Lithium iron phosphate composite material and preparation method thereof

Abstract

This invention discloses a lithium iron phosphate composite material and its preparation method, belonging to the field of lithium iron phosphate technology. The preparation method includes the following steps: First, preparing a vinylsiloxane-modified lithium iron phosphate precursor; Second, using the vinylsiloxane-modified lithium iron phosphate precursor and vinylimidazole ionic liquid as raw materials, a polymerization reaction is carried out under the action of an initiator: the vinylsiloxane-modified lithium iron phosphate precursor and vinylimidazole ionic liquid are added to methanol, an initiator is added, and under an inert atmosphere, after ultrasonic dispersion, the reaction is carried out at room temperature to obtain an ionic liquid-coated lithium iron phosphate precursor; Third, under an inert atmosphere, calcination is performed to obtain the lithium iron phosphate composite material. The introduction of vinylsiloxane constructs a more complex conductive network, and the ionic liquid as a carbon source enables multi-element doping. The prepared lithium iron phosphate composite material has better discharge capacity and cycle performance as a battery electrode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate technology, specifically relating to a lithium iron phosphate composite material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LFP) has an olivine-type structure, theoretically high specific capacity, good structural stability during charge and discharge, and long cycle life. Furthermore, its raw materials are abundant, inexpensive, and environmentally friendly, aligning with sustainable development requirements. However, LFP has low electrical conductivity, which hinders electron transport during charge and discharge, particularly under high-current conditions, resulting in poor rate performance and an inability to meet high-power output demands. Simultaneously, low conductivity causes a rapid voltage drop during high-rate discharge, affecting battery output performance and limiting its widespread application in power-critical fields such as electric vehicles and energy storage systems.

[0003] Currently, common methods to improve the conductivity of lithium iron phosphate include ion doping, nano-sizing, surface coating, and carbon coating. Ion doping involves doping other metal ions (such as Mg) into the lithium iron phosphate lattice. 2+ Al 3+ Ti 4+ (e.g., can introduce defects into the crystal lattice, thereby improving the material's conductivity and ion diffusion performance); nano-sizing refers to preparing lithium iron phosphate particles into nanoscale sizes, which can significantly shorten the lithium ion diffusion path, thereby improving the material's rate performance; surface coating methods involve coating the surface of lithium iron phosphate with other conductive materials to further improve the material's conductivity, and battery performance can be optimized by adjusting the type of polymer and the coating method; carbon coating involves coating the surface of lithium iron phosphate with a layer of carbon, which can construct a conductive network and increase the material's conductivity.

[0004] However, the above methods have some drawbacks. For example, ion doping requires precise control of the type and content of doping elements, the process is complex, and it may affect other properties of the material. Although nano-sizing can shorten the lithium-ion diffusion path, nanoparticles are prone to agglomeration, and the preparation process is complex and costly. Surface coatings are limited by the stability of the coating material and its compatibility with lithium iron phosphate. Currently, the conventional method for coating lithium iron phosphate with carbon is to directly mix the carbon source with lithium iron phosphate and then treat it at high temperature. The advantage of this method is that it is suitable for large-scale industrial production. Its disadvantage is that the coating degree on the surface of lithium iron phosphate is uneven, and the amount of carbon coating is insufficient, which will reduce the electrochemical performance of lithium iron phosphate materials (such as energy density, rate performance, etc.). Summary of the Invention

[0005] The purpose of this invention is to provide a lithium iron phosphate composite material and its preparation method to solve the problem of poor electrochemical performance of lithium iron phosphate materials.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The first aspect of this application provides a method for preparing lithium iron phosphate composite materials, comprising the following steps:

[0008] Step 1: Preparation of vinylsiloxane-modified lithium iron phosphate precursor;

[0009] The second step involves a polymerization reaction using vinylsiloxane-modified lithium iron phosphate precursor and vinylimidazole ionic liquid as raw materials, under the action of an initiator:

[0010] Vinylsiloxane-modified lithium iron phosphate precursor and vinylimidazolium ionic liquid were added to methanol, an initiator was added, and the mixture was ultrasonically dispersed under an inert atmosphere and reacted at room temperature. After washing and freeze-drying, the lithium iron phosphate precursor coated with ionic liquid was obtained.

