of two or more.

When the positive electrode mixture of the present invention is obtained by mixing the solvent, the content is not particularly limited, but is preferably 10 to 99% by weight in the positive electrode mixture.

<Method for producing positive electrode mixture>
The positive electrode composite of the present invention is obtained by mixing the phosphorus sulfide and / or its discharge product [I], the conductive material [II], and further optional components such as a binder and a solvent as necessary. be able to.
A method for mixing these is not particularly limited, and a conventionally known method can be used. For example, planetary ball mill (manufactured by Fritsch), hybridization system (manufactured by Nara Machinery Co., Ltd.), cosmos (manufactured by Kawasaki Heavy Industries, Ltd.) ), Mechano-Fusion System (manufactured by Hosokawa Micron), Nobilta NOB (manufactured by Hosokawa Micron), Mechano Mill (manufactured by Okada Seiko Co., Ltd.), Theta Composer (manufactured by Tokusu Kosakusha), Nanosonic Mill (manufactured by Inoue Seisakusho Co., Ltd.), Kneader (Inoue) Mfg. Co., Ltd.), Super Mass Collider (Masuyuki Sangyo Co., Ltd.), Nanomec Reactor (Techno Eye Co., Ltd.), Cornell Despa (Asada Iron Works Co., Ltd.), Planetary Mixer (Asada Iron Works Co., Ltd.), Miracle KCK (Asada Iron Works) ), Mixing using a vibration mill (Matsubo), etc. It is.

In preparation of the positive electrode mixture, heat treatment may be performed after mixing the respective components.
This is because the contact interface between the phosphorous sulfide and / or its discharge product [I] and the conductive material [II] contained in the positive electrode mixture can be strengthened, and the interface resistance can be reduced. Because.
Although the said heat processing is not specifically limited, For example, it can carry out for 1 second-10 hours on 80-250 degreeC, 100-200 degreeC conditions in atmosphere, such as argon, nitrogen, air.
The heat treatment may be performed using a conventionally known heating device. Specifically, for example, a constant temperature dryer, a blow dryer, a vacuum dryer, an infrared dryer, or the like may be used.

<< All solid-state lithium-sulfur battery >>
Next, the all solid-state lithium-sulfur battery of the present invention will be described.
The all solid-state lithium-sulfur battery of the present invention includes a positive electrode mixture layer including the positive electrode mixture of the present invention, a solid electrolyte layer, a negative electrode, and a current collector.

In the present specification, the “all solid type” means a polymer solid electrolyte and / or an inorganic solid electrolyte as an electrolyte, and contains substantially no solvent in the negative electrode, the solid electrolyte layer, and the positive electrode mixture layer. Say things.
In the present specification, “substantially no solvent” means that a trace amount of the solvent may remain.

The all-solid-state lithium-sulfur battery of the present invention has, for example, a structure in which a negative electrode, a solid electrolyte layer, and a positive electrode mixture layer are sequentially laminated, and current collectors (negative electrode current collector and positive electrode current collector) are arranged on both sides thereof. It can be.
Hereinafter, each of the current collector (negative electrode current collector, positive electrode current collector), negative electrode, solid electrolyte layer, and positive electrode mixture layer will be described in order.

<Current collector>
Although it does not specifically limit as said electrical power collector, For example, Al, Cu, Ni, stainless steel etc. can be used.
As the negative electrode current collector, Cu is preferably used because it is difficult to make an alloy with lithium and it can be easily processed into a thin film.
As the positive electrode current collector, Al is preferably used because it is easy to process into a thin film and is inexpensive.

<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. Here, examples of the material that occludes and releases lithium ions include metallic lithium, lithium alloy, metal oxide, metal sulfide, and a carbonaceous substance that occludes and releases lithium ions.
Examples of the lithium alloy include alloys of lithium, aluminum, silicon, tin, magnesium, indium, calcium, and the like.
Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.
Examples of the metal sulfide include tin sulfide and titanium sulfide.
Examples of the carbonaceous material that absorbs and releases lithium ions include graphite, coke, mesophase pitch-based carbon fiber, spherical carbon, and resin-fired carbon.

The method of obtaining the negative electrode is not particularly limited, but a method of pressing the material that absorbs and releases lithium ions, and a negative electrode precursor dispersion containing the material that absorbs and releases lithium ions and a solvent are used as a negative electrode current collector. Examples thereof include a method of pressing after coating and drying.
As the solvent contained in the negative electrode precursor dispersion, the same solvents as those used for the positive electrode mixture can be used.
The solvent is used to assist the application of the negative electrode precursor dispersion and is removed by drying after the application.

