JP2021136126A - Composite material, positive electrode for lithium sulfur battery, lithium sulfur battery, and method for manufacturing composite material - Google Patents

Abstract

To provide a composite material for a positive electrode of a lithium sulfur battery, by which a large discharge capacity per unit mass of sulfur and a superior cycle characteristic can be realized in a lithium sulfur battery.SOLUTION: A composite material for a positive electrode of a lithium sulfur battery comprises: a porous carbon material; sulfur; and a metal oxide. The porous carbon material is 0.3 mass% or more in nitrogen content, of which the specific surface area obtained by BET method of a nitrogen-adsorbing/desorbing method is 1000 m2/g or larger, and the pore volume obtained Quenched Solid Density Functional Theory Method (QSDFT) is 0.45 cm3/g or larger.SELECTED DRAWING: Figure 5

Description

The present invention relates to composite materials, positive electrodes for lithium-sulfur batteries, lithium-sulfur batteries, and methods for producing composite materials.

Lithium-ion secondary batteries use an organic electrolyte of lithium salt as a non-aqueous electrolyte, are lightweight and have high energy density, and are used as a power source for mobile phones or laptop computers. In the future, they will be represented by hybrid vehicles. It is also expected to be used as a power source for moving objects such as electric vehicles.
Therefore, in recent years, there has been an increasing demand for batteries having a higher capacity density and a lower cost.

Generally, as the positive electrode active material of a lithium ion secondary battery, a metal oxide containing Co, Ni, Mn, Fe and the like and Li is used, but in recent years, instead of these positive electrode active materials, theoretically A lithium-sulfur battery using sulfur as a positive electrode active material, which has an extremely high capacity density and is low in cost, is being developed.

A lithium-sulfur battery is a secondary battery in which a sulfur-based compound is used as a positive electrode active material, and a substance in which an alkali metal such as lithium or a metal ion such as lithium ion is inserted and removed, for example, silicon is used as a negative electrode active material.
Since the redox reaction of sulfur is reversible and the number of reaction electrons is large, it has a theoretical capacity of 1672 mAh / g, which is about 10 times higher than that of a metal oxide positive electrode.

However, the positive electrode active material composed of lithium and sulfur has the following problems.
First, since the positive electrode active material consisting of lithium and sulfur has poor electrical conductivity, electrons can be transferred only to the part near the surface, and the utilization rate of sulfur involved in the electrochemical redox reaction is low. , There is a problem that the battery capacity becomes low.
Further, due to the reaction during charging and discharging, the _{lithium polysulfide represented by the formula; Li 2} S _x (x is 4 to 8 in the formula) is eluted into the electrolytic solution, and the sulfur existing on the positive electrode is lost. This causes a problem that the capacity of the lithium-sulfur battery is reduced accordingly. To prevent degradation capacity of such lithium-sulfur batteries, it is desirable to stop the dissolution of Li ₂ S _x.

As a technique for solving the above-mentioned problems, a technique for combining carbon material, which is a conductive material, and sulfur has been proposed.
As a technique for obtaining a composite of a carbon material and sulfur and using this as an active material for a positive electrode, for example, particles of sulfur and / or a sulfur compound having a particle diameter of 75 μm or less, and a predetermined carbon having a hollow structure are used. A composite having a structure in which fine particles are used as a raw material and these are composited by mechanofusion to form a sulfur and / or sulfur compound particles as a nucleus and a carbon fine particle layer is provided on the surface thereof is obtained, and this is used as the activity of the positive electrode. Techniques used as substances are disclosed (see Patent Documents 1 and 2).

In addition, sodium thiosulfate is dissolved in water, anhydrous acetic acid is added to make an aqueous solution, carbon black is further added and mixed, and the aqueous solution is mixed by the mechanochemical method, centrifuged and filtered, and the supernatant is obtained. Is disclosed, and a technique is disclosed in which a filter residue is obtained as a carbon black-sulfur nanoparticle composite, and the composite is used as an active material for a positive electrode of a lithium-sulfur battery (see Patent Document 3).
Such a technique is a technique for obtaining a composite by compounding a carbon material and sulfur by reacting them by applying strong shear stress and centrifugal force.

On the other hand, the present inventors have found a technique for producing a composite composed of activated carbon containing 31% sulfur by melting and diffusing sulfur into a carbon material by heating sulfur and activated carbon at 155 ° C. for 5 hours. (See Non-Patent Document 1).

Furthermore, the present inventors have developed a technique in which a nitrogen-containing carbon material is chemically activated, a nitrogen-containing porous carbon material is used as a carbon material, and sulfur is melted and diffused in the obtained carbon material to be composited with sulfur. (See Patent Document 4).

In the technique disclosed in Patent Document 4, the "composite of carbon material and sulfur" obtained by using the nitrogen-containing porous carbon material has a large sulfur carrying amount of 54 to 62% by mass. When this is used as the positive electrode active material of a lithium-sulfur battery, it has the advantages of having a large capacity per sulfur mass and a capacity per composite containing sulfur and a carbon material, and having excellent cycle characteristics. ..

On the other hand, a _{technique of using a composite in which MnO 2} is filled in hollow carbon nanofibers as a positive electrode material is disclosed (see Non-Patent Document 2). In this technique, _{a composite in which MnO 2} is filled in hollow carbon nanofibers is filled with molten sulfur to be composited with sulfur. Non-Patent Document 2 states _{that by chemically bonding MnO 2} to Li ₂ S _x (x is 4 to 8 in the formula), _{the elution of Li 2} S _x is suppressed and the cycle characteristics are improved. There is a description.

Japanese Unexamined Patent Publication No. 2006-92881 Japanese Unexamined Patent Publication No. 2006-92883 Japanese Unexamined Patent Publication No. 2012-204332 Japanese Unexamined Patent Publication No. 2018-39685

Progress in Natural Science: Materials International, 25, 612-621 (2015) Angew. Chem. Int. Ed., 54, 12886-12890 (2015)

However, a composite having a sulfur and / or sulfur compound particles formed by complexing with mechanofusion described in Patent Documents 1 and 2 as a nucleus and a carbon fine particle layer on the surface was used as an active material for a positive electrode. In lithium-sulfur batteries, most of the sulfur is deposited on the outer surface of the carbon material or exists as free sulfur, so the problems of the prior art have not yet been sufficiently solved, and the sulfur utilization rate is high. It has a problem that it is low and the capacity per sulfur mass is small, and further, it has a problem that the cycle characteristics are remarkably low because _{sulfur is eluted as Li 2} S _x.

Further, in the technique described in Patent Document 3, the capacity per mass of sulfur is small, and the sulfur content is as low as 22.9 mass%, so that the capacity per mass of the composite containing sulfur and the carbon material is high. It has the problem of being small. Further, there is a problem that the cycle characteristics of the lithium-sulfur battery containing the composite obtained by the technique described in Patent Document 3 as the active material of the positive electrode are also practically insufficient (Patent Document 3). See FIG. 10).

Further, a lithium-sulfur battery using the composite described in Non-Patent Document 1 as a positive electrode active material has a relatively large capacity per sulfur mass, but has a sulfur content of 31% by mass, so that it is a sulfur and carbon material. It has a problem that the capacity per mass of the complex containing the above is low.

Furthermore, the complex obtained by the technique described in Patent Document 4 has a larger amount of sulfur carried than the complex obtained by the technique described in Patent Documents 1 to 3 and Non-Patent Document 1. When this is used as the positive electrode active material of a lithium-sulfur battery, the capacity per sulfur mass and the capacity per composite containing sulfur and a carbon material are large. However, it has a problem that the cycle characteristics are insufficient.

On the other hand, the composite obtained by the technique described in Non-Patent Document 2 uses hollow carbon nanofibers as an active material, while the lithium ion secondary battery is a mobile phone or a notebook computer as described above. Since it is used as a power source for moving objects such as electric vehicles, the discharge capacity per volume of the battery is emphasized. Since carbon nanofibers have a very low bulk density, the discharge capacity per volume is significantly low, which makes them impractical as active materials for batteries. In particular, when hollow carbon nanofibers are used, there is a problem that the discharge capacity per volume is further lowered.
Further, the composite obtained by the technique described in Non-Patent Document 2 has a problem that the manufacturing method is complicated. _{Specifically, MnO 2} nanowires having a uniform average diameter of about 35 nm are first produced, then coated with silica, then coated with resorcinol formaldehyde (RF) resin, and then fired in a nitrogen atmosphere. Next, by removing silica with an aqueous NaOH solution, a composite in which MnO ₂ is filled in hollow carbon nanofibers is produced, and the obtained composite is filled with molten sulfur to form a composite.

Therefore, in the present invention, in view of the above-mentioned problems of the prior art, it is used for the positive electrode of a lithium-sulfur battery having a large discharge capacity per sulfur mass and excellent cycle characteristics without using hollow carbon nanofibers as an active material. It is an object of the present invention to provide a composite material, a positive electrode using the composite material, a lithium-sulfur battery using the positive electrode, and a simple method for producing the composite material.

As a result of diligent studies to achieve the above object, the present inventors have obtained a porous carbon material having a specific nitrogen content and a specific structure, and a composite material containing sulfur and a metal oxide. It has been found that the above-mentioned problems of the prior art can be solved by using it as an active material for a positive electrode for a lithium-sulfur battery, and the present invention has been completed.
That is, the present invention is as follows.

