Confined-range aluminized carbon nanotube, preparation method and application thereof, and preparation method of positive electrode active material

Abstract

The invention provides a confinement aluminized carbon nanotube, a preparation method and application thereof, and a preparation method of a positive electrode active material, and particularly relates to the technical field of lithium ion batteries. In the confinement aluminized carbon nanotube, the carbon nanotube is subjected to space confinement in a nanopore channel of a porous anodic aluminum oxide template, and an aluminum-containing compound film is generated in situ on the outer wall of the carbon nanotube and the inner surface of a tube cavity through template conversion; wherein the aluminum-containing compound comprises lithium metaaluminate and / or aluminum oxide; the confinement aluminized carbon nanotube is of a long-strip-shaped and cylindrical structure. According to the invention, spatial confinement is realized in the nanopore channels of the porous anodic aluminum oxide template, and a one-dimensional structure is completely maintained; in a confinement environment, an aluminum-containing compound film is generated in situ on the outer wall of the carbon nano tube and the inner surface of a tube cavity through a template conversion mechanism, so that not only is uniform compounding of an aluminum source and the carbon nano tube realized, but also agglomeration and structural change of the carbon nano tube in subsequent processing and application processes are fundamentally inhibited through a space confinement effect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a confined aluminized carbon nanotube, its preparation method and application, and a method for preparing positive electrode active materials. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is an important cathode material for lithium-ion batteries, widely used in electric vehicles, energy storage systems, and portable electronic devices due to its advantages such as high safety, long cycle life, good thermal stability, environmental friendliness, and low raw material cost. However, its inherent low electronic conductivity and ion diffusion coefficient limit its performance under high-rate charge and discharge conditions, especially with problems such as rapid capacity decay and insufficient power density under high current operation.

[0003] To improve the electrochemical performance of lithium iron phosphate (LFP) lithium iron phosphate, existing technologies commonly employ two modification methods: carbon coating and metal doping. Carbon coating can form a conductive network on the surface of LFP particles, effectively improving the overall electronic conductivity of the material; while metal ion doping can improve ion transport performance by adjusting the crystal structure, expanding lithium-ion diffusion channels, or enhancing the intrinsic conductivity of the material. In practice, organic materials such as glucose, sucrose, polyethylene glycol, and carbon black are often used as carbon sources, decomposing during high-temperature sintering to generate an amorphous carbon layer for coating.

[0004] However, traditional carbon source materials can only provide passive surface coating and lack the ability to effectively control the internal conductive structure of the material. In recent years, one-dimensional carbon nanomaterials such as carbon nanotubes (CNTs) have been regarded as ideal conductive additives due to their excellent conductivity, mechanical strength, and long-range conductive pathways. However, due to their high specific surface area and strong van der Waals forces, carbon nanotubes are prone to aggregation and curling during use, transforming from their original long strip or cylindrical structure into a "mosquito coil" or entangled state. This significantly weakens their conductive bridging function, making it difficult to form an effective three-dimensional conductive network in active materials, thus limiting their practical application in lithium iron phosphate materials.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a confined aluminized carbon nanotube and its preparation method and application, as well as a method for preparing positive electrode active materials, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A first aspect of the present invention provides a confined aluminized carbon nanotube, wherein the carbon nanotube is spatially confined within the nanopores of a porous anodic alumina template, and an aluminum-containing compound film is generated in situ on the outer wall and inner surface of the carbon nanotube by template conversion; wherein the aluminum-containing compound includes lithium aluminate and / or alumina; and the confined aluminized carbon nanotube has an elongated or cylindrical structure.

[0008] Furthermore, the carbon nanotubes have a length of 1-50 micrometers and a diameter of 0.75-3 nanometers.

[0009] Preferably, the proportion of aluminum-containing compounds in the confined aluminized carbon nanotubes is 5-15 wt%.

[0010] The second aspect of the present invention provides a method for preparing the confined aluminized carbon nanotubes, wherein a pretreated aluminum sheet is subjected to a first anodic oxidation to form an alumina film, and then the alumina film is post-treated with a film removal solution, and carbon nanotubes are added after the treatment is completed; then a second anodic oxidation is performed to obtain carbon nanotubes encapsulating the alumina film; finally, lithium hydroxide is added to an ethanol solution and ultrasonically treated to generate lithium aluminate in situ, thereby obtaining the confined aluminized carbon nanotubes.

[0011] Furthermore, the first anodizing and the second anodizing processes are independent of each other: an aluminum sheet is used as the anode and a platinum sheet is used as the cathode, both are placed in an acidic electrolyte, and an anodizing is performed by passing a power source through them.

[0012] Preferably, the voltage for anodizing is 15~50V and the time is 0.5~3h.

[0013] Preferably, the temperature of the electrolyte is controlled at 13~26℃ during the process.

[0014] Preferably, the electrolyte includes oxalic acid, sulfuric acid, or phosphoric acid.

[0015] Furthermore, the membrane removal solution includes phosphoric acid and chromic acid.

[0016] Preferably, the concentration of phosphoric acid is 0.5~0.7 mol / L, and the concentration of chromic acid is 0.1~0.2 mol / L.

[0017] Preferably, the post-treatment temperature is 50~70℃ and the time is 0.5~2h.

[0018] Preferably, the amount of carbon nanotubes added is 30%-50% of the mass of the pretreated aluminum sheet.

[0019] Furthermore, the concentration of the lithium hydroxide ethanol solution is 1~3 g / mL.

[0020] Preferably, lithium hydroxide accounts for 300-800 ppm of the mass of the carbon nanotubes encapsulating the alumina film.

[0021] Preferably, the ultrasonic treatment time is 20-40 minutes.

[0022] Furthermore, the pretreatment process of the aluminum sheet includes annealing, cleaning, alkaline washing, and acid washing processes performed sequentially.

[0023] Preferably, the aluminum sheet has an aluminum content of ≥99.99%.