<Solid electrolyte layer>
Examples of the solid electrolyte layer include those made of a polymer solid electrolyte and / or an inorganic solid electrolyte.
As the inorganic solid electrolyte, for example, a solid electrolyte having a conductivity of 0.1 mS / cm or more may be used. Specific examples of the solid electrolyte are not particularly limited as long as the electrical conductivity is 0.1 mS / cm or more, and examples thereof include lithium salts, lithium sulfides, lithium oxides, and lithium nitrides.

The solid electrolyte is preferably a lithium salt, a lithium sulfide, or a combination thereof. This is because the conductivity is high and the grain boundary resistance is small.

Examples of the lithium salt is not particularly limited, for example, LiBH _4, LiI and the like.
As the lithium sulfide is not particularly limited, for example, the P _x S _y with those conjugated, specifically, such composite compound of the Li 2 _S and P _x S _y and the like, also In addition to Li ₂ S and P _x S _y , GeS ₂ , SiS ₂ , Li ₃ PO ₄ , Li ₄ SiO _{4 and the} like may be combined.
As the lithium oxide is not particularly limited, for _{example, Li 2 O, Li 2 O} 2 and the like.
As the lithium nitride is not particularly limited, for example, Li 3 _N and the like.
These solid electrolytes may be used alone or in combination of two or more.

The solid electrolyte layer made of the inorganic solid electrolyte can be obtained, for example, by a method of pressure-molding the solid electrolyte, a method of applying the coating after the solid electrolyte is dispersed in a solvent, and drying.
The method for pressure-forming the solid electrolyte is not particularly limited. For example, a method of sandwiching and pressing the solid electrolyte between the negative electrode current collector and the positive electrode current collector, a method of pressing with a jig of a pressure molding machine Etc.
When a solid electrolyte layer is obtained by a method in which the solid electrolyte is dispersed in a solvent and then applied and dried, the dried solid electrolyte layer may be pressed by the same method as described above.
As the solvent for dispersing the solid electrolyte, the same solvents as those used for the above-mentioned positive electrode mixture can be used.
When a solid electrolyte layer is obtained by these methods, heat treatment may be performed at an arbitrary timing for the purpose of reducing the interface resistance of the solid electrolyte layer and improving the denseness.
Examples of the solid electrolyte layer made of the polymer solid electrolyte include polyethylene oxide polymers containing lithium salts such as lithium perchlorate and lithium bistrifluoromethanesulfonylamide.

<Positive electrode mixture layer>
The positive electrode mixture layer can be obtained, for example, by a method of supporting the positive electrode mixture on a positive electrode current collector, a method of pressure forming the positive electrode mixture, or the like.
The method of supporting the positive electrode mixture on the positive electrode current collector is not particularly limited. For example, a method of pressure-forming the positive electrode mixture, a positive electrode mixture paste using an organic solvent or the like is used as the positive electrode current collector. For example, there may be mentioned a method of fixing by applying, drying and pressing.
The method for pressure forming the positive electrode mixture is not particularly limited. For example, a method of pressing the positive electrode mixture between the solid electrolyte layer and the positive electrode current collector and pressing with a jig of the pressure molding machine And the like.
The method for applying the positive electrode mixture to the positive electrode current collector is not particularly limited, and examples thereof include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. It is done.
When the positive electrode mixture layer is obtained by these methods, heat treatment may be performed at an arbitrary timing for the purpose of reducing the interface resistance of the positive electrode mixture layer and improving the denseness.

The all solid-state lithium-sulfur battery may have a separator, in addition to the above-described negative electrode current collector, negative electrode, solid electrolyte layer, positive electrode mixture layer, and positive electrode current collector.
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 rectangular type.

<Method for producing all solid-state lithium-sulfur battery>
The method for producing the all solid-state lithium-sulfur battery is not particularly limited, and examples thereof include the following methods.
First, a solid electrolyte is sandwiched between a negative electrode current collector and a positive electrode current collector and pressed to produce a solid electrolyte layer. Next, a positive electrode mixture is deposited on one side of the solid electrolyte layer, and both ends thereof are sandwiched between a current collector (a negative electrode current collector on the solid electrolyte layer side and a positive electrode current collector on the positive electrode mixture side), and pressed. A positive electrode mixture layer and a positive electrode current collector are laminated on one surface of the electrolyte layer, and a negative electrode current collector is laminated on the other surface of the solid electrolyte layer. Finally, once remove the negative electrode current collector, put the negative electrode on the side opposite to the positive electrode mixture layer side of the solid electrolyte layer, and further press the negative electrode current collector on the negative electrode side and press the other side of the solid electrolyte layer A negative electrode and a negative electrode current collector are stacked on the surface. Moreover, it may be pressed one layer at a time as described above, or two or more layers may be deposited and a plurality of layers may be pressed together and laminated. By such a method, an all solid-state lithium-sulfur battery can be produced.

