A method for preparing a positive electrode material for lithium-sulfur batteries using ultra-thin carbon sheets doped with ZnO / CuO heterojunction

Abstract

A method for preparing a positive electrode material for a lithium-sulfur battery using a doped ZnO / CuO heterojunction ultra-thin carbon sheet is disclosed. The method relates to a method for preparing a positive electrode material for a lithium-sulfur battery. The present invention aims to address the problems of existing methods for preparing positive electrode materials for lithium-sulfur batteries, such as poor conductivity, low active material utilization, and the shuttle effect caused by polysulfide dissolution. The method of the present invention is as follows: 1. Preparation of ultra-thin carbon sheets; 2. Preparation of flower-shaped doped ZnO ultra-thin carbon sheets; 3. Preparation of doped ZnO / CuO ultra-thin carbon sheets; 4. Preparation of sulfur-loaded positive electrode materials using doped ZnO / CuO ultra-thin carbon sheets; and 5. Preparation of a positive electrode and battery assembly. The doped ZnO / CuO heterojunction ultra-thin carbon sheet positive electrode material for a lithium-sulfur battery prepared by the method of the present invention facilitates the rapid conversion of polysulfides while mitigating the shuttle effect. It has low preparation costs, is simple and safe to operate, and is suitable for commercial applications. The present invention has applications in the field of lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-sulfur batteries, and in particular relates to a method for preparing a positive electrode material of a lithium-sulfur battery with a doped ZnO / CuO heterojunction ultra-thin carbon sheet. Background Art

[0002] Lithium-sulfur batteries have attracted widespread attention in the battery industry due to their high energy density and low material cost. Elemental sulfur, as an abundant and readily available material, can react with lithium to produce a multi-electron reaction, providing 1672 mAh g -1 Lithium-sulfur batteries (LSBs) are considered one of the most promising secondary battery systems due to their high theoretical capacity. They are expected to find widespread application in areas requiring high energy density, such as portable electronic communications and energy storage devices. However, the commercialization of LSBs is still hampered by inherent defects, such as the poor conductivity of elemental sulfur and the severe shuttle effect. Therefore, addressing the issues of poor conductivity of LSB cathode materials, low active material utilization, slow reaction kinetics, and the shuttle effect caused by polysulfide dissolution is a current research hotspot. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of poor insulation, poor cycle performance and shuttle effect of sulfur in lithium-sulfur batteries, and to provide a method for preparing a lithium-sulfur battery positive electrode material with a doped ZnO / CuO heterojunction ultra-thin carbon sheet.

[0004] The preparation method of the ZnO / CuO doped heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material of the present invention is carried out according to the following steps:

[0005] 1. Preparation of ultrathin carbon sheets: Sodium citrate was used as the carbon source. Sodium citrate was weighed, ball-milled for 30-120 min, dried, transferred to a tube furnace, and carbonized under nitrogen for 1-3 h. The sample was taken out and soaked in hydrochloric acid for 12-18 h, washed with ethanol and distilled water respectively, and centrifuged to dry to obtain ultrathin carbon sheets.

[0006] 2. Preparation of flower-like ZnO-doped ultrathin carbon sheets

[0007] A mixture of zinc acetate and ultrathin carbon sheets in a mass ratio of 1:1 to 3:1 was added to deionized water and stirred for 30 to 40 minutes. Hydrazine hydrate was then added and stirred evenly. The mixture was transferred to a high-pressure reactor and reacted at 120 to 140°C for 12 to 18 hours. The reactant was washed by centrifugation with a mixed solution of ethanol and N,N-dimethylformamide and then dried to obtain a brown powder, which is the doped flower-shaped ZnO ultrathin carbon sheet.

[0008] The mass volume ratio of the mixture of zinc acetate and ultra-thin carbon sheet to deionized water is 1 g: 30-50 mL; the mass volume ratio of the mixture of zinc acetate and ultra-thin carbon sheet to hydrazine hydrate is 1 g: 1-3 mL;

[0009] 3. Preparation of ultra-thin carbon sheets doped with ZnO / CuO heterojunction

[0010] Copper acetate and flower-shaped ZnO-doped ultrathin carbon sheets were added to N,N-dimethylformamide solution, heated and stirred for 3 to 5 hours, and then allowed to stand for 6 to 10 hours. The supernatant was poured out, and the supernatant was washed alternately by centrifugation with ethanol and distilled water, and dried to obtain a doped ZnO / CuO heterojunction ultrathin carbon sheet.

