Method for dynamically preparing doped and coated lithium iron phosphate positive electrode material by one-step method, positive electrode material and application

Abstract

The invention provides a preparation method for dynamically preparing a doped and coated lithium iron phosphate positive electrode material by a one-step method and the positive electrode material. A lithium source, an iron source, a phosphorus source, an aluminum source, a titanium source, other optional doping agents, a coating agent and an optional dispersing agent are mixed through a one-step method, spray drying and dynamic sintering are carried out, presintering and high-temperature sintering are adopted in dynamic sintering, and carbon thermal reduction and carbon coating are synchronously completed. According to the doped and coated lithium iron phosphate positive electrode material disclosed by the invention, the lattice structure is optimized through Al / Ti co-doping, and the conductivity of the material and the lithium ion diffusion rate are remarkably improved by combining with a continuous nano carbon layer generated by splitting decomposition of a carbon source. According to the technology, the problem of non-uniform heat transfer of traditional static sintering is abandoned, and an efficient and low-cost solution is provided for industrial production of high-performance lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of cathode materials, specifically relating to a method for preparing doped and coated lithium iron phosphate cathode materials, the cathode materials themselves, and their applications. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that convert electrical energy into chemical energy through the repeated insertion and extraction of lithium ions between the positive and negative electrodes. Since their commercialization, they have become the mainstream power source for electric vehicles, consumer electronics, and energy storage systems due to their high energy density and long cycle life. Currently, commonly used lithium-ion battery cathode materials include lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese oxide. Among these, lithium iron phosphate has become the mainstream choice for power batteries due to its advantages such as good safety, long cycle life, and environmental friendliness. However, its inherent low electronic conductivity (10⁻⁶ Ω·cm) is a significant drawback. -9 ~10 -10 S cm -1 The rapid charge-discharge capability of lithium iron phosphate (LFP) is severely limited. To improve this, doping, surface coating with conductive layers, and structural nanostructuring are commonly used to enhance the electrochemical performance of LFP. However, structural nanostructuring usually requires wet processing, which is energy-intensive and requires calcination for more than 20 hours. In contrast, solid-state methods can complete doping and carbon layer coating in one step, making it a highly efficient modification method. However, traditional LFP preparation processes mostly rely on tube furnaces or rotary kilns for solid-state sintering. Material accumulation leads to slow and uneven heat transfer, requiring prolonged high-temperature treatment (typically ≥800℃, holding for more than 20 hours), resulting in high energy consumption and limited production capacity. Furthermore, traditional static calcination has almost no mass transfer, poor batch-to-batch stability between saggers, and poor material quality and uniformity. This further leads to uneven deposition of the carbon coating layer and poor dispersion of dopants, resulting in less than ideal electrochemical performance.

[0003] Therefore, it is necessary to further explore simpler and more efficient methods for preparing lithium iron phosphate materials to improve production efficiency and reduce costs, while simultaneously obtaining high-performance lithium iron phosphate materials. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a one-step dynamic preparation method for doped and coated lithium iron phosphate cathode materials. This method employs dynamic sintering, eliminating the uneven heat transfer problem inherent in traditional static sintering, and providing an efficient and low-cost solution for the industrial production of high-performance lithium iron phosphate.

[0005] Specifically, one aspect of the present invention provides a one-step dynamic preparation method for doped and coated lithium iron phosphate cathode materials, comprising the following steps:

[0006] S1. Mix lithium source, iron source, phosphorus source, aluminum source, titanium source, optional other dopants, coating agent, optional dispersant and water evenly, and grind the mixed slurry.

[0007] S2. Spray dry the slurry obtained from S1 to obtain the lithium iron phosphate precursor.

[0008] S3. Under the protection of an inert atmosphere, the lithium iron phosphate precursor obtained in S2 is pre-sintered in a dynamic bed and then sintered at high temperature to obtain the doped and coated lithium iron phosphate cathode material.

[0009] In one or more embodiments, in S1, the molar ratio of lithium source, iron source, phosphorus source, aluminum source, titanium source, and optional other dopants is (1.000~1.110):1:1:(0.0005~0.0015):(0.0005~0.002):(0~0.001).

[0010] In one or more embodiments, in S1, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium phosphate.

[0011] In one or more embodiments, in S1, the iron source is selected from one or more of ferrous oxalate, ferrous sulfate, and ferric phosphate.

[0012] In one or more embodiments, in S1, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0013] In one or more embodiments, in S1, the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, and aluminum phosphate.

[0014] In one or more embodiments, in S1, the titanium source is selected from one or more of titanium dioxide and titanium isopropoxide.

[0015] In one or more embodiments, in S1, the solid content of the slurry is between 40% and 60%.

[0016] In one or more embodiments, in S1, optional other dopants include one or more of magnesium sources and vanadium sources, wherein the magnesium source is selected from one or more of magnesium oxide, magnesium carbonate, magnesium nitrate, magnesium sulfate, magnesium oxalate, and magnesium acetate, and the vanadium source is selected from one or more of vanadium pentoxide, ammonium metavanadate, vanadium oxysulfate, vanadium trioxide, and ammonium vanadate.

[0017] In one or more embodiments, in S1, the coating agent is a carbon source, which is selected from one or more of glucose, sucrose, and citric acid, and the amount of carbon source is 5 to 10% of the iron source by mass.

[0018] In one or more embodiments, in S1, the dispersant is selected from one or more of PEG200, PEG300, and PEG400, and the amount used is 5% of the carbon source by mass.

