Method for efficiently preparing hard carbon composite material

Abstract

The invention discloses an efficient preparation method of a hard carbon composite material, which solves the problems of high energy consumption and low efficiency of high-temperature treatment and need of inert gas protection in the existing hard carbon preparation method, high specific capacity and high initial coulombic efficiency are obtained, the prepared product is good in conductivity and high in activity, and the obtained material mainly has the following characteristics: (1) the specific capacity is high and is 145-195mAh / g; (3) first coulombic efficiency gt; 80%.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical energy storage, and specifically relates to a method for efficiently preparing a hard carbon composite material. Background Art

[0002] With the widespread application of drones in different scenarios (such as surveying, exploration, bridge building, natural disasters, etc.), there are more and more scenarios that require drones with long flight time and high payload capacity, so the requirements for the energy storage capacity of electrochemical energy storage devices are also getting higher and higher.

[0003] Due to the special carbon skeleton structure of hard carbon, the development of lithium-ion battery technology with high electrochemical energy storage capacity through hard carbon is considered to be an important way to replace graphite-based lithium-ion battery technology. However, due to the presence of strong lithium-philic structural defects such as oxygen-containing groups in hard carbon, irreversible lithium deposition will occur, leading to the formation of first effect or even dendrites, thus greatly reducing the energy storage capacity and being unfavorable for the development of lithium-ion batteries suitable for long-endurance, high-load drones.

[0004] Removing oxygen-containing groups and repairing structural defects by high temperature and introducing active sites by nitrogen doping while removing oxygen-containing groups are currently the most common and effective methods. However, the current methods mainly achieve the removal of oxygen-containing groups, nitrogen doping and structural defect repair under the action of high temperature, inert gas and ammonia in an atmosphere furnace such as a tubular furnace. Although the effect is good, the energy consumption and efficiency are low, and inert gas protection is required, resulting in extremely high costs. Therefore, the development of more efficient and low-energy deoxidation, nitrogen doping and defect repair methods has become a key technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for efficiently preparing a hard carbon composite material.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for efficiently preparing a hard carbon composite material, characterized in that: comprising:

[0009] Preparation of graphite oxide: Using flake graphite as a precursor, graphite oxide is prepared by chemical exfoliation;

[0010] Preparation of graphene oxide / sucrose composite: graphite oxide and water are stirred evenly to obtain a graphene oxide dispersion, sucrose is added, stirred, and dried to obtain a graphene oxide / sucrose composite;

[0011] Carbonization of graphene oxide / sucrose composite: adding concentrated sulfuric acid to the graphene oxide / sucrose composite to obtain a black loose porous carbon material, which is then rinsed and dried for later use;

[0012] preparing reduced graphene oxide;

[0013] The porous carbon material, urea and reduced graphene oxide are ground and mixed evenly, and then irradiated with microwaves to obtain a hard carbon composite material.

[0014] As a preferred embodiment of the preparation method of the present invention, the chemical stripping method includes Hummers method, Standenmaier method and Brodie method.

[0015] As a preferred embodiment of the preparation method of the present invention, the graphite oxide and water are stirred evenly, wherein the material ratio of graphene oxide to water is 10 mg:1 mL to 30 mg:1 mL.

[0016] As a preferred embodiment of the preparation method of the present invention, wherein: sucrose is added, wherein the mass ratio of graphene oxide to sucrose is 1:5 to 1:10.

[0017] As a preferred embodiment of the preparation method of the present invention, concentrated sulfuric acid is added dropwise to the graphene oxide / sucrose complex, wherein the material ratio of the graphene oxide / sucrose complex to the concentrated sulfuric acid is 2g:3mL to 2g:5mL; and the concentration of the concentrated sulfuric acid is 95% to 98%.

[0018] As a preferred embodiment of the preparation method of the present invention, the material ratio of the porous carbon material to urea is 2:1 to 1:2.

[0019] As a preferred embodiment of the preparation method of the present invention, the material ratio of the porous carbon material to the reduced graphene oxide is 20:1 to 10:1.

[0020] As a preferred embodiment of the preparation method of the present invention, the microwave radiation has a microwave power of 600 to 800 W and a microwave radiation time of 80 to 110 s.

