CN110767460B - Preparation method of partially alloyed tin oxide nanorod array supercapacitor cathode material - Google Patents

Abstract

The invention relates to a preparation method of a partially alloyed tin oxide nanorod array supercapacitor positive electrode material, and belongs to the technical field of new energy material preparation and application. The anode material provided by the invention is formed by an oxygen-deficient tin oxide nanorod array structure which grows on a foamed nickel substrate and is partially alloyed by Sn-Ni, can be directly used as a working electrode of a super capacitor, and has the advantages of large specific capacitance, good circulation stability and no toxicity or harm to a human body. The method comprises the steps of firstly, taking sodium stannate trihydrate and sodium hydroxide as raw materials, growing a tin dioxide nanorod array on a current collector foamed nickel substrate by adopting a solvothermal method, and then carrying out high-temperature heat treatment in a vacuum tube furnace in a reducing atmosphere to finally obtain the cathode material. The tin oxide nanorod array structure obtained by the method is high in yield and controllable in composition and appearance; the raw materials, equipment and process are simple, the cost is low, the production process is safe, clean and environment-friendly, and the method is favorable for large-scale production.

Description

Preparation of Partially Alloyed Tin Oxide Nanorod Arrays as Cathode Materials for Supercapacitors method

technical field

The invention relates to a preparation method of a partially alloyed tin oxide nanorod array supercapacitor positive electrode material, and belongs to the technical field of new energy material preparation and application.

Background technique

In recent years, in order to alleviate the energy shortage and environmental pollution caused by the overexploitation and use of fossil energy, and to meet the increasing energy demand of modern society, various sustainable and renewable energy storage materials have been extensively studied. Compared with batteries and traditional capacitors, supercapacitors have received widespread attention due to their faster charge and discharge rates, higher power density, longer cycle life, wider application temperature, and lower maintenance costs. For high-performance supercapacitors, the electrode materials should have large specific surface area, high specific capacitance, long cycle life, and high electrochemical oxidation/reduction rate. Among them, metal oxides are one of the typical cathode materials of pseudocapacitive supercapacitors.

The metal oxide pseudocapacitive supercapacitor cathode material first reported in the literature is ruthenium oxide (RuO ₂ ), which has the advantages of fast electrochemical response and high specific capacitance. However, the disadvantages of high cost and high environmental toxicity of ruthenium oxide electrode greatly limit its large-scale industrial application. Therefore, it is very meaningful to search for nontoxic and inexpensive metal oxides as electrodes for future high-performance supercapacitors. Among various metal oxides, SnO ₂ has become a research hotspot due to its low cost, non-toxicity, good thermal stability, and strong power transfer capability. For example, Pusawale et al. have chemically deposited nano-SnO ₂ thin films, and under the condition of a scan rate of 10 mV/s, the specific capacitance of the best sample was 66 F/g; Shinde et al. The metal tin substrate was anodized to prepare a self-organized nanoporous tin oxide film. The maximum specific capacitance of the obtained film sample reached 274F/g at 10mV/s. However, factors such as poor electrical conductivity, obvious particle agglomeration, and poor rate capability still hinder the commercialization of tin oxide-based supercapacitor electrode materials. In order to improve the electrochemical performance of _SnO2 electrodes, the researchers also made some attempts. Shakir et al. synthesized tin oxide-coated molybdenum oxide nanowires (SnO ₂ /MoO ₃ ) by sol-thermal and wet chemical routes, and the results showed that the synthesized SnO ₂ /MoO ₃ The specific capacitance of the composite nanowires can reach 295 F/g; Wang et al. synthesized SnO ₂ @polyaniline nanocomposites through a simple in-situ preparation method, and the specific capacitance was 335.5 F/g at 100 mV/s. However, these composites still have serious problems such as insufficient exposure of active sites, poor material conductivity, and poor performance stability.

