Preparation method and application of lithium iron phosphate positive electrode material

Abstract

The application provides a preparation method and application of a lithium iron phosphate positive electrode material, and belongs to the technical field of lithium batteries. The method comprises the following steps: S1: providing a mesoporous template; S2: filling iron sources and phosphorus sources into the pore channels of the mesoporous template through gas phase transmission, and performing heat treatment to form an iron-phosphorus oxide precursor; S3: making lithium sources react with the iron-phosphorus oxide precursor through gas phase lithium infiltration to generate lithium iron phosphate; S4: depositing a continuous carbon layer on the surface of the lithium iron phosphate through chemical vapor deposition; and S5: removing the mesoporous template to obtain a lithium iron phosphate / carbon composite material with a three-dimensional double-continuous network structure. Through gas phase transmission and gas phase lithium infiltration, the application realizes efficient utilization of the iron sources, the phosphorus sources and the lithium sources, reduces the preparation cost, and the chemical vapor deposition step deposits a continuous carbon layer on the surface of the lithium iron phosphate, thereby further improving the conductivity and the cycle stability of the material.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a method for preparing and applying lithium iron phosphate cathode material. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has become one of the most important cathode materials for lithium-ion batteries due to its high safety, long cycle life, and abundant raw materials. However, its low intrinsic electronic conductivity and small lithium-ion diffusion coefficient result in poor rate performance. Existing improvement methods include carbon coating to improve electronic conductivity, but excessive carbon reduces tap density and energy density; ion doping to broaden lithium-ion migration channels, but single doping has limited effect; nano-sizing to shorten the lithium-ion diffusion path, but nanoparticles are prone to agglomeration and have low tap density; and morphology control to prepare spherical or near-spherical particles to improve processing performance and tap density. Current technologies mostly focus on the simple superposition of one or a few of these aspects, lacking an organic, mutually reinforcing synergistic mechanism between the steps and components, leading to bottlenecks in performance improvement.

[0003] Patent CN113044822B utilizes the porous properties of sponges and relies on spatial confinement to prepare petal-shaped lithium iron phosphate in situ, which improves conductivity. However, this morphology is difficult to maintain after high-temperature calcination. CN115172704A uses a metal-organic framework to prepare porous lithium iron phosphate, but this method is costly and difficult to mass-produce. CN103066280B and CN108878848B use surfactants as support to obtain mesoporous lithium iron phosphate, but the absorption of electrolyte by the mesopores is extremely limited, and the improvement in battery rate performance is not significant.

[0004] To address the aforementioned problems, this invention introduces a sacrificial mesoporous silica template and combines it with unique vapor phase lithium infiltration and vapor phase deposition techniques to prepare a lithium iron phosphate / carbon composite material. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for preparing lithium iron phosphate cathode material and its application. The method achieves efficient utilization of iron, phosphorus and lithium sources through gas phase transport and gas phase lithium infiltration. The chemical vapor deposition step deposits a continuous carbon layer on the surface of lithium iron phosphate, which further improves the conductivity and cycle stability of the material.

[0006] Specifically, the first aspect of this application provides a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0007] S1: A mesoporous template is provided, which is formed by pressing mesoporous silica microspheres, wherein the template has macropores of 50-200 nm and mesopores of 2-50 nm.

[0008] S2: Volatile iron and volatile phosphorus sources are filled into the pores of the mesoporous template through gas phase transport, and condensation filling is performed under a vacuum of less than 0.1 Pa. Subsequently, heat treatment is carried out at 400-600℃ in an inert atmosphere to form an iron-phosphorus oxide precursor.

[0009] S3: Lithium iron phosphate is generated by reacting a volatile lithium source with the iron-phosphorus oxide precursor through vapor-phase lithium infiltration.

[0010] S4: A continuous carbon layer is deposited on the surface of the lithium iron phosphate by chemical vapor deposition;

[0011] S5: Remove the mesoporous template and subject the resulting material to supercritical drying to obtain a lithium iron phosphate / carbon composite material with a three-dimensional dual continuous network structure.

[0012] Further, the volatile iron source mentioned in step S2 is a mixed iron source composed of ferric acetylacetone and ferrocene in a mass ratio of 1:1-3;

[0013] The volatile phosphorus source is triphenyl phosphate;

[0014] The molar ratio of the iron source to the phosphorus source is 1:(0.9-1.1).

