Preparation method of high-compaction-type lithium iron phosphate positive electrode material

Abstract

This invention discloses a method for preparing a high-pressure solid lithium iron phosphate cathode material, comprising: (1) adding an iron source, a lithium source, a phosphorus source, a first carbon source, a titanium source, and a dispersant to a high-speed mixer for dry mixing, and mixing evenly to obtain a dry powder; (2) pre-sintering the dry powder under an inert atmosphere at a sintering temperature of 600~700℃ and a holding time of 1~8h to obtain primary precursor particles; (3) mixing the primary precursor particles with a solvent, adding a second carbon source, a titanium source, and a lithium source, and transferring the mixture to a sand mill for wet milling to obtain a wet milling slurry; (4) transferring the wet milling slurry to a spray dryer to obtain secondary precursor particles; (5) performing secondary sintering of the secondary precursor particles under an inert atmosphere at a sintering temperature of 750~850℃ and a holding time of 2~10h to obtain the high-pressure solid lithium iron phosphate cathode material. By adjusting the process, optimizing parameters, and designing wet milling feed, a method for preparing lithium iron phosphate with synergistic improvement in high compaction density and electrochemical performance is achieved, thus addressing the pain points of existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically, it relates to a method for preparing high-pressure compact lithium iron phosphate cathode material. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in energy storage systems and power batteries. Lithium iron phosphate (LiFePO4), as a commonly used cathode material, boasts advantages such as low cost, good thermal stability, safety, and environmental friendliness, holding a significant position in the energy storage and low-to-mid-range power battery markets. However, lithium iron phosphate has inherent drawbacks: low conductivity, poor rate performance, and a much lower compaction density than other cathode materials such as lithium cobalt oxide and ternary materials, limiting its specific capacity and making it difficult to meet the high energy density requirements of high-end energy storage and power batteries.

[0003] In the prior art, the “two wet milling → two spray drying → two sintering” process disclosed in Chinese patent CN202411235237.8 can improve the wide temperature range high rate performance through nano-sizing and carbon coating, but it has the following defects: (1) The process starts with “wet mixing-grinding”, which is prone to uneven dispersion due to the difference in the solubility of raw materials. The temperature of the subsequent two sintering (first sintering 300~500℃, second sintering 600~800℃) is too low, making it difficult to achieve crystal densification. The BET specific surface area of ​​the finished product is as high as 10~25m² / g, the particle dispersion is too high, the compaction density is low, and it is difficult to meet the compaction density requirements of medium and high energy density batteries.

[0004] (2) The process only adds dopants in the initial mixing stage, without considering the loss of lithium and titanium elements due to volatilization during the first sintering process, which easily forms vacancy defects and affects the stability of the crystal structure and cycle life.

[0005] Some existing technologies improve low-temperature performance through nano-processing, but nanoparticles have a large specific surface area and a strong tendency to agglomerate, making it difficult for the carbon coating layer to cover evenly. This not only leads to a decrease in compaction density but also exacerbates the side reactions between the electrolyte and the material surface at high temperatures, shortening the cycle life. Other technologies improve density by increasing the sintering temperature, but excessively high temperatures can lead to excessive crystal growth, damaging ion transport channels and sacrificing rate performance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-density lithium iron phosphate cathode material. By adjusting the process, optimizing parameters, and designing wet milling and feeding, a method for preparing lithium iron phosphate with synergistic improvement in high density and electrochemical performance is achieved, thereby solving the pain points of existing technologies.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a high-pressure solid lithium iron phosphate cathode material, comprising the following steps:

[0009] (1) Add the iron source, lithium source, phosphorus source, first carbon source, titanium source and dispersant to a high-speed mixer for dry mixing, and mix evenly to obtain dry powder;

[0010] (2) Under an inert atmosphere, the dry powder obtained in step (1) is pre-sintered at a sintering temperature of 600~700℃ and a holding time of 1~8h to obtain primary precursor particles.

[0011] (3) Mix the primary precursor particles obtained in step (2) with the solvent, add the second carbon source, titanium source and lithium source, and transfer to a sand mill for wet grinding to obtain a wet grinding slurry;

[0012] (4) Transfer the wet grinding slurry obtained in step (3) into a spray dryer to obtain secondary precursor particles;

[0013] (5) Under an inert atmosphere, the secondary precursor particles obtained in step (4) are sintered for a second time at a temperature of 750~850℃ and a holding time of 2~10h to obtain the high-pressure compact lithium iron phosphate cathode material.

