Binder-free silicon / carbon nanotube composite carbon fiber negative electrode material, preparation method thereof and application in lithium ion structure energy storage composite material

Abstract

The invention discloses a binder-free silicon / carbon nanotube composite carbon fiber negative electrode material, a preparation method thereof and an application of the binder-free silicon / carbon nanotube composite carbon fiber negative electrode material in a lithium ion structure energy storage composite material. Carbon fibers are used as a substrate, catalyst nanowires are grown through a hydrothermal method, then dicyandiamide is used as a carbon source and a nitrogen source through a chemical vapor deposition method, and the binder-free silicon / carbon nanotube composite carbon fiber negative electrode material is prepared. Uniform and compact carbon nanotubes doped with nitrogen and embedded with ferrocobalt nanoparticles and arranged in a three-dimensional disordered structure grow on the surface of the carbon fiber, and then ultra-thin nano silicon is uniformly sputtered on a carbon nanotube substrate supported by the carbon fiber through a radio frequency plasma magnetron sputtering technology. The carbon nano tube and the silicon material are effectively compounded together, the advantages of carbon and silicon are combined, and a synergistic effect is achieved. When the obtained silicon-carbon composite material is used as a negative electrode material of a lithium ion structure energy storage composite material, excellent electrochemical performance and cycling stability are shown, and the flexible structure and excellent mechanical performance ensure efficient use of the material in different fields and different application scenes.

Description

Technical Field

[0001] This invention relates to flexible binder-free carbon fiber composite anode materials for lithium-ion structural energy storage, specifically to a binder-free silicon / carbon nanotube composite carbon fiber anode material, its preparation method, and its application in lithium-ion structural energy storage composite materials. Background Technology

[0002] Functionalization of structural materials and structuralization of functional materials are the future development trends of composite materials. Lightweight structural energy storage multifunctional integrated composite materials have both structural load-bearing and energy storage functions, which can meet the material requirements of the development of lightweight, electrification and intelligence of advanced equipment, and have broad application prospects in the fields of automobiles, robots, wind power, military industry and aerospace.

[0003] Anode materials are a crucial component of structural energy storage composite materials. Graphite-based materials are currently the most common anode materials, with a theoretical specific capacity of 372 mAh / g. The best-performing artificial graphite in the industry has reached around 350 mAh / g, leaving little room for further improvement. However, with the rapid development of the new energy sector, electric vehicles and large-scale energy storage systems are becoming inevitable trends, and graphite materials, due to their relatively low specific capacity, are struggling to meet the demands of this field. Therefore, one effective solution to improve the energy density of battery cells is to develop and utilize novel anode materials with high specific capacity.

[0004] Silicon is currently the anode material with the highest theoretical specific capacity. Because each silicon atom can bind to approximately four lithium ions, its theoretical specific capacity is 10 times that of graphite. It also has a low operating voltage (its mass specific capacity can reach 4200 mAh / g, and its volumetric specific capacity can reach 9786 mAh / cm³). 2 However, the volume change rate is also the largest. Therefore, the silicon anode inevitably undergoes volume expansion during battery cycling, leading to battery failure.

[0005] Compared to silicon, carbon materials exhibit better electrical conductivity, and their volume expansion during cycling is far less pronounced. This results in significantly superior electrochemical cycling stability compared to silicon, making the combination of the two materials into silicon-carbon composites an effective approach. The silicon-carbon-based composite anode material, formed by mixing carbon and silicon, not only combines the high conductivity of carbon with the high specific capacity of silicon, but also effectively buffers the expansion of silicon when carbon serves as the substrate, thereby improving the overall electrochemical cycling performance of the material.

[0006] Magnetron sputtering, as an industrial-scale method, is widely used for the deposition of high-purity functional materials due to its simplicity, ease of operation, and high efficiency. Specifically, the controllable construction of nanostructures on substrates using magnetron sputtering-based electrode materials is very promising because of the following aspects: (1) High density of sputtering; (2) Excellent adhesion between the substrate and the sputtered material; (3) Regardless of the melting temperature of the material, this technology can achieve low-temperature, high-deposition-rate sputtering; (4) The proportions of sputtered composite materials are easy to control; (5) The materials are easily oxidized, and complex compounds are difficult to synthesize using ordinary chemical techniques, but can be achieved using appropriate target materials through magnetron sputtering technology.

