WO2021210525A1

WO2021210525A1 - Positive electrode material for lithium-sulfur secondary batteries, lithium-sulfur secondary batteries using same, and method for producing positive electrode material for lithium-sulfur secondary batteries

Info

Publication number: WO2021210525A1
Application number: PCT/JP2021/015144
Authority: WO
Inventors: 石川　正司; 由紀子松井; 剛殿納屋
Original assignee: 学校法人関西大学
Priority date: 2020-04-14
Filing date: 2021-04-12
Publication date: 2021-10-21
Also published as: JPWO2021210525A1

Abstract

The present invention addresses the problem of providing a positive electrode material for lithium-sulfur secondary batteries, that retains conductivity and can suppress the elution of polysulfide ions into the electrolyte solution. In order to solve this problem, a positive electrode material for lithium-sulfur secondary batteries according to an embodiment of the present invention contains a composite active carbon provided by mixing (a) sulfur-supporting active carbon with (b) active carbon that does not support sulfur.

Description

A positive electrode material for a lithium-sulfur secondary battery, a method for manufacturing a positive electrode material for a lithium-sulfur secondary battery using the same, and a positive electrode material for a lithium-sulfur secondary battery.

The present invention relates to a positive electrode material for a lithium-sulfur secondary battery, a lithium-sulfur secondary battery using the same, and a method for manufacturing a positive electrode material for a lithium-sulfur secondary battery.

Currently, lithium-ion batteries are widely used as secondary batteries used in mobile phones, personal computers, digital cameras, etc., but further improvement in energy density and cost reduction are required.

Therefore, the lithium-sulfur secondary battery is attracting attention. A lithium sulfur secondary battery is a secondary battery that uses sulfur as a positive electrode active material and lithium metal as a negative electrode active material, ^{and charges and discharges by moving lithium ions (Li +} ) between the positive electrode and the negative electrode. .. The lithium-sulfur secondary battery, Li ⁺ ions are eluted from the negative electrode during discharge, reacts with sulfur in the positive electrode, to generate a Li 2 _S, a current flows to an external circuit.

Sulfur atoms have a large number of electrons related to the redox reaction per weight, and are expected to have a theoretically five times higher energy density than conventional lithium-ion batteries. Moreover, since sulfur is inexpensive and easy to secure, it is possible to reduce the cost of the material. For this reason, lithium-sulfur secondary batteries are being actively researched as next-generation secondary batteries.

For example, in Patent Document 1, the positive electrode includes a first positive electrode layer and a second positive electrode layer, and the first positive electrode layer contains sulfur particles coated with a polymer, sulfur particles, and carbon. A lithium-sulfur battery in which the positive electrode layer of No. 2 contains carbon and does not contain sulfur is disclosed.

Further, in Patent Document 2, carbon aggregates having a hierarchical pore structure composed of aligned pores which are three-dimensionally connected to each other; and at least a part of the outer surface and the inside of the carbon aggregates. A carbon-sulfur complex containing introduced sulfur; is disclosed.

Further, Patent Document 3 describes a material containing carbon and sulfur so that the carbon is in the form of a porous matrix having nanoporous properties and has a free volume available within the nanoporous properties. A material in which the sulfur is adsorbed in a part of the nanoporous of the carbon matrix is disclosed.

Japanese Unexamined Patent Publication No. 2018-113142 (published on July 19, 2018) Special Table 2019-513673 (published on May 30, 2019) Japanese Unexamined Patent Publication No. 2013-118191 (published on June 13, 2013)

While the lithium-sulfur secondary battery has a high energy density, it has a problem that polysulfide ions generated at the positive electrode during discharge are eluted into the electrolytic solution. Specifically, eluted polysulfide ions produces a sulfide reacts with lithium ion in the electrolyte (e.g., polysulfide, such as Li 2 _S), a 1.8 times the volume of sulfur. For this reason, when the lithium-sulfur secondary battery is repeatedly charged and discharged, the positive electrode is crushed or cracked due to the volume change, which leads to a problem that the discharge capacity is lowered.

In Patent Document 1, the first positive electrode layer close to the positive electrode current collector contains sulfur particles coated with a polymer to suppress the amount of sulfur eluted during discharge, and the second positive electrode layer close to the electrolytic solution layer. As a result of suppressing the precipitation of lithium sulfide in the vicinity of the second positive electrode layer by not containing sulfur, the amount of lithium sulfide precipitated at the interface between the electrolytic solution layer and the positive electrode is reduced, and instead, lithium sulfide is precipitated inside the positive electrode. It is stated that it can be done.

However, the positive electrode described in Patent Document 1 is indispensable to include a first positive electrode layer and a second positive electrode layer, and the functions are shared between the first positive electrode layer and the second positive electrode layer. , It is necessary to bother to prepare two positive electrode layers. Therefore, it can be said that the invention described in Patent Document 1 has room for improvement from the viewpoint of preventing the elution of sulfur by a simple structure.

Patent Document 2 states that a carbon-sulfur complex in which sulfur is introduced into at least a part of the outer surface and the inside of a carbon aggregate having a hierarchical pore structure reduces the outflow of sulfur to an electrolyte. (Patent Document 2 [0018]).

However, in the carbon-sulfur composite, the carbon aggregate obtained by heat-treating the template particle-carbon composite obtained by spray-drying a mixed dispersion of the template particles and the cylindrical carbon material is impregnated with sulfur. Manufactured by letting. As described above, the carbon-sulfur complex disclosed in Patent Document 2 needs to be obtained through a complicated process.

Further, Patent Document 3 describes that the cycle life and the like can be improved by using a carbon material having nanoporous as a matrix and adsorbing sulfur in the nanoporous. However, there is no mention of elution of sulfur into the electrolyte.

One aspect of the present invention can be obtained by a simple method, and can maintain conductivity and suppress elution of polysulfide ions into an electrolytic solution by a configuration completely different from that of the prior art. An object of the present invention is to provide a positive electrode material for a sulfur secondary battery.

In order to solve the above-mentioned problems, the present inventor uses a composite activated carbon obtained by mixing (a) sulfur-supported activated carbon and (b) sulfur-free activated carbon as a positive electrode material. As a result, it was found that the amount of sulfur carried on the positive electrode can be kept high and the battery characteristics such as discharge capacity can be made excellent.

