CN108987729B - Lithium-sulfur battery positive electrode material, preparation method thereof and lithium-sulfur battery - Google Patents

Lithium-sulfur battery positive electrode material, preparation method thereof and lithium-sulfur battery Download PDF

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CN108987729B
CN108987729B CN201810996798.8A CN201810996798A CN108987729B CN 108987729 B CN108987729 B CN 108987729B CN 201810996798 A CN201810996798 A CN 201810996798A CN 108987729 B CN108987729 B CN 108987729B
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lithium
sulfur battery
positive electrode
sulfur
cobalt
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CN108987729A (en
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付继江
秦萍
高标
张旭明
霍开富
黄超
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Wuhan University of Science and Engineering WUSE
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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
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • 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
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
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    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
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    • H—ELECTRICITY
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    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/626—Metals
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery. The lithium-sulfur battery positive electrode material comprises a plurality of vanadium oxide nanosheets, a plurality of cobalt particles dispersed on each vanadium oxide nanosheet, carbon nanotubes grown on the surfaces of the cobalt particles, and elemental sulfur dispersed in the carbon nanotubes and simultaneously dispersed in a network formed by the carbon nanotubes. The lithium-sulfur battery cathode material provided by the invention takes the metallic cobalt simple substance and the transition metal oxide as templates to grow the carbon nano tube for carrying sulfur, so that the problem of volume expansion in the charging and discharging process is effectively relieved, and the metallic cobalt simple substance and the carbon nano tube are good conductive materials, so that the defect of sulfur insulativity is overcome, and the rate capability and the cycling stability of the obtained lithium-sulfur battery are greatly improved. And the preparation method has the advantages of simple process, convenient operation, environmental protection, contribution to large-scale production and practicability.

Description

Lithium-sulfur battery positive electrode material, preparation method thereof and lithium-sulfur battery
Technical Field
The invention belongs to the field of lithium-sulfur battery positive electrode materials, and particularly relates to a lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery.
Background
With the development of modern industry and the popularization of automobiles, fossil energy is gradually reduced, environmental problems are serious, and the situation is not optimistic. There is an urgent need to research clean, renewable energy sources to replace the existing non-renewable fossil energy sources, and at the same time, the solution of the energy storage problem is on the way. At present, lithium ion batteries are widely researched and applied, and have the advantages of relatively high power density and energy density, long cycle life, environmental friendliness and the like, so that the lithium ion batteries are widely applied to various mobile power supplies, large-scale energy storage equipment and new energy electric vehicles. However, the capacity of the currently researched lithium ion anode and cathode materials almost reaches the theoretical capacity, and it is difficult to meet the increasing energy storage requirement. Therefore, research into electrode materials having higher energy density is urgently needed to promote further development of society. At this time, the lithium-sulfur battery gradually climbs the stage of energy storage with its high specific energy and theoretical specific capacity of the material.
The lithium sulfur battery is a lithium battery which takes sulfur as a battery anode material and metal lithium as a cathode material, wherein the storage capacity of elemental sulfur on the earth is quite rich, so that the lithium sulfur battery has the advantage of low price, and the sulfur element is pollution-free to the environment and belongs to a clean energy source material2S2And L i2S is an insulator, so that the rate performance of the battery is poor; (2) an intermediate polysulfide of the lithium sulfur battery is dissolved in an electrolyte to reduce ionic conductivity, and the polysulfide moves between a positive electrode and a negative electrode to lose active materials, thereby reducing cycle stability; (3) in the process of charging and discharging, the volume of sulfur is increased, the battery is easily damaged, and potential safety hazards are brought.
In order to solve the existing problems of the lithium-sulfur battery, the anode material needs to be modified. Most of the techniques currently studied are mainly to compound sulfur with a single conductive base material or metal oxide material to improve performance. However, the above methods have a limited effect of improving the conductivity of the material and inhibiting the shuttling effect of polysulfides, and also have a limited ability of improving both the rate capability and the cycle performance of lithium-sulfur batteries.
Disclosure of Invention
Aiming at the technical problems in the prior art, the lithium-sulfur battery positive electrode material, the preparation method thereof and the lithium-sulfur battery are provided. The lithium-sulfur battery positive electrode material can provide high conductivity, catalytic performance and a shuttle effect of polysulfide through chemical inhibition, so that the rate capability and the cycle performance of the lithium-sulfur battery are improved.
