JP2022076603A - Electrolytic solution for lithium-sulfur secondary battery and lithium-sulfur secondary battery - Google Patents

Abstract

To provide an electrolytic solution for a lithium-sulfur secondary battery capable of suppressing elution of lithium polysulfide from a composite material of porous carbon and sulfur.SOLUTION: In an electrolytic solution for a lithium-sulfur secondary battery, the lithium-sulfur secondary battery includes a composite material of porous carbon and sulfur as a material for a positive electrode, the porous carbon contains pores having a pore diameter of 2 nm or more, and the solvent of the electrolytic solution contains ethylene carbonate having a chloro group.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolytic solution for a lithium-sulfur secondary battery and a lithium-sulfur secondary battery.

Lithium-ion secondary batteries are secondary batteries that have high energy density, can operate under high voltage, and have excellent performance such as long life due to low self-discharge. In recent years, in order to further popularize electric vehicles and the like, it is required to have a higher energy density.

However, since the lithium ion secondary battery is a battery that uses cobalt, manganese, nickel, or the like, it has resource restrictions and price restrictions in order to achieve high-density energy.

A lithium-sulfur secondary battery using sulfur for the positive electrode can obtain a significantly larger discharge capacity than a lithium ion secondary battery. In addition, since sulfur is abundant as a resource, it is cheaper than the above-mentioned cobalt, manganese, nickel and the like, and is easily available. Therefore, lithium-sulfur-based secondary batteries are attracting attention as next-generation secondary batteries.

On the other hand, sulfur is an insulator that does not have electron conductivity. Therefore, a method of complexing sulfur with an electron conductive substance has been proposed. Non-Patent Document 1 proposes carbon nanotubes, graphene, porous carbon, conductive polymers, polyacrylonitrile, metal oxides and the like as examples of the electron conductive substance. Examples of the use of the electron conductive substance include an electrode material in which sulfur is adsorbed in the nanoporous of porous carbon as disclosed in Patent Document 1.

Patent Document 2 discloses a binder for use as an electrode of a lithium-sulfur-based secondary battery, and also discloses that a composite of sulfur and porous carbon is used as a material for a positive electrode.

On the other hand, in a lithium-sulfur-based secondary battery, the lithium metal is oxidized at the negative electrode during discharge, and lithium ions are dissolved in the electrolytic solution. The lithium ion reacts with sulfur at the positive electrode and is reduced to lithium sulfide ₍ Li 2S) via the reaction intermediate product lithium polysulfide (lithium polysulfide).

However, since the lithium polysulfide is easily eluted in the electrolytic solution, self-discharge is generated by the so-called redox shuttle, which causes a rapid capacity attenuation and a decrease in charge / discharge efficiency of the lithium-sulfur-based secondary battery.

Patent Document 3 describes, as a technique for suppressing elution of lithium polysulfide, an electrolytic solution of a lithium-sulfur-based secondary battery using a composite of sulfur and porous carbon as a positive electrode material, which is a fluorinated ether. The electrolytic solution containing the above is disclosed.

Japanese Unexamined Patent Publication No. 2013-118191 Japanese Unexamined Patent Publication No. 2016-100094 International Publication No. 2018/163778

X. Ji, K. T. Lee and L. F. Nazar, “A highly ordered nanostructured carbon-sulphur cathode for lithium-sulphur batteries”, Nature Materials. 8 (2009) 500.

Here, when a composite material of porous carbon and sulfur is used as a material for a positive electrode, it is preferable that the larger the amount of sulfur carried in the porous carbon, the higher the energy density of the lithium-sulfur secondary battery. It can be said that. From the viewpoint of supporting a large amount of sulfur, it can be said that it is preferable that the pore size of the porous carbon is large.

However, the present inventor uses ethylene carbonate as a solvent for the electrolytic solution for a lithium-sulfur-based secondary battery in which the composite is used as a material for a positive electrode and the porous carbon has pores of 2 nm or more. It has been found that when used, there arises a problem that charge / discharge characteristics cannot be obtained. Ethylene carbonate is a solvent for an electrolytic solution generally used in a lithium ion secondary battery.

Patent Document 1 and Non-Patent Document 1 refer to the composite material, but cannot solve the problem because they do not mention the problem between the electrolytic solution and the charge / discharge characteristics.

Patent Document 2 merely discloses that microporous carbon is used as the porous carbon and ethylene carbonate is used as a preferable solvent used in the electrolytic solution. Since Patent Document 2 does not recognize any problem when the porous carbon has pores of 2 nm or more, the problem cannot be solved.

Patent Document 3 discloses that the electrolytic solution of the lithium-sulfur-based secondary battery described in Patent Document 3 can suppress the production of Li ₂ S ₈ among lithium polysulfides. However, as will be described later, the present inventor has found that the lithium-sulfur-based secondary battery using the electrolytic solution has room for improvement in the polarization of charge / discharge characteristics.

Therefore, one aspect of the present invention is to suppress elution of lithium polysulfide from a composite material of porous carbon containing sulfur having pores having a pore diameter of 2 nm or more and sulfur, and to charge / discharge characteristics of a lithium-sulfur secondary battery. It is an object of the present invention to provide an electrolytic solution for a lithium-sulfur-based secondary battery which can greatly improve the above.

As a result of diligent studies to solve the above problems, the present inventor has found that the above problems can be solved by using an electrolytic solution using ethylene carbonate having a chloro group as a solvent, and completed the present invention. I came to do.

That is, the present invention includes the following configurations.

<1> An electrolytic solution for a lithium-sulfur-based secondary battery, wherein the lithium-sulfur-based secondary battery includes a composite material of porous carbon and sulfur as a positive electrode material, and the porous carbon is An electrolytic solution for a lithium-sulfur secondary battery, which contains pores having a pore diameter of 2 nm or more and contains an ethylene carbonate having a chloro group as the solvent of the electrolytic solution.

<2> The electrolytic solution for a lithium-sulfur secondary battery according to <1>, wherein the total volume of the pores of the porous carbon is 0.4 cm ³ / g or more and 2.0 cm ³ / g or less.

<3> The electrolytic solution for a lithium-sulfur secondary battery according to <2>, wherein the total volume of the pores of the porous carbon is 0.9 cm ³ / g or more and 2.0 cm ³ / g or less.

<4> The weight of sulfur carried in the pores of the porous carbon is 30% by weight or more and 90% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. The electrolytic solution for a lithium-sulfur secondary battery according to any one of <1> to <3>.

<5> The weight of sulfur carried in the pores of the porous carbon is 50% by weight or more and 90% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. , <4>. The electrolytic solution for a lithium-sulfur secondary battery.

