Preparation and application of hollow carbon / graphene composite carbon

Abstract

The application belongs to the technical field of electrode materials, and particularly discloses a preparation and application of hollow carbon / graphene composite carbon, which comprises the following steps: preparing a graphene oxide aqueous solution; taking deionized water, adding tetraethyl orthosilicate, stirring, and adjusting the pH value by using ammonia water; adding dopamine hydrochloride into the tetraethyl orthosilicate hydrolysate, stirring, removing the supernatant by centrifugation, and then vacuum drying; taking the graphene aqueous solution, adding a silicon-carbon precursor; after sufficient stirring, freezing, and drying; placing in a tube furnace, carbonizing, washing three times with deionized water, and then vacuum drying; soaking in hydrofluoric acid, washing three times with deionized water, and then vacuum drying. The preparation and application of the hollow carbon / graphene composite carbon can solve the problem of insufficient chemical kinetic characteristics of existing carbon-based sodium ion battery negative materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to preparation and application of hollow carbon / graphene composite carbon. BACKGROUND

[0002] Currently, heteroatom-doped carbon can improve its electron-withdrawing properties, electrolyte wettability, electrochemical activity, specific surface area, etc. due to the introduction of heteroatoms. Currently, strategies such as precursor mixing or post-processing doping are often used to introduce heteroatoms into the carbon skeleton to regulate the electronic structure and surface properties of the material. Although heteroatom-doped carbon exhibits excellent performance in the fields of electrochemical energy storage, catalysis and sensing, its electrochemical specific capacity and stability still need to be further improved to meet the demand for its large-scale application. Current solutions include micro-interface structure design, heteroatom modification, and composite structure construction. Therefore, there is a need in the art to develop a preparation and application of hollow carbon / graphene composite carbon that can effectively solve the above problems. SUMMARY

[0003] The purpose of the present application is to provide a preparation and application of hollow carbon / graphene composite carbon. The metal / non-metal co-doped multi-state three-dimensional carbon composite material prepared by the preparation method can solve the problem of insufficient chemical kinetic characteristics of existing carbon-based sodium ion battery negative materials.

[0004] To achieve the above-mentioned purpose, the present application provides a preparation of hollow carbon / graphene composite carbon, comprising the following steps:

[0005] Step S1, preparing an aqueous solution of graphene oxide;

[0006] Step S2, taking deionized water and adding tetraethyl orthosilicate, so that the volume concentration of tetraethyl orthosilicate is 0.05-0.22 g / mL -1 If the volume concentration of tetraethyl orthosilicate is too high, the silica particles obtained by hydrolysis will be large, and if the volume concentration of tetraethyl orthosilicate is too low, the manufacturing cost will increase during the process of hydrolyzing the silica. Stirring, adjusting the pH value with ammonia water, and obtaining a tetraethyl orthosilicate hydrolysate;

[0007] Step S3, adding hydrochloric acid dopamine to the tetraethyl orthosilicate hydrolysate, so that the mass concentration of hydrochloric acid dopamine is 2.5-4.5 mg / mL -1 If the mass concentration of dopamine is too high, the carbon coating on the outer layer of the silicon-based particle precursor will be too thick, the coating layer will be too thick, and ion shuttling will be difficult in the later stage; if the mass concentration of dopamine is too low, the carbon coating on the outer layer of the silicon-based particle precursor will be too thin, the coating layer will be incomplete, and the confinement effect of ion migration in the later stage will be insufficient; stirring, centrifugation to remove the supernatant, and then vacuum drying at a temperature of 60°C for 24h to obtain a silicon-carbon precursor;

[0008] Step S4, take 50 mL graphene aqueous solution, add silicon-carbon precursor, so that the mass concentration of silicon-carbon precursor is 0.5-3 mg mL -1 The mass concentration of the suspension is too high, and the subsequent three-dimensional carbon skeleton cannot be fully supported. The mass concentration of the suspension is too low, and the amount of nanoscale carbon sheet units supported by the subsequent three-dimensional carbon skeleton is insufficient. After sufficient stirring, freeze for 12 h, and then dry for 12 h;

[0009] Step S5, place in a tube furnace, carbonize under nitrogen or argon atmosphere, wash with deionized water three times, and then vacuum dry at a temperature of 60 DEG C for 24 h;

