Preparation method of composite lithium iron phosphate material
By combining non-stoichiometric ratio and composite carbon source with spray drying and multi-stage sintering process, composite lithium iron phosphate material was prepared, which solved the problems of low energy density, poor cycle performance and insufficient conductivity of lithium iron phosphate, and achieved high energy density and long cycle stability, which is suitable for new energy vehicles and energy storage fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HECHI INST OF SCI & TECH INFORMATION
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-05
AI Technical Summary
Lithium iron phosphate materials suffer from problems such as lower energy density than theoretical value, rapid capacity decay during cycling, poor conductivity, and difficulty in achieving both nano-scale and tap density.
Composite lithium iron phosphate materials were prepared by using non-stoichiometric raw material ratios, synergistic effects of composite carbon sources, and spray drying and multi-stage sintering processes. By adjusting the ratio of lithium, iron, and phosphorus, and combining a porous carbon coating layer and a highly conductive network, the multi-dimensional properties of the materials were optimized.
It improves the energy density, cycle stability and conductivity of the material, and solves the problems of insufficient energy density, poor cycle performance and limited conductivity of traditional lithium iron phosphate. It also balances nano-sizing and tap density, making it suitable for new energy vehicles and energy storage.
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Figure CN122144681A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and particularly relates to a method for preparing a composite lithium iron phosphate material. Background Technology
[0002] Lithium-ion batteries have demonstrated an irreplaceable position in fields such as new energy vehicles and large-scale energy storage due to their advantages such as high energy density, long cycle life, and environmental friendliness. Lithium iron phosphate (LiFePO4), as one of the core candidates for cathode materials of lithium-ion batteries, has been a research hotspot since it was first reported by the Goodenough team in 1997 due to its high theoretical specific capacity, excellent thermal stability, low raw material cost, and lack of heavy metal pollution.
[0003] However, lithium iron phosphate has inherent defects, including insufficient energy density and cycle stability: the olivine-type crystal structure has narrow lithium-ion diffusion channels, resulting in an actual energy density lower than the theoretical value; simultaneously, Fe... 2+ / Fe 3+ Phase transitions in lithium iron phosphate (LFP) can easily induce lattice stress, leading to capacity decay during cycling. Poor conductivity: As a semiconductor, LFP exhibits high electron transport resistance, limiting rate performance. A trade-off exists between particle size and tap density: while nano-sizing shortens the lithium-ion diffusion path, particle agglomeration reduces tap density, hindering improvements in volumetric energy density; conversely, larger particles, while offering higher tap density, sacrifice rate performance. Therefore, developing a method for preparing LFP that synergistically optimizes energy density, cycle stability, conductivity, and tap density has significant industrial value. Summary of the Invention
[0004] To address the problems existing in the prior art, this invention provides a method for preparing composite lithium iron phosphate materials, which synergistically optimizes energy density, cycle stability, conductivity, and tap density. Through non-stoichiometric raw material ratios, synergistic effects of composite carbon sources, and spray drying and multi-stage sintering processes, it simultaneously improves the multi-dimensional performance of the material, meeting the needs of high-performance cathode materials in the fields of new energy vehicles and energy storage. This method solves the problems in the prior art, such as lithium iron phosphate having energy density lower than theoretical values, rapid capacity decay during cycling, poor conductivity leading to rate limiting, and the difficulty in simultaneously achieving nano-scale and tap density.
