Preparation method and application of iron phosphate material

Abstract

The invention provides a lithium iron phosphate material preparation method, which comprises: mixing a first iron source, a first phosphorus source, a first lithium source, a first dopant, a first carbon source and deionized water, and carrying out first wet grinding, first spray drying, first sintering and first crushing to obtain a first lithium iron phosphate intermediate; mixing a second iron source, a second phosphorus source, a second lithium source, a second dopant, a second carbon source and deionized water, and performing second wet grinding, second spray drying, second sintering and second crushing to obtain a second lithium iron phosphate intermediate; and mixing the second lithium iron phosphate intermediate, a third carbon source and deionized water, carrying out third wet grinding, adding the first lithium iron phosphate intermediate, uniformly mixing, and carrying out third spray drying, third sintering and third crushing to obtain the lithium iron phosphate material, the compaction density of the material is high, and the electrochemical performance of the lithium iron phosphate material further serving as a battery positive electrode material is good. The invention also provides a lithium iron phosphate material and a lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and more specifically, to a method for preparing an iron phosphate material, a lithium iron phosphate material, and applications of the lithium iron phosphate material. Background Art

[0002] As the representative of secondary batteries with the best comprehensive performance, the commercialization of lithium-ion batteries can be traced back to the 1990s. After years of research, lithium iron phosphate cathode materials have become a technical route with better performance in the field of lithium-ion batteries. Lithium iron phosphate has excellent electrochemical properties. As the cathode material of lithium-ion secondary batteries, it has the advantages of high specific capacity, excellent cycle performance, good high-temperature charge and discharge performance, wide source of raw materials, no environmental pollution, good thermal stability of materials, and outstanding safety performance of the prepared batteries, which makes it have great market prospects in various mobile power fields, especially in the field of electric vehicle power batteries.

[0003] A method commonly used to prepare lithium iron phosphate materials, using a two-step sintering process, wet-mixing iron phosphate, lithium carbonate, a dopant and a carbon source in proportion, grinding them to a certain particle size and then spray-drying and sintering them for the first time, coarsely crushing them after sintering and then sintering them for the second time, and finally pulverizing them to obtain an ultra-high-pressure compacted lithium iron phosphate positive electrode material.

[0004] However, this preparation process has certain limitations. It has high requirements for iron phosphate raw materials, high purity and low impurity content, and high requirements for particle morphology; the uniformity and stability during secondary sintering are poor, and the compaction and capacity fluctuations are large; during secondary sintering, the particles grow as a whole and there are some abnormally large particles, and the carbon coating is affected. The electrochemical performance is general and needs to be improved. Summary of the invention

[0005] In view of the above, the present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing an iron phosphate material and its application, wherein two different groups of lithium iron phosphate intermediates are prepared by a primary sintering, and then the two groups of lithium iron phosphate intermediates are mixed and sintered for a secondary sintering to obtain a high-density lithium iron phosphate material. The process has low requirements for raw materials, and the particle size and shape of the two groups of lithium iron phosphate intermediates are different, which can form a good grading effect in the secondary sintering. The prepared lithium iron phosphate material has the characteristics of high compaction density and good electrochemical performance. At the same time, the preparation method of the iron phosphate material has a simple process flow and is suitable for application in large-scale industrial production.

[0006] To this end, in a first aspect, an embodiment of the present invention provides a method for preparing a lithium iron phosphate material, the preparation method comprising:

[0007] S10, mixing a first iron source, a first phosphorus source, a first lithium source, a first dopant, a first carbon source and deionized water in a certain proportion, and obtaining a first lithium iron phosphate intermediate by first wet grinding, first spray drying, first sintering and first crushing;

[0008] S20, mixing a second iron source, a second phosphorus source, a second lithium source, a second dopant, a second carbon source and deionized water in a certain proportion, and obtaining a second lithium iron phosphate intermediate by a second wet grinding, a second spray drying, a second sintering and a second crushing; and

[0009] S30, mixing the second lithium iron phosphate intermediate, the third carbon source and deionized water in a certain proportion, performing a third wet grinding, adding the first lithium iron phosphate intermediate, mixing evenly, performing a third spray drying, a third sintering and a third pulverizing to obtain a lithium iron phosphate material.

[0010] Preferably, the addition ratio of the first iron source, the first phosphorus source, and the first lithium source is the same as the addition ratio of the second iron source, the second phosphorus source, and the second lithium source; and / or,

[0011] The addition ratio of the first dopant is smaller than the addition ratio of the second dopant; and / or,

[0012] The addition ratio of the first carbon source is greater than the addition ratio of the second carbon source; and / or,

[0013] The sintering temperature of the first sintering is higher than the sintering temperature of the second sintering; and / or,

[0014] The particle size of the first wet grinding is the same as the particle size of the second wet grinding, and the particle size of the third wet grinding is smaller than the particle size of the first wet grinding; and / or,

[0015] The particle size of the first pulverized particles is the same as that of the second pulverized particles, and the particle size of the third pulverized particles is smaller than that of the first pulverized particles.

[0016] Preferably, the first iron source and the second iron source respectively include at least one of ferric phosphate, ferric oxide, ferrous phosphate, and hydroxyferric phosphate; and / or,

[0017] The first phosphorus source and the second phosphorus source respectively include at least one of ferric phosphate, ferrous phosphate, hydroxyferric phosphate, diammonium phosphate, phosphoric acid, and lithium phosphate; and / or,

[0018] The first lithium source and the second lithium source respectively include at least one of lithium carbonate, lithium hydroxide and lithium phosphate; and / or,

[0019] The addition ratios of the first iron source, the first phosphorus source, and the first lithium source and the addition ratios of the second iron source, the second phosphorus source, and the second lithium source respectively satisfy an iron-phosphorus molar ratio Fe:P of 0.96-0.99 and a lithium-iron molar ratio Li:Fe of 1.02-1.05.

