Super capacitor electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of super capacitors, and particularly relates to a super capacitor electrode material and a preparation method thereof. Zinc selenide is tightly compounded on an MXene material to obtain the nano composite material, and the zinc selenide is obtained through in-situ conversion of a ZIF-7 precursor. The material realizes a point-line-surface three-dimensional conductive network in which ZnSe nanoparticles, in-situ derived carbon and MXene nanosheets are tightly coupled, has a high-defect carbon structure and an excellent electron conduction path, realizes ultrahigh specific capacitance, excellent rate capability and excellent long cycle stability, and greatly improves comprehensive electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to a supercapacitor electrode material and its preparation method. Background Technology

[0002] With industrial development and increasing environmental pollution, developing low-cost clean energy and efficient energy storage technologies has become a key step towards achieving green and sustainable development. The development of power sources capable of rapid acceleration and instantaneous discharge has become a major focus of our time. Batteries are becoming a transformative solution for electric vehicles and robotics. Compared to batteries, supercapacitors have faster kinetics, resulting in better rate performance and safety. In supercapacitors, electrode materials play a decisive role in capacitor performance, and selecting effective precursors is crucial for preparing the final supercapacitor electrode materials.

[0003] Metal-organic frameworks (MOFs) have attracted much attention in gas adsorption, catalysis, and sensing due to their high specific surface area and abundant porous structure. As an important branch of MOFs, zeolite imidazole ester frameworks (ZIFs) combine high specific surface area, tunable pores, structural diversity, and good chemical stability, showing great potential in energy storage. However, the inherently low electrical conductivity of ZIFs limits their electrochemical performance. Therefore, derivative materials prepared using ZIFs as templates have become a research hotspot. These derivatives not only maintain the high double-layer capacitance of ZIFs but also generate significant pseudocapacitance by activating metal ions, thereby improving overall energy storage capacity. Currently, how to rationally select the target metal compounds for derivatization remains a key issue that needs further exploration in this field.

[0004] Transition metal chalcogenides and their composites, as a typical class of multifunctional new energy materials, have attracted widespread attention from researchers. Transition metal selenides, in particular, occupy a very important position in inorganic materials. Due to the presence of lone pairs of d electrons, easily bonding empty d orbitals, and high charge-to-radius ratios of atoms or ions, compounds formed by transition metals and chalcogens exhibit significant stability, more electrons participating in redox reactions, and unique electron-deficient structures. These properties enable them to maximize charge storage / release when used as electrode materials in supercapacitors, thus achieving satisfactory overall electrochemical performance. However, ZIF-templated metal selenide electrode materials currently still face the following challenges.

[0005] 1. The conductive network is not ideal, and the intrinsic capacitance performance needs to be improved. Although porous carbon-supported metal selenides (such as CoSe2, Ni-doped CoSe, etc.) can be derived using ZIF-L as a precursor, the conductivity of the derived carbon matrix is ​​limited, and the number and kinetics of redox reaction sites provided by a single metal active center are difficult to overcome the bottleneck of existing capacity and rate performance.

[0006] 2. Existing synthesis processes are complex and demanding, and it is difficult to precisely control the microstructure of composite materials. The traditional two-step process of "carbonization followed by selenization" is lengthy and energy-intensive; while the one-step hydrothermal method is simple, the reaction environment is prone to oxidative deactivation of MXene, and there is a lack of precise control over the size, morphology and binding mode of the product with the substrate, which makes it impossible to fully utilize the structural advantages of ZIF templates to construct ideal ion / electron dual continuous transport channels.

[0007] 3. Existing composite materials have poor structural stability, making it difficult to meet the requirements for long cycle life. Whether it is directly synthesized selenides grown on MXene substrates or simply mixed with ZIF-derived selenides and conductive substrates, structural collapse will occur under long-term high current density impact, resulting in a significant decrease in capacitance retention.

