Preparation method of modified nanometer carbon-coated lithium iron phosphate positive electrode material

Abstract

The application discloses a preparation method of modified nanometer carbon-coated lithium iron phosphate positive electrode material. The LiFePO4 material is in-situ coated by modified nanometer carbon powder, the conductivity of the prepared LiFePO4 positive electrode material is improved, the complexing agent is combined to control FePO4 to form a uniform crystal nucleus structure, the oxidation of iron in the reaction process is reduced, the content of Fe impurities is controlled, the agglomeration of particles is inhibited by benzene dicarboxylic imide and stearoyl hydrazide and ultrasonic dispersion, and the coating type three-dimensional network structure on the surface of the lithium iron phosphate particles plays a certain guiding growth and optimization role.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and in particular relates to a method for preparing modified nano-carbon coated lithium iron phosphate cathode material. Background Technology

[0002] Lithium iron phosphate (LFP) cathode material is widely recognized as the safest power battery material. Its long charge / discharge platform, stable properties, low cost, and environmental friendliness make it the most promising lithium battery cathode material, widely used in portable electronic devices, automobiles, ships, and energy storage. However, due to its inherent structural limitations, lithium-ion batteries using LFP as the cathode material exhibit poor conductivity, slow lithium-ion diffusion rate, and poor discharge performance at low temperatures, limiting its application prospects. Therefore, modification of LFP materials is necessary to fully realize its inherent potential in the battery field. Currently, the modification of lithium manganese phosphate mainly involves three methods: carbon coating, ion doping, and material nanostructuring.

[0003] Vanadium bismuth tetroxide (VBS) is a novel visible light photocatalyst. It is non-toxic, has a narrow band gap, a bright color, and exhibits excellent photocatalytic properties, making it widely used in pigments and photocatalytic degradation. It is often applied in photoelectric materials with boron trifluoride (BAM) to improve photoelectric conversion efficiency. However, there are few reports on the application of VBS combined with BAM in batteries. This may be because the carbon coating, ion doping, and nano-sizing processes used in the modification of lithium iron phosphate (LFP) cathode materials differ from the processes used in applying VBS and BAM to photoelectric materials. This difference may prevent the prepared LFP cathode material from simultaneously achieving the photocatalytic advantages of VBS and BAM while maintaining the superior performance of other essential properties of LFP cathode materials.

[0004] Traditional carbon coating technology improves the performance of lithium iron phosphate (LFP) by adding an appropriate carbon layer. However, the added carbon source easily leads to particle aggregation, resulting in a slowdown in lithium-ion diffusion rate and a decrease in conductivity. Existing technologies address this problem by modifying the surface of LFP using composite materials. This invention aims to improve the application of vanadium bismuth tetroxide (vanadium bismuth tetroxide) and boron trifluoride (boron amine trifluoride) in the battery field by improving the carbon coating technology. It utilizes the excellent photocatalytic properties of vanadium bismuth tetroxide and boron trifluoride to modify LFP, thereby improving the conductivity of lithium-ion batteries using LFP as the cathode material. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a method for preparing modified carbon nanotube coated lithium iron phosphate cathode material, comprising the following steps:

[0006] (1) Preparation of precursor: Take 40-50 parts of FeSO4, 40-60 parts of H3PO4, 125-168 parts of modified nano carbon powder, add 13-15 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat in a high pressure vessel to 110-130℃ and stir the reaction at this temperature for 6-8 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0007] (2) Premixed slurry: Take 120-180 parts of LiOH, add LiOH and precursor to the premix tank, add 200-280 parts of ultrapure water, and then stir and sonicate. The stirring speed is 50-70 rpm, the ultrasonic frequency is 20 kHz, and the stirring and sonication time is 10-20 min. Then add 18-32 parts of N-sec-butylphthalimide and 22-47 parts of stearyl hydrazide, and stir and sonicate for the second time. The stirring speed is 150-200 rpm, the ultrasonic frequency is 100 kHz, and the stirring and sonication time is 80-100 min.

[0008] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0009] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 100-140℃, the vacuum degree of spray drying is 0.098-0.1MPa, and the particle size of the dried powder is controlled to be 10-15um.

[0010] (5) Sintering: A roller furnace is used to sinter at 650°C for 5-7 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas is treated to be harmless before being discharged.

