Preparation and Application of Supercapacitor, Its Electrodes and NiOOH-Co(OH)2 Composite Electrode Active Material

Abstract

The present invention belongs to the field of energy storage materials, and particularly relates to a NiOOH-Co(OH)2 composite electrode active material for supercapacitors, which is a composite containing NiOOH and Co(OH)2. The present invention also includes the preparation and application of the active material, as well as supercapacitors and their electrodes containing the active material. In the present invention, the NiOOH-Co(OH)2 is compounded, and the electrochemical performance of the supercapacitor can be synergistically improved based on a new mechanism.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage materials, and particularly relates to electrode materials for supercapacitors. Background Art

[0002] A supercapacitor is a new type of energy storage device between a capacitor and a traditional chemical power source. According to the energy storage method, it is divided into an electric double layer capacitor and a Faraday pseudocapacitor. As a new type of energy storage device, a supercapacitor has the advantages of high power density, long cycle life, wide operating temperature range, fast charging, environmental friendliness, etc., but also has shortcomings such as low energy density, high price, and large self-discharge. Electrode materials are the research focus of new high-performance supercapacitors, and it is of great significance to improve their performance.

[0003] In recent years, it has been found that by generating Faraday pseudocapacitance through rapid reversible adsorption / desorption and oxidation / reduction reactions on the electrode surface and in the bulk phase, that is, through the redox reaction of mutual conversion between Co 2+ / Co 3+ and Ni 2+ / Ni 3+ it has a high theoretical specific capacitance and energy density. However, the performance of existing supercapacitors needs to be further improved. Summary of the Invention

[0004] Aiming at the problem of the unsatisfactory performance of supercapacitor electrode materials, the first object of the present invention is to provide a NiOOH-Co(OH)2 composite electrode active material for supercapacitors, aiming to improve the electrochemical performance of supercapacitors based on the synergism of Ni-Co with special valence states.

[0005] The second object of the present invention is to provide a preparation method of the NiOOH-Co(OH)2 composite electrode active material for supercapacitors and its application in supercapacitors.

[0006] The third object of the present invention is to provide a supercapacitor electrode containing the active material and its preparation.

[0007] The fourth object of the present invention is to provide a supercapacitor containing the active material.

[0008] A NiOOH-Co(OH)2 composite electrode active material for supercapacitors is a composite containing NiOOH and Co(OH)2.

[0009] The present invention unexpectedly discovers that innovatively combining NiOOH-Co(OH)2 can synergistically improve the performance of supercapacitors based on a new action mechanism.

[0010] In the present invention, the NiOOH is γ-NiOOH of hexagonal crystal system, and the Co(OH)2 is α-Co(OH)2 of hexagonal crystal system.

[0011] Preferably, the Ni / Co molar ratio of the NiOOH and Co(OH)2 is 1:2 to 2.5. At this preferred ratio, the synergistic effect of the two can be unexpectedly further improved, which is helpful for further improving the electrochemical performance of the supercapacitor.

[0012] The present invention also provides a preparation method of the NiOOH-Co(OH)2 composite electrode active material for the supercapacitor, which is obtained by oxidizing a nickel source and an oxidant, then mixing them with a cobalt source, and adding an alkali for coprecipitation treatment.

[0013] In the present invention, the nickel source is oxidized and then coprecipitated with cobalt, so that the composite material can be obtained in one pot, which is helpful for improving the electrochemical performance of the material in the supercapacitor.

[0014] In the present invention, the nickel source is a water-soluble salt of Ni 2+ preferably at least one of nickel sulfate, nickel acetate, and nickel nitrate;

[0015] The oxidant is persulfate, preferably ammonium persulfate.

[0016] Preferably, the amount of the oxidant is 0.9 to 1.1 times the theoretical molar amount of oxidizing Ni 2+ in the nickel source to Ni 3+ ;

[0017] Preferably, the molar ratio of the nickel source to the oxidant is 1:0.5 to 0.55.

