A preparation method and application of lithium iron manganese phosphate cathode material

Abstract

This invention discloses a method for preparing and applying lithium iron manganese phosphate (LiFeMC) cathode material. A lithium source, phosphorus source, manganese source, and iron source are dry-milled, then lithium phosphate, an organic solvent, and a carbon material precursor are added for wet-milling. The mixture is then subjected to solvent evaporation and high-temperature sintering to obtain a carbon-lithium phosphate-coated LiFeMC cathode material. The cycling performance of the uncoated and coated materials at a high rate of 3.0C differs significantly. The uncoated LiFeMC exhibits superior cycling performance. 0.5 Mn 0.5 The PO4 material retained 75.1% of its capacity after 200 cycles at 3.0C, while the coated LiFe... 0.5 Mn 0.5 The capacity retention rate of PO4@C-Li3PO4 material is as high as 82.8%. The method of this invention can not only successfully prepare lithium iron manganese phosphate cathode material through a simple one-step process, but also coat the surface of lithium iron manganese phosphate cathode material, which greatly improves the electrochemical performance of the material.

Description

Technical Field

[0001] This invention relates to the field of high-energy battery materials technology, specifically to a method for preparing and applying lithium iron manganese phosphate cathode material. Background Technology

[0002] With rapid social and economic development, people's demand for energy is increasing daily. Currently, traditional fossil fuels face the risk of resource depletion, and the combustion of fossil fuels causes serious environmental pollution. Developing new clean energy sources is crucial for achieving sustainable development for both humanity and the environment. Over the past few decades, researchers have developed various rechargeable battery technologies through innovation. In recent years, lithium-ion batteries have been widely used in portable electronic devices and aerospace due to their high energy density, low self-discharge, long cycle life, and environmental friendliness. Their applications are also gradually shifting towards large-scale energy storage and power batteries. However, with the large-scale development of new energy vehicles, higher demands are being placed on the energy density, safety, and stability of lithium-ion batteries. Cathode materials, as key basic materials for lithium-ion batteries, are a crucial factor affecting battery energy density, safety, and stability. Traditional commercial cathode materials such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and conventional ternary cathode materials are gradually becoming insufficient to meet the demands of high-energy-density and high-safety lithium-ion batteries due to their respective shortcomings. Therefore, developing new cathode materials with high energy density, high safety, and high stability is of paramount importance for promoting the development of the new energy vehicle industry.

[0003] LiFe iron manganese phosphate material x Mn 1-xLiFe1-xMnxPO4 (0 < x < 1, LFMP), as a new type of phosphate cathode material, can be regarded as lithium iron phosphate material doped with manganese element. Therefore, this type of lithium iron manganese phosphate material has a crystal structure similar to that of lithium iron phosphate material, and also has advantages such as high structural stability, excellent cycling performance, and high thermal stability. In addition, the introduction of manganese element can increase the charge-discharge plateau of the material from 3.4V to 4.1V, thus greatly improving the energy density of the material. Therefore, lithium iron manganese phosphate material is a new type of ideal cathode material with high energy density, high safety, and excellent cycling performance, and has great potential for commercial application. However, the current preparation process of LFMP material is complex, the lithium source and phosphorus source need to be supplemented separately, which is easy to introduce impurities and reduce the purity of the material. At the same time, in the LFMP material, FeO6 is connected with four surrounding FeO6 through common vertices, forming a zigzag plane layer. And there is no continuous FeO6 octahedral grid, so a continuous ion transport channel cannot be formed. Therefore, the LFMP material has poor ionic conductivity, and the rate performance and high-temperature electrochemical performance of the material are not good, which restricts the further development of LFMP material. Developing new preparation methods of LFMP, using element doping to optimize the crystal structure of LFMP material, and coating LFMP with materials having excellent conductivity can improve the purity of LFMP material, enhance the lithium ion diffusion ability and rate performance of the material to a certain extent, and thus enhance the industrial application potential of the material. Summary of the Invention

