Nanocomposite negative electrode material

Abstract

The application relates to the technical field of lithium battery negative electrode materials, and discloses a kind of nano composite negative electrode materials, raw materials are calculated according to weight fraction, composition includes: 3-4 parts of carbon nanotube, 135-150 parts of concentrated nitric acid, 315-330 parts of concentrated sulfuric acid, 600-650 parts of dilute hydrochloric acid, 30-40 parts of anhydrous ethanol, 7.5-10 parts of polyethylene imine, 25-30 parts of molybdenum disulfide, 10-12 parts of surfactant, 3325-3600 parts of deionized water.The MoS2 nanosheet layer and MWCNTs modified by electrostatic force assisted self-assembly method are self-assembled in solution, MoS2 / PVP / PEI / MWCNTs quaternary composite is obtained, and finally heat treatment is carried out to obtain the final MoS2 / MWCNTs nano composite negative electrode material, which has higher reversible capacity, better cycle stability and rate performance.In addition, the preparation method does not need high temperature and high pressure condition, is efficient, convenient and energy-saving and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode material technology, and in particular to a nanocomposite anode material. Background Technology

[0002] Lithium-ion batteries are considered one of the high-energy batteries best suited to meet the sustainable development requirements of future society. In recent years, lithium-ion batteries have developed rapidly and have been widely used in portable electronic devices such as mobile phones, laptops, and cameras, as well as in the aerospace and aviation fields, and have received significant attention in the electric vehicle sector. However, current lithium-ion batteries cannot meet the continuously growing energy density demands of pure electric vehicles and hybrid electric vehicles. Therefore, developing battery materials with high energy density and high rate performance has become a highly focused research area.

[0003] Anode materials are among the key materials affecting the performance of lithium-ion batteries. Currently, the main anode materials for lithium-ion batteries include graphite, amorphous carbon, carbon nanotubes, silicon-based materials, tin-based materials, alloy materials, coated metal oxides, and two-dimensional nanomaterials. Among these, multi-walled carbon nanotubes (MWCNTs) are a novel type of carbon crystalline material discovered in recent years. They are composed of several to thousands of coaxial single-walled carbon nanotubes, with inter-tube forces similar to van der Waals forces in graphite, and a radial spacing of approximately 0.34 nm between adjacent tubes. MWCNTs possess excellent physical and chemical properties, such as a large specific surface area and small molecular size voids, extremely high tensile strength, good thermodynamic properties, high chemical stability, and good hydrogen storage performance. Therefore, they have been extensively studied in areas such as catalyst supports, hydrogen storage materials, lithium-ion batteries, double-layer capacitors, and field emission. MWCNTs used as anode materials for lithium-ion batteries offer advantages such as numerous lithium insertion sites, easy delithiation, and good cycle stability; however, they have a relatively large irreversible capacity and a relatively small specific capacity in the first cycle.

[0004] Molybdenum disulfide (MoS2) is an important transition metal sulfide with a typical layered structure and wide applications. It can be used as an embedded electrode material for electrochemical lithium storage, providing a high theoretical specific capacity, but its cycle stability is poor. Therefore, many researchers have hybridized it with carbon materials with excellent cycle stability, such as graphene, carbon nanotubes, and amorphous carbon, to obtain composite anode materials with better performance.

[0005] Currently, hydrothermal synthesis is commonly used to prepare MoS2 / CNTs nanocomposites, but the drawback is the high temperature and high pressure, which not only requires high-end equipment but is also extremely energy-intensive, thus failing to meet the requirements of modern green chemistry. Summary of the Invention

[0006] To overcome the shortcomings and deficiencies of existing technologies, this invention aims to provide a nanocomposite anode material and its preparation method. The prepared nanocomposite anode material has high reversible capacity, good cycle stability and rate performance. The preparation method is an electrostatically assisted self-assembly method, which is efficient, convenient and energy-saving and environmentally friendly.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A nanocomposite anode material, the raw materials of which, by weight, comprise: 3-4 parts carbon nanotubes, 135-150 parts concentrated nitric acid, 315-330 parts concentrated sulfuric acid, 600-650 parts dilute hydrochloric acid, 30-40 parts anhydrous ethanol, 7.5-10 parts polyethyleneimine, 25-30 parts molybdenum disulfide, 10-12 parts surfactant, and 3325-3600 parts deionized water.