[0007] Based on these advantages, magnetron sputtering technology has been considered an attractive auxiliary method for preparing electrode materials in recent years. This is because the active material is deposited on the current collector or precursor, and the sputtered material can be directly used as an electrode without the need for additional binders and conductive agents, thus achieving high specific capacity, excellent battery cycle performance, and superior rate performance. Simultaneously, the active material can be sputtered as an electrode material onto flexible substrates, meeting the needs of current flexible wearable devices.

[0008] This invention utilizes nitrogen-doped carbon nanotubes (CNTs) with embedded cobalt-iron nanoparticles, arranged in a three-dimensional disordered structure, uniformly grown on carbon fibers as the substrate material. The carbon fibers serve as a flexible substrate suitable for flexible electronic devices. The dense CNTs provide ample surface area for silicon deposition, preventing agglomeration of nano-silicon and providing more active sites during lithiation. CNTs possess advantages such as small diameter, large specific surface area, excellent conductivity, good mechanical properties, and good flexibility. Nitrogen doping enhances the interaction between silicon and CNTs, effectively suppressing silicon volume expansion. By optimizing the silicon deposition amount, carbon coating on the silicon-based material surface is unnecessary, effectively improving the low conductivity of silicon and solving the pulverization and polarization problems caused by its expansion. The embedded Co and CoFe nanoparticles further enhance the electrode capacity and cycle life. The unique structural design combines the excellent conductivity of CNTs with the high theoretical capacity of silicon, working synergistically to compensate for each other. The carefully designed CNT framework provides excellent assurance for electrochemical cycle stability, and the introduction of silicon achieves higher energy density. Summary of the Invention

[0009] The purpose of this invention is to provide a binder-free silicon / carbon nanotube composite carbon fiber anode material, its preparation method, and its application in lithium-ion energy storage composite materials. This invention provides an effective, simple, low-cost, and highly efficient technical method for preparing silicon / carbon nanotube composite lithium-ion energy storage composite anode materials. It effectively combines nano-silicon and carbon nanotube materials, fully integrating the advantages of both and achieving a synergistic effect. Flexible carbon fiber serves as a substrate, and nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles are uniformly grown on the carbon fiber using chemical vapor deposition in a three-dimensional disordered structure. The dense carbon nanotubes provide a large surface area for silicon deposition, preventing the agglomeration of nano-silicon and providing more active sites during lithiation. The incorporation of nitrogen enhances the interaction between silicon and carbon nanotubes, effectively suppressing silicon volume expansion. By optimizing the silicon deposition amount, carbon coating on the silicon-based material shell is unnecessary, effectively improving the low conductivity of silicon and solving the pulverization and polarization problems caused by its expansion. Embedded CoFe nanoparticles can further enhance the electrode's capacity and cycle life. By exploring and optimizing various magnetron sputtering conditions, the most suitable conditions for sputtering nano-silicon on carbon nanotube substrates supported by carbon fibers were selected, thereby designing a final material with excellent morphology, uniform silicon / carbon nanotube bonding, and excellent and stable electrochemical performance.

[0010] Based on the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material includes the following steps: using carbon fiber as a substrate, hydrothermal growth of hydroxide nanowires, followed by chemical vapor deposition growth of nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure, and finally magnetron sputtering of an ultrathin nano-silicon film onto the surface of the carbon nanotubes. (1) Dissolve cobalt nitrate, ferric nitrate, ammonium fluoride and urea in deionized water in sequence, stir to obtain a mixed solution, put carbon fiber into it, and perform hydrothermal reaction at 100~150℃ for 1h~10h. After cooling to room temperature, take out the sample, wash and dry it to obtain carbon fiber with hydroxide nanowires grown on the surface. (2) Place carbon fibers with hydroxide nanowires grown on the surface in the downstream of a quartz tube furnace, then weigh 2-3g of dicyandiamide and place it in a corundum boat, place it in the upstream air inlet of the quartz tube furnace, purge the air in the quartz tube with argon, adjust the gas flow rate to 10-50 sccm, keep it at 350-450℃ for 1-3 h, then keep it at 750-850℃ for 1-3 h, cool it to room temperature and take it out, and you will get carbon fibers with nitrogen-doped carbon nanotubes and cobalt-iron nanoparticles embedded in them, arranged in a three-dimensional disordered structure. (3) Carbon fibers with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles arranged in a three-dimensional disordered structure are fixed on the substrate of a magnetron sputtering instrument. The Si target is fixed on the radio frequency target column and nano-silicon is sputtered. The sputtering pressure is 0.5~5 Pa, the sputtering power is 50~150 W, the sputtering time is 10~40 min, and the working gas during sputtering is argon. The binderless silicon / carbon nanotube composite carbon fiber anode material is obtained. Further, in step (1), the carbon fiber needs to be pretreated before use. The specific process is as follows: the carbon fiber cut to the specified size is placed in a potassium permanganate solution and ultrasonically treated for 5-30 minutes, then repeatedly ultrasonically cleaned with deionized water and alcohol (to remove excess potassium permanganate), and then the cleaned carbon fiber is dried. Drying is preferably carried out in a vacuum drying oven at 50-80℃ for 10-15 hours. Preferably, the concentration of the potassium permanganate solution is 5 wt%-15 wt%.

