Carbon nano island modified ferric trifluoride hydrate positive electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of a carbon nano island modified ferric trifluoride hydrate positive electrode material. The carbon nano island modified ferric trifluoride hydrate material is produced by adopting a wet chemical reaction-continuous anhydrous oxygen-free fluorination-oxygen-free high-speed ball milling process, and the method comprises the following steps: carrying out continuous fluorination on ferric hydroxide obtained by reacting a positive ferric ion-containing metal salt raw material with a hydroxyl-containing alkali solution by using anhydrous oxygen-free fluorine; the iron trifluoride hydrate obtained after cooling and sieving and conductive carbon are subjected to sufficient oxygen-free high-speed ball milling, the iron trifluoride hydrate material modified by the carbon nano island is obtained, the size of the material is within the range of 1-20 microns, the material is of a mottle layered structure, the size of the carbon nano island is within the range of 50-200 nm, and the material is of an island-shaped structure. The method is simple in preparation flow, controllable in process, good in stability, capable of achieving batch production and suitable for macro preparation.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery cathode material preparation technology, specifically relating to a carbon nano-island modified hydrated iron trifluoride cathode material and its preparation method. Background Technology

[0002] Lithium metal batteries use lithium metal as the negative electrode. Due to their advantages such as ultra-high theoretical specific capacity, simple battery structure, and strong environmental adaptability, they are transitioning from basic research to commercialization. In particular, lithium metal batteries are one of the most promising batteries, especially in fields such as low-altitude flight technology and long-endurance driving.

[0003] Lithium metal batteries have a simple structure, consisting of a lithium metal anode, a separator, a cathode material, and an electrolyte. The theoretical specific capacity of lithium metal is as high as 3860 mAh / g; therefore, the energy density of the entire battery is greatly limited by the cathode material. Currently, commercially available lithium metal cathode materials are mainly lithium-rich manganese-based cathodes, lithium cobalt oxide cathodes, and lithium iron phosphate cathodes, all of which have a specific capacity of less than 350 mAh / g, making it difficult to overcome the demand for higher energy densities in lithium metal batteries. Therefore, developing new high-energy-density cathode materials is key to improving the energy density of lithium metal batteries and is of great significance for promoting their commercialization.

[0004] Ferric trifluoride, with the molecular formula FeF3, has a relatively small molecular weight of 74.8 g / mol. Patent CN106058222B indicates that in FeF3, Fe exists in the +3 form, exhibiting two typical charge-discharge plateaus during the charging and discharging process of a battery composed of lithium metal: 4.5–2.5 V and 2.5–1.5 V, corresponding to Fe... 3+ / Fe 2+ and Fe 2+ / Fe 0 Two redox reactions mean that 1 mol of hydrated iron trifluoride can store up to 3 mol of lithium ions. Therefore, iron trifluoride material has an extremely high theoretical specific capacity of 712 mAh / g, making it a highly promising candidate material for lithium metal batteries.

[0005] However, iron trifluoride (Fe3F) materials often exhibit unsatisfactory performance when directly used as cathode materials in lithium-ion batteries. On the one hand, due to its wide band gap, Fe3F is essentially an electronic insulator, resulting in low electronic conductivity. On the other hand, Fe3F can be considered a cubic crystal structure with a hexagonal close-packed structure, which significantly hinders lithium-ion transfer into the Fe3F interior. Patents CN114447291A and CN103855389A indicate that doping or coating with conductive materials (such as carbon nanotubes and graphene) can improve the electronic conductivity of Fe3F, but the actual performance of modified Fe3F cathode materials is less than 260 mAh / g. Therefore, in addition to considering the electronic conductivity of Fe3F, lithium-ion conductivity is also a key factor affecting its performance. Summary of the Invention

[0006] The purpose of this invention is to provide a promising carbon nano-island modified hydrated iron trifluoride cathode material and its preparation method, providing a new option for the design of high energy density lithium metal.

[0007] The objective of this invention is achieved through the following solution:

[0008] [First aspect]

[0009] This invention relates to a carbon nano-island modified hydrated iron trifluoride cathode material, wherein the material is a composite material of nano-carbon and hydrated iron trifluoride, the composite material exhibits a mottled layered structure with a size of 1-20 μm; the carbon nano-islands are island-shaped morphologies partially embedded in the bulk phase of hydrated iron trifluoride, and the carbon nano-islands have a size of 50-200 nm.

[0010] In one embodiment of the present invention, the elements in the region where the carbon nano islands and hydrated iron trifluoride are combined are distributed in a gradient.

[0011] [Second aspect]

[0012] This invention relates to a method for preparing a carbon nano-island modified hydrated iron trifluoride cathode material, which employs a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process; the iron hydroxide obtained from the wet chemical reaction is continuously fluorinated with anhydrous and oxygen-free fluorine gas, and the hydrated iron trifluoride obtained after cooling is subjected to oxygen-free high-speed ball milling with nano-carbon to obtain the carbon nano-island modified hydrated iron trifluoride composite material.

