Three-dimensional porous carbon loaded molybdenum-based compound electrode material and preparation method and application thereof

Abstract

The invention discloses a three-dimensional porous carbon loaded molybdenum-based compound electrode material and a preparation method and application thereof. The preparation method comprises the following steps: adding a molybdenum source into a solution dissolved with molten salt and PVP powder to form a uniform solution; performing freeze drying to obtain a solid precursor; calcining the solid precursor in a protective atmosphere to obtain a calcined product; and removing impurities from the calcined product to obtain the three-dimensional porous carbon-loaded molybdenum-based compound electrode material. Wherein different types of molybdenum-based compound electrode materials are obtained by controlling the use amount of the PVP powder. In the reaction process, soluble molten salt exists among generated molybdenum-based compound particles, agglomeration among the particles is reduced, and the method is simple and mild in preparation condition and low in cost. When the composite material is used as a negative electrode material of a lithium ion battery, the common problems of poor conductivity, easy agglomeration of particles, volume effect and the like when a molybdenum-based compound is applied to the lithium ion battery are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of electrochemistry and nanomaterials, and particularly relates to a three-dimensional porous carbon-supported molybdenum-based compound electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Since the new century, with the vigorous development of electric vehicles and renewable clean energy, the field of electrochemical energy storage has broad development prospects. As the main energy source of the power battery system of current new energy electric vehicles, lithium-ion batteries have the advantages of high energy density, high specific power, long life, safety and environmental protection. As the main component of rechargeable secondary batteries, electrode materials play a key role in the electrochemical performance of lithium-ion batteries.

[0003] Three-dimensional porous carbon materials have been widely studied in the field of energy storage due to their high conductivity, large specific surface area, high mechanical strength, and abundant active sites. The rich, interconnected, and stable porous structure enables the porous carbon material to be used as a loading matrix to load a variety of metal-based nanomaterials. The prepared electrode material inhibits the agglomeration of nanomaterials, provides abundant active sites, shortens the ion or electron transport path, and has high structural stability. Therefore, when used as the anode material of lithium-ion batteries, it exhibits good storage performance.

[0004] In terms of preparation methods, hydrothermal and solvothermal combined with template technology are common methods for preparing three-dimensional porous carbon-supported molybdenum-based compound electrode materials. However, this method has the disadvantages of particle growth agglomeration, easy caking, cumbersome production process, and low yield. These have severely restricted its practical application and performance improvement in lithium-ion batteries.

[0005] Currently, there is still a lack of a method for preparing three-dimensional porous carbon-supported molybdenum-based compound electrode materials with simple, efficient, controllable morphology and product. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a three-dimensional porous carbon-supported molybdenum-based compound electrode material, a preparation method thereof, and an application thereof. The technological process of the present invention is simple, low-cost, efficient, and suitable for large-scale production. The presence of porous carbon effectively buffers the volume effect in the electrochemical process, improves the conductivity of the material, and prevents particle agglomeration during the preparation of molybdenum-based compounds, thereby facilitating the exertion of the intrinsic capacity of molybdenum-based compounds.

[0007] The technical solution provided by the present invention is as follows:

[0008] In the first aspect, the present invention provides a preparation method of a three-dimensional porous carbon-supported molybdenum-based compound electrode material, comprising the following steps:

[0009] Add a molybdenum source to the solution containing the molten salt and PVP powder to form a homogeneous solution; after freeze-drying, a solid precursor is obtained;

[0010] In a protective atmosphere, calcine the solid precursor to obtain a calcined product;

[0011] Purify the calcined product to obtain a three-dimensional porous carbon-supported molybdenum-based compound electrode material.

[0012] In a possible implementation, the molybdenum source includes molybdic acid and thio molybdate; the molten salt includes NaCl, KCl, CaCl 2 , MgCl 2 and LiCl.

[0013] Furthermore, the molybdic acid includes phosphomolybdic acid, sodium molybdate and ammonium molybdate; the thio molybdate includes ammonium thio molybdate. Preferably, the molybdenum source is phosphomolybdic acid.

[0014] In a possible implementation, the average molecular weight of the PVP powder is 30000 - 58000 (K25 - K30).