In order to solve the technical problems, the invention adopts the technical scheme that:
the lithium-sulfur battery positive electrode material comprises a plurality of vanadium oxide nanosheets, a plurality of cobalt particles dispersed on each vanadium oxide nanosheet, carbon nanotubes grown on the surfaces of the cobalt particles, and elemental sulfur dispersed in the carbon nanotubes and simultaneously dispersed in a network formed by the carbon nanotubes.
In the above scheme, the vanadium oxide nanosheet is hexagonal.
In the scheme, the side length of the vanadium oxide nanosheet is 2-3 μm, and the thickness of the vanadium oxide nanosheet is 1-1.5 μm.
In the scheme, the diameters of the cobalt particles and the carbon nano tubes are both 10-30 nm.
The preparation method of the lithium-sulfur battery positive electrode material comprises the following steps:
(1) adding cyclohexamine, cobalt chloride hexahydrate and ammonium metavanadate precursor into water for mixing to obtain a mixture;
(2) putting the mixture prepared in the step (1) into a water bath, and stirring to obtain a cobalt vanadate powder material;
(3) and (3) putting the cobalt vanadate material obtained in the step (2) into a tube furnace, and performing heat treatment in a carbon monoxide atmosphere to perform phase separation and synchronously grow a carbon nano tube coating layer.
(4) And (4) mixing the composite material obtained in the step (3) with sublimed sulfur, and then carrying out vacuum low-temperature heat treatment to obtain the lithium-sulfur battery positive electrode material.
In the scheme, the mass ratio of the cyclohexenetetramine, the cobalt chloride hexahydrate and the ammonium metavanadate in the step (1) is 1: 4-5: 12-13.
In the scheme, the temperature of the water bath kettle in the step (2) is 80 ℃, and the heat preservation time is 4 hours.
In the scheme, the heat treatment temperature in the step (3) is 580-620 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 1-3 h.
In the scheme, the heat treatment temperature in the step (4) is 150-160 ℃, the heating rate is 1-10 ℃/min, and the heat preservation time is 10-13 h.
The lithium-sulfur battery comprises a positive electrode, a lithium negative electrode and electrolyte, wherein the positive electrode comprises an active substance, and the active substance is the lithium-sulfur battery positive electrode material or the lithium-sulfur battery positive electrode material prepared by the preparation method.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a lithium-sulfur battery positive electrode material, a preparation method thereof and a lithium-sulfur battery. The lithium-sulfur battery positive electrode material provided by the invention comprises a vanadium oxide sheet, a carbon nanotube network coated on the surface of the sheet, a metal cobalt simple substance and a sulfur simple substance filled in the network. The lithium-sulfur battery positive electrode material provided by the invention takes the metallic cobalt simple substance and the transition metal oxide as templates to grow the carbon nano tube for carrying sulfur, so that the problem of volume expansion in the charging and discharging process is effectively relieved, and the metallic cobalt simple substance and the carbon nano tube are good conductive materials, so that the defect of sulfur insulativity is overcome; secondly, the simple substance of the metallic cobalt has catalytic action and promotes the reaction; the vanadium oxide has a chemical adsorption effect on sulfur and polysulfide, and can effectively inhibit the shuttle effect of the polysulfide in the reaction process; in addition, the vanadium oxide sheet and the peripheral carbon nanotube network are added with a cobalt simple substance and matched with proper sulfur content, so that the composite structure can simultaneously promote electron transmission and can rapidly transmit lithium ions to low-conductivity sulfur, thereby improving the rate capability and the cycling stability of the lithium-sulfur battery. The experimental result shows that the discharge capacity of the lithium-sulfur battery prepared by the lithium-sulfur battery anode material can still maintain 501mAh/g after 200 cycles at 1C, the discharge capacity can maintain 451mAh/g after 300 cycles, and the coulombic efficiency can still maintain about 100%; under 5C high rate circulation, the discharge capacity can still maintain 532mAh/g, and when the discharge capacity returns to 1C again, the discharge capacity can still maintain 679 mAh/g.