<6> The method according to any one of <1> to <5>, wherein the ratio of the amount of pores having a pore diameter of 2 nm or more to the total amount of pores possessed by the porous carbon is 5% or more and 100% or less. Electrolyte for lithium-sulfur secondary batteries.

<7> The electrolytic solution for a lithium-sulfur secondary battery according to <6>, wherein the ratio of the amount of pores having a pore diameter of 2 nm or more is 40% or more and 100% or less.

<8> The electrolysis for a lithium-sulfur secondary battery according to any one of <1> to <7>, wherein the content of ethylene carbonate having a chloro group in the solvent is 20% by weight or more and 100% by weight or less. liquid.

<9> The electrolytic solution for a lithium-sulfur secondary battery according to <8>, wherein the content of ethylene carbonate having a chloro group in the solvent is 30% by weight or more and 100% by weight or less.

<10> The solvent according to any one of <1> to <9>, wherein the solvent contains one or more selected from vinylene carbonate, hydrofluoroether, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. Electrolyte for lithium-sulfur secondary batteries.

<11> The electrolytic solution for a lithium-sulfur secondary battery according to any one of <1> to <10> is contained, and a composite material of porous carbon and sulfur is used as a positive electrode material, and the porous carbon is used. Is a lithium-sulfur secondary battery containing pores with a pore diameter of 2 nm or more.

According to one aspect of the present invention, even when a composite material of porous carbon containing pores having a pore diameter of 2 nm or more and sulfur is used as a positive electrode material, elution of lithium polysulfide from the composite material. Can be effectively suppressed. Further, according to one aspect of the present invention, it is possible to provide a lithium-sulfur-based secondary battery having excellent charge / discharge characteristics.

It is a figure which shows the result of the charge / discharge test of the lithium-sulfur-based secondary battery prepared in an Example and a comparative example. It is a graph which shows the result of subjecting the lithium-sulfur-based secondary battery prepared in an Example and a comparative example to a cycle characteristic test. It is a graph which shows the result of subjecting the lithium-sulfur-based secondary battery prepared in an Example and a comparative example to a cycle characteristic test. It is a graph which shows the result of subjecting the lithium-sulfur-based secondary battery prepared in an Example to a cycle characteristic test.

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, embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more and B or less".

[1. Lithium-sulfur-based secondary battery electrolyte]
The electrolytic solution for a lithium-sulfur-based secondary battery according to an embodiment of the present invention is an electrolytic solution for a lithium-sulfur-based secondary battery, and the lithium-sulfur-based secondary battery is used as a material for a positive electrode. The porous carbon comprises a composite material of porous carbon and sulfur, the porous carbon contains pores having a pore size of 2 nm or more, and the solvent of the electrolytic solution contains ethylene carbonate having a chloro group.

(1-1. Material for positive electrode of lithium-sulfur secondary battery)
The lithium-sulfur-based secondary battery using an electrolytic solution for a lithium-sulfur-based secondary battery according to an embodiment of the present invention includes a composite material of porous carbon and sulfur as a positive electrode material. In the present specification, the positive electrode material is a material applied or filled in a current collector for producing a positive electrode, and contains a positive electrode active material, a conductive auxiliary agent, a binder, and the like.

The sulfur is a positive electrode active material. The porous carbon is not particularly limited, but activated carbon or the like obtained by carbonizing a resin, a fossil resource material or the like and then activating it with an alkali such as potassium hydroxide can be preferably used. The activated carbon or the like is preferable because it has a large specific surface area and a volume of pores, and has a structure suitable for supporting a large amount of sulfur. Further, porous carbon whose pore structure of carbon is controlled by a template method can also be preferably used. The porous carbon may be produced based on a known method, or may be a commercially available product.

The "composite material of porous carbon and sulfur" is a porous carbon in which sulfur is supported in the pores of the porous carbon. That is, the composite material of porous carbon and sulfur also includes porous carbon adsorbed with polysulfide. The adsorption may be physical adsorption or chemical adsorption.

The porous carbon contains pores having a pore diameter of 2 nm or more. The shape of the pores of the porous carbon includes a slit shape, a wide open hole shape, a connecting hole, and the like, but the shape is not particularly limited. Types of pores of porous carbon include micropores having a pore diameter of less than 2 nm, mesopores having a pore diameter of 2 nm or more and less than 50 nm, and macropores having a pore diameter of 50 nm or more.

As described above, Patent Document 2 discloses that microporous carbon is used as the porous carbon and ethylene carbonate is used as a preferable solvent used in the electrolytic solution.

The microporous carbon disclosed in Patent Document 2 is a porous carbon having micropores. In this case, since ethylene carbonate cannot penetrate into the micropores, the sulfur supported on the micropores does not elute into the electrolytic solution as lithium polysulfide.

However, since the micropores have a very small pore diameter, the amount of sulfur that can be supported is naturally small. Therefore, it is required to support sulfur in mesopores having a pore diameter larger than that of micropores and to reduce the amount of sulfur eluted in the electrolytic solution.

Since the porous carbon contains pores having a pore diameter of 2 nm or more, it can carry more sulfur than the porous carbon having only micropores. Therefore, the lithium-sulfur-based secondary battery can be made into high-density energy.

Moreover, as will be described later, since the electrolytic solution for the lithium-sulfur secondary battery according to the embodiment of the present invention contains ethylene carbonate having a chloro group as a solvent, the sulfur is contained in the electrolytic solution as lithium polysulfide. It is possible to suppress the elution to. Therefore, the electrolytic solution for a lithium-sulfur-based secondary battery according to an embodiment of the present invention can provide a lithium-sulfur-based secondary battery having excellent charge / discharge characteristics.

The total volume of the pores of the porous carbon is preferably 0.4 cm ³ / g to 2.0 cm ³ / g, preferably 0.9 cm ³ / g to 2.0 cm, from the viewpoint of supporting a large amount of sulfur. It is more preferably ³ / g, and even more preferably 1.2 cm ³ / g to 2.0 cm ³ / g.

When the total volume of the pores of the porous carbon is in the above range, sulfur can be sufficiently supported on the porous carbon, so that the energy density of the lithium-sulfur secondary battery can be further improved. Can be done.

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

Further, the weight of sulfur carried in the pores of the porous carbon is 30% by weight or more and 90% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. It is more preferable, it is more preferably 50% by weight or more and 90% by weight or less, and further preferably 70% by weight or more and 90% by weight or less.

Further, in one aspect of the present invention, the weight of sulfur carried in the pores of the porous carbon is 70% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. There may be.

