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 positive electrode material for lithium-sulfur batteries and a lithium-sulfur battery containing the positive electrode material.

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

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based substance having 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 in resources worldwide, non-toxic, and having a low weight per atom.

[0004] As the application areas of secondary batteries expand to include electric vehicles (EVs) and energy storage systems (ESS), lithium-sulfur battery technology, which can achieve a high theoretical energy storage density of ~2,500 Wh / kg compared to lithium-ion secondary batteries with a relatively low energy storage density of ~250 Wh / kg, is attracting attention.

[0005] In a lithium-sulfur battery, during discharge, lithium, the negative electrode active material, releases electrons and oxidizes while ionizing into lithium cations, while the sulfur-based material, the positive electrode active material, is reduced while accepting electrons. Here, through the reduction reaction of the sulfur-based material, the SS bond accepts two electrons and is converted into a sulfur anion. The lithium cations produced by the oxidation reaction of lithium are transferred to the positive electrode via the electrolyte, where they combine with sulfur anions produced by the reduction reaction of the sulfur-based compound to form a salt. Specifically, sulfur before discharge has a cyclic S8 structure, which is converted into lithium polysulfide (Li2Sx) by the reduction reaction, and then completely reduced to produce lithium sulfide (Li2S).

[0006] Because sulfur used as a positive electrode active material is an insulator, the movement of electrons generated by electrochemical reactions is difficult, and there are problems that need to be solved, such as a rapid decrease in battery capacity due to the leaching of lithium polysulfide (LiSx) generated during the charging and discharging process.

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

[0008] There is a real need for technologies that can suppress the loss of energy density in batteries due to the shuttle effect described above. [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, the problem that the present invention aims to solve is to solve the above-mentioned problem, To suppress the elution of lithium polysulfide from the positive electrode of a lithium-sulfur battery, a sulfur-carbon composite in which all or part of the surface is coated with a polymer and a method for producing the same are provided.

[0010] In particular, by suppressing the shuttle effect through the coating structure of the sulfur-carbon composite and suppressing the volume expansion of the positive electrode, a lithium-sulfur battery excellent in discharge capacity and capacity retention rate is provided.

Means for Solving the Problem

[0011] In order to solve the above problems, According to one aspect of the present invention, a sulfur-carbon composite of the following embodiments is provided.

[0012] The sulfur-carbon composite according to the first embodiment 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 all or part of the surface is coated with a cross-linked product of an amphiphilic cardanol derivative represented by the following chemical formula 1.

[0013]

Chemical formula

[0014] In Chemical formula 1, R1 is at least one selected from an alkyl group of C 10 ~C 50 , an alkenyl group of C 10 ~C 50 , and an alkynyl group of C 10 ~C 50 , R2 is at least one selected from an alkyl group of C1~C 10 , an alkenyl group of C2~C 10 , and an alkynyl group of C2~C 10 , The aforementioned R2 has a structure in which at least one anionic functional group is substituted.

[0015] According to the second example, in the first example, The surface zeta potential (ζ) can satisfy the following equation 1.

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

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

[0018] According to the fifth example of manifestation, in any one of the first to fourth examples of manifestation, The aforementioned anionic functional group is -O - , -SO3 - , -COO - , -SO4 2- , and may include at least one selected from these conjugate acids.

[0019] According to the sixth example, in any one of the first to fifth examples, The anionic functional group contained in R2 may further contain at least one of alkali metal ions and alkaline earth metal ions as a cation.

[0020] According to the 7th embodiment example, in any one of the 1st to 6th embodiment examples, The crosslinked product of the amphiphilic cardanol derivative may have a degree of crosslinking of 15% to 45% according to the following formula 2.

[0021] [Formula 2] Degree of crosslinking (%) = (Degree of carbon unsaturation of the crosslinked product of the amphiphilic cardanol derivative / Degree of carbon unsaturation of the amphiphilic cardanol derivative) × 100 According to the eighth example of implementation, in any one of the seventh examples of implementation, 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 9th embodiment example, in any one of the 1st to 8th embodiment examples, The aforementioned amphiphilic cardanol derivative is R1 contains 1 to 10 parts by weight of the structure represented by the chemical formula 2. R1 is a structure represented by the chemical formula 3, in amounts of 40 to 70 parts by weight. The R1 is the structure represented by the chemical formula 4, in amounts of 5 to 25 parts by weight, and The aforementioned R1 may contain 25 to 40 parts by weight of the structure represented by the chemical formula 5.

[0027] According to the 10th embodiment, in any one of the 1st to 9th embodiments, The porous carbon substrate may include carbon black, carbon fibers, carbon nanotubes (CNTs), 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 of these materials.

[0028] According to the 11th embodiment, in any one of the 1st to 10th embodiments, The sulfur-containing compound may include inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 2≦x≦8), disulfide compounds, or mixtures of two or more of these.