[0020] Preferably, the first dopant comprises a compound of at least one of Ti, V, Nb and Mn; and / or,

[0021] The molar ratio of the added amount of the first dopant relative to iron is 0-1.0%; and / or,

[0022] The second dopant includes a compound of at least one of Ti, V, Nb, and Mn; and / or,

[0023] The molar ratio of the added amount of the second dopant relative to iron is 1.0%-3.0%.

[0024] Preferably, the first carbon source comprises at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and / or,

[0025] The amount of the first carbon source added satisfies that the carbon content of the lithium iron phosphate material is between 0.5wt% and 0.8wt%; and / or,

[0026] The second carbon source comprises at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and / or,

[0027] The added amount of the second carbon source satisfies that the carbon content of the lithium iron phosphate material is 0.1wt%-0.4wt%.

[0028] Preferably, in step S10, a sintering aid is added and mixed evenly before spray drying, and the sintering aid includes at least one of phosphoric acid, boric acid, and magnesium oxide; and / or,

[0029] The sintering temperature of the first sintering is 700° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or,

[0030] The sintering temperature of the second sintering is 500° C.-600° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or,

[0031] The particle size D50 of the first wet grinding and the second wet grinding is 0.2 μm-0.6 μm; and / or,

[0032] The particle size D50 of the third wet grinding is 0.2 μm-0.4 μm; and / or,

[0033] The particle size D50 of the first crushing and the second crushing is 1 μm-2 μm, and D99≤20 μm; and / or,

[0034] The particle size of the third crushing is D10≥0.35μm, D50 is 1μm-2μm, and D99≤10μm.

[0035] Preferably, in step S30, a third lithium source is further added to mix with the second lithium iron phosphate intermediate; the amount of the third lithium source added satisfies the molar ratio of the lithium iron phosphate material to be 0-2%; and / or,

[0036] The amount of the third carbon source added satisfies that the carbon content of the lithium iron phosphate material is between 1.1wt% and 1.5wt%; and / or,

[0037] In the step S30, the mass ratio of the added amount of the first lithium iron phosphate intermediate to the second lithium iron phosphate intermediate is 8:2-5:5; and / or,

[0038] The sintering temperature of the third sintering is 750° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or,

[0039] The inlet air temperature of the first spray drying, the second spray drying and the third spray drying is 220°C-280°C, and the outlet air temperature is 90°C-110°C.

[0040] Preferably, the first sintering, the second sintering and the third sintering are performed under a rare gas atmosphere; more preferably, the rare gas atmosphere is a nitrogen atmosphere.

[0041] In a second aspect, an embodiment of the present invention further provides a lithium iron phosphate material, wherein the lithium iron phosphate material is prepared by the preparation method described in the first aspect.

[0042] In a third aspect, an embodiment of the present invention further provides a lithium-ion battery, comprising: a battery positive electrode made of the lithium iron phosphate material described in the second aspect.

[0043] The present invention proposes a preparation method and application of an iron phosphate material. The preparation process has low requirements on iron source and phosphorus source materials. A lithium iron phosphate intermediate is used to replace the iron source, phosphorus source and lithium source of the traditional process. The prepared lithium iron phosphate material has better capacity and rate performance when used as a positive electrode material of a battery. The first lithium iron phosphate intermediate sintered at a relatively high temperature and the large particle material subsequently produced therefrom are in an incompletely fused polycrystalline state, which improves the electrochemical performance of the material. The particle size and morphology of the first lithium iron phosphate intermediate and the second lithium iron phosphate intermediate are quite different. After secondary grinding, mixing and sintering, they can form a good gradation correspondingly and obtain a high compaction density, so that the prepared lithium iron phosphate material has high physical and electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of a method for preparing an iron phosphate material provided in one embodiment of the present invention;

[0045] Figure 2 This is a SEM image of the lithium iron phosphate material prepared in Example 1 of the present invention;

[0046] Figure 3 This is a SEM image of the lithium iron phosphate material prepared in Comparative Example 1 of the present invention;

[0047] Figure 4 This is a SEM image of the lithium iron phosphate material prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0048] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0049] The disclosure below provides many different embodiments or examples to implement different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or letters in different examples. This repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific processes and examples of materials, but those of ordinary skill in the art can be aware of the applicability of other processes and / or the use of other materials.

[0050] Please refer to Figure 1In a first aspect, an embodiment of the present invention provides a method for preparing a lithium iron phosphate material, which can be used as a positive electrode material to prepare a positive electrode of a lithium ion battery. The preparation method comprises:

[0051] S10, mixing a first iron source, a first phosphorus source, a first lithium source, a first dopant, a first carbon source and deionized water in a certain proportion, and obtaining a first lithium iron phosphate intermediate by first wet grinding, first spray drying, first sintering and first crushing;

[0052] S20, mixing a second iron source, a second phosphorus source, a second lithium source, a second dopant, a second carbon source and deionized water in a certain proportion, and obtaining a second lithium iron phosphate intermediate by a second wet grinding, a second spray drying, a second sintering and a second crushing; and

[0053] S30, mixing the second lithium iron phosphate intermediate, the third carbon source and deionized water in a certain proportion, performing a third wet grinding, adding the first lithium iron phosphate intermediate, mixing evenly, performing a third spray drying, a third sintering and a third pulverizing to obtain a lithium iron phosphate material.

