A lithium-rich lithium iron phosphate positive electrode lithium supplement additive, a preparation method thereof and a lithium ion battery positive electrode

Abstract

The application discloses a lithium-rich lithium iron phosphate anode lithium supplement additive and a preparation method thereof and a lithium ion battery anode. The preparation method of the lithium-rich lithium iron phosphate anode lithium supplement additive comprises the following steps: S1, dispersing lithium-rich lithium iron phosphate particles in an organic solvent for ultrasonic cleaning to remove impurities on the surfaces of the particles; S2, spraying etching the lithium-rich lithium iron phosphate particles after the ultrasonic cleaning with an aqueous hydrofluoric acid solution, and drying after etching; S3, sintering the dried material in an inert atmosphere at high temperature to build a lithium fluoride coating layer on the surfaces of the lithium-rich lithium iron phosphate particles, so that the lithium-rich lithium iron phosphate anode lithium supplement additive is obtained. By coating lithium fluoride particles on the surfaces of the lithium-rich lithium iron phosphate material, the lithium-rich lithium iron phosphate anode lithium supplement additive is obtained, the surface structure stability is improved, the residual alkali is reduced, the surface roughness of the material is increased, the delithiation efficiency is improved, and the lithium supplement capacity exertion ability of the lithium supplement material at a high rate is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode lithium replenishment technology, and particularly to a lithium-rich lithium iron phosphate cathode lithium replenishment additive, its preparation method, and a lithium-ion battery cathode. Background Technology

[0002] Lithium replenishment technology is a method of pre-storing lithium ions in the electrode to compensate for the initial capacity loss of the battery. It effectively solves the problem of low initial coulombic efficiency and improves battery capacity and cycle stability. Lithium-rich lithium iron phosphate (LFP) has attracted increasing attention as a high-capacity cathode lithium replenishment additive. However, LFP materials are extremely unstable in air, reacting rapidly with water to form lithium hydroxide, leading to capacity reduction and excessive surface alkali residue, increasing processing difficulty. Simultaneously, LFP materials have low intrinsic ionic and electronic conductivity, and the density of ion and electron pathways at the contact interface is a key factor affecting lithium source conversion efficiency, resulting in significant polarization and making it difficult to achieve high lithium replenishment capacity to meet the demands of high-power batteries. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a lithium-rich lithium iron ferrite cathode lithium supplement additive, its preparation method, and a lithium-ion battery cathode. A lithium fluoride coating layer is constructed on the surface of lithium-rich lithium iron ferrite particles through a low-temperature hydrofluoric acid spray etching and re-sintering method, aiming to solve the problems of poor surface chemical stability, high residual alkali value, and low Li-carbon content in lithium-rich lithium iron ferrite materials. + The technical problem is low transmission efficiency, making it difficult to fully utilize the lithium replenishment capacity.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a method for preparing a lithium-rich lithium iron phosphate cathode lithium supplement additive, comprising the following steps:

[0006] S1. Disperse lithium iron phosphate particles in an organic solvent and perform ultrasonic cleaning to remove impurities from the particle surface.

[0007] S2. The ultrasonically cleaned lithium iron ferrite particles are sprayed with hydrofluoric acid aqueous solution for etching, and then dried.

[0008] S3. The dried material is sintered at high temperature in an inert atmosphere to form a lithium fluoride particle coating layer on the surface of the lithium iron phosphate particles, thereby obtaining the lithium iron phosphate cathode lithium supplementation additive.

[0009] In the above-mentioned method for preparing lithium-rich lithium iron phosphate cathode lithium supplement additive, the average particle size of the lithium-rich lithium iron phosphate particles can be 0.5-50 μm, specifically 8.5 μm; as an example, the lithium-rich lithium iron phosphate particles are prepared by the following steps: iron oxide and lithium hydroxide are uniformly mixed in a Fe to Li molar ratio of 1:5.5, the mixture is placed in a nitrogen atmosphere and sintered at 900°C for 20 h to obtain lithium-rich lithium iron phosphate particles;

[0010] The average thickness of the lithium fluoride particle coating is ≤100nm, such as 30nm;

[0011] The average particle size of the lithium fluoride particles in the lithium fluoride particle coating layer is 20-50 nm, such as 40 nm.

