Graphene-carbon nanotube-nano silicon oxide composite electrode material for lithium ion battery and preparation method of graphene-carbon nanotube-nano silicon oxide composite electrode material

Abstract

The embodiment of the invention discloses a graphene-carbon nanotube-nano silicon oxide composite electrode material for a lithium ion battery and a preparation method of the graphene-carbon nanotube-nano silicon oxide composite electrode material, the material takes a carbon nanotube as a conductive skeleton, and the surface of the carbon nanotube is sequentially coated with ellipsoidal silicon oxide nanoparticles and boron nitride nanosheets; on the outermost layer, a three-dimensional conjugated network is formed by reducing graphene oxide and boron nitride nanosheets, and a carbon nanotube / silicon oxide-boron nitride / graphene-boron nitride cross-scale multi-dimensional structure is constructed; the ellipsoidal silicon oxide nano-particles are arranged along the axial direction of the carbon nano-tubes and are combined with the boron nitride nano-sheets through Si-O-B chemical bonds.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries and its preparation method. Background Technology

[0002] Silicon-based materials (such as silicon oxide) have a high theoretical capacity (Li₂ at room temperature) due to their high Li₂O₃ content. 15 The Si4 phase (with a theoretical capacity of 3590 mAh / g) is considered an ideal choice for the next generation of lithium-ion battery anodes, but it faces the following core challenges in practical applications: (1) The volume change during lithiation / delithiation can reach 300%, leading to particle crushing and repeated rupture of the SEI film, resulting in rapid capacity decay. (2) The intrinsic insulation of silicon oxide leads to insufficient electron transport efficiency, requiring the use of conductive additives to build a network, but the interface bonding force of traditional physical encapsulation methods is weak. (3) Local overheating during charging and discharging can easily trigger side reactions, further reducing battery stability.

[0003] Currently, researchers have proposed that ternary composite systems (such as graphene-carbon nanotube-silicon oxide) can partially alleviate the above problems, but they still suffer from problems such as radial stress concentration caused by the random distribution of spherical silicon oxide particles, insufficient structural stability, lack of effective thermal management methods, low thermal conductivity, and inability to solve local overheating. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries and its preparation method. This composite electrode material has high specific capacity, long cycle life, good thermal conductivity and structural stability, and good energy storage performance, electron transport efficiency and thermal management capability. It can be used as a high energy density and high stability lithium-ion battery electrode material. It can effectively solve the problems of large volume change of lithiation / delithiation, poor conductivity due to intrinsic insulation and side reactions caused by local overheating during charging and discharging in existing silicon-based (such as silicon oxide) electrode materials, as well as the problems of radial stress concentration, insufficient structural stability and low thermal conductivity in traditional graphene-carbon nanotube-silica ternary systems.

[0005] To achieve the above objectives, the present invention provides the following solution: The material uses carbon nanotubes as a conductive framework, with ellipsoidal silica nanoparticles and boron nitride nanosheets sequentially wrapped around the surface of the carbon nanotubes. The outermost layer forms a three-dimensional conjugated network with reduced graphene oxide and boron nitride nanosheets, constructing a multi-scale multidimensional structure of carbon nanotube / silica-boron nitride / graphene-boron nitride. The ellipsoidal silica nanoparticles are arranged along the axial direction of the carbon nanotubes and are bonded to the boron nitride nanosheets through Si-OB chemical bonds.

[0006] Furthermore, the carbon nanotubes have a diameter of 5-20 nm; the ellipsoidal silica nanoparticles have a major axis of 200-500 nm and a minor axis of 50-200 nm; the boron nitride nanosheets have a thickness of 5-10 nm and a diameter of 200-800 nm; and the reduced graphene oxide is a sheet with a thickness of 0.8-1.5 nm.

[0007] Furthermore, the boron nitride nanosheets account for 5-15% of the total mass; the molar ratio of silicon oxide to boron nitride is 1:0.1-0.5.

[0008] This application also provides a method for preparing a graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries, comprising the following steps: S1. In an Ar / H2 mixed gas atmosphere, carbon nanotubes are treated with 50-100W power for 5-15 minutes to introduce hydroxyl groups on their surface. S2. Immerse the carbon nanotubes treated in step S1 into a reaction solution containing sodium silicate, boric acid and urea, and react at 120-180℃ for 8-16 hours to form a composite layer on the surface of the carbon nanotubes, which is coated with ellipsoidal silica nanoparticles and boron nitride nanosheets; wherein the molar ratio of sodium silicate, boric acid and urea is 1:0.3:2. S3. Using the product obtained in step S2 as the working electrode and porous titanium foil as the counter electrode, a pulse voltage of 0.5-1.2 V is applied in an electrolyte containing 2-8 mg / mL reduced graphene oxide and 0.5-2 mg / mL boron nitride nanosheets to deposit the outer three-dimensional conjugated network for 8-25 min.

