Cathode material for lithium-sulfur batteries and lithium-sulfur batteries containing the cathode material

Abstract

The present invention relates to a sulfur-carbon composite for use in a positive electrode of a lithium-sulfur battery and a method for manufacturing the same. The carbon composite includes a porous carbon substrate and a sulfur-containing compound contained in at least one of the outer surface and the inner surfaces of the pores of the porous carbon substrate, and the surface is entirely or partially coated with a crosslinked product of an amphiphilic cardanol derivative represented by Chemical Formula 1. Chemical Formula 1 is as described in the Description of the Invention.

Description

[Technical Field]

[0001] The present invention relates to a cathode material for a lithium-sulfur battery and a lithium-sulfur battery including the cathode material.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0110405, filed on August 31, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings of that application. [Background technology]

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond (SS bond) as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the positive electrode active material, has the advantages of being abundant worldwide, non-toxic, and having a low weight per atom.

[0004] As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESSs), lithium-sulfur battery technology is gaining attention due to its high theoretical energy storage density (up to 2,500Wh / kg) compared to lithium-ion secondary batteries, which have a relatively low energy storage density (up to 250Wh / kg) relative to their weight.

[0005] During discharge, lithium, the negative electrode active material, releases electrons and oxidizes, ionizing into lithium cations, while the positive electrode active material, a sulfur-based material, accepts electrons and is reduced. Through the reduction of the sulfur-based material, the S-S bond accepts two electrons and converts into sulfur anions. The lithium cations generated by the oxidation of lithium are transported to the positive electrode via the electrolyte, where they combine with sulfur anions generated by the reduction of sulfur-based compounds to form salts. Specifically, sulfur, which has a cyclic S8 structure before discharge, is converted to lithium polysulfide (Li2Sx) through a reduction reaction, and is then completely reduced to form lithium sulfide (Li2S).

[0006] As sulfur used as a positive electrode active material is a non-conductor, it is difficult for electrons generated by electrochemical reactions to move, and there are problems that need to be solved, such as a rapid decrease in battery capacity due to the elution of lithium polysulfide (LiSx) generated during the charge and discharge process.

[0007] For example, sulfur used in the positive electrode is reduced during discharge to form lithium polysulfide, which dissolves in the ether-based liquid electrolyte and is released from the positive electrode. The released lithium polysulfide passes through the separator to the negative electrode, where it reacts with lithium metal to form an unstable interface. This causes a loss of sulfur, the positive electrode active material. This series of processes is called the shuttle effect.

[0008] There is a need for a technology that can suppress the loss of energy density in batteries due to the shuttle effect described above. Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the problem to be solved by the present invention is to solve the above-mentioned problems, The present invention aims to provide a sulfur-carbon composite whose surface is entirely or partially coated with a polymer to suppress the elution of lithium polysulfide from the positive electrode of a lithium-sulfur battery, and a method for producing the same.

[0010] In particular, the goal is to provide a lithium-sulfur battery with excellent discharge capacity and capacity retention rate by suppressing the shuttle effect and volume expansion of the positive electrode through the coating structure of the sulfur-carbon composite. [Means for solving the problem]

[0011] To solve the above problems, According to one aspect of the present invention, there is provided a sulfur-carbon composite according to the following embodiment:

[0012] The sulfur-carbon composite according to the first embodiment is A porous carbon substrate and a sulfur-containing compound contained in at least one of an outer surface of the porous carbon substrate and inner surfaces of pores, The surface is entirely or partially covered with a crosslinked product of an amphiphilic cardanol derivative represented by the following chemical formula 1.

[0013] [ka]

[0014] In Chemical Formula 1, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 and at least one alkynyl group selected from the group consisting of R2 is C1~C 10 Alkyl groups of C2 to C 10 Alkenyl groups of C2 to C 10 and at least one alkynyl group selected from the group consisting of The R2 has a structure substituted with at least one anionic functional group.

[0015] According to the second embodiment, in the first embodiment, The zeta potential (ζ) of the surface may satisfy the following equation 1:

[0016] [Formula 1] -60mV≦ζ≦0mV According to the third embodiment, in the first or second embodiment, The amphiphilic cardanol derivative may have a structure in which at least one of R1 and R2 contains at least one carbon-carbon unsaturated bond.

[0017] According to the fourth embodiment, in any one of the first to third embodiments, The R2 is —(CH x ) n It can be represented by Q (x=0, 1 or 2, n=an integer of 1 to 10, Q is an anionic functional group).

[0018] According to the fifth embodiment, in any one of the first to fourth embodiments, The anionic functional group is —O - , -SO3 - , -COO - , -SO4 2- and conjugate acids thereof.

[0019] According to the sixth embodiment, in any one of the first to fifth embodiments, The anionic functional group contained in R2 may further include at least one of an alkali metal ion and an alkaline earth metal ion as a cation.

[0020] According to the seventh embodiment, in any one of the first to sixth embodiments, The crosslinked product of the amphiphilic cardanol derivative may have a crosslinking degree of 15% to 45% according to the following Equation 2:

[0021] [Formula 2] Degree of crosslinking (%) = (carbon unsaturation degree of crosslinked amphiphilic cardanol derivative / carbon unsaturation degree of amphiphilic cardanol derivative) × 100 According to the eighth embodiment, in any one of the first to seventh embodiments, The amphiphilic cardanol derivative may have at least one structure in which R1 is selected from the following Chemical Formulas 2 to 5.

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] [ka]

[0026] According to the ninth embodiment, in any one of the first to eighth embodiments, The amphiphilic cardanol derivative is R1 is 1 part by weight to 10 parts by weight of a structure represented by Chemical Formula 2, R1 is 40 to 70 parts by weight of a structure represented by Chemical Formula 3, R1 is 5 to 25 parts by weight of a structure represented by Chemical Formula 4, and The R1 may contain the structure represented by Chemical Formula 5 in an amount of 25 to 40 parts by weight.

[0027] According to the tenth embodiment, in any one of the first to ninth embodiments, The porous carbon substrate may include carbon black, carbon fiber, carbon nanotubes (CNT), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofiber (GNF), carbon nanofiber (CNF), activated carbon fiber (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more materials thereof.

[0028] According to the eleventh embodiment, in any one of the first to tenth embodiments, The sulfur-containing compound may include inorganic sulfur (S), lithium sulfide (LiS), lithium polysulfide (LiS, 2≦x≦8), a disulfide compound, or a mixture of two or more thereof.

[0029] According to the twelfth embodiment, in any one of the first to eleventh embodiments, Based on the total weight of the sulfur-carbon composite, the total content of the crosslinked amphiphilic cardanol derivative may be 0.1 wt % to 10 wt %.

[0030] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, Based on the total weight of the sulfur-carbon composite, the total content of the crosslinked amphiphilic cardanol derivative may be 0.1 wt % to 1 wt %.

[0031] According to another aspect of the present invention, there is provided a method for producing a sulfur-carbon composite according to the following embodiment.

