A high-rate lithium iron phosphate cathode material, its preparation method and battery

Abstract

The present invention discloses a high-rate lithium iron phosphate cathode material, a preparation method thereof, and a battery, belonging to the technical field of batteries. The preparation method includes: mixing iron phosphate, a lithium source, a carbon source, and an additive with a solvent, and performing coarse grinding and fine grinding to obtain a mixed slurry; subjecting the mixed slurry to spray drying, sintering in a nitrogen atmosphere, and naturally cooling to room temperature to obtain the high-rate lithium iron phosphate cathode material. Among them, the preparation method of the additive is: treating titanium dioxide with sebacic acid to obtain modified titanium dioxide; treating zirconia with KH550 to obtain modified zirconia; adding the modified titanium dioxide, the modified zirconia, and polyethylene glycol diamine 200 to N,N-dimethylformamide for treatment to obtain a mixture, and performing low-temperature heat treatment, ball milling, and drying to obtain the additive. 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 are well improved, and it has a high discharge specific capacity at 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 electrode material, an electrolyte capable of transferring lithium ions, a separator, and a casing, etc. In a lithium-ion battery, the positive electrode material is an important factor determining its electrochemical performance, safety performance, and future development direction. Lithium iron phosphate (LiFePO4), as a new generation of lithium-ion battery positive electrode 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, and is a good choice for power batteries and energy storage batteries.

[0003] The rate performance is a key consideration index for the lithium iron phosphate cathode material and has an important impact on the performance of the battery for rapid charge and discharge 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 for 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:

[0006] 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 coarsely grind and finely grind to obtain a mixed slurry;

[0007] 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.

[0008] 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.

[0009] Preferably, in Step 1, the additive contains one or more of the elements Ti, Ce, Al, Ni, Zr, and Zn.

[0010] 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 10~20wt% of the mass of iron phosphate; the addition amount of additive is 0.01~1wt% of the mass of iron phosphate; the solid content of the slurry is 20~60wt%.

[0011] Preferably, in the first step, the lithium source is lithium carbonate; the carbon sources are glucose monohydrate and polyethylene glycol 2000.

[0012] 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 8~10wt% of the mass of iron phosphate, and the addition amount of polyethylene glycol 2000 is 5~6wt% of the mass of iron phosphate.

[0013] Preferably, in the first step, the rough grinding time is 0.5~2h, and the fine grinding time is 1~3h.

[0014] 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 5~15h.

[0015] Preferably, the preparation method of the additive in the first step includes the following steps:

[0016] S11. Add sebacic acid to absolute ethanol, stir evenly, then add titanium dioxide, ball-mill and mix, wash with absolute ethanol, and vacuum dry to obtain modified titanium dioxide;

[0017] S12. Add KH550 to an ethanol solution, stir, then add zirconia, heat and stir, filter by suction, wash with absolute ethanol, and vacuum dry to obtain modified zirconia;

[0018] S13. Add the modified titanium dioxide, modified zirconia and polyethylene glycol diamine 200 to N,N-dimethylformamide, ultrasonically disperse, magnetically stir, let stand, filter by suction, wash successively with deionized water and absolute ethanol, and vacuum dry to obtain a mixture;

[0019] S14. Heat-treat the mixture at 150~300°C at low temperature, then ball-mill and vacuum dry to obtain the additive.

[0020] 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 100~500rpm, the time is 1~5h; wash 2~5 times; the vacuum drying temperature is 80°C.

[0021] Preferably, in the step S12, the ethanol solution is an aqueous ethanol 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.

[0022] 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; let stand for 6-18 h; wash 2-5 times; the vacuum drying temperature is 80 °C.

[0023] 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.

[0024] 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.

[0025] A battery, the cathode material of the battery is the high-rate lithium iron phosphate cathode material as described above.

[0026] The present invention has at least the following beneficial effects:

[0027] 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 a high discharge specific capacity is achieved at different rates.

[0028] 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 at the same time has a certain reaction activity, which is beneficial to the doping of elements into the lithium iron phosphate lattice; then performs low-temperature heat treatment and ball milling on the mixed powders, 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.