[0010] Step S6, soak in hydrofluoric acid for 12-36 h. If the etching time in the hydrofluoric acid is too long, the carbonaceous material will be damaged. If the etching time is too short, the siliceous material cannot be completely removed, affecting the electrochemical activity of the composite material. Wash with deionized water three times, and then vacuum dry at a temperature of 60 DEG C for 24 h to obtain the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0011] The prepared hollow carbon / graphene composite carbon has the following characteristics:

[0012] 1) Size characteristics: The composite carbon material is a micro-nano composite material, the hollow carbon has a sub-nanoscale diameter, and the graphene unit is a nanoscale carbonaceous layer. Sub-nanoscale materials can improve the rate characteristics of the electrode, and nanoscale materials can enrich the active sites required by the carriers in the electrochemical reaction process, thereby improving the electrochemical reaction reversibility of the electrode material. In order to fully exert the electrochemical activity of the micro-nano carbonaceous composite carbon, the diameter of the hollow carbon carried on the graphene is less than 300 nm.

[0013] 2) Structure and performance characteristics:

[0014] The carbonaceous material mainly realizes energy storage through intercalation reaction, and has the disadvantage of low specific capacity. The composite carbon improves the energy storage mechanism of the composite carbon through structure regulation and improves the electrochemical stability. After the unit materials are combined, the composite material exhibits high capacity and long cycle performance.

[0015] 3) Process characteristics: The composite material is obtained by combining hydrothermal method and medium-temperature carbonization heat treatment, which is a traditional method and simple process, and is easy to realize.

[0016] 4) Cost characteristics: The unit materials in the composite carbon are mainly carbon, and carbon is a conventional element. Therefore, improving the electrochemical performance of the composite material and developing related energy storage material technology have advantages in reducing the cost of the composite material.

[0017] Preferably, in step S1, the concentration of the graphene oxide aqueous solution is 3-6 mg / mL, and the mass concentration of the graphene oxide is too low to make the surface of the melamine foam fiber load insufficient nanocarbon sheet units, and the mass concentration of the graphene oxide is too high to cause the graphene to be reduced to graphene during the subsequent carbonization process, and the graphene is aggregated, so that the electrochemical performance of the graphene is insufficient.

[0018] Preferably, in step S2, the deionized water is 40-70 mL, and the deionized water is too low to cause the tetraethyl silicate to be insufficiently hydrolyzed, and the deionized water is too high to cause water resource waste. The stirring time is 0.5-1.5 h, and the stirring time is too short to cause the tetraethyl silicate to be insufficiently hydrolyzed, and the stirring time is too short to cause the energy consumption in the material preparation process to increase. The pH value is 9-11, and the pH value is too high to affect the hydrolysis product of the tetraethyl silicate to be a silicic acid complex, and the pH value is too low to affect the hydrolysis speed of the tetraethyl silicate to decrease, thereby prolonging the material preparation cycle.

[0019] Preferably, in step S3, the stirring time is 12-36 h, the centrifugal speed is 6000-10000 r / min, and the centrifugal time is 5-10 min.

[0020] Preferably, in step S5, the heating rate of the tube furnace carbonization is 2-6 ℃ / min, the carbonization temperature is 600-900 ℃, and the holding time is 1.5-3 h.

[0021] The heating rate is too low to increase the energy consumption in the preparation process, and the heating rate is too fast to cause the space structure of the composite carbon to collapse during the formation process. The carbonization temperature is too low to cause the carbonization degree to be insufficient, and the electronic conductivity of the material is insufficient, and the carbonization temperature is too high to cause the increase of the carbonization degree to stop the electrochemical performance gain of the composite material, and the preparation cost of the material to increase unreasonably. The carbonization time is too long to cause the cost to increase, and the carbonization time is too short to cause the graphitization degree of the carbon material to be insufficient, and the conductivity of the composite material to be insufficient.

[0022] The application also provides a hollow carbon / graphene composite carbon prepared by the method.

