Spherical high-performance lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium battery positive electrode material production processes, and particularly discloses a spherical high-performance lithium iron phosphate positive electrode material preparation method, which comprises: S1, adding required powder into a solvent according to a corresponding ratio, mixing, and carrying out grinding treatment after mixing to obtain a first mixture; s2, drying and sintering the mixture to obtain a first lithium iron phosphate precursor; s3, adding the first lithium iron phosphate precursor and other powder into deionized water, dispersing to obtain a second mixture, grinding and drying to obtain a second lithium iron phosphate precursor; and S4, sintering the second lithium iron phosphate precursor to obtain the carbon-coated lithium iron phosphate positive electrode material. The two-fluid spray drying method is adopted in the slurry drying stage, the spherical lithium iron phosphate small in particle size is prepared, the processes such as airflow pulverization of materials in the traditional process are omitted, and the method is low in raw material requirement, simple in process, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of production technology of lithium-ion battery positive electrode materials, and in particular to a spherical high-performance lithium iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] As a representative of olivine-type structured cathode materials, lithium iron phosphate cathode materials have become a hot topic in the research of lithium-ion battery cathode materials due to their excellent safety, good cycle performance, environmental friendliness, abundant raw material sources, and low cost. However, when lithium iron phosphate is used as a cathode material for lithium batteries, it still has defects, mainly manifested in its poor electronic conductivity, relatively low rechargeable voltage, poor low-temperature stability, low tap density, less electrical energy stored per unit volume of battery, and limited fast charging performance. Compared with ternary lithium batteries, lithium iron phosphate batteries have a slower charging speed, and the maximum charging rate usually does not exceed 2C, which limits its application in modern electric vehicles that require fast charging. During the synthesis process, Fe 2+ Easily oxidized to Fe 3+ It is difficult to obtain single-phase lithium iron phosphate. The preparation process is complex and requires long-term high-temperature calcination, high energy consumption, and a long cycle. Although the rate performance of lithium iron phosphate can be improved by improving the ionic and electronic conductivity through lithium and iron doping, and increasing the electronic conductivity through the addition of additional conductive agents, the inherent characteristics of lithium iron phosphate determine that its rate performance is inferior to other positive electrode materials such as ternary materials.

[0003] CN118754087A discloses a method for preparing a nano-scale lithium iron phosphate battery cathode material and its application. The method comprises dissolving acrylic acid, 2-amino-4-chloro-6-methylpyrimidine, and sulfathiazole in pure water, then adding sodium hydroxide while stirring, cooling to room temperature, removing oxygen from the container, and sequentially adding an initiator and a cross-linking agent to polymerize. After the reaction is complete, the gel is dried and crushed to obtain a water-absorbent resin powder. A lithium source, a carbon source, an iron source, and a phosphorus source are added to the pure water, dispersed to obtain a slurry, and the slurry is ground to obtain a precursor slurry. The water-absorbent resin powder is then added to the precursor slurry and stirred to mix. The mixture is aged in a constant temperature chamber to absorb water. After water absorption is complete and the colloid is stable, it is sintered. The sintered product is subjected to air flow crushing to obtain a nano-scale lithium iron phosphate battery cathode material. The patent discloses that the charge-discharge performance and cycle performance of the lithium iron phosphate material are improved by preparing nano-scale lithium iron phosphate. The patent requires the prior preparation of water-absorbent resin powder, which has a complicated preparation process and increases the production cost, making it unfavorable for large-scale industrial production. At the same time, the high production cost will also affect its competitiveness in the price-sensitive market.

[0004] CN118529708A discloses a high-performance lithium iron phosphate cathode material and its preparation method, which is prepared by uniformly mixing an iron source, a phosphorus source, a lithium source, and a carbon source to form a granular material, and then performing liquid phase sintering under the action of ultrasound. The raw materials will produce a large amount of liquid phase at a certain sintering temperature, and the proportion of liquid phase in the raw materials is close to 30-50%. At this time, the introduction of ultrasound will accelerate the mass transfer rate between the phases, increase the probability of lattice defects, improve the activity and density of the material, and will not easily form skeletal crystals. The amount of irregular crystals will be reduced, and the sphericity of the particles will be improved. On this basis, due to the addition of ultrasound, the number of liquid bridge connection points between the particles is reduced, so only low-pressure crushing is required to complete the crushing, thereby better protecting the carbon coating layer on the surface of the material. The obtained lithium iron phosphate cathode material has better charge and discharge performance. In the patent, it is necessary to introduce ultrasound at a specific process stage, which increases the complexity of the preparation process and is not conducive to large-scale industrial production. Summary of the Invention