[0011] Wherein, the mass ratio of the copper acetate to the flower-shaped ZnO ultra-thin carbon sheet is 0.25-0.5:0.5-1.0; 4. Preparation of sulfur-loaded positive electrode material of doped ZnO / CuO heterojunction ultra-thin carbon sheet: the doped ZnO / CuO ultra-thin carbon sheet obtained in step 3 is mixed with elemental sulfur in a mass ratio of 1:4-1:6, ball milled for 1-3 hours, melt-diffused at 155-170°C for 3-5 hours, and cooled to room temperature in the furnace to complete the preparation of sulfur-loaded positive electrode material of doped ZnO / CuO heterojunction ultra-thin carbon sheet;

[0012] Furthermore, the drying time in step 1 is 12 to 18 hours. The hydrochloric acid concentration is 20 to 40%, and the carbonization temperature in the tubular furnace is 600 to 800°C to obtain ultrathin carbon sheets with a high degree of graphitization and a thickness of less than 10 nm. Washing and centrifugation are performed until neutral. The washing steps are: washing with anhydrous ethanol and centrifugation 1 to 2 times, washing with distilled water and centrifugation 5 to 10 times, and then drying. Too short a ball milling time will result in thickening of the carbon sheet, while too long a ball milling time will damage the carbon sheet structure.

[0013] Furthermore, the mass volume ratio of the mixture of zinc acetate and ultrathin carbon sheets described in step 2 to hydrazine hydrate is 1 g: 1-3 mL; utilizing the strong reducing property of hydrazine hydrate, flower-shaped ZnO is synthesized. The flower-shaped ZnO has a high specific surface area, which is conducive to the loading of CuO and provides good reaction sites for elemental sulfur;

[0014] Furthermore, the mass ratio of copper acetate to flower-shaped ZnO-doped ultra-thin carbon sheet in step 3 is 0.25-0.5:0.5-1.0, and a doped ZnO / CuO heterojunction ultra-thin carbon sheet is obtained by solvent thermal treatment. When the CuO content is too high, uneven loading results and the catalytic performance of the material is attenuated, while when the CuO content is too low, the ZnO / CuO heterojunction sites are reduced, affecting the catalytic performance of the material.

[0015] Furthermore, the ultra-thin carbon sheet doped with ZnO / CuO heterojunction in step 4 serves as a sulfur-supporting matrix. ZnO has a wide bandgap, while CuO has a narrow bandgap. Therefore, the ZnO / CuO heterojunction generates a strong built-in electric field, achieving a synergistic effect of excellent catalytic performance and efficient adsorption of polysulfides, reducing the poor dissolution of polysulfides and accelerating redox reactions. The ultra-thin carbon sheet enhances the conductivity of the electrode material and accelerates charge transfer.

[0016] For the sake of brevity, the ultrathin carbon sheet, flower-like ZnO-doped ultrathin carbon sheet, and CuO / ZnO-doped ultrathin carbon sheet materials are named UC, UC / ZnO, and UC / ZnO / CuO, respectively. The sulfur-loaded materials are named S@UC, S@UC / ZnO, and S@UC / ZnO / CuO, respectively.

[0017] The gain effect of the present invention:

[0018] First, a conductive carbon with an ultra-thin structure was obtained by annealing sodium citrate in a tube furnace. This material effectively improves the conductivity of elemental sulfur.

[0019] Secondly, the ZnO / CuO heterojunction coupling effect and the different band gaps can accelerate interfacial reaction kinetics and charge carrier transport. ZnO and CuO have different band gaps, and the establishment of a built-in electric field has an electrocatalytic effect, inhibiting the shuttle effect, accelerating the conversion and adsorption of polysulfides, and extending the cycle life. The ZnO / CuO heterojunction combined with ultra-thin carbon sheets evenly distributes the current density, rapidly transfers positive charges and electrons, catalyzes the rapid conversion of lithium polysulfide into lithium sulfide, improves battery cycle performance, and inhibits the formation of dendrite lithium.

[0020] Finally, the preparation process of the present invention is simple, low-cost, and suitable for large-scale production and commercial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the modified results of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments.