[0014] In the preferred embodiment, in step (1), the molar ratio of iron source, lithium source, and phosphorus source is 1:(1.01~1.1):(1.01~1.3).

[0015] The iron source is one or more of ferric sulfate, ferric chloride, and ferric nitrate.

[0016] The lithium source is one of lithium carbonate and lithium hydroxide;

[0017] The phosphorus source is one or more of ammonium dihydrogen phosphate and sodium dihydrogen phosphate;

[0018] The first carbon source is glucose, and the amount of glucose added is 1.0 wt% to 2.0 wt% of the total mass of the raw materials.

[0019] The titanium source is titanium dioxide, with a doping amount of 1000~2000ppm;

[0020] The dispersing agent is zinc stearate, accounting for 0.2wt% to 1.0wt% of the total mass of the raw materials.

[0021] Ti 4+ Ionic radius and Fe 2+ Approaching, it can be embedded in lattice interstices or partially replace Fe. 2+ This inhibits crystal growth and improves structural stability. The total doping amount is controlled between 1000 and 2000 ppm; excessive doping can lead to severe lattice distortion, reducing material capacity and cycle stability.

[0022] The dispersant selected is zinc stearate, whose polar groups in its molecular structure can be adsorbed on the surface of raw material particles, reducing the van der Waals forces between particles and preventing particle agglomeration during the mixing process. At the same time, under the shear force generated by high-speed mixing, it further improves the uniformity of raw material dispersion.

[0023] In the preferred embodiment, in step (1), the high-speed mixer rotates at 1600~2400 r / min and mixes for 10~60 min at a temperature of 32~50℃. Dry mixing replaces traditional wet mixing, and the combination of dispersing agents and high-speed shearing ensures the initial uniform dispersion of raw materials such as iron, lithium, and phosphorus sources, avoiding elemental segregation caused by particle agglomeration during the wet process, thus laying the foundation for subsequent uniform crystal growth and tight particle packing. The mixing temperature of 32~50℃ ensures that zinc stearate fully exerts its dispersing effect while avoiding premature carbonization of glucose due to excessively high temperatures.

[0024] In the preferred embodiment, in step (2), under a nitrogen atmosphere, the dry powder is placed into a graphite crucible and heated to 600-700°C at a rate of 3-6°C / min, held at that temperature for 1-8 hours, and then naturally cooled to room temperature to obtain primary precursor particles. The pre-sintering temperature is set at 600-700°C. This temperature range allows the raw materials to fully react and form highly crystalline lithium iron phosphate nuclei, while also preventing excessive crystal growth and promoting the initial carbonization of the first carbon source to form an initial carbon layer that is tightly bonded to the crystal.

[0025] In the preferred embodiment, in step (3), the precursor particles are mixed with deionized water;

[0026] The second carbon source is polyethylene glycol (PEG2000), and the amount added is 0.1wt%~1wt% of the mass of the primary precursor particles;

[0027] The titanium source is titanium dioxide, and the total Ti doping amount is 1000~2000ppm;

[0028] The lithium source is either lithium carbonate or lithium hydroxide, and the amount added is 2wt% to 5wt% of the amount of lithium source used in step (1), which is used to make up for the lithium loss in the first sintering.

[0029] Lithium replenishment is used to correct lithium volatilization losses during pre-sintering and eliminate lithium vacancy defects; titanium replenishment is achieved through the use of Ti. 4+ Lattice doping modulates crystal parameters, improving lattice conductivity while suppressing abnormal crystal growth, thus balancing compaction density and electrochemical performance.

[0030] In the preferred embodiment, in step (3), the solid content of the slurry during wet milling is 40%~50%, and the particle size distribution in the slurry is controlled. 50The particle size is 0.34~0.38μm. Strict control of the D-size of the wet grinding slurry particles is required. 50 With a particle size of 0.34~0.38μm, this particle size range can achieve close packing between particles, while shortening the lithium-ion transport distance and avoiding the problems of loose packing of excessively fine particles and insufficient rate performance of excessively coarse particles.

[0031] In the preferred embodiment, in step (4), the wet grinding slurry is transferred into a spray dryer, and the inlet air temperature is controlled at 190~220℃, the outlet air temperature at 75~90℃, the atomization pressure at 0.3~0.6MPa, and the feed rate at 20~40mL / min to obtain secondary precursor particles.

