A composite material based on single-layer MoS2 and its preparation method, battery negative electrode, and lithium battery

Abstract

The present invention provides a composite material based on a single-layer MoS2 and its preparation method, a battery negative electrode, and a lithium battery, which relates to the field of new battery materials. The preparation method of the composite material of the single-layer MoS2 comprises the following steps: taking a precursor liquid, the precursor liquid containing cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide in a mass ratio of 1: (0.7-1): (1-2); placing the precursor liquid in a gas phase high-pressure reaction device, and then heating it in a protective gas environment to decompose the precursor liquid into a gas phase, and making Co 2+ In situ substitution of Mo 4+ The preparation method of the present invention has a high yield. The resulting composite material has no agglomeration of the MoS2 monolayer and good intrinsic conductivity, and has excellent ion transport capability, which can improve the battery's lithium storage capacity, cycle life, and rate performance.

Description

Technical Field

[0001] The present application relates to the field of new battery materials, and specifically to a composite material based on single-layer MoS2 and a preparation method thereof, a battery negative electrode, and a lithium battery. Background Art

[0002] Currently, the primary anode material for rechargeable lithium-ion batteries (LIBs), widely used in various fields such as electronics and electric vehicles, is graphite. However, graphite's small interlayer spacing (0.334 nm) and anisotropic ion transport channels severely limit further improvements in ion transport capacity. Furthermore, graphite's low theoretical specific capacity (372 mAh / g) cannot meet the growing demand for fast-charging lithium-ion batteries in electronics and electric vehicles. Researchers have conducted extensive research on materials such as metals (Ge, Sn, etc.), transition metal sulfides, transition metal oxides, silicon and its oxides, and graphene in the hope of finding alternative anode materials to graphite. Among these anode materials, MoS2 has attracted considerable attention due to its large interlayer spacing (0.62 nm) and high theoretical capacity (670 mAh / g). General MoS2 (such as few-layer MoS2, with a band gap generally between 1.2 and 1.9 eV) is a layered material, which is formed by strong covalent bonds or ionic bonds within the same layer. The specific structure is a sandwich layer formed by a layer of Mo atoms in the middle and a layer of S atoms on each side; the layers are combined together by van der Waals forces; while single-layer MoS2 is a material with only one layer of sandwich structure. The difference between single-layer MoS2 and general MoS2 with a few-layer MoS2 structure is similar to the difference between graphite and graphene.

[0003] Currently, the preparation routes of single-layer MoS2 are divided into two categories: (1) growing and depositing a single-layer MoS2 film on a substrate, including the use of chemical vapor deposition, epitaxy, and magnetron sputtering; (2) bulk exfoliation to form a single-layer MoS2, including tape exfoliation, liquid ultrasonication, and chemical exfoliation.

[0004] However, the single-layer MoS2 film synthesized in (1) is not suitable for use as a negative electrode for LIBs; the single-layer MoS2 synthesized using (2) has a low yield, and the single-layer MoS2 is very easy to agglomerate, and needs to be dispersed in a solution for use. In addition, the single-layer MoS2 synthesized using (2) still has the inherent technical problem of poor intrinsic conductivity. Summary of the Invention

[0005] The embodiments of the present application provide a composite material based on a single-layer MoS2 and a preparation method thereof, a battery negative electrode, and a lithium battery. The preparation method has a high yield, and the single-layer MoS2 in the generated composite material does not agglomerate and has good intrinsic conductivity and good ion transport capability. When used as a negative electrode of a lithium-ion battery, the capacity, rate performance and cycle stability of the lithium-ion battery can be improved, meeting the requirements of high energy and high power density.

[0006] In the first aspect, the embodiment of the present application provides a method for preparing a composite material based on a single-layer MoS2, which comprises the following steps: taking a precursor liquid, wherein the precursor liquid contains cobalt isooctanoate, ammonium tetrathiomolybdate and N, N-dimethylformamide in a mass ratio of 1: (0.7-1): (1-2); placing the precursor liquid in a gas phase high-pressure reaction device, and then heating it in a protective gas environment to decompose the precursor liquid into a gas phase, and to make Co 2+ In situ substitution of Mo 4+ .