[0024] Preferably, the annealing temperature is 450~550℃.

[0025] Preferably, the solvent used for cleaning is acetone and / or ethanol.

[0026] Preferably, the cleaning is ultrasonic cleaning, and the time is 20-40 minutes.

[0027] Preferably, the alkaline solution used for alkaline washing is a sodium hydroxide solution, and the washing time is 3-8 minutes.

[0028] Preferably, the concentration of the sodium hydroxide solution is 0.08~0.15 mol / L.

[0029] Preferably, the acid solution used for pickling is a mixture of perchloric acid and ethanol.

[0030] Preferably, in the mixed solution, the volume ratio of perchloric acid to ethanol is 1:(3~8).

[0031] The third aspect of this invention provides the application of the confined aluminized carbon nanotubes in the preparation of positive electrode active materials.

[0032] The fourth aspect of the present invention provides a method for preparing a positive electrode active material, wherein the positive electrode active material includes lithium iron phosphate; the preparation method includes: mixing and grinding a phosphorus source, a lithium source, an iron source, a carbon source and confined aluminized carbon nanotubes, followed by spray drying and sintering to obtain the lithium iron phosphate.

[0033] The confined aluminized carbon nanotube is the confined aluminized carbon nanotube described in the first aspect.

[0034] Furthermore, the amount of the confined aluminized carbon nanotubes is 1 to 3 wt% of the combined mass of the iron source and the phosphorus source.

[0035] Preferably, the phosphorus source includes iron phosphate, the lithium source includes lithium carbonate and / or lithium hydroxide, the iron source includes iron phosphate, and the carbon source is at least one selected from polyethylene glycol, glucose, sucrose, carbon black, and citric acid.

[0036] Preferably, the molar ratio of lithium, iron and phosphorus in the raw material is (0.98~1.4):(1~1.4):(0.95~1.3).

[0037] Preferably, the carbon source accounts for 10-20% of the total mass of the lithium source, iron source and phosphorus source.

[0038] Preferably, the mixing and grinding time is 3 to 10 hours and the rotation speed is 500 to 1000 rpm.

[0039] Preferably, the sintering is carried out under a protective atmosphere, at a temperature of 700~900℃, for 8~10 hours.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects: The confined aluminized carbon nanotubes provided by this invention achieve spatial confinement within the nanopores of a porous anodic alumina template, thus maintaining their elongated, cylindrical, one-dimensional structure. In this confined environment, aluminum-containing compound films are generated in situ on the outer wall and inner surface of the carbon nanotubes through a template conversion mechanism. This not only achieves uniform composite of aluminum source and carbon nanotubes, but also fundamentally suppresses the aggregation and structural changes of carbon nanotubes during subsequent processing and application through the spatial confinement effect.

[0041] The preparation method provided by this invention not only ensures the integrity of the one-dimensional long-range structure of carbon nanotubes, but also achieves highly uniform distribution of aluminum source and strong interfacial bonding through chemical transformation within a confined space. It has the advantages of good process repeatability, mild reaction conditions, and precise component control, providing a reliable technical path for the large-scale preparation of multifunctional carbon nanomaterials.

[0042] The application provided by this invention, given the advantages of the confined aluminized carbon nanotubes, allows them to maintain a long, cylindrical, one-dimensional structure in the positive electrode active material, thereby constructing a continuous and efficient electronic conduction pathway and significantly improving the overall conductivity of the positive electrode active material.

[0043] The method for preparing positive electrode active materials provided by this invention allows aluminum-containing compounds in confined aluminized carbon nanotubes to release Al during high-temperature sintering. 3+ The presence of ions enables effective doping of the lithium iron phosphate lattice, optimizing the crystal structure and enhancing lithium-ion diffusion capabilities. Simultaneously, aluminum-containing compounds participate in the formation of an interface regulation layer during the reaction, synergistically promoting uniform carbon coating. Therefore, this confined aluminized carbon nanotube integrates structural confinement stability, in-situ doping, enhanced conductivity, and interfacial synergy, significantly improving the electronic / ionic conductivity of the cathode material, thereby substantially enhancing its rate performance and cycle stability. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a scanning electron microscope image of the original carbon nanotubes. Figure 2 The image shows a scanning electron microscope (SEM) image of the ball-milled carbon nanotubes. Figure 3 Scanning electron microscope image of the original confined aluminized carbon nanotubes; Figure 4 Scanning electron microscope (SEM) image of confined aluminized carbon nanotubes after ball milling; Figure 5 EDS spectra of confined aluminized carbon nanotubes; Figure 6 This is the energy spectrum curve of confined aluminized carbon nanotubes. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0047] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0048] A first aspect of the present invention provides a confined aluminized carbon nanotube, wherein the carbon nanotube is spatially confined within the nanopores of a porous anodic alumina template, and an aluminum-containing compound film is generated in situ on the outer wall and inner surface of the carbon nanotube by template conversion; wherein the aluminum-containing compound includes lithium aluminate and / or alumina; and the confined aluminized carbon nanotube has an elongated or cylindrical structure.

[0049] The confined aluminized carbon nanotubes provided by this invention achieve spatial confinement within the nanopores of a porous anodic alumina template, thus maintaining their elongated, cylindrical, one-dimensional structure. In this confined environment, aluminum-containing compound films are generated in situ on the outer wall and inner surface of the carbon nanotubes through a template conversion mechanism. This not only achieves uniform composite of aluminum source and carbon nanotubes, but also fundamentally suppresses the aggregation and structural changes of carbon nanotubes during subsequent processing and application through the spatial confinement effect.

[0050] Furthermore, the carbon nanotubes have a length of 1-50 micrometers and a diameter of 0.75-3 nanometers.

[0051] Preferably, the proportion of aluminum-containing compounds in the confined aluminized carbon nanotubes is 5-15 wt%.

