Preparation method and application of high-rate-performance conversion type metal fluoride positive electrode material

Abstract

The invention discloses a preparation method and application of a high-rate-performance conversion type metal fluoride positive electrode material, and belongs to the technical field of high-specific-energy secondary batteries. The metal fluoride, Super P and lithium carbonate generate trace oxyfluoride in situ in the ball milling process, the electrochemical reaction path of the metal fluoride is uniquely changed, and the activation energy of the conversion reaction is greatly reduced. The core bottleneck problem of slow reaction kinetics of the traditional conversion type metal fluoride positive electrode material is effectively solved. Due to optimization of reaction kinetics, the composite material prepared by the method shows extremely excellent rate capability. The ball milling method disclosed by the invention is simple in process, does not need complicated subsequent treatment, is easy to amplify production, and provides a brand new technical route for application of the conversion type metal fluoride positive electrode material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high specific energy secondary batteries, in particular to a preparation method of a high-rate performance conversion type metal fluoride positive electrode material and application thereof. BACKGROUND

[0002] The development prospect of the new energy automobile industry is good, and the market has gradually entered a stage of high-quality rapid development. The heart of the new energy industry, lithium batteries, has also entered a fast development track.

[0003] At present, a commercial lithium ion battery adopts an intercalation type positive electrode material. Traditional intercalation type positive electrode materials are divided into lithium cobaltate, lithium manganate and lithium iron phosphate according to different crystal structures. The capacity of the intercalation type positive electrode material is close to the theoretical capacity in actual use, and it is difficult to further improve, so we need to seek new positive electrode materials with higher capacity. Conversion type positive electrodes have a multi-electron reaction energy storage advantage relative to traditional intercalation type positive electrodes, and have been widely concerned. Fluorides such as iron fluoride (FeF3) and ferrous fluoride (FeF2) are considered to be potential positive electrode materials for lithium batteries due to their extremely high energy density and low cost.

[0004] However, the conversion type positive electrode metal fluoride material has problems such as poor electrical conductivity, slow reaction kinetics and large volume change during the cycle process, which seriously limits its application under high-rate charging and discharging conditions. High-rate charging and discharging means that the battery can complete the charging or discharging process in a shorter time, which is of great significance for the popularization and application of new energy vehicles.

[0005] The core methods for improving the rate performance of the conversion type positive electrode metal fluoride include nanocrystallization to shorten the ion diffusion path, carbon material compounding to build a conductive network, element doping to optimize the crystal structure, and development of a suitable electrolyte to stabilize the interface. However, these strategies all face significant challenges. Nanocrystallization leads to a significant reduction in tap density and volume energy density, carbon coating improves electrical conductivity but sacrifices mass energy density, the mechanism and uniformity of element doping are difficult to control, and electrolyte optimization is limited by cost, safety and full battery adaptability. Ultimately, these methods have universal difficulties in process scaling, side reaction suppression and energy density trade-off, which restrict their practical application. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of a high-rate performance conversion type metal fluoride positive electrode material and application thereof to solve the problems raised in the background art.

[0007] To achieve the above purpose, the present application provides the following technical solution: a preparation method of a high-rate performance conversion type metal fluoride positive electrode material, comprising the following steps:

[0008] (1) Under an argon atmosphere with water and oxygen levels below 0.1 ppm, metal fluoride and conductive carbon black were ground and mixed evenly in an agate mortar according to a mass ratio to obtain a mixture;

[0009] (2) a. In an argon atmosphere with water and oxygen levels below 0.1 ppm, add the grinding beads and the mixture from step (1) to the grinding jar in a mass ratio. The high-energy grinding time is 25-35 min. After that, stop the operation, cool for more than 10 min, and then run the high-energy grinding mill again. Repeat this step. The total high-energy grinding time reaches 1-3 h to obtain a mixture. Use a clean spatula to slowly scrape the mixture along the inner wall of the grinding jar. Then add a certain mass ratio of lithium carbonate and grinding beads to the grinding jar and place it in a planetary grinding mill for grinding and mixing. Use a clean spatula to slowly scrape the mixture along the inner wall of the grinding jar to obtain a high-rate conversion type metal fluoride cathode material.

