KR101719048B1 - A Cathode of Lithium-Sulfur Batteries and a manufacturing method thereof - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium-sulfur battery and a method of manufacturing the same. More particularly, the present invention relates to a lithium-sulfur secondary battery using a polymer containing sulfur as a positive electrode active material.
The cathode active material according to the present invention is characterized in that the porous structure is manufactured by filling sulfur into the porous structure to vulcanize the porous structure.

Description

[0001] The present invention relates to a cathode active material for a lithium-sulfur battery,

The present invention relates to a positive electrode active material for a lithium-sulfur battery and a method of manufacturing the same. More particularly, the present invention relates to a lithium-sulfur secondary battery using a polymer containing sulfur as a positive electrode active material.

The lithium-sulfur battery includes a positive electrode containing sulfur, and a lithium metal is used as a negative electrode. At the discharge, the reduced sulfur in the anode combines with the lithium ion moved from the cathode to form Li ₂ S (2Li ⁺ + 2e ^- + S ↔ Li ₂ S), and the theoretical value of 1672 mAh / g Capacity.

In such a lithium-sulfur battery, the anode sulfur and the reaction end product LiS have an electrically non-conductive nature, and thus an electrolyte having a high dielectric constant is used. As a result, the soluble polysulfide is dissolved in the electrolyte and the positive and negative electrodes are reciprocated. As a result, the insoluble Li ₂ S and Li ₂ S ₂ produced in this process accumulate on the surface of the negative electrode and other separator, Mechanism problems arise.

As a solution to this problem, a method of improving the electrolyte and preventing the sulfur leaching has been developed, but the progress thereof is insignificant, and measures for reducing the leaching of sulfur by improving the structure of the anode have been developed.

Composites in which sulfur is supported on a structured porous carbon structure in order to smoothly supply electrons to the insulator sulfur is proposed. The carbon structure not only captures the polysulfide physically, but also facilitates electron transfer. By using various types of carbon structures such as porous carbon, hollow carbon spheres, carbon nanotubes or carbon nanofibers and graphene or oxidized graphene, it is possible to achieve a long cycle life of over 300 cycles and an improved capacity retention of more than 70% . However, gradual reduction of capacity in long-lasting charge / discharge is difficult to avoid because of the low binding energy between sulfur and carbon.

Recently, Pyun et al. Developed a high performance lithium-sulfur battery using a sulfur-containing polymer as a cathode. The lithium-sulfur battery using a sulfur-containing polymer as a cathode active material was found to have 1005 mAh / g at 100 cycles, 817 mAh / g at 300 cycles, and 635 mAh / g at 500 cycles when subjected to 0.1C charge / Discharge capacity. However, since it contains sulfur having low conductivity, there is a problem that it is difficult to use it in an energy storage system requiring high charge / discharge rate. In fact, when the charge / discharge rate was increased to 2C, the discharge capacity was drastically reduced to 400 mAh / g.

A problem to be solved by the present invention is to provide a novel high performance cathode active material containing sulfur.

Another object of the present invention is to provide a novel high performance cathode active material containing sulfur.

Another object of the present invention is to provide a new cathode active material which can prevent elution of sulfur and exhibit a high capacity, a lifetime of 450 cycles or more, and a capacity retention rate of 83% or more.

Another object of the present invention is to provide a lithium-sulfur anode including a novel high-performance cathode active material containing sulfur, and a lithium-sulfur battery.

In order to solve the above-mentioned problems, the cathode active material according to the present invention is manufactured by filling a porous structure with sulfur and vulcanizing the porous structure.

In the present invention, the porous structure is not particularly limited as long as it can be vulcanized by the filled sulfur, but preferably it contains a sulfur component so as to enhance the compatibility with the filled and vulcanized sulfur. The porous structure containing the sulfur component preferably has a solyzer so that the filled sulfur can be easily vulcanized to the structure.

In the present invention, it is understood that the term 'containing sulfur' means that the compound constituting the porous structure includes a sulfur element.