In addition, literature studies have shown that the direct synthesis of electroactive materials on metal current collectors to prepare binder-free samples as electrodes is a promising method, which not only avoids the complicated preparation process of powdered electrodes, but also enables More active material on the sample is in contact with the electrolyte and participates in the redox reaction, thereby greatly improving the electrochemical performance of the electrode material (Yifei Guo, et al. Vertically standing MoP nanosheet arrays on Mosubstrate: An integrated binder-free electrode for highly efficient and stablehydrogen evolution. Journal of Alloys and Compounds, 2019, 792:732-741). Moreover, the metal current collector is also beneficial to the conduction of electrons, which enhances the electrical conductivity of the electrode material. In addition, the existence of defects in nanomaterials can significantly improve the electrical conductivity of nanomaterials (Yang Wang, et al. Tunable electricalresistivity of oxygen-deficient zinc oxide thin films. Surface Engineering, 2017, 33(3): 217-225 ).

Therefore, the present invention proposes a preparation method of a partially alloyed tin oxide nanorod array supercapacitor positive electrode material. In the technology proposed by the present invention, firstly using sodium stannate trihydrate and sodium hydroxide as raw materials, a solvothermal method is used to grow tin dioxide nanorod arrays on a foamed nickel substrate, and then in a vacuum tube furnace in a reducing atmosphere A high-temperature heat treatment was performed in the middle, and finally a partially Sn-Ni alloyed, oxygen-deficient tin oxide nanorod array structure grown on a foamed nickel substrate was obtained. This tin oxide nanorod array structure can be directly used as the working electrode (positive electrode) of supercapacitors. The supercapacitor cathode material prepared by this method has a large specific surface area, sufficient exposure of active sites, and large specific capacitance of the electrode because the active material is grown on the foamed nickel substrate in the form of nanorod array; this electrode material Among them, the valence state of metal cations is rich, the electrochemical reaction is complex, and the material capacitance is high; the substrate (current collector) of this electrode material is a metal with excellent electrical conductivity, and the active material is an oxygen-deficient oxidizer with strong electrical conductivity. Tin and the newly added Sn-Ni alloy with good electrical conductivity, and they are organically combined by high temperature heat treatment, so this electrode material has good conductivity and is conducive to the rapid transfer of charges; the nanorods in this electrode material are The voids provided buffer space for the volume expansion caused by the intercalation and deintercalation of ions in the electrochemical reaction, so the structural stability of this capacitor is good, and due to the existence of Ni alloy in this electrode material, the cycle stability is excellent. In addition, this supercapacitor electrode material is a tin oxide-based material, so it is non-toxic and harmless to the human body; the obtained tin oxide nanorod array structure has a large yield, and the composition and morphology are controllable. Moreover, the preparation method of the supercapacitor positive electrode material proposed by the present invention has simple raw materials, equipment and process, strong controllability of process and parameters, high product yield, low cost, safe, clean and environmentally friendly production process, Conducive to large-scale production.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to propose a partially alloyed tin oxide nanorod array supercapacitor positive electrode material. This supercapacitor cathode material is composed of a partially Sn-Ni alloyed, oxygen-deficient tin oxide nanorod array structure grown on a foamed nickel substrate. This tin oxide nanorod array structure can be directly used as the working electrode (positive electrode) of supercapacitors. The supercapacitor cathode material prepared by this method has a large specific surface area, sufficient exposure of active sites, and large specific capacitance of the electrode because the active material is grown on the foamed nickel substrate in the form of nanorod array; this electrode material Among them, metal cations are rich in valence state, complex electrochemical reaction, and high capacitance of the material; the substrate (current collector) of this electrode material is a metal with excellent electrical conductivity, and the active material is an oxygen-deficient oxidizer with strong electrical conductivity. Tin and the new Sn-Ni alloy with good electrical conductivity, and they are organically combined by high temperature heat treatment, so this electrode material has good conductivity and is conducive to the rapid transfer of charges; the nanorods in this electrode material are The voids provided buffer space for the volume expansion caused by the intercalation and deintercalation of ions in the electrochemical reaction, so the structural stability of this capacitor is good, and due to the existence of Ni alloy in this electrode material, the cycle stability is excellent. In addition, this supercapacitor electrode material is a tin oxide-based material, so it is non-toxic and harmless to the human body.

The second purpose of the present invention is to provide a corresponding preparation method of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material. The tin oxide nanorod array structure obtained by this method has a large yield and controllable composition and morphology; at the same time, the raw materials, equipment and process used by this method are simple, the process parameters are highly controllable, and the product yield is high. The cost is low, the production process is safe, clean, and environmentally friendly, which is conducive to large-scale production.

