Production method of low-cost and high-compaction lithium iron phosphate positive electrode material

Abstract

The invention provides a production method of a low-cost and high-compaction lithium iron phosphate positive electrode material, and belongs to the technical field of lithium iron phosphate positive electrode materials, and the production method comprises the following steps: S1, adding iron phosphate and a lithium source into a carboxylated carbon nanotube dispersion liquid, stirring, filtering, drying, compacting and molding, transferring into a rotary furnace, and carrying out low-temperature sintering to obtain a lithium iron phosphate precursor; an inorganic carbon doped iron phosphate precursor is obtained; s2, uniformly stirring the inorganic carbon doped iron phosphate precursor and a lithium source in a polyvinyl alcohol solution, and compacting and forming to obtain an organic carbon coated lithium iron phosphate mixed material; and S3, feeding the organic carbon coated lithium iron phosphate mixed material into a roller furnace in saggars, sintering at high temperature, and cooling to obtain the low-cost and high-compaction lithium iron phosphate positive electrode material. According to the method, different reaction stages are subjected to two-stage furnace sintering treatment, so that the defects of poor form consistency and poor electrochemical performance of the lithium iron phosphate material caused by the conventional transverse expansion arrangement number and layer number can be overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium iron phosphate positive electrode materials, and in particular relates to a method for producing a low-cost high-density lithium iron phosphate positive electrode material. Background Art

[0002] Among the main positive electrode materials of many new energy lithium batteries, LiFePO4 with olivine structure is more stable because of its internal FeO6 octahedral structure.

[0003] In the existing technology, the production methods of lithium iron phosphate materials are mainly solid-phase method and liquid-phase method. Among them, the solid-phase method must use a roller furnace made of all non-metallic materials due to the difficulty in controlling the precursor structure and the avoidance of magnetic substances. It has high energy consumption and low efficiency. At the same time, the compaction density of one sintering has reached a bottleneck and cannot be expanded to a higher range of applications.

[0004] Currently, improvements to the performance of LiFePO4 materials include particle refinement and ion doping. Improvements to high energy consumption usually involve increasing the number of horizontal rows of roller furnaces and multi-layer designs. These improvements have problems such as slow heat transfer rate, long preheating time, and uneven temperature distribution, and are suspected of being "high consumption and low energy". The resulting lithium iron phosphate positive electrode material is difficult to achieve high electrochemical performance. Summary of the Invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a low-cost production method of high-density lithium iron phosphate positive electrode material. Through two-stage separate furnace sintering and processing of different reaction stages, it can improve the shortcomings of lithium iron phosphate material caused by the number and number of layers of conventional lateral expansion arrangement, such as poor morphological consistency and poor electrochemical performance, break through the bottleneck of compaction density manufacturing, and realize low-cost and efficient preparation of high-density lithium iron phosphate material.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: Adding iron phosphate and lithium source to the carboxylated carbon nanotube dispersion, stirring for 10-20 min, filtering, drying, compacting by a compactor, transferring to a rotary kiln, introducing an inert protective gas, and sintering at a low temperature of 300-400 ° C for 2-6 h. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and the lithium source in step S1 are stirred evenly in a polyvinyl alcohol solution, transferred to a mixer, and the mixing is continued for 3-5h. After the mixing is completed, the compactor is compacted to obtain an organic carbon-coated lithium iron phosphate mixture; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and fed into a roller hearth furnace. An inert protective gas is introduced and sintered at high temperature at 600-800°C for 6-10 hours. After cooling, the material is pulverized to control the particle size and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate cathode material.

[0007] Furthermore, in step S1, the molar ratio of Li:Fe in the iron phosphate and the lithium source is 0.95-1.00:1, and the mass ratio of the iron phosphate to the carboxylated carbon nanotube dispersion is 1:8-12.

[0008] Furthermore, in step S2, the mass ratio of the inorganic carbon-doped iron phosphate precursor, the lithium source and the polyvinyl alcohol solution is 100:2.5-3.5:4-6.

[0009] Furthermore, in step S1, the mass concentration of the carboxylated carbon nanotube dispersion is 0.4-0.6%, and the dispersion solvent is N,N-dimethylformamide.

[0010] Furthermore, the mass concentration of the polyvinyl alcohol solution in step S2 is 4-6%.

[0011] Furthermore, the lithium source in steps S1 and S2 is one or a mixture of two or more of lithium carbonate, lithium hydroxide and lithium nitrate.

