CN110931782A - Preparation method and application of hollow sphere cobalt sulfide/graphene composite material - Google Patents
Preparation method and application of hollow sphere cobalt sulfide/graphene composite material Download PDFInfo
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Abstract
A preparation method and application of a hollow sphere cobalt sulfide/graphene composite material. According to the preparation method, firstly, glycerol and cobalt nitrate hexahydrate are adopted to prepare a cobalt-glycerol complex in a solid sphere shape, then a surface charge modifier is adopted to change the surface electrical property of the cobalt-glycerol complex, the cobalt-glycerol complex is mixed with graphene and attached to the surface of the graphene, finally thioamide is added, the cobalt-glycerol complex attached to the surface of the graphene undergoes a hydrothermal reaction, vulcanization is carried out while cobalt is diffused, a hollow sphere structure is formed in situ on the graphene, and the cobalt sulfide/graphene composite material in a hollow sphere shape is obtained. The composite material prepared by the method is used for assembling the battery, so that the battery has excellent cycle stability and rate capability.
Description
Technical Field
The invention relates to the field of composite materials, and particularly relates to a preparation method and application of a hollow sphere cobalt sulfide/graphene composite material.
Background
Lithium ion batteries have the advantages of high energy density, high power density, long cycle life and nontoxicity, making them the primary power source of choice for portable electronic devices and electric vehicles. However, the low theoretical specific capacity, low safety and poor rate performance of the graphite-based negative electrode materials commonly used in lithium ion batteries limit further application of the graphite negative electrode, and cannot meet the requirements of people on the lithium ion batteries.
Compared with the traditional graphite cathode, the metal sulfide has higher reversible specific capacity, higher energy density and excellent safety performance, and is an ideal material for the cathode material of the lithium ion battery. However, the application of metal sulfide as a negative electrode material is severely limited by the problems of poor intrinsic electronic conductivity, slow lithium ion migration rate, volume expansion in the lithium ion deintercalation process and the like. In order to enable the metal sulfide to better meet the requirements of new-generation energy batteries, at present, the practical application of the metal sulfide is promoted through structural hollowing and graphene coating.
The electrode material with the hollow structure can enlarge the contact interface between the electrode and the electrolyte, provide more contact sites, increase the specific capacity and reduce the material and charge transfer paths. In addition, the inner hollow structure can organize volume expansion to cause structure collapse and alleviate the pressure effect caused by the lithium ion deintercalation process. Although graphene with a two-dimensional nanostructure has high electrochemical performance, thermal stability and a large specific surface area, and can play a good role in enhancing the electrochemical performance of a battery electrode material, the application of intrinsic graphene in the electronic field is severely limited by its zero band gap characteristic.
CN108147472A discloses a preparation method of a hollow cobalt sulfide microsphere catalyst, which is characterized in that a cobalt source and a sulfur source are added into a reaction kettle to carry out hydrothermal reaction to obtain hollow microspheres. However, the spherical shape is micron-sized, the structure is easily damaged, the lithium ion diffusion distance is increased, the resistance effect is enlarged, and the method is not suitable for preparing good electrode materials.
CN103214041A discloses a preparation method of self-assembly cobalt sulfide electrode materials with various morphologies, which prepares electrode materials with different morphologies by carrying out hydrothermal reaction on a sulfur source, a cobalt source and a plurality of solvents. However, the electrode material prepared by the method still has poor conductivity and serious volume expansion effect, and is not suitable for lithium ion batteries.
CN108598427A discloses a method for improving charge-discharge cycle capacity of cobalt sulfide by coating reduced graphene oxide, the method is complex in process and multiple in flow, and the prepared cobalt sulfide is easy to agglomerate, so that the theoretical specific capacity cannot be fully exerted.