[0029] According to the 12th embodiment, in any one of the 1st to 11th embodiments, Based on the total weight of the sulfur-carbon complex, the total content of the crosslinked amphiphilic cardanol derivative can be 0.1% to 10% by weight.

[0030] According to the 13th embodiment example, in any one of the 1st to 12th embodiment examples, Based on the total weight of the sulfur-carbon complex, the total content of the crosslinked amphiphilic cardanol derivative may be 0.1% to 1% by weight.

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

[0032] The method for producing a sulfur-carbon composite according to the 14th embodiment is: The steps include: preparing a porous carbon substrate and an uncoated sulfur-carbon composite containing a sulfur-containing compound supported on one or more of the outer surface and inner surfaces of the pores of the porous carbon substrate; The steps include coating all or at least part of the surface of the uncoated sulfur-carbon composite with an amphiphilic cardanol derivative, The process includes the step of 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 aforementioned 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 group, C 10 ~C 50 The alkenyl group and C 10 ~C 50 At least one selected from the alkynyl groups, R2 is C1~C 10 alkyl groups, C2~C 10 The alkenyl group, and C2~C 10 At least one selected from the alkynyl groups, The aforementioned R2 has a structure in which at least one anionic functional group is substituted.

[0035] According to the 15th example of implementation, in the 14th example of implementation, The process may further include a step of preparing the amphiphilic cardanol derivative through an alkylation reaction of the cardanol derivative represented by the following chemical formula 6.

[0036] [ka]

[0037] In chemical formula 6, R1 is C 10 ~C 50 alkyl group, C 10 ~C 50 The alkenyl group and C 10 ~C 50 It is at least one of the alkynyl groups selected from the following.

[0038] According to yet another aspect of the present invention, a positive electrode for a lithium-sulfur battery is provided as an embodiment described below.

[0039] The positive electrode for the lithium-sulfur battery according to the 16th embodiment is: The invention comprises a sulfur-carbon composite and a binder polymer, according to one of the first to thirteenth embodiment examples.

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

[0041] The lithium-sulfur battery according to the 17th embodiment example is, The system includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode includes the positive electrode according to the 16th embodiment. [Effects of the Invention]

[0042] A sulfur-carbon composite according to one aspect of the present invention has a coating structure with a crosslinked amphiphilic cardanol derivative, and when a lithium-sulfur battery containing a positive electrode to which the sulfur-carbon composite is applied is driven, it can suppress the elution of lithium polysulfide. This not only improves the discharge capacity of the lithium-sulfur battery but also provides an excellent effect on the battery's capacity retention rate in response to repeated cycles.

[0043] Furthermore, the aforementioned coating structure mitigates 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 accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention. The invention shall not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0045] [Figure 1] These are the 1H NMR spectra of the cardanol used in the production of Production Example 1 and Production Example 2. [Figure 2] This is the 1H NMR spectrum of the amphiphilic cardanol derivative produced in Production Example 1. [Figure 3] This figure shows a portion of the 1H NMR spectrum of the amphiphilic cardanol derivative crosslinked product formed in Example 1. [Figure 4] This is a TGA analysis graph of the porous carbon substrate (KB) used in the production of Comparative Example 1, Comparative Example 1 (KB / S), Example 1 (c-CPS-KB / S 0.5wt%), Example 2 (c-CPS-Li-KB / S 0.5wt%), Example 3 (c-CPS-KB / S 1wt%), Example 4 (c-CPS-KB / S 2wt%), and Example 5 (c-CPS-KB / S 3wt%). [Figure 5] These are SEM images of Comparative Example 1 (KB / S), Example 1 (c-CPS-KB / S 0.5wt%), Example 2 (c-CPS-Li-KB / S 0.5wt%), Example 3 (c-CPS-KB / S 1wt%), Example 4 (c-CPS-KB / S 2wt%), and Example 5 (c-CPS-KB / S 3wt%). [Figure 6] This graph shows 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] This graph shows the results of cycle tests on lithium sulfur coin cells using Comparative Example 1, Example 1, and Example 2. [Modes for carrying out the invention]

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

[0047] In this specification, when a configuration is described as "including" a component, unless otherwise specified, it does not mean that other components are excluded, but rather that other components may be included.

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

[0049] The specific terms used herein are for convenience only and are not limiting. For example, terms indicating position, such as “up,” “down,” “left,” “right,” “front,” “back,” “inside,” and “outside,” are used to describe the relative position or orientation between components, rather than absolute position, or may represent position or orientation in a referenced drawing. These terms include, in addition to themselves, words containing them, their derivatives, and words with similar meanings.

[0050] In this specification, "alkyl group," "alkenyl group," and "alkynyl group" can each independently be a linear or branched chain and represent a substituted or unsubstituted hydrocarbon.

