Preparation methods of lithium iron phosphate materials and lithium iron phosphate materials

Abstract

This invention belongs to the field of lithium-ion battery material technology and provides a method for preparing lithium iron phosphate material, comprising: (1) mixing precursors with different titanium content once, followed by sintering and crushing to obtain lithium iron phosphate; the precursors include phosphorus source, iron source, lithium source, primary carbon source and titanium source; (2) adding the lithium iron phosphate to a mixture of a linker and a secondary carbon source for secondary mixing, followed by drying, sintering and crushing to obtain lithium iron phosphate material. The lithium iron phosphate material prepared by this method has a certain particle size distribution width, which is beneficial to improving the compaction density of the lithium iron phosphate material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically, it relates to a method for preparing lithium iron phosphate material and the lithium iron phosphate material itself. Background Technology

[0002] Environmentally friendly lithium-ion batteries are widely welcomed by consumers due to their advantages such as suitable operating voltage, long cycle life, high energy density, and low self-discharge, and their application fields are constantly expanding. Among them, cathode materials are an important component of lithium-ion batteries, and lithium iron phosphate has attracted widespread attention due to its good cycle performance, high safety, low price, and environmental friendliness, becoming one of the most mainstream cathode materials for lithium-ion batteries on the market today.

[0003] Currently, lithium iron phosphate (LFP) batteries still have a low market share in the power battery market, mainly due to their short driving range. Therefore, researchers in this field focus on improving the volumetric energy density of LFP materials. One important direction for improving volumetric energy density is to increase the powder compaction density of LFP materials. Currently, the powder compaction density of relatively mature LFP products is around 2.58 g / cm³. 3 The theoretical powder compaction density of lithium iron phosphate material is 3.6 g / cm³. 3 Therefore, there is considerable room for improvement in the compaction density of lithium iron phosphate powder.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing lithium iron phosphate material and the lithium iron phosphate material itself. This method produces lithium iron phosphate material with large and small size distribution, which is beneficial to improving the compaction density of the lithium iron phosphate material.

[0006] To achieve the above objectives, the present invention provides a method for preparing lithium iron phosphate material, comprising the following steps:

[0007] (1) After mixing precursors with different titanium content once, lithium iron phosphate is obtained by sintering and crushing once; the precursors with different titanium content include phosphorus source, iron source, lithium source, primary carbon source and titanium source.

[0008] (2) The lithium iron phosphate is added to the mixture of the binder and the secondary carbon source for secondary mixing, and then dried, sintered twice and crushed to obtain the lithium iron phosphate material.

[0009] In some embodiments, the precursors with different titanium content include at least two of a first precursor, a second precursor, and a third precursor, wherein the different titanium content ranges from 500 ppm to 3500 ppm.

[0010] In some embodiments, the titanium content of the first precursor is [500ppm, 1500ppm]; the titanium content of the second precursor is [1500ppm, 2500ppm]; and the titanium content of the third precursor is (2500ppm, 3500ppm).

[0011] In some embodiments, the precursors with different titanium contents include any two of the first precursor, the second precursor, and the third precursor.

[0012] In some embodiments, the precursors with different titanium contents include the first precursor, the second precursor, and the third precursor.

[0013] In some embodiments, the mass ratio of the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor is [10%, 50%]: [50%, 90%];

[0014] Preferably, the mass ratio of the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor is [20%, 40%]: [60%, 80%].

[0015] In some embodiments, the mass ratio of the first precursor, the second precursor, and the third precursor is (0%, 30%): [50%, 90%): (0%, 30%).

[0016] Preferably, the mass ratio of the first precursor, the second precursor, and the third precursor is [5%, 15%]: [70%, 80%]: [5%, 15%].

[0017] In some embodiments, the linker is a titanate coupling agent; and / or, the secondary carbon source is a hydroxyl-containing carbon source.

[0018] In some embodiments, the mass ratio of the linker to the secondary carbon source is 1:[1,3]; and / or, the mass ratio of the linker to the lithium iron phosphate is 1:[80,100].

[0019] In a second aspect, the present invention provides a lithium iron phosphate material, which is prepared by the method for preparing lithium iron phosphate material according to any of the above embodiments, wherein the compacted density of the lithium iron phosphate material powder is [2.58 g / cm³]. 3 2.72 g / cm 3 ].

