Preparation method of uniform carbon-coated lithium iron phosphate positive electrode material
By employing a stepwise addition of two carbon source solutions, the problem of uneven carbon coating in lithium iron phosphate materials was solved, improving the material's compaction density and electrochemical performance, especially its cycle performance.
Patent Information
- Application Number
- CN202511167775.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-20
- Publication Date
- 2025-12-12
AI Technical Summary
In the existing technology, lithium iron phosphate materials have low electronic conductivity, high resistance, uneven carbon coating leading to low tap density and compaction density, and contain a lot of free carbon.
Two carbon source solutions are added separately. The first carbon source solution coats the particles once, and the second carbon source solution is added during spraying. They are sprayed simultaneously with the first slurry to form a uniform carbon layer, thus forming a uniform carbon coating layer on the surface of the lithium iron phosphate material.
Uniform carbon coating was achieved in lithium iron phosphate materials, which improved the compaction density and cycling performance of the materials, reduced the probability of free carbon shedding, and enhanced the electrochemical performance of the materials.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of lithium ion battery cathode material, and particularly relates to a preparation method of uniform carbon-coated lithium iron phosphate cathode material. BACKGROUND
[0002] Lithium iron phosphate is an orthorhombic crystal olivine structure, as a lithium ion battery cathode material, has the advantages of stable discharge voltage platform and good high-temperature performance, and has a theoretical specific capacity of 170 mAh / g. At present, the preparation methods of lithium iron phosphate mainly include high-temperature solid-phase method, carbon thermal reduction method, hydrothermal method and the like. However, it is found in the preparation process that the uncoated lithium iron phosphate has the defects of low electronic conductivity and large resistance, and cannot be directly used as a cathode material.
[0003] The most common method for improving the performance of lithium iron phosphate material in the prior art is to coat the lithium iron phosphate with a carbon layer. The common carbon source mainly uses one of an organic carbon source and an inorganic carbon source, and the carbon source is directly added before spray drying. However, it is found after preparation that the carbon coating method causes the carbon layer on the surface of the material to be non-uniform and have a large amount of free carbon, thereby resulting in low tap density and low compacted density of the material.
[0004] In view of this, a uniform carbon layer coating method is provided to improve the compacted density of the lithium iron phosphate cathode material. SUMMARY
[0005] The purpose of the present application is to provide a preparation method of uniform carbon-coated lithium iron phosphate cathode material. The carbon source is added in two carbon source solutions, the first carbon source solution is used to coat the primary particles, and the second carbon source solution is added during spray drying and sprayed at the same time as the first slurry, so that a uniform carbon coating layer is formed on the surface of the primary particles and the secondary particles, and the method has the advantages of controllable process, simple operation and low cost.
[0006] To solve the above technical problems, the present application provides a preparation method of uniform carbon-coated lithium iron phosphate cathode material, which comprises the following steps: S1, preparation of a first slurry The lithium source is first dissolved in water to form a solution, then the iron source and the phosphorus source are added, and after uniform mixing and stirring, the additive and the first carbon source solution are added and stirred and ball milled. After the solutes in the slurry are uniformly dispersed, sand milling is performed. After the sand milling is performed to a particle size of 0.3-0.5 μm, the first slurry is obtained. The solid content of the first slurry is 20%-60%; S2, preparation of a second carbon source solution The second carbon source and the third carbon source which are soluble in water are respectively dissolved in deionized water, and after uniform mixing and stirring, the second carbon source solution is obtained; S3, preparation of a lithium iron phosphate semi-finished product spray material The first slurry of S1 and the second carbon source solution of S2 are sprayed simultaneously, the feeding rate of the second carbon source solution is 0.1-5 times of the first slurry, and the lithium iron phosphate semi-finished product spray material with uniform carbon layer is obtained after the spraying of the first slurry and the second carbon source solution is completed. S4, preparation of lithium iron phosphate / carbon composite material The semi-finished product spray material is sintered at high temperature under a protective atmosphere, and finally the lithium iron phosphate / carbon composite material is obtained.
[0007] Preferably, the first carbon source solution in S1 is prepared by dissolving a certain amount of first carbon source in ultrapure water, wherein the first carbon source is one or more of glucose, polyethylene glycol, phenolic resin, alginic acid, sucrose, starch, and polyvinylpyrrolidone, and the mass of the first carbon source powder accounts for 5wt%-8wt% of the total mass of lithium source, iron source, and phosphorus source powder materials.
