A carbon quantum dot / nickel hydroxide nanocomposite material, its preparation method and application

Abstract

This invention discloses a carbon quantum dot / nickel hydroxide nanocomposite material, its preparation method, and its application. Carbon quantum dots are dissolved in water to obtain a carbon quantum dot solution, and Ni(OH)₂ nanospheres are dissolved in water to obtain a Ni(OH)₂ nanosphere solution. The carbon quantum dot solution and Ni(OH)₂ nanosphere solution are mixed and stirred until homogeneous to obtain a mixed solution. Urea is dissolved in water and added to the mixed solution while stirring. The mixture is refluxed at 95–110°C for 12–60 h, cooled to room temperature, and finally centrifuged, washed, and dried to obtain the carbon quantum dot / nickel hydroxide nanocomposite material. The CQDs / Ni(OH)₂ electrochemical energy storage material obtained by this invention has a high specific surface area and pore volume, more active sites, and superior electrochemical performance. A digital clock and a thermo-hygrometer are connected in parallel and lit by connecting three ASCII arrays, and they remain operational for more than 45 minutes.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor materials, and particularly relates to a carbon quantum dot / nickel hydroxide nanocomposite material, its preparation method, and its application. Background Technology

[0002] The rapid development of electronic technology and the Internet of Things has greatly stimulated the demand for electricity. Currently, extensive research has been conducted on developing new, easy-to-use, and efficient electrochemical energy storage (EES) devices. Among these, supercapacitors (SCs) have become a focus due to their high power density, fast charge / discharge time, long cycle life, and low cost, promising to usher in an unprecedented era of energy storage. However, they still face the problem of low energy density caused by poor anode material performance. As a typical pseudocapacitive material, Ni(OH)₂ has received continuous attention due to its simple preparation, environmental friendliness, and high theoretical specific capacitance, mainly stemming from its rapid and reversible Faraday redox reaction on its surface. In fact, the actual specific capacitance of Ni(OH)₂ is far lower than the theoretical value due to its low conductivity, approximately 10⁻⁶. -17 S·cm -1 Recently, the combination of Ni(OH)2 nanoparticles with highly conductive materials (including metal nanoparticles, carbon nanotubes, graphene, and activated carbon) has attracted great interest from researchers. However, the improvement in capacitance is limited because the surface carbon nanosheets / nanotubes hinder the contact between Ni(OH)2 and the electrolyte, and the specific capacitance is reduced due to its poor capacitance performance.

[0003] Quantum dots, a novel zero-dimensional (0D) material, were discovered and synthesized by MG Bawendi, LEBrus, and AIEkimov. Carbon quantum dots (CQDs) possess advantages such as ease of modification, small size, good stability, and high conductivity, making them highly attractive for energy storage and conversion applications such as solar cells, ion batteries, and supercapacitors. Therefore, the introduction of nanoscale CQDs is expected to be an effective means of improving the conductivity of Ni(OH)₂ and enhancing its electrochemical performance. Recently, morphology engineering by regulating nanostructures and crystal structures has been considered an effective method for improving capacitance performance. A simple strategy for preparing three-dimensional Ni(OH)₂ nanospheres as electrode materials for supercapacitors has been reported, but its electrochemical performance is still limited by its less-than-ideal specific surface area. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a carbon quantum dot / nickel hydroxide nanocomposite material, its preparation method, and its applications.

[0005] This invention enables the construction of 3D Ni(OH)2 nanospheres into 2D carbon quantum dots / nickel hydroxide nanosheets, which can be used as anode materials for asymmetric supercapacitors. The CQDs / Ni(OH)2 composite material is prepared via a two-step method, which includes the synthesis of 3D Ni(OH)2 nanospheres and their morphological evolution into 2D Ni(OH)2 nanosheets in the presence of CQDs.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a carbon quantum dot / nickel hydroxide nanocomposite material includes the following steps:

[0008] (1) Carbon quantum dots were dissolved in water to obtain a carbon quantum dot solution, and Ni(OH)2 nanospheres were dissolved in water to obtain a Ni(OH)2 nanosphere solution.