[0052] The second aspect of the present invention provides a method for preparing the confined aluminized carbon nanotubes, wherein a pretreated aluminum sheet is subjected to a first anodic oxidation to form an alumina film, and then the alumina film is post-treated with a film removal solution, and carbon nanotubes are added after the treatment is completed; then a second anodic oxidation is performed to obtain carbon nanotubes encapsulating the alumina film; finally, lithium hydroxide is added to an ethanol solution and ultrasonically treated to generate lithium aluminate in situ, thereby obtaining the confined aluminized carbon nanotubes.

[0053] The preparation method provided by this invention not only ensures the integrity of the one-dimensional long-range structure of carbon nanotubes, but also achieves highly uniform distribution of aluminum source and strong interfacial bonding through chemical transformation within a confined space. It has the advantages of good process repeatability, mild reaction conditions, and precise component control, providing a reliable technical path for the large-scale preparation of multifunctional carbon nanomaterials.

[0054] Specifically, an ordered porous alumina film is formed through the first anodizing process, providing a template for subsequent structural guidance. Subsequently, the alumina film is treated more uniformly and regularly using a film removal solution, which then introduces carbon nanotubes into a confined state and performs a second anodizing process. This allows the newly generated alumina to grow in situ on the surface and within the pores of the carbon nanotubes, firmly encapsulating them within the nanopores and maintaining a one-dimensional state. Finally, the alumina is partially converted into lithium aluminate, achieving in-situ composite of aluminum-containing compounds on the outer wall and inner surface of the carbon nanotubes.

[0055] Furthermore, the first anodizing and the second anodizing processes are independent of each other: an aluminum sheet is used as the anode and a platinum sheet is used as the cathode, both are placed in an acidic electrolyte, and an anodizing is performed by passing a power source through them.

[0056] Preferably, the voltage for anodizing is 15~50V and the time is 0.5~3h.

[0057] Typically, but not limitingly, the voltage for anodizing can be, for example, 30V, 32V, 35V, 38V, 40V, 42V, 45V, 48V, or 50V, or any value within the range of 30V to 50V; the anodizing time can be, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h, or any value within the range of 0.5h to 3h.

[0058] Preferably, the electrolyte temperature is controlled between 13 and 26°C during the process to ensure the orderly growth of alumina nanopores and prevent film ablation or structural damage caused by local overheating. This low-temperature condition can effectively suppress Joule heating generated in the electrochemical reaction, maintain a stable oxidation rate and uniform pore morphology, thereby obtaining a highly ordered, uniformly sized porous anodic alumina (AAO) template. At the same time, the low temperature helps to improve the compactness and mechanical stability of the oxide film, avoids the accelerated alumina dissolution rate at high temperatures which would affect the template quality, and provides a high-quality nano-reaction space for subsequent confined composite of carbon nanotubes and in-situ generation of aluminum-containing compounds.

[0059] Typical, but not limiting, the temperature of the electrolyte during the process can be controlled at, for example, 13°C, 15°C, 17°C, 19°C, 21°C, 23°C, or 26°C, or any value within the range of 13°C to 26°C.

[0060] Preferably, the electrolyte includes oxalic acid, sulfuric acid, or phosphoric acid.

[0061] Furthermore, the film removal solution includes phosphoric acid and chromic acid, which selectively dissolve the porous alumina film formed after the first anodizing, thereby exposing the regularly arranged pit array structure on the aluminum substrate surface. Phosphoric acid can gently corrode the alumina layer to achieve uniform film removal, while chromic acid acts as a passivator for the aluminum substrate surface, preventing it from being over-corroded or developing irregular defects during the oxide film removal process. The synergistic effect of the two can retain a highly ordered nanoscale pit template, providing a precise structural guidance basis for the subsequent introduction of carbon nanotubes and the directional regrowth of the new alumina layer during the second anodizing process.

[0062] Preferably, the concentration of phosphoric acid is 0.5~0.7 mol / L, and the concentration of chromic acid is 0.1~0.2 mol / L.

[0063] Typically, but not limitingly, the concentration of phosphoric acid can be, for example, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, or 0.7 mol / L, or any value within the range of 0.5 mol / L to 0.7 mol / L; the concentration of chromic acid can be, for example, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, or 0.2 mol / L, or any value within the range of 0.1 mol / L to 0.2 mol / L.

[0064] Preferably, the post-treatment temperature is 50~70℃ and the time is 0.5~2h.

[0065] Typically, but not limitingly, the post-processing temperature can be, for example, 50°C, 55°C, 60°C, 65°C, or 70°C, or any value within the range of 50°C to 70°C; the post-processing time can be, for example, 0.5h, 1h, 1.2h, 1.5h, 1.8h, or 2h, or any value within the range of 0.5h to 2h.

[0066] Preferably, the amount of carbon nanotubes added is 30%-50% of the mass of the pretreated aluminum sheet.

[0067] Furthermore, the concentration of the lithium hydroxide ethanol solution is 1-3 g / mL. Through an ultrasound-assisted interfacial reaction, the alumina portion encapsulated on the surface and within the pores of the carbon nanotubes is converted into an aluminum-containing compound—lithium aluminate. This reaction is carried out under mild conditions; using ethanol as a solvent effectively penetrates the confined structure, avoiding the damage to the one-dimensional nanostructure caused by violent reactions. Simultaneously, lithium hydroxide provides the lithium source and OH... - Ions undergo a solid-phase transformation reaction with alumina to generate a lithium aluminate film with ionic conductivity potential. This process enables in-situ uniform composite formation of aluminum-containing compounds on the outer wall and inner surface of carbon nanotubes, which not only enhances the compositional uniformity and interfacial bonding strength of the material, but also provides a functional basis for subsequent application in cathode materials to achieve aluminum doping and interfacial control.

[0068] Preferably, lithium hydroxide accounts for 300-800 ppm of the mass of the carbon nanotubes encapsulating the alumina film.