[0010] (2) b. In an argon atmosphere with water and oxygen levels below 0.1 ppm, add the grinding beads, lithium carbonate and the mixture from step (1) to the grinding jar in the mass ratio. The high-energy grinding time is 25-35 min. After that, stop the operation, cool for more than 10 min, and then run the high-energy grinding mill again. Repeat this step. The total high-energy grinding time reaches 1-3 h. Obtain the mixture. Use a clean spatula to slowly scrape the mixture along the inner wall of the grinding jar to obtain the high-rate conversion type metal fluoride cathode material.

[0011] Furthermore, in step (1), the conversion-type positive electrode metal fluoride is one of iron fluoride (FeF3), ferrous fluoride (FeF2), bismuth fluoride (BiF3), and copper fluoride (CuF2);

[0012] Furthermore, in step (1), the conductive carbon black is one or more of reduced graphene oxide, Super P, acetylene black, and Ketjen black;

[0013] Furthermore, in step (1), the mass ratio of the conversion-type positive electrode metal fluoride to the conductive carbon black is 7~9:1~2;

[0014] Furthermore, in step (2), either a or b can be chosen;

[0015] Furthermore, in step (2), the conductive carbon black is one or more of reduced graphene oxide, Super P, acetylene black, and Ketjen black;

[0016] Furthermore, in step (2), the mass ratio of the conversion-type positive electrode metal fluoride, conductive carbon black, and lithium carbonate is 7~9:1~2:0.5~3;

[0017] Furthermore, in step (2), the high-energy grinding jar is made of zirconium oxide, the high-energy grinding beads are made of zirconium oxide, the diameter of the high-energy grinding beads is 5~10 mm, and the high-energy grinding ball-to-material ratio is (20~40):1;

[0018] Furthermore, in step (2), the planetary ball milling speed is 200~600 rpm, the milling time is 2~8 h, the planetary ball milling tank liner is made of zirconium oxide, the planetary ball milling beads are made of zirconium oxide, the diameter of the planetary ball milling beads is 5~10 mm, and the planetary ball milling material ratio is (20~45):1.

[0019] A second aspect of the present invention provides an application of a high-rate conversion-type metal fluoride cathode in lithium metal batteries: a lithium metal battery is assembled in an argon atmosphere with water and oxygen levels below 0.1 ppm, comprising a negative electrode, an electrolyte, a separator, a battery casing assembly, and the metal fluoride cathode provided by the present invention.

[0020] Furthermore, the positive electrode material is a metal fluoride or a carbon-coated aluminum foil, the negative electrode material is lithium metal, and the separator is polypropylene or glass fiber.

[0021] Furthermore, the method for preparing the conversion metal fluoride positive electrode sheet specifically involves coating a conversion metal fluoride slurry onto a carbon-coated aluminum foil to obtain a conversion metal fluoride positive electrode sheet with high rate performance.

[0022] The preparation method of the metal fluoride slurry is as follows:

[0023] S1. The metal fluoride composite material obtained by ball milling, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are placed in an agate or zirconium oxide mortar at a mass ratio of (70-90):(5-30):(10-20). The mixture is first dry-mixed with a pestle at a pressure of 20-60 N and a speed of 60-120 rpm for 2-5 min to obtain a uniform powder.

[0024] S2. Add the organic solvent 1-methyl-2-pyrrolidone (NMP) in 2-4 drops, with each drop not exceeding 10% of the powder mass. After each drop, maintain the same pressure and speed and continue grinding for 2-10 minutes to ensure that the solvent is fully absorbed by the powder and that there are no agglomerated particles.