[0023] The application specifically is:

[0024] The prepared hollow carbon / graphene composite carbon, conductive carbon black or carbon nanotube and polyvinylidene fluoride are uniformly mixed in N-methyl pyrrolidone according to a mass ratio of 7-8:2-1:1, and are stirred for 0.2-0.5 h, and the uniform electrode slurry is obtained; the obtained uniform electrode slurry is coated on a copper foil, and the loading amount reaches 3-8 g / cm 2, the loading amount is too low, and the production reference value is small, and too high will cause the material at the near collector to not fully play its performance, therefore, the loading amount is in the appropriate range. After coating, place in a vacuum drying box, dry at 60-90 DEG C for 12-48h, punch into a circular electrode sheet (as a negative electrode) with a diameter of 12mm or a card battery corresponding electrode sheet size; finally, in a glove box, with a sodium foil, a two-electrode system battery is assembled into a CR2025 button cell or a corresponding card battery.

[0025] The application adopts the above-mentioned preparation and application of the hollow carbon / graphene composite carbon, and has the following beneficial effects:

[0026] 1. The metal / non-metal co-doped multi-state three-dimensional carbon prepared by the application has high sodium storage specific capacity. The application introduces metal and non-metal heterogeneous atoms into the composite material to provide sufficient electron-accepting sites during the synthesis of the composite carbon, which is beneficial to sodium ion migration and diffusion, and can improve the sodium storage specific capacity of the composite carbon material. The battery prepared by using the composite material (electrode) prepared by the application can have a reversible capacity of 329.5 mAh / g at a current density of 0.05 A / g.

[0027] 2. The composite material prepared by the application can relieve the volume strain of the composite carbon electrode in the electrochemical process. The hollow carbon can provide rich electronic transport channels, and has a positive effect on the distribution of the thin carbon. The unique spatial structure of the composite carbon provides rich active sites and stable electrochemical structure for ion adsorption / desorption and intercalation / extraction, and can relieve the volume expansion of the composite carbon electrode material in the electrochemical reaction process, which mainly uses adsorption / desorption reaction as the main sodium storage mechanism.

[0028] 3. The composite carbon material prepared by the application has good electrochemical structure stability, and the composite carbon electrode sheet prepared by the application has excellent cycle performance. The reaction kinetics of the electrode material directly reflects the ion transport efficiency of the electrode material. The composite carbon combines the kinetic advantages of the hollow carbon unit and the two-dimensional graphene unit. The space distribution of the composite carbon is expanded by the introduction of graphene. The carrier shuttling and reaction kinetics sites are increased by the introduction of the hollow carbon unit. The reaction reversibility of the composite carbon material is improved by the structure regulation of the composite carbon material, and a sodium ion battery with excellent cycle stability is obtained. When the current density is 0.1 Ag -1 , the reversible capacity retention rate can reach 93.4% after 1000 cycles.

[0029] 4, The prepared composite material has good electrochemical reaction reversibility, and the prepared composite carbon electrode sheet (battery) has excellent rate performance. Compared with hollow carbon, the composite carbon can improve the thermodynamic stability of the electrode material and the electrochemical reaction kinetics of ions, and provide more abundant electrochemical oxidation-reduction active centers, which accelerates the transport of ions / electrons and improves the specific capacity of the composite electrode material. As can be seen from the rate curve, the specific capacity of the composite carbon material is as high as 329.6 mAh / g, 292.9 mAh / g, 256.1 mAh / g, 207.2 mAh / g, 155.3 mAh / g, 105.4 mAh / g, 71.6 mAh / g, and 47.3 mAh / g under the current density of 0.05 Ag -1 , 0.1 Ag -1 , 0.3 Ag -1 , 0.5 Ag -1 , 0.8 Ag -1 , 1.0 Ag -1 , 3.0 Ag -1 , 5.0 Ag -1 . And when the current density returns to small, the capacity is basically not attenuated, which again shows that the obtained composite material has excellent reaction reversibility.

[0030] 5, The preparation steps of the application are simple, the reaction conditions are mild and easy to control, and the raw materials used are low in cost, suitable for industrial application. The hydrothermal reaction used in the preparation process of the composite carbon material can be completed by using a common air drying oven, and all the heat treatment processes in the tubular furnace are low-temperature heating, which is conventional equipment without harsh conditions. This provides the possibility for large-scale production for the ton-level reaction kettle in the conventional chemical plant. The carbonaceous material composition unit in the composite material provides production and application guarantee for the low cost and environmental friendliness of the composite material, which creates favorable conditions for large-scale production of the composite material.

