Lithium iron phosphate material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention discloses a lithium iron phosphate material and a preparation method thereof, an electrochemical device and electronic equipment. The preparation method comprises the following steps: grinding raw materials, and sequentially carrying out drying treatment, sintering treatment and crushing treatment, wherein the raw materials comprise a phosphorus source, an iron source, a lithium source, a carbon source and a doping agent; the doping agent comprises rutile type titanium dioxide and anatase type titanium dioxide. The lithium iron phosphate material prepared by the invention has excellent grading effect and relatively high compaction density, and the electrochemical device adopting the lithium iron phosphate material has excellent electrical properties.

Description

Technical Field

[0001] The present invention relates to a lithium iron phosphate material, a preparation method thereof, an electrochemical device, and an electronic device. Background Art

[0002] With the rapid development of new energy technologies, lithium iron phosphate (LiFePO 4 , abbreviated as LFP) has been widely used as the cathode material of lithium-ion batteries due to its excellent safety, cycle stability, and cost-effectiveness. However, the low tap density and conductivity of LFP materials limit their application in high-energy-density batteries. To improve the electrochemical performance of LFP materials, researchers have mostly used technical means such as particle nanosizing, carbon coating, and ion doping to overcome the inherent defects of this material. Among them, metal ion doping is an important method to improve the conductivity of LFP materials. However, the above means will further reduce the tap density of LFP materials, resulting in the inability to further improve the volumetric energy density of lithium iron phosphate batteries. Summary of the Invention

[0003] To solve the defect in the prior art that the tap density of lithium iron phosphate materials is low, resulting in a low energy density of lithium iron phosphate batteries, the present invention provides a lithium iron phosphate material, a preparation method thereof, an electrochemical device, and an electronic device. The lithium iron phosphate material of the present invention has a better grading effect and a high tap density. The electrochemical device using the lithium iron phosphate material of the present invention has excellent electrical properties, especially a high discharge capacity and a high initial coulombic efficiency.

[0004] In a first aspect, the present invention provides a preparation method of a lithium iron phosphate material, the preparation method comprising:

[0005] After grinding the raw materials, drying treatment, sintering treatment, and pulverization treatment are carried out in sequence;

[0006] wherein the raw materials include a phosphorus source, an iron source, a lithium source, a carbon source, and a dopant;

[0007] The dopant includes rutile titanium dioxide and anatase titanium dioxide.

[0008] In a second aspect, the present invention provides a lithium iron phosphate material, which is prepared by the preparation method of the lithium iron phosphate material as described above.

[0009] In a third aspect, the present invention provides an electrochemical device, and the positive electrode sheet of the electrochemical device includes the lithium iron phosphate material as described above.

[0010] In a fourth aspect, the present invention provides an electronic device, which includes the electrochemical device as described above.

[0011] The positive progressive effect of the present invention is that:

[0012] The present invention improves the conductivity of lithium iron phosphate materials through the composite doping of different crystal forms of titanium dioxide (TiO 2 ), controls the morphology of particle growth, achieves a better grading effect, thereby improving the tap density, optimizing the electrical properties, especially the discharge capacity and the first efficiency. At the same time, compared with the common precursor grading, slurry grading, second sintering grading and other schemes in the market, the process flow is simpler, the cost is lower, the control is more convenient, and it is easy to mass produce. Description of the Drawings

[0013] Figure 1 SEM image of the lithium iron phosphate material prepared in Example 1.

[0014] Figure 2 PSD curve of the lithium iron phosphate material prepared in Example 1.

[0015] Figure 3 SEM image of the lithium iron phosphate material prepared in Comparative Example 1.

[0016] Figure 4 SEM image of the lithium iron phosphate material prepared in Comparative Example 2. Detailed Embodiments

[0017] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0018] Lithium iron phosphate material

[0019] In the first aspect of the present invention, a preparation method of a lithium iron phosphate material is provided. The preparation method includes: after grinding the raw materials, successively performing drying treatment, sintering treatment and pulverization treatment;

[0020] Wherein, the raw materials include a phosphorus source, an iron source, a lithium source, a carbon source and a dopant;

[0021] The dopant includes rutile-type titanium dioxide and anatase-type titanium dioxide.

[0022] In some embodiments, the mass ratio of the rutile-type titanium dioxide to the anatase-type titanium dioxide is (4-8):(6-2).

[0023] In some preferred embodiments, the mass ratio of the rutile-type titanium dioxide to the anatase-type titanium dioxide is (6-7):(4-3).

[0024] In some specific embodiments, the mass ratio of the rutile titanium dioxide to the anatase titanium dioxide is, for example, 4:6, 6:4, 6.5:3.5, 7:3 or 8:2.

[0025] In some embodiments, the D50 particle size of the rutile titanium dioxide is 0.2 - 2 μm, for example, 0.98 μm.

[0026] In some embodiments, the D50 particle size of the anatase titanium dioxide is 0.2 - 2 μm, for example, 1.16 μm.