[0019] In one or more embodiments, in S1, grinding is one or more of ball milling, sand milling, or ultrasonic vibration.

[0020] In one or more embodiments, in S1, the grinding time is 40 to 80 minutes, preferably 60 minutes.

[0021] In one or more embodiments, in S1, the particle size D of the slurry after grinding is... 50 The micrometer size is 0.3–0.5 μm, preferably 0.35–0.41 μm.

[0022] In one or more embodiments, in S2, the inlet air temperature of the spray dryer is in the range of 80 to 130°C, preferably 80 to 110°C, and the outlet air temperature is in the range of 250 to 320°C, preferably 270 to 300°C.

[0023] In one or more embodiments, in S2, the particle size D of the lithium iron phosphate precursor obtained by spray drying is... 50 The value is 75–120 μm, preferably 85–110 μm.

[0024] In one or more embodiments, in S3, the pre-sintering heating rate is 5-10℃ / min, the pre-sintering temperature is 400-420℃, and the holding time is 1-2h. Preferably, the heating rate is 5℃ / min, the pre-sintering temperature is 400℃, and the holding time is 1h.

[0025] In one or more embodiments, in S3, the conditions for high-temperature sintering are: a heating rate of 5-10°C / min, a temperature of 750-830°C, and a holding time of 1-2 hours. Preferably, the heating rate is 5°C / min, the temperature is 780-810°C, and the holding time is 1 hour.

[0026] In one or more embodiments, in S3, the gas velocity during pre-sintering is 0.05 to 0.3 m / s, preferably 0.05 to 0.25 m / s, and the gas velocity during high-temperature sintering is 0.02 to 0.2 m / s, preferably 0.08 to 0.2 m / s.

[0027] In one or more embodiments, in S3, the particle size D of the doped lithium iron phosphate cathode material is... 50 The value is 75–120 μm, preferably 85–110 μm.

[0028] The present invention also provides a cathode material comprising a doped and coated lithium iron phosphate cathode material obtained by the preparation method described herein.

[0029] In one or more embodiments, the positive electrode material has the chemical formula LiFe. 1-x-y-z Al x Ti y M z PO4 / C, where 0.0005≤x≤0.0015, 0.0005≤y≤0.002, 0≤z≤0.001, Al and Ti are doping elements, M is an optional other doping element selected from one or more of Mg and V, and C is a coating element.

[0030] In one or more embodiments, the carbon layer thickness of the cathode material is 7–10 nm.

[0031] In one or more embodiments, the particle size D of the cathode material 50 It ranges from 85 to 110 μm.

[0032] The present invention also provides a cathode sheet containing the doped and coated lithium iron phosphate cathode material described herein.

[0033] The present invention also provides a lithium-ion battery comprising the positive electrode sheet described herein. Attached Figure Description

[0034] Figure 1 The image shows the XRD pattern of the doped lithium iron phosphate cathode material of Example 1.

[0035] Figure 2 (a) is a SEM image of the doped lithium iron phosphate cathode material of Example 1 with a scale of 100 μm, and (b) is a SEM image of the lithium iron phosphate material of Comparative Example 2 with a scale of 100 μm.

[0036] Figure 3 (a) is a SEM image of the doped lithium iron phosphate cathode material of Example 1 with a scale of 1 μm, and (b) is a SEM image of the lithium iron phosphate material of Comparative Example 2 with a scale of 1 μm.

[0037] Figure 4 These are the first-week charge-discharge curves of the lithium-ion button batteries in Examples 1-6 and Comparative Examples 1-5 of the present invention.

[0038] Figure 5 The cycling performance of the lithium-ion button batteries in Examples 1-6 and Comparative Examples 1-5 of this invention is shown. Detailed Implementation

[0039] To enable those skilled in the art to understand the features and effects of this invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the conventional meaning understood by those skilled in the art regarding this invention, and in case of conflict, the definitions in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0041] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0042] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0043] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0044] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0045] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0046] Preparation method of doped and coated lithium iron phosphate cathode material

[0047] The doped and coated lithium iron phosphate cathode material of the present invention is formed by mixing a lithium source, an iron source, a phosphorus source, an aluminum source, a titanium source, optional other dopants, a coating agent, optional dispersant and water, spray drying and sintering.

[0048] The lithium source can be one or more selected from lithium carbonate, lithium hydroxide, and lithium phosphate.

[0049] The iron source can be one or more of ferrous oxalate, ferrous sulfate, and ferric phosphate.

[0050] The phosphorus source can be one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid.

[0051] The aluminum source can be one or more of aluminum oxide, aluminum hydroxide, and aluminum phosphate.

[0052] The titanium source can be one or more of titanium dioxide and titanium isopropoxide.

[0053] The dispersant can be one or more of PEG200, PEG300, and PEG400.

[0054] Other optional dopants may be selected from one or more of magnesium sources and vanadium sources, wherein the magnesium source is selected from one or more of magnesium oxide, magnesium carbonate, magnesium nitrate, magnesium sulfate, magnesium oxalate, and magnesium acetate, and the vanadium source is selected from one or more of vanadium pentoxide, ammonium metavanadate, vanadium oxysulfate, vanadium trioxide, and ammonium vanadate.

[0055] The coating agent is a carbon source, selected from one or more organic carbons such as glucose, sucrose, and citric acid.

[0056] The preparation method of the doped and coated lithium iron phosphate cathode material of the present invention includes the following steps:

[0057] S1. Mix lithium source, iron source, phosphorus source, aluminum source, titanium source, optional other dopants, coating agent, optional dispersant and water evenly, and grind the mixed slurry.