[0012] In the above-mentioned method for preparing lithium-rich lithium iron phosphate cathode lithium supplementation additive, the organic solvent is any one of ethanol, methanol, n-propanol and isopropanol;

[0013] The ratio of the lithium iron ferrite particles to the organic solvent can be 1g:(5-20)mL, specifically 1g:(5-10)mL, 1g:(10-20)mL, 1g:20mL, 1g:10mL or 1g:5mL;

[0014] The conditions for ultrasonic cleaning are as follows: ultrasonic power is 80-200W (e.g., 80W, 200W, 100W, 150W), ultrasonic time is 5-15min (e.g., 5min or 10min), and temperature is 10-30℃ (e.g., 10℃, 20℃ or 30℃).

[0015] The ultrasonic cleaning process includes the following steps: ultrasonic treatment of an organic dispersion of lithium iron phosphate particles, followed by centrifugation to collect the solid particles.

[0016] In the above-mentioned method for preparing lithium-rich lithium iron phosphate cathode lithium supplementation additive, the mass concentration of the hydrofluoric acid aqueous solution can be 0.5% to 5%, preferably 0.5% to 2%, specifically 0.5%, 1% or 2%;

[0017] The temperature of the spray etching can be 5 to 10°C, specifically 5°C or 10°C;

[0018] The mass ratio of the hydrofluoric acid aqueous solution to the ultrasonically cleaned lithium iron ferrite particles can be (0.1-0.2):1, specifically 0.1:1, 0.15:1, or 0.2:1.

[0019] In the above-mentioned preparation method of lithium iron phosphate cathode lithium supplement additive, the drying can be vacuum drying, the temperature can be 40-100℃, preferably 40-60℃, such as 40℃, 60℃ or 50℃, the time can be 3-6h (such as 6h, 3h or 4h), and the vacuum degree can be ≤-0.02MPa (such as -0.02MPa or -0.01MPa).

[0020] In the above-mentioned method for preparing lithium-rich lithium iron phosphate cathode lithium supplement additive, the high-temperature sintering temperature can be 500-800℃ (e.g., 600℃, 800℃ or 500℃), and the time can be 2-5h (e.g., 5h or 3h).

[0021] The inert atmosphere is argon or nitrogen.

[0022] Secondly, the present invention provides a lithium-rich lithium iron ferrite cathode lithium supplement additive prepared by any of the above-described preparation methods. The lithium-rich lithium iron ferrite cathode lithium supplement additive of the present invention has a stable surface structure, a lower residual alkali value, which is beneficial for improving processing performance, reducing slurry viscosity, and more easily exerting lithium supplementation capability.

[0023] Thirdly, the present invention provides the application of the lithium-rich lithium iron phosphate cathode lithium supplementation additive in any of the following:

[0024] A1) Increase the initial charge capacity of the battery;

[0025] A2) Increase Li + Transmission efficiency.

[0026] Fourthly, the present invention provides a lithium-ion battery cathode comprising the aforementioned lithium-rich lithium iron phosphate cathode lithium replenishment additive.

[0027] In at least one embodiment of the present invention, the lithium-ion battery cathode is composed of the lithium-rich lithium iron phosphate cathode lithium supplementation additive, carbon black and PVDF in a mass ratio of 8:1:1.

[0028] In at least one other embodiment of the present invention, the lithium-ion battery cathode is composed of a mixture of the lithium-rich lithium iron phosphate cathode lithium supplement additive and lithium iron phosphate in a mass ratio of 8:1:1, carbon black, and PVDF. For example, the lithium-rich lithium iron phosphate cathode lithium supplement additive has a mass percentage of 5% in the mixture of the lithium-rich lithium iron phosphate cathode lithium supplement additive and lithium iron phosphate.

