A phosphorus-doped manganese iron lithium phosphate material and a preparation method thereof

Abstract

This invention belongs to the technical field of cathode materials for secondary batteries. More specifically, it relates to a doped lithium manganese iron phosphate material and its preparation method. The product of this invention includes a lithium manganese iron phosphate core and a lithium iron phosphate shell coating the surface of the lithium manganese iron phosphate core; wherein, the lithium manganese iron phosphate core includes pores and titanium dioxide deposited in the pores, the content of the titanium dioxide is 1.5-2.5% of the mass of the lithium manganese iron phosphate core, and the porosity of the lithium manganese iron phosphate is 20-25%; wherein, porosity = (1 - apparent density / true density) × 100%; the true density is 3.6 g·cm³. ‑3 The apparent density was measured using a tap density meter. The D50 of the lithium manganese iron phosphate core is 5-6 μm; and the Span value of the particle size distribution of the lithium manganese iron phosphate core is 0.8-1.0; the Span value = (D90-D10) / D50.

Description

A doped lithium manganese iron phosphate material and its preparation method Technical Field

[0001] This invention belongs to the technical field of cathode materials for secondary batteries. More specifically, it relates to a doped lithium manganese iron phosphate material and its preparation method. Background Technology

[0002] Using lithium manganese iron phosphate as the main material, and through doping or compounding with lithium iron phosphate, is a strategy to optimize the performance of lithium manganese iron phosphate materials. It aims to improve cycle stability, inhibit manganese dissolution, improve rate performance, and at the same time maintain its advantages of high voltage and high energy density.

[0003] Specifically, the stable structure of lithium iron phosphate can reduce the dissolution of manganese ions in lithium manganese iron phosphate, especially at high temperatures or during long cycles. Furthermore, ferrous ion doping can mitigate lattice distortion caused by manganese ions, improving the material's structural stability. For example, it is possible to use lithium manganese iron phosphate as the core and coat it with a lithium iron phosphate nanolayer, for example, 5-10 nm thick, to suppress electrolyte erosion of manganese (Mn).

[0004] However, during long-term use, the inventors discovered that there are differences in the lattice parameters between lithium manganese iron phosphate and lithium iron phosphate. The lattice volume of lithium manganese iron phosphate is slightly larger. During long-term charging and discharging, repeated insertion and extraction of lithium ions may lead to the accumulation of interfacial stress, which may eventually cause the coating layer to peel off or crack. In addition, manganese ions are prone to Jahn-Teller distortion during cycling, while lithium iron phosphate does not exhibit this phenomenon. The structural responses of the two at the interface are inconsistent, which may accelerate phase separation and ultimately affect the service life of the product. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: when lithium iron phosphate is coated on the surface of existing lithium manganese iron phosphate, the lithium iron phosphate coating layer and the lithium manganese iron phosphate core will separate during use due to differences in their properties and parameters, which will lead to a decrease in the cycle life of the product. The present invention provides a doped lithium manganese iron phosphate material and its preparation method.

[0006] The purpose of this invention is to provide a doped lithium manganese iron phosphate material.

[0007] Another objective of this invention is to provide a method for preparing doped lithium manganese iron phosphate materials.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A doped lithium manganese iron phosphate material includes a lithium manganese iron phosphate core and a lithium iron phosphate shell covering the surface of the lithium manganese iron phosphate core.

[0010] The lithium manganese iron phosphate core includes pores and titanium dioxide deposited in the pores. The content of titanium dioxide is 1.5-2.5% of the mass of the lithium manganese iron phosphate core, and the porosity of the lithium manganese iron phosphate is 20-25%.

[0011] Wherein, porosity = (1 - apparent density / true density) × 100%;

[0012] The true density is 3.6 g·cm³. -3 ;

[0013] The apparent density was obtained by measuring the tap density using a tap density meter.

[0014] By employing an appropriate porosity, it is ensured that titanium dioxide can fully penetrate and diffuse into the interior of lithium manganese iron phosphate during the deposition process. However, if the porosity is too high, it will lead to a decrease in the physical structural stability of the lithium manganese iron phosphate core itself. Based on the corresponding porosity, the proportion of titanium dioxide deposition relative to the core mass is adjusted to ensure that enough titanium dioxide is deposited in the pores, but without excessive deposition on the surface of the material, which would significantly reduce the proportion of active material and affect the energy density of the product.