[0058] S2. Spray dry the ground slurry obtained in S1 to obtain the lithium iron phosphate material precursor.

[0059] S3. Under the protection of an inert atmosphere, the lithium iron phosphate material precursor obtained in S2 is pre-sintered in a dynamic bed and then sintered at high temperature to obtain doped and coated lithium iron phosphate cathode material.

[0060] In step S1, all raw materials are mixed in a one-step wet process to obtain a slurry. In conventional processes, a lithium iron phosphate precursor is prepared first, and then mixed with the dopant. Grinding can be one or more of ball milling, sand milling, or ultrasonic vibration; for example, sand milling can be used for 1 hour. The particle size D of the slurry after grinding is... 50 The micrometer size is 0.3–0.5 μm, for example, it can be 0.3 μm, 0.4 μm, 0.45 μm, or 0.5 μm, and is preferably 0.35–0.41 μm.

[0061] In step S2, a centrifugal sprayer can be used for spray drying, with an inlet air temperature range of 80–130°C, preferably 80–110°C, and an outlet air temperature range of 250–320°C, preferably 270–300°C. The solid content of the slurry used for spray drying is between 40% and 60%. The particle size D of the lithium iron phosphate material precursor obtained by spray drying is... 50 The size is 75–120 μm, for example, it can be 75 μm, 85 μm, 100 μm, or 110 μm, preferably 85–110 μm.

[0062] In step S3, the inert atmosphere comes from nitrogen, argon, or a mixture of both.

[0063] In step S3, the sintering equipment used is a dynamic bed sintering furnace. A dynamic bed sintering furnace generally consists of a bed, a gas distribution device (such as a perforated plate or wind cap), a heating system, a gas-solid separation device (such as a cyclone separator or filter), and a feeding / discharging system. High-temperature gas enters the bed uniformly through the gas distribution device, fluidizing the solid particles and causing them to sinter. The separation device recovers the sintered particles. The dynamic bed sintering furnace significantly improves heat and mass transfer efficiency, enabling the material to complete the sintering reaction rapidly at high temperatures, avoiding the problems of uneven temperature, agglomeration, and long sintering times found in traditional sintering equipment such as tunnel kilns and rotary kilns. The dynamic bed sintering furnace used in this invention has an inner diameter of 50 mm and a material height-to-diameter ratio of 1:1 to 5:1, for example, 1:1, 2:1, 3:1, or 5:1, with a preferred height-to-diameter ratio of 2:1 to 4:1. The lithium iron phosphate material precursor undergoes two sintering steps in the dynamic bed sintering furnace: pre-sintering and high-temperature sintering. Pre-sintering decomposes the organic carbon source in the lithium iron phosphate precursor, uniformly coating the primary particle surface as a carbon coating layer. High-temperature sintering promotes the graphitization of the carbon layer, improves electronic conductivity, and ultimately forms a doped and coated lithium iron phosphate cathode material. The pre-sintering heating rate is 5–10 °C / min, for example, 5 °C / min, 8 °C / min, or 10 °C / min; the pre-sintering temperature is 400–420 °C, for example, 400 °C, 410 °C, or 420 °C; and the holding time is 1–2 h, for example, 1 h, 1.2 h, 1.5 h, 1.6 h, or 2 h. Preferably, the heating rate is 5 °C / min, the pre-sintering temperature is 400 °C, and the holding time is 1 h. The heating rate for high-temperature sintering is 5–10 °C / min, for example, 5 °C / min, 8 °C / min, or 10 °C / min; the sintering temperature is 750–830 °C, for example, 750 °C, 780 °C, 800 °C, or 830 °C; the holding time is 1–2 h, for example, 1 h, 1.2 h, 1.5 h, 1.6 h, or 2 h; preferably, the heating rate is 5 °C / min, the temperature is 780–810 °C, and the holding time is 1 h. By precisely controlling different temperature ranges, carbothermic reduction and carbon coating are completed simultaneously, which can optimize the material crystallinity and carbon coating effect, thereby balancing energy density, rate performance, and cycle life.

[0064] In S3, the gas velocity of the dynamic bed is controlled at the critical fluidization gas velocity, which ensures that the material is fully fluidized and avoids particle agglomeration caused by local overheating. The gas velocity for pre-sintering is 0.05 to 0.3 m / s, for example, 0.05 m / s, 0.1 m / s, 0.2 m / s, or 0.3 m / s. Preferably, the gas velocity is 0.05 to 0.25 m / s. The gas velocity for high-temperature sintering is 0.02 to 0.2 m / s, for example, 0.02 m / s, 0.05 m / s, 0.1 m / s, or 0.2 m / s. Preferably, the gas velocity is 0.08 to 0.2 m / s.

[0065] Doped and coated lithium iron phosphate cathode materials

[0066] The lithium iron phosphate cathode material of the present invention is a lithium iron phosphate cathode material doped with doping elements and coated with carbon.

[0067] The chemical formula of the lithium iron phosphate cathode material of this invention is LiFe 1-x-y-z Al x Ti y M z PO4 / C, where 0.0005≤x≤0.0015, 0.0005≤y≤0.002, 0≤z≤0.001, Al and Ti are doping elements, M is an optional other doping element selected from one or more of Mg and V, and C is a coating element.