[0008] Therefore, how to inherit the advantages of ZIF templates in terms of high specific surface area and porous structure, while constructing a robust conductive network, enhancing interfacial coupling, and simplifying the process flow, so as to obtain electrode materials with high specific capacitance, excellent rate performance and ultra-long cycle stability, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] To address the aforementioned issues, this application provides a supercapacitor electrode material and its preparation method. A nanocomposite material is obtained by tightly coupling zinc selenide onto MXene material, wherein the zinc selenide is obtained through in-situ conversion of the ZIF-7 precursor. This material achieves a three-dimensional conductive network of "point-line-surface" tightly coupled ZnSe nanoparticles, in-situ derived carbon, and MXene nanosheets. It possesses a high-defect carbon structure and excellent electronic conduction pathways, achieving ultra-high specific capacitance, excellent rate performance, and outstanding long-cycle stability, resulting in a significant improvement in overall electrochemical performance.

[0010] To achieve the above objectives, the first technical solution of this application discloses a supercapacitor electrode material, wherein the material is a zinc selenide nanocomposite material supported by MXene, wherein the zinc selenide is obtained by in-situ conversion of ZIF-7 precursor and is tightly composited with MXene substrate.

[0011] The second technical solution of this application discloses a method for preparing the above-mentioned capacitor electrode material, including the following steps:

[0012] S1. Add MXene to the ZIF-7 synthesis raw materials, and then obtain the MXene / ZIF-7 precursor with ZIF-7 uniformly distributed on MXene by the ZIF-7 synthesis method;

[0013] S2. The MXene / ZIF-7 precursor and selenium source are calcined and selenized under an inert atmosphere to obtain MXene / ZnSe, which is the electrode material for supercapacitors.

[0014] Furthermore, the mass ratio of MXene to ZIF-7 in the MXene / ZIF-7 precursor is 1:1 (i.e., every 100 mg of MXene will be mixed with 100 mg of ZIF-7).

[0015] Furthermore, the selenium source includes, but is not limited to, selenium powder, selenourea, selenium dioxide, and sodium hydroselenate.

[0016] Furthermore, the mass ratio of the MXene / ZIF-7 precursor to the selenium source is 1:2 (the selenium source is twice the amount of the precursor to achieve the best synthesis effect).

[0017] Furthermore, the calcination selenization involves first heating to 250°C and holding for 2 hours, then continuing to heat to 450°C and holding for 2 hours.

[0018] Furthermore, the heating rate is 5°C / min.

[0019] And, the supercapacitor electrode material obtained according to the above preparation method.

[0020] And the application of the aforementioned supercapacitor electrode materials as electrodes in supercapacitors.

[0021] The technical solution provided by this invention brings the following significant beneficial effects:

[0022] 1. A unique composite structure combining high conductivity and abundant active sites was obtained, fundamentally improving the intrinsic performance of electrode materials: This invention successfully constructed a three-dimensional conductive network of tightly coupled "point-line-surface" structures, consisting of ZnSe nanoparticles, in-situ derived carbon, and MXene nanosheets, through in-situ growth and confined transformation of ZIF-7 on MXene. This unique structure brings dual advantages: Furthermore, significantly enhanced conductivity: Raman spectroscopy (I0.05) D / I G =1.02) and electrochemical impedance spectroscopy (EIS) confirmed that the composite material has a high defect carbon structure and excellent electronic conduction pathway. Its charge transfer resistance (Rct) is as low as 1.32 Ω, which is significantly lower than that of the precursor ZIF-7 (2.28 Ω) and unselenized MXene / ZIF-7 (2.06 Ω).

[0023] 2. Achieving ultra-high specific capacitance, excellent rate performance, and outstanding long-cycle stability, resulting in a significant improvement in overall electrochemical performance: Thanks to the above-mentioned optimized structure, the electrode material of this invention exhibits comprehensively leading electrochemical performance:

[0024] (1) Ultra-high specific capacity: at 1 A g -1 At a current density of 2014 F g, its specific capacitance is as high as 2014 F g. -1 It is far superior to the comparative material.

[0025] (2) Excellent rate performance: even at high current densities of 10 A g -1 Under these conditions, the specific capacitance can still maintain 916 F g. -1 The capacity retention rate demonstrates good fast charge and discharge capability.