<Applications of all-solid-state lithium-sulfur batteries>
The use of the all-solid-state lithium-sulfur battery is not particularly limited, but can be suitably used for electrical products that require high energy density, such as hybrid vehicles and electric vehicles.

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

1. Preparation of phosphorus sulfide and / or its discharge product [I] (Synthesis Example 1)
Li ₂ S (manufactured by Furuuchi Chemical Co., Ltd.) and P ₂ S ₅ (manufactured by Aldrich) were weighed to a molar ratio of 80:20 and mixed in a mortar with a planetary ball mill at a rotational speed of 250 rpm. By treating for 10 hours at a speed of 500 rpm (rotation and reverse rotation), phosphorus sulfide having a phosphorus weight ratio of 0.153 and / or its discharge product [I] was obtained.

(Synthesis Example 2)
Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of 70:30, and mixed in a mortar with a planetary ball mill for 10 hours at a rotation speed of 250 rpm and a revolution speed of 500 rpm (rotation and reverse rotation). As a result, phosphorus sulfide having a phosphorus weight ratio of 0.188 and / or its discharge product [I] was obtained.

(Synthesis Example 3)
Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of 60:40, and mixed in a mortar and processed for 10 hours at a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of 500 rpm (rotation and reverse rotation). As a result, phosphorus sulfide having a phosphorus weight ratio of 0.213 and / or its discharge product [I] was obtained.

(Synthesis Example 4)
Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of 40:60, and mixed in a mortar, and then treated with a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of 500 rpm (rotation and reverse rotation) for 10 hours. As a result, phosphorus sulfide having a phosphorus weight ratio of 0.245 and / or its discharge product [I] was obtained.

(Synthesis Example 5)
Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of 20:80, and mixed in a mortar and processed for 10 hours at a planetary ball mill at a rotation speed of 250 rpm and a revolution speed of 500 rpm (rotation and reverse rotation). As a result, phosphorus sulfide having a phosphorus weight ratio of 0.265 and / or its discharge product [I] was obtained.

(Synthesis Example 6)
By mixing P ₂ S ₅ in a mortar, phosphorus sulfide having a phosphorus weight ratio of 0.279 and / or its discharge product [I] was obtained.

2. Preparation of Conductive Material [II] Activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd., specific surface area 3000 m ² / g) was used as the conductive material [II].
3. Production of positive electrode mixture (Example 1)
Phosphorus sulfide and / or its discharge product [I] is phosphorous sulfide and / or its discharge product of Synthesis Example 1, and activated carbon is used as the conductive material [II], and the composition ratio (weight ratio) is 90:10. The phosphorous sulfide and / or its discharge product [I] 180 mg and the conductive material [II] 20 mg were weighed so that the planetary ball mill (premium line P-7 manufactured by Filsch, revolution radius 0.07 m, rotation radius 0. At 0235 m, the ratio of rotation to revolution = -2) was mixed with about 40 g of 5 mm zirconia balls in a 45 ml pot at a revolution speed of 370 rpm for 4 hours to obtain a positive electrode mixture for an all solid-state lithium-sulfur battery. .

(Comparative Example 1)
A positive electrode mixture was obtained by the same mixing treatment as in Example 1 except that sulfur (manufactured by Aldrich) was used as phosphorus sulfide and / or its discharge product [I].

(Example 2)
A positive electrode mixture was obtained by the same mixing treatment as in Example 1, except that phosphorus sulfide and / or its discharge product [I] in Synthesis Example 2 was used as phosphorus sulfide and / or its discharge product [I]. .

(Example 3)
A positive electrode mixture was obtained by the same mixing treatment as in Example 1 except that phosphorus sulfide and / or its discharge product [I] was synthesized using phosphorus sulfide and / or its discharge product [I]. .

Example 4
A positive electrode mixture was obtained by the same mixing treatment as in Example 1 except that phosphorus sulfide and / or its discharge product [I] of Synthesis Example 4 was used as phosphorus sulfide and / or its discharge product [I]. .

(Example 5)
A positive electrode mixture was obtained by the same mixing treatment as in Example 1 except that phosphorus sulfide and / or its discharge product [I] of Synthesis Example 5 was used as phosphorus sulfide and / or its discharge product [I]. .

(Example 6)
A positive electrode mixture was obtained by the same mixing treatment as in Example 1 except that phosphorus sulfide and / or its discharge product [I] of Synthesis Example 6 was used as phosphorus sulfide and / or its discharge product [I]. .