[0015] Furthermore, the D50 of the lithium manganese iron phosphate core is 5-6 μm; and the Span value of the particle size distribution of the lithium manganese iron phosphate core is 0.8-1.0.

[0016] The Span value is calculated as (D90 - D10) / D50.

[0017] Controlling the particle size within a suitable range ensures uniformity during the coating or deposition of lithium iron phosphate. However, the inventors discovered that particle size distribution is also a contributing factor. A lower span value corresponds to a narrower particle size distribution, resulting in a more uniform deposition process under the same reaction environment. Conversely, an excessively wide particle size distribution leads to uneven coating thickness, causing some particles to crack due to insufficient coating and others to suffer from excessively thick coating, affecting lithium-ion transport or capacity utilization. On the other hand, an excessively low span value results in poor particle gradation when the material is used as a positive electrode active material, leading to high porosity and high particle impedance, thus hindering energy density utilization.

[0018] Furthermore, the D50 of the doped lithium iron phosphate material is 1.03-1.05 times that of the lithium manganese iron phosphate core; and the particle size distribution span value of the doped lithium iron phosphate material is smaller than that of the lithium manganese iron phosphate core.

[0019] By selecting raw materials and controlling the preparation process, the particle size of lithium iron phosphate particles can be increased after coating. This is also a way to control the thickness of the surface coating layer. Furthermore, by controlling the coating process and even screening and classifying the coated particles, the particle size distribution of the finished product after coating can be made more uniform than before coating, resulting in relatively uniform stress between different particles.

[0020] Furthermore, the sphericity of the lithium manganese iron phosphate core is 90-92%, and the sphericity of the doped lithium iron phosphate material is greater than that of the lithium iron phosphate core.

[0021] Furthermore, the lithium iron phosphate shell includes amorphous carbon, and the amorphous carbon is doped with nitrogen (N) element.

[0022] The following preparation method introduces amorphous carbon and nitrogen doping by doping with dopamine, thereby improving the interfacial adsorption strength between the lithium iron phosphate coating and the core, and further reducing the surface ion diffusion resistance.

[0023] Furthermore, the titanium dioxide is anatase phase titanium dioxide.

[0024] A method for preparing doped lithium manganese iron phosphate material, the specific preparation steps include:

[0025] Dilute nitric acid solution was used as the corrosive medium to corrode lithium manganese iron phosphate material to form porous lithium manganese iron phosphate material with a porosity of 20-25%.

[0026] In the pores of the porous lithium manganese iron phosphate material, a titanium source precursor is deposited and then calcined to form titanium dioxide in the pores to obtain the lithium manganese iron phosphate core.

[0027] Specifically, tetrabutyl titanate can be used as the titanium source. By adjusting the water content of lithium manganese iron phosphate material, a small amount of water can be left inside. For details, please refer to the relevant preparation method in the embodiment. During the heating process, tetrabutyl titanate diffuses and permeates into the pores, while water begins to diffuse outward. When the two meet, the tetrabutyl titanate hydrolyzes in the pores to produce a precursor. The precursor is further calcined to form titanium dioxide, thereby achieving deposition inside the pores.

[0028] By coating the surface of the lithium manganese iron phosphate core with lithium iron phosphate, a doped lithium manganese iron phosphate material is obtained.

[0029] Furthermore, the specific preparation steps also include:

[0030] In the pores of the porous lithium manganese iron phosphate material, a titanium source precursor is deposited and then calcined at a temperature of 400-450℃ to form titanium dioxide in the pores, so as to obtain the lithium manganese iron phosphate core.

[0031] The lithium manganese iron phosphate core was mixed with water, then polyvinylpyrrolidone was added, and the mixture was ultrasonically dispersed to obtain a lithium manganese iron phosphate core dispersion.

