Lithium-sulfur battery cathode material, preparation method and application thereof

Abstract

The application relates to a lithium-sulfur battery positive electrode material and a preparation method and application thereof, and belongs to the technical field of batteries. The preparation method comprises the following steps: S1, adding an aqueous phase into an oil phase, mixing, adding a sulfur source, carrying out hydrothermal reaction, and then carrying out centrifugation and drying to obtain modified molybdenum sulfide; the aqueous phase is a mixed solution of a molybdenum source, glucose and water; the oil phase is a mixed solution of a cationic surfactant and a solvent; S2, calcining the molybdenum sulfide at 680 DEG C-720 DEG C for 2h-6h to obtain carbon-containing molybdenum sulfide; S3, dispersing the carbon-containing molybdenum sulfide in an alcohol solution, adding a soluble iron salt, uniformly mixing, and then carrying out centrifugation, drying and calcination to obtain the lithium-sulfur battery positive electrode material. After the Fe-MoS2-C is used for modifying the positive electrode, the battery has higher reaction kinetics with the reduction of the charge transfer resistance, the adsorption conversion of polysulfides is accelerated, the shuttle effect is effectively inhibited, the efficient reversible conversion of the polysulfides is stabilized, and the utilization rate of sulfur is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a lithium-sulfur battery cathode material, its preparation method and application. Background Technology

[0002] With the rapid increase in the global population and the rapid development of the world economy, energy demand is gradually increasing. Lithium-sulfur batteries have attracted much attention from the electric vehicle and electronic equipment industries due to their abundant raw materials, low price, environmental friendliness, and high theoretical energy density, and have become a leader among new rechargeable battery systems. However, the commercialization process of lithium-sulfur batteries still faces many challenges, which can be summarized into the following five aspects: (1) Insulation characteristics of elemental sulfur (S) and discharge product lithium sulfide (Li2S): Elemental sulfur and lithium sulfide have extremely low electronic conductivity, which will greatly increase the impedance of the material, resulting in huge battery energy loss and thus reducing the energy efficiency of the entire product. (2) Volume change problem during the active material cycle: The discharge conversion process from S to Li2S will cause huge volume expansion of the electrode, which can reach almost 80%; correspondingly, the charging process will also cause extremely serious volume shrinkage. This volume cycle change will seriously damage the battery stability and accelerate its performance degradation. (3) The "double low" problem, namely low sulfur loading per unit area and low sulfur content: At present, lithium-sulfur batteries still have a long way to go before their large-scale practical application. How to improve the sulfur loading is a key issue. A higher sulfur loading can ensure stable battery performance and effectively suppress the shuttle effect, thus extending the battery's service life. (4) Shuttle effect of discharge intermediate product polysulfides: Discharge intermediate product polysulfides (Li2S x (3≤x≤8) is easily soluble in electrolyte and shuttles back and forth between positive and negative electrodes, which not only greatly reduces the amount of active material, but also corrodes the lithium anode, leading to a series of performance degradation and safety issues. (5) Electrode and its slow reaction kinetics: Polysulfide conversion, especially Li2S deposition and dissolution, has an extremely high reaction energy barrier, resulting in extremely low polysulfide redox kinetics, which easily forms dead sulfur, leading to the loss of active material and reducing the cycle stability of the battery.

