阅读说明：本技术 一种石墨烯修饰的高铁酸盐材料及其制备方法和应用 (Graphene-modified ferrate material and preparation method and application thereof ) 是由 王宝辉 朱凌岳 于登宇 汪洪溟 苑丹丹 闫超 吴红军 于 2019-09-03 设计创作，主要内容包括：本发明涉及一种石墨烯修饰的高铁酸盐材料及其制备方法和应用,所述方法：制备强酸性氧化石墨,用含有氮甲基吡咯烷酮和无水乙醇的混合液多次清洗,得到中性氧化石墨,用水将中性氧化石墨分散均匀,得到氧化石墨水分散液；以抗坏血酸为还原剂,在超声辅助的水热条件下将氧化石墨水分散液中的氧化石墨还原成化学还原石墨烯,然后经过抽滤和干燥,得到化学还原石墨烯；将高铁酸盐和化学还原石墨烯乙醇分散液通过共沉积法制得石墨烯修饰的高铁酸盐材料。本发明通过共沉积法将化学还原石墨烯包覆于高铁酸盐表面,显著提高了高铁酸盐在潮湿环境和饱和KOH溶液中的稳定性,以及与Zn组成的碱性超铁电池在多种情况下的实际放电性能。(The invention relates to a graphene modified ferrate material and a preparation method and application thereof, wherein the method comprises the following steps: preparing strong acid graphite oxide, washing the strong acid graphite oxide for multiple times by using a mixed solution containing nitrogen methyl pyrrolidone and absolute ethyl alcohol to obtain neutral graphite oxide, and uniformly dispersing the neutral graphite oxide by using water to obtain a graphite oxide water dispersion solution; reducing graphite oxide in the graphite oxide aqueous dispersion into chemically reduced graphene under an ultrasonic-assisted hydrothermal condition by using ascorbic acid as a reducing agent, and then performing suction filtration and drying to obtain the chemically reduced graphene; and (3) preparing the ferrate material modified by the graphene from ferrate and chemically reduced graphene ethanol dispersion liquid by a codeposition method. According to the invention, the chemical reduction graphene is coated on the surface of ferrate by a codeposition method, so that the stability of ferrate in a humid environment and a saturated KOH solution is obviously improved, and the actual discharge performance of an alkaline super-iron battery consisting of the ferrate and Zn under various conditions is obviously improved.)

1. A preparation method of a graphene-modified ferrate material is characterized by comprising the following steps of:

(1) preparing strong-acid graphite oxide, washing the strong-acid graphite oxide for multiple times by using a mixed solution containing nitrogen methyl pyrrolidone and absolute ethyl alcohol to obtain neutral graphite oxide, and then uniformly dispersing the neutral graphite oxide by using water to obtain a graphite oxide water dispersion liquid;

(2) reducing graphite oxide in the graphite oxide aqueous dispersion into chemically reduced graphene under an ultrasonic-assisted hydrothermal condition by using ascorbic acid as a reducing agent, and then sequentially performing suction filtration and drying to obtain the chemically reduced graphene;

(3) preparing chemical reduction graphene ethanol dispersion liquid by using the chemical reduction graphene obtained in the step (2), and preparing the graphene modified ferrate material with ferrate coated by the chemical reduction graphene by using a codeposition method through ferrate and the chemical reduction graphene ethanol dispersion liquid.

2. The method of claim 1, wherein:

the ferrate is one or more of potassium ferrate, sodium ferrate, barium ferrate, lithium ferrate, cesium ferrate, silver ferrate and strontium ferrate;

preferably, the ferrate is potassium ferrate.

3. The method of claim 1, wherein:

in the step (1), the volume ratio of the strongly acidic graphite oxide to the N-methyl pyrrolidone and the absolute ethyl alcohol contained in the mixed solution is 1:2: 4.

4. The method of manufacturing according to claim 1, further comprising:

and co-depositing the graphene-modified ferrate material and the chemical reduction graphene ethanol dispersion liquid for multiple times to obtain graphene-modified ferrate materials with different chemical reduction graphene coating amounts.

5. The production method according to any one of claims 1 to 4, characterized in that:

the mass ratio of ferrate contained in the graphene-modified ferrate material to chemically reduced graphene is 100: (0.8-5.2).

6. The production method according to any one of claims 1 to 4, characterized in that:

the concentration of graphite oxide contained in the graphite oxide water dispersion liquid is 0.05-0.2 mg/L.

7. The production method according to any one of claims 1 to 4, characterized in that:

the concentration of the chemically reduced graphene contained in the chemically reduced graphene ethanol dispersion liquid is 0.05-0.12 mg/mL.

8. The production method according to any one of claims 1 to 4, characterized in that:

the hydrothermal temperature is 24-60 ℃.

9. The graphene-modified ferrate material prepared by the preparation method of any one of claims 1 to 8.

10. Use of the graphene-modified ferrate material prepared by the preparation method of any one of claims 1 to 8 as a cathode material in a super-iron battery.