In the present invention, the 'structure' is understood to mean that the porous material is formed into a substantially certain shape, for example, a predetermined shape such as a rod, flake, sphere, or a combination thereof.

In the present invention, the porous structure may be prepared by drying porous crystals of a compound containing sulfur.

In the present invention, the sulfur-containing compound constituting the porous structure may be a trithiocyanuric acid (TTCA).

In the present invention, the determination of TTCA is based on the assumption that N-H < - > S hydrogen bond between the TTCA and the solvent. O = C hydrogen bond, and the prepared TTCA crystal is heat-treated to remove the solvent, thereby forming a porous TTCA structure. The solvent may be a single solvent or a mixed solvent, and the type of the structure may vary depending on the type of the solvent. For example, a single solvent such as a water / DMF mixed solvent or acetone may be used, and a structure such as a rectangular tube or a splice plate may be obtained.

In the present invention, the step of filling the sulfur substantially means a process in which the pores of the structure are filled with sulfur. The filling process may be performed at a temperature of preferably 200 ° C or lower, more preferably 180 ° C or lower, and most preferably 160 ° C so that the solvent is removed and substantially no vulcanization occurs.

In the present invention, the step of vulcanizing the filled sulfur means a process in which the sulfur is opened to chemically bond the structure. The vulcanization step is preferably a linear polysulfane bond between the silane groups in which the ring-opening reaction of the filled sulfur occurs and is exposed on the surface of the TTCA, and the vulcanization step is carried out at a high temperature of 220 DEG C or higher, Preferably at 250 < 0 > C.

In the present invention, the amount of sulfur is preferably larger so that the porous crystal and sulfur can sufficiently enter into the porous crystal, preferably 1: 2 to 1: 5, and most preferably 1: 3 .

According to an aspect of the present invention, there is provided a cathode active material of a lithium-sulfur battery, characterized in that pores of the porous structure are filled with sulfur and vulcanized. The vulcanized sulfur is incorporated into the pores in the form of a crosslinked polysulfane.

In the present invention, the porous structure is preferably a structure including a sulfur component, preferably a sialo functional group, so that the sulfur charged in the pores can be easily vulcanized. In addition, the porous structure preferably includes an amine group capable of promoting migration of lithium ions.

In the practice of the present invention, the porous structure is a TTCA crystal, and the active material is a vulcanized TTCAs. The content of sulfur in the vulcanized TTCAs is preferably 50 to 70% by weight, more preferably 55 to 65% by weight.

In a preferred embodiment of the present invention, the porous structure is vulcanized TTCAs TTCA and sulfur 1:06 to 1:08 molar ratio, preferably 1: 7 molar ratio of the forms to, vulcanized -S _n - in average chain n Is from 5 to 8, preferably from 6 to 7.

According to an aspect of the present invention, there is provided a sulfur-lithium secondary battery including a cathode including a cathode active material filled with sulfur in pores of the porous structure. The anode is manufactured by bonding the cathode active material and the porous carbon to a binder.

A high performance cathode active material for a sulfur-lithium secondary battery according to the present invention and a method for manufacturing the same are provided. Particularly, it is advantageous in that it has high efficiency at a fast charge / discharge speed.

We have investigated a new method to improve the performance of lithium-sulfur batteries based on organic sulfur electrodes. Hundreds of grams of sulfur rich polymers with different morphologies were synthesized from elemental sulfur using porous organic crystal soft molds. This is a unique feature of our system compared to the vulcanized polymers reported in literature where shape and shape control were not feasible. Successful implementation of a sulfur-rich three-dimensionally interconnected structure in the electrode structure allowed us to achieve a high discharge capacity of 850 mAh / g after 450 cycles and an unprecedented 83% high capacity retention rate, While the polysulfide intermediate was well connected to the interior of the vulcanized polymer that did not pass the liquid. Our results are one of the high specific capacities reported in lithium-sulfur cells, and are characterized by high specific capacities (1C 872mAh / g, 3C 803mAh / g, 5C 730 mAh / g) . This can be interpreted as the well-organized lithium ion coordination sites of the organic crystals facilitate migration of lithium ions to the active material. We also gained an understanding of the factors affecting cell performance: the form of organic crystals provides a fundamentally different surface area and thus plays an important role in determining the specific capacity by affecting the rate of lithium ion migration.

