CN113380551B - Method for improving capacity of Mo-Co-S super capacitor - Google Patents
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- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
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- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
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Abstract
The invention discloses a method for improving the capacity of a Mo-Co-S super capacitor. Carrying out P doping treatment on the low-crystalline Mo-Co-S by adopting a CVD method to obtain Mo-Co-S/P; the Mo-Co-S/P is subjected to overvoltage constant-current charging treatment, the surface of a sample is split into a block structure with a plurality of obvious gaps from the complete gully shape, and a large number of nano spherical particles with the diameter of 50-100 nm and nano sheets with the thickness of 100nm are accumulated on the block structure, so that more active sites are provided for electrochemical reaction. The electrochemical performance of the electrode was evaluated in a 1M KOH electrolyte at 10mA/cm2The Mo-Co-S capacity is only 0.72F/cm under the current density2The P doping is improved to 4.16F/cm2The maximum capacity can reach 9.64F/cm after overvoltage and constant current charging treatment2The capacity of the Mo-Co-S/P electrode is 2.3 times that of the Mo-Co-S/P electrode without charging treatment and 13.4 times that of the Mo-Co-S electrode; meanwhile, the capacity of the P-undoped Mo-Co-S is only 1.43F/cm by directly carrying out overvoltage constant-current charging treatment under the same conditions2。
Description
Technical Field
The invention belongs to the field of super capacitors, and particularly relates to a method for improving the capacity of a Mo-Co-S super capacitor by the cooperation of P doping and overvoltage constant-current charging.
Background
The super capacitor is considered as one of the most promising energy storage candidates in urban power grids and electric vehicles because of the characteristics of high power density, excellent electrochemical reversibility, long cycle stability and the like. However, the energy density of the super capacitor still needs to be improved, so increasing the energy density of the electrode material becomes an important way to further improve the performance of the capacitor.
Mo-Co-S is of great interest in electrode materials of super capacitors, and is a super capacitor electrode material with good application prospect due to the advantages of high theoretical capacity, low cost, easy preparation and the like. However, due to the limitations of conductivity and microstructure, the actual capacity of Mo-Co-S is generally much lower than its theoretical capacity, and the cycle stability is not ideal. Research has shown that metal P-compounds generally have metalloid properties and excellent conductivity, so P-doping can effectively increase the conductivity of the material, thereby increasing its capacity. However, the amount of P doping is generally low and the effect of increasing the capacity is still not ideal. On the other hand, compared with a block material, the microstructure with the nanoscale is more beneficial to full contact of electrolyte ions and an electrode material, and can provide more active sites for electrochemical reaction, but the electrochemical reaction is usually carried out at the atomic scale, and the electrochemical active sites have a great lifting space for nano-sheets, nano-rods and other nano-structures with smooth surfaces. In addition, compared with a crystalline electrode material, the low-crystalline electrode material has more structural defects and often has more excellent cycling stability, and at present, few reports of the low-crystalline Mo-Co-S electrode material exist.
Disclosure of Invention
The invention aims to provide a method for improving the capacity of low-crystalline Mo-Co-S by the cooperation of P doping and overvoltage constant-current charging aiming at the low actual specific capacity of a Mo-Co-S electrode material and the defects of the prior art, namely, firstly preparing the low-crystalline Mo-Co-S, and improving the conductivity by P doping; and then, the microstructure is further changed through overvoltage constant current charging, so that a large sample is split into small blocks, and a large number of nano spherical particles with the diameter of 50-100 nm and nano sheets with the thickness of 100nm are accumulated on the surface of each small sample, so that electrochemical active sites are remarkably increased. In addition, electrochemical impedance spectrum analysis shows that the overvoltage charging treatment not only can optimize the microstructure, but also can further reduce the internal resistance of the electrode, the charge transfer resistance and the electrolyte ion transmission resistance. Therefore, the capacity of Mo-Co-S is from 0.72F/cm by adopting the method of the P doping and overvoltage constant-current charging synergistic treatment2Lifting to 9.62F/cm2。
The technical scheme of the invention is as follows: taking foamed nickel as a substrate, and obtaining a Mo-Co-S precursor by adopting a hydrothermal method; and then, using sodium metaphosphate as a P source, annealing the Mo-Co-S precursor in a CVD (chemical vapor deposition) tube furnace to obtain Mo-Co-S/P, and then carrying out overvoltage constant-current charging technical treatment on the Mo-Co-S/P precursor.
