CN117410479B - Lithium ion battery composite positive electrode material, preparation method thereof and assembled battery - Google Patents

Lithium ion battery composite positive electrode material, preparation method thereof and assembled battery Download PDF

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CN117410479B
CN117410479B CN202311705084.4A CN202311705084A CN117410479B CN 117410479 B CN117410479 B CN 117410479B CN 202311705084 A CN202311705084 A CN 202311705084A CN 117410479 B CN117410479 B CN 117410479B
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graphene oxide
positive electrode
electrode material
lithium ion
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CN117410479A (en
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桑玉
程建良
席永全
王志莹
陈文豪
徐孟洁
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Yongkang Shenweiye Technology Co ltd
Henan Xinquan Energy Technology Co ltd
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Henan Xinquan Energy Technology Co ltd
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    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/60Selection of substances as active materials, active masses, active liquids of organic compounds
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/62Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624Electric conductive fillers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M2004/026Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028Positive electrodes
    • YGENERAL 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
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10Energy storage using batteries

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Abstract

The application relates to the technical field of lithium ion batteries, and particularly discloses a lithium ion battery composite positive electrode material, a preparation method thereof and an assembled battery. A preparation method of a lithium ion battery composite positive electrode material comprises the following steps: preparing lamellar graphene oxide, mixing the graphene oxide with silica sol, performing hydrothermal reduction and heat treatment under nitrogen atmosphere, coating the graphene oxide thin layer on the surface of silicon dioxide, etching the silicon dioxide by hydrogen fluoride to form a porous three-dimensional hollow graphene oxide porous ball, inducing the growth of octafluoro-iron phthalocyanine by oxygen-containing functional groups on the surface of the hollow graphene oxide porous ball to obtain octafluoro-iron phthalocyanine@GO, grinding and mixing the octafluoro-iron phthalocyanine@GO with sulfur in a mass ratio of 1:3, performing melt diffusion for 30-40min in a vacuum environment at 160-170 ℃, and cooling to obtain the lithium ion battery composite anode material. The lithium ion battery composite positive electrode material prepared by the method has the advantages of outstanding conductivity, mechanical stability, high specific capacity, and excellent cycle stability and rate capability.

Description

Lithium ion battery composite positive electrode material, preparation method thereof and assembled battery
Technical Field
The application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery composite positive electrode material, a preparation method thereof and an assembled battery.
Background
Along with the continuous improvement of the advantages of high specific capacity, stable cycle characteristics, low self-discharge rate and the like of the rechargeable lithium ion battery, the rapid development of novel energy storage technology is promoted, and after 2000 years, the rechargeable lithium ion battery is more and more widely applied to the fields of civil traffic, military power supplies, electric energy storage and the like, so that the improvement of the quality energy density of the power battery is urgent. Currently, lithium secondary batteries generally include LiNiO 2 、LiMnO 2 And LiFeO 4 And the like as a positive electrode material. However, due to their low intrinsic specific energy of the cathode material and due to the limitations of intercalation mechanisms, they cannot achieve high energy densities, all of which have theoretical capacities below 300mAh/g. Therefore, development of a novel electrode material capable of satisfying high energy density of a battery is required.
Conversion type electrode materials such as sulfides are increasingly attracting attention by researchers because of their high theoretical specific capacities. The lithium-sulfur battery has the theoretical specific capacity of 1675mAh/g and the energy density of 2600Wh/kg, the positive active material sulfur content is rich in the nature, the material cost is low, and the lithium-sulfur battery is a secondary battery energy storage system with development prospect. However, commercial application of lithium sulfur batteries is greatly restricted due to the "shuttle effect" caused by dissolution of lithium polysulfide in the electrolyte, the low conductivity of sulfur and lithium sulfide, and the density difference of the two.