[0025] S3. After the last NMP drop is completed, continue grinding for 5~20 min to obtain a particle-free cathode slurry with a viscosity of 3000~8000 mPa·s.

[0026] In the preparation method of the metal fluoride slurry, the conductive carbon black in step S1 is one or more of reduced graphene oxide, SuperP, acetylene black, and Ketjen black.

[0027] In step S1, the metal fluoride is one of iron fluoride (FeF3), ferrous fluoride (FeF2), bismuth fluoride (BiF3), and copper fluoride (CuF2).

[0028] The method for coating the metal fluoride slurry onto the current collector is as follows: the obtained conversion metal fluoride positive electrode slurry is uniformly coated onto carbon-coated aluminum foil using a coating machine to obtain a metal fluoride active material sheet with a thickness of 50-200 μm. After drying in a vacuum oven at 100-130 ℃ for 10-13 h, the conversion metal fluoride positive electrode sheet is obtained by roll pressing.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) Fundamentally improved reaction kinetics: This invention generates trace amounts of fluorine oxides in situ from metal fluorides, conductive carbon black, and lithium carbonate during ball milling, uniquely altering the electrochemical reaction pathway of metal fluorides and significantly reducing the activation energy of the conversion reaction. This effectively solves the core bottleneck problem of slow reaction kinetics in traditional conversion-type metal fluoride cathode materials.

[0031] (2) Improved rate performance: Due to the optimization of reaction kinetics, the composite material prepared by this invention exhibits extremely excellent rate performance.

[0032] (3) Simple process and easy to promote: The ball milling process described in this invention is simple, does not require complicated post-processing, and is easy to scale up for production, providing a brand-new technical route for the application of conversion metal fluoride cathode materials. Attached Figure Description

[0033] Figure 1 This is a rate performance graph of the FeF3 / Li battery assembled with iron fluoride cathode in the example, in 3M LiTFSI DME electrolyte.

[0034] Figure 2 This is a graph showing the rate performance of a FeF3 / Li battery assembled with a comparative iron fluoride cathode in 3M LiTFSI DME electrolyte.

[0035] Figure 3 These are XRD patterns of the iron fluoride materials and standard cards prepared in the examples and comparative examples.

[0036] Figure 4 This is a TEM image of the iron fluoride material prepared in the example.

[0037] Figure 5 This is a TEM image of the iron fluoride material prepared in a comparative proportion. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please see Figures 1-5 This invention provides a technical solution: a method for preparing a high-rate conversion-type metal fluoride cathode material, comprising steps S01 and S02, either of which can be selected:

[0040] S01: Under an argon atmosphere with water and oxygen levels below 0.1 ppm, metal fluoride and conductive carbon black are ground and mixed evenly in an agate mortar according to a mass ratio to obtain a mixture;

[0041] In an argon atmosphere with water and oxygen levels below 0.1 ppm, the grinding beads and the mixture from step (1) are added to the grinding jar in a mass ratio. The high-energy grinding time is 25-35 min, after which the operation is stopped, and the mixture is cooled for more than 10 min. The high-energy grinding mill is then run again, and this step is repeated. The total high-energy grinding time reaches 1-3 h to obtain a mixture. The mixture is slowly scraped along the inner wall of the grinding jar with a clean spatula. A certain mass ratio of lithium carbonate and grinding beads is then added to the grinding jar, and the mixture is placed in a planetary grinding mill for grinding. The mixture is slowly scraped along the inner wall of the grinding jar with a clean spatula to obtain a high-rate conversion type metal fluoride cathode material.

[0042] S02:

[0043] In an argon atmosphere with water and oxygen levels below 0.1 ppm, metal fluoride and conductive carbon black were ground and mixed evenly in an agate mortar according to a mass ratio to obtain a mixture.

