Method for reducing molybdenum trioxide to molybdenum dioxide or molybdenum carbide and use thereof

Abstract

The application provides a method and application for reducing molybdenum trioxide to generate molybdenum dioxide or molybdenum carbide, which comprises the following steps: dispersing MoO3 powder in a mixed solution of monohydric alcohol and polyhydric alcohol, adding a triblock copolymer P123 stabilizer, and obtaining a suspension which is subjected to microwave-assisted solvothermal reaction, centrifugation or filtration and washing, and then brown H 0.93 The MoO3 / C precursor microspheres are placed in an argon plasma environment and calcined at a high temperature of 500-600 DEG C for 30-60 min to obtain brown-black MoO2 / C microspheres; or the H 0.93 The MoO3 / C precursor is placed in a hydrogen-argon plasma environment and calcined at a high temperature of 500-600 DEG C for 30-60 min to obtain gray Mo2C / C microspheres. The MoO2 / C and Mo2C / C materials prepared by the application have nanocrystalline characteristics and excellent electrochemical performance, and have a good commercial application prospect as negative electrode materials of lithium batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery materials, in particular to a method for preparing spherical molybdenum-based precursor by using molybdenum trioxide and reducing the molybdenum-based precursor to generate molybdenum dioxide or molybdenum carbide and application thereof. BACKGROUND

[0002] Transition metal oxides (TMOs) exhibit diverse lithiation reaction mechanisms due to the rich and variable valence states of transition elements and unique crystal structures, which are expected to replace graphite as a promising electrode active material for lithium ion batteries. Among them, TMOs in the pre-subgroup (IVB and VB) (including TiO2, V2O5, and Nb2O5, etc.) have stable crystal structures and can realize reversible intercalation / deintercalation of lithium ions in the structure; TMOs in the post-subgroup (VIII and IB) (including FeO, CoO, Co3O4, NiO, Cu2O, etc.) only exhibit multi-electron conversion reaction type lithiation activity at the nanoscale; and TMOs in the intermediate subgroup (VIB and VIII) (including MoO3, RuO2, MoO2, etc.) exhibit reversible intercalation / deintercalation at a higher potential range (>1.00 V vs. Li / Li⁺) and gradual amorphization of multi-electron conversion reactions at a lower potential range (<1.00 V vs. Li / Li⁺). At present, molybdenum dioxide (MoO2) with high theoretical capacity (838 mAh g⁻¹) and metallic conductivity has attracted widespread attention. However, the application of commercial bulk MoO2 is limited, mainly because the monoclinic-orthorhombic-monoclinic phase transition of the distorted rutile crystal structure during the lithium ion intercalation / deintercalation process at high crystallinity is a slow phase change of lithiation reaction, which hinders further lithiation reaction, showing that the Mo-O bond cannot be fully broken at a lower potential range (<1.00 V vs. Li / Li⁺) to trigger multi-electron conversion reactions, and accumulative volume changes occur during the lithiation process, showing an activation process with a long cycle number, followed by serious capacity decay. Therefore, nanocrystallization of the microstructure and microcrystallization of the crystal material are considered as effective strategies to break through the limitations of MoO2 bulk materials in the application as anode materials for lithium ion batteries.

[0003] A large number of studies focus on designing and preparing high-efficiency nanostructures, aiming to expand the reaction contact area, shorten the ion diffusion path, and reduce internal stress. Porous MoO2@C nano-octahedrons can be derived from metal-organic frameworks (MOFs) of polyoxometalates; and ordered mesoporous MoO2 can be synthesized by a sacrificial template method, such as introducing ordered mesoporous carbon CMK-3, and precisely synthesizing by controlling the molybdate impregnation process and carbon thermal reduction conditions. Through chelation and subsequent carbonization process, 3D hierarchical MoO2 nanospheres can be prepared, in which the amorphous carbon matrix is self-assembled. Using salt, glucose or surfactant as a template for self-assembly, two-dimensional MoO2 flakes can be prepared. By coating the surface of the precursor MoO3 nanobelt with carbon and then reducing it, the one-dimensional MoO2 nanobelt structure can be retained; otherwise, nanoparticles are obtained. The above nano-materials have high specific surface area, which is beneficial to the diffusion and intercalation of lithium ions, and exhibit good rate and cycle stability, but at the same time, it may increase the interface resistance and side reactions, and the first coulombic efficiency is low.

[0004] The crystallization of the crystalline material is mainly controlled by the attachment of the molybdenum-based precursor to the amorphous carbon matrix, and the selection of the calcination temperature or time after self-assembly, to realize the recrystallization control of MoO2, aiming to weaken the limitation of the distorted rutile crystal structure on the lithium-rich state conversion reaction, break the Mo-O bond, and realize the rapid excitation of the four-electron complete conversion reaction through the nanocrystalline effect. However, by using nano-MoO3 as a precursor, it still needs to be reacted at a temperature greater than 680°C to obtain a high-crystallinity MoO2 material; if a polyoxometalate or an organic chelating ligand of molybdenum is used as a precursor, it needs to be reacted at a temperature greater than 600°C to obtain a MoO2 material with high crystallinity and high carbon content. The above methods still have the defects of unstable crystallinity and product size, which limit the commercial application of the material.

