Sulfur-triazine polymer and lithium-sulfur battery capable of being used in poor electrolyte comprising same as positive electrode

Abstract

The present invention relates to a sulfur-triazine polymer and a lithium-sulfur battery capable of being used in a poor electrolyte including the same as a positive electrode, and more particularly, to a sulfur-triazine polymer prepared by grafting and covalently bonding sulfur to triazine, and a lithium-sulfur battery exhibiting high performance even in a poor electrolyte including the same as a positive electrode.

Description

Technical Field

[0001] The present invention relates to a sulfur-triazine polymer and a lithium-sulfur battery containing the same as a positive electrode and capable of being used in a poor electrolyte. More specifically, the present invention relates to a sulfur-triazine polymer prepared by grafting and covalently bonding sulfur to triazine and a lithium-sulfur battery containing the same as a positive electrode and capable of exhibiting high performance even in a poor electrolyte. Background Art

[0002] Lithium-sulfur (Li-S) batteries are a new generation of high-performance secondary batteries that surpass the limitations of lithium-ion batteries. They have attracted much attention for their high theoretical energy density of 2567Wh / kg and environmental friendliness. However, in terms of achieving a specific energy of 500Wh / kg, they are subject to many restrictions due to the "dissolution-precipitation" reaction of the currently used ether-based electrolytes. The main reason for this restriction is that sulfur substances in the positive electrode are lost due to the formation of many polysulfides.

[0003] There are generally two solutions to this problem. One is to increase the activity of sulfur by introducing appropriate main materials such as nanocarbon and metal oxides. The other is to use a large amount of electrolyte to improve the cycle characteristics of the battery. However, this method has the problem that the energy density of the lithium-sulfur battery is limited to 130Wh / kg when the electrolyte / electrode ratio is above 30μL / mg. In addition, when the main material is introduced into the sulfur electrode, the cycle performance of the battery will be seriously affected due to mechanical problems in the lean electrolyte.

[0004] Due to the above problems, it is necessary to develop a new positive electrode that uses a carbon main agent or a supporting base agent that can exert high performance even in a lean electrolyte to disperse insulating sulfur and can improve the wettability and processing characteristics of the negative electrode while strongly fixing polysulfides. Summary of the invention

[0005] Technical issues

[0006] In order to solve the above problems, an object of the present invention is to provide a sulfur-triazine polymer that can be incorporated into a positive electrode to fix polysulfide.

[0007] Another object of the present invention is to provide a lithium-sulfur battery including a sulfur-triazine polymer as a positive electrode and capable of exhibiting high performance even in a poor electrolyte.

[0008] The technical problems to be solved by the present invention are not limited to the problems described above, and those skilled in the art who are skilled in the art to which the present invention belongs can clearly understand the unmentioned or other technical problems.

[0009] Technical Solution

[0010] To achieve the above object, the present invention provides a sulfur-triazine polymer and a lithium-sulfur battery comprising the same as a positive electrode and capable of being used in a lean electrolyte.

[0011] The present invention provides a sulfur-triazine polymer in which a triazine polymer is bonded with sulfur, wherein the bond is a covalent bond formed by grafting the sulfur onto the triazine polymer.

[0012] In the present invention, the sulfur-triazine polymer is characterized in that the sulfur-triazine polymer has one or more structures selected from the group consisting of Chemical Formula 2 to Chemical Formula 7 by covalently bonding sulfur to a triazine polymer having a graphite-phase carbon nitride structure as shown in the following Chemical Formula 1.

[0013] Chemical formula 1

[0014]

[0015] Chemical formula 2

[0016]

[0017] Chemical formula 3

[0018]

[0019] Chemical formula 4

[0020]

[0021] Chemical formula 5

[0022]

[0023] Chemical formula 6

[0024]

[0025] Chemical formula 7

[0026]

[0027] The present invention provides a lithium-sulfur battery that can be used in a lean electrolyte and comprises the sulfur-triazine polymer prepared as described above as a positive electrode.

[0028] The present invention is characterized in that the lithium-sulfur battery can exhibit battery performance in an electrolyte with a lean electrolyte / electrode ratio of 4 μL / mg to 10 μL / mg.