[0022] Figure 1 This is a preparation method of a ZnO / CuO-doped heterojunction ultra-thin carbon sheet lithium-sulfur battery cathode material and a flow chart of the preparation of UC / ZnO / CuO composite materials;

[0023] Figure 2 (a) SEM image of ultrathin carbon sheet; (b) TEM image of ultrathin carbon sheet;

[0024] Figure 3 is the SEM image of UC / ZnO / CuO;

[0025] Figure 4TEM image of ZnO / CuO;

[0026] Figure 5 is the lattice fringe diagram of ZnO / CuO;

[0027] Figure 6 XRD patterns of ZnO / CuO, UC / ZnO / CuO, UC / ZnO, and UC materials, as well as XPS patterns of UC / ZnO / CuO and UC / ZnO materials; Figure (a) XRD patterns of ZnO / CuO, UC / ZnO / CuO, UC / ZnO and UC; (b) Full XPS spectra of ZnO / CuO and UC / ZnO / CuO materials; (c) XPS of O element in UC / ZnO / CuO; (d) XPS of Cu element in UC / ZnO / CuO; (e) XPS of Zn element in UC / ZnO / CuO; (f) XPS of C element in UC / ZnO / CuO;

[0028] Figure 7 The discharge curves of UC, UC / ZnO, and UC / ZnO / CuO lithium-sulfur battery cathode materials are shown;

[0029] Figure 8 This is the long cycle charge and discharge curve of UC / ZnO / CuO lithium-sulfur battery cathode material;

[0030] Figure 9 This is the mechanism diagram of UC / ZnO / CuO lithium-sulfur battery cathode material;

[0031] Figure 10 The optimized model adsorption diagrams for Li2S6, ZnO, and CuO;

[0032] Figure 11 Calculation diagram of ZnO and CuO energy bands.

[0033] Figure 12 TEM image and specific capacity efficiency graph of the ultra-thin carbon sheet of Example 1 DETAILED DESCRIPTION

[0034] The above contents of the present invention are further described in detail below through examples, but the subject matter of the present invention is not limited to the following examples, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0035] Experimental drugs

[0036]

[0037] Experimental equipment

[0038]

[0039]

[0040] Comparative Example 1

[0041] The preparation method of a ZnO / CuO doped heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode in this comparative example is carried out according to the following steps:

[0042] 1. Preparation of Ultrathin Carbon Sheets

[0043] Using sodium citrate as the carbon source, 5 g of sodium citrate was weighed, ball-milled for 30 minutes, dried, transferred to a tube furnace, and carbonized at 600°C for 1 hour under nitrogen protection. The sample was taken out and soaked in 20% hydrochloric acid for 16 hours, washed with ethanol and distilled water respectively, and centrifuged to dry to obtain ultrathin carbon sheets.

[0044] 2. Preparation of flower-like ZnO-doped ultrathin carbon sheets

[0045] A mixture of zinc acetate and ultrathin carbon sheets in a mass ratio of 1:1 was added to deionized water and stirred for 30 minutes. 1 mL of hydrazine hydrate was then added and stirred evenly. The mixture was transferred to a high-pressure reactor and reacted at 120°C for 12 hours. The reactant was washed by centrifugation with a mixed solution of ethanol and N,N-dimethylformamide in a volume ratio of 1:4, and then dried to obtain a brown powder, which is the doped flower-shaped ZnO ultrathin carbon sheet.

[0046] 3. Preparation of ultra-thin carbon sheets doped with ZnO / CuO heterojunction

[0047] Copper acetate and flower-shaped ZnO-doped ultrathin carbon sheets were added to N,N-dimethylformamide solution, heated and stirred for 3 hours, and then allowed to stand for 6 hours. The supernatant was poured out, and the supernatant was washed alternately by centrifugation with ethanol and distilled water. After drying, the ZnO / CuO-doped heterojunction ultrathin carbon sheet was obtained.

[0048] The mass ratio of the copper acetate to the flower-shaped ZnO-doped ultra-thin carbon sheet is 0.25:0.5 g.

