Preparation method of aluminum oxide coated lithium-rich lithium ferrite and lithium ion battery

Abstract

The invention discloses a preparation method of aluminum oxide coated lithium-rich lithium ferrite and a lithium ion battery, and the method comprises the following steps: dissolving a soluble aluminum salt in a first organic solvent to form an aluminum salt solution; dispersing the lithium-rich lithium ferrite and an alkaline compound in a second organic solvent to form a mixture; stirring the mixture, heating the mixture to a reflux temperature, dropwise adding the aluminum salt solution into the mixture, and carrying out a reaction, so that the aluminum element is precipitated in situ in the form of aluminum hydroxide and coats the surfaces of the lithium-rich lithium ferrite particles to obtain a mixed dispersion liquid; carrying out solid-liquid separation on the mixed dispersion liquid to obtain a coated precursor; the precursor is subjected to heat treatment in an inert or reducing atmosphere, so that the precursor is converted into aluminum oxide, the aluminum oxide coated lithium-rich lithium ferrite is obtained, the coated aluminum oxide coating layer is more uniform and can better resist moisture in air, and the excellent lithium supplementing characteristic is played in the electrochemical lithium supplementing process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a method for preparing alumina-coated lithium iron phosphate and a lithium-ion battery thereof. Background Technology

[0002] The SEI film (solid electrolyte interface film) is a passivation layer formed on the negative electrode surface by the electrolyte through an electrochemical reduction reaction during the first charge and discharge process of a lithium-ion battery. It allows lithium ions to pass through but blocks electron conduction, and is a key factor in ensuring the battery's long cycle life. However, the formation of the SEI film also consumes active lithium ions in the positive electrode material, reducing the number of lithium ions that can be intercalated or deintercalated, thus lowering the capacity retention rate of the lithium-ion battery during cycles. Therefore, it is necessary to replenish lithium ions to compensate for this loss.

[0003] Cathode lithium replenishment technology is simple, safe, and controllable, requiring no additions or alterations to the battery manufacturing process. Simply adding a certain proportion of lithium replenishing agent during the cathode homogenization process can improve the performance of the prepared lithium-ion battery. In the field of cathode lithium replenishing agents, lithium-rich lithium iron phosphate (Li5FeO4) materials possess extremely high lithium replenishment capacity and exhibit good compatibility with existing lithium iron phosphate and ternary cathode materials, effectively enhancing their long-cycle performance. However, lithium-rich lithium iron phosphate has poor structural stability and is highly susceptible to decomposition in humid air, thus reducing lithium-ion replenishment. To address the air tolerance issue of lithium iron ferrite (LFI), the current mainstream coating method involves coating the surface of LFI with a carbon layer or a metal oxide layer followed by a carbon layer. While the carbon coating provides some resistance to moisture in the air and increases the conductivity of LFI, traditional carbon coating methods fail to fully realize the actual lithium replenishment effect and exhibit limited air tolerance. Coating with a metal oxide layer followed by a carbon layer further enhances the air tolerance of LFI as a lithium replenisher. However, solid-phase coating of metal oxides is generally ineffective, failing to uniformly coat the LFI material. Furthermore, LFI decomposes upon contact with water, making aqueous liquid-phase coating of metal oxides impractical. Therefore, a novel metal oxide coating method is needed to improve the air tolerance of LFI when using it as a lithium replenisher. Summary of the Invention

[0004] One object of the present invention is to provide a method for preparing lithium iron ferrite coated with alumina and a lithium-ion battery, so as to solve the technical problems in the background art mentioned above.

[0005] A method for preparing alumina-coated lithium iron ferrite includes the following steps: A soluble aluminum salt is dissolved in a first organic solvent to form an aluminum salt solution; Lithium-rich lithium iron ferrite and an alkaline compound are dispersed in a second organic solvent to form a mixture; The mixture is stirred and heated to reflux temperature, and the aluminum salt solution is added dropwise to react, so that the aluminum element precipitates in situ in the form of aluminum hydroxide and coats the surface of lithium iron ferrite particles to obtain a mixed dispersion. The mixed dispersion was subjected to solid-liquid separation to obtain the coated precursor; The precursor is heat-treated in an inert or reducing atmosphere to convert it into alumina, resulting in alumina-coated lithium iron ferrite.