That is, the present invention includes the following configurations.
<1>
A positive electrode material for a lithium-sulfur secondary battery, which comprises a composite activated carbon obtained by mixing (a) a sulfur-supported activated carbon and (b) a sulfur-free activated carbon.
<2>
In <1>, the composite activated carbon contains 50% by weight or more and 98% by weight or less of the above (a) and 2% by weight or more and 50% by weight or less of the (b) with respect to the weight of the composite activated carbon. The positive electrode material for the lithium-sulfur secondary battery described.
<3>
In <2>, the composite activated carbon contains 60% by weight or more and 80% by weight or less of the above (a) and 10% by weight or more and 30% by weight or less of the (b) with respect to the weight of the composite activated carbon. The positive electrode material for the lithium-sulfur secondary battery described.
<4>
For the weight of the positive electrode material for lithium-sulfur secondary batteries
The composite activated carbon is contained in an amount of 90% by weight or more and 95% by weight or less.
The positive electrode material for a lithium-sulfur secondary battery according to any one of <1> to <3>, which contains 5% by weight or more and 10% by weight or less of other components.
<5>
The positive electrode material for a lithium-sulfur secondary battery according to any one of <1> to <4>, wherein the (a) carries 60% by weight or more of sulfur with respect to the weight of the (a).
<6>
The positive carbon material for a lithium-sulfur secondary battery according to any one of <1> to <5>, wherein the activated carbon carrying (a) sulfur and the activated carbon not supporting (b) sulfur are the same type of activated carbon.
<7>
The specific surface area of the activated carbon supporting (a) sulfur and the activated carbon not supporting sulfur (b) is 1500 m ² g ^-1 or more and 2900 m ² g ^-1 or less. The positive electrode material for lithium-sulfur secondary batteries described in C.
<8>
The positive electrode material for a lithium-sulfur secondary battery according to any one of <1> to <7>, further containing a conductive auxiliary agent and an aqueous binder.
<9>
A lithium-sulfur secondary battery comprising the positive electrode material for the lithium-sulfur secondary battery according to any one of <1> to <8>.
<10>
An electrolyte containing lithium and one or more solvents selected from the group consisting of carbonates, ethers, sulfur compounds, halogenated hydrocarbons, phosphate ester compounds, sulfolane hydrocarbons, and ionic liquids. The lithium sulfur secondary battery according to <9>, comprising an electrolytic solution containing.
<11>
By mixing activated carbon and sulfur and heating the obtained mixture, (a) a step of obtaining activated carbon carrying sulfur, and
A method for producing a positive electrode material for a lithium-sulfur secondary battery, comprising the steps of (a) a sulfur-supporting activated carbon, (b) a sulfur-free activated carbon, a conductive auxiliary agent, and an aqueous binder. ..
<12>
A positive electrode for a lithium-sulfur secondary battery containing a composite activated carbon obtained by mixing (a) an activated carbon carrying sulfur and (b') an activated carbon supporting a smaller proportion of sulfur than the above (a). material.
<13>
The (a) carries 60% by weight or more of sulfur with respect to the weight of the (a), and the (b') is more than 0% by weight and 10% by weight or less with respect to the weight of the (b'). The positive electrode material for a lithium-sulfur secondary battery according to <12>, which carries the sulfur of.
<14>
It contains (a) a composite activated carbon obtained by mixing an activated carbon carrying sulfur and (b) an activated carbon not carrying sulfur, and a conductive auxiliary agent made of a material different from the composite activated carbon. Positive electrode material for lithium-sulfur secondary batteries.

According to one aspect of the present invention, it is possible to provide a lithium-sulfur secondary battery in which the amount of sulfur carried in the positive electrode is kept high and the battery characteristics such as discharge capacity are excellent.

It is a figure which shows the measurement result of the AC impedance of an Example and a comparative example. It is a figure which shows the measurement result of the cyclic voltammetry of the 2nd cycle of an Example and a comparative example. It is a figure which shows the result of the charge / discharge test in an Example and a comparative example. It is an enlarged view of a part of the result of the charge / discharge test shown in FIG. It is a figure which shows the result of the cycle characteristic test in an Example and a comparative example. It is the result of the polysulfide adsorption test in an Example and a comparative example.

Hereinafter, one embodiment of the present invention will be described in detail. However, the present invention is not limited to this, and various modifications can be made within the scope described. For example, an embodiment obtained by appropriately combining the technical means disclosed in different embodiments is also included in the technical scope of the present invention. Unless otherwise specified in the present specification, "AB" representing a numerical range is intended to be "A or more and B or less".

[1. Positive electrode material for lithium-sulfur secondary batteries]
The positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention includes (a) sulfur-supporting activated carbon (hereinafter, may be abbreviated as “(a)”) and (b) sulfur-supporting activated carbon. It contains a composite activated carbon obtained by mixing with activated carbon that has not been used (hereinafter, may be abbreviated as "(b)").

The activated carbon supporting (a) sulfur is an activated carbon in which sulfur is supported in the pores of the activated carbon. Support of sulfur in the pores can be performed, for example, by mixing activated carbon and sulfur using a mortar or the like, and then heating the obtained mixture in a muffle furnace or the like. As the sulfur, commercially available sulfur flower or the like can be used.

That is, the "sulfur-supporting activated carbon" is an activated carbon in which the molten sulfur is diffused into the pores of the activated carbon to adsorb the sulfur in the pores. The adsorption may be physical adsorption or chemical adsorption.

As will be described later, it is preferable that the activated carbon supporting (a) sulfur carries 60% by weight or more of sulfur with respect to the weight of (a). As a method for setting the weight of sulfur carried by (a) to a desired value, for example, the ratio of the weight of sulfur to the weight of (a) is increased by 1 to 4% by weight from the desired value. In this way, a method of mixing activated charcoal and sulfur using a mortar or the like, putting the obtained mixture into a muffle furnace, and treating under the conditions shown in Example 1 described later can be mentioned.

In the present specification, the form of sulfur is not particularly limited. For example, one or more sulfur selected from the group consisting of α-sulfur (oblique sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), rubbery sulfur, and plastic sulfur can be used.

The activated carbon that supports sulfur is not particularly limited, but since it has a large specific surface area and pore volume and has a structure suitable for supporting a large amount of sulfur, after carbonizing a resin, fossil resource material, etc., potassium hydroxide is used. Activated carbon or the like obtained by activating with an alkali such as the above can be preferably used.