The adoption of the positive electrode sulfur carrier material with high conductivity, large specific surface area and excellent adsorptivity to the lithium polysulfide is an effective solution. The transition metal phthalocyanine complex has chemical polarity and shows strong interaction in the catalytic conversion process of LiPSs molecules, provides adsorption active sites for the LiPSs molecules and provides electrons to accelerate the oxidation-reduction process of the LiPSs molecules, so that the shuttle effect is effectively inhibited. However, most transition metal phthalocyanine complexes have the problems of low intrinsic conductivity, small specific surface area and the like. The graphene has the advantages of large specific surface area, excellent conductivity, good mechanical stability and the like, and shows good electrochemical performance when being used as a positive electrode sulfur carrier material of a lithium sulfur battery, but the nonpolar graphene mainly realizes the adsorption of lithium polysulfide through weaker physical action, so that the dissolution and diffusion of the graphene cannot be effectively avoided, and the battery shuttle effect cannot be fully relieved.
Disclosure of Invention
In order to further improve the conductivity and stability of an electrode of a lithium ion battery, the application provides a lithium ion battery composite positive electrode material, a preparation method thereof and an assembled battery.
In a first aspect, the present application provides a technical solution as follows:
the lithium ion battery composite positive electrode material comprises octafluoro iron phthalocyanine@GO, wherein the octafluoro iron phthalocyanine@GO is prepared by the following steps: s1, preparing graphene oxide: taking graphite, adding sulfuric acid and sulfate, vigorously stirring in an ice bath, slowly adding potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring for 8-10 hours at 50-60 ℃ after the addition is completed, adding ice water in the ice bath, adding 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, preparing hollow graphene oxide porous spheres: ultrasonically dispersing graphene oxide in deionized water, then dropwise adding silica sol, mixing, then adding concentrated hydrochloric acid and citric acid, mechanically stirring after ultrasonic dispersion, then reacting for 8-10h at 180-200 ℃ in an autoclave, then calcining for 1h in a nitrogen atmosphere at 1000-1200 ℃, finally etching with 15wt% of HF solution, and freeze-drying to obtain hollow graphene oxide porous spheres; s3, taking hollow graphene oxide porous spheres, performing ultrasonic dispersion in pure water to obtain graphene dispersion liquid, adding urea, 3, 6-difluorophthalic acid, ferrous sulfate heptahydrate and ammonium molybdate into the graphene dispersion liquid, stirring for 20-30min, transferring the solution into a reaction kettle, preserving heat for 4-6h at 160-180 ℃, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for more than three times, performing freeze drying, transferring the product into a tubular furnace, heating to 250-270 ℃ from room temperature at 5 ℃/min, preserving heat for 2-4h, and naturally cooling to room temperature to obtain octafluorophthalic iron@GO.
According to the technical scheme, the lamellar graphene oxide is prepared firstly, then the graphene oxide is mixed with silica sol, after hydrothermal reduction and heat treatment are carried out in nitrogen atmosphere, the partially reduced graphene oxide lamellar is well coated on the surface of silicon dioxide, then the silicon dioxide is etched through hydrogen fluoride to form a three-dimensional hollow graphene oxide porous sphere with a hierarchical porous structure, and then the growth of octafluoro-iron phthalocyanine is induced through oxygen-containing functional groups on the surface of the hollow graphene oxide porous sphere. The structure has outstanding conductivity and mechanical stability, and the charge transfer resistance and stability of the electrode are effectively improved, and the structure has high electrical specific capacity, excellent cycle stability and excellent rate capability.
Preferably, in the step S1, the mass volume ratio of graphite, sulfuric acid, sulfate, potassium permanganate, ice water and 30% hydrogen peroxide is as follows: (1.5-2 g): (180-200 mL): (20-24 mL): (8-10 g): (100-120 mL): (20-30 mL).
By adopting the technical scheme, the components are added properly in proportion, and the graphene is converted into lamellar graphene oxide.
Preferably, in the step S2, the mass volume ratio of graphene oxide, deionized water, silica sol, concentrated hydrochloric acid, citric acid and a solution of 15wt% of HF is (100-120 mg) (25-35 mL) (50-70 mL) (6-9 g) (0.05-0.1 g) (30-40 mL).
Through the technical scheme, when the components are added in proportion, after graphene oxide and silica sol are mixed, hydrothermal reduction and heat treatment are carried out under nitrogen atmosphere, a partially reduced graphene oxide thin layer is well coated on the surface of a silicon dioxide sphere, and the silicon dioxide is etched by hydrogen fluoride to form the three-dimensional hollow graphene oxide porous sphere with a hierarchical porous structure.