[0011] The third step involves calcining the lithium iron phosphate precursor coated with ionic liquid under an inert atmosphere to obtain a lithium iron phosphate composite material.

[0012] Furthermore, the anion in the vinylimidazolium ionic liquid is [BF4]. - [PF6] - [CF3SO3] - and [NTf2] - One of them.

[0013] Furthermore, the vinylsiloxane-modified lithium iron phosphate precursor comprises the following steps:

[0014] The lithium iron phosphate precursor was dispersed in a methanol aqueous solution, and lithium hydroxide was added to adjust the pH to 8-9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed under an inert atmosphere and aged at room temperature for 20-24 hours with intermittent shaking during the process to remove the solvent, thereby obtaining the vinylsiloxane-modified lithium iron phosphate precursor. The ratio of lithium iron phosphate precursor to vinylsiloxane was 3g:2-3mL.

[0015] Furthermore, the calcination conditions are as follows: nitrogen is used as a protective gas, and the temperature is increased from 30°C to 300-350°C at a rate of 5-10°C / min, held for 2-3 hours, and then increased to 700°C at the same rate, held for 10-12 hours.

[0016] Furthermore, the mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid is 3:0.9-1.2; the amount of initiator added is 1% to 2% of the mass of the vinylimidazolium ionic liquid.

[0017] Furthermore, the vinylsiloxane is one of vinyltriethoxysilane, vinyltrimethoxysilane, and methacryloxypropyltrimethoxysilane.

[0018] Furthermore, the lithium iron phosphate precursor is synthesized via a hydrothermal method.

[0019] Furthermore, the lithium iron phosphate precursor is prepared by the following steps:

[0020] The lithium source, iron source, and phosphorus source are mixed in a molar ratio of lithium ions, ferrous ions, and phosphate ions of 1-4:1:1 and heated to 140-200℃ for 9-12 hours under an inert atmosphere. After the reaction is completed, the mixture is cooled, washed, filtered, and vacuum dried at 110℃ for 10-12 hours to obtain the lithium iron phosphate precursor.

[0021] Furthermore, the lithium source is one of lithium hydroxide, lithium carbonate, and lithium acetate; the iron source is one of ferrous sulfate, ferrous oxalate, ferrous phosphate, ferrous acetate, and ferrous chloride; and the phosphorus source is one of phosphoric acid and ammonium dihydrogen phosphate.

[0022] A lithium iron phosphate composite material is prepared by the above-described method.

[0023] The beneficial effects of this invention are:

[0024] This invention provides a method for preparing lithium iron phosphate composite materials. The method includes preparing a vinylsiloxane-modified lithium iron phosphate precursor, using the vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid as raw materials, undergoing a polymerization reaction under the action of an initiator, and finally preparing the lithium iron phosphate composite material through in-situ polymerization and sintering. The introduction of vinylsiloxane can construct a more complex conductive network, providing more channels for lithium-ion diffusion, reducing the diffusion resistance of lithium-ions, and thus improving the rate performance of the battery. Furthermore, silicon doping can enhance the bonding force between the carbon layer and lithium iron phosphate particles, improve the structural stability of the material, reduce volume changes during charge and discharge, and help extend the cycle life of the battery. The ionic liquid, as a carbon source, can achieve multi-element doping, improving the cycle stability, rate performance, and charge / discharge performance of the lithium iron phosphate composite material as an electrode material. Detailed Implementation

[0025] 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 some embodiments of the present invention, and not all 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.

[0026] The following is a detailed description of a lithium iron phosphate composite material and its preparation method according to an embodiment of this application.

[0027] The following is a detailed description with reference to specific examples.

