A chromium-molybdenum double-doped lithium iron phosphate material, a preparation method thereof and application thereof

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a chromium-molybdenum dual-doped lithium iron phosphate material, its preparation method, and its application; it addresses the problems of low capacity, low electronic conductivity, and poor cycle stability in existing lithium iron phosphate materials. The preparation method involves doping lithium iron phosphate with chromium-molybdenum, where the bond energies of Cr-O and Mo-O bonds are stronger than those of Fe-O bonds, thus reducing the Fe content during long-term cycling. 2+ The dissolution and loss of lithium iron phosphate improves battery capacity and intrinsic electronic conductivity; nitrogen-doped carbon nanotubes coat lithium iron phosphate, with nitrogen doping in the graphite lattice of carbon nanotubes, providing additional free electrons, improving intrinsic conductivity, reducing resistance, and improving rate performance and cycle life; the polyaniline coating layer forms a barrier layer on the surface of lithium iron phosphate particles, improving cycle performance and battery capacity; the three work synergistically to improve the material's capacity, conductivity, rate performance, and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a chromium-molybdenum dual-doped lithium iron phosphate material, its preparation method, and its application. Background Technology

[0002] In the field of lithium-ion battery technology, improving charging efficiency, extending battery life, and enhancing energy storage performance are goals that researchers constantly pursue. Among these goals, the selection and improvement of cathode materials are particularly important. Currently, lithium iron phosphate (LFP) is widely recognized as a stable cathode material due to its good safety and cycle stability. However, LFP materials still have some shortcomings in practical applications, such as low capacity, low electronic conductivity, and the need to improve cycle stability. Therefore, modifying LFP materials through doping to further enhance their performance has become an important research direction in the field of lithium-ion batteries.

[0003] Traditional doping methods mainly involve replacing a portion of the lithium or iron ions in a material with a small amount of metal ions. While this method can improve certain properties, it may also introduce new problems, such as instability in the material structure and inconsistency in electrochemical performance. Against this backdrop, exploring more effective doping elements and methods has become crucial for improving the performance of lithium iron phosphate materials. Dual doping, which involves using two elements simultaneously, can better balance the structure and electrochemical performance of these materials, thereby achieving the goal of improving overall performance.

[0004] Therefore, the development of a chromium-molybdenum dual-doped lithium iron phosphate material, its preparation method, and its application is of great significance for promoting the development of lithium-ion battery technology. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the present invention aims to provide a chromium-molybdenum dual-doped lithium iron phosphate material, its preparation method and application; and solves the problems of low capacity, low electronic conductivity and poor cycle stability of existing lithium iron phosphate materials.

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

[0007] In a first aspect, this application provides a method for preparing a chromium-molybdenum co-doped lithium iron phosphate material, comprising the following steps:

[0008] Step a1: Add the iron source and H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1-2 hours. Add CrCl3·6H2O and (NH4)6Mo7O 24• 4H2O and NH4H2PO4 were added to a beaker and mixed and stirred for 1 hour to obtain a doped solution. The doped solution was then added to the three-necked flask and mixed and stirred for 30 minutes before being transferred to a wet ball mill jar. A dispersant was added, and the ball-to-material ratio was 10:1. The ball mill was run at 350-400 r / min for 4-6 hours. After ball milling, the balls and material were separated. The material was placed in a vacuum drying oven at 100℃ and dried for 12 hours. After drying, the material was ground in a mortar for 1-2 hours to obtain chromium-molybdenum co-doped iron phosphate.