[0007] The applicant found that although the existing single-layer MoS2 is a single-layer structure, van der Waals forces are still easily generated between the layers, resulting in the macroscopic manifestation of the single-layer MoS2 being prone to agglomeration and stacking when stacked to form MoS2 powder and not easy to disperse; and the van der Waals forces between the layers lead to the macroscopic anisotropy of the MoS2 powder, making the material's ion transport capacity unsatisfactory.

[0008] In the above technical solution, N, N-dimethylformamide can dissolve ammonium tetrathiomolybdate and cobalt isooctanoate. Ammonium tetrathiomolybdate in the precursor liquid can provide both Mo and S sources to ensure that MoS2 can be generated in the subsequent reaction. The cobalt isooctanoate in the precursor liquid is liquid and will produce Co after being dissolved in N, N-dimethylformamide. 2+ , in a gas phase high pressure environment, Co 2+ Will replace part of Mo in situ 4+ , the MoS2 layer structure thus generated has a negative charge, and at this time 2+ Coordinated negatively charged gaseous group (CH3)2C(CH2)4COOH - ) will cooperate with the negatively charged layer structure to build an interlayer electrostatic repulsion. When the electrostatic repulsion is much greater than the van der Waals force between MoS2 layers, Co-doped 2+Furthermore, upon cooling, the gaseous radicals transform into a carbon matrix, allowing the single-layer MoS2 to embed within the carbon matrix. This carbon matrix prevents further aggregation and stacking of the single-layer MoS2, while also enhancing the composite's electrical conductivity. This single-layer MoS2-based composite material, as a lithium-ion battery negative electrode, can improve capacity, rate capability, and cycle stability, achieving high energy and power density requirements, and has broad application prospects.

[0009] In addition, in the present application embodiment, the mass ratio of cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide needs to be controlled within a suitable range; If cobalt isooctanoate is less, the electrostatic repulsion between layers is not enough to resist van der Waals force, and what is formed is a few layers of MoS with multiple layer structures , this few layers of MoS The composite material formed is easily agglomerated, not easy to disperse, and there is anisotropy between the layer structures of few layers of MoS, which is unfavorable for the transport of ions. If cobalt isooctanoate is more, in addition to producing a single layer of MoS , Co 3 S 4 structure will also be generated, which is also unfavorable for the transport of ions. If the amount of N,N-dimethylformamide is less, ammonium tetrathiomolybdate is not easy to dissolve; If the amount of N,N-dimethylformamide is more, it is unfavorable for improving the lithium storage capacity of the composite material, because carbon mainly comes from the conversion of N,N-dimethylformamide under gas phase high pressure, MoS 2 capacity is higher than carbon material, and the higher the carbon content, the lower the lithium storage capacity.

[0010] In a possible implementation, the reaction is carried out in a tube furnace, and the reaction temperature is 500-550° C., and the reaction time is 5-120 min.

[0011] In the above technical solution, in the tube furnace, the above reaction temperature and reaction time ensure that the precursor liquid can be decomposed into a gas phase.

[0012] In a possible implementation, the temperature is lowered to 10-30°C.

[0013] In a possible implementation, the protective gas is at least one of nitrogen and argon.

[0014] In a second aspect, an embodiment of the present application provides a composite material based on a single layer of MoS2, which is prepared by the above-mentioned method for preparing a composite material based on a single layer of MoS2.

[0015] In the above technical solution, the composite material based on single-layer MoS2 prepared using the above method is easy to disperse, has many lithium storage sites and has good ion transport capacity. When used as the negative electrode of a lithium-ion battery, it can improve the capacity, rate performance and cycle stability of the lithium-ion battery, and meet the requirements of high energy and high power density.

[0016] In a third aspect, the present invention provides a composite material based on a single-layer MoS2, which includes a carbon matrix and a single-layer MoS2 embedded in the carbon matrix; the single-layer MoS2 is doped with Co 2+ , and Co 2+ It accounts for 10% to 15% of the MoS2 atomic percentage.

[0017] In the above technical solution, in the above composite material, the single layer MoS2 is doped with Co 2+ , and Co 2+ It accounts for 10% to 15% of the atomic percentage of MoS2, so that the layers of the single-layer MoS2 have electrostatic repulsion, so that the entire composite material has good dispersion and ion transport properties, and the entire Co 2+ The macroscopic manifestation of doped monolayer MoS2 is: band gap is 0eV.

