WO2020096331A1 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery and, more specifically, to a lithium secondary battery comprising a cathode catalyst including a transition metal composite having a stable structure in which four nitrogens are bonded to the transition metal as a cathode catalyst for a reduction reaction of sulfur generated during operation of the lithium secondary battery having a sulfur-containing material included in a cathode thereof, thereby improving performance and longevity of the battery.

Description

Lithium secondary battery

This application is for Korean Patent Application No. 10-2018-0135536 filed on November 7, 2018, Korean Patent Application No. 10-2018-0135538 for November 7, 2018 and Korean Patent Application No. 10-2019 for November 4, 2019 Claims the benefit of priority based on -0139543, and all content disclosed in the literature of the relevant Korean patent application is included as part of this specification.

The present invention relates to a lithium secondary battery comprising a positive electrode catalyst that can facilitate the commercialization and high performance of the battery by promoting the chemical reaction occurring at the electrode.

Until recently, there has been considerable interest in developing high energy density cells using lithium as the negative electrode. Lithium metal compared to other electrochemical systems with lithium intercalated carbon anodes, and nickel or cadmium electrodes, for example, reducing the energy density of the cell by increasing the weight and volume of the anode in the presence of a non-electroactive material Since it has low weight and high capacity characteristics, it is very interesting as a negative electrode active material for electrochemical cells. A lithium metal negative electrode, or a negative electrode mainly containing lithium metal, provides an opportunity to construct a lighter and higher energy density battery than a battery such as a lithium-ion, nickel metal hydride, or nickel-cadmium battery. These features are highly desirable for batteries for portable electronic devices such as cell phones and laptop computers, where the premium is paid at low weight.

Cathode active materials for lithium batteries of this type are known, and they contain a sulfur-containing positive electrode active material comprising a sulfur-sulfur bond, a high energy capacity from electrochemical cutting (reduction) and reforming (oxidation) of the sulfur-sulfur bond and Rechargeability is achieved.

Lithium-sulfur secondary batteries using lithium and alkali metal as the negative electrode active material and sulfur as the positive electrode active material have a theoretical energy density of 2,800 Wh / kg and a theoretical capacity of sulfur of 1,675 mAh / g, which is superior to other battery systems. High, sulfur is abundant in resources, it is inexpensive, and it is attracting attention as a portable electronic device due to its advantages as an environment-friendly material.

However, since the sulfur used as the positive electrode active material of the lithium-sulfur secondary battery is a non-conductor, the movement of electrons generated by the electrochemical reaction is difficult, and the polysulfide (Li ₂ S ₈ ~ Li ₂ S ₄ ) elution problem generated during the charging and discharging process and Due to the low electrical conductivity of sulfur and lithium sulfide (Li ₂ S ₂ / Li ₂ S), there was a problem in that battery life characteristics and speed characteristics were inhibited due to the slow kinetic of the electrochemical reaction.

In this regard, in the process of charging and discharging a lithium-sulfur secondary battery using platinum (Pt), which has been recently used as an electrochemical catalyst, a high performance of the lithium-sulfur secondary battery is realized by improving the kinetic of the redox reaction of sulfur. Studies have been reported (Hesham Al Salem et al .: "Polysulfide Traps for Controlling Redox Shuttle Process of Li-S Batteries": J.Am.Chem.Soc., 2015, 137, 11542).

However, since a precious metal catalyst such as platinum is expensive, it is not only a material that is difficult to commercialize, but also has a problem in that it is not easy to use it as a positive electrode material for a lithium-sulfur secondary battery due to the possibility of poisoning by the redox reaction of sulfur in the process of charging and discharging.

Accordingly, it is possible to improve the kinetic of the electrochemical reaction during charging and discharging of the lithium-sulfur secondary battery, and at the same time, it is continuously required to develop a technology for a positive electrode material that is advantageous for commercialization.

[Advanced technical literature]

[Patent Document]

(Patent Document 1) Korean Patent Publication No. 2013-0014650

(Patent Document 2) International Publication Patent No. 2018-0013499

(Patent Document 3) International Publication No. 2017-0023304

The present inventors conducted various studies to solve the above problems, and as a catalyst for the reduction reaction of sulfur generated in the positive electrode during discharge of a lithium secondary battery containing a sulfur-containing material in the positive electrode, the outer surface of the porous carbon and the inner surface of the pores Introducing a transition metal complex comprising a transition metal and a doping element, but among the transition metal complexes, four nitrogen is bonded to the transition metal to introduce a high stability transition metal complex, thereby improving the performance and life characteristics of a lithium secondary battery. It was confirmed that it can be done.

Accordingly, an object of the present invention is to provide a lithium secondary battery comprising a positive electrode catalyst suitable as a catalyst for the reduction reaction of sulfur.

In order to achieve the above object, the present invention, in a lithium secondary battery comprising a positive electrode, a negative electrode containing a sulfur-containing material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the positive electrode is bonded to the surface of the porous carbon It provides a lithium secondary battery, including a positive electrode catalyst comprising a transition metal complex, wherein the transition metal complex comprises four nitrogen bonded to the transition metal.

The positive electrode is a current collector; And a positive electrode active material layer formed on the current collector, and the positive electrode catalyst may be included in the positive electrode active material layer.

The positive electrode catalyst may be 20 to 30% by weight based on the total weight of the positive electrode active material.

The transition metal may be one or more selected from the group consisting of Fe, Ni, Mn, Cu and Zn.

The transition metal complex may be contained in 1 to 20% by weight based on the total weight of the positive electrode catalyst.

The transition metal composite may be bonded to at least one of the porous carbon outer surface and the pore inner surface.

The transition metal complex may be adsorbed and bound to the surface of the porous carbon by π-π interaction.

The porous carbon includes at least one selected from the group consisting of activated carbon, carbon nanotube (CNT), graphene, carbon black, acetylene black, graphite, graphite nanofiber (GNF) and fullerene. May be

The pore size of the porous carbon may be 2 to 50 nm.