[0005] This invention is achieved through a method for preparing a composite lithium iron phosphate material, comprising the following steps: S1. Raw material selection and pretreatment: Weigh lithium source, iron source and phosphorus source in molar ratio Li:Fe:P=1.02-1.1:1:1-1.05; Weigh composite carbon source at 2%-8% of the iron source mass. The composite carbon source consists of a first carbon source, a second carbon source and a third carbon source. The first carbon source is a combination of glucose, sucrose, starch and at least one of cassava residue, sugarcane residue or straw. It is crushed to 100-200 mesh and dried to a moisture content ≤5%, accounting for 50%-80% of the total mass of the composite carbon source. The second carbon source is superconducting carbon black, accounting for 10%-30% of the total mass of the composite carbon source. The third carbon source is polyethylene glycol, accounting for 5%-20% of the total mass of the composite carbon source. The molecular weight of polyethylene glycol is 2000-6000. S2. Precursor ball milling and mixing: The iron source and phosphorus source are ball milled with deionized water as the medium for 1-3 hours. After adjusting the pH to 1-3, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and composite carbon source are added and ball milling is continued for 3-8 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. Multi-stage sintering and in-situ carbon coating: The precursor powder is sintered in two stages under inert gas protection. The first stage is heated to 350-450℃ and held for 2-4 hours. The second stage is heated to 600-700℃ and held for 5-15 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
[0006] As a preferred embodiment of the present invention, in step S1, the lithium source is lithium carbonate or lithium hydroxide with a purity ≥99.5%, the iron source is at least one of ferric phosphate, ferrous phosphate, and ferrous chloride with a purity ≥99.0%, and the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid with a purity ≥99.0% and a mass fraction of phosphoric acid ≥85%.
[0007] This setting reduces the interference of impurities in the raw materials on the lithium iron phosphate crystal structure, while also facilitating the dissolution of the raw materials. It allows for spray drying and dispersion, preventing impurity atoms from occupying lithium-ion diffusion channels or causing lattice distortion, thereby ensuring the electrochemical stability of the material and improving cycle life and coulombic efficiency.
[0008] As a preferred embodiment of the present invention, in step S2, the ball milling speed is 200-500 rpm, the amount of hydrogen peroxide is 3-8% of the iron source mass, the ball milling uses zirconium oxide balls, the acid used to adjust the pH is phosphoric acid, and the ball milling speed after adding lithium source and composite carbon source is 300-800 rpm.
[0009] This setup ensures that the zirconia balls have high hardness and strong chemical inertness, preventing contamination from impurities introduced during the ball milling process. The initial ball milling speed of 200-500 rpm enables preliminary dispersion of the iron and phosphorus sources. Combined with phosphoric acid to adjust the pH to an acidic environment, it promotes the dissolution and activation of iron ions. The amount of hydrogen peroxide used as an oxidant stabilizes the valence state of iron. The secondary ball milling speed of 300-800 rpm enables molecular-level mixing of the lithium, carbon, and precursor sources, ensuring uniform reaction of each component during subsequent sintering and reducing local component segregation.
[0010] As a preferred embodiment of the present invention, in step S3, the inlet air temperature of the spray drying is 200-300℃, the outlet air temperature is 50-80℃, and the particle size D50 of the obtained precursor powder is 100-500nm.
[0011] This setting allows for rapid evaporation of moisture in the slurry, preventing particle agglomeration due to slow drying; ensures complete powder drying without premature decomposition of the carbon source due to overheating; provides a foundation for uniform grain growth and uniform carbon source coating during subsequent sintering, and lays the structural foundation for the high tap density of the final material.
[0012] As a preferred embodiment of the present invention, the inert gas is nitrogen or argon (gas purity ≥ 99.9%), the heating rate of the first stage sintering is 5-10℃ / min, and the heating rate of the second stage sintering is 3-8℃ / min.
[0013] With this setup, nitrogen or argon acts as an inert protective gas, preventing Fe from being trapped during sintering. 2+ Oxidized to Fe 3 + To avoid the formation of impurities, the first stage of heating rate allows impurities such as water and ammonium salts in the precursor to be fully decomposed and discharged, while the carbon source is initially pyrolyzed to form a uniform pre-coating layer. The second stage of slow heating rate is conducive to the orderly growth of olivine phase LiFePO4 grains, avoiding uneven grain size or carbon coating layer cracking due to rapid heating, and ensuring the integrity of the material's crystal structure and conductivity.