[0004] In order to overcome the existing defects and deficiencies of lithium iron manganese phosphate cathode material, the purpose of the present invention is to provide a new preparation method of lithium iron manganese phosphate cathode material and the application of lithium iron manganese phosphate cathode material. The present invention first prepares a uniformly mixed precursor mixture of lithium iron manganese phosphate cathode material by carrying out solid-phase ball milling on a lithium source, a phosphorus source, a manganese source, and an iron source. Then, lithium phosphate (Li3PO4), a carbon material precursor, and an organic solvent are heated for wet mixing, so that Li3PO4 and the carbon material precursor adhere to the surface of the LFMP material, and a C-Li3PO4-coated LFMP material is prepared after high-temperature sintering. Therefore, by the method of the present invention, a coated LFMP cathode material can be prepared by a one-step method, and the modified material has excellent electrochemical performance.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A preparation method of lithium iron manganese phosphate cathode material, comprising the following steps:

[0007] Carry out dry ball milling on a lithium source, a phosphorus source, a manganese source, and an iron source, then add lithium phosphate, an organic solvent, and a carbon material precursor for wet ball milling, and then obtain a carbon-lithium phosphate (C-Li3PO4)-coated lithium iron manganese phosphate cathode material after evaporating the solvent and high-temperature sintering.

[0008] The method described uses lithium metaphosphate as both the lithium and phosphorus source, with a Li:P stoichiometric ratio of 1:1 in the lithium metaphosphate.

[0009] The method comprises a manganese source including at least one of Mn(OH)2, MnCO3 and MnSO4, preferably Mn(OH)2; and an iron source including at least one of Fe(OH)2, FeO and FeSO4, preferably Fe(OH)2.

[0010] Furthermore, the molar ratio of LiPO3, manganese source and iron source is (1-1.5):(0.1-0.9):(0.9-0.1), wherein the sum of the molar numbers of manganese source and iron source is 1, preferably 1:0.2-0.8:0.8-0.2.

[0011] Lithium metaphosphate should not be used in excess, as excessive amounts can easily introduce impurities. Similarly, the sum of the molar amounts of manganese and iron sources should be controlled at 1.0 to reduce the introduction of new impurities.

[0012] The method described above uses a dry ball milling speed of 100-400 rad / min. -1 200-300 rad min is preferred -1 The ball milling time is 1-5 hours, preferably 2-4 hours, and the ball-to-material ratio is 5:1.

[0013] Dry ball milling can thoroughly mix lithium, phosphorus, manganese and iron sources to obtain a homogeneous mixture of lithium iron manganese phosphate cathode material precursors.

[0014] The lithium phosphate added during wet ball milling can not only compensate for the Li and P losses of LFMP materials during mixing and sintering, but also allow the residual Li3PO4 to form a coating on the material surface.

[0015] The method comprises a carbon material precursor including at least one of sucrose, glucose and polydopamine, preferably polydopamine; and an organic solvent including at least one of ethanol, petroleum ether and ethyl acetate, preferably petroleum ether.

[0016] Furthermore, the mass ratio of the LFMP precursor mixture, lithium phosphate, and carbon material precursor is 1–1.02:0.005–0.02:0.01–0.07, preferably 1:0.01:0.05.

[0017] The amount of lithium phosphate and carbon material precursors added should not be too much. Too much will not only increase the thickness of the coating layer on the material surface and improve the lithium ion diffusion path, but will also reduce the material capacity.

[0018] The addition of carbon precursors can form a carbon coating layer on the surface of LFMP materials, improving the lithium-ion diffusion coefficient on the material surface. Organic solvents, used as solvents in wet ball milling, can enhance the dispersion efficiency of lithium phosphate and carbon precursors on the surface of the mixed material.

[0019] The method described above involves wet ball milling conducted under an inert atmosphere at a milling speed of 200-500 rad / min. -1 300-400 rad min is preferred -1 The ball milling time is 1-10 hours, preferably 5-7 hours.

[0020] Furthermore, the inert atmosphere includes at least one of Ar or N2, preferably N2.

[0021] Wet ball milling can disperse and adhere lithium phosphate and carbon material precursors to the surface of a mixture of lithium iron manganese phosphate cathode material precursors.

[0022] The method involves evaporating the solvent under magnetic stirring and heating, with the magnetic stirring speed at 300-600 rpm. -1 400-500 rad min is preferred -1 The heating temperature is 50-110℃, preferably 80-100℃.

[0023] During the solvent evaporation process, the organic solvent vaporizes and forms many pores on the material surface. The presence of these pores not only facilitates more complete sintering of the material, but also increases the contact area between the material and the electrolyte, thereby improving the lithium-ion transport efficiency of the material.

