CN109243850B - Ni-Co oxide nanocrystals and their controllable synthesis methods and applications - Google Patents

Abstract

The invention relates to the field of material chemistry, in particular to a Ni-Co oxide nanocrystal and a controllable synthesis method and application thereof. The Ni-Co oxide nanocrystal is a solid nano-spherical structure. The invention can controllably synthesize Ni-Co oxide nanocrystals with solid spherical structure by changing synthesis conditions and processes such as the amount of solvent and calcination temperature. The preparation process is simple, the process controllability is strong, the synthesis time is short, and the invention has a good industrial application prospect. At the same time, the Ni-Co oxide nanocrystals prepared by the present invention have excellent solid-state asymmetric flexible supercapacitor performance, are bendable, can be rapidly charged and discharged, have efficient electrical energy storage performance, and are important for the development of renewable energy technologies. Guiding significance.

Description

Ni-Co oxide nanocrystals and their controllable synthesis methods and applications

technical field

The invention relates to the field of material chemistry, in particular to the field of synthesis and application of nanocrystals, and more particularly to Ni-Co oxide nanocrystals and a controllable synthesis method and application thereof.

Background technique

Ni-Co oxide refers to a composite oxide having the chemical formula of NiCo ₂ O ₄ . Due to the excellent electrical conductivity and electrochemical activity of the composite compound, the research on Ni-Co oxide has been a hot topic in the field of material chemistry, especially in the field of supercapacitor research in recent years.

For example, NiCo ₂ O ₄ black nano-powders including the spinel structure disclosed by Chu have been disclosed in the prior art. _NiCo2O4 gels disclosed by _TYWei et al _{. NiCo2O4} nanowires disclosed by HL Wang et al. And the NiCo ₂ O ₄ nanoneedles disclosed by GQ Zhang et al.

Different _NiCo2O4 structures can provide different electrical properties, that is, the electrical properties of nanocrystals have a great dependence _on nanocrystal structure and size. Therefore, controlling the formation of nanocrystal structures through meticulous and controllable synthetic methods is an important means and method to obtain nanocrystals with different electrical and other properties. In other words, different nanocrystalline structures can exhibit different electrical properties. Therefore, for a new electrical application, it is necessary to search for nanocrystalline structures that can satisfy them, and to obtain the controllable formula of the nanocrystalline structures. The method of synthesis is critical.

With the popularization of portable electronic devices and the vigorous development of electric vehicles, people have higher and higher performance requirements for energy storage materials, but the development of energy storage materials is lagging behind. On the one hand, the energy density of energy storage materials is not enough, which leads to the short use time of electrical appliances and frequent charging, which brings serious inconvenience to daily use and greatly limits the use of electric vehicles. On the other hand, the power of the energy storage material is insufficient, resulting in an excessively long charging time of the energy storage material.

In recent years, with the rise of wearable portable electronic devices, the problems of insufficient energy density and insufficient power of energy storage materials have become more prominent. At the same time, due to the proposal of "wearable", new requirements are put forward for energy storage devices, that is, energy storage devices should be flexible.

Literature studies have shown that transition metals are widely used in energy storage materials due to their good reversibility and fast reaction speed during oxidation and reduction. For example, Yating et al. found that the mixture of Fe ₂ O ₃ nanoclusters and rGO has better properties as the anode of flexible supercapacitors, and has larger energy density and power density. It can be shown that the graphene composite material has better current activity, which is mainly related to the fact that graphene as a skeleton structure becomes a good carrier and graphene has excellent electrical conductivity.

Therefore, energy storage materials made of transition metals have the potential to prepare flexible supercapacitors. Therefore, the development of efficient synthesis methods of transition metal nanocrystals with special structures is a hot research topic, especially the electrode materials that can be used in all-solid-state asymmetric flexible supercapacitors are of great significance and great challenges.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to disclose an electrode material that can be used for an all-solid-state asymmetric flexible supercapacitor, so as to meet the requirements of wearable portable electronic devices for energy storage devices and provide a basis for the development of wearable portable electronic devices.

In order to solve the above technical problems, the present invention discloses Ni-Co oxide nanocrystals, and the Ni-Co oxide nanocrystals have a solid nano-spherical structure.

Further, the present invention also discloses that the Ni-Co oxide nanocrystal is a solid nano-spherical structure with a diameter of 3-5nm.

