Preparation method of silica-graphene composite aerogel for in-situ generation of silicon nitride and application of silica-graphene composite aerogel

Abstract

The invention discloses a preparation method and application of a siloxyalkene-graphene composite aerogel for in-situ generation of silicon nitride, and belongs to the technical field of composite material preparation technologies and electrochemical energy storage materials. The method comprises the following steps: reacting purified calcium silicide with concentrated hydrochloric acid, washing, drying, and carrying out ultrasonic stripping to obtain silylene; dispersing the composite aerogel and graphene oxide, directionally freezing by liquid nitrogen, and freeze-drying to obtain composite aerogel; and carrying out heat treatment in an argon / ammonia gas atmosphere, and generating silicon nitride on the surface of the silylene in situ. According to the method, uniform compounding of silicon nitride and controllable construction of a three-dimensional porous structure are realized on the basis of topological chemical conversion and directional freezing technologies. The silicon nitride content in the obtained composite aerogel is 10-40%, and the composite aerogel has excellent structural stability and conductive network, can provide reversible capacity of 500-1000 mAh / g under 1.5 C multiplying power when being used as a lithium ion battery negative electrode material, and has good application prospects in the field of energy storage.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a method for preparing siloxane-graphene composite aerogels with in-situ silicon nitride generation and their applications. Background Technology

[0002] With the rise of electric vehicles and various portable electronic devices, the public's demand for batteries and their performance is increasing. Therefore, silicon-based materials, with their high specific capacity (>3500mAh / g), low operating voltage, and abundant resources, are considered the most promising anode materials. However, the rapid volume change of silicon-based materials leads to a rapid decline in cycle stability, which poses an obstacle to the large-scale commercial application of silicon-based materials in lithium-ion batteries.

[0003] To address this issue, nanostructuring is used to mitigate volume expansion. Two-dimensional structures with high specific surface area and large interlayer space provide channels for rapid lithium-ion storage. Siloxene is a typical two-dimensional silicon material with a honeycomb structure similar to graphene, and its large interlayer distance provides sufficient space for lithium-ion migration. However, siloxene anodes still exhibit a 300% volume expansion, exacerbating SEI layer growth and reducing conductivity. One effective solution to this problem is to composite graphene with siloxene. Therefore, this invention provides a method for preparing a composite siloxene and graphene. Summary of the Invention

[0004] This application provides a method for preparing siloxane-graphene composite aerogels with in-situ silicon nitride generation and their applications. Using calcium silicide as raw material, the calcium silicide is topologically converted into siloxane by utilizing the structural invariance of topological chemical reactions. The siloxane is then further exfoliated into a single layer using ultrasound. The single layer of siloxane is then uniformly mixed with graphene oxide using ultrasound and other methods. The graphene oxide is converted into graphene by heat treatment. Finally, a directionally grown siloxane-graphene composite structure is formed by directional freezing.

[0005] On the one hand, this application provides a silicon oxyene-graphene composite material with in-situ silicon nitride generation, characterized by in-situ silicon nitride generation to improve the antioxidant properties of silicon oxyene, wherein the silicon nitride content is 10%~40%, and the battery prepared by this material can reach a capacity of 500~1000mAh / g at 1.5C.

[0006] On the other hand, this application provides a method for preparing a silicon nitride-based silicon oxide-graphene composite material in situ, comprising the following steps: (1) Calcium silicide was added to sodium hydroxide solution for purification, and after freeze drying, the resulting dry powder was obtained; (2) Place the dried powder from step (1) into a three-necked flask, add concentrated hydrochloric acid, purge with argon gas, and react at -30℃ for 3 to 5 days; (3) Wash the product obtained in step (2) with deionized water and anhydrous ethanol until neutral, and then dry it; (4) The dried powder obtained in step (3) is sonicated for 10 hours with deionized water as solvent, centrifuged, and the upper layer is taken. The upper layer is then freeze-dried to obtain siloxane. (5) Disperse the siloxane and graphene oxide obtained in step (4) separately in deionized water, sonicate for 1 hour, then mix the siloxane dispersion and the graphene oxide dispersion together and sonicate for 30 minutes. After uniform dispersion, use liquid nitrogen for directional freezing; (6) After placing the sample obtained in step (5) into a freeze dryer for 3 to 5 days, a silicate-graphene oxide composite aerogel is obtained. (7) The aerogel obtained in step (6) is placed in a tube furnace, and a mixture of argon and ammonia is introduced to heat it to obtain a silicon nitride-graphene composite aerogel generated in situ.