[0051] The terms "substituted or unsubstituted" above mean substituted with one or more substituents selected from the group including deuterium; halogen groups; nitrile groups; nitro groups; hydroxyl groups; -COOH; alkoxy groups; alkyl groups; cycloalkyl groups; alkenyl groups; cycloalkenyl groups; aryl groups; heterocyclic groups containing one or more N, O, S, or P atoms; and heteroaryl groups; or having no substituents at all.

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

[0053] The sulfur-carbon composite comprises a porous carbon substrate and a sulfur-containing compound contained in one or more of the outer surface and inner surfaces of the pores of the porous carbon substrate, and has a structure in which all or part of its surface is coated with a crosslinked product of an amphiphilic cardanol derivative represented by the following chemical formula 1.

[0054] In this specification, "amphiphilic" means a property that includes both a nonpolar hydrophobic moiety and a polar hydrophilic moiety. For example, an amphiphilic compound means a compound having a structure that includes both a nonpolar hydrophobic moiety and a polar hydrophilic moiety. Thus, the "amphiphilic cardanol derivative" means a cardanol derivative having a structure that includes both a nonpolar hydrophobic moiety and a polar hydrophilic moiety.

[0055] In this specification, the term "derivative(s)" means a structurally similar compound obtained by chemically altering a part of any compound. Generally, a derivative refers to a compound in which a hydrogen atom or a specific group of atoms in the compound is substituted by another atom or group of atoms. More broadly, products created by additive reactions can also be called derivatives. Therefore, the term "cardanol derivative" refers not only to cardanol itself, but also to compounds obtained by chemically altering cardanol that are structurally similar to cardanol.

[0056] The aforementioned "cardanol" is a derivative obtained from cashew nutshell liquid (CNSL), a natural vegetable oil extracted from the peel of the cashew fruit, which belongs to the Anacardiaceae family and inhabits tropical Urima. It can be represented by the following structure.

[0057] [ka]

[0058] R=C 15 H 31-2n (n=0, 1, 2, or 3) In this specification, the term "amphiphilic cardanol derivative" refers collectively 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 collectively to chemical reactions that induce a change in the chemical properties of a compound by substituting part or all of its structure.

[0059] Specifically, in this 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 group, C 10 ~C 50 The alkenyl group and C 10 ~C 50 At least one selected from the alkynyl groups, R2 is C1~C 10 alkyl groups, C2~C 10 The alkenyl group, and C2~C 10 It is at least one of the alkynyl groups selected from the following.

[0062] The aforementioned R2 has a structure in which at least one anionic functional group is substituted.

[0063] The compound of chemical formula 1 is a phenol derivative with R1 substituted at the meta position, and is one of the cardanol derivatives. The compound of chemical formula 1 contains a nonpolar hydrophobic moiety by including a substituent (R1) having 10 to 50 carbon atoms. The compound of chemical formula 1 also contains a hydrophilic moiety by including a substituent (R2) having 1 to 10 carbon atoms and having at least one anionic functional group.

[0064] The compound of chemical formula 1 can form crosslinked products through addition reactions via unsaturated bonds between carbon atoms in its structure and / or condensation reactions via alkoxy functional groups.

[0065] In one embodiment of the present invention, the compound of chemical formula 1 can form a crosslinked product by unsaturated bonds between carbon atoms, wherein at least one of R1 and R2 contains at least one unsaturated bond between carbon atoms.

[0066] In this specification, the term "unsaturated carbon-carbon bond" refers to at least one of a carbon(sp2)=carbon(sp2) double bond and a carbon(sp)≡carbon(sp) triple bond. Therefore, the term "at least one of R1 and R2 contains at least one unsaturated carbon-carbon 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 unsaturated carbon-carbon bonds contained in the amphiphilic cardanol derivative may provide crosslinking sites(s) in the crosslinked product of the amphiphilic cardanol derivative.

[0067] According to one embodiment of the present invention, as will be described later, the sulfur-carbon composite may be a composite whose entire or partial surface is coated with the amphiphilic cardanol derivative and subjected to a crosslinking reaction, thereby having the entire or partial surface 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, which has a relatively long carbon chain, is located, provides excellent bonding strength with the porous carbon substrate, and the polar portion where the carbon chain is relatively short and the anionic functional group is located can impart hydrophilicity to the surface of the sulfur-carbon composite.

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

[0070] Specifically, the zeta potential of the surface of the sulfur-carbon composite can satisfy the range of Equation 1 below.

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

[0072] In one embodiment of the present invention, the amphiphilic cardanol derivative is modified such that at least one anionic functional group is present in the structure of R2, and 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 from 1 to 10, where Q is an anionic functional group).

[0073] In this specification, the anionic functional group refers to a functional group capable of providing anions in an aqueous solvent. For example, a compound containing the anionic functional group contains hydrogen (H) in an aqueous solvent such as water to provide an anion (-). + ) may have the property of dissociating cations such as .