[0026] (3) Excellent cycling stability: at 10 A g -1 After 10,000 continuous charge-discharge cycles under high current, its capacitance retention rate remained as high as 80.04%, and post-cycle SEM showed that the material structure was intact, without collapse or agglomeration. This is attributed to the mechanical support of MXene and the effective buffering of volumetric stress by its porous structure.

[0027] 3. The preparation process is simplified, MXene oxidation is avoided, and precise control over the material structure is achieved, exhibiting excellent repeatability and scalability. During the high-temperature refining process, the entire process is carried out under an inert atmosphere, effectively preventing MXene oxidation at high liquid-phase temperatures and better preserving its intrinsic high conductivity. Most importantly, in-situ, controllable conversion of the ZIF-7 template into the target product is achieved, perfectly inheriting the template's high specific surface area and porous characteristics. The process has high repeatability and is easy to scale up for production.

[0028] In summary, this invention, through ingenious material design and process innovation, comprehensively solves the technical problems of insufficient conductivity, easy structural degradation, and complex preparation process of existing ZIF-derived electrode materials, and successfully prepares a supercapacitor electrode material with high energy density, high power density, and ultra-long lifespan, which has significant practical application value and industrialization prospects. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This diagram illustrates a method for preparing supercapacitor electrode materials according to one embodiment, along with microscopic images of each intermediate material; wherein, Figure 1 a is a schematic diagram of the preparation method; Figure 1 b is the SEM image of ZIF-7. Figure 1c is the SEM image of ZIF-7 / MXene. Figure 1 d is the SEM image of MXene / ZnSe; Figure 1 e is a TEM image of ZIF-7; Figure 1 f is a TEM image of ZIF-7 / MXene; Figure 1 g is a TEM image of MXene / ZnSe.

[0031] Figure 2 The following are the spectral analysis results of each material during the preparation of MXene / ZnSe in Example 1. Figure 2 a is the XRD diffraction pattern. Figure 2 b represents FTIR analysis. Figure 2 c represents the BET isotherm. Figure 2 d represents TGA analysis.

[0032] Figure 3 The electrochemical analysis results of each material during the preparation of MXene / ZnSe in Example 1 are shown; among them Figure 3 a represents the CV curves of the bare ZIF-7, MXene / ZIF-7, and MXene / ZnSe electrodes at 10 mV s−1; Figure 3 b shows the GCD curves of ZIF-7, MXene / ZIF-7, and MXene / ZnSe electrodes at a current density of 10 A g⁻¹. Figure 3 c represents the coulombic efficiency of ZIF-7, MXene / ZIF-7, and MXene / ZnSe. Figure 3 d represents the specific surface area AC / / MXene / ZnSe, capacitance, and capacitance retention at a series of current densities. Figure 3 e represents the EIS curves of ZIF-7, MXene / ZIF-7, and MXene / ZnSe electrodes. Figure 3 f represents the cycling performance of ZIF-7, MXene / ZIF-7, and MXene / ZnSe ASC after 10,000 cycles at 10 A g⁻¹. Figure 3 g represents the CV curves at different scan rates. Figure 3 GCD results measured at h = 1 - for asymmetric supercapacitors at 10 F g -1 Current density, Figure 3 i is the SEM image of MXene / ZnSe after 10000 cycles.

[0033] Figure 4 The performance diagram of the capacitor described in Example 2 is shown below. Figure 4 a represents MXene / ZnSe and AC electrodes at 10 mVs -1 CV curves measured at scan rate; Figure 4b represents the CV curves at different scan speeds; Figure 4 c represents the GCD curves under different current densities; Figure 4 d represents the calculated specific capacitance of the ASC under different current densities; Figure 4 e represents the capacitance retention rate of MXene / ZnSe.

[0034] Figure 5 Ragone diagram of AC / / MXene / ZnSe ASC and other ASCs. Detailed Implementation

[0035] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0036] The first embodiment of this application discloses a supercapacitor electrode material, which is a zinc selenide nanocomposite material supported by MXene, wherein the zinc selenide is obtained by in-situ conversion of ZIF-7 precursor and is tightly composited with MXene substrate.

