A lithium iron phosphate positive electrode material and its preparation method and application

Abstract

This article discloses a lithium iron phosphate positive electrode material, its preparation method, and application, belonging to the technical field of lithium iron phosphate positive electrode materials. The lithium iron phosphate positive electrode material includes small lithium iron phosphate particles and large lithium iron phosphate particles. At least some of the small lithium iron phosphate particles fill the gaps between the large lithium iron phosphate particles, and the crystal lattice of the small lithium iron phosphate particles is doped with Ti. The lithium iron phosphate positive electrode material has a high compaction density, which is beneficial for improving the discharge capacity and coulombic efficiency of the material. The preparation method includes: mixing a first slurry for forming large lithium iron phosphate particles with a second slurry for forming small lithium iron phosphate particles, drying, and sintering. The lithium iron phosphate positive electrode material can be used to further prepare batteries.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium iron phosphate positive electrode materials, and in particular to a lithium iron phosphate positive electrode material and a preparation method and application thereof. Background Art

[0002] With the continued expansion of lithium iron phosphate materials in the power and energy storage markets, manufacturers are actively developing high-density lithium iron phosphate cathode materials to meet market demand for high-energy-density batteries. However, the current density of lithium iron phosphate cathode materials is generally low and needs to be further improved.

[0003] In view of this, the present disclosure is proposed. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a lithium iron phosphate positive electrode material and a preparation method and application thereof to solve or improve the above-mentioned technical problems.

[0005] The present disclosure can be implemented as follows:

[0006] In a first aspect, the present disclosure provides a lithium iron phosphate positive electrode material, which includes small lithium iron phosphate particles and large lithium iron phosphate particles, at least part of the small lithium iron phosphate particles are filled in the gaps between the large lithium iron phosphate particles, and the lattice of the small lithium iron phosphate particles is doped with Ti.

[0007] In an optional embodiment, the D of the lithium iron phosphate small particles 50 200nm-400nm, D of large lithium iron phosphate particles 50 It is 600nm-800nm.

[0008] In an optional embodiment, in the lithium iron phosphate positive electrode material, the number of small lithium iron phosphate particles accounts for 45%-85%.

[0009] In an optional embodiment, the surfaces of the small lithium iron phosphate particles and the large lithium iron phosphate particles are both coated with a carbon coating layer.

[0010] In an optional embodiment, the thickness of the carbon coating layer is 3 nm-5 nm.

[0011] In an optional embodiment, the lithium iron phosphate positive electrode material has at least one of the following characteristics:

[0012] Feature 1: The compaction density of lithium iron phosphate cathode material is not less than 2.55g / cm 3 ;

[0013] Feature 2: The initial discharge capacity of the lithium iron phosphate cathode material is not less than 156 mAh / g;

[0014] Feature 3: The coulombic efficiency of the lithium iron phosphate positive electrode material is not less than 98.5%.

[0015] In a second aspect, the present disclosure provides a method for preparing a lithium iron phosphate positive electrode material as described in any of the aforementioned embodiments, which includes the following steps: mixing a first slurry for forming large lithium iron phosphate particles with a second slurry for forming small lithium iron phosphate particles, and drying them to obtain a lithium iron phosphate precursor; and sintering the lithium iron phosphate precursor.

[0016] In an optional embodiment, the first slurry contains iron phosphate, a lithium source and a carbon source, and the second slurry contains iron phosphate, a lithium source, a carbon source and a titanium source; the particle size of the solid in the first slurry is larger than the particle size of the solid in the second slurry.

[0017] In an optional embodiment, the preparation of the lithium iron phosphate precursor includes: sand grinding the iron phosphate, a lithium source and a carbon source in the presence of a dispersion medium to obtain a first slurry; continuing to grind part of the first slurry to obtain an intermediate slurry; mixing the intermediate slurry with a titanium source solution, adjusting the pH value to 7 to 8, and obtaining a second slurry; mixing the remaining first slurry with the second slurry, and drying.

[0018] In an alternative embodiment, the iron-to-phosphorus ratio of the ferric phosphate is from 0.975:1 to 0.985:1;

[0019] and / or, the lithium source comprises at least one of lithium carbonate and lithium hydroxide;

[0020] And / or, the carbon source includes at least one of glucose, sucrose, citric acid and polyethylene glycol.

[0021] In an alternative embodiment, the molar ratio of lithium in the lithium source to iron in the ferric phosphate is 1.01:1 to 1.03:1;

[0022] And / or, the amount of carbon source added is 6%-12% of the mass of the theoretically generated pure-phase lithium iron phosphate.

[0023] In an optional embodiment, the preparation process of the first slurry includes at least one of the following features:

[0024] Feature 1: The dispersion medium used is water;

[0025] Feature 2: The mass fraction of solid matter in the mixture of iron phosphate, lithium source, carbon source and dispersion medium is 55%-65%;

[0026] Feature 3: Particle size D of solid matter in the first slurry 50 1.1μm-1.3μm.

[0027] In an optional embodiment, the intermediate slurry is obtained by further grinding 65wt%-80wt% of the first slurry;

[0028] and / or, particle size D of the solid matter in the intermediate slurry 50 0.35μm-0.45μm.

[0029] In an optional embodiment, the titanium source in the titanium source solution is an organic titanium compound;

[0030] And / or, the amount of titanium element added to the titanium source is 0.1%-0.3% of the mass of the theoretically generated pure-phase lithium iron phosphate.