[0014] As a preferred embodiment of the present invention, the sieve mesh size is 200-400 mesh, the primary particle size of the composite lithium iron phosphate material is 0.2-0.8 μm, and the thickness of the carbon coating layer is 7.5-25.5 nm.
[0015] This setup allows for the removal of small amounts of hard agglomerated particles that may be generated during sintering, ensuring uniform particle size distribution and improving the consistency of battery electrode coating. A primary particle size of 0.2-0.8 μm can shorten the lithium-ion diffusion path and avoid excessive agglomeration of excessively small particles, which would lead to a decrease in tap density. A carbon coating thickness of 7.5-25.5 nm can achieve a balance between conductivity and ion diffusion capability.
[0016] As a preferred embodiment of the present invention, in the composite carbon source, the first carbon source is mainly used to form a porous carbon coating structure, the second carbon source is mainly used to construct a highly conductive network, and the third carbon source mainly suppresses the agglomeration of lithium iron phosphate particles through the steric hindrance effect of polymer.
[0017] Through this setup, the three carbon sources form a synergistic effect of continuous porous carbon layer, high conductivity network, and steric hindrance. The continuous porous carbon coating layer of the first carbon source provides a macroscopic channel for lithium-ion transport, the high conductivity network of the second carbon source fills the conductive gaps between particles, and the steric hindrance effect of the third carbon source prevents hard agglomeration of material particles during sintering. Together, the three enhance the conductivity, dispersibility, and tap density of the material, solving the technical bottleneck that a single carbon source cannot simultaneously achieve multiple performance characteristics.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: by regulating the non-stoichiometric ratio of lithium, iron and phosphorus, the lattice defects of lithium iron phosphate are reduced, the lattice stress during the charging and discharging process is alleviated, the cycle stability and coulombic efficiency of the material are effectively improved, and the problems of insufficient energy density and rapid capacity decay of traditional lithium iron phosphate are improved. The composite carbon source, through the synergistic effect of multiple components, the continuous porous carbon coating layer formed by the first carbon source and the highly conductive network constructed by the second carbon source jointly optimize the ion mobility and conductivity of the material, solving the problem of limited rate performance caused by its semiconductor characteristics. The steric hindrance effect of the third carbon source inhibits particle agglomeration and takes into account dispersibility. The coupling of spray drying and multi-stage sintering process can control the morphology of precursor particles and grain growth, and balance the ion diffusion advantages brought by micro-nano particle size with the tap density requirements, thus avoiding the contradiction between particle size and tap density in traditional processes. The overall solution is adapted to the demand for high-performance cathode materials in the fields of new energy vehicles and energy storage, and has significant industrial application value. Attached Figure Description
[0019] Figure 1 These are the XRD patterns of the composite lithium iron phosphate materials obtained in Examples 1-3 of this invention; Figure 2 This is a TEM image of the composite lithium iron phosphate material obtained in Example 1 of the present invention; Figure 3 This is a high-magnification TEM image of the composite lithium iron phosphate material obtained in Example 1 of this invention; Detailed Implementation
[0020] To further understand the invention's content, features, and effects, the following embodiments are provided and described in detail below.
[0021] The present invention will now be described in detail.
[0022] Example 1 The present invention provides a method for preparing a composite lithium iron phosphate material, comprising the following steps: S1. Raw material selection and pretreatment: Weigh lithium source, iron source and phosphorus source in a molar ratio of Li:Fe:P = 1.02:1:1; weigh composite carbon source at 2% of the iron source mass. The composite carbon source consists of a first carbon source, a second carbon source and a third carbon source. The first carbon source is a combination of glucose and bagasse, accounting for 50% of the total mass of the composite carbon source. The second carbon source is superconducting carbon black, accounting for 30% of the total mass of the composite carbon source. The third carbon source is polyethylene glycol, accounting for 20% of the total mass of the composite carbon source. S2. Precursor ball milling and mixing: Iron source and phosphorus source are ball milled with deionized water as medium for 1 hour. After adjusting the pH to 1, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and composite carbon source are added and ball milling is continued for 3 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. Multi-stage sintering and in-situ carbon coating: The precursor powder is sintered in two stages under inert gas protection. The first stage is heated to 350°C and held for 2 hours. The second stage is heated to 600°C and held for 5 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
[0023] Specifically, in step S1, the lithium source is lithium carbonate with a purity of 99.5%, the iron source is ferrous phosphate with a purity of 99.0%, and the phosphorus source is phosphoric acid with a purity of 85%.