[0049] 4. Preparation of sulfur-loaded positive electrode material of ultrathin carbon sheet doped with ZnO / CuO heterojunction: The ultrathin carbon sheet doped with ZnO / CuO obtained in step 3 was mixed with elemental sulfur in a mass ratio of 1:4, ball milled for 1 hour, melt-diffused at 155°C for 3 hours, and cooled to room temperature in the furnace to complete the preparation of sulfur-loaded positive electrode material of ultrathin carbon sheet doped with ZnO / CuO heterojunction;

[0050] 5. Preparation of positive electrode and battery assembly

[0051] The doped ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material obtained in step 4 was mixed with polyvinylidene fluoride and acetylene black in a ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent; the mixture was stirred for 24 hours and mixed evenly to prepare a positive electrode slurry for standby use, the slurry was scraped onto aluminum foil, placed in an oven, and dried at 100°C; after cooling to room temperature, the slurry was sliced ​​with a slicer for standby use; the negative electrode shell, lithium sheet, lithium-sulfur battery electrolyte, diaphragm, lithium-sulfur battery electrolyte, positive electrode, and positive electrode shell were assembled in an argon-filled glove box in the order of negative electrode shell, lithium sheet, lithium-sulfur battery electrolyte, diaphragm, lithium-sulfur battery electrolyte, positive electrode, and positive electrode shell to obtain the lithium-sulfur battery for subsequent electrochemical performance testing. The obtained lithium-sulfur battery had a discharge capacity of 1228.8 mAh g at 0.5C. -1 .

[0052] Example 1

[0053] The difference between this embodiment and the comparative example is that the sample obtained by annealing in the tube furnace in step 1 is immersed in 10% concentrated hydrochloric acid. The other steps are the same as those in comparative example 1. Figure 12 As shown in the TEM image and specific capacity efficiency graph of the ultra-thin carbon sheet, the obtained carbon sheet has an uneven thickness and the lithium-sulfur battery prepared with this material has a discharge specific capacity of 771.3 mAh g at 0.5C. -1 .

[0054] Example 2

[0055] The difference between this embodiment and the comparative example is that in step 5, UC is selected as the sulfur-carrying matrix of the lithium-sulfur battery, and the other steps are the same as those of the comparative example 1. The 0.5C discharge specific capacity of the lithium-sulfur battery prepared in this way is shown in the attached figure. Figure 7 Shown is 261.1mAh g -1 .

[0056] The performance of the above comparative examples and embodiments was characterized

[0057] 1) XRD measurement: The crystal plane and crystallinity of the positive electrode material are tested, and the 2θ range is 10° to 90°.

[0058] 2) Scanning Electron Microscope (SEM) Testing: The cathode material's surface morphology and elemental distribution were determined using an SEM with an accelerating voltage of 0.2-30 kV. The instrument model was a FEI Sirion 200, with a resolution of 20 kV and an accelerating voltage of 0.2-30 kV. Sample Preparation: The test sample was adhered to conductive adhesive, with surrounding material removed by air blowing. After gold spraying for 20 seconds, the sample was placed on a sample stage for testing.

[0059] 3) Transmission Electron Microscopy (TEM) Testing: The microstructure of the cathode material was determined using a transmission electron microscope (TEM). Instrument model: JEM-2100. Sample Preparation: Ultrasonicate the ethanol-sample mixture for 30 minutes to evenly disperse the sample. Use a dropper to drop the dispersion onto a copper mesh. After drying, place the sample on a sample stand for testing.

[0060] 4) X-ray photoelectron spectroscopy (XPS) test. The chemical states of C, O, Zn, and Cu elements were determined by XPS test analysis. The instrument model is K-Alpha+, the test parameters are vacuum, Al Kα (hv = 1486.6eV), working power is 100W, and high resolution pass energy is 50eV. Sample preparation: The dried positive electrode material is ground into powder and placed on the sample stage for testing. The C 1s standard peak is 285.0eV for charge correction and fitting is performed using XPSPEAK41.

[0061] 5) Charge and discharge test. The LAND battery test system is used for charge and discharge tests with a voltage range of 1.5V-3.0V. It analyzes electrochemical performance parameters such as battery discharge capacity, charge and discharge efficiency, and voltage platform.

[0062] 6) CV test. Cyclic voltammetry (CV) test was performed on the assembled lithium-sulfur battery to characterize the cycle stability and reversibility of the lithium-sulfur battery. The instrument model was an electrochemical workstation CHI760E with a scan rate of 0.0001-0.0005 V·s -1 , the voltage range is 1.5V~3.0V.

