Preparation method of gap structure lithium iron phosphate material

Abstract

The application provides a kind of void structure lithium iron phosphate material and its preparation method, comprising: primary particles form secondary particles by hierarchical random close packing method;Primary particles are spherical or near spherical;Secondary particles contain hierarchical pore structure of mesopore and macropore;The volume ratio of mesopore and macropore is 1.5~2.3:1, mesopore is formed by the gap between primary particles, and macropore is formed by the gap between secondary particles.After precursor solution preparation, slurry preparation, spray drying, gradient sintering process steps, void structure lithium iron phosphate is obtained.The method of the application can realize controllable hierarchical pore making, optimize electron and ion transmission path, improve the electronic conductivity and high rate charge-discharge performance of lithium iron phosphate, and at the same time, build a graphene skeleton with continuous three-dimensional conductive network, effectively enhance the structural stability of the material.In addition, low-cost raw materials and spray drying process are used to simplify the process flow and reduce production cost.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, and in particular to a method for preparing a porous lithium iron phosphate material. Background Technology

[0002] Lithium-ion batteries, as high-performance rechargeable batteries, possess advantages such as high energy density, high output power, and long cycle life, and are widely used in portable electronic products, communication tools, electric vehicles, and other fields. Among them, lithium iron phosphate (LiFePO4), as a new generation of lithium-ion battery cathode material, is considered one of the most promising cathode materials due to its advantages such as being non-toxic, pollution-free, safe, having abundant raw materials, and being inexpensive. However, currently commercially available lithium iron phosphate materials still face two major technical bottlenecks: one is low electronic conductivity (approximately 10⁻⁶ ppm). -9 The lithium-ion transfer rate (LTP) is limited by several factors: firstly, the S / cm ratio restricts high-rate charge / discharge performance; secondly, the solid-state diffusion kinetics are slow, with a lithium-ion transference number of only 0.3–0.5. While traditional carbon doping modification methods can improve electron conduction, their effect on ion transport is limited. To address these issues, researchers have attempted to introduce hierarchical porous structures to optimize electron and ion transport pathways.

[0003] Chinese patent CN105576220A discloses a method for preparing porous carbon-coated lithium iron phosphate cathode material. This method involves mixing volatile ammonium salts with a carbon source during the carbon coating process, uniformly coating the surface of lithium iron phosphate, freeze-drying, and then heating. Utilizing the volatility of the ammonium salts, pores are created on the surface of the lithium iron phosphate particles. After sintering, porous carbon-coated lithium iron phosphate is formed. This porous carbon coating provides more channels for lithium ions, improving the rate performance and low-temperature performance of the cathode material. Although this method proposes using volatile ammonium salts as pore-forming agents to prepare porous carbon-coated lithium iron phosphate, the physical mixing and adhesion of the carbon source and pore-forming agent to the pre-prepared lithium iron phosphate particle surface makes uniform coating difficult to achieve. This easily leads to uneven coating thickness, incomplete coating in some areas, or agglomeration. Furthermore, the one-step sintering method cannot precisely control the pore structure. In addition, the freeze-drying process used in this method is cumbersome and costly, which is not conducive to large-scale industrial production.

[0004] Chinese patent CN118458733A discloses a method for preparing high-capacity lithium iron phosphate cathode material. This method uses ammonium polyphosphate as the phosphorus source, which reacts with an iron source and lithium hydroxide to generate lithium iron phosphate. The coating layer, triphenylcyclodextrin, serves as the carbon source, and triazine functional groups act as the nitrogen source. The ammonium polyphosphate undergoes thermal decomposition to generate ammonia gas, which escapes from the carbon matrix, forming a porous structure. This yields porous nitrogen-doped carbon-coated lithium iron phosphate, suitable as a cathode material for lithium-ion batteries. While this method proposes to improve conductivity and structural stability through porous carbon coating and promote electron and lithium-ion transport, the use of ammonia gas generated by the thermal decomposition of ammonium polyphosphate to create pores may disrupt the integrity of the carbon coating layer, thus affecting the structural stability and cycle life of the cathode material.