Since the lithium secondary battery according to the present invention contains a sulfur-containing material as a positive electrode active material, since a reduction reaction of sulfur occurs at the positive electrode when the battery is driven, a positive electrode catalyst capable of improving the reaction rate (kinetic) of the sulfur reduction reaction is appropriate By including the content, there is an effect of improving the initial discharge capacity and life characteristics of the battery.

The positive electrode catalyst according to the present invention can improve efficiency as a catalyst for the reduction reaction of sulfur due to a structure in which a transition metal complex having a stable structure in which four nitrogens are bonded to a transition metal is bonded.

In addition, by using a metal-phthalocyanine in the preparation of the positive electrode catalyst, the positive electrode catalyst can be prepared by a simple process without an additional process for bonding four nitrogens to the transition metal.

In addition, in the positive electrode catalyst, the transition metal complex is adsorbed by a π-π interaction on the surface of the porous carbon, and thus may exhibit an effect of maintaining physical and chemical properties of the porous carbon.

In addition, the positive electrode catalyst can be used as a catalyst for the reduction reaction of sulfur, and is advantageous for commercialization by replacing a relatively inexpensive transition metal on the surface of the porous carbon by replacing expensive platinum used as a conventional catalyst.

In addition, the positive electrode catalyst is a form in which a transition metal complex containing a transition metal and nitrogen is bonded to the outer surface of the porous carbon and the inner surface of the pores. Due to the material properties of the positive electrode catalyst, the possibility of toxicity to the redox reaction of sulfur is low. It is suitable for application as a positive electrode material of a lithium secondary battery, for example, a lithium-sulfur secondary battery. In particular, it can be applied as a positive electrode material of a lithium-sulfur secondary battery by supporting sulfur as a positive electrode active material in the pores of the porous carbon.

In addition, even if the transition metal complex is bonded to the pore inner surface of the porous carbon as a size of a molecular unit, it is possible to prevent the pore volume and size of the porous carbon from being reduced, and thus, lithium-sulfur secondary such as sulfur. When the positive electrode active material of the battery is supported, pore blocking can be prevented.

The lithium-sulfur secondary battery in which the positive electrode catalyst is introduced is capable of high performance due to activation of a reduction reaction of sulfur generated in the positive electrode.

1 is a schematic view showing a longitudinal section of an anode catalyst according to an embodiment of the present invention.

Figure 2 is a schematic diagram showing a method of manufacturing a positive electrode catalyst according to an embodiment of the present invention.

3 is a schematic view showing a longitudinal section of a positive electrode active material according to an embodiment of the present invention.

4 is a scanning electron microscope (SEM) photograph of the positive electrode catalysts prepared in Preparation Examples 1 to 6 and Comparative Preparation Examples 1 to 2, respectively.

FIG. 5 is a photograph showing a process in which the precursor (FePC) and porous carbon (CNT) of the transition metal complex in Preparation Example 1 are dissolved in an organic solvent (DMF) (FePC4-CNT mixture) and filtered.

6 is an XRD (x-ray diffraction) graph for the precursor (FePC) and the positive electrode catalyst (FePC16-CNT) of the transition metal complex used in Preparation Example 6.

7 is a TGA (Thermogravimetric analysis) graph for the positive electrode catalyst (FePC16-CNT) prepared in Preparation Example 6.

8A and 8B are graphs showing initial discharge capacity (FIG. 8A) and Coulomb efficiency (FIG. 8B) of the lithium-sulfur secondary batteries prepared in Example 1 and Comparative Example 1, respectively.

9A and 9B are graphs showing the initial discharge capacity (FIG. 9A) and Coulomb efficiency (FIG. 9B) of the lithium-sulfur secondary batteries prepared in Example 2 and Comparative Example 1, respectively.

10A and 10B are graphs showing initial discharge capacity (FIG. 10A) and Coulomb efficiency (FIG. 10B) of the lithium-sulfur secondary batteries prepared in Example 3 and Comparative Example 1, respectively.

11A and 11B are graphs showing initial discharge capacities (FIG. 11A) and Coulomb efficiency (FIG. 11B) of the lithium-sulfur secondary batteries prepared in Example 4 and Comparative Example 1, respectively.

12A and 12B are graphs showing initial discharge capacities (FIG. 12A) and Coulomb efficiency (FIG. 12B) of the lithium-sulfur secondary batteries prepared in Example 5 and Comparative Example 1, respectively.

13A and 13B are graphs showing initial discharge capacity (FIG. 13A) and Coulomb efficiency (FIG. 13B) of the lithium-sulfur secondary batteries prepared in Comparative Example 2 and Comparative Example 1, respectively.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

Terms or words used in the present specification and claims should not be interpreted as being limited to a conventional or dictionary meaning, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

Lithium secondary battery

The present invention is a lithium secondary battery comprising a positive electrode comprising a sulfur-containing material, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the positive electrode comprising a transition metal composite bonded to the surface of the porous carbon Including a catalyst, the transition metal complex is related to a lithium secondary battery comprising four nitrogens bound to a transition metal.

The positive electrode catalyst may be included in 20 to 30% by weight, preferably 22 to 28% by weight based on the total weight of the positive electrode active material in the positive electrode of the lithium secondary battery. If it is less than the above range, the catalytic activity for the sulfur reduction reaction is lowered, so the effect of improving battery performance and life characteristics is negligible, and a capacity deterioration phenomenon of the battery may occur beyond the above range.

The lithium secondary battery may contain a sulfur-containing material in the positive electrode, and thus may be a lithium-sulfur secondary battery.

In the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

The positive electrode current collector may be foamed aluminum having excellent conductivity, foamed nickel, or the like.

The positive electrode active material layer may include a positive electrode active material containing the sulfur-containing material and the positive electrode catalyst. In addition, the positive electrode active material layer further includes a conductive material for smoothly moving electrons within the positive electrode together with the positive electrode active material, and a binder for increasing binding force between the positive electrode active material or between the positive electrode active material and the positive electrode current collector. can do.