The specific surface area of the (a) and (b), from the viewpoint of increasing carrying sulfur is preferably ^{^{^{1500m 2 g -1 ~ 2900m 2 g}}} -1, with ^{^{^{2200m 2 g -1 ~ 2900m 2 g}}} -1 More preferably.

The specific surface area is a value measured by the BET method. The specific surface area can be measured, for example, by using AUTOSORB iQ manufactured by Quantachrome.

The volume of the pores (a) and (b) is preferably ^{0.6 cc · g -1} to 1.2 cc · g -1 from the viewpoint of supporting a large amount of sulfur, preferably 0.9 cc · g ^-1. It is more preferably g ^-1 to 1.2 cc · g ^-1.

The volume of the pores can be measured using, for example, AUTOSORB iQ manufactured by Quantachrome.

The particle size of (a) is preferably 1.7 μm or more and 6.0 μm or less in D50 from the viewpoint of the cumulative frequency% diameter. From the viewpoint of the cumulative frequency% diameter, the particle size of (b) is preferably smaller than that of (a) and preferably 1.7 μm or more and 6.0 μm or less, and 1.7 μm or more and 3.1 μm or less. Is more preferable. It is considered that this is because the smaller the particle size of (b), the larger the surface area and the more polysulfide can be adsorbed. The preferred range of the particle size of (b'), which will be described later, is the same as that of (b).

The cumulative frequency% diameter can be measured by a wet batch type measuring method using a scattering type particle size distribution measuring device (LASER SCATTERING PARTICLE SIZE DISTRIBUTION ANALYZER LA-950 (manufactured by HORIBA)).

The wet batch type measurement method can be performed by the following method.

(I) The above (a) and / or the above (b) is mixed with a dispersion medium (carboxymethyl cellulose, surfactant, etc.) to prepare a dispersion liquid in which the above (a) and / or the above (b) is dispersed. do.

(Ii) Next, a glass cell subjected to a special coating process is filled with pure water, and a few drops of the dispersion liquid are dropped therein to prepare a sample. Further, the sample is stirred using a stirrer to disperse the dispersion in the cell.

(Iii) After dispersing the dispersion, the sample is irradiated with a semiconductor laser beam to measure the transmittance of the sample, and the particle size of the (a) and / or the (b) is calculated from the transmittance. do.

As a method for measuring the cumulative frequency% diameter, there are a flow method, a dry method, etc., but in the wet batch type measurement method, the above-mentioned (a) and (b) used for the measurement are small, and the amount of sewage generated after the measurement is sufficient. Is a small amount, so the measurement can be easily performed.

The activated carbon (b) that does not support sulfur is an activated carbon that does not support sulfur in its pores. Since sulfur itself is an insulator, the above (a) supports sulfur on activated carbon for the purpose of ensuring conductivity. However, in a lithium-sulfur secondary battery, expansion and contraction of the positive electrode may occur due to charging and discharging. At that time, the larger the amount of sulfur supported in (a), the greater the expansion / contraction of the positive electrode material.

Therefore, when only the above (a) is used as the positive electrode material, the supported sulfur may be eluted as polysulfide in the electrolytic solution due to the expansion / contraction. When such a situation occurs, problems such as a decrease in the discharge capacity of the lithium-sulfur secondary battery occur.

The present inventor has attempted to use the composite activated carbon obtained by mixing the above (a) and the above (b) as the positive electrode material for the purpose of preventing the expansion and contraction of the positive electrode material. Then, surprisingly, it became clear that the cycle characteristics of the lithium-sulfur secondary battery were significantly improved. Therefore, as a result of measuring the cross section of the positive electrode material for the lithium sulfur secondary battery after charging and discharging by the Auger electron spectroscopic analysis method using an electric field radiation type Auger electron spectroscopic analyzer (manufactured by AES PHI), the above (b) Sulfur was also detected at the site. From this result, it was clarified that the (b) adsorbs the polysulfide eluted from the (a).

As described above, the positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention is a composite composed of (a) a sulfur-supporting activated charcoal and (b) a sulfur-non-supporting activated charcoal. By containing the activated charcoal, even when the polysulfide is eluted from the (a) to the electrolytic solution by charging / discharging of the lithium-sulfur secondary battery, the polysulfide can be adsorbed by the (b).

As a result, it is possible to obtain characteristics commensurate with the amount of sulfur supported on (a) without wasting the sulfur carried on (a). Therefore, it is possible to provide a lithium-sulfur secondary battery having excellent properties.

"Activated carbon that does not support sulfur" is activated carbon that does not support sulfur in the pores of the activated carbon. Therefore, the step (b) does not need to go through the step of combining activated carbon and sulfur as in the step (a). As the above (b), for example, commercially available activated carbon can be used as it is.

The activated carbon (b) may be the same type of activated carbon as the activated carbon used in the above (a) before carrying sulfur, or may be a different type of activated carbon, but the polysulfide eluted from the above (a) may be used. From the viewpoint of adsorption, it is preferable that the activated carbon is of the same type. For example, as (b) above, activated carbon obtained by carbonizing the above-mentioned resin, fossil resource material, or the like and then activating with alkali can be preferably used.

The "composite activated carbon" means a mixture of a sulfur-supported activated carbon and a sulfur-non-supporting activated carbon. The mixing of the (a) and the (b) is performed so that the (a) and the (b) are uniformly mixed. As a method of homogeneously mixing the above (a) and the above (b), for example, the above (a), the above (b), and other components (conductive aid, water-based binder, etc.) described later are used using a mortar or pestle or the like. ), And the obtained mixture is further stirred using a rotation / revolution mixer.

The (a) preferably carries 60% by weight or more of sulfur with respect to the weight of the (a). That is, it is preferable that the ratio of the weight of sulfur to the total of the weight of sulfur constituting the activated carbon carrying sulfur and the weight of activated carbon is 60% by weight or more.

According to this configuration, since the amount of sulfur carried is large, it is possible to provide a lithium-sulfur battery that meets the recent demand for an increase in the sulfur content in the positive electrode material. Further, to provide a lithium-sulfur battery capable of preventing elution of polysulfide and sufficiently exerting the characteristics of a large amount of supported sulfur because it contains a composite activated carbon obtained by mixing the above (a) and the above (b). Can be done.

