CN111554928A - Graphene-based composite material and preparation method and application thereof - Google Patents
Graphene-based composite material and preparation method and application thereof Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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- H01M4/00—Electrodes
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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Abstract
The invention discloses a graphene-based composite material and a preparation method and application thereof, wherein the method comprises the following steps: (1) mixing the magnesium salt solution and the carbonate solution, then carrying out suction filtration and washing, dispersing the obtained solid material into water, then mixing the dispersed slurry with the silicon powder-containing slurry, and carrying out spray drying; (2) placing the precursor in a high-temperature reactor, continuously heating, introducing protective gas, and introducing first gas containing protective gas and hydrogen into the high-temperature reactor after the first preset temperature is reached; (3) placing the composite material containing magnesium oxide and silicon in a high-temperature reactor, continuously heating, introducing protective gas, and introducing second gas containing protective gas and a carbon source or containing protective gas and a nitrogen-containing carbon source into the high-temperature reactor after reaching a second preset temperature to obtain graphene or the MgO-Si composite material of nitrogen atom doped graphene; (4) and removing magnesium oxide in the graphene or nitrogen atom doped graphene MgO-Si composite material, and then washing the magnesium oxide until the magnesium oxide is neutral to obtain the graphene-based composite material.
Description
Technical Field
The invention belongs to the technical field of carbon materials, and particularly relates to a graphene-based composite material as well as a preparation method and application thereof.
Background
At present, graphite carbon materials are mainly adopted by the lithium ion battery as negative active materials, but the theoretical specific capacity of the lithium ion battery is only 372mAh/g, so that the lithium ion battery cannot meet the requirements of miniaturization of electronic equipment and high power and high capacity of the lithium ion battery for vehicles. The high theoretical specific capacity of silicon (4200mAh/g) and the low intercalation potential have therefore led to extensive research in recent years. However, silicon undergoes large volume changes (> 300%) during lithium deintercalation, resulting in pulverization of silicon and rapid capacity decay, limiting its full use as an active material.
The graphene has excellent characteristics of high electron mobility, high thermal conductivity, high surface activity and the like, and shows good application prospects in the fields of energy storage, catalysis, sensors, electronic devices and the like. Among them, the application of graphene in the field of electrochemical energy storage is an important aspect, and the design of the microstructure and chemical properties of graphene is the key to realize high-performance electrode materials.
The existing electrode material has the following problems:
(1) silicon performance limitations: the silicon serving as the negative electrode material has the problem that the volume change of the silicon is large in the processes of lithium intercalation and lithium deintercalation, which can lead to the powdering of the electrode material, so that the energy storage capacity of the lithium ion battery is reduced rapidly along with the increase of the cycle number, the service life of the lithium ion battery is shortened, and the industrial application of the lithium ion battery is restricted. Therefore, the effect of reducing the volume of the silicon cathode is an important problem to be solved before the silicon material is applied.
(2) The graphene structure is difficult to regulate and control: the quality of the currently widely used graphene (mainly based on a chemical oxidation-reduction method) is not high, which is obviously reflected in that most graphene products are extremely non-uniform in size and not high in conductivity. The defects are generated in the graphene structure and the controllability of the number of layers, the size and the like of the graphene is poor due to the limitation of the preparation method. Although many graphene preparation methods have been developed over the last decade, mechanical exfoliation, Chemical Vapor Deposition (CVD), graphite oxidation-reduction, direct liquid phase exfoliation, and other chemical synthesis techniques have been developed. However, these methods still have scientific bottlenecks in terms of macro-scale preparation, graphene layer number and lateral dimension control, and structural integrity.
(3) The processing technology of the graphene/silicon composite material is immature: the traditional mechanical mixing cannot ensure the uniform compounding of silicon and graphene, and silicon still can fall off in the process of charging and discharging for many times, so that the capacity attenuation is fast.
Therefore, the existing technology for preparing electrode materials is in need of improvement.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, one object of the present invention is to provide a graphene-based composite material, and a preparation method and an application thereof, wherein the graphene-based composite material prepared by the method has excellent electrical conductivity and good cycle performance, and during charging and discharging processes of a negative electrode material prepared from the graphene-based composite material, graphene relieves volume change during lithium deintercalation from silicon, and improves electrochemical stability of the negative electrode material.
In one aspect of the present invention, a method of preparing a graphene-based composite is presented. According to an embodiment of the invention, the method comprises:
(1) mixing a magnesium salt solution and a carbonate solution, carrying out suction filtration and washing, dispersing the obtained solid material in water to obtain dispersed slurry, mixing the dispersed slurry and silicon-containing powder slurry, and carrying out spray drying on the obtained mixed slurry to obtain a precursor;
(2) placing the precursor in a high-temperature reactor, continuously heating, introducing protective gas, and introducing first gas containing protective gas and hydrogen into the high-temperature reactor after the temperature of the precursor reaches a first preset temperature so as to obtain a composite material containing magnesium oxide and silicon;
(3) placing the composite material containing the magnesium oxide and the silicon in a high-temperature reactor, continuously heating, introducing the protective gas, and after reaching a second preset temperature, introducing a second gas containing the protective gas and a carbon source or containing the protective gas and a nitrogen-containing carbon source into the high-temperature reactor so as to deposit and form graphene or nitrogen-doped graphene on the composite material containing the magnesium oxide and the silicon, thereby obtaining the MgO-Si composite material of the graphene or the nitrogen atom-doped graphene;
(4) and removing magnesium oxide in the graphene or nitrogen atom doped graphene MgO-Si composite material, and then washing the magnesium oxide to be neutral so as to obtain the graphene-based composite material.
