MXene composite fiber and preparation method thereof, flexible electrode and supercapacitor

Abstract

The invention provides an MXene composite fiber and a preparation method thereof, a flexible electrode and a supercapacitor, and belongs to the technical field of MXene composite fibers.The method comprises the steps that Co (NO3) 2.6 H2O and a solvent are mixed to obtain a solution D1; zn (CH3COO) 2.2 H2O and a solvent are mixed, and a solution D2 is obtained; dimethylimidazole and a solvent are mixed to obtain a solution D3; the solution D1 and the solution D2 are mixed to obtain a mixed solution D4, MXene fibers are immersed in the mixed solution D4, then the solution D3 is added, drying is conducted after aging, and the MXene ZIF-6 / ZIF-8 composite fibers are obtained. The composite fiber has rich and unique wrinkled and crimped structures, a symmetrical fiber supercapacitor assembled by the fiber has the remarkable advantages of high area specific capacitance, high ion transmission rate and the like, and a zinc ion hybrid supercapacitor assembled by the fiber has the remarkable advantages of wide voltage window, high energy density and the like.

Description

Technical Field

[0001] This invention belongs to the field of MXene composite fiber technology, specifically relating to an MXene composite fiber and its preparation method, as well as flexible electrodes and supercapacitors. Background Technology

[0002] As a newly emerging two-dimensional transition metal carbides / nitrides (MXenes) in recent years, MXenes, similar to graphene, are two-dimensional materials with a layered structure. MXenes possess unique advantages in several aspects: their two-dimensional layered structure endows them with a large specific surface area and interlayer spacing; their metal-like conductivity ensures efficient electron transport; and their tunable surface functional groups provide space for chemical modification. Unlike carbon materials, MXene electrode materials can store energy simultaneously through physical adsorption / desorption and reversible redox reactions, thus exhibiting a capacity value far exceeding that of carbon materials. However, due to van der Waals forces, adjacent MXene nanosheets tend to aggregate and stack, reducing the interlayer spacing and hindering electrolyte ion transport, making it difficult to meet current demands for high-performance electrodes. Through rational structural design and controllable fabrication, researchers have developed MXene composite fibers that effectively transfer the superior properties of MXene at the microscale to the macroscale, exhibiting excellent mechanical, electrical, and thermal properties, thus enabling applications in functional fabrics, sensing, and energy fields. Currently, the structure and morphology of MXene fiber electrodes can be controlled by strategies such as adjusting the size of MXene sheets, interlayer spacing, and constructing three-dimensional / porous structures. Their performance can be further improved by optimizing the material system and preparation process. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention proposes an MXene composite fiber, its preparation method, and its application. The composite fiber possesses well-developed interlayer electroactive sites, ordered ion diffusion channels, and strong interfacial charge transfer. The constructed fiber-type flexible supercapacitor exhibits excellent energy density and high capacitance characteristics.

[0004] In a first aspect, the present invention provides a method for preparing MXene composite fibers, comprising: mixing Co(NO3)2·6H2O with a solvent to obtain solution D1; mixing Zn(CH3COO)2·2H2O with a solvent to obtain solution D2; mixing dimethylimidazole with a solvent to obtain solution D3; mixing solution D1 and solution D2 to obtain mixed solution D4; immersing MXene fibers in mixed solution D4; adding solution D3; aging and drying to obtain MXene@ZIF-6 / ZIF-8 composite fibers.

[0005] As a preferred technical solution, the ratio of Co(NO3)2·6H2O to solvent is 0.12–0.33 mol / mL.

[0006] As a preferred technical solution, the ratio of Zn(CH3COO)2·2H2O to solvent is 0.12–0.33 mol / mL.

[0007] As a preferred technical solution, the ratio of dimethylimidazole to solvent is 0.4–0.87 mmol / mL.

[0008] As a preferred technical solution, the solvent is selected from at least one of methanol and ethanol.

[0009] As a preferred technical solution, the volume ratio of solution D1, solution D2, and solution D3 is 1:1:1 to 1:1:3, preferably 1:1:1.

[0010] As a preferred technical solution, the mass-volume ratio of the MXene fiber to the solution D4 is 0.01:30 to 0.03:30, preferably 0.01:30.

[0011] As a preferred technical solution, the aging conditions include: aging temperature of 25-27°C and aging time of 12-48 hours.

[0012] As a preferred technical solution, the drying conditions include: drying temperature of 50-60℃ and drying time of 12-24h.

[0013] As a preferred technical solution, the MXene fiber is obtained by spinning solution through multi-stage spinning channels of different sizes; As a preferred technical solution, the multi-level dimensions include sequentially nested channels I and II; the inner diameter of channel I is greater than the inner diameter of channel II; preferably, the inner diameter of channel I is 1.2–1.6 mm; preferably, the inner diameter of channel II is 0.6–1.2 mm; preferably, the spinning solution is MXene-Ti3C2T. X The spinning advance rate is 85-100 ml / h.

[0014] Secondly, the present invention provides MXene composite fibers obtained by any of the above preparation methods, wherein the diameter of the composite fibers is 250-300 μm.

[0015] Thirdly, the present invention provides a flexible electrode using the aforementioned MXene composite fiber as the electrode material.

[0016] Fourthly, the present invention provides a parallel fiber-type symmetrical supercapacitor, wherein the anode material and the cathode material of the supercapacitor are both MXene composite fibers obtained by any of the above preparation methods, the distance between the MXene composite fibers used as the anode material and the MXene composite fibers used as the cathode material is 0.2 to 0.6 cm, and the fiber length is required to be 1 to 1.5 cm; the electrolyte is a 1.0 to 2.0 mol / L PVA / H2SO4 gel electrolyte.

[0017] As a preferred technical solution, the areal capacitance of the supercapacitor is 789–1433.9 mF / cm². -2 Fifthly, the present invention provides a zinc ion hybrid supercapacitor, wherein the supercapacitor uses 1-3 mol / L ZnSO4 as the electrolyte, the MXene composite fiber obtained by any of the above preparation methods as the cathode material, and the anode material is 70% rGO / MXene composite fiber.

