Nanometer spherical lithium iron phosphate material as well as preparation method and application thereof

Abstract

The invention provides a nano spherical lithium iron phosphate material as well as a preparation method and application thereof. The chemical formula of the nano spherical lithium iron phosphate material is LiFe < 1-a-x-y-z > Al Ti < x > V < y > Mg < z > PO4 / C, Al, Ti, V and Mg are doping elements, C is a coating element, and the range of (D90-D10) / D50 of the lithium iron phosphate material is 0.3-0.9. The lithium iron phosphate positive electrode material is obtained by mixing a lithium source, an iron source, a phosphorus source, a doping agent and a coating agent through a one-step method, drying and sintering. A fluidized bed sintering furnace is adopted for sintering, the heat transfer and mass transfer efficiency during sintering can be improved, the sintering time is shortened, the production cost is reduced, accurate control over different sintering temperature sections is further combined, the particle size distribution and the carbon coating effect of the lithium iron phosphate material are optimized, and the obtained lithium iron phosphate material has excellent rate capability and cycle life.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of positive electrode materials, and particularly relates to a nanospherical lithium iron phosphate positive electrode material, a preparation method and application. BACKGROUND

[0002] A lithium ion battery is a rechargeable battery that relies on the reciprocal intercalation / deintercalation of lithium ions between the positive electrode and the negative electrode to realize the conversion of electrical energy and chemical energy. Since commercialization, it has become the mainstream power source for electric vehicles, consumer electronics and energy storage systems due to its high energy density, long cycle life and other advantages. The commonly used positive electrode materials for lithium ion batteries currently include lithium cobaltate, lithium nickel cobalt manganese oxide, lithium iron phosphate and lithium manganate, among which lithium iron phosphate batteries have broad application prospects due to their high operating voltage, high energy density, high cost performance, high safety and long cycle life. However, due to the olivine crystal structure of lithium iron phosphate, it has the problem of low electrical conductivity and active material etching at high potentials, resulting in poor rate performance, shortened life and poor low-temperature performance, which seriously restricts its practical application. To improve its electrochemical performance, the following modification strategies can be used: 1) ion doping: by introducing additional lithium ion storage sites, promoting the diffusion of lithium ions in the solid phase; 2) surface coating: enhancing the interface electron transport capacity to improve the electrical conductivity of the material; 3) structure regulation: optimizing the structure to promote the penetration of the electrolyte and accelerate the electrochemical reaction.

[0003] Patent document CN118929614A discloses a Mg, Ti ion composite doped lithium iron phosphate positive electrode material, which is prepared by mixing lithium salt, phosphorus source and iron source material, grinding and sintering to obtain a lithium iron phosphate precursor material, and then mixing the precursor with a magnesium source, a titanium source and a carbon source, grinding and sintering. The preparation steps of this method are relatively complicated.

[0004] Patent document CN116565180A discloses a high tap density lithium iron phosphate positive electrode material, which includes a lithium iron phosphate material and an external carbon coating layer, and the lithium iron phosphate material is further doped with cations and anions. The preparation method includes mixing a lithium source, an iron source, a phosphorus source, a carbon source, a cation dopant and an anion dopant, and then grinding and spray drying to obtain a precursor material, and sintering the precursor material to obtain a lithium iron phosphate positive electrode material. This method uses conventional sintering, which requires a long sintering time of 15-20 hours and has a high cost.

[0005] Patent document CN115332530A discloses a lithium iron phosphate positive electrode material, and the expression of the lithium iron phosphate material is LiFe 1-x M xPO4 / C, where 0 < x ≤ 0.05, M is selected from at least one element of Mg, Al, Zr, Ti, Co, V, Mn, Zr, W, Sn, Nb, and Mo, and the particle size distribution of the lithium iron phosphate cathode material satisfies (D90 - D10) / D50 = 1 to 2.17. The uniformity of the particle size distribution needs to be further improved.

[0006] Therefore, exploring simpler and more efficient methods for preparing lithium iron phosphate materials to improve production efficiency and reduce costs, as well as preparing lithium iron phosphate materials with more uniform particle size distribution and better rate performance, are crucial for the commercialization of lithium iron phosphate batteries. Summary of the Invention

[0007] To address these issues, the present invention provides a nano-spherical lithium iron phosphate material with a very narrow particle size distribution, which improves the electrochemical performance of lithium iron phosphate. The present invention also provides a method for preparing the nano-spherical lithium iron phosphate material. By regulating the calcination method and time of the lithium iron phosphate material, the nano-spherical lithium iron phosphate material can be produced at low cost and high efficiency.

[0008] Specifically, one aspect of the present invention provides a nano-spherical lithium iron phosphate material, wherein the D10 of the nano-spherical lithium iron phosphate material is 65-85 μm, preferably 70-80 μm, the D50 is 90-110 μm, preferably 95-105 μm, the D90 is 120-140 μm, preferably 125-135 μm, and the range of (D90-D10) / D50 is 0.3-0.9, preferably 0.4-0.7.

[0009] In one or more embodiments, the lithium iron phosphate material includes spherical secondary particles, the secondary particles are composed of primary particles, and the particle size of the primary particles ranges from 0.01 to 3.5 μm, preferably from 0.05 to 1 μm.

[0010] In one or more embodiments, the chemical formula of the lithium iron phosphate material is LiFe 1-a-x-y- z Al a Ti x V y Mg z PO4 / C, where 0≤a≤0.005, 0≤x≤0.01, 0≤y≤0.005, 0≤z≤0.05, Al, Ti, V and Mg are doping elements, and C is a coating element.

[0011] Another aspect of the present invention provides a method for preparing nano-spherical lithium iron phosphate material, the method comprising the following steps:

[0012] S1, uniformly mixing a lithium source, an iron source, a phosphorus source, an optional dopant, an optional carbon source and water, and grinding the mixed slurry;

[0013] S2, spray drying the ground slurry obtained in S1 to obtain a lithium iron phosphate material precursor;

[0014] S3, under the protection of an inert atmosphere, pre-sintering the lithium iron phosphate material precursor obtained in S2 in a fluidized bed, and then high-temperature sintering to obtain a nanospherical lithium iron phosphate material.

