JP7328865B2 - Porous carbon material, method for producing porous carbon material, composite, method for producing composite, positive electrode for lithium-sulfur battery, and lithium-sulfur battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous carbon material, a method for producing a porous carbon material, a composite, a method for producing a composite, a positive electrode for a lithium-sulfur battery, and a lithium-sulfur battery.

Porous carbon materials, typified by activated carbon, are used for wastewater treatment, decolorization, and purification in the liquid phase, and air purification, deodorization, gas separation, and solvent recovery in the gas phase, using their adsorption and separation performance. ing.
Porous carbon materials are also used as catalyst carriers or as active materials for electric double layer capacitors by utilizing their porosity.

Lithium secondary batteries, on the other hand, use organic electrolytes of lithium salts as non-aqueous electrolytes, are lightweight and have high energy density, and are used as power sources for mobile phones and laptop computers. It is also expected to be used as a power source for mobile vehicles such as electric vehicles.
Therefore, in recent years, there has been an increasing demand for batteries with higher capacity densities and lower costs.

Metal oxides containing Co, Ni, Mn, Fe, etc. and Li are generally used as positive electrode active materials for lithium ion secondary batteries. Lithium-sulfur batteries using sulfur as a positive electrode active material, which has an extremely high capacity density and is low in cost, are being developed.

A lithium-sulfur battery is a secondary battery that uses a sulfur-based compound as a positive electrode active material, and a material that causes insertion and extraction of metal ions such as alkali metals such as lithium or lithium ions, such as silicon, as a negative electrode active material.
Since the redox reaction of sulfur is reversible and the number of reactive electrons is large, it has a high theoretical capacity of 1672 mAh/g, which is about 10 times that of the 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 composed of lithium and sulfur has poor electrical conductivity, electrons can only be given and received at the part near the surface, and the utilization rate of sulfur involved in the electrochemical redox reaction is low. However, there is a problem that the battery capacity becomes low.
In addition, due to the reaction during charging and discharging, the lithium polysulfide represented by the formula Li ₂ S _x (where x is 4 to 8) is eluted into the electrolytic solution, resulting in loss of sulfur present on the positive electrode. As a result, there is a problem that the capacity of the lithium-sulfur battery decreases. In order to prevent such a decrease in the capacity of the lithium-sulfur battery, it is desirable to stop the elution _{of Li2Sx} .

As a technique for solving the above-described problems, a technique for compounding a carbon material, which is a conductive material, and sulfur has been proposed.
As the conductive material, conductive polymers are also known in addition to carbon materials. It is attracting attention because it is flammable.

As a technique for obtaining a composite of a carbon material and sulfur and using it as a positive electrode material, for example, sulfur and/or sulfur compound particles having a particle diameter of 75 μm or less and predetermined carbon fine particles having a hollow structure are used. A technology for obtaining a composite having a configuration in which particles of sulfur and/or sulfur compounds are used as raw materials and composited by mechanofusion, and having a carbon fine particle layer on the surface thereof, and the composite is used as a positive electrode material. is disclosed (see, for example, Patent Documents 1 and 2).

Also, sodium thiosulfate is dissolved in water, acetic anhydride is added to make an aqueous solution, carbon black is added and mixed, the aqueous solution is mixed by a mechanochemical method, the supernatant is removed by centrifugation and filtration, and the filter residue is removed. is obtained as a carbon black-sulfur nanoparticle composite, and the composite is disclosed as a positive electrode material for lithium-sulfur batteries (see, for example, Patent Document 3).
Such a technique is a technique for obtaining a composite by reacting by applying strong shear stress and centrifugal force to combine a carbon material and sulfur.

Further, a technique for producing a composite material composed of activated carbon containing 31% sulfur by heating sulfur and activated carbon at 155° C. for 5 hours has been disclosed (see, for example, Non-Patent Document 1).

Furthermore, a technique of chemically activating a nitrogen-containing carbon material, using a nitrogen-containing porous carbon material as the carbon material, and combining it with sulfur has been disclosed (see, for example, Patent Document 4).

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

JP-A-2006-92881 JP-A-2006-92883 JP 2012-204332 A JP 2018-39685 A

Progress in Natural Science: Materials International, 25, 612-621 (2015)

However, as described in Patent Documents 1 and 2, lithium sulfur using as a positive electrode material a composite having a configuration in which particles of sulfur and/or sulfur compounds formed by combining by mechanofusion are used as nuclei and a carbon fine particle layer is formed on the surface. Batteries suffer from low sulfur utilization and low capacity per mass of sulfur because most of the sulfur is either deposited on the outer surface of the carbon material or exists as free sulfur. Furthermore, there is a problem that the cycle characteristics are remarkably low due to elution of sulfur.

In addition, the technology described in Patent Document 3 has a small capacity per mass of sulfur and a low sulfur content of 22.9% by mass, so the capacity per mass of the positive electrode material containing sulfur and a carbon material is low. It has the problem of being small. In addition, there is a problem that the cycle characteristics of lithium-sulfur batteries containing the composite obtained by the technology described in Patent Document 3 as a positive electrode material are also insufficient for practical use (Fig. 10).

Furthermore, the lithium-sulfur battery using the positive electrode material described in Non-Patent Document 1 has a relatively large capacity per sulfur mass, but the sulfur content is 31% by mass, so the positive electrode material containing sulfur and a carbon material. However, it has a problem of low capacity per mass. In addition, there is also the problem that the manufacturing method of the positive electrode material described in Non-Patent Document 1 is complicated.

Furthermore, the composite obtained by the technique described in Patent Document 4 has a larger amount of sulfur supported than the composite 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 mass of sulfur and the capacity per positive electrode material containing sulfur and carbon materials are large. In addition, it has the advantage of excellent cycle characteristics using a tetraglyme (G4) solvent as the electrolyte.
However, it has a problem of insufficient cycle characteristics. Moreover, there is no disclosure of cycle characteristics using a carbonate solvent, which is a commonly used solvent.

Therefore, in the present invention, in view of the above-described problems of the conventional technology, a porous positive electrode material having a large discharge capacity per sulfur mass, a large discharge capacity per positive electrode material containing sulfur and a carbon material, and excellent cycle characteristics An object is to provide a carbon material, a composite of the porous carbon material and sulfur, a positive electrode for a lithium-sulfur battery using the composite, and a lithium-sulfur battery using the positive electrode.

The inventors of the present invention have made intensive studies to achieve the above object, and as a result, have found that a porous carbon material having a specific nitrogen content and a specific structure can solve the above-described problems of the prior art. and completed the present invention.
That is, the present invention is as follows.