[0037] like Figure 1 As shown, the above-mentioned supercapacitor electrode material is obtained by the following preparation method:

[0038] S1. Add MXene to the ZIF-7 synthesis raw materials, and then obtain the MXene / ZIF-7 precursor with ZIF-7 uniformly distributed on MXene by the ZIF-7 synthesis method;

[0039] S2. The MXene / ZIF-7 precursor and selenium source are calcined and selenized under an inert atmosphere to obtain MXene / ZnSe, which is the electrode material for supercapacitors.

[0040] In this embodiment, MXene is a class of two-dimensional inorganic compounds in materials science, consisting of transition metal carbides, nitrides, or carbonitrides with a thickness of several atomic layers. Its general chemical formula is Mx. n+1 X n T x In this formula, M represents a transition metal element, X represents carbon or nitrogen, and T represents a functional group bonded to the surface of the MXene. MXene exhibits excellent electrical and ionic conductivity. The MXene described in this application is used for supporting and dispersing ZIF-7 and its derivatives, and can be used to support Ti3C2T. x It can also be other transition metal carbides, nitrides, or carbonitrides (MXenes) such as Mo2CT. x V2CT x Nb2CTx wait.

[0041] The MXene material described in this application can be prepared from corresponding three-dimensional materials, such as... Figure 1 One specific embodiment disclosed involves obtaining a three-dimensional material through ultrasonic dissection, or it may be commercially available.

[0042] In this embodiment, such as Figure 1 As shown, the MXene / ZIF-7 precursor is achieved by intercalating MXene and anchoring ZIF-7 in situ onto MXene. Specifically, MXene is added to the ZIF-7 synthesis raw material, and during the stir synthesis process, ZIF-7 can be uniformly distributed on MXene, thus completing the intercalation of MXene and the anchoring of ZIF-7.

[0043] Understandably, the synthesis of ZIF-7 in the above process is a conventional synthesis method in the art. A preferred synthesis method disclosed in this application involves mixing, stirring, and allowing the mixture to stand with a soluble zinc source solution. Compared to ZIF-8 or ZIF-67, ZIF-7's unique benzimidazole ligand and topological structure enable it to form a zinc selenide / carbon composite structure with richer defects and superior ion diffusion channels after pyrolysis, which is key to improving intrinsic capacitance. In this embodiment, the mass ratio of MXene to ZIF-7 in the MXene / ZIF-7 precursor is 1:1.

[0044] In a further embodiment, the obtained MXene / ZIF-7 precursor and selenium source are calcined and selenized under an inert atmosphere to obtain MXene / ZnSe, which is the supercapacitor electrode material.

[0045] like Figure 1 As shown, the obtained MXene / ZIF-7 precursor was subjected to a two-stage calcination with a selenium source under an inert atmosphere. The first stage of calcination involved heating to 250°C and holding for 2 hours, followed by a second stage of calcination at 450°C and holding for 2 hours. In the first stage at a low temperature, the ZIF-7 on the MXene / ZIF-7 was gently decomposed, constructing a sacrificial template with highly dispersed metal sites and abundant porosity. In the second stage at a high temperature, the selenium powder sublimated, efficiently completing the selenization reaction while protecting the MXene, generating highly crystalline ZnSe nanocrystals.

[0046] Compared to the existing two-step high-temperature method of "carbonization followed by selenization", this application integrates the pyrolysis and selenization processes into a single high-temperature step. This process not only simplifies the procedure and reduces energy consumption, but more importantly, the solid-gas reaction under an inert atmosphere effectively avoids the oxidation of MXene in a liquid-phase hydrothermal environment, maximizing the preservation of its high conductivity, while also achieving precise control over the microstructure of the product.

[0047] In a further embodiment, the selenium source includes, but is not limited to, selenium powder, selenourea, selenium dioxide, and sodium hydroselenate. The mass ratio of the MXene / ZIF-7 precursor to the selenium source is 1:2, and the heating rate is 5°C / min.

