A high-compact lithium iron phosphate cathode material and its preparation method

Abstract

This invention discloses a high-compact lithium iron phosphate (LFP) cathode material and its preparation method, specifically belonging to the field of lithium-ion battery technology. The preparation method of the high-compact LFP cathode material involves pre-reacting a lithium source, phosphorus source, iron source, and a cationic dispersant, followed by ball milling and blending with a suitable silane coupling agent and carbon source, and finally sintering to obtain the high-compact LFP cathode material. The obtained LFP cathode material exhibits excellent electrical performance indicators, showing superior performance in terms of compaction density, low-rate discharge specific capacity, initial charge-discharge efficiency, high-rate discharge specific capacity, and cycle stability. The preparation process of the LFP cathode material provided by this invention is simple and easy to implement, suitable for large-scale production. Furthermore, the selection and addition of suitable dispersants and carbon sources during preparation results in a synergistic optimization effect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery preparation technology, specifically relating to a high-compact lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries have become the mainstream power source for electric vehicles, energy storage systems, and portable electronic devices due to their high energy density, long cycle life, and environmental friendliness. As a core component of lithium-ion batteries, the performance of the cathode material directly affects the battery's energy density, rate performance, and cycle stability.

[0003] Lithium iron phosphate (LiFePO4), as a typical olivine-structured cathode material, has advantages such as high safety, low cost, environmental friendliness and good thermal stability. However, its low electronic conductivity and lithium-ion diffusion rate limit its application under high-rate charge-discharge and high-density conditions.

[0004] To improve the electrochemical performance of lithium iron phosphate (LFP), researchers have proposed several modification strategies, including: nano-sizing: reducing particle size to shorten the lithium-ion diffusion path, but nanoparticles are prone to agglomeration, leading to reduced compaction density; carbon coating: coating the material surface with a conductive carbon layer to improve electronic conductivity, but traditional carbon sources (such as glucose and sucrose) are prone to producing uneven carbon layers during sintering, affecting performance; and doping modification: introducing metal ions (such as Nb). 5+ Mg 2+ The crystal structure can be optimized by adding non-metallic elements (such as S and N), but excessive doping may lead to a decrease in the stability of the material structure. Surfactant-assisted synthesis: Surfactants are used to regulate the morphology of precursor particles, but anionic surfactants are charged and repulsive to the surface of lithium iron phosphate, resulting in poor dispersion.

[0005] Although the above methods have improved the performance of lithium iron phosphate to some extent, the following problems still exist: it is difficult to achieve both nano-sizing and high compaction density; the uniformity and conductivity of the carbon coating layer are insufficient; the selection and timing of surfactant addition have a significant impact on material performance, but systematic research is lacking; and insufficient interfacial bonding leads to a decrease in cycle stability.

[0006] Therefore, developing a method for preparing lithium iron phosphate cathode materials that can simultaneously achieve high real density, high conductivity, and excellent cycle stability has significant application value. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium iron phosphate cathode material and its preparation method that can simultaneously achieve high real density, high specific capacity and excellent cycle stability.

[0008] To achieve the above objectives, the present invention discloses the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a high-pressure lithium iron phosphate cathode material, the method comprising the following steps:

[0010] (1) Under a nitrogen atmosphere, lithium source, phosphorus source and iron source are added to deionized water in a molar ratio of lithium element, phosphorus element and iron element of (1-2):(0.8-1):1 and stirred evenly. Then, cationic dispersant is added and mixed evenly to obtain a mixed solution.

[0011] (2) Transfer the mixed solution obtained in step (1) to a high-pressure reaction vessel and react at 160-180℃ for 4-5 hours to obtain a reaction slurry. Centrifuge the reaction slurry, remove the liquid and keep the residue to obtain the reaction product. Wash the reaction product with a lithium salt solution with a concentration of 0.05wt%, and dry the washed reaction product to obtain powder.

[0012] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with silane coupling agent and carbon source at a mass ratio of 100:(0.6-1.5):(1-6) and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) at a mass ratio of 1:(0.8-1.5):(3-10).

[0013] (4) The precursor is placed in a nitrogen atmosphere and sintered at 650-720℃ for 7-12h. After the sintered product is subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material is obtained.

[0014] Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0015] Preferably, the phosphorus source is selected from phosphoric acid.

[0016] Preferably, the iron source is selected from at least one of ferrous chloride, ferrous sulfate heptahydrate, and ferrous nitrate.