[0015] In one or more embodiments, in S1, the molar ratio of the lithium source, the iron source, the phosphorus source and the dopant is 1:1-0.93:1:0-0.07.

[0016] In one or more embodiments, in S1, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate.

[0017] In one or more embodiments, in S1, the iron source is selected from one or more of iron phosphate, ferrous oxalate dihydrate, ferrous sulfate heptahydrate, ammonium ferrous sulfate hexahydrate.

[0018] In one or more embodiments, in S1, the phosphorus source is selected from one or more of diammonium hydrogen phosphate, phosphoric acid.

[0019] In one or more embodiments, in S1, the aluminum source is selected from one or more of di-aluminum trioxide, aluminum hydroxide, aluminum phosphate, basic aluminum di(octadecanoate).

[0020] In one or more embodiments, in S1, the titanium source is selected from one or more of titanium dioxide, titanium isopropoxide.

[0021] In one or more embodiments, in S1, the vanadium source is selected from ammonium metavanadate.

[0022] In one or more embodiments, in S1, the magnesium source is selected from one or more of magnesium acetate, magnesium acetate tetrahydrate.

[0023] In one or more embodiments, in S1, the carbon source is selected from one or more of glucose, sucrose, citric acid, starch, polyethylene glycol.

[0024] In one or more embodiments, in S1, the grinding is one or more of ball milling, sand milling or ultrasonic vibration.

[0025] In one or more embodiments, in S1, the grinding time is 20 min-4 h, preferably 0.5-1.5 h.

[0026] In one or more embodiments, in S1, the particle size D50 of the slurry after grinding is 0.01-10 μm, preferably 0.35-1.5 μm.

[0027] In one or more embodiments, in S2, the inlet temperature of the spray drying is 250-350 °C, preferably 270-320 °C, and the outlet temperature is 70-130 °C, preferably 80-100 °C.

[0028] In one or more embodiments, in S3, the temperature increasing rate of the pre-sintering is 5-20 °C / min, the pre-sintering temperature is 350-500 °C, and the holding time is 20-80 min, preferably, the temperature increasing rate is 5-10 °C / min, the pre-sintering temperature is 320-420 °C, and the holding time is 40-60 min.

[0029] In one or more embodiments, in S3, the high-temperature sintering is performed at a temperature increasing rate of 5-20 °C / min, a temperature of 600-800 °C, and a holding time of 30-90 min, preferably, the temperature increasing rate is 8-15 °C / min, the temperature is 700-800 °C, and the holding time is 50-70 min.

[0030] The present application also provides a positive electrode sheet comprising the nanospherical lithium iron phosphate material as described herein, or a positive electrode sheet comprising the nanospherical lithium iron phosphate material prepared by the method as described herein.

[0031] In one or more embodiments, the nanospherical lithium iron phosphate material accounts for 75-85% of the mass of the positive electrode sheet.

[0032] In one or more embodiments, the positive electrode sheet further comprises polyvinylidene fluoride and super carbon black, and the mass ratio of the nanospherical lithium iron phosphate material, polyvinylidene fluoride and super carbon black is 75-85:10-15:5-10.

[0033] The present application also provides a lithium ion battery comprising the positive electrode sheet as described herein. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 FIG. 3 is an XRD pattern of the lithium iron phosphate material of Example 1.

[0035] Figure 2 FIG. 4 is an SEM image of the lithium iron phosphate material of Example 1 at a scale of 100 μm (a) and an SEM image of the lithium iron phosphate material of Comparative Example 2 at a scale of 100 μm (b).

[0036] Figure 3Fig. 1 is a SEM image of the lithium iron phosphate material of Example 1 at a scale of 1 μm, Fig. 2 is a SEM image of the lithium iron phosphate material of Comparative Example 2 at a scale of 1 μm.

[0037] Figure 4 Fig. 3 is a SEM image of the primary particles of the lithium iron phosphate material of Example 1 obtained by air flow crushing at a scale of 1 μm, Fig. 4 is a SEM image of the primary particles of the lithium iron phosphate material of Comparative Example 2 obtained by air flow crushing at a scale of 1 μm.

[0038] Figure 5 Fig. 5 is a graph of the first cycle charge-discharge curve of the lithium ion button cell of Example 1-7 and Comparative Example 1-2, Fig. 6 is an enlarged view of a part of Fig. 5. DETAILED DESCRIPTION

[0039] To enable persons skilled in the art to have a better understanding of the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used in the specification have the conventional meanings understood by those skilled in the art of the present application, and in the event of a conflict, the definitions in the specification shall prevail.

[0040] Theories and mechanisms described and disclosed herein, whether correct or not, should not be considered limiting on the scope of the present application, which is defined only by the claims. The present application can be implemented in the absence of any specific theory or mechanism.

[0041] In the present disclosure, the terms "comprising", "including", "containing", and the like, are inclusive, in the sense of "consisting essentially of", and "consisting of", for example, when the present disclosure recites a composition, a method or process, an article of manufacture, or a computer program comprising A and B, it will be understood that "A and B" are essential to the composition, the method or process, the article of manufacture, or the computer program, and that "A and B" cannot be removed without altering the composition, the method or process, the article of manufacture, or the computer program.

[0042] In the present disclosure, all features defined by numerical ranges or percentage ranges, such as numerical values, amounts, contents and concentrations, are for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0043] In the present disclosure, unless otherwise specified, percentages are mass percentages, and ratios are mass ratios.

[0044] In the present disclosure, when describing embodiments or examples, it should be understood that they are not intended to limit the present application to these embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein, which are apparent to those skilled in the art, are intended to be encompassed by the scope of the claims.

[0045] In this document, all possible combinations between technical features in individual embodiments or examples are not described in order to simplify the description. Therefore, as long as there is no contradiction, any combination of technical features in individual embodiments or examples can be combined, and all possible combinations shall be considered as the scope described in this specification.

