CN115020661A - Co with selenium vacancies 0.85 Se@WSe 2 Preparation method and application of nitrogen-doped carbon polyhedral composite material - Google Patents

Co with selenium vacancies 0.85 Se@WSe 2 Preparation method and application of nitrogen-doped carbon polyhedral composite material Download PDF

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CN115020661A
CN115020661A CN202210544256.3A CN202210544256A CN115020661A CN 115020661 A CN115020661 A CN 115020661A CN 202210544256 A CN202210544256 A CN 202210544256A CN 115020661 A CN115020661 A CN 115020661A
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CN115020661B (en
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杨春成
裴亚茹
文子
赵明
蒋青
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Jilin University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to Co with selenium vacancy 0.85 Se@WSe 2 A preparation method of a nitrogen-doped carbon polyhedral composite material (CoWSe/NCP) and application thereof as a negative electrode material of a sodium-ion battery. The preparation steps of the composite material are as follows: a. preparing a metal organic framework material ZIF-67; b. annealing ZIF-67 in Ar atmosphere to obtain Co nano-particles/nitrogen-doped carbon polyhedrons (Co/NCP); c. dispersing Co/NCP in Na-containing solution 2 WO 4 ·2H 2 In O water solution, after ultrasonic dispersion, the adsorbed Na is obtained by hydrothermal reaction 2 WO 4 Co/NCP (Na) of 2 WO 4 -Co/NCP); d. na is mixed with 2 WO 4 -Co/NCP and selenium powder in Ar/H 2 Annealing under the atmosphere to obtain the CoWSe/NCP composite material. As a negative electrode material of a sodium-ion battery, CoWSe/NCP shows higher discharge capacity at 0.1Ag ‑1 The discharge capacity of 100 cycles under the current density is 505.2mAh g ‑1 (ii) a Outstanding rate capability at 20Ag ‑1 Capacity at a lower value of 339.6mAh g ‑1 (ii) a And excellent cycle stability at 1Ag ‑1 The capacity of 5000 circles of lower circulation is 434.9mAh g ‑1 . The invention provides a new idea for researching and developing the sodium-ion battery cathode material with excellent comprehensive performance.

Description

Co with selenium vacancies 0.85 Se@WSe 2 Preparation method and application of nitrogen-doped carbon polyhedral composite material
The technical field is as follows:
the invention relates to Co with selenium vacancy 0.85 Se@WSe 2 A preparation method of a heterostructure/nitrogen doped carbon polyhedral composite material and application thereof as a cathode material of a sodium ion battery.
Background art:
lithium ion batteries have high energy and power densities and have been widely used in various energy storage devices. However, the lithium resource has limited reserves and uneven distribution, and cannot meet the huge demand of large-scale energy storage, and a great deal of exploration on alternative energy sources is initiated. Sodium ion batteries are receiving increasing attention due to the abundant sodium resources and energy storage mechanisms similar to those of lithium ion batteries. However, Na + Radius ratio Li + The graphite used as the cathode of a commercial lithium ion battery for the cathode of a sodium ion battery shows poor electrochemical performance due to large radius. Therefore, finding a sodium ion battery anode material with excellent rate performance and cycle stability remains a great challenge. Transition metal selenides have received much attention due to their weaker metal-selenium bond, better conductivity and higher theoretical capacity. However, during cycling, they undergo a large volume expansion resulting in a rapid capacity decay.
Experiments prove that the heterostructure design is an effective method for improving the electrochemical performance of the metal selenide. Two or more substances are chemically or physically (mainly van der waals forces) bonded together to form an interface. At the interface, the chemical bonds and charge distribution of the two phases will rearrange. Due to the synergistic effect of the heterostructure electrodes, the performance is generally superior to that of a single electrode. The reason for the analysis is as follows: firstly, the electrodes with the heterostructure can make up for the deficiencies of each component by taking the advantages of each component into consideration. Second, heterostructures typically have a small bandgap, thereby exhibiting excellent conductivity and rapid charge transfer. Third, the cycle life of the electrode can be improved due to the strong interaction between the two phases of the heterostructure. Finally, at the interface between the two phases, the charge is redistributed and also provides more active sites for the adsorption of alkali metal ions. Thus, the design of the heterostructure can enhance sodium storage capability.
In addition, the defect of introducing vacancy into the metal selenide is an effective method for improving the sodium storage performance of the metal selenide. In one aspect, vacancies can adjust the electronic state around the metal atom, producing additional Na + An adsorption site. On the other hand, the vacancies may also enhance Na + The adsorption capacity of (1). Therefore, defect engineering is also an effective strategy to improve the electrochemical performance of power cells. Therefore, the cooperative design of the heterostructure and the vacancy can improve the electronic conductivity, accelerate the reaction kinetics and enhance Na + Adsorption capacity and addition of Na + An adsorption site. However, to our knowledge, there are currently very few reports on this. Based on the above strategies, the invention aims to prepare the sodium-ion battery cathode material with excellent rate performance and cycle stability.
The invention content is as follows:
aiming at the problems, the invention prepares Co with selenium vacancy 0.85 Se@WSe 2 Heterostructure/nitrogen doped carbon polyhedra (CoWSe/NCP) and is used for sodium ion battery anode materials.
The structure of the CoWSe/NCP composite material is Co with selenium vacancy 0.85 Se@WSe 2 Heterostructures anchored in nitrogen-doped carbon polyhedra, due to differences in the electronegativity of Co and W, in the formation of Co 0.85 Se@WSe 2 And forming abundant selenium vacancy at the same time of the heterostructure. The composite material has the following characteristics: first, Co 0.85 Se@WSe 2 The heterostructure can improve the electronic conductivity and accelerate the charge transfer; second, selenium vacancyThe site is enhanced by Na + The adsorption capacity of the sodium ion adsorbent improves the sodium storage capacity; thirdly, the nitrogen-doped carbon polyhedron can play a role in buffering in the charging and discharging process, so that the strain caused by volume change is reduced, and the structural stability is enhanced. Therefore, the CoWSe/NCP is used as a negative electrode material of the sodium-ion battery and shows excellent comprehensive electrochemical performance.