[1]
The nitrogen content is 0.2 to 2.0% by mass,
The specific surface area obtained by the BET method of nitrogen adsorption and desorption is 1000 to 1800 m ² /g,
The pore volume obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption and desorption method is 0.50
~0.80 cm ³ /g ,
In the laser Raman spectrum diagram with a wavenumber of 800 to 1900 cm ^-1 ,
having a peak P1 between 1250 and 1385 cm ^-1 ,
having a peak P2 between 1550 and 1620 cm ^-1 ;
The height L from the baseline of the minimum point M between the P1 and P2 and the baseline of P1
The ratio of the height H1 from the (L/H1) is 0.25 to 0.54,
Porous carbon material.
[2]
The method for producing a porous carbon material according to [1] above,
a step of chemically activating the nitrogen-containing carbon material;
Having a step of heat-treating in an inert gas after the chemical activation,
A method for producing a porous carbon material.
[3]
The method for producing a porous carbon material according to [2] above, wherein the temperature of the heat treatment in the inert gas is 900° C. or higher.
[4]
The reduction rate of the nitrogen content in the chemical activation step is
Formula (I) below:
Reduction rate of nitrogen content (mass%) = ((B-A) / B) × 100 (I)
(In formula (I), A is the nitrogen content (% by mass) measured by XPS in the porous carbon material after the chemical activation step , and B is the nitrogen content measured by XPS in the nitrogen-containing carbon material. is the nitrogen content (mass%) in
7. The method for producing a porous carbon material according to the above [2] or [3] , wherein the content is 0 to 99% by mass.
[5]
The method for producing a porous carbon material according to any one of [2] to [4] above, wherein the nitrogen content in the nitrogen-containing carbon material is 2 to 45% by mass.
[6]
The method for producing a porous carbon material according to any one of [2] to [5] above, wherein the chemical activation is alkali activation.
[7]
A composite of the porous carbon material according to [1] and sulfur.
[8]
The composite according to [7] above, wherein the sulfur content is 40 to 70% by mass.
[9]
The method for producing the composite according to [7] or [8] above,
A mixing step of mixing the porous carbon material and sulfur heated to a temperature equal to or higher than the melting point;
A method for manufacturing a composite.
[10]
A positive electrode for a lithium-sulfur battery containing the composite according to [7] or [8] .
[11]
A lithium-sulfur battery comprising the positive electrode according to [10] above.

According to the present invention, in a lithium-sulfur battery having a positive electrode for a lithium-sulfur battery using a composite of a porous carbon material and sulfur, the discharge capacity per sulfur mass is large, and the discharge capacity per positive electrode material is large and excellent cycle characteristics can be realized.
According to the present invention, a porous carbon material for a lithium-sulfur battery having the above characteristics, a composite of the porous carbon material and sulfur, a positive electrode for a lithium-sulfur battery using the composite, and using the positive electrode A lithium sulfur battery is obtained.

FIG. 2 is an explanatory diagram of a method for calculating heights (H1, H2) from peaks and height (L) from minimum value M from laser Raman spectrum diagrams of porous carbon materials. 4 is a graph of thermogravimetric analysis (TG) when measuring the sulfur content of the composite of the porous carbon material and sulfur of Example 1. FIG. 4 is a graph showing pore distributions of porous carbon materials obtained in Comparative Example 1 and Examples 1 to 3. FIG. 1 is a laser Raman spectrum diagram of porous carbon materials obtained in Comparative Example 1 and Examples 1 to 3. FIG. 5 is a graph showing cycle characteristics of discharge capacity of Comparative Example 1 and Examples 1 to 3. FIG. 1 is a scanning electron microscope (SEM) image of the porous carbon material of Example 1.

EMBODIMENT OF THE INVENTION Hereinafter, the form (only henceforth "this embodiment") for implementing this invention is demonstrated in detail, referring drawings as needed.
The present embodiment is an example for explaining the present invention, and the present invention is not limited only to the embodiment. That is, the present invention can be modified in various ways without departing from the scope of the invention.

[(A) Porous carbon material]
The porous carbon material of this embodiment is
The nitrogen content is 0.2 to 2.0% by mass,
The specific surface area obtained by the BET method of nitrogen adsorption and desorption is 1000 to 1800 m ² /g,
The pore volume obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption/desorption method is 0.50 to 0.80 cm ³ /g.
Since the porous carbon material of the present embodiment has the above-described configuration, a lithium-sulfur battery including a positive electrode for a lithium-sulfur battery using a composite in which the porous carbon material and sulfur are combined can realize a large discharge capacity per mass of sulfur, a large discharge capacity per positive electrode material, and excellent cycle characteristics.

(Method for producing porous carbon material)
The method for producing a porous carbon material according to the present embodiment includes a step of chemically activating a nitrogen-containing carbon material, and a step of heat-treating in an inert gas after the chemical activation.
A nitrogen-containing carbon material is an X-ray diffraction pattern (XRD) obtained using CuKα rays as an X-ray source, and the peak position of the diffraction angle (2θ) is 22.5 to 26.8° derived from the (002) plane. The material has a main peak at 43.0-46.0°, and a weak peak is observed at 44.0-45.5°.
For example, a nitrogen-containing carbon material can be obtained by applying a heat history of 600° C. or higher using an organic compound as a raw material.
The nitrogen-containing carbon material used in this embodiment may contain other atoms such as oxygen and hydrogen in addition to carbon and nitrogen.

The present inventors have found that the nitrogen content is 0.2 to 2.0% by mass by chemically activating a nitrogen-containing carbon material and heat-treating it in an inert gas after chemical activation, and the nitrogen adsorption/desorption method BET The specific surface area obtained by the method is 1000 to 1800 m ² /g, and the pore volume obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption and desorption method is 0.50 to 0.80 cm ³ /g. By obtaining a porous carbon material and using the composite of the porous carbon material and sulfur as a positive electrode material for a lithium-sulfur battery, the discharge capacity per mass of sulfur, the positive electrode material containing sulfur and the carbon material It was found that the discharge capacity per unit was large and that the battery had excellent cycle characteristics.
Having excellent cycle characteristics means having a large discharge capacity after 100 cycles of charging and discharging.
The reason for this is not clear, but is presumed as follows. However, the present invention is not limited by this presumption. When pores are formed by chemically activating and heat-treating a nitrogen-containing carbon material, the nitrogen portion is preferentially removed, so micropores are preferentially formed, resulting in the formation of micropores when the chemical activation is performed. Possible defect structures are reduced by heat treatment in inert gas after chemical activation. It is considered that these effects are excellent when used as a positive electrode material for a lithium-sulfur battery.

In the present specification, the “pores” of “pore volume” are uniquely defined 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. Pores are referred to as micropores, pores with a pore diameter of more than 2 nm and 50 nm or less are referred to as mesopores, and pores with a pore diameter of more than 50 nm are referred to as macropores.

A composite of sulfur and a porous carbon material having pores generated by removing many nitrogen atoms from the nitrogen-containing carbon material obtained by chemical activation and heat treatment in an inert gas has few mesopores. Therefore, the elution of sulfur filled in the pores into the electrolyte is suppressed, and the pores are filled with sulfur, increasing the amount of sulfur that can transfer electrons, increasing the utilization rate of sulfur and increasing the capacity is increased and the cycle characteristics are improved.

<Nitrogen-containing carbon material and method for producing the same>
As described above, the method for producing a porous carbon material according to the present embodiment includes a step of chemically activating the nitrogen-containing carbon material and a step of heat-treating in an inert gas after the chemical activation.
The nitrogen-containing carbon material used in this embodiment is a carbon material containing nitrogen.
Nitrogen-containing carbon materials can be produced, for example, by polymerizing a low-molecular-weight nitrogen-containing organic compound as a raw material and carbonizing the resulting polymer, or by chemical vapor deposition (CVD) using a low-molecular-weight nitrogen-containing organic compound as a raw material. ), a method of impregnating or reacting a low-molecular-weight nitrogen-containing organic compound with a polymer and then carbonizing it, a method of carbonizing a natural product containing nitrogen, ammonium treatment of the carbide, It is obtained by a method of manufacturing by performing post-treatment such as ammoxidation treatment.
Specifically, pyrrole, acetonitrile, chemical vapor deposition of nitrogen-containing organic compounds such as 2,3,6,7-tetracyano-1,4,5,8-tetraazanaphthalene, melamine resin, urea resin, Aniline resin, polyacrylonitrile, azulmic acid, melem polymer, polypyrrole, polyimide, etc., or a method of carbonizing precursors obtained by mixing these with other polymers, a method of carbonizing beans, etc., activated carbon, etc. The nitrogen-containing carbon material can be produced by, for example, a method of reacting the carbon material with ammonia gas and an oxygen-containing gas.

