High-rate lithium iron phosphate positive electrode material, preparation method thereof and battery

Abstract

The invention discloses a high-rate lithium iron phosphate positive electrode material, a preparation method thereof and a battery, and belongs to the technical field of batteries, the preparation method comprises the following steps: mixing iron phosphate, a lithium source, a carbon source and an additive with a solvent, and carrying out coarse grinding and fine grinding to obtain mixed slurry; and carrying out spray drying on the mixed slurry, sintering in a nitrogen atmosphere, and naturally cooling to room temperature to obtain the high-rate lithium iron phosphate positive electrode material. The preparation method of the additive comprises the following steps: treating titanium dioxide with sebacic acid to obtain modified titanium dioxide; kH550 is adopted to treat zirconium oxide, and modified zirconium oxide is obtained; the modified titanium dioxide, the modified zirconium oxide and polyethylene glycol diamine 200 are added into N, N-dimethylformamide to be treated, a mixture is obtained, low-temperature heat treatment, ball milling and drying are conducted, and the additive is obtained. The high-rate lithium iron phosphate positive electrode material prepared by the method has excellent electrochemical performance, the charge-discharge specific capacity and the rate capability are well improved, and the high-rate lithium iron phosphate positive electrode material has high discharge specific capacity under different rates.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries. More specifically, the present invention relates to a high-rate lithium iron phosphate cathode material, a preparation method thereof, and a battery. Background Art

[0002] A lithium-ion battery mainly consists of a positive and negative electrode material, an electrolyte capable of transferring lithium ions, a separator, and a casing, etc. In a lithium-ion battery, the cathode material is an important factor determining its electrochemical performance, safety performance, and future development direction. Lithium iron phosphate (LiFePO 4 ) as a new generation of lithium-ion battery cathode material with the most development and application potential has attracted much attention from all walks of life due to its advantages such as rich raw materials, low price, relatively high specific capacity, high working voltage platform, stable structure, and no environmental pollution. It is a good choice for power batteries and energy storage batteries.

[0003] The rate performance is a key consideration index for lithium iron phosphate cathode materials and has an important impact on the performance of rapid charging and discharging of the battery in a short time. At present, the lithium iron phosphate cathode material still faces the disadvantage of poor rate performance during use. Therefore, exploring how to improve the rate performance of the lithium iron phosphate cathode material is of great significance to the development of lithium-ion batteries. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0005] To achieve these objects and other advantages of the present invention, a preparation method of a high-rate lithium iron phosphate cathode material is provided, including the following steps: Step 1: Mix iron phosphate, a lithium source, a carbon source, and an additive, then mix with a solvent to form a slurry, and then perform rough grinding and fine grinding to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1, sinter in a nitrogen atmosphere, and naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material.

[0006] Preferably, in Step 1, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate; the carbon source is one or more of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; the solvent is anhydrous ethanol or deionized water.

[0007] Preferably, in Step 1, the additive contains one or more of elements Ti, Ce, Al, Ni, Zr, and Zn.

[0008] Preferably, in the first step, the molar ratio of lithium element to phosphorus element in iron phosphate and lithium source is 1-1.1:1; the addition amount of carbon source is 10-20 wt% of the mass of iron phosphate; the addition amount of additive is 0.01-1 wt% of the mass of iron phosphate; the solid content of the slurry is 20-60 wt%.

[0009] Preferably, in the first step, the lithium source is lithium carbonate; the carbon source is glucose monohydrate and polyethylene glycol 2000.

[0010] Preferably, in the first step, the molar ratio of lithium element to phosphorus element in iron phosphate and lithium carbonate is 1-1.1:1; the addition amount of glucose monohydrate is 8-10 wt% of the mass of iron phosphate, and the addition amount of polyethylene glycol 2000 is 5-6 wt% of the mass of iron phosphate.

[0011] Preferably, in the first step, the rough grinding time is 0.5-2 h, and the fine grinding time is 1-3 h.

[0012] Preferably, in the second step, the inlet air temperature of spray drying is 200-280 °C, and the outlet air temperature is 80-120 °C; the sintering temperature is 690-710 °C, the sintering heating rate is 1-5 °C / min, and the sintering time is 5-15 h.