In order to achieve the above goals, the partially alloyed tin oxide nanorod array supercapacitor cathode material proposed in the present invention is characterized in that the tin oxide nanorods are vertically, uniformly and closely attached to the current collector foam nickel substrate to form an array The structure is mainly composed of oxygen-deficient tin oxide and contains a small amount of Ni-Sn alloy; the diameter of this nanorod is about 40-120 nm and the length is 0.5-3 μm. This supercapacitor cathode material is rich in metal cation valence, large specific surface area, fully exposed active sites, good conductivity, large electrode specific capacitance, good cycle stability, non-toxic and harmless to the human body, and is an excellent supercapacitor positive electrode material.

The method for preparing the partially alloyed tin oxide nanorod array supercapacitor positive electrode material provided by the invention is characterized in that, the method firstly uses sodium stannate trihydrate and sodium hydroxide as raw materials, and adopts a solvothermal method to foam the current collector. SnO2 nanorod arrays are grown on nickel substrates, and then heat treated at high temperature in a reducing atmosphere in a vacuum tube furnace, and finally a partially Sn-Ni alloyed, oxygen-deficient type grown on a foamed nickel substrate is obtained. The tin oxide nanorod array structure.

The preparation method of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material proposed by the present invention includes the following steps and contents:

(1) Put deionized water in a beaker, dissolve sodium stannate trihydrate and sodium hydroxide in it, and magnetically stir for 30-60min to obtain a colorless clear solution. Then, slowly pour anhydrous ethanol into the beaker, and continue stirring for 30-60 min to obtain a milky white precursor thick and turbid liquid, which is ready for use.

(2) Transfer the precursor solution to a high-pressure stainless steel reactor, and fix the clean nickel foam sheet vertically in the reactor, and completely immerse it in the precursor solution. Then, the reactor was sealed and placed in an oven for heat preservation treatment. After cooling to room temperature naturally, the reactor was opened, and the nickel foam sample was taken out, rinsed with deionized water for 3-5 times, and dried.

(3) The obtained nickel foam sample is placed at the bottom of the alumina crucible, and some pre-oxidized polyacrylonitrile or epoxy resin is surrounded around it, and then the crucible is placed in a vacuum tube furnace and heated under the protection of an inert atmosphere, Finally, it is cooled to room temperature in the furnace and taken out, to obtain the partially alloyed tin oxide nanorod array supercapacitor positive electrode material.

In the above-mentioned preparation method, the consumption ratio of deionized water, sodium stannate trihydrate and sodium hydroxide in the step (1) is (20-60mL):(1-4g):(0.2-1.0g).

In the above preparation method, the volume ratio of absolute ethanol and deionized water in the solvent in the step (1) is 1:1-1:7.

In the above preparation method, in the step (1), when sodium stannate trihydrate and sodium hydroxide are dissolved in water, magnetic stirring is performed until the solution is completely clarified; after adding dehydrated alcohol, under continuous magnetic stirring, to obtain milky white until the thick turbid liquid.

In the above preparation method, the volume of the inner lining of the reaction kettle in the step (2) is 60-150 mL.

In the above preparation method, in the step (2), the filling amount of the reaction solution in the autoclave is 50%-80%.

In the above preparation method, the cleaning method of the nickel foam sheet in the step (2) is: take a piece of nickel foam, place it in acetone and anhydrous ethanol solution in turn, ultrasonically clean for 15-20min respectively, and then dry.

In the above preparation method, the nickel foam sheet is vertically fixed in the reaction kettle in the step (2).

In the above preparation method, in the step (2), the holding temperature of the reaction kettle in the oven is 130-250° C., and the holding time is 3-48 h.

In the above preparation method, in the step (3), the thermal reducing atmosphere is provided by thermal decomposition of one of pre-oxidized polyacrylonitrile or epoxy resin; the state of pre-oxidized polyacrylonitrile or epoxy resin is fiber or powder, and the quality is 0.5-8.0g.

In the above preparation method, in the step (3), the inert atmosphere is provided by high-purity nitrogen or argon, and the purity is above 99.99 vol.%.

In the above preparation method, in the step (3), the heat treatment temperature is 200-700° C., the heat treatment time is 30-240 min, and the heating rate of the tube furnace is 10-25° C./min.