[0048] The technical effects of the present application's technical solution will be described in detail below through specific embodiments.

[0049] Example 1: Preparation of Supercapacitor Electrode Materials

[0050] This embodiment uses Ti3C2T x It was prepared from MXnenc material, specifically as follows:

[0051] (1) Ti3C2T x Preparation of MXene

[0052] Weigh 1.5 g of Ti3AlC2 MAX phase (3D material), grind for 30 minutes, and divide into five small portions. Place 1.5 g of LiF in 30 mL of HCl (9 M) and stir for 10 minutes. Then, add a portion of MAX phase to the solution every 5 minutes of stirring until the last portion is added, and continue stirring for 35 minutes. Then, stir in a water bath at 35 °C for 36 hours. After stirring, wash with deionized water until the pH is approximately 7. Collect the precipitate, redisperse it in deionized water, and sonicate for 1 hour. After centrifugation, redisperse the precipitate in anhydrous ethanol and perform a second ultrasonic stripping for another 30 minutes. After another centrifugation step, mix the precipitate with water, centrifuge, and collect the supernatant to produce a few-layer 2D MXene.

[0053] (2) Preparation of MXene / ZIF-7 and ZIF-7

[0054] The preparation method of ZIF-7 is as follows: Weigh 878 mg of zinc acetate and place it in 20 mL of deionized water, labeling it solution A. Weigh 946 mg of benzimidazole and place it in 20 mL of DMF. After sonicating solutions A and B for 5 minutes respectively, quickly pour solution A into solution B and stir for 10 minutes. Then let it stand for 24 hours. After standing, centrifuge the product three times with anhydrous ethanol and dry it in a vacuum drying oven. The collected white powder is ZIF-7.

[0055] The preparation method of MXene / ZIF-7 is as follows: MXene is added to the raw materials for ZIF-7 preparation, and then the MXene / ZIF-7 precursor with ZIF-7 uniformly distributed on MXene is obtained by ZIF-7 synthesis method; that is, according to the ZIF-7 preparation method, 40 mL of MXene (2 mg / mL) is added after mixed solutions A and B. -1 ), and perform subsequent operations to obtain the MXene / ZIF precursor.

[0056] (3) Preparation of MXene / ZnSe

[0057] Weigh 200 mg of MXene / ZIF-7 and place it in a porcelain boat. Then weigh 400 mg of Se powder and place it on the upper part of the porcelain boat. Finally, place the boat in a tube furnace and heat at 5 °C for 1 minute. -1 Heat to 250 °C and maintain for 2 hours, then continue heating at 5 °C / min. -1 Heat to 450 °C and hold for 2 hours. After cooling, collect the brown powder, i.e., MXene / ZnSe.

[0058] Experimental Example 1: Microstructure of MXene / ZnSe

[0059] like Figure 1 Figure 1b discloses the microstructure of the products at each stage of the preparation process in Example 1. SEM observation of MXene / ZnSe and its precursor morphology shows that ZIF-7 has a typical sodalite structure with a size of approximately 200 nm. In Figure 1c, ZIF-7 is uniformly distributed on the two-dimensional MXene layer. The synergistic effect of the two metals can prevent nanoparticle aggregation, reduce internal resistance, improve rate performance, and construct ion diffusion channels. To increase the contact area between the material and the electrolyte and optimize ion transport, selenization treatment was performed. Figure 1 d shows that the selenized MXene / ZnSe exhibits a loose and porous structure, providing more electrochemical active sites, and the MXene layer was not oxidized under nitrogen atmosphere protection. TEM characterization was used to observe the internal structure and morphology of ZIF-7, MXene / ZIF-7, and MXene / ZnSe: Figure 1 The ZIF-7 morphology in e is consistent with that in SEM, but the size is slightly smaller, possibly due to prolonged ultrasound treatment before TEM. Figure 1 f shows that in MXene / ZIF-7, ZIF-7 is densely packed within the MXene sheet, while the morphology of ZIF-7 in sparse areas shows no significant change, confirming that in-situ intercalation of MXene does not affect its physical properties; after high-temperature selenization, MXene / ZnSe exhibits loose and porous characteristics, with the MXene sheet becoming more wrinkled and ZnSe being uniformly dispersed on the sheet, effectively preventing the co-reclamation of the two. Figure 1 g).