[0018] In a possible implementation, the single-layer MoS2 is in the shape of an elongated strip, and the length of the single-layer MoS2 is 2 to 10 nm.

[0019] In a fourth aspect, an embodiment of the present application provides a battery negative electrode, which contains the above-mentioned single-layer MoS2-based composite material.

[0020] In the above technical solution, the battery negative electrode containing the above-mentioned single-layer MoS2-based composite material can improve the capacity, rate performance and cycle stability of the lithium-ion battery.

[0021] In a fifth aspect, an embodiment of the present application provides a lithium battery comprising the battery negative electrode according to the fourth aspect.

[0022] In the above technical solution, the battery in the embodiment of the present application has the performance of high energy and high power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is an SEM image of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0025] Figure 2 TEM image of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0026] Figure 3This is the Raman graph of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0027] Figure 4 This is the XRD pattern of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0028] Figure 5 This is the full XPS spectrum of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0029] Figure 6 This is the XPS spectrum of Co 2p of the single-layer MoS2 and carbon composite material in Example 1 of the present application;

[0030] Figure 7 TEM image of the few-layer MoS2 and carbon composite material in Comparative Example 1 of the present application;

[0031] Figure 8 This is an SEM image of the MoS2 and carbon composite material in Comparative Example 2 of the present application;

[0032] Figure 9 TEM image of the MoS2 and carbon composite material in Comparative Example 2 of the present application;

[0033] Figure 10 for Figure 9 Magnified image of medium and fine particles;

[0034] Figure 11 yes Figure 9 Enlarged view of the particles in the middle block;

[0035] Figure 12 The first charge-discharge curve of the battery negative electrode made using the composite material of Example 1 of the present application at a current density of 0.1 A / g;

[0036] Figure 13 This is a cycling curve of a battery negative electrode made using the composite material of Example 1 of the present application at a current density of 0.1 A / g;

[0037] Figure 14 This is a cycling curve of a battery negative electrode made using the composite material of Example 1 of the present application at a current density of 5 A / g;

[0038] Figure 15 This is the rate performance curve of the battery negative electrode made using the composite material of Example 1 of the present application;

[0039] Figure 16 The rate performance curve of the battery negative electrode prepared using the composite material of Comparative Example 1 of the present application;

[0040] Figure 17The rate performance curve of the battery negative electrode prepared using the composite material of Comparative Example 2 of the present application;

[0041] Figure 18 The figure is a curve showing the relationship between energy density and charging time of a lithium battery made using the composite material of Example 1 of the present application;

[0042] Figure 19 This is a cycling stability curve of a lithium battery made using the composite material of Example 1 of the present application at a current density of 4C;

[0043] Figure 20 Schematic diagram of the effect of Co doping on the lithium ion diffusion energy barrier on the monolayer MoS2 plane in the composite material of Example 1 of the present application;

[0044] Figure 21 Schematic diagram of the curve showing the effect of Co doping on the density of states of single-layer MoS2 in the composite material of Example 1 of the present application. DETAILED DESCRIPTION

[0045] The applicant found that although the existing single-layer MoS2 is theoretically a single-layer structure, after the single-layer MoS2 is used to form a powder, there are still van der Waals forces between the single-layer MoS2 layers. Therefore, the powder formed by it still has the technical problems existing in the few-layer MoS2, such as being extremely easy to agglomerate and needing to be dispersed in a solution for use; and the intrinsic conductivity of the single-layer MoS2 is also poor, making it difficult to directly apply it to fields such as batteries.

[0046] Based on this, the applicant proposed a solution, which is to dope Co between the monolayer MoS2 2+ , which makes the MoS2 layer structure have electrostatic repulsion that can counteract the van der Waals force, and the single layer MoS2 is embedded in the carbon matrix, thus forming a composite material with good dispersion and excellent electrical conductivity, which can be actually used in the battery field.

[0047] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0048] The following is a detailed description of the composite material based on single-layer MoS2 and its preparation method in the embodiment of the present application.