[0018] In the present invention, the cobalt source is a water-soluble salt of Co 2+ preferably at least one of nickel sulfate, nickel acetate, and nickel nitrate;

[0019] Preferably, the Ni / Co molar ratio in the nickel source and the cobalt source is 1:2 to 2.5;

[0020] Preferably, the alkali is at least one of sodium hydroxide and potassium hydroxide;

[0021] Preferably, the alkali is 1.5 to 3 times the theoretical molar amount of completely precipitating nickel and cobalt;

[0022] Preferably, the alkali is 2 to 2.5 times the total molar amount of nickel and cobalt.

[0023] In the present invention, the entire preparation process can be carried out at room temperature, and the temperature of the room temperature is, for example, 15 to 45 °C, and further can be 20 to 40 °C. The materials of the present invention can be prepared under mild conditions, and the properties of the prepared materials are excellent.

[0024] The present invention also provides an application of the NiOOH-Co(OH)2 composite electrode active material, which is used as an electrode active material for preparing a supercapacitor.

[0025] In the present invention, based on existing means, the supercapacitor can be prepared from the active material described in the present invention.

[0026] The present invention also provides a supercapacitor electrode, including a current collector and an electrode material compounded on its surface, and the electrode material contains the NiOOH-Co(OH)2 composite electrode active material.

[0027] Preferably, the electrode material further contains a binder and a conductive agent;

[0028] Preferably, in the electrode material, the content of the NiOOH-Co(OH)2 composite electrode active material is 75 to 90 wt%;

[0029] Preferably, the current collector is at least one of a foam metal and a carbon material;

[0030] Preferably, the foam metal is foam nickel.

[0031] The present invention also provides a supercapacitor, including the electrode containing the active electrode material described in the present invention.

[0032] Beneficial effects

[0033] The present invention provides a NiOOH-Co(OH)2 composite electrode active material, which can synergistically improve the performance of the supercapacitor based on a new action mechanism. Brief description of the drawings

[0034] Figure 1 It is a schematic diagram of the preparation process of four samples of NiOOH-Co(OH)2, Ni(OH)2-Co(OH)2, Ni(OH)2-CoOOH and NiCoOOH ((Example 1, Comparative Examples 1 to 3)) in the present invention;

[0035] Figure 2 It is the XRD pattern of the samples prepared in Example 1 and Comparative Examples 1 to 3;

[0036] Figure 3TEM images of the samples prepared in Example 1 and Comparative Examples 1-3, where a, b, c, and d are the morphology, SAED, and HRTEM images of NiOOH-Co(OH)2, respectively; e, f, g, and h are the morphology, SAED, and HRTEM images of Ni(OH)2-Co(OH)2, respectively; i, j, k, and l are the morphology, SAED, and HRTEM images of Ni(OH)2-CoOOH, respectively; m, n, o, and p are the morphology, SAED, and HRTEM images of NiCoOOH, respectively;

[0037] Figure 4 Raman spectra of the samples prepared in Example 1 and Comparative Examples 1-3;

[0038] Figure 5 XPS spectra of the samples prepared in Example 1 and Comparative Examples 1-3, where a is the spectrum of Co 2p, b is the spectrum of Ni 2p, and c is the spectrum of O 1s;

[0039] Figure 6 CV curves of four samples (Example 1 and Comparative Examples 1-3) at a scan rate of 5 mV s -1 ;

[0040] Figure 7 Galvanostatic charge-discharge curves of four samples (Example 1 and Comparative Examples 1-3) at 1 A g -1 ;

[0041] Figure 8 Specific mass capacitance diagrams of four samples (Example 1 and Comparative Examples 1-3) at different current densities;

[0042] Figure 9 Cycling life curves of four samples (Example 1 and Comparative Examples 1-3) at a current density of 2 A g -1 ;

[0043] Figure 10 Electrochemical impedance spectroscopy diagrams of four samples (Example 1 and Comparative Examples 1-3). Detailed implementation manners

[0044] The technical solutions of the present invention will be further described below in conjunction with the detailed implementation manners, but the present invention is not limited thereto.

[0045] Unless otherwise specified, the temperature in the following synthesis process is room temperature, such as 20-40 °C.