[0054] Furthermore, the addition ratio of the first iron source, the first phosphorus source, and the first lithium source is the same as the addition ratio of the second iron source, the second phosphorus source, and the second lithium source.

[0055] Furthermore, the addition ratio of the first dopant is smaller than the addition ratio of the second dopant.

[0056] Furthermore, the addition ratio of the first carbon source is greater than the addition ratio of the second carbon source.

[0057] Furthermore, the sintering temperature of the first sintering is higher than the sintering temperature of the second sintering.

[0058] Further, the particle size of the first wet grinding is the same as the particle size of the second wet grinding, and the particle size of the third wet grinding is smaller than the particle size of the first wet grinding.

[0059] Furthermore, the particle size of the first crushing is the same as the particle size of the second crushing, and the particle size of the third crushing is smaller than the particle size of the first crushing.

[0060] Furthermore, the first iron source and the second iron source respectively include at least one of ferric phosphate, ferric oxide, ferrous phosphate, and hydroxyferric phosphate.

[0061] Furthermore, the first phosphorus source and the second phosphorus source respectively include at least one of ferric phosphate, ferrous phosphate, hydroxyferric phosphate, diammonium phosphate, phosphoric acid, and lithium phosphate.

[0062] Furthermore, the first lithium source and the second lithium source respectively include at least one of lithium carbonate, lithium hydroxide, and lithium phosphate.

[0063] Furthermore, the addition ratio of the first iron source, the first phosphorus source, and the first lithium source, and the addition ratio of the second iron source, the second phosphorus source, and the second lithium source respectively satisfy the iron-phosphorus molar ratio Fe:P of 0.96-0.99 and the lithium-iron molar ratio Li:Fe of 1.02-1.05.

[0064] Furthermore, the first dopant includes a compound of at least one of Ti, V, Nb, and Mn.

[0065] Furthermore, the molar ratio of the added amount of the first dopant relative to iron is 0-1.0%.

[0066] Furthermore, the second dopant includes a compound of at least one of Ti, V, Nb, and Mn.

[0067] Furthermore, the molar ratio of the added amount of the second dopant relative to iron is 1.0%-3.0%.

[0068] Furthermore, the first carbon source includes at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol.

[0069] Furthermore, the added amount of the first carbon source satisfies that the carbon content of the lithium iron phosphate material is 0.5wt%-0.8wt%.

[0070] Furthermore, the second carbon source includes at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol.

[0071] Furthermore, the added amount of the second carbon source satisfies that the carbon content of the lithium iron phosphate material is 0.1wt%-0.4wt%.

[0072] Furthermore, in the step S10, a sintering aid is added and mixed evenly before spray drying, and the sintering aid includes at least one of phosphoric acid, boric acid, and magnesium oxide.

[0073] Furthermore, the sintering temperature of the first sintering is 700° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa.

[0074] Furthermore, the sintering temperature of the second sintering is 500° C.-600° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa.

[0075] Furthermore, the particle size D50 of the first wet grinding and the second wet grinding is 0.2 μm-0.6 μm.

[0076] Furthermore, the particle size D50 of the third wet grinding is 0.2 μm-0.4 μm.

[0077] Furthermore, the particle size D50 of the first crushing and the second crushing is 1 μm-2 μm, and D99≤20 μm.

[0078] Furthermore, the particle size of the third crushing is D10≥0.35μm, D50 is 1μm-2μm, and D99≤10μm.

[0079] Furthermore, in the step S30, a third lithium source is added to mix with the second lithium iron phosphate intermediate; the amount of the third lithium source added is such that the molar ratio of the lithium iron phosphate material is 0-2%.

[0080] Furthermore, the added amount of the third carbon source satisfies that the carbon content of the lithium iron phosphate material is between 1.1wt% and 1.5wt%.

[0081] Furthermore, in the step S30, the mass ratio of the added amount of the first lithium iron phosphate intermediate to the second lithium iron phosphate intermediate is 8:2-5:5.

[0082] Furthermore, the sintering temperature of the third sintering is 750° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa.

[0083] Furthermore, the air inlet temperature of the first spray drying, the second spray drying and the third spray drying is 220°C-280°C, and the air outlet temperature is 90°C-110°C.

[0084] Furthermore, the first sintering, the second sintering, and the third sintering are performed under a rare atmosphere; preferably, the rare atmosphere is a nitrogen atmosphere.

[0085] The specific process and effect of the preparation method of the lithium iron phosphate positive electrode material of the present invention are further described in detail below in combination with some specific embodiments, but are not limited to the protection scope of the present invention.

