CN111261428A - A kind of method for ammonia plasma to enhance the performance of cobalt-nickel sulfide supercapacitor - Google Patents

Abstract

The invention discloses a method for enhancing the performance of a cobalt-nickel sulfide supercapacitor by ammonia gas plasma, that is, a plasma chemical vapor deposition (PECVD) system is used, ammonia gas is used as a plasma gas source, and the cobalt-nickel sulfide supercapacitor is processed under certain conditions. deal with. The electrochemical properties of the samples were evaluated in 1 M KOH electrolyte, and it was found that after PECVD treatment, the maximum capacity of cobalt-nickel sulfide could reach 3.32 F/cm ² , which was about 3 times that of the samples before PECVD treatment, and the cycle stability was improved by 14.2%. %, indicating that the PECVD method can significantly improve the supercapacitor performance of cobalt-nickel sulfide.

Description

A kind of method for ammonia plasma to enhance the performance of cobalt-nickel sulfide supercapacitor

technical field

The present invention relates to the field of supercapacitors, in particular to a method for enhancing the electrical properties of cobalt-nickel sulfide supercapacitors by ammonia gas plasma.

Background technique

Supercapacitors are an upgrade to traditional capacitors. Its energy density is greater than that of traditional capacitors, power density is greater than that of batteries, and it has long cycle life, safety and environmental protection, and a wide range of applicable temperatures. It is a very promising new type of energy storage device.

The main disadvantage of supercapacitors is their lower energy density than lithium-ion batteries, which hinders their large-scale commercial application. Traditional commercial supercapacitors generally use carbon materials as electrode materials. Such electrode materials store charges by forming an electric double layer between them and the electrolyte, which is a physical process and has a low specific capacitance. Pseudocapacitive electrode materials store charge through a highly reversible redox reaction between the active material and the electrolyte. Under the condition of the same effective area, the pseudocapacitance is about 10-100 times the capacitance of the electric double layer, so it has greater energy density.

Cobalt-nickel sulfide is a promising pseudocapacitive electrode material due to its high theoretical capacity, diverse redox couples, easy preparation, and low cost. However, the low conductivity and hindered electron and ion transport not only lead to low electrochemical reactivity and reduce their actual capacity, but also affect their rate performance and cycling stability. Combining with highly conductive carbon materials to construct external conductive channels is the main measure to optimize the conductivity of materials. When compounding with a three-dimensional conductive carbon network, in order to ensure full contact between the active material and the carbon material, the loading of the active material is usually low, which is not conducive to the energy density of the device; when the surface of the active material is coated with a carbon layer, the cycling process The volume effect easily destroys the carbon coating layer, causing the loss of electrical contact between the active material and the carbon material, affecting its cycle stability; at the same time, the introduction of the carbon material will also reduce the effective mass of the active material, thereby reducing the energy density of the device. .

SUMMARY OF THE INVENTION

The purpose of the present invention is to address the above problems, starting from the internal electronic structure of cobalt nickel sulfide, through ammonia plasma treatment, using plasma chemical vapor deposition method to process cobalt nickel sulfide, regulating the surface structure of cobalt nickel sulfide, that is, manufacturing surface S vacancies, while introducing nitrogen doping, optimizes conductivity and ion transport properties, thereby improving its capacity, rate performance and cycle stability. The specific capacitance of the treated electrode is about 3 times that of the untreated electrode, and the cycle stability is improved by at least 14.2%.

The technical scheme of the present invention comprises the following steps:

(1) cleaning of nickel foam base: the nickel foam is ultrasonically cleaned and dried with tap water, acetone, dilute hydrochloric acid, distilled water successively;

(2) Preparation of cobalt-nickel precursor: dissolve a certain amount of cobalt nitrate, nickel nitrate and urea in deionized water, stir until fully dissolved, pour into the reactor, put in foam nickel, seal, and hydrothermally react for a period of time Rinse with deionized water and absolute ethanol in turn and dry naturally to obtain cobalt-nickel precursor;

(3) prepare cobalt-nickel sulfide: add sodium sulfide solution to cobalt-nickel precursor, seal, rinse with deionized water and absolute ethanol successively after hydrothermal reaction for a period of time and naturally dry to obtain cobalt-nickel sulfide;

(4) In the cavity of the prepared cobalt-nickel sulfide plasma chemical vapor deposition system, the pressure and temperature in the cavity are adjusted, and ammonia gas plasma is applied, and the cobalt-nickel sulfide supercapacitor can be prepared by vapor deposition.