[0046] Preparation of NiOOH-Co(OH)2 in Example 1

[0047] Nickel foam (size 1×1 cm 2)The nickel foam (NF) was ultrasonically treated with 1 M HCl solution for 1 min to remove the possible oxide layer, and then ultrasonically treated with ethanol and deionized water for 1 min and 5 min respectively to remove organic pollutants and water-soluble impurities, obtaining the pretreated nickel foam (NF). 0.3943 g of NiSO4·6H2O was dissolved in 50 mL of deionized water, and 7.5 mL of (NH4)S2O8 solution (0.1 M) was added dropwise over 1 h in order to just oxidize Ni 2+ to Ni 3+ . Then 0.9839 g of CoSO4·7H2O was added, and 23 mL of NaOH solution (0.5 M) was added dropwise over 2 h, finally forming NiOOH-Co(OH)2, with continuous stirring during the process. The obtained solution was centrifuged and washed until neutral, and then dried.

[0048] The NiOOH-Co(OH)2 prepared above was mixed with acetylene black and PVDF in a ratio of 8:1:1 in N-methylpyrrolidone (NMP) to form a paste, which was coated on a clean nickel foam (NF, 1×1 cm 2 ) and dried in vacuum at 60 °C for 10 h to obtain NiOOH-Co(OH)2@NF, with a loading amount of 1.5 mg cm -2 .

[0049] Preparation of Comparative Example 1 Ni(OH)2-Co(OH)2

[0050] The nickel foam was obtained by pretreatment as in Example 1. After mixing 0.3943 g of NiSO4·6H2O and 0.9839 g of CoSO4·7H2O, they were dissolved in 50 mL of deionized water, and 20 mL of NaOH solution (0.5 M) was added dropwise over 2 h, finally forming Ni(OH)2-Co(OH)2, with continuous stirring during the process. The obtained solution was centrifuged and washed until neutral, and then dried.

[0051] NiOOH-Co(OH)2 in Example 1 was changed to Ni(OH)2-Co(OH)2 to prepare Ni(OH)2-Co(OH)2@NF, with a loading amount of 1.5 mg cm -2 .

[0052] Preparation of Comparative Example 2 Ni(OH)2-CoOOH

[0053] The nickel foam was obtained by pretreatment as in Example 1. 0.9839 g of CoSO4·7H2O was dissolved in 50 mL of deionized water, and 17.5 mL of (NH4)S2O8 solution (0.1 M) was added dropwise over 1 h in order to just oxidize Co 2+ to Co 3+. Then add 0.3943 g of NiSO4·6H2O, and dropwise add 27 mL of NaOH solution (0.5 M) over 2 h. Finally, Ni(OH)2-CoOOH is formed, and it is kept under stirring during the process. The obtained solution is centrifuged and washed until neutral, and then dried.

[0054] Change NiOOH-Co(OH)2 in Example 1 to Ni(OH)2-CoOOH to prepare Ni(OH)2-CoOOH@NF with a loading amount of 1.5 mg cm -2 .

[0055] Preparation of NiCoOOH in Comparative Example 3

[0056] The nickel foam is pretreated as in Example 1. After mixing 0.3943 g of NiSO4·6H2O and 0.9839 g of CoSO4·7H2O, they are dissolved in 50 mL of deionized water, and 25 mL of (NH4)S2O8 solution (0.1 M) is dropwise added over 1 h to just oxidize Ni 2+ , Co 2+ to Ni 3+ , Co 3+ . Then 30 mL of NaOH solution (0.5 M) is dropwise added over 2 h, and finally NiCoOOH is formed, and it is kept under stirring during the process. The obtained solution is centrifuged and washed until neutral, and then dried.

[0057] Change NiOOH-Co(OH)2 in Example 1 to NiCoOOH to prepare NiCoOOH@NF with a loading amount of 1.5 mg cm -2 .

[0058] The preparation flowcharts of the 4 examples are as Figure 1 shown.