Technical Field

The invention belongs to the technical field of super-iron batteries, and particularly relates to a graphene modified ferrate material as well as a preparation method and application thereof.

Background

With the increasing demand for green chemical energy and almost exhausted electrode materials, ferrate compounds have a broad development prospect as battery cathode materials. In 1999, Litch used ferrate (MFeO)₄) As cathode material to replace MnO in alkaline zinc-manganese cell₂Cathode and this new cell is named "super-iron cell", MFeO₄The discharge products of the/Zn battery are ZnO, water and Fe which do not pollute the environment₂O₃With basic MnO₂MFeO vs. Zn and lead acid batteries₄the/Zn battery is a green and pollution-free sustainable energy source and is praised as a new generation of 'green battery'. However, despite its potential advantages, ferrate is limited by chemical instability. Ferrate is very unstable and easy to decompose in aqueous solution or humid environment; and oxygen can be released immediately under acidic condition and is decomposed slowly in neutral or weak alkaline solution. The wide application of the super-iron battery is limited due to poor stability of ferrate. Thus, maintaining a stable and sustained discharge is critical to improving the electrochemical performance of ferrate batteries.

In order to improve the stability of ferrate cathodes, zirconium chloride (ZrCl) has been proposed₄) Zirconium dioxide (ZrO)₂) Yttrium oxide-zirconium dioxide (Y)₂O₃-ZrO₂)、Phthalocyanine (H)₂PC) and the like for potassium ferrate (K)₂FeO₄) The coating is carried out to improve the discharge performance of the potassium ferrate cathode, but when the substances are used as coating materials, MFeO₄The capacitance of the/Zn battery still has the problems of insignificant increase and the like.

Graphene is a carbon material emerging in the 21 st century, and is widely concerned by people due to excellent electrical, thermal, mechanical and optical properties, and the like, and particularly applied to the field of electrochemical energy storage. At present, Graphene Oxide (GO) and Chemically Reduced Graphene (CRG) have been successfully applied to lithium ion batteries, supercapacitors and lithium-air batteries, and have achieved good results. However, no report is available for improving the stability and discharge performance of the super-iron battery by coating ferrate with Chemically Reduced Graphene (CRG) as a cathode.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a graphene modified ferrate material and a preparation method and application thereof. According to the method, Chemically Reduced Graphene (CRG) is used as a coating material and coated on the surface of ferrate by a codeposition method, so that the stability of ferrate in a humid environment and a saturated KOH solution is obviously improved, and the actual discharge performance of an alkaline super-iron battery consisting of the ferrate and Zn under various conditions is improved.

In order to achieve the above object, the present invention provides, in a first aspect, a method for preparing a graphene-modified ferrate material, the method comprising the steps of:

(1) preparing strong-acid graphite oxide, washing the strong-acid graphite oxide for multiple times by using a mixed solution containing nitrogen methyl pyrrolidone and absolute ethyl alcohol to obtain neutral graphite oxide, and then uniformly dispersing the neutral graphite oxide by using water to obtain a graphite oxide water dispersion liquid;

(2) reducing graphite oxide in the graphite oxide aqueous dispersion into chemically reduced graphene under an ultrasonic-assisted hydrothermal condition by using ascorbic acid as a reducing agent, and then sequentially performing suction filtration and drying to obtain the chemically reduced graphene;

(3) preparing chemical reduction graphene ethanol dispersion liquid by using the chemical reduction graphene obtained in the step (2), and preparing the graphene modified ferrate material with ferrate coated by the chemical reduction graphene by using a codeposition method through ferrate and the chemical reduction graphene ethanol dispersion liquid.

Preferably, the ferrate is one or more of potassium ferrate, sodium ferrate, barium ferrate, lithium ferrate, cesium ferrate, silver ferrate and strontium ferrate; preferably, the ferrate is potassium ferrate.

Preferably, in step (1), the volume ratio of the strongly acidic graphite oxide to the N-methylpyrrolidone and the absolute ethyl alcohol contained in the mixed solution is 1:2: 4.

Preferably, the method further comprises: and co-depositing the graphene-modified ferrate material and the chemical reduction graphene ethanol dispersion liquid for multiple times to obtain graphene-modified ferrate materials with different chemical reduction graphene coating amounts.

Preferably, the mass ratio of ferrate contained in the graphene-modified ferrate material to reduced graphene is 100: (0.8-5.2).

Preferably, the concentration of the graphite oxide contained in the graphite oxide water dispersion liquid is 0.05-0.2 mg/L.

Preferably, the concentration of the chemically reduced graphene contained in the chemically reduced graphene ethanol dispersion liquid is 0.05-0.12 mg/mL.

Preferably, the hydrothermal temperature is 24-60 ℃.

In a second aspect, the present invention provides a graphene-modified ferrate material prepared by the preparation method according to the first aspect of the present invention.