[0060] Experimental Example 2: Spectral Analysis

[0061] The structures of the MXene / ZnSe and intermediate materials prepared in Example 1 were systematically characterized by XRD (X-ray diffraction) Raman spectroscopy, and the results are as follows: Figure 2 As shown: XRD spectrum ( Figure 2 a) This indicates that the synthesized ZIF-7 has good crystallinity, and its characteristic peaks are consistent with those reported in the literature. In the MXene / ZIF-7 composite material, both the characteristic peaks of ZIF-7 and Ti3C2T can be observed simultaneously. x The diffraction peaks of MXene near 7.25°, 35.4°, and 42.7° confirm the successful growth and intercalation of ZIF-7 on the MXene surface. Notably, the intensity of the diffraction peaks of ZIF-7 decreased after composite formation, indicating an interfacial interaction between the two. After calcination and selenization, the characteristic peaks of ZIF-7 completely disappeared, and the (111), (200), and (220) diffraction peaks corresponding to the ZnSe standard card (PDF#03-7409) appeared in the MXene / ZnSe spectrum, confirming that ZIF-7 had been successfully converted to ZnSe and loaded onto MXene. Raman spectroscopy ( Figure 2 (b) Further information about the carbon structure of the materials was revealed. All samples exhibited characteristic peaks at 1335.69 cm⁻¹ (D band, representing defects / disorder) and 1594.34 cm⁻¹ (G band, representing sp² carbon structure). The Ig of MXene / ZnSe... D / I G The highest ratio (1.02) indicates that the anchoring and transformation of ZIF-7 on the MXene surface in the composite material introduces more structural defects and small-sized sp² carbon domains, which is beneficial to increasing the electrochemical active sites.

[0062] SEM and TEM observations revealed that MXene / ZnSe exhibited a loose and porous morphology after selenization. BET test ( Figure 2 c) shows that ZIF-7, MXene / ZIF-7, and MXene / ZnSe all possess type IV isotherms and mesoporous structures, with specific surface areas of 3.1 m² g⁻¹, 2.43 m² g⁻¹, and 3.47 m² g⁻¹, respectively. The higher specific surface area and abundant mesopores of MXene / ZnSe facilitate electrolyte contact and permeation, thus providing more pseudocapacitive active sites. TGA analysis ( Figure 2(d) indicates that the thermal decomposition of the three materials can be divided into two stages: the first stage (70–225 °C) mainly involves the removal of adsorbed water, with MXene / ZnSe exhibiting the lowest weight loss rate (4.75%); the second stage (250–620 °C) corresponds to the decomposition of the organic ligands, where the weight loss trend of MXene / ZnSe is significantly slowed down, indicating that it has the best thermal stability. This is attributed to its unique rough porous structure, which facilitates heat distribution and resists structural collapse. This further confirms that ZIF-7 grows stably on MXene, and the thermal stability of the composite material is enhanced.