[0086] Example 1

[0087] The high-density lithium iron phosphate material is prepared, and the specific steps include:

[0088] 1. According to the Fe / P (molar ratio) of 0.970, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.007, and carbon content of 0.6%, weigh 1000 g of anhydrous iron phosphate precursor, 252.4 g of lithium carbonate, 60 g of glucose, 10 g of polyethylene glycol, and 4.0 g of titanium dioxide;

[0089] 2. Stir and disperse the weighed materials first, use deionized water as solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.35μm;

[0090] 3. Add 0.3% phosphoric acid relative to the weight of the iron phosphate precursor in step 1 to the ground slurry, stir and mix for 60 minutes, and then spray dry, controlling the inlet air temperature at 220°C and the outlet air temperature at 100°C;

[0091] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen, and the pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 780℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is crushed with a small air flow mill, and the equipment parameters are adjusted to control the particle size D50: about 1.3μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0092] 5. The second Fe source, P source, Li source and other materials are weighed according to Fe / P: 0.97, Li / Fe: 1.05, dopant / Fe is 0.02, and the carbon content is 0.2%. 1000g of anhydrous iron phosphate precursor, 252.4g of lithium carbonate, 30g of glucose, 20g of polyethylene glycol, and 11.4g of titanium dioxide;

[0093] 6. Stir and disperse the material weighed in step 5, use deionized water as solvent, control the solid content to 40%, stir and disperse in ball mill for 30 minutes, then transfer to sand mill for grinding, and finally control the grinding particle size D50 to about 0.35 μm. Spray dry the ground slurry, and control the inlet air temperature to 220°C and the outlet air temperature to 100°C;

[0094] 7. The sprayed material in step 6 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 550°C and 6 hours. After sintering, the temperature naturally drops to below 80°C and the sintered material is taken out of the furnace. The obtained sintered material is lithium iron phosphate semi-finished product B;

[0095] 8. According to the weight ratio of lithium iron phosphate semi-finished product A to lithium iron phosphate semi-finished product B of 6:4, the carbon content of the final product is 1.35%, and the 1% mol Li source relative to the total amount of lithium iron phosphate semi-finished products A and B, weigh 600g of lithium iron phosphate semi-finished product A, 400g of lithium iron phosphate semi-finished product B, 2.3g of lithium carbonate, 35g of glucose, and 40g of polyethylene glycol; stir and disperse the weighed materials (lithium iron phosphate semi-finished product A is not added in this step), use deionized water as solvent, control the solid content to 40%, stir and disperse with ball mill for 30 minutes, and then transfer to a sand mill for grinding, and finally control the grinding particle size D50 to be about 0.25μm;

[0096] 9. Add the lithium iron phosphate semi-finished product A weighed in step 8, deionized water (control the final solid content to be about 40%) and thickener (0.5% relative to the mass of the slurry) to the slurry ground in step 8, and perform ball milling and stirring. After the slurry is ball milled and stirred, the particle size D99 is controlled to be about 8 μm, and then spray drying is performed. The air inlet temperature is controlled to be 220° C. and the air outlet temperature is controlled to be 100° C.;

[0097] 10. The sprayed material in step 9 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 770°C and 8 hours. After sintering, the temperature naturally drops to below 80°C and the furnace is taken out of the furnace;

[0098] 11. The sintered material obtained in step 10 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0099] The SEM image of the prepared iron phosphate material is shown in Figure 2 As shown by Figure 2 It can be seen that the prepared iron phosphate material has large polycrystalline particles and small particles tightly combined with the large particles, and there are very few gaps between the materials.

[0100] Example 2

[0101] The high-density lithium iron phosphate material is prepared, and the specific steps include:

[0102] 1. According to the Fe / P (molar ratio) of 0.970, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.010, and carbon content of 0.6%, weigh 1000g of anhydrous iron phosphate precursor, 252.4g of lithium carbonate, 60g of glucose, 10g of polyethylene glycol, and 5.7g of titanium dioxide;

[0103] 2. Stir and disperse the weighed materials first, use deionized water as solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.40μm;

[0104] 3. Add 0.3% phosphoric acid relative to the weight of the iron phosphate precursor in step 1 to the ground slurry, stir and mix for 60 minutes, and then spray dry, controlling the inlet air temperature at 220°C and the outlet air temperature at 100°C;

[0105] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 780℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is crushed with a small air flow mill. The equipment parameters are adjusted to control the particle size D50: about 1.3μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0106] 5. The second Fe source, P source, Li source and other materials are weighed according to Fe / P: 0.97, Li / Fe: 1.05, dopant / Fe is 0.03, and the carbon content is 0.3%. 1000g of anhydrous iron phosphate precursor, 252.4g of lithium carbonate, 40g of glucose, 20g of polyethylene glycol, and 17.1g of titanium dioxide;

[0107] 6. Stir and disperse the material weighed in step 5, use deionized water as solvent, control the solid content to 40%, stir and disperse in ball mill for 30 minutes, then transfer to sand mill for grinding, and finally control the grinding particle size D50 to about 0.30 μm. Spray dry the ground slurry, and control the inlet air temperature to 220°C and the outlet air temperature to 100°C;

[0108] 7. The sprayed material in step 6 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 550°C and 6 hours. After sintering, the temperature naturally drops to below 80°C and the sintered material is taken out of the furnace. The obtained sintered material is lithium iron phosphate semi-finished product B;

[0109] 8. According to the weight ratio of lithium iron phosphate semi-finished product A to lithium iron phosphate semi-finished product B of 7:3, the carbon content of the final product is 1.35%, and the 1% mol Li source relative to the total amount of lithium iron phosphate semi-finished products A and B, weigh 700g of lithium iron phosphate semi-finished product A, 300g of lithium iron phosphate semi-finished product B, 2.3g of lithium carbonate, 35g of glucose, and 40g of polyethylene glycol; stir and disperse the weighed materials (lithium iron phosphate semi-finished product A is not added in this step), use deionized water as solvent, control the solid content to 40%, stir and disperse with ball mill for 30 minutes, and then transfer to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.25μm;

[0110] 9. Add the lithium iron phosphate semi-finished product A weighed in step 8, deionized water (control the final solid content to be about 40%) and thickener (0.5% relative to the mass of the slurry) to the slurry ground in step 8, and perform ball milling and stirring. Control the particle size D99 of the slurry after ball milling and stirring to be about 9 μm, and then perform spray drying. Control the inlet air temperature to 220° C. and the outlet air temperature to 100° C.;