[0031] In an alternative embodiment, the organic titanium compound includes at least one of tetrabutyl titanate and tetraethyl titanate.

[0032] In an optional embodiment, the preparation of the titanium source solution includes: mixing an aqueous oxalic acid solution with a titanium source to obtain a suspension; heating the suspension to obtain a titanium-containing solution; and mixing the titanium-containing solution with a stabilizer.

[0033] In an optional embodiment, the preparation of the titanium source solution includes at least one of the following features:

[0034] Feature 1: The concentration of oxalic acid in the oxalic acid aqueous solution is 8wt%-12wt%;

[0035] Feature 2: The mass ratio of the titanium source to the oxalic acid in the oxalic acid aqueous solution is 1:2.1 to 1:2.3;

[0036] Feature 3: Heating temperature is not less than 60℃;

[0037] Feature 4: The mass ratio of titanium source to stabilizer is 1:0.04 to 1:0.06;

[0038] Feature 5: The stabilizer is hydrogen peroxide.

[0039] In an optional embodiment, the pH value is adjusted by adding ammonia water.

[0040] In an alternative embodiment, drying is performed by spray drying.

[0041] In an optional embodiment, the spray drying includes at least one of the following features:

[0042] Feature 1: The inlet temperature of the spray tower is 180℃-280℃;

[0043] Feature 2: The air outlet temperature of the spray tower is 80℃-110℃;

[0044] Feature 3: Compressed air pressure is 0.35MPa-0.45MPa.

[0045] In an optional embodiment, sintering includes at least one of the following features:

[0046] Feature 1: Sintering temperature is 760℃-840℃;

[0047] Feature 2: Sintering time is 6h-10h;

[0048] Feature 3: The heating rate during sintering is 2℃ / min-5℃ / min;

[0049] Feature 4: Sintering is carried out in a protective atmosphere.

[0050] In a third aspect, the present disclosure provides a battery comprising the lithium iron phosphate positive electrode material according to any one of the aforementioned embodiments.

[0051] The beneficial effects of the present disclosure include:

[0052] The present disclosure improves the compaction density of the lithium iron phosphate cathode material by combining lithium iron phosphate particles of different sizes and filling at least some of the small lithium iron phosphate particles between the large lithium iron phosphate particles. Furthermore, the lattice of the small lithium iron phosphate particles is doped with Ti, which refines the lattice and prevents the small particles from agglomerating and growing into large particles, thereby ensuring that the lithium iron phosphate cathode material always contains both small and large lithium iron phosphate particles that cooperate with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0054] Figure 1 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 1;

[0055] Figure 2 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1;

[0056] Figure 3 This is the discharge diagram of the lithium iron phosphate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0057] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0058] The lithium iron phosphate positive electrode material provided by the present disclosure, as well as its preparation method and application are described in detail below.

[0059] The present disclosure provides a lithium iron phosphate positive electrode material, which includes small lithium iron phosphate particles and large lithium iron phosphate particles. At least part of the small lithium iron phosphate particles are filled in the gaps between the large lithium iron phosphate particles, and Ti is doped in the lattice of the small lithium iron phosphate particles.

[0060] By combining lithium iron phosphate particles of different sizes and filling at least some of the small lithium iron phosphate particles between larger lithium iron phosphate particles, the compaction density of the lithium iron phosphate cathode material is improved. In addition, the lattice of the small lithium iron phosphate particles is doped with Ti, which can refine the lattice and prevent small particles from agglomerating into large particles, thereby ensuring that the lithium iron phosphate cathode material always contains both small and large lithium iron phosphate particles that cooperate with each other.

[0061] In some embodiments, the D of the lithium iron phosphate small particles is 50 It can be 200nm-400nm, such as 200nm, 250nm, 300nm, 350nm or 400nm, etc., or any other value within the range of 200nm-400nm. 50 It can be 600nm-800nm, such as 600nm, 650nm, 700nm, 750nm or 800nm, or any other value within the range of 600nm-800nm.

[0062] By combining the small lithium iron phosphate particles and large lithium iron phosphate particles of the above-mentioned particle size, the small lithium iron phosphate particles can be effectively filled in the gaps between the large lithium iron phosphate particles.

[0063] In some embodiments, in the lithium iron phosphate positive electrode material, the number of small lithium iron phosphate particles can account for 45%-85%, such as 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, etc., or it can be any other value within the range of 45%-85%.

[0064] The proportion of small lithium iron phosphate particles in the lithium iron phosphate positive electrode material is set to the above range, which can effectively coordinate the small lithium iron phosphate particles and large lithium iron phosphate particles, that is, the gaps between the large lithium iron phosphate particles are filled with an appropriate amount of small lithium iron phosphate particles, which is conducive to providing a high compaction density of the lithium iron phosphate positive electrode material.

[0065] In the present disclosure, the surfaces of the small lithium iron phosphate particles and the large lithium iron phosphate particles may also be coated with a carbon coating layer.

[0066] Illustratively, the thickness of the carbon coating layer may be 3 nm-5 nm, such as 3 nm, 3.5 nm, 4 nm, 4.5 nm or 5 nm, or any other value within the range of 3 nm-5 nm.

[0067] By coating the surface of small lithium iron phosphate particles and large lithium iron phosphate particles with a carbon coating layer, on the one hand, the conductivity of the lithium iron phosphate positive electrode material can be improved. On the other hand, the carbon coating layer can also limit the size of the small lithium iron phosphate particles and large lithium iron phosphate particles, thereby preventing the small lithium iron phosphate particles and large lithium iron phosphate particles from growing further.