[0063] 7) EIS test: The assembled battery was subjected to an electrochemical impedance spectroscopy (EIS) test to characterize the impedance and stability of the lithium-sulfur battery during cycling. The constant current charge and discharge performance of the lithium-sulfur battery in the voltage range of 1.5V to 3.0V was measured.

[0064] 8) Binding energy calculation. Based on density functional theory (DFT), using Materials Studio software, CASTEP module, and PBE-GGA functional. Equation (1) is the energy calculation formula;

[0065] E Binding Energy =E Total -(E1+E2) (1)

[0066] Figure 1This is a flow chart showing a method for preparing a ZnO / CuO heterojunction-doped ultra-thin carbon sheet cathode material for lithium-sulfur batteries. The material is obtained by carbonization in a tube furnace using sodium citrate as the carbon source. This method offers advantages such as a simple synthesis process and readily available raw materials. Flower-shaped zinc oxide is then incorporated into the ultra-thin carbon sheet via a hydrothermal reaction. Finally, a ZnO / CuO / UC composite material is obtained by stirring and heating.

[0067] Figure 2 (a) is the SEM image of the ultrathin carbon sheet, and (b) is the TEM image of the ultrathin carbon sheet. The results show that according to the SEM image ( Figure 2 a), showing that UC is composed of many interconnected thin sheets. TEM images show that the thickness of the ultrathin carbon sheets is less than 10 nm.

[0068] Figure 3 This is an SEM image of UC / ZnO / CuO. SEM characterization shows that the anchoring of CuO nanodots on ZnO roughens the surface of the ZnO microrods. The large specific surface area of ​​the ZnO microrod structure allows for the deposition of numerous CuO nanodots on the ZnO surface, resulting in a rich heterogeneous interface. Due to the large specific surface area of ​​the heterogeneous structure, the large number of exposed heterogeneous interfaces provides abundant active sites for the adsorption of polysulfides and accelerated polysulfide conversion, demonstrating the great potential of lithium-sulfur batteries.

[0069] Figure 4 TEM image of ZnO / CuO. The obtained ZnO / CuO surface has CuO, which proves that CuO grows successfully on the ZnO surface.

[0070] Figure 5 The lattice fringe diagram of ZnO / CuO and the magnified TEM image show a clear heterogeneous interface between CuO and ZnO. It can be observed that the interplanar spacing of the ZnO (101) crystal plane is 0.38nm, and the interplanar spacing of the CuO (111) crystal plane is 0.26nm.

[0071] Figure 6(a) XRD patterns of ZnO / CuO, UC / ZnO / CuO, UC / ZnO, and UC; (b) full XPS spectra of ZnO / CuO and UC / ZnO / CuO materials; (c) XPS of O element in UC / ZnO / CuO; (d) XPS of Cu element in UC / ZnO / CuO; (e) XPS of Zn element in UC / ZnO / CuO; (f) XPS of C element in UC / ZnO / CuO. As can be seen from the spectra, the XRD pattern of UC has a peak at 21°, corresponding to the graphite (002) plane, indicating the amorphous state of UC. The high degree of graphitization of carbon demonstrates its excellent conductivity in lithium-sulfur batteries. The XRD peak positions of the UC / ZnO / CuO material are at 2θ = 31.6°, 34.4°, 36.1°, 47.4°, 56.5°, and 62.8°, corresponding to the (100), (002), (101), (102), (110), and (103) crystal planes, respectively. The elemental composition and chemical state of the surface composition of the UC / ZnO / CuO heterojunction were analyzed by XPS. It can be found that the C 1s, O 1s, Cu 2p, and Zn 2p peaks appear at approximately 284.75 eV, 531.47 eV, 934.22 eV, and 1027.3 eV, respectively. In the O1s spectrum, there are two characteristic peaks at 531.98 eV and 530.28 eV. In the Cu 2p spectrum, there are two characteristic peaks at 933.37eV and 953.79eV, which correspond to Cu 2p 3 / 2 and Cu 2p 1 / 2 , indicating that Cu exists in Cu 2+ The characteristic peaks of the XPS spectrum in the Zn 2p region are located at 1021.92 and 1045.06 eV, respectively, corresponding to Zn 2p 1 / 2 and Zn 2p 3 / 2 In the C1s spectrum, there are two characteristic peaks at 284.74 eV and 287.08 eV.