In a third aspect, the present invention provides a graphene-modified ferrate material prepared by the preparation method of the first aspect of the present invention, and the graphene-modified ferrate material is used as a cathode material in a super-iron battery.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) according to the method, the strong-acid graphite oxide is innovatively cleaned by using the mixed solution of N-methyl pyrrolidone (NMP) and absolute ethyl alcohol, and the graphite oxide with the pH value not more than 1 can be converted into neutral after 6-7 times of cleaning, so that the efficiency of preparing the neutral graphite oxide is effectively improved.

(2) According to the method, Chemically Reduced Graphene (CRG) is used as a coating material and coated on the surface of ferrate by a codeposition method, so that the stability of ferrate in a humid environment and a saturated KOH solution is obviously improved, and the actual discharge performance of an alkaline super-iron battery consisting of the ferrate and Zn under various conditions is improved.

(3) After 60 days, the prepared graphene modified ferrate material has CRG (Crg-coated glass) type K in a humid environment₂FeO₄The purity (5 times) was 46.7% as compared with uncoated K₂FeO₄The height is 33.9 percent; CRG-coated K in saturated KOH solution₂FeO₄The purity of (5 times) was 75.9% as compared with that of uncoated K₂FeO₄Higher by 25.6%; when the graphene-modified ferrate material prepared by the invention is applied as a cathode material of a super-iron battery, the CRG-coated K₂FeO₄(5 times) the ratio K of actual capacitance and active component utilization rate of alkaline super-iron battery composed of Zn at 1775 omega₂FeO₄The higher ratio is 22.9% and 22.8%, respectively, compared with MnO₂The higher ratios were 33.4% and 15.9%, respectively.

Drawings

Fig. 1 is an infrared spectrum (FTIR spectrum) of neutral Graphite Oxide (GO) and Chemically Reduced Graphene (CRG) in example 1 of the present invention. In the figure, a is the FTIR spectrum of CRG, and b is the FTIR spectrum of GO.

Fig. 2 is an X-ray photoelectron spectroscopy (XPS) spectrum of neutral Graphite Oxide (GO) and Chemically Reduced Graphene (CRG) in example 1 of the present invention. In the figure, a is the XPS spectrum of GO and b is the XPS spectrum of CRG.

Fig. 3 is an X-ray diffraction spectrum (XRD spectrum) of graphite powder, neutral Graphite Oxide (GO), and Chemically Reduced Graphene (CRG) in example 1 of the present invention. In the figure, a is an XRD spectrogram of CRG, b is an XRD spectrogram of GO, and c is an XRD spectrogram of graphite powder.

FIG. 4 is a drawing of the present inventionK in example 1₂FeO₄And CRG coated form K₂FeO₄Photographs (3 times) and SEM images. In the figure, a and c respectively represent K₂FeO₄The photographs and SEM images of (A) and (B) show CRG-coated K₂FeO₄Photographs (3 times) and SEM images.

FIG. 5 shows K in example 2 of the present invention₂FeO₄And CRG coated form K₂FeO₄(3 times) purity in different environments versus time. In which a denotes K₂FeO₄+ dry air, b denotes CRG-coated type K₂FeO₄(3 times) + saturated KOH solution, c represents K₂FeO₄+ saturated KOH solution, d denotes CRG-coated K₂FeO₄(3 times) + moist air, e denotes K₂FeO₄Purity in + humid air versus time. In the figure, the abscissa Time represents Time in days (day) and the ordinate Purity (%) represents Purity in%.

FIG. 6 shows K in example 2 of the present invention₂FeO₄CRG coated K₂FeO₄(1, 3 and 5) purity in humid air as a function of time. In the figure, a, b, c and d respectively represent K₂FeO₄CRG coated K₂FeO₄(1 time) CRG-coated K₂FeO₄(3 times) CRG-coated K₂FeO₄(5 times) purity in humid air versus time curve.

FIG. 7 CRG-coated type K in example 3 of the present invention₂FeO₄Graph of discharge performance at 1775 Ω. In which a denotes K₂FeO₄B represents a CRG-coated type K₂FeO₄(1 st) discharge Performance Curve, c represents CRG-coated K₂FeO₄(3 times) discharge Performance Curve, d represents CRG-coated K₂FeO₄(5 times) discharge Performance Curve, e represents MnO₂Discharge performance curve of (1). In the figure, the abscissa Sepcific Capacity represents the actual discharge amount in mAh, and the ordinate Voltage represents the Voltage in V.

FIG. 8 is the present inventionCRG-coated type K in invention example 3₂FeO₄Discharge performance plots at 200 Ω and 20 Ω. In the figure, a represents a CRG-coated type K₂FeO₄(5 times) discharge Performance Curve at 200. omega. b represents CRG-coated K₂FeO₄Discharge performance curve at 20 Ω (5 times).