When the weight of the sulfur is in the above range, the amount of sulfur supported on the porous carbon can be sufficiently increased, so that the charge / discharge characteristics of the lithium-sulfur secondary battery can be improved. It is preferable that the amount of sulfur supported is large, but the upper limit is about 90% by weight in view of the carrying capacity of porous carbon and the like. The amount of sulfur carried can be confirmed by the method described later in the examples.

The ratio of the amount of pores having a pore diameter of 2 nm or more is preferably 5% or more, more preferably 20% or more, and more preferably 40% with respect to the total amount of pores contained in the porous carbon. The above is particularly preferable. Further, the ratio of the amount of pores having a pore diameter of 2 nm or more is preferably as high as possible, and is preferably 40% or less rather than 20% or less, and 60% with respect to the total amount of pores of the porous carbon. It is more preferably less than or equal to, more preferably 80% or less, and particularly preferably 100% or less.

As used herein, the "amount of pores" may mean either the number of pores or the volume of pores. That is, the ratio of the amount of pores having a pore diameter of 2 nm or more to the total amount of pores possessed by the porous carbon is the ratio of the pores having a pore diameter of 2 nm or more to the total number of pores possessed by the porous carbon. It may be a percentage of the number. Alternatively, the ratio of the amount of pores having a pore diameter of 2 nm or more to the total amount of pores possessed by the porous carbon is such that the pore diameter is 2 nm or more relative to the total volume of pores possessed by the porous carbon. It may be a percentage of the volume of the holes.

When the ratio is 5% or more, the amount of sulfur carried can be greatly increased as compared with the porous carbon having only micropores, so that a lithium-sulfur-based secondary battery having a high energy density can be provided. It will be easier.

When the ratio of macropores to the pores is large, the density of the electrodes tends to decrease. Therefore, it is more preferable that the pores having a pore diameter of 2 nm or more are mesopores.

The ratio of the number of pores having a pore diameter of 2 nm or more, and the pore diameter of the pores are measured by measuring the specific surface area of the porous carbon by the BET method, and the distribution of the pores and the pore diameter by the quenching solid phase density function method (QSDFT). It can be confirmed by measuring the volume of the pores. As the measuring device, AUTOSORB iQ manufactured by Quantachrome can be used.

The specific surface area, pore distribution, and pore volume of the porous carbon are measured by measuring the adsorption isotherm of nitrogen at the temperature of liquid nitrogen for a sample vacuum degassed at 200 ° C. for 3 hours. It can be carried out.

Further, the ratio of the volume of the pores having a pore diameter of 2 nm or more can be confirmed by the pore distribution map obtained from the AUTOSORB iQ.

Supporting sulfur in the pores can be performed, for example, by mixing porous 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.

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 specific surface area of the porous carbon is preferably 750 m ² / g to 3300 m ² / g, and more preferably 1200 m ² / g to 3300 m ² / g, from the viewpoint of supporting a large amount of sulfur.

The conductive auxiliary agent, which is a material for the positive electrode, can be used without particular limitation as long as it is an electronically conductive material that does not adversely affect the battery performance. As the conductive auxiliary agent, carbon black such as acetylene black or Ketjen black is usually used, but other conductive auxiliary agents may be used. For example, natural graphite (scaly graphite, scaly graphite, earthy graphite, etc.), artificial graphite, carbon whiskers, carbon fiber powder, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fibers, conductive ceramic materials. , A conductive material such as carbon nanotubes may be used. These may be used alone or as a mixture of two or more kinds.

Further, as the binder, for example, an aqueous binder can be used. The water-based binder is not particularly limited as long as it can bind the composite material of the porous carbon and sulfur to the conductive auxiliary agent or the like. For example, one or two types of binders selected from the group consisting of styrene-butadiene rubber (SBR) which is a rubber-based binder, carboxymethyl cellulose (CMC) as a dispersant, alginate as an aqueous binder, polyglutamic acid and the like. The above can be used.

The positive electrode material can be prepared, for example, by homogeneously mixing the sulfur-supporting porous carbon, the conductive auxiliary agent, and the binder. Examples of the mixing method include a method in which the porous carbon carrying sulfur and the conductive auxiliary agent are placed in a mortar or the like and mixed, and the obtained mixture is further stirred using a rotation / revolution mixer. be able to.

(1-2. Electrolyte for lithium-sulfur secondary battery)
The electrolytic solution for a lithium-sulfur-based secondary battery (hereinafter, also simply referred to as an electrolytic solution) contains a solvent and an electrolyte containing lithium.

The solvent of the electrolytic solution for the lithium-sulfur secondary battery (hereinafter, also simply referred to as the solvent of the electrolytic solution) contains ethylene carbonate having a chloro group. The number of chloro groups of the ethylene carbonate having a chloro group is not particularly limited and may be 1 to 4.

Further, the bonding position of the chloro group to ethylene carbonate is not particularly limited, and may be present at any position. That is, for example, all carbons in ethylene carbonate may have one or two chloro groups, or only one carbon may have a chloro group. Further, the chloro group may not be directly bonded to the carbon of ethylene carbonate, but may be bonded to the carbon as a chloromethylene group, for example.

Examples of the ethylene carbonate having a chloro group include chloroethylene carbonate (4-chloro-1,3-dioxolane-2-one), 3-chloropropylene carbonate, 4,4,5,5, -tetrachloro-1, Examples thereof include 3-dioxolane-2-one. Only one kind of ethylene carbonate containing a chloro group may be contained in the solvent of the electrolytic solution, or two or more kinds may be contained.

Since the solvent of the electrolytic solution contains ethylene carbonate having a chloro group, sulfur is lithium polysulfide from the pores even if the composite material of porous carbon and sulfur contains pores having a pore diameter of 2 nm or more. It is possible to prevent elution in the electrolytic solution.

As shown in Example 1 described later, when an electrolytic solution containing ethylene carbonate having a chloro group as a solvent is used, it is shown that a film is formed in the pores of the composite material (activated carbon carrying sulfur). A possible charge / discharge curve has been obtained.

From this, it is considered that in the electrolytic solution for the lithium-sulfur secondary battery according to the embodiment of the present invention, first, ethylene carbonate having a chloro group forms a film on the pores. Next, it is considered that the coating film suppresses the contact between the sulfur and the electrolytic solution and suppresses the elution of lithium polysulfide from the pores. As a result, it is considered that the loss of sulfur contained in the composite material can be prevented and sulfur can be effectively acted as a positive electrode active material, so that excellent charge / discharge characteristics can be obtained in a lithium-sulfur-based secondary battery. ..

