JP2020161317A - Lithium-sulfur solid-state battery - Google Patents

Abstract

To provide a new lithium-sulfur solid-state battery with improved battery characteristics.SOLUTION: In a lithium-sulfur solid-state battery 1 including a sulfur positive electrode 11, a lithium negative electrode 12, and a solid electrolyte 13, the solid electrolyte 13 is arranged between the sulfur positive electrode 11 and the lithium negative electrode 12, and at least the electrolytic solution 15 containing lithium bis (oxalate) borate is held between the lithium negative electrode 12 and the solid electrolyte 13.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium-sulfur solid-state battery.

In recent years, portable and cordless electronic devices and communication devices have been rapidly progressing. As a power source for these electronic devices and communication devices, secondary batteries with high energy density and excellent load characteristics are required, and the use of lithium secondary batteries with high voltage, high energy density, and excellent cycle characteristics is expanding. are doing.
On the other hand, batteries with even higher energy densities are required for the spread of electric vehicles and the promotion of the use of natural energy. Therefore, it is desired to develop a new lithium secondary battery that replaces 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 using sulfur as a constituent material of the positive electrode has the potential to achieve the theoretically highest energy density among batteries. ing. Therefore, research and development of lithium-sulfur batteries have been actively carried out.

When an organic electrolytic solution is used as the electrolyte of a lithium-sulfur battery, sulfur molecules and reaction intermediates (for example, lithium polysulfide, etc.) are dissolved and diffused in the organic electrolytic solution during charging and discharging. Therefore, there is a problem that self-discharge and deterioration of the negative electrode are caused, and the battery performance is deteriorated.
Therefore, in order to solve such a problem, a method of modifying the electrolytic solution by adding an acid such as hydrochloric acid or nitric acid to the electrolytic solution (see Patent Document 1), and using Ketjen Black 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.

Japanese Unexamined Patent Publication No. 2013-114920 Japanese Unexamined Patent Publication No. 2012-204332

However, in the methods disclosed in Patent Documents 1 and 2, since the electrolyte itself is liquid, it is not possible to completely suppress the dissolution of sulfur molecules and reaction intermediates in the electrolytic solution, and a sufficient effect can be obtained. There was a problem that there was no such thing.
As a method of solving the problem when such an electrolytic solution is used, there is a method of using a solid electrolyte. However, lithium-sulfur solid-state batteries equipped with solid electrolytes have not yet been sufficiently studied technically, and there is room for great improvement.

For example, a lithium-sulfur solid-state battery has a problem in terms of battery characteristics, such as a short circuit may occur even with a relatively small number of cycles when charging / discharging.

An object of the present invention is to provide a novel lithium-sulfur solid-state battery having improved battery characteristics.

The present invention adopts the following configuration.
[1]. A sulfur positive electrode, a lithium negative electrode, and a solid electrolyte are provided, and the solid electrolyte is arranged between the sulfur positive electrode and the lithium negative electrode, and at least between the lithium negative electrode and the solid electrolyte, lithium is provided. A lithium-sulfur solid-state battery having an electrolytic solution containing bis (oxalate) borate.

[2]. Further, the lithium ion conducting layer is provided, and the lithium ion conducting layer is arranged between the lithium negative electrode and the solid electrolyte, and the lithium ion conducting layer contains an electrolytic solution containing lithium bis (oxalate) borate. The lithium sulfur solid cell according to [1], which contains lithium ions and conducts lithium ions between the lithium negative electrode and the solid electrolyte.
[3]. When the electrolytic solution between the lithium negative electrode and the solid electrolyte and the lithium ion conducting layer are provided, the electrolytic solution contained in the lithium ion conducting layer contains an ionic liquid [1]. ] Or the lithium-sulfur solid-state battery according to [2].
[4]. When the electrolytic solution between the lithium negative electrode and the solid electrolyte and the lithium ion conductive layer are provided, the lithium bis (oxalate) borate is used in the electrolytic solution contained in the lithium ion conductive layer. , Lithium borohydride, lithium salt that does not fall under any of the above, and the ratio of the molar amount of lithium bis (oxalate) borate to the total molar amount of lithium bis (oxalate) borate is 1 mol% or more, [1] ] To the lithium sulfur solid-state battery according to any one of [3].
[5]. The lithium-sulfur solid-state battery according to any one of [1] to [4], wherein the constituent material of the solid electrolyte is an oxide-based material.
[6]. The lithium-sulfur solid-state battery according to any one of [3] to [5], wherein the ionic liquid is a solvated ionic liquid composed of a glyme-lithium salt complex.

According to the present invention, a novel lithium-sulfur solid-state battery having improved battery characteristics is provided.

It is sectional drawing which shows typically the main part of the example of the lithium-sulfur solid-state battery of this embodiment. It is sectional drawing which shows typically the main part of another example of the lithium-sulfur solid-state battery of this embodiment. It is the imaging data of the positive electrode of Experimental Example 1 in Test Example 1. It is the imaging data of the positive electrode of Experimental Example 2 in Test Example 1. It is the imaging data of the positive electrode of Experimental Example 3 in Test Example 1. It is the imaging data of the positive electrode of Experimental Example 4 in Test Example 1. It is a graph which shows the Coulomb efficiency of the half cell of Experimental Example 1 in Test Example 2. FIG. It is a graph which shows the Coulomb efficiency of the half cell of Experimental Example 4 in Test Example 2. FIG. 3 is a graph showing the results on the reduction reaction side of the cyclic voltammetry test in the first cycle for the half cells of Experimental Examples 2 and 4 in Test Example 3. It is a graph which shows the result of the reduction reaction side of the cyclic voltammetry test of the 2nd cycle about the half cell of Experimental Examples 2 and 4 in Test Example 3. It is a graph which shows the result of the reduction reaction side of the cyclic voltammetry test of the 3rd cycle about the half cell of Experimental Examples 2 and 4 in Test Example 3.

<< Lithium-sulfur solid-state battery >>
The lithium-sulfur solid-state battery according to the embodiment of the present invention includes a sulfur positive electrode, a lithium negative electrode, and a solid electrolyte, and the solid electrolyte is arranged between the sulfur positive electrode and the lithium negative electrode, and at least, Between the lithium negative electrode and the solid electrolyte, there is an electrolytic solution containing lithium bis (oxalate) boronate.
The lithium-sulfur solid-state battery of the present embodiment has an electrolytic solution containing lithium bis (oxalate) borate as an additive between the lithium negative electrode and the solid electrolyte, and this electrolytic solution is reduced during charging and discharging. Since the stability is excellent, the lithium-sulfur solid-state battery has a large number of cycles until a short circuit occurs, and has high battery characteristics.

Hereinafter, first, the structure of the lithium-sulfur solid-state battery of the present embodiment will be described in detail with reference to the drawings.
In addition, in the figure used in the following description, in order to make it easy to understand the features of the present invention, the main part may be enlarged and shown, and the dimensional ratio of each component is the same as the actual one. Is not always the case.

FIG. 1 is a cross-sectional view schematically showing a main part of an example of the lithium-sulfur solid-state battery of the present embodiment.
The lithium-sulfur solid-state battery 1 shown here includes a sulfur positive electrode 11, a lithium negative electrode 12, a solid electrolyte 13, and a lithium ion conductive layer 14.
In the lithium-sulfur solid-state battery 1, the solid electrolyte 13 is arranged between the sulfur positive electrode 11 and the lithium negative electrode 12, and the lithium ion conductive layer 14 is arranged between the lithium negative electrode 12 and the solid electrolyte 13. That is, in the lithium-sulfur solid-state battery 1, the sulfur positive electrode 11, the solid electrolyte 13, the lithium ion conductive layer 14 and the lithium negative electrode 12 are laminated in this order in the thickness direction.

The lithium-sulfur solid-state battery 1 further has an electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13.
In FIG. 1, reference numeral 13b indicates a surface of the solid electrolyte 13 on the lithium negative electrode 12 side (in the present specification, it may be referred to as a “second surface”).

The lithium ion conductive layer 14 may be referred to from one surface (sometimes referred to as the "first surface" in the present specification) 14a to the other surface (in the present specification, the "second surface"). It has a large number of voids (not shown) that reach up to 14b. Therefore, liquid substances and fine substances can be transferred between the lithium negative electrode 12 and the solid electrolyte 13 via the lithium ion conductive layer 14.
Further, the lithium ion conductive layer 14 holds an electrolytic solution (not shown) in the voids and the like, and lithium ions can be dissolved in the electrolytic solution. As described above, since the lithium ion conductive layer 14 contains the electrolytic solution (not shown), the lithium ion conductive layer 14 is interposed between the lithium negative electrode 12 and the solid electrolyte 13 (the lithium ion conductive layer 14). In the thickness direction), lithium ions can be easily conducted.

The portion of the lithium ion conductive layer 14 that has the void portion, holds the electrolytic solution, and maintains the shape of the lithium ion conductive layer is referred to as a “main body portion” in the present specification. That is, the lithium ion conductive layer 14 includes the main body portion and the electrolytic solution held by the main body portion.

The main body of the lithium ion conductive layer 14 is, for example, a porous body or a fibrous material in which fibrous materials are aggregated to form a layer (in the present specification, the term "fiber aggregate"). (Sometimes referred to) and the like.

