阅读说明：本技术 一种氟化钴/氧化铁复合材料及其应用 (Cobalt fluoride/ferric oxide composite material and application thereof ) 是由 程秋遐 林晓明 欧虹 蔡跃鹏 于 2019-10-22 设计创作，主要内容包括：本发明涉及一种氟化钴/氧化铁复合材料及其应用,所述氟化钴/氧化铁复合材料由以下制备方法制备,步骤为：S1：Fe-Co-ZIF模板的合成；S2：Fe/Co/C三维多孔材料的制备；S3：CoF<Sub>2</Sub>/Fe<Sub>2</Sub>O<Sub>3</Sub>复合材料的制备。该方法在Fe-Co-ZIF模板的合成过程中,原位生成碳骨架代替了外部导电碳添加,有效地提高了材料自身的导电性。同时,ZIF前驱体中的氮元素均匀地掺杂在制备的纳米CoF<Sub>2</Sub>/Fe<Sub>2</Sub>O<Sub>3</Sub>复合材料的结构中,增强了材料的缺陷,提供了更多的锂插入位点,有效地缩短了锂离子的输运路径。该方法制得的CoF<Sub>2</Sub>/Fe<Sub>2</Sub>O<Sub>3</Sub>复合材料形成的正极在1000mA g<Sup>-1</Sup>的相对高电流下,平均放电比容量为90mAh g<Sup>-1</Sup>。当电流密度逐渐恢复到50mA g<Sup>-1</Sup>时,CoF<Sub>2</Sub>/Fe<Sub>2</Sub>O<Sub>3</Sub>复合材料的容量可以相应地恢复到263mAh g<Sup>-1</Sup>。与前十个循环的放电比容量相比,其容量保持率约为92.6％。(The invention relates to a cobalt fluoride/ferric oxide composite material and application thereof, wherein the cobalt fluoride/ferric oxide composite material is prepared by the following preparation method comprising the following steps: s1: synthesizing a Fe-Co-ZIF template; s2: preparing a Fe/Co/C three-dimensional porous material; s3: CoF 2 /Fe 2 O 3 And (4) preparing the composite material. According to the method, in the synthesis process of the Fe-Co-ZIF template, the carbon skeleton is generated in situ to replace external conductive carbon, so that the conductivity of the material is effectively improved.Meanwhile, nitrogen in the ZIF precursor is uniformly doped in the prepared nano CoF 2 /Fe 2 O 3 In the structure of the composite material, the defects of the material are enhanced, more lithium insertion sites are provided, and the transportation path of lithium ions is effectively shortened. CoF prepared by the method 2 /Fe 2 O 3 The positive electrode formed by the composite material is 1000mA g ‑1 At a relatively high current, the average specific discharge capacity is 90mAh g ‑1 . When the current density is gradually recovered to 50mA g ‑1 Of CoF 2 /Fe 2 O 3 The capacity of the composite material can be correspondingly restored to 263mAh g ‑1 . Compared with the discharge specific capacity of the first ten cycles, the capacity retention rate is about 92.6 percent.)

1. The cobalt fluoride/iron oxide composite material is characterized in that the preparation method comprises the following steps:

step S1: synthesizing a Fe-Co-ZIF template;

step S2: preparing a Fe/Co/C three-dimensional porous material;

step S3: CoF₂/Fe₂O₃And (4) preparing the composite material.

2. The cobalt fluoride/iron oxide composite of claim 1, wherein: synthesizing a Fe-Co-ZIF die in the step S1The raw material required for the plate comprises Co (NO)₃)₂·6H₂O、FeCl₃·6H₂O and 2-methylimidazole, wherein the Co (NO) is₃)₂·6H₂O、FeCl₃·6H₂The mass ratio of O to 2-methylimidazole is 1: 1.8-2: 17-20.

3. The cobalt fluoride/iron oxide composite of claim 2, wherein: the specific operation of step S1 is to firstly carry out Co (NO)₃)₂·6H₂O and FeCl₃·6H₂Dissolving O in a solvent to obtain a solution A; completely dissolving the mixture of 2-methylimidazole and sodium hydroxide in another solvent to form a solution B; and then mixing the solution A and the solution B, and then heating the mixture in a microwave reactor to fully react the mixture, wherein the solvent is deionized water or methanol.