The ratio is more preferably 70% by weight or more, and more preferably higher, but the upper limit is about 60 to 66% by weight in view of the carrying capacity of activated carbon and the like. The amount of sulfur supported can be confirmed by the method described later in Example 1.

In the positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention, the pores (a) may be mesopores or micropores.

The pores are micropores means that the diameter of the pores is 2 nm or more. The pores are micropores by measuring the specific surface area by the BET method and measuring the pore distribution and the volume of the pores by the quenching solid phase density function method (QSDFT) using AUTOSORB iQ manufactured by Quantachrome. , Can be confirmed.

The specific surface area, pore distribution, and pore volume can be measured by measuring the adsorption isotherm of nitrogen at the temperature of liquid nitrogen for a sample that has been vacuum degassed at 200 ° C. for 3 hours.

It should be noted that it can be confirmed by the same method that the pores described later are mesopores.

When the pores are micropores, the electrolytic solution does not easily penetrate into the pores, so that the elution of polysulfide into the electrolytic solution that has penetrated the pores is small. Therefore, a high discharge capacity can be obtained even if an arbitrary electrolytic solution is used.

The activated carbon with further developed micropores is an activated carbon obtained by carbonizing the above-mentioned raw materials such as resin and fossil resource material and then activating them with alkali from the viewpoint of facilitating the support of a large amount of sulfur. Is preferable.

The pores are mesopores means that the diameter of the pores is more than 2 nm and 50 nm or less. Activated carbon with mesopores has a large pore diameter, so that it is easier to support sulfur than activated carbon with micropores. On the other hand, due to the size of the pores, the electrolytic solution is more likely to penetrate into the pores than activated carbon having micropores.

Therefore, it can be said that activated carbon having mesopores in the pores is more likely to elute polysulfide into the electrolytic solution than activated carbon having micropores in the pores.

As described above, when activated carbon having micropores is used, any electrolytic solution can be used, but the pores (a) may be mesopores or micropores.

In a lithium-sulfur secondary battery in which the positive electrode material for a lithium-sulfur secondary battery is used as the positive electrode, for example, fluoroethylene carbonate is used as a solvent for the electrolytic solution, the SEI film formed by the reduced decomposition product of the electrolytic solution in the initial discharge is formed. The pores are formed in the pores of activated carbon, which are mesopores.

Therefore, after the initial discharge, the invasion of the electrolytic solution into the pores can be suppressed. Examples of a suitable solvent for forming such an SEI film include vinylene carbonate, lithium bis (fluorosulfonyl) imide, and the like, in addition to fluoroethylene carbonate.

When the above (a) contains activated carbon having mesopores in the pores, elution of polysulfide may occur in the electrolytic solution that has penetrated into the pores at the time of initial discharge of the lithium-sulfur secondary battery. However, since the SEI film is formed in the pores after that, further elution of polysulfide can be prevented.

In summary, when the pores of (a) are micropores, elution of polysulfide is unlikely to occur, so any electrolytic solution can be used. On the other hand, when the pores of (a) are mesopores, the energy density increases because the pores of (a) can carry a large amount of sulfur. Therefore, the pores of (a) may be mesopores or micropores.

As described above, the pores of (b) are used to adsorb the polysulfide eluted from (a) due to expansion of the positive electrode material or the like. Therefore, the pores of (b) are preferably micropores.

In the positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention, the composite activated carbon contains 50% by weight or more and 98% by weight or less of the above (a) with respect to the weight of the composite activated carbon. b) is preferably contained in an amount of 2% by weight or more and 50% by weight or less.

According to the configuration, even when the sulfur supported on (a) is eluted as polysulfide due to expansion of the positive electrode or the like, the polysulfide can be efficiently adsorbed by (b). As a result, it is possible to more easily provide a lithium-sulfur secondary battery exhibiting excellent cycle characteristics and the like.

From the viewpoint of more efficiently adsorbing the polysulfide by the above (b), the composite activated carbon contains 60% by weight or more and 90% by weight or less of the above (a) with respect to the weight of the composite activated carbon. It is more preferable to contain b) in an amount of 10% by weight or more and 40% by weight or less.

From the viewpoint of more efficiently adsorbing the polysulfide by the (b), the composite activated carbon contains the (a) in an amount of 60% by weight or more and 80% by weight or less, and contains the (b) in an amount of 10% by weight or more and 30% by weight or more. It is more preferable to contain% or less.

The positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention contains 90% by weight or more and 95% by weight or less of the composite activated carbon with respect to the weight of the positive electrode material for a lithium-sulfur secondary battery, and other components. Is preferably contained in an amount of 5% by weight or more and 10% by weight or less.

According to the configuration, the content of the composite activated carbon in the positive electrode material for the lithium-sulfur secondary battery and the content of other components are in an appropriate balance. Therefore, even when the sulfur supported on (a) is eluted as polysulfide due to expansion of the positive electrode or the like, the polysulfide can be efficiently adsorbed by (b).

Examples of the other components include a conductive auxiliary agent, an aqueous binder, and the like. As the conductive auxiliary agent, any electronically conductive material that does not adversely affect the battery performance can be used. Normally, carbon black such as acetylene black and ketjen black is used, but natural graphite (scaly graphite, scaly graphite, earthy graphite, etc.), artificial graphite, carbon whisker, carbon fiber powder, metal (copper, nickel, etc.) (Aluminum, silver, gold, etc.) A conductive material such as powder, metal fiber, or conductive ceramic material may be used. These may be used alone or as a mixture of two or more kinds.

The conductive auxiliary agent is preferably made of a material different from that of the composite activated carbon. For example, all of the above-exemplified conductive materials such as natural graphite are different materials from the activated carbon obtained by carbonizing the above-mentioned resin, fossil resource material and the like and then alkali-activating them.

The water-based binder is not particularly limited as long as it can bind the composite activated carbon and the conductive auxiliary agent or the like. For example, one or more kinds of styrene-butadiene rubber (SBR) aqueous dispersion, carboxymethyl cellulose (CMC), alginate and the like can be used.

The other components are homogeneously mixed with the above (a) and the above (b). As the method, for example, as described above, the other components are put into a mortar or the like together with the above (a) and the above (b) and mixed, and the obtained mixture is further used with a rotation / revolution mixer. A method of stirring can be mentioned.