[0032] In the preferred embodiment, in step (5), the secondary precursor particles are loaded into a graphite crucible and heated to 750-850°C at a rate of 2-5°C / min under a nitrogen atmosphere, with a holding time of 2-10 hours. Precise temperature control promotes crystal densification and simultaneously enables the second carbon source to be fully carbonized, forming a uniform and continuous conductive carbon layer, thus achieving a synergistic effect of "density enhancement" and "conductivity assurance".

[0033] The present invention also provides a high-pressure solid lithium iron phosphate cathode material, which is prepared by the aforementioned preparation method.

[0034] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the high-pressure compact lithium iron phosphate positive electrode material.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) This invention improves the compaction density of lithium iron phosphate cathode material and reduces the specific surface area (BET) of the finished product by combining the innovative process flow of "dry mixing → pre-sintering → wet grinding → spray drying → secondary sintering" with precise control of multi-dimensional parameters. At the same time, it takes into account the excellent electrochemical performance and solves the core pain point of "difficulty in synergistic high compaction and high performance" in the existing technology.

[0037] (2) The process is simple and controllable, the raw material cost is low, the process parameters of each step are compatible with industrial production equipment, no special customized equipment is required, it is suitable for large-scale industrial production, and has broad market application prospects.

[0038] (3) The high-pressure compact lithium iron phosphate cathode material prepared can significantly improve the energy density of the battery, extend the driving range, and improve the cycle life and environmental adaptability of the battery, thus promoting the technological progress of the new energy industry. Attached Figure Description

[0039] Figure 1 The image shows a SEM image of the high-performance lithium iron phosphate cathode material prepared in Example 1.

[0040] Figure 2 The image shows the XRD pattern of the high-performance lithium iron phosphate cathode material prepared in Example 1. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0042] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0043] Example 1

[0044] A method for preparing a high-pressure compact lithium iron phosphate cathode material includes the following steps:

[0045] (1) Dry mixing: Ferric sulfate, lithium carbonate, ammonium dihydrogen phosphate, glucose (1.5wt%), titanium dioxide (1500ppm), and zinc stearate (0.6wt%) were added to a high-speed mixer for dry mixing. The molar ratio of ferric sulfate, lithium carbonate, and ammonium dihydrogen phosphate was 1:1.05:1.1. The mixture was mixed for 30 minutes at 40°C and 2000r / min under nitrogen protection to obtain dry powder.

[0046] (2) Pre-sintering: Under nitrogen atmosphere, dry powder is loaded into graphite sagger, heated to 650°C at a rate of 4°C / min, held for 6 hours, and naturally cooled to room temperature to obtain primary precursor particles.

[0047] (3) Wet milling: Mix the primary precursor particles with an appropriate amount of deionized water, add polyethylene glycol (PEG2000, 0.8wt%), titanium dioxide (to meet the total Ti doping amount of 1500ppm), and lithium carbonate (3wt% of the lithium source amount), and transfer to a sand mill for wet milling. During the wet milling process, the slurry solid content is 45%, and the slurry D is controlled. 50 The particle size is 0.34~0.38μm, resulting in a wet grinding slurry;

[0048] (4) Spray drying: The wet grinding slurry is transferred into a spray dryer, and the inlet air temperature is controlled at 205℃, the outlet air temperature at 82℃, the atomization pressure at 0.45MPa, and the feed rate at 32mL / min to obtain secondary precursor particles;

[0049] (5) Secondary sintering: The secondary precursor particles are loaded into a graphite sagger and heated to 800°C at a rate of 3°C / min under a nitrogen atmosphere. The temperature is held for 8 hours and then naturally cooled to room temperature to obtain high-pressure compact lithium iron phosphate cathode material.

[0050] Example 2

[0051] A method for preparing a high-pressure compact lithium iron phosphate cathode material includes the following steps:

[0052] (1) Dry mixing: Ferric sulfate, lithium carbonate, ammonium dihydrogen phosphate, glucose (1.7wt%), titanium dioxide (1800ppm), and zinc stearate (0.9wt%) were added to a high-speed mixer for dry mixing. The molar ratio of ferric sulfate, lithium carbonate, and ammonium dihydrogen phosphate was 1:1.08:1.2. The mixture was mixed for 25 minutes at 45°C and 2200r / min under nitrogen protection to obtain dry powder.

[0053] (2) Pre-sintering: Under nitrogen atmosphere, dry powder is loaded into graphite sagger, heated to 700°C at a rate of 5°C / min, held for 4 hours, and naturally cooled to room temperature to obtain primary precursor particles.