4. The cobalt fluoride/iron oxide composite of claim 3, wherein: the specific operation of the step S2 is to perform high-temperature treatment on the Fe-Co-ZIF template prepared in the step S1 in a nitrogen atmosphere to prepare the black Fe/Co/C three-dimensional porous material.

5. The cobalt fluoride/iron oxide composite of claim 4, wherein: the specific operation of the step S3 is to mix the Fe/Co/C three-dimensional porous material prepared in the step S2 with a fluorine source, heat the mixture in a nitrogen atmosphere, and carry out heat preservation reaction to obtain CoF₂/Fe₂O₃A composite material.

6. The cobalt fluoride/iron oxide composite of claim 5, wherein: the fluorine source in the step S3 is HF, NH₄F、NH₄HF₂、MSiF₆、BmimBF₄At least one fluorine-containing ionic liquid.

7. The cobalt fluoride/iron oxide composite of claim 6, wherein: fluorine in said step S3The source being NH₄F, and the mass ratio of the Fe/Co/C three-dimensional porous material to the fluorine source is 1: 4-6.

8. Use of a cobalt fluoride/iron oxide composite as claimed in any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of lithium ion battery anode materials, in particular to a cobalt fluoride/ferric oxide composite material and application thereof.

Background

With the increasing development of socio-economy and the rapid growth of population, energy and environmental issues have become two serious issues that must be faced in the 21 st century. Chemical power sources, especially secondary power sources, as a device capable of realizing mutual conversion of chemical energy and electric energy, are key devices for reasonably and effectively utilizing energy, and are one of important means for solving energy problems at present. Lead-acid batteries and nickel-cadmium batteries. Among many series of batteries such as nickel-metal hydride batteries, lithium ion secondary batteries have become a hot spot in battery research and development and application in the world today due to their superior performances such as high reversible capacity, high voltage, high cycle performance and high energy density. However, the current commercialized lithium ion has the problems of poor cycling stability, weak large-current discharge capacity and the like, and the lithium ion battery industry is very competitive, so the research and development of a novel electrode material with high capacity, high power density, high cycling performance and low cost becomes a powerful means for further reducing the battery cost and enhancing the competitiveness. Metal Fluorides (MF)_x) Is a promising new anode material with high capacity.

Metal Fluorides (MF)_x) Has the advantages of low cost, low toxicity, abundant resources and the like, and the MF has the advantages of_xThe theoretical energy density, the volume capacity and the working voltage of the lithium-sulfur battery are even better than those of the lithium-sulfur battery to a certain extent, so that the lithium-sulfur battery is a conversion type positive electrode material with application prospect. At present, fluorides of various transition metals, such as Fe, Mn,Ni and Cu, which have been studied as the positive electrode of the secondary battery. For example, FeF₃The highest theoretical capacity is 712mAh g^-1(3e^-Transfer), theoretical energy density 1950Whkg^-1。CuF₂Comparative Li⁺Li has an optimal thermodynamic discharge potential of 3.55V (its theoretical specific capacity is 528mAh g)^-1Theoretical specific energy is 1874Wh kg^-1) And the like.

As MF_xCobalt fluoride (CoF), a member of₂) Compared with the traditional positive electrode material (LiCoO)₂、LiFePO₄Etc.) with a smaller relative molecular mass and a higher theoretical specific capacity (554mAh g)^-1) And CoF₂The lithium ion battery anode material has rich resources, low cost and environmental friendliness, so the lithium ion battery anode material is considered to be a new generation of lithium ion battery anode material with great research value and application prospect. However, CoF₂The problems of higher electrochemical impedance, low utilization rate of active substances at room temperature, strong ionic bond of fluoride, poor high-current density charge-discharge performance, rapid capacity attenuation in a short cycle process and the like when the lithium-manganese fluoride battery is assembled with a cathode, and the further application of the Li-MFx battery is limited. Most of the current researches are directed at the preparation and reaction mechanism of cobalt fluoride electrodes, and few modifications and researches on cobalt fluoride are carried out.

Disclosure of Invention

Based on this, the present invention aims to overcome the disadvantages of the prior art and provide a cobalt fluoride/iron oxide composite material, the preparation method of which comprises the following steps:

step S1: synthesizing a Fe-Co-ZIF template;

step S2: preparing a Fe/Co/C three-dimensional porous material;

step S3: CoF₂/Fe₂O₃And (4) preparing the composite material.