[0011] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained.

[0012] Further, in step (1), the modified nano-carbon powder is prepared as follows:

[0013] Take 37-49 parts of starch, 11-17 parts of vanadium bismuth tetroxide, and 8-11 parts of boron trifluoride amine into a reaction vessel, add 120-150 parts of anhydrous ethanol, heat the reaction vessel to 80-90℃, and stir at 500-700 rpm for 4-6 hours. After the reaction is completed, add 25-38 parts of raw bamboo powder, heat the reaction vessel to 120-150℃, and stir at 1000-1200 rpm for 6-12 hours. After the reaction is completed, filter, wash the solid product with deionized water, and dry at 105℃ for 12-24 hours to obtain modified nano-carbon powder.

[0014] Further, in step (1), the preparation of the complexing agent:

[0015] Take 43-59 parts of phenyl polyoxyethylene phosphate ammonium salt, 14-20 parts of sodium 3-nitrobenzenesulfonate, 5-10 parts of nano zinc oxide, and 250-300 parts of ultrapure water. Place the phenyl polyoxyethylene phosphate ammonium salt and sodium 3-nitrobenzenesulfonate in a reaction vessel, add ultrapure water, heat the reaction vessel to 30-50℃, and stir at a speed of 800-1400 r / min for 8-10 h. Add the nano zinc oxide, heat the reaction vessel to 100-120℃, and stir at a speed of 1600-2000 r / min for 3-6 h. Cool to room temperature to obtain the final product.

[0016] Furthermore, the preparation process for the raw bamboo powder can be as follows:

[0017] The raw bamboo is pressed until it cracks and then cut into square or strip-shaped pieces 5-150 mm long. After tearing them along the axial direction, they are placed in an oven and dried at 40-60℃ for 8-12 hours. The dried raw bamboo pieces are then ground in a pulverizer until they pass through an 80-mesh sieve to obtain raw bamboo powder. Beneficial effects

[0018] (1) The ultrasonic dispersion method utilizes the cavitation effect of ultrasound to reduce the surface energy of lithium iron phosphate through high-energy high-oscillation and prevent particle agglomeration under stirring, thereby achieving uniform particle dispersion. Phthalimide decomposes during sintering to generate gas, which further improves the dispersion of particles during the reaction process. At the same time, it can guide the growth and optimize the coating layer on the particle surface, improving the uniformity of the coating layer. In this invention, N-sec-butylphthalimide and stearyl hydrazide are used to replace phthalimide, further forming a coated three-dimensional network structure on the basis of carbon coating on the surface of lithium iron phosphate particles, which further improves the conductivity of the material. At the same time, it can inhibit particle agglomeration during the preparation process, making the carbon coating structure uniform and complete, and significantly improving the cycle stability of lithium iron phosphate cathode material.

[0019] (2) Using modified nano carbon powder as a carbon source to coat LiFePO4 material in situ can change the size of lithium iron phosphate grains, create lattice defects in lithium iron phosphate, and improve the conductivity of the prepared LiFePO4.

[0020] (3) Modified nano-carbon powder, on the one hand, utilizes the carbonization effect of carbon source to inhibit crystal growth, alleviate particle aggregation, and improve the conductivity of electrons in the grains. On the other hand, the modified three-dimensional network structure reduces the diffusion path of lithium ions, thereby achieving the purpose of improving the performance of LiFePO4 material.

[0021] (4) After modification with vanadium bismuth tetroxide and boron trifluoride amine, nano-carbon powder is coated on the surface of lithium iron phosphate. By doping with vanadium and bismuth atoms, the planar structure of boron clusters within a certain size range is changed, resulting in a nanostructure that is very different from free boron clusters. The electrons around the boron clusters tend to be delocalized, which is conducive to electron transfer and enhances the conductivity of modified nano-carbon coated lithium iron phosphate particles.