[0009] Further, in step S1, the carbon nanotubes are carbon nanotube films, the thickness of which is 10-20 micrometers and the density is 0.8-1.2 g / cm³. 3 Furthermore, the diameter of carbon nanotubes is 5-20 nm.

[0010] Furthermore, in step S3, the electrolyte also contains 0.1M NaCl; the frequency of the pulse voltage is 10Hz, the electric field strength during the deposition process is 15-35 V / m, and the distance between the working electrode and the counter electrode is 2 cm.

[0011] This application also provides an electrode comprising the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries as described in any of the preceding claims, or the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries prepared according to the preparation method described in any of the preceding claims.

[0012] This application also provides a lithium-ion battery comprising the electrodes described above.

[0013] This application also provides the use of the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries as described in any of the preceding claims, or the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries prepared by any of the preceding claims in the field of lithium-ion batteries.

[0014] The embodiments described in this specification can achieve the following beneficial effects: In this application, carbon nanotubes function as a conductive framework within the material, providing the main channel for electron transport in the entire composite structure. Simultaneously, their mechanical strength maintains the overall structural stability of the material. On the surface of the carbon nanotubes, the composite electrode material provided in this application employs a layered, ordered encapsulation method to construct the composite structure. From a lithium storage mechanism perspective, silicon oxide undergoes a reversible alloying reaction with lithium ions during charging and discharging, accommodating a large number of lithium ions into its structure. Furthermore, as the primary energy storage carrier in the composite electrode material, silicon oxide constitutes a relatively core portion. Its ellipsoidal structure and arrangement along the axial direction of the carbon nanotubes ensure both an effective volume proportion and minimize the impact of volume expansion on the lithium storage process through structural design, allowing the high theoretical capacity of silicon oxide to be effectively utilized. Boron nitride nanosheets provide physical protection for the silicon oxide.

[0015] The outermost layer of the material is constructed from reduced graphene oxide and boron nitride nanosheets. Their interaction forms a three-dimensional conjugated network. This network not only further encapsulates the inner structure, enhancing the overall density and integrity of the material, but also creates additional conductive pathways, supplementing the conductivity of the carbon nanotubes and enabling more efficient electron transport within the material. Through this layered encapsulation and combination, a multi-scale, multi-dimensional structure of carbon nanotubes / silicon oxide-boron nitride / graphene-boron nitride is ultimately formed. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is an infrared spectrum of carbon nanotubes after functionalization, provided in Embodiment 1 of the present invention; Figure 2 This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silicon oxide / boron nitride nanosheet film provided in Embodiment 1 of the present invention; Figure 3This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silicon oxide / boron nitride nanosheet-graphene film provided in Embodiment 1 of the present invention; Figure 4 This is a charge / discharge capacity diagram provided in Embodiment 1 of the present invention; Figure 5 This is a charge-discharge performance cycle diagram provided in Embodiment 1 of the present invention; Figure 6 This is an infrared spectrum of carbon nanotubes after functionalization, provided in Embodiment 2 of the present invention; Figure 7 This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silica / boron nitride nanosheet film provided in Embodiment 2 of the present invention; Figure 8 This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silicon oxide / boron nitride nanosheet-graphene film provided in Embodiment 2 of the present invention; Figure 9 This is a charge / discharge capacity diagram provided in Embodiment 2 of the present invention; Figure 10 This is a charge-discharge performance cycle diagram provided in Embodiment 2 of the present invention; Figure 11 This is an infrared spectrum of carbon nanotubes after functionalization, provided in Embodiment 3 of the present invention; Figure 12 This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silica / boron nitride nanosheet film provided in Embodiment 3 of the present invention; Figure 13 This is a scanning electron microscope image of a carbon nanotube / ellipsoidal silicon oxide / boron nitride nanosheet-graphene film provided in Embodiment 3 of the present invention; Figure 14 This is a charge / discharge capacity diagram provided in Embodiment 3 of the present invention; Figure 15 This is a charge-discharge performance cycle diagram provided in Embodiment 3 of the present invention; Figure 16 This is a schematic flowchart of the preparation method of the graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries provided by the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed following the word and its equivalents, but do not exclude other elements or objects.

[0019] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments, unless otherwise explicitly stated, "%" refers to weight percentage.

