Preparation method of monatomic catalyst material of lithium-sulfur battery sulfur positive electrode

Abstract

A preparation method of a lithium-sulfur battery positive electrode single-atom catalyst material, comprising the following steps: dissolving a carbon source in an organic solvent, then adding an organic acid, and stirring to form a mixed solution; taking the mixed solution and adding it to a mesoporous template agent, soaking overnight, then aging at low temperature and aging at high temperature again, and drying to obtain sample I; performing sintering treatment on the sample I, and naturally cooling to obtain sample II; mixing a metal source and an organic ligand, then adding them to pure methanol, stirring, then adding a nitrogen source, and stirring to form a uniform solution; adding the sample II to the uniform solution, and sequentially performing evaporation, sintering, etching, washing, suction filtration and drying to obtain the single-atom catalyst material. The method has green and simple preparation process, low cost and short reaction time, the obtained single-atom catalyst material can be fully compounded with sulfur, the obtained composite material can not only enhance the conductivity of the electrode, but also fix the sulfur through a physical confinement mode, and when the composite material is used as a lithium-sulfur battery positive electrode material, excellent electrochemical performance is exhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery electrode materials, and in particular relates to a method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery. Background Art

[0002] With the continuous development of the electronics market, lithium-ion batteries (LIBs) can no longer meet the current requirements for energy storage systems. In order to enable the rapid development of electric vehicles and some electronic devices, a new generation of high-energy-density energy storage systems is urgently needed to replace existing LIBs. Lithium-sulfur batteries (Li-S) have great potential as the next generation of energy storage devices due to their high theoretical energy density and low sulfur raw material cost. In addition, sulfur has the advantages of being naturally abundant and non-toxic, and can provide high specific capacity (1675mAhg -1 ). However, the commercialization of Li-S batteries has been plagued by several inherent obstacles. The insulating properties of sulfur and its final discharge products (Li2S / Li2S2) lead to low utilization of active materials. The severe volume change during cycling (about 80%) leads to poor cycling stability. In addition, the so-called shuttle effect caused by soluble lithium polysulfides (LiPs) has been considered its main bottleneck. Therefore, it is imperative to develop an effective technology to enhance the fixation of lithium polysulfides on the sulfur cathode.

[0003] Research on cathode modification has mainly focused on encapsulating sulfur molecules into the pores of various carbon hosts, which can physically hinder diffusion and alleviate the shuttling phenomenon. However, the physical adsorption of carbon supports can only provide weak interactions with non-polar S8, and polar LiPs will inevitably dissolve into the electrolyte. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a single-atom catalyst material for the sulfur positive electrode of a lithium-sulfur battery. The preparation process of the method is green and simple, low in cost, and short in reaction time. The prepared single-atom catalyst material can be fully compounded with sulfur. The obtained composite material can not only enhance the electrical conductivity of the electrode and have a high electrochemical capacity, but also fix sulfur by physical confinement. When used as a positive electrode material for a lithium-sulfur battery, it can exhibit excellent electrochemical performance.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery comprises the following steps:

[0007] (1) dissolving a carbon source in an organic solvent, adding an organic acid, and stirring to form a mixed solution;

[0008] (2) adding the mixed solution prepared in step (1) to the mesoporous template, impregnating for a period of time, then aging at low temperature and then at high temperature, and finally drying to obtain sample I;

[0009] (3) Sintering sample I in a sintering atmosphere and naturally cooling to room temperature to obtain sample II;

[0010] (4) Mixing the metal source and the organic ligand, adding them to pure methanol, stirring, then adding the nitrogen source, and stirring again to form a uniform solution;

[0011] (5) Sample II is added to the uniform solution obtained in step (4), and the monoatomic catalyst material is obtained by evaporation, sintering in a sintering atmosphere, etching, washing, filtering, and drying.

[0012] Preferably, in step (1), the organic acid is oxalic acid or formic acid; the carbon source is one of sugar alcohol, glucose, and sucrose; and the mass concentrations of the carbon source and the organic acid in the mixed solution are 9-11% and 70-90%, respectively.

