A type of scaly MoO 2 / Mo 2 C@Poplar catkin biomass carbon composite material and its application

Abstract

This invention belongs to the field of functional material preparation, and particularly relates to a flake-like MoO2. 2 / Mo 2 C@poplar catkin biomass carbon composite material and its application: scaly MoO2 was prepared by a method of poplar catkin carbonization-impregnation with molybdate-calcination in an inert atmosphere. 2 / Mo 2 C@poplar catkin biomass carbon composite material, and further calcined the material in air to prepare hollow tubular MoO 3 The materials and synthesis methods are simple and easy to implement. The materials obtained in this invention exhibit excellent performance as anode materials for lithium-ion batteries and cathode carrier materials for lithium-sulfur batteries, which is beneficial for the preparation of high-energy-density electrode materials. Moreover, the preparation method is inexpensive and can simultaneously solve the harm caused by poplar catkins, realizing the high-value utilization of poplar catkins.

Description

A flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material and its application Technical Field

[0001] This invention belongs to the field of functional material preparation, specifically relating to a flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material and its application. Background Technology

[0002] Developing efficient energy storage systems plays a crucial role in the utilization of renewable energy and the adjustment of the energy structure. Secondary batteries, with their high efficiency, cleanliness, and convenience, possess significant advantages in the energy storage field. Currently, lithium-ion batteries dominate the market due to their high voltage, low self-discharge rate, lack of memory effect, and long cycle life, and are widely used in electronic products and new energy vehicles. However, with economic development, higher demands are being placed on the energy density of secondary batteries, and the key to improving energy density lies in increasing the energy density of electrode materials. Therefore, the preparation of high-specific-energy electrode materials is crucial for the development of lithium secondary batteries.

[0003] Transition metal oxides possess unique energy level structures, high stability, and tunable structures, making them a research hotspot in the field of new energy materials. Among them, molybdenum oxide (MoO) boasts advantages such as high theoretical capacity, high chemical and thermal stability, low cost, and environmental friendliness, making it an ideal electrode material. Specifically, when used as the anode material in lithium-ion batteries, MoO has a theoretical specific capacity as high as 838 mAh g⁻¹. -1 Furthermore, it possesses good conductivity, a high melting point, high stability, and is environmentally friendly. Therefore, molybdenum dioxide was used as the anode material for lithium batteries to replace graphite anodes (theoretical capacity 372 mAh g). -1 Molybdenum dioxide (MoO2) is beneficial for improving the energy density of lithium-ion batteries. However, it suffers from capacity decay and structural damage due to volume expansion during electrode cycling. For example, Zhang et al. prepared MoO2 nanoparticles by hydrothermal reaction at 200℃ for 12 h using ammonium heptamolybdate tetrahydrate as the molybdenum source. The full cell assembled with MoO2 as the negative electrode material and LiCoO2 positive electrode had an energy density of 179 Wh / kg. -1 (Electrochimica Acta, 2016, 213, 416). MoO3 is also a promising anode material for lithium-ion batteries, with a theoretical capacity as high as 1100 mAh g⁻¹. -1 However, its inherently poor electronic conductivity and high volume expansion during charge and discharge processes hinder its ability to achieve high practical capacity. Sahu et al. prepared a composite material of orthorhombic α-MoO3 nanoribbons and multi-walled carbon nanotubes using a microwave hydrothermal method (180℃, 50Hz, 500W, 120psi), achieving a capacity of 654 mAh g⁻¹ at 1C rate. -1(Advanced Energy Materials, 2020, 10, 2001627). All of the above preparation methods suffer from complex processes that are difficult to implement and mass-produce.

[0004] Furthermore, molybdenum dioxide and molybdenum trioxide possess strong polarity and catalytic activity, making them suitable as carrier materials for sulfur in lithium-sulfur batteries. They can catalyze and promote the electrochemical conversion of sulfur, and suppress the shuttle effect of lithium polysulfides, the discharge intermediates of sulfur, through polar adsorption, thereby enabling the sulfur cathode to achieve high energy density. For example, Yang et al. grew MoO3 / MoO2 on carbon paper as a sulfur carrier, which effectively adsorbed lithium polysulfides. The corresponding sulfur cathode maintained a capacity of 828.1 mAh g after 500 cycles at 0.5C. -1 .