[0005] Although existing technologies have disclosed methods for constructing porous structures to optimize the electron and ion transport pathways of lithium iron phosphate cathode materials, technical challenges remain, including the inability to precisely control the pore structure, complex processes, and high production costs. Therefore, developing a novel method for preparing lithium iron phosphate materials that enables controllable hierarchical pore formation, simultaneously improves electronic conductivity and enhances structural stability, while simplifying the process and reducing production costs is of great significance. Summary of the Invention

[0006] In view of the above, the present invention provides a method for preparing porous lithium iron phosphate materials, which can achieve controllable hierarchical pore formation, simultaneously improve electronic conductivity and enhance structural stability, while simplifying the process and reducing production costs.

[0007] This invention provides a porous lithium iron phosphate material, comprising: primary particles forming secondary particles through a hierarchical, random, and tightly packed arrangement; the primary particles being spherical or nearly spherical; the secondary particles comprising a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.5~2.3:1, the mesopores being formed by the gaps between the primary particles, and the macropores being formed by the gaps between the secondary particles; the pore size distribution of the mesopores being 20~50 nm, accounting for 60~70% of the total mesopores and macropores; and the pore size distribution of the macropores being 50~200 nm, accounting for 30~40% of the total mesopores and macropores.

[0008] The hierarchical pore structure designed in this invention directly determines the proportion and distribution of mesopores by the primary particle packing method, while the proportion and distribution of macropores are related to the secondary particle packing structure. Mesopores provide short-range ion diffusion channels, while macropores promote electrolyte penetration, reduce mass transfer resistance, and increase ion diffusion rate. High porosity accelerates ion migration, improving the high-rate performance of the material. Simultaneously, the hierarchical pore structure of mesopores and macropores buffers charge-discharge volume changes, inhibits lithium iron phosphate particle breakage, and improves the structural stability and cycle life of the material.

[0009] This invention also provides a method for preparing a porous lithium iron phosphate material, which is carried out according to the following steps:

[0010] (1) Preparation of precursor solution: Disperse iron phosphate, lithium carbonate, carbon source and pore-forming agent in pure water to form precursor solution;

[0011] (2) Slurry preparation: The precursor solution is stirred and ground to prepare a slurry;

[0012] (3) Spray drying: The slurry is spray dried to obtain spherical precursor powder;

[0013] (4) Gradient sintering: The spherical precursor powder is subjected to gradient sintering and natural cooling under an inert gas atmosphere to obtain porous lithium iron phosphate.

[0014] The molar ratio of iron phosphate to lithium carbonate is Fe:Li = 1:1.01~1.05. This stoichiometric ratio maximizes the synthesis of lithium iron phosphate, avoiding the introduction of impurities due to excessive iron or lithium sources, which could negatively impact the material's structural stability and cycle life.

[0015] Optionally, the carbon source includes glucose, sucrose, or citric acid. After high-temperature sintering in an inert atmosphere, the carbon source carbonizes to form an amorphous carbon layer coating the surface of the lithium iron phosphate particles, improving the electronic conductivity between the particles. Simultaneously, the uniformly coated carbon layer physically blocks direct contact between the lithium iron phosphate particles during sintering, effectively inhibiting excessive growth of lithium iron phosphate crystals at high temperatures, thus improving the rate performance of the material. Furthermore, the carbon layer can reduce ferric iron (Fe3+) generated during sintering to ferrous iron (Fe2+). When glucose, sucrose, or citric acid is used as the carbon source, it pyrolyzes at 350-400°C to generate 3-5 layers of graphene conductive layer, reducing the lithium-ion diffusion path, increasing the diffusion coefficient, and thereby improving electronic conductivity.

[0016] The amount of carbon source added is 10-15% of the total mass of iron phosphate to ensure the formation of a continuous, complete, and defect-free conductive carbon coating layer. If the residual carbon content is less than 1.4%, the carbon coating may be incomplete or discontinuous, resulting in poor electronic conductivity of the material, which in turn affects rate performance and cycle life. If the residual carbon content is greater than 1.45%, the carbon coating layer is too thick, ion migration is hindered, and the volumetric energy density is significantly reduced.

[0017] The pore-forming agent is ammonium dihydrogen phosphate, and its addition amount is 15-25% of the total mass of iron phosphate, lithium carbonate, and carbon source. Ammonium dihydrogen phosphate not only provides a phosphorus source but also decomposes in the low-temperature sintering section (450-550℃) to produce NH3 and H2O gases, forming mesopores within the lithium iron phosphate structure. In the high-temperature sintering section (700-800℃), the lithium source decomposes to produce CO2, and the solid-phase reaction produces CO, further forming macropores on top of the mesopores, ultimately resulting in a hierarchical pore structure of mesopores and macropores.

