CN111206303B - Preparation method of magnesium cobaltate/carbon composite nano fiber with wolf tooth rod structure, fiber prepared by preparation method and electrode - Google Patents

Abstract

The invention discloses a preparation method of magnesium cobaltate/carbon composite nanofiber with a wolf tooth rod structure. The invention also discloses magnesium cobaltate/carbon composite nano-fiber with a wolfsbane rod structure prepared by the method and an electrode of a capacitor prepared by using the composite nano-fiber. The magnesium cobaltate/carbon composite nanofiber with the wolframic rod structure has excellent electrochemical performance, the electrode is easy to contact with various ions of electrolyte, has high charge and discharge rate, provides good electronic carriers and buffer matrixes for effectively releasing mechanical stress caused by volume change of cobaltate, and solves the problem that expansion and contraction are easy to occur in the charge and discharge process.

Description

Preparation method of magnesium cobaltate/carbon composite nanofiber with mace structure, fiber and electrode prepared therefrom

technical field

The invention relates to the technical field of preparation of composite nanofibers, in particular to a preparation method of magnesium cobaltate/carbon composite nanofibers with a mace structure, and the prepared fibers and electrodes.

Background technique

Supercapacitors, also known as electrochemical capacitors, have higher power density than batteries and energy density of traditional electrostatic capacitors, and at the same time have stable cycle performance, wider operating temperature range, energy saving, safety, and environmental friendliness. The high-profile energy storage device can be used as a backup or independent power source in important fields of communication, power and transportation.

Metal oxide materials with stable crystal structure and high specific capacity have recently attracted much attention due to the problems of expansion and contraction during charging and discharging of traditional electrode materials. At present, the most excellent metal oxide electrode material is ruthenium oxide, which can have extremely high specific capacitance and good electrical conductivity, but ruthenium is a precious metal, expensive and toxic, which limits its large-scale application.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention researches and designs a preparation method of a magnesium cobalt oxide/carbon composite nanofiber with a mace structure, and the prepared fibers and electrodes. The technical means adopted in the present invention are as follows:

A method for preparing magnesium cobaltate/carbon composite nanofibers with mace structure, using cobalt salt and magnesium salt as the source of magnesium cobaltate, using polyvinylpyrrolidone as the carbon source, and using graphene quantum dots as the spinning solution to conduct electricity Additives, electrospinning technology is used to prepare precursor fibers, and the precursor fibers are pre-oxidized and carbonized to obtain magnesium cobalt oxide/carbon composite nanofibers with mace structure. Cobalt salts and magnesium salts can be specifically nitrates or acetates.

Further, the preparation method of the magnesium cobaltate/carbon composite nanofiber of the mace structure comprises the following steps:

S1, dissolving polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF) to obtain a PVP solution with a mass fraction of 15-20wt%;

S2. Mix Mg(Ac) ₂ .4H ₂ O, Co(Ac) ₂ .4H ₂ O and graphene quantum dots with the PVP solution obtained in step S1 to obtain a precursor solution. The mass fraction ratio is Mg(Ac) ₂ ·4H ₂ O: Co(Ac) ₂ ·4H ₂ O: graphene quantum dots: PVP: DMF=(1.7-1.8):(4.0-4.2):(0.5-0.2 ):(14.3-18.5):(79.5-75.3);

S3, using the precursor solution obtained in step S2 to perform electrospinning, the spinning voltage is 8-15kV, and the spinning receiving distance is 10-20cm to obtain the precursor fiber;

S4, drying the precursor fiber, and pre-oxidizing and carbonizing the dried precursor fiber to obtain a magnesium cobalt oxide/carbon composite nanofiber with a mace structure.

Further, in step S3, the air humidity of electrospinning is 30%±10%; in step S4, the drying temperature is 80-150°C, the drying time is 3-12 hours, and the pre-oxidation method is at 180-250°C Pre-oxidation for 2-4 hours, the carbonization method is anaerobic calcination, the temperature of anaerobic calcination is 650-750 ° C, the holding time is 4-8 hours, and natural cooling is obtained to obtain the magnesium cobalt oxide/carbon composite nanometer of mace structure. fiber.