[0005] Therefore, molybdenum dioxide and molybdenum trioxide show promising applications as both negative electrode materials in lithium-ion batteries and sulfur supports in positive electrodes of lithium-sulfur batteries. However, the preparation methods for most molybdenum oxide nanomaterials are quite demanding and complex. Developing simpler synthesis methods and designing structures to mitigate the damage to the electrode structure caused by volume expansion while simultaneously improving electrochemical cycling stability are urgent problems to be solved.

[0006] Poplar catkins are hollow tubular fibers with a surface rich in organic functional groups, possessing a large specific surface area, light weight, and easy collection. However, during the poplar fruit ripening season, large quantities of catkins are dispersed into the air, adversely affecting the human respiratory system and even causing allergic reactions. Furthermore, the sheer volume of catkins impacts urban cleanliness and road traffic, causing traffic problems and posing a fire hazard. Carbonizing poplar catkins and preparing catkin-derived carbon / metal oxide composite materials could significantly reduce their harmful effects while increasing their value, resulting in highly efficient and inexpensive functional materials.

[0007] How to organically combine the above elements became one of the problems the inventor needed to solve. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material and its applications. The flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material was prepared by carbonizing poplar catkins, impregnating with molybdate, and calcining in an inert atmosphere. Furthermore, this material was calcined in air to prepare hollow tubular MoO3 material. The synthesis method is simple and easy to implement. The material obtained by this invention exhibits excellent performance as a negative electrode material for lithium-ion batteries and a positive electrode carrier material for lithium-sulfur batteries, which is beneficial for the preparation of high-energy-density electrode materials. Moreover, the preparation method is low-cost and can simultaneously solve the harm caused by poplar catkins, achieving high-value utilization of poplar catkins.

[0009] The specific technical solution of the present invention is as follows:

[0010] A flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is a structure in which MoO2 / Mo2C nanosheets are loaded on the surface of poplar catkin biomass carbon. The loading amount of MoO2 / Mo2C nanosheets is 15-50 wt%, and the loading effect is good.

[0011] The poplar catkin biomass carbon mentioned above is prepared from poplar catkins as raw material, and its preparation method is as follows:

[0012] Poplar catkins are carbonized in a tubular furnace under an argon atmosphere to obtain poplar catkin biomass carbon; preferably, the heating rate is 2-5℃ / min. -1 The insulation temperature is 400℃ and the insulation time is 6 hours.

[0013] More specifically, the above-mentioned carbon composite material was prepared into a flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material by carbonization of poplar catkins-impregnation with molybdate-calcination in an inert atmosphere; based on this, hollow tubular MoO3 material was prepared by calcining the material in air.

[0014] The specific applications of the above-obtained flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material or hollow tubular MoO3 material can be as a negative electrode material for lithium-ion batteries or as a carrier material for the positive electrode of lithium-sulfur batteries.

[0015] The specific steps for preparing the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material are as follows:

[0016] (1) The poplar catkins were carbonized in a tubular furnace under an argon atmosphere to obtain poplar catkin biomass carbon; wherein the heating rate was 2-5℃ / min. -1 The insulation temperature is 400℃ and the insulation time is 6 hours;

[0017] (2) The carbonized poplar catkins were soaked in ammonium molybdate solution, then filtered to separate the poplar catkins and dried. The specific steps are as follows: a certain mass of ammonium molybdate tetrahydrate was added to a certain volume of distilled water and ultrasonically dissolved to obtain ammonium molybdate solution; poplar catkin biomass carbon was placed in the above ammonium molybdate solution, ultrasonicated for 5 min, soaked for 2 h, filtered to separate the poplar catkins and dried at 60℃ for 12-24 h.

[0018] The molar concentration of the ammonium molybdate solution is 0.1–0.3 mol / L. -1 The mass ratio of biomass carbon from poplar catkins to ammonium molybdate is 0.01–0.032:1.

[0019] (3) The poplar catkin biomass carbon obtained in the previous step is calcined in a tube furnace under an argon atmosphere; specifically, at 3.5℃ min. -1Heat to 400℃ and hold for 4 hours, then reduce temperature by 5℃ per minute. -1 Raise the temperature to 850℃ and keep it warm for 2 hours.