[0018] As a preferred technical solution, the zinc ion hybrid supercapacitor can undergo 6500 cycles in ZnSO4 electrolyte, exhibiting an excellent capacitance retention rate of up to 92.9% and an areal capacitance > 400 mF / cm². -2 Their energy densities are all greater than those of symmetrical supercapacitors.

[0019] The MXene@ZIF-67 / ZIF-8 composite fibers prepared by this invention have relatively rich and unique fold and crimp structures. Symmetrical fiber supercapacitors assembled from these fibers have significant advantages such as high areal specific capacitance and high ion transport rate. Zinc ion hybrid supercapacitors assembled from these fibers have significant advantages such as wide voltage window and high energy density. Attached Figure Description

[0020] Figure 1 middle, Figure 1 a is a low-resolution SEM image of the surface of MXene fiber No. 1 prepared in Example 1; Figure 1 b is a high-resolution SEM image of the surface of the MXene fiber No. 1 prepared in Example 1; Figure 1 c is a cross-sectional SEM image of the MXene fiber No. 1 prepared in Example 1; Figure 1 d is a low-resolution SEM image of a surface of the 70% rGO / MXene anode fiber prepared in Example 3; Figure 1 e is a high-resolution SEM image of a surface of the 70% rGO / MXene anode fiber prepared in Example 3; Figure 1 f is a cross-sectional SEM image of the 70% rGO / MXene fiber prepared in Preparation Example 3; Figure 1 g is a SEM image of the bimetallic MOFs ZIF-67 / ZIF-8 prepared in Example 2; Figure 1 h is a low-resolution SEM image of a surface of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 i is a high-resolution SEM image of a surface of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 j is a cross-sectional SEM image of the MXene@ZIF-67 / ZIF-8 fibers prepared in Example 1; Figure 1 k is a surface location of the scanned EDS of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 l is an EDS diagram of the Zn element in the cross section of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 m is the EDS diagram of the Co element in the cross section of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 n is the EDS diagram of Ti element in the cross section of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 o is the EDS diagram of the O element in the cross section of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1; Figure 1 p is the EDS diagram of the C element of the cross section of the MXene@ZIF-67 / ZIF-8 fiber prepared in Example 1.

[0021] Figure 2 middle, Figure 2 a) is the flexible symmetrical supercapacitor (FSC) assembled from MXene fibers with different spinning channels in PVA / H2SO4 electrolyte, prepared in Example 1, at 0.6 mA cm⁻¹. -2 Comparison of GCD curves under current density; Figure 2 b. Flexible symmetrical supercapacitors (FSCs) assembled from MXene fibers with different spinning channels using the PVA / H2SO4 electrolyte prepared in Example 1 were tested at 0.6 mA cm⁻¹. -2Comparison of area-to-capacitance ratios under current density.

[0022] Figure 3 middle, Figure 3 a) The MXene@ZIF-67 / ZIF-8 fibers prepared in Example 1, the MXene@ZIF-8 fibers prepared in Comparative Example 1, the MXene@ZIF-67 fibers prepared in Comparative Example 2, and the MXene fibers prepared in Preparation Example 1 were all prepared in Example 4 and used to construct a flexible symmetrical supercapacitor in PVA / H2SO4 electrolyte at 0.4 mA cm⁻¹. -2 Comparison of GCD curves under current density; Figure 3 b represents the MXene@ZIF-67 / ZIF-8 fibers prepared in Example 1, the MXene@ZIF-8 fibers prepared in Comparative Example 1, the MXene@ZIF-67 fibers prepared in Comparative Example 2, and the MXene fibers prepared in Preparation Example 1. All of these were prepared in Example 4 and used to construct flexible symmetrical supercapacitors (FSCs) in PVA / H2SO4 electrolyte at 0.4 mA cm⁻¹. -2 Comparison of area-to-capacitance ratios under current density.

[0023] Figure 4 middle, Figure 4 a represents the MXene@ZIF-67 / ZIF-8 fiber FSCs prepared in Examples 1, 2, and 3 at 0.4 mA cm⁻¹. -2 Comparison of GCD curves under current density; Figure 4 b represents the MXene@ZIF-67 / ZIF-8 fiber FSCs prepared in Examples 1, 2, and 3 at 0.4 mA cm⁻¹. -2 Comparison of area-to-capacitance ratios under current density.

[0024] Figure 5 middle, Figure 5 a, Figure 5 b、 Figure 5 c represents the electrochemical performance test data of the MXene@ZIF-67 / ZIF-8 fibers prepared in Example 1 in a three-electrode system with 1.0 M H2SO4 electrolyte. Figure 5 a in 1-8 mA cm -2 GCD curves at current density; Figure 5 b is in the range of 25-150 mV s -1 CV curves at scan rate. Figure 5 c. Area capacitance at different scan rates. The inset in the upper right corner is a schematic diagram of the three-electrode test (using 1M H2SO4 as electrolyte, MXene@ZIF-67 / ZIF-8 as working electrode, platinum sheet as counter electrode, and Ag / AgCl as reference electrode).

[0025] Figure 6 middle, Figure 6 a, Figure 6 b、 Figure 6 c. Figure 6 d and Figure 6 e represents the electrochemical performance of the flexible symmetric supercapacitor made of MXene@ZIF-67 / ZIF-8 fibers prepared in Example 4, tested in a PVA / H2SO4 electrolyte using a two-electrode configuration. Figure 6 a in 0.2-1.0 mA cm -2 GCD curves at current density; Figure 6 b is in the range of 10-100 mV s -1 CV curves at scan rate; Figure 6 c. Area capacitance at different current densities. The inset is a schematic diagram of the assembled supercapacitor device. Figure 6 GCD comparison curves of a single MXene@ZIF-67 / ZIF-8 FSCs and three cascaded MXene@ZIF-67 / ZIF-8 FSCs; Figure 6 GCD comparison curves of a single MXene@ZIF-67 / ZIF-8 FSCs connected in parallel with three.