[0031] The technical solutions of the application will be further described in detail below by means of the drawings and examples. DETAILED DESCRIPTION

[0032] Figure 1 SEM morphology of the prepared hollow carbon / graphene composite carbon in Example 1 of the application;

[0033] Figure 2 Raman spectrum of the prepared hollow carbon / graphene composite carbon in Example 1 of the application;

[0034] Figure 3 Thermogravimetric curve of the prepared hollow carbon / graphene composite carbon and hollow carbon in Example 1 of the application;

[0035] Figure 4 The constant current charge-discharge curve of the hollow carbon / graphene composite carbon in the first embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0036] Figure 5 The constant current charge-discharge curve of the hollow carbon in the first embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0037] Figure 6 The rate performance graph of the hollow carbon / graphene composite carbon in the first embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0038] Figure 7 The cycle performance curve of the hollow carbon / graphene composite carbon in the first embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0039] Figure 8 The SEM morphology graph of the hollow carbon / graphene composite carbon prepared in the second embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0040] Figure 9 The SEM morphology graph of the hollow carbon / graphene composite carbon prepared in the third embodiment of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0041] Figure 10 The SEM morphology graph of the hollow carbon / graphene composite carbon prepared in the first comparative example of the preparation and application of the hollow carbon / graphene composite carbon of the present application;

[0042] Figure 11 The SEM morphology graph of the hollow carbon / graphene composite carbon prepared in the second comparative example of the preparation and application of the hollow carbon / graphene composite carbon of the present application. DETAILED DESCRIPTION

[0043] The technical solutions of the present application are further described below through the drawings and examples.

[0044] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those skilled in the art to which the present application belongs.

[0045] Example 1

[0046] A hollow carbon / graphene composite carbon is prepared, comprising the following steps:

[0047] Step S1, preparing a graphene oxide aqueous solution with a concentration of 4 mg / mL;

[0048] Step S2, taking 50 mL of deionized water, adding tetraethyl orthosilicate, and making the volume concentration of the tetraethyl orthosilicate 0.15 g / mL-1 Stir for 0.5 h, adjust the pH to 9 with ammonia water to obtain tetraethyl silicate hydrolysate;

[0049] Step S3: Add dopamine hydrochloride to the tetraethyl silicate hydrolysate to make the mass concentration of dopamine hydrochloride 3.5 mg / mL. -1 Stir for 24 hours, centrifuge to remove supernatant at a speed of 8000 r / min for 8 min, and then vacuum dry at 60℃ for 24 hours to obtain silicon-carbon precursor;

[0050] Step S4: Take 50 mL of graphene aqueous solution and add silicon carbon precursor to make the mass concentration of silicon carbon precursor 2.5 mg / mL. -1 The suspension was thoroughly stirred, then frozen for 12 hours, and then dried for 12 hours.

[0051] Step S5: Place it in a tube furnace and carbonize it under a nitrogen or argon atmosphere. The heating rate is 5℃ / min, the carbonization temperature is 800℃, the holding time is 2h, and it is cleaned three times with deionization. Then it is vacuum dried at 60℃ for 24h.

[0052] Step S6: Immerse in hydrofluoric acid for 24 hours, rinse three times with deionized water, and then vacuum dry at 60°C for 24 hours to obtain the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0053] like Figure 1 As shown, sub-nanometer-sized hollow carbon is relatively uniformly dispersed on the surface of the graphene sheet, with a diameter of approximately 300 nm.

[0054] like Figure 2 As shown, hollow carbon / graphene composite carbon was successfully synthesized.

[0055] like Figure 3 As shown, the specific areas of hollow carbon / graphene composite carbon and hollow carbon are approximately 1026.3 and 873.5 m², respectively. 2 g -1 The hollow carbon preparation process is as follows: step S6 is omitted, and other parameters and operations are the same as in Example 1.

