Preparation method of high-compaction lithium iron phosphate positive electrode material

Abstract

The invention provides a preparation method of a high-compaction lithium iron phosphate positive electrode material, and the method comprises the following steps: providing a first lithium iron phosphate precursor and a second lithium iron phosphate precursor, the first lithium iron phosphate precursor and the second lithium iron phosphate precursor respectively comprising a Li element, a Fe element, a P element and an O element; the particle size Dv150 of the first lithium iron phosphate precursor is 2.0-3.5 m, and the particle size Dv250 of the second lithium iron phosphate precursor is 0.3-0.6 m; iron sources for preparing the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are different; and mixing and sintering the first lithium iron phosphate precursor and the second lithium iron phosphate precursor, and crushing to obtain the lithium iron phosphate positive electrode material. According to the preparation method, the sintering yield of iron is relatively high, the process cost is saved, and the prepared lithium iron phosphate positive electrode material has relatively high compaction density and relatively high gram volume.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion cathode material preparation technology, specifically a method for preparing high-pressure lithium iron phosphate cathode material. Background Technology

[0002] Lithium iron phosphate (LiFePO4) Due to its excellent thermal stability, cycle life (typically thousands of times), and relatively low cost, it has been widely used in fields such as electric vehicles and energy storage systems.

[0003] To improve the energy density of batteries, especially in confined spaces (such as battery packs for electric vehicles), developing LFP materials with high compaction density (typically ≥2.6 g / cm³) while maintaining high capacity (close to theoretical values) has become an important research direction. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-density lithium iron phosphate cathode materials, so as to solve the problem that high density and high specific capacity of lithium iron phosphate cathode materials are incompatible in the prior art.

[0005] In a first aspect, embodiments of this application provide a method for preparing a high-pressure lithium iron phosphate cathode material, comprising the following steps:

[0006] A first lithium iron phosphate precursor and a second lithium iron phosphate precursor are provided, wherein the first lithium iron phosphate precursor and the second lithium iron phosphate precursor respectively comprise Li, Fe, P and O elements; the particle size Dv of the first lithium iron phosphate precursor is provided. 1 50 is 2.0-3.5µm, and the particle size Dv of the second lithium iron phosphate precursor is... 2 50 is 0.3-0.6µm; the iron source and solvent used to prepare the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are different;

[0007] The first lithium iron phosphate precursor and the second lithium iron phosphate precursor are mixed and sintered, and then pulverized to obtain the lithium iron phosphate cathode material.

[0008] In some embodiments, the iron source used to prepare the first lithium iron phosphate precursor is ferrous oxalate, and the iron source used to prepare the second lithium iron phosphate precursor is iron oxide.

[0009] In some embodiments, the solvent used to prepare the first lithium iron phosphate precursor is an organic solvent, and the solvent used to prepare the second lithium iron phosphate precursor is water.

[0010] In some embodiments, the organic solvent includes one or both of methanol and ethanol.

[0011] In some embodiments, the iron source comprises one or more of an oxide of iron, a chloride of iron, iron hydroxide, and an iron salt.

[0012] In some embodiments, the time for preparing the first lithium iron phosphate precursor is less than the time for preparing the second lithium iron phosphate precursor.

[0013] In some embodiments, the method for preparing the first lithium iron phosphate precursor comprises mixing ferrous oxalate, a phosphoric acid source, a lithium source, a carbon source, and an auxiliary material in methanol, and grinding at a speed of 600-1200 rpm for 0.5-2.5 h; and spray drying after the grinding to obtain the first lithium iron phosphate precursor.

[0014] In some embodiments, the method for preparing the second lithium iron phosphate precursor comprises mixing iron red, a phosphoric acid source, a lithium source, a carbon source, and an auxiliary material in deionized water, and grinding at a speed of 600-1200 rpm for 2-5 h; and spray drying after the grinding to obtain the second lithium iron phosphate precursor.

[0015] In some embodiments, the carbon source comprises one or more of glucose, sucrose, polyethylene glycol, and polyacrylonitrile.

[0016] In some embodiments, the auxiliary material comprises one or more of lithium hydroxide, lithium carbonate, tetrabutyl titanate, titanium dioxide, vanadium pentoxide, and magnesium oxide.

[0017] In some embodiments, the lithium source comprises one or more of an oxide of lithium, a chloride of lithium, lithium-containing phosphate, and lithium hydroxide.