[0074] In one embodiment of the present invention, the anionic functional group is -O in an aqueous solvent. - , -SO3 - , -COO - or -SO4 2- It may be a functional group exhibiting the following characteristics. Specifically, the anionic functional group is -O - , -SO3 - , -COO - , -SO4 2- , and may include at least one selected from these conjugate acids.

[0075] In one embodiment of the present invention, the amphiphilic cardanol derivative may further contain alkali metal ions and / or alkaline earth metal ions as conjugate ions of the anionic functional group contained in its structure. Specifically, the anionic functional group contained in R2 may further contain at least one of alkali metal ions and alkaline earth metal ions as a conjugate ion. When R2 further contains a conjugate ion of the anionic functional group, it can provide advantageous effects in terms of the electrical conductivity of the positive electrode using the sulfur-carbon composite, but the present invention is not limited thereto.

[0076] The alkali metal ions mentioned above include, for example, lithium ions (Li + ), sodium ions (Na + ), or potassium ions (K + ) may have, but is not limited to, these. The alkaline earth metal ions may include, for example, calcium ions (Ca 2+ ), magnesium (Mg 2+ ) or beryllium (Be 2+ ) may have, 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 may be at least one of the following: alkali metal ions or alkaline earth metal ions.)

[0078] In another embodiment of the present invention, at least one anionic functional group contained within the structure of R2 is -SO3 - -SO3H, and -SO3 - M + It may contain at least one of the following (where 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 imparts anions to the surface of a sulfur-carbon composite coated with a crosslinked product of the amphiphilic cardanol derivative. This can improve the electrical conductivity of the sulfur-carbon composite, but the effects of the present invention are not limited thereto.

[0080] As described above, the unsaturated carbon-carbon bonds contained in the amphiphilic cardanol derivative provide crosslinking sites(s) in the crosslinked product of the amphiphilic cardanol derivative. Specifically, the amphiphilic cardanol derivative contains at least one unsaturated carbon-carbon bond. This allows for the formation of a crosslinked product of the amphiphilic cardanol derivative through intermolecular and / or intramolecular crosslinking reactions between two or more amphiphilic cardanol derivatives.

[0081] In one embodiment of the present invention, the crosslinking reaction between the unsaturated bonds of the amphiphilic cardanol derivative can be confirmed by observing the structural changes of the amphiphilic cardanol derivative before and after the crosslinking reaction. For example, this can be confirmed by comparing the 1H NMR graphs of the amphiphilic cardanol derivative before and after the crosslinking reaction, which show 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., CC). Alternatively, the formation of a crosslinked product of the amphiphilic cardanol derivative can be confirmed by known analytical methods that can detect changes in the number of unsaturated bonds between carbon atoms.

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

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

[0084] One example of a method for measuring the degree of carbon unsaturation is 1H NMR analysis. For example, the degree of carbon unsaturation can be measured by dividing the peak region of unsaturated bonds between carbon atoms of the crosslinked amphiphilic cardanol derivative by the peak region of unsaturated bonds between carbon atoms of the crosslinked amphiphilic cardanol derivative.

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

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

[0087] The R1 is 10 ~ 50 an alkyl group of, 10 ~ 50 an alkenyl group of, and 10 ~ 50 an alkynyl group of, and is at least any one selected therefrom.

[0088] In one embodiment of the present invention, the R1 is specifically 10 ~ 40 an alkyl group of, 10 ~ 40 an alkenyl group of, and 10 ~ 40 an alkynyl group of, and may be at least any one selected therefrom. More specifically, 10 ~ 30 an alkyl group of, 10 ~ 30 an alkenyl group of, and 10 ~ 30 an alkynyl group of, and may be at least any one selected therefrom. More specifically, 13 ~ 20 an alkyl group of, 13 ~ 20 an alkenyl group of, and 13 ~ 20 an alkynyl group of, and may be at least any one selected therefrom.

[0089] In one embodiment of the present invention, the amphiphilic cardanol derivative may have a structure in which the R1 has 10 to 30 carbon atoms and the number of unsaturated bond groups between carbon atoms is 0 (that is, a saturated hydrocarbon group) to 5, specifically 0 to 4, or 0 to 3. <000051​​In other embodiments of the present invention, the amphiphilic cardanol derivative may include one having at least one structure selected from the following chemical formulas 2 to 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 different R1s. Specifically, the amphiphilic cardanol derivative may be a mixture of R1 having structures represented by chemical formulas 2 to 5.

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

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

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

[0099] R2 is at least one selected from an alkyl group of C1 to C 10 an alkenyl group of C2 to C 10 and an alkynyl group of C2 to C 10 and has a structure substituted with at least one anionic functional group at an arbitrary position.

[0100]

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

[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 may be 3-sulfonic acid propyl.