[0017] Preferably, the cationic dispersant is selected from at least one of dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide.

[0018] More preferably, the amount of the cationic dispersant added is 4-5% of the total mass of the lithium source, phosphorus source and iron source.

[0019] Preferably, the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane.

[0020] Preferably, in step (2), the washed reaction product is vacuum dried at 120-140°C for 1-2 hours.

[0021] In a second aspect, the present invention provides a high-compact lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material is prepared by the preparation method described in the first aspect.

[0022] Thirdly, the present invention provides the application of the high-compact lithium iron phosphate cathode material described in the second aspect in the preparation of lithium iron phosphate battery materials with high compaction, high capacity, and long lifespan.

[0023] The beneficial effects of this invention are:

[0024] 1. The lithium iron phosphate cathode material provided by the present invention has excellent electrical performance indicators, and exhibits excellent performance in terms of compaction density, low-rate discharge specific capacity, first charge-discharge efficiency, high-rate discharge specific capacity and cycle stability.

[0025] 2. The lithium iron phosphate cathode material preparation process provided by this invention is simple and easy to implement, and is suitable for large-scale production. At the same time, the dispersant and carbon source selected and added in the preparation process have a synergistic optimization effect. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0028] In this invention:

[0029] Sodium poly(4-vinylbenzoate) was purchased from Hangzhou Yuhao Chemical Technology Co., Ltd., with a weight-average molecular weight of 4000-5000 Da.

[0030] Preparation of high-pressure lithium iron phosphate cathode material:

[0031] Preparation of Example 1

[0032] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous chloride are added to deionized water in a molar ratio of lithium, phosphorus and iron of 1:1:1 and stirred until homogeneous. Then, dodecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of dodecyltrimethylammonium bromide added is 4% of the total mass of lithium hydroxide, phosphoric acid and ferrous chloride.

[0033] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 180°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 130°C for 1.5 hours to obtain powder.

[0034] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltriethoxysilane and carbon source at a mass ratio of 100:0.6:1 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor. The carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) at a mass ratio of 1:0.8:3.

[0035] (4) The precursor was placed in a nitrogen atmosphere and sintered at 720°C for 7 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0036] Preparation of Example 2

[0037] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0038] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0039] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source in a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor. The carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in a mass ratio of 1:1.3:6.

[0040] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0041] Preparation of Example 3

[0042] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous nitrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 1:0.8:1 and stirred until homogeneous. Then, hexadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of hexadecyltrimethylammonium bromide added is 4% of the total mass of lithium hydroxide, phosphoric acid and ferrous nitrate.

[0043] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 160°C for 5 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 140°C for 1 hour to obtain powder.

[0044] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source in a mass ratio of 100:1.5:6 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in a mass ratio of 1:1.5:10.

[0045] (4) The precursor was placed in a nitrogen atmosphere and sintered at 650°C for 12 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0046] To verify the role of the key components of this invention, based on Example 2, the key components were omitted or replaced as follows:

[0047] Preparation of Comparative Example 1

[0048] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then sodium hexadecylbenzenesulfonate is added and mixed until homogeneous to obtain a mixed solution. The amount of sodium hexadecylbenzenesulfonate added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0049] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0050] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source in a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor. The carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in a mass ratio of 1:1.3:6.

[0051] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0052] That is, compared with Example 2, the cationic dispersant octadecyltrimethylammonium bromide is replaced with an equal amount of anionic dispersant sodium hexadecylbenzenesulfonate, and the rest is the same as Example 2.

[0053] Preparation of Comparative Example 2

[0054] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0055] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0056] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source at a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of sorbitol and poly(4-vinylbenzoate sodium salt) at a mass ratio of 1.3:6.

[0057] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0058] That is, compared with Example 2, the carbon source composition in step (3) lacks carbon black, while the rest is the same as in Example 2.

[0059] Preparation of Comparative Example 3

[0060] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0061] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0062] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source at a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of carbon black and poly(4-vinylbenzoate sodium salt) at a mass ratio of 1:6.

[0063] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0064] That is, compared with Example 2, the carbon source composition in step (3) lacks sorbitol, while the rest is the same as in Example 2.

[0065] Preparation of Comparative Example 4

[0066] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0067] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0068] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source in a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of carbon black and sorbitol in a mass ratio of 1:1.3.

[0069] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0070] That is, compared with Example 2, the carbon source composition in step (3) lacks poly(4-vinylbenzoate sodium salt), while the rest is the same as in Example 2.

