NL2030850B1

NL2030850B1 - Flexible composite electrode material as well as preparation method and use thereof

Info

Publication number: NL2030850B1
Application number: NL2030850A
Authority: NL
Inventors: Li Ming; Jia Wenhan
Original assignee: Univ Guilin Technology
Priority date: 2021-12-09
Filing date: 2022-02-08
Publication date: 2022-11-24
Also published as: NL2030850A; CN114156095B; CN114156095A

Abstract

Disclosed are a flexible composite electrode material as well as a preparation method and use thereof. The preparation method includes: uniformly dispersing leybdate and a sulfur source in aqueous solution, then adding a cobalt source and a nitrogen source, and uniformly dispersing the cobalt source and the nitrogen source ultrasonically, so as to obtain a Hfixture; and then placing a pretreated carbon cloth into the mixture, performing heat preservation at l90—220°C for 20—36 h, and performing washing and drying after a reaction, so as to obtain an electrode composite material. The present invention. is modified with doped, N and Co elements, pseudo capacitance of a supercapacitor can be effectively improved, with doped nitrogen elements, and more reactive sites are provided under a synergistic effect, so that impedance of a Haterial is effectively reduced, and a low capacitive property and low cycle stability of M082 are remarkably improved.

Description

P1094 /NL

FLEXIBLE COMPOSITE ELECTRODE MATERIAL AS WELL AS PREPARATION METHOD AND USE THEREOF

TECHNICAL FIELD The present invention relates to the technical field of ener- gy storage materials, and in particular relates to a flexible com- posite electrode material as well as a preparation method and use thereof.

BACKGROUND ART The development of a wearable device technology has broadened the development of energy storage devices towards a trend of flex- ibility. A flexible supercapacitor exhibits great application pro- spects in the field of flexible energy storage due to the high power density and cycle stability. However, the development of a flexible supercapacitor is limited by the low self-energy and poor rate capability currently, making it urgent for improvement.

Transition metal dichalcogenide (TMD) is a typical “graphene- like“ two-dimensional material and shows excellent properties in electrocatalysis and electric storage due to the unique structure. MoS; with a graphite-like structure has attracted great interests among various inorganic two-dimensional materials as electrode ma- terials. Compared with a carbon material, MoS, features several advantages such as its ability to store charges remotely or through a surface storage mechanism, relatively high capacitance as well as relatively high ionic conductivity and non-toxicity.

However, a capacitive property of pure MoS; is still limited due to a low electronic conductivity. An excellent approach to achieve necessary characteristics and eliminate shortcomings of individual materials is to integrate the individual materials with other materials with required characteristics into one system. The combination of two or more materials makes a final mixture basi- cally exhibit complementary or customized characteristics.

SUMMARY To overcome the defects in the prior art, the present inven- tion provides a flexible composite electrode material as well as a preparation method and use thereof. The present invention is modi- fied with doped N and Co elements, pseudo capacitance of a super- capacitor may be effectively improved with doped nitrogen ele- ments, and more reactive sites are provided under a synergistic effect of the nitrogen elements and cobalt elements, so that im- pedance of a material is effectively reduced, and a low capacitive property and low cycle stability of MoS; are remarkably improved. The flexible composite electrode material as well as the preparation method and the use thereof in the present invention are realized by the following technical solutions: A first objective of the present invention is to provide the preparation method of the flexible composite electrode material, which includes: uniformly dispersing molybdate and a sulfur source in aqueous solution, then adding a cobalt source and a nitrogen source, and uniformly dispersing the cobalt source and the nitrogen source ul- trasonically, so as to obtain a mixture; and then placing a pre- treated carbon cloth into the mixture, performing heat preserva- tion at 190-220°C for 20-36 h, and performing washing and drying after a reaction, so as to obtain an electrode composite material, where a molar ratio of the molybdate to the sulfur source is 1:2-4; a molar ratio of the cobalt source to the molybdate is 0.08-

0.1:1; and a molar ratio of the nitrogen source to the cobalt source is

0.4-0.6:1. Furthermore, the molybdate is any one of sodium molybdate, potassium molybdate and ammonium molybdate tetrahydrate. Furthermore, the sulfur source is any one of thiourea, L- cysteine and thioacetamide. Furthermore, the cobalt source is any one of cobalt nitrate, cobalt acetate and cobalt chloride. Furthermore, the nitrogen source is any one of urea, melamine and ammonia water.