[0012] Furthermore, the inert protective gas used is one of nitrogen and argon, or a mixture of the two.

[0013] Furthermore, the material of the rotary kiln in step S1 is one of 316L stainless steel and 310S stainless steel. Using a rotary kiln for sintering in step S1 saves time and energy compared to a conventional roller furnace.

[0014] This application has the following beneficial effects: 1. The present invention provides a low-cost production method for high-density compacted lithium iron phosphate positive electrode materials. Through two-stage separate furnace sintering and processing of different reaction stages, it can improve the shortcomings of poor morphological consistency and poor electrochemical performance of lithium iron phosphate materials caused by the number and number of conventional lateral expansion arrangements, and break through the bottleneck of compaction density manufacturing. At the same time, the use of a rotary kiln has lower energy consumption than a roller furnace, and the continuous discharge of the rotary kiln can realize a "one-to-two" or even "one-to-three" production line configuration, which can greatly reduce energy consumption and achieve low-cost and efficient preparation.

[0015] 2. During low-temperature sintering, lithium-deficient sintering is beneficial to the dispersion of mixing and sintering, avoiding the problems of agglomerate growth and excessive hardness. Carbon nanotube doping can improve the conductivity and structural stability of the material and improve the electrochemical properties of the material. During high-temperature sintering, under the action of lithium supplementation and carbon coating, the iron impurity phase inside the material can be converted back into lithium iron phosphate material through the sintering process, effectively reducing the impurity content. At the same time, the volume shrinkage of polyvinyl alcohol after high-temperature dehydration can reduce the coating gap, enabling it to tightly coat the main material, making the regular arrangement of the crystallization zone during the sintering process denser, and finally obtaining a lithium iron phosphate positive electrode material with a single material component and dense arrangement, achieving higher self-discharge performance and cycle performance.

[0016] 3. The carbon nanotubes doped during low-temperature sintering are carboxylated carbon nanotubes, which have high activity. After the water-soluble polyvinyl alcohol infiltrates the inorganic carbon-doped iron phosphate precursor, it can effectively combine with the carboxylated carbon nanotubes to achieve uniform coating and effective adhesion of the organic carbon source to the lithium iron phosphate, thereby further improving the coating effect of the organic carbon source and improving the electrochemical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 , XRD diffraction pattern of the lithium iron phosphate material prepared in Example 1 of the present invention; Figure 2 , SEM image of the lithium iron phosphate material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The present application is further described in detail below with reference to the embodiments.

[0019] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available. Example 1

[0020] A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: adding iron phosphate and lithium carbonate to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.5%, stirring for 15 minutes, filtering, drying, compacting and forming with a compactor, transferring the mixture into a rotary kiln made of 316L stainless steel, introducing nitrogen, and performing low-temperature sintering at a sintering temperature of 350°C for 4 hours. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in the iron phosphate and lithium carbonate is 0.98:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:10; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and lithium carbonate in step S1 were stirred evenly in a polyvinyl alcohol solution having a mass concentration of 5% and transferred to a mixer for continuous mixing for 4 hours. After the mixing was completed, the compactor was compacted to obtain an organic carbon-coated lithium iron phosphate mixture, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium carbonate and polyvinyl alcohol solution was 100:3:5; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and placed into a roller hearth furnace. Nitrogen is introduced and sintered at high temperature at 700°C for 8 hours. After cooling, the material particle size is controlled by a crusher and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate positive electrode material. Example 2

[0021] A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: adding iron phosphate and lithium hydroxide to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.4%, stirring for 20 min, filtering, drying, compacting and molding with a compactor, transferring the mixture to a rotary kiln made of 310S stainless steel, introducing argon gas, and sintering at a low temperature of 300 ° C for 6 h. After sintering, the mixture was naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in the iron phosphate and lithium hydroxide was 0.95:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion was 1:8-12; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and lithium hydroxide in step S1 were stirred evenly in a polyvinyl alcohol solution having a mass concentration of 4%, and transferred to a mixer, and the mixing was continued for 3 hours. After the mixing was completed, the compactor was compacted to obtain an organic carbon-coated lithium iron phosphate mixture, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium hydroxide and polyvinyl alcohol solution was 100:2.5:4; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and placed into a roller hearth furnace. Argon is introduced and sintered at high temperature at 600°C for 10 hours. After cooling, the material particle size is controlled by a crusher and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate positive electrode material. Example 3