[0009] Step a2: Chromium-molybdenum co-doped iron phosphate and Li2CO3 are added to a grinder and ground for 10-14 hours to obtain grinding material. Then, the grinding material, carbon source and anhydrous ethanol are added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 350-450 r / min for 2-4 hours. After the balls and materials are separated, the material is added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10 mL / min to obtain dry powder. The dry powder is added to a tube furnace for sintering under argon protection. The temperature is increased to 350℃ at a rate of 5℃ / min and held for 4 hours. Then, the temperature is increased to 700℃ and held for 10 hours. The material is then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0010] Step a3: Melamine, Ni(NO3)2·6H2O and deionized water are added to a three-necked flask equipped with a stirrer and thermometer. The mixture is sonicated for 1 hour to obtain a suspension. Modified lithium iron phosphate is added to the suspension and stirred in a 60°C water bath for 1-2 hours. The mixture is then placed in a tube furnace and heated to 550°C at a rate of 5°C / min under an argon atmosphere. The temperature is held for 30 minutes, and then heated to 750-800°C under a mixed gas atmosphere. The temperature is held for 1-2 hours, and then naturally cooled to 25°C. Hydrochloric acid solution is added, and the mixture is stirred at 60-80°C for 4-6 hours. The mixture is then filtered, and the filter cake is washed 2-3 times with anhydrous ethanol and dried at 80°C for 1-2 hours to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate.

[0011] Step a4: Nitrogen-doped carbon nanotube-coated lithium iron phosphate and HCl solution are added to a three-necked flask equipped with a stirrer and thermometer. The mixture is ultrasonically dispersed for 30 min, transferred to an ice-water bath at 0-5℃, and magnetically stirred for 1-2 h. Aniline is added, and stirring is continued for 1 h to obtain a dispersion solution. Ammonium persulfate is added to the above dispersion solution, and the mixture is reacted in an ice-water bath at 0-5℃ for 12-14 h. After the reaction is completed, the mixture is filtered, and the filter cake is washed 3-4 times with deionized water and anhydrous ethanol. After washing, the mixture is vacuum dried at 60℃ for 12-24 h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0012] In a preferred embodiment of the present invention, the iron source, H2O2 solution, CrCl3·6H2O, and (NH4)6Mo7O mentioned in step a1 are... 24 The ratio of ·4H2O to NH4H2PO4 is 0.96-1 mol: 100-110 mL: 0.01-0.02 mol: 3-4 g: 1 mol.

[0013] In a preferred embodiment of the present invention, the iron source in step a1 is one of FeC2O4·2H2O and FeSO4·7H2O; the mass fraction of the H2O2 solution is 27.5%.

[0014] In a preferred embodiment of the present invention, the ratio of the amount of chromium-molybdenum dual-doped iron phosphate, Li2CO3, carbon source and anhydrous ethanol in step a2 is 145-155g: 1.05-1.1mol: 70-75g: 200-300mL.

[0015] In a preferred embodiment of the present invention, the carbon source in step a2 is either sucrose or glucose.

[0016] In a preferred embodiment of the present invention, the ratio of melamine, Ni(NO3)2·6H2O, deionized water, modified lithium iron phosphate and hydrochloric acid solution in step a3 is 1g:0.1g:50mL:10g:100-200mL.

[0017] In a preferred embodiment of the present invention, the mixed gas in step a3 is a mixture of H2 and Ar in a volume ratio of 5:95; the molar concentration of the hydrochloric acid solution is 1-2 mol / L.

[0018] In a preferred embodiment of the present invention, the ratio of nitrogen-doped carbon nanotubes coated with lithium iron phosphate, HCl solution, aniline and ammonium persulfate in step a4 is 1-2g: 100-110mL: 0.1-0.2g: 0.25-0.5g.

[0019] In a preferred embodiment of the present invention, the molar concentration of the HCl solution in step a4 is 1 mol / L.

[0020] Secondly, this application provides a chromium-molybdenum dual-doped lithium iron phosphate material, which is prepared according to the preparation method of the chromium-molybdenum dual-doped lithium iron phosphate material described in the first aspect.

[0021] Thirdly, this application provides the application of chromium-molybdenum dual-doped lithium iron phosphate materials in batteries as described in the first aspect.