[1]
A composite material for the positive electrode of lithium-sulfur batteries
Contains porous carbon materials, sulfur, and metal oxides
The porous carbon material has a nitrogen content of 0.3% by mass or more, a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method of 1000 m ² / g or more, and a quenching solid phase density function method (QSDFT). The pore volume obtained by the ^{above is 0.45 cm 3} / g or more.
Composite material.
[2]
The composite material according to the above [1], wherein the metal oxide is one or more kinds of oxides selected from the group consisting of Mn and Ti.
[3]
A positive electrode for a lithium-sulfur battery containing the composite material according to the above [1] or [2].
[4]
A lithium-sulfur battery comprising the positive electrode according to the above [3].
[5]
The method for producing a composite material according to the above [1] or [2].
The nitrogen content is 0.3% by mass or more, the specific surface area obtained by the BET method of the nitrogen adsorption / desorption method is 1000 m ² / g or more, and the pore volume obtained by the quenching solid phase density function method (QSDFT) is 0.45 cm. A step of mixing a porous carbon material having a surface area of ^{3 / g or more, sulfur, and a metal oxide.}
The step of melting the sulfur and filling the porous carbon material with
Have, have
Method for manufacturing composite materials.
[6]
It has an activation step of obtaining the porous carbon material by activating the nitrogen-containing carbon material.
In the activation step,
Equation (I) below:
Nitrogen content reduction rate (mass%) = ((BA) / B) x 100 (I)
(In the formula (I), A is the nitrogen content (mass%) measured by XPS in the porous carbon material, and B is the nitrogen content (mass) measured by XPS in the nitrogen-containing carbon material. %).)
The rate of decrease in nitrogen content as defined in is 30-99% by weight.
The method for producing a composite material according to the above [5].
[7]
The method for producing a composite material according to the above [6], wherein the nitrogen content in the nitrogen-containing carbon material is 2 to 45% by mass.
[8]
The method for producing a composite material according to the above [6] or [7], wherein the activation is a chemical activation.
[9]
The method for producing a composite material according to any one of [5] to [8] above, wherein the metal oxide is one or more kinds of oxides selected from the group consisting of Mn and Ti.

According to the present invention, in a lithium-sulfur battery, a composite material for a positive electrode of a lithium-sulfur battery, a positive electrode for a lithium-sulfur battery, a lithium-sulfur battery, which has a large discharge capacity per sulfur mass and can realize excellent cycle characteristics, And a method for producing a composite material used for a positive electrode of a lithium-sulfur battery.

It is explanatory drawing about the method of calculating the height from a peak (H1, H2) and the height (L) from a minimum value M from a laser Raman spectrum diagram of a porous carbon material. When the sulfur content of the composite material composed of the porous carbon material of Example 1 and sulfur and metal oxide, the composite material composed of the porous carbon material and sulfur of Comparative Example 1, and sulfur only was measured. It is a graph of thermogravimetric analysis (TG) of. It is a laser Raman spectrum diagram of the porous carbon material used in Examples and Comparative Examples. It is a charge / discharge curve of the 1st cycle and the 80th cycle of Example 1 and Comparative Example 1. It is a graph which shows the cycle characteristic of the discharge capacity of Example 1 and Comparative Example 1. It is a graph which shows the cycle characteristic of the discharge capacity of Example 2 and Comparative Example 2.

Hereinafter, a mode for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary.
The present embodiment is an example for explaining the present invention, and the present invention is not limited to the embodiment. That is, the present invention can be variously modified without departing from the gist thereof.

[Composite material]
The composite material of the present embodiment is a composite material for the positive electrode of a lithium-sulfur battery, and includes a porous carbon material, sulfur, and a metal oxide.
The porous carbon material has a nitrogen content of 0.3% by mass or more, a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method of 1000 m ² / g or more, and a quenching solid phase density function method (QSDFT). The pore volume obtained by the ^{above is 0.45 cm 3} / g or more.
By having the above-described configuration, in a lithium-sulfur battery, a large discharge capacity per sulfur mass and excellent cycle characteristics can be realized.

(Porous medium)
The porous carbon material used for the composite material of the present embodiment has a nitrogen content of 0.3% by mass or more, a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method of 1000 m ² / g or more, and a quenching solid phase density function. The pore volume obtained by the method (QSDFT) is 0.45 cm ³ / g or more.
Since the porous carbon material has the above-mentioned structure, a lithium-sulfur battery using a composite material containing the porous carbon material and sulfur and a metal oxide as a positive electrode has a discharge capacity per sulfur mass. Large and excellent cycle characteristics can be realized.

<Manufacturing method of porous carbon material>
Preferred production methods for the porous carbon material contained in the composite material of the present embodiment include a production method including a step of producing a nitrogen-containing carbon material and a step of activating the nitrogen-containing carbon material, for example, activating a chemical. ..
The step of heat-treating in an inert gas after the activation, for example, the activation of a chemical, may be included.
The nitrogen-containing carbon material is 22.5 to 26.8 derived from the (002) plane at the peak position of the diffraction angle (2θ) in the X-ray diffraction diagram (XRD) obtained by using CuKα ray as an X-ray source. The material preferably has a main peak at the ° position, and a weak peak is observed at the 43.0 to 46.0 ° position, usually 44.0 to 45.5 °. Is preferable.
The nitrogen-containing carbon material used in the method for producing a porous carbon material may contain other atoms such as oxygen and hydrogen in addition to carbon and nitrogen.

By activating a nitrogen-containing carbon material, for example, by activating a chemical, the present inventors have a nitrogen content of 0.3% by mass or more, and a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method is 1000 m ² / g or more. In addition, a porous carbon material ^{having a pore volume of 0.45 cm 3} / g or more obtained by the quenching solid phase density function method (QSDFT) can be obtained. It has been found that by using the composite material in the form as a positive electrode for a lithium-sulfur battery, it is possible to realize a lithium-sulfur battery having a large discharge capacity per sulfur mass, excellent cycle characteristics, and simple production of a composite material. ..
The reason for this is not clear, but it is presumed as follows. However, this speculation does not limit the present invention in any way.

When pores are formed by activating, for example, chemical activating, and heat-treating a nitrogen-containing carbon material, the nitrogen portion is preferentially removed, so that micropores are preferentially formed.
The amount of elution suppression and electron transfer is possible sulfur by immobilization of sulfur to the resulting micropores increases, immobilization of sulfur to residual nitrogen functionality, Li ₂ in S _x (wherein the metal oxide, x is 4-8) is Li ₂ in S _x (wherein in the charge-discharge process by chemically binding, x is 4-8) suppression of the elution, the results which they are functional in a composite manner, the composite of the present embodiment It is considered that an excellent effect is exhibited when the material is used as an active material for a positive electrode for a lithium-sulfur battery.
In the present specification, the "pore" of the "pore volume" is uniquely determined by the quenching solid phase density function method (QSDFT), and in the pore distribution diagram obtained by the method, the pore diameter is 2 nm or less. The pores are referred to as micropores, the pores having a pore diameter of more than 2 nm and 50 nm or less are referred to as mesopores, and the pores having a pore diameter of more than 50 nm are referred to as macropores.

By carrying out activation of the nitrogen-containing carbon material, for example, chemical activation, the reduction rate of the nitrogen content defined by the following formula (I) is preferably 30 to 99% by mass.
Nitrogen content reduction rate (mass%) = ((BA) / B) x 100 (I)
(In the formula (I), A is the nitrogen content (mass%) measured by XPS in the porous carbon material, and B is the nitrogen content (mass) measured by XPS in the nitrogen-containing carbon material. %).)

[Nitrogen-containing carbon material and method for producing nitrogen-containing carbon material]
The nitrogen-containing carbon material used in the method for producing a porous carbon material is a carbon material containing nitrogen.
The nitrogen-containing carbon material is produced, for example, by polymerizing a low-molecular-weight nitrogen-containing organic compound as a raw material and carbonizing the obtained polymer, or using a low-molecular-weight nitrogen-containing organic compound as a raw material for chemical vapor deposition (CVD). ), A method of impregnating a polymer with a low-molecular-weight nitrogen-containing organic compound and then carbonizing it to produce it, a method of carbonizing a natural product containing nitrogen, and treating the carbonized product with ammonia. It can be produced by a method or the like produced by performing a post-treatment such as an ammoxidation treatment.
Specifically, a method for chemically vapor-depositing a nitrogen-containing organic compound such as pyrrole, acetonitrile, 2,3,6,7-tetracyano-1,4,5,8-tetraazanaphthalene, melamine resin, urea resin, etc. Aniline resin, polyacrylonitrile, azulmic acid, melem polymer, polypyrrole, polyimide, etc., or a method of carbonizing a precursor obtained by mixing these with other polymers, a method of carbonizing beans, etc., activated charcoal, etc. A nitrogen-containing carbon material can be produced by a method of reacting an ammonia gas with an oxygen-containing gas with the carbon material of the above.
When giving a heat history using various organic compounds as raw materials as described above, it is preferable to give a heat history of 600 ° C. or higher.

The nitrogen-containing carbon material is preferably a nitrogen-containing carbon material having a high nitrogen content.
The nitrogen content in the nitrogen-containing carbon material is measured by CHN analysis.
In the present embodiment, the nitrogen content of the nitrogen-containing carbon material is preferably 2 to 45% by mass.
The lower limit of the nitrogen content is more preferably 3% by mass or more, further preferably 5% by mass or more, and even more preferably 10% by mass or more.
The upper limit of the nitrogen content is more preferably 40% by mass or less, further preferably 35% by mass or less, and even more preferably 30% by mass or less.
When a nitrogen-containing carbon material having a nitrogen content of 2% by mass or more is used, micropores are likely to develop. A nitrogen-containing carbon material having a nitrogen content of 45% by mass or less tends to develop a carbon structure.