[0005] In addition, transition metal carbides (TMCs) have high electrical conductivity, good chemical stability, and inherent catalytic activity, and have been widely studied and used as active materials in various energy storage fields. Among them, Mo2C prepared by MAX etching or high-temperature carbon thermal reduction in a H2 / Ar atmosphere shows higher capacity (about 300 mAh g -1 ) and gradually increasing cycle performance (capacity retention rate > 100%) compared with Nb2C (about 250 mAh g -1 ), V2C (about 260 mAh g -1 ) and Ti2C (about 160 mAh g -1 ). However, Mo2C material needs to be carbon thermally reduced at a high temperature of more than 800°C, which is harsh and has high energy consumption; and high-temperature reaction can only obtain Mo2C with very high crystallinity, which cannot realize the microcrystallization control of this type of material. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and first provides a method for preparing spherical Mo-based precursor from molybdenum trioxide and reducing the Mo-based precursor to generate molybdenum dioxide or molybdenum carbide.

[0007] The method provided by the present application comprises the following steps:

[0008] S1: MoO3 powder is stirred and dispersed in a mixed solution of monohydric alcohol and polyhydric alcohol, then a triblock copolymer P123 stabilizer is added, and the obtained suspension is subjected to microwave-assisted solvothermal reaction, centrifugation or filtration and washing to obtain brownish H 0.93 MoO3 / C precursor microspheres;

[0009] S2: the H 0.93 MoO3 / C precursor obtained in step S1 is placed in an argon plasma atmosphere and calcined at a high temperature of 500-600°C for 30-60 min to obtain brownish black MoO2 / C microspheres with a diameter of 1.00-1.10 μm;

[0010] Alternatively, the H 0.93 MoO3 / C precursor obtained in step S1 is placed in a hydrogen-argon plasma atmosphere and calcined at a high temperature of 500-600°C for 30-60 min to obtain dark gray Mo2C / C microspheres with a diameter of 0.75-0.85 μm.

[0011] The present application also provides applications of the MoO2 / C material and the Mo2C / C material prepared by the above method in negative electrode materials of lithium ion batteries.

[0012] The present application has the following technical effects:

[0013] (1) The present application directly synthesizes high-activity, uniform microspherical H 0.93 MoO3 / C precursor by using commercial MoO3 as a molybdenum source and without introducing an additional carbon source as a reducing agent, only through microwave-assisted solvothermal reaction, and the H 0.93 MoO3 / C precursor is subjected to low-temperature calcination, the calcination temperature is controlled, and an argon plasma or hydrogen-argon plasma reducing atmosphere is combined to fully reduce and synthesize MoO2 / C material and Mo2C / C material, and the method is simple and low in cost.

[0014] (2) The present application can avoid the collapse or adhesion of the microspherical structure obtained by microwave-assisted solvothermal reaction due to the deviation of the mixed volume ratio of the dispersion solution of monohydric alcohol and polyhydric alcohol by introducing a triblock copolymer P123 stabilizer, and effectively ensures the uniformity of the H 0.93The diameter of the MoO3 / C precursor microspheres is in the range of 1.50-1.60μm, the diameter of the MoO2 / C material microspheres is in the range of 1.00-1.10μm, and the diameter of the Mo2C / C material microspheres is in the range of 0.75-0.85μm. The products have high consistency, and the structure of the prepared materials is stable, the surface is negatively charged, and they all have good monodisperse characteristics.

[0015] (3) The MoO2 / C material and Mo2C / C material prepared in this application both have nanocrystalline characteristics. The MoO2 / C material has a high conductivity at 1.00~3.00 V ( vs. Li / Li + ) potential range, it exhibits single-electron insertion / extraction lithium storage activity; in the range of 0.01~3.00 V ( vs. Li / Li + ) potential range, it shows four-electron conversion reaction lithium storage activity, Mo2C / C material in the range of 0.01~3.00 V ( vs. Li / Li + ) potential range, it shows surface lithium atom adsorption and desorption and gradual conversion reaction lithium storage activity, both of which have excellent electrochemical properties. The introduction of MoO2 / C and Mo2C / C as lithium battery negative electrode materials has good commercial application prospects and provides a new economical and effective way for the preparation of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 For the MoO3 block in Example 1, H 0.93 X-ray diffraction patterns of MoO3 / C precursor, MoO2 / C and Mo2C / C materials;