Further, in the examples described later, the case where ethylene carbonate having a chloro group is used brings about superior charge / discharge characteristics to the lithium-sulfur secondary battery than the case where fluoroethylene carbonate is used as the solvent. It has been shown that it can be done.

The content of the ethylene carbonate having a chloro group in the solvent of the electrolytic solution is preferably 20% by weight or more and 100% by weight or less, preferably 30% by weight or more, when the weight of the solvent is 100% by weight. It is more preferably 100% by weight or less, and further preferably 50% by weight or more and 100% by weight or less.

When the content is 20% by weight or more, the film can be formed to such an extent that the elution of lithium polysulfide can be sufficiently suppressed when used as a solvent for the electrolytic solution. Therefore, a lithium-sulfur secondary battery It is preferable to improve the discharge capacity of the above.

The solvent of the electrolytic solution may contain a solvent other than the ethylene carbonate having a chloro group as a co-solvent. Such a co-solvent is selected from the group consisting of carbonates other than ethylene carbonate, ethers, sulfur compounds, halogenated hydrocarbons, phosphate ester compounds, sulfolane hydrocarbons, and ionic liquids. 1 or more can be mentioned.

Examples of the carbonates other than the ethylene carbonate include cyclic carbonates such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC); chains such as dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC). It is preferably carbonates.

The ethers are preferably cyclic ethers such as dioxolane (DOL) and tetrahydrofuran; chain ethers such as dimethoxyethane (DME), triglyme (G3), tetraglyme (G4) and hydrofluoro ethers.

Among the co-solvents, one or more selected from vinylene carbonate, hydrofluoroether, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and fluoroethylene carbonate is the charge / discharge characteristic of the lithium-sulfur secondary battery. It is particularly preferable from the viewpoint of improving.

Examples of the hydrofluoroether include 1,1,2,2-tetrafluoro-3- (1,1,2,2-tetrafluoroethoxy) -propane.

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.

[2. Lithium-sulfur secondary battery]
The lithium-sulfur-based secondary battery according to the embodiment of the present invention contains an electrolytic solution for the lithium-sulfur-based secondary battery according to the embodiment of the present invention, and a composite material of porous carbon and sulfur is used as a positive electrode. Used as a material, the porous carbon contains pores having a pore diameter of 2 nm or more.

According to this configuration, as shown in Examples described later, the amount of sulfur carried in the pores of the porous carbon contained in the positive electrode material is increased, and the sulfur is eluted as lithium polysulfide by the electrolytic solution. Therefore, it is possible to provide a lithium-sulfur-based secondary battery exhibiting a high discharge capacity.

The electrolytic solution and the porous carbon supporting sulfur are as described above. The electrolytic solution can be prepared, for example, by a method of mixing a lithium-containing electrolyte and a solvent.

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

The positive electrode can be prepared, for example, by applying or filling a current collector with a slurry for a positive electrode, drying it, pressure-molding it, and then vacuum-drying it.

The positive electrode slurry is prepared, for example, by adding a conductive auxiliary agent to a binder solution prepared by dissolving the binder in pure water, and then adding and mixing the composite material of the porous carbon and sulfur. be able to.

The weight ratio of the composite material, the conductive auxiliary agent, and the binder in the positive electrode slurry is 80:10:10 to 97: 0: 3 from the viewpoint of uniformly applying or filling the current collector. Is preferable, and 85: 5: 10 to 95: 0: 5 is more preferable.

As the current collector, an electron 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. For the purpose of improving adhesiveness, conductivity, oxidation resistance, etc., a current collector whose surface is treated with carbon, nickel, titanium, silver, or the like may be used.

The shape of the current collector may be any of foil-like, film-like, sheet-like, net-like and the like. Among them, a current collector having a three-dimensional structure such as a honeycomb shape is preferable because a larger amount of the positive electrode material for the lithium-sulfur secondary battery can be filled and the capacity can be increased. Examples of the current collector include a 3D aluminum current collector.

The negative electrode can be prepared, for example, by applying or filling a current collector with a slurry for a negative electrode, drying it, pressure-molding it, and then vacuum-drying it.

The negative electrode slurry can be prepared, for example, by adding a conductive auxiliary agent to a binder solution prepared by dissolving a binder in pure water, and then adding and mixing a negative electrode active material. As the negative electrode active material, for example, metallic lithium can be used.

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.

<Charging / discharging test>
A constant current charge / discharge test was performed using BTS2400W (manufactured by Nagano) with the positive electrode of the lithium-sulfur secondary battery produced in Examples and Comparative Examples described later as the working electrode. The charging mode is C.I. C. The method (“CC” is an abbreviation for consistent currant) is used, and the mode at the time of discharge is 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 the 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 in each cycle, the better the lithium-sulfur secondary battery.

The Coulomb efficiency and the capacity retention rate were calculated by the following formulas.
・ Coulomb efficiency (%) = (100th cycle Coulomb efficiency / 2nd cycle Coulomb efficiency) × 100
-Capacity retention rate (%) = (100th cycle discharge capacity / 2nd cycle discharge capacity) x 100
[Example 1]
(Preparation of activated carbon supporting sulfur)
Activated carbon having mesopores with a pore diameter of 2 nm or more and 4 nm or less and sulfur flower (manufactured by Wako pure chemical, with a purity of more than 99%) are mixed using an agate mortar so that the weight ratio is 35:65. A mixture was obtained. The mixture was transferred to a heat-resistant metal container, put into a muffle furnace, and heat-treated in the atmosphere.

The volume of the pores of the activated carbon was 1.6 cm ³ / g, and the specific surface area was 1307 m ² / g. Further, in the pores provided in the activated carbon, the ratio of the number of macropores: mesopores: micropores was 0:40:60.

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. The sulfur was adsorbed in the pores of the activated carbon by capillarity. Then, the inside of the furnace was sufficiently air-cooled to room temperature, and the metal container was taken out from the inside of the furnace to obtain activated carbon carrying sulfur. The activated carbon corresponds to the "composite material of porous carbon and sulfur" in one embodiment of the present invention.

The amount of sulfur supported on the activated carbon (weight of sulfur supported in the pores of the porous carbon) was measured by the following method. That is, the activated carbon carrying sulfur was put into 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 65% by weight based on the total weight of the activated carbon supporting sulfur.

(Preparation of binder solution)
As a binder, styrene-butadiene rubber (SBR), which is a rubber-based binder, and carboxylmethylcellulose (CMC), which is a dispersant, are dissolved in pure water, and the concentration of carboxylmethylcellulose (CMC) is 1 to 2% by weight. A solution was prepared.

