Synthesis method of super nano conductive agent

Abstract

The invention discloses a synthesis method of a super nano conductive agent, which comprises the following steps: preparing a rod-like lithium iron phosphate precursor with a nano size, dispersing tributyl phosphate in an organic solution, dispersing the prepared rod-like lithium iron phosphate precursor in a tributyl phosphate solution to obtain a lithium iron phosphate precursor dispersion liquid, and drying the lithium iron phosphate precursor dispersion liquid to obtain the super nano conductive agent. Mixing the lithium iron phosphate precursor dispersion liquid in a carbon source solution to prepare suspension slurry, and performing high-speed spray drying and granulation on the suspension slurry to obtain particle powder; the lithium iron phosphate precursor coated with the tributyl phosphate is in contact with the carbon source, a phosphate group of the tributyl phosphate reacts with a hydroxyl group on the carbon surface to form a carbon-oxygen-phosphorus covalent bond, so that the binding force between the lithium iron phosphate surface and carbon is enhanced, and the lithium iron phosphate surface and the carbon are more stable through certain directivity and saturability of the covalent bond. The bonding thickness is limited, the low resistivity is ensured, and the transmission efficiency of ions and electrons is improved.

Description

Technical Field

[0001] This invention relates to the field of conductive agents for lithium-ion batteries, and in particular to a method for synthesizing a super nano-conductive agent. Background Technology

[0002] Conductive agents are a relatively small component of batteries, but their role is crucial. From the perspective of lithium-ion battery principles, conductive agents and binders are auxiliary materials that do not directly participate in electrochemical reactions, so they have no direct impact on capacity. However, they can indirectly influence capacity. Although added in small quantities, conductive agents play a vital and indispensable role. Conductive agents have two functions in batteries: a direct one and an indirect one. The direct function is to collect microcurrents between the current collector and the active material, and between active materials themselves, reducing impedance. The indirect effect is due to the large specific surface area of ​​conductive agents, which adsorbs electrolytes. Their distribution affects electrolyte distribution, improving electrolyte wetting and indirectly increasing the lithium-ion transport rate.

[0003] Lithium iron phosphate (LiFePO4) is a novel cathode material that has emerged to meet the demands of high-power output applications, characterized by its excellent safety. LiFePO4 has an olivine structure with space group Pnmb, where oxygen atoms are arranged in a slightly distorted hexagonal close-packed configuration. Phosphorus ions occupy the 4c ​​positions of the tetrahedrons, while iron and lithium atoms occupy the 4c ​​and 4a positions of the octahedrons, forming FeO6 and LiO6 octahedrons. The alternating arrangement of FeO6, LiO6, and PO4 tetrahedrons forms an orthorhombic crystal system. This structure of lithium iron phosphate exhibits lithium-ion intercalation / deintercalation behavior, providing a foundation for its application in lithium-ion secondary batteries.

[0004] The molecular structures of lithium iron phosphate and carbon source solutions differ significantly, resulting in weak interactions between them. Lithium iron phosphate precursors typically possess metal-oxygen and metal-phosphorus chemical bonds, while the molecules in carbon source solutions mainly contain carbon-hydrogen and carbon-carbon chemical bonds. These chemical bonds have weak interactions and are difficult to form strong bonds. Furthermore, the poor dispersibility of lithium iron phosphate precursors in polymeric carbon source solutions leads to uneven coverage of the lithium iron phosphate surface during coating. This may result in some areas having excessively thick carbon coatings while others have thinner coatings.