According to the method for preparing the graphene-based composite material, provided by the embodiment of the invention, a magnesium salt solution and a carbonate solution are mixed, then suction filtration and washing are carried out, an obtained solid material is dispersed in water to obtain a dispersion slurry, then the dispersion slurry is mixed with a silicon-containing powder slurry, spray drying is carried out on the obtained mixed slurry to obtain a precursor containing magnesium carbonate and silicon powder, then the obtained precursor containing magnesium carbonate and silicon is placed in a high-temperature reactor to carry out a reduction reaction in a first gas atmosphere containing protective gas and hydrogen to obtain a composite material containing magnesium oxide and silicon, wherein the magnesium oxide has excellent graphene catalytic activity, so that graphene with a complete structure is formed in a subsequent deposition process, then the composite material containing magnesium oxide and silicon is placed in the high-temperature reactor to carry out a deposition reaction in a second gas atmosphere containing protective gas and a carbon source or containing protective gas and a nitrogen-containing carbon source, the graphene in the composite material can not only improve the conductivity of the material, but also has excellent flexibility, thereby relieving the volume change of the composite material when the composite material is used as a negative electrode material and silicon is subjected to lithium extraction, improving the electrochemical stability of the composite material, simultaneously, the negative electrode material prepared by adopting the graphene-based composite material can play a role in buffering an electrode in the charging and discharging processes, thereby improving the cycle performance and the rate capability of the negative electrode material, and simultaneously, because the graphene-based composite material is porous, the porous structure of the negative electrode material prepared by adopting the graphene-based composite material is not only beneficial to the insertion and extraction of lithium ions, but also can buffer the stress generated in the reaction process, and the addition of silicon improves the silicon storage amount of the composite material, namely the composite material combines the advantages of the graphene and the silicon, in addition, the method uses a spraying method to prepare the template agent, the preparation process is environment-friendly and easy to amplify, the chemical vapor deposition method is used for catalyzing and growing the graphene, the process is simple and easy to operate, the source of the gas source is wide, the reaction temperature is low, and the large-scale production can be realized in the existing CVD equipment.
In addition, the method for preparing the graphene-based composite material according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the invention, in step (1), the magnesium salt solution is at least one of a magnesium nitrate solution, a magnesium chloride solution, a magnesium sulfate solution, and a magnesium acetate solution.
In some embodiments of the present invention, in the step (1), the concentration of magnesium ions in the magnesium salt solution is 0.01-3 mol/L.
In some embodiments of the present invention, in step (1), the carbonate solution is at least one of a sodium carbonate solution, a potassium carbonate solution, an ammonium carbonate solution, a sodium bicarbonate solution, a potassium bicarbonate solution, and an ammonium bicarbonate solution.
In some embodiments of the present invention, in the step (1), the carbonate ion concentration in the carbonate solution is 0.01 to 3 mol/L.
In some embodiments of the invention, in step (1), the volume ratio of the magnesium salt solution to the carbonate solution is 0.5-10: 1.
In some embodiments of the present invention, in the step (1), the concentration of the dispersion slurry is 0.01 to 4 mol/L.
In some embodiments of the invention, in the step (1), the concentration of the silicon powder-containing slurry is 0.1-10 g/L.
In some embodiments of the present invention, in step (1), the dispersion slurry and the silica-containing powder slurry are mixed in a volume ratio of 1-15: 1.
In some embodiments of the present invention, in the step (1), the feeding speed of the spray drying process is 2 to 30mL/min, the inlet air temperature is 200 to 300 ℃, and the outlet air temperature is 95 to 160 ℃.
In some embodiments of the present invention, in the step (2), the temperature rise rate is 5 to 15 degrees Celsius/min.
In some embodiments of the invention, in step (2), the shielding gas is at least one of nitrogen, argon and helium.
In some embodiments of the present invention, in the step (2), the first predetermined temperature is 400 to 900 degrees celsius, and the reaction is performed at the first predetermined temperature for 0.5 to 10 hours.
In some embodiments of the invention, in the step (2), the flow rate of the shielding gas in the first gas containing the shielding gas and hydrogen is 0.3-10L/min, and the volume ratio of the shielding gas to the hydrogen is 1: (0.03 to 1).
In some embodiments of the present invention, in the step (3), the temperature rise rate is 5 to 15 degrees Celsius/min.
In some embodiments of the invention, in step (3), the shielding gas is at least one of nitrogen, argon and helium.
In some embodiments of the present invention, in the step (3), the second predetermined temperature is 600 to 1200 degrees centigrade, and the reaction is performed at the second predetermined temperature for 5 to 120 minutes.
In some embodiments of the invention, in the step (3), the flow rate of the protective gas in the protective gas-containing and carbon source is 0.3-10L/min, and the volume ratio of the protective gas to the carbon source is 1: (0.05-1).
In some embodiments of the invention, in the step (3), the flow rate of the protective gas in the second gas containing the protective gas and the nitrogen-containing carbon source is 0.3-10L/min, and the volume ratio of the protective gas to the nitrogen-containing carbon source is 1: (0.05-1).
In some embodiments of the invention, in step (3), the carbon source comprises at least one of methane, ethane, propane, butane, ethylene, acetylene, propylene, methanol, ethanol, and acetic acid.
In some embodiments of the invention, in step (3), the nitrogen-containing carbon source comprises at least one of urea, triethanolamine, diethanolamine, hexamethylenetetramine, aniline, propylene/N, N-dimethylformamide, ammonia, melamine, acetonitrile, propionitrile, butyronitrile, methane/ammonia, pyrrole, acetone/methanol, pyridine, and thiourea.
In some embodiments of the present invention, in step (4), magnesium oxide in the graphene or nitrogen atom-doped graphene MgO — Si composite is removed by etching.
In some embodiments of the invention, the acid solution of the etching process comprises at least one of hydrochloric acid and nitric acid.
In some embodiments of the invention, the concentration of the acid solution is 0.5-1.5 mol/L.
In some embodiments of the invention, the etching temperature is 10-90 ℃ and the etching time is 0.5-12 h.
