Layered iron fluoride-based positive electrode material and preparation method and application thereof

Abstract

The application discloses a layered fluorinated iron-based positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion battery positive electrode materials. The preparation method is as follows: a graphene template is prepared; an iron source-containing precursor graphene template is prepared; ethanol and an HF aqueous solution are mixed to obtain a mixed solution; the mixed solution is transferred into an autoclave; the mixed solution is isolated from the iron source-containing precursor graphene template; the iron source-containing precursor graphene template is subjected to fluorination treatment through steam generated by the mixed solution; and then, washing and vacuum drying are sequentially performed to obtain an intermediate sample, in which fluorinated iron grows between layers of the graphene template; and the intermediate sample is subjected to heat treatment under the protection of an inert gas to obtain the layered fluorinated iron-based positive electrode material. The problems of the fluorinated iron positive electrode material, such as phase transition caused by electrochemical reaction, product phase separation, slow atomic migration and side reactions caused by Fe nanoparticle agglomeration, are solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a layered iron fluoride-based cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) have garnered significant attention in both academia and industry due to their high energy / power density, long cycle life, and environmental friendliness. Currently, commercially available cathode materials are primarily based on intercalation mechanisms, such as olivine-type LiFePO4 (specific capacity approximately 170 mAh / g), layered LiCoO2 (specific capacity approximately 274 mAh / g), and spinel-type LiMn2O4 (specific capacity approximately 148 mAh / g). These materials typically exhibit low self-discharge and good cycle stability; however, due to their single-electron reaction mechanism, their theoretical energy density limit is approximately 350 Wh / kg, which is insufficient to meet the growing demand for high-energy storage in electric vehicles and portable electronic products.

[0003] In contrast, conversion electrode materials, through multi-electron transfer reactions, can provide higher specific capacity and are expected to achieve energy densities exceeding 350 Wh / kg, thus being regarded as potential candidate systems for next-generation high-energy-density batteries. Among many conversion materials, iron fluoride (FeF3) has become one of the research hotspots due to its theoretical specific capacity of up to 712 mAh / g, high discharge plateau, and good structural stability.

[0004] However, iron fluoride cathode materials still face a series of challenges in practical applications. The reaction involves a transition from a single phase to multiple phases, accompanied by the breaking and recombination of chemical bonds, leading to significant changes in electrode volume and structural reconstruction, resulting in capacity decay and decreased cycle performance. The conductive Fe nanoparticles and insulating LiF nanoparticles generated in the reaction are prone to phase separation, and the slow atomic migration in the solid / solid reaction leads to poor kinetic performance and low energy efficiency (approximately 80%). Furthermore, the agglomeration of Fe nanoparticles during cycling exacerbates side reactions with the electrolyte, causing loss of active material and iron dissolution, further accelerating capacity decay. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a layered iron fluoride-based cathode material, its preparation method and application, so as to solve the technical defects of iron fluoride cathode materials caused by electrochemical reaction phase transformation, product phase separation, slow atomic migration and side reactions caused by Fe nanoparticle agglomeration, resulting in capacity decay, poor cycle performance, poor kinetic performance and low energy efficiency.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention provides a method for preparing a layered iron fluoride-based cathode material, comprising the following steps:

[0008] Preparation of graphene templates;

[0009] Ferric nitrate nonahydrate was dissolved in deionized water to prepare ferric nitrate aqueous solution. The graphene template was then immersed in the ferric nitrate aqueous solution and allowed to stand. The precipitate was collected and then filtered, washed, and freeze-dried to obtain a graphene template containing an iron source precursor.

[0010] Ethanol and HF aqueous solution were mixed to prepare a mixed solution. The mixed solution was transferred to a hydrothermal reactor and isolated from the graphene template containing the iron source precursor. The graphene template containing the iron source precursor was fluorinated by the steam generated by the mixed solution. Then, it was washed and vacuum dried to obtain an intermediate sample. In the intermediate sample, iron fluoride grew between the graphene template layers.

[0011] The intermediate sample was heat-treated under the protection of an inert gas to obtain a layered iron fluoride-based cathode material.

[0012] In one embodiment, the preparation of the graphene template includes the following steps:

[0013] Graphite, chromium trioxide and hydrochloric acid were mixed for the first reaction, followed by washing with water to remove unreacted chromium trioxide, and drying to obtain a dried sample;

[0014] The dried sample was dispersed in a hydrogen peroxide solution and allowed to stand to expand, thus obtaining chemically expanded graphite.

[0015] Chemically expanded graphite was immersed in a mixture of concentrated sulfuric acid and potassium permanganate for mixed oxidation treatment to obtain graphene oxide arrays with an array structure.

[0016] The polyetheramine was mixed with the graphene oxide array for a second reaction, followed by washing and freeze-drying to obtain the graphene template.

[0017] In one embodiment, the ratio of graphite, chromium trioxide, and hydrochloric acid is 1g~2g:8g~16g:5mL~15mL;

[0018] The concentration of the hydrogen peroxide solution is 10wt%~20wt%, and the ratio of the amount of dried sample to hydrogen peroxide solution is 0.5g~1g:300mL~1000mL;

[0019] The ratio of chemically expanded graphite, concentrated sulfuric acid, and potassium permanganate is 0.5g~1g:40mL~100mL:1g~2g;

[0020] The concentration of the graphene oxide array is 2 mg / mL to 8 mg / mL, and the ratio of the polyetheramine to the graphene oxide array is 0.6 g to 2 g: 30 mL to 125 mL.

