Metal fluoride / carbon composite material with yolk-shell structure and preparation method thereof
By preparing a Yolk-Shell structured metal fluoride/carbon composite material, the problems of volume expansion and poor conductivity of metal fluoride electrode materials in lithium-ion batteries were solved, achieving higher energy density and coulombic efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2022-07-12
- Publication Date
- 2026-06-02
AI Technical Summary
Existing metal fluoride electrode materials face problems such as volume expansion, poor conductivity, and voltage hysteresis in electrochemical reactions, resulting in dissolution of active materials, low coulombic efficiency, and poor capacity retention, making them difficult to apply in lithium-ion batteries.
A metal fluoride/carbon composite material with a Yolk-shell structure was prepared by coating a porous carbon shell around a metal fluoride core to form a Yolk-shell structure. The carbon shell was used to alleviate volume expansion and improve conductivity. A uniform composite material was prepared by etching the silicon oxide layer using a gas-solid reaction.
It effectively alleviates the volume expansion of metal fluorides during charging and discharging, improves the kinetic performance of electrochemical reactions and the stability of materials, and enhances the energy density and coulombic efficiency of lithium-ion batteries.
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Figure CN115241453B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy storage materials technology, specifically relating to battery materials and their preparation methods. Background Technology
[0002] With the continuous depletion of primary energy sources and the increasing severity of environmental problems, electrochemical energy storage, a type of secondary energy, has attracted widespread attention due to its clean and efficient characteristics. Lithium-ion batteries, in particular, are widely used in everyday life, including portable electronic devices and electric vehicles. The energy density of lithium-ion batteries is primarily determined by the electrode materials. Currently, common commercially available cathode materials include lithium iron phosphate, lithium cobalt oxide, and nickel-cobalt-manganese ternary materials, with a theoretical capacity of approximately 250 mAg. -1 As application devices are updated and upgraded, higher requirements are placed on energy storage devices in terms of energy density and cost. However, the commercially available electrode materials have reached their limits in terms of lithium storage and cannot be further improved in terms of energy density.
[0003] With the continuous exploration and research of energy storage devices, conversion-type metal fluoride electrode materials have attracted widespread attention due to their ability to store more lithium ions and their high energy density. As a typical example of low-cost, high-energy-density materials, iron fluoride (FeF3) has a theoretical capacity of 712 mAh g⁻¹. -1 The theoretical specific capacity of copper fluoride (CuF2) is 528 mAh g. -1 Metal fluorides are considered to be highly competitive cathode materials for the future and can be applied to lithium batteries. However, as electrode materials, metal fluorides face challenges such as volume expansion, poor conductivity, and voltage hysteresis during electrochemical reactions, leading to dissolution of active materials, low coulombic efficiency, and poor capacity retention, thus hindering their current application.
[0004] Currently, researchers mainly address the problems associated with metal fluorides through material nanosizing and carbon material composites. Taking iron fluoride as an example, material nanosizing increases the specific surface area, which facilitates lithium-ion transport. For instance, patent application CN202010409715.8 prepared nano-iron fluoride with different particle sizes. However, its large specific surface area also makes it more easily dissolved during electrochemical reactions, leading to side reactions. Patent applications CN202011597045.3 and CN201610670999.X improve the conductivity of materials through carbon material composites. However, the volume change during charging and discharging can cause structural collapse, resulting in a decrease in capacity. Summary of the Invention
[0005] To address the problems existing in the prior art, the present invention aims to provide a metal fluoride / carbon composite material with a Yolk-shell structure, overcoming the difficulties faced by metal fluoride conversion electrode materials such as volume expansion, slow reaction kinetics, and poor conductivity.
[0006] Another object of the present invention is to provide a method for preparing a metal fluoride / carbon composite material with a Yolk-shell structure.
[0007] To achieve the above objectives, the present invention provides the following specific technical solutions.
[0008] First, this invention provides a metal fluoride / carbon composite material having a Yolk-shell structure; "Yolk" refers to the metal fluoride core, "Shell" refers to the carbon shell, and a cavity exists between the metal fluoride core and the carbon shell.
[0009] In addition, the present invention provides a method for preparing a metal fluoride / carbon composite material, comprising the following steps:
[0010] Step S1: Disperse the metal oxide in an ethanol / water mixed solution, then add orthosilicate and ammonia solution to hydrolyze the orthosilicate; after hydrolysis, add organic polymer monomer, ultrasonically disperse and stir, then filter the reaction slurry, wash and dry the solid phase to obtain a metal oxide with a core-shell structure and a double coating layer.
