Preparation method and application of a few-layer transition metal chalcogenide compound with sulfur vacancy point defect

Abstract

The present invention discloses a preparation method and application of a transition metal sulfide having a sulfur vacancy point defect. The preparation method creatively adopts a step-by-step stripping technology, namely a secondary stripping technology, to realize the preparation of a few-layer two-dimensional material having a sulfur vacancy point defect. In the secondary shear stripping process, the shear stripping can realize the separation of material layers and the formation of sulfur vacancy point defects while maintaining the crystal structure of the transition metal sulfide. The prepared TMDs negative electrode material with point defects effectively promotes the diffusion of sodium ions and increases the storage sites of sodium ions, so that the material exhibits excellent electrochemical performance in the assembled sodium ion battery. The method of preparing TMDs with point defects by using the shear stripping technology is simple and feasible, suitable for large-scale production and preparation, and the prepared materials have great application prospects in the fields of power batteries and catalysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of alkali metal ion battery energy storage, and more specifically, relates to a preparation method and application of a few-layer transition metal sulfide compound with sulfur vacancy point defects. Background Art

[0002] Transition metal chalcogenides (TMDs) such as molybdenum disulfide and cobalt disulfide have been widely explored and applied in the field of alkali metal ion batteries due to their high theoretical capacity. TMDs have a high theoretical capacity that fully meets the high capacity requirements of sodium ion batteries for anode materials; however, TMDs have the characteristics of poor stacking structure and poor conductivity. During the charge and discharge process of sodium ion batteries, severe volume changes will occur, resulting in slow reaction kinetics, rapid capacity decay and severe polarization of the anode. For example, molybdenum disulfide (MoS 2 ) has a theoretical capacity of 670 mAh g -1 , whose layered structure can effectively insert and store sodium ions, is a particularly promising anode material for sodium-ion batteries. 2 The poor stacking structure and poor conductivity lead to severe volume changes during the charge and discharge process, which will cause MoS 2 The anode has slow reaction kinetics, fast capacity decay and severe polarization. Researchers have also done a lot of research to solve the above problems, such as constructing few-layer or single-layer MoS 2 It can effectively alleviate volume expansion and improve the sodium storage stability of the material. 2 It is reported that S vacancies in TMDs can reduce the electrostatic repulsion between nearby layers, directly break the barrier of ion diffusion and migration, and promote Na + embedding and reaction. In addition, during the reaction, S vacancies serve as storage sites for anchoring sodium ions, which can improve the conductivity of sulfides. At present, the main methods for preparing S vacancies include controlled solvothermal growth, plasma bombardment, chemical etching, etc. However, these traditional S vacancy introduction methods require high energy input and uncontrollable processing dynamics, which leads to complex preparation conditions and high costs for the preparation of S vacancies. Therefore, it is urgent to develop a simple and low-cost method for preparing transition metal sulfides with sulfur vacancy defects to promote the development and application of TMDs negative electrode materials in sodium ion batteries. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects and shortcomings in the prior art and to provide a method for preparing a few-layer transition metal sulfide having sulfur vacancy point defects.

[0004] The second object of the present invention is to provide application of the preparation method.

[0005] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0006] The present invention first provides a method for preparing a transition metal sulfide having a sulfur vacancy point defect, comprising the following steps:

[0007] S1. uniformly dispersing the transition metal sulfide in a stripping solvent to obtain a solution;

[0008] S2. The solution prepared in S1 is placed in an ice bath for the first shear stripping, and the stripped solution is allowed to stand to obtain a supernatant;

[0009] S3. Add metal salt to the supernatant obtained in S2, perform a second shear stripping in an ice bath, wash and dry the stripped solution, and obtain a transition metal sulfide with sulfur vacancy site defects.

[0010] Mechanical shear stripping technology is a universal two-dimensional material stripping technology. It uses shear force to achieve effective stripping of layers in two-dimensional layered materials, thereby achieving effective preparation of few-layer two-dimensional materials. The present invention creatively proposes a step-by-step stripping technology, namely a secondary stripping technology. The first stripping breaks the van der Waals force of the material and achieves layer-by-layer fracture of the material. Metal salts are added to the stripping solvent of the second shear stripping, and the dual effects of metal ion impact and shear force are used to promote the generation of point defects in transition metal chalcogenides. Therefore, by means of this technology, the synthesis and preparation of few-layer TMDs and point defect few-layer TMDs are achieved in turn by regulating the type of stripping solvent in the two shear strippings. In the step-by-step shear stripping process, shear stripping can achieve the separation of material layers and the formation of sulfur vacancy point defects while maintaining the crystal structure of transition metal sulfides, thereby improving the sodium ion diffusion coefficient of transition metal chalcogenides in sodium ion batteries, increasing sodium ion storage sites, and further improving the specific capacity and stability of sodium ion batteries.

