A preparation method of lithium iron phosphate, a lithium iron phosphate cathode material and a lithium battery

Abstract

The present application provides a method for preparing lithium iron phosphate, a lithium iron phosphate cathode material and a lithium battery. Among them, the method includes: providing crude lithium iron phosphate; preparing the crude lithium iron phosphate into a slurry and then performing sanding treatment to obtain a sanded slurry; aging the sanded slurry; adding a carbon coating agent to the aged sanded slurry and then performing spray drying, sintering and air crushing treatment to obtain refined lithium iron phosphate. The method provided by the embodiments of the present application can prepare refined lithium iron phosphate with excellent rate charge and discharge performance and processing performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly to a preparation method of lithium iron phosphate, a lithium iron phosphate cathode material, and a lithium battery. Background Art

[0002] The energy density of lithium-ion batteries is closely related to the cathode material. Among the currently commercialized lithium-ion cathode materials, olivine-structured LiFePO4 has become the focus of research in recent years due to its advantages such as good charge and discharge platforms, excellent reversible capacity, and outstanding cycling performance.

[0003] With the continuous development of the new energy market, higher requirements are put forward for the rate performance and low-temperature discharge performance of lithium iron phosphate cathode materials.

[0004] It is known that the control of particle size and morphology is very effective for improving the rate performance of materials. The size of the particle size changes the distance of lithium-ion diffusion. The smaller the particle size, the smaller the lithium-ion diffusion distance, which correspondingly increases the lithium-ion diffusion rate and further improves the electrochemical performance of the material.

[0005] However, the lithium iron phosphate materials prepared by existing methods such as high-temperature solid-phase method and hydrothermal method have problems of poor high-rate charge and discharge performance and poor processing performance.

[0006] Therefore, the existing technology still needs to be improved. Summary of the Invention

[0007] The technical problem to be solved by the present application is to provide a preparation method of lithium iron phosphate, a lithium iron phosphate cathode material, and a lithium battery to solve the technical problems of poor high-rate charge and discharge performance and poor processing performance of the lithium iron phosphate materials prepared in the existing technology.

[0008] To solve the above problems, the present application is realized by the following technical solutions:

[0009] The present application provides a preparation method of lithium iron phosphate, which includes:

[0010] Providing crude lithium iron phosphate;

[0011] Formulating the crude lithium iron phosphate into a slurry and then performing sanding treatment to obtain a sanded slurry;

[0012] Aging the sanded slurry;

[0013] Adding a carbon coating agent to the aged sanded slurry and then performing spray drying, sintering, and air crushing treatment to obtain refined lithium iron phosphate.

[0014] Further, in the method, the aging conditions are to keep warm at 30-200 °C for 1-48 h.

[0015] Further, in the method, the carbon coating agent is one or more of carbon black, graphene, carbon nanotubes, glucose, sucrose, acetone, polyaniline, and polyethylene glycol.

[0016] Further, in the method, the addition amount of the carbon coating agent is 0.1-15% of the solid content in the sanded slurry after aging.

[0017] Further, in the method, before spray drying, the method further includes:

[0018] Adding a metal dopant to the sanded slurry after aging.

[0019] Further, in the method, the metal elements of the metal dopant are one or more of Ca, Mg, Cu, Al, Zr, Ti, Co, V, Mn, Zr, W, Sn, Nb, and Mo.

[0020] Further, in the method, during the process of adding the metal dopant to the sanded slurry after aging, the metal dopant is added according to the metal element doping amount of 0.1-3% wt of the solid content in the sanded slurry after aging.

[0021] Further, in the method, the steps of providing crude lithium iron phosphate include:

[0022] In an inert gas atmosphere, mixing an iron source and a phosphorus source into a first liquid material, then adding a lithium source, and controlling the pH of the system to be 3-8, and shearing and stirring until emulsification is complete to obtain a lithium iron phosphate precursor slurry;

[0023] Pressurizing and heating the lithium iron phosphate precursor slurry to obtain the crude lithium iron phosphate.

[0024] Further, in the method, during the process of obtaining the lithium iron phosphate precursor slurry, the solvent used is selected from one or more of deionized water, ethanol, methanol, acetone, propanol, isopropanol, propylene glycol, and DMF;

[0025] During the process of formulating the crude lithium iron phosphate into a slurry, the solvent used is selected from one or more of deionized water, methanol, ethanol, propanol, propylene glycol, acetone, NMP, and DMF.

[0026] Further, in the method, in the first liquid material, the iron source concentration is 0.5-2 mol / L, and the molar ratio of the iron source to the phosphorus source is (0.96-1.02):1.

[0027] Further, in the method, the iron source is at least one of ferrous sulfate, ferrous chloride, ferrous bromide, ferrous perchlorate, ferrous oxalate, ferrous nitrate, and ferrous acetate;

[0028] The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, potassium phosphate, and lithium dihydrogen phosphate;

[0029] The lithium source is at least one of lithium reagents such as lithium chloride, lithium bromide, lithium sulfate, lithium nitrate, lithium carbonate, lithium chlorate, lithium hydroxide, lithium formate, and lithium acetate.