[0103] In one embodiment of the present invention, the amphiphilic cardanol derivative may contain cardanylpropyl sulfonic acid represented by the following Chemical Formula 7. <00005b9>

[0104] [ka]

[0105] In chemical 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 a crosslinked amphiphilic cardanol derivative and a core structure comprising a porous carbon substrate and a sulfur-containing compound.

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

[0108] The porous carbon substrate is a material containing numerous micropores, and the sulfur-containing compound is supported on one or more of either the outer surface or the inner surface of the pores of the porous carbon substrate.

[0109] In one embodiment of the present invention, the porous carbon substrate includes a large number of micropores on its outer surface and interior, 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 fine pores 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 fibers, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more of these materials.

[0112] In one embodiment of the present invention, when the porous carbon substrate material 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 porous carbon substrate material includes carbon nanotubes, the carbon nanotubes may include entangled carbon nanotubes (ENTNs) formed as a secondary structure by the aggregation of multiple primary structures, with carbon nanotubes serving as the primary structure.

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

[0115] In one embodiment of the present invention, the size of the porous carbon substrate is not limited thereto, but may be, for example, 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 obtained in terms of adjusting the solid content and electrode properties, such as adhesive strength, and battery performance (output and capacity, etc.) when manufacturing a slurry for forming an electrode active material layer.

[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 It can be / g. The pore volume may be a value calculated and measured, for example, through N2 adsorption isotherm analysis 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 not limited to this, but for example, 150 m². 2 / g~2,000m 2 / g, specifically 250m 2 / g~700m 2 It 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 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 (77K) using BELSORP-mini II manufactured by BEL Japan.

[0118] In one embodiment of the present invention, the sulfur-containing compound may be, but is not limited to, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 2≦x≦8), disulfide compounds, or mixtures of two or more of these.

[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, they 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.

[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 and the sulfur-containing compound and then heat-treating the mixture. The heat treatment may be carried out 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, a sulfur-carbon composite is provided in which the sulfur-containing compound is contained in one or more of the outer surface and inner surface of the pores of the porous carbon substrate, and all or part of the surface is coated 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) of, for example, 10 μm to 100 μm, specifically 20 μm to 50 μm. 50 ) may have.

[0123] In one embodiment of the present invention, the total content of the amphiphilic cardanol derivative crosslinks, based on the total weight of the sulfur-carbon composite, is not limited to, but may be, for example, 0.1% to 10% by weight. Specifically, based on the total weight of the sulfur-carbon composite, the total content of the amphiphilic cardanol derivative crosslinks may be 0.1% to 5% by weight, specifically 0.1% to 1% by weight, 0.3% to 1% by weight, or 0.3% to 0.8% by weight. While having a content of the amphiphilic cardanol derivative crosslinks within the above range is further advantageous in terms of improving the lifespan of the lithium-sulfur battery to which the sulfur-carbon composite is applied, the present invention is not limited thereto.

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

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

[0126] In the above-mentioned manufacturing method, the porous carbon substrate, sulfur-containing compound, amphiphilic cardanol derivative, and crosslinked product of amphiphilic cardanol derivative shall be as described above.

[0127] In one embodiment of the present invention, the method for producing the sulfur-carbon composite may further include the step of preparing the amphiphilic cardanol derivative through an alkylation reaction of the cardanol derivative represented by the following chemical formula 6.

[0128] [ka]

[0129] In chemical formula 6, R1 is C 10 ~C 50 alkyl group, C 10 ~C 50 The alkenyl group and C 10 ~C 50 It is at least one of the alkynyl groups selected from the following.

[0130] First, the step of preparing the uncoated sulfur-carbon composite includes the step of mixing the porous carbon substrate and 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, they 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 process may further include the step of grinding the porous carbon substrate and the sulfur-containing compound after mixing them. The homogeneity of the mixture between the porous carbon substrate and the sulfur-containing compound can be improved through this grinding, 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 the step of heat-treating the porous carbon substrate and the sulfur-containing compound after mixing (or mixing and grinding). The heat treatment may be carried out at a temperature of, for example, 130°C to 200°C, specifically 130°C to 180°C, or 150°C to 160°C. The mechanical strength of the sulfur-carbon composite produced through the heat treatment can be improved, 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 contact between the sulfur-carbon composite and the amphiphilic cardanol derivative. For example, the surface of the sulfur-carbon composite can be coated by immersing it in a dispersion in which the amphiphilic cardanol derivative is dispersed and then stirring.

[0135] In one embodiment of the present invention, the dispersion in which the amphiphilic cardanol derivative is dispersed may be, for example, an aqueous solvent such as water in which the amphiphilic cardanol derivative is dispersed at a weight of 0.1% to 10%; however, 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% to 10% by weight, 0.1% to 5% by weight, 0.1% to 3% by weight, 0.1% to 1% by weight, or 0.3% to 0.8% by weight, based on the total weight of the coated sulfur-carbon complex. The amount of the coated amphiphilic cardanol derivative can be calculated by the increased weight of the coated sulfur-carbon complex compared to the weight of the uncoated sulfur-carbon complex.