[0011] Further, in step (1), the molar ratio of cobalt nitrate, ferric nitrate, ammonium fluoride, and urea is (0.8~1):(0.8~1):(4~6):(9~11), specifically (0.8~1):(0.8~1):5:10, and the concentration of ferric nitrate in deionized water is 0.02~0.03mol / L.

[0012] Furthermore, in step (2), the amount of dicyandiamide used is 0.1~0.3 g / cm³. 2 Carbon fiber.

[0013] Furthermore, the thickness of the ultrathin nano-silicon film is 2nm~30nm.

[0014] The binderless silicon / carbon nanotube composite carbon fiber anode material prepared by the above method contains nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure with a transverse diameter of 2 nm to 300 nm.

[0015] The binderless silicon / carbon nanotube composite carbon fiber anode material prepared by the above preparation method contains nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure. The embedded cobalt-iron nanoparticles are one or more of the following: single atoms with a size of 0.2 nm to 0.5 nm or CoFe alloy with a size of 5 nm to 50 nm.

[0016] The above-mentioned binderless silicon / carbon nanotube composite carbon fiber anode material is used as an anode in lithium-ion structured energy storage composite materials.

[0017] This process uses dicyandiamide as both the nitrogen and carbon sources, and hydroxide nanowires as a catalyst precursor to synthesize nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure. During high-temperature calcination in an argon inert gas atmosphere, the hydroxide nanowires formed on the carbon fiber surface are reduced to metal nanoparticles. During annealing, the dicyandiamide is catalyzed to transform into nitrogen-doped carbon nanotubes encapsulating the metal nanoparticles. The flexible, binder-free electrode material prepared by this invention can be directly applied to lithium-ion energy storage composite materials, serving as a negative electrode material. This silicon / carbon nanotube negative electrode material possesses numerous active sites, uniformly distributed nano-silicon, and a stable silicon / carbon nanotube bond, thus exhibiting excellent and stable electrochemical performance.

[0018] Compared with the prior art, the advantages of the present invention are as follows: (1) The carbon nanotube substrate supported by carbon fiber is an excellent conductor of electrons and its conductivity is better than that of semiconductor silicon. The combination with silicon improves the conductivity of the electrode to a certain extent. (2) The carbon fiber-supported carbon nanotube substrate prepared has excellent mechanical, electrical, and thermal properties, and stable physicochemical properties. The incorporation of nitrogen enhances the interaction between silicon and carbon nanotubes, effectively suppressing the volume expansion of silicon. By optimizing the amount of silicon deposition, carbon coating on the surface of the silicon-based material shell can be eliminated, effectively improving the low conductivity of silicon and solving the pulverization and polarization problems caused by its expansion. The embedded Co and CoFe nanoparticles can further improve the capacity and cycle life of the electrode; (3) Carbon nanotube materials have a very high specific surface area. When combined with silicon, they can not only provide lithium storage capacity, but also shorten the transport distance of lithium ions in the electrode material and increase the lithiation reaction rate of silicon. (4) Carbon nanotubes can serve as an isolation layer between silicon and electrolyte, preventing silicon agglomeration and side reactions with electrolyte. Moreover, they have a small volume effect and can form a relatively stable SEI film on the surface.