(Preparation of slurry for positive electrode of lithium-sulfur secondary battery)
A slurry for a positive electrode was prepared by adding acetylene black, which is a conductive additive, to the binder solution, and then adding activated carbon carrying the sulfur. The weight ratio of the sulfur-supporting activated carbon, acetylene black, dispersant (CMC), and binder (SBR) was 90: 5: 3: 2.

(Manufacturing of positive electrode for lithium-sulfur secondary battery)
As a positive electrode for a lithium-sulfur secondary battery, a positive electrode for a bipolar flat cell was manufactured.

The positive electrode for a two-pole flat cell was produced by the following method. First, the positive plasma slurry is applied to an aluminum foil (current collector) so that the weight of the activated carbon carrying the sulfur is 1.3 mg / cm ² per unit area of the current collector, and the pressure is reduced. , Dryed at 40 ° C. for 1 hour using an oven. Next, the dried current collector was rolled using a roll press machine and then punched to a size of 12 mm in diameter to obtain a molded body. The molded product was vacuum dried for another 12 hours using a bell jar at 50 ° C. to prepare a positive electrode for a bipolar flat cell.

(Manufacturing of negative electrode for lithium-sulfur secondary battery)
As a negative electrode for a lithium-sulfur secondary battery, a negative electrode for a bipolar flat cell was manufactured.

The negative electrode for a two-pole flat cell was prepared by punching a lithium foil having a thickness of 20 μm into a diameter of 16 mm in an air atmosphere having a dew point of −40 ° C. or lower.

(Preparation of electrolytic solution 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, 4-chloro-1,3-dioxolane-2-one (chloroethylene carbonate) (hereinafter referred to as ClEC) and 1,1,2,2-tetrafluoro-3- (1,1) are used. , 2,2-Tetrafluoroethoxy) -propane (hereinafter referred to as HFE) was mixed so as to have a volume ratio of 50:50, and a mixed solvent was used.

The method for preparing the electrolytic solution will be described more specifically. ClEC and HFE were mixed in a volume ratio of 50:50 to obtain a mixed solvent. Next, a solution in which LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / ClEC: HFE of 1.0 mol / L was used as an electrolytic solution for a lithium-sulfur secondary battery.

(Making a lithium-sulfur secondary battery)
A positive electrode prepared by the above (manufacturing of a positive electrode for a lithium-sulfur secondary battery) and a negative electrode prepared by the above (manufacturing of a negative electrode for a lithium-sulfur secondary battery) in an air atmosphere with a dew point of -40 ° C. or lower. Using the electrolytic solution prepared in (Preparation of electrolytic solution for lithium-sulfur-based secondary battery) and polypropylene-based microporous membrane as a separator, a lithium-sulfur-based secondary battery was prepared by the following procedure.

A two-pole flat cell (coated electrode) was used as the cell of the lithium-sulfur secondary battery. First, the positive electrode, the separator, and the negative electrode were housed in the cell so as to be laminated in this order. Next, the electrolytic solution was injected into the cell to prepare a lithium-sulfur secondary battery.

The lithium-sulfur secondary battery was subjected to the charge / discharge test and cycle characteristic test described above.

[Example 2]
(Preparation of activated carbon supporting sulfur)
Sulfur-supporting activated carbon was obtained by the same method as in Example 1 except that the activated carbon had mesopores having a pore diameter of 2 nm or more and 3 nm or less.

The volume of the pores of the activated carbon was 1.3 cm ³ / g, and the specific surface area was 2924 m ² / g. Further, in the pores provided in the activated carbon, the ratio of the number of macropores: mesopores: micropores was 0: 5: 95.

The amount of sulfur supported on the activated carbon was measured by the same method as in Example 1. The amount of sulfur supported was 61% by weight based on the total weight of the activated carbon supporting sulfur.

(Preparation of binder solution)
As a binder, polyglutamic acid salt of an aqueous binder was dissolved in pure water to prepare a binder solution having a polyglutamic acid concentration of 5% by weight.

(Preparation of slurry for positive electrode of lithium-sulfur secondary battery)
A positive electrode slurry was prepared by adding carbon nanotubes as a conductive auxiliary agent and then activated carbon carrying the sulfur to the binder solution. The weight ratio of the sulfur-supported activated carbon, the carbon nanotubes, and the binder was 94: 1: 5.

(Making a lithium-sulfur secondary battery)
Same as Example 1 except that the activated carbon carrying sulfur is applied to an aluminum foil (current collector) so that the weight of the activated carbon is 1.1 to 1.3 mg / cm ² per unit area of the current collector. A positive electrode for a two-pole flat cell was produced by the above method.

A lithium-sulfur secondary battery was produced in the same manner as in Example 1 in other respects.

[Example 3]
A lithium-sulfur secondary battery was produced by the same method as in Example 2 except that the electrolytic solution was prepared as follows.

ClEC and 4-fluoro-1,3-dioxolane-2-one (fluoroethylene carbonate) (hereinafter referred to as FEC) were mixed so as to have a volume ratio of 50:50 to prepare a mixed solvent. Next, a solution in which LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / ClEC: FEC of 1.0 mol / L was used as an electrolytic solution for a lithium-sulfur secondary battery.

[Example 4]
A lithium-sulfur secondary battery was produced by the same method as in Example 2 except that the electrolytic solution was prepared as follows.

ClEC and the VC were mixed so as to have a volume ratio of 50:50 to prepare a mixed solvent. Next, a solution in which LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / ClEC: VC of 1.0 mol / L was used as an electrolytic solution for a lithium-sulfur secondary battery.

The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 5]
A lithium-sulfur secondary battery was produced by the same method as in Example 2 except that the electrolytic solution was prepared as follows.

A solution prepared by dissolving LiTFSI in ClEC so as to have LiTFSI / ClEC of 1.0 mol / L was used as an electrolytic solution for a lithium-sulfur secondary battery.

The amount of sulfur supported in the sulfur-supported activated carbon was 63% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 6]
A lithium-sulfur secondary battery was produced in the same manner as in Example 2 except that the electrolytic solution was prepared as follows.

LiTFSI was dissolved in ClEC so as to be 1.0 mol / L LiTFSI / ClEC to prepare a solution. Next, 10 Volume% of vinylene carbonate (VC) was added to the 100 Volume% solution to prepare an electrolytic solution for a lithium-sulfur secondary battery.

The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 7]
A lithium-sulfur secondary battery was produced in the same manner as in Example 2 except that the electrolytic solution was prepared as follows.