Depending on the electrolytic solution in the lithium ion conductive layer 14, metallic lithium having a dendritic shape (in other words, a protrusion) or a shape close to it (hereinafter, may be abbreviated as “dendritic or the like”) in the lithium ion conductive layer 14 Precipitation is suppressed. The metallic lithium precipitated in such a shape tends to be elongated (grown), and in that case, the battery characteristics of the lithium-sulfur solid-state battery are deteriorated, such as low cycle characteristics. In the lithium ion conductive layer 14, the precipitation of metallic lithium is suppressed in this way, the lithium ions are smoothly conducted, and the precipitation of metallic lithium is similarly suppressed in the solid electrolyte 13. That is, in the lithium-sulfur solid-state battery 1, the continuous precipitation of metallic lithium from the lithium ion conductive layer 14 to the sulfur positive electrode 11 via the solid electrolyte 13 is suppressed. As a result, cracking of the solid electrolyte 13 can be suppressed.

Further, the electrolytic solution between the lithium negative electrode 12 and the solid electrolyte 13, more specifically, the electrolytic solution 15 between the lithium negative electrode 12 and the lithium ion conductive layer 14, and the lithium ion conductive layer 14 and the solid electrolyte 13. The electrolytes 15 in between are all lithium bis (oxalate) borate ((OC (= O) -C (= O) -O) ₂ B ^- Li ⁺ , and in the present specification, "LiBOB". May be abbreviated).
As described above, since the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13 contains LiBOB, the surface of the lithium negative electrode 12 on the solid electrolyte 13 side (in the present specification, the “first surface”). In 12a (sometimes referred to as), even if metallic lithium is precipitated, its elongation (growth) is suppressed. The reason is not clear, but the decomposition product derived from oxalate volate, which is generated by reducing LiBOB during discharge, is laminated on the surface of the precipitated metallic lithium to form a coating layer, and is dendritic as described above. It is presumed that this is because the precipitation of metallic lithium is stabilized by suppressing the further precipitation of metallic lithium in the shape of the above. As described above, the shape of metallic lithium at the beginning of precipitation is dendritic or the like, and current tends to concentrate on the tip of the protrusion during charging / discharging. Therefore, it is usually considered that by repeating charging and discharging, metallic lithium is further precipitated at the tip of the protrusion, and the precipitate is elongated. On the other hand, in the lithium sulfur solid-state battery 1, the coating layer is formed on the surface of the precipitated metallic lithium, and the precipitation of dendritic metallic lithium is suppressed. As a result, the precipitation of metallic lithium is specific. It is presumed that it becomes difficult to concentrate on the portion, and the elongation (growth) of metallic lithium is suppressed on the first surface 12a of the lithium negative electrode 12.

In the lithium-sulfur solid-state battery 1, the elongation of metallic lithium is suppressed on the first surface 12a of the lithium negative electrode 12 in this way, so that the number of cycles until a short circuit occurs during charging / discharging is longer than usual. There are also many.

When the lithium sulfur solid battery has a lithium ion conducting layer between the lithium negative electrode and the solid electrolyte as in the lithium sulfur solid battery 1 shown here, in the present specification, "the lithium negative electrode and the solid electrolyte" The "electrolyte solution between" means "both the electrolytic solution between the lithium negative electrode and the lithium ion conductive layer and the electrolytic solution between the lithium ion conductive layer and the solid electrolyte" unless otherwise specified. To do.

Either the electrolytic solution 15 between the lithium negative electrode 12 and the lithium ion conductive layer 14, the electrolytic solution 15 between the lithium ion conductive layer 14 and the solid electrolyte 13, and the electrolytic solution contained in the lithium ion conductive layer 14. 1 or 2 or more preferably contain an ionic liquid. When these electrolytic solutions contain ionic liquids, the battery characteristics of the lithium-sulfur solid-state battery 1 are further improved.
The ionic liquid may be a known one, but is preferably a solvated ionic liquid composed of a glyme-lithium salt complex.
The ionic liquid will be described in detail separately.

The electrolytic solution 15 between the lithium negative electrode 12 and the lithium ion conductive layer 14, the electrolytic solution 15 between the lithium ion conductive layer 14 and the solid electrolyte 13, or the electrolytic solution contained in the lithium ion conductive layer 14 is an ionic liquid. In these electrolytic solutions, the ratio of the total mass of the lithium salt and the solvent to the total mass of the lithium salt, the solvent and the additive (([mass of the lithium salt in the electrolytic solution] + [of the solvent in the electrolytic solution] [Mass]) / ([Mass of lithium salt in electrolytic solution] + [Mass of solvent in electrolytic solution] + [Mass of additive in electrolytic solution]) x 100), depending on the type of ionic liquid It is preferable to adjust as appropriate.
Here, as will be described later, the "lithium salt" means "a lithium salt that does not fall under any of LiBOB and lithium borohydride (LiBH ₄ )", and specific examples thereof are in the art. Known lithium salts can be mentioned. The "solvent" means "a liquid medium in which the lithium salt is dissolved", and specific examples thereof include grime and a liquid ionic compound described later. The "additive" means "a component that does not correspond to either a lithium salt or a solvent", and a specific example thereof is LiBOB.

For example, when the ionic liquid is a solvated ionic liquid, the ratio is preferably 99.1 to 99.6% by mass, and the ionic liquid is other than the solvated ionic liquid (for example, 170 described later). In the case of an ionic compound that is liquid at a temperature lower than ° C.), the ratio is preferably 98.9 to 99.96% by mass. When the ratio is at least the lower limit value, the effect of using the ionic liquid can be obtained more remarkably.

Preferred lithium-sulfur solid-state batteries 1 include, for example, those in which the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13 and the electrolytic solution contained in the lithium ion conductive layer 14 contain an ionic liquid. A preferable lithium sulfur solid-state battery 1 is one in which the ionic liquid is a solvated ionic liquid composed of a glyme-lithium salt complex.

The electrolytic solution contained in the lithium ion conductive layer 14 does not have to contain LiBOB, but it preferably contains LiBOB because the above-mentioned effect of suppressing the elongation of metallic lithium is higher.

In the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13, the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt and LiBOB ([molar amount of LiBOB in the electrolytic solution] / ([in the electrolytic solution] [Molar amount of lithium salt] + [Molar amount of LiBOB in electrolytic solution]) × 100) is not particularly limited as long as the above-mentioned effect of suppressing the elongation of metallic lithium can be obtained. In terms of obtaining a higher effect, the ratio is preferably 1 mol% or more, for example, 3 mol% or more, 5 mol% or more, 7 mol% or more, and 9 mol% or more. You may.
In addition, in this specification, "lithium salt" means "lithium salt which does not correspond to either LiBOB and LiBH ₄ " unless otherwise specified.

In the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13, the upper limit of the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt and LiBOB is not particularly limited. In terms of suppressing overuse of LiBOB, the ratio is preferably 20 mol% or less.

In the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13, the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt and LiBOB is an arbitrary lower limit value and upper limit value of any of the above. It can be adjusted as appropriate within the range set in combination with. For example, in one embodiment, the proportion is preferably 1-20 mol%, for example any of 3-20 mol%, 5-20 mol%, 7-20 mol%, and 9-20 mol%. It may be. However, these are examples of the above ratio.

In the electrolytic solution contained in the lithium ion conductive layer 14, the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt and LiBOB ([molar amount of LiBOB in the electrolytic solution] / ([lithium salt in the electrolytic solution] The molar amount] + [molar amount of LiBOB in the electrolytic solution]) × 100) is not particularly limited. For example, the ratio may be the same as in the case of the electrolytic solution 15 in that the effect of suppressing the elongation of metallic lithium is higher.

The preferred lithium sulfur solid-state battery 1 is, for example, the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13 and the electrolytic solution contained in the lithium ion conductive layer 14 with respect to the total molar amount of the lithium salt and LiBOB. , The ratio of the molar amount of LiBOB is in the above-mentioned numerical range, and examples thereof include those having 1 mol% or more.

In the lithium-sulfur solid-state battery 1, the sulfur positive electrode 11 and the solid electrolyte 13 are in direct contact with each other.

In the lithium-sulfur solid-state battery 1, the lithium ion conductive layer 14 has an arbitrary configuration and can be omitted.
However, in the lithium-sulfur solid-state battery 1, since the lithium ion conductive layer 14 is provided, even if metallic lithium is deposited on the first surface 12a of the lithium negative electrode 12, the lithium ion conductive layer 14 is extended. Is suppressed.
As described above, in the lithium-sulfur solid-state battery 1, in addition to the electrolytic solution 15 containing LiBOB, further, by providing the lithium ion conductive layer 14 in this way, the effect of suppressing the elongation of metallic lithium is further further enhanced. It is high, and during charging and discharging, the number of cycles until a short circuit occurs is even larger than usual.

In FIG. 1, the solid electrolyte 13 and the lithium ion conductive layer 14 in the lithium-sulfur solid-state battery 1 are arranged apart from each other without contacting each other, but they may be in contact with each other. That is, in the lithium-sulfur solid-state battery 1, the second surface 13b of the solid electrolyte 13 and the first surface 14a of the lithium ion conductive layer 14 may be in direct contact with each other. In that case, since there are usually a large number of voids between the second surface 13b of the solid electrolyte 13 and the first surface 14a of the lithium ion conductive layer 14, the electrolytic solution 15 is provided in these voids. You may be doing it.
In the lithium-sulfur solid-state battery 1, the lithium ion conductive layer 14 and the lithium negative electrode 12 are arranged apart from each other without contacting each other, but may be in contact with each other. That is, in the lithium-sulfur solid-state battery 1, the second surface 14b of the lithium ion conductive layer 14 and the first surface 12a of the lithium negative electrode 12 may be in direct contact with each other.