[0069] Typically, but not limitingly, the mass of lithium hydroxide in the carbon nanotubes encapsulating the alumina film can be, for example, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, or 800 ppm, or any value in the range of 300 ppm to 800 ppm.

[0070] Preferably, the ultrasonic treatment time is 20-40 minutes.

[0071] Typically, but not limitingly, the duration of the ultrasonic treatment can be, for example, 20 min, 25 min, 30 min, 35 min, or 40 min, or any value within the range of 20 min to 40 min.

[0072] Furthermore, the pretreatment process of the aluminum sheet includes annealing, cleaning, alkaline washing, and acid washing processes performed sequentially.

[0073] Preferably, the aluminum sheet has an aluminum content of ≥99.99%.

[0074] Preferably, the annealing temperature is 450~550℃ to eliminate the internal stress generated during the processing of high-purity aluminum sheets, promote the uniform and orderly growth of the oxide layer on its surface, and improve the lattice integrity, thereby laying the structural foundation for the subsequent anodizing to form a highly ordered porous alumina (AAO) template.

[0075] Typically, but not limitingly, the annealing temperature can be, for example, 450°C, 470°C, 490°C, 500°C, 520°C, 540°C, or 550°C, or any value within the range of 450°C to 550°C.

[0076] Preferably, the solvent used for cleaning is acetone and / or ethanol to remove organic contaminants, grease and residual processing aids from the surface of the aluminum sheet, ensuring that the substrate surface is clean.

[0077] Preferably, the cleaning is ultrasonic cleaning, and the time is 20-40 minutes.

[0078] Typical, but not limiting, ultrasonic cleaning time can be, for example, 20 min, 25 min, 30 min, 35 min or 40 min, or any value within the range of 20 min to 40 min.

[0079] Preferably, the alkaline solution used in the alkaline washing is a sodium hydroxide solution, and the washing time is 3-8 minutes, to remove the dense aluminum oxide layer naturally formed on the surface of the aluminum sheet or generated during processing, as well as some inorganic impurities.

[0080] Typical, but not limiting, alkaline washing time can be, for example, 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, or any value within the range of 3 min to 8 min.

[0081] Preferably, the concentration of the sodium hydroxide solution is 0.08~0.15 mol / L.

[0082] Typically, but not limitingly, the concentration of the sodium hydroxide solution can be, for example, 0.08 mol / L, 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, or 0.15 mol / L, or any value within the range of 0.08 mol / L to 0.15 mol / L.

[0083] Preferably, the acid solution used in the pickling is a mixture of perchloric acid and ethanol, which can selectively corrode the raised areas and grain boundary defects on the aluminum surface under mild conditions, achieving surface smoothing while avoiding excessive corrosion. Ethanol, as an organic solvent, can also effectively reduce the intensity of the reaction, improve process safety, and promote solution wetting and product removal. This step ultimately forms a uniform, low-roughness metal surface, which is beneficial to the uniformity of the electric field distribution during subsequent anodizing, thereby improving the orderliness and structural consistency of the porous alumina template.

[0084] Preferably, in the mixed solution, the volume ratio of perchloric acid to ethanol is 1:(3~8).

[0085] Typically, but not limitingly, the volume ratio of perchloric acid to ethanol in the mixed solution can be, for example, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, or any ratio in the range of 1:(3~8).

[0086] The third aspect of this invention provides the application of the confined aluminized carbon nanotubes in the preparation of positive electrode active materials.

[0087] The application provided by this invention, given the advantages of the confined aluminized carbon nanotubes, allows them to maintain a long, cylindrical, one-dimensional structure in the positive electrode active material, thereby constructing a continuous and efficient electronic conduction pathway and significantly improving the overall conductivity of the positive electrode active material.

[0088] The fourth aspect of the present invention provides a method for preparing a positive electrode active material, wherein the positive electrode active material includes lithium iron phosphate; the preparation method includes: mixing and grinding a phosphorus source, a lithium source, an iron source, a carbon source and confined aluminized carbon nanotubes, followed by spray drying and sintering to obtain the lithium iron phosphate.

[0089] The confined aluminized carbon nanotube is the confined aluminized carbon nanotube described in the first aspect.

[0090] The method for preparing positive electrode active materials provided by this invention allows aluminum-containing compounds in confined aluminized carbon nanotubes to release Al during high-temperature sintering. 3+The presence of ions enables effective doping of the lithium iron phosphate lattice, optimizing the crystal structure and enhancing lithium-ion diffusion capabilities. Simultaneously, aluminum-containing compounds participate in the formation of an interface regulation layer during the reaction, synergistically promoting uniform carbon coating. Therefore, this confined aluminized carbon nanotube integrates structural confinement stability, in-situ doping, enhanced conductivity, and interfacial synergy, significantly improving the electronic / ionic conductivity of the cathode material, thereby substantially enhancing its rate performance and cycle stability.

[0091] Furthermore, the amount of confined aluminized carbon nanotubes used is 1-3 wt% of the combined mass of the iron and phosphorus sources. Within this range, the material can provide a sufficient one-dimensional conductive network to significantly improve the electronic conductivity of the positive electrode active material, and also achieve effective release of aluminum-containing compounds during sintering. This allows for appropriate aluminum doping of the lithium iron phosphate lattice, optimizing the crystal structure and improving the lithium-ion diffusion rate. Simultaneously, this amount helps in the formation of the interface control layer, promoting uniform coating of the carbon source. If the amount is less than 1 wt%, the conductivity enhancement and doping effect are insufficient; if it exceeds 3 wt%, it will cause problems such as conductive agent accumulation, decreased specific energy, or increased side reactions.

[0092] Typically, but not limitingly, the amount of confined aluminized carbon nanotubes used is 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, or 3 wt% of the combined mass of the iron and phosphorus sources, or any value within the range of 1 wt% to 3 wt% of the combined mass of the iron and phosphorus sources.