[0032] The method for producing a sulfur-carbon composite according to the fourteenth embodiment includes: preparing an uncoated sulfur-carbon composite including a porous carbon substrate and a sulfur-containing compound supported on at least one of an outer surface and inner surfaces of pores of the porous carbon substrate; coating all or at least a portion of the surface of the uncoated sulfur-carbon composite with an amphiphilic cardanol derivative; and crosslinking at least a portion of the coated amphiphilic cardanol derivative to obtain a sulfur-carbon composite whose surface is entirely or partially coated with a crosslinked product of the amphiphilic cardanol derivative, The amphiphilic cardanol derivative is represented by the following chemical formula 1:

[0033] [ka]

[0034] In Chemical Formula 1, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 and at least one alkynyl group selected from the group consisting of R2 is C1~C 10 Alkyl groups of C2 to C 10 Alkenyl groups of C2 to C 10 and at least one alkynyl group selected from the group consisting of The R2 has a structure substituted with at least one anionic functional group.

[0035] According to the fifteenth embodiment, in the fourteenth embodiment, The method may further include a step of preparing the amphiphilic cardanol derivative through an alkylation reaction of a cardanol derivative represented by the following Chemical Formula 6:

[0036] [ka]

[0037] In Chemical Formula 6, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 The alkynyl group is at least one selected from the following alkynyl groups.

[0038] According to yet another aspect of the present invention, there is provided a positive electrode for a lithium-sulfur battery according to the following embodiment.

[0039] The positive electrode for a lithium-sulfur battery according to the sixteenth embodiment includes: The sulfur-carbon composite according to any one of the first to thirteenth embodiments and a binder polymer are included.

[0040] According to yet another aspect of the present invention, there is provided a lithium-sulfur battery according to the following embodiment.

[0041] The lithium-sulfur battery according to the seventeenth embodiment is The battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution; The positive electrode includes the positive electrode according to the sixteenth embodiment. [Effects of the Invention]

[0042] The sulfur-carbon composite according to one embodiment of the present invention has a coating structure of a crosslinked product of an amphiphilic cardanol derivative, and thus can suppress the elution of lithium polysulfide when a lithium-sulfur battery including a positive electrode containing the sulfur-carbon composite is operated. This not only improves the discharge capacity of the lithium-sulfur battery, but also improves the capacity retention rate of the battery over repeated cycles.

[0043] Furthermore, the coating structure alleviates the problem of the positive electrode expanding when the lithium-sulfur battery is in operation, thereby improving the safety of the lithium-sulfur battery.

[0044] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, and the present invention should not be interpreted as being limited only to the matters described in the drawings. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a spectrum obtained by 1H NMR of cardanol used in the production of Production Examples 1 and 2. [Figure 2] 1 is a spectrum of the 1H NMR result of the amphiphilic cardanol derivative prepared in Preparation Example 1. [Figure 3] FIG. 1 shows a portion of the spectrum obtained by 1H NMR of the crosslinked product of the amphiphilic cardanol derivative formed in Example 1. [Figure 4] 1 shows TGA analysis graphs of the porous carbon substrate (KB) used in the preparation of Comparative Example 1, Comparative Example 1 (KB / S), Example 1 (c-CPS-KB / S 0.5 wt%), Example 2 (c-CPS-Li-KB / S 0.5 wt%), Example 3 (c-CPS-KB / S 1 wt%), Example 4 (c-CPS-KB / S 2 wt%), and Example 5 (c-CPS-KB / S 3 wt%). [Figure 5] 1 shows SEM images of Comparative Example 1 (KB / S), Example 1 (c-CPS-KB / S 0.5 wt%), Example 2 (c-CPS-Li-KB / S 0.5 wt%), Example 3 (c-CPS-KB / S 1 wt%), Example 4 (c-CPS-KB / S 2 wt%), and Example 5 (c-CPS-KB / S 3 wt%). [Figure 6] 1 is a graph showing the results of cycle tests of lithium-sulfur coin cells using Comparative Example 1, Example 1, Example 3, Example 4, and Example 5. [Figure 7] 1 is a graph showing the results of cycle tests of lithium-sulfur coin cells using Comparative Example 1, Example 1, and Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0046] The present invention will be described in detail below. However, the present invention is not limited to the following content, and each component may be variously modified or selectively combined as necessary. Therefore, it should be understood that the present invention includes all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention.

[0047] In this specification, when a certain configuration "includes" a certain component, unless otherwise specified, it does not mean that other components are excluded, but that other components may also be included.

[0048] In this specification, the phrase "A and / or B" means A or B or both.

[0049] Certain terminology used herein is for convenience only and is not limiting. For example, positional terms such as "top," "bottom," "left," "right," "front," "rear," "inside," and "outside" are used to describe relative positions and orientations of components relative to one another, or may represent positions and orientations in the drawings to which reference is made, rather than absolute positions. The terms include the terms themselves as well as words containing them, their derivatives, and words of similar meaning.

[0050] As used herein, the terms "alkyl group," "alkenyl group," and "alkynyl group" each independently refer to a substituted or unsubstituted hydrocarbon which may be linear or branched.

[0051] The term "substituted or unsubstituted" means that the group is substituted with one or more substituents selected from the group consisting of deuterium, halogen, nitrile, nitro, hydroxy, -COOH, alkoxy, alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, heterocyclic, containing one or more N, O, S, or P atoms, and heteroaryl.

[0052] According to one embodiment of the present invention, there is provided a sulfur-carbon composite that can be used as a positive electrode material for lithium-sulfur secondary batteries.

[0053] The sulfur-carbon composite includes a porous carbon substrate and a sulfur-containing compound contained in at least one of the outer surface and the inner surface of the pores of the porous carbon substrate, and has a structure in which the surface is entirely or partially covered with a crosslinked product of an amphiphilic cardanol derivative represented by the following Chemical Formula 1:

[0054] As used herein, the term "amphiphilic" refers to a property that includes both a nonpolar hydrophobic portion and a polar hydrophilic portion. For example, an amphiphilic compound refers to a compound having a structure that includes both a nonpolar hydrophobic portion and a polar hydrophilic portion. Thus, the term "amphiphilic cardanol derivative" refers to a cardanol derivative having a structure that includes both a nonpolar hydrophobic portion and a polar hydrophilic portion.

[0055] As used herein, the term "derivative(s)" refers to structurally similar compounds obtained by chemically modifying a portion of any compound. Typically, a derivative refers to a compound in which a hydrogen atom or a specific atomic group in a compound is replaced with another atom or atomic group. In a broader sense, products produced by an addition reaction or the like can be considered derivatives. Therefore, the term "cardanol derivative" refers not only to cardanol itself, but also to compounds structurally similar to cardanol obtained by chemically modifying cardanol.

[0056] The "cardanol" is one of the derivatives obtained from cashew nutshell liquid (CNSL), a natural vegetable oil extracted from the skin of cashews, which belong to the Anacardiaceae family and grow in tropical tropics, and can be represented by the following structure:

[0057] [ka]

[0058] R=C 15 H 31-2n (n=0, 1, 2 or 3) As used herein, the term "amphiphilic cardanol derivative" refers to compounds structurally similar to cardanol that have been modified to include both a nonpolar hydrophobic moiety and a polar hydrophilic moiety within their structure. Here, "modification" refers to a chemical reaction that substitutes a portion or all of the structure of any compound to induce a change in its chemical properties.