The nitrogen content of the nitrogen-containing carbon material can be controlled by a method of appropriately selecting the nitrogen content of the polymer used as a raw material.
For example, as a method for producing a nitrogen-containing carbon material having a high nitrogen content, a method of carbonizing a polymer having a high nitrogen content can be exemplified.
Specific examples thereof include a nitrogen-containing carbon material produced by carbonizing azulmic acid, a melem polymer, and polyacrylonitrile, and a nitrogen-containing carbon material produced by carbonizing azulmic acid is preferable.
Azulmic acid is a polymer obtained by polymerizing hydrocyanic acid or hydrocyanic acid oligomer. The hydrocyanic acid oligomer is a dimer or more of hydrocyanic acid.
The condition for carbonization of the polymer is that the heat treatment is performed in an inert gas atmosphere using, for example, a rotary furnace, a tunnel furnace, a tube furnace, a box furnace, a flow firing furnace, or the like. The temperature of the heat treatment is not particularly limited, but is preferably 600 to 1200 ° C, more preferably 700 to 1000 ° C, and even more preferably 750 to 900 ° C.
The inert gas is not limited to the following gas, and examples thereof include an inert gas such as nitrogen, argon, helium, and neon. Further, the inert gas atmosphere may be under reduced pressure, that is, in a pressure environment lower than atmospheric pressure. Among these, it is preferable to use nitrogen gas as the inert gas. The inert gas atmosphere may be such that the inert gas is stationary or circulated, but it is preferable that the inert gas is circulated. The oxygen concentration in the inert gas is preferably 5% or less, more preferably 1% or less, and particularly preferably 1000 ppm or less.
The carbonization treatment time is preferably 10 seconds to 100 hours, more preferably 5 minutes to 10 hours, still more preferably 15 minutes to 5 hours, and even more preferably 30 minutes to 2 hours.
When an inert gas is used, the pressure during the carbonization treatment is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, still more preferably 0.08 to 0.3 MPa, still more preferably 0. It is .09 to 0.15 MPa.

[Step of activating nitrogen-containing carbon material]
Next, the step of activating the nitrogen-containing carbon material will be described.
Activation is a process for making a nitrogen-containing carbon material porous.
In the activation step of the nitrogen-containing carbon material, chemical activation is particularly preferable from the viewpoint that it is easy to obtain a porous carbon material having a large specific surface area, a high micropore ratio, and a large pore volume.
The chemical activation step is performed by mixing a nitrogen-containing carbon material with a chemical and heat-treating it.
The chemicals used for chemical activation refer to chemicals that are solid at 25 ° C. and atmospheric pressure, and their hydrates and aqueous solutions.
The chemicals are not limited to the following, but for example, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali metal carbonates such as potassium carbonate and sodium carbonate; potassium sulfate, sodium sulfate and the like. Alkali metal sulfates; zinc chloride, calcium chloride, potassium sulfide, phosphoric acid and the like, and examples thereof include aqueous solutions or hydrates thereof.
One of these types may be used alone, or two or more types may be used in combination.

The chemical activation is preferably an alkali activation using a chemical containing an alkali metal from the viewpoint of controlling the specific surface area and the pore volume within a desired range, and specifically, potassium hydroxide, sodium hydroxide, potassium carbonate. , Sodium carbonate, etc.

The amount of the chemical used with respect to the nitrogen-containing carbon material in the chemical activation step is not particularly limited, but the chemical / nitrogen-containing carbon material (mass ratio) is preferably 0.1 to 10.
The lower limit of the chemical / nitrogen-containing carbon material (mass ratio) is more preferably 0.3 or more, and even more preferably 0.5 or more.
The upper limit of the chemical / nitrogen-containing carbon material (mass ratio) is more preferably 5 or less, and particularly preferably 3 or less.
When the chemical / nitrogen-containing carbon material (mass ratio) is 0.1 or more, the pores are sufficiently developed, and when it is 10 or less, overactivation can be prevented and the destruction of the pore wall can be suppressed.

The atmosphere for activating the chemical is preferably an inert gas atmosphere. Examples of the inert gas include gases such as nitrogen, argon, helium, and neon.
The chemical activation treatment is not particularly limited, but is carried out, for example, at a temperature of 500 to 1100 ° C., more preferably 600 ° C. to 1000 ° C., and even more preferably 700 ° C. to 900 ° C.
When the temperature of the chemical activation treatment is 500 ° C. or higher, the progress of activation is sufficient, and when it is 1100 ° C. or lower, excessive progress of activation can be suppressed and corrosion of the activation device can be prevented. can.
The time of the chemical activation treatment is not particularly limited, but is preferably 10 minutes to 50 hours, more preferably 30 minutes to 10 hours, and particularly preferably 1 to 5 hours.
The pressure of the chemical activation treatment is usually normal pressure, but it can also be performed under pressure or reduced pressure.

As the activation furnace, a rotary furnace, a tunnel furnace, a tube furnace, a box furnace, a flow firing furnace, or the like can be used.

After the chemical activation is completed, the activated nitrogen-containing carbon material is washed with water, the metal components used for the chemical activation are washed, neutralized with hydrochloric acid, sulfuric acid, nitric acid, etc., and then washed again with water to wash the acid. It is preferable to provide a step.
After performing the washing step, the washed product is subjected to a solid-liquid separation treatment such as filtration, and a drying treatment is performed.

After the chemical activation, the heat treatment may be performed in an inert gas.
The inert gas is not limited to the following, and examples thereof include an inert gas such as nitrogen, argon, helium, and neon.
Further, the inert gas atmosphere may be under reduced pressure, that is, in a pressure environment lower than atmospheric pressure. Among these, it is preferable to use nitrogen gas as the inert gas.
The inert gas atmosphere may be such that the inert gas is stationary or circulated, but it is preferable that the inert gas is circulated.
The oxygen concentration in the inert gas is preferably 5% or less, more preferably 1% or less, and even more preferably 1000 ppm or less.

The temperature of the heat treatment is preferably 900 ° C. or higher from the viewpoint of controlling the specific surface area and the pore volume within a desired range. It is more preferably 1000 ° C. or higher, still more preferably 1100 ° C. or higher, even more preferably 1200 ° C. or higher, and even more preferably 1300 ° C. or higher. Further, 1800 ° C. or lower is preferable, and 1600 ° C. or lower is more preferable.

The heat treatment time is preferably 10 seconds to 100 hours, more preferably 5 minutes to 10 hours, still more preferably 15 minutes to 5 hours, and even more preferably 30 minutes to 2 hours.
When an inert gas is used, the pressure during the heat treatment is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, still more preferably 0.08 to 0.3 MPa, still more preferably 0. It is 09 to 0.15 MPa.
The heat treatment can be performed in the above-mentioned activation furnace.

The reduction rate of the nitrogen content defined by the following formula (I) in the activation step, for example, the chemical activation step is preferably 30 to 99% by mass.
Nitrogen content reduction rate (mass%) = ((BA) / B) x 100 (I)
(In the formula (I), A is the nitrogen content (% by mass) measured by XPS in the porous carbon material, and B is the nitrogen content measured by XPS in the nitrogen-containing carbon material. (Mass%).)
The lower limit of the reduction rate of the nitrogen content is more preferably 75% by mass or more, and further preferably 80% by mass or more.
The upper limit is more preferably 98% by mass or less, further preferably 95% by mass or less.
When the reduction rate of the nitrogen content is 30% by mass or more, micropores develop, which is preferable.
The reduction rate of the nitrogen content is preferably 99% by mass or less from the viewpoint of retaining nitrogen and from the viewpoint of setting the specific surface area and the pore volume within the desired ranges.
The reduction rate of the nitrogen content defined by the formula (I) can be controlled within the above numerical range by selecting the nitrogen-containing carbon material and selecting the conditions in the activation step for the nitrogen-containing carbon material.

<Form of porous carbon material>
The porous carbon material used for the composite material of the present embodiment is produced by a pulverization method.
The pulverization may be carried out in any of the production steps of the nitrogen-containing organic compound, the nitrogen-containing carbon material, and the porous carbon material.
The average particle size of the porous carbon material is preferably 0.1 to 100 μm, more preferably 0.5 to 20 μm, and even more preferably 1 to 5 μm when observed with an SEM (scanning electron microscope). The aspect ratio is preferably 5 or less, more preferably 2 or less, and even more preferably 1.5 or less.

<Physical characteristics of porous carbon material>
The porous carbon material used for the composite material of the present embodiment has a nitrogen content of 0.3% by mass or more, a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method of 1000 m ² / g or more, and a quenching solid phase density function. The pore volume obtained by the method (QSDFT) is 0.45 cm ³ / g or more.
The nitrogen content of the porous carbon material used in the composite material of the present embodiment is measured by X-ray photoelectron spectroscopy (XPS) under the following conditions.
[Measurement condition]
X-ray source: Mg tube (Mg-Kα line), tube voltage: 12 kV, emission current: 50 mA, analysis area: Φ600 μm, uptake area: N1s, C1s, O1s Pass-Energy: 10 eV

The nitrogen content in the porous carbon material used for the composite material of the present embodiment is 0.3% by mass or more, preferably 0.5% by mass or more, and 0.8% by mass or more from the viewpoint described later. More preferably, it is more preferably 1% by mass or more. Further, the nitrogen content described later is preferably 6% by mass or less, more preferably 4% by mass or less, and further preferably 3% by mass or less.