Figure 1 shows the synthesis route of tens of grams of sulfur-rich polymers. A schematic representation of a form-controllable sulfur-rich polymer synthesis method; (1) preparation of TTCA co-crystal, (2) pore formation in TTCA structure by solvent removal through heat treatment, and (3) flowering polymerization of sulfur element in thiol on porous TTCA mold surface as shown in the figure.
Figure 2 shows Vulcanized TTCAs having different morphologies (another form of vulcanized TTCA). (a), (b) TTCA-I and TTCA-II synthesized through various crystallization solvents Scanning electron microscope (SEM) and optical microscope (OM) photographs of the co-crystal, each rectangular tube and fragmented plate-like. (c), (d) Scanning electron microscope (SEM) and optical microscope (OM) plots of TTCA-I and TTCA-II after removal of solvent at 160 ° C . (SEM) and optical microscope (SEM) images of S-TTCA-I and S-TTCA-II with sulfur at 245 ° C using porous TTCA as a soft template. The images inserted inside confirm that most of the pores disappear after the vulcanization reaction and the smooth surface is restored.
3 . Molecular characteristics of Vulcanized TTCAs. (Molecular properties of vulcanized TTCA). (b) XPS results of S-TTCA-I and (c) S-TTCA-I X-ray photoelectron spectroscopy results of porous TTCA- I Thermogravimetric analysis, comparison with sulfur elements present in carbon.
Figure 4 is a crystal structure analysis . (a) Prepared TTCA-I and TTCA-II co-crystals. (b) TTCA-I and TTCA-II heat treated at 160 ° C, and (c) powder X-ray diffraction results of S-TTCA-I and S-TTCA-II vulcanized at 245 ° C. The Miller indices of hkl reflecting surfaces are given in the respective figures.
5 Battery performance of Li-S cells. Typical constant current charging / discharging results of Li / S-TTCA-I and Li / S-TTCA-II cells are in the range of 1.7-2.7V at room temperature 0.2C. (b) Charging / discharging capacity and coulombic efficiency of Li / S-TTCA-I and Li / S-TTCA-II compared with general Li / SC batteries.
FIG. 6 shows Hihg-capacity and high-rate lithium sulfur battery. (a) charge / discharge capacities and coulombic efficiency of Li / S-TTCA-I and Li / S-TTCA-II cells at different current rates for 300 cycles. (b) The typical voltage-current curves of S-TTCA-I were obtained at different scan rates. (c) The lithium ion diffusion coefficients of S-TTCA-I, S-TTCA-II and SC electrodes were calculated by Randle-Sevcik equation Calculated. (d) Performance characteristics of Li / S-TTCA-I cells according to their speed as compared with Li / SC batteries.
Figure 7 shows the amount of solvent contained in TTCA-I and TTCA-II. Thermogravimetric analysis (TGA) data for TTCA-I and TTCA-II co-crystals.
8 shows the molar ratio of TTCA to sulfur in the vulcanized material. Cation Eradication Time Flight Mass Spectrometry (ESI-TOF) mass spectrum of the S-TTCA-Ι intermediate which ceased to react during the vulcanization reaction.
9 shows the thermal stability of the TTCA crystal. X-ray diffraction results of TTCA-Ι crystals heat-treated at 160 ° C and 245 ° C.
10 Cell performance test of Li / S-TTCA-I and Li / S-TTCA-II cells. Typical constant current charge / discharge voltage results for Li / S-TTCA-I (solid lines) and Li / S-TTCA-II (dashed lines) cells. Cycles range from 0.2C to 1.7-2.7V.
11 shows the crystal structure of the heat-treated TTCA. In adjacent sheets of TTCA molecules, adjacent sheets of π-stacked amine groups are rotated 60 degrees. The distance of NN is 3.7 Å. Yellow and purple represent sulfur atom and nitrogen atom, respectively.
12 shows the long cycle life of the Li / S-TTCA-Ι cell. The Li / S-TTCA-I cells were tested for 0.5 to 450 cycles and exhibited charge / discharge capacities and coulombic efficiency.