[0028] Example 1

[0029] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0030] Ferrous sulfate and ascorbic acid were dissolved in water to obtain a mixed solution. Phosphoric acid was dissolved in water to obtain a phosphoric acid solution. Lithium hydroxide was dissolved in water to obtain a lithium hydroxide solution. Phosphoric acid solution and mixed solution were added to lithium hydroxide solution in sequence, resulting in precipitation. Ammonia or dilute hydrochloric acid was added to adjust the pH to 2-3. The mixture was heated to 180℃ and reacted for 10 hours under an inert atmosphere. After the reaction was completed, the mixture was cooled, washed, filtered, and vacuum dried at 110℃ for 10 hours to obtain lithium iron phosphate precursor. The molar ratio of lithium hydroxide, ferrous sulfate, and phosphoric acid was 3:1:1, and the molar ratio of ascorbic acid and ferrous sulfate was 0.3:1.

[0031] The lithium iron phosphate precursor was dispersed in a methanol aqueous solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 min under an inert atmosphere and aged at room temperature for 24 h, with intermittent shaking during the aging process. The solvent was removed to obtain the vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL. The vinylsiloxane was vinyltriethoxysilane.

[0032] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium tetrafluoroborate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0033] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0034] Example 2

[0035] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0036] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The solvent was removed to obtain a vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0037] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium tetrafluoroborate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:1.2; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0038] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0039] Example 3

[0040] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0041] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The resulting vinylsiloxane-modified lithium iron phosphate precursor was removed. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g:3 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0042] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium tetrafluoroborate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0043] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0044] Example 4

[0045] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0046] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The resulting vinylsiloxane-modified lithium iron phosphate precursor was removed. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g:3 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0047] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium tetrafluoroborate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:1.2; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0048] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0049] Example 5

[0050] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0051] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The solvent was removed to obtain a vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL; the vinylsiloxane was methacryloxypropyltrimethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0052] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium tetrafluoroborate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0053] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0054] Example 6

[0055] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0056] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The solvent was removed to obtain a vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0057] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium hexafluorophosphate. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0058] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0059] Example 7

[0060] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0061] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The solvent was removed to obtain a vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0062] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0063] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0064] Example 8

[0065] This embodiment provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0066] A lithium iron phosphate precursor was dispersed in a methanol-water solution, and lithium hydroxide was added to adjust the pH to 9. Vinylsiloxane was then added, and the mixture was ultrasonically dispersed for 10 minutes under an inert atmosphere, followed by aging at room temperature for 24 hours, with intermittent shaking during the aging process. The solvent was removed to obtain a vinylsiloxane-modified lithium iron phosphate precursor. In some specific embodiments, the ratio of lithium iron phosphate precursor to vinylsiloxane was 3 g: 2 mL; the vinylsiloxane was vinyltriethoxysilane. The lithium iron phosphate precursor was the same as in Example 1.

[0067] A vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid were added to methanol, with azobisisobutyronitrile (AIBN) added as an initiator. The mixture was ultrasonically dispersed for 10 min under an inert atmosphere, then mechanically stirred at room temperature for 1 h. The methanol was removed by heating to the boiling point of methanol. After the reaction was complete, the mixture was washed with methanol and freeze-dried at -70 °C to obtain the ionic liquid-coated lithium iron phosphate precursor. The vinylimidazolium ionic liquid was 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid was 3:0.9; the amount of initiator added was 2% of the mass of the vinylimidazolium ionic liquid.

[0068] The lithium iron phosphate precursor coated with ionic liquid was calcined under an inert atmosphere: nitrogen was used as a protective gas, and the temperature was increased from 30°C to 300°C at a rate of 5°C / min, held for 3 hours, and then increased to 700°C at the same rate and held for 12 hours to obtain the lithium iron phosphate composite material.