Meanwhile, the present invention also discloses a controllable synthesis method of the Ni-Co oxide nanocrystals, which comprises the following steps:

S1: Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, were added to a mixed solution of oleic acid (OA), dodecylamine and octadecene (ODE) ;

S2: Gradually increase the temperature to 180°C;

S3: keep the temperature at 180 °C to react to obtain a precursor containing Ni-Co oxide nanocrystals;

S4: dispersion sedimentation, centrifugation;

S5: Gradually increase the temperature to 350°C;

S6: calcining under the condition of keeping the temperature at 350° C. to obtain Ni-Co oxide nanocrystals.

Meanwhile, the present invention further discloses Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, oleic acid (OA), dodecylamine and octadecene (ODE) The addition ratio of Ni(CH ₃ COO) ₂ ·4H ₂ O is 3.62 mmol, the addition amount of Co(CH ₃ COO) ₂ ·4H ₂ O is 1.81 mmol, the addition amount of ODE is 10 mL, dodecylamine The addition amount of OA is 5mL, and the addition amount of OA is 5mL.

Preferably, in the step S2, the heating rate is 3-4°C·min ^-1 .

Further preferably, in step S3, the reaction is carried out under the condition that the temperature is kept at 180° C. for 18 hours.

In a preferred technical solution, anhydrous ethanol-n-heptane mixed solution is used for dispersion and sedimentation in step S4. Further preferably, the mixing volume ratio of the absolute ethanol and n-heptane is 1:1.

A further preferred technical solution is that the step S4 also includes washing after dispersion sedimentation and centrifugation.

In a preferred technical solution, the washing adopts anhydrous ethanol-n-heptane mixed solution. Further preferably, the mixing volume ratio of the absolute ethanol-n-heptane is 1:1.

As another preferred technical solution, in the step S5, the heating rate is 10°C·min ^-1 .

And as a preferred technical solution, in step S6, the temperature is kept at 350° C. for 1 hour.

Finally, the present invention also discloses the application of the Ni-Co oxide nanocrystals in solid-state asymmetric flexible supercapacitor electrode materials.

The Ni-Co oxide nanocrystal prepared by the invention has excellent solid-state asymmetric flexible supercapacitor performance, is bendable, can be rapidly charged and discharged, and has high-efficiency electrical energy storage performance. After testing, its performance is better than that of the current commercially available asymmetric flexible supercapacitor, which has important guiding significance for the development of renewable energy technology.

At the same time, in the present invention, a controllable synthesis method is used to controllably synthesize Ni-Co oxide nanocrystals with a solid spherical structure by changing synthesis conditions and processes such as the amount of solvent and calcination temperature. The preparation process is simple, the process controllability is strong, the synthesis time is short, conforms to the standard of industrial production, and has a good industrial application prospect.

Description of drawings

Fig. 1 is the TEM image of the Ni-Co oxide nanocrystal synthesized by the present invention.

FIG. 2 is a cyclic voltammetry (CV) diagram of Ni-Co oxide nanocrystals synthesized in the present invention.

FIG. 3 is a graph of constant current charge-discharge (GCD) of Ni-Co oxide nanocrystals synthesized in the present invention.

FIG. 4 is a cyclic voltammogram of the Ni-Co oxide nanocrystals synthesized in the present invention when they are not bent; the photo therein is a schematic diagram of the unbent detection state.

FIG. 5 is a cyclic voltammogram of the Ni-Co oxide nanocrystals synthesized in the present invention after bending; the photo therein is a schematic diagram of the bending detection state.

Detailed ways

For a better understanding of the present invention, the present invention will be further described below with reference to specific embodiments.

Example 1

At room temperature (25±5℃), weigh 0.9008g of Ni(CH ₃ COO) ₂ ·4H ₂ O and 0.4509g of Co(CH ₃ COO) ₂ ·4H ₂ O and pour it into 10 mL of octadecene (ODE), 5mL of dodecylamine and 5mL of oleic acid (OA) in the PTFE liner, magnetically stirred for 15min, placed in a stainless steel reaction kettle, and the lid of the kettle was tightened. Put it in an oven, adjust the temperature to 180°C, and the heating rate to be 3-4°C·min ^-1 . When the temperature reaches 180°C, the reaction is continued for 18 hours. After the reaction was completed, the temperature was lowered to room temperature, the reactor was opened, an appropriate amount of absolute ethanol-n-heptane (volume ratio 1:1) was added to disperse, and the solid was centrifuged. The solid was washed with n-heptane-absolute ethanol (volume ratio 1:1) and put into a muffle furnace after being vacuum-dried in a vacuum drying oven overnight, and the adjustment temperature was 350 °C, and the heating rate was 10 °C min ^{- 1.} When the temperature reaches 350°C, continue calcining for 1 hour to obtain Ni-Co oxide nanocrystals.