Further, in the lithium-sulfur solid-state battery 1, the electrolytic solution 15 containing LiBOB is electrochemically stable and has excellent reduction stability, and the components in the electrolytic solution 15 (for example, alkyl fluorinated). Degradation of the group-bearing component) is suppressed. As a result, the battery characteristics of the lithium-sulfur solid-state battery 1 are high.

As described above, the lithium-sulfur solid-state battery 1 has the above-mentioned characteristics in addition to the number of cycles until a short circuit occurs during charging / discharging, and the battery characteristics are remarkably high.

In the lithium-sulfur solid-state battery 1, for example, the entire laminated structure of the above-mentioned sulfur positive electrode 11, solid electrolyte 13, lithium ion conductive layer 14 and lithium negative electrode 12 is housed in a container, and the electrolytic solution (with the electrolytic solution 15) is used. , The structure in which the electrolytic solution contained in the lithium ion conductive layer 14) is retained is applied.
In the lithium-sulfur solid-state battery 1, for example, the sulfur positive electrode 11 and the lithium negative electrode 12 are each provided with terminals for connection with an external circuit.

FIG. 2 is a cross-sectional view schematically showing a main part of another example of the lithium-sulfur solid-state battery of the present embodiment.
In the drawings after FIG. 2, the same components as those shown in the already explained figures are designated by the same reference numerals as in the case of the already explained figures, and detailed description thereof will be omitted.

The lithium-sulfur solid-state battery 2 shown here does not have the lithium ion conductive layer 14, and therefore does not have the electrolytic solution 15 between the lithium ion conductive layer 14 and the solid electrolyte 13. It is the same as the lithium-sulfur solid-state battery 1 shown in FIG. That is, in the lithium-sulfur solid-state battery 2, the sulfur positive electrode 11, the solid electrolyte 13, and the lithium negative electrode 12 are laminated in this order in the thickness direction.

The lithium-sulfur solid-state battery 2 further has an electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13.

For example, a preferable lithium-sulfur solid-state battery 2 includes a battery in which the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13 contains an ionic liquid, and a more preferable lithium-sulfur solid-state battery 2 includes the ionic liquid. , A solvated ionic liquid composed of a glyme-lithium salt complex.

As described above, the lithium-sulfur solid-state battery 2 also has the same effect as the lithium-sulfur solid-state battery 1 because the electrolytic solution 15 between the lithium negative electrode 12 and the solid electrolyte 13 contains LiBOB.
Next, the configuration of each layer of the lithium-sulfur solid-state battery of the present embodiment will be described in more detail.

<Sulfur positive electrode>
The sulfur positive electrode in the lithium-sulfur solid-state battery of the present embodiment is not particularly limited as long as it contains sulfur and functions as a positive electrode.
Examples of the sulfur positive electrode include known ones in which a positive electrode active material layer is provided on a current collector (positive electrode current collector).

Other than these, as a preferable sulfur positive electrode, for example, a conductive sheet having a large number of voids is provided, the voids are open to the outside of the conductive sheet, and the conductive sheet has the voids. Examples thereof include those containing at least sulfur in the portions, and it is preferable that the conductive sheet contains at least sulfur and an electrolytic solution in the void portions.
As such a sulfur positive electrode, for example, the conductive sheet contains sulfur, a conductive auxiliary agent, a binder and an electrolytic solution in the void portion (in the present specification, "sulfur positive electrode (I)). The conductive sheet contains sulfur in the voids and does not contain a conductive auxiliary agent and a binder (in the present specification, "sulfur positive electrode (II)". (Sometimes referred to as). It is preferable that the sulfur positive electrode (II) further contains an electrolytic solution in the void portion.
Hereinafter, these constituent materials of the sulfur positive electrode will be described in detail for each sulfur positive electrode.

○ Sulfur positive electrode (I)
[Conductive sheet]
In the sulfur positive electrode (I), the conductive sheet can function as a positive electrode current collector.
The voids in the conductive sheet hold components other than the conductive sheet of the sulfur positive electrode (I), that is, sulfur, a conductive auxiliary agent, a binder, and an electrolytic solution. Then, the conductive sheet can function as a positive electrode current collector.
Further, the void portion is open to the outside of the conductive sheet, and it is possible to retain these components by adding various components such as sulfur to the conductive sheet later. There is.

The shape of the void portion in the conductive sheet is not particularly limited as long as the above conditions are satisfied.
For example, the voids may be connected to one or more other voids, or may be independent without being connected to the other voids.
Further, both the connected voids and the non-connected voids may or may not penetrate from one surface of the conductive sheet to the other surface on the opposite side, and are conductive without penetrating. There may be a dead end inside the sex sheet.
Further, both the connected voids and the non-connected 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 is, for example, a porous body or a fiber aggregate (a fibrous material in which fibrous materials are aggregated to form a layer) similar to the main body of the lithium ion conductive layer described above. And so on. The fiber aggregate constituting the conductive sheet may be, for example, one in which fibrous materials are entwined with each other, or one in which fibrous materials are regularly or irregularly stacked. You may.

The constituent material of the conductive sheet may have conductivity, but is preferably one that does not have reactivity with sulfur.
More specific examples of the constituent material of the conductive sheet include carbon, metal (elemental metal, alloy) and the like.
Among them, preferable constituent materials of the conductive sheet include constituent materials of the positive electrode current collector, and more specifically, for example, carbon, copper, aluminum, titanium, nickel, stainless steel and the like.

The constituent materials of the conductive sheet may be only one kind, two or more kinds, and when there are two or more kinds, the combination and the ratio thereof can be arbitrarily selected according to the purpose.

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

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 50 to 30,000 μm, more preferably 100 to 3000 μm.

When the thickness of the conductive sheet clearly varies depending on the part of the conductive sheet, such as when the surface of the conductive sheet has a high degree of unevenness, the maximum thickness is defined as the thickness of the conductive sheet. (The thickness of the thickest part of the conductive sheet is defined as the thickness of the conductive sheet). This applies not only to the conductive sheet but also to the thickness of all layers (sulfur positive electrode, lithium negative electrode, solid electrolyte and lithium ion conductive layer described later).

[Conductive aid]
The conductive auxiliary agent may be a known one, and specific examples thereof include graphite (graphite); carbon black such as Ketjen black and acetylene black; carbon nanotube; graphene; fullerene and the like.
The conductive auxiliary agent contained in the sulfur positive electrode (I) may be only one type, two or more types, or two or more types, and the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode (I), the ratio of the total content of sulfur and the conductive auxiliary agent to the total content of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution ([total content of sulfur and the conductive auxiliary agent in the sulfur positive electrode (I)). Amount (parts by mass)] / [total content of sulfur, conductive auxiliary agent, binder and electrolytic solution of sulfur positive electrode (I) (parts by mass)] × 100) is not particularly limited, but is 60 to 95% by mass. It is preferably 70 to 85% by mass, and more preferably 70 to 85% by mass. When the ratio of the total content is at least the lower limit value, the charge / discharge characteristics of the battery are further improved. When the ratio of the total content is not more than the upper limit value, the effect of using the components other than sulfur and the conductive auxiliary agent can be obtained more remarkably.

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

In the sulfur positive electrode (I), the sulfur and the conductive auxiliary agent may form a complex.
For example, a sulfur-carbon composite can be obtained by mixing sulfur and a carbon-containing material (for example, Ketjen black, etc.) and firing. Such a composite is also suitable as a component contained in the sulfur positive electrode (I).

[binder]
The binder may be a known one, and specific examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-propylene hexafluoride copolymer (PVDF-HFP), and polyacrylic acid (PAA). Lithium polyacrylate (PAALI), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), carboxymethyl cellulose (CMC), polyvinylidene nitrile (PAN), polyimide (PI) And so on.
The binder contained in the sulfur positive electrode (I) may be only one type, may be 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 (I), the ratio of the content of the binder to the total content of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution ([sulfur positive electrode (I) binder content (parts by mass)] / [sulfur positive electrode). The total content (parts by mass) of sulfur, conductive auxiliary agent, binder and electrolytic solution of (I)] × 100) is not particularly limited, but is preferably 3 to 15% by mass, preferably 5 to 9% by mass. More preferably. When the content ratio is at least the lower limit value, the structure of the sulfur positive electrode (I) can be maintained more stably. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

[Electrolytic solution]
The electrolytic solution contained in the sulfur positive electrode (I) preferably contains an ionic liquid, and may be composed of an ionic liquid (the electrolytic solution is an ionic liquid).
The electrolytic solution contained in the sulfur positive electrode (I) may be only one type, may be 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.

(Ionic liquid)
The ionic liquid contained in the sulfur positive electrode (I) is a component for easily moving lithium ions, and is excellent in high temperature stability. Since the sulfur positive electrode (I) contains an ionic liquid, the contact area between the sulfur positive electrode (I) and the solid electrolyte is small, but the ionic liquid produces lithium ions between the sulfur positive electrode (I) and the solid electrolyte. Move. Therefore, the solid-state battery using the sulfur positive electrode (I) has a small interface resistance value at the sulfur positive electrode interface and has excellent battery characteristics even though the solid electrolyte is used.

The ionic liquid can be appropriately selected from, for example, known ones.
However, as the ionic liquid, for example, a liquid having a low sulfur solubility in a temperature range of less than 170 ° C. is preferable, and a liquid that does not dissolve sulfur is particularly preferable.

Examples of the ionic liquid include an ionic compound that is liquid at a temperature of less than 170 ° C., a solvated ionic liquid, and the like.