The technical method comprises the following steps:
(1) preparing a low-crystalline Mo-Co-S precursor: and (3) washing the foamed nickel with the area of 2cm multiplied by 4cm by using a 1M dilute hydrochloric acid solution, deionized water and absolute ethyl alcohol in sequence, and drying for later use. Adding cobalt nitrate, ammonium molybdate, thioacetamide and ammonium fluoride into deionized water, stirring until the cobalt nitrate, the ammonium molybdate, the thioacetamide and the ammonium fluoride are fully dissolved, pouring the mixture into a reaction kettle inner container, then putting clean foamed nickel into the inner container, sealing the nickel by using a stainless steel outer sleeve, heating the nickel for 15 to 20 hours at the temperature of 150 plus one year and taking the nickel out, respectively ultrasonically cleaning the nickel in the deionized water and absolute ethyl alcohol, drying the cleaned nickel in an oven to obtain a Mo-Co-S precursor,
(2) preparation of low crystalline Mo-Co-S/P: and (3) taking sodium metaphosphate as a P source, and annealing the Mo-Co-S precursor and the sodium metaphosphate in a CVD (chemical vapor deposition) tube furnace at the temperature of 300 ℃ for 2 hours to obtain the Mo-Co-S/P.
The molar ratio of the cobalt nitrate, the ammonium molybdate, the thioacetamide, the ammonium fluoride and the sodium metaphosphate in the steps (1) and (2) is 1:1:4-5:1-2: 2-3.
(3) And (3) carrying out constant current charging treatment on Mo-Co-S/P in a positive potential window: preparing a KOH solution with a certain concentration as an electrolyte, adopting an electrochemical workstation three-electrode system, taking Mo-Co-S/P as a working electrode, taking a platinum sheet as a counter electrode, taking a mercury/mercury oxide electrode as a reference electrode, and carrying out constant current charging treatment on the Mo-Co-S/P for a certain time under a certain potential window and current by adopting a constant current charging and discharging method in the electrochemical workstation three-electrode system. The concentration of the electrolyte KOH is 1-6M, the low potential window is 0V, the high potential window is 0.55-0.7V, the charging current is 0.01-0.02A, and the charging time is 1-3 h.
The technical scheme of the invention applies the obtained electrode to the super capacitor.
In the invention, the Mo-Co-S/P obtained after the treatment of the step (2) is increased in conductivity and obviously increased in capacity. After the treatment of the step (3), the surface of the sample is split into a plurality of block structures with obvious gaps from the complete gully shape, and a large number of nano spherical particles with the diameter of 50-100 nm and nano sheets with the thickness of 100nm are stacked on the block structures, so that more active sites are provided for the electrochemical reaction; and the internal resistance, the charge transfer resistance and the electrolyte ion transmission resistance of the electrode material are further reduced, and the capacity is further improved.
Drawings
FIG. 1 is SEM images of uncharged Mo-Co-S/P electrodes of example 1 at different magnifications, wherein a is an image magnified by 5000 times, b is an image magnified by 20000 times, and c is an image magnified by 50000 times.
FIG. 2 is SEM images of Mo-Co-S/P electrode after charging treatment in example 1 at different magnifications, wherein a is an image magnified 5000 times, b is an image magnified 20000 times, and c is an image magnified 50000 times.
FIG. 3 is an XRD pattern of the Mo-Co-S/P electrode before and after the charging treatment in example 1.
FIG. 4 is a graph showing a comparison of the performance of the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode of example 1 before and after the charging treatment; wherein (a) is example 1 at a current density of 20mA/cm2And (3) charging and discharging curves before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode are subjected to charging treatment. (b) The charge and discharge curves of the Mo-Co-S/P electrode after the charge treatment of example 1 at different current densities are shown.
FIG. 5 is a graph comparing the capacity-current density relationship before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode of example 1 were subjected to the charging treatment.
In FIG. 6, a is the EIS curve before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode of the example 1 are charged; b is an enlarged view of the high-frequency region of the EIS curve.
FIG. 7 shows that the current density of example 2 is 20mA/cm2And (3) charging and discharging curves before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode are subjected to charging treatment.
FIG. 8 shows that in example 3, the current density was 20mA/cm2And (3) charging and discharging curves before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode are subjected to charging treatment.
FIG. 9 shows that in example 4, the current density was 20mA/cm2And (3) charging and discharging curves before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode are subjected to charging treatment.
FIG. 10 shows the current density of 20mA/cm in example 52In time, Mo-Co-And charging and discharging curves before and after the charging treatment of the S precursor electrode and the Mo-Co-S/P electrode.
Detailed Description
To further clarify the summary and features of the present invention, the following examples of the present invention are given by way of illustration only and are not intended to limit the scope of the present invention.
The experimental procedures in the following examples are conventional unless otherwise specified.