[0019] (5) Low-cost and high-efficiency plasma magnetron sputtering technology is used to prepare electrode materials by depositing nano-silicon on carbon nanotube substrates supported by carbon fibers. The sputtered materials can be used directly as electrodes without the need for additional binders and conductive agents, thereby achieving high specific capacity, excellent battery cycle performance and excellent rate performance. At the same time, active materials can be sputtered as electrode materials on flexible substrates, which can meet the needs of current flexible wearable devices. Attached Figure Description

[0020] Figure 1 The high-resolution microstructure of the material prepared in Example 1 under a sputtering pressure of 3 Pa is shown under a scanning electron microscope (SEM). Figure 2The high-resolution microstructure of the material prepared in Example 2 under a sputtering pressure of 2 Pa is shown under a scanning electron microscope (SEM). Figure 3 The high-resolution microstructure of the sample prepared in Example 3 under a sputtering pressure of 1 Pa under a scanning electron microscope (SEM). Figure 4 The high-resolution microstructure of the material prepared in Example 4 under a sputtering pressure of 0.5 Pa is shown under a scanning electron microscope (SEM). Figure 5 The high-resolution microstructure of the material prepared in Example 5 is shown under a scanning electron microscope (SEM). Figure 6 The high-resolution microstructure of the material prepared in Example 6 is shown under a scanning electron microscope (SEM). Figure 7 The high-resolution microstructure of the material prepared in Example 7 is shown under a scanning electron microscope (SEM). Figure 8 The high-resolution microstructure of the material prepared for Comparative Example 1 is shown under a scanning electron microscope (SEM). Figure 9 Comparison of the cycling stability of the final samples from Examples 2 and 3 at 2.5C; Figure 10 A comparison of the cycling stability of the materials prepared in Examples 3 and 4 at 1C; Figure 11 Comparison of the cycling stability of Examples 5 and 3 and Comparative Examples 1 and 2 at 2.5C; Figure 12 The cycling stability data for Comparative Example 3 at 2.5C are provided. Figure 13 X-ray diffraction (XRD) analysis of the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles prepared in step (3) of Example 3. Figure 14 To analyze the three-dimensional disordered structure of the carbon nanotubes with nitrogen doped and embedded cobalt-iron nanoparticles prepared in step (3) of Example 3 under a transmission electron microscope (TEM). Figure 15 The analysis of the binder-free silicon / carbon nanotube composite carbon fiber anode material in Example 3 was performed using transmission electron microscopy (TEM). Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described in this specification are merely for explaining the present invention and are not intended to limit the present invention. The parameters, proportions, etc. of the embodiments can be selected according to local conditions without having a substantial impact on the results.

[0022] Example 1 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) Pretreatment of carbon fiber Carbon fiber (T8006K, 320g / m) 2 Cut the carbon fiber into 3cm×4cm pieces, then add it to a prepared 10 wt.% potassium permanganate solution and sonicate for 10 min. Repeatedly sonicate with deionized water and alcohol to remove excess potassium permanganate. Then place the cleaned carbon fiber in a vacuum drying oven and dry it at 60 ℃ for 12 h.

[0023] (2) Hydrothermal growth of hydroxide nanowires Weigh 0.388g (0.96mmol) of Fe(NO3)3·9H2O, 0.27g (0.93mmol) of Co(NO3)2·6H2O, 0.186g (5mmol) of NH4F, and 0.6g (10mmol) of urea and dissolve them in 40 mL of deionized water. Stir for half an hour, then put the carbon fiber pretreated in step (1) into it, and then transfer it to a 50mL hydrothermal reactor. Keep it at 120℃ for 6 hours in an oven. After cooling to room temperature, take out the sample, wash the excess catalyst several times with deionized water and alcohol, and then dry it in a vacuum drying oven at 60℃ for 12 hours.

[0024] (3) Chemical vapor deposition growth of nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure. High-quality carbon nanotubes were prepared by chemical vapor deposition (CVD). The carbon fibers with grown hydroxide nanowires obtained in step (2) were used as templates and calcined under an argon atmosphere. Dicyandiamide was used as the carbon source for growing carbon nanotubes. Specifically, the carbon fibers with grown hydroxide nanowires were placed in a high-temperature tube furnace, downstream of a quartz tube furnace. Then, 2.5 g of dicyandiamide was weighed and placed in a corundum boat, positioned at the upstream inlet of the quartz tube furnace. The air inside the quartz tube was purged with argon, and the gas flow rate was adjusted to 30 sccm. After holding at 400℃ for 2 h, the temperature was increased to 800℃, held at 800℃ for 2 h, and then cooled to room temperature. Finally, a carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles arranged in a three-dimensional disordered structure was obtained.