-Ionic compound liquid at a temperature of less than 170 ° C. The cation portion constituting the ionic compound may be either an organic cation or an inorganic cation, but is preferably an organic cation.
The anion portion constituting the ionic compound may be either an organic anion or an inorganic anion.

Among the cation portions, examples of the organic cation include an imidazolium cation, a pyridinium cation, a pyrrolidinium cation, a sulfonium cation, and an ammonium cation. , Sulfonium cation, and the like.
However, the organic cation is not limited to these.

Among the anion portion, as the organic anion, e.g., methylsulfate anion _(CH 3 SO ₄ ^-), ethylsulfate anion ^{_{(C 2 H 5 SO 4 -}} ) alkyl sulfate anions such as (alkylsulfate anion);
Tosylate anion _{(CH 3 C 6 H 4 SO} 3 -);
Alkane sulfonate anions such as methane sulfonate anion (CH ₃ SO ₃ ⁻ ), ethane sulfonate anion (C ₂ H ₅ SO ₃ ⁻ ), butane sulfonate anion (C ₄ H ₉ SO ₃ ⁻ );
Trifluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ), pentafluoroethane sulfonate anion (C ₂ F ₅ SO ₃ ⁻ ), heptafluoropropane sulfonate anion (C ₃ H ₇ SO ₃ ⁻ ), nonafluorobutane sulfonate anion (C ₄₎ H ₉ SO ₃ ^-) perfluoroalkane sulfonate anions such as (perfluoroalkanesulfonate anion);
Bis (trifluoromethanesulfonyl) imide anion _{((CF 3 SO 2) N} -), bis (nonafluorobutanesulfonyl) imide anion _{((C 4 F 9 SO 2} ) N -), nonafluoro -N - [(trifluoromethane) sulfonyl] butane sulfonyl imide anion _{((CF 3 SO 2) (} C 4 F 9 SO 2) N -), N, N- hexafluoro-1,3-imide anion _{(SO 2 CF 2 CF 2 CF} 2 SO ₂ N ^-) perfluoroalkanesulfonyl anion such as (perfluoroalkanesulfonylimide anion);
Acetate anion (CH ₃ COO ⁻ );
Hydrogen sulfate anion (HSO ₄ ^-); and the like.
However, the organic anion is not limited to these.

Among the anion portion, the inorganic anions include bis (fluorosulfonyl) imide anion _{(N (SO 2 F) 2} -); hexafluorophosphate anion (PF ₆ ^-); tetrafluoroborate anion (BF ₄ ^-) ; chloride ion (Cl ^-), bromide ion (Br ^-), iodide ion (I ^-) halide anions such (halide anion); tetrachloroaluminate anion (AlCl ₄ ^-), thiocyanate anion (SCN ^-) and the like Can be mentioned.
However, the inorganic anion is not limited to these.

Examples of the ionic compound include those composed of a combination of any of the above-mentioned cation portions and any of the above-mentioned anion portions.

Examples of the ionic liquid in which the cation portion is an imidazolium cation include 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, 1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, and 1 -Methyl-3-propylimidazolium bis (trifluoromethanesulfonyl) imide, 1-hexyl-3-methylimidazoliumbis (trifluoromethanesulfonyl) imide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-3 Methyl imidazolium chloride, 1-ethyl-3-methyl imidazolium methanesulfonate, 1-butyl-3-methyl imidazolium methane sulfonate, 1,2,3-trimethyl imidazolium methyl sulfate, methyl imidazolium chloride, methyl imidazolium hydro Gensulfate, 1-ethyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazole Rium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazole Rium ethyl sulfate, 1-butyl-3-methylimidazolium methyl sulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-2,3-dimethylimidazolium ethyl Sulfate and the like can be mentioned.

Examples of the ionic liquid in which the cation portion is a pyridinium cation include 1-butylpyridinium bis (trifluoromethanesulfonyl) imide and 1-butyl-3-methylpyridinium bis (trifluoromethanesulfonyl) imide.

Examples of the ionic liquid in which the cation portion is a pyrrolidinium cation include 1-methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide and 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl). Examples include imide and the like.

Examples of the ionic liquid in which the cation portion is a phosphonium cation include tetrabutylphosphonium bis (trifluoromethanesulfonyl) imide and tributyldodecylphosphonium bis (trifluoromethanesulfonyl) imide.

Examples of the ionic liquid in which the cation portion is an ammonium cation include methyltributylammoniummethylsulfate, butyltrimethylammonium bis (trifluoromethanesulfonyl) imide, and trimethylhexyl ammonium bis (trifluoromethanesulfonyl) imide.

-Solvated ionic liquid The preferred solvated ionic liquid is, for example, one composed of a glyme-lithium salt complex or the like.

Examples of the lithium salt in the glyme-lithium salt complex include lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ , which may be abbreviated as "LiFSI" in the present specification) and lithium bis (. Examples thereof include trifluoromethanesulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ , which may be abbreviated as “LiTFSI” in the present specification).

Examples of the grime in the grime-lithium salt complex include triethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₃ OCH ₃ , triglime), tetraethylene glycol dimethyl ether (CH ₃ (OCH ₂ CH ₂ ) ₄ OCH ₃ , and so on. Tetraglyme) and the like.

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

The grime-lithium salt complex is prepared by mixing, for example, a lithium salt and a grime so that the molar ratio of lithium salt (mol): grime (mol) is preferably 10:90 to 90:10. Can be made.

Preferred grime-lithium salt complexes include, for example, triglyme-LiFSI complex, tetraglyme-LiFSI complex, triglyme-LiTFSI complex, tetraglyme-LiTFSI complex and the like.

The ionic liquid contained in the sulfur positive electrode (I) may be only one type, may be 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.

Among the above, the ionic liquid contained in the sulfur positive electrode (I) is preferably a solvated ionic liquid composed of a glyme-lithium salt complex.

In the sulfur positive electrode (I), the ratio of the content of the electrolytic solution to the total content of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution ([content of the electrolytic solution of the sulfur positive electrode (I) (parts by mass)] / [ The total content (parts by mass) of sulfur, conductive auxiliary agent, binder and electrolytic solution of the sulfur positive electrode (I) is not particularly limited, but is preferably 5 to 20% by mass, preferably 9 to 15% by mass. More preferably. When the content ratio is at least the lower limit value, the conductivity of the sulfur positive electrode (I) is further improved. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

[Other ingredients]
As long as the effect of the present invention is not impaired, the sulfur positive electrode (I) contains other components (however, a solvent described later) in addition to sulfur, a conductive auxiliary agent, a binder and an electrolytic solution as constituent components other than the conductive sheet. (Excluding) may be contained.
The other components are not particularly limited and can be arbitrarily selected depending on the intended purpose.
The other components contained in the sulfur positive electrode (I) may be only one type, two or more types, and when two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.

In the sulfur positive electrode (I), the ratio of the content of the other components to the total content of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution ([content of other components of the sulfur positive electrode (I) (parts by mass)). ] / [Total content of sulfur, conductive auxiliary agent, binder and electrolytic solution (parts by mass) of the sulfur positive electrode (I)] × 100) is not particularly limited, but is preferably 10% by mass or less, and 5% by mass. % Or less, 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 (I), the ratio of the total mass of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution to the mass of the conductive sheet ([total mass of sulfur, the conductive auxiliary agent, the binder and the electrolytic solution] / [conductive sheet]. [Mass] × 100) is preferably 15 to 45% by mass, and more preferably 25 to 40% by mass.

○ Manufacturing method of sulfur positive electrode (I) Sulfur positive electrode (I) is manufactured by a manufacturing method including, for example, a step of impregnating the conductive sheet with a positive electrode material containing sulfur, a conductive auxiliary agent, a binder and an electrolytic solution. it can. The manufacturing method may further include other steps such as a step of drying the impregnated positive electrode material. Hereinafter, a method for producing such a sulfur positive electrode will be described.

[Positive material]
Preferred positive electrode materials include, for example, those containing sulfur, a conductive auxiliary agent, an electrolytic solution, an ionic liquid, a solvent, and, if necessary, the other components.

The solvent is a component for dissolving or dispersing each component such as sulfur described above to impart appropriate fluidity to the positive electrode material.
In the present specification, unless otherwise specified, no ionic liquid is included in the solvent (all ionic liquids are not treated as a solvent).

The solvent can be arbitrarily selected according to the type of each component such as sulfur described above, and an organic solvent is preferable.
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); and ketones such as acetone. Can be mentioned.
The solvent contained in the positive electrode material may be only one type, 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 of the positive electrode material is not particularly limited, and can be appropriately adjusted according to the type of the component other than the solvent.

Ratio of sulfur content to total content of components other than solvent in the positive electrode material ([Sulfur content (mass) of positive electrode material] / [Total content of components other than solvent in positive electrode material (parts by mass) )] × 100) is the ratio of the sulfur content to the total content of sulfur, conductive aid, binder, electrolytic solution and other components in the sulfur positive electrode ([Sulfur content of the sulfur positive electrode (parts by mass)). )] / [Total content (parts by mass) of sulfur, conductive auxiliary agent, binder, electrolytic solution and other components of the sulfur positive electrode] × 100). This also applies to conductive auxiliaries, binders, electrolytes and other components other than sulfur.

The positive electrode material can be obtained by blending each component such as sulfur described above.
The order of addition of each component at the time of blending is not particularly limited, and two or more kinds of components may be added at the same time.
When a solvent is used, the solvent is mixed with any component other than the solvent (ie, any of the above-mentioned sulfur, conductive aid, binder, electrolyte and other components) to mix this component. It may be used by diluting it in advance, or it may be used by mixing a solvent with these components without diluting any component other than the above-mentioned solvent in advance.

