Nanometer flower-shaped NiCo-LDH-NaAc and preparation method and application thereof

Abstract

The invention discloses nano flower-shaped NiCo-LDH-NaAc, which is prepared by the following steps: by taking nickel nitrate and cobalt nitrate as raw materials, sodium acetate trihydrate NaAc. 3H2O as a precipitator and deionized water as a solvent, preparing the nano flower-shaped NiCo-LDH-NaAc through a hydrothermal method; the microtopography of the NiCo-LDH-NaAc is of a nano flower-shaped structure composed of thin nanosheets which are irregular in self-assembly and have the size of 1-3 [mu] m. The preparation method comprises the following steps: firstly, dissolving Ni (NO3). 6H2O and Co (NO3). 6H2O in deionized water to obtain a mixed solution, then, adding sodium acetate NaAc. 3H2O into the mixed solution, stirring and dissolving to obtain a reaction solution, finally, carrying out hydrothermal reaction, and washing and drying the obtained product to obtain the nano flower-shaped NiCo-LDH-NaAc. When the NiCo-LDH-NaAc composite material is used as a supercapacitor electrode material, the charge and discharge voltage range is 0-0.5 V, and when the discharge current density is 1A g <-1 >, the specific capacitance of NiCo-LDH-NaAc is 1900-2112F g <-1 >; when the number of cycles is 5000, the capacitance retention rate of the NiCo-LDH-NaAc is 70%-80%, and the coulombic efficiency of the NiCo-LDH-NaAc is 98%-100%.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitors, and particularly to a nanoflower-like NiCo-LDH-NaAc, a preparation method thereof, and an application thereof. Background Art

[0002] Among the active materials of supercapacitors, layered double hydroxide (LDH) has the characteristic of multiple valence states of metal centers, and can promote electron transfer through reversible redox reactions, thereby achieving the effect of efficient electrochemical charge storage. Among them, nickel-cobalt layered double hydroxide (NiCo-LDH) further has a hexagonal crystal system structure, layered stacked octahedral units, and the presence of hydroxide ions, so it has good hydrophilicity, which can improve the contact between the electrolyte and the material and further improve the electrochemical performance.

[0003] The basic structural characteristics of NiCo-LDH determine that during the preparation of NiCo-LDH, anions and water molecules will be inserted into its interlayer structure. This phenomenon directly has the following two aspects of influence: 1. The inserted anions and water molecules act as supporting substances in the structure, thereby inhibiting the dense stacking of the interlayer structure and finally achieving the effect of improving the structural stability; 2. Inserting anions and water molecules can balance the charge in the material, form a charge center through anions, and promote the storage and release of ions during the energy storage process. Therefore, by changing the interlayer anions, the interlayer distance and the chemical composition of the main layer can be regulated, thereby improving the electrochemical performance. For example, the prior art 1 (Wenxuan H, Lu C, Biao G, et al. Effect of intercalated anion in nickel-cobalt-layered double hydroxide on its supercapacitive properties[J]. Chemical Engineering Journal, 2023, 468) synthesized NiCo-LDH-MoO4 with molybdate MoO4 2- as the intercalated anion on a carbon cloth substrate. The surface of the carbon cloth is a vertical nanosheet array. When the current density is 1 A g -1 , the specific capacitance is 576 C g -1 , and after 20,000 cycles, the capacity retention rate is 80%. MoO4 2-Intercalation expands the layer spacing of NiCo-LDH from 0.73 nm to 0.96 nm, providing a larger ion diffusion channel, reducing the diffusion resistance, increasing the specific surface area, and significantly enhancing the specific capacity. However, due to the use of a vertical nanosheet array structure in this technical solution, there is a problem that the internal active sites in the vertical part cannot be fully wetted by the electrolyte due to the stacking of nanosheets, resulting in "dead volume" and ultimately insufficient charge storage capacity, that is, the problem that the internal active sites cannot be exposed.