[0020] (4) The material obtained in (3) is washed by filtration with distilled water and ethanol, and then dried to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material.

[0021] The method described above for preparing MoO2 / Mo2C is simple and easy to implement. Furthermore, during calcination in an inert atmosphere, the poplar catkin biomass carbon can act as a reducing agent, reducing ammonium molybdate to MoO2 / Mo2C, thus avoiding the use of reducing atmospheres such as H2 / Ar and improving the safety of the preparation process. Simultaneously, when used as electrode materials, the high conductivity of the poplar catkin biomass carbon and Mo2C can serve as a conductive framework, promoting electron transport and thus improving the electrochemical performance of the prepared electrode.

[0022] The prepared flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material, when used as an electrode material and assembled with lithium metal into a battery, achieves a specific capacity of 365 mAh g⁻¹ in the first week of charge-discharge at a 0.1C rate. -1 After 50 cycles at 0.2C, the capacity remains at 290 mAh g. -1 .

[0023] By using the prepared flake-like MoO2 / Mo2C@poplar catkin biomass carbon as a carrier material and combining it with sulfur, a sulfur-based composite material can be obtained. The composite method includes common methods such as melt processing, vapor phase processing, and in-situ deposition. The sulfur content in the sulfur-based composite material is 10–90 wt%. The flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material has a large specific surface area and strong polarity, providing a large number of polar adsorption sites for lithium polysulfides and effectively mitigating the shuttle effect. Simultaneously, Mo2C and hollow tubular poplar catkin biomass carbon are beneficial to improving the conductivity of the sulfur cathode. The heterostructure formed by MoO2 and Mo2C facilitates charge transfer in the electrochemical conversion reaction of sulfur, catalyzing the efficient and reversible sulfur charge-discharge reaction, thereby improving the electrochemical performance of the sulfur electrode. When the prepared MoO2 / Mo2C@poplar catkin biomass carbon composite material is used as the electrode material and assembled with lithium metal into a battery, the first-week specific capacity can reach 1067 mAh g⁻¹. -1 .

[0024] Hollow tubular MoO3 can also be prepared using the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material. The specific steps are as follows:

[0025] The flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is calcined in a muffle furnace to obtain hollow tubular MoO3; preferably, the calcination temperature is 500℃ and the calcination time is 1h.

[0026] The hollow tubular MoO3 is composed of nanoparticles with a tubular morphology and a diameter of about 4 to 5 μm. When used as an electrode material for lithium-ion batteries, this morphology is beneficial for the penetration of electrolyte.

[0027] When the prepared hollow tubular MoO3 is used as an electrode material and assembled with lithium metal into a battery, the specific capacity in the first week of charge-discharge at a 0.1C rate can reach 1304.48 mAh g. -1 After 40 cycles at 0.2C, the capacity remains at 504.4 mAh g. -1 .

[0028] By combining the prepared hollow tubular MoO3 as a carrier material with sulfur, a sulfur-based composite material can be obtained. The composite method includes common methods such as melt processing, vapor phase processing, and in-situ deposition. The sulfur content in the sulfur-based composite material is 10–90 wt%. When used as a carrier material in lithium-sulfur batteries, it can provide sulfur storage space and also has strong polarity, providing physical and chemical confinement for lithium polysulfides, thereby improving the electrochemical performance of the sulfur electrode. When the composite material obtained by combining the prepared hollow tubular MoO3 with sulfur is used as an electrode material and assembled with lithium metal in a battery, the specific capacity still reaches 864.9 mAh g⁻¹ after 40 cycles. -1 .

[0029] The applicant further claims protection for the application of the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material or hollow tubular MoO3 material as a negative electrode material for lithium-ion batteries. Specifically, the application method is to mix the above-mentioned materials with binders and conductive agents and then coat them into electrode sheets for use as a negative electrode for lithium-ion batteries.

[0030] Furthermore, it is required to protect the application of the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material or hollow tubular MoO3 material as a carrier material for lithium-sulfur batteries. Specifically, the above-mentioned material is used as a carrier to combine with sulfur to prepare a sulfur-based composite material. The sulfur-based composite material is then mixed with a binder and a conductive agent and coated into an electrode sheet for use as the positive electrode of a lithium-ion battery.

