Carbon nanotube-manganese dioxide-graphene composite electrode material for lithium ion battery and preparation method of carbon nanotube-manganese dioxide-graphene composite electrode material
By constructing a carbon nanotube-manganese dioxide-graphene composite electrode material, the problems of conductivity and structural stability of lithium-ion battery cathode materials were solved, achieving efficient charge transport and long-life battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF SYST ENG ACAD OF MILITARY SCI MILITARY NEW ENERGY TECH INST
- Filing Date
- 2025-12-29
- Publication Date
- 2026-05-08
AI Technical Summary
The existing lithium-ion battery cathode material, manganese dioxide, has poor conductivity, unstable structure, and high interface impedance, resulting in low charge transport efficiency and short cycle life.
A carbon nanotube-manganese dioxide-graphene composite electrode material was used. Carbon nanotube sponges were constructed by ice template method, manganese dioxide nanosheets were grown by double pulse electrodeposition, and graphene nanosheets were formed by pH response self-assembly method to construct a core-branch-shell three-level conductive structure.
We have achieved high power density, high energy density and long cycle life in lithium-ion battery electrode materials, which improve charge transport efficiency and structural stability.
Smart Images
Figure CN122000319A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries and its preparation method. Background Technology
[0002] In the field of lithium-ion batteries (LIBs), improving the performance of cathode materials is key to overcoming the bottlenecks in energy density and cycle life. Manganese dioxide (…) Due to its high theoretical specific capacity (308 mAh / g), low cost, and environmental friendliness, it has become a highly promising cathode material candidate. However, its material properties limit its practical application in the field of lithium batteries. It has at least the following disadvantages: (1) Poor electrical conductivity: The intrinsic conductivity is extremely low ( ~ The charge transfer efficiency is low (S / cm), making it difficult to achieve high power density.
[0003] (2) Insufficient structural stability: During the charging and discharging process, Volume expansion can easily lead to structural collapse, resulting in a short cycle life.
[0004] (3) High interfacial impedance: In traditional electrode materials, Insufficient physical contact with conductive agents (such as carbon black) results in high interfacial contact resistance, further reducing its electrochemical performance.
[0005] Although those skilled in the art have attempted to use graphene encapsulation Nanocomposite structures are constructed to improve conductivity, but the ability to construct three-dimensional conductive networks from single carbon materials is limited, and Effective methods for controlling the uniform growth and interfacial bonding of nanosheets remain lacking. Therefore, developing electrode composite materials that combine high conductivity, structural stability, and interfacial compatibility is crucial for improving the performance of lithium-ion batteries. The core challenge in the performance of base electrode composite materials. Summary of the Invention
[0006] To solve the existing To address the problems of poor conductivity, structural instability, and high interfacial impedance in base electrode materials, this invention proposes a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries and its preparation method. The carbon nanotube-manganese dioxide-graphene composite electrode material of this invention has a core-branch-pore three-level conductive structure. Through multi-scale structural design and synergistic effects, this invention prepares lithium-ion batteries with high power density, high energy density, and long cycle life.
[0007] To achieve the above objectives, the present invention provides the following technical solution: A carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries has a three-level complex structure consisting of a core layer, a dendrite layer, and a shell layer; wherein the core layer is a carbon nanotube sponge, the dendrite layer is manganese dioxide nanosheets arranged along the axial direction of the carbon nanotube sponge, and the shell layer is graphene nanosheets coated on the surface of the manganese dioxide nanosheets.
[0008] Furthermore, the carbon nanotube sponge has a porosity of 85-95%, a pore size of 100-400 nm, and a density of 0.3-0.5 g / L. ; And / or, the thickness of the manganese dioxide nanosheets is 10~50 nm; And / or, the thickness of the graphene nanosheets is 1 to 3 layers, and the length and width are both 100 to 500 nm.
[0009] The present invention also provides a method for preparing the above-mentioned carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries, comprising the following steps: Carbon nanotube sponges were prepared using the ice template method. Manganese dioxide nanosheets were deposited on the surface of the carbon nanotube sponge using a dual-pulse electrodeposition method. Graphene nanosheets were self-assembled on manganese dioxide nanosheets using a pH-responsive self-assembly method.
[0010] Furthermore, the specific steps for preparing carbon nanotube sponge by the ice template method are as follows: mixing carbon nanotube suspension with ice template, freezing at -80 degrees Celsius for 12 hours, and removing the ice template by vacuum drying to obtain the carbon nanotube sponge.