Further, in step S1, the mass fraction of the PVP solution is 18%; in step S2, the molar ratio of Mg and Co is 1:2; in step S3, the spinning voltage is 10kV, and the spinning receiving distance is 14cm; step S4 Among them, the drying temperature was 80°C, the drying time was 3 hours, the preoxidation method was preoxidation at 200°C for 2 hours, the oxygen-free calcination temperature was 700°C, and the holding time was 4 hours.

Further, the carbonization method is oxygen-free calcination in an argon atmosphere.

A magnesium cobaltate/carbon composite nanofiber with a mace structure is prepared by the method of the present invention.

An electrode of a supercapacitor comprises magnesium cobaltate/carbon composite nanofibers with a mace structure prepared by the method of the present invention.

Compared with the prior art, the magnesium cobaltate/carbon composite nanofiber of the mace structure of the present invention has abundant pore size, larger specific surface area, and excellent electrochemical performance, and the supercapacitor of the present invention has The electrode is easily in contact with various ions of the electrolyte, showing a high charge-discharge rate even at high current density, and inhibits the aggregation effect of the magnesium cobaltate nanoparticles in the host fiber during the charge-discharge cycle. It provides a good electron carrier and buffer matrix for effectively releasing the mechanical stress caused by the volume change of the cobaltate, and solves the problem of easy expansion and contraction during charging and discharging.

Description of drawings

FIG. 1 is a schematic structural diagram of a magnesium cobaltate/carbon composite nanofiber with a mace structure according to an embodiment of the present invention.

Fig. 2 is the XRD pattern of the magnesium cobaltate/carbon composite nanofibers prepared under different carbonization temperatures in the embodiment of the present invention.

3a and 3b are SEM images of the magnesium cobaltate/carbon composite nanofibers of the mace structure prepared in the embodiment of the present invention.

4 is a TEM image of the magnesium cobaltate/carbon composite nanofiber with a single mace structure prepared in the embodiment of the present invention: FIG. 4a is a TEM image of the MgCo ₂ O ₄ nanofiber prepared at 700° C.; FIG. 4b are selected area electron diffraction (SAED) images; Figures 4c and 4i are high-resolution transmission electron microscopy (HR-TEM) images; Figures 4e-4h, 4k, and 4l are elemental surface scanning images; Figures 4d and 4j are enlarged areas .

₅ is the N adsorption and desorption isotherm curves of the magnesium cobaltate/carbon composite nanofibers of the mace structure prepared in the embodiment of the present invention.

Fig. 6 is the electrochemical performance curve of the magnesium cobaltate/carbon composite nanofiber of mace structure prepared by the embodiment of the present invention: Fig. 6a is the CV curve under different scanning rates; Fig. 6b is the CP curve under different current densities ; Figure 6c is the EIS spectrum; Figure 6d is the cycle life curve at 1A/g current density.

Detailed ways

Accurately weigh 4.170g of polyvinylpyrrolidone (PVP) and dissolve it in 20mL of N,N-dimethylformamide (DMF), stir magnetically for 12h until the polymer is completely dissolved, stand for 12h, and prepare a PVP solution with a mass fraction of 18wt%, Add 0.05 g of graphene quantum dots and stir until uniform. The electrospinning precursor solution is prepared according to the molar ratio of Mg:Co=1:2 (the addition amount of each salt is 0.002mol). Specifically, the nitrate or acetate of magnesium and cobalt can be used, as long as the subsequent reaction can be satisfied. This example is described by taking acetate as an example: 0.429g Mg(Ac) ₂ 4H ₂ O and 0.996g Co(Ac) ₂ 4H ₂ O were respectively weighed and dissolved in the 18wt% PVP solution prepared above. , and magnetically stirred for 12 h until fully dissolved to obtain the precursor solution for spinning. The prepared spinning precursor solution is added to the plastic syringe, and is connected to the metal electrode connected to the positive electrode of the high-voltage power supply. The receiving device is an aluminum foil, which is connected to the negative electrode of the high-voltage power supply and grounded. The spinning voltage was controlled to be 10 kV, the spinning receiving distance was 14 cm, and the air humidity was maintained at (30% ± 10%) for electrospinning to obtain precursor composite nanofibers, which were dried in an 80°C vacuum oven for 3 hours. The dried precursor composite nanofibers are subjected to a pre-oxidation and carbonization process to obtain the final cobaltate/carbon composite nanofibers with a mace structure. After the precursor fiber was pre-oxidized at 200 °C for 2 h, it was placed in the quartz tube of the high temperature tube furnace, and Ar gas was passed into the high temperature tube furnace for 1 h to remove the air. The precursor nanofiber sample was heated in the Ar atmosphere to increase the temperature. The temperature is raised to 650-750°C at a rate of 1-5°C/min, and kept for 4-8 hours, preferably to 700°C at a rate of 2°C/min, and calcined at 700°C for 4 hours, then naturally cooled to obtain a mace structure of magnesium cobaltate/carbon composite nanofibers.