[0021] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application in the efficient preparation of hard carbon composite materials.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention proposes for the first time to utilize reduced graphene oxide to absorb microwaves and quickly release heat to drive urea decomposition, thereby realizing rapid high-temperature heat treatment in the preparation process of hard carbon under air conditions. By utilizing reduced graphene oxide as a microwave absorbing and heating material and uniformly mixing reduced graphene oxide with a hard carbon precursor, on the one hand, the hard carbon precursor can be uniformly and rapidly heated, so that the hard carbon obtained after heat treatment has high uniformity, and on the other hand, it can be compounded with hard carbon to improve the conductivity of hard carbon.

[0024] (2) The present invention prepares reduced graphene oxide doped hard carbon by using graphene oxide and sucrose in combination. On the one hand, the graphene oxide can be used to regulate the structure of the hard carbon. On the other hand, the graphene oxide can be reduced to absorb microwaves and release heat, thereby fully ensuring uniform heat treatment of the hard carbon. Urea is decomposed into carbon dioxide and ammonia. On the one hand, the generated carbon dioxide and ammonia can be used to protect the hard carbon and graphene from being oxidized by air. On the other hand, nitrogen doping can be achieved to improve the electrochemical activity of the hard carbon and obtain a hard carbon composite material with high energy storage capacity.

[0025] (3) The method provided by the present invention is simple to operate, short in time, high in efficiency, low in energy consumption, and conventional in equipment, and can be mass-produced. Among them, the raw materials, reagents, and equipment used in the preparation of graphite oxide, the preparation of graphene oxide / sucrose composites, the carbonization of graphene oxide / sucrose composites, the preparation of reduced graphene oxide, and the preparation of hard carbon composite materials are all commercially available, with a wide range of sources and low cost.

[0026] (4) The present invention prepares a hard carbon composite material, which solves the problems of high energy consumption, low efficiency and the need for inert gas protection in the existing hard carbon preparation method, and obtains a high specific capacity and a high first coulombic efficiency. The prepared product has good conductivity and high activity. The obtained material has the following main characteristics: ① High specific capacity, 145 to 195 mAh / g; ③ First coulombic efficiency> 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0028] Figure 1 This is an optical photograph of the hard carbon composite material prepared in Example 1;

[0029] Figure 2 This is a SEM image of the hard carbon composite material prepared in Example 1;

[0030] Figure 3 This is an EDS image of the hard carbon composite material prepared in Example 1;

[0031] Figure 4 This is a constant current charge and discharge (GCD) diagram of the hard carbon composite material prepared in Example 1;

[0032] Figure 5 The cycle life and coulomb efficiency diagram of the hard carbon composite material prepared in Example 1;

[0033] Figure 6 GCD diagram of the hard carbon material prepared in comparative example. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0037] Example 1

[0038] The first step is to prepare graphite oxide using the Hummers method in chemical exfoliation:

[0039] Weigh 1g of flake graphite and 0.5g of sodium nitrate and place them in a 250mL round-bottom flask, measure 23mL of concentrated sulfuric acid with a weight percentage concentration of 98% and add it to the round-bottom flask, add a magnet, place the round-bottom flask in an ice-water bath, stir for 30min, weigh 3g of potassium permanganate and add it to the reactor, continue stirring for 1h, after the reaction is completed, transfer the reactor to a 35°C water bath, continue stirring for 30min, measure 50mL of distilled water and add it to the round-bottom flask, then transfer the round-bottom flask to a 98°C oil bath, continue stirring for 15min, add 140mL of distilled water and 10mL of H2O2 with a mass fraction of 30% in sequence, centrifuge after the reaction system finally turns bright yellow, then wash with 500mL of hydrochloric acid with a mass fraction of 5% HCl and distilled water in sequence until the solution becomes neutral, then place it on the surface of a watch glass, dry it to obtain graphite oxide (oxygen atom content of 25-30at.%), and set it aside;

[0040] Step 2: Preparation of graphene oxide / sucrose composite:

[0041] 1 g of graphite oxide was placed in a beaker, 50 mL of deionized water was added, and mechanical stirring was performed to obtain a graphene oxide dispersion. 5 g of sucrose was then added, and mechanical stirring was continued to be performed to obtain a graphene oxide dispersion. Finally, the dispersion was placed in an oven at 50° C. and dried for 24 h to obtain a viscous graphene oxide / sucrose composite for later use.

[0042] Step 3: Carbonization of graphene oxide / sucrose composite:

[0043] Take the graphene oxide / sucrose complex, add 9 mL of concentrated sulfuric acid while stirring, so that the brown viscous graphene oxide / sucrose complex completely turns into a black loose porous carbon material, rinse with deionized water, and place in a 50°C oven to dry for 12 h for later use;

[0044] Step 4: Preparation of reduced graphene oxide:

[0045] Take the graphite oxide prepared in the first step and contact it with the outer flame of an alcohol lamp for 3 seconds to transform the brown graphite oxide into black, thereby obtaining reduced graphene oxide for later use.