[0093] Preferably, the phosphorus source includes iron phosphate, the lithium source includes lithium carbonate and / or lithium hydroxide, the iron source includes iron phosphate, and the carbon source is at least one selected from polyethylene glycol, glucose, sucrose, carbon black, and citric acid.

[0094] Preferably, the molar ratio of lithium, iron and phosphorus in the raw material is (0.98~1.4):(1~1.4):(0.95~1.3).

[0095] Typical, but not limiting, molar ratios of lithium, iron, and phosphorus in the raw materials can be, for example, (0.98:1:0.95), (1.1:1.1:1.0), (1.2:1.2:1.1), (1.3:1.3:1.2), or (1.4:1.4:1.3), or any combination of ratios within the range of (0.98~1.4):(1~1.4):(0.95~1.3).

[0096] Preferably, the carbon source accounts for 10-20% of the total mass of the lithium source, iron source and phosphorus source.

[0097] Typically, but not limitingly, the proportion of the carbon source to the sum of the masses of the lithium source, iron source and phosphorus source can be, for example, 10%, 12%, 14%, 16%, 18% or 20%, or any value in the range of 10% to 20%.

[0098] Preferably, the mixing and grinding time is 3 to 10 hours and the rotation speed is 500 to 1000 rpm.

[0099] Typically, but not limitingly, the mixing and grinding time can be, for example, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h, or any value within the range of 3h to 10h; the grinding speed can be, for example, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, or 1000rpm, or any value within the range of 500rpm to 1000rpm.

[0100] Preferably, the sintering is carried out under a protective atmosphere, at a temperature of 700~900℃, for 8~10 hours.

[0101] Typical, but not limiting, sintering temperatures can be, for example, 700°C, 750°C, 800°C, 850°C, or 900°C, or any value within the range of 700°C to 900°C; sintering times can be, for example, 8h, 8.5h, 9h, 9.5h, or 10h, or any value within the range of 8h to 10h.

[0102] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0103] Example 1 This embodiment provides a confined aluminized carbon nanotube, and the specific preparation process is as follows: (1) Pretreatment of aluminum sheet: High-purity aluminum sheet with a purity of 99.99% was selected and annealed at 500℃ for 1 h in air atmosphere to eliminate internal stress and promote uniform growth of oxide layer. After annealing, the aluminum sheet was ultrasonically cleaned in acetone and anhydrous ethanol for 30 min respectively to remove surface organic contaminants; after removal, it was rinsed with deionized water and then immersed in 0.1 mol / L sodium hydroxide (NaOH) solution for alkali washing for 5 min to remove natural oxide layer; then it was thoroughly rinsed with deionized water and acid-polished with a mixed solution of perchloric acid and ethanol with a volume ratio of 1:5 to obtain a mirror-smooth and clean surface.

[0104] (2) First anodizing: 30g of pretreated aluminum sheet was used as the anode and platinum sheet as the cathode. The two were placed in a polyethylene container containing 0.3mol / L oxalic acid to form an electrolytic cell. A rubber ring was placed between the aluminum sheet and the container to ensure tight contact. A copper sheet was introduced as an auxiliary anode to improve the uniformity of conductivity. The entire device was placed in an ice-water bath. The first anodizing was carried out under a constant voltage of 40V for 1 hour, resulting in an ordered porous alumina film.

[0105] (3) Film removal treatment: After oxidation, the aluminum sheet is removed and rinsed with deionized water. The formed alumina film is immersed in a film removal solution for selective dissolution treatment. The film removal solution consists of 0.6 mol / L phosphoric acid and 0.15 mol / L chromic acid. It is heated in a 60°C water bath for 1 h to expose the regularly arranged pit template structure.

[0106] (4) Introduction of carbon nanotubes and second anodizing: 10g of carbon nanotubes (approximately 2-3 nm in diameter and 1-2 μm in length) were added to the system and dispersed in the electrolyte to ensure that they could enter the template micro-area environment. Then, a second anodizing was performed with a voltage of 40 V and a time of 6 h, so that a new alumina layer grew in situ around the carbon nanotubes, thereby effectively encapsulating them in the nanopores and forming carbon nanotubes that encapsulate the alumina film.

[0107] (5) Lithium aluminate conversion: The carbon nanotubes coated with the alumina film obtained above were immersed in a 95% ethanol solution, and lithium hydroxide was added, wherein the amount of lithium hydroxide added accounted for 500 ppm (i.e. 0.5‰) of the total mass of the carbon nanotubes coated with the alumina film. The solution was ultrasonically treated for 30 min to promote the partial conversion of alumina into lithium aluminate (LiAlO2), realizing the in-situ generation of aluminum-containing compounds on the outer wall and inner surface of the carbon nanotubes, and finally obtaining confined aluminized carbon nanotubes with elongated cylindrical structures.

[0108] Example 2 This embodiment provides a confined aluminized carbon nanotube, and the specific preparation process is as follows: (1) The aluminum sheet pretreatment process is the same as the step in Example 1.

[0109] (2) First anodizing: 30g of pretreated aluminum sheet was used as the anode and platinum sheet as the cathode. The two were placed in a polyethylene container containing 0.3mol / L oxalic acid to form an electrolytic cell. A rubber ring was placed between the aluminum sheet and the container to ensure tight contact. A copper sheet was introduced as an auxiliary anode to improve the uniformity of conductivity. The entire device was placed in an ice-water bath. The first anodizing was carried out under a constant voltage of 45V for 1.5 h, resulting in an ordered porous alumina film.

[0110] (3) Film removal treatment: Take out the oxidized aluminum sheet, rinse it with deionized water and immerse it in a film removal solution composed of 0.55 mol / L phosphoric acid and 0.18 mol / L chromic acid. Treat it in a water bath at 55℃ for 1.5 h to expose a regularly arranged pit array structure.