Drawings
Fig. 1 is a schematic structural view of a positive electrode material for a lithium sulfur battery prepared in example 1 of the present invention;
FIG. 2 is a scanning electron microscope image of a carbon nanotube material grown by a metal simple substance and a vanadium oxide nanosheet prepared in example 1 of the present invention;
fig. 3 is a graph showing the adsorption effect of the polysulfide adsorbed by the carbon nanotube material grown from the elemental metal and the vanadium oxide nanosheet prepared in example 1 of the present invention;
FIG. 4 is a charge-discharge curve of a lithium-sulfur battery prepared in example 1 of the present invention;
FIG. 5 is a graph showing rate performance of a lithium sulfur battery prepared in example 1 of the present invention;
fig. 6 is a graph showing cycle performance of a lithium sulfur battery prepared in example 1 of the present invention.
Detailed Description
So that those skilled in the art can better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, the positive electrode material for a lithium-sulfur battery provided by the present invention includes a plurality of vanadium oxide nanosheets, a plurality of cobalt particles dispersed on each vanadium oxide nanosheet, carbon nanotubes grown on the surfaces of the cobalt particles, and elemental sulfur dispersed in the carbon nanotubes and simultaneously dispersed in a network formed by the carbon nanotubes.
In the invention, the vanadium oxide nanosheet is hexagonal, the side length of the vanadium oxide nanosheet is 2-4 microns, and the thickness of the vanadium oxide nanosheet is 1-1.5 microns. The content of the vanadium oxide flakes is not particularly limited in the present invention. In the present invention, the vanadium oxide flakes have a stable shape. In the invention, the vanadium oxide sheet has chemical adsorption on sulfur and polysulfide, and can effectively inhibit shuttle effect of polysulfide.
The lithium-sulfur battery positive electrode material also comprises nanometer cobalt particles dispersed on the vanadium nitride sheet. In the present invention, the particle size of the nano cobalt particles is preferably 10 to 30 nm. The distribution density of the cobalt nanoparticles on the outer surface of the vanadium oxide sheet is not particularly limited, and the cobalt nanoparticles are uniformly distributed according to the content of vanadium oxide and cobalt nanoparticles. In the invention, the metal simple substance nano cobalt particles have high conductivity, and ensure high utilization rate and excellent rate capability of sulfur. In the invention, the metal simple substance nano cobalt particles have a catalytic action on the charge-discharge reaction of the battery, and promote the smooth proceeding of the reaction.
The lithium-sulfur battery positive electrode material provided by the invention also comprises a carbon nano tube network coated on the outer side of the vanadium oxide. In the invention, the carbon nanotube network provides a larger storage space for elemental sulfur, improves the loading capacity of the elemental sulfur and can relieve the volume change of the sulfur in the charging and discharging processes. In the invention, the diameter of the carbon nano tube is 10-30 nm. In the present invention, the carbon nanotube has a length of 1 to 3 μm. In the invention, the carbon nano tube has excellent conductivity, and compensates the insulativity of elemental sulfur and reaction products of lithium sulfide or dilithium sulfide.
The lithium-sulfur battery positive electrode material provided by the invention comprises a sulfur simple substance filled in the carbon nano tube network and in the carbon nano tube. The filling degree of the elemental sulfur in the carbon nanotube network is not particularly limited, and can be adjusted according to the content of the elemental sulfur. In the invention, the sulfur simple substance with specific content is used as an active substance of the anode material, and under the combined action of the flaky vanadium oxide, the metal simple substance nano cobalt particles and the carbon nano tube network, the composite material can ensure the rapid transmission and movement of electrons and ions, thereby achieving the purpose of improving the cycle performance and the rate capability of the lithium-sulfur battery.
The invention provides a preparation method of the lithium-sulfur battery positive electrode material, which comprises the following steps:
1) adding the cyclohexamethylenetetramine, cobalt chloride hexahydrate and ammonium metavanadate precursor into pure water, and mixing to obtain a mixture;
(2) putting the mixture prepared in the step (1) into a water bath, and stirring to obtain a cobalt vanadate powder material;
(3) and (3) putting the cobalt vanadate material obtained in the step (2) into a tube furnace, and performing heat treatment in a carbon monoxide atmosphere to perform phase separation and synchronously grow a carbon nano tube coating layer.
(4) And (4) mixing the composite material obtained in the step (3) with sublimed sulfur, and then carrying out vacuum low-temperature heat treatment to obtain the lithium-sulfur battery positive electrode material.