[0015] Furthermore, the mesoporous silica microspheres described in step S1 are synthesized using a soft template method;

[0016] The soft template method uses at least one of hexadecyltrimethylammonium bromide and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0017] Furthermore, in step S2, the iron source is a volatile organic iron compound.

[0018] Furthermore, the phosphorus source is a volatile organophosphorus compound.

[0019] Furthermore, the molar ratio of the iron source to the phosphorus source is 1:(0.9-1.1).

[0020] Furthermore, in step S2, the gas phase transfer is carried out under vacuum or inert atmosphere, the temperature of the heat treatment is 400-600℃, and / or the holding time of the heat treatment is 1-5 hours.

[0021] Further, in step S3, the lithium source is a volatile organic lithium compound or a lithium hydride, and the gas-phase lithium infiltration process adopts a programmed temperature rise method: first, it is kept at 500-550℃ for 1-2 hours, and then raised to 600-700℃ and kept at 600-700℃ for 2-6 hours.

[0022] Further, in step S4, the carbon source for the chemical vapor deposition is at least one of benzene, toluene, methane, and acetylene; the deposition temperature is 600-800℃, the deposition time is 10-60 minutes, and the thickness of the deposited continuous carbon layer is 2-3 nm.

[0023] Furthermore, in step S4, the chemical vapor deposition process is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume percentage of hydrogen is 5%-15%.

[0024] Further, in step S5, the mesoporous template is removed by etching with acid or alkali solution; when the template is silicon dioxide, a sodium hydroxide solution with a concentration of 1-4 mol / L is used for etching.

[0025] Furthermore, the supercritical drying in step S5 uses supercritical carbon dioxide fluid, and the drying conditions are: temperature 35-45℃, pressure 8-12 MPa.

[0026] The carbon composite material is a graphitized carbon layer.

[0027] The second aspect of this application provides an application of a lithium iron phosphate cathode material, which is used in lithium-ion batteries.

[0028] The present invention has the following beneficial effects:

[0029] This invention constructs a mesoporous silica framework as a template, which provides precise reaction space for iron, phosphorus, and lithium sources during subsequent preparation processes. During gas-phase transport and gas-phase lithium infiltration, the macropores and mesopores of the mesoporous silica template effectively restrict the growth direction and size of the reaction products, allowing the iron-phosphorus oxide precursor and the final lithium iron phosphate to be uniformly distributed within the template's pores, forming a regular and ordered structure.

[0030] In the chemical vapor deposition (CVD) step, the presence of a mesoporous silica template facilitates the uniform deposition of a continuous carbon layer on the lithium iron phosphate (LFP) surface. Due to the template's porous structure, the carbon source gas can fully contact the LFP surface, and under suitable temperature and atmosphere conditions, a uniform, continuous, and dense carbon layer is formed. This continuous carbon layer not only significantly improves the material's conductivity but also provides protection during cycling, reducing side reactions between the electrode material and the electrolyte, thereby enhancing the material's cycling stability.

[0031] Removing the mesoporous silica template yields a lithium iron phosphate / carbon composite material with a three-dimensional bicontinuous network structure, offering unique advantages. This structure provides abundant transport channels for lithium ions and electrons, significantly shortening the lithium ion diffusion path and increasing the ion diffusion rate. Simultaneously, this structure increases the contact area between the material and the electrolyte, leading to more complete electrode reactions and further enhancing the material's rate performance. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0033] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0034] An embodiment of the first aspect of this application provides a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0035] S1: A mesoporous template is provided, which is formed by pressing mesoporous silica microspheres, wherein the template has macropores of 50-200 nm and mesopores of 2-50 nm.

[0036] S2: Volatile iron and volatile phosphorus sources are filled into the pores of the mesoporous template through gas phase transport, and condensation filling is performed under a vacuum of less than 0.1 Pa. Subsequently, heat treatment is carried out at 400-600℃ in an inert atmosphere to form an iron-phosphorus oxide precursor.

[0037] S3: Lithium iron phosphate is generated by reacting a volatile lithium source with the iron-phosphorus oxide precursor through vapor-phase lithium infiltration.