[0022] A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: adding iron phosphate and lithium nitrate to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.6%, stirring for 10 minutes, filtering, drying, compacting and forming with a compactor, transferring the mixture into a rotary kiln made of 316L stainless steel, introducing nitrogen, and performing low-temperature sintering at a sintering temperature of 400°C for 2 hours. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in the iron phosphate and lithium nitrate is 1:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:12; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and lithium nitrate in step S1 were stirred evenly in a polyvinyl alcohol solution having a mass concentration of 6%, and transferred to a mixer, and the mixing was continued for 5 hours. After the mixing was completed, the compactor was compacted to obtain an organic carbon-coated lithium iron phosphate mixture, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium nitrate and polyvinyl alcohol solution was 100:3.5:6; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and placed into a roller hearth furnace. Nitrogen is introduced and sintered at high temperature at 800°C for 6 hours. After cooling, the material particle size is controlled by a crusher and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate positive electrode material. Example 4

[0023] A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: adding iron phosphate and lithium carbonate to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.4%, stirring for 20 minutes, filtering, drying, compacting and forming with a compactor, transferring the mixture into a rotary kiln made of 310S stainless steel, introducing argon gas, and performing low-temperature sintering at a sintering temperature of 300°C for 6 hours. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in the iron phosphate and lithium carbonate is 1:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:12; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and lithium carbonate in step S1 were stirred evenly in a polyvinyl alcohol solution having a mass concentration of 4% and transferred to a mixer for continuous mixing for 5 hours. After the mixing was completed, the compactor was compacted to obtain an organic carbon-coated lithium iron phosphate mixture, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium carbonate and polyvinyl alcohol solution was 100:2.5:5; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and placed into a roller hearth furnace. Argon is introduced and sintered at high temperature at 800°C for 6 hours. After cooling, the material particle size is controlled by a crusher and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate positive electrode material. Example 5

[0024] A method for producing a low-cost, high-density lithium iron phosphate cathode material comprises the following steps: S1. Introduction of lithium source and inorganic carbon source: adding iron phosphate and lithium nitrate to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.5%, stirring for 20 minutes, filtering, drying, compacting and forming with a compactor, transferring the mixture into a rotary kiln made of 316L stainless steel, introducing nitrogen, and performing low-temperature sintering at a sintering temperature of 350°C for 6 hours. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in the iron phosphate and lithium nitrate is 0.97:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:8; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and lithium nitrate in step S1 were stirred evenly in a polyvinyl alcohol solution having a mass concentration of 5%, and transferred to a mixer, and the mixing was continued for 3 hours. After the mixing was completed, the compactor was compacted to obtain an organic carbon-coated lithium iron phosphate mixture, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium nitrate and polyvinyl alcohol solution was 100:3.5:5; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and placed into a roller hearth furnace. Nitrogen is introduced and sintered at high temperature at 700°C for 10 hours. After cooling, the material particle size is controlled by a crusher and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate positive electrode material. Comparative Example 1

[0025] The difference between this comparative example and Example 1 is that the carboxylated carbon nanotubes are replaced with ordinary carbon nanotubes in step S1, which is as follows: S1. Introducing lithium source and inorganic carbon source: adding iron phosphate and lithium carbonate to a dispersion of carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carbon nanotubes in the dispersion is 0.5%, stirring for 15 minutes, filtering, drying, compacting and forming with a compactor, transferring to a rotary kiln, introducing nitrogen, and performing low-temperature sintering at a sintering temperature of 350°C and a sintering time of 4 hours. After sintering, naturally cooling to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in iron phosphate and lithium carbonate is 0.98:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:10. Comparative Example 2

[0026] The difference between this comparative example and Example 1 is that no inorganic carbon source doping is performed in step S1, that is, no carboxylated carbon nanotubes are added. The details are as follows: S1. Introducing lithium source: Add iron phosphate and lithium carbonate to N,N-dimethylformamide, stir for 15 minutes, filter, dry, compact and shape with a compactor, transfer to a rotary kiln, introduce nitrogen, and perform low-temperature sintering at a temperature of 350°C for 4 hours. After sintering, naturally cool to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in iron phosphate and lithium carbonate is 0.98:1, and the mass ratio of iron phosphate to N,N-dimethylformamide is 1:10. Comparative Example 3