[0018] Thus, glucose, sucrose, or citric acid are carbonized to form a graphene conductive layer. Combined with the mesopores formed in the low-temperature sintering section and the macropores formed in the high-temperature sintering section, a graphene framework with a continuous three-dimensional conductive network is synergistically constructed. This can effectively enhance the structural stability of the material while ensuring its electronic conductivity, avoid pulverization and crack propagation during the charging and discharging process, and extend the cycle life of the material.

[0019] Step (2) involves first homogenizing the precursor solution at 500-600 rpm for 30-60 minutes, then grinding it with a ball mill until the particle size is 350-400 nm to obtain a slurry. In this step, homogenization and stirring achieve macroscopic dispersion and preliminary homogenization of the material, while ball milling controls the particle size and achieves uniform mixing at the nanoscale, thereby shortening the ion / electron transport path, increasing the reactive surface area, increasing the ion diffusion rate, and improving the rate performance of the material.

[0020] In step (3), the slurry is spray-dried under conditions of an inlet air temperature of 230-250℃ and an outlet air temperature of 100-110℃, with an atomization pressure of 1.2-1.5MPa and a frequency of 365-370Hz, to obtain spherical precursor powder. This step, by precisely controlling the spray drying conditions, transforms the uniformly mixed precursor slurry into spherical precursor powder in one step. This not only maintains the nanoscale component uniformity achieved in step (2), preparing for the subsequent formation of a uniform carbon coating layer and hierarchical pore structure, but also significantly improves the tap density and electrode processing performance of the material by obtaining spherical particles. Furthermore, this continuous spray drying process is simpler, more efficient, and more suitable for large-scale industrial continuous production compared to traditional methods such as freeze drying.

[0021] Optionally, the inert gas includes nitrogen or argon. Using an inert gas during sintering protects against oxidation of ferrous iron.

[0022] In step (4), gradient sintering refers to first heating the material to 450-550℃ at a rate of 2-3℃ / min, holding it at that temperature for 1-3 hours, and then heating it to 720-750℃ at a rate of 2-3℃ / min, holding it at that temperature for 8-10 hours. This invention designs a gradient sintering process to perform segmented heating of the material, precisely controlling pore formation in the low-temperature and high-temperature stages, ultimately obtaining a hierarchical pore structure containing mesopores and macropores. In the low-temperature sintering stage, ammonium dihydrogen phosphate not only decomposes to form mesopores but also provides a highly active phosphorus source for the solid-phase reaction in the subsequent high-temperature sintering stage. First, the temperature is raised to 450-550℃ at a slow heating rate (2-3℃ / min) and held for 1-3 hours. The slow heating allows ammonium dihydrogen phosphate to decompose slowly, producing gases (NH3 and H2O), and ensures uniform gas release to avoid sudden increases in local pressure that could cause particle breakage. This initially forms uniformly distributed mesopores of 2-50 nm. During this period, the carbon source is initially carbonized to form a structural framework. Then, the temperature is raised to 720-750℃ at a heating rate of 2-3℃ / min. The lithium source (Li2CO3) decomposes to produce lithium oxide (Li2O) and CO2. The lithium oxide (Li2O) reacts with iron phosphate (FePO4) and the carbon source (C) in a solid-state reaction to produce lithium iron phosphate (LiFePO4) and CO. The CO2 and CO gases produced in this process escape and create pores, resulting in a dual pore-forming enhancement effect. At the same time, the solid-state reaction is accompanied by volume shrinkage, further expanding the pores. Macropores of 50-200 nm are formed on the basis of the 2-50 nm mesopores, resulting in a hierarchical pore structure. In addition, during the gradient sintering process, the carbon source is carbonized to form a graphene conductive layer, which, together with the formed hierarchical porous structure, synergistically constructs a graphene framework with a continuous three-dimensional conductive network.