[0020] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0021] This application provides a graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries. The material uses carbon nanotubes as a conductive framework, with ellipsoidal silica nanoparticles and boron nitride nanosheets sequentially wrapped on the surface of the carbon nanotubes. The outermost layer forms a three-dimensional conjugated network through reduced graphene oxide and boron nitride nanosheets, constructing a multi-scale multidimensional structure of carbon nanotube / silica-boron nitride / graphene-boron nitride. The ellipsoidal silica nanoparticles are arranged along the axial direction of the carbon nanotubes and are bonded to the boron nitride nanosheets through Si-OB chemical bonds.

[0022] The technical principles of the above-mentioned technical solution are explained in detail below. In this solution, carbon nanotubes function as a conductive framework, providing the main channel for electron transport in the entire composite structure. Simultaneously, their mechanical strength maintains the overall structural stability of the material. On the surface of the carbon nanotubes, as described above, the composite electrode material provided in this application employs a layered, ordered encapsulation method to construct the composite structure. From the perspective of lithium storage mechanism, silicon oxide undergoes a reversible alloying reaction with lithium ions during charging and discharging, accommodating a large number of lithium ions into its structure. Furthermore, as the primary energy storage carrier in the composite electrode material, silicon oxide has a relatively high content. Its ellipsoidal structure and arrangement along the axial direction of the carbon nanotubes ensure both an effective volume ratio and minimize the impact of volume expansion on the lithium storage process through structural design, allowing the high theoretical capacity of silicon oxide to be effectively utilized. Boron nitride nanosheets provide physical protection for the silicon oxide.

[0023] The outermost layer of the material is constructed from reduced graphene oxide and boron nitride nanosheets. Their interaction forms a three-dimensional conjugated network. This network not only further encapsulates the inner structure, enhancing the overall density and integrity of the material, but also creates additional conductive pathways, supplementing the conductivity of the carbon nanotubes and enabling more efficient electron transport within the material. Through this layered encapsulation and combination, a multi-scale, multi-dimensional structure of carbon nanotubes / silicon oxide-boron nitride / graphene-boron nitride is ultimately formed.

[0024] Meanwhile, addressing the issue of volume expansion in silicon-based materials during lithiation / delithiation, the aforementioned structure incorporates ellipsoidal silica nanoparticles aligned along the axial direction of carbon nanotubes. This axial alignment allows the volume change of the silica particles to better conform to the elongated shape of the carbon nanotubes, reducing radial compression between particles and thus minimizing stress concentration within the structure, preventing particle fragmentation or structural cracking. Furthermore, the ellipsoidal silica nanoparticles and boron nitride nanosheets are chemically bonded via Si-OB bonds. Compared to traditional physical encapsulation, this chemical bonding significantly enhances the interfacial bonding force, effectively preventing interlayer delamination that may occur during long-term charge-discharge cycles, further improving the long-term stability of the material structure.

[0025] In the technical solution of this application, the diameter of the carbon nanotube is 5-20 nm; the major axis of the ellipsoidal silica nanoparticle is 200-500 nm and the minor axis is 50-200 nm; the thickness of the boron nitride nanosheet is 5-10 nm and the diameter is 200-800 nm; and the reduced graphene oxide is a sheet with a thickness of 0.8-1.5 nm.

[0026] In this application's technical solution, the boron nitride nanosheets account for 5-15% of the total mass. This range is designed to address two main issues: firstly, boron nitride has high thermal conductivity, enabling it to quickly conduct away localized heat generated during charging and discharging, preventing localized overheating and side reactions; secondly, its layered structure acts as a buffer, mitigating the volume expansion of silicon oxide. Furthermore, the molar ratio of silicon oxide to boron nitride in this application's technical solution is 1:0.1-0.5. This molar ratio ensures the dominant position of silicon oxide, allowing it to function as the primary lithium-ion storage carrier and guaranteeing a high initial capacity. Secondly, the 0.1 to 0.5 molar ratio ensures a proper match between the amount of boron nitride and silicon oxide, with each unit of silicon oxide corresponding to a sufficient amount of boron nitride. This is achieved through Si-OB chemical bonds, and the layered structure of boron nitride effectively encapsulates the silicon oxide, forming an effective buffer and providing thermal protection.

[0027] like Figure 16 As shown, the present invention also provides a method for preparing the above-mentioned graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries, comprising the following steps: Step S1: Under an Ar / H2 mixed gas atmosphere, treat carbon nanotubes at a power of 50-100W for 5-15 minutes to introduce hydroxyl groups onto their surface. The carbon nanotubes are carbon nanotube films with a thickness of 10-20 micrometers and a density of 0.8-1.2 g / cm³. 3 Furthermore, the diameter of carbon nanotubes is 5-20 nm.