[0027] In some embodiments, the grinding treatment is wet grinding, and the wet grinding includes the following steps:

[0028] Mix the raw materials with a solvent to obtain a first slurry;

[0029] Grind the first slurry to obtain a second slurry.

[0030] In some embodiments, the solid content of the first slurry is 30% - 40%. Herein, the solid content refers to the percentage of the mass of the raw materials other than the solvent in the first slurry to the total mass of the first slurry.

[0031] In some embodiments, the solvent in the first slurry is deionized water.

[0032] In some embodiments, the particle size distribution of the second slurry satisfies: 0.3 μm ≤ D50 ≤ 0.6 μm, for example, 0.33 μm ≤ D50 ≤ 0.37 μm (i.e., 0.35 ± 0.02 μm).

[0033] In some embodiments, the particle size distribution of the second slurry satisfies: 0 < D100 < 2 μm, preferably 0 < D100 < 1 μm.

[0034] In some preferred embodiments, the particle size distribution of the second slurry satisfies: 0.3 μm ≤ D50 ≤ 0.6 μm, and 0 < D100 < 2 μm.

[0035] In some specific embodiments, the particle size distribution of the second slurry satisfies: 0.33 μm ≤ D50 ≤ 0.37 μm, and 0 < D100 < 1 μm.

[0036] In some embodiments, the molar ratio of elements in the raw materials Li:P:Fe = (1.00 - 1.03):1:(0.96 - 0.995).

[0037] In some preferred embodiments, the molar ratio of elements in the raw materials Li:P:Fe = (1.01 - 1.03):1:(0.96 - 0.98).

[0038] In some specific embodiments, the molar ratio of elements in the raw materials is Li:P:Fe = 1.02:1:0.97.

[0039] In some embodiments, the carbon source is an organic carbon source, such as one or more of anhydrous glucose, sucrose, citric acid, polyethylene glycol, and polyvinyl alcohol.

[0040] In some preferred embodiments, the carbon source is anhydrous glucose and polyethylene glycol.

[0041] In some specific embodiments, the carbon source is anhydrous glucose and PEG2000; wherein, the mass ratio of anhydrous glucose to PEG2000 is, for example, 6:6.5.

[0042] In some embodiments, the lithium source is one or more of lithium carbonate, lithium phosphate, and lithium hydroxide.

[0043] In some specific embodiments, the lithium source is lithium carbonate. Among them, the D50 particle size of the lithium carbonate can be 2 - 10 μm, for example, 3.22 μm.

[0044] In some embodiments, the phosphorus source is monoammonium phosphate and / or lithium phosphate.

[0045] In some embodiments, the iron source is one or more of iron(III) oxide, ferrous oxalate, and iron(III) phosphate.

[0046] In some specific embodiments, the phosphorus source and the iron source are iron(III) phosphate. That is, iron(III) phosphate is used as both the phosphorus source and the iron source simultaneously.

[0047] In the above - mentioned embodiments, the D50 particle size of the iron(III) phosphate can be 2 - 10 μm, for example, 2.53 μm.

[0048] In the above - mentioned embodiments, the mass percentage of the carbon source in the iron(III) phosphate is 11% - 13%, for example, 12.5%.

[0049] In some embodiments, the drying treatment is spray drying. Among them, the spray drying preferably satisfies the following conditions: the atomizer frequency is 40 - 45 Hz, the inlet temperature of the heated air is 240 - 300 °C, and the outlet temperature is 100 - 120 °C.

[0050] In some specific embodiments, the spray drying satisfies the following conditions: the atomizer frequency is 45 Hz, the inlet temperature of the heated air is 300 °C, and the outlet temperature is 100 °C.

[0051] In some embodiments, a first precursor is obtained after the drying treatment; wherein, the first pre - D50 of the bodyThe particle size can be 15 - 40 μm, such as 30 μm; the moisture content of the first precursor can Less than 2%.

[0052] In some embodiments, the holding temperature of the sintering treatment is 720 - 820 °C, such as 780 °C.

[0053] In some embodiments, a second precursor is obtained after the sintering treatment; wherein, the D50 particle size of the second precursor is 10 - 30 μm, such as 25 μm.

[0054] In some embodiments, the comminution treatment uses air jet milling. The parameters of the air jet milling are preferably: the classification frequency is 10 - 40 Hz, the induced air frequency is 20 - 45 Hz, and the feeding speed is 10 - 40 Hz.

[0055] In some specific embodiments, the parameters of the air jet milling are: the classification frequency is 25 Hz, the induced air frequency is 40 Hz, and the feeding speed is 20 Hz.

[0056] In some specific embodiments, after the comminution treatment, sieving and demagnetization are further included.

[0057] In the second aspect of the present invention, a lithium iron phosphate material is provided, which is prepared by the preparation method of the lithium iron phosphate material as described above.

[0058] In some embodiments, the chemical formula of the lithium iron phosphate material is Li y Fe x Ti 1-x PO 4 @C, 0.96 ≤ x ≤ 0.995, 1.00 ≤ y ≤ 1.03.