[0072] Figure 7 The discharge curves of UC / ZnO / CuO, UC / ZnO and UC lithium-sulfur battery cathode materials are shown in Figure 2. The initial discharge capacity of UC / ZnO / CuO, UC / ZnO and UC batteries is at 0.5C. After 550 cycles, the discharge capacity of the three groups of materials remains at 1228.8 mAh g -1 , 504.3mAh g -1 , 261.1mAh g -1The discharge curve of the UC material shows the specific discharge capacity of Example 2. This indicates that the UC / ZnO / CuO composite has the optimal specific discharge capacity, significantly suppressing the shuttle effect. This is because the ZnO / CuO heterojunction induces a strong built-in electric field, which promotes the electronic conductivity of the composite cathode material and enhances the redox kinetics of polysulfides.

[0073] Figure 8 This is the long cycle charge and discharge curve of the UC / ZnO / CuO lithium-sulfur battery cathode material. After 800 cycles of the UC / ZnO / CuO lithium-sulfur battery cathode material, the battery's discharge capacity is 200mAh g -1 .

[0074] Figure 9 This diagram shows the mechanism of the UC / ZnO / CuO lithium-sulfur battery cathode material. ZnO has a very wide energy band. In contrast, CuO has a narrow energy band, and the overlapping conduction and valence bands make CuO an excellent electronic conductor. Therefore, the ZnO / CuO heterojunction generates a strong built-in electric field, which promotes the electronic conductivity of the composite material and enhances the charge transfer process during the electrochemical redox reaction occurring on the surface of the ZnO / CuO adsorbed nano-thin carbon sheets. The nano-thin carbon sheets prepared with sodium citrate as the raw material enhance the conductivity of the electrode material and accelerate the electron transfer ability. The two complement each other to achieve rapid charge transport and electron transfer catalytic polysulfide rapid conversion.

[0075] Figure 10 The optimized model adsorption diagrams for Li2S6, ZnO, and CuO. Materials Studio was used to calculate the adsorption of Li2S6 on ZnO and CuO, and the adsorption capacity of ZnO and CuO on Li2S6 was studied respectively. The calculation results show that the adsorption energies of Li2S6 on the surfaces of ZnO (101) and CuO (111) are -1.7 eV and -2.1 eV, respectively, indicating that CuO has a higher adsorption capacity for polysulfides. Based on the different adsorption energies of ZnO and CuO, there is a gap in the adsorption energies of ZnO and CuO on Li2S6, which means that Li2S6 can diffuse from ZnO to CuO, so the dielectric binding energy of the ZnO / CuO heterostructure can improve its electrochemical performance and redox kinetics.

[0076] Figure 11 The calculated energy bands for ZnO and CuO are shown below. The calculated results show that the energy band for CuO is 1.196 eV, while that for ZnO is 3.413 eV, demonstrating that the heterostructure has distinct energy bands. Therefore, the heterostructure composed of ZnO and CuO can induce a strong built-in electric field, effectively promoting the electronic conductivity of the composite material.

[0077] Figure 12TEM image and specific capacity efficiency diagram of ultrathin carbon sheet. Figure 12 (a) is a TEM image of the carbon sheet obtained in Example 1, and compared with the comparative example Figure 2 (b) Compared with the hydrochloric acid concentration below 20%, it is not possible to obtain uniform ultra-thin carbon sheets, and there are certain impurities. The uneven thickness of the carbon sheet has a certain impact on the electron / ion transmission path, which leads to a decrease in the discharge capacity of the lithium-sulfur battery. Figure 12 (b) It can be seen that the discharge capacity of the lithium-sulfur battery in Example 1 is 771.3 mAh g -1 .

Claims

1. A method for preparing a positive electrode material for a lithium-sulfur battery by using a ZnO / CuO heterojunction ultra-thin carbon sheet, characterized in that A method for preparing a ZnO / CuO-doped heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode is carried out according to the following steps:

1. Preparation of Ultrathin Carbon Sheets Sodium citrate was used as the carbon source. Sodium citrate was weighed, ball-milled for 30 to 120 minutes, dried, transferred to a tube furnace, and carbonized under nitrogen for 1 to 3 hours. The sample was taken out and soaked in hydrochloric acid for 12 to 18 hours, washed with ethanol and distilled water respectively, and centrifuged to dry to obtain an ultrathin carbon sheet.