Example 1
(1) Preparing a low crystalline Mo-Co-S/P electrode: and ultrasonically cleaning the foamed nickel by using a 1M dilute hydrochloric acid solution, deionized water and absolute ethyl alcohol in sequence, and drying for later use. Weighing 0.325mmol of cobalt nitrate, 0.325mmol of ammonium molybdate and 1.464mmol of thioacetamide, dissolving in 40mL of deionized water, obtaining a red transparent solution under the action of magnetic stirring, adding 0.5mmol of ammonium fluoride, continuing stirring to fully dissolve the ammonium fluoride, pouring the solution into a 50mL reaction kettle inner container, adding clean foamed nickel, sealing by using a stainless steel outer sleeve, putting into a constant-temperature drying box at 180 ℃, preserving heat for 15 hours, taking out the foamed nickel after the reaction kettle is cooled to room temperature, ultrasonically cleaning the foamed nickel for 3min by using deionized water and absolute ethyl alcohol respectively, and then drying in a 60 ℃ drying oven to obtain a Mo-Co-S precursor; weighing 80mg of sodium metaphosphate, placing the sodium metaphosphate into a porcelain boat, placing the porcelain boat into a CVD (chemical vapor deposition) tube furnace to be close to the direction of airflow source, then placing a Mo-Co-S precursor into the tube furnace, sealing two ends of the tube furnace, introducing a certain amount of nitrogen (or argon), and setting a furnace body temperature rise program after 15 minutes: the heating rate is 5 ℃/min, the temperature is increased from room temperature to 300 ℃, the temperature is kept for 2 hours after the temperature reaches 300 ℃, then the temperature is naturally cooled to the room temperature, the nitrogen (or argon) atmosphere is kept in the whole process, and finally the Mo-Co-S/P electrode is obtained. FIG. 1 is an SEM image of Mo-Co-S/P electrode at different magnifications, showing the complete gully morphology on the surface.
(2) And (3) constant-current charging treatment in a positive potential interval: A1M KOH solution is prepared to serve as an electrolyte, a Mo-Co-S/P electrode serves as a working electrode, a platinum sheet serves as a counter electrode, a mercury/mercury oxide electrode serves as a reference electrode, a constant-current charge-discharge method in a three-electrode system of an electrochemical workstation is adopted, and a low potential window is set to be 0V and a high potential window is set to be 0.6V. The charging current is 0.01A, and the charging time is 1.6 h. FIG. 2 is an SEM image of Mo-Co-S/P electrode with different magnification after positive potential window constant current charging, which shows that the charged electrode surface is split into a plurality of block-shaped substances, and a large number of nanosphere particles stacked with the diameter of 50-100 nm and nanosheets with the thickness of about 100nm are generated on the surface of the electrode, so that more active sites are provided for electrochemical reaction, rapid diffusion of electrolyte ions is facilitated, specific capacitance can be greatly improved, and good electrochemical performance is achieved.
FIG. 3 is XRD (X-ray diffraction) patterns before and after the charging treatment of the Mo-Co-S/P electrode, and only a few weak peaks except the diffraction peak of the nickel net can be seen, which shows the low crystalline property of the sample.
In order to further verify the influence of the positive potential window constant current charging technology on the capacity, the Mo-Co-S precursor is also subjected to charging treatment under the same condition, and electrochemical performance test and comparison are carried out on the Mo-Co-S precursor. FIG. 4-a shows Mo-Co-S precursor, Mo-Co-S/P, charged Mo-Co-S, and charged Mo-Co-S/P at a current density of 20mA/cm2The charge-discharge curve shows that the discharge time of Mo-Co-S/P after charge treatment is longest, i.e. the capacity is the largest. FIG. 4-b is a charging and discharging curve of the Mo-Co-S/P electrode after charging treatment under different current densities. The capacitance values of the samples at different current densities were obtained from the specific capacitance calculation formula (I, t, S, V values are shown in the attached Table 1), and FIG. 5 was obtained, from which it can be seen that when the current density was 10mA/cm2When the Mo-Co-S capacity is only 0.72F/cm2The P doping is improved to 4.16F/cm2The maximum capacity can reach 9.64F/cm after further overvoltage constant current charging treatment2The capacity of the Mo-Co-S/P electrode is 2.3 times that of the Mo-Co-S/P electrode without charging treatment and 13.4 times that of the Mo-Co-S electrode; meanwhile, the capacity of the P-undoped Mo-Co-S is only 1.43F/cm by directly carrying out overvoltage constant-current charging treatment under the same conditions2. It is shown that the maximum capacity can be obtained only by the simultaneous P-formation and over-voltage charging processes.
FIG. 6 is a comparison of Electrochemical Impedance (EIS), FIG. 6-a is an EIS curve, FIG. 6-b is a high-frequency enlarged view of the EIS curve, and by comparing the first intersection point of the curve semicircular region and the Z' axis, the internal resistances of the Mo-Co-S precursor electrode, the Mo-Co-S/P electrode and the charged Mo-Co-S/P electrode are 1.33 Ω, 1.2 Ω and 1.05 Ω, respectively, it is proved that the internal resistance can be effectively reduced by P doping, and can be further reduced by the overvoltage constant-current charging treatment; compared with the characteristic of a curve in a higher frequency region, the radius of the charged Mo-Co-S/P electrode is the smallest, the slope is the largest, and the charging treatment proves that the charge transfer resistance and the electrolyte ion transmission impedance are both reduced.