[0024] The method involves high-temperature sintering carried out under an inert atmosphere at a temperature of 400-800℃, preferably 550-750℃; the heating rate is 1-10℃ / min. -1 Preferred temperature: 3-8℃ min -1 The sintering time is 5-20 hours, preferably 10-14 hours.

[0025] Furthermore, the high-temperature sintering inert atmosphere includes at least one of Ar or N2, preferably Ar.

[0026] The method described uses lithium iron manganese phosphate material, specifically LiFe. x Mn 1-x PO4, 0 < x < 1; further preferred to include LiFe 0.5 Mn 0.5 PO4, LiFe 0.6 Mn 0.4 PO4 and LiFe 0.2 Mn 0.8 At least one of PO4.

[0027] The present invention also provides lithium iron manganese phosphate cathode material prepared by the above method.

[0028] The aforementioned carbon-lithium phosphate hybrid-coated lithium iron manganese phosphate cathode material has a carbon-lithium phosphate hybrid coating layer thickness of 2-8 nm and a material porosity of 50-800 cm³. 3 .

[0029] The present invention also provides the application of the above-mentioned lithium iron manganese phosphate cathode material in the preparation of lithium-ion batteries.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] In this invention, lithium metaphosphate is used as the lithium and phosphorus source for the LFMP material. Compared with conventional lithium sources (generally LiOH or Li2CO3) and phosphorus sources (generally H3PO4 or NH4H2PO4), lithium metaphosphate is not only cheaper but also provides a precise Li:P ratio (1:1), which helps reduce raw material waste and the introduction of impurities. As a high-performance fast ion conductor, the introduction of lithium phosphate during material preparation not only replenishes some of the Li and P lost during sintering but also allows the residual lithium phosphate to adhere to the material surface, transforming into a lithium phosphate coating layer after sintering. The addition of the carbon precursor is to form a carbon coating layer on the LFMP material surface, improving the lithium-ion diffusion coefficient. Furthermore, the organic solvent not only serves as a solvent for wet ball milling, improving the dispersion efficiency of lithium phosphate and carbon precursors on the mixed material surface, but also enables pore-forming at multiple material interfaces during evaporation, facilitating effective contact between the material and the electrolyte. Therefore, the novel preparation method for lithium iron manganese phosphate materials developed by this invention can not only achieve one-step preparation of LFMP materials and reduce the production cost of materials, but also overcome the defect of poor conductivity at the material surface and interface by the C-Li3PO3 mixed coating layer, improve the rate performance of the material, and have excellent electrochemical performance and ultra-stable structure. Attached Figure Description

[0032] Figure 1 XRD patterns of the samples prepared in Examples 1 and 2.

[0033] Figure 2 SEM image of the sample prepared in Example 1.

[0034] Figure 3 TEM and HAADF images of the sample prepared in Example 1.

[0035] Figure 4 SEM image of the sample prepared in Example 2.

[0036] Figure 5 TEM image of the sample prepared in Example 2.

[0037] Figure 6 TEM image of the sample prepared in Example 3. Detailed Implementation

[0038] The following examples are intended to further illustrate the present invention, and are not intended to limit the scope of protection of the present invention.

[0039] The materials used in the following examples are all commercially available.

[0040] Example 1

[0041] (1) Using a molar ratio of 1:0.5:0.5, weigh 3.0 g LiPO3, 1.56 g Mn(OH)2 and 1.57 g Fe(OH)2 into a ball mill jar and mill at 250 rad / min. -1 Ball milling was performed at a rotation speed of 3 h (ball-to-material ratio 5:1) to obtain a uniformly mixed LFMP precursor mixture. 0.06 g of lithium phosphate and 0.31 g of polydopamine were added to a ball mill jar at a mass ratio of 1:0.01:0.05, along with 30 mL of petroleum ether. The jar was then filled with N2, sealed, and ball milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.5 Mn 0.5 PO4@C-Li3PO4) cathode material.

[0042] (2) X-ray diffraction (XRD) was used to analyze the LiFe obtained in Example 1. 0.5 Mn 0.5 The XRD pattern of PO4@C-Li3PO4 was obtained through testing and analysis, as shown below. Figure 1 As shown.