[0013] First, the wet chemical reaction is a process for controlling morphology and removing impurities, resulting in an ideal pre-material. The subsequent continuous anhydrous and oxygen-free fluorination is a fluorination process conducted at different temperature ranges, activating the material surface and achieving a high degree of fluorination. The process is efficient and controllable. Finally, the oxygen-free high-speed ball milling is a composite process that effectively and fully composites the nano-carbon materials with hydrated iron trifluoride; an oxygen-free environment is essential. From the perspective of preparing carbon nano-island modified hydrated iron trifluoride cathode materials, the above steps—morphology and purity control, fluorination control, and composite control—are all necessary steps.

[0014] The wet chemical reaction is a process of converting salts containing +3 ferric ions into ferric hydroxide. This process is extremely crucial to the morphology and purity of the layered hydrated ferric trifluoride material. Most +3 ferric salt anions only volatilize at extremely high temperatures. However, by utilizing their easy solubility in polar solvents, the non-volatile anions can be completely removed during the wet chemical reaction, yielding high-purity ferric hydroxide.

[0015] The continuous anhydrous and oxygen-free fluorination process involves transferring the pre-material prepared above into a reactor and continuously fluorinating it in an anhydrous and oxygen-free fluorine gas environment to obtain hydrated iron trifluoride material. Hydrated iron trifluoride is easily oxidized in environments containing water and oxygen; therefore, anhydrous and oxygen-free conditions are necessary to obtain a product with higher purity. Fluorine gas is a good fluorinating agent and, under suitable conditions, can fully convert iron-containing intermediate materials into fluorides, making it a good choice for fluorination. The continuous fluorination process avoids the changes in material morphology and structure caused by direct high-temperature fluorination. The continuous fluorination process, from low-temperature pre-fluorination to high-temperature fluorination, is an important condition for constructing layered hydrated iron trifluoride.

[0016] The oxygen-free high-speed ball milling process involves high-speed ball milling of the aforementioned hydrated ferric trifluoride material with a defined water of crystallization content and nano-carbon in a specific ratio under an oxygen-free environment to obtain carbon nano-island-modified hydrated ferric trifluoride material. An oxygen-free environment is essential to prevent the oxidation of ferric trifluoride; high-speed ball milling provides sufficient energy for the bonding of nano-carbon and hydrated ferric trifluoride, and the initial fluorination process leaves abundant active surfaces on the hydrated ferric trifluoride surface, which is crucial for the composite nano-carbon.

[0017] As one embodiment of the present invention, the method includes the following steps:

[0018] S1. Wet chemical reaction: After the iron-containing raw material is fully reacted with the hydroxide-containing solution, it is subjected to differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying to finally obtain the iron hydroxide intermediate product.

[0019] S2. Continuous anhydrous and oxygen-free fluorination: The iron hydroxide intermediate product is continuously fluorinated with fluorine gas in an anhydrous and oxygen-free environment and within different temperature ranges to obtain the corresponding hydrated iron trifluoride.

[0020] S3. High-speed ball milling in an oxygen-free atmosphere: The hydrated iron trifluoride and nano carbon are ball milled at high speed in an oxygen-free atmosphere, and then the materials are separated to obtain carbon nano-island modified hydrated iron trifluoride cathode material.

[0021] As one embodiment of the present invention, in step S2, iron trifluoride with different water of crystallization content is obtained according to the difference in fluorination temperature range, including FeF3·0.33H2O and FeF3·3H2O, preferably FeF3·0.33H2O.

[0022] In one embodiment of the present invention, in step S1, the iron-containing raw material is a ferric (Fe3+) metal salt, and the hydroxide-containing solution is a polar alkaline solution with a pH of 10; the iron-containing raw material and the hydroxide-containing solution react fully at a molar ratio of iron to hydroxide of 1:4 to 1:7. In some examples, the mixture is stirred for 6 to 12 hours at a temperature of 35–50°C to ensure a full reaction between the iron and hydroxide ions. The wet chemical reaction involves adding the ferric (Fe3+) salt to a heated solvent with a pH of 10 and reacting under continuous stirring. The ferric salt dissociates into ferric ions and corresponding anions in the solution. Due to solvation, the anions constrain the ferric ions before the hydroxide ions combine, which affects the morphology of the resulting ferric hydroxide. Furthermore, the solvent removes a large amount of anionic impurities by increasing the solubility of the anionic groups in the ferric salt, and repeated ultrasonic washing with ultrapure water is performed during the subsequent collection process to further improve the purity of the ferric hydroxide product.

[0023] As one embodiment of the present invention, in step S1, the differential centrifugation speed is 10000-15000 rpm, and the duration is 3-8 min.

[0024] As one embodiment of the present invention, in step S1, the freeze-drying process requires pre-freezing at -15 to -20°C for at least 12 hours, followed by freeze-drying at -35 to -45°C for at least 72 hours.