The above purpose of the invention is realized by the following technical scheme:
co with selenium vacancy 0.85 Se@WSe 2 The preparation method of the heterostructure/nitrogen-doped carbon polyhedral composite material comprises the following steps:
a. preparing ZIF-67: 1.2-1.6 g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100ml of methanol solution, dissolving 3.2-3.5 g of dimethyl imidazole in 50ml of methanol solution, uniformly stirring, and pouring the methanol solution of dimethyl imidazole into Co (NO) 3 ) 2 ·6H 2 Continuously stirring the mixture for 2 to 4 hours in the methanol solution of O, centrifuging and washing the mixture, and then putting the mixture into a vacuum dryer for 10 to 12 hours at the temperature of 60 ℃;
b. preparation of Co/NCP: maintaining the temperature of the ZIF-67 at 550-650 ℃ in Ar atmosphere for 2-2.5 h for annealing to obtain Co/NCP;
c. adding 0.5-1.0 g of Na 2 WO 4 ·2H 2 Dispersing 0.2-0.3 g of Co/NCP (cobalt-N-phosphate) into 50-80 ml of ultrapure water, uniformly stirring, ultrasonically dispersing for 30-60 min, placing the solution into a 100ml reaction kettle, reacting for 10-12 h at 100-150 ℃, centrifuging the product, cleaning with water and ethanol for 2-3 times, and vacuum drying for 10-12 h at 60 ℃ to obtain Na 2 WO 4 -Co/NCP；
d. Adding 0.1-0.2 g of Na 2 WO 4 -Co/NCP and 0.2-0.5 g selenium powder in Ar/H 2 Keeping the temperature of 600-650 ℃ for 2-2.5 h in the atmosphere for annealing to finally obtain Co with selenium vacancy 0.85 Se@WSe 2 Heterostructure/nitrogen doped carbon polyhedral composite material, i.e. CoWSe/NCP.
Further, in step a, Co (NO) is adjusted 3 ) 2 ·6H 2 The concentration of O and dimethyl imidazole and reaction time control the size of ZIF-67.
Further, in step b, ZIF-67 was heated at 5 ℃ for min in an Ar-filled tube furnace -1 Raising the temperature to 600 ℃, preserving the heat for 2h, and then cooling the product to room temperature to obtain Co/NCP.
Further, the Co/NCP and selenium powder in the step b is in Ar/H 2 Annealing in atmosphere to obtain Co 0.85 Se/NCP；
Further, the Co/NCP in the step b is etched in HCl to remove Co in the Co/NCP to obtain NCP, and then the NCP is dispersed into Na 2 WO 4 ·2H 2 In an aqueous solution of O to obtain Na 2 WO 4 NCP, finally Na 2 WO 4 -NCP and selenium powder in Ar/H 2 Annealing in atmosphere to obtain WSe 2 /NCP。
Further, in step c, Na can be adjusted 2 WO 4 ·2H 2 The concentration of O and the amount of Co/NCP regulate the Co content in the final composite material 0.85 Se and WSe 2 The ratio of (a) to (b).
Further, the annealing temperature and time can be adjusted to adjust Co in the composite material in the step d 0.85 Se and WSe 2 The degree of crystallization of (a).
Further, in step d, during annealing, due to the difference in electronegativity between Co and W, Co is formed 0.85 Se@WSe 2 And meanwhile, forming abundant selenium vacancies at the same time of the heterostructure.
Co with selenium vacancy obtained by preparation method 0.85 Se@WSe 2 The heterostructure/nitrogen-doped carbon polyhedral composite material is used as a negative electrode material of a sodium ion battery to carry out electrochemical performance test, and comprises the following steps:
a. preparing a working electrode: firstly, the active material, i.e. CoWSe/NCP, Co 0.85 Se/NCP or WSe 2 The preparation method comprises the following steps of mixing the conductive carbon black and the binder sodium carboxymethyl cellulose uniformly in water according to the ratio of 7:2:1, coating the mixture on a copper foil, performing vacuum drying at the temperature of 70-100 ℃ for 10-12 hours, and cutting the copper foil into a circular electrode slice with the diameter of 11-12 mm;
b. assembling the sodium-ion battery: the active material is used as a working electrode, the sodium sheet is used as a counter electrode/reference electrode, and the diaphragm is Whatman glass fiber with 1M NaClO electrolyte 4 Dissolving in a mixture of ethylene carbonate and diethylene carbonate containing 5.0 wt% fluoroethylene carbonate at a mass ratio of 1:1, and assembling into CR2025 button cell in an argon-filled glove box with water oxygen value [ O ] 2 ]<1ppm,[H 2 O]<1ppm；
c. Performing cyclic voltammetry test by using an Ivium-n-Stat electrochemical workstation at a sweep rate of 0.1-1.2 mV s -1 The voltage range is 0.01-3.0V;
d. the electrochemical impedance test condition is that the frequency range is 100kHz to 10mHz at room temperature;
e. performing constant current charge-discharge cycle test by using a LAND CT2001A battery test system, wherein the voltage range is 0.01-3.0V;
f. disassembly characterization of the battery: disassembling the button cell after charge and discharge tests in a glove box, taking out electrode plates, soaking the button cell in dimethyl carbonate solution for 20-24 h, then cleaning the button cell with ethanol for 3-6 times, drying the button cell, and then performing ex-situ XRD, ex-situ Raman and TEM characterization, wherein the water oxygen values of the glove box are respectively [ O ] 2 ]<1ppm,[H 2 O]<1ppm。
The invention has the technical effects that:
co with selenium vacancy prepared by the invention 0.85 Se@WSe 2 Heterostructure/nitrogen doped carbon polyhedral composite, Co 0.85 Se@WSe 2 The heterostructure can improve the electronic conductivity and accelerate the charge transfer; selenium vacancy enhances Na + The adsorption capacity of the sodium ion adsorbent improves the sodium storage capacity; the nitrogen-doped carbon polyhedron can play a role in buffering in the charging and discharging process, reduce the strain caused by volume change and enhance the structural stability. The negative electrode material of the sodium-ion battery shows higher discharge capacity (at 0.1A g) -1 The discharge capacity of the capacitor is 505.2mAh g under the current density and circulating for 100 circles -1 ) Outstanding rate capability (at 20A g) -1 Capacity at a lower value of 339.6mAh g -1 ) And excellent cycling stability (at 1A g) -1 The capacity of 5000 circles of lower circulation is 434.9mAh g -1 ). The invention provides the research and development of the cathode material of the sodium-ion battery with excellent comprehensive performanceA new idea.