[0031] Compared with existing technologies, the present invention has the following advantages:

[0032] (1) The carbon source used in this invention is poplar catkins, which are widely available and are beneficial to solving the social harm caused by poplar catkins;

[0033] (2) The present invention uses a simple and easy method to prepare MoO2 / Mo2C / carbon composite material and hollow tubular MoO3 material. Compared with the current molybdenum oxide preparation method, it is simple, efficient, easy to mass-produce and low in cost.

[0034] (3) This invention utilizes the micro-composition and structure of the carbon surface of poplar catkin biomass to obtain a scaly MoO2 / Mo2C composite material;

[0035] (4) When the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is used as a negative electrode material for lithium-ion batteries, Mo2C with ultra-high electronic conductivity can improve the conductivity of the electrode material, while hollow tubular poplar catkin biomass carbon can alleviate the volume expansion during charging and discharging, thus facilitating the acquisition of high theoretical specific capacity and cycle performance.

[0036] (5) When the above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is used as a cathode carrier in lithium-sulfur batteries, its large specific surface area and strong polarity provide a large number of polar adsorption sites for lithium polysulfides, effectively mitigating the shuttle effect. At the same time, Mo2C and hollow tubular poplar catkin biomass carbon are beneficial to improving the conductivity of the sulfur cathode, and the heterojunction structure formed by MoO2 and Mo2C is beneficial to promoting charge transfer in the electrochemical conversion reaction of sulfur, catalyzing the efficient and reversible sulfur charge-discharge reaction, thereby improving the electrochemical performance of the sulfur electrode.

[0037] (6) The above-mentioned flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material can be calcined in air to obtain hollow tubular MoO3. Using it as a negative electrode material for lithium-ion batteries is beneficial to promote ion transfer, alleviate the structural damage caused by the volume effect of electrode materials, and improve electrochemical performance.

[0038] (7) The hollow tubular MoO3 mentioned above is used as a sulfur cathode carrier material. Its hollow tubular cavity structure is conducive to accommodating sulfur and achieving uniform composite with sulfur. At the same time, it can limit the shuttle effect of lithium polysulfides through spatial confinement and chemical adsorption, thereby improving the electrochemical performance of the sulfur cathode. Attached Figure Description

[0039] Figure 1 is a SEM image of the poplar catkin biomass carbon prepared in Example 1;

[0040] Figure 2 shows the XRD image of the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared in Example 1;

[0041] Figures 3 and 4 are SEM images of the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared in Example 1;

[0042] Figure 5 shows the first-week charge-discharge curve of the electrode prepared by the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared in Example 1;

[0043] Figure 6 shows the cycle performance curve of the electrode prepared by the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared in Example 1;

[0044] Figure 7 shows the cycle performance curve of the sulfur cathode prepared by using flake-like MoO2 / Mo2C@poplar catkin biomass carbon as a lithium-sulfur battery carrier in Example 2.

[0045] Figure 8 shows the XRD image of the hollow tubular MoO3 material prepared in Example 4;

[0046] Figure 9 shows a SEM image of the hollow tubular MoO3 material prepared in Example 4;

[0047] Figure 10 shows the first-cycle charge-discharge curve of the electrode prepared from the hollow tubular MoO3 material prepared in Example 4.

[0048] Figure 11 shows the cycle performance curve of the electrode prepared from the hollow tubular MoO3 material prepared in Example 4;

[0049] Figure 12 shows the cycle performance curve of the sulfur cathode prepared by using the hollow tubular MoO3 material prepared in Example 5 as a lithium-sulfur battery carrier. Detailed Implementation

[0050] The invention will be further illustrated below with specific implementation examples. These examples are only intended to provide a complete and clear explanation of the invention, and are not intended to represent all possible implementations. All other implementations created based on this invention are within the scope of protection of this invention.

[0051] Example 1

[0052] The specific preparation process for flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is as follows:

[0053] Collect poplar fluff from Canadian poplars at 5℃ for 1 minute. -1 The temperature was raised to 400℃ and held for 6 hours to obtain poplar catkin biomass carbon. As shown in Figure 1, the obtained poplar catkin biomass carbon has a hollow tubular morphology with a diameter of approximately 5–8 μm.

