Rare earth alloy coated lithium iron manganese phosphate cathode material, preparation method and application thereof

Abstract

The application provides a rare earth alloy coated lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. The rare earth alloy coated lithium manganese iron phosphate positive electrode material comprises lithium manganese iron phosphate particles and rare earth alloy particles coated on the surface of the lithium manganese iron phosphate particles, wherein the average size of the lithium manganese iron phosphate particles is 300-800 nm, and the average size of the rare earth alloy particles is ≤50 nm. The rare earth alloy coated lithium manganese iron phosphate positive electrode material provided by the application uses rare earth elements with atomic size and stable chemical properties to construct a rare earth high-entropy alloy coating layer, which not only has high solid solubility and structural stability, but also can enhance the Li + adsorption and promote ion transmission, and can also guide the charge redistribution in the positive electrode material through the disordered arrangement of a plurality of different electronegative elements in the high-entropy alloy, thereby reducing the John-Teller effect of the Mn element in the lithium manganese iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and more specifically, to a rare earth alloy-coated lithium iron manganese phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Lithium iron phosphate (LFP) has been widely used as a cathode material in power batteries due to its high theoretical capacity and structural stability. However, it suffers from low redox potential and low conductivity. Lithium manganese phosphate (LMP), which shares the same olive tree structure as LFP, offers similar capacity but also boasts a higher plateau voltage, contributing to improved cell energy density. Furthermore, its stability and low cost contribute to its promising future. However, LMP also has some significant drawbacks, such as low electronic conductivity and lithium-ion diffusion coefficient, and low Mn content. 3+ The John-Teller effect causes lattice distortion, resulting in poor stability in its applications.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The main objective of this invention is to provide a rare-earth alloy-coated lithium iron manganese phosphate cathode material, its preparation method, and its application, to address some serious shortcomings of existing lithium manganese phosphate materials, such as low electronic conductivity and lithium-ion diffusion coefficient, and low Mn content. 3+ The John-Teller effect causes lattice distortion, leading to poor stability in its applications.

[0005] To achieve the above objectives, according to one aspect of the present invention, a rare earth alloy-coated lithium iron manganese phosphate cathode material is provided, the cathode material comprising lithium iron manganese phosphate particles and rare earth alloy particles coated on the surface of the lithium iron manganese phosphate particles, wherein the average size of the lithium iron manganese phosphate particles is 300-800 nm, and the average size of the rare earth alloy particles is ≤50 nm.

[0006] Furthermore, the rare earth elements in the rare earth alloy particles include Gd, Ho, La, Tb and Y, with a preferred molar ratio of 1:1:1:1:1.

[0007] Furthermore, the mass ratio of lithium iron manganese phosphate particles to rare earth alloy particles is 50–100:1.

[0008] According to a second aspect of the present invention, a method for preparing the above-mentioned rare earth alloy-coated lithium iron manganese phosphate cathode material is also provided. The method includes: step S1, providing lithium iron manganese phosphate particles, mixing and ball milling the lithium iron manganese phosphate particles with rare earth source powder containing at least two different rare earths to obtain a cathode material precursor; step S2, subjecting the cathode material precursor to a vacuum hot pressing sintering followed by rapid cooling to obtain an initial state cathode material; step S3, subjecting the initial state cathode material to a secondary vacuum hot pressing sintering and tempering, and cooling to room temperature to obtain a rare earth alloy-coated lithium iron manganese phosphate cathode material.

[0009] Further, in step S1, the lithium iron manganese phosphate particles are first subjected to ultrasonic treatment, and then mixed with various rare earth source powders and ball-milled.

[0010] Furthermore, the lithium iron manganese phosphate particles are subjected to ultrasonic treatment in sequence with acetone and ethanol; preferably, the ultrasonic treatment time is 20 to 40 minutes.

[0011] Furthermore, the mass ratio of acetone and ethanol to the lithium iron phosphate particles is 5 to 10:1.

[0012] Furthermore, the molar ratio of Gd powder, Ho powder, La powder, and Tb powder is 1:1:1:1:1.

[0013] Furthermore, the mass ratio of rare earth source powder to lithium iron manganese phosphate particles is 1:50 to 100.