[0030] Further, in the method, during the process of controlling the pH of the system to be 3 - 8, the pH regulator is at least one of ammonia water, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate.

[0031] Further, in the method, the sanding treatment specifically includes:

[0032] Using zirconium balls with a diameter of 0.1 - 0.5 mm to sand until the particle size of the slurry is 0.1 - 2 μm.

[0033] Further, in the method, during the process of obtaining the lithium iron phosphate precursor slurry by reacting under shear stirring conditions, the system temperature is 120 - 240 °C, and the reaction time is 2 - 24 h.

[0034] The present application also provides a lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material is prepared by the method as described above.

[0035] Further, the lithium iron phosphate cathode material is spherical, and the primary particle size Dv(50) is 10 - 100 nm.

[0036] The present application also provides a lithium battery, which includes a cathode, and the cathode is made of the lithium iron phosphate cathode material as described above.

[0037] Compared with the prior art, the present application has the following advantages:

[0038] In the present application, the crude lithium iron phosphate is first formulated into a slurry and then subjected to sanding treatment, and then the sanded slurry is aged to enable the fine particles caused by sanding to redissolve and recrystallize into spherical particles again. Then, a carbon coating agent is added for spray drying, sintering, and air crushing treatment, and refined lithium iron phosphate with excellent rate charge and discharge performance and processing performance can be prepared.

[0039] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. Description of the Drawings

[0040] Figure 1 It is a schematic flow chart of the preparation method of lithium iron phosphate provided by the embodiments of the present application;

[0041] Figure 2 It is a scanning electron microscope image of the lithium iron phosphate prepared by the embodiments of the present application;

[0042] Figure 3 It is a scanning electron microscope image of the lithium iron phosphate prepared by the prior art. Specific embodiments

[0043] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] A preparation method of a cathode material for a lithium battery provided by an embodiment of the present application, as Figure 1 shown, includes steps 101 to 104:

[0045] Step 101, provide crude lithium iron phosphate.

[0046] In the above step 101, the crude lithium iron phosphate is lithium iron phosphate with a relatively large particle size and uneven size, and specifically, it can be lithium iron phosphate in the prior art or lithium iron phosphate prepared by conventional technical methods.

[0047] Step 102, prepare the crude lithium iron phosphate into a slurry and then perform sanding treatment to obtain a sanded slurry.

[0048] According to the Domino cascade model, due to the nano-size effect, when the de-lithiated phase and the grain boundary phase are formed, the interface of the phase will move rapidly along the a-axis direction. At this time, the charge storage of lithium ions can be regarded as a pseudocapacitance behavior, which will thus improve the electrochemistry of lithium iron phosphate. When the particle size of lithium iron phosphate is reduced to less than 100 nm, the lithium ion transport channels will increase significantly, indicating that smaller particles are beneficial to the transport of lithium ions. For larger particles, the lithium ion transport channels are more likely to be blocked by defects. Therefore, in step 102, the crude lithium iron phosphate prepared into a slurry is sanded into fine particles by sanding treatment to obtain a sanded slurry of lithium iron phosphate with smaller particles, refining the particle size of the subsequent aged product and facilitating the subsequent doping and coating, and a more uniform material can be obtained.

[0049] Among them, in the process of preparing the crude lithium iron phosphate into a slurry, the solvent used is selected from one or more of deionized water, methanol, ethanol, propanol, propylene glycol, acetone, NMP, and DMF.

[0050] Step 103, age the sanded slurry.

[0051] In step 103, under the protection of inert gases such as nitrogen, argon, and helium with a purity > 99%, the sanded slurry obtained in step 102 is kept warm for a preset duration under preset temperature conditions to achieve the aging of lithium iron phosphate. For example, it is aged by keeping warm at a temperature of 30 - 200°C for 1 - 48 h.

[0052] Among them, after the material treated by sanding is aged, the extremely fine particles originally generated by sanding will adsorb on the surface of slightly larger particles and form spherical particles, which will then become an integral part during subsequent sintering. In this way, the final particle size of the material can be precisely controlled to achieve controllable preparation. At the same time, when the particles are spherical, the carbon coating in the post-treatment is more uniform, the contact between particles is good, and the electronic conductivity is improved accordingly; at the same time, the side reactions of the carbon-coated lithium iron phosphate material in the electrolyte will also be reduced, so that the cycle performance of the lithium iron phosphate material will be improved to a certain extent.

[0053] Step 104: Add a carbon coating agent to the aged material, and then perform spray drying, sintering, and air crushing treatment to obtain refined lithium iron phosphate.