The positive electrode material for the lithium-sulfur secondary battery according to the embodiment of the present invention includes (a) activated carbon supporting sulfur and (b') activated carbon supporting a smaller proportion of sulfur than the above (a). , May contain a composite activated carbon in which is mixed.

The conditions of activated carbon, the type of sulfur, the content in the positive electrode material, and other components are as described above. Further, with respect to the above-mentioned (b'), the above-mentioned matters relating to (b) can be applied except for the amount of sulfur supported.

As described above, the (a) preferably carries 60% by weight or more of sulfur with respect to the weight of the (a). Further, the (b') preferably carries sulfur of more than 0% by weight and 10% by weight or less with respect to the weight of the above (b'), and more than 0% by weight and 5% by weight or less of sulfur. It is more preferable to carry it.

When the composite activated carbon is a mixture of the above (a) and the above (b'), there is a difference in the amount of sulfur supported, so that the above (a) is different from the case where only the above (a) is used. ), The polysulfide eluted from () can be adsorbed by the above (b').

The amount of sulfur supported in (b') is preferably as small as possible from the viewpoint of efficiently adsorbing the polysulfide eluted from (a). The efficiency with which the activated carbon (b') carrying sulfur of more than 0% by weight and 10% by weight or less adsorbs polysulfide is slightly inferior to the case of using the activated carbon not supporting sulfur as described in (b) above. However, it is possible to solve the problems of the present invention.

However, it is better to use the above (b) than to use the above (b'). Further, when the above (b') is used, two types of activated carbons in which the amount of sulfur is changed must be prepared, so that the number of manufacturing steps is increased as compared with the case of using the above (b). Therefore, it is more preferable to contain a composite activated carbon obtained by mixing (a) a sulfur-supporting activated carbon and (b) a sulfur-supporting activated carbon.

The positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention includes a composite activated carbon obtained by mixing (a) a sulfur-supported activated carbon and (b) a sulfur-free activated carbon. It may contain a conductive auxiliary agent made of a material different from that of the composite activated carbon. The other conditions in this case are the same as those of the positive electrode material for the lithium-sulfur secondary battery described above.

[2. Method for manufacturing positive electrode material for lithium-sulfur secondary batteries]
The method for producing a positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention is a step of (a) obtaining activated carbon carrying sulfur by mixing activated carbon and sulfur and heating the obtained mixture. A step of mixing (a) a sulfur-supported activated carbon, (b) a sulfur-free activated carbon, a conductive auxiliary agent, and an aqueous binder is provided. Regarding the above (a), the above (b), the conductive auxiliary agent, the water-based binder, the mixing ratio, etc., [1. Lithium-sulfur secondary battery positive electrode material].

In the production method, the activated carbon supporting (a) sulfur is, for example, [1. It can be produced by the method described in [Positive Material for Lithium-Sulfur Secondary Battery].

In the above-mentioned production method, the method of mixing each substance is not particularly limited, and may be mixed by an agate mortar or the like, may be mixed by stirring, or a plurality of methods may be used in combination.

In the above-mentioned production method, the method of stirring is not particularly limited, but for example, as in the examples described later, stirring may be performed using a rotation / revolution mixer. The stirring conditions are not particularly limited, but may be, for example, 1000 to 3000 rpm. The stirring time is also not particularly limited, but may be, for example, 20 to 40 minutes.

[3. Lithium-sulfur secondary battery]
The lithium-sulfur secondary battery according to the embodiment of the present invention includes a positive electrode material for the lithium-sulfur secondary battery according to the embodiment of the present invention. According to this configuration, even when the positive electrode material expands and contracts due to charging and discharging and the polysulfide is eluted from the above (a), the polysulfide can be adsorbed by the above (b). As shown in the example, excellent cycle characteristics and the like can be shown.

The positive electrode can be prepared by applying or filling the positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention to a current collector, drying it, pressure-molding it, and then vacuum-drying it. can.

As the current collector, an electronic conductor that does not adversely affect the configured battery can be used. For example, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass and the like can be mentioned. A current collector whose surface is treated with carbon, nickel, titanium, silver or the like may be used for the purpose of improving adhesiveness, conductivity, oxidation resistance and the like.

The shape of the current collector may be any of foil, film, sheet, net and the like. Among them, a current collector having a three-dimensional structure such as a honeycomb shape is preferable because more positive electrode materials for the lithium-sulfur secondary battery can be filled and the capacity can be increased.

The negative electrode can be obtained by subjecting a negative electrode material for a lithium-sulfur secondary battery containing metallic lithium as an active material, the above-mentioned conductive auxiliary agent, an aqueous binder and the like to, for example, the same method as the above-mentioned method for obtaining a positive electrode. can.

The lithium sulfur secondary battery according to the embodiment of the present invention includes an electrolyte containing lithium, carbonates, ethers, sulfur compounds, halogenated hydrocarbons, phosphate ester compounds, sulfolane hydrocarbons, and the like. It is preferable to provide an electrolytic solution containing one or more solvents selected from the group consisting of ionic liquids.

Examples of the lithium-containing electrolyte include LiPF ₆ , LiBF ₄ , lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and lithium bis (fluorosulfonyl) imide (LiFSI). Of these, LiPF ₆ , LiFSI, and LiTFSI are preferable, and LiTFSI is even more preferable. Only one type of the lithium-containing electrolyte may be used, or two or more types may be used in combination.

It is more preferable that the solvent contains one or more solvents selected from the group consisting of carbonates and ethers.

Examples of the carbonates include cyclic carbonates such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like. It is preferably chain carbonates.

Examples of the ethers include cyclic ethers such as dioxolane (DOL) and tetrahydrofuran; dimethoxyethane (DME), triglime (G3), tetraglime (G4), 1,1,2,2-tetrafluoro-3- (1). , 1,2,2-Tetrafluoroethoxy) -Propane (HFE) and other chain ethers are preferred.

Among them, the solvent is more preferably a solvent containing the carbonates. As described above, the solvents containing the carbonates are FEC and HFE from the viewpoint that an SEI film can be formed on the activated carbon having micropores and mesopores at the time of initial discharge of the lithium-sulfur secondary battery. It is particularly preferable that it is a mixture with.