[0024] Specifically, in step S2, the ball mill speed is 200 rpm, the amount of hydrogen peroxide used is 3% of the iron source mass, the ball mill uses zirconium oxide balls, the acid used to adjust the pH is phosphoric acid, and the ball mill speed after adding lithium source and composite carbon source is 300 rpm.
[0025] Specifically, in step S3, the spray drying inlet air temperature is 200℃, the exhaust air temperature is 50℃, and the resulting precursor powder particle size D50 is 100 nm.
[0026] Specifically, the inert gas is nitrogen (gas purity ≥ 99.9%), the heating rate for the first stage of sintering is 5℃ / min, and the heating rate for the second stage of sintering is 3℃ / min.
[0027] Specifically, the sieve mesh size is 200 mesh, the average particle size of the composite lithium iron phosphate material is 0.55 μm, and the average thickness of the carbon coating layer is about 19.5 nm.
[0028] Specifically, in the composite carbon source, the first carbon source is mainly used to form a porous carbon coating structure, the second carbon source is mainly used to construct a highly conductive network, and the third carbon source mainly suppresses the agglomeration of lithium iron phosphate particles through the steric hindrance effect of polymer.
[0029] Example 2 A method for preparing a composite lithium iron phosphate material includes the following steps: S1. Raw material selection and pretreatment: Weigh lithium source, iron source and phosphorus source according to the molar ratio Li:Fe:P=1.06:1:1.03; weigh composite carbon source according to 5% of the iron source mass. The composite carbon source consists of a first carbon source, a second carbon source and a third carbon source. The first carbon source is a combination of sucrose and cassava residue, accounting for 65% of the total mass of the composite carbon source. The second carbon source is superconducting carbon black, accounting for 20% of the total mass of the composite carbon source. The third carbon source is polyethylene glycol, accounting for 15% of the total mass of the composite carbon source. S2. Precursor ball milling and mixing: Iron source and phosphorus source are ball milled with deionized water for 2 hours. After adjusting the pH to 2, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and composite carbon source are added and ball milling is continued for 5 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. Multi-stage sintering and in-situ carbon coating: The precursor powder is sintered in two stages under inert gas protection. The first stage is heated to 400℃ and held for 3 hours. The second stage is heated to 650℃ and held for 10 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
[0030] Specifically, in step S1, the lithium source is lithium carbonate with a purity of 99.5%, the iron source is ferrous phosphate with a purity of 99.0%, and the phosphorus source is phosphoric acid with a purity of 85%.
[0031] Specifically, in step S2, the ball mill speed is 300 rpm, the amount of hydrogen peroxide used is 5% of the iron source mass, the ball mill uses zirconium oxide balls, the acid used to adjust the pH is phosphoric acid, and the ball mill speed after adding lithium source and composite carbon source is 500 rpm.
[0032] Specifically, in step S3, the spray drying inlet air temperature is 250°C, the exhaust air temperature is 65°C, and the resulting precursor powder particle size D50 is 300 nm.
[0033] Specifically, the inert gas is nitrogen, the heating rate for the first sintering stage is 8℃ / min, and the heating rate for the second sintering stage is 5℃ / min.