[0003] Currently, the scientific community widely utilizes highly efficient catalysts to prepare composite cathode materials, accelerating the conversion of polysulfides and improving the long-term performance of batteries. Among these materials, molybdenum disulfide (MoS2) stands out due to its excellent catalytic effect and simple synthesis method, making it highly favored by the scientific community. However, limited by the extremely low proportion of active sites in pure crystalline MoS2, researchers have focused on controlling its catalytic activity through strategies such as introducing defects, doping, and phase transitions. The preparation of 1T MoS2 using intercalation technology to achieve high conductivity and high catalytic activity is a particularly noteworthy technique. However, due to the unstable physical structure of 1T MoS2 and limitations in preparation methods and conditions, most reports on this type of cathode modification material still face numerous problems, hindering the commercialization of lithium-sulfur batteries. For example, 1T MoS2 is limited by its unstable electronic structure and is prone to crystal plane slip over time, leading to the loss of active sites. This makes it difficult for the cathode structure of batteries using this material to maintain long-term cycle stability. Secondly, since 1T MoS2 is more thermodynamically unstable than 2H MoS2, many reported synthesized 1T MoS2 have limited purity and usually contain some 2HMoS2. This makes it difficult for the cathode material to fully exert its catalytic advantages, and its improvement on the performance of lithium-sulfur batteries is also limited. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a lithium-sulfur battery cathode material, its preparation method, and its application.

[0005] The first objective of this invention is to provide a method for preparing a lithium-sulfur battery cathode material, comprising the following steps:

[0006] S1. Add the aqueous phase to the oil phase, mix, add a sulfur source, perform a hydrothermal reaction, centrifuge, and dry to obtain modified molybdenum sulfide; the aqueous phase is a mixture of molybdenum source, glucose, and water; the oil phase is a mixture of cationic surfactant and solvent;

[0007] S2. Under a protective atmosphere, the molybdenum sulfide described in S1 is calcined at 680℃-720℃ for 2h-6h to obtain carbon-containing molybdenum sulfide.

[0008] S3. Disperse the carbon-containing molybdenum sulfide described in S2 in an alcohol solution, add soluble iron salt and mix well, then centrifuge, dry and calcine to obtain the lithium-sulfur battery cathode material.

[0009] In one embodiment of the present invention, in S1, the molybdenum source is selected from sodium molybdate and / or ammonium molybdate; the sulfur source is selected from thiourea and / or thioacetamide; and the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, and octadecyldimethylhydroxyethylammonium nitrate.

[0010] In one embodiment of the present invention, in S1, the concentration of the molybdenum source in the aqueous phase is 6.5 mmol / L-7 mmol / L, and the concentration of glucose is 9 mmol / L-9.5 mmol / L; the concentration of the cationic surfactant in the oil phase is 0.12 mol / L-0.18 mol / L; and the volume ratio of the aqueous phase to the oil phase is 3-4:1.

[0011] In one embodiment of the present invention, in S1, the temperature of the hydrothermal reaction is 200℃-250℃; the time is 24h-32h.

[0012] In one embodiment of the present invention, in S1, the soluble iron salt is selected from ferric nitrate and / or ferric chloride.

[0013] In one embodiment of the present invention, in S2, the heating rate of the calcination is 4°C / min-6°C / min.

[0014] In one embodiment of the present invention, in S3, the molar ratio of the carbon-containing molybdenum sulfide and the soluble iron salt is 3-3.5:1.

[0015] In one embodiment of the present invention, in S3, the calcination temperature is 680℃-720℃, the calcination time is 2h-4h, and the heating rate is 4℃ / min-6℃ / min.

[0016] A second objective of this invention is to provide a lithium-sulfur battery cathode material prepared by the method described above.

[0017] A third objective of this invention is to provide an application of the aforementioned lithium-sulfur battery cathode material in lithium-sulfur batteries.

[0018] The technical solution of the present invention has the following advantages compared with the prior art:

[0019] (1) The lithium-sulfur battery cathode material of this invention introduces a large number of vacancies by adding carbon intercalation to increase the interlayer spacing. Furthermore, the resulting 2H to 1T phase transition and Fe doping help improve the material's conductivity and accelerate electron transfer and polysulfide conversion. Finally, the material is synthesized into a spherical morphology to avoid internal agglomeration and thus improve catalytic stability. The hollow spherical structure also increases the sulfur loading, further suppressing the shuttle effect and improving the device's electrochemical performance. In summary, the lithium-sulfur battery obtained by this technical solution has great practical application potential and is conducive to the further development of lithium-sulfur battery commercialization.