2. Preparation of Flower-like ZnO-doped Ultrathin Carbon Sheets A mixture of zinc acetate and ultrathin carbon sheets in a mass ratio of 1:1 to 3:1 was added to deionized water and stirred for 30 to 40 minutes. Hydrazine hydrate was then added and stirred evenly. The mixture was transferred to a high-pressure reactor and reacted at 120 to 140°C for 12 to 18 hours. The reactant was washed by centrifugation with a mixed solution of ethanol and N,N-dimethylformamide and then dried to obtain a brown powder, which is the doped flower-shaped ZnO ultrathin carbon sheet. The mass volume ratio of the mixture of zinc acetate and ultrathin carbon sheet to deionized water is 1 g: 30-50 mL; The mass volume ratio of the mixture of zinc acetate and ultrathin carbon sheet to hydrazine hydrate is 1 g: 1 to 3 mL; 3. Preparation of ultra-thin carbon sheets doped with ZnO / CuO heterojunction Copper acetate and flower-shaped ZnO-doped ultrathin carbon sheets were added to N,N-dimethylformamide solution, heated and stirred for 3 to 5 hours, and then allowed to stand for 6 to 10 hours. The supernatant was poured out, and the supernatant was washed alternately by centrifugation with ethanol and distilled water, and dried to obtain a doped ZnO / CuO heterojunction ultrathin carbon sheet. Wherein, the mass ratio of the copper acetate to the flower-shaped ZnO-doped ultra-thin carbon sheet is 0.25-0.5:0.5-1.0; 4. Preparation of Sulfur-loaded Cathode Materials Doped with ZnO / CuO Heterojunction Ultrathin Carbon Sheets The doped ZnO / CuO ultra-thin carbon sheet obtained in step 3 is mixed with elemental sulfur in a mass ratio of 1:4 to 1:6, ball-milled for 1 to 3 hours, melt-diffused at 155 to 170°C for 3 to 5 hours, and cooled to room temperature in the furnace to complete the preparation of the doped ZnO / CuO heterojunction ultra-thin carbon sheet sulfur-loaded positive electrode material.

2. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material according to claim 1, characterized in that The concentration of hydrochloric acid in step 1 is 20-40%.

3. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material according to claim 1, characterized in that The carbonization temperature of the tubular furnace in step 1 is 600-800°C.

4. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material according to claim 1, characterized in that The thickness of the ultra-thin carbon sheet in step 1 is less than 10 nm.

5. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material according to claim 1, characterized in that The volume ratio of the mixed solution of ethanol and N,N-dimethylformamide used in step 2 is 1:4 to 1:

6.

6. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material according to claim 1, characterized in that The mass volume ratio of the mixture of copper acetate and doped flower-shaped ZnO ultra-thin carbon sheets described in step 3 to the N,N-dimethylformamide solution is 1 g: 30-50 mL.

7. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery cathode material according to claim 1, characterized in that The mass ratio of zinc acetate to sodium citrate is 1:5 to 1:

9.

8. The method for preparing a ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery cathode material according to claim 1, characterized in that The doped ZnO / CuO heterojunction ultra-thin carbon sheet in step 4 is a sulfur-loaded matrix.

9. A battery assembled using the ZnO / CuO heterojunction ultra-thin carbon sheet lithium-sulfur battery positive electrode material prepared according to claim 1.

10. The battery according to claim 9, characterized in that The battery assembly method is as follows: The doped ZnO / CuO heterojunction ultra-thin carbon sheet loaded with sulfur positive electrode material is mixed with polyvinylidene fluoride and acetylene black in a mass ratio of 8:1:1, and then N-methylpyrrolidone is added as a solvent; the mixture is stirred for 12 to 24 hours, and after being evenly mixed, it is used as a positive electrode slurry for standby use, the slurry is scraped onto aluminum foil, and then placed in an oven and dried at 100 to 120°C; after cooling to room temperature, it is sliced ​​with a slicer for standby use; the negative electrode shell, lithium sheet, lithium-sulfur battery electrolyte, diaphragm, lithium-sulfur battery electrolyte, positive electrode, and positive electrode shell are assembled in an argon-filled glove box in this order to obtain a lithium-sulfur battery.

Images