A molybdenum-based negative electrode material and its preparation method and application

Abstract

The present invention relates to the technical field of sodium / lithium ion battery negative electrode materials, and discloses a molybdenum-based negative electrode material, a preparation method thereof, and an application thereof. The material comprises nitrogen- and sulfur-coated carbon nanorods, wherein the carbon nanorods are filled with core-shell molybdenum-based nanoscrolls; the core-shell molybdenum-based nanoscrolls comprise a molybdenum dioxide core and a molybdenum disulfide shell with a curved structure, and the number of molybdenum disulfide layers is 12 to 35. The molybdenum-based negative electrode material provided by the present invention consists of a core-shell MoO2-MoS2 nanoscroll with a carbon nanorod coating and internal filling; the MoO2-MoS2 nanoscroll is obtained by homologous conversion of MoO3 nanorods and has a unique core-shell structural feature. The two form a large number of heterogeneous interfaces, providing abundant reaction active sites for storing sodium ions or lithium ions and accelerating the electrochemical reaction kinetics; the MoS2 shell has a curved structural feature, and the number of MoS2 layers is regulated to 12 to 35 layers by limiting the pyrolysis temperature and the amount of sulfur-containing initiator, so as to obtain excellent sodium / lithium storage performance, and has excellent rate performance and cycle stability when used in sodium / lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium / lithium ion battery negative electrode materials, and in particular relates to a molybdenum-based negative electrode material and a preparation method and application thereof. Background Art

[0002] Anode materials play a vital role in the energy density and cycle life of batteries. Molybdenum disulfide (MoS2) has become a highly promising anode material for sodium / lithium ion batteries due to its low cost, large interlayer spacing (~0.62nm), significant pseudocapacitive properties, and theoretical capacity of up to 670mAh / g. However, MoS2 faces many challenges in practical applications, including inherent poor conductivity, slow electrochemical reaction kinetics, large volume changes during charge and discharge cycles, and even structural pulverization, which severely limit its rate performance and cycle stability in sodium / lithium ion batteries.

[0003] Constructing heterostructures is an effective way to overcome the above challenges. By coupling electrode materials with different band gaps to form a stable nanostructure, a built-in electric field is created at the heterojunction interface, which not only reduces the ion diffusion energy barrier but also significantly promotes the redox reaction (Small 2023, 19, 2207919; J. Energy Chem. 2023, 82, 268). Yang et al. found that in Fe 1-x The S / MoS2 heterostructure interface forms an "ion reservoir" that greatly reduces the Na + The diffusion barrier of the Na-ion battery is reduced, thus enhancing the rate performance of the Na-ion battery (Nano-MicroLett.2019,11:80). However, due to the lattice mismatch of different components, the construction of MoS2-based heterostructures is still very challenging. Monoclinic molybdenum dioxide (MoO2) with a tunnel structure has high conductivity (~1.1×10 4 S / cm), which is beneficial to promote charge transfer during the electrochemical reaction (Energy Storage Mater. 2018, 11, 161). At the same time, it has a theoretical capacity of up to 836 mAh / g, as well as pseudocapacitive properties similar to MoS2 (Adv. Energy Mater. 2017, 7, 1602880). These advantages undoubtedly make MoO2 an ideal choice for integration with MoS2 to construct a unique molybdenum-based heterostructure negative electrode material. The existing technology mainly prepares MoO2 materials with a MoS2 layer on the surface by sulfurization and roasting by adding additional sulfur powder as a sulfur source (J. Phys. Chem. C 2014, 118, 18387; Part. Part. Syst. Charact. 2017, 341600223), but the long-term cycle performance of this material as a negative electrode for sodium / lithium ion batteries is poor. Summary of the Invention

[0004] The present invention provides a molybdenum-based negative electrode material and its preparation method and application, which solves the problem of poor long-term cycle performance of MoO2 materials with a surface covered with a MoS2 layer prepared in the prior art when used as the negative electrode of sodium / lithium ion batteries.

[0005] A first aspect of the present invention provides a molybdenum-based negative electrode material comprising nitrogen- and sulfur-co-doped carbon nanorods, wherein the carbon nanorods are filled with core-shell molybdenum-based nanoscrolls;

[0006] The core-shell molybdenum-based nanoscroll includes a molybdenum dioxide core and a molybdenum disulfide shell with a curved structure, and the number of layers of the molybdenum disulfide is 12 to 35.

[0007] The MoO2 in this molybdenum-based anode material is a monoclinic phase, and the MoS2 is a 2H phase. Both are derived from the MoO3 nanorod template in the precursor, forming a large number of heterogeneous interfaces. The MoS2 shell has a curved structure, and the number of layers can be controlled. Too many MoS2 shells hinder the diffusion of sodium and lithium ions into the molybdenum dioxide core, while too few shells prevent the stable core-shell structure from being maintained during charge and discharge.

[0008] The second aspect of the present invention provides a method for preparing the molybdenum-based negative electrode material. The reaction formula involved in the formation process is: 2MoO3+C=2MoO2+CO2↑; 2MoO2+15C+6(NH4)2S2O8=2MoS2+12NH3↑+8SO2↑+15CO2↑+6H2O↑, and the preparation method is:

[0009] MoO3 nanorods were ultrasonically dispersed in deionized water. A nitrogen-containing organic carbon source monomer solution was injected under ice bath and continuous stirring. Then, an ice bath-treated sulfur-containing initiator solution with strong oxidizing properties was added dropwise to initiate a polymerization reaction of the nitrogen-containing organic carbon source. The reaction mixture was directly transferred to an evaporating dish and dried to obtain a molybdenum trioxide-organic polymer precursor with the sulfur-containing initiator uniformly dispersed therein.