[0025] In one embodiment of the present invention, in step S2, the intermediate product of ferric hydroxide is transferred to an anhydrous reactor, and then anhydrous and oxygen-free fluorine gas is introduced for fluorination treatment according to a continuous anhydrous and oxygen-free fluorination process. Continuous anhydrous and oxygen-free fluorination involves subjecting the high-purity ferric hydroxide obtained above to a continuous fluorination process from low to high temperature under an anhydrous and oxygen-free fluorine atmosphere, ultimately yielding hydrated ferric trifluoride. An anhydrous and oxygen-free environment is a necessary condition in the fluorination process to prevent oxidation of the fluorinated product, especially during the cooling stage. The fluorination process requires a certain temperature as a reaction condition; when the temperature is lower than the fluorination reaction temperature, oxygen or water in the environment will react with the highly surface-active hydrated ferric trifluoride to generate iron oxide. To ensure the purity of the product, surface oxidation of the hydrated ferric trifluoride should be avoided, i.e., the reaction environment should be controlled to be an anhydrous and oxygen-free environment. Simultaneously, the surface of high-purity hydrated ferric trifluoride will not be coated with iron oxide, and the surface remains in an active state, which can promote the bonding of hydrated ferric trifluoride with nano-carbon. Continuous fluorination can improve the degree of fluorination of materials while maintaining the layered structure morphology. At lower temperatures, pre-fluorination can be achieved. As the temperature increases, the intermediate material after pre-fluorination is further fluorinated, increasing the degree of fluorination. During fluorination, hydroxide ions in the iron source react with fluorine gas to generate water, hydrogen fluoride, and oxygen. Water initially remains in the iron trifluoride lattice, forming water of crystallization. Further increases in temperature not only further fully fluorinate the material but also gradually reduce the bound water content in the iron trifluoride material. Continuous fluorination temperature settings allow for precise control of the water of crystallization content in hydrated iron trifluoride materials. Fluorination at 150 and 250℃ yields FeF3·3H2O and FeF3·0.33H2O, respectively. During the volatilization of the generated gases, pores or pits are left on the material surface. Furthermore, fluorine-containing functional groups remain on the material surface after fluorination. The presence of these structures and functional groups enhances the surface activity of the material, providing conditions for the incorporation of nano-carbon.

[0026] In one embodiment of the present invention, in step S3, hydrated ferric trifluoride and nano-carbon are mixed at a mass ratio of 70:30 to 90:10 under an oxygen-free protective atmosphere, then transferred to a ball mill jar for sealing, followed by high-speed ball milling. The oxygen-free high-speed ball milling involves sealing the above-mentioned hydrated ferric trifluoride material and nano-carbon in a ball mill jar within an argon-filled glove box according to a set ratio, then removing it for high-speed ball milling, finally obtaining nano-carbon-modified hydrated ferric trifluoride material. Since hydrated ferric trifluoride is reactive in oxygen- and water-containing environments, the energy introduced by high-speed ball milling accelerates this reaction; therefore, an oxygen-free environment is crucial to prevent the oxidation of the hydrated ferric trifluoride material. Under high-speed ball milling, the highly surface-active hydrated ferric trifluoride undergoes a bonding reaction with nano-carbon at the interface, and the abundant fluorine-containing functional groups on the surface combine with carbon to form an interface similar to fluorinated carbon. Due to the presence of voids or pits, and under the energy provided by high-speed ball milling, the nano-carbon portion is embedded inside the hydrated iron trifluoride, resulting in a carbon nano-island modified hydrated iron trifluoride cathode material.

[0027] In one embodiment of the present invention, in step S3, the particle size of the nano-carbon is 20-50 nm. If the nano-carbon is too large, the relative contact surface area between it and hydrated iron trifluoride will be too small, making it difficult to form a stable interaction and introducing too much inactive material mass; if the nano-carbon is too small, the nano-carbon may be trapped in the interlayer of hydrated iron trifluoride, affecting the structure of the material.

[0028] In some implementation examples, the wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process mainly includes the following steps:

[0029] S1. Wet chemical reaction: Mix a metal salt containing ferric ions with a polar alkaline solution with a pH of 10, wherein the molar ratio of iron to hydroxide is 1:4 to 1:7, and stir for 6 to 12 hours at a temperature of 35 to 50°C to allow the iron and hydroxide to react fully. Then, collect the ferric hydroxide intermediate product obtained from the reaction by ultrasonic washing with ultrapure water, differential centrifugation, and freeze drying.

[0030] S2, Continuous anhydrous and oxygen-free fluorination: The iron hydroxide intermediate product obtained in S1 is transferred to an anhydrous reactor, and then anhydrous fluorine gas is introduced. Fluorination is carried out according to the continuous anhydrous and oxygen-free fluorination process to obtain hydrated iron trifluoride.

