Preparation method of high-compaction lithium iron phosphate positive electrode material
By using an iron-organic coordination salt modification method, spherical precursor particles with a high-iron shell and low-iron core structure are formed, solving the problem of balancing high density and electrochemical performance in existing technologies. This method enables the preparation of lithium iron phosphate materials with high density and excellent electrochemical performance, which are suitable for lithium-ion battery cathode materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI XINNA MATERIAL SCIENCE & TECHNOLOGY CO LTD
- Filing Date
- 2025-10-29
- Publication Date
- 2026-05-15
AI Technical Summary
Existing technologies struggle to prepare high-density lithium iron phosphate materials without compromising electrochemical performance, and existing methods suffer from high costs, instability, and difficulty in industrialization.
A preparation method using iron-organic coordination salt modification was adopted, and spherical precursor particles with a 'high iron shell and low iron core' structure were formed by spray drying. Combined with multi-level particle construction technology, ion transport and structural stability were optimized to achieve high solid density and good electrochemical performance.
It significantly improves the compaction density and electrochemical performance of the material, enhances the volumetric energy density and cycle life of lithium-ion batteries, and has a simple process that is easy to industrialize.
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Figure CN121269668B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically a method for preparing high-pressure lithium iron phosphate cathode material. Background Technology
[0002] Lithium iron phosphate (LFP) materials have become the mainstream cathode material for lithium-ion batteries due to their high structural stability, environmental friendliness, and long cycle life. However, their low volumetric energy density severely limits the potential for increasing battery capacity within a limited space. Improving compaction density is a key path to overcome this bottleneck, especially given the increasing demands for space utilization in power batteries and energy storage systems. At the same time, the cost of lithium battery raw materials continues to rise, making the development of a preparation process that combines high compaction density with low cost an urgent industry need.
[0003] The current mainstream methods for improving compaction density are: first, reducing the carbon coating content, which can reduce the particle spacing by decreasing the carbon layer thickness, but this significantly reduces the material's electronic conductivity, leading to capacity decay (typically <155 mAh / g) and rate performance degradation; second, increasing the sintering temperature, where high temperatures (>750℃) can promote grain densification, but easily induces iron-site lithium vacancy defects, causing irreversible capacity loss and drastically increasing energy consumption and costs; and third, optimizing particle size distribution by mixing precursors or finished particles of different sizes to attempt to achieve close packing. However, the core drawback is that small particles undergo uncontrollable agglomeration during sintering due to surface melting, causing the preset bimodal distribution to fail, resulting in a large particle size distribution range in the final product and compaction density fluctuations exceeding ±0.15 g / cm³, which cannot meet the stability requirements of industrial production. All of the above methods fall into a triple dilemma of "performance-process-cost": reducing carbon sacrifices conductivity, high-temperature sintering loses capacity, and the gradation process is limited by agglomeration instability.
[0004] Therefore, there is an urgent need to develop a new preparation method that is simple in process, cost-controllable, and can stably achieve high solid density (≥2.55 g / cm³) while maintaining electrochemical performance. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple method for preparing high-pressure lithium iron phosphate materials.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] A method for preparing a high-pressure lithium iron phosphate cathode material, the method comprising the following steps:
[0008] Step 1: Add iron source, phosphorus source, lithium source, carbon source, dispersant, and elemental dopant to a solvent for dispersion to prepare a slurry;
[0009] Step 2: Grind the slurry to obtain the first slurry;
[0010] Step 3: Add iron-organic coordination salt to the first slurry, mix well to obtain the second slurry, and then spray dry it to obtain the spray material;
[0011] Step 4: Sinter and pulverize the sprayed material to obtain high-pressure lithium iron phosphate material.
[0012] Preferably, in step one, the iron source and phosphorus source are iron phosphate;
[0013] Preferably, the lithium source is any one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; more preferably, the lithium source is lithium carbonate.
[0014] Preferably, the carbon source is any one or more of glucose, sucrose, PVDF (polyvinylidene fluoride), graphene, and carbon nanotubes;
[0015] Preferably, the dispersant is any one or more of PEG2000 (polyethylene glycol with a molecular weight of 2000), PEG6000 (polyethylene glycol with a molecular weight of 6000) and PVA2000 (polyvinyl alcohol with a molecular weight of 2000).