[0022] The beneficial effects of this invention are:

[0023] This invention relates to a chromium-molybdenum co-doped lithium iron phosphate material, its preparation method, and its application. The method involves adding an iron source and H₂O₂ solution to a three-necked flask and stirring magnetically. CrCl₃·6H₂O and (NH₄)₆Mo₇O₇ are then added. 24 • 4H2O and NH4H2PO4 were mixed and stirred to obtain a doped solution; the doped solution was added to the above three-necked flask, transferred to a wet ball mill jar for ball milling, drying, and grinding to obtain chromium-molybdenum co-doped iron phosphate; Cr 3+ and Mo 6+ ionic radius and Fe 2+ Unlike other materials, doping into the crystal lattice and substituting Fe sites causes lattice distortion and expands the Li... + Diffusion channels, reducing Li + Migration resistance; Mo in high valence state 6+ Doping creates lithium vacancies, which occupy Fe. 2+ When at a site, Li needs to be consumed. + To compensate for the charge, a large number of lithium vacancies are introduced, accelerating ion diffusion kinetics and allowing a large amount of Li to still be present at high rates. + It can participate in the reaction, thus having a higher reversible capacity; Cr 3+ Mo 6+ Fe replacement 2+ At this time, a larger number of charge compensation defects are generated, introducing a large number of electron carriers and greatly improving the intrinsic electronic conductivity of the material; the bond energies of Cr-O and Mo-O bonds are stronger than those of Fe-O bonds, which strengthens the olivine crystal structure of lithium iron phosphate and inhibits the Li-O bond. + The fatigue and damage caused by lattice expansion and contraction during repeated insertion and extraction processes make the structure more robust, and stronger Mo-O bonds reduce Fe degradation during long-term cycling. 2+ To improve battery capacity, chromium-molybdenum co-doped iron phosphate and Li2CO3 were mixed and ground, then a carbon source and anhydrous ethanol were added and ball-milled. The balls and materials were separated, and the materials were dried, sintered, and naturally cooled to obtain modified lithium iron phosphate. The carbon source served as a reducing agent to prevent Fe from dissolving and leaching. 2+Oxidation ensures proper phase formation; the first carbon coating forms a conductive network, significantly improving electronic conductivity, inhibiting excessive grain growth, controlling particle size, and enhancing the material's tap density and processing performance. Melamine, Ni(NO3)2·6H2O, and deionized water are mixed and ultrasonically suspended to obtain a suspension. Modified lithium iron phosphate is then added, stirred in a water bath, sintered, and cooled to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate. Ni(NO3)2·6H2O serves as a catalyst, and melamine provides the carbon and nitrogen sources, transforming the material through pyrolysis. Nitrogen-doped carbon nanotubes are used to coat lithium iron phosphate (LFP) particles. Nitrogen atoms have one more electron than carbon atoms. When nitrogen atoms are doped into the graphite lattice of carbon nanotubes, they provide additional free electrons, transforming the carbon nanotubes from metallic to n-type semiconductors and improving their intrinsic conductivity. Carbon nanotubes possess a one-dimensional tubular structure, extremely high aspect ratio, and excellent intrinsic conductivity. When nitrogen-doped carbon nanotubes are coated onto LFP particles, they form a three-dimensional conductive network, significantly reducing the overall resistance of the electrode, improving rate performance, introducing defect anchoring points, and enhancing conductivity. The binding force prevents carbon nanotubes from detaching from the lithium iron phosphate surface during battery cycling, ensuring the long-term stability of the conductive network and thus improving cycle life. Nitrogen-doped carbon nanotubes are coated onto lithium iron phosphate, ultrasonically dispersed in HCl solution, magnetically stirred in an ice-water bath, aniline is added, stirring continues, ammonium persulfate is added, the reaction is carried out in an ice-water bath, filtered, and the filter cake is washed and dried to obtain chromium-molybdenum dual-doped lithium iron phosphate. Aniline undergoes in-situ polymerization on the lithium iron phosphate surface to form a polyaniline coating layer. This polyaniline coating layer forms a dense and stable physical barrier layer on the surface of the lithium iron phosphate particles, significantly reducing the direct contact area between the active material and the electrolyte, effectively inhibiting the electrolyte's erosion of the lithium iron phosphate, thereby reducing iron dissolution, protecting the active material, and improving cycle capacity retention. Polyaniline itself is an electroactive material that stores and releases charge through its own redox reaction, a process called capacitance, thus improving battery capacity. Bulk doping, carbon coating, and polymer interface protection synergistically improve the material's capacity, conductivity, rate performance, and cycle stability. Attached Figure Description