[0031] S3. High-speed ball milling without oxygen: The hydrated iron trifluoride obtained in S2 above is mixed with nano carbon in a mass ratio of 70:30 to 90:10 under an anhydrous protective atmosphere, then transferred to a ball milling jar for sealing treatment, and then subjected to a high-speed ball milling process. After the ball milling is completed, the carbon nano island modified hydrated iron trifluoride material is obtained.

[0032] There are three key points in preparing carbon nanoisland-modified hydrated iron trifluoride materials in the system of this invention: 1. Hydrated iron trifluoride with surface activity (mainly derived from gas volatilization during fluorination and the enhancement of surface activity by surface F functional groups); 2. Carbon spheres of approximately 20-50 nm are used; 3. The composite method is anhydrous and oxygen-free high-speed ball milling. When the carbon nanospheres are replaced with other types of carbon, such as carbon cloth, carbon nanotubes, or graphene, carbon nanoisland-modified hydrated iron trifluoride materials cannot be obtained due to size mismatch and difficulty in reshaping the carbon shape during material synthesis.

[0033] As one embodiment of the present invention, the trivalent iron ion metal salt includes FeCl3, Fe(NO3)3, Fe2(SO4)3, and Fe(CO2CH2)3, preferably Fe(CO2CH2)3.

[0034] As one embodiment of the present invention, the polar alkaline solution contains NH3·H2O, LiOH, NaOH, KOH, preferably KOH, and the polar solvent contains H2O, CH3OH, CH3CH2OH, preferably H2O.

[0035] In one embodiment of the present invention, in step S1, ultrasonic washing with ultrapure water is repeated at least 5 times. Differential centrifugation is performed at 12000 rpm for 5 minutes. Before freeze-drying, the sample must be pre-frozen at -18°C for at least 12 hours, and the freeze-drying time is at least 72 hours.

[0036] As one embodiment of the present invention, the anhydrous and oxygen-free fluorine gas is a mixture of fluorine and nitrogen or a mixture of fluorine and argon, wherein the volume fraction of fluorine in the mixture is more than 10%.

[0037] In one embodiment of the present invention, the continuous anhydrous and oxygen-free fluorination process starts at 0°C, reaches an end temperature of 150–260°C, and has a heating rate of 1°C / min. Pre-fluorination is performed for 2 hours every 50°C increase. After reaching the set temperature, the temperature is held for 5–10 hours to achieve full fluorination, and then cooled to room temperature at a rate of 1°C / min. In some embodiments, the continuous anhydrous and oxygen-free fluorination process starts at 0°C, reaches an end temperature of 200–260°C, and has a heating rate of 1°C / min. Pre-fluorination is performed for 2 hours every 50°C increase. After reaching the set temperature, the temperature is held for 5–10 hours to achieve full fluorination, and then cooled to room temperature at a rate of 1°C / min.

[0038] As one embodiment of the present invention, the oxygen-free high-speed ball milling is achieved in a clean glove box protected by argon gas, wherein the content of water and oxygen is less than 0.1 ppm. The high-speed ball milling process is carried out in an intermittent manner, with a ball milling speed of 300-600 rpm, a working time of 10-15 min, an interval of 3-5 min, repeated 25-35 times, and a material temperature of 25-50℃.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1) This invention uses a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process to prepare carbon nano-island modified hydrated iron trifluoride materials. The raw materials are simple, the process is stable, the degree of fluorination is high, the product purity is high, the composite material has good stability, and the single batch production can reach the kilogram level.

[0041] 2) The water content of the prepared hydrated iron trifluoride can be customized as needed. The fluorinated hydrated iron trifluoride has a layered structure and stable morphology.

[0042] 3) The carbon nano islands modified hydrated iron trifluoride obtained after being combined with carbon nanotubes have improved electron and ion conduction capabilities, which can meet the requirements of lithium metal batteries for cathode materials and are expected to be used on a large scale in lithium metal battery cathode materials and even other energy fields. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1 Flowchart of wet chemical reaction - continuous anhydrous and oxygen-free fluorination - oxygen-free high-speed ball milling process;

[0045] Figure 2 XRD pattern of FeF3·0.33H2O modified with carbon nano islands;

[0046] Figure 3 XRD pattern of FeF3·3H2O modified with carbon nano islands;

[0047] Figure 4 SEM image of FeF3·0.33H2O modified with carbon nano islands;

[0048] Figure 5 STEM image of FeF3·0.33H2O modified with carbon nano islands;

[0049] Figure 6 XPS image of FeF3·0.33H2O modified with carbon nano islands;

[0050] Figure 7STEM image of nano-carbon and FeF3 composite material prepared at high temperature;

[0051] Figure 8 TEM image of nano-carbon and FeF3·0.33H2O composite material prepared in an oxygen- and water-containing environment;

[0052] Figure 9 Charge-discharge curves of coin cells assembled with carbon nano island modified FeF3·0.33H2O positive electrode, Comparative Example 1 and Comparative Example 2, and lithium metal negative electrode, respectively.