[0068] In this invention, the required doping elements include Al and Ti. The ionic valences of Al and Ti are higher than those of Fe. Therefore, Al is used to dope LiFePO4. 3+ Ti 4+ High-valence doping elements will replace Fe in LiFePO4. 2+ At the site of doping, this high-valence substitution introduces positively charged defects into the crystal lattice, thereby forming Li vacancies or electronic defects to maintain electroneutrality through charge compensation, resulting in a significant increase in the material's electronic conductivity and rate performance. Simultaneously, the doping element Al... 3+ ionic radius Ti 4+ ionic radius All are smaller than Fe 2+ ionic radius Doping reduces the lattice volume, thereby broadening the Li... + The one-dimensional diffusion channel in the

[010] direction, and reduce Li + The diffusion barrier ultimately improves the rate performance of the material. The specific chemical formula of lithium iron phosphate cathode materials can be, for example, LiFe... 0.998 Al 0.001 Ti 0.001 PO4 / C, LiFe 0.9965 Al 0.0015 Ti 0.002 PO4 / C, LiFe 0.9975 Al 0.0015 Ti 0.001 PO4 / C, LiFe 0.9955 Al 0.0015 Ti 0.002 V 0.0005 Mg 0.0005 PO4 / C.

[0069] In this invention, the coating element is carbon. A carbon layer with a thickness of 7-10 nm is coated on the lithium iron phosphate. This carbon layer can form a conductive network, improve electronic conductivity, reduce electrode polarization, and improve rate performance. At the same time, the carbon layer can limit the grain growth of the lithium iron phosphate precursor during the sintering process and avoid uneven particle size distribution.

[0070] In this invention, Al and Ti co-doping optimizes the lattice structure of lithium iron phosphate, and combined with a continuous nano-carbon layer coating lithium iron phosphate, the conductivity and lithium-ion diffusion rate of the material can be significantly improved.

[0071] In this invention, the lithium iron phosphate cathode material is composed of secondary particles formed by the agglomeration of nanoscale primary particles, with a spherical or near-spherical shape. Spherical particles have advantages such as high volumetric capacity and high packing density. In some embodiments, the particle size of the primary particles is between 400 and 700 nm, for example, 400 nm, 500 nm, 600 nm, or 700 nm, preferably between 600 and 700 nm. When the particles reach the nanoscale, the transport efficiency of lithium ions and electrons can be improved, increasing the utilization rate of the material. In some embodiments, the particle size D of the secondary particles... 50 The size can be between 75 and 120 μm, for example, 80 μm, 95 μm, 100 μm, 105 μm, or 110 μm, with 85 to 110 μm being preferred.

[0072] Positive electrode and lithium-ion battery

[0073] The present invention also provides a cathode sheet containing the doped and coated lithium iron phosphate cathode material as described in any embodiment herein, and a lithium-ion battery containing the cathode sheet.

[0074] The positive electrode sheet includes 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 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode material layer is obtained by coating a positive electrode slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent onto the positive electrode current collector, followed by rolling and baking. The positive electrode current collector can be copper foil, aluminum foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The solvent of the positive electrode slurry can be N-methylpyrrolidone (NMP). In the positive electrode sheet of the present invention, the positive electrode active material includes the doped and coated lithium iron phosphate material of the present invention. The conductive agent of the positive electrode can be one or more selected from superconducting carbon black (SP), carbon fiber (CF), acetylene black, conductive graphite, graphene, carbon nanotubes, and carbon microspheres. The binder of the positive electrode can be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl alcohol, polyolefins, styrene-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 each component in the positive electrode material layer can be conventional; for example, the mass fraction of the positive electrode active material can be 75-85%, such as 75%, 77%, 80%, or 82%; the mass fraction of the conductive agent can be 5-10%, such as 5%, 7%, or 9%; and the mass fraction of the binder can be 10-15%, such as 10%, 11%, 12%, 13%, 14%, or 15%.

[0075] The preparation method of the positive electrode sheet is as follows: place the positive electrode material, binder and conductive agent in a weighing bottle in proportion, then add an appropriate amount of organic solvent, such as N-methylpyrrolidone (NMP), and form a uniform slurry 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.

[0076] A lithium-ion battery cell can be produced by stacking positive electrode plates, negative electrode plates, and a separator. The cell is then encapsulated in a casing, dried, injected with electrolyte, sealed, left to stand, formed, and sorted to obtain a lithium-ion battery. The form of the lithium-ion battery of this invention is not particularly limited and can be a cylindrical lithium-ion battery, a pouch lithium-ion battery, an aluminum-cased lithium-ion battery, or a button lithium-ion battery, etc.

[0077] The present invention has the following beneficial effects:

[0078] 1. A one-step method for preparing cathode material precursors: This invention prepares a high-solids-content slurry (40-60%) from lithium source, iron source, phosphorus source, Al / Ti source and carbon source, which is then thoroughly milled and spray-granulated to form uniform microspheres. The steps are simple.

[0079] 2. This invention employs a dynamic sintering reaction. Under a nitrogen atmosphere, the material is fully fluidized by controlling the gas velocity (critical fluidizing gas velocity) of the fluidized bed, resulting in more uniform sintering and avoiding particle agglomeration caused by local overheating. Simultaneously, carbothermic reduction and carbon coating are completed.

[0080] 3. This invention employs efficient doping and carbon layer design, Al / Ti co-doping optimizes the crystal structure, and combined with the continuous nano-carbon layer generated by carbon source pyrolysis, significantly improving the material's conductivity and lithium-ion diffusion rate.

[0081] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0082] In the following examples and comparative examples, the relevant parameters were obtained through the following test methods:

[0083] (1) XRD: The sample was characterized using an X-ray diffractometer (XRD, D8 ADVANCE, Bruker), which employed Cu-Kα radiation. To identify crystal structure and phase composition, XRD data were collected within an angular range of 5–90° at a scan rate of 2° / min. Numerical processing was performed by using Jade9 to query PDF cards to identify crystal forms.