[0069] Comparative Example 1

[0070] This comparative example provides a method for preparing lithium iron phosphate composite materials, including the following steps:

[0071] The lithium iron phosphate precursor, vinyltriethoxysilane, and 1-vinyl-3-ethylimidazolium tetrafluoroborate were mixed in a ratio of 3g:2mL:0.9g, ground evenly, and then sintered under a nitrogen protective atmosphere. The sintering process and the lithium iron phosphate precursor were the same as in Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing a lithium iron phosphate composite material, comprising the following steps:

[0074] The lithium iron phosphate precursor and 1-vinyl-3-ethylimidazolium tetrafluoroborate were mixed at a ratio of 3g:0.9g, ground evenly, and then sintered under a nitrogen protective atmosphere. The sintering process and the lithium iron phosphate precursor were the same as in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a method for preparing a lithium iron phosphate composite material, comprising the following steps:

[0077] Ferrous sulfate and ascorbic acid were dissolved in water to obtain a mixed solution. Phosphoric acid was dissolved in water to obtain a phosphoric acid solution. Lithium hydroxide was dissolved in water to obtain a lithium hydroxide solution. Glucose, phosphoric acid solution, and the mixed solution were added sequentially to the lithium hydroxide solution, resulting in a precipitate. Ammonia or dilute hydrochloric acid was added to adjust the pH to 2-3. The mixture was heated to 180℃ under an inert atmosphere and reacted for 10 hours. After the reaction, the mixture was cooled, washed, filtered, and vacuum dried at 110℃ for 10 hours to obtain a lithium iron phosphate composite material. The molar ratio of lithium hydroxide, ferrous sulfate, and phosphoric acid was 3:1:1; the molar ratio of ascorbic acid to ferrous sulfate was 0.3:1; and the molar ratio of glucose to ferrous sulfate was 0.9 g:0.02 mol. Glucose was used as the carbon source.

[0078] Performance testing

[0079] The performance of lithium iron phosphate composite materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3 was tested. Sample preparation:

[0080] The lithium iron phosphate composite materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were mixed with PVDF (polyvinylidene fluoride) and acetylene black at a mass ratio of 8:1:1 and ground evenly. The solvent N-methylpyrrolidone was added dropwise and the grinding continued. The resulting slurry was coated on aluminum foil with a thickness of 50 μm and vacuum dried at 110°C for 10-12 h to obtain the positive electrode sheet.

[0081] The experimental battery used 99.9% lithium metal as the negative electrode and Celgard 2400 (microporous polyethylene membrane) as the separator. It was assembled into a simulated battery in a vacuum glove box. A 2032 coin cell was prepared using lithium metal as the negative electrode material, polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 as the electrolyte.

[0082] Performance tests were conducted on Examples 1 to 8 and Comparative Examples 1 to 3:

[0083] Specific capacity test: Under constant temperature conditions of 25℃ and a voltage range of 2.0 to 3.8V, the first discharge capacity of the sample battery was tested at 0.1C and 10C rates, respectively.

[0084] Cyclic performance test: The sample battery was subjected to charge-discharge cycle test within a voltage range of 2.0 to 3.8V, a constant temperature of 25℃ and a rate of 0.1C, and the discharge capacity after 100 cycles was recorded.

[0085] The results are shown in Table 1:

[0086] Table 1

[0087]

[0088] Combining Example 1 and Comparative Examples 1-3, different preparation methods affect battery performance. In Example 1, the in-situ polymerization and sintering method for preparing the lithium iron phosphate composite material, compared to the grinding and mixing method in Comparative Examples 1-2 and the in-situ coating with a conventional carbon source in Comparative Example 3, allows for the preparation of a uniform and tightly coated carbon layer. Furthermore, compared to Comparative Examples 2 and 3, the silane coupling agent used in Example 1 can construct a more complex conductive network, providing more channels for lithium-ion diffusion, reducing diffusion resistance, and thus improving the battery's rate performance. Additionally, silicon doping enhances the bonding force between the carbon layer and lithium iron phosphate particles, improves the material's structural stability, reduces volume changes during charge and discharge, and helps extend the battery's cycle life.