[0014] Furthermore, the particle sizes of Gd powder, Ho powder, La powder, and Tb powder are each independently 10–20 nm.

[0015] Furthermore, the ball mill rotation speed is 600–1000 r / min, the ball milling media are zirconium oxide or silicon carbide, the ball-to-material ratio is 2–5:1, and the ball milling time is 1–3 h.

[0016] Further, in step S2, the temperature of the first vacuum hot pressing sintering is 1000-1200℃, the pressure is 30-50MPa, the vacuum degree is 1-10Pa, and the time is 3-5h.

[0017] Furthermore, the quenching is carried out in liquid nitrogen, preferably for 3 to 10 minutes.

[0018] Further, in step S3, the temperature of the secondary vacuum hot pressing sintering is 1000-1200℃, the pressure is 30-50MPa, the vacuum degree is 1-10Pa, and the time is 0.5-2h.

[0019] Furthermore, the cooling method is natural cooling.

[0020] According to a third aspect of the present invention, the application of the rare earth alloy-coated lithium iron manganese phosphate cathode material provided in the first aspect or the rare earth alloy-coated lithium iron manganese phosphate cathode material obtained by the preparation method provided in the second aspect is also provided in lithium-ion batteries.

[0021] According to a fourth aspect of the present invention, a lithium-ion battery is also provided, comprising the rare earth alloy-coated lithium iron manganese phosphate cathode material provided in the first aspect or the rare earth alloy-coated lithium iron manganese phosphate cathode material obtained by the preparation method provided in the second aspect above.

[0022] Applying the technical solution of this application, the rare earth alloy-coated lithium iron manganese phosphate cathode material provided by this application uses rare earth elements with stable atomic size and chemical properties to construct a rare earth high-entropy alloy coating layer. This not only possesses high solid solubility and structural stability, but also enhances the Li-type lithium oxide coating by leveraging the electronegative rare earth elements in the high-entropy alloy. + Adsorption promotes ion transport and can also guide the redistribution of charge in the cathode material through the disordered arrangement of various electronegative elements in the high-entropy alloy, thereby reducing the John-Teller effect of Mn element in lithium iron manganese phosphate, improving stability, and reducing manganese dissolution.

[0023] In addition, the rare earth alloy coating layer of the rare earth alloy-coated lithium iron manganese phosphate cathode material provided in this application not only provides high conductivity and structural protection, but its redox matrix can also provide more lithium storage sites, thus comprehensively improving the capacity and cycle performance of the cathode material. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 SEM images of the cathode materials provided in Example 1 and Comparative Example 1 are shown; (a) is an SEM image of the cathode material provided in Example 1, and (b) is an SEM image of the lithium iron manganese phosphate particles provided in Comparative Example 1. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0027] As analyzed in the background section of this application, lithium iron phosphate materials suffer from low redox potential and low conductivity. Lithium manganese phosphate, which has the same olive tree structure as lithium iron phosphate, possesses a higher plateau voltage, which helps improve the energy density of the battery cell. However, lithium manganese phosphate itself has some serious drawbacks, such as low electronic conductivity and lithium-ion diffusion coefficient, and low Mn content. 3+ The John-Teller effect causes lattice distortion, leading to poor stability in applications. To address this issue, this application provides a rare-earth alloy-coated lithium iron manganese phosphate cathode material, its preparation method, and its applications.

[0028] In a first typical embodiment of this application, a rare earth alloy-coated lithium iron manganese phosphate cathode material is provided. The cathode material includes lithium iron manganese phosphate particles and rare earth alloy particles coated on the surface of the lithium iron manganese phosphate particles. The average size of the lithium iron manganese phosphate particles is 300-800 nm, and the average size of the rare earth alloy particles is ≤50 nm.

[0029] The rare-earth alloy-coated lithium iron manganese phosphate cathode material provided in this application uses rare-earth elements with stable atomic size and chemical properties to construct a rare-earth high-entropy alloy coating layer. This not only possesses high solid solubility and structural stability, but also enhances the Li-type cathode material by leveraging the electronegative rare-earth elements within the high-entropy alloy. + Adsorption promotes ion transport and can also guide the redistribution of charge in the cathode material through the disordered arrangement of various electronegative elements in the high-entropy alloy, thereby reducing the John-Teller effect of Mn element in lithium iron manganese phosphate, improving stability, and reducing manganese dissolution.