The method of mixing each component at the time of blending is not particularly limited, and known methods such as a method of rotating a stirring rod, a stirrer, a stirring blade, etc.; a method of mixing using a mixer; a method of adding ultrasonic waves to mix, etc. The method may be appropriately selected from the above methods.
The temperature and time at the time of adding and mixing each component are not particularly limited as long as each component does not deteriorate. Usually, the temperature at the time of 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 some operation is performed on the obtained composition, for example, a part of the added solvent is removed by distillation or the like. The material obtained by adding the above may be used as the positive electrode material.

The impregnation of the positive electrode material into the conductive sheet can be performed by, for example, a method of applying a liquid positive electrode material to the conductive sheet, a method of immersing the conductive sheet in the liquid positive electrode material, or the like.
The positive electrode material can be applied to the conductive sheet by a known method.
The temperature of the positive electrode material impregnated into the conductive sheet is not particularly limited, but can be, for example, 15 to 30 ° C. However, this is an example of the temperature.

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

○ Sulfur positive electrode (II)
The sulfur positive electrode (II) contains sulfur in the void portion, and is obtained by impregnating a conductive sheet with molten sulfur or a sulfur solution.

[Conductive sheet]
The conductive sheet in the sulfur positive electrode (II) is the same as the conductive sheet in the sulfur positive electrode (I), and can be used in the same manner as in the case of the sulfur positive electrode (I).

[Sulfur, sulfur solution]
The sulfur solution is obtained by dissolving sulfur in a solvent.
The solvent of the sulfur solution is not particularly limited as long as it can dissolve sulfur and does not deteriorate the conductive sheet.
The solvent may be either an inorganic solvent or an organic solvent.
Examples of the inorganic solvent include carbon disulfide and the like.
Examples of the organic solvent include benzene, toluene, n-hexane and the like.

The solvent in the sulfur solution may be only one type, 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 concentration of sulfur in the sulfur solution is not particularly limited as long as the voids of the conductive sheet can be impregnated with the sulfur solution.
The concentration of sulfur in the sulfur solution can be appropriately adjusted depending on, for example, the type of solvent.
The sulfur concentration in the sulfur solution is preferably 0.1 to 35% by mass, for example. When the concentration is at least the lower limit value, a sulfur positive electrode (II) having a high sulfur content can be more easily obtained. When the concentration is not more than the upper limit value, the handleability of the sulfur solution at the time of impregnation of the conductive sheet becomes better.

At the time of producing the sulfur positive electrode (II), as a method of impregnating the conductive sheet with molten sulfur, for example, solid sulfur is placed on the surface of the conductive sheet and the sulfur in this state is heated. Method of melting (in this specification, it may be abbreviated as "impregnation method A"); method of supplying sulfur in a state of being melted by heating to the surface of a conductive sheet (in this specification, ". Impregnation method B ”may be abbreviated) and the like.
In the impregnation method A, for example, sulfur on the conductive sheet may be heated together with the conductive sheet.
In the impregnation method B, for example, sulfur in a molten state may be supplied to the surface of the conductive sheet while being heated. Further, sulfur may be supplied while heating the conductive sheet at a temperature equivalent to that of sulfur.

Among them, in the impregnation method A, the molten sulfur is naturally impregnated into the conductive sheet by gravity only by heating the sulfur on the conductive sheet, so that the impregnation can be performed extremely easily.
Therefore, the method of impregnating the conductive sheet with the molten sulfur is preferably the impregnation method A.

When the conductive sheet is impregnated with molten sulfur, the temperature of sulfur is preferably 120 to 160 ° C, more preferably 135 to 160 ° C, and particularly preferably 150 to 160 ° C. When the temperature is in such a range, the melt viscosity of sulfur is sufficiently lowered, sulfur can be easily introduced into the voids of the conductive sheet, and the sulfur content in the voids becomes better. .. As a result, in the sulfur positive electrode (II), the conductive auxiliary agent and the binder usually used are not required, and the energy density of the lithium-sulfur solid-state battery becomes higher.

In the production of the sulfur positive electrode (II), as a method of impregnating the conductive sheet with the sulfur solution, for example, a method of supplying the sulfur solution to the surface of the conductive sheet; a method of immersing the conductive sheet in the sulfur solution, etc. Can be mentioned.

When the conductive sheet is impregnated with the sulfur solution, the temperature of the sulfur solution is preferably adjusted appropriately according to the type of the solvent in the sulfur solution. For example, the temperature of the sulfur solution is preferably equal to or lower than the boiling point of the solvent in the sulfur solution. When the temperature is not more than the upper limit value, the sulfur solution can be easily introduced into the voids of the conductive sheet, and the sulfur content in the voids becomes better. As a result, in the sulfur positive electrode (II), the conductive auxiliary agent and the binder usually used are not required, and the energy density of the lithium-sulfur solid-state battery becomes higher.

When the conductive sheet is impregnated with the sulfur solution, the lower limit of the temperature of the sulfur solution is not particularly limited as long as the sulfur solution does not solidify. For example, the temperature is preferably 15 ° C. or higher in terms of easy preparation of the sulfur solution and good handleability of the sulfur solution.

When the conductive sheet is impregnated with the sulfur solution, it is necessary to dry the sulfur solution (remove the solvent in the sulfur solution).
The sulfur solution may be dried by a known method, for example, under normal pressure, under reduced pressure, or under blowing conditions, or under any of the atmosphere and the atmosphere of an inert gas.
The drying temperature (solvent removal temperature) is preferably adjusted as appropriate according to the type of solvent in the sulfur solution. For example, the drying temperature of the sulfur solution is preferably equal to or higher than the boiling point of the solvent in the sulfur solution.

When the sulfur positive electrode (II) is obtained by impregnating a conductive sheet with molten sulfur or a sulfur solution, sulfur is contained in a unique state in the voids of the conductive sheet. That is, sulfur is agglomerated in the voids of the conductive sheet, and is held in contact with the surface of the voids in a state where the generation of gaps is suppressed. In other words, in the voids of the conductive sheet, the massive sulfur has a large contact area with the surface of the voids. This is an effect that the molten sulfur or the sulfur solution is filled in the voids of the conductive sheet by impregnating the conductive sheet. For example, when the conductive sheet is impregnated with a sulfur dispersion containing undissolved sulfur, the undissolved sulfur is finally formed into particles or the like as it is in the voids of the conductive sheet. Be retained. In such a sulfur positive electrode (II), the contact area between the sulfur and the surface of the void portion becomes small.
In the lithium-sulfur solid-state battery of the present embodiment, in the sulfur positive electrode (II), the sulfur is contained in such a peculiar state, so that the conductive auxiliary agent and the binder which are usually used are not required, and the energy density is increased.

Further, in the sulfur positive electrode (II) in the present embodiment, the sulfur content can be increased by setting the sulfur content in a peculiar state as described above, as compared with the case where the sulfur content is not so. This is because the sulfur content in the voids of the conductive sheet increases. As described above, when the sulfur content is increased, the lithium-sulfur solid-state battery of the present embodiment uses a large amount of sulfur, and also has excellent battery characteristics in this respect.

As the sulfur positive electrode (II) in the present embodiment, for example, the sulfur content is preferably 6 mg / cm ² or more, more preferably 10 mg / cm ² or more, still more preferably 15 mg / cm ² or more, and particularly preferably 20 mg. / Cm ² or more can be mentioned. In the present specification, the "sulfur content (mg / cm ² ) of the sulfur positive electrode (II)" means that the sulfur positive electrode (II) is viewed in a plan view from directly above, unless otherwise specified. It means the sulfur content (mg) of the sulfur positive electrode (II) per 1 cm ² of the surface area of the sulfur positive electrode (II).

In the present embodiment, the upper limit of the sulfur content of the sulfur positive electrode (II) is not particularly limited. The sulfur content of the sulfur positive electrode (II) is preferably 300 mg / cm ² or less, for example, in that the sulfur positive electrode (II) can be more easily produced.

In the present embodiment, the sulfur content of the sulfur positive electrode (II) can be appropriately adjusted so as to be within a range set by arbitrarily combining any of the above-mentioned lower limit values and upper limit values. For example, in one embodiment, the sulfur content of the sulfur cathode (II) is preferably 6~300mg / cm ^2, more preferably ^{10~300mg / cm 2, 15~300mg / cm} 2 Is more preferable, and 20 to 300 mg / cm ² is particularly preferable. However, these are examples of the sulfur content of the sulfur positive electrode (II).

As described above, due to the unique content of sulfur in the voids of the conductive sheet, the sulfur positive electrode (II) in the present embodiment is used as a normal positive electrode such as a conductive auxiliary agent and a binder. Ingredients are not required. As described above, the sulfur content in the sulfur positive electrode (II) can be increased by not requiring (not containing) a component other than sulfur in the conductive sheet.

[Electrolytic solution]
The electrolytic solution contained in the sulfur positive electrode (II) preferably contains an ionic liquid, and may be composed of an ionic liquid (the electrolytic solution is an ionic liquid).
The electrolytic solution contained in the sulfur positive electrode (II) may be only one type, may be 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.

