Composite diaphragm for supercapacitor and preparation method thereof

Abstract

The invention relates to a composite diaphragm for a supercapacitor and a preparation method thereof, and the preparation method comprises the following steps: carrying out the ionic liquid functionalization of a metal organic frame material, and obtaining a functionalized metal organic frame; performing conductive polymer surface modification on the MXene quantum dots to obtain modified MXene; dispersing the functionalized metal organic framework, the modified MXene and a dynamic cross-linking agent in a fluorine-containing polymer solution to form precursor slurry; coating the precursor slurry on the surface of a conductive substrate, applying a direct-current electric field to carry out orientation treatment, and carrying out phase separation and curing to obtain a composite diaphragm; wherein the dynamic cross-linking agent is a polyurethane elastomer containing a disulfide bond. According to the preparation method disclosed by the invention, the metal organic framework material is subjected to functionalized treatment through the ionic liquid, so that the material keeps a high specific surface area and a 0.8 nm regular pore channel, an ion selective transmission path in gradient distribution is formed, the ionic conductivity is optimized, and the pore channel is prevented from being blocked.

Description

Technical Field

[0001] This application relates to the technical field of capacitors, and particularly to a composite separator for supercapacitors and a preparation method thereof. Background Art

[0002] In the development of composite separators for supercapacitors, traditional preparation technologies generally face the contradictory challenges of material functionality and structural stability. Existing methods usually introduce inorganic fillers in a physical blending manner to enhance mechanical properties, but the poor interfacial compatibility between the fillers and the polymer matrix easily leads to phase separation, resulting in blocked ion transport channels; meanwhile, the insufficient compatibility between conventional plasticizers and solvents easily causes the aggregation of residues, affecting the chemical stability of the electrolyte. More prominently, traditional film-forming processes such as melt extrusion are difficult to achieve the three-dimensional ordered arrangement of nano-fillers, and the disordered dispersion of conductive phases cannot construct a continuous electron conduction network, resulting in a high surface resistance of the separator. In addition, commercial materials show the expansion of microcracks due to the lack of a dynamic bonding mechanism during long-term cycling, and the thermal motion of polymer segments intensifies at high temperatures, leading to structural collapse, seriously restricting the application reliability of devices in high-load and wide-temperature environments. How to simultaneously improve the ion / electron dual-conduction ability, self-healing characteristics, and high-temperature stability of the separator through material design and process innovation, while solving the problems of filler orientation control and process compatibility, has become a technical bottleneck that urgently needs to be broken through in this field. Summary of the Invention

[0003] This application provides a preparation method for a composite separator for supercapacitors, including the following steps:

[0004] Perform ionic liquid functionalization treatment on a metal-organic framework material to obtain a functionalized metal-organic framework;

[0005] Perform conductive polymer surface modification on MXene quantum dots to obtain modified MXene;

[0006] Disperse the functionalized metal-organic framework, modified MXene, and a dynamic cross-linking agent in a fluoropolymer solution to form a precursor slurry;

[0007] Coat the precursor slurry on the surface of a conductive substrate, apply a direct current electric field for orientation treatment, and obtain a composite separator after phase separation and curing;

[0008] Wherein, the dynamic cross-linking agent is a polyurethane elastomer containing disulfide bonds.

[0009] In some embodiments, the metal-organic framework material is UiO-66-NH 2, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and when performing the functionalization treatment, the mass-to-volume ratio of the metal-organic framework to the ionic liquid is 1 g:50 mL, the reaction temperature is 60 ± 2 °C, and the reaction time is 24 h.

[0010] In some embodiments, the preparation of the modified MXene comprises the following steps:

[0011] Etching the Ti 3 AlC 2 powder for 24 h with 40% hydrofluoric acid solution, obtaining a monolayer MXene colloidal solution after exfoliation with DMSO solvent, and obtaining MXene quantum dots after ultrasonic fragmentation;

[0012] Performing a grafting reaction on the MXene quantum dots, 3,4-ethylenedioxythiophene monomer, and an oxidant in an ice-water bath at 5 °C for 12 h to obtain the modified MXene.