The porous carbon material used for the composite material of the present embodiment is obtained by removing nitrogen atoms from the nitrogen-containing carbon material and leaving nitrogen atoms in a specific ratio during the activation step of the nitrogen-containing carbon material, for example, the chemical activation step. Can be formed.
Due to its unpaired electron effect, the nitrogen atom has an excellent affinity with the sulfur atom as compared with the carbon atom. Therefore, the nitrogen content in the porous carbon material obtained after the activation step, for example, the chemical activation step is 0. When it is 3% by mass or more, it is considered that sulfur can be effectively supported in the pores when forming a complex of the porous carbon material and sulfur.
Further, when the nitrogen content is 6% by mass or less, it is considered that a porous carbon material having pores generated by the loss of many nitrogen atoms can be obtained as described above. Therefore, it is considered to be suitable as an active material for a positive electrode for a lithium-sulfur battery.

The oxygen content of the porous carbon material used in the composite material of the present embodiment is preferably 2 to 20% by mass, more preferably 5 to 15% by mass, and further preferably 9 to 13% by mass.

The specific surface area of the porous carbon material of this embodiment is 1000 m ² / g or more, preferably more than 1100 m ² / g, more preferably at least 1300 m ² / g, still more preferably at least 1500 m ² / g. The specific surface area is preferably not more than 3000 m ² / g, more preferably at most 2500 m ² / g.
The above range is preferable from the viewpoint of increasing the discharge capacity per sulfur mass and realizing excellent cycle characteristics.
The specific surface area of the porous carbon material can be controlled within the above numerical range by adjusting the chemical activation conditions of the nitrogen-containing carbon material and the heat treatment conditions in the inert gas.

Pore volume obtained by quenching the solid phase density functional theory (QSDFT) nitrogen adsorption-desorption method is a 0.45 cm ³ / g or more, preferably 0.5 cm ³ / g or more, 0.6 cm ³ / g or more more preferably, 0.7 cm ³ / g or more, and even more preferably 0.8 cm ³ / g or more.
The pore volume is preferably from 2 cm ³ / g or less, more preferably 1.5 cm ³ / g.
Regarding a lithium-sulfur battery using the composite material of the present embodiment composed of the porous carbon material and sulfur and metal oxide as the active material of the positive electrode, the porous carbon material having a ^{pore volume of 0.45 cm 3 / g or more is} Since it can contain a large amount of sulfur, the total discharge capacity of sulfur and carbon material per mass increases. Therefore, the discharge capacity per weight of the positive electrode becomes large.
The pore volume of the porous carbon material can be controlled within the above numerical range by adjusting the activation conditions of the nitrogen-containing carbon material and the heat treatment conditions in the inert gas.

Further, the porous carbon material used for the composite material of the present embodiment has a pore volume of 0.7 to 3 nm in the pore distribution diagram obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption / desorption method. There is preferably 0.40cm ³ / g or more, more preferably 0.60 cm ³ / g or more, further preferably 0.70 cm ³ / g or more.
In the above pore distribution diagram, it is preferable that the pore volume of pore diameters 0.7~2nm is 0.35 cm ³ / g or more, more preferably 0.50 cm ³ / g or more, 0. It is more preferably 60 cm ³ / g or more.

FIG. 1 is a laser Raman spectrum diagram of the porous carbon material of the present embodiment, and is an explanatory diagram of a method of calculating H1, H2, and L from such spectra.
As shown in the laser Raman spectrum diagram of the porous carbon material shown in FIG. 1, the porous carbon material used for the composite material of the present embodiment has a wave number of 800 to 1900 cm ^{-1 in} a laser Raman spectrum of 1.25 to 1385 cm ^-1 . It has at least two major peaks, a peak P1 ^{in between and a peak P2 between 1550 and 1620 cm -1} , the height L from the baseline of the minimum point M between P1 and P2, and the base of P1. The ratio of height H1 from the line (L / H1) is preferably 0.40 to 0.65 from the viewpoint of further increasing the discharge capacity per sulfur mass and realizing even better cycle characteristics. ..

In this embodiment, the laser Raman spectrum is measured under the following conditions.
[Measurement condition]
LD-excited solid-state laser λ: 532 nm 47 mW Measurement conditions 532 nm Irradiation 2.34 mW Exposure time 10 seconds Total 10 times Greatening 600 G / mm

In FIG. 1, P1 and P2 are two major peaks in which the ^{Raman shift in the laser Raman spectrum diagram is between 1200 and 1700 cm -1.} P1 is a peak between 1250 and 1385 cm ^-1 and P2 is a peak between 1550 and 1620 cm ^-1.

(L / H1) is more preferably 0.50 to 0.60, still more preferably 0.55 to 0.58.
(L / H2) is preferably 0.40 to 0.65, more preferably 0.50 to 0, from the viewpoint of further increasing the discharge capacity per sulfur mass and realizing more excellent cycle characteristics. It is .60, more preferably 0.55 to 0.59.

The half-value width of the peak P1, preferably 30~130cm ^-1, more preferably 50~120cm ^-1, more preferably from 100~110cm ^-1.
The half-value width of the peak P2, preferably 20~90cm ^-1, more preferably 40~80cm ^-1, more preferably from 65~70cm ^-1.

Note that FIG. 1 does not limit the laser Raman spectral diagram obtained from the porous carbon material of the present embodiment.
In Figure 1, B1 is the minimum intensity value of 800~1250cm ^-1, B2 is the minimum of the intensity value between 1700~1900cm ^-1.
The baseline in the laser Raman spectrum diagram used in this embodiment is a straight line connecting B1 and B2.
Next, C1 and C2 shown in FIG. 1 are intersections of a perpendicular line and a baseline drawn from peaks P1 and P2 to the Raman shift axis (horizontal axis), respectively.
D is the intersection of the perpendicular line and the baseline drawn from the minimum intensity value M between the peaks P1 and P2 to the Raman shift axis (horizontal axis), and the height L is lowered from the M to the Raman shift axis. The length to the intersection of the perpendicular and the baseline. Specifically, in the laser Raman spectrum diagram illustrated in FIG. 1, it is the length of the line segment MD.
On the other hand, the height H1 is the length from P1 to the intersection of the perpendicular line and the baseline drawn on the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of the line segment P1C1 corresponds to the height H1.
The height H2 is the length from P2 to the intersection of the perpendicular line and the baseline drawn on the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of the line segment P2C2 corresponds to the height H2.

(Metal oxide)
The composite material of this embodiment includes the above-mentioned porous carbon material, sulfur and metal oxide.
The metal component of the metal oxide is preferably Mn, Ti, V, Fe, Co, Ni, Zn, Mg, Al, Ca, Zr, Nb, Mo, Ag, Ba, Ta, W, La, Ce, more preferably. Is Mn, Ti, and more preferably Mn.
_{MnO 2} is preferable as the oxide of Mn. _{TiO 2} is preferable as the oxide of Ti. The metal oxide is preferable from the viewpoint of realizing excellent cycle characteristics.
For reasons not clear which can realize the cycle characteristics of the metal oxide of the excellent, the metal oxide is Li ₂ S _x (wherein, x is 4-8) adsorbs lithium polysulfide represented by It is effective, and it is considered that this phenomenon contributes to the improvement of cycle characteristics.
In the composite material of the present embodiment, the mass ratio of the porous carbon material and the metal oxide is 0.05 parts by mass or more with respect to 1 part by mass of the porous carbon material from the viewpoint of improving the cycle characteristics. Is preferable, 0.1 part by mass or more is more preferable, and 0.3 part by mass or more is further preferable. Further, from the viewpoint of improving the discharge capacity per composite material, the metal oxide is preferably 3 parts by mass or less, more preferably 1 part by mass or less, and 0.7 parts by mass or less with respect to 1 part by mass of the porous carbon material. Is even more preferable.

(sulfur)
The composite material of this embodiment contains sulfur.
As the sulfur, alone that contains sulfur is not particularly limited as long as it is a compound, e.g., elemental sulfur (S), can be such as lithium sulfide compound (Li ₂ S) is given. It is preferably elemental sulfur (S). In this specification, elemental sulfur (S) is referred to as sulfur.

[Manufacturing method of composite material]
The method for producing a composite material of the present embodiment includes a step of mixing a porous carbon material with a raw material of sulfur and a metal oxide.
In the process of manufacturing the composite material of the present embodiment, other additives may be contained within a range that does not interfere with the effects of the present invention.
The method of mixing will be described.
A method of mixing a porous carbon material with sulfur and a metal oxide in a dry atmosphere, a method of mixing a porous carbon material with a sulfur and a metal oxide in a wet atmosphere in the presence of a solvent to remove the solvent, a method of mixing the porous carbon material and a metal Examples thereof include a method in which an oxide precursor is mixed in the presence of a solvent, the metal oxide precursor is converted into a metal oxide, the solvent is removed, and sulfur is added and mixed.
As a method of mixing the porous carbon material and sulfur and metal oxide in a dry or wet atmosphere, a method of putting the porous carbon material and sulfur and metal oxide in a mixer and mixing them in the mixer can be exemplified. Examples of the mixer include a mortar and a ball mill.
As a method for converting a metal oxide precursor into a metal oxide, the metal oxide precursor is dissolved in a solvent such as water or an organic solvent, mixed with a porous carbon material, the solvent is removed, and then an inert gas is used. A method of firing in an atmosphere, dissolving a water-soluble peroxide in water and mixing it with a porous carbon material, reducing and precipitating the water-soluble peroxide with a porous carbon material, etc., and converting it into an oxide, as a by-product Examples of a method of removing the salt by washing with water or the like and, if necessary, further firing in an inert gas atmosphere can be exemplified. Examples of the water-soluble peroxide include KMnO _{4 and the} like.