[0038] S4: A continuous carbon layer is deposited on the surface of the lithium iron phosphate by chemical vapor deposition;

[0039] S5: Remove the mesoporous template and subject the resulting material to supercritical drying to obtain a lithium iron phosphate / carbon composite material with a three-dimensional dual continuous network structure.

[0040] This invention constructs a mesoporous silica framework as a template, which provides precise reaction space for iron, phosphorus, and lithium sources during subsequent preparation processes. During gas-phase transport and gas-phase lithium infiltration, the macropores and mesopores of the mesoporous silica template effectively restrict the growth direction and size of the reaction products, allowing the iron-phosphorus oxide precursor and the final lithium iron phosphate to be uniformly distributed within the template's pores, forming a regular and ordered structure.

[0041] In the chemical vapor deposition (CVD) step, the presence of a mesoporous silica template facilitates the uniform deposition of a continuous carbon layer on the lithium iron phosphate (LFP) surface. Due to the template's porous structure, the carbon source gas can fully contact the LFP surface, and under suitable temperature and atmosphere conditions, a uniform, continuous, and dense carbon layer is formed. This continuous carbon layer not only significantly improves the material's conductivity but also provides protection during cycling, reducing side reactions between the electrode material and the electrolyte, thereby enhancing the material's cycling stability.

[0042] Removing the mesoporous silica template yields a lithium iron phosphate / carbon composite material with a three-dimensional bicontinuous network structure, offering unique advantages. This structure provides abundant transport channels for lithium ions and electrons, significantly shortening the lithium ion diffusion path and increasing the ion diffusion rate. Simultaneously, this structure increases the contact area between the material and the electrolyte, leading to more complete electrode reactions and further enhancing the material's rate performance.

[0043] In this embodiment, the mesoporous template is a silica template; the silica template is obtained by pressing mesoporous silica microspheres, and its interior contains macropores of 50-200 nm formed by the gaps between the microspheres and mesopores of 2-50 nm inherent in the microspheres themselves. The mesoporous silica microspheres are synthesized by a soft template method, and the soft template agent used in the soft template method is at least one of hexadecyltrimethylammonium bromide and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0044] Specifically, the template agent is hexadecyltrimethylammonium bromide (CTAB); the silicon source is tetraethyl orthosilicate (TEOS); the catalyst is ammonia (NH4OH, 28 wt%); and the solvents are anhydrous ethanol, 500 mL and deionized water, 250 mL.

[0045] Preparation steps of step S1: Dissolve CTAB in a solvent consisting of 500 mL ethanol and 250 mL water, and stir at a constant temperature in a 35°C water bath. Then add 50.0 mL of ammonia and stir for 30 minutes to ensure homogeneity. Under vigorous stirring, slowly add 25.0 mL of TEOS at a rate of 2 mL / min using a constant pressure dropping funnel. After the addition is complete, continue the reaction at 35°C for 4 hours. After the reaction is complete, seal the mixture and allow it to age at room temperature for 24 hours. Then, collect the white precipitate by centrifugation at 8000 rpm for 10 minutes. Wash the precipitate three times each with anhydrous ethanol and deionized water alternately to remove residual ammonia and unreacted substances. Place the washed product in a vacuum drying oven and dry at 80°C for 12 hours to obtain mesoporous silica microsphere powder. The dried silica micropowder was placed in a mold with a diameter of 20 mm and cold isostatically pressed under a pressure of 100 MPa for 5 minutes to obtain a mesoporous silica template block with a certain mechanical strength. The microstructure of the template block is as follows: macropores of 50-200 nm are formed between the microspheres, and the microspheres themselves have ordered mesopores of 2-50 nm.

[0046] This invention uses hexadecyltrimethylammonium bromide (CTAB) as a template agent and tetraethyl orthosilicate (TEOS) as a silicon source to synthesize uniformly sized mesoporous silica microspheres in an alkaline ethanol-water solution. The pore size is precisely controlled within the 10-15 nm range by adjusting the CTAB / TEOS ratio. The silica microspheres are then assembled into a composite template block with a macroporous structure (pores formed by the gaps between microspheres) and ordered mesopores (2-50 nm) within the microspheres themselves using centrifugal sedimentation and pressure molding techniques. This step provides two levels of space: the macropores (50-200 nm) between the microspheres are used for the rapid transport of subsequent gaseous substances, while the mesopores (2-50 nm) within the microspheres restrict the growth of active substances.

