CN107331835B - One-step solvothermal method for synthesizing three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material and method - Google Patents

One-step solvothermal method for synthesizing three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material and method Download PDF

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CN107331835B
CN107331835B CN201710428793.0A CN201710428793A CN107331835B CN 107331835 B CN107331835 B CN 107331835B CN 201710428793 A CN201710428793 A CN 201710428793A CN 107331835 B CN107331835 B CN 107331835B
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dimensional graphene
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CN107331835A (en
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曹丽云
康倩
李嘉胤
黄剑锋
程娅伊
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Shaanxi University of Science and Technology
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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
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    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • H01M4/625—Carbon or graphite
    • 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
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    • 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 relates to a three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material synthesized by a one-step solvothermal method and a method, wherein the three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material is prepared by the following steps in percentage by volume (0.5-3): 70, adding oleic acid into the ethanol solution to obtain a solution A; adding cobalt salt and a precipitator into the solution A, and uniformly stirring to obtain a solution B; adding graphene oxide into the solution B, and uniformly stirring to obtain a suspension C; carrying out ultrasonic treatment on the suspension C, and then carrying out homogeneous hydrothermal reaction to generate a precipitate; and separating out the precipitate, washing and drying to obtain the three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material. The three-dimensional graphene network skeleton in the product of the invention not only enables the material to have good mechanical strength and stability, but also reduces the distance of electron transmission, accelerates the speed of electron transmission, and the CoCO wrapped by the graphene skeleton3the quantum dots are small in size, have a promoting effect on the transmission of electrons and ions in the charge and discharge processes, and improve the electrochemical performance.

Description

One-step solvothermal method for synthesizing three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material and method
Technical Field
the invention relates to the field of negative electrode materials of ion batteries, in particular to an electrode material and a method for synthesizing a three-dimensional graphene-coated cobalt carbonate quantum dot composite by a one-step solvothermal method.
Background
Energy is an indispensable material basis for the development of the whole human society, but with the gradual exhaustion of non-renewable energy and the ecological and environmental problems brought by the non-renewable energy, people have to develop new renewable energy. Lithium ion batteries have been widely used in various portable electronic devices and in the medical and aerospace fields because of their high voltage, high specific energy, stable discharge voltage, and long operating life. However, the shortage of lithium resources and the higher cost thereof become important factors restricting the development of the lithium ion battery, compared with lithium, the storage of sodium is quite rich, lithium and sodium belong to the same main group, the chemical properties are similar, and the working principles of the sodium ion battery and the lithium ion battery are also similar, so that the development of the sodium ion battery by replacing lithium with sodium is a trend of new energy development in the future.