[0029] The present invention is characterized in that the lithium-sulfur battery generates L during charging and discharging. i2 S4 interacts with one or more selected from the group consisting of pyridine-N and pyrrolic acid-N to be immobilized in a block form.

[0030] The present invention is characterized in that the lithium-sulfur battery provides a capacity of 500 mAh / g to 650 mAh / g at the 150th to 200th cycle.

[0031] The present invention is characterized in that when 3 mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.5 μL / mg to 1.5 μL / mg, the lithium-sulfur battery exhibits a coulombic efficiency of 85% to 98% when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

[0032] The present invention is characterized in that when 3 mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.0 μL / mg to 1.0 μL / mg, the lithium-sulfur battery exhibits a capacity of 500 mAh / g to 650 mgAh / g when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

[0033] The present invention is characterized in that the lithium-sulfur battery can be used as a soft pack battery.

[0034] When used as the soft pack battery, an energy density of 300 to 400 Wh / kg is exhibited.

[0035] The present invention is characterized in that the lithium-sulfur battery can be used as a flexible battery.

[0036] Hereinafter, this specification is described in more detail.

[0037] Effects of the Invention

[0038] The present invention can provide a sulfur-triazine polymer that can fix polysulfide by using the technical solution in the positive electrode of a battery.

[0039] Furthermore, the present invention can provide a lithium-sulfur battery that exhibits high performance even in a poor electrolyte by including a sulfur-triazine polymer.

[0040] The effects of the present invention are not limited to the effects mentioned above, and a person skilled in the art can clearly understand the unmentioned or other effects through the description in the scope of protection claimed in the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Part (a) is a schematic diagram of a lithium-sulfur battery that can be used in a lean electrolyte and uses a positive electrode containing sulfur-triazine according to the present invention, Figure 1 (b) is a schematic diagram showing the preparation and structure of a sulfur-triazine polymer.

[0042] Figure 2Schematic diagram showing the process of Li2S4 being fixed in bulk form by interacting with one or more selected from the group consisting of pyridine-N and pyrrolic acid-N during charge and discharge of the sulfur-triazine electrode.

[0043] Figure 3 Schematic diagram showing the polysulfide reaction pathway of sulfur-triazine cathode via bulk immobilization compared to sulfur / carbon electrode via surface immobilization of polysulfides and a schematic diagram showing bulk immobilization with respect to surface immobilization occurring inside a lean electrolyte lithium-sulfur cell.

[0044] Figure 4 Part (a) shows the spectra of the STP electrode and the S / C electrode shown by the Fourier transform infrared spectroscopy (FT-IR) experiment performed according to Experimental Example 1, Figure 4 Part (b) is a spectrum showing a covalent bond by performing a Raman experiment according to Experimental Example 1.

[0045] FIG. 5 shows a cyclic voltage-current diagram obtained in the fifth cycle at a scan rate of 0.1 mV / s in a voltage range of 1.7 V to 2.8 V according to Experimental Example 2 ( Figure 5a ), for restoration ( Figure 5a A1 and A2) and oxidation ( Figure 5a The graph comparing the redox peak current induced in the C1 peak current ( Figure 5b ), a graph showing the reduction and oxidation current as a function of various E / S ratios ( Figure 5c ), constant current discharge / charge profiles measured at various E / S ratios (implemented at E / S ratios of 2 μL / mg, 4 μL / mg, 6 μL / mg, and 8 μL / mg, with current rates of C / 2 and 1C) ( Figure 5d ), Capacity retention curve with E / S ratio implemented in C / 2 ( Figure 5e ), capacity curve with E / S ratio implemented in 1C ( Figure 5f ), Capacity and sulfur utilization curves obtained at high stagnation (QH) and low stagnation (QL) of lithium-sulfur batteries with various E / S implemented at current rates of C / 2 and 1C ( Figure 5g ), the ratio of sulfur used in high stagnation and low stagnation relative to the total sulfur (ideally 3.00%) based on the reagent volume according to the E / S ratio ( Figure 5h ), shows Figure 5f The bar graph of the voltage polarization at each E / S ratio in the current speed of C / 2 and 1C derived from ( Figure 5i ), Nyquist plots of E / S at 4μL / mg, 6μL / mg, 8μL / mg and 15μL / mg by electrochemical impedance spectroscopy (EIS) ( Figure 5j ).