[0054] In this step 104, a carbon coating agent is added to the aged sanded slurry to improve the conductivity of the lithium iron phosphate material by using carbon source coating. Then, the sanded slurry mixed with the carbon coating agent is spray dried at 50 - 220°C to remove moisture; then the dried material is placed in high-temperature sintering equipment such as a pusher furnace, tunnel kiln, rotary kiln, or tubular furnace, and sintered at 600 - 800°C for 4 - 12 h under the protection of inert gases such as nitrogen, argon, and helium with a purity > 99% to sinter the extremely fine particles generated by sanding and adsorbed on the surface of slightly larger particles with the slightly larger particles to form spherical particles; then it is cooled and the sintered block material is subjected to air crushing treatment to obtain the lithium iron phosphate product of the present application.

[0055] Among them, sintering treatment under the protection of inert gases such as nitrogen, argon, and helium with a purity > 99% can effectively prevent the oxidation of ferrous ions.

[0056] Among them, the above carbon coating agent can specifically be one or more of carbon black, graphene, carbon nanotubes, glucose, sucrose, acetone, polyaniline, and polyethylene glycol. The addition amount of the carbon coating agent is 0.1 - 15% of the solid content in the aged sanded slurry. That is, the solid content of the aged lithium iron phosphate is measured with a rapid moisture tester, and then 0.1 - 15% of the carbon source is coated according to the solid content to determine the addition amount of the carbon coating agent.

[0057] In the embodiments of the present application, first, the crude lithium iron phosphate is formulated into a slurry and then subjected to sanding treatment. After that, the sanded slurry is aged to dissolve the fine particles caused by sanding and recrystallize them into spherical particles again, so as to synthesize ultrafine and uniformly distributed small particles with a particle size of 20-70 nm. Then, a carbon coating agent is added for spray drying, sintering and air crushing treatment, and refined lithium iron phosphate with excellent high-rate charge and discharge performance and processing performance can be prepared.

[0058] Optionally, in one embodiment, the method provided by the embodiments of the present application further includes, before spray drying:

[0059] Adding a metal dopant to the aged sanded slurry.

[0060] In this embodiment, during the charge and discharge cycle of lithium iron phosphate, the electron or ion transport will be slower than that causing the polarization of the electrode, which will in turn affect the high-rate charge and discharge performance of the battery. The heteroatom doping changes the crystal structure of the material, increases the lithium ion transport channels, and increases the lattice volume, thus significantly increasing the diffusion coefficient of lithium ions in the material, reducing the electrode polarization, improving the high-rate performance of the battery material, and increasing the reversible capacity at high rates.

[0061] Among them, the atomic radius of the doped metal element in the above metal dopant is larger than that of iron, and specifically, it can be one or more of Ca, Mg, Cu, Al, Zr, Ti, Co, V, Mn, Zr, W, Sn, Nb and Mo.

[0062] Optionally, since too low doping amount cannot effectively improve the high-rate performance of the battery material, while too high doping amount will reduce the capacity of the material, during the process of adding the metal dopant to the aged sanded slurry, the metal dopant is added according to the metal element doping amount of 0.1 wt% - 3 wt% of the solid content in the aged sanded slurry.

[0063] Optionally, in one embodiment, the above step 101 specifically includes step 111 - step 112:

[0064] Step 111, in an inert gas atmosphere, mix an iron source and a phosphorus source into a first liquid material, then add a lithium source, and control the pH of the system to be 3-8, and shear and stir until emulsification is complete to obtain a lithium iron phosphate precursor slurry.

[0065] In the above step 111, the iron source and the phosphorus source are mixed according to the ratio to prepare the first liquid material, the lithium source is formulated into the second liquid material, and the pH regulator is formulated into the third liquid material. For example, the pH regulator is formulated into a solution with a concentration of 2.0 - 5.0 mol / L. Then, the first liquid material is added into a reaction vessel such as an emulsifying shear stirring tank, and then the second liquid material is added into the reaction vessel, and the pH value of the system is controlled to be 3 - 8 by using the third liquid material. Then, after shearing and stirring for 1 h, a lithium iron phosphate precursor slurry containing ferrous phosphate and lithium phosphate can be obtained by reacting to prepare the lithium iron phosphate precursor slurry.

[0066] Among them, the solvents of the first liquid material, the second liquid material and the third liquid material are selected from one or more of deionized water, ethanol, methanol, acetone, propanol, isopropanol, propylene glycol, and DMF.

[0067] Optionally, in the above first liquid material, the concentration of the iron source is controlled to be 0.5 - 2 mol / L, and in order to ensure that the material has a high reversible capacity, the molar ratio of the iron source to the phosphorus source needs to be controlled to be between (0.96 - 1.02):1.