Description of the drawings:
FIG. 1 CoWSe/NCP, Co in example 1 of the present invention 0.85 Se/NCP and WSe 2 the/NCP composite material is used as the rate capability of the negative electrode of the sodium-ion battery.
FIG. 2 is a flow chart of the preparation of CoWSe/NCP composite material in example 1 of the present invention.
FIG. 3 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 XRD pattern of/NCP composite material.
FIG. 4 Raman spectrum of CoWSe/NCP composite prepared in example 1 of the present invention.
FIG. 5N of CoWSe/NCP composite prepared in example 1 of the present invention 2 Adsorption and desorption curves and pore size distribution diagrams (inset).
FIG. 6 is a FESEM photograph of the CoWSe/NCP composite material prepared in example 1 of the present invention.
FIG. 7 TEM photograph of CoWSe/NCP composite prepared in example 1 of the present invention.
FIG. 8 is a HRTEM photograph of the CoWSe/NCP composite prepared in example 1 of the present invention.
FIG. 9 SAED photograph of CoWSe/NCP composite prepared in example 1 of the present invention.
FIG. 10, TGA graph of CoWSe/NCP composite prepared in inventive example 1.
FIG. 11 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 XPS survey of/NCP composites.
FIG. 12 CoWSe/NCP, Co prepared in example 1 of the invention 0.85 Se/NCP and WSe 2 C1s XPS high resolution spectra of/NCP composites.
FIG. 13 CoWSe/NCP, Co prepared in example 1 of the invention 0.85 Se/NCP and WSe 2 N1s XPS high resolution spectra of/NCP composites.
FIG. 14 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 Co 2p XPS high resolution spectra of/NCP composites.
FIG. 15 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 W4 f XPS high resolution spectra of/NCP composites.
FIG. 16 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 Se 3d XPS high resolution spectra of/NCP composites.
FIG. 17 EPR spectrum of CoWSe/NCP composite prepared in inventive example 1.
FIG. 18, cyclic voltammogram of CoWSe/NCP composite electrode prepared in example 1 of the present invention in sodium ion battery with scan rate of 0.1mV s -1 。
FIG. 19 CoWSe/NCP composite electrode prepared in inventive example 1 in sodium ion battery 0.1A g -1 Constant current charge and discharge curve under current density.
FIG. 20 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 0.1A g of/NCP composite material electrode in sodium ion battery -1 Graph of cycling performance at current density.
FIG. 21 CoWSe/NCP, Co prepared in example 1 of the present invention 0.85 Se/NCP and WSe 2 1A g of/NCP composite material electrode in sodium ion battery -1 Plot of cycling performance at current density.
FIG. 22 CoWSe/NCP composite electrode prepared in inventive example 1 in sodium ion battery 2A g -1 Graph of cycling performance at current density.
FIG. 23 CoWSe/NCP composite electrode prepared in inventive example 1 in sodium ion battery 5A g -1 Graph of cycling performance at current density.
FIG. 24 CoWSe/NCP composite electrode prepared in inventive example 1 in sodium ion battery 10A g -1 Graph of cycling performance at current density.
FIG. 25 shows different scanning rates (0.2-1.2 mV s) of CoWSe/NCP composite electrode prepared in example 1 of the present invention in a sodium ion battery -1 ) Cyclic voltammogram.
FIG. 26 is a graph showing the linear relationship of logi to logv of CoWSe/NCP composite electrodes prepared in example 1 of the present invention in different redox states in a sodium ion battery.
FIG. 27, the CoWSe/NCP composite electrode prepared in example 1 of the present invention, scanned in a sodium ion battery at a rate of 0.8mV s -1 The contribution of the capacitive storage process and the diffusion storage process.
FIG. 28 is a graph of the capacity normalization contribution rate of capacitance and diffusion storage of CoWSe/NCP composite electrode prepared in example 1 of the present invention at different scanning rates in a sodium ion battery.
FIG. 29, ex-situ XRD patterns of CoWSe/NCP composite electrodes prepared in example 1 of the present invention at different potentials in sodium ion batteries.
FIG. 30, Ex-situ Raman spectra of CoWSe/NCP composite electrodes prepared in example 1 of the present invention at different potentials in sodium ion batteries.
FIG. 31, HRTEM photograph of CoWSe/NCP composite electrode prepared in example 1 of the present invention after complete discharge in sodium ion battery.
FIG. 32, HRTEM photograph of CoWSe/NCP composite electrode prepared in example 1 of the present invention after full charge in sodium ion battery.
FIG. 33 is a FESEM photograph of the CoWSe/NCP composite material prepared in example 2 of the present invention.
FIG. 34 is an FESEM photograph of the CoWSe/NCP composite prepared in example 3 of the present invention.
Detailed Description
The specific contents and embodiments of the present invention will be further described with reference to examples, which are provided for illustration only and should not be construed as limitations on the technical solutions of the present invention. The following is a detailed description of example 1. Examples 2 and 3 of the present invention are similar to those of example 1.
Examples of the invention will now be described below:
example 1
The preparation process and steps in this example are as follows:
(1) 1.455g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100ml methanol solution, dissolving 3.384g dimethyl imidazole in 50ml methanol solution, stirring well, pouring dimethyl imidazole methanol solution into Co (NO) 3 ) 2 ·6H 2 Continuously stirring the mixture in the methanol solution of O for 2 hours, centrifuging and washing the mixture, and then putting the mixture into a vacuum drying chamber at the temperature of 60 ℃ for 12 hours;
(2) keeping the temperature of ZIF-67 at 600 ℃ in Ar atmosphere for 2h, and annealing to obtain Co/NCP;
(3) mixing 0.587g of Na 2 WO 4 ·2H 2 Dispersing 0.2g of Co/NCP into 70ml of ultrapure water, uniformly stirring, performing ultrasonic dispersion for 30min, putting the solution into a 100ml reaction kettle, reacting for 10h at 120 ℃, centrifuging the product, cleaning for 2-3 times by using water and ethanol, and performing vacuum drying for 12h at 60 ℃ to obtain Na 2 WO 4 -Co/NCP；
(4) 0.1g of Na 2 WO 4 -Co/NCP with 0.3g selenium powder in Ar/H 2 And (4) keeping the temperature at 600 ℃ for 2h in the atmosphere for annealing to finally obtain the CoWSe/NCP.