[0011] The present invention not only prepares a few-layer sulfide material by adopting a step-by-step stripping technology, but also introduces sulfur vacancy defects during the preparation process, so that a few-layer TMDs material with sulfur vacancy defects is prepared. Constructing a few-layer sulfide material structure can effectively reduce volume expansion and improve sodium storage stability; at the same time, constructing sulfur vacancy defects can effectively improve the intrinsic conductivity of the material, promote sodium ion diffusion and provide abundant sodium storage sites, thereby improving the sodium storage performance of the material. Therefore, the preparation technology of preparing few-layer sulfides with sulfur vacancies by shear stripping is simple to operate and has potential applications in large-scale production and preparation, and the prepared sulfide negative electrode rich in sulfur vacancy defects is an excellent negative electrode material for sodium ion batteries.

[0012] Furthermore, the transition metal sulfide in step S1 includes but is not limited to at least one of molybdenum disulfide, titanium disulfide, tungsten disulfide, cobalt disulfide, and antimony disulfide.

[0013] Preferably, the transition metal sulfide is a bulk material.

[0014] Furthermore, the stripping solution in step S1 includes but is not limited to at least one of water, ethanol, a mixture of water and ethanol, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0015] Preferably, the stripping solution in step S1 is selected from at least one of a mixture of water and ethanol, ethanol, and N-N-dimethylformamide.

[0016] Preferably, the volume ratio of water to ethanol in the water-ethanol mixture is 4:3.

[0017] Furthermore, in step S1, the material-liquid ratio (g / mL) of the transition metal sulfide and the stripping solution is 1:200-400.

[0018] Furthermore, step S1 is to uniformly disperse the transition metal sulfide in the stripping solvent by stirring.

[0019] Furthermore, the rotation speed of the first shearing and peeling in step S2 is in the range of 5000 to 6000 r / min, and the time is 1 to 3 hours.

[0020] Preferably, the rotation speed of the first shearing and peeling in step S2 is in the range of 5000 to 6000 r / min, and the time is 1 to 2 hours.

[0021] Furthermore, the standing time in step S2 is 18 to 30 hours.

[0022] Preferably, the standing time in step S2 is 24 hours.

[0023] Furthermore, in step S3, the concentration ratio (g / L) of the metal salt to the supernatant is 30 to 50:1.

[0024] Furthermore, the metal salt in step S3 includes but is not limited to at least one of ferric nitrate, cobalt nitrate and copper nitrate.

[0025] Furthermore, the rotation speed of the second shearing and peeling in step S3 is in the range of 5000 to 6000 r / min, and the time is 0.3 to 1 h.

[0026] Preferably, the rotation speed range of the second shearing and peeling in step S3 is 5000-6000 r / min, and the time is 0.5 h.

[0027] Furthermore, the washing in step S3 is suction filtration washing, and the solvent used includes water or ethanol; the drying is vacuum drying, and the drying temperature is 80-120° C. and the time is 10-24 hours.

[0028] Preferably, the drying is vacuum drying at 100-120° C. for 12 hours.

[0029] The present invention also provides a transition metal sulfide having a sulfur vacancy point defect prepared by any of the above-mentioned preparation methods.

[0030] The present invention also provides the use of the transition metal sulfide with sulfur vacancy point defects as a negative electrode material in the preparation of a sodium ion battery.

[0031] Furthermore, the electrolyte of the sodium ion battery includes sodium salt, solvent and additives.

[0032] Preferably, the sodium salt is selected from fluorine-containing sodium salts, boron-containing sodium salts and other sodium salts (NaClO 4 ) etc. The fluorine-containing sodium salt includes NaPF 6 , NaOTF, NaFSI, NaTFSI, etc., boron-containing sodium salts include NaBF 4 , NaBOB, NaDFOB, etc.

[0033] Preferably, the solvent includes at least one of the following: an ether solvent and an ester solvent. The ether solvent includes ethylene glycol dimethyl ether and dioxolane, and the lipid solvent includes propylene carbonate, ethylene carbonate and diethyl carbonate.

[0034] Preferably, the additive is selected from at least one of the following: fluoroethylene carbonate, vinylene carbonate, propane sultone, etc.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a method for preparing a transition metal sulfide with sulfur vacancy point defects. The present invention creatively adopts a step-by-step stripping technology to prepare a few-layer two-dimensional material with point defects. On the basis of conventional shear stripping, a shear stripping is added, and metal salt is added during the second shear stripping process, and the dual effects of metal ion impact and shear force are used to promote the generation of point defects in transition metal sulfide. In the secondary shear stripping process of the present invention, shear stripping can achieve the separation of material layers and the formation of sulfur vacancy point defects under the premise of maintaining the crystal structure of transition metal sulfide, improve the sodium ion diffusion coefficient of transition metal sulfide in sodium ion battery, increase sodium ion storage sites, and further improve the specific capacity and stability of sodium ion battery. The method is simple to operate and low in cost, and the sulfur vacancy layered material prepared by the method can significantly overcome the problems of slow reaction kinetics and insufficient specific capacity of TMDs materials in sodium ion batteries, so that the prepared sulfide negative electrode for sodium ion battery rich in sulfur vacancy defects has high specific capacity and high rate performance, is an excellent sodium ion battery negative electrode material, and has potential application value for large-scale production and preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the shear peeling equipment.