[0056] Electrode preparation / battery assembly: The prepared hollow carbon / graphene composite carbon, conductive carbon black, and polyvinylidene fluoride were mixed uniformly in N-methylpyrrolidone at a mass ratio of 7:2:1 and stirred for 0.5 h. The resulting uniform electrode slurry was coated onto copper foil, achieving a loading of 3.5 mg / cm³. 2 After preparation, the electrode is dried in a vacuum drying oven at 60°C for 12 hours and then punched into a circular electrode sheet with a diameter of 12 mm. In a glove box, it is matched with a sodium metal two-electrode battery system, model CR2025, with a voltage test range of 0.01-3V.

[0057] As shown in Figures 4-5 , the galvanostatic charge-discharge curve of the battery in Example 1 at a current density of 0.05 Ag -1 , it can be seen from the figure that after cycling to the third cycle, the curve overlaps, and the performance begins to stabilize, which is due to the formation of SEI film, and the charge-discharge platform of the material is about 0.82V.

[0058] As shown in Figure 6 , at a current density of 0.05 Ag -1 , 0.1 Ag -1 , 0.3 Ag -1 , 0.5 Ag -1 , 0.8 Ag -1 , 1.0 Ag -1 , 3.0 Ag -1 , 5.0 Ag -1 , the reversible capacity can reach 329.6mAh g -1 , 292.9mAh g -1 , 256.1mAh g -1 , 207.2mAh g -1 , 155.3mAh g -1 , 105.4mAh g -1 , 71.6mAh g -1 , 47.3mAh g -1 .

[0059] As shown in Figure 7 , the cycle life of the battery in Example 1 at a current density of 0.1 Ag -1 , after 1000 cycles, the capacity retention rate reaches 93.4%. It can be seen that the electrode material / battery prepared in this embodiment shows good cycle stability.

[0060] Example 2

[0061] A hollow carbon / graphene composite carbon is prepared, comprising the following steps:

[0062] Step S1, preparing a graphene oxide aqueous solution with a concentration of 6mg / mL;

[0063] Step S2, taking 65mL of deionized water, adding tetraethyl orthosilicate, so that the volume concentration of tetraethyl orthosilicate is 0.20gmL -1 , stirring for 1.5h, adjusting the pH value to 11 with ammonia water to obtain a tetraethyl orthosilicate hydrolysate;

[0064] Step S3, adding dopamine hydrochloride to the tetraethyl orthosilicate hydrolysate, so that the mass concentration of dopamine hydrochloride is 4.5mg / mL-1 , stirring for 36 h, removing the supernatant by centrifugation at 9000 r / min for 10 min, and vacuum drying at 60°C for 24 h to obtain a silicon-carbon precursor;

[0065] Step S4, 50 mL of the graphene aqueous solution was taken, and the silicon-carbon precursor was added to obtain a suspension with a mass concentration of 2.5 mg / mL of the silicon-carbon precursor; after sufficient stirring, freezing was performed for 12 h, and drying was performed for 12 h; -1

[0066] Step S5, carbonization was performed in a tube furnace under a nitrogen or argon atmosphere, the heating rate was 5°C / min, the carbonization temperature was 900°C, the holding time was 2 h, the material was washed with deionized water three times, and vacuum drying was performed at 60°C for 24 h;

[0067] Step S6, immersion in hydrofluoric acid was performed for 36 h, washing with deionized water was performed three times, and vacuum drying was performed at 60°C for 24 h to obtain the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0068] Electrode preparation / battery assembly: the prepared hollow carbon / graphene composite carbon, conductive carbon black, and polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1, and stirring was performed for 0.5 h. The obtained uniform electrode slurry was coated on a copper foil, the loading amount reached 8 mg / cm 2 , and after preparation, drying was performed in a vacuum drying box at 90°C for 36 h, and punching was performed to obtain a circular electrode sheet with a diameter of 12 mm. A two-electrode battery system was matched with metallic sodium in a glove box, the model was CR2025, and the voltage test range was 0.01-3 V.

[0069] As shown in Figure 8 , the dispersity of the hollow carbon was relatively low compared to Example 1, which was related to the concentration and treatment time of the nano-carbon layer precursor. After the mass ratio of the metal / non-metal co-doped multi-state three-dimensional carbon composite material, conductive carbon black, and polyvinylidene fluoride was adjusted from 7:2:1 to 8:1:1, the specific capacity retention rate of the battery after 1000 cycles was 80.7%.