The inert gas is not limited to the following, and examples thereof include an inert gas such as nitrogen, argon, helium, and neon. Among these, it is preferable to use nitrogen gas as the inert gas.
The treatment in the inert gas is carried out by performing the heat treatment in an atmosphere of the inert gas using, for example, a rotary furnace, a tunnel furnace, a tube furnace, a box furnace, a fluidized firing furnace and the like. The temperature of the heat treatment is not particularly limited, but is preferably 300 to 1000 ° C, more preferably 400 to 800 ° C, and even more preferably 500 to 700 ° C.
The heat treatment time is preferably 10 seconds to 100 hours, more preferably 5 minutes to 10 hours, still more preferably 15 minutes to 5 hours, and even more preferably 30 minutes to 2 hours.
When an inert gas is used, the pressure during the heat treatment is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, still more preferably 0.08 to 0.3 MPa, still more preferably 0. It is .09 to 0.15 MPa.

The method for producing the composite material includes a step of melting sulfur and filling the porous carbon material.
After the step of mixing the porous carbon material with the raw materials of sulfur and the metal oxide, the sulfur is heated above the melting point of sulfur to melt the sulfur, and the pores of the porous carbon material are impregnated with sulfur by capillarity. It is preferable to go through a process in which the porous carbon material and the metal oxide are simultaneously exposed to the molten sulfur.
The heating temperature may be 107 ° C. or higher, which is the melting point of sulfur, but is preferably 130 ° C. or higher, and more preferably 150 ° C. or higher. The heating temperature is preferably 200 ° C. or lower, more preferably 180 ° C. or lower, and even more preferably 170 ° C. or lower.
From the viewpoint of suppressing the volatilization of sulfur, it is preferable to impregnate the pores with sulfur in a closed container. The reaction time is preferably 0.1 to 100 hours, more preferably 0.5 to 20 hours, still more preferably 1 to 10 hours.
The atmosphere may be air or an inert gas such as nitrogen, argon, helium or neon.

Next, the porous carbon material impregnated with sulfur is heated in order to remove the sulfur that has not been filled in the pores. The heating temperature is preferably 250 ° C. or higher, more preferably 270 ° C. or higher, and even more preferably 290 ° C. or higher.
The heating temperature is preferably 500 ° C. or lower, preferably 400 ° C. or lower, and even more preferably 330 ° C. or lower.
The heating time is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably 2 hours or more.
The container may be a closed container or an open container. In the case of a closed container, it is preferable that the temperature of the upper part of the container is lower than that of the heating part. The atmosphere may be air or an inert gas such as nitrogen, argon, helium, or neon, but air is preferable from the viewpoint of ease of operation.

The mass ratio when mixing the composite material and sulfur is 0.3 parts by mass or more of sulfur with respect to 1 part by mass of the porous carbon material from the viewpoint of filling the pores of the porous carbon material without lack of sulfur. Is preferable, 0.9 parts by mass or more is more preferable, and 1.1 parts by mass or more is further preferable. Regarding the mass ratio, sulfur that is not filled in the pores of the porous carbon material and remains on the surface is removed by evaporation, but from the viewpoint of reducing the amount of evaporation and the energy required for evaporation, the porous carbon The amount of sulfur is preferably 20 parts by mass or less, more preferably 8 parts by mass or less, and further preferably 5 parts by mass or less with respect to 1 part by mass of the material.

The sulfur content of the composite material of the present embodiment containing the porous carbon material and sulfur and metal oxide is preferably 40 to 70% by mass.
The lower limit of the sulfur content is preferably 40% by mass or more, more preferably 43% by mass or more, and further preferably 45% by mass or more from the viewpoint of further increasing the discharge capacity per composite material.
The upper limit of the sulfur content is 70% by mass or less, more preferably 67% by mass or less, and further preferably 65% by mass or less from the viewpoint of producing a porous carbon material.
Here, the sulfur content is the following formula:
Sulfur content = (mass of sulfur) / (mass of porous carbon material and composite material containing sulfur and metal oxides) x 100
It is a value calculated by.

As for the sulfur content in the composite material of the present embodiment, the sulfur taken into the micropores of the porous carbon material is hard to evaporate, and the sulfur outside the micropores is easy to evaporate. It can be prepared by the method and measured by thermogravimetric analysis (TG).
After mixing the porous carbon material and sulfur, the mixture is kept at 155 ° C. for 5 hours in a closed container to melt the sulfur and fill the pores of the porous carbon material by capillary action. After that, the temperature is raised to 300 ° C. as it is, and the temperature is maintained for 2 hours to evaporate and remove sulfur remaining on the surface of the porous carbon material, air-cooled to room temperature, and the container is opened to open the porous carbon material, sulfur and metal. A composite material composed of oxides is taken out and used as a sample.
Subsequently, thermogravimetric analysis (TG) is used to measure the sulfur content in the composite material composed of the porous carbon material and sulfur and metal oxides. Specifically, using a DTG-60AH manufactured by Shimadzu Corporation, 10 mg of a sample was placed in a cell, a measurement gas Ar, a flow rate of 50 ml / min, a starting temperature of 30 ° C., and a heating rate of 5 ° C./min. , And the measurement is performed under the condition of the upper limit temperature of 600 ° C.

For convenience, the graph of thermogravimetric analysis (TG) obtained by measuring the porous carbon material produced in Example 1 in Examples described later and the composite material composed of sulfur and metal oxide under the above conditions. A method of calculating the sulfur content will be described with reference to FIG.
In the graph of thermogravimetric analysis (TG) shown in FIG. 2, the mass decreases with increasing temperature, which corresponds to the sublimation of sulfur filled in the pores. In the region of 300 ° C. to 500 ° C., a point where the slope of the tangent line of the graph changes discontinuously appears. This corresponds to the fact that only the porous carbon material and the metal oxide remain at this point.
Assuming that the mass% of the initial value is 100 and the mass% of the point where the slope of the tangent line of the graph changes discontinuously is X, the sulfur content Y of the composite material is the porous carbon material from the initial value (100). Since it is the value obtained by subtracting the ratio of the total value of the metal oxides, it is defined as Y = 100-X.
In Example 1, since X = 52 and Y = 48, the sulfur content Y is 48% by mass.

As a reference, in this measurement method, when only sulfur is subjected to TG measurement, it can be seen that sulfur is sublimated by 300 ° C. and no sulfur remains, as shown in FIG. X = 0, Y = 100, and the sulfur content Y is 100% by mass.
The composite material containing the porous carbon material of the present embodiment and sulfur and a metal oxide substantially has a peak characteristic of sulfur in an X-ray diffraction diagram (XRD) obtained by using CuKα ray as an X-ray source. It is preferable that there is no such thing.
The characteristic peak of sulfur has a strong peak (P2) at the position of 23.0 ° ± 0.3 °, and also 15.3 ° ± 0.3 ° and 25.8 ° ± 0.3. It has peaks at °, 26.7 ° ± 0.3 °, and 27.7 ° ± 0.3 °.

[Positive electrode for lithium-sulfur batteries]
The positive electrode for the lithium-sulfur battery of the present embodiment contains the porous carbon material obtained as described above, and a composite material containing a metal oxide and sulfur.
The positive electrode for the lithium-sulfur battery of the present embodiment includes the composite material of the present embodiment,, if necessary, a binder, a conductive auxiliary agent, and a current collector.
Although the composite material functions as an active material, the positive electrode of the lithium-sulfur battery of the present embodiment may contain an active material other than the composite material composed of the porous carbon material, the metal oxide and sulfur.

The binder used for the positive electrode of the present embodiment is not limited to the following, but is, for example, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-. Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene-based fluororubber, vinylidenefluo Ride-hexafluoropropylene-tetrafluoroethylene-based fluororubber, vinylidene fluoride-pentafluoropropylene-based fluororubber, vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoro Vinylidene fluoride-based fluororubbers such as ethylene-based fluororubbers and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers, tetrafluoroethylene-propylene-based fluororubbers, tetrafluoroethylene-perfluoroalkyl vinyl ether-based fluororubbers, thermoplastic fluororubbers , Polyethylene, polypropylene, styrene butadiene rubber (SBR), isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, aqueous binder, polyacrylonitrile and the like.
It should be noted that one of these may be used alone, or two or more thereof may be used in any combination and ratio.
The content ratio of the binder is preferably 1 to 20% by mass and more preferably 2 to 10% by mass with respect to the active material. When the content ratio of the binder is 1% by mass or more, the strength of the positive electrode is sufficient, and when the content ratio of the binder is 20% by mass or less, an increase in electrical resistance or a decrease in capacity can be further suppressed.

Examples of the conductive auxiliary agent used for the positive electrode of the present embodiment include, but are not limited to, carbon black, acetylene black, and carbon nanotubes.
It should be noted that one of these may be used alone, or two or more thereof may be used in any combination and ratio. The content ratio of the conductive auxiliary agent is preferably 1 to 20% by mass, more preferably 2 to 10% by mass with respect to the active material.