Preferably, the preparation method of the silica sol in S2 comprises the following steps: 100mL of absolute ethyl alcohol and 15mL of ultrapure water are mixed to prepare a uniform solution, 25mL of 28wt% ammonia water is added to the solution to ensure that the PH value of the solution is 9, after mechanical stirring for 10min, 6mL of tetraethyl orthosilicate is dropwise added to the solution under strong stirring, stirring is carried out for 2 hours, the centrifugation is carried out to obtain silicon dioxide, the silicon dioxide is washed 3 times by the absolute ethyl alcohol and water, then the heat treatment is carried out for 3 hours at 550 ℃, the obtained silicon dioxide becomes spherical, then 100mg of silicon dioxide is added to 50mL of deionized water, and then 20mg of polyvinylpyrrolidone is added to obtain silica sol after uniform dispersion.
By adopting the technical scheme, the spherical silicon dioxide is prepared firstly, then the dispersion liquid is prepared, and polyvinylpyrrolidone is added, so that the polyvinylpyrrolidone is favorable for uniformly dispersing the silicon dioxide, and is favorable for fully contacting with the graphene oxide thin layer after uniformly dispersing the silicon dioxide.
Preferably, the mass volume ratio of the hollow graphene oxide porous spheres in the S3 to the pure water to the urea to the 3, 6-difluorophthalic acid to the ferrous sulfate heptahydrate to the ammonium molybdate is: (0.8-1.2 g): (100-150 mL): (1.2-1.5 g): (1.4-1.6 g): (1-1.3 g): (0.15-0.2 g).
By adopting the technical scheme, the components are added properly in proportion, the oxygen-containing functional groups on the surface of the hollow graphene oxide porous sphere induce the iron octafluorophthalocyanine to grow uniformly, and finally the iron octafluorophthalocyanine@GO composite material with a large number of nano particles distributed uniformly on the surface is produced.
Preferably, the lithium ion battery composite positive electrode material is prepared by the following method: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur in a mass ratio of 1:3 for 1-2h, performing melt diffusion in a vacuum environment at 160-170 ℃ for 30-40min, and cooling to room temperature to obtain the lithium ion battery composite anode material.
By adopting the technical scheme, the obtained lithium ion battery composite anode material has high sulfur carrying capacity.
In a second aspect, the present application provides an assembled battery comprising the lithium ion battery composite positive electrode material described above.
In summary, the present application has the following beneficial effects:
1. according to the preparation method, lamellar graphene oxide is firstly prepared, then graphene oxide is mixed with silica sol, after hydrothermal reduction and heat treatment are carried out in nitrogen atmosphere, a partially reduced graphene oxide thin layer is well coated on the surface of silicon dioxide, then the silicon dioxide is etched through hydrogen fluoride to form a three-dimensional hollow graphene oxide porous ball with a hierarchical porous structure, and then the oxygen-containing functional group on the surface of the hollow graphene oxide porous ball induces the growth of octafluoro-iron phthalocyanine. The structure has outstanding conductivity and mechanical stability, and the charge transfer resistance and stability of the electrode are effectively improved, and the structure has high electrical specific capacity, excellent cycle stability and excellent rate capability.
2. In the application, silica sol with polyvinylpyrrolidone is preferably mixed with graphene oxide, the addition of polyvinylpyrrolidone is favorable for the more stable dispersion of silica in water, the surface potential of silica and graphene oxide is negative, an amide part in polyvinylpyrrolidone can be used as oxygen in silica and bridge oxide containing oxygen groups in graphene oxide, the interaction between silica nanospheres and graphene oxide nanoplatelets is promoted, the graphene oxide is more coated on the surface of the silica, and further, calcination is performed, nitrogen atoms in polyvinylpyrrolidone form doping, so that the mechanical property of the porous hollow graphene oxide porous spheres is improved, three-dimensional hollow graphene oxide porous spheres with a hierarchical porous structure are formed after etching, the charge transfer resistance and stability of electrodes are improved, the electrical specific capacity is high, and the circulation stability and the multiplying power performance are excellent.
3. The lithium ion battery composite positive electrode material prepared by the preparation method has excellent electrode conductivity, cycle performance, cycle stability and rate capability.