[0009] (2) The carbon quantum dot solution and Ni(OH)2 nanosphere solution described in step (1) are mixed and stirred evenly to obtain a mixed solution. Then, urea is dissolved in water and added to the mixed solution while stirring. The mixture is refluxed at 95-110°C for 12-60 hours, cooled to room temperature, and finally obtained by centrifugation, washing and drying. The carbon quantum dot / nickel hydroxide nanocomposite material is denoted as CQDs / Ni(OH)2.

[0010] Preferably, in step (1), the Ni(OH)2 nanospheres are prepared with reference to the following literature: Zhang R, Tu Q, Li X, et al. Template-free preparation of α-Ni(OH)2 nanosphere as high-performance electron material for advanced supercapacitor[J]. Nanomaterials, 2022, 12(13): 2216.

[0011] Preferably, in step (1), the concentration of the Ni(OH)2 nanosphere solution is 0.018–0.09 mmol / mL.

[0012] Preferably, in step (1), carbon quantum dots are prepared according to the following steps: take 1.16 g (5.5 mmol) citric acid monohydrate and 0.7 g (5 mmol) cyclohexamethylenetetramine, then add 10 mL of water, stir until completely dissolved, transfer to a polytetrafluoroethylene liner, place in a reaction vessel, react at 200 °C for 5 h, cool to room temperature, take out, centrifuge at 8000 rad / min for 10 min, collect the filtrate, and freeze dry.

[0013] Preferably, in step (1), the concentration of the carbon quantum dot solution is 0.0068 to 0.053 mmol / mL.

[0014] Preferably, in step (2), the mass ratio of Ni(OH)2 in the Ni(OH)2 nanosphere solution to carbon quantum dots in the carbon quantum dot solution is 1:0.125~1.

[0015] Preferably, in step (2), the molar ratio of urea in the urea solution to Ni(OH)2 in the Ni(OH)2 nanosphere aqueous solution is 1:0.84 to 1.68.

[0016] Preferably, in step (2), the centrifugation rate is 5000 rad / min and the centrifugation time is 5 min.

[0017] Preferably, in step (2), the washing is performed until the solution is neutral.

[0018] Preferably, in step (2), the drying is freeze drying.

[0019] The above-mentioned carbon quantum dot / nickel hydroxide nanocomposite material is used in the preparation of supercapacitor anode materials.

[0020] Compared with the prior art, the beneficial effects of the present invention include:

[0021] (1) The CQDs / Ni(OH)2 described in this invention achieves complete adsorption of positively charged CQDs onto the surface of negatively charged Ni(OH)2 microspheres through electrostatic adsorption. Then, the 3D spherical structure is formed under excess OH... - Under the influence of the collapse, a large and thin 2D structure of CQDs / Ni(OH)2 nanoplates is formed, which has good electrochemical energy storage performance and excellent cycle stability.

[0022] (2) This invention yields CQDs / Ni(OH)2 electrochemical energy storage materials with high specific surface area and pore volume. It exhibits superior specific capacitance (up to 2040.0 F / g at a current density of 2 A / g) and long cycle life (retaining 112.3% after 5000 cycles at 20 A / g). Furthermore, the assembled CQDs / Ni(OH)2 / / AC asymmetric capacitor possesses high specific capacitance (169.6 F / g at a current density of 1 A / g), significant energy density (56.6 Wh / kg at 775.0 W / kg), and excellent cycle stability (84.0% after 10000 cycles), surpassing most Ni(OH)2-based supercapacitors. A digital clock and a thermo-hygrometer were connected in parallel and powered by connecting three ASCs in series, maintaining their operation for over 45 minutes. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation process of CQDs / Ni(OH)2 according to the present invention.