[0111] 10. The sprayed material in step 9 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 770°C and 8 hours. After sintering, the temperature naturally drops to below 80°C and the furnace is taken out of the furnace;

[0112] 11. The sintered material obtained in step 10 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0113] Example 3

[0114] The high-density lithium iron phosphate material is prepared, and the specific steps include:

[0115] 1. According to the Fe / P (molar ratio) of 0.965, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.007, and carbon content of 0.5%, 770 g of anhydrous ferrous phosphate precursor, 251.3 g of lithium phosphate, 13.5 g of diammonium phosphate, 50 g of glucose, 10 g of polyethylene glycol, and 4.0 g of titanium dioxide were weighed;

[0116] 2. Stir and disperse the weighed materials first, use deionized water as solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.50μm;

[0117] 3. Add 0.2% phosphoric acid relative to the weight of the iron phosphate precursor in step 1 to the ground slurry, stir and mix for 60 minutes, and then spray dry, controlling the inlet air temperature at 220°C and the outlet air temperature at 100°C;

[0118] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 780℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is crushed with a small air flow mill. The equipment parameters are adjusted to control the particle size D50: about 1.3μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0119] 5. The second Fe source, P source, Li source and other materials were weighed according to Fe / P: 0.98, Li / Fe: 1.05, dopant / Fe was 0.015, and the carbon content was 0.2%. 770g of anhydrous ferrous phosphate precursor, 251.3g of lithium phosphate, 7.2g of diammonium phosphate, 30g of glucose, 20g of polyethylene glycol, and 8.5g of titanium dioxide;

[0120] 6. Stir and disperse the material weighed in step 5, use deionized water as solvent, control the solid content to 40%, stir and disperse in ball mill for 30 minutes, then transfer to sand mill for grinding, and finally control the grinding particle size D50 to about 0.50 μm. Spray dry the ground slurry, and control the inlet air temperature to 220°C and the outlet air temperature to 100°C;

[0121] 7. The sprayed material in step 6 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 570°C and 6 hours. After sintering, the temperature naturally drops to below 80°C and the sintered material is taken out of the furnace. The obtained sintered material is lithium iron phosphate semi-finished product B;

[0122] 8. According to the weight ratio of lithium iron phosphate semi-finished product A to lithium iron phosphate semi-finished product B of 5.5:4.5, the carbon content of the final product is 1.35%, and the 1% mol Li source relative to the total amount of lithium iron phosphate semi-finished products A and B, weigh 700g of lithium iron phosphate semi-finished product A, 300g of lithium iron phosphate semi-finished product B, 2.3g of lithium carbonate, 35g of glucose, and 40g of polyethylene glycol; stir and disperse the weighed materials (lithium iron phosphate semi-finished product A is not added in this step), use deionized water as solvent, control the solid content to 40%, stir and disperse with ball mill for 30 minutes, and then transfer to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.25μm;

[0123] 9. Add the lithium iron phosphate semi-finished product A weighed in step 8, deionized water (control the final solid content to be about 40%) and thickener (0.5% relative to the mass of the slurry) to the slurry ground in step 8, and perform ball milling and stirring. After the slurry is ball milled and stirred, the particle size D99 is controlled to be about 8 μm, and then spray drying is performed. The air inlet temperature is controlled to be 220° C. and the air outlet temperature is controlled to be 100° C.;

[0124] 10. The sprayed material in step 9 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 770°C and 8 hours. After sintering, the temperature naturally drops to below 80°C and the furnace is taken out of the furnace;

[0125] 11. The sintered material obtained in step 10 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0126] Example 4

[0127] The high-density lithium iron phosphate material is prepared, and the specific steps include:

[0128] 1. According to the Fe / P (molar ratio) of 0.965, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.010, and carbon content of 0.6%, 850 g of hydroxyferric phosphate precursor, 251.3 g of lithium phosphate, 13.5 g of diammonium phosphate, 60 g of glucose, 10 g of polyethylene glycol, and 5.7 g of titanium dioxide were weighed;

[0129] 2. Stir and disperse the weighed materials first, use deionized water as the solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.60μm;

[0130] 3. Add 0.2% phosphoric acid relative to the weight of the iron phosphate precursor in step 1 to the ground slurry, stir and mix for 60 minutes, and then spray dry, controlling the inlet air temperature at 220°C and the outlet air temperature at 100°C;

[0131] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 780℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is crushed with a small air flow mill. The equipment parameters are adjusted to control the particle size D50: about 1.3μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0132] 5. The second Fe source, P source, Li source and other materials were weighed according to Fe / P: 0.975, Li / Fe: 1.05, dopant / Fe was 0.025, and the carbon content was 0.3%. 850g of hydroxyferric phosphate precursor, 251.3g of lithium phosphate, 9.0g of diammonium phosphate, 40g of glucose, 20g of polyethylene glycol, and 14.3g of titanium dioxide;

[0133] 6. Stir and disperse the material weighed in step 5, use deionized water as solvent, control the solid content to 40%, stir and disperse in ball mill for 30 minutes, then transfer to sand mill for grinding, and finally control the grinding particle size D50 to about 0.60 μm. Spray dry the ground slurry, and control the inlet air temperature to 220°C and the outlet air temperature to 100°C;