[0013] Preferably, the preparation method of the additive in the first step includes the following steps: S11. Add sebacic acid into absolute ethanol, stir evenly, then add titanium dioxide, ball mill and mix, wash with absolute ethanol, and vacuum dry to obtain modified titanium dioxide; S12. Add KH550 into ethanol solution, stir, then add zirconia, heat and stir, filter by suction, wash with absolute ethanol, and vacuum dry to obtain modified zirconia; S13. Add modified titanium dioxide, modified zirconia and polyethylene glycol diamine 200 into N,N-dimethylformamide, ultrasonically disperse, magnetically stir, stand still, filter by suction, wash successively with deionized water and absolute ethanol, and vacuum dry to obtain a mixture; S14. Perform low-temperature heat treatment on the mixture at 150-300 °C, then ball mill and vacuum dry to obtain the additive.

[0014] Preferably, in S11, the mass ratio of sebacic acid, titanium dioxide and absolute ethanol is 0.05-0.2:10:8-12; the specific parameters of ball milling are: the grinding balls are zirconia balls, the ball-to-material ratio is 5-15:1, the rotation speed is 100-500 rpm, the time is 1-5 h; wash 2-5 times; the vacuum drying temperature is 80 °C.

[0015] Preferably, in the step S12, the ethanol solution is an ethanol aqueous solution with a concentration of 50-90 wt%; the mass ratio of zirconia, KH550 and the ethanol solution is 10:0.2-1:100-300; stir for 0.5-2 h, then add zirconia, heat to 50-80 °C and stir for 1-5 h; wash 2-5 times; the vacuum drying temperature is 80 °C.

[0016] Preferably, in the step S13, the mass ratio of the modified titanium dioxide, the modified zirconia and the polyethylene glycol diamine 200 is 1-2:1-2:0.1-0.5; the mass-volume ratio of the modified titanium dioxide and N,N-dimethylformamide is 1 g:10-50 mL; the power of ultrasonic dispersion is 200-400 W, the frequency is 50-70 kHz, and the time is 0.5-2 h; the rotational speed of magnetic stirring is 800-1200 rpm, and the time is 1-5 h; stand for 6-18 h; wash 2-5 times; the vacuum drying temperature is 80 °C.

[0017] Preferably, in the step S14, the low-temperature heat treatment is specifically as follows: under a nitrogen atmosphere, heat up to 150-300 °C at a heating rate of 1-5 °C / min, and keep the temperature for 1-3 h; the specific parameters of ball milling are as follows: the ball milling medium is anhydrous ethanol, the solid-liquid ratio is 1:1-1.5, the grinding balls are zirconia balls, the ball-to-material ratio is 5-15:1, the rotational speed is 300-800 rpm, and the time is 1-5 h.

[0018] A high-rate lithium iron phosphate cathode material is prepared by the preparation method of the high-rate lithium iron phosphate cathode material as described above.

[0019] A battery, wherein the cathode material of the battery is the high-rate lithium iron phosphate cathode material as described above.

[0020] The present invention has at least the following beneficial effects: The present invention provides a preparation method of a high-rate lithium iron phosphate cathode material. The prepared high-rate lithium iron phosphate cathode material has excellent electrochemical performance. The charge-discharge specific capacity and the rate performance are both improved well, and it has a high discharge specific capacity at different rates.

[0021] The present invention optimizes and improves the added metal oxides, uses sebacic acid to modify the surface of titanium dioxide powder, uses silane coupling agent to treat the surface of zirconia powder, adds the modified titanium dioxide and zirconia powders and polyethylene glycol diamine into N,N-dimethylformamide for treatment, improves the dispersibility and stability of the powders, and has certain reaction activity at the same time, which is beneficial to the doping of elements into the lithium iron phosphate lattice; then the mixed powders are subjected to low-temperature heat treatment and ball milling, which is beneficial to their highly dispersing in the system, and the obtained additive can optimize the spatial structure of lithium iron phosphate and improve the stability of its lattice and interface, thereby further enhancing the electrochemical performance of the lithium iron phosphate cathode material.