[0070] The electrochemical performance of the composite material obtained in Example 2 was lower than that in Example 1, and the overall performance of the battery decreased. The microstructure of the carbon composite material determines the carrier transport kinetics, and the carbon sheet structure and dispersity thereof were not as good as those in Example 1. In addition, the proportion of the conductive agent was reduced, which resulted in a lower electron collection effect than that in Example 1, and finally led to a decrease in the cycle performance of the battery.

[0071] Example Three

[0072] A preparation method of a hollow carbon / graphene composite carbon, comprising the following steps:​

[0073] Step S1: Prepare an aqueous solution of graphene oxide with a concentration of 3 mg / mL;

[0074] Step S2: Take 45 mL of deionized water and add tetraethyl orthosilicate to make the volume concentration of tetraethyl orthosilicate 0.10 g / mL. -1 Stir for 0.5 h, adjust the pH to 11 with ammonia water to obtain tetraethyl silicate hydrolysate;

[0075] Step S3: Add dopamine hydrochloride to the tetraethyl silicate hydrolysate to make the mass concentration of dopamine hydrochloride 2.5 mg / mL. -1 Stir for 18 hours, centrifuge to remove supernatant at 6000 r / min for 6 min, and then vacuum dry at 60℃ for 24 hours to obtain silicon-carbon precursor.

[0076] Step S4: Take 50 mL of graphene aqueous solution and add silicon carbon precursor to make the mass concentration of silicon carbon precursor 1.5 mg / mL. -1 The suspension was thoroughly stirred, then frozen for 12 hours, and then dried for 12 hours.

[0077] Step S5: Place it in a tube furnace and carbonize it under a nitrogen or argon atmosphere. The heating rate is 5℃ / min, the carbonization temperature is 900℃, the holding time is 2h, and it is cleaned three times with deionization. Then it is vacuum dried at 60℃ for 24h.

[0078] Step S6: Immerse in hydrofluoric acid for 36 hours, rinse three times with deionized water, and then vacuum dry at 60°C for 24 hours to obtain the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0079] Electrode preparation / battery assembly: The prepared hollow carbon / graphene composite carbon, conductive carbon black, and polyvinylidene fluoride (mass ratio 7:2:1) were mixed uniformly in N-methylpyrrolidone and stirred for 0.5 h. The resulting uniform electrode slurry was coated onto copper foil, achieving a loading of 4 mg / cm³. 2 In a vacuum drying oven, at 90℃ for 24 hours, the electrode sheets were punched into circular electrode sheets with a diameter of 12mm. In a glove box, they were combined with sodium metal to form a two-electrode system. The battery assembly model was CR2025 button cell, and the voltage test range was 0.01-3V.

[0080] like Figure 9 As shown, the dispersion of the metal / non-metal co-doped three-dimensional multi-configuration composite carbon is not as good as in Examples 1 and 2, and it is not well dispersed within the three-dimensional carbon voids. This is related to insufficient concentration, amount, and processing time of the carbon sheet precursor. At a current density of 0.05 Ag... -1The reversible capacity was 268.4 mAh g -1 0.1 Ag -1 The capacity retention rate was 70.7% after 1000 cycles.

[0081] The microstructure of the composite carbon as the main active material in the electrode material and the distribution of the hollow carbon constituting unit directly affect the comprehensive performance of the electrode material. Since the overall preparation process parameters are lower than those of Example One, the electrochemical performance is relatively low. Since the hollow carbon on the surface of the graphene is sparse, and the electrode material activity cannot be compensated after adjusting the electrode material ratio, the electrochemical performance is lower than that of Example One.