[0021] In one embodiment, the temperature of the first reaction is 20°C to 60°C, and the time is 2h to 4h; the drying process is carried out under vacuum conditions, and the temperature of the drying process is 60°C to 80°C, and the time is 12h to 24h.

[0022] The static expansion time is 7 to 10 days;

[0023] The temperature of the mixed oxidation treatment is 35℃~45℃, and the time is 4h~12h;

[0024] The second reaction is carried out at a temperature of 80℃~100℃ for a time of 20h~24h.

[0025] The freeze-drying process is carried out at a temperature of -50℃ to -40℃ for 12 hours to 24 hours.

[0026] In one embodiment, the concentration of the ferric nitrate aqueous solution is 0.1 mol / L to 2 mol / L; the ratio of the graphene template to ferric nitrate nonahydrate is 20 mg to 200 mg: 0.808 g to 16.16 g.

[0027] In one embodiment, the volume ratio of the ethanol to the HF aqueous solution is (10~100):1; and the mass fraction of the HF aqueous solution is 40%~42%.

[0028] In one embodiment, the molar ratio of the ferric nitrate nonahydrate to HF in the HF aqueous solution is 1:(0.05~1.13).

[0029] In one embodiment, the settling time is 12h to 24h; the freeze-drying temperature is -50℃ to -40℃, and the time is 1 day to 2 days;

[0030] The fluorination treatment is carried out at a temperature of 60℃ to 200℃ for a time of 2h to 20h.

[0031] The vacuum drying temperature is 60℃~120℃, and the time is 12h~24h;

[0032] The inert gas is argon, and the heat treatment temperature is 150℃~350℃, and the time is 2h~12h.

[0033] This invention also provides a method for preparing a layered iron fluoride-based cathode material, wherein the layered iron fluoride-based cathode material has a two-dimensional nanosheet morphology with a thickness of less than 50 nm; the layered iron fluoride-based cathode material includes a graphene template and iron fluoride, wherein the iron fluoride is grown in layers between the layers of the graphene template, and the iron fluoride exists in the form of FeF3·0.33H2O crystalline phase.

[0034] This invention also provides an application of layered iron fluoride-based cathode material as a cathode material in lithium-ion batteries.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention provides a method for preparing a layered iron fluoride-based cathode material. This method uses graphene as a template to achieve confined growth of iron fluoride within the graphene layers, effectively suppressing the aggregation and excessive growth of iron fluoride particles. The final product is a layered iron fluoride-based cathode material with a regular two-dimensional layered morphology, namely a graphene / iron fluoride composite cathode material. Relying on the interlayer confinement effect of the graphene template, it not only significantly alleviates the volume expansion and structural stress caused by phase transitions during charge and discharge of iron fluoride, enhancing the structural stability of the electrode, but also improves reaction reversibility and reaction kinetics, mitigating voltage hysteresis. Simultaneously, the highly conductive network constructed by graphene itself can significantly improve the overall electronic conductivity of the material, fundamentally solving the problem of poor intrinsic conductivity of iron fluoride. The synergistic effect of these multiple structural advantages enables the prepared cathode material to exhibit excellent rate performance and long-cycle stability, effectively reducing irreversible capacity decay during cycling and significantly improving the initial coulombic efficiency. This preparation method achieves precise confined growth and efficient synthesis of iron fluoride through multi-step process design. Specific advantages are as follows: First, layered iron fluoride is prepared using a graphene template through interlayer confinement, avoiding excessive growth and aggregation of iron fluoride particles. The method of first soaking the iron source precursor, then freeze-drying, and finally fluorination prevents iron fluoride from growing outside the graphene template, ensuring that the obtained sample is iron fluoride grown within the interlayer of the graphene template. Second, the ethanol-assisted HF evaporation method directly synthesizes FeF3·0.33H2O in one step, replacing the complex process of first synthesizing hydrates and then undergoing multiple dehydration steps in the traditional process. This significantly simplifies the preparation steps and effectively reduces production energy consumption and time costs. Furthermore, the amount of ethanol used in this process needs precise control; too little ethanol easily generates FeF3·3H2O, affecting the subsequent electrochemical performance of the material, while too much ethanol reduces the reaction rate. Third, after the fluorination reaction, the sample is washed and dried to remove unreacted ferric nitrate impurities between graphene layers, thus avoiding the adverse effects of impurities on the subsequent electrochemical performance of the battery. Fourth, the final high-temperature inert gas heat treatment can further remove residual impurities in the material and improve the conductivity of the graphene template. The temperature of this heat treatment also needs to be strictly controlled. If the temperature is too low, the reduction of graphene oxide will be insufficient, affecting the conductivity of the material. If the temperature is too high, FeF3·0.33H2O will dehydrate to generate FeF3, destroying the crystal structure of the target product and thus affecting its electrochemical performance.

[0037] The preparation method of this invention provides a new, efficient, and controllable approach for the template-based synthesis of FeF3·0.33H2O, and the process has good scalability. The obtained FeF3·0.33H2O has a more stable crystal structure than FeF3 and FeF3·3H2O. The appropriate amount of water of crystallization can effectively maintain the integrity of the layered framework of the material during electrochemical cycling, further inhibiting the dissolution and structural degradation of active materials, fundamentally improving the structural retention ability of electrode materials during long-term cycling, and ultimately significantly improving the overall cycle life and capacity retention of lithium-ion batteries.

[0038] Furthermore, a stable graphene oxide array was obtained through expansion, oxidation, and polyetheramine crosslinking as a graphene template. This graphene template has an accordion-like structure, which can prevent the graphene sheets from re-stacking, so as to facilitate the subsequent growth of iron fluoride between the layers.