[0017] Figure 2 is H in Example 1 0.93 Particle size distribution curves of MoO3 / C precursor, MoO2 / C and Mo2C / C materials;

[0018] Figure 3 is H in Example 1 0.93 Zeta potential distribution curves of MoO3 / C precursor, MoO2 / C and Mo2C / C materials;

[0019] Figure 4 is H in Example 1 0.93 Scanning electron micrographs of MoO3 / C precursor, MoO2 / C, and Mo2C / C materials;

[0020] Figure 5 H in Example 1 0.93 EDS spectrum of MoO3 / C precursor;

[0021] Figure 6 Cyclic voltammograms of MoO2 / C and Mo2C / C materials in Example 1;

[0022] Figure 7 Charge-discharge rate performance curves of MoO2 / C and Mo2C / C materials in Example 1;

[0023] Figure 8 Electrochemical impedance spectra of MoO2 / C and Mo2C / C materials in Example 1 after 20 cycles of charge-discharge;

[0024] Figure 9 X-ray diffraction pattern of the precursor obtained in Comparative Example 1;

[0025] Figure 10 X-ray diffraction pattern of the precursor obtained in Comparative Example 2;

[0026] Figure 11 X-ray diffraction pattern of the precursor obtained in Comparative Example 3;

[0027] Figure 12 Scanning electron micrograph of the precursor obtained in Comparative Example 3;

[0028] Figure 13 Scanning electron micrograph of the precursor obtained in Comparative Example 4;

[0029] Figure 14 X-ray diffraction pattern of the MoO2 / C material obtained in Comparative Example 5;

[0030] Figure 15 X-ray diffraction pattern of the Mo2C / C material obtained in Comparative Example 6. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0032] The present application provides a method for reducing molybdenum trioxide to generate molybdenum dioxide or molybdenum carbide, comprising the following steps:

[0033] S1 MoO3 powder is stirred and dispersed in a mixed solution of monohydric alcohol and polyhydric alcohol, then a triblock copolymer P123 stabilizer is added, and the obtained suspension is subjected to microwave-assisted solvothermal reaction, and then centrifuged or filtered and washed to obtain brown H 0.93 The MoO3 / C precursor microspheres have good monodispersity in water.

[0034] In this step, MoO3 powder is stirred and dispersed in a mixed solution of monohydric alcohol and polyhydric alcohol, so that MoO3 is uniformly dispersed in the mixed solution to form a suspension, and the reduction reaction activity of the system is enhanced, so that MoO3 can be completely converted into H 0.93 MoO3 / C precursor. Moreover, amorphous carbon can be derived from the microwave-assisted solvent thermal decomposition product of monohydric alcohol and dihydric alcohol, so that the application does not need to introduce an additional carbon source as a reducing agent. The addition of a triblock copolymer P123 stabilizer in the mixed solution can maintain the material morphology and prevent particle agglomeration, avoid the collapse of the microsphere structure in the mixed solution of monohydric alcohol and polyhydric alcohol due to the deviation of the actual volume ratio, and ensure that the final MoO2 / C and Mo2C / C products are within the set size range, and the material structure after preparation is stable, the surface is negatively charged, and both have good monodisperse characteristics, improving the processability of subsequent lithium ion battery product preparation, such as mixing and uniform coating, and also improving the tap density and electrolyte permeability.

[0035] The monohydric alcohol is at least one of methanol, ethanol, and isopropanol, preferably isopropanol; and the polyhydric alcohol is at least one of ethylene glycol and glycerol, preferably glycerol.

[0036] The volume ratio of monohydric alcohol to polyhydric alcohol is 1:2 to 2:1.

[0037] The mass ratio of the amount of the triblock copolymer P123 stabilizer to the mixed solution of monohydric alcohol and polyhydric alcohol is 10g to 30g / L, preferably 20g / L.

[0038] The microwave-assisted solvent thermal reaction temperature is 180 to 210°C, preferably 200°C, and the holding time is 20 to 40 minutes, preferably 30 minutes.

[0039] S2 placing the H 0.93 MoO3 / C precursor obtained in step S1 in an argon plasma atmosphere and calcining at a reaction temperature of 500 to 600°C for 30 to 60 minutes to obtain brown-black MoO2 / C microspheres with a diameter of 1.00 to 1.10μm;

[0040] Alternatively, placing the H 0.93 MoO3 / C precursor obtained in step S1 in a hydrogen-argon plasma atmosphere and calcining at a reaction temperature of 500 to 600°C for 30 to 60 minutes to obtain dark gray Mo2C / C microspheres with a diameter of 0.75 to 0.85μm.

[0041] The reaction temperature is preferably 600°C, the calcination time is preferably 40 minutes, and the hydrogen in the hydrogen-argon plasma is 15% of the total amount.