Compared with the prior art, the invention provides a method for preparing bimetallic ZIF-derived CoF₂/Fe₂O₃A method for preparing a nanocomposite. Firstly synthesizing a Fe-Co-ZIF template, graphitizing the Fe-Co-ZIF template to obtain a three-dimensional porous Fe/Co/C frame, and finally preparing CoF₂/Fe₂O₃A nanocomposite material. In the synthesis process of the Fe-Co-ZIF template, the carbon skeleton is generated in situ to replace the addition of external conductive carbon, so that the conductivity of the material can be effectively improved. Meanwhile, nitrogen in the ZIF precursor is uniformly doped in the prepared nano CoF₂/Fe₂O₃In the structure of the composite material, the defects of the material are enhanced, more lithium insertion sites are provided, and the transportation path of lithium ions is effectively shortened. In addition, the porous nanostructure of the cobalt fluoride/iron oxide composite material can not only provide enough space to adapt to volume change, but also improve the utilization rate of active substances in a circulating process and promote faster ion and electron transfer. The preparation method has the advantages of simple synthesis process, convenient operation, low cost, less pollution and wide market prospect.

Further, the raw material required for synthesizing the Fe-Co-ZIF template in the step S1 includes Co (NO)₃)₂·6H₂O、FeCl₃·6H₂O and 2-methylimidazole, wherein the Co (NO) is₃)₂·6H₂O、FeCl₃·6H₂The mass ratio of O to 2-methylimidazole is 1: 1.8-2: 17-20.

Further, the specific operation of step S1 is to firstly process Co (NO)₃)₂·6H₂O and FeCl₃·6H₂Dissolving O in a solvent to obtain a solution A; completely dissolving the mixture of 2-methylimidazole and sodium hydroxide in another solvent to form a solution B; and then mixing the solution A and the solution B, and then heating the mixture in a microwave reactor to fully react the mixture, wherein the solvent is deionized water or methanol. The microwave reaction method has simple operation and mild reaction, and the prepared crystal is pure and has higher quality.

Further, the specific operation of the step S2 is to perform high-temperature treatment on the Fe-Co-ZIF template prepared in the step S1 in a nitrogen atmosphere to obtain a black Fe/Co/C three-dimensional porous material. The in-situ generated carbon skeleton in the calcination process of Fe-Co-ZIF can replace the addition of external conductive carbon, thereby effectively improving the conductivity of the catalyst.

Further, the stepsS3 is specifically carried out by mixing the Fe/Co/C three-dimensional porous material prepared in the step S2 with a fluorine source, heating in a nitrogen atmosphere, and carrying out heat preservation reaction to obtain CoF₂/Fe₂O₃A composite material.

Further, the fluorine source in the step S3 is HF, NH₄F、NH₄HF₂、MSiF₆、BmimBF₄At least one fluorine-containing ionic liquid.

Further, the fluorine source in the step S3 is NH₄F, and the mass ratio of the Fe/Co/C three-dimensional porous material to the fluorine source is 1: 4-6. NH relative to other fluorine sources₄F has low toxicity and low price, and the loss of products in the co-heating process is small.

The invention also aims to provide application of the cobalt fluoride/iron oxide composite material.

Drawings

FIG. 1 is a flow chart of a method for preparing a cobalt fluoride/iron oxide composite material according to the present invention.

FIG. 2 is an SEM image of 1 μm resolution of a ZIF precursor prepared by the preparation method of a cobalt fluoride/iron oxide composite material of the present invention.

FIG. 3 is an SEM image of 1 μm resolution of calcined ZIF precursors prepared by the method of preparing cobalt fluoride/iron oxide composites of the present invention.

FIG. 4 shows CoF prepared by the preparation method of the cobalt fluoride/iron oxide composite material₂/Fe₂O₃The resolution of the composite was 1 μm SEM image.

FIG. 5 shows CoF prepared by the preparation method of the cobalt fluoride/iron oxide composite material₂/Fe₂O₃XRD pattern of the composite.

FIG. 6 shows CoF prepared by the preparation method of the cobalt fluoride/iron oxide composite material₂/Fe₂O₃Raman spectra of the composite material.