[0032] Lithium hydroxide, ferrous sulfate and ammonium dihydrogen phosphate are added to the lithium manganese iron phosphate core dispersion. After mixing evenly, the mixture is heated and stirred for 2-4 hours at a temperature of 60-80℃ and a pH of 8-9. After centrifugation and drying, the mixture is sintered for 2-3 hours at a temperature of 400-450℃ in a mixed atmosphere of argon and hydrogen. After cooling, the material is discharged to obtain the doped lithium manganese iron phosphate material.

[0033] The mixed atmosphere of argon and hydrogen is formed by mixing argon and hydrogen in a volume ratio of 95:5.

[0034] Furthermore, the specific preparation steps also include:

[0035] Lithium manganese iron phosphate cores and water are mixed at a mass ratio of 1:10 to obtain a mixture. Then, 4-6% by mass of polyvinylpyrrolidone and 6-8% by mass of dopamine are added to the mixture and ultrasonically dispersed to obtain a lithium manganese iron phosphate core dispersion.

[0036] Beneficial technical effects:

[0037] (1) The technical solution of the present invention uses lithium manganese iron phosphate as the core and covers its surface with a lithium iron phosphate coating layer. On this basis, titanium dioxide is deposited in the pores of the lithium manganese iron phosphate core to solve the phase separation problem between the core and the surface coating layer. Specifically, the titanium dioxide deposited in the pores can form a strong interaction with the manganese ions in the lithium manganese iron phosphate material, thereby anchoring the manganese element and reducing the dissolution of manganese. In this way, the structure of the lithium manganese iron phosphate material can be stabilized. In addition, the lithium ion diffusion coefficient of titanium dioxide is higher than that of pure lithium manganese iron phosphate, and the titanium dioxide in the pores can provide additional lithium ion transport paths. More importantly, the hydroxyl groups on the surface of titanium dioxide can form a strong adsorption force with the precursor of lithium iron phosphate, thereby forming a modulus gradient of lithium manganese iron phosphate-titanium dioxide-lithium iron phosphate, reducing the risk of interface cracking during cycling.

[0038] (2) By further controlling the temperature during the calcination process, the crystal form of the generated titanium dioxide is controlled to be anatase phase, which has low strain characteristics. Based on this, it is deposited in the pores and can effectively absorb the lattice stress changes of lithium manganese iron phosphate during the charging and discharging process. Detailed Implementation

[0039] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0040] Unless otherwise specified, all reagents and materials used in the following examples are commercially available. Example 1

[0041] Lithium manganese iron phosphate particles and 0.2 mol / L nitric acid solution were mixed at a mass ratio of 1:10. The mixture was then subjected to ultrasonic corrosion at 55℃ and 80 kHz for 65 min. After filtration, the filter cake was washed three times with deionized water. The washed filter cake was then dried in an oven at 55℃ until the moisture content was 6% to form a porous lithium manganese iron phosphate material with a porosity of 20%.

[0042] When adjusting the above process parameters, they should be adjusted reasonably according to the porosity. The porosity is characterized by the following formula: porosity = (1 - apparent density / true density) × 100%.

[0043] The true density is 3.6 g·cm³. -3 ;

[0044] The apparent density was obtained by tap density meter;

[0045] Tetrabutyl titanate and anhydrous ethanol were mixed uniformly at a mass ratio of 1:10 to obtain a tetrabutyl titanate solution. Porous lithium manganese iron phosphate material and the tetrabutyl titanate solution were mixed at a mass ratio of 1:12 and subjected to ultrasonic reaction at 55°C and 70kHz for 80 minutes to deposit a titanium precursor in the pores of the porous lithium manganese iron phosphate material. After the reaction was completed, the mixture was filtered, the filter cake was collected, and washed three times with anhydrous ethanol. The washed filter cake was dried to constant weight at 90°C, then heated to 400°C and calcined for 100 minutes under a nitrogen atmosphere. After cooling to room temperature, the material was discharged and sieved to obtain lithium manganese iron phosphate core particles with a D50 of 5 μm, a particle size distribution Span value of 0.8, and a sphericity of 90%. The Span value is calculated as (D90 - D10) / D50.

