CN104282882B - Composite positive electrode material and preparation method thereof - Google Patents

Abstract

The invention provides a positive electrode composite material, which is a graphene-FeOF composite material, including FeOF particles and graphene bonded by chemical bonds. The present invention also provides a method for preparing a positive electrode composite material, which includes the following steps: uniformly mixing ferric fluoride and graphene oxide in a liquid phase solvent to form a solid-liquid mixture; The hydrothermal/solvothermal reaction is carried out in the thermal reaction kettle at 80℃~250℃.

Description

Positive electrode composite material and preparation method thereof

technical field

The invention relates to a positive electrode composite material based on ferric oxyfluoride and a preparation method thereof.

Background technique

Iron oxyfluoride (FeOF) can be regarded as a structure formed by replacing _FeF2 with O. Compared with strongly ionic FeF ₂ , FeOF contains more chemical bonds Fe-O, which makes FeOF more conductive than FeF ₂ (the band gaps are 1.5 eV and 3 eV, respectively). At the same time, Fe in FeOF is +3 valence, and it can react with three electrons in the electrochemical process. The reaction in each voltage range is as follows: 2V~4.5V: Fe ³⁺ OF + Li = LiFe ²⁺ OF; 0.7V~2V : LiFe ²⁺ OF + 2Li = LiF + Li ₂ O + Fe ⁰ , with a theoretical specific capacity of 885 mAh g ^-1 , which is expected to be used as a cathode material with a large specific capacity.

The synthesis method of FeOF in the prior art is relatively limited. JG Thompson and FJ Brink of the Australian National University first synthesized FeOF by solid-state reaction of FeF ₃ and Fe ₂ O ₃ in a closed Pt tube under an Ar atmosphere at a high temperature of 950°C. GG Amatucci and N. Pereira of Rutgers University in the United States synthesized FeOF by solution method by using Fe metal and fluorosilicic acid aqueous solution as precursors. Shigeto Okada and Ayuko Kitajou of Kyushu University in Japan used FeF ₃ and Fe ₂ O ₃ as raw materials to synthesize FeO _1.1+-1 F _0.95 by roller quenching method. This rapid synthesis method is beneficial to reduce production costs and avoid the release of F atmosphere. pollution caused. However, after FeOF is synthesized by these three methods, it needs to be ball milled with acetylene black to increase the conductivity, and then prepare electrode sheets.

Contents of the invention

In view of this, it is indeed necessary to provide a new iron oxyfluoride-based positive electrode composite material and a preparation method thereof.

A positive electrode composite material is a graphene-FeOF composite material, including FeOF particles and graphene bonded by chemical bonds.

A positive electrode composite material is functionalized graphene, which includes FeOF particles and graphene carbon atom layers, and the FeOF particles and graphene carbon atom layers are chemically bonded.

A method for preparing a positive electrode composite material, comprising the following steps: uniformly mixing ferric fluoride and graphene oxide in a liquid phase solvent to form a solid-liquid mixture; and placing the solid-liquid mixture in a hydrothermal/solvothermal reaction kettle 80℃~250℃ for hydrothermal/solvothermal reaction.

Compared with the prior art, the present invention synthesizes FeOF by iron fluoride and graphene oxide for the first time, and the graphene oxide is not only used as a reaction raw material to chemically react with iron fluoride, but also as a conductive agent in the positive electrode composite material to increase FeOF conductivity.

Description of drawings

FIG. 1 is an SEM image of the positive electrode composite material synthesized in the embodiment of the present invention.

Fig. 2 is an XRD pattern of the positive electrode composite material synthesized in the embodiment of the present invention.

detailed description

The positive electrode composite material provided by the present invention and its preparation method will be further described in detail below with reference to the accompanying drawings and specific examples.

An embodiment of the present invention provides a positive electrode composite material, which is a graphene-FeOF composite material, including FeOF particles and graphene bonded by chemical bonds. FeOF particles were in situ generated on the graphene surface.

Specifically, the particle size of the FeOF particles is preferably 1 nm to 10 μm.

It can be understood that the graphene may include one or more layers (such as 1-10 layers, preferably 1-3 layers) of superimposed carbon atomic layers. The graphene may be graphene oxide, that is, some carbon atoms in graphene are connected with oxygen atoms through chemical bonds. The mass percentage of FeOF in the cathode composite material may be 2%-98%, preferably 70%-95%.

Some of the carbon atoms in the graphene are connected with Fe, O or F in the FeOF particles through chemical bonds, preferably with O in the FeOF particles.