[0004] To solve the problem that the internal active sites cannot be exposed due to the vertical stacking of nanosheets, a structure-directing agent can be added to regulate the microtopography, control the crystal growth direction, and then enable the active sites to be fully wetted by the electrolyte, ultimately achieving the effect of improving the ion diffusion efficiency. For example, in the prior art 2 (Zhang Q, Wang S, Lan Y, et al. Enhancing supercapacitor electrochemical performance through acetate-ion intercalation in layered nickel-cobalt double hydroxides[J]. Journal of Colloid And Interface Science, 2024, 660597-607.), nickel-cobalt layered double hydroxide intercalated with acetate ions was prepared by a solvothermal method. When the current density is 1 A g -1 -1, the specific capacity is 1032.2 F g -1 -1, and the capacitance retention rate is 82.8% after 3000 cycles. The microtopography is a composite morphology of square crystal nanoparticles and spherical nanoparticles. The acetate ions act as a structure-directing agent to form a dense three-dimensional block structure of the material. The three-dimensional block structure obtained by this technical solution is conducive to the full wetting of the electrolyte and can effectively improve the structural stability and thermal stability. However, the precipitating agent used in this technical solution is urea. This technical feature directly leads to the decomposition of urea and the release of CO2 and NH3 during the high-temperature decomposition process. In addition to directly causing environmental problems, more importantly, CO2 will form carbonate ions CO3 2- 2-, competing with acetate ions for the interlayer position, thus affecting the uniform distribution of acetate ions in the interlayer and having a negative impact on the electrochemical performance. This technical problem is simply referred to as the anion competition problem.

[0005] To solve the problem that the by-products of the decomposition of urea as a precipitant lead to a decrease in electrochemical performance, that is, the anion competition problem, the most direct solution is not to use a precipitant. For example, in the prior art 3 (Wang G, Meng Y, Chi C, et al. Acetate ion-intercalated NiCo-LDH with quasi-theoretical capacitance for high energy / power density aqueous supercapacitors [J]. Inorganic Chemistry Frontiers, 2024, 11(3): 863-873.), the solvothermal method was used to obtain Ni 0.7 Co 0.3 -LDH. When the current density is 1 A g -1 -1, the specific capacitance is 1026 C g -1 -1, and the capacitance retention rate is 72% after 6000 cycles. Acetate is used as the metal source and methanol is the main solvent. In this technical solution, no precipitant is used, but the strong solvation ability of methanol is utilized to promote the insertion of acetate ions into the layered structure, so as to prevent other anions from entering the interlayer to compete with acetate ions, and finally realize the role of acetate ions, that is, to avoid the generation of anion competition problems. However, directly removing the necessary technical feature of the precipitant directly leads to the disappearance of the technical effects originally achieved by introducing the precipitant. Specifically, in the preparation method of this technical solution, the solvothermal method requires a reaction time of 72 hours to achieve the full growth of the layered structure and the stable intercalation of acetate ions, that is, there are technical problems of long synthesis time and high energy consumption. Summary of the Invention

[0006] The object of the present invention is to provide a nanoflower-like NiCo-LDH-NaAc, its preparation method and application. Based on the following invention principle, the technical problems existing in the current technical solution are solved. The specific principles involved are as follows:

[0007] 1. Sodium acetate is used as a precipitant. Sodium acetate hydrolyzes in aqueous solution to generate hydroxide ions and acetate ions. Among them, OH - reacts with Ni 2+ and Co 2+ ions to generate hydroxide monomers, which are co-deposited on the surface to form NiCo-LDH crystal nuclei, and further crystallize and grow to form a nanosheet structure;

[0008] 2. The layered structure is stabilized by the insertion of acetate ions between the layers to inhibit the stacking of flakes. Moreover, as a structure-directing agent, acetate ions regulate the crystal growth direction by adsorbing on specific crystal planes, promoting the self-assembly of two-dimensional nanosheets to form a three-dimensional nanoflower structure;

[0009] That is, in the present invention, sodium acetate not only achieves the technical effect of a precipitating agent, but also does not have the problem of anion competition caused by conventional precipitating agents.

[0010] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is as follows:

[0011] A nanoscale flower-like NiCo-LDH-NaAc is prepared from nickel nitrate and cobalt nitrate as raw materials, sodium acetate trihydrate NaAc·3H2O as a precipitating agent, and deionized water as a solvent through a hydrothermal method; the microscopic morphology of the NiCo-LDH-NaAc is a nanoscale flower-like structure, and the nanoscale flower-like structure is composed of self-assembled irregular thin nanosheets with a size of 1-3 μm.