The sulfur-containing material included in the positive electrode active material may include elemental sulfur (S8), a sulfur-based compound, or a mixture thereof. Specifically, the sulfur-based compound is Li ₂ S _n (n is a real number of 1 or more), an organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n , x is a real number of 2.5 to 50, n is 2 This is a real mistake).

The positive electrode active material may be included in 60 to 90% by weight based on the total weight of the positive electrode active material layer. If it is less than the above range, the capacity of the battery decreases, and if it is above the above range, overvoltage may occur.

In addition, the conductive material is a carbon-based material, such as carbon black, acetylene black, Ketjen black; Or it may be a conductive polymer such as polyaniline, polythiophene, polyacetylene, and polypyrrole. The conductive material may be preferably included in 5 to 20% by weight relative to the total weight of the positive electrode active material layer. If the content of the conductive material is less than 5% by weight, the effect of improving conductivity according to the use of the conductive material is insignificant, whereas when it exceeds 20% by weight, the content of the positive electrode active material is relatively small, and there is a fear that capacity characteristics are deteriorated.

In addition, the binder includes poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate), poly Copolymer of vinylidene fluoride, polyhexafluoropropylene and polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine , Polystyrene, their derivatives, blends, copolymers, and the like. The binder may be preferably included in 5 to 20% by weight relative to the total weight of the positive electrode active material layer. When the content of the binder is less than 5% by weight, the effect of improving binding strength between the positive electrode active material or between the positive electrode active material and the positive electrode current collector according to the use of the binder is negligible, whereas when it exceeds 20% by weight, the content of the positive electrode active material is relatively small. There is a possibility that capacity characteristics are deteriorated.

The positive electrode as described above may be prepared according to a conventional method. Specifically, a positive electrode active material layer-forming composition prepared by mixing the positive electrode active material, positive electrode catalyst, conductive material, and binder on an organic solvent, on the positive electrode current collector After application, it can be prepared by drying and optionally rolling.

At this time, the organic solvent may uniformly disperse the positive electrode active material, the positive electrode catalyst, the binder, and the conductive material, and it is preferable to use one that is easily evaporated. Specific examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

In the present invention, the negative electrode may be a lithium metal thin film, or may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

The negative electrode current collector may be selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer may be used.

The negative electrode active material layer is a negative electrode active material composed of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal and lithium alloy It may include those selected from the group.

As a material capable of reversibly intercalating / deintercalating the lithium ions, a carbon-based negative electrode active material generally used in the lithium-sulfur secondary battery may be used, and specific examples include crystalline Carbon, amorphous carbon, or a combination of these may be used. In addition, a typical example of a material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion includes, but is not limited to, tin oxide (SnO ₂ ), titanium nitrate, silicon (Si), and the like. The lithium metal alloy may be specifically an alloy of lithium and Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, or Cd.

In addition, the negative electrode may further include a conductive material and a binder selectively together with the negative electrode active material. The types and contents of the conductive material and the binder are the same as described above.

In the present invention, the separator is a physical separator having a function of physically separating an electrode, and can be used without particular limitation as long as it is used as a separator in a lithium secondary battery. It is preferable that it has excellent moisture permeability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, alone It may be used as or by laminating them, or a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a nonwoven fabric made of polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

In the present invention, the electrolyte solution may include an organic solvent and a lithium salt.

Specifically, the organic solvent may be a polar solvent such as an aryl compound, bicyclic ether, acyclic carbonate, sulfoxide compound, lactone compound, ketone compound, ester compound, sulfate compound, sulfite compound, or the like.

More specifically, the organic solvent is 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, dioxolane (DOL), 1,4-dioxane, tetrahydrofuran , 2-methyltetrahydrofuran, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate, dipropyl carbonate, butyl ethyl carbonate, ethyl propano Eight (EP), toluene, xylene, dimethyl ether (DME), diethyl ether, triethylene glycol monomethyl ether (TEGME), triethylene glycol dimethyl ether (Triethylene glycol dimethyl ether, TEGDME ), Diglyme, tetraglyme, hexamethyl phosphoric triamide, gamma-butyrolactone (GBL), acetonitrile, propionitrile, ethylene carbonate (EC), propylene carbonate (PC), N- Me Tilpyrrolidone, 3-methyl-2-oxazolidone, acetic acid ester, butyric acid ester and propionic acid ester, dimethylformamide, sulfolane (SL), methyl sulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol And diacetate, dimethyl sulfite, or ethylene glycol sulfite. Among them, a mixed solvent of triethylene glycol monomethyl ether / dioxolane / dimethyl ether may be more preferable.

In addition, the lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt includes LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ (Lithium bis (perfluoroethylsulfonyl) imide, BETI), LiN (CF ₃ SO ₂ ) ₂ (Lithium bis (Trifluoromethanesulfonyl) imide, LiTFSI), LiN (C _a F _{2a + 1} SO ₂ ) (C _b F _{2b + 1} SO ₂ ) (where a and b are natural numbers, preferably 1≤a≤20 and 1≤b≤20), lithium poly [4,4 '-(hexahexafluor Loisopropylidene) diphenoxy] sulfonylimide (lithium poly [4,4 '-(hexafluoroisopropylidene) diphenoxy] sulfonylimide, LiPHFIPSI), LiCl, LiI, LiB (C ₂ O ₄ ) _2, etc. may be used, Among them, a sulfonyl group-containing imide lithium compound such as LiTFSI, BETI or LiPHFIPSI may be more preferable.

In addition, the lithium salt may be preferably included in 10 to 35% by weight relative to the total weight of the electrolyte. When the content of the lithium salt is less than 10% by weight, the conductivity of the electrolyte is lowered to degrade the electrolyte performance, and when it exceeds 35% by weight, the viscosity of the electrolyte is increased to decrease the mobility of lithium ions.

Anode catalyst

In the present invention, the positive electrode catalyst may be used as a catalyst for improving the reaction rate (kinetic) of the reduction reaction of sulfur in a lithium secondary battery containing a sulfur-containing material.