[0013] In some embodiments, the molar ratio of the MXene quantum dots to the 3,4-ethylenedioxythiophene monomer is 1:50, the oxidant includes ammonium persulfate, and the molar ratio of the 3,4-ethylenedioxythiophene monomer to the oxidant is 1:1.2.

[0014] In some embodiments, the precursor slurry contains by mass percentage: 5% functionalized metal-organic framework, 1% modified MXene, 0.5% dynamic crosslinking agent, and the balance is a fluoropolymer solution. The fluoropolymer is a vinylidene fluoride-chlorotrifluoroethylene copolymer, wherein the molar content of chlorotrifluoroethylene is 10%.

[0015] In some embodiments, the functionalized metal-organic framework is dispersed by ball milling, the ball milling speed is 300 rpm, and the ball milling time is 2 h; the modified MXene is dispersed by probe sonication, the ultrasonic power is 200 W, the on / off cycle is 2 s / 1 s, and the ultrasonic time is 15 min.

[0016] In some embodiments, the DC electric field strength is 50 kV, the electric field treatment time is 10 min, and the conductive substrate is an electrolytic copper foil with a surface roughness Ra ≤ 0.2 μm.

[0017] In some embodiments, the phase separation and curing include: pre-volatilizing at 40 °C until the film thickness is 200 μm, then immersing the copper foil coated with the slurry in liquid nitrogen for 5 min, and the cooling rate ≥ 150 °C / min.

[0018] In some embodiments, the number-average molecular weight of the dynamic crosslinking agent is 8000 - 10000, wherein the molar content of disulfide bonds is 2.5 - 3.5%, and the solvent of the fluoropolymer solution is a mixed solvent of DMF and acetone with a volume ratio of 7:3.

[0019] The present application also provides a composite separator for supercapacitors, which is prepared according to any one of the foregoing preparation methods.

[0020] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0021] 1. By functionalizing metal-organic framework materials with ionic liquids, while maintaining a high specific surface area (≥1200 m 2 / g) and 0.8 nm regular pore channels, a gradient-distributed ion-selective transport path is formed to optimize ionic conductivity and avoid pore blockage.

[0022] 2. By surface-modifying MXene quantum dots with conductive polymers, a three-dimensional conductive network is formed in MXene to enhance antioxidant ability and inhibit quantum dot agglomeration, and improve the charge distribution uniformity of the separator.

[0023] 3. By introducing a polyurethane elastomer containing disulfide bonds as a dynamic crosslinking agent, the material undergoes reversible fracture / recombination under stress, endowing the separator with self-healing ability and effectively inhibiting the propagation of microcracks during cycling.

[0024] 4. By inducing the directional alignment of functionalized metal-organic frameworks and modified MXene with a DC electric field (50 kV) and combining liquid nitrogen quenching phase separation curing, the separator forms gradient pores and ordered ion / electron transport channels, significantly improving ionic conductivity and structural stability.

[0025] 5. By chemical bonding of a fluoropolymer matrix and functional fillers, the interfacial compatibility is enhanced, avoiding the phase separation problem caused by traditional physical blending. At the same time, the crystallinity is reduced by 10 mol% trifluorochloroethylene units, improving the flexibility of the matrix and the high-temperature deformation resistance.

[0026] 6. By synergistically treating ball milling dispersion and probe ultrasound, the functionalized metal-organic frameworks and modified MXene form an interpenetrating structure in the matrix, maximizing the ion / electron double conduction performance.

[0027] 7. By fixing the oriented structure with liquid nitrogen quenching, the separator forms a composite structure of hierarchical pores and nanoscale pores, while retaining the ordered arrangement characteristics induced by the electric field.

[0028] 8. By regulating the phase separation process with a DMF / acetone (7:3) mixed solvent, the fluoropolymer forms an interpenetrating network structure, promoting the gradient dispersion of functional fillers and providing a structural basis for electric field orientation.