[0020] (2) The preparation method described in this invention utilizes the hindering effect of carbon intercalation on crystal plane displacement to simply, efficiently, and cost-effectively prepare stable 1T phase MoS2 materials. The prepared MoS2 material has high 1T phase purity, and Raman spectroscopy results show that the 2H phase is rarely present, effectively and innovatively solving the key problem of low 1T phase structure purity in current preparation techniques. After being applied to the lithium-sulfur battery industry, the carbon intercalation technology introduces a large number of stable active sites while expanding the interlayer spacing of the material, significantly improving the catalytic stability of the material. In addition, the high-purity 1T phase structure also effectively improves the conductivity of the material, enhancing its application capability in electrochemical fields such as lithium-sulfur batteries. To further improve the conductivity of the material, this preparation method also introduces Fe. 3+ Doping techniques are used to construct interlayer carrier channels, accelerating the electron transfer rate within the material during the reaction and improving the redox conversion of polysulfides inside the battery. Finally, the sulfur loading is increased by synthesizing a three-dimensional spherical structure, effectively ensuring the material's stability.

[0021] (3) The Fe-MoS2-C material prepared by the method described in this invention has a uniform elemental distribution, forming a hollow sphere nanoarray. Its chemical information conforms to the characteristics of the 1T phase, and the preparation process is highly reproducible. Testing showed that the material exhibits strong conductivity, with its transfer resistance decreasing to 11Ω. After application in lithium-sulfur batteries, the battery's discharge capacity is significantly improved, and its cycle stability remains good. Furthermore, the potential difference between the positive and negative peaks in the CV curve is reduced to 0.34V, demonstrating that the Fe-MoS2-C material prepared by this method has higher electrochemical reaction kinetics, effectively ensuring the rate stability of the device's electrochemical performance. The prepared high-purity, high-conductivity, and high-catalytic-effect 1T phase Fe-MoS2-C material can be used to prepare high-performance lithium-sulfur batteries, promoting further commercial development in this industry.

[0022] (4) After the lithium-sulfur battery cathode material Fe-MoS2-C described in this invention is used to modify the cathode, the charge transfer resistance (R) increases. ct The reduction of sulfur content leads to higher reaction kinetics in the battery, accelerating the adsorption and conversion of polysulfides and effectively suppressing the shuttle effect; it also stabilizes the efficient and reversible transformation of polysulfides, improving sulfur utilization; and it enhances the electrochemical performance and stability of lithium-sulfur batteries, making the prepared lithium-sulfur batteries more valuable for practical applications. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0024] Figure 1The images are SEM images of MoS2-CTAB, MoS2-C, and Fe-MoS2-C (700℃) in Test Example 1 of the present invention; wherein, a) is the SEM image of MoS2-CTAB, b) is the SEM image of MoS2-C, and c) is the SEM image of Fe-MoS2-C.

[0025] Figure 2 The images show SEM images of Fe-MoS2-C prepared at 850℃ and 950℃ in Test Example 1 of the present invention; wherein, a) is the SEM image of MoS2-CTAB prepared at 850℃, and b) is the SEM image of MoS2-C prepared at 950℃.

[0026] Figure 3 This is a TEM image of Fe-MoS2-C (700℃) in Test Example 1 of the present invention.

[0027] Figure 4 The images shown are XRD patterns and high-resolution TEM images of MoS2-CTAB, MoS2-C, and Fe-MoS2-C (700℃) in Test Example 1 of the present invention; wherein, a) is a SEM image of MoS2-CTAB, MoS2-C, and Fe-MoS2-C, and b) is a high-resolution TEM image of Fe-MoS2-C.

[0028] Figure 5 This is the EDX elemental mapping diagram of Fe-MoS2-C (700℃) in Test Example 1 of the present invention.

