Lithium iron phosphate material, preparation method and application thereof

Abstract

The application relates to a lithium iron phosphate material and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a lithium source, an iron source, a phosphorus source, a doping element and a carbon source through ball milling to obtain a mixture; (2) pre-sintering the mixture, crushing after cooling, and sieving to obtain a first intermediate; (3) high-temperature sintering the first intermediate, crushing after cooling, and sieving to obtain a second intermediate; (4) performing atomic deposition reaction on the second intermediate under the condition that the flow rate of a gas source is not less than 70 sccm to obtain the lithium iron phosphate material; the atomic deposition reaction comprises: first introducing an aluminum oxide precursor to perform reaction, and then introducing water vapor to perform reaction, and the above steps are sequentially performed for 7-15 times of cyclic reaction. The lithium iron phosphate material prepared by the application is applied to the preparation of lithium ion batteries as a battery positive electrode material, and the battery capacity and long cycle performance can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic compounds and materials technology, and relates to lithium-ion battery cathode materials, specifically to a lithium iron phosphate material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are mainly composed of positive electrode materials, negative electrode materials, separators, electrolytes, and battery casings. As a crucial component of lithium-ion batteries, the positive electrode material directly determines the battery's energy density, safety, lifespan, charging time, and temperature adaptability, making it a decisive factor in the battery's electrochemical performance. Furthermore, the cost of the positive electrode material also has a significant impact on the overall cost of lithium-ion batteries. Therefore, the positive electrode material plays a guiding role in the development of the lithium-ion battery industry. Lithium iron phosphate (LFP) is currently the preferred material for lithium-ion power batteries in China, possessing the following advantages: First, power batteries have high safety requirements, and LFP offers excellent safety performance; second, in terms of lifespan, LFP batteries can achieve a lifespan comparable to the vehicle's operational lifespan; third, in terms of charging speed, it balances speed, efficiency, and safety. Therefore, LFP power batteries remain the most suitable for the safety requirements of domestically produced new energy buses.

[0003] However, current lithium iron phosphate materials cannot simultaneously meet the battery requirements for high capacity and long cycle performance. Summary of the Invention

[0004] Based on this, the purpose of this invention is to improve the capacity and long-cycle performance of lithium iron phosphate cathode materials.

[0005] To achieve the above-mentioned objectives, the present invention includes the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing lithium iron phosphate material, comprising the following steps:

[0007] (1) The lithium source, iron source, phosphorus source, doping element and carbon source are ball-milled and mixed to obtain a mixture;

[0008] (2) The mixture is pre-sintered, cooled, crushed, and sieved to obtain the first intermediate;

[0009] (3) The first intermediate is sintered at high temperature, cooled and then crushed and sieved to obtain the second intermediate;

[0010] (4) The second intermediate is subjected to atomic deposition reaction under the condition that the gas source flow rate is not less than 70 sccm to obtain the lithium iron phosphate material;

[0011] The atomic deposition reaction includes: first, introducing an alumina precursor for reaction, then introducing water vapor for reaction, and repeating this cycle 7 to 15 times.

[0012] Secondly, the present invention provides lithium iron phosphate materials prepared by the above-described preparation method.

[0013] Thirdly, this invention provides the application of the lithium iron phosphate material as a battery cathode material in the preparation of lithium-ion batteries.

[0014] The present invention has the following beneficial effects:

[0015] This invention introduces doping elements during the preparation of lithium iron phosphate to obtain high-capacity cathode materials. Then, after fluidizing the powder in a fluidized container, atomic deposition technology is used to form a dense and uniform coating layer of a certain thickness on its surface. This reduces side reactions during cycling, maintains material stability, and reduces fragmentation in the later stages of cycling. The synergistic effect of these two methods yields a lithium iron phosphate cathode material with high discharge capacity and excellent cycle performance. Applying the lithium iron phosphate material prepared by this invention as a cathode material in lithium-ion batteries can effectively improve battery capacity and long-cycle performance.