The lithium-sulfur secondary battery according to the embodiment of the present invention can be manufactured by assembling by a conventionally known method using a positive electrode, a negative electrode, an electrolytic solution, a separator, a housing and the like.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

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

<Measurement of AC impedance>
The AC impedance of the lithium-sulfur secondary batteries produced in Examples and Comparative Examples was measured using an electrochemical measurement system S1 1280B (manufactured by Solartron). Specifically, the lithium-sulfur secondary battery is operated for 10 cycles in a voltage range of 1 to 3 V to charge and discharge, relaxed for 24 hours, and then the AC impedance is adjusted under the conditions of an amplitude width of 10 mV and a frequency range of 500 kHz to 10 MHz. It was measured.

<Measurement of cyclic voltammetry>
Cyclic voltammetry of the lithium-sulfur secondary batteries prepared in Examples and Comparative Examples was measured using an electrochemical measurement system S1 1280B (manufactured by Solartron). Specifically, using the above equipment, the ^{lithium-sulfur secondary battery was operated for two cycles at a scanning speed of 0.03 mV · s -1} and a voltage range of 1 to 3 V, and a cyclic voltammogram was prepared for the second cycle.

<Charge / discharge test>
A constant current charge / discharge test was performed using a positive electrode material for a lithium-sulfur secondary battery prepared in Examples and Comparative Examples as a working electrode and BTS2400W (manufactured by Nagano). Set the charging mode to C.I. C. The method (“CC” is an abbreviation for consistent currant) is used, and the mode at the time of discharge is changed to C.I. 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). The cutoff voltage has a lower limit of 1.0 V and an upper limit of 3.0 V. The test was conducted in an environment of 25 ° C.

The charge capacity and discharge capacity are defined as ^{mA · h (g sulfur) -1 based on the weight of sulfur.}

<Cycle property test>
The charge / discharge rate was set to 0.1 / 0.1C, and 1-100 cycles of charge / discharge were performed. The higher the discharge capacity at each cycle, the better the lithium-sulfur secondary battery.

The initial discharge capacity retention rate and energy density were calculated by the following formulas.
-Initial discharge capacity retention rate (%) = (20th cycle discharge capacity / 2nd cycle discharge capacity) x 100
・ Energy density (W ・ h / kg) = (Discharge capacity (m ・ Ah / g) × Weight of sulfur (g) × Voltage (V) × 1000) / (Weight of positive electrode including current collector (kg) + Electrolyte weight (kg) + separator weight (kg) + theoretical lithium weight (kg))
[Example 1]
(Preparation of activated carbon supporting sulfur)
0.35 g of activated carbon and 0.65 g of sulfur flower (manufactured by Wako pure chemical, with a purity of more than 99%) were mixed using an agate mortar to obtain a mixture. The mixture was transferred to a heat-resistant metal container, put into a muffle furnace, and heat-treated in the air.

The volume of the pores of the activated carbon was 1.202 cc / g, and the specific surface area was 2863 m ² / g. The pore distribution of the activated carbon was such that pores of 2 nm or less accounted for 93% or more, and in particular, pores of around 0.8 nm were most developed. These measurements were performed using the AUTOSORB iQ from Quantachrome.

Specifically, after the metal container was put into the furnace, the temperature inside the furnace was raised to 155 ° C., and this temperature was maintained for 5 hours to melt sulfur. Then, the temperature was raised to 300 ° C. at a rate of 5 ° C./min, and this temperature was maintained for 2 hours. Then, the inside of the furnace was sufficiently air-cooled, and the metal container was taken out from the inside of the furnace to obtain (a) sulfur-supported activated carbon.

The amount of sulfur supported in (a) above was measured by the following method. That is, the above (a) was placed in an alumina cell, and thermogravimetric analysis (TGA) was performed using DTG-60AH manufactured by Shimadzu Corporation. The measurement was performed under the conditions of the measurement gas Ar, the gas flow rate of 50 ml / min, the heating rate of 5 ° C./min, and the upper limit temperature of 600 ° C. The amount of sulfur supported was 61 to 63% by weight based on the total weight of (a).

(Preparation of positive electrode material and positive electrode for lithium-sulfur secondary battery)
The ratio of (a) sulfur-supported activated carbon, (b) sulfur-free activated carbon, acetylene black as a conductive auxiliary agent, and water-based binder as a binder to 70: 20: 5: 5 by weight. I measured it so that it would be. The above (b) is the same as the activated carbon used for the production of the above (a).

The measured material was mixed using an agate mortar, and the obtained mixture was transferred to an ointment case. Next, the mixture was stirred at a rotation speed of 2000 rpm for a total of 25 minutes using a rotation / revolution mixer to obtain a positive electrode material for a lithium-sulfur secondary battery.

Next, the positive electrode material for the lithium-sulfur secondary battery was filled in a 3D aluminum current collector (manufactured by Sumitomo Electric Industries, Ltd.) and dried at 40 ° C. for 1 hour using a hot plate. After rolling the dried current collector using a roll press machine, it is cut into a size of 2.4 cm × 2.4 cm using scissors to obtain a molded body, and then using a bell jar at 50 ° C., 12 more. It was dried for an hour to prepare a positive electrode.

(Preparation of electrolyte for lithium-sulfur secondary battery)
As the lithium-containing electrolyte, lithium bis (trifluoromethanesulfonyl) imide (hereinafter referred to as LiTFSI) was used. Further, as non-aqueous solvents, fluoroethylene carbonate (hereinafter referred to as FEC) and 1,1,2,2-tetrafluoro-3- (1,1,2,2-tetrafluoroethoxy) -propane (hereinafter referred to as HFE). A mixed solvent mixed with (referred to as) was used.

The method for preparing the electrolytic solution will be described more specifically. FEC and HFE were mixed so as to have a volume ratio of 1: 1 to obtain a mixed solvent. Next, LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / FEC: HFE of 1.0 mol / L, and vinylene carbonate (VC) was added in an amount of 10 Volume% to 90 Volume% of LiTFSI / FEC: HFE. It was used as the electrolyte for the lithium-sulfur secondary battery.

(Manufacturing of lithium-sulfur secondary battery)
The cell shape includes a cylindrical metal can type, a coin type, a laminated type, and the like, and a laminated type cell was used in this test. Using the positive electrode and the electrolytic solution prepared as described above, the lithium foil as the negative electrode, the separator and the electrolytic solution, a lithium sulfur battery was prepared by the following procedure in an air atmosphere having a dew point of −40 ° C. or lower.