[0022] Other advantages, objectives and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD patterns of the high-rate lithium iron phosphate cathode materials prepared in Examples 1 to 3 and the commercial lithium iron phosphate in Comparative Example 1; Figure 2 SEM image of the high-rate lithium iron phosphate cathode material prepared in Example 1; Figure 3 Particle size distribution of the high-rate lithium iron phosphate cathode material prepared in Example 1; Figure 4 Polarization values of the high-rate lithium iron phosphate cathode materials prepared in Example 2 and the commercial lithium iron phosphate in Comparative Example 1 at 15C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0025] It should be understood that the terms such as "having", "comprising" and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations. Example 1 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 lithium carbonate (lithium to phosphorus molar ratio of 1.006:1), 0.85 g of glucose monohydrate, 0.566 g of PEG2000 and 0.025 g of titanium dioxide, add them into absolute ethanol according to a solid content of 40%, and then coarsely grind for 1 h by a sand mill. The median particle size of the particles after coarse grinding is 0.564 µm, and then finely grind for 1.5 h. The median particle size of the particles after fine grinding is 0.358 µm to obtain a mixed slurry; Step 2: The mixed slurry obtained in Step 1 is spray-dried (inlet air temperature: 240 °C, outlet air temperature: 100 °C) and then sintered. Under a nitrogen atmosphere, it is heated to 690 °C at a heating rate of 3 °C / min and held for 10 h, and then naturally cooled to room temperature to obtain a high-rate lithium iron phosphate cathode material, denoted as LFP-690.

[0026] Example 2 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of titanium dioxide, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h with a sand mill and then finely grind for 1.5 h to obtain a mixed slurry; Step 2: The mixed slurry obtained in Step 1 is spray-dried (inlet air temperature: 240 °C, outlet air temperature: 100 °C) and then sintered. Under a nitrogen atmosphere, it is heated to 700 °C at a heating rate of 3 °C / min and held for 10 h, and then naturally cooled to room temperature to obtain a high-rate lithium iron phosphate cathode material, denoted as LFP-700.

[0027] In this example, the sintering temperature is 700 °C, and the other steps are the same as those in Example 1.

[0028] Example 3 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of titanium dioxide, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h with a sand mill and then finely grind for 1.5 h to obtain a mixed slurry; Step 2: The mixed slurry obtained in Step 1 is spray-dried (inlet air temperature: 240 °C, outlet air temperature: 100 °C) and then sintered. Under a nitrogen atmosphere, it is heated to 710 °C at a heating rate of 3 °C / min and held for 10 h, and then naturally cooled to room temperature to obtain a high-rate lithium iron phosphate cathode material, denoted as LFP-710.

[0029] In this example, the sintering temperature is 710 °C, and the other steps are the same as those in Example 1.

[0030] Example 4 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of zirconia, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h and finely grind for 1.5 h using a sand mill to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), then sinter it. Under a nitrogen atmosphere, heat it at a heating rate of 3 °C / min to 700 °C and hold for 10 h, and then naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material.

[0031] In this example, zirconia is used to replace titanium dioxide, and the remaining steps are the same as in Example 2.

[0032] Example 5 A method for preparing a high-rate lithium iron phosphate cathode material, comprising the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of an additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h and finely grind for 1.5 h using a sand mill to obtain a mixed slurry; wherein, the additive is obtained by mixing titanium dioxide and zirconia in a mass ratio of 2:1; Step 2: Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), then sinter it. Under a nitrogen atmosphere, heat it at a heating rate of 3 °C / min to 700 °C and hold for 10 h, and then naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material.

[0033] In this example, a mixture of titanium dioxide and zirconia in a mass ratio of 2:1 is used to replace titanium dioxide, and the remaining steps are the same as in Example 2.