[0018] In some embodiments, the phosphoric acid source comprises one or more of ammonium phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate.

[0019] In some embodiments, the phosphoric acid source and the lithium source are the same substance.

[0020] In some embodiments, the mass ratio of the first lithium iron phosphate precursor to the second lithium iron phosphate precursor is (3-20):100.

[0021] In a second aspect, the embodiments of the present application provide a high-density lithium iron phosphate cathode material prepared by the preparation method of the first aspect, wherein the particle size Dv50 of the lithium iron phosphate cathode material is 0.9-1.6 µm.

[0022] Compared with the prior art, the preparation method of the high-density lithium iron phosphate cathode material provided by the present application uses different iron sources to prepare first lithium iron phosphate precursors and second lithium iron phosphate precursors with different particle sizes, and the first lithium iron phosphate precursor with a particle size Dv 1 50 of 2.0-3.5 µm and the second lithium iron phosphate precursor with a particle size Dv2 50 is a second lithium iron phosphate precursor of 0.3-0.6 µm mixed and sintered to obtain a lithium iron phosphate material with matching size particles and a tap density greater than 2.70 g / cm 3 3, and a 0.5C discharge capacity greater than 146 mAh / g, so that the lithium iron phosphate cathode material has both good tap density and high capacity. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required to be used in the embodiments of the present disclosure will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure, and other drawings can also be obtained according to the drawings without creative labor for those skilled in the art.

[0024] Figure 1 A scanning electron microscope diagram provided by some embodiments of the present application is shown.

[0025] Figure 2 A lithium iron phosphate electrochemical performance diagram provided by some embodiments of the present application is shown. DETAILED DESCRIPTION

[0026] Hereinafter, specific embodiments of the preparation method of the high-tap-density lithium iron phosphate cathode material of the present disclosure are specifically disclosed with appropriate reference to the drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of matters known to those skilled in the art, repeated descriptions of practically identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided in order for those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0027] The ranges disclosed herein are defined by their lower and upper limit. Any range listed is defined to include the range endpoints, unless specifically stated otherwise in the specifi c context. Any range listed can be combined with any other range, for example, if a range of 60-120 and a range of 80-110 are listed, then a range of 60-110 and a range of 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and a maximum range value of 3, 4 and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every number that is an integer within the given range of a and b, wherein a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0 and 5" have been listed herein, and "0-5" is merely a shorthand way of describing each and every number that is an integer within the given range of 0 and 5. Additionally, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0028] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present disclosure.

[0029] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present disclosure.

[0030] Unless otherwise specified, all steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, a method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0031] Unless otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects, and are not used to describe a specific order or primary and secondary relationship.

[0032] In the present disclosure, the terms "a plurality of" and "a plurality of" refer to two or more.

[0033] The test temperature of each parameter mentioned in the present disclosure is 25℃ unless otherwise specified.

[0034] In order to obtain high tap density, it is often necessary to increase the particle size of the primary particles. In the ferrous oxalate process route, the tap density is usually significantly increased at high temperature. However, the increase in particle size will prolong the lithium ion diffusion path, resulting in poor capacity performance, especially at high rates. On the contrary, nano-sized lithium iron phosphate material is beneficial to capacity performance, but the tap density will be reduced.

[0035] In view of this, the present application provides a preparation method of high-tap-density lithium iron phosphate cathode material, which uses different solvents and different iron sources to prepare first lithium iron phosphate precursors and second lithium iron phosphate precursors with different particle sizes, so that the lithium iron phosphate cathode material has good tap density and high capacity.

[0036] In a first aspect, the present application provides a preparation method of high-tap-density lithium iron phosphate cathode material, which includes the following steps:

[0037] The first lithium iron phosphate precursor and the second lithium iron phosphate precursor each include Li element, Fe element, P element and O element; the particle size Dv 1 50 of the first lithium iron phosphate precursor is 2.0-3.5 µm, and the particle size Dv 2 50 of the second lithium iron phosphate precursor is 0.3-0.6 µm; the iron source and the solvent used for preparing the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are different;

[0038] The first lithium iron phosphate precursor and the second lithium iron phosphate precursor are mixed and sintered to prepare the lithium iron phosphate cathode material.