[0016] This invention introduces atomic deposition technology, which uses fluidization to allow powder particles to exist in a powder holder in a continuous motion. Then, atomic deposition technology is used to achieve surface coating of the powder in a dispersed state. This method can improve coating uniformity and overall coating rate. Moreover, this method can complete the coating without high-temperature sintering. It forms a uniform and dense coating layer on the particle surface, maintains the stability of the material, reduces side reactions of particles during cycling, reduces fragmentation in the later stage of cycling, and improves the cycle capacity retention rate of the cathode material. Attached Figure Description

[0017] Figure 1 The image shows a SEM image of the lithium iron phosphate material prepared in Example 1.

[0018] Figure 2 SEM image of the uncoated lithium iron phosphate material prepared in Comparative Example 1 Detailed Implementation

[0019] To facilitate understanding of the present invention, a more complete description will be provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0020] Unless otherwise specified, experimental methods in the following examples are generally performed under standard conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the examples are commercially available products.

[0021] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this invention includes any and all combinations of one or more of the associated listed items.

[0022] Furthermore, as used herein, the term "or" is an inclusive "or" sign and is equivalent to the term "and / or" unless the context clearly specifies otherwise. The term "based on" is not exclusive and allows for basing on other factors not described unless the context clearly specifies otherwise. Additionally, throughout the specification, the meanings of "an," "a," and "the" include plural indicators. The meaning of "in" includes both "in" and "on."

[0023] Some of the embodiments involve a method for preparing a lithium iron phosphate material, including the following steps:

[0024] (1) The lithium source, iron source, phosphorus source, doping element and carbon source are ball-milled and mixed to obtain a mixture;

[0025] (2) The mixture is pre-sintered, cooled, crushed, and sieved to obtain the first intermediate;

[0026] (3) The first intermediate is sintered at high temperature, cooled and then crushed and sieved to obtain the second intermediate;

[0027] (4) The second intermediate is subjected to atomic deposition reaction under the condition that the gas source flow rate is not less than 70 sccm to obtain the lithium iron phosphate material;

[0028] The atomic deposition reaction includes: first, introducing an alumina precursor for reaction, then introducing water vapor for reaction, and repeating this cycle 7 to 15 times.

[0029] This invention introduces doping elements during the preparation of lithium iron phosphate to prepare high-capacity cathode materials. Then, after the powder is fluidized in a fluidized container, atomic deposition technology is used to form a dense and uniform coating layer of a certain thickness on its surface, which reduces side reactions of particles during cycling, maintains the stability of the material, and reduces fragmentation in the later stages of cycling. The two work together to prepare a high-capacity lithium iron phosphate cathode material with excellent long-cycle performance.

[0030] This invention introduces atomic deposition technology, which uses fluidization to allow powder particles to exist in a powder holder in a continuous motion. Then, atomic deposition technology is used to achieve surface coating of the powder in a dispersed state. This method can improve coating uniformity and overall coating rate. Moreover, this method can complete the coating without high-temperature sintering. It forms a uniform and dense coating layer on the particle surface, maintains the stability of the material, reduces side reactions of particles during cycling, reduces fragmentation in the later stage of cycling, and improves the cycle capacity retention rate of the cathode material.

[0031] In some embodiments, step (4) specifically includes: loading the second intermediate into a fluidized container, evacuating it, and then introducing an inert gas (e.g., nitrogen and / or argon). The gas source flow rate is set to not less than 70 sccm. After the gas pressure in the fluidized container stabilizes, the temperature is increased. After the temperature stabilizes, an alumina precursor is introduced first for reaction, and then water vapor is introduced for reaction. This process is repeated 7 to 15 times. After cooling, the lithium iron phosphate material is obtained.

[0032] In some preferred embodiments, the air source flow rate is 70 sccm to 200 sccm, more preferably 90 sccm to 150 sccm. The air source flow rate affects the fluidization state of the material within the fluidizing container. When the airflow velocity is too low, the particles cannot exhibit a fluidized state inside the container, leading to uneven powder coating and consequently, an unsatisfactory material circulation capacity retention rate. When the air source flow rate is in the range of 90 sccm to 150 sccm, a more ideal circulation capacity retention rate can be obtained.