[0008] Preferably, the second carbon source and the third carbon source in S2 are one or more of glucose, polyethylene glycol, phenolic resin, alginic acid, sucrose, starch, and polyvinylpyrrolidone, and the total mass of the second carbon source and the third carbon source in the second carbon source solution of S2 accounts for 3wt%-8wt% of the total mass of lithium source, iron source, and phosphorus source powder materials, and the solvent accounts for 40%-90%.
[0009] Preferably, the mass ratio of the second carbon source to the third carbon source in S2 is 1-10:1.
[0010] Preferably, the lithium / iron molar ratio in S1 is 0.9-1.2, and the iron / phosphorus molar ratio is 0.9-1.05.
[0011] Preferably, the lithium source in S1 is one or more of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium hydroxide; the iron source is one or more of iron phosphate, ferrous oxalate, diiron trioxide, and triiron tetroxide; the phosphorus source is one or more of iron phosphate, lithium dihydrogen phosphate, phosphoric acid, lithium phosphate, and ammonium dihydrogen phosphate.
[0012] Preferably, the additive in S1 is one or more of titanium dioxide, tetrabutyl titanate, magnesium oxide, manganese carbonate, vanadium pentoxide, and ammonium metavanadate.
[0013] Preferably, the additive in S1 is 1500-6000ppm.
[0014] Preferably, the atomization temperature in S3 is 210-270℃, the exhaust temperature is 70-95℃, and the feeding speed of the first slurry is 20-5rpm / min.
[0015] Preferably, the protective gas of the sintering stage in S4 is one of nitrogen and argon, the sintering temperature is 650-850 DEG C, and the holding treatment time is 8-12h.
[0016] The beneficial effects of the present application are: The preparation method of the uniform carbon-coated lithium iron phosphate positive electrode material is simple and efficient, two kinds of carbon source solutions are added, the first carbon source solution is used to coat the primary particles, and the second carbon source solution is added during spraying and sprayed at the same time as the first slurry, so that a uniform carbon coating layer is formed on the surface of the primary particles and the secondary particles. Here, the primary particles are independent mixed particles mainly composed of iron phosphate formed in the grinding stage, and the secondary particles are quasi-spherical particles formed by the accumulation of the primary particles after spray drying. The second carbon source is mainly used for coating the secondary particles, so that the carbon coating is more uniform and the probability of carbon layer falling off is reduced. Therefore, during the subsequent sintering, the uniform carbon coating layer has only a small amount of free carbon, thereby improving the compaction density of the lithium iron phosphate material, and the uniform carbon coating layer improves the cycle performance of the lithium iron phosphate material. BRIEF DESCRIPTION OF DRAWINGS
[0017] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.
[0018] Figure 1 is the XRD pattern of embodiment 1 of the present application; Figure 2 is the SEM pattern of embodiment 1 of the present application. DETAILED DESCRIPTION
[0019] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. EMBODIMENT
[0020] A preparation method of a uniform carbon-coated lithium iron phosphate positive electrode material, the preparation method comprising the following steps: S1, preparation of the first slurry Take deionized water with solid content of 40%, and add lithium carbonate. After the lithium carbonate is dissolved, add iron phosphate according to the Li / Fe molar ratio of 1.05, mix and stir uniformly, then add 3000ppm titanium dioxide and 5% of the total mass of the powder. After the solutes in the slurry are uniformly dispersed, sand grinding is performed. After the sand grinding particle size is less than 0.45μm, the first slurry solution is obtained; S2, preparation of a second carbon source solution Take 4.5% of the total mass of the powder of polyethylene glycol and 1.5% of the total mass of the powder of phenolic resin and add them to 0.7 times the mass of deionized water in the above solution. After the carbon source is completely dissolved, the second carbon source solution is obtained; S3, preparation of lithium iron phosphate semi-finished spray material Simultaneously spray the first slurry in S1 and the second carbon source solution in S2. Set the atomization temperature to 230℃ and the exhaust temperature to 80℃. Control the first slurry feeding speed to be 30 rpm / min, and the second carbon source solution feeding speed to be 0.7 times that of the first slurry. After the spraying is completed, the lithium iron phosphate semi-finished spray material with uniform carbon layer is obtained; S4, preparation of lithium iron phosphate / carbon composite material Place the above obtained spray material in an N2 atmosphere furnace, increase the temperature to 785℃ at a rate of 3℃ / min, and keep the temperature for 10h. After the temperature decreases to room temperature, the lithium iron phosphate / carbon composite material is obtained. Example