ClEC and HFE were mixed so as to have a volume ratio of 90:10, and used as a mixed solvent. Then, LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / ClEC: HFE of 1.0 mol / L to prepare a solution. Next, VC was added in 10 Volume% to the 100 Volume% solution to obtain an electrolytic solution for a lithium-sulfur secondary battery.

The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 8]
ClEC and HFE were mixed so as to have a volume ratio of 70:30, and used as a mixed solvent. Then, LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / ClEC: HFE of 1.0 mol / L to prepare a solution. Further, VC was added in 10 Volume% to the 100 Volume% solution to obtain an electrolytic solution for a lithium-sulfur secondary battery. A lithium-sulfur-based secondary battery was produced in the same manner as in Example 7 in other respects.

The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 9]
A lithium-sulfur secondary battery was produced in the same manner as in Example 7 except that ClEC and HFE were mixed so as to have a volume ratio of 50:50 and used as a mixed solvent.

The amount of sulfur supported in the sulfur-supported activated carbon was 63% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 10]
A lithium-sulfur secondary battery was produced in the same manner as in Example 7 except that ClEC and HFE were mixed so as to have a volume ratio of 30:70 and used as a mixed solvent.

The amount of sulfur supported in the sulfur-supported activated carbon was 63% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 11]
A lithium-sulfur secondary battery was produced by the same method as in Example 2 except that the electrolytic solution, the positive electrode, the negative electrode, and the electrolytic solution were prepared as follows. The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

A positive electrode for a laminated cell was produced by the following method.

First, the positive electrode slurry prepared by the same method as in Example 1 is 3D so that the weight of the activated carbon carrying sulfur is 11 mg / cm ^{2 or more and 13 mg / cm 2 or} less per unit area of the current collector. It was filled in an aluminum collector (Celmet manufactured by Sumitomo Electric Co., Ltd.). Next, the 3D aluminum current collector was dried at 40 ° C. for 1 hour under atmospheric pressure using an oven. Subsequently, the dried current collector was rolled using a roll press machine and then cut into a size of 24 mm × 24 mm using scissors to obtain a molded body. The molded product was vacuum dried for another 12 hours using a bell jar at 50 ° C. to prepare a positive electrode for a laminated cell.

The negative electrode for the laminated cell was prepared by cutting a lithium foil having a thickness of 30 μm into a size of 30 mm × 35 mm using scissors in an air atmosphere having a dew point of −40 ° C. or lower.

The electrolytic solution of the lithium-sulfur secondary battery was prepared by the same method as in Example 6.

[Example 12]
A lithium-sulfur secondary battery was produced by the same method as in Example 11 except that ClEC and HFE were mixed so as to have a volume ratio of 90:10 and used as a mixed solvent. The amount of sulfur supported in the sulfur-supported activated carbon was 66% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 13]
A lithium-sulfur secondary battery was produced by the same method as in Example 11 except that ClEC and HFE were mixed so as to have a volume ratio of 70:30 and used as a mixed solvent. The amount of sulfur supported in the sulfur-supported activated carbon was 64% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 14]
A lithium-sulfur secondary battery was produced by the same method as in Example 11 except that ClEC and HFE were mixed so as to have a volume ratio of 50:50 and used as a mixed solvent. The amount of sulfur supported in the sulfur-supported activated carbon was 65% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 15]
In the preparation of the electrolytic solution, ClEC and dimethyl carbonate (hereinafter referred to as DMC) were mixed so as to have a volume ratio of 70:30 and used as a mixed solvent by the same method as in Example 11, lithium-sulfur. A secondary battery was manufactured. The amount of sulfur supported in the sulfur-supported activated carbon was 67% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 16]
In the preparation of the electrolytic solution, a lithium-sulfur secondary battery was produced by the same method as in Example 11 except that ClEC and DMC were mixed so as to have a volume ratio of 50:50 and used as a mixed solvent. The amount of sulfur supported in the sulfur-supported activated carbon was 64% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 17]
In the preparation of the electrolytic solution, Lithium was mixed by the same method as in Example 11 except that ClEC and ethyl methyl carbonate (hereinafter referred to as EMC) were mixed so as to have a volume ratio of 70:30 and used as a mixed solvent. -A sulfur secondary battery was manufactured. The amount of sulfur supported in the sulfur-supported activated carbon was 65% by weight based on the total weight of the sulfur-supported activated carbon.

[Example 18]
In the preparation of the electrolytic solution, ClEC and diethyl carbonate (hereinafter referred to as DEC) were mixed so as to have a volume ratio of 70:30 to prepare a mixed solvent, and lithium- was used in the same manner as in Example 11. A sulfur secondary battery was manufactured. The amount of sulfur supported in the sulfur-supported activated carbon was 67% by weight based on the total weight of the sulfur-supported activated carbon.

[Comparative Example 1]
In the preparation of the electrolytic solution, lithium hexafluorophosphate (hereinafter referred to as LiPF ₆ ) was used as the lithium-containing electrolyte. Further, as the non-aqueous solvent, a mixed solvent (commercially available product manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (hereinafter referred to as EC) and DMC were mixed so as to have a volume ratio of 50:50 was used.

In other respects, a lithium-sulfur secondary battery was produced by the same method as in Example 1.

[Comparative Example 2]
A lithium-sulfur secondary battery was produced by the same method as in Example 1 except that FEC was used instead of ClEC as the non-aqueous solvent in the preparation of the electrolytic solution.

[Comparative Example 3]
In the preparation of the electrolytic solution, the same method as in Example 2 except that a mixed solvent (commercially available product manufactured by Kishida Chemical Co., Ltd.) in which EC and DMC are mixed so as to have a volume ratio of 50:50 was used as the non-aqueous solvent. To produce a lithium-sulfur secondary battery.

[Comparative Example 4]
In the preparation of the electrolytic solution, a lithium-sulfur-based battery was prepared by the same method as in Example 2 except that a mixed solvent in which FEC and HFE were mixed so as to have a volume ratio of 50:50 was used as the non-aqueous solvent. The next battery was manufactured.

[Comparative Example 5]
A lithium-sulfur secondary battery was produced by the same method as in Example 11 except that the electrolytic solution was prepared as follows.

In the electrolytic solution, LiPF ₆ was used as the lithium-containing electrolyte. Further, as a non-aqueous solvent, a mixed solvent (commercially available product manufactured by Kishida Chemical Co., Ltd.) in which EC and DMC were mixed so as to have a volume ratio of 50:50 was used. Next, a solution was prepared in which LiPF ₆ was dissolved in the mixed solvent so as to be 1.0 mol / L LiPF ₆ / EC: DMC. Further, vinylene carbonate (VC) was added at 10 Volume% to the 100 Volume% solution to prepare an electrolytic solution for a lithium-sulfur secondary battery.