[0023] The present invention has at least the following beneficial effects:

[0024] This invention, through the design of a hierarchical pore structure, optimizes the electron and ion transport paths, significantly improving the electronic conductivity of the material and overcoming the low electronic conductivity (approximately 10⁻⁶) of traditional lithium iron phosphate materials. -9 This invention overcomes the technical bottleneck of (S / cm) and effectively improves the electronic conductivity and high-rate charge-discharge performance of lithium iron phosphate materials. It innovatively utilizes hierarchical pore control technology, combined with gradient sintering, to achieve controllable hierarchical pore formation, precisely controlling the internal pore characteristics of lithium iron phosphate. This solves the problem of difficulty in controlling uniform pore size distribution in existing soft template methods, ensuring the internal uniformity and structural stability of lithium iron phosphate materials. The formed graphene conductive layer and hierarchical pore structure synergistically construct a graphene framework with a continuous three-dimensional conductive network, effectively enhancing the structural stability of the material, preventing pulverization and crack propagation during charge-discharge processes, and extending the cycle life of the material. Furthermore, this invention uses low-cost raw materials and spray drying technology, reducing production costs, simplifying the process, and overcoming the high production costs of traditional freeze-drying methods. Attached Figure Description

[0025] Figure 1 This is a SEM image of the porous lithium iron phosphate structure in Embodiment 1 of the present invention. Detailed Implementation

[0026] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0027] The term "comprising" as used in this application is an open-ended inclusion, meaning "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". Definitions of other terms will be given in the description below.

[0028] All embodiments of the present invention are implemented using the following technical solutions, and the main reaction conditions for different embodiments are shown in Table 1:

[0029] Example 1: A method for preparing a porous lithium iron phosphate material is provided, the specific steps of which include:

[0030] (1) Preparation of precursor solution: Iron phosphate, lithium carbonate, carbon source and pore-forming agent are dispersed in pure water. The molar ratio of iron phosphate to lithium carbonate is Fe:Li=1:1.01. The carbon source is sucrose and the amount of carbon source added is 10% of the total mass of iron phosphate. The pore-forming agent is ammonium dihydrogen phosphate and the amount of it added is 15% of the total mass of iron phosphate, lithium carbonate and carbon source to form a precursor solution.

[0031] (2) Slurry preparation: First, the obtained precursor solution is homogenized and stirred at 500 rpm for 60 min, and then ground with a ball mill until the particle size of the material is 350 nm to obtain the slurry;

[0032] (3) Spray drying: Under the conditions of inlet air temperature of 230℃ and outlet air temperature of 100℃, the atomization pressure of the spray drying equipment is set to 1.2MPa and the frequency is 365Hz. The obtained slurry is spray dried to obtain spherical precursor powder.

[0033] (4) Gradient sintering: Under a nitrogen atmosphere, the obtained spherical precursor powder is first heated to 450°C at a heating rate of 2°C / min and held for 1 hour. Then, it is heated to 720°C at a heating rate of 2°C / min and held for 8 hours. After natural cooling, the porous lithium iron phosphate is obtained.

[0034] The porous lithium iron phosphate material prepared by the method provided in Example 1 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.6±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0035] Example 2: A method for preparing a porous lithium iron phosphate material is provided, wherein the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.03, and the carbon source is citric acid; in step (2), the homogenization stirring speed in slurry preparation is 600 rpm, the homogenization stirring time is 30 min, and then the material is ground to a particle size of 400 nm using a ball mill; in step (3), the spray drying conditions are an inlet air temperature of 250℃, an outlet air temperature of 110℃, an atomization pressure of 1.5 MPa, and a frequency of 370 Hz; in step (4), under an argon atmosphere, the obtained spherical precursor powder is first heated to 450℃ at a heating rate of 3℃ / min, held for 3 h, then heated to 720℃ again at a heating rate of 3℃ / min, held at a constant temperature for 10 h, and then naturally cooled to obtain porous lithium iron phosphate. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 2 are the same as those in Example 1, and other parameters are the same as in Example 1.

[0036] The porous lithium iron phosphate material prepared by the method provided in Example 2 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.6±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0037] Example 3: A method for preparing a porous lithium iron phosphate material is provided, wherein the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.05, and the carbon source is glucose; in step (2), the homogenization stirring speed in slurry preparation is 550 rpm, the homogenization stirring time is 45 min, and then the material is ground to a particle size of 375 nm using a ball mill; in step (3), the spray drying conditions are an inlet air temperature of 240℃, an outlet air temperature of 105℃, an atomization pressure of 1.3 MPa, and a frequency of 367 Hz; in step (4), under a nitrogen atmosphere, the obtained spherical precursor powder is first heated to 450℃ at a heating rate of 3℃ / min, held for 3 h, then heated to 720℃ again at a heating rate of 3℃ / min, held at a constant temperature for 9 h, and then naturally cooled to obtain porous lithium iron phosphate. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 3 are the same as those in Example 1, and other parameters are the same as those in Example 1.