[0022] (5) Phenyl polyoxyethylene phosphate ammonium salt acts as a nucleation aid for FePO4, controlling the formation of a uniform crystal nucleus structure of FePO4 and improving the conductivity of the prepared LiFePO4. Sodium 3-nitrobenzenesulfonate can avoid destroying the lamellar conformation of the prepared precursor. At the same time, sodium 3-nitrobenzenesulfonate can act as a reducing agent during sintering, reducing the oxidation of iron during the reaction and controlling the Fe impurity content. Phenyl polyoxyethylene phosphate ammonium salt and sodium 3-nitrobenzenesulfonate can reduce the agglomeration of particles during the preparation of the precursor, improve the uniformity of the prepared modified nano-carbon powder, and further improve the cycle stability of lithium iron phosphate cathode material. Implementation Example

[0023] Preparation of modified carbon nanoparticles:

[0024] 49 parts of starch, 17 parts of vanadium bismuth tetroxide, and 8 parts of boron trifluoride amine were placed in a reaction vessel, and 150 parts of anhydrous ethanol were added. The reaction vessel was heated to 80°C and stirred at 500 rpm for 4 hours. After the reaction was completed, 38 parts of raw bamboo powder were added, and the reaction vessel was heated to 150°C and stirred at 1000 rpm for 12 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 12 hours to obtain modified nano-carbon powder.

[0025] Preparation of complexing agents:

[0026] Take 43 parts of phenyl polyoxyethylene phosphate ammonium salt and 20 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 250 parts of ultrapure water, heat the reaction vessel to 3°C, stir at 1400 r / min for 8 h, add 10 parts of nano zinc oxide, heat the reaction vessel to 120°C, stir at 1600 r / min for 6 h, and cool to room temperature to obtain the final product.

[0027] Preparation of modified carbon nanotube coated lithium iron phosphate cathode material:

[0028] (1) Preparation of precursor: Take 40 parts of FeSO4, 60 parts of H3PO4, 125 parts of modified nano carbon powder, add 13 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 130℃ in a high pressure vessel and stir the reaction at this temperature for 8 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0029] (2) Premixed slurry: 120 parts of LiOH and precursor were added to the premixing tank, and 280 parts of ultrapure water were added. The mixture was stirred and ultrasonically treated. The stirring speed was 70 rpm, the ultrasonic frequency was 20 kHz, and the stirring and ultrasonic treatment time was 10 min. Then, 18 parts of N-sec-butylphthalimide and 47 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated for the second time. The stirring speed was 150 rpm, the ultrasonic frequency was 100 kHz, and the stirring and ultrasonic treatment time was 100 min.

[0030] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0031] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 100℃, the vacuum degree of spray drying is 0.1MPa, and the particle size of the dried powder is controlled to be 10~15um.

[0032] (5) Sintering: A roller furnace was used to sinter at 650°C for 7 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas was treated to render it harmless before being discharged.

[0033] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained. Example

[0034] Preparation of modified carbon nanoparticles:

[0035] Take 37 parts of starch, 11 parts of vanadium bismuth tetroxide, and 11 parts of boron trifluoride amine into a reaction vessel, add 120 parts of anhydrous ethanol, heat the reaction vessel to 90°C, and stir at 700 rpm for 6 hours. After the reaction is completed, add 25 parts of raw bamboo powder, heat the reaction vessel to 120°C, and stir at 1200 rpm for 6 hours. After the reaction is completed, filter, wash the solid product with deionized water, and dry at 105°C for 24 hours to obtain modified nano-carbon powder.

[0036] Preparation of complexing agents:

[0037] Take 59 parts of phenyl polyoxyethylene phosphate ammonium salt and 14 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 300 parts of ultrapure water, heat the reaction vessel to 50°C, stir at 800 r / min for 10 h, add 5 parts of nano zinc oxide, heat the reaction vessel to 100°C, stir at 2000 r / min for 3 h, and cool to room temperature to obtain the final product.

[0038] Preparation of modified carbon nanotube coated lithium iron phosphate cathode material:

[0039] (1) Preparation of precursor: Take 50 parts of FeSO4, 40 parts of H3PO4, 168 parts of modified nano carbon powder, add 15 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 110°C in a high pressure vessel and stir the reaction at this temperature for 6 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0040] (2) Premixed slurry: 180 parts of LiOH and precursor were added to a premixing tank, and 200 parts of ultrapure water were added. The mixture was stirred and ultrasonically treated. The stirring speed was 50 rpm, the ultrasonic frequency was 20 kHz, and the stirring and ultrasonic treatment time was 20 min. Then, 32 parts of N-sec-butylphthalimide and 22 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated for the second time. The stirring speed was 200 rpm, the ultrasonic frequency was 100 kHz, and the stirring and ultrasonic treatment time was 80 min.