[0029] 9. By optimizing the molecular weight of the dynamic crosslinking agent (8000 - 10000) and the disulfide bond content (2.5 - 3.5%), the crosslinked network has both mechanical strength and chain segment reconstruction ability, balancing the self-healing performance and material integrity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings herein are incorporated into and constitute a part of this specification, showing embodiments consistent with the present invention and, together with the specification, are used to explain the principles of the present invention.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a flowchart of the preparation method of the composite separator for supercapacitors provided by the embodiments of the present application;

[0033] Figure 2 It is a flowchart of the preparation method of MXene quantum dots provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0035] Figure 1 It shows a flowchart of the preparation method of the composite separator for supercapacitors provided by the embodiments of the present application.

[0036] As Figure 1 shown, the present application provides a preparation method of a composite separator for supercapacitors, including the following steps:

[0037] S10. Perform ionic liquid functionalization treatment on the metal-organic framework material to obtain a functionalized metal-organic framework;

[0038] S20. Perform conductive polymer surface modification on MXene quantum dots to obtain modified MXene;

[0039] S30. Disperse the functionalized metal-organic framework, modified MXene, and dynamic crosslinking agent in a fluoropolymer solution to form a precursor slurry;

[0040] S40. Coating a precursor slurry on the surface of a conductive substrate, applying a direct current electric field for orientation treatment, and obtaining a composite separator after phase separation and curing;

[0041] Among them, the dynamic crosslinking agent is a polyurethane elastomer containing disulfide bonds.

[0042] This preparation method realizes the directional arrangement of functional materials under the induction of a direct current electric field through the synergistic effect of ionic liquid-functionalized metal-organic frameworks and MXene quantum dots modified with conductive polymers, combined with the reversible characteristics of the disulfide bonds of the dynamic crosslinking agent, to obtain functional fillers. Specifically, the ionic liquid-grafted metal-organic framework provides an ion-selective transport path through its regular pores, the conductive polymer coated on the surface of MXene quantum dots forms a three-dimensional conductive network, and the disulfide bonds in the dynamic crosslinking agent undergo reversible fracture / recombination under stress; under the action of a direct current electric field, the functionalized metal-organic framework particles generate electrophoretic migration due to surface charge differences and form a concentration gradient distribution along the electric field direction - the enrichment degree of the metal-organic framework is higher in the area close to the positive electrode, and the pore arrangement is denser; while in the area far from the electrode, it shows a gradually sparse distribution. At the same time, the spatial difference in the solvent evaporation rate during the phase separation process (the surface layer evaporates faster than the bottom layer) leads to the generation of a pore size gradient during the curing of the polymer: the surface layer forms smaller pores (50 - 100 nm) due to rapid curing, and the bottom layer undergoes slow phase separation to form larger pores (200 - 300 nm). This macroscopic gradient and the regular micropores (0.8 nm) of the MOFs themselves jointly construct a "micropore-mesopore-macropore" multi-level transport channel to achieve the directional and rapid migration of ions in the thickness direction of the separator. At the same time, the fluoropolymer solution fixes the orientation structure through liquid nitrogen quenching during the phase separation process, and finally forms a composite separator with gradient pores and self-healing ability.

[0043] This method constructs an ordered ion transport channel through electric field-induced orientation, significantly improving the ionic conductivity of the separator; the disulfide bonds of the dynamic crosslinking agent endow the material with self-healing ability, which can effectively inhibit the propagation of microcracks during cycling; the ion-selective transport of the metal-organic framework and the conductive network of MXene work together to maintain structural stability at high temperatures; the chemical bonding between the fluoropolymer matrix and the functional filler enhances the interfacial compatibility and avoids the phase separation problem caused by traditional physical blending, thereby comprehensively improving the cycle life and high-temperature working performance of the supercapacitor.

[0044] In some embodiments, the metal-organic framework material is UiO-66-NH 2 , the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and the mass-volume ratio of the metal-organic framework to the ionic liquid during the functionalization treatment is 1 g:50 mL, the reaction temperature is 60 ± 2 °C, and the reaction time is 24 h.