[0024] Figure 2 The figure shows the Zeta potential data for Ni(OH)2 and CQDs.

[0025] Figure 3 This is a scanning electron microscope image of CN-2.

[0026] Figure 4 Electron microscopy image (7 μm) of the CN-0 formation process.

[0027] Figure 5 Electron microscopy image (40 μm) of the CN-0 formation process.

[0028] Figure 6 This is a scanning electron microscope image (7 μm) of CN-1.

[0029] Figure 7 This is a scanning electron microscope image (40 μm) of CN-1.

[0030] Figure 8 This is a scanning electron microscope image (7 μm) of CN-3.

[0031] Figure 9 This is a scanning electron microscope image (40 μm) of CN-3.

[0032] Figure 10 XRD diffraction patterns of CQDs, CN-2, CN-O and α-Ni(OH)2.

[0033] Figure 11 The XRD diffraction patterns are for CN-1, CN-2, and CN-3.

[0034] Figure 12 The electrode rate performance curves for CN-0, CN-1, CN-2, and CN-3 are shown.

[0035] Figure 13 The cyclic stability diagrams for CN-2 and CN-0 after 10,000 cycles at a current density of 20 A / g are shown.

[0036] Figure 14 This is a schematic diagram of the ASC device assembly.

[0037] Figure 15 This is a bar chart comparing the specific capacitance and speed performance of the ASC device (CN-2 as the positive electrode) under different current densities.

[0038] Figure 16 Lagon plot showing the relationship between energy density and power density of different ASC devices.

[0039] Figure 17 The graph shows the cycle stability and coulombic efficiency performance of the ASC device (CN-2 as the positive electrode) after 10,000 cycles at 15 A / g.

[0040] Figure 18 CV curves for one, two, and three cascaded ASC devices (CN-2 as the positive electrode).

[0041] Figure 19 GCD curves for one, two, and three cascaded ASC devices (CN-2 as the positive electrode).

[0042] Figure 20 Circuit diagrams for one, two, and three ASCII devices connected in series (CN-2 as the positive terminal).

[0043] Figure 21 A photograph showing how three ASCII devices (CN-2 as the positive terminal) are connected in series to provide synchronous power to a digital clock and a thermometer / hygrometer. Detailed Implementation

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] The Ni(OH)2 nanospheres described in the examples were prepared with reference to the following literature: Zhang R, Tu Q, Li X, et al. Template-free preparation of α-Ni(OH)2 nanosphere as high-performance electron material for advanced supercapacitor[J]. Nanomaterials, 2022, 12(13): 2216.

[0046] The carbon quantum dots were prepared according to the following steps: 1.16 g (5.5 mmol) of citric acid monohydrate and 0.7 g (5 mmol) of cyclohexamethylenetetramine were taken, and then 10 mL of water was added. The mixture was stirred until completely dissolved, transferred to a polytetrafluoroethylene liner, placed in a reaction vessel, and reacted at 200 °C for 5 h. After cooling to room temperature, the mixture was removed, centrifuged at 8000 rad / min for 10 min, and the filtrate was collected and freeze-dried.

[0047] Example 1

[0048] A method for preparing a carbon quantum dot / nickel hydroxide nanocomposite material, comprising the following steps:

[0049] (1) Dissolve 0.0097 g (0.8 mmol) of carbon quantum dots in 60 mL of water to obtain a carbon quantum dot solution; dissolve 0.3 g of Ni(OH)2 nanospheres in 60 mL of water to obtain a Ni(OH)2 nanosphere solution;

[0050] (2) The Ni(OH)2 nanosphere solution and carbon quantum dot solution were transferred to a 150 mL single-necked flask and stirred for 1 h to obtain a mixed solution. Then, 0.1935 g (3.2 mmol) of urea was dissolved in 30 mL of water and added to the mixed solution while stirring. The mixture was dynamically refluxed at 105 °C for 24 h, cooled to room temperature, and then centrifuged at 5000 rad / min for 5 min, washed until neutral, and freeze-dried to obtain the carbon quantum dot / nickel hydroxide nanocomposite material, denoted as CN-2.