Drawings
Fig. 1: SEM images of hollow graphene oxide porous spheres and iron octafluorophthalocyanine @ GO prepared in example 2 of the present application.
Fig. 2: graphs of lithium ion battery composite positive electrode materials TG (thermal weight) of example 2 and comparative example 1 of the present application.
Fig. 3: cycling performance and coulombic efficiency graphs for example 2, comparative examples 1 and 2 of the present application.
Fig. 4: the rate performance graphs of example 2, comparative examples 1 and 2 of the present application.
Detailed Description
The present application is described in further detail below with reference to examples.
The raw materials of the examples and comparative examples herein are commercially available in general unless otherwise specified.
Examples
Example 1
The lithium ion battery composite positive electrode material comprises octafluoro iron phthalocyanine@GO, wherein the octafluoro iron phthalocyanine@GO is prepared by the following steps: s1, preparing graphene oxide: taking 1.5g of graphite, adding 180mL of sulfuric acid and 20mL of sulfate, vigorously stirring in an ice bath, slowly adding 8g of potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring at 50 ℃ for 8 hours after the addition is finished, adding 100mL of ice water in the ice bath, adding 20mL of 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, preparing hollow graphene oxide porous spheres: dispersing graphene oxide 100mg in 25mL of deionized water by ultrasonic, dropwise adding 50mL of silica sol, mixing, adding 6g of concentrated hydrochloric acid and 0.05g of citric acid, mechanically stirring after ultrasonic dispersion, reacting for 8-10h at 180 ℃ in an autoclave, calcining for 1h at 1000 ℃ in nitrogen atmosphere, and finally etching with 30mL of 15wt% HF solution, and freeze-drying to obtain hollow graphene oxide porous spheres; s3, taking 0.8g of hollow graphene oxide porous spheres, ultrasonically dispersing the hollow graphene oxide porous spheres into 100mL of pure water to obtain graphene dispersion liquid, adding 1.2g of urea, 1.4g of 3, 6-difluorophthalic acid, 1g of ferrous sulfate heptahydrate and 0.15g of ammonium molybdate into the graphene dispersion liquid, stirring for 20min, transferring the solution into a reaction kettle, preserving heat for 4h at 160 ℃, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for three times, then freeze-drying, transferring the product into a tubular furnace, heating the product to 250 ℃ from room temperature at 5 ℃/min, preserving heat for 2h, and naturally cooling to room temperature to obtain the iron octafluorophthalate@GO.
The preparation method of the silica sol in the step S2 comprises the following steps: 100mL of absolute ethyl alcohol and 15mL of ultrapure water are mixed to prepare a uniform solution, 25mL of 28wt% ammonia water is added to the solution to ensure that the PH value of the solution is 9, after mechanical stirring for 10min, 6mL of tetraethyl orthosilicate is dropwise added to the solution under strong stirring, stirring is carried out for 2 hours, the centrifugation is carried out to obtain silicon dioxide, the silicon dioxide is washed 3 times by the absolute ethyl alcohol and water, then the heat treatment is carried out for 3 hours at 550 ℃, the obtained silicon dioxide becomes spherical, then 100mg of silicon dioxide is added to 50mL of deionized water, and then 20mg of polyvinylpyrrolidone is added to obtain silica sol after uniform dispersion.
The lithium ion battery composite positive electrode material is prepared by the following method: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur in a mass ratio of 1:3 for 1h, performing melt diffusion for 30min in a vacuum environment at 160 ℃, and cooling to room temperature to obtain the lithium ion battery composite anode material.