[0020] The method for preparing lithium iron phosphate material provided by this invention involves mixing precursors with different titanium contents in different proportions during a primary mixing process to obtain lithium iron phosphate with varying sizes, thereby increasing the compaction density of the lithium iron phosphate. Simultaneously, a secondary mixing process uses a linker and a secondary carbon source to jointly coat the lithium iron phosphate, further improving the compaction density of the lithium iron phosphate material. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram illustrating the compaction effect of powder particles with different gradations;

[0023] Figure 2 The particle size distribution curve of the lithium iron phosphate material prepared in Example 1;

[0024] Figure 3 The particle size distribution curve of the lithium iron phosphate material prepared in Example 2;

[0025] Figure 4 The particle size distribution curve of the lithium iron phosphate material prepared in Example 3;

[0026] Figure 5 The particle size distribution curve of the lithium iron phosphate material prepared in Comparative Example 1;

[0027] Figure 6 The particle size distribution curve of the lithium iron phosphate material prepared in Comparative Example 2;

[0028] Figure 7 The image shows a SEM image of the lithium iron phosphate material prepared in Example 1. Detailed Implementation

[0029] The following detailed description of the preparation method of the lithium iron phosphate material, the specific embodiments of the lithium iron phosphate material and the lithium-ion battery of the present invention will be provided with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Specifically, "()", ")", "[", and "]" represent intervals, where "()" or ")" represents an open interval, meaning the endpoints of the interval are not included; and "[" and "]" represent a closed interval, meaning the endpoints of the interval are included. A range defined in this way can include endpoints or not, and can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range.

[0031] Specifically, for example, if the ranges 60-120 and 80-110 are listed for a specific parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein, and “0-5” is merely a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If (10, 20) is listed, it is understood as any value in the interval 10-20 excluding 10 and 20; (10, 20] is understood as any value in the interval 10-20 excluding 10 but including 20.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0034] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0036] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0037] In a first aspect, this invention provides a method for preparing lithium iron phosphate material, comprising the following steps:

[0038] (1) After mixing precursors with different titanium content once, lithium iron phosphate is obtained by sintering and crushing once; the precursors with different titanium content include phosphorus source, iron source, lithium source, primary carbon source and titanium source.

[0039] (2) The lithium iron phosphate is added to the mixture of the binder and the secondary carbon source for secondary mixing, and then dried, sintered twice and crushed to obtain the lithium iron phosphate material.

[0040] In some embodiments, the precursors with different titanium content are obtained by adding phosphorus source, iron source, lithium source, primary carbon source and titanium source to deionized water, grinding to a certain particle size to obtain a slurry, and then spray drying it once.

[0041] In some embodiments, the iron source is at least one of ferric phosphate, ferric oxide, and ferrous oxalate; the phosphorus source is at least one of ferric phosphate, ammonium dihydrogen phosphate, and phosphoric acid; the lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; and the primary carbon source is at least one of glucose, sucrose, polyethylene glycol-1000, polyethylene glycol-1500, polyethylene glycol-2000, polyethylene glycol-4000, polyethylene glycol-6000, polyethylene glycol-10000, citric acid, cyclodextrin, and polyvinyl alcohol.

[0042] In some embodiments, the molar ratio of phosphorus, iron and lithium in the precursor is [1,1.2]:1:[1,1.2], and the mass fraction of the primary carbon source in the precursor is [2.5%,6%].

[0043] In some embodiments, the titanium source is at least one of rutile nano-titanium dioxide, anatase nano-titanium dioxide, brookite nano-titanium dioxide, tetrabutyl titanate, titanium boride, titanium sulfate, titanate coupling agents, titanium oxysulfate, and titanium citrate.

[0044] In some embodiments, precursors with different titanium contents are mixed once, then sintered and crushed once to obtain lithium iron phosphate. Titanium doping into the lithium iron phosphate lattice has a grain-refining effect; different doping amounts result in different degrees of grain refinement. Sintering precursors with different titanium contents produces lithium iron phosphate with different particle size ranges. Mixing lithium iron phosphate with different particle size ranges can increase the compaction density of lithium iron phosphate, and high compaction density lithium iron phosphate can improve the energy density of lithium-ion batteries.

[0045] In some embodiments, the precursor is at least two types of titanium with a content of 500 ppm to 3500 ppm. In this invention, the titanium content is selected within this range. If the titanium content is too low, the precursor will form larger lithium iron phosphate particles after sintering, resulting in a lower compaction density. Conversely, if the titanium content is too high, the precursor will form smaller lithium iron phosphate particles after sintering, resulting in a lower compaction density.

[0046] In some embodiments, a precursor with a titanium content of [500 ppm, 1500 ppm] is a first precursor; a precursor with a titanium content of [1500 ppm, 2500 ppm] is a second precursor; and a precursor with a titanium content of [2500 ppm, 3500 ppm] is a third precursor. The precursors with different titanium contents include at least two of the first, second, and third precursors.