[0026] Figure 7 middle, Figure 7 a, Figure 7 b、 Figure 7 c. Figure 7 d、 Figure 7 e Figure 7 f、 Figure 7 g and Figure 7 h represents the electrochemical performance test of the zinc ion hybrid supercapacitors (ZIHSCs) prepared in Example 5. Figure 7 'a' is the working mechanism diagram. Figure 7 b represents the CV curves obtained for 70% rGO / MXene and MXene@ZIF-67 / ZIF-8 fibers under a three-electrode system. Figure 7 c is the GCD curve for ZIHSCs as the potential window extends from 0.8 V to 1.6 V. Figure 7 d represents the GCD curves under different current densities. Figure 7 e represents the CV curves at different scan rates. Figure 7 f is the specific capacitance at different current densities. The inset is a schematic diagram of the device with electrode assembly of ZIHSCs. Figure 7 g is a comparison of the energy densities of zinc ion hybrid supercapacitors (ZIHSCs) and symmetrical supercapacitors (FSCs) assembled from MXene@ZIF-67 / ZIF-8 fibers at different current densities; Figure 7h represents the capacitance retention of ZIHSCs after 6500 cycles, and the inset shows the GCD curves for the first and last 10 cycles.

[0027] Figure 8 middle, Figure 8 a, Figure 8 b and Figure 8 c represents the characterization of the ZIF-8 / ZIF-67 crystals prepared in Example 2 and the MXene@ZIF-67 / ZIF-8 fibers prepared in Example 1. Figure 8 a is Ti3C2T x XRD patterns of Ti3AlC2; Figure 8 b is the XRD pattern of ZIF-67 / ZIF-8; Figure 8 c is the XRD pattern of MXene@ZIF-67 / ZIF-8 fibers. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0029] A method for preparing MXene@MOFs composite fibers: 3-5 mol of Co(NO3)2·6H2O is added to 15-25 ml of methanol and mixed to obtain solution D1. 3-5 mol of Zn(CH3COO)2·2H2O is added to 15-25 ml of methanol and mixed to obtain solution D2. 10-13 mmol of dimethylimidazole is mixed with 15-25 ml of methanol and stirred to obtain solution D3. Under stirring, solution D1 is slowly added to solution D2 to obtain mixed solution D4. 0.1-0.3 g of MXene fibers are immersed in mixed solution D4. Solution D3 is added to solution D4 impregnated with MXene fibers. The mixture is aged at room temperature (25-27℃) for 12-48 h, then rinsed with methanol and deionized water, and dried in a vacuum drying oven at 50-60℃ for 12-24 h to obtain MXene@ZIF-6 / ZIF-8 fibers.

[0030] The test methods for the embodiments and comparative examples of this invention are as follows: Constant current charge-discharge test (GCD) By applying a constant current to control the charging and discharging process of the electrode under test, a voltage-time curve is obtained for forward charging and a voltage-time curve for reverse discharging, resulting in a triangular-like GCD curve. By monitoring and recording the constant current charging and discharging process, the performance parameters of the electrode under test, such as charging efficiency and discharging capacity, can be evaluated. Cyclic voltammetry (CV) Within a selected voltage window, electrochemical reactions are studied by applying a sinusoidal or triangular voltage signal to the electrode under test and then measuring the current response. When the voltage reaches a certain level, an electrochemical reaction, such as a redox reaction, occurs. The test is performed at least three cycles to obtain a stable closed-loop current-voltage curve, i.e., a CV curve. Cyclic voltammetry can be used to characterize the redox behavior, electrochemical kinetics, and other properties of electrochemical materials. Electrochemical impedance spectroscopy (EIS) AC impedance analysis obtains the impedance response of the electrode to AC voltages of different frequencies by applying interference signals of different frequencies to the electrode under test. The data is then plotted as a Nyquist plot, and the ion diffusion and electron transport resistance of the electrode are analyzed based on the low-frequency slope and the high-frequency radius.

[0031] Figure 2 a, Figure 2 b、 Figure 3 a, Figure 3 b、 Figure 4 a, Figure 4 b is the electrochemical comparative test system for symmetrical supercapacitors, tested using a CHI660E electrochemical workstation. All electrochemical behaviors were performed using PVA / H2SO4 electrolyte. The voltage range for constant current charge-discharge tests was 0-0.8V, and the current density range was 0.4 and 0.6 mA cm⁻¹. -2 .

[0032] Figure 6 a, Figure 6 b、 Figure 6 c. Figure 6 d and Figure 6 e represents the electrochemical testing system for a symmetrical supercapacitor, tested using a CHI660E electrochemical workstation. All electrochemical behaviors were performed using PVA / H₂SO₄ electrolyte. The cyclic voltammetry test voltage range was 0-0.8V, and the scan rate selection range was 10, 25, 50, 75, and 100 mV s. -1 The voltage ranges for constant current charge-discharge tests are 0-0.8V and 0-2.5V, and the current density range is 0.2-1.0 mA cm⁻¹. -2 Figure 5 a, Figure 5 b、 Figure 5 c represents the three-electrode testing system for the fiber electrode, tested using a CHI660E electrochemical workstation. The electrolyte was 1M H₂SO₄, the working electrode was MXene@ZIF-67 / ZIF-8, the counter electrode was a platinum sheet, and the reference electrode was Ag / AgCl. Cyclic voltammetry was used in the voltage range of 0-0.6V, with a scan rate selection range of 25-150mV s. -1The voltage range for constant current charge-discharge tests is 0-0.6V, and the current density range is 1-8 mA cm⁻¹. -2 .

[0033] Figure 7 a, Figure 7 b、 Figure 7 c. Figure 7 d、 Figure 7 e Figure 7 f、 Figure 7 g、 Figure 7 h is the electrochemical testing system for a zinc-ion hybrid supercapacitor, tested using a CHI660E electrochemical workstation. All electrochemical behaviors were performed using ZnSO4 electrolyte. The voltage range for cyclic voltammetry testing was 0-1.8V, and the scan rate range was 10-100mV s. -1 The voltage range for constant current charge-discharge tests is 0-1.8V, and the current density range is 0.2–1.0 mA cm⁻¹. -2 .