The positive electrode catalyst according to the present invention includes a transition metal complex bound to the surface of the porous carbon, and the transition metal complex includes a transition metal and four nitrogens bonded to the transition metal. At this time, since the catalytic activity can be controlled by the transition metal complex, the transition metal complex can be referred to as a catalytic site.

Hereinafter, the positive electrode catalyst according to the present invention will be described in more detail with reference to the drawings.

1 is a schematic view showing a longitudinal section of an anode catalyst according to an embodiment of the present invention.

Referring to Figure 1, the positive electrode catalyst 1 according to an embodiment of the present invention is a porous carbon (10); And a transition metal complex 20 bonded to the surface of the porous carbon 10.

The porous carbon 10 is a particle-shaped structure in which a number of pores 11 are formed, and is made of a material having a large size and high electrical conductivity, and has a pore volume and a specific surface area sufficient to promote the redox reaction of sulfur. , As a support for the transition metal composite 20, it is possible to maintain or improve the performance, durability and efficiency of the transition metal composite 20.

The porous carbon 10 is at least one carbon selected from the group consisting of activated carbon, carbon nanotube (CNT), graphene, carbon black, acetylene black, graphite, graphite nanofiber (GNF) and fullerene. It may be made of material.

The pores 11 formed on the porous carbon 10 are partially formed in an open shape, and inside the pores 11, an active material of an electrode, specifically, a positive electrode active material of a lithium-sulfur secondary battery may be supported.

The porous carbon 10 may be particles having a particle diameter of 1 to 50 μm, preferably 5 to 30 μm. If it is less than the above range, lithium ion transfer efficiency may be reduced due to penetration and wetting of the electrolyte, and if it is above the above range, the volume of the electrode pores may increase due to an increase in electrode pores compared to the electrode weight.

The pores 11 formed in the porous carbon 10 may be meso pores of 2 to 50 nm, preferably 2 to 45 nm, and more preferably 2 to 40 nm. If it is less than the above range, clogging of the pores 11 may occur in the process of impregnation of sulfur. In particular, when the positive electrode catalyst 1 is applied to a lithium secondary battery, for example, a lithium-sulfur secondary battery, impregnated liquid sulfur, which is a positive electrode active material, is impregnated. During the process, pores 11 may be clogged, and sulfur may not be uniformly supported in each pore. Also, due to the volume limitation of the pores 11, the amount of sulfur supported in the pores 11 may be reduced. In addition, when it is more than the above range, the reactants may be eluted in the reduction reaction of sulfur by becoming macro pores, and in particular, when the positive electrode catalyst 1 is applied to a lithium secondary battery, for example, a lithium-sulfur secondary battery, The intermediate product, poly sulfide, can be eluted.

In addition, the volume of the pores 11 contained in the porous carbon 10 may be 0.5 to 3.5 cc / g, preferably 1.0 to 3.0 cc / g, more preferably 1.5 to 2.5 cc / g. If it is less than the above range, clogging of the pores 11 may occur in the process of impregnation of sulfur. In particular, when the positive electrode catalyst 1 is applied to a lithium secondary battery, for example, a lithium-sulfur secondary battery, impregnated liquid sulfur, which is a positive electrode active material, is impregnated. During the process, pores 11 may be clogged, and sulfur may not be uniformly supported in each pore. Also, due to the volume limitation of the pores 11, the amount of sulfur supported in the pores 11 may be reduced. In addition, when it is more than the above range, the reactants may be eluted in the reduction reaction of sulfur by becoming macro pores, and in particular, when the positive electrode catalyst 1 is applied to a lithium secondary battery, for example, a lithium-sulfur secondary battery, The intermediate product, poly sulfide, can be eluted.

In addition, as the surface area of the porous carbon 10 increases, it is advantageous for catalytic activity, and specifically, it may be 100 to 1200 m 2 / g, preferably 150 to 500 m 2 / g. If it is less than the above range, the catalytic activity may decrease, and if it is above the above range, the durability of the anode catalyst may decrease.

In addition, the porous carbon 10 may be 80 to 99% by weight, preferably 80 to 95% by weight, more preferably 80 to 90% by weight based on the total content of the positive electrode catalyst (1). If it is less than the above range, the durability of the anode catalyst 1 may decrease, and if it is above the above range, the catalytic activity may decrease.

The transition metal complex 20 is a complex formed by bonding four nitrogens to a transition metal, and can act as a catalyst for the reduction reaction of sulfur to improve kinetic. Therefore, it can be suitable as a catalyst for a positive electrode of a lithium secondary battery, especially a lithium-sulfur secondary battery.

In the transition metal complex 20, when the number of nitrogens bound to the transition metal is less than 4, activity as a catalyst decreases, and when it exceeds 4, structural stability decreases, so that catalytic activity for sulfur reduction reaction It may degrade.

In addition, when nitrogen is bonded to the transition metal, it is not only stable, but also exhibits excellent catalytic properties, and thus can exhibit high stability and catalytic effect compared to a transition metal complex formed by bonding different types of elements to the transition metal.

The transition metal composite 20 may be included in an amount of 1 to 20% by weight, preferably 4 to 16% by weight, based on the total content of the positive electrode catalyst 1. If it is less than the above range, the effect of improving the reaction rate of the reduction reaction of sulfur may be reduced, and thus the effect of improving the battery performance may be negligible. If the content of the transition metal complex 20 is increased, the reaction rate of the reduction reaction of sulfur may no longer increase. It may not.

The transition metal composite 20 may be bonded to one or more positions of the outer surface of the porous carbon 10 and the inner surface of the pores, and specifically, the transition metal composite 20 may have π- on the surface of the porous carbon 10. It may be adsorbed and bound by π interaction. The π-π interaction has a binding form between a surface and a surface rather than a specific inter-element bond, and may exhibit strong adsorption compared to other types of bonds, and the transition metal complex 20 is bonded to the surface of the porous carbon 10 Even if it is, it is possible to maintain the characteristics of the porous carbon (10).