[0046] Nanospherical lithium iron phosphate material

[0047] The nanospherical lithium iron phosphate material of the present application is secondary particles formed by agglomeration of nanoscale primary particles, and has a shape of a regular sphere or a shape close to a regular sphere. The spherical particles have the advantages of high volume specific capacity and high bulk density, and can solve the problems of low tap density, low conductivity, irregular shape and unstable performance of the lithium iron phosphate prepared by the existing preparation method of lithium iron phosphate.

[0048] The particle size of the primary particles of the present application is between 0.01 and 3.5 μm, for example, it can be 300 nm, 600 nm, 900 nm, 1 μm, 3 μm, and preferably the particle size is between 0.05 and 1 μm. When the particle size reaches the nanoscale, the transmission efficiency of lithium ions and electrons can be improved, and the utilization rate of the material can be improved.

[0049] D10 represents the particle size at which the volume cumulative value of the particles in the particle size distribution is 10%, D50 represents the particle size at which the volume cumulative value of the particles in the particle size distribution is 50%, and D90 represents the particle size at which the volume cumulative value of the particles in the particle size distribution is 90%. The particle size D10 of the secondary particles of the present application can be between 65 and 85 μm, for example, it can be 65 μm, 70 μm, 72 μm, 75 μm, and preferably the particle size D10 is between 70 and 80 μm. The particle size D50 of the secondary particles of the present application can be between 90 and 110 μm, for example, it can be 95 μm, 100 μm, 105 μm, 110 μm, and preferably it is between 95 and 105 μm. The particle size D90 of the secondary particles of the present application can be between 120 and 140 μm, for example, it can be 121 μm, 125 μm, 127 μm, 130 μm, and preferably the particle size D90 is between 125 and 135 μm.

[0050] (D90-D10) / D50 represents the particle size distribution width coefficient, and the smaller the value of the particle size distribution width coefficient, the narrower the particle size distribution, the more uniform the particle size, and the higher the concentration. The particle size distribution width coefficient of the secondary particles of the present application is between 0.3 and 0.9, for example, it can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and preferably it is between 0.4 and 0.7.

[0051] The nanospherical lithium iron phosphate material of the present application is doped and carbon-coated lithium iron phosphate (LiFePO4). The chemical formula of the lithium iron phosphate material of the present application can be represented as LiFe 1-a-x-y-zAl a Ti x V y Mg z PO4 / C, where 0≤a≤0.002, 0≤x≤0.0025, 0≤y≤0.0005, 0≤z≤0.05, wherein Al, Ti, V and Mg are doping elements, a, x, y, z can be determined according to the addition amount and valence state of the doping elements, and C is a coating element.

[0052] In the present invention, the amount of doping element or coating element added refers to the mass fraction of the doping element or coating element in the total mass of the final lithium iron phosphate material. The ion valence of the doping elements Al, Ti, and V is higher than that of Fe. 3+ 、Ti 4+ 、V 3+ and V 4+ , high-valent doping elements will replace Fe in LiFePO4 2+ This high-valent substitution introduces positive charge defects in the lattice, thereby forming Li vacancies or electron defects to maintain electrical neutrality through charge compensation, which significantly improves the electronic conductivity of the material and enhances the rate performance.

[0053] Doping element Al 3+ Ionic radius Ti 4+ Ionic radius V 3+ Ionic radius V 4+ Ionic radius and Mg 2+ Ionic radius Both are smaller than Fe 2+ Ionic radius After doping, the lattice volume is reduced, thereby widening the Li + One-dimensional diffusion channel (

[010] direction), and reduce Li + diffusion barrier, ultimately improving the rate performance of the material.

[0054] The four doping elements may be contained at the same time, or only one or two doping elements may be contained. Preferably, two or more doping elements are contained, and more preferably, at least Al and Ti doping elements are contained. The chemical formula of lithium iron phosphate material may be, for example, LiFe 0.97 Mg 0.03 PO4 / C, LiFe 0.995 Al 0.001 Ti 0.004 PO4 / C, LiFe 0.997 Al 0.002 Ti 0.001 PO4 / C, LiFe0.994 Al 0.002 Ti 0.004 PO4 / C, LiFe 0.992 Al 0.004 Ti 0.004 PO4 / C, LiFe 0.997 Ti 0.002 V 0.001 PO4 / C, LiFe 0.9495 V 0.0005 Mg 0.05 PO4 / C, LiFe 0.9885 Al 0.0015 Mg 0.01 PO4 / C, LiFe 0.9785 Al 0.0015 Mg 0.02 PO4 / C, LiFe 0.945 Al 0.002 Ti 0.0025 V 0.0005 Mg 0.05 PO4 / C.

[0055] In the application, the coating element is carbon. The carbon layer coated outside the lithium iron phosphate can form a conductive network, improve the electronic conductivity, reduce the electrode polarization, improve the rate performance, and the carbon layer can limit the grain growth of the lithium iron phosphate precursor in the sintering process to avoid uneven particle size distribution.

[0056] Preparation method of nanospherical lithium iron phosphate material

[0057] The nanospherical lithium iron phosphate material of the application is formed by mixing, spray drying and sintering of a lithium source, an iron source, a phosphorus source, an optional dopant and an optional coating agent.

[0058] The lithium source can be one or more selected from lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate and lithium nitrate.

[0059] The iron source is selected from one or more of iron phosphate, ferrous oxalate dihydrate, ferrous sulfate heptahydrate and ferrous ammonium sulfate hexahydrate.

[0060] The phosphorus source is selected from one or more of diammonium hydrogen phosphate and phosphoric acid.

[0061] The dopant can be selected from one or more of an aluminum source, a titanium source, a vanadium source and a magnesium source. The aluminum source is selected from one or more of diatomium trioxide, aluminum hydroxide, aluminum phosphate and basic aluminum di(octadecanoate), the titanium source is selected from one or more of titanium dioxide and titanium isopropoxide, the vanadium source is ammonium metavanadate, and the magnesium source is selected from one or more of magnesium acetate and magnesium acetate tetrahydrate.