The current collector used for the positive electrode of the present embodiment is not particularly limited as long as it enables electrical connection of the electrodes, and the materials thereof include aluminum, titanium, zirconium, hafnium, niobium, tantalum, and the like. Examples include alloys containing the above metals. Among these, those selected from the group consisting of aluminum, titanium, tantalum, and alloys containing these metals are preferable, and aluminum is particularly preferable. A foil-shaped, perforated foil-shaped, mesh-shaped or the like obtained from these metals or alloys can be used as a current collector for the positive electrode.

Next, a method for manufacturing a positive electrode for a lithium-sulfur battery according to this embodiment will be described.
The method for producing a positive electrode for a lithium-sulfur battery of the present embodiment is not particularly limited as long as it is a known method, except that the composite material of the present embodiment containing a porous carbon material, a metal oxide and sulfur is used as an active material. ..
For example, a binder, a conductive auxiliary material, and a solvent are added to a composite material containing a porous carbon material, a metal oxide, and sulfur to form a slurry, and the slurry is applied or filled in a current collector, dried, and then pressed. There is a method of manufacturing a positive electrode for a lithium-sulfur battery by increasing the density.
The thickness of the positive electrode layer laminated on the current collector is preferably about 20 to 400 μm. When the thickness of the positive electrode layer is 20 μm or more, the ratio of the amount of active material to the entire battery tends to increase, and the energy density tends to increase, which is preferable. On the other hand, when the thickness of the positive electrode layer is 400 μm or less, the resistance inside the electrode tends to decrease and the output density tends to increase, which is preferable.

The solvent used for producing the positive electrode of the lithium-sulfur battery of the present embodiment may be either aqueous or non-aqueous.
Non-aqueous solvents include, but are not limited to, N-methylpyrrolidone, methylethylketone, cyclohexanone, isophorone, N, N-dimethylformamide, N, N-dimethyl and the like.
The slurry is prepared by kneading with a disperser such as a stirrer, a pressurized kneader, a ball mill and a super sand mill.
Further, a thickener for adjusting the viscosity may be added to the slurry. Thickeners include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch and casein. One of these may be used alone, or two or more thereof may be used in any combination and ratio.

[Lithium-sulfur battery]
Hereinafter, the lithium-sulfur battery including the positive electrode for the lithium-sulfur battery of the present embodiment will be described.
The materials that can be used for the lithium-sulfur battery of the present embodiment, the method for manufacturing the lithium-sulfur battery, and the like are not limited to the following specific examples.
The lithium-sulfur battery of the present embodiment includes a positive electrode for the lithium-sulfur battery of the present embodiment as a positive electrode, and the other configurations are not particularly limited, and any known device other than the positive electrode for the lithium-sulfur battery may be known. good.
For example, the lithium-sulfur battery of the present embodiment includes a separator, a positive electrode for the lithium-sulfur battery of the present embodiment arranged to face each other via the separator, a negative electrode, an electrolytic solution in contact with them, and an exterior body. To be equipped.
The lithium-sulfur battery of the present embodiment has an electrode body including a negative electrode and a positive electrode arranged as described above, and an exterior body for accommodating the electrode body, and an electrolytic solution is injected into a space inside the exterior body to seal the battery. Can be obtained by doing.

The negative electrode can be manufactured by forming a negative electrode layer containing a negative electrode active material on a current collector in the same manner as the positive electrode.
The current collector of the negative electrode is not particularly limited as long as it enables electrical connection of the electrodes, and the material thereof is not limited to the following, but for example, copper, aluminum, nickel, and titanium. And stainless steel. Of these, copper is preferable from the viewpoint of easy processing into a thin film and from the viewpoint of cost. Examples of the shape of the current collector include a foil shape, a perforated foil shape, and a mesh shape. Further, as the current collector, a porous material such as porous metal (foamed metal) and carbon paper can also be used.
The negative electrode active material may be any material containing lithium, and examples thereof include lithium oxide, lithium composite oxide, lithium sulfide, and lithium composite sulfide, in addition to metallic lithium or lithium alloy. Examples of the lithium alloy include an alloy of aluminum or silicon, tin, magnesium, indium, calcium and the like with lithium. The negative electrode active material is preferably metallic lithium or an alloy of silicon and lithium.
The negative electrode may be metallic lithium or a lithium alloy itself. For example, a negative electrode active material is mixed with a conductive material such as graphite, acetylene black, or Ketjen black and a binder, and an appropriate solvent is added to form a paste. The negative electrode material may be applied and dried on the surface of the current collector, and if necessary, compressed to increase the electrode density.

The electrolytic solution can be prepared by dissolving a lithium-containing electrolyte in a non-aqueous solvent.
Examples of the lithium-containing electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF (CF ₃ ) ₅ , LiCF ₂ (CF ₃ ) ₄ , LiCF ₃ (CF ₃ ) ₃ , LiCF ₄ (CF ₃ ) _2. , LiCF ₅ (CF ₃ ), LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO ) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ , lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI).
One of these may be used alone, or two or more thereof may be mixed and used. Among them, LiPF ₆ , LiFSI, and LiTFSI are preferable, and LiTFSI is more preferable.
Further, the concentration of these lithium salts is preferably 0.1 to 3.0 mol / L, more preferably 0.5 to 2.0 mol / L.

Examples of the non-aqueous solvent include carbonates, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, nitro compounds, and phosphate ester compounds. , Sulfolane-based hydrocarbons, and ionic liquids can be appropriately selected.
In particular, carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), fluoroethylene carbonate (FEC); dimethoxyethane (DME), triglime (G3) and tetraglime. Ethers such as (G4); cyclic ethers such as dioxolane (DOL) and tetrahydrofuran; 1,1,2,2-tetrafluoro-3- (1,1,2,2-tetrafluoroethoxy) -propane (HFE) , And a mixture thereof are suitable. A solvent containing carbonates is more preferable, and a mixture of (FEC) and (HFE) is more preferable.

The material or shape of the separator is not particularly limited as long as it is used for a normal lithium-sulfur battery. This separator separates the positive electrode and the negative electrode so that they do not physically contact each other, and preferably has high ion permeability.
Examples of the separator include a synthetic resin microporous membrane, a woven fabric, a non-woven fabric, and the like, and a synthetic resin microporous membrane is preferable. Examples of the material of the synthetic resin microporous film include polyolefins such as polyethylene, polypropylene, and polybutene; and further, polyamide, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, and polyvinylidene fluoride.
Of these, polyethylene and polypropylene are preferred. If the structure is such that the positive electrode and the negative electrode of the lithium-sulfur battery to be manufactured are not in direct contact with each other, it is not necessary to use a separator.

The structure of the electrode body of the lithium-sulfur battery of the present embodiment is not particularly limited, but usually, the positive electrode and the negative electrode and the separator provided as needed are wound in a flat spiral shape to form a wound electrode group. Alternatively, it is common to form a structure in which these electrode plates are enclosed in an exterior body by laminating them in a flat plate shape to form a laminated electrode plate group.

As the exterior body, a metal can, a laminated film, or the like can be used.
The metal can is preferably made of aluminum. In this case, for example, the metal can is used as the negative electrode terminal, and the metal lid crimped on the metal can with the insulator sandwiched therein is used as the positive electrode terminal. The electrode body and the terminal are electrically connected by the electrode tab.
Further, as the laminated film, a film in which a metal foil and a resin film are laminated is preferable, and a three-layer structure composed of an outer layer resin film / metal foil / inner layer resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be preferably used.
The metal foil is for preventing the permeation of moisture and gas, and a foil of copper, aluminum, stainless steel or the like can be preferably used. Further, the inner layer resin film is for protecting the metal foil from the electrolytic solution stored inside and for melting and sealing at the time of heat sealing, and polyolefins, acid-modified polyolefins and the like can be preferably used.
When a laminated film exterior body is used, the peripheral edge portion of the laminated film is sealed with the end portions of the electrode terminals pulled out into the external space of the exterior body. The sealing method is preferably heat sealing.

The lithium-sulfur battery of the present embodiment may have a form such as a paper type battery, a button type battery, a coin type battery, a laminated type battery, or a cylindrical type battery.

Hereinafter, the present embodiment will be described in more detail with reference to specific examples and comparative examples, but these are exemplary, and the present embodiment is limited by the following examples and comparative examples. It's not something.
Therefore, those skilled in the art can implement the present invention by making various modifications to the examples shown below, and such modifications are included in the present invention.

[Analysis method]
(CHN analysis method)
A nitrogen-containing carbon material was used as a measurement sample.
CHN analysis was performed by filling a sample table with 2500 μg of a sample using an elemental analyzer (trade name “MICRO CORDER JM10”) manufactured by J-Science Lab.
The temperature of the sample furnace is 950 ° C, the temperature of the combustion furnace (copper oxide catalyst) is 850 ° C, and the temperature of the reduction furnace (consisting of silver grains + copper oxide zone, reduced copper zone and copper oxide zone) is 550 ° C. Set to.
The oxygen flow rate was set to 15 mL / min and the He flow rate was set to 150 mL / min.
A thermal conductivity detector (TCD) was used as the detector.
Calibration was performed using Antipyrine by the method described in the manual.
The content of oxygen element (mass%) was calculated by subtracting the content (mass%) of carbon element, nitrogen element, and hydrogen element from 100% by mass.