[0042] The MoO2 / C material prepared by the method has a microspherical structure and is a microcrystalline material. When the material is used as a negative electrode material of a lithium ion battery, the secondary microspherical structure can well adapt to volume expansion caused by lithiation, the microspherical structure can reduce interface resistance and side reactions to improve the first cycle coulombic efficiency, and the nanocrystalline structure can shorten the activation period of a four-electron conversion reaction. The MoO2 / C material exhibits single-electron intercalation / deintercalation lithium storage activity in a potential range of 1.00-3.00 V (Li / Li vs. Li / Li + ), and exhibits four-electron conversion reaction lithium storage activity in a potential range of 0.01-3.00 V (Li / Li vs. Li / Li + ), and has excellent electrochemical performance.

[0043] The prepared Mo2C / C material has a nanocrystalline characteristic. When the material is used as a negative electrode material of a lithium ion battery, the material has good rate capability and long cycle stability. In a potential range of 0.01-3.00 V (Li / Li vs. Li / Li + ), the material exhibits surface lithium atom adsorption / desorption and gradually occurring conversion reaction lithium storage activity, and has excellent electrochemical performance.

[0044] The application further provides application of the MoO2 / C and Mo2C / C materials in lithium ion batteries.

[0045] The MoO2 / C microcrystalline material having a microspherical structure is used as a negative electrode material of a lithium ion battery. The secondary microspherical structure can well adapt to volume expansion caused by lithiation, the microspherical structure can reduce interface resistance and side reactions to improve the first cycle coulombic efficiency, and the nanocrystalline structure can shorten the activation period of a four-electron conversion reaction.

[0046] The Mo2C / C microcrystalline material having a microspherical structure is used as a negative electrode material of a lithium ion battery, and has good rate capability and long cycle stability.

[0047] The application applies the MoO2 / C and Mo2C / C materials to lithium ion batteries, thereby reducing the manufacturing cost of the lithium ion batteries and improving the electrochemical performance of the lithium ion batteries.

[0048] The MoO2 / C and Mo2C / C materials are respectively used as active substances of negative electrode materials of lithium ion batteries, and are used in a process for preparing a lithium ion half battery:

[0049] (1) MoO2 / C or Mo2C / C material, conductive agent acetylene black, and adhesive polyvinylidene fluoride (PVDF) are ground for 30 min at a weight ratio of 8:1:1, and are uniformly mixed, and the mixture is dispersed in an N-methyl pyrrolidone (NMP) solution to prepare a slurry;

[0050] (2) The slurry was uniformly coated on the copper foil by a coating machine, and vacuum dried at 110°C for 12h, and then cut into a circular electrode with a diameter of 16mm by a cutting machine;

[0051] (3) The assembly of CR2032 button half-cell was carried out in a glove box filled with high-purity argon:

[0052] The gasket and spring were placed in the negative electrode shell, a lithium metal sheet with a diameter of 16mm was placed on the gasket, electrolyte (1M LiPF6 dissolved in ethylene carbonate (EC) / dimethyl carbonate (DMC) with a volume ratio of 1:1) was added dropwise by a pipette, a circular polypropylene separator with a diameter of 19mm was placed, electrolyte was added dropwise by a pipette, the cut electrode was placed as the counter electrode, and finally the button cell was packaged.

[0053] The method for reducing molybdenum trioxide to molybdenum dioxide or molybdenum carbide used in the present application will be further described in detail below in combination with specific examples.

[0054] Example 1:

[0055] S1 100g of commercial MoO3 powder was dispersed in a mixed solution of 500 mL isopropyl alcohol and 500 mL glycerol by stirring, and 20g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out at a reaction temperature of 200°C for 30 min. Three times of distilled water and twice of ethanol were used for centrifugation or filtration to obtain brownish H 0.93 MoO3 / C precursor;

[0056] S2 The H 0.93 MoO3 / C precursor was calcined in an argon plasma atmosphere at 600°C for 40 min to obtain MoO2 / C material;

[0057] The H 0.93 MoO3 / C precursor was placed in a 15% hydrogen argon plasma atmosphere and calcined at 600°C for 40 min to obtain Mo2C / C material.

[0058] Referring to Figure 1 In this embodiment 1, the commercial MoO3 powder was mixed with isopropyl alcohol, glycerol, and triblock copolymer P123 stabilizer, and microwave-assisted solvothermal reaction was carried out, which could completely convert the MoO3 powder into H 0.93 MoO3 / C precursor without other impurity phases; the H 0.93 MoO3 / C precursor was calcined in an argon plasma at a low temperature, which could be completely reduced to MoO2 / C material without other impurity phases; the H 0.93 MoO3 / C precursor was calcined in a 15% hydrogen argon plasma atmosphere, which could be completely converted from H 0.93MoO3 / C is fully reduced to Mo2C / C material without other impurity phases.