In yet another aspect of the present invention, a graphene-based composite is provided. According to the embodiment of the invention, the graphene-based composite material is prepared by the method. Therefore, the graphene in the composite material can improve the conductivity of the material and has excellent flexibility, so that the volume change of the composite material when the composite material is used as a negative electrode material in the process of releasing lithium by silicon is relieved, the electrochemical stability of the composite material is improved, meanwhile, the graphene can play a buffer role on an electrode in the charge and discharge processes of the negative electrode material prepared by the graphene-based composite material, so that the cycle performance and the rate capability of the negative electrode material are improved, in addition, the porous structure of the graphene-based composite material is favorable for the insertion and the release of lithium ions, the stress generated in the reaction process can be buffered, and the silicon storage capacity of the composite material is improved by adding the silicon, namely, the composite material combines the advantages of the graphene and the silicon.
In a third aspect of the invention, a method of making an anode material is presented. According to an embodiment of the invention, the method comprises: mixing the graphene-based composite material with a binder and a conductive agent, and then coating the paste on a copper foil, wherein the graphene-based composite material is the graphene-based composite material obtained by the method or the graphene-based composite material.
According to the method for preparing the cathode material, the graphene-based composite material with good conductivity and high electrochemical stability is mixed with the binder and the conductive agent to prepare the cathode material, the graphene in the composite material can improve the conductivity of the material and has excellent flexibility, so that the volume change of the composite material when the composite material is used as the cathode material to remove and embed lithium from silicon is relieved, the electrochemical stability of the composite material is improved, meanwhile, the graphene in the cathode material prepared by the graphene-based composite material can play a role in buffering the electrode in the charging and discharging processes, so that the cycle performance and the rate performance of the cathode material are improved, in addition, as the graphene-based composite material is porous, the cathode material prepared by the graphene-based composite material is assembled into a battery, the porous structure of the cathode material is not only beneficial to the insertion and removal of lithium ions, but also can buffer the stress generated in the reaction process, and the addition of silicon improves the silicon storage amount of the composite material, namely the composite material combines the advantages of the graphene and the silicon.
In addition, the method for preparing the anode material according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the invention, the binder comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose, and polyacrylic acid.
In some embodiments of the present invention, the conductive agent comprises at least one of carbon nanotubes, acetylene black, and conductive carbon black.
In some embodiments of the present invention, the mass ratio of the graphene-based composite material, the binder, and the conductive agent is (5-95): (1-10): (0-10).
In a fourth aspect of the invention, an anode material is provided. According to the embodiment of the invention, the negative electrode material is prepared by the method. Therefore, the cathode material not only has excellent conductivity, but also has excellent electrical flexibility, so that the volume change of the cathode material when lithium is embedded in silicon is relieved, the electrochemical stability of the cathode material is improved, in the charge and discharge process of the cathode material, graphene can play a buffering role on an electrode, so that the cycle performance and the rate capability of the cathode material are improved, in addition, the graphene-based composite material is porous, so that a battery is assembled by adopting the cathode material, the porous structure of the cathode material is not only favorable for embedding and extracting lithium ions, but also can buffer stress generated in the reaction process, and the silicon storage amount of the composite material is improved by adding silicon, namely the composite material combines the advantages of the graphene and the silicon.
In a fifth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the negative electrode material obtained by the method described above or the negative electrode material described above. Therefore, the lithium battery has long cycle life on the basis of high volume specific capacity.
In a sixth aspect of the present invention, an automobile is provided. According to an embodiment of the present invention, the automobile has the lithium battery described above. Therefore, the vehicle loaded with the lithium battery with high volume specific capacity and long cycle life has excellent cruising ability, thereby meeting the use requirements of consumers.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a schematic flow diagram of a method of preparing a graphene-based composite according to one embodiment of the present invention;
fig. 2 is an SEM image of the graphene-based composite material obtained in example 1;
fig. 3 is a charge/discharge graph of a lithium ion battery assembled with the negative electrode material obtained in example 4.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
In one aspect of the present invention, a method of preparing a graphene-based composite is presented. Referring to fig. 1, the method according to an embodiment of the present invention includes:
s100: mixing a magnesium salt solution and a carbonate solution, carrying out suction filtration and washing, dispersing the obtained solid material in water to obtain dispersed slurry, mixing the dispersed slurry and silicon-containing powder slurry, and carrying out spray drying on the obtained mixed slurry
In the step, silicon powder is uniformly dispersed in deionized water to obtain silicon powder-containing slurry, magnesium salt and carbonate are dissolved in deionized water respectively to obtain magnesium salt solution and carbonate solution, the carbonate solution is slowly added into the magnesium salt solution to obtain magnesium carbonate-containing mixed slurry, then the mixed slurry is quickly filtered and collected to obtain solid, the separated solid is washed by using washing liquid (for example, water and ethanol are used as a detergent), then the washed solid material is dispersed in water to form dispersed slurry, then silicon-containing powder slurry is slowly and uniformly added into the dispersed slurry to be mixed, the obtained mixed slurry is subjected to spray drying, and a precursor containing magnesium carbonate and silicon is collected. The magnesium salt solution is at least one of a magnesium nitrate solution, a magnesium chloride solution, a magnesium sulfate solution and a magnesium acetate solution, and the concentration of magnesium ions in the magnesium salt solution is 0.01-3 mol/L; the carbonate solution is at least one of a sodium carbonate solution, a potassium carbonate solution, an ammonium carbonate solution, a sodium bicarbonate solution, a potassium bicarbonate solution and an ammonium bicarbonate solution, and the concentration of carbonate ions in the carbonate solution is 0.01-3 mol/L; the volume ratio of the magnesium salt solution to the carbonate solution is 0.5-10:1, and the concentration of the dispersed slurry is 0.01-4 mol/L; the concentration of the silicon powder-containing slurry is 0.1-10 g/L; the mixing volume ratio of the dispersed slurry to the silicon powder-containing slurry is 1-15: 1.