[0049] The preparation method of the composite material based on the single-layer MoS2 includes the following steps: taking a precursor liquid, wherein the precursor liquid contains cobalt isooctanoate, ammonium tetrathiomolybdate and N, N-dimethylformamide in a mass ratio of 1: (0.7-1): (1-2); placing the precursor liquid in a gas phase high-pressure reaction device, and then heating it in a protective gas environment to decompose the precursor liquid into a gas phase, and make Co 2+ In situ substitution of Mo 4+ , then cool down.

[0050] In the method of the embodiment of the present application, N,N-dimethylformamide can dissolve ammonium tetrathiomolybdate and cobalt isooctanoate. Ammonium tetrathiomolybdate in the precursor liquid can provide both Mo and S sources to ensure that MoS2 can be generated in the subsequent reaction. Cobalt isooctanoate in the precursor liquid can provide Co 2+ , driven by high pressure in the gas phase, Co 2+ Will replace part of Mo in situ 4 + , the MoS2 layer structure thus generated has a negative charge, and at this time 2+ Coordinated negatively charged gaseous groups (negatively charged gaseous groups are generally (CH3)2C(CH2)4COOH - ) will interact with the negatively charged layer structure to build an interlayer electrostatic repulsion. When the electrostatic repulsion is much greater than the van der Waals force between MoS2 layers, Co-doped 2+ In addition, after cooling, the gaseous groups will be converted into a carbon matrix. In the composite material formed in this way, the single layer of MoS2 will be embedded in the carbon matrix. On the one hand, the carbon matrix can prevent the single layer of MoS2 from agglomerating and stacking, and on the other hand, it can also enhance the conductivity of the composite material. This composite material can be used in lithium batteries.

[0051] During the entire preparation process, it should be noted that, first, the precursor liquid must be liquid, otherwise Co 2+ It is impossible to replace Mo in situ under the driving of gas phase high pressure 4+ Therefore, N, N-dimethylformamide is needed to dissolve cobalt 2-octanoate and ammonium tetrathiomolybdate at the same time; secondly, the mass ratio of cobalt 2-octanoate, ammonium tetrathiomolybdate and N, N-dimethylformamide must be controlled in the range of 1: (0.7~1): (1~2). 2+ If the amount is too small, the electrostatic repulsion is insufficient to counteract the van der Waals force and a single layer of MoS2 cannot be formed. 2+Too much will produce byproducts such as Co3S4, affecting the ion transport capacity of the MoS2 composite material. If the amount of N,N-dimethylformamide is small, ammonium tetrathiomolybdate will not dissolve easily; if the amount of N,N-dimethylformamide is large, it will not be conducive to improving the lithium storage capacity of the composite material. This is because the carbon mainly comes from the conversion of N,N-dimethylformamide under high pressure in the gas phase. The capacity of MoS2 is higher than that of carbon materials. The higher the carbon content, the lower the lithium storage capacity.

[0052] Furthermore, since the reaction is driven by high pressure in the gas phase, it is typically carried out in a tube furnace, with a temperature generally ranging from 500°C to 550°C and a reaction time of 5 to 120 minutes. After the reaction is complete, the temperature is lowered to 10°C to 30°C. The protective gas can be at least one of nitrogen and argon. For example, argon is used in this embodiment.

[0053] The MoS2 composite material prepared by the above method includes a carbon matrix and a single layer of MoS2 embedded in the carbon matrix; the single layer of MoS2 is doped with Co 2+ , and Co 2+ It accounts for 10% to 15% of the atomic percentage of MoS2, so that when the single-layer MoS2 is stacked, there is an electrostatic repulsion between the layers, so that the entire composite material has good dispersion and ion transport properties, and the entire Co 2+ The macroscopic performance of doped monolayer MoS2 is: band gap is 0eV.

[0054] The applicants also discovered that the aforementioned single-layer MoS2 is in the form of elongated strips, 2 to 10 nm in length, and is generally composed of particles with a diameter of 10 to 20 nm. This composite material, when used as a battery negative electrode, can improve the capacity, rate capability, and cycle stability of lithium-ion batteries, enabling them to achieve high energy and power density requirements.