[0059] Figure 2 The results showed that the obtained H 0.93 The particle size distribution of MoO3 / C precursor, MoO2 / C and Mo2C / C materials showed a sharp single peak, with good particle uniformity. Figure 2 and Figure 4 The results showed that H 0.93 The MoO3 / C precursor is a micron sphere with a diameter of about 1.50 μm, the MoO2 / C material is a micron sphere with a diameter of about 1.00 μm, and the Mo2C / C material is a micron sphere with a diameter of about 0.80 μm.

[0060] from Figure 3 It can be seen that the H obtained in this embodiment 0.93 The Zeta potential distribution of MoO3 / C precursor, MoO2 / C and Mo2C / C materials is a negative single peak, which has good monodispersity in the aqueous phase and has a negative charge on the surface. 0.93 The MoO3 / C precursor is -58.7 mV, the MoO2 / C material is -49.3 mV, and the Mo2C / C material is -39.2 mV.

[0061] Figure 5 The results showed that the obtained H 0.93 The mass percentages of Mo, O, and C in MoO3 / C are 56.18%, 25.71%, and 40.74%, respectively. 0.93 The source of amorphous carbon in the MoO3 / C precursor is mainly the decomposition products of monohydric alcohols and polyhydric alcohols during microwave-assisted solvothermal treatment.

[0062] The obtained MoO2 / C and Mo2C / C materials were assembled into button-type lithium-ion half-cells, and their electrochemical performance was tested. Figure 6 The results show that in the range of 1.00~3.00 V( vs. Li / Li + ) potential range, MoO2 / C exhibits single-electron insertion / extraction lithium storage activity, while Mo2C / C exhibits reversible adsorption / desorption activity; in the potential range of 0.01~3.00 V ( vs. Li / Li + ), MoO2 / C exhibits four-electron conversion reaction lithium storage activity, while Mo2C / C exhibits lithium atom adsorption and desorption and gradual conversion reaction activity.

[0063] from Figure 7 It can be seen that in the range of 1.00 to 3.00 V ( vs. Li / Li +) potential range, current density 100 mA g -1 The capacity of MoO2 / C is about 149.1 mAh g -1 The first cycle coulombic efficiency is 63.2% and the current density is 500 mA g -1 The capacity of MoO2 / C is about 89.8 mAh g -1 ; In 0.01~3.00 V( vs. Li / Li + ) potential range, current density 100 mA g -1 The capacity of MoO2 / C is about 833.6 mAh g -1 The first cycle coulombic efficiency is 78.2% and the current density is 1000 mA g -1 The capacity of MoO2 / C is about 666.2 mAh g -1 ; In 0.01~3.00 V( vs. Li / Li + ) potential range, current density 100 mA g -1 The capacity of Mo2C / C is about 259.1 mAh g -1 The first cycle coulombic efficiency is 51.2% and the current density is 1000 mA g -1 The capacity of Mo2C / C is about 104.3 mAh g -1 .

[0064] Figure 8 The results show that after 20 cycles of charge and discharge, the EIS in the high-frequency band is an arc, corresponding to the electrochemical reaction impedance. The comprehensive impedance of MoO2 / C is about 120Ω, and the comprehensive impedance of Mo2C / C is about 60Ω, indicating that both have the conductive characteristics of their parent metals; the low-frequency band is a slant line, corresponding to the diffusion behavior of lithium ions in the solid phase, and both have good Warburg diffusion characteristics.

[0065] Therefore, as a single electron insertion / extraction type lithium battery negative electrode material, the electrochemical performance of MoO2 / C is equivalent to that of commercial Li4Ti5O 12 Materials (theoretical capacity 175 mAh g -1 ), which has a richer charge and discharge platform and pseudocapacitive characteristics; as a negative electrode material for multi-electron conversion reaction lithium batteries, the electrochemical performance of MoO2 / C is better than that of commercial artificial graphite materials (theoretical capacity 372 mAh g -1 ), compared with it, it has a higher specific capacity; as a new type of lithium battery negative electrode material, Mo2C / C has better rate performance than commercial artificial graphite materials and can adapt to characteristics such as fast charging and discharging.

[0066] Example 2:

[0067] S1 100g commercial MoO3 powder was stirred and dispersed in a mixed solution of 350 mL isopropyl alcohol and 650 mL glycerol, and 25g of triblock copolymer P123 stabilizer was added. The resulting stable suspension was placed in a reaction kettle, and a microwave-assisted solvothermal reaction was carried out at a temperature of 180°C for 20 min. Centrifugation or filtration was performed using distilled water three times and ethanol twice to obtain brown H 0.93 MoO3 / C precursor;

[0068] S2 The obtained H 0.93 MoO3 / C precursor was calcined at a temperature of 500°C for 30 min under an argon plasma atmosphere to obtain brown-black MoO2 / C material;

[0069] The obtained H 0.93 MoO3 / C precursor was calcined at a temperature of 500°C for 30 min under a 15% hydrogen-argon plasma atmosphere to obtain dark gray Mo2C / C material.