Furthermore, a usage amount ratio of the molybdate to the aqueous solution is 1 mol/10 L-1 mol/15 L.

Furthermore, pretreatment specifically includes soaking the carbon cloth in nitric acid for 10-14 h and then cleaning the car- bon cloth.

Furthermore, the pretreated carbon cloth is placed in the mixture, and the heat preservation is performed at 200°C for 24 h.

A second objective of the present invention is to provide the flexible composite electrode material made through the preparation method.

A third objective of the present invention is to provide the use of the flexible composite electrode material in preparation of an enhanced supercapacitor.

Compared with the prior art, the present invention has the following beneficial effects: According to the present invention, a non-adhesive flexible electrode is made through a one-step hydrothermal method, thereby saving a great deal of cost and time; moreover, contact space with an electrolyte is greatly improved by means of a nanosheet struc- ture growing vertically on a carbon fiber cloth, thereby improving a charge reserve of the electrode material of the present inven- tion; and a synthesized substance has excellent crystallinity on the carbon cloth.

The present invention provides a quiet and stable environment for growth of MoS: through a solvothermal method, such that MoS; grows vertically on the carbon cloth; and the present invention is modified with doped N and Co elements, pseudo capacitance of a su- percapacitor may be effectively improved with doped nitrogen ele- ments, and more reactive sites are provided under a synergistic effect of the nitrogen elements and cobalt elements, so that im- pedance of a material is effectively reduced, and a low capacitive property and low cycle stability of MoS, are remarkably improved.

The doped elements of the present invention may not only af- fect properties of the material itself, but also significantly im- prove properties of the entire supercapacitor.

The preparation method of the present invention is simple and convenient, the preparation cost is low, and the material is capa-

ble of being well degraded in nature and is more ecological and environment-friendly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a scanning electron microscope (SEM) photograph of an electrode material of the present invention; FIG. la is an SEM photograph of an electrode material of comparative example 1; FIG. lb is an SEM photograph of an electrode material of comparative example 2; FIG. lc is an SEM photograph of an electrode material of comparative example 3; FIG. 1d is an SEM photograph of an elec- trode material of Example 1; FIG. le is an SEM photograph, en- larged to a size of 5 pm, of a box in FIG. 1d; and FIG. 1f is an SEM photograph, enlarged to a size of 2 pm, of the box in FIG. 1d. FIG. 2 is an energy dispersive spectrometer (EDS) spectrum of the electrode material of the present invention; FIG. 2a is a to- tal EDS spectrum of the electrode material of example 1; FIG. 2b is an EDS spectrum of S element distribution in the electrode ma- terial of example 1; FIG. 2c is an EDS spectrum of Mo element dis- tribution in the electrode material of example 1; FIG. 2d is an EDS spectrum of N element distribution in the electrode material of example 1; and FIG. 2e is an EDS spectrum of Co element distri- bution in the electrode material of example 1. FIG. 3 is a transmission electron microscope (TEM) photograph of the electrode material of the present invention; FIG. 3a is a TEM photograph of the electrode material with a size of 0.5 pm of example 1; and FIG. 3b is a TEM photograph of the electrode mate- rial with a size of 5 nm of example 1. FIG. 4 is an x-ray diffraction (XRD) pattern of the electrode material of the present invention; FIG. 4a is an XRD pattern of the electrode material of example 1; and FIG. 4b is an XRD pattern of Cos. FIG. 5 is a Raman spectrogram of the electrode material of example 1. FIG. 6 is an energy spectrum diagram of the electrode materi- al of example 1; FIG. 6a is an x-ray photoelectron spectroscopy (XPS) total energy spectrum diagram of the electrode material of example 1, FIG. 6b is a Mo 3d energy spectrum diagram of the elec-

trode material of example 1, FIG. éc is a 3 2p energy spectrum di- agram of the electrode material of example 1, FIG. 6d is a Co 2p energy spectrum diagram of the electrode material of example 1, and FIG. 6e is a N ls energy spectrum diagram of the electrode ma- 5 terial of example 1.