[0068] In some embodiments of the present disclosure, the compaction density of the lithium iron phosphate cathode material is not less than 2.55 g / cm 3 , indicating that the lithium iron phosphate positive electrode material has a higher compaction density.

[0069] In some embodiments of the present disclosure, the first discharge specific capacity of the lithium iron phosphate positive electrode material is not less than 156 mAh / g, indicating that the lithium iron phosphate positive electrode material has a relatively high first discharge specific capacity.

[0070] In some embodiments of the present disclosure, the coulombic efficiency of the lithium iron phosphate positive electrode material is not less than 98.5%, indicating that the lithium iron phosphate positive electrode material has a relatively high coulombic efficiency.

[0071] Accordingly, the present disclosure also provides a method for preparing a lithium iron phosphate positive electrode material, which includes the following steps: mixing a first slurry for forming large lithium iron phosphate particles with a second slurry for forming small lithium iron phosphate particles, drying them to obtain a lithium iron phosphate precursor; and sintering the lithium iron phosphate precursor.

[0072] The first slurry contains iron phosphate, a lithium source and a carbon source, and the second slurry contains iron phosphate, a lithium source, a carbon source and a titanium source; the particle size of the solid matter in the first slurry is larger than that of the solid matter in the second slurry.

[0073] In some embodiments, the preparation of a lithium iron phosphate precursor may include: sand-grinding iron phosphate, a lithium source, and a carbon source in the presence of a dispersion medium to obtain a first slurry; continuing to grind a portion of the first slurry to obtain an intermediate slurry; mixing the intermediate slurry with a titanium source solution, adjusting the pH value to 7 to 8, and obtaining a second slurry; mixing the remaining first slurry with the second slurry, and drying.

[0074] Iron phosphate can be purchased directly. For example, the iron-to-phosphorus ratio of the iron phosphate used can be 0.975:1 to 0.985:1, such as 0.975:1, 0.980:1, or 0.985:1, or any other value within the range of 0.975:1 to 0.985:1. The so-called "iron-to-phosphorus ratio" refers to the molar ratio of Fe to P.

[0075] The lithium source may illustratively but not limitatively include at least one of lithium carbonate and lithium hydroxide.

[0076] The carbon source may illustratively but not limitedly include at least one of glucose, sucrose, citric acid, and polyethylene glycol.

[0077] The dispersion medium may be, for example, water or anhydrous ethanol, etc. In some embodiments, water is used as the dispersion medium to reduce costs.

[0078] For reference, the relationship between the amount of lithium source and iron phosphate can be referred to as follows: the molar ratio of lithium in the lithium source to iron in the iron phosphate is 1.01:1 to 1.03:1, such as 1.01:1, 1.02:1 or 1.03:1, etc., and can also be any other value within the range of 1.01:1 to 1.03:1.

[0079] The dosage relationship of the carbon source can be referred to as follows: the amount of carbon source added is 6%-12% of the theoretical mass of pure phase lithium iron phosphate, such as 6%, 7%, 8%, 9%, 10%, 11% or 12%, etc., or it can be any other value within the range of 6%-12%.

[0080] If the amount of carbon source used is too much, the carbon coating layer will be too thick, which is not conducive to lithium ion insertion and extraction, resulting in low capacity.

[0081] In the present disclosure, the mass fraction of solid matter in the mixture of iron phosphate, lithium source, carbon source and dispersion medium can be 55%-65%, such as 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64% or 65%, etc., or it can be any other value within the range of 55%-65%.

[0082] If the mass fraction of solid matter is too low, the sanding efficiency will be reduced; if the mass fraction of solid matter is too high, sanding will be difficult to carry out.

[0083] In some embodiments, the particle size D of the solid matter in the first slurry is 50 It can be 1.1μm-1.3μm, such as 1.1μm, 1.15μm, 1.2μm, 1.25μm or 1.3μm, or any other value within the range of 1.1μm-1.3μm. That is, it is sufficient to sand-grind to the above particle size. After subsequent drying and sintering, the first slurry under this particle size can form D 50 These are large lithium iron phosphate particles of 600nm-800nm.

[0084] 65 wt% to 80 wt% of the first slurry is further ground to obtain an intermediate slurry, which is used to further prepare the second slurry.

[0085] For example, the particle size D of the solid matter in the intermediate slurry is50 It can be 0.35 μm-0.45 μm, such as 0.35 μm, 0.40 μm or 0.45 μm.

[0086] In the present disclosure, the preparation of the titanium source solution may include: mixing an oxalic acid aqueous solution with a titanium source to obtain a suspension; heating the suspension to obtain a titanium-containing solution; and mixing the titanium-containing solution with a stabilizer.

[0087] The titanium source in the titanium source solution is an organic titanium compound, such as at least one of tetrabutyl titanate and tetraethyl titanate.

[0088] The amount of titanium added to the titanium source can be 0.1%-0.3% of the theoretical mass of pure-phase lithium iron phosphate, such as 0.1%, 0.15%, 0.2%, 0.25% or 0.3%, or any other value within the range of 0.1%-0.3%.

[0089] The concentration of oxalic acid in the aqueous oxalic acid solution can be 8 wt%-12 wt%, such as 8 wt%, 9 wt%, 10 wt%, 11 wt% or 12 wt%. The mass ratio of the titanium source to the oxalic acid in the aqueous oxalic acid solution is 1:2.1 to 1:2.3, such as 1:2.1, 1:2.2 or 1:2.3.