[0005] Therefore, in order to solve the above problems, the present invention provides a method for preparing a super nano-conductive agent, which solves the problems of poor binding effect and poor dispersibility between lithium iron phosphate and carbon source solution. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a method for synthesizing super nano-conductive agents.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a method for synthesizing a super nano-conductive agent, comprising the following steps: S1. Preparation of nano-sized rod-shaped lithium iron phosphate precursors; S2. Disperse tributyl phosphate in an organic solution to obtain a tributyl phosphate solution. Disperse the prepared rod-shaped lithium iron phosphate precursor in the tributyl phosphate solution to obtain a lithium iron phosphate precursor dispersion. S3. The lithium iron phosphate precursor dispersion is mixed with the carbon source solution to prepare a suspension slurry; S4. The dispersed suspension slurry is spray-dried at high speed and granulated into granular powder. S5. The powder is calcined at high temperature under inert gas protection and then graded and screened to obtain conductive agent material.

[0008] In a preferred embodiment of the present invention, the method for preparing nano-sized rod-shaped lithium iron phosphate precursor in step S1 includes the following steps: S11. Take the metal reactants, nano-iron phosphate suspension and lithium source suspension, and add them sequentially into a high-pressure reactor. Keep the temperature and react to obtain a mixed solution. S12. The prepared mixed solution is precipitated, compressed and filtered to obtain a filter cake, which is then washed and dried. S13. Control the temperature, calcine the dried filter cake at high temperature and then crush it to obtain rod-shaped lithium iron phosphate precursor with nano-sized structure.

[0009] In a preferred embodiment of the present invention, in step S13, the prepared rod-shaped lithium iron phosphate precursor has a diameter of 35nm-55nm and a length-to-diameter ratio of 20-22:4-6.

[0010] In a preferred embodiment of the present invention, the metal reactant is one or more of aluminum salts, titanium oxides, and magnesium salts; The content of the metal reactants is 800ppm-3000ppm; The molar ratio between the nano-iron phosphate and the lithium source is 1:1; The particle size of the nano-iron phosphate is between 10 nm and 50 nm.

[0011] In a preferred embodiment of the present invention, The lithium source is one or more of lithium hydroxide, lithium chloride, lithium nitrate, lithium acetate, lithium carbonate, and lithium oxalate. The heat preservation temperature is 100℃-300℃, and the reaction time is 5h-20h. The filter cake is calcined at a temperature of 500℃-800℃ for 4h-24h. The particle size of the nano-sized lithium iron phosphate precursor is between 20 nm and 50 nm.

[0012] In a preferred embodiment of the present invention, in step S2, the organic solvent is a 75% concentration ethanol solution, and the mass ratio between tributyl phosphate and the ethanol solution is 1-1.5:2-4. The mass ratio between the tributyl phosphate solution and the rod-shaped lithium iron phosphate precursor is 1-1.2:0.45-0.5.

[0013] In a preferred embodiment of the present invention, in step S3, the carbon source is one or more of glucose, sucrose, starch, ethanol, polyvinyl alcohol, citric acid, etc., to prepare carbon nanotubes.

[0014] In a preferred embodiment of the present invention, in step S3, the mass ratio of the lithium iron phosphate precursor to the carbon source is 5-7:1, and the solid content of the suspension slurry is 20%-80%.

[0015] In a preferred embodiment of the present invention, in step S4, an atomizing disc is used to spray dry the suspended slurry. The inlet air temperature for spray drying is 180℃-280℃, the outlet air temperature is 70℃-120℃, the rotation speed of the atomizing disc is 6000rpm-30000rpm, and the measured D50 of the particles is 0.2μm-0.8μm.

[0016] In a preferred embodiment of the present invention, in step S5, the inert gas is one or more of nitrogen, argon, carbon dioxide, etc. The calcination temperature is 500℃-700℃, and the calcination time is 8h-20h; The particle size range of the graded screening is D50: 0.3μm-1.0μm, and the specific surface area of ​​the conductive agent is 9m². 2 / g-12m 2 / g, with a carbon content of 1.8%-3.8%.