[0041] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0042] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 140℃, the vacuum degree of spray drying is 0.098MPa, and the particle size of the dried powder is controlled to be 10~15um.

[0043] (5) Sintering: A roller furnace is used to sinter at 650°C for 5 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas is treated to be harmless before being discharged.

[0044] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained. Example

[0045] Preparation of modified carbon nanoparticles:

[0046] 43 parts of starch, 14 parts of vanadium bismuth tetroxide, and 10 parts of boron trifluoride amine were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of raw bamboo powder were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0047] Preparation of complexing agents:

[0048] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt and 17 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, add 7 parts of nano zinc oxide, heat the reaction vessel to 110°C, stir at 1800 r / min for 4.5 h, and cool to room temperature to obtain the final product.

[0049] Preparation of modified carbon nanotube coated lithium iron phosphate cathode material:

[0050] (1) Preparation of precursor: Take 45 parts of FeSO4, 50 parts of H3PO4, 146 parts of modified nano carbon powder, add 14 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 120°C in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0051] (2) Premixed slurry: 150 parts of LiOH and precursor were added to a premixing tank, and 240 parts of ultrapure water were added. The mixture was stirred and ultrasonically treated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of N-sec-butylphthalimide and 35 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0052] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0053] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 120℃, the vacuum degree of spray drying is 0.099MPa, and the particle size of the dried powder is controlled to be 10~15um.

[0054] (5) Sintering: A roller furnace is used to sinter at 650°C for 6 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas is treated to render it harmless before being discharged.

[0055] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained.

[0056] Comparative Example 1

[0057] The premixed slurry used in the comparative preparation process of modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0058] 150 parts of LiOH and the precursor were added to a premixing tank, followed by 240 parts of ultrapure water. The mixture was then stirred and sonicated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 35 parts of stearyl hydrazide were added, and the mixture was stirred and sonicated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0059] Everything else is the same as in Example 3.

[0060] Comparative Example 2

[0061] The premixed slurry used in the comparative preparation process of modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0062] 150 parts of LiOH and the precursor were added to a premixing tank, followed by 240 parts of ultrapure water. The mixture was then stirred and sonicated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of phthalimide and 35 parts of stearyl hydrazide were added, and the mixture was stirred and sonicated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0063] Everything else is the same as in Example 3.

[0064] Comparative Example 3

[0065] The premixed slurry used in the comparative preparation process of modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0066] 150 parts of LiOH and the precursor were added to a premixing tank, followed by 240 parts of ultrapure water. The mixture was then stirred and sonicated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of N-sec-butylphthalimide were added, and the mixture was stirred and sonicated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0067] Everything else is the same as in Example 3.

[0068] Comparative Example 4

[0069] The premixed slurry used in the comparative preparation process of modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0070] 150 parts of LiOH and the precursor were added to a premixing tank, 240 parts of ultrapure water were added, and after stirring evenly, 25 parts of N-sec-butylphthalimide and 35 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0071] Everything else is the same as in Example 3.

[0072] Comparative Example 5

[0073] The premixed slurry used in the comparative preparation process of modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0074] 150 parts of LiOH and the precursor were added to a premixing tank, followed by 240 parts of ultrapure water. The mixture was then stirred and sonicated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of N-sec-butylphthalimide and 35 parts of stearyl hydrazide were added, and the mixture was stirred and sonicated a second time at a stirring speed of 60 rpm and an ultrasonic frequency of 100 kHz for 15 min.

[0075] Everything else is the same as in Example 3.

[0076] Comparative Example 6

[0077] This comparative example prepares modified nano-carbon powder:

[0078] 43 parts of glucose, 14 parts of vanadium bismuth tetroxide, and 10 parts of boron trifluoride amine were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of raw bamboo powder were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0079] Everything else is the same as in Example 3.

[0080] Comparative Example 7

[0081] This comparative example prepares modified nano-carbon powder:

[0082] 43 parts of starch and 10 parts of boron trifluoride amine were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of raw bamboo powder were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0083] Everything else is the same as in Example 3.