[0034] Preparation Example 1: Preparation of MXene Fibers by Microfluidic Wet Spinning High-concentration MXene dispersions (MAX-Ti3AlC2) were prepared by etching with LiF / HCl solution. (1) Place 2 g of lithium fluoride and 40 mL of 9 M hydrochloric acid solution in a polytetrafluoroethylene container and stir magnetically for 30 min. Then, slowly add 2 g of Ti3AlC2 powder at 450 r and stir at 35 °C for 24 hours. Centrifuge at 6000 r and wash with deionized water until the pH reaches 6 to obtain a high concentration (approximately 50 mg / mL). -1 Monolayer or few-layer MXene (Ti3C2Tx) dispersion (dispersion medium is water).

[0035] MXene-Ti3C2T X The dispersion, used as the spinning solution, was propelled at a rate of 90 mL / h through a multi-stage spinning channel (18G needles nested within 15G needles; the flow sequence of the spinning solution was from a coarser 15G channel to a finer 18G channel before entering the coagulation bath; 15G: 1.4 mm, 18G: 0.86 mm). This forced the Ti3C2T... X The nanosheets were arranged in an orderly manner and solidified in acetic acid. The fibers were then soaked in the solidification bath for 10 minutes to solidify the MXene fibers. After washing with anhydrous ethanol, the fibers were dried in a vacuum oven at 50°C for 12 hours to obtain pure MXene fibers.

[0036] Meanwhile, a series of MXene fibers were prepared using spinning channels of different sizes (15+18G, 15G, 18G, 21G), namely MXene fiber 1#, 2#, 3#, and 4#.

[0037] Table 1. MXene fibers with different spinning channels

[0038] like Figure 1 a and Figure 1 As shown in b, pure MXene fibers obtained by wet spinning in an acetic acid coagulation bath form a large number of voids during the fiber coagulation process, and the surface exhibits a rich and unique fold and crimp structure. like Figure 1 As shown in c, the MXene fiber exhibits a highly ordered and tightly packed layered structure, similar to a stacked array of nanosheets. This structure endows the fiber with excellent mechanical properties and ion transport channels.

[0039] Preparation Example 2: Preparation of ZIF-8 / ZIF-67 crystals 3 mmol of zinc acetate dihydrate was mixed with 15 ml of methanol at 300 rpm for 5 min until homogeneous, yielding solution C1. 3 mmol of cobalt nitrate hexahydrate was also mixed with 15 ml of methanol at 300 rpm for 5 min until homogeneous, yielding solution C2. 12 mmol of dimethylimidazole was then mixed with 15 ml of methanol at 300 rpm for 5 min until homogeneous, yielding solution C3. Solutions C1 and C2 were then mixed and allowed to stand at room temperature (25°C) for 5 min. The resulting mixture was then added to solution C3 and aged at 25°C for 24 h. After standing for a period of time, the solution was centrifuged, washed with deionized water, and the product was collected to obtain dodecahedral ZIF-8 / ZIF-67 crystals.

[0040] Figure 1 g shows ZIF-67 / ZIF-8 crystal particles aged for 24 hours, exhibiting a typical regular and uniform dodecahedral structure. This highly crystalline metal-organic framework structure provides an ideal building block for the functionalization of composite materials.

[0041] Figure 8 XRD analysis of a confirmed the elimination of Al and Ti3C2T. x Successful preparation of MXene. After 24 h of etching, Ti3C2T x The diffraction peak (104) disappears at 39.2° due to the increased interlayer spacing of Ti3C2T. x The (002) peak shifted from 9.5° to 7.0°. Figure 8In the XRD pattern of ZIF-67 / ZIF-8 (red curve), b shows that the characteristic diffraction peaks highly match the peak positions of the standard cards for ZIF-67 and ZIF-8. For example, the (011), (002), and (112) diffraction peaks of ZIF-67 and the characteristic diffraction peaks of ZIF-8 are clearly visible, proving that the crystal structures of ZIF-67 and ZIF-8 coexist in the composite particles without the formation of impurity phases, thus successfully constructing a bimetallic organic framework composite system. Figure 8 In the XRD curve of MXene@ZIF-67 / ZIF-8 fibers, the (002) crystal plane diffraction peak with a 2θ of approximately 6.2° is a typical characteristic peak of MXene, representing its layered structure and verifying the existence of MXene fibers. It also contains characteristic peaks of ZIF-67 / ZIF-8 (18.5°, 34°, 39°, 41.7°), proving that ZIF-67 / ZIF-8 was successfully loaded onto the surface of MXene fibers to form a composite structure.

[0042] Preparation Example 3: Preparation of 70% rGO / MXene anode fibers Graphene oxide (GO, 10 mg g) -1 The dispersion was stirred thoroughly for 30 min, and then the MXene dispersion (the dispersion obtained in Preparation Example 1) was added and stirred for another 30 min to obtain a mixed spinning solution with a weight ratio of MXene to GO of 3:7. Microfluidic-assisted wet spinning technology was used to inject the spinning solution into an acetic acid coagulation bath for molding. The microfluidic spinning channel was designed with a diameter gradient from large to small (the spinning solution first passed through a larger 15G spinning channel and then through a smaller 18G spinning channel). The dried GO / MXene fibers were reduced at high temperature (85-100℃, preferably 85℃) for 8-12 hours (preferably 8h) in a mixed solution of hydroiodic acid and acetic acid with a volume ratio of 2:3. During this time, GO was reduced to rGO, and 70% rGO / MXene fibers were prepared.

[0043] Figure 1 d and Figure 1 As can be seen, 70% of the rGO / MXene fibers exhibit a tightly wrinkled surface morphology; Figure 1 The f-shown data shows that the 70% rGO / MXene fibers exhibit a honeycomb-like rich pore structure. These pores not only significantly increase the specific surface area of ​​the electrode material, but more importantly, they provide abundant adsorption and storage sites for zinc ions. This is of great significance for improving the energy storage performance of zinc ion hybrid supercapacitors. Comparative Example 1: MXene@ZIF-8 fiber MOFs (ZIF-8) crystals were synthesized on the surface of the 1#MXene fiber prepared in Preparation Example 1 by in-situ co-deposition process.