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 this 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, even more 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, even more 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 tend 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 appropriately selecting the nitrogen content of the polymer used as the raw material.
For example, as a method of producing a nitrogen-containing carbon material with a high nitrogen content, a method of carbonizing a polymer with a high nitrogen content can be exemplified.
Specific examples include nitrogen-containing carbon materials produced by carbonizing azulmic acid, melem polymers, and polyacrylonitrile, and nitrogen-containing carbon materials produced by carbonizing azulmic acid are preferred.
Azulmic acid is a polymer obtained by polymerizing hydrocyanic acid or hydrocyanic acid oligomers. A hydrocyanic acid oligomer is a dimer or higher of hydrocyanic acid.
Conditions for the carbonization treatment of the polymer are, for example, using a rotary furnace, a tunnel furnace, a tubular furnace, a box furnace, a fluidized bed furnace, etc., and performing a heat treatment in an inert gas atmosphere. The temperature of the heat treatment is not particularly limited, but is preferably 600 to 1200°C, more preferably 700 to 1000°C, still more preferably 750 to 900°C.
Examples of the inert gas include, but are not limited to the following gases, inert gases such as nitrogen, argon, helium, and neon. Also, the inert gas atmosphere may be under reduced pressure, that is, a pressure environment lower than the atmospheric pressure. Among these, it is preferable to use nitrogen gas as the inert gas. In the inert gas atmosphere, the inert gas may be stationary or may be circulating, but is preferably circulating. 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 time is preferably 10 seconds to 100 hours, more preferably 5 minutes to 10 hours, even more preferably 15 minutes to 5 hours, and even more preferably 30 minutes to 2 hours.
In addition, when using an inert gas, the pressure during carbonization is preferably 0.01 to 5 MPa, more preferably 0.05 to 1 MPa, still more preferably 0.08 to 0.3 MPa, and even more preferably 0. 0.09 to 0.15 MPa.

<Step of Chemical Activation of Nitrogen-Containing Carbon Material>
Next, the step of chemically activating the nitrogen-containing carbon material will be described.
The chemical activation step is performed by mixing the nitrogen-containing carbon material with chemicals and heat-treating the mixture.
The chemicals used for chemical activation refer to chemicals that are solid at 25° C. and atmospheric pressure, their hydrates, and aqueous solutions.
Examples of chemicals include, but are not limited to, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali metal carbonates such as potassium carbonate and sodium carbonate; Sulfates of alkali metals; zinc chloride, calcium chloride, potassium sulfide, phosphoric acid, etc. Examples thereof include aqueous solutions and hydrates thereof.
One of these may be used alone, or two or more may be mixed and used.

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

In the chemical activation step, the amount of the chemical used relative to the nitrogen-containing carbon material is not particularly limited, but the chemical/nitrogen-containing carbon material (mass ratio) is preferably 0.1-10.
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.
Further, 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 develop sufficiently, and when it is 10 or less, over-activation can be prevented and breakage of the pore walls can be suppressed.

The atmosphere for chemical activation is preferably an inert gas atmosphere. Examples of inert gases include gases such as nitrogen, argon, helium, and neon.
The chemical activation treatment is not particularly limited, but is carried out at a temperature of, for example, 500-1100°C, more preferably 600-1000°C, still more preferably 700-900°C.
When the temperature of the chemical activation treatment is 500° C. or higher, the activation progresses sufficiently, 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 chemical activation treatment time 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 pressurized or reduced pressure is also possible.
As the activation furnace, a rotary furnace, a tunnel furnace, a tubular furnace, a box furnace, a fluidized bed sintering furnace, or the like can be used.

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

<Process of heat treatment after chemical activation>
After the chemical activation, heat treatment is performed in an inert gas to obtain the porous carbon material of the present embodiment.
Examples of the inert gas include, but are not limited to, inert gases such as nitrogen, argon, helium, and neon.
Also, the inert gas atmosphere may be under reduced pressure, that is, a pressure environment lower than the atmospheric pressure. Among these, it is preferable to use nitrogen gas as the inert gas.
In the inert gas atmosphere, the inert gas may be stationary or circulating, but preferably circulating.
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 pore volume within desired ranges. 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. Moreover, 1800 degrees C or less is preferable and 1600 degrees C or less is more preferable.

The heat treatment time is preferably 10 seconds to 100 hours, more preferably 5 minutes to 10 hours, even more preferably 15 minutes to 5 hours, still more preferably 30 minutes to 2 hours.
In addition, 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, and even more preferably 0.01 to 5 MPa when an inert gas is used. 09 to 0.15 MPa.
The heat treatment can be performed in the activation furnace described above.

The nitrogen content reduction rate in the chemical activation step is defined by the following formula (I).
Reduction rate of nitrogen content (mass%) = ((B-A) / B) × 100 (I)
(In 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. (% by mass).)
In this embodiment, the nitrogen content reduction rate is preferably 70 to 99% by mass.
The lower limit of the reduction rate of the nitrogen content is more preferably 75% by mass or more, and even more preferably 80% by mass or more.
The upper limit is more preferably 98% by mass or less, and even more preferably 95% by mass or less.
If the rate of decrease in the nitrogen content is 70% by mass or more, micropores develop, which is preferable.
A nitrogen content reduction rate of 99% by mass or less is preferable from the viewpoint of controlling the specific surface area and the pore volume within the desired ranges.
From the viewpoint of shortening the time required for the activation step and of allowing nitrogen to remain, the content is preferably 98% by mass or less.

<Physical properties of porous carbon material>
The porous carbon material of the present embodiment has a nitrogen content of 0.2 to 2.0% by mass, a specific surface area obtained by the BET method of nitrogen adsorption and desorption of 1000 to 1800 m ² /g, and a nitrogen adsorption and desorption method. It is a porous carbon material having a pore volume of 0.50 to 0.80 cm ³ /g obtained by a quenching solid phase density function method (QSDFT).
The nitrogen content of the porous carbon material of this embodiment is measured by X-ray photoelectron spectroscopy (XPS) under the following conditions.
[Measurement condition]
X-ray source: Mg tube (Mg-Kα ray), tube voltage: 12 kV, emission current: 50 mA, analysis area: Φ600 μm, capture area: N1s, C1s, O1s Pass-Energy: 10 eV
The obtained spectrum is energy-corrected at the peak position of C1s.
The nitrogen content is preferably 0.3 to 1.7 mass %, more preferably 0.4 to 1.5 mass %, still more preferably 0.5 to 1.0 mass %.

The porous carbon material of the present embodiment can be formed by removing nitrogen atoms from the nitrogen-containing carbon material during the chemical activation step of the nitrogen-containing carbon material, leaving a specific proportion of nitrogen atoms.
Although not wishing to be bound by theory, nitrogen atoms have an excellent affinity with sulfur atoms compared to carbon atoms due to the unpaired electron effect, so the porous carbon material obtained after the chemical activation step If the nitrogen content is adjusted to 0.2% by mass or more, sulfur can be effectively supported in the pores when forming a composite of the porous carbon material and sulfur. Conceivable.
Further, when the nitrogen content is adjusted to 2.0% by mass or less, as described above, it is believed that a porous carbon material having pores generated by the removal of many nitrogen atoms can be obtained. Therefore, it is considered suitable as a positive electrode material for lithium-sulfur batteries.