[0059] Specifically, in the present specification, the amphiphilic cardanol derivative is represented by the following chemical formula 1:

[0060] [ka]

[0061] In Chemical Formula 1, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 and at least one alkynyl group selected from the group consisting of R2 is C1~C 10 Alkyl groups of C2 to C 10 Alkenyl groups of C2 to C 10 The alkynyl group is at least one selected from the following alkynyl groups.

[0062] The R2 has a structure substituted with at least one anionic functional group.

[0063] The compound of Chemical Formula 1 is a phenol derivative substituted with R1 at the meta position, and is one of cardanol derivatives. The compound of Chemical Formula 1 includes a non-polar hydrophobic portion by including a substituent (R1) having 10 to 50 carbon atoms. In addition, the compound of Chemical Formula 1 includes a hydrophilic portion by including a substituent (R2) having 1 to 10 carbon atoms and having at least one anionic functional group.

[0064] The compound of Formula 1 may form a crosslinked product through an addition reaction through the unsaturated bond between carbon atoms in the structure and / or a condensation reaction through the alkoxy functional group.

[0065] In one embodiment of the present invention, the compound of Formula 1 may form a crosslinked compound through a carbon-carbon unsaturated bond, since at least one of R1 and R2 contains at least one carbon-carbon unsaturated bond.

[0066] As used herein, the "carbon-carbon unsaturated bond" refers to at least one of a carbon(sp2)=carbon(sp2) double bond and a carbon(sp)≡carbon(sp) triple bond. Therefore, the phrase "at least one of R1 and R2 contains at least one carbon-carbon unsaturated bond" means that at least one of R1 and R2 is a substituted or unsubstituted hydrocarbon in which some or all of the carbon-carbon bonds are double bonds and / or triple bonds. According to one embodiment of the present invention, the carbon-carbon unsaturated bond contained in the amphiphilic cardanol derivative can provide crosslinking sites in a crosslinked product of the amphiphilic cardanol derivative.

[0067] According to one embodiment of the present invention, as described below, the sulfur-carbon composite may have its entire surface or a portion thereof coated with the amphiphilic cardanol derivative and then subjected to a crosslinking reaction, so that the entire surface or a portion thereof is coated with a crosslinked product of the amphiphilic cardanol derivative.

[0068] According to one embodiment of the present invention, in the structure of the amphiphilic cardanol derivative, the nonpolar portion where R1 having a relatively long carbon chain is located can provide excellent binding strength with the porous carbon substrate, and the polar portion where an anionic functional group having a relatively short carbon chain is located can impart hydrophilicity to the surface of the sulfur-carbon composite.

[0069] According to one embodiment of the present invention, the sulfur-carbon composite, the surface of which is entirely or partially covered with the crosslinked product of the amphiphilic cardanol derivative, may have a negative (-) zeta potential on the surface.

[0070] Specifically, the zeta potential of the surface of the sulfur-carbon composite may satisfy the range of the following mathematical formula 1:

[0071] [Formula 1] -60mV≦ζ≦0mV In this specification, the zeta potential may be a value measured using a zeta potential measuring device (ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.) after preparing a dispersion containing the sulfur-carbon composite at a concentration of 0.01 wt % using water as a solvent, although there may be a measurement error depending on the measuring device.

[0072] In one embodiment of the present invention, the amphiphilic cardanol derivative is modified so that at least one anionic functional group is present in the structure of R2, and the at least one anionic functional group may be substituted at one end of R2. For example, R2 may be -(CH x ) n It can be represented by Q (x=0, 1 or 2, n=an integer of 1 to 10, Q is an anionic functional group).

[0073] As used herein, the anionic functional group refers to a functional group that can provide an anion in an aqueous solvent. For example, a compound containing the anionic functional group can be formed by reacting a hydrogen atom (H) with the compound to provide an anion (-) in an aqueous solvent such as water. + ) may have the property of dissociating cations such as

[0074] In one embodiment of the present invention, the anionic functional group is -O - , -SO3 - , -COO - or -SO4 2- Specifically, the anionic functional group may be a functional group having the formula -O - , -SO3 - , -COO - , -SO4 2- and conjugate acids thereof.

[0075] In one embodiment of the present invention, the amphiphilic cardanol derivative may further include an alkali metal ion and / or an alkaline earth metal ion as a conjugated ion of the anionic functional group contained within the structure. Specifically, the anionic functional group contained in R2 may further include at least one of an alkali metal ion and an alkaline earth metal ion as a conjugated ion. When R2 further includes a conjugated ion of the anionic functional group, the electrical conductivity of a positive electrode using the sulfur-carbon composite can be improved, but the present invention is not limited thereto.

[0076] The alkali metal ions are, for example, lithium ions (Li + ), sodium ions (Na + ), or potassium ions (K + The alkaline earth metal ions may include, but are not limited to, calcium ions (Ca 2+ ), magnesium (Mg 2+ ) or beryllium (Be 2+ ), but is not limited to these.

[0077] In one embodiment of the present invention, the anionic functional group is -SO3 - , -COO - , -SO4 2- , -SO3H, -COOH, -SO4H, -SO3 - M + , -COO - M+ , -SO4 2- M2 + , and -SO4 2- M 2+ (M is an alkali metal ion or an alkaline earth metal ion).

[0078] In another embodiment of the present invention, at least one anionic functional group contained in the structure of R2 is -SO3 - , -SO3H, and -SO3 - M + (wherein M is an alkali metal ion).

[0079] According to one embodiment of the present invention, the anionic functional group contained in the amphiphilic cardanol derivative provides anions to the surface of a sulfur-carbon composite coated with a crosslinked product of the amphiphilic cardanol derivative, thereby improving the electrical conductivity of the sulfur-carbon composite, but the effects of the present invention are not limited thereto.

[0080] As described above, the carbon-carbon unsaturated bond contained in the amphiphilic cardanol derivative provides crosslinking sites in the crosslinked product of the amphiphilic cardanol derivative. Specifically, the amphiphilic cardanol derivative contains at least one carbon-carbon unsaturated bond. As a result, a crosslinked product of the amphiphilic cardanol derivative is formed through a crosslinking reaction between two or more amphiphilic cardanol derivative molecules and / or within a single amphiphilic cardanol derivative molecule.

[0081] In one embodiment of the present invention, the crosslinking reaction between unsaturated bonds of the amphiphilic cardanol derivative can be confirmed by structural changes before and after the crosslinking reaction of the amphiphilic cardanol derivative. For example, by comparing H NMR graphs of the amphiphilic cardanol derivative before and after the crosslinking reaction, it can be confirmed by a decrease in the peak intensity of unsaturated bonds (e.g., C=C, C≡C) and an increase in the peak intensity of saturated bonds (e.g., C-C). Alternatively, the formation of a crosslinked product of the amphiphilic cardanol derivative can be confirmed by a known analytical method capable of confirming a change in the number of unsaturated bonds between carbon atoms.

[0082] In one embodiment of the present invention, the crosslinking degree of the crosslinked product of the amphiphilic cardanol derivative according to the following Equation 2 may be, but is not limited to, for example, 15% to 45%, specifically 20% to 40%, and more specifically 25% to 35%.