The preparation principle of the lithium-sulfur battery anode material is that a precursor is stirred in a water bath to synthesize cobalt vanadate, the cobalt vanadate is treated in a carbon monoxide atmosphere to separate vanadium oxide and metal cobalt, carbon monoxide provides a carbon source under the catalytic action of the metal cobalt, carbon nanotubes grow on the surface of the metal cobalt, and finally, a sulfur simple substance is filled into a carbon nanotube network through heat treatment to obtain the lithium-sulfur battery anode material.
According to the invention, the cyclohexamethylenetetramine, cobalt chloride hexahydrate and ammonium metavanadate precursors are added into pure water and mixed to obtain a mixture. In the invention, the mass ratio of the hexamethylene tetramine, the cobalt chloride hexahydrate and the ammonium metavanadate is 1: 4-5: 12-13. In the water bath reaction, the temperature is set to 80 ℃, and after stirring for 4 hours, a cobalt vanadate product is obtained. And then, in a carbon monoxide atmosphere, treating the carbon-doped lithium-sulfur battery anode material at 580-620 ℃ for 1-3h, setting the heating rate to be 5-10 ℃/min to obtain a carbon nanotube network on the surface of the metal-oxide, and steaming the sulfur at 150-160 ℃ for 10-13h to obtain the carbon nanotube network serving as a sulfur-carrying medium and applied to a lithium-sulfur battery anode material. In the invention, the heat treatment enables elemental sulfur to be filled in the carbon nanotube network, and the volume change of sulfur in the charging and discharging process is limited and relieved.
The operation of mixing the three precursors in the present invention is not particularly limited, and a water bath method familiar to those skilled in the art may be used. In the invention, the water bath reaction temperature of the mixture of the hexamethylene tetramine, the cobalt chloride hexahydrate and the ammonium metavanadate is preferably 80 ℃. In the invention, the water bath reaction of the mixture of the hexamethylene tetramine, the cobalt chloride hexahydrate and the ammonium metavanadate is preferably carried out under continuous stirring; the stirring is preferably magnetic stirring; the stirring speed is preferably 300-600r/min, and more preferably 400-500 r/min; the stirring time is preferably 3 to 6 hours, more preferably 4 to 5 hours.
The operation of the cobalt vanadate preparation is not particularly limited in the invention, and a water bath reaction technical scheme well known to those skilled in the art can be adopted. The preparation of the cobalt vanadate preferably comprises the following steps: mixing the cyclic hexamethylene tetramine, cobalt chloride hexahydrate, ammonium metavanadate and pure water to obtain a mixed solvent.
After the water bath reaction, the invention preferably carries out solid-liquid separation on the product of the water bath reaction, and then the solid obtained by separation is dried to obtain the cobalt vanadate material. The operation of the solid-liquid separation and drying is not particularly limited in the invention, and the technical scheme of the solid-liquid separation and drying which is well known to the skilled person in the art can be adopted. In the present invention, the solid-liquid separation is preferably suction filtration, and the number of times of suction filtration is preferably 2.
After obtaining the cobalt vanadate material, the invention carries out heat treatment on the cobalt vanadate material to obtain metallic simple substance cobalt particles and a flaky vanadium oxide coated carbon nanotube network. In the present invention, the heat treatment temperature is preferably 580 to 620 ℃, preferably 590 to 610 ℃; the heat treatment temperature is 1-3h, preferably 2.5h-1.5 h. In the present invention, the heat treatment is preferably performed under a carbon monoxide atmosphere. The heating rate of the heat treatment is preferably 5-10 ℃/min.
After the flaky vanadium oxide is obtained and distributed with metal simple substance cobalt particles and the material with the periphery coated with the carbon nano tube network, the composite material is mixed with the simple substance sulfur and then is subjected to heat treatment, and the lithium-sulfur battery anode material is obtained.
The operation of mixing the composite material with the elemental sulfur is not particularly specified in the invention, and the technical scheme of powder mixing, which is well known to those skilled in the art, can be adopted. In the present invention, the above composite material is mixed with elemental sulfur, preferably by grinding and mixing, and the grinding and mixing time is preferably 0.5 to 3 hours, preferably 1 to 2 hours. The temperature for heat treatment after mixing is preferably 150 ℃ to 165 ℃, and most preferably 155 ℃ to 160 ℃; the heat treatment time is preferably 10 to 13 hours, most preferably 11 to 12 hours. In the invention, elemental sulfur is filled in the carbon nanotube network by the heat treatment, so that the volume change of sulfur in the charging and discharging process is limited and relieved.