As a comparative experiment, the Co/NCP and selenium powder in step b are added in Ar/H 2 Annealing in atmosphere to obtain Co 0.85 Se/NCP；
As a comparative experiment, the Co/NCP in the step b is etched in HCl to remove Co in the Co/NCP to obtain NCP, and then the NCP is dispersed in Na 2 WO 4 ·2H 2 In an aqueous solution of O to obtain Na 2 WO 4 NCP, finally Na 2 WO 4 -NCP and selenium powder in Ar/H 2 Annealing in an atmosphere to obtain WSe 2 /NCP。
The CoWSe/NCP composite material obtained by the preparation method is used as a sodium ion battery negative electrode material for carrying out electrochemical performance test, and comprises the following steps:
a. preparing a working electrode: firstly, the active material, i.e. CoWSe/NCP, Co 0.85 Se/NCP or WSe 2 The NCP, conductive carbon black and sodium carboxymethyl cellulose as a binder are uniformly mixed in water according to the ratio of 7:2:1, then the mixture is coated on a copper foil, and the copper foil is dried in vacuum at 80 ℃ for 12 hours and then cut into a circular electrode slice with the diameter of 12 mm;
b. assembling the sodium-ion battery: the active material is used asIs used as a working electrode, a sodium sheet is used as a counter electrode/reference electrode, a diaphragm is Whatman glass fiber, and electrolyte is 1M NaClO 4 Dissolving in a mixture of ethylene carbonate and diethylene carbonate containing 5.0 wt% fluoroethylene carbonate at a mass ratio of 1:1, and assembling into CR2025 type button cell in an argon-filled glove box with water oxygen value of [ O ] 2 ]<1ppm,[H 2 O]<1ppm；
c. Performing cyclic voltammetry test by using an Ivium-n-Stat electrochemical workstation at a sweep rate of 0.1-1.2 mV s -1 The voltage range is 0.01-3.0V;
d. the electrochemical impedance test condition is that the frequency range is 100kHz to 10mHz at room temperature;
e. performing constant current charge-discharge cycle test by using a LAND CT2001A battery test system, wherein the voltage range is 0.01-3.0V;
f. disassembly characterization of the battery: disassembling the button cell after charge and discharge tests in a glove box, taking out electrode plates, soaking in dimethyl carbonate solution for 24h, cleaning with ethanol for 3 times, drying, performing ex-situ XRD, and performing ex-situ Raman and TEM characterization, wherein the water oxygen values of the glove box are [ O ] respectively 2 ]<1ppm,[H 2 O]<1ppm。
Co with selenium vacancies 0.85 Se@WSe 2 Morphology and structure characterization of heterostructure/nitrogen doped carbon polyhedral composite (CoWSe/NCP):
the process for making the CoWSe/NCP composite is shown in FIG. 2. Firstly, preparing an organic metal framework material ZIF-67 precursor, and annealing the precursor in Ar atmosphere to obtain Co/NCP. Next, Co/NCP is dispersed in the Na-containing solution 2 WO 4 ·2H 2 In O water solution, after ultrasonic dispersion, Na is obtained by hydrothermal reaction 2 WO 4 -Co/NCP. Finally, adding Na 2 WO 4 -Co/NCP and selenium powder in Ar/H 2 Annealing under the atmosphere to obtain the CoWSe/NCP composite material. We characterized the structure and morphology of the CoWSe/NCP composite by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). FIG. 3 shows CoWSe/NCP, Co 0.85 Se/NCP and WSe 2 The XRD pattern of the/NCP composite material,it can be seen that the peak at 20 to 30 ° is broad and is a characteristic peak of amorphous carbon. In addition, diffraction peaks at 33.2 °, 45.2 °, 51.2 °, 60.8 °, 62.6 °, 69.9 ° and 13.6 °, 31.4 °, 37.8 °, and 55.9 ° in the CoWSe/NCP composite material correspond to those of Co, respectively 0.85 Se (JCPSD No.52-1008) and WSe 2 (JCPSD No.38-1388) two phases. FIG. 4 is a Raman (Raman) spectrum of a CoWSe/NCP composite at 1346 and 1589cm -1 The characteristic peaks at (A) correspond to the D band and the G band of the carbon material, respectively. By calculation, the intensity ratio (I) D /I G ) 1.15, which shows that the nitrogen-doped carbon polyhedron has more defects and is beneficial to Na + And (5) storing. At 678cm -1 Peak of (b) corresponds to A of CoSe 1g Vibration modes, 472, 514 and 612cm -1 The peaks at (A) respectively correspond to the E of trivalent cobalt g ，F 2g 1 And F 2g 2 Vibration mode at 188 and 248cm -1 The peaks at (A) respectively correspond to WSe 2 E of (A) 1g And A 1g A vibration mode. FIG. 5 is N of CoWSe/NCP composite 2 The adsorption and desorption curves show that the specific surface area of the CoWSe/NCP composite material is 107.0m 2 g -1 . The inset is a Barrett-Joyer-Halenda pore diameter distribution diagram, the pore diameter of the composite material is mainly below 10nm, the high porosity and the large specific surface area are favorable for the diffusion of electrolyte, and simultaneously the pore diameter is Na + Intercalation provides a more efficient active site. FIGS. 6 and 7 are FESEM and TEM photographs of the CoWSe/NCP composite material, respectively, which can be seen to show a polyhedral structure with a rough surface. FIG. 8 is a High Resolution TEM (HRTEM) photograph of a CoWSe/NCP composite material, in which interplanar spacings of 0.269 and 0.324nm correspond to Co, respectively 0.85 Se (101) and WSe 2 (004) The crystal plane, the white dotted line, marks the phase interface of the two phases. FIG. 9 is a Selected Area Electron Diffraction (SAED) spectrum of the CoWSe/NCP composite material, and Co can be clearly observed 0.85 Se and WSe 2 The diffraction ring of (3) is consistent with the results of XRD. The mass ratio of Co and W elements in the CoWSe/NCP composite material can be obtained to be 2:1 through inductively coupled plasma optical emission spectroscopy (ICP-OES). Further, from the thermogravimetric analysis (TGA) curve of FIG. 10, it can be calculated that Co in the CoWSe/NCP composite material 0.85 Se，WSe 2 And amorphousThe mass percentages of carbon are 53.9%, 19.4% and 26.7%, respectively. Next, the surface characteristics of the composite material were investigated by X-ray photoelectron spectroscopy (XPS). FIG. 11 shows CoWSe/NCP, Co 0.85 Se/NCP and WSe 2 XPS survey of the/NCP composite, it can be seen that Co, W, Se, C and N elements are present in the CoWSe/NCP composite. In the CoWSe/NCP composite, the surface N element content is about 14.6 at%. On one