[0090] During the specific operation, the titanium source can be slowly added to the oxalic acid aqueous solution while stirring. After the titanium source is added, a suspension of white precipitate is obtained. It should be noted that if tetrabutyl titanate is used as the organic titanium compound, an oil layer will appear. In this case, the upper oil layer should be separated and removed before subsequent treatment.

[0091] The purpose of heating the suspension is mainly to accelerate the dissolution rate of the precipitate. For example, the heating temperature is not less than 60° C. Specifically, the suspension can be heated in a water bath with stirring.

[0092] It should be noted that, in some embodiments, the suspension may not be heated and may be allowed to slowly dissolve.

[0093] After the precipitate is dissolved, it is cooled, and then the cooled titanium-containing solution is stirred evenly with the stabilizer.

[0094] The mass ratio of the titanium source to the stabilizer may be 1:0.04 to 1:0.06, such as 1:0.04, 1:0.05, or 1:0.06. The stabilizer may be, for example but not limited to, hydrogen peroxide. By using hydrogen peroxide as a stabilizer, other impurities will not be introduced after its decomposition.

[0095] In the present disclosure, the pH value can be adjusted by adding ammonia water, wherein the concentration of the ammonia water can be 25 wt%.

[0096] In the present disclosure, drying can be performed by spray drying.

[0097] For reference, the spray tower inlet temperature may be 180°C-280°C, such as 180°C, 200°C, 220°C, 240°C, 260°C or 280°C, or any other value within the range of 180°C-280°C.

[0098] The air outlet temperature of the spray tower can be 80°C-110°C, such as 80°C, 90°C, 100°C or 110°C, or any other value within the range of 80°C-110°C.

[0099] The compressed air pressure may be 0.35 MPa-0.45 MPa, such as 0.35 MPa, 0.38 MPa, 0.4 MPa, 0.42 MPa or 0.45 MPa, or any other value within the range of 0.35 MPa-0.45 MPa.

[0100] Through the above spray drying, a lithium iron phosphate precursor is obtained.

[0101] In the present disclosure, the temperature for sintering the lithium iron phosphate precursor can be 760℃-840℃, such as 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃ or 840℃, etc., or it can be any other value within the range of 760℃-840℃.

[0102] The sintering time may be 6 h to 10 h, such as 6 h, 7 h, 8 h, 9 h or 10 h, etc., or any other value within the range of 6 h to 10 h.

[0103] The heating rate during the sintering process can be 2°C / min-5°C / min, such as 2°C / min, 3°C / min, 4°C / min or 5°C / min, or any other value within the range of 2°C / min-5°C / min.

[0104] The sintering may be performed in a protective atmosphere, wherein the protective atmosphere may illustratively but not limitatively include a nitrogen atmosphere or an argon atmosphere.

[0105] After sintering, cool naturally to below 80℃ and take out the material.

[0106] It should be noted that, during the above sintering process, protective gas is passed throughout the entire process from heating to cooling.

[0107] After obtaining the lithium iron phosphate positive electrode material, it can also be post-processed, such as crushing and screening.

[0108] For example, the sintered material can be crushed by air flow crushing or mechanical grinding, and the crushed material is sieved through a 200-mesh sieve, the material on the sieve is crushed again, and the material under the sieve is collected.

[0109] In some embodiments, taking the titanium source as tetraethyl titanate, the lithium source as lithium carbonate, and the stabilizer as hydrogen peroxide as an example, the reactions involved in the preparation of the lithium iron phosphate positive electrode material include:

[0110] (1) Tetraethyl titanate is hydrolyzed to form unstable metatitanic acid:

[0111] Ti(OC2H5)4+4H2O→Ti(OH)4+4C2H5OH;

[0112] (2) Titanic acid and oxalic acid form a soluble metal complex:

[0113] Ti(OH)4+2H2C2O4→Ti 4+ ·[(C2O4) 2+ ]2+4H2O;

[0114] (3) Adding ammonia water to adjust the pH destroys the complex structure, causing TiO2 to precipitate and coat the surface of small particles. Ammonium oxalate decomposes during the sintering process and does not introduce impurities:

[0115] Ti 4+ ·[(C2O4) 2+ ]2+NH3·H2O→TiO2↓+2(NH4)C2O4;

[0116] (4) Lithium iron phosphate synthesis:

[0117] Li2CO3+2FePO4+C→2LiFePO4+CO↑+CO2↑.

[0118] The TiO2 precipitated and coated on the surface of the small particles by chemical deposition can, on the one hand, refine the particles during the sanding process, reduce the sanding time, and reduce energy consumption during the sanding process; on the other hand, the titanium element will enter the internal lattice of the small particles during the sintering process, and also refine the lattice, preventing the small particles from agglomerating and growing into large particles during the sintering process.

[0119] As mentioned above, the present invention ensures the particle size grading ratio by mixing a second slurry containing solids of different particle sizes and the remaining first slurry in a certain proportion. The two are fully mixed and then sprayed, and the purpose of uniform distribution of large and small particles can be achieved without sintering, which is beneficial to improving compaction. Among them, the addition of a titanium source to the second slurry can refine the solids in the second slurry, preventing them from agglomerating and growing into large particles during the subsequent sintering process, and is also beneficial to reducing the sanding time and reducing energy consumption during the sanding process. In addition, the TiO2 coating layer formed on the surface of the solids in the second slurry by chemical deposition is uniform and tight, which can prevent the TiO2 coating layer from falling off with the mixing and stirring of large and small particle slurries. If a similar purpose is achieved by traditional means, the only way is to spray-dry the large and small particle slurries separately and then mix the materials. In addition to increasing the mixing process and mixing equipment, the uniformity of solid phase mixing is also worse than the liquid phase mixing of the present invention.