[0039] This invention provides a layered iron fluoride-based cathode material. This material is produced by growing layered iron fluoride between the layers of a graphene template. Utilizing the confinement effect of graphene, it avoids excessive growth and aggregation of iron fluoride, and significantly shortens the Li... + The graphene / iron fluoride heterostructure effectively increases the diffusion distance within the active material, thereby enhancing the ion diffusion rate. Simultaneously, the resulting graphene / iron fluoride heterostructure constructs a continuous conductive network, specifically addressing the poor conductivity of iron fluoride. Furthermore, the graphene template effectively buffers the stress generated by volume expansion and contraction, inhibiting the pulverization and shedding of the active material. During charge and discharge, its confinement effect enhances the reversibility of the reaction, reduces irreversible capacity decay, strengthens reaction kinetics, and effectively alleviates capacity decay caused by product phase separation. Attached Figure Description

[0040] Figure 1 These are optical micrographs of the graphene templates used in Examples 1 to 7 and Comparative Examples 1 to 3;

[0041] Figure 2 This is the X-ray diffraction pattern of the two-dimensional layered iron fluoride-based cathode material in Example 1;

[0042] Figure 3 This is a scanning electron microscope image of the two-dimensional layered iron fluoride-based cathode material in Example 1;

[0043] Figure 4 The X-ray diffraction pattern of the iron fluoride cathode material in Comparative Example 1 is shown.

[0044] Figure 5 This is a scanning electron microscope image of the iron fluoride cathode material in Comparative Example 4;

[0045] Figure 6The graph shows the rate performance test results of the lithium-ion batteries assembled in Example 1 and Comparative Examples 1, 2, and 3. Detailed Implementation

[0046] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions mentioned in the specification are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0047] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0048] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0049] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0050] This invention provides a layered iron fluoride-based cathode material, its preparation method, and its application.

[0051] One approach provides a method for preparing a layered iron fluoride-based cathode material, which is based on a graphene template and includes the following steps:

[0052] S1: Preparation of graphene template.

[0053] S2: Dissolve ferric nitrate nonahydrate in deionized water to prepare an aqueous solution of ferric nitrate with a concentration of 0.1 mol / L to 2 mol / L. Soak a graphene template in the aqueous solution of ferric nitrate, with the ratio of graphene template to ferric nitrate nonahydrate being 20 mg to 200 mg: 0.808 g to 16.16 g. Let stand for 12 h to 24 h and collect the precipitate.

[0054] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at a temperature of -50℃ to -40℃, preferably -40℃, for 1 to 2 days to obtain a graphene template containing an iron source precursor.

[0055] S4: Ethanol and HF aqueous solution are mixed at a volume ratio of (10~100):1, wherein the mass fraction of HF aqueous solution is 40%~42%, preferably 40%, to obtain a mixed solution. The mixed solution is transferred to a hydrothermal reactor, and the mixed solution is isolated from the graphene template containing the iron source precursor. The graphene template containing the iron source precursor obtained in S3 is fluorinated at a temperature of 60℃~200℃ using high-temperature steam generated by the mixed solution for 2h~20h. The molar ratio of ferric nitrate nonahydrate to HF in the HF aqueous solution is 1:(0.05~1.13), preferably ferric nitrate nonahydrate:HF is 40mmol:2.26mmol.

[0056] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 60℃~120℃ for 12h~24h to obtain an intermediate sample. In the intermediate sample, iron fluoride grows between the graphene template layers.

[0057] S6: The intermediate sample obtained in S5 is heat-treated at 150℃~350℃ for 2h~12h under the protection of inert gas (argon) to obtain layered iron fluoride-based cathode material, which is used as cathode material for lithium-ion batteries.

[0058] In S1, the method for preparing the graphene template includes the following steps:

[0059] S11: Weigh graphite, chromium trioxide, and hydrochloric acid, mix them, and carry out a first reaction at 20℃~60℃ for 2h~4h. Then, wash with water to remove unreacted chromium trioxide, and dry under vacuum at 60℃~80℃ for 12h~24h to obtain a dried sample. The ratio of graphite, chromium trioxide, and hydrochloric acid is 1g~2g:8g~16g:5mL~15mL, preferably 1g:16g:10mL.

[0060] S12: Disperse the dried sample in a hydrogen peroxide solution and allow it to stand for expansion for 7 to 10 days, preferably 7 days, to obtain chemically expanded graphite (CEG). The concentration of the hydrogen peroxide solution is 10 wt% to 20 wt%, preferably 10 wt%; the ratio of the dried sample to the hydrogen peroxide solution is 0.5 g to 1 g: 300 mL to 1000 mL, preferably 0.5 g: 300 mL.

[0061] S13: A mixed solution is prepared by mixing concentrated sulfuric acid and potassium permanganate. CEG is then immersed in the mixed solution of concentrated sulfuric acid and potassium permanganate and subjected to a mixed oxidation treatment at 35℃~45℃ for 4h~12h to obtain a graphene oxide array (CEGO) with an array structure. The ratio of chemically expanded graphite, concentrated sulfuric acid, and potassium permanganate is 0.5g~1g:40mL~100mL:1g~2g. Preferably, the ratio is 0.5g:100mL:1g.

[0062] S14: Polyetheramine is mixed with CEGO solution and subjected to a second reaction at 80℃~100℃ for 20h~24h. The preferred temperature for the second reaction is 90℃ for 24h. After washing, the mixture is freeze-dried at -50℃~-40℃ for 12h~24h, preferably at -40℃ for 24h, to obtain a graphene template with a stable array structure. The concentration of the graphene oxide array is 2mg / mL~8mg / mL, preferably 5mg / mL. The ratio of polyetheramine to graphene oxide array is 0.6g~2g:30mL~125mL, preferably 2g:50mL.