[0083] [Formula 2] Degree of crosslinking (%) = (carbon unsaturation degree of crosslinked amphiphilic cardanol derivative / carbon unsaturation degree of amphiphilic cardanol derivative) × 100 In Equation 2, the "carbon unsaturation degree" of the amphiphilic cardanol derivative and the crosslinked product of the amphiphilic cardanol derivative can be measured by a known method for measuring carbon unsaturation degree, and the crosslinking degree can be calculated using Equation 2.

[0084] The degree of carbon unsaturation can be measured, for example, by H NMR analysis, by dividing the peak area of ​​the carbon-carbon unsaturated bond of the crosslinked product of the amphiphilic cardanol derivative by the peak area of ​​the carbon-carbon unsaturated bond of the amphiphilic cardanol derivative before crosslinking.

[0085] In one embodiment of the present invention, 1H NMR analysis can be performed by known methods, for example, using a 400 MHz NMR device in a state where the compound is dissolved in DMSO-d6 solvent.

[0086] In one embodiment of the present invention, the number of carbon atoms in R1 in Formula 1 is important in terms of imparting hydrophobicity to the crosslinked product of the amphiphilic cardanol derivative and improving adhesion to the porous carbon substrate.

[0087] The R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 The alkynyl group is at least one selected from the following alkynyl groups.

[0088] In one embodiment of the present invention, R1 is specifically C 10 ~C 40 Alkyl groups of C 10 ~C 40 Alkenyl groups of C 10 ~C 40 and more specifically, C 10 ~C 30 Alkyl groups of C 10 ~C 30 Alkenyl groups of C 10 ~C 30 More specifically, the alkynyl group may be at least one selected from the alkynyl groups 13 ~C 20 Alkyl groups of C 13 ~C 20 Alkenyl groups of C 13 ~C 20 The alkynyl group may be at least one selected from the following alkynyl groups:

[0089] In one embodiment of the present invention, the amphiphilic cardanol derivative may have a structure in which R1 has 10 to 30 carbon atoms and 0 to 5 carbon-carbon unsaturated bond groups (i.e., saturated hydrocarbon groups), specifically 0 to 4 or 0 to 3 carbon-carbon unsaturated bond groups.

[0090] In another embodiment of the present invention, the amphiphilic cardanol derivative may include those having at least one structure selected from the following Chemical Formula 2 to Chemical Formula 5.

[0091] [ka]

[0092] [ka]

[0093] [ka]

[0094] [ka]

[0095] In another embodiment of the present invention, the amphiphilic cardanol derivative may be a mixture of two or more types in which R1 is different. Specifically, the amphiphilic cardanol derivative may be a mixture of those in which R1 has a structure represented by Chemical Formula 2 to Chemical Formula 5.

[0096] In yet another embodiment of the present invention, the amphiphilic cardanol derivative may contain 1 part by weight to 10 parts by weight of a structure in which R1 is represented by chemical formula 2, 40 parts by weight to 70 parts by weight of a structure in which R1 is represented by chemical formula 3, 5 parts by weight to 25 parts by weight of a structure in which R1 is represented by chemical formula 4, and 25 parts by weight to 40 parts by weight of a structure in which R1 is represented by chemical formula 5.

[0097] Specifically, the amphiphilic cardanol derivative may contain 3 to 7 parts by weight of a structure in which R1 is represented by chemical formula 2, 45 to 60 parts by weight of a structure in which R1 is represented by chemical formula 3, 10 to 20 parts by weight of a structure in which R1 is represented by chemical formula 4, and 25 to 30 parts by weight of a structure in which R1 is represented by chemical formula 5.

[0098] In one embodiment of the present invention, the number of carbon atoms in R2 in Formula 1 is important in terms of imparting hydrophilicity to the crosslinked product of the amphiphilic cardanol derivative and improving the electrical conductivity of the sulfur-carbon composite.

[0099] The R2 is C1 to C 10 Alkyl groups of C2 to C 10 Alkenyl groups of C2 to C 10 and has a structure substituted with at least one anionic functional group at any position.

[0100] In one embodiment of the present invention, R2 may be at least one selected from a C2 to C8 alkyl group, a C2 to C8 alkenyl group, and a C2 to C8 alkynyl group, and more specifically, may be at least one selected from a C3 to C5 alkyl group, a C3 to C5 alkenyl group, and a C3 to C5 alkynyl group.

[0101] In one embodiment of the present invention, the amphiphilic cardanol derivative may have a structure in which R2 has 2 to 5 carbon atoms and an anionic functional group is substituted at the terminal.

[0102] In one embodiment of the present invention, R2 can be 3-propyl sulfonate.

[0103] In one embodiment of the present invention, the amphiphilic cardanol derivative may include cardanylpropyl sulfonic acid represented by the following Chemical Formula 7:

[0104] [ka]

[0105] In formula 7, R is C 15 H 31-2n (n=0, 1, 2 or 3).

[0106] In one embodiment of the present invention, the structure of the sulfur-carbon composite can be divided into a coating structure coated with the crosslinked product of the amphiphilic cardanol derivative and a core structure including a porous carbon substrate and a sulfur-containing compound.

[0107] The porous carbon substrate constituting the core structure may have the functions of improving the electrical conductivity of the sulfur-carbon composite and supporting a sulfur-containing compound to improve sulfur utilization efficiency, but the mechanism of the present invention is not limited thereto.

[0108] The porous carbon substrate is a material containing a large number of micropores, and the sulfur-containing compound is supported on at least one of the outer surface of the porous carbon substrate and the inner surface of the pores.

[0109] In one embodiment of the present invention, the porous carbon substrate comprises a large number of micropores on the outer surface and inside thereof, and the average diameter of the micropores may be, for example, 5 nm to 100 nm, specifically 5 nm to 80 nm, 5 nm to 60 nm, or 5 nm to 50 nm.

[0110] The porous carbon substrate is not particularly limited in material as long as it contains a large number of micropores as described above and is capable of supporting the sulfur-containing compound.

[0111] In one embodiment of the present invention, the porous carbon substrate may include, for example, carbon black, carbon fiber, carbon nanotube (CNT), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofiber (GNF), carbon nanofiber (CNF), activated carbon fiber (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more materials thereof.

[0112] In one embodiment of the present invention, when the material of the porous carbon substrate includes carbon nanotubes, the carbon nanotubes may include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or both.

[0113] In another embodiment of the present invention, when the material of the porous carbon substrate includes carbon nanotubes, the carbon nanotubes may include entangled carbon nanotubes formed as secondary structures by aggregating a plurality of carbon nanotubes as primary structures.

[0114] According to one embodiment of the present invention, the entangled carbon nanotubes may have an improved porosity compared to the primary structure carbon nanotubes due to an interstitial volume formed by the entanglement of the primary structure carbon nanotubes.

[0115] In one embodiment of the present invention, the size of the porous carbon substrate may be, but is not limited to, 10 μm to 100 μm, specifically 20 μm to 50 μm. When the size of the porous carbon substrate is within the above range, advantageous effects can be achieved in terms of controlling the solid content when preparing a slurry for forming an electrode active material layer, and in terms of electrode properties, such as adhesive strength, and battery performance (output, capacity, etc.).

[0116] In one embodiment of the present invention, the pore volume of the porous carbon substrate is, for example, 1 cm 3 / g~5cm 3 / g, specifically 1cm 3 / g~4cm 3 The pore volume may be a value calculated or measured through, for example, N adsorption isotherm analysis obtained based on the adsorption of liquid nitrogen.