[0011] Furthermore, the ice crystals formed during the freezing process have a size of 300~500nm.
[0012] Furthermore, in the process of depositing manganese dioxide nanosheets on the surface of the carbon nanotube sponge using the dual-pulse electrodeposition method: the electrodeposition solution is... Sodium acetate and Na The mixture has a pH of 4-4.5; the current density of the positive pulse is 0.2-0.6 mA / s. The current density of the reverse pulse is -0.3 to -0.1 mA / s. The number of cycles is 1500-2500, and the deposition time is 300-450 min.
[0013] Furthermore, the step of assembling graphene nanosheets from manganese dioxide nanosheets using the pH-responsive self-assembly method is as follows: immerse a carbon nanotube sponge with manganese dioxide nanosheets deposited on its surface into a graphene oxide solution with an initial pH of 2, let it stand, and adjust the pH of the solution to 10.
[0014] Furthermore, the concentration of the graphene oxide solution is 5~8 mg / mL; And / or, the settling time is 120~300min.
[0015] The present invention also provides the application of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries as described in any of the preceding claims in the preparation of lithium-ion batteries.
[0016] Furthermore, the lithium-ion battery includes liquid lithium-ion batteries, gel lithium-ion batteries, and solid lithium-ion batteries.
[0017] Compared with the prior art, the present invention has the following advantages and technical effects: In the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries of this invention, the three-dimensional network of the carbon nanotube sponge is as follows: It provides mechanical support, mitigating volume expansion; The dendritic structure increases the electrolyte contact area and improves the utilization rate of active materials; the graphene shell reduces interfacial impedance, accelerates charge transport, and achieves high power density.
[0018] The composite electrode material preparation process of this invention includes ice template method to construct carbon nanotube sponge and pulse electrodeposition growth. The three core steps of nanosheets, pH-responsive self-assembled graphene layers, and precise control of the three-dimensional structure and interface bonding have enabled the performance optimization of composite electrode materials. The ice template method and electrodeposition process can be used to fabricate large-area flexible electrodes on a large scale, which is suitable for roll-to-roll production; the room-temperature pH-responsive self-assembly process avoids high-temperature treatment, reducing energy consumption and cost.
[0019] This invention systematically solves the problem through an integrated process of structural design, interface optimization, and performance coordination. The challenges of conductivity, stability, and interfacial impedance of base electrode materials provide a new technological path for high-energy-density lithium-ion batteries.
[0020] In summary, the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries of the present invention has high power density, high energy density and long cycle life, and has good application prospects in the field of lithium-ion batteries. Attached Figure Description
[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A scanning electron microscope image of the carbon nanotube sponge prepared in Example 1; Figure 2 Carbon nanotubes prepared in Example 1 - Scanning electron microscope image of the composite membrane; Figure 3 The image shows a scanning electron microscope (SEM) image of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries prepared in Example 1. Figure 4 The single-cycle specific capacity-voltage diagram is shown for the button half-cell prepared with the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries in Example 1, in a current density of 1.0C and a voltage range of 0.1~2.5V. Figure 5 The charge-discharge performance cycle diagram shows the button half-cell prepared using the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries in Example 1. Detailed Implementation
[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.
[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0027] The present invention provides a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries, which has a three-level composite structure with a core layer, a dendrite layer and a shell layer. The core layer is a carbon nanotube sponge, the dendrite layer is manganese dioxide (MnO2) nanosheets arranged along the axial direction of the carbon nanotube sponge, and the shell layer is graphene nanosheets coated on the surface of the manganese dioxide nanosheets.
[0028] The carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries of this invention has a three-level conductive structure of core-branch-pore. The innermost layer is a carbon nanotube sponge, which constructs a three-dimensional interconnected electron transport channel. Dendritic structures are arranged along the axial direction of the carbon nanotube sponge. Nanosheets, forming "carbon nanotubes" The carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries features a dendritic interconnected structure. The surface of the manganese dioxide nanosheets is covered with a graphene layer (i.e., the outermost layer is graphene nanosheets), forming a point-to-point physical interconnection network that reduces interfacial stress while improving electron transport efficiency. The specific capacity of this carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries is 100~200 mAh / g, and its capacity retention rate is ≥80% after 500 cycles at 1C. Macroscopically, this carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries is a thin film that can adhere to the surface of a substrate to form a thin-film electrode, making it highly suitable for fabricating lithium-ion battery electrodes. The composite electrode material prepared by this invention exhibits excellent electrochemical performance, including high power density, high energy density, and long cycle life, and has promising application prospects in the field of lithium-ion batteries.