[0029] Figure 6 The images show the Raman spectra of pure 2H MoS2, 2H MoS2 with a combined 1T structure, and MoS2 materials in Test Example 1 of this invention; where a) is the Raman spectrum of pure 2H MoS2 and 2H MoS2 with a combined 1T structure, and b) is the Raman spectrum of MoS2.

[0030] Figure 7 The graph shows the rate performance of the lithium-sulfur battery after using MoS2 and Fe-MoS2-C materials in Test Example 2 of this invention.

[0031] Figure 8 This is a graph showing the cycle performance of a lithium-sulfur battery at 0.2C rate after using MoS2 and Fe-MoS2-C materials in Test Example 2 of this invention.

[0032] Figure 9 This is the EIS curve of the lithium-sulfur battery before cycling after using MoS2 and Fe-MoS2-C materials in Test Example 2 of the present invention.

[0033] Figure 10 The cycling CV curves of the lithium-sulfur battery after using MoS2 and Fe-MoS2-C materials in Test Example 2 of this invention are shown. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] In this invention, unless otherwise stated, the concentration of concentrated hydrochloric acid is 32.36 mol / L. -1 .

[0036] Example 1

[0037] The lithium-sulfur battery cathode material and its preparation method of the present invention specifically include the following steps:

[0038] Synthesis of S1, Molybdenum disulfide: First, 0.192 g of Na2MoO4, 120 mL of deionized water, and 0.2 g of glucose were mixed together and stirred to form a homogeneous solution A. Then, 2.19 g of CTAB was mixed with 40 mL of n-butanol and stirred to form a homogeneous solution B. Once both solutions were clear, all of solution A was added dropwise to solution B and stirred for 2 hours. Then, approximately 30 mL of ethylene glycol was added to the white, turbid solution to restore clarity, followed by 0.2 mL of concentrated hydrochloric acid, and stirring continued for 2 hours. Afterward, 0.76 g of thiourea was added, and stirring continued for 3 hours to ensure uniform dispersion. The homogeneous solution was hydrothermally heated at 220°C for 24 hours. The resulting solution was then washed with deionized water and ethanol, and centrifuged. The waste liquid was discarded, and the centrifuge tubes were dried in an oven to obtain black MoS2-CTAB.

[0039] Synthesis of S2 and Fe-MoS2-C materials: The product was cooled to room temperature and thoroughly ground. It was then placed in a tube furnace and calcined at 700°C at a rate of 5°C / min under an Ar atmosphere for 4 hours to obtain MoS2-C. Finally, 50 mg of MoS2-C was dispersed in an ethanol / water mixture (40 mL water, 20 mL ethanol), and 100 μL of a 1 mol / L Fe(NO3)3 solution was added dropwise. The mixture was then dried by centrifugation with deionized water and ethanol, and calcined at 700°C at a rate of 5°C / min under an H2 / Ar atmosphere for 2 hours to obtain the Fe-MoS2-C material.

[0040] Comparative Example 1

[0041] Synthesis of S1, Molybdenum disulfide: First, 0.192 g of Na2MoO4, 120 mL of deionized water, and 0.2 g of glucose were mixed together and stirred to form a homogeneous solution A. Then, 2.19 g of CTAB was mixed with 40 mL of n-butanol and stirred to form a homogeneous solution B. Once both solutions were clear, all of solution A was added dropwise to solution B and stirred for 2 hours. Then, approximately 30 mL of ethylene glycol was added to the white, turbid solution to restore clarity, followed by 0.2 mL of concentrated hydrochloric acid, and stirring continued for 2 hours. Afterward, 0.76 g of thiourea was added, and stirring continued for 3 hours to ensure uniform dispersion. The homogeneous solution was hydrothermally heated at 220°C for 24 hours. The resulting solution was then washed with deionized water and ethanol, and centrifuged. The waste liquid was discarded, and the centrifuge tubes were dried in an oven to obtain black MoS2-CTAB.