[0010] The molybdenum trioxide-organic polymer precursor in which the sulfur-containing initiator is uniformly dispersed is placed in a quartz boat, loaded into a programmed temperature tubular furnace, and protected by inert gas. A confined pyrolysis treatment is performed at 600-800°C to allow the sulfur-containing initiator to in-situ sulfurize the molybdenum trioxide-organic polymer precursor. The material is then cooled in the furnace to obtain the molybdenum-based negative electrode material. The molar ratio of the molybdenum trioxide nanorods, the nitrogen-containing organic carbon source monomer, and the sulfur-containing initiator is 1.0:5-15:1.0.

[0011] Preferably, during the confined pyrolysis, the temperature is first raised from room temperature to 300°C at a rate of 1°C / min for 3 hours to remove adsorbed moisture from the precursor and convert the organic polymer into amorphous carbon. The temperature is then further raised to 600-800°C at a rate of 2-10°C / min for 2-5 hours. During the second heating stage, if the heating rate is too slow, excessive decomposition of the sulfur-containing initiator will occur, while if the heating rate is too fast, insufficient decomposition of the sulfur-containing initiator will occur, both of which are detrimental to the sulfurization of the precursor.

[0012] The present invention does not add an additional sulfur source during the confined pyrolysis, but directly uses the sulfur-containing initiator that has been uniformly dispersed in the molybdenum trioxide-organic polymer precursor in the previous step to achieve in-situ sulfurization of the molybdenum trioxide-organic polymer precursor.

[0013] Preferably, the sulfur-containing initiator is ammonium persulfate.

[0014] Preferably, when preparing the sulfur-containing initiator dispersed molybdenum trioxide-organic polymer precursor, the ammonium persulfate is first prepared into a solution and then the reaction is initiated; wherein the concentration of the ammonium persulfate solution is 1.0 to 3.0 mol / L.

[0015] Preferably, the nitrogen-containing organic carbon source monomer is one or more of pyrrole, aniline, and dopamine hydrochloride.

[0016] Preferably, the preparation method of the molybdenum trioxide nanorods is:

[0017] Molybdate and ferric chloride hexahydrate are added into a dilute nitric acid solution and subjected to a constant temperature hydrothermal reaction to obtain molybdenum trioxide nanorods.

[0018] Preferably, the molar ratio of molybdenum in the molybdate, iron in ferric chloride hexahydrate, and dilute nitric acid is 0.5-4.0:0.01-0.05:1.0-5.0.

[0019] Preferably, the constant temperature hydrothermal reaction is carried out at 150-220° C. for 15-25 hours.

[0020] The third aspect of the present invention protects the use of the molybdenum-based negative electrode material in the negative electrode of a sodium-lithium ion battery or a lithium ion battery.

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

[0022] 1. The molybdenum-based negative electrode material provided by the present invention is a core-shell MoO2-MoS2 nanoscroll composite material filled with carbon nanorods; the MoO2-MoS2 nanoscroll is obtained by homologous transformation of MoO3 nanorods and has a unique core-shell structural feature. The two form a large number of heterogeneous interfaces, providing rich reaction active sites for storing sodium ions or lithium ions and accelerating the electrochemical reaction kinetics; the MoS2 shell has a curved structural feature, and the number of MoS2 layers is regulated to 12 to 35 layers by limiting the pyrolysis temperature and the amount of sulfur-containing initiator, so as to obtain excellent sodium / lithium storage performance, and has excellent rate performance and cycle stability when used in sodium / lithium batteries.

[0023] 2. The preparation method of the molybdenum-based negative electrode material provided by the present invention uses MoO3 nanorods as templates, and coordinates and polymerizes on the surface of the nanorods through nitrogen-containing organic carbon source monomers. After drying, a molybdenum trioxide-organic polymer precursor in which a sulfur-containing initiator is uniformly dispersed is obtained. Then, confined pyrolysis is carried out under high temperature conditions to reduce MoO3 to MoO2, and then controllably sulfurized by decomposition of the sulfur-containing initiator is carried out to form a curved MoS2 coating layer in situ on the surface of the highly conductive MoO2. This method is simple and efficient, and MoO2 and MoS2 are obtained from the in-situ conversion of MoO3, which is very beneficial for constructing a large number of heterogeneous interfaces.

[0024] 3. The present invention directly utilizes the sulfur-containing initiator in the polymerization reaction process as a sulfur source, without the need to add an additional sulfur source, thereby preventing the additional sulfur source from being unable to form core-shell MoO2-MoS2 nanoscrolls, and avoiding the complicated separation and purification process after the polymerization reaction is completed; the sulfur-containing initiator is uniformly dispersed in the molybdenum-based precursor, which is conducive to in-situ sulfurization to form a core-shell structure; the sulfur-containing initiator with strong oxidizing properties partially etches the carbon layer during the pyrolysis process to form a higher porosity, which is conducive to the rapid penetration of the electrolyte in the electrochemical process.