for lithium ion batteries and sodium ion batteries, many transition metal oxides can be used as the negative electrode materials, such as CoO and Co3O4、Mn3O4、Fe2O3etc., all of which have a higher theoretical capacity. Transition metal carbonates (e.g., CoCO)3、MnCO3、FeCO3Etc.) are generally regarded as precursors of transition metal oxides, and there are few studies on their use for electrode materials, but there are also some cases where transition metal carbonates have more excellent electrochemical properties than transition metals. YIrenZHong et al [ YIrenZhong, Liwei Su, Mei Yang, Jinping Wei, and Zhen Zhou, rambutan-LikeFeCO ]3Hollow Microspheres:Facile Preparation and Superior Lithium Storage Performances[J].ACS Appl.Mater.Interfaces,2013,5:11212-11217.]preparing the FeCO with the shape of the rambutan by a hydrothermal method3the hollow microspheres can be maintained at 710mAh/g after circulating for 200 circles under the current density of 200 mA/g. Maria Jos Arag xi, etc. [ Maria Jos Arag xi, Bernardo Le xi n, cars P re ez vicentite, Jos e L.Tirado.A new form of a regulating carbonate for the regulating electrode of batteries-batteries [ J]J.Power Sources,2011,196:2863-2866.]MnCO prepared by micro-emulsion method3Lianbang Wang et al [ Lianbang Wang, Weijie Tang, Yu jin, Liwei Su, and Zhen Zhou. Do Transition metals cations, A Case studio Monodissse CoCO3and CoO Microspindles[J].ACS Appl.Mater.Interfaces,2014,6:12346-12352.]fusiform CoCO obtained by solvothermal method combined with heat treatment3The reversible capacity after 10 cycles of circulation under the current density of 50mA/g can reach 1065mAh/g, which is far higher than that of CoCO3The theoretical capacity (450mAh/g) is even higher than the CoO cycle reversible capacity (-720 mAh/g). Liweii Su et al [ Liweii Su, Zhen Zhou,Xue Qin,Qiwei Tang,Dihua Wu,Panwen Shen.CoCO3Submicrocube/Graphene Composites with High Lithium Storage Capability[J].Nano Energy,2013,2:276-282.]CoCO produced by solvothermal method3The reversible capacity of the/graphene complex after 40 cycles is about 930 mAh/g. There have been studies showing transition Metal Carbonates (MCO)3) Except for MCO3To M0/LiCO3The reversible transformation of (A) provides a theoretical capacity of 450mAh/g, and also LiCO therein3Can also participate in the storage process of lithium and simultaneously carry out the reaction on the reduced M at certain potential0according to such a new electrochemical mechanism, then MCO3The theoretical capacity of the capacitor can reach 1300 mAh/g. Thus, transition metal carbonates are also gaining increasing attention.
But CoCO3poor stability when used as an electrode material, CoCO3Instability of the electrochemical device can affect the stability of the electrochemical cycle.
disclosure of Invention
The invention aims to overcome the problems in the prior art, and provides a three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material synthesized by a one-step solvothermal method and a method thereof, so that the stability of the material is improved.
in order to achieve the purpose, the invention adopts the following technical scheme:
The method comprises the following steps:
1) The volume ratio of (0.5-3): 70, adding oleic acid into the ethanol solution to obtain a solution A;
2) Adding cobalt salt and a precipitator into the solution A, and uniformly stirring to obtain a solution B; wherein the proportion of the cobalt salt to the ethanol solution in the step 1) is (2-6) mmol: 70 mL;
3) adding graphene oxide into the solution B, and uniformly stirring to obtain a suspension C; wherein the ratio of the graphene oxide to the ethanol solution in the step 1) is (0.07-0.14) g: 70 mL;
4) Carrying out ultrasonic treatment on the suspension C, and then carrying out homogeneous hydrothermal reaction to generate a precipitate;
5) and separating out the precipitate, washing and drying to obtain the three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material.
further, the step 1) contains 64-68 mL of absolute ethyl alcohol in every 70mL of ethanol solution.
Further, stirring for 3-5 min in the step 1) to obtain a solution A; stirring for 10-30 min in the step 2) to obtain a solution B.
Further, the molar ratio of the cobalt salt to the precipitant in the step 2) is 1: 5.
Further, the cobalt salt is Co (NO)3)2·6H2O, using CO (NH) as a precipitator2)2。
Further, magnetically stirring for 20-60 min in the step 3) to obtain a suspension C.
Further, in the step 4), the suspension C is subjected to ultrasonic treatment for 6-12 hours under 1500W.
Further, in the step 4), the suspension C after ultrasonic treatment is poured into a polytetrafluoroethylene inner liner, then the polytetrafluoroethylene inner liner is filled into a stainless steel reaction kettle outer liner, the stainless steel reaction kettle outer liner is sealed and then placed into a homogeneous reactor, the temperature is increased to 120-180 ℃ from the room temperature, the temperature is kept for 5-8 hours, and then the mixture is naturally cooled to the room temperature to generate a precipitate.
Further, in the step 5), the precipitate is separated by centrifugation, washed for 3-6 times by absolute ethyl alcohol and then dried for 8-12 hours in a vacuum drying oven at the temperature of 60-80 ℃.