[0063] Among them, the graphite is flake graphite with a particle size of 80 mesh to 1000 mesh, and the molecular weight of the polyetheramine is 600 g / mol to 2000 g / mol.

[0064] The prepared graphene template, such as Figure 1 As shown, the graphene template has an accordion-like array structure. This array structure can serve as a framework for the subsequent interlayer growth of iron fluoride, resulting in an iron fluoride-based material with a layered structure.

[0065] On the other hand, a high-performance two-dimensional layered iron fluoride-based cathode material prepared by the above-mentioned preparation method of layered iron fluoride-based cathode material is provided.

[0066] like Figure 2 and Figure 3 As shown, the layered iron fluoride-based cathode material exhibits a typical two-dimensional nanosheet morphology with a thickness of less than 50 nm. The layered iron fluoride-based cathode material includes a graphene template and iron fluoride. The iron fluoride is grown in layers between the graphene template and exists in the form of FeF3·0.33H2O crystalline phase.

[0067] On the other hand, the application of the high-performance two-dimensional layered iron fluoride-based cathode material prepared by the above preparation method as a cathode material in lithium-ion batteries is also provided.

[0068] The high-performance layered iron fluoride-based cathode material prepared above is applied to the assembly process of lithium-ion batteries, including the following steps:

[0069] Step 1: High-performance two-dimensional layered iron fluoride-based cathode material is ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone is added to form a homogenate. The viscous slurry is then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours to obtain the electrode sheet. The obtained electrode sheet is then cut to obtain the iron fluoride cathode electrode sheet.

[0070] Step Two: The lithium-ion battery assembly process is carried out in an argon-filled glove box. The battery is assembled in the following order: positive electrode shell, iron fluoride positive electrode sheet, electrolyte, separator, lithium sheet, and negative electrode shell. The electrolyte is 1M LiPF6-EC (ethylene carbonate, EC) / DMC (dimethyl carbonate, DMC) / DEC (diethyl carbonate, DEC) (v / v=1:1:1), with a total electrolyte volume of 90μL. A PP separator is used. First, the iron fluoride positive electrode sheet is placed in the center of the positive electrode shell, and 45μL of electrolyte is added for wetting. Then, the PP separator is placed on top, and another 45μL of electrolyte is added. Next, a fresh lithium sheet is placed in the center of the separator. The spacer, spring contact, and negative electrode shell are then added in sequence. The entire battery assembly process is completed using a battery packaging machine.

[0071] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0072] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0073] Example 1

[0074] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0075] S1: Preparation of graphene template.

[0076] S11: Weigh 1g of 1000-mesh graphite, 16g of chromium trioxide and 10mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0077] S12: Disperse 0.5g of the dried sample in 300mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0078] S13: Mix 100 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0079] S14: Finally, 2g of polyetheramine with a molecular weight of 2000g / mol was mixed with 50mL of CEGO solution with a concentration of 5mg / mL, and the mixture was reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0080] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0081] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0082] S4: Add 0.1 mL of HF aqueous solution to 6 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 150 °C using high-temperature steam generated by the mixed solution.

[0083] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 80°C for 12 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0084] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0085] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0086] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0087] The resulting layered iron fluoride-based cathode material has lateral dimensions of several micrometers and a thickness of approximately 10 nanometers.

[0088] The battery assembled in this embodiment can achieve a specific capacity of 353 mAh / g at a current density of 0.03 A / g, 310 mAh / g at a current density of 0.06 A / g, 225 mAh / g at a current density of 0.15 A / g, 155 mAh / g at a current density of 0.3 A / g, and 82 mAh / g at a current density of 0.6 A / g.

[0089] Depend on Figure 2 It can be seen that FeF30·33H2O can be obtained in one step by using ethanol-assisted HF volatilization.

[0090] Depend on Figure 3 It can be seen that it exhibits a typical two-dimensional nanosheet morphology, and does not show the granular morphology of iron fluoride obtained by the conventional solvothermal method.

[0091] Example 2

[0092] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0093] S1: Preparation of graphene template.

[0094] S11: Weigh 2g of 80-mesh graphite, 8g of chromium trioxide and 5mL of hydrochloric acid and mix them at 40℃ for 4h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0095] S12: Disperse 1g of dried sample in 1000mL of 20wt% hydrogen peroxide solution and let it stand for 10 days to expand, thus obtaining chemically expanded graphite (CEG).

[0096] S13: Mix 40 mL of concentrated sulfuric acid with 2 g of potassium permanganate and stir. Soak 1 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 45 °C for 12 h to obtain graphene oxide array CEGO with an array structure.

[0097] S14: Finally, 0.6 g of 600 g / mol polyetheramine was mixed with 125 mL of 2 mg / mL CEGO solution and reacted at 100 °C for 20 h. After washing, the mixture was freeze-dried at -50 °C for 12 h to obtain a graphene template with a stable array structure.

[0098] S2: Dissolve 0.808g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 0.1mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 12h. Take the precipitate.

[0099] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -50°C for 1 day to obtain a graphene template containing an iron source precursor.

[0100] S4: Add 0.05 mL of HF aqueous solution to 3 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 42%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 at 200 °C for 2 h using high-temperature steam generated by the mixed solution.

[0101] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 120℃ for 24 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0102] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0103] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0104] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0105] The battery assembled in this embodiment can achieve a specific capacity of 280 mAh / g at a current density of 0.03 A / g, 220 mAh / g at a current density of 0.06 A / g, 186 mAh / g at a current density of 0.15 A / g, 131 mAh / g at a current density of 0.3 A / g, and 75 mAh / g at a current density of 0.6 A / g.