hand, nitrogen doping provides more electrons for a pi conjugated system of carbon, so that the conductivity of the carbon nano polyhedron is improved. In addition, pyridine N and pyrrole N can form more defects on carbon nano-polyhedra, Na + The intercalation provides more channels and active sites. In the presence of Co 0.85 Se/NCP and WSe 2 The disappearance of W and Co elements was observed in the/NCP composite material, respectively. Fig. 12 is a C1s XPS high resolution spectrum of the composite material with characteristic peaks at 284.8, 286.2 and 288.2eV corresponding to C-C, C-O/C-N and C ═ O bonding. Fig. 13 is a N1s XPS high resolution spectrum of the composite material, which can be divided into three peaks at 398.3, 399.8 and 401.6eV, corresponding to pyridine N, pyrrole N and graphite N, respectively. By fitting the peak areas, the percentages were 46.9%, 32.6% and 20.5%, respectively. FIG. 14 is Co 2p XPS high resolution spectra of composites in which Co 2p is present in CoWSe/NCP composites 3/2 And Co 2p 1/2 The two pairs of peaks indicate divalent cobalt (Co) respectively 2+ ) And trivalent cobalt (Co) 3+ ) Is present. And Co 0.85 Se/NCP comparison, Co 2p 3/2 Middle Co 2+ The peak of (C) was shifted to a higher binding energy (to about 1.5eV), confirming that Co was present 0.85 Se@WSe 2 There are strong electronic interactions in heterostructures. Similar peak shift phenomena are also found in the W4 f region. In the CoWSe/NCP composite material, the characteristic peaks at 32.2 and 34.5eV respectively correspond to W4 f 7/2 And W4 f 5/2 . And WSe 2 W4 f vs. NCP 7/2 And W4 f 5/2 Transfer to low binding energy (transfer about 1.5 eV). The peaks at 35.6 and 37.6eV correspond to the presence of W-O due to the partial oxidation caused by the exposure of the sample to air. FIG. 16 is a Se 3d XPS high resolution spectrum of composite material, the characteristic peaks at 54.4, 55.1 and 55.8eV are respectively corresponding to Se 3d 5/2 ，Se 3d 3/2 And Se-O. CoWS (cognitive radio Web site)Se 3d in e/NCP composite material 3/2 Is in proportion to Co (59.2%) 0.85 Se/NCP (24.2%) and WSe 2 the/NCP (21.7%) is much larger, indicating that Se vacancies may be present in the CoWSe/NCP composite. To confirm this, we performed Electron Paramagnetic Resonance (EPR) tests. As shown in fig. 17, there is a strong EPR signal at g-2.004, confirming the presence of a large number of Se vacancies in the CoWSe/NCP composite.
To test the electrochemical performance of the CoWSe/NCP composite as a sodium ion battery negative electrode material, we assembled samples into half cells and tested them at room temperature. FIG. 18 is a plot of the cyclic voltammetry of the first five cycles of a CoWSe/NCP composite electrode in a sodium ion battery with a sweep rate of 0.1mV s -1 Potential range of 0.01-3.0V (vs. Na/Na) + ). The reduction peak around 0.91V observed only in the first scan corresponds to the formation of a Solid Electrolyte Interface (SEI) film. Two cathodic peaks at 1.33 and 0.66V with Na + At Co 0.85 Gradual intercalation/conversion in Se to Co and Na 2 The Se reaction is related, the cathode peak at 1.16V corresponds to WSe 2 To W and Na 2 Conversion reaction of Se. Anodic peak at 1.83V, with Na + Is exfoliated and Co 0.85 Se and WSe 2 Is related to the regeneration of (1). During subsequent scans, the CV curves were highly overlapping, indicating excellent reversibility of the CoWSe/NCP composite electrode. FIG. 19 shows that the discharge current density was 0.1A g -1 Constant current charge and discharge curves at circles 1, 2, 50 and 100 of the CoWSe/NCP composite electrode. It is noted that all capacities in this work are calculated based on the total mass of the CoWSe/NCP composite. The first circle discharge capacity and the charge capacity of the CoWSe/NCP composite material electrode are 824.2 mAh g and 546.8mAh g respectively -1 Corresponding to an initial coulombic efficiency of 66.2%. The first turn of irreversible capacity is due to the formation of SEI film. FIG. 20 shows CoWSe/NCP, Co 0.85 Se/NCP and WSe 2 the/NCP composite material electrode is at 0.1A g -1 The reversible capacity of the CoWSe/NCP composite material electrode after 100 cycles is 505.2mAh g -1 Much higher than Co 0.85 Se/NCP(382.6mAh g -1 ) And WSe 2 /NCP(384.5mAh g -1 ). FIG. 1 shows CoWSe/NCP, Co 0.85 Se/NCP and WSe 2 Results of rate capability test of/NCP composite material electrode, the test current density is gradually increased from 0.1 to 20A g -1 . Current densities of 0.1, 0.2, 0.5, 1, 2, 5, 10 and 20A g -1 The average discharge capacities corresponding to the CoWSe/NCP composite material electrodes are 579.7, 531.5, 498.9, 465.1, 426.8, 390.4, 363.8 and 339.6mAh g respectively -1 And Co 0.85 Se/NCP and WSe 2 the/NCP electrode showed lower discharge capacity of 513.8, 448.4, 409.7, 381.5, 356.6, 325.7, 295.1, 278.7mAh g respectively -1 And 478.9, 424.8, 390.1, 364.9, 338.1, 303.9, 274.4, 250.5mAh g -1 . When the current density jumps back to 0.1A g -1 Then, the capacity of the CoWSe/NCP electrode can be recovered to 460.4mAh g -1 And gradually stabilizes during subsequent charge and discharge cycles. This means that CoWSe/NCP has excellent rate capability. FIG. 21 shows CoWSe/NCP, Co 0.85 Se/NCP and WSe 2 the/NCP composite material electrode is 1A g -1 And (5) testing the cycle stability under the current density. After 5000 cycles of circulation, the discharge capacity of the CoWSe/NCP composite material electrode still maintains 434.9mAh g -1 . In contrast, Co 0.85 The capacity fade of the Se/NCP electrode is severe at the beginning due to WSe 2 Has a large interlayer spacing of WSe 2 the/NCP electrode is relatively stable but exhibits a lower capacity. As shown in FIG. 22, even at higher current densities (2A g) -1 ) After 5000 cycles of the CoWSe/NCP composite material electrode, the capacity of the CoWSe/NCP composite material electrode still maintains 347.1mAh g -1 And exhibits excellent cycle stability. It is worth mentioning that, as shown in fig. 23 and 24, when the current density is increased to 5A g -1 And 10A g -1 Then, the capacity of the CoWSe/NCP composite material electrode after 10000 cycles of circulation is 280.7mAh g -1 And 162.2mAh g -1 Further, the excellent cycle stability was confirmed.