[0084] (2) SEM morphology test: obtained by scanning electron microscope (FE-SEM, JSM-7900F, JOEL).

[0085] (3) Particle size distribution: D was obtained using a Mastersizer 3000 laser particle size analyzer. 50 Numerical value.

[0086] (4) Rate performance test: The assembled lithium-ion coin cells were left to stand in a constant temperature environment (25±2℃) for 12-24 hours. The rate performance was tested using the LAND-CT2001A testing system with a range of 0.1C→0.2C→0.5C→1C→2C→5C→0.1C (1C=170mAh·g). -1 Electrochemical tests were performed sequentially at each rate, with five cycles at each rate, to avoid the accumulation of battery polarization affecting high-rate data.

[0087] (5) Cyclic performance test: At room temperature, charge and discharge performance was tested at a 1C rate on the LAND-CT2001A test system. The electrode was allowed to stand for 24 hours before charging to ensure that the positive electrode was fully wetted by the electrolyte. The electrode was allowed to stand for 5 minutes between charging and discharging to ensure voltage stability and reduce the influence of concentration polarization.

[0088] Example 1

[0089] The doped and coated lithium iron phosphate cathode material in this embodiment is prepared through the following steps:

[0090] (1) Preparation of precursor particles

[0091] First, weigh 589.3692g of purified water. While stirring, add 442.6682g of ferric phosphate, 108.8212g of lithium carbonate, 35.4135g of glucose, 1.7707g of PEG200, 0.2252g of Al2O3, and 0.4705g of TiO2. After stirring for 1 hour, transfer the slurry to a sand mill (MEM-015) and mill at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0092] The obtained uniform slurry was spray-dried in a spray dryer (QFN-L-10) with an inlet air temperature of 80℃ and an outlet air temperature of 270℃ for approximately 15 minutes to obtain dried precursor particles with a particle size D. 50 It is 95.4 μm.

[0093] (2) Dynamic sintering

[0094] 228.6914 g of the precursor was placed in a dynamic bed (height-to-diameter ratio of 3), and nitrogen gas was introduced and purged for 15 min. The temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h at a gas velocity of 0.1 m / s, and then increased to 800 °C at a rate of 5 °C / min, held for 1 h at a gas velocity of 0.08 m / s to obtain Al / Ti-doped LFP / C.

[0095] The chemical formula of the doped and coated lithium iron phosphate material in this embodiment is LiFe. 0.9965 Al 0.0015 Ti 0.002 PO4 / C.

[0096] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 7.34 nm, and the particle size D is... 50 It is 93.8 μm.

[0097] The positive electrode sheet in this embodiment is prepared by the following method:

[0098] The doped lithium iron phosphate material, polyvinylidene fluoride (PVDF), and superconducting carbon black prepared above were mixed at a mass ratio of 79:11:10. N-methylpyrrolidone (NMP) was added dropwise to prepare a uniform slurry, which was stirred at 1500 rpm for 12 hours. The mixture was then coated, dried, and pressed into a tablet press to obtain a positive electrode sheet, which was then cut into circular sheets with a diameter of 12 mm.

[0099] The lithium-ion battery in this embodiment is prepared by the following method:

[0100] The positive electrode sheet prepared above was assembled with a lithium metal negative electrode to form a lithium-ion battery. The electrolyte was 1.0M LiPF6inEC:DMC:DEC=1:1:1vol%. The separator (Celgard 2325) was cut into a circular sheet with a diameter of 19mm. The negative electrode shell, spring sheet, gasket, lithium sheet, separator, positive electrode sheet and positive electrode shell were assembled in sequence to obtain a lithium-ion coin cell battery.

[0101] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0102] Example 2

[0103] The lithium iron phosphate material in this embodiment is prepared through the following steps:

[0104] (1) Preparation of precursor particles

[0105] First, weigh 589.6828g of purified water. While stirring, add 442.6682g of ferric phosphate, 108.8212g of lithium carbonate, 35.4135g of glucose, 1.7707g of PEG200, 0.5388g of AlPO4, and 0.4705g of TiO2. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0106] The obtained uniform slurry was spray-dried in a spray dryer with an inlet air temperature of 80°C and an outlet air temperature of 270°C for approximately 15 minutes to obtain dried precursor particles with a particle size D. 50 It is 93.8 μm.

[0107] (2) Dynamic sintering

[0108] 228.6914 g of the precursor was placed in a dynamic bed (height-to-diameter ratio of 3), and nitrogen gas was introduced and purged for 15 min. The temperature was increased to 400 °C at a rate of 5 °C / min, held for 1 h at a gas velocity of 0.1 m / s, and then increased to 800 °C at a rate of 5 °C / min, held for 1 h at a gas velocity of 0.08 m / s to obtain Al / Ti-doped LFP / C.

[0109] The chemical formula of the doped and coated lithium iron phosphate material in this embodiment is LiFe. 0.9965 Al 0.0015 Ti 0.002 PO4 / C.

[0110] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 8.31 nm, and the particle size D is... 50 It is 85.1 μm.

[0111] The steps for preparing the positive electrode and lithium-ion button cell in this embodiment are the same as in Example 1.