[0120] In addition, the present disclosure also provides a battery, which contains the lithium iron phosphate positive electrode material according to any of the aforementioned embodiments.

[0121] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0122] Example 1

[0123] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0124] (1) Weighing:

[0125] Commercial iron phosphate (iron-phosphorus ratio of 0.98:1) and lithium carbonate are weighed according to the molar ratio of Li to Fe of 1.02:1; glucose is weighed according to 10wt% of the mass of the theoretically generated pure-phase lithium iron phosphate; tetrabutyl titanate is weighed according to 0.2wt% of the mass of the theoretically generated pure-phase lithium iron phosphate; oxalic acid and hydrogen peroxide are weighed according to the molar ratio of tetrabutyl titanate: oxalic acid: hydrogen peroxide of 1:2.1:0.05; and a certain amount of 25wt% ammonia water is prepared.

[0126] (2) Preparation of Ti salt solution:

[0127] Weighed oxalic acid is prepared into a 10wt% oxalic acid aqueous solution; while stirring the solution, weighed tetrabutyl titanate is slowly added, and after the tetrabutyl titanate is added, a suspension of white precipitate is obtained; the suspension is heated in a water bath with stirring at 60°C. After the precipitate is completely dissolved, heating is stopped; after the solution cools, hydrogen peroxide is added and stirred uniformly to obtain a titanium source solution. The titanium source solution preparation and sand milling can be performed simultaneously.

[0128] (3) Sanding:

[0129] Commercial iron phosphate, lithium carbonate and glucose were sand-milled, and appropriate amount of deionized water was added as a dispersion medium to adjust the solid content to 60 wt %. The particles were ground to a size of D 50 =1.2μm, and the first slurry is obtained. 30wt% of the first slurry is transferred to the stirring tank A for stirring and used as the precursor slurry A; the remaining first slurry is further ground to a particle size of D 50 =0.4μm to obtain an intermediate slurry; transfer all the intermediate slurry to a stirring tank B for stirring, slowly add the titanium source solution prepared in step (2) into the stirring tank B, and after the addition of the titanium source solution is completed, slowly add ammonia water to adjust the pH to 7-8 to obtain a second slurry (as precursor slurry B); transfer all the precursor slurry B to tank A and mix it with the precursor slurry A to obtain precursor slurry C.

[0130] (4) Spray drying:

[0131] The precursor slurry C was spray dried, the spray tower inlet temperature was set to 220° C., the air outlet temperature was set to 110° C., and the compressed air pressure was 0.4 MPa. After spray drying, a lithium iron phosphate precursor was obtained.

[0132] (5) Sintering:

[0133] The lithium iron phosphate precursor was placed in a kiln with nitrogen for sintering, and the temperature was raised to 760°C at a heating rate of 5°C / min, kept at this temperature for 8 hours, and cooled to below 80°C to take out the material; nitrogen gas was passed throughout the entire process from the start of heating to the end of cooling.

[0134] (6) Crushing and screening:

[0135] The sintered material is crushed by air flow crushing or mechanical grinding, and the crushed material is screened through a 200-mesh sieve. The material on the sieve is crushed again, and the material under the sieve is the target product, lithium iron phosphate positive electrode material.

[0136] The SEM image of the lithium iron phosphate cathode material is as follows Figure 1 As shown by Figure 1 It can be seen that the lithium iron phosphate positive electrode material contains both small lithium iron phosphate particles and large lithium iron phosphate particles, and the gaps between the large lithium iron phosphate particles are filled with small lithium iron phosphate particles.

[0137] The XRD pattern of the lithium iron phosphate cathode material is as follows Figure 2 As shown by Figure 2 It can be seen that the synthesized material highly coincides with the standard card PDF#81-1173, indicating that the synthesized material is a pure phase lithium iron phosphate material.

[0138] Example 2

[0139] The difference between this embodiment and embodiment 1 is that:

[0140] During the weighing process: tetraethyl titanate is weighed so that the titanium element accounts for 0.15 wt% of the mass of the theoretically generated pure phase lithium iron phosphate.

[0141] The remaining steps and conditions are the same as in Example 1.

[0142] Example 3

[0143] The difference between this embodiment and embodiment 1 is that:

[0144] During the sand milling process, 25 wt% of the first slurry was transferred to a stirring tank A for stirring and used as precursor slurry A.

[0145] The remaining steps and conditions are the same as in Example 1.

[0146] Example 4

[0147] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0148] (1) Weighing:

[0149] Commercial iron phosphate (iron-phosphorus ratio of 0.975) and lithium carbonate are weighed according to the molar ratio of Li to Fe of 1.01:1; sucrose is weighed according to 6wt% of the theoretical mass of pure-phase lithium iron phosphate; tetrabutyl titanate is weighed according to 0.1wt% of the theoretical mass of pure-phase lithium iron phosphate; oxalic acid and hydrogen peroxide are weighed according to the molar ratio of tetrabutyl titanate: oxalic acid: hydrogen peroxide of 1:2.2:0.04; and some 25wt% ammonia water is prepared.