[0051] Example 2

[0052] Except for the carbon quantum dots mentioned in step (1) having a mass of 0.0049g, the other steps are the same as in Example 1, and the prepared product is denoted as CN-1.

[0053] Example 3

[0054] Except for the carbon quantum dots mentioned in step (1) having a mass of 0.0193g, the other steps are the same as in Example 1, and the prepared product is denoted as CN-3.

[0055] Comparative Example 1

[0056] Without adding carbon quantum dot solution, the remaining steps are the same as in Example 1, and the final product is denoted as CN-0.

[0057] Fabrication of asymmetric CQDs / Ni(OH)2 / / AC (AC represents activated carbon) supercapacitor

[0058] An asymmetric supercapacitor (ASC) was assembled on a CR2032 coin cell, wherein a mixture of 80 wt% CQD / Ni(OH)2, 10 wt% acetylene black, and 10 wt% PVDF emulsion was coated onto a circular nickel foam (12 mm in diameter) as the positive electrode. Similarly, an emulsion of 80 wt% activated carbon, 10 wt% acetylene black, and 10 wt% PTFE was formulated and deposited onto a circular nickel foam (12 mm in diameter) as the negative electrode. Furthermore, a nonwoven membrane and a 6 mol / L KOH solution were used as the separator and electrolyte, respectively. Note that the ASC in this invention was sealed using an MSK-160E coin cell sealing machine (HF Kejing, China).

[0059] Figure 1 This is a schematic diagram of the preparation process of CQDs / Ni(OH)2 according to the present invention. Figure 1It can be seen that the preparation process of CQDs / Ni(OH)2 can be summarized into two parts: the first part is the synthesis of Ni(OH)2, and the second part is the process of obtaining CQDs / Ni(OH)2 composite through electrostatic adsorption between positive and negative charges of CQDs and Ni(OH)2.

[0060] Figure 2 and Figure 3 The images show the Zeta potential data for Ni(OH)2 and CQDs, and the scanning electron microscope image of CN-2, respectively. Figure 2 and 3 It can be concluded that, due to the opposite charge properties of the surface groups, negatively charged CQDs (Zeta potential ~ -22.1 mV) are completely adsorbed onto the positively charged Ni(OH)2 surface (Zeta potential ~ 3.4 mV) through Coulomb interactions. Simultaneously, due to excess OH... - Under the influence of ions, the spherical structure collapses, and the CQDs / Ni(OH)2 nanoplates become larger and thinner.

[0061] Figure 4 and Figure 5 The images are scanning electron microscope (SEM) images of the formation process of CN-0, from... Figure 4 and Figure 5 It can be seen that in CN-0, the spherical Ni(OH)2 dissolves and is replaced by a layered structure, but due to incomplete growth, a small portion of undissolved nanospheres are still retained.

[0062] Figure 6 and Figure 7 Scanning electron microscope images of CN-1, from Figure 6 and Figure 7 It can be seen that this situation is greatly improved after the addition of CQDs, and larger nanosheets can be observed in the figure.

[0063] Figure 8 and Figure 9 The scanning electron microscope (SEM) spectrum of CN-3 is shown below. Figure 8 and Figure 9 It can be observed that with the increase of CQDs added, the nanosheets become more complete and thinner due to the dispersion of CQDs with opposite charges, and in CN-2 ( Figure 3 The preferred sheet-like structure was achieved in CN-3. However, when the amount added reached CN-3, the growth of nanosheets was inhibited and they adhered to each other due to the excessive CQDs on the surface.