[0013] Preferably, in step (2), the mesoporous template is SBA-15, the mass ratio between the mixed solution and the mesoporous template is in the range of 1:(1-4), the immersion temperature is 25-35° C., and the immersion time is 10-12 h.

[0014] Preferably, in step (2), the aging parameters at low temperature are: aging temperature of 40-50°C, aging time of 16-18h; the aging parameters at high temperature are: aging temperature of 90-120°C, aging time of 19-23h; drying temperature of 50-60°C, drying time of 12-14h.

[0015] Preferably, in step (3), the sintering temperature is 850-950° C., and the sintering time is 3-5 hours.

[0016] Preferably, in step (4), the metal source is one of ferrous sulfate, cobalt sulfate, copper sulfate, and nickel acetate; the organic ligand is one of 1,10-phenanthroline, ethylenediamine, and glycine; and the nitrogen source is one of dimethylimidazole and urea.

[0017] Preferably, in step (4), the concentrations of the metal source and the nitrogen source in the homogeneous solution are in the range of 5.5-10 g / L and 65-70 g / L, respectively; and the mass ratio of the metal source to the organic ligand is in the range of 1:(1-3).

[0018] Preferably, in step (5), the mass ratio of sample II to the uniform solution is in the range of 1:(0.1-0.5).

[0019] Preferably, in step (3) and step (5), the sintering atmosphere is one of nitrogen, argon, and argon / hydrogen mixed atmosphere; in step (5), the sintering temperature is 900-1050° C., and the sintering time is 4-5 h.

[0020] Preferably, in step (5), the evaporation process parameters are: evaporation temperature of 70-80°C, evaporation time of 8-10h; etching process parameters are: hydrofluoric acid etching, etching time of 6-8h; drying process parameters are: drying temperature of 40-60°C, drying time of 8-12h.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention prepares a uniformly distributed single-atom catalyst by impregnating a carbon source into a mesoporous template, optimizing the pore structure through aging temperature and time, coordinating a metal source with an organic ligand, introducing a nitrogen source, and sintering at high temperature. The preparation process of the present invention is green, simple, low-cost, and has a short reaction time. The prepared single-atom catalyst material has a high specific surface area and pore structure, has a good adsorption effect on LiPs, can provide a channel for the transmission of electrolyte, promote ion diffusion, improve the battery specific capacity and cycle stability, and significantly affect the migration resistance of lithium ions and electrons in the sulfur / carbon composite positive electrode material. In addition, due to its high activity, the single-atom catalyst can significantly activate and reduce the delithiation barrier of Li2S, thereby affecting the macroscopic reaction kinetics of the active sulfur redox process and improving the battery's charge and discharge performance. The single-atom catalyst material prepared by the present invention can fully composite with sulfur. The resulting composite material can not only enhance the conductivity of the electrode and have a high electrochemical capacity, but also fix sulfur through physical confinement. When used as a positive electrode material for lithium-sulfur batteries, it can exhibit excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of the Co-NC single-atom material prepared in Example 1 of the present invention;

[0024] Figure 2 This is an SEM image of the Co-NC single-atom material prepared in Example 1 of the present invention;

[0025] Figure 3 This is a charge-discharge cycle curve of a lithium-sulfur battery assembled with the Co-NC single-atom material prepared in Example 1 of the present invention at a current density of 1C;

[0026] Figure 4 This is a charge-discharge cycle curve of a lithium-sulfur battery assembled with the Cu-NC single-atom material prepared in Example 6 of the present invention at a current density of 1C;

[0027] Figure 5This is a charge-discharge cycle curve of a lithium-sulfur battery assembled with the Fe-NC single-atom material prepared in Example 7 of the present invention at a current density of 1C. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] A method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery comprises the following steps:

[0031] (1) 4 ml of furfuryl alcohol was dissolved in 6 ml of trimethylbenzene, and then 40 mg of oxalic acid was added and stirred to form a mixed solution; the mass concentrations of furfuryl alcohol and oxalic acid in the mixed solution were 9% and 70%, respectively;

[0032] (2) 1200 μL of the mixed solution was added to 0.5 g of the mesoporous template SBA-15 and immersed at 30 °C for 12 h. The mass ratio of the mixed solution to the mesoporous template was 1:2.4. The sample was then aged at 50 °C for 16 h, then aged at 90 °C for 19 h, and finally opened and dried at 60 °C for 12 h to obtain sample I.