[0137] Next, a crosslinking reaction is carried out to form a crosslink in the coated amphiphilic cardanol derivative through unsaturated bonds between carbon atoms. Through this crosslinking reaction, all or part of the surface of the sulfur-carbon composite can be coated with the crosslink of the amphiphilic cardanol derivative.

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

[0139] In one embodiment of the present invention, the crosslinking reaction is preferably carried out at a temperature in which the amphiphilic cardanol derivative does not decompose. The crosslinking reaction is preferably carried out at, 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 one embodiment of the present invention, the method for producing the sulfur-carbon composite may further include the step of 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 through an alkylation reaction 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 group, C 10 ~C 50 The alkenyl group and C 10 ~C 50 It is at least one of the alkynyl groups selected from the following.

[0144] In one embodiment of the present invention, the explanation for R1 in chemical formula 6 is the same as the explanation for R1 in chemical formula 1.

[0145] In one embodiment of the present invention, the alkylation reaction of the cardanol derivative represented by chemical formula 6 is a reaction to replace the hydrogen atom of the hydroxyl group (OH) in chemical formula 6 with R2. The explanation for R2 in chemical formula 6 is the same as the explanation for R2 in chemical formula 1.

[0146] In one embodiment of the present invention, the alkylation reaction of the cardanol derivative represented by chemical formula 6 involves converting the hydrogen atoms of the hydroxyl group of the cardanol derivative represented by chemical formula 6 to C1-C1. 10 alkyl groups, C2~C 10 The alkenyl group, and C2~C 10 This can be carried out in the following order: substitution with at least one selected from the alkynyl groups, followed by modification to make the substituted structure amphiphilic by substituting at least one hydrogen atom with an anionic functional group.

[0147] In one embodiment of the present invention, the step of modifying to amphiphilic involves performing an alkylation reaction on the cardanol derivative, substituting at least one sulfonic acid, carboxylic acid, and sulfuric acid functional group into the alkyl-substituted structure, and adding hydrogen ions (H) to the acid compound. + This can be done in the order of changing ) 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 an alkylsultone. In this case, the cardanol derivative alkylated through the ring-opening reaction of the alkylsultone may contain a sulfonic acid group as an anionic functional group.

[0149] By the above method, a sulfur-carbon composite can be produced that contains a porous carbon substrate and a sulfur-containing compound contained in one or more of the outer surface and inner surfaces of the pores of the porous carbon substrate, and whose surface is entirely or partially coated with a crosslinked product of an amphiphilic cardanol derivative represented by chemical formula 1.

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

[0151] In one embodiment of the present invention, the binder polymer can be any binder that is suitable for use in the positive electrode of a lithium-sulfur battery, without any particular limitations. The binder may include, for example, PVDF (polyvinylidene fluoride), and more specifically, PVDF dispersed in NMP (N-methyl-2-pyrrolidone), but is not limited to these.

[0152] In other embodiments of the present invention, the binder polymer may include, for example, an aqueous binder such as SBR (styrene-butadiene rubber), and more specifically, an aqueous binder dispersed in an aqueous solvent such as water, but is not limited thereto.

[0153] In other embodiments of the present invention, the positive electrode for the lithium-sulfur battery may further include conductive materials, additives, etc., in addition to the sulfur-carbon composite and binder polymer. In this case, the specific types of conductive materials and additives can be those of ordinary use, so a detailed explanation is omitted.

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

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

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

[0157] A lithium-sulfur battery according to yet another embodiment of the present invention comprises a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode described above.

[0158] In one embodiment of the present invention, the negative electrode and the separator membrane can be used without particular limitation as long as they are suitable for use in a lithium-sulfur battery and do not hinder the objectives of the present invention. For example, lithium metal can be used as the negative electrode.

[0159] In one embodiment of the present invention, the separation membrane can be used without limitation as long as it is one that is normally usable as a separation membrane for lithium-sulfur batteries. The separation membrane may include a porous polyolefin substrate, and may further include inorganic particles on at least one surface of the porous polyolefin substrate as needed. The separation membrane may also further include a binder for binding the inorganic particles as needed.

[0160] In another embodiment of the present invention, the separation membrane may be a film-like electrolyte membrane containing a solid electrolyte, and may further contain a binder for binding the solid electrolyte as needed. The solid electrolyte may be any solid electrolyte that is commonly used in lithium-sulfur batteries, such as a polymer-based solid electrolyte, an inorganic solid electrolyte, or a mixture thereof.

[0161] In one embodiment of the present invention, the electrolyte includes one that is normally usable in lithium-sulfur batteries. The electrolyte may include a lithium salt and a non-aqueous solvent.

[0162] The lithium salt can be used without limitation as long as it is one that is normally usable in the electrolyte of a lithium-sulfur battery. Examples of lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 It may contain, but is not limited to, LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3Cli, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide, or two or more of these.