The characteristics of the present invention are:

(1) This supercapacitor cathode material is composed of a partially Sn-Ni alloyed, oxygen-deficient tin oxide nanorod array structure grown on a foamed nickel substrate. Among them, the tin oxide nanorods are vertically, uniformly and closely attached to the current collector foam nickel substrate to form an array structure, and the main component is oxygen-deficient tin oxide, and contains a small amount of Ni-Sn alloy to form a uniform Complex. This kind of complex has rich cation valence and complex electrochemical oxidation-reduction reaction process; this partially alloyed and oxygen-deficient complex and metal current collector are organically combined with each other and have good electrical conductivity; this The nanoscale structure of such nanorods is beneficial to utilize the small size effect of materials to improve the performance of supercapacitors.

(2) In the process of preparing the partially alloyed tin oxide nanorod array supercapacitor positive electrode material, the method first uses sodium stannate trihydrate and sodium hydroxide as raw materials, and adopts the solvothermal method to foam nickel in the current collector. SnO2 nanorod arrays were grown on the substrate, and then subjected to high temperature heat treatment in a reducing atmosphere in a vacuum tube furnace, and finally a partially Sn-Ni alloyed, oxygen-deficient type of nanorods grown on a foamed nickel substrate was obtained. Tin oxide nanorod array structure.

The advantages of the present invention are:

(1) This tin oxide nanorod array structure can be directly used as a positive electrode material for supercapacitors. The supercapacitor cathode material prepared by this method has a large specific surface area, sufficient exposure of active sites, and large specific capacitance of the electrode because the active material is grown on the foamed nickel substrate in the form of nanorod array; this electrode material Among them, the valence state of metal cations is rich, the electrochemical reaction is complex, and the material capacitance is high; the substrate (current collector) of this electrode material is a metal with excellent electrical conductivity, and the active material is an oxygen-deficient oxidizer with strong electrical conductivity. Tin and the newly added Sn-Ni alloy with good electrical conductivity, and they are organically combined by high temperature heat treatment without any binder, so this electrode material has good conductivity and is conducive to the rapid transfer of charges; this electrode The voids between the nanorods in the material provide buffer space for the volume expansion of the electrochemical reaction due to ion intercalation and deintercalation, so the structural stability of this capacitor is good, and due to the existence of Ni alloy in this electrode material, Excellent cycle stability. In addition, this supercapacitor electrode material is a tin oxide-based material, so it is non-toxic and harmless to the human body.

(2) The tin oxide nanorod array structure obtained by this method has a large yield and controllable composition and morphology; at the same time, the raw materials, equipment and process used by the method are simple, the process parameters are highly controllable, and the product yields High rate, low cost, safe, clean and environmentally friendly production process, which is conducive to large-scale production. It is particularly worth pointing out that the raw materials of the technology of the present invention are non-toxic, harmless and easy to obtain; in the thermal reduction process of tin oxide nanorods, the reducing atmosphere generated by the thermal decomposition of pre-oxidized polyacrylonitrile or epoxy resin organic matter is used, Instead of the traditional hydrogen thermal reduction, it is clean, environmentally friendly, and the safety is greatly improved.

Description of drawings

Fig. 1 is the surface scanning electron microscope photograph of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material prepared in Example 3 of the present invention

Fig. 2 is the cross-sectional scanning electron microscope photo of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material prepared in Example 3 of the present invention

Fig. 3 is the X-ray diffraction pattern of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material prepared in Example 3 of the present invention and its analytical results

4 is the cyclic voltammetry curve of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material prepared in Example 3 of the present invention

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the embodiments.

The present invention provides a partially alloyed tin oxide nanorod array supercapacitor positive electrode material, which is characterized in that the tin oxide nanorods are vertically, uniformly and tightly attached to the current collector foam nickel substrate to form an array structure, and its composition The main body is oxygen-deficient tin oxide and contains a small amount of Ni-Sn alloy; this nanorod is about 40-120 nm in diameter and 0.5-3 μm in length. This supercapacitor cathode material is rich in metal cation valence, large specific surface area, fully exposed active sites, good conductivity, large electrode specific capacitance, good cycle stability, non-toxic and harmless to the human body, and is an excellent supercapacitor positive electrode material.