The electrolytic solution contained in the sulfur positive electrode (II) can easily move lithium ions. Therefore, since the sulfur positive electrode (II) contains the electrolytic solution, the contact area between the sulfur positive electrode (II) and the solid electrolyte is small, but the electrolytic solution is lithium between the sulfur positive electrode (II) and the solid electrolyte. Move the ions. Therefore, such a solid-state battery using the sulfur positive electrode (II) has a smaller interface resistance value at the sulfur positive electrode (II) interface and has better battery characteristics, even though the solid electrolyte is used. .. In particular, the ionic liquid is excellent in high temperature stability, and the above effect can be further enhanced.

(Ionic liquid)
The ionic liquid in the sulfur positive electrode (II) is the same as the ionic liquid in the sulfur positive electrode (I).
The ionic liquid contained in the sulfur positive electrode (II) may be only one type, may be 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.

When an ionic liquid is used, the ratio of the content of the ionic liquid to the total content of sulfur and the ionic liquid in the sulfur positive electrode (II) ([content of the ionic liquid of the sulfur positive electrode (II) (parts by mass)] / [ The total content of sulfur and ionic liquid of the sulfur positive electrode (II) (parts by mass)] × 100) is not particularly limited, but is preferably 5 to 95% by mass, more preferably 10 to 90% by mass. preferable. When the content ratio is at least the lower limit value, the conductivity of the sulfur positive electrode (II) is further improved. When the content ratio is not more than the upper limit value, the charge / discharge characteristics of the battery are further improved.

In the sulfur positive electrode (II), an ionic liquid can be used as in the case of the sulfur positive electrode (I), except for the above points.

[Other ingredients]
The sulfur positive electrode (II) may contain other components that do not fall under any of the conductive sheet, sulfur, and the electrolytic solution, regardless of whether they are inside or outside the voids of the conductive sheet.
The other components are not particularly limited as long as they do not inhibit the function of the sulfur positive electrode (II).
The other components contained in the sulfur positive electrode (II) may be only one type, two or more types, and when two or more types, the combination and ratio thereof can be arbitrarily selected according to the purpose.
For example, the sulfur positive electrode (II) may contain a component used in a normal positive electrode, such as a conductive auxiliary agent and a binder. When the sulfur positive electrode (II) contains a conductive auxiliary agent, it may be contained as a composite of sulfur and the conductive auxiliary agent. The composite of sulfur and the conductive auxiliary agent is obtained by mixing, for example, sulfur and a carbon-containing material (for example, Ketjen black) and firing.

The conductive auxiliary agent in the sulfur positive electrode (II) is the same as the conductive auxiliary agent in the sulfur positive electrode (I).
The binder in the sulfur positive electrode (II) is the same as the binder in the sulfur positive electrode (I).

However, in the sulfur positive electrode (II), the higher the content of the other components, the lower the sulfur content.
From this point of view, in the sulfur positive electrode (II), the ratio of the content of the other components to the total content of the components other than the conductive sheet ([content (mass) of the other components in the sulfur positive electrode (II)). Part)] / [Total content of components other than the conductive sheet in the sulfur positive electrode (II) (parts by mass)] × 100) is preferably 10% by mass or less, and more preferably 5% by mass or less. It is preferably 3% by mass or less, more preferably 1% by mass or less, and most preferably 0% by mass, that is, the sulfur positive electrode (II) does not contain the other components. ..
In other words, in the sulfur positive electrode (II), the ratio of the total content of sulfur and the electrolytic solution to the total content of the components other than the conductive sheet ([total content of sulfur and the electrolytic solution in the sulfur positive electrode (II) (mass)). Part)] / [Total content of components other than the conductive sheet in the sulfur positive electrode (II) (parts by mass)] × 100) is preferably 90% by mass or more, and more preferably 95% by mass or more. It is preferably 97% by mass or more, more preferably 99% by mass or more, and most preferably 100% by mass.
A lithium-sulfur solid-state battery satisfying such conditions has better battery characteristics.

Regardless of the type of the sulfur positive electrode, the thickness of the sulfur positive electrode is not particularly limited and may be appropriately set according to the purpose of the battery to be applied. Generally, the thickness of the sulfur positive electrode is preferably 100 to 30,000 μm, more preferably 200 to 3000 μm.

<Lithium negative electrode>
The lithium negative electrode in the lithium-sulfur solid-state battery of the present embodiment may be a known one.

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

<Solid electrolyte>
The constituent material of the solid electrolyte in the lithium-sulfur solid-state battery of the present embodiment is not particularly limited, and may be any of a crystalline material, an amorphous material, and a glass material.
More specifically, as a constituent material of the solid electrolyte, for example, a material containing no sulfide and containing an oxide (sometimes referred to as an "oxide-based material" in the present specification), at least a sulfide. Known materials such as those containing (sometimes referred to as "sulfide-based materials" in the present specification) can be mentioned.

Examples of the oxide-based material include Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ), Li _2.9 PO _3.3 N _0.46 (LIPON), and La _0.51 Li _0.34 TiO _2.94. , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , 50Li ₄ SiO ₄・ 50Li ₃ BO ₃ , Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.07 Al _{0 .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 a composite oxide such as Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) to which elements such as aluminum, tantalum, niobium, and bismuth are added (doped). Be done. Here, the element to be added may be only one kind, two or more kinds, and when two or more kinds are added, the combination and ratio thereof can be arbitrarily selected according to the purpose.

Examples of the sulfide-based materials, for _{example, Li 10 GeP 2 S 12 (} LGPS), Li 3.25 Ge 0.25 P 0.75 S 4, 30Li 2 S · 26B 2 S 3 · 44LiI, 63Li 2 S · _{36SiS 2 · 1Li 3 PO 4,} 57Li 2 S · 38SiS 2 · 5Li 4 SiO 4, 70Li 2 S · 30P 2 S 5 (LISPS), 50Li 2 S · 50GeS 2, Li 7 P 3 S 11, Li 3.25 P _0.95 S _{4 and the} like can be mentioned.

The constituent materials of the solid electrolyte may be only one kind, two or more kinds, and when there are two or more kinds, the combination and the ratio thereof can be arbitrarily selected according to the purpose.

The constituent material of the solid electrolyte is preferably the oxide-based material from the viewpoint that a solid electrolyte having high stability in the atmosphere and high density can be produced.

The thickness of the solid electrolyte is not particularly limited, and may be appropriately set according to the purpose of the battery to be applied. Generally, the thickness of the solid electrolyte is preferably 10 to 1200 μm. When the thickness of the solid electrolyte is at least the above lower limit value, the manufacture and handleability thereof are improved. When the thickness of the solid electrolyte is not more than the upper limit value, the resistance value of the lithium-sulfur solid-state battery is further reduced.

The solid electrolyte can be produced, for example, by selecting a raw material such as a metal oxide, a metal hydroxide, or a metal sulfide according to the desired type, and firing this raw material. The amount of the raw material used may be appropriately set in consideration of the atomic number ratio of each metal in the solid electrolyte and the like.

<Lithium ion conductive layer>
As described above, the lithium ion conductive layer in the lithium sulfur solid-state battery of the present embodiment is a layer that contains an electrolytic solution and conducts lithium ions between the lithium negative electrode and the solid electrolyte.
As described above, the lithium ion conductive layer includes a main body portion and an electrolytic solution.

[Main body]
Examples of the main body of the lithium ion conductive layer include a porous body, a fiber aggregate, and the like, as described above.
The main body of the lithium ion conductive layer is preferably one that does not react with the lithium negative electrode, does not dissolve, and does not deteriorate under the temperature conditions during operation of the lithium sulfur solid-state battery. Here, "alteration of the main body" means that the composition of the components of the main body changes. The operating temperature of the lithium-sulfur solid-state battery can be appropriately set according to the type of the sulfur positive electrode. When a known sulfur positive electrode or sulfur positive electrode (I) is used, the operating temperature of the lithium-sulfur solid-state battery is, for example, preferably 110 ° C. or lower, more preferably 100 ° C. or lower. Therefore, the main body of the lithium ion conductive layer in this case is preferably stable under a temperature condition of, for example, about 120 ° C. On the other hand, when the sulfur positive electrode (II) is used, the operating temperature of the lithium-sulfur solid-state battery is preferably 110 to 160 ° C. Therefore, the main body of the lithium ion conductive layer in this case is preferably one that is stable under such temperature conditions.

Among such main body portions, examples of the constituent material of the porous body or fiber aggregate include synthetic resin, glass, paper and the like, and synthetic resin or glass is preferable.
Among them, the constituent material of the main body is more preferably polyimide or glass. That is, it is more preferable that the lithium ion conductive layer contains polyimide or glass as its constituent material.

The constituent material of the main body of the lithium ion conductive layer may be only one type, may be 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.

[Electrolytic solution]
The electrolytic solution contained in the lithium ion conductive layer is the same as that described above with reference to FIG. 1, and may be, for example, the same as the electrolytic solution contained in the above-mentioned sulfur positive electrode.
Examples of the ionic liquid contained in the electrolytic solution include the same as the ionic liquid contained in the sulfur positive electrode (I), and a solvated ionic liquid composed of a glyme-lithium salt complex is preferable.

The electrolytic solution contained in the lithium ion conductive layer may be only one type, may be 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.

The electrolytic solution contained in the lithium ion conductive layer may be the same as or different from the electrolytic solution contained in the sulfur positive electrode described above.