[0150] (2) Preparation of Ti salt solution:

[0151] Weighed oxalic acid is prepared into an 8wt% oxalic acid aqueous solution; while stirring the solution, weighed tetrabutyl titanate is slowly added, and after the tetrabutyl titanate is added, a suspension of white precipitate is obtained; the suspension is heated in a water bath with stirring at 60°C. After the precipitate is completely dissolved, heating is stopped; after the solution cools, hydrogen peroxide is added and stirred uniformly to obtain a titanium source solution. The titanium source solution preparation and sand milling can be performed simultaneously.

[0152] (3) Sanding:

[0153] Commercial iron phosphate, lithium carbonate and sucrose were sand-milled, and appropriate amount of deionized water was added as a dispersion medium to adjust the solid content to 55 wt %. The particles were ground to a size of D 50 =1.1μm, and the first slurry is obtained. 20wt% of the first slurry is transferred to the stirring tank A for stirring and used as the precursor slurry A; the remaining first slurry is further ground to a particle size of D 50=0.35μm to obtain an intermediate slurry; transfer all the intermediate slurry to a stirring tank B for stirring, slowly add the titanium source solution prepared in step (2) into the stirring tank B, and after the addition of the titanium source solution is completed, slowly add ammonia water to adjust the pH to 7-8 to obtain a second slurry (as precursor slurry B); transfer all the precursor slurry B to tank A and mix it with the precursor slurry A to obtain precursor slurry C.

[0154] (4) Spray drying:

[0155] The precursor slurry C was spray dried, the spray tower inlet temperature was set to 180° C., the air outlet temperature was set to 80° C., and the compressed air pressure was 0.35 MPa. After spray drying, a lithium iron phosphate precursor was obtained.

[0156] (5) Sintering:

[0157] The lithium iron phosphate precursor was placed in a kiln with nitrogen for sintering, and the temperature was raised to 760°C at a heating rate of 2°C / min. It was kept at this temperature for 10 hours, and the material was taken out after cooling to below 80°C. Argon gas was passed throughout the entire process from the start of heating to the end of cooling.

[0158] (6) Crushing and screening:

[0159] The sintered material is crushed by air flow crushing or mechanical grinding, and the crushed material is screened through a 200-mesh sieve. The material on the sieve is crushed again, and the material under the sieve is the target product, lithium iron phosphate positive electrode material.

[0160] Example 5

[0161] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0162] (1) Weighing:

[0163] Commercial iron phosphate (iron-phosphorus ratio of 0.985) and lithium carbonate are weighed according to the molar ratio of Li to Fe of 1.03:1; citric acid is weighed according to 12wt% of the theoretical mass of pure-phase lithium iron phosphate; tetraethyl titanate is weighed according to 0.3wt% of the theoretical mass of pure-phase lithium iron phosphate; oxalic acid and hydrogen peroxide are weighed according to the molar ratio of tetraethyl titanate: oxalic acid: hydrogen peroxide of 1:2.3:0.06; and a certain amount of 25wt% ammonia water is prepared.

[0164] (2) Preparation of Ti salt solution:

[0165] Weighed oxalic acid is prepared into a 12wt% oxalic acid aqueous solution; while stirring the solution, weighed tetraethyl titanate is slowly added, and after the tetraethyl titanate is added, a suspension of white precipitate is obtained; the suspension is heated in a water bath with stirring at 60°C. After the precipitate is completely dissolved, heating is stopped; after the solution cools, hydrogen peroxide is added and stirred uniformly to obtain a titanium source solution. The titanium source solution preparation and sand milling can be performed simultaneously.

[0166] (3) Sanding:

[0167] Commercial iron phosphate, lithium carbonate and citric acid were sand-milled, and appropriate amount of deionized water was added as a dispersion medium to adjust the solid content to 65 wt %. The particles were ground to a size of D 50 =1.3μm, and the first slurry is obtained. 35wt% of the first slurry is transferred to the stirring tank A for stirring and used as the precursor slurry A; the remaining first slurry is further ground to a particle size of D 50 =0.45μm to obtain an intermediate slurry; transfer all the intermediate slurry to a stirring tank B for stirring, slowly add the titanium source solution prepared in step (2) into the stirring tank B, and after the addition of the titanium source solution is completed, slowly add ammonia water to adjust the pH to 7-8 to obtain a second slurry (as precursor slurry B); transfer all the precursor slurry B to tank A and mix it with the precursor slurry A to obtain precursor slurry C.

[0168] (4) Spray drying:

[0169] The precursor slurry C was spray dried, the spray tower inlet temperature was set to 280° C., the air outlet temperature was set to 100° C., and the compressed air pressure was 0.45 MPa. After spray drying, a lithium iron phosphate precursor was obtained.

[0170] (5) Sintering:

[0171] The lithium iron phosphate precursor was placed in a kiln with nitrogen for sintering, and the temperature was raised to 840°C at a heating rate of 4°C / min, kept at this temperature for 6 hours, and cooled to below 80°C to take out the material; nitrogen gas was passed throughout the entire process from the start of heating to the end of cooling.

[0172] (6) Crushing and screening:

[0173] The sintered material is crushed by air flow crushing or mechanical grinding, and the crushed material is screened through a 200-mesh sieve. The material on the sieve is crushed again, and the material under the sieve is the target product, lithium iron phosphate positive electrode material.

[0174] Comparative Example 1

[0175] The difference between this comparative example and Example 1 is that no titanium source is added to the second slurry.