[0005] The present invention aims to provide a high-capacity spherical lithium iron phosphate cathode material and a method for preparing the same. The prepared lithium iron phosphate has excellent rate performance and a high compaction density. To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a spherical high-performance lithium iron phosphate positive electrode material comprises the following steps: S1, adding the required lithium source, carbon source, iron source, phosphorus source, dopant and dispersant into a solvent in corresponding proportions and mixing them, and then grinding them to obtain a first mixture; S2, drying the mixture, controlling the particle size Dv50 after drying in the range of 5-12 μm, and then sintering the mixture under an inert atmosphere formed by continuously passing nitrogen gas to obtain a first lithium iron phosphate precursor; Preferably, the drying method in step S2 is spray drying, the air inlet temperature during drying is 240~280℃, and the air outlet temperature is 90~110℃; the sintering parameters are: sintering temperature is 400℃~800℃, and the constant temperature time during sintering is 3 h~10 h; the carbon content of the lithium iron phosphate precursor after sintering is less than 0.3%.

[0006] S3, adding the first lithium iron phosphate precursor, the second carbon source, the coating agent, and the dispersant into deionized water for dispersion to obtain a second mixture, grinding and drying the dispersed second mixture, and controlling the particle size Dv50 after drying to be in the range of 3 to 8 μm to obtain a second lithium iron phosphate precursor; Preferably, in step S3, the mass ratio of the lithium iron phosphate precursor, the second carbon source, the coating agent, and the dispersant is 1:(0.01-0.06):(0.001-0.01):(0.01-0.05); the drying method is spray drying, and the air inlet temperature during drying is 240-280°C, and the air outlet temperature is 90-110°C.

[0007] Preferably, in step S3, the solid content of the material in the solvent or deionized water solution is controlled between 30% and 60%.

[0008] S4, sintering the second lithium iron phosphate precursor in an inert atmosphere furnace continuously flowing with nitrogen to obtain a carbon-coated lithium iron phosphate positive electrode material; Preferably, the sintering parameters in step S4 are: sintering temperature is 600° C. to 800° C., and constant temperature time during sintering is 5 h to 10 h.

[0009] Preferably, in step S4, the material is pre-treated and dispersed in a solvent or deionized water for no less than 60 minutes.

[0010] Preferably, in step S1, the molar ratio of the phosphorus source, the iron source, and the lithium source is (0.80-1.1): (0.90-1.20): (0.85-1.15); the mass ratio of the carbon source to the iron source is (0.01-0.07): 1; the mass ratio of the dispersant to the iron source is (0.00-0.04): 1; and the mass ratio of the dopant to the iron source is (0.01-0.05): 1.

[0011] Preferably: The phosphorus source is a mixture of any one or more of ferric phosphate, phosphoric acid, lithium dihydrogen phosphate, monoammonium phosphate, and ammonium dihydrogen phosphate; The iron source is a mixture of any one or more of ferric phosphate, ferric oxide, ferroferric oxide, and ferric hydroxide; The lithium source is a mixture of any one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; The carbon source and dispersant are a mixture of any one or more of glucose, sucrose, starch, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol, and melamine; the carbon source (glucose, etc.) has a certain dispersing effect, and the commonly used dispersants (polyvinyl pyrrolidone, etc.) also contain carbon and have a certain carbon supplementation ability.

[0012] The dopant and coating agent are a mixture of any one or more of titanium dioxide, tetrabutyl titanate, magnesium oxide, magnesium acetate, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium hydroxide, zirconium oxide or niobium pentoxide.