[0111] (4) Introduction of carbon nanotubes and second anodizing: 10g of carbon nanotubes (approximately 2-3 nm in diameter and 1-2 μm in length) were added to the electrolytic cell to allow them to fully enter the template micro-region environment. Then, a second anodizing was performed with the following process parameters: voltage 45V and time 6.5 h. This allowed the newly generated alumina to be coated in situ around the carbon nanotubes, forming a carbon nanotube film encapsulating the alumina.

[0112] (5) Lithium aluminate conversion: The obtained carbon nanotubes coated with alumina film were immersed in a 0.02 mol / L lithium hydroxide ethanol solution and treated with ultrasound for 35 min at room temperature. The amount of lithium hydroxide added was equivalent to 600 ppm of the mass of the carbon nanotubes coated with alumina. Through interfacial reaction, some alumina was converted into lithium aluminate, and finally confined aluminized carbon nanotubes were obtained.

[0113] Example 3 This embodiment provides a confined aluminized carbon nanotube, and the specific preparation process is as follows: (1) The aluminum sheet pretreatment process is the same as the step in Example 1.

[0114] (2) First anodizing: 30g of pretreated aluminum sheet was used as the anode and platinum sheet as the cathode. The two were placed in a polyethylene container filled with 0.2mol / L sulfuric acid to form an electrolytic cell. A rubber ring was placed between the aluminum sheet and the container to ensure tight contact. A copper sheet was introduced as an auxiliary anode to improve the uniformity of conductivity. The entire device was placed in an ice-water bath. The first anodizing was carried out under a constant voltage of 50V for 2 hours to generate an ordered porous alumina film.

[0115] (3) Film removal treatment: Take out the oxidized aluminum sheet, rinse it with deionized water and immerse it in a film removal solution composed of 0.7 mol / L phosphoric acid and 0.2 mol / L chromic acid. Treat it in a water bath at 70℃ for 2 h to expose a regularly arranged pit array structure.

[0116] (4) Introduction of carbon nanotubes and second anodizing: 10g of carbon nanotubes (approximately 2-3 nm in diameter and 1-2 μm in length) were added to the electrolytic cell to allow them to fully enter the template micro-region environment. Then, a second anodizing was performed with the following process parameters: voltage 50V and time 7h. This allowed the newly generated alumina to be coated in situ around the carbon nanotubes, forming a carbon nanotube film encapsulating the alumina.

[0117] (5) Lithium aluminate conversion: The carbon nanotubes coated with the obtained alumina film were immersed in a 0.03 mol / L lithium hydroxide ethanol solution and treated with ultrasound for 40 min at room temperature. The amount of lithium hydroxide added was equivalent to 800 ppm of the mass of the carbon nanotubes coated with alumina. Through interfacial reaction, some alumina was converted into lithium aluminate, and finally confined aluminized carbon nanotubes were obtained.

[0118] Example 4 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (3), it is heated in a 40°C water bath for 2 hours. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0119] Example 5 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (3), it is heated in a 50°C water bath for 2 hours. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0120] Example 6 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (3), it is heated in a 70°C water bath for 0.5 hours. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0121] Example 7 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (3), it is heated in an 80°C water bath for 0.5 hours. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0122] Example 8 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (4), the amount of carbon nanotube added is 5g. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0123] Example 9 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (4), the amount of carbon nanotube added is 9g. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0124] Example 10 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (4), the amount of carbon nanotube added is 15g. The other steps are the same as in embodiment 1, and will not be repeated here.

[0125] Example 11 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (4), the amount of carbon nanotube added is 20g. The other steps are the same as in embodiment 1, and will not be repeated here.

[0126] Example 12 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (5), the amount of lithium hydroxide added accounts for 200 ppm of the total mass of the carbon nanotubes encapsulating the alumina film. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0127] Example 13 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (5), the amount of lithium hydroxide added accounts for 300 ppm of the total mass of the carbon nanotubes encapsulating the alumina film. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0128] Example 14 This embodiment provides a confined aluminized carbon nanotube. The difference from embodiment 1 is that in step (5), the amount of lithium hydroxide added accounts for 800 ppm of the total mass of the carbon nanotubes encapsulating the alumina film. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0129] Example 15 This embodiment provides a confined aluminized carbon nanotube. Unlike embodiment 1, in step (5), the amount of lithium hydroxide added accounts for 1000 ppm of the total mass of the carbon nanotubes encapsulating the alumina film. The remaining steps are the same as in embodiment 1 and will not be repeated here.

[0130] Characterization Example 1 The confined aluminized carbon nanotubes obtained in Example 1 and the raw carbon nanotubes from Example 1 were placed in a ball mill and ball-milled for 3 hours at a speed of 800 r / min. Then, the ball-milled material and the original material were subjected to scanning electron microscopy.

[0131] Scanning electron microscope image of the original carbon nanotubes as shown below Figure 1 As shown, from Figure 1 As can be seen, carbon nanotubes exhibit a clear elongated, one-dimensional fibrous morphology with a typical cylindrical structure, good dispersibility, and no obvious aggregation or curling.

[0132] Scanning electron microscope image of ball-milled carbon nanotubes as shown below Figure 2 As shown, from Figure 2 It can be seen that carbon nanotubes exhibit severe curling, entanglement, and even mosquito coil-like stacking structures.

[0133] Scanning electron microscope image of the original confined aluminized carbon nanotubes as shown below Figure 3As shown, from Figure 3 It can be seen that the carbon nanotubes still maintain a straight, elongated structure and are coated with a uniform outer shell material, indicating that spatially confined composite was successfully achieved through the porous anodic alumina template method.

[0134] Scanning electron microscope image of confined aluminized carbon nanotubes after ball milling is shown below. Figure 4 As shown, from Figure 4 It can be seen that despite undergoing intense mechanical action, carbon nanotubes still maintain a straight, extended strip shape, without any obvious curling or entanglement.