[0034] Example 6 A method for preparing a high-rate lithium iron phosphate cathode material, comprising the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of an additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h and finely grind for 1.5 h using a sand mill to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), then sinter it. Under a nitrogen atmosphere, heat it at a heating rate of 3 °C / min to 700 °C and hold for 10 h, and then naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material; Among them, the preparation method of the additive comprises the following steps: S11. Add 0.1 g of sebacic acid to 10 g of absolute ethanol, stir evenly, then add 10 g of titanium dioxide, ball-mill and mix for 3 h, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified titanium dioxide; among them, the specific parameters of ball milling are: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm; S12. Add 0.5 g of KH550 to 200 g of 80 wt% ethanol solution, stir for 1 h, then add 10 g of zirconia, stir at 60 °C for 3 h, filter by suction, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified zirconia; S13. Add 10 g of modified titanium dioxide, 5 g of modified zirconia and 1 g of polyethylene glycol diamine 200 to 200 mL of N,N-dimethylformamide, disperse by ultrasonic wave at 300 W and 55 kHz for 1 h, stir magnetically at 1000 rpm for 2 h, stand for 12 h, filter by suction, wash 3 times with deionized water and absolute ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture; S14. Perform low-temperature heat treatment on the mixture under a nitrogen atmosphere, heat up to 200 °C at a heating rate of 3 °C / min, keep the temperature for 2 h, then ball-mill for 2 h, and dry in vacuum at 80 °C to obtain an additive; among them, the specific parameters of ball milling are: the ball-milling medium is absolute ethanol, the solid-liquid ratio is 1:1.2, the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 400 rpm.

[0035] In this example, the additive is used to replace titanium dioxide, and the remaining steps are the same as those in Example 2.

[0036] In this example, first, the surface of titanium dioxide powder is modified with sebacic acid, and then the surface of zirconia is modified with silane coupling agent KH550. The modified titanium dioxide and zirconia powders are added to N,N-dimethylformamide for treatment, which improves the dispersibility and stability of the powders, and at the same time makes the mixed powders have certain reaction activity, which is beneficial to the doping of Ti and Zr into the lithium iron phosphate lattice; then, the mixed powders are subjected to low-temperature heat treatment and ball milling to obtain an additive with good dispersibility, reaction activity and stability. Adding this additive to lithium iron phosphate can make it highly dispersed in the system, make the crystallization more uniform, optimize the spatial structure of lithium iron phosphate, improve the stability of its lattice and interface, and Zr and Ti also have a synergistic effect. At the same time, carbon and nitrogen elements are introduced, further improving the electrochemical performance of the lithium iron phosphate cathode material.

[0037] Example 7 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h with a sand mill and then finely grind for 1.5 h to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), and then sinter it. Under a nitrogen atmosphere, heat it to 700 °C at a heating rate of 3 °C / min and hold for 10 h, and then naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material; Among them, the preparation method of the additive includes the following steps: S11: Add 0.5 g of KH550 to 200 g of 80 wt% ethanol solution, stir for 1 h, then add 10 g of zirconia, stir at 60 °C for 3 h, filter by suction, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified zirconia; S12: Add 10 g of titanium dioxide, 5 g of modified zirconia, and 1 g of polyethylene glycol diamine 200 to 200 mL of N,N-dimethylformamide, ultrasonically disperse at 300 W and 55 kHz for 1 h, magnetically stir at 1000 rpm for 2 h, let stand for 12 h, filter by suction, wash 3 times with deionized water and absolute ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture; S13: Perform low-temperature heat treatment on the mixture under a nitrogen atmosphere, heat it to 200 °C at a heating rate of 3 °C / min, hold for 2 h, then ball-mill for 2 h, and dry in vacuum at 80 °C to obtain the additive; among them, the specific parameters of the ball-milling are: the ball-milling medium is absolute ethanol, the solid-liquid ratio is 1:1.2, the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 400 rpm.

[0038] In this example, in the preparation of the additive, titanium dioxide was not modified, and the remaining steps were the same as those in Example 6.

[0039] Example 8 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1: Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h with a sand mill and then finely grind for 1.5 h to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), and then sinter it. Under a nitrogen atmosphere, heat it to 700 °C at a heating rate of 3 °C / min and hold for 10 h, and then naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material; Among them, the preparation method of the additive includes the following steps: S11. Add 0.1 g of sebacic acid to 10 g of absolute ethanol, stir evenly, then add 10 g of titanium dioxide, ball-mill and mix for 3 h, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified titanium dioxide. Among them, the specific parameters of the ball milling are: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm. S12. Add 10 g of modified titanium dioxide, 5 g of zirconia, and 1 g of polyethylene glycol diamine 200 to 200 mL of N,N-dimethylformamide, disperse by ultrasonic wave at 300 W and 55 kHz for 1 h, stir magnetically at 1000 rpm for 2 h, let stand for 12 h, filter by suction, wash 3 times with deionized water and absolute ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture. S13. Carry out low-temperature heat treatment on the mixture under a nitrogen atmosphere, heat up to 200 °C at a heating rate of 3 °C / min, keep warm for 2 h, then ball-mill for 2 h, and dry in vacuum at 80 °C to obtain the additive. Among them, the specific parameters of the ball milling are: the ball milling medium is absolute ethanol, the solid-liquid ratio is 1:1.2, the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 400 rpm.