[0106] Example 3

[0107] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0108] S1: Preparation of graphene template.

[0109] S11: Weigh 1g of 500-mesh graphite, 16g of chromium trioxide and 15mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0110] S12: Disperse 0.5g of the dried sample in 500mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0111] S13: Mix 40 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0112] S14: Finally, 2g of 900g / mol polyetheramine was mixed with 50mL of 5mg / mL CEGO solution and reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0113] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 200mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0114] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0115] S4: Add 0.1 mL of HF aqueous solution to 1 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 150 °C using high-temperature steam generated by the mixed solution.

[0116] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 60°C for 12 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0117] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0118] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0119] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0120] The battery assembled in this embodiment can achieve a specific capacity of 320 mAh / g at a current density of 0.03 A / g, 276 mAh / g at a current density of 0.06 A / g, 213 mAh / g at a current density of 0.15 A / g, 138 mAh / g at a current density of 0.3 A / g, and 73 mAh / g at a current density of 0.6 A / g.

[0121] Example 4

[0122] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0123] S1: Preparation of graphene template.

[0124] S11: Weigh 1g of 300-mesh graphite, 8g of chromium trioxide and 10mL of hydrochloric acid and mix them at 60℃ for 4h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 80℃ for 24h to obtain a dried sample.

[0125] S12: Disperse 0.5g of the dried sample in 500mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0126] S13: Mix 40 mL of concentrated sulfuric acid with 2 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 45 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0127] S14: Finally, 2g of 900g / mol polyetheramine was mixed with 50mL of 5mg / mL CEGO solution and reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0128] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0129] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0130] S4: Add 0.1 mL of HF aqueous solution to 10 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 150 °C using high-temperature steam generated by the mixed solution.

[0131] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 80°C for 20 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0132] S6: The intermediate sample obtained in S5 was heat-treated at 150°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0133] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0134] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0135] The battery assembled in this embodiment can achieve a specific capacity of 336 mAh / g at a current density of 0.03 A / g, 304 mAh / g at a current density of 0.06 A / g, 216 mAh / g at a current density of 0.15 A / g, 136 mAh / g at a current density of 0.3 A / g, and 80 mAh / g at a current density of 0.6 A / g.

[0136] Example 5

[0137] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0138] S1: Preparation of graphene template.

[0139] S11: Weigh 1g of 1000-mesh graphite, 16g of chromium trioxide and 10mL of hydrochloric acid and mix them at 60℃ for 4h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 80℃ for 24h to obtain a dried sample.

[0140] S12: Disperse 1g of dried sample in 300mL of 10wt% hydrogen peroxide solution and let it stand for 10 days to expand, thus obtaining chemically expanded graphite (CEG).

[0141] S13: Mix 100 mL of concentrated sulfuric acid with 2 g of potassium permanganate and stir. Immerse 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate and perform mixed oxidation at 35 °C for 12 h to obtain graphene oxide array CEGO with an array structure.

[0142] S14: Finally, 2g of 1000g / mol polyetheramine was mixed with 50mL of 5mg / mL CEGO solution and reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0143] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 12h. Take the precipitate.

[0144] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -50°C for 1 day to obtain a graphene template containing an iron source precursor.

[0145] S4: Add 0.1 mL of HF aqueous solution to 6 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 120 °C using high-temperature steam generated by the mixed solution.

[0146] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 80°C for 24 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0147] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0148] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0149] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0150] The battery assembled in this embodiment can achieve a specific capacity of 327 mAh / g at a current density of 0.03 A / g, 295 mAh / g at a current density of 0.06 A / g, 213 mAh / g at a current density of 0.15 A / g, 133 mAh / g at a current density of 0.3 A / g, and 67 mAh / g at a current density of 0.6 A / g.

[0151] Example 6

[0152] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0153] S1: Preparation of graphene template.

[0154] S11: Weigh 2g of 500-mesh graphite, 16g of chromium trioxide and 5mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0155] S12: Disperse 1g of dried sample in 1000mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0156] S13: Mix 100 mL of concentrated sulfuric acid with 2 g of potassium permanganate and stir. Soak 1 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain CEGO, a graphene oxide array with an array structure.

[0157] S14: Finally, 2g of 1000g / mol polyetheramine was mixed with 30mL of 8mg / mL CEGO solution and reacted at 80℃ for 24h. After washing, the mixture was freeze-dried at -50℃ for 12h to obtain a graphene template with a stable array structure.

[0158] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 20mg of the prepared graphene template in the solution and let it stand for 12h. Take the precipitate.

[0159] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 2 days to obtain a graphene template containing an iron source precursor.

[0160] S4: Add 0.1 mL of HF aqueous solution to 6 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 15 h at 100 °C using high-temperature steam generated by the mixed solution.

[0161] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 60°C for 24 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0162] S6: The intermediate sample obtained in S5 was heat-treated at 180°C for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0163] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0164] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0165] The battery assembled in this embodiment can achieve a specific capacity of 343 mAh / g at a current density of 0.03 A / g, 307 mAh / g at a current density of 0.06 A / g, 214 mAh / g at a current density of 0.15 A / g, 134 mAh / g at a current density of 0.3 A / g, and 80 mAh / g at a current density of 0.6 A / g.

[0166] Example 7

[0167] This embodiment provides a method for preparing a layered iron fluoride-based cathode material, including the following steps:

[0168] S1: Preparation of graphene template.