[0007] Preferably, in step (3), the deionized water is washed until neutral, then washed with anhydrous ethanol, and dried in a vacuum oven at a temperature of 50~70℃ for 10~12 hours.

[0008] Preferably, the ultrasound in step (4) uses a cell disruptor with the temperature controlled at 0~5℃.

[0009] Preferably, the mass ratio of siloxane to graphene oxide in step (5) is 1:1 to 5:3, and the concentration of the mixed dispersion is 10 to 12 mg / ml.

[0010] Preferably, the ratio of argon and ammonia in step (7) is 9:1 to 7:3, and the heating temperature is 1200 to 1600°C.

[0011] Beneficial effects

[0012] This invention proposes a method for preparing siloxane-graphene composite aerogels with in-situ generated silicon nitride and its application. Based on the layered structure of calcium silicide, the method utilizes the structural invariance of topological chemical reactions to topologically transform calcium silicide into siloxane. Further, it is exfoliated into monolayer siloxane using ultrasonic methods. The monolayer siloxane is then uniformly mixed with graphene oxide using ultrasonic and other methods. Graphene oxide is then converted into graphene through heat treatment. Finally, a directionally grown siloxane-graphene composite structure is formed through directional freezing. This invention fully utilizes the unique layered structure of calcium silicide and cleverly leverages the in-situ generated silicon nitride to enhance the antioxidant capacity of siloxane. Attached Figure Description

[0013] Appendix Figure 1 This is a scanning electron microscope (SEM) image of the siloxane-graphene composite aerogel in Example 1.

[0014] Appendix Figure 2 This is the X-ray diffraction (XRD) pattern of the siloxane in Example 1.

[0015] Appendix Figure 3 This is the XRD pattern of graphene oxide in Example 1.

[0016] Appendix Figure 4 This is the XRD pattern of the siloxane-graphene composite aerogel in Example 1.

[0017] Appendix Figure 5 This is the Fourier Transform Infrared (FTIR) spectrum of the silicon oxyene-graphene composite aerogel that was originally intended to generate silicon nitride in Example 1.

[0018] Appendix Figure 6 This is a battery cycle performance diagram for Example 4. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0022] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0023] Example 1

[0024] Solution preparation: 1 mol / L sodium hydroxide solution (500 ml): Take 20 g of solid sodium hydroxide and pour it into a dry 200 ml beaker. Slowly add deionized water (about 100-200 ml) and stir constantly with a glass rod until the solid is completely dissolved. After the solution cools to room temperature, transfer it to a 1000 ml beaker and slowly add deionized water to 500 ml.

[0025] 12 mg / ml siloxane-graphene oxide dispersion (5 ml): The mass ratio of siloxane to graphene oxide is 1:1. Weigh 30 mg of monolayer siloxane and 30 mg of graphene oxide according to this ratio, and add 2.5 ml of deionized water to each. Disperse the siloxane dispersion and the graphene oxide dispersion evenly by sonication, stirring and oscillation.

[0026] A method for preparing siloxane-graphene composite aerogels with in-situ silicon nitride generation, the specific steps of which are as follows: (1) First, add 10g of calcium silicide to 500ml of 1mol / L sodium hydroxide solution while stirring continuously, and stir for 12h to remove impurities. Second, after drying the purified calcium silicide, weigh 2g of the purified calcium silicide and add it to concentrated hydrochloric acid. Stir at -30℃ for 3 days until the solution changes from mostly black to yellow-green, at which point the reaction can be stopped.

[0027] (2) The product obtained in step (1) is washed with MCE aqueous mixed fiber microporous filter membrane and deionized water and vacuum filtered 3-4 times until neutral. Then it is washed with organic Nylon microporous filter membrane and anhydrous ethanol and vacuum filtered once. The filtered solid powder is placed in a vacuum drying oven and dried at 50°C for 24 hours under vacuum.