The content of the electrolytic solution in the lithium ion conductive layer is not particularly limited.
However, the ratio of the total volume of the electrolytic solution held in the lithium ion conductive layer to the total volume of the voids in the main body of the lithium ion conductive layer ([total of the electrolytic solutions held in the lithium ion conductive layer]. [Volume] / [Total volume of voids in the main body of the lithium ion conductive layer] × 100) is preferably 80 to 120% by volume at room temperature. When the ratio is at least the lower limit value, the effect of suppressing the precipitation of metallic lithium in the solid electrolyte becomes higher. When the ratio is not more than the upper limit value, excessive use of the electrolytic solution is suppressed.
The ratio can be larger than 100% by volume because the electrolytic solution may be present in the lithium ion conductive layer in addition to the void portion of the main body portion.
In addition, in this specification, "normal temperature" means a temperature which is not particularly cooled or heated, that is, a normal temperature, and examples thereof include a temperature of 15 to 25 ° C.

The lithium ion conductive layer may be composed of one layer (single layer) or may be composed of two or more layers. When the lithium ion conductive layer is composed of a plurality of layers, the plurality of layers may be the same or different from each other, and the combination of the plurality of layers is not particularly limited.
In the present specification, not only in the case of the lithium ion conductive layer, "a plurality of layers may be the same or different from each other" means "all layers may be the same or all layers". May be different, or only some layers may be the same ", and" a plurality of layers are different from each other "means" at least one of the constituent materials and thicknesses of each layer is different from each other. It means "different".

The thickness of the lithium ion conductive layer is not particularly limited.
The thickness of the lithium ion conductive layer composed of a plurality of layers means the total thickness of all the layers constituting the lithium ion conductive layer.

However, the thickness of the lithium ion conductive layer is preferably 10 μm or more in that the effect of suppressing the precipitation of metallic lithium in the solid electrolyte is further enhanced. When the thickness of the lithium ion conductive layer is equal to or greater than the lower limit, even if metallic lithium is deposited in the lithium ion conductive layer, its influence does not extend to the solid electrolyte as described above. .. As a result, in the lithium-sulfur solid-state battery, the continuous precipitation of metallic lithium from the lithium ion conductive layer to the sulfur positive electrode via the solid electrolyte is suppressed.

On the other hand, the thickness of the lithium ion conductive layer is preferably 100 μm or less from the viewpoint that the thickness of the lithium ion conductive layer does not become excessive (more appropriate).
Generally, the thinner the lithium ion conductive layer, the lower the resistance value in the lithium ion conductive layer, and the higher the energy density of the lithium-sulfur solid-state battery.

For the lithium ion conductive layer, for example, a first raw material composition containing a constituent material of the main body, an electrolytic solution, and a solvent if necessary is prepared, and the lithium ion conductive layer is formed on a surface to be formed. It can be formed by applying the first raw material composition and drying it if necessary. This method is a method of simultaneously forming the main body and the lithium ion conductive layer. When no solvent is used, it is not necessary to dry the coated first raw material composition.

At the time of preparing the first raw material composition, the temperature and time at the time of adding and mixing each raw material are not particularly limited as long as each raw material is not deteriorated. For example, the temperature at the time of mixing may be 15 to 50 ° C., which is an example. The method of mixing each raw material may be the same as the method of mixing each component at the time of producing the above-mentioned positive electrode material, for example.

The first raw material composition can be applied to the surface to be formed of the lithium ion conductive layer by a known method.
The temperature of the first raw material composition to be coated is not particularly limited as long as the surface to be formed of the lithium ion conductive layer, the constituent material of the main body, the ionic liquid, the solvent and the like are not deteriorated. For example, the temperature of the first raw material composition at this time may be 15 to 50 ° C., which is an example.

When the first raw material composition is dried, the drying can be carried out by a known method under normal pressure or reduced pressure. The drying temperature of the first raw material composition is not particularly limited and may be, for example, 20 to 100 ° C., but this is an example.

When the surface to be formed of the lithium ion conductive layer is the arrangement surface of the lithium ion conductive layer in the lithium sulfur solid-state battery (for example, the surface on the lithium negative electrode side of the solid electrolyte), the formed lithium ion conductive layer is , It is not necessary to move it to another place, and it can be arranged as it is.
On the other hand, when the surface to be formed of the lithium ion conductive layer is not the surface on which the lithium ion conductive layer is arranged in the lithium sulfur solid state battery, the formed lithium ion conductive layer is peeled off from this surface to form the lithium sulfur solid state battery. It may be moved by sticking it to the target arrangement surface inside.

Further, as the lithium ion conductive layer, for example, the main body is impregnated with an electrolytic solution, or a mixed solution containing the electrolytic solution and, if necessary, a solvent is prepared, and the mixed solution is used as the main body. It can also be formed by impregnating the portion and, if necessary, drying the impregnated main body portion. This method is a method using a pre-formed main body. When no solvent is used, it is not necessary to dry the main body after impregnation.
In this case, the main body is not arranged on the arrangement surface of the lithium ion conductive layer in the lithium-sulfur solid-state battery, but is handled independently to form the lithium ion conductive layer, and then the obtained lithium ions are obtained. It is preferable that the conductive layer is further attached to the target arrangement surface in the lithium-sulfur solid-state battery.

The main body can be produced by a known method, for example, by preparing a second raw material composition containing the constituent material of the main body and molding the second raw material composition.
Further, the main body may be a commercially available product.

As a method of impregnating the main body with the electrolytic solution or the mixed solution, for example, a method of applying the electrolytic solution or the mixed solution to the main body, or immersing the main body in the electrolytic solution or the mixed solution. The method and the like can be mentioned.

The electrolytic solution or mixed solution can be applied to the main body by a known method.
The temperature of the electrolytic solution or the mixed solution impregnated in the main body is not particularly limited as long as the raw materials such as the main body, the electrolytic solution and the solvent are not deteriorated. For example, the temperature of the electrolytic solution or the mixed solution at the time of impregnation may be 15 to 50 ° C., which is an example.

The main body after impregnation with the mixed solution can be dried under normal pressure or reduced pressure by a known method. The drying temperature at this time is not particularly limited and may be, for example, 20 to 100 ° C., but this is an example.

<Electrolytic solution>
The electrolytic solution contained in the lithium-sulfur solid-state battery of the present embodiment between the lithium negative electrode and the solid electrolyte is the same as that described above with reference to FIG.
Examples of the ionic liquid contained in the electrolytic solution include the same as the ionic liquid contained in the sulfur positive electrode (I), and a solvated ionic liquid composed of a glyme-lithium salt complex is preferable.

The lithium-sulfur solid-state battery of the present embodiment is not limited to the above, and has some configurations changed, deleted or added in the above-described ones without departing from the spirit of the present invention. It may be.

For example, the lithium-sulfur solid-state battery of the present embodiment has one type or two or more other layers, one layer for each type, which does not correspond to any of the sulfur positive electrode, the solid electrolyte, the lithium ion conductive layer, and the lithium negative electrode. Alternatively, two or more layers may be provided.
The other layer is not particularly limited as long as the effect of the present invention is not impaired, and can be arbitrarily selected depending on the intended purpose.

When a sulfur positive electrode composed of a component such as sulfur is used in the voids of the conductive sheet having a large number of voids, in the lithium-sulfur solid-state battery of the present embodiment, the sulfur positive electrode and the solid electrolyte Sufficient battery characteristics can be obtained even if they are in direct contact with each other.

<< Manufacturing method of lithium-sulfur solid-state battery >>
In the lithium sulfur solid battery of the present embodiment, the solid electrolyte is located between the sulfur positive electrode and the lithium negative electrode, and the lithium ion conductive layer is located between the solid electrolyte and the lithium negative electrode, if necessary. The sulfur positive electrode, the lithium negative electrode, and the solid electrolyte, and if necessary, the lithium ion conductive layer are arranged, and at least an electrolytic solution containing LiBOB is placed between the lithium negative electrode and the solid electrolyte. It can be manufactured by a method having a step of holding.
In other words, in the lithium-sulfur solid-state battery of the present embodiment, the sulfur positive electrode, the solid electrolyte, the lithium ion conductive layer, and the lithium negative electrode, if necessary, are laminated in this order in the thickness direction of these. At least, it can be produced by a method having a step of holding an electrolytic solution containing LiBOB between the lithium negative electrode and the solid electrolyte.
For example, in the lithium-sulfur solid-state battery of the present embodiment, a lithium ion conductive layer is newly used as needed, and the sulfur positive electrode, the solid electrolyte, and the lithium ion conductive layer and the lithium negative electrode as described above are described above. Manufactured in the same manner as in the case of known lithium-sulfur solid-state batteries, except that they are laminated so as to be arranged, and at least an electrolytic solution containing LiBOB is held between the lithium negative electrode and the solid electrolyte. it can. When a sulfur positive electrode provided with the above-mentioned conductive sheet is used, a known lithium-sulfur solid-state battery is used except that such a sulfur positive electrode is additionally used instead of the conventional sulfur positive electrode. Can be manufactured in the same way as.

When the lithium-sulfur solid-state battery includes a lithium ion conducting layer, as a method of holding an electrolytic solution containing LiBOB between the lithium negative electrode and the solid electrolyte, for example, the entire lithium ion conducting layer contains the electrolytic solution. (A) is a method (a) in which a lithium negative electrode is arranged on one surface (second surface side) side of such a lithium ion conducting layer and a solid electrolyte is arranged on the other surface (first surface side) side. Be done.

In the method (a), the lithium ion conductive layer containing the electrolytic solution containing LiBOB can be simultaneously produced by impregnating the entire lithium ion conductive layer with the electrolytic solution.
In the method (a), the electrolyte solution is further applied to either or both of the surface of the lithium negative electrode on the solid electrolyte side (first surface) and the surface of the solid electrolyte on the lithium negative electrode side (second surface). May be attached. In that case, the three types of the electrolytic solution attached to the lithium negative electrode, the electrolytic solution attached to the solid electrolyte, and the electrolytic solution impregnated in the entire lithium ion conductive layer may all be the same or different. It may be the same, or only two kinds may be the same.