[0046] Figure 6 Part (a) is the ideal structure of carbon nitride according to Experimental Example 3. Figure 6 Part (b) is the density functional theory analysis of the interaction between pyridinic-N, pyrrolic acid-N, graphitic-N and Li2S4 and Li2S polysulfides.

[0047] FIG. 7 shows a schematic diagram of a poor electrolyte lithium-sulfur (Li-S) soft pack battery consisting of a thin lithium Li negative electrode, a separator soaked with different E / S ratios, and a STP positive electrode according to Experimental Example 4 ( Figure 7a ), digital photo of a poor electrolyte lithium sulfur soft pack battery showing a stable open circuit voltage of 2.83V ( Figure 7b ), galvanostatic discharge / charge profiles of poor-electrolyte lithium-sulfur pouch cells measured at a current rate of C / 5 ( Figure 7c ), Capacity retention curve of poor electrolyte lithium sulfur soft pack battery measured under C / 5 conditions ( Figure 7d ), digital photos showing the operation of dozens of light-emitting diodes composed of electrolyte-poor lithium-sulfur soft-pack cells ( Figure 7e ), the mass ratio of various battery structural elements as a function of the E / S ratio and each actual capacity ( Figure 7f ), E / S ratio and mass and energy density of battery structural elements ( Figure 7g ), showing the cyclic voltage-current diagram of the 5th and 10th cycles recorded at a scan rate of 0.1 mV / s ( Figure 7h ), the estimated value of energy density based on E / S ratio and sulfur content and the measured value of energy density of poor electrolyte lithium-sulfur battery ( Figure 7i ), energy density comparison under poor (≤8μL / mg) electrolyte and rich (>8μL / mg) electrolyte conditions ( Figure 7j ). DETAILED DESCRIPTION

[0048] The terms used in this specification are selected from commonly used terms that are currently widely used while considering the functions in the present invention. However, this may be different according to the intention or practice of ordinary people in the technical field to which the present invention belongs, the emergence of new technologies, etc. In addition, there are terms that the applicant arbitrarily selects in certain cases. In this case, their meanings will be described in detail in the description of the relevant invention. Therefore, the terms used in the present invention should not be simply limited to the names of the terms, but should be defined based on the meanings of the terms and the entire content of the present invention.

[0049] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. Terms that are the same as those defined in commonly used dictionaries should be interpreted as having meanings consistent with the contextual meanings of the relevant descriptions, and should not be interpreted as ideal or exaggerated formal meanings if not clearly defined in this application.

[0050] Numerical ranges include the values ​​defined by the ranges. All maximum numerical limitations described throughout this specification should include all lower numerical limitations as if lower numerical limitations were explicitly recorded. All minimum numerical limitations described throughout this specification should include all higher numerical limitations as if higher numerical limitations were explicitly recorded. All numerical limitations described throughout this specification should include all narrower numerical limitations as if narrower numerical limitations were explicitly recorded.

[0051] The advantages, features and methods of achieving the advantages and features of the present invention will be further clarified with reference to the embodiments described below. However, the present invention is not limited to the embodiments disclosed below, and can also be implemented in various other forms. These embodiments are only provided to make the disclosure of the present invention complete and to enable ordinary technicians in the technical field to which the present invention belongs to fully understand the scope of the present invention. The present invention is only defined by the scope of the scope of the invention.

[0052] Sulfur-triazine polymer

[0053] The present invention relates to a sulfur-triazine polymer in which a triazine polymer is bonded with sulfur, and the bond is a covalent bond formed by grafting the sulfur to the triazine polymer.

[0054] In order to maintain a sulfur content of more than 60%, the triazine polymer is grafted with sulfur through a CS bond. The grafted sulfur and the sulfur ring of S8 have high reactivity with Li lithium ions and can therefore react easily.