[0028] (3) Take 0.5g of the powder obtained in step (2) and add 80ml of deionized water to a double-jacketed peeling beaker. Stir thoroughly to disperse the powder evenly in the deionized water. Use a cell disruptor to sonicate the solution at 0℃. Centrifuge the sonicated solution and freeze-dry the supernatant. The resulting powder is the peeled monolayer silicate.

[0029] (4) Prepare 5 ml of siloxane-graphene oxide dispersion with a concentration of 12 mg / ml. After fully dispersing and uniformly dispersing, use liquid nitrogen to directionally freeze for 30 min.

[0030] (5) Place the sample from step (4) into a freeze dryer and freeze dry for 3 days to obtain siloxane-graphene oxide aerogel.

[0031] (6) The aerogel obtained in step (5) is placed in a tube furnace and a mixture of argon and ammonia (9:1) is introduced to heat it. The heat treatment time is 100 min and the heat treatment temperature is 1600℃ to obtain silicon nitride-siloxane-graphene composite aerogel generated in situ.

[0032] Elemental analysis revealed that the silicon nitride content of this material was 38%.

[0033] SEM images of the prepared silicate-graphene composite aerogel are shown below. Figure 1 As shown in the figure, a vertical porous structure was obtained through directional freezing with liquid nitrogen. (Attached) Figure 2 The XRD pattern of the siloxane is shown. The peaks at approximately 14°, 17°, and 47° correspond to the siloxane phase, indicating successful preparation of the siloxane. The XRD pattern of the prepared graphene composite is shown below. Figure 3 As shown, the strong and sharp diffraction peak appearing around 10° is a typical characteristic peak of graphene oxide. (See attached image.) Figure 4The image shows the XRD pattern of a silica-graphene composite aerogel. The characteristic peaks of graphene oxide disappear, while those of silica-graphene weaken, indicating interlayer interpenetration and the formation of a composite structure. The original FTIR image of the silica-graphene composite aerogel, which was initially a silicon nitride aerogel, is shown below. Figure 5 As shown, the main diffraction peaks of the material correspond to the vibrations of Si-N bonds, Si-O bonds, and the C=C framework, proving that silicon nitride was successfully generated in situ and composited with siloxane-graphene aerogel.

[0034] Example 2

[0035] Solution preparation: 1 mol / L sodium hydroxide solution (500 ml): Take 20 g of solid sodium hydroxide and pour it into a dry 200 ml beaker. Slowly add deionized water (about 100-200 ml) and stir constantly with a glass rod until the solid is completely dissolved. After the solution cools to room temperature, transfer it to a 1000 ml beaker and slowly add deionized water to 500 ml.

[0036] 12 mg / ml siloxane-graphene oxide dispersion (5 ml): The mass ratio of siloxane to graphene oxide is 5:3. Weigh 37.5 mg of monolayer siloxane and 22.5 g of graphene oxide according to this ratio, add 3 ml and 2 ml of deionized water respectively, and disperse the siloxane dispersion and graphene oxide dispersion evenly by sonication, stirring and oscillation.

[0037] A method for preparing siloxane-graphene composite aerogels with in-situ silicon nitride generation, the specific steps of which are as follows: (1) First, add 10g of calcium silicide to 500ml of 1mol / L sodium hydroxide solution while stirring continuously, and stir for 12h to remove impurities. Second, after drying the purified calcium silicide, weigh 2g of the purified calcium silicide and add it to concentrated hydrochloric acid. Stir at -30℃ for 4 days until the solution changes from mostly black to yellow-green, at which point the reaction can be stopped.

[0038] (2) The product obtained in step (1) is washed with MCE aqueous mixed fiber microporous filter membrane and deionized water and vacuum filtered 3-4 times until neutral. Then it is washed with organic Nylon microporous filter membrane and anhydrous ethanol and vacuum filtered once. The filtered solid powder is placed in a vacuum drying oven and dried at 60°C for 24 hours under vacuum.

[0039] (3) Take 0.5g of the powder obtained in step (2) and add 90ml of deionized water to a double-jacketed peeling beaker. Stir thoroughly to disperse the powder evenly in the deionized water. Use a cell disruptor to sonicate the solution at 3℃. Centrifuge the sonicated solution and freeze-dry the supernatant. The resulting powder is the peeled monolayer silicate.