[0047] In this embodiment, in step S2, the iron source is a volatile organic iron compound, such as iron acetylacetonate, and the phosphorus source is a volatile organic phosphorus compound, such as triphenyl phosphate. The molar ratio of the iron source to the phosphorus source is 1:(0.9-1.1).

[0048] Place the silica template block in a quartz boat within the tube furnace, positioning it in the furnace's constant-temperature zone. Mix ferric acetylacetone and triphenyl phosphate powder thoroughly, place the mixture in another quartz boat, and position it in the upstream low-temperature zone of the tube furnace. Shut down the tube furnace and use a mechanical pump and a molecular pump to evacuate the system to a vacuum level <5.0 × 10⁻⁶. -2Pa. Subsequently, the upstream low-temperature zone was heated to 180°C at a rate of 5°C / min and held for 30 minutes; simultaneously, the downstream template zone was heated to 250°C. During this process, ferric acetylacetone and triphenyl phosphate sublimated, and gaseous molecules were transported and condensed into the low-temperature template zone under vacuum, completely filling the mesopores of the template. After filling, high-purity argon gas (99.999% purity) was introduced into the tube furnace at a flow rate of 200 sccm. Under the argon atmosphere, the entire tube furnace was programmed to heat to 400-600°C at a rate of 3°C / min and held at this temperature for 1-5 hours. During this process, the ferric acetylacetone and triphenyl phosphate condensed in the channels decomposed and reacted to generate amorphous FePO4, which uniformly adhered to the inner wall of the mesoporous channels.

[0049] This invention uses iron acetylacetone and triphenyl phosphate as the iron and phosphorus sources, respectively. Both have suitable volatility. During gas-phase transport, they can sublimate into gaseous molecules at relatively low temperatures, facilitating their transport to the template region under vacuum and their condensation to fill the pores of the template. Moreover, these two substances can uniformly decompose and react during heat treatment to generate amorphous FePO4, providing a good precursor for the subsequent generation of lithium iron phosphate.

[0050] In this embodiment, in step S3, the lithium source is a volatile organic lithium compound or a lithium hydride, preferably lithium tert-butoxide.

[0051] Specifically, the FePO4 / silica composite material is placed in the downstream isothermal zone of a tube furnace, while lithium tert-butoxide powder is placed in the upstream low-temperature zone. High-purity argon gas (99.999%) is introduced into the tube furnace at a flow rate of 100 sccm. The upstream lithium source zone is heated to 120°C at a rate of 10°C / min and maintained to allow the lithium tert-butoxide to sublimate continuously. The downstream composite material zone is heated to 500-700°C at a rate of 5°C / min and held at this temperature for 2-8 hours. The gaseous lithium tert-butoxide undergoes a solid-gas reaction with the FePO4 in the channels to generate crystalline LiFePO4.

[0052] Gaseous lithium tert-butoxide molecules diffuse into the mesopores and undergo a solid-gas reaction with FePO4 within the channels to generate crystalline LiFePO4. In this step, vapor-phase lithium infiltration ensures that the lithium source can fully and uniformly contact and react with the FePO4 confined within the nanopores, avoiding the inhomogeneous mixing and residual impurities commonly found in solid-phase methods.

[0053] The vapor phase lithium infiltration process adopts a programmed temperature rise method: first, it is kept at 500-550℃ for 1-2 hours, and then raised to 600-700℃ and kept at 2-6 hours.

[0054] In this embodiment, in step S4, the carbon source for chemical vapor deposition is at least one selected from benzene, toluene, methane, and acetylene, preferably benzene. The chemical vapor deposition process is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume percentage of hydrogen is 5%-15%.

[0055] In an argon-hydrogen mixed atmosphere, the tube furnace is heated to 600-800℃ at a rate of 10℃ / min. After the temperature stabilizes, argon gas is introduced at a flow rate of 20 sccm into a bubbler containing liquid benzene (the bubbler temperature is controlled at 25℃), carrying benzene vapor into the reaction chamber. The total deposition time is 10-60 minutes. During this process, benzene undergoes cracking and deposition on the surface of the LiFePO4 framework, forming a continuous graphitized carbon layer with a thickness of 2-3 nm.