[0112] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0113] Example 3

[0114] The lithium iron phosphate material in this embodiment is prepared through the following steps:

[0115] (1) Preparation of precursor particles

[0116] First, weigh 589.7812g of purified water. While stirring, add 443.3345g of ferric phosphate, 108.8212g of lithium carbonate, 35.4668g of glucose, 1.7733g of PEG200, 0.1502g of Al2O3, and 0.2352g of TiO2. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0117] The obtained uniform slurry was spray-dried in a spray dryer with an inlet air temperature of 80°C and an outlet air temperature of 270°C for approximately 15 minutes to obtain dried precursor particles with a particle size D. 50 It is 96.2 μm.

[0118] (2) Dynamic sintering

[0119] 227.9514 g of the precursor was placed in a dynamic bed (height-to-diameter ratio of 3), and nitrogen gas was introduced and purged for 15 min. The temperature was raised to 400 °C at a rate of 5 °C / min and held for 1 h at a gas velocity of 0.1 m / s. Subsequently, the temperature was raised to 800 °C at a rate of 5 °C / min and held for 1 h at a gas velocity of 0.08 m / s to obtain Al / Ti-doped LFP / C.

[0120] The chemical formula of the doped and coated lithium iron phosphate material in this embodiment is LiFe. 0.998 Al 0.001 Ti 0.001 PO4 / C.

[0121] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 8.52 nm, and the particle size D is... 50 It is 90.0 μm.

[0122] The steps for preparing the positive electrode and lithium-ion button cell in this embodiment are the same as in Example 1.

[0123] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0124] Example 4

[0125] The lithium iron phosphate material in this embodiment is prepared through the following steps:

[0126] (1) Preparation of precursor particles

[0127] First, weigh 589.2047g of purified water. While stirring, add 442.4461g of ferric phosphate, 108.8212g of lithium carbonate, 35.3957g of glucose, 1.7698g of PEG200, 0.1502g of Al2O3, 0.2352g of TiO2, 0.1187g of MgO, and 0.2679g of V2O5. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0128] The obtained uniform slurry was spray-dried in a spray dryer with an inlet air temperature of 80°C and an outlet air temperature of 270°C for approximately 15 minutes to obtain dried precursor particles with a particle size D. 50 It is 93.3 μm.

[0129] (2) Dynamic sintering

[0130] 229.5486 g of the precursor was placed in a dynamic bed (height-to-diameter ratio of 3), and nitrogen gas was introduced and purged for 15 min. The temperature was raised to 400 °C at a rate of 5 °C / min and held for 1 h at a gas velocity of 0.1 m / s. Then the temperature was raised to 800 °C at a rate of 5 °C / min and held for 1 h at a gas velocity of 0.08 m / s to obtain Al / Ti / Mg / V doped LFP / C.

[0131] The chemical formula of the doped and coated lithium iron phosphate material in this embodiment is LiFe. 0.996 Al 0.001 Ti 0.001 Mg 0.001 V 0.001 PO4 / C.

[0132] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 7.69 nm, and the particle size D is... 50It is 92.5μm.

[0133] The steps for preparing the positive electrode and lithium-ion button cell in this embodiment are the same as in Example 1.

[0134] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0135] Example 5

[0136] The raw materials are the same as in Example 1, the only difference being:

[0137] Sintering conditions: Hold at 400℃ for 2 hours, then raise the temperature to 800℃ and hold for 2 hours.

[0138] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 8.34 nm, and the particle size D is... 50 It is 92.6 μm.

[0139] The steps for preparing the positive electrode and lithium-ion button cell in this embodiment are the same as in Example 1.

[0140] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0141] Example 6

[0142] The raw materials are the same as in Example 1, the only difference being:

[0143] Sintering conditions: Hold at 420℃ for 1 hour, then raise the temperature to 750℃ and hold for 1 hour.

[0144] In this embodiment, the carbon layer thickness of the doped and coated lithium iron phosphate material is 9.31 nm, and the particle size D is... 50 It is 87.1 μm.

[0145] The steps for preparing the positive electrode and lithium-ion button cell in this embodiment are the same as in Example 1.

[0146] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0147] Comparative Example 1

[0148] This comparative example provides an undoped lithium iron phosphate material.

[0149] The lithium iron phosphate material in this comparative example was prepared through the following steps:

[0150] (1) Preparation of precursor particles

[0151] First, weigh 599.7467g of purified water. While stirring, add 441.1352g of ferric phosphate, 108.8212g of lithium carbonate, 40.4624g of glucose, and 4.7608g of PEG200. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0152] The spray drying process is the same as in Example 1, to obtain dried precursor particles.

[0153] (2) Dynamic sintering

[0154] The dynamic sintering process is the same as in Example 1, resulting in undoped LFP / C.

[0155] The chemical formula of the lithium iron phosphate material in this comparative example is LiFePO4 / C.

[0156] The carbon layer thickness of the lithium iron phosphate material in this comparative example is 7.44 nm, and the particle size D is... 50 It is 83.3 μm.

[0157] The positive electrode and lithium-ion coin cell prepared in this comparative example follow the same steps as in Example 1.

[0158] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0159] Comparative Example 2

[0160] This comparative example provides a lithium iron phosphate material doped only with Al.

[0161] The lithium iron phosphate material in this comparative example was prepared through the following steps:

[0162] (1) Preparation of precursor particles

[0163] First, weigh 589.8618g of purified water. While stirring, add 443.5566g of ferric phosphate, 108.8212g of lithium carbonate, 35.4845g of glucose, 1.7742g of PEG200, and 0.2252g of Al(OH)3. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0164] The spray drying process is the same as in Example 1, to obtain dried precursor particles.