[0063] Experimental Example 3: Electrochemical Performance Analysis

[0064] Electrochemical analysis was performed on the MXene / ZnSe obtained in Example 1 and each intermediate material (ZIF-7, MXene / ZIF-7) (test conditions: room temperature, 6M KOH electrolyte). The experimental results are as follows. Figure 3 As shown. Figure 3 In Figure a, the CV curves at a scan rate of 10 mV s⁻¹ show that MXene / ZnSe has the largest CV area, current density, and specific capacitance. Figure 3 In b, at a current density of 1A g⁻¹, this electrode has the longest discharge time and the highest specific capacitance; Figure 3 c shows that its coulombic efficiency at 1 A g⁻¹ reaches 95.13%, significantly better than ZIF-7 and MXene / ZIF-7. Figure 3d shows that the MXene / ZnSe material maintains the highest specific capacitance at different current densities. This is attributed to the ordered arrangement of nanoparticles loaded on the nanosheets, which provides many active sites for redox reactions. Furthermore, Figure 3 Figure e shows the Nyquist plots of electrochemical impedance spectroscopy (EIS) for several materials. The plots are similar in shape, consisting of semicircles in the high-frequency region corresponding to charge transfer resistance and diagonal lines in the low-frequency region. The fitted charge transfer resistances for the precursors ZIF-7, MXene / ZIF-7, and MXene / ZnSe are 2.28 Ω, 2.06 Ω, and 1.32 Ω, respectively. The lowest resistance of MXene / ZnSe indicates its superior capacitive properties. Figure 3The figure shows the long-term cycling performance of the three materials at 10 A g⁻¹. The MXene / ZnSe electrode retained 80.04% of its initial capacitance after 10,000 cycles, while ZIF-7 and MXene / ZIF-7 retained only 77.86% and 74.36%, respectively. This indicates a significantly enhanced stability of the MXene / ZnSe electrode. The main reasons include the strong interaction between MXene and ZnSe, which may enhance ion and electron conduction. The loose porous structure of zinc selenide can better disperse the stress induced by high current. Simultaneously, the extensive coverage of the MXene sheet allows all ZnSe particles to simultaneously store and accumulate charge, thereby mitigating the structural degradation of locally active particles caused by significant energy shocks. The CV curves of MXene / ZnSe at different scan rates and the galvanostatic charge-discharge (GCD) curves at different current densities are shown in the figure. Figure 3 The values ​​of g and 3h are shown. Notably, with increasing scan rate, the electrode exhibits a gradually expanding CV curve with a distinct bimodal distribution, indicating battery-like behavior and excellent conductivity within this scan rate range. Benefiting from the pseudocapacitive mechanism, the GCD curve shows a high specific capacitance. At current densities of 1, 2, 5, 8, and 10 A g -1 The calculated specific capacitances were 2014, 1718, 1349, 1345, and 916 F g, respectively. -1 It exhibits commendable rate performance. Figure 3 Image i shows a SEM image of MXene / ZnSe after 10,000 cycles. The synthesized electrode material retains its overall structure, and no structural changes were observed. Therefore, the MXene-based composite material exhibits improved performance after selenium modification due to rapid electron transfer and ion diffusion.

[0065] Example 2: Application of MXene / ZnSe in Supercapacitors

[0066] In this embodiment, an asymmetric supercapacitor (ASC) device was assembled using MXene / ZnSe as the cathode, activated carbon (AC) as the anode, and 3 M KOH as the electrolyte. The electrochemical performance of the device was then tested, and the results are as follows: Figure 4 As shown.

[0067] Figure 4 a represents the CV curve of MXene / ZnSe versus AC in the three-electrode system; Figure 4 b shows a 1.6 V voltage window and a 10-100 mV s. -1 At the same scan rate, the shape of the CV curve and the redox peaks are basically consistent, demonstrating excellent electrochemical stability; Figure 4The symmetric GCD curve of c proves that AC / / MXene / ZnSe has high reversible electrochemical performance; Figure 4 d indicates that 1-10 Ag -1 At a current density of 1 A g, the device -1 The specific capacitance reaches 127.26 F g. -1 The discharge time is relatively long. Furthermore, such as... Figure 4 As shown in Figure e, the sample still retains 71.62% of its capacitance after 10,000 cycles, demonstrating the device's excellent long-term cycling stability.

[0068] Example 3: Comparison of electrochemical performance of MXene / ZnSe with similar materials

[0069] The electrode material prepared in this application was compared with asymmetric supercapacitors made from similar electrode materials reported in the literature, and the overall electrochemical performance was found to be significantly improved. The results are shown in Table 1.

[0070] Table 1. Comparison of electrochemical performance of MXene / ZnSe with similar materials

[0071] .