[0169] S11: Weigh 2g of 1000-mesh graphite, 16g of chromium trioxide and 15mL of hydrochloric acid and mix them at 60℃ for 4h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 80℃ for 24h to obtain a dried sample.

[0170] S12: Disperse 0.5g of the dried sample in 1000mL of 20wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0171] S13: Mix 100 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 1 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate and perform mixed oxidation at 45 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0172] S14: Finally, 0.6 g of 600 g / mol polyetheramine was mixed with 50 mL of 5 mg / mL CEGO solution and reacted at 100 °C for 20 h. After washing, the mixture was freeze-dried at -50 °C for 12 h to obtain a graphene template with a stable array structure.

[0173] S2: Dissolve 0.808g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 0.1mol / L. Immerse 20mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0174] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 2 days to obtain a graphene template containing an iron source precursor.

[0175] S4: Add 0.1 mL of HF aqueous solution to 6 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 at 60°C for 20 h using high-temperature steam generated by the mixed solution.

[0176] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 120℃ for 12h to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0177] S6: The intermediate sample obtained in S5 was heat-treated at 350℃ for 2 hours under argon protection to obtain a graphene / iron fluoride composite material, namely a layered iron fluoride-based cathode material.

[0178] This embodiment also provides an application of layered iron fluoride-based cathode material in lithium-ion batteries, including the following steps:

[0179] The prepared high-performance two-dimensional layered iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0180] The battery assembled in this embodiment can achieve a specific capacity of 336 mAh / g at a current density of 0.03 A / g, 285 mAh / g at a current density of 0.06 A / g, 198 mAh / g at a current density of 0.15 A / g, 146 mAh / g at a current density of 0.3 A / g, and 79 mAh / g at a current density of 0.6 A / g.

[0181] Comparative Example 1

[0182] This comparative example provides a method for preparing an iron fluoride cathode material, including the following steps:

[0183] S1: Preparation of graphene template.

[0184] S11: Weigh 1g of 1000-mesh graphite, 16g of chromium trioxide and 10mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0185] S12: Disperse 0.5g of the dried sample in 300mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0186] S13: Mix 100 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0187] S14: Finally, 2g of polyetheramine with a molecular weight of 2000g / mol was mixed with 50mL of CEGO solution with a concentration of 5mg / mL, and the mixture was reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0188] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0189] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0190] S4: Transfer 1 mL of HF aqueous solution to a hydrothermal reactor, wherein the mass fraction of HF aqueous solution is 40%. Isolate the graphene template containing the iron source precursor obtained in S3 from the HF aqueous solution and prevent direct contact. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 150℃ using high-temperature steam generated by the HF aqueous solution.

[0191] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 80°C for 12 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0192] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a composite material of iron fluoride, namely an iron fluoride cathode material.

[0193] This comparative example also provides an application of iron fluoride cathode material in lithium-ion batteries, including the following steps:

[0194] The prepared iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0195] The battery assembled using this comparative example achieves a specific capacity of 130 mAh / g at a current density of 0.03 A / g, 83 mAh / g at a current density of 0.06 A / g, 68 mAh / g at a current density of 0.15 A / g, 60 mAh / g at a current density of 0.3 A / g, and 52 mAh / g at a current density of 0.6 A / g.

[0196] like Figure 4As shown, compared with Example 1, the iron fluoride material prepared by the HF aqueous solution evaporation method without the addition of ethanol yields a mixed crystal form of FeF3 and FeF3·3H2O. After heat treatment, the FeF3 crystal form of the iron fluoride cathode material is obtained, thus exhibiting poor electrochemical performance. Simultaneously, due to the absence of ethanol, the volatilization of HF is very limited, and it cannot completely react with the ferric nitrate precursor between the graphene template layers, resulting in a low initial specific capacity.

[0197] Comparative Example 2

[0198] This comparative example provides a method for preparing an iron fluoride cathode material, including the following steps:

[0199] S1: Preparation of graphene template.

[0200] S11: Weigh 1g of 1000-mesh graphite, 16g of chromium trioxide and 10mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0201] S12: Disperse 0.5g of the dried sample in 300mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0202] S13: Mix 100 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0203] S14: Finally, 2g of polyetheramine with a molecular weight of 2000g / mol was mixed with 50mL of CEGO solution with a concentration of 5mg / mL, and the mixture was reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0204] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0205] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0206] S4: Transfer 5 mL of HF aqueous solution to a hydrothermal reactor, wherein the mass fraction of HF aqueous solution is 40%. Isolate the graphene template of the iron-containing precursor obtained in S3 from the HF aqueous solution and prevent direct contact. Fluoride the graphene template of the iron-containing precursor obtained in S3 for 10 h at 150℃ using high-temperature steam generated by the HF aqueous solution.

[0207] S5: The sample after the S4 reaction is completed is washed and then vacuum dried at 80°C for 12 hours to obtain an intermediate sample in which iron fluoride grows between the graphene template layers.

[0208] S6: The intermediate sample obtained in S5 was heat-treated at 220°C for 12 hours under argon protection to obtain a composite material of iron fluoride, namely an iron fluoride cathode material.

[0209] This comparative example also provides an application of iron fluoride cathode material in lithium-ion batteries, including the following steps:

[0210] The prepared iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0211] The battery assembled in this comparative example achieves a specific capacity of 162 mAh / g at a current density of 0.03 A / g, 140 mAh / g at a current density of 0.06 A / g, 108 mAh / g at a current density of 0.15 A / g, 86 mAh / g at a current density of 0.3 A / g, and 70 mAh / g at a current density of 0.6 A / g.