[0084] Comparative Example 8

[0085] 43 parts of starch and 14 parts of vanadium bismuth tetroxide were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of raw bamboo powder were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0086] Everything else is the same as in Example 3.

[0087] Comparative Example 9

[0088] This comparative example prepares modified nano-carbon powder:

[0089] 43 parts of starch, 14 parts of vanadium bismuth tetroxide, and 10 parts of boron trifluoride amine were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of lignocellulose were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0090] Everything else is the same as in Example 3.

[0091] Comparative Example 10

[0092] Preparation of modified carbon nanoparticles:

[0093] 43 parts of starch, 14 parts of vanadium bismuth tetroxide, and 10 parts of boron trifluoride amine were placed in a reaction vessel, and 135 parts of anhydrous ethanol were added. The reaction vessel was heated to 85°C and stirred at 600 rpm for 5 hours. After the reaction was completed, 31 parts of raw bamboo powder were added, and the reaction vessel was heated to 135°C and stirred at 1100 rpm for 9 hours. After the reaction was completed, the mixture was filtered, the solid product was washed with deionized water, and dried at 105°C for 18 hours to obtain modified nano-carbon powder.

[0094] Preparation of modified carbon nanotube coated lithium iron phosphate cathode material:

[0095] (1) Preparation of precursor: Take 45 parts of FeSO4, 50 parts of H3PO4, 146 parts of modified nano carbon powder, add 14 parts of hexadecyltrimethylammonium bromide, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 120°C in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0096] (2) Premixed slurry: 150 parts of LiOH and precursor were added to a premixing tank, and 240 parts of ultrapure water were added. The mixture was stirred and ultrasonically treated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of N-sec-butylphthalimide and 35 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0097] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0098] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 120℃, the vacuum degree of spray drying is 0.099MPa, and the particle size of the dried powder is controlled to be 10~15um.

[0099] (5) Sintering: A roller furnace is used to sinter at 650°C for 6 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas is treated to render it harmless before being discharged.

[0100] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained.

[0101] Comparative Example 11

[0102] This comparative example prepares a complexing agent:

[0103] Take 17 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, add 7 parts of nano zinc oxide, heat the reaction vessel to 110°C, stir at 1800 r / min for 4.5 h, and cool to room temperature to obtain the final product.

[0104] Everything else is the same as in Example 3.

[0105] Comparative Example 12

[0106] This comparative example prepares a complexing agent:

[0107] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, add 7 parts of nano zinc oxide, heat the reaction vessel to 110°C, stir at 1800 r / min for 4.5 h, and cool to room temperature to obtain the product.

[0108] Everything else is the same as in Example 3.

[0109] Comparative Example 13

[0110] This comparative example prepares a complexing agent:

[0111] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt and 17 parts of sodium 3-nitrobenzenesulfonate in a reaction vessel, add 275 parts of ultrapure water, stir evenly, then add 7 parts of nano zinc oxide, heat the reaction vessel to 110℃, stir at 1800r / min for 4.5h, and cool to room temperature to obtain the product.

[0112] Everything else is the same as in Example 3.

[0113] Comparative Example 14

[0114] This comparative example prepares a complexing agent:

[0115] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt and 17 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, after the reaction is completed, continue to heat the reaction vessel to 110°C, stir at 1800 r / min for 4.5 h, and cool to room temperature to obtain the product.

[0116] Everything else is the same as in Example 3.

[0117] Comparative Example 15

[0118] This comparative example prepares a complexing agent:

[0119] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt and 17 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, add 7 parts of nano zinc oxide, continue stirring, keep the reaction at the temperature for 9 h, and cool to room temperature to obtain the product.

[0120] Everything else is the same as in Example 3.

[0121] Comparative Example 16

[0122] In this comparative example, the preparation of the precursor in the process of preparing modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0123] Take 45 parts of FeSO4, 35 parts of H3PO4, 146 parts of modified nano carbon powder, add 14 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 120℃ in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain a precursor slurry. Separate the precursor slurry into solid and liquid phases, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0124] Everything else is the same as in Example 3.

[0125] Comparative Example 17

[0126] In this comparative example, the preparation of the precursor in the process of preparing modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0127] Take 45 parts of FeSO4, 65 parts of H3PO4, 146 parts of modified nano carbon powder, add 14 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 120℃ in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain a precursor slurry. Separate the precursor slurry into solid and liquid phases, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0128] Everything else is the same as in Example 3.