[0053] Figure 10 The charge-discharge curves of coin cells assembled with lithium metal anodes in Examples 2, 3, and 4 are shown.

[0054] Figure 11 Cycling curves of a coin cell assembled with a carbon nanoisland-modified FeF3·0.33H2O cathode and a lithium metal anode. Detailed Implementation

[0055] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0056] Example 1

[0057] Using Fe(CO2CH2)3 as the iron source and water as the solvent, and adjusting the pH value by adding KOH, carbon nano-island modified FeF3·0.33H2O materials were prepared by a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process. The process is as follows: Figure 1 As shown.

[0058] (1) Wet chemical reaction: KOH was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then Fe(CO2CH2)3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation (12,000 rpm for 5 minutes), ultrasonic washing with ultrapure water repeated 5 times, and freeze-drying (the product needs to be pre-frozen at -18°C for at least 12 hours before freeze-drying, and then freeze-dried in a freeze dryer with a cold trap temperature of -40°C for at least 72 hours).

[0059] (2) Continuous anhydrous and oxygen-free fluorination: The obtained iron hydroxide is transferred to a reactor, and anhydrous and oxygen-free fluorine gas (a mixture of fluorine and argon with a fluorine volume fraction of 15%) is introduced to remove the air from the reactor. Then, the reactor is heated from 0°C to 250°C at a heating rate of 1°C / min and held for 10 hours. During this period, when the temperature is raised to 50, 100, 150, and 200°C, a pre-fluorination is performed and held for 2 hours every 50°C increase. Finally, the temperature is lowered to room temperature at a cooling rate of 1°C / min to obtain FeF3·0.33H2O.

[0060] (3) High-speed ball milling in oxygen-free environment: The obtained FeF3·0.33H2O and 20-50nm nano carbon were mixed in an argon-filled anhydrous and oxygen-free glove box (the content of water and oxygen is less than 0.1ppm) at a mass ratio of 80:20 and then added to the ball milling jar. Appropriate small balls were added at a mass ratio of ball milling material to ball milling balls of 1:9. After sealing, the jar was taken out and subjected to high-speed ball milling. The ball milling was carried out in an intermittent manner, with a 10min interval, a 5min interval, and repeated 30 times. The rotation speed was 300rpm and the material temperature was controlled at 25-35℃. After the ball milling was completed, the small balls and the material were separated in the glove box to obtain the FeF3·0.33H2O material modified with carbon nano islands.

[0061] Figure 2 , Figure 4 , Figure 5 , Figure 6 XRD patterns, SEM images, STEM images, and XPS spectra of carbon nanoisland-modified FeF3·0.33H2O materials. Figure 9-10 The image shows the charge-discharge curves and cycle performance of a coin cell assembled with a carbon nanoisland-modified FeF3·0.33H2O cathode material, a lithium metal anode, a polypropylene separator, and a 2032 battery case. The cathode was prepared by grinding FeF3·0.33H2O, polyvinylidene fluoride, and conductive carbon in a mass ratio of 8:1:1, adding an appropriate amount of N-methylpyrrolidone solvent, until a uniform viscous state was achieved, and then coating it onto carbon-coated aluminum foil and drying it. Figure 2 It can be seen that the obtained carbon nano-island modified FeF3·0.33H2O contains only a single phase, FeF3·0.33H2O, and the preparation process effectively protects FeF3·0.33H2O from oxidation. Figure 4 It can be seen that the carbon nano-island modified FeF3·0.33H2O exhibits a mottled layered structure. From Figure 5 It can be seen that the nano-carbon is partially embedded in the FeF3·0.33H2O surface, exhibiting a strong interaction. Furthermore, a gradient distribution of carbon signal is observed in the region where nano-carbon and FeF3·0.33H2O are bonded, with the carbon signal significantly enhanced closer to the nano-carbon location. Figure 6It can be seen that, compared to FeF3·0.33H2O, the Fe 2p of FeF3·0.33H2O modified with carbon nanoislands is significantly better. 1 / 2 and Fe 2p 3 / 2 Both showed a 0.1 eV shift towards lower binding energy. This is because carbon is less electronegative than fluorine, resulting in reduced electron transfer from iron to fluorine in the composite material due to the influence of carbon. Therefore, in XPS, this shift towards lower binding energy is observed. Figure 9 and Figure 11 It can be seen that FeF3·0.33H2O modified with carbon nano islands can release a specific capacity of up to 496 mAh / g in the first cycle of lithium metal batteries and has good cycle performance.

[0062] Example 2

[0063] Using FeCl3 as the iron source and water as the solvent, and adjusting the pH value by adding KOH, carbon nano-island modified FeF3·0.33H2O materials were prepared by a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process. The process is as follows: Figure 1 As shown.