[0082] Comparative Example One

[0083] A preparation method of hollow carbon / graphene composite carbon, comprising the following steps:

[0084] Step S1, preparing a graphene oxide aqueous solution with a concentration of 7.5 mg / mL;

[0085] Step S2, taking 90 mL of deionized water, adding tetraethyl orthosilicate, so that the volume concentration of the tetraethyl orthosilicate is 0.30 g / mL -1 , stirring for 1.5 h, adjusting the pH value to 11 with ammonia water, and obtaining a tetraethyl orthosilicate hydrolysate;

[0086] Step S3, adding dopamine hydrochloride to the tetraethyl orthosilicate hydrolysate, so that the mass concentration of the dopamine hydrochloride is 6.5 mg / mL -1 , stirring for 36 h, removing the supernatant by centrifugation at a speed of 9000 r / min for 6 min, and then vacuum drying at a temperature of 60°C for 24 h to obtain a silicon-carbon precursor;

[0087] Step S4, taking 50 mL of the graphene aqueous solution, adding the silicon-carbon precursor to obtain a suspension with a mass concentration of 4.5 mg / mL -1 of the silicon-carbon precursor; after sufficient stirring, freezing for 12 h, and then drying for 12 h;

[0088] Step S5, placing in a tube furnace, and performing carbonization under a nitrogen or argon atmosphere, with a heating rate of 6°C / min, a carbonization temperature of 900°C, and a holding time of 4 h; then washing with deionized water three times, and then vacuum drying at a temperature of 60°C for 24 h;

[0089] Step S6, soaking in hydrofluoric acid for etching for 36 h, washing with deionized water three times, and then vacuum drying at a temperature of 60°C for 24 h to obtain the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0090] Electrode preparation / battery assembly: the prepared hollow carbon / graphene composite carbon, conductive carbon black and polyvinylidene fluoride (mass ratio 7:2:1) were mixed uniformly in N-methyl pyrrolidone, and stirred for 0.5 h. The slurry was coated on a copper foil, with a loading of about 1 mg / cm 2 , vacuum dried at 60 °C for 24 h, punched into a circular electrode sheet with a diameter of 12 mm, and assembled into a two-electrode system battery with sodium metal in a glove box. The voltage test range was 0.01-3 V.

[0091] As shown in Figure 10 , the composite carbon showed significant agglomeration, and a micro-nano composite material with a reasonable distribution of carbon units could not be obtained. Because the structure of the composite carbon was not ideal, the obtained electrochemical performance was low, with a specific capacity of only 227.2 mAh g -1 (0.05Ag -1 ).

[0092] Comparative Example Two

[0093] A hollow carbon / graphene composite carbon was prepared, including the following steps:

[0094] Step S1, preparing a graphene oxide aqueous solution with a concentration of 1.5 mg / mL;

[0095] Step S2, taking 40 mL of deionized water, adding tetraethyl orthosilicate, so that the volume concentration of the tetraethyl orthosilicate is 0.02 g mL -1 , stirring for 0.5 h, adjusting the pH value to 7.5 with ammonia water, to obtain a tetraethyl orthosilicate hydrolysate;

[0096] Step S3, adding dopamine hydrochloride to the tetraethyl orthosilicate hydrolysate, so that the mass concentration of the dopamine hydrochloride is 1.5 mg mL -1 , stirring for 6 h, removing the supernatant by centrifugation at a speed of 5000 r / min for 5 min, and then vacuum drying at a temperature of 60 °C for 24 h to obtain a silicon-carbon precursor;

[0097] Step S4, taking 50 mL of a graphene aqueous solution, adding the silicon-carbon precursor to obtain a suspension with a mass concentration of 0.5 mg mL -1 ; after sufficient stirring, freezing for 12 h, and then drying for 12 h;

[0098] Step S5, placing in a tube furnace, and performing carbonization under a nitrogen or argon atmosphere, with a heating rate of 6 °C / min, a carbonization temperature of 500 °C, and a holding time of 1 h. Then, washing with deionized water three times, and vacuum drying at a temperature of 60 °C for 24 h;

[0099] Step S6, soaking in hydrofluoric acid, etching time is 2h, washed with deionized water three times, and then vacuum dried at 60℃ for 24h, which is the prepared hollow carbon / graphene composite carbon (HCS / rGO).

[0100] Electrode preparation / battery assembly: the prepared hollow carbon / graphene composite carbon, conductive carbon black and polyvinylidene fluoride (mass ratio of 8:1:1) were mixed uniformly in N-methyl pyrrolidone, and stirred for 0.1h. The obtained slurry was coated on a copper foil with a loading of about 1mg / cm2, vacuum dried (60℃, 12h), punched into a circular electrode sheet with a diameter of 12mm, and assembled into a two-electrode system battery with a metal sodium foil in a glove box. The voltage test range was 0.01-3V, and the specific capacity was only 199.5mAh g -1 (0.05Ag -1 ).