[0068] According to the above ratio, the phase of the lithium iron phosphate product obtained after sintering in this application is the LiFePO4 phase, and the mass percentages of each component are: Li 4.1 - 4.7%, Fe 32% - 36%, PO4 3+ 56 - 61%, C 0.1 - 5%; it also includes a doping element of 0.1% - 3%, and the doping element is one or several of Ca, Mg, Cu, Al, Zr, Ti, Co, V, Mn, Zr, W, Sn, Nb, and Mo; it also includes an impurity element of 0.01 - 1%, and the impurity element is Ca, Mg, Cu, Al, Si, S, Zn, Ni, Co, Mn, Ti, O, etc.

[0069] Specifically, the above iron source can be at least one of ferrous sulfate, ferrous chloride, ferrous bromide, ferrous perchlorate, ferrous oxalate, ferrous nitrate, and ferrous acetate; the above phosphorus source can be at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, potassium phosphate, and lithium dihydrogen phosphate; the lithium source can be at least one of lithium reagents such as lithium chloride, lithium bromide, lithium sulfate, lithium nitrate, lithium carbonate, lithium chlorate, lithium hydroxide, lithium formate, and lithium acetate; the pH regulator is at least one of ammonia water, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate.

[0070] Optionally, in a specific embodiment, the above phosphorus source is selected as phosphoric acid, and the lithium source is selected as lithium hydroxide and / or lithium carbonate. In this embodiment, lithium hydroxide or lithium carbonate can be used as both the lithium source and the pH regulator, which can reduce the introduction of unnecessary elements other than lithium, iron, and phosphorus, and prepare a lithium iron phosphate material with a more single phase and superior performance.

[0071] Optionally, in the above step 111, after adding the first feed liquid into the reaction vessel, start the shearing machine and the stirring paddle, keep the rotation speed of the stirring paddle at 100 - 400 r / min, and then add the lithium source, so as to react and prepare lithium iron phosphate precursor with smaller and more uniform particle size.

[0072] Step 112: Pressurize and heat the lithium iron phosphate precursor slurry to obtain the crude lithium iron phosphate.

[0073] In the above step 112, add the slurry reacted in step 111 into the high-pressure reactor, heat for a preset time, and then cool and filter to obtain the crude lithium iron phosphate slurry through reaction.

[0074] Among them, the heating condition in the above step 112 is to keep warm at 20 - 250 °C for 1 - 24 h.

[0075] Among them, in order to avoid the oxidation of ferrous ions, both the above step 111 and step 112 need to be carried out under the protection of inert gases such as nitrogen, argon, and helium with a purity > 99%.

[0076] Optionally, after adding the lithium iron phosphate precursor slurry into the high-pressure reactor, first start the stirring paddle of the reactor, keep the rotation speed of the stirring paddle at 300 - 600 r / min for emulsification shearing, and crude lithium iron phosphate with smaller and more uniform particle size can be prepared.

[0077] Optionally, in one embodiment, in the method provided by the embodiments of the present application, the sanding treatment specifically includes:

[0078] Use zirconia beads with a diameter of 0.1 - 0.5 mm to sand the slurry until the particle size of the slurry is 0.1 - 2 μm.

[0079] In this embodiment, that is, use zirconia beads with a diameter of 0.1 - 0.5 mm to continuously sand the slurry of crude lithium iron phosphate until the particle size of the slurry is 0.1 - 2 μm, and the crude lithium iron phosphate can be sanded into nano-sized fine particles. Among them, the sanding time is controlled within 1 - 16 h.

[0080] The embodiments of the present application also provide a lithium iron phosphate cathode material, which is prepared by the method as described above.

[0081] The lithium iron phosphate cathode material of the embodiments of the present application has prepared spherical nano lithium iron phosphate particles with uniform particle distribution, and (D90 - D10) / D50 = 1.0 - 2.0, and has excellent rate performance at room temperature and low temperature.

[0082] Specifically, the lithium iron phosphate cathode material provided by the embodiments of the present application is spherical, and the primary particle size Dv(50) is 10 - 100 nm. It is ultra-fine particles at the nanometer level with uniform distribution, thus having excellent rate charge and discharge performance and processing performance.

[0083] The embodiments of the present application also provide a lithium battery, including a cathode, which is made of the lithium iron phosphate cathode material as described above.

[0084] In the embodiments of the present application, due to the above-mentioned lithium iron phosphate cathode material being spherical and having a primary particle size Dv(50) of 10 - 100 nm, being ultra-fine particles at the nanometer level with uniform distribution, it has excellent high-rate charge and discharge performance and processing performance.

[0085] The lithium battery of the present application is prepared by methods well-known to those skilled in the art.

[0086] The present application will be described in detail below through examples.