[0024] The invention will now be further described with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic diagram showing the capacity test results of lithium-ion batteries prepared based on chromium-molybdenum dual-doped lithium iron phosphate materials in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0026] Figure 2 This is a schematic diagram showing the powder conductivity test results of lithium-ion batteries prepared based on chromium-molybdenum dual-doped lithium iron phosphate materials in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0027] Figure 3This is a schematic diagram showing the capacity retention test results of lithium-ion batteries prepared based on chromium-molybdenum dual-doped lithium iron phosphate materials in Examples 1-3 and Comparative Examples 1-3 of this invention after 2000 cycles at 1C. Detailed Implementation

[0028] 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.

[0029] Example 1:

[0030] This embodiment describes a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, including the following steps:

[0031] Step S1: Add 0.96 mol FeC2O4·2H2O and 100 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1 h. Then add 0.01 mol CrCl3·6H2O and 3 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar, a dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 350 r / min for 4 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 1 h to obtain chromium-molybdenum co-doped iron phosphate.

[0032] Step S2: 145g of chromium-molybdenum co-doped iron phosphate and 1.05mol of Li2CO3 were added to a grinder and ground for 10h to obtain a grinding material. Then, the grinding material, 70g of sucrose and 200mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 350r / min for 2h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min, held for 4h, and then heated to 700℃ and held for 10h. The mixture was then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0033] Step S3: Add 1g of melamine, 0.1g of Ni(NO3)2·6H2O and 50mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 1h to obtain a suspension. Add 10g of modified lithium iron phosphate to the above suspension. Stir for 1h in a 60℃ water bath. Place in a tube furnace and heat to 550℃ at a rate of 5℃ / min under an argon atmosphere. Hold for 30min. Then, heat to 750℃ under a mixed gas of H2 and Ar in a volume ratio of 5:95. Hold for 1h. Allow to cool naturally to 25℃. Add 100mL of 1mol / L hydrochloric acid solution. Stir at 60℃ for 4h. Filter. Wash the filter cake twice with anhydrous ethanol. Dry at 80℃ for 1h to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate.

[0034] Step S4: Add 1g of nitrogen-doped carbon nanotube-coated lithium iron phosphate and 100mL of 1mol / L HCl solution to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 30min, transfer to an ice-water bath at 0℃, and magnetically stir for 1h. Add 0.1g of aniline and continue stirring for 1h to obtain a dispersion solution. Add 0.25g of ammonium persulfate to the above dispersion solution and react in an ice-water bath at 0℃ for 12h. After the reaction is complete, filter the solution. Wash the filter cake three times with deionized water and anhydrous ethanol. After washing, vacuum dry at 60℃ for 12h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0035] Example 2:

[0036] This embodiment describes a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, including the following steps:

[0037] Step S1: Add 0.98 mol FeC2O4·2H2O and 105 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1.5 h. Then add 0.02 mol CrCl3·6H2O and 3 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar. A dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 375 r / min for 5 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 1.5 h to obtain chromium-molybdenum co-doped iron phosphate.