FIG. 7 shows CoF prepared by the preparation method of the cobalt fluoride/iron oxide composite material₂/Fe₂O₃TGA profile of the composite.

FIG. 8 shows cobalt fluoride according to the present inventionCoF prepared by preparation method of/iron oxide composite material₂/Fe₂O₃XPS survey of composites.

FIG. 9 shows CoF prepared by the preparation method of the cobalt fluoride/iron oxide composite material₂/Fe₂O₃C1 s high resolution plot of XPS test of composites.

FIG. 10 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃F1 s high resolution plot of XPS test of composites.

FIG. 11 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the invention₂/Fe₂O₃XPS-tested Co 2p high resolution maps of the composites.

FIG. 12 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃XPS-tested high resolution plot of Fe 2p for composites.

FIG. 13 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃Constant current charge and discharge curve of the composite material in a voltage interval of 1.2-4.5V.

FIG. 14 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃Cyclic Voltammetry (CV) test plots of the composite.

FIG. 15 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃The composite material has a density of 50mAg^-1Specific capacity at current and coulombic efficiency.

FIG. 16 shows CoF prepared by the method for preparing cobalt fluoride/iron oxide composite material₂/Fe₂O₃The composite material is 100mAh g^-1Charge and discharge curves at current.

FIG. 17 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃The composite material is 100mAh g^-1Specific capacity at current and coulombic efficiency.

FIG. 18 shows cobalt fluoride according to the present inventionCoF prepared by preparation method of/iron oxide composite material₂/Fe₂O₃The composite material is 50 to 1000mA g^-1Rate capability at current density.

FIG. 19 shows CoF prepared by the method for preparing cobalt fluoride/iron oxide composite material₂/Fe₂O₃The composite material has a density of 100mAg^-1Electrochemical Impedance Spectroscopy (EIS) before and after cycling at current density.

FIG. 20 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃The scanning rate of the composite material is 0.2 to 1.2mV s^-1CV curve of time.

FIG. 21 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃Characteristic peak currents of the composite and fitting equations for different scan rates.

FIG. 22 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃The composite material is in the range of 0.8mVs^-1Lower total current (full area) and capacitive current (pink region) contribution ratio.

FIG. 23 shows CoF prepared by the method for preparing a cobalt fluoride/iron oxide composite material according to the present invention₂/Fe₂O₃Capacitance contribution and diffusion control contribution at different sweep rates of the composite.

FIG. 24 is a graph showing CoF measurement using the constant current intermittent titration technique (GITT)₂/Fe₂O₃Graph of voltage versus time during discharge of the composite material.

FIG. 25 is a graph showing CoF measurement using the constant current intermittent titration technique (GITT)₂/Fe₂O₃First step GITT titration curve for composite.

FIG. 26 is a graph showing CoF measurement using the constant current intermittent titration technique (GITT)₂/Fe₂O₃Titration of composite Material^{1 /2}And a linear behavior diagram between potentials.

FIG. 27 is a graph showing CoF measurement using the constant current intermittent titration technique (GITT)₂/Fe₂O₃Lithium ion diffusion coefficient plots for different voltages of the composite.

Detailed Description

Referring to fig. 1, it is a flow chart of the preparation method of the cobalt fluoride/iron oxide composite material of the present invention, which comprises the following steps:

step S1: synthesizing a Fe-Co-ZIF template;

zeolite Imidazole Frameworks (ZIFs) are a subclass of Metal-organic Frameworks (MOFS) with a Metal-imidazole-Metal bond angle of 145 ° similar to the bond angle of Si-O-Si bonds in zeolites and have molecular sieve topologies. Besides the excellent properties of MOFs, such as various framework structures and pore systems, large surface areas and modifiable organic bridging ligands, the ZIFs have the high thermal stability and chemical stability of the traditional zeolite, in addition, the ZIFs are easy to synthesize micro-nano crystals with certain sizes and shapes like the zeolite, and the regular atomic arrangement sequence in the ZIFs greatly improves the uniformity and crystallinity of the synthesized cobalt fluoride/iron oxide composite material, thereby further improving the electrochemical performance of the material.

ZIF series materials are generally synthesized by a one-step method, and are generated by reacting metal salt and organic ligand in a solvent. The synthesis method mainly comprises a solvothermal method, a liquid phase diffusion method, a microwave method, an ultrasonic method, a mechanical stirring method and the like. In the embodiment, a microwave method is preferred, conditions of the method are simple and mild, and the prepared crystal is pure and high in quality.