[0006] Compared with existing technologies, the beneficial effects of this invention are as follows: the alumina-coated lithium iron ferrite obtained is produced by synthesizing an aluminum hydroxide coating layer on the surface of lithium iron ferrite through reflux heating, and then converting it into an alumina coating layer through heating and calcination. Compared with the traditional solid-phase method, which directly mixes metal compounds and then calcines for coating, the alumina coating layer produced by this method is more uniform, can better resist moisture in the air, and exhibits excellent lithium replenishment characteristics during the electrochemical lithium replenishment process.

[0007] Furthermore, the first organic solvent and the second organic solvent are independently selected from at least one of alcohols, ketones or nitrile solvents.

[0008] Furthermore, the molar ratio of the alkaline compound to the soluble aluminum salt is from 0.5:1 to 3.5:1.

[0009] Furthermore, based on the mass of the lithium iron ferrite, the amount of soluble aluminum salt added is from 1 wt% to 20 wt%.

[0010] Furthermore, the reflux temperature is 50°C to 100°C; after the aluminum salt solution is added, the reflux reaction continues for 1 hour to 20 hours.

[0011] Furthermore, the heat treatment temperature is 400°C to 900°C, and the heat treatment time is 1 hour to 20 hours.

[0012] Furthermore, the solid-liquid separation method includes, but is not limited to, filtration, vacuum drying, and evaporation under an inert atmosphere.

[0013] Furthermore, the soluble aluminum salt is aluminum nitrate; the alkaline compound is lithium hydroxide.

[0014] In addition, the present invention also provides alumina-coated lithium ferrite prepared by the method described above.

[0015] In addition, the present invention also provides a lithium-ion battery obtained by coating lithium iron ferrite with alumina as described above.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the preparation method of alumina-coated lithium iron ferrite provided in Example 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the alumina-coated lithium iron ferrite material prepared in Example 1 of the present invention. Figure 3 The X-ray diffraction (XRD) spectra of the materials prepared in Example 1 and Comparative Example 1 of this invention after exposure to air are compared. Figure 4 The graph shows a comparison of the first-charge performance of a lithium battery assembled using the materials of Example 1 of the present invention and a lithium battery assembled using the materials of Comparative Example 1 at a rate of 0.066C. Figure 5 The graph shows the first charging performance of a lithium battery assembled using the materials of Example 2 of this invention at a rate of 0.066C. Detailed Implementation

[0019] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below with reference to examples. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0020] The present invention provides a method for preparing alumina-coated lithium iron ferrite, comprising the following steps: A soluble aluminum salt is dissolved in a first organic solvent to form an aluminum salt solution; Lithium-rich lithium iron ferrite and an alkaline compound are dispersed in a second organic solvent to form a mixture; The mixture is stirred and heated to reflux temperature, and the aluminum salt solution is added dropwise to react, so that the aluminum element precipitates in situ in the form of aluminum hydroxide and coats the surface of lithium iron ferrite particles to obtain a mixed dispersion. The mixed dispersion was subjected to solid-liquid separation to obtain the coated precursor; The precursor is heat-treated in an inert or reducing atmosphere to convert it into alumina, resulting in alumina-coated lithium iron ferrite.

[0021] The first organic solvent and the second organic solvent are independently selected from at least one of alcohols, ketones or nitrile solvents.

[0022] The molar ratio of the alkaline compound to the soluble aluminum salt is 0.5:1 to 3.5:1.

[0023] The amount of soluble aluminum salt added is 1 wt% to 20 wt%, based on the mass of the lithium iron ferrite.

[0024] The reflux temperature is 50°C to 100°C; after the aluminum salt solution is added, the reflux reaction continues for 1 hour to 20 hours.

[0025] The heat treatment temperature is 400°C to 900°C, and the heat treatment time is 1 hour to 20 hours.

[0026] The solid-liquid separation methods include, but are not limited to, filtration, vacuum drying, and evaporation under an inert atmosphere.

[0027] The soluble aluminum salt is aluminum nitrate; the alkaline compound is lithium hydroxide.

[0028] One of them is prepared by the method described above for alumina-coated lithium iron ferrite.

[0029] One type of lithium-ion battery includes lithium iron ferrite coated with alumina.

[0030] It is worth noting that the present invention synthesizes aluminum hydroxide on the surface of lithium-rich lithium ferrite by means of reflux heating reaction, and then forms an aluminum oxide coating layer on the surface of lithium-rich lithium ferrite by heating and calcination.