[0176] Comparative Example 2

[0177] The difference between this comparative example and Example 1 is that tetraethyl titanate is replaced by an equal amount of titanium dioxide, that is, titanium dioxide is directly added to the second slurry as a titanium source.

[0178] Comparative Example 3

[0179] The difference between this comparative example and Example 1 is that during the sand milling process, commercial iron phosphate, lithium carbonate and glucose were sand milled, and an appropriate amount of deionized water was added as a dispersion medium to adjust the solid content to 60 wt % and grinded to a particle size of D 50 =0.4 μm, and then all of it was transferred to a stirring tank for stirring, and a titanium source solution was slowly added to the stirring tank. After the addition of the titanium source solution was completed, ammonia water was slowly added to adjust the pH to 7-8 to obtain a precursor slurry C.

[0180] Comparative Example 4

[0181] The difference between this comparative example and Example 1 is that 50 wt% of the first slurry is transferred to a stirring tank A for stirring and used as precursor slurry A.

[0182] Comparative Example 5

[0183] The difference between this comparative example and Example 1 is that: during the sand milling process, commercial iron phosphate, lithium carbonate and glucose were mixed and dispersed, an appropriate amount of deionized water was added as a dispersion medium, and the solid content was adjusted to 60wt%, and then a titanium source solution was added. After the titanium source solution was added, ammonia water was slowly added to adjust the pH to 7-8 to obtain an unground slurry; the unground slurry was transferred to a sand mill and ground to a particle size of D 50 =1.2μm, 30wt% of the slurry was transferred to the stirring tank A for stirring and standby use to obtain the precursor slurry A; the remaining slurry was continued to be ground to a particle size of D 50 =0.4 μm, all of it is transferred to stirring tank B for stirring to obtain precursor slurry B; all of precursor slurry B is transferred to tank A and mixed with precursor slurry A to obtain precursor slurry C.

[0184] That is, the titanium source is added to the first slurry and mixed with the iron phosphate, lithium carbonate and glucose.

[0185] Test example

[0186] The lithium iron phosphate positive electrode materials obtained in Examples 1-5 and Comparative Examples 1-5 were subjected to measurement of compaction density, initial discharge specific capacity, and coulombic efficiency.

[0187] The compaction density test was carried out at 3T pressure, and the first discharge specific capacity and coulombic efficiency test were carried out in accordance with Appendix G of GB / T33822-2017. The results are shown in Table 1 and Figure 3 shown.

[0188] Table 1 Physical and chemical indicators of lithium iron phosphate products

[0189]

[0190]

[0191] Depend on Figure 3 It can be seen that the lithium iron phosphate cathode material prepared in the embodiment has a stable discharge platform and a high discharge capacity.

[0192] As can be seen from Table 1:

[0193] By comparing Example 1, Example 2 and Comparative Example 1 in which no Ti element is added, it is found that the TiO2 coating layer is deposited on the surface of small particles during the sand milling process using a chemical deposition method within a reasonable range, which can effectively limit the growth of crystals. A large number of small particles effectively fill the gaps between large particles, thereby improving the compaction density. The increase in small particles is also beneficial to the deintercalation and intercalation of lithium ions, and the gram capacity and coulombic efficiency are also improved.

[0194] By comparing Example 1 with Comparative Example 2, TiO2 deposited on the surface of small particles during sand milling by mechanical mixing will be broken up during mixing with large particle slurry, and will not be able to achieve the effect of coating only small particles.

[0195] By comparing Example 1 with Comparative Example 3, it can be seen that adopting a grading scheme during the sand milling process can effectively improve the compaction density without affecting the gram capacity.

[0196] By comparing Example 1, Example 3 and Comparative Example 4, it can be seen that by adjusting the ratio of the sand-milled large and small particle slurry within a reasonable range, a high compaction density product can be obtained. An excessively high proportion of large particles will not only fail to increase the compaction density but will reduce the electrochemical properties of the material.

[0197] By comparing Example 1 with Comparative Example 5, it can be seen that mixing the coating raw material with iron phosphate, lithium source, etc. and then sand-milling will destroy the generated TiO2 coating layer, and the purpose of restricting the growth of small particles alone cannot be achieved.

[0198] In summary, the lithium iron phosphate positive electrode material provided by the present disclosure has a relatively high compaction density, which is beneficial to improving the discharge capacity and coulombic efficiency of the material.

[0199] Industrial Applicability.

[0200] The lithium iron phosphate positive electrode material provided by the present disclosure has high compaction density, discharge capacity and coulombic efficiency, and can be used to prepare batteries with high energy density, thereby meeting the market demand for high energy density batteries.

Claims

1. A lithium iron phosphate positive electrode material, characterized in that: The lithium iron phosphate positive electrode material includes small lithium iron phosphate particles and large lithium iron phosphate particles, at least part of the small lithium iron phosphate particles are filled in the gaps between the large lithium iron phosphate particles, and the lattices of the small lithium iron phosphate particles are doped with Ti; The preparation of the lithium iron phosphate positive electrode material includes: sand grinding iron phosphate, a lithium source, and a carbon source in the presence of a dispersion medium to obtain a first slurry; further grinding a portion of the first slurry to obtain an intermediate slurry; mixing the intermediate slurry with a titanium source solution and adjusting the pH value to 7 to 8 to obtain a second slurry; mixing the remaining first slurry with the second slurry and drying to obtain a lithium iron phosphate precursor; sintering the lithium iron phosphate precursor; the intermediate slurry is obtained by further grinding 65wt%-80wt% of the first slurry; The preparation of the titanium source solution includes: mixing an oxalic acid aqueous solution with a titanium source to obtain a suspension; heating the suspension to obtain a titanium-containing solution; mixing the titanium-containing solution with a stabilizer; the titanium source in the titanium source solution is an organic titanium compound.