FIG. 7 is a cyclic voltammetry (CV) curve of electrode mate- rials of example 1, comparative example 1 and Comparative Example 4 of the present invention at a scanning rate of 10 mV's".

FIG. 8 is CV curves of the electrode material of example 1 at different scanning rates.

FIG. 9 is a charge-discharge test chart of the electrode ma- terial of example 1 at different scanning rates.

FIG. 10 is a specific capacity test chart of the electrode materials of example 1 and comparative example 4 at different cur- rent densities.

FIG. 11 is a specific capacity test chart of the electrode materials of example 1, comparative example 2 and comparative ex- ample 3 at different current densities.

FIG. 12 is a Nyquist diagram of the electrode materials of example 1 and comparative example 4.

FIG. 13 is a capacity retention rate change chart of the electrode material of example 1 after 10,000 cycles under a cur- rent density of 3 A/g.

FIG. 14 is a comparison diagram of galvanostatic charge/discharge (GCD) curves of a first cycle and a last cycle of the electrode material of example 1 during 10,000 cycles under the current density of 3 A/g.

DETAILED DESCRIPTION OF THE EMBODIMENTS The technical solutions in the examples of the present inven- tion will be clearly and completely described below with reference to the drawings in the examples of the present invention.

It should be noted that a carbon fiber cloth (hereinafter re- ferred to as a carbon cloth} used in the following examples of the present invention are purchased from carbon industry companies, with a thickness of 0.41 mm. During a reaction, the carbon cloth is cut to a size of 1 cm*l cm*0.41 mm with scissors for the reac-

tion.

Example 1 The example of the present invention provides a preparation method of a flexible composite electrode material. The method in- cluded the following steps: The carbon cloth was soaked in nitric acid with a mass con- centration of 65% for 12 h to make the carbon cloth hydrophilic and then washed with ethanol and acetone alternately 3 times, and a cleaned carbon cloth was dried in a vacuum drying oven at 60°C for 8 h for later use.

0.29 g of sodium molybdate (1 mmol) and 0.26 g of thiourea (3 mmol) were taken and poured into an inner sleeve of polytetrafluo- roethylene with a volume of 25 mL, and deionized water was added to reach 60% of a total volume so as to fully dissolve solid.

0.025 g of cobalt nitrate hexahydrate (0.086 mmol) and 0.025 g of urea CH4N;O (0.42 mmol) were added, and were ultrasonically mixed uniformly at 100 W for 10 min, and then a pretreated carbon cloth was placed into a mixture. The inner sleeve was placed in an outer stainless steel sleeve and sealed. Heating was performed to 200°C and then heat preservation was performed for 24 h.

After the reaction, the mixture was cooled at a room tempera- ture, the carbon cloth was taken out and washed centrifugally with the deionized water, soluble substances on the carbon cloth were removed to obtain a carbon cloth loaded with active substances, and the carbon cloth was dried in a vacuum oven at 60°C for 8 h to obtain the flexible composite electrode material.

Example 2 The example of the present invention provides a preparation method of a flexible composite electrode material. The method in- cluded the following steps: The carbon cloth was soaked in nitric acid with a mass con- centration of 60% for 12 h to make the carbon cloth hydrophilic and then washed with ethanol and acetone alternately 3 times, and a cleaned carbon cloth was dried in a vacuum drying oven at 60°C for 8 h for later use.

Potassium molybdate and thioacetamide were weighed and taken separately at a molar ratio of 1:2, a corresponding volume of de-

ionized water was weighed and taken according to a usage amount ratio of 10 L of deionized water per mole of potassium molybdate, a corresponding mass of cobalt acetate was weighed and taken at a molar ratio of the cobalt acetate to the potassium molybdate of

0.08:1, and corresponding ammonia water was weighed and taken at a molar ratio of the ammonia water to the cobalt acetate of 0.4:1 for later use.

The weighed potassium molybdate and thicacetamide were uni- formly dispersed in the deionized water, then the weighed cobalt acetate and ammonia water were added and ultrasonically mixed uni- formly at 100 W for 15 min, a mixture was transferred into an in- ner sleeve of polytetrafluoroethylene with a volume of 25 mL, then the pretreated carbon cloth was placed into the mixture, and the inner sleeve was placed in an outer stainless steel sleeve and sealed. Heating was performed to 190°C and then heat preservation was performed for 36 h.