[0117] In one embodiment of the present invention, the BET specific surface area of ​​the porous carbon substrate is, but is not limited to, for example, 150 m 2 / g~2,000m 2 / g, specifically 250m 2 / g~700m 2 The BET specific surface area may be / g. The BET specific surface area is measured by the BET method and may represent a value measured by a known method for measuring a BET specific surface area. For example, the BET specific surface area may be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan.

[0118] In one embodiment of the present invention, the sulfur-containing compound may be, for example, but is not limited to, inorganic sulfur (S), lithium sulfide (LiS), lithium polysulfide (LiS, 2≦x≦8), a disulfide compound, or a mixture of two or more thereof.

[0119] In one embodiment of the present invention, the porous carbon substrate and the sulfur-containing compound may be mixed in a weight ratio of, for example, 1:9 to 9:1, more specifically, 2:8 to 8:2, more specifically, 3:7 to 7:3, or 4:6 to 2:8.

[0120] In one embodiment of the present invention, the core structure of the sulfur-carbon composite may be formed by mixing the porous carbon substrate with a sulfur-containing compound and then heat-treating the mixture at a temperature of, for example, 130°C to 200°C, specifically, 130°C to 180°C, or 150°C to 160°C.

[0121] As described above, according to one embodiment of the present invention, there is provided a sulfur-carbon composite in which at least one of the outer surface and the inner surfaces of the pores of the porous carbon substrate contains the sulfur-containing compound, and the entire or partial surface is covered with a crosslinked product of an amphiphilic cardanol derivative represented by the following Chemical Formula 1:

[0122] In one embodiment of the present invention, the sulfur-carbon composite has an average particle size (D 50 ).

[0123] In one embodiment of the present invention, the total content of the crosslinked amphiphilic cardanol derivatives, based on the total weight of the sulfur-carbon composite, may be, but is not limited to, 0.1 wt % to 10 wt %. Specifically, the total content of the crosslinked amphiphilic cardanol derivatives, based on the total weight of the sulfur-carbon composite, may be 0.1 wt % to 5 wt %, more specifically, 0.1 wt % to 1 wt %, 0.3 wt % to 1 wt %, or 0.3 wt % to 0.8 wt %. The content of the crosslinked amphiphilic cardanol derivatives within the above range is advantageous in terms of improving the lifespan of a lithium-sulfur battery incorporating the sulfur-carbon composite, but the present invention is not limited thereto.

[0124] Another embodiment of the present invention provides a method for producing the above-mentioned sulfur-carbon composite.

[0125] According to another embodiment of the present invention, a method for producing a sulfur-carbon composite includes the steps of: preparing an uncoated sulfur-carbon composite including a porous carbon substrate and a sulfur-containing compound supported on at least one of the outer surface and the inner surfaces of the pores of the porous carbon substrate; coating all or at least a portion of the surface of the uncoated sulfur-carbon composite with an amphiphilic cardanol derivative; and crosslinking at least a portion of the coated amphiphilic cardanol derivative to obtain a sulfur-carbon composite whose surface is all or partly coated with the crosslinked product of the amphiphilic cardanol derivative.

[0126] In the production method, the above descriptions are applicable to the porous carbon substrate, the sulfur-containing compound, the amphiphilic cardanol derivative, and the crosslinked product of the amphiphilic cardanol derivative.

[0127] In one embodiment of the present invention, the method for preparing the sulfur-carbon composite may further include preparing the amphiphilic cardanol derivative through an alkylation reaction of a cardanol derivative represented by Chemical Formula 6 below:

[0128] [ka]

[0129] In Chemical Formula 6, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 The alkynyl group is at least one selected from the following alkynyl groups.

[0130] First, the step of preparing the uncoated sulfur-carbon composite includes mixing the porous carbon substrate with the sulfur-containing compound. In one embodiment of the present invention, the porous carbon substrate and the sulfur-containing compound may be mixed in a weight ratio of, for example, 1:9 to 9:1. Specifically, the porous carbon substrate and the sulfur-containing compound may be mixed in a weight ratio of 2:8 to 8:2, more specifically, 3:7 to 7:3, or 4:6 to 2:8.

[0131] In one embodiment of the present invention, the method may further include the step of pulverizing the porous carbon substrate and the sulfur-containing compound after mixing them together. The pulverization may improve the mixing uniformity of the porous carbon substrate and the sulfur-containing compound, but the present invention is not limited thereto.

[0132] In one embodiment of the present invention, the step of preparing the uncoated sulfur-carbon composite may further include a step of heat-treating the porous carbon substrate and the sulfur-containing compound after mixing (or mixing and pulverizing) them. The heat treatment may be performed at a temperature of, for example, 130°C to 200°C, specifically, 130°C to 180°C, or 150°C to 160°C. The heat treatment may improve the mechanical strength of the sulfur-carbon composite, but the present invention is not limited thereto.

[0133] Next, the entire or at least a portion of the surface of the prepared uncoated sulfur-carbon composite is coated with the amphiphilic cardanol derivative.

[0134] In one embodiment of the present invention, the coating is performed by contacting the sulfur-carbon composite with the amphiphilic cardanol derivative. For example, the sulfur-carbon composite can be coated by immersing the sulfur-carbon composite in a dispersion of the amphiphilic cardanol derivative and then stirring the mixture.

[0135] In one embodiment of the present invention, the dispersion in which the amphiphilic cardanol derivative is dispersed may be, for example, a dispersion in which the amphiphilic cardanol derivative is dispersed in an aqueous solvent such as water at a weight of 0.1 wt % to 10 wt %, but the present invention is not limited thereto.

[0136] In one embodiment of the present invention, the amount of the coated amphiphilic cardanol derivative may be 0.1 wt % to 10 wt %, 0.1 wt % to 5 wt %, 0.1 wt % to 3 wt %, 0.1 wt % to 1 wt %, or 0.3 wt % to 0.8 wt % based on the total weight of the coated sulfur-carbon composite. The amount of the coated amphiphilic cardanol derivative may be calculated based on the increased weight of the coated sulfur-carbon composite relative to the weight of the uncoated sulfur-carbon composite.

[0137] Next, a crosslinking reaction is carried out to form a crosslinked product through the carbon-carbon unsaturated bond in the coated amphiphilic cardanol derivative, and as a result, all or part of the surface of the sulfur-carbon composite can be coated with the crosslinked product of the amphiphilic cardanol derivative.

[0138] In one embodiment of the present invention, the crosslinking reaction may be carried out in the presence of a polymerization initiator, for example. The polymerization initiator may be, for example, an azo-based initiator, such as commercially available V-501 (CAS RN® 2638-94-0, C 12 H 16 N4O4, MW 280.28 g / mol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) can be used, but is not limited thereto.

[0139] In one embodiment of the present invention, the crosslinking reaction is preferably carried out at a temperature at which the amphiphilic cardanol derivative is not decomposed, for example, 60°C to 100°C, 70°C to 95°C, 80°C to 95°C, or 90°C to 95°C, but the present invention is not limited thereto.

[0140] In an embodiment of the present invention, the method for preparing the sulfur-carbon composite may further include preparing an amphiphilic cardanol derivative to be used in the coating step of the uncoated sulfur-carbon composite.