[0029] In a preferred embodiment of the present invention, the carbon nanotube sponge has a porosity of 85-95%, a thickness of 20-50 micrometers, a pore size of 100-400 nm, and a conductivity of [missing information]. S / cm, density is 0.3~0.5g / cm³ The preferred pore size of the carbon nanotube sponge is 200-400 nm. The raw material for preparing the carbon nanotube sponge is multi-walled carbon nanotubes with a diameter of 10-50 nm, and its structure is affected by the assembly method of the carbon nanotube sponge. Conventional dispersed carbon nanotube powder is not suitable for preparing carbon nanotube sponges because carbon nanotube powder is prone to agglomeration when dispersed, and it cannot maintain the interconnection structure after being combined with metal oxides, resulting in poor conductivity.
[0030] The MnO2 nanosheets have a dendritic structure with a thickness of 10-50 nm and a diameter of 100-600 nm; preferably, the diameter of the MnO2 nanosheets is 200-300 nm and the thickness is 10-20 nm.
[0031] Graphene nanosheets are network structures formed by connecting multiple layers of graphene nanosheets, with a length and width of 100~500nm; preferably, the number of graphene nanosheets is 1~3 layers and the thickness is 1~2nm.
[0032] Embodiments of the present invention also provide a method for preparing the above-mentioned carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries, comprising the following steps: preparing carbon nanotube sponges by an ice template method; and depositing carbon nanotubes onto the surface of the carbon nanotube sponges using a dual-pulse electrodeposition method. Nanosheets; assembled via pH-responsive self-assembly in the above-mentioned nanosheets Graphene nanosheets self-assembled on the surface of nanosheets.
[0033] The principle of this invention is as follows: This invention designs a novel electrode composite material structure, which includes: a core layer (three-dimensional conductive framework): carbon nanotube sponges forming interconnected electron transport channels, possessing both high conductivity and a flexible network structure; and a dendritic layer (active material carrier): a tree-like structure grown by pulsed electrodeposition. Nanosheets are vertically anchored to the inner wall of the carbon nanotube sponge pores, forming a "carbon nanotube- "The dendritic interconnect structure significantly improves the loading of active materials and ion diffusion efficiency; the shell (interface optimization layer): 1-3 layers of graphene nanosheets formed by pH-responsive self-assembly are coated with a 'point-to-point' physical overlapping network." On the surface, while reducing interfacial stress, a high-speed electron transport path is constructed.
[0034] In a preferred embodiment of the present invention, the specific steps for preparing carbon nanotube sponge by the ice template method are as follows: the carbon nanotube suspension is mixed with the ice template and frozen at -80 degrees Celsius for 12 hours to form a "carbon nanotube-ice template" composite gel, and the ice template is removed by vacuum drying to obtain the carbon nanotube sponge.
[0035] In a preferred embodiment of the present invention, the volume ratio of the carbon nanotube suspension to the ice template is 1:1~3. The preparation of the carbon nanotube sponge is carried out in a freeze dryer with a vacuum degree ≤10Pa; the step of vacuum drying to remove the ice template is as follows: the temperature is raised to 20 degrees Celsius, and vacuum drying is performed for 24 hours to remove the ice template.
[0036] In a preferred embodiment of the present invention, the ice crystals formed during the freezing process have a size of 300~500nm.
[0037] The microstructure of the nanotube-manganese dioxide-graphene composite electrode material of this invention is determined by both the raw materials and the preparation process. A pulsed electrodeposition process can be used to form... The structure of nanosheets permeating the pores of carbon nanotube sponges.