The three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material synthesized by the method has the advantages that the size of cobalt carbonate quantum dots in the material is 3-5 nm; the average specific capacity is 923 to 973 mAh/g.
compared with the prior art, the invention has the following beneficial technical effects:
According to the method, a certain amount of oleic acid is added into a mixed solution of water and ethanol by a one-step solvothermal method, then cobalt salt, a precipitator and graphene oxide are added, the mixture is stirred and subjected to ultrasonic treatment, and homogeneous reaction is carried out, so that the CoCO wrapped by the three-dimensional graphene network framework is successfully prepared3the structure of the quantum dot, in the reaction process, the oleic acid molecules dispersed in the ethanol solution can cause the graphene to rollThe material is bent and presents a three-dimensional skeleton structure, cobalt ions decomposed by cobalt nitrate and carbonate ions decomposed by urea gradually react to generate cobalt carbonate, and the cobalt ions are also attracted by carboxyl contained in oleic acid, so that the nucleation and growth of the cobalt carbonate are limited, and finally cobalt carbonate quantum dots are obtained, and are uniformly wrapped in a curled three-dimensional graphene skeleton. The preparation process is simple, the reaction condition is mild, the reaction period is short, and the method is environment-friendly and suitable for large-scale production. The three-dimensional graphene network skeleton in the prepared product not only enables the material to have good mechanical strength and stability, but also reduces the distance of electronic transmission, accelerates the speed of electronic transmission, and the CoCO is wrapped by the graphene skeleton3The quantum dots have small size, promote the transmission of electrons and ions in the charge and discharge processes, and more efficiently improve the CoCO3Electrochemical properties of the negative electrode.
The method obtains three-dimensional graphene coated CoCO by a solvothermal method3Quantum dots of the structure in which CoCO3The size of the quantum dots is 3-5nm, and the quantum dots are wrapped in the hollow framework of the quantum dots by graphene and are uniformly distributed. The small particle size is beneficial to the rapid transmission of electrons, and the reaction rate of the oxidation-reduction reaction in the charge-discharge process is accelerated. On the other hand, the specific surface area of small particle size is larger, the contact area with electrolyte is increased, the active sites of reaction are increased, and the high-efficiency implementation of electrochemical reaction is facilitated. The three-dimensional graphene network can not only improve the stability of the material structure, but also relieve the volume expansion caused by the insertion/desorption of lithium ions or sodium ions in the charge and discharge process, thereby protecting CoCO3The effect of the particles. On the other hand, the contact area of the material and the electrolyte is increased by the gaps and the holes in the three-dimensional network, and more sites are provided for electrochemical reaction. The characteristics of the structures greatly help the improvement of electrochemical properties such as charge-discharge specific capacity, cycling stability, rate performance and the like of the material, and the average specific capacity of the composite is 923-973 mAh/g; also has important significance for the research and development of the cathode material of the lithium/sodium ion battery.
Drawings
FIG. 1 shows that CoCO is wrapped by three-dimensional graphene as a negative electrode material of a lithium/sodium ion battery prepared in example 1 of the present invention3an X-ray diffraction (XRD) pattern of the quantum dot composite.
FIG. 2 shows that CoCO is wrapped by three-dimensional graphene as a negative electrode material of a lithium/sodium ion battery prepared in example 1 of the invention3scanning Electron Microscope (SEM) picture of quantum dot composite under 30.0K multiplying power.
FIG. 3 shows that CoCO is wrapped by three-dimensional graphene as the negative electrode material of the lithium/sodium ion battery prepared in example 1 of the present invention3Scanning Electron Microscope (SEM) pictures of the quantum dot composites at a magnification of 100K.
FIG. 4 shows that CoCO is wrapped by three-dimensional graphene as the negative electrode material of the lithium/sodium ion battery prepared in example 1 of the invention3Transmission Electron Microscopy (TEM) images of the quantum dot composites at 200nm magnification.