Disclosure of Invention
The invention aims to overcome the defects and provide a preparation method and application of a hollow sphere cobalt sulfide/graphene composite material. The preparation method provided by the invention is simple to operate and low in cost, and can successfully prepare the hollow cobalt sulfide/graphene composite material with excellent conductivity.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a preparation method of a hollow cobalt sulfide/graphene composite material comprises the following steps:
(1) adding cobalt nitrate hexahydrate and glycerol into isopropanol, and carrying out hydrothermal reaction to obtain a cobalt-glycerol complex;
(2) dispersing the cobalt-glycerol complex obtained in the step (1) in an alcohol solvent, adding a surface charge modifier, and carrying out charge modification under an ultrasonic condition to obtain a cobalt-glycerol complex with a negatively charged surface;
(3) uniformly dispersing graphene oxide in an alcohol solvent, adding the cobalt-glycerol complex with the negative surface obtained in the step (2), and performing ultrasonic dispersion to obtain a mixed solution;
(4) and (4) adding thioacetamide into the mixed solution obtained in the step (3), and carrying out hydrothermal reaction to obtain the hollow sphere cobalt sulfide/graphene composite material.
Preferably, in the step (1), the temperature of the hydrothermal reaction is 160-200 ℃, and the reaction time is 4-6 h. Preferably, in the step (1), the mass ratio of the cobalt nitrate hexahydrate to the glycerol is 1: 290-600, and the volume ratio of the glycerol to the isopropanol is 1-2: 5. Under the condition of the proportion, the solid sphere can be formed under a stable oil-water interface.
Preferably, in the step (2), the surface charge modifier is selected from one or more of 3-aminopropyltrimethoxysilane, vinyltriethoxysilane and vinyltrimethoxysilane.
Preferably, in the step (2), the volume ratio of the surface charge modifier to the alcohol solvent is 1: 10-15. Under the condition of the mass ratio, the surface charge of the cobalt-glycerol complex is fully modified to be negative, and the excessive surface charge can cause the introduction of impurities.
Preferably, in the step (2), the concentration of the cobalt-glycerol complex in the alcohol solvent is 1-2 mg/mL.
Preferably, in the step (3), the mass-to-volume ratio of the graphene oxide to the alcohol solvent is 0.5-1 mg/mL.
Preferably, in the step (3), the mass ratio of the cobalt-glycerol complex to the graphene oxide is 5: 1-2.
Preferably, in the step (3), the power of the ultrasonic dispersion is 100-600W, and the time is 2-4 h. Under the condition, the cobalt-glycerol complex solid spheres are completely adsorbed on the surface of the graphene oxide.
Preferably, in the step (4), the temperature of the hydrothermal reaction is 160-200 ℃, and the reaction time is 2-8 h. The hydrothermal reaction temperature and time ensure that the solid sphere is diffused and combined with the sulfur source to form a hollow sphere structure.
Preferably, in the step (4), the mass ratio of the thioacetamide to the cobalt-glycerol complex is 1-2: 1.
Preferably, in steps (2) and (3), the alcohol solvent is ethanol.
A preparation method of a hollow cobalt sulfide/graphene composite material specifically comprises the following steps:
(1) adding cobalt nitrate hexahydrate and glycerol into isopropanol, stirring, carrying out hydrothermal reaction, cooling after the reaction is completed, centrifugally washing, and drying to obtain a cobalt-glycerol complex;
(2) dispersing the cobalt-glycerol complex obtained in the step (1) in an alcohol solvent, adding a surface charge modifier, stirring, performing charge modification under an ultrasonic condition, centrifuging, and washing to obtain a cobalt-glycerol complex with a negatively charged surface;
(3) uniformly dispersing graphene oxide in an alcohol solvent by adopting ultrasound, adding the cobalt-glycerol complex with the negative surface obtained in the step (2), and performing ultrasonic dispersion to obtain a mixed solution;
(4) and (4) adding thioacetamide into the mixed solution obtained in the step (3), stirring, carrying out hydrothermal reaction, centrifuging, washing and drying to obtain the hollow sphere cobalt sulfide/graphene composite material.