[0038] In a preferred embodiment of the present invention, during the deposition of manganese dioxide nanosheets on the surface of carbon nanotube sponge using a dual-pulse electrodeposition method: the electrodeposition solution is a mixture of Mn(NO3)2 (0.02~0.2 mol / L), sodium acetate (0.05~0.5 mol / L), and NaNO3 (0.1~1 mol / L), with a pH of 4~4.5 (adjusted to 4~4.5 using dilute nitric acid or NaOH solution); the current density of the positive pulse is 0.2~0.6 mA / L. The duration is 1~5ms, promoting nanosheet nucleation, and the current density of the reverse pulse is -0.3~-0.1mA / s. The duration was 1-5 ms to inhibit excessive sheet thickening, the number of cycles was 1500-2500, and the deposition time was 300-450 min. After depositing manganese dioxide nanosheets on the surface of carbon nanotube sponge, the surface was washed three times each with deionized water and ethanol, and then vacuum dried at 60 degrees Celsius for 3 hours.
[0039] In a preferred embodiment of the present invention, the step of assembling graphene nanosheets from MnO2 nanosheets using a pH-responsive self-assembly method is as follows: depositing a layer of [unclear - likely a specific material or substance] onto the surface. Carbon nanotube sponges made of nanosheets are immersed in a graphene oxide (GO) solution and left to stand for electrostatic adsorption. GO adheres to the sponge via electrostatic adsorption. surface( Initial adsorption occurs when the GO surface carries a negative charge (GO carries a positive charge). Subsequently, NaOH solution is added dropwise to adjust the pH of the solution to 10, triggering the dissociation of carboxyl groups on the GO surface (-COOH → -). GO forms ionic bonds with metal ions on the MnO2 surface, while the alkaline environment promotes the reduction of GO to graphene (reduction degree > 92%), forming a highly conductive graphene layer. Finally, it is washed 5-10 times with deionized water to remove unadsorbed GO, and then vacuum dried at 60 degrees Celsius for 5 hours to obtain the final electrode composite material. In a preferred embodiment of the present invention, the concentration of the GO solution is 5-8 mg / mL, the initial pH is 2 (adjusted with hydrochloric acid to make the GO surface positively charged), the GO size is 100-500 nm in length and width, and the thickness is 1-2 nm (single layer or few layers); the standing time is 120-300 min. The present invention uses the ice template method to construct carbon nanotube sponges. Through the freeze-drying process of carbon nanotube suspension and ice template (ice crystal size 300-500 nm), the three-dimensional pore structure of the carbon nanotube sponge is precisely controlled, solving the problem of uneven dispersion of traditional carbon nanotube powder; pulse electrodeposition is used to control the morphology of MnO2, and the bidirectional pulse current (positive pulse (0.2-0.6 mA / ) is used. Promotes nucleation, reverse pulse (-0.3~-0.1mA / (Inhibiting excessive growth) enabled controllable growth of MnO2 nanosheet thickness and density; pH-responsive self-assembly of graphene layers was employed, and by adjusting the solution pH (2→10), the electrostatic adsorption-ionic bonding process between GO and MnO2 was triggered, simultaneously achieving high GO reduction (>92%) and uniform coating. Embodiments of this invention also provide an application of the above-mentioned carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries in the preparation of lithium-ion battery electrodes.
[0040] In a preferred embodiment of the present invention, the lithium-ion battery includes a liquid lithium-ion battery, a gel lithium-ion battery (semi-solid), and a solid lithium-ion battery.
[0041] Unless otherwise specified, room temperature in this invention refers to 25±2 degrees Celsius. All raw materials used in the embodiments of this invention were obtained through commercial purchase. It should be noted that any aspects not described in detail in this invention are conventional practices in the art and are not the focus of this invention.
[0042] The technical solution of the present invention will be further illustrated by the following embodiments.
[0043] Example 1 This embodiment provides a method for preparing a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries. The specific steps are as follows: (1) Preparation of carbon nanotube sponge: The carbon nanotube suspension and ice template were mixed at a volume ratio of 1:2 and ultrasonically dispersed for 30 min until uniform; transferred to a mold and frozen at -80 degrees Celsius for 12 h to form a "carbon nanotube-ice template" composite gel. The vacuum degree of the freeze dryer was ≤10 Pa, the temperature was raised to 20 degrees Celsius, and dried for 24 h to remove the ice template, thus obtaining a porous carbon nanotube sponge. Its scanning electron microscope image is shown below. Figure 1 As shown, the sponge has a thickness of approximately 20 micrometers, a pore size of approximately 200 nm, a porosity of 90%, and a conductivity of [missing information]. S / cm, density is 0.4g / cm .