Example 2
The lithium ion battery composite positive electrode material comprises octafluoro iron phthalocyanine@GO, wherein the octafluoro iron phthalocyanine@GO is prepared by the following steps: s1, preparing graphene oxide: taking 1.8g of graphite, adding 190mL of sulfuric acid and 22mL of sulfate, vigorously stirring in an ice bath, slowly adding 9g of potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring for 9 hours at 55 ℃ after the addition is finished, adding 110mL of ice water in the ice bath, adding 25mL of 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, preparing hollow graphene oxide porous spheres: dispersing 110mg of graphene oxide in 30mL of deionized water by ultrasonic, dropwise adding 60mL of silica sol, mixing, adding 8g of concentrated hydrochloric acid and 0.08g of citric acid, mechanically stirring after ultrasonic dispersion, reacting for 9h at 190 ℃ in an autoclave, calcining for 1h in a nitrogen atmosphere at 1100 ℃, and finally etching with 35mL of 15wt% HF solution, and freeze-drying to obtain hollow graphene oxide porous spheres; s3, taking 1g of hollow graphene oxide porous spheres, ultrasonically dispersing the hollow graphene oxide porous spheres in 125mL of pure water to obtain graphene dispersion liquid, adding 1.4g of urea, 1.5g of 3, 6-difluorophthalic acid, 1.2g of ferrous sulfate heptahydrate and 0.18g of ammonium molybdate into the graphene dispersion liquid, stirring for 25min, transferring the solution into a reaction kettle, preserving heat for 5h at 170 ℃, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for three times, then freeze-drying, transferring the product into a tubular furnace, heating the product to 260 ℃ from room temperature at 5 ℃/min, preserving heat for 3h, and naturally cooling to room temperature to obtain the iron octafluorophthalate@GO.
The preparation method of the silica sol in the step S2 is the same as that of the embodiment 1.
The lithium ion battery composite positive electrode material is prepared by the following method: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur in a mass ratio of 1:3 for 1.5h, carrying out melt diffusion for 35min in a vacuum environment at 165 ℃, and cooling to room temperature to obtain the lithium ion battery composite anode material.
The microstructure of the hollow graphene oxide porous spheres and the iron octafluorophthalocyanine @ GO prepared in S2 in example 2 was observed by a scanning electron microscope as shown in fig. 1 (left hollow graphene oxide porous spheres, right iron octafluorophthalocyanine @ GO).
From fig. 1 (left), it can be seen that the prepared hollow graphene oxide porous spheres have multi-level spherical pores, and the octafluoro-iron phthalocyanine nanoparticles in octafluoro-iron phthalocyanine @ GO are successfully loaded on the hollow graphene oxide porous spheres, and the diameters are about 200nm and are uniformly distributed.
Characterization of specific surface area and pore size distribution for iron octafluoro phthalocyanine @ GO prepared in S3 in example 2: the specific surface area and pore size distribution were analyzed using a Michael BELSOP MINI X fully automatic specific surface area analyzer. The adsorption gas adopts nitrogen, the degassing temperature is 200 ℃, the testing temperature is 77K, the specific surface area is analyzed by adopting multi-layer adsorption BET, and the pore size distribution is analyzed by adopting NLDFT curve.
The test results are: the BET specific surface area of the prepared octafluoro iron phthalocyanine @ GO is 55.83m 2 Per gram, micropore specific surface area 15.43m 2 Per gram, external specific surface area 30.54m 2 /g, microPore volume of 6×10 3 cc/g, mesoporous volume 10×10 3 cc/g, total pore volume 17X 10 3 cc/g. Is beneficial to improving the sulfur loading capacity and the energy density of the battery.
Example 3
The lithium ion battery composite positive electrode material comprises octafluoro iron phthalocyanine@GO, wherein the octafluoro iron phthalocyanine@GO is prepared by the following steps: s1, preparing graphene oxide: taking 2g of graphite, adding 200mL of sulfuric acid and 24mL of sulfate, vigorously stirring in an ice bath, slowly adding 10g of potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring for 10 hours at 60 ℃ after the addition is completed, adding 120mL of ice water in the ice bath, adding 30mL of 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, separating, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, preparing hollow graphene oxide porous spheres: dispersing 120mg of graphene oxide in 35mL of deionized water by ultrasonic, dropwise adding 70mL of silica sol, mixing, adding 9g of concentrated hydrochloric acid and 0.1g of citric acid, mechanically stirring after ultrasonic dispersion, reacting for 10 hours at 200 ℃ in an autoclave, calcining for 1 hour in a nitrogen atmosphere at 1200 ℃, and finally etching with 40mL of 15wt% HF solution, and freeze-drying to obtain hollow graphene oxide porous spheres; s3, taking 1.2g of hollow graphene oxide porous spheres, ultrasonically dispersing the hollow graphene oxide porous spheres into 150mL of pure water to obtain graphene dispersion liquid, adding 1.5g of urea, 1.6g of 3, 6-difluorophthalic acid, 1.3g of ferrous sulfate heptahydrate and 0.2g of ammonium molybdate into the graphene dispersion liquid, stirring for 30min, transferring the solution into a reaction kettle, preserving heat for 6h at 180 ℃, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for three times, then freeze-drying, transferring the product into a tubular furnace, raising the temperature from the room temperature to 270 ℃ at 5 ℃/min, preserving heat for 4h, and naturally cooling to the room temperature to obtain the octafluoro iron phthalocyanine@GO.