[0017] This invention addresses the shortcomings of the prior art and has the following beneficial effects: This invention provides a method for synthesizing a super nano-conductive agent. It utilizes tributyl phosphate to coat a lithium iron phosphate precursor and contact it with a carbon source. The phosphate groups of tributyl phosphate react with the hydroxyl groups on the carbon surface to form carbon-oxygen-phosphorus covalent bonds, thereby strengthening the bonding force between the lithium iron phosphate surface and the carbon. Furthermore, the covalent bonds themselves have a certain directionality and saturation, which limits the thickness of the bond, ensuring its low resistivity and improving the transport efficiency of ions and electrons.

[0018] This invention reduces the contact area between particles and lowers the strength of hydrogen bonds and van der Waals forces by mixing rod-shaped lithium iron phosphate with a carbon source solution. This results in more uniform dispersion of nanorod-shaped potassium iron phosphate particles in the composite material, reducing agglomeration and improving the overall performance of the material.

[0019] This invention combines rod-shaped lithium iron phosphate particles with carbon nanotubes from a carbon source. The composite material of rod-shaped lithium iron phosphate particles and carbon nanotubes has more nanoscale channels, which is beneficial to improving the transport efficiency of ions and electrons, reducing internal resistance, and improving the rate performance of the battery.

[0020] This invention reduces volume change by combining rod-shaped lithium iron phosphate with carbon nanotubes in a carbon source. By controlling the nanostructure of potassium iron phosphate, the diffusion path of lithium ions can be optimized, diffusion resistance can be reduced, and the migration efficiency of lithium ions in the electrode can be improved, thus optimizing lithium ion diffusion.

[0021] This invention prepares rod-shaped potassium iron phosphate, which has high chemical reactivity. When combined with carbon nanotubes, it can promote electrochemical reactions, improve the energy density and charge / discharge efficiency of the battery, and thus enhance chemical reactivity. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of a method for synthesizing a super nano-conductive agent according to the present invention; Figure 2 This is a flowchart of the method for preparing rod-shaped lithium iron phosphate precursor according to the present invention; Figure 3 This is a SEM image of a rod-shaped lithium iron phosphate rod according to a preferred embodiment of the present invention. Detailed Implementation

[0023] 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.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0027] like Figure 1 , Figure 2 and Figure 3 As shown, a method for synthesizing a super nano-conductive agent includes the following steps: S1. Preparation of nano-sized rod-shaped lithium iron phosphate precursors; In S1, the method for preparing nano-sized rod-shaped lithium iron phosphate precursors includes the following steps: S11. Take the metal reactants, nano-iron phosphate suspension and lithium source suspension, and add them sequentially into a high-pressure reactor. Keep the temperature and react to obtain a mixed solution. S12. The prepared mixed solution is precipitated, compressed and filtered to obtain a filter cake, which is then washed and dried. S13. Control the temperature, calcine the dried filter cake at high temperature and then crush it to obtain rod-shaped lithium iron phosphate precursor with nano-sized structure.

[0028] In S13, the prepared rod-shaped lithium iron phosphate precursor has a diameter of 35nm-55nm and a length-to-diameter ratio of 20-22:4-6. By controlling the nanostructure of potassium iron phosphate, it is prepared into a rod shape. Due to its low surface energy and weak interparticle interaction, the strength of hydrogen bonds and van der Waals forces can be reduced, making the nanorod-shaped potassium iron phosphate particles more uniformly dispersed in the composite material.

[0029] In this invention, the metal reactants are one or more of aluminum salts, titanium oxides, and magnesium salts; The content of metal reactants ranges from 800 ppm to 3000 ppm; The molar ratio between nano-iron phosphate and lithium source is 1:1; The particle size of nano-iron phosphate is between 10nm and 50nm.

[0030] In this invention, the lithium source is one or more of lithium hydroxide, lithium chloride, lithium nitrate, lithium acetate, lithium carbonate, and lithium oxalate. The heat preservation temperature is 100℃-300℃, and the reaction time is 5h-20h. The filter cake calcination temperature is 500℃-800℃, and the calcination time is 4h-24h. The particle size of the nano-sized lithium iron phosphate precursor is 20nm-50nm.