[0042] Synthesis of S2 and Fe-MoS2-C materials: The product was cooled to room temperature and thoroughly ground. It was then placed in a tube furnace and calcined at 850°C for 4 hours under an Ar atmosphere at a rate of 5°C / min to obtain MoS2-C. Finally, 50 mg of MoS2-C was dispersed in an ethanol / water mixture (40 mL water, 20 mL ethanol), and 100 μL of a 1 mol / L Fe(NO3)3 solution was added dropwise. The mixture was then dried by centrifugation with deionized water and ethanol, and calcined at 700°C for 2 hours under an H2 / Ar atmosphere to obtain the Fe-MoS2-C material.

[0043] Comparative Example 2

[0044] Synthesis of S1, Molybdenum disulfide: First, 0.192 g of Na2MoO4, 120 mL of deionized water, and 0.2 g of glucose were mixed together and stirred to form a homogeneous solution A. Then, 2.19 g of CTAB was mixed with 40 mL of n-butanol and stirred to form a homogeneous solution B. Once both solutions were clear, all of solution A was added dropwise to solution B and stirred for 2 hours. Then, approximately 30 mL of ethylene glycol was added to the white, turbid solution to restore clarity, followed by 0.2 mL of concentrated hydrochloric acid, and stirring continued for 2 hours. Afterward, 0.76 g of thiourea was added, and stirring continued for 3 hours to ensure uniform dispersion. The homogeneous solution was hydrothermally heated at 220°C for 24 hours. The resulting solution was then washed with deionized water and ethanol, and centrifuged. The waste liquid was discarded, and the centrifuge tubes were dried in an oven to obtain black MoS2-CTAB.

[0045] Synthesis of S2 and Fe-MoS2-C materials: The product was cooled to room temperature and thoroughly ground. It was then placed in a tube furnace and calcined at 950°C for 4 hours under an Ar atmosphere at a rate of 5°C / min to obtain MoS2-C. Finally, 50 mg of MoS2-C was dispersed in an ethanol / water mixture (40 mL water, 20 mL ethanol), and 100 μL of a 1 mol / L Fe(NO3)3 solution was added dropwise. The mixture was then dried by centrifugation with deionized water and ethanol, and calcined at 700°C for 2 hours under an H2 / Ar atmosphere to obtain the Fe-MoS2-C material.

[0046] Comparative Example 3

[0047] Synthesis of S1, Molybdenum disulfide: First, 0.206 g of Na2MoO4, 120 mL of deionized water, and 0.6 g of glucose were mixed together and stirred to form a homogeneous solution A. Then, 5.46 g of CTAB was mixed with 40 mL of n-butanol and stirred to form a homogeneous solution B. Once both solutions were clear, all of solution A was added dropwise to solution B and stirred for 2 hours. Then, approximately 50 mL of ethylene glycol was added to the white, turbid solution to restore clarity, followed by 0.2 mL of concentrated hydrochloric acid, and stirring continued for 5 hours. Afterward, 0.76 g of thiourea was added, and stirring continued for 3 hours to ensure uniform dispersion. The homogeneous solution was hydrothermally heated at 220°C for 24 hours. The resulting solution was then washed with deionized water and ethanol, and centrifuged. The waste liquid was discarded, and the centrifuge tubes were dried in an oven to obtain black MoS2-CTAB.

[0048] Synthesis of S2 and Fe-MoS2-C materials: The product was cooled to room temperature and thoroughly ground. It was then placed in a tube furnace and calcined at 700°C at a rate of 5°C / min under an Ar atmosphere for 4 hours to obtain MoS2-C. Finally, 100 mg of MoS2-C was dispersed in an ethanol / water mixture (40 mL water, 20 mL ethanol), and 5 mL of a 1 mol / L Fe(NO3)3·9H2O solution was added dropwise. The mixture was then dried by centrifugation with deionized water and ethanol, and calcined at 700°C at a rate of 5°C / min under an H2 / Ar atmosphere for 3 hours to obtain the Fe-MoS2-C material.

[0049] Although the Fe-MoS2-C material produced has a spherical structure, its size is not uniform, which is not conducive to good catalytic effect and catalytic stability.