[0034] Specifically, the sieve mesh size is 300 mesh, the average particle size of the composite lithium iron phosphate material is 0.46 μm, and the average thickness of the carbon coating layer is about 15.5 nm.
[0035] Specifically, in the composite carbon source, the first carbon source is mainly used to form a porous carbon coating structure, the second carbon source is mainly used to construct a highly conductive network, and the third carbon source mainly suppresses the agglomeration of lithium iron phosphate particles through the steric hindrance effect of polymer.
[0036] Example 3 A method for preparing a composite lithium iron phosphate material includes the following steps: S1. Raw material selection and pretreatment: Weigh lithium source, iron source and phosphorus source according to the molar ratio Li:Fe:P=1.1:1:1.05; weigh composite carbon source according to 8% of the iron source mass. The composite carbon source consists of a first carbon source, a second carbon source and a third carbon source. The first carbon source is a combination of starch and straw, accounting for 80% of the total mass of the composite carbon source. The second carbon source is superconducting carbon black, accounting for 10% of the total mass of the composite carbon source. The third carbon source is polyethylene glycol, accounting for 10% of the total mass of the composite carbon source. S2. Precursor ball milling and mixing: Iron source and phosphorus source are ball milled with deionized water for 3 hours. After adjusting the pH to 3, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and composite carbon source are added and ball milling is continued for 8 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. Multi-stage sintering and in-situ carbon coating: The precursor powder is sintered in two stages under inert gas protection. The first stage is heated to 450℃ and held for 4 hours, and the second stage is heated to 700℃ and held for 15 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
[0037] Specifically, in step S1, the lithium source is lithium hydroxide with a purity of 99.5%, the iron source is ferrous phosphate with a purity of 99.0%, and the phosphorus source is phosphoric acid with a purity of 85%.
[0038] Specifically, in step S2, the ball mill speed is 500 rpm, the amount of hydrogen peroxide used is 8% of the iron source mass, the ball mill uses zirconium oxide balls, the acid used to adjust the pH is phosphoric acid, and the ball mill speed after adding lithium source and composite carbon source is 800 rpm.
[0039] Specifically, in step S3, the spray drying inlet air temperature is 300℃, the exhaust air temperature is 80℃, and the resulting precursor powder particle size D50 is 500nm.
[0040] Specifically, the inert gas is argon, the heating rate for the first sintering stage is 10℃ / min, and the heating rate for the second sintering stage is 8℃ / min.
[0041] Specifically, the sieve mesh size is 400 mesh, the average particle size of the composite lithium iron phosphate material is 0.38 μm, and the average thickness of the carbon coating layer is about 10.5 nm.
[0042] Specifically, in the composite carbon source, the first carbon source is mainly used to form a porous carbon coating structure, the second carbon source is mainly used to construct a highly conductive network, and the third carbon source mainly suppresses the agglomeration of lithium iron phosphate particles through the steric hindrance effect of polymer.
[0043] Comparative Example 1 The present invention provides a method for preparing lithium iron phosphate material, comprising the following steps: S1. Raw material selection and pretreatment: Weigh out lithium source, iron source and phosphorus source in a molar ratio of Li:Fe:P=1:1:1; Weigh out a single carbon source at 2% of the mass of iron source, wherein the carbon source is one of glucose and bagasse combination, superconducting carbon black and polyethylene glycol. S2. Precursor ball milling and mixing: Iron source and phosphorus source are ball milled with deionized water as medium for 1 hour. After adjusting the pH to 1, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and single carbon source are added and ball milling is continued for 3 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. First-stage sintering and carbon coating: The precursor powder is sintered in one stage under inert gas protection, directly heated to 600℃ and held for 5 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
[0044] Specifically, in step S1, the lithium source is lithium carbonate with a purity of 99.5%, the iron source is ferrous phosphate with a purity of 99.0%, and the phosphorus source is phosphoric acid with a purity of 85%.