[0062] The coating agent is a carbon source, selected from one or more of organic carbon such as glucose, sucrose, citric acid, starch, and polyethylene glycol.

[0063] The preparation method of the nano-spherical lithium iron phosphate material of the present invention comprises the following steps:

[0064] S1. Evenly mix a lithium source, an iron source, a phosphorus source, an optional dopant, an optional coating agent, and water, and grind the resulting slurry;

[0065] S2, spray drying the ground slurry obtained in S1 to obtain a lithium iron phosphate material precursor;

[0066] S3. Under the protection of an inert atmosphere, the lithium iron phosphate material precursor obtained in S2 is pre-sintered in a fluidized bed, and then sintered at a high temperature to obtain a nano-spherical lithium iron phosphate material.

[0067] In step S1, all raw materials are wet mixed in a one-step process to obtain a slurry. In conventional processes, a lithium iron phosphate precursor is first prepared and then mixed with the dopant. The grinding process can be one or more of ball milling, sand milling, or ultrasonic vibration. For example, a sand mill can be used for sand milling for 1 hour. The particle size D50 of the slurry after grinding is 0.01 to 10 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 5 μm, and preferably 0.35 to 1.5 μm.

[0068] In step S2, spray drying can be performed using a centrifugal sprayer with an inlet air temperature range of 250-350°C, preferably 270-320°C, and an outlet air temperature range of 70-130°C, preferably 80-100°C. The solid content of the slurry used for spray drying is between 40% and 60%. The particle size D50 of the lithium iron phosphate material precursor obtained by spray drying is 85-100 μm, preferably 90-95 μm.

[0069] In step S3, the inert atmosphere is from nitrogen, argon or a mixture of both. The sintering device is a fluidized bed sintering furnace. The fluidized bed sintering furnace generally consists of a bed body, a gas distribution device (such as a porous plate or a hood), a heating system, a gas-solid separation device (such as a cyclone separator or a filter) and an in / out feeding system. The high-temperature gas uniformly enters the bed layer through the gas distribution device, making the solid particles fluidized and heated for sintering, and the separation device recovers the sintered particles. The fluidized bed sintering furnace can significantly improve the heat and mass transfer efficiency, so that the material can quickly complete the sintering reaction at high temperature, avoiding the problems of uneven temperature, caking and long sintering time in traditional sintering equipment such as tunnel kiln and rotary kiln. The fluidized bed sintering furnace used in the present application has an inner diameter of 50 cm, and the material height-diameter ratio is 1:1 to 8:1, for example, it can be 1:1, 2:1, 3:1, 5:1, 7:1, and the preferred height-diameter ratio is 2:1 to 4:1. The lithium iron phosphate material precursor is subjected to two sintering steps of pre-sintering and high-temperature sintering in the fluidized bed sintering furnace. Pre-sintering can decompose the organic carbon source in the lithium iron phosphate material precursor, and uniformly coat the primary particles with a carbon-coated layer. High-temperature sintering promotes the graphitization of the carbon layer, improves the electronic conductivity, and finally forms the doped and coated lithium iron phosphate. The pre-sintering temperature rising rate is 5-20℃ / min, for example, it can be 5℃ / min, 8℃ / min, 10℃ / min, 15℃ / min; the pre-sintering temperature is 350-500℃, for example, it can be 350℃, 380℃, 400℃, 450℃; the holding time is 20-80min, for example, it can be 20min, 25min, 30min, 40min, 60min; preferably, the temperature rising rate is 5-10℃ / min, the pre-sintering temperature is 320-420℃, and the holding time is 40-60min. The high-temperature sintering temperature rising rate is 5-20℃ / min, for example, it can be 5℃ / min, 8℃ / min, 10℃ / min, 15℃ / min; the sintering temperature is 600-800℃, for example, it can be 600℃, 630℃, 650℃, 700℃, 750℃; the holding time is 30-90min, for example, it can be 30min, 35min, 40min, 60min, 80min; preferably, the temperature rising rate is 8-15℃ / min, the temperature is 700-800℃, and the holding time is 50-70min. Through accurate control of different temperature stages, the material crystallinity, particle size distribution, impurity removal and carbon coating effect can be optimized, so as to balance the energy density, rate performance and cycle life.

[0070] Positive electrode sheet and lithium ion battery

[0071] The present application also provides a positive electrode sheet containing the nanospherical lithium iron phosphate material according to any one of the embodiments herein, and a lithium ion battery containing the positive electrode sheet.

[0072] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer formed on the surface of the positive electrode current collector. The positive electrode material layer comprises a positive electrode active material, a conductive agent and a binder. The positive electrode material layer is obtained by coating the positive electrode slurry comprising the positive electrode active material, the conductive agent, the binder and a solvent on the positive electrode current collector, rolling, baking and the like. The positive electrode current collector can be a copper foil, an aluminum foil, a titanium foil, a nickel foil, an iron foil, a zinc foil and the like. The solvent of the positive electrode slurry can be N-methyl pyrrolidone (NMP). In the positive electrode sheet of the present application, the positive electrode active material comprises the nanospherical lithium iron phosphate material of the present application. The conductive agent of the positive electrode can be one or more selected from super conductive carbon black (SP), carbon fiber (CF), acetylene black, conductive graphite, graphene, carbon nanotube and carbon microsphere. The binder of the positive electrode can be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl alcohol, polyolefin, butadiene rubber, fluorinated rubber, polyurethane and sodium alginate. In some embodiments, the conductive agent in the positive electrode material layer is SP, and the binder is PVDF. The content ratio of the components in the positive electrode material layer can be conventional, for example, the mass fraction of the positive electrode active material can be 75-85%, for example, 75%, 77%, 80%, 82%; the mass fraction of the conductive agent can be 5-10%, for example, 5%, 7%, 9%; and the mass fraction of the binder can be 10%-15%, for example, 10%, 11%, 12%, 13%, 14%, 15%.