The oxygen content of the porous carbon material of the present embodiment is preferably 2 to 11 mass %, more preferably 5 to 10 mass %, still more preferably 6 to 9 mass %.

The specific surface area of the porous carbon material of the present embodiment is 1000 to 1800 m ² /g, preferably 1100 to 1680 m 2 /g, more preferably 1150 to 1600 m ² /g, still more preferably 1200 to 1600 ^{m 2} /g. 1400 m ² /g.
From the viewpoint of increasing the discharge capacity per mass of sulfur and the discharge capacity per positive electrode material and realizing excellent cycle characteristics, it should be 1000 to 1800 m ² /g.
The specific surface area of the porous carbon material can be controlled within the above numerical range by adjusting chemical activation conditions for the nitrogen-containing carbon material and heat treatment conditions in an inert gas.

The pore volume obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption/desorption method shall be 0.50 to 0.80 cm ³ /g, preferably 0.54 to 0.73 cm ³ /g. more preferably 0.56 to 0.70 cm ³ /g, still more preferably 0.58 to 0.68 cm ³ /g.
From the viewpoint of increasing the discharge capacity per mass of sulfur and the discharge capacity per positive electrode material and realizing excellent cycle characteristics, it should be 0.50 to 0.80 cm ³ /g.
The pore volume of the porous carbon material can be controlled within the above numerical range by adjusting chemical activation conditions for the nitrogen-containing carbon material and heat treatment conditions in an inert gas.

In the pore distribution diagram obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption and desorption method, the pore volume with a pore diameter of 0.6 to 1.1 nm is 0.150 to 0.290 cm ³ /g. is preferred, 0.160 to 0.270 cm ³ /g is more preferred, and 0.170 to 0.240 cm ³ /g is even more preferred.
The pore volume with a pore diameter of 0.6 to 1.5 nm is preferably 0.200 to 0.420 cm ³ /g, more preferably 0.240 to 0.410 cm ³ /g, more preferably 0.260 More preferably ~0.350 cm ³ /g.
The pore volume with a pore diameter of 0.6 to 2.0 nm is preferably 0.300 to 0.570 cm ³ /g, more preferably 0.350 to 0.510 cm ³ /g, more preferably 0.370 More preferably ~0.480 cm ³ /g.

The porous carbon material of the present ^{embodiment has at least two main peaks P1 between 1250 and 1385 cm -1 and} a peak P2 between 1550 and 1620 cm ^-1 in a laser Raman spectrum diagram with a wavenumber of 800 to 1900 cm -1. The ratio of the height L from the baseline of the minimum point M between P1 and P2 to the height H1 from the baseline of P1 (L/H1) is the discharge capacity per sulfur mass It is preferably 0.25 to 0.54 from the viewpoint of further increasing the discharge capacity per positive electrode material and realizing further excellent cycle characteristics.

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

P1 and P2 are two major peaks with Raman shifts between 1200 and 1700 cm ^-1 in the laser Raman spectrum diagram. P1 is the peak between 1250-1385 cm ^-1 and P2 is the peak between 1550-1620 cm ^-1 .

(L/H1) is preferably 0.30 to 0.50, more preferably 0.33 to 0.48.
(L/H2) is preferably 0.35 to 0.54 from the viewpoint of realizing a larger discharge capacity per sulfur mass and a higher discharge capacity per positive electrode material, and furthermore excellent cycle characteristics, and more It is preferably 0.40 to 0.51, more preferably 0.42 to 0.50.

The half width of the peak P1 is preferably 30 to 120 cm ^-1 , more preferably 50 to 110 cm ^-1 , still more preferably 70 to 100 cm ^-1 .
The half width of the peak P2 is preferably 20 to 70 cm ^-1 , more preferably 30 to 65 cm ^-1 , still more preferably 40 to 60 cm ^-1 .

FIG. 1 is a laser Raman spectrum diagram of the porous carbon material of this embodiment, and is an explanatory diagram of a method for calculating H1, H2, and L from this spectrum.
In addition, FIG. 1 does not at all limit the laser Raman spectrum diagram obtained from the porous carbon material of the present embodiment.
In FIG. 1, B1 is the minimum intensity value between 800 and 1250 cm ⁻¹ and B2 is the minimum intensity value between 1700 and 1900 cm ⁻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 the intersections of the baseline and the perpendicular drawn from the peaks P1 and P2 to the Raman shift axis (horizontal axis).
D is the intersection of the baseline and the perpendicular down the Raman shift axis (horizontal axis) from the minimum intensity value M between peaks P1 and P2, and the height L is down the Raman shift axis from said M It is the length to the intersection of the perpendicular and the baseline. Specifically, it is the length of the line segment MD in the laser Raman spectrum diagram illustrated in FIG.
On the other hand, the height H1 is the length from P1 to the intersection of the baseline and the perpendicular to the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of line segment P1C1 corresponds to height H1.
Height H2 is the length from P2 to the intersection of the baseline and the perpendicular down to the Raman shift axis. In the laser Raman spectrum diagram illustrated in FIG. 1, the length of line segment P2C2 corresponds to height H2.

[(B) Complex]
The composite of this embodiment is a composite of the above-described porous carbon material of this embodiment and sulfur.

(Manufacturing method of composite)
A method for producing a composite of porous carbon material and sulfur includes a step of mixing the porous carbon material and sulfur having a melting point or higher.
The following methods can be exemplified as the method for producing the composite.
First, a porous carbon material and sulfur powder are mixed.
Next, the sulfur is heated to the melting point of sulfur or more to melt the sulfur, and the pores of the porous carbon material are impregnated with the sulfur by capillary action.
The melting temperature may be 107° C. or higher, which is the melting point of sulfur, preferably 130° C. or higher, and more preferably 150° C. or higher. Also, the melting 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 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 sulfur-impregnated porous carbon material is heated in order to remove sulfur that has not been impregnated into 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 more preferably 330° C. or lower.
The container may be a closed container or an open container. In the case of a closed container, the temperature of the upper part of the container is preferably lower than that of the heating section. The atmosphere may be air or an inert gas such as nitrogen, argon, helium or neon, but air is preferred from the viewpoint of ease of operation.

The mass ratio when mixing the porous carbon material and sulfur is preferably 0.3 parts or more, more preferably 0.9 parts or more, and 1.1 parts or more per part of the porous carbon material. More preferred. As for the mass ratio, sulfur is preferably 20 parts or less, more preferably 8 parts or less, and even more preferably 5 parts or less per 1 part of the porous carbon material.