[0025] 4. The molybdenum-based negative electrode material provided by the present invention has high specific capacity, high rate performance and high cycle stability when applied to the negative electrode of sodium ion batteries and lithium ion batteries, showing broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Transmission electron microscopy images of the molybdenum-based negative electrode material prepared in Example 1 at different magnifications: a) 50 nm, b) 10 nm; and c) magnified images of the corresponding core and shell regions of the nanoscroll and d) Fourier transform images;

[0027] Figure 2 Scanning electron micrographs of the molybdenum-based negative electrode material prepared in Example 1 at different magnifications: a) 1 μm, b) 200 nm;

[0028] Figure 3This is a diagram showing the element surface distribution results of the molybdenum-based negative electrode material prepared in Example 1;

[0029] Figure 4 X-ray diffraction patterns of the molybdenum-based negative electrode materials prepared in Example 1: a), Comparative Example 1: b), Comparative Example 2: c), and Comparative Example 3: d);

[0030] Figure 5 Transmission electron microscopy image of the molybdenum-based negative electrode material prepared in Comparative Example 1: a) and selected area electron diffraction image: b);

[0031] Figure 6 Scanning electron microscope images of the molybdenum-based negative electrode material prepared in Comparative Example 2 at different magnifications: a) 1 μm, b) 200 nm;

[0032] Figure 7 Transmission electron micrographs of the molybdenum-based negative electrode material prepared in Comparative Example 2 at different magnifications: a) 50 nm, b) 5 nm;

[0033] Figure 8 Scanning electron microscope images of the molybdenum-based negative electrode material prepared in Comparative Example 3 at different magnifications: a) 1 μm, b) 200 nm;

[0034] Figure 9 Transmission electron micrographs of the molybdenum-based negative electrode material prepared in Comparative Example 3 at different magnifications: a) 50 nm, b) 5 nm;

[0035] Figure 10 The first, second, and third cycle constant current charge-discharge performance curves of the molybdenum-based negative electrode materials prepared in Example 1: a) and Comparative Example 1: b) when used in sodium-ion batteries;

[0036] Figure 11 Graphs showing rate performance of the molybdenum-based negative electrode materials prepared in Example 1: a), Comparative Example 1: b), Comparative Example 2: c), and Comparative Example 3: d) when used in sodium-ion batteries;

[0037] Figure 12 Cycling stability of the molybdenum-based negative electrode materials prepared in Example 1: a) and Comparative Example 1: b) when used in sodium ion batteries at a current density of 0.1 A / g;

[0038] Figure 13 Cycling stability of the molybdenum-based negative electrode materials prepared in Example 1: a) and Comparative Example 1: b) when used in sodium ion batteries at a current density of 1.0 A / g;

[0039] Figure 14 The cyclic stability performance of the molybdenum-based negative electrode material prepared in Example 1 when used in a sodium ion battery at a current density of 5.0 A / g;

[0040] Figure 15 The first, second, and third cycle constant current charge-discharge performance curves of the molybdenum-based negative electrode material prepared in Example 1 when used in a lithium-ion battery: a) and rate performance graph: b);

[0041] Figure 16 The molybdenum-based negative electrode material prepared in Example 1 has a cycling stability when used in a lithium-ion battery at a current density of 0.2 A / g. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the specific implementation of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Unless otherwise specified, the methods described in the embodiments of the present invention are conventional methods. The materials and reagents used are all commercially available unless otherwise specified.

[0044] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural; the single symbol " / " means "or".

[0045] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of A, B or C", or "at least one of A, B and C" can mean any one of A, B, C, or A+B, or A+C, or B+C, or A+B+C, where A, B, and C can be single or multiple, respectively.

[0046] In the following description of this embodiment, the order of serial numbers does not mean the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of this embodiment.

[0047] In the following description of the present embodiment, the numerical range should be understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value in the stated range and any other stated value or intermediate value in the stated range is also included in the present embodiment, and the upper and lower limits of the smaller ranges may be independently included or excluded in the range.

[0048] Unless otherwise indicated, the technical / scientific terms used in this embodiment have the same meanings as those generally understood by those skilled in the art. Although this application only describes preferred methods and materials, any similar or equivalent methods and materials may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0049] The present invention provides a molybdenum-based negative electrode material, its preparation method, and application. MoO3 nanorods are primarily used as templates. Nitrogen-containing organic carbon source monomers coordinate and polymerize on their surfaces, resulting in a molybdenum trioxide-organic polymer precursor uniformly dispersed with a sulfur-containing initiator after drying. Confined pyrolysis is then performed under high-temperature conditions to reduce the MoO3 to MoO2. Further controllable sulfurization is achieved through decomposition of the sulfur-containing initiator, resulting in the in-situ construction of a curved MoS2 coating on the highly conductive MoO2 surface. The prepared molybdenum-based negative electrode material is used as the negative electrode material for sodium / lithium ion batteries.

[0050] The preparation method comprises the following steps:

[0051] Molybdate and ferric chloride hexahydrate were added sequentially to a continuously stirred dilute nitric acid solution. After complete dissolution, a clear and transparent mixed solution was obtained. The mixed solution was then transferred to a polytetrafluoroethylene-lined reactor. After constant temperature hydrothermal reaction and purification treatment, MoO3 nanorods were collected.

[0052] The MoO3 nanorods are ultrasonically dispersed in deionized water, and a nitrogen-containing organic carbon source monomer solution is injected under ice bath and continuous stirring. Then, an ice bath-treated sulfur-containing initiator is added dropwise to initiate a polymerization reaction of the carbon source monomer. The reaction mixture is directly transferred to an evaporating dish and dried to obtain a molybdenum trioxide-organic polymer precursor in which the sulfur-containing initiator is uniformly dispersed.

[0053] The molybdenum trioxide-organic polymer precursor is placed in a quartz boat, loaded into a programmed temperature tubular furnace, and protected by inert gas. It is subjected to confined pyrolysis treatment under high temperature conditions to allow the sulfur-containing initiator to in situ sulfurize the molybdenum-based precursor. The furnace is cooled to obtain a nitrogen and sulfur co-doped carbon-coated MoO2-MoS2 core-shell structure material.