In the transition metal complex 20, the molar ratio of transition metal and nitrogen may be 1: 2 to 10, preferably 1: 2 to 8, and more preferably 1: 3 to 5. If it is less than the above range, the surface of the porous carbon 10 cannot be sufficiently doped with the transition metal complex 20 as necessary, and if it is above the above range, the amount of nitrogen per unit weight of the anode catalyst 1 increases, thereby increasing the catalytic activity. This can degrade.

The size of the transition metal composite 20 is 0.1 to 1 nm, preferably 0.1 to 0.9 nm, and more preferably 0.1 to 0.8 nm, which is an atomic level composite, even when bonded on the inner surface of the porous carbon 10. Since there is no reduction in volume and size of 11), even if the active material is carried inside the pores 11, it is possible to prevent pore clogging.

The transition metal may be at least one selected from the group consisting of Fe, Ni, Mn, Cu, and Zn, but is not limited thereto as long as it is a transition metal capable of exhibiting catalytic activity for the reduction reaction of sulfur.

The positive electrode catalyst 1 as described above can be widely used as a catalyst for the general sulfur reduction reaction. In addition, it can be used as a cathode material of a lithium secondary battery, in particular, it can also be applied as a cathode material of a lithium-sulfur secondary battery accompanied by a reduction reaction of sulfur to realize high performance of the battery, and can be advantageous for commercialization due to low cost. .

Anode catalyst manufacturing method

The present invention also relates to a method for preparing a positive electrode catalyst as described above, wherein the method for producing the positive electrode catalyst comprises: (S1) dissolving a precursor of a transition metal complex comprising a transition metal and nitrogen in a solvent; (S2) adding and mixing porous carbon to the precursor solution of the transition metal complex obtained in the step (S1); (S3) filtering the mixed solution obtained in the step (S2); And (S4) after the step (S3), drying the powder obtained in the upper layer of the mixture; may include, it will be described below in more detail for each step of the production method of the positive electrode catalyst according to the present invention.

(S1) step

In the step (S1), the precursor of the transition metal complex containing the transition metal and nitrogen is dissolved in a solvent to prepare a precursor solution of the transition metal complex. Preferably, the precursor of the transition metal complex may be dispersed in a solvent and subjected to ultrasonic treatment to prepare a precursor solution of the transition metal complex.

The concentration of the precursor solution of the transition metal complex may be 5 to 15%, preferably 5 to 12%, and more preferably 5 to 10% based on the solid content weight. If it is less than the above range, the weight of the transition metal complex contained in the cathode catalyst to be produced is reduced, resulting in poor catalytic activity, and if it is above the above range, the weight of the transition metal complex contained in the cathode catalyst to be produced is increased to block the pores of the porous carbon. Symptoms may occur.

The precursor of the transition metal complex may be at least one metal-phthalocyanine (MePC) selected from the group consisting of iron phthalocyanine, nickel phthalocyanine, manganese phthalocyanine, copper phthalocyanine, and zinc phthalocyanine.

The metal-phthalocyanine is a type of macrocyclic compound having a structure in which a ring of nitrogen atoms and carbon atoms intersects, and has a chemical structure in which metal ions coordinate in the center.

Since the metal-phthalocyanine is used as a precursor of the transition metal complex, it is possible to manufacture a positive electrode catalyst including a transition metal complex having a stable structure in which four nitrogens are bonded to the transition metal. In general, in order to bond four nitrogens to the transition metal, it is necessary to undergo a process of several steps such as reacting with a precursor material containing N, and further reacting under an ammonia (NH ₃ ) atmosphere. By using a metal-phthalocyanine having a chemical structure as described above as a precursor of a transition metal complex, a cathode catalyst comprising a transition metal complex having a stable structure in which four nitrogens are bonded to the transition metal as described above in a simple process is used. Can be produced.

The solvent is dimethyl carbonate, dimethyl formamide, N-methyl formamide, sulfolane (tetrahydrothiophene-1,1-dioxide), 3-methylsulfolan, N-butyl sulfone, dimethyl sulfoxide, pyridolinone ( HEP), dimethylpiperidone (DMPD), N-methyl pyrrolidinone (NMP), N-methyl acetamide, dimethyl acetamide (DMAc), N, N-dimethylformamide (DMF), diethyl acetamide (DEAc) ) Dipropylacetamide (DPAc), ethanol, propanol, butanol, hexanol, ethylene glycol, tetrachloroethylene, propylene glycol, toluene, trapentine, methyl acetate, ethyl acetate, petroleum ether, acetone, cresol and glycerol It may be at least one organic solvent selected from, preferably, when using DMF as the solvent, the solubility of the precursor of the transition metal complex may be high.

(S2) step

In the step (S2), porous carbon may be added to the precursor solution of the transition metal complex obtained in the step (S1) and mixed. The material of the porous carbon; And morphological characteristics such as pore size.

The porous carbon may be synthesized by a hard molding method, but is not limited thereto, and the porous carbon in the form described above may be synthesized by a conventional method for synthesizing porous carbon in the art.

Specifically, porous carbon may be synthesized using a carbon material. At this time, the carbon material used to synthesize the porous carbon and the shape of the produced porous carbon are as described above.

When mixing by adding porous carbon to the precursor solution of the transition metal complex, if necessary, ultrasonic treatment is performed followed by stirring and mixing to obtain a mixed solution.

Figure 2 is a schematic diagram showing a method of manufacturing a positive electrode catalyst according to an embodiment of the present invention.

Referring to FIG. 2, CNT is added as a porous carbon to a solution in which a metal-phthalocyanine (MePC), which is a precursor of a transition metal complex, is dissolved in an organic solvent, and a positive electrode catalyst (MePC-CNT) in which a transition metal complex is bonded to the surface of the CNT ) Can be prepared.

At this time, the amount of the transition metal composite and the porous carbon in the cathode catalyst to be produced can be used by appropriately adjusting the amount used in the manufacturing process, so as to satisfy the weight range as described above.