[0025] (4) Magnetron sputtering of nano-silicon Magnetron sputtering of silicon nanoparticles is performed using radio frequency (RF) magnetron sputtering. Specifically, the carbon fiber substrate, which consists of nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure, prepared in step (3), is first fixed onto the substrate of a magnetron sputtering instrument. Then, a Si target is fixed onto an RF target post, and silicon nanoparticles are sputtered and deposited. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5 × 10⁻⁶. -4 The sputtering pressure was 3 Pa, the sputtering power was 100 W, and the sputtering time was 20 min.

[0026] The morphology of the material obtained in Example 1 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown, after carbon nanotubes with a three-dimensional disordered structure were uniformly grown on carbon fibers, no nano-silicon deposition was found on the surface of the carbon nanotubes under a sputtering pressure of 3 Pa by magnetron sputtering. The morphology of the carbon nanotubes was the same as that of the initial carbon nanotubes on the carbon fibers. Therefore, it can be concluded that nano-silicon cannot be sputtered under a sputtering pressure of 3 Pa.

[0027] Example 2 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0028] (2) This step is the same as step (2) in Example 1.

[0029] (3) This step is the same as step (3) in Example 1.

[0030] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4 The sputtering pressure was 2 Pa, the sputtering power was 100 W, and the sputtering time was 20 min.

[0031] The morphology of the material obtained in Example 2 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown, after carbon nanotubes arranged in a three-dimensional disordered structure are grown on carbon fibers, some carbon nanotubes are obviously surrounded by nano-silicon and their diameters become thicker. However, some carbon nanotubes do not have nano-silicon deposited on them, showing unevenness. It can be concluded that the sputtering under the sputtering pressure of 2 Pa is not sufficient. Many carbon nanotubes are not sputtered, while some are sputtered too much, resulting in poor uniformity.

[0032] Example 3 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0033] (2) This step is the same as step (2) in Example 1.

[0034] (3) This step is the same as step (3) in Example 1.

[0035] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4 The sputtering pressure was 1 Pa, the sputtering power was 100 W, and the sputtering time was 20 min.

[0036] The morphology of the material obtained in Example 3 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown, after growing carbon nanotubes with a three-dimensional disordered structure on carbon fibers, the deposition of nano-silicon is very uniform under a sputtering pressure of 1 Pa. The surface of the carbon nanotubes is obviously and uniformly covered with nano-silicon. Each carbon nanotube is of uniform thickness and there is no aggregation or accumulation of nano-silicon, which lays the foundation for excellent electrochemical performance.

[0037] Example 4 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0038] (2) This step is the same as step (2) in Example 1.

[0039] (3) This step is the same as step (3) in Example 1.

[0040] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4The sputtering pressure was 0.5 Pa, the sputtering power was 100 W, and the sputtering time was 20 min.

[0041] The morphology of the material obtained in Example 4 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 4 As shown, after carbon nanotubes with a three-dimensional disordered structure are grown on carbon fibers, the surface of each carbon nanotube is covered with nano-silicon under a sputtering pressure of 0.5 Pa. However, the nano-silicon agglomerates, and many nano-silicon particles do not deposit on the carbon nanotube framework but accumulate on the surface. In subsequent electrochemical reactions, the nano-silicon particles are prone to agglomeration and detachment, which affects the electrochemical stability.

[0042] Example 5 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0043] (2) This step is the same as step (2) in Example 1.

[0044] (3) This step is the same as step (3) in Example 1.

[0045] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4 The sputtering pressure was 1 Pa, the sputtering power was 100 W, and the sputtering time was 10 min.

[0046] The morphology of the material obtained in Example 5 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 5 As shown, after carbon nanotubes with a three-dimensional disordered structure are grown on carbon fibers, a small amount of nano-silicon is deposited on the surface of the carbon nanotubes after sputtering for 10 min at a sputtering pressure of 1 Pa. The sputtering is uniform, and the diameter of the silicon-carbon nanotubes sputtered for 10 min increases only slightly, indicating that the loading of nano-silicon is relatively small.

[0047] Example 6 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0048] (2) This step is the same as step (2) in Example 1.

[0049] (3) This step is the same as step (3) in Example 1.

[0050] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4 The sputtering pressure was 1 Pa, the sputtering power was 100 W, and the sputtering time was 30 min.

[0051] The morphology of the material obtained in Example 6 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 6 As shown, after carbon nanotubes with a three-dimensional disordered structure are grown on carbon fibers, nano-silicon is uniformly deposited on the carbon nanotubes under a sputtering pressure of 1 Pa and a sputtering time of 30 min. The diameter of the carbon nanotubes is further increased, and the deposition of nano-silicon on the surface is further increased.