[0141] In one embodiment of the present invention, the amphiphilic cardanol derivative can be prepared by alkylation of a cardanol derivative represented by the following Chemical Formula 6:

[0142] [ka]

[0143] In Chemical Formula 6, R1 is C 10 ~C 50 Alkyl groups of C 10 ~C 50 Alkenyl groups of C 10 ~C 50 The alkynyl group is at least one selected from the following alkynyl groups.

[0144] In one embodiment of the present invention, the description of R1 in Chemical Formula 1 is incorporated herein by reference for R1 in Chemical Formula 6.

[0145] In one embodiment of the present invention, the alkylation reaction of the cardanol derivative represented by Chemical Formula 6 is a reaction for substituting the hydrogen atom of the hydroxy group (OH) with R2 in Chemical Formula 6. The same description of R2 in Chemical Formula 1 applies to R2 in Chemical Formula 6.

[0146] In one embodiment of the present invention, the alkylation reaction of the cardanol derivative represented by Chemical Formula 6 is carried out by converting the hydrogen atom of the hydroxy group of the cardanol derivative represented by Chemical Formula 6 into a C1-C 10 Alkyl groups of C2 to C 10 Alkenyl groups of C2 to C 10 and then substituting at least one hydrogen atom in the substituted structure with an anionic functional group to modify the structure to be amphiphilic.

[0147] In one embodiment of the present invention, the step of modifying the cardanol derivative to be amphiphilic is to perform an alkylation reaction on the cardanol derivative, and to substitute at least one sulfonic acid, carboxylic acid, and sulfuric acid functional group into the alkyl-substituted structure, thereby generating hydrogen ions (H + ) to alkali metal ions and / or alkaline earth metal ions.

[0148] In one embodiment of the present invention, the alkylation reaction may be carried out, for example, by a ring-opening reaction of alkylsultone. In this case, the cardanol derivative alkylated through the ring-opening reaction of alkylsultone may include a sulfonic acid group as an anionic functional group.

[0149] By the above method, a sulfur-carbon composite can be prepared, which includes a porous carbon substrate and a sulfur-containing compound contained in at least one of the outer surface and the inner surface of the pores of the porous carbon substrate, and has a structure in which the entire or part of the surface is covered with a crosslinked product of the amphiphilic cardanol derivative represented by Chemical Formula 1.

[0150] According to yet another embodiment of the present invention, there is provided a positive electrode for a lithium-sulfur battery, comprising the above-described sulfur-carbon composite and a binder polymer.

[0151] In one embodiment of the present invention, the binder polymer may be any binder that can be used for the positive electrode of a lithium-sulfur battery, including, but not limited to, PVDF (polyvinylidene fluoride), specifically, PVDF dispersed in NMP (N-methyl-2-pyrrolidone).

[0152] In another embodiment of the present invention, the binder polymer may include, but is not limited to, an aqueous binder such as SBR (styrene butadiene rubber), specifically, an aqueous binder dispersed in an aqueous solvent such as water.

[0153] In another embodiment of the present invention, the positive electrode for a lithium-sulfur battery may further include, in addition to the sulfur-carbon composite and the binder polymer, a conductive material, an additive, etc. Here, specific types of the conductive material and the additive may be conventional ones, and therefore, description thereof will be omitted.

[0154] In yet another embodiment of the present invention, the positive electrode for a lithium-sulfur battery may include a positive electrode current collector, and a positive electrode active material layer in which the sulfur-carbon composite as the positive electrode active material is coated on one or both surfaces of the current collector together with the binder polymer.

[0155] In this case, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity.

[0156] In one embodiment of the present invention, the positive electrode including the sulfur-carbon composite may exhibit excellent effects in terms of initial capacity and cycle stability, but the effects of the present invention are not limited thereto.

[0157] According to another embodiment of the present invention, there is provided a lithium-sulfur battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode includes the above-described positive electrode.

[0158] In one embodiment of the present invention, the anode and separator may be any material usable in a lithium-sulfur battery without limitation, as long as the anode and separator do not impair the object of the present invention. For example, lithium metal may be used as the anode.

[0159] In one embodiment of the present invention, the separator may be any material that can be commonly used as a separator for lithium-sulfur batteries. The separator may include a porous polyolefin substrate, and optionally, may further include inorganic particles on at least one surface of the porous polyolefin substrate. The separator may also optionally include a binder to bind the inorganic particles.

[0160] In another embodiment of the present invention, the separator may be a film-type electrolyte membrane containing a solid electrolyte, and may further contain a binder for binding the solid electrolyte, if necessary. The solid electrolyte may be any solid electrolyte that can be commonly used in lithium-sulfur batteries, such as a polymer-based solid electrolyte, an inorganic-based solid electrolyte, or a mixture thereof, without limitation.

[0161] In one embodiment of the present invention, the electrolyte solution includes those commonly used in lithium-sulfur batteries, and may include a lithium salt and a non-aqueous solvent.

[0162] The lithium salt may be any salt that can be commonly used in the electrolyte of a lithium-sulfur battery. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium tetraphenylborate, lithium imide, or two or more thereof.

[0163] The non-aqueous solvent may be any solvent that can be commonly used in electrolytes for lithium-sulfur batteries, including, but not limited to, cyclic carbonate solvents, linear carbonate solvents, ester solvents, ketone solvents, or mixtures of two or more thereof.

[0164] In one embodiment of the present invention, the electrolyte may include (CF3SO2)2NLi as a lithium salt and a dioxolane (DOL) / dimethoxyethane (DME) binary system as a non-aqueous solvent. For example, the electrolyte may further include a conventional additive such as LiNO3.

[0165] In one embodiment of the present invention, the lithium-sulfur battery may have an outer shape, such as a coin shape, a cylindrical shape, a pouch shape, or a rectangular shape, but the outer shape of the battery is not particularly limited. Furthermore, the lithium-sulfur battery may be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a plurality of battery cells, and the usage form is not particularly limited.

[0166] In one embodiment of the present invention, a lithium-sulfur battery using a cathode including the sulfur-carbon composite can effectively alleviate the problem of capacity reduction due to repeated cycles by suppressing the elution of lithium polysulfide during battery operation and mitigating the shuttle effect, but the effects of the present invention are not limited thereto.

[0167] In one embodiment of the present invention, the lithium-sulfur battery may exhibit an effect of improving energy density by increasing the sulfur loading amount in the positive electrode, but the effect of the present invention is not limited thereto.

[0168] Hereinafter, a method for preparing a sulfur-carbon composite and a method for preparing a lithium-sulfur battery using the same according to an embodiment of the present invention will be described in detail with reference to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0169] [Preparation of amphiphilic cardanol derivatives] An amphiphilic cardanol derivative was prepared using cardanol having the following structure. The results of 1H NMR analysis of the cardanol used are shown in Figure 1. In the structure below, a to d indicate the symbols corresponding to the 1H NMR peaks in Figure 1.

[0170] [ka]

[0171] Production Example 1: Production of cardanylpropyl sulfonic acid (CPS) According to the reaction scheme below, cardanylpropylsulfonic acid was produced as an amphiphilic cardanol derivative as follows.