[0054] In a specific embodiment, the molybdate is one or more of ammonium molybdate tetrahydrate, sodium molybdate dihydrate, and potassium molybdate, and the concentration of the formed molybdate solution is 0.05-0.40 mol / L; the concentration of the dilute nitric acid solution is 0.10-0.50 mol / L; the concentration of the ferric chloride hexahydrate solution is 0.001-0.005 mol / L; the nitrogen-containing organic carbon source monomer is one or more of pyrrole, aniline, and dopamine hydrochloride, and the molar ratio of the nitrogen-containing organic carbon source monomer to the molybdenum trioxide template is (5-15):1; the concentration of the sulfur-containing initiator is 1.0-3.0 mol / L; the temperature of the high-temperature pyrolysis is 600-800°C, and the reaction time is 2-5h.

[0055] The abbreviations of some raw materials in the examples of the present invention are:

[0056] Polyvinylidene fluoride: PVDF, N-methyl-2-pyrrolidone: NMP; Polypropylene: PP.

[0057] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0058] Example 1

[0059] A method for preparing a molybdenum-based negative electrode material:

[0060] 0.618 g of ammonium molybdate tetrahydrate (Mo content is 3.5 mmol) and 0.014 g of ferric chloride hexahydrate (Fe content is 0.005 mmol) were weighed and added in sequence to 20 mL of a continuously stirred dilute nitric acid solution with a concentration of 0.25 mol / L. After complete dissolution, a clear and transparent mixed solution was obtained. The solution was then transferred to a 40 mL polytetrafluoroethylene-lined reactor and placed in a 200 ° C oven for constant temperature reaction for 20 hours. After the hydrothermal reaction was completed, the MoO3 nanorods were separated by centrifugation, washed with water and ethanol in sequence, and purified, and then dried to collect.

[0061] 0.144 g MoO3 nanorods (1.0 mmol) were ultrasonically dispersed in 40 mL deionized water. Under ice bath and continuous stirring, 675 μL pyrrole monomer solution (10.0 mmol) was injected, followed by dropwise addition of 10 mL of 1.0 mol / L ice bath treated ammonium persulfate solution (S content was 10.0 mmol) to initiate polymerization of the pyrrole monomer. The mixture quickly turned from white to black. The ice bath and stirring reaction were continued for 5 hours. The reaction mixture was directly transferred to an evaporating dish and dried thoroughly to obtain a molybdenum trioxide-polypyrrole precursor uniformly dispersed in ammonium persulfate.

[0062] The molybdenum trioxide-polypyrrole precursor was placed in a quartz boat and loaded into a programmed temperature tubular furnace. Argon gas was introduced at a flow rate of 30 mL / min for protection. The temperature was first raised from room temperature to 300°C at a rate of 1°C / min and maintained for 3 hours. Then, the temperature was further raised to 700°C at a rate of 10°C / min and maintained for 2 hours for confined pyrolysis treatment, so that ammonium persulfate in situ sulfurized the molybdenum trioxide-polypyrrole precursor. After the furnace body was naturally cooled to room temperature, the molybdenum-based negative electrode material, i.e., nitrogen and sulfur co-doped carbon nanorods (named MoO2@MoS2@C), was obtained.

[0063] Figure 1 Transmission electron micrographs of the molybdenum-based negative electrode material prepared in Example 1 at different magnifications: a) 50nm, b) 10nm; and c) the magnified image of the corresponding core and shell regions of the nanoscroll and the Fourier transform image (d). Figure 1 As shown in the figure, a large number of core-shell MoO2-MoS2 nanoscrolls with a size of about 20-50 nm are formed in the prepared MoO2@MoS2@C material, and MoO2 and MoS2 are in close contact to produce rich heterogeneous interfaces; the inner core MoO2 has a very high crystallinity, and clear lattice stripes of (100) and (220) crystal planes can be observed; the shell MoS2 has a curved structural feature, with about 15 layers, and clear (002) interlayer spacing lattice stripes can be observed, corresponding to an interlayer spacing of 0.641 nm, which is larger than the theoretical value of 0.620 nm.

[0064] Figure 2 Scanning electron microscope images of the molybdenum-based negative electrode material prepared in Example 1 at different magnifications: a) 1 μm, b) 200 nm. Figure 2 As shown, the prepared MoO2@MoS2@C material inherits the nanorod morphology of the MoO3 template. The width of the nanorod is about 300nm and the length is about 2μm. Many nanocarbon particles derived from polypyrrole grow on its surface.

[0065] Figure 3 This is the element surface distribution result diagram of the molybdenum-based negative electrode material prepared in Example 1. Figure 3 As shown, the five elements C, N, S, Mo, and O are evenly distributed in the prepared MoO2@MoS2@C material, indicating that the surface carbon coating formed after carbonization of polypyrrole and ammonium persulfate has the co-doping characteristics of nitrogen and sulfur.

[0066] Figure 4Figure a) is the X-ray diffraction pattern of the molybdenum-based negative electrode material prepared in Example 1. In the prepared MoO2@MoS2@C material, two active components, MoS2 and MoO2, were successfully formed, both of which have good crystallinity; MoS2 showed significant diffraction peaks at 14.3°, 33.0° and 58.6°, corresponding to the (002), (100) and (110) crystal planes of the 2H phase, respectively; MoO2 showed significant diffraction peaks at 26.2°, 37.1° and 53.7°, corresponding to the (110), (200) and (220) crystal planes of the monoclinic phase MoO2, respectively.