[0027] The difference between this comparative example and Example 1 is that no organic carbon source coating is performed in step S2, that is, no polyvinyl alcohol is added, as follows: S2. Replenishing lithium source: Stir the inorganic carbon-doped iron phosphate precursor and lithium carbonate in water in step S1 evenly, transfer them into a mixer, and continue mixing for 4 hours. After the mixing is completed, compact them with a compactor to obtain an organic carbon-coated lithium iron phosphate mixture material, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium carbonate and water is 100:3:5. Comparative Example 4

[0028] The difference between this comparative example and Example 1 is that no inorganic carbon source doping is performed in step S1, and no organic carbon source coating is performed in step S2, as follows: S1. Introduction of lithium source: Add iron phosphate and lithium carbonate to N,N-dimethylformamide, stir for 15 minutes, filter, dry, compact and shape with a compactor, transfer to a rotary kiln, introduce nitrogen, and perform low-temperature sintering at 350°C for 4 hours. After sintering, cool naturally to room temperature to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in iron phosphate and lithium carbonate is 0.98:1, and the mass ratio of iron phosphate to N,N-dimethylformamide is 1:10; S2. Replenishing lithium source: Stir the inorganic carbon-doped iron phosphate precursor and lithium carbonate in water in step S1 evenly, transfer them into a mixer, and continue mixing for 4 hours. After the mixing is completed, compact them with a compactor to obtain an organic carbon-coated lithium iron phosphate mixture material, wherein the mass ratio of the inorganic carbon-doped iron phosphate precursor, lithium carbonate and water is 100:3:5.

[0029] Comparative Example 5

[0030] The difference between this comparative example and Example 1 is that the sintering method in the low-temperature sintering in step S1 is changed from rotary kiln sintering to roller hearth furnace sintering, as follows: S1. Introducing lithium source and inorganic carbon source: adding iron phosphate and lithium carbonate to a dispersion of carboxylated carbon nanotubes in N,N-dimethylformamide, wherein the mass concentration of carboxylated carbon nanotubes in the dispersion is 0.5%, stirring for 15 minutes, filtering, drying, compacting and forming with a compactor, transferring to a roller furnace, introducing nitrogen, and performing low-temperature sintering at a sintering temperature of 350°C and a sintering time of 4 hours. After sintering, naturally cooling to room temperature is completed to obtain an inorganic carbon-doped iron phosphate precursor, wherein the molar ratio of Li:Fe in iron phosphate and lithium carbonate is 0.98:1, and the mass ratio of iron phosphate to the carboxylated carbon nanotube dispersion is 1:10.

[0031] Proven effectiveness

[0032] Physical performance parameters: After the lithium iron phosphate composite materials of Examples 1-5 were passed through a 200-mesh sieve, the physical performance parameters of the lithium iron phosphate positive electrode materials were tested. The specific test results are shown in Table 1; Electrical performance test: The lithium iron phosphate positive electrode material obtained in Examples 1-5 and Comparative Examples 1-4, acetylene black, and 60.63% polyPTFE emulsion were mixed in a mass percentage of 90:7:3, stirred evenly, coated, and dried to form a single-sided electrode with a diameter of 14 mm. The electrode was placed in a vacuum drying oven and vacuum dried at 120°C for 1 hour. The electrode was assembled into a simulated battery with a metal element lithium sheet as the negative electrode, 1M LiPF6 as the electrolyte, and Cellgard2300 as the diaphragm for electrochemical testing. The specific test results are shown in Table 2.

[0033] Table 1

[0034] Table 2 Result Analysis

[0035] Figure 1 This is the X-ray diffraction pattern of the product obtained in Example 1. By comparison, it can be seen that the diffraction peak position is consistent with the standard spectrum (PDF#83-2092), and the diffraction peak is sharp, indicating that the lithium iron phosphate obtained in this example has good crystallinity and a single phase composition.

[0036] Figure 2 This is a scanning electron microscope image of the product obtained in Example 1. As can be seen from the image, the obtained material is composed of particles with a size of 200-300 nm. The particles are well dispersed as a whole and there is no agglomeration. The particles of different particle sizes have a high degree of coordination and are tightly combined.

[0037] Table 1 shows the physical property parameters of the lithium iron phosphate composite materials of Examples 1-5 measured after passing through a 200-mesh sieve. The data show that the prepared lithium iron phosphate positive electrode materials have good particle size uniformity, high compaction density and conductivity.