[0030] In addition, the rare earth alloy coating layer of the rare earth alloy-coated lithium iron manganese phosphate cathode material provided in this application not only provides high conductivity and structural protection, but its redox matrix can also provide more lithium storage sites, thus comprehensively improving the capacity and cycle performance of the cathode material.

[0031] In this application, the average size of lithium iron manganese phosphate particles is 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm or any range of two values.

[0032] The specific preparation method of the above-mentioned lithium iron manganese phosphate particles is not limited. For example, lithium iron manganese phosphate particles can be prepared by solid-state method, using Li2CO3, FeC2O4·2H2O, MnCO3, NH4H2PO4 and C 12 H 22 O 11 The above raw materials were mixed in an appropriate amount of anhydrous ethanol solvent according to the LiFe... 0.6 Mn 0.4After mixing PO4 in stoichiometric proportions, the mixture was ball-milled. The mixture was then dried and transferred to a sintering furnace for high-temperature sintering under nitrogen protection. First, it was pre-calcined at 350°C for 3 hours, then the temperature was increased to 700°C for 10 hours. After natural cooling to room temperature, it was pulverized to obtain the final product.

[0033] To further improve the structural stability of rare-earth alloy-coated lithium iron manganese phosphate cathode materials, in some embodiments, the rare-earth elements in the rare-earth alloy particles include Gd, Ho, La, Tb, and Y. Through the synergistic effect of Gd, Ho, La, Tb, and Y, the solid solubility and structural stability of the cathode material are further improved. In particular, when the molar ratio of Gd, Ho, La, Tb, and Y in the rare-earth alloy particles is 1:1:1:1:1, it is more conducive to enhancing the cathode material's adhesion to Li. + Adsorption promotes ion transport and also helps improve the stability of the cathode material and reduce manganese leaching.

[0034] To further improve the structural stability of rare earth alloy-coated lithium iron phosphate cathode material, the preferred mass ratio of lithium iron manganese phosphate particles to rare earth alloy particles is 50 to 100:1, such as 50:1, 55:1, 60:1, 70:1, 80:1, 90:1, 100:1 or any range of two values.

[0035] In a second typical embodiment of this application, a method for preparing a rare earth alloy-coated lithium iron manganese phosphate cathode material is also provided. The preparation method includes the following steps: Step S1, providing lithium iron manganese phosphate particles, mixing and ball milling the lithium iron manganese phosphate particles with rare earth source powder containing at least two different rare earths to obtain a cathode material precursor; Step S2, subjecting the cathode material precursor to a vacuum hot-pressing sintering followed by rapid cooling to obtain an initial state cathode material; Step S3, subjecting the initial state cathode material to a second vacuum hot-pressing sintering and tempering, and cooling to room temperature to obtain a rare earth alloy-coated lithium iron manganese phosphate cathode material.

[0036] The method for preparing rare-earth alloy-coated lithium iron manganese phosphate cathode material provided in this application first involves ball milling to uniformly attach rare-earth source powder to the surface of lithium iron manganese phosphate particles. Then, through a first vacuum hot-pressing sintering, rapid cooling, and a second vacuum hot-pressing sintering, the rare-earth source powder is transformed into rare-earth alloy particles with an average size ≤500nm, which coat the surface of the lithium iron manganese phosphate particles, thereby constructing a rare-earth high-entropy alloy coating layer. This results in a rare-earth alloy-coated lithium iron manganese phosphate cathode material that not only possesses high solid solubility and structural stability but also enhances the Li-P-P coating by leveraging the electronegative rare-earth elements in the high-entropy alloy. +Adsorption promotes ion transport and, through the disordered arrangement of various electronegative elements in the high-entropy alloy, guides the redistribution of charge in the cathode material, thereby reducing the John-Teller effect of Mn in lithium iron manganese phosphate, improving stability, and reducing manganese dissolution. Furthermore, the redox matrix of this rare-earth alloy coating provides more lithium storage sites, comprehensively enhancing the capacity and cycle performance of lithium iron manganese phosphate materials.