[0044] Solution D1 was obtained by mixing 3 mmol of zinc acetate dihydrate with 15 ml of methanol and stirring. Solution D2 was obtained by mixing 12 mmol of dimethylimidazole with 15 ml of methanol and stirring.

[0045] 0.1g of MXene fiber was immersed in solution D1, and then solution D2 was poured into it. The fiber was aged and precipitated at room temperature of 25°C for 24 hours. The fiber was then washed with deionized water and methanol, and then dried in a vacuum drying oven at 50°C for 12 hours to obtain MXene@ZIF-67 fiber.

[0046] Comparative example: 2MXene@ZIF-67 fiber MOFs (ZIF-67) crystals were synthesized on the surface of the 1#MXene fiber prepared in Preparation Example 1 by in-situ co-deposition process.

[0047] Solution E1 was prepared by mixing 3 mmol of cobalt nitrate hexahydrate with 15 ml of methanol and stirring. Solution E2 was prepared by mixing 12 mmol of dimethylimidazole with 15 ml of methanol and stirring.

[0048] 0.1g of MXene fiber was immersed in solution E1, and then solution E2 was poured into solution E1. The fiber was aged and precipitated at room temperature for 24h. The fiber was then washed with deionized water and methanol, and then dried in a vacuum drying oven at 50℃ for 12h to obtain MXene@ZIF-67 fiber.

[0049] Example 1: MXene@ZIF-67 / ZIF-8 fiber MOFs (ZIF-67 / ZIF-8) crystals were synthesized on the surface of the 1#MXene fiber prepared in Preparation Example 1 by in-situ co-deposition process.

[0050] 3 mmol of Co(NO3) 2· Solution F1 was obtained by adding 6H2O to 15ml of methanol and stirring. Solution F2 was obtained by adding 3mmol of Zn(CH3COO)2·2H2O to 15ml of methanol and stirring. Solution F3 was obtained by adding 12mmol of dimethylimidazole to 15ml of methanol and stirring. Then, solution F1 was slowly added to solution F2 under stirring at 300 rpm to obtain mixed solution F4. 0.1g of MXene fiber was immersed in mixed solution F4. Then, solution F3 was added to solution F4 containing MXene fiber. The mixture was aged at room temperature (25°C) for 24 hours, then rinsed with methanol and deionized water, and dried overnight (12 hours) in a vacuum drying oven at 50°C to obtain MXene@ZIF-6 / ZIF-8 fiber.

[0051] Figure 1h shows the surface microstructure of MXene@ZIF-67 / ZIF-8 fibers. It can be seen that these fibers have fewer wrinkles compared to pure MXene fibers. Due to the in-situ polymerization of ZIF-67 / ZIF-8 crystals, a complex morphology is formed where wrinkles and nanoparticles coexist, building upon the existing wrinkles of MXene fibers. Figure 1 It can be clearly seen that the surface of MXene@ZIF-67 / ZIF-8 fibers is uniformly loaded with MOF crystals. Based on the original wrinkles of MXene fibers, the in-situ polymerization of ZIF-67 / ZIF-8 crystals forms a complex morphology in which wrinkles and nanoparticles coexist. Unlike the relatively simple wrinkled surface of MXene fibers, this composite structure not only significantly improves the surface roughness of the material, but also constructs a multi-level pore system.

[0052] Figure 1 j is a cross-sectional view, showing ZIF-67 / ZIF-8 crystals filling or growing between the wrinkled layers on the MXene surface, altering the porosity and wrinkles.

[0053] Figure 1 k is the EDS scan position of MXene@ZIF-67 / ZIF-8 fibers; Figure 1 l、 Figure 1 m、 Figure 1 n、 Figure 1 o、 Figure 1 p represents the EDS (Enhanced Metal-Organic Spectroscopy) images of Zn, Co, Ti, O, and C elements in the cross-section of MXene@ZIF-67 / ZIF-8 fibers. The EDS images show that various elements exhibit specific distribution characteristics in the microstructure of the MXene@ZIF-67 / ZIF-8 fiber cross-section. Zn and Co elements are uniformly dispersed, as clearly seen in the spectra. This directly proves that ZIF-67 / ZIF-8 is successfully loaded and uniformly distributed in the fiber, forming a stable metal-organic framework structure.

[0054] Example 2: Preparation of MXene@ZIF-6 / ZIF-8 fibers The difference from Example 1 is that the aging time is 12 hours.

[0055] 3 mmol of Co(NO3) 2·6H2O was added to 15 ml of methanol and stirred to obtain solution F1. 3 mmol of Zn(CH3COO)2·2H2O was added to 15 ml of methanol and stirred to obtain solution F2. 12 mmol of dimethylimidazole was mixed with 15 ml of methanol and stirred to obtain solution F3. Subsequently, under stirring at 300 rpm, solution F1 was slowly added to solution F2 to obtain mixed solution F4. 0.1 g of MXene fiber was immersed in mixed solution F4. Then, solution F3 was added to solution F4 containing MXene fiber. The mixture was aged at 25°C for 12 h, then rinsed with methanol and deionized water, and dried overnight in a vacuum drying oven at 50°C for 12 h to obtain MXene@ZIF-6 / ZIF-8 fiber.

[0056] Example 3: Preparation of MXene@ZIF-6 / ZIF-8 fibers The difference from Example 1 is that the aging time is 18 hours.

[0057] 3 mmol of Co(NO3) 2· Solution F1 was obtained by adding 6H2O to 15ml of methanol and stirring. Solution F2 was obtained by adding 3mmol of Zn(CH3COO)2·2H2O to 15ml of methanol and stirring. Solution F3 was obtained by adding 12mmol of dimethylimidazole to 15ml of methanol and stirring. Then, solution F1 was slowly added to solution F2 under stirring at 300 rpm to obtain mixed solution F4. 0.1g of MXene fiber was immersed in mixed solution F4. Then, solution F3 was added to solution F4 containing MXene fiber. The mixture was aged at room temperature of 25°C for 18 hours, then rinsed with methanol and deionized water, and dried overnight in a vacuum drying oven at 50°C for 12 hours to obtain MXene@ZIF-6 / ZIF-8 fiber.