[0064] Figure 10 and Figure 11 XRD diffraction patterns of CQDs, CN-2, CN-1, CN-O, and α-Ni(OH)2, from Figure 10 and Figure 11It can be seen that the Ni(OH)2 diffraction peaks are located at 2θ = 12.4°, 25.0°, 33.4°, 36.5°, and 59.4°, which have good indexing relationships with the (003), (006), (101), (015), and (110) planes of the rhombic α-Ni(OH)2 (JCPDS Card No. 38-0715) lattice. Notably, several peaks centered at 2θ = 16.2°, 21.4°, 52.4°, and 59.4° in the CN-0 mode correspond to the (011), (-102), (-243), and (011) planes of the monoclinic Ni5(CO3)4(OH)3·4.5H2O (JCPDS Card No. 46-1398) crystal plane, indicating that nickel carbonate tetrahydrate underwent partial transformation after 24 h of reaction. For the CQDs samples, the broad peak at ~2θ = 24.8° is attributed to the highly disordered carbon atoms. More importantly, apart from the small shift at 2θ, the CN-2 composite material actually inherits the characteristic peaks of CN-0, while the characteristic peaks of CQDs are absent in all CQDs / Ni(OH)2 composites, which may be due to insufficient CQDs content on the Ni(OH)2 nanosheet surface. Furthermore, the (003) lattice plane intensities of the CQDs / Ni(OH)2 series products differ, attributed to variations in the amount of CQDs added.

[0065] The electrochemical performance of the electrodes was evaluated using a three-electrode system consisting of a working electrode (CN-0, CN-1, CN-2, and CN-3), a reference electrode (HgO), and an auxiliary electrode (platinum sheet electrode).

[0066] Figure 12 The rate performance curves for electrodes CN-0, CN-1, CN-2, and CN-3 are shown below. Figure 12 It can be seen that, at any current density, the capacitance performance of CQDs / Ni(OH)2 is superior to that of the original Ni(OH)2, confirming the synergistic effect between CQDs and Ni(OH)2. More importantly, compared with CN-1 (1265.5 F / g) and CN-3 (1578.5 F / g) electrodes, the CN-2 electrode achieves a specific capacitance of 2040.0 F / g at 2 A / g.

[0067] Figure 13 The graph shows the cycle stability of CN-2 and CN-0 after 10,000 cycles at a current density of 20 A / g. The inset shows the GCD curves after 5 cycles before and after cycling. Figure 13It can be seen that the capacitance on the CN-2 electrode increases slightly with the increase of the number of cycles, which may be due to the increase in active sites activated by the electrochemical process. Therefore, after 5000 cycles, the shape of the GCD curve remains good, and the capacitance retention rate of the CN-2 electrode is as high as ~112.3%, which is much higher than that of Ni(OH)2 (~44.4%).

[0068] Figure 14 This is a schematic diagram of the ASCII device assembly. Figure 14 It can be seen that: CN-2 is used as the positive electrode, AC as the negative electrode, and 6mol / L KOH is used as the electrolyte. The asymmetric button supercapacitor is assembled in the following order: negative electrode shell, spring, gasket, negative electrode, separator, positive electrode, gasket, and positive electrode shell.

[0069] Figure 15 This is a bar chart comparing the specific capacitance and speed performance of the ASC device (CN-2 as the positive electrode) at different current densities. Figure 15 It can be seen that the specific capacitance of CQDs / Ni(OH)2 / / AC ASC at a current density of 1A / g is 169.6F / g. When the current density increases to 15A / g, the specific capacitance still remains at about 55.5% of the initial capacitance, which shows excellent rate performance.

[0070] Figure 16 Lagon plots relating energy density and power density to different ASC devices, where the anode material in the CQDs / Ni(OH)2 / / AC ASC is CQDs / Ni(OH)2(CN-2), from... Figure 16 It can be seen that CQDs / Ni(OH)2 / / AC ASC achieves a maximum energy density of 56.6 Wh / kg at a power density of 775.0 W / kg, and the power density can reach 11625.0 W / kg when the energy density is as high as 31.4 Wh / kg, which is better than the reported Ni(OH)2-based supercapacitors.