[0046] In addition, during the above preparation process, the content of titanium dioxide was controlled to 1.5% of the mass of lithium manganese iron phosphate core particles by controlling the amount of raw materials used.

[0047] Lithium manganese iron phosphate core particles and water were mixed at a mass ratio of 1:10 to obtain a mixture. Then, 4% by mass of polyvinylpyrrolidone and 6% by mass of dopamine were added to the mixture and ultrasonically dispersed at an ultrasonic frequency of 80kHz for 20 minutes to obtain a lithium manganese iron phosphate core dispersion.

[0048] Lithium hydroxide, ferrous sulfate and ammonium dihydrogen phosphate were added to the lithium manganese iron phosphate core dispersion and mixed evenly. The mixture was heated and stirred for 2 hours at 60°C and pH 8. After centrifugation and drying, the mixture was sintered for 2 hours at 400°C in a mixed atmosphere of argon and hydrogen. After cooling, the material was discharged to obtain the doped lithium manganese iron phosphate material.

[0049] By controlling the above coating process conditions and combining them with sieving, particles with a D50 greater than that of the lithium manganese iron phosphate core are obtained. Specifically, the D50 of the doped lithium iron phosphate material is 1.03 times that of the lithium manganese iron phosphate core, and the particle size distribution Span value of the doped lithium iron phosphate material is smaller than that of the lithium manganese iron phosphate core. Through uniform coating, the sphericity of the doped lithium iron phosphate material is made greater than that of the lithium iron phosphate core.

[0050] The molar ratio of lithium hydroxide to ferrous sulfate is 1:1, and the amount of ammonium dihydrogen phosphate is 10% of the mass of lithium hydroxide. The small amount of ammonium dihydrogen phosphate used in the reaction process results in insufficient phosphorus source diffused from lithium manganese iron phosphate. The amount of lithium hydroxide used is 1.0% of the mass of the lithium manganese iron phosphate core.

[0051] The argon and hydrogen mixed atmosphere is formed by mixing argon and hydrogen in a volume ratio of 95:5. Example 2

[0052] Lithium manganese iron phosphate particles and a 0.25 mol / L nitric acid solution were mixed at a mass ratio of 1:10. The mixture was then subjected to ultrasonic corrosion at 60℃ and 90 kHz for 70 min. After filtration, the filter cake was washed three times with deionized water. The washed filter cake was then dried in an oven at 58℃ until the moisture content was 7%, thus forming a porous lithium manganese iron phosphate material with a porosity of 22%.

[0053] When adjusting the above process parameters, they should be adjusted reasonably according to the porosity. The porosity is characterized by the following formula: porosity = (1 - apparent density / true density) × 100%.

[0054] The true density is 3.6 g·cm³. -3 ;

[0055] The apparent density was obtained by tap density meter;

[0056] Tetrabutyl titanate and anhydrous ethanol were mixed uniformly at a mass ratio of 1:10 to obtain a tetrabutyl titanate solution. Porous lithium manganese iron phosphate material and the tetrabutyl titanate solution were mixed at a mass ratio of 1:12 and subjected to ultrasonic reaction at 58℃ and 72kHz for 90 min to deposit a titanium precursor in the pores of the porous lithium manganese iron phosphate material. After the reaction was completed, the mixture was filtered, the filter cake was collected, and washed three times with anhydrous ethanol. The washed filter cake was dried to constant weight at 90℃, then heated to 420℃ and calcined for 110 min under a nitrogen atmosphere. After cooling to room temperature, the material was discharged and sieved to obtain lithium manganese iron phosphate core particles with a D50 of 5 μm, a particle size distribution Span value of 0.9, and a sphericity of 91%. The Span value is calculated as (D90 - D10) / D50.

[0057] In addition, during the above preparation process, the content of titanium dioxide is controlled to be 2% of the mass of lithium manganese iron phosphate core particles by controlling the amount of raw materials used;

[0058] Lithium manganese iron phosphate core particles and water were mixed at a mass ratio of 1:10 to obtain a mixture. Then, 5% polyvinylpyrrolidone and 7% dopamine were added to the mixture and ultrasonically dispersed at an ultrasonic frequency of 80kHz for 20 minutes to obtain a lithium manganese iron phosphate core dispersion.