[0037] To further reduce the impact of impurities on the cathode material, in some embodiments, lithium iron manganese phosphate particles are first ultrasonically treated to clean and remove dust and other impurities adhering to the surface, and then mixed with rare earth source powder and ball-milled.

[0038] In some specific embodiments, organic solvents are used to clean lithium iron manganese phosphate particles. For example, acetone and ethanol are used to ultrasonically treat the lithium iron manganese phosphate particles in sequence. In particular, controlling the ultrasonic treatment time to 20-40 minutes is more conducive to cleaning the lithium iron manganese phosphate particles.

[0039] The specific amounts of acetone and ethanol used are not specifically limited. In some embodiments, in order to further improve the efficiency of ultrasonic treatment, it is preferred that the mass ratio of acetone and ethanol to lithium iron phosphate particles is 5 to 10:1, such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or any range of two values.

[0040] The aforementioned rare earth source powder refers to rare earth source powder containing at least two different rare earth elements. The specific type of rare earth source powder is not limited, including but not limited to rare earth elemental powder and rare earth-containing compounds. The rare earth-containing compounds refer to compounds that obtain rare earth elements after high-temperature sintering.

[0041] To further improve the stability of the cathode material, the rare earth source powder is preferably a mixture of Gd powder, Ho powder, La powder, Tb powder and Y powder, especially when the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:1:1:1:1, which is conducive to forming rare earth alloy particles of Gd, Ho, La, Tb and Y with a molar ratio of 1:1:1:1:1.

[0042] To further improve the ion transport performance and structural stability of the cathode material, the preferred mass ratio of rare earth source powder to lithium iron manganese phosphate particles is 1:50 to 100, such as 1:50, 1:55, 1:60, 1:70, 1:80, 1:90, 1:100 or any range of two values.

[0043] In order to facilitate the formation of rare earth alloy particles with an average size ≤50nm, the particle size of Gd powder, Ho powder, La powder, and Tb powder is independently 10-20nm, such as 10nm, 12nm, 15nm, 18nm, 20nm, or any range of two values.

[0044] To further improve the uniformity of dispersion of various rare earth powders, in step S1, the preferred milling speed is 600-1000 r / min, the milling media is zirconium oxide or silicon carbide, the ball-to-material ratio is 2-5:1, and the milling time is 1-3 h.

[0045] In step S1 above, the rotational speed of the ball mill is 600 r / min, 700 r / min, 800 r / min, 900 r / min, 100 r / min or any range of two values; the ratio of ball material to material is 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1 or any range of two values; the ball milling time is 1 h, 1.5 h, 2 h, 2.5 h, 3 h or any range of two values.

[0046] In step S2 above, in order to further improve the efficiency of the first vacuum hot pressing sintering, the preferred temperature for the first vacuum hot pressing sintering is 1000-1200℃, the pressure is 30-50MPa, the vacuum degree is 1-10Pa, and the time is 3-5h.

[0047] Typical, but not limiting, in step S2 above, the temperature of the first vacuum hot pressing sintering is 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any two of these values; the pressure is 30MPa, 35MPa, 40MPa, 45MPa, 50MPa or any two of these values; the vacuum degree is 1Pa, 2Pa, 3Pa, 5Pa, 8Pa, 10Pa or any two of these values; and the time is 3h, 3.5h, 4h, 4.5h, 5h or any two of these values.

[0048] In step S2 above, rapid cooling further eliminates the stress between rare earth alloy particles and lithium iron manganese phosphate particles, thereby improving the bonding strength between rare earth alloy particles and lithium iron manganese phosphate particles in the initial state cathode material.

[0049] In some embodiments, quenching is performed in liquid nitrogen, preferably for a duration of 3 to 10 minutes, such as 3 minutes, 5 minutes, 8 minutes, 10 minutes, or any range of two values.

[0050] To further improve the efficiency of secondary vacuum hot pressing sintering, step S3 is preferred, with a temperature of 1000-1200℃, a pressure of 30-50MPa, a vacuum degree of 1-10Pa, and a time of 0.5-2h.