[0016] Preferably, the elemental dopant is any one or more of titanium dioxide, ammonium metavanadate, magnesium carbonate, aluminum oxide, and niobium oxide;
[0017] Preferably, the solvent is pure water.
[0018] Preferably, in step one, the molar ratio of the metal elements in the iron source, phosphorus source, lithium source, and elemental dopant is 0.95-1:1:1-1.1:0.005-0.05.
[0019] Preferably, in step one, the mass ratio of ferric phosphate, carbon source and dispersant is 1:0.01-0.1:0.01-0.1.
[0020] Preferably, in step one, the solid content of the slurry is 35%-45%.
[0021] Preferably, in step two, the abrasive particle size of the first slurry is controlled at D50 = 0.25-0.45 μm.
[0022] Preferably, in step three, the iron-organic coordination salt is any one or more of ferric ammonium citrate, ferric ammonium gluconate, triethanolamine iron, ethylenediamine iron, and sodium ferric ethylenediaminetetraacetate, and its amount is 0.1-5% of the molar amount of iron phosphate.
[0023] Preferably, in step four, the inlet air temperature of the spray drying is 210-240℃, the outlet air temperature of the spray drying is 90-110℃, and the moisture content of the material obtained by spray drying is less than 2wt%.
[0024] Preferably, in step four, sintering is carried out under a protective atmosphere of nitrogen or argon, at a sintering temperature of 700-750℃, and for a sintering time of 6-10 hours.
[0025] The high-pressure lithium iron phosphate preparation method provided by this invention introduces an iron-organic coordination compound that is easily soluble in solvent during the sand milling stage. This compound then spontaneously forms spherical precursor particles with a "high-iron shell-low-iron core" structure through a spray drying process. The process is simple, cost-controllable, and easily industrialized. This method offers the following advantages:
[0026] 1. Gradient Structure Synergistic Optimization of Ion Transport and Structural Stability: The core advantage of this design lies in the clever regionalization of functions within the same particle through the gradient distribution of composition. The high iron-phosphorus ratio of the particle shell effectively suppresses excessive grain growth during high-temperature sintering, thus forming a loose and porous outer layer composed of nanoscale fine primary particles. This structure provides abundant migration interfaces and short-range diffusion paths for lithium ions, significantly reducing ion diffusion resistance and enabling the material to possess excellent high-rate charge-discharge performance. Simultaneously, the particle core employs a lower iron-phosphorus ratio, creating ideal conditions for the formation of large-sized grains with high crystallinity and complete structure. This robust core, as the main mechanical support of the material, effectively buffers the volume change stress during lithium-ion insertion / extraction, thereby greatly improving the intrinsic structural stability and long cycle life of the material.
[0027] 2. Multi-level Particle Structure Enhances Electrode Compaction Density and Overall Electrochemical Performance: Based on the aforementioned gradient structure, the multi-level primary particle combination of "small outer shell particles and large core particles" generates a significant spatial optimization effect during the electrode fabrication compaction process. The fine outer shell particles efficiently fill the gaps between the large core particles, achieving a net increase in electrode compaction density and contributing to improved battery volumetric energy density. More importantly, this multi-level structure synergistically constructs an efficient dual charge transport network within the electrode: the large core particles ensure efficient long-range electron conduction, while the small outer shell particles and their abundant interfaces greatly promote rapid short-range ion migration. This synergistic effect reduces the battery's charge transfer impedance, enhances reaction kinetics, and ultimately results in materials with higher reversible discharge capacity, excellent rate performance, and more stable cycle performance.
[0028] 3. Easy to industrialize and promote: The process of this invention is simple and highly operable. No additional equipment investment is required. It can be quickly scaled up by relying on existing lithium iron phosphate production lines, and has significant practicality and economic benefits. Attached Figure Description
[0029] Figure 1 Here is a SEM image of the lithium iron phosphate cathode material prepared in Example 1;
[0030] Figure 2 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1;
[0031] Figure 3 The first charge-discharge curve of the lithium iron phosphate cathode material prepared in Example 1 at 0.1C is shown.
[0032] Figure 4 This is a particle size distribution diagram of the lithium iron phosphate cathode material prepared in Example 1. Detailed Implementation
[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, the embodiments described below are only some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.