[0021] A preparation method of a uniform carbon-coated lithium iron phosphate positive electrode material, the preparation method comprising the following steps: S1, preparation of a first slurry Take deionized water with solid content of 40%, and add lithium carbonate. After the lithium carbonate is dissolved, add iron phosphate according to the Li / Fe molar ratio of 1.05, mix and stir uniformly, then add 3000ppm titanium dioxide and 5% of the total mass of the powder. After the solutes in the slurry are uniformly dispersed, sand grinding is performed. After the sand grinding particle size is less than 0.45μm, the first slurry solution is obtained; S2, preparation of a second carbon source solution Take 4.5% of the total mass of the powder of polyethylene glycol and 1.5% of the total mass of the powder of phenolic resin and add them to 0.7 times the mass of deionized water in the above solution. After the carbon source is completely dissolved, the second carbon source solution is obtained; S3, preparation of lithium iron phosphate semi-finished spray material Simultaneously spray the first slurry in S1 and the second carbon source solution in S2. Set the atomization temperature to 230℃ and the exhaust temperature to 80℃. Control the first slurry feeding speed to be 30 rpm / min, and the second carbon source solution feeding speed to be 0.7 times that of the first slurry. After the spraying is completed, the lithium iron phosphate semi-finished spray material with uniform carbon layer is obtained; Preparation of lithium iron phosphate / carbon composite material The spray material obtained above was placed in a N2 atmosphere furnace, and was raised to 790℃ at a temperature raising rate of 5℃ / min, and was kept for 8h, and the lithium iron phosphate / carbon composite material was obtained after the temperature was reduced to room temperature. Example
[0022] A preparation method of a uniform carbon-coated lithium iron phosphate anode material, the preparation method comprising the following steps: S1, preparation of a first slurry Deionized water with a solid content of 40% was weighed, and lithium dihydrogen phosphate was added, after the lithium dihydrogen phosphate was dissolved, iron oxide was added according to a Li / Fe molar ratio of 1.04, after uniform mixing and stirring, 3000ppm of titanium dioxide, 2000ppm of vanadium pentoxide and 5.8% of the total mass of the powder of polyethylene glycol were added, after the solutes in the slurry were uniformly dispersed, sand milling was performed, and after the sand milling particle size was less than 0.4μm, the first slurry solution was obtained; S2, preparation of a second carbon source solution The total mass of 4.5% of the powder of sucrose and 2% of polyvinylpyrrolidone was weighed and added to deionized water with a mass of 1 times that of the above-mentioned solution, and after the carbon source was completely dissolved, the second carbon source solution was obtained; S3, preparation of a lithium iron phosphate semi-finished product spray material The first slurry of S1 and the second carbon source solution of S2 were simultaneously sprayed, the atomization temperature was set to 255℃, the exhaust temperature was 90℃, the feeding speed of the first slurry was controlled to be 22 rpm / min, and the feeding speed of the second carbon source solution was 1 times that of the first slurry, after the spraying was completed, the lithium iron phosphate semi-finished product spray material with a uniform carbon layer was obtained; S4, preparation of a lithium iron phosphate / carbon composite material The spray material obtained above was placed in a N2 atmosphere furnace, and was raised to 790℃ at a temperature raising rate of 5℃ / min, and was kept for 8h, and the lithium iron phosphate / carbon composite material was obtained after the temperature was reduced to room temperature.
[0023] In summary, the electrochemical performance test results of the lithium iron phosphate prepared in Examples 1-3 are shown in Table 1: Table 1 LFP material performance test table of Examples 1-3 From Table 1, it can be seen that: The powder compaction density of the material prepared in Example 1 was 2.56g / cm 3 , the first charge specific capacity was 163.31mAh / g, the first discharge specific capacity was 161.21mAh / g, the first efficiency was 98.71%, and the capacity retention rate after 1000 cycles was 94.2% under 1C charge / discharge rate; The powder compaction density of the material prepared in Example 2 is 2.58 g / cm 3 The first charge specific capacity is 162.52 mAh / g, the first discharge specific capacity is 160.09 mAh / g, the first efficiency is 98.50%, and the capacity retention rate after 1000 cycles at 1C charge-discharge rate is 95.3%; The powder compaction density of the material prepared in Example 3 is 2.59 g / cm 3 The first charge specific capacity is 163.71 mAh / g, the first discharge specific capacity is 159.83 mAh / g, the first efficiency is 97.63%, and the capacity retention rate after 1000 cycles at 1C charge-discharge rate is 94.5%.