A composite of a porous carbon material and sulfur contains sulfur in the porous carbon material. The sulfur content of the composite of the present embodiment is preferably 40-70% by mass.
From the viewpoint of further increasing the discharge capacity per positive electrode material, the lower limit of the sulfur content is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more.
The upper limit of the sulfur content is 70% by mass or less, more preferably 67% by mass or less, and even more preferably 65% by mass or less, from the viewpoint of producing a porous carbon material.
Here, the sulfur content is defined by the following formula:
Sulfur content = (mass of sulfur) / (mass of composite of porous carbon material and sulfur) x 100
It is a value calculated by
The content of sulfur in the composite of the porous carbon material and sulfur of the present embodiment is determined by taking advantage of the fact that the sulfur taken into the micropores is difficult to evaporate and the sulfur outside the micropores is easy to evaporate. can be prepared by the following method and measured by thermogravimetric analysis (TG).
After mixing the porous carbon material and sulfur, the mixture is held at 155° C. for 5 hours in an airtight 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. and held for 2 hours to evaporate and remove the sulfur remaining on the surface of the porous carbon material, air-cooled to room temperature, and the container is opened to allow the porous carbon material and sulfur to mix. The complex is taken out and used as a sample.
Subsequently, thermogravimetric analysis (TG) is used to measure the sulfur content in the composite of porous carbon material and sulfur. Specifically, DTG-60AH manufactured by Shimadzu Corporation was used, 10 mg of a sample was put in a cell, measurement gas was Ar, flow rate was 50 ml/min, starting temperature was 30°C, and heating rate was 5°C/min. , and an upper limit temperature of 600°C.

For the sake of convenience, FIG. A method for calculating the amount will be explained.
In the TG graph shown in FIG. 2, the mass decreases as the temperature rises, but a point appears in the region of 300° C. to 500° C. where the slope of the tangent line of the graph changes discontinuously.
Assuming that the initial mass% is 100 and the mass% at which the slope of the tangent line of the graph changes discontinuously is X, the sulfur content Y is defined as Y=100−X.

The composite of the porous carbon material and sulfur of the present embodiment is an X-ray diffraction diagram (XRD) obtained using CuKα rays as an X-ray source, and the peak position of the diffraction angle (2θ) is measured under the following conditions (1): and (2) are preferably satisfied.
(1) It has a peak P1 at a position of 22.5 to 26.0° as a characteristic peak of the porous carbon material.
(2) It should have substantially no peak characteristic of sulfur.
XRD, tube voltage: 20 kV, tube current: 40 mA, analyzing crystal: yes, scattering slit: 8.0 mm, divergence slit: 2/3 °, light receiving slit: open, scan speed: 40.0 ° / min, sampling width : 0.02°, scanning method: measured by 2θ/θ method.
Regarding the condition (1), the complex more preferably has a peak P1 at a position of 23.0 to 25.0°, more preferably at a position of 23.2 to 24.5°. The complex may also have a peak at a position of 43.0-46.0°, preferably at a position of 44.0-45.5. The peak at the position of 43.0 to 46.0° is weak in intensity and often not observed, but the peak may be observed when the vertical axis of XRD is enlarged. Furthermore, it is preferable that the peak P1 at the position of 22.5-26.0° has a higher intensity than the peak at the position of 43.0-46.0°.
For condition (2), the characteristic sulfur peak has a strong peak (P2) at 23.0°±0.3°. Other characteristic peaks for sulfur are 15.3°±0.3°, 25.8°±0.3°, 26.7°±0.3°, and 27.7°±0.3° It has a peak at the position of °.

Preferably, the composite of the porous carbon material and sulfur of the present embodiment does not substantially have peaks characteristic of sulfur. As used herein, the phrase “substantially does not have peaks characteristic of sulfur” means that the peak intensity derived from sulfur is smaller than the peak intensity derived from a carbon material, specifically , where I(P2) is the intensity of peak P2 and I(P1) is the intensity of peak P1, I(P2)/I(P1) is 0.2 or less. I(P2)/I(P1) is preferably 0.1 or less, more preferably 0.05 or less.

[(C) Positive electrode for lithium-sulfur battery]
The positive electrode for a lithium-sulfur battery of the present embodiment contains the composite of the porous carbon material and sulfur obtained as described above.
The positive electrode of the lithium-sulfur battery of the present embodiment includes the composite of the porous carbon material of the present embodiment and sulfur, and, if necessary, a binder, a conductive aid, and a current collector.
The composite of the porous carbon material and sulfur mainly functions as an active material, but the positive electrode of the lithium-sulfur battery of the present embodiment is an active material other than the composite of the porous carbon material and sulfur of the present embodiment. may include

The binder used in the positive electrode of the present embodiment is not limited to the following, but examples include polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride Ride-hexafluoropropylene-tetrafluoroethylene fluororubber, vinylidene fluoride-pentafluoropropylene fluororubber, vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoro Ethylene fluororubber, vinylidene fluoride fluororubber such as vinylidene fluoride-chlorotrifluoroethylene fluororubber, tetrafluoroethylene-propylene fluororubber, tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber, thermoplastic fluororubber , polyethylene, polypropylene, styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, aqueous binders, and the like.
In addition, these may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.
The content of the binder is preferably 1 to 20% by mass, more preferably 2 to 10% by mass, based on the active material. When the binder content is 1% by mass or more, the strength of the positive electrode is sufficient, and when the binder content is 20% by mass or less, an increase in electrical resistance or a decrease in capacity can be further suppressed.

Examples of conductive aids used in the positive electrode of the present embodiment include, but are not limited to, carbon black, acetylene black, and carbon nanotubes.
In addition, these may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and arbitrary ratios. The content of the conductive aid is preferably 1 to 20% by mass, more preferably 2 to 10% by mass, based on 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 electrode, and the material thereof includes aluminum, titanium, zirconium, hafnium, niobium, tantalum, and the like. and alloys containing metals such as Among these, those selected from the group consisting of aluminum, titanium, tantalum, and alloys containing these metals are preferred, and aluminum is particularly preferred. A foil, perforated foil, mesh, or the like of these metals or alloys can be used as a current collector for the positive electrode.

Next, a method for manufacturing the positive electrode of the lithium-sulfur battery of this embodiment will be described.
The method for manufacturing the positive electrode of the lithium-sulfur battery of the present embodiment is not particularly limited as long as it is a known method, except that a composite of a porous carbon material and sulfur is used as an active material. For example, a binder, a conductive agent and a solvent are added to a composite of a porous carbon material and sulfur to form a slurry, the slurry is applied or filled on a current collector, dried and then pressed to increase the density. A method for manufacturing a positive electrode of a lithium-sulfur battery is exemplified.
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 active material amount 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 be small and the output density tends to increase, which is preferable.

The solvent used for manufacturing the positive electrode of the lithium-sulfur battery of the present embodiment may be either aqueous or non-aqueous.
Examples of non-aqueous solvents include, but are not limited to, N-methylpyrrolidone, methyl ethyl ketone, cyclohexanone, isophorone, N,N-dimethylformamide, N,N-dimethyl and the like.
The slurry is prepared by kneading with a dispersing device such as a stirrer, pressure kneader, ball mill and super sand mill.
Moreover, a thickener may be added to the slurry to adjust the viscosity. Examples of thickening agents include, but are not limited to, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salts), oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

[(D) Lithium sulfur battery]
An example of a lithium-sulfur battery including the positive electrode for a lithium-sulfur battery of the present embodiment will be described below.
Materials that can be used in lithium-sulfur batteries, methods for producing lithium-sulfur batteries, and the like are not limited to the following specific examples.
The lithium-sulfur battery of the present embodiment includes the positive electrode of the lithium-sulfur battery of the present embodiment as a positive electrode, and other configurations are not particularly limited, and the positive electrode of the lithium-sulfur battery may be a known one.
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 opposite to each other via the separator, a negative electrode, and an electrolytic solution and an exterior body in contact with them. Prepare.
The lithium-sulfur battery of the present embodiment has an electrode body including the negative electrode and the positive electrode arranged as described above, and an exterior body that houses the electrode body. can be obtained by

The negative electrode can be produced 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 its material is not limited to the following, but examples include copper, aluminum, nickel, and titanium. and stainless steel. Among these, copper is preferable from the viewpoint of ease of 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. Porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors.
The negative electrode active material may be any material containing lithium, and examples thereof include metallic lithium, lithium alloys, lithium oxides, lithium composite oxides, lithium sulfides, and lithium composite sulfides. Lithium alloys include, for example, aluminum or alloys of silicon, tin, magnesium, indium, calcium, etc. 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, a conductive material such as graphite, acetylene black, or ketjen black is mixed with a binder, and an appropriate solvent is added to form a paste. The negative electrode material may be coated on the surface of a current collector, dried, and optionally compressed to increase the electrode density.