[0033] In some preferred embodiments, the number of cycles is 8 to 12. The number of cycles determines the thickness of the alumina coating. Alumina has poor conductivity; when the coating thickness is insufficient, its protective effect on the particles is poor, resulting in an unsatisfactory cycle capacity retention rate. When the coating thickness is too high, it reduces the conductivity of the material and restricts lithium-ion diffusion, thereby inhibiting the material's capacity utilization and reducing energy efficiency. When the number of cycles is 8 to 12, the most ideal capacity and cycle capacity retention rate can be obtained.

[0034] In some preferred embodiments, the alumina precursor is selected from at least one of trimethylaluminum, triethylaluminum, and triisobutylaluminum, more preferably trimethylaluminum.

[0035] In some preferred embodiments, the pipe temperature in step (4) is 70°C to 150°C, and the reaction temperature in the fluidized container is 150°C to 260°C.

[0036] A suitable pipeline temperature can ensure that no alumina precursor remains in the pipeline, preventing pipeline blockage; a suitable reaction temperature in the fluidized container can allow the alumina precursor to react better on the particle surface to form a coating layer.

[0037] In some preferred embodiments, the pipe temperature in step (4) is 80°C to 120°C, and the reaction temperature in the fluidized container is 175°C to 250°C.

[0038] In some preferred embodiments, the pipe temperature in step (4) is 80°C to 90°C, and the reaction temperature in the fluidized container is 240°C to 250°C.

[0039] In some preferred embodiments, the lithium source is selected from at least one of lithium carbonate, lithium acetate, lithium oxalate, lithium hydroxide, and lithium oxide; for example, it may be a combination of lithium hydroxide and lithium oxide, and the molar ratio of lithium hydroxide to lithium oxide is preferably 1:0.8 to 1.2.

[0040] In some preferred embodiments, the iron source is selected from at least one of ferric oxalate, ferric nitrate, ferric hydroxide, ferric acetate, ferrous oxalate, and ferrous nitrate.

[0041] In some preferred embodiments, the phosphorus source is selected from at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid.

[0042] In some preferred embodiments, the carbon source is selected from at least one of glucose, sucrose, citric acid, maltose, and polyethylene glycol. For example, it can be a mixture of maltose and polyethylene glycol as carbon sources, wherein the mass ratio of maltose to polyethylene glycol is preferably 1:2 to 4, more preferably 1:3.

[0043] The amount of carbon source affects the performance of the resulting material particles. Insufficient carbon source content fails to form an effective and uniform carbon coating network and cannot suppress particle growth, leading to larger particles. This results in increased lithium-ion insertion / extraction pathways, increased polarization, reduced discharge capacity, and poorer rate performance. Excessive carbon source content increases the specific surface area of ​​the particles, creating more contact sites between the material and the particles, further increasing side reactions, reducing active lithium, and accelerating cycle decay. Considering these factors, the preferred carbon source content is 5wt%-15wt% of the weight of the lithium iron phosphate material, more preferably 6wt%-8wt%, and even more preferably 7%.

[0044] In some preferred embodiments, the doping element is selected from at least one of V, Ti, Nb, Mg, Mn, and Zr. For example, it can be a combination of V and Zr, with the molar ratio of V to Zr preferably being 1 to 2:1. The combination of two doping elements is more conducive to improving the capacity utilization of lithium iron phosphate cathode materials.

[0045] In some preferred embodiments, the molar ratio of the dopant element to iron is 0.4:99.6 to 1:99. The added dopant element replaces iron sites, and the added substance can be an oxide or acid salt of the element, such as magnesium nitrate, vanadium pentoxide, titanium dioxide, zirconium carbonate, etc. When replacing the raw material element with a dopant element, the amount of the raw material element should be reduced accordingly. The amount of dopant element has a significant impact on the specific capacity of the cathode material. If the amount is too small, the capacity of the material will not reach the ideal effect; if the amount is too large, it will lead to an increase in crystal nucleation defects, poor structural stability, and the risk of cation dissolution. When the molar ratio of the dopant element to iron is 0.4:99.6 to 1:99, the resulting cathode material has a high capacity.