[0054] Prepare 0.2 mol L -1 50 mL ammonium molybdate solution: Add 12.5 g of ammonium molybdate tetrahydrate to 50 mL of distilled water and dissolve by sonication. Place 0.3 g of poplar catkin biomass carbon in the ammonium molybdate solution and sonicate for 5 min. Remove and soak for 2 h. Filter to obtain the soaked poplar catkin biomass carbon, and dry at 60 °C. Place the soaked and dried poplar catkin biomass carbon in a tube furnace and heat at 3.5 °C for [time missing] min under an Ar atmosphere. -1 Heat to 400℃ and hold for 4 hours, then reduce temperature by 5℃ / min. -1The sample was heated to 850℃ and held for 2 hours. After cooling to room temperature, the sample was removed, washed three times with distilled water and ethanol respectively, and dried at 60℃ to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material. The structure, morphology, and electrochemical properties of the material were characterized.

[0055] Figure 2 shows the XRD image of the prepared flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material. As can be seen from the figure, the obtained XRD pattern has sharp peaks, which are consistent with the standard cards PDF#76-1807 for MoO2 and PDF#72-1683 for Mo2C. Furthermore, the peak around 25° is a carbon diffraction peak, indicating that the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material was successfully obtained, and that both MoO2 and Mo2C exhibit good crystallinity. Figures 3-4 show SEM images of the prepared flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material at different magnifications. As can be seen from the figures, the poplar catkin biomass carbon is a hollow tubular structure with a diameter of approximately 5 μm. Its surface is uniformly loaded with MoO2 / Mo2C nanosheets arranged in a flake-like pattern, with a loading of 22 wt%.

[0056] The flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared above was used to fabricate electrode sheets according to the following method, and a half-cell was assembled with lithium metal as the counter electrode to test its electrochemical performance. The specific method is as follows:

[0057] Weigh 0.7g of the prepared flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material, 0.2g of conductive carbon black (SuperP), and 0.1g of polyvinylidene fluoride (PVdF). Place them in a flat weighing bottle, mix thoroughly, and then add 2mL of N-methylpyrrolidone (NMP). Stir for 6 hours to obtain a slurry with suitable viscosity (SuperP, PVdF, and NMP are all conventional reagents in this field). Then, use a coating machine to uniformly coat the slurry onto aluminum foil and dry it in a 60℃ oven for 12 hours. After that, cut the dried electrode into 10mm diameter round pieces and assemble 2032 coin cells in an argon-filled glove box. After assembly, let the cells stand for 4 hours and then activate them at 0.05C for two weeks on a battery testing system. Subsequently, activate them at 0.1C and 0.01-3V (vs. Li + The battery was tested under a charge / discharge program within the / Li discharge voltage range. The results are shown in Figure 5, which illustrates the battery's charge / discharge performance during the first week. The first-week discharge specific capacity was 364 mAh g. -1 Figure 6 shows the cycle performance of the battery. After 50 cycles, the discharge specific capacity is 290 mAh g. -1 .

[0058] Example 2

[0059] The specific preparation process for flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is as follows:

[0060] Poplar catkin biomass carbon was prepared according to the method described in Example 1.

[0061] Prepare 0.2 mol L -1 50 mL ammonium molybdate tetrahydrate solution: Add 12.5 g of ammonium molybdate tetrahydrate to 50 mL of distilled water and dissolve by sonication. Place 0.2 g of poplar catkin biomass carbon in the ammonium molybdate solution and sonicate for 5 min. Remove and soak for 2 h. Filter to obtain the soaked poplar catkin biomass carbon, and dry at 60℃. Place the soaked poplar catkin biomass carbon in a tube furnace and heat at 3.5℃ for 1 min under an Ar atmosphere. -1 Heat to 400℃ and hold for 4 hours, then reduce temperature by 5℃ / min. -1 The sample was heated to 850℃ and held for 2 hours. After cooling to room temperature, the sample was removed, washed three times with distilled water and ethanol respectively, and dried at 60℃ to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material. The structure, morphology, and electrochemical properties of the material were characterized according to the method described in Example 1. The surface MoO2 / Mo2C loading of the obtained flake-like MoO2 / Mo2C@poplar catkin biomass carbon was 38 wt%.