[0165] (2) Dynamic sintering

[0166] The dynamic sintering process is the same as in Example 1, resulting in Al-doped and coated LFP / C.

[0167] The chemical formula of the lithium iron phosphate material in this comparative example is LiFe. 0.9985 Al 0.0015 PO4 / C.

[0168] The carbon layer thickness of the lithium iron phosphate material in this comparative example is 9.51 nm, and the particle size D is... 50 It is 84.2 μm.

[0169] The positive electrode and lithium-ion coin cell prepared in this comparative example follow the same steps as in Example 1.

[0170] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0171] Comparative Example 3

[0172] This comparative example provides a lithium iron phosphate material doped only with Ti.

[0173] The lithium iron phosphate material in this comparative example was prepared through the following steps:

[0174] (1) Preparation of precursor particles

[0175] First, weigh 589.8663g of purified water. While stirring, add 443.3345g of ferric phosphate, 108.8212g of lithium carbonate, 35.4668g of glucose, 1.7733g of PEG200, and 0.4705g of TiO2. After stirring for 1 hour, transfer the slurry to a sand mill and mill it at 2300 rpm for 40 minutes to obtain a slurry with a solid content of 50%.

[0176] The spray drying process is the same as in Example 1, to obtain dried precursor particles.

[0177] (2) Dynamic sintering

[0178] The dynamic sintering process is the same as in Example 1, resulting in Ti-doped and coated LFP / C.

[0179] The chemical formula of the lithium iron phosphate material in this comparative example is LiFe. 0.998 Ti 0.002 PO4 / C.

[0180] The carbon layer thickness of the lithium iron phosphate material in this comparative example is 7.33 nm, and the particle size D is... 50 It is 82.3 μm.

[0181] The positive electrode and lithium-ion coin cell prepared in this comparative example follow the same steps as in Example 1.

[0182] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0183] Comparative Example 4

[0184] This comparative example provides a lithium iron phosphate material that does not employ dynamic bed sintering.

[0185] The preparation process of the lithium iron phosphate material in this comparative example is the same as that in Example 1, except that:

[0186] The granular material was placed in a crucible and then sintered in a tube furnace under an inert atmosphere. The temperature was increased to 400°C at a rate of 5°C / min and held for 1 hour. Subsequently, the temperature was increased to 800°C under an inert atmosphere at a rate of 5°C / min and held for 1 hour. Lithium iron phosphate material was obtained.

[0187] The carbon layer thickness of the lithium iron phosphate material in this comparative example is 8.53 nm, and the particle size D is... 50 It is 74.3 μm.

[0188] The positive electrode and lithium-ion coin cell prepared in this comparative example follow the same steps as in Example 1.

[0189] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0190] Comparative Example 5

[0191] This comparative example provides a lithium iron phosphate material sintered in a dynamic bed sintering furnace but without pre-sintering.

[0192] The preparation process of the lithium iron phosphate material in this comparative example is the same as that in Example 1, except that:

[0193] The granular material was loaded into a dynamic bed and sintered under an inert atmosphere. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 hour to obtain lithium iron phosphate material.

[0194] The particle size D of the lithium iron phosphate material in this comparative example 50 The thickness was 77.8 μm, and no uniform carbon layer was formed.

[0195] The positive electrode and lithium-ion coin cell prepared in this comparative example follow the same steps as in Example 1.

[0196] The test results of lithium-ion button batteries are shown in Table 1 and... Figure 4-5 As shown.

[0197] Table 1 shows the rate performance of lithium-ion button batteries in Examples 1-6 and Comparative Examples 1-5 of the present invention.

[0198] Table 1 Comparison of rate performance results between Examples 1-6 and Comparative Examples 1-5 (Unit: mAh / g)

[0199] 0.1C 0.2C 0.5C 1C 2C 5C 0.1C Example 1 157.56 157.74 157.32 153.01 146.16 128.53 157.84 Example 2 158.47 158.03 157.35 153.34 145.38 124.99 158.73 Example 3 158.60 157.66 154.41 150.73 142.71 124.61 158.68 Example 4 154.76 155.81 154.51 150.90 142.95 127.19 154.35 Example 5 157.84 157.68 153.04 149.62 138.41 120.15 158.63 Example 6 156.34 154.79 152.36 148.22 138.06 120.15 158.34 Comparative Example 1 148.37 150.04 146.93 142.12 133.08 114.33 150.09 Comparative Example 2 151.56 153.72 149.91 144.73 136.44 120.22 150.10 Comparative Example 3 149.12 150.10 147.42 142.33 134.48 118.47 146.80 Comparative Example 4 150.39 152.26 148.26 143.29 133.45 113.14 150.91 Comparative Example 5 151.69 153.81 150.00 144.82 136.52 120.29 152.19

[0200] Figure 1 The image shows the XRD pattern of the lithium iron phosphate material prepared in Example 1. As can be seen from the image, the XRD diffraction peaks of Example 1 match those of the standard card PDF#01-083-2092, and the diffraction peaks are sharp and have high peak intensities, indicating that the present invention has successfully synthesized a lithium iron phosphate material with an olive-shaped structure, which belongs to the orthorhombic crystal system and has a space group of Pnma.

[0201] Figure 2 This is a SEM image of the lithium iron phosphate material from Example 1, with a scale of 100 μm. Figure 3 The image shown is a SEM image of the lithium iron phosphate material from Example 1, with a scale of 1 μm. It can be seen that the lithium iron phosphate material produced by the dynamic bed provided by this invention has an overall spherical shape, a narrow particle size distribution, high carbon layer density, high electrical conductivity, small primary particle size, and fast transport.