[0009] Preferably, the carbon nanotubes are multi-walled carbon nanotubes.

[0010] Preferably, the surfactant is polyvinylpyrrolidone.

[0011] Preferably, the concentration of the concentrated nitric acid is 65%.

[0012] Preferably, the concentration of the concentrated sulfuric acid is 98%.

[0013] Preferably, the concentration of the dilute hydrochloric acid is 3%.

[0014] The method for preparing a nanocomposite anode material includes the following steps:

[0015] (1) Mix concentrated sulfuric acid and concentrated nitric acid evenly, then add multi-walled carbon nanotubes, ultrasonically disperse for 10 min, then transfer to an oil bath for reaction. After the reaction is complete, dilute with 1000-1200 parts of deionized water, let stand overnight, filter to remove acid, then wash with 1500 parts of deionized water 3-4 times, wash twice with anhydrous ethanol, transfer to an oven for vacuum drying for 24 h, then transfer to a refrigerator for freezing for 5 h, and then freeze-dry to obtain pretreated multi-walled carbon nanotubes. Add them to 500 parts of deionized water and ultrasonically disperse for 15 min to obtain a multi-walled carbon nanotube aqueous dispersion.

[0016] (2) Polyethyleneimine was added to 30 times its mass of deionized water and stirred evenly to form a polyethyleneimine aqueous solution. Then, it was added dropwise to the multi-walled carbon nanotube aqueous dispersion under ultrasonic conditions. After the addition was completed, ultrasonication was continued for 1.5 hours. A small amount of precipitate was removed by centrifugation to obtain a multi-walled carbon nanotube aqueous dispersion coated with polyethyleneimine.

[0017] (3) Add molybdenum disulfide and polyvinylpyrrolidone to 100 parts of deionized water and stir evenly. Then, ultrasonically disperse until the dispersion is dark green. Let it stand for 72 hours, transfer the supernatant to a centrifuge tube, centrifuge at 1500 rpm for 45 minutes, and then transfer the supernatant to obtain a polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet dispersion.

[0018] (4) Under ultrasonic conditions, the molybdenum disulfide nanosheet dispersion was added dropwise to the aqueous dispersion of multi-walled carbon nanotubes coated with polyethyleneimine. After the addition was completed, ultrasonication was continued for 1.5 h, then allowed to stand for 24 h, filtered, and dried in a vacuum oven for 24 h to obtain a quaternary composite of molybdenum disulfide / polyvinylpyrrolidone / polyvinylimine / multi-walled carbon nanotubes. Then, it was heat-treated at 800 °C for 1.5 h in an inert gas atmosphere to remove polyvinylpyrrolidone and polyethyleneimine, thus obtaining a nanocomposite anode material of molybdenum disulfide / multi-walled carbon nanotubes.

[0019] Preferably, the reaction in step (1) is a stirring reaction at 70°C for 6 hours.

[0020] Preferably, the centrifugation operation in step (2) is a centrifugation operation with a rotation speed of 8000 r / min and a time of 5 min.

[0021] Preferably, the oven in step (1) is a 60°C oven, and the oven in step (4) is an 80°C oven.