[0015] In a possible implementation, the freeze-drying temperature is -60 to -40 °C, and the freeze-drying time is 12 to 24 h.

[0016] In a possible implementation, the heating rate of the calcination is 2 to 10 °C / min; the heat preservation conditions are: 700 to 1000 °C, and heat preservation for 1 to 5 h.

[0017] Furthermore, the heat preservation temperature of the heat preservation conditions is 800 °C.

[0018] In a possible implementation, the method of impurity removal includes removing the molten salt by washing with water.

[0019] In a possible implementation, the protective gas includes argon, nitrogen and helium.

[0020] In a possible implementation, different types of three-dimensional porous carbon-supported molybdenum-based compound electrode materials are obtained by changing the dosage ratio of the PVP powder in the preparation method.

[0021] Furthermore, if the mass ratio of the molybdenum source to the PVP powder is 1:(1.18 - 1.60), the product is three-dimensional porous carbon-supported Mo 2 C; if the mass ratio of the molybdenum source to the PVP powder is 1:(1.62 - 2.00), the product is three-dimensional porous carbon-supported Mo 2 N-Mo 2C hetero-structure; if the mass ratio of the molybdenum source to the PVP powder is 1:(2.05 - 4.00), the product is Mo supported on three-dimensional porous carbon 2 N.

[0022] Furthermore, the amount of the molten salt used is 1 - 1.5 times the sum of the masses of the PVP powder and the molybdenum source.

[0023] In a second aspect, the present invention provides a molybdenum-based compound electrode material supported on three-dimensional porous carbon, which is prepared by the method described in the first aspect.

[0024] In a third aspect, the present invention provides the application of the molybdenum-based compound electrode material supported on three-dimensional porous carbon described in the second aspect as a negative electrode material for lithium or sodium or potassium ion batteries.

[0025] Advantages of the present invention:

[0026] 1) The present invention mainly uses soluble molten salt, molybdenum source, and PVP as reaction raw materials, and through freeze-drying and one-step high-temperature calcination method, realizes the controllable preparation of various molybdenum-based compound electrode materials supported on three-dimensional porous carbon. During the preparation process, the presence of the molten salt prevents the connection and aggregation between particles, and the three-dimensional porous carbon generated by PVP provides a stable conductive carbon skeleton, thus effectively buffering the volume change during the charge and discharge process of the molybdenum-based compound material.

[0027] 2) The material prepared by the present invention exhibits excellent cycle stability and high specific capacity in terms of electrochemical performance.

[0028] 3) The raw materials used in the method of the present invention are non-toxic and inexpensive, and the process method is simple, and it can be used for large-scale industrial production.

[0029] 4) The method of the present invention can controllably prepare different types of molybdenum-based composite materials, including Mo supported on three-dimensional porous carbon 2 C, Mo supported on three-dimensional porous carbon 2 N-Mo 2 C, and Mo supported on three-dimensional porous carbon 2 N composite materials, only by adjusting the mass ratio of the molybdenum source to PVP. This method can realize the switching of product types in a large-scale industrial production line. Description of the drawings

[0030] Figure 1 Mo 2 XRD pattern of the Mo

[0031] Figure 2 Mo 2 SEM image of the Mo

[0032] Figure 3Mo 2 C-Mo 2 XRD pattern of N / C electrode material

[0033] Figure 4 Mo 2 XRD pattern of N / C electrode material.

[0034] Figure 5 Mo 2 When the C / C electrode material is applied to a lithium-ion battery, at a current density of 0.5 Ag -1 cycling curve. Detailed implementation manners

[0035] The following further describes the specific implementation steps of the present invention in conjunction with the accompanying drawings. The content of the present invention is not limited thereto at all.

[0036] The preparation method of the three-dimensional porous carbon-supported molybdenum-based compound electrode material provided by the present invention is characterized by including the following steps:

[0037] S1, adding a molybdenum source to a solution containing a molten salt and PVP powder to form a homogeneous solution; after freeze-drying, obtaining a solid precursor;

[0038] S2, calcining the solid precursor in a protective atmosphere to obtain a calcined product;

[0039] S3, removing impurities from the calcined product to obtain a three-dimensional porous carbon-supported molybdenum-based compound electrode material.