[0056] By precisely controlling the flow rate and deposition time of benzene, a continuous graphitized carbon layer is uniformly deposited on the surface of the LiFePO4 crystal network. In this step, the carbon layer is formed directly in situ on the LiFePO4 framework, with tight bonding, forming a three-dimensional continuous electron transport network that is completely parallel to and nested within the LiFePO4 ion transport network.

[0057] Further, in step S5, the product from step S4 is immersed in a 1-4 mol / L NaOH solution and gently stirred (magnetic stirring, 200 rpm) in a 60℃ water bath for 6 hours to completely dissolve the silica template without damaging the brittle LiFePO4 / carbon three-dimensional network structure. The solid product is collected by vacuum filtration and repeatedly washed with deionized water until the filtrate is neutral. The washed material is then immersed in anhydrous ethanol and stirred three times, 30 minutes each time, to perform solvent replacement. Subsequently, the material is placed in a supercritical CO2 dryer and dried for 4 hours at a temperature of 35-45℃ and a pressure of 8-12 MPa to prevent the network structure from being damaged by surface tension during liquid-phase drying, yielding the final product—a black lithium iron phosphate / carbon three-dimensional dual continuous network material.

[0058] An embodiment of the second aspect of this application provides an application of a lithium iron phosphate cathode material, which is used in a lithium-ion battery.

[0059] Example

[0060] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0061] Example 1

[0062] A method for preparing a lithium iron phosphate cathode material includes the following steps:

[0063] S1: A mesoporous template is provided, which is formed by pressing mesoporous silica microspheres, wherein the template has macropores of 50-200 nm and mesopores of 2-50 nm.

[0064] The preparation method is as follows: CTAB is dissolved in a solvent consisting of 500 mL of ethanol and 250 mL of water, and stirred at a constant temperature in a 35°C water bath. Then, 50.0 mL of ammonia is added, and the mixture is stirred for 30 minutes to ensure homogeneity. Under vigorous stirring, 25.0 mL of TEOS is slowly added dropwise at a rate of 2 mL / min using a constant pressure dropping funnel. After the addition is complete, the reaction is continued at 35°C for 4 hours. After the reaction is completed, the mixture is sealed and allowed to stand at room temperature for 24 hours for aging. Then, the white precipitate is collected by centrifugation at 8000 rpm for 10 minutes. The precipitate is washed three times each with anhydrous ethanol and deionized water to remove residual ammonia and unreacted substances. The washed product is placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain mesoporous silica microsphere powder. The dried silica micropowder is placed in a mold with a diameter of 20 mm and cold isostatically pressed under a pressure of 100 MPa for 5 minutes to obtain a mesoporous silica template block.

[0065] S2: Take 10g of the above template, fill the pores of the mesoporous silica template with 3.58g of ferric acetylacetone and 3.26g of triphenyl phosphate, close the tube furnace, and use a mechanical pump and a molecular pump to evacuate the system to a vacuum level of <5.0×10⁻⁶. -2 Pa; then, the upstream low-temperature zone is heated to 180°C at a rate of 5°C / min and held for 30 minutes; at the same time, the downstream template zone is heated to 250°C; under an argon atmosphere, the entire tube furnace is heated to 500°C at a rate of 3°C / min and held at this temperature for 2 hours to form an iron-phosphorus oxide precursor.

[0066] S3: Place 1.28g of lithium tert-butoxide powder in the upstream low-temperature zone, introduce high-purity argon into the tube furnace, raise the upstream lithium source zone to 120℃ at 10℃ / min and maintain it, so that lithium tert-butoxide continues to sublimate; raise the downstream composite material zone to 550℃ at 5℃ / min and maintain it at this temperature for 4 hours to generate lithium iron phosphate.

[0067] S4: Using benzene as the carbon source, the tube furnace is heated to 650°C at a rate of 10°C / min under an argon-hydrogen mixed atmosphere. After the temperature stabilizes, argon gas carrying benzene vapor is introduced into the reaction chamber. The total deposition time is 30 minutes. During this process, benzene is cracked and deposited on the surface of the LiFePO4 framework to form a continuous graphitized carbon layer with a thickness of 2-3 nm.