[0039] According to the present application, different solvents and different iron sources are used to prepare first lithium iron phosphate precursors and second lithium iron phosphate precursors with different particle sizes. The two precursors with different particle sizes are mixed and sintered, which improves the sintering process. After sintering, the first lithium iron phosphate precursor provides medium and small particles, and the second lithium iron phosphate precursor provides large particles, forming a particle size distribution, thereby improving the lithium iron phosphate cathode material with good tap density.

[0040] The green body obtained by mixing the two precursors with different particle sizes is sintered more densely, reduces internal closed pores, forms stronger secondary particles, optimizes particle morphology, optimizes packing efficiency, reduces porosity, and can prepare lithium iron phosphate material with matching particle sizes and tap density greater than 2.70 g / cm 3 The lithium iron phosphate cathode material has good tap density and high capacity.

[0041] In some embodiments, the particle size Dv50 of the first lithium iron phosphate precursor is 2.0-3.5 μm. 1 50 can be 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, or a range consisting of any of the numbers.

[0042] Optionally, the particle size Dv50 of the first lithium iron phosphate precursor is 2.0-3.5 μm. 1 50 can be 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, or a range consisting of any of the numbers. Thus, it is beneficial to match the particle size of the second lithium iron phosphate precursor, further improving the tap density and gram capacity of the lithium iron phosphate cathode material.

[0043] In some embodiments, the particle size Dv50 of the second lithium iron phosphate precursor is 0.3-0.6 μm. 2 50 can be 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, or a range consisting of any of the numbers. Thus, it is beneficial to match the particle size of the first lithium iron phosphate precursor, further improving the tap density and gram capacity of the lithium iron phosphate cathode material.

[0044] Optionally, the particle size Dv50 of the second lithium iron phosphate precursor is 0.3-0.6 μm. 2 50 can be 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, or a range consisting of any of the numbers. Thus, it is beneficial to match the particle size of the first lithium iron phosphate precursor, further improving the tap density and gram capacity of the lithium iron phosphate cathode material.

[0045] The particle size Dv50 of the first lithium iron phosphate precursor and the particle size Dv50 of the second lithium iron phosphate precursor can be tested by a particle size analyzer, and the average particle size is taken as Dv50. The volume average particle size Dv50 is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%. 1 The particle size Dv50 of the first lithium iron phosphate precursor and the particle size Dv50 of the second lithium iron phosphate precursor can be tested by a particle size analyzer, and the average particle size is taken as Dv50. The volume average particle size Dv50 is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%. 2 The particle size Dv50 of the first lithium iron phosphate precursor and the particle size Dv50 of the second lithium iron phosphate precursor can be tested by a particle size analyzer, and the average particle size is taken as Dv50. The volume average particle size Dv50 is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%. v The particle size Dv50 of the first lithium iron phosphate precursor and the particle size Dv50 of the second lithium iron phosphate precursor can be tested by a particle size analyzer, and the average particle size is taken as Dv50. The volume average particle size Dv50 is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%.

[0046] In some embodiments, after mixing and sintering the first lithium iron phosphate precursor and the second lithium iron phosphate precursor, the method further comprises: pouring the sintered material into a screw mixer for preliminary crushing and mixing, then conveying to an air jet mill for air jet crushing, and finally obtaining the lithium iron phosphate cathode material.

[0047] In some embodiments, the iron source for preparing the first lithium iron phosphate precursor is ferrous oxalate, and the iron source for preparing the second lithium iron phosphate precursor is iron oxide.

[0048] According to the embodiment of the present application, by combining the ferrous oxalate process with the iron red process, the ferrous oxalate spray material prone to forming small particles is mixed with the iron red spray material prone to forming large particles, and after kiln calcination, a high-pressure high-performance power-type lithium iron phosphate positive electrode material with perfect gradation of large particles and small particles is formed. On the other hand, the cost of iron red raw materials is relatively low, the burning rate is high, and the grinding medium can be replaced with water instead of methanol, further saving the process cost.

[0049] According to the embodiment of the present application, by combining the ferrous oxalate process with the iron red process, the ferrous oxalate spray material prone to forming small particles is mixed with the iron red spray material prone to forming large particles, and after kiln calcination, a high-pressure high-performance power-type lithium iron phosphate positive electrode material with perfect gradation of large particles and small particles is formed. On the other hand, the cost of iron red raw materials is relatively low, the burning rate is high, and the grinding medium can be replaced with water instead of methanol, further saving the process cost.