[0022] The beneficial effects of this invention are:

[0023] This invention uses polyvinylpyrrolidone (PVP) as a surfactant to prepare a PVP-stabilized MoS2 nanosheet dispersion via an ultrasonic-assisted liquid-phase exfoliation method, thereby imbuing the nanosheets with a negative charge. Then, acidified multi-walled carbon nanotubes (MWCNTs) are coated with polyethyleneimine (PEI) to impart a positive charge to their surfaces. The two components then undergo self-assembly in solution to obtain a MoS2 / PVP / PEI / MWCNTs quaternary composite. Finally, heat treatment yields the final MoS2 / MWCNTs nanocomposite anode material, exhibiting high reversible capacity, good cycle stability, and rate performance. Furthermore, the preparation method utilizes electrostatic interaction-assisted self-assembly, which is highly efficient, convenient, energy-saving, and environmentally friendly. Attached Figure Description

[0024] Figure 1 This is a graph showing the cycling performance of electrodes made of different materials at the same current density;

[0025] Figure 2 This is a graph showing the rate performance of the MoS2 / MWCNTs nanocomposite anode material at different current densities; Detailed Implementation

[0026] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention.

[0027] Example 1:

[0028] A nanocomposite anode material, the raw materials of which, by weight, comprise: 3 parts multi-walled carbon nanotubes, 135 parts concentrated nitric acid, 315 parts concentrated sulfuric acid, 600 parts dilute hydrochloric acid, 30 parts anhydrous ethanol, 7.5 parts polyethyleneimine, 25 parts molybdenum disulfide, 10 parts polyvinylpyrrolidone, and 3325 parts deionized water.

[0029] The preparation method of the nanocomposite anode material described in this embodiment, based on parts by weight, includes the following steps:

[0030] (1) Mix concentrated sulfuric acid and concentrated nitric acid evenly, then add multi-walled carbon nanotubes, ultrasonically disperse for 10 min, then transfer to an oil bath and stir at 70°C for 6 h. After the reaction is complete, dilute with 1000 parts of deionized water, let stand overnight, filter to remove acid, then wash with 1500 parts of deionized water 3-4 times, wash twice with anhydrous ethanol, transfer to an oven at 60°C and vacuum dry for 24 h, then transfer to a refrigerator and freeze for 5 h, and then freeze-dry to obtain pretreated multi-walled carbon nanotubes. Add them to 500 parts of deionized water and ultrasonically disperse for 15 min to obtain a multi-walled carbon nanotube aqueous dispersion.

[0031] (2) Polyethyleneimine was added to 30 times its mass of deionized water and stirred evenly to form a polyethyleneimine aqueous solution. Then, it was added dropwise to the multi-walled carbon nanotube aqueous dispersion under ultrasonic conditions. After the addition was completed, ultrasonication was continued for 1.5 hours. A small amount of precipitate was removed by centrifugation at 8000 r / min for 5 minutes to obtain a multi-walled carbon nanotube aqueous dispersion coated with polyethyleneimine.

[0032] (3) Add molybdenum disulfide and polyvinylpyrrolidone to 100 parts of deionized water and stir evenly. Then, ultrasonically disperse until the dispersion is dark green. Let it stand for 72 hours, transfer the supernatant to a centrifuge tube, centrifuge at 1500 rpm for 45 minutes, and then transfer the supernatant to obtain a polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet dispersion.

[0033] (4) Under ultrasonic conditions, the molybdenum disulfide nanosheet dispersion was added dropwise to the aqueous dispersion of multi-walled carbon nanotubes coated with polyethyleneimine. After the addition was completed, the mixture was ultrasonicated for 1.5 h, then allowed to stand for 24 h, filtered, and dried in a vacuum oven at 80 °C for 24 h to obtain a quaternary composite of molybdenum disulfide / polyvinylpyrrolidone / polyvinylimine / multi-walled carbon nanotubes. Then, the composite was heat-treated at 800 °C for 1.5 h under an inert gas atmosphere to remove polyvinylpyrrolidone and polyethyleneimine, thus obtaining a nanocomposite anode material of molybdenum disulfide / multi-walled carbon nanotubes.

[0034] Example 2:

[0035] A nanocomposite anode material, the raw materials of which, by weight, comprise: 3 parts multi-walled carbon nanotubes, 140 parts concentrated nitric acid, 325 parts concentrated sulfuric acid, 625 parts dilute hydrochloric acid, 35 parts anhydrous ethanol, 9 parts polyethyleneimine, 27 parts molybdenum disulfide, 11 parts polyvinylpyrrolidone, and 3470 parts deionized water.