[0040] In this example, in the preparation of the additive, zirconia was not subjected to modification treatment, and the other steps were the same as those in Example 6.

[0041] Example 9 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1. Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000, and 0.025 g of additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h by a sand mill, and then finely grind for 1.5 h to obtain a mixed slurry. Step 2. Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), then sinter it. Under a nitrogen atmosphere, heat up to 700 °C at a heating rate of 3 °C / min and keep warm for 10 h, and naturally cool to room temperature to obtain the high-rate lithium iron phosphate cathode material. Among them, the preparation method of the additive includes the following steps: S11. Add 0.1 g of sebacic acid to 10 g of absolute ethanol, stir evenly, then add 10 g of titanium dioxide, ball-mill and mix for 3 h, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified titanium dioxide. Among them, the specific parameters of the ball milling are: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm. S12. Add 0.5 g of KH550 to 200 g of 80 wt% ethanol solution, stir for 1 h, then add 10 g of zirconia, stir at 60 °C for 3 h, filter by suction, wash with absolute ethanol three times, and dry in vacuum at 80 °C to obtain modified zirconia; S13. Add 10 g of modified titanium dioxide and 5 g of modified zirconia to 200 mL of N,N-dimethylformamide, disperse by ultrasonic wave at 300 W and 55 kHz for 1 h, stir magnetically at 1000 rpm for 2 h, let stand for 12 h, filter by suction, wash with deionized water and absolute ethanol three times respectively, and dry in vacuum at 80 °C to obtain a mixture; S14. Perform low-temperature heat treatment on the mixture under a nitrogen atmosphere, heat it to 200 °C at a heating rate of 3 °C / min, hold for 2 h, then ball mill for 2 h, and dry in vacuum at 80 °C to obtain an additive; wherein, the specific parameters of the ball milling are: the ball milling medium is absolute ethanol, the solid-liquid ratio is 1:1.2, the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 400 rpm.

[0042] In this example, during the preparation of the additive, polyethylene glycol diamine 200 was not used, and the remaining steps were the same as those in Example 6.

[0043] Example 10 A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps: Step 1. Mix 10 g of iron phosphate, 2.464 g of lithium carbonate, 0.85 g of glucose monohydrate, 0.566 g of PEG2000 and 0.025 g of additive, add them to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h by a sand mill and then finely grind for 1.5 h to obtain a mixed slurry; Step 2. Spray-dry the mixed slurry obtained in Step 1 (inlet air temperature 240 °C, outlet air temperature 100 °C), then sinter it. Under a nitrogen atmosphere, heat it to 700 °C at a heating rate of 3 °C / min and hold for 10 h, and naturally cool to room temperature to obtain a high-rate lithium iron phosphate cathode material; Among them, the preparation method of the additive includes the following steps: S11. Add 0.1 g of sebacic acid to 10 g of absolute ethanol, stir evenly, then add 10 g of titanium dioxide, ball mill and mix for 3 h, wash with absolute ethanol three times, and dry in vacuum at 80 °C to obtain modified titanium dioxide; wherein, the specific parameters of the ball milling are: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm; S12. Add 0.5 g of KH550 to 200 g of 80 wt% ethanol solution, stir for 1 h, then add 10 g of zirconia, stir at 60 °C for 3 h, filter by suction, wash with absolute ethanol three times, and dry in vacuum at 80 °C to obtain modified zirconia; S13. Add 10 g of modified titanium dioxide, 5 g of modified zirconium oxide, and 1 g of polyethylene glycol diamine 200 to 200 mL of N,N-dimethylformamide, disperse them by ultrasonic wave at 300 W and 55 kHz for 1 h, stir magnetically at 1000 rpm for 2 h, let it stand for 12 h, filter by suction, wash it 3 times with deionized water and absolute ethanol respectively, and dry it in vacuum at 80 °C to obtain a mixture; S14. Ball-mill the mixture for 2 h and dry it in vacuum at 80 °C to obtain an additive; among them, the specific parameters of ball-milling are: the ball-milling medium is absolute ethanol, the solid-liquid ratio is 1:1.2, the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 400 rpm.