[0038] The porous lithium iron phosphate material prepared by the method provided in Example 3 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.7±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0039] Example 4: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 12% of the total mass of iron phosphate. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 4 are the same as those in Example 1, and other parameters are the same as in Example 1.

[0040] The porous lithium iron phosphate material prepared by the method provided in Example 4 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.7±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0041] Example 5: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 5 are the same as those in Example 1, and other parameters are the same as in Example 1.

[0042] The porous lithium iron phosphate material prepared by the method provided in Example 5 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.8±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0043] Example 6: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 20% of the total mass of iron phosphate, lithium carbonate, and carbon source. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 6 are the same as those in Example 1, and other parameters are the same as in Example 1.

[0044] The porous lithium iron phosphate material prepared by the method provided in Example 6 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.0±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0045] Example 7: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 25% of the total mass of iron phosphate, lithium carbonate, and carbon source. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 7 are the same as those in Example 1, and other parameters are the same as in Example 1.

[0046] The porous lithium iron phosphate material prepared by the method provided in Example 7 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.2±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0047] Example 8: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 25% of the total mass of iron phosphate, lithium carbonate, and carbon source; and the temperature of the low-temperature sintering section in step (4) gradient sintering is 500℃. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 8 are the same as those in Example 1, and other parameters are the same as those in Example 1.

[0048] The porous lithium iron phosphate material prepared by the method provided in Example 8 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.1±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0049] Example 9: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 25% of the total mass of iron phosphate, lithium carbonate, and carbon source; and the temperature of the low-temperature sintering section in step (4) gradient sintering is 550℃. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 9 are the same as those in Example 1, and other parameters are the same as those in Example 1.

[0050] The porous lithium iron phosphate material prepared by the method provided in Example 9 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.2±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0051] Example 10: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 25% of the total mass of iron phosphate, lithium carbonate, and carbon source; in step (4), the temperature of the low-temperature sintering section in the gradient sintering is 550℃, and the temperature of the high-temperature sintering section in the gradient sintering is 735℃. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 10 are the same as those in Example 1, and other parameters are the same as those in Example 1.

[0052] The porous lithium iron phosphate material prepared by the method provided in Example 10 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.2±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0053] Example 11: A method for preparing a porous lithium iron phosphate material is provided, wherein the carbon source is glucose, and the amount of carbon source added is 15% of the total mass of iron phosphate; the pore-forming agent is ammonium dihydrogen phosphate, and the amount added is 25% of the total mass of iron phosphate, lithium carbonate, and carbon source; in step (4), the temperature of the low-temperature sintering section in the gradient sintering is 550℃, and the temperature of the high-temperature sintering section in the gradient sintering is 750℃. The steps of the method for preparing a porous lithium iron phosphate material provided in Example 11 are the same as those in Example 1, and other parameters are the same as those in Example 1.

[0054] The porous lithium iron phosphate material prepared by the method provided in Example 11 includes: primary particles forming secondary particles through a hierarchical random compact packing method; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical porous structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 2.2±0.1∶1, the mesopores are formed by the gaps between the primary particles, and the macropores are formed by the gaps between the secondary particles.