[0059] Lithium hydroxide, ferrous sulfate and ammonium dihydrogen phosphate were added to the lithium manganese iron phosphate core dispersion and mixed evenly. The mixture was then heated and stirred for 3 hours at 70°C and pH 8.5. After centrifugation and drying, the mixture was sintered at 420°C for 2.5 hours in a mixed atmosphere of argon and hydrogen. After cooling, the material was discharged to obtain the doped lithium manganese iron phosphate material.

[0060] By controlling the above coating process conditions and cooperating with sieving, particles with a D50 greater than that of the lithium manganese iron phosphate core are obtained. Specifically, the D50 of the doped lithium iron phosphate material is 1.04 times that of the lithium manganese iron phosphate core, and the particle size distribution Span value of the doped lithium iron phosphate material is smaller than that of the lithium manganese iron phosphate core. Through uniform coating, the sphericity of the doped lithium iron phosphate material is made greater than that of the lithium iron phosphate core.

[0061] The molar ratio of lithium hydroxide to ferrous sulfate is 1:1, and the amount of ammonium dihydrogen phosphate is 10% of the mass of lithium hydroxide. The small amount of ammonium dihydrogen phosphate used in the reaction process results in insufficient phosphorus source diffused from lithium manganese iron phosphate. The amount of lithium hydroxide used is 1.1% of the mass of the lithium manganese iron phosphate core.

[0062] The argon and hydrogen mixed atmosphere is formed by mixing argon and hydrogen in a volume ratio of 95:5. Example 3

[0063] Lithium manganese iron phosphate particles and 0.3 mol / L nitric acid solution were mixed at a mass ratio of 1:10. The mixture was then subjected to ultrasonic corrosion at 65℃ and 100 kHz for 75 min. After filtration, the filter cake was washed three times with deionized water. The washed filter cake was then dried in an oven at 60℃ until the moisture content was 8%, thus forming a porous lithium manganese iron phosphate material with a porosity of 25%.

[0064] When adjusting the above process parameters, they should be adjusted reasonably according to the porosity. The porosity is characterized by the following formula: porosity = (1 - apparent density / true density) × 100%.

[0065] The true density is 3.6 g·cm³. -3 ;

[0066] The apparent density was obtained by tap density meter;

[0067] Tetrabutyl titanate and anhydrous ethanol were mixed uniformly at a mass ratio of 1:10 to obtain a tetrabutyl titanate solution. Porous lithium manganese iron phosphate material and the tetrabutyl titanate solution were mixed at a mass ratio of 1:12 and subjected to ultrasonic reaction at 60°C and 75kHz for 100 min to deposit a titanium precursor in the pores of the porous lithium manganese iron phosphate material. After the reaction was completed, the mixture was filtered, the filter cake was collected, and washed three times with anhydrous ethanol. The washed filter cake was dried to constant weight at 90°C, then calcined at 450°C under a nitrogen atmosphere for 120 min. After cooling to room temperature, the material was discharged and sieved to obtain lithium manganese iron phosphate core particles with a D50 of 6 μm, a particle size distribution Span value of 1.0, and a sphericity of 92%. The Span value is calculated as (D90 - D10) / D50.

[0068] In addition, during the above preparation process, the content of titanium dioxide was controlled to 2.5% of the mass of lithium manganese iron phosphate core particles by controlling the amount of raw materials used.

[0069] Lithium manganese iron phosphate core particles and water were mixed at a mass ratio of 1:10 to obtain a mixture. Then, 6% by mass of polyvinylpyrrolidone and 8% by mass of dopamine were added to the mixture and ultrasonically dispersed at an ultrasonic frequency of 80kHz for 20 minutes to obtain a lithium manganese iron phosphate core dispersion.

[0070] Lithium hydroxide, ferrous sulfate and ammonium dihydrogen phosphate were added to the lithium manganese iron phosphate core dispersion and mixed evenly. The mixture was heated and stirred for 4 hours at 80°C and pH 9. After centrifugation and drying, the mixture was sintered for 3 hours at 450°C in a mixed atmosphere of argon and hydrogen. After cooling, the material was discharged to obtain the doped lithium manganese iron phosphate material.