[0163] The non-aqueous solvent can be used without limitation as long as it is normally usable as an electrolyte for lithium-sulfur batteries. The non-aqueous solvent may include, but is not limited to, cyclic carbonate solvents, linear carbonate solvents, ester solvents, ketone solvents, or mixtures of two or more of these.

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

[0165] In one embodiment of the present invention, the external shape of the lithium-sulfur battery may be, for example, coin-shaped, cylindrical, pouch-shaped, or rectangular, but the external 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 small devices, but also as a unit battery in medium- and large-sized battery modules containing multiple battery cells, and its usage is not particularly limited.

[0166] In one embodiment of the present invention, a lithium-sulfur battery using a positive electrode containing the sulfur-carbon composite can effectively improve 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 to this.

[0167] In one embodiment of the present invention, the lithium-sulfur battery can achieve an effect of improving energy density by increasing the amount of sulfur loaded in the positive electrode, but the effects of the present invention are not limited to this.

[0168] The following describes in detail, with reference to examples, a method for producing a sulfur-carbon composite according to embodiments of the present invention, and a method for producing a lithium-sulfur battery using the same. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited to these.

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

[0170] [ka]

[0171] Manufacturing Example 1: Production of cardanylpropyl sulfonic acid (CPS) Cardanylpropylsulfonic acid was produced as an amphiphilic cardanol derivative according to the reaction equation below.

[0172] [ka]

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

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

[0175] Cardanylpropyl sulfonate was dissolved in water, then an equivalent amount or more of HCl (manufactured by Daejung) was added and the mixture was stirred at room temperature to protonate it and obtain cardanylpropyl sulfonic acid (CPS) (yield 50%).

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

[0177] Manufacturing Example 2. Production of cardanylpropyl lithium sulfonate (CPS-Li)

[0178] [ka]

[0179] In Production Example 1, cardanylpropyl sulfonic acid (CPS) and LiOH were dissolved in water in equivalent amounts and stirred to obtain cardanylpropyl lithium sulfonate (CPS-Li).

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

[0181] Comparative example 1.KB-S Sulfur (S8, manufactured by Sigma-Aldrich) and Ketjenblack (KB, manufactured by Lion Corporation) were mixed in a mass ratio of 7:3 and pulverized in a mortar grinder. The mixture was then heat-treated at 155°C for 30 minutes to produce an uncoated sulfur-carbon composite (KB-S) in which the 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% To 300 ml of water, 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 Production Example 1 were added as an amphiphilic cardanol derivative. After sonication for 5 hours, the mixture was stirred for 16 hours, washed with water, and the surface of the uncoated sulfur-carbon composite was coated with the amphiphilic cardanol derivative of Production Example 1.

[0183] Based on the total weight of the sulfur-carbon composite coated with the amphiphilic cardanol derivative, 10% by weight of polymerization initiator (V-501, manufactured by Fujifilm Wako Pure Chemical Industries) was added with 2 ml of water and stirred at 90°C for 24 hours. After washing with water, a sulfur-carbon composite coated with a crosslinked amphiphilic cardanol derivative was obtained.

[0184] Figure 3 shows the peak region of the bridged structure of the amphiphilic cardanol derivative among the 1H NMR results of the acquired sulfur-carbon complex. Referring to Figure 3, it can be confirmed that the bridged structure was formed by unsaturated bonds between carbon atoms, as the 1H peak of the unsaturated carbon observed in the 1H NMR result of the amphiphilic cardanol derivative (Figure 2) has decreased.

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

[0186] Degree of crosslinking (%) = Content of unsaturated bonds in the crosslinked product of the 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 complex 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 1wt% A sulfur-carbon composite was obtained in the same manner as in Example 1, except that 1 part by weight of Production Example 1 was used as the amphiphilic cardanol derivative.

[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 Production Example 1 was used as the amphiphilic cardanol derivative.

[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 complexes] The composition of the sulfur-carbon composite produced is shown in Table 1.

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

[0192] [Table 1]

[0193] Referring to Table 1 and Figure 4, although sulfur (S8) is insoluble in water at room temperature, it is sublimable, and therefore it is thought that some of it was lost at the temperature at which the crosslinking reaction took place. Specifically, in Examples 1 and 2, the coating layer formed by the crosslinked 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 is thought to have increased sulfur loss. In Example 5, an excess amount of crosslinked amphiphilic cardanol derivative almost completely covered the surface of KB / S, resulting in less sulfur loss than in Examples 3 and 4.

[0194] [Analysis of the structure of sulfur-carbon complexes] Figure 5 shows SEM images of the sulfur-carbon composites produced in Comparative Example 1 and Examples 1 to 5.

[0195] From Figure 5, the sulfur-carbon composite manufactured as described above has an average particle size (D 50 It can be confirmed that the particles are spherical and 35 μm in size.