[0067] The prepared MoO2@MoS2@C was used as the negative electrode material, polyvinylidene fluoride was used as the binder, and N-methyl-2-pyrrolidone was used as the solvent to prepare a uniform slurry, wherein the mass ratio of the negative electrode material to the binder was 9:1. The slurry was applied to a clean copper foil and then dried under vacuum at 120°C for 12 hours. The copper foil loaded with the slurry was cut into circular electrode sheets with a diameter of 12 mm and compacted. When assembling the sodium-ion battery, a metal sodium sheet and a glass fiber membrane (Whatman, GF-D) were used as the positive electrode and separator, respectively. The electrolyte was 1 mol / L NaClO4 (mixed solvent: ethylene carbonate / diethyl carbonate / fluoroethylene carbonate, volume ratio of 1:1:0.1). The circular electrode sheet was used as the negative electrode. CR2032 button-type half-cells were assembled in an argon-filled glove box. After standing for 8 hours, the positive electrode voltage was 0.1-3.0 V (vs. Na) at ... + When assembling lithium-ion batteries, polypropylene film was used as the separator, and the electrolyte was 1 mol / L LiPF6 (mixed solvent: dimethyl carbonate / ethylene carbonate / ethyl methyl carbonate, volume ratio of 1:1:1). CR2032 button half-cells were assembled in an argon-filled glove box. After standing for 8 hours, the charge and discharge performance was tested at 0.1~3.0V (vs.Li + / Li) to test the charge and discharge performance.

[0068] Figure 10 Figure a) shows the charge and discharge curve of the molybdenum-based negative electrode material prepared in Example 1. When the prepared MoO2@MoS2@C material is used in sodium ion batteries, the first-cycle discharge capacity at a current density of 0.1A / g is as high as 649.1mAh / g, which is comparable to the theoretical capacity of MoS2. The discharge capacity after cycle stabilization is approximately 393.3mAh / g.

[0069] Figure 11Figure a) is a rate performance diagram of the molybdenum-based negative electrode material prepared in Example 1. When the prepared MoO2@MoS2@C material is used in sodium ion batteries, the specific capacities at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are 393.5, 327.8, 304.8, 276.5, 252.2, and 219.5 mAh / g, respectively, indicating that the material has excellent rate performance.

[0070] Figure 12 a) is the cycle stability performance of the molybdenum-based negative electrode material prepared in Example 1 when used in a sodium ion battery at a current density of 0.1 A / g. When the prepared MoO2@MoS2@C material is used in a sodium ion battery, it can be stably cycled for up to 160 cycles at a current density of 0.1 A / g and for up to 350 cycles at a current density of 1.0 A / g, indicating that the material has very high sodium ion battery cycle stability at low rates.

[0071] Figure 13 a) is the cycle stability performance of the molybdenum-based negative electrode material prepared in Example 1 when used in a sodium ion battery under a current density of 1.0 A / g. When the prepared MoO2@MoS2@C material is used in a sodium ion battery, it can be stably cycled for up to 350 cycles at a current density of 1.0 A / g, indicating that the material has very high sodium ion battery cycle stability at a higher rate.

[0072] Figure 14 The molybdenum-based negative electrode material prepared in Example 1 has a cycle stability performance at a current density of 5.0 A / g when used in a sodium ion battery. Figure 14 As shown, when the prepared MoO2@MoS2@C material is used in sodium ion batteries, it can be stably cycled for up to 1000 cycles at a current density of 5.0 A / g, indicating that the material still has very high sodium ion battery cycle stability at high rates.

[0073] Figure 15 Figure a) shows the charge and discharge curve of the molybdenum-based negative electrode material prepared in Example 1 when used in a lithium-ion battery, and Figure b) shows the rate performance. The prepared MoO2@MoS2@C material has a very high specific capacity. The first-cycle discharge specific capacity at a current density of 0.1A / g is as high as 890.0mAh / g, far exceeding the theoretical specific capacity of MoS2 and MoO2. The discharge specific capacity after cycle stabilization is about 646.3mAh / g, and a significant charge and discharge platform appears; the specific capacities at current densities of 0.1, 0.2, 0.5, and 1.0A / g are 634.9, 595.4, 542.4, and 491.8mAh / g, respectively, indicating that the material has excellent rate performance.

[0074] Figure 16The molybdenum-based negative electrode material prepared in Example 1 has a cycle stability performance at a current density of 0.2 A / g when used in a lithium-ion battery. Figure 15 As shown, when the prepared MoO2@MoS2@C material is used in lithium-ion batteries, it can be stably cycled for up to 300 cycles at a current density of 0.2 A / g, indicating that the material has very high lithium-ion battery cycle stability.

[0075] Examples 2 to 5:

[0076] The preparation methods of Examples 2 to 5 are the same as those of Example 1, except for the amount of pyrrole monomer solution added, the concentration of ammonium persulfate solution, and the temperature of high-temperature pyrolysis. The specific reaction parameters are listed in Table 1. The molybdenum-based materials prepared in Examples 2 to 5 were used as negative electrode materials, respectively, with polyvinylidene fluoride as a binder and N-methyl-2-pyrrolidone as a solvent to prepare a uniform slurry, wherein the mass ratio of the negative electrode material to the binder was 9:1. The slurry was coated on a clean copper foil and then dried at 120°C under vacuum for 12 hours. The copper foil loaded with the slurry was cut into round electrode sheets with a diameter of 12 mm and compacted. When assembling the sodium ion battery, a sodium metal sheet and a glass fiber membrane (Whatman, GF-D) were used as the positive electrode and the separator, respectively. The electrolyte was 1 mol / L NaClO4 (mixed solvent: ethylene carbonate / diethyl carbonate / fluoroethylene carbonate, volume ratio of 1:1:0.1). The round electrode sheet was used as the negative electrode. The battery was assembled into a CR2032 button half-cell in an argon-filled glove box. After standing for 8 hours, the battery was tested at 0.1-3.0 V (vs. Na + / Na) to test the charge and discharge performance, the results are shown in Table 1.