[0062] The prepared MoO2 / Mo2C@poplar catkin biomass carbon composite material was combined with sulfur as a cathode material for lithium-sulfur batteries. Specifically, 0.8g of elemental sulfur was mixed with 0.2g of the prepared MoO2 / Mo2C@poplar catkin biomass carbon, and ground in an agate mortar for 30min. Then, it was placed in a crucible wrapped with tin foil and kept at 155℃ for 12h. After the heating was completed and the temperature was restored to room temperature, the product was ground again in an agate mortar for 20min. Finally, a sulfur-based composite cathode material S / MoO2 / Mo2C@poplar catkin biomass carbon with MoO2 / Mo2C@poplar catkin biomass carbon as the carrier was obtained, with a sulfur content of 80wt%.

[0063] The obtained S / MoO2 / Mo2C@poplar catkin biomass carbon composite material was used to prepare a positive electrode sheet, and then assembled into a battery for testing. The specific method is as follows:

[0064] Weigh 0.28 g of the prepared S / MoO2 / Mo2C@poplar catkin biomass carbon composite material, 0.08 g of conductive carbon black (Super P), and 0.04 g of polyvinylidene fluoride (PVdF). Place them in a flat weighing bottle, mix thoroughly, and then add 2.6 mL of N-methylpyrrolidone (NMP). Stir for 6 h to obtain a slurry with suitable viscosity (Super P, PVdF, and NMP are all conventional reagents in this field). Then, use a coating machine to uniformly coat the slurry onto carbon paper (Toray carbon paper, model: TGP-H-060 hydrophilic type), with a coating amount of 0.2 g. Dry the paper in a 60°C oven for 12 h. Then, cut the dried positive electrode into round pieces with a diameter of 10 mm. The mass of sulfur in each positive electrode is about 1-2 mg. Assemble them into coin cells in an argon-filled glove box. The electrolyte volume is 30 μL mg. -1 (The mass is the sulfur mass mentioned above). After assembly, the battery was allowed to stand for 24 hours, then activated for one week at 0.03C and one week at 0.05C on a battery testing system. Subsequently, it was tested using a charge-discharge program with a voltage range of 0.1C and 1.7-2.8V. The cycle performance diagram is shown in Figure 7. The discharge specific capacity in the first week at a 0.03C rate is 1067.2 mAh g. -1 After 40 cycles at 0.1C, the discharge specific capacity is 848.4 mAh g. -1 .

[0065] Example 3

[0066] The specific preparation process for flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is as follows:

[0067] Poplar catkin biomass carbon was prepared according to the method described in Example 1.

[0068] Prepare 0.1 mol L -1 50 mL ammonium molybdate solution: Add 6.25 g of ammonium molybdate tetrahydrate to 50 mL of distilled water and dissolve by sonication. Place 0.2 g of poplar catkin biomass carbon in the ammonium molybdate solution and sonicate for 5 min. Remove and soak for 2 h. Filter to obtain the soaked poplar catkin biomass carbon, and dry at 60℃. Place the soaked poplar catkin biomass carbon in a tube furnace and heat at 3.5℃ in an Ar atmosphere for [time missing]. -1 Heat to 400℃ and hold for 4 hours, then reduce temperature by 5℃ / min. -1 The sample was heated to 850℃ and held for 2 hours. After cooling to room temperature, the sample was removed, washed three times with distilled water and ethanol respectively, and dried at 60℃ to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material. The structure, morphology, and electrochemical properties of the material were characterized according to the method described in Example 1. The MoO2 / Mo2C loading on the surface of the obtained flake-like MoO2 / Mo2C@poplar catkin biomass carbon was 15 wt%.

[0069] Following the method described in Example 1, the obtained flake-like MoO2 / Mo2C@poplar catkin biomass carbon was used as the active material to assemble a half-cell with lithium metal. Electrochemical performance tests were then conducted, and the first-cycle discharge specific capacity at 0.1C rate was measured to be 320 mAh g⁻¹. -1 After 50 cycles at 0.2C, the discharge specific capacity is 295 mAh g. -1 .

[0070] Example 4

[0071] The specific preparation process for hollow tubular MoO3 materials is as follows:

[0072] The flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material prepared in Example 1 was placed in a muffle furnace and heated to 2°C for 2 min. -1 The MoO3 material was obtained by heating to 500℃ and holding for 1 hour. The structure, morphology and electrochemical properties of the obtained material were characterized.