[0047] In some embodiments, two precursors with different titanium content are mixed once, wherein the precursors with different titanium content include any two of the first precursor, the second precursor, and the third precursor.

[0048] In some embodiments, three precursors with different titanium content are mixed at once, the precursors with different titanium content including the first precursor, the second precursor and the third precursor.

[0049] Lithium iron phosphate (LFP) obtained by sintering two or more precursors with different titanium content ranges exhibits a secondary or higher gradation effect, resulting in LFP materials with high compaction density. Figure 1 It can be seen that compared with the two-level gradation, the three-level gradation has a higher space utilization efficiency and a higher packing density.

[0050] In some embodiments, when two precursors with different titanium contents are mixed in one step, the mass ratio of the first precursor to the second precursor, or the first precursor to the third precursor, or the second precursor to the third precursor is [10%, 50%]: [50%, 90%]. A lower mass ratio of the precursor with the lower titanium content and a higher mass ratio of the precursor with the higher titanium content is beneficial for balancing the compaction density of lithium iron phosphate powder with the corresponding lithium-ion battery capacity.

[0051] In some embodiments, the mass ratio of the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor is [20%, 40%]: [60%, 80%].

[0052] In some embodiments, the particle size distribution of lithium iron phosphate materials prepared by mixing the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor in different mass ratios, exhibits a bimodal distribution, with the first peak having a particle size range of 0.1-1.5 μm and the second peak having a particle size range of 1.5-15.0 μm.

[0053] In some embodiments, when the three precursors with different titanium contents are mixed once, the mass ratio of the first precursor, the second precursor, and the third precursor is (0%, 30%): [50%, 90%): (0%, 30%). The second precursor has a larger mass proportion, while the first and third precursors have smaller mass proportions, which is beneficial for balancing the compaction density of lithium iron phosphate powder and the corresponding lithium-ion battery capacity.

[0054] In some embodiments, the mass ratio of the first precursor, the second precursor, and the third precursor is [5%, 15%]: [70%, 80%]: [5%, 15%].

[0055] In some embodiments, the particle size distribution of lithium iron phosphate material prepared by mixing the first precursor, the second precursor and the third precursor in different mass ratios exhibits three peaks: the first peak has a particle size range of 0.1-1.0 μm, the second peak has a particle size range of 1.0-8.0 μm, and the third peak has a particle size range of 8.0-30.0 μm.

[0056] In some embodiments, after mixing the binder and secondary carbon source in water, the above-mentioned lithium iron phosphate is added for secondary mixing, followed by secondary spray drying, secondary sintering, and crushing to obtain lithium iron phosphate material.

[0057] In some embodiments, the linker is a titanate coupling agent.

[0058] In some embodiments, the secondary carbon source is a hydroxyl-containing carbon source, such as polyethylene glycol-1500, polyethylene glycol-2000, polyethylene glycol-4000, polyethylene glycol-6000, polyethylene glycol-10000, phenol, etc.

[0059] The binder acts as a "bridging agent," possessing both polar and non-polar groups. The non-polar groups adsorb onto the weakly polar surface of lithium iron phosphate, while the polar groups combine with the hydroxyl groups in the hydroxyl-containing carbon source, improving the compatibility between the hydroxyl-containing carbon source and lithium iron phosphate. This, in turn, increases the coating thickness and uniformity of the hydroxyl-containing carbon source on the lithium iron phosphate surface. Simultaneously, the coating of the hydroxyl-containing carbon source enhances the dispersibility of lithium iron phosphate, thus preventing agglomeration. Through the combined use of the binder and the hydroxyl-containing carbon source, the lithium iron phosphate material after secondary sintering exhibits a uniform carbon coating layer.

[0060] The coupling agent used in this invention is a titanium-containing coupling agent, mainly because titanium is a "beneficial factor" in lithium iron phosphate. If other coupling agents are used, impurities will be introduced, reducing the stability of lithium iron phosphate materials.

[0061] In some embodiments, the mass ratio of the binder to the secondary carbon source is 1:[1,3].

[0062] In some embodiments, the mass ratio of the binder to the lithium iron phosphate is 1:[80,200].

[0063] In some embodiments, the mass ratio of the mixture of the binder and the secondary carbon source to water is 1:[30,50].

[0064] In some embodiments, the primary sintering and secondary sintering temperatures are independently [780°C, 850°C]. Preferably, the primary sintering and secondary sintering temperatures are independently [800°C, 820°C].