Example 3 The example of the present invention provides a preparation method of a flexible composite electrode material. The method in- cluded the following steps: The carbon cloth was soaked in nitric acid with a mass con- centration of 60% for 12 h to make the carbon cloth hydrophilic and then washed with ethanol and acetone alternately 3 times, and a cleaned carbon cloth was dried in a vacuum drying oven at 60°C for 8 h for later use.

Ammonium molybdate tetrahydrate and L-cysteine were weighed and taken separately at a molar ratio of 1:2, a corresponding vol- ume of deionized water was weighed and taken according to a usage amount ratio of 12 L of deionized water per mole of ammonium mo- lybdate tetrahydrate, a corresponding mass of cobalt chloride was weighed and taken at a molar ratio of the cobalt chloride to the ammonium molybdate tetrahydrate of 0.1:1, and corresponding mela- mine was weighed and taken at a molar ratio of the melamine to co- balt acetate of 0.4 for later use.

The weighed ammonium molybdate tetrahydrate and L-cysteine were uniformly dispersed in the deionized water, then the weighed cobalt chloride and melamine were added and ultrasonically mixed uniformly at 100 W for 7 min, a mixture was transferred into an inner sleeve of polytetrafluoroethylene with a volume of 25 ml, where an addition amount was not larger than 15 mL, then the pre- treated carbon cloth was placed into the mixture, and the inner sleeve was placed in an outer stainless steel sleeve and sealed.

Heating was performed to 220°C and then heat preservation was per- formed for 20 h.

Comparative Example 1 The carbon cloth was soaked in nitric acid with a mass con- centration of 65% for 12 h to make the carbon cloth hydrophilic and then washed with ethanol and acetone alternately 3 times, and a cleaned carbon cloth was dried in a vacuum drying oven at 60°C for 8 h, so as to obtain a carbon cloth (CC) electrode.

Comparative Example 2 A difference from example 1 was that after sealing, heating was performed to 160°C and then heat preservation was performed for 24 h, so as to obtain a composite electrode material.

Comparative Example 3 A difference from example 1 was that after sealing, heating was performed to 180°C and then heat preservation was performed for 24 h, so as to obtain a composite electrode material.

Comparative Example 4 A difference from example 1 was that nitrogen source and co- balt salt were not added, a pretreated carbon cloth was directly placed in deionized water, and after sealing, heating was per-

formed to 180°C and then heat preservation was performed for 24 h, so as to obtain an electrode material.

Test part (I) Scanning electron microscope test (SEM test) To facilitate observation of a shape and a form of a flexible composite electrode material prepared through the method of the present invention, the present invention performed the SEM test on electrode materials prepared in example 1 and comparative examples 1-3 separately, and results were shown in FIG. 1.

FIG. la was a scanning electron microscope photograph of a CC electrode material of comparative example 1, FIG. 1b was a scan- ning electron microscope photograph of an electrode material of comparative example 2, FIG. lc was the scanning electron micro- scope photograph of the electrode material of comparative example 1, and FIG. 1d was a scanning electron microscope photograph of an electrode material of example 1.

As seen from FIGs. la-d, the undoped CC electrode material of comparative example 1 had a tightly connected network structure, and was composed of carbon fiber bundles with a diameter of about 10 pm in a staggered mode. Moreover, when a temperature was lower than 180°C, due to insufficient reduction, sparse MoS; nanosheets may be formed on a surface of the CC electrode material without any layering phenomenon (as shown in FIG. 1b), at 180°C, nuclea- tion of an electrode material was significantly improved, and com- pared with the material at the temperature lower than 180°C, a composite material with a carbon cloth coated with MoS; was signif- icantly improved (as shown in FIG. 1c). In a preparation process of the present invention, a nucleation rate of the composite elec- trode material was increased with the rise of temperature, and af- ter a further strong heating process, the nanoparticles collided fiercely together to generate a new molecular structure.

As seen from FIG. ld, a large number of MoS; nanosheets grew vertically and uniformly on a surface of the carbon cloth at 200°C, and compared with comparative example 2 and comparative ex- ample 3, the composite electrode material prepared in the Example 1 had more excellent crystallinity and a more desirable electro- chemical property. In addition, compared with a carbon cloth mate-

rial without any coating of comparative example 1 in FIG. la, the composite electrode material of example 1 had an originally smooth and fine carbon fiber surface uniformly coated with a thick layer of MoS; after being subjected to high-temperature hydrothermal treatment.