[0052] Example 7 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0053] (2) This step is the same as step (2) in Example 1.

[0054] (3) This step is the same as step (3) in Example 1.

[0055] (4) First, the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3), is fixed on the substrate of the magnetron sputtering instrument. Then, the Si target is fixed on the RF target post for sputtering deposition of nano-silicon. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. - 4 The sputtering pressure was 1 Pa, the sputtering power was 100 W, and the sputtering time was 40 min.

[0056] The morphology of the material obtained in Example 7 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 7 As shown, after growing carbon nanotubes with a three-dimensional disordered structure on carbon fibers, the diameter of the carbon nanotubes increased significantly under a sputtering pressure of 1 Pa and a sputtering time of 40 min. The deposited silicon was very full and three-dimensional, and no aggregation of nano-silicon was found, indicating that the sputtering was uniform.

[0057] Comparative Example 1 (1) Pretreatment of carbon fiber The carbon fiber was cut into small pieces of 3cm×4cm, then added to a prepared 10 wt.% potassium permanganate solution and sonicated for 10 min. Excess potassium permanganate was removed by repeated sonication with deionized water and alcohol. The cleaned carbon fiber was then placed in a vacuum drying oven and dried at 60 ℃ for 12 h.

[0058] (2) Hydrothermal growth of hydroxide nanowires Weigh 0.388g of Fe(NO3)3·9H2O, 0.27g of Co(NO3)2·6H2O, 0.186g of NH4F, and 0.6g of urea and dissolve them in 40 mL of deionized water. Stir for half an hour, then put the carbon fiber pretreated in step (1) into it, and then transfer it to a 50 mL hydrothermal reactor. Keep it at 120℃ in an oven for 6 h. After cooling to room temperature, take out the sample, wash the excess catalyst several times with deionized water and alcohol, and then dry it in a vacuum drying oven at 60℃ for 12 h.

[0059] (3) Chemical vapor deposition growth of nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure. High-quality nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure were prepared by chemical vapor deposition (CVD). The carbon fibers with grown hydroxide nanowires obtained in step (2) were used as templates and calcined under an argon atmosphere. Dicyandiamide was used as the carbon source for growing the carbon nanotubes. Specifically, the carbon fibers with grown hydroxide nanowires were placed in a high-temperature tube furnace, downstream of a quartz tube furnace. Then, 2.5g of dicyandiamide was weighed and placed in a corundum boat, positioned at the upstream inlet of the quartz tube furnace. The air inside the quartz tube was purged with argon, the gas flow rate was adjusted to 30 sccm, and the temperature was maintained at 400℃ for 2 h. The temperature was then increased to 800℃ and maintained for another 2 h before being cooled to room temperature and removed. Finally, a carbon fiber substrate with nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles arranged in a three-dimensional disordered structure was obtained.

[0060] Using nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles grown solely on carbon fibers in a three-dimensional disordered structure, without silicon sputtering as a control sample, the morphology of the material obtained in Comparative Example 1 was analyzed by scanning electron microscopy (SEM). The results are as follows: Figure 8 As shown, only carbon nanotubes with a uniform three-dimensional disordered structure were grown on carbon fibers, without the deposition of silicon by magnetron sputtering.

[0061] Comparative Example 2 (1) This step is the same as step (1) in Comparative Example 1.

[0062] Simply treating the carbon fiber to increase its hydrophilicity without any other steps are used to assess the capacity contribution of pure carbon fiber in the electrode.

[0063] Comparative Example 3 A method for preparing a binderless silicon / carbon nanotube composite carbon fiber anode material specifically includes the following steps: (1) This step is the same as step (1) in Example 1.

[0064] (2) This step is the same as step (2) in Example 1.

[0065] (3) This step is the same as step (3) in Example 1.

[0066] (4) After calcination in step (3), the embedded cobalt-iron nanoparticles are removed by etching, washing and drying with 4-6 mol / L sulfuric acid.

[0067] (5) First, fix the carbon fiber substrate with nitrogen-doped carbon nanotubes arranged in a three-dimensional disordered structure, prepared in step (4), onto the substrate of the magnetron sputtering instrument. Then, fix the Si target onto the RF target post and perform sputtering deposition of silicon nanoparticles. The working gas during sputtering is argon. The vacuum background of the magnetron sputtering is controlled to be 5×10⁻⁶. -4 The sputtering pressure was 1 Pa, the sputtering power was 100 W, and the sputtering time was 20 min.