[0036] The preparation method of the nanocomposite anode material described in this embodiment, based on parts by weight, includes the following steps:

[0037] (1) Mix concentrated sulfuric acid and concentrated nitric acid evenly, then add multi-walled carbon nanotubes, ultrasonically disperse for 10 min, then transfer to an oil bath and stir at 70°C for 6 h. After the reaction is complete, dilute with 1100 parts of deionized water, let stand overnight, filter to remove acid, then wash with 1500 parts of deionized water 3-4 times, wash twice with anhydrous ethanol, transfer to an oven at 60°C and vacuum dry for 24 h, then transfer to a refrigerator and freeze for 5 h, and then freeze-dry to obtain pretreated multi-walled carbon nanotubes. Add them to 500 parts of deionized water and ultrasonically disperse for 15 min to obtain a multi-walled carbon nanotube aqueous dispersion.

[0038] (2) Polyethyleneimine was added to 30 times its mass of deionized water and stirred evenly to form a polyethyleneimine aqueous solution. Then, it was added dropwise to the multi-walled carbon nanotube aqueous dispersion under ultrasonic conditions. After the addition was completed, ultrasonication was continued for 1.5 hours. A small amount of precipitate was removed by centrifugation at 8000 r / min for 5 minutes to obtain a multi-walled carbon nanotube aqueous dispersion coated with polyethyleneimine.

[0039] (3) Add molybdenum disulfide and polyvinylpyrrolidone to 100 parts of deionized water and stir evenly. Then, ultrasonically disperse until the dispersion is dark green. Let it stand for 72 hours, transfer the supernatant to a centrifuge tube, centrifuge at 1500 rpm for 45 minutes, and then transfer the supernatant to obtain a polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet dispersion.

[0040] (4) Under ultrasonic conditions, the molybdenum disulfide nanosheet dispersion was added dropwise to the aqueous dispersion of multi-walled carbon nanotubes coated with polyethyleneimine. After the addition was completed, the mixture was ultrasonicated for 1.5 h, then allowed to stand for 24 h, filtered, and dried in a vacuum oven at 80 °C for 24 h to obtain a quaternary composite of molybdenum disulfide / polyvinylpyrrolidone / polyvinylimine / multi-walled carbon nanotubes. Then, the composite was heat-treated at 800 °C for 1.5 h under an inert gas atmosphere to remove polyvinylpyrrolidone and polyethyleneimine, thus obtaining a nanocomposite anode material of molybdenum disulfide / multi-walled carbon nanotubes.

[0041] Example 3:

[0042] A nanocomposite anode material, the raw materials of which, by weight, comprise: 4 parts multi-walled carbon nanotubes, 150 parts concentrated nitric acid, 330 parts concentrated sulfuric acid, 650 parts dilute hydrochloric acid, 40 parts anhydrous ethanol, 10 parts polyethyleneimine, 30 parts molybdenum disulfide, 10-12 parts polyvinylpyrrolidone, and 3600 parts deionized water.

[0043] The preparation method of the nanocomposite anode material described in this embodiment, based on parts by weight, includes the following steps:

[0044] (1) Mix concentrated sulfuric acid and concentrated nitric acid evenly, then add multi-walled carbon nanotubes, ultrasonically disperse for 10 min, then transfer to an oil bath and stir at 70°C for 6 h. After the reaction is complete, dilute with 1200 parts of deionized water, let stand overnight, filter to remove acid, then wash with 1500 parts of deionized water 3-4 times, wash twice with anhydrous ethanol, transfer to an oven at 60°C and vacuum dry for 24 h, then transfer to a refrigerator and freeze for 5 h, and then freeze-dry to obtain pretreated multi-walled carbon nanotubes. Add them to 500 parts of deionized water and ultrasonically disperse for 15 min to obtain a multi-walled carbon nanotube aqueous dispersion.