The preparation method of the silica sol in the step S2 is the same as that of the embodiment 1.3, 6-difluorophthalic acid
The lithium ion battery composite positive electrode material is prepared by the following method: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur for 2 hours according to the mass ratio of 1:3, carrying out melt diffusion in a vacuum environment at 170 ℃ for 40 minutes, and cooling to room temperature to obtain the lithium ion battery composite anode material.
Comparative example
Comparative example 1
A lithium ion battery composite positive electrode material comprises octafluoro iron phthalocyanine @ GO 1 The octafluoro iron phthalocyanine @ GO 1 The preparation method of (2) is as follows: s1, preparing graphene oxide: taking 1.8g of graphite, adding 190mL of sulfuric acid and 22mL of sulfate, vigorously stirring in an ice bath, slowly adding 9g of potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring for 9 hours at 55 ℃ after the addition is finished, adding 110mL of ice water in the ice bath, adding 25mL of 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, taking 1g of graphene oxide, ultrasonically dispersing the graphene oxide into 125mL of pure water to obtain graphene dispersion liquid, adding 1.4g of urea, 1.5g of 3, 6-difluorophthalic acid, 1.2g of ferrous sulfate heptahydrate and 0.18g of ammonium molybdate into the graphene dispersion liquid, stirring for 25min, transferring the solution into a reaction kettle, preserving heat at 170 ℃ for 5h, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for three times, then freeze-drying, transferring the product into a tubular furnace, raising the temperature from room temperature to 260 ℃ at 5 ℃/min, preserving heat for 3h, and naturally cooling to room temperature to obtain the iron octafluorophthalate @ GO 1
The lithium ion battery composite positive electrode material is prepared by the following method: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur in a mass ratio of 1:3 for 1-2h, performing melt diffusion in a vacuum environment at 160-170 ℃ for 30-40min, and cooling to room temperature to obtain the lithium ion battery composite anode material.
Comparative example 2
The same as in example 2, except that "3, 6-difluorophthalic acid" was replaced with an equimolar amount of "tetrafluorophthalic acid".
The lithium ion battery composite positive electrode materials obtained in examples 1 to 3 and comparative examples 1 to 2 were prepared into positive electrode sheets and assembled into batteries by the following method:
preparation of a positive plate: compounding lithium ion battery with positive electrode material, conductive carbon black and polymerThe vinylidene fluoride is mixed according to the mass ratio of 6:3:1 to obtain positive electrode slurry, the slurry is coated on aluminum foil, dried and cut into wafers with the diameter of 12mm to be used as positive electrode plates of the battery, and when the specific capacity is calculated, the mass of active substances is based on the mass of sulfur in the positive electrode plates, and a specific calculation formula is as follows: m active material=0.7×sulfur loading× (mass of M positive plate-positive plate substrate aluminum foil), wherein sulfur loading is based on TG test results, and the surface loading of active material sulfur is ensured to be 2.2mg/cm by controlling slurry coating thickness 2
And (3) battery assembly: celgard 2400 is used as a diaphragm, a lithium sheet is used as a negative electrode, and lithium bis (fluorosulfonyl) imide and lithium nitrate are dissolved in a solvent of 1, 3-dioxolane and ethylene glycol dimethyl ether (volume ratio is 1:1) to obtain a required electrolyte (in the prepared electrolyte, 1.2mol/L of lithium bis (fluorosulfonyl) imide and 1.2wt% of lithium nitrate are obtained by mass fraction). The button cell was assembled in a glove box using a CR2032 type battery case with a battery liquid to mass ratio (E/S) of 10. Mu.L/mg.