To further observe the shape and form of the electrode mate- rial of example 1, a material at a box in FIG. 1d was enlarged in the present invention, and results were shown in FIG. le {a size of 5 pm) and FIG. 1f (a size of 2 pm). It may be seen that the composite electrode material of example 1 was formed by stacking pieces of nanosheets, some materials even had the shape and form of a nanoflower through stacking, which may be due to a high tem- perature reaction between thiourea and sodium molybdate at 200°C, and a structure of MoS; nanosheets was formed at 200°C. It was pre- cisely because of increase of the structure that a specific sur- face area of the material was significantly increased.

(IT) Energy dispersive spectrometer (EDS) test To verify doping and distribution of elements in a flexible composite electrode material prepared through the method of the present invention, the present invention performed the EDS test on the composite electrode material of example 1, and test results were shown in FIG. 2. It may be seen that a certain proportion of N and Co elements were uniformly distributed in the composite ma- terial of example 1, which also reflected from the side that the N and Co elements well entered a material of MoS; through a hydro- thermal method.

(III) Transmission electron microscope (TEM) test To observe a crystal lattice of a flexible composite elec- trode material prepared through the method of the present inven- tion, the present invention performed the TEM test on the compo- site electrode material of example 1, and test results were shown in FIG. 3. It may be seen that a lattice spacing of the material was 0.65 nm, which corresponded to 0.62 nm of an intrinsic (002) crystal face of MoS;. Slight expansion was resulted from existence of an intercalator, and specifically, due to the fact that a part of thiourea hydrolyzed and entered molybdenum ions, slight in- crease of the lattice spacing was caused, some possible reasons of which are that cobalt atoms intercalated to sulphur vacancies in molybdenum sulfide, so that nitrogen elements in a neutral posi- tion were attracted closer to molybdenum elements due to decrease of potential energy of the nitrogen elements, which changed a whole energy barrier, and meanwhile, cobalt elements were likely to enter a MoS, lattice as a substitute atom of molybdenum, instead of aggregating, forming clusters and eventually leading to change of the lattice spacing.

(IV) X-ray diffraction (¥RD) test X-ray diffraction (XRD) was used to analyze the composite electrode material of example 1. As seen from FIG. 4, diffraction peaks of 13.9, 32.6, 36.5 and 57.4 collected by the XRD were con- sistent with those of MoS, (JCPDS No. 73-1508), which corresponded to (002), (100), (102) and (110) faces respectively. Doping of ni- trogen elements did not significantly change a crystal form of MoS:, however, meanwhile it may be seen from the figure that a small peak which did not appear in original molybdenum sulfide ap- peared at 28.75°, and when enlarged, a region (26.5°-29.5°) where cobalt sulfide was located was found to correspond to a (111) crystal form of CoS. (JCPDS No. 89-1492) at 27.787°, which was be- cause a small amount of cobalt nitrate was sulfurized by thiourea during the reaction so as to generate the cobalt sulfide.

(V) Raman spectrum test The present invention performed the Raman spectrum test on the composite electrode material of example 1, and test results were shown in FIG. 5. It may be seen that the composite electrode material of example 1 basically retained two characteristic peaks of molybdenum sulfide at 379 and 405 cm, which corresponded to typical Alg and El2g modes of MoS; respectively. But almost no peaks were detected at 1350 cmt (D-band) and 1590 cmt {(G-band) of a substrate, which indicated that a surface of the carbon cloth was coated with a thick layer of MoS; nanosheets.

(VI) X-ray photoelectron spectroscopy test The present invention used an x-ray photoelectron spectrosco- py energy spectrum diagram to analyze characteristics of a valence state and chemical composition of the composite electrode material of example 1, and results were shown in FIG. 6. FIG. 6a was an x-

ray photoelectron spectroscopy (XPS) total energy spectrum dia- gram, FIG. &6b was a Mo 3d energy spectrum diagram, FIG. 6c was a S 2p energy spectrum diagram, FIG. &d was a Co 2p energy spectrum diagram, and FIG. 6e was a N 1s energy spectrum diagram.