[0038] Step S2: 150g of chromium-molybdenum co-doped iron phosphate and 1.08mol of Li2CO3 were added to a grinder and ground for 12h to obtain a grinding material. Then, the grinding material, 73g of sucrose and 250mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 400r / min for 3h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min, held for 4h, and then heated to 700℃ and held for 10h. The mixture was then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0039] Step S3: Add 1g of melamine, 0.1g of Ni(NO3)2·6H2O and 50mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 1h to obtain a suspension. Add 10g of modified lithium iron phosphate to the above suspension. Stir for 1.5h in a 60℃ water bath. Place in a tube furnace and heat to 550℃ at a rate of 5℃ / min under an argon atmosphere. Hold for 30min. Then, heat to 775℃ under a mixed gas of H2 and Ar in a volume ratio of 5:95. Hold for 1.5h. Allow to cool naturally to 25℃. Add 150mL of hydrochloric acid solution with a molar concentration of 1.5mol / L. Stir at 70℃ for 5h. Filter. Wash the filter cake three times with anhydrous ethanol. Dry at 80℃ for 1.5h to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate.

[0040] Step S4: Add 1.5g of nitrogen-doped carbon nanotube-coated lithium iron phosphate and 105mL of 1mol / L HCl solution to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 30min, transfer to an ice-water bath at 3℃, and magnetically stir for 1.5h. Add 0.15g of aniline and continue stirring for 1h to obtain a dispersion solution. Add 0.35g of ammonium persulfate to the above dispersion solution and react in an ice-water bath at 3℃ for 13h. After the reaction is complete, filter the solution. Wash the filter cake four times with deionized water and anhydrous ethanol. After washing, vacuum dry at 60℃ for 18h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0041] Example 3:

[0042] This embodiment describes a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, including the following steps:

[0043] Step S1: Add 1 mol FeC2O4·2H2O and 110 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 2 hours. Then add 0.02 mol CrCl3·6H2O and 4 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar. A dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 400 r / min for 6 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 2 h to obtain chromium-molybdenum co-doped iron phosphate.

[0044] Step S2: 155g of chromium-molybdenum co-doped iron phosphate and 1.1mol of Li2CO3 were added to a grinder and ground for 14h to obtain a grinding material. Then, the grinding material, 75g of sucrose and 300mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 450r / min for 4h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min, held for 4h, and then heated to 700℃ and held for 10h. The mixture was then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0045] Step S3: Add 1g of melamine, 0.1g of Ni(NO3)2·6H2O and 50mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 1h to obtain a suspension. Add 10g of modified lithium iron phosphate to the above suspension. Stir for 2h in a 60℃ water bath. Place in a tube furnace and heat to 550℃ at a rate of 5℃ / min under an argon atmosphere. Hold for 30min. Then, heat to 800℃ under a mixed gas of H2 and Ar in a volume ratio of 5:95. Hold for 2h. Allow to cool naturally to 25℃. Add 200mL of 2mol / L hydrochloric acid solution. Stir at 80℃ for 6h. Filter. Wash the filter cake three times with anhydrous ethanol. Dry at 80℃ for 2h to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate.

[0046] Step S4: Add 2g of nitrogen-doped carbon nanotube-coated lithium iron phosphate and 110mL of 1mol / L HCl solution to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 30min, transfer to an ice-water bath at 5℃, and magnetically stir for 2h. Add 0.2g of aniline and continue stirring for 1h to obtain a dispersion solution. Add 0.5g of ammonium persulfate to the above dispersion solution and react in an ice-water bath at 5℃ for 14h. After the reaction is complete, filter. Wash the filter cake four times with deionized water and anhydrous ethanol. After washing, vacuum dry at 60℃ for 24h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0047] Comparative Example 1

[0048] This comparative example illustrates a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, comprising the following steps:

[0049] Step S1: Add 0.98 mol FeC2O4·2H2O and 105 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1.5 h. Then add 0.02 mol CrCl3·6H2O and 3 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar. A dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 375 r / min for 5 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 1.5 h to obtain chromium-molybdenum co-doped iron phosphate.