Performance test
Thermogravimetric analysis was performed on the lithium ion battery composite cathode materials prepared in example 2 and comparative example 1: the sulfur content in the lithium ion battery composite anode material is tested and analyzed by using a Beijing instrument technology ZCT-B comprehensive thermal analyzer, the test atmosphere is nitrogen, the test temperature is 0-600 ℃, and the heating rate is 10 ℃/min; the test results are shown in FIG. 2 (thick line in FIG. 2 is example 2, thin line is comparative example 1).
As can be seen from fig. 2, the sulfur loadings of the lithium ion battery composite cathode materials prepared in example 2 and comparative example 1 were 68.73 and 52.14%, respectively. This is probably due to the high specific surface area and pore volume of the iron octafluoro phthalocyanine @ GO described in example 2, which is more advantageous for achieving higher sulfur loading, and thus the energy density of the battery can be improved.
Constant current charge and discharge and multiplying power performance characterization: the batteries prepared in examples 1-3 and comparative examples 1-3 were subjected to constant current charge and discharge test and rate performance test using a LAND series battery test system, with a test voltage range of 0.01 to 3.5V; the cycle performance and coulombic efficiency test results at 0.2C current density are shown in fig. 3; the results of the rate performance test for recovery to 0.1C after 5 cycles at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C are shown in fig. 4.
As can be seen from fig. 3, the battery assembled by the lithium ion battery composite positive electrode material described in example 2 has a specific capacity of 1379.8mAh/g for the first time, a specific capacity of 1078.2mAh/g after 200 cycles, a capacity retention rate of 78.1%, an attenuation rate of 0.11% per cycle, and a coulomb efficiency of over 0.99% all the time. The battery assembled by the lithium ion battery composite positive electrode material of comparative example 1 has a first discharge specific capacity of 1138.2mAh/g, a discharge specific capacity after 200 circles is attenuated to 626.3mAh/g, a capacity retention rate is 53.6%, and an attenuation rate of each circle is 0.23%; the battery assembled by the lithium ion battery composite positive electrode material described in comparative example 2 has a first discharge specific capacity of 1491.7mAh/g, a discharge specific capacity after 200 circles is attenuated to 932.5mAh/g, a capacity retention rate is 62.5%, and an attenuation rate per circle is 0.18%, but the initial stage of coulomb efficiency is only about 95%. Therefore, the lithium ion battery composite positive electrode material prepared in the embodiment 2 of the application has ideal cycle performance and cycle stability.
As can be seen from fig. 4, the specific capacity of the battery assembled from the lithium ion battery composite cathode material of example 2 at each rate is higher than that of the battery assembled from the lithium ion battery composite cathode material of comparative example 2, and the rate performance is better; the battery assembled from the lithium ion battery composite cathode material of example 2 has higher initial discharge specific capacity at each current density than the battery assembled from the lithium ion battery composite cathode material of comparative example 1, and the system has similar discharge specific capacity at 0.1C rate as the battery of comparative example 1, but the discharge specific capacity difference between the two is gradually increased with the increase of the current density, and the rate performance of example 2 is better.
This is probably because the lithium ion battery composite positive electrode material in example 2 has a significantly increased specific surface area compared with that in comparative example 1 due to the large specific surface area of the hollow graphene oxide porous spheres, but in the electrochemical process, the adsorption and conversion of lithium polysulfide are mainly completed by iron octafluorophthalate, the adsorption of graphene to lithium polysulfide is limited, the utilization ratio of graphene to sulfur is equivalent in the initial stage, and the initial stage shows a close first discharge specific capacity. However, with the increase of the cycle number and the discharge multiplying power, the octafluoro iron phthalocyanine @ GO is more stable in electrode structure and slower in capacity attenuation due to the excellent stability, the gap between the octafluoro iron phthalocyanine @ GO and the multiplying power performance of comparative example 1 is gradually increased, and the stability of the electrode is effectively improved due to the introduction of the graphene with excellent mechanical stability, so that the electrochemical performance of the electrode is more outstanding. In comparative example 2, too many fluorine atoms cause the fluorine phthalocyanine iron itself to have low electron conductivity due to too strong electronegativity, and the electrochemical performance is slightly inferior to that of example 2.
The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.