[0065] In some embodiments, the present invention also provides a lithium iron phosphate material, wherein the mass fraction of carbon in the lithium iron phosphate material obtained by the preparation method provided by the present invention is [1.10%, 1.50%]. Preferably, the mass fraction of carbon in the lithium iron phosphate material is [1.15%, 1.30%].

[0066] In some embodiments, the titanium doping content of the lithium iron phosphate material is [1000ppm, 5000ppm].

[0067] In some embodiments, the powder compaction density of lithium iron phosphate material is [2.58 g / cm³]. 3 2.72 g / cm 3 ].

[0068] In some embodiments, lithium-ion batteries prepared using the lithium iron phosphate material obtained by the present invention have a 0.1C charging specific capacity range of [162.0 mAh / g, 164.5 mAh / g] within a voltage range of [2.0V, 3.75V].

[0069] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0070] Example 1

[0071] (1) Preparation of precursors with different titanium contents:

[0072] Preparation of the first precursor: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 1000 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the first precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220℃, and the outlet air temperature was 105℃.

[0073] Preparation of the second precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 2000 ppm.

[0074] Preparation of the third precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 3000 ppm.

[0075] (2) Lithium iron phosphate was prepared by mixing precursors with different proportions of titanium in one step:

[0076] The first, second, and third precursors were mixed evenly in a high-speed mixer at a mass ratio of 10%:80%:10%. The mixed precursors were then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing, and demagnetization, lithium iron phosphate was obtained.

[0077] (3) Preparation of lithium iron phosphate materials:

[0078] 1.0 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight 1500) were added to 150 kg of deionized water and mixed. Then, 100 kg of the above-mentioned lithium iron phosphate was added for secondary mixing. The secondary mixture was milled to a particle size D50 of 1.00 ± 0.05 μm. After secondary spray drying, a lithium iron phosphate material intermediate was obtained. The feed rate of the secondary spray drying was 80 kg / h, the inlet air temperature was 220°C, and the outlet air temperature was 105°C. The above-mentioned lithium iron phosphate material intermediate was placed in a graphite saggar and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 h. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0079] Example 2:

[0080] (1) Preparation of precursors with different titanium contents:

[0081] Preparation of the first precursor: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 1000 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the first precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220℃, and the outlet air temperature was 105℃.

[0082] Preparation of the second precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 2200 ppm.

[0083] (2) Lithium iron phosphate was prepared by mixing precursors with different proportions of titanium in one step:

[0084] The first and second precursors were mixed evenly in a high-speed mixer at a mass ratio of 20%:80%. The mixed precursors were then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing and demagnetizing, lithium iron phosphate was obtained.

[0085] (3) Preparation of lithium iron phosphate materials:

[0086] 1 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight 1500) were mixed with 150 kg of deionized water, followed by a secondary mixing with 100 kg of the aforementioned lithium iron phosphate. The secondary mixture was then milled to a particle size D50 of 1.00 ± 0.05 μm and subjected to a secondary spray drying process to obtain a lithium iron phosphate material intermediate. The secondary spray drying process involved a feed rate of 80 kg / h, an inlet air temperature of 220°C, and an outlet air temperature of 105°C. The lithium iron phosphate material intermediate was then placed in a graphite saggar and sintered at 820°C in a nitrogen atmosphere in a roller kiln for 10 hours. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0087] Example 3:

[0088] The only difference between this embodiment and embodiment 2 is that the mass ratio of the first precursor and the second precursor in step (2) is replaced by 40%:60% instead of 20%:80%. All other conditions and parameters are exactly the same as in embodiment 2.

[0089] Example 4:

[0090] (1) Preparation of precursors with different titanium contents:

[0091] Preparation of the first precursor: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 500 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the first precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220℃, and the outlet air temperature was 105℃.

[0092] Preparation of the second precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 2500 ppm.

[0093] Preparation of the third precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 2600 ppm.

[0094] (2) Lithium iron phosphate was prepared by mixing precursors with different proportions of titanium in one step:

[0095] The first, second, and third precursors were mixed evenly in a high-speed mixer at a mass ratio of 15%:70%:15%. The mixed precursors were then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing, and demagnetization, lithium iron phosphate was obtained.