[0055] The sulfur-triazine polymer may have one or more structures selected from the group consisting of Chemical Formula 2 to Chemical Formula 7 by covalently bonding sulfur to a triazine polymer having a graphite-phase carbon nitride structure as shown in Chemical Formula 1 below.

[0056] Chemical formula 1

[0057]

[0058] Chemical formula 2

[0059]

[0060] Chemical formula 3

[0061]

[0062] Chemical formula 4

[0063]

[0064] Chemical formula 5

[0065]

[0066] Chemical formula 6

[0067]

[0068] Chemical formula 7

[0069]

[0070] As shown in Chemical Formula 2, the sulfurized-triazine polymer (STP) positive electrode by graft covalent bonding is prepared by thermal free radical polymerization of the di-free radical sulfur of S8 and the tri-S-triazine (heptazine) skeleton. The cyclic sulfur (S8) can be formed into a chemically unstable linear polysulfane with two free ends by ring-opening polymerization at a temperature above 159° C. in an inert gas. Figure 1 As shown in part (b), the unstable linear polysulfane formed is simultaneously stabilized by reverse vulcanization with the unsaturated CN double bonds of triazine (CxNy) to form a covalently bonded sulfur-triazine structure. The generated triazine polymer can be grafted with a large amount of sulfur through the active CS bonds required for high energy density lithium-sulfur batteries.

[0071] Lithium-sulfur battery containing sulfur-triazine polymer cathode capable of use in lean electrolyte

[0072] The present invention relates to a lithium-sulfur battery comprising the sulfur-triazine polymer positive electrode and capable of being used in a lean electrolyte.

[0073] The sulfur-triazine polymer of the present invention is a triazine polymer bonded with sulfur, and the bond is a covalent bond formed by grafting the sulfur to the triazine polymer.

[0074] The present invention relates to a sulfur-triazine polymer in which a triazine polymer is bonded with sulfur, and the bond is a covalent bond formed by grafting the sulfur to the triazine polymer.

[0075] In order to maintain a sulfur content of more than 60%, the triazine polymer is grafted with sulfur through a CS bond. The grafted sulfur and the sulfur ring of S8 have high reactivity with Li lithium ions and can therefore react easily.

[0076] The sulfur-triazine polymer may have one or more structures selected from the group consisting of Chemical Formula 2 to Chemical Formula 7 by covalently bonding sulfur to a triazine polymer having a graphite-phase carbon nitride structure as shown in Chemical Formula 1 below.

[0077] Chemical formula 1

[0078]

[0079] Chemical formula 2

[0080]

[0081] Chemical formula 3

[0082]

[0083] Chemical formula 4

[0084]

[0085] Chemical formula 5

[0086]

[0087] Chemical formula 6

[0088]

[0089] Chemical formula 7

[0090]

[0091] As shown in Chemical Formula 2, the sulfur-triazine polymer positive electrode by graft covalent bonding is prepared by thermal free radical polymerization of the diradical sulfur of S8 and the triazine (heptazine) skeleton. The cyclic sulfur (S8) can be formed into a chemically unstable linear polysulfane with two free ends by ring-opening polymerization at a temperature above 159°C in an inert gas. Figure 1 As shown in part (b), the unstable linear polysulfane formed is simultaneously stabilized by reverse vulcanization with the unsaturated CN double bonds of triazine (CxNy) to form a covalently bonded sulfur-triazine structure. The generated triazine polymer can be grafted with a large amount of sulfur through the active CS bonds required for high energy density lithium-sulfur batteries.

[0092] The lithium-sulfur battery can exhibit reaction performance in an electrolyte with a lean electrolyte / electrode ratio of 4 μL / mg to 10 μL / mg.

[0093] The lithium-sulfur battery can achieve an area capacity of 4 mAh / cm2, which is close to that of a lithium-ion battery, in a poor electrolyte with a poor electrolyte / electrode ratio of 4 μL / mg to 10 μL / mg. 2The area capacity, such as Figure 1 As shown in part (a), it can provide multifunctional properties such as excellent electrolyte wettability, polysulfide fixation and volume control.