Meanwhile, the spray drying method is a two-fluid spray drying method, atomized slurry shrinks into a spherical shape by means of the surface tension of the atomized slurry, water in the slurry is quickly volatilized by hot air, and fog drops are dried to form spherical powder; the feeding speed is 2-30mL/min, the air inlet temperature of spray drying is 200-300 ℃, the air outlet temperature is controlled at 95-160 ℃, the temperature is adjusted to limit the full drying of the powder, and then the dried agglomerated powder is sucked into a cyclone separator for collection through air draft.
S200: placing the precursor in a high-temperature reactor, continuously heating, introducing protective gas, introducing first gas containing protective gas and hydrogen into the high-temperature reactor after the first preset temperature is reached
In the step, the obtained precursor containing magnesium carbonate and silicon is placed in a high-temperature reactor to be continuously heated, meanwhile, protective gas is introduced, after the temperature reaches a first preset temperature, first gas containing protective gas and hydrogen is introduced into the high-temperature reactor, and the magnesium carbonate in the precursor is fully reduced under the action of hydrogen reducing gas, so that the composite material containing magnesium oxide and silicon is obtained. The inventor finds that magnesium oxide in the obtained composite material containing magnesium oxide and silicon has excellent graphene catalytic activity by placing the precursor in a high-temperature reactor to perform a reduction reaction in a first gas atmosphere containing protective gas and hydrogen, so that graphene with a complete structure is formed in a subsequent deposition process. Further, the temperature rise rate of the high-temperature reactor is 5-15 degrees centigrade per minute, for example, 5 degrees centigrade per minute, 6 degrees centigrade per minute … … 14 degrees centigrade per minute, and 15 degrees centigrade per minute, and the inventors found that an excessively high temperature rise rate may cause incomplete removal of moisture from the carbon-containing precursor material, and an excessively low temperature rise rate may increase the preparation cost of the material. The adopted protective gas is at least one of nitrogen, argon and helium, the first preset temperature is 400-900 ℃, for example 400 ℃, 410 ℃, … … 890 ℃, 900 ℃, and the reaction is carried out for 0.5-10 hours at the first preset temperature. The inventors have found that too low a preset temperature may lead to incomplete removal of moisture from the carbonaceous precursor material, and that too high a preset temperature may increase the cost of the material preparation. In the first gas simultaneously containing the protective gas and the hydrogen, the flow rate of the protective gas is 0.3-10L/min, such as 0.3L/min, 0.4L/min … … 9.9.9L/min and 10L/min, and the volume ratio of the protective gas to the hydrogen is 1: (0.03 to 1), for example, 1: (0.03, 0.04 … … 0.99.99, 1). The inventor finds that the volume ratio is too high, so that the magnesium carbonate cannot be completely reduced, and the volume ratio is too low, so that the waste of reducing hydrogen is caused, and the material preparation cost is increased.
S300: placing the composite material containing magnesium oxide and silicon in a high-temperature reactor, continuously heating, introducing protective gas, and introducing a second gas containing protective gas and a carbon source or containing protective gas and a nitrogen-containing carbon source into the high-temperature reactor after reaching a second preset temperature
In the step, the composite material containing magnesium oxide and silicon is placed in a high-temperature reactor to be continuously heated, meanwhile, protective gas is introduced, and after a second preset temperature is reached, second gas containing protective gas and a carbon source or containing protective gas and a nitrogen-containing carbon source is introduced into the high-temperature reactor, so that graphene or nitrogen-doped graphene is deposited and formed on the composite material containing magnesium oxide and silicon, and the MgO-Si composite material of graphene or nitrogen atom-doped graphene is obtained. The inventor finds that graphene or nitrogen-doped graphene is formed on the surface of the composite material containing magnesium oxide and silicon through deposition, so that the graphene-coated magnesium oxide graphene-based composite material is obtained, the graphene in the composite material can improve the conductivity of the material and has excellent flexibility, so that the volume change of the composite material during the process of taking the composite material as a negative electrode material and releasing lithium from the silicon is relieved, the electrochemical stability of the composite material is improved, meanwhile, in the charging and discharging processes of the negative electrode material prepared by adopting the graphene-based composite material, the graphene can play a role in buffering an electrode, so that the cycle performance and the rate capability of the negative electrode material are improved, and meanwhile, as the graphene-based composite material is porous, the porous structure of the negative electrode material prepared by adopting the graphene-based composite material is beneficial to the insertion and release of lithium ions and can also buffer the stress generated in the reaction process, and the addition of silicon improves the silicon storage amount of the composite material, namely the composite material combines the advantages of the graphene and the silicon. Further, the temperature rise rate of the high-temperature reactor in the step is 5-15 ℃ per minute, such as 5 ℃, 6 ℃ per minute … … 14 ℃, and 15 ℃. The adopted shielding gas is at least one of nitrogen, argon and helium, and the second preset temperature is 600-1200 ℃, such as 600 ℃, 610 ℃, … … 1190 ℃ and 1200 ℃, and the reaction is carried out for 5-120 minutes at the second preset temperature. The inventor finds that the reaction gas is not fully cracked due to too low temperature, the cracked carbon atoms are not fully arranged on the surface of the magnesium oxide due to too high reaction temperature, defective graphene is formed, and the magnesium oxide material is melted due to high reaction temperature, so that the morphology of the material is damaged. Meanwhile, if the second gas contains the protective gas and the carbon source, the flow rate of the protective gas is 0.3-10L/min, such as 0.3L/min, 0.4L/min … … 9.9.9L/min and 10L/min, and the volume ratio of the protective gas to the carbon source is 1: (0.05 to 1), for example, 1: (0.05, 0.06 … … 0.99.99, 1). The inventor finds that too high a ratio can lead to insufficient cracked carbon atoms and failure to form high-quality graphene, too low a ratio can lead to generation of a large amount of cracked carbon atoms in a short time, disturb the sedimentation of the carbon atoms on the surface of magnesium oxide, form defects, cause air source waste and increase cost, and in addition, if the second gas contains the protective gas and the nitrogen-containing carbon source, the flow rate of the protective gas is 0.3-10L/min, such as 0.3L/min, 0.4L/min … … 9.9.9L/min and 10L/min, and the volume ratio of the protective gas to the nitrogen-containing carbon source is 1: (0.05 to 1), for example, 1: (0.05, 0.06 … … 0.99.99, 1). The inventor finds that too high proportion can lead to insufficient cracked carbon atoms and failure to form high-quality graphene, and too low proportion can lead to generation of a large amount of cracked carbon atoms in a short time, disturb the sedimentation of the carbon atoms on the surface of magnesium oxide, form defects, cause air source waste and increase cost.