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The invention provides a preparation method of a graphene modified ferrate material in a first aspect, which comprises the following steps:

(1) preparing strong acid graphite oxide (graphite oxide with pH not more than 1), washing the strong acid graphite oxide for multiple times by using a mixed solution containing N-methyl pyrrolidone (NMP) and absolute ethyl alcohol to obtain neutral graphite oxide, and then uniformly dispersing the neutral graphite oxide by using water to obtain a graphite oxide water dispersion liquid (GO dispersion liquid); in the invention, the graphite oxide is graphene oxide, and the graphite oxide water dispersion liquid is a dispersion liquid which takes neutral graphite oxide as a dispersoid and water as a dispersion medium; in the present invention, the strongly acidic graphite oxide can be produced, for example, by the Hummers method using graphite powder as a raw material; in the present invention, the neutral graphite oxide is a hydrous neutral graphite oxide (hydrous graphite oxide) which is not dried after being washed, because the inventors have found through a large number of experiments that a large number of oxygen-containing functional groups having poor stability on the surface of the graphite oxide are rapidly decomposed during drying, causing difficulty in completely dispersing the solid graphite oxide in water, and the mass concentration of the dispersion can be significantly improved after the hydrous graphite oxide is used as a dispersoid. In the present invention, the specific steps of washing with the mixed solution containing the nitrogen methyl pyrrolidone and the absolute ethyl alcohol may be, for example: adding a mixed solution of NMP and absolute ethyl alcohol into the strongly acidic graphite oxide according to a certain volume ratio, stirring for 5 minutes, standing for 20 minutes, carrying out vacuum filtration on the mixed solution standing for 20 minutes, stirring and dispersing the obtained filter cake into 100mL of distilled water, and centrifuging (8000r/min, 15min) to separate graphite oxide with reduced acidity; and finally, repeatedly treating the graphite oxide with reduced acidity by using NMP, absolute ethyl alcohol and deionized water until the pH value is about 7 to obtain the neutral graphite oxide.

(2) Reducing Graphite Oxide (GO) in the graphite oxide water dispersion liquid (GO dispersion liquid) obtained in the step (1) into Chemically Reduced Graphene (CRG) by using ascorbic acid (reduced ascorbic acid, L-AA) as a reducing agent under an ultrasonic-assisted hydrothermal condition, and then sequentially performing suction filtration and drying to obtain the Chemically Reduced Graphene (CRG); specifically, for example, the graphite oxide aqueous dispersion is placed in a water bath, L-AA is added, the reaction is carried out under the assistance of ultrasound until pure black CRG aqueous dispersion is obtained, then the CRG aqueous dispersion is subjected to vacuum filtration to obtain a black filter cake, and finally the black filter cake is placed in a 50 ℃ vacuum drying oven to be dried for 12 hours, so that the black film-shaped solid CRG can be obtained.

(3) Preparing a chemical reduction graphene ethanol dispersion solution (CRG ethanol dispersion solution) by using the chemical reduction graphene obtained in the step (2), and preparing the graphene modified ferrate material of which ferrate is coated by the chemical reduction graphene by using a codeposition method through ferrate and the chemical reduction graphene ethanol dispersion solution; in the present invention, in particular, for example, ferrate powder such as potassium ferrate powder (K)₂FeO₄) Adding into CRG ethanol dispersion, rapidly stirring to make potassium ferrate suspend in the dispersion, stopping stirring after 20min, and standing for 10 min; then removing the residual ethanol from the solid-liquid mixture by vacuum filtration, and then placing the filter residue in a vacuum drying oven at 50 ℃ for 2h to remove the residual ethanol, thus obtaining the K with the surface coated by CRG₂FeO₄And gently flicked to remove excess CRG. In the invention, the chemically reduced graphene BThe alcohol dispersion liquid refers to a dispersion liquid in which chemically reduced graphene is used as a dispersoid and ethanol (for example, absolute ethanol) is used as a dispersion medium; in the present invention, when the ferrate is K₂FeO₄In the meantime, the ferrate material modified by graphene is also recorded as CRG-coated K₂FeO₄。

As is well known, the well-established preparation processes for preparing graphite oxide include the Brodie method, the Standenmaier method and the Hummers method, among which the Hummers method, which is relatively safe and simple, is widely used, but the Hummers method produces strongly acidic graphite oxide, which cannot be used as it is, and thus it is necessary to remove acidic substances adsorbed thereto. The acid removal method in the prior art mainly comprises centrifugal washing, suction filtration washing or infiltration, but the centrifugal washing and the infiltration waste a large amount of water and time and cannot be treated in a large scale. In addition, during the continuous filtration, washing and washing processes, the flaky graphite oxide can expand in volume due to water adsorption, and the expanded graphite oxide can block the micropores on the filter membrane, so that it is very difficult to completely remove acidic substances by vacuum filtration. Compared with the traditional filtration water washing, permeation and centrifugal water washing, the method for washing the acidic graphite oxide by washing the acidic graphite oxide for 6-7 times by using the mixed solution of the NMP solution and the ethanol solution is more efficient, convenient and environment-friendly, and the efficiency for preparing the neutral graphite oxide is effectively improved.