FIG. 5 shows that CoCO is wrapped by three-dimensional graphene as the negative electrode material of the lithium/sodium ion battery prepared in example 1 of the invention3Transmission Electron Microscopy (TEM) images of the quantum dot composites at 5nm magnification.
FIG. 6 shows three-dimensional graphene-wrapped CoCO prepared in example 1 and comparative example 1 of the present invention3the quantum dot composite is used as a lithium/sodium ion battery cathode material, and is respectively cycled for 100 circles under the current density of 100 mA/g.
Detailed Description
the present invention will be described in further detail with reference to the accompanying drawings.
The method comprises the following steps:
1) Adding 2-6 mL of deionized water into 68-64 mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) Adding 0.5-3 mL of oleic acid into the mixed solvent A, and stirring for 3-5 min to obtain a solution B;
3) Taking 2-6 mmol of Co (NO)3)2·6H2o, 10-30 mmol of CO (NH)2)2sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 10-30 min to obtain a solution C;
4) adding 0.07-0.14 g of graphene oxide into the solution C, and magnetically stirring for 20-60 min to obtain a suspension D;
5) Performing ultrasonic treatment on the suspension D at 1500W for 6-12 h to uniformly disperse graphene in the solution;
6) Pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 120-180 ℃ from room temperature, preserving the heat for 5-8 h, carrying out homogeneous hydrothermal reaction, and then naturally cooling the inner liner to room temperature to obtain a precipitate E;
7) centrifuging the precipitate E, washing the precipitate E for 3-6 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at the temperature of 60-80 ℃ for 8-12 hours to obtain three-dimensional graphene coated CoCO3a quantum dot composite.
The invention adopts the three-dimensional graphene and CoCO with high conductivity, high mechanical flexibility and stable chemical properties3The purpose of improving the conductivity and the electrochemical stability of the electrode material is achieved through compounding, so that the electrode material with excellent electrochemical performance is obtained.
Example 1:
1) Adding 6mL of deionized water into 64mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) Adding 1mL of oleic acid into the mixed solvent A, and stirring for 3min to obtain a solution B;
3) 2mmol of Co (NO) was taken3)2·6H2o, 10mmol of CO (NH)2)2sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 10min to obtain a solution C;
4) adding 0.07g of graphene oxide into the solution C, and magnetically stirring for 20min to obtain a suspension D;
5) Carrying out ultrasonic treatment on the suspension D for 6 h;
6) Pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 120 ℃ from room temperature, preserving the heat for 5 hours, and then naturally cooling the inner liner to room temperature to obtain a precipitate E;
7) Centrifuging the precipitate E, washing the precipitate E for 3 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at the temperature of 60 ℃ for 12 hours to obtain three-dimensional graphene coated CoCO3A quantum dot composite.
as shown in FIG. 1, each characteristic diffraction peak is associated with CoCO in the XRD pattern of the obtained product3is identical to standard card (JCPDS No.: 78-0209). Fig. 2 and fig. 3 are SEM images of three-dimensional graphene at magnifications of 30K and 100K, respectively, and it can be seen from the two images that the graphene sheet curls to form a three-dimensional skeleton structure under the action of oleic acid, and CoCO3 quantum dot particles can be seen in the graphene structure. In addition, the TEM image of FIG. 4 shows that CoCO3 quantum dots grown in the graphene skeleton are uniformly distributed, and the HRTEM image of FIG. 5 shows that the size of the CoCO3 quantum dots is 3-5 nm.