[0033] (3) Sample I was placed in a tube furnace under an argon atmosphere and heat treated at 850°C for 4 h, and then naturally cooled to room temperature to obtain sample II;

[0034] (4) 0.055 g of CoSO4·7H2O and 0.096 g of 1,10-phenanthroline were mixed and added to 10 mL of pure methanol. After stirring for 0.5 h, 0.66 g of 2-methylimidazole was added and stirred for another 1 h to obtain a homogeneous solution. The concentrations of the metal source and nitrogen source in the homogeneous solution were 5.5 g / L and 66 g / L, respectively, and the mass ratio of the metal source to the organic ligand was 1:1.75.

[0035] (5) 1 g of sample II was added to the homogeneous solution obtained in step (4), with the mass ratio of sample II to the homogeneous solution being 1:0.1. The samples were evaporated at 80°C for 8 h, then thermally decomposed at 900°C under argon for 5 h, and stirred in HF solution (5 wt%) for 6 h to remove the silicon template. The etched samples were washed, filtered, and dried at 40°C for 12 h to obtain a single-atom catalyst material, which was named Co-NC.

[0036] The Co-NC composite material prepared in this example was characterized and tested. Figure 1 The XRD results show that there is no peak of Co element, indicating that Co is distributed in the mesoporous carbon in the form of atoms. Figure 2 The SEM results show that Co-NC still maintains the spherical morphology of the mesoporous template.

[0037] 25mg of Co-NC and 75mg of elemental sulfur powder were mixed and heat treated at 155℃ for 12h under vacuum to obtain a lithium-sulfur battery sulfur positive electrode composite material with single-atom material Co-NC as the carrier material. The electrochemical performance of the sulfur battery sulfur positive electrode composite material was tested: the prepared sulfur battery sulfur positive electrode composite material, conductive agent SuperP and binder polyvinylidene fluoride were mixed evenly and fully ground, then mixed with dispersant N-methylpyrrolidone to make the sample viscous, coated on aluminum foil, dried, and the dried sample was cut into electrode sheets with a diameter of 10mm. The electrode sheet is the positive electrode of the lithium-sulfur battery. The positive electrode sheet, 14mm round lithium sheet, 16mm round Celgard2400, ether electrolyte, electrode shell, and gasket are assembled into a battery and sealed. Let it stand at room temperature for 4h, and then the electrochemical performance test was carried out; the ether electrolyte is 1MLiTFSI+0.2MLiNO3; DOL / DME, v / v=1:1. From Figure 3 It can be seen that at a current density of 1C, the lithium-sulfur battery has an initial specific capacity of 1004.78mAh / g. After 100 cycles, the capacity remains at 820.51mAh / g, with a capacity retention rate of up to 81.6%.

[0038] Examples 2-5: These four groups of examples differ from Example 1 only in their carbon content. The single-atom Co-NC materials obtained in Examples 1-5 were further prepared into sulfur cathode composite materials for lithium-sulfur batteries. After assembling into batteries, the electrochemical performance was tested. The results are shown in the following table:

[0039] Table 1 shows the effect of carbon content on the electrochemistry of lithium-sulfur batteries

[0040] Example Example 1 Example 2 Example 3 Example 4 Example 5 Furfuryl alcohol content (μL) 1200 900 1000 1400 1600 Initial specific capacity (mAh / g) 1004.78 899.5 866.3 780.3 796.5 Retention rate 81.6％ 74.7％ 80.6％ 80.6％ 80.8％

[0041] As shown in Table 1, at a current density of 1C, the lithium-sulfur battery in Example 1, with 1200 μL of carbon source added, exhibited an initial specific capacity of 1004.78 mAh / g. After 100 cycles, the capacity retention reached 81.6%. This indicates that when 1200 μL of carbon source was added, the Co-NC exhibited the optimal pore structure, resulting in the best catalytic effect and battery stability.