[Comparative Example 6]
A lithium-sulfur secondary battery was produced by the same method as in Example 11 except that the electrolytic solution was prepared as follows.

In the electrolytic solution, as a non-aqueous solvent, a mixed solvent in which FEC and HFE were mixed so as to have a volume ratio of 50:50 was used. Then, LiTFSI was dissolved in the mixed solvent so as to have LiTFSI / FEC: HFE of 1.0 mol / L to prepare a solution. Next, 10 Volume% of vinylene carbonate (VC) was added to the 100 Volume% solution to prepare an electrolytic solution for a lithium-sulfur secondary battery.

〔result〕
FIG. 1 is a diagram showing the results of charge / discharge tests of the lithium-sulfur-based secondary batteries prepared in Example 1, Comparative Examples 1 and 2.

From FIG. 1, the lithium-sulfur-based secondary batteries prepared in Example 1 and Comparative Example 2 were able to be charged and discharged 100 times or more, but the lithium-sulfur-based secondary batteries prepared in Comparative Example 1 were capable of being charged and discharged 100 times or more. Only the discharge characteristics of the first cycle can be shown, and it can be seen that the battery could not be recharged.

Ethylene carbonate (EC) cannot penetrate the micropores (pore diameter less than 2 nm) of activated carbon, but can penetrate the mesopores. As described above, the ratio of the number of pores of the activated carbon used in Example 1, Comparative Example 1 and Comparative Example 2 is macropore: mesopore: micropore = 0:40:60. It is considered that the result of Comparative Example 1 is due to the fact that the EC, which is a solvent, invades into the mesopores, so that sulfur is eluted as lithium polysulfide and no electric current is generated.

Further, from FIG. 1, it can be seen that a characteristic discharge is generated in the vicinity of 1.8 to 2.3 V of the first cycle of Example 1 and Comparative Example 1. From this, it can be seen that a film was formed on the pores of the activated carbon carrying sulfur on the positive electrode.

The lithium-sulfur-based secondary batteries prepared in Example 1 and Comparative Example 2 have 100 cycles or more, unlike Comparative Example 1, as a result of suppressing the invasion of the solvent into the pores by forming the coating film. It is probable that charging and discharging could be performed.

On the other hand, it can be seen that the lithium-sulfur-based secondary battery prepared in Example 1 has a much smaller polarization of charge / discharge characteristics than the lithium-sulfur-based secondary battery prepared in Comparative Example 2. That is, it was clarified that by using ClEC as the solvent of the electrolytic solution, the resistance of the lithium-sulfur secondary battery can be significantly reduced as compared with the case of using FEC.

Therefore, it can be said that the lithium-sulfur-based secondary battery prepared in Example 1 can exhibit better charge / discharge characteristics than the lithium-sulfur-based secondary battery prepared in Comparative Example 1.

FIG. 2 and Table 1 show the results of subjecting the lithium-sulfur secondary batteries prepared in Example 1, Comparative Examples 1 and 2 to the above-mentioned cycle characteristic test.

As shown in FIG. 2 and Table 1, the lithium-sulfur-based secondary battery prepared in Comparative Example 1 could not operate. This result is considered to be due to the fact that EC used as the solvent of the electrolytic solution invaded the mesopores and sulfur was eluted as lithium polysulfide as described above.

The lithium-sulfur-based secondary battery prepared in Example 1 showed a higher discharge capacity in the second cycle than the lithium-sulfur-based secondary battery prepared in Comparative Example 2, and showed a capacity retention rate and an average Coulomb efficiency. Also showed a high value.

Further, as shown in FIG. 2, the lithium-sulfur-based secondary battery prepared in Example 1 has a higher discharge capacity than the lithium-sulfur-based secondary battery prepared in Comparative Example 2 even when the number of cycles is increased. It was shown that the difference increases as the number of cycles increases.

That is, it can be seen that by using ClEC as the solvent of the electrolytic solution, the discharge capacity of the lithium-sulfur secondary battery can be improved as compared with the case of using EC or FEC as the solvent.

FIG. 3 shows the results of cycle characteristic tests of the lithium-sulfur secondary batteries prepared in Example 2 and Comparative Examples 3 and 4. Table 2 shows the results of measuring the discharge capacity of the lithium-sulfur secondary batteries prepared in Examples 2 and 3 and Comparative Examples 3 and 4 in the second cycle.

As shown in FIGS. 3 and 2, the lithium-sulfur-based secondary battery prepared in Comparative Example 3 was able to operate up to 20 cycles, but had a low discharge capacity and short-circuited after 20 cycles. I couldn't operate it.

The lithium-sulfur-based secondary battery prepared in Comparative Example 3 uses EC as the solvent of the electrolytic solution, but all of the activated carbon used is more than the lithium-sulfur-based secondary battery prepared in Comparative Example 1 described above. The ratio of micropores to the pores is large. That is, the proportion of activated carbon in which EC cannot enter the pores is high. Therefore, unlike the lithium-sulfur-based secondary battery prepared in Comparative Example 1, it is considered that the battery could operate up to 20 cycles.

However, in the lithium-sulfur-based secondary battery prepared in Comparative Example 3, the sulfur carried in the mesopores was eluted by the EC invading the inside of the mesopores, resulting in a short circuit after 20 cycles. It is probable that it has been done.

From Table 2, the lithium-sulfur-based secondary batteries prepared in Examples 2 and 3 have a higher discharge capacity in the second cycle than the lithium-sulfur-based secondary batteries prepared in Comparative Examples 3 and 4. You can see that. Further, from FIG. 3, the lithium-sulfur-based secondary battery prepared in Example 2 is higher than the lithium-sulfur-based secondary battery prepared in Comparative Examples 3 and 4 even when the number of cycles is increased. It can be seen that it indicates the discharge capacity.

It is considered that the lithium-sulfur-based secondary batteries prepared in Examples 2 and 3 were able to form a film and retain a large amount of sulfur in the mesopores by using ClEC as the solvent of the electrolytic solution. Therefore, it is considered that the lithium-sulfur-based secondary battery prepared in Examples 2 and 3 was able to exhibit an excellent discharge capacity unlike the lithium-sulfur-based secondary battery prepared in Comparative Example 3.

Further, as described above, when ClEC is used as the solvent, the polarization of the charge / discharge characteristics can be made smaller than when ClEC is not used as the solvent and FEC is used. Due to this, it is considered that the lithium-sulfur-based secondary battery prepared in Example 2 showed a higher discharge capacity than the lithium-sulfur-based secondary battery prepared in Comparative Example 4.