[0028] The purpose of this step is to pretreat carbon nanotubes with plasma. An Ar / H2 mixed gas is used as the ambient gas for plasma treatment, with a treatment power of 50-100W and a treatment time of 5-15 minutes. This plasma treatment process introduces hydroxyl (-OH) groups onto the surface of the carbon nanotubes, enhancing the interfacial bonding between the carbon nanotubes and the subsequently deposited silicon dioxide (SiO2), laying the foundation for the stable formation of the subsequent composite layer. The carbon nanotubes used are not in powder form but rather in the form of a carbon nanotube film with specific physical parameters: a thickness of 10-20 micrometers and a density of 0.8-1.2 g / cm³. 3 The carbon nanotubes constituting the carbon nanotube film have a diameter ranging from 5 to 20 nm. Using carbon nanotube films as the treatment object in this step can solve the problems of conventional carbon nanotube powders being prone to agglomeration during dispersion and difficulty in maintaining the interconnection structure after being combined with other materials, resulting in poor conductivity. At the same time, it can also serve as a template and current collector in subsequent preparation processes, ensuring the structural stability and conductivity of the composite electrode material.

[0029] Step S2: Immerse the carbon nanotubes treated in step S1 into a reaction solution containing sodium silicate, boric acid and urea, and react at 120-180℃ for 8-16 hours to form a composite layer on the surface of the carbon nanotubes, which is coated with ellipsoidal silica nanoparticles and boron nitride nanosheets; wherein the molar ratio of sodium silicate, boric acid and urea is 1:0.3:2.

[0030] The purpose of this step is to co-deposit silica and boron nitride nanosheets on the surface of pretreated carbon nanotubes using a hydrothermal method. The reaction system is prepared by dissolving sodium silicate, boric acid, and urea in deionized water at a molar ratio of 1:0.3:2 to form a homogeneous reaction solution. The carbon nanotubes treated in step S1 (introducing hydroxyl groups to the surface) are immersed in this reaction solution and then reacted at 120-180℃ for 8-16 hours. During this hydrothermal reaction, a composite layer of ellipsoidal silica nanoparticles and boron nitride nanosheets forms on the surface of the carbon nanotubes. The ellipsoidal silica nanoparticles have a major axis of 200-500 nm and a minor axis of 50-200 nm, and are oriented axially along the carbon nanotube axis, effectively reducing radial stress concentration. The boron nitride nanosheets have a thickness of 5-10 nm and a diameter of 200-800 nm, and work synergistically with the silica. This process utilizes the Si-OB chemical bonds generated by the reaction of sodium silicate and boric acid to form a stable interface between silicon oxide and boron nitride nanosheets. This avoids the detachment problem that easily occurs in traditional physical encapsulation methods, and at the same time, it can initially construct a composite structure that combines structural stability and potential thermal conductivity.

[0031] Step S3: Using the product obtained in step S2 as the working electrode and porous titanium foil as the counter electrode, a pulsed voltage of 0.5-1.2 V is applied in an electrolyte containing 2-8 mg / mL reduced graphene oxide and 0.5-2 mg / mL boron nitride nanosheets to deposit the outer three-dimensional conjugated network for 8-25 min. The electrolyte also contains 0.1 M NaCl; the frequency of the pulsed voltage is 10 Hz; the electric field strength during deposition is 15-35 V / m; and the distance between the working electrode and the counter electrode is 2 cm.

[0032] This step employs pulsed electrophoretic deposition. Reduced graphene oxide (rGO) and boron nitride nanosheets (BNNS) self-assemble on the surface of the product obtained in step S2, forming an outer three-dimensional conjugated network. In the deposition system, the electrolyte contains 2-8 mg / mL of reduced graphene oxide and 0.5-2 mg / mL of boron nitride nanosheets, with 0.1 M NaCl added to enhance electrolyte conductivity and improve deposition uniformity. For the electrode setup, the carbon nanotube / SiO2-BNNS composite structure obtained in step S2 is used as the working electrode, and porous titanium foil is used as the counter electrode, with a 2 cm distance between the two electrodes. During deposition, a pulsed voltage of 0.5-1.2 V is applied at a frequency of 10 Hz, the electric field strength is controlled at 15-35 V / m, and the deposition time is 8-25 min. Under these conditions, reduced graphene oxide and boron nitride nanosheets self-assemble orderly on the surface of the composite structure through electrophoresis, forming a three-dimensional conjugated network.