[0043] (3) The LiFe obtained in Example 1 was analyzed using a scanning electron microscope (SEM). 0.5 Mn 0.5 The PO4@C-Li3PO4 sample was tested and analyzed, and its electron micrograph was obtained, as shown below. Figure 2 As shown.

[0044] (4) The LiFe obtained in Example 1 was examined using a transmission electron microscope (TEM). 0.5 Mn 0.5 PO4@C-Li3PO4 was tested and analyzed to obtain its TEM and HAADF plots, as shown below. Figure 3 As shown.

[0045] (5) The LiFe obtained in Example 1 0.5 Mn 0.5 PO4@C-Li3PO4 was assembled into a 2016-type button cell and charged and discharged within a voltage range of 3.0-4.3V.

[0046] (6) The test temperature was 25℃. The battery was first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3C. The test results are shown in Table 1 and Table 2.

[0047] Example 2

[0048] (1) Using a molar ratio of 1:0.4:0.6, weigh 3.0 g LiPO3, 1.24 g Mn(OH)2 and 1.88 g Fe(OH)2 into a ball mill jar and mill at 250 rad / min. -1 Ball milling was performed at a rotation speed of 400 rad / min for 3 hours (ball-to-material ratio 5:1) to obtain a uniformly mixed LFMP precursor mixture. 0.06 g of lithium phosphate and 0.3 g of polydopamine were added to a ball mill jar at a mass ratio of 1:0.01:0.05, along with 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.6 Mn 0.4 PO4@C-Li3PO4) cathode material.

[0049] (2) X-ray diffraction (XRD) was used to analyze the LiFe obtained in Example 2. 0.6 Mn 0.4 The XRD pattern of PO4@C-Li3PO4 was obtained through testing and analysis, as shown below. Figure 1 As shown.

[0050] (3) The LiFe obtained in Example 2 was analyzed using a scanning electron microscope (SEM). 0.6Mn 0.4 The PO4@C-Li3PO4 sample was tested and analyzed, and its electron micrograph was obtained, as shown below. Figure 4 As shown.

[0051] (4) The LiFe obtained in Example 2 was examined using a transmission electron microscope (TEM). 0.6 Mn 0.4 PO4@C-Li3PO4 was tested and analyzed to obtain its TEM image, as shown below. Figure 5 As shown.

[0052] (5) The LiFe obtained in Example 2 0.6 Mn 0.4 PO4@C-Li3PO4 was assembled into a 2016-type button cell and charged and discharged within a voltage range of 3.0-4.3V.

[0053] (6) The test temperature was 25℃. The battery was first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3C. The test results are shown in Table 1 and Table 2.

[0054] Example 3

[0055] (1) Weigh 3.0 g LiPO3, 2.48 g Mn(OH)2 and 0.63 g Fe(OH)2 into a ball mill jar with a molar ratio of 1:0.8:0.2 and mill at 250 rad / min. -1 Ball milling was performed at a rotation speed of 400 rad / min for 3 hours (ball-to-material ratio 5:1) to obtain a uniformly mixed LFMP precursor mixture. 0.06 g of lithium phosphate and 0.3 g of polydopamine were added to a ball mill jar at a mass ratio of 1:0.01:0.05, along with 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.2 Mn 0.8 PO4@C-Li3PO4) cathode material.

[0056] (2) The LiFe obtained in Example 3 was examined using a transmission electron microscope (TEM). 0.2 Mn 0.8PO4@C-Li3PO4 was tested and analyzed to obtain its TEM image, as shown below. Figure 6 As shown.

[0057] (3) The LiFe obtained in Example 3 0.2 Mn 0.8 PO4@C-Li3PO4 was assembled into a 2016-type button cell and charged and discharged within a voltage range of 3.0-4.3V.

[0058] (4) The test temperature was 25℃. The battery was first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3C. The test results are shown in Table 1 and Table 2.

[0059] Comparative Example 1

[0060] (1) Using a molar ratio of 1:0.5:0.5, weigh 3.0 g LiPO3, 1.56 g Mn(OH)2 and 1.57 g Fe(OH)2 into a ball mill jar and mill at 250 rad / min. -1 Ball milling was performed at a speed of 400 rpm for 3 hours with a ball-to-material ratio of 5:1 to obtain a homogeneous LFMP precursor mixture. 30 mL of petroleum ether was added to the ball mill jar, which was then filled with nitrogen, sealed, and ball milled at 400 rpm. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring speed of 400 rpm. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours, then cooled to room temperature to obtain lithium iron manganese phosphate (LiFe). 0.5 Mn 0.5 PO4) cathode material.