[0055] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0056] Example 1

[0057] This embodiment provides a composite material based on a single layer of MoS2, the preparation method of which is as follows:

[0058] A precursor solution was prepared by mixing cobalt isooctanoate, ammonium tetrathiomolybdate, and N,N-dimethylformamide in a mass ratio of 1:0.8:1.4. This precursor solution was then added to a high-pressure reactor. The reactor was sealed and placed in an argon-protected tube furnace. The reactor was heated to 520°C at a rate of 10°C / min, held for 20 minutes, and then cooled to room temperature (25°C). The high-pressure reactor was then removed and opened to obtain a black powder, which was then stored in a sample bottle.

[0059] After the preparation is completed, the composite material in this embodiment is characterized by using SEM (Scanning Electron Microscope, scanning electron microscope), TEM (Transmission Electron Microscope, transmission electron microscope), infrared spectrometer, XRD (Diffraction of X-rays, X-ray diffraction), and XPS (X-ray Photoelectron Spectroscopy, X-ray photoelectron spectroscopy). The characterization results are shown in FIG. Figures 1 to 6 shown.

[0060] Depend on Figure 1 From the SEM image, it can be seen that the single-layer MoS2 is composed of 10-20nm particles; Figure 2 It can be seen that the long strip-shaped single-layer MoS2 with a length of 2-5nm is evenly dispersed in the carbon substrate without agglomeration. Figure 3 It can be seen that the Raman shift at 380 cm -1 and 400.6cm -1 MoS2 appeared and A 1g peak, the displacement difference is 20.6cm -1 , which again indicates that a single layer of MoS2 is formed. In addition, at 1326.5 cm -1 and 1593.1cm -1 The typical D and G peaks of carbon materials appeared at , which proved the formation of carbon matrix. Figure 4 It can be seen that the diffraction peaks at 33.5° and 58.5° are attributed to the (100) and (110) crystal planes of MoS2, respectively, indicating that a MoS2 structure has been formed. Since the diffraction peak of its (002) crystal plane does not exist, the layer-to-layer stacking structure disappears, further confirming the existence of a single-layer MoS2. Figure 5 It can be seen that Co accounts for 11.52% of the atomic percentage of MoS2. Figure 6 It can be seen that the sample shows clear Co 2p XPS spectra at 793.6 eV and 778.5 eV, which is attributed to the presence of CoMoS, which proves that Co 2+Replace Mo in the form of doping 4+ .

[0061] from Figures 2 to 6 It can be concluded that Co-doped single-layer MoS2 with a length of 2-5 nm is uniformly dispersed in the carbon substrate, and its morphology is particles composed of 10 to 20 nm.

[0062] Example 2

[0063] This embodiment provides a MoS2 composite material, and its preparation method is different from that of Example 1, mainly in that the mass ratio of cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide is 1:1:2.

[0064] Example 3

[0065] This embodiment provides a MoS2 composite material, and its preparation method is different from that of Example 1, mainly in that the mass ratio of cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide is 1:0.7:1.

[0066] Comparative Example 1

[0067] This comparative example provides a MoS2 composite material, and its preparation method is different from that of Example 1, mainly in that the mass ratio of cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide is 1:1.3:3.

[0068] After the preparation, the MoS2 composite material in this comparative example was characterized by TEM, and the results were as follows: Figure 7 As shown. Figure 7 It can be seen that when the amount of cobalt 2-isooctanoate added is small, MoS2 with an interlayer spacing of 1.16 nm and 4 to 6 layers is obtained, indicating that a few-layer MoS2 is obtained. This shows that too little cobalt 2-isooctanoate is added to obtain a single-layer MoS2, but it also shows that when Co 2+ During doping, electrostatic repulsion is formed between layers, which leads to the expansion of the interlayer distance.

[0069] Comparative Example 2

[0070] This comparative example provides a MoS2 composite material, and its preparation method is different from that of Example 1, mainly in that the mass ratio of cobalt isooctanoate, ammonium tetrathiomolybdate and N,N-dimethylformamide is 1:0.6:0.7.

[0071] After the preparation, the MoS2 composite material in Comparative Example 2 was characterized by SEM and TEM, and the results were as follows: Figure 8 and Figures 9 to 11 As shown, Figures 9 to 11 They are all TEM images, but Figure 9 This is a low-magnification TEM photo. Figure 10 yes Figure 9 Enlarged view of small and medium particles, Figure 11 yes Figure 9 Enlarged view of the medium block particles.