The method for preparing the partially alloyed tin oxide nanorod array supercapacitor positive electrode material provided by the invention is characterized in that, the method firstly uses sodium stannate trihydrate and sodium hydroxide as raw materials, and adopts a solvothermal method to foam the current collector. SnO2 nanorod arrays are grown on nickel substrates, and then heat treated at high temperature in a reducing atmosphere in a vacuum tube furnace, and finally a partially Sn-Ni alloyed, oxygen-deficient type grown on a foamed nickel substrate is obtained. The tin oxide nanorod array structure.

The preparation method of the partially alloyed tin oxide nanorod array supercapacitor positive electrode material proposed by the present invention includes the following steps and contents:

(1) Put 20-60mL of deionized water in a beaker, dissolve 1-4g of sodium stannate trihydrate and 0.2-1.0g of sodium hydroxide in it, and magnetically stir for 30-60min to obtain a colorless clear solution. Then, slowly pour the absolute ethanol into the beaker according to the volume ratio of absolute ethanol:deionized water 1:1-1:7, and continue to stir for 30-60min to obtain a milky white precursor thick and turbid liquid, for use.

(2) Transfer the precursor solution to a high-pressure stainless steel reactor, and fix the clean nickel foam sheet vertically in the reactor, and completely immerse it in the precursor solution. Then, the reactor was sealed and placed in an oven for heat preservation treatment. After cooling to room temperature naturally, the reactor was opened, and the nickel foam sample was taken out, rinsed with deionized water for 3-5 times, and dried.

(3) Place the obtained nickel foam sample at the bottom of an alumina crucible, and surround it with 0.5-8.0 g of pre-oxidized polyacrylonitrile or epoxy resin, and then place the crucible in a vacuum tube furnace, at a concentration of more than 99.99 vol.% Heat treatment is carried out under the protection of high-purity nitrogen or argon inert atmosphere, and finally cooled to room temperature with the furnace to take out, that is, the partially alloyed tin oxide nanorod array supercapacitor positive electrode material is obtained.

(4) In the above step (2), the volume of the inner lining of the reaction kettle is 60-150 mL, and the filling amount of the reaction solution in the autoclave is 50%-80%.

(5) The cleaning method of the nickel foam sheet in the above step (2) is as follows: take a piece of nickel foam, place it in acetone and anhydrous ethanol solution in turn, ultrasonically clean for 15-20min respectively, and then dry.

(6) In the above (2), the holding temperature of the reaction kettle in the oven is 130-250° C., and the holding time is 3-48 h.

(7) In the above step (3), the heat treatment temperature is 200-700°C, the heat treatment time is 30-240min, and the heating rate of the tube furnace is 10-25°C/min.

The resulting partially alloyed tin oxide nanorod array supercapacitor cathode material is white to gray solid in appearance. Under the scanning electron microscope, many nanorods can be observed, with a diameter of about 40-120nm and a length of 0.5-3μm; from the surface, the nanorods have a highly ordered structure; from the cross section, the highly ordered nanorods are evenly vertical Directly grown on nickel foam substrates. X-ray diffraction analysis shows that this material is mainly composed of oxygen-deficient tin oxide and contains a small amount of Ni-Sn alloy. Cyclic-voltammetry tests showed that the samples had obvious redox peaks, indicating that the samples had excellent electrochemical performance.

In conclusion, high-performance partially alloyed tin oxide nanorod array supercapacitor cathode materials can be prepared by this technique.

Example: 40 mL of deionized water was placed in a beaker, 2 g of sodium stannate trihydrate and 0.44 g of sodium hydroxide were dissolved in it, and a colorless clear solution was obtained after magnetic stirring for 30 min. Then, 40 mL of anhydrous ethanol was slowly poured into the beaker, and the stirring was continued for 30 min to obtain a thick turbid liquid of the milky white precursor. Then, the obtained precursor solution was transferred to a 100 mL high-pressure stainless steel reactor, and a clean nickel foam sheet with a size of 1 cm × 1.5 cm was vertically fixed in the reactor and completely immersed in the precursor solution. Then, the reaction kettle was sealed and placed in an oven at 190° C. for 24 hours. After naturally cooling to room temperature, the reactor was opened, and the nickel foam sample was taken out, rinsed with deionized water for 5 times, and dried in an oven at 100 °C for 10 h. Then, the obtained nickel foam sample was placed at the bottom of an alumina crucible, and 4.0 g of pre-oxidized polyacrylonitrile fibers were surrounded around it, and then the crucible was placed in a vacuum tube furnace, inert in a high-purity argon gas above 99.99 vol.% Under the protection of atmosphere, the temperature is kept at 200-700° C. for 30-240 min, and finally cooled to room temperature with the furnace to be taken out to obtain the partially alloyed tin oxide nanorod array supercapacitor positive electrode material.