[0034] Example 1
[0035] Step 1: Add 3000g of ferric phosphate, 760.8g of lithium carbonate, 60g of sucrose, 270g of PEG2000, 16g of titanium dioxide and 7.2g of ammonium metavanadate to 6L of pure water and mechanically stir and disperse for 10 minutes until the mixture is uniformly dispersed to obtain a uniformly dispersed slurry.
[0036] Step 2: Grind the uniformly dispersed slurry to control D50 to 0.30μm to obtain the first slurry;
[0037] Step 3: Add 191g of ferric ammonium citrate to the first slurry, mechanically stir for 10 minutes, mix evenly to obtain the second slurry, and then spray dry it, controlling the inlet air temperature to 220℃ and the outlet air temperature to 98℃ to obtain the spray material;
[0038] Step 4: Transfer the sprayed material to a box furnace and sinter it at 750℃ for 8 hours under a nitrogen atmosphere with a heating rate of 2.5℃ / min. Then, pulverize the sintered material by air jet mill, controlling the particle size D50 to be 1.2±0.2μm. After a sieving and demagnetization process, high-pressure lithium iron phosphate material is obtained.
[0039] Example 2
[0040] Step 1: Add 3000g of ferric phosphate, 760.8g of lithium carbonate, 90g of glucose, 270g of PEG6000, 16g of titanium dioxide and 7.2g of magnesium carbonate to 6L of pure water and mechanically stir and disperse for 10 minutes until well mixed to obtain a uniformly dispersed slurry.
[0041] Step 2: Grind the uniformly dispersed slurry to control D50 to 0.35μm to obtain the first slurry;
[0042] Step 3: Add 134g of triethanolamine iron to the first slurry, mechanically stir for 10 minutes, mix evenly to obtain the second slurry, and then spray dry it, controlling the inlet air temperature to 230℃ and the outlet air temperature to 105℃ to obtain the spray material.
[0043] Step 4: Transfer the sprayed material to a box furnace and sinter it at 750℃ for 8 hours under a nitrogen atmosphere with a heating rate of 2.5℃ / min. Then, pulverize the sintered material by air jet mill, controlling the particle size D50 to be 1.2±0.2μm. After a sieving and demagnetization process, high-pressure lithium iron phosphate material is obtained.
[0044] Example 3
[0045] Step 1: Add 3000g of ferric phosphate, 760.8g of lithium carbonate, 90g of glucose, 270g of PEG6000, 16g of titanium dioxide and 7.2g of ammonium metavanadate to 6L of pure water and mechanically stir and disperse for 10 minutes until the mixture is uniformly dispersed to obtain a uniformly dispersed slurry.
[0046] Step 2: Grind the uniformly dispersed slurry to control D50 to 0.30μm to obtain the first slurry;
[0047] Step 3: Add 287g of ferric ammonium citrate to the first slurry, mechanically stir for 10 minutes, mix evenly to obtain the second slurry, and then spray dry it, controlling the inlet air temperature to 220℃ and the outlet air temperature to 96℃ to obtain the spray material;
[0048] Step 4: Transfer the sprayed material to a box furnace and sinter it at 750℃ for 10 hours under a nitrogen atmosphere with a heating rate of 2.5℃ / min. Then, pulverize the sintered material by air jet mill, controlling the particle size D50 to be 1.2±0.2μm. After a sieving and demagnetization process, high-pressure lithium iron phosphate material is obtained.
[0049] Comparative Example 1
[0050] The difference between this comparative example and Example 1 is that no iron-organic coordination salt is added in step three.
[0051] Compacted density test:
[0052] The compaction density of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Example 1 was tested using a compaction density meter at a pressure of 3T.
[0053] Electrochemical performance testing and particle size testing:
[0054] The lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Example 1 were subjected to the following operations: the active material, binder PVDF, and conductive additive SP were dispersed in NMP solution at a mass ratio of 90:5:5. After being mixed evenly, a slurry was prepared, coated on aluminum foil, vacuum dried, rolled, and cut into sheets to obtain cathode sheets. The active material mass of the cathode sheet was 12 mg. The negative electrode was a lithium metal sheet, the separator was a polypropylene porous membrane, and the electrolyte was 1 mol / L LiPF6 / EC+DEC+DMC (where the volume ratio of EC:DEC:DMC = 1:1:1). The charge and discharge specific capacity was tested in the voltage range of 2.5V-3.9V.