[0073] Figure 8 shows the XRD image of the MoO3 material prepared in Example 2. As can be seen from the figure, the obtained XRD spectrum has sharp peaks, which are consistent with the standard card PDF#76-1003 for MoO3, and there are no impurity peaks, indicating that pure-phase MoO3 material was successfully obtained with good crystallinity. Figure 9 shows the SEM image of the MoO3 material prepared in Example 2. As can be seen from the figure, the prepared MoO3 material is a hollow tubular shape with a diameter of approximately 5 μm, and it is composed of nanoparticles.

[0074] The MoO3 material prepared above was fabricated into electrode sheets using the following method, and a half-cell was assembled using lithium metal as the counter electrode to test its electrochemical performance. The specific method is as follows:

[0075] Weigh 0.7g of the prepared MoO3 material, 0.2g of conductive carbon black (Super P), and 0.1g of polyvinylidene fluoride (PVdF), place them in a flat weighing bottle, mix thoroughly, add 2mL of N-methylpyrrolidone (NMP), and stir for 6h to obtain a slurry of suitable viscosity (Super P, PVdF, and NMP are all conventional reagents in the art); then use a coating machine to uniformly coat the slurry onto aluminum foil, and dry it in a 60℃ oven for 12h for later use; then cut the dried electrode into 10mm diameter round pieces, assemble 2032 coin cells in an argon-filled glove box, and after assembly, let the cells stand for 4h, then activate them for two weeks at 0.05C on a battery testing system, and then at 0.1C and 0.01-3V (vs. Li + The battery was tested under a charge-discharge program within the / Li discharge voltage range. Figure 10 shows the cycle performance of the battery; the first-cycle discharge specific capacity at 0.1C rate is 1321.5 mAh g.-1 Figure 11 shows the cycle performance of the battery. After 50 cycles at a 0.2C rate, the discharge specific capacity is 504.4 mAh g. -1 .

[0076] Example 5

[0077] The preparation of hollow tubular MoO3 material follows the same experimental steps as in Example 4.

[0078] The above-mentioned MoO3 material was used as a carrier to prepare an S / MoO3 sulfur-based composite cathode material via a melt method. The specific preparation process is as follows:

[0079] 0.8g of elemental sulfur was mixed with 0.2g of the prepared MoO3 and ground in an agate mortar for 30min. Then, the mixture was placed in a crucible wrapped with tin foil and kept at 155℃ for 12h. After the heating was completed and the mixture was allowed to return to room temperature, the product was ground again in an agate mortar for 20min. Finally, a sulfur-based composite material S / MoO3 with MoO3 as the carrier was obtained, with a sulfur content of 80wt%.

[0080] The obtained S / MoO3 composite cathode material was fabricated into a positive electrode sheet according to the following method, and then assembled into a battery for testing. The specific method is as follows:

[0081] Weigh 0.28 g of the prepared S / MoO3 cathode composite material, 0.08 g of conductive carbon black (Super P), and 0.04 g of polyvinylidene fluoride (PVdF), place them in a flat weighing bottle, mix thoroughly, add 2.6 mL of N-methylpyrrolidone (NMP), and stir for 6 h to obtain a slurry of suitable viscosity (Super P, PVdF, and NMP are all conventional reagents in this field); then use a coating machine to uniformly coat the slurry onto carbon paper (Toray carbon paper, model: TGP-H-060 hydrophilic type), with a coating amount of 0.2 g, and dry in a 60℃ oven for 12 h for later use; then cut the dried cathode sheet into round pieces with a diameter of 10 mm, each cathode sheet containing approximately 1–2 mg of sulfur, and assemble them into coin cells in an argon-filled glove box, using 30 μL of electrolyte. -1 (The mass is the sulfur mass mentioned above). After assembly, the battery was allowed to stand for 24 hours, then activated at 0.03C for two weeks and 0.06C for one week on a battery testing system. Subsequently, it was tested using a charge-discharge program with a voltage range of 0.1C and 1.7-2.8V. The battery cycle performance is shown in Figure 12. After 40 cycles, the discharge specific capacity is 864 mAh g. -1 .