[0202] Analysis Table 1 and Figure 4-5 The data shows that, compared with the comparative examples, Examples 1 to 6 of the present invention exhibit higher charge / discharge specific capacity and rate performance.

[0203] like Figure 4-5 As shown, the initial capacity at 0.1C in the examples ranged from 153 to 156 mAh / g, and the 1C cycling performance was also above 150 mAh / g, while the comparative examples were all lower than this value. The capacities of Examples 1-6 at each rate were also significantly higher than the comparative examples. Comparative Example 5 was a sample that had not undergone pre-sintering. Because the carbon source was not fully decomposed into carbon, the carbon layer coating effect of this sample was poor, failing to effectively facilitate electron transport and resulting in poor conductivity. Therefore, it exhibited a low initial capacity of 141.65 mAh / g and showed a severe capacity drop during cycling tests. In contrast, the initial electrochemical performance of the single-doped samples in Comparative Examples 2 and 3 was slightly higher than that of Comparative Examples 1 and 4, but due to the lack of synergistic effect, their capacities were still lower than those of the examples. Comparing Examples 1 and Comparative Example 4, it can be seen that dynamic sintering, due to its superior mass and heat transfer efficiency, resulted in electrochemical performance far superior to that of statically sintered samples.

[0204] Although the preferred embodiments of the present invention have been disclosed above, they are not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A one-step dynamic preparation method for doped and coated lithium iron phosphate cathode materials, characterized in that, The method includes: S1. Mix lithium source, iron source, phosphorus source, aluminum source, titanium source, optional other dopants, coating agent, optional dispersant and water evenly, and grind the resulting slurry. S2. Spray dry the slurry obtained from S1 to obtain the lithium iron phosphate precursor. S3. Under an inert atmosphere, the lithium iron phosphate precursor obtained in S2 is pre-sintered in a dynamic bed and then sintered at high temperature to obtain the doped and coated lithium iron phosphate cathode material.

2. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, characterized in that, In S1, the molar ratio of the lithium source, iron source, phosphorus source, aluminum source, titanium source, and optional other dopants is (1.000~1.110):1:1:(0.0005~0.0015):(0.0005~0.002):(0~0.001); And / or, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium phosphate; And / or, the iron source is selected from one or more of ferrous oxalate, ferrous sulfate, and ferric phosphate; And / or, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; And / or, the aluminum source is selected from one or more of aluminum oxide, aluminum hydroxide, and aluminum phosphate; And / or, the titanium source is selected from one or more of titanium dioxide and titanium isopropoxide; And / or, the dispersant is selected from one or more of PEG200, PEG300, and PEG400; And / or, the solid content of the slurry is between 40% and 60%.

3. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, characterized in that, In S1, the other dopant is selected from one or more of magnesium source and vanadium source; the magnesium source is selected from one or more of magnesium oxide, magnesium carbonate, magnesium nitrate, magnesium sulfate, magnesium oxalate, and magnesium acetate; the vanadium source is selected from one or more of vanadium pentoxide, ammonium metavanadate, vanadium oxysulfate, vanadium trioxide, and ammonium vanadate.

4. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the coating agent is a carbon source; the carbon source is selected from one or more of glucose, sucrose, and citric acid; the amount of the carbon source, by mass, is 5-10% of the iron source.

5. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, 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 40 to 80 minutes, preferably 60 minutes; And / or, the particle size D of the slurry after grinding 50 The micrometer size is 0.3–0.5 μm, preferably 0.35–0.41 μm.

6. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, characterized in that, In step S2, the inlet air temperature range of the spray drying is 80–130°C, preferably 80–110°C, and the outlet air temperature range is 250–320°C, preferably 270–300°C. And / or, the particle size D of the lithium iron phosphate precursor obtained by spray drying 50 The value is 75–120 μm, preferably 85–110 μm.

7. The method for one-step dynamic preparation of doped and coated lithium iron phosphate cathode material according to claim 1, characterized in that, In step S3, the heating rate of the pre-sintering is 5-10℃ / min, the gas velocity is 0.05-0.3m / s, the pre-sintering temperature is 400-420℃, and the holding time is 1-2h. Preferably, the heating rate is 5℃ / min, the gas velocity is 0.05-0.25m / s, the pre-sintering temperature is 400℃, and the holding time is 1h. And / or, the conditions for high-temperature sintering are: heating rate of 5-10℃ / min, gas velocity of 0.02-0.2m / s, high-temperature sintering temperature of 750-830℃, and holding time of 1-2h; preferably, heating rate of 5℃ / min, gas velocity of 0.08-0.2m / s, high-temperature sintering temperature of 780-810℃, and holding time of 1h. And / or, the particle size D of the doped lithium iron phosphate cathode material 50 The value is 75–120 μm, preferably 85–110 μm.

8. A positive electrode material, characterized in that, The cathode material is prepared by the one-step dynamic preparation method for doped and coated lithium iron phosphate cathode material according to any one of claims 1-7, and the chemical formula of the cathode material is LiFe. 1-x-y- z Al x Ti y M z PO4 / C, where 0.0005≤x≤0.0015, 0.0005≤y≤0.002, 0≤z≤0.001, Al and Ti are doping elements, M is an optional doping element selected from one or more of Mg and V, C is a coating element, the carbon layer thickness of the cathode material is 7-10 nm, and the particle size D 50 It ranges from 85 to 110 μm.

9. A positive electrode plate, characterized in that, The positive electrode sheet includes the positive electrode material as described in claim 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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