Preferably, in the step (4), the stirring speed is 200-400 r/min, and the stirring time is 4-6 h. The sulfur source is fully contacted with the cobalt source attached to the graphene sheet layer under the stirring condition, so that a foundation is provided for the next complete vulcanization reaction.
A lithium battery positive electrode material comprises the hollow sphere cobalt sulfide/graphene composite material prepared by the method.
The invention has the beneficial effects that:
(1) according to the preparation method, firstly, glycerol and cobalt nitrate hexahydrate are adopted to prepare a cobalt-glycerol complex in a solid sphere shape, then a surface charge modifier is adopted to change the surface electrical property of the cobalt-glycerol complex, the cobalt-glycerol complex is mixed with graphene and attached to the surface of the graphene, finally thioamide is added, the cobalt-glycerol complex attached to the surface of the graphene undergoes a hydrothermal reaction, vulcanization is carried out while cobalt is diffused, a hollow sphere structure is formed in situ on the graphene, and the cobalt sulfide/graphene composite material in a hollow sphere shape is obtained;
(2) in the hollow sphere cobalt sulfide/graphene composite material prepared by the preparation method, the cobalt sulfide is in a hollow sphere structure, the average size is 300-400 nm, the hollow sphere structure can enlarge the contact interface of an electrode and electrolyte, provide more contact sites, increase the specific capacity and reduce the transfer paths of substances and charges; in addition, the inner hollow structure can organize the volume expansion to cause the structure to collapse and relieve the pressure effect caused by the lithium ion extraction process;
(3) in the hollow sphere cobalt sulfide/graphene composite material prepared by the preparation method, the cobalt sulfide is uniformly and stably distributed between graphene sheet layers and on the surface of the graphene sheet layers, and cobalt spheres attached to the graphene sheet layers form a hollow sphere structure in situ on graphene through a vulcanization process, so that the hollow sphere structure and a matrix form a structure-activity relationship, and the ionic and electronic conductivity of metal sulfide is improved.
(4) The cathode material prepared from the hollow sphere cobalt sulfide/graphene composite material is assembled into a lithium ion battery, and the lithium ion battery is under the voltage range of 0.01-3.0V and the multiplying power of 0.1C (1C =500mAh g)-1) The first discharge specific capacity can reach 759.8 mAh/g, and under the multiplying power of 0.2C, 0.5C, 1C, 2C and 5C, the first discharge specific capacities are 701.2 mAh/g, 640.9 mAh/g, 623.3 mAh/g, 591.7 mAh/g and 488.0 mAh/g respectively; under the high multiplying power of 10C and 15C, the first discharge specific capacity respectively reaches 371.2 mAh/g and 279.2 mAh/g; after the circulation is carried out for 90 circles under the multiplying power of 15C, the capacity retention rate is 94%, and the specific capacity is maintained to be 538.5 mAh/g; the lithium ion battery assembled by the hollow sphere cobalt sulfide/graphene composite material prepared by the invention has very high specific capacity, and excellent rate performance and cycling stability.
Drawings
Fig. 1 is an XRD chart of the hollow sphere cobalt sulfide/graphene composite material obtained in example 1 of the present invention;
FIG. 2 is SEM and TEM images of the hollow sphere cobalt sulfide/graphene composite material obtained in example 1 of the present invention at different magnification;
fig. 3 is a TEM image of the hollow sphere cobalt sulfide/graphene composite material obtained in example 1 of the present invention at different times;
fig. 4 is a TEM image of the hollow sphere cobalt sulfide/graphene composite material obtained in example 2 of the present invention at different times;
fig. 5 is a discharge rate performance curve diagram of a lithium ion battery assembled by the hollow sphere cobalt sulfide/graphene composite material obtained in example 1 of the present invention;
fig. 6 is a discharge cycle curve diagram of a lithium ion battery assembled by the hollow sphere cobalt sulfide/graphene composite material obtained in example 1 of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings. The graphene oxide used in the following examples was prepared by reference to "Hummers, W.S.; Offeman, R.E. Journal of the American chemical society 1958, 80, 1339-.