[0094] The lithium-sulfur battery can be fixed in bulk form by the interaction of Li2S4 generated during charge and discharge with one or more selected from the group consisting of pyridine-N and pyrrolidone-N.

[0095] The triazine structure of the sulfur-triazine polymer constituting the lithium-sulfur battery allows nitrogen to be held in a multi-coordinated state such as pyridine, pyrrolic acid, and graphite nitrogen. The abundant nitrogen held as described above can be bonded to polysulfide.

[0096] like Figure 2 As shown, during the charge and discharge of the lithium-sulfur battery, Li ions interact with S8 rings to form Li2S4 as a high-order polysulfide. The generated Li2S4 is fixed by the strong interaction given by pyridine-N and pyrrolic acid-N. In particular, the polysulfide is very close to the interaction, so it can be fixed in a molecular manner without being dissolved by the liquid electrolyte. In this case, Figure 3 As shown, the immobilization is not surface immobilization but bulk-immobilization, and the immobilization of polysulfide by the bulk-immobilization occurs due to the high bonding strength provided by triazine to polysulfide.

[0097] The lithium-sulfur battery can be used in a lean electrolyte characterized by providing a capacity of 500 mAh / g to 650 mAh / g at the 150th to 200th cycle.

[0098] When 3mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.5 μL / mg to 1.5 μL / mg, the lithium-sulfur battery can exhibit a coulombic efficiency of 85% to 98% when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

[0099] When 3mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.0 μL / mg to 1.0 μL / mg, the lithium-sulfur battery can exhibit a capacity of 500 mAh / g to 650 mgAh / g when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

[0100] The lithium-sulfur battery may be used as a pouch battery, and when used as the pouch battery, may exhibit an energy density of 300 to 400 Wh / kg.

[0101] The lithium-sulfur battery can be used as a flexible battery.

[0102] Example

[0103] Hereinafter, examples of the present invention will be described in detail, but the present invention is not limited to the following examples.

[0104] The advantages, features and methods of achieving the advantages and features of the present invention will be further clarified with reference to the embodiments described below. However, the present invention is not limited to the embodiments disclosed below, and can also be implemented in various other forms. These embodiments are only provided to make the disclosure of the present invention complete and to enable ordinary technicians in the technical field to which the present invention belongs to fully understand the scope of the present invention. The present invention is only defined by the scope of the scope of the invention.

[0105] Example 1. Sulfur-triazine polymer (STP)

[0106] Triazine powder is prepared by thermal condensation reaction of melamine powder. 1 g of melamine powder is placed in an alumina bottle and transferred to an atmosphere-regulated furnace core tube with a lid on. Nitrogen (100 mL / min) is then diffused in the heating chamber for 30 minutes. In this case, the thermal condensation of the melamine is started at a rate of 3°C per minute for 4 hours until 550°C. After the condensation is completed, it is naturally cooled and crushed before storage.

[0107] Then, 100 mg of triazine was dispersed in 5 mL of H2SO4 preheated at 60°C for 6 hours. Then, the same amount of deionized water was added to the triazine-acid mixture, the reaction temperature was raised and stirred, and then stirred for another 10 hours. The reaction mixture after the acid treatment changed from light yellow to white, which showed the successful exfoliation of triazine nanosheets. The mixture was neutralized with deionized water until the pH was 7. The solution obtained by neutralization was centrifuged at a speed of 6000RPM and dried at 60°C to obtain nanosheet powder.

[0108] Then, thio-triazine comprising the triazine obtained by the method is prepared by ring-opening polymerization at a temperature of 160° C. or higher.

[0109] The sulfur / carbon composite was prepared by the following process: a melt infiltration process was performed for 12 hours at a heating rate of 3°C per minute from 155°C in a nitrogen gas of 100 mL / min. Then, 3 weight percent (wt%) of the obtained triazine nanosheets were mixed with the sulfur / carbon composite for about 1 hour, and then ring-opening polymerization was performed again in a nitrogen gas at a heating rate of 5°C per minute from 160°C for 10 hours. During the heat treatment, the sulfur (S8) ring formed a linear polysulfide with multiple chain ends at a temperature above 159°C. The polysulfide formed a sulfur-triazine polymer by covalent bonding with the carbon adjacent to the nitrogen of the triazine ring.