Example 2

The Ni-Co oxide nanocrystal product obtained in Example 1 is tested by transmission electron microscope (TEM), and the result is shown in Figure 1. It can be seen from Figure 1 that the Ni-Co oxide nanocrystal is a solid spherical nanocrystal. crystal structure, and the diameter of the Ni-Co oxide nanocrystals is 3-5 nm.

Example 3

In the two-electrode system, the electrochemical properties of the Ni-Co oxide nanocrystal sample (hereinafter referred to as the sample) obtained in Example 1 were tested by cyclic voltammetry and constant current charge-discharge method. The specific process is as follows:

The electrochemical experiments were carried out on a CHI660d electrochemical workstation, using a two-electrode test system, and the corresponding positive electrode was the nickel foam electrode modified by the sample obtained in this paper. The negative electrode is an activated carbon modified nickel foam electrode. All potentials herein are relative to RHE. The electrolyte is 3M KOH solution. All electrochemical tests were performed at 25°C. For each experiment, all electrodes were tested in 3M KOH solution.

The preparation method of sample modified nickel foam is as follows:

Before each test, the nickel foam was cut into a size of 1cm × 5cm, ultrasonically cleaned with deionized water for 15 minutes, then ultrasonically cleaned with ethanol for 15 minutes, and dried at 50 °C for 2 hours before use.

Take 40 mg of Ni-Co oxide nanocrystals and 7.5 mg of acetylene black, and grind them with a mortar for 15 min. Then an appropriate amount of isopropanol was added, and the grinding was continued for 15 min. Finally, add 1-2 drops of polytetrafluoroethylene (PTFE) emulsion, and after a little stirring, drop it on the surface of the nickel foam to be used before. After drying at 50°C for 2h, wait for the electrochemical test.

Take 40 mg of activated carbon and 7.5 mg of acetylene black, and grind with a mortar for 15 minutes. Then an appropriate amount of isopropanol was added, and the grinding was continued for 15 min. Finally, 1-2 drops of polytetrafluoroethylene (PTFE) emulsion are added, and after a little stirring, they are dropped on the surface of the nickel foam to be used before. After drying at 50°C for 2h, wait for the electrochemical test.

Cyclic voltammetry and constant current charge-discharge tests were performed on the modified nickel foam in the above two-electrode system. See Figure 2 and Figure 3 for the test results. The test results show that the Ni-Co oxide nanocrystals exhibit excellent supercapacitor performance. According to the calculation in Figure 3, the current densities of Ni-Co oxide nanocrystals are 5 mA cm ^-2 , 10 mA cm ^-2 , 15 mA cm ^- , respectively. ² , 20mA cm ^-2 and 25mA cm ^-2 , the specific capacitances were 330.8mF cm ^-2 , 300.6mF cm ^-2 , 278.5mF cm ^-2 , 251.3mF cm ^-2 and 212.0mF cm ^-2 , respectively.

Example 4

The flexible properties of Ni-Co oxide nanocrystalline devices (hereinafter referred to as devices) were tested by assembling all-solid-state flexible asymmetric capacitor devices and comparing the cyclic voltammograms before and after bending. The specific process is as follows:

The electrochemical experiments were carried out on a CHI660d electrochemical workstation, using a two-electrode test system, and the corresponding positive electrode was the nickel foam electrode modified by the sample obtained in this paper. The negative electrode is an activated carbon modified nickel foam electrode. All potentials herein are relative to RHE. The electrolyte is 3M KOH solution. All electrochemical tests were performed at 25°C. For each experiment, all electrodes were tested in 3M KOH solution.

The preparation method of sample modified nickel foam is as follows:

Before each test, the nickel foam was cut into a size of 1 cm × 5 cm, ultrasonically cleaned with deionized water for 15 min, then ultrasonically cleaned with ethanol for 15 min, and dried at 50 °C for 2 h before use.

Take 40 mg of Ni-Co oxide nanocrystals and 7.5 mg of acetylene black, and grind them with a mortar for 15 min. Then an appropriate amount of isopropanol was added, and the grinding was continued for 15 min. Finally, add 1-2 drops of polytetrafluoroethylene (PTFE) emulsion, and after a little stirring, drop it on the surface of the nickel foam to be used before. After drying at 50 °C for 2 h, wait for the assembly of the all-solid-state flexible asymmetric capacitor.