[0135] Characterization Example 2 The confined aluminized carbon nanotubes obtained in Example 1 were subjected to EDS, and the resulting images are as follows: Figure 5 As shown. From Figure 5 As can be seen, carbon elements are evenly distributed in the detection area, forming a continuous coating layer; aluminum elements are concentrated in the core area and are encapsulated by carbon elements. The successful coating of the aluminum core with carbon nanotubes, without issues such as aluminum core exposure, carbon layer breakage, or elemental segregation, indicates that the coating process is stable and the structural integrity is good.

[0136] Figure 6 The image shows the energy spectrum of the confined aluminized carbon nanotubes obtained in Example 1. Figure 6 It can be seen that carbon (C) is the dominant component in the sample (mass percentage 96.6±0.16%, atomic percentage 98.5±0.12%), while aluminum (Al) is the minor component (mass percentage 3.4±0.01%, atomic percentage 1.5±0.00%).

[0137] Example 16 This embodiment provides a lithium iron phosphate preparation method as follows: (1) Raw material mixing and ball milling: Lithium carbonate was weighed as the lithium source according to the molar ratio of Li:Fe:P=1.025:1:1, and iron phosphate provided both iron and phosphorus sources. The confined aluminized carbon nanotubes obtained in Example 1 (accounting for 1wt% of the mass of iron phosphate) were initially dry-mixed. Then glucose was added as the carbon source, with the amount of carbon source added being 15wt% of the total mass of lithium carbonate and iron phosphate. After being mixed evenly, the mixture was transferred to a ball mill and ball-milled for 3 hours at a speed of 800 r / min to obtain homogenized precursor powder with a D50 particle size of 500~520 nm.

[0138] (2) Spray drying granulation: The ball-milled slurry is spray-dried with an inlet temperature of 250°C and an outlet temperature of 100°C to obtain granulated powder with good sphericity and excellent flowability. The granulated powder is then lightly crushed to make the final particle size distribution in the range of 20~30μm, so as to facilitate heat and mass transfer in the subsequent sintering process.

[0139] (3) High-temperature sintering: The granulated powder is placed in a corundum crucible and heated to 780°C under a nitrogen protective atmosphere by programmed heating. The mixture is then held at the temperature for 9 hours to obtain lithium iron phosphate cathode material.

[0140] Examples 17-30 This embodiment provides a lithium iron phosphate. Unlike embodiment 16, the confined aluminized carbon nanotubes are provided by embodiments 2-15. The other preparation methods are the same as those in embodiment 16 and will not be described again here.

[0141] Example 31 This embodiment provides a lithium iron phosphate, which differs from Example 16 in that the amount of confined aluminized carbon nanotubes accounts for 3 wt% of the mass of the lithium iron phosphate. The rest of the preparation method is the same as in Example 16, and will not be described again here.

[0142] Example 32 This embodiment provides a lithium iron phosphate, which differs from Example 16 in that the amount of confined aluminized carbon nanotubes accounts for 1 wt% of the mass of the lithium iron phosphate. The rest of the preparation method is the same as in Example 16, and will not be described again here.

[0143] Example 33 This embodiment provides a lithium iron phosphate, which differs from Embodiment 16 in that the amount of confined aluminized carbon nanotubes accounts for 0.5 wt% of the mass of the lithium iron phosphate. The rest of the preparation method is the same as that in Embodiment 16, and will not be described again here.

[0144] Example 34 This embodiment provides a lithium iron phosphate, which differs from Embodiment 16 in that the amount of confined aluminized carbon nanotubes accounts for 5 wt% of the mass of the lithium iron phosphate. The rest of the preparation method is the same as that in Embodiment 16, and will not be described again here.

[0145] Comparative Example 1 This comparative example provides a lithium iron phosphate, which differs from Example 16 in that it uses carbon nanotubes instead of confined aluminized carbon nanotubes. The rest of the preparation method is the same as in Example 16, and will not be described again here.

[0146] Comparative Example 2 This comparative example provides a lithium iron phosphate, which differs from Example 16 in that glucose is not used as the reaction raw material. The rest of the preparation method is the same as that in Example 16, and will not be described again here.

[0147] Comparative Example 3 This comparative example provides a lithium iron phosphate, which differs from Example 16 in that carbon nanotubes are used instead of confined aluminized carbon nanotubes, and glucose is not used as a reaction raw material. The rest of the preparation methods are the same as those in Example 16, and will not be described again here.

[0148] Comparative Example 4 This comparative example provides a lithium iron phosphate, which differs from Example 16 in that carbon nanotubes (0.5 wt% of the mass of iron phosphate) and lithium aluminate (0.4 wt% of the mass of iron phosphate) are used to replace the confined aluminized carbon nanotubes. The other raw materials and preparation methods are the same as in Example 16, and will not be repeated here.

[0149] Test Example 1 The lithium iron phosphate obtained from the examples and comparative examples were used to prepare batteries, and then performance tests were conducted. The performance test results are shown in Table 1.

[0150] The battery fabrication process is as follows: Lithium iron phosphate obtained in the examples and comparative examples was used as the positive electrode, and lithium foil was used as the negative electrode for battery assembly. A 1 mol / L LiPF6 / EC (ethylene carbonate) / DMC (diethyl carbonate) electrolyte (EC and DMC volume ratio 1:1) was used as the electrolyte, and a polypropylene microporous membrane was used as the separator. The battery performance was tested using a two-electrode battery testing module.

[0151] The charge-discharge performance of the cathode material was tested on a battery testing system. A constant current charge-discharge regime was adopted, with a charge-discharge voltage range of 2.0-4.2V, and a 1-minute rest period was set before each constant current process. Battery assembly was carried out in a glove box under a high-purity argon atmosphere.

[0152] Table 1

[0153] As shown in Table 1, the lithium iron phosphate material prepared using this confined aluminized carbon nanotube exhibits an initial discharge specific capacity of 162.00–164.11 mAh / g at 0.1C, significantly higher than Comparative Examples 2–4 (158.98–159.64 mAh / g). This indicates that the constructed continuous one-dimensional conductive network greatly enhances the utilization rate of the active material and the electron transport efficiency. Furthermore, after 100 cycles, the material retains a discharge capacity of 162.80–163.98 mAh / g, with a capacity retention exceeding 99.2%, far superior to the 96% of Comparative Example 1 using ordinary carbon nanotubes. This fully verifies the crucial role of the spatially confined structure in the long-term stability of the conductive network.