[0031] S2. Disperse tributyl phosphate in an organic solution to obtain a tributyl phosphate solution. Disperse the prepared rod-shaped lithium iron phosphate precursor in the tributyl phosphate solution to obtain a lithium iron phosphate precursor dispersion. In S2, the organic solvent is a 75% ethanol solution, and the mass ratio of tributyl phosphate to ethanol solution is 1-1.5:2-4. It is worth mentioning that tributyl phosphate was mixed in a 75% ethanol solution and then subjected to ultrasonic treatment to ensure that the tributyl phosphate was fully dispersed in the 75% ethanol solution. Tributyl phosphate can be used to modify the surface of lithium iron phosphate, forming a composite material with carbon-oxygen-phosphorus covalent bonds. Upon contact with a carbon source, these covalent bonds are formed, significantly improving the bonding force between the lithium iron phosphate surface and carbon, thereby enhancing the performance of the lithium iron phosphate-based composite material. Because too many carbon atoms are bonded to the surface of lithium iron phosphate, these carbon atoms occupy the active sites on the lithium iron phosphate surface, hindering the insertion and extraction of lithium ions during charging and discharging. This reduces the conductivity between lithium iron phosphate particles, obstructing electron transport during charging and discharging, and consequently affecting the battery's rate performance and energy density. Therefore, it is necessary to control the carbon atom content on the surface of lithium iron phosphate. Furthermore, because carbon-oxygen-phosphorus covalent bonds have a certain directionality and saturation, the carbon-oxygen-phosphorus covalent bonds limit the thickness of the carbon atom coating on the lithium iron phosphate surface, effectively avoiding the problem of excessively thick carbon coatings.

[0032] The mass ratio between the tributyl phosphate solution and the rod-shaped lithium iron phosphate precursor is 1-1.2:0.45-0.5.

[0033] S3. The lithium iron phosphate precursor dispersion is mixed with the carbon source solution to prepare a suspension slurry; In S3, the carbon source is one or more of glucose, sucrose, starch, ethanol, polyvinyl alcohol, citric acid, etc., to prepare carbon nanotubes. It should be noted that, in the preparation of carbon nanotubes by chemical vapor deposition, taking glucose as an example, glucose is placed in a reaction vessel and heated to 150°C to fully dissolve it into a glucose carbon source solution. An iron salt catalyst is added to the glucose carbon source solution to promote the formation of carbon nanotubes. Subsequently, the glucose carbon source solution is carbonized at 300°C under the action of the catalyst and the protection of an inert gas (nitrogen). The carbonized product is separated and washed to remove unreacted substances and impurities. The separated product is then placed in an oven and dried at 80°C for 1 hour to obtain carbon nanotubes. The method for preparing carbon nanotubes using one or more of glucose, sucrose, starch, ethanol, polyvinyl alcohol, and citric acid as raw materials is the same as the method described above.

[0034] In S3, the mass ratio of lithium iron phosphate precursor to carbon source is 5-7:1, and the solid content of the suspension slurry is 20%-80%.

[0035] S4. The dispersed suspension slurry is spray-dried at high speed and granulated into granular powder. In section 4, an atomizing disc was used to spray dry the suspended slurry. The inlet air temperature for spray drying was 180℃-280℃, the outlet air temperature was 70℃-120℃, the rotation speed of the atomizing disc was 6000rpm-30000rpm, and the particle D50 was measured to be 0.2μm-0.8μm.

[0036] S5. The powder is calcined at high temperature under inert gas protection and then graded and screened to obtain conductive agent material.

[0037] In S5, the inert gas is one or more of nitrogen, argon, carbon dioxide, etc. The calcination temperature is 500℃-700℃, and the calcination time is 8h-20h; The particle size range for grading and screening is D50: 0.3μm-1.0μm, carbon coating thickness is 3nm-8nm, and the specific surface area of ​​the conductive agent is 9m². 2 / g-12m 2 / g, with a carbon content of 1.8%-3.8%.