Preferably, the carbon source includes at least one of methane, ethane, propane, butane, ethylene, acetylene, propylene, methanol, ethanol, and acetic acid, and the nitrogen-containing carbon source includes at least one of urea, triethanolamine, diethanolamine, hexamethylenetetramine, aniline, propylene/N, N-dimethylformamide, ammonia, melamine, acetonitrile, propionitrile, butyronitrile, methane/ammonia, pyrrole, acetone/methanol, pyridine, and thiourea.
S400: removing magnesium oxide in the MgO-Si composite material of graphene or nitrogen atom doped graphene, and then washing the MgO-Si composite material to be neutral
In the step, magnesium oxide in the obtained graphene or nitrogen atom doped graphene MgO-Si composite material is removed, and then the obtained graphene or nitrogen atom doped graphene MgO-Si composite material is washed to be neutral, so that the graphene-based composite material is obtained. Preferably, removing magnesium oxide in the graphene or nitrogen atom doped graphene MgO-Si composite material by etching; and the acid solution of the etching process comprises at least one of hydrochloric acid and nitric acid; furthermore, the concentration of the acid solution is 0.5-1.5 mol/L, the etching temperature is 10-90 ℃, and the time is 0.5-12 h.
According to the method for preparing the graphene-based composite material, provided by the embodiment of the invention, a magnesium salt solution and a carbonate solution are mixed, then suction filtration and washing are carried out, an obtained solid material is dispersed in water to obtain a dispersion slurry, then the dispersion slurry is mixed with a silicon-containing powder slurry, spray drying is carried out on the obtained mixed slurry to obtain a precursor containing magnesium carbonate and silicon powder, then the obtained precursor containing magnesium carbonate and silicon is placed in a high-temperature reactor to carry out a reduction reaction in a first gas atmosphere containing protective gas and hydrogen to obtain a composite material containing magnesium oxide and silicon, wherein the magnesium oxide has excellent graphene catalytic activity, so that graphene with a complete structure is formed in a subsequent deposition process, then the composite material containing magnesium oxide and silicon is placed in the high-temperature reactor to carry out a deposition reaction in a second gas atmosphere containing protective gas and a carbon source or containing protective gas and a nitrogen-containing carbon source, the graphene in the composite material can not only improve the conductivity of the material, but also has excellent flexibility, thereby relieving the volume change of the composite material when the composite material is used as a negative electrode material and silicon is subjected to lithium extraction, improving the electrochemical stability of the composite material, simultaneously, the negative electrode material prepared by adopting the graphene-based composite material can play a role in buffering an electrode in the charging and discharging processes, thereby improving the cycle performance and the rate capability of the negative electrode material, and simultaneously, because the graphene-based composite material is porous, the porous structure of the negative electrode material prepared by adopting the graphene-based composite material is not only beneficial to the insertion and extraction of lithium ions, but also can buffer the stress generated in the reaction process, and the addition of silicon improves the silicon storage amount of the composite material, namely the composite material combines the advantages of the graphene and the silicon, in addition, the method uses a spraying method to prepare the template agent, the preparation process is environment-friendly and easy to amplify, the chemical vapor deposition method is used for catalyzing and growing the graphene, the process is simple and easy to operate, the source of the gas source is wide, the reaction temperature is low, and the large-scale production can be realized in the existing CVD equipment.
In yet another aspect of the present invention, a graphene-based composite is provided. According to the embodiment of the invention, the graphene-based composite material is prepared by the method. Therefore, the graphene in the composite material can improve the conductivity of the material and has excellent flexibility, so that the volume change of the composite material when the composite material is used as a negative electrode material in the process of releasing lithium by silicon is relieved, the electrochemical stability of the composite material is improved, meanwhile, the graphene can play a buffer role on an electrode in the charge and discharge processes of the negative electrode material prepared by the graphene-based composite material, so that the cycle performance and the rate capability of the negative electrode material are improved, in addition, the porous structure of the graphene-based composite material is favorable for the insertion and the release of lithium ions, the stress generated in the reaction process can be buffered, and the silicon storage capacity of the composite material is improved by adding the silicon, namely, the composite material combines the advantages of the graphene and the silicon. It should be noted that the features and advantages described above for the method for preparing the graphene-based composite material are also applicable to the graphene-based composite material, and are not described herein again.
In a third aspect of the invention, a method of making an anode material is presented. According to an embodiment of the invention, the method comprises: mixing the graphene-based composite material with a binder and a conductive agent, and then coating the paste on a copper foil, wherein the graphene-based composite material is the graphene-based composite material obtained by the method or the graphene-based composite material. The inventor finds that the graphene-based composite material with good conductivity and high electrochemical stability is mixed with the binder and the conductive agent to prepare the negative electrode material, the graphene in the composite material can improve the conductivity of the material and has excellent flexibility, so that the volume change of the composite material during the process of taking the composite material as the negative electrode material to remove and embed lithium is relieved, the electrochemical stability of the composite material is improved, meanwhile, the graphene in the negative electrode material prepared by the graphene-based composite material can play a role in buffering an electrode in the charging and discharging processes, so that the cycle performance and the rate capability of the negative electrode material are improved, in addition, the graphene-based composite material has a plurality of pores, the negative electrode material prepared by the graphene-based composite material is assembled into a battery, the porous structure of the battery is favorable for the insertion and removal of lithium ions, and the stress generated in the reaction process can be buffered, and the addition of silicon improves the silicon storage amount of the composite material, namely the composite material combines the advantages of the graphene and the silicon.