[0154] In terms of high-rate performance, the 5C discharge capacity of Examples 5-7 reached 137.26-137.34 mAh / g, which is significantly better than that of Comparative Examples 1-4. This indicates that the confined aluminized carbon nanotubes not only ensure rapid electron conduction, but also release Al during the high-temperature sintering process. 3+Furthermore, the doping into the LiFePO4 lattice optimized the crystal structure and improved lithium-ion diffusion kinetics. Crucially, compared to Comparative Example 4, which directly physically mixed carbon nanotubes and lithium aluminate, the embodiments of this invention exhibit significant advantages in first-discharge capacity, cycle stability, and rate performance. This demonstrates that the integrated design of structural confinement, in-situ recombination, and synergistic reaction is not a simple superposition of components, but rather produces an unexpected synergistic effect.

[0155] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered 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 confined aluminized carbon nanotube, characterized in that, Carbon nanotubes are spatially confined within the nanopores of a porous anodic aluminum oxide template, and aluminum-containing compound films are generated in situ on the outer wall and inner surface of the carbon nanotubes through template conversion. The aluminum-containing compounds include lithium aluminate and / or aluminum oxide; The confined aluminized carbon nanotubes have a long, cylindrical structure.

2. The confined aluminized carbon nanotube according to claim 1, characterized in that, The carbon nanotubes have a length of 1-50 micrometers and a diameter of 0.75-3 nanometers; And / or, in the confined aluminized carbon nanotubes, the proportion of aluminum-containing compounds is 5~15wt%.

3. A method for preparing confined aluminized carbon nanotubes according to claim 1 or 2, characterized in that, The pretreated aluminum sheet is subjected to a first anodizing to form an aluminum oxide film. Then, the aluminum oxide film is post-treated with a film removal solution, and carbon nanotubes are added after the treatment. Next, a second anodizing is performed to obtain carbon nanotubes that encapsulate the aluminum oxide film. Finally, lithium hydroxide is added to an ethanol solution and ultrasonically treated in situ to generate lithium aluminate, thus obtaining the confined aluminized carbon nanotubes.

4. The preparation method according to claim 3, characterized in that, The first and second anodizing processes are independent of each other: an aluminum sheet is used as the anode and a platinum sheet is used as the cathode. The two sheets are placed in an acidic electrolyte and a power source is applied to perform anodizing. And / or, the voltage for the anodizing is 15~50V, and the time is 0.5~3h; And / or, the temperature of the electrolyte is controlled at 13~26℃ during the process; And / or, the electrolyte includes oxalic acid, sulfuric acid, or phosphoric acid.

5. The preparation method according to claim 3, characterized in that, The membrane removal solution includes phosphoric acid and chromic acid; And / or, the concentration of phosphoric acid is 0.5~0.7 mol / L, and the concentration of chromic acid is 0.1~0.2 mol / L; And / or, the post-processing temperature is 50~70℃, and the time is 0.5~2h; And / or, the amount of carbon nanotubes added is 30%-50% of the mass of the pretreated aluminum sheet.

6. The preparation method according to claim 3, characterized in that, The concentration of the lithium hydroxide ethanol solution is 1~3 g / mL; And / or, lithium hydroxide accounts for 300 to 800 ppm of the mass of the carbon nanotubes encapsulating the alumina film; And / or, the duration of the ultrasonic treatment is 20-40 minutes.

7. The preparation method according to any one of claims 3 to 6, characterized in that, The pretreatment process of aluminum sheets includes annealing, cleaning, alkaline washing and acid washing in sequence; And / or, the aluminum content of the aluminum sheet is ≥99.99%; And / or, the annealing temperature is 450~550℃; And / or, the solvent used for the cleaning is acetone and / or ethanol; And / or, the cleaning is ultrasonic cleaning, and the time is 20~40 minutes; And / or, the alkaline solution used for the alkaline washing is a sodium hydroxide solution, and the washing time is 3~8 minutes; And / or, the concentration of the sodium hydroxide solution is 0.08~0.15 mol / L; And / or, the acid solution used for pickling is a mixture of perchloric acid and ethanol; And / or, in the mixed solution, the volume ratio of perchloric acid to ethanol is 1:(3~8).

8. The application of the confined aluminized carbon nanotubes according to claim 1 or 2 in the preparation of positive electrode active materials.

9. A method for preparing a positive electrode active material, characterized in that, The positive electrode active material includes lithium iron phosphate; The preparation method includes: mixing and grinding phosphorus source, lithium source, iron source, carbon source and confined aluminized carbon nanotubes, followed by spray drying and sintering to obtain lithium iron phosphate; The confined aluminized carbon nanotube is the confined aluminized carbon nanotube as described in claim 1 or 2.

10. The preparation method according to claim 9, characterized in that, The amount of confined aluminized carbon nanotubes used is 1-3 wt% of the combined mass of the iron and phosphorus sources; And / or, the phosphorus source includes iron phosphate, the lithium source includes lithium carbonate and / or lithium hydroxide, the iron source includes iron phosphate, and the carbon source is at least one of polyethylene glycol, glucose, sucrose, carbon black, and citric acid; And / or, the molar ratio of lithium, iron and phosphorus in the raw materials is (0.98~1.4):(1~1.4):(0.95~1.3); And / or, the carbon source accounts for 10-20% of the total mass of the lithium source, iron source and phosphorus source; And / or, the mixing and grinding time is 3~10h, and the rotation speed is 500~1000rpm; And / or, the sintering is carried out under a protective atmosphere, at a temperature of 700~900℃, for a time of 8~10h.

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