[0061] (2) Using the same material preparation method, only the molar ratio of Mn(OH)2 and Fe(OH)2 was changed to prepare LiFe2+. 0.6 Mn 0.4 PO4 and LiFe 0.2 Mn 0.8 PO4 cathode material.

[0062] (3) The difference between this comparative example and Examples 1, 2, and 3 is that lithium phosphate and carbon material precursors were not added. The LiFe obtained in Comparative Example 1... 0.5 Mn 0.5 PO4, LiFe 0.6 Mn 0.4 PO4 and LiFe 0.2 Mn 0.8The PO4 cathode material was assembled into a 2016-type button cell and subjected to charge-discharge tests within the voltage range of 3.0-4.3V. The test conditions were as follows: at 25℃, the cells were first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3.0C, as shown in Tables 1 and 2.

[0063] Comparative Example 2

[0064] (1) Weigh 3.0 g LiPO3, 1.56 g Mn(OH)2 and 1.57 g Fe(OH)2 into a ball mill jar with a molar ratio of 1:0.5:0.5 and mill at 250 rad / min. -1 The mixture was ball-milled at a speed of 300 rad / min for 3 hours with a ball-to-material ratio of 5:1 to obtain a homogeneous LFMP precursor mixture. 0.06 g of lithium phosphate was added to the ball mill jar at a mass ratio of 1:0.01 (LFMP precursor mixture: lithium phosphate), followed by 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball-milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.5 Mn 0.5 PO4@Li3PO4) cathode material.

[0065] (2) The difference between this comparative example and Example 1 is that no carbon material precursor was added during the material preparation process. The LiFe obtained in Comparative Example 2... 0.5 Mn 0.5 PO4@Li3PO4 was assembled into a 2016-type button cell and charged / discharge tested within the 3.0-4.3V voltage range. The test conditions were as follows: at 25℃, the cells were first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3.0C, as shown in Tables 1 and 2.

[0066] Comparative Example 3

[0067] (1) Weigh 3.0 g LiPO3, 1.56 g Mn(OH)2 and 1.57 g Fe(OH)2 into a ball mill jar with a molar ratio of 1:0.5:0.5 and mill at 250 rad / min. -1The mixture was ball-milled at a speed of 300 rad / min for 3 hours with a ball-to-material ratio of 5:1 to obtain a homogeneous LFMP precursor mixture. 0.31 g of polydopamine was added to a ball mill jar at a mass ratio of 1:0.05, along with 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball-milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-coated lithium iron manganese phosphate (LiFe) was obtained. 0.5 Mn 0.5 PO4@C) cathode material.

[0068] (2) The difference between this comparative example and Example 1 is that lithium phosphate was not added during the material preparation process. The LiFe obtained in Comparative Example 3... 0.5 Mn 0.5 PO4@C was assembled into 2016-type button cells and charged and discharged within the voltage range of 3.0-4.3V. The test conditions were as follows: at 25℃, the cells were first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3.0C, as shown in Tables 1 and 2.

[0069] Comparative Example 4

[0070] (1) 1.47 g LiOH·H2O, 4.01 g NH4H2PO4, 1.56 g Mn(OH)2 and 1.57 g Fe(OH)2 were placed in a ball mill jar at a molar ratio of 1:1:0.5:0.5 and milled at 250 rad / min. -1 The mixture was ball-milled at a rotation speed of 3 h with a ball-to-material ratio of 5:1 to obtain a homogeneous LFMP precursor mixture. 0.08 g of lithium phosphate and 0.43 g of polydopamine were added to a ball mill jar at a mass ratio of 1:0.01:0.05, along with 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball-milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.5Mn 0.5 PO4@C-Li3PO4A) cathode material.

[0071] (2) The difference between this comparative example and Example 1 is that LiOH and NH4H2PO4 are used instead of LiPO3 in the material preparation process. The LiFe obtained in Comparative Example 4... 0.5 Mn 0.5 PO4@C-Li3PO4A was assembled into a 2016-type button cell and charged / discharge tested within the 3.0-4.3V voltage range. The test conditions were as follows: at 25℃, the cells were first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3.0C, as shown in Tables 1 and 2.