[0045] Specifically, in step S2, the ball mill speed is 200 rpm, the amount of hydrogen peroxide used is 3% of the iron source mass, the ball mill uses zirconium oxide balls, the acid used to adjust the pH is phosphoric acid, and the ball mill speed after adding lithium source and composite carbon source is 300 rpm.
[0046] Specifically, in step S3, the spray drying inlet air temperature is 200℃, the exhaust air temperature is 50℃, and the resulting precursor powder particle size D50 is 100 nm.
[0047] Specifically, the inert gas is nitrogen (gas purity ≥ 99.9%), the heating rate for the first stage of sintering is 5℃ / min, and the heating rate for the second stage of sintering is 3℃ / min.
[0048] This invention improves the cycling stability and coulombic efficiency of lithium, iron, and phosphorus by controlling the non-stoichiometric ratio of lithium, iron, and phosphorus. Excess lithium compensates for lithium loss during sintering, reduces lattice defects in lithium iron phosphate, and alleviates lattice stress during charging and discharging, thus addressing the problems of insufficient energy density and rapid capacity decay in traditional lithium iron phosphate. The composite carbon source, through the synergistic effect of multiple components—a continuous porous carbon coating layer formed by the first carbon source and a highly conductive network constructed by the second carbon source—optimizes the material's conductivity, solving the rate performance limitation caused by its semiconductor characteristics. The steric hindrance effect of the third carbon source inhibits particle agglomeration while maintaining dispersion. The coupling of spray drying and multi-stage sintering processes controls the precursor particle morphology and grain growth, balancing the ion diffusion advantages of micro- and nano-sized particles with the tap density requirements, avoiding the contradiction between particle size and tap density in traditional processes. The overall solution is suitable for the high-performance cathode materials required in new energy vehicles and energy storage, possessing significant industrial application value.
[0049] The composite lithium iron phosphate materials prepared in Examples 1-3 were used as positive electrode materials to prepare lithium-ion batteries and their electrochemical performance was analyzed. The composite lithium iron phosphate material was mixed with a conductive agent (acetylene black) and a binder (PVDF, polyvinylidene fluoride) at a mass ratio of 8:1:1. The resulting mixture was ground into a slurry using NMP (N-methyl-2-pyrrolidone) solvent. The slurry was then uniformly coated onto a single-sided aluminum foil and dried in a vacuum oven at 100°C for 10 hours to obtain the electrode material. In an argon-filled glove box, lithium metal sheets or commercial graphite were used as the negative electrode, with a Kroeder 2500 separator and a 1 M LiPF6 solution as the electrolyte. The batteries were arranged in the following order: negative electrode shell - spring sheet - gasket - lithium sheet - separator - positive electrode - positive electrode shell. The batteries were then sealed using a manual hydraulic sealer at a pressure of 50 MPa to assemble CR2032 coin cells. Constant current charge-discharge experiments and long-cycle stability tests were conducted at a current density of 1C = 0.3 mA (0.1C, 0.2C, 0.5C, 1C, and 3C), with a voltage test range of 2.5~4.2 V. The electrochemical performance was tested using a Newway battery tester. The test results are listed in Table 1.
[0050] Table 1 Electrochemical performance test results
[0051] The test results above show that, in particular, Comparative Example 1, due to the lack of control over the stoichiometric ratio of lithium, iron, and phosphorus, and the use of a single carbon source and a one-stage sintering process, exhibits a certain degree of reduction in rate performance and cycle performance compared to Examples 1-3. This indicates that the lithium battery prepared using the composite lithium iron phosphate material obtained in this invention as the cathode possesses excellent discharge capacity, good rate performance, and long-term cycle charge-discharge stability. Furthermore, the composite lithium iron phosphate materials obtained in Examples 1-3 of the present invention were characterized by XRD. Figure 1 It can be seen that the XRD diffraction patterns of the samples in Examples 1-3 all correspond to the LiFePO4 (PDF#81-1173) standard card, indicating that the LiFePO4 phase was generated in all samples and no other impurity phases were generated.