[0044] (2) Pulse electrodeposition growth of manganese dioxide nanosheets 100 mL of 0.05 mol / L ·6 100mL 0.5mol / L And 100 mL of 0.2 mol / L The mixture was prepared and the pH was adjusted to 4.5 with dilute nitric acid (6 mol / L) as the electrodeposition solution. Manganese dioxide nanosheets were then grown by pulse electrodeposition under the following conditions: Working electrode: carbon nanotube sponge; counter electrode: platinum sheet; reference electrode: Ag / AgCl.
[0045] Positive pulse: 0.4mA / The duration is 3ms.
[0046] Reverse pulse: -0.2mA / The duration is 3ms.
[0047] Number of cycles: 2000, total deposition time: 360 min.
[0048] After deposition, the sample was washed three times each with deionized water and ethanol, and then vacuum dried at 60 degrees Celsius for 3 hours to obtain carbon nanotube-manganese dioxide. The composite membrane, its scanning electron microscope image is as follows: Figure 2 As shown, the size of manganese dioxide nanosheets is approximately 300~500 nm, and they are uniformly distributed along the axial direction of carbon nanotubes.
[0049] (3) pH-responsive self-assembled graphene layer The carbon nanotubes prepared in step 2 - The composite membrane undergoes electrophoretic self-assembly to reduce graphene oxide.
[0050] Preparation of reaction solution: The concentration of GO solution is 6 mg / mL, pH=2 (adjusted with hydrochloric acid, GO surface is positively charged), GO size: length and width are both 300 nm, thickness is 1-2 nm (monolayer). Electrostatic adsorption and ionic bonding: combining carbon nanotubes - The composite membrane was immersed in GO solution and left to stand at room temperature for 180 min. The membrane was then subjected to electrostatic interaction. Initial adsorption occurs due to the negative charge on the surface and the positive charge of GO; adding NaOH solution to adjust the pH to 10 triggers the dissociation of carboxyl groups on the GO surface (-COOH → -COO). - ),and Ionic bonds are formed, and the alkaline environment promotes GO reduction (reduction degree > 92%). The material is washed eight times with deionized water to remove unadsorbed GO, and then vacuum-dried at 60°C for 5 hours to obtain the final composite electrode material (carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries). Its scanning electron microscope image is shown below. Figure 3 As shown, graphene nanosheets are uniformly coated on the surface of manganese dioxide nanosheets, forming a dense "point-to-point" physical bonding network. The thickness of the graphene layer is about 1~2nm, and it is tightly bonded to the manganese dioxide interface without obvious agglomeration. The composite structure as a whole maintains good porous characteristics.
[0051] Single-cycle specific capacity-voltage measurement The prepared lithium-ion battery was used as an electrode with a carbon nanotube-manganese dioxide-graphene composite electrode material to form a button half-cell with a lithium sheet. The electrolyte solution was a 0.8 mol / L lithium hexafluorophosphate solution, and the solvent was a mixture of ethylene carbonate and diethyl carbonate (volume ratio = 1:1).
[0052] The prepared electrode was tested as a lithium metal half-cell using a LANHECT3002A battery tester. The single charge-discharge capacity of the electrode was measured at a current density of 1.0C and a voltage range of 0.1–2.5V. The single-cycle specific capacity-voltage graph is shown below. Figure 4 As shown, the electrode of Example 1 exhibits a capacity as high as 156.0 mAh / g at 1.0C. The charge-discharge performance cycle diagram is shown below. Figure 5 As shown, the capacity retention rate remains at 81.4% after 500 cycles, indicating good cycling performance.
[0053] Example 2 This embodiment provides a method for preparing a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries. Its purpose is to verify the feasibility and universality of the technical solution of this invention when key parameters in the preparation process are within different ranges described in this invention, particularly verifying the impact of variations in the ice crystal size formed by the ice template within the specified range on the final material structure and performance. The difference between this embodiment and Embodiment 1 lies only in adjusting the initial conditions of the ice template, aiming to obtain a sponge structure close to the lower limit of the ice crystal size range (300 nm) described in this invention. All other steps and process parameters remain consistent with Embodiment 1.