Further, the binder comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose and polyacrylic acid, the conductive agent comprises at least one of carbon nanotubes, acetylene black and conductive carbon black, and preferably, based on the total mass of the negative electrode material, the mass ratio of the graphene-based composite material to the binder to the graphite to the conductive agent is (5-95): (1-10): (0-10).
It should be noted that the features and advantages described above for the graphene-based composite material and the preparation method thereof are also applicable to the method for preparing the anode material, and are not described herein again.
In a fourth aspect of the invention, an anode material is provided. According to the embodiment of the invention, the negative electrode material is prepared by the method. Therefore, the cathode material not only has excellent conductivity, but also has excellent electrical flexibility, so that the volume change of the cathode material when lithium is embedded in silicon is relieved, the electrochemical stability of the cathode material is improved, in the charge and discharge process of the cathode material, graphene can play a buffering role on an electrode, so that the cycle performance and the rate capability of the cathode material are improved, in addition, the graphene-based composite material is porous, so that a battery is assembled by adopting the cathode material, the porous structure of the cathode material is not only favorable for embedding and extracting lithium ions, but also can buffer stress generated in the reaction process, and the silicon storage amount of the composite material is improved by adding silicon, namely the composite material combines the advantages of the graphene and the silicon. It should be noted that the features and advantages described above for the method of preparing the anode material are also applicable to the anode material, and are not described herein again.
In a fifth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery has the negative electrode material obtained by the method described above or the negative electrode material described above. Therefore, the lithium battery has long cycle life on the basis of high volume specific capacity. It should be noted that the features and advantages described above for the negative electrode material and the preparation method thereof are also applicable to the lithium battery, and are not described herein again.
In a sixth aspect of the present invention, an automobile is provided. According to an embodiment of the present invention, the automobile has the lithium battery described above. Therefore, the vehicle loaded with the lithium battery with high volume specific capacity and long cycle life has excellent cruising ability, thereby meeting the use requirements of consumers. It should be noted that the features and advantages described above for the lithium battery are also applicable to the vehicle and will not be described in detail here.
The following embodiments of the present invention are described in detail, and it should be noted that the following embodiments are exemplary only, and are not to be construed as limiting the present invention. In addition, all reagents used in the following examples are commercially available or can be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated.
Example 1
The method for preparing the graphene-based composite material comprises the following steps:
(1) preparing a precursor: uniformly dispersing 225mg of silicon powder in 50mL of deionized water to obtain slurry containing the silicon powder; respectively preparing 1mol/L sodium carbonate solution and 1mol/L magnesium nitrate solution, slowly dripping 0.5L sodium carbonate solution into 0.5L magnesium nitrate solution to obtain mixed slurry, rapidly carrying out suction filtration and washing on the mixed slurry (the washing solution is water and ethanol), uniformly dispersing a filter cake in 300mL deionized water to obtain dispersed slurry, slowly and uniformly adding silicon powder-containing slurry into the dispersed slurry, uniformly mixing, and then carrying out spray drying on the obtained mixed slurry, wherein the feeding speed is 5mL/min, the air inlet temperature of the spray drying is 260 ℃, the air outlet temperature of the spray drying is controlled at 105 ℃, and then pumping the dried agglomerated powder into a cyclone separator through air draft for collection;
(2) reduction of the precursor: placing the obtained precursor in a high-temperature reaction furnace, heating at a heating rate of 5 ℃ per minute, uniformly introducing argon at a flow rate of 1L per minute in the heating process, heating to a reaction temperature of 500 ℃, preserving heat, simultaneously uniformly introducing hydrogen at a flow rate of 0.3L per minute, uniformly introducing argon at a flow rate of 1L per minute, and reacting for 3 hours to obtain a composite material containing magnesium oxide and silicon;
(3) preparing a graphene or nitrogen atom doped graphene MgO-Si composite material: placing a composite material containing magnesium oxide and silicon in a high-temperature reaction furnace, heating at a heating rate of 5 ℃ per minute, uniformly introducing argon at a flow rate of 0.5L per minute in the heating process, heating to a reaction temperature of 900 ℃, preserving heat, uniformly introducing methane at a flow rate of 0.2L per minute, uniformly introducing argon at a flow rate of 0.5L per minute, and reacting for 30 minutes to obtain graphene or nitrogen atom doped graphene MgO-Si composite material;
(4) preparing the graphene-based composite material: preparing 1.5mol/L hydrochloric acid solution, adding the obtained graphene or nitrogen atom doped graphene MgO-Si composite material into 1000mL hydrochloric acid solution, etching at 20 ℃ for 10h, removing magnesium oxide, filtering, washing, and drying by air blast to obtain the graphene-based composite material.
The method for preparing the anode material comprises the following steps:
and (3) taking the graphene-based composite material obtained in the step (4) as an active substance, mixing the active substance with conductive carbon black and polyvinylidene fluoride according to the mass ratio of 80:10:10 to obtain paste, and coating the paste on a copper foil to obtain the negative electrode material.
Example 2
The method of preparing the graphene-based composite material was the same as in example 1;
the method for preparing the anode material comprises the following steps:
and (3) taking the graphene-based composite material obtained in the step (3) as an active substance, mixing the active substance with conductive carbon black and polyvinylidene fluoride according to the mass ratio of 90:5:5 to obtain paste, and coating the paste on a copper foil to obtain the negative electrode material.