Peaks of S 2p, Mo 3d, Ols and Nls may be seen in FIG. 6a, and a high oxygen peak was resulted from thermal drying in air and long time placement during the test.

From FIG. 6b, the Mo peaks with MoS; doped may be seen, and a Mo 3d signal without MoS, doped significantly showed two peaks at

229.0 and 232.2 eV separately, which belonged to Mo 3d 5/2 and Mo 3d 3/2 respectively. Deconvolution peaks revealed different types of Mo states, which may be attributed to change of a defect struc- ture in a 2d configuration. As seen from FIG. 5c, 169.08 and 167.78 in a fine spectrum of S corresponded to 2pl/2 and 2p3/2 of S respectively. Similarly, in FIG. 5d, 800 and 780 of Co corresponded to 2pl/2 and 2p3/2, and in FIG. 6e, a N spectrum at 394 corresponded to a bonding property of a Mo-N bond, which also verified that N elements kept in a neutral position moved close to Mo elements and performed bonding as co- balt entered a vacancy of a single sulfur site in molybdenum sul- fide and replaced part of Mo groups. The fact further proved ef- fective synthesis of a ternary composite material based on self- growing N and Co-MoS; on the carbon cloth. (VII) Electrochemical property test To verify an electrochemical property of the flexible compo- site electrode material prepared through the method of the present invention, the present invention used a CHI760E electrochemical workstation (CHI760E), used a platinum (Pt) foil as a counter electrode, used a Hg/Hg:Cl: electrode as a reference electrode, and used the electrode materials of example 1 and comparative examples 1-4 as working electrodes respectively, so as to test the electro- chemical property of the flexible composite electrode material, where an electrolyte was 1 M Na:50,. Cyclic voltammetry test: The cyclic voltammetry (CV) test was performed in a range of -0.8 V to 0 V. As shown in FIG. 7a, at a consistent scanning rate (10 mv-s*), the composite material of example 1 showed a larger CV curve area than comparative example 1 and comparative example 4, and a curve was close to a rectangle with no redox peak, indicat- ing an electric double-layer capacitance property of an electrode. Compared with a CC electrode coated with nanosheets, a curve area of CC was very small, and influence of the CC on a total capacity may be negligible. Moreover, a maximum CV area also indicated that a composite electrode exhibited the highest capacitance. The fact meant that the composite electrode material of example 1 had high- er area specific capacitance. In addition, a maximum CV region al- so indicated that the composite electrode material of example 1 exhibited the highest capacitance.

As seen from FIG. 7b, a shape of a CV curve of the composite electrode material of example 1 was almost similar to a curve of a gradually increasing scanning rate. The fact also reflected the excellent electrochemical property of the composite electrode ma- terial of example 1.

In a charge-discharge test of the composite electrode materi- al of example 1, a rate of a scanning test changed from 10 mV to 1 mV. As seen from FIG. 7c, a shape of the figure hardly changed at different rates, but still showed good triangular symmetry, and compared with a capacity of 500-1500 mF /cm of pure molybdenum sulfide at 1 mv s*, the material had a high specific capacity of 4870 mF /cm.

As seen from cyclic test results of FIG. 5d, a capacity re- tention rate may still reach 100% after 10,000 cycles at a current density of 3 A/g, which indicated that the composite electrode ma- terial of example 1 had excellent crystallinity, and further indi- cated excellent cycle stability of the composite electrode materi- al of example 1 as a flexible used material. Compared with pure MoS; of comparative example 4, N and Co-MOS; of example 1 exhibited the highest capacitance and remarkable rate capability, showing high-speed ion transfer and a superior rate property with increase of currents.

FIG. 5e showed cyclic test results of the composite electrode materials of example 1 and comparative examples 2 and 3 of the present invention. It may be seen that specific capacities of the composite electrode materials of example 1 and comparative exam-

ples 2 and 3 were 5105 mF/cm*, 1800 mF/cm” and 4000 mF/cm? re- spectively, which indicated that a temperature had a greater in- fluence on the specific capacities of the composite electrode ma- terials. Compared with comparative examples 2 and 3, a reaction temperature of example 1 had a better property. The Example 1 had desirable crystallinity and is capable of growing more vertical nanosheet structures, so that electrolyte solution made contact with the electrode materials more fully, thereby increasing a spe- cific surface area, and further improving a charge storage capaci- ty of the materials.