[0044] In an argon atmosphere with water and oxygen levels below 0.1 ppm, the grinding beads, lithium carbonate, and the mixture from step (1) are added to the grinding jar in the specified mass ratio. The high-energy grinding time is 25-35 min. After that, the grinding is stopped, cooled for more than 10 min, and then the high-energy grinding mill is run again. This step is repeated until the total high-energy grinding time reaches 1-3 h. The mixture is obtained by slowly scraping it along the inner wall of the grinding jar with a clean spatula to obtain a high-rate conversion type metal fluoride cathode material.

[0045] All raw materials used in this invention can be purchased from the market.

[0046] In this embodiment of the invention, the metal fluoride is selected as FeF3, and the conductive carbon black is selected as Super P.

[0047] In this embodiment of the invention, the mass ratio of metal fluoride, conductive carbon black, and lithium carbonate during high-energy ball milling is 70:15:10.

[0048] This invention introduces low-cost lithium carbonate, and during ball milling, iron fluoride, Super P, and lithium carbonate are used to generate trace amounts of iron fluoride oxide (FeOF) in situ. This uniquely alters the electrochemical reaction pathway of iron fluoride, significantly reducing the activation energy of the conversion reaction. This effectively solves the core bottleneck problem of slow reaction kinetics in traditional conversion-type metal fluoride cathode materials. Due to the optimized reaction kinetics, the iron fluoride composite material prepared by this invention exhibits extremely superior rate performance.

[0049] The following is a specific embodiment of a method for preparing a high-rate conversion-type iron fluoride cathode material:

[0050] Example

[0051] (1) In an argon atmosphere with water oxygen content below 0.1 ppm, weigh 0.7412 g of iron fluoride and 0.1588 g of Super P and grind and mix them evenly in an agate mortar to obtain a mixture.

[0052] (2) In an argon atmosphere with water oxygen concentration below 0.1 ppm, weigh 26.1534 g of zirconia grinding beads and 0.1059 g of Li2CO3, add the grinding beads, lithium carbonate and the mixture in step (1) into a zirconia high-energy ball mill jar, run the high-energy ball mill for 30 min, then stop the operation, cool for 15 min, and run the high-energy ball mill again. Repeat this step 4 times, and the total high-energy ball milling time reaches 2 h to obtain a mixture. Use a clean spatula to slowly scrape the mixture along the inner wall of the ball mill jar to obtain a trace amount of FeOF-doped FeF3 cathode material.

[0053] The obtained active material (FeF3 cathode material doped with trace amounts of FeOF, wherein the mass ratio of FeF3:Super P:Li2CO3 is 70:15:10), Super P, and binder PVDF were placed in an agate mortar at a mass ratio of 95:5:10. The mixture was first dry-mixed with a pestle at a pressure of 20-60 N and a speed of 60-120 rpm for 4 min to obtain a uniform powder. The organic solvent NMP was added dropwise in three batches, with each addition not exceeding 10% of the powder mass. After each addition, the same pressure and speed were maintained, and grinding continued for 7 min to ensure the solvent was fully absorbed by the powder and that no agglomerates were formed. After the final NMP addition, grinding continued for 5 min to obtain a particle-free cathode slurry. The obtained cathode slurry was uniformly coated onto carbon-coated aluminum foil using a coating machine to obtain a 100 μm thick sheet of iron fluoride active material. After drying in a vacuum oven at 120 ℃ for 12 h, the sheet was rolled and sliced ​​using a slicing machine with a 12 mm die. Battery assembly was carried out in an argon atmosphere with water and oxygen levels below 0.1 ppm. Lithium metal was used as the counter electrode, carbon-coated aluminum foil as the working electrode, polypropylene as the separator, and 3M LiTFSI DME as the electrolyte. The battery was assembled into a structure consisting of a negative electrode shell, lithium metal, separator, electrolyte, carbon-coated aluminum foil, gasket, spring, and positive electrode shell. After assembly, the battery was compacted using a battery packaging machine, removed, marked, and left to stand for 8 hours before testing.