[0072] Among them, MXene / SnS2 / CNT is from the literature (Chem. Eng. J. (2025) 165826); NCL-SSAC / / SSAC is from the literature (Ceram. Int. 51 (2025) 52163-52180); NFC / porous Co3O4 is from the literature (Adv. Compos. Hybrid Mater. 4 (2021) 306-316). ， PGr is derived from the literature (Int. J. Energy Res. 46 (2022) 11400-11410), and (MnFeCoNiZn)3O4 is derived from the literature (Chemical Engineering Journal Advances. 21 (2025) 100708). ， CuCoSn–OH is derived from the literature (J. Phys. Chem. Solids 199 (2025) 112524.).

[0073] To further investigate the performance of the samples prepared in this experiment, the energy density and power density of the AC / / MXene / ZnSe capacitor at the corresponding current density were calculated using the results obtained from the GCD curves. The results are as follows: Figure 5 As shown. It can be observed that at a power density of 749.83 W kg... -1At that time, the energy density of the AC / / MXene / ZnSe capacitor reached 39.76 Wh kg. -1 Combining the results in Table 1 with those of other materials, it can be seen that the asymmetric supercapacitor AC / / MXene / ZnSe, through the fusion of the double electric layer and pseudocapacitance / cell-type mechanism, maintains high power and long lifetime while significantly improving energy density due to the synergistic effect of the nanostructure and the combination of high voltage windows on both positive and negative poles.

[0074] As demonstrated by the above embodiments, this application discloses a scalable and cost-effective strategy for preparing MXene-based selenide materials with high specific capacitance and high cycling stability. MXene / ZnSe nanocomposites were prepared by in-situ stirring precipitation and high-temperature calcination, and the structure was successfully constructed by XRD, TEM, and SEM characterization. ZnSe nanoparticles can adapt to electrode volume expansion, and the MXene layer can reduce ZnSe fragmentation and detachment during cycling; the synergistic effect of these two components bridges the gap between the theoretical and actual specific capacitance of selenides, inhibits MXene stacking, increases active sites, and enhances pseudocapacitive energy storage. In a three-electrode system, this material exhibits high specific capacitance at 1 Ag... -1 The specific capacitance reaches 2014 F g -1 When assembled into an AC / / MXene / ZnSe asymmetric supercapacitor, the power density reaches 749.83 W kg. -1 The energy density remains at 39.76 Wh / kg. -1 And 10 A g -1 After 10,000 cycles, the capacitance retention rate exceeds 70%.

[0075] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A supercapacitor electrode material, characterized in that, The material is a zinc selenide nanocomposite material supported by MXene, wherein the zinc selenide is obtained by in-situ conversion of the ZIF-7 precursor.

2. A method for preparing the capacitor electrode material as described in claim 1, characterized in that, Includes the following steps: S1. Add MXene to the ZIF-7 synthesis raw materials, and then obtain the MXene / ZIF-7 precursor with ZIF-7 uniformly distributed on MXene by the ZIF-7 synthesis method; S2. The MXene / ZIF-7 precursor and selenium source are calcined and selenized under an inert atmosphere to obtain MXene / ZnSe, which is the electrode material for supercapacitors.

3. The preparation method according to claim 2, characterized in that, The mass ratio of MXene to ZIF-7 in the MXene / ZIF-7 precursor is 1:

1.

4. The preparation method according to claim 2, characterized in that, The selenium source includes, but is not limited to, selenium powder, selenourea, selenium dioxide, and sodium hydroselenate.

5. The preparation method according to claim 2, characterized in that, The mass ratio of the MXene / ZIF-7 precursor to the selenium source is 1:

2.

6. The preparation method according to claim 2, characterized in that, The calcination selenization process involves first heating to 250°C and holding for 2 hours, then continuing to heat to 450°C and holding for 2 hours.

7. The preparation method according to claim 6, characterized in that, The heating rate is 5°C / min.

8. A supercapacitor electrode material prepared by any one of the preparation methods according to claims 2-7.

9. The application of the capacitor electrode material according to claim 1 or 8 as an electrode in a supercapacitor.

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