[0033] Example 1: Preparation and performance testing of graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries (1) Surface functionalization treatment of carbon nanotubes A carbon nanotube hybrid film was used as the substrate, wherein the diameter of the carbon nanotubes was 5 nm, the thickness of the carbon nanotube film was 10 μm, and the density was 1.0 g / cm³. 3 The carbon nanotube film was surface-treated using Ar / H2 mixed gas plasma with a treatment power of 80W and a treatment time of 10min. Hydroxyl (-OH) groups were introduced into the surface of the carbon nanotubes through plasma etching.

[0034] like Figure 1 As shown, the functionalized carbon nanotube film, characterized by infrared spectroscopy, exhibits high performance at 3400 cm⁻¹. -1 The presence of a strong, broad peak nearby corresponds to the stretching vibration of hydroxyl groups (OH), indicating that hydroxyl groups have been successfully introduced onto the surface of carbon nanotubes, which can enhance the subsequent interfacial bonding force with silicon oxide.

[0035] (2) Hydrothermal co-deposition growth of SiO2-BN composite layer Weigh 1 mol of sodium silicate, 0.3 mol of boric acid, and 2 mol of urea according to the molar ratio of sodium silicate:boric acid:urea = 1:0.3:2, dissolve them in 200 mL of deionized water, and stir until completely dissolved to form a homogeneous reaction solution. Transfer the above reaction solution to a stainless steel reactor, then immerse the carbon nanotube membrane treated in step (1) into the reaction solution, seal the reactor, and place it in an oven. Keep it at 150 °C for 12 h to simultaneously deposit ellipsoidal silica nanoparticles and boron nitride nanosheets (BNNS) on the surface of the carbon nanotubes through hydrothermal reaction.

[0036] After the reaction was completed, the product was taken out and washed three times with deionized water to remove the residual reaction reagents on the surface. Then it was vacuum dried at 60°C for 12 hours to obtain carbon nanotube / silicon oxide-boron nitride composite film and CNT / SiO2-BNNS composite film.

[0037] like Figure 2 As shown, the composite film is characterized by scanning electron microscopy (SEM). The ellipsoidal silica nanoparticles have a major axis of 400 nm and a minor axis of 100 nm, and are oriented along the axial direction of the carbon nanotubes. The boron nitride nanosheets have a thickness of about 8 nm and form a stable interface with silica through Si-OB chemical bonds.

[0038] (3) Pulse electrophoretic deposition of rGO-BN composite layer Electrolyte preparation: Reduced graphene oxide (rGO) and boron nitride nanosheets (BNNS) were dispersed in 0.1M NaCl aqueous solution to make the concentration of rGO 5 mg / mL and the concentration of BNNS 1 mg / mL, and stirred until uniformly dispersed.

[0039] The CNT / SiO2-BNNS composite film obtained in step (2) was used as the working electrode, and a porous titanium foil with a pore size of 50 μm was used as the counter electrode. The distance between the two electrodes was 2 cm. Electrophoretic deposition was performed in the above electrolyte by applying a pulse voltage of 1.0 V, a frequency of 10 Hz, an electric field strength of 25 V / m, and a deposition time of 20 min, so that rGO and BNNS were self-assembled on the surface of the composite film driven by the electric field.

[0040] After deposition, the product was washed twice with ethanol to remove residual electrolyte on the surface, and then vacuum dried at 80°C for 8 hours to obtain graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries.

[0041] like Figure 3 As shown, SEM characterization revealed that the composite electrode material is coated with a continuous graphene layer, and boron nitride nanosheets are uniformly distributed on the graphene surface, forming an outer three-dimensional conjugated network.

[0042] (4) Electrochemical performance testing The graphene-carbon nanotube-silica composite film prepared in step (3) was used directly as the working electrode, and a lithium metal sheet was used as the counter electrode to assemble a button half-cell. The electrolyte was a 0.8 mol / L lithium hexafluorophosphate solution, and the solvent was ethylene carbonate: diethyl carbonate = 1:1 (volume ratio).

[0043] The electrochemical performance of this half-cell was tested using a LANHECT 3002A battery tester. At a current density of 0.1C, the test voltage range was 0.1~2.5V. Its single-cycle specific capacity-voltage curve is shown below. Figure 4As shown, the results indicate that the initial capacity of this electrode material is as high as 650 mAh / g. Cycling performance tests were conducted at a 1C current density, and the capacity retention curve after 500 cycles is shown in the figure. Figure 5 As shown, the results indicate that the capacity retention rate remains at 87.2%, demonstrating that the material exhibits excellent cycle stability.

[0044] The above results show that the graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries prepared in Example 1 has high initial capacity and excellent cycle stability, which can meet the application requirements of high energy density lithium-ion batteries.