[0071] Preparation of Comparative Example 5

[0072] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0073] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0074] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source at a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor. The carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) at a mass ratio of 1:0.5:2.

[0075] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0076] That is, compared with Example 2, the mass ratio of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in step (3) is adjusted to 1:0.5:2, and the rest is the same as in Example 2.

[0077] Preparation of Comparative Example 6

[0078] (1) Under a nitrogen atmosphere, lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate are added to deionized water in a molar ratio of lithium, phosphorus and iron of 2:1:1 and stirred until homogeneous. Then, octadecyltrimethylammonium bromide is added and mixed until homogeneous to obtain a mixed solution. The amount of octadecyltrimethylammonium bromide added is 5% of the total mass of lithium hydroxide, phosphoric acid and ferrous sulfate heptahydrate.

[0079] (2) The mixed solution obtained in step (1) is transferred to a high-pressure reactor and reacted at 170°C for 4 hours to obtain a reaction slurry. The reaction slurry is centrifuged to remove the liquid and retain the residue to obtain the reaction product. The reaction product is washed with a lithium chloride solution with a concentration of 0.05wt%. The washed reaction product is vacuum dried at 120°C for 2 hours to obtain powder.

[0080] (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with 3-aminopropyltrimethoxysilane and carbon source in a mass ratio of 100:1.1:3 and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor. The carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in a mass ratio of 1:2:15.

[0081] (4) The precursor was placed in a nitrogen atmosphere and sintered at 700°C for 8 hours. After the sintered product was subjected to gas crushing treatment, high-pressure lithium iron phosphate cathode material was obtained.

[0082] That is, compared with Example 2, the mass ratio of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in step (3) is adjusted to 1:2:15, and the rest is the same as in Example 2.

[0083] Performance testing

[0084] The compaction density of the lithium iron phosphate cathode materials from Examples 1-3 and Comparative Examples 1-6 was tested using a compaction density meter (TDDC-5). The cathode materials prepared in the examples and comparative examples were then used to fabricate coin cells. The fabrication steps are as follows:

[0085] 1. Preparation of positive electrode slurry: Lithium iron phosphate positive electrode material, carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 15:1:1, N-methylpyrrolidone solvent is added, and the viscosity is adjusted to 4000 mPa·s to 8000 mPa·s to obtain positive electrode slurry.

[0086] 2. The positive electrode slurry is evenly coated on one surface (perpendicular to the thickness direction) of aluminum foil (positive electrode current collector) and dried. Then it is rolled and sliced ​​to obtain a positive electrode sheet containing a positive electrode film layer.

[0087] 3. A button cell was fabricated using lithium hexafluorophosphate-ethyl methyl carbonate as the electrolyte and polypropylene as the separator, combined with the prepared positive electrode and negative lithium electrode.

[0088] The manufactured coin cells were tested using a Newway tester at a voltage range of 2.0V to 3.8V. The tests included 0.1C discharge specific capacity, 0.1C first charge-discharge efficiency, 5C discharge specific capacity, and capacity retention rate after 500 cycles / 1C. The specific test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] Results analysis:

[0092] According to the data in Table 1, Examples 1-3 are significantly better than Comparative Examples 1-6 in all performance indicators such as compaction density, discharge specific capacity, first charge-discharge efficiency, high rate performance and cycle stability, indicating that the preparation process and additive selection provided by the present invention have a synergistic optimization effect.

[0093] Comparative Example 1 used an anionic dispersant, while Example 2 used a cationic dispersant, namely octadecyltrimethylammonium bromide. According to the experimental results in Table 1, all indicators of Comparative Example 1 were lower than those of Example 2, especially the compaction density, indicating that the type of dispersant has a significant impact on the dispersion effect and structural compactness of the material. The cationic dispersant interacts better with the material surface, forming more uniform particles, thereby improving density and electrochemical performance.