[0024] As Figure 1 can be seen, the diffraction peaks of the prepared LiFePO4 are sharp and high in intensity, and are completely consistent with the standard card, without impurity peaks, indicating that the material has high purity and crystallinity; from the scanning electron microscope image of Figure 2 , it can be seen that the LiFePO4 prepared by this method presents a spherical shape, is regular and round in shape, has less flocculent free carbon, and is graded by small particles of 200-300 nm and large particles of 1-3 μm. This morphology of the iron lithium material can improve the compaction density, and the presence of small particles and the uniform carbon layer also make it have good electrochemical performance, especially significantly improving the cycle performance.
[0025] The above only discloses preferred embodiments of the present application, and of course cannot limit the scope of the rights of the present application, so equivalent changes made according to the claims of the present application still fall within the scope of the present application.
Claims
1. A method for preparing a uniformly carbon-coated lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: S1, Preparation of the first slurry The lithium source is first dissolved in water to form a solution, then the iron source and phosphorus source are added and mixed evenly. After mixing, the additives and the first carbon source solution are added and ball-milled. After the solutes in the slurry are evenly dispersed, the slurry is sand-milled until the particle size is 0.3-0.5 μm to obtain the first slurry. The solid content of the first slurry is 20%-60%. S2, Preparation of the second carbon source solution The second and third carbon sources, which are soluble in water, are dissolved in deionized water, and after mixing and stirring evenly, a solution of the second carbon source is obtained. Preparation of S3, Lithium Iron Phosphate Semi-finished Spray Material The first slurry of S1 and the second carbon source solution of S2 are sprayed simultaneously. The feed rate of the second carbon source solution is controlled to be 0.1 to 5 times that of the first slurry. After the first slurry and the second carbon source solution are sprayed simultaneously, a lithium iron phosphate semi-finished spray material with a uniform carbon layer is obtained. Preparation of S4, Lithium Iron Phosphate / Carbon Composite Material The above-mentioned semi-finished spray material was sintered at high temperature under a protective atmosphere to finally obtain lithium iron phosphate / carbon composite material.
2. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The first carbon source solution in S1 is prepared by dissolving a certain amount of the first carbon source in ultrapure water. The first carbon source is one or more of glucose, polyethylene glycol, phenolic resin, alginic acid, sucrose, starch, and polyvinylpyrrolidone. The mass of the first carbon source powder accounts for 5wt% to 8wt% of the total mass of the lithium source, iron source, and phosphorus source powder materials.
3. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, In S2, the second carbon source and the third carbon source are one or more of glucose, polyethylene glycol, phenolic resin, alginic acid, sucrose, starch, and polyvinylpyrrolidone. The total mass of the second carbon source solution and the third carbon source in S2 accounts for 3wt% to 8wt% of the total mass of lithium source, iron source, and phosphorus source powder materials, and the solvent accounts for 40% to 90% of the second carbon source solution.
4. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 3, characterized in that, The mass ratio of the second carbon source to the third carbon source in S2 is 1 to 10:
1.
5. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The lithium / iron molar ratio in S1 is 0.9–1.2, and the iron / phosphorus molar ratio is 0.9–1.
05.
6. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The lithium source in S1 is one or more of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium hydroxide. The iron source is one or more of ferric phosphate, ferrous oxalate, ferric oxide, and ferric oxide; The phosphorus source is one or more of iron phosphate, lithium dihydrogen phosphate, phosphoric acid, lithium phosphate, and ammonium dihydrogen phosphate.
7. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The additive in S1 is one or more of the following: titanium dioxide, tetrabutyl titanate, magnesium oxide, manganese carbonate, vanadium pentoxide, and ammonium metavanadate.
8. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The additive in S1 is 1500-6000 ppm.
9. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, In S3, the atomization temperature is 210–270℃, the exhaust temperature is 70–95℃, and the first slurry feed rate is 20–5 rpm / min.
10. The method for preparing a uniformly carbon-coated lithium iron phosphate cathode material according to claim 1, characterized in that, The protective gas in the sintering stage of S4 is either nitrogen or argon, the sintering temperature is 650-850℃, and the heat treatment time is 8-12h.