[0029] Fifthly, the present invention provides a lithium-ion battery, comprising the aforementioned lithium-ion battery positive electrode, negative electrode, separator, and electrolyte.

[0030] In at least one embodiment of the present invention, the lithium-ion battery is a coin cell (such as a CR2032 coin cell), the negative electrode is a lithium metal sheet, the separator is a polypropylene microporous membrane, the electrolyte is a 1 mol / L LiPF6 solution, and the electrolyte solvent is EC, DMC, and EMC in a volume ratio of 1:1:1. The electrical performance is tested under the following conditions: voltage range of 2V-4.5V, and charge / discharge current of 0.05C or 0.1C.

[0031] The present invention has the following beneficial effects:

[0032] This invention employs a low-temperature hydrogen fluoride spray etching method to achieve (1) surface coating of lithium fluoride particles with the etching product lithium fluoride, thereby reducing interfacial impedance and improving the surface of lithium ferrite particles. + Transmission effect, (2) Etching can improve surface roughness, promote material-electrolyte contact, and further enhance Li + Transmission efficiency, improve capacity utilization, (3) Etching and re-sintering to form a surface coating layer, which helps to improve surface structure stability and reduce residual alkali. Attached Figure Description

[0033] Figure 1 The images are SEM spectra of Example 1(a) and Comparative Example 2(b).

[0034] Figure 2 This is a TEM image of Example 1. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; and the materials and reagents used are commercially available unless otherwise specified.

[0037] The lithium iron ferrite particles in the following examples were prepared according to the following steps: iron oxide and lithium hydroxide were uniformly mixed in a Fe to Li molar ratio of 1:5.5, and the mixture was sintered at 900°C for 20 hours under a nitrogen atmosphere to obtain lithium iron ferrite particles with an average particle size of 8.5 μm.

[0038] Example 1

[0039] The lithium fluoride / lithium-rich lithium ferrite composite material was prepared according to the following steps: 1) 10g of lithium-rich lithium ferrite particles were added to 200mL of ethanol and the surface of the particles was cleaned by ultrasonic cleaning. Specifically, the particles were ultrasonically cleaned at 10℃ with a power of 80W for 5min. After ultrasonic cleaning, the cleaned lithium-rich lithium ferrite particles were obtained by centrifugation; 2) The cleaned lithium-rich lithium ferrite was etched by low-temperature spraying with 1g of 0.5wt% hydrofluoric acid solution at 5℃. The etched material was then vacuum dried at 40℃ for 6h under a vacuum of -0.02MPa; 3) The dried lithium-rich lithium ferrite material was sintered at 600℃ for 5h in a nitrogen atmosphere to stabilize the surface structure and obtain the lithium fluoride / lithium-rich lithium ferrite composite material.

[0040] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0041] Example 2

[0042] The lithium fluoride / lithium-rich lithium ferrite composite material was prepared according to the following steps: 1) 10g of lithium-rich lithium ferrite particles were added to 100mL of methanol, and impurities on the particle surface were cleaned by ultrasonic cleaning. Specifically, the particles were ultrasonically cleaned at 200W power for 10min at 20℃. After ultrasonic cleaning, the cleaned lithium-rich lithium ferrite particles were obtained by centrifugation; 2) The cleaned lithium-rich lithium ferrite was etched by low-temperature spraying with 1.5g of 1wt% hydrofluoric acid solution at 10℃, and the etched material was vacuum dried at 60℃ for 3h under vacuum of -0.02MPa; 3) The dried lithium-rich lithium ferrite material was sintered at 800℃ for 5h in a nitrogen atmosphere to stabilize the surface structure and obtain the lithium fluoride / lithium-rich lithium ferrite composite material.