[0051] Typical, but not limiting, in step S3 above, the temperature of the secondary vacuum hot pressing sintering is 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any two of these values; the pressure is 30MPa, 35MPa, 40MPa, 45MPa, 50MPa or any two of these values; the vacuum degree is 1Pa, 2Pa, 3Pa, 5Pa, 8Pa, 10Pa or any two of these values; and the time is 0.5h, 1h, 1.5h, 2h or any two of these values.

[0052] To further improve the particle size uniformity of rare earth alloy particles, it is preferable to use natural cooling in step S3, which helps to reduce the stress on the rare earth alloy particles and further improve the stability of the cathode material.

[0053] In a third typical embodiment of this application, the application of the rare earth alloy-coated lithium iron manganese phosphate cathode material provided in the first typical embodiment or the rare earth alloy-coated lithium iron manganese phosphate cathode material obtained by the preparation method provided in the second typical embodiment is also provided in lithium-ion batteries.

[0054] The rare-earth alloy-coated lithium iron manganese phosphate cathode material provided in this application, when used as a cathode active material in lithium-ion batteries, not only possesses high solid solubility and structural stability, but also enhances its resistance to Li. + Adsorption promotes ion transport and guides charge redistribution in the cathode material, reducing the John-Teller effect of Mn in lithium iron manganese phosphate, improving stability, and reducing manganese dissolution. Furthermore, the rare-earth alloy-coated lithium iron manganese phosphate cathode material provided in this application offers high conductivity and structural protection, while its redox matrix provides more lithium storage sites, comprehensively enhancing the capacity and cycle performance of lithium-ion batteries.

[0055] In the fourth typical embodiment of this application, a lithium-ion battery is also provided, which includes the rare earth alloy coated lithium iron manganese phosphate cathode material provided in the first typical embodiment or the rare earth alloy coated lithium iron manganese phosphate cathode material obtained by the preparation method provided in the second typical embodiment.

[0056] The lithium-ion battery provided in this application utilizes rare earth alloy-coated lithium iron manganese phosphate cathode material as the cathode active material, which not only improves the stability and service life of the lithium-ion battery, but also promotes ion transport and reduces manganese dissolution, thereby comprehensively improving the capacity and cycle performance of the lithium-ion battery.

[0057] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0058] Example 1

[0059] This embodiment provides a rare earth alloy-coated lithium iron manganese phosphate cathode material, which is prepared according to the following steps:

[0060] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 80 g of lithium iron manganese phosphate particles (average particle size 543 nm) for 30 min, and then dry them.

[0061] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 71g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 1000r / min, 3h, and the ball-to-material ratio is 2:1 to obtain the cathode material precursor.

[0062] (3) The cathode material precursor is subjected to vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 30MPa, a vacuum degree of 10Pa, and a time of 3h; the obtained primary sintering product is placed in liquid nitrogen and cooled for 3min to obtain the initial state cathode material.

[0063] (4) The initial state cathode material is subjected to secondary vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 30MPa, a vacuum degree of 10Pa, and a time of 0.5h. The obtained secondary sintering product is then naturally cooled to room temperature.

[0064] Example 2

[0065] This embodiment provides a rare earth alloy-coated lithium iron manganese phosphate cathode material, which is prepared according to the following steps:

[0066] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 80 g of lithium iron manganese phosphate particles (average particle size 700 nm) for 30 min, and then dry them.

[0067] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 35.5g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 600r / min, 1h, and the ball-to-material ratio is 5:1 to obtain the cathode material precursor.

[0068] (3) The cathode material precursor was subjected to vacuum hot pressing sintering at a temperature of 1200℃, a pressure of 40MPa, a vacuum degree of 1Pa, and a time of 5h; the obtained first sintering product was placed in liquid nitrogen and cooled for 3min to obtain the initial state cathode material.

[0069] (4) The initial state cathode material is subjected to secondary vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 30MPa, a vacuum degree of 10Pa, and a time of 2h. The obtained secondary sintering product is then naturally cooled to room temperature.

[0070] Example 3

[0071] This embodiment provides a rare earth alloy-coated lithium iron manganese phosphate cathode material, which is prepared according to the following steps:

[0072] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 40 g of lithium iron manganese phosphate particles (average particle size 780 nm) for 30 min, and then dry them.

[0073] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 35.5g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 800r / min, 3h, and the ball-to-material ratio is 3:1 to obtain the cathode material precursor.