FIG. 12 were Nyquist diagrams of the electrode materials of example 1 and comparative example 4. The electrochemical property of a supercapacitor may be directly reflected by an equivalent se- ries resistance (RS) and a charge transfer resistance (RCT). As seen from FIG. 5f, an equivalent resistance of pure molybdenum di- sulfide in comparative example 4 was larger. Compared with compar- ative example 4, a slope of an equivalent resistance in a high frequency region of example 1 was increased, charge transport in a low frequency region was significantly reduced, the equivalent re- sistance was significantly decreased, and the charge transfer re- sistance was also kept at a very good level. Therefore, it may be concluded that a ternary composite material with N and Co-MoS; growing on the carbon cloth was capable of significantly reducing impedance of an electrode material.

FIG. 5g showed cyclic test results of the composite electrode material of example 1 of the present invention. It may be seen that the capacity retention rate may still reach 100% after 10,000 cycles at the current density of 3 A/g, which indicated that the composite electrode material of example 1 had the excellent crys- tallinity, and further indicated the excellent cycle stability of the composite electrode material of example 1 as the flexible used material. Compared with the pure MoS;, the N and Co-MOS, exhibited the highest capacitance and the remarkable rate capability, show- ing the high-speed ion transfer and the superior rate property with the increase of currents.

FIG. 5h is a galvanostatic charge/discharge (GCD) curve of the composite electrode material of example 1 after 10,000 cycles.

It may be seen that after 10,000 cycles, the GCD curve had hardly changed obviously, which indicated that the material had the ex- cellent cycle stability.

In conclusion, the test results of the present invention in- dicated that the specific capacitance of the flexible composite electrode material of the present invention reached 500 F/g (4870 mF/cm?), and after 10,000 cycles at the current density of 5 A/g, the excellent stability with the retention rate of 100% and almost no attenuation (compared with 89.6% after 2,500 cycles of pure mo- lybdenum sulfide) was greatly improved.

Apparently, the above-mentioned examples are merely some ra- ther than all examples of the present invention. Based on the ex- amples of the present invention, all other examples acquired by those of ordinary skill in the art without making creative efforts should fall within the scope of protection of the present inven- tion.

Claims

CONCLUSIONS

A method for preparing a flexible composite electrode material, comprising: uniformly dispersing molybdate and a sulfur source in an aqueous solution, then adding a cobalt source and a nitrogen source, and uniformly ultrasonic dispersing the cobalt source and the nitrogen source, to obtain a mixture; and then placing a pretreated carbon cloth in the mixture, keeping heat at 190 to 220°C for 20 to 36 hours, and performing washing and drying after a reaction, to obtain an electrode composite material having a molar ratio of molybdate to sulfur source is 1:(2 to 4); a molar ratio of the cobalt source to the molybdate is {0.08 to 0.1):1; and a molar ratio of the nitrogen source to the cobalt source is {0.4 to 0.6):1.

The preparation method according to claim 1, wherein the molybdate is one of sodium molybdate, potassium molybdate and ammonium molybdate tetrahydrate.

The preparation method according to claim 1, characterized in that the sulfur source is thiourea, L-cysteine and thioacetamide.

The preparation method according to claim 1, wherein the cobalt source is one of cobalt nitrate, cobalt acetate and cobalt chloride.

The manufacturing method according to claim 1, wherein the nitrogen source is one of urea, melamine and ammonia water.

The preparation method according to claim 1, characterized in that the ratio of the use amount of the molybdate to the aqueous solution is 1 mol/10 L to 1 mol/15 L.

Preparation method according to one of Claims 1 to 4, characterized in that the pre-treatment comprises, in particular, soaking the carbon cloth in nitric acid for 10 to 14 hours and then cleaning the carbon cloth.

The preparation method according to claim 1, wherein the pre-treated carbon cloth is placed in the mixture and the heat preservation is carried out at 200°C for 24 hours.

A flexible composite electrode material made by the preparation method according to any one of claims 1 to 8.

Use of the flexible composite electrode material according to claim 9 to prepare an improved supercapacitor.