The electrolytic solution can be prepared by dissolving a lithium-containing electrolyte in a non-aqueous solvent.
Lithium-containing electrolytes include, for example, _LiPF6 , _LiClO4 , _LiBF4 , _LiAsF6 , LiCF( _CF3 ) ₅ , _LiCF2 ( _CF3 ) ₄ , _LiCF3 ( _CF3 ) ₃ , _LiCF4 ( _CF3 ) _{2 , LiCF5} ( _CF3 ) _{, LiCF3} ( _C2F5 ) _{3 , LiCF3SO3} , LiN( _{CF3SO2 ) 2} , LiN( _{C2F5SO2 ) 2} , LiN _{( C2F5CO} ) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ , lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI).
These may be used individually by 1 type, and may be used in mixture of 2 or more types. Among them, LiPF ₆ , LiFSI and LiTFSI are preferable, and LiTFSI is more preferable.
Further, the concentration of these lithium salts is preferably 0.1-3.0 mol/L, more preferably 0.5-2.0 mol/L.

Examples of the non-aqueous solvent include carbonates, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, nitro compounds, and phosphoric acid ester compounds. , sulfolane hydrocarbons, and ionic liquids.
Especially carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), fluoroethylene carbonate (FEC); dimethoxyethane (DME), triglyme (G3) and tetraglyme 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 mixtures thereof are preferred. A solvent containing carbonates is more preferable, and a mixture of (FEC) and (HFE) is more preferable.

The separator is not particularly limited in material or shape as long as it is used in a normal lithium-sulfur battery. This separator separates the positive electrode and the negative electrode so that they do not come into physical contact with each other, and preferably has high ion permeability.
Examples of the separator include synthetic resin microporous membranes, woven fabrics, non-woven fabrics, and the like, with synthetic resin microporous membranes being preferred. Materials for the synthetic resin microporous membrane include, for example, polyolefins such as polyethylene, polypropylene, and polybutene; polyamides, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, and polyvinylidene fluoride.
Among these, polyethylene and polypropylene are preferred. In addition, when the positive electrode and the negative electrode of the lithium-sulfur battery to be manufactured are configured so as not to be in direct contact with each other, the separator does not need to be used.

The structure of the electrode assembly of the lithium-sulfur battery of the present embodiment is not particularly limited, but usually, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode plate group. Alternatively, these electrodes are formed into flat plates and laminated to form a laminated electrode plate group, so that the structure in which these electrode plate groups are enclosed in an outer package is generally formed.

A metal can, a laminate film, or the like can be used as the outer package.
As the metal can, one made of aluminum is preferable. In this case, for example, the metal can is used as a negative terminal, and the metal lid crimped to the metal can with an insulator sandwiched therebetween is used as a positive terminal. An electrode tab electrically connects the electrode body and the terminal.
As the laminate film, a film obtained by laminating a metal foil and a resin film is preferable, and a three-layer structure consisting 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 suitably used.
The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel, etc. can be suitably used. The inner layer resin film is for protecting the metal foil from the electrolyte to be stored inside and also for melting and sealing during heat sealing, and polyolefin, acid-modified polyolefin, etc. can be suitably used.
In the case of using a laminated film outer package, the edge of the laminated film is sealed while the end of the electrode terminal is pulled out to the outer space of the outer package. A preferred sealing method is heat sealing.

The lithium-sulfur battery of this embodiment can be in the form of a paper-type battery, a button-type battery, a coin-type battery, a stack-type battery, a cylindrical battery, or the like.

Hereinafter, the present embodiment will be described in more detail with specific examples and comparative examples, but these are illustrative, and the present embodiment is not limited by the following examples and comparative examples. not something.
Therefore, those skilled in the art can implement the present invention by adding 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 carried out by filling a sample stage with 2500 μg of a sample using an elemental analyzer manufactured by J Science Lab (trade name “MICRO CORDER JM10”).
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 (composed of silver particles + copper oxide zone, reduced copper zone and copper oxide zone) is 550°C. set to
Also, 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 (% by mass) of oxygen element was calculated by subtracting the content (% by mass) of carbon element, nitrogen element and hydrogen element from 100% by mass.

(Method for measuring specific surface area, pore volume, and pore distribution)
A porous carbon material was used as a measurement sample.
Using AUTOSORB iQ from Quantachrome, the specific surface area was measured by the BET method, and the pore distribution and pore volume were measured by the quench solid phase density function method (QSDFT).
Specifically, the sample was vacuum degassed at 100° C. for 3 hours and measured.
Adsorption isotherms of nitrogen were measured at liquid nitrogen temperature, and specific surface area, pore volume, and pore distribution were measured.

(Measurement method of X-ray photoelectron spectroscopy (XPS))
A nitrogen-containing carbon material and a porous carbon material were used as measurement samples.
Using JPS-9010MC manufactured by JEOL, a cell for powder 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, capture area: N1s, C1s, O1s Pass-Energy: 10 eV
The obtained spectrum was energy-corrected at the peak position of C1s.
The total content (% by 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 microscopic laser Raman spectrometer Nanofinder 30 manufactured by Co., Ltd., a cell for powder was filled and measured under the following conditions.
LD excitation solid-state laser λ: 532 nm 47 mW Measurement conditions: 532 nm, irradiation: 2.34 mW, exposure time: 10 seconds, integration: 10 times, grating: 600 G/mm.
Let P1 be the peak between 1250 and 1385 cm ^-1 .
Let the peak between 1550 and 1620 cm ^-1 be P2.
Let L be the height from the baseline of the minimum point M between P1 and P2.
Let H1 be the height of P1 from the baseline.
Let H2 be the height of P2 from the baseline.

(SEM measurement method)
A porous carbon material was used as the measurement target.
The surface state was observed using a scanning microscope (SU-1500 manufactured by Hitachi, Hitachi High-Tech Solutions).
Using a conductive carbon tape on an aluminum sample table, each powder sample was attached and installed in the chamber.
After evacuating the chamber, the sample was observed at a working distance of 15 mm and an acceleration voltage of 15 kV.