[0071] By controlling the above coating process conditions and combining them with sieving, particles with a D50 greater than that of the lithium manganese iron phosphate core are obtained. Specifically, the D50 of the doped lithium iron phosphate material is 1.05 times that of the lithium manganese iron phosphate core, and the particle size distribution Span value of the doped lithium iron phosphate material is smaller than that of the lithium manganese iron phosphate core. Through uniform coating, the sphericity of the doped lithium iron phosphate material is made greater than that of the lithium iron phosphate core.

[0072] The molar ratio of lithium hydroxide to ferrous sulfate is 1:1, and the amount of ammonium dihydrogen phosphate is 10% of the mass of lithium hydroxide. The small amount of ammonium dihydrogen phosphate is used during the reaction process because the phosphorus source diffused from lithium manganese iron phosphate is insufficient. The amount of lithium hydroxide is 1.2% of the mass of the lithium manganese iron phosphate core.

[0073] The argon and hydrogen mixed atmosphere is formed by mixing argon and hydrogen in a volume ratio of 95:5. Example 4

[0074] The difference between this example and Example 1 is that dopamine was not added, while all other conditions remained unchanged. Example 5

[0075] The difference between this embodiment and Embodiment 1 is as follows:

[0076] Tetrabutyl titanate and anhydrous ethanol were mixed uniformly at a mass ratio of 1:10 to obtain a tetrabutyl titanate solution. Porous lithium manganese iron phosphate material and the tetrabutyl titanate solution were mixed at a mass ratio of 1:12 and subjected to ultrasonic reaction at 55°C and 70kHz for 80 minutes to deposit a titanium precursor in the pores of the porous lithium manganese iron phosphate material. After the reaction was completed, the mixture was filtered, the filter cake was collected, and washed three times with anhydrous ethanol. The washed filter cake was dried to constant weight at 90°C, then heated to 550°C and calcined for 100 minutes under a nitrogen atmosphere. After cooling to room temperature, the material was discharged and sieved to obtain lithium manganese iron phosphate core particles with a D50 of 5 μm, a particle size distribution Span value of 0.8, and a sphericity of 90%. The Span value is calculated as (D90 - D10) / D50.

[0077] All other conditions remained unchanged; due to the increase in calcination temperature, some titanium dioxide was transformed into the rutile phase.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that aluminum isopropoxide is used instead of tetrabutyl titanate, while the other conditions remain unchanged.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Example 1 is that tetrabutyl titanate was not used, and lithium iron phosphate was directly coated, while the other conditions remained unchanged.

[0082] The performance of the products obtained in the above embodiments and comparative examples was tested and evaluated. The specific test and evaluation methods and results are as follows:

[0083] Using a 13µm thick aluminum foil as the positive electrode current collector, and following a formulation of positive electrode active material: conductive agent Super P: binder PVDF = 90:5:5, a layer with a thickness of 80µm and an areal density of 18mg / cm² is formed on the surface of the positive electrode current collector. 2 Using lithium metal sheets as the negative electrode, EC / DMC at a volume ratio of 1:1, lithium hexafluorophosphate at a concentration of 1 mol / L as the electrolyte, and Celgard 2325 as the separator, a CR2032 coin cell was assembled.

[0084] The EIS test was performed using a Bio-Logic SP-300 electrochemical workstation at a temperature of 25℃, a frequency range of 0.1Hz-100Hz, an amplitude of 10mV, and a test potential of 50% SOC.

[0085] An EIS test is performed after every 50 cycles. Before the test, the system is allowed to stand for 2 hours until the OCV stabilizes.

[0086] Specifically, during the cycle, refer to the following charge and discharge strategy: the voltage range is 2.5-4.0V, the cycle rate is 1C, first charge at 1C rate to the upper limit voltage, then maintain constant voltage charging to 0.05C cutoff, rest for 5 minutes, then discharge at 1C rate to the lower limit voltage, and rest for 5 minutes.

[0087] The Rct value was obtained through EIS testing to evaluate the interfacial reaction resistance, i.e., charge transfer resistance. Detailed test results are shown in Table 1.