[0072] Comparative Example 5

[0073] (1) Weigh out 1.29g Li2CO3, 4.01g NH4H2PO4, 1.56g Mn(OH)2 and 1.57g Fe(OH)2 in a ball mill jar with a molar ratio of 0.5:1:0.5:0.5 and place them in the ball mill jar. -1 The mixture was ball-milled at a rotation speed of 3 h with a ball-to-material ratio of 5:1 to obtain a homogeneous LFMP precursor mixture. 0.08 g of lithium phosphate and 0.44 g of polydopamine were added to a ball mill jar at a mass ratio of 1:0.01:0.05, along with 30 mL of petroleum ether. The jar was then filled with nitrogen, sealed, and ball-milled at 400 rad / min. -1 After ball milling for 6 hours, the material was transferred to a single-necked flask, magnetically stirred, and heated at a stirring rate of 400 rad / min. -1 The heating temperature is 90℃. After the solvent has completely evaporated, the solid mixture is placed in a tube furnace and heated at 5℃ for 5 minutes under an Ar atmosphere. -1 The temperature was increased to 650℃ and sintered for 12 hours. After cooling to room temperature, C-Li3PO4-coated lithium iron manganese phosphate (LiFe) was obtained. 0.5 Mn 0.5 PO4@C-Li3PO4B) cathode material.

[0074] (2) The difference between this comparative example and Example 1 is that Li2CO3 and NH4H2PO4 are used instead of LiPO3 in the material preparation process. The LiFe obtained in Comparative Example 4... 0.5 Mn 0.5 PO4@C-Li3PO4B was assembled into a 2016-type button cell and charged / discharge tested within the 3.0-4.3V voltage range. The test conditions were as follows: at 25℃, the cells were first activated at 0.2C and 0.5C for one cycle, and then cycled at 1.0C and 3.0C, as shown in Tables 1 and 2.

[0075] Table 1. Comparison of electrical properties of the sample and comparative materials (tested at 25°C, 1.0C cycling).

[0076]

[0077]

[0078] Table 2. Comparison of electrical properties of the sample and comparative materials (tested at 25°C, 3.0°C cycling).

[0079]

[0080] Regarding the material LiFe obtained in Example 1 of this invention 0.5 Mn 0.5 PO4@C-Li3PO4, by XRD Figure 1 As can be seen, the characteristic peaks of lithium iron manganese phosphate in the material are obvious, indicating that the lithium iron manganese phosphate material was successfully prepared in this experiment. Figure 2 It is known that the prepared material surface has a large number of pores and channels. These pores facilitate electrolyte wetting and greatly increase the effective contact area between the material and the electrolyte, thereby improving the lithium-ion diffusion coefficient and rate performance of the material. Furthermore, from Figure 3 It is known that the prepared material surface has a C-Li3PO4 mixed coating layer of approximately 4 nm thickness. Carbon is a highly conductive material, while Li3PO4 is a fast ion conductor. Therefore, the C-Li3PO4 mixed coating layer not only protects the material interface but also significantly enhances the lithium-ion transport kinetics at the material surface, thereby further improving the electrochemical performance of the material. Figure 3 The HADDF diagram shows that C is evenly distributed on the material surface, indicating that C has been uniformly coated on the material surface.

[0081] The LiFe obtained in Example 2 of this invention 0.6 Mn 0.4 PO4@C-Li3PO4 material, made from Figure 1 XRD results indicate that lithium iron manganese phosphate material has been successfully synthesized; Figure 4 It is known that the material is an amorphous sheet, and its surface contains abundant porous structures, which can effectively improve the poor ionic conductivity of lithium iron manganese phosphate materials; in addition, due to Figure 5 It can be seen that LiFe 0.6 Mn 0.4 The surface of the PO4@C-Li3PO4 material also has a distinct nano-C-Li3PO4 mixed coating layer, which can further improve the rate performance of the material.