[0129] Comparative Example 18

[0130] Preparation of complexing agents:

[0131] Take 51 parts of phenyl polyoxyethylene phosphate ammonium salt and 17 parts of sodium 3-nitrobenzenesulfonate into a reaction vessel, add 275 parts of ultrapure water, heat the reaction vessel to 40°C, stir at 1100 r / min for 9 h, add 7 parts of nano zinc oxide, heat the reaction vessel to 110°C, stir at 1800 r / min for 4.5 h, and cool to room temperature to obtain the final product.

[0132] Preparation of modified carbon nanotube coated lithium iron phosphate cathode material:

[0133] (1) Preparation of precursor: Take 45 parts of FeSO4, 50 parts of H3PO4, 146 parts of glucose, add 14 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 120°C in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0134] (2) Premixed slurry: 150 parts of LiOH and precursor were added to a premixing tank, and 240 parts of ultrapure water were added. The mixture was stirred and ultrasonically treated at a stirring speed of 60 rpm and an ultrasonic frequency of 20 kHz for 15 min. Then, 25 parts of N-sec-butylphthalimide and 35 parts of stearyl hydrazide were added. The mixture was stirred and ultrasonically treated a second time at a stirring speed of 175 rpm and an ultrasonic frequency of 100 kHz for 90 min.

[0135] (3) Grinding: The slurry is ground using a sand mill until the particle size is 0.15~0.2μm;

[0136] (4) Vacuum spray drying: Vacuum spray drying is used to grind the slurry after sand milling. The spray drying temperature is 120℃, the vacuum degree of spray drying is 0.099MPa, and the particle size of the dried powder is controlled to be 10~15um.

[0137] (5) Sintering: A roller furnace is used to sinter at 650°C for 6 hours under a nitrogen atmosphere to prepare modified nano-carbon coated lithium iron phosphate powder. The generated gas is treated to render it harmless before being discharged.

[0138] (6) Screening to remove iron: The sintered lithium iron phosphate material is screened to remove iron until the content of magnetic material is <0.1ppm, and the modified nano carbon coated lithium iron phosphate product is obtained.

[0139] Comparative Example 19

[0140] In this comparative example, the preparation of the precursor in the process of preparing modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0141] Take 45 parts FeSO4, 50 parts H3PO4, 146 parts modified nano carbon powder, add 14 parts complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 135℃ in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain a precursor slurry. Separate the precursor slurry into solid and liquid phases, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0142] Everything else is the same as in Example 3.

[0143] Comparative Example 20

[0144] In this comparative example, the preparation of the precursor in the process of preparing modified carbon nanotube-coated lithium iron phosphate cathode material is as follows:

[0145] Take 45 parts of FeSO4, 50 parts of H3PO4, 146 parts of modified nano carbon powder, add 14 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.5. Heat to 105℃ in a high pressure vessel and stir the reaction at this temperature for 7 hours to obtain a precursor slurry. Separate the precursor slurry into solid and liquid phases, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor.

[0146] Everything else is the same as in Example 3.

[0147] Conductivity was determined according to section 6.17 of GB / T 30835-2014, "Carbon Composite Lithium Iron Phosphate Cathode Materials for Lithium-ion Batteries".

[0148] GB / T 42161-2022 Electrochemical Performance Testing of Lithium Iron Phosphate - Test Methods for First Discharge Specific Capacity and First Charge-Discharge Efficiency

[0149] GB / T 33828-2017 Determination of Trivalent Iron Content in Nano Lithium Iron Phosphate

[0150] The technical specifications of Embodiments 1-3 of the present invention are compared with those of Comparative Examples 1-20, as shown in Tables 1 and 2.