Take 40 mg of activated carbon and 7.5 mg of acetylene black, and grind with a mortar for 15 minutes. Then an appropriate amount of isopropanol was added, and the grinding was continued for 15 min. Finally, add 1-2 drops of polytetrafluoroethylene (PTFE) emulsion, and after a little stirring, drop it on the surface of the nickel foam to be used before. After drying at 50 °C for 2 h, wait for the assembly of the all-solid-state flexible asymmetric capacitor.

The assembly method of the all-solid-state flexible asymmetric capacitor device is as follows:

Take two 1cm×4cm polyvinyl chloride (PVC) sheets, slowly drop 3-5 drops of a mixture of 3M KOH and polyethylene glycol on one of them, and spread the entire PVC sheet. Then, place the modified nickel foam of the sample and the modified activated carbon foam on both ends of the PVC sheet, overlapping about 1 cm, to ensure that the foamed nickel is immersed in the mixture of 3M KOH and polyethylene glycol. Then carefully cover another piece of PVC sheet to make it completely overlapped, and then wrap the entire device with plastic wrap to prevent liquid leakage. After drying at 50°C for 12h, wait for the electrochemical test.

The all-solid flexible asymmetric capacitor device was tested by cyclic voltammetry in the above two-electrode system, and then it was bent for cyclic voltammetry test. The test results are shown in Figures 4 and 5. The test results show that there is no obvious difference between the cyclic voltammogram (Figure 4) before bending and the cyclic voltammogram (Figure 5) after bending, indicating that the capacitance performance of the device does not change significantly before and after bending, and the flexibility performance is good. .

The above are specific embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims (12)

1. A controllable synthesis method of Ni-Co oxide nanocrystals is characterized in that the Ni-Co oxide nanocrystals are solid nanosphere-shaped structures with the diameter of 3-5nm, and the controllable synthesis method specifically comprises the following steps:

   s1: mixing Ni (CH)₃COO)₂∙4H₂O、Co(CH₃COO)₂∙4H₂Adding O into a mixed solution of Oleic Acid (OA), dodecylamine and Octadecene (ODE);

   s2: gradually heating to 180 ℃;

   s3: keeping the temperature at 180 ℃ for reaction to obtain a precursor containing Ni-Co oxide nanocrystals;

   s4: dispersing, settling and centrifuging;

   s5: gradually heating to 350 ℃;

   s6: and calcining at 350 ℃ to obtain the Ni-Co oxide nanocrystal.
2. 2. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: ni (CH)₃COO)₂∙4H₂O、Co(CH₃COO)₂∙4H₂O, Oleic Acid (OA), dodecylamine and Octadecene (ODE) are added in the ratio of Ni (CH)₃COO)₂∙4H₂When O is 3.62mmol, Co (CH)₃COO)₂∙4H₂The amount of O added was 1.81mmol, the amount of ODE added was 10mL, the amount of dodecylamine added was 5mL, and the amount of OA added was 5 mL.
3. 3. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: in the step S2, the heating rate is 3-4 ℃ min^-1。
4. 4. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: in step S4, an absolute ethanol-n-heptane mixed solution is used for dispersion and sedimentation.
5. 5. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 4, wherein: the mixing volume ratio of the absolute ethyl alcohol to the n-heptane is 1: 1.
6. 6. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: step S4 includes washing after dispersion sedimentation and centrifugation.
7. 7. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 6, wherein: the washing adopts an absolute ethyl alcohol-n-heptane mixed solution.
8. 8. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 7, wherein: the volume ratio of the absolute ethyl alcohol to the n-heptane is 1: 1.
9. 9. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: in the step S5, the temperature rise rate is 10 ℃ min^-1。
10. 10. The controllable synthesis method of Ni-Co oxide nanocrystals according to claim 1, wherein: the reaction time in step S6 was 1 hour.
11. 11. The Ni-Co oxide nanocrystal prepared by the controlled synthesis method of the Ni-Co oxide nanocrystal according to any one of claims 1 to 10, characterized in that: the Ni-Co oxide nanocrystal is a solid nanosphere structure with the diameter of 3-5 nm.
12. 12. Use of the Ni-Co oxide nanocrystals according to claim 11 in solid-state asymmetric flexible supercapacitor electrode materials.

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