[0050] Step S2: 150g of chromium-molybdenum co-doped iron phosphate and 1.08mol of Li2CO3 were added to a grinder and ground for 12h to obtain a grinding material. Then, the grinding material, 73g of sucrose and 250mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 400r / min for 3h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min and held for 4h. Then, the temperature was further increased to 700℃ and held for 10h. The material was then naturally cooled to 25℃ to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0051] Comparative Example 2

[0052] This comparative example illustrates a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, comprising the following steps:

[0053] Step S1: Add 0.98 mol FeC2O4·2H2O and 105 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1.5 h. Then add 0.02 mol CrCl3·6H2O and 3 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar. A dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 375 r / min for 5 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 1.5 h to obtain chromium-molybdenum co-doped iron phosphate.

[0054] Step S2: 150g of chromium-molybdenum co-doped iron phosphate and 1.08mol of Li2CO3 were added to a grinder and ground for 12h to obtain a grinding material. Then, the grinding material, 73g of sucrose and 250mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 400r / min for 3h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min, held for 4h, and then heated to 700℃ and held for 10h. The mixture was then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0055] Step S3: Add 1g of melamine, 0.1g of Ni(NO3)2·6H2O and 50mL of deionized water to a three-necked flask equipped with a stirrer and thermometer. Sonicate for 1h to obtain a suspension. Add 10g of modified lithium iron phosphate to the above suspension. Stir for 1.5h in a 60℃ water bath. Place in a tube furnace and heat to 550℃ at a rate of 5℃ / min under an argon atmosphere. Hold for 30min. Then, heat to 775℃ under a mixed gas of H2 and Ar in a volume ratio of 5:95. Hold for 1.5h. Allow to cool naturally to 25℃. Add 150mL of hydrochloric acid solution with a molar concentration of 1.5mol / L. Stir at 70℃ for 5h. Filter. Wash the filter cake three times with anhydrous ethanol. Dry at 80℃ for 1.5h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0056] Comparative Example 3

[0057] This comparative example illustrates a method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material, comprising the following steps:

[0058] Step S1: Add 0.98 mol FeC2O4·2H2O and 105 mL of 27.5% H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, and stir magnetically for 1.5 h. Then add 0.02 mol CrCl3·6H2O and 3 g (NH4)6Mo7O 24 • 4H2O and 1 mol NH4H2PO4 were added to a beaker and mixed and stirred for 1 h to obtain a doped solution. The doped solution was added to the above three-necked flask and mixed and stirred for 30 min, then transferred to a wet ball mill jar. A dispersant was added, the ball-to-material ratio was 10:1, and the ball milling speed was 375 r / min for 5 h. After ball milling, the balls and materials were separated, and the materials were placed in a vacuum drying oven at 100℃ and dried for 12 h. After drying, the materials were ground in a mortar for 1.5 h to obtain chromium-molybdenum co-doped iron phosphate.

[0059] Step S2: 150g of chromium-molybdenum co-doped iron phosphate and 1.08mol of Li2CO3 were added to a grinder and ground for 12h to obtain a grinding material. Then, the grinding material, 73g of sucrose and 250mL of anhydrous ethanol were added to a planetary ball mill with a ball-to-material ratio of 5:1 and a rotation speed of 400r / min for 3h. After the balls and materials were separated, the material was added to a spray dryer for spray drying with an inlet temperature of 200℃, an outlet temperature of 100℃ and a feed rate of 10mL / min to obtain a dry powder. The dry powder was added to a tube furnace for sintering under argon protection and heated to 350℃ at a rate of 5℃ / min, held for 4h, and then heated to 700℃ and held for 10h. The mixture was then naturally cooled to 25℃ to obtain modified lithium iron phosphate.