[0059] In some embodiments, the Ti content in the lithium iron phosphate material is 2000 - 7000 ppm, preferably 3000 - 6000 ppm. In the present invention, the Ti content refers to the mass percentage of Ti in LiFePO 4 @C, where "LiFePO 4 @C" represents carbon-coated lithium iron phosphate calculated theoretically according to the stoichiometric ratio based on the phosphorus source, iron source, lithium source and carbon source.

[0060] In some specific embodiments, the Ti content in the lithium iron phosphate material is, for example, 2000 ppm, 3000 ppm, 4000 ppm, 6000 ppm or 7000 ppm.

[0061] In some embodiments, the particle size distribution of the lithium iron phosphate material satisfies: 0.2 μm ≤ D10 ≤ 0.4 μm, 0.6 μm ≤ D50 ≤ 1.0 μm, 2.0 μm ≤ D90 ≤ 5.0 μm.

[0062] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.33 μm, D50 = 0.73 μm, D90 = 2.85 μm.

[0063] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.3 μm, D50 = 0.75 μm, D90 = 3.39 μm.

[0064] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.33 μm, D50 = 0.79 μm, D90 = 3.85 μm.

[0065] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.33 μm, D50 = 0.8 μm, D90 = 3.79 μm.

[0066] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.27 μm, D50 = 0.7 μm, D90 = 2.96 μm.

[0067] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.35 μm, D50 = 0.88 μm, D90 = 4.73 μm.

[0068] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.33 μm, D50 = 0.7 μm, D90 = 2.93 μm.

[0069] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.33 μm, D50 = 0.85 μm, D90 = 4.37 μm.

[0070] In some specific embodiments, the particle size distribution of the lithium iron phosphate material satisfies: D10 = 0.27 μm, D50 = 0.62 μm, D90 = 2.88 μm.

[0071] In some embodiments, the lithium iron phosphate material includes first particles and second particles. The first particles are particles with a particle size range of 2.0 - 3.0 μm, and the second particles are particles with a particle size range of 0.3 - 0.5 μm. The volume ratio of the first particles to the second particles can be 1:(1.5 - 7), preferably 1:(1.8 - 4.5), and more preferably 1:(2 - 3).

[0072] In some specific embodiments, the lithium iron phosphate material includes first particles and second particles, the first particles are particles with a particle size range of 2.0-3.0 μm, the second particles are particles with a particle size range of 0.3-0.5 μm, and the volume ratio of the first particles to the second particles is, for example, 1:1.5, 1:1.8, 1:2.2, 1:2.4, 1:2.5, 1:3, 1:4.5 or 1:7.

[0073] In some embodiments, the powder compaction density of the lithium iron phosphate material is greater than 2.5 g / cm3, preferably greater than 2.55 g / cm 3 .

[0074] In some specific embodiments, the powder compaction density of the lithium iron phosphate material is, for example, 2.50 g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.59g / cm 3 or 2.6g / cm 3 .

[0075] In some embodiments, the powder resistivity of the lithium iron phosphate material is less than 100 Ω·cm, preferably less than 20 Ω·cm, and more preferably less than 15 Ω·cm.

[0076] In some specific embodiments, the powder resistivity of the lithium iron phosphate material is, for example, 9.6Ω·cm, 10.2Ω·cm, 10.7Ω·cm, 10.9Ω·cm, 11.8Ω·cm, 12.8Ω·cm, 13.3Ω·cm, 13.5Ω·cm or 17.2Ω·cm.

[0077] In some embodiments, the specific surface area of ​​the lithium iron phosphate material is 10-13m 2 / g, for example 10.2m 2 / g, 10.3m 2 / g, 10.5m 2 / g, 10.6m 2 / g, 11.0m 2 / g, 11.3m 2 / g, 11.4m 2 / g or 11.9m 2 / g.

[0078] In some embodiments, the carbon content of the lithium iron phosphate material is 1.0% - 1.5%, such as 1.15%, 1.19%, 1.2%, 1.22%, 1.25%, 1.26%, 1.27%, 1.29% or 1.33%.

[0079] Electrochemical device

[0080] In the electrochemical device described in the third aspect of the present invention, the positive electrode sheet of the electrochemical device comprises the lithium iron phosphate material as described above.

[0081] In the present invention, the electrochemical device is preferably a lithium ion battery. Among them, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0082] Positive electrode sheet

[0083] In the present invention, the positive electrode sheet may comprise a positive electrode current collector, and a positive electrode material layer provided on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode material, and the positive electrode material comprising the lithium iron phosphate material as described above.

[0084] In some embodiments, the positive electrode material layer further comprises a binder. For the binder, it may be a component that helps the binding between the active material and the conductive agent and helps the binding between the positive electrode material and the positive electrode current collector. It can generally be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene terpolymer (EPDM), sulfonated EPDM, styrene - butadiene rubber, fluororubber and various copolymers.