Comparative example 1:
the raw material oleic acid in the step 2) of the embodiment 1 is removed, and other conditions are not changed, so that the electrochemical performance of the obtained graphene/cobalt oxide composite electrode is greatly reduced, as shown in a circulation performance comparison chart shown in fig. 6, the average specific capacity is reduced from 973mAh/g to 596mAh/g, and the capacity is continuously attenuated along with the increase of the circulation times.
example 2:
1) Adding 5mL of deionized water into 65mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) adding 0.5mL of oleic acid into the mixed solvent A, and stirring for 3min to obtain a solution B;
3) 3mmol of Co (NO) was taken3)2·6H2O, 15mmol of CO (NH)2)2Sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 10min to obtain a solution C;
4) Adding 0.1g of graphene oxide into the solution C, and magnetically stirring for 30min to obtain a suspension D;
5) Carrying out ultrasonic treatment on the suspension D for 8 h;
6) Pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 140 ℃ from room temperature, preserving the heat for 6 hours, and then naturally cooling the inner liner to the room temperature to obtain a precipitate E;
7) Centrifuging the precipitate E, washing the precipitate E for 4 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at 70 ℃ for 10 hours to obtain three-dimensional graphene coated CoCO3Quantum dotsA complex; the average specific capacity of the composite is 965 mAh/g.
Example 3:
1) adding 4mL of deionized water into 66mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) Adding 1.5mL of oleic acid into the mixed solvent A, and stirring for 4min to obtain a solution B;
3) 4mmol of Co (NO) was taken3)2·6H2O, 20mmol of CO (NH)2)2sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 20min to obtain a solution C;
4) Adding 0.12g of graphene oxide into the solution C, and magnetically stirring for 40min to obtain a suspension D;
5) Carrying out ultrasonic treatment on the suspension D for 10 h;
6) pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 160 ℃ from room temperature, preserving the heat for 8 hours, and then naturally cooling the inner liner to room temperature to obtain a precipitate E;
7) centrifuging the precipitate E, washing the precipitate E for 5 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at 80 ℃ for 8 hours to obtain three-dimensional graphene coated CoCO3The average specific capacity of the quantum dot composite is 951 mAh/g.
example 4:
1) Adding 3mL of deionized water into 67mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) Adding 2mL of oleic acid into the mixed solvent A, and stirring for 5min to obtain a solution B;
3) 5mmol of Co (NO) was taken3)2·6H2o, 25mmol of CO (NH)2)2sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 30min to obtain a solution C;
4) adding 0.14g of graphene oxide into the solution C, and magnetically stirring for 50min to obtain a suspension D;
5) Carrying out ultrasonic treatment on the suspension D for 10 h;
6) Pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 180 ℃ from room temperature, preserving the heat for 5 hours, and then naturally cooling the inner liner to the room temperature to obtain a precipitate E;
7) Centrifuging the precipitate E, washing the precipitate E for 6 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at the temperature of 60 ℃ for 12 hours to obtain three-dimensional graphene coated CoCO3The average specific capacity of the quantum dot composite is 923 mAh/g.
example 5:
1) Adding 2mL of deionized water into 68mL of absolute ethyl alcohol to prepare 70mL of mixed solvent A;
2) adding 3mL of oleic acid into the mixed solvent A, and stirring for 5min to obtain a solution B;
3) 6mmol of Co (NO) was taken3)2·6H2o, 30mmol of CO (NH)2)2Sequentially adding the mixed solution into the solution B according to a molar ratio of 1:5, and stirring for 30min to obtain a solution C;
4) Adding 0.14g of graphene oxide into the solution C, and magnetically stirring for 60min to obtain a suspension D;
5) Carrying out ultrasonic treatment on the suspension D for 12 h;
6) pouring the suspension D after ultrasonic treatment into a 100mL polytetrafluoroethylene inner liner, then putting the inner liner into a stainless steel reaction kettle outer liner, sealing the inner liner, putting the inner liner into a homogeneous reactor, heating the inner liner to 120 ℃ from room temperature, preserving the heat for 8 hours, and then naturally cooling the inner liner to room temperature to obtain a precipitate E;
7) centrifuging the precipitate E, washing the precipitate E for 6 times by using absolute ethyl alcohol, and drying the precipitate E in a vacuum drying oven at 80 ℃ for 10 hours to obtain three-dimensional graphene coated CoCO3The quantum dot composite has an average specific capacity of 942 mAh/g.