In addition, the method takes Chemically Reduced Graphene (CRG) as a coating material, and coats the surface of the ferrate by a codeposition method, so that the stability of the ferrate in a humid environment and a saturated KOH solution is obviously improved, and the actual discharge performance of the alkaline super-iron battery consisting of the ferrate and Zn under various conditions is improved.

According to some preferred embodiments, the ferrate is potassium ferrate (K)₂FeO₄) Sodium ferrate (Na)₂FeO₄) Barium ferrate (B)aFeO₄) Lithium ferrate (Li)₂FeO₄) Cesium ferrate (Cs)₂FeO₄) Silver ferrate (Ag)₂FeO₄) Strontium ferrate (SrFeO)₄) One or more of; preferably, the ferrate is potassium ferrate; in the present invention, the potassium ferrate can be produced, for example, by a hypochlorite oxidation method (one-step method).

According to some preferred embodiments, in the step (1), the volume ratio of the strongly acidic graphite oxide to the N-methylpyrrolidone and the absolute ethyl alcohol contained in the mixed solution is 1:2: 4.

According to some preferred embodiments, the method further comprises: and co-depositing the graphene-modified ferrate material and the chemical reduction graphene ethanol dispersion liquid for multiple times to obtain graphene-modified ferrate materials with different chemical reduction graphene coating amounts. In the invention, specifically, for example, the graphene-modified ferrate material powder is added into a newly prepared CRG ethanol dispersion, and is rapidly stirred so that the graphene-modified ferrate material is suspended in the dispersion, and after 20min, the stirring is stopped, and the mixture is stood for 10 min; then removing the residual ethanol from the solid-liquid mixture through vacuum filtration, and then placing the filter residue in a vacuum drying oven at 50 ℃ for 2 hours to remove the residual ethanol, thus obtaining the graphene-modified ferrate material coated with chemically reduced graphene for the second time; and repeating the step for multiple times of codeposition to obtain the graphene-modified ferrate material which is repeatedly coated by the chemically reduced graphene, and thus obtaining various graphene-modified ferrate materials with different chemically reduced graphene coating amounts. In the present invention, CRG is coated on K₂FeO₄The reason for the surface may be that in a very low polarity ethanol solution, the surface has negatively charged K₂FeO₄Will attract CRG with positive charges on the surface to make CRG coat on K₂FeO₄On the surface, a codeposition phenomenon occurs; when CRG is coated with type K₂FeO₄When the dispersion is put into a new CRG dispersion again, the balance of the dispersion is lost, and the original dispersion is causedCRG will be coated with CRG again₂FeO₄Agglomeration occurred, so treatment K was repeated using a CRG ethanol dispersion₂FeO₄K with different CRG coating amounts can be obtained₂FeO₄。

According to some preferred embodiments, the graphene-modified ferrate material comprises ferrate and chemically-reduced graphene in a mass ratio of 100: (0.8-5.2).

According to some preferred embodiments, the aqueous graphite oxide dispersion contains graphite oxide at a concentration of 0.05 to 0.2mg/L (e.g., 0.05, 0.1, 0.15, or 0.2mg/L), preferably 0.15 mg/L.

According to some preferred embodiments, the chemically reduced graphene contained in the chemically reduced graphene ethanol dispersion liquid has a concentration of 0.05 to 0.12mg/mL (e.g., 0.05, 0.1, or 0.12mg/mL), preferably 0.1 mg/mL.

According to some preferred embodiments, the hydrothermal temperature (reaction temperature under hydrothermal conditions) is 24 to 60 ℃ (e.g., 24 ℃, 36 ℃, 48 ℃, or 60 ℃), preferably 36 ℃. The inventor finds that the reduction speed of reduced ascorbic acid (L-AA) to Graphite Oxide (GO) can be obviously improved by increasing the hydrothermal temperature, and the chemical reaction rates at 36 ℃, 48 ℃ and 60 ℃ are about 2 times, 3 times and 3 times of those at 24 ℃. However, when the reaction temperature exceeds 36 ℃, GO with gradually reduced oxygen content can agglomerate in water to form amorphous carbon, and the agglomeration phenomenon is more obvious at higher reaction temperature. The inventor finds that the reduction under the ultrasonic-assisted hydrothermal condition can effectively prevent amorphous carbon from occurring in Chemically Reduced Graphene (CRG) aqueous dispersion prepared at 36 ℃, and can also remarkably improve the reduction speed by more than 15 times at 24 ℃. However, when the reaction temperature exceeds 48 ℃, the ability of the ultrasonic aid to prevent amorphous carbon formation is insufficient. Therefore, the inventors found that in the present invention, the optimal reaction conditions for preparing CRG were to subject the aqueous GO dispersion to ultrasonic-assisted reduction at 36 ℃ for 2 h.