Hereinafter, the present invention will be described in more detail.

A soft-template synthesis of sulfur-rich polymers. (Polymer rich in sulfur Of the template  synthesis).

As shown in Figure 1, there is provided a schematic description of 10 g of sulfur-rich polymer synthesis in a controllable form. The synthesis method is as follows.

(1) Prepare a variety of solvents that can make TTCA crystals. Under this solvent, N-H < RTI ID = 0.0 > S hydrogen bond between the TTCA and the solvent. O = C hydrogen bond.

(2) If the solvent is removed by a simple heat treatment method, a porous TTCA structure can be formed.

(3) Flowering polymerization of sulfur on the thiol surface of a porous TTCA structure, the above reaction is explained through the structural formula shown in the figure. A more detailed description is given in the Experimental section.

Two kinds of TTCA co-crystals (crystals) having different forms were synthesized by using a co-solvent of dimethylformamide (DMF) / water (1: 1, volume) and acetone and two different solvents. The TTCA co-crystals each have the shape of a rectangular tube and a splice plate. Crystals made from DMF / water are now called TTCA-I, and crystals made from acetone are named TTCA-II. Examination of the crystals using scanning electron microscopy (SEM) and optical microscope (OM) confirmed that the TTCA-I crystals had rectangular holes and had a rectangular cross-section of 50 × 20 microns and a length of several hundred microns. On the other hand, TTCA-II crystals are in the form of 1x1 rhombus and have a thickness of 150 microns (Fig. 2b).

When the solvent is removed from the TTCA-I and TTCA-II crystals at 160 ° C, the crystal surface becomes rough. 2c and 2d, and it can be seen that pores having a size of 10 nanometers are formed. Changes in the form of porosity can be easily perceived through changes in the transparency of the crystal through the optical microscope image. The amount of solvent present in the TTCA-I and TTCA-II crystals was determined by thermogravimetric analysis (TGA) experiments and contained 30 wt% and 14 wt% of solvents, respectively (Fig. 7). This suggests that the surface area of the heat-treated TTCA-I and TTCA-II will be fundamentally different. Despite the heat treatment, the two crystals still retain their original shape, especially the TTCA-I crystals contain rectangular holes.

Sulfur-containing polymers are synthesized using porous TTCA crystals as a soft template. The two - stage vulcanization process was carried out in a closed vessel. At a lower temperature of 160 ° C, sulfur is introduced into the porous TTCA structure, and then the temperature is raised to 245 ° C to form a linear polysulfane through ring opening polymerization of sulfur along the thiol surface. The vulcanized TTCA is named S-TTCA-I and S-TTCA-II, respectively. This process involves the color change of crystals from pale yellow to dark brown. It is believed that the polysulfone double radicals are cross-linked between the TTCA molecules, indicating that S-TTCA-I and S-TTCA-II are insoluble in all solvents. After the vulcanization reaction, Returning to the surface was confirmed by scanning electron microscopy images of Figs. 2e and 2f. As shown in the figure, the rectangular hole of TTCA-I disappeared after the reaction.

Molecular and structural characterization of vulcanized TTCAs

The molecular properties of the vulcanized TTCAs were analyzed by Raman spectroscopy. Representative spectra of TTCA-I and S-TTCA-I are shown in Figure 3A. The peak located at 448 cm ^-1 represents the NCS deformation and is evident in the porous TTCA-I. After the vulcanization reaction, the NCS strain peak shifts to 435 cm ^{- 1} and a new peak appears at 482 cm ^{- 1} as evidence of SS bond. The above phenomenon shows that sulfur reacts with the zeol group of the TTCA crystal as shown in the structural formula of FIG.