[0058] Table 2. Control groups of MXene fibers loaded with different MOF crystals

[0059] Table 3. Control groups of MXene@ZIF-8 / ZIF-8 fibers at different aging times

[0060] Example 4: Assembly of a parallel fiber supercapacitor Assembly of symmetrical supercapacitor: Both the anode and cathode are made of two identical MXene composite fibers (prepared in Example 1, Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3) arranged in parallel on a flexible substrate. The parallel distance between the two fibers is 0.5 cm (or 0.2-0.6 cm if desired). The two ends are fixed with conductive copper tape, and the distance between the two ends (i.e., the fiber length) is 1 cm (range 1-1.5 cm). PVA / H2SO4 gel electrolyte is used to cover the fiber electrodes to assemble a parallel fiber symmetrical supercapacitor.

[0061] The PVA / H2SO4 gel electrolyte was prepared by mixing 60 mL of deionized water, 6 g of PVA, and 6 g of H2SO4, and then incubating at 95 °C with a flow rate of 150 r / min. -1 Stir at a certain speed for 2 hours to obtain the product.

[0062] Example 5: Zinc ion hybrid supercapacitors (ZIHSCs) The MXene@ZIF-67 / ZIF-8 prepared in Example 1 was used as the cathode fiber of ZIHSCs, and the 70% rGO / MXene fiber prepared in Preparation Example 3 was used as the anode fiber of ZIHSCs. Aqueous ZIHSCs were constructed using 2M ZnSO4 as the electrolyte.

[0063] MXene fibers with different spinning channels, different MOF crystal loadings, and MXene@ZIF-67 / ZIF-8 fibers with different aging times were assembled into symmetrical flexible supercapacitors in PVA / H2SO4 electrolyte, and their corresponding electrochemical performance was evaluated.

[0064] Test Example 1: Electrochemical properties of MXene fibers with different spinning channels In microfluidic wet spinning, the inner diameter of the spinning channel is one of the key parameters affecting the fiber structure. The spinning channel influences the nanosheet arrangement by regulating shear force, thereby controlling the pore distribution. The inner diameter of the spinning channel needle is usually represented by G, with a smaller number indicating a larger inner diameter. To obtain the influence of different spinning channels on the electrochemical properties of MXene fibers in microfluidic wet spinning, and to screen for the optimal microfluidic spinning conditions, MXene fibers prepared with different spinning channels (15G, 18G, 21G, 15+18G) were assembled into FSCs for comparison using constant current charge-discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS).

[0065] Figure 2 a shows at 0.6 mA cm -2GCD comparison curves under current density Figure 2 b shows that the 15+18G MXene fiber has the longest discharge time and the highest areal capacitance of 1433.9 mF / cm². -2 All are higher than 15G (789 mF cm) of a single spinning channel. -2 ), 18G (1101 mF cm) -2 ), 21G (566.9 mF cm) -2 MXene fibers. A 15+18G combined needle first provides initial high-speed flow through a large-size spinning channel (15G), forming the fiber's skeletal structure and establishing an efficient channel for ion transport; subsequently, a smaller-size spinning channel (18G) applies higher shear force, inducing "secondary" micropores or mesopores on top of the macropores, achieving a gradient distribution of pore size and significantly improving capacitance performance (areal capacitance reaches 1433.9 mF / cm²). -2 Therefore, the advantage of the 15G+18G combined spinning channel lies in its multi-level channel design, which overcomes the limitations of a single spinning channel and achieves a comprehensive improvement in electrochemical performance (specific capacitance, charge transfer efficiency, and ion diffusion kinetics). This strategy provides a new approach for the fabrication of high-performance fiber-based energy storage devices: through the hierarchical structure of multi-size spinning channels, the electrochemical behavior of the material is synergistically optimized.

[0066] Test Example 2: Electrochemical performance of MXene fibers loaded with different MOF crystals By comparing the electrochemical properties of MXene, MXene@ZIF-8, MXene@ZIF-67 and MXene@ZIF-67 / ZIF-8 fiber FSCs ( Figure 3 a and Figure 3 (b) It was found that MXene@ZIF-67 / ZIF-8 fibers at 0.4 mA cm⁻¹ -2 The discharge time is longest at the current density, and its corresponding isotropic capacitance is 2126 mF / cm². -2 The maximum values ​​were all greater than those of MXene@ZIF-8 (1884.2 mF / cm²) of single-metal MOFs. -2 ), MXene@ZIF-67 (1379.6 mF cm -2 ) and pure MXene (1499.9 mF cm -2 The areal capacitance of the fibers is due to the synergistic effect of the ZIF-67 / ZIF-8 bimetallic framework: it not only increases the density of active sites, but also optimizes the electron / ion transport path through multi-level channels, reduces interfacial impedance, and significantly improves charge storage capacity and kinetic performance.

[0067] Test Example 3: Electrochemical performance of MOFs@ZIF-67 / ZIF-8 at different aging times To explore the optimal aging time for bimetallic MOFs loaded on MXene fibers. Figure 4 a and Figure 4 Figure b shows the GCD curves and areal capacitance comparison curves of MXene@ZIF-8 / ZIF-67 fibers at different aging times (12h, 18h, 24h). Figure 4 As shown in Figure a, the discharge time of MXene@ZIF-8 / ZIF-67 fibers aged for 24 hours is much longer than that of MXene@ZIF-67 / ZIF-8 fibers aged for 12 hours and 18 hours. Figure 4 b indicates the areal capacitance (2126 mF / cm²) corresponding to MXene@ZIF-8 / ZIF-67 fibers. -2 All were greater than 12h (1308 mF cm). -2 ) and 18h ​​(1933 mF cm -2 The aging time of MXene@ZIF-67 / ZIF-8 fibers indicates that a 24-hour aging time allows for more complete crystal growth and higher crystallinity in ZIF-67 / ZIF-8, forming a regular porous framework that provides more active sites and ion storage space.