[0029] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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;

[0031] Figure 2 SEM image of the high-rate lithium iron phosphate cathode material prepared in Example 1;

[0032] Figure 3 Particle size distribution of the high-rate lithium iron phosphate cathode material prepared in Example 1;

[0033] Figure 4 Polarization values of the high-rate lithium iron phosphate cathode material prepared in Example 2 and the commercial lithium iron phosphate in Comparative Example 1 at 15C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] 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.

[0035] 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.

[0036] Example 1

[0037] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0038] Step 1: Mix 10 g of iron phosphate, 2.464 g of 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 to absolute ethanol according to a solid content of 40%, then coarsely grind for 1 h using a sand mill. The median particle size after coarse grinding is 0.564 µm, and then finely grind for 1.5 h. The median particle size after fine grinding is 0.358 µm to obtain a mixed slurry;

[0039] 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 up to 690 °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, denoted as LFP-690.

[0040] Example 2

[0041] A method for preparing a high-rate lithium iron phosphate cathode material, comprising the following steps:

[0042] 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 using a sand mill, and then finely grind for 1.5 h to obtain a mixed slurry;

[0043] 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 up 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, denoted as LFP-700.

[0044] In this example, the sintering temperature is 700 °C, and the other steps are the same as in Example 1.

[0045] Example 3

[0046] A method for preparing a high-rate lithium iron phosphate cathode material, comprising the following steps:

[0047] 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 using a sand mill, and then finely grind for 1.5 h to obtain a mixed slurry;

[0048] 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.

[0049] In this example, the sintering temperature is 710°C, and the other steps are the same as in Example 1.

[0050] Example 4

[0051] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0052] 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 anhydrous 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;

[0053] 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.

[0054] In this example, zirconia is used to replace titanium dioxide, and the other steps are the same as in Example 2.

[0055] Example 5

[0056] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0057] 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 anhydrous 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; wherein, the additive is obtained by mixing titanium dioxide and zirconia in a mass ratio of 2:1;

[0058] 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.

[0059] 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 other steps are the same as in Example 2.

[0060] Example 6

[0061] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0062] 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 anhydrous 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;

[0063] 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 the high-rate lithium iron phosphate cathode material;

[0064] Among them, the preparation method of the additive includes the following steps:

[0065] S11: Add 0.1 g of sebacic acid to 10 g of anhydrous ethanol, stir evenly, then add 10 g of titanium dioxide, ball-mill and mix for 3 h, wash 3 times with anhydrous 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;

[0066] 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 anhydrous ethanol, and dry in vacuum at 80 °C to obtain modified zirconia;

[0067] 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, ultrasonically disperse 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 anhydrous ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture;

[0068] 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 the additive; among them, the specific parameters of the ball milling are: the ball milling medium is anhydrous 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.

[0069] In this example, the additive is used to replace titanium dioxide, and the remaining steps are the same as those in Example 2.

[0070] In this embodiment, first, sebacic acid is used to modify the surface of titanium dioxide powder, and then silane coupling agent KH550 is used to modify the surface of zirconia. The modified titanium dioxide and zirconia powders and polyethylene glycol diamine 200 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 a certain reactivity, which is conducive 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, reactivity 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.

[0071] Example 7

[0072] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0073] 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 anhydrous 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.

[0074] 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 up 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.

[0075] Among them, the preparation method of the additive includes the following steps:

[0076] 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 anhydrous ethanol, and dry in vacuum at 80 °C to obtain modified zirconia.

[0077] 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 anhydrous ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture.

[0078] S13. Heat-treat the mixture under a nitrogen atmosphere at low temperature, raise the temperature 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; wherein, the specific parameters of the ball-milling are as follows: the ball-milling medium is anhydrous 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.

[0079] 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.

[0080] Example 8

[0081] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0082] 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 the additive, add them to anhydrous 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.

[0083] Step 2. Spray-dry (inlet air temperature 240 °C, outlet air temperature 100 °C) the mixed slurry obtained in Step 1 and then sinter it. Under a nitrogen atmosphere, raise the temperature 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 the high-rate lithium iron phosphate cathode material.