[0045] Example 2: Preparation and performance testing of graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries (1) Surface functionalization treatment of carbon nanotubes A carbon nanotube hybrid film was used as the substrate, wherein the diameter of the carbon nanotubes was 10 nm, the thickness of the carbon nanotube film was 15 μm, and the density was 0.8 g / cm³. 3 The carbon nanotube film was surface-treated using Ar / H2 mixed gas plasma. The treatment power was set to 50W and the treatment time was 5min. Hydroxyl (-OH) groups were introduced into the surface of the carbon nanotubes through plasma etching.

[0046] like Figure 6 As shown, the functionalized carbon nanotube film, characterized by infrared spectroscopy, exhibits high performance at 3400 cm⁻¹. -1 The presence of a broad peak nearby corresponds to the stretching vibration of hydroxyl groups (OH), indicating that hydroxyl groups have been successfully introduced onto the surface of carbon nanotubes, which can enhance the subsequent interfacial bonding force with silicon oxide.

[0047] (2) Hydrothermal co-deposition growth of SiO2-BN composite layer Weigh 1 mol of sodium silicate, 0.3 mol of boric acid, and 2 mol of urea according to the molar ratio of sodium silicate:boric acid:urea = 1:0.3:2, dissolve them in 200 mL of deionized water, and stir magnetically for 30 min until completely dissolved to form a homogeneous reaction solution. Transfer the reaction solution to a 500 mL stainless steel reactor, and then completely immerse the carbon nanotube membrane treated in step (1) into the reaction solution. After sealing the reactor, place it in a forced-air drying oven and keep it at 120 °C for 8 h. Through hydrothermal reaction, ellipsoidal silica nanoparticles and boron nitride nanosheets (BNNS) are simultaneously deposited on the surface of the carbon nanotubes.

[0048] After the reaction was completed, the reaction vessel was allowed to cool naturally to room temperature. The product was then removed and ultrasonically cleaned three times with deionized water (10 min each time) to remove residual reaction reagents on the surface. It was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain a carbon nanotube / silica-boron nitride composite film, namely CNT / SiO2-BNNS composite film.

[0049] like Figure 7 As shown, the composite film is characterized by scanning electron microscopy (SEM). The ellipsoidal silica nanoparticles have a major axis of 300 nm and a minor axis of 80 nm, and are oriented along the axial direction of the carbon nanotubes. The boron nitride nanosheets are about 6 nm thick and form a stable interface with silica through Si-OB chemical bonds, which improves the structural integrity of the composite layer.

[0050] (3) Pulse electrophoretic deposition of rGO-BN composite layer Electrolyte preparation: Reduced graphene oxide (rGO) and boron nitride nanosheets (BNNS) were dispersed in 0.1M NaCl aqueous solution and ultrasonically dispersed for 30 min to make the concentration of rGO 2 mg / mL and the concentration of BNNS 0.5 mg / mL. The mixture was stirred until it was uniformly dispersed.

[0051] Using the CNT / SiO2-BNNS composite film obtained in step (2) as the working electrode and a porous titanium foil (50 μm pore size) as the counter electrode, the distance between the two electrodes was strictly controlled to be 2 cm. Electrophoretic deposition was performed in the above electrolyte by applying a pulsed voltage of 0.5 V, a frequency of 10 Hz, an electric field strength of 15 V / m, and a deposition time of 8 min, so that rGO and BNNS were self-assembled on the surface of the composite film by electric field drive, forming an outer three-dimensional conjugated network.

[0052] After deposition, the product was washed twice with anhydrous ethanol (5 min each time) to remove residual electrolyte on the surface, and then dried in a vacuum drying oven at 80℃ for 8 h to obtain graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries.

[0053] like Figure 8 As shown, SEM characterization revealed that the composite electrode material is coated with a uniform graphene layer, and boron nitride nanosheets are uniformly dispersed on the graphene surface, forming a continuous three-dimensional conductive network, which is beneficial for rapid charge transport.

[0054] (4) Electrochemical performance testing The graphene-carbon nanotube-silica composite film prepared in step (3) was directly cut into 12 mm diameter discs to serve as the working electrode. A lithium metal sheet was used as the counter electrode, and a CR2032 button cell was used as the casing. The half-cell was assembled in an argon glove box (oxygen and moisture < 0.01 ppm). The electrolyte was a 0.8 mol / L lithium hexafluorophosphate solution, the solvent was ethylene carbonate: diethyl carbonate = 1:1 (volume ratio), and the separator was Celgard 2400.