Example 1
(1) Adding 0.375mmol (0.1091g) of cobalt nitrate hexahydrate and 8mL of glycerol into 40mL of isopropanol, stirring, carrying out hydrothermal reaction for 6 hours at 180 ℃, carrying out centrifugal separation at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain a cobalt-glycerol complex;
(2) adding 2.5mL of 3-aminopropyltrimethoxysilane into 30mL of absolute ethanol solution containing 50mg of cobalt-glycerol complex, stirring for 12h at the speed of 300r/min, carrying out ultrasonic treatment for 4h at the speed of 400W, centrifuging at the speed of 6000rpm/min, and respectively and alternately washing precipitates for 5 times by using deionized water and absolute ethanol to obtain 30mL of ethanol solution containing the cobalt-glycerol complex;
(3) adding 15mg of graphene oxide into 20mL of absolute ethanol solution, performing 400W ultrasonic dispersion for 2h to obtain uniform and stable graphene oxide dispersion liquid, then adding 30mL of ethanol solution containing the cobalt-glycerol complex obtained in the step (2), stirring for 5h at a speed of 300r/min, and performing 400W ultrasonic treatment for 4h to obtain uniform and stable mixed solution;
(4) and (3) adding 50mg of thioacetamide into 50mL of mixed solution obtained in the step (4), stirring, carrying out hydrothermal reaction at 180 ℃ for 6h, centrifuging at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain the hollow sphere cobalt sulfide/graphene composite material.
Through detection, an XRD pattern of the hollow sphere cobalt sulfide/graphene composite material obtained in the present embodiment is shown in fig. 1, where the position of the characteristic peak on XRD is consistent with the position of the characteristic peak on the standard card, the formed cobalt sulfide is a pure phase, and the purity of the prepared cobalt sulfide is not affected by the introduction of graphene.
Through detection, an SEM image and a TEM image of the hollow sphere cobalt sulfide/graphene composite material obtained in the present embodiment are respectively shown in fig. 2 and fig. 3, and it can be known from observing fig. 2 and fig. 3 that the spherical size of the hollow sphere cobalt sulfide is relatively uniform, the average particle size is 200-300 nm, the hollow spheres are uniformly and uniformly distributed between graphene sheet layers and outside, and the defect of poor conductivity of the metal sulfide is overcome.
Assembling the battery: respectively weighing 0.8 g of the cobalt sulfide/graphene composite material of the hollow sphere obtained in the embodiment as a positive electrode material, adding 0.1 g of acetylene black (SP) as a conductive agent and 0.01 g of PVDF (HSV-900) as a binder, fully grinding, adding 1.5 mL of NMP for dispersing and mixing, uniformly mixing, pulling slurry on an aluminum foil with the thickness of 75 microns to prepare a positive electrode plate, taking lithium metal as a negative electrode and taking polypropylene as a diaphragm in an anaerobic glove box, and taking 1mol/L LiPF6A 2025 button cell is assembled by using a mixed solution of ethylene carbonate, dimethyl carbonate and dimethyl carbonate (volume ratio =1:1: 1) as an electrolyte; and testing the constant current charge and discharge performance of the assembled lithium ion battery under the voltage range of 0.01-3.0V.
As shown in fig. 5, at 0.1C magnification (1C =500mAh · g)-1) The first charge-discharge specific capacity of the assembled lithium ion battery reaches 759.8 mAh.g-1. Under the multiplying power of 0.2C, 0.5C, 1C, 2C, 5C and 10C, the first discharge specific capacity reaches 701.2, 640.9, 623.3, 591.7, 488.0 and 371.2 mAh.g respectively-1. Even under the high rate of 15C, the first discharge specific capacity is 279.2mAh g-1. Then the discharge rate is returned to 0.01C multiplying power, and the first discharge specific capacity is 747.0mAh g-1。
As shown in FIG. 6, under the 15C multiplying power, the first specific discharge capacity of the assembled lithium ion battery can still reach 525.6mAh g after 107 cycles-1. The lithium ion battery assembled by the prepared hollow sphere cobalt sulfide/graphene composite material has higher specific capacity and good performanceRate capability and cycle capability of (2).