[0212] Compared with Example 1, Comparative Example 2 did not add ethanol to assist in the evaporation of HF, but the amount of HF was increased compared with Comparative Example 1, resulting in more reaction between HF and the ferric nitrate precursor between the graphene layers. Therefore, the electrochemical performance was lower than that of Example 1, but slightly higher than that of Comparative Example 1.

[0213] Comparative Example 3

[0214] This comparative example provides a method for preparing an iron fluoride cathode material, including the following steps:

[0215] S1: Preparation of graphene template.

[0216] S11: Weigh 1g of 1000-mesh graphite, 16g of chromium trioxide and 10mL of hydrochloric acid and mix them at 20℃ for 2h. Then wash with water to remove unreacted chromium trioxide and vacuum dry at 60℃ for 12h to obtain a dried sample.

[0217] S12: Disperse 0.5g of the dried sample in 300mL of 10wt% hydrogen peroxide solution and let it stand for 7 days to expand, thus obtaining chemically expanded graphite (CEG).

[0218] S13: Mix 100 mL of concentrated sulfuric acid with 1 g of potassium permanganate and stir. Soak 0.5 g of CEG in the mixture of concentrated sulfuric acid and potassium permanganate. Perform mixed oxidation at 35 °C for 4 h to obtain graphene oxide array CEGO with an array structure.

[0219] S14: Finally, 2g of polyetheramine with a molecular weight of 2000g / mol was mixed with 50mL of CEGO solution with a concentration of 5mg / mL, and the mixture was reacted at 90℃ for 24h. After washing, the mixture was freeze-dried at -40℃ for 24h to obtain a graphene template with a stable array structure.

[0220] S2: Dissolve 16.16g of ferric nitrate nonahydrate in 20mL of deionized water to prepare a ferric nitrate aqueous solution with a concentration of 2mol / L. Immerse 40mg of the prepared graphene template in the solution and let it stand for 24h. Take the precipitate.

[0221] S3: The precipitate obtained in S2 is filtered and then washed with a small amount of deionized water. The solid obtained from the washing is freeze-dried at -40°C for 1 day to obtain a graphene template containing an iron source precursor.

[0222] S4: Add 0.1 mL of HF aqueous solution to 6 mL of ethanol solution, wherein the mass fraction of HF aqueous solution is 40%, to prepare a mixed solution. Transfer the mixed solution to a hydrothermal reactor and isolate the mixed solution from the graphene template containing the iron source precursor. Fluoride the graphene template containing the iron source precursor obtained in S3 for 10 h at 150 °C using high-temperature steam generated by the mixed solution.

[0223] S5: The sample after the S4 reaction was completed was washed and then vacuum dried at 80℃ for 12 h to obtain an intermediate sample, which yielded FeF30.33H2O grown between the graphene template layers.

[0224] S6: The intermediate sample obtained in S5 was heat-treated at 400℃ for 12 hours under argon protection to obtain a graphene / iron fluoride composite material, which is an iron fluoride cathode material.

[0225] This comparative example also provides an application of iron fluoride cathode material in lithium-ion batteries, including the following steps:

[0226] The prepared iron fluoride cathode material was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was cut to obtain the iron fluoride cathode sheet, which was then used to assemble a lithium-ion battery.

[0227] The battery assembled in this comparative example achieves a specific capacity of 142 mAh / g at a current density of 0.03 A / g, 118 mAh / g at a current density of 0.06 A / g, 80 mAh / g at a current density of 0.15 A / g, 63 mAh / g at a current density of 0.3 A / g, and 42 mAh / g at a current density of 0.6 A / g.

[0228] Compared with Example 1, the heat treatment temperature of Comparative Example 3 was increased to 400°C. At this temperature, the FeF30.33H2O grown between layers was dehydrated to obtain FeF3 composite material. Due to the lack of bound water, it exhibited poor rate performance.

[0229] Comparative Example 4

[0230] This comparative example provides an iron fluoride cathode material, including the following steps:

[0231] 2.02 g of ferric nitrate nonahydrate was dissolved in 40 mL of ethanol solution. 1 mL of HF was slowly added to the solution, and after stirring for 2 h, the mixture was transferred to a hydrothermal reactor and reacted at 120 °C for 10 h to obtain ferric fluoride cathode material.

[0232] This comparative example also provides an application of iron fluoride cathode material in lithium-ion batteries, including the following steps:

[0233] The iron fluoride cathode material prepared by the method was ground with carbon black and polyvinylidene fluoride in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone was added to form a homogenate. The viscous slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The resulting electrode sheet was then cut and assembled into a lithium-ion battery.

[0234] The battery assembled using this comparative example achieves a specific capacity of 126 mAh / g at a current density of 0.03 A / g, 103 mAh / g at a current density of 0.06 A / g, 65 mAh / g at a current density of 0.15 A / g, 55 mAh / g at a current density of 0.3 A / g, and 40 mAh / g at a current density of 0.6 A / g.

[0235] like Figure 5 As shown, in Comparative Example 4, compared with Example 1, no graphene template was used. The prepared iron fluoride material exhibited an irregular spherical shape. Due to its poor conductivity and easy agglomeration during the reaction, it caused large voltage hysteresis and rapid capacity decay, thus exhibiting poor electrochemical performance.

[0236] Depend on Figure 6 It can be seen that the lithium-ion battery assembled in Example 1 exhibits excellent electrochemical performance at different current densities, which is far superior to the electrochemical performance of the lithium-ion batteries assembled in Comparative Examples 1, 2 and 3.