As shown in Example 3, the lithium-sulfur-based secondary battery in which ClEC and FEC are used in combination as the solvent is higher than the lithium-sulfur-based secondary battery prepared in Comparative Example 4 in which ClEC is not used as the solvent. The discharge capacity in the second cycle was excellent. From this, it is possible to understand the usefulness of using ClEC as the solvent.

Table 3 shows the results of the cycle characteristic test of the lithium-sulfur secondary battery prepared in Examples 2, 4 and 5.

As shown in Example 5 of Table 3, it was found that the lithium-sulfur secondary battery exhibits a high discharge capacity even when ClEC is used alone as the solvent of the electrolytic solution.

Table 4 and FIG. 4 show the results of subjecting the lithium-sulfur secondary batteries prepared in Examples 6 to 10 to the cycle characteristic test.

As shown in Table 4 and FIG. 4, all of the lithium-sulfur-based secondary batteries prepared in Examples 6 to 10 showed high discharge capacities. As shown in Example 10, even if the ratio of ClEC in the electrolytic solution solvent is 30% by volume or less (the volume ratio of ClEC, HFE, and VC is 30:70:10), it is a lithium-sulfur-based battery. The secondary battery was found to exhibit a high discharge capacity.

That is, it can be said that the ClEC content in the solvent in the electrolytic solution does not necessarily have to be higher than that in the co-solvent, and a high discharge capacity can be obtained with a small content.

Table 5 shows the discharge capacities in the second and fifth cycles, and the capacity retention rate, which are the results of the cycle characteristic tests of Examples 11 to 18 and Comparative Examples 5 and 6.

From Table 5, the lithium-sulfur-based secondary battery prepared in each of the examples had a significantly higher discharge capacity in the second cycle than the lithium-sulfur-based secondary battery prepared in Comparative Example 5. That is, it was found that even when applied to a laminated cell, the discharge capacity can be significantly improved by using ClEC as the solvent of the electrolytic solution as compared with the case of using EC.

In addition, the discharge capacity of the lithium-sulfur-based secondary batteries prepared in Examples 11 to 14, 16 and 17 in the second cycle was significantly higher than that of the lithium-sulfur-based secondary batteries prepared in Comparative Example 6. That is, it was found that even when applied to a laminated cell, the discharge capacity can be improved by using ClEC as the solvent of the electrolytic solution as compared with the case of using FEC.

The discharge capacity of the lithium-sulfur-based secondary battery prepared in Examples 15 and 18 in the second cycle is about the same as that of the lithium-sulfur-based secondary battery prepared in Comparative Example 6. However, the results in Table 5 show that the capacity retention rate (discharge capacity in the 5th cycle / discharge capacity in the 2nd cycle × 100) when ClEC is used as the solvent of the electrolytic solution is larger than that when FEC is used. In view, it can be said that ClEC is useful as a solvent for the electrolytic solution.

From the above results, the electrolytic solution for the lithium-sulfur secondary battery according to the embodiment of the present invention has sulfur from activated carbon even when the ratio of mesopores to the pores of the activated carbon is high. It can be seen that the elution of can be prevented. Therefore, it has been clarified that the lithium-sulfur-based secondary battery can be imparted with excellent charge / discharge characteristics and cycle characteristics.

The lithium-sulfur-based secondary battery electrolyte and the lithium-sulfur-based secondary battery according to an embodiment of the present invention are portable terminal devices such as mobile phones and mobile information terminals (PDAs), notebook personal computers, and video cameras. Small electronic devices such as digital cameras, home appliances; electric bicycles, electric vehicles (electric vehicles), hybrid vehicles, mobile equipment (vehicles) such as trains; thermal power generation, wind power generation, hydraulic power generation, nuclear power generation, geothermal power generation, It can be widely used in the fields of power generation equipment such as solar power generation; natural energy storage system; etc.

Claims (11)

An electrolyte for lithium-sulfur secondary batteries,
The lithium-sulfur-based secondary battery includes a composite material of porous carbon and sulfur as a material for a positive electrode.
The porous carbon contains pores having a pore diameter of 2 nm or more, and the porous carbon contains pores having a pore diameter of 2 nm or more.
The solvent of the electrolytic solution is an electrolytic solution for a lithium-sulfur secondary battery containing ethylene carbonate having a chloro group. The electrolytic solution for a lithium-sulfur secondary battery according to claim 1, wherein the total volume of the pores of the porous carbon is 0.4 cm ³ / g or more and 2.0 cm ³ / g or less. The electrolytic solution for a lithium-sulfur secondary battery according to claim 2, wherein the total volume of the pores of the porous carbon is 0.9 cm ³ / g or more and 2.0 cm ³ / g or less. Claimed that the weight of sulfur carried in the pores of the porous carbon is 30% by weight or more and 90% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. The electrolytic solution for a lithium-sulfur secondary battery according to any one of 1 to 3. 4. Claim 4 that the weight of sulfur carried in the pores of the porous carbon is 50% by weight or more and 90% by weight or less with respect to the total of the weight of the porous carbon and the weight of the sulfur. The electrolytic solution for the lithium-sulfur secondary battery described in 1. The lithium-sulfur according to any one of claims 1 to 5, wherein the ratio of the amount of pores having a pore diameter of 2 nm or more to 100% or less with respect to the total amount of pores contained in the porous carbon is 5% or more and 100% or less. Electrolyte for system secondary batteries. The electrolytic solution for a lithium-sulfur secondary battery according to claim 6, wherein the ratio of the amount of pores having a pore diameter of 2 nm or more is 40% or more and 100% or less. The electrolytic solution for a lithium-sulfur secondary battery according to any one of claims 1 to 7, wherein the content of ethylene carbonate having a chloro group in the solvent is 20% by weight or more and 100% by weight or less. The electrolytic solution for a lithium-sulfur secondary battery according to claim 8, wherein the content of ethylene carbonate having a chloro group in the solvent is 30% by weight or more and 100% by weight or less. The lithium-sulfur system according to any one of claims 1 to 9, wherein the solvent comprises one or more selected from vinylene carbonate, hydrofluoroether, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and fluoroethylene carbonate. Electrolyte for secondary batteries. The electrolytic solution for a lithium-sulfur secondary battery according to any one of claims 1 to 10 is included.
A lithium-sulfur secondary battery in which a composite material of porous carbon and sulfur is used as a positive electrode material, and the porous carbon contains pores having a pore diameter of 2 nm or more.

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