[0043] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0044] Example 3

[0045] The lithium fluoride / lithium-rich lithium ferrite composite material was prepared according to the following steps: 1) 10g of lithium-rich lithium ferrite particles were added to 50mL of n-propanol and the surface impurities of the particles were cleaned by ultrasonic cleaning. Specifically, the particles were ultrasonically cleaned at 30℃ with a power of 100W for 10min. After centrifugation, the cleaned lithium-rich lithium ferrite particles were obtained. Then, the cleaned lithium-rich lithium ferrite was subjected to low-temperature spray etching with 2g of 2wt% hydrofluoric acid solution at a temperature of 5℃. The etched material was then vacuum dried at 50℃ for 4h with a vacuum degree of -0.01MPa. 3) The dried lithium-rich lithium ferrite material was placed in a nitrogen atmosphere and sintered at 500℃ for 3h to stabilize the surface structure, thus obtaining the lithium fluoride / lithium-rich lithium ferrite composite material.

[0046] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0047] Example 4

[0048] The lithium fluoride / lithium-rich lithium ferrite composite material was prepared according to the following steps: 1) 10g of lithium-rich lithium ferrite particles were added to 100mL of isopropanol and the surface impurities of the particles were cleaned by ultrasonic cleaning. Specifically, the particles were ultrasonically cleaned at 150W power for 10min at 20℃, and then centrifuged to obtain the cleaned lithium-rich lithium ferrite particles; 2) The cleaned lithium-rich lithium ferrite was etched by low-temperature spraying with 1.0g of 1.5wt% hydrofluoric acid solution at 5℃, and the etched material was vacuum dried at 60℃ for 3h under vacuum of -0.01MPa; 3) The dried lithium-rich lithium ferrite material was sintered at 500℃ for 5h in an argon atmosphere to stabilize the surface structure and obtain the lithium fluoride / lithium-rich lithium ferrite composite material.

[0049] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0050] Example 5

[0051] The lithium fluoride / lithium-rich lithium ferrite composite material was prepared according to the following steps: 1) 10g of lithium-rich lithium ferrite particles were added to 200mL of ethanol, and impurities on the particle surface were cleaned by ultrasonic cleaning at 10℃ and 80W power for 5min. After ultrasonic cleaning, the cleaned lithium-rich lithium ferrite particles were obtained by centrifugation; 2) The cleaned lithium-rich lithium ferrite was etched by low-temperature spraying with 1g of 5wt% hydrofluoric acid solution at 5℃, and the etched material was vacuum dried at 100℃ for 6h under vacuum of -0.02MPa; Finally, the dried lithium-rich lithium ferrite material was sintered at 500℃ for 5h in a nitrogen atmosphere to stabilize the surface structure and obtain the lithium fluoride / lithium-rich lithium ferrite composite material.

[0052] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0053] Comparative Example 1

[0054] 10g of lithium iron ferrite particles were added to 200mL of ethanol and the surface of the particles was cleaned by ultrasonic cleaning at 10℃ and 80W power for 5min. The cleaned lithium iron ferrite particles were then separated by centrifugation. Subsequently, the cleaned lithium iron ferrite particles were subjected to low-temperature spray etching with 1g of 0.5wt% hydrofluoric acid solution at 5℃. The etched material was then vacuum dried at 40℃ for 6h under a vacuum of -0.02MPa.

[0055] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0056] Comparative Example 2

[0057] 10g of lithium iron ferrite particles were added to 200mL of ethanol and the surface of the particles was cleaned by ultrasonic cleaning. The particles were ultrasonically cleaned at 80W power for 5min at 10℃ and then centrifuged to obtain the cleaned lithium iron ferrite particles. Subsequently, the dried lithium iron ferrite material was placed in a nitrogen atmosphere and sintered at 600℃ for 5h to stabilize the surface structure, thus obtaining a lithium fluoride / lithium iron ferrite composite material.