[0237] This invention provides a layered iron fluoride nanosheet cathode material, its preparation method, and its applications, belonging to the technical field of lithium-ion battery cathode materials. The method includes: preparing a graphene template; immersing the graphene template in an aqueous solution of iron nitrate, filtering, and freeze-drying to obtain a graphene template containing an iron source precursor; and fluorinating the graphene template containing the iron source precursor using a co-evaporation method with hydrofluoric acid and ethanol to obtain the layered iron fluoride nanosheet cathode material. Using this cathode material to assemble batteries can achieve high-performance lithium-ion batteries. This invention utilizes a unique graphene template method to grow iron fluoride between layers, and through the co-evaporation method with hydrofluoric acid and ethanol, can prepare a high-performance two-dimensional layered iron fluoride cathode material, providing a new technical solution for the preparation of iron fluoride.

[0238] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for preparing a layered iron fluoride-based cathode material, characterized in that, Includes the following steps: Graphene templates were prepared, and the graphene templates had an accordion-like array structure. Ferric nitrate nonahydrate was dissolved in deionized water to prepare ferric nitrate aqueous solution. The graphene template was then immersed in the ferric nitrate aqueous solution and allowed to stand. The precipitate was collected and then filtered, washed, and freeze-dried to obtain a graphene template containing an iron source precursor. Ethanol and HF aqueous solution were mixed to prepare a mixed solution. The mixed solution was transferred to a hydrothermal reactor and isolated from the graphene template containing the iron source precursor. The graphene template containing the iron source precursor was fluorinated by the steam generated by the mixed solution. Then, it was washed and vacuum dried to obtain an intermediate sample. In the intermediate sample, iron fluoride grew between the graphene template layers. The volume ratio of ethanol to HF aqueous solution is (10~100):1; the mass fraction of HF aqueous solution is 40%~42%. The intermediate sample was heat-treated under the protection of an inert gas to obtain a layered iron fluoride-based cathode material. The heat treatment temperature is 150℃~350℃, and the time is 2h~12h; The layered iron fluoride-based cathode material has a two-dimensional nanosheet morphology with a thickness of less than 50 nm. The layered iron fluoride-based cathode material includes a graphene template and iron fluoride. The iron fluoride is grown in layers between the graphene template and exists in the form of FeF3·0.33H2O crystalline phase.

2. The method for preparing a layered iron fluoride-based cathode material according to claim 1, characterized in that, The preparation of the graphene template includes the following steps: Graphite, chromium trioxide and hydrochloric acid were mixed for the first reaction, followed by washing with water to remove unreacted chromium trioxide, and drying to obtain a dried sample; The dried sample was dispersed in a hydrogen peroxide solution and allowed to stand to expand, thus obtaining chemically expanded graphite. Chemically expanded graphite was immersed in a mixture of concentrated sulfuric acid and potassium permanganate for mixed oxidation treatment to obtain graphene oxide arrays with an array structure. The polyetheramine was mixed with the graphene oxide array for a second reaction, followed by washing and freeze-drying to obtain the graphene template.

3. The method for preparing a layered iron fluoride-based cathode material according to claim 2, characterized in that, The ratio of graphite, chromium trioxide and hydrochloric acid is 1g~2g:8g~16g:5mL~15mL; The concentration of the hydrogen peroxide solution is 10wt%~20wt%, and the ratio of the amount of dried sample to hydrogen peroxide solution is 0.5g~1g:300mL~1000mL; The ratio of chemically expanded graphite, concentrated sulfuric acid, and potassium permanganate is 0.5g~1g:40mL~100mL:1g~2g; The concentration of the graphene oxide array is 2 mg / mL to 8 mg / mL, and the ratio of the polyetheramine to the graphene oxide array is 0.6 g to 2 g: 30 mL to 125 mL.

4. The method for preparing a layered iron fluoride-based cathode material according to claim 2, characterized in that, The temperature of the first reaction is 20℃~60℃, and the time is 2h~4h; the drying treatment is carried out under vacuum conditions, and the temperature of the drying treatment is 60℃~80℃, and the time is 12h~24h. The static expansion time is 7 to 10 days; The temperature of the mixed oxidation treatment is 35℃~45℃, and the time is 4h~12h; The second reaction is carried out at a temperature of 80℃~100℃ for a time of 20h~24h. The freeze-drying process is carried out at a temperature of -50℃ to -40℃ for 12 hours to 24 hours.

5. The method for preparing a layered iron fluoride-based cathode material according to claim 1, characterized in that, The concentration of the ferric nitrate aqueous solution is 0.1 mol / L to 2 mol / L; the ratio of the graphene template to ferric nitrate nonahydrate is 20 mg to 200 mg: 0.808 g to 16.16 g.

6. The method for preparing a layered iron fluoride-based cathode material according to claim 1, characterized in that, The molar ratio of ferric nitrate nonahydrate to HF in the HF aqueous solution is 1:(0.05~1.13).

7. The method for preparing a layered iron fluoride-based cathode material according to claim 1, characterized in that, The settling time is 12h~24h; the freeze-drying temperature is -50℃~-40℃, and the time is 1 day~2 days; The fluorination treatment is carried out at a temperature of 60℃ to 200℃ for a time of 2h to 20h. The vacuum drying temperature is 60℃~120℃, and the time is 12h~24h.

8. A layered iron fluoride-based cathode material, characterized in that, It is prepared by the method for preparing layered iron fluoride-based cathode material as described in any one of claims 1 to 7.

9. The application of a layered iron fluoride-based cathode material as a cathode material in lithium-ion batteries, characterized in that, The layered iron fluoride-based cathode material is prepared using the preparation method of the layered iron fluoride-based cathode material as described in any one of claims 1 to 7.

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