[0054] (3) Wet milling: Mix the primary precursor particles with an appropriate amount of deionized water, add polyethylene glycol (PEG2000, 0.9wt%), titanium dioxide (to meet the total Ti doping amount of 1600ppm), and lithium carbonate (4wt% of the lithium source amount), and transfer to a sand mill for wet milling. During the wet milling process, the slurry solid content is 48%, and the slurry D is controlled. 50 The particle size is 0.34~0.38μm, resulting in a wet grinding slurry;

[0055] (4) Spray drying: The wet grinding slurry is transferred into a spray dryer, and the inlet air temperature is controlled at 210℃, the outlet air temperature at 85℃, the atomization pressure at 0.5MPa, and the feed rate at 35mL / min to obtain secondary precursor particles;

[0056] (5) Secondary sintering: The secondary precursor particles are loaded into a graphite sagger and heated to 820°C at a rate of 4°C / min under a nitrogen atmosphere. The temperature is held for 6 hours and then naturally cooled to room temperature to obtain high-pressure solid lithium iron phosphate cathode material.

[0057] Example 3

[0058] A method for preparing a high-pressure compact lithium iron phosphate cathode material includes the following steps:

[0059] (1) Dry mixing: Ferric sulfate, lithium carbonate, ammonium dihydrogen phosphate, glucose (1.3wt%), titanium dioxide (1200ppm), and zinc stearate (0.5wt%) were added to a high-speed mixer for dry mixing. The molar ratio of ferric sulfate, lithium carbonate, and ammonium dihydrogen phosphate was 1:1.03:1.15. The mixture was mixed for 35 minutes at 38°C and 1800r / min under nitrogen protection to obtain dry powder.

[0060] (2) Pre-sintering: Under nitrogen atmosphere, dry powder is loaded into graphite sagger, heated to 630°C at a rate of 3°C / min, held for 7 hours, and naturally cooled to room temperature to obtain primary precursor particles.

[0061] (3) Wet milling: Mix the primary precursor particles with an appropriate amount of deionized water, add polyethylene glycol (PEG2000, 0.6wt%), titanium dioxide (to meet the total Ti doping amount of 1200ppm), and lithium carbonate (2wt% of the lithium source amount), and transfer to a sand mill for wet milling. During the wet milling process, the slurry solid content is 40%, and the slurry D is controlled. 50 The particle size is 0.34~0.38μm, resulting in a wet grinding slurry;

[0062] (4) Spray drying: The wet grinding slurry is transferred into a spray dryer, and the inlet air temperature is controlled at 200℃, the outlet air temperature at 80℃, the atomization pressure at 0.4MPa, and the feed rate at 28mL / min to obtain secondary precursor particles;

[0063] (5) Secondary sintering: The secondary precursor particles are loaded into a graphite sagger and heated to 780°C at a rate of 2°C / min under a nitrogen atmosphere. The temperature is held for 9 hours and then naturally cooled to room temperature to obtain high-pressure solid lithium iron phosphate cathode material.

[0064] Comparative Example 1

[0065] Prepared according to the steps of Example 1 in CN202411235237.8:

[0066] (1) First wet grinding: 50g anhydrous ferric phosphate, 12.8g lithium carbonate, 5.4g glucose and 0.4g ammonium metavanadate are dispersed in 180g deionized water and sand-milled for 2h until D50=300~400nm;

[0067] (2) First spray drying: to obtain the first precursor (carbon content 2.8wt%);

[0068] (3) First sintering: nitrogen atmosphere, 400℃, heat preservation for 4 hours;

[0069] (4) Second wet milling: Add 0.8g PEG2000 and mill for 2.5h until D50=200~300nm;

[0070] (5) Second spray drying: to obtain the second precursor (carbon content 3.5wt%);

[0071] (6) Second sintering: nitrogen atmosphere, 750℃, for 6 hours.

[0072] Performance test results:

[0073] The prepared lithium iron phosphate cathode material was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added to form a uniform slurry, which was then coated onto aluminum foil. After vacuum drying at 120°C for 12 hours, the slurry was rolled to form a cathode sheet. Using lithium metal sheets as the anode, Celgard 2400 as the separator, and 1M LiPF6 in ethylene carbonate / diethyl carbonate (volume ratio 1:1) as the electrolyte, CR2032 button cells were assembled in an argon glove box.