When the lithium-sulfur solid-state battery does not have the lithium ion conductive layer, as a method of holding the electrolytic solution containing LiBOB between the lithium negative electrode and the solid electrolyte, for example, the above-described electrolytic solution is held. (B) can be mentioned.

The handling temperature of the lithium-sulfur solid-state battery of the present embodiment is not particularly limited, but when an ionic liquid is used, it is preferably 160 ° C. or lower, for example. By doing so, the vaporization of the ionic liquid can be suppressed, the leakage of sulfur can be suppressed, and the lithium-sulfur solid-state battery exhibits more excellent 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, a household power supply; an emergency power supply; a power source for an airplane, an electric vehicle, or the like.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples shown below.

<< Manufacture of half cell >>
[Experimental Example 1]
As a lithium ion conductive layer, a polyimide sheet (diameter 17 mm, thickness 30 μm), which is the main body, impregnated with 80 μL of an electrolytic solution was prepared. As the electrolytic solution, one having a molar ratio of LiTFSI: LiBOB: tetraglime of 0.99: 0.01: 1 was used. This electrolytic solution contains LiTFSI as a lithium salt and LiBOB as an additive, and the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt and LiBOB is 1 mol%.

A lithium negative electrode (diameter 15 mm, thickness 600 μm), a lithium ion conductive layer containing the above-mentioned electrolytic solution, and a positive electrode made of copper foil (diameter 14 mm, thickness 20 μm) are arranged in this order in these thickness directions. Coin-shaped cells were manufactured as half cells by stacking them concentrically.

[Experimental Example 2]
As the electrolytic solution, the molar ratio of LiTFSI: LiBOB: tetraglime is 0.95: 0.05: 1, that is, the ratio of the molar amount of LiBOB to the total molar amount of lithium salt (LiTFSI) and LiBOB. However, a half cell was produced by the same method as in the case of Experimental Example 1 except that 5 mol% was used.

[Experimental Example 3]
As the electrolytic solution, the molar ratio of LiTFSI: LiBOB: tetraglime is 0.90: 0.10: 1, that is, the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt (LiTFSI) and LiBOB. However, a half cell was produced by the same method as in Experimental Example 1 except that the content was 10 mol%.

[Experimental Example 4]
As the electrolytic solution, the molar ratio of LiTFSI: LiBOB: tetraglime is 1: 0: 1, that is, the ratio of the molar amount of LiBOB to the total molar amount of the lithium salt (LiTFSI) and LiBOB is 0 mol. A half cell was produced by the same method as in the case of Experimental Example 1 except that the value of% was used.

<< Evaluation of half cell >>
[Test Example 1]
<Observation of the surface condition of the positive electrode>
The temperature of the half cells obtained in Experimental Examples 1 to 4 was set to 120 ° C., and under these temperature conditions, the current density was set to 1 mA / cm ² and discharged for 5 mAh.
Next, the positive electrode was taken out from the half cell, and the surface arranged on the lithium ion conductive layer side was observed using a scanning electron microscope (SEM, manufactured by JEOL Ltd.). The imaging data acquired at this time and having a magnification of 800 times are shown in FIGS. 3 to 6. FIG. 3 shows the imaging data of the positive electrodes in Experimental Example 1, FIG. 4 is Experimental Example 2, FIG. 5 is Experimental Example 3, and FIG. 6 is Experimental Example 4.

As is clear from FIGS. 3 to 6, in Experimental Example 4 using the electrolytic solution containing no LiBOB, precipitation of metallic lithium having a shape close to a dendritic shape (projection shape) was observed on the surface of the positive electrode. .. On the other hand, in Experimental Examples 1 to 3 using the electrolytic solution containing LiBOB, precipitates were observed on the surface of the positive electrode, but this was different from the case of Experimental Example 4 and was rounded. The lower the height and the larger the molar amount of LiBOB in the electrolytic solution, that is, the greater the degree in the order of Experimental Example 3, Experimental Example 2 and Experimental Example 1.
As a result, in Experimental Examples 1 to 3, a coating layer was formed on the surface of the positive electrode by decomposition of LiBOB, precipitation of metallic lithium in a dendritic shape was suppressed, and elongation of metallic lithium was suppressed. It showed that it was suppressed.

The above-mentioned test using a half cell is widely used as a battery test method in the art. The results of this test example showed that the elongation of the precipitated metallic lithium was suppressed even on the surface of the lithium negative electrode of the lithium-sulfur solid-state battery of the present embodiment, as in the case of the above-mentioned half cell.

[Test Example 2]
<Evaluation of cycle characteristics>
The temperature of the half cell obtained in Experimental Examples 1 to 4 was 120 ° C., and under this temperature condition, the battery was discharged at a current density of 1 mA / cm ² for 30 minutes, and then charged at a cutoff voltage of 1 V. This charge / discharge cycle was set as one cycle, and the charge / discharge cycle was repeated to determine the Coulomb efficiency of the half cell. The results in the half cell of Experimental Example 1 are shown in FIG. 7, and the results in the half cell of Experimental Example 4 are shown in FIG. 8, respectively.

As is clear from FIGS. 7 to 8, in the half cell of Experimental Example 4, the Coulomb efficiency decreased sharply from around 80 cycles, whereas in the half cell of Experimental Example 1, the Coulomb efficiency was high even after 100 cycles. It was maintained and had excellent cycle characteristics.
Similar results were obtained for the half cells of Experimental Examples 2 and 3 as for the half cells of Experimental Example 1.
As described above, the use of the electrolytic solution containing LiBOB was found to improve the battery characteristics. The results of this test example showed that the lithium-sulfur solid-state battery of the present embodiment also improved the battery characteristics as in the case of the above-mentioned half cell.

After the end of 150 cycles, the positive electrode was taken out from the half cells of Experimental Examples 1 to 4, and the surface arranged on the lithium ion conductive layer side was observed using SEM in the same manner as above. As a result, in Experimental Example 4, precipitation of metallic lithium having a shape close to a dendritic shape (projection shape) was observed on the surface of the positive electrode, whereas in Experimental Examples 1 to 3, it was found on the surface of the positive electrode. , The elongation of metallic lithium was suppressed.

[Test Example 3]
<Evaluation of current value>
The half cells obtained in Experimental Examples 2 and 4 were subjected to the cyclic voltammetry test shown below.
That is, the temperature of these half cells is 120 ° C., the sweep speed is 5 mV / min, and under these temperature conditions, potential scanning is performed for 3 cycles in the potential range of −0.001 to 2.8 V, and the flowing current value is measured. did.
The measurement results of the current value at this time are shown in FIGS. 9 to 11. The results shown here are the results on the reduction reaction side. FIG. 9 shows the measurement result in one cycle, FIG. 10 shows the measurement result in two cycles, and FIG. 11 shows the measurement result in three cycles.

As is clear from FIGS. 9 to 11, the half cell of Experimental Example 2 showed a smaller current value than the half cell of Experimental Example 4 at any number of cycles, and the decomposition of the electrolytic solution was suppressed. This showed that in the half cell of Experimental Example 2, the decomposition of the components in the electrolytic solution, particularly the lithium salt-derived components, was suppressed.
As described above, the use of the electrolytic solution containing LiBOB was found to improve the battery characteristics. The results of this test example showed that the lithium-sulfur solid-state battery of the present embodiment also improved the battery characteristics as in the case of the above-mentioned half cell.

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

1,2 ... Lithium-sulfur solid-state battery, 11 ... Lithium positive electrode, 12 ... Lithium negative electrode, 13 ... Solid electrolyte, 14 ... Lithium ion conductive layer, 15 ... Electrolyte

Claims (6)

It is provided with a sulfur positive electrode, a lithium negative electrode, and a solid electrolyte.
The solid electrolyte is arranged between the sulfur positive electrode and the lithium negative electrode.
A lithium-sulfur solid-state battery having at least an electrolytic solution containing lithium bis (oxalate) borate between the lithium negative electrode and the solid electrolyte. In addition, it has a lithium-ion conductive layer
The lithium ion conductive layer is arranged between the lithium negative electrode and the solid electrolyte.
The lithium sulfur solid-state battery according to claim 1, wherein the lithium ion conductive layer contains an electrolytic solution containing a lithium bis (oxalate) borate and conducts lithium ions between the lithium negative electrode and the solid electrolyte. .. The claim that the electrolytic solution between the lithium negative electrode and the solid electrolyte and, when the lithium ion conducting layer is provided, the electrolytic solution contained in the lithium ion conducting layer contains an ionic liquid. The lithium sulfur solid-state battery according to 1 or 2. When the electrolytic solution between the lithium negative electrode and the solid electrolyte and the lithium ion conductive layer are provided, the lithium bis (oxalate) borate is used in the electrolytic solution contained in the lithium ion conductive layer. , Lithium borohydride, and the ratio of the molar amount of lithium bis (oxalate) borate to the total molar amount of lithium bis (oxalate) borate, which does not correspond to any of the above, is 1 mol% or more. The lithium sulfur solid-state battery according to any one of 1 to 3. The lithium-sulfur solid-state battery according to any one of claims 1 to 4, wherein the constituent material of the solid electrolyte is an oxide-based material. The lithium-sulfur solid-state battery according to any one of claims 3 to 5, wherein the ionic liquid is a solvated ionic liquid composed of a glyme-lithium salt complex.