The cathode composite material can also be regarded as a functionalized graphene. In traditional functionalized graphene, carbon atomic layers of graphene are connected with functional groups, such as organic groups such as S or Cl, through chemical bonds. In the present invention, the functional groups in the functionalized graphene are FeOF particles.

The cathode composite material can be used in lithium ion batteries or other electrochemical batteries.

An embodiment of the present invention provides a method for preparing a positive electrode composite material, which includes the following steps:

S1, uniformly mixing iron fluoride (FeF ₃ ) and graphene oxide in a liquid phase solvent to form a solid-liquid mixture; and

S2, the solid-liquid mixture is subjected to a hydrothermal/solvothermal reaction at 80° C. to 250° C. in a hydrothermal/solvothermal reaction kettle.

FeF ₃ may or may not contain crystal water, preferably contains crystal water, such as ferric fluoride trihydrate (FeF ₃ 3H ₂ O), FeF ₃ 0.33H ₂ O, Fe _1.9 F _4.75 0.95H ₂ O, FeF At least one of _2.5 ·0.5H ₂ O, FeF ₃ ·H ₂ O and amorphous FeF ₃ .

The graphene oxide reacts with _FeF3 under hydrothermal/solvothermal conditions to generate FeOF in situ on the surface of the carbon atomic layer of graphene, thereby combining with graphene through chemical bonds. When all the oxygen in graphene oxide participates in the reaction with FeOF, graphene oxide can be completely reduced to graphene.

The liquid phase solvent can be water and/or an organic solvent, and the organic solvent preferably contains an oxidative group (such as -NO ₂ , -OH, -COOH, etc.), such as one of ethanol, propanol, acetic acid and citric acid or more. When the liquid-phase solvent is a mixed solvent of water and an organic solvent, the ratio between water and the organic solvent is not limited. That is to say, the basic function of the liquid-phase solvent is to provide a hydrothermal/solvothermal liquid-phase reaction environment. When the liquid phase solvent contains water, FeF can be dissolved to form a solid _- liquid mixture with graphene oxide, making the reaction easier to carry out. Preferably, FeF with as small a size particle as possible can be used as a raw material, and when the liquid phase solvent is only an organic solvent, such as ethanol, the FeF _of a small size particle can also be oxidized under the high temperature and high pressure conditions _of hydrothermal/solvothermal Graphene reacts to form FeOF. When the organic solvent contains an oxidizing group, it can participate in the reaction between graphene _oxide and FeF as a reactant to promote the generation of FeOF. The ratio of water to organic solvent can be 1:10~10:1, preferably 1:3~3:1.

The FeF ₃ , graphene oxide and liquid phase solvent can be uniformly mixed by means of mechanical stirring, ball milling or ultrasonic oscillation.

The hydrothermal/solvothermal reaction kettle is a sealed autoclave, and the liquid phase solvent inside the reaction kettle is vaporized by heating during the reaction process, thereby providing a high-pressure reaction environment. The holding time of the hydrothermal/solvothermal reaction may be 2 hours to 24 hours. After the reaction, naturally cool to room temperature, open the reactor and filter the obtained solid product, which is the positive electrode composite material, that is, the graphene-FeOF composite material.

Please refer to Figure 1. The morphology of the product graphene oxide-FeOF composite material is shown in the figure. Nano-scale FeOF particles (40 nm×100 nm) are uniformly dispersed on the graphene oxide sheet. Please refer to Figure 2. The synthesized solid product is characterized by XRD. The diffraction peaks in the spectrum can be assigned to graphene oxide (the peak at 11.8°, marked by the arrow) and FeOF (other diffraction peaks in the spectrum). It can thus be proved that _FeF3 and GO can be completely converted into GO-FeOF composites after the hydrothermal reaction of FeF3 and GO in the mixed solution of ethanol and deionized water. This nanocomposite can be used as an excellent cathode material for lithium-ion batteries.

The raw material _FeF3 and the synthesis method of graphene oxide used in the above reaction are not limited, and the preparation method of _FeF3 · _3H2O in this embodiment includes the following steps;

Ultrasonic dispersion of surfactants (such as CTAB) in deionized water;

Add ferric chloride to dissolve in this deionized water, obtain Fe ³⁺ solution; And

The Fe ³⁺ solution was dropped into the hydrofluoric acid solution drop by drop under the condition of stirring, and the stirring was continued until the reaction was complete.

The obtained solid product can be further separated by centrifugation, washed with ethanol until neutral, and dried to obtain FeF ₃ ·3H ₂ O.