[0085] In some embodiments, the positive electrode material layer further comprises a conductive agent. For the conductive agent, it is a reagent used to ensure good charge - discharge performance of the electrode. It can be arbitrarily selected from graphite - based materials such as natural graphite and artificial graphite, carbon black - based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride powder, aluminum powder, nickel powder, etc., conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives.

[0086] In some embodiments, the positive electrode material layer comprises a positive electrode material, polyvinylidene fluoride and acetylene black.

[0087] In a specific embodiment, the mass ratio of the positive electrode material, polyvinylidene fluoride and acetylene black is 97:1.5:1.5.

[0088] In the present invention, the positive current collector may be a conventional positive current collector in the art. For the positive current collector, materials that do not cause chemical changes and have high electrical conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can usually be used, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive current collector. The positive current collector can be used in various forms, such as films, sheets, foils, meshes, or porous bodies, etc.

[0089] In some alternative embodiments, the positive current collector is aluminum foil.

[0090] In some alternative embodiments, the thickness of the positive current collector may be 8 - 16 μm, for example, 10 μm.

[0091] In the present invention, the positive electrode sheet can be prepared by a conventional method in the art.

[0092] In some embodiments, the positive electrode sheet is prepared by the following method: after mixing the positive electrode material, conductive agent, and binder in a certain mass ratio, adding a solvent and mixing evenly to obtain a positive electrode slurry, wherein the positive electrode material includes the lithium iron phosphate material as described above; then uniformly coating the positive electrode slurry on at least one surface of the positive current collector; and then through processes such as drying, rolling, and slitting, the positive electrode sheet is prepared.

[0093] Negative electrode sheet

[0094] In some embodiments, the negative electrode sheet is a lithium sheet.

[0095] In some other embodiments, the negative electrode sheet may include a negative current collector and a negative electrode material layer located on at least one surface of the negative current collector, and the negative electrode material layer includes a negative electrode material.

[0096] In the present invention, the negative electrode material in the negative electrode material layer can be a negative electrode material conventionally used in the art, preferably including one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide, and silicon-carbon materials, for example, artificial graphite.

[0097] In some embodiments, the negative electrode material layer further includes a conductive agent.

[0098] There are no particular restrictions on the conductive agent, as long as it has conductivity and does not cause chemical changes in the battery. For example, specific examples include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black (Super P), carbon nanotubes (CNT), acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black or carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0099] In some embodiments, the negative electrode material layer further includes a binder.

[0100] Among them, the type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as SBR.

[0101] In some embodiments, the negative electrode material layer further includes a thickener.

[0102] The addition of the thickener can increase the system viscosity of the components in the negative electrode slurry, and the thickener can be a conventional thickener used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0103] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector is used as a substrate to support the negative electrode material layer, and is generally a metal foil having a thickness of 3-500 microns. There is no particular restriction on the material, as long as it has high conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector is generally a smooth surface, but fine lines may also be formed on its surface to increase the adhesion between the negative electrode material layer and the current collector. In addition to the foil, the negative electrode current collector may also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0104] In some embodiments, the method for preparing the negative electrode sheet comprises the following steps: thoroughly stirring and mixing the components of the negative electrode material layer in a solvent to obtain a negative electrode slurry which is applied on at least one surface of the negative electrode current collector, dried, cold pressed, and cut.

[0105] Diaphragm

[0106] In some alternative embodiments, the separator can be a polypropylene film or a polyethylene film.

[0107] In a specific embodiment, the separator is a polypropylene film; the thickness of the separator is 12 μm.

[0108] Electrolyte

[0109] In some embodiments, the electrolyte can be a conventional electrolyte used in batteries in the art, generally including a non-aqueous solvent and a lithium salt.

[0110] In the present invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0111] In some embodiments, the non-aqueous solvent preferably includes ester solvents, more preferably carbonate solvents. The carbonate solvents can optionally be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The non-aqueous solvent can also include ethyl acetate.

[0112] In the present invention, the lithium salt can be a conventional lithium salt in the art, such as LiPF 6 .

[0113] In some embodiments, the electrolyte includes LiPF 6 , ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate.

[0114] Among them, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate is, for example, 1:1:2:6. Among them, the concentration of the lithium salt is, for example, 1 mol / L.

[0115] In some embodiments, the electrolyte can be prepared by a conventional method in the art. Optionally, it is prepared by the following method: in an argon atmosphere glove box with a water content < 10 ppm, the non-aqueous solvents are mixed according to the ratio, and then a sufficiently dried lithium salt is added and mixed evenly to obtain the electrolyte.

[0116] In the present invention, the method for preparing the lithium-ion battery can be a conventional preparation method in the art. It can be winding the positive electrode sheet, the negative electrode sheet, and the separator to obtain an electrode core, and then performing packaging with a packaging shell and injecting the electrolyte; or stacking the negative electrode sheet, the separator, the positive electrode sheet, and the separator in sequence to obtain an electrode core, and then performing packaging with a packaging shell and injecting the electrolyte.