[0134] 7. The sprayed material in step 6 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 600°C and 6 hours. After sintering, the temperature naturally drops to below 80°C and the sintered material is taken out of the furnace. The obtained sintered material is lithium iron phosphate semi-finished product B;

[0135] 8. According to the weight ratio of lithium iron phosphate semi-finished product A to lithium iron phosphate semi-finished product B of 5.5:4.5, the carbon content of the final product is 1.35%, and the 1% mol Li source relative to the total amount of lithium iron phosphate semi-finished products A and B, weigh 700g of lithium iron phosphate semi-finished product A, 300g of lithium iron phosphate semi-finished product B, 2.3g of lithium carbonate, 35g of glucose, and 40g of polyethylene glycol; stir and disperse the weighed materials (lithium iron phosphate semi-finished product A is not added in this step), use deionized water as solvent, control the solid content to 40%, stir and disperse with ball mill for 30 minutes, and then transfer to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.25μm;

[0136] 9. Add the lithium iron phosphate semi-finished product A weighed in step 8, deionized water (control the final solid content to be about 40%) and thickener (0.5% relative to the mass of the slurry) to the slurry ground in step 8, and perform ball milling and stirring. After the slurry is ball milled and stirred, the particle size D99 is controlled to be about 8 μm, and then spray drying is performed. The air inlet temperature is controlled to be 220° C. and the air outlet temperature is controlled to be 100° C.;

[0137] 10. The sprayed material in step 9 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 770°C and 8 hours. After sintering, the temperature naturally drops to below 80°C and the furnace is taken out of the furnace;

[0138] 11. The sintered material obtained in step 10 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0139] Example 5

[0140] The high-density lithium iron phosphate material is prepared, and the specific steps include:

[0141] 1. According to the Fe / P (molar ratio) of 0.965, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.010, and carbon content of 0.6%, 850 g of hydroxyferric phosphate precursor, 251.3 g of lithium phosphate, 13.5 g of diammonium phosphate, 60 g of glucose, 10 g of polyethylene glycol, and 8.2 g of manganese carbonate were weighed;

[0142] 2. Stir and disperse the weighed materials first, use deionized water as the solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.60μm;

[0143] 3. Add 0.2% phosphoric acid relative to the weight of the iron phosphate precursor in step 1 to the ground slurry, stir and mix for 60 minutes, and then spray dry, controlling the inlet air temperature at 220°C and the outlet air temperature at 100°C;

[0144] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen, and the pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 780℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is crushed with a small air flow mill, and the equipment parameters are adjusted to control the particle size D50: about 1.3μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0145] 5. The second Fe source, P source, Li source and other materials were weighed according to Fe / P: 0.975, Li / Fe: 1.05, dopant / Fe was 0.025, and the carbon content was 0.3%. 850g of hydroxyferric phosphate precursor, 251.3g of lithium phosphate, 9.0g of diammonium phosphate, 40g of glucose, 20g of polyethylene glycol, and 20.6g of manganese carbonate were taken;

[0146] 6. Stir and disperse the material weighed in step 5, use deionized water as solvent, control the solid content to 40%, stir and disperse in ball mill for 30 minutes, then transfer to sand mill for grinding, and finally control the grinding particle size D50 to about 0.60 μm. Spray dry the ground slurry, and control the inlet air temperature to 220°C and the outlet air temperature to 100°C;

[0147] 7. The sprayed material in step 6 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 600°C and 6 hours. After sintering, the temperature naturally drops to below 80°C and the sintered material is taken out of the furnace. The obtained sintered material is lithium iron phosphate semi-finished product B;

[0148] 8. According to the weight ratio of lithium iron phosphate semi-finished product A to lithium iron phosphate semi-finished product B of 5.5:4.5, the carbon content of the final product is 1.35%, and the 1% mol Li source relative to the total amount of lithium iron phosphate semi-finished products A and B, weigh 700g of lithium iron phosphate semi-finished product A, 300g of lithium iron phosphate semi-finished product B, 2.3g of lithium carbonate, 35g of glucose, and 40g of polyethylene glycol; stir and disperse the weighed materials (lithium iron phosphate semi-finished product A is not added in this step), use deionized water as solvent, control the solid content to 40%, stir and disperse with ball mill for 30 minutes, and then transfer to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.25μm;

[0149] 9. Add the lithium iron phosphate semi-finished product A weighed in step 8, deionized water (control the final solid content to be about 40%) and thickener (0.5% relative to the mass of the slurry) to the slurry ground in step 8, and perform ball milling and stirring. After the slurry is ball milled and stirred, the particle size D99 is controlled to be about 8 μm, and then spray drying is performed. The air inlet temperature is controlled to be 220° C. and the air outlet temperature is controlled to be 100° C.;

[0150] 10. The sprayed material in step 9 is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100 Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5°C / min. The sintering temperature and time are set to 770°C and 8 hours. After sintering, the temperature naturally drops to below 80°C and the furnace is taken out of the furnace;

[0151] 11. The sintered material obtained in step 10 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0152] Comparative Example 1

[0153] On the basis of Example 1, during the preparation of lithium iron phosphate semi-finished product A, the carbon content was controlled to 0.2%, and no solvent was added to the slurry after grinding. The sintering temperature was 800° C., and the remaining steps and methods were the same as in Example 1.

[0154] The SEM image of the prepared iron phosphate material is shown in Figure 3 As shown by Figure 3 It can be seen that the prepared iron phosphate material has large particles of single crystal material and small particles combined with the large particles.

[0155] Comparative Example 2

[0156] The iron phosphate process is used to sinter the finished product once and then sinter it twice. The doping amount of the finished product is the same as that in Example 1.