[0012] A preparation method of a nanoscale flower-like NiCo-LDH-NaAc includes the following steps: First, dissolve Ni(NO3)·6H2O and Co(NO3)·6H2O in deionized water to obtain a mixed solution. Then, add sodium acetate NaAc·3H2O to the mixed solution and stir to dissolve to obtain a reaction solution. Finally, under certain conditions, perform a hydrothermal reaction on the reaction solution, and the obtained product is washed and dried to obtain the nanoscale flower-like NiCo-LDH-NaAc prepared with sodium acetate NaAc as a precipitating agent;

[0013] The addition amount of the NaAc·3H2O satisfies that the molar ratio of the elements Na:Ni:Co is 8:4:2;

[0014] The preparation conditions of the reaction solution are that the stirring time is 20-40 min;

[0015] The conditions of the hydrothermal reaction are that the hydrothermal temperature is 120-140 °C and the hydrothermal time is 10-12 h;

[0016] The conditions of the drying are that the drying temperature is 50-70 °C and the drying time is 11-13 h.

[0017] When the nanoscale flower-like NiCo-LDH-NaAc is used as a supercapacitor electrode material, the charge-discharge voltage range is 0-0.5 V. When the discharge current density is 1 A g -1 at this time, the specific capacitance of NiCo-LDH-NaAc is 1900-2112 F g -1 ; when the number of cycles is 5000 times, the capacitance retention rate of NiCo-LDH-NaAc is 70-80%, and the Coulomb efficiency is 98-100%.

[0018] The beneficial technical effects of the NiCo-LDH-NaAc material obtained by the present invention can be known through experimental detection:

[0019] XRD detection of the NiCo-LDH-NaAc material indicates that characteristic peaks of the NiCo-LDH diffraction crystal plane exist in NiCo-LDH-NaAc.

[0020] EDS detection of the NiCo-LDH-NaAc material indicates that Co element, Ni element, C element and O element are evenly distributed on the surface of the spherical NiCo-LDH-NaAc nanoflowers.

[0021] SEM detection of the NiCo-LDH-NaAc material indicates that the microscopic morphology of NiCo-LDH-NaAc is a nanoflower-like structure, the diameter of the nanoflower structure is 1-3 μm, and the nanoflower-like structure is composed of self-assembled irregular thin nanosheets.

[0022] Electrochemical detection of the NiCo-LDH-NaAc material indicates that the charge-discharge voltage range is 0-0.5 V. When the discharge current density is 1 A g -1 , its specific capacitance is 1900-2112 F g -1 .

[0023] Cyclic stability detection of the NiCo-LDH-NaAc material indicates that when the number of cycles is 5000, the capacitance retention rate of NiCo-LDH-NaAc-8 is 71.3%, and the coulombic efficiency is 100%.

[0024] Therefore, the NiCo-LDH-NaAc material of the present invention has the following advantages over the prior art:

[0025] 1. Sodium acetate is used as a precipitating agent in the present invention to obtain the basic technical effects of the precipitating agent, that is, the synthesis time is short, the energy consumption is low, acetate ions are stably inserted into the interlayer, the interlayer spacing is expanded, and the ion diffusion rate is increased;

[0026] 2. Sodium acetate is used to replace the conventional precipitating agent urea to synthesize the NiCo-LDH-NaAc material in the present invention. Acetate ions can form stable complexes with nickel ions and cobalt ions, improving the material uniformity;

[0027] 3. The nanoflower-like structure of the NiCo-LDH-NaAc material in the present invention is composed of irregular thin nanosheets, exposing more active sites, which is beneficial to electrolyte penetration and ion diffusion, and improving the specific capacitance of the material. Description of the Drawings

[0028] Figure 1XRD test patterns of NiCo-LDH-Ur, NiCo-LDH-NaAc-8, NiCo-LDH-NaAc-6, and NiCo-LDH-NaAc-10 materials prepared in Comparative Example 1 and Examples 1, 2, and 3;