Adopt Hummers method to prepare graphene oxide in the present embodiment, preparation method comprises the following steps:

Mix and stir graphite, sodium nitrate, and 1 concentrated sulfuric acid in an ice-water bath;

Add potassium permanganate and continue to stir until the graphite is completely oxidized;

Add deionized water and hydrogen peroxide to the reactant, and stir until the reaction is complete.

The obtained solid product can be further centrifuged to obtain a graphene oxide suspension.

Example 1

Preparation of ferric fluoride trihydrate FeF ₃ 3H ₂ O: Add 0.1g CTAB to 30mL deionized water, ultrasonically disperse; then add 18 g FeCl ₃ 6H ₂ O to it to obtain Fe ³⁺ solution; under strong stirring , the Fe ³⁺ solution was dropped into HF (38%, 50mL) dropwise, and continued to stir for 2h until the reaction was complete. Centrifuge and wash with ethanol until neutral, and dry the precipitate in a common oven at 60°C for 10 hours to obtain iron fluoride trihydrate FeF ₃ ·3H ₂ O.

Preparation of graphene oxide: Graphene oxide was prepared by the Hummers method. The experimental process was as follows: 5 g of graphite, 2.5 g of sodium nitrate, and 115 mL of concentrated sulfuric acid were mixed in an ice-water bath, and stirred vigorously for 30 min; 30 g of permanganese was added to it. After stirring for 5 hours, graphite was completely oxidized; 200 mL of deionized water was added to the reactant and stirring was continued for 20 minutes, and 400 mL of deionized water and 20 mL of hydrogen peroxide (30%) were added until the reaction was complete. Centrifuge at 5000 rpm / 30 min, discard the lower precipitate, and take the upper graphene oxide suspension (4 mg/mL) and save it for later use.

Preparation of graphene-FeOF composite material: 10 mL of the prepared graphene oxide suspension (4 mg/mL) was mixed with 80 mg of the prepared FeF ₃ 3H ₂ O and 25 mL of ethanol, and ultrasonically dispersed for 30 min; then The mixed solution was placed in a hydrothermal kettle, the temperature was raised to 120°C, and the temperature was kept for 10 h. Then cool down to room temperature naturally.

The preparation method of the positive electrode composite material provided by the present invention utilizes graphene oxide not only as a reaction raw material to chemically react with _FeF3 , but also as a conductive agent in the positive electrode composite material to increase the conductivity of FeOF. Since graphene oxide includes one or several layers of carbon atoms, the surface contains oxygen-containing functional groups, and has good dispersion in aqueous solution, FeOF can be uniformly generated on the surface of graphene oxide. Because graphene has good conductivity, large specific surface area and good mechanical properties, it can be used as a carrier of FeOF nanoparticles; after forming a composite material with FeOF nanoparticles, graphene plays a role in the electrochemical process. Electronics, increase conductivity, prevent agglomeration, buffer volume changes, etc.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included within the scope of protection claimed by the present invention.

Claims (8)

1. a preparation method for anode composite material, it comprises the following steps:

Ferric flouride and graphene oxide are uniformly mixed to form a solidliquid mixture in liquid phase solvent, this fluorine Change ferrum is FeF₃·3H₂O、FeF₃·0.33H₂O、Fe_1.9F_4.75·0.95H₂O、FeF_2.5·0.5H₂O、FeF₃·H₂O And amorphous FeF₃In at least one；And

By this solidliquid mixture in hydrothermal/solvent thermal response still 80 DEG C～250 DEG C to carry out hydrothermal/solvent heat anti- Should.

2. the preparation method of anode composite material as claimed in claim 1, it is characterised in that this liquid phase solvent For water and the combination of ethanol.

3. the preparation method of anode composite material as claimed in claim 1, it is characterised in that this hydrothermal/solvent The temperature retention time of thermal response is 2 hours～24 hours.

4. an anode composite material, this anode composite material is combined by the positive pole as described in claim 1-3 Prepared by the preparation method of material, it is characterised in that this anode composite material is that Graphene-FeOF is combined Material, including by the FeOF granule of chemical bonds and Graphene.

5. anode composite material as claimed in claim 4, it is characterised in that the grain size of this FeOF granule For 1nm～10 μm.

6. anode composite material as claimed in claim 4, it is characterised in that FeOF in this anode composite material Weight/mass percentage composition be 2%～98%.

7. anode composite material as claimed in claim 4, it is characterised in that FeOF in this anode composite material Weight/mass percentage composition be 70%～95%.

8. anode composite material as claimed in claim 4, it is characterised in that this FeOF particle in-situ generates This graphenic surface.