[0038] It is worth mentioning that the composite preparation of rod-shaped potassium iron phosphate and carbon nanotubes, with carbon nanotubes having excellent conductivity, can significantly improve the conductivity of the composite material by combining it with rod-shaped potassium iron phosphate particles, which is beneficial to improving the charge and discharge performance of the battery. The composite material of rod-shaped potassium iron phosphate particles and carbon nanotubes has a larger contact area, which allows for better utilization of active materials during charge and discharge, improving the capacity and performance of the electrode. Furthermore, the composite material of rod-shaped potassium iron phosphate particles and carbon nanotubes has more nanoscale channels, which is beneficial to improving the transport efficiency of ions and electrons, reducing internal resistance, and improving the rate performance of the battery. Because carbon nanotubes have good high-temperature resistance, when combined with rod-shaped potassium iron phosphate particles, the thermal stability of the composite material can be improved, thus enhancing battery safety.

[0039] Example 1: 62.23g of nano-titanium dioxide, 50kg of nano-ferric phosphate and 12.23kg of lithium carbonate were weighed and dispersed in 50L of IPA (isopropanol) solution and stirred to form a suspension. The above three suspensions were then added to a high-pressure reactor in sequence and kept at 225°C for 12h. After the reaction was completed and cooled to room temperature, the white precipitate formed in the reaction system was filtered to form a filter cake. The filter cake was washed with pure water, crushed and placed in a mortar, calcined at 655°C for 8h and then ball-milled to a D50 of about 1μm. Weigh 30 kg of the above-mentioned nano-lithium iron phosphate precursor and add it to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:4 to obtain a lithium iron phosphate precursor dispersion. Then, ultrasonically disperse it in 6 kg of 50% glucose solution and stir to prepare a suspension slurry. The dispersed slurry is pumped to the spray drying tower via a fluid pump. The spray drying inlet air temperature is set to 180℃, the outlet air temperature to 70℃, and the atomizing disc rotation speed to 12000rpm. The spray-dried granulated powder was calcined at 620℃ for 18 hours under nitrogen protection, and the final product with a particle size D50 of 1.03μm was obtained by grading and screening. Its carbon content and specific surface area were then tested.

[0040] Example 2 follows largely the same procedure as Example 1, except that 30 kg of the above-mentioned nano-lithium iron phosphate precursor was weighed and added to 5 kg of a tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution was 1:3.5, to obtain a lithium iron phosphate precursor dispersion. This dispersion was then ultrasonically dispersed in 6 kg of a 50% glucose solution and stirred to prepare a suspension slurry. The lithium iron phosphate material prepared in this way was tested for its carbon content and specific surface area.

[0041] Example 3 follows largely the same procedure as Example 1, except that 30 kg of the above-mentioned nano-lithium iron phosphate precursor is weighed and added to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:3, to obtain a lithium iron phosphate precursor dispersion. This dispersion is then ultrasonically dispersed in 6 kg of 50% glucose solution and stirred to prepare a suspension slurry. The lithium iron phosphate material prepared in this way is tested for its carbon content and specific surface area.

[0042] Example 4 follows largely the same procedure as Example 1, except that 30 kg of the above-mentioned nano-lithium iron phosphate precursor is weighed and added to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:2.5, to obtain a lithium iron phosphate precursor dispersion. This dispersion is then ultrasonically dispersed in 6 kg of 50% glucose solution and stirred to prepare a suspension slurry. The lithium iron phosphate material prepared in this way is tested for its carbon content and specific surface area.

[0043] Example 5 follows largely the same procedure as Example 1, except that 30 kg of the above-mentioned nano-lithium iron phosphate precursor is weighed and added to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:2, to obtain a lithium iron phosphate precursor dispersion. This dispersion is then ultrasonically dispersed in 6 kg of 50% glucose solution and stirred to prepare a suspension slurry. The lithium iron phosphate material prepared in this way is tested for its carbon content and specific surface area.