[0044] In this example, during the preparation of the additive, low-temperature heat treatment is not carried out, and the remaining steps are the same as those in Example 6.

[0045] Comparative Example 1 Commercial lithium iron phosphate, denoted as LFP-SY.

[0046] Figure 1 The XRD patterns of the high-rate lithium iron phosphate cathode materials prepared in Examples 1 to 3 and the commercial lithium iron phosphate in Comparative Example 1 are shown. It can be seen that the positions and peak intensities of the high-rate lithium iron phosphate cathode materials prepared by the present invention conform to those of the lithium iron phosphate cathode materials, and the absence of impurity peaks proves that there are no other impurities.

[0047] Figure 2 The SEM image of the high-rate lithium iron phosphate cathode material prepared in Example 1 is shown. The particle size of the material is subjected to a normal distribution. The maximum particle size of this material has a normal distribution of 10.15 μm ( Figure 3 )

[0048] Perform electrochemical tests on the high-rate lithium iron phosphate cathode materials prepared in Examples 1 to 8 and the commercial lithium iron phosphate in Comparative Example 1: Dissolve the obtained lithium iron phosphate cathode material, acetylene black, and polyvinylidene fluoride in a mass ratio of 8:1:1 in an appropriate amount of N-methylpyrrolidone solvent to form a uniform slurry, coat it on an aluminum foil, cut it into electrode sheets with a diameter of 14 mm after vacuum drying, and the areal density is 8 mg / cm 2 ; Use a lithium metal sheet as the negative electrode; the separator is an imported polypropylene microporous membrane (Celgard 2400); the electrolyte is a 1 mol / L LiPF 6 solution, and its solvent is a mixed solution of ethylene carbonate (EC): dimethyl carbonate (DMC) with a volume ratio of 1:1; Assemble button cells (CR2032) in a glove box filled with nitrogen, and then perform charge and discharge tests on the assembled batteries using a Neware battery test system.

[0049] The initial charge specific capacity at 0.1C (0.1CC), the initial discharge specific capacity at 0.1C (0.1CD), the initial Coulombic efficiency (0.1CD / 0.1CC*100%), and the discharge specific capacities at 1C, 5C, and 15C rates of the lithium iron phosphate in Examples 1-3 and Comparative Example 1 are shown in Table 1; Figure 4 The polarization values at 15C of the high-rate lithium iron phosphate cathode material prepared in Example 2 and the commercial lithium iron phosphate in Comparative Example 1.

[0050] Table 1 In summary, it can be seen that the high-rate lithium iron phosphate cathode material prepared by the present invention has excellent electrochemical performance, and both the charge-discharge specific capacity and the rate performance have been improved well; among them, the LFP-700 cathode material prepared in Example 2 has the best electrochemical performance; as Figure 4 shown, the polarization value of the LFP-SY electrode at 15C is 789.4 mV, while the polarization value of the LFP-700 electrode (788.4 mV) is slightly lower than that of LFP-SY, indicating that the superior stability of the LFP-700 electrode under high-rate conditions may be due to the reduction of the internal resistance of the electrode.

[0051] The test results of the electrochemical performance of the high-rate lithium iron phosphate cathode materials prepared in Examples 4-10 are shown in Table 2. It can be seen that compared with Examples 2, 4, and 5, adding additives to lithium iron phosphate in Examples 6-10 can further improve the electrochemical performance of the lithium iron phosphate cathode material. Among them, the high-rate lithium iron phosphate cathode material prepared in Example 4 has the best electrochemical performance, and it has a higher discharge specific capacity at different rates.

[0052] Table 2 Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the examples shown and described here.