3. Production of an all-solid-state lithium-sulfur battery A cylindrical jig made of SUS304 (10 mmΦ, height 10 mm) is used as a negative electrode current collector from the lower side of a polycarbonate cylindrical tube jig (inner diameter 10 mmΦ, outer diameter 23 mmΦ, height 20 mm). 70 mg of a solid electrolyte (composite of 5Li ₂ S—GeS ₂ —P ₂ S ₅ baked at 510 ° C. for 8 hours) is inserted from the upper side of the cylindrical tube jig made of polycarbonate, and further made of SUS304 as a positive electrode current collector. A cylindrical jig (10 mmΦ, height 15 mm) is inserted from the upper side of a polycarbonate cylindrical tube jig, the solid electrolyte is sandwiched, and pressed at 200 MPa for 3 minutes to obtain a solid having a diameter of 10 mmΦ and a thickness of about 0.6 mm. An electrolyte layer was formed.
Next, the cylindrical jig (positive electrode current collector) made of SUS304 inserted from the upper side was once extracted, and the positive electrode produced in Examples 1-8 and Comparative Examples 1-5 on the solid electrolyte layer in the polycarbonate cylindrical tube. Each of the mixed materials was put to 7.5 mg, and a cylindrical jig (positive electrode current collector) made of SUS304 was inserted again from the upper side and pressed at a pressure of 200 MPa for 3 minutes, so that the diameter was 10 mmΦ and the thickness was about 0.00. A 1 mm positive electrode mixture layer was formed.
Next, a cylindrical jig made of SUS304 (negative electrode current collector) inserted from the lower side was extracted, and a lithium sheet (manufactured by Furuuchi Chemical Co., Ltd.) having a thickness of 0.25 mm was punched as a negative electrode to a diameter of 8 mmΦ with a punch. A 0.3mm-thick indium sheet (Furuuchi Chemical Co., Ltd.) punched to 9mmφ in diameter with a punch, and placed on the bottom of a polycarbonate cylindrical tube jig. A tool (negative electrode current collector) was inserted and pressed at 80 MPa for 3 minutes to form a lithium-indium alloy negative electrode.
As described above, an all-solid-state lithium-sulfur battery in which the negative electrode current collector, the lithium-indium alloy negative electrode, the solid electrolyte layer, the positive electrode mixture layer, and the positive electrode current collector were stacked in this order from the bottom was produced.

4). Evaluation method
(Charge / discharge test)
Discharge capacity per weight of positive electrode mixture when discharged at a current density of 0.64 mA / cm ^{2 with} a charge / discharge device (ACD-M01A, manufactured by Asuka Electronics Co., Ltd.) using the produced all solid-state lithium-sulfur battery. Was measured. The results are shown in Table 1.
In Table 1, (I) and (II) mean phosphorus sulfide and / or its discharge product [I] and conductive material [II], respectively.

5. Results and Discussion From the evaluation results of the positive electrode composites produced in the examples and comparative examples, by using phosphorus sulfide and / or its discharge product containing phosphorus at a predetermined weight ratio as the positive electrode active material / ion conductive material It was revealed that an all-solid-state lithium-sulfur battery excellent in charge / discharge capacity per positive electrode mixture when a practical high current was passed could be obtained.
In the present invention, if the charge / discharge capacity per positive electrode mixture is 150 mAh / g or more, it is considered to be a good positive electrode mixture.

Claims (7)

[I] Phosphorus sulfide and / or its discharge product, wherein the weight ratio of phosphorus (P) is 0.15 to 0.55, and
[II] A positive electrode mixture comprising a conductive material component and being used for a positive electrode mixture layer of an all-solid-state lithium-sulfur battery. The positive electrode mixture according to claim 1, wherein the specific surface area of component [II] is 1000 m ² / g or more. The component [I] is P _x S _y (where x and y independently represent an integer giving a stoichiometric ratio) or a composite containing Li, S and P. 4. The positive electrode composite material according to any one of 3 above. A composite containing Li, S and P contains at least Li ₂ S and S and P, or at least Li ₂ S and P _x S _y (where x and y are independently a stoichiometry). The positive electrode composite material according to claim 3, which is obtained by mechanical milling treatment. A composite containing Li, S and P is M _z S (where M represents Si, Ge, B or Al and Z represents an integer giving a stoichiometric ratio), phosphorus oxide, At least one selected from the group consisting of lithium oxide and lithium iodide is obtained by mechanical milling with Li ₂ S, S and P, or Li ₂ S and P _x S _y , The positive electrode mixture according to claim 4. The positive electrode mixture according to any one of claims 1 to 5, wherein the content of component [I] is 70% by weight or more of the entire positive electrode mixture. An all-solid-state lithium-sulfur battery comprising a positive electrode mixture layer including the positive electrode mixture according to claim 1, a solid electrolyte layer, a negative electrode, and a current collector.