[0054] The specific preparation steps are as follows: (1) Preparation of carbon nanotube sponge: Carbon nanotube suspension and ice template were mixed at a volume ratio of 1:2. By controlling the pre-cooling temperature and suspension concentration, the ice crystal size formed during the freezing process was controlled to be approximately 300 nm. After ultrasonic dispersion for 30 min until uniform, the mixture was transferred to a mold and frozen at -80°C for 12 h to form a "carbon nanotube-ice template" composite gel. Subsequently, the temperature was raised to 20°C and dried for 24 h in a freeze dryer with a vacuum degree ≤10 Pa to completely remove the ice template, resulting in a porous carbon nanotube sponge. The macroscopic and microscopic morphology of this sponge is similar to that of the material obtained in Example 1 (e.g., ...). Figure 1 Similar to (as shown), both exhibit a three-dimensional interconnected porous network structure, with the main difference being a slightly smaller average pore size of approximately 150 nm. Measurements show a porosity of 88% and a density of 0.42 g / L. .
[0055] (2) Pulse electrodeposition growth of manganese dioxide nanosheets: This step was performed entirely according to the process in Example 1. The prepared carbon nanotube sponge was used as the working electrode, and the nanosheets were grown in a solution of 0.05 mol / L Mn(NO3)2, 0.5 mol / L NaNO3, and 0.2 mol / L... In an electrodeposition solution with the same composition (pH=4.5), the same dual-pulse parameters (positive pulse: 0.4mA / ) were used. 3ms; Reverse pulse: -0.2mA / The carbon nanotube-manganese dioxide composite film was deposited 2000 times (3ms) in a cycle (total time 360min). After deposition, the film was washed and dried to obtain a carbon nanotube-manganese dioxide composite film. Its microstructure is similar to... Figure 2 Similarly, manganese dioxide nanosheets grow uniformly along the axial direction of carbon nanotubes, forming a dendritic interconnected structure.
[0056] (3) pH-responsive self-assembled graphene layer: This step was performed entirely according to the process in Example 1. The composite film was immersed in a graphene oxide (GO) solution with a concentration of 6 mg / mL and an initial pH of 2 and allowed to stand for 180 min. The pH was then adjusted to 10 to trigger the self-assembly and reduction process. Finally, after washing and drying, the final carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries was obtained. The scanning electron microscope image of this final material shows that it possesses... Figure 3 With a consistent core-branch-shell three-level composite structure, graphene nanosheets were successfully coated onto the surface of manganese dioxide nanosheets, forming a complete conductive network.
[0057] Performance Testing and Results: The composite electrode material prepared in this embodiment was assembled into a CR2032 coin cell using the same method as in Example 1, and charge-discharge tests were conducted at a 1.0C rate and a voltage range of 0.1-2.5V. Its initial discharge specific capacity was 148.7 mAh / g. Long-cycle performance testing showed that its capacity decay curve was similar to... Figure 5 Consistent with the trend shown, the capacity retention rate was 79.8% after 500 cycles. Conclusion: This embodiment successfully prepared an electrode material with a "core-branch-shell" three-level composite structure consistent with the core characteristics of this invention by adjusting the ice crystal size to near the lower limit of the range (300-500 nm) described in this invention. Although the specific capacity and cycle retention rate were slightly lower than the optimized Example 1 due to changes in substrate pore size, the core structure was maintained, and the cycle performance was still significantly better than that of unstructured conventional electrode materials. This fully demonstrates the feasibility of ice crystal size within the range described in this invention, and the robustness of the technical solution of this invention within the parameter range.
[0058] Example 3 This embodiment provides a method for preparing a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries. The purpose is to verify the effect of varying the graphene oxide (GO) solution concentration within the range (5-8 mg / mL) described in this invention on the self-assembly effect of the graphene shell and the final electrode performance. The only difference between this embodiment and Example 1 is the increased GO solution concentration, designed to examine the feasibility of this upper limit, while the core composite structural characteristics of the material are not expected to change. The specific preparation steps are as follows: (1) Preparation of carbon nanotube sponge: All process parameters in this step are exactly the same as in Example 1. The structure and performance characteristics of the obtained carbon nanotube sponge are described in Example 1 and related appendices. Figure 1 .
[0059] (2) Pulse electrodeposition growth of manganese dioxide nanosheets: All process parameters in this step are exactly the same as in Example 1. The morphological characteristics of the resulting carbon nanotube-manganese dioxide composite film are described in Example 1 and related appendices. Figure 2 .