[0031] The resulting alumina-coated lithium iron ferrite was synthesized by reflux heating to form an aluminum hydroxide coating layer on the surface of lithium iron ferrite, which was then converted into an alumina coating layer by calcination. Compared with the traditional solid-phase method, which involves directly mixing metal compounds and then calcining for coating, the alumina coating layer produced by this method is more uniform, can better resist moisture in the air, and exhibits excellent lithium replenishment characteristics during electrochemical lithium replenishment.

[0032] The embodiments of the present invention will be further described below with reference to several examples. The embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of unchanged main claims.

[0033] Example 1 In the first embodiment of the present invention, as Figures 1 to 4 As shown, a method for preparing alumina-coated lithium iron ferrite includes the following steps S01-S05: S01, dissolve the soluble aluminum salt in the first organic solvent to form an aluminum salt solution; In this embodiment, 3.15g of anhydrous aluminum nitrate was dissolved in 100mL of anhydrous ethanol and stirred to form a homogeneous aluminum nitrate ethanol solution.

[0034] SO2 disperses lithium iron ferrite and an alkaline compound in a second organic solvent to form a mixture; In this embodiment, 100g of lithium iron ferrite (Li5FeO4) powder and 1.05g of lithium hydroxide were weighed and added to a three-necked flask containing 100mL of anhydrous ethanol. The mixture was heated to 75°C and kept under reflux with continuous stirring.

[0035] S03, the mixture is stirred and heated to reflux temperature, and the aluminum salt solution is added dropwise to react, so that the aluminum element precipitates in situ in the form of aluminum hydroxide and coats the surface of lithium iron ferrite particles to obtain a mixed dispersion. In this embodiment, the aluminum nitrate ethanol solution was slowly and uniformly added dropwise to the refluxed mixture at a rate of 1 mL / min using a peristaltic pump. After the addition was complete, the mixture was refluxed at 75°C for 2 hours.

[0036] S04, the mixed dispersion is subjected to solid-liquid separation to obtain the coated precursor; In this embodiment, after the reaction was completed, heating was stopped, and the mixed dispersion was cooled to room temperature. The solid was then separated by filtration and washed twice with a small amount of anhydrous ethanol. The resulting solid was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain an aluminum hydroxide-coated lithium iron ferrite precursor.

[0037] S05, the precursor is heat-treated in an inert or reducing atmosphere to convert it into alumina, thereby obtaining alumina-coated lithium iron ferrite.

[0038] In this embodiment, the precursor was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under an argon protective atmosphere, and then calcined at this temperature for 10 hours. After calcination, it was naturally cooled to room temperature, the product was removed, and after grinding, alumina-coated lithium iron ferrite material A1 was obtained.

[0039] Calculations show that the molar ratio of lithium hydroxide to aluminum nitrate in this embodiment is approximately 2.96:1. Based on the mass of lithium-rich lithium ferrite, the amount of aluminum nitrate added is 6.3 wt%, and the theoretical coating amount of the resulting alumina is approximately 0.75% of the mass of lithium-rich lithium ferrite.

[0040] like Figure 2 As shown, the alumina-coated lithium iron ferrite material has a particle size in the micrometer range. The obtained alumina-coated lithium iron ferrite material was exposed to air with a dew point of -20°C for 2 hours, and then subjected to XRD testing. Figure 3 As shown, from Figure 3 As can be seen, after being placed in air for 2 hours, the alumina-coated lithium iron ferrite material did not show obvious impurity peaks, indicating good air resistance.

[0041] Example 2 In a second embodiment of the present invention, a method for preparing alumina-coated lithium iron ferrite includes the following steps: Dissolve 3.15g of anhydrous aluminum nitrate in 100mL of anhydrous ethanol to form an aluminum nitrate ethanol solution.

[0042] Weigh 100g of lithium iron ferrite powder and 0.93g of lithium hydroxide, and add them to a three-necked flask containing 100mL of anhydrous ethanol. Heat to 70°C with stirring and maintain reflux.

[0043] Aluminum nitrate ethanol solution was added dropwise to the reflux system at a rate of 0.5 mL / min using a peristaltic pump. After the addition was complete, the system was refluxed at 70°C for 3 hours.

[0044] The subsequent cooling, filtration, washing, and vacuum drying steps were the same as in Example 1. The dried precursor was calcined at 800°C for 10 hours under an argon atmosphere, cooled, and then ground to obtain alumina-coated lithium iron ferrite material A2.

[0045] In this embodiment, the molar ratio of lithium hydroxide to aluminum nitrate is approximately 2.68:1, and the amount of aluminum nitrate added is 6.3 wt%.