[0055] The electrochemical performance of this half-cell was tested using a LANHE CT3002A battery tester. At a current density of 0.1C, the test voltage range was 0.1~2.5V. Its single-cycle specific capacity-voltage curve is shown below. Figure 9 As shown, the initial capacity of the electrode material is 580 mAh / g. Cycling performance tests were conducted at a 1C current density, and the capacity retention curve after 500 cycles is shown below. Figure 10 As shown, the results indicate that the capacity retention rate is 82.5%, demonstrating that the material has good cycle stability and electrochemical reversibility.

[0056] Example 3: Preparation and performance testing of graphene-carbon nanotube-silica nanocomposite electrode material for lithium-ion batteries (1) Surface functionalization treatment of carbon nanotubes A carbon nanotube hybrid film was used as the substrate, wherein the diameter of the carbon nanotubes was 20 nm, the thickness of the carbon nanotube film was 20 μm, and the density was 1.2 g / cm³. 3 The carbon nanotube film was surface-treated using Ar / H2 mixed gas plasma. The treatment power was set to 100W and the treatment time was 15min. Hydroxyl (-OH) groups were introduced into the surface of the carbon nanotubes through plasma etching.

[0057] like Figure 11 As shown, the functionalized carbon nanotube film, characterized by infrared spectroscopy, exhibits high performance at 3400 cm⁻¹. -1 A strong, broad peak appeared nearby, corresponding to the stretching vibration of hydroxyl (OH). The peak intensity was higher than that in Example 2, indicating that the higher power and longer processing time introduced more hydroxyl groups, which can further enhance the interfacial bonding force with silicon oxide.

[0058] (2) Hydrothermal co-deposition growth of SiO2-BN composite layer Weigh 1 mol of sodium silicate, 0.3 mol of boric acid, and 2 mol of urea according to the molar ratio of sodium silicate:boric acid:urea = 1:0.3:2, dissolve them in 200 mL of deionized water, and stir magnetically for 30 min until completely dissolved to form a homogeneous reaction solution. Transfer the reaction solution to a 500 mL stainless steel reactor, and then completely immerse the carbon nanotube membrane treated in step (1) into the reaction solution. After sealing the reactor, place it in a forced-air drying oven and keep it at 180 °C for 16 h. Through hydrothermal reaction, ellipsoidal silica nanoparticles and boron nitride nanosheets (BNNS) are simultaneously deposited on the surface of carbon nanotubes.

[0059] After the reaction was completed, the reaction vessel was allowed to cool naturally to room temperature. The product was then removed and ultrasonically cleaned three times (10 min each time) with deionized water to remove residual reaction reagents on the surface. It was then placed in a vacuum drying oven at 60℃ and dried for 12 h to obtain a carbon nanotube / silica-boron nitride composite film (CNT / SiO2-BNNS composite film).

[0060] like Figure 12 As shown, the composite film is characterized by scanning electron microscopy (SEM). The ellipsoidal silica nanoparticles have a major axis of 500 nm and a minor axis of 120 nm, and are more densely arranged along the axial direction of the carbon nanotubes. The boron nitride nanosheets are about 10 nm thick and are firmly bonded to silica through Si-OB chemical bonds. The thickness of the composite layer is slightly higher than that of Examples 1 and 2.

[0061] (3) Pulse electrophoretic deposition of rGO-BN composite layer Electrolyte preparation: Reduced graphene oxide (rGO) and boron nitride nanosheets (BNNS) were dispersed in 0.1M NaCl aqueous solution and ultrasonically dispersed for 30 min to make the concentration of rGO 8 mg / mL and the concentration of BNNS 2 mg / mL. The mixture was stirred until it was uniformly dispersed.

[0062] Using the CNT / SiO2-BNNS composite film obtained in step (2) as the working electrode and a porous titanium foil (50 μm pore size) as the counter electrode, the distance between the two electrodes was strictly controlled to be 2 cm. Electrophoretic deposition was performed in the above electrolyte by applying a pulsed voltage of 1.2 V, a frequency of 10 Hz, an electric field strength of 35 V / m, and a deposition time of 25 min, so that rGO and BNNS were self-assembled on the surface of the composite film by electric field drive, forming a denser outer three-dimensional conjugated network.

[0063] After deposition, the product was washed twice with anhydrous ethanol (5 min each time) to remove residual electrolyte on the surface, and then dried in a vacuum drying oven at 80℃ for 8 h to obtain graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries.

[0064] like Figure 13 As shown, SEM characterization revealed that the composite electrode material is coated with a thick graphene layer, and boron nitride nanosheets are uniformly embedded in the graphene network, forming a continuous and dense three-dimensional conductive structure, which significantly reduces charge transport resistance.