[0059] To analyze the phase and crystal structure of the obtained products, Figure 2 shows the XRD patterns of NiOOH-Co(OH)2, Ni(OH)2-Co(OH)2, Ni(OH)2-CoOOH, and NiCoOOH. Among them, the NiOOH-Co(OH)2 sample exhibits typical hexagonal α-Co(OH)2 (labeled as JCPDS No. 46-0605) and hexagonal γ-NiOOH (labeled as JCPDS No. 06-0075). The other three samples respectively show the corresponding β-Co(OH)2 (labeled as JCPDS No. 51-1731), Ni(OH)2 (labeled as "*", JCPDS No. 38-0715), and CoOOH (labeled as Characteristic peaks of JCPDS No. 73-1213

[0060] Subsequently, in order to obtain the morphology of the samples, transmission electron microscopy (TEM) tests were further carried out. Figure 3 a, e, i, m are TEM images of four samples, and their shapes are all granular. From the SAED patterns and high-resolution images of NiOOH-Co(OH)2 ( Figure 3 b and c, d), the samples show clear lattice spacings of 0.210 nm and 0.242 nm, which belong to the (105) plane of NiOOH and the (105) plane of Co(OH)2, respectively. In addition, the SAED patterns show four distinct halo rings. The SAED patterns of NiOOH are (105) and (0017), and the SAED patterns of Co(OH)2 are (102) and (110), indicating the polycrystalline nature of the NiOOH-Co(OH)2 particles and further verifying the XRD results.

[0061] The TEM images of Ni(OH)2-Co(OH)2 are as Figure 3 shown in f-h, and the lattice spacings are 0.259 nm and 0.241 nm, which belong to the (012) plane of Ni(OH)2 and the (102) plane of Co(OH)2, respectively. In addition, the diffraction rings in the SAED patterns show the (018), (113) planes of Ni(OH)2 and the (102), (110) planes of Co(OH)2.

[0062] The TEM images of Ni(OH)2-CoOOH are as Figure 3 shown in i-l, and the lattice spacings are 0.224 nm and 0.239 nm, which belong to the (015) plane of Ni(OH)2 and the (012) plane of CoOOH, respectively. In addition, the diffraction rings in the SAED patterns show the (012), (110) planes of Ni(OH)2 and the (006), (113) planes of CoOOH.

[0063] The TEM images of NiCoOOH are as Figure 3 shown in m-p, and the lattice spacings are 0.209 nm and 0.225 nm, which belong to the (105) plane of NiOOH and the (012) plane of CoOOH, respectively. In addition, the diffraction rings in the SAED patterns show the (105), (110) planes of NiOOH and the (012) plane of CoOOH.

[0064] Raman spectroscopy was used to further analyze the structure and composition of the samples. Since Ni:Co = 3:7, the Raman spectra mainly show peaks related to Co. As Figure 4 shown, both NiOOH-Co(OH)2 and Ni(OH)2-Co(OH)2 are at 467 and 532 cm-1 Two main characteristic peaks appear at this position, which belong to the Eg mode and A in the O-M-O (M = Co) framework of typical Co(OH)2 respectively 1g mode. While the Eg and A of Ni(OH)2-CoOOH and NiCoOOH 1g modes are blue-shifted to 500 and 600 cm respectively -1 . This evolution implies the change of Co valence state from divalent to trivalent and the phase transformation of Co(OH)2 to CoOOH.

[0065] XPS technology was used to evaluate the elemental composition and oxidation state of the samples in detail. For the high-resolution Co 2p spectrum ( Figure 5 a), Ni(OH)2-CoOOH and NiCoOOH show that the content of the Co 3+ (≈66 / 68%) characteristic peak is much larger than that of the Co 2+ (≈34 / 32%) characteristic peak; NiOOH-Co(OH)2 and Ni(OH)2-Co(OH)2 show that the content of the Co 2+ (≈73%) characteristic peak is much larger than that of the Co 3+ (≈27%) characteristic peak. In addition, as Figure 5 shown in b, two characteristic peaks of Ni 2+ and Ni 3+ appear in the high-resolution Ni 2p spectrum. NiOOH-Co(OH)2 and NiCoOOH show that the content of the Ni 3+ (≈74 / 78%) characteristic peak is much larger than that of the Ni 2+ (≈26 / 22%) characteristic peak; Ni(OH)2-CoOOH and Ni(OH)2-Co(OH)2 show that the content of the Ni 2+ (≈60 / 63%) characteristic peak is much larger than that of the Ni 3+ (≈40 / 37%) characteristic peak. Correspondingly, NiOOH and CoOOH phases are generated, thus having M-O (M = Ni, Co) bonds. Therefore, the content of the M-O peak in the O1s spectrum of NiCoOOH is relatively high (18%). Since NiOOH-Co(OH)2 and Ni(OH)2-CoOOH each contain only one kind of MOOH, the content of the M-O peak is relatively low (11% and 12%). Ni(OH)2-Co(OH)2 does not generate M-O bonds, so the content is zero. The binding energies of the other two peaks from small to large are O-H bonds and adsorbed water ( Figure 5 c). The results show that NiOOH-Co(OH)2, Ni(OH)2-Co(OH)2, Ni(OH)2-CoOOH and NiCoOOH are successfully prepared, which is consistent with the results of XRD, TEM and Raman.