From the above, the lithium ion battery assembled by the hollow sphere cobalt sulfide/graphene composite material obtained in the embodiment of the invention has high specific discharge capacity, good rate capability and cycle performance, and the introduction of the graphene effectively improves the conductivity of the hollow sphere cobalt sulfide active material.
Example 2
(1) Adding 0.375mmol (0.1091g) of cobalt nitrate hexahydrate and 16mL of glycerol into 40mL of isopropanol, stirring, carrying out a hydrothermal reaction at 180 ℃ for 4 hours, centrifuging at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain a cobalt-glycerol complex;
(2) adding 2.5mL of 3-aminopropyltrimethoxysilane into 30mL of absolute ethanol solution containing 30mg of cobalt-glycerol complex, stirring for 12h at the speed of 300r/min, carrying out ultrasonic treatment for 4h at the speed of 400W, centrifuging at the speed of 6000rpm/min, and respectively and alternately washing precipitates for 5 times by using deionized water and absolute ethanol to obtain 30mL of ethanol solution containing the cobalt-glycerol complex;
(3) adding 10mg of graphene oxide into 20mL of absolute ethanol solution, and performing 400W ultrasonic dispersion for 2h to obtain uniform and stable graphene oxide dispersion liquid; then adding 30mL of ethanol solution containing the cobalt-glycerol complex obtained in the step (2), stirring for 5h at 300r/min, and carrying out 400W ultrasonic treatment for 4h to obtain uniform and stable mixed solution;
(4) and (3) adding 50mg of thioacetamide into 50mL of mixed solution obtained in the step (4), stirring, carrying out hydrothermal reaction at 160 ℃ for 6h, centrifuging at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain the hollow sphere cobalt sulfide/graphene composite material.
Through detection, the position of the characteristic peak of the hollow sphere cobalt sulfide/graphene composite material of the lithium ion battery cathode material obtained in the embodiment of the invention on XRD is consistent with the characteristic peak on a standard card, and the formed composite material cobalt sulfide/graphene is a pure phase, which indicates that the introduction of the graphene does not influence the purity of the prepared cobalt sulfide.
Through detection, a TEM of the hollow sphere cobalt sulfide/graphene composite material obtained in the embodiment is shown in fig. 4, and it can be seen from observing fig. 4 that the average particle size of the hollow sphere cobalt sulfide is 400-500 nm, and cobalt sulfide is uniformly distributed on the surface of graphene and between graphene layers. As is clear from the data of comparative example 1, in step (4), the longer the hydrothermal reaction time, the more significant the diffusion of cobalt, and the cobalt sulfide shell was formed by binding with sulfur in the solution, thereby forming a hollow spherical structure having a larger particle size.
Assembling the battery: the same as example 1; and carrying out constant-current charge and discharge performance test on the assembled lithium ion battery under the voltage range of 0.01-3.0V.
At 0.1C magnification (1C =500mAh · g)-1) The first charge-discharge specific capacity of the assembled lithium ion battery reaches 689.8 mAh.g-1. Under the multiplying power of 0.2C, 0.5C, 1C, 2C, 5C and 10C, the first discharge specific capacity reaches 688.7, 633.4, 598.8, 532.5, 487.6 and 402.3 mAh.g-1. Even under the high multiplying power of 15C, the first discharge specific capacity is 300.6 mAh.g-1. Then the discharge rate is returned to 0.01C multiplying power, and the first discharge specific capacity is 678.6mAh g-1。
Under the multiplying power of 15C, the first discharge specific capacity of the assembled lithium ion battery can still reach 498.8 mAh.g after 98 cycles-1. The lithium ion battery assembled by the prepared hollow sphere cobalt sulfide/graphene composite material has higher specific capacity and good rate performance and cycle performance.