[0087] Performance test method:

[0088] 1. Preparation of test battery:

[0089] (1) Preparation of the positive electrode sheet: The cathode material, acetylene black, and PVDF are dissolved in N-methylpyrrolidone at a weight ratio of 100:4:5, stirred evenly, then coated on aluminum foil, baked at a temperature of 100 ± 5 °C, rolled to a certain thickness using a tablet press, and cut into positive electrode sheets;

[0090] (2) Preparation of the negative electrode sheet: Graphite, acetylene black, and PVDF are dissolved in N-methylpyrrolidone at a weight ratio of 100:3:6, stirred evenly, then coated on copper foil, baked at a temperature of 100 ± 5 °C, rolled to a certain thickness using a tablet press, and cut into negative electrode sheets;

[0091] (3) The above positive and negative electrode sheets are wound into a square lithium-ion battery core with a 20-μm-thick polypropylene separator, placed in a battery case and welded, and then injected with 1.0 mol / L LiPF6 / (EC + EMC + DMC) (where the mass ratio of EC, EMC, and DMC is 1:1:1) electrolyte, and sealed to make a test battery.

[0092] 2. Rate performance test method: The battery is charged at a constant current and constant voltage to 3.8 V at a 0.2C rate, with a cut-off current of 0.02C, and then discharged at a constant current to 2.5 V at a 15C rate. Record the ratio of the discharge capacity at the 15C rate to the discharge capacity at the 0.2C rate, which is the discharge efficiency at the 15C rate.

[0093] 3. Low-temperature performance test method: The battery is charged at a constant current and constant voltage to 3.8V at a rate of 0.1C at room temperature, then discharged at a constant current of 0.1C to 2.5V, and then cycled once again. Then, at a rate of 0.5C, it is charged at a constant current to 3.8V, and then charged at a constant voltage of 3.8V until the current reaches 0.1C and then cut off. The battery is placed in a freezer at -20°C and discharged at a constant current of 1C to 2.0V. Calculate the ratio of the discharge capacity at -20°C to the charge capacity at 0.5C at room temperature, which is the low-temperature capacity retention rate of the battery;

[0094] 4. Cycle performance test method: Under normal temperature conditions, at a rate of 1C, after the battery undergoes 500 charge-discharge cycles, the ratio of the capacity of the 500th cycle to the capacity of the 1st cycle is the cycle capacity retention rate of the battery.

[0095] Example 1

[0096] (1) Accurately weigh a certain mass of ferrous sulfate heptahydrate, 85wt% phosphoric acid, and deionized water, and prepare solution A with a concentration of 0.5mol / L; accurately weigh a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly, and prepare solution B with a concentration of 1mol / L;

[0097] (2) Add the prepared solution A to the emulsifying and shearing reaction tank, start the stirring paddle and emulsifying and shearing machine, and at the same time add the prepared solution B to the emulsifying and shearing reaction tank, and control and adjust the pH value of the system in the range of 4 - 5;

[0098] (3) Add the slurry obtained from step (2) to the high-pressure reactor, keep it at a temperature of 190°C for 5 hours for reaction, and then cool it to obtain lithium iron phosphate slurry L1.

[0099] (4) Filter, wash, and make a slurry of the cooled material to prepare a slurry with a mass fraction of 15wt%, and then pump it into a sand mill for sanding treatment. After sanding, the obtained slurry is placed at a temperature of 50°C for aging for 1 hour to obtain lithium iron phosphate slurry L2.

[0100] (5) Then, add glucose to the slurry obtained from step (4) with a carbon coating amount of 2wt% and a doping agent with a V heteroatom doping amount of 0.1wt%. After that, the slurry is spray-dried to obtain spray material P1, sintered in a tube furnace at 700°C for 10 hours in an inert atmosphere, and then cooled and processed by air crushing technology to obtain lithium iron phosphate product LFP-S1.

[0101] Example 2

[0102] (1) Accurately weigh a certain mass of ferrous sulfate heptahydrate, 85wt% phosphoric acid, and deionized water, and prepare solution A with a concentration of 0.5mol / L; accurately weigh a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly, and prepare solution B with a concentration of 1mol / L;

[0103] (2) Add the prepared solution A into the emulsifying and shearing reaction tank, start the stirring paddle and the emulsifying and shearing machine, and at the same time add the prepared solution B into the emulsifying and shearing reaction tank, and control and adjust the pH value of the system in the range of 4-5.

[0104] (3) Add the slurry obtained from the reaction in (2) into the high-pressure reactor, keep it at 190 °C for 5 h for reaction and then cool it to obtain the lithium iron phosphate slurry L1.

[0105] (4) Filter, wash and pulp the cooled material, then prepare a slurry with a mass fraction of 15 wt%, and then pump it into a sand mill for sanding treatment. After sanding, place the obtained slurry at 50 °C for 3 h for aging to obtain the lithium iron phosphate slurry L2.

[0106] (5) Then add glucose according to a carbon coating amount of 2 wt% and a dopant according to a V heteroatom doping amount of 0.1 wt% into the slurry obtained in (4). After that, the obtained slurry is spray-dried to obtain the spray material P1, sintered in a tubular furnace at 700 °C for 10 h under an inert atmosphere, and then processed by a gas crushing process after cooling to obtain the lithium iron phosphate product LFP-S2.