[0038] Table 2 shows the electrochemical property parameters of the obtained lithium iron phosphate material. The lithium iron phosphate positive electrode material prepared by the present invention has a 0.2C discharge capacity of more than 155.4 mAh / g, a 0.2C discharge capacity of more than 148.6 mAh / g, and a 2C rate of more than 134.3 mAh / g.

[0039] By analyzing Examples 1-5 and Comparative Examples 1-4 and combining the data in Table 2, it can be seen from Comparative Example 1 and Example 1 that the carboxylation treatment of carbon nanotubes can improve the rate discharge capacity of the lithium iron phosphate positive electrode material. Both carboxylation carbon nanotube doping during low-temperature sintering and organic carbon coating during high-temperature sintering can improve the rate discharge capacity of the lithium iron phosphate positive electrode material. More importantly, the increase in rate discharge capacity when the combined use of carboxylation carbon nanotube doping during low-temperature sintering and organic carbon coating during high-temperature sintering is significantly greater than the sum of the increases when the two treatment methods are used alone, indicating that the two can produce synergistic effects and greatly improve the rate discharge capacity of the lithium iron phosphate positive electrode material.

[0040] In Comparative Example 5, the sintering method in the low-temperature sintering in step S1 is changed from rotary kiln sintering to roller hearth furnace sintering. By comparing with Example 1, we found that the dynamic sintering of the rotary kiln is much better than the static sintering of the roller hearth furnace, and is more conducive to exhaust gas discharge and uniformity of synthesis.

[0041] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0042] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for producing a low-cost high-density lithium iron phosphate cathode material, characterized in that: The following steps are involved: S1. Introduction of lithium source and inorganic carbon source: Adding iron phosphate and lithium source to the carboxylated carbon nanotube dispersion, stirring for 10-20 min, filtering, drying, compacting by a compactor, transferring to a rotary kiln, introducing an inert protective gas, and sintering at a low temperature of 300-400 ° C for 2-6 h. After sintering, the mixture is naturally cooled to room temperature to obtain an inorganic carbon-doped iron phosphate precursor; S2. Supplementing the lithium source and introducing an organic carbon source: The inorganic carbon-doped iron phosphate precursor and the lithium source in step S1 are stirred evenly in a polyvinyl alcohol solution, transferred to a mixer, and the mixing is continued for 3-5h. After the mixing is completed, the compactor is compacted to obtain an organic carbon-coated lithium iron phosphate mixture; S3. Synthesis of lithium iron phosphate material: The organic carbon-coated lithium iron phosphate mixture is separated into saggers and fed into a roller hearth furnace. An inert protective gas is introduced and sintered at high temperature at 600-800°C for 6-10 hours. After cooling, the material is pulverized to control the particle size and passed through a 200-mesh sieve to obtain a low-cost, high-density lithium iron phosphate cathode material.

2. The production method according to claim 1, characterized in that In step S1, the molar ratio of Li:Fe in the iron phosphate and the lithium source is 0.95-1.00:1, and the mass ratio of the iron phosphate to the carboxylated carbon nanotube dispersion is 1:8-12.

3. The method for producing a low-cost, high-density lithium iron phosphate cathode material according to claim 1, characterized in that: In step S2, the mass ratio of the inorganic carbon-doped iron phosphate precursor, the lithium source and the polyvinyl alcohol solution is 100:2.5-3.5:4-6.

4. The method for producing a low-cost, high-density lithium iron phosphate cathode material according to claim 1, characterized in that: In step S1, the mass concentration of the carboxylated carbon nanotube dispersion is 0.4-0.6%, and the dispersion solvent is N,N-dimethylformamide.

5. The method for producing a low-cost high-density lithium iron phosphate cathode material according to claim 1, characterized in that: The mass concentration of the polyvinyl alcohol solution in step S2 is 4-6%.

6. The method for producing a low-cost, high-density lithium iron phosphate cathode material according to claim 1, characterized in that: In steps S1 and S2, the lithium source is one or a mixture of two or more of lithium carbonate, lithium hydroxide and lithium nitrate.

7. The method for producing a low-cost, high-density lithium iron phosphate cathode material according to claim 1, characterized in that: In steps S1 and S2, the inert protective gas is one of nitrogen and argon, or a mixture of the two.

8. The method for producing a low-cost, high-density lithium iron phosphate cathode material according to claim 1, characterized in that: The material of the rotary kiln in step S1 is one of 316L stainless steel and 310S stainless steel. Using a rotary kiln for sintering saves time and energy compared to a conventional roller furnace.

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