[0096] (3) Preparation of lithium iron phosphate materials:

[0097] 1 kg of isopropyltrioleoyl titanate and 1 kg of polyethylene glycol (molecular weight 1500) were added to 100 kg of deionized water and mixed. Then, 80 kg of the above-mentioned lithium iron phosphate was added for secondary mixing. The secondary mixture was milled to a particle size D50 of 1.00 ± 0.05 μm. After secondary spray drying, a lithium iron phosphate material intermediate was obtained. The feed rate of the secondary spray drying was 80 kg / h, the inlet air temperature was 220°C, and the outlet air temperature was 105°C. The above-mentioned lithium iron phosphate material intermediate was placed in a graphite saggar and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 h. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0098] Example 5:

[0099] (1) Preparation of precursors with different titanium contents:

[0100] Preparation of the second precursor: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 1500 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the second precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220℃, and the outlet air temperature was 105℃.

[0101] Preparation of the third precursor: The only difference from the preparation of the second precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 2600 ppm.

[0102] (2) Lithium iron phosphate was prepared by mixing precursors with different proportions of titanium in one step:

[0103] The second and third precursors were mixed evenly in a high-speed mixer at a mass ratio of 20%:80%. The mixed precursors were then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing and demagnetizing, lithium iron phosphate was obtained.

[0104] (3) Preparation of lithium iron phosphate materials:

[0105] 1 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 3 kg of polyethylene glycol (molecular weight 1500) were mixed with 120 kg of deionized water, followed by a secondary mixing with 200 kg of the aforementioned lithium iron phosphate. The secondary mixture was milled to a particle size D50 of 1.00 ± 0.05 μm and then subjected to a secondary spray drying process to obtain a lithium iron phosphate material intermediate. The secondary spray drying process had a feed rate of 80 kg / h, an inlet air temperature of 220°C, and an outlet air temperature of 105°C. The lithium iron phosphate material intermediate was then placed in a graphite saggar and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 h. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0106] Example 6:

[0107] (1) Preparation of precursors with different titanium contents:

[0108] Preparation of the first precursor: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 1400 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the first precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220℃, and the outlet air temperature was 105℃.

[0109] Preparation of the third precursor: The only difference from the preparation of the first precursor is that the proportion of titanium in the rutile nano-titanium dioxide is 3500 ppm.

[0110] (2) Lithium iron phosphate was prepared by mixing precursors with different proportions of titanium in one step:

[0111] The first and third precursors were mixed evenly in a high-speed mixer at a mass ratio of 20%:80%. The mixed precursors were then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing and demagnetizing, lithium iron phosphate was obtained.

[0112] (3) Preparation of lithium iron phosphate materials:

[0113] 1 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight 1500) were mixed with 150 kg of deionized water, followed by a secondary mixing with 100 kg of the aforementioned lithium iron phosphate. The secondary mixture was then milled to a particle size D50 of 1.00 ± 0.05 μm and subjected to a secondary spray drying process to obtain a lithium iron phosphate material intermediate. The secondary spray drying process involved a feed rate of 80 kg / h, an inlet air temperature of 220°C, and an outlet air temperature of 105°C. The lithium iron phosphate material intermediate was then placed in a graphite saggar and sintered at 820°C in a nitrogen atmosphere in a roller kiln for 10 hours. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0114] Comparative Example 1:

[0115] (1) Preparation of titanium-containing precursors:

[0116] 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate, and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 2000 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground five times in a coarse mill and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After that, it was spray-dried with ethanol to obtain the titanium-containing precursor. The spray drying rate was 80 kg / h, the inlet air temperature was 220 °C, and the outlet air temperature was 105 °C.

[0117] (2) Preparation of lithium iron phosphate:

[0118] The titanium-containing precursor was placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing and demagnetizing, lithium iron phosphate was obtained.

[0119] (3) Preparation of lithium iron phosphate materials:

[0120] 1.0 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight 1500) were mixed in 150 kg of deionized water, and then lithium iron phosphate was added for secondary mixing. The secondary mixture was milled to a particle size D50 of 1.00 ± 0.05 μm, and then spray-dried twice to obtain a lithium iron phosphate material intermediate. The secondary spray-drying feed rate was 80 kg / h, the inlet air temperature was 220°C, and the outlet air temperature was 105°C. The lithium iron phosphate material intermediate was placed in a graphite saggar and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 h. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0121] Comparative Example 2:

[0122] The only difference between this comparative example and comparative example 1 is that in step (3), "1.0 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight of 1500) are added to 150 kg of deionized water and mixed" is replaced with "2 kg of polyethylene glycol (molecular weight of 1500) is added to 150 kg of deionized water and mixed". All other conditions and parameters are exactly the same as those in comparative example 1.