[0011] Step S2: Calcining the metal oxide with a core-shell structure and double coating layer obtained in step S1 at high temperature under an inert atmosphere to obtain a metal oxide with a core-shell structure and carbon coating layer.
[0012] Step S3 involves reacting the core-shell structured metal oxide with a carbon coating obtained in step S2 with a fluorine-containing gas to obtain a yolk-shell structured metal fluoride / carbon composite material.
[0013] Furthermore, in some preferred embodiments of the present invention, the metal element in the metal oxide is selected from one or more of iron, copper, cobalt, nickel, manganese, vanadium and titanium.
[0014] Furthermore, in some preferred embodiments of the present invention, the orthosilicate is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate.
[0015] Furthermore, in some preferred embodiments of the present invention, the organic polymer monomer is selected from one or more of resorcinol-formaldehyde, dopamine, and glucose.
[0016] Furthermore, in some preferred embodiments of the present invention, the volume ratio of ethanol to water in the ethanol / water mixed solution is 1:10 to 10:1.
[0017] Furthermore, in some preferred embodiments of the present invention, the metal oxide is dispersed in an ethanol / water mixed solution to obtain a mixed slurry with a liquid-to-solid ratio of 2000:1 to 3000:1.
[0018] Furthermore, in some preferred embodiments of the present invention, the concentration of the added ammonia solution is 28 wt%, and the amount of the added ammonia solution is 0.1% to 10% of the mass of the mixed slurry.
[0019] Furthermore, in some preferred embodiments of the present invention, the amount of orthosilicate added is 1 to 1000 times the mass of the metal oxide, and the amount of organic polymer monomer added is 1 to 500 times the mass of the metal oxide.
[0020] By adjusting the amount of organic polymer monomers and orthosilicates added, the carbon shell thickness and reserved space of Yolk-Shell structure metal fluoride / carbon composite materials can be effectively controlled, thus preparing materials that meet application requirements.
[0021] Furthermore, in some preferred embodiments of the present invention, in step S1, the ultrasonic dispersion time is 1~2 hours and the stirring time is 12~36 hours.
[0022] Furthermore, in some preferred embodiments of the present invention, the calcination temperature in step S2 is 600~900℃, the heating rate is 1.0~5.0℃ / min, and the calcination time is 1~5 hours.
[0023] Furthermore, in some preferred embodiments of the present invention, the temperature of the gas-solid reaction in step S3 is 250~600°C, and the duration of the gas-solid reaction is 1~3h.
[0024] At relatively low temperatures of 250℃ to 600℃, the strong oxidizing properties of fluorine-containing gases cannot be fully manifested, so they will not react with the carbon shell. However, they can etch the silicon oxide layer and react with metal oxides to generate metal fluorides, thus maintaining the original morphology of the material and greatly improving the efficiency of material preparation.
[0025] As a further preferred option, the heating rate of the gas-solid reaction is controlled to be 1~5℃ / min.
[0026] Furthermore, in some preferred embodiments of the present invention, the fluorine-containing gas is selected from one or more of hydrogen fluoride, fluorine, and nitrogen trifluoride.
[0027] This invention first coats a silicon oxide sacrificial layer and an organic polymer layer sequentially on the surface of a metal oxide using a liquid-phase method. Then, the organic polymer layer is converted into a carbon layer by high-temperature calcination in an inert atmosphere. Finally, a gas-solid reaction is carried out with a fluorine-containing gas, simultaneously etching the silicon oxide layer and fluorinating the metal oxide, to obtain a metal fluoride / carbon composite material with a Yolk-Shell structure.
[0028] Compared with the prior art, the present invention has the following obvious beneficial technical effects:
[0029] Compared to the unevenness and agglomeration problems of metal fluoride / carbon composite materials prepared by existing technologies, the present invention can achieve uniform coating through ultrasonic stirring;
[0030] In the process of synthesizing metal fluorides through gas-solid reaction, the silicon oxide sacrificial layer is also etched simultaneously, which has a higher synthesis efficiency compared with traditional strong acid and strong base etching.
[0031] As a novel electrode material structure, the Yolk-Shell structure, compared to traditional coating, can effectively alleviate the volume expansion during the metal fluoride reaction process by leaving space between the core and shell, and prevent the material from cracking and dissolving after multiple charge and discharge cycles.
[0032] The shell material in the metal fluoride / carbon composite material prepared by this invention is a porous carbon shell. The composite of carbon materials can improve the electron migration rate, and the porous channels can promote the rapid transfer of ions, thereby improving the kinetics of the electrochemical reaction process as a whole.