[0107] Example 3

[0108] (1) Accurately weigh a certain mass of ferrous sulfate heptahydrate, 85 wt% phosphoric acid and deionized water, and prepare a 0.5 mol / L solution A; accurately weigh a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly and prepare a 1 mol / L solution B.

[0109] (2) Add the prepared solution A into the emulsifying and shearing reaction tank, start the stirring paddle and the emulsifying and shearing machine, and at the same time add the prepared solution B into the emulsifying and shearing reaction tank, and control and adjust the pH value of the system in the range of 4-5.

[0110] (3) Add the slurry obtained from the reaction in (2) into the high-pressure reactor, keep it at 190 °C for 5 h for reaction and then cool it to obtain the lithium iron phosphate slurry L1.

[0111] (4) Filter, wash and pulp the cooled material, then prepare a slurry with a mass fraction of 15 wt%, and then pump it into a sand mill for sanding treatment. After sanding, place the obtained slurry at 60 °C for 1 h for aging to obtain the lithium iron phosphate slurry L2.

[0112] (5) Then, glucose is added to the slurry obtained in (4) according to a carbon coating amount of 2 wt%, and a dopant is added according to a V heteroatom doping amount of 0.1 wt%. After that, the resulting slurry is spray-dried to obtain spray material P1, which is sintered in a tube furnace at 700 °C for 10 h under an inert atmosphere. After cooling, it is further processed by air crushing to obtain the lithium iron phosphate product LFP-S3.

[0113] Example 4

[0114] (1) Weigh accurately a certain mass of ferrous sulfate heptahydrate, 85 wt% phosphoric acid, and deionized water, and prepare them into a 0.5 mol / L solution A; weigh accurately a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly, and prepare them into a 1 mol / L solution B.

[0115] (2) Add the prepared solution A to the emulsifying and shearing reaction tank, start the stirring paddle and emulsifying and shearing machine, and at the same time add the prepared solution B to the emulsifying and shearing reaction tank, and control and adjust the pH value of the system within the range of 4 - 5.

[0116] (3) Add the slurry obtained from the reaction in (2) to the autoclave, keep it at 190 °C for 5 h for reaction and then cool it to obtain the lithium iron phosphate slurry L1.

[0117] (4) Filter, wash, and pulp the cooled material to prepare a slurry with a mass fraction of 15 wt%, then pump it into a sand mill for sanding treatment. After sanding, the resulting slurry is aged at 70 °C for 1 h to obtain the lithium iron phosphate slurry L2.

[0118] (5) Then, glucose is added to the slurry obtained in (4) according to a carbon coating amount of 2 wt%, and a dopant is added according to a V heteroatom doping amount of 0.1 wt%. After that, the resulting slurry is spray-dried to obtain spray material P1, which is sintered in a tube furnace at 700 °C for 10 h under an inert atmosphere. After cooling, it is further processed by air crushing to obtain the lithium iron phosphate product LFP-S4.

[0119] Example 5

[0120] (1) Weigh accurately a certain mass of ferrous sulfate heptahydrate, 85 wt% phosphoric acid, and deionized water, and prepare them into a 0.5 mol / L solution A; weigh accurately a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly, and prepare them into a 1 mol / L solution B.

[0121] (2) Add the prepared solution A to the emulsifying and shearing reaction tank, start the stirring paddle and emulsifying and shearing machine, and at the same time add the prepared solution B to the emulsifying and shearing reaction tank, and control and adjust the pH value of the system within the range of 4 - 5.

[0122] (3), Add the well-reacted slurry in (2) into a high-pressure reactor, keep it at 190 °C for 5 h for reaction and then cool it to obtain lithium iron phosphate slurry L1.

[0123] (4), Filter, wash and make into a slurry the cooled material, then prepare a slurry with a mass fraction of 15 wt%, and then pump it into a sand mill for sanding treatment. After sanding, place the obtained slurry at 50 °C for 1 h of aging to obtain lithium iron phosphate slurry L2.

[0124] (5), Then add glucose according to a carbon coating amount of 2 wt% and a dopant according to a V heteroatom doping amount of 0.1 wt% into the slurry obtained in (4). After that, the obtained slurry is spray-dried to obtain spray material P1, sintered in a tube furnace at 650 °C for 10 h under an inert atmosphere, and then subjected to a gas crushing process after cooling to obtain lithium iron phosphate product LFP-S5.

[0125] Comparative Example 1

[0126] (1), Accurately weigh a certain mass of ferrous sulfate heptahydrate, 85 wt% phosphoric acid and deionized water, and prepare solution A with a concentration of 0.5 mol / L; accurately weigh a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly and prepare solution B with a concentration of 1 mol / L.