[0046] Example 3 In a third embodiment of the present invention, a method for preparing alumina-coated lithium iron ferrite includes the following steps: Dissolve 3.15g of anhydrous aluminum nitrate in 100mL of acetone to form an aluminum nitrate acetone solution.

[0047] Weigh 100g of lithium iron ferrite powder and 1.05g of lithium hydroxide, and add them to a three-necked flask containing 100mL of acetone. Heat to 55°C with stirring and maintain reflux.

[0048] Aluminum nitrate acetone solution was added dropwise to the reflux system at a rate of 2 mL / min using a peristaltic pump. After the addition was complete, the system was refluxed at 55°C for 2 hours.

[0049] The subsequent cooling, filtration, washing, and vacuum drying steps were the same as in Example 1. The dried precursor was calcined at 750°C for 10 hours under an argon atmosphere, cooled, and then ground to obtain alumina-coated lithium iron ferrite material A3.

[0050] In this embodiment, the molar ratio of lithium hydroxide to aluminum nitrate is approximately 2.96:1, and the amount of aluminum nitrate added is 6.3 wt%. Example 4 In a fourth embodiment of the present invention, a method for preparing alumina-coated lithium iron ferrite includes the following steps: Take 10.0g of the alumina-coated lithium iron ferrite material A1 prepared in Example 1, and grind and mix it thoroughly with 1.0g of polypropylene powder in a mortar (mass ratio 10:1).

[0051] The mixture was placed in a tube furnace and heated to 550°C at a rate of 5°C / min under an argon atmosphere. It was then kept at this temperature for 5 hours to carbonize the polypropylene and form a carbon coating layer. After natural cooling, a carbon-alumina double-layer coated lithium iron ferrite composite material C1 was obtained.

[0052] The composite material C1 was used as the positive electrode lithium supplement / active material, and was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder at a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was ground to form a uniform paste.

[0053] The slurry was evenly coated onto the aluminum foil current collector and vacuum dried at 120°C for 12 hours. After drying, it was cut into circular electrodes with a diameter of 12 mm.

[0054] A CR2032 type coin cell lithium battery, denoted as battery B1, was assembled in an argon-filled glove box (H2O and O2 contents both below 0.1 ppm) using a lithium metal sheet as the counter electrode, a polyethylene microporous membrane as the separator, and a mixed solution of 1M LiClO4 DME (dimethoxyethane) and PC (propylene carbonate) (volume ratio 1:1) as the electrolyte.

[0055] Example 5 In a fifth embodiment of the present invention, a method for preparing alumina-coated lithium iron ferrite includes the following steps: 10.0g of the alumina-coated lithium iron phosphate material A2 prepared in Example 2 was used as raw material. The remaining carbon coating steps, electrode preparation and battery assembly steps were exactly the same as in Example 4. The resulting coin cell lithium battery was designated as battery B2.

[0056] Comparative Example 1 Weigh 93.46g of lithium peroxide (Li2O2) and 64.52g of ferric oxide (Fe2O3) powder, place them in a ball mill jar, and ball mill them at 400 r / min for 2 hours to ensure they are fully mixed.

[0057] The mixed powder was placed in an alumina crucible and heated to 700°C at a rate of 5°C / min in a tube furnace under an argon atmosphere, and then calcined at that temperature for 10 hours. After natural cooling, it was removed, ground, and pulverized to obtain lithium iron ferrite (Li5FeO4) matrix powder.

[0058] Weigh 100g of the above matrix powder and 1.15g of aluminum hydroxide (Al(OH)3) powder, and manually grind and mix them in a mortar for 30 minutes to achieve initial mixing.

[0059] The mixture was calcined again at 700°C for 10 hours under an argon atmosphere to form an alumina coating layer through a solid-phase reaction, thus obtaining solid-phase coated lithium iron ferrite material D1.

[0060] Take material D1 and perform carbon coating, electrode preparation and battery assembly according to the same steps as in Example 4. The resulting battery is denoted as battery DB1.

[0061] like Figure 3 As shown, from Figure 3 As can be seen, impurity peaks appeared at positions 2θ=30.54° and 31.7°, indicating that the material decomposed after being placed in air for 2 hours. The lithium iron ferrite material coated with solid-phase alumina was used as the raw material, and the rest were selected in the same way as in Example 4. The carbon-coated material was assembled into a lithium battery in a glove box filled with argon gas.