[0082] It can be seen that the MoO2 / Mo2C@poplar catkin biomass carbon composite material and the hollow tubular MoO3 material provided by this invention have achieved high theoretical specific capacity in lithium-ion batteries and lithium-sulfur batteries. However, considering that low carbon content is beneficial to improving battery energy density, a technical solution with a lower mass ratio of poplar catkin biomass carbon to ammonium molybdate can be considered.

[0083] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The description of the above embodiments can help understand the principles and methods of the present invention. However, the above embodiments are not unique and should not be construed as limiting the present invention. At the same time, those skilled in the art can make flexible changes to the specific implementation methods and application scope based on the principles and methods of the present invention.

Claims

1. A flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material, characterized in that: The structure of poplar catkin biomass carbon is supported on the surface of MoO2 / Mo2C nanosheets, with a loading of 15~50 wt% for MoO2 / Mo2C nanosheets; wherein the poplar catkin biomass carbon is prepared from poplar catkins as raw material, and the preparation method is as follows: (1) Carbonize the poplar catkins in a tube furnace under an argon atmosphere to obtain poplar catkin biomass carbon; wherein the heating rate is 2~5℃min -1 The heat preservation temperature is 400℃ and the heat preservation time is 6 h; (2) The carbonized poplar catkins are soaked in ammonium molybdate solution, then filtered to separate the poplar catkins and dried; the specific steps are: take a certain mass of ammonium molybdate tetrahydrate and add it to a certain volume of distilled water, and dissolve it by ultrasonication to obtain ammonium molybdate solution; place the poplar catkin biomass carbon in the above ammonium molybdate solution, ultrasonicate for 5 min, soak for 2 h, filter to separate the poplar catkins and dry at 60 ℃ for 12~24 h; (3) calcine the poplar catkin biomass carbon obtained in the previous step in a tube furnace under an argon atmosphere; (4) wash the material obtained in (3) with distilled water and ethanol, and dry it to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material.

2. The method for preparing the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material according to claim 1, characterized in that, The specific steps are as follows: (1) Carbonize poplar catkins in a tubular furnace under an argon atmosphere to obtain poplar catkin biomass carbon; wherein the heating rate is 2~5℃min. -1 The heat preservation temperature is 400℃ and the heat preservation time is 6 h; (2) The carbonized poplar catkins are soaked in ammonium molybdate solution, then filtered to separate the poplar catkins and dried; the specific steps are: take a certain mass of ammonium molybdate tetrahydrate and add it to a certain volume of distilled water, and dissolve it by ultrasonication to obtain ammonium molybdate solution; place the poplar catkin biomass carbon in the above ammonium molybdate solution, ultrasonicate for 5 min, soak for 2 h, filter to separate the poplar catkins and dry at 60 ℃ for 12~24 h; (3) calcine the poplar catkin biomass carbon obtained in the previous step in a tube furnace under an argon atmosphere; (4) wash the material obtained in (3) with distilled water and ethanol, and dry it to obtain the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material.

3. The method for preparing the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material according to claim 2, characterized in that, In step (2), the molar concentration of the ammonium molybdate solution is 0.1~0.3 mol L. -1 The mass ratio of biomass carbon from poplar catkins to ammonium molybdate is 0.01~0.032:

1.

4. The method for preparing the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material according to claim 2, characterized in that, In step (3), calcination is carried out at 3.5 °C for 1 minute. -1 Heat to 400 ℃ and hold for 4 hours, then reduce temperature by 5 ℃ / min. -1 Heat to 850 ℃ and keep warm for 2 hours.

5. A method for preparing hollow tubular MoO3 using the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material according to claim 1, characterized in that, The specific steps are as follows: the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material is calcined in a muffle furnace to obtain hollow tubular MoO3; the calcination temperature is 500 ℃ and the calcination time is 1 h.

6. The application of the flake-like MoO2 / Mo2C@poplar catkin biomass carbon composite material according to claim 1, characterized in that, It serves as a carrier material for the negative electrode of lithium-ion batteries or the positive electrode of lithium-sulfur batteries.

7. The application of hollow tubular MoO3 obtained by the method for preparing hollow tubular MoO3 according to claim 5, characterized in that, It serves as a carrier material for the negative electrode of lithium-ion batteries or the positive electrode of lithium-sulfur batteries.

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