[0054] Comparative Example

[0055] (1) In an argon atmosphere with water oxygen content below 0.1 ppm, weigh 0.8235 g FeF3 and 0.1765 g Super P and grind them evenly in an agate mortar to obtain a mixture.

[0056] (2) In an argon atmosphere with water and oxygen levels below 0.1 ppm, weigh 26 g of zirconia grinding beads and add the grinding beads and the mixture from step (1) into a zirconia high-energy ball milling jar. The high-energy ball milling time is 30 min. After that, stop the operation, cool for 15 min, and then run the high-energy ball mill again. Repeat this step 4 times. The total high-energy ball milling time reaches 2 h. Obtain the mixture and slowly scrape the mixture along the inner wall of the ball milling jar with a clean spatula to obtain the FeF3 cathode material.

[0057] The above-obtained active material (comparative FeF3 cathode material, wherein the mass ratio of FeF3:Super P is 70:15), Super P, and binder PVDF were placed in an agate mortar at a mass ratio of 85:5:10. The mixture was first dry-mixed with a pestle at a pressure of 20-60 N and a speed of 60-120 rpm for 4 min to obtain a uniform powder. The organic solvent NMP was then added dropwise in three batches, with each addition not exceeding 10% of the powder mass. After each addition, the same pressure and speed were maintained, and grinding continued for 7 min to ensure the solvent was fully absorbed by the powder and that no agglomerates were formed. After the final NMP addition, grinding continued for 5 min to obtain a particle-free cathode slurry. The obtained cathode slurry was uniformly coated onto carbon-coated aluminum foil using a coating machine to obtain a 100 μm thick sheet of iron fluoride active material. After drying in a vacuum oven at 120 ℃ for 12 h, the sheet was rolled and sliced ​​using a slicing machine with a 12 mm die. Battery assembly was carried out in an argon atmosphere with water and oxygen levels below 0.1 ppm. Lithium metal was used as the counter electrode, carbon-coated aluminum foil as the working electrode, polypropylene as the separator, and 3M LiTFSI DME as the electrolyte. The battery was assembled into a structure consisting of a negative electrode shell, lithium metal, separator, electrolyte, carbon-coated aluminum foil, gasket, spring, and positive electrode shell. After assembly, the battery was compacted using a battery packaging machine, removed, marked, and left to stand for 8 hours before testing.

[0058] Performance testing:

[0059] (1) The following is an electrochemical performance test of a conversion-type metal fluoride cathode, FeF3, in a lithium metal battery:

[0060] In the following application examples, the first cycle was a constant current charge-discharge at 0.085 mA, followed by constant rate charge-discharge tests at 0.5C, 1C, 2C, and 3C. Specifically, at 25 °C, the electrochemical performance of the trace FeOF-doped FeF3 cathode in 3M LiTFSI DME electrolyte was tested using a LAND electrochemical workstation to evaluate the rate performance of the trace FeOF-doped FeF3 cathode. The FeF3 voltage range was 1-4.5 V, and the 1C current density was 712 mA g⁻¹. The results are as follows: Figure 1 As shown, from Figure 1 It can be seen that, with Figure 2 Compared to the comparative example, the rate performance and capacity of the embodiment are significantly improved.

[0061] The following comparative application uses a constant current charge-discharge cycle of 0.085 mA for the first cycle, followed by constant rate charge-discharge tests at 0.5C, 1C, 2C, and 3C. Specifically, the electrochemical performance of the FeF3 cathode in 3M LiTFSIDME electrolyte was tested at 25 °C using a LAND electrochemical workstation to evaluate its rate performance. The FeF3 voltage range was 1-4.5 V, and the 1C current density was 712 mA g⁻¹. The results are as follows: Figure 2 As shown.