[0046] In some preferred embodiments, the Li:Fe:P molar ratio of the lithium source, iron source, and phosphorus source is 1.01–1.05:0.96–1.01:1, preferably 1.03:0.99:1. This preferred ratio ensures a stable crystal nucleus structure in the resulting material, with sufficient active lithium without excessive formation of impurity phases.

[0047] In some preferred embodiments, the ball milling in step (1) can be dry or wet ball milling. Wet ball milling requires the use of ethanol as a medium, followed by sampling, drying, and then sintering.

[0048] In some preferred embodiments, the dry ball milling process conditions include: a zirconium bead to total raw material mass ratio of 0.8 to 1.2:1, a ball milling time of 20 to 40 minutes, and a rotation speed of 100 to 300 rpm.

[0049] In some preferred embodiments, the heating rate of the pre-sintering in step (2) is 5℃ / min to 15℃ / min, the pre-sintering temperature is 350℃ to 480℃, and the holding time is 3 hours to 8 hours.

[0050] In some preferred embodiments, the sieving in step (3) is performed using a 200-mesh sieve.

[0051] In some preferred embodiments, the heating rate of high-temperature sintering in step (3) is 5℃ / min to 15℃ / min, the high-temperature sintering temperature is 700℃ to 780℃, and the holding time is 4 hours to 10 hours.

[0052] In some preferred embodiments, the sieving in step (3) is performed using a 200-mesh sieve.

[0053] The pre-sintering described in step (2) and the high-temperature sintering described in step (3) are carried out in a sintering furnace under an inert gas atmosphere. The sintering furnace can be a tube furnace, roller kiln, or other equipment.

[0054] In some embodiments, the present invention also provides the application of lithium iron phosphate material prepared by the preparation method of the present invention as a battery cathode material in the preparation of lithium-ion batteries.

[0055] Using the lithium iron phosphate material prepared according to the present invention as a positive electrode material in the preparation of lithium-ion batteries can effectively improve battery capacity and long cycle performance.

[0056] The present invention will be further described in detail below with reference to specific embodiments.

[0057] Example 1

[0058] The lithium iron phosphate material provided in this embodiment is prepared by the following steps:

[0059] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 0.5% of iron) were dry ball-milled to obtain a mixture.

[0060] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0061] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0062] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 90 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0063] SEM image of the final product, lithium iron phosphate material, is shown below. Figure 1 As shown, it is spherical or near-spherical. The SEM image of the second intermediate (lithium iron phosphate material not coated by atomic deposition technology) is shown below. Figure 2 As shown, the particles without atomic deposition coating are smoother. This indicates that a coating layer was successfully applied to the surface of the material particles, which roughens the surface.

[0064] Example 2

[0065] (1) Lithium hydroxide with lithium oxide, iron oxalate, and phosphoric acid (Li:Fe:P molar ratio of 1.03:0.99:1) in a molar ratio of 1:1, and maltose with polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), vanadium pentoxide (providing V doping to replace iron sites, with a molar amount accounting for 0.3% of iron) and zirconium carbonate (providing Zr doping to replace iron sites, with a molar amount accounting for 0.2% of iron) in a mass ratio of 1:3 were dry ball-milled (zirconium beads: total raw material mass ratio of 1:1, ball milling for 30 min, rotation speed of 200 rpm) to obtain a mixture.

[0066] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0067] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0068] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 150 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased. The pipeline temperature was set to 80 °C, and the container reaction temperature was set to 250 °C. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0069] Example 3

[0070] (1) Lithium acetate, iron hydroxide with a molar ratio of 2:5, iron acetate, hydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose with a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and titanium dioxide (providing Ti doping to replace iron sites, with a molar amount accounting for 0.5% of the iron element) were dry ball-milled to obtain a mixture.