[0073] The preparation method of the positive electrode sheet is as follows: the positive electrode material, the binder and the conductive agent are placed in a weighing bottle in proportion, then an appropriate amount of organic solvent, for example, N-methyl pyrrolidone (NMP), is added dropwise, and a uniform slurry is formed after magnetic stirring. The prepared slurry is uniformly coated on the positive electrode current collector, dried overnight, pressed into a sheet and then punched into a circular sheet.

[0074] The positive electrode sheet, the negative electrode sheet and the separator are laminated to obtain the electric core of the lithium ion battery. The electric core is packaged in a shell, dried, injected with electrolyte, packaged, left to stand, formed, sorted and then the lithium ion battery is obtained. The form of the lithium ion battery of the present application is not particularly limited and can be a cylindrical lithium ion battery, a soft package lithium ion battery, an aluminum shell lithium ion battery or a button lithium ion battery and the like.

[0075] The present application has the following beneficial effects:

[0076] 1. The lithium iron phosphate material provided by the present application has a regular circular shape, a narrow particle size distribution range and more uniform charge and discharge performance.

[0077] 2. The present application uses a fluidized bed sintering furnace to improve the heat and mass transfer efficiency during sintering, shorten the sintering time and reduce the production cost. Meanwhile, the present application combines the accurate control of different sintering temperature sections to optimize the particle size distribution and carbon coating effect of the lithium iron phosphate material, so that the obtained lithium iron phosphate material has excellent rate performance and cycle life.

[0078] 3、The doping element of the present application includes one or more of Al, Ti, V, Mg, wherein the ionic valence of Al, Ti and V is higher than that of Fe, and the ionic radius of Al, Ti, V and Mg is smaller than that of Fe, and the conductivity and rate performance of the lithium iron phosphate material can be improved by doping the above elements.

[0079] The present application will be described below in the manner of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present application. The methods, reagents and materials used in the examples are conventional in the art unless otherwise specified. The raw material compounds in the examples can be purchased through commercial channels.

[0080] In the following examples and comparative examples, the relevant parameters are obtained by the following test methods:

[0081] (1) XRD: The sample was characterized using an X-ray diffractometer (Rigaku Smart Lab SE) with Cu-Ka radiation for identification of crystal structure and phase composition analysis. XRD data were collected in an angular range of 10-90° with a scan rate of 5° / min. Numerical processing method: identify crystal form by jade9 query PDF card.

[0082] (2) SEM morphology test: obtained by JSM7401 scanning electron microscope test.

[0083] (3) Particle size distribution: D10, D50 and D90 values were obtained by Mastersizer3000+Ultra laser particle size analyzer, and the particle size distribution value was calculated by (D90-D10) / D50.

[0084] (4) Rate performance test: the assembled lithium ion button cell was placed in a constant temperature environment (25±2℃) for 12-24 hours. The electrochemical test was carried out on a blue electric test system (LAND-CT2001A) with 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 0.1Cm (1C=170mAh·g -1 ) rate in turn, and each rate was cycled for 5 times, and the last stable data was taken to avoid the influence of battery polarization accumulation on high rate data.

[0085] (5) Charge-discharge performance test: at room temperature, the charge-discharge performance test was carried out on a blue electric test system (LAND-CT2001A) with 0.1C rate, and the voltage was stable between charge and discharge, and the influence of concentration difference polarization was reduced.

[0086] Example 1

[0087] The lithium iron phosphate material of the present embodiment is prepared by the following steps:

[0088] (1) 647.01 mL of deionized water was added to a beaker and placed on a magnetic stirrer for low-speed stirring, then 117.11 g of lithium carbonate, 482.62 g of iron phosphate, 0.38 g of aluminum oxide, 1.01 g of titanium dioxide, 42.91 g of glucose and 3 g of polyethylene glycol were added respectively, and the slurry was stirred for 1 h, then the slurry was injected into a sand mill (Mini-Easy laboratory nanometer sand mill) for sand milling for 1 h, and the particle size D50 of the slurry was 1.34 μm;

[0089] (2) Then the slurry was sprayed and granulated by a centrifugal spray dryer (LPG-5 type), the inlet air temperature of the centrifugal spray dryer was 280℃, and the outlet air temperature was 100℃, and the granular material was obtained after spray granulation;

[0090] (3) The granular material was loaded into a fluidized bed (inner diameter of 50 cm, material height-diameter ratio of 3:1), and sintering was carried out under the protection of inert atmosphere, the temperature was raised to 400℃ at a rate of 10℃ / min, and the temperature was kept for 60 min; then the temperature was raised to 800℃ at a rate of 10℃ / min under the protection of inert atmosphere, and the temperature was kept for 60 min, to obtain spherical lithium iron phosphate material.

[0091] The chemical formula of the spherical lithium iron phosphate material of the present embodiment is LiFe 0.995 Al 0.001 Ti 0.004 PO4 / C.

[0092] The particle size D10 of the spherical lithium iron phosphate material of the present embodiment is 76.6 μm, the particle size D50 is 98.8 μm, the particle size D90 is 127 μm, and (D90-D10) / D50 is 0.51.

[0093] The D10 of the primary particles obtained by air flow crushing of the spherical lithium iron phosphate material of the present embodiment under a certain vibration feeding frequency is 18.7 nm, the D50 is 60.1 nm, and the D90 is 2.94 μm.

[0094] The positive electrode sheet of the present embodiment is prepared by the following method:

[0095] The lithium iron phosphate material prepared above, polyvinylidene fluoride (PVDF) and superconducting carbon black were mixed in a mass ratio of 79:11:10, N-methyl pyrrolidone (NMP) was added dropwise to prepare a uniform slurry, and the slurry was stirred at a speed of 1300 rpm for 8 h. Then the positive electrode sheet was obtained by coating, drying, and placing it in a tablet press to press the sheet, and then punching it into a circular sheet with a diameter of 12 mm.

[0096] The lithium ion battery of the present example was prepared by the following method:

[0097] The positive electrode sheet prepared above was assembled with a lithium metal negative electrode to form a lithium ion battery, the electrolyte was 1.0 M LiPF6in EC:DMC:DEC = 1:1:1 vol%, the separator (Celgard 2400) was cut into a circle with a diameter of 19 mm, and the lithium ion button cell was obtained by assembling in the order of negative electrode shell, spring, gasket, lithium sheet, separator, positive electrode sheet, and positive electrode shell.