[0074] (3) The cathode material precursor is subjected to vacuum hot pressing sintering at a temperature of 1200℃, a pressure of 50MPa, a vacuum degree of 10Pa, and a time of 3h; the obtained first sintering product is placed in liquid nitrogen and cooled for 10min to obtain the initial state cathode material.

[0075] (4) The initial state cathode material is subjected to secondary vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 50MPa, a vacuum degree of 10Pa, and a time of 1.5h. The obtained secondary sintering product is then naturally cooled to room temperature.

[0076] Example 4

[0077] This embodiment provides a rare earth alloy-coated lithium iron manganese phosphate cathode material, which is prepared according to the following steps:

[0078] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 60 g of lithium iron manganese phosphate particles (average particle size 543 nm) for 30 min, and then dry them.

[0079] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 56.8g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 1000r / min, 3h, and the ball-to-material ratio is 3:1 to obtain the cathode material precursor.

[0080] (3) The cathode material precursor is subjected to vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 50MPa, a vacuum degree of 10Pa, and a time of 3h; the obtained primary sintering product is placed in liquid nitrogen and cooled for 10min to obtain the initial state cathode material.

[0081] (4) The initial state cathode material is subjected to secondary vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 50MPa, a vacuum degree of 10Pa, and a time of 1.5h. The obtained secondary sintering product is then naturally cooled to room temperature.

[0082] Example 5

[0083] The difference between this embodiment and embodiment 1 is that Gd powder was not added in step (2).

[0084] Example 6

[0085] The difference between this embodiment and embodiment 1 is that Ho powder was not added in step (2).

[0086] Example 7

[0087] The difference between this embodiment and embodiment 1 is that La powder was not added in step (2).

[0088] Example 8

[0089] The difference between this embodiment and embodiment 1 is that Tb powder was not added in step (2).

[0090] Example 9

[0091] The difference between this embodiment and embodiment 1 is that Y powder was not added in step (2).

[0092] Example 10

[0093] The difference between this embodiment and Embodiment 1 is that the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 2:1:1:1:1.

[0094] Example 11

[0095] The difference between this embodiment and Embodiment 1 is that the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:2:1:1:1.

[0096] Example 12

[0097] The difference between this embodiment and Embodiment 1 is that the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:1:2:1:1.

[0098] Example 13

[0099] The difference between this embodiment and Embodiment 1 is that the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:1:1:2:1.

[0100] Example 14

[0101] The difference between this embodiment and Embodiment 1 is that the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:1:1:1:2.

[0102] Example 15

[0103] The difference between this embodiment and embodiment 1 is that in step (2), the amount of lithium iron manganese phosphate particles used is 20g.

[0104] Example 16

[0105] The difference between this embodiment and embodiment 1 is that in step (2), the amount of lithium iron manganese phosphate particles used is 85g.

[0106] Example 17

[0107] The difference between this embodiment and embodiment 1 is that in step (3), the sintered product is naturally cooled to room temperature to obtain the initial state cathode material.

[0108] Comparative Example 1

[0109] This comparative example provides lithium iron manganese phosphate particles, which are obtained according to the following steps:

[0110] 80g of lithium iron manganese phosphate particles (average particle size 543nm) were ultrasonically cleaned sequentially with 400mL of acetone and 400mL of ethanol for 30min, and then dried.

[0111] Comparative Example 2

[0112] This comparative example provides a rare earth composite cathode material, which is obtained according to the following steps:

[0113] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 60 g of lithium iron manganese phosphate particles (average particle size 543 nm) for 30 min, and then dry them.

[0114] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 71g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 1000r / min, 3h, and the ball-to-material ratio is 2:1.

[0115] Comparative Example 3

[0116] This comparative example provides a rare earth alloy-coated lithium iron manganese phosphate cathode material, which is prepared according to the following steps:

[0117] (1) Use 400 mL of acetone and 400 mL of ethanol to ultrasonically clean 80 g of lithium iron manganese phosphate particles (average particle size 543 nm) for 30 min, and then dry them.