[0071] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0072] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0073] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 100 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased. The pipeline temperature was set to 120℃ and the container reaction temperature was set to 175℃. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0074] Example 4

[0075] (1) Lithium acetate, iron hydroxide with a molar ratio of 2:5, iron acetate, ammonium hydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose with a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and vanadium pentoxide (providing doping element V to replace iron sites, its molar amount accounting for 0.5% of iron element) were dry ball-milled to obtain a mixture.

[0076] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0077] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0078] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 100 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased. The pipeline temperature was set to 120℃ and the container reaction temperature was set to 175℃. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0079] Comparative Example 1 (different from Example 1 in that it is not coated)

[0080] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 0.5% of iron) were dry ball-milled to obtain a mixture.

[0081] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0082] (3) The above intermediates were transferred to a sintering furnace in an inert atmosphere for high-temperature sintering (heating rate of 10℃ / min, sintering temperature of 760℃, and holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then, it was sieved through a 200-mesh screen to obtain uncoated lithium iron phosphate material.

[0083] Comparative Example 2 (different from Example 1 in that it did not form a fluidized state)

[0084] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 0.5% of iron) were dry ball-milled to obtain a mixture.

[0085] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0086] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0087] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 50 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated the completion of the reaction). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0088] Comparative Example 3 (different from Example 1 in that it has more coating layers)

[0089] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 0.5% of iron) were dry ball-milled to obtain a mixture.

[0090] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0091] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0092] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 90 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated the completion of the reaction). The reaction was repeated 25 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 25 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0093] Comparative Example 4 (different from Example 1 in that it has no doped elements)

[0094] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3 and polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material) were mixed by dry ball milling (zirconium beads:total raw material mass ratio of 1:1, ball milling for 30 min at 200 rpm) to obtain a mixture.

[0095] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0096] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0097] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 90 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0098] Comparative Example 5 (different from Example 1 in that the doping amount is reduced)

[0099] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 0.1% of iron) were dry ball-milled to obtain a mixture.

[0100] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0101] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0102] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 90 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0103] Comparative Example 6 (different from Example 1 in that the doping amount is excessive)

[0104] (1) Lithium carbonate, iron nitrate, ammonium dihydrogen phosphate (Li:Fe:P molar ratio of 1.03:0.99:1), maltose in a mass ratio of 1:3, polyethylene glycol (as a carbon source, added at 10% of the theoretical weight of lithium iron phosphate material), and magnesium nitrate (providing Mg doping to replace iron sites, its molar amount accounting for 1.1% of iron) were dry ball-milled to obtain a mixture.

[0105] (2) The above mixture was transferred to a sintering furnace using a sintering boat and pre-sintered in a nitrogen inert atmosphere (heating rate of 10℃ / min, pre-sintering temperature of 450℃, holding time of 4 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the first intermediate.

[0106] (3) The above intermediate was transferred to a sintering furnace using a sintering boat and sintered at high temperature in an inert atmosphere (heating rate of 10℃ / min, sintering temperature of 760℃, holding time of 5 hours). After naturally cooling to room temperature, the material was taken out and crushed using a wall-breaking machine. Then it was sieved through a 200-mesh screen to obtain the second intermediate.

[0107] (4) The second intermediate was loaded into a 500 mL fluidized bed container, and an atomic deposition reaction was performed by assembling a pipeline. After the fluidized bed container was evacuated, inert argon gas was introduced at a flow rate of 90 sccm. After the pressure in the fluidized bed container stabilized (determined by the rheological curve, with fluctuations within 0.5 Pa), the temperature was increased to 120 °C in the pipeline and 215 °C in the container. After the temperature stabilized, trimethylaluminum was introduced first for reaction. After the reaction was complete, water vapor was introduced for further reaction (an atomic mass spectrometer was connected to the tail gas of the atomic deposition process; a surge in the peak value of trimethylaluminum or water content indicated that the reaction was complete). The reaction was repeated 10 times (i.e., reacting sequentially with trimethylaluminum and water vapor, repeated 10 times). After the reaction was completed, the mixture was cooled to room temperature, and the material was removed to obtain the final product, lithium iron phosphate material.