[0055] Table 1 shows the performance test results of the porous structure lithium iron phosphate in different embodiments. From the test results in Table 1 and... Figure 1As can be seen, this invention successfully prepared lithium iron phosphate with a hierarchical pore structure of mesoporous and macroporous structures. Combined with the continuous three-dimensional conductive network formed after carbon source sintering, the electronic conductivity and high-rate performance of the material are significantly improved. The porous lithium iron phosphate prepared by the method described in this invention has an electronic conductivity in the range of 0.042~0.107 S / cm, a 0.1C discharge specific capacity in the range of 160.45~162.3 mAh / g, a 5C discharge specific capacity in the range of 129.63~136.92 mAh / g, and a capacity retention rate of 80.79~84.36% at 5C. As shown in Table 1, compared with Examples 1, 2 and 3, Example 3, which uses glucose as a carbon source, has a relatively high electronic conductivity of 0.079 S / cm, while the porous lithium iron phosphate prepared in Example 3 has a relatively high 5C capacity (135.3 mAh / g) and capacity retention rate (83.78%). As can be seen from Examples 3, 4, and 5, in Example 4, when the amount of carbon source added is 12% of the total mass of iron phosphate, its electronic conductivity (0.107 S / cm), 5C capacity (136.92 mAh / g), and capacity retention (84.36%) are the highest. This is attributed to the optimal combination of carbon source, pore-forming agent ratio, and sintering process, proving that the design of the material's conductive network and pore structure can improve its overall electrochemical performance. In Examples 5, 6, and 7, with the increase of the amount of pore-forming agent added, the electronic conductivity of the material gradually increases, while its 5C capacity and capacity retention show a trend of first increasing and then decreasing. Comparing Examples 7, 8, and 9, with the increase of the low-temperature sintering temperature, the electronic conductivity, 5C capacity, and capacity retention of the material gradually decrease. This indicates that low-temperature sintering at a relatively low temperature of 450°C is beneficial for forming a suitable conductive network and pore structure to achieve optimal overall electrochemical performance. In Examples 9, 10, and 11, as the temperature of the high-temperature sintering section increased, the electronic conductivity, 5C capacity, and capacity retention of the material gradually decreased. This indicates that high-temperature sintering at a relatively low temperature of 720°C is beneficial for forming a suitable conductive network and pore structure to achieve optimal comprehensive electrochemical performance.

[0056] Table 1 Performance test results of porous lithium iron phosphate in different embodiments

[0057]

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A porous lithium iron phosphate material, characterized in that, include: Primary particles are formed into secondary particles through a hierarchical, random, and tightly packed arrangement; the primary particles are spherical or nearly spherical; the secondary particles contain a hierarchical pore structure of mesopores and macropores; wherein the volume ratio of mesopores to macropores is 1.5 to 2.3:1, the mesopores are formed by the gaps between primary particles, and the macropores are formed by the gaps between secondary particles.

2. The porous lithium iron phosphate material according to claim 1, characterized in that, The mesopores have a pore size distribution of 20~50nm, accounting for 60~70% of the total number of mesopores and macropores.

3. The porous lithium iron phosphate material according to claim 1, characterized in that, The pore size distribution of the macropores is 50~200nm, accounting for 30~40% of the total number of mesopores and macropores.

4. The porous lithium iron phosphate material according to any one of claims 1 to 3, characterized in that, Follow these steps: (1) Preparation of precursor solution: Disperse iron phosphate, lithium carbonate, carbon source and pore-forming agent in pure water to form precursor solution; (2) Slurry preparation: The precursor solution is stirred and ground to prepare a slurry; (3) Spray drying: The slurry is spray dried to obtain spherical precursor powder; (4) Gradient sintering: The spherical precursor powder is subjected to gradient sintering and natural cooling under an inert gas atmosphere to obtain porous lithium iron phosphate.

5. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, The molar ratio of iron phosphate to lithium carbonate is Fe:Li = 1:1.01~1.

05.

6. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, The carbon source includes glucose, sucrose, or citric acid.

7. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, The amount of carbon source added is 10-15% of the total mass of iron phosphate.

8. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, The pore-forming agent is ammonium dihydrogen phosphate, and its addition amount is 15-25% of the total mass of iron phosphate, lithium carbonate, and carbon source.

9. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, Step (2) refers to first homogenizing the precursor solution at 500-600 rpm for 30-60 min, and then grinding it with a ball mill until the particle size of the material is 350-400 nm to obtain a slurry.

10. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, Step (3) refers to setting the atomization pressure of the spray drying equipment to 1.2~1.5MPa and the frequency to 365~370Hz under the conditions of inlet air temperature of 230~250℃ and outlet air temperature of 100~110℃, and spray drying the slurry to obtain spherical precursor powder.

11. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, The inert gas includes nitrogen or argon.

12. The method for preparing the porous lithium iron phosphate material according to claim 4, characterized in that, In step (4), gradient sintering refers to first heating the temperature to 450-550℃ at a heating rate of 2-3℃ / min, holding it at that temperature for 1-3 hours, and then heating it to 720-750℃ at a heating rate of 2-3℃ / min again, holding it at that temperature for 8-10 hours.

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