[0118] (2) Take 0.16g Gd powder, 0.16g Ho powder, 0.14g La powder, 0.16g Tb powder and 0.09g Y powder respectively, mix them with 71g lithium iron manganese phosphate particles obtained in step (1) and ball mill them. The ball milling medium is zirconium oxide, the ball milling conditions are 1000r / min, 3h, and the ball-to-material ratio is 3:1 to obtain the cathode material precursor.

[0119] (3) The cathode material precursor is subjected to vacuum hot pressing sintering at a temperature of 1000℃, a pressure of 50MPa, a vacuum degree of 10Pa, and a time of 3h; the obtained sintering product is placed in liquid nitrogen and cooled for 10min to obtain the product.

[0120] Experimental Example 1

[0121] The cathode materials provided in Examples 1-4 and Comparative Example 1 were observed using a scanning electron microscope. The results showed that the surface of the lithium iron manganese phosphate particles in the cathode materials provided in Examples 1-4 was coated with rare earth alloy particles, and the average size of the rare earth alloy particles was ≤50nm.

[0122] Figure 1The images are SEM images of the cathode materials provided in Example 1 and Comparative Example 1. (a) is an SEM image of the cathode material provided in Example 1, and (b) is an SEM image of the lithium iron manganese phosphate particles provided in Comparative Example 1. As can be seen from (a), the surface coating of the lithium iron manganese phosphate particles has an aggregated particle morphology with a size ≤50nm. As can be seen from (b), the surface of the lithium iron manganese phosphate particles is smooth.

[0123] Experimental Example 2

[0124] The positive electrode materials provided in the above embodiments and comparative examples were used as positive electrode active materials to assemble coin cells of model CR2032. The specific steps included: mixing and grinding the positive electrode materials provided in the embodiments and comparative examples with carbon black and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, then coating them onto aluminum foil as the positive electrode of the lithium-ion battery. The coin cells of model CR2032 were then assembled in an argon-filled glove box. The negative electrode was a lithium metal sheet, the separator was a polypropylene microporous membrane, and the electrolyte was a 1 mol / L LiPF6 solution with an electrolyte solvent of EC:DMC:EMC = 1:1:1 (v / v / v). The physicochemical and electrical properties of each coin cell were then measured within a voltage range of 2V to 4.5V, and the results are shown in Table 1 below.

[0125] Table 1

[0126]

[0127]

[0128] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The rare earth alloy-coated lithium iron manganese phosphate cathode material provided in the application uses rare earth elements with atomic size and stable chemical properties to construct a rare earth high-entropy alloy coating layer, which not only has high solid solubility and structural stability, but also enhances the Li-terminus reaction by utilizing the electronegative rare earth elements in the high-entropy alloy. + Adsorption promotes ion transport and can also guide the redistribution of charge in the cathode material through the disordered arrangement of various electronegative elements in the high-entropy alloy, thereby reducing the John-Teller effect of Mn element in lithium iron manganese phosphate, improving stability, and reducing manganese dissolution.

[0129] Furthermore, the rare earth alloy coating layer of the lithium iron manganese phosphate cathode material provided in this application not only provides high conductivity and structural protection, but its redox matrix can also provide more lithium storage sites, thus comprehensively improving the capacity and cycle performance of the cathode material.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare earth alloy-coated lithium iron manganese phosphate cathode material, characterized in that, The cathode material includes lithium iron manganese phosphate particles and rare earth alloy particles coated on the surface of the lithium iron manganese phosphate particles, wherein the average size of the lithium iron manganese phosphate particles is 300~800nm, and the average size of the rare earth alloy particles is ≤50nm. The rare earth alloy particles contain at least four of the rare earth elements selected from Gd, Ho, La, Tb, and Y. The method for preparing the cathode material includes: step S1, providing lithium iron manganese phosphate particles, mixing and ball milling the lithium iron manganese phosphate particles with rare earth source powder to obtain a cathode material precursor; wherein, the rare earth source powder includes at least four of Gd powder, Ho powder, La powder, Tb powder and Y powder. Step S2: The cathode material precursor is subjected to vacuum hot pressing sintering and then rapidly cooled to obtain the initial state cathode material. Step S3: The initial state cathode material is subjected to secondary vacuum hot pressing sintering and tempering, and then cooled to room temperature to obtain the rare earth alloy-coated lithium iron manganese phosphate cathode material.