[0046] Step 5: Preparation of nitrogen-doped hard carbon negative electrode material:

[0047] Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea and 200 mg, grind and mix evenly, place in a microwave oven, set the power to 800 W, and irradiate for 110 s to obtain a hard carbon composite material.

[0048] Example 2

[0049] The first step is to prepare graphite oxide using the Standenmaier method in chemical exfoliation:

[0050] Measure 17.5 mL of concentrated sulfuric acid and 9 mL of concentrated nitric acid into a 250 mL flask and stir for 15 min; weigh 1 g of graphite and slowly add it into the flask; after stirring evenly, add 11 g of potassium chlorate and react for 96 h; wash with 800 mL of distilled water, then with 5% dilute hydrochloric acid, and finally with distilled water until neutral, then place on the surface of a watch glass, dry, and obtain graphite oxide (oxygen atom content of 25-30 at.%) for later use;

[0051] Step 2: Preparation of graphene oxide / sucrose composite:

[0052] 1 g of graphite oxide was placed in a beaker, 50 mL of deionized water was added, and mechanical stirring was performed to obtain a graphene oxide dispersion. 5 g of sucrose was then added, and mechanical stirring was continued to be performed to obtain a graphene oxide dispersion. Finally, the dispersion was placed in an oven at 50° C. and dried for 24 h to obtain a viscous graphene oxide / sucrose composite for later use.

[0053] Step 3: Carbonization of graphene oxide / sucrose composite:

[0054] Take the graphene oxide / sucrose complex, add 9 mL of concentrated sulfuric acid while stirring, so that the brown viscous graphene oxide / sucrose complex completely turns into a black loose porous carbon material, rinse with deionized water, and place in a 50°C oven to dry for 12 h for later use;

[0055] Step 4: Preparation of reduced graphene oxide:

[0056] Take the graphite oxide prepared in the first step and contact it with the outer flame of an alcohol lamp for 3 seconds to transform the brown graphite oxide into black, thereby obtaining reduced graphene oxide for later use.

[0057] Step 5: Preparation of nitrogen-doped hard carbon negative electrode material:

[0058] Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea and 100 mg, grind and mix evenly, place in a microwave oven, set the power to 800 W, and irradiate for 110 s to obtain a hard carbon composite material.

[0059] Example 3

[0060] The first step is to prepare graphite oxide using the Hummers method in chemical exfoliation:

[0061] Weigh 1g of flake graphite and 0.5g of sodium nitrate and place them in a 250mL round-bottom flask, measure 23mL of concentrated sulfuric acid with a weight percentage concentration of 98% and add it to the round-bottom flask, add a magnet, place the round-bottom flask in an ice-water bath, stir for 30min, weigh 3g of potassium permanganate and add it to the reactor, continue stirring for 1h, after the reaction is completed, transfer the reactor to a 35°C water bath, continue stirring for 30min, measure 50mL of distilled water and add it to the round-bottom flask, then transfer the round-bottom flask to a 98°C oil bath, continue stirring for 15min, add 140mL of distilled water and 10mL of H2O2 with a mass fraction of 30% in sequence, centrifuge after the reaction system finally turns bright yellow, then wash with 500mL of hydrochloric acid with a mass fraction of 5% HCl and distilled water in sequence until the solution becomes neutral, then place it on the surface of a watch glass, dry it, and obtain graphite oxide (oxygen atom content of 25-30at.%) for standby use;

[0062] Step 2: Preparation of graphene oxide / sucrose composite:

[0063] 0.5 g of graphite oxide was placed in a beaker, 50 mL of deionized water was added, and mechanical stirring was performed to obtain a graphene oxide dispersion. 5 g of sucrose was then added, and mechanical stirring was continued to be performed to obtain a graphene oxide dispersion. Finally, the dispersion was placed in an oven at 50° C. and dried for 24 h to obtain a viscous graphene oxide / sucrose composite for later use.