[0040] In a possible implementation manner, the molybdenum source includes molybdic acid and thiomolybdate; the molten salt includes NaCl, KCl, CaCl 2 , MgCl 2 and LiCl.

[0041] Furthermore, the molybdic acid includes phosphomolybdic acid, sodium molybdate and ammonium molybdate; the thiomolybdate includes ammonium thiomolybdate.

[0042] In a possible implementation manner, the average molecular weight of the PVP powder is 30000-58000 (K25-K30).

[0043] Preferably, the average molecular weight of the PVP powder is 30000-40000, K25.

[0044] In a possible implementation manner, the freeze-drying temperature is -60 to -40 °C, and the freeze-drying time is 12 to 24 h.

[0045] In a possible implementation manner, the heating rate of the calcination is 2-10 °C / min; the heat preservation condition is: 700-1000 °C, and the heat preservation time is 1-5 h.

[0046] Further, the heat preservation temperature of the heat preservation condition is 800 °C.

[0047] In a possible implementation manner, the method for removing impurities includes removing the molten salt by water washing.

[0048] In a possible implementation manner, the protective gas includes argon, nitrogen, and helium.

[0049] In a possible implementation manner, the preparation method obtains different types of three-dimensional porous carbon-supported molybdenum-based compound electrode materials by changing the dosage ratio of PVP powder.

[0050] Further, if the mass ratio of the molybdenum source to the PVP powder is 1:(1.18 - 1.60), the product is three-dimensional porous carbon-supported Mo 2 C; if the mass ratio of the molybdenum source to the PVP powder is 1:(1.62 - 2.00), the product is three-dimensional porous carbon-supported Mo 2 N-Mo 2 C heterostructure; if the mass ratio of the molybdenum source to the PVP powder is 1:(2.05 - 4.00), the product is three-dimensional porous carbon-supported Mo 2 N.

[0051] Furthermore, if the mass ratio of the molybdenum source to the PVP powder is 1:1.18, the product is three-dimensional porous carbon-supported Mo 2 C; if the mass ratio of the molybdenum source to the PVP powder is 1:1.62, the product is three-dimensional porous carbon-supported Mo 2 N-Mo 2 C heterostructure; if the mass ratio of the molybdenum source to the PVP powder is 1:2.05, the product is three-dimensional porous carbon-supported Mo 2 N.

[0052] Further, the dosage of the molten salt is 1 - 1.5 times the sum of the masses of the PVP powder and the molybdenum source.

[0053] The relevant principle of the present invention is as follows: when the mass ratio of the PVP powder to the molybdenum source is (1.18 - 1.60):1, at this time, the NH 3 atmosphere generated by the pyrolysis of PVP is less, and mainly a reducing carbon-containing gas flow is generated to form a single-phase Mo 2 C with the molybdenum source, and amorphous carbon converted into a three-dimensional structure under the confinement of the molten salt template; as the mass ratio of the PVP powder to the molybdenum source increases to (1.62 - 2.00):1, in addition to forming Mo 2 C with the molybdenum source and converting into amorphous carbon during the pyrolysis of PVP, since the electronegativity of N is greater than that of C, N atoms preferentially combine with Mo atoms, Mo 2N begins to appear, resulting in Mo in the generated porous carbon 2 C and Mo 2 N two-phase coexistence; when the dosage of PVP increases to a certain extent [PVP: molybdenum source = (2.05 - 4.00):1], a large amount of NH 3 atmosphere will be generated, providing sufficient nitrogen source. At this time, the molybdenum source reacts with the surrounding nitrogen source at high temperature and is completely converted into single-phase Mo 2 N, and PVP is pyrolyzed at high temperature to transform into an amorphous carbon skeleton.

[0054] In the following examples, the average molecular weight of PVP is 30000 - 40000, K25.

[0055] Example 1

[0056] Add 0.3824 g of PVP and 1 g of sodium chloride to a beaker (50 mL) containing 10 mL of water, and perform magnetic stirring for 1 h under the condition of a 40°C water bath. After complete dissolution, add 0.3232 g of phosphomolybdic acid and stir for 1 h; freeze-dry the obtained homogeneous mixture solution at -40°C for 12 h; place the solid precursor obtained by freeze-drying in a tube furnace and heat it to 800°C at a heating rate of 5°C / min under N 2 protective atmosphere, hold for 2 h; wait until it cools to room temperature, wash the calcined black product with deionized water multiple times to dissolve the sodium chloride template, and dry it at 60°C for 12 h to obtain a three-dimensional porous carbon-supported molybdenum carbide electrode material. Named Mo 2 C / C.