[0058] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0059] Comparative Example 3

[0060] 10g of lithium-rich lithium ferrite particles were cleaned with 1g of 0.5wt% hydrofluoric acid solution and then subjected to low-temperature spray etching at 5℃. The etched material was then vacuum dried at 40℃ for 6 hours under a vacuum of -0.02MPa. Finally, the dried lithium-rich lithium ferrite material was sintered at 600℃ for 5 hours in a nitrogen atmosphere to stabilize the surface structure, thus obtaining a lithium fluoride / lithium-rich lithium ferrite composite material.

[0061] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0062] Comparative Example 4

[0063] 10g of lithium-rich lithium ferrite particles were added to 200mL of ethanol, and impurities on the particle surface were cleaned by ultrasonic cleaning at 10℃ and 80W power for 5min. After centrifugation, the cleaned lithium-rich lithium ferrite particles were obtained. Subsequently, the cleaned lithium-rich lithium ferrite was subjected to low-temperature spray etching with 1g of 0.5wt% hydrofluoric acid solution at 30℃. The etched material was then vacuum dried at 40℃ for 6h under a vacuum of -0.02MPa. Finally, the dried lithium-rich lithium ferrite material was sintered at 600℃ for 5h in a nitrogen atmosphere to stabilize the surface structure, thus obtaining a lithium fluoride / lithium-rich lithium ferrite composite material.

[0064] The prepared composite material was mixed and ground with carbon black and PVDF at a mass ratio of 8:1:1, and then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The coin cell measured a voltage range of 2V-4.5V and charge / discharge currents of 0.05C and 0.1C.

[0065] The SEM spectra of Example 1 and Comparative Example 2 are shown below. Figure 1 The TEM image of Example 1 is shown below. Figure 2 ,Depend on Figure 1 It can be seen that the surface roughness of Example 1 increased significantly after etching, while the particle surface of Comparative Example 2 was relatively smooth. The surface of Example 1 was densely packed with LiF small particles with a particle size of about 40 nm and a coating thickness of about 30 nm.

[0066] The physicochemical and electrical properties of the positive electrode lithium replenishment materials prepared in Experimental Examples 1-5 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1:

[0067] The testing method is as follows:

[0068] Electrical performance characterization: Same as above.

[0069] LiOH Residual Alkali Test Method: Accurately weigh 0.3g of sample into a clean, dry 100ml gas washing bottle. Add 100ml of diluted ethanol to the gas washing bottle and stir for 5min. After stirring, vacuum filter and collect the filtrate into a 100ml volumetric flask. Transfer 40ml of the filtrate to a titration cup; titrate with 0.01M HCl standard solution to obtain the titration curve, and record the volume V1 of hydrochloric acid standard solution consumed during this process. Simultaneously, analyze the method blank, and the endpoint hydrochloric acid consumption volume V0. LiOH content = 23.94 × 0.01 × (V1 - V0) / 120.

[0070] Table 1. Surface LiOH content and initial charge capacity of comparative examples and embodiments.

[0071]

[0072] As can be seen from Table 1, compared with Comparative Examples 1-4, the initial charge capacity at 0.05C of Example 5 is slightly lower, but the capacity at 0.1C decreases significantly. This indicates that when the etchant concentration is higher than the preferred value, it will cause excessive damage to the surface structure, thereby reducing the capacity of Li at high magnification. + The transport process affects capacity utilization. Compared with Comparative Examples 1-4, Examples 1-5 showed significantly lower residual LiOH content and higher capacity. This indicates that surface cleaning, low-concentration low-temperature etching, and subsequent high-temperature sintering play a crucial role in the material's structural stability and capacity utilization.