[0088] Table 1: Product Performance Evaluation Results

[0089]

[0090] As can be seen from the test results in Table 1, the product obtained by the present invention can maintain interface stability and has a relatively low increase in related interface impedance during the cycling process.

[0091] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A doped lithium iron phosphate material, characterized in that, The invention comprises a lithium manganese iron phosphate (LFP) core and a lithium iron phosphate shell covering the surface of the LFP core; wherein the LFP core includes pores and titanium dioxide deposited in the pores, the titanium dioxide content being 1.5-2.5% of the mass of the LFP core, and the porosity of the LFP is 20-25%; wherein the porosity is calculated as (1 - apparent density / true density) × 100%; and the true density is 3.6 g·cm³. -3 The apparent density is obtained by tap density meter; the D50 of the lithium manganese iron phosphate core is 5-6 μm; and the particle size distribution Span value of the lithium manganese iron phosphate core is 0.8-1.0; the Span value = (D90-D10) / D50.

2. The doped lithium manganese iron phosphate material according to claim 1, characterized in that, The D50 of the doped lithium manganese iron phosphate material is 1.03-1.05 times that of the lithium manganese iron phosphate core; and the particle size distribution span value of the doped lithium manganese iron phosphate material is smaller than that of the lithium manganese iron phosphate core.

3. The doped lithium manganese iron phosphate material according to claim 1, characterized in that, The sphericity of the lithium manganese iron phosphate core is 90-92%, and the sphericity of the doped lithium manganese iron phosphate material is greater than that of the lithium manganese iron phosphate core.

4. The doped lithium manganese iron phosphate material according to claim 1, characterized in that, The lithium iron phosphate shell includes amorphous carbon, and the amorphous carbon is doped with nitrogen (N) element.

5. The doped lithium manganese iron phosphate material according to claim 1, characterized in that, The titanium dioxide is anatase phase titanium dioxide.

6. A method for preparing a doped lithium manganese iron phosphate material as described in any one of claims 1-5, characterized in that, The specific preparation steps include: using dilute nitric acid solution as the corrosion medium to corrode lithium manganese iron phosphate material to form porous lithium manganese iron phosphate material with a porosity of 20-25%; depositing a titanium source precursor in the pores of the porous lithium manganese iron phosphate material, and then calcining it to form titanium dioxide in the pores to obtain a lithium manganese iron phosphate core; coating the surface of the lithium manganese iron phosphate core with lithium iron phosphate to obtain the doped lithium manganese iron phosphate material.

7. The method for preparing a doped lithium manganese iron phosphate material according to claim 6, characterized in that, The specific preparation steps further include: depositing a titanium source precursor in the pores of the porous lithium manganese iron phosphate material, and then calcining it at a temperature of 400-450℃ to form titanium dioxide in the pores to obtain a lithium manganese iron phosphate core; mixing the lithium manganese iron phosphate core with water, adding polyvinylpyrrolidone, and ultrasonically dispersing to obtain a lithium manganese iron phosphate core dispersion; adding lithium hydroxide, ferrous sulfate, and ammonium dihydrogen phosphate to the lithium manganese iron phosphate core dispersion, mixing evenly, and then heating and stirring the mixture at a temperature of 60-80℃ and a pH of 8-9 for 2-4 hours; then centrifuging and drying the mixture, and finally sintering it at a temperature of 400-450℃ for 2-3 hours in a mixed atmosphere of argon and hydrogen, cooling, and discharging to obtain the doped lithium manganese iron phosphate material; the mixed atmosphere of argon and hydrogen is formed by mixing argon and hydrogen at a volume ratio of 95:

5.

8. The method for preparing a doped lithium manganese iron phosphate material according to claim 7, characterized in that, The specific preparation steps also include: mixing lithium manganese iron phosphate cores and water at a mass ratio of 1:10 to obtain a mixture, then adding 4-6% by mass of polyvinylpyrrolidone and 6-8% by mass of dopamine to the mixture, and ultrasonically dispersing to obtain a lithium manganese iron phosphate core dispersion.

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