[0050] In some embodiments, the solvent used to prepare the first lithium iron phosphate precursor is an organic solvent, and the solvent used to prepare the second lithium iron phosphate precursor is water.

[0051] The solvent of the second lithium iron phosphate precursor is water, compared with the existing pure ferrous oxalate process, the alcohol as the original solvent is replaced, the cost of raw materials and grinding medium is saved, and large particles are also provided. Therefore, the cost of preparing lithium iron phosphate is reduced.

[0052] In some embodiments, the organic solvent includes one or both of methanol and ethanol.

[0053] In some embodiments, the iron source includes one or more of an oxide of iron, a chloride of iron, iron hydroxide, and an iron salt.

[0054] In some embodiments, the time for preparing the first lithium iron phosphate precursor is less than the time for preparing the second lithium iron phosphate precursor.

[0055] In some embodiments, the method for preparing the first lithium iron phosphate precursor includes mixing ferrous oxalate, a phosphoric acid source, a lithium source, a carbon source, and an auxiliary material in methanol, and grinding at a speed of 600-1200 rpm for 0.5-2.5 h. After grinding, the first lithium iron phosphate precursor is obtained by spray drying.

[0056] Optionally, the grinding is performed at a rotational speed of any value in the range consisting of 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm, or a range composed thereof. The grinding time can be any value in the range consisting of 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, or a range composed thereof.

[0057] In some embodiments, the method for preparing the second lithium iron phosphate precursor comprises mixing iron red, a phosphoric acid source, a lithium source, a carbon source, an auxiliary material in deionized water, and grinding at a rotational speed of 600-1200 rpm for 2-5 h. After the grinding is completed, spray drying is performed to obtain the lithium iron phosphate precursor.

[0058] Optionally, the grinding is performed at a rotational speed of any value in the range consisting of 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm, or a range composed thereof. The grinding time can be any value in the range consisting of 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, or a range composed thereof.

[0059] In some embodiments, the carbon source comprises one or more of glucose, sucrose, polyethylene glycol, and polyacrylonitrile.

[0060] In some embodiments, the auxiliary material comprises one or more of lithium hydroxide, lithium carbonate, tetrabutyl titanate, titanium dioxide, vanadium pentoxide, and magnesium oxide.

[0061] In some embodiments, the lithium source comprises one or more of lithium oxide, lithium chloride, lithium-containing phosphate, and lithium hydroxide.

[0062] In some embodiments, the phosphoric acid source comprises one or more of ammonium phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate.

[0063] In some embodiments, the phosphoric acid source and the lithium source are the same substance. For example, lithium dihydrogen phosphate.

[0064] In some embodiments, during the preparation of the first lithium iron phosphate precursor, zirconium balls are added, and the diameter of the zirconium balls is 1.0-1.5 mm.

[0065] In some embodiments, during the preparation of the first lithium iron phosphate precursor, the inlet temperature of the spray dryer is 160-200 °C, and the outlet temperature is 70-90 °C.

[0066] In some embodiments, the purity of the iron oxide is ≥98%, and the particle size D50 is ≤0.6 μm.

[0067] In some embodiments, during the preparation of the second lithium iron phosphate precursor, zirconium balls are added, and the diameter of the zirconium balls is 0.6-0.8 mm.

[0068] In some embodiments, during the preparation of the second lithium iron phosphate precursor, the inlet temperature of the spray dryer is 200-280 ℃, and the outlet temperature of the spray dryer is 100-120 ℃.

[0069] In some embodiments, in the step of mixing and sintering the first lithium iron phosphate precursor and the second lithium iron phosphate precursor, the rotation speed of the high-speed mixer is 400-600 rpm, and the mixing time is 10-40 min.

[0070] Alternatively, the rotation speed of the high-speed mixer can be any value in the range of 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, or a range composed of any of these values.

[0071] In some embodiments, the sintering temperature is 720-790 ℃, the sintering time is 8-14 h, and the protective gas is nitrogen.

[0072] In some embodiments, the mass ratio of the first lithium iron phosphate precursor to the second lithium iron phosphate precursor is 1:1.

[0073] In a second aspect, the embodiments of the present application provide a high-compaction lithium iron phosphate cathode material prepared by the preparation method of the first aspect, wherein the particle size Dv50 of the lithium iron phosphate cathode material is 0.9-1.6 μm.