[0110] Example 2. Sulfur-triazine electrode (STP electrode)

[0111] The sulfur-triazine polymer (STP) prepared according to Example 1 was prepared by a doctor blade method. The electrode was composed of the STP as an active material, multi-walled carbon nanotubes (MWCNT) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 8:1.5:0.5, respectively, and after they were completely mixed for 45 minutes, N-methylpyrrolidone (NMP, Sigma Aldrich-Battery grade) solvent was added to the mixture to form a viscous slurry. Then, the obtained slurry was cast on a pre-washed 17 μm thick aluminum foil, dried at room temperature for more than 12 hours, and then vacuum dried at a temperature of 80° C. for 12 hours. The sulfur electrode was prepared by punching the dried sulfur electrode.

[0112] Example 3. Electrolyte-poor lithium-sulfur soft pack battery

[0113] A poor electrolyte lithium-sulfur battery was prepared using a 2cm×3cm sulfur-triazine electrode as a working electrode, a polypropylene separator, and a ground 2cm×3cm thin lithium metal as a reference electrode. The sulfur-triazine and lithium metal electrodes were connected from the outside using an aluminum sheet, and the outside was packaged using an aluminum-plastic composite film. Then, one side of the aluminum sheet was sealed using hot pressing, and after confirming the stacking and external contact, the other side was sealed in the same way. Before the final sealing, a small amount of liquid electrolyte calculated based on the E / S ratio was infiltrated. The electrolyte used used 1M LiTFSi prepared in a DOL and DME solvent with a volume ratio of 1:1, and 2% LiNO3 was used as an additive.

[0114] Comparative Example 1: SC Electrode

[0115] The electrode was prepared in the same manner as in Example 2, except that bare SC (S-Cbare) was used as the active material instead of STP.

[0116] Experimental Example 1. Sulfur-triazine covalent bond experiment by FT-IR and Raman spectroscopy

[0117] In order to confirm the CS covalent bond of the sulfur-triazine polymer, the sulfur-triazine polymer prepared in Example 2 and the S / C electrode prepared in Comparative Example 1 were used to conduct FT-IR experiments and Raman spectroscopy experiments.

[0118] The FT-IR experiments were performed using UATR2 (Perkin Elmer) at 4000 cm -1 Up to 500cm -1 The results are shown in Figure 4 As shown in part (a) of .

[0119] The Raman spectroscopy experiment was performed using LabRAM HR800 (Horiba) using a laser wavelength of 532 nm. The results are shown in Figure 4 As shown in part (b) of .

[0120] like Figure 4 As shown in part (a) of FIG. 1 , in the spectrum showing the FT-IR experimental results, the electrode containing the sulfur-triazine polymer (STP) of Example 2 is characterized by a 778 cm -1 The narrow band formed in the -1 The broad bands shown in the graph indicate the formation of sulfur-carbon (CS) covalent bonds. However, in the S / C electrode of Comparative Example 1, no CS covalent bonds were observed because sulfur was not bonded to triazine.

[0121] And, if Figure 4 As shown in part (b), the electrode containing the sulfur-triazine polymer (STP) of Example 2 has a wavelength of 962 cm corresponding to the covalent CS stretching vibration. -1 The S / C electrode of Comparative Example 1 shows a characteristic Raman band at 472 cm -1 and 433cm -1 A characteristic band indicating an SS bond was shown in the sample, but no CS covalent bond was confirmed because the triazine was not bonded to sulfur.

[0122] The above results shown by the Raman experiment and the FT-IR experiment confirmed that the CS covalent bond was successfully expressed in the electrode including the sulfur-triazine polymer (STP).