[0070] Tests show that the H 0.93 MoO3 / C precursor obtained in this embodiment is a micron sphere with a diameter of 1.60 pm, the MoO2 / C material is a micron sphere with a diameter of 1.10 pm, and the Mo2C / C material is a micron sphere with a diameter of 0.85 pm, and the surfaces of all are negatively charged.

[0071] Example 3:

[0072] S1 100g commercial MoO3 powder was stirred and dispersed in a mixed solution of 650 mL isopropyl alcohol and 350 mL glycerol, and 30g of triblock copolymer P123 stabilizer was added. The resulting stable suspension was placed in a reaction kettle, and a microwave-assisted solvothermal reaction was carried out at a temperature of 210°C for 40 min. Centrifugation or filtration was performed using distilled water three times and ethanol twice to obtain brown H 0.93 MoO3 / C precursor;

[0073] S2 The obtained H 0.93 MoO3 / C precursor was calcined at a temperature of 600°C for 60 min under an argon plasma atmosphere to obtain brown-black MoO2 / C material;

[0074] The obtained H 0.93 MoO3 / C precursor was calcined at a temperature of 600°C for 60 min under a 10% 15% hydrogen-argon plasma atmosphere to obtain dark gray Mo2C / C material.

[0075] Tests show that the H 0.93The MoO3 / C precursor is a microsphere with a diameter of 1.60 pm, the MoO2 / C material is a microsphere with a diameter of 1.05 pm, and the Mo2C / C material is a microsphere with a diameter of 0.78 pm, and the surfaces of them are all negatively charged.

[0076] Example 4:

[0077] S1: 100 g of commercial MoO3 powder was stirred and dispersed in a mixed solution of 600 mL of methanol and 400 mL of ethylene glycol, and then 10 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle for microwave-assisted solvothermal reaction. The reaction was carried out at a reaction temperature of 180°C for 30 min. Centrifugation or filtration was performed using distilled water three times and ethanol twice to obtain brownish H 0.93 MoO3 / C precursor;

[0078] S2: The obtained H 0.93 MoO3 / C precursor was calcined under an argon plasma atmosphere at a reaction temperature of 600°C for 50 min to obtain brownish black MoO2 / C material.

[0079] The obtained H 0.93 MoO3 / C precursor was placed in a 15% hydrogen argon plasma atmosphere and calcined at a reaction temperature of 600°C for 50 min to obtain dark gray Mo2C / C material.

[0080] It was tested that the H 0.93 MoO3 / C precursor is a microsphere with a diameter of 1.55 pm, the MoO2 / C material is a microsphere with a diameter of 1.05 pm, and the Mo2C / C material is a microsphere with a diameter of 0.85 pm, and the surfaces of them are all negatively charged.

[0081] Example 5:

[0082] S1: 100 g of commercial MoO3 powder was stirred and dispersed in a mixed solution of 600 mL of methanol and 400 mL of ethylene glycol, and then 10 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle for microwave-assisted solvothermal reaction. The reaction was carried out at a reaction temperature of 180°C for 30 min. Centrifugation or filtration was performed using distilled water three times and ethanol twice to obtain brownish H 0.93 MoO3 / C precursor;

[0083] S2: The obtained H 0.93 MoO3 / C precursor was calcined under an argon plasma atmosphere at a reaction temperature of 600°C for 50 min to obtain brownish black MoO2 / C material.

[0084] The obtained H 0.93The MoO3 / C precursor was placed in a 15% hydrogen argon plasma atmosphere and calcined at 500°C for 40 min to obtain dark gray Mo2C / C material.

[0085] The H 0.93 The MoO3 / C precursor was micron spheres with a diameter of 1.55 μm, the MoO2 / C material was micron spheres with a diameter of 1.05 μm, and the Mo2C / C material was micron spheres with a diameter of 0.75 μm, and the surfaces of all were negatively charged.

[0086] Example 6:

[0087] S1: 100 g of commercial MoO3 powder was stirred and dispersed in a mixed solution of 350 mL of ethanol and 650 mL of ethylene glycol, and 25 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out at 190°C for 40 min. After centrifugation or filtration, the product was washed with distilled water three times and ethanol twice to obtain brownish H 0.93 MoO3 / C precursor;

[0088] S2: The obtained H 0.93 The MoO3 / C precursor was placed in an argon plasma atmosphere and calcined at 550°C for 60 min to obtain brownish black MoO2 / C material.

[0089] The obtained H 0.93 The MoO3 / C precursor was placed in a 15% hydrogen argon plasma atmosphere and calcined at 550°C for 60 min to obtain dark gray Mo2C / C material.