[0068] Application examples The negative electrode materials from Examples 2 to 5, as well as Comparative Examples 1, 2, and 3, were cut into 1.2 cm diameter discs and used directly as working electrodes, without the need for other binders, current collectors, or conductive agents. Lithium metal was used as the counter electrode. These were assembled into button cells. The button cell structure, from bottom to top, consisted of: a positive electrode shell, electrode material, electrolyte (LX-031, formulation: 1M LiPF6 in DEC:DMC:EC = 1:1:1 Vol% with 5% FEC), a separator (Celgard 2500), electrolyte (same as above), lithium sheet, gasket, spring, and negative electrode shell. The same electrolyte was added to both sides of the separator until it completely wetted the separator. Cycle performance was then tested on the Blue Electric testing platform. The results are detailed in [link to results]. Figures 9 to 12 .

[0069] First, activate the assembled button battery at 0.5C for 4 cycles, then cycle it at 2.5C for 100 cycles. Figure 9 As shown, the material of Example 3 (i.e., sputtering pressure of 1 Pa) has an initial discharge specific capacity of approximately 1850 mAhg at 2.5 C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 1250 mAh g. -1After 100 cycles, the specific capacity is approximately 1050 mAh g. -1 The capacity retention rate was approximately 84%, demonstrating excellent stability. The material in Example 2 (i.e., sputtering pressure of 2 Pa) exhibited an initial discharge specific capacity of approximately 1300 mAh g⁻¹ at 2.5 C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 750 mAh g. -1 After 100 cycles, the specific capacity is approximately 480 mAh g. -1 The capacity retention rate was 64%. Therefore, by comparison, the material of Example 3 is significantly better than the material of Example 2 in terms of specific capacity and cycle stability.

[0070] Figure 10 As can be seen, the material in Example 3 (i.e., sputtering pressure of 1 Pa) has an initial discharge specific capacity of approximately 2150 mAh g at 1C. -1 The specific capacity at 1C in the 5th cycle is approximately 1450 mAh g. -1 After 70 cycles, the specific capacity is approximately 1400 mAh g. -1 The capacity retention rate was 96.5%, demonstrating excellent stability. The material in Example 4 (sputtering pressure of 0.5 Pa) had an initial discharge specific capacity of approximately 1980 mAh g⁻¹ at 1 C. -1 The specific capacity at 1C in the 5th cycle is approximately 1300 mAh g. -1 After 70 cycles, the specific capacity is approximately 1250 mAh g. -1 The capacity retention rate was 96.1%. Therefore, by comparison, the material of Example 3 is significantly better than the material of Example 4 in terms of specific capacity and cycle stability.

[0071] Figure 11 The material in Example 3 showed an initial discharge specific capacity of approximately 1850 mAh g at 2.5C. -1 The 5th cycle at 2.5 C is approximately 1250 mAh g. -1 After 100 cycles, the specific capacity is approximately 1050 mAh g. -1 The capacity retention rate was 84%. The material in Example 5 had an initial discharge capacity of approximately 1300 mAh g⁻¹ at 2.5C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 750 mAh g. -1 After 100 cycles, the specific capacity is approximately 550 mAh g. -1 The capacity retention rate was 73.3%. Comparative Example 1 (CNT) material had an initial discharge capacity of approximately 900 mAh g⁻¹ at 2.5C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 350 mAh g. -1After 100 cycles, the specific capacity is approximately 250 mAh g. -1 The capacity retention rate was 71.4%. The material in Comparative Example 2 (raw carbon cloth) had an initial discharge specific capacity of approximately 100 mAh g at 2.5 C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 35 mAh g. -1 After 100 cycles, the specific capacity is approximately 30 mAh g. -1 The capacity retention rate was 85.7%, which is very low. Figure 12 The material in Comparative Example 3 showed an initial discharge capacity of approximately 1640 mAh g at 2.5C. -1 The specific capacity at 2.5 C in the 5th cycle is approximately 1070 mAh g. -1 After 100 cycles, the specific capacity is approximately 852 mAh g. -1 The capacity retention rate was 79.6%. Therefore, by comparison, the material in Example 3 showed a significant advantage in specific capacity and cycle stability.