[0196] Furthermore, referring to Figure 5, it can be confirmed that in Examples 1 and 2, the crosslinked amphiphilic cardanol derivative uniformly and without clumping covers the surface of the sulfur-carbon composite. On the other hand, in Examples 3 to 5, where the content of the crosslinked amphiphilic cardanol derivative was increased, it was confirmed that the crosslinked amphiphilic cardanol derivative aggregated, and the uniformity of the coating structure on the surface of the sulfur-carbon composite decreased.

[0197] [Evaluation of the performance of lithium-sulfur coin cells] To evaluate the battery performance when the sulfur-carbon composite manufactured as described above is applied to the positive electrode, lithium-sulfur coin cells were manufactured using the following method.

[0198] The manufactured sulfur-carbon composite, polyacrylic acid (PAA) binder (Mw 450,000), and carbon conductive material (Super P) were mixed at a ratio of 85:10:5, and after adding 0.5 wt% of PVA dispersant (Mw 9,500), they were mixed with a mixer (manufactured by Shin-Kei Co., Ltd.) to a solid content concentration of 13 wt% in an aqueous phase to produce a positive electrode slurry. The produced positive electrode slurry was coated on an aluminum foil to a thickness of 300 μm using a doctor blade and dried at 50 °C for 14 hours.

[0199] The manufactured positive electrode and lithium metal negative electrode were prepared, and an electrode assembly prepared by sandwiching a Celgard separator between the positive electrode and the negative electrode was immersed in a liquid electrolyte of DOL / DME, 1 M LiTFSI (with 0.2 M LiNO3) to manufacture a lithium-sulfur coin cell.

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

[0201] The evaluation results of the discharge capacity according to cycle repetition are shown in FIGS. 6 and 7.

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

[0203] Referring to Figure 6, it can be seen that the initial capacity retention rate of lithium-sulfur batteries using sulfur-carbon composites in Examples 1 and 3 to 5 has improved compared to Comparative Example 1. As the number of cycles increases, it can be seen that Example 1 exhibits the best long-term life characteristics.

[0204] Referring to Figure 7, it can be confirmed that the capacity retention rate was improved in the lithium-sulfur batteries using the sulfur-carbon composites of Examples 1 and 2 compared to Comparative Example 1. On the other hand, although the electrical conductivity of the surface of the sulfur-carbon composite of Example 2 was improved by coating it with Production Example 2, which contains Li ions as an amphiphilic cardanol derivative, it can be confirmed that the amphiphilic cardanol derivative of Production Example 1 is even more useful in terms of battery capacity.

Claims

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

2. The surface zeta potential (ζ) is given by the following equation 1: [Formula 1] -60mV ≤ ζ ≤ 0mV A sulfur-carbon composite according to claim 1, satisfying the requirements.

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

4. The aforementioned R ２ is, -(CH ｘ ) ｎ The sulfur-carbon composite according to claim 1, represented by Q (x = 0, 1, or 2, n = an integer from 1 to 10, where Q is an anionic functional group).

5. The aforementioned anionic functional group is -O － , -SO ３ － , -COO － , -SO ４ ２－ The sulfur-carbon composite according to claim 1, comprising, and at least one selected from these conjugate acids.

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

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

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

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

10. The sulfur-carbon composite according to claim 1, wherein the porous carbon substrate comprises carbon black, carbon fibers, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), carbon black, graphite, graphite nanofibers (GNF), carbon nanofibers (CNF), activated carbon fibers (ACF), natural graphite, artificial graphite, expanded graphite, activated carbon, fullerene, or two or more of these materials.

11. The aforementioned sulfur-containing compound is inorganic sulfur (S ８ ), lithium sulfide (Li ２ S), Lithium polysulfide (Li ２ The sulfur-carbon composite according to claim 1, comprising Sx, 2 ≤ x ≤ 8), a disulfide compound, or a mixture of two or more thereof.

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

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

14. The steps include: preparing a porous carbon substrate and an uncoated sulfur-carbon composite containing a sulfur-containing compound supported on one or more of the outer surface and inner surfaces of the pores of the porous carbon substrate; The steps include coating all or at least part of the surface of the uncoated sulfur-carbon composite with an amphiphilic cardanol derivative, The process includes the step of 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 given by the following chemical formula 1: 【Transformation 6】 It is represented as, In chemical formula 1, R １ C １０ ~C ５０ alkyl group, C １０ ~C ５０ The alkenyl group and C １０ ~C ５０ At least one selected from the alkynyl groups, R ２ C １ ~C １０ alkyl group, C ２ ~C １０ The alkenyl group and C ２ ~C １０ At least one selected from the alkynyl groups, The aforementioned R ２ A method for producing a sulfur-carbon composite having a structure substituted with at least one anionic functional group.

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

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

17. The system includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium sulfur battery wherein the positive electrode includes the positive electrode described in claim 16.

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