[0033] The method for preparing composite materials according to the present invention is simple, has mild process conditions, compact and continuous procedures, high controllability, and the required raw materials are basically traditional industrial raw materials with low raw material costs, and has the potential to achieve industrial production. Attached Figure Description
[0034] Figure 1 This is a reference process flow diagram for a specific embodiment.
[0035] Figure 2 The images shown are SEM images of the Fe2O3@SiO2@C material obtained by calcination in Example 1, where a is a SEM image magnified 20,000 times and b is a SEM image magnified 50,000 times.
[0036] Figure 3 The image shows the XRD pattern of the FeF3@C material obtained in Example 1.
[0037] Figure 4 The images shown are SEM images of the FeF3@C material obtained in Example 1, where a is a SEM image magnified 20,000 times and b is a SEM image magnified 50,000 times. Detailed Implementation
[0038] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.
[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0041] The following embodiments mainly utilize Figure 1 The process flow diagram shown illustrates the preparation of metal fluoride / carbon composite materials with a Yolk-shell structure.
[0042] Example 1:
[0043] A method for preparing a yolk-shell structured iron / carbon fluoride composite material includes the following steps:
[0044] 1) Coating: At room temperature, 60 mg of iron oxide (ellipsoids with a morphology of 200 nm) was dispersed in 140 mL of ethanol, and 20 mL of deionized water was added. After sonication and mechanical stirring for 15 min, 6 mL of ammonia water (28 wt% NH3·H2O) and 0.5 mL of methyl orthosilicate were added sequentially. Sonication and mechanical stirring were continued for another 15 min. Then, 0.1 g of resorcinol and 0.15 mL of formaldehyde solution (37 wt%) were added sequentially. After sonication and mechanical stirring for another 15 min, mechanical stirring was continued for 24 hours. The resulting suspension was centrifuged, washed, and dried to obtain iron oxide nanospheres (Fe2O3@SiO2@RF) coated with phenolic resin and silica.
[0045] 2) Carbonization: The obtained Fe2O3@SiO2@RF iron oxide nanospheres coated with phenolic resin and silicon oxide were calcined in an argon atmosphere, heated to 600℃ at a heating rate of 3℃ / min and held for 2 hours to obtain Fe2O3@SiO2@C, which was then cooled to room temperature in the furnace.
[0046] 3) Fluorination: Fe2O3@SiO2@C was heated to 380℃ for 2 hours in an atmosphere with 5% NF3 content (NF3-Ar) at a heating rate of 5 ℃ / min to obtain Yolk-Shell structure FeF3@C, which was then cooled to room temperature in the furnace.
[0047] Figure 2The image shows a SEM image of calcined Fe2O3@SiO2@C. The image reveals uniform dispersion with minimal agglomeration, and a clearly visible double-layered structure. It can be inferred that the inner shell of this double-layered structure is silicon oxide, the outer shell is carbon, and the core is iron oxide.
[0048] Figure 3 The XRD pattern of FeF3@C shows that the diffraction peaks obtained by low-temperature fluorination are basically matched with the standard card of FeF3 (JCPDS No. 33-0647). The strong diffraction peak at 23.8° indicates that the FeF3 crystal preferentially grows along the (012) plane. No other impurity peaks appear in the XRD pattern, indicating that no other phases are generated and the crystal is completely transformed into FeF3.
[0049] Figure 4 The image shows a SEM image of the FeF3@C sample. As can be seen from the image, the carbon shell maintains a good structure due to the use of a low-temperature fluorination process.
[0050] Example 2
[0051] A method for preparing a yolk-shell structured copper fluoride / carbon composite material includes the following steps:
[0052] 1) Coating: At room temperature, 60 mg of cuprous oxide (cubic with a morphology of 100 nm) was dispersed in 140 mL of ethanol, and 20 mL of deionized water was added. After sonication and mechanical stirring for 15 min, 6 mL of ammonia water (28 wt% NH3·H2O) and 0.5 mL of tetraethyl orthosilicate were added sequentially. Sonication and mechanical stirring were continued for another 15 min. Then, 0.1 g of resorcinol and 0.15 mL of formaldehyde solution (37 wt%) were added sequentially. After sonication and mechanical stirring for another 15 min, mechanical stirring was continued for 24 hours. The resulting suspension was centrifuged, washed, and dried to obtain iron oxide nanospheres (Cu2O@SiO2@RF) coated with phenolic resin and silica.
[0053] 2) Carbonization: The obtained iron oxide nanospheres Cu2O@SiO2@RF coated with phenolic resin and silicon oxide were calcined in an argon atmosphere, heated to 900℃ at a heating rate of 5℃ / min and held for 2 hours to obtain Cu2O@SiO2@C, which was then cooled to room temperature in the furnace.