[0084] Among them, the preparation method of the additive includes the following steps:

[0085] S11. Add 0.1 g of sebacic acid to 10 g of anhydrous ethanol, stir evenly, then add 10 g of titanium dioxide, ball-mill and mix for 3 h, wash 3 times with anhydrous ethanol, and dry in vacuum at 80 °C to obtain modified titanium dioxide; wherein, the specific parameters of the ball-milling are as follows: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm.

[0086] 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, ultrasonically disperse for 1 h at 300 W and 55 kHz, magnetically stir at 1000 rpm for 2 h, let stand for 12 h, filter by suction, wash 3 times with deionized water and anhydrous ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture.

[0087] S13. Heat-treat the mixture under a nitrogen atmosphere at a low temperature. 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; 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.

[0088] In this example, during the preparation of the additive, the zirconia was not modified, and the remaining steps were the same as those in Example 6.

[0089] Example 9

[0090] A method for preparing a high-rate lithium iron phosphate cathode material includes the following steps:

[0091] 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 the 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;

[0092] 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 naturally cool to room temperature to obtain the high-rate lithium iron phosphate cathode material;

[0093] Among them, the preparation method of the additive includes the following steps:

[0094] 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; 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;

[0095] 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;

[0096] S13. Add 10 g of modified titanium dioxide and 5 g of modified zirconia 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;

[0097] S14. Heat-treat the mixture under a nitrogen atmosphere at a low temperature. Heat it up 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; wherein, the specific parameters of the ball-milling are as follows: 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.

[0098] In this example, in the preparation of the additive, polyethylene glycol diamine 200 was not used, and the remaining steps were the same as in Example 6.

[0099] Example 10

[0100] A preparation method of a high-rate lithium iron phosphate cathode material includes the following steps:

[0101] 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 the 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;

[0102] Step 2. Spray-dry (inlet air temperature 240 °C, outlet air temperature 100 °C) the mixed slurry obtained in Step 1 and then sinter it. Under a nitrogen atmosphere, heat it up to 700 °C at a heating rate of 3 °C / min and hold for 10 h, and naturally cool to room temperature to obtain the high-rate lithium iron phosphate cathode material;

[0103] Among them, the preparation method of the additive includes the following steps:

[0104] 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; wherein, the specific parameters of the ball-milling are as follows: the grinding balls are zirconia balls, the ball-to-material ratio is 8:1, and the rotation speed is 200 rpm;

[0105] 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, carry out suction filtration, wash 3 times with absolute ethanol, and dry in vacuum at 80 °C to obtain modified zirconia;

[0106] 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, ultrasonically disperse at 300 W and 55 kHz for 1 h, magnetically stir at 1000 rpm for 2 h, let stand for 12 h, carry out suction filtration, wash 3 times with deionized water and absolute ethanol respectively, and dry in vacuum at 80 °C to obtain a mixture;

[0107] S14. The mixture was ball-milled for 2 h and dried in vacuum at 80 °C to obtain the additive. Among them, the specific parameters of the ball milling were as follows: the ball milling medium was anhydrous ethanol, the solid-liquid ratio was 1:1.2, the grinding balls were zirconia balls, the ball-to-material ratio was 8:1, and the rotation speed was 400 rpm.

[0108] In this example, in the preparation of the additive, low-temperature heat treatment was not carried out, and the remaining steps were the same as those in Example 6.

[0109] Comparative Example 1

[0110] Commercial lithium iron phosphate, denoted as LFP-SY.

[0111] Figure 1 XRD patterns of the high-rate lithium iron phosphate cathode materials prepared in Examples 1-3 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 in 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.

[0112] Figure 2 SEM image of the high-rate lithium iron phosphate cathode material prepared in Example 1. The particle size of the material was subjected to a normal distribution, and the maximum particle size normal distribution of this material was 10.15 μm ( Figure 3 )

[0113] Electrochemical tests were carried out on the high-rate lithium iron phosphate cathode materials prepared in Examples 1-8 and the commercial lithium iron phosphate in Comparative Example 1: The obtained lithium iron phosphate cathode material, acetylene black, and polyvinylidene fluoride were dissolved in an appropriate amount of N-methylpyrrolidone solvent in a mass ratio of 8:1:1 to form a uniform slurry, which was coated on an aluminum foil. After vacuum drying, it was cut into electrode sheets with a diameter of 14 mm, and the areal density was 8 mg / cm 2 ; A metallic lithium sheet was used as the anode; the separator was an imported polypropylene microporous membrane (Celgard 2400); the electrolyte was a 1 mol / L LiPF6 solution, and its solvent was a mixed solution of ethylene carbonate (EC):dimethyl carbonate (DMC) with a volume ratio of 1:1; a button cell (CR2032) was assembled in a glove box filled with nitrogen, and then the assembled battery was subjected to charge-discharge tests on a Neware battery test system.