[0074] The performance of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Example 1 was tested, and the test results are shown in Table 1:

[0075] Table 1 Performance Test Results

[0076] sample Compacted density (g / cm³) Specific surface area (m² / g) 0.1C discharge specific capacity (mAh / g) Capacity retention rate (%) after 1800 cycles at 45℃ (1C) Example 1 2.68 10.1 160.8 84.5 Example 2 2.70 9.8 159.5 83.8 Example 3 2.65 10.6 161.2 85.1 Comparative Example 1 - 12.3 154.3 83.7

[0077] Figure 1 The image shows a SEM image of the high-performance lithium iron phosphate cathode material prepared in Example 1. As can be seen from the image, the prepared lithium iron phosphate particles are uniform, well dispersed, and have a particle size range of 0.1 μm to 1 μm. Figure 2 The image shows the XRD pattern of the high-performance lithium iron phosphate cathode material prepared in Example 1. As can be seen from the image, the prepared lithium iron phosphate has good crystallinity and high consistency with the standard card.

[0078] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a high-pressure compact lithium iron phosphate cathode material, characterized in that, Includes the following steps: (1) Add the iron source, lithium source, phosphorus source, first carbon source, titanium source and dispersant to a high-speed mixer for dry mixing, and mix evenly to obtain dry powder; (2) Under an inert atmosphere, the dry powder obtained in step (1) is pre-sintered at a sintering temperature of 600~700℃ and a holding time of 1~8h to obtain primary precursor particles. (3) Mix the primary precursor particles obtained in step (2) with the solvent, add the second carbon source, titanium source and lithium source, and transfer to a sand mill for wet grinding to obtain a wet grinding slurry; (4) Transfer the wet grinding slurry obtained in step (3) into a spray dryer to obtain secondary precursor particles; (5) Under an inert atmosphere, the secondary precursor particles obtained in step (4) are sintered for a second time at a temperature of 750~850℃ and a holding time of 2~10h to obtain the high-pressure compact lithium iron phosphate cathode material.

2. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the molar ratio of iron source, lithium source and phosphorus source is 1:(1.01~1.1):(1.01~1.3). The iron source is one or more of ferric sulfate, ferric chloride, and ferric nitrate. The lithium source is one of lithium carbonate and lithium hydroxide; The phosphorus source is one or more of ammonium dihydrogen phosphate and sodium dihydrogen phosphate; The first carbon source is glucose, and the amount of glucose added is 1.0 wt% to 2.0 wt% of the total mass of the raw materials. The titanium source is titanium dioxide, with a doping amount of 1000~2000ppm; The dispersing agent is zinc stearate, accounting for 0.2wt%~1.0wt% of the total mass of the raw materials.

3. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the speed of the high-speed mixer is 1600~ Mix at 2400 r / min for 10 to 60 min at a temperature of 32 to 50℃.

4. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), under a nitrogen atmosphere, the dry powder is loaded into a graphite crucible and heated to 600-700°C at a rate of 3-6°C / min. The temperature is maintained for 1-8 hours and then naturally cooled to room temperature to obtain primary precursor particles.

5. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the primary precursor particles are mixed with deionized water; The second carbon source is polyethylene glycol (PEG2000), and the amount added is 0.1wt%~1wt% of the mass of the primary precursor particles; The titanium source is titanium dioxide, and the total Ti doping amount is 1000~2000ppm; The lithium source is either lithium carbonate or lithium hydroxide, and the amount added is 2wt% to 5wt% of the amount of lithium source used in step (1), which is used to make up for the lithium loss in the first sintering.

6. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the solid content of the slurry during wet milling is 40%~50%, and the particle size D of the slurry is controlled. 50 The thickness is 0.34~0.38μm.

7. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (4), the wet grinding slurry is transferred into a spray dryer, and the inlet air temperature is controlled at 190~220℃, the outlet air temperature at 75~90℃, the atomization pressure at 0.3~0.6MPa, and the feed rate at 20~40mL / min to obtain secondary precursor particles.

8. The method for preparing a high-pressure compact lithium iron phosphate cathode material according to claim 1, characterized in that, In step (5), the secondary precursor particles are loaded into a graphite crucible and heated to 750-850°C at a rate of 2-5°C / min under a nitrogen atmosphere, and the temperature is maintained for 2-10 hours.

9. A high-pressure compact lithium iron phosphate cathode material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode comprises the high-density lithium iron phosphate positive electrode material as described in claim 9.

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