[0072] from Figure 8 It can be seen that in addition to particles composed of microparticles with a size of 10 to 20 nm, bulk structures with a scale of about 200 nm also appear. This result shows that the morphology of the obtained sample is uneven.

[0073] from Figure 10 It can be seen that a single layer of MoS2 is formed. Figure 11 It can be concluded that the interlayer spacing of the bulk structure is 0.3 nm, which is attributed to the Co3S4 (311) crystal plane, that is, Figure 11 The formation of Co3S4 was proved. Figures 9 to 11 It can be concluded that although single-layer MoS2 can be obtained under the condition of excessive addition of cobalt isooctanoate, there will be a large amount of Co3S4 bulk impurities.

[0074] Application Examples

[0075] The MoS2 composite materials in Example 1 and Comparative Examples 1-2 were respectively used to prepare lithium battery negative electrodes, and the performance of the lithium battery negative electrodes was tested.

[0076] The specific process of the negative electrode of the lithium battery is as follows:

[0077] The composite materials obtained in Example 1 and Comparative Examples 1 to 2 were mixed with acetylene black and polyvinylidene fluoride, respectively, and added to N-methylpyrrolidone for magnetic stirring. After 24 hours, they were evenly applied on the copper foil current collector and then transferred to a vacuum drying oven. They were first dried at 70°C under normal pressure for 5 hours to remove the macromolecular solvent, and then dried at 100°C in vacuum for 10 hours. After completion, the wafers were taken out, cut into 12 mm diameter wafers, and placed in a glove box.

[0078] Electrochemical performance test of lithium battery negative electrode: The performance test of lithium battery negative electrode made of materials of Example 1 and Comparative Examples 1-2 was carried out by constant current charge and discharge method. The test results of Example 1 are as follows: Figures 12 to 15 As shown, the test results of Comparative Example 1 are as follows Figure 16 As shown, the test results of Comparative Example 2 are as follows Figure 17 shown.

[0079] from Figure 12 It can be shown that the reversible capacity of the battery negative electrode corresponding to Example 1 after the first charge and discharge is 1512.9 mAh / g.

[0080] from Figure 13It can be seen that at a current density of 0.1 A / g, the reversible capacity of the battery negative electrode corresponding to Example 1 is as high as 1661.6 mAh / g after 300 cycles, and the corresponding capacity retention rate is 109.8%.

[0081] from Figure 14 It can be seen that at a current density of 5 A / g, the reversible capacity of the battery negative electrode corresponding to Example 1 is as high as 1115.2 mAh / g after 3000 cycles, and the corresponding capacity retention rate is 92.0%.

[0082] from Figure 15 It can be seen that the capacities obtained by the battery negative electrode at current densities of 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, 5A / g, 10A / g and 20A / g are 1512.9mAh / g, 1470.5mAh / g, 1362.3mAh / g, 1315.6mAh / g, 1233.1mAh / g, 1164.1mAh / g and 1063.3mAh / g, respectively. In particular, when the current density returns to 0.1A / g, its reversible capacity is still as high as 1517.2mAh / g.

[0083] Depend on Figures 12 to 15 It can be seen that the battery negative electrode made of the composite material based on the single-layer MoS2 of this embodiment has ultra-high lithium storage capacity, outstanding cycle life and rate performance.

[0084] from Figure 16 It can be seen that the battery negative electrode prepared based on the composite material obtained in Comparative Example 1 has a lower capacity than that in Example 1 at different current densities, indicating that the lithium storage performance of the few-layer MoS2 prepared with a small amount of cobalt isooctanoate is not as good as the MoS2 prepared in Example 1, which shows that the composite material of single-layer MoS2 has better fast charging performance than the composite material of few-layer MoS2.

[0085] from Figure 17 It can be seen that the battery negative electrode prepared based on the composite material obtained in Comparative Example 2 has a lower capacity than that in Example 1 at different current densities, indicating that the energy storage performance of MoS2 prepared with excess cobalt isooctanoate is not as good as that of MoS2 prepared in Example 1. This result shows that the presence of a large amount of Co3S4 block impurities will reduce the fast charging performance of single-layer MoS2.