[0127] (2), Add the prepared solution A into an emulsifying and shearing reaction tank, start the stirring paddle and emulsifying and shearing machine, and at the same time add the prepared solution B into the emulsifying and shearing reaction tank, and control and adjust the pH value of the system in the range of 4 - 5.

[0128] (3), Add the well-reacted slurry in (2) into a high-pressure reactor, keep it at 190 °C for 5 h for reaction and then cool it to obtain lithium iron phosphate slurry L1.

[0129] (4), Then add glucose according to a carbon coating amount of 2 wt% into the slurry obtained in (3). After that, the obtained slurry is spray-dried to obtain spray material P1, sintered in a tube furnace at 700 °C for 10 h under an inert atmosphere, and then subjected to a gas crushing process after cooling to obtain lithium iron phosphate product LFP-D1.

[0130] Comparative Example 2

[0131] (1), Accurately weigh a certain mass of ferrous sulfate heptahydrate, 85 wt% phosphoric acid and deionized water, and prepare solution A with a concentration of 0.5 mol / L; accurately weigh a certain mass of lithium hydroxide monohydrate and deionized water, mix them evenly and prepare solution B with a concentration of 1 mol / L.

[0132] (2), Add the prepared solution A into an emulsifying and shearing reaction tank, start the stirring paddle and emulsifying and shearing machine, and at the same time add the prepared solution B into the emulsifying and shearing reaction tank, and control and adjust the pH value of the system in the range of 4 - 5.

[0133] (3) Add the well-reacted slurry in (2) into a high-pressure reactor, keep it at 190 °C for 5 h for reaction and then cool it to obtain lithium iron phosphate slurry L1.

[0134] (4) Then, add glucose with a carbon coating amount of 2% and a dopant with a V heteroatom doping amount of 0.1% into the slurry obtained in (3). After that, the obtained slurry is spray-dried to obtain spray material P1, which is sintered in a tube furnace at 700 °C for 10 h in an inert atmosphere, and then cooled and processed by air crushing technology to obtain lithium iron phosphate product LFP-D2.

[0135] Sample appearance test:

[0136] (1) Scanning electron microscope test

[0137] Perform scanning electron microscope tests on lithium iron phosphate product LFP-S4 and lithium iron phosphate product LFP-D2. The results are respectively as Figure 2 and Figure 3 shown.

[0138] Comparison Figure 2 with Figure 3 It can be known that the lithium iron phosphate product prepared by the method of sanding treatment provided in this application followed by aging is spherical, with smaller and more uniform particle sizes.

[0139] (2) Particle size test

[0140] Perform particle size statistics on lithium iron phosphate products LFP-S1 to LFP-S5 and lithium iron phosphate products LFP-D1 to LFP-D2. The results are shown in Table 1.

[0141] It can be known from Table 1 that the lithium iron phosphate product prepared by the method of sanding treatment provided in this application followed by aging not only has smaller particle size, but also due to the aging effect, the fine particles are deposited on the surface of the larger particles, making the particle size of the final product more uniform;

[0142] By comparing Example 1 and Example 2, it can be known that extending the aging time of the sanded slurry from 1 h to 2 h can increase the particle size;

[0143] By comparing Example 1 with Examples 3 and 4, it can be known that as the aging temperature of the sanded slurry is increased from 50 °C to 70 °C, the particle size of the product continuously decreases, indicating that the particle deposition can be effectively regulated by controlling the aging temperature, thereby regulating the particle size.

[0144] Table 1

[0145] Experiment Material Naming Dv(10) / nm Dv(50) / nm Dv(90) / nm Example 1 LFP-S1 27.5 59.8 113.3 Example 2 LFP-S2 31.5 67.3 116.8 Example 3 LFP-S3 18.86 50.06 100.33 Example 4 LFP-S4 15.56 44.44 89.01 Example 5 LFP-S5 25.8 62.2 117.8 Comparative Example 1 LFP-D1 55.56 121.58 208.48 Comparative Example 2 LFP-D2 50.45 105.58 201.83

[0146] Sample performance test:

[0147] The above lithium iron phosphate product is prepared into a test battery, and then rate performance test, low-temperature performance test and cycle performance test are carried out. The test results are shown in Table 2 below.

[0148] According to Table 2, by comparing Examples 1-5 with Comparative Examples 1-2, it can be seen that by using the method of aging again after sanding treatment provided in this application, the room temperature 15C discharge efficiency, low-temperature -20°C 1C discharge efficiency and room temperature 1C cycle capacity retention rate of the prepared lithium iron phosphate product can be effectively improved;

[0149] And from Comparative Example 1 and Comparative Example 2, it can be seen that the doping of metal element dopants can improve the room temperature 15C discharge efficiency, low-temperature -20°C 1C discharge efficiency and room temperature 1C cycle capacity retention rate of the prepared lithium iron phosphate product.