By conducting photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) experiments, information on the chemical state and sulfur content of vulcanized TTCAs was obtained. Representative XPS results of S-TTCA-I are shown in Figure 3b, with 60% of the sulfur present in the SS form and 40% forming the CS bond. From the thermogravimetric analysis (TGA) test of FIG. 3c, the total sulfur content in S-TTCA-I was found to be 63 wt% and is not significantly different from S-TTCA-II (58 wt%). Since the vulcanized TTCAs do not dissolve in any solvent, the S-TTCA-I reaction intermediates were analyzed by cationic EIN-ionization time-of-flight mass spectrometry. As can be seen in Figure 8, in most compounds TTCA and sulfur molar ratio is from 1: 7, and -S _n - estimates that the average n is 7 in the chain.

In particular, as shown in Figure 3c, the reduction in the mass of sulfur in S-TTCA-I starts at 110 ° C and continues to decrease to 310 ° C. This phenomenon differs markedly from the decrease in the mass of sulfur supported on the carbon structure. The sulfur carried on the carbon structure starts to decrease in mass at 180 ° C and ends in mass reduction at 280 ° C. The low temperature at which sulfur mass reduction begins in S-TTCA-I and the breakdown of sulfur over a wide temperature range indicates that small sulfur molecules are covalently linked to the TTCA structure. The mass reduction of TTCA starts at 360 ° C and ends at 500 ° C.

Powder X-ray diffraction was used to confirm the change in crystal structure through the heat treatment and vulcanization reaction. The used X-ray diffraction method 2theta range was measured from 5 ^o to 35 ^o at 0.02 ^o intervals and can be seen in Figures 4a-c. TTCA-I initially has a P2 _{1 / c} space group of monoclinic and TTCA-II has a triplet P1 space group. The unit lattice parameters were obtained from the Cambridge Structural Database (CSD), and for TTCA-I a = 9.780 Å b = 12.755 Å c = 9.280 Å α = 90.00 °, β = 91.19 °, γ = 90.00 °, TTCA-II A = 8.937 Å, b = 9.985 Å, c = 10.447 Å, α = 95.12 °, β = 96.79 ° and γ = 107.29 °. Removal of solvents in TTCA-I and TTCA-II induces deformation to the same structure. In this case, the crystal structure has a triplet P space group and the unit lattice parameters are a = 5.587 Å, b = 7.047 Å, c = 8.799 Å, α = 102.99 °, β = 92.87 ° and γ = 110.47 °. The shrinkage of the unit volume induces the morphology of the porosity, and the degree of shrinkage depends on TTCA-I and TTCA-II. This phenomenon is closely related to the surface area of the heat treated TTCA structure. Finally, the XRD monotonous pattern of S-TTCA-I and S-TTCA-II as shown in Figure 4c shows that linking to the sulfur TTCA structure via covalent destroys the pi-pi stack of the TTCA ring. The absence of the crystal peak of sulfur, as in Figure 4c, is a notable feature in that sulfur participates in the polymerization process and is present in amorphous form. Notably, as can be seen in FIG. 9, the TTCA crystal is thermally stable, and therefore the disappearance of the crystallinity of S-TTCA is not due to the amorphization of TTCA.

Battery performance of the Li -S cells based on the S- TTCA  cathodes.

Sulfur electrodes were fabricated by incorporating S-TTCA-I (or S-TTCA-II), Super P carbon, and polyvinylidene binder. Typical sulfur electrodes were sulfur element, Super P carbon, and polyvinylidene binder, and used as a control. A coin cell including a lithium metal, a liquid electrolyte and a sulfur electrode was assembled and then charged / discharged at room temperature. 5A shows a representative constant current charge / discharge voltage result in the 1.7V-2.7V voltage range so that the Li / S-TTCA-I cell is 0.2 current. Li / S-TTCA-I shows one plateau at 2.06V during the discharge test, but Li / SC cell shows two plateau. This is because most of the sulfur present in the S-TTCA-I electrode forms a disulfide bond to the TTCA structure. At the 2.33 and 2.06 V after the first cycle, typical two plateau appear, because of the electrochemical cleavage of the disulfide bond during the cycle and S ₈ due to regeneration. Overall, the charge / discharge voltage results for Li / S-TTCA-II cells are similar to the charge / discharge voltage results for Li / S-TTCA-I except for the ring open plateau at 2.33V during the first discharge cycle 10).