[0042] Example 6

[0043] A method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery comprises the following steps:

[0044] (1) Dissolve 4 mg of glucose in 6 ml of trimethylbenzene, then add 40 ml of formic acid and stir to form a mixed solution; the mass concentrations of glucose and formic acid in the mixed solution are 10% and 80%, respectively;

[0045] (2) 1400 μL of the mixed solution was added to 2 g of the mesoporous template SBA-15 and immersed at 25 °C for 10 h. The mass ratio of the mixed solution to the mesoporous template was 1:1.4. The sample was then aged at 40 °C for 17 h, then at 100 °C for 22 h, and finally opened and dried at 60 °C for 12 h to obtain sample I.

[0046] (3) Sample I was placed in a tube furnace under an argon atmosphere and heat treated at 900 °C for 4 h, and then naturally cooled to room temperature to obtain sample II;

[0047] (4) 0.078 g of CuSO4·7H2O and 0.136 g of ethylenediamine were mixed and added to 10 mL of methanol and stirred for 0.5 h. Then, 0.67 g of urea was added and stirred for another 1 h to obtain a homogeneous solution. The concentrations of the metal source and nitrogen source in the homogeneous solution were 7.8 g / L and 67 g / L, respectively. The mass ratio of the metal source to the organic ligand was 1:1.75.

[0048] (5) 1 g of sample II was added to the homogeneous solution obtained in step (4), with the mass ratio of sample II to the homogeneous solution being 1:0.3. The samples were evaporated at 80°C for 10 h, then thermally decomposed at 950°C under argon for 4 h, and stirred in HF solution (5 wt%) for 7 h to remove the silicon template. The etched samples were washed, dried at 50°C for 9 h, and the single-atom catalyst material was obtained. The product was named Cu-NC.

[0049] 25 mg of Cu-NC and 75 mg of elemental sulfur powder were mixed and heat treated at 155°C for 12 h under vacuum to obtain a lithium-sulfur battery sulfur positive electrode composite material with single-atom material Cu-NC as the carrier material. The electrochemical performance of the sulfur battery sulfur positive electrode composite material was tested in the same manner as in Example 1. Figure 4 It can be seen that at a current density of 1C, the lithium-sulfur battery has an initial specific capacity of 968.84mAh / g. After 100 cycles, the capacity remains at 777.72mAh / g, with a capacity retention rate of up to 80.27%.

[0050] Example 7

[0051] A method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery comprises the following steps:

[0052] (1) 4 mg of sucrose was dissolved in 6 ml of trimethylbenzene, and then 40 mg of oxalic acid was added and stirred to form a mixed solution; the mass concentrations of furfuryl alcohol and oxalic acid in the mixed solution were 11% and 90%, respectively;

[0053] (2) 1600 μL of the mixed solution was added to 3 g of the mesoporous template SBA-15 and immersed at 35 °C for 11 h. The mass ratio of the mixed solution to the mesoporous template was 1:3.2. The sample was then aged at 50 °C for 18 h, then aged at 120 °C for 23 h, and finally opened and dried at 50 °C for 14 h to obtain sample I.

[0054] (3) Sample I was placed in a tube furnace under an argon atmosphere and heat treated at 950°C for 4 h, and then naturally cooled to room temperature to obtain sample II;

[0055] (4) 0.088 g of FeSO4·5H2O and 0.176 g of glycine were mixed and added to 10 mL of methanol and stirred for 0.5 h. Then, 0.68 g of 2-methylimidazole was added and stirred for another 2 h to obtain a homogeneous solution. The concentrations of the metal source and the nitrogen source in the homogeneous solution were 8.8 g / L and 68 g / L, respectively. The mass ratio of the metal source to the organic ligand was 1:2.