[0114] The 0.1C first charge specific capacity (0.1CC), 0.1C first discharge specific capacity (0.1CD), first Coulombic efficiency (0.1CD / 0.1CC*100%), and discharge specific capacities at 1C, 5C, and 15C rates of the lithium iron phosphates in Examples 1-3 and Comparative Example 1 are shown in Table 1; Figure 4 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.

[0115] Table 1

[0116]

[0117] 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 well improved; 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 is 789.4 mV at 15C, 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.

[0118] The test results of the electrochemical performance of the high-rate lithium iron phosphate cathode materials prepared in Examples 4 to 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 to 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.

[0119] Table 2

[0120]

[0121] Although the embodiments of the present invention have been disclosed as above, they are 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 illustrated examples here.

Claims

1. A preparation method of a high-rate lithium iron phosphate cathode material, characterized in that It includes the following steps: Step 1: Mix ferric phosphate, lithium source, carbon source and additive, then mix with a solvent to form a slurry, and then conduct rough grinding and fine grinding to obtain a mixed slurry; Step 2: Spray-dry the mixed slurry obtained in Step 1, sinter it under a nitrogen atmosphere, and naturally cool it to room temperature to obtain a high-rate lithium iron phosphate cathode material; The preparation method of the additive includes the following steps: S11: Add sebacic acid to absolute ethanol, stir evenly, then add titanium dioxide, conduct ball milling and mixing, wash with absolute ethanol, and vacuum dry to obtain modified titanium dioxide; S12: Add KH550 to an ethanol solution, stir, then add zirconia, heat and stir, conduct suction filtration, wash with absolute ethanol, and vacuum dry to obtain modified zirconia; S13: Add the modified titanium dioxide, modified zirconia and polyethylene glycol diamine 200 to N,N-dimethylformamide, conduct ultrasonic dispersion, magnetic stirring, let it stand, conduct suction filtration, wash successively with deionized water and absolute ethanol, and vacuum dry to obtain a mixture; S14: Conduct low-temperature heat treatment on the mixture at 150-300°C, then conduct ball milling and vacuum drying to obtain the additive.

2. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, wherein In the said 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 absolute ethanol or deionized water.

3. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In the said Step 1, in ferric phosphate and the lithium source, the molar ratio of lithium element to phosphorus element is 1-1.1:1; the addition amount of the carbon source is 10-20 wt% of the mass of ferric phosphate; the addition amount of the additive is 0.01-1 wt% of the mass of ferric phosphate; the solid content of the slurry is 20-60 wt%; the rough grinding time is 0.5-2 h, and the fine grinding time is 1-3 h.

4. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In the said S11, the mass ratio of sebacic acid, titanium dioxide and absolute ethanol is 0.05-0.2:10:8-12; the specific parameters of the 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.

5. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In the said 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.

6. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, In the said S13, the mass ratio of the modified titanium dioxide, modified zirconia and 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 the ultrasonic dispersion is 200-400 W, the frequency is 50-70 kHz, and the time is 0.5-2 h; the magnetic stirring rotation speed is 800-1200 rpm, and the time is 1-5 h; let it stand for 6-18 h; wash 2-5 times; the vacuum drying temperature is 80°C.

7. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that In S14, the low-temperature heat treatment is specifically as follows: under a nitrogen atmosphere, the temperature is raised to 150-300°C at a heating rate of 1-5°C / min and held for 1-3 h; the specific parameters of ball milling are as follows: the ball milling medium is absolute 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 300-800 rpm, and the time is 1-5 h.

8. The preparation method of a high-rate lithium iron phosphate cathode material according to claim 1, characterized in that, 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.

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

10. A battery, characterized in that, The cathode material of the battery is the high-rate lithium iron phosphate cathode material according to claim 9.

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