[0090] The H 0.93 The MoO3 / C precursor was micron spheres with a diameter of 1.60 μm, the MoO2 / C material was micron spheres with a diameter of 1.08 μm, and the Mo2C / C material was micron spheres with a diameter of 0.82 μm, and the surfaces of all were negatively charged.

[0091] Comparative Example 1:

[0092] 100 g of commercial MoO3 powder was stirred and dispersed in a mixed solution of 500 mL of isopropyl alcohol and 500 mL of glycerol, and 20 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out with a fixed holding time of 30 min and controlled reaction temperatures of 140°C, 160°C and 220°C, respectively. After centrifugation or filtration, the product was washed with distilled water three times and ethanol twice to obtain the precursor.

[0093] Figure 9The results show that in the process of microwave-assisted solvothermal reaction, when the temperature is lower than 160℃, the obtained product is mainly in amorphous state, H 0.93 MoO3 phase has not been crystallized; when the temperature is higher than 220℃, H 0.93 MoO3 phase has clear X-ray diffraction peaks, that is, the crystallinity of the material is further improved with the increase of temperature, and there is no other impurity phase. However, the microwave-assisted solvothermal reaction at higher temperature has high requirements for equipment, high energy consumption, and safety problems such as microwave leakage.

[0094] Comparative Example 2:

[0095] 100 g of commercial MoO3 powder was dispersed in a mixed solution of 500 mL of isopropanol and 500 mL of glycerol by stirring, and 20 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out. The reaction temperature was fixed at 200℃, and the holding time was controlled at 120 min, 150 min, and 180 min, respectively. After centrifugation or filtration, three times of distilled water and twice of ethanol washing were carried out to obtain the precursor.

[0096] Figure 10 The results show that in the process of microwave-assisted solvothermal reaction, under the condition of 200℃, prolonging the holding time can obtain H 0.93 MoO3 / C precursor with higher crystallinity, and no other impurity phase, which is only a secondary recrystallization of minerals. However, the advantage of microwave-assisted solvothermal reaction is that it can greatly shorten the time required for mineralization and crystallization in traditional solvothermal reaction. Longer time requires high equipment and high energy consumption, and there are safety problems such as microwave leakage.

[0097] Comparative Example 3:

[0098] 100 g of commercial MoO3 powder was dispersed in 1000 mL of isopropanol solution or 1000 mL of glycerol solution, that is, 100% isopropanol and 100% glycerol, and 20 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out at a reaction temperature of 200℃ for 30 min. After centrifugation or filtration, three times of distilled water and twice of ethanol washing were carried out to obtain the precursor.

[0099] Figure 11 The results show that after high-temperature reaction of MoO3 in isopropanol solution, MoO 3-x phase is obtained, and MoO3 phase is still partially retained, indicating that the high-temperature thermal reduction of MoO3 by isopropanol solvent is not sufficient, which is a necessary condition for the synthesis of non-MoO3; after high-temperature reaction of MoO3 in glycerol solution, H 0.93 MoO3 phase is obtained, and there is no other impurity phase, indicating that the high-temperature thermal reduction of MoO3 by glycerol is sufficient, which is a necessary condition for the synthesis of H0.93 Necessity condition of MoO3 phase synthesis. Therefore, the ratio of the components of the mixed solution in the microwave-assisted solvothermal reaction directly determines the H 0.93 Conversion of MoO3 phase.

[0100] Figure 12 The results show that the microwave-assisted solvothermal reaction of 100% isopropanol solvent still retains the block structure of MoO3 precursor, which also indicates that the reaction is insufficient; and the microwave-assisted solvothermal reaction of 100% glycerol solvent mainly obtains cross-linked microspheres. Therefore, the difference in micro-morphology is mainly related to the viscosity difference between isopropanol and glycerol.

[0101] Comparative Example 4:

[0102] 100 g of commercial MoO3 powder was dispersed in a mixed solution of 500 mL of isopropanol and 500 mL of glycerol by stirring, and the amount of added triblock copolymer P123 stabilizer was controlled to be 0 g and 50 g, respectively. The obtained suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out at a reaction temperature of 200°C for 30 min. After centrifugation or filtration, the obtained precursor was washed with distilled water three times and ethanol twice.

[0103] Figure 13 The results show that without adding the triblock copolymer P123 stabilizer, the obtained precursor is a disordered accumulation of nanoscale particles; and with the addition of 50 g of triblock copolymer P123 stabilizer, the obtained precursor is a microsphere with uneven size, indicating that the triblock copolymer P123 stabilizer can cross-link and agglomerate the nanoscale particles during the microwave-assisted solvothermal reaction to form a secondary spherical structure, but excessive addition of the stabilizer can strengthen the Oswald ripening, so that the smaller crystalline or sol particles in the solute are dissolved and deposited on the larger crystalline or sol particles again. Therefore, the appropriate content of the stabilizer in the microwave-assisted solvothermal reaction directly determines the self-assembly of the secondary microsphere structure, and plays an important role in stabilizing the uniform microsphere structure.