[0060] Step S3: Add 1g of carbon nanotubes TOB-TNT-M and 50mL of deionized water to a three-necked flask equipped with a stirrer and thermometer, and sonicate for 1h to obtain a suspension. Add 10g of modified lithium iron phosphate to the above suspension, stir in a 60℃ water bath for 1.5h, place in a tube furnace, and heat to 550℃ at a rate of 5℃ / min under an argon atmosphere, hold for 30min, and then heat to 650℃ under a mixed gas of H2 and Ar in a volume ratio of 5:95, hold for 8h, and naturally cool to 25℃ to obtain carbon nanotube-coated lithium iron phosphate.

[0061] Step S4: Add 1.5g of carbon nanotube-coated lithium iron phosphate and 105mL of 1mol / L HCl solution to a three-necked flask equipped with a stirrer and thermometer. Disperse by sonication for 30min, transfer to an ice-water bath at 3℃, and stir magnetically for 1.5h. Add 0.15g of aniline and continue stirring for 1h to obtain a dispersion solution. Add 0.35g of ammonium persulfate to the above dispersion solution and react in an ice-water bath at 3℃ for 13h. After the reaction is complete, filter the solution. Wash the filter cake four times with deionized water and anhydrous ethanol. After washing, vacuum dry at 60℃ for 18h to obtain chromium-molybdenum co-doped lithium iron phosphate.

[0062] The chromium-molybdenum dual-doped lithium iron phosphate prepared in Examples 1-3 and Comparative Examples 1-3 were used as positive electrode materials. The positive electrode material, binder PVDF DS202, conductive agent Super P, and N-methylpyrrolidone were mixed in a mass ratio of 7:1:2:8 and thoroughly stirred to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of an aluminum foil. The coated aluminum foil was dried in an oven at 100°C and then cut using a mold to obtain the positive electrode sheet. A lithium sheet was used as the negative electrode, and the separator was TOB-PP-16. 1 mol of LiPF6 was dissolved in 1 L of a 1:1 volume ratio mixed solution of ethylene carbonate and dimethyl carbonate to obtain a 1 mol / L LiPF6 electrolyte. The above positive electrode sheet, lithium sheet, separator, and electrolyte were used to prepare a CR2032 button battery. The battery capacity was tested according to GB / T 18287-2013. According to GB / T... Powder conductivity was measured according to standard 30835-2014; cyclic stability was tested according to standard GB / T31484-2015; test results are attached. Figure 1-3 As shown:

[0063] Comparison of Examples 1-3 and Comparative Examples 1-3: Example 1 had relatively low doping and surface coating amounts, resulting in insufficient powder conductivity and cycle performance; Example 2 had relatively better doping amounts and process parameters, forming a complete conductive network, resulting in good capacity, conductivity, and cycle performance; Example 3 had excessively high doping amounts, disrupting the integrity of the lithium iron phosphate crystal structure and causing defects, therefore its performance, while good, was slightly lower than Example 2; Comparison of Example 2 and Comparative Example 1: Comparative Example 1 only performed bulk doping and basic carbon coating, which only addresses the internal and surface issues of the particles. The conductivity issue stems from the fact that particles still rely on point-to-point physical contact, resulting in high resistance, low powder conductivity, and short cycle life. Comparing Example 2 with Comparative Example 2: Comparative Example 2 incorporates Cr / Mo doping, carbon coating, and in-situ growth of nitrogen-doped carbon nanotubes, creating an extremely smooth electron conduction path from the inside out. Comparative Example 2 lacks a polyaniline protective layer, preventing effective suppression of interfacial side reactions, leading to poor capacity and cycle performance. Comparing Example 2 with Comparative Example 3: Comparative Example 3 does not utilize nitrogen-doped carbon nanotubes, resulting in lower intrinsic conductivity.