The invention also provides a lithium-sulfur battery, which comprises a positive electrode, a lithium negative electrode and electrolyte, wherein the positive electrode comprises an active substance, and the active substance is the positive electrode material of the lithium-sulfur battery in the technical scheme or the positive electrode material of the lithium-sulfur battery prepared by the preparation method in the technical scheme.
Several specific examples are described below.
Example 1
The embodiment provides a preparation method of the lithium-sulfur battery cathode material, which comprises the following steps:
(1) mixing the hexamethylene tetramine, cobalt chloride hexahydrate and ammonium metavanadate precursors according to a ratio of 1:5:12.5 to obtain a mixture;
(2) putting the container filled with the reactants into a water bath kettle at the temperature of 80 ℃, and stirring for 4 hours without stopping to obtain a cobalt vanadate material;
(3) carrying out suction filtration on the cobalt vanadate obtained by the reaction for 2 times, and removing the precursor which is not completely reacted;
(4) and (3) putting the finally obtained cobalt vanadate material into a tube furnace, carrying out heat treatment in the atmosphere of carbon monoxide, heating to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2 hours, carrying out phase separation and synchronous growth of a carbon nanotube network coating layer, and taking out the product after the product is cooled to room temperature along with the furnace.
(5) And mixing the composite material with sublimed sulfur, fully mixing, and carrying out low-temperature heat treatment at 155 ℃ for 12 hours to obtain the lithium-sulfur battery cathode material.
FIG. 1 is a flow chart of the preparation of example 1 of the present invention; as can be seen from the scanning electron microscope image in fig. 2 (including fig. 2A and fig. 2B), the final product prepared in this embodiment is a vanadium oxide sheet and a carbon nanotube network structure whose outer layer is catalytically grown by metallic simple substance cobalt. It is known that the obtained product has high conductivity, catalytic performance, adsorptivity and large sulfur-carrying gaps. FIG. 3 is a charge-discharge curve of the lithium-sulfur battery, FIG. 4 is a rate performance diagram of the lithium-sulfur battery, FIG. 5 is a cycle performance diagram of the lithium-sulfur battery, and under 1C, after 200 cycles, the discharge capacity can still maintain 501mAh/g, after 300 cycles, the discharge capacity can maintain 451mAh/g, and the coulombic efficiency can still maintain about 98%; under 5C high rate circulation, the discharge capacity can still maintain 532mAh/g, and when the discharge capacity returns to 1C again, the discharge capacity can still maintain 679 mAh/g.
Example 2
The embodiment provides a preparation method of the lithium-sulfur battery cathode material, which comprises the following steps:
(1) mixing the hexamethylene tetramine, cobalt chloride hexahydrate and ammonium metavanadate precursors according to a ratio of 1:5:12.5 to obtain a mixture;
(2) putting the container filled with the reactants into a water bath kettle at the temperature of 80 ℃, and stirring for 4 hours without stopping to obtain a cobalt vanadate material;
(3) carrying out suction filtration on the cobalt vanadate obtained by the reaction for 2 times, and removing the precursor which is not completely reacted;
(4) and (3) putting the finally obtained cobalt vanadate material into a tubular furnace, carrying out heat treatment in the atmosphere of carbon monoxide, heating to 580 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 3 hours, carrying out phase separation and synchronous growth of a carbon nanotube coating layer, and taking out the product after the product is cooled to room temperature along with the furnace.
(5) And mixing the composite material with sublimed sulfur, fully mixing, and performing low-temperature heat treatment at 160 ℃ to obtain the lithium-sulfur battery cathode material. Under 1C, after 200 times of circulation, the discharge capacity can still maintain 497mAh/g, after 300 times of circulation, the discharge capacity can maintain 445mAh/g, and the coulomb efficiency can still maintain more than 98%; under 5C high rate circulation, the discharge capacity can still maintain 526mAh/g, and when the discharge capacity returns to 1C again, the discharge capacity can still maintain 661 mAh/g.