[0045] By setting this parameter combination, UiO-66-NH 2 while maintaining its original high specific surface area (≥1200 m 2 / g) and 0.8 nm regular pore channels, endows it with ion-selective transport ability through ionic liquid grafting; the feeding ratio of 1 g:50 mL optimizes the coordination density between the surface functional groups of the metal-organic framework and the ionic liquid, avoiding pore blockage caused by excessive ionic liquid and ensuring the exposure of sufficient active sites; the mild reaction temperature of 60 °C realizes efficient grafting while protecting the crystal structure of the metal-organic framework from being damaged; the 24 h reaction cycle enables the ionic liquid to form a gradient distribution inside and outside the pores, and finally obtains a functionalized metal-organic framework material with both high ionic conductivity and structural stability.

[0046] Figure 2 This is the flow chart of the preparation method of MXene quantum dots provided by the embodiments of this application.

[0047] As Figure 2 shown, in some embodiments, the preparation of the modified MXene includes the following steps:

[0048] S11. Use 40% hydrofluoric acid solution to etch Ti 3 AlC 2 powder for 24 h, obtain a monolayer MXene colloidal solution after exfoliation with DMSO solvent, and obtain MXene quantum dots after ultrasonic fragmentation;

[0049] S12. Carry out a grafting reaction on the MXene quantum dots, 3,4-ethylenedioxythiophene monomer and an oxidant in an ice bath at 5 °C for 12 h to obtain the modified MXene.

[0050] First, use 40% hydrofluoric acid to etch Ti 3 AlC 2 powder for 24 h, selectively remove the Al atomic layer to form a layered Ti 3 C 2 Tx structure, and then exfoliate it into monolayer MXene colloidal quantum dots through the intercalation of DMSO solvent; then, in a low-temperature environment at 5 °C, utilize the in-situ oxidative polymerization reaction of 3,4-ethylenedioxythiophene monomer on the surface of MXene quantum dots, and through the π-π conjugation and hydrogen bond interaction between the thiophene ring and the oxygen-containing functional groups (such as -OH, -O) on the MXene surface, form a uniformly coated PEDOT conductive layer. The 12 h reaction time ensures the full diffusion of the monomer and the completion of the grafting process, and finally obtains a modified MXene with both high conductivity and structural stability.

[0051] The synergistic effect of hydrofluoric acid etching and DMSO stripping enables MXene quantum dots to maintain a single-layer structure and a high specific surface area, providing sufficient active sites for subsequent conductive polymer grafting; the low-temperature reaction environment of 5 °C inhibits the side reaction of self-polymerization of EDOT monomers, ensuring the preferential growth of PEDOT on the MXene surface to form a continuous coating layer, effectively preventing the aggregation of quantum dots; the 12-hour grafting time enables the PEDOT segments to form stable chemical bonds with the MXene surface, enhancing the antioxidant ability of the material in the electrolyte while constructing a three-dimensional conductive network, thereby improving the overall electrochemical performance and cycle stability of the separator.

[0052] In some embodiments, the molar ratio of the MXene quantum dots to the 3,4-ethylenedioxythiophene monomer is 1:50, the oxidant includes ammonium persulfate, and the molar ratio of the 3,4-ethylenedioxythiophene monomer to the oxidant is 1:1.2.

[0053] By precisely controlling the molar ratio of MXene quantum dots to the 3,4-ethylenedioxythiophene monomer (1:50) and the ratio of the monomer to the ammonium persulfate oxidant (1:1.2), the controllable grafting of the conductive polymer on the MXene surface is achieved: the excessive amount of EDOT monomer (50-fold molar amount) ensures its sufficient adsorption on the MXene quantum dot surface and the formation of a dense coating layer, while ammonium persulfate, as an oxidant, slowly releases free radicals at a low temperature of 5 °C, preferentially initiating the in-situ polymerization of the monomer on the MXene surface rather than the self-polymerization reaction in the bulk solution; the 1:1.2 oxidant ratio not only provides sufficient oxidation ability to drive the ring-opening polymerization of EDOT but also avoids the destruction of the MXene crystal structure by excessive oxidant, ultimately forming a uniform and chemically bonded PEDOT-MXene composite interface.