[0172] [ka]

[0173] First, 3 g of cardanol and 2.24 g of potassium t-butoxide (Sigma-Aldrich) were stirred in an ethanol (Daejung) solvent at room temperature (23°C) to activate the hydroxyl group (-OH).

[0174] Propane sultone (manufactured by TCI) dissolved in ethanol was added to the activated cardanol monomer, and the mixture was reacted at 80°C for 40 hours to obtain cardanyl propyl sulfonate.

[0175] Cardanyl propyl sulfonate was dissolved in water, and then an equivalent or greater amount of HCl (Daejung Co.) was added and stirred at room temperature to obtain cardanyl propyl sulfonic acid (CPS) through protonation (yield 50%).

[0176] The acquisition of cardanylpropylsulfonic acid was confirmed by 1H NMR, and the 1H NMR results are shown in Figure 2.

[0177] Preparation Example 2: Preparation of cardanylpropyl lithium sulfonate (CPS-Li)

[0178] [ka]

[0179] Equivalent amounts of Preparation Example 1 (cardanylpropylsulfonic acid, CPS) and LiOH were dissolved in water and stirred to obtain cardanylpropyllithium sulfonate (CPS-Li).

[0180] [Production of sulfur-carbon composite] The sulfur-carbon composites of Comparative Example 1 and Examples 1 to 5 were produced according to the following methods.

[0181] Comparative example 1.KB-S Sulfur (S8, manufactured by Sigma-Aldrich) and Ketjenblack (KB, manufactured by Lion Chemical Industries, Ltd.) were mixed in a mass ratio of 7:3, ground in a mortar grinder, and heat-treated at 155°C for 30 minutes to prepare an uncoated sulfur-carbon composite (KB-S) in which sulfur was supported on the outer surface and inner surface of the pores of the Ketjenblack.

[0182] Example 1.c-CPS-KB / S 0.5wt% 100 parts by weight of the uncoated sulfur-carbon composite prepared in Comparative Example 1 and 0.5 parts by weight of cardanylpropylsulfonic acid (CPS) obtained in Preparation Example 1 as an amphiphilic cardanol derivative were added to 300 ml of water, sonicated for 5 hours, stirred for 16 hours, and washed with water to coat the surface of the uncoated sulfur-carbon composite with the amphiphilic cardanol derivative of Preparation Example 1.

[0183] A polymerization initiator (V-501, Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount of 10 wt % based on the total weight of the sulfur-carbon composite coated with the amphiphilic cardanol derivative was stirred with 2 ml of water at 90°C for 24 hours and then washed with water to obtain a sulfur-carbon composite coated with a crosslinked product of the amphiphilic cardanol derivative.

[0184] The peak region of the crosslinked amphiphilic cardanol derivative from the 1H NMR results of the obtained sulfur-carbon composite is shown in Figure 3. Referring to Figure 3, the 1H peak of the unsaturated carbon confirmed in the 1H NMR results of the amphiphilic cardanol derivative (Figure 2) has decreased, confirming that a crosslinked product was formed through unsaturated bonds between carbon atoms.

[0185] In particular, referring to Figures 2 and 3, the ratio of the unsaturated bond content of the crosslinked product of the amphiphilic cardanol derivative after the crosslinking reaction to the unsaturated bond content of the amphiphilic cardanol derivative before the crosslinking reaction was confirmed to be 30%.

[0186] Degree of cross-linking (%) = content of unsaturated bonds in the cross-linked product of amphiphilic cardanol derivative (Figure 3) / content of unsaturated bonds in the amphiphilic cardanol derivative (Figure 2) × 100 Example 2.c-CPS-Li-KB / S 0.5wt% A sulfur-carbon composite was obtained in the same manner as in Example 1, except that Production Example 2 was used as the amphiphilic cardanol derivative.

[0187] Example 3. c-CPS-KB / S 1 wt% A sulfur-carbon composite was obtained in the same manner as in Example 1, except that 1 part by weight of the amphiphilic cardanol derivative of Production Example 1 was used.

[0188] Example 4.c-CPS-KB / S 2wt% A sulfur-carbon composite was obtained in the same manner as in Example 1, except that 2 parts by weight of the amphiphilic cardanol derivative of Production Example 1 was used.

[0189] Example 5.c-CPS-KB / S 3wt% A sulfur-carbon composite was obtained in the same manner as in Example 1, except that 3 parts by weight of Production Example 1 was used as the amphiphilic cardanol derivative.

[0190] [Analysis of the composition of sulfur-carbon composites] The compositions of the prepared sulfur-carbon composites are shown in Table 1.

[0191] The sulfur content of the prepared sulfur-carbon composite was measured using a TGA (TA Instruments, TGA55) by isothermalizing at 100°C for 10 minutes and then ramping from 100°C to 700°C at a rate of 10°C / min. The measurement results are shown in Figure 4.

[0192] [Table 1]

[0193] 4, sulfur (S8) is insoluble in water at room temperature but sublimes, and therefore is thought to have been partially lost at the temperature at which the crosslinking reaction was carried out. Specifically, in Examples 1 and 2, the coating layer of the crosslinked product of the amphiphilic cardanol derivative was formed with a relatively uniform thickness, minimizing sulfur loss. However, in Examples 3 and 4, the thickness of the coating layer varied, which appears to have partially increased sulfur loss. In Example 5, an excess amount of the crosslinked product of the amphiphilic cardanol derivative almost completely covered the surface of the KB / S, resulting in less sulfur loss than in Examples 3 and 4.

[0194] [Structural analysis of sulfur-carbon composites] SEM images of the sulfur-carbon composites produced in Comparative Example 1 and Examples 1 to 5 are shown in FIG.

[0195] As can be seen from Fig. 5, the sulfur-carbon composites prepared as described above have an average particle size (D 50 ) It can be confirmed that the particles are spherical and have a diameter of 35 μm.

[0196] 5, it can be seen that the crosslinked product of the amphiphilic cardanol derivative uniformly coated the surface of the sulfur-carbon composite without clumping in Examples 1 and 2. On the other hand, in Examples 3 to 5, where the content of the crosslinked product of the amphiphilic cardanol derivative was increased, it was seen that the crosslinked product of the amphiphilic cardanol derivative aggregated, resulting in a decrease in the uniformity of the coating structure on the surface of the sulfur-carbon composite.

[0197] [Evaluation of the performance of lithium-sulfur coin cells] To evaluate the battery performance when the sulfur-carbon composite prepared as above was applied to the cathode, a lithium-sulfur coin cell was fabricated as follows.

[0198] The prepared sulfur-carbon composite was mixed with polyacrylic acid (PAA) binder (MW 450,000) and carbon conductive material (Super P) in a ratio of 85:10:5, and 0.5 wt% of PVA dispersant (MW 9,500) was added. The mixture was then mixed in a mixer (Thinky) to prepare a cathode slurry with a solids concentration of 13 wt% in the aqueous phase. The prepared cathode slurry was coated on aluminum foil to a thickness of 300 μm using a doctor blade and dried at 50°C for 14 hours.

[0199] The fabricated cathode and lithium metal anode were prepared, and a Celgard separator was sandwiched between the cathode and anode to prepare an electrode assembly. The assembly was then immersed in a liquid electrolyte of DOL / DME, 1M LiTFSI (with 0.2M LiNO3) to fabricate a lithium-sulfur coin cell.