(Measurement method of specific surface area / pore volume)
A porous carbon material was used as a measurement sample.
Using AUTOSORB iQ manufactured by Quantachrome, the specific surface area was measured by the BET method, and the pore distribution and pore volume were measured by the quenching solid phase density function method (QSDFT).
Specifically, the sample was evacuated at 100 ° C. for 3 hours for measurement.
The adsorption isotherm of nitrogen was measured at the temperature of liquid nitrogen, and the specific surface area, pore volume, and pore distribution were measured.

(Measurement method of X-ray photoelectron spectroscopy (XPS))
Nitrogen-containing carbon material and porous carbon material were used as measurement samples.
Using JEOL's JPS-9010MC, the powder cell was filled and measured under the following conditions.
X-ray source: Mg tube (Mg-Kα ray), tube voltage: 12 kV, emission current: 50 mA, analysis area: Φ600 μm, uptake area: N1s, C1s, O1s Pass-Energy: 10 eV.
The obtained spectrum was energy-corrected at the peak position of C1s.
The total content (mass%) of carbon element, nitrogen element, and oxygen element was set to 100% by mass.

(Measurement method of laser Raman spectrum)
A porous carbon material was used as a measurement sample.
Tokyo Instruments Inc. Using a 3D microlaser Raman spectroscope Nanofinder30 manufactured by the same company, the cells were filled in a powder cell and measured under the following conditions.
LD-excited solid-state laser λ: 532 nm 47 mW Measurement conditions 532 nm, irradiation 2.34 mW, exposure time 10 seconds, integration 10 times, Greating 600 G / mm.
Let P1 be the peak between 1250 to 1385 cm ^-1.
Let P2 be the peak between 1550 and 1620 cm ^-1.
Let L be the height from the baseline of the minimum point M between P1 and P2.
Let the height of P1 from the baseline be H1.
Let the height of P2 from the baseline be H2.

(SEM measurement method)
Porous carbon materials and composite materials were measured.
A scanning microscope (Su-1500 manufactured by Hitachi, Hitachi High-Tech Solutions) was used.
Conductive carbon tape was used on an aluminum sample table, and each powder sample was attached and installed in the chamber.
After evacuating the inside of the chamber, the sample was observed at a working distance of 15 mm and an acceleration voltage of 15 kV. The average particle size and aspect ratio of the porous carbon material were measured. No aggregation _{of MnO 2 was} observed in the observation of the composite material.

(Measuring method of sulfur content)
Measurement of the sulfur content in a composite material composed of a porous carbon material and sulfur and a metal oxide, and a composite composed of a porous carbon material and sulfur is performed using thermogravimetric analysis (TG) as follows. I went by the method of.
Using DTG-60AH manufactured by Shimadzu Corporation, 10 mg of the sample was placed in the cell, and the measurement gas Ar, the flow rate 50 mL / min, the starting temperature 30 ° C., and the heating rate 5 ° C./min. , And the measurement was carried out under the condition of the upper limit temperature of 600 ° C.
A method for calculating the sulfur content from the obtained thermogravimetric analysis (TG) will be described with reference to [Example 1] in FIG.
In the graph of thermogravimetric analysis (TG), the mass decreases with increasing temperature, which corresponds to the sublimation of sulfur filled in the pores. In the region of 300 ° C. to 500 ° C., a point where the slope of the tangent line of the graph changes discontinuously appears. This corresponds to the fact that only the porous carbon material and the metal oxide remain at this point.
Assuming that the mass% of the initial value is 100 and the mass% of the point where the slope of the tangent line of the graph changes discontinuously is X, the sulfur content Y is the porous carbon material and the metal oxide from the initial value (100). Since it is a value obtained by subtracting the ratio of the total values of, it is defined as Y = 100-X.
In Example 1, X = 52, Y = 48, and the sulfur content Y is 48% by mass.
The sulfur content was calculated in the same manner in Example 2 and Comparative Examples 1 and 2.

[Manufacturing of lithium-sulfur batteries]
(Making a positive electrode for a lithium-sulfur battery)
Carboxymethyl cellulose (CMC) (dispersant) was dissolved in pure water to prepare a 2% by mass solution.
Acetylene black (conductive auxiliary agent) is added thereto, and then the active material (composite material composed of the porous carbon material produced in Examples 1 and 2 described later and sulfur and metal oxide, Comparative Examples 1 and 2) is added. A composite of the porous carbon material produced in 1 and sulfur) and styrene-butadiene rubber (SBR) (binding material) were added to prepare a positive electrode slurry.
The mass ratio of the active material, the conductive auxiliary agent, the dispersant, and the binder was set to be active material: conductive auxiliary agent: dispersant: binder = 84:10: 3: 3.
The obtained positive electrode slurry was filled in an Al current collector foil so that the amount of active material was about 2.0 mg / cm ^2.
Then, it was dried under atmospheric pressure in an oven at 40 ° C. for 1 hour.
After drying, the dried product was pressure-molded through a roll press, punched to a size of Φ12 mm with a punch, and dried in an oven at 50 degrees under vacuum to obtain a positive electrode for a lithium-sulfur battery. The thickness of the positive electrode layer was about 75 μm.

(Manufacture of negative electrode for lithium-sulfur battery)
In an air atmosphere with a dew point of −40 ° C. or lower, a Li foil having a thickness of 200 μm was punched out with a punch having a thickness of Φ13 mm to obtain a negative electrode for a lithium-sulfur battery.

(Making a lithium-sulfur battery)
A lithium-sulfur battery was produced by the following procedure in an air atmosphere with a dew point of −40 ° C. or lower.
Positive electrode prepared by the above item (preparation of positive electrode for lithium-sulfur battery), negative electrode prepared by the above item (preparation of negative electrode for lithium-sulfur battery), bis (trifluorosulfonyl) imide (LiTFSI) as lithium-containing electrolyte, non-water As a solvent, a mixed solvent of tetraglime (G4) / 1,1,2,2-tetrafluoro-3- (1,1,2,2-tetrafluoroethoxy) -propane (HFE) was used.
Regarding the preparation of the electrolytic solution, G4: HFE was mixed at a substance amount of 8:40, LiTFSI was dissolved in a mixed solvent of G4 and HFE, and the electrolytic solution was prepared so as to have a concentration of 1.0 mol / L.
A polypropylene-based microporous membrane was used as the separator.
A two-pole flat cell was used as a cell, and a positive electrode, a separator, and a negative electrode were housed in the cell so as to be laminated in this order, and an electrolytic solution was further injected to prepare a lithium-sulfur battery.

[Charge / discharge test]
A constant current charge / discharge test was performed using the active material (positive electrode) as the working electrode.
The charging mode is C.I. C. According to the method (CC is an abbreviation for constant curent), C.C. is used at the time of discharge. C. It was set to the mode.
The set current density was 167.2 mA / g (current density 1672 mA / g is defined as 1C. Hereinafter, 167.2 mA / g is referred to as 0.1C).
Regarding the cutoff voltage, the lower limit was 1.0 V and the upper limit was 3.0 V.
The charge / discharge test was performed in an environment of 25 ° C.
Charge capacity and discharge capacity were defined per mass of sulfur.
The cycle efficiency was calculated by the following formula.
Cycle efficiency (%) = ((charge capacity (mAh / g-sulfur)) / (discharge capacity (mAh / g-sulfur))) × 100

[Production example of nitrogen-containing carbon material]
(Manufacturing of azulmic acid)
An aqueous solution prepared by dissolving 150 g of hydrocyanic acid in 350 g of water was prepared in a container, 120 g of a 25% aqueous ammonia solution was added over 10 minutes while stirring the aqueous solution, and the obtained mixed solution was heated to 35 ° C. Then, the polymerization of hydrocyanic acid started, the blackish brown polymer started to precipitate, and the temperature gradually increased to 45 ° C.
Two hours after the start of the polymerization, a 30 mass% hydrocyanic acid aqueous solution was started to be added at a rate of 200 g / hour, and 800 g was added over 4 hours.
During the addition of the hydrocyanic acid aqueous solution, the container was cooled and controlled so that the reaction temperature was maintained at 50 ° C. The polymerization reaction solution was stirred at this temperature for 100 hours.
The obtained black precipitate was separated by filtration. The yield of the precipitate at this time was 96% by mass with respect to the total amount of hydrocyanic acid used. The precipitate after separation was washed with water and then dried in a dryer at 120 ° C. for 4 hours to obtain azulmic acid.
The obtained azulmic acid was subjected to CHN analysis by filling a sample table with 2500 μg of the azulmic acid sample using an elemental analyzer (trade name “MICRO CORDER JM10”) manufactured by J-Science Lab.
The temperature of the sample furnace is 950 ° C, the temperature of the combustion furnace (copper oxide catalyst) is 850 ° C, and the temperature of the reduction furnace (consisting of silver grains + copper oxide zone, reduced copper zone and copper oxide zone) is 550 ° C. Set to. The oxygen flow rate was set to 15 mL / min and the He flow rate was set to 150 mL / min. A thermal conductivity detector (TCD) was used as the detector.
Calibration was performed using Antipyrine by the method described in the manual.
As a result, the composition of the azulmic acid obtained as described above was 40.0% by mass of the carbon element, 29.8% by mass of the nitrogen element, and 4.1% by mass of the hydrogen element.
Here, since the adsorbed water remains under the above-mentioned drying conditions, it is considered that the difference is mainly derived from the oxygen element and the hydrogen element in the adsorbed water.