[0054] The above parameters enable the EDOT monomer to form a continuous conductive network on the MXene surface. The high ratio of 1:50 ensures that the active sites on the quantum dot surface are completely covered, avoiding the charge transport bottleneck caused by locally unmodified regions; the 1:1.2 oxidant dosage balances the polymerization rate and the product quality, ensuring both the sufficient growth of PEDOT segments to form a three-dimensional conductive path and preventing the structural damage of MXene quantum dots caused by over-oxidation; the synergistic effect of the low-temperature controllable oxidation characteristics and the precise ratio of ammonium persulfate ultimately results in a modified MXene material with both high conductivity, interface stability, and structural integrity.

[0055] In some embodiments, the precursor slurry contains by mass percentage: 5% functionalized metal-organic framework, 1% modified MXene, 0.5% dynamic cross-linking agent, and the balance is a fluoropolymer solution. The fluoropolymer is a vinylidene fluoride-chlorotrifluoroethylene copolymer, in which the molar content of chlorotrifluoroethylene is 10%.

[0056] The high specific surface area and regular pore channels of the functionalized metal-organic framework provide the main path for ion transport. The 1% modified MXene forms an auxiliary electron conduction network through its surface conductive polymer coating layer. The disulfide bonds of the 0.5% dynamic crosslinking agent establish reversible crosslinking points between polymer chains. 10 mol% of the chlorotrifluoroethylene units in the vinylidene fluoride-chlorotrifluoroethylene copolymer enhance the flexibility of the matrix by reducing crystallinity. At the same time, their strongly electronegative fluorine atoms have electrostatic interactions with the cations in the ionic liquid on the surface of the metal-organic framework, promoting the uniform dispersion of the functional fillers in the matrix and forming a stable composite system with intertwined hierarchical pores and conductive networks.

[0057] The addition of 5% functionalized metal-organic framework ensures the density of ion transport channels while avoiding embrittlement of the matrix caused by excessive filling. The introduction of 1% modified MXene improves the uniformity of charge distribution in the separator through the conductive network, and its low addition amount avoids competitive effects with the pore structure of the metal-organic framework. The disulfide bond density of the 0.5% dynamic crosslinking agent matches the flexibility of the polymer matrix, realizing self-healing of microcracks while maintaining the mechanical strength of the material. The introduction of 10 mol% chlorotrifluoroethylene in the fluoropolymer optimizes the polarity and swelling characteristics of the matrix, enhancing the compatibility with the ionic liquid and inhibiting high-temperature deformation through moderate crystallization, comprehensively improving the structural stability and electrochemical performance of the separator.

[0058] In some embodiments, the functionalized metal-organic framework is dispersed by ball milling at a ball milling speed of 300 rpm for 2 h; the modified MXene is dispersed by probe sonication at a sonication power of 200 W with an on / off cycle of 2 s / 1 s for 15 min.

[0059] The ball milling speed of 300 rpm and the duration of 2 h in the ball milling process balance the dispersion efficiency of the metal-organic framework and the need for structural protection, achieving both uniform particle distribution and maintaining its regular pore structure. The 200 W power and intermittent cycle design of the probe sonication efficiently exfoliate MXene aggregates while avoiding the peeling of the surface conductive polymer layer or the fragmentation of the quantum dot structure caused by continuous high-energy input. The parameter co-optimization of the two dispersion methods ensures that the ion transport channels of the functionalized metal-organic framework and the conductive network of the modified MXene form an interpenetrating structure in the matrix, thereby maximizing the ion / electron double conduction performance of the composite separator.

[0060] In some embodiments, the DC electric field strength is 50 kV, the electric field treatment time is 10 min, and the conductive substrate is an electrolytic copper foil with a surface roughness Ra ≤ 0.2 μm.