[0117] Electronic device

[0118] In the electronic device provided in the fourth aspect of the present invention, it includes the electrochemical device as described above.

[0119] Exemplarily, the electronic device of the present invention can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, a backup power supply, etc.

[0120] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention. The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions noted in the following examples are carried out according to conventional methods and conditions, or are selected according to the product specifications. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0121] Example 1

[0122] S1. Slurry preparation

[0123] Weigh 25.14 kg of battery-grade lithium carbonate (Li 2 CO 3 , D50 = 3.22 μm) and 100 kg of iron phosphate (FePO 4 , D50 = 2.53 μm) according to the molar ratio of Li:P:Fe = 1.02:1:0.97.

[0124] Select anhydrous glucose (commercially available) and PEG2000 (PEG-2000 from Liaoning Aoke Chemical) as carbon sources, and weigh them according to the mass ratio of anhydrous glucose:PEG2000:iron phosphate = 6:6.5:100, that is, 6 kg of anhydrous glucose and 6.5 kg of PEG2000 are weighed.

[0125] Select rutile titanium dioxide (commercially available) and anatase titanium dioxide (commercially available) as dopants, and weigh a total of 0.6 kg (calculated based on the Ti content of 4000 ppm in the prepared LiFePO 4 @C), wherein the mass ratio of rutile titanium dioxide (D50 = 0.98 μm) to anatase titanium dioxide (D50 = 1.16 μm) is 7:3.

[0126] Weigh 207.36 kg of deionized water. Add the solid-phase raw materials to the deionized water in the order of titanium dioxide, anhydrous glucose, PEG2000, battery-grade lithium carbonate, and iron phosphate. Stir in a stirring tank at a speed of 45 Hz for 60 minutes. Take three samples at different points to test the particle size. If the difference in the test results is within 5%, it means the sample is evenly mixed, and then obtain the first slurry (solid content: 40%).

[0127] Transfer the first slurry to a nano sand mill for grinding. By controlling the rotation speed of the mill and the number of tank inversions, control the grinding end point: D50 = 0.35 ± 0.02 μm, 0 < D100 < 1 μm, to obtain the second slurry.

[0128] S2. Spray drying

[0129] Transfer the second slurry to a spray dryer for drying and granulation. Set the rotation speed of the atomizer to 45 Hz, the inlet air temperature of the heated air to 300 °C, and the outlet air temperature to 100 °C. Feed through a screw pump, and the feeding speed is automatically adjusted according to the set temperature. Then obtain the first precursor; at this time, the first precursor meets the requirements: moisture content < 2% (tested with a Mettler rapid moisture analyzer), D50 = 30 μm.

[0130] S3. Sintering treatment

[0131] Next, sinter the first precursor in a roller hearth furnace. The sintering process parameters of the roller hearth furnace are set as follows: ① The first temperature section: 200 °C - 780 °C, heating rate 1.5 °C / min; ② The second temperature section: keep at 780 °C for 10 h; ③ The third temperature section: 780 °C - room temperature, cooling method is water cooling; set the protective atmosphere of the roller hearth furnace to nitrogen, inlet air at the bottom and sides of the furnace, control the furnace pressure to 50 Pa, and the oxygen content in the whole section of the furnace < 10 ppm.

[0132] Load the first precursor into a graphite crucible and sinter and synthesize it in the roller hearth furnace with the set parameters. The loading amount per crucible is 8 kg. After taking out of the furnace, obtain the second precursor. Among them, D50 of the second precursor = 25 μm.

[0133] S4. Crushing treatment

[0134] Transfer the second precursor to a jet mill for crushing and classification. Set the classification frequency of the jet mill to 25 Hz, the air extraction frequency to 40 Hz, and the feeding speed to 20 Hz;

[0135] Then, through screening and demagnetization, obtain the lithium iron phosphate material.

[0136] Example 2

[0137] The difference between this embodiment and Embodiment 1 is that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 6.5:3.5. Other conditions are the same as those in Embodiment 1.

[0138] Embodiment 3

[0139] The difference between this embodiment and Embodiment 1 is that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 6:4. Other conditions are the same as those in Embodiment 1.

[0140] Embodiment 4

[0141] The difference between this example and Example 1 is that: in step S1, 0.45 kg of titanium dioxide is weighed (Calculated based on the Ti content of 3000 ppm in the prepared LiFePO 4 @C). Other conditions are the same as those in Embodiment 1.

[0142] Embodiment 5

[0143] The difference between this embodiment and Embodiment 1 is that: in step S1, 0.9 kg of titanium dioxide is weighed (calculated based on the Ti content of 6000 ppm in the prepared LiFePO 4 @C). Other conditions are the same as those in Embodiment 1.

[0144] Embodiment 6

[0145] The difference between this embodiment and Embodiment 1 is that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 4:6. Other conditions are the same as those in Embodiment 1.

[0146] Embodiment 7

[0147] The difference between this embodiment and Embodiment 1 is that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 8:2. Other conditions are the same as those in Embodiment 1.