[0013] Preferably, the solid content of the first mixture and the second mixture slurry is controlled to be less than 60%; the rotation speed of the grinding equipment is 500r / min~2000r / min, the particle size of the first mixture is 0.35μm~0.60μm; the particle size of the second mixture is 0.20μm~0.50μm, and the first mixture and the second mixture are ground after being fully dispersed in the mixing tank, and the grinding is stopped when the particle size reaches the requirement.

[0014] The present invention also discloses a high-capacity core-shell structure ultra-high nickel positive electrode material prepared by the above preparation method.

[0015] The beneficial effect of the present invention is that, in view of the poor rate performance of current lithium iron phosphate batteries, which makes it difficult to achieve capacity retention at higher rates, the material can be nano-sized to increase the specific surface area of the material, enlarge the reaction interface and provide more diffusion channels; at the same time, due to the small size effect of nano-ions, the depth and distance of lithium ion insertion and extraction are reduced, thereby improving the cycle life.

[0016] In response to the problems caused by the nano-ization of existing materials, such as the agglomeration of nano-scale LiFePO4 materials during the electrochemical process and the need to improve the compaction density of nano-scale lithium iron phosphate powder, the present invention adopts a two-fluid spray drying method to prepare nano-scale lithium iron phosphate into spherical lithium iron phosphate diol particles, which solves a series of problems caused by nano-ization and maintains the material's co-capacity.

[0017] Compared to existing technologies, the method for preparing high-capacity lithium iron phosphate cathode materials provided by this invention utilizes a two-fluid spray drying method during the slurry drying stage to produce spherical lithium iron phosphate with a smaller particle size, eliminating traditional processes such as airflow milling. The solution provided by this invention has low raw material requirements, a simple process, and low costs, making it suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a SEM image of lithium iron phosphate prepared in Example 1; Figure 2 The particle size distribution of lithium iron phosphate prepared in Example 1 of the present invention; Figure 3 It is a process flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0021] Example 1 Combine Figure 3 S1. 1 part of a phosphorus source, 0.97 parts of an iron source, 1.035 parts of a lithium source, 5% of a first carbon source relative to the mass of the iron source, 0.03% of a dopant relative to the total mass of the mixture, and 0.01% of a dispersant relative to the mixture were added to deionized water and mixed. After 90 minutes of dispersion, the mixture was ground to a final particle size Dv50 = 0.65 μm. S2. The first mixture was dried by spray drying at an air inlet temperature of 240 ° C and an air outlet temperature of 95 ° C; the dried material was sintered in a roller kiln continuously fed with a nitrogen atmosphere, the sintering temperature during the sintering process was 600 ° C, and the sintering time was 7 h to obtain a first lithium iron phosphate precursor; S3. 2% polyethylene glycol, 0.05% coating agent, and 0.01% dispersant, relative to the weight of the lithium iron phosphate precursor, were added to deionized water and dispersed for 100 minutes before grinding to a final particle size Dv50 of 0.28 μm. The mixture was then spray-dried at an inlet air temperature of 240°C and an outlet air temperature of 100°C to obtain a second lithium iron phosphate precursor. S4. The second lithium iron phosphate precursor was sintered in a roller kiln continuously supplied with a nitrogen atmosphere at a sintering temperature of 760°C for 8 h to obtain a lithium iron phosphate cathode material. refer to Figure 1 and Figure 2 It can be seen that the method of this embodiment can synthesize spherical lithium iron phosphate with good morphology and small particle size ( Figure 1 ), particle size Dv50=6.5μm ( Figure 2 ).

[0022] Example 2

[0023] The difference between Comparative Example 1 and the embodiment is that the parameters used in each process control the central value in the claims.

[0024] Example 3

[0025] The difference between Comparative Example 1 and the embodiment is that the parameters used in each process control the upper limit values in the claims.

[0026] Example 4

[0027] The difference between Comparative Example 1 and the embodiment is that the parameters used in each process control the lower limit values in the claims.

[0028]

[0029] Table 1 compares the performance data of the examples. The carbon content, powder compaction, and resistivity of the positive electrode materials of the examples were measured. Coin-type batteries were then fabricated using the same method. Parameters characterizing electrical performance (0.1C gram capacity, initial efficiency, and 1.0C gram capacity) were then measured using methods known in the art. Table 1 shows that the powder compaction of the examples and comparative examples ranges from 2.00 to 2.58 g / cc; the 1.0C gram capacity of the button-type batteries is 151.5 to 153.8 mAh / g.