[0066] At 2 mol L-1 In a KOH solution, the electrochemical properties of these electrodes were studied through a three - electrode system (reference electrode: mercury oxide electrode; counter electrode: platinum mesh). First, the four electrodes were tested by cyclic voltammetry (CV) in a potential window from 0 V to 0.5 V at a scan rate of 5 mV s -1 . From Figure 6 it can be seen that due to the relatively large scan rate, the redox peaks shifted. By Figure 7 , compared with the other three electrodes, the charge - discharge time of the NiOOH - Co(OH)2 electrode was significantly prolonged. Through calculation, the specific mass capacitance at a current density of 1 A g -1 reached 742.9 F g -1 , which was much larger than that of Ni(OH)2 - Co(OH)2 (411.4 F g -1 ), Ni(OH)2 - CoOOH (454.3 F g -1 ), and NiCoOOH (188.6 F g -1 ). In addition, as the current density increased ( Figure 8 ), the decay of the specific mass capacitance of NiOOH - Co(OH)2 was smaller, showing better rate performance (39.2%), which was significantly better than that of Ni(OH)2 - Co(OH)2 (25.0%), Ni(OH)2 - CoOOH (18.9%), and NiCoOOH (27.3%). At the same time, after 2000 constant - current charge - discharge cycles at a current density of 2 A g -1 , the retention rate of its specific mass capacitance was as high as 70.7% ( Figure 9 ), lower than that of Ni(OH)2 - Co(OH)2 (76.2%) and higher than that of Ni(OH)2 - CoOOH (68.3%) and NiCoOOH (66.7%).

[0067] To further explore the key parameters affecting the electrode performance, electrochemical impedance spectroscopy (EIS) analysis was carried out at a potential of 5 mV in the frequency range of 1000 kHz to 0.01 Hz. As Figure 10As shown, the Nyquist plots of these electrodes exhibit a semicircle at high frequencies. The semicircle corresponds to the charge transfer resistance (Rct) associated with the redox reaction occurring at the electrode surface. The sizes of the semicircles in the EIS curves are in the order of Ni(OH)2-CoOOH > Ni(OH)2-Co(OH)2 > NiOOH-Co(OH)2 > NiCoOOH, indicating that the charge transfer rates at the interface between the active material and the electrolyte are Ni(OH)2-CoOOH < Ni(OH)2-Co(OH)2 < NiOOH-Co(OH)2 < NiCoOOH. The Nyquist plots of these electrodes show a straight line at low frequencies. The straight line connected to the semicircle represents the kinetic diffusion process occurring within the electrolyte in the electrode, known as the Warburg impedance (Zw). According to the literature, the steeper the straight line at low frequencies is perpendicular to the imaginary impedance axis, the closer the electrode is to the ideal capacitive behavior, which means a faster kinetics of the electrolyte diffusion process. The straight line of the NiOOH-Co(OH)2 electrode is the steepest, and the straight lines of the other electrodes are flatter. The results show that the NiOOH-Co(OH)2 electrode has the largest Warburg impedance and the fastest kinetic diffusion of the electrolyte.