[0123] Experimental Example 2. Electrochemical performance test of lithium-sulfur battery containing sulfur-triazine polymer electrode in lean electrolyte

[0124] For the sulfur-triazine polymer (STP) electrodes prepared in Examples 1 and 2 and the S / C electrode prepared in Comparative Example 1, the electrochemical performance was tested by cyclic voltage and current method in a voltage window of 1.7 V to 2.8 V at a scan rate of 0.1 mV / s in a poor electrolyte with an electrolyte / sulfur (E / S) ratio of 2 μL / mg, 4 μL / mg, 6 μL / mg and 8 μL / mg and a rich electrolyte of 15 μL / mg. The results are shown in FIG5 (i.e., Figures 5a to 5j ) as shown.

[0125] like Figure 5a and Figure 5bAs shown, the STP electrodes of Examples 1 and 2 show sulfur reduction peaks at 2.25 (A1) and 2.0 V (A2), and oxidation peaks at 2.45 V (C1). When the E / S ratio drops to less than 2 μL / mg, the STP electrode remains inaccessible to Li particles in order to induce sulfur reaction performance. This also occurs when the ratio is increased to a high level of 10 μL / mg or more.

[0126] and, Figure 5c As shown, compared with the S / C electrode of Comparative Example 1, Examples 1 and 2 show better peak currents in various E / S ratios due to the correct adjustment of Li2S4 and Li2S due to the molecular adsorption of triazine. In particular, A1 converted from S8→Li2S4 maintains similar peak currents in Li-S batteries of all E / S ratios, while the peak current of A2 converted from Li2S4→Li2S shows the correct peak current based on each solvent due to chemical reactions in each solvent, thereby showing multiple peaks. As E / S approaches 4μL / mg from 8μL / mg, the peak shape is converted to diffused Li2S→S8, thereby showing more diverse peaks in C1.

[0127] The above results demonstrate that the STP electrode exhibits better sulfur kinetics in lean electrolytes than the S / C electrode.

[0128] And, if Figure 5d to Figure 5g As shown, at 1C (1.675A / g s ) investigated the performance of the STP electrode. The discharge capacity at the end of the 5th cycle was 592 mAh / g, 708 mAh / g and 809 mAh / g in the lean electrolyte with E / S ratios of 4 μL / mg, 6 μL / mg and 8 μL / mg, respectively. The capacity difference was within 101 to 217, showing a low voltage polarization, which confirmed that the capacity and polarization standards required for the operation of lithium-sulfur batteries were met.

[0129] And, if Figure 5h to Figure 5jAs shown, the cycle characteristics of the STP electrode are 576mAh / g, 697mAh / g, and 826mAh / g in C / 2, and 406mAh / g, 495mAh / g, and 502mAh / g in 1C at E / S ratios of 4μL / mg, 6μL / mg, and 8μL / mg, and the coulombic efficiency is 96%, 98.5%, and 96%, showing very excellent life characteristics. In addition, when repeatedly charged and discharged, the STP electrode shows a low capacity reduction of 0.11 to 0.02 per cycle, and shows a stable capacity until the 200th cycle. In particular, in the E / S ratio of 4μL / mg to 6μL / mg, the STP electrode shows a capacity of 522mAh / g and 574mAh / g in the 34th cycle, and then maintains the capacity with minimal reduction until the 200th cycle.

[0130] The above results confirm that the sulfur-triazine polymer cathode of the present invention can meet the capacity and polarization standards required for lithium-sulfur batteries to operate in a lean electrolyte.

[0131] Experimental Example 3. Density Function Theory (DFT) Analysis of Sulfur-Triazine Polymer Electrodes

[0132] In order to understand the interaction possibility between the sulfur-triazine polymer electrodes prepared according to Examples 1 and 2 and polysulfide in nitrogen gas, density functional theory (DFT) analysis was performed. The results are as follows: Figure 6 shown.

[0133] The polysulfide absorption energy of triazine of the sulfur-triazine polymer electrode is calculated by the following Mathematical Formula 1.

[0134] Mathematical formula 1

[0135] E ads =E 总 (E total )-(E g +E ps )

[0136] like Figure 6 As shown, the HOPS and LOPS of pyridine-N are E ads = -2.31 and -1.47 eV, the HOPS and LOPS of pyrrolidine-N are E ads =-1.77 and -1.29 eV, and the HOPS and LOPS of graphite-N are -1.42 and -1.12 eV respectively.