[0062] (2) X-ray diffraction was used to test the FeF3 cathode material with trace FeOF doping obtained in the examples and the FeF3 cathode material obtained in the comparative examples. The results are as follows: Figure 3 As shown, from Figure 3 It can be seen that the material synthesized in the comparative example is FeF3, and its diffraction peak positions match the standard spectrum of FeF3 (PDF#04-005-4240). The material synthesized in the example is FeF3 doped with trace amounts of FeOF, and its diffraction peak positions match the standard spectrum of FeF3 (PDF#04-005-4240) and the standard spectrum of FeOF (PDF#97-000-2875).

[0063] (3) The FeF3 cathode material with trace FeOF doping obtained in the examples was characterized by transmission electron microscopy, and the results are as follows: Figure 4 As shown.

[0064] (4) The FeF3 cathode material obtained in the comparative example was characterized using transmission electron microscopy, and the results are as follows: Figure 5 As shown.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-rate conversion-type metal fluoride cathode material, characterized in that, Includes the following steps: Step (1) In an argon atmosphere with water and oxygen levels below 0.1 ppm, the converted metal fluoride and conductive carbon black are ground and mixed at a mass ratio of 7~9:1~2 to obtain a mixture; In step (2), under an argon atmosphere with water and oxygen levels below 0.1 ppm, the mixture obtained in step (1) is placed together with lithium carbonate and milling beads in a high-energy ball milling jar at a mass ratio for ball milling. After high-energy ball milling for a preset total time, a high-rate conversion-type metal fluoride cathode material is obtained.

2. The preparation method according to claim 1, characterized in that, Step (2) involves first placing the mixture obtained in step (1) together with the grinding beads in a high-energy ball milling jar for ball milling. The total high-energy ball milling time is 1-3 hours. Then, the mixture after high-energy ball milling is placed together with lithium carbonate and grinding beads in a planetary ball milling jar according to the mass ratio. The total planetary ball milling time is 2-8 hours.

3. The preparation method according to claim 1, characterized in that, Step (2) involves placing the mixture obtained in step (1) together with lithium carbonate and milling beads in a high-energy ball milling jar at a mass ratio for ball milling treatment. The total high-energy ball milling time is 1 to 3 hours.

4. The preparation method according to claim 1, characterized in that, The converted metal fluoride is selected from one of iron fluoride, ferrous fluoride, bismuth fluoride, and copper fluoride; The conductive carbon black is selected from one or more of reduced graphene oxide, Super P, acetylene black, and Ketjen black.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the converted metal fluoride, conductive carbon black and lithium carbonate is 7~9:1~2:0.5~3.

6. The preparation method according to claim 1, characterized in that, The high-energy ball mill uses a zirconia ball milling jar and zirconia ball milling beads with a diameter of 5-10 mm. The ball-to-material ratio of the high-energy ball mill is (20-40):

1. The high-energy ball milling process adopts an intermittent operation mode, with each operation lasting 25-35 minutes and then cooling for more than 10 minutes. This process is repeated until the total duration reaches 1-3 hours.

7. The preparation method according to claim 2, characterized in that, The planetary ball mill uses a grinding jar lined with zirconium oxide and zirconium oxide grinding beads. The planetary ball mill speed is 200~600 rpm, the diameter of the grinding beads is 5~10 mm, and the ball-to-material ratio is (20~45):

1.

8. A high-rate conversion-type metal fluoride cathode material prepared by the method described in any one of claims 1 to 7.

9. The application of a high-rate conversion-type metal fluoride cathode in lithium metal batteries, characterized in that: This includes the positive electrode, negative electrode, electrolyte, separator, and battery casing assembly.

10. The application according to claim 9, characterized in that: The positive electrode is the high-rate conversion-type metal fluoride positive electrode material and carbon-coated aluminum foil as described in claim 9, the negative electrode material is lithium metal, the separator is polypropylene and glass fiber, and the electrolyte is 3M LiTFSI DME.

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