[0077] Table 1 Reaction parameters and battery performance results of Examples 2 to 5

[0078]

[0079]

[0080] Comparative Example 1: 0.618 g of ammonium molybdate tetrahydrate (Mo content of 3.5 mmol) and 0.014 g of ferric chloride hexahydrate (Fe content of 0.005 mmol) were weighed and added sequentially to 20 mL of a continuously stirred 0.25 mol / L dilute nitric acid solution to obtain a clear and transparent mixed solution after complete dissolution. The mixed solution was then transferred to a 40 mL polytetrafluoroethylene-lined reactor and placed in a 200 ° C oven for constant temperature reaction for 20 hours. After the hydrothermal reaction was completed, the MoO3 nanorods were separated by centrifugation, washed with water and ethanol in sequence, and dried to collect.

[0081] 0.144 g of MoO3 nanorods (1.0 mmol) were ultrasonically dispersed in 40 mL of deionized water. Under ice bath conditions and continuous stirring, 675 μL of pyrrole monomer solution (10.0 mmol) was injected, followed by dropwise addition of 10 mL of 1.0 mol / L ice bath treated ammonium persulfate solution (S content: 10.0 mmol) to initiate polymerization of the pyrrole monomer. The mixture quickly turned from white to black. The ice bath and stirring reaction were continued for 5 hours. The ammonium persulfate initiator was removed by centrifugation and purification, and the molybdenum trioxide-polypyrrole precursor was obtained after sufficient drying.

[0082] The molybdenum trioxide-polypyrrole precursor was placed in a quartz boat and loaded into a programmed temperature tube furnace. Argon gas was introduced at a flow rate of 30 mL / min for protection. The temperature was first raised from room temperature to 300°C at a rate of 1°C / min and maintained for 3 hours. Then the temperature was further raised to 700°C at a rate of 10°C / min and maintained for 2 hours for confined pyrolysis treatment. After the furnace body was naturally cooled to room temperature, a nitrogen-doped carbon-coated molybdenum dioxide negative electrode material (named MoO2@C) was obtained.

[0083] Figure 4 Figure b) is the X-ray diffraction pattern of MoO2@C prepared in comparative example 1. The prepared MoO2@C material shows significant diffraction peaks at 26.2°, 37.1° and 53.7°, corresponding to the (110), (200) and (220) crystal planes of monoclinic MoO2, respectively. The 2H phase MoS2 formed in Example 1 was not detected.

[0084] Figure 5 Figure a) is a transmission electron microscope image of MoO2@C prepared in comparative example 1. The prepared MoO2@C material has a nanorod-like morphology with a width of about 300 nm. Its surface is covered with a carbon layer, and the interior is highly crystalline MoO2; Figure b) is a selected area electron diffraction image in which clear diffraction spots can be observed on its (110) and (200) crystal planes.

[0085] The prepared nitrogen-doped carbon-coated molybdenum dioxide negative electrode material was mixed and dispersed with PVDF binder and NMP solvent to form a uniform slurry, in which the mass ratio of the negative electrode material to the binder was 9:1. The slurry was coated on a clean copper foil and then dried at 120°C under vacuum conditions for 12 hours. The copper foil loaded with the slurry was cut into round electrode sheets with a diameter of 12 mm and compacted. When assembling the sodium ion battery, a metal sodium sheet and a glass fiber membrane (Whatman, GF-D) were used as the positive electrode and separator, respectively. The electrolyte was 1 mol / L NaClO4 (mixed solvent: ethylene carbonate / diethyl carbonate / fluoroethylene carbonate, volume ratio of 1:1:0.1). The round electrode sheet was the negative electrode and assembled into a CR2032 button half-cell in an argon-filled glove box. After standing for 8 hours, the positive electrode was tested at 0.1~3.0V (vs. Na + / Na) to test the charge and discharge performance.

[0086] Figure 10 Figure b) shows the charge and discharge curve of MoO2@C prepared in Comparative Example 1. When the MoO2@C material prepared in Comparative Example 1 is used in a sodium ion battery, the first cycle discharge capacity at a current density of 0.1 A / g is 538.3 mAh / g, and the discharge capacity after cycle stabilization is about 320.2 mAh / g, which is much lower than the MoO2@MoS2@C material prepared in Example 1.

[0087] Figure 11 Figure b) is a rate performance diagram of MoO2@C prepared in Comparative Example 1. When the MoO2@C material prepared in Comparative Example 1 is used in sodium ion batteries, the specific capacities at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are 300.2, 256.2, 240.1, 223.8, 200.8, and 170.7 mAh / g, respectively. The specific capacity at any current density is much lower than that of the MoO2@MoS2@C material prepared in Example 1, indicating that the construction of core-shell MoO2-MoS2 heterogeneous materials helps to accelerate the electrochemical reaction kinetics and improve the rate performance of sodium ion batteries.

[0088] Figure 12 Figure b) shows the cycle stability performance of the MoO2@C material prepared in Comparative Example 1 when used in sodium ion batteries under a current density of 0.1 A / g. The specific capacity decays sharply after 140 cycles, indicating that the core-shell MoO2-MoS2 heterogeneous material gives the MoO2@MoS2@C material prepared in Example 1 high cycle stability at low rates in sodium ion batteries.