[0137] The above results confirm that pyridine-N has greater absorption energy for polysulfide than pyrrolic acid-N and graphite-N structures, and that the sulfur-triazine polymer electrode containing it can have improved electrochemical performance in a poor electrolyte.

[0138] Experimental Example 4. Performance test of soft-pack electrolyte-poor lithium-sulfur battery

[0139] In order to confirm the electrochemical performance of the poor electrolyte lithium sulfur soft pack battery containing the sulfur-triazine polymer electrode prepared according to Examples 1 to 3 in a poor electrolyte, an experiment was conducted using a 2 cm×3 cm soft pack lithium sulfur (Li-S) battery prepared according to Example 3. The results are shown in Figure 7 (i.e., Figures 7a to 7j ) as shown.

[0140] like Figure 7b As shown, the Li-S soft pack battery exhibits an OCV of 2.83 V. Figure 7c As shown, the constant current charge / discharge profile of the Li-S pouch cell without applied pressure exhibits a voltage polarization of 0.388 V at a C / 5 ratio.

[0141] And, if Figure 7d As shown, the Li-S battery exhibited excellent cycling stability, showing a coulombic efficiency of 524 mAh / g with 98%, and the capacity was stably maintained until the end of the 40th cycle.

[0142] And, if Figure 7e As shown, the Li-S battery can make the light emitting diode emit light at a critical value of 5.3V.

[0143] And, if Figure 7h to Figure 7j As shown, an excellent energy density of 371 Wh / kg was exhibited at an E / S ratio of 6 μL / mg, which was higher than the theoretical value at 4.4 μL / mg.

[0144] The above results confirm that the sulfur-triazine electrode of the present invention exhibits excellent electrochemical performance under poor electrolyte conditions, has a stable capacity with high energy density, has excellent cycle life, polysulfide fixation and self-discharge prevention characteristics, and can meet the conditions required for lithium-sulfur batteries requiring high energy density.

Claims

1. A sulfur-triazine polymer, characterized in that Triazine polymers are bonded to sulfur, The bonding is a covalent bonding formed by grafting the sulfur to the triazine polymer.

2. The sulfur-triazine polymer according to claim 1, characterized in that The sulfur-triazine polymer has one or more structures selected from the group consisting of Chemical Formula 2 to Chemical Formula 7 by covalently bonding sulfur to a triazine polymer having a graphite-phase carbon nitride structure as shown in the following Chemical Formula 1, Chemical formula 1: Chemical formula 2: Chemical formula 3: Chemical formula 4: Chemical formula 5: Chemical formula 6: Chemical formula 7:

3. A lithium-sulfur battery capable of being used in a lean electrolyte, characterized in that: The sulfur-triazine polymer according to claim 1 or 2 is used as a positive electrode.

4. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: The lithium-sulfur battery exhibits sulfur reaction performance in an electrolyte with a lean electrolyte / electrode ratio of 4 μL / mg to 10 μL / mg.

5. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: The lithium-sulfur battery is fixed in bulk form by the interaction between Li2S4 generated during charge and discharge and one or more selected from the group consisting of pyridine-N and pyrrolic acid-N.

6. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: The lithium-sulfur battery provides a capacity of 500 mAh / g to 650 mAh / g at the 150th to 200th cycle.

7. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: When 3mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.5 μL / mg to 1.5 μL / mg, the lithium-sulfur battery exhibits a coulombic efficiency of 85% to 98% when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

8. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: When 3mg / cm 2 Up to 7mg / cm 2 When the sulfur loading is 2.0 μL / mg to 1.0 μL / mg, the lithium-sulfur battery exhibits a capacity of 500 mAh / g to 650 mgAh / g when the electrolyte / electrode ratio is 4 μL / mg to 10 μL / mg.

9. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: The lithium-sulfur battery can be used as a soft pack battery. When used as the soft pack battery, an energy density of 300 to 400 Wh / kg is exhibited.

10. The lithium-sulfur battery capable of being used in a lean electrolyte according to claim 3, characterized in that: The lithium-sulfur battery can be used as a flexible battery.

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