To better understand the storage mechanism of CoWSe/NCP composite electrode, we scanned at different speeds (0.2-1.2 mV s) -1 ) Cyclic voltammetry was performed, and the results are shown in fig. 25. Typically, the scan rate (v) and the test current(i) Obeying the following relationship:
i＝av b (1)
where a and b are adjustable parameters. Equation 1 can also be expressed in the following form.
log(i)＝blog(v)+log(a) (2)
Here, the b value is the slope of the linear relationship between logi and logv, and the magnitude of the slope can be used for representing Na + A storage mechanism. b-0.5 means that the electrochemical reaction of the electrode is Na + Intercalation/deintercalation reactions, i.e. diffusion control processes; b-1 indicates that the electrode electrochemical reaction is capacitive behavior, controlled by surface reactions, and represents a capacitive control process. The slope b values calculated by the relationship of logi-logv in fig. 26 are 0.96 (peak 1), 0.98 (peak 2) and 0.97 (peak 3), respectively, which illustrates that the dynamic process of the CoWSe/NCP composite electrode is mainly a capacitance control process. In addition, the capacitive behavior (k) at a fixed potential 1 v) and diffusion behavior (k) 2 v 1/2 ) The relative contribution of (c) can be obtained from the following equation:
i(V)＝k 1 v+k 2 v 1/2 (3)
wherein k is 1 And k 2 Is an adjustable parameter. Equation 3 can also be expressed in the following form.
i(V)/v 1/2 ＝k 1 v 1/2 +k 2 (4)
By calculating k 1 The specific proportion of the capacitor storage that is present throughout the electrochemical process can be determined. As shown in FIG. 27, the sweep rate was 0.8mV s -1 The contribution of the CoWSe/NCP composite electrode capacitance control process was 89.7%. As the scan rate increases, the capacitive contribution gradually increases, as shown in fig. 28. When the scanning rate is increased to 1.2mV s -1 At times, the capacitance contribution is as high as 92.2%. The results show that the electrochemical process in the CoWSe/NCP composite material electrode is mainly a capacitance storage process, which is attributed to the nitrogen-doped carbon polyhedron with large specific surface area, provides an effective path for the transmission of electrolyte and simultaneously provides Na + The intercalation provides an effective active site, whichIn addition, the composite material has a large number of selenium vacancies, which can induce the generation of additional Na + Adsorbing active sites, thereby promoting the creation of pseudocapacitance.
In order to clarify the reaction mechanism of the CoWSe/NCP composite material electrode in the charging and discharging processes, ex-situ XRD, ex-situ Raman and ex-situ HRTEM characterization before and after charging and discharging are carried out on the CoWSe/NCP composite material electrode. As shown in FIG. 29, as the discharge proceeds, Co 0.85 Se and WSe 2 The characteristic peak of (A) becomes weak and a new Na appears around 22 DEG 2 Se peak (JCPDS No. 65-2999). When fully discharged, metallic Co and W phases appear, meaning Co 0.85 Se and WSe 2 With Na + Gradually convert to Na 2 Se, metallic Co and W phases. During charging, Co 0.85 Se and WSe 2 Phase is gradually recovered and Na 2 The residual peak of Se may be related to the first irreversible reaction. FIG. 30 is an ex-situ Raman spectrum of a composite electrode at different discharge potentials, I D /I G Gradually decreases from 1.15 to 1.03, and I is in the later charging process D /I G And gradually increased to 1.07. This indicates that the degree of graphitization of the composite material increases during discharge and decreases during charging. HRTEM photographs of the CoWSe/NCP composite electrode after charge and discharge are shown in FIGS. 31 and 32, and Na is observed after complete discharge 2 Se (111), metal W (210) and Co (111) crystal planes, and Co after full charge 0.85 Se and WSe 2 The phases are regenerated again. Based on the above analysis, the charge and discharge reactions involved can be described as:
and (3) discharging:
Co 0.85 Se+2Na + +2e - →0.85Co+Na 2 Se (5)
WSe 2 +4Na + +4e - →W+2Na 2 Se (6)
and (3) charging process:
0.85Co+Na 2 Se→Co 0.85 Se+2Na + +2e - (7)
W+2Na 2 Se→WSe 2 +4Na + +4e - (8)
in conclusion, the Co with selenium vacancy is designed and prepared by a novel and simple method 0.85 Se@WSe 2 Heterostructure/nitrogen doped carbon polyhedral composite materials. Co in the composite material 0.85 Se@WSe 2 The heterostructure can improve the electronic conductivity and accelerate the charge transfer; selenium vacancy enhances Na + The adsorption capacity of the sodium ion adsorbent improves the sodium storage capacity; the nitrogen-doped carbon polyhedron can play a role in buffering, reduce the strain caused by volume change and enhance the structural stability. Therefore, the composite material electrode shows excellent electrochemical performance in a sodium ion battery, and is expected to be applied to a high-performance sodium ion battery.