[0029] Figure 2 EDS diagram of the NiCo-LDH-NaAc-8 material prepared in Example 1;

[0030] Figure 3 SEM images of the NiCo-LDH-NaAc-8 material prepared in Example 1;

[0031] Figure 4 Cyclic voltammogram of the NiCo-LDH-NaAc-8 material prepared in Example 1;

[0032] Figure 5 Charge-discharge curve of the NiCo-LDH-NaAc-8 material prepared in Example 1;

[0033] Figure 6 Cycling life curve of the NiCo-LDH-NaAc-8 material prepared in Example 1;

[0034] Figure 7 SEM images of the NiCo-LDH-Ur material prepared in Comparative Example 1;

[0035] Figure 8 SEM images of the NiCo-LDH-NaAc-6 material prepared in Example 2;

[0036] Figure 9 SEM images of the NiCo-LDH-NaAc-10 material prepared in Example 3. Detailed implementation mode

[0037] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it is not a limitation of the present invention.

[0038] Example 1

[0039] A preparation method of nano-flower-shaped NiCo-LDH-NaAc, comprising the following steps:

[0040] First, 1.164 g of Ni(NO3)·6H2O and 0.582 g of Co(NO3)·6H2O were dissolved in 60 mL of deionized water to obtain a mixed solution. Then, 1.089 g of sodium acetate NaAc·3H2O was added to the mixed solution and stirred until dissolved to obtain a reaction solution. Finally, under the conditions of a hydrothermal temperature of 120 °C and a hydrothermal time of 10 h, the reaction solution was subjected to a hydrothermal reaction. The obtained product was washed and dried to obtain nano-flower-shaped NiCo-LDH-NaAc prepared using sodium acetate NaAc as a precipitating agent, simply referred to as NiCo-LDH-NaAc. Since the addition amount of NaAc·3H2O in the material obtained in Example 1 satisfied the elemental molar ratio of Na:Ni:Co of 8:4:2, therefore, based on the addition amount of NaAc, it was named NiCo-LDH-NaAc-8.

[0041] To prove the composition of NiCo-LDH-NaAc-8, XRD testing was carried out. The test results are as Figure 1 shown. Characteristic peaks of the NiCo-LDH diffraction crystal plane exist in NiCo-LDH-NaAc-8, that is, NiCo-LDH-NaAc-8 was successfully prepared.

[0042] To further prove the composition of NiCo-LDH-NaAc-8, EDS testing was carried out. The test results are as Figure 2 shown. Co element, Ni element, C element, and O element are evenly distributed on the surface of the nano-flower-shaped sphere of NiCo-LDH-NaAc-8.

[0043] To observe the microscopic morphology of NiCo-LDH-NaAc-8, SEM testing was carried out. The test results are as Figure 3 shown. The microscopic morphology of NiCo-LDH-NaAc-8 is a nano-flower-shaped structure. The diameter of the nano-flower structure is 1 - 3 μm, and moreover, the nano-flower-shaped structure is composed of self-assembled irregular thin nanosheets.

[0044] To prove the electrochemical performance of NiCo-LDH-NaAc-8, cyclic voltammetry CV testing was carried out. The test results are as Figure 4 shown. At different scanning rates, redox peaks appear in the CV curve of NiCo-LDH-NaAc-8; as the scanning rate increases, the redox peaks will shift and the distance between the peaks will increase. This phenomenon indicates that NiCo-LDH-NaAc-8 has pseudocapacitive characteristics.

[0045] To prove the electrochemical performance of NiCo-LDH-NaAc-8, charge-discharge testing was carried out under three electrodes. The test results are as Figure 5 shown. The charge-discharge voltage range is 0 - 0.5 V. When the discharge current density is 1 Ag -1At this time, its specific capacitance is 2112 F g -1 .

[0046] To prove the cycling stability of NiCo-LDH-NaAc-8, the cycling stability was tested in a three-electrode system. The test results are as Figure 6 shown. When the number of cycles is 5000, the capacitance retention rate of NiCo-LDH-NaAc-8 is 71.3%, and the coulombic efficiency is 100%.