[0038] Figure 2 XRD characterization of the material prepared in Example 1.

[0039] Figure 3 TEM characterization of the material prepared in Example 1.

[0040] Figure 4 This is the spherical aberration electron microscopy characterization of the material prepared in Example 1.

[0041] Figure 5 This is the XPS graph of the material prepared in Example 1.

[0042] Figure 6 The rate and cycle performance of the sodium ion battery assembled using the negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0044] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0045] Example 1 Preparation of Molybdenum Disulfide (E-Mo-2-50-0.5) with Point Defects

[0046] Molybdenum disulfide with point defects was prepared by shear stripping. Molybdenum disulfide was uniformly dispersed in a mixture of water and ethanol (water: ethanol volume ratio = 4:3), the mass of molybdenum disulfide and the volume ratio of the mixture was 1g / 400mL, the shear stripping speed was 6000r / min, and the time was 2h (in an ice bath); after the stripping was completed, the solution was allowed to stand for 24h, cobalt nitrate was added to the supernatant, and the concentration ratio of cobalt nitrate to the supernatant was 50g / L. After the cobalt nitrate was completely dissolved, the stripping was continued in an ice bath, and the shear stripping speed was 6000r / min, and the time was 0.5h; after the stripping was completed, the filter was washed, and finally the solid obtained by the filter was placed in a vacuum oven at 100℃ and dried for 12h.

[0047] Example 2 Preparation of titanium disulfide with point defects (E-Ti-1-40-0.5)

[0048] Titanium disulfide with point defects was prepared by shear stripping. Titanium disulfide was uniformly dispersed in ethanol, the mass ratio of titanium disulfide to ethanol volume was 1g / 400mL, the shear stripping speed was 5000r / min, and the time was 1h (in an ice bath); after stripping, the solution was allowed to stand for 24h, and ferric nitrate was added to the supernatant liquid, the concentration ratio of ferric nitrate to the supernatant liquid was 40g / L, and after the ferric nitrate was completely dissolved, the stripping was continued in an ice bath, the shear stripping speed was 5000r / min, and the time was 0.5h; after stripping, the solution was filtered and washed, and finally the solid obtained by filtration was placed in a vacuum oven at 120°C and dried for 12h.

[0049] Example 3 Preparation of cobalt disulfide with point defects (E-Co-2-30-0.5)

[0050] Cobalt disulfide with point defects was prepared by shear stripping. Cobalt disulfide was uniformly dispersed in NN dimethylformamide, the mass ratio of cobalt disulfide to volume ratio of NN dimethylformamide was 1.5g / 300mL, the shear stripping speed was 5500r / min, and the time was 2h (in an ice bath); after stripping, the solution was allowed to stand for 24h, copper nitrate was added to the supernatant, and the concentration ratio of copper nitrate to the supernatant was 30g / L. After the copper nitrate was completely dissolved, the stripping was continued in an ice bath, and the shear stripping speed was 5500r / min, and the time was 0.5h; after stripping, the solution was filtered and washed, and finally the solid obtained by filtration was placed in a vacuum oven at 100°C and dried for 12h.

[0051] Example 4 Preparation of cobalt disulfide with point defects (E-Co-2-30-0.5)

[0052] Cobalt disulfide with point defects was prepared by shear stripping. Cobalt disulfide was uniformly dispersed in ethanol, the mass ratio of cobalt disulfide to ethanol volume was 1g / 350mL, the shear stripping speed was 6000r / min, and the time was 2h (in an ice bath); after stripping, the solution was allowed to stand for 24h, cobalt nitrate was added to the supernatant, and the concentration ratio of cobalt nitrate to the supernatant was 30g / L. After the cobalt nitrate was completely dissolved, the stripping was continued in an ice bath, and the shear stripping speed was 6000r / min, and the time was 0.5h; after stripping, the solid was filtered and washed, and finally the filtered solid was placed in a vacuum oven at 100°C and dried for 12h.