[0150] Table 2

[0151]

[0152] In summary, in this embodiment, for the provided method for preparing lithium iron phosphate, the crude lithium iron phosphate is first formulated into a slurry and then subjected to sanding treatment, and then the sanded slurry is aged to cause the fine particles caused by sanding to redissolve and recrystallize into spherical particles again, thereby synthesizing ultrafine and uniformly distributed small particles of 10-100 nm. Then, a carbon coating agent is added for spray drying, sintering and air crushing treatment, and refined lithium iron phosphate with excellent rate charge and discharge performance and processing performance can be prepared. Therefore, the technical problems of poor high-rate charge and discharge performance and poor processing performance of the lithium iron phosphate material prepared by the existing method are solved.

[0153] Although the preferred embodiments of the embodiments of the present application have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present application.

[0154] The above provides a detailed introduction to a method for preparing lithium iron phosphate, a lithium iron phosphate cathode material and a lithium battery provided by the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A preparation method of lithium iron phosphate, characterized in that, Comprising: Providing crude lithium iron phosphate; Formulating the crude lithium iron phosphate into a slurry and then performing sand milling treatment to obtain a sand milled slurry; Aging the sand milled slurry; Adding a carbon coating agent to the aged sand milled slurry and then performing spray drying, sintering and air crushing treatment to obtain refined lithium iron phosphate.

2. The method according to claim 1, characterized in that, The conditions for the aging are heat preservation at 30 - 200 °C for 1 - 48 h.

3. The method according to claim 1, characterized in that, The carbon coating agent is one or more of carbon black, graphene, carbon nanotubes, glucose, sucrose, acetone, polyaniline, polyethylene glycol.

4. The method according to claim 1, characterized in that, The addition amount of the carbon coating agent is 0.1 - 15% of the solid content in the aged sand milled slurry.

5. The method according to claim 1, characterized in that, Before performing spray drying, the method further includes: Adding a metal doping agent to the aged sand milled slurry.

6. The method according to claim 5, characterized in that, The metal element of the metal doping agent is one or more of Ca, Mg, Cu, Al, Zr, Ti, Co, V, Mn, Zr, W, Sn, Nb and Mo.

7. The method according to claim 5, characterized in that, During the process of adding the metal doping agent to the aged sand milled slurry, the metal doping agent is added according to the doping amount of the metal element being 0.1 - 3% wt of the solid content in the aged sand milled slurry.

8. The method according to claim 1, characterized in that, The step of providing crude lithium iron phosphate includes: In an inert gas atmosphere, mixing an iron source and a phosphorus source into a first liquid material, then adding a lithium source, and controlling the pH of the system to be 3 - 8, and performing shear stirring until emulsification is complete to obtain a lithium iron phosphate precursor slurry; Pressurizing and heating the lithium iron phosphate precursor slurry to obtain the crude lithium iron phosphate.

9. The method according to claim 8, characterized in that, During the process of obtaining the lithium iron phosphate precursor slurry, the solvent used is selected from one or more of deionized water, methanol, ethanol, propanol, propylene glycol, acetone, NMP, DMF.

10. The method according to claim 8, characterized in that, In the first liquid material, the concentration of the iron source is 0.5 - 2 mol / L, and the molar ratio of the iron source to the phosphorus source is (0.96 - 1.02):

1.

11. The method according to claim 8, characterized in that, The iron source is at least one of ferrous sulfate, ferrous chloride, ferrous bromide, ferrous perchlorate, ferrous oxalate, ferrous nitrate, ferrous acetate; The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, sodium phosphate, potassium phosphate, lithium dihydrogen phosphate; The lithium source is at least one of lithium reagents such as lithium chloride, lithium bromide, lithium sulfate, lithium nitrate, lithium carbonate, lithium chlorate, lithium hydroxide, lithium formate, lithium acetate.

12. The method according to claim 8, characterized in that, During the process of controlling the pH of the system to be 3 - 8, the pH regulator is at least one of ammonia water, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate.

13. The method according to claim 8, characterized in that, During the process of obtaining the lithium iron phosphate precursor slurry by reaction under shear stirring conditions, the system temperature is 120 - 250 °C, and the reaction time is 1 - 24 h.

14. The method according to claim 1, characterized in that, The sand milling treatment specifically includes: Using zirconium balls with a diameter of 0.1 - 0.5 mm for sand milling until the particle size of the slurry is 0.1 - 2 μm.

15. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared by the method according to any one of claims 1 - 13.

16. The lithium iron phosphate cathode material according to claim 15, wherein, The lithium iron phosphate cathode material is spherical, and the primary particle size Dv(50) is 10 - 100 nm.

17. The lithium iron phosphate cathode material according to claim 15, wherein, (D90 - D10) / D50 of lithium iron phosphate is 1.0 - 2.

0.

18. A lithium battery, wherein, including a positive electrode, which is made of the lithium iron phosphate positive electrode material according to any one of claims 15 to 17.

Images