[0055] Table 1:
[0056] sample 0.1C charging specific capacity (mAh / g) 0.1C discharge specific capacity (mAh / g) First-time effect (%) 1C discharge specific capacity (mAh / g) <![CDATA[3T powder compaction (g / cm 3 )]]> Example 1 163.17 157.79 96.7 143.25 2.58 Example 2 162.01 156.82 96.8 142.34 2.57 Example 3 163.80 159.54 97.4 144.82 2.55 Comparative Example 1 160.82 153.27 95.3 138.42 2.46
[0057] Table 1 and Figure 3 Experimental results confirm that, compared to the traditional one-time sintering process used in Comparative Example 1, all examples modified with iron-organic coordination salts (1, 2, 3) exhibit significant performance advantages, specifically reflected in: General improvement: Different types and ratios of iron-organic coordination salts can effectively improve the compaction density and rate performance of the material. Optimal performance: Among them, Example 1 (using ferric ammonium citrate) showed the best performance, with a 3T powder compaction density of 2.58 g / cm³ and a 1C first-cycle discharge specific capacity of 143.25 mAh / g.
[0058] The lithium iron phosphate cathode material prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing. The SEM images are shown below. Figure 1 As shown. By Figure 1 It can be seen that the prepared lithium iron phosphate sample has a "large-small" particle distribution and the particles are spherical. When tightly packed, the synergistic effect of the naturally formed particle gradation and the spherical primary particles can significantly improve the packing density of the material.
[0059] XRD phase analysis was performed on the lithium iron phosphate cathode material prepared in Example 1, and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that no other impurity peaks were found in the prepared lithium iron phosphate sample, indicating that the olivine-structured lithium iron phosphate material was successfully prepared. Figure 4 The particle size analysis results show that the pulverized material exhibits a typical bimodal distribution. This also confirms the successful preparation of an optimized particle system composed of both large and small particles.
[0060] The above embodiments are only for illustrating the technical solutions and features of the present invention, and are intended to enable those skilled in the art to implement them better. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention are within the scope of protection of the present invention. The parts not described in detail are prior art.
Claims
1. A method for preparing a high-pressure lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: Step 1: Add iron source, phosphorus source, lithium source, carbon source, dispersant, and elemental dopant to a solvent for dispersion to prepare a slurry; Step 2: Grind the slurry to obtain the first slurry; Step 3: Add iron-organic coordination salt to the first slurry, mix well to obtain the second slurry, and then spray dry it to obtain the spray material; Step 4: Sinter and pulverize the sprayed material to obtain high-pressure lithium iron phosphate material.
2. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step one, the iron source and phosphorus source are iron phosphate; the lithium source is any one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the carbon source is any one or more of glucose, sucrose, PVDF, graphene, and carbon nanotubes; the dispersant is any one or more of PEG2000, PEG6000, and PVA2000; the elemental dopant is any one or more of titanium dioxide, ammonium metavanadate, magnesium carbonate, aluminum oxide, and niobium oxide; and the solvent is pure water.
3. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step one, the molar ratio of the metal elements in the iron source, phosphorus source, lithium source, and elemental dopant is 0.95-1:1:1-1.1:0.005-0.
05.
4. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step one, the mass ratio of iron phosphate, carbon source and dispersant is 1:0.01-0.1:0.01-0.
1.
5. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step one, the solid content of the slurry is 35%-45%.
6. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step two, the abrasive particle size of the first slurry is controlled at D50 = 0.25-0.45 μm.
7. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step three, the iron-organic coordination salt is any one or more of ferric ammonium citrate, ferric ammonium gluconate, triethanolamine iron, ethylenediamine iron, and ethylenediaminetetraacetic acid sodium iron, and its amount is 0.1-5% of the molar amount of iron phosphate.
8. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step three, the inlet air temperature of spray drying is 210-240℃, the outlet air temperature of spray drying is 90-110℃, and the moisture content of the material obtained by spray drying is less than 2wt%.
9. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step four, sintering is carried out under a protective atmosphere of nitrogen or argon, at a temperature of 700-750℃, for a time of 6-10 hours.