[0089] According to Table 1, and in conjunction with Examples 1, 2-5, it can be seen that there is no significant difference in discharge capacity and cycle capacity retention of the material between Examples 2-5 and Example 1 at different rates, indicating that the capacity and cycle performance of Examples 2-5 are not significantly different from those of Example 1. This is because the changes in Examples 2-5 compared to Example 1 are only variations in raw materials and their proportions within the required range, having little impact on the final battery performance. Examples 6-8, compared to Example 1, changed the type of ionic liquid, demonstrating that different types of ionic liquids can affect the capacity and cycle performance of the material to some extent. In particular, in Example 6, the selection of 1-vinyl-3-ethylimidazolium hexafluorophosphate as the ionic liquid resulted in the best improvement. In this invention, the ionic liquid acts as a carbon source, forming a heteroatom-doped carbon source that in-situ coats lithium iron phosphate. F doping can reduce the lithium iron phosphate antisite defect, decrease the resistance to electron and lithium ion transport, and accelerate lithium ion migration. Compared to N and B, P has a higher electron-donating ability, thereby promoting electron conductivity and improving bonding stability. Meanwhile, the high specific surface area generated by the PC bonds formed after P doping of the carbon layer helps to improve the graphitization level of the carbon layer, and further improves the battery performance by co-doping F and P.

[0090] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0091] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lithium iron phosphate composite material, characterized in that, Includes the following steps: Step 1: Preparation of vinylsiloxane-modified lithium iron phosphate precursor: The lithium iron phosphate precursor was dispersed in a methanol aqueous solution, lithium hydroxide was added to adjust the pH to 8-9, vinylsiloxane was added, and the mixture was ultrasonically dispersed under an inert atmosphere and aged at room temperature for 20-24 hours. The solvent was removed to obtain the vinylsiloxane-modified lithium iron phosphate precursor. The ratio of lithium iron phosphate precursor to vinylsiloxane was 3g:2-3mL. The second step involves in-situ polymerization of a vinylsiloxane-modified lithium iron phosphate precursor and a vinylimidazolium ionic liquid as raw materials, under the action of an initiator, to obtain an ionic liquid-coated lithium iron phosphate precursor. The mass ratio of the vinylsiloxane-modified lithium iron phosphate precursor to the vinylimidazolium ionic liquid is 3:0.9-1.2; the amount of initiator added is 1% to 2% of the mass of the vinylimidazolium ionic liquid. The third step involves calcining the lithium iron phosphate precursor coated with ionic liquid under an inert atmosphere to obtain a lithium iron phosphate composite material.

2. The method for preparing a lithium iron phosphate composite material according to claim 1, characterized in that, The anion in vinylimidazolium ionic liquids is [BF4]. - [PF6] - [CF3SO3] - and [NTf2] - One of them.

3. The method for preparing a lithium iron phosphate composite material according to claim 1, characterized in that, Calcination conditions: Nitrogen is used as a protective gas. The temperature is increased from 30℃ to 300-350℃ at a rate of 5-10℃ / min, and held for 2-3 hours. The temperature is then increased to 700℃ at the same rate and held for 10-12 hours.

4. The method for preparing a lithium iron phosphate composite material according to claim 1, characterized in that, The vinylsiloxane is one of vinyltriethoxysilane, vinyltrimethoxysilane, and methacryloxypropyltrimethoxysilane.

5. The method for preparing a lithium iron phosphate composite material according to claim 1, characterized in that, The lithium iron phosphate precursor was synthesized via a hydrothermal method.

6. The method for preparing a lithium iron phosphate composite material according to claim 1, characterized in that, The lithium iron phosphate precursor is prepared by the following steps: The lithium source, iron source, and phosphorus source are mixed in a molar ratio of lithium ions, ferrous ions, and phosphate ions of 1-4:1:1 and heated to 140-200℃ for 9-12 hours under an inert atmosphere. After the reaction is completed, the mixture is cooled, washed, filtered, and vacuum dried at 110℃ for 10-12 hours to obtain the lithium iron phosphate precursor.

7. The method for preparing a lithium iron phosphate composite material according to claim 6, characterized in that, The lithium source is one of lithium hydroxide, lithium carbonate, and lithium acetate; the iron source is one of ferrous sulfate, ferrous oxalate, ferrous phosphate, ferrous acetate, and ferrous chloride; and the phosphoric acid is one of phosphoric acid and ammonium dihydrogen phosphate.

8. A lithium iron phosphate composite material, characterized in that, It is prepared by any one of the preparation methods described in claims 1-7.

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