[0047] To prove the influence of sodium acetate, i.e., the precipitant, on the microstructure and properties of the obtained materials, Comparative Example 1, NiCo-LDH-Ur prepared based on the conventional precipitant urea, was provided.

[0048] Comparative Example 1

[0049] A preparation method of NiCo-LDH-Ur based on the conventional precipitant urea. The steps not specifically described are the same as those in Example 1, except that: urea was used as the precipitant, that is, 0.48 g of urea was added to replace 1.089 g of sodium acetate NaAc·3H2O, and the obtained material was named NiCo-LDH-Ur.

[0050] To analyze the composition of NiCo-LDH-Ur, XRD test was carried out. The test results are as Figure 1 shown. NiCo-LDH-Ur has the characteristic peaks of the diffraction crystal planes of NiCo-LDH. Comparing with Example 1, it can be seen that the composition of NiCo-LDH-Ur has no substantial difference from that of NiCo-LDH-NaAc.

[0051] To prove the microstructure of NiCo-LDH-Ur, SEM test was carried out. The test results are as Figure 7 shown. Although the microstructure of NiCo-LDH-Ur is still a nanoflower-like structure, the diameter of the nanoflower structure is 9 - 10 μm. Comparing with Example 1, it can be seen that using NaAc as the precipitant can adjust the flower-like structure, significantly reduce the diameter of the nanoflower structure, and avoid the phenomenon of nanosheet stacking.

[0052] To prove the electrochemical performance of NiCo-LDH-Ur, electrochemical performance test was carried out. The test results are as Figure 5 shown. The charge-discharge voltage range is 0 - 0.5 V. When the discharge current density is 1 A g -1 at this time, its specific capacitance is 1336 F g -1 . Comparing with Example 1, it can be seen that using NaAc as the precipitant can significantly improve the specific capacitance performance, and the improvement amplitude is 58%.

[0053] It can be seen from Example 1 and Comparative Example 1 that when sodium acetate is used as a precipitant, it has a significant impact on the microscopic morphology and material properties of the obtained material. The reason is that in addition to acting as a precipitant, acetate ions also have the role of a structure-directing agent. The specific principle is that by adsorbing on specific crystal planes, the crystal growth direction is regulated, promoting the self-assembly of two-dimensional nanosheets, and finally forming a three-dimensional hierarchical nanoflower structure. Moreover, acetate can form stable complexes with Ni ions and Co ions, controlling the release rate of metal ions, prolonging the nucleation and growth period, thereby avoiding particle agglomeration and preventing the stacking of nanosheets, that is, obtaining the technical effects of improving crystallinity and structural uniformity, increasing active sites, and improving specific capacitance.

[0054] To prove the influence of the NaAc addition amount on the performance, Example 2 and Example 3 are provided, and the addition amounts of NaAc satisfy the elemental molar ratios of Na:Ni:Co of 6:4:2 and 10:4:2, respectively.

[0055] Example 2

[0056] A preparation method of NiCo-LDH-NaAc with the NaAc addition amount satisfying 6:4:2. The steps not specifically described are the same as those in Example 1, and the difference is that in Step 1, the addition amount of NaAc·3H2O is 0.816 g, and the obtained material is named NiCo-LDH-NaAc-6.

[0057] To prove the composition of NiCo-LDH-NaAc-6, XRD tests were carried out. The test results are as Figure 1 shown. There are characteristic peaks of the NiCo-LDH diffraction crystal plane. By comparing with Example 1, it can be seen that there is no substantial difference in the composition between NiCo-LDH-NaAc-6 and NiCo-LDH-NaAc.

[0058] To prove the microscopic morphology of NiCo-LDH-NaAc-6, SEM tests were carried out. The test results are as Figure 8 shown. The basic microscopic morphology of NiCo-LDH-NaAc-6 is the same as that of NiCo-LDH-NaAc-8 obtained in Example 1, that is, it is still a nanoflower-like structure. However, the size is 4 - 6 μm. By comparing with Example 1, it can be seen that the size is increased by 2 - 3 times.