Specifically, the raw material required for synthesizing the Fe-Co-ZIF template in the embodiment comprises Co (NO)₃)₂·6H₂O、FeCl₃·6H₂O and 2-methylimidazole, wherein the Co (NO) is₃)₂·6H₂O、FeCl₃·6H₂The mass ratio of O to 2-methylimidazole is 1: 1.8-2: 17-20. The specific steps are firstly to prepare Co (NO)₃)₂·6H₂O and FeCl₃·6H₂Dissolving O in deionized water or methanol, and performing ultrasonic treatment to completely dissolve O to obtain a solution A; mixing the 2-methylimidazole with sodium hydroxideCompletely dissolving the mixture in additional deionized water or methanol to form a solution B; then mixing the solution A and the solution B, and then placing the mixture in a microwave reactor for heating to ensure that the mixture fully reacts; and finally, centrifuging the mixed solution after the microwave reaction for 2-5 minutes at the rotating speed of 5000-7000 r/min, collecting a solid product, washing the solid product for more than 3 times by using deionized water or methanol, and drying the washed solid product in vacuum at the temperature of 50-70 ℃ to prepare the powdery Fe-Co-ZIF template.

Step S2: preparing a Fe/Co/C three-dimensional porous material;

and (4) transferring the Fe-Co-ZIF template prepared in the step (S1) to a tube furnace, heating to 600-800 ℃ at the speed of 2-5 ℃/min in the nitrogen atmosphere, treating at high temperature for 1-3 hours, and cooling to room temperature to obtain the black three-dimensional porous Fe/Co/C material.

Because the Fe-Co-ZIF template is synthesized by a time-saving and simple microwave-assisted method, the prepared Fe-Co-ZIF is likely to lose weight when the organic ligand is decomposed at the temperature of more than 550 ℃. Therefore, the precursor Fe-Co-ZIF is firstly annealed at high temperature to obtain the conductive three-dimensional porous graphitized material Fe/Co/C.

Step S3: CoF₂/Fe₂O₃And (4) preparing the composite material.

Mixing and grinding the Fe/Co/C three-dimensional porous material prepared in the step S2 with a fluorine source, wherein the fluorine source is HF and NH₄F、NH₄HF₂、MSiF₆、BmimBF₄At least one fluorine-containing ionic liquid. Transferring the ground mixture to a tube furnace, heating to 100-200 ℃ at the speed of 2-5 ℃/min under the nitrogen atmosphere, keeping the temperature for reaction for 1-3 hours, then continuously heating to 350-600 ℃, and reacting for 2-6 hours to obtain the CoF₂/Fe₂O₃A composite material.

Specifically, this embodiment selects NH₄F, and the mass ratio of the Fe/Co/C three-dimensional porous material to the fluorine source is 1: 4-6.

Compared with the prior art, the invention provides a method for preparing bimetallic ZIF-derived CoF by adopting a co-pyrolysis strategy₂/Fe₂O₃A method for preparing a nanocomposite. Firstly synthesizing a Fe-Co-ZIF template, graphitizing the Fe-Co-ZIF template to obtain a three-dimensional porous Fe/Co/C frame, and finally mixing the Fe/Co/C material with NH₄F is co-heated to obtain CoF₂/Fe₂O₃A nanocomposite material. NH in the preparation method₄The F has low toxicity and low price, the product loss is small in the Co-heating process, and in the Fe-Co-ZIF calcining process, the carbon skeleton generated in situ replaces the addition of external conductive carbon, so that the conductivity of the material is effectively improved. Meanwhile, nitrogen elements derived from 2-methylimidazole ligand are uniformly doped in the prepared nano CoF₂/Fe₂O₃In the structure, the defects of the material are enhanced, more lithium insertion sites are provided, and the transportation path of lithium ions is effectively shortened. In addition, the porous nanostructure of the cobalt fluoride/iron oxide composite material can not only provide enough space to adapt to volume change, but also improve the utilization rate of active substances in a circulating process and promote faster ion and electron transfer.

The cobalt fluoride/iron oxide composite material and the method for preparing the same according to the present invention will be further explained by the following specific examples.