[0064] (1) Wet chemical reaction: KOH was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then FeCl3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying (same as in Example 1).

[0065] (2) Continuous anhydrous and oxygen-free fluorination: The obtained iron hydroxide is transferred to a reactor, and anhydrous and oxygen-free fluorine gas (a mixture of fluorine and argon with a fluorine volume fraction of 15%) is introduced to remove the air from the reactor. Then, the reactor is heated from 0°C to 250°C at a heating rate of 1°C / min and held for 10 hours. During this period, when the temperature is raised to 50, 100, 150, and 200°C, a pre-fluorination is performed and held for 2 hours every 50°C increase. Finally, the temperature is lowered to room temperature at a cooling rate of 1°C / min to obtain FeF3·0.33H2O.

[0066] (3) Oxygen-free high-speed ball milling: The obtained FeF3·0.33H2O and 20-50nm nano-carbon were mixed in an argon-protected anhydrous and oxygen-free glove box (water and oxygen content both below 0.1ppm) at a mass ratio of 80:20, and then added to a ball milling jar. Appropriate small balls were added at a mass ratio of material to ball milling balls of 1:9. After sealing, the mixture was removed and subjected to high-speed ball milling. The ball milling was carried out intermittently, with a 10-minute milling interval followed by a 5-minute interval, repeated 30 times at a rotation speed of 300 rpm. The material temperature was controlled at 25-35℃. After ball milling, the small balls and material were separated in the glove box to obtain carbon nano-island modified FeF3·0.33H2O material. Figure 10 It can be seen that, under the same battery assembly process conditions as in Example 1, the specific capacity of the carbon nano-island modified FeF3·0.33H2O composite material is 300.6mAh / g.

[0067] Example 3

[0068] Using Fe(CO2CH2)3 as the iron source and water as the solvent, and adjusting the pH value by adding NH3·H2O, carbon nano-island modified FeF3·0.33H2O materials were prepared by a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process. The process is as follows: Figure 1 As shown.

[0069] (1) Wet chemical reaction: NH3·H2O was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then Fe(CO2CH2)3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying (same as in Example 1).

[0070] (2) Continuous anhydrous and oxygen-free fluorination: The obtained iron hydroxide is transferred to a reactor, and anhydrous and oxygen-free fluorine gas (a mixture of fluorine and argon with a fluorine volume fraction of 15%) is introduced to remove the air from the reactor. Then, the reactor is heated from 0°C to 250°C at a heating rate of 1°C / min and held for 10 hours. During this period, when the temperature is raised to 50, 100, 150, and 200°C, a pre-fluorination is performed and held for 2 hours every 50°C increase. Finally, the temperature is lowered to room temperature at a cooling rate of 1°C / min to obtain FeF3·0.33H2O.

[0071] (3) Oxygen-free high-speed ball milling: The obtained FeF3·0.33H2O and 20-50nm nano-carbon were mixed in an argon-protected anhydrous and oxygen-free glove box (water and oxygen content both below 0.1ppm) at a mass ratio of 80:20, and then added to a ball milling jar. Appropriate small balls were added at a mass ratio of material to ball milling balls of 1:9. After sealing, the mixture was removed and subjected to high-speed ball milling. The ball milling was carried out intermittently, with a 10-minute milling interval followed by a 5-minute interval, repeated 30 times at a rotation speed of 300 rpm. The material temperature was controlled at 25-35℃. After ball milling, the small balls and material were separated in the glove box to obtain carbon nano-island modified FeF3·0.33H2O material. Figure 10 It can be seen that, under the same battery assembly process conditions as in Example 1, the specific capacity of the carbon nano-island modified FeF3·0.33H2O composite material is 381.1 mAh / g.

[0072] Example 4

[0073] Using Fe(CO2CH2)3 as the iron source and water as the solvent, and adjusting the pH value by adding KOH, carbon nano-island modified FeF3·3H2O materials were prepared by a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process. The process is as follows: Figure 1 As shown.

[0074] (1) Wet chemical reaction: KOH was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then Fe(CO2CH2)3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying (same as in Example 1).

[0075] (2) Continuous anhydrous and oxygen-free fluorination: The obtained iron hydroxide is transferred to a reactor, and anhydrous and oxygen-free fluorine gas (a mixture of fluorine and argon with a fluorine volume fraction of 15%) is introduced to remove the air from the reactor. Then, the temperature is increased from 0°C to 150°C at a rate of 1°C / min and held for 10 hours. During this period, when the temperature is increased to 50°C and 100°C, pre-fluorination is performed and held for 2 hours every time the temperature is increased by 50°C. Finally, the temperature is reduced to room temperature at a rate of 1°C / min to obtain FeF3·3H2O.