In a second aspect, the present invention provides a graphene-modified ferrate material prepared by the preparation method according to the first aspect of the present invention.

In a third aspect, the present invention provides a graphene-modified ferrate material prepared by the preparation method of the first aspect of the present invention, and the graphene-modified ferrate material is used as a cathode material in a super-iron battery.

The present invention will be further described with reference to the following examples. These examples are merely illustrative of preferred embodiments of the present invention and the scope of the present invention should not be construed as being limited to these examples.

Example 1: preparation of graphene-modified ferrate material

Adding a two-system mixed solution of NMP and absolute ethyl alcohol into strongly acidic graphite oxide according to the volume ratio of the strongly acidic graphite oxide to the NMP to the ethyl alcohol of 1:2:4, stirring for 5 minutes, and standing for 20 minutes; vacuum filtering the mixed solution for 20min, dispersing the obtained filter cake in 100mL of distilled water under stirring, and centrifuging (8000r/min, 15min) to separate graphite oxide with reduced acidity; finally, repeatedly using NMP, absolute ethyl alcohol and deionized water to treat the graphite oxide with reduced acidity (the volume ratio of the acidic graphite oxide to the NMP to the ethyl alcohol is 1:2:4 each time) until the pH value is about 7, thus obtaining neutral graphite oxide; finally, uniformly dispersing the neutral graphite oxide by using water to obtain a graphite oxide water dispersion liquid (GO dispersion liquid) with the mass concentration of the graphite oxide being 0.15 mg/mL; the strongly acidic graphite oxide is prepared by taking graphite powder as a raw material through a Hummers method.

Placing the graphite oxide water dispersion liquid with the concentration of 0.15mg/mL into a water bath kettle at 36 ℃, adding ascorbic acid L-AA to enable the concentration of the L-AA in the dispersion liquid to be 30mg/L, reacting for 2 hours under the assistance of ultrasound until pure black CRG water dispersion liquid is obtained, then obtaining a black filter cake by vacuum filtration of the CRG water dispersion liquid, finally placing the black filter cake into a vacuum drying oven at 50 ℃ for drying for 12 hours to obtain black film solid CRG, and grinding the black film solid CRG into powder.

Preparing 20mL of chemical reduction graphene ethanol dispersion liquid (CRG ethanol dispersion liquid) with the mass concentration of 0.1mg/mL of CRG; 100mg of ground potassium ferrate (K) was uniformly mixed₂FeO₄) Adding powder to the CRG ethanol dispersion, andstirring rapidly to make K₂FeO₄Suspending in the dispersion, stopping stirring after 20min, and standing for 10 min; then removing the residual ethanol from the solid-liquid mixture by vacuum filtration, and then placing the filter residue in a vacuum drying oven at 50 ℃ for 2h to remove the residual ethanol, thus obtaining the K with the surface coated by CRG₂FeO₄And gently flicked to remove excess CRG. K to be coated 1 time with GO₂FeO₄The coating steps are repeated to obtain K with different CRG coating amounts₂FeO₄(graphene-modified ferrate materials with different amounts of chemically reduced graphene coating). The mass data of the coated CRG are shown in table 1. Wherein, K₂FeO₄For preparing K with purity of 94.7% by hypochlorite oxidation method₂FeO₄And (4) crystals.

Table 1: k₂FeO₄And CRG coated form K₂FeO₄Quality data of

Number of coating	K2FeO4(mg)	CRG coated K2FeO4(mg)	Percentage of coating
				1	100	100.8	0.8％
3	100	102.7	2.7％
				5	100	105.2	5.2％

In this example, the chemical and crystal structures of the resulting CRG were characterized by infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD): in comparison with graphite oxide, part of the oxygen-containing peak in the FTIR spectrum of CRG is apparently disappeared, for example, as shown in FIG. 1, CRG is at 1730cm^-1(stretching vibration of O-C ═ O or C ═ O), 1224cm^-1(stretching vibration of O-C-O) 1051cm^-1(C-O stretching vibration) and 3391cm^-1The disappearance and attenuation of the absorption peak at the position (-stretching vibration of OH bond) can prove that L-AA can effectively reduce graphite oxide to CRG, but at 1388cm^-1A newly appeared C-OH absorption peak indicates that a small amount of oxygen-containing functional groups are remained in the CRG; compared with graphite oxide, the intensity and area of an oxygen-containing peak in an XPS spectrum are obviously reduced, for example, as shown in FIG. 2, L-AA can effectively cause C-O/C-O-C in GO to undergo a ring-opening reaction, and then GO is reduced into CRG; as compared with graphite oxide, the XRD pattern has a smaller interlayer spacing and significantly enhanced conductivity, for example, as shown in fig. 3, the characteristic diffraction peak of graphite oxide appears at 2 θ of 11.4 ° and an interlayer spacing of 0.794nm, and after reduction with L-AA, the characteristic diffraction peak of graphite oxide has disappeared and a new diffraction peak appears at 2 θ of 24.5 ° (an interlayer spacing of 0.37nm) at a position close to the characteristic (002) diffraction peak of graphite (2 θ of 26.1 ° and an interlayer spacing of 0.34nm), but the peak is flat, and the interlayer spacing of CRG is smaller than that of graphite oxide but larger than the theoretical interlayer spacing value (0.335nm) of graphene, which indicates that L-AA removes most of the oxygen-containing functional groups in CRG, but still has a small amount of oxygen-containing functional groups remaining between the interlayer spacings of CRG, and the plane electron conjugated system of CRG is reconstructed to some extent.