[0068] Test Example 4: Electrochemical performance of MOFs@ZIF-67 / ZIF-8 electrodes Through the above comparative experiments, it was found that the bimetallic MOFs@MXene fibers with an aging time of 24 hours exhibited the best performance. Therefore, the electrochemical performance of MXene@ZIF-67 / ZIF-8 fibers was evaluated using a three-electrode test. 1M H₂SO₄ was used as the electrolyte, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode. Under these test conditions, the electrochemical performance of MXene@ZIF-67 / ZIF-8 fibers was found to be within the range of 1.0–8.0 mA cm⁻¹. -2 GCD curve at current density ( Figure 5 (a) The constant current charge and discharge curves under different current densities maintain a relatively consistent triangular shape. Figure 5 (b) Displayed within a potential window of -0.2 to 0.6 V, with a recording scan rate of 25 to 150 mV s. -1 The CV curve, even at higher scan rates (150 mV s), -1 Even under these conditions, the CV curve shape can still be maintained well. Specific capacitance is an important indicator for evaluating the electrochemical performance of fibers. Figure 5(c) The areal capacitance of MXene@ZIF-67 / ZIF-8 fibers obtained from CV curves at different scan rates is shown in the inset as a schematic diagram of the fiber's three-electrode system test. With increasing scan rate (25~150 mV s...), the areal capacitance... -1 The specific capacitance decreases accordingly (170.1~1141.1 mF cm). -2 This study confirmed that the fiber exhibits stable electrochemical activity over a wide scan rate range, and demonstrates a significant synergistic advantage in ion transport efficiency and structural stability.

[0069] Test Example 5: Testing a flexible symmetric supercapacitor assembled using MXene@ZIF-67 / ZIF-8 fibers as electrodes. Due to the excellent electrochemical performance of MXene@ZIF-67 / ZIF-8 fibers, flexible symmetric supercapacitors (FSCs) were assembled using MXene@ZIF-67 / ZIF-8 fibers as electrodes to evaluate their performance in practical applications. The device exhibited electrochemical properties ranging from 0.2 to 1.0 mA cm⁻¹. -2 The constant current charge-discharge test curves under current density are as follows: Figure 6 (a) The charge-discharge curves exhibit similar triangular shapes at different current densities, without obvious charge-discharge plateaus, demonstrating typical capacitive characteristics and good reversibility. As the current density increases, the discharge time shortens, but the voltage drop remains consistently gradual, indicating stable charge storage at different current densities and demonstrating that it retains a certain specific capacitance (0.2~1.0 mA cm⁻¹) even at high current densities. -2 ,1385.9~2144mF cm -2 This demonstrates excellent energy storage performance. For example... Figure 6 As shown in (b), in the range of 10~100 mV s -1 At the specified scan rate, the CV curve is approximately rectangular. As the scan rate increases, the current density increases synchronously, and the area under the curve changes regularly without significant distortion, indicating rapid ion response kinetics. Specific capacitance is also an important indicator for evaluating the electrochemical performance of FSCs. Figure 6 (c) shows the areal capacitance of MXene@ZIF-67 / ZIF-8 FSCs at different current densities. The inset is a schematic diagram of the device assembled into a symmetrical supercapacitor using PVA / H2SO4 electrolyte. As the current density increases, the areal capacitance of MXene@ZIF-67 / ZIF-8 FSCs increases from 2144 mF / cm². -2 (0.2 mA cm) -2 It dropped to 1385.9 mF cm -2 (1.0 mA cm) -2 The volumetric capacitance is 408 F cm⁻¹ -3Reduced to 256 F cm -3 .

[0070] Based on practical applications of MXene@ZIF-67 / ZIF-8 FSCs, the limited range of current and voltage provided by a single FSC can lead to the configuration of gel-type FSCs in series or parallel to meet application requirements. Figure 6 d and Figure 6 e represents the GCD curves of a single MXene@ZIF-67 / ZIF-8 FSCs device and three devices connected in series and parallel, respectively. The series-assembled three FSCs can achieve an operating voltage three times that of a single device (0-2.4 V) within a similar charge-discharge time, while the parallel-assembled three FSCs can increase the capacitance and achieve a discharge time three times that of a single device. Based on these results, it can be concluded that series-assembled devices can increase the operating voltage, while parallel-assembled devices increase the total capacitance.

[0071] Test Example 6: Testing Aqueous Zinc Ion Hybrid Supercapacitors (ZIHSCs) In exploring the application potential of MXene@ZIF-67 / ZIF-8 fibers in the field of supercapacitors, they were successfully assembled into a flexible symmetrical supercapacitor. To further expand its application range and increase energy density, an aqueous zinc ion hybrid supercapacitor (ZIHSC) was constructed using an MXene@ZIF-67 / ZIF-8 fiber electrode as the cathode, a 70% rGO / MXene fiber electrode as the anode, and a 2M ZnSO4 aqueous solution as the electrolyte. The zinc ion storage capacity of this ZIHSC was then investigated.

[0072] Figure 7 a represents the electrochemical reaction mechanism of ZIHSCs under charge and discharge conditions. During the charging phase, anions in the electrolyte (such as SO42-) 2- (etc.) migrate directionally to the cathode surface, inducing the electric double layer capacitance effect through adsorption behavior, Zn 2+ The Zn atoms detach from the electrolyte, migrate towards the anode, and complete deposition. The discharge process is the reverse of the charging process; the Zn atoms on the anode surface... 2+ The Zn in the electrolyte undergoes stripping and redisperses into the electrolyte; 2+ The charge then migrates to and adsorbs onto the surface of the cathode material, thus realizing the charge release process. To evaluate the voltage window of ZIHSCs, a typical three-electrode system was used to perform CV tests on the anode and cathode separately, such as... Figure 7 b shows that, relative to the reference Ag / AgCl (2 M ZnSO4) electrode, the MXene@ZIF-67 / ZIF-8 fiber electrode can... Operating within a positive voltage window of 0.2 to 0.8 V, 70% rGO / MXene fiber electrodes are used. 1.2 to Detected at a negative voltage window of 0.2V 1.2V / The sharp redox peak at 0.74 V corresponds to Zn / Zn 2+ The redox intercalation / deintercalation process demonstrates that ZIHSCs assembled from MXene@ZIF-67 / ZIF-8 cathode fibers and 70% rGO / MXene anode fibers can operate within a voltage window up to 1.8 V. To verify the voltage window selection in the previous three-electrode system, further two-electrode electrochemical performance tests were conducted, such as... Figure 7 c represents the GCD curve of ZIHSCs as the operating voltage window extends from 0.8V to 1.8V, showing that the curves maintain good stability across different operating voltage ranges.