[0157] 1. According to the Fe / P (molar ratio) of 0.970, Li / Fe (molar ratio) of 1.05, dopant / Fe (molar ratio) of 0.0122, and carbon content of 1.35%, weigh 1000g of anhydrous iron phosphate precursor, 252.4g of lithium carbonate, 80g of glucose, 40g of polyethylene glycol, and 7.0g of titanium dioxide;

[0158] 2. Stir and disperse the weighed materials first, use deionized water as solvent, control the solid content to 40%, stir and disperse them in a ball mill for 30 minutes, then transfer them to a sand mill for grinding, and finally control the grinding particle size D50 to about 0.35μm;

[0159] 3. Spray dry the ground slurry, control the inlet air temperature at 220℃ and the outlet air temperature at 100℃;

[0160] 4. The sprayed material is loaded into a sagger and placed in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 820℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and the sintered material is taken out of the furnace. The obtained sintered material is coarsely crushed with a small air flow mill. The equipment parameters are adjusted to control the particle size D50: about 2.0μm and D99≤20μm. The obtained material is lithium iron phosphate semi-finished product A;

[0161] 5. Load the lithium iron phosphate semi-finished product A into a sagger and place it in a box-type atmosphere furnace for sintering. The sintering atmosphere is nitrogen. The pressure in the furnace is controlled to be about 100Pa. Nitrogen is passed for more than 2 hours before heating. The heating rate is controlled to be 2.5℃ / min. The sintering temperature and time are set to 770℃ and 8 hours. After sintering, the temperature naturally drops to below 80℃ and then the product is taken out of the furnace;

[0162] 6. The sintered material obtained in step 5 is subjected to air flow pulverization to control the particle size D10 ≥ 0.35 μm, D50: 1-2 μm, and D99 ≤ 10 μm. The obtained material is an ultra-high pressure compacted lithium iron phosphate positive electrode material, and relevant tests are performed.

[0163] The SEM image of the prepared iron phosphate material is shown in Figure 4 As shown by Figure 4 It can be seen that the prepared iron phosphate material has less single-crystalline large particles. Compared with the lithium iron phosphate material prepared in Example 1, the overall material particles are larger and there are fewer small particles. In addition, the bonding density between large particles and small particles is low, and there are some material gaps.

[0164] The embodiments and comparative examples were further tested, and the relevant physical and chemical properties and electrochemical properties were tested with reference to the national standard "Carbon composite lithium iron phosphate positive electrode material for lithium ion batteries" GB / T 30835-2014, wherein button batteries were made (the mass ratio of active material, conductive agent and binder was 90:5:5, and the charge and discharge voltage range was 2.5V-3.8V), and the results were as follows:

[0165] Table 1 Basic properties of lithium manganese iron phosphate materials

[0166]

[0167]

[0168] Comparing the basic material performance data of the embodiment and comparative example 2 in Table 1, when the carbon content and specific surface area of ​​the materials are basically the same, the lithium manganese iron phosphate material powder prepared by the present invention has higher compaction (through SEM, it can be seen that the particle size is smaller, the small particles are more, and the gradation is more reasonable); at the same time, the materials 0.1C and 1C are respectively increased by about 3mAh / g and 8mAh / g compared with comparative example 2, which fully demonstrates the good control of the primary particle size, doping effect and carbon coating effect of the present invention.

[0169] Comparing the basic material performance data of Example 1 and Comparative Example 1 in Table 1, on the basis of similar formulation processes, the powder compaction of the two is basically the same, and the capacity of the embodiment is higher. Comparing SEM, it can be seen that most of the large particles of the embodiment are polycrystalline without complete fusion, and most of the large particles of the comparative example are single crystal with complete fusion (under the same size, the capacity and rate performance of polycrystalline iron lithium are better than those of single crystal), which just reflects the effect advantage of the higher carbon content and co-solvent used in the preparation of semi-finished product A in the embodiment.

[0170] Comparing the basic material performance data of Example 4 and Example 5 in Table 1, based on the similar formulation process, the powder compaction of the two is basically the same, and the 1C discharge capacity gram of the material of Example 5 is higher, indicating that Mn doping has more advantages in rate and low temperature performance.

[0171] The preparation method and application of the lithium iron phosphate material provided by the present invention have no special requirements on the initial raw materials, have a wide range of choices, and are conducive to reducing costs.

[0172] This solution uses lithium iron phosphate semi-finished products to replace the iron source / phosphorus source / lithium source of the traditional process. After pre-burning, this part of the material has been basically crystallized. Combined with the secondary sintering, the material's chemical composition is more complete, the crystallinity is better, and the surface carbon coating is also better, so the capacity and rate performance are better; and the second sintering basically has no effect on the morphology after the secondary grinding and mixing, and the particle size can still be controlled in a small range, thereby improving the electrochemical performance.

[0173] The lithium iron phosphate material prepared in this scheme, with large polycrystalline particles provided by the first lithium iron phosphate intermediate, provides particle grading (improves compaction) and can further improve capacity and rate performance.

[0174] This scheme prepares lithium iron phosphate material, and the material during the secondary sintering is composed of a first lithium iron phosphate intermediate and a second lithium iron phosphate intermediate. Due to the difference in material composition (the main elements of the two, the amount of doping, and the sintering temperature), and the difference in particle size after sintering and secondary grinding, a gradation of different particle sizes can be formed, and the wet mixing before sintering makes the material more uniform and ensures sufficient filling of large and small particles. There are differences in particle size, so a gradation of different particle sizes can be formed, and finally an ultra-high compaction density is obtained.