[0052] Figure 2-3 This is a TEM (transmission electron microscope) image of the composite lithium iron phosphate material prepared in Example 1 of the present invention. Figure 1 It can be seen that the prepared composite lithium iron phosphate electrode material exhibits a near-spherical shape with a particle size of approximately 0.55 μm. Furthermore, from... Figure 2 As is known, the surface of composite lithium iron phosphate particles is coated with a carbon coating layer with a thickness of approximately 19.5 nm.
[0053] All the above results indicate that the preparation method of the present invention can successfully synthesize composite lithium iron phosphate cathode materials.
[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a composite lithium iron phosphate material, characterized in that, Includes the following steps: S1. Raw material selection and pretreatment: Weigh lithium source, iron source and phosphorus source in molar ratio Li:Fe:P=1.02-1.1:1:1-1.05; Weigh composite carbon source at 2%-8% of the iron source mass. The composite carbon source consists of a first carbon source, a second carbon source and a third carbon source. The first carbon source is at least one of cassava residue, sugarcane residue or straw, crushed to 100-200 mesh and dried to a moisture content ≤5%, accounting for 50%-80% of the total mass of the composite carbon source. The second carbon source is superconducting carbon black, accounting for 10%-30% of the total mass of the composite carbon source. The third carbon source is polyethylene glycol, accounting for 5%-20% of the total mass of the composite carbon source. The molecular weight of polyethylene glycol is 2000-6000. S2. Precursor ball milling and mixing: The iron source and phosphorus source are ball milled with deionized water as the medium for 1-3 hours. After adjusting the pH to 1-3, hydrogen peroxide is added to react and generate iron phosphate dihydrate ball milling slurry. Then, lithium source and composite carbon source are added and ball milling is continued for 3-8 hours to obtain a uniform slurry. S3. Spray drying and granulation: The slurry from step S2 is spray dried to obtain spherical lithium iron phosphate precursor powder. S4. Multi-stage sintering and in-situ carbon coating: The precursor powder is sintered in two stages under inert gas protection. The first stage is heated to 350-450℃ and held for 2-4 hours. The second stage is heated to 600-700℃ and held for 5-15 hours. S5. Post-processing: The sintered product is crushed and sieved to obtain composite lithium iron phosphate material.
2. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: In step S1, the lithium source is lithium carbonate or lithium hydroxide with a purity ≥99.5%, the iron source is at least one of ferric phosphate, ferrous phosphate, and ferrous chloride with a purity ≥99.0%, and the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid with a purity ≥99.0% and a mass fraction of phosphoric acid ≥85%.
3. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: In step S2, the ball mill speed is 200-500 rpm, the amount of hydrogen peroxide is 3-8% of the iron source mass, the ball mill uses zirconia balls, the acid used to adjust the pH is phosphoric acid, and the ball mill speed after adding lithium source and composite carbon source is 300-800 rpm.
4. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: In step S3, the inlet air temperature for spray drying is 200-300℃, the outlet air temperature is 50-80℃, and the particle size D50 of the resulting precursor powder is 100-500nm.
5. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: The inert gas is nitrogen or argon (gas purity ≥ 99.9%). The heating rate for the first stage of sintering is 5-10℃ / min, and the heating rate for the second stage of sintering is 3-8℃ / min.
6. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: The sieve mesh size is 200-400 mesh, the primary particle size of the composite lithium iron phosphate material is 0.2-0.8 μm, and the thickness of the carbon coating layer is 7.5-25.5 nm.
7. The method for preparing a composite lithium iron phosphate material as described in claim 1, characterized in that: In the composite carbon source, the first carbon source is mainly used to form a porous carbon coating structure, the second carbon source is mainly used to construct a highly conductive network, and the third carbon source mainly suppresses the agglomeration of lithium iron phosphate particles through the steric hindrance effect of polymer.