Example 3
The method for preparing the graphene-based composite material comprises the following steps:
(1) preparing a precursor: uniformly dispersing 120g of silicon powder in 20mL of deionized water to obtain slurry containing the silicon powder; respectively preparing 1mol/L sodium carbonate solution and 1mol/L magnesium nitrate solution, slowly dripping 0.5L sodium carbonate solution into 0.5L magnesium nitrate solution to obtain mixed slurry, rapidly carrying out suction filtration and washing on the mixed slurry (the washing solution is water and ethanol), uniformly dispersing a filter cake in 300mL deionized water to obtain dispersed slurry, slowly and uniformly adding silicon powder-containing slurry into the dispersed slurry, uniformly mixing, and then carrying out spray drying on the obtained mixed slurry, wherein the feeding speed is 5mL/min, the air inlet temperature of the spray drying is 260 ℃, the air outlet temperature of the spray drying is controlled at 105 ℃, and then pumping the dried agglomerated powder into a cyclone separator through air draft for collection;
(2) reduction of the precursor: placing the obtained precursor in a high-temperature reaction furnace, heating at a heating rate of 5 ℃ per minute, uniformly introducing argon at a flow rate of 1L per minute in the heating process, heating to a reaction temperature of 400 ℃, preserving heat, simultaneously uniformly introducing hydrogen at a flow rate of 0.5L per minute, uniformly introducing argon at a flow rate of 1L per minute, and reacting for 2 hours to obtain a composite material containing magnesium oxide and silicon;
(3) preparing a graphene or nitrogen atom doped graphene MgO-Si composite material: placing the composite material containing magnesium oxide and silicon in a high-temperature reaction furnace, heating at a heating rate of 10 ℃ per minute, uniformly introducing argon at a flow rate of 1L per minute in the heating process, heating to a reaction temperature of 900 ℃, preserving heat, uniformly introducing acetonitrile at a flow rate of 0.5L per minute, uniformly introducing argon at a flow rate of 0.5L per minute, and reacting for 10 minutes to obtain graphene or nitrogen atom doped graphene MgO-Si composite material;
(4) preparing the graphene-based composite material: preparing 1mol/L hydrochloric acid solution, adding the obtained graphene or nitrogen atom doped graphene MgO-Si composite material into 500mL hydrochloric acid solution, etching at 60 ℃ for 20h, removing magnesium oxide, filtering, washing, and drying by air blast to obtain the graphene-based composite material.
The method for preparing the anode material comprises the following steps:
and (3) taking the graphene-based composite material obtained in the step (4) as an active substance, mixing the active substance with conductive carbon black and polyvinylidene fluoride according to the mass ratio of 80:10:10 to obtain paste, and coating the paste on a copper foil to obtain the negative electrode material.
Example 4
The method of preparing the graphene-based composite material was the same as in example 3.
The method for preparing the anode material comprises the following steps:
and (3) taking the graphene-based composite material obtained in the step (3) as an active substance, mixing the active substance with conductive carbon black and polyvinylidene fluoride according to the mass ratio of 90:5:5 to obtain paste, and coating the paste on a copper foil to obtain the negative electrode material.
Evaluation:
1. respectively representing the surface morphology of the graphene-based composite material obtained in the embodiment 1-4, the specific capacity and the electrochemical stability of the button cell prepared from the graphene-based composite material;
2. the test method comprises the following steps:
and (3) morphology observation: observing the surface appearance of the graphene-based composite material through a scanning electron microscope;
electrochemical performance: and (3) carrying out vacuum drying on the copper foil coated with the slurry for 8-15 h at 100 ℃, rolling and shearing the copper foil to prepare the negative plate. A button cell (CR2025) was assembled in a glove box filled with argon gas, using LiPF6 (dimethyl carbonate (DMC): Ethylene Carbonate (EC): 1, volume ratio) with an electrolyte of 1mol/L, a diaphragm being Celgard2400 monolayer polypropylene membrane (PP), and a metallic lithium sheet as a counter electrode. And (3) carrying out charge-discharge cycle performance and rate performance tests on the button cell by using a battery test system (LAND CT2100A5V/10mA), wherein the voltage is 0.01-3V. The specific capacity of the button cell assembled by the negative electrode materials of examples 1-4 is shown in table 1, and the cycle performance data of the button cell assembled by the negative electrode materials of examples 1-4 is shown in table 2.
Table 1 examples 1-4 specific capacity of button cell assembled with negative electrode material
| 0.1C specific capacity, mAh/g | 10C specific capacity, mAh/g | |
| Example 1 | 1247 | 502 |
| Example 2 | 1386 | 534 |
| Example 3 | 1194 | 487 |
| Example 4 | 1178 | 462 |
Table 2 examples 1-4 button cell cycling performance of negative electrode material assembly
| Retention rate for 30 weeks in cycles | Retention rate of 100 weeks in cycles | |
| Example 1 | 98％ | 91％ |
| Example 2 | 96％ | 88％ |
| Example 3 | 97％ | 86％ |
| Example 4 | 93％ | 85％ |
Morphological and structural experimental analysis: fig. 2 is an SEM image of the graphene-based composite material obtained in example 1, and as can be seen from fig. 2, it can be seen that the graphene-based composite material maintains the particle integrity and is a porous material, and as can be seen from the SEM images of the graphene-based composite materials obtained in examples 2 to 4, the graphene-based composite material maintains the particle integrity and is a porous material.