[0040] (4) Prepare 5 ml of siloxane-graphene oxide dispersion with a concentration of 10 mg / ml. After fully dispersing and uniformly dispersing, use liquid nitrogen to directionally freeze for 30 min.

[0041] (5) Place the sample from step (4) into a freeze dryer and freeze dry for 4 days to obtain siloxane-graphene oxide aerogel.

[0042] (6) The aerogel obtained in step (5) is placed in a tube furnace and a mixture of argon and ammonia (7:3) is introduced to heat it. The heat treatment time is 110 min and the heat treatment temperature is 1400℃ to obtain silicon nitride-siloxane-graphene composite aerogel generated in situ.

[0043] Elemental analysis revealed that the silicon nitride content of this material was 23%.

[0044] Example 3

[0045] Solution preparation: 1 mol / L sodium hydroxide solution (500 ml): Take 20 g of solid sodium hydroxide and pour it into a dry 200 ml beaker. Slowly add deionized water (about 100-200 ml) and stir constantly with a glass rod until the solid is completely dissolved. After the solution cools to room temperature, transfer it to a 1000 ml beaker and slowly add deionized water to 500 ml.

[0046] A 10 mg / ml silicate-graphene oxide dispersion (5 ml): The mass ratio of silicate to graphene oxide is 5:3. Based on this ratio, weigh 31.25 mg of monolayer silicate and 18.75 g of graphene oxide, add 3 ml and 2 ml of deionized water respectively, and disperse the silicate and graphene oxide dispersions evenly using ultrasonication, stirring, and oscillation.

[0047] A method for preparing siloxane-graphene composite aerogels with in-situ silicon nitride generation, the specific steps of which are as follows: (1) First, add 10g of calcium silicide to 500ml of 1mol / L sodium hydroxide solution while stirring continuously, and stir for 12h to remove impurities. Second, after drying the purified calcium silicide, weigh 2g of the purified calcium silicide and add it to concentrated hydrochloric acid. Stir at -30℃ for 5 days until the solution changes from mostly black to yellow-green, at which point the reaction can be stopped.

[0048] (2) The product obtained in step (1) is washed with MCE aqueous mixed fiber microporous filter membrane and deionized water and vacuum filtered 3-4 times until neutral. Then it is washed with organic Nylon microporous filter membrane and anhydrous ethanol and vacuum filtered once. The filtered solid powder is placed in a vacuum drying oven and dried at 70°C for 24 hours under vacuum.

[0049] (3) Take 0.5g of the powder obtained in step (2) and add 100ml of deionized water to a double-jacketed peeling beaker. Stir thoroughly to disperse the powder evenly in the deionized water. Use a cell disruptor to sonicate the solution at 5℃. Centrifuge the sonicated solution and freeze-dry the supernatant. The resulting powder is the peeled monolayer silicate.

[0050] (4) Prepare 5 ml of siloxane-graphene oxide dispersion with a concentration of 12 mg / ml. After fully dispersing and uniformly dispersing, use liquid nitrogen to directionally freeze for 30 min.

[0051] (5) Place the sample from step (4) into a freeze dryer and freeze dry for 5 days to obtain siloxane-graphene oxide aerogel.

[0052] (6) The aerogel obtained in step (5) is placed in a tube furnace and a mixture of argon and ammonia (7:3) is introduced to heat it. The heat treatment time is 120 min and the heat treatment temperature is 1200℃ to obtain silicon nitride-siloxane-graphene composite aerogel generated in situ.

[0053] Elemental analysis revealed that the silicon nitride content of this material is 13%.

[0054] Example 4

[0055] This embodiment uses the in-situ generated silicon nitride siloxane-graphene composite aerogel prepared in Example 1 as the negative electrode material for battery assembly. The steps are as follows: (1) The prepared aerogel is cut into thin slices and used as the negative electrode material of the battery. The battery assembly process is carried out in a glove box. (2) First, put the cut aerogel into the positive electrode shell, cover the diaphragm and add an appropriate amount of electrolyte to wet it, then put in the lithium sheet, gasket and spring in sequence, add an appropriate amount of electrolyte and cover the negative electrode shell, and press it firmly. (3) Compact the battery using the tablet press inside the glove box to ensure a tight seal. Remove the prepared battery from the glove box and perform performance testing.