First, the laminate assembled so that the positive electrode, the separator, and the negative electrode were laminated in this order was housed in an aluminum laminate film formed into a bag shape by thermocompression bonding. Further, after injecting the electrolytic solution into the laminated film, thermocompression bonding was performed while evacuating the laminated film to prepare a lithium-sulfur secondary battery.

[Example 2]
For lithium-sulfur secondary batteries by the same method as in Example 1 except that the weight ratios of (a), (b), acetylene black, and the aqueous binder were changed to 80:10: 5: 5. A positive electrode material and a lithium-sulfur secondary battery were produced.

[Example 3]
Lithium-sulfur secondary battery by the same method as in Example 1 except that the weight ratio of (a), (b), acetylene black, and water-based binder was changed to 60:30: 5: 5. A positive electrode material for use and a lithium-sulfur secondary battery were manufactured.

[Comparative Example 1]
In the preparation of the positive electrode material for the lithium-sulfur secondary battery, the weight ratio of (a), acetylene black, and the aqueous binder was changed to 90: 5: 5 without using (b). Except for this point, a positive electrode material for a lithium-sulfur secondary battery and a lithium-sulfur secondary battery were produced by the same method as in Example 1.

〔result〕
FIG. 1 shows the results of measuring the AC impedance of the lithium-sulfur secondary batteries produced in Example 1 and Comparative Example 1.

From FIG. 1, it can be seen that the semicircular component drawn by the plot in which the impedance is measured is smaller in Example 1 than in Comparative Example 1. That is, in the positive electrode for the lithium-sulfur secondary battery of Comparative Example 1, it is considered that the resistance between the particles of the activated carbon was increased by the side reaction product generated by the side reaction of the polysulfide eluted on the surface of (a). ..

On the other hand, in the positive electrode for a lithium-sulfur secondary battery of Example 1, which contains a composite activated carbon obtained by mixing (a) a sulfur-supporting activated carbon and (b) a sulfur-free activated carbon, from the above (a). It is suggested that the eluted polysulfide is adsorbed to the above (b) as it is before causing a side reaction, so that the irreversible reaction on the surface of the activated carbon is suppressed and the resistance is lowered.

FIG. 2 is a cyclic voltammogram of the second cycle in the lithium-sulfur secondary battery produced in Example 1 and Comparative Example 1.

From FIG. 2, it can be seen that in Example 1, the response current was generally larger and the sulfur utilization rate was higher in the insertion / desorption reaction than in Comparative Example 1. Therefore, the positive electrode material for the lithium-sulfur secondary battery contains the composite activated carbon obtained by mixing the above (a) and the above (b), so that the capacity of sulfur supported on the positive electrode material for the lithium-sulfur secondary battery is increased. It turned out that can be used efficiently.

Further, in FIG. 2, the reaction potentials of Example 1 and Comparative Example 1 were different. That is, it was shown that the polysulfide reaction of Example 1 was different from that of Comparative Example 1 because the positive electrode material for the lithium-sulfur secondary battery contained the composite activated carbon.

FIG. 3 shows the charge / discharge curves of the first cycle and the 100th cycle in Examples 1 to 3 and Comparative Example 1. FIG. 4 is an enlarged view of the circled portion in FIG.

As indicated by the arrow in FIG. 3, Example 1 had a larger discharge capacity per sulfur weight than Comparative Example 1. That is, it was found that the discharge capacity is improved by containing the composite activated carbon obtained by mixing the above (a) and the above (b) in the positive electrode material for the lithium-sulfur secondary battery.

Further, as indicated by the arrow in FIG. 4, in Examples 1 to 3, the discharge capacity (that is, the initial discharge capacity) ^{in 0 to 200 mAh (g sulfur) -1 was larger than that in Comparative Example 1.} Further, Example 1 had a larger initial discharge capacity than Comparative Example 1. That is, it was found that the initial discharge capacity is improved by containing the composite activated carbon obtained by mixing the above (a) and the above (b) in the positive electrode material for the lithium-sulfur secondary battery. Furthermore, it was found that the initial discharge capacity was further improved as the content of (b) was increased.

FIG. 5 shows the results of cycle characteristic tests of 1 to 100 cycles in Examples 1 to 3 and Comparative Example 1. The vertical axis on the left represents the discharge capacity, and the vertical axis on the right represents the cycle efficiency.

Table 1 shows the results of the cycle characteristic test and the initial discharge capacity retention rate. In the table, "(a): (b)" refers to (a) sulfur-supporting activated carbon and (b) sulfur in the positive electrode material for a lithium-sulfur secondary battery produced in Examples 1 to 3 and Comparative Example 1. It is a weight ratio with activated carbon that is not supported.

As shown in FIG. 5, in Comparative Example 1, the discharge capacity was significantly reduced by about the 20th cycle. On the other hand, in Example 2, the decrease in discharge capacity up to about the 20th cycle was improved as compared with Comparative Example 1. Further, it can be seen that in Example 1 in which the content of (b) was increased as compared with Example 2, the decrease in the discharge capacity was dramatically improved. Furthermore, it was clarified that in Example 3 in which the content of (b) was increased as compared with Example 1, the decrease in the initial discharge capacity was further improved as compared with Example 1.

Further, as shown in Table 1, Example 1 showed a higher initial discharge capacity retention rate than Comparative Example 1, and Example 3 showed a higher initial discharge capacity retention rate.

Table 2 shows the energy densities of the positive electrodes used in Examples 1 to 3 and Comparative Example 1 in the second cycle obtained from the results of the cycle characteristic test. In the table, the meaning of "(a): (b)" is the same as that in Table 1.

As shown in Table 2, Examples 1 to 3 had a higher energy density than Comparative Example 1. That is, it was found that the energy density of the positive electrode can be improved by containing the composite activated carbon obtained by mixing the above (a) and the above (b) in the positive electrode material for the lithium-sulfur secondary battery.

From the above results, the positive electrode material for a lithium-sulfur secondary battery according to an embodiment of the present invention contains the above (a) sulfur-supporting activated carbon as high as 60% by weight or more based on the weight of the above (a). It was revealed that even when sulfur was supported at a rate, it exhibited excellent properties. That is, it was shown that the positive electrode material for a lithium-sulfur secondary battery exhibits high conductivity, can suppress a decrease in discharge capacity due to elution of polysulfide into an electrolytic solution, and can achieve a high energy density. ..