In this embodiment, for K₂FeO₄And CRG coated form K₂FeO₄Scanning electron microscopy characterization (SEM characterization) was performed (3 times) as shown in fig. 4: phase contrast K₂FeO₄CRG coated K₂FeO₄(3 times), in CRG ethanol dispersion, can be at K by codeposition₂FeO₄A CRG coating layer with a certain thickness is formed on the surface and appears in appearance as a transition from crystal particles with metallic luster (fig. 4a) to dark black particles with larger volume (fig. 4b), and the morphology under SEM is an irregular lump (a ball shape) piled together.

Example 2: CRG-coated pair K₂FeO₄Effect test on stability

Using K in example 1₂FeO₄And CRG coated form K₂FeO₄The experiment was performed (3 times): mixing three parts of K₂FeO₄Respectively placing in dry air at normal temperature, in humid air environment (humid environment) and saturated KOH solution environment, and coating two portions of CRG with K₂FeO₄(3 times) placing in a humid air environment and a saturated KOH solution environment respectively, and researching K₂FeO₄CRG coated K₂FeO₄(3 times) the change of purity with time in different environments, the results are shown in FIG. 5.

As can be seen from fig. 5: in dry air at normal temperature, K₂FeO₄The purity of (D) is reduced by only 1.1% within 60d, which shows that K is₂FeO₄Is stable in dry air. However, will K₂FeO₄And CRG coated form K₂FeO₄After being placed in a humid environment for 60 days (3 times), the purity is greatly reduced to 12.8 percent and 40.8 percent respectively, and is reduced to 81.9 percent and 53.9 percent respectively. In addition, to simulate the super-iron battery environment, K is added₂FeO₄Saturated KOH solution, K is added dropwise₂FeO₄The purity of the crystal is reduced to 50.3 percent and 44.4 percent from the initial 94.7 percent within 60 days, while the CRG coated K₂FeO₄The purity (3 times) is reduced to 75.9% in a small degree and 18.8% in a small degree. CRG-coated K in humid and saturated KOH environments₂FeO₄The (3) purity profile always lies at K₂FeO₄In the above, it is shown that the CRG coating can significantly improve K₂FeO₄Is probably due to the coating at K₂FeO₄The large amount of CRG on the surface has excellent hydrophobic property, can isolate most of water outside and further prevent K₂FeO₄Rapid large scale hydrolysis reactions occur.

This example further investigated the number of CRG coatings versus K₂FeO₄The effect of stability in a humid environment, as shown in fig. 6: CRG coated K after 60d placement₂FeO₄The purity of (5 times) is about 46.7% in comparison with K₂FeO₄Higher by 33.9% (difference), but with CRG-coated K₂FeO₄The purity of the product (3 times) is similar; this indicates that the more times the coating was performed, the more CRG-coated form K₂FeO₄The better the stability of (b), but too much coating becomes less effective. Although after CRG coating, K₂FeO₄The purity of (A) is still obviously reduced in a humid environment, which shows that CRG is in K₂FeO₄The coating formed on the surface can only prevent the water in the electrolyte from being greatly soaked in the electrolyte for a certain time, but compared with the prior K coated by other materials₂FeO₄Already obviously improve K₂FeO₄Stability in a humid environment.

In the invention, the purity of the potassium ferrate solid sample is analyzed by a chromite method, and the calculation formula of the potassium ferrate purity is as follows:

in the formula: the purity of the P-potassium ferrate; v-iron ammonium sulfate solution Fe (NH) consumed₄)₂(SO₄)₂Volume (mL); N-Fe (NH)₄)₂(SO₄)₂Equivalent concentration; m_W-K₂FeO₄Molecular weight 198.04; M-K₂FeO₄Sample quality or CRG coated K₂FeO₄Sample mass.

Example 3: CRG coated K₂FeO₄Discharge performance test experiment under constant temperature and constant resistance

Will K₂FeO₄Or CRG coated K₂FeO₄The CR2032 type button cell is formed by mixing acetylene black with acetylene black, rolling into a thin sheet as a cathode, using Zn foil as an anode, using saturated potassium hydroxide as electrolyte and using a glass fiber diaphragm as a cell diaphragm, wherein the specific raw material ratio is as follows: k₂FeO₄Or CRG coated K₂FeO₄: acetylene black: 100mg of Zn: 10 mg: 200 mg.