[0050] Test Example 1

[0051] (1) The morphology and structure of MoS2-CTAB, MoS2-C, and Fe-MoS2-C prepared in Example 1 and the materials prepared in Comparative Examples 1-2 were observed using scanning electron microscopy (SEM). The results are as follows: Figures 1-2 As shown. From Figure 1 It can be seen that the three materials retain their spherical structure composed of a two-dimensional array after treatment, with no significant change in size, indicating that the overall spherical morphology is well maintained, basically meeting the expected results, and preliminarily proving the rationality of the preparation method. From Figure 2 As can be seen, a large gap appeared on the spherical interface with increasing temperature, and the integrity of the material structure was destroyed, demonstrating the importance of temperature selection. Based on this result, calcination environments of 850℃ and 950℃ are not suitable for the preparation of Fe-MoS2-C materials, therefore this embodiment ends here.

[0052] (2) Based on the proof that the material's outer surface is spherical, the interior of the Fe-MoS2-C material was observed using transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the color is darker on the circumference and lighter inside the circle, which well proves the existence of the hollow structure.

[0053] (3) To further analyze the material structure, X-ray diffraction (XRD) was used to examine the sample, and the results are as follows: Figure 4 As shown in a). From Figure 4 a) It can be seen that the main diffraction peaks in the spectrum are all standard peaks of MoS2, while the (002) diffraction peak corresponding to the pure MoS2-CTAB material is located at 7.16°, which is different from the data corresponding to the 2H structure MoS2, proving the generation of 1T phase MoS2, which will be described in more detail in the Raman spectroscopy test below. After calcination, the (002) diffraction peak corresponding to MoS2-C shifts to the right to 8.89°, and the interlayer spacing of MoS2 decreases slightly. This is because the volume shrinkage occurs when the CTAB intercalation becomes a carbon intercalation, which narrows its width and leads to a reduction in the interlayer spacing. However, compared with the position of the pure MoS2 (002) peak, the (002) peaks of all three materials show a leftward shift, indicating that the presence of intercalation can indeed expand the interlayer spacing and introduce more active sites. The samples were characterized using high-resolution TEM, and the results are as follows. Figure 4 As shown in b). From Figure 4 b) It can be seen that, after precise measurement and calculation according to the scale, the interlayer spacing of the currently prepared Fe-MoS2-C material has been expanded to [a certain extent]. The Bragg formula 2dsinθ=nλ shows that this is consistent with the XRD results, providing strong evidence for the existence of carbon intercalation. Similarly, the above also demonstrates that Fe doping does not lead to the formation of impurities such as FeS and does not alter the material's composition or structure.

[0054] (4) To investigate the elemental distribution characteristics of the prepared material, elemental mapping of Fe-MoS2-C was performed using energy-scattering X-ray spectroscopy (EDX). The results are as follows: Figure 5 As shown. From Figure 5 It can be seen that S, Mo, and Fe are all evenly distributed in the material, indicating that no other impurities are generated, which also highlights the rationality and superiority of the material preparation method.

[0055] (5) Raman spectroscopy is an effective method for clearly identifying the formation of 1T phase MoS2. Raman spectroscopy tests were performed on pure 2HMoS2 prepared by Tong et al., 2HMoS2 with combined 1T structure, and MoS2 from Example 1. The results are as follows: Figure 6 As shown. From Figure 6 a) It can be seen that the characteristic peak of pure 2HMoS2 prepared by Tong et al. is 378 cm⁻¹. -1 (E 1 2g (due to the opposite vibrations of the two S atoms relative to the Mo atom) and 404 cm -1 (A 1 g (This is only related to the vibrations of the S atom in opposite directions). From Figure 6 b) It can be seen that the main characteristic peak of the material prepared in Example 1 appears at 147 cm⁻¹. -1 282cm -1 With 336cm -1 These correspond to J1 and E of phase 1T, respectively. 1g The characteristic peaks of the J3 mode and the 2H phase are completely different, which effectively proves the formation of the high-purity 1TMoS2 structure.