[0148] Embodiment 8

[0149] The difference between this embodiment and Embodiment 1 is that: in step S1, 0.3 kg of titanium dioxide is weighed (calculated based on the Ti content of 2000 ppm in the prepared LiFePO 4 @C). Other conditions are the same as those in Embodiment 1.

[0150] Embodiment 9

[0151] The difference between this embodiment and Embodiment 1 is that: in step S1, 1.05 kg of titanium dioxide is weighed (calculated based on the Ti content of 7000 ppm in the prepared LiFePO 4 @C). Other conditions are the same as those in Embodiment 1.

[0152] Comparative Example 1

[0153] The difference between this comparative example and Example 1 lies in that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 10:0, that is, only rutile titanium dioxide is used. Other conditions are the same as those in Example 1.

[0154] Comparative Example 2

[0155] The difference between this comparative example and Example 1 lies in that: in step S1, the mass ratio of rutile titanium dioxide to anatase titanium dioxide is 0:10, that is, only anatase titanium dioxide is used. Other conditions are the same as those in Example 1.

[0156] Effect Example 1: Material Characterization

[0157] (1) SEM Test

[0158] The prepared lithium iron phosphate materials of each example and comparative example were subjected to SEM test, and the test method was as follows: Using a Phenom Pure+ scanning electron microscope (Phenom Pure+), stick the conductive adhesive on the sample stage, take 1 ± 0.1 g of the prepared powdery lithium iron phosphate material, spread it evenly on it, blow it with a special gas, put the sample cup into the sample slot in the test chamber, select the test mode as "electronic imaging", set an appropriate acceleration voltage of ~5 kV, low beam current intensity, move the field of view to select an appropriate imaging area for shooting and saving. The SEM images of Example 1, Comparative Example 1 and Comparative Example 2 are respectively as Figure 1 、 Figure 3 and Figure 4 shown.

[0159] (2) Particle Size Distribution (PSD) Test

[0160] The PSD test was carried out on the prepared lithium iron phosphate materials of each example and comparative example by a Malvern laser particle size analyzer (Master Size 3000). According to the PSD curve, D10, D50, and D90 can be obtained, and the volume ratio of the first particles in the particle size range of 2.0 - 3.0 μm to the second particles in the particle size range of 0.3 - 0.5 μm was calculated by integration. The PSD curve of Example 1 is as Figure 2 shown.

[0161] Among them, D10 is the corresponding particle size when the cumulative distribution ratio in the sample reaches 10%, in the unit of μm; D50 is the corresponding particle size when the cumulative distribution ratio in the system reaches 50%, in the unit of μm; D90 is the corresponding particle size when the cumulative distribution ratio in the system reaches 90%, in the unit of μm.

[0162] (3) Specific Surface Area

[0163] The specific surface areas of the lithium iron phosphate materials prepared in each example and comparative example were tested, and the test method was as follows:

[0164] The specific surface area of the sample was tested using a TriStar IIPlus fully automatic specific surface area and pore size analyzer, and the test method referred to the national standard GB / T19587-2017:

[0165] The sample to be tested was added to the sample tube through a funnel, and the mass of the sample + sample tube was weighed. The sample was loaded onto the degassing station for degassing treatment, cooled to room temperature for inflation and weighed again. The filling rod was added to the sample tube, the isothermal jacket was put on, and the sample tube was installed on the analysis station; Liquid nitrogen was added to the Dewar flask and placed on the lifting platform of the analysis station. The test program was started. After the sample analysis was completed, the test data was automatically generated on the software interface.

[0166] (4) Element content

[0167] The element contents of the lithium iron phosphate materials prepared in each example and comparative example were tested, and the test method was as follows:

[0168] ① Carbon content

[0169] The carbon content of the lithium iron phosphate material was tested using a high-frequency infrared carbon-sulfur analyzer (BRUKER G4 ICARUS).

[0170] ② Li, P, Fe content

[0171] The Li, P, Fe contents of the lithium iron phosphate material were tested using a Shimadzu inductively coupled plasma emission spectrometer (ICPE-9800), and the element molar ratio Li:P:Fe = (1.01 - 1.03):1:(0.96 - 0.98) was obtained.

[0172] (5) Powder compaction density and powder resistivity

[0173] The powder compaction density of the lithium iron phosphate materials prepared in each example and comparative example was measured using a powder resistivity & compaction density tester from Yuanneng Technology, and the data at a test pressure of 160 Mpa was selected. The test method was as follows:

[0174] Use a balance to weigh the powder required for the test and record the sample weight as 1 g ± 0.1 g. Pour the powder into the cavity of the jig, and weigh the remaining weight of the weighing paper. Put the jig into the pre-vibrator to level the powder, take out the jig, install the pressure head, and put it into the test bench. Select the 2-probe mode and use the variable voltage test method to start the test. After the test is completed, select the data at a test pressure of 160 Mpa to obtain the sample compaction density and powder resistivity.

[0175] The test results are shown in Table 1.