[0068] S5: Immerse the product from step S4 in a 2 mol / L NaOH solution and gently stir (magnetic stirring, 200 rpm) in a 60℃ water bath for 6 hours. Place the material in a supercritical CO2 dryer and dry it for 4 hours at a temperature of 40℃ and a pressure of 10 MPa to obtain lithium iron phosphate / carbon composite material.

[0069] Example 2

[0070] This embodiment is basically the same as that of Embodiment 1, except that the temperature of chemical vapor deposition in step S4 is 700°C.

[0071] Example 3

[0072] This embodiment is basically the same as that of embodiment 1, except that in step S2, 0.05g of magnesium acetylacetone is also included in iron acetylacetone and triphenyl phosphate to achieve magnesium ion doping.

[0073] Example 4

[0074] This embodiment is basically the same as Embodiment 1, except that in step S5, atmospheric pressure freeze drying is used instead of supercritical CO2 drying.

[0075] Comparative Example 1

[0076] Compared with Example 1, this comparative example uses a template-free solid-phase method. Lithium carbonate, ferrous oxalate and ammonium dihydrogen phosphate are measured and added in proportion, and 10 wt% glucose is added as a carbon source. After ball milling and mixing, the mixture is pre-calcined at 350°C for 4 hours in an argon atmosphere, and then sintered at 700°C for 10 hours to obtain lithium iron phosphate product.

[0077] Comparative Example 2

[0078] The same SiO2 template as in Example 1 was used, except that the SiO2 template was immersed in a mixed aqueous solution of ferric nitrate and ammonium phosphate, dried, and then mixed and ground with lithium carbonate and glucose solids. Subsequently, it was sintered at 700°C for 10 hours in argon atmosphere, and finally the template was removed with NaOH to obtain the lithium iron phosphate product.

[0079] Comparative Example 3

[0080] This comparative example is basically the same as the example, except that in step S3, instead of vapor phase lithium infiltration, it is mixed and ground with an excess of 5% lithium carbonate solid, then sintered at 700°C for 10 hours, and then carbon and template are removed by CVD deposition to obtain lithium iron phosphate product.

[0081] Comparative Example 4

[0082] This comparative example is basically the same as the example, except that after the vapor phase lithium in step S3, the template is removed directly to obtain a carbon-free LFP three-dimensional network material.

[0083] Comparative Example 5

[0084] This comparative example is basically the same as the example, except that the deposition time of benzene in step S4 is extended to 120 minutes.

[0085] Experimental Case

[0086] The lithium iron phosphate materials from Examples 1-4 and Comparative Examples 1-5 were used as active materials for electrochemical testing:

[0087] The active material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) binder are mixed evenly in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The mixture is then coated onto aluminum foil, dried under vacuum at 120°C for 12 hours, and finally stamped into an electrode sheet.

[0088] In an argon-protected glove box, a CR2032 button cell was assembled using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 in EC / DEC (1:1 v / v) as the electrolyte.

[0089] The Blue Battery testing system was used to conduct tests within a voltage range of 2.5–4.2 V. The rate performance test sequence was: 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, with 5 cycles at each rate, finally returning to 0.1C. Cycling performance testing was conducted at 1C rate, recording the discharge capacity of the first and nth cycles, and calculating the capacity retention rate. The test results are shown in Table 1.

[0090] Table 1 Test results of Examples 1-4 and Comparative Examples 1-5

[0091]

[0092] As shown in Table 1, the lithium iron phosphate materials prepared in Examples 1 to 4 are significantly superior to those in Comparative Examples 1 to 5 in terms of rate performance and cycle stability. Specifically, Example 1 retains approximately 85% of its initial capacity at 10C, while Comparative Example 1 exhibits a capacity decay exceeding 40% under the same conditions. Example 2 further optimized the graphitization of the carbon layer by adjusting the chemical vapor deposition temperature to 700°C, resulting in a significant reduction in polarization at high rates. In Example 3, magnesium ion doping (0.05 g magnesium acetylacetonate) effectively improved the structural stability of the material, achieving a capacity retention of 92% after 50 cycles at 1C, a 3 percentage point improvement compared to the undoped Example 1. Although the atmospheric pressure freeze-drying in Example 4 resulted in a slight decrease in porosity, it still maintained the integrity of the three-dimensional network structure, and its rate performance was close to that of Example 1, which underwent supercritical drying.