[0056] Test Example 2

[0057] The electrochemical performance of the material prepared in Example 1 was tested, specifically including the following steps:

[0058] (1) Preparation of cathode material: The cathode was prepared using a simple blade coating method. First, elemental sulfur and Fe-MoS2-C from Example 1 were mixed evenly at a mass ratio of 4:1, and then heated at 155°C for 12 hours. The obtained Fe-MoS2-C / S composite material, acetylene black, and PVDF were mixed at a mass ratio of 6:3:1. NMP solvent was added and the mixture was stirred thoroughly. The mixture was then ground into a homogenate using a mortar and pestle and coated onto carbon-coated aluminum foil with a coating thickness of 300 μm. The coating was then dried overnight in a 60°C oven. After completion, the coating was cut into 12 mm diameter discs using a slicer.

[0059] (2) Assembly of lithium-sulfur batteries: Assemble the lithium-sulfur batteries in a glove box filled with argon atmosphere, ensuring that the oxygen and water content is below 0.1 ppm. Assemble the positive electrode shell, modified sulfur positive electrode, 30 μL of electrolyte containing 2% LiNO3 in 1M LiTFSI-DME / DOL (V:V = 1:1), separator, lithium metal negative electrode, gasket, spring, and negative electrode shell in sequence to form a standard 2025 coin cell. Ensure that the side of the modified positive electrode material coated with active material is bonded to the separator, and the other side of the separator is bonded to the negative electrode sheet.

[0060] (3) Testing: The lithium-sulfur battery underwent constant current charge-discharge testing using the Blue Electric CT2001A battery testing system. The battery capacity was calculated to evaluate its cycle and rate electrochemical performance. Cyclic voltammetry (CV) testing assessed the redox reaction kinetics by analyzing the magnitude of the reaction current. The lithium-ion diffusion coefficient was calculated by fitting the scan rate and current peak value. A CHI660E electrochemical workstation was used with a scan rate of 0.1 mV / s. -1 -0.5mV s -1 The voltage range is 1.7V-2.8V. Electrochemical impedance spectroscopy (EIS) is used to analyze the impedance of interfacial charge transport, with a frequency range of 10mHz-100kHz. The results are as follows: Figures 7-10 As shown.

[0061] Figure 7 The rate performance of lithium-sulfur batteries after modifying the cathode with MoS2 and Fe-MoS2-C materials, respectively, is shown. Figure 7 It can be seen that at discharge rates of 0.2C, 0.5C, 1.0C, and 2.0C, the average discharge specific capacities of the MoS2-modified batteries are 856, 757, 660, and 562 mAh g, respectively. -1 The introduction of Fe-MoS2-C increased the average discharge specific capacity of lithium-sulfur batteries at the same rate, reaching 1014, 873, 775, and 666 mAh g, respectively. -1Clearly, compared to pure MoS2 modification, lithium-sulfur batteries modified with Fe-MoS2-C material exhibit better rate performance. Equally important, when the current density is switched back to 0.2C, the device discharge capacity recovers to 892 mAh g⁻¹. -1 This also indicates that Fe-MoS2-C has excellent rate stability.

[0062] Figure 8 The figures show the cycle performance curves of lithium-sulfur batteries at 0.2C rate after using MoS2 and Fe-MoS2-C materials, respectively. Figure 8 It can be seen that the initial discharge capacity of the battery modified with MoS2 is 830 mAh g. -1 After 30 cycles at 0.2C, the discharge capacity decayed to 699mAh g. -1 In contrast, the battery modified with Fe-MoS2-C has an initial discharge capacity of 1089 mAh g. -1 The discharge capacity at the end was 884 mAh g. -1 Both are significantly higher than the former, fully demonstrating the superiority and cycle stability of Fe-MoS2-C materials. The figure also shows that the coulombic efficiencies of the two are similar, both around 99%.