[0074] Alternatively, the particle size Dv50 of the lithium iron phosphate cathode material can be any value in the range of 0.90 μm, 0.95 μm, 1.00 μm, 1.05 μm, 1.10 μm, 1.15 μm, 1.20 μm, 1.25 μm, 1.30 μm, 1.35 μm, 1.40 μm, 1.45 μm, 1.50 μm, 1.55 μm, 1.60 μm, or a range composed of any of these values.

[0075] In some embodiments, the compaction density of the lithium iron phosphate cathode material is 3T compaction density 2.6 g / cm 3 ~2.75 g / cm 3 .

[0076] In some embodiments, the discharge capacity of the lithium iron phosphate positive electrode material at a current density of 0.5C is 145 mAh / g to 148.5 mAh / g.

[0077] Embodiments

[0078] The present disclosure is described in more detail by the following embodiments, which are only used for illustrative explanation, and various modifications and changes within the scope of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further treatment, and the instruments used in the examples are commercially available.

[0079] Embodiment 1

[0080] The present embodiment provides a preparation method of lithium iron phosphate, comprising:

[0081] First step: ferrous oxalate, lithium dihydrogen phosphate are mixed according to the ratio of Fe:P=0.958, 40% solid content methanol is added, 3wt% glucose, 6wt% polyethylene glycol, 0.08% lithium carbonate, 2% tetrabutyl titanate, and grinding at 1200 rpm for 1.5 h, and then spray drying at an inlet temperature of 180℃ and an outlet temperature of 80℃ to obtain a first lithium iron phosphate precursor;

[0082] Second step: iron red, lithium dihydrogen phosphate are mixed according to the ratio of Fe:P=0.958, 30% solid content deionized water is added, 5wt% glucose, 10wt% polyethylene glycol, 0.8% titanium dioxide, and grinding at 800 rpm for 3 h; spray drying at an inlet temperature of 260℃ and an outlet temperature of 110℃ to obtain a second lithium iron phosphate precursor;

[0083] Third step: the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are mixed in a mass ratio of 92:8, and then put into a high-speed mixer for stirring at 500 rpm for 30 min;

[0084] Fourth step: the mixed material is sieved through a vibrating screen, and then packed and vibrated, and then sintered at 750℃ in a roller furnace under a nitrogen atmosphere for 10 h;

[0085] Fifth step: the sintered material is poured into a screw cutter mixer for preliminary crushing and mixing, and then conveyed to an air jet mill for air jet crushing, and finally a lithium iron phosphate positive electrode material is obtained.

[0086] Embodiment 2

[0087] Example 2 has the same steps as Example 1, except that the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are mixed in a mass ratio of 85:15, and finally a lithium iron phosphate positive electrode material is obtained.

[0088] Example 3

[0089] Example 3 has the same steps as Example 2, and the same mass ratio of the added spray material, except that the sintering conditions are changed to 730°C for 10h, and finally a lithium iron phosphate positive electrode material is obtained.

[0090] Example 4

[0091] Example 4 has the same steps as Example 1, and the same mass ratio of the added spray material, except that the sintering conditions are changed to 770°C for 10h, and finally a lithium iron phosphate positive electrode material is obtained.

[0092] Example 5

[0093] Example 5 has the same steps as Example 1, except that the grinding speed of the first lithium iron phosphate precursor is changed to 800rpm for 2.5h.

[0094] Example 6

[0095] Example 6 has the same steps as Example 1, except that the grinding speed of the second lithium iron phosphate precursor is 600rpm for 5h.

[0096] Comparative Example 1

[0097] The present embodiment provides a preparation method of lithium iron phosphate, comprising:

[0098] Ferrous oxalate and lithium dihydrogen phosphate are mixed in a ratio of Fe:P=0.958, 30%-50% methanol with solid content is added, 3wt% glucose, 6wt% polyethylene glycol, 0.08% lithium carbonate, 2% tetrabutyl titanate, and the mixture is ground at a speed of 1200rpm for 1.5h; the spray material is dried at an inlet temperature of 180°C and an outlet temperature of 80°C to obtain a precursor powder; the spray material is sieved through a vibrating screen, and then packed and vibrated to be compacted in a roller furnace under a nitrogen atmosphere at 750°C for 10h; the sintered material is poured into a screw mixer for preliminary crushing and mixing, and then conveyed to an air jet mill for air jet crushing, and finally a lithium iron phosphate positive electrode material is obtained.