[0086] Lithium battery performance test

[0087] A lithium battery was prepared using the negative electrode material based on Example 1, and performance testing was continued. The positive electrode of the lithium battery used commercial LiFePO4 material, prepared by coating aluminum foil with a mixture of 95.0% by mass LiFePO4, 2.5% by mass polyvinylidene fluoride, and 2.5% by mass acetylene black.

[0088] Before assembling the battery anode into a lithium battery, the battery anode was activated for three cycles in a half-cell at 0.1 A / g to improve its coulombic efficiency. The N / P ratio of the full cell was 1.06. The mass loading of the anode active material was 2.0 mg / cm 2 , the mass loading of the positive electrode is 16.4 mg / cm 2 The tested current density is 0.1~4C (1C=170mA / g).

[0089] The performance of lithium batteries is tested using the constant current charge and discharge method. The specific results are as follows: Figures 18 and 19 shown.

[0090] from Figure 18 It can be seen that the energy density at a current density of 0.1C is 177.8Wh / kg, and it takes only 11.5 minutes to fully charge at a current density of 4C, with an energy density of 136.2Wh / kg. Compared with the capacity retention rate of 76.6% under the current density of 0.1C, this result shows that the composite material based on single-layer MoS2 has excellent fast charging capability.

[0091] from Figure 19 It can be seen that at a current density of 4C, the capacity retention rate of single-layer MoS2 after 500 cycles is 80.2%, indicating that the composite material based on single-layer MoS2 has outstanding cycle stability.

[0092] Bandgap verification

[0093] Density functional theory was used to simulate the single-layer MoS2 in the composite material in Example 1, including the calculation of the lithium ion diffusion energy barrier and state density. The specific results are as follows: Figure 20 and Figure 21 shown.

[0094] from Figure 20 It can be seen that the lithium ion diffusion energy barrier (0.19 eV) of Co-doped monolayer MoS2 is lower than that of monolayer MoS2 (0.28 eV), indicating that Co doping can greatly improve the lithium ion diffusion kinetics, thereby leading to rapid lithium ion transport.

[0095] from Figure 21It can be seen that Co doping atoms can significantly reduce the band gap of monolayer MoS2, achieving high carrier transport. Pure monolayer MoS2 has semiconductor properties with a band gap of 1.30eV, while Co-doped monolayer MoS2 has metallic properties with a band gap of 0eV, which can improve carrier transport capabilities.

[0096] In summary, the composite material based on single-layer MoS2 in the embodiment of the present application has good dispersion performance and conductivity, and is used to prepare the negative electrode of lithium-ion batteries, which can greatly improve the battery performance.

[0097] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a composite material based on a single layer of MoS2, characterized in that: It includes the following steps: A precursor liquid is prepared, wherein the precursor liquid contains cobalt isooctanoate, ammonium tetrathiomolybdate, and N,N-dimethylformamide in a mass ratio of 1:(0.7-1):(1-2); the precursor liquid is placed in a gas phase high pressure reaction device, and then heated in a protective gas environment to decompose the precursor liquid into a gas phase, and Co 2+ In situ substitution of Mo 4+ The reaction is carried out in a tube furnace at a temperature of 500-550°C for 5-120 minutes. The temperature is then lowered to obtain a composite material based on a single-layer MoS2, the composite material comprising a carbon matrix and a single-layer MoS2 embedded in the carbon matrix, wherein the single-layer MoS2 is doped with Co. 2+ .

2. The method for preparing a composite material based on a single layer of MoS2 according to claim 1, characterized in that: Cool down to 10~30℃.

3. The method for preparing a composite material based on a single layer of MoS2 according to claim 1, characterized in that: The protective gas is at least one of nitrogen and argon.

4. A composite material based on a single layer of MoS2, characterized in that It is prepared by the preparation method of the composite material based on single-layer MoS2 according to any one of claims 1 to 3.

5. The composite material based on single-layer MoS2 according to claim 4, Co 2+ It accounts for 10%~15% of MoS2 atomic percentage.

6. The composite material based on single-layer MoS2 according to claim 5, characterized in that The single-layer MoS2 is in the shape of an elongated strip, and the length of the single-layer MoS2 is 2-10 nm.

7. A battery negative electrode, characterized in that: It contains the composite material based on single-layer MoS2 as claimed in claim 5.

8. A lithium battery, characterized in that: It contains the battery negative electrode according to claim 7.

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