From the above, the lithium ion battery assembled by the lithium ion battery cathode material hollow sphere cobalt sulfide/graphene composite material obtained in the embodiment of the invention has higher specific discharge capacity, good rate capability and cycle performance, and the introduction of the graphene effectively improves the conductivity of the hollow sphere cobalt sulfide active material.
Comparative example 1
(1) Adding 0.375mmol (0.1091g) of cobalt nitrate hexahydrate and 8mL of glycerol into 40mL of isopropanol, stirring, carrying out a hydrothermal reaction at 180 ℃ for 6 hours, centrifuging at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain a cobalt-glycerol complex;
(2) adding 50mg of cobalt-glycerol complex into 30mL of absolute ethyl alcohol solution, stirring for 12h at 300r/min, carrying out 400W ultrasonic treatment for 4h, centrifuging at 6000rpm/min, and respectively and alternately washing precipitates for 5 times by using deionized water and absolute ethyl alcohol;
(3) and (3) adding 50mg of thioacetamide into 30mL of solution obtained in the step (2), stirring, carrying out hydrothermal reaction at 180 ℃ for 6h, centrifuging at 6000rpm/min, respectively and alternately washing precipitates for 6 times by using deionized water and absolute ethyl alcohol, and drying at 70 ℃ to obtain the hollow sphere cobalt sulfide material.
Through detection, the position of the characteristic peak of the hollow sphere cobalt sulfide of the lithium ion battery cathode material obtained in the embodiment of the invention on XRD is consistent with the position of the characteristic peak on a standard card, and the formed cobalt sulfide is pure phase.
Through detection, the spherical size of the cobalt sulfide of the hollow ball of the lithium ion battery cathode material obtained in the embodiment of the invention is 300-400 nm, and the spherical cobalt sulfide is uniformly distributed.
Assembling the battery: assembling the hollow sphere cobalt sulfide/graphene composite material obtained in the embodiment into a battery, and assembling according to the steps in embodiment 1; and testing the constant current charge and discharge performance of the assembled lithium ion battery under the voltage range of 0.01-3V.
At 0.1C magnification (1C =500mAh · g)-1) The first charge-discharge specific capacity of the assembled lithium ion battery reaches 995.2 mAh.g-1. The specific first discharge capacity reaches 434.1, 325.6, 278.8, 122.0, 39.6 and 24.3 mAh.g at the multiplying power of 0.2C, 0.5C, 1C, 2C, 5C and 10C respectively-1. Under the high rate of 15C, the first discharge specific capacity is 18.3 mAh.g-1. Then the discharge rate is returned to 0.01C multiplying power, and the first discharge specific capacity is 54.7mAh g-1。
Through detection, under the multiplying power of 15C, the first discharge specific capacity of the assembled lithium ion battery is only 58.4 mAh.g after 100 cycles-1。
From the above, the lithium ion battery cathode material obtained by the comparative example has poor structural stability, and has poor rate capability and cycle performance.
In summary, the lithium ion battery assembled by the hollow sphere cobalt sulfide/graphene composite material obtained in the embodiments 1-2 of the present invention has higher specific discharge capacity and cycle performance and shows excellent electrochemical performance at a large rate compared to the battery assembled by the cobalt sulfide pure phase material obtained in the comparative example. It can be seen that the lithium ion battery made of the hollow sphere cobalt sulfide/graphene composite material obtained in embodiments 1-2 of the present invention is more stable in a long cycle process, because the introduction of the graphene improves the conductivity of the cobalt sulfide, and increases the specific discharge capacity, rate capability and cycle performance of the material.
Claims (10)
1. The preparation method of the hollow cobalt sulfide/graphene composite material is characterized by comprising the following steps:
(1) adding cobalt nitrate hexahydrate and glycerol into isopropanol, and carrying out hydrothermal reaction to obtain a cobalt-glycerol complex;
(2) dispersing the cobalt-glycerol complex obtained in the step (1) in an alcohol solvent, adding a surface charge modifier, and carrying out charge modification under an ultrasonic condition to obtain a cobalt-glycerol complex with a negatively charged surface;
(3) uniformly dispersing graphene oxide in an alcohol solvent, adding the cobalt-glycerol complex with the negative surface obtained in the step (2), and performing ultrasonic dispersion to obtain a mixed solution;
(4) and (4) adding thioacetamide into the mixed solution obtained in the step (3), and carrying out hydrothermal reaction to obtain the hollow sphere cobalt sulfide/graphene composite material.