[0044] The resistivity, carbon content, compaction density, and lithium-ion diffusion coefficient D of the lithium iron phosphate materials obtained in Examples 1 to 5 were analyzed. Li The 1C discharge capacity was tested, and the results are shown in Table 1.

[0045] Table 1.

[0046]

[0047] In summary, as the mass percentage of tributyl phosphate in the tributyl phosphate solution increases, its coverage on the surface of lithium iron phosphate gradually increases, resulting in more carbon atoms adhering to the surface. Therefore, a high concentration of tributyl phosphate can provide more phosphate groups to react with the hydroxyl groups on the lithium iron phosphate surface, forming carbon-oxygen-phosphorus covalent bonds, thereby strengthening the bonding force between the lithium iron phosphate surface and carbon. Furthermore, as the mass percentage of tributyl phosphate in the tributyl phosphate solution increases, the resistivity of the lithium iron phosphate material decreases. Lower resistivity means less resistance when current flows inside the battery, and lower resistance increases the diffusion rate of lithium ions, allowing for faster charging and discharging, improving the battery's discharge capacity and charging / discharging efficiency, and extending the battery's lifespan. However, as the mass percentage of tributyl phosphate in the tributyl phosphate solution increases to a certain value, although the carbon content of the prepared lithium iron phosphate material continues to increase, the resistivity of the lithium iron phosphate material increases. The main reason is that there are too many carbon atoms on the surface of the lithium iron phosphate material. Too many carbon atoms will occupy the active sites on the surface of lithium iron phosphate, which will hinder the insertion and extraction of lithium ions during charging and discharging. That is, the resistivity increases, which leads to a decrease in the conductivity between lithium iron phosphate particles. Comparing the above embodiments, it can be concluded that the lithium iron phosphate material obtained in Example 3 has a lower resistivity. The reduced resistivity improves the diffusion performance of lithium ions, thereby increasing its discharge capacity. However, in the process of the resistivity of the lithium iron phosphate material increasing from low to high, compared with Example 3, it shows that the carbon coating thickness on the lithium iron phosphate particles is too large. Therefore, the carbon coating thickness of the lithium iron phosphate material prepared in Example 3 is the optimal value.

[0048] Comparative Example 1: 57.92g of nano-alumina, 50kg of nano-ferric phosphate, and 7.92kg of lithium hydroxide were weighed and dispersed in 50L of IPA (isopropanol) solution and stirred to form a suspension. The three suspensions were then added to a high-pressure reactor in sequence and reacted at 200℃ for 14h. After the reaction was completed and cooled to room temperature, the white precipitate formed in the reaction system was filtered to form a filter cake. The filter cake was washed with pure water, crushed, placed in a mortar, calcined at 670℃ for 9h, and then ball-milled to a D50 of about 1μm. Weigh 30 kg of the above-mentioned nano-lithium iron phosphate precursor and add it to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:3 to obtain a lithium iron phosphate precursor dispersion. Then, ultrasonically disperse it in 5.85 kg of 47.5% polyethylene glycol solution and stir to prepare a suspension slurry. The dispersed slurry is pumped to the spray drying tower via a fluid pump. The spray drying inlet air temperature is set to 200℃, the outlet air temperature to 95℃, and the atomizing disc rotation speed to 14500rpm. The spray-dried granulated powder was calcined at 635℃ for 20 hours under nitrogen protection, and the final product with a particle size D50 of 0.988μm was obtained by grading and screening. Its carbon content and specific surface area were then tested.