The magnesium cobalt oxide/carbon composite nanofibers with mace structure, conductive carbon black and binder (polytetrafluoroethylene solution, 60wt% PTFE) were mixed in a ratio of 85:10:5, accurately weighed and put in. In the colorimetric tube, add a certain amount of absolute ethanol as a solvent to fully mix the three, take it out, pour it into a watch glass, bake it in a 70°C oven until the solution is viscous, and evenly coat it on the foam nickel disc , put it in the oven again to dry. On a hot press with a pressure of 2 MPa, a current collector with nickel foam as an electrode material and a nickel tape are pressed to obtain an electrode sheet. The electrochemical performance test of the electrode adopts a three-electrode working system, with the prepared magnesium cobaltate/carbon composite nanofiber as the working electrode, saturated calomel electrode (SCE) as the reference electrode, platinum wire as the auxiliary electrode, using CHI660B electro- ChemStation (Shanghai Chenhua Instrument Co., Ltd.) was used for electrochemical performance testing.

As shown in FIG. 1 , the magnesium cobaltate/carbon composite nanofibers of the mace structure prepared in this example include a fiber body 1 of a magnesium cobaltate/carbon composite, 3 in the figure is magnesium cobaltate nanoparticles, and 4 is graphite ene quantum dots, many carbon nanotubes/carbon nanowires 2 are embedded on the fiber body 1 to form a magnesium cobalt oxide/carbon composite nanofiber with a mace structure.

As shown in Figure 2, the characteristic peaks appearing at 2θ=18.96°, 31.20°, 36.76°, 38.46°, 44.71°, 55.53°, 59.22°, 65.08°, and 73.94° in the XRD pattern correspond to spinel MgCo ₂ O ₄ (111), (220), (311), (222), (400), (422), (511), (440), (620) crystal planes of (JCPDS card 81-0667); 2θ=42.82° The weak peaks at 62.16° correspond to the diffraction peaks of (200) and (220) crystal planes of MgO (JCPDS card 75-0447).

As shown in Figure 3a and Figure 3b, the diameter of the main fiber of the magnesium cobaltate/carbon composite nanofiber of the mace structure is about 500 nm, and the diameter of the carbon nanowire/carbon nanotube embedded in the main fiber is about 40 nm.

As shown in Figure 4a to Figure 4l, the main body of the magnesium cobaltate/carbon composite nanofiber of the mace structure is composed of MgCo ₂ O ₄ nanoparticles and carbon nanoparticles. The diffraction pattern of ₂ O ₄ particles is a polycrystalline structure, and the HR-TEM characterization of the fiber body shows that the lattice spacing is 0.164 nm, which is consistent with the (422) interplanar spacing of spinel MgCo ₂ O ₄ ; The EDS mapinning test shows that C, Mg, Co, and O elements are uniformly distributed in the fiber body; it can be clearly observed that the ciliary structure is composed of carbon tubes and Co nanoparticles accumulated at the tips of the carbon tubes. The diameter of the carbon tubes is about 28 nm. The particle size of Co nanoparticles is about 38nm; high-resolution TEM and mapinning tests were performed on the ciliary structure, which further proved that carbon nanotubes/carbon nanowires were grown on the outer surface of the fiber body, and the tips of the carbon nanotubes/carbon nanowires had elemental particles. Cobalt nanoparticles.