[0064] Step 3: Carbonization of graphene oxide / sucrose composite:

[0065] Take the graphene oxide / sucrose complex, add 9 mL of concentrated sulfuric acid while stirring, so that the brown viscous graphene oxide / sucrose complex completely turns into a black loose porous carbon material, rinse with deionized water, and place in a 50°C oven to dry for 12 h for later use;

[0066] Step 4: Preparation of reduced graphene oxide:

[0067] Take the graphite oxide prepared in the first step and contact it with the outer flame of an alcohol lamp for 3 seconds to transform the brown graphite oxide into black, thereby obtaining reduced graphene oxide for later use.

[0068] Step 5: Preparation of nitrogen-doped hard carbon negative electrode material:

[0069] Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea and 200 mg, grind and mix evenly, place in a microwave oven, set the power to 800 W, and irradiate for 90 seconds to obtain a hard carbon composite material.

[0070] Example 4

[0071] The first step is to prepare graphite oxide using the Brodie method in chemical exfoliation:

[0072] Weigh 2g of graphite powder and add it to 3mL of concentrated sulfuric acid containing 3gK2S2O8 and 3gP2O5, heat it at 80℃ for 6h, then cool it to room temperature, dilute it with distilled water, wash it to neutrality, and dry it to obtain pre-oxidized graphite oxide. Weigh 1g of the obtained pre-oxidized graphite and add it to 46mL of concentrated sulfuric acid. Add 3g of potassium permanganate under ice-water bath conditions, and react at 35℃ for 2h. After the reaction, add 46mL of distilled water, then slowly add 280mL of distilled water and 5mL of 30% hydrogen peroxide, centrifuge it while hot, and finally wash it with 500mL of 5% dilute hydrochloric acid and a large amount of distilled water to neutrality, then place it on the surface of a watch glass, dry it, and obtain graphite oxide (oxygen atom content of 25-30at.%), which is ready for use;

[0073] Step 2: Preparation of graphene oxide / sucrose composite:

[0074] 1 g of graphite oxide was placed in a beaker, 50 mL of deionized water was added, and mechanical stirring was performed to obtain a graphene oxide dispersion. 5 g of sucrose was then added, and mechanical stirring was continued to be performed to obtain a graphene oxide dispersion. Finally, the dispersion was placed in an oven at 50° C. and dried for 24 h to obtain a viscous graphene oxide / sucrose composite for later use.

[0075] Step 3: Carbonization of graphene oxide / sucrose composite:

[0076] Take the graphene oxide / sucrose complex, add 15 mL of concentrated sulfuric acid while stirring, so that the brown viscous graphene oxide / sucrose complex completely turns into a black loose porous carbon material, rinse with deionized water, and place in a 50°C oven to dry for 12 hours for later use;

[0077] Step 4: Preparation of reduced graphene oxide:

[0078] Take the graphite oxide prepared in the first step and contact it with the outer flame of an alcohol lamp for 3 seconds to transform the brown graphite oxide into black, thereby obtaining reduced graphene oxide for later use.

[0079] Step 5: Preparation of nitrogen-doped hard carbon negative electrode material:

[0080] Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea and 200 mg, grind and mix evenly, place in a microwave oven, set the power to 700 W, and irradiate for 110 s to obtain a hard carbon composite material.

[0081] Example 5

[0082] The first step is to prepare graphite oxide using the Hummers method in chemical exfoliation:

[0083] Weigh 1g of flake graphite and 0.5g of sodium nitrate and place them in a 250mL round-bottom flask, measure 23mL of concentrated sulfuric acid with a weight percentage concentration of 98% and add it to the round-bottom flask, add a magnet, place the round-bottom flask in an ice-water bath, stir for 30min, weigh 3g of potassium permanganate and add it to the reactor, continue stirring for 1h, after the reaction is completed, transfer the reactor to a 35°C water bath, continue stirring for 30min, measure 50mL of distilled water and add it to the round-bottom flask, then transfer the round-bottom flask to a 98°C oil bath, continue stirring for 15min, add 140mL of distilled water and 10mL of H2O2 with a mass fraction of 30% in sequence, centrifuge after the reaction system finally turns bright yellow, then wash with 500mL of hydrochloric acid with a mass fraction of 5% HCl and distilled water in sequence until the solution becomes neutral, then place it on the surface of a watch glass, dry it, and obtain graphite oxide (oxygen atom content of 25-30at.%) for standby use;

[0084] Step 2: Preparation of graphene oxide / sucrose composite:

[0085] 0.5 g of graphite oxide was placed in a beaker, 50 mL of deionized water was added, and mechanical stirring was performed to obtain a graphene oxide dispersion. 5 g of sucrose was then added, and mechanical stirring was continued to be performed to obtain a graphene oxide dispersion. Finally, the dispersion was placed in an oven at 50° C. and dried for 24 h to obtain a viscous graphene oxide / sucrose composite for later use.