[0068] In the present invention, NiSO4·6H2O was used as the nickel source, CoSO4·7H2O as the cobalt source, 0.1 M (NH4)S2O8 as the oxidant (the relevant reactions are shown in Equations 1, 2, 3, where M = Ni, Co), and 0.5 M NaOH as the precipitant (the relevant reactions are shown in Equations 4, 5), to prepare 4 kinds of active materials: NiOOH-Co(OH)2, Ni(OH)2-Co(OH)2, Ni(OH)2-CoOOH, and NiCoOOH. The capacitive characteristics of the materials are mainly based on their Faraday reactions. The Faraday reactions can be described by the following Equations 6 - 8:

[0069] S2O8 2- + M 2+ = ·SO4 - + M 3+ + SO4 2- (1)

[0070] ·SO4 - + M 2+ = M 3+ + SO4 2- (2)

[0071] S2O8 2- + 2M 2+ = 2M 3+ + 2SO4 2- (3)

[0072] M 2+ + 2OH -= M(OH)2 (4)

[0073] M 3+ + 3OH - = MOOH + H2O (5)

[0074]

[0075]

[0076]

[0077] The valence state of Co is richer than that of Ni, so the theoretical capacity is naturally higher. When the electro-oxidation reaction occurs, Co(OH)2 is oxidized to CoOOH and then further oxidized to CoO2. At this time, NiOOH gives the opportunity to Co(OH)2 and no reaction occurs. When the electro-reduction reaction occurs, CoO2 is reduced to CoOOH and then further reduced to Co(OH)2, and NiOOH is also reduced to Ni(OH)2. The rich redox reactions make the sample NiOOH-Co(OH)2 have the highest capacity. In the Ni(OH)2-CoOOH sample, the reaction route with less CoOOH and the oxidation reaction of Ni(OH)2 result in Ni(OH)2-CoOOH having a lower capacity. Ni(OH)2-Co(OH)2 also has a lower capacity due to the oxidation reaction of Ni(OH)2. And the reaction route with less NiCoOOH results in the lowest capacity.

[0078] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art to which the present invention pertains can also make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor, characterized in that, The nickel source and the oxidant are subjected to oxidation treatment, and then mixed with the cobalt source, and alkali is added for coprecipitation treatment to obtain the product; The nickel source described is Ni 2+ water-soluble salt, and the oxidizing agent is persulfate.

2. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 1, characterized in that, The NiOOH-Co(OH)2 composite electrode active material of the supercapacitor described is a composite containing NiOOH-Co(OH)2.

3. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 2, characterized in that, The NiOOH is γ-NiOOH of the hexagonal crystal system, and the Co(OH)2 is α-Co(OH)2 of the hexagonal crystal system.

4. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 2, characterized in that, The Ni / Co molar ratio of the NiOOH and Co(OH)2 is 1:2 to 2.

5.

5. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 1, characterized in that, The described Ni 2+ The water-soluble salt is at least one of nickel sulfate, nickel acetate, and nickel nitrate.

6. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 1, characterized in that, The persulfate is ammonium persulfate.

7. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 1, characterized in that, The dosage of the oxidant is 0.9 to 1.1 times the theoretical molar amount for oxidizing Ni in the nickel source to Ni 2+ 3+ 3+ .

8. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 7, characterized in that, The molar ratio of the nickel source to the oxidant is 1:0.5 to 0.

55.

9. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 1, characterized in that, The cobalt source described above is Co 2+ water-soluble salt.

10. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 9, characterized in that, The Co 2+ water-soluble salt is at least one of cobalt sulfate, cobalt acetate, and cobalt nitrate.

11. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 9, characterized in that, The Ni / Co molar ratio in the nickel source and the cobalt source is 1:2 to 2.

5.

12. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 9, characterized in that, The alkali is at least one of sodium hydroxide and potassium hydroxide.

13. The preparation method of NiOOH-Co(OH)2 composite electrode active material for supercapacitor according to claim 9, characterized in that, The alkali is 1.5 to 3 times the theoretical molar amount for completely precipitating nickel and cobalt.

14. The preparation method of the NiOOH-Co(OH)2 composite electrode active material of the supercapacitor according to claim 9, characterized in that, The alkali is 2 to 2.5 times the total molar amount of nickel and cobalt.

15. The preparation method of the NiOOH-Co(OH)2 composite electrode active material of the supercapacitor according to claim 9, characterized in that, The temperature of the oxidation and coprecipitation processes is room temperature.

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