[0089] Figure 13Figure b) shows the cycle stability performance of the MoO2@C material prepared in Comparative Example 1 when used in sodium ion batteries under a current density of 1.0 A / g. Its cycle stability is far inferior to that of the MoO2@MoS2@C material prepared in Example 1, indicating that the core-shell MoO2-MoS2 heterogeneous material also gives the MoO2@MoS2@C material prepared in Example 1 high cycle stability at higher rates in sodium ion batteries.

[0090] Comparative Example 2

[0091] 0.618 g of ammonium molybdate tetrahydrate (Mo content is 3.5 mmol) and 0.014 g of ferric chloride hexahydrate (Fe content is 0.005 mmol) were weighed and added in sequence to 20 mL of a continuously stirred dilute nitric acid solution with a concentration of 0.25 mol / L. After complete dissolution, a clear and transparent mixed solution was obtained. The solution was then transferred to a 40 mL polytetrafluoroethylene-lined reactor and placed in a 200 ° C oven for constant temperature reaction for 20 hours. After the hydrothermal reaction was completed, the MoO3 nanorods were separated by centrifugation, washed with water and ethanol in sequence, and collected after drying.

[0092] 0.144 g MoO3 nanorods (1.0 mmol) were ultrasonically dispersed in 40 mL deionized water. Under ice bath and continuous stirring, 675 μL pyrrole monomer solution (10.0 mmol) was injected, followed by dropwise addition of 10 mL of 1.0 mol / L ice-bathed ammonium persulfate solution (S content was 10.0 mmol) to initiate polymerization of the pyrrole monomer. The mixture quickly turned from white to black. The ice bath and stirring reaction were continued for 5 hours. The ammonium persulfate initiator was removed by centrifugation and purification, and the molybdenum trioxide-polypyrrole precursor was obtained after sufficient drying.

[0093] The molybdenum trioxide-polypyrrole precursor and 320 mg of sulfur powder (S content is 10.0 mmol) were ground evenly and placed in a quartz boat, loaded into a programmed temperature tubular furnace, and argon gas was introduced at a flow rate of 30 mL / min for protection. The temperature was first raised from room temperature to 300°C at a rate of 1°C / min and maintained for 3 hours. Then the temperature was continued to be raised to 700°C at a rate of 10°C / min and maintained for 2 hours for confined pyrolysis treatment. After the furnace body was naturally cooled to room temperature, nitrogen and sulfur co-doped carbon-coated molybdenum dioxide-molybdenum disulfide composite negative electrode material (named MoO2 / MoS2@C-1) was obtained.

[0094] Figure 4c) is the X-ray diffraction pattern of MoO2 / MoS2@C-1 prepared in comparative example 2. In the prepared MoO2 / MoS2@C-1 material, two active components, MoS2 and MoO2, are formed, both of which have good crystallinity; MoS2 shows significant diffraction peaks at 14.3°, 33.0° and 58.6°, corresponding to the (002), (100) and (110) crystal planes of the 2H phase, respectively; MoO2 shows significant diffraction peaks at 26.2°, 37.1° and 53.7°, corresponding to the (110), (200) and (220) crystal planes of the monoclinic phase MoO2, respectively; compared with the MoO2@MoS2@C material prepared in Example 1, the MoS2 content in MoO2 / MoS2@C-1 is greatly increased.

[0095] Figure 6 These are scanning electron microscope images of the MoO2 / MoS2@C-1 material prepared in comparative example 2 at different magnifications. Although the prepared MoO2 / MoS2@C-1 material exhibits a nanorod-like morphology similar to that of Example 1, with many nanocarbon particles derived from polypyrrole grown on the surface, some nanosheets are also formed and scattered on the surface.

[0096] Figure 7 These are transmission electron microscope images of the MoO2 / MoS2@C-1 material prepared in comparative example 2 at different magnifications. The core-shell MoO2-MoS2 nanoscrolls of Example 1 are not formed in the prepared MoO2 / MoS2@C-1 material. Instead, many clear (002) interlayer spacing lattice stripes of 2H phase MoS2 are observed on the surface of the nanorods, indicating that the additionally added sulfur powder as a sulfur source cannot form core-shell MoO2-MoS2 nanoscrolls.

[0097] The prepared nitrogen- and sulfur-co-doped carbon-coated molybdenum dioxide-molybdenum disulfide composite anode material was mixed and dispersed with a PVDF binder and NMP solvent to form a uniform slurry. The mass ratio of the anode material to the binder was 9:1. The slurry was coated on a clean copper foil and then dried at 120°C under vacuum for 12 hours. The slurry-loaded copper foil was cut into circular electrode sheets with a diameter of 12 mm and compacted. When assembling the sodium-ion battery, a sodium metal sheet and a glass fiber membrane (Whatman, GF-D) were used as the positive electrode and separator, respectively. The electrolyte was 1 mol / L NaClO4 (mixed solvent: ethylene carbonate / diethyl carbonate / fluoroethylene carbonate, volume ratio 1:1:0.1). The circular electrode sheet served as the negative electrode. CR2032 button-type half-cells were assembled in an argon-filled glove box and, after standing for 8 hours, the voltage at 0.1-3.0 V (vs. Na) was measured. + / Na) to test the charge and discharge performance.

[0098] Figure 11Figure c) is a rate performance diagram of MoO2 / MoS2@C-1 prepared in Comparative Example 2. When the MoO2 / MoS2@C-1 material prepared in Comparative Example 2 is used in a sodium ion battery, the specific capacities at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are 236.8, 210.5, 189.9, 169.6, 149.2, and 128.4 mAh / g, respectively. The specific capacity at any current density is much lower than that of the MoO2@MoS2@C material prepared in Example 1, and also lower than that of the MoO2@C material prepared in Comparative Example 1.