[0086] Step 3: Carbonization of graphene oxide / sucrose composite:

[0087] Take the graphene oxide / sucrose complex, add 9 mL of concentrated sulfuric acid while stirring, so that the brown viscous graphene oxide / sucrose complex completely turns into a black loose porous carbon material, rinse with deionized water, and place in a 50°C oven to dry for 12 h for later use;

[0088] Step 4: Preparation of reduced graphene oxide:

[0089] Take the graphite oxide prepared in the first step and contact it with the outer flame of an alcohol lamp for 3 seconds to transform the brown graphite oxide into black, thereby obtaining reduced graphene oxide for later use.

[0090] Step 5: Preparation of nitrogen-doped hard carbon negative electrode material:

[0091] Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea and 200 mg, grind and mix evenly, place in a microwave oven, set the power to 800 W, irradiate for 80 seconds, and obtain a hard carbon composite material.

[0092] Comparative Example 1

[0093] The first step is water treatment of sucrose:

[0094] Take 5g of sucrose and put it in a beaker, add 50mL of deionized water, stir mechanically to obtain a uniform sucrose solution, and finally dry it in a 50℃ oven for 24h to obtain viscous sucrose for later use;

[0095] Step 4: Carbonization of sucrose:

[0096] Take viscous sucrose, stir, and drop 9 mL of concentrated sulfuric acid to completely turn the colorless sucrose into black loose porous carbon material, rinse with deionized water, and place in a 50 ° C oven to dry for 12 hours for use;

[0097] S5. Preparation of nitrogen-doped hard carbon negative electrode material: Take 2 g of the porous carbon material obtained by carbonization, add 2 g of urea, grind and mix evenly, place in a tubular furnace protected by argon at 800°C and calcine for 6 hours to obtain a nitrogen-doped hard carbon negative electrode material.

[0098] Table 1

[0099] sample Specific capacity (mAh / g) First coulombic efficiency (%) Example 1 147.3 99.8％ Example 2 195.1 89.1％ Example 3 168.5 92.9％ Example 4 182.9 88.4％ Example 5 180.7 83.9％ Comparative Example 1 73 44.8％

[0100] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A method for efficiently preparing a hard carbon composite material, characterized in that: include, Preparation of graphite oxide: Using flake graphite as a precursor, graphite oxide is prepared by chemical exfoliation; Preparation of graphene oxide / sucrose composite: graphite oxide and water are stirred evenly to obtain a graphene oxide dispersion, sucrose is added, stirred, and dried to obtain a graphene oxide / sucrose composite; Carbonization of graphene oxide / sucrose composite: adding concentrated sulfuric acid to the graphene oxide / sucrose composite to obtain a black loose porous carbon material, which is then rinsed and dried for later use; preparing reduced graphene oxide; The porous carbon material, urea and reduced graphene oxide are ground and mixed evenly, and then irradiated with microwaves to obtain a hard carbon composite material.

2. The preparation method according to claim 1, characterized in that: The chemical peeling methods include Hummers method, Standenmaier method and Brodie method.

3. The preparation method according to claim 1, characterized in that: The graphite oxide and water are stirred evenly, wherein the material ratio of graphene oxide to water is 10 mg:1 mL to 30 mg:1 mL.

4. The preparation method according to claim 1, characterized in that: Sucrose is added, wherein the mass ratio of graphene oxide to sucrose is 1:5 to 1:

10.

5. The preparation method according to claim 1, characterized in that: The concentrated sulfuric acid is added dropwise to the graphene oxide / sucrose complex, wherein the material ratio of the graphene oxide / sucrose complex to the concentrated sulfuric acid is 2g:3mL-2g:5mL; and the concentration of the concentrated sulfuric acid is 95%-98%.

6. The preparation method according to claim 1, characterized in that: The material ratio of the porous carbon material to urea is 2:1 to 1:

2.

7. The preparation method according to claim 1, characterized in that: The material ratio of the porous carbon material to the reduced graphene oxide is 20:1 to 10:

1.

8. The preparation method according to claim 1, characterized in that: The microwave radiation has a power of 600 to 800 W and a microwave radiation time of 80 to 110 s.

9. Use of the hard carbon composite material obtained by the preparation method according to any one of claims 1 to 8.

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