[0082] The LiFe obtained in Example 3 of this invention 0.2 Mn0.8 PO4@C-Li3PO4 material, by its Figure 6 The TEM image shows that there is a coating layer on the surface of the material, and there are some regions with obvious lattice in the coating layer with a lattice spacing of 0.305 nm. These lithium phosphate (200) characteristic crystal planes indicate that there is a lithium phosphate coating on the surface of the material. In addition, other amorphous regions are carbon materials.

[0083] As shown in Tables 1 and 2, the lithium iron manganese phosphate material co-coated with lithium phosphate and carbon obtained by this method not only enables the one-step preparation of coated lithium iron manganese phosphate cathode materials, but also exhibits excellent electrochemical cycling and rate performance. (Using LiFe...) 0.5 Mn 0.5 Taking PO4@C-Li3PO4 material as an example, the initial discharge specific capacity of the material is 160.8 mAh g. -1 The charging specific capacity is 163.2mAh g. -1 The material achieved an initial coulombic efficiency of 98.5%, and after 300 cycles, its discharge specific capacity remained as high as 154.2 mAh g⁻¹. -1 The capacity retention rate was 95.8%. Meanwhile, the uncoated LiFe... 0.5 Mn 0.5 The discharge specific capacity of the PO4 material is only 150.7 mAh g after 300 cycles. -1 The capacity retention rate was only 94.7%. Furthermore, the difference in cycling performance between uncoated and coated materials at a high rate of 3.0C was even more pronounced, with uncoated LiFe showing the most significant difference. 0.5 Mn 0.5 The PO4 material exhibits a discharge specific capacity of 119.5 mAh g after 200 cycles at 3.0C. -1 The capacity retention rate was 75.1%, while the coated LiFe... 0.5 Mn 0.5 The discharge specific capacity of the PO4@C-Li3PO4 material is 132.6 mAh g. -1 The capacity retention rate is as high as 82.8%. It is worth noting that while the electrochemical performance of lithium iron manganese phosphate materials modified solely by carbon coating or lithium phosphate coating can be improved to some extent compared to the blank material, the modification effect is lower than that of materials co-coated with carbon and lithium phosphate. Overall, the method of this invention, through a simple one-step process, not only successfully prepares lithium iron manganese phosphate cathode materials but also coats the surface of these materials, greatly improving their electrochemical performance, especially their cycling performance at a high rate of 3.0C.

[0084] 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 method for preparing a lithium iron manganese phosphate cathode material, characterized in that: The lithium source, phosphorus source, manganese source and iron source are dry ball milled, then lithium phosphate, organic solvent and carbon material precursor are added and wet ball milled, and then carbon-lithium phosphate coated lithium iron manganese phosphate cathode material is obtained by solvent evaporation and high temperature sintering; lithium metaphosphate is used as lithium source and phosphorus source, and the Li:P stoichiometric ratio in lithium metaphosphate is 1:

1. The high-temperature sintering temperature is 550-800℃.

2. The preparation method according to claim 1, characterized in that: The manganese source includes at least one of Mn(OH)2, MnCO3 and MnSO4; the iron source includes at least one of Fe(OH)2, FeO and FeSO4.

3. The preparation method according to claim 1, characterized in that: Dry ball milling speed is 100-400 rad / min -1 The ball milling time is 1-5 hours.

4. The preparation method according to claim 1, characterized in that: The carbon material precursor includes at least one of sucrose, glucose, and polydopamine; the organic solvent includes at least one of ethanol, petroleum ether, and ethyl acetate.

5. The preparation method according to claim 1, characterized in that: Wet ball milling is carried out under an inert atmosphere at a milling speed of 200-500 rad / min. -1 The ball milling time is 1-10 hours.

6. The preparation method according to claim 1, characterized in that: The solvent was evaporated under magnetic stirring and heating, with the magnetic stirring speed at 300-600 rad / min. -1 The heating temperature is 50-110℃.

7. The preparation method according to claim 1, characterized in that: High-temperature sintering is carried out under an inert atmosphere, with a heating rate of 1-10℃ / min. -1 The sintering time is 5-20 hours.

8. The preparation method according to claim 1, characterized in that: Lithium iron manganese phosphate material is LiFe x Mn 1-x PO4, 0 < x < 1.

9. A lithium-ion battery, characterized in that: The lithium iron manganese phosphate material coated with lithium carbon phosphate obtained by the preparation method according to any one of claims 1-8 is used as a positive electrode.

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