The molar ratio range of the cobalt nitrate, nickel nitrate and urea is 1:1-2:3.5-6, and the urea can also be replaced with ammonium fluoride.

The hydrothermal reaction temperature in step (2) is 100-140° C., and the hydrothermal reaction time is 5-10 h.

The concentration of the sodium sulfide solution is 0.05-0.3 mol/L, and the cobalt-nickel precursor is a thin film sample, which is directly put into the sodium sulfide solution.

The hydrothermal reaction temperature in step (3) is 100-140° C., and the hydrothermal reaction time is 5-10 h.

In step (3), the pressure in the chamber of the plasma chemical vapor deposition system is adjusted to 10 ^-4 -10 ^-3 Pa, and the temperature in the chamber is adjusted to 150-350°C. The flow rate of ammonia gas is 10-30sccm, the time is 5-30min, the temperature is 150-350°C, the sputtering power is 100-400W, and the sputtering pressure is 40-80Pa.

Compared with the cobalt-nickel sulfide without any treatment, the cobalt-nickel sulfide prepared by the preparation method of the present invention has significantly improved capacity and cycle stability. More sulfur vacancies and doping with more nitrogen elements make it more conductive, and ultimately significantly improve the electrochemical reactivity, rate capability, and cycling stability.

Description of drawings

1 is a graph showing the charge and discharge curves of the cobalt-nickel sulfide electrodes before and after PECVD treatment in Examples 1 and 2.

FIG. 2 shows the specific capacitance curves of the cobalt-nickel sulfide electrodes before and after PECVD treatment in Examples 1 and 2 at different current densities.

3 is a graph showing the cycle stability performance of the cobalt-nickel sulfide electrode before and after PECVD treatment in Examples 1 and 2 (the current density is 20 mA/cm ² ).

4 is the EIS curve of the cobalt-nickel sulfide electrode before and after PECVD treatment in Examples 1 and 2.

5 shows the charge-discharge curves of the cobalt-nickel sulfide electrodes before and after PECVD treatment in Examples 3 and 4.

6 shows the specific capacitance curves of the cobalt-nickel sulfide electrodes before and after PECVD treatment in Examples 3 and 4 at different current densities.

7 is the EIS curve of the cobalt-nickel sulfide electrode before and after PECVD treatment in Examples 3 and 4.

Detailed ways:

In order to further understand the content and characteristics of the present invention, several embodiments of the present invention are given below. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

The experimental methods in the following examples are conventional methods unless otherwise specified.

Example 1

(1) Cleaning of the foamed nickel substrate: The foamed nickel was ultrasonically cleaned with tap water, acetone, dilute hydrochloric acid, and distilled water in turn and dried.

(2) Preparation of cobalt-nickel precursor: Weigh 2mmol of nickel chloride, 4mmol of cobalt nitrate and 12mmol of urea, dissolve in 35mL of deionized water, magnetically stir until completely dissolved, and transfer the solution to a polytetrafluoroethylene lining. Put the nickel foam into the inner lining, cover the inner lining and the stainless steel jacket, put it into an oven, and react at 120 °C for 7 h. After the reaction was completed, after being naturally cooled to room temperature, the nickel foam was taken out, rinsed with deionized water and absolute ethanol in sequence, and dried at 60°C.

(3) preparation of cobalt-nickel sulfide: the sodium sulfide solution with a concentration of 0.2 mol/L is configured, poured into the inner lining of the reactor, the sample obtained in step (2) is put into the reactor, and heated at 120 ° C after sealing 6h, rinsed with deionized water and absolute ethanol in turn and air-dried naturally.