[0072] Figure 13 XRD analysis of the carbon fiber substrate with nitrogen-doped carbon nanotubes embedded with cobalt-iron nanoparticles, prepared in step (3) of Example 3, reveals the formation of single cobalt and iron atoms or cobalt-iron alloys.

[0073] Figure 14 The TEM analysis shows that the nitrogen-doped carbon nanotubes with embedded cobalt-iron nanoparticles, which are arranged in a three-dimensional disordered structure, prepared in step (3) of Example 3, have a lateral diameter of 2 nm-300 nm. The embedded cobalt-iron nanoparticles are single atoms with a size of 0.2 nm-0.5 nm and an alloy with a size of 5 nm-50 nm.

[0074] Figure 15 The transmission electron microscopy analysis of the binderless silicon / carbon nanotube composite carbon fiber anode material in Example 3 shows that the thickness of the ultrathin nano-silicon film material is 2nm-30nm.

Claims

1. A method for producing a binderless silicon / carbon nanotube composite carbon fiber negative electrode material, characterized by, The present application discloses a preparation method of binder-free silicon / carbon nanotube composite carbon fiber negative electrode material, which comprises the following steps: (1) dissolving cobalt nitrate, iron nitrate, ammonium fluoride and urea in deionized water in sequence to obtain a mixed solution, and then putting carbon fibers into the mixed solution, hydrothermal reaction is carried out at 100-150℃ for 1-10h, and then the sample is taken out after cooling to room temperature, washed and dried to obtain carbon fibers with hydroxide nanowires grown on the surface; (2) placing the carbon fibers with hydroxide nanowires grown on the surface into the downstream of a quartz tube furnace, then weighing 2-3g of dicyandiamide in a corundum boat and placing it in the upstream gas inlet of the quartz tube furnace, and then scanning the air in the quartz tube with argon gas, adjusting the gas flow rate to 10-50sccm, and then keeping the temperature at 350-450℃ for 1-3h, and then keeping the temperature at 750-850℃ for 1-3h, and then cooling to room temperature to obtain carbon fibers with nitrogen-doped and cobalt-iron nanoparticle-embedded three-dimensional disordered structure arranged carbon nanotubes; (3) fixing the carbon fibers with nitrogen-doped and cobalt-iron nanoparticle-embedded three-dimensional disordered structure arranged carbon nanotubes on the substrate of a magnetron sputtering instrument, fixing a Si target on the radio frequency target column, and then carrying out sputter deposition of nanosilicon, wherein the sputtering pressure is 0.5-5Pa, the sputtering power is 50-150W, the sputtering time is 10-40min, and the working gas during sputtering is argon, to obtain the binder-free silicon / carbon nanotube composite carbon fiber negative electrode material.

2. The production method according to claim 1, wherein In step (1), the carbon fibers need to be pretreated before use, and the specific process is as follows: putting the carbon fibers with the size cut into a potassium permanganate solution and ultrasonic treatment for 5-30min, repeatedly ultrasonic cleaning with deionized water and alcohol, and then drying the cleaned carbon fibers.

3. The production method according to claim 1, wherein In step (1), the molar ratio of cobalt nitrate, iron nitrate, ammonium fluoride and urea is (0.8-1):(0.8-1):(4-6):(9-11), and the concentration of iron nitrate in deionized water is 0.02-0.03mol / L.

4. The production method according to claim 1, wherein In step (2), the amount of dicyandiamide is 0.1 to 0.3 g / cm 2 Carbon fibers.

5. The production method according to claim 1, wherein The thickness of the ultrathin nanosilicon film is 2-30nm.

6. The binder-free silicon / carbon nanotube composite carbon fiber negative electrode material prepared by the preparation method of any one of claims 1-5.

7. The binderless silicon / carbon nanotube composite carbon fiber negative electrode material according to claim 6, wherein The nitrogen-doped and cobalt-iron nanoparticle-embedded three-dimensional disordered structure arranged carbon nanotubes have a transverse diameter of 2-300nm.

8. The binderless silicon / carbon nanotube composite carbon fiber negative electrode material according to claim 6, wherein The cobalt-iron nanoparticles embedded in the nitrogen-doped and cobalt-iron nanoparticle-embedded three-dimensional disordered structure arranged carbon nanotubes are one or more of single atoms with a size of 0.2-0.5nm and CoFe alloy with a size of 5-50nm.

9. The binder-free silicon / carbon nanotube composite carbon fiber negative electrode material of any one of claims 6-8 is used as a negative electrode in a lithium ion structure energy storage composite material.

Images