[0098] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0099] Example 2

[0100] The lithium iron phosphate material of the present example was prepared by the following steps:

[0101] (1) 805.95 mL of deionized water was added to a beaker and placed on a magnetic stirrer for low-speed stirring, then 220.63 g of lithium nitrate, 482.62 g of iron phosphate, 0.58 g of aluminum hydroxide, 1.01 g of titanium dioxide, 42.91 g of glucose, and 3 g of polyethylene glycol were added respectively, and the slurry was stirred for 1 h on a magnetic stirrer, then the slurry was injected into a ball mill (model PMQW04) for ball milling for 20 min and ultrasonic vibration for 30 min, and the particle size D50 of the slurry was 1.10 μm;

[0102] (2) Then the slurry was spray granulated by a centrifugal spray dryer, the inlet air temperature of the centrifugal spray dryer was 290°C, and the outlet air temperature was 110°C, and the granular material was obtained after spray granulation;

[0103] (3) The granular material was loaded into a fluidized bed (inner diameter of 50 cm, material height-diameter ratio of 2:1), and sintering was carried out under the protection of an inert atmosphere, the temperature was raised to 380°C at a rate of 8°C / min, and the temperature was maintained for 70 min. Then the temperature was raised to 710°C at a rate of 8°C / min under the protection of an inert atmosphere, and the temperature was maintained for 70 min, to obtain spherical lithium iron phosphate material.

[0104] The chemical formula of the spherical lithium iron phosphate material of the present example is LiFe 0.992 Al 0.004 Ti 0.004 PO4 / C.

[0105] The particle size D10 of the spherical lithium iron phosphate material of the present example was 76.2 μm, the D50 was 99.9 μm, the D90 was 132 μm, and the (D90-D10) / D50 was 0.56.

[0106] The positive electrode sheet of the present example was prepared by the following method:

[0107] The lithium iron phosphate material prepared above, polyvinylidene fluoride (PVDF) and superconducting carbon black were mixed in a mass ratio of 80:10:10, and N-methyl pyrrolidone (NMP) was added dropwise to prepare a uniform slurry, which was stirred at a speed of 1300 rpm for 8 h. After coating, drying, and placing in a tablet press to press a tablet, a positive electrode sheet was obtained, which was punched into a circular sheet with a diameter of 12 mm.

[0108] The lithium ion battery of this example was prepared by the following method:

[0109] The positive electrode sheet prepared above was assembled with a lithium metal negative electrode to form a lithium ion battery, the electrolyte was 1.0 M LiPF6in EC:DMC:DEC=1:1:1 vol%, the separator (Celgard 2400) was cut into a circular sheet with a diameter of 19 mm, and the lithium ion button cell was assembled in the order of negative electrode shell, spring, gasket, lithium sheet, separator, positive electrode sheet, and positive electrode shell.

[0110] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0111] Example 3

[0112] The lithium iron phosphate material of this example was prepared in the same way as in Example 1, except that:

[0113] The raw materials were changed to 970 mL of deionized water, 383.16 g of lithium dihydrogen phosphate, 556.02 g of iron phosphate, 0.59 g of titanium dioxide, 0.43 g of ammonium metavanadate, 26.82 g of glucose, and 1.88 g of polyethylene glycol.

[0114] The spherical lithium iron phosphate material of this example had a chemical formula of LiFe 0.997 Ti 0.002 V 0.001 PO4 / C.

[0115] The spherical lithium iron phosphate material of this example had a particle size D10 of 73.3 μm, a D50 of 98.8 μm, a D90 of 132 μm, and a (D90-D10) / D50 of 0.59.

[0116] The steps of preparing the positive electrode sheet and the lithium ion button cell of this example were the same as in Example 1.

[0117] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0118] Example 4

[0119] The lithium iron phosphate material of this example was prepared in the same way as in Example 1, except that:

[0120] The raw materials were changed to 654.75 mL of deionized water, 118.23 g of lithium carbonate, 482.62 g of iron phosphate, 0.49 g of aluminum oxide, 6.68 g of magnesium acetate, 42.91 g of sucrose, and 3 g of polyethylene glycol.

[0121] The chemical formula of the spherical lithium iron phosphate material of this example was LiFe 0.9785 Al 0.0015 Mg 0.02 PO4 / C.

[0122] The particle size D10 of the spherical lithium iron phosphate material of this example was 77.3 μm, the D50 was 102 μm, the D90 was 134 μm, and the (D90-D10) / D50 was 0.56.

[0123] The steps of preparing the positive electrode sheet and the lithium ion button cell of this example were the same as those of Example 1.

[0124] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0125] Example 5

[0126] The lithium iron phosphate material of this example was prepared in the same way as in Example 1, except that:

[0127] The raw materials were changed to 654.75 mL of deionized water, 117.11 g of lithium carbonate, 482.62 g of iron phosphate, 13.67 g of magnesium acetate, 42.91 g of sucrose, and 3 g of polyethylene glycol.

[0128] The chemical formula of the spherical lithium iron phosphate material of this example was LiFe 0.97 Mg 0.03 PO4 / C.

[0129] The particle size D10 of the spherical lithium iron phosphate material of this example was 74.6 μm, the D50 was 100 μm, the D90 was 135 μm, and the (D90-D10) / D50 was 0.60.

[0130] The steps of preparing the positive electrode sheet and the lithium ion button cell of this example were the same as those of Example 1.

[0131] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0132] Example 6

[0133] The lithium iron phosphate material of this example was prepared in the same way as in Example 1, except that:

[0134] The pre-sintering conditions were a temperature increase rate of 10℃ / min, a pre-sintering temperature of 450℃, and a holding time of 70 min.

[0135] The high-temperature sintering condition is: the temperature rising rate is 10℃ / min, the temperature is 790℃, and the holding time is 75min.