[0104] Comparative Example 5:

[0105] 100 g of commercial MoO3 powder was dispersed in a mixed solution of 500 mL of isopropanol and 500 mL of glycerol by stirring, and 20 g of triblock copolymer P123 stabilizer was added. The obtained stable suspension was placed in a reaction kettle, and microwave-assisted solvothermal reaction was carried out at a reaction temperature of 200°C for 30 min. After centrifugation or filtration, the obtained brown H 0.93 MoO3 / C precursor; the obtained H 0.93The MoO3 / C precursor was placed in an argon plasma, and calcination temperatures were controlled at 650℃ and 700℃ respectively, and calcination reaction was performed for 40 min to obtain MoO2 / C series materials.

[0106] Figure 14 The results show that MoO2 pure phase can be obtained when the temperature range is 500-600℃, and the crystallinity of the material becomes higher as the calcination temperature increases; when the temperature is increased to 650℃, Mo2C impurity phase appears in MoO2 / C, and MoO2 / Mo2C composite material is obtained; when the temperature is further increased to 700℃, Mo2C / C is further carbothermal reduced, and Mo impurity phase appears in MoO2 / Mo2C / C, and MoO2 / Mo2C / Mo composite material is obtained. Therefore, in order to obtain MoO2 pure phase, the reaction temperature needs to be controlled to be less than 650℃.

[0107] Comparative Example 6:

[0108] 100g of commercial MoO3 powder was dispersed in a mixed solution of 500mL of isopropyl alcohol and 500mL of glycerol (1:1, by volume) by stirring, and 20g of triblock copolymer P123 stabilizer was added, and the obtained stable suspension was placed in a reaction kettle for microwave-assisted solvothermal reaction, and was kept at 200℃ for 30 min. After centrifugation or filtration, the obtained brownish H 0.93 MoO3 / C precursor; the obtained H 0.93 The MoO3 / C precursor was placed in an argon plasma, and calcination temperatures were controlled at 400℃ and 700℃ respectively, and calcination reaction was performed for 40 min to obtain Mo2C / C series materials.

[0109] Figure 15 The results show that Mo2C phase appears when the temperature is increased to 400℃, but there is an impurity phase; Mo2C pure phase can be obtained when the temperature is increased to 600℃; and Mo2C pure phase is still obtained when the temperature is further increased to 700℃, and the crystallinity of the material becomes higher as the calcination temperature increases. Therefore, in order to obtain Mo2C pure phase, the reaction temperature needs to be controlled to be greater than 400℃.

[0110] The above embodiments of the present application shown only part of the preferred embodiments of the present application, and cannot be limited to the present application, and any modification, equivalent replacement and improvement made by those skilled in the art without departing from the essence of the present application are within the protection scope of the present application.

Claims

1. A method for reduction of molybdenum trioxide to molybdenum dioxide or molybdenum carbide, characterized in that, It comprises the following steps: S1 MoO3 powder is stirred and dispersed in a mixed solution of monohydric alcohol and polyhydric alcohol, then a triblock copolymer P123 stabilizer is added, and the obtained suspension is subjected to microwave-assisted solvothermal reaction, centrifugation or filtration and washing to obtain brownish H 0.93 MoO3 / C precursor microspheres; wherein, The volume ratio of the monohydric alcohol and the polyhydric alcohol is 1:2-2:1; The mass ratio of the added amount of the triblock copolymer P123 stabilizer to the mixed solution of the monohydric alcohol and the polyhydric alcohol is 10g-30g / L; The suspension is prepared by microwave-assisted solvothermal reaction at a temperature of 180-210℃ and a holding time of 20-40min. S2: H obtained in step S1 0.93 The MoO3 / C precursor was placed in an argon plasma atmosphere and calcined at a high temperature of 500-600°C for 30-60 min to obtain brown-black MoO2 / C microspheres with a diameter of 1.00-1.10 μm. Alternatively, H 0.93 MoO3 / C precursor was calcined at 500-600℃ for 30-60min under hydrogen-argon plasma atmosphere to obtain dark gray Mo2C / C microspheres with a diameter of 0.75-0.85μm.

2. The method for reducing molybdenum trioxide to generate molybdenum dioxide or molybdenum carbide according to claim 1, wherein: In the S1 step, the monohydric alcohol is at least one of methanol, ethanol and isopropyl alcohol, and the polyhydric alcohol is at least one of ethylene glycol and glycerol.

3. The method for reducing molybdenum trioxide to produce molybdenum dioxide or molybdenum carbide according to claim 1 or 2, wherein The hydrogen in the hydrogen-argon plasma atmosphere accounts for 15% of the total amount.

4. The application of the MoO2 / C material and the Mo2C / C material prepared by the method of any one of claims 1-3 to negative electrode materials of lithium ion batteries.

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