[0053] Test Example 1 Basic Characterization of Materials

[0054] The present invention prepares transition metal chalcogenides with point defects by shear exfoliation method. Figure 1 It is a schematic diagram of the shear stripping equipment. On the one hand, the shear stripping technology will not destroy the crystal structure of the transition metal chalcogenide, and this technology is simple to operate and low in cost. It can expand the interlayer spacing of the transition metal chalcogenide and improve the specific capacity of the sodium ion battery. On the other hand, during the shear stripping process, metal salts are added to the solvent, and the dual effects of metal ion impact and shear force are used to promote the generation of point defects in the transition metal chalcogenide to increase the sodium ion diffusion coefficient of the transition metal chalcogenide in the sodium ion battery, increase the sodium ion storage sites, and further improve the specific capacity and stability of the sodium ion battery. The present invention performs XRD, TEM, and spherical aberration electron microscopy characterization on the materials prepared in Example 1, and the results are as follows:

[0055] From XRD( Figure 2 ) The results show that the XRD peak of MoS2 after shearing and peeling is consistent with the position of the standard peak, and the crystal structure has not changed. From the TEM characterization ( Figure 3 ) It can be seen that the lattice constant of the shear-peeled MoS2 is similar to that of the unpeeled MoS2 (P-MoS 2 ) has not changed, further proving that shear peeling will not damage the crystal structure of MoS2. Figure 4 ) characterization results show that there are S vacancies in the MoS2 after shear exfoliation, and we use XPS characterization to find that the Mo3d and S2p of E-Mo-2-50-0.5 after exfoliation shift to lower binding energy ( Figure 5 ), further proving the existence of S vacancies. The presence of these S vacancies can increase the sodium ion diffusion coefficient of MoS2 in sodium ion batteries, increase the storage sites of sodium ions, and thus improve the specific capacity of sodium ion batteries.

[0056] Test Example 2 Electrochemical Performance Characterization

[0057] The prepared samples were electrochemically characterized. A CR2035 coin cell shell was used, and the counter electrode was sodium at room temperature. The electrolyte was 1.0 M NaClO 4 Ethylene carbonate / propylene carbonate and 5wt% fluoroethylene carbonate solution (EC / PC, 1:1 vol.%, 5.0% FEC). A mixture of active material, conductive carbon black and binder (carboxymethyl cellulose, CMC) was formed into a slurry according to E-Mo-2-50-0.5: carbon black: CMC = 7:2:1 to prepare a working electrode, and the slurry was evenly pasted on a copper foil collector. The button battery was assembled in a glove box filled with argon, and the humidity and oxygen concentration were both less than 1ppm. After assembly, the electrochemical performance of the battery was tested, and constant current charging and discharging was adopted, with the charging cutoff voltage at 3V and the discharging cutoff voltage at 0.1V.

[0058] The performance of sodium ion batteries with different materials at different current densities is shown in Figure 2. Figure 6 As shown in the figure, it is found that the specific capacity of the few-layer sulfide material with point defects (E-Mo-2-50-0.5) at different current densities is significantly higher than that of the material prepared without shear exfoliation (P-MoS 2 ). This result shows that the point defects formed under the dual action of metal salt ions and shear force can promote the diffusion of sodium ions and increase the sodium ion storage sites, thereby improving its specific capacity in sodium ion battery applications.

Claims

1. A method for preparing a transition metal sulfide having a sulfur vacancy defect, characterized in that: The following steps are involved: S1. The transition metal sulfide is uniformly dispersed in a stripping solvent to obtain a solution; the stripping solvent is selected from at least one of water, ethanol, NN dimethylformamide, NN dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; S2. The solution prepared in S1 is placed in an ice bath for the first shear stripping, and the stripped solution is allowed to stand to obtain a supernatant; the speed range of the first shear stripping is 5000 to 6000 r / min, and the time is 1 to 3 h; S3. Add metal salt to the supernatant obtained in S2, perform a second shear stripping in an ice bath, wash and dry the stripped solution to obtain a transition metal sulfide with sulfur vacancy site defects; the concentration ratio (g / L) of the metal salt to the supernatant is 30 to 50:1; the rotation speed range of the second shear stripping is 5000 to 6000 r / min, and the time is 0.3 to 1 h.

2. The preparation method according to claim 1, characterized in that: In step S1, the transition metal sulfide is selected from at least one of molybdenum disulfide, titanium disulfide, tungsten disulfide, cobalt disulfide and antimony disulfide.

3. The preparation method according to claim 1, characterized in that: The standing time in step S2 is 18 to 30 hours.

4. The preparation method according to claim 1, characterized in that: The metal salt is selected from at least one of ferric nitrate, cobalt nitrate and copper nitrate.

5. The preparation method according to claim 1, characterized in that: The washing in step S3 is suction filtration washing, and the solvent used includes water or ethanol; the drying is vacuum drying, and the drying temperature is 80-120° C. and the time is 10-24 hours.

6. A transition metal sulfide having a sulfur vacancy point defect prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the transition metal sulfide having sulfur vacancy point defects as claimed in claim 6 as a negative electrode material in the preparation of a sodium ion battery.

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