[0064] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a chromium-molybdenum co-doped lithium iron phosphate material, characterized in that, Includes the following steps: Step a1: Add the iron source and H2O2 solution to a three-necked flask equipped with a stirrer and thermometer, stir magnetically, and add CrCl3·6H2O and (NH4)6Mo7O. 24 • 4H2O and NH4H2PO4 are added to a beaker and mixed and stirred to obtain a doped solution; the doped solution is added to the above three-necked flask and mixed and stirred, then transferred to a wet ball mill jar for ball milling. After ball milling, the balls and materials are separated, the materials are dried, and after drying, they are ground to obtain chromium-molybdenum dual-doped iron phosphate; Step a2: Chromium-molybdenum co-doped iron phosphate and Li2CO3 are added to a grinder and ground to obtain a grinding material. Then, the grinding material, carbon source and anhydrous ethanol are added to a planetary ball mill for ball milling. The carbon source is either sucrose or glucose. The balls and materials are separated, and the material is spray-dried and sintered. Argon gas is introduced for protection, and the temperature is raised to 350°C at a rate of 5°C / min and held for 4 hours. Then, the temperature is raised to 700°C and held for 10 hours. After cooling, modified lithium iron phosphate is obtained. Step a3: Melamine, Ni(NO3)2·6H2O and deionized water were ultrasonically mixed to obtain a suspension. Modified lithium iron phosphate was added, and the mixture was stirred in a water bath. The suspension was placed in a tube furnace and heated to 550°C at a rate of 5°C / min under an argon atmosphere. The temperature was held for 30 min. Then, under a mixed gas of H2 and Ar in a volume ratio of 5:95, the temperature was raised to 750-800°C and held for 1-2 h. The mixture was naturally cooled to 25°C, and hydrochloric acid solution was added. The mixture was stirred, filtered, and the filter cake was washed and dried to obtain nitrogen-doped carbon nanotube-coated lithium iron phosphate. Step a4: Nitrogen-doped carbon nanotube-coated lithium iron phosphate and HCl solution are ultrasonically dispersed, transferred to an ice-water bath, magnetically stirred, aniline is added, and stirring is continued to obtain a dispersion solution; ammonium persulfate is added, and the reaction is carried out in an ice-water bath. After the reaction is completed, the mixture is filtered, the filter cake is washed and dried to obtain chromium-molybdenum dual-doped lithium iron phosphate.

2. The method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material according to claim 1, characterized in that, The iron source, H2O2 solution, CrCl3·6H2O, and (NH4)6Mo7O mentioned in step a1 24 The ratio of ·4H2O and NH4H2PO4 is 0.96-1 mol: 100-110 mL: 0.01-0.02 mol: 3-4 g: 1 mol; the mass fraction of the H2O2 solution is 27.5%; the iron source is one of FeC2O4·2H2O and FeSO4·7H2O.

3. The method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material according to claim 1, characterized in that, The ratio of chromium-molybdenum dual-doped iron phosphate, Li2CO3, carbon source, and anhydrous ethanol in step a2 is 145-155g. 1.05-1.1mol: 70-75g: 200-300mL.

4. The method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material according to claim 1, characterized in that, In step a3, the ratio of melamine, Ni(NO3)2·6H2O, deionized water, modified lithium iron phosphate, and hydrochloric acid solution is 1g:0.1g:50mL:10g:100-200mL; the molar concentration of the hydrochloric acid solution is 1-2mol / L.

5. The method for preparing a chromium-molybdenum dual-doped lithium iron phosphate material according to claim 1, characterized in that, In step a4, the ratio of nitrogen-doped carbon nanotubes coated with lithium iron phosphate, HCl solution, aniline, and ammonium persulfate is 1-2g: 100-110mL: 0.1-0.2g: 0.25-0.5g; the molar concentration of the HCl solution is 1mol / L.

6. A chromium-molybdenum dual-doped lithium iron phosphate material, characterized in that, The chromium-molybdenum dual-doped lithium iron phosphate material is prepared according to any one of claims 1-5 by a method for preparing chromium-molybdenum dual-doped lithium iron phosphate material.

7. The application of a chromium-molybdenum dual-doped lithium iron phosphate material as described in any one of claims 1-5 in lithium-ion batteries.

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