[0136] The steps of preparing the positive electrode sheet and the lithium ion button cell in this example are the same as those in Example 1.

[0137] The chemical formula of the spherical lithium iron phosphate material in this example is LiFe 0.995 Al 0.001 Ti 0.004 PO4 / C.

[0138] The particle size D10 of the spherical lithium iron phosphate material in this example is 73.8μm, the D50 is 98.6μm, the D90 is 131μm, and the (D90-D10) / D50 is 0.58.

[0139] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0140] Example 7

[0141] The lithium iron phosphate material in this example is prepared in the same way as in Example 1, except that:

[0142] The pre-sintering condition is: the temperature rising rate is 8℃ / min, the pre-sintering temperature is 380℃, and the holding time is 70min.

[0143] The high-temperature sintering condition is: the temperature rising rate is 8℃ / min, the temperature is 710℃, and the holding time is 70min.

[0144] The chemical formula of the spherical lithium iron phosphate material in this example is LiFe 0.995 Al 0.001 Ti 0.004 PO4 / C.

[0145] The particle size D10 of the spherical lithium iron phosphate material in this example is 77.2μm, the D50 is 101μm, the D90 is 133μm, and the (D90-D10) / D50 is 0.55.

[0146] The steps of preparing the positive electrode sheet and the lithium ion button cell in this example are the same as those in Example 1.

[0147] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0148] Comparative Example 1

[0149] This comparative example provides an undoped lithium iron phosphate material.

[0150] The lithium iron phosphate material of the present comparative example was prepared in the same manner as in Example 1, except that:

[0151] No aluminum oxide and titanium dioxide were added, and the other steps were the same, finally obtaining the lithium iron phosphate material of the present comparative example.

[0152] The chemical formula of the lithium iron phosphate material of the present comparative example was LiFePO4 / C.

[0153] The particle size D10 of the lithium iron phosphate material of the present comparative example was 64 μm, the D50 was 85.8 μm, the D90 was 114 μm, and the (D90-D10) / D50 was 0.58.

[0154] The positive electrode sheet and the lithium ion button cell of the present comparative example were prepared in the same manner as in Example 1.

[0155] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0156] Comparative Example 2

[0157] The present comparative example provides a lithium iron phosphate material which is not sintered by using a fluidized bed sintering furnace.

[0158] The lithium iron phosphate material of the present comparative example was prepared in the same manner as in Example 1, except that:

[0159] The granular material was loaded into a crucible and placed in a tube furnace, and sintered under the protection of an inert atmosphere, with a heating rate of 5 ℃ / min to 400 ℃ for 4 h. Subsequently, under the protection of an inert atmosphere, with a heating rate of 5 ℃ / min to 750 ℃, and kept for 12 h. The lithium iron phosphate material was obtained.

[0160] The particle size D10 of the lithium iron phosphate material of the present comparative example was 52.8 μm, the D50 was 87.5 μm, the D90 was 137 μm, and the (D90-D10) / D50 was 0.96.

[0161] The lithium iron phosphate material of the present comparative example was subjected to the same airflow crushing method as in Example 1, and the D10 of the primary particles obtained by airflow crushing was 23.3 nm, the D50 was 2.28 μm, and the D90 was 6.51 μm.

[0162] The positive electrode sheet and the lithium ion button cell of the present comparative example were prepared in the same manner as in Example 1.

[0163] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0164] Comparative Example 3

[0165] The present comparative example provides a lithium iron phosphate material which is sintered by using a fluidized bed sintering furnace but is not pre-sintered.

[0166] The lithium iron phosphate material of the present comparative example was prepared in the same manner as in Example 1, except that:

[0167] The granular material was loaded into a fluidized bed and sintered under the protection of an inert atmosphere, and heated to 800℃ at a heating rate of 10℃ / min and kept for 2h to obtain the lithium iron phosphate material.

[0168] The lithium iron phosphate material of the present comparative example had a particle size D10 of 59.7μm, a D50 of 93.7μm, a D90 of 141μm, and a (D90-D10) / D50 of 0.87.

[0169] The positive electrode sheet and lithium ion button cell prepared in the present comparative example were prepared in the same manner as in Example 1.

[0170] The test results of the lithium ion button cell are shown in Table 1 and Figure 5 .

[0171] Table 1: Comparison of rate performance results of Examples 1-7 and Comparative Examples 1-3

[0172] 0.1C 0.2C 0.5C 1C 2C 5C 0.1C Example 1 166.38 166.33 163.46 158.59 151.47 136.07 165.01 Example 2 165.43 167.02 164.81 161.23 153.84 138.70 164.77 Example 3 164.05 164.73 162.97 158.79 152.61 137.47 163.95 Example 4 166.33 167.85 165.46 161.34 152.96 136.08 165.82 Example 5 163.55 164.63 157.01 153.41 145.62 129.04 162.01 Example 6 165.28 164.55 161.70 156.23 148.66 131.52 164.08 Example 7 163.44 163.76 160.65 156.94 149.9 134.86 163.05 Comparative Example 1 161.16 159.60 156.47 152.05 144.08 128.09 160.65 Comparative Example 2 159.78 157.89 154.43 148.17 142.27 124.30 157.18 Comparative Example 3 158.24 154.81 152.63 147.07 139.40 125.18 156.97

[0173] As can be seen from Table 1 and Figure 5 , the lithium iron phosphate materials of Examples 1-7 of the present application exhibited higher charge-discharge specific capacity and rate performance compared to the comparative examples.

[0174] Figure 1 The XRD pattern of the lithium iron phosphate material prepared in Example 1. As can be seen from the figure, the XRD diffraction peaks of Example 1 matched the standard card PDF#01-075-7725, and the diffraction peaks were sharp with high peak intensity, indicating that the lithium iron phosphate material with an olivine structure was synthesized well, which belonged to the orthorhombic system with a space group of Pnma.

[0175] Figure 2 The SEM image of the lithium iron phosphate material of Example 1 and Comparative Example 2 at a scale of 100μm, Figure 3 The SEM image of the lithium iron phosphate material of Example 1 and Comparative Example 2 at a scale of 1μm. Figure 4 The SEM image of the primary particles of the lithium iron phosphate material of Example 1 and Comparative Example 2 obtained by the same airflow crushing at a scale of 1μm.