2. The preparation method of the hollow cobalt sulfide/graphene composite material according to claim 1, wherein in the step (1), the temperature of the hydrothermal reaction is 160-200 ℃, and the reaction time is 4-6 h; preferably, in the step (1), the mass ratio of the cobalt nitrate hexahydrate to the glycerol is 1: 290-600, and the volume ratio of the glycerol to the isopropanol is 1-2: 5.
3. The preparation method of the hollow cobalt sulfide/graphene composite material according to claim 1 or 2, wherein in the step (2), the surface charge modifier is selected from one or more of 3-aminopropyltrimethoxysilane, vinyltriethoxysilane and vinyltrimethoxysilane; preferably, the volume ratio of the surface charge modifier to the alcohol solvent is 1: 10-15; preferably, the concentration of the cobalt-glycerol complex in the alcohol solvent is 1-2 mg/mL.
4. The preparation method of the hollow cobalt sulfide/graphene composite material according to any one of claims 1 to 3, wherein in the step (3), the mass-to-volume ratio of the graphene oxide to the alcohol solvent is 0.5-1 mg/mL; preferably, the mass ratio of the cobalt-glycerol complex to the graphene oxide is 5: 1-2; preferably, the power of the ultrasonic dispersion is 100-600W, and the time is 2-4 h.
5. The preparation method of the hollow cobalt sulfide/graphene composite material according to any one of claims 1 to 4, wherein in the step (4), the temperature of the hydrothermal reaction is 160 to 200 ℃, and the reaction time is 2 to 8 hours.
6. The preparation method of the hollow cobalt sulfide/graphene composite material according to any one of claims 1 to 5, wherein in the step (4), the mass ratio of thioacetamide to the cobalt-glycerol complex is 1-2: 1.
7. The method for preparing the hollow cobalt sulfide/graphene composite material according to any one of claims 1 to 6, wherein in the steps (2) and (3), the alcohol solvent is ethanol.
8. The preparation method of the hollow cobalt sulfide/graphene composite material according to any one of claims 1 to 7, which is characterized by comprising the following steps:
(1) adding cobalt nitrate hexahydrate and glycerol into isopropanol, stirring, carrying out hydrothermal reaction, cooling after the reaction is completed, centrifugally washing, and drying to obtain a cobalt-glycerol complex;
(2) dispersing the cobalt-glycerol complex obtained in the step (1) in an alcohol solvent, adding a surface charge modifier, stirring, performing charge modification under an ultrasonic condition, centrifuging, and washing to obtain a cobalt-glycerol complex with a negatively charged surface;
(3) uniformly dispersing graphene oxide in an alcohol solvent by adopting ultrasound, adding the cobalt-glycerol complex with the negative surface obtained in the step (2), and performing ultrasonic dispersion to obtain a mixed solution;
(4) and (4) adding thioacetamide into the mixed solution obtained in the step (3), stirring, carrying out hydrothermal reaction, centrifuging, washing and drying to obtain the hollow sphere cobalt sulfide/graphene composite material.
9. The preparation method of the hollow cobalt sulfide/graphene composite material according to claim 8, wherein in the step (4), the stirring speed is 200-400 r/min, the stirring time is 4-6 h, and the sulfur source and the cobalt source attached to the graphene sheet layer are in full contact under the stirring condition, so that a basis is provided for a next complete vulcanization reaction.
10. A lithium battery positive electrode material, which is characterized by comprising the hollow sphere cobalt sulfide/graphene composite material prepared by the preparation method of any one of claims 1 to 9.
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