[0176] Table 1

[0177]

[0178] Effect Example 2: Electrochemical Performance Test

[0179] The lithium iron phosphate materials prepared by each of the examples and comparative examples were used as the positive electrode materials respectively, and button cells were assembled according to the national standard GB / T33822-2017. The specific method was as follows:

[0180] Mix the positive electrode material, binder PVDF, and conductive agent acetylene black in a mass ratio of 97:1.5:1.5. After the positive electrode material, binder, and conductive agent are mixed evenly, add the solvent NMP and stir in a vacuum mixer until uniform to obtain the positive electrode slurry. Coat the positive electrode slurry evenly on a 10-μm aluminum foil current collector, then dry the current collector at room temperature and transfer it to an oven, dry it at 120°C for 10 h, and then obtain the positive electrode sheet through rolling and slitting; among them, the compaction density of the positive electrode sheet is 2.2 g / cm3; among them, the test method for the compaction density of the electrode sheet is: punch the positive electrode sheet into a unit circle, measure the weight, subtract the weight of the aluminum foil, and divide by the volume to obtain the compaction density of the electrode sheet.

[0181] Select a pure metal lithium sheet as the negative electrode sheet and a 12-μm thick polypropylene film as the separator;

[0182] Prepare the electrolyte: Mix battery-grade ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl acetate in a mass ratio of 1:1:2:6. In a glove box filled with argon gas with a water content of less than 10 ppm, dissolve fully dried LiPF 6 in the mixed organic solvent, and obtain the electrolyte after mixing evenly. Among them, the concentration of LiPF 6 is 1 mol / L;

[0183] Button cell assembly: Carry out the assembly of the button cell in a glove box filled with dry argon gas. Assemble the positive electrode sheet, separator, negative electrode sheet, and electrolyte into a button cell of model CR2016 and let it stand for 12 hours.

[0184] Use the button cell prepared above to carry out electrical performance tests in a battery charge and discharge test instrument according to the test procedure. The test voltage range is in the interval of 2.0 - 3.75 V. First, perform constant current and constant voltage charging at 0.1C, with a cut-off current of 0.05C, to obtain the 0.1C charging specific capacity. Then, perform constant current discharge at 0.1C to obtain the 0.1C discharge specific capacity. Divide the first discharge specific capacity by the first charge specific capacity to obtain the Coulomb efficiency. Then, perform constant current and constant voltage charging at 0.3C, with a charging cut-off current of 0.05C, and perform constant current discharge at 1C to obtain the 1C discharge specific capacity. The test results are shown in Table 2.

[0185] Table 2

[0186]

[0187] Doping with metal cation Ti can effectively improve the intrinsic conductivity of lithium iron phosphate materials, significantly enhancing their electrochemical performance; anatase titanium dioxide and rutile titanium dioxide have obvious differential effects on the particle growth during the synthesis stage of lithium iron phosphate materials: doping with rutile titanium dioxide has a relatively obvious inhibitory effect on the particle growth of lithium iron phosphate materials; doping with anatase titanium dioxide has no obvious inhibitory effect on the particle growth of lithium iron phosphate materials. Therefore, by simultaneously selecting doping agents of these two crystal forms and controlling the size and proportion of large and small particles in the finished product through composite doping, a better natural grading effect can be achieved, thereby improving the tap density and energy density of lithium iron phosphate materials.

[0188] As can be seen from the SEM image of Example 1 ( Figure 1 ), the particle size distribution of its finished product is relatively wide, with small and medium-sized particles in the range of 0.1 - 0.4 μm and large particles with a size greater than 1 μm. Combining with the PSD curve of Example 1 ( Figure 2 ), it can be known that the volume ratio of the first particles in the particle size range of 2.0 - 3.0 μm to the second particles in the particle size range of 0.3 - 0.5 μm in Example 1 is 1:2.5. From Table 1 and Table 2, it can be seen that in Examples 1 - 9 of the present invention, doping agents of two crystal forms are simultaneously selected, and the prepared lithium iron phosphate materials have excellent natural grading effects, and their particle size distributions satisfy: D10 = 0.2 - 0.4 μm, D50 = 0.6 - 1.0 μm, D90 = 2.0 - 5.0 μm; the specific surface area is 10 - 13 m 2 / g. Samples with such particle size distributions have high tap density and good discharge capacity, indicating that they have good particle grading effects and achieve a balance between tap density and electrochemical performance. The tap density of the powder of the lithium iron phosphate material prepared in the examples of the present invention is greater than 2.5 g / cm3; the powder resistivity is less than 20 Ω·cm. The lithium ion battery using the lithium iron phosphate material prepared in the examples of the present invention as the cathode material has excellent electrical properties. Specifically: the charge capacity per gram at 0.1C > 158 mAh / g, the discharge capacity per gram at 0.1C > 156 mAh / g, the discharge capacity per gram at 1C > 140 mAh / g, and the initial efficiency at 0.1C > 97%.