Table 1 shows the values of the parameters for calculating the specific capacitance of the sample in example 1.
Uncharged Mo-Co-S precursors refer to: and the Mo-Co-S precursor sample is not subjected to overvoltage constant-current charging treatment.
The charge treatment of the Mo-Co-S precursor refers to: and (3) carrying out overvoltage constant current charging treatment on the Mo-Co-S precursor sample.
The uncharged Mo-Co-S/P indicates that: and the Mo-Co-S/P precursor sample is not subjected to overvoltage constant-current charging treatment.
The charge treatment Mo-Co-S/P means: and (3) carrying out overvoltage constant current charging treatment on the Mo-Co-S/P precursor sample.
Example 2
The same as example 1 except that a potential window (low potential of 0V, high potential of 0.7V) was set as compared with example 1. The maximum capacity of the Mo-Co-S/P electrode after charging treatment can reach 7.4F/cm2. FIG. 7 shows the current density of 20mA/cm in example 22And comparing the charge-discharge curves of the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode before and after charging treatment.
Example 3
The same as example 1 except that the constant current charging time (1h) was set differently from example 1. The maximum capacity of the Mo-Co-S/P electrode after charging treatment can reach 7.11F/cm2. FIG. 8 shows the current density of 20mA/cm in example 32Before and after the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode are chargedAnd (5) comparing charge and discharge curves.
Example 4
The same as example 1 except that the charging current was set to a different value (0.005A) as compared with example 1. The maximum capacity of the Mo-Co-S/P electrode after charging treatment can reach 6.89F/cm2. It can be seen that when the charging current was too small, the Mo-Co-S/P electrode capacity was significantly reduced. FIG. 9 shows the current density of 20mA/cm in example 42And comparing the charge-discharge curves of the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode before and after charging treatment.
Example 5
The same as example 1 except that a potential window (low potential of 0V, high potential of 0.5V) was set as compared with example 1. The maximum capacity of the Mo-Co-S/P electrode after charging treatment can reach 4.84F/cm2. It can be seen that when the high potential voltage is set too low, the Mo-Co-S/P electrode capacity is significantly reduced. FIG. 10 shows the current density of 20mA/cm in example 42And comparing the charge-discharge curves of the Mo-Co-S precursor electrode and the Mo-Co-S/P electrode before and after charging treatment.
Claims (3)
1. A method for improving the capacity of a Mo-Co-S super capacitor is characterized by comprising the following steps:
(1) preparing a low-crystalline Mo-Co-S precursor: adding cobalt nitrate, ammonium molybdate, thioacetamide and ammonium fluoride into deionized water, stirring until the cobalt nitrate, the ammonium molybdate, the thioacetamide and the ammonium fluoride are fully dissolved, pouring the prepared solution into a reaction kettle inner container, putting clean foamed nickel into the inner container, sealing the inner container by using a stainless steel outer sleeve, heating the inner container for 15 to 20 hours at the temperature of 150 plus one year and 200 ℃, taking the inner container out, respectively performing ultrasonic cleaning in the deionized water and absolute ethyl alcohol, and drying the inner container in an oven to obtain a Mo-Co-S precursor;
(2) preparation of Mo-Co-S/P: putting the Mo-Co-S precursor and sodium metaphosphate into a CVD tube furnace for annealing to obtain Mo-Co-S/P;
(3) and (3) carrying out constant current charging treatment on Mo-Co-S/P in a positive potential window: and (3) preparing a KOH solution with the concentration of 1-6M as an electrolyte, taking the Mo-Co-S/P obtained in the step (2) as a working electrode, a platinum sheet as a counter electrode and a mercury/mercury oxide electrode as a reference electrode, and performing constant-current charging and discharging treatment on the Mo-Co-S/P for 1-3 h by adopting a constant-current charging and discharging method in a three-electrode system of an electrochemical workstation at a low potential window of 0V, a high potential window of 0.55-0.7V and a charging current of 0.01-0.02A to obtain the charged Mo-Co-S/P electrode.
2. The method for improving the capacity of the Mo-Co-S supercapacitor according to claim 1, wherein the molar ratio of the cobalt nitrate, the ammonium molybdate, the thioacetamide, the ammonium fluoride and the sodium metaphosphate in steps (1) and (2) is 1:1:4-5:1-2: 2-3.
3. The method for improving the capacity of the Mo-Co-S supercapacitor as claimed in claim 1, wherein the annealing temperature in the step (2) is 300-400 ℃.
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