[0073] Figure 7 d and Figure 7 The electrochemical performance of this ZIHSCs in 2M ZnSO4 electrolyte was evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). Figure 7 As shown in d, the range is 0.2~1.0 mA cm⁻¹ -2 The GCD curves at different current densities all maintained similar triangular shapes and had no obvious charge / discharge voltage plateau, indicating the high reversibility of the electrode reaction and the absence of obvious side reactions in the ion insertion / extraction process. This further demonstrates that the zinc ion supercapacitor with MXene@ZIF-67 / ZIF-8 composite fiber as the cathode electrode has good electrochemical performance. Figure 7 e is in the range of 10~100 mV s -1 CV curves at different scan rates, even when the scan rate is increased to 100 mV / s -1 The curve shape remains stable, further demonstrating the rapid reversibility of its charge storage process and structural stability. Through Figure 7 The area-to-capacitance ratio calculated from the GCD curve of d is as follows: Figure 7 As shown in f, when the current density increases from 0.2 mA cm⁻¹ -2 Increased to 1.0 mA cm -2 At that time, the specific capacitance increased from 833.7 mF cm⁻¹ -2 It dropped to 442.9 mF cm -2 All of these devices exhibit excellent areal capacitance.

[0074] Figure 7 g compares the energy density of zinc ion hybrid supercapacitors (ZIHSCs) and symmetric supercapacitors (FSCs) assembled based on MXene@ZIF-67 / ZIF-8 composite fibers at different current densities. At 0.2 mA cm⁻¹-2 At current density, ZIFSCs achieve an energy density as high as 93.8 μWh / cm³. -2 This is significantly higher than the approximately 47 μWh / cm² of FSCs. -2 As the current density increases to 1.0 mA cm⁻¹ -2 The energy density of ZIFSCs is reduced to approximately 50 μWh / cm³. -2 FSCs decreased to approximately 30 μWh cm⁻¹ -2 As can be seen, the energy density of ZIHSCs is significantly better than that of FSCs at all current densities, demonstrating their efficient charge storage capability based on the MXene@ZIF-67 / ZIF-8 composite structure, and confirming the advantages of zinc-ion supercapacitors in energy storage performance. The assembled ZIHSCs can undergo 6500 cycles in ZnSO4 electrolyte with excellent capacitance retention (92.9%), exhibiting outstanding cycle stability. Figure 7 g).

[0075] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0076] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing MXene composite fibers, characterized in that, include: Co(NO3)2·6H2O was mixed with a solvent to obtain solution D1; Zn(CH3COO)2·2H2O was mixed with a solvent to obtain solution D2; dimethylimidazole was mixed with a solvent to obtain solution D3; solution D1 and solution D2 were mixed to obtain mixed solution D4. MXene fibers were immersed in mixed solution D4, and then solution D3 was added. After aging and drying, MXene@ZIF-6 / ZIF-8 composite fibers were obtained.

2. The method for preparing MXene composite fibers according to claim 1, characterized in that, The ratio of Co(NO3)2·6H2O to solvent is 0.12–0.33 mol / mL; And / or, the ratio of Zn(CH3COO)2·2H2O to solvent is 0.12–0.33 mol / mL; And / or, the ratio of dimethylimidazole to solvent is 0.4–0.87 mmol / mL; And / or, the solvent is selected from at least one of methanol and ethanol; And / or, the volume ratio of solution D1, solution D2, and solution D3 is 1:1:1 to 1:1:3; And / or, the mass-to-volume ratio of the MXene fiber to solution D4 is 0.01:30 to 0.03:

30.

3. The method for preparing MXene composite fibers according to claim 1, characterized in that, The aging conditions include: aging temperature of 25-27°C and aging time of 12-48 hours. The drying conditions include: a drying temperature of 50–60°C and a drying time of 12–24 hours.

4. The method for preparing MXene composite fibers according to claim 1, characterized in that, The MXene fiber is obtained by spinning solution through multi-stage sized spinning channels; The multi-level dimensions include sequentially nested channel I and channel II; The inner diameter of channel I is greater than the inner diameter of channel II; Preferably, the inner diameter of channel I is 1.2~1.6mm; Preferably, the inner diameter of channel II is 0.6~1.2mm; Preferably, the spinning solution is MXene-Ti3C2T X The spinning advance rate is 85-100 ml / h.

5. The MXene composite fiber obtained by the preparation method according to any one of claims 1-4, characterized in that, The diameter of the composite fiber is 250–300 μm.

6. A flexible electrode, characterized in that, The MXene composite fiber described in claim 5 is used as the electrode material.

7. A parallel fiber-type symmetrical supercapacitor, characterized in that, The anode and cathode materials of the supercapacitor are both MXene composite fibers obtained by any one of the preparation methods described in 1-4. The distance between the MXene composite fibers used as the anode material and the MXene composite fibers used as the cathode material is 0.2-0.6 cm, and the fiber length is required to be 1-1.5 cm. The electrolyte is a 1.0-2.0 mol / L PVA / H2SO4 gel electrolyte.

8. The parallel fiber symmetrical supercapacitor according to claim 7, characterized in that, The areal capacitance of the supercapacitor is 789–1433.9 mF / cm². -2 .

9. A zinc-ion hybrid supercapacitor, characterized in that, The supercapacitor uses 1-3 mol / L ZnSO4 as the electrolyte, MXene composite fiber obtained by any one of the preparation methods described in 1-4 as the cathode material, and the anode material is 70% rGO / MXene composite fiber.

10. The zinc-ion hybrid supercapacitor according to claim 9, characterized in that, The zinc-ion hybrid supercapacitor can undergo 6500 cycles in ZnSO4 electrolyte with an excellent capacitance retention of up to 92.9% and an areal capacitance >400 mF / cm². -2 Their energy densities are all greater than those of symmetrical supercapacitors.

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