The typical surface SEM photo of the obtained sample is shown in Figure 1, and the cross-sectional SEM photo is shown in Figure 2, from which a highly ordered nanorod array structure can be observed; this material is mainly composed of oxygen-deficient tin oxide and contains a small amount of Ni -Sn alloy (see Figure 3); when this sample is directly used as a supercapacitor positive electrode, its cyclic voltammetry curve exhibits a strong redox peak (see Figure 4), indicating that the sample has excellent capacitive performance (see Table 1 ). Different from the traditional electrode material, the electrode material obtained in the present invention exhibits super-strong electrochemical cycle performance, and its specific capacity can be continuously enhanced with the increase of cycle times, reaching more than ten times the initial capacity.

Table 1

Claims (3)

1. a preparation method of a partially alloyed tin oxide nanorod array supercapacitor positive electrode material, is characterized in that, described tin oxide nanorod is vertically, evenly, closely attached on the current collector foam nickel substrate to form an array structure, Its main composition is oxygen-deficient tin oxide, and contains a small amount of Ni-Sn alloy; the diameter of this nanorod is 40-120 nm and the length is 0.5-3 μm; the preparation method firstly uses sodium stannate trihydrate and sodium hydroxide as As raw materials, tin dioxide nanorod arrays were grown on the current collector foam nickel substrate by solvothermal method, and then subjected to high-temperature heat treatment in a reducing atmosphere in a vacuum tube furnace, and finally a partially grown on the foam nickel substrate was obtained. Sn-Ni alloyed, oxygen-deficient tin oxide nanorod array structure; including the following steps: (1) Fill deionized water in a beaker, dissolve sodium stannate trihydrate and sodium hydroxide therein, and obtain a colorless clear solution after magnetic stirring for 30-60min; then, slowly pour dehydrated alcohol into the beaker In the process, continue stirring for 30-60min to obtain a milky white precursor thick turbid liquid, which is for later use; (2) Transfer the precursor solution to the high-pressure stainless steel reactor, and vertically fix the clean nickel foam sheet in the reactor, and completely immerse it in the precursor solution; then, seal the reactor and place it in an oven Carry out thermal insulation treatment inside; after natural cooling to room temperature, open the reactor, take out the nickel foam sample, rinse with deionized water 3-5 times, and dry; (3) Place the obtained nickel foam sample at the bottom of the alumina crucible, and surround it with epoxy resin or pre-oxidized polyacrylonitrile, then place the crucible in a vacuum tube furnace, heat treatment under the protection of an inert atmosphere, and finally After being cooled to room temperature, the partially alloyed tin oxide nanorod array supercapacitor positive electrode material is obtained. 2. according to the described preparation method of claim 1, it is characterized in that, in described step (1), the consumption ratio of deionized water, sodium stannate trihydrate and sodium hydroxide is (20-60mL): (1-4g ): (0.2-1.0g), the volume ratio of absolute ethanol and deionized water in the solvent is 1:1-1:7; In the step (2), the reaction solution filling amount in the autoclave is 50%-80% %; in the step (2), the holding temperature of the reaction kettle in the oven is 130-250° C., and the holding time is 3-48 h. 3. The preparation method according to claim 1, characterized in that, in the step (3), the thermal reducing atmosphere is provided by thermal decomposition of one of epoxy resin or pre-oxidized polyacrylonitrile; epoxy resin or pre-oxidized polypropylene The state of nitrile is fiber or powder, and the mass is 0.5-8.0g; the inert atmosphere is provided by high-purity nitrogen or argon, and the purity is above 99.99vol.%; the heat treatment temperature is 200-700 ℃, and the heat treatment time is 30-240min. The heating rate of the furnace is 10-25°C/min.

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