[0076] (3) Oxygen-free high-speed ball milling: The obtained FeF3·3H2O and 20-50 nm nano-carbon were mixed in an argon-protected anhydrous and oxygen-free glove box at a mass ratio of 80:20, and then added to a ball milling jar. Appropriate small balls were added at a mass ratio of material to ball milling balls of 1:9. After sealing, the mixture was removed and subjected to high-speed ball milling. The ball milling was carried out intermittently, with a 10-minute milling interval followed by a 5-minute interval, repeated 30 times at a rotation speed of 300 rpm. The material temperature was controlled at 25-35℃. After ball milling, the small balls and material were separated in the glove box to obtain carbon nano-island modified FeF3·3H2O material. Figure 10 It can be seen that, under the same battery assembly process conditions as in Example 1, the specific capacity of the carbon nano-island modified FeF3·3H2O composite material is 162.7 mAh / g.

[0077] like Figure 3 As shown, the XRD pattern of the carbon nano-island modified FeF3·3H2O material matches the standard PDF card of FeF3·3H2O, proving that the product phase obtained by fluorination in the low-temperature region is FeF3·3H2O.

[0078] Comparative Example 1

[0079] Nano-carbon / FeF3 composite materials were prepared using Fe(CO2CH2)3 as the iron source, water as the solvent, and KOH to adjust the pH value. The process involved wet chemical reaction, continuous anhydrous and oxygen-free fluorination, and oxygen-free high-temperature composite process.

[0080] (1) Wet chemical reaction: KOH was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then Fe(CO2CH2)3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying (same as in Example 1).

[0081] (2) Continuous anhydrous and oxygen-free fluorination: The obtained iron hydroxide is transferred to a reactor, and anhydrous and oxygen-free fluorine gas (a mixture of fluorine and argon with a fluorine volume fraction of 15%) is introduced to remove the air from the reactor. Then, the reactor is heated from 0°C to 250°C at a heating rate of 1°C / min and held for 10 hours. During this period, when the temperature is raised to 50, 100, 150, and 200°C, a pre-fluorination is performed and held for 2 hours every 50°C increase. Finally, the temperature is lowered to room temperature at a cooling rate of 1°C / min to obtain FeF3·0.33H2O.

[0082] (3) Oxygen-free high-temperature composite: The obtained FeF3·0.33H2O and 20-50nm nano carbon were mixed at a mass ratio of 80:20 and then transferred to a tube furnace. Argon gas was introduced to remove the air, and the temperature was raised from room temperature to 600℃ and held for 2 hours at a heating rate of 5℃ / min. Then the furnace was cooled to room temperature to obtain nano carbon / FeF3 composite material.

[0083] Depend on Figure 7 It can be seen that in the nano-carbon / FeF3·0.33H2O composite material prepared by high-temperature composite method, FeF3·0.33H2O undergoes sintering at high temperature, transforming into anhydrous FeF3 phase and losing its layered structure; for example... Figure 9 As shown, under the same battery assembly process conditions as in Example 1, the specific capacity of the nano-carbon / FeF3·0.33H2O composite material is 220.8 mAh / g, which is less than half of the specific capacity of the carbon nano-island modified FeF3·0.33H2O material.

[0084] Comparative Example 2

[0085] Carbon nanoisland-modified FeF3·0.33H2O composite materials were prepared by using Fe(CO2CH2)3 as the iron source, water as the solvent, and adjusting the pH value by adding NH3·H2O, and by a wet chemical reaction-continuous fluorination-high-speed ball milling process.

[0086] (1) Wet chemical reaction: NH3·H2O was dissolved in water to prepare an alkaline solution with a pH of 10. The solution was heated to 40°C with stirring, and then Fe(CO2CH2)3 was added to the solution at a molar ratio of iron to hydroxide of 1:5. The reaction was continued for 4 hours. After the reaction, the product was collected by differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying (same as in Example 1).

[0087] (2) Continuous fluorination: The obtained ferric hydroxide is transferred to a reactor, and fluorine gas is introduced (without removing air and water from the reactor). The temperature is increased from 0°C to 250°C at a rate of 1°C / min and held for 10 hours. During this period, when the temperature is increased to 50, 100, 150 and 200°C, pre-fluorination is performed for 2 hours every time the temperature is increased by 50°C. Finally, the temperature is reduced to room temperature at a rate of 1°C / min to obtain FeF3·0.33H2O.

[0088] (3) High-speed ball milling: The obtained FeF3·0.33H2O and nano carbon were mixed in a mass ratio of 80:20 and added to the ball milling jar. Appropriate small balls were added in a mass ratio of ball milling material to ball milling balls of 1:9. High-speed ball milling was then carried out in an intermittent manner, with a 10-minute interval followed by a 5-minute interval, repeated 30 times. The rotation speed was 300 rpm, and the material temperature was controlled at 25-35℃. After the ball milling was completed, the small balls and the material were separated in a glove box to obtain the nano carbon modified FeF3·0.33H2O material.