[0094] Compared to Example 2, Comparative Examples 2-4 lacked carbon black, sorbitol, and sodium poly(4-vinylbenzoate), respectively. Compared to Example 2, Comparative Examples 2-4 showed a decrease in compaction density and discharge capacity. Comparative Example 2, lacking carbon black, saw its compaction density decrease from 2.72 to 2.45, and its discharge capacity also decreased. This indicates that carbon black, as a conductive agent, improves the conductivity of the material, thereby enhancing rate performance and capacity. Without carbon black, electron conduction is insufficient, affecting performance. Comparative Example 3, lacking sorbitol, had a compaction density of 2.28, the lowest among all comparative examples, and its discharge capacity was also very low. This indicates that sorbitol, as part of the carbon source, decomposes during high-temperature sintering to form a conductive carbon layer. Simultaneously, it plays a dispersing role during ball milling, helping to form a uniform carbon coating layer, improving the structural stability and conductivity of the material. Without sorbitol, the carbon layer coating is uneven, resulting in poor conductivity, poor interparticle contact, and affecting compaction density and capacity. Comparative Example 4, lacking poly(sodium 4-vinylbenzoate), also showed a decrease in compaction density and volume. This polymer acts as a binder and structural support in the carbon source, helping to form a stable three-dimensional conductive network during sintering. It also prevents particle agglomeration and maintains the structural integrity of the material. Without it, the carbon structure is not continuous enough, affecting electron transport and stability.

[0095] Comparative Examples 5 and 6 adjusted the proportions of the three carbon sources. The results showed that the performance of Comparative Example 5 was worse than that of Example 2, indicating that the proportion of sorbitol and poly(4-vinylbenzoate sodium salt) in the carbon source was too low and may not be able to form an effective conductive network. Although the cycle retention rate of Comparative Example 6 was close to that of Example 2, the compaction density and discharge capacity were still low, indicating that the proportion of sorbitol and poly(4-vinylbenzoate sodium salt) in the carbon source was too high, resulting in too much carbon content, which affected the compaction density of the material and also caused the carbon layer to be too thick, hindering lithium ion diffusion.

[0096] Based on the comprehensive experimental data, carbon black, as a conductive agent, provides a direct electronic conduction pathway; sorbitol decomposes during sintering to generate amorphous carbon, which enhances conductivity and promotes interparticle connection, thereby increasing compaction density; while poly(sodium 4-vinylbenzoate) forms a continuous network structure after carbonization, while inhibiting particle growth and maintaining the material's efficient ion and electron transport pathways.

[0097] In summary, the lithium iron phosphate cathode material of this invention, through the synergistic effect of the dispersant and three carbon sources, ultimately achieves high compaction, high capacity, and long lifespan.

[0098] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-pressure lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) Under a nitrogen atmosphere, lithium source, phosphorus source and iron source are added to deionized water in a molar ratio of lithium, phosphorus and iron of (1-2):(0.8-1):1 and stirred until homogeneous. Then, cationic dispersant is added and mixed until homogeneous to obtain a mixed solution. (2) Transfer the mixed solution obtained in step (1) to a high-pressure reaction vessel and react at 160-180℃ for 4-5 hours to obtain a reaction slurry. Centrifuge the reaction slurry, remove the liquid and keep the residue to obtain the reaction product. Wash the reaction product with a lithium salt solution with a concentration of 0.05wt%, and dry the washed reaction product to obtain powder. (3) Under a nitrogen atmosphere, the powder obtained in step (2) is placed in a ball mill with silane coupling agent and carbon source in a mass ratio of 100:(0.6-1.5):(1-6) and wet ball milled for 3 hours to obtain ball milling product. The ball milling product is spray dried to obtain precursor, wherein the carbon source is composed of carbon black, sorbitol and poly(4-vinylbenzoate sodium salt) in a mass ratio of 1:(0.8-1.5):(3-10). (4) The precursor is placed in a nitrogen atmosphere and sintered at 650-720℃ for 7-12h. The sintered product is then subjected to gas crushing treatment to obtain high-pressure lithium iron phosphate cathode material. The cationic dispersant is selected from at least one of dodecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and hexadecyltrimethylammonium bromide.

2. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The lithium source is selected from at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

3. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The phosphorus source is selected from phosphoric acid.

4. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The iron source is selected from at least one of ferrous chloride, ferrous sulfate heptahydrate, and ferrous nitrate.

5. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 3, characterized in that, The amount of the cationic dispersant added is 4-5% of the total mass of the lithium source, phosphorus source and iron source.

6. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, The silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane.

7. The method for preparing high-pressure lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the washed reaction product is vacuum dried at 120-140℃ for 1-2 hours.

8. A high-compact lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared by the preparation method according to any one of claims 1-7.

9. The application of the high-compact lithium iron phosphate cathode material according to claim 8 in the preparation of lithium iron phosphate battery materials with high compaction, high capacity and long life.

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