adding a certain amount of oleic acid into a mixed solution of water and ethanol, adding cobalt salt, a precipitator and graphene oxide, stirring and ultrasonically treating, then placing into a reaction kettle, reacting for a certain time by using a homogeneous reactor, repeatedly washing an obtained product with absolute ethyl alcohol for multiple times, and then drying to finally obtain a three-dimensional network-shaped framework formed by curled graphene, wherein the framework is internally wrapped with CoCO which is uniformly distributed and has the size of about 5nm3A composite of quantum dots. Three-dimensional graphene network boneThe frame not only enables the material to have good mechanical strength and stability, but also reduces the distance of electronic transmission and accelerates the speed of electronic transmission. CoCO wrapped by graphene framework3The size of the quantum dot is about 5nm, the smaller size has a promoting effect on the transmission of electrons and ions in the charging and discharging process, the specific surface area of particles is increased due to the nanoscale size, the particles are enabled to be more fully contacted with electrolyte, the graphene wrapped by the outer layer has a good buffering effect on the volume expansion effect in the charging and discharging process, and the characteristics can effectively improve the electrochemical performance of the electrode material. The preparation method is simple, mild in reaction condition, short in reaction period, environment-friendly and suitable for large-scale production.

Claims (9)

1. the method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method is characterized by comprising the following steps of: the method comprises the following steps:
1) The volume ratio of (0.5-3): 70, adding oleic acid into the ethanol solution to obtain a solution A;
2) Adding cobalt salt and a precipitator into the solution A, and uniformly stirring to obtain a solution B; wherein the cobalt salt is Co (NO)3)2·6H2O, using CO (NH) as a precipitator2)2，Co(NO3)2·6H2The proportion of O to the ethanol solution in the step 1) is (2-6) mmol: 70 mL;
3) Adding graphene oxide into the solution B, and uniformly stirring to obtain a suspension C; wherein the ratio of the graphene oxide to the ethanol solution in the step 1) is (0.07-0.14) g: 70 mL;
4) Carrying out ultrasonic treatment on the suspension C, and then carrying out homogeneous hydrothermal reaction for 5-8 h at 120-180 ℃ to generate a precipitate;
5) And separating out the precipitate, washing and drying to obtain the three-dimensional graphene coated cobalt carbonate quantum dot composite electrode material.
2. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: step 1) each 70mL of ethanol solution contains 64-68 mL of absolute ethanol.
3. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: stirring for 3-5 min in the step 1) to obtain a solution A; stirring for 10-30 min in the step 2) to obtain a solution B.
4. the method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: the molar ratio of the cobalt salt to the precipitant in the step 2) is 1: 5.
5. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: and 3) magnetically stirring for 20-60 min in the step 3) to obtain a suspension C.
6. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: and 4) ultrasonically treating the suspension C under 1500W for 6-12 h.
7. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: and 4), pouring the suspension C subjected to ultrasonic treatment into a polytetrafluoroethylene inner liner, then putting the polytetrafluoroethylene inner liner into a stainless steel reaction kettle outer liner, sealing the stainless steel reaction kettle outer liner, putting the stainless steel reaction kettle outer liner into a homogeneous reactor, heating the reaction kettle to the reaction temperature from room temperature, and naturally cooling the reaction kettle to the room temperature after the reaction is finished to generate a precipitate.
8. The method for synthesizing the three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material by the one-step solvothermal method according to claim 1, wherein the method comprises the following steps: and 5) centrifugally separating out precipitates, washing the precipitates for 3-6 times by using absolute ethyl alcohol, and then drying the precipitates for 8-12 hours in a vacuum drying oven at the temperature of 60-80 ℃.
9. The three-dimensional graphene-coated cobalt carbonate quantum dot composite electrode material synthesized by the method of claim 1, which is characterized in that: the size of the cobalt carbonate quantum dots in the material is 3-5 nm; the average specific capacity is 923 to 973 mAh/g.
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