[0049] Comparative Example 2: 71.85 g of magnesium hydroxide, 50 kg of nano-iron phosphate and 21.85 kg of lithium acetate were weighed and dispersed in 50 LIPA (isopropanol) solution and stirred to form a suspension. The three suspensions were then added to a high-pressure reactor in sequence and reacted at 190 °C for 16 h. After the reaction was completed and cooled to room temperature, the white precipitate formed in the reaction system was filtered to form a filter cake. The filter cake was washed with pure water, crushed, placed in a mortar, calcined at 660 °C for 10 h, and then ball-milled to a D50 of about 1 μm. Weigh 30 kg of the above-mentioned nano-lithium iron phosphate precursor and add it to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:3 to obtain a lithium iron phosphate precursor dispersion. Then, ultrasonically disperse it in a 1:1 mixed solution containing 5.92 kg of 48.7% polyethylene glycol solution and glucose, and stir to prepare a suspension slurry. The dispersed slurry is pumped to the spray drying tower via a fluid pump. The spray drying inlet air temperature is set to 210℃, the outlet air temperature to 100℃, and the atomizing disc rotation speed to 16800rpm. The spray-dried granulated powder was calcined at 650℃ for 21 hours under nitrogen protection, and the final product with a particle size D50 of 0.993μm was obtained by grading and screening. Its carbon content and specific surface area were then tested.

[0050] Comparative Example 3: 66.88 g of nano-alumina, 50 kg of nano-iron phosphate, and 16.88 kg of lithium oxalate were weighed and dispersed in 50 L of IPA (isopropanol) solution, and stirred to form a suspension. The three suspensions were then added to a high-pressure reactor in sequence and reacted at 220 °C for 11 h. After the reaction was completed and cooled to room temperature, the white precipitate formed in the reaction system was filtered to form a filter cake. The filter cake was washed with pure water, crushed, placed in a mortar, calcined at 655 °C for 11 h, and then ball-milled to a D50 of about 1 μm. Weigh 30 kg of the above-mentioned nano-lithium iron phosphate precursor and add it to 5 kg of tributyl phosphate solution, wherein the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution is 1:3 to obtain a lithium iron phosphate precursor dispersion. Then, ultrasonically disperse it in 5.61 kg of 42.8% starch solution and stir to prepare a suspension slurry. The dispersed slurry is pumped to the spray drying tower via a fluid pump. The spray drying inlet air temperature is set to 240℃, the outlet air temperature to 100℃, and the atomizing disc rotation speed to 18000rpm. The spray-dried granulated powder was calcined at 660℃ for 17h under nitrogen protection, and the final product with a particle size D50 of 1.102μm was obtained by grading and screening. Its carbon content and specific surface area were then tested.

[0051] Since the lithium iron phosphate material prepared in Example 3 has the best overall performance, Comparative Examples 1 to 3 were set up. With the mass ratio of tributyl phosphate to ethanol in the tributyl phosphate solution being 1:3 as a constant, different preparation materials and steps were used to obtain lithium iron phosphate materials with different specific surface areas.

[0052] The resistivity, specific surface area, carbon content, and lithium-ion diffusion coefficient D of the lithium iron phosphate materials obtained in Example 3 and Comparative Examples 1 to 3 were measured. Li The 1C discharge capacity was tested, and the results are shown in Table 2.

[0053] Table 2.

[0054]

[0055] In summary, comparing Example 3, Comparative Example 1, and Comparative Example 2, the carbon content of the lithium iron phosphate materials prepared in Comparative Example 1 and Comparative Example 2 is higher than that of the lithium iron phosphate material prepared in Example 3, and their specific surface area is smaller than that of Example 3. Therefore, it can be deduced that an increase in specific surface area leads to a decrease in resistivity, mainly because the number of active sites on the lithium iron phosphate surface is relatively increased, allowing for the accommodation of more carbon atoms. This reduces the obstacles to lithium ion insertion and extraction during charging and discharging, resulting in a relatively lower resistivity and improved conductivity between lithium iron phosphate particles. While the specific surface area of ​​the lithium iron phosphate material prepared in Comparative Example 3 is larger than that of the lithium iron phosphate material prepared in Example 3, its carbon content is lower, resulting in a lower resistivity than that of the lithium iron phosphate material prepared in Example 3. Therefore, the lithium iron phosphate material prepared in Example 3 possesses both a good specific surface area and a low resistivity, making it the optimal choice.