[0062] The electrochemical performance of the lithium batteries in Example 4 and Comparative Example 1 was tested, and the results are as follows: Figure 4 As shown.

[0063] Figure 4 The graph shows the charging performance of lithium batteries prepared from lithium-rich lithium iron ferrite obtained in Example 1 and lithium-rich lithium iron ferrite in Comparative Example 1 at a rate of 0.066C. Figure 4 As shown, the lithium battery prepared by lithium iron ferrite in Example 1 has a specific charging capacity of 734 mAh / g at a rate of 0.066C and below 4.25V. The lithium battery prepared by lithium iron ferrite in Comparative Example 1 has a specific charging capacity of 743 mAh / g at a rate of 0.066C and below 4.25V. From the specific capacity, it can be seen that the materials after carbon coating can perform well in terms of lithium replenishment performance of lithium iron ferrite. The lithium iron ferrite coated by the reflux heating method with alumina did not cause a decrease in lithium replenishment performance and can perform the same lithium replenishment performance as the lithium iron ferrite coated by the solid phase method with alumina.

[0064] Figure 5 The graph shows the charging performance of the lithium battery prepared from lithium-rich lithium iron phosphate obtained in Example 2 at a rate of 0.066C. Figure 5 As shown, at a rate of 0.066C, the charging specific capacity below 4.25V reaches 738mAh / g.

[0065] In summary, compared with lithium ferrite materials coated only by solid-phase alumina, lithium ferrite materials coated by reflux heating alumina prepared by the method of this invention have a more uniform metal oxide coating layer, better air resistance, and are less prone to decomposition in air.

[0066] To verify the effectiveness of the material of this invention, a series of morphology, structure and electrochemical performance tests were conducted.

[0067] 1. Morphological and structural characterization: The material A1 obtained in Example 1 was tested by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown in the image, a uniform and dense coating layer is formed on the surface of the material particles, with the particles having a micron-sized structure, confirming that the reflow heating method of this invention can achieve excellent surface coating effects.

[0068] 2. Air stability test (XRD analysis): Material A1 obtained in Example 1 and material D1 obtained in Comparative Example 1 were simultaneously exposed to air with a dew point of -20°C for 2 hours, followed by X-ray diffraction (XRD) testing. The results are as follows: Figure 3 As shown. The XRD pattern of material A1 in Example 1 was basically consistent before and after exposure, with no obvious new impurity peaks, indicating that its crystal structure was stable and had good air resistance. However, material D1 in Comparative Example 1 showed obvious impurity peaks at diffraction angles of approximately 30.54° and 31.7°, indicating that it had decomposed, proving that the protective effect of the coating layer formed by the traditional solid-phase mixing method was limited.

[0069] 3. Electrochemical lithium replenishment performance test: The batteries B1 and B2 assembled in Examples 4 and 5, and the battery DB1 assembled in Comparative Example 1, were subjected to an initial charge test at a rate of 0.066C (1C is calculated as 700 mA / g) (voltage range: 2.0-4.25V). The results are as follows: Figure 4 and Figure 5 As shown.

[0070] The specific charge capacity of battery B1 (corresponding to material A1 in Example 1) is 734 mAh / g.

[0071] The specific charge capacity of battery B2 (corresponding to material A2 in Example 2) is 738 mAh / g.

[0072] The specific charge capacity of battery DB1 (corresponding to solid-state material D1) is 743 mAh / g.

[0073] 4. Data Summary and Analysis: To more completely and clearly demonstrate the technical solution and advantages of the present invention, the key information of all embodiments and comparative examples is summarized in the table below: Table 1: Comparison of preparation parameters and performance between each embodiment and comparative example

[0074] Based on the above comparison, a clear conclusion can be drawn: Excellent lithium replenishment performance: As shown in Table 1, the materials coated with alumina using the reflow heating method of this invention (Examples 1 and 2, and the batteries B1 and B2 prepared therefrom) exhibit the same excellent initial charge specific capacity (734-738 mAh / g) as the materials coated using the traditional solid-phase mixing method (Comparative Example 1, 743 mAh / g). Example 3, as an example of process parameter adjustment, can also be presumed to have performance within this high-level range. This indicates that the innovative coating process of this invention fully retains the high lithium replenishment capability of the lithium iron phosphate core, and has a wide process window and good reproducibility.