[0101] As shown in Figure 11 , due to the change of the preparation process of the composite carbon, the electrochemical performance of the composite carbon as the main electrode active material is reduced due to the insufficient carbonization treatment temperature and etching time, resulting in a low final specific capacity of the battery.

[0102] Based on the data of Examples 1-3 and Comparative Examples 1-2, the summary analysis is as follows:

[0103] Structural factor consideration: the micro-morphology structure of the composite carbon directly affects its electrochemical performance and application. As can be seen from the comparison of the examples and comparative examples, to ensure that the carbon units cooperate efficiently and the morphology of the composite material is relatively uniform, the amount of each carbon precursor should be moderate, and the carbonization treatment temperature, speed and time should be appropriate.

[0104] Cost factor consideration: the amount of raw materials affects the difficulty of process implementation and the possibility of large-scale production. Therefore, the amount of dopamine hydrochloride, tetraethyl orthosilicate and graphene should be within a reasonable range, the carbonization treatment temperature, rate and time should be appropriate to ensure the carbonization of the composite material, and the annealing temperature and time should be appropriate to ensure the effective adsorption of metal ions.

[0105] Process factor consideration: the process setting directly determines the possibility of large-scale application of the material, therefore, the recommended process parameters are as follows: the mass concentration of graphene oxide aqueous solution is 3-6mg / mL, the carbonization temperature is 600-900℃, the volume concentration of tetraethyl orthosilicate is 0.05-0.22g mL -1 , and the mass concentration of dopamine hydrochloride is 2.5-4.5mg mL -1 .

[0106] Therefore, the application adopts the preparation and application of the hollow carbon / graphene composite carbon, and the metal / non-metal co-doped multi-state three-dimensional carbon composite material prepared by the preparation method can solve the problem of insufficient chemical kinetic characteristics of the existing carbon-based sodium ion battery negative electrode material.

[0107] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application 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 application can still be modified or replaced by equivalents, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing hollow carbon / graphene composite carbon, characterized in that, Includes the following steps: Step S1: Prepare an aqueous solution of graphene oxide; The concentration of the aqueous solution of graphene oxide is 3-6 mg / mL; Step S2: Take deionized water and add tetraethyl orthosilicate to make the volume concentration of tetraethyl orthosilicate 0.05-0.22 g / mL. -1 Stir, adjust the pH value with ammonia water to obtain tetraethyl silicate hydrolysate; Step S3: Add dopamine hydrochloride to the tetraethyl silicate hydrolysate to achieve a dopamine hydrochloride concentration of 2.5-4.5 mg / mL. -1 Stir, centrifuge to remove the supernatant, and then vacuum dry at 60℃ for 24h to obtain silicon-carbon precursor; Use 40-70 mL of deionized water, stir for 0.5-1.5 h, and set the pH to 9-11. Step S4: Take 50 mL of graphene aqueous solution and add silicon carbon precursor to make the mass concentration of silicon carbon precursor 0.5-3 mg / mL. -1 The suspension was thoroughly stirred, then frozen for 12 hours, and then dried for 12 hours. Step S5: Place in a tube furnace and carbonize under a nitrogen or argon atmosphere. Clean with deionization three times and then vacuum dry at 60°C for 24 hours. The heating rate of the carbonization process in the tubular furnace is 2-6℃ / min, the carbonization temperature is 600℃-900℃, and the holding time is 1.5-3h. Step S6: Immerse in hydrofluoric acid for 12-36 hours, rinse three times with deionized water, and then vacuum dry at 60°C for 24 hours to obtain the prepared hollow carbon / graphene composite carbon.

2. The preparation method of hollow carbon / graphene composite carbon according to claim 1, characterized in that: In step S3, the stirring time is 12-36 hours, the centrifugation speed is 6000-10000 r / min, and the centrifugation time is 5-10 minutes.

3. The application of hollow carbon / graphene composite carbon prepared according to any one of claims 1-2 in sodium-ion batteries.

Images