[0089] Depend on Figure 8 It can be seen that in the FeF3·0.33H2O material prepared by fluorination and ball milling under an anhydrous and oxygen-free environment, there is a significant oxide layer coating on the surface of FeF3·0.33H2O; such as Figure 9 As shown, under the same battery assembly process conditions as in Example 1, the specific capacity of the nano-carbon / FeF3·0.33H2O composite material is 115.8 mAh / g, which is significantly lower than the specific capacity of the carbon nano-island modified FeF3·0.33H2O material.

[0090] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A carbon nano-island modified hydrated iron trifluoride cathode material, characterized in that, The material is a composite material of nano-carbon and hydrated iron trifluoride. The composite material exhibits a mottled layered structure with a size of 1–20 μm. The carbon nano-islands are island-shaped morphologies partially embedded in the bulk phase of hydrated iron trifluoride, with a size of 50–200 nm.

2. The carbon nano-island modified hydrated iron trifluoride cathode material according to claim 1, characterized in that, The elements in the region where carbon nano islands and hydrated ferric trifluoride are combined exhibit a gradient distribution.

3. A method for preparing a carbon nano-island modified hydrated iron trifluoride cathode material according to claim 1, characterized in that, The process employs a wet chemical reaction-continuous anhydrous and oxygen-free fluorination-oxygen-free high-speed ball milling process. The iron hydroxide obtained from the wet chemical reaction is continuously fluorinated with anhydrous and oxygen-free fluorine gas, and the resulting hydrated iron trifluoride is cooled and then subjected to oxygen-free high-speed ball milling with nano-carbon to obtain the carbon nano-island modified hydrated iron trifluoride cathode material.

4. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 3, characterized in that, S1. Wet chemical reaction: After the iron-containing raw material is fully reacted with the hydroxide-containing solution, it is subjected to differential centrifugation, ultrasonic washing with ultrapure water, and freeze drying to obtain the iron hydroxide intermediate product. S2. Continuous anhydrous and oxygen-free fluorination: The iron hydroxide intermediate product is continuously fluorinated with a fluorine atmosphere in an anhydrous and oxygen-free environment and within different temperature ranges to obtain the corresponding hydrated iron trifluoride. S3. High-speed ball milling in an oxygen-free atmosphere: The hydrated iron trifluoride and nano carbon are ball milled at high speed in an oxygen-free atmosphere, and then the materials are separated to obtain carbon nano-island modified hydrated iron trifluoride cathode material.

5. The method for preparing the carbon-carbon nano-island modified hydrated iron trifluoride cathode material according to claim 4, characterized in that, In step S2, based on the differences in fluorination temperature range, ferric fluoride with different water of crystallization contents is obtained, including FeF3·0.33H2O and FeF3·3H2O.

6. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 4, characterized in that, In step S1, the iron-containing raw material is a ferric ion metal salt, and the hydroxide-containing solution is a polar alkaline solution with a pH of 10; the iron-containing raw material and the hydroxide-containing solution react fully at a molar ratio of iron to hydroxide of 1:4 to 1:

7. And / or, in step S2, the iron hydroxide intermediate product is transferred to an anhydrous reactor, and then anhydrous and oxygen-free fluorine gas is introduced to carry out fluorination treatment according to a continuous anhydrous and oxygen-free fluorination process. And / or, in step S3, hydrated ferric fluoride and nano carbon are mixed at a mass ratio of 70:30 to 90:10 under an oxygen-free protective atmosphere, then transferred to a ball mill jar for sealing treatment, and then subjected to high-speed ball milling. And / or, in step S3, the particle size of the nano-carbon is 20-50 nm.

7. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 6, characterized in that, The ferric ion metal salts include FeCl3, Fe(NO3)3, Fe2(SO4)3, and Fe(CO2CH2)3; the polar alkaline solutions include NH3·H2O, LiOH, NaOH, and KOH, and the polar solvents include H2O, CH3OH, and CH3CH2OH.

8. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 6, characterized in that, The anhydrous and oxygen-free fluorine gas is a mixture of fluorine and nitrogen, or a mixture of fluorine and argon, wherein the volume fraction of fluorine in the mixture is above 10%.

9. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 6, characterized in that, The continuous anhydrous and oxygen-free fluorination process starts at 0°C, reaches an end temperature of 150–260°C, and has a heating rate of 1°C / min. Pre-fluorination is performed for 2 hours every 50°C increase. After reaching the set temperature, the temperature is maintained for 5–10 hours to achieve full fluorination. Then, the temperature is lowered to room temperature at a rate of 1°C / min.

10. The method for preparing the carbon nano-island modified hydrated iron trifluoride cathode material according to claim 4, characterized in that, In step S3, the oxygen-free atmosphere is achieved in a clean glove box protected by argon gas, where the content of water and oxygen is less than 0.1 ppm; the high-speed ball milling process is carried out in an intermittent manner, with a ball milling speed of 300-600 rpm, a working time of 10-15 min, an interval of 3-5 min, repeated 25-35 times, and a material temperature of 25-50℃.

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