(S3) step

In the step (S3), the mixed liquid obtained in the step (S2) can be filtered and washed to remove impurities.

(S4) step

In the step (S4), after the step (S3), the powder obtained in the upper layer of the mixed solution may be dried to obtain an anode catalyst.

The positive electrode catalyst has a structure including a transition metal complex bound to the surface of the porous carbon, in order to obtain the positively formed positive electrode catalyst, the drying is 60 to 100 ° C, preferably 65 to 95 ° C, more preferably It may be made at a temperature of 70 to 90 ℃ for 10 to 14 hours, preferably 10.5 to 13.5 hours, more preferably 11 to 13 hours.

Anode active material

The present invention also relates to a positive electrode active material applicable to the positive electrode of a lithium secondary battery. Preferably, the lithium secondary battery may be a lithium-sulfur secondary battery including a sulfur-containing material as a positive electrode active material.

3 is a schematic view showing a longitudinal section of a positive electrode active material according to an embodiment of the present invention.

3, the positive electrode active material 2 according to an embodiment of the present invention includes the positive electrode catalyst 1 as described above; And a sulfur-containing material 30 supported inside the pores 11 of the porous carbon 10 included in the positive electrode catalyst 1.

The structure and constituent materials of the anode catalyst 1 are as described above.

The sulfur-containing material 30 may be one or more selected from the group consisting of elemental sulfur (S ₈ ) and sulfur compounds. Specifically, the sulfur compound is Li ₂ S _n (n is a real number of 1 or more), an organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) _n , x is a real number of 2.5 to 50, n is 2 or more Real number).

Manufacturing method of positive electrode active material

The present invention also relates to a method for producing a positive electrode active material as described above, wherein the method for producing a positive electrode active material comprises: (P1) forming a mixed powder of the positive electrode catalyst and a sulfur or sulfur compound; (P2) mixing the solvent for dissolving sulfur in the mixed powder to form a mixture; And (P3) heat-treating the mixture under vacuum to support sulfur in the pores of the positive electrode catalyst. It may include.

Hereinafter, a method of manufacturing the positive electrode active material according to the present invention will be described in more detail for each step.

(P1) step

The positive electrode catalyst for preparing the positive electrode active material may be prepared by a method for preparing a positive electrode catalyst including steps (S1) to (S4) as described above.

Both the positive electrode catalyst and sulfur can be mixed in a powder state to obtain a mixed powder. At this time, the positive electrode catalyst and sulfur may be mixed so that the weight of sulfur may be 50 to 80% by weight, preferably 65 to 77% by weight based on the total weight of the positive electrode active material to be produced.

(P2) step

The solvent is mixed with the mixed powder obtained in the step (P1) to form a mixture, and the solvent dissolves sulfur contained in the mixed powder by using a solvent for dissolving sulfur having a high solubility of sulfur, so that the dissolved liquid sulfur is It can be carried in the pores contained in the porous carbon of the positive electrode catalyst.

At this time, the solvent for dissolving sulfur may be at least one selected from the group consisting of CS ₂ solvent, ethylenediamine, acetone, and ethanol, and in particular, when using a CS ₂ solvent, the selective solubility for sulfur contained in the mixed powder is high. It may be advantageous to dissolve sulfur so that it is supported inside the pores contained in the porous carbon.

(P3) step

By heat-treating the mixture formed in step (P2) under vacuum, it is possible to fix the liquid sulfur supported inside the pores contained in the porous carbon of the positive electrode catalyst to the surface of the pores.

By the steps (P1) to (P3), it is possible to prepare a positive electrode active material having a form in which sulfur is supported on the positive electrode catalyst. The positive electrode active material can be applied to the positive electrode of a lithium secondary battery. Preferably, the lithium secondary battery may be a lithium-sulfur secondary battery.

Among the lithium secondary batteries according to the present invention, the lithium-sulfur secondary battery can improve the kinetic of the reduction reaction of sulfur generated at the positive electrode during discharge by introducing the positive electrode catalyst as described above to the positive electrode, and consequently, the lithium-sulfur secondary battery. High performance can be implemented.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are only illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and technical thought scope of the present invention. It is natural that changes and modifications fall within the scope of the appended claims.

Manufacturing example  1 to 6

(1) Preparation of the precursor solution (MePC solution) of the transition metal complex

Metal-phthalocyanine (Metal-phthalocyanine, MePC, Metal = Fe, Ni, Mn, Cu, Zn, Aldrich Co.), which is a precursor of the transition metal complex as described in Table 1 below, is a solvent N, N-dimethylformamide (N , N-Dimethylformamide, DMF), followed by bath sonication for 10 minutes to prepare a MePC solution. At this time, 40 mg of the MePC was dissolved in 500 mL of DMF to prepare a MePC solution.

At this time, MePC used in Preparation Examples 1 to 6 are respectively called FePC, NiPC, MnPC, CuPC, ZnPC and FePC.

(2) Porous carbon mixture

To the MePC solution, 960 mg of porous carbon CNT (CNano) was added, bath sonication was performed for 10 minutes, and the mixture was obtained by stirring at 500 rpm for 4 hours at room temperature.

(3) Filtration and cleaning

The mixed solution was filtered with a vacuum pump, and then washed with 1000 ml of ethanol.

(4) Dry

The upper layer powder of the filtered and washed mixture was dried at 80 ° C. for 12 hours to prepare a positive electrode catalyst in which a transition metal complex (MePC) was bonded to CNTs.

compare Manufacturing example  One

It carried out in the same manner as in Production Example 1, without using a positive electrode catalyst formed from the precursor of the transition metal complex and CNT, was prepared by using only CNT positive electrode catalyst.

compare Manufacturing example  2

A cathode catalyst was prepared in the same manner as in Preparation Example 1, using CoPC as a metal-phthalocyanine which is a precursor of the transition metal complex.