[0065] (4) Electrochemical performance testing The graphene-carbon nanotube-silica composite film prepared in step (3) was directly cut into 12 mm diameter discs to serve as the working electrode. A lithium metal sheet was used as the counter electrode, and a CR2032 button cell was used as the casing. The half-cell was assembled in an argon glove box (oxygen and moisture <0.01 ppm). The assembly and testing conditions were the same as in Example 2.

[0066] The battery was tested using a LANHE CT3002A battery tester at a current density of 0.1C. The single-cycle specific capacity-voltage curve is shown below. Figure 14 As shown, the results indicate that the initial capacity of this electrode material is as high as 720 mAh / g. Cycling performance tests were conducted at a 1C current density, and the capacity retention curve after 500 cycles is shown in the figure. Figure 15 As shown, the results indicate a capacity retention rate of 90.3%, demonstrating that the material possesses excellent lithium storage capacity and cycle stability.

[0067] This application also provides an electrode comprising the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries as described in any of the preceding claims, or the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries prepared according to the preparation method described in any of the preceding claims.

[0068] This application also provides a lithium-ion battery comprising the electrodes described above.

[0069] This application also provides the use of the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries as described in any of the preceding claims, or the graphene-carbon nanotube-silica composite electrode material for lithium-ion batteries prepared by any of the preceding claims in the field of lithium-ion batteries.

[0070] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries, characterized by, The material takes carbon nanotubes as a conductive framework, and the surface of the carbon nanotubes is wrapped with ellipsoidal silica nanoparticles and boron nitride nanosheets in turn, and the outermost layer forms a three-dimensional conjugated network through reduction of graphene oxide and boron nitride nanosheets, thereby constructing a cross-scale multi-dimensional structure of carbon nanotube / silica-boron nitride / graphene-boron nitride; the ellipsoidal silica nanoparticles are arranged along the axial direction of the carbon nanotubes and are combined with the boron nitride nanosheets through Si-O-B chemical bonds.

2. The graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries according to claim 1, characterized in that, The diameter of the carbon nanotubes is 5-20 nm; the long axis of the ellipsoidal silica nanoparticles is 200-500 nm, and the short axis is 50-200 nm; the thickness of the boron nitride nanosheets is 5-10 nm, and the diameter is 200-800 nm; and the reduced graphene oxide is a sheet layer with a thickness of 0.8-1.5 nm. 3.The graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries according to claim 1, characterized in that, The mass percentage of the boron nitride nanosheets is 5-15%; and the molar ratio of the silica to the boron nitride is 1:0.1-0.

5.

4. A method for preparing a graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries, characterized in that, The method comprises the following steps: S1. treating the carbon nanotubes under an Ar / H2 mixed gas atmosphere at a power of 50-100 W for 5-15 min to introduce hydroxyl groups on the surface of the carbon nanotubes; S2. immersing the carbon nanotubes treated in step S1 in a reaction solution containing sodium silicate, boric acid and urea, and reacting at 120-180℃ for 8-16 h to form a composite layer of ellipsoidal silica nanoparticles and boron nitride nanosheets on the surface of the carbon nanotubes; wherein the molar ratio of sodium silicate, boric acid and urea is 1:0.3:2; S3. taking the product obtained in step S2 as a working electrode, a porous titanium foil as a counter electrode, and depositing an outer three-dimensional conjugated network in an electrolyte containing 2-8 mg / mL reduced graphene oxide and 0.5-2 mg / mL boron nitride nanosheets by applying a pulse voltage of 0.5-1.2 V for 8-25 min.

5. The preparation method of the graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries according to claim 4, characterized in that, In step S1, the carbon nanotubes are carbon nanotube films having a thickness of 10 to 20 micrometers, a density of 0.8 to 1.2 g / cm 3 , and a diameter of 5 to 20 nm.

6. The method for preparing the graphene-carbon nanotube-nanosilica composite electrode material for lithium-ion batteries according to claim 4, characterized in that, In step S3, the electrolyte further contains 0.1M NaCl; the frequency of the pulse voltage is 10 Hz, the electric field strength during the deposition process is 15-35 V / m, and the distance between the working electrode and the counter electrode is 2 cm.

7. An electrode characterized by: The graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries according to any one of claims 1-3 or prepared according to the method of any one of claims 4-6.

8. A lithium-ion battery, characterized by, The electrode according to claim 7.

9. Use of the graphene-carbon nanotube-nanosilica composite electrode material for lithium ion batteries according to any one of claims 1-3 or prepared according to the method of any one of claims 4-6 in the field of lithium ion batteries.

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