[0059] To prove the electrochemical performance of NiCo-LDH-NaAc-6, electrochemical performance tests were carried out. The test results are as Figure 5 shown. The charge-discharge voltage range is 0 - 0.5 V. When the discharge current density is 1 A g -1 -1, its specific capacitance is 1900 F g -1 .

[0060] Example 3

[0061] A preparation method of NiCo-LDH-NaAc with the addition amount of NaAc meeting 10:4:2. The steps not specifically described are the same as those in Example 1. The differences are as follows: In step 1, the addition amount of NaAc·3H2O is 1.732 g, and the obtained material is named NiCo-LDH-NaAc-10.

[0062] To prove the composition of NiCo-LDH-NaAc-10, XRD test was carried out. The test results are as Figure 1 shown. There are characteristic peaks of the diffraction crystal plane of NiCo-LDH. By comparing with Example 1, it can be seen that the composition of NiCo-LDH-NaAc-10 has no substantial difference from that of NiCo-LDH-NaAc.

[0063] To prove the microscopic morphology of NiCo-LDH-NaAc-10, SEM test was carried out. The test results are as Figure 9 shown. The basic microscopic morphology of NiCo-LDH-NaAc-10 is the same as that of NiCo-LDH-NaAc-8 obtained in Example 1, that is, it is still a nanoflower-like structure. However, the size is 3-5 μm. By comparing with Example 1, it can be seen that the size increases by 1-3 times.

[0064] To prove the electrochemical performance of NiCo-LDH-NaAc-10, electrochemical performance test was carried out. The test results are as Figure 5 shown. The charge-discharge voltage range is 0-0.5 V. When the discharge current density is 1 A g -1 , its specific capacitance is 2020 F g -1 .

[0065] By comparing Example 1, Example 2, and Example 3, it can be seen that the addition amount of NaAc has no substantial influence on the basic microscopic morphology of the nanoflower-like structure. However, excessive or small addition amount of NaAc both leads to an increase in the size of the nanoflowers.

Claims

1. A nano-flower-like NiCo-LDH-NaAc, characterized in that: Using nickel nitrate and cobalt nitrate as raw materials, sodium acetate trihydrate (NaAc·3H2O) as a precipitant, and deionized water as a solvent, nano-flower-like NiCo-LDH-NaAc was prepared by a hydrothermal method.

2. The nanoflower-like NiCo-LDH-NaAc according to claim 1, wherein: The microscopic morphology of the NiCo-LDH-NaAc is a nano-flower-like structure, which is composed of self-assembled irregular thin nanosheets with a size of 1-3 μm.

3. A preparation method of nano-flower-shaped NiCo-LDH-NaAc, characterized in that It includes the following steps: First, dissolve Ni(NO3)·6H2O and Co(NO3)·6H2O in deionized water to obtain a mixed solution. Then, add sodium acetate (NaAc·3H2O) to the mixed solution and stir to dissolve to obtain a reaction solution. Finally, under certain conditions, carry out a hydrothermal reaction on the reaction solution, and the obtained product is washed and dried to obtain nano-flower-like NiCo-LDH-NaAc prepared using sodium acetate (NaAc) as a precipitant.

4. The preparation method according to claim 3, characterized in that: The addition amount of the NaAc·3H2O satisfies that the molar ratio of the elements Na:Ni:Co is 8:4:

2.

5. The preparation method according to claim 3, characterized in that: The preparation conditions of the reaction solution are that the stirring time is 20-40 min; the conditions of the hydrothermal reaction are that the hydrothermal temperature is 120-140 °C and the hydrothermal time is 10-12 h; the conditions of the drying are that the drying temperature is 50-70 °C and the drying time is 11-13 h.

6. The nano-flower-shaped NiCo-LDH-NaAc according to claim 1, wherein: When used as a supercapacitor electrode material, the charge-discharge voltage range is 0 - 0.5 V. When the discharge current density is 1 A g -1 , the specific capacitance of NiCo-LDH-NaAc is 1900 - 2112 F g -1 .

7. The nano-flower-like NiCo-LDH-NaAc according to claim 1, wherein: When used as a supercapacitor electrode material, when the number of cycles is 5000, the capacitance retention rate of NiCo-LDH-NaAc is 70-80%, and the Coulomb efficiency is 98-100%.

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