[0056] The cycle performance diagram of the battery prepared in this embodiment is shown below. Figure 6 As shown, the battery prepared with this material can achieve a capacity of approximately 700 mAh / g at 1.5C.

[0057] Example 5

[0058] This embodiment uses the in-situ generated silicon nitride siloxane-graphene composite aerogel prepared in Example 2 as the negative electrode material for battery assembly. The steps are as follows: (1) The prepared aerogel is cut into thin slices and used as the negative electrode material of the battery. The battery assembly process is carried out in a glove box. (2) First, put the cut aerogel into the positive electrode shell, cover the diaphragm and add an appropriate amount of electrolyte to wet it, then put in the lithium sheet, gasket and spring in sequence, add an appropriate amount of electrolyte and cover the negative electrode shell, and press it firmly. (3) Compact the battery using the tablet press inside the glove box to ensure a tight seal. Remove the prepared battery from the glove box and perform performance testing.

[0059] The battery prepared in this embodiment has a capacity of approximately 980 mAh / g at 1.5C.

[0060] Example 6

[0061] This embodiment uses the in-situ generated silicon nitride siloxane-graphene composite aerogel prepared in Example 3 as the negative electrode material for battery assembly. The steps are as follows: (1) The prepared aerogel is cut into thin slices and used as the negative electrode material of the battery. The battery assembly process is carried out in a glove box. (2) First, put the cut aerogel into the positive electrode shell, cover the diaphragm and add an appropriate amount of electrolyte to wet it, then put in the lithium sheet, gasket and spring in sequence, add an appropriate amount of electrolyte and cover the negative electrode shell, and press it firmly. (3) Compact the battery using the tablet press inside the glove box to ensure a tight seal. Remove the prepared battery from the glove box and perform performance testing.

[0062] The battery prepared in this embodiment has a capacity of approximately 502 mAh / g at 1.5C.

[0063] The above are preferred embodiments of the present invention. Those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above. Any obvious improvements, substitutions or modifications made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims

1. A siloxene-graphene composite aerogel generating silicon nitride in situ, characterized in that, Silicon oxyene-graphene aerogel in-situ generating silicon nitride; wherein the silicon nitride content is 10%~40%.

2. A method of preparing a siloxene-graphene composite aerogel generating silicon nitride in situ according to claim 1, characterized in that, It comprises the following steps: (1) adding calcium silicide into sodium hydroxide solution to purify it, and after freeze-drying, dry powder is obtained; (2) putting the dry powder of step (1) into a three-necked flask, adding concentrated hydrochloric acid, passing in argon, and reacting at-30℃ for 3~5 days; (3) drying the product obtained in step (2) after washing with deionized water and anhydrous ethanol until neutral; (4) using deionized water as solvent, ultrasonicating the dry powder obtained in step (3) for 10 hours, centrifuging, taking the upper liquid, freeze-drying the upper liquid to obtain silicon oxyene; (5) dispersing the silicon oxyene and graphene oxide obtained in step (4) in deionized water respectively, ultrasonicating for 1 hour, mixing the silicon oxyene dispersion liquid and graphene oxide dispersion liquid together and ultrasonicating for 30 minutes, and then directional freezing with liquid nitrogen after uniform dispersion; (6) putting the sample obtained in step (5) into a freeze-drying machine for 3~5 days to obtain silicon oxyene-graphene composite aerogel; (7) putting the aerogel obtained in step (6) into a tube furnace, passing in a mixed gas of argon and ammonia, and heating to obtain silicon oxyene-graphene composite aerogel in-situ generating silicon nitride.

3. The method of claim 2, wherein the method further comprises the step of: The ultrasonication in step (4) uses a cell disrupter, and the temperature is controlled at 0~5℃. ​ 4. The method of claim 2, wherein the method is characterized by, The mass ratio of silicon oxyene to graphene oxide in step (5) is 1:1~5:3, and the concentration of the mixed dispersion liquid is 10~12mg / ml.

5. The method of claim 2, wherein the method is characterized by: The mixed gas of argon and ammonia in step (7) has a ratio of 9:1~7:3, and the heating temperature is 1200~1600℃.

6. Use of a siloxene-graphene composite aerogel for in-situ generation of silicon nitride, characterized in that, The half-cell assembled by the negative electrode of the composite aerogel material has a capacity of 500~1000mAh / g at 1.5C.

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