[0073] The positive electrode lithium-replenishing additives from Examples 1-5 and Comparative Examples 1-4 were mixed with lithium iron phosphate positive electrode materials at a mass ratio of 5:95. The mixture was then mixed with carbon black and PVDF at a mass ratio of 8:1:1 and ground. This mixture was then coated onto aluminum foil to serve as the positive electrode for lithium-ion batteries. CR2032 coin cells were assembled in an argon-filled glove box to further evaluate the lithium-replenishing effect of the positive electrode lithium-replenishing material. 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 ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The measured voltage range of the coin cells was 2V-4.5V, and the charge / discharge current was 0.05C. The test results are shown in Table 2.

[0074] Table 2. Initial Charge Capacity of 5% Lithium Supplement Material + Lithium Iron Phosphate

[0075] Example 1 173.7mAh / g Example 2 172.0mAh / g Example 3 172.9mAh / g Example 4 171.5mAh / g Example 5 170.1mAh / g Comparative Example 1 166.3mAh / g Comparative Example 2 167.8mAh / g Comparative Example 3 168.6mAh / g Comparative Example 4 167.2mAh / g

[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-rich lithium iron phosphate cathode lithium supplement additive, comprising the following steps: S1. Disperse lithium iron phosphate particles in an organic solvent and perform ultrasonic cleaning to remove impurities from the particle surface. S2. The ultrasonically cleaned lithium iron ferrite particles are sprayed with hydrofluoric acid aqueous solution for etching, and then dried. The mass concentration of the hydrofluoric acid aqueous solution is 0.5%~5%; The temperature of the spray etching is 5~10℃; S3. The dried material is sintered at high temperature in an inert atmosphere to form a lithium fluoride particle coating layer on the surface of the lithium iron phosphate particles, thereby obtaining the lithium iron phosphate cathode lithium supplementation additive.

2. The preparation method of the lithium-rich lithium iron phosphate cathode lithium supplement additive according to claim 1, characterized in that: The average particle size of the lithium iron phosphate particles is 0.5~50μm; The average thickness of the lithium fluoride particle coating layer is ≤100 nm; The average particle size of the lithium fluoride particles in the lithium fluoride particle coating layer is 20~50nm.

3. The method for preparing the lithium-rich lithium iron phosphate cathode lithium supplement additive according to claim 1 or 2, characterized in that: The organic solvent is any one of ethanol, methanol, n-propanol, and isopropanol; The ratio of the lithium iron ferrite particles to the organic solvent is 1g:(5~20)mL; The conditions for ultrasonic cleaning are as follows: ultrasonic power is 80~200W, ultrasonic time is 5~15min, and temperature is 10~30℃.

4. The preparation method of the lithium-rich lithium iron phosphate cathode lithium supplement additive according to claim 1 or 2, characterized in that: The mass ratio of the hydrofluoric acid aqueous solution to the ultrasonically cleaned lithium iron ferrite particles is (0.1~0.2):

1.

5. The method for preparing the lithium-rich lithium iron phosphate cathode lithium supplement additive according to claim 1 or 2, characterized in that: The drying process is vacuum drying, with a temperature of 40~100℃, a time of 3~6h, and a vacuum degree of ≤-0.02MPa.

6. The method for preparing the lithium-rich lithium iron phosphate cathode lithium supplement additive according to claim 1 or 2, characterized in that: The high-temperature sintering temperature is 500~800℃, and the time is 2~5h; The inert atmosphere is argon or nitrogen.

7. The lithium-rich lithium iron phosphate cathode lithium supplement additive prepared by the preparation method according to any one of claims 1-6.

8. The use of the lithium-rich lithium iron phosphate cathode lithium supplementation additive according to claim 7 in any of the following: A1) Increase the initial charge capacity of the battery; A2) Increase Li + Transmission efficiency.

9. A lithium-ion battery positive electrode, characterized in that, It includes the lithium-rich lithium iron phosphate cathode lithium supplementation additive as described in claim 7.

10. A lithium-ion battery, characterized in that, It includes the positive electrode, negative electrode, separator, and electrolyte of the lithium-ion battery as described in claim 9.

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