[0108] Example 5 Performance Test

[0109] 1. Specific Surface Area: The specific surface area of ​​the lithium iron phosphate materials prepared in Examples 1-4 and Comparative Examples 1-5 was tested using a specific surface area analyzer. The determination was performed using the low-temperature static volumetric method at liquid nitrogen temperature, with nitrogen as the adsorbent gas. The specific operation was as follows: 2g of sample was taken and placed in a sample tube. After the sample was loaded, the sample tube was fixed in the specific surface area analyzer, a heating mantle was put on, and the inlet valve at the instrument end was opened (helium:nitrogen = 80:20), with a pressure of 0.3 MPa. The sample was purged for 30 minutes and heated to 150°C. After purging, 2 / 3 of the liquid nitrogen was added to the liquid nitrogen cup for sample testing, and 1 / 2 of the liquid nitrogen was added to the liquid nitrogen cup for the side cooling well. The test was then started, and the data was read after the test was completed.

[0110] 2. Resistivity: The resistance of the lithium iron phosphate powder materials prepared in Examples 1-4 and Comparative Examples 1-5 was tested using a four-probe resistance tester. The test was conducted in a constant-temperature, dry room at 25°C and humidity below 50% RH. 1g of material was weighed into the four-probe resistance tester, the start button was pressed, and the data was read from the display screen.

[0111] 3. Cyclic testing: Coin cells were assembled using lithium iron phosphate materials prepared in Examples 1-4 and Comparative Examples 1-5 as positive electrode active materials and graphite as negative electrode active material. The cells were subjected to charge-discharge cycle testing using a 0.5P constant power step with a charge-discharge voltage range of 2.50V to 3.65V for a total of 200 cycles. The tests were conducted in a 25℃ constant temperature chamber. The capacity retention rate was obtained by dividing the discharge capacity of each cycle by the discharge capacity of the first cycle.

[0112] The test results are shown in Table 1. The discharge capacity of 0.5P in the table is the discharge capacity data of the first cycle of the cyclic test.

[0113] Table 1 Summary of Cyclic Test Data

[0114]

[0115] As shown in Table 1, Comparative Example 1, without atomic deposition coating, exhibited a significantly lower cycle retention rate, approximately 5% lower than Example 1. Comparative Example 3, with its excessive number of cycles resulting in an excessive coating layer, maintained a capacity retention rate roughly equivalent to Example 1 after 200 cycles, but its discharge capacity was significantly reduced, indicating limited lithium-ion diffusion. These results demonstrate that using atomic deposition technology to coat an appropriate thickness of passivation film can effectively improve cycle capacity retention. Insufficient or no coating results in suboptimal cycle performance, while excessive coating hinders lithium-ion diffusion, leading to a substantial decrease in discharge capacity. Furthermore, due to the poor conductivity of alumina, its resistivity also increases significantly.

[0116] As can be seen from the comparison between Comparative Example 2 and Example 1, when the airflow velocity is low, the particles do not exhibit a fluidized state inside the container, and the powder coating is uneven, resulting in a lower cycle capacity retention rate than that of lithium iron phosphate cathode material coated in a fluidized state.

[0117] Comparative Example 4, which did not use any doping elements, showed a significant difference in discharge specific capacity compared to Examples 1-4, being approximately 9 mAh / g lower. This indicates that doping elements also contribute to increased specific capacity, and high-capacity lithium iron phosphate cathode materials cannot be obtained without introducing doping elements. From Examples 1-4, it was observed that different doping elements resulted in different initial-cycle specific capacities. Introducing two doping elements while maintaining a constant total amount of doping elements resulted in higher initial-cycle specific capacities for the lithium iron phosphate cathode material, with minimal performance differences when doping with a single element. Comparing Comparative Examples 5 and 6 with Example 1, it can be seen that reducing the doping amount decreased the specific capacity of the cathode material, with coating only maintaining cycle performance. Excessive doping leads to increased crystal nucleus defects, decreased structural stability, and accelerated cycle decay.