[0054] 3) Fluorination: Cu2O@SiO2@C was heated to 500℃ for 2 hours in an atmosphere with 5% NF3 content (NF3-Ar) at a heating rate of 5 ℃ / min to obtain Yolk-Shell structure CuF2@C, which was then cooled to room temperature in the furnace.
[0055] Example 3
[0056] A method for preparing a yolk-shell structured iron / carbon fluoride composite material includes the following steps:
[0057] 1) Coating: At room temperature, 60 mg of iron oxide (ellipsoids with a morphology of 200 nm) was dispersed in 20 mL of ethanol, and 140 mL of deionized water was added. After ultrasonic and mechanical stirring for 15 min, 1 mL of ammonia (28 wt% NH3·H2O) and 0.5 mL of methyl orthosilicate were added sequentially. Ultrasonic and mechanical stirring was continued for 15 min. 0.1 g of dopamine was added, and the pH was adjusted to 8.5 with ammonia. After ultrasonic and mechanical stirring for 15 min, mechanical stirring was continued for 24 hours. The resulting suspension was centrifuged, washed, and dried to obtain iron oxide nanospheres (Fe2O3@SiO2@PDA) coated with polydopamine and silica.
[0058] 2) Carbonization: The obtained Fe2O3@SiO2@PDA iron oxide nanospheres coated with polydopamine and silicon oxide were calcined in an argon atmosphere, heated to 800℃ at a heating rate of 5℃ / min and held for 3 hours to obtain Fe2O3@SiO2@C, which was then cooled to room temperature in the furnace.
[0059] 3) Fluorination: Fe2O3@SiO2@C was heated to 600℃ for 1 hour in an atmosphere with 5% NF3 content (NF3-Ar) at a heating rate of 5 ℃ / min to obtain Yolk-Shell structure FeF3@C, which was then cooled to room temperature in the furnace.
[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing a metal fluoride / carbon composite material, characterized in that, Includes the following steps: Step S1: Disperse the metal oxide in an ethanol / water mixed solution, then add orthosilicate and ammonia solution to hydrolyze the orthosilicate; after hydrolysis, add organic polymer monomer, ultrasonically disperse and stir, then filter the reaction slurry, wash and dry the solid phase to obtain a metal oxide with a core-shell structure and a double coating layer. Step S2: The metal oxide with a core-shell structure and double coating layer obtained in step S1 is calcined at high temperature under an inert atmosphere to obtain a metal oxide with a core-shell structure and carbon coating layer. Step S3 involves reacting the core-shell structured metal oxide with a carbon coating obtained in step S2 with nitrogen trifluoride gas in a gas-solid reaction, simultaneously etching the silicon oxide layer and fluorinating the metal oxide to obtain a yolk-shell structured metal fluoride / carbon composite material; the temperature of the gas-solid reaction is 380~600℃. The composite material has a Yolk-shell structure, where "Yolk" is a metal fluoride core and "Shell" is a carbon shell; there is a cavity between the metal fluoride core and the carbon shell.
2. The preparation method according to claim 1, characterized in that, The metal element in the metal oxide is selected from one or more of iron, copper, cobalt, nickel, manganese, vanadium and titanium; the orthosilicate is selected from one or more of methyl orthosilicate, ethyl orthosilicate and propyl orthosilicate; the organic polymer monomer is selected from one or more of resorcinol-formaldehyde, dopamine and glucose.
3. The preparation method according to claim 1, characterized in that, In the ethanol / water mixed solution, the volume ratio of ethanol to water is 1:10 to 10:
1.
4. The preparation method according to claim 3, characterized in that, Metal oxides are dispersed in an ethanol / water mixed solution to obtain a mixed slurry with a liquid-to-solid ratio of 2000:1 to 3000:
1.
5. The preparation method according to claim 4, characterized in that, The concentration of the added ammonia solution is 28 wt%, and the amount of added ammonia solution is 0.1% to 10% of the mass of the mixed slurry.
6. The preparation method according to claim 1, characterized in that, The amount of orthosilicate added is 1 to 1000 times the mass of the metal oxide, and the amount of organic polymer monomer added is 1 to 500 times the mass of the metal oxide.
7. The preparation method according to any one of claims 1-6, characterized in that, In step S1, the ultrasonic dispersion time is 1~2h and the stirring time is 12~36h; in step S2, the calcination temperature is 600~900℃, the heating rate is 1.0~5.0℃ / min, and the calcination time is 1~5h.
8. The preparation method according to claim 7, characterized in that, The heating rate of the gas-solid reaction was controlled at 1~5℃ / min.