Claims

1. A method for preparing a high-rate lithium iron phosphate positive electrode material, characterized in that: The following steps are involved: Step 1: mixing iron phosphate, lithium source, carbon source and additives, and then mixing with a solvent to form a slurry, and then coarsely grinding and finely grinding to obtain a mixed slurry; Step 2: spray-drying the mixed slurry obtained in step 1, sintering it in a nitrogen atmosphere, and naturally cooling it to room temperature to obtain a high-rate lithium iron phosphate positive electrode material; The preparation method of the additive comprises the following steps: S11, adding sebacic acid to anhydrous ethanol, stirring evenly, then adding titanium dioxide, ball milling and mixing, washing with anhydrous ethanol, and vacuum drying to obtain modified titanium dioxide; S12, adding KH550 to the ethanol solution, stirring, then adding zirconium oxide, heating and stirring, filtering, washing with anhydrous ethanol, and vacuum drying to obtain modified zirconium oxide; S13, adding modified titanium dioxide, modified zirconium oxide and polyethylene glycol diamine 200 into N,N-dimethylformamide, dispersing by ultrasonication, stirring by magnetic force, standing, filtering by suction, washing with deionized water and anhydrous ethanol in sequence, and drying in vacuo to obtain a mixture; S14, subjecting the mixture to low temperature heat treatment at 150-300° C., and then ball milling and vacuum drying to obtain an additive.

2. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In step 1, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate; the carbon source is one or more of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and the solvent is anhydrous ethanol or deionized water.

3. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step 1, the molar ratio of lithium element to phosphorus element in the iron phosphate and the lithium source is 1-1.1:1; the amount of the carbon source added is 10-20wt% of the mass of the iron phosphate; the amount of the additive added is 0.01-1wt% of the mass of the iron phosphate; the solid content of the slurry is 20-60wt%; the coarse grinding time is 0.5-2h, and the fine grinding time is 1-3h.

4. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the S11, the mass ratio of sebacic acid, titanium dioxide and anhydrous ethanol is 0.05-0.2:10:8-12; the specific parameters of ball milling are: grinding balls are zirconia balls, ball-to-material ratio is 5-15:1, rotation speed is 100-500 rpm, time is 1-5h; washing is 2-5 times; vacuum drying temperature is 80°C.

5. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the S12, the ethanol solution is an ethanol aqueous solution with a concentration of 50-90wt%; the mass ratio of zirconium oxide, KH550 and ethanol solution is 10:0.2-1:100-300; stirring for 0.5-2h, then adding zirconium oxide, heating to 50-80°C and stirring for 1-5h; washing 2-5 times; and the vacuum drying temperature is 80°C.

6. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the S13, the mass ratio of modified titanium dioxide, modified zirconium oxide and polyethylene glycol diamine 200 is 1~2:1~2:0.1~0.5; the mass volume ratio of modified titanium dioxide and N,N-dimethylformamide is 1g:10~50mL; the power of ultrasonic dispersion is 200~400W, the frequency is 50~70kHz, and the time is 0.5~2h; the magnetic stirring speed is 800~1200rpm, and the time is 1~5h; standing for 6~18h; washing 2~5 times; and the vacuum drying temperature is 80°C.

7. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the S14, the low temperature heat treatment is specifically as follows: in a nitrogen atmosphere, the temperature is increased to 150-300°C at a heating rate of 1-5°C / min, and the temperature is kept for 1-3 hours; the specific parameters of the ball milling are as follows: the ball milling medium is anhydrous ethanol, the solid-liquid ratio is 1:1-1.5, the grinding balls are zirconia balls, the ball-to-material ratio is 5-15:1, the rotation speed is 300-800rpm, and the time is 1-5 hours.

8. The method for preparing a high-rate lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step 2, the inlet air temperature of the spray drying is 200-280°C, and the outlet air temperature is 80-120°C; the sintering temperature is 690-710°C, the sintering heating rate is 1-5°C / min, and the sintering time is 5-15h.

9. A high-rate lithium iron phosphate positive electrode material, characterized in that: The high-rate lithium iron phosphate positive electrode material is prepared by the preparation method of the high-rate lithium iron phosphate positive electrode material according to any one of claims 1 to 8.

10. A battery, characterized in that: The positive electrode material of the battery is the high-rate lithium iron phosphate positive electrode material as described in claim 9.

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