[Manufacturing of nitrogen-containing carbon materials]
6.7 g of azulmic acid obtained as described above was filled in a quartz tube having an inner diameter of 25 mm, and 500 Ncc / min. The temperature was raised to 800 ° C. over 1 hour and 20 minutes in the nitrogen stream of the above, held at 800 ° C. for 1 hour for carbonization, and then pulverized with a planetary ball mill to obtain a nitrogen-containing carbon material.
<CHN analysis method>
The CHN analysis results of the nitrogen-containing carbon material are shown in Table 1 below.
<XPS analysis method>
The XPS analysis results of the nitrogen-containing carbon material are shown in Table 1 below.

[Manufacturing of porous carbon material]
2 g of the nitrogen-containing carbon material obtained in the above-mentioned [Production of nitrogen-containing carbon material] was added to 20 mL of a mixed solution of potassium hydroxide and pure water, and water was removed at 100 ° C. with stirring to prevent precipitation. ..
Then, the sample was transferred to a quartz boat, placed in a quartz tube of a horizontal tubular furnace, argon gas was flowed at a flow rate of 500 Ncc / min, and the gas was exchanged by leaving it for 5 minutes. After the replacement, the temperature was raised to 150 ° C. over 15 minutes, and the contents were dried by heat treatment at 150 ° C. for 1 hour.
Then, the temperature was raised to 800 ° C. over 1 hour, heat treatment was performed for 1 hour, and then the temperature was lowered to recover the contents.
The contents were washed with 0.3 L of water, further washed with 0.5 L of 1 mol / L hydrochloric acid aqueous solution, then washed with water until the furnace liquid became almost neutral, collected by filtration, and dried. A porous carbon material was obtained.
This operation was repeated to mass-produce the porous carbon material. The average particle size was about 5 to 10 μm and the aspect ratio was about 1.5 or less when observed by SEM.
<XPS analysis>
The XPS analysis results of the porous carbon material are shown in Table 2 below.
The rate of decrease in nitrogen content was 85% by mass (= ((14.59-2.19) /14.59) × 100).
<Measurement of specific surface area and pore volume>
Table 2 below shows the measurement results of the specific surface area and pore volume of the porous carbon material.
<Raman analysis>
The Raman analysis results of the porous carbon material are shown in FIG. 3, and the analysis results are shown in Table 2.

[Example 1]
<Manufacturing of composite material composed of porous carbon material, sulfur and MnO _2>
Using 0.43 g of the porous carbon material produced as described above, the porous carbon material, sulfur, and MnO ₂ (Fujifilm Wako Pure Chemical Industries, Ltd., manganese oxide (IV), 99.5%) were added by mass ratio. Then, the porous carbon material: sulfur: MnO ₂ = 40: 60: 20 was mixed in a dairy pot for 10 minutes, placed in a closed container having an inner diameter of 20 mm and a height of 60 mm, and held at 155 ° C. for 5 hours to melt the sulfur. The pores of the alkali-activated activated carbon were filled with the capillary phenomenon, and then the temperature was raised to 300 ° C. and held for 2 hours to evaporate and remove the residual sulfur.
After air cooling to room temperature, the container was opened to obtain a porous carbon material, a composite material composed of _{sulfur and MnO 2.}
All compounding steps were performed in the atmosphere.
<Measurement of sulfur content>
The sulfur content of the obtained porous carbon material and the _{composite material composed of sulfur and MnO 2} was measured by thermogravimetric analysis (TG). The measurement results are shown in FIGS. 2 and 3.
<Making lithium-sulfur batteries>
A lithium-sulfur battery was prepared according to [Preparation of Lithium-Sulfur Battery].
<Charge / discharge test>
The above-mentioned [charge / discharge test] was carried out at 0.1 C. The charge / discharge curves of the first cycle and the 80th cycle are shown in FIG. The evaluation result of the cycle characteristics is shown in FIG.

[Comparative Example 1]
<Manufacturing of composite composed of porous carbon material and sulfur>
A composite composed of a porous carbon material and sulfur was obtained in the same manner as in [Example 1] except that _{MnO 2 was not added.}
<Measurement of sulfur content>
The sulfur content of the obtained composite of the porous carbon material and sulfur was measured by thermogravimetric analysis (TG). The measurement results are shown in FIGS. 2 and 3.
<Making lithium-sulfur batteries>
A lithium-sulfur battery was prepared according to [Preparation of Lithium-Sulfur Battery].
<Charge / discharge test>
The above-mentioned [charge / discharge test] was carried out at 0.1 C. The charge / discharge curves of the first cycle and the 80th cycle are shown in FIG. The evaluation result of the cycle characteristics is shown in FIG.

[Example 2]
<Manufacturing method of composite material composed of porous carbon material, sulfur and MnO _2>
Add 1.8 g of porous carbon material and about 90 zirconia balls (about 36 g) with a diameter of 5 mm to an 80 cc tungsten carbide container, and use a planetary ball mill (Classic Line P-5 manufactured by FRITSCH) at 400 rpm in an atmospheric atmosphere. The mixture was pulverized for 4 hours to obtain a pulverized porous carbon material. The average particle size was about 1 to 3 μm and the aspect ratio was about 1.5 or less when observed by SEM. 0.43 g was taken out from the porous carbon material obtained in this step. A composite material composed of the _{porous carbon material, sulfur, and MnO 2} was obtained in the same manner as in the above [Example 1] except that the porous carbon material obtained in this step was used.
<Measurement of sulfur content>
The sulfur content of the porous carbon material obtained in this step and the _{composite material composed of sulfur and MnO 2} was measured by thermogravimetric analysis (TG). The measurement results are shown in Table 3.
<Making lithium-sulfur batteries>
A lithium-sulfur battery was prepared according to [Preparation of Lithium-Sulfur Battery].
<Charge / discharge test>
The above-mentioned [charge / discharge test] was carried out at 0.1 C. The evaluation result of the cycle characteristics is shown in FIG.

[Comparative Example 2]
<Manufacturing method of composite composed of porous carbon material and sulfur>
A composite composed of a porous carbon material and sulfur was obtained in the same manner as in [Example 2] except that _{MnO 2 was not added.}
<Measurement of sulfur content>
The sulfur content of the obtained composite of the porous carbon material and sulfur was measured by thermogravimetric analysis (TG). The measurement results are shown in Table 3.
<Making lithium-sulfur batteries>
In [Preparation of Lithium-Sulfur Battery] (Preparation of positive electrode of lithium-sulfur battery), "Organic binder (binding agent) is dimethyl" instead of "Dissolve water-based binder (binding material) in pure water". A lithium-sulfur battery was produced in the same manner as in [Comparative Example 1], except that "dissolved in formamide".
<Charge / discharge test>
The above-mentioned [charge / discharge test] was carried out at 0.1 C. The evaluation result of the cycle characteristics is shown in FIG.

From FIG. 5, the composite material composed of the porous carbon material of Example 1 and sulfur and metal oxide is composed of the porous carbon material of Comparative Example 1 and sulfur when used as a positive electrode of a lithium-sulfur battery. It was found that the lithium-sulfur battery has a larger discharge capacity per sulfur mass when the cycle is repeated than the composite, and can realize excellent cycle characteristics.

The composite material composed of the porous carbon material of the present invention and sulfur and metal oxide has industrial applicability as an active material for the positive electrode of a lithium-sulfur battery.
Further, the method for producing a composite material composed of a porous carbon material and sulfur and a metal oxide of the present invention can be industrially used as a simple method for producing a composite material used as an active material for a positive electrode of a lithium-sulfur battery. There is sex.

Claims (9)

A composite material for the positive electrode of lithium-sulfur batteries
Contains porous carbon materials, sulfur, and metal oxides
The porous carbon material has a nitrogen content of 0.3% by mass or more, a specific surface area obtained by the BET method of the nitrogen adsorption / desorption method of 1000 m ² / g or more, and a quenching solid phase density function method (QSDFT). The pore volume obtained by the ^{above is 0.45 cm 3} / g or more.
Composite material. The composite material according to claim 1, wherein the metal oxide is one or more kinds of oxides selected from the group consisting of Mn and Ti. A positive electrode for a lithium-sulfur battery containing the composite material according to claim 1 or 2. A lithium-sulfur battery comprising the positive electrode according to claim 3. The method for producing a composite material according to claim 1 or 2.
The nitrogen content is 0.3% by mass or more, the specific surface area obtained by the BET method of the nitrogen adsorption / desorption method is 1000 m ² / g or more, and the pore volume obtained by the quenching solid phase density function method (QSDFT) is 0.45 cm. A step of mixing a porous carbon material having a surface area of ^{3 / g or more, sulfur, and a metal oxide.}
The step of melting the sulfur and filling the porous carbon material with
Have, have
Method for manufacturing composite materials. It has an activation step of obtaining the porous carbon material by activating the nitrogen-containing carbon material.
In the activation step,
Equation (I) below:
Nitrogen content reduction rate (mass%) = ((BA) / B) x 100 (I)
(In the formula (I), A is the nitrogen content (mass%) measured by XPS in the porous carbon material, and B is the nitrogen content (mass) measured by XPS in the nitrogen-containing carbon material. %).)
The rate of decrease in nitrogen content as defined in is 30-99% by weight.
The method for producing a composite material according to claim 5. The method for producing a composite material according to claim 6, wherein the nitrogen content in the nitrogen-containing carbon material is 2 to 45% by mass. The method for producing a composite material according to claim 6 or 7, wherein the activation is chemical activation. The method for producing a composite material according to any one of claims 5 to 8, wherein the metal oxide is one or more kinds of oxides selected from the group consisting of Mn and Ti.

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