As shown in Examples, the positive electrode material for a lithium-sulfur secondary battery can be manufactured at low cost by a simple process, and a lithium-sulfur secondary battery having both a high sulfur content and a high discharge capacity can be produced. Can be provided.

Since the lithium-sulfur secondary battery exhibits high energy density and can exhibit stable charge / discharge characteristics, it is considered that it can greatly contribute to the practical use of the lithium-sulfur secondary battery in the future.

[Example 4, Comparative Example 2: Polysulfide adsorption test]
A polysulfide adsorption test was conducted to investigate whether activated carbon adsorbs polysulfide.

(Method)
The Li _{2 S} n and _{(n = 4-8)} and dimethoxyethane (DME), a weight ratio of 1: 200 Li was prepared by mixing to such that _{_{2 S n (n = 4-8)}} / DME solution Was used. In 2 mL of the liquid, activated carbon 1 (D50 3.1 μm) that does not support sulfur, activated carbon 2 (D50 1.7 μm) that does not support sulfur, and carbon (acetylene black) that is not activated carbon as a comparative example are added. 0.02 g of each was added and left for a whole day and night. After that, the change in color was visually observed. The results are shown in Table 3 and FIG.

〔result〕
From Table 3 and Figure 6, since the color of the solution with the addition of activated carbon 1 is thinner, it can be seen that Li ₂ S _n is adsorbed on the activated carbon 1. Thin color finely activated carbon 2, further liquid particle size, since the almost colorless, as compared with the activated carbon 1, towards the activated carbon 2 has been found to be highly adsorbent of the Li ₂ S _n. On the other hand, acetylene black of the comparative example is the same as for the _Li 2 _S n / DME solution only, was yellow.

Therefore, it was found that when a material other than activated carbon (for example, acetylene black used as a normal conductive auxiliary agent) is used as the positive electrode material, the effect of polysulfide adsorption cannot be obtained. It is considered that this is because the specific surface area of activated carbon is about 750 m ² / g to 3300 m ² / g, while the specific surface area of acetylene black is about 40 m ² / g to 80 m ² / g.

The method for manufacturing a positive electrode material for a lithium sulfur secondary battery according to the present invention, a lithium sulfur secondary battery using the same, and a positive electrode material for a lithium sulfur secondary battery according to the present invention is a portable device such as a mobile phone or a mobile information terminal (PDA). Terminal equipment, laptop computers, small electronic devices such as video cameras and digital cameras, home appliances, electric bicycles, electric vehicles (electric vehicles), hybrid vehicles, mobile equipment (vehicles) such as trains, thermal power generation, wind power generation, It can be widely used in the fields of power generation equipment such as hydroelectric power generation, nuclear power generation, geothermal power generation, solar power generation, and renewable energy storage systems.

Claims

A positive electrode material for a lithium-sulfur secondary battery, which contains a composite activated carbon obtained by mixing (a) sulfur-supported activated carbon and (b) sulfur-free activated carbon.
The first aspect of the present invention, wherein the composite activated carbon contains 50% by weight or more and 98% by weight or less of the above (a) and 2% by weight or more and 50% by weight or less of the (b) with respect to the weight of the composite activated carbon. The positive electrode material for the lithium-sulfur secondary battery described.
The second aspect of the present invention, wherein the composite activated carbon contains 60% by weight or more and 80% by weight or less of the above (a) and 10% by weight or more and 30% by weight or less of the (b) with respect to the weight of the composite activated carbon. The positive electrode material for the lithium-sulfur secondary battery described.
For the weight of the positive electrode material for lithium-sulfur secondary batteries
The composite activated carbon is contained in an amount of 90% by weight or more and 95% by weight or less.
The positive electrode material for a lithium-sulfur secondary battery according to any one of claims 1 to 3, which contains 5% by weight or more and 10% by weight or less of other components.
The positive electrode material for a lithium-sulfur secondary battery according to any one of claims 1 to 4, wherein the (a) carries 60% by weight or more of sulfur with respect to the weight of the (a).
The positive carbon material for a lithium-sulfur secondary battery according to any one of claims 1 to 5, wherein the activated carbon carrying (a) sulfur and the activated carbon not supporting (b) sulfur are the same type of activated carbon.
The specific surface area of the activated carbon supporting (a) sulfur and the activated carbon not supporting (b) sulfur is 1500 m 2 g -1 or more and 2900 m 2 g -1 or less, any one of claims 1 to 6. The positive electrode material for a lithium-sulfur secondary battery according to the section.
The positive electrode material for a lithium-sulfur secondary battery according to any one of claims 1 to 7, further containing a conductive auxiliary agent and an aqueous binder.
A lithium-sulfur secondary battery comprising the positive electrode material for the lithium-sulfur secondary battery according to any one of claims 1 to 8.
An electrolyte containing lithium and one or more solvents selected from the group consisting of carbonates, ethers, sulfur compounds, halogenated hydrocarbons, phosphate ester compounds, sulfolane hydrocarbons, and ionic liquids. The lithium sulfur secondary battery according to claim 9, further comprising an electrolytic solution containing.
By mixing activated carbon and sulfur and heating the obtained mixture, (a) a step of obtaining activated carbon carrying sulfur, and
A method for producing a positive electrode material for a lithium-sulfur secondary battery, comprising the steps of (a) a sulfur-supporting activated carbon, (b) a sulfur-free activated carbon, a conductive auxiliary agent, and an aqueous binder. ..
A positive electrode for a lithium-sulfur secondary battery containing a composite activated carbon obtained by mixing (a) an activated carbon carrying sulfur and (b') an activated carbon supporting a smaller proportion of sulfur than the above (a). material.
The (a) carries 60% by weight or more of sulfur with respect to the weight of the (a), and the (b') is more than 0% by weight and 10% by weight or less with respect to the weight of the (b'). The positive electrode material for a lithium-sulfur secondary battery according to claim 12, which carries the sulfur of the above.
It contains (a) a composite activated carbon obtained by mixing an activated carbon carrying sulfur and (b) an activated carbon not carrying sulfur, and a conductive auxiliary agent made of a material different from the composite activated carbon. Positive electrode material for lithium-sulfur secondary batteries.