[0056] (5) 1 g of sample II was added to the homogeneous solution obtained in step (4), with the mass ratio of sample II to the homogeneous solution being 1:0.5. The samples were evaporated at 70°C for 10 h, then thermally decomposed at 1050°C under argon for 4 h, and stirred in HF solution (5 wt%) for 8 h to remove the silicon template. The etched sample was washed, filtered, and dried at 60°C for 8 h to obtain a single-atom catalyst material, which was named Fe-NC.

[0057] 25 mg of Fe-NC and 75 mg of elemental sulfur powder were mixed and heat treated at 155 ° C for 12 h under vacuum to obtain a lithium-sulfur battery sulfur positive electrode composite material with single-atom material Fe-NC as the carrier material. The electrochemical performance of the sulfur battery sulfur positive electrode composite material was tested in the same way as in Example 1. Figure 5 It can be seen that at a current density of 1C, the lithium-sulfur battery has an initial specific capacity of 899.52mAh / g. After 100 cycles, the capacity remains at 762.581mAh / g, with a capacity retention rate of up to 84.77%.

Claims

1. A method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery, characterized in that: The following steps are involved: (1) dissolving a carbon source in an organic solvent, adding an organic acid, and stirring to form a mixed solution; the organic acid is oxalic acid or formic acid; the carbon source is one of sugar alcohol, glucose, and sucrose; (2) The mixed solution prepared in step (1) was added to a mesoporous template, immersed for a period of time, then aged at low temperature and then aged at high temperature, and finally dried to obtain sample I; the mesoporous template was SBA-15; the low temperature aging temperature was 40-50°C, and the high temperature aging temperature was 90-120°C; (3) Sintering sample I in a sintering atmosphere and naturally cooling to room temperature to obtain sample II; the sintering temperature is 850-950°C; (4) The metal source and the organic ligand are mixed and added to pure methanol, stirred, and then a nitrogen source is added, and stirred to form a uniform solution; the metal source is one of ferrous sulfate, cobalt sulfate, copper sulfate, and nickel acetate; the organic ligand is one of 1,10-phenanthroline, ethylenediamine, and glycine; (5) Sample II is added to the uniform solution obtained in step (4), and the monoatomic catalyst material is obtained by evaporating, sintering in a sintering atmosphere, etching, washing, filtering, and drying.

2. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1, characterized in that: In step (1), the mass concentrations of the carbon source and the organic acid in the mixed solution are 9-11% and 70-90%, respectively.

3. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (2), the mass ratio of the mixed solution to the mesoporous template agent is in the range of 1:(1-4), the immersion temperature is 25-35°C, and the immersion time is 10-12h.

4. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (2), the low-temperature aging time is 16-18 hours; the high-temperature aging time is 19-23 hours; the drying temperature is 50-60°C, and the drying time is 12-14 hours.

5. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (3), the sintering time is 3-5 hours.

6. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (4), the nitrogen source is one of dimethylimidazole and urea.

7. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (4), the concentrations of the metal source and the nitrogen source in the homogeneous solution are in the range of 5.5-10 g / L and 65-70 g / L, respectively; and the mass ratio of the metal source to the organic ligand is in the range of 1:(1-3).

8. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (5), the mass ratio of sample II to the uniform solution is in the range of 1:(0.1-0.5).

9. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (3) and step (5), the sintering atmosphere is one of nitrogen, argon, and argon / hydrogen mixed atmosphere; in step (5), the sintering temperature is 900-1050° C., and the sintering time is 4-5 h.

10. The method for preparing a single-atom catalyst material for a sulfur positive electrode of a lithium-sulfur battery according to claim 1 or 2, characterized in that: In step (5), the evaporation process parameters are: evaporation temperature is 70-80°C, and evaporation time is 8-10 hours; the etching process parameters are: hydrofluoric acid etching, and etching time is 6-8 hours; the drying process parameters are: drying temperature is 40-60°C, and drying time is 8-12 hours.

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