Example 3
The embodiment provides a preparation method of the lithium-sulfur battery cathode material, which comprises the following steps:
(1) mixing the hexamethylene tetramine, cobalt chloride hexahydrate and ammonium metavanadate precursors according to a ratio of 1:5:12.5 to obtain a mixture;
(2) putting the container filled with the reactants into a water bath kettle at the temperature of 80 ℃, and stirring for 4 hours without stopping to obtain a cobalt vanadate material;
(3) carrying out suction filtration on the cobalt vanadate obtained by the reaction for 2 times, and removing the precursor which is not completely reacted;
(3) and (3) putting the finally obtained cobalt vanadate material into a tube furnace, carrying out heat treatment in the atmosphere of carbon monoxide, heating to 620 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 2 hours, carrying out phase separation and synchronous growth of a carbon nanotube coating layer, and taking out the product after the product is cooled to room temperature along with the furnace.
(4) And mixing the composite material with sublimed sulfur, fully mixing, and carrying out low-temperature heat treatment at 155 ℃ to obtain the lithium-sulfur battery cathode material. At 1C, after 200 times of circulation, the discharge capacity can still maintain 491mAh/g, after 300 times of circulation, the discharge capacity can maintain 442mAh/g, and the coulombic efficiency can still maintain more than 98 percent; the discharge capacity can still maintain 528mAh/g under 5C high rate circulation, and the discharge capacity can still maintain 670mAh/g when the temperature returns to 1C again.
The above embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and the scope of the present invention is defined by the claims. Various modifications and equivalents may be made by those skilled in the art within the spirit and scope of the present invention, and such modifications and equivalents should also be considered as falling within the scope of the present invention.

Claims (10)

1. The lithium-sulfur battery positive electrode material is characterized by comprising a plurality of vanadium oxide nanosheets, a plurality of cobalt particles dispersed on each vanadium oxide nanosheet, carbon nanotubes grown on the surfaces of the cobalt particles, and a sulfur simple substance dispersed in the carbon nanotubes and simultaneously dispersed in a network formed by the carbon nanotubes.
2. The lithium sulfur battery positive electrode material of claim 1, wherein the vanadium oxide nanoplates are hexagonal.
3. The positive electrode material for lithium-sulfur batteries according to claim 2, wherein the vanadium oxide nanosheets have a side length of 2-4 μm and a thickness of 1-1.5 μm.
4. The positive electrode material for a lithium-sulfur battery according to claim 1, wherein the cobalt particles and the carbon nanotubes each have a diameter of 10 to 30 nm.
5. The method of preparing a positive electrode material for a lithium-sulfur battery according to any one of claims 1 to 4, comprising the steps of:
(1) adding cyclohexamine, cobalt chloride hexahydrate and ammonium metavanadate precursor into water for mixing to obtain a mixture;
(2) putting the mixture prepared in the step (1) into a water bath, and stirring to obtain a cobalt vanadate powder material;
(3) putting the cobalt vanadate material obtained in the step (2) into a tube furnace, and performing heat treatment in the atmosphere of carbon monoxide to perform phase separation and synchronously grow a carbon nano tube coating layer;
(4) and (4) mixing the composite material obtained in the step (3) with sublimed sulfur, and then carrying out vacuum low-temperature heat treatment to obtain the lithium-sulfur battery positive electrode material.
6. The method according to claim 5, wherein the mass ratio of the cyclohexenetetramine, the cobalt chloride hexahydrate and the ammonium metavanadate in the step (1) is 1:4 to 5:12 to 13.
7. The method according to claim 5, wherein the water bath temperature in the step (2) is 80 ℃ and the holding time is 4 hours.
8. The preparation method of claim 5, wherein the heat treatment temperature in the step (3) is 580 ℃ -620 ℃, the heating rate is 5 ℃/min-10 ℃/min, and the holding time is 1-3 h.
9. The preparation method according to claim 5, wherein the heat treatment temperature in the step (4) is 150 ℃ to 165 ℃, the temperature rise rate is 1 ℃/min to 10 ℃/min, and the holding time is 10 to 13 hours.
10. A lithium-sulfur battery comprising a positive electrode, a lithium negative electrode and an electrolyte, wherein the positive electrode comprises an active material, and the active material is the lithium-sulfur battery positive electrode material according to any one of claims 1 to 4 or the lithium-sulfur battery positive electrode material prepared by the preparation method according to any one of claims 5 to 8.
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