Example 2
The preparation process and steps in this example are as follows:
(1) 1.2g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100ml methanol solution, dissolving 3.2g dimethylimidazole in 50ml methanol solution, stirring well, pouring the methanol solution of dimethylimidazole into Co (NO) 3 ) 2 ·6H 2 Continuously stirring the mixture in the methanol solution of O for 2 hours, centrifuging and washing the mixture, and then putting the mixture into a vacuum drying chamber at the temperature of 60 ℃ for 12 hours;
(2) keeping the temperature of ZIF-67 at 600 ℃ in Ar atmosphere for 2h, and annealing to obtain Co/NCP;
(3) 0.5g of Na 2 WO 4 ·2H 2 O, 0.2g of Co/NCP is dispersed in 70ml of ultrapure water, the mixture is uniformly stirred and ultrasonically dispersed for 30min, the solution is placed in a 100ml reaction kettle to react for 10h at 120 ℃, the product is centrifuged, washed for 2-3 times by water and ethanol, and dried for 12h in vacuum at 60 ℃ to obtain Na 2 WO 4 -Co/NCP；
(4) 0.1g of Na 2 WO 4 -Co/NCP with 0.4g selenium powder in Ar/H 2 And (4) keeping the temperature at 600 ℃ for 2h in the atmosphere for annealing to finally obtain the CoWSe/NCP.
The CoWSe/NCP composite material obtained by the preparation method is used as a sodium ion battery negative electrode material for carrying out electrochemical performance test, and comprises the following steps:
a. preparing a working electrode: firstly, uniformly mixing an active material, namely a CoWSe/NCP composite material, conductive carbon black and a binder sodium carboxymethyl cellulose in water according to a ratio of 7:2:1, coating the mixture on a copper foil, then performing vacuum drying at 80 ℃ for 12 hours, and then cutting the copper foil into a circular electrode plate with the diameter of 12 mm;
b. assembling the sodium-ion battery: active material is used as a working electrode, a sodium sheet is used as a counter electrode/reference electrode, a membrane is Whatman glass fiber, and electrolyte is 1M NaClO 4 Dissolving in a mixture of ethylene carbonate and diethylene carbonate containing 5.0 wt% fluoroethylene carbonate at a mass ratio of 1:1, and assembling into CR2025 button cell in an argon-filled glove box with water oxygen value [ O ] 2 ]<1ppm,[H 2 O]<1ppm；
c. Performing cyclic voltammetry test by using an Ivium-n-Stat electrochemical workstation at a sweep rate of 0.1-1.2 mV s -1 The voltage range is 0.01-3.0V;
d. the electrochemical impedance test condition is that the frequency range is 100kHz to 10mHz at room temperature;
e. performing constant current charge-discharge cycle test by using a LAND CT2001A battery test system, wherein the voltage range is 0.01-3.0V;
f. disassembly characterization of the cell: disassembling the button cell after charge and discharge tests in a glove box, taking out electrode plates, soaking in dimethyl carbonate solution for 24h, cleaning with ethanol for 3 times, drying, performing ex-situ XRD, and performing ex-situ Raman and TEM characterization, wherein the water oxygen values of the glove box are [ O ] respectively 2 ]<1ppm,[H 2 O]<1ppm。
FESEM photograph of the CoWSe/NCP composite material prepared in this example is shown in FIG. 33. As can be seen from the figure, the composite material prepared in the example has a similar morphology to the material prepared in the example 1, and shows a polyhedral structure.
Example 3
The preparation process and steps in this example are as follows:
(1) 1.6g of Co (NO) 3 ) 2 ·6H 2 O was dissolved in 100ml of a methanol solution, and 3.5g of dimethylimidazole was dissolvedStirring the mixture evenly in 50ml of methanol solution, and pouring the methanol solution of the dimethyl imidazole into Co (NO) 3 ) 2 ·6H 2 Continuously stirring the mixture in the methanol solution of O for 2 hours, centrifuging and washing the mixture, and then putting the mixture into a vacuum drying chamber at the temperature of 60 ℃ for 12 hours;
(2) maintaining the temperature of the ZIF-67 at 600 ℃ in Ar atmosphere for 2h for annealing to obtain Co/NCP;
(3) adding 1.0g of Na 2 WO 4 ·2H 2 O, 0.2g of Co/NCP is dispersed in 70ml of ultrapure water, the mixture is uniformly stirred and ultrasonically dispersed for 30min, the solution is placed in a 100ml reaction kettle to react for 10h at 120 ℃, the product is centrifuged, washed for 2-3 times by water and ethanol, and dried for 12h in vacuum at 60 ℃ to obtain Na 2 WO 4 -Co/NCP；
(4) 0.1g of Na 2 WO 4 -Co/NCP with 0.5g selenium powder in Ar/H 2 And (4) keeping the temperature at 600 ℃ for 2h in the atmosphere for annealing to finally obtain the CoWSe/NCP.
The CoWSe/NCP composite material obtained by the preparation method is used as a sodium ion battery negative electrode material for carrying out electrochemical performance test, and comprises the following steps:
a. preparing a working electrode: firstly, uniformly mixing an active material, namely a CoWSe/NCP composite material, conductive carbon black and a binder sodium carboxymethyl cellulose in water according to the ratio of 7:2:1, coating the mixture on a copper foil, then drying the mixture in vacuum at 80 ℃ for 12 hours, and then cutting the mixture into a circular electrode slice with the diameter of 12 mm;
b. assembling the sodium-ion battery: active material is used as a working electrode, a sodium sheet is used as a counter electrode/reference electrode, a membrane is Whatman glass fiber, and electrolyte is 1M NaClO 4 Dissolving in a mixture of ethylene carbonate and diethylene carbonate containing 5.0 wt% fluoroethylene carbonate at a mass ratio of 1:1, and assembling into CR2025 type button cell in an argon-filled glove box with water oxygen value of [ O ] 2 ]<1ppm,[H 2 O]<1ppm；
c. Performing cyclic voltammetry test by using an Ivium-n-Stat electrochemical workstation at a sweep rate of 0.1-1.2 mV s -1 The voltage range is 0.01-3.0V;
d. the electrochemical impedance test condition is that the frequency range is 100kHz to 10mHz at room temperature;
e. performing constant current charge-discharge cycle test by using a LAND CT2001A battery test system, wherein the voltage range is 0.01-3.0V;
f. disassembly characterization of the cell: disassembling the button cell after charge and discharge tests in a glove box, taking out electrode plates, soaking in dimethyl carbonate solution for 24h, cleaning with ethanol for 3 times, drying, performing ex-situ XRD, and performing ex-situ Raman and TEM characterization, wherein the water oxygen values of the glove box are [ O ] respectively 2 ]<1ppm,[H 2 O]<1ppm。
FESEM photograph of the CoWSe/NCP composite material prepared in this example is shown in FIG. 34. As can be seen from the figure, the composite material prepared in the example has a similar morphology to the material prepared in the example 1, and shows a polyhedral structure.