[0071] Figure 16 The NF / Ni(OH)2 / PEDOT / / NF / CNTs ASC is derived from:

[0072] J.Song,W.Li,J.Xin,W.Wang,K.Song,X.Chen,G.Yin,Ni(OH)2 / PEDOT“skeleton / skin”structural composite electrode improves electrochemical performance forasymmetric supercapacitors,Ionics.27(2021)4047-4056.

[0073] AC / / Ni(OH)2 / EG ASC solvent:

[0074] R. Qu, S. Tang, X. Qin, J. Yuan, Y. Deng, L. Wu, J. Li, Z. Wei, Expanded graphitesupported Ni(OH)2composites for high performance supercapacitors,Journal ofAlloys and Compounds.728(2017)222-230.

[0075] Ni(OH)2 / f-XC-72 / / AC ASC solvent:

[0076] X. Qin, S. Tang, J. Yuan, Y. Deng, R. Qu, L. Wu, J. Li,Enhanced performances offunctionalized XC-72supported Ni(OH)2composites for supercapacitors,NewJournal of Chemistry.41(2017)11372-11382.

[0077] Ni(OH)2 / AC / CNT / / AC AS:

[0078] L. Sui, S. Tang, Y. Chen, Z. Dai, H. Huangfu, Z. Zhu, X. Qin, Y. Deng, G. Haarberg, An asymmetric supercapacitor with good electrochemical performances based on Ni(OH)2 / AC / CNT and AC, Electrochimica Acta.182(2015)1159-1165.

[0079] rGO / / rGO-Ni(OH)2ASC catalyst:

[0080] BJReddy,P.Vickraman,ASJustin,Moringa oleifera Leaf ExtractMediated Reduced Graphene Oxide / α-Ni(OH)2Nanocomposite for AsymmetricSupercapacitors,Brazilian Journal of Physics.49(2019)348-359.

[0081] MWCNTs-GONRs / Ni(OH)2 / / AC ASC solvent:

[0082] H.Qiu,S.An,X.Sun,H.Yang,Y.Zhang,W.He,Excellent performance MWCNTs-GONRs / Ni(OH)2 electrode for outstanding supercapacitors,CeramicsInternational.45(2019)18422-18429.

[0083] Ni(OH)2 / CNTs / / AC FSC solvent:

[0084] Q. Qin, J. Liu, W. Mao, C. Xu, B. Lan, Y. Wang, Y. Zhang, J. Yan, Y. Wu, Ni(OH)2 / CNTshierarchical spheres for a foldable all-solid-state supercapacitor with highspecific energy,Nanoscale.10(2018)7377-7381.

[0085] AC / / Co(OH)F / Ni(OH)2ASC solvent:

[0086] X. Li, R. Ding, W. Shi, Q. Xu, D. Ying, Y. Huang, E. Liu, Hierarchical porous Co(OH)F / Ni(OH)2:A new hybrid for supercapacitors,Electrochimica Acta.265(2018)455-473.

[0087] Ni3S2 / Ni(OH)2 / / AC ASC originates from:

[0088] X. Pan, L. Zhao, H. Liu, M. Guo, C. Han, W. Wang, Hierarchical structure Ni3S2 / Ni(OH)2 nanoarrays towards high-performance supercapacitors, Journal of SolidState Chemistry.309(2022)122974.

[0089] NiSe / Ni(OH)2 / / AC ASC originates from:

[0090] L.He, Y.Wang, Y.Guo, G.Li,

[0091] Figure 17 The graph shows the cycle stability and coulombic efficiency performance of the ASC device (CN-2 as the positive electrode) after 10,000 cycles at 15 A / g. Figure 17 It can be seen that after 5000 cycles, the capacitance loss of ASC is very small, approximately 12.0% of the original capacitance. After 10000 cycles, the final capacitance retention is approximately 84.0%, demonstrating excellent cycle stability. Meanwhile, the coulombic efficiency remains close to 100% throughout, indicating good matching of positive and negative electrode quality.