(Method for measuring sulfur content)
The sulfur content in the composite of porous carbon material and sulfur was measured.
Taking advantage of the fact that sulfur trapped in micropores is difficult to evaporate and sulfur outside the micropores is easy to evaporate, samples were prepared by the following method.
After mixing the porous carbon material and sulfur, the mixture was held at 155° C. for 5 hours in a closed vessel to melt sulfur and fill the pores of the porous carbon material by capillary action. After that, the temperature is raised to 300° C. and held for 2 hours to evaporate and remove the sulfur remaining on the surface of the porous carbon material, air-cooled to room temperature, the container is opened, and the porous carbon material and sulfur are composited. The body was taken out and used as a sample.
Subsequently, thermogravimetric analysis (TG) was used to measure the sulfur content in the composite of the porous carbon material and sulfur.
Specifically, DTG-60AH manufactured by Shimadzu Corporation was used, 10 mg of a sample was put in a cell, measurement gas was Ar, flow rate was 50 mL/min, starting temperature was 30°C, and temperature increase rate was 5°C/min. , and an upper limit temperature of 600°C.
A method for calculating the sulfur content from the obtained TG will be described with reference to FIG. 2 of [Example 1] described later.
In the TG graph, the mass decreases as the temperature rises, but a point appears in the region of 300° C. to 500° C. where the slope of the tangent line of the graph changes discontinuously.
Assuming that the initial sulfur content (mass%) is 100 and the sulfur content (mass%) at the point where the slope of the tangent line of the graph changes discontinuously is X, the sulfur content Y is Y = 100- is defined as X.
In Example 1, X=46 and Y=54 (% by mass).
In Examples 2 and 3 and Comparative Example 1, the sulfur content was calculated in the same manner.

[Production of lithium-sulfur battery]
(Preparation of positive electrode for lithium-sulfur battery)
An aqueous binder (binder) was dissolved in pure water to prepare a 5% by mass solution.
Acetylene black (conductive aid) was added to this, and then an active material (a composite of sulfur and a porous carbon material produced in Examples 1 to 3 and Comparative Example 1 described later) was added to obtain a positive electrode slurry. prepared.
The mass ratio of the active material, conductive aid, and binder was set to active material:conductive aid:binder=90:5:5.
The resulting positive electrode slurry was filled in an Al porous current collector so that the amount of the active material was 7.0 mg/cm ² .
After that, it was dried in an oven at 40° C. under atmospheric pressure for 1 hour.
After drying, the dried product was pressed through a roll press, cut into a size of 24×24 mm, and vacuum-dried at room temperature to obtain a positive electrode.
The thickness of the positive electrode layer was about 250 μm.

(Preparation of negative electrode for lithium-sulfur battery)
Li foil with a thickness of 30 μm was cut into a size of 30×30 mm in an air atmosphere with a dew point of −40° C. or less to obtain a negative electrode for a lithium-sulfur battery.

(Fabrication of lithium-sulfur battery)
A lithium-sulfur battery was produced in the following procedure in an air atmosphere with a dew point of −40° C. or less.
Positive electrode prepared according to the above item (preparation of positive electrode for lithium sulfur battery), negative electrode prepared according to the above item (preparation of negative electrode for lithium sulfur battery), bis (trifluorosulfonyl) imide (LiTFSI) as lithium-containing electrolyte, non-aqueous A mixed solvent of fluoroethylene carbonate (FEC)/1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)-propane (HFE) was used as a solvent.
Regarding the preparation of the electrolytic solution, FEC:HFE was mixed at a volume of 1:1, and LiTFSI was dissolved in a mixed solvent of FEC and HFE so that the concentration of LiTFSI/FEC:HFE was 1.0 mol/L. was prepared.
10% by mass of vinylene carbonate (VC) was added as an additive.
A polypropylene-based microporous film was used as a separator.
A laminate cell was used as a cell, and a positive electrode, a separator, and a negative electrode were accommodated in the cell so as to be stacked in order, and an electrolytic solution was injected to produce a lithium-sulfur battery.

[Charging and discharging test]
A constant current charging/discharging test was performed using the active material (positive electrode) as a working electrode.
The charging mode is C.I. C. (C.C. is an abbreviation for constant current.), and the C.C. C. mode.
The set current density was 167.2 mA/g (current density of 1672 mA/g is defined as 1C. Hereinafter, 167.2 mA/g is referred to as 0.1C).
The cut-off voltage has a lower limit of 1.0V and an upper limit of 3.0V.
Note that the charge/discharge test was performed in an environment of 25°C.
Charge capacity and discharge capacity were defined per mass of sulfur.
Table 2 below shows the discharge capacity (mAh/g-sulfur) at the 100th cycle.
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]
(Production of azulmic acid)
An aqueous solution in which 150 g of hydrocyanic acid was dissolved in 350 g of water was prepared in a vessel, and 120 g of a 25% aqueous ammonia solution was added over 10 minutes while stirring the aqueous solution, and the resulting mixture was heated to 35°C. Then, the polymerization of hydrocyanic acid started and a dark brown polymer began to precipitate, and the temperature gradually rose to 45°C.
Two hours after the polymerization started, addition of 30% by mass hydrocyanic acid aqueous solution was started 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 vessel was cooled to keep the reaction temperature at 50°C. The polymerization reaction solution was stirred at this temperature for 100 hours.
The resulting 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. After the separated precipitate was washed with water, it was dried in a dryer at 120° C. for 4 hours to obtain azulmic acid.
The resulting azulmic acid was subjected to CHN analysis using an elemental analyzer (trade name: "MICRO CORDER JM10") manufactured by Jay Science Lab, with 2500 µg of an azulmic acid sample filled on a sample table.
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 (composed of silver particles + copper oxide zone, reduced copper zone and copper oxide zone) is 550°C. set to Also, the oxygen flow rate was set to 15 mL/min, and the He flow rate was set to 150 mL/min. A 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 carbon elements, 29.8% by mass of nitrogen elements, and 4.1% by mass of hydrogen elements.
Here, since the adsorbed water remains under the above drying conditions, it is considered that the difference is mainly derived from the oxygen element and the hydrogen element in the adsorbed water.

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

[Comparative Example 1]
(Activation method and production of porous carbon material)
Add 2 g of the nitrogen-containing carbon material obtained in the above [Production Example of Nitrogen-Containing Carbon Material] to 20 mL of a mixed solution of 4 g of potassium hydroxide and pure water, and remove water at 100 ° C. while stirring to prevent precipitation. did.
After that, 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 left for 5 minutes to perform gas exchange. After the replacement, the temperature was raised to 150° C. over 15 minutes, and heat treatment was performed at 150° C. for 1 hour to dry the contents.
After that, the temperature was raised to 800° C. over 1 hour, heat treatment was performed for 1 hour, and then the temperature was lowered and the contents were collected.
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 filtrate became almost neutral, collected by filtration, and dried. A porous carbon material was obtained.
This operation was repeated to mass-produce porous carbon materials.

<XPS analysis>
Table 2 below shows the XPS analysis results of the porous carbon material.
The nitrogen content reduction rate was 85% by mass.

<Measurement of specific surface area, pore volume, and pore distribution>
Table 2 below shows the measurement results of the specific surface area and pore volume of the porous carbon material.
FIG. 3 shows the analysis results of the pore distribution.

<Raman analysis>
FIG. 4 shows the Raman analysis results of the porous carbon material, and Table 2 shows the analysis results.

<Method for producing composite of porous carbon material and sulfur, and measurement of sulfur content>
After mixing 0.43 g of the porous carbon material produced as described above at a mass ratio of porous carbon material: sulfur = 35:65, the mixture was heated to 155°C in a sealed container having an inner diameter of 20 mm and a height of 60 mm. By holding at for 5 hours, sulfur was melted and filled into the pores of the porous carbon material by capillary action.
After that, the temperature is raised to 300° C. and held for 2 hours to evaporate and remove the sulfur remaining on the surface of the porous carbon material, air-cooled to room temperature, and the container is opened to allow the porous carbon material and sulfur to mix. A complex was obtained.
All the compounding steps were performed in the atmosphere.
The sulfur content of the resulting composite of porous carbon material and sulfur was measured by thermogravimetric analysis (TG). Table 2 shows the measurement results.