[0099] Comparative Example 2

[0100] The present embodiment provides a preparation method of lithium iron phosphate, comprising:

[0101] FeSO4.7H2O, LiH2PO4 were mixed in the ratio of Fe:P=0.958, 30%-50% solid content of methanol was added, 3wt% of glucose, 6wt% of polyethylene glycol, 0.08% of lithium carbonate, 2% of tetrabutyl titanate were added, and grinding was carried out at a speed of 1200 rpm for 1.5 h; the precursor powder was obtained by drying at an inlet temperature of 180℃ and an outlet temperature of 80℃; the spray material was sieved through a vibrating screen, and then was loaded into a bowl and vibrated to be compacted, and then was sintered in a roller furnace at 790℃ in a nitrogen atmosphere for 10 h; the sintered material was poured into a knife mixer for preliminary crushing and mixing, and then was conveyed to an air jet mill for air jet crushing, and finally the lithium iron phosphate positive electrode material was obtained.

[0102] Comparative Example 3

[0103] The present embodiment provides a preparation method of lithium iron phosphate, comprising:

[0104] Fe2O3, LiH2PO4 were mixed in the ratio of Fe:P=0.958, 30% solid content of deionized water was added, 5wt% of glucose, 10wt% of polyethylene glycol, 0.8% of titanium dioxide were added, and grinding was carried out at a speed of 800 rpm for 3 h; the precursor powder was obtained by drying at an inlet temperature of 260℃ and an outlet temperature of 110℃; the spray material was sieved through a vibrating screen, and then was loaded into a bowl and vibrated to be compacted, and then was sintered in a roller furnace at 750℃ in a nitrogen atmosphere for 10 h; the sintered material was poured into a knife mixer for preliminary crushing and mixing, and then was conveyed to an air jet mill for air jet crushing, and finally the lithium iron phosphate positive electrode material was obtained.

[0105] Comparative Example 4

[0106] Comparative Example 4 and Example 1 have the same steps, except that the grinding speed of the second lithium iron phosphate precursor is changed to 500 rpm and the time is 2.5 h.

[0107] Performance test

[0108] 1. Loss on ignition calculation of lithium iron phosphate product: the loss on ignition of lithium iron phosphate product = the mass lost in the fourth step of sintering process accounts for the percentage of the total mass of the material before the fourth step of sintering.

[0109] The mass lost in the fourth step of sintering process = the difference between the total mass of the material before the fourth step of sintering and the mass of the material after the fourth step of sintering, wherein the total mass of the material before the fourth step of sintering is the sum of the mass of the first lithium iron phosphate precursor in the first step and the mass of the second lithium iron phosphate precursor in the second step.

[0110] 2. The detection of the tap density of the lithium iron phosphate positive electrode material: the tap density of the positive electrode material is a meaning known in the art, which can be measured by a method known in the art. For example, the tap density can be tested by using a Sansi UIM7305 tap density tester, and the test method is as follows: 1 g of the positive electrode material is weighed and placed in a clean mold, then the mold is placed on the equipment pressure disc, and the test pressure is selected as 3T for testing

[0111] 3. The detection of the discharge capacity of the lithium iron phosphate positive electrode material: the negative electrode sheet uses a lithium metal sheet, and the electrolyte includes LiPF6, methyl ethyl carbonate, dimethyl carbonate and ethylene carbonate; DMC is dimethyl carbonate, EC is ethylene carbonate, EMC is methyl ethyl carbonate, the concentration of LiPF6 is 1 mol / L, and the solvent is mixed in a volume ratio of 1:1:1, and the battery shell, the above-mentioned lithium iron phosphate positive electrode material and acetylene black, the positive electrode sheet prepared by mixing polyvinylidene fluoride PVDF in a mass ratio of 85:10:5, the negative electrode sheet, the separator (PE double-layer ceramic separator), the elastic sheet and the gasket are assembled into a button cell in a vacuum glove box. The electrochemical performance is tested by using a blue electric test system CT3002A, and the charge and discharge test is carried out at 0.5C under the condition of 2.5-4.2V. The measurement temperature is 25℃±1℃, the humidity is <40%, and the test of the discharge specific capacity under the current density of 0.5C can be carried out according to the national standard GB / T24533-2019 Appendix G. The results are shown in Table 1.

[0112] Table 1.