The above examples are only a few embodiments of the present invention, not all of them, and should not be construed as limiting the scope of the present invention, and all equivalent changes and modifications made according to the spirit of the present invention should be covered by the present invention.

Claims (7)

1. Co with selenium vacancy 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material comprises the following steps:
a. preparation of ZIF-67: 1.2-1.6 g of Co (NO) 3 ) 2 ·6H 2 Dissolving O in 100ml of methanol solution, dissolving 3.2-3.5 g of dimethylimidazole in 50ml of methanol solution, stirring uniformly, and pouring the dimethylimidazole methanol solution into Co (NO) 3 ) 2 ·6H 2 Continuously stirring the mixture for 2-4 hours in the methanol solution of O, centrifuging and washing the mixture, and then putting the mixture into a vacuum drying machine at the temperature of 60 ℃ for 10-12 hours;
b. preparation of Co/NCP: keeping the temperature of ZIF-67 at 550-650 ℃ for 2-2.5 h in Ar atmosphere for annealing to obtain Co/NCP;
c. adding 0.5-1.0 g of Na 2 WO 4 ·2H 2 Dispersing 0.2-0.3 g of Co/NCP into 50-80 ml of ultrapure water, uniformly stirring, ultrasonically dispersing for 30-60 min, and then placing the solution into a 100ml reaction kettle for reaction at 100-150 DEG CCentrifuging the product for 10-12 h, washing the product with water and ethanol for 2-3 times, and vacuum drying at 60 ℃ for 10-12 h to obtain Na 2 WO 4 -Co/NCP；
d. Adding 0.1-0.2 g of Na 2 WO 4 -Co/NCP and 0.2-0.5 g selenium powder in Ar/H 2 Keeping the temperature of 600-650 ℃ for 2-2.5 h in the atmosphere for annealing to finally obtain Co with selenium vacancy 0.85 Se@WSe 2 Heterostructure/nitrogen doped carbon polyhedral composites, i.e. CoWSe/NCP;
as a comparative experiment, the Co/NCP and selenium powder in step b are added in Ar/H 2 Annealing in atmosphere to obtain Co 0.85 Se/NCP；
As a comparative experiment, the Co/NCP in the step b is etched in HCl to remove Co in the Co/NCP to obtain NCP, and then the NCP is dispersed in Na 2 WO 4 ·2H 2 In an aqueous solution of O to obtain Na 2 WO 4 NCP, finally Na 2 WO 4 -NCP and selenium powder in Ar/H 2 Annealing in atmosphere to obtain WSe 2 /NCP。
2. Co with selenium vacancy as claimed in claim 1 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material is characterized in that Co (NO) is adjusted in the step a 3 ) 2 ·6H 2 The concentrations of O and dimethylimidazole, and the reaction time, controlled the size of ZIF-67.
3. Co with selenium vacancy as claimed in claim 1 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material is characterized in that in the step b, ZIF-67 is filled in a tube furnace filled with Ar for 5 ℃ min -1 Raising the temperature to 600 ℃, preserving the heat for 2h, and then cooling the product to room temperature to obtain Co/NCP.
4. Co with selenium vacancy as claimed in claim 1 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material is characterized in that Na is adjusted in the step c 2 WO 4 ·2H 2 The concentration of O and the amount of Co/NCP regulate the Co content in the final composite material 0.85 Se and WSe 2 The ratio of (a) to (b).
5. Co with selenium vacancy as claimed in claim 1 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material is characterized in that the Co in the composite material can be adjusted by adjusting the annealing temperature and the annealing time in the step d 0.85 Se and WSe 2 The degree of crystallization of (a).
6. Co with selenium vacancy as claimed in claim 1 0.85 Se@WSe 2 The preparation method of the nitrogen-doped carbon polyhedral composite material is characterized in that in the step d, in the annealing process, Co is formed due to the difference of electronegativity of Co and W 0.85 Se@WSe 2 And meanwhile, forming abundant selenium vacancies at the same time of the heterostructure.
7. Use of a composite material according to any one of claims 1 to 6 as a negative electrode material for sodium ion batteries for electrochemical performance testing, comprising the steps of:
a. preparing a working electrode: firstly, the active material, i.e. CoWSe/NCP, Co 0.85 Se/NCP or WSe 2 The preparation method comprises the following steps of mixing the conductive carbon black and the binder sodium carboxymethyl cellulose uniformly in water according to the ratio of 7:2:1, coating the mixture on a copper foil, drying the copper foil in vacuum at 70-100 ℃ for 10-12 hours, and cutting the copper foil into a circular electrode slice with the diameter of 11-12 mm;
b. assembling the sodium-ion battery: active material is used as a working electrode, a sodium sheet is used as a counter electrode/reference electrode, a membrane is Whatman glass fiber, and electrolyte is 1M NaClO 4 Dissolving in a mixture of ethylene carbonate and diethylene carbonate containing 5.0 wt% fluoroethylene carbonate at a mass ratio of 1:1, and assembling into CR2025 type button cell in an argon-filled glove box with water oxygen value of [ O ] 2 ]<1ppm,[H 2 O]<1ppm；
c. Cyclic voltammetry using an Ivium-n-Stat electrochemical workstationThe test and sweep speed is 0.1-1.2 mV s -1 The voltage range is 0.01-3.0V;
d. the electrochemical impedance test condition is carried out at room temperature, and the frequency range is 100kHz to 10 mHz;
e. performing constant-current charge-discharge test by using a LAND CT2001A battery test system, wherein the voltage range is 0.01-3.0V;
f. disassembly characterization of the cell: disassembling the button cell after the charge and discharge test in a glove box, taking out electrode plates, soaking the button cell in a dimethyl carbonate solution for 20-24 h, cleaning the button cell with ethanol for 3-6 times, drying the button cell, and then performing ex-situ X-ray diffraction (XRD), ex-situ Raman (Raman) and Transmission Electron Microscope (TEM) characterization, wherein the water oxygen values of the glove box are respectively [ O ] 2 ]<1ppm,[H 2 O]<1ppm。
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