[0200] [Evaluation of discharge capacity according to repeated cycles] The lithium-sulfur coin cell prepared as described above was tested at 25°C using a battery cycle tester (WBS3000 Battery Cycler, WonA Tech) at 1.8 to 2.8 V (vs Li / Li + A charge-discharge cycle test was performed by repeatedly charging and discharging at a cut-off voltage and a current density of 0.5C.

[0201] The results of evaluation of discharge capacity as a function of cycle repetition are shown in FIGS.

[0202] In Figures 6 and 7, bare indicates Comparative Example 1, 0.5 wt% c-CPS-KB / S indicates Example 1, 0.5 wt% c-CPS-Li-KB / S indicates Example 2, 1 wt% c-CPS-KB / S indicates Example 3, 2 wt% c-CPS-KB / S indicates Example 4, and 3 wt% c-CPS-KB / S indicates Example 5.

[0203] 6, it can be seen that the initial capacity retention rates of the lithium-sulfur batteries using the sulfur-carbon composites of Examples 1, 3, and 5 were improved compared to Comparative Example 1. It can also be seen that as the number of cycles increased, Example 1 exhibited the best long-term life characteristics.

[0204] 7, it can be seen that the capacity retention rates of the lithium-sulfur batteries using the sulfur-carbon composites of Examples 1 and 2 were improved compared to Comparative Example 1. On the other hand, it can be seen that the amphiphilic cardanol derivative of Preparation Example 1 is more effective in improving the battery capacity, even though the electrical conductivity of the surface of the sulfur-carbon composite was improved by coating the sulfur-carbon composite of Example 2 with the amphiphilic cardanol derivative of Preparation Example 2 containing Li ions.

Claims

1. A porous carbon substrate and a sulfur-containing compound contained in at least one of an outer surface of the porous carbon substrate and inner surfaces of pores, The following chemical formula 1: 【Chemical 1】 The surface is entirely or partially covered with a crosslinked product of an amphiphilic cardanol derivative represented by In Chemical Formula 1, R １ is C １０ ~C ５０ alkyl group of C １０ ~C ５０ and an alkenyl group of C １０ ~C ５０ and at least one alkynyl group selected from the group consisting of R ２ is C １ ~C １０ alkyl group of C ２ ~C １０ and an alkenyl group of C ２ ~C １０ and at least one alkynyl group selected from the group consisting of The R ２ is a sulfur-carbon complex having a structure substituted with at least one anionic functional group.

2. The zeta potential (ζ) of the surface is calculated using the following formula 1: [Formula 1] −60 mV≦ζ≦0 mV The sulfur-carbon composite according to claim 1, which satisfies the following:

3. The amphiphilic cardanol derivative is １ and R ２ 2. The sulfur-carbon composite according to claim 1, wherein at least one of the following has a structure containing at least one carbon-carbon unsaturated bond:

4. The R ２ is -(CH ｘ ) ｎ Q (x = 0, 1, or 2, n = an integer of 1 to 10, and Q is an anionic functional group).

5. The anionic functional group is —O － , -SO ３ － , -COO － , -SO ４ ２－ and conjugate acids thereof.

6. The R ２ 2. The sulfur-carbon composite according to claim 1, wherein the anionic functional group contained in the sulfur-carbon composite further contains at least one of an alkali metal ion and an alkaline earth metal ion as a cation.

7. The crosslinked product of the amphiphilic cardanol derivative has the following formula 2: [Formula 2] Degree of crosslinking (%) = (degree of carbon unsaturation of crosslinked product of amphiphilic cardanol derivative / degree of carbon unsaturation of amphiphilic cardanol derivative) × 100 2. The sulfur-carbon composite according to claim 1, wherein the degree of crosslinking by the method is 15% or more and 45% or less.

8. The amphiphilic cardanol derivative is １ are represented by the following chemical formulas 2 to 5: 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 The sulfur-carbon composite according to claim 1, having at least one structure selected from the following:

9. The amphiphilic cardanol derivative is The R １ a structure represented by Chemical Formula 2 in an amount of 1 part by weight or more and 10 parts by weight or less, The R １ the structure represented by Chemical Formula 3 is 40 parts by weight or more and 70 parts by weight or less, The R １ the structure represented by Chemical Formula 4 is 5 parts by weight or more and 25 parts by weight or less, and The R １ The sulfur-carbon composite according to claim 8, wherein the structure represented by Chemical Formula 5 is contained in an amount of 25 parts by weight or more and 40 parts by weight or less.

10. 2. The sulfur-carbon composite according to claim 1, wherein the porous carbon substrate comprises carbon black, carbon fiber, carbon nanotube (CNT), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofiber (GNF), carbon nanofiber (CNF), activated carbon fiber (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more materials thereof.

11. The sulfur-containing compound is inorganic sulfur (S ８ ), lithium sulfide (Li ２ S), lithium polysulfide (Li ２ 2. The sulfur-carbon composite according to claim 1, comprising a sulfur-carbon complex, ...

12. 2. The sulfur-carbon composite according to claim 1, wherein the total content of the crosslinked amphiphilic cardanol derivative is 0.1 wt % or more and 10 wt % or less, based on the total weight of the sulfur-carbon composite.

13. 12. The sulfur-carbon composite according to claim 11, wherein the total content of the crosslinked amphiphilic cardanol derivative is 0.1 wt % or more and 1 wt % or less, based on the total weight of the sulfur-carbon composite.

14. providing an uncoated sulfur-carbon composite including a porous carbon substrate and a sulfur-containing compound supported on at least one of an outer surface of the porous carbon substrate and inner surfaces of pores of the porous carbon substrate; coating all or at least a portion of the surface of the uncoated sulfur-carbon composite with an amphiphilic cardanol derivative; and crosslinking at least a portion of the coated amphiphilic cardanol derivative to obtain a sulfur-carbon composite whose surface is entirely or partially coated with a crosslinked product of the amphiphilic cardanol derivative, The amphiphilic cardanol derivative has the following chemical formula 1: 【Chemistry 6】 is expressed as In Chemical Formula 1, R １ is C １０ ~C ５０ alkyl group of C １０ ~C ５０ and an alkenyl group of C １０ ~C ５０ and at least one alkynyl group selected from the group consisting of R ２ is C １ ~C １０ alkyl group of C ２ ~C １０ and an alkenyl group of C ２ ~C １０ and at least one alkynyl group selected from the group consisting of The R ２ A method for producing a sulfur-carbon composite having a structure substituted with at least one anionic functional group.

15. The following chemical formula 6: 【Chemistry 7】 The method further comprises the step of preparing the amphiphilic cardanol derivative through an alkylation reaction of a cardanol derivative represented by In Chemical Formula 6, R １ is C １０ ~C ５０ alkyl group of C １０ ~C ５０ and an alkenyl group of C １０ ~C ５０ The method for producing a sulfur-carbon composite according to claim 14, wherein the alkynyl group is at least one selected from the following alkynyl groups:

16. A positive electrode for a lithium-sulfur battery, comprising the sulfur-carbon composite according to any one of claims 1 to 13 and a binder polymer.

17. The battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution; 17. A lithium-sulfur battery, wherein the positive electrode comprises the positive electrode of claim 16.

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