		Precursor of transition metal complex	Content of transition metal complex (included in anode catalyst)
Preparation Example 1	FePC4-CNT	FePC	4 wt%
Preparation Example 2	NiPC4-CNT	NiPC	4 wt%
Preparation Example 3	MnPC4-CNT	MnPC	4 wt%
Preparation Example 4	CuPC4-CNT	CuPC	4 wt%
Preparation Example 5	ZnPC4-CNT	ZnPC	4 wt%
Preparation Example 6	FePC16-CNT		FePC	16% by weight
Comparative Production Example 1	CNT	-	-
Comparative Production Example 2	CoPC4-CNT	CoPC	4 wt%

Example  1 to 6 and Comparative example  1 to 2: lithium secondary battery production

A positive electrode active material, a conductive material, and a binder were mixed using a mixer to prepare a composition for forming a positive electrode active material layer. At this time, sulfur as a positive electrode active material, carbon black as a conductive material, and polyvinyl alcohol as a binder were used respectively, and the mixing ratio was set so that the positive electrode active material: conductive material: binder was 75: 20: 5 by weight. The prepared positive electrode active material layer-forming composition was applied to an aluminum current collector and dried to prepare a positive electrode (energy density of the positive electrode: 1.0 mAh / cm 2).

At this time, the positive electrode catalysts prepared in Preparation Examples 1 to 6 and Comparative Preparation Examples 1 to 2 were mixed together to prepare positive electrodes in Examples 1 to 6 and Comparative Examples 1 to 2, respectively. The positive electrode catalyst was made to be 25% by weight based on the total weight of the positive electrode active material.

In addition, a lithium metal thin film was prepared as a negative electrode.

After the positive electrode and the negative electrode were placed to face each other, a polyethylene separator was interposed between the positive electrode and the negative electrode.

Thereafter, an electrolyte was injected into the case to prepare a lithium-sulfur secondary battery. At this time, the electrolyte solution, the organic solvent TEGDME / DOL / DME (1: 1: 1, vol%: vol%: vol%) is mixed with a lithium salt LiTFSI, LiTFSI: organic solvent = 1: 3 by weight ratio The electrolyte solution which mixed and added LiNO ₃ in the weight ratio of 1/10 of LiTFSI was used.

Comparative example  3

A lithium-sulfur secondary battery was manufactured in the same manner as in Example 1, except that the content of the transition metal complex included in the positive electrode catalyst was 25% by weight.

Experimental Example  1: Surface observation of anode catalyst

In the production examples and comparative production examples, the surfaces of the positive electrode catalysts respectively prepared were observed.

4 is a scanning electron microscope (SEM) photograph of the positive electrode catalysts prepared in Preparation Examples 1 to 6 and Comparative Preparation Examples 1 to 2, respectively.

Referring to Figure 4, the transition metal composite is a positive electrode catalyst of Preparation Examples 1 to 6, which is a positive electrode catalyst bonded to a porous carbon, and a comparative catalyst of Comparative Preparation Example 1, which is a positive electrode catalyst containing a porous carbon that is not bonded to a transition metal complex The anode catalyst was found to have no difference on the SEM photograph.

From this, it can be seen that in the positive electrode catalysts of Preparation Examples 1 to 6, the transition metal complex was evenly dispersed and bonded to the surface of the porous carbon through π-π interaction. That is, the transition metal complex has a size of several tens of μm, but it is confirmed that there is no difference between the SEM picture of the positive electrode catalyst in which the transition metal complex is bonded to the porous carbon and the SEM picture of the porous carbon to which the transition metal complex is not bonded. , It can be seen that the transition metal complex is evenly dispersed and bonded to the surface of the porous carbon.

Experimental Example  2: Observation of anode catalyst manufacturing process

FIG. 5 is a photograph showing a process in which the precursor (FePC) and porous carbon (CNT) of the transition metal complex in Preparation Example 1 are dissolved in an organic solvent (DMF) (FePC4-CNT mixture) and filtered.

Referring to FIG. 5, it can be seen that FePC is strongly adsorbed to CNT through π-π interaction. In general, FePC has a strong blue color even when only a small amount is dispersed in a solution. The FePC4-CNT mixture was blue, but it was found that the blue color disappeared in the filtration solution, indicating that FePC was adsorbed to the CNT.

Experimental Example  3: Structure and composition analysis of anode catalyst

An experiment for structural analysis of the positive electrode catalyst (FePC4-CNT) prepared in Example 1 was performed.

6 is an XRD (x-ray diffraction) graph for the precursor (FePC) and the positive electrode catalyst (FePC16-CNT) of the transition metal complex used in Preparation Example 6.

Referring to FIG. 6, in the positive electrode catalyst (FePC16-CNT) prepared in Preparation Example 6, since FePC is a single molecule evenly distributed on CNT, it can be seen that the XRD pattern of FePC does not appear in the XRD of FePC16-CNT. .

In addition, experiments for component analysis of the positive electrode catalyst (FePC16-CNT) prepared in Preparation Example 6 were performed.

TGA (Thermogravimetric analysis) is a device that measures the change in mass by increasing the temperature in an air or N ₂ atmosphere. When heat treatment is performed in FePC under air conditions, organic substances such as N or C around Fe are blown away and Fe is Oxidation produces Fe ₂ O ₃ . Therefore, as described below, after confirming the weight of Fe ₂ O ₃ , the amount of FePC was derived by tracing in reverse.

7 is a TGA (Thermogravimetric analysis) graph for the positive electrode catalyst (FePC16-CNT) prepared in Preparation Example 6.

Table 2 shows Elemental Analysis (EA) and Inductively coupled plasma (ICP) data for the positive electrode catalyst (FePC16-CNT) prepared in Preparation Example 6.

	EA			ICP
	C	N	O	Fe
Preparation Example 6 (FePC16-CNT)	93.4	2.7	1.9	1.6

Referring to FIG. 7 and Table 2, the FePc content included in the positive electrode catalyst of Preparation Example 6 is a TGA result (2.3 wt% (Fe ₂ O ₃ ) = ~ FePC 16 wt%) and an ICP result (1.6 wt% (Fe) = ~ FePC 16 wt%), which matches the target loading amount of 16 wt%.