[0176] It can be seen that the lithium iron phosphate material produced by the fluidized bed provided by the present application has primary particles of nanoscale, a whole round shape, a narrow particle size distribution range, high carbon layer density, high electrical conductivity, small primary particle size, and small particles significantly shorten the migration distance of lithium ions in the solid phase, accelerate the deintercalation kinetics, and thus improve the performance of the battery at high rate charge and discharge.

[0177] As can be seen from Comparative Examples 1-7 and Comparative Examples 2-3, the particle size distribution of the lithium iron phosphate material provided by the present application is narrower compared with the comparative examples.

[0178] In addition, compared with the traditional sintering kiln, the lithium iron phosphate material is produced by the fluidized bed sintering furnace in the present application, the mass transfer and heat transfer rate is fast, which can reach 3-5 times of the traditional kiln, the energy consumption is reduced by about 30-50%; the sintering time is shortened by more than 50%; the local overheating or underburning is reduced, the waste rate is reduced from 5-10% of the traditional process to 1-3%; the degree of automation is high, the manual intervention is reduced, and the labor cost is reduced by 20-30%. The production cost of the lithium iron phosphate material can be reduced by 20-50% as a whole.

[0179] Although the preferred embodiments of the present application have been disclosed as above, the present application is not intended to be limited thereto, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not deviate from the technical solutions of the present application, shall fall within the protection scope of the present application.

Claims

1. A nano-spherical lithium iron phosphate material, characterized in that: The D10 of the nano-spherical lithium iron phosphate material is 65-85 μm, preferably 70-80 μm, the D50 is 90-110 μm, preferably 95-105 μm, the D90 is 120-140 μm, preferably 125-135 μm, and the range of (D90-D10) / D50 is 0.3-0.9, preferably 0.4-0.

7.

2. The nano-spherical lithium iron phosphate material according to claim 1, characterized in that: The nano-spherical lithium iron phosphate material includes spherical secondary particles, which are composed of primary particles. The particle size of the primary particles ranges from 0.01 to 3.5 μm, preferably from 0.05 to 1 μm.

3. The nano-spherical lithium iron phosphate material according to claim 1, characterized in that: The chemical formula of the nano-spherical lithium iron phosphate material is LiFe 1-a-x-y-z Al a Ti x V y Mg z PO4 / C, where 0≤a≤0.005, 0≤x≤0.01, 0≤y≤0.005, 0≤z≤0.05, Al, Ti, V and Mg are doping elements, and C is a coating element.

4. A method for preparing the nano-spherical lithium iron phosphate material according to any one of claims 1 to 3, characterized in that: The method comprises: S1. Evenly mixing a lithium source, an iron source, a phosphorus source, an optional dopant, an optional carbon source, and water, and grinding the resulting slurry; S2, spray drying the ground slurry obtained in S1 to obtain a lithium iron phosphate precursor; S3. Under the protection of an inert atmosphere, the lithium iron phosphate precursor obtained in S2 is pre-sintered in a fluidized bed, and then sintered at a high temperature to obtain a nano-spherical lithium iron phosphate material.

5. The method for preparing nano-spherical lithium iron phosphate material according to claim 4, characterized in that: In S1, the molar ratio of the lithium source, iron source, phosphorus source and dopant is 1:1-0.93:1:0-0.07; And / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium nitrate; And / or, the iron source is selected from one or more of ferric phosphate, ferrous oxalate dihydrate, ferrous sulfate heptahydrate, and ferrous ammonium sulfate hexahydrate; And / or, the phosphorus source is selected from one or more of diammonium hydrogen phosphate and phosphoric acid; And / or, the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, aluminum phosphate, and basic aluminum distearate; And / or, the titanium source is selected from one or more of titanium dioxide and titanium isopropoxide; and / or, the vanadium source is selected from ammonium metavanadate; And / or, the magnesium source is selected from one or more of magnesium acetate and magnesium acetate tetrahydrate; And / or, the carbon source is selected from one or more of glucose, sucrose, citric acid, starch, and polyethylene glycol.

6. The method for preparing nano-spherical lithium iron phosphate material according to claim 4, characterized in that: In S1, the grinding is one or more of ball milling, sand milling or ultrasonic vibration; And / or, the grinding time is 20 min to 4 h, preferably 0.5 to 1.5 h; And / or, the particle size D50 of the slurry after grinding is 0.01 to 10 μm, preferably 0.35 to 1.5 μm.

7. The method for preparing nano-spherical lithium iron phosphate material according to claim 4, characterized in that: In S2, the inlet air temperature of the spray drying is in the range of 250-350°C, preferably 270-320°C, and the outlet air temperature is in the range of 70-130°C, preferably 80-100°C.

8. The method for preparing nano-spherical lithium iron phosphate material according to claim 4, characterized in that: In S3, the pre-sintering heating rate is 5-20°C / min, the pre-sintering temperature is 350-500°C, and the holding time is 20-80min. Preferably, the heating rate is 5-10°C / min, the pre-sintering temperature is 320-420°C, and the holding time is 40-60min. And / or, the conditions for high-temperature sintering are: a heating rate of 5-20°C / min, a temperature of 600-800°C, and a holding time of 30min-90min. Preferably, the heating rate is 8-15°C / min, a temperature of 700-800°C, and a holding time of 50min-70min.

9. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the nano-spherical lithium iron phosphate material according to any one of claims 1 to 3, or comprises the nano-spherical lithium iron phosphate material obtained by the method according to any one of claims 4 to 8, and the mass of the nano-spherical lithium iron phosphate material accounts for 75-85% of the mass of the positive electrode sheet; Preferably, the positive electrode sheet further comprises polyvinylidene fluoride and superconducting carbon black, and the mass ratio of the nano-spherical lithium iron phosphate material, polyvinylidene fluoride and superconducting carbon black is 75-85:10-15:5-10.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 10.

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