[0099] Comparative Example 3

[0100] The preparation method of Comparative Example 3 is the same as that of Comparative Example 2, except that 320 mg of sulfur is replaced with 761 mg of thiourea (S content is 10.0 mmol) and ground evenly with the molybdenum trioxide-polypyrrole precursor. After high-temperature pyrolysis, a carbon-molybdenum dioxide-molybdenum disulfide composite negative electrode material co-loaded with nitrogen and sulfur (named MoO2 / MoS2@C-2) is obtained.

[0101] Figure 4 Figure d) is the X-ray diffraction pattern of MoO2 / MoS2@C-2 prepared in Comparative Example 3. In the prepared MoO2 / MoS2@C-2 material, 2H phase MoS2 has significant diffraction peaks at 14.3°, 33.0° and 58.6°, corresponding to the (002), (100) and (110) crystal planes, respectively, while MoO2 has only weak diffraction peaks at 26.2°, 37.1° and 53.7°, corresponding to the single crystal planes. The (110), (200) and (220) crystal planes of the oblique phase MoO2 indicate that compared with the MoO2@MoS2@C material prepared in Example 1 and the MoO2 / MoS2@C-1 material prepared in Comparative Example 2, the MoS2 content in MoO2 / MoS2@C-2 is further increased, that is, the sulfur source is changed from the strongly oxidizing ammonium persulfate to sulfur powder, and then to the reducing thiourea. The content of 2H phase MoS2 formed during the pyrolysis process will gradually increase significantly.

[0102] Figure 8 These are scanning electron microscope images of the MoO2 / MoS2@C-2 material prepared in comparative example 3 at different magnifications. The prepared MoO2 / MoS2@C-2 material no longer has the nanorod-like morphology similar to that in example 1, and many nanosheets stacked on each other are formed on the surface.

[0103] Figure 9These are transmission electron microscope images of the MoO2 / MoS2@C-2 material prepared in comparative example 3 at different magnifications. The core-shell MoO2-MoS2 nanoscrolls of Example 1 are not formed in the prepared MoO2 / MoS2@C-2 material. Instead, a large number of 2H phase MoS2 with clear (002) interlayer spacing lattice fringes are observed on the carbon support, indicating that the additionally added thiourea as a sulfur source cannot form core-shell MoO2-MoS2 nanoscrolls.

[0104] Figure 11 d) is a rate performance diagram of MoO2 / MoS2@C-2 prepared in Comparative Example 3. When the MoO2 / MoS2@C-2 material prepared in Comparative Example 3 is used in a sodium ion battery, the specific capacities at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are 205.8, 178.5, 154.8, 135.7, 106.3, and 82.4 mAh / g, respectively. The specific capacity at any current density is much lower than that of the MoO2@MoS2@C material prepared in Example 1, and also much lower than that of the MoO2 / MoS2@C-1 material prepared in Comparative Example 2.

[0105] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0106] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A molybdenum-based negative electrode material, characterized in that: including nitrogen and sulfur co-doped carbon nanorods; The carbon nanorods are filled with core-shell molybdenum-based nanoscrolls, which include a molybdenum dioxide core and a molybdenum disulfide shell with a curved structure, and the number of layers of the molybdenum disulfide is 12 to 35. The preparation method of the molybdenum-based negative electrode material comprises: Molybdenum trioxide nanorods are dispersed in water, and a nitrogen-containing organic carbon source monomer solution is injected under ice bath conditions. A sulfur-containing initiator with strong oxidizing properties is used to initiate the reaction, and after the reaction, a sulfur-containing initiator-dispersed molybdenum trioxide-organic polymer precursor is obtained; Under the protection of an inert atmosphere, the molybdenum trioxide-organic polymer precursor dispersed with the sulfur-containing initiator is subjected to confined pyrolysis at 600-800° C. to obtain the molybdenum-based negative electrode material; wherein the molar ratio of the molybdenum trioxide nanorods, the nitrogen-containing organic carbon source monomer and the sulfur-containing initiator is 1.0:5-15:1.0; and the sulfur-containing initiator is ammonium persulfate.

2. The molybdenum-based negative electrode material according to claim 1, characterized in that During the confined pyrolysis, the temperature is first raised from room temperature to 300° C. at a rate of 1° C. / min for 3 hours, and then the temperature is further raised to 600-800° C. at a rate of 2-10° C. / min for 2-5 hours.

3. The molybdenum-based negative electrode material according to claim 1, characterized in that When preparing the sulfur-containing initiator dispersed molybdenum trioxide-organic polymer precursor, the ammonium persulfate is first prepared into a solution and then the reaction is initiated; wherein the concentration of the ammonium persulfate solution is 1.0 to 3.0 mol / L.

4. The molybdenum-based negative electrode material according to claim 1, characterized in that The nitrogen-containing organic carbon source monomer is one or more of pyrrole, aniline, and dopamine hydrochloride.

5. The molybdenum-based negative electrode material according to claim 1, characterized in that The preparation method of the molybdenum trioxide nanorods is as follows: Molybdate and ferric chloride hexahydrate are added into nitric acid solution and subjected to constant temperature hydrothermal reaction to obtain molybdenum trioxide nanorods.

6. The molybdenum-based negative electrode material according to claim 5, characterized in that The molar ratio of molybdenum in the molybdate, iron in ferric chloride hexahydrate, and nitric acid is 0.5-4.0:0.01-0.05:1.0-5.

0.

7. The molybdenum-based negative electrode material according to claim 5, characterized in that The constant temperature hydrothermal reaction condition is 150-220° C. for 15-25 hours.

8. Use of the molybdenum-based negative electrode material according to claim 1 in a sodium ion battery negative electrode or a lithium ion battery negative electrode.

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