Experimental Example  1: Experiment of initial discharge capacity and life characteristics of lithium-sulfur secondary battery

Initial discharge capacity and life characteristics of the lithium-sulfur secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 2, respectively, were conducted.

For each lithium-sulfur secondary battery, charge 0.1C (0.55 mA · cm ^-2 ) / 0.1C (0.55 mA · cm ^-2 ) after 2.5 cycles of discharge, charge 0.2C (1.1 mA · cm ^-2 ) / 0.2C ( 1.1 mA · cm ^{- 2} ) After 3 cycles of discharge, the experimental results were measured under 0.3C (1.65 mA · cm ^-2 ) charge / 0.5C (2.65 mA · cm ^-2 ) discharge conditions.

8A and 8B are graphs showing initial discharge capacity (FIG. 8A) and Coulomb efficiency (FIG. 8B) of the lithium-sulfur secondary batteries prepared in Example 1 and Comparative Example 1, respectively.

8A and 8B, Example 1 (S / FePC4-CNT) showed that the initial discharge capacity was significantly improved and the overvoltage was improved compared to Comparative Example 1 (ref).

9A and 9B are graphs showing the initial discharge capacity (FIG. 9A) and Coulomb efficiency (FIG. 9B) of the lithium-sulfur secondary batteries prepared in Example 2 and Comparative Example 1, respectively.

9A and 9B, Example 2 (S / NiPC4-CNT) has increased initial discharge capacity, improved overvoltage, increased high rate capacity, and improved life characteristics compared to Comparative Example 1 (ref). Turned out to be.

10A and 10B are graphs showing initial discharge capacity (FIG. 10A) and Coulomb efficiency (FIG. 10B) of the lithium-sulfur secondary batteries prepared in Example 3 and Comparative Example 1, respectively.

10A and 10B, Example 3 (S / MnPC4-CNT) showed that the initial discharge capacity increased, the overvoltage improved, and the high rate capacity increased significantly compared to Comparative Example 1 (ref).

11A and 11B are graphs showing initial discharge capacities (FIG. 11A) and Coulomb efficiency (FIG. 11B) of the lithium-sulfur secondary batteries prepared in Example 4 and Comparative Example 1, respectively.

11A and 11B, Example 4 (S / CuPC4-CNT) showed that the initial discharge capacity increased and the high rate capacity increased compared to Comparative Example 1 (ref).

12A and 12B are graphs showing initial discharge capacities (FIG. 12A) and Coulomb efficiency (FIG. 12B) of the lithium-sulfur secondary batteries prepared in Example 5 and Comparative Example 1, respectively.

12A and 12B, Example 5 (S / ZnPC4-CNT) showed that the initial discharge capacity increased compared to Comparative Example 1 (ref).

13A and 13B are graphs showing initial discharge capacity (FIG. 13A) and Coulomb efficiency (FIG. 13B) of the lithium-sulfur secondary batteries prepared in Comparative Example 2 and Comparative Example 1, respectively.

13A and 13B, Comparative Example 2 (S / CoPC4-CNT) showed no improvement compared to Comparative Example 1 (ref).

Table 3 below summarizes the experimental results for Examples 1 to 6 and Comparative Examples 1 to 3. The overvoltage is a relative advantage, inferiority, and degree of equality based on Comparative Example 1.

	Initial discharge mAh / g (active)	Low rate discharge @ 0.2C	High rate discharge @ 0.5C	Discharge capacity @ 100cycle	Overvoltage
Example 1	792	670	557	424	predominance
Example 2	770	692	581	496	predominance
Example 3	783	720	600	414	predominance
Example 4	774	685	577	460	Tenth
Example 5	788	690	578	382	equal
Example 6	800	670	555	343	predominance
Comparative Example 1	745	659	533	490	-
Comparative Example 2	755	644	546	203	Tenth
Comparative Example 3	760	665	510	278	predominance

Referring to Table 2, it can be seen that in Example 1, the initial discharge capacity was significantly superior, in Example 2, the index of all parts was superior, and in Example 3, the high rate discharge capacity was significantly superior.

[Description of codes]

1: anode catalyst

2: positive electrode active material

10: porous carbon

11: Qigong

20: transition metal complex

30: sulfur-containing material

Claims (10)

1. In the lithium secondary battery comprising a positive electrode, a negative electrode containing a sulfur-containing material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte,

   The positive electrode includes a positive electrode catalyst including a transition metal complex bound to the surface of the porous carbon, wherein the transition metal complex includes four nitrogen bound to the transition metal, lithium secondary battery.
2. According to claim 1,

   The positive electrode is a current collector; And a positive electrode active material layer formed on the current collector,

   The positive electrode catalyst is included in the positive electrode active material layer, lithium secondary battery.
3. According to claim 1,

   The positive electrode catalyst is 20 to 30% by weight based on the total weight of the positive electrode active material, lithium secondary battery.
4. According to claim 1,

   The transition metal is at least one selected from the group consisting of Fe, Ni, Mn, Cu and Zn, lithium secondary battery.
5. According to claim 1,

   The transition metal composite is 1 to 20% by weight based on the total weight of the positive electrode catalyst, lithium secondary battery.
6. According to claim 1,

   The transition metal composite is a lithium secondary battery coupled to one or more positions of the outer surface of the porous carbon and the inner surface of the pore.
7. According to claim 1,

   The transition metal composite is a lithium secondary battery, which is adsorbed and bonded to the surface of the porous carbon by π-π interaction.
8. According to claim 1,

   The porous carbon includes at least one selected from the group consisting of activated carbon, carbon nanotube (CNT), graphene, carbon black, acetylene black, graphite, graphite nanofiber (GNF) and fullerene. , Lithium secondary battery.
9. According to claim 1,

   The pore size of the porous carbon is 2 to 50 nm, lithium secondary battery.
10. According to claim 1,

    The lithium secondary battery is a lithium-sulfur secondary battery, a lithium secondary battery.

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