[0175] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0176] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a lithium iron phosphate material, characterized in that: The preparation method comprises: S10, mixing a first iron source, a first phosphorus source, a first lithium source, a first dopant, a first carbon source and deionized water in a certain proportion, and obtaining a first lithium iron phosphate intermediate by first wet grinding, first spray drying, first sintering and first crushing; S20, mixing a second iron source, a second phosphorus source, a second lithium source, a second dopant, a second carbon source and deionized water in a certain proportion, and obtaining a second lithium iron phosphate intermediate by a second wet grinding, a second spray drying, a second sintering and a second crushing; and S30, mixing the second lithium iron phosphate intermediate, the third carbon source and deionized water in a certain proportion, performing a third wet grinding, adding the first lithium iron phosphate intermediate, mixing evenly, performing a third spray drying, a third sintering and a third pulverizing to obtain a lithium iron phosphate material.

2. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The addition ratio of the first iron source, the first phosphorus source, and the first lithium source is the same as the addition ratio of the second iron source, the second phosphorus source, and the second lithium source; and / or, The addition ratio of the first dopant is smaller than the addition ratio of the second dopant; and / or, The addition ratio of the first carbon source is greater than the addition ratio of the second carbon source; and / or, The sintering temperature of the first sintering is higher than the sintering temperature of the second sintering; and / or, The particle size of the first wet grinding is the same as the particle size of the second wet grinding, and the particle size of the third wet grinding is smaller than the particle size of the first wet grinding; and / or, The particle size of the first pulverized particles is the same as that of the second pulverized particles, and the particle size of the third pulverized particles is smaller than that of the first pulverized particles.

3. The method for preparing the lithium iron phosphate material according to claim 2, characterized in that: The first iron source and the second iron source respectively include at least one of ferric phosphate, ferric oxide, ferrous phosphate, and hydroxyferric phosphate; and / or, The first phosphorus source and the second phosphorus source respectively include at least one of ferric phosphate, ferrous phosphate, hydroxyferric phosphate, diammonium phosphate, phosphoric acid, and lithium phosphate; and / or, The first lithium source and the second lithium source respectively include at least one of lithium carbonate, lithium hydroxide and lithium phosphate; and / or, The addition ratios of the first iron source, the first phosphorus source, and the first lithium source and the addition ratios of the second iron source, the second phosphorus source, and the second lithium source respectively satisfy an iron-phosphorus molar ratio Fe:P of 0.96-0.99 and a lithium-iron molar ratio Li:Fe of 1.02-1.

05.

4. The method for preparing the lithium iron phosphate material according to claim 2, characterized in that: The first dopant includes a compound of at least one of Ti, V, Nb, and Mn; and / or, The molar ratio of the added amount of the first dopant relative to iron is 0-1.0%; and / or, The second dopant includes a compound of at least one of Ti, V, Nb, and Mn; and / or, The molar ratio of the added amount of the second dopant relative to iron is 1.0%-3.0%.

5. The method for preparing the lithium iron phosphate material according to claim 2, characterized in that: The first carbon source comprises at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and / or, The amount of the first carbon source added satisfies that the carbon content of the lithium iron phosphate material is between 0.5wt% and 0.8wt%; and / or, The second carbon source comprises at least one of glucose, sucrose, polyethylene glycol, and polyvinyl alcohol; and / or, The added amount of the second carbon source satisfies that the carbon content of the lithium iron phosphate material is 0.1wt%-0.4wt%.

6. The method for preparing the lithium iron phosphate material according to claim 2, characterized in that: In the step S10, a sintering aid is added and mixed evenly before spray drying, and the sintering aid includes at least one of phosphoric acid, boric acid, and magnesium oxide; and / or, The sintering temperature of the first sintering is 700° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or, The sintering temperature of the second sintering is 500° C.-600° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or, The particle size D50 of the first wet grinding and the second wet grinding is 0.2 μm-0.6 μm; and / or, The particle size D50 of the third wet grinding is 0.2 μm-0.4 μm; and / or, The particle size D50 of the first crushing and the second crushing is 1 μm-2 μm, and D99≤20 μm; and / or, The particle size of the third crushing is D10≥0.35μm, D50 is 1μm-2μm, and D99≤10μm.

7. The method for preparing lithium iron phosphate material according to claim 1, characterized in that: In the step S30, a third lithium source is further added to mix with the second lithium iron phosphate intermediate; the amount of the third lithium source added satisfies the molar ratio of the lithium iron phosphate material to be 0-2%; and / or, The amount of the third carbon source added satisfies that the carbon content of the lithium iron phosphate material is between 1.1wt% and 1.5wt%; and / or, In the step S30, the mass ratio of the added amount of the first lithium iron phosphate intermediate to the second lithium iron phosphate intermediate is 8:2-5:5; and / or, The sintering temperature of the third sintering is 750° C.-800° C., the sintering time is 6 h-8 h, and the sintering atmosphere pressure is 50 Pa-200 Pa; and / or, The inlet air temperature of the first spray drying, the second spray drying and the third spray drying is 220°C-280°C, and the outlet air temperature is 90°C-110°C.

8. The method for preparing lithium iron phosphate material according to claim 1, characterized in that: The first sintering, the second sintering and the third sintering are performed under a rare gas atmosphere; preferably, the rare gas atmosphere is a nitrogen atmosphere.

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

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises: a battery positive electrode made from the lithium iron phosphate material according to claim 9.

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