[0123] Comparative Example 3:

[0124] (1) Preparation of titanium-containing precursors:

[0125] 4.5 kg of glucose, 6.5 kg of polyethylene glycol (molecular weight 1500), and 1.0 kg of isopropyltris(dioctylphosphoyloxy)titanate were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate, and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 2000 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground five times in a coarse mill, and then sand-milled in a fine mill until the particle size D50 was 0.60 ± 0.01 μm. After one spray drying treatment, the titanium-containing precursor was obtained. The spray drying rate was 80 kg / h, the inlet air temperature was 220 °C, and the outlet air temperature was 105 °C.

[0126] (2) Preparation of lithium iron phosphate materials:

[0127] The titanium-containing precursor was placed in a graphite sagger and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 hours. After cooling, crushing and demagnetizing, lithium iron phosphate material was obtained.

[0128] Comparative Example 4:

[0129] The only difference between this comparative example and Example 1 is that in step (1), the 90 kg of ferric phosphate and rutile nano-titanium dioxide used in the preparation of the first precursor are replaced with an equal amount of rutile nano-titanium dioxide and 90 kg of ferric phosphate processed to obtain titanium-doped ferric phosphate; the 90 kg of ferric phosphate and rutile nano-titanium dioxide used in the preparation of the second precursor are replaced with an equal amount of rutile nano-titanium dioxide and 90 kg of ferric phosphate processed to obtain titanium-doped ferric phosphate; and the 90 kg of ferric phosphate and rutile nano-titanium dioxide used in the preparation of the third precursor are replaced with an equal amount of rutile nano-titanium dioxide and 90 kg of ferric phosphate processed to obtain titanium-doped ferric phosphate. All other conditions and parameters are exactly the same as in Example 1.

[0130] Comparative Example 5:

[0131] (1) Preparation of slurries with different titanium content:

[0132] Preparation of the first slurry: 4.5 kg of glucose and 4.5 kg of polyethylene glycol (molecular weight 1500) were dissolved in 230 kg of deionized water. Then, 90 kg of ferric phosphate, 22.6 kg of lithium carbonate and rutile nano-titanium dioxide were added sequentially for premixing. The titanium content in the rutile nano-titanium dioxide was 1000 ppm. After premixing for 1.5 h, the premix was obtained. The premix was coarsely ground 5 times in a coarse mill and then sand-ground in a fine mill until the particle size D50 was 0.60 ± 0.01 μm to obtain the first slurry.

[0133] Preparation of the second slurry: The only difference from the preparation of the first slurry is that the proportion of titanium in the rutile nano-titanium dioxide premix is ​​2000 ppm.

[0134] Preparation of the third slurry: The only difference from the preparation of the first slurry is that the proportion of titanium in the rutile nano-titanium dioxide premix is ​​3000ppm.

[0135] (2) Lithium iron phosphate was prepared by mixing slurries with different proportions of titanium element content once:

[0136] The first, second, and third slurries were mixed in a mass ratio of 10%:80%:10%, and then subjected to a single spray drying process to obtain the precursor. The spray drying rate was 80 kg / h, the inlet air temperature was 220°C, and the outlet air temperature was 105°C. The mixed precursor was then placed in a graphite sagger and sintered at a constant temperature of 800°C in a nitrogen atmosphere in a roller kiln for 10 hours. After cooling, crushing, and demagnetization, lithium iron phosphate was obtained.

[0137] (3) Preparation of lithium iron phosphate materials:

[0138] 1.0 kg of isopropyl tris(dioctylphosphoyloxy)titanate and 2 kg of polyethylene glycol (molecular weight 1500) were mixed with 150 kg of deionized water, followed by a secondary mixing with 100 kg of the aforementioned lithium iron phosphate. The secondary mixture was milled to a particle size D50 of 1.00 ± 0.05 μm, and then subjected to a secondary spray drying process to obtain a lithium iron phosphate material intermediate. The secondary spray drying process had a feed rate of 80 kg / h, an inlet air temperature of 220°C, and an outlet air temperature of 105°C. The lithium iron phosphate material intermediate was placed in a graphite saggar and sintered at a constant temperature of 820°C in a nitrogen atmosphere roller kiln for 10 h. After cooling, crushing, and demagnetization, the lithium iron phosphate material was obtained.

[0139] Example of effect 1:

[0140] To verify the performance of the lithium iron phosphate material of the present invention, the compaction density of the lithium iron phosphate material powder prepared in each embodiment and comparative example was tested using instruments and methods known in the art. For example, the compaction density of powder can be determined by referring to GB / T 24533-2009, using an electronic pressure testing machine. The powder weight was 1.0±0.05g and the test pressure was 3T.

[0141] The test results are shown in Table 1.