5B shows charge / discharge capacities of Li / S-TTCA-I, Li / S-TTCA-II and Li / S-C cells at a current rate of 0.2. The first discharge capacity of the Li / S-TTCA-I cell is 813 mAh / g and stabilizes at a capacity of about 1050 mAh / g after 5 cycles. After 100 cycles, it maintains a high capacity of 945 mAh / g, which is 92% capacity retention compared to the second cycle and also has a coulombic efficiency of over 99%. This high performance is presumably due to the fact that the intermediate lithium polysulfide was embedded in S-TTCA-I and was not eluted into the liquid electrolyte. This result is in sharp contrast with the Li / S-C battery, which exhibits low capacity and capacity retention after 100 cycles due to the shuttle effect due to the elution of polysulfide. The Li / S-TTCA-II battery has a high capacity retention rate of 86% and a high Coulomb efficiency of 99%, except that it exhibits a low capacity of 565 mAh / g after 100 cycles as compared to Li / S-TTCA- .

It was repeatedly observed that S-TTCA-I had better battery performance than S-TTCA-II when charge / discharge experiments were carried out at different current rates for 300 cycles. Figure 6 shows charge / discharge capacities of Li / S-TTCA-I and Li / S-TTCA-II cells at 0.2C and 0.5C. The Li / S-TTCA-I cell showed a capacity of 872mAh / g (0.2C) and 886mAh / g (0.5C) after 300 cycles and 85% capacity retention rate. On the other hand, the Li / S-TTCA-II cell exhibits a low discharge capacity of 300 mAh / g (0.2C) and 440 mAh / g (0.5C) after 300 cycles. The superior cell performance of this Li / S-TTCA-I is a clear signal from its morphological advantage.

Mechanisms underlying the improved battery performance of the Li / S-TTCA-I cells

The following experiment confirms that the performance of Li / S-TTCA-I battery is significantly improved compared to that of Li / S-TTCA-I and Li / S battery is related to the migration rate of lithium cation in the electrode. Cyclic current and voltage tests were performed to determine the lithium cation diffusion coefficients of S-TTCA-I, S-TTCA-II and S-C electrodes using the Randles-Sevcik equation below.

_{^{I p = 2.69 x10 5 n 1.5}} AD Li 0 .5 v 0.5 C Li (One)

Where I _p Is the peak current, n is the number of electrons involved in the reaction, A is the electrode area, v is the scan rate, and C _Li is the lithium ion concentration in the electrolyte. The representative voltage and current results of the S-TTCA-I are shown in FIG. 6B.

I _p and v for S-I-TTCA electrode in linear relationship ^{0 .5 C1 = 9.5x10 -10, C2} = 3.0 x10 -9 cm 2 / s (cathodic) and ^{A = 4.3x10 -9 cm 2 / s} ( were obtained the results of anodic) this number is S-TTCA-II of the electrode ^{(C1 = 8.8x10 -10, C2 =} 1.2x10 -9, and ^{a = 2.6x10 -9 cm 2 / s} ) value greater than 2.7 times larger . This can be seen from FIG. 6C.

The tubular structure of TTCA-I improves the lithium ion migration rate by facilitating access of the liquid electrolyte to the active material through the three-dimensionally well-connected pores. Conversely, a two-dimensional 150 micrometer thick wall of the S-TTCA-II inhibits rapid migration of lithium ions. In addition, the lowest value of D _Li SC electrode ^{(C1 = 8.0x10 -10, C2 =} 9.5x10 -10, and A = 1.5x10 -9 cm 2 / s) sorted according to the secondary amine group, and p e of the ring TTCA It is possible to derive that the lithium cation coordination site improves the rate of lithium cation migration.