[0030] The above description is merely a relevant concentrated combination of the embodiments of the present invention, and does not limit the present invention in any form. Although the present invention has been presented as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a spherical high-performance lithium iron phosphate positive electrode material, characterized in that: Including steps: S1, adding the required lithium source, carbon source, iron source, phosphorus source, dopant and dispersant into a solvent in corresponding proportions and mixing them, and then grinding them to obtain a first mixture; S2, drying the mixture, controlling the particle size Dv50 after drying in the range of 5-12 μm, and then sintering the mixture under an inert atmosphere formed by continuously passing nitrogen gas to obtain a first lithium iron phosphate precursor; S3, adding the first lithium iron phosphate precursor, the second carbon source, the coating agent, and the dispersant into deionized water for dispersion to obtain a second mixture, grinding and drying the dispersed second mixture, and controlling the particle size Dv50 after drying to be in the range of 3 to 8 μm to obtain a second lithium iron phosphate precursor; S4. Sintering the second lithium iron phosphate precursor in an inert atmosphere furnace with nitrogen continuously flowing in to obtain a carbon-coated lithium iron phosphate positive electrode material.

2. The method for preparing a spherical high-performance lithium iron phosphate positive electrode material according to claim 1, characterized in that: In step S1, the molar ratio of the phosphorus source, the iron source, and the lithium source is (0.80-1.1): (0.90-1.20): (0.85-1.15); the mass ratio of the carbon source to the iron source is (0.01-0.07): 1; the mass ratio of the dispersant to the iron source is (0.00-0.04): 1; and the mass ratio of the dopant to the iron source is (0.01-0.05):

1.

3. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: The drying method in step S2 is spray drying, and the air inlet temperature during drying is 240-280°C, and the air outlet temperature is 90-110°C; The sintering parameters are: sintering temperature of 400°C to 800°C, constant temperature time during sintering of 3 h to 10 h; and the carbon content of the lithium iron phosphate precursor after sintering is less than 0.3%.

4. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: In step S3, the mass ratio of the lithium iron phosphate precursor, the second carbon source, the coating agent, and the dispersant is 1:(0.01-0.06):(0.001-0.01):(0.01-0.05); the drying method is spray drying, and the air inlet temperature during drying is 240-280° C., and the air outlet temperature is 90-110° C.

5. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: The sintering parameters in step S4 are: sintering temperature is 600°C to 800°C, and constant temperature time during sintering is 5 h to 10 h.

6. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: The phosphorus source is a mixture of any one or more of ferric phosphate, phosphoric acid, lithium dihydrogen phosphate, monoammonium phosphate, and ammonium dihydrogen phosphate; The iron source is a mixture of any one or more of ferric phosphate, ferric oxide, ferroferric oxide, and ferric hydroxide; The lithium source is a mixture of any one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; The carbon source and dispersant are a mixture of any one or more of glucose, sucrose, starch, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol, and melamine; The dopant and coating agent are a mixture of any one or more of titanium dioxide, tetrabutyl titanate, magnesium oxide, magnesium acetate, magnesium hydroxide, magnesium nitrate, zirconium nitrate, zirconium hydroxide, zirconium oxide or niobium pentoxide.

7. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: In step S1 and step S3, the solid content of the material in the solvent or deionized water solution is controlled between 30% and 60%; the material is pretreated and dispersed in the solvent or deionized water for no less than 60 minutes.

8. The method for preparing a spherical high-performance lithium iron phosphate cathode material according to claim 1, characterized in that: The solid content of the first mixture and the second mixture is controlled to be less than 60%; the rotation speed of the grinding equipment is 500r / min~2000r / min, the particle size of the first mixture is 0.35μm~0.60μm; the particle size of the second mixture is 0.20μm~0.50μm, and the first mixture and the second mixture are first ground after being fully dispersed in the material tank, and the grinding is stopped when the particle size reaches the requirement.

9. A high-capacity core-shell structure ultra-high nickel cathode material, characterized in that: The method is prepared according to any one of claims 1 to 8.

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