[0056] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for synthesizing a super nano-conductive agent, characterized in that, Includes the following steps: S1. Preparation of nano-sized rod-shaped lithium iron phosphate precursors; S2. Disperse tributyl phosphate in an organic solution to obtain a tributyl phosphate solution. Disperse the prepared rod-shaped lithium iron phosphate precursor in the tributyl phosphate solution to obtain a lithium iron phosphate precursor dispersion. S3. The lithium iron phosphate precursor dispersion is mixed with the carbon source solution to prepare a suspension slurry; S4. The dispersed suspension slurry is spray-dried at high speed and granulated into granular powder. S5. The powder is calcined at high temperature under inert gas protection and then graded and screened to obtain conductive agent material.

2. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In S1, the method for preparing nano-sized rod-shaped lithium iron phosphate precursors includes the following steps: S11. Take the metal reactants, nano-iron phosphate suspension and lithium source suspension, and add them sequentially into a high-pressure reactor. Keep the temperature and react to obtain a mixed solution. S12. The prepared mixed solution is precipitated, compressed and filtered to obtain a filter cake, which is then washed and dried. S13. Control the temperature, calcine the dried filter cake at high temperature and then crush it to obtain rod-shaped lithium iron phosphate precursor with nano-sized structure.

3. The method for synthesizing a superconducting nanoparticle according to claim 2, characterized in that: In step S13, the prepared rod-shaped lithium iron phosphate precursor has a diameter of 35nm-55nm and a length-to-diameter ratio of 20-22:4-6.

4. The method for synthesizing a superconducting nanoparticle according to claim 2, characterized in that: The metal reactant is one or more of aluminum salts, titanium oxides, and magnesium salts; The content of the metal reactants is 800ppm-3000ppm; The molar ratio between the nano-iron phosphate and the lithium source is 1:1; The particle size of the nano-iron phosphate is between 10 nm and 50 nm.

5. The method for synthesizing a superconducting nanoparticle according to claim 2, characterized in that: The lithium source is one or more of lithium hydroxide, lithium chloride, lithium nitrate, lithium acetate, lithium carbonate, and lithium oxalate. The heat preservation temperature is 100℃-300℃, and the reaction time is 5h-20h. The filter cake is calcined at a temperature of 500℃-800℃ for 4h-24h. The particle size of the nano-sized lithium iron phosphate precursor is between 20 nm and 50 nm.

6. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In S2, the organic solvent is a 75% ethanol solution, and the mass ratio of tributyl phosphate to ethanol solution is 1-1.5:2-4. The mass ratio between the tributyl phosphate solution and the rod-shaped lithium iron phosphate precursor is 1-1.2:0.45-0.

5.

7. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In S3, the carbon source is one or more of glucose, sucrose, starch, ethanol, polyvinyl alcohol, citric acid, etc., to prepare carbon nanotubes.

8. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In S3, the mass ratio of the lithium iron phosphate precursor to the carbon source is 5-7:1, and the solid content of the suspension slurry is 20%-80%.

9. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In step S4, an atomizing disc is used to spray dry the suspended slurry. The inlet air temperature for spray drying is 180℃-280℃, the outlet air temperature is 70℃-120℃, the rotation speed of the atomizing disc is 6000rpm-30000rpm, and the measured D50 of the particles is 0.2μm-0.8μm.

10. The method for synthesizing a superconducting nanoparticle according to claim 1, characterized in that: In S5, the inert gas is one or more of nitrogen, argon, carbon dioxide, etc. The calcination temperature is 500℃-700℃, and the calcination time is 8h-20h; The particle size range of the graded screening is D50: 0.3μm-1.0μm, and the specific surface area of ​​the conductive agent is 9m². 2 / g-12m 2 / g, with a carbon content of 1.8%-3.8%.

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