[0075] Significantly improved air stability: As shown in Table 1, the material prepared by the method of this invention (Example 1) did not decompose under harsh conditions, while the solid-state material (Comparative Example 1) decomposed significantly. Combined with the uniform coating morphology shown by SEM characterization, this strongly demonstrates that the uniform and dense alumina coating layer achieved by the present invention through "non-aqueous solvent reflux heating" can significantly and effectively improve the environmental stability of lithium-rich lithium iron ferrite, solving a key problem in its storage and application as a lithium replenishing agent.

[0076] Overall technical advantages: The "alumina reflux heating coating" technology described in this invention successfully achieves a balance and synergy between high lithium replenishment performance and high environmental stability in lithium-rich lithium iron phosphate lithium replenishers. Examples 4 and 5 demonstrate that this material is easily subjected to subsequent carbon coating treatment and can exhibit excellent lithium replenishment effects in full cells. This method offers controllable processes, providing crucial material support for the preparation of high-performance, long-life lithium-ion batteries.

[0077] This invention achieves uniform, in-situ precipitation and coating of aluminum hydroxide on the surface of lithium-rich lithium ferrite using a specific process of "non-aqueous solvent reflux heating," forming an alumina protective layer after calcination. This method effectively avoids the problem of lithium-rich lithium ferrite decomposition upon contact with water and overcomes the defect of uneven coating in solid-phase methods. The prepared material, as a positive electrode lithium replenishment agent, successfully balances high lithium replenishment capacity and excellent environmental stability, possessing significant industrial application value.

[0078] In summary, this application has the following beneficial effects: By using a non-aqueous organic solvent (such as ethanol) system for reflux reaction, the problem of lithium iron ferrite decomposition upon contact with water is completely avoided, and the fundamental technical obstacle that prevents it from being uniformly coated using the traditional aqueous liquid phase method is solved.

[0079] By using reflux heating and controlled dropwise addition, aluminum source (aluminum nitrate) is slowly and uniformly precipitated in situ into aluminum hydroxide in an alkaline environment, directly forming a complete precursor coating layer on the surface of lithium iron ferrite particles. Compared with the solid-phase physical mixing method mentioned in the background art of claim 1 (corresponding to example 1), the method of the present invention avoids the problems of uneven mixing between particles and incomplete coating caused by heterogeneous nucleation at high temperature, and can obtain a coating layer with uniform thickness and strong bonding.

[0080] The present invention also provides alumina-coated lithium ferrite prepared by the method described above.

[0081] The present invention also provides a lithium-ion battery obtained by coating lithium iron ferrite with alumina as described above.

[0082] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing alumina-coated lithium iron ferrite, characterized in that, Includes the following steps: A soluble aluminum salt is dissolved in a first organic solvent to form an aluminum salt solution; Lithium-rich lithium iron ferrite and an alkaline compound are dispersed in a second organic solvent to form a mixture; The mixture is stirred and heated to reflux temperature, and the aluminum salt solution is added dropwise to react, so that the aluminum element precipitates in situ in the form of aluminum hydroxide and coats the surface of lithium iron ferrite particles to obtain a mixed dispersion. The mixed dispersion was subjected to solid-liquid separation to obtain the coated precursor; The precursor is heat-treated in an inert or reducing atmosphere to convert it into alumina, resulting in alumina-coated lithium iron ferrite.

2. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, The first organic solvent and the second organic solvent are independently selected from at least one of alcohols, ketones or nitrile solvents.

3. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, The molar ratio of the alkaline compound to the soluble aluminum salt is from 0.5:1 to 3.5:

1.

4. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, Based on the mass of the lithium iron ferrite, the amount of soluble aluminum salt added is from 1 wt% to 20 wt%.

5. The method for preparing alumina-coated lithium iron ferrite according to claim 2, characterized in that, The reflux temperature is 50°C to 100°C; after the aluminum salt solution is added, the reflux reaction continues for 1 hour to 20 hours.

6. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, The heat treatment temperature is 400°C to 900°C, and the heat treatment time is 1 hour to 20 hours.

7. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, The solid-liquid separation methods include, but are not limited to, filtration, vacuum drying, and evaporation under an inert atmosphere.

8. The method for preparing alumina-coated lithium iron ferrite according to claim 1, characterized in that, The soluble aluminum salt is aluminum nitrate; the alkaline compound is lithium hydroxide.

9. An alumina-coated lithium iron ferrite, characterized in that, It is prepared by any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, It includes the alumina-coated lithium iron ferrite as described in claim 9.

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