电流密度为6mA/cm²时，其最大比电容为3.23F/cm²，即使电流密度增加至50mA/cm²，比电容仍然高达2.38F/cm²(附图2)；相比之下，PECVD处理前的电极在电流密度为10mA/cm²时，其比电容仅为1.3F/cm²，当电流密度为50mA/cm²时，容量降为0.83F/cm²。附图3为PECVD处理前后，硫化钴镍电极在电流密度为20mA/cm²的条件下得到的循环稳定性，可见，经PECVD处理后，电极的循环稳定性提升了14.2％。附图4为电化学阻抗图(EIS)对比，插图为EIS放大图和等效电路图，通过分析可知，PECVD处理后电极的内阻(Rs)从1.41降至1.38Ω，离子扩散电阻也明显降低(即EIS曲线直线斜率明显变大)。(4) PECVD treatment: put the sample obtained in step (3) into the cavity of the PECVD system and fix it on the sample stage. When the vacuum degree of the PECVD system is reduced to 10 ^-4 Pa and the temperature is raised to 250°C, ammonia gas is applied Plasma, the ammonia flow rate is 15sccm, the ventilation duration is 15min, the pressure is 60Pa, and the power is 250W. (5) This electrode is used as the working electrode, the platinum electrode is used as the counter electrode, and the mercury oxide electrode is used as the reference electrode to form a three-electrode test system. 1M KOH is used as the electrolyte, and the CHI760E electrochemical test system is used. The electrochemical test results show that the charge and discharge time of the electrode after PECVD treatment is significantly longer than that of the sample before treatment (Fig. 1). According to the capacity calculation formula:

When the current density is 6mA/cm ² , the maximum specific capacitance is 3.23F/cm ² . Even if the current density is increased to 50mA/cm ² , the specific capacitance is still as high as 2.38F/cm ² (Fig. 2); in contrast, The specific capacitance of the electrode before PECVD treatment was only 1.3F/cm ² when the current density was 10mA/cm ² , and the capacity decreased to 0.83F/cm ² when the current density was 50mA/cm ² . Figure 3 shows the cycle stability of the cobalt-nickel sulfide electrode before and after PECVD treatment under the condition of a current density of 20 mA/cm ² . It can be seen that after PECVD treatment, the cycle stability of the electrode is improved by 14.2%. Figure 4 is a comparison of the electrochemical impedance diagram (EIS), and the inset is the enlarged EIS diagram and the equivalent circuit diagram. It can be seen from the analysis that the internal resistance (Rs) of the electrode after PECVD treatment decreased from 1.41 to 1.38Ω, and the ion diffusion resistance was also significantly reduced. (that is, the slope of the straight line of the EIS curve becomes significantly larger).

Example 2

Compared with Example 1, the rest is the same as Example 1 except that PECVD is not performed. The test results are shown in Figure 1-4.

Example 3

(1) Cleaning of the foamed nickel substrate: The foamed nickel was ultrasonically cleaned with tap water, acetone, dilute hydrochloric acid, and distilled water in turn and dried.

(2) Preparation of cobalt-nickel precursor: Weigh 1 mmol of nickel nitrate, 1 mmol of cobalt nitrate and 3.5 mmol of ammonium fluoride, dissolve in 35 mL of deionized water, stir magnetically until completely dissolved, and transfer the solution to a polytetrafluoroethylene lining . Put the nickel foam into the inner lining, cover the inner lining and stainless steel jacket, put it into an oven, and react at 120 °C for 8 h. After the reaction was completed, after being naturally cooled to room temperature, the nickel foam was taken out, rinsed with deionized water and absolute ethanol in sequence, and dried at 60°C.

(3) preparation of cobalt-nickel sulfide: configure sodium sulfide solution with a concentration of 0.1 mol/L, pour it into the inner lining of the reactor, put the sample obtained in step (2) into the reactor, and heat it at 120 ° C after sealing 6h, rinsed with deionized water and absolute ethanol in turn and air-dried naturally.

(4) PECVD treatment: put the sample obtained in step (3) into the cavity of the PECVD system and fix it on the sample stage. When the vacuum degree of the PECVD system is reduced to 10 ^-4 Pa and the temperature is raised to 300°C, ammonia gas is applied Plasma, the ammonia flow is 15sccm, the ventilation duration is 10min, the pressure is 60Pa, and the power is 250W.

电流密度为5mA/cm²时，其最大比电容为1.23F/cm²，电流密度增加至50mA/cm²，比电容仍然高达1F/cm²(附图6)；相比之下，PECVD处理前的电极在电流密度为5mA/cm²时，虽然电容为1.13F/cm²，但当电流密度为30mA/cm²时，容量降为0.75F/cm²，说明倍率性能明显比处理后的样品差。附图7为电化学阻抗图(EIS)对比，插图为EIS放大图和等效电路图，通过分析可知，PECVD处理后电极的内阻(Rs)从2.46降至1.96Ω，离子扩散电阻也明显降低(即EIS曲线直线斜率明显变大)。(5) This electrode is used as the working electrode, the platinum electrode is used as the counter electrode, and the mercury oxide electrode is used as the reference electrode to form a three-electrode test system. 1M KOH is used as the electrolyte, and the CHI760E electrochemical test system is used. The electrochemical test results show that the discharge time of the electrode after PECVD treatment is significantly longer than that of the sample before treatment (Fig. 5), indicating that the capacity of the electrode is significantly improved. According to the calculation formula of capacity:

When the current density was 5mA/cm ² , the maximum specific capacitance was 1.23F/cm ² , and the current density increased to 50mA/cm ² , and the specific capacitance was still as high as 1F/cm ² (Fig. 6); in contrast, PECVD treatment When the current density of the former electrode is 5mA/cm ² , although the capacitance is 1.13F/cm ² , when the current density is 30mA/cm ² , the capacity drops to 0.75F/cm ² , which shows that the rate performance is significantly better than that of the treated electrode. Poor sample. Figure 7 is a comparison of the electrochemical impedance diagram (EIS), and the inset is an enlarged EIS diagram and an equivalent circuit diagram. It can be seen from the analysis that the internal resistance (Rs) of the electrode after PECVD treatment decreased from 2.46 to 1.96Ω, and the ion diffusion resistance was also significantly reduced. (that is, the slope of the straight line of the EIS curve becomes significantly larger).

Example 4

Compared with Example 3, except that PECVD is not performed, the rest is the same as Example 3, and the effects are shown in Figures 5, 6, and 7.

Claims (7)

1. A method for enhancing the performance of a cobalt nickel sulfide supercapacitor by ammonia plasma is characterized by comprising the following steps:

(1) cleaning of the foamed nickel substrate: ultrasonically cleaning and drying the foamed nickel by using tap water, acetone, dilute hydrochloric acid and distilled water in sequence;

(2) preparing a cobalt-nickel precursor: dissolving a certain amount of cobalt nitrate, nickel nitrate and urea in deionized water, stirring until the cobalt nitrate, the nickel nitrate and the urea are fully dissolved, pouring the mixture into a reaction kettle, adding foamed nickel, sealing, performing hydrothermal reaction for a period of time, sequentially washing the mixture by using the deionized water and absolute ethyl alcohol, and naturally drying the mixture to obtain a cobalt-nickel precursor;

(3) preparing cobalt nickel sulfide: putting the cobalt-nickel precursor into a sodium sulfide solution, sealing, carrying out hydrothermal reaction for a period of time, sequentially washing the cobalt-nickel precursor with deionized water and absolute ethyl alcohol, and naturally drying the cobalt-nickel precursor to obtain cobalt-nickel sulfide;

(4) and (3) regulating the pressure and temperature in the cavity of the prepared cobalt nickel sulfide plasma chemical vapor deposition system, applying ammonia plasma, and performing vapor deposition to obtain the cobalt nickel sulfide supercapacitor electrode.

2. The method for enhancing the performance of the cobalt nickel sulfide supercapacitor by ammonia gas plasma according to claim 1, wherein the molar ratio of the cobalt nitrate to the nickel nitrate to the urea in the step (2) is in the range of 1:1-2:3.5-6, and the urea can be replaced by ammonium fluoride.

3. The method for enhancing the performance of the cobalt nickel sulfide supercapacitor by using the ammonia gas plasma as claimed in claim 2, wherein the hydrothermal reaction temperature in the step (2) is 100 ℃ and 140 ℃, and the hydrothermal reaction time is 5-10 h.

4. The method for enhancing the performance of the cobalt nickel sulfide supercapacitor by ammonia gas plasma according to claim 3, wherein the concentration of the sodium sulfide solution is 0.05-0.3 mol/L.

5. The method for enhancing the performance of the cobalt nickel sulfide supercapacitor by using the ammonia gas plasma as claimed in claim 4, wherein the hydrothermal reaction temperature in the step (3) is 100 ℃ and 140 ℃, and the hydrothermal reaction time is 5-10 h.

6. The method for enhancing the performance of a cobalt nickel sulfide supercapacitor by ammonia plasma according to claim 5, wherein the pressure in the cavity of the plasma chemical vapor deposition system is adjusted to 10^-4-10^-3Pa, regulating the temperature in the cavity to be 150-350 ℃.

7. The method as claimed in claim 6, wherein the flow rate of the introduced ammonia gas is 10-30sccm, the time is 5-30min, the temperature is 150-350 ℃, the sputtering power is 100-400W, and the sputtering pressure is 40-80 Pa.

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