2. The lithium iron phosphate positive electrode material according to claim 1, characterized in that The D of the lithium iron phosphate small particles 50 The D of the large lithium iron phosphate particles is 200nm-400nm. 50 It is 600nm-800nm.

3. The lithium iron phosphate cathode material according to claim 1 or 2, characterized in that In the lithium iron phosphate positive electrode material, the number of the small lithium iron phosphate particles accounts for 45%-85%.

4. The lithium iron phosphate positive electrode material according to claim 1 or 2, characterized in that The surfaces of the small lithium iron phosphate particles and the large lithium iron phosphate particles are both coated with a carbon coating layer.

5. The lithium iron phosphate positive electrode material according to claim 4, characterized in that The thickness of the carbon coating layer is 3nm-5nm.

6. The lithium iron phosphate cathode material according to claim 1 or 2, characterized in that: The lithium iron phosphate positive electrode material has at least one of the following characteristics: Feature 1: The compaction density of the lithium iron phosphate positive electrode material is not less than 2.55g / cm 3 ; Feature 2: The initial discharge specific capacity of the lithium iron phosphate cathode material is not less than 156 mAh / g; Feature 3: The coulombic efficiency of the lithium iron phosphate positive electrode material is not less than 98.5%.

7. A method for preparing the lithium iron phosphate positive electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Sand-grinding iron phosphate, a lithium source, and a carbon source in the presence of a dispersion medium to obtain a first slurry; further grinding a portion of the first slurry to obtain an intermediate slurry; mixing the intermediate slurry with a titanium source solution and adjusting the pH value to 7 to 8 to obtain a second slurry; mixing the remaining first slurry with the second slurry and drying them to obtain a lithium iron phosphate precursor; sintering the lithium iron phosphate precursor; The intermediate slurry is obtained by further grinding 65wt%-80wt% of the first slurry; The preparation of the titanium source solution includes: mixing an oxalic acid aqueous solution with a titanium source to obtain a suspension; heating the suspension to obtain a titanium-containing solution; mixing the titanium-containing solution with a stabilizer; the titanium source in the titanium source solution is an organic titanium compound.

8. The preparation method according to claim 7, characterized in that The iron-phosphorus ratio of the ferric phosphate is 0.975:1 to 0.985:1; And / or, the lithium source includes at least one of lithium carbonate and lithium hydroxide; And / or, the carbon source includes at least one of glucose, sucrose, citric acid and polyethylene glycol.

9. The preparation method according to claim 7, characterized in that The molar ratio of lithium in the lithium source to iron in the iron phosphate is 1.01:1 to 1.03:1; And / or, the added amount of the carbon source is 6%-12% of the mass of the theoretically generated pure-phase lithium iron phosphate.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The preparation process of the first slurry includes at least one of the following features: Feature 1: The dispersion medium used is water; Feature 2: In the mixture of the iron phosphate, the lithium source, the carbon source and the dispersion medium, the mass fraction of solid matter is 55%-65%; Feature 3: Particle size D of the solid matter in the first slurry 50 1.1μm-1.3μm.

11. The preparation method according to claim 7, characterized in that The particle size D of the solid matter in the intermediate slurry 50 0.35μm-0.45μm.

12. The preparation method according to claim 7, characterized in that The amount of titanium element added to the titanium source is 0.1%-0.3% of the mass of the theoretically generated pure-phase lithium iron phosphate.

13. The preparation method according to claim 12, characterized in that The organic titanium compound includes at least one of tetrabutyl titanate and tetraethyl titanate.

14. The preparation method according to claim 7, characterized in that The preparation of the titanium source solution includes at least one of the following features: Feature 1: The concentration of oxalic acid in the oxalic acid aqueous solution is 8wt%-12wt%; Feature 2: The mass ratio of the titanium source to the oxalic acid in the oxalic acid aqueous solution is 1:2.1 to 1:2.3; Feature 3: Heating temperature is not less than 60℃; Feature 4: The mass ratio of the titanium source to the stabilizer is 1:0.04 to 1:0.06; Feature 5: The stabilizer is hydrogen peroxide.

15. The preparation method according to claim 7, characterized in that The pH value was adjusted by adding ammonia.

16. The preparation method according to claim 7, characterized in that Drying is carried out by spray drying.

17. The preparation method according to claim 16, characterized in that Spray drying includes at least one of the following features: Feature 1: The inlet temperature of the spray tower is 180℃-280℃; Feature 2: The air outlet temperature of the spray tower is 80℃-110℃; Feature 3: Compressed air pressure is 0.35MPa-0.45MPa.

18. The preparation method according to claim 7, characterized in that Sintering includes at least one of the following features: Feature 1: Sintering temperature is 760℃-840℃; Feature 2: Sintering time is 6h-10h; Feature 3: The heating rate during sintering is 2℃ / min-5℃ / min; Feature 4: Sintering is carried out in a protective atmosphere.

19. A battery, characterized in that: The battery contains the lithium iron phosphate positive electrode material according to any one of claims 1 to 6.

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