Claims (5)

1. The lithium sulfur battery composite positive electrode material is characterized by comprising octafluoro iron phthalocyanine@GO, wherein the octafluoro iron phthalocyanine@GO is prepared by the following steps: s1, preparing graphene oxide: taking graphite, adding sulfuric acid and sulfate, vigorously stirring in an ice bath, slowly adding potassium permanganate, ensuring that the temperature is lower than 15 ℃, stirring for 8-10 hours at 50-60 ℃ after the addition is completed, adding ice water in the ice bath, adding 30% hydrogen peroxide until the color of the solution turns bright yellow, centrifuging, taking a precipitate, washing the precipitate with 20% dilute hydrochloric acid and deionized water, and freeze-drying to obtain graphene oxide; s2, preparing hollow graphene oxide porous spheres: ultrasonically dispersing graphene oxide in deionized water, then dropwise adding silica sol, mixing, then adding concentrated hydrochloric acid and citric acid, mechanically stirring after ultrasonic dispersion, then reacting for 8-10h at 180-200 ℃ in an autoclave, then calcining for 1h in a nitrogen atmosphere at 1000-1200 ℃, finally etching with 15wt% of HF solution, and freeze-drying to obtain hollow graphene oxide porous spheres; s3, taking hollow graphene oxide porous spheres, performing ultrasonic dispersion in pure water to obtain graphene dispersion liquid, adding urea, 3, 6-difluorophthalic acid, ferrous sulfate heptahydrate and ammonium molybdate into the graphene dispersion liquid, stirring for 20-30min, transferring the solution into a reaction kettle, preserving heat for 4-6h at 160-180 ℃, naturally cooling to room temperature, alternately washing the product with deionized water and alcohol for more than three times, performing freeze drying, transferring the product into a tubular furnace, heating to 250-270 ℃ from room temperature at 5 ℃/min, preserving heat for 2-4h, and naturally cooling to room temperature to obtain octafluorophthalic iron@GO;
the preparation method of the silica sol in the step S2 comprises the following steps: mixing 100mL of absolute ethyl alcohol and 15mL of ultrapure water to prepare a uniform solution, then adding 25mL of 28wt% ammonia water into the solution to ensure that the PH value of the solution is 9, mechanically stirring for 10min, dropwise adding 6mL of tetraethyl orthosilicate into the solution under strong stirring, stirring for 2 hours, centrifuging to obtain silicon dioxide, washing 3 times with absolute ethyl alcohol and water, then performing heat treatment for 3 hours at 550 ℃ to obtain silicon dioxide, forming the silicon dioxide into a sphere, adding 100mg of silicon dioxide into 50mL of deionized water, adding 20mg of polyvinylpyrrolidone, and dispersing uniformly to obtain silica sol;
the lithium-sulfur battery composite positive electrode material is prepared by the following steps: grinding and mixing the octafluoro iron phthalocyanine@GO and sulfur in a mass ratio of 1:3 for 1-2h, performing melt diffusion for 30-40min in a vacuum environment at 160-170 ℃, and cooling to room temperature to obtain the lithium-sulfur battery composite anode material.
2. The lithium-sulfur battery composite positive electrode material according to claim 1, wherein the mass volume ratio of graphite, sulfuric acid, sulfate, potassium permanganate, ice water and 30% hydrogen peroxide in the S1 is: (1.5-2 g): (180-200 mL): (20-24 mL): (8-10 g): (100-120 mL): (20-30 mL).
3. The lithium sulfur battery composite positive electrode material according to claim 2, wherein the mass volume ratio of graphene oxide, deionized water, silica sol, concentrated hydrochloric acid, citric acid and 15wt% of HF solution in the S2 is (100-120 mg): (25-35 mL): (50-70 mL): (6-9 g): (0.05-0.1 g): (30-40 mL).
4. The lithium sulfur battery composite positive electrode material according to claim 1, wherein the mass volume ratio of the hollow graphene oxide porous spheres, pure water, urea, 3, 6-difluorophthalic acid, ferrous sulfate heptahydrate and ammonium molybdate in the S3 is as follows: (0.8-1.2 g): (100-150 mL): (1.2-1.5 g): (1.4-1.6 g): (1-1.3 g): (0.15-0.2 g).
5. A lithium-sulfur battery comprising the lithium-sulfur battery composite positive electrode material of claim 1.
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