The discharge performance curve and the active ingredient utilization rate of the CR2032 type button battery under the constant resistance 1775 omega load are tested, and the test method comprises the following steps: discharging the battery under a constant resistance, collecting time, voltage and current data through a battery test system, and performing piecewise fitting on time and current curves by using origin software, wherein a fitting model is a polynomial of degree 2; calculating the area of the graph formed by the time-current curve and the abscissa through fixed integral, namely the actual discharge capacity (actual capacitance), drawing an actual capacitance-voltage curve, namely a discharge performance curve, and K₂FeO₄The calculation formula of the effective utilization rate of the active ingredients is as follows:

in the formula: a: the effective utilization rate of active ingredients; c: 100mg K₂FeO₄Or CRG coated K₂FeO₄Actual discharge capacity; 40.6: 100mg of K with a purity of 100%₂FeO₄The theoretical capacitance of (1); 94.7%: k used₂FeO₄The purity of (2).

K obtained in this example₂FeO₄CRG coated K₂FeO₄(n-times of coating) (n ═ 1, 3, and 5) and MnO₂The discharge performance curve of the/Zn coin cell under the load of 1775 omega is shown in figure 7, and the discharge performance curve and the active ingredient utilization rate data are shown in table 2.

Table 2: CRG coated K₂FeO₄Discharge efficiency and active ingredient utilization of the discharge at 1775 Ω.

Cathode material	Actual discharge capacity (mAh)	Active ingredient utilization ratio (%)
			K2FeO4	25.6	66.5
CRG coated K2FeO4(1 time)	29.5	76.6
			CRG coated K2FeO4(3 times)	32.3	83.9
CRG coated K2FeO4(5 times)	33.2	86.2
			MnO2	22.1	72.5

Note: CRG-coated form K in Table 2₂FeO₄The CRG-coated K prepared in example 1 was used₂FeO₄(1 time) CRG-coated K₂FeO₄(3 times) and CRG-coated form K₂FeO₄(5 times) materials.

As can be seen from fig. 7 and table 2: when the cut-off voltage is 0.8V, 100mg K₂FeO₄The actual discharge capacity is about 25.6mAh, the starting and stopping voltage is 1.61V, the discharge platform voltage is 1.56 +/-0.05V and the utilization rate of active ingredients is about 66.5 percent. And after CRG coating, K₂FeO₄The actual discharge amount of (a) significantly increases with the increase in the CRG coating amount. When n is 5, CRG-coated K₂FeO₄The actual discharge capacity can reach 33.2mAh, the starting and stopping voltage is increased to 1.73V, the discharge platform is 1.57 +/-0.05V, and the utilization rate of active ingredients is more 86.2%. To contrast with alkaline zinc-manganese cells, the cathode material of button cells was replaced with MnO₂The experimental result shows that 100mg MnO is₂The actual discharge capacity is about 22.1mAh, the starting and stopping voltage is 1.52V, the discharge platform is 1.28 +/-0.05V, and the utilization rate of active substances is 72.5%. With CRG-coated K₂FeO₄(5 times) comparison, MnO₂The ratio of the capacitance lower than that of (A) was 33.4%, the ratio of the discharge plateau voltage lower was 18.9% and the ratio of the active ingredient utilization lower was 15.9%, indicating that CRG-coated K₂FeO₄(5 times) to MnO₂The electrochemical performance is more excellent.

This example further investigated load pair CRG-coated K₂FeO₄The effect of discharge performance of CRG coated K is tested₂FeO₄Discharge performance curves and active ingredient utilization rates at 200 Ω and 20 Ω (5 times), and the results are shown in fig. 8 and table 3.

Table 3: CRG coated K₂FeO₄Discharge efficiency and active ingredient utilization rate of the discharge at 200 Ω and 20 Ω (5 times).

As can be seen from FIG. 8 and Table 3, inCRG (Crg-Crg) coated K under loads of 200 omega and 20 omega₂FeO₄(5 times) and MnO₂The actual discharge amount of the discharge electrode is obviously reduced, and the discharge platform is obviously reduced. When the load is 200 omega, the CRG cladding type K₂FeO₄The actual discharge capacity (5 times) was reduced by 12.3% to 1775 Ω, the discharge plateau voltage was reduced by 8.2%, and the active ingredient utilization rate was reduced by 12.4%. When the load is 20 omega, the CRG coated K₂FeO₄The actual discharge capacity (5 times), the discharge plateau voltage and the active ingredient utilization rate were further reduced. MnO for simultaneous comparison₂The actual discharge capacity, discharge plateau voltage and active ingredient utilization ratio under 200 omega and 20 omega are higher than that of CRG cladding type K₂FeO₄(5 times) lower. It can be seen that even under heavy-load discharge, CRG-coated K₂FeO₄The discharge performance of the (5 times) is also higher than that of MnO₂。

Finally, the description is as follows: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the embodiments can still be modified, or some technical features can be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the present invention in its spirit and scope.