The XRD analysis of FIG. 4B shows that the annealed TTCA has an N-N distance of 3.7 A and the p-stacked adjacent sheets of the amine group are arranged in a 60 degree rotation.

The advantage of the lithium ion migration rate of the S-TTCA-I electrode is evident in the rate capability of the Li / S-TTCA-I electrode. As can be seen from FIG. 6D, the Li / S-TTCA-I electrode was found to have a concentration of 1210 mAh / g at 0.1 C, 1090 mAh / g at 0.2 C, 1030 mAh / g at 0.5 C, 872 mAh / g at 1 C, 803 mAh / And a reversible discharge capacity of 730 mAh / g at 5C.

Although the discharge capacity is greatly reduced to 452 mAh / g when the current speed is increased to 6 C, the original discharge capacity is recovered to 1053 mAh / g when the current speed is lowered to 0.1 C again. This is an excellent performance characteristic in terms of speed in a lithium-sulfur battery.

In the control experiment, when the experiment was carried out at various current rates using SC, the discharge capacity was significantly reduced at 1C (1C 198 mAh / g, 3C 129 mAh / g, and 5C 102 mAh / g). Currently, the Li / S-TTCA-I cell is under 450 cycles, with a discharge capacity of 850 mAh / g (83% capacity retention) and 99% Coulomb efficiency (FIG. 12).

Preparation of trithiocyanuric  acid ( TTCA ) co-crystals ( try  Saisian Nyric Acid  co-crystal preparation)

TTCA-I and TTCA-II co-crystals are prepared using various crystallization solvents. In the case of TTCA-I, TTCA (98%, TCA) is dissolved in dimethylformamide (DMF, 99%, Alfa Aesar) and distilled water 1: 1 co-solvent and crystals are formed at 0 ° C for 24 hours. The resulting crystals are collected by filtration and dried in a vacuum at 40 ° C for 24 hours to remove any remaining solvent. For TTCA-II co-crystals, dissolve TTCA in acetone (HPLC grade, J. T Baker) and remove the solvent at 50 ° C. TTCA-I and TTCA-II co-crystals are bright yellow.

Synthesis of S- TTCA -I and S- TTCA -II .

S-TTCA-I and S-TTCA-II are synthesized directly from the sulfur element using TTCA-I and TTCA-II as soft templates. The process is a three-step process: (1) TTCA-I and TTCA-II are heated at 160 ° C to remove solvents present in the crystals. Removal of the solvent from the TTCA-I and TTCA-II crystals changes the clarity of the crystal. (2) After removal of the solvent from the crystals, the amount of the predetermined amount of sulfur is determined and mixed with the ratio of sulfur to the weight of the crystal (3: 1), and then sulfur is introduced into the TTCA structure at 160 ° C for 10 hours. (3) The mixture is further heated at 245 ° C for 2 hours to synthesize linear polysulfone through ring-opening polymerization of the sulfur element along the thiol surface of the TTCA structure. The results of S-TTCA-I and S-TTCA-II are dark brown.

Morphology and structure characterization

The morphology of TTCA crystals before and after the heat treatment and after the vulcanization was determined by optical microscopy and (Zeiss axio scope, A1) Field Emission Scanning Electron Microscope (FE-SEM, XL30S FEG, Philips). The X-ray diffraction analysis for each crystal was carried out at the Pohang Accelerator Laboratory (PAL) 9B HRPD (High Resolution Powder Diffraction) beamline (wavelength λ = 1.4640 Å).

Fourier transform Raman experiments (FT-Raman)

The Raman spectroscope was measured using a WITEC Alpha 300R Raman spectroscope (WITec, Ulm, Germany) and a HeNe laser was used. The spatial resolution of the spectroscope is 250 nanometers. The laser excitation power was used below 3 mW, to prevent thermal damage by the laser of the sample.