And (3) analyzing electrochemical properties: fig. 3 is a charge-discharge curve diagram of the lithium ion battery assembled with the negative electrode material obtained in example 4, table 1 is specific capacity data of the negative electrode materials obtained in examples 1 to 4, and it can be seen from the data in table 1 that the lithium batteries assembled with the negative electrode materials obtained in examples 1 to 4 have excellent specific capacity, and meanwhile, in combination with table 2, the lithium batteries assembled with the negative electrode materials obtained in examples 1 to 4 have excellent cycle performance, which indicates that the graphene in the graphene-based composite material obtained by the method of the present application relieves the volume change of the lithium battery when the lithium is deintercalated from silicon, and improves the electrochemical stability of the lithium battery.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A method of preparing a graphene-based composite, comprising:
(1) mixing a magnesium salt solution and a carbonate solution, carrying out suction filtration and washing, dispersing the obtained solid material in water to obtain dispersed slurry, mixing the dispersed slurry and silicon-containing powder slurry, and carrying out spray drying on the obtained mixed slurry to obtain a precursor;
(2) placing the precursor in a high-temperature reactor, continuously heating, introducing protective gas, and introducing first gas containing protective gas and hydrogen into the high-temperature reactor after the temperature of the precursor reaches a first preset temperature so as to obtain a composite material containing magnesium oxide and silicon;
(3) placing the composite material containing the magnesium oxide and the silicon in a high-temperature reactor, continuously heating, introducing the protective gas, and after reaching a second preset temperature, introducing a second gas containing the protective gas and a carbon source or containing the protective gas and a nitrogen-containing carbon source into the high-temperature reactor so as to deposit and form graphene or nitrogen-doped graphene on the composite material containing the magnesium oxide and the silicon, thereby obtaining the MgO-Si composite material of the graphene or the nitrogen atom-doped graphene;
(4) and removing magnesium oxide in the graphene or nitrogen atom doped graphene MgO-Si composite material, and then washing the magnesium oxide to be neutral so as to obtain the graphene-based composite material.
2. The method according to claim 1, wherein in the step (1), the magnesium salt solution is at least one of a magnesium nitrate solution, a magnesium chloride solution, a magnesium sulfate solution and a magnesium acetate solution;
optionally, in the step (1), the concentration of magnesium ions in the magnesium salt solution is 0.01-3 mol/L;
optionally, in the step (1), the carbonate solution is at least one of a sodium carbonate solution, a potassium carbonate solution, an ammonium carbonate solution, a sodium bicarbonate solution, a potassium bicarbonate solution, and an ammonium bicarbonate solution;
optionally, in the step (1), the carbonate ion concentration in the carbonate solution is 0.01-3 mol/L;
optionally, in step (1), the volume ratio of the magnesium salt solution to the carbonate solution is 0.5-10: 1.
Optionally, in the step (1), the concentration of the dispersed slurry is 0.01-4 mol/L;
optionally, in the step (1), the concentration of the slurry containing silicon powder is 0.1-10 g/L;
optionally, in the step (1), the mixing volume ratio of the dispersing slurry to the silicon-containing powder slurry is 1-15: 1;
optionally, in the step (1), the feeding speed in the spray drying process is 2-30mL/min, the air inlet temperature is 200-300 ℃, and the air outlet temperature is 95-160 ℃.
3. The method according to claim 1 or 2, wherein in the step (2), the temperature rise rate is 5 to 15 degrees centigrade per minute;
optionally, in step (2), the shielding gas is at least one of nitrogen, argon and helium;
optionally, in the step (2), the first predetermined temperature is 400 to 900 ℃, and the reaction is carried out for 0.5 to 10 hours at the first predetermined temperature;
optionally, in the step (2), in the first gas containing the shielding gas and the hydrogen, the flow rate of the shielding gas is 0.3-10L/min, and the volume ratio of the shielding gas to the hydrogen is 1: (0.03 to 1).
4. The method according to claim 1, wherein in the step (3), the temperature rise rate is 5 to 15 degrees centigrade per minute;
optionally, in step (3), the shielding gas is at least one of nitrogen, argon and helium;
optionally, in the step (3), the second predetermined temperature is 600 to 1200 ℃, and the reaction is carried out for 5 to 120 minutes at the second predetermined temperature;
optionally, in the step (3), the flow of the protective gas in the protective gas-containing and carbon source is 0.3-10L/min, and the volume ratio of the protective gas to the carbon source is 1: (0.05-1);
optionally, in the step (3), in the second gas containing the protective gas and the nitrogen-containing carbon source, the flow rate of the protective gas is 0.3-10L/min, and the volume ratio of the protective gas to the nitrogen-containing carbon source is 1: (0.05-1);
optionally, in step (3), the carbon source comprises at least one of methane, ethane, propane, butane, ethylene, acetylene, propylene, methanol, ethanol, and acetic acid;
optionally, in step (3), the nitrogen-containing carbon source comprises at least one of urea, triethanolamine, diethanolamine, hexamethylenetetramine, aniline, propylene/N, N-dimethylformamide, ammonia, melamine, acetonitrile, propionitrile, butyronitrile, methane/ammonia, pyrrole, acetone/methanol, pyridine, and thiourea.
5. The method according to claim 1, wherein in step (4), magnesium oxide in the graphene or nitrogen atom-doped graphene MgO-Si composite is removed by etching;
optionally, the acid solution of the etching process comprises at least one of hydrochloric acid and nitric acid;
optionally, the concentration of the acid solution is 0.5-1.5 mol/L;
optionally, the etching temperature is 10-90 ℃ and the time is 0.5-12 h.
6. A graphene-based composite material, wherein the graphene-based composite material is prepared by the method according to any one of claims 1 to 5.
7. A method for preparing a negative electrode material, characterized by mixing a graphene-based composite material with a binder and a conductive agent, and then coating a paste on a copper foil, wherein the graphene-based composite material is the graphene-based composite material obtained by the method according to any one of claims 1 to 5 or the graphene-based composite material according to claim 6;
optionally, the binder comprises at least one of polyvinylidene fluoride, sodium carboxymethylcellulose, and polyacrylic acid;
optionally, the conductive agent comprises at least one of carbon nanotubes, acetylene black, and conductive carbon black;
optionally, based on the total mass of the anode material, the mass ratio of the graphene-based composite material to the binder to the conductive agent is (5-95): (1-10): (0-10).
8. A negative electrode material, characterized in that the negative electrode material is prepared by the method of claim 6 or 7.
9. A lithium battery having the negative electrode material obtained by the method of claim 6 or 7 or using the negative electrode material of claim 8.
10. An automobile, characterized in that it has a lithium battery as claimed in claim 9.
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