<Charging and discharging test>
The above [charge/discharge test] was performed at 0.1C. FIG. 5 shows the evaluation results of cycle characteristics. Table 2 shows the discharge capacity at the 100th cycle.

[Example 1]
(Manufacturing of porous carbon material)
2 g of the porous carbon material produced in [Comparative Example 1] described above was placed in a quartz boat and placed in a box furnace.
The box furnace was vacuum degassed and then replaced with nitrogen gas.
After repeating this operation twice, the nitrogen flow rate was 1000 Ncc/min, and the temperature was changed to 10° C./min. was raised to 1000° C. and held at 1000° C. for 1 hour.
After that, the temperature was lowered and the content was recovered to obtain a porous carbon material.

<XPS analysis>
Table 2 below shows the XPS analysis results of the porous carbon material.

<Measurement of specific surface area, pore volume, and pore distribution>
Table 2 below shows the measurement results of the specific surface area and pore volume of the porous carbon material.
FIG. 3 shows the analysis results of the pore distribution.

<Raman analysis>
The Raman analysis results of the porous carbon material are shown in FIG. 4, and the analysis results are shown in Table 2 below.

<SEM measurement>
The measurement results are shown in FIG.

<Method for producing composite of porous carbon material and sulfur, and measurement of sulfur content>
The mass ratio of porous carbon material: sulfur was changed to 43:57 instead of 35:65. For other conditions, the method for producing a composite of porous carbon material and sulfur in Comparative Example 1 was repeated to obtain a composite of porous carbon material and sulfur.
The sulfur content of the resulting composite of porous carbon material and sulfur was measured by thermogravimetric analysis (TG). Table 2 shows the measurement results.

<Charging and discharging test>
The above [charge/discharge test] was performed at 0.1C. FIG. 5 shows the evaluation results of cycle characteristics. Table 2 shows the discharge capacity at the 100th cycle.

[Example 2]
(Manufacturing of porous carbon material)
The temperature condition for raising the temperature was changed from 1000°C to 1200°C. For other conditions, the heat treatment method of [Example 1] was repeated to obtain a porous carbon material.

<XPS analysis>
Table 2 below shows the XPS analysis results of the porous carbon material.

<Measurement of specific surface area, pore volume, and pore distribution>
Table 2 below shows the measurement results of the specific surface area and pore volume of the porous carbon material.
FIG. 3 shows the analysis results of the pore distribution.

<Raman analysis>
The Raman analysis results of the porous carbon material are shown in FIG. 4, and the analysis results are shown in Table 2 below.

<Method for producing composite of porous carbon material and sulfur, and measurement of sulfur content>
The mass ratio of porous carbon material: sulfur was changed to 43:57 instead of 35:65. For other conditions, the method for producing a composite of porous carbon material and sulfur in Comparative Example 1 was repeated to obtain a composite of porous carbon material and sulfur.
The sulfur content of the resulting composite of porous carbon material and sulfur was measured by thermogravimetric analysis (TG). Table 2 shows the measurement results.

<Charging and discharging test>
The above [charge/discharge test] was performed at 0.1C. FIG. 5 shows the evaluation results of cycle characteristics. Table 2 shows the discharge capacity at the 100th cycle.

[Example 3]
(Manufacturing of porous carbon material)
The temperature condition for raising the temperature was changed from 1000°C to 1400°C. For other conditions, the heat treatment method of [Example 1] was repeated to obtain a porous carbon material.

<XPS analysis>
Table 2 below shows the XPS analysis results of the porous carbon material.

<Measurement of specific surface area, pore volume, and pore distribution>
Table 2 below shows the measurement results of the specific surface area and pore volume of the porous carbon material.
FIG. 3 shows the analysis results of the pore distribution.

<Raman analysis>
The Raman analysis results of the porous carbon material are shown in FIG. 4, and the analysis results are shown in Table 2 below.

<Method for producing composite of porous carbon material and sulfur, and measurement of sulfur content>
The mass ratio of porous carbon material: sulfur was changed to 46:54 instead of 35:65. For other conditions, the method for producing a composite of porous carbon material and sulfur in Comparative Example 1 was repeated to obtain a composite of porous carbon material and sulfur.
The sulfur content of the resulting composite of porous carbon material and sulfur was measured by thermogravimetric analysis (TG). Table 2 shows the measurement results.

<Charging and discharging test>
The above [charge/discharge test] was performed at 0.1C. FIG. 5 shows the evaluation results of cycle characteristics. Table 2 shows the discharge capacity at the 100th cycle.

From FIG. 5, when the porous carbon material and sulfur composites of Examples 1 to 3 were used as the positive electrode of a lithium-sulfur battery, the discharge capacity per mass of sulfur, the discharge per positive electrode material containing sulfur and the carbon material It was found that the battery has a large capacity, a large discharge capacity even after repeated charging and discharging, and excellent cycle characteristics.

The composite of the porous carbon material and sulfur of the present invention has industrial applicability as a positive electrode for lithium-sulfur batteries.
In addition, the porous carbon material of the present invention has industrial applicability as a raw material for the positive electrode of the lithium-sulfur battery.

Claims (11)

The nitrogen content is 0.2 to 2.0% by mass,
The specific surface area obtained by the BET method of nitrogen adsorption and desorption is 1000 to 1800 m ² /g,
The pore volume obtained by the quenching solid phase density function method (QSDFT) of the nitrogen adsorption and desorption method is 0.50
~0.80 cm ³ /g ,
In the laser Raman spectrum diagram with a wavenumber of 800 to 1900 cm ^-1 ,
having a peak P1 between 1250 and 1385 cm ^-1 ,
having a peak P2 between 1550 and 1620 cm ^-1 ;
The height L from the baseline of the minimum point M between the P1 and P2 and the baseline of P1
The ratio of the height H1 from the (L/H1) is 0.25 to 0.54,
Porous carbon material. A method for producing a porous carbon material according to claim 1 ,
a step of chemically activating the nitrogen-containing carbon material;
Having a step of heat-treating in an inert gas after the chemical activation,
A method for producing a porous carbon material. 3. The method for producing a porous carbon material according to claim 2 , wherein the heat treatment temperature in the inert gas is 900[deg.] C. or higher. The reduction rate of the nitrogen content in the chemical activation step is
Formula (I) below:
Reduction rate of nitrogen content (mass%) = ((B-A) / B) × 100 (I)
(In formula (I), A is the nitrogen content (% by mass) measured by XPS in the porous carbon material after the chemical activation step , and B is the nitrogen content measured by XPS in the nitrogen-containing carbon material. is the nitrogen content (mass%) in
7. The method for producing a porous carbon material according to claim 2 or 3 , wherein the content is 0 to 99% by mass. The method for producing a porous carbon material according to any one of claims 2 to 4 , wherein the nitrogen content in the nitrogen-containing carbon material is 2 to 45% by mass. the chemical activation is alkali activation;
The method for producing a porous carbon material according to any one of claims 2 to 5 . A composite of the porous carbon material according to claim 1 and sulfur. A composite according to claim 7 , wherein the sulfur content is 40-70% by weight. A method for producing the composite according to claim 7 or 8 ,
A mixing step of mixing the porous carbon material and sulfur heated to a temperature equal to or higher than the melting point;
A method for manufacturing a composite. A positive electrode for a lithium-sulfur battery containing the composite according to claim 7 or 8 . A lithium-sulfur battery comprising the positive electrode according to claim 10 .