[0063] Figure 9 The images show the EIS curves of lithium-sulfur batteries before cycling, using MoS2 and Fe-MoS2-C materials respectively. Figure 9 It can be seen that the MoS2-modified battery has a charge transfer resistance (R) as high as about 21Ω. ct ), while the R of devices modified with Fe-MoS2-C ct With an impedance of only around 11Ω, which is only half of the former, it is evident that the introduction of carbon intercalation and iron doping technology greatly improves the conductivity of the material, thus significantly enhancing the battery's performance and stability.

[0064] Figure 10 The cyclic CV curves of lithium-sulfur batteries using MoS2 and Fe-MoS2-C materials, respectively. Figure 10 It can be seen that the two peaks in the discharge process correspond to the initial reduction of S8 to long-chain Li2S. x (4≤x≤8), then reduced to short-chain Li2S2 / Li2S. It can be observed that the lithium-sulfur battery modified with Fe-MoS2-C exhibits a stronger response current and a faster peak-on trend, indicating that this composite material, as the battery cathode, possesses higher redox kinetics. Furthermore, the figure shows that the potential difference between the oxidation and reduction peaks is reduced to 0.34V, which also indicates that Fe-MoS2-C brings higher electrochemical reaction kinetics, which is beneficial for promoting the catalytic conversion of polysulfides.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a lithium-sulfur battery cathode material, characterized in that, Includes the following steps, S1. Add the aqueous phase to the oil phase, mix, add a sulfur source, and after hydrothermal reaction, centrifuge and dry to obtain modified molybdenum sulfide; the aqueous phase is a mixture of molybdenum source, glucose and water; the oil phase is a mixture of cationic surfactant and solvent; the hydrothermal reaction temperature is 200 ℃-250 ℃; the time is 24 h-32 h. S2. Under a protective atmosphere, the molybdenum sulfide described in S1 is calcined at 680 ℃-720 ℃ for 2 h-6 h to obtain carbon-containing molybdenum sulfide; S3. Disperse the carbon-containing molybdenum sulfide described in S2 in an alcohol solution, add soluble iron salt and mix well, then centrifuge, dry and calcine to obtain the lithium-sulfur battery cathode material; the calcination temperature is 680 ℃-720 ℃ and the calcination time is 2 h-4 h. The cathode material of the lithium-sulfur battery is a 1T phase Fe-MoS2-C material; The Fe-MoS2-C material has a uniform elemental distribution, forming a hollow sphere nanoarray.

2. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S1, the molybdenum source is selected from sodium molybdate and / or ammonium molybdate; the sulfur source is selected from thiourea and / or thioacetamide; and the cationic surfactant is selected from one or more of hexadecyltrimethylammonium bromide, dodecyldimethylbenzylammonium chloride, and octadecyldimethylhydroxyethylammonium nitrate.

3. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S1, the concentration of molybdenum source in the aqueous phase is 6.5 mmol / L-7 mmol / L, and the concentration of glucose is 9 mmol / L-9.5 mmol / L; the concentration of cationic surfactant in the oil phase is 0.12 mol / L-0.18 mol / L; and the volume ratio of the aqueous phase to the oil phase is 3-4:

1.

4. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S1, the soluble iron salt is selected from ferric nitrate and / or ferric chloride.

5. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S2, the heating rate of the calcination is 4 ℃ / min-6 ℃ / min.

6. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S3, the molar ratio of the carbon-containing molybdenum sulfide to the soluble iron salt is 3-3.5:

1.

7. The method for preparing the lithium-sulfur battery cathode material according to claim 1, characterized in that, In S3, the heating rate of the calcination is 4 ℃ / min-6 ℃ / min.

8. The lithium-sulfur battery cathode material prepared by the method according to any one of claims 1-7.

9. The application of the lithium-sulfur battery cathode material according to claim 8 in lithium-sulfur batteries.

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