As shown in Fig. 5, the specific surface area of the magnesium cobalt oxide/carbon composite nanofibers of the mace structure is 314.027m ² /g, and the pore size distribution is concentrated in 5-15nm, which belongs to the mesoporous structure, and the total pore volume is 0.398m ³ /g.

As shown in Fig. 6a to Fig. 6d, at the current density of 4.0, 2.0, 1.0, 0.5, and 0.25 A/g, the corresponding specific capacitance values of the magnesium cobalt oxide/carbon composite nanofiber electrode material with mace structure are 50.3, 74.3 , 92.8, 102.8, 115.7F/g; the internal resistance of the electrode is 0.385Ω, and the internal resistance of charge transfer is 0.232Ω; under the current density of 1.0A/g, 1000 times of charge-discharge cycle life test were carried out. After 300 cycles, The specific capacity retention rate remained stable at 98.05% of the initial value.

The above-mentioned embodiments merely describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, those of ordinary skill in the art can make various Such deformations and improvements shall fall within the protection scope determined by the claims of the present invention.

Claims (6)

1. the preparation method of the magnesium cobaltate/carbon composite nanofiber of a mace structure, is characterized in that: may further comprise the steps: S1, dissolving polyvinylpyrrolidone in N,N-dimethylformamide to obtain a PVP solution with a mass fraction of 15-25 wt%; S2. Mix Mg(Ac) ₂ • 4H ₂ O, Co(Ac) ₂ • 4H ₂ O, and graphene quantum dots with the PVP solution obtained in step S1 to obtain a precursor solution, wherein the components in the precursor solution are The mass fraction ratio is Mg(Ac) ₂ • 4H ₂ O: Co(Ac) ₂ • 4H ₂ O: graphene quantum dots: PVP: DMF = (1.7-1.8): (4.0-4.2): (0.5-0.2 ): (14.3-18.5): (79.5-75.3); S3, using the precursor solution obtained in step S2 to carry out electrospinning, the spinning voltage is 8-15kV, and the spinning receiving distance is 10-20cm, to obtain precursor fibers, and the air humidity of electrospinning is 30%±10%; S4, drying the precursor fiber, and pre-oxidizing and carbonizing the dried precursor fiber to obtain a magnesium cobalt oxide/carbon composite nanofiber with a mace structure; The carbonization method is as follows: the precursor nanofiber sample is heated to 650-750°C at a heating rate of 1-5°C/min in an Ar atmosphere, and kept for 4-8h; The method of pre-oxidation is pre-oxidation at 180-250°C for 2-4 hours. 2. the preparation method of the magnesium cobaltate/carbon composite nanofiber of mace structure according to claim 1, is characterized in that: in step S4, drying temperature is 80-150 ℃, drying time 3-12 hours, carbonization The method is anaerobic calcination, the temperature of anaerobic calcination is 650-750 DEG C, the holding time is 4-8 hours, and natural cooling is used to obtain the magnesium cobaltate/carbon composite nanofiber of mace structure. 3. the preparation method of the magnesium cobaltate/carbon composite nanofiber of mace structure according to claim 2, is characterized in that: In step S1, the mass fraction of the PVP solution is 18%; In step S2, the mol ratio of Mg and Co is 1:2; In step S3, the spinning voltage is 10kV, and the spinning receiving distance is 14cm; In step S4, the drying temperature is 80°C, the drying time is 3 hours, the pre-oxidation method is pre-oxidizing at 200°C for 2 hours, the oxygen-free calcination temperature is 700°C, and the holding time is 4 hours. 4. the preparation method of the magnesium cobaltate/carbon composite nanofiber of mace structure according to any one of claim 1 to 3, it is characterized in that: the method for carbonization is to carry out oxygen-free calcination in the atmosphere of argon . 5. A magnesium cobaltate/carbon composite nanofiber of mace structure, characterized in that: prepared by the method described in any one of claims 1 to 4. 6 . An electrode for a supercapacitor, characterized in that: the magnesium cobalt oxide/carbon composite nanofiber of the mace structure prepared by the method according to any one of claims 1 to 4 is included.

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