[0045] (2) Polyethyleneimine was added to 30 times its mass of deionized water and stirred evenly to form a polyethyleneimine aqueous solution. Then, it was added dropwise to the multi-walled carbon nanotube aqueous dispersion under ultrasonic conditions. After the addition was completed, ultrasonication was continued for 1.5 hours. A small amount of precipitate was removed by centrifugation at 8000 r / min for 5 minutes to obtain a multi-walled carbon nanotube aqueous dispersion coated with polyethyleneimine.

[0046] (3) Add molybdenum disulfide and polyvinylpyrrolidone to 100 parts of deionized water and stir evenly. Then, ultrasonically disperse until the dispersion is dark green. Let it stand for 72 hours, transfer the supernatant to a centrifuge tube, centrifuge at 1500 rpm for 45 minutes, and then transfer the supernatant to obtain a polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet dispersion.

[0047] (4) Under ultrasonic conditions, the molybdenum disulfide nanosheet dispersion was added dropwise to the aqueous dispersion of multi-walled carbon nanotubes coated with polyethyleneimine. After the addition was completed, the mixture was ultrasonicated for 1.5 h, then allowed to stand for 24 h, filtered, and dried in a vacuum oven at 80 °C for 24 h to obtain a quaternary composite of molybdenum disulfide / polyvinylpyrrolidone / polyvinylimine / multi-walled carbon nanotubes. Then, the composite was heat-treated at 800 °C for 1.5 h under an inert gas atmosphere to remove polyvinylpyrrolidone and polyethyleneimine, thus obtaining a nanocomposite anode material of molybdenum disulfide / multi-walled carbon nanotubes.

[0048] Comparative Example 1:

[0049] The only difference between this comparative example and Example 1 is that MWCNTs are not added during the preparation process. The other raw materials and steps are the same as in Example 1, and a single-component MoS2 anode material is prepared.

[0050] Comparative Example 2:

[0051] The only difference between this comparative example and Example 1 is that MoS2 is not added during the preparation process. The other raw materials and steps are the same as in Example 1, and MWCNTs single-component anode materials are prepared.

[0052] Anode material performance testing:

[0053] Electrode paste was prepared using the negative electrode materials prepared in Example 1 and Comparative Examples 1-2, the conductive agent carbon black, and the binder PVDF in a mass ratio of 85:10:5. First, PVDF was dissolved in NMP solvent, then carbon black and each negative electrode material were added, thoroughly mixed, and diluted with NMP solvent to a suitable viscosity. The electrode paste was then uniformly coated onto a 0.1 nm thick copper foil current collector, dried in an oven at 110°C for 4 hours, removed, pressed firmly on a double-roll press, and then cut into 1.2 cm diameter circular copper foils to serve as the electrode sheets for testing. Using lithium metal foil as the counter electrode, Celgard-2300 lithium-ion battery separator as the separator, and a 1.0 M LiPF6 EC / EMC / DMC solution (volume ratio 1:1:1) as the electrolyte system, a self-made battery was assembled under an inert gas environment. Performance testing was then conducted using a LAND CT2001A charge / discharge tester. The charge-discharge test had a current density of 100 mA / g and a voltage range of 3.0–0.0 V. The cyclic voltammetry test had a scan rate of 0.2 mV / s and a voltage range of 3.0–0.0 V.

[0054] Figure 1This graph shows the cycling performance of three anode materials at 100 mA / g. As can be seen, MoS2 exhibits low specific capacity and poor cycling stability, while MWCNTs exhibit low specific capacity and excellent cycling stability. This is because MoS2 has a typical layered structure, making it suitable as an embedded electrode material for electrochemical lithium storage, providing a high theoretical specific capacity, but its cycling stability is poor. MWCNTs, as a lithium-ion battery anode material, have advantages such as numerous lithium insertion sites, easy delithiation, and good cycling stability, but their irreversible capacity in the first cycle is large, and their specific capacity is small. In contrast, the MoS2 / MWCNTs nanocomposite anode material organically combines the two components, allowing them to interact and exhibiting high specific capacity and good cycling stability.