[0142] Example 2:

[0143] To verify the performance of the lithium iron phosphate material of the present invention, the lithium iron phosphate materials prepared in each embodiment and comparative example were used to make button batteries. The preparation method is as follows:

[0144] Lithium iron phosphate material is mixed evenly with conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone using a high-speed mixer. The mass ratio of lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride is 90:5:5. Then, an automatic coating machine is used to coat aluminum foil. The coated aluminum foil is dried in an oven and cut into small round pieces of the required size, which are then weighed to obtain the positive electrode sheet. Using pure lithium sheet as the negative electrode sheet, the positive electrode shell, negative electrode shell, positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled into a button cell according to requirements.

[0145] The obtained button cell batteries were placed on a battery testing system and left to stand. The charge and discharge specific capacity at 0.1C and 1C was tested within a voltage range of [2.0V, 3.75V]. The test results are shown in Table 1.

[0146] Table 1

[0147]

[0148] As can be seen from the results in Table 1, compared with the two-stage gradation schemes used in Examples 2 and 3, the three-stage gradation scheme used in Example 1 has large, medium, and small particles, resulting in high space utilization and better stacking effect, which leads to a higher compaction density of the lithium iron phosphate material. At the same time, the lithium iron phosphate material obtained by the three-stage gradation scheme in Example 1 gives the lithium-ion battery a higher discharge specific capacity at 1C.

[0149] Compared with Comparative Example 1, the method for preparing lithium iron phosphate material provided by the present invention, on the one hand, enables the lithium iron phosphate material to have secondary / tertiary particle size distribution characteristics, and enables the lithium iron phosphate material to have secondary / tertiary gradation high compaction characteristics, while enabling the lithium-ion battery to have a higher discharge specific capacity at 1C.

[0150] Compared with Comparative Example 2, Comparative Example 1 used isopropyltris(dioctylphosphoyloxy)titanate coupling agent in the carbon coating process of lithium iron phosphate, which can make polyethylene glycol more uniformly coated on the surface of lithium iron phosphate. After calcination, a uniform carbon coating layer is formed, which increases the surface smoothness and sphericity of lithium iron phosphate material and gives lithium iron phosphate material a higher compaction density.

[0151] Compared to Comparative Example 3, Comparative Example 1 used isopropyltris(dioctylphosphoyloxy)titanate and polyethylene glycol to coat the surface of the prepared lithium iron phosphate. After calcination, the binder and the hydroxyl-containing carbon source formed a uniform carbon coating layer. On the one hand, the uniform carbon coating layer increased the surface smoothness and sphericity of the lithium iron phosphate material, and the lithium iron phosphate material had a higher compaction density; on the other hand, the uniform carbon coating layer helped to improve the electron conduction rate of the lithium-ion battery.

[0152] Compared to Comparative Example 4, which uses titanium-doped iron phosphate as a raw material, the preparation method provided in this invention uses titanium as an independent raw material. On one hand, by using titanium as an independent raw material and incorporating it into the lithium iron phosphate lattice during synthesis, the growth of lithium iron phosphate can be controlled, achieving the effect of refining lithium iron phosphate grains. Through particle size control, particle size classification is achieved, resulting in high space utilization and good packing effect. In contrast, Comparative Example 4 directly uses titanium-doped iron phosphate as a raw material. Due to the shrinkage of the unit cell volume after titanium doping, the subsequent entry of Li ions is affected, causing uneven lithium distribution in the lithium iron phosphate material and ultimately affecting the electrochemical performance of the material. Furthermore, the effect is more significant for iron phosphate with a higher titanium doping content and less for iron phosphate with a lower titanium doping content. Therefore, the small lithium iron phosphate particles become even smaller, and the large particles become even larger, affecting the gradation effect and reducing the compaction density of the lithium iron phosphate material.

[0153] Compared to Comparative Example 5, which mixes slurries with different titanium content in a certain proportion, this invention provides a method for preparing lithium iron phosphate materials. The method involves spray-drying slurries with different titanium contents to obtain precursors with different titanium contents. These precursors are then mixed in a certain proportion and subjected to a second spray-drying process to obtain intermediate lithium iron phosphate materials with different titanium contents. Sintering then yields lithium iron phosphate materials with different titanium doping levels. In contrast, directly mixing and spraying slurries does not produce lithium iron phosphate materials with different titanium doping levels, thus lacking a multi-stage gradation effect.

[0154] Example of effect 3:

[0155] To verify the particle size distribution of the lithium iron phosphate material of the present invention, the lithium iron phosphate material samples prepared in each embodiment and comparative example were measured. The key test steps were: adding solvent: 20 ml of deionized water, and light-blocking degree: 8~12%.