2. The cathode material according to claim 1, characterized in that, The rare earth elements in the rare earth alloy particles include Gd, Ho, La, Tb, and Y.

3. The cathode material according to claim 2, characterized in that, The rare earth elements in the rare earth alloy particles, Gd, Ho, La, Tb and Y, are in a molar ratio of 1:1:1:1:

1.

4. The cathode material according to any one of claims 1 to 3, characterized in that, The mass ratio of the lithium iron manganese phosphate particles to the rare earth alloy particles is 50~100:

1.

5. A method for preparing a cathode material according to any one of claims 1 to 4, characterized in that, The preparation method includes: Step S1: Provide lithium iron manganese phosphate particles, mix the lithium iron manganese phosphate particles with rare earth source powder and ball mill to obtain a cathode material precursor; wherein, the rare earth source powder includes at least four of Gd powder, Ho powder, La powder, Tb powder and Y powder. Step S2: The cathode material precursor is subjected to vacuum hot pressing sintering and then rapidly cooled to obtain the initial state cathode material. Step S3: The initial state cathode material is subjected to secondary vacuum hot pressing sintering and tempering, and then cooled to room temperature to obtain the rare earth alloy-coated lithium iron manganese phosphate cathode material.

6. The preparation method according to claim 5, characterized in that, In step S1, the lithium iron manganese phosphate particles are first subjected to ultrasonic treatment, and then mixed and ball-milled with various rare earth source powders.

7. The preparation method according to claim 6, characterized in that, The lithium iron manganese phosphate particles were subjected to ultrasonic treatment in sequence using acetone and ethanol.

8. The preparation method according to claim 6, characterized in that, The ultrasonic treatment time is 20-40 minutes.

9. The preparation method according to claim 7, characterized in that, The mass ratio of acetone and ethanol to lithium iron manganese phosphate particles is 5~10:

1.

10. The preparation method according to claim 5, characterized in that, In step S1, the rare earth source powder is a mixture of Gd powder, Ho powder, La powder, Tb powder and Y powder.

11. The preparation method according to claim 10, characterized in that, In the mixture of Gd powder, Ho powder, La powder, Tb powder and Y powder, the molar ratio of Gd powder, Ho powder, La powder, Tb powder and Y powder is 1:1:1:1:

1.

12. The preparation method according to claim 5, characterized in that, The mass ratio of the rare earth source powder to the lithium iron manganese phosphate particles is 1:50~100.

13. The preparation method according to claim 10, characterized in that, The particle size of each of the Gd powder, Ho powder, La powder, and Tb powder is 10~20 nm.

14. The preparation method according to claim 5, characterized in that, In step S1, the ball milling speed is 600~1000 r / min, the ball milling media is zirconium oxide or silicon carbide, the ball-to-material ratio is 2~5:1, and the ball milling time is 1~3 h.

15. The preparation method according to claim 5, characterized in that, In step S2, the temperature of the first vacuum hot pressing sintering is 1000~1200℃, the pressure is 30~50MPa, the vacuum degree is 1~10Pa, and the time is 3~5h.

16. The preparation method according to claim 5, characterized in that, In step S2, the quenching is carried out in liquid nitrogen.

17. The preparation method according to claim 16, characterized in that, The quenching process involves placing the sample in liquid nitrogen for 3 to 10 minutes.

18. The preparation method according to any one of claims 5 to 17, characterized in that, In step S3, the secondary vacuum hot pressing sintering temperature is 1000~1200℃, the pressure is 30~50MPa, the vacuum degree is 1~10Pa, and the time is 0.5~2h.

19. The preparation method according to any one of claims 5 to 17, characterized in that, In step S3, the cooling is natural cooling.

20. The application of the rare earth alloy-coated lithium iron manganese phosphate cathode material according to any one of claims 1 to 4 or the rare earth alloy-coated lithium iron manganese phosphate cathode material obtained by the preparation method according to any one of claims 5 to 19 in lithium-ion batteries.

21. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the rare earth alloy coated lithium iron manganese phosphate cathode material according to any one of claims 1 to 4 or the rare earth alloy coated lithium iron manganese phosphate cathode material obtained by the preparation method according to any one of claims 5 to 19.

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