[0055] Figure 2 This chart shows the rate performance of three anode materials at different current densities. The current densities for 1-5 cycles, 6-10 cycles, 11-15 cycles, 16-20 cycles, and 21-30 cycles are 100 mA / g, 200 mA / g, 400 mA / g, 800 mA / g, and 200 mA / g, respectively. The chart shows that when the current density changes from 800 mA / g to 200 mA / g, the MoS2 / MWCNTs nanocomposite anode material can recover more than 90% of its initial specific capacity, exhibiting good rate performance and good reversible capacity. Furthermore, the capacity shows virtually no decay in subsequent cycle tests, demonstrating good cycle stability.

[0056] The above embodiments are only some embodiments of the present invention, and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

Claims

1. A nanocomposite anode material, wherein the raw materials, by weight, comprise: 3 parts of multi-walled carbon nanotubes, 140 parts of concentrated nitric acid, 325 parts of concentrated sulfuric acid, 625 parts of dilute hydrochloric acid, 35 parts of anhydrous ethanol, 9 parts of polyethyleneimine, 27 parts of molybdenum disulfide, 11 parts of polyvinylpyrrolidone, 3470 parts of deionized water; The preparation method of the nanocomposite negative electrode material comprises the following steps in terms of weight fractions: (1) mix and stir the concentrated sulfuric acid and the concentrated nitric acid uniformly, then add the multi-walled carbon nanotubes, ultrasonically disperse for 10 min, then transfer to an oil bath pot and stir at 70°C for 6 h, after the reaction is completed, dilute with 1100 parts of deionized water, stand overnight, filter to remove the acid liquid, then wash with 1500 parts of deionized water for 3-4 times, wash with anhydrous ethanol twice, transfer to a 60°C oven and vacuum dry for 24 h, then transfer to a refrigerator and freeze for 5 h, then freeze-dry to obtain pretreated multi-walled carbon nanotubes, add the pretreated multi-walled carbon nanotubes to 500 parts of deionized water, ultrasonically disperse for 15 min, and obtain a multi-walled carbon nanotube water dispersion liquid; (2) add the polyethyleneimine to 30 times the mass of deionized water to form a polyethyleneimine aqueous solution, then add the polyethyleneimine aqueous solution dropwise to the multi-walled carbon nanotube water dispersion liquid under ultrasonic conditions, continue to ultrasonically disperse for 1.5 h, centrifuge at a speed of 8000 r / min for 5 min to remove a small amount of precipitate, and obtain a polyethyleneimine-coated multi-walled carbon nanotube water dispersion liquid; (3) add the molybdenum disulfide and the polyvinylpyrrolidone to 100 parts of deionized water, stir to mix uniformly, then ultrasonically disperse until the dispersion liquid is dark green, stand for 72 h, remove the upper clear liquid and transfer to a centrifuge tube, centrifuge at a speed of 1500 rpm for 45 min, then remove the upper clear liquid, and obtain a polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet layer dispersion liquid; (4) add the polyethyleneimine-coated multi-walled carbon nanotube water dispersion liquid dropwise to the polyvinylpyrrolidone-stabilized molybdenum disulfide nanosheet layer dispersion liquid under ultrasonic conditions, continue to ultrasonically disperse for 1.5 h after the dropwise addition is completed, then stand for 24 h, filter, and dry in a vacuum oven at 80°C for 24 h to obtain a molybdenum disulfide / polyvinylpyrrolidone / polyethyleneimine / multi-walled carbon nanotube quaternary composite, then heat treat at 800°C for 1.5 h under an inert gas atmosphere to remove the polyvinylpyrrolidone and the polyethyleneimine, and obtain a molybdenum disulfide / multi-walled carbon nanotube nanocomposite negative electrode material.

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