[0151] Table 1

[0152]

[0153] Table 2

[0154]

[0155] Based on Examples 1-3 and Comparative Examples 1-5 in Table 1, it can be seen that N-sec-butylphthalimide and stearyl hydrazide further form a coated three-dimensional network structure on the carbon coating surface of lithium iron phosphate particles, which can improve the conductivity of the material. Furthermore, by inhibiting particle agglomeration during the preparation process, the coated three-dimensional network structure is made uniform and complete, significantly improving the cycle stability of the lithium iron phosphate cathode material. Based on Examples 1-3 and Comparative Examples 6-9 in Table 1, it can be seen that the modified nano-carbon powder of vanadium bismuth tetroxide and boron trifluoride, coated on the surface of lithium iron phosphate, can enhance the performance of the modified nano-carbon coated lithium iron phosphate particles. Conductivity; as shown in Examples 1-3 and Comparative Examples 10-15 in Table 2, sodium 3-nitrobenzenesulfonate can act as a reducing agent during sintering, reducing the oxidation of iron during the reaction. The combination of phenyl polyoxyethylene phosphate ammonium salt and sodium 3-nitrobenzenesulfonate can reduce particle agglomeration during precursor preparation, improve the uniformity of the prepared modified nano-carbon powder, and further improve the cycle stability of lithium iron phosphate cathode material. As shown in Examples 1-3 and Comparative Examples 16-20 in Table 1, the process improvement of the present invention has a significant effect on improving the conductivity, controlling the impurity content, and improving the capacity stability of lithium iron phosphate cathode material.

Claims

1. A method for preparing modified nano-carbon coated lithium iron phosphate cathode material, characterized in that: The preparation process includes: (1) Preparation of precursor: Take 40-50 parts of FeSO4, 40-60 parts of H3PO4, 125-168 parts of modified nano carbon powder, add 13-15 parts of complexing agent, and then add sulfuric acid to control the pH of the system to 1.

5. Heat in a high pressure vessel to 110-130℃ and stir the reaction at this temperature for 6-8 hours to obtain precursor slurry. Separate the precursor slurry into solid and liquid, and dry the filter residue in an oven under an inert atmosphere to obtain the precursor. (2) Premixed slurry: Take 120-180 parts of LiOH, add LiOH and precursor to the premix tank, add 200-280 parts of ultrapure water, and then stir and sonicate. The stirring speed is 50-70 rpm, the ultrasonic frequency is 20 kHz, and the stirring and sonication time is 10-20 min. Then add 18-32 parts of N-sec-butylphthalimide and 22-47 parts of stearyl hydrazide, and stir and sonicate for the second time. The stirring speed is 150-200 rpm, the ultrasonic frequency is 100 kHz, and the stirring and sonication time is 80-100 min. (3) Grinding: The slurry is ground using a sand mill; (4) Spray drying: Spray drying is used to pulverize the slurry after sand milling; (5) Sintering to prepare modified nano-carbon coated lithium iron phosphate powder; (6) Iron removal by sieving yields modified nano-carbon coated lithium iron phosphate product; The preparation process of the modified nano-carbon powder includes: taking 37-49 parts of starch, 11-17 parts of vanadium bismuth tetroxide, and 8-11 parts of boron trifluoride amine into a reaction vessel, adding 120-150 parts of anhydrous ethanol, heating the reaction vessel to 80-90℃, stirring at 500-700 rpm for 4-6 hours, adding 25-38 parts of raw bamboo powder, heating the reaction vessel to 120-150℃, stirring at 1000-1200 rpm for 6-12 hours, filtering after the reaction, washing the solid product with deionized water, and drying at 105℃ for 12-24 hours to obtain the modified nano-carbon powder; The preparation process of the complexing agent includes: taking 43-59 parts of phenyl polyoxyethylene phosphate ammonium salt, 14-20 parts of sodium 3-nitrobenzenesulfonate, 5-10 parts of nano zinc oxide, and 250-300 parts of ultrapure water; placing the phenyl polyoxyethylene phosphate ammonium salt and sodium 3-nitrobenzenesulfonate in a reaction vessel, adding ultrapure water, heating the reaction vessel to 30-50°C, stirring at a speed of 800-1400 r / min for 8-10 h, adding nano zinc oxide, heating the reaction vessel to 100-120°C, stirring at a speed of 1600-2000 r / min for 3-6 h, and cooling to room temperature to obtain the final product.

2. The preparation method of the modified nano-carbon coated lithium iron phosphate cathode material as described in claim 1, characterized in that: The process conditions for spray drying are as follows: a vacuum spray drying device is used, the spray drying temperature is 100-140℃, and the vacuum degree of spray drying is 0.098-0.1MPa.

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