Analysis of chemical states and sulfur contents in S- TTCA -I and S- TTCA -II

X-ray photoelectron spectroscopy (XPS) experiments were performed using a monochromatic Al-K _λ X-ray and an Escalab 250 × i spectrometer using a hemispherical electrostatic analyzer. Thermogravimetric analysis (TGA) experiments were conducted at 25-50 ° C temperature range and 10 ° C / min heating rate under nitrogen environment to determine the sulfur weight in S-TTCA-I and S-TTCA-II. The weight spectra of the resulting interim reactions were obtained via cation ESI-TOF (compact, Bruker). The mass spectrometer was operated at a source temperature of 180 ° C and a capillary potential of 4500V. The m / z range of the mass spectrometer is 50-1,700 daltons.

Preparation of sulfur cathodes

The S-TTCA-I and S-TTCA-II electrodes contained 60 mass% of S-TTCA-I (or S-TTCA-II), 30 mass% of Super P carbon (Alfa Aesar), and 10 mass% of polyvinylidene , Solef) binder is dissolved in NMP (Sigma Aldrich) and ball milling (MillMM400) is performed in an argon atmosphere. Typical sulfur electrodes are made by mixing sulfur powder (99.998%, Sigma Aldrich), Super P carbon, and PVDF binder in a 60:30:10 ratio. The ball milled slurry is coated on the aluminum current collector by the doctor blade method. All the prepared sulfur electrodes are dried in an Ar environment at 50 ° C for 24 hours and then dried under vacuum at 50 ° C. The dried electrode is cut with a disk cutter (MTI, 15 mm diameter).

Battery tests

Lithium-sulfur batteries were assembled in a glove box filled with high-purity argon to prevent contamination by moisture and oxygen. The coin cell (CR 2032, MTI) cell was made by assembling lithium metal as cathode, porous polypropylene separator (Celgard 2400), and sulfur anode. The liquid electrolyte was prepared by dissolving 1M lithium bis (trifluoromethane) sulfonamide (LiTFSI, 98.0%, TCI) and 0.2M lithium nitrate (99.999%, Alfa Aesar) in tetraethylene glycol dimethyl ether (TEGDME, Sigma Aldrich) (DIOX, 99.8%, Sigma Aldrich) (33:67 vol%) in a mixed solvent. The constant current charging / discharging test of the lithium-sulfur battery was conducted using a battery cycler (WBCS300, Wonatech) at a predetermined current rate between 1.7-2.7V. Cyclic current and voltage analysis of the sulfur anode proceeded at various scan rates in the voltage range of 1.7-2.7V.

Claims (17)

Wherein the porous structure having a molecular structure containing sulfur is filled with sulfur and the sulfur constituting the molecular structure of the porous structure and the filled sulfur are vulcanized. delete The method of claim 1, wherein the porous structure has a solyol. The method of claim 1, wherein the porous structure is made of a trithiocyanuric acid crystal. 5. The method of claim 4, wherein the crystal is N-H < RTI ID = 0.0 > S hydrogen bond, and between TTCA and the solvent. Wherein the cathode active material is prepared by using a solvent that forms an O = C hydrogen bond. 6. The method of claim 5, wherein the solvent is a water / DMF mixed solvent or acetone. 5. The method of claim 4, wherein the crystal is a rectangular tube. The method of claim 1, wherein the vulcanization is performed at a high temperature of 220 ° C or higher. The method of claim 1, wherein the weight ratio of the porous structure to sulfur is in the range of 1: 2 to 1: 5. The method of claim 1, wherein the filled sulfur is opened and vulcanized. Wherein the porous structure has a polysulfone crosslinked to the pores of the porous structure. 12. The cathode active material of a lithium-sulfur battery according to claim 11, wherein the positive electrode active material is composed of 5 to 7 polysulfone sulfides. The positive electrode active material according to claim 11 or 12, wherein the polysulfone is bonded to a sialo group of the porous structure. The positive electrode active material according to claim 11 or 12, wherein the porous structure has an amine group. The positive electrode active material according to claim 11 or 12, wherein the porous structure is a triisocyanuric acid crystal. 16. The cathode active material of claim 15, wherein the porous structure is a tubular structure. A cathode comprising the cathode active material according to claim 11 or 12; cathode; And an electrolyte.

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