[0093] In the comparative examples, the template-free solid-phase method (Comparative Example 1) resulted in the formation of impurity phases due to uneven mixing, leading to an initial capacity approximately 20 mAh / g lower than that of the examples. The solution impregnation method (Comparative Example 2) suffered from a sharp drop in capacity at high rates due to incomplete template removal and residual SiO2 hindering lithium-ion transport. Solid-phase lithium infiltration, replacing gas-phase lithium infiltration (Comparative Example 3), resulted in uneven lithium distribution, with capacity retention of less than 60% at 5C. While the carbon-free material (Comparative Example 4) maintained its three-dimensional structure, its poor electronic conductivity resulted in significantly inferior rate performance compared to the carbon-coated sample. Extending the benzene deposition time to 120 minutes (Comparative Example 5) led to an excessively thick carbon layer (>5 nm), which increased lithium-ion diffusion resistance and deteriorated high-rate performance. These comparative results fully validate the effectiveness of this invention in constructing a three-dimensional dual-continuous network structure through gas-phase transport confinement synthesis and in-situ carbon coating technology.

[0094] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: S1: providing a mesoporous template formed by compressing mesoporous silica microspheres, the template having both 50-200 nm macropores and 2-50 nm mesopores; S2: filling a volatile iron source and a volatile phosphorus source into the pore channels of the mesoporous template by gas phase transmission, condensing and filling under a vacuum degree lower than 0.1 Pa, and then performing heat treatment at 400-600 ℃ in an inert atmosphere to form an iron-phosphorus oxide precursor; S3: reacting a volatile lithium source with the iron-phosphorus oxide precursor by gas phase lithium infiltration to generate lithium iron phosphate; S4: depositing a continuous carbon layer on the surface of the lithium iron phosphate by chemical vapor deposition; S5: removing the mesoporous template and performing supercritical drying on the obtained material to obtain a lithium iron phosphate / carbon composite material having a three-dimensional double-continuous network structure.

2. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: The volatile iron source in step S2 is a mixed iron source composed of iron acetylacetone and ferrocene at a mass ratio of 1:1-3; ​ The volatile phosphorus source is triphenyl phosphate; The molar ratio of the iron source to the phosphorus source is 1:(0.9-1.1).

3. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, The mesoporous silica microspheres in step S1 are synthesized by a soft template method; The soft template agent used in the soft template method is at least one of cetyltrimethylammonium bromide and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.

4. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the heat treatment has a holding time of 1-5 hours.

5. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphorous pentoxide; and heating the mixture to a temperature of 600-800°C for 2-10 hours. In step S3, the lithium source is a volatile organic lithium compound or a lithium hydride, and the gas phase lithium infiltration process uses a programmed temperature method: first holding at 500-550 ℃ for 1-2 hours, and then raising the temperature to 600-700 ℃ for 2-6 hours.

6. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphorous pentoxide; and heating the mixture to a temperature of 600-800°C for 6-12 hours. In step S4, the carbon source for chemical vapor deposition is at least one of benzene, toluene, methane, and acetylene; And / or, the deposition temperature is 600-800 ℃, and the deposition time is 10-60 minutes.

7. The method of claim 6, wherein the lithium iron phosphate cathode material is prepared by the steps of: In step S4, the chemical vapor deposition process is performed in a mixed gas atmosphere of argon and hydrogen, wherein the volume fraction of hydrogen is 5%-15%. ​ 8. The method for preparing lithium iron phosphate cathode material according to claim 1, characterized in that, In step S5, the mesoporous template is removed by etching with an acid or an alkali; when the template is silica, etching is performed using a sodium hydroxide solution with a concentration of 1-4 mol / L.

9. Use of a lithium iron phosphate cathode material, characterized in that The lithium iron phosphate positive electrode material is prepared by the method described in any one of claims 1-8, and is applied in a lithium ion battery.

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