[0092] Figures 18-20 The CV and GCD curves and circuit diagrams for one, two, and three ASCII devices connected in series (CN-2 as the positive electrode) are provided. Figures 18-20 It can be seen that when two ASCs are connected in series, the operating potential window can easily be extended to 3.10V, while when three ASCs are connected in series, the operating potential window is enhanced to 4.65V.

[0093] Figure 21 A photograph showing the synchronous power supply of a digital clock and a thermometer / hygrometer via three ASCII devices connected in series (CN-2 as the positive terminal). Figure 21It can be seen that connecting a 3.0V digital clock and a 4.5V hygrometer in parallel, driven simultaneously by a series-connected ASC, allows for a lighting time of over 30 minutes, and the digital clock continues to operate after 45 minutes. These results further demonstrate the enormous potential of CQDs / Ni(OH)2 / AC ASCs in the fields of energy conversion and storage.

[0094] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a carbon quantum dot / nickel hydroxide nanocomposite material, characterized in that, Includes the following steps: (1) Carbon quantum dots are dissolved in water to obtain a carbon quantum dot solution. In addition, Ni(OH)2 nanospheres are dissolved in water to obtain a Ni(OH)2 nanosphere solution. (2) Mix the carbon quantum dot solution and Ni(OH)2 nanosphere solution described in step (1) and stir evenly to obtain a mixed solution. Then, dissolve urea in water and add it to the mixed solution while stirring. Reflux at 95~110℃ for 12~60h, cool to room temperature, and finally obtain the carbon quantum dot / nickel hydroxide nanocomposite material after centrifugation, washing and drying. The carbon quantum dots were prepared according to the following steps: citric acid monohydrate and cyclohexamethylenetetramine were taken, then water was added and stirred until completely dissolved. The mixture was transferred to a polytetrafluoroethylene liner, placed in a reaction vessel, and reacted at 200°C for 5 hours. After cooling to room temperature, the mixture was removed, centrifuged for 10 minutes, the filtrate was collected, and then freeze-dried.

2. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 1, characterized in that, The concentration of the Ni(OH)2 nanosphere solution in step (1) is 0.018~0.09 mmol / mL.

3. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 2, characterized in that, The concentration of the carbon quantum dot solution in step (1) is 0.0068~0.053 mmol / mL.

4. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to any one of claims 1 to 3, characterized in that, In step (2), the mass ratio of Ni(OH)2 in the Ni(OH)2 nanosphere solution to carbon quantum dots in the carbon quantum dot solution is 1:0.125~1.

5. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 4, characterized in that, In step (2), the molar ratio of urea in the urea solution to Ni(OH)2 in the Ni(OH)2 nanosphere aqueous solution is 1:0.84~1.

68.

6. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to any one of claims 1 to 3, characterized in that, In step (2), the centrifugation rate is 5000 rad / min and the centrifugation time is 5 min.

7. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 6, characterized in that, The washing described in step (2) is washing until neutral.

8. The method for preparing the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 7, characterized in that, The drying process described in step (2) is freeze drying.

9. The carbon quantum dot / nickel hydroxide nanocomposite material prepared by the preparation method of any one of claims 1 to 8.

10. The application of the carbon quantum dot / nickel hydroxide nanocomposite material according to claim 9 in the preparation of anode materials for supercapacitors, characterized in that, The process includes the following steps: assembling an asymmetric supercapacitor (ASC) onto a CR2032 coin cell, wherein 80 wt% CQD / Ni(OH)2, 10 wt% acetylene black, and 10 wt% PVDF emulsion are mixed and coated onto a circular nickel foam as the positive electrode; and an emulsion of 80 wt% activated carbon, 10 wt% acetylene black, and 10 wt% PTFE is prepared and deposited onto another circular nickel foam as the negative electrode, wherein the diameter of the two circular nickel foams is 12 mm.

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