[0118] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing lithium iron phosphate material, characterized in that, Includes the following steps: (1) The lithium source, iron source, phosphorus source, doping element and carbon source are ball-milled and mixed to obtain a mixture; (2) The mixture is pre-sintered, cooled, crushed, and sieved to obtain the first intermediate; (3) The first intermediate is sintered at high temperature, cooled and crushed, and then sieved to obtain the second intermediate; (4) The second intermediate is subjected to atomic deposition reaction under the condition of gas source flow rate of 90sccm~150sccm to obtain the lithium iron phosphate material; The atomic deposition reaction includes: first, introducing an alumina precursor for reaction, then introducing water vapor for reaction, and repeating this cycle 8 to 12 times. The doping elements are V and Zr in a molar ratio of 1 to 2:1; The molar ratio of the dopant element to iron is 0.4:99.6 to 1:

99.

2. The method for preparing lithium iron phosphate material according to claim 1, characterized in that, Step (4) includes: loading the second intermediate into a fluidized container, evacuating it, and then introducing an inert gas. The gas flow rate is set to 90 sccm to 150 sccm. After the gas pressure in the fluidized container stabilizes, the temperature is increased. After the temperature stabilizes, an alumina precursor is introduced first for reaction, followed by water vapor for reaction. This process is repeated 8 to 12 times. After cooling, the lithium iron phosphate material is obtained.

3. The method for preparing lithium iron phosphate material according to claim 2, characterized in that, The gas source flow rate is 90 sccm, 100 sccm, or 150 sccm; and / or, The number of cycles is 10; and / or, The alumina precursor is selected from at least one of trimethylaluminum, triethylaluminum, and triisobutylaluminum; and / or, In step (4), the pipe temperature is 70℃~150℃, and the reaction temperature inside the fluidized container is 150℃~260℃; and / or, The inert gas is nitrogen and / or argon.

4. The method for preparing lithium iron phosphate material according to any one of claims 1-3, characterized in that, The lithium source is selected from at least one of lithium carbonate, lithium acetate, lithium oxalate, lithium hydroxide, and lithium oxide; and / or, The iron source is selected from at least one of ferric oxalate, ferric nitrate, ferric hydroxide, ferric acetate, ferrous oxalate, and ferrous nitrate; and / or, The phosphorus source is selected from at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid; and / or, The carbon source is selected from at least one of glucose, sucrose, citric acid, maltose, and polyethylene glycol.

5. The method for preparing lithium iron phosphate material according to claim 4, characterized in that, The lithium source is a lithium hydroxide and lithium oxide in a molar ratio of 1:0.8~1.2; and / or, The carbon source is maltose and polyethylene glycol in a mass ratio of 1:2~4.

6. The method for preparing lithium iron phosphate material according to any one of claims 1-3, characterized in that, The Li:Fe:P molar ratio of the lithium source, iron source, and phosphorus source is 1.01~1.05:0.96~1.01:1; and / or, The carbon source is 5wt% to 15wt% of the weight of the lithium iron phosphate material.

7. The method for preparing lithium iron phosphate material according to any one of claims 1-3, characterized in that, In step (2), the pre-sintering heating rate is 5℃ / min~15℃ / min, the pre-sintering temperature is 350℃~480℃, and the holding time is 3 hours~8 hours; and / or, The pre-sintering in step (2) is carried out in an inert gas atmosphere; and / or, The sieving in step (2) is performed using a 200-mesh sieve.

8. The method for preparing lithium iron phosphate material according to any one of claims 1-3, characterized in that, In step (3), the heating rate for high-temperature sintering is 5℃ / min~15℃ / min, the high-temperature sintering temperature is 700℃~780℃, and the holding time is 4 hours~10 hours; and / or, The pre-sintering in step (3) is carried out in an inert gas atmosphere; and / or, The sieving in step (3) is performed using a 200-mesh sieve.

9. A lithium iron phosphate material prepared by the preparation method according to any one of claims 1-8.

10. The application of the lithium iron phosphate material according to claim 9 as a battery cathode material in the preparation of lithium-ion batteries.

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