[0189] In Comparative Example 1, only rutile titanium dioxide was doped. By comparing Example 1 with Comparative Example 1, it can be seen that when only rutile titanium dioxide is used, due to the relatively obvious inhibitory effect of rutile titanium dioxide doping on the particle growth of lithium iron phosphate materials, the particle growth is inhibited, and the particle size results D10, D50, and D90 all become smaller, and the tap density of the final product is relatively low; from the SEM image of Comparative Example 1 ( Figure 3) It can be seen from this that the reason is the lack of large particles above 1μm, resulting in a low tap density. The resistivity of the lithium iron phosphate material powder prepared in Comparative Example 1 is much higher than that in Example 1.

[0190] In Comparative Example 2, only anatase-type titanium dioxide was doped. By comparing Example 1 with Comparative Example 2, it can be seen that when only anatase-type titanium dioxide is used, since the doping of anatase-type titanium dioxide has no obvious inhibitory effect on the particle growth of the lithium iron phosphate material, the particle growth is relatively large, and the particle size results D10, D50, and D90 all increase. However, the tap density of the final product is relatively low. From the SEM image of Comparative Example 2 ( Figure 4 ) It can be seen from this that the reason is the lack of small particles below 200nm, the grading effect is poor, and at the same time, too many large particles also lead to the deterioration of the electrochemical performance, the discharge specific capacity is low, and the initial efficiency is poor.

[0191] By comparing Examples 1, 2, and 3, it can be seen that within a certain range, by appropriately adjusting the doping ratio of rutile-type and anatase-type titanium dioxide, the same effect can be achieved, and the parameter indicators of the final product are close: tap density > 2.55g / cc, 1C discharge capacity > 142mAh / g, meeting the requirements of high tap density and high specific capacity. By comparing Examples 1, 4, and 5, it can be seen that within a certain range, by appropriately adjusting the total doping amount, the same effect can be achieved, and the parameter indicators of the final product are close.

[0192] By comparing Example 1 with Examples 6 and 7, it can be seen that when the proportion of rutile-type or anatase-type titanium dioxide is too high, the grading effect of the final product will become poor and the tap density cannot be improved; by comparing Example 1 with Examples 8 and 9, it can be seen that with the same proportion of rutile-type: anatase-type titanium dioxide, a too high total doping amount will lead to a decrease in tap density; a too low total doping amount will lead to poor electrical performance.

[0193] The above specific embodiments have further detailed the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium iron phosphate material, characterized in that: The preparation method comprises: grinding the raw material, and then sequentially performing drying, sintering and pulverizing; Wherein, the raw materials include a phosphorus source, an iron source, a lithium source, a carbon source and a dopant; The dopant includes rutile titanium dioxide and anatase titanium dioxide.

2. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The mass ratio of the rutile titanium dioxide to the anatase titanium dioxide is (4-8):(6-2).

3. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The phosphorus source and the iron source are iron phosphate; The mass percentage of the carbon source to the iron phosphate is 11%-13%.

4. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The molar ratio of elements in the raw material is Li:P:Fe=(1.01-1.03):1:(0.96-0.98).

5. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The grinding process adopts wet grinding, and the wet grinding comprises the following steps: Mixing the raw material with a solvent to obtain a first slurry; Then, grinding the first slurry to obtain a second slurry; The solid content of the first slurry is 30%-40%; The particle size distribution of the solid component in the second slurry satisfies: 0.3 μm≤D50≤0.6 μm, and 0<D100<2 μm.

6. The method for preparing the lithium iron phosphate material according to claim 1, characterized in that: The D50 particle size of the rutile titanium dioxide is 0.2-2 μm, and the D50 particle size of the anatase titanium dioxide is 0.2-2 μm.

7. A lithium iron phosphate material, characterized in that: The lithium iron phosphate material is prepared by the preparation method of the lithium iron phosphate material according to any one of claims 1 to 6.

8. The lithium iron phosphate material according to claim 7, characterized in that: The chemical formula of the lithium iron phosphate material is Li y Fe x Ti 1-x PO4@C, where 0.96≤x≤0.995, 1.00≤y≤1.03; The Ti content in the lithium iron phosphate material is 2000-7000ppm; The particle size distribution of the lithium iron phosphate material satisfies: 0.2 μm≤D10≤0.4 μm, 0.6 μm≤D50≤1.0 μm, 2.0 μm≤D90≤5.0 μm; The lithium iron phosphate material includes first particles and second particles, the first particles are particles with a particle size in the range of 2.0-3.0 μm, the second particles are particles with a particle size in the range of 0.3-0.5 μm, and the volume ratio of the first particles to the second particles is 1:(1.5-7); The specific surface area of ​​the lithium iron phosphate material is 10-13m 2 / g; The carbon content of the lithium iron phosphate material is 1.0%-1.5%.

9. An electrochemical device, characterized in that: The positive electrode sheet of the electrochemical device comprises the lithium iron phosphate material as claimed in claim 7 or 8.

10. An electronic device, characterized in that: It comprises the electrochemical device as claimed in claim 9.

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