[0057] Figure 1 For the XRD pattern of the prepared Mo 2 C / C electrode material. As shown in the figure, eight peaks of (100), (002), (101), (102), (110), (103), (112) and (201) can be clearly observed, corresponding to β-phase Mo 2 C (PDF#35 - 0787), and there are no other impurity peaks, confirming that the prepared sample is a pure Mo 2 C phase. Figure 2 For the SEM image of the prepared Mo 2 C / C electrode material. As shown in the figure, the Mo 2 C / C composite material presents a honeycomb network structure constructed by PVP-derived carbon sheets. And interconnected large pores and Mo 2 C particles can be observed to be uniformly loaded on the three-dimensional porous carbon skeleton.

[0058] Example 2

[0059] Add 0.5236 g of PVP and 1 g of sodium chloride into a beaker (50 mL) containing 10 mL of water, and perform magnetic stirring for 1 h under the condition of a 40 °C water bath. After complete dissolution, add 0.3232 g of phosphomolybdic acid and stir for 1 h; freeze-dry the obtained homogeneous mixture solution at -40 °C for 12 h; place the solid precursor obtained by freeze-drying in a tubular furnace and heat it to 800 °C at a heating rate of 5 °C / min under a N 2 protective atmosphere, and keep it at this temperature for 2 h; wait until it cools down to room temperature, wash the calcined black product with deionized water multiple times to dissolve the sodium chloride template, and dry it at 60 °C for 12 h to obtain a three-dimensional porous carbon-supported molybdenum carbide and molybdenum nitride electrode material. Name it Mo 2 C-Mo 2 N / C.

[0060] Figure 3 To prepare the XRD pattern of the Mo 2 C-Mo 2 N / C electrode material. As shown in the figure, it can be clearly observed that the seven peaks of (100), (101), (102), (110), (103), (112) and (201) of Mo 2 C and the three peaks of (111), (200) and (220) of Mo 2 N correspond to the β-phase Mo 2 C (PDF#35-0787) and the cubic-phase Mo 2 N (PDF#25-1366). The absence of other impurity peaks confirms that the prepared sample is a pure Mo 2 N-Mo 2 C phase.

[0061] Example 3

[0062] Add 0.6648 g of PVP and 1 g of sodium chloride into a beaker (50 mL) containing 10 mL of water, and perform magnetic stirring for 1 h under the condition of a 40 °C water bath. After complete dissolution, add 0.3232 g of phosphomolybdic acid and stir for 1 h; freeze-dry the obtained homogeneous mixture solution at -40 °C for 12 h; place the solid precursor obtained by freeze-drying in a tubular furnace and heat it to 800 °C at a heating rate of 5 °C / min under a N 2 protective atmosphere, and keep it at this temperature for 2 h; wait until it cools down to room temperature, wash the calcined black product with deionized water multiple times to dissolve the sodium chloride template, and dry it at 60 °C for 12 h to obtain a three-dimensional porous carbon-supported molybdenum nitride electrode material. Name it Mo 2 N / C.

[0063] Figure 4 To prepare the 2XRD pattern of the N / C electrode material. As shown in the figure, four peaks of (111), (200), (220) and (311) can be clearly observed, corresponding to cubic phase Mo 2 N (PDF#25-1366), and the absence of other impurity peaks confirms that the prepared sample is pure Mo 2 N phase.

[0064] Example 4

[0065] The prepared electrode material was tested for its electrochemical performance. For example, at different current densities, its cycle life, Coulomb efficiency, and AC impedance were tested, and the reasons for its excellent electrochemical performance were analyzed.