[0060] (3) pH-responsive self-assembled graphene layer: The carbon nanotube-manganese dioxide composite film prepared in step (2) was immersed in a graphene oxide GO solution with a concentration of 8 mg / mL (other properties such as initial pH=2, GO sheet size, etc. are the same as in Example 1) for pH-responsive self-assembly. The subsequent standing (180 min), pH adjustment to 10, cleaning and drying processes were completely consistent with those in Example 1. Scanning electron microscopy analysis of the final material showed that graphene nanosheets were uniformly coated on the surface of manganese dioxide dendrites, forming a continuous and dense conductive shell, and its overall composite structure was consistent with that of Example 1. Figure 3 The morphology shown is not substantially different.
[0061] Performance Testing and Results: The materials in this embodiment were evaluated using the same battery assembly and testing procedures as in Example 1. The initial discharge specific capacity at 1.0C rate was 152.3 mAh / g. After 500 cycles, the capacity retention was 80.5%. Conclusion: This embodiment successfully constructed a complete "carbon nanotube-manganese dioxide-graphene" tertiary composite structure using the pH-responsive self-assembly process by increasing the GO solution concentration to the upper limit (8 mg / mL) of the range described in this invention. The higher GO concentration did not lead to excessive graphene sheet stacking or pore blockage; on the contrary, it may have promoted the formation of a denser shell. The obtained good electrochemical performance (capacity >150 mAh / g, cycle retention >80%) demonstrates the rationality of the GO solution concentration within the range described in this invention, especially the feasibility of the upper limit, further supporting the inclusiveness and operability of the parameter range of the preparation method of this invention.
[0062] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries, characterized in that, It has a three-level complex structure with a core layer, a dendritic layer and a shell layer; wherein, the core layer is a carbon nanotube sponge, the dendritic layer is manganese dioxide nanosheets arranged along the axial direction of the carbon nanotube sponge, and the shell layer is graphene nanosheets coated on the surface of the manganese dioxide nanosheets.
2. The carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 1, characterized in that, The carbon nanotube sponge has a porosity of 85-95%, a pore size of 100-400 nm, and a density of 0.3-0.5 g / L. ; And / or, the thickness of the manganese dioxide nanosheets is 10~50 nm; And / or, the thickness of the graphene nanosheets is 1 to 3 layers, and the length and width are both 100 to 500 nm.
3. A method for preparing a carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to any one of claims 1 to 2, characterized in that, Includes the following steps: Carbon nanotube sponges were prepared using the ice template method. Manganese dioxide nanosheets were deposited on the surface of the carbon nanotube sponge using a dual-pulse electrodeposition method. Graphene nanosheets were self-assembled on manganese dioxide nanosheets using a pH-responsive self-assembly method.
4. The preparation method of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 3, characterized in that, The specific steps for preparing carbon nanotube sponge by the ice template method are as follows: mix carbon nanotube suspension with ice template, freeze at -80 degrees Celsius for 12 hours, remove ice template by vacuum drying, and obtain carbon nanotube sponge.
5. The preparation method of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 4, characterized in that, The ice crystals formed during the freezing process have a size of 300~500nm.
6. The preparation method of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 3, characterized in that, In the process of depositing manganese dioxide nanosheets on the surface of the carbon nanotube sponge using the dual-pulse electrodeposition method: the electrodeposition solution is... Sodium acetate and The mixture has a pH of 4-4.5; the current density of the positive pulse is 0.2-0.6 mA / s. The current density of the reverse pulse is -0.3 to -0.1 mA / s. The number of cycles is 1500-2500, and the deposition time is 300-450 min.
7. The preparation method of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 3, characterized in that, The steps for assembling graphene nanosheets from manganese dioxide nanosheets using the pH-responsive self-assembly method are as follows: immerse a carbon nanotube sponge with manganese dioxide nanosheets deposited on its surface into a graphene oxide solution with an initial pH of 2, let it stand, and then adjust the pH of the solution to 10.
8. The method for preparing the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries according to claim 7, characterized in that, The concentration of the graphene oxide solution is 5~8 mg / mL; And / or, the settling time is 120~300min.
9. The application of the carbon nanotube-manganese dioxide-graphene composite electrode material for lithium-ion batteries as described in any one of claims 1 to 2 in the preparation of lithium-ion batteries.
10. The application according to claim 9, characterized in that, The lithium-ion battery includes liquid lithium-ion battery, gel lithium-ion battery and solid lithium-ion battery.