[0113]

[0114] As can be seen from Table 1, the particle size and mass ratio of the two precursor powders are adjusted in the examples, the phase transition comparative examples, and the lithium iron phosphate positive electrode material prepared in the examples has good discharge capacity and tap density. After optimization, the 3T tap density of Example 1 is 2.723 g / cm 3 , and the 0.5C discharge capacity is 148.3 mAh / g, while ensuring that.

[0115] Under the use of similar schemes, by adjusting the sintering temperature, Comparative Example 1 and Comparative Example 2 show that after increasing the sintering temperature of the ferrous oxalate process, the tap density of the lithium iron phosphate can be obviously improved, but the discharge capacity cannot be considered. Comparative Example 3 uses the iron red process alone, and both the tap density and the capacity are poor. Comparative Example 4 uses a second lithium iron phosphate precursor with a larger particle size and a first lithium iron phosphate precursor, which has limited improvement in the discharge capacity and tap density of the lithium iron phosphate positive electrode material.

[0116] Figure 1 The scanning electron microscope images provided by some embodiments of the present application are shown. As can be observed from the images, the lithium iron phosphate of Example 1 has a uniform particle size.

[0117] Figure 2 Performance test The electrochemical performance of the lithium iron phosphate provided by some embodiments of the present application is shown in the figure. It can be observed from the figure that the lithium iron phosphate of Example 1 has a good discharge capacity.

[0118] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0119] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-pressure lithium iron phosphate cathode material, characterized in that, Includes the following steps: A first lithium iron phosphate precursor and a second lithium iron phosphate precursor are provided, wherein the first lithium iron phosphate precursor and the second lithium iron phosphate precursor respectively comprise Li, Fe, P and O elements; the particle size Dv of the first lithium iron phosphate precursor is provided. 1 50 is 2.0-3.5µm, and the particle size Dv of the second lithium iron phosphate precursor is... 2 50 is 0.3-0.6µm; the iron sources used to prepare the first lithium iron phosphate precursor and the second lithium iron phosphate precursor are different; The first lithium iron phosphate precursor and the second lithium iron phosphate precursor are mixed and sintered, and then pulverized to obtain the lithium iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The iron source used to prepare the first lithium iron phosphate precursor is ferrous oxalate, and the iron source used to prepare the second lithium iron phosphate precursor is iron oxide.

3. The preparation method according to claim 1, characterized in that, The solvent used to prepare the first lithium iron phosphate precursor is an organic solvent, and the solvent used to prepare the second lithium iron phosphate precursor is water.

4. The preparation method according to claim 3, characterized in that, The organic solvent includes one or both of methanol and ethanol.

5. The preparation method according to claim 1, characterized in that, The time required to prepare the first lithium iron phosphate precursor is less than the time required to prepare the second lithium iron phosphate precursor.

6. The preparation method according to claim 1, characterized in that, The preparation method of the first lithium iron phosphate precursor includes mixing ferrous oxalate, phosphate source, lithium source, carbon source and excipients in methanol, grinding at 600-1200 rpm for 0.5-2.5 h; after grinding, spray drying to obtain the first lithium iron phosphate precursor.

7. The preparation method according to claim 1, characterized in that, The preparation method of the second lithium iron phosphate precursor includes mixing iron oxide, phosphoric acid source, lithium source, carbon source and auxiliary materials in deionized water, grinding at 600-1200 rpm for 2-5 hours; spray drying after grinding to obtain the second lithium iron phosphate precursor.

8. The preparation method according to claim 6 or 7, characterized in that, The preparation method satisfies one or more of the following conditions: (1) The carbon source includes one or more of glucose, sucrose, polyethylene glycol, and polyacrylonitrile; (2) The excipients include one or more of lithium hydroxide, lithium carbonate, tetrabutyl titanate, titanium dioxide, vanadium pentoxide, and magnesium oxide; (3) The lithium source includes one or more of lithium oxide, lithium chloride, lithium-containing phosphate, and lithium hydroxide; (4) The phosphoric acid source includes one or more of ammonium phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate; (5) The phosphoric acid source and the lithium source are the same substance.

9. The preparation method according to claim 1, characterized in that, The mass ratio of the first lithium iron phosphate precursor to the second lithium iron phosphate precursor is (97~80): (3~20).

10. A high-pressure lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1 to 9, wherein the particle size Dv50 of the lithium iron phosphate cathode material is 0.9 to 1.6 μm.

Images