[0066] I. Preparation of button-type sodium-ion batteries

[0067] Using the Mo 2 C / C, Mo 2 C-Mo 2 N / C, Mo 2 N / C electrode materials to prepare CR2025 button-type lithium-ion batteries. The specific preparation method is as follows:

[0068] (1) The active material, acetylene black, and a 5% mass fraction of polytetrafluoroethylene aqueous dispersion emulsion were uniformly mixed together to obtain a mixture; N-methylpyrrolidone was added dropwise to the mixture to obtain a mixture for coating;

[0069] Among them, the active material in step (1) is the electrode materials prepared in all the above examples;

[0070] In the mixture in step (1), the mass fraction of the active material is 70%, the mass fraction of acetylene black is 20%, and the mass fraction of PVDF is 10%;

[0071] In step (1), the volume ratio of N-methylpyrrolidone to the mass of the active material is (1-2 mL):(5-10 mg);

[0072] (2) The coating mixture obtained in step (1) was uniformly coated on a copper foil with a diameter of 12 mm, and then vacuum dried at 60 °C for 12 h to obtain a pole piece with active material on its surface; the mass of the active material on the pole piece was obtained by the difference method;

[0073] (3) Transfer the electrode sheet with active substances on its surface to a vacuum glove box to complete the assembly of the button battery. Among them, the polypropylene separator (PP) is used as the battery separator, the lithium sheet is used as the counter electrode, and the electrode sheet with active substances on its surface is used as the working electrode. After assembling the working electrode, separator, counter electrode, gasket and battery case into a CR2025 button battery in the glove box, use a sealing machine to seal the button battery. Finally, let the prepared button battery stand at room temperature for 12 h to activate the battery, thus completing the preparation of the CR2025 button-type lithium-ion battery.

[0074] Second, conduct cyclic life tests and electrochemical performance analyses on the battery.

[0075] The analysis results are as follows: Figure 5 For the lithium-ion battery prepared with the electrode material (Mo 2 C / C) of Example 1, the cyclic curve at a current density of 0.5 Ag -1 . When the current density is 0.5 Ag -1 , after 60 cycles, its reversible specific capacity still remains at about 640 mAhg -1 , while the commercially available molybdenum carbide of the existing materials is only about 50 mAhg -1 . The results show that the composite of porous carbon effectively buffers the volume expansion, effectively inhibits the aggregation between Mo 2 C particles (the formation of bulk Mo 2 C), and increases the lithium storage active sites.

[0076] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent replacements and improvements made by those skilled in the art within the technical scope disclosed by the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional porous carbon-supported molybdenum-based compound electrode material, characterized in that: The following steps are involved: Adding a molybdenum source to a solution containing molten salt and PVP powder to form a uniform solution; freeze-drying to obtain a solid precursor; calcining the solid precursor in a protective atmosphere to obtain a calcined product; The calcined product is decontaminated to obtain a three-dimensional porous carbon-supported molybdenum-based compound electrode material.

2. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The molybdenum source includes molybdic acid and thiomolybdate; the molten salt includes NaCl, KCl, CaCl2, MgCl2 and LiCl.

3. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The average molecular weight of the PVP powder is 30,000-58,000.

4. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The freeze drying temperature is -60 to -40°C, and the freeze drying time is 12 to 24 hours.

5. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The heating rate of the calcination is 2-10°C / min; the heat preservation conditions are: 700-1000°C, heat preservation for 1-5h.

6. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The impurity removal method includes removing the molten salt by water washing.

7. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 1, characterized in that: The preparation method obtains different types of three-dimensional porous carbon-loaded molybdenum-based compound electrode materials by changing the usage ratio of PVP powder and molybdenum source.

8. The method for preparing the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 7, characterized in that: If the mass ratio of the molybdenum source to the PVP powder is 1:(1.18-1.60), the product is three-dimensional porous carbon-loaded Mo2C; if the mass ratio of the molybdenum source to the PVP powder is 1:(1.62-2.00), the product is a three-dimensional porous carbon-loaded Mo2N-Mo2C heterostructure; if the mass ratio of the molybdenum source to the PVP powder is 1:(2.05-4.00), the product is a three-dimensional porous carbon-loaded Mo2N; the amount of the molten salt used is 1-1.5 times the sum of the masses of the PVP powder and the molybdenum source.

9. A three-dimensional porous carbon-supported molybdenum-based compound electrode material, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Use of the three-dimensional porous carbon-supported molybdenum-based compound electrode material according to claim 9 as a negative electrode material for lithium, sodium or potassium ion batteries.

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