[0156] Figures 2-6 The particle size distribution curves of the lithium iron phosphate materials prepared in each embodiment and comparative example are shown.

[0157] Figure 2 The lithium iron phosphate material prepared by Example 1 shows a three-peaked particle size distribution curve as seen in the figure. The first peak has a particle size of 0.3-0.5 μm, the second peak has a particle size of 2-4 μm, and the third peak has a particle size of 15.0-25.0 μm.

[0158] Figure 3 The lithium iron phosphate material prepared by Example 2 shows a bimodal particle size distribution curve, with the first peak having a particle size of 0.3-0.5 μm and the second peak having a particle size of 2-5 μm.

[0159] Figure 4 The lithium iron phosphate material prepared by Example 3 shows a bimodal particle size distribution curve, with the first peak having a particle size of 0.4-0.6 μm and the second peak having a particle size of 2.0-4.0 μm.

[0160] Figure 5 The lithium iron phosphate material prepared by Comparative Example 1 is shown in the figure. As can be seen from the figure, the particle size distribution curve is a single-peak curve, and the single-peak particle size is 1.0-2.0 μm.

[0161] Figure 6 The lithium iron phosphate material prepared by Comparative Example 2 is shown in the figure. As can be seen from the figure, the particle size distribution curve is a single-peak curve, and the single-peak particle size is 2.0-4.0 μm.

[0162] Example of effect 4:

[0163] The morphology of the lithium iron phosphate material sample in Example 1 was observed using a scanning electron microscope.

[0164] Figure 7 The image shows a SEM image of the lithium iron phosphate material prepared in Example 1. Figure 7 As can be seen, the lithium iron phosphate material with three-stage gradation includes large, medium and small particles, resulting in high space utilization and good stacking effect.

[0165] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing a lithium iron phosphate material, characterized by, The method comprises the following steps: (1) mixing different titanium element content precursors, and then sintering and crushing to obtain lithium iron phosphate; the different titanium element content precursors comprise a phosphorus source, an iron source, a lithium source, a primary carbon source and a titanium source; (2) adding the lithium iron phosphate into a mixture of a coupling agent and a secondary carbon source, mixing again, drying, sintering again, and crushing to obtain a lithium iron phosphate material; The different titanium element content precursors comprise at least two of a first precursor, a second precursor and a third precursor; the titanium element content of the first precursor is [500 ppm, 1500 ppm); the titanium element content of the second precursor is [1500 ppm, 2500 ppm]; and the titanium element content of the third precursor is (2500 ppm, 3500 ppm].

2. The method of claim 1, wherein the lithium iron phosphate material is prepared by the steps of: The different titanium element content precursors comprise any two of the first precursor, the second precursor and the third precursor. ​ 3. The method of claim 1, wherein the lithium iron phosphate material is prepared by the steps of: The different titanium element content precursors comprise the first precursor, the second precursor and the third precursor. ​ 4. The method of claim 2, wherein the lithium iron phosphate material is prepared by the steps of: The mass ratio of the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor is [10%, 50%]:[50%, 90%]. ​ 5. The method of claim 4, wherein the lithium iron phosphate material is prepared by the steps of: The mass ratio of the first precursor and the second precursor, or the first precursor and the third precursor, or the second precursor and the third precursor is [20%, 40%]:[60%, 80%]. ​ 6. The method for preparing lithium iron phosphate material according to claim 3, characterized in that, The mass ratio of the first precursor, the second precursor and the third precursor is (0%, 30%]:[50%, 90%]: (0%, 30%].

7. The method of claim 6, wherein the lithium iron phosphate material is prepared by a process comprising: The mass ratio of the first precursor, the second precursor and the third precursor is [5%, 15%]:[70%, 80%]:[5%, 15%]. ​ 8. The method of claim 1, wherein the lithium iron phosphate material is prepared by a process comprising: The coupling agent is a titanium ester coupling agent; and / or, the secondary carbon source is a hydroxyl-containing carbon source. ​ 9. The method of claim 1-8, wherein the lithium iron phosphate material is prepared by, The mass ratio of the coupling agent and the secondary carbon source is 1:[1, 3]; And / or, the mass ratio of the coupling agent and the lithium iron phosphate is 1:[80, 100].

10. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material is prepared by the method for preparing the lithium iron phosphate material according to any one of claims 1-9, and the compaction density of the lithium iron phosphate material powder is [2.58 g / cm 3 , 2.72 g / cm 3 ].

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