[0061] When applying a high-intensity electric field of 50 kV, the 50 kV electric field intensity provides sufficient driving force within 10 minutes to enable the nano-fillers to overcome Brownian motion and complete orientation, forming a continuous ion / electron transport channel penetrating the separator. The charged groups of the ionic liquid grafted on the surface of the functionalized metal-organic framework and the conductive polymer coating layer of the modified MXene migrate along the electric field direction under the drive of the electric field force, enabling the charged particles to complete the orientation movement and stabilize at the predetermined positions; the electrolytic copper foil with a surface roughness Ra ≤ 0.2 μm reduces the interfacial turbulence during slurry coating through its ultra-smooth surface, ensuring the formation of a uniform wet film of the precursor slurry. At the same time, when the highly conductive copper foil serves as the positive electrode of the electric field, it generates a uniform electric field distribution, avoiding the disorder of filler orientation caused by local electric field distortion, and finally achieving a highly ordered arrangement of the functional materials in the matrix.

[0062] In some embodiments, the phase separation and curing include: after pre-volatilizing at 40 °C until the film thickness reaches 200 μm, dipping the copper foil coated with the slurry into liquid nitrogen and holding for 5 minutes, with a cooling rate ≥ 150 °C / min.

[0063] During the 40 °C pre-volatilization stage, the DMF / acetone mixed solvent in the fluoropolymer solution selectively volatilizes (acetone volatilizes first), causing the viscosity gradient of the slurry to rise to the critical phase separation point. When the film thickness is reduced to 200 μm, a prototype of the bicontinuous phase structure is formed; subsequently, dipping the coated copper foil into liquid nitrogen and holding for 5 minutes, the rapid cooling (≥ 150 °C / min) causes the residual solvent to instantly crystallize into a template. At the same time, the fluoropolymer chain segments are "frozen" in the non-equilibrium state due to the glass transition, and the orientation structures of the functionalized metal-organic framework and MXene are rapidly fixed; the deep low-temperature environment of liquid nitrogen (-196 °C) induces a stress difference between the solvent crystal and the polymer matrix, forming a composite structure with through pores and nano-scale pores after subsequent solvent volatilization.

[0064] The 40 °C pre-volatilization temperature balances the solvent volatilization rate and the phase separation process, avoiding the relaxation of filler orientation caused by high temperature. The setting of the 200 μm film thickness ensures that the solvent residue is at the optimal phase separation threshold; the high cooling rate of liquid nitrogen quenching inhibits the rearrangement of polymer chain segments, completely retaining the pore orientation of the metal-organic framework and the conductive network arrangement of MXene induced by the electric field; the 5-minute immersion time allows liquid nitrogen to fully penetrate into the film layer, forming a hierarchical pore structure through the solvent crystallization-sublimation mechanism, while avoiding the embrittlement of the matrix caused by too long a time; the cooling rate ≥ 150 °C / min fixes the dispersion state of the functional fillers at the nano-scale, and finally obtains a composite separator with both high porosity, ordered pore arrangement and structural stability.

[0065] In some embodiments, the cured composite separator is subjected to hot pressing at 120 °C for 5 minutes, and the hot pressing pressure is 5 MPa.

[0066] During the hot pressing process, the fluoropolymer matrix undergoes segmental relaxation at 120 °C. The disulfide bonds of the dynamic crosslinking agent are thermally activated and undergo reversible cleavage-recombination, promoting stress release and rearrangement at the interfaces between the polymer chains and the functionalized metal-organic frameworks and modified MXene. A pressure of 5 MPa eliminates the non-oriented macropores with pore sizes greater than 100 nm formed during the phase separation process through mechanical compression, while enhancing the physical contact between the filler and the matrix. The regular micropores (0.8 nm) of the functionalized metal-organic frameworks and the interfacial nanochannels (2 - 5 nm) of the MXene-PEDOT are retained due to their structural rigidity. The 5-minute treatment time not only ensures sufficient thermal diffusion for the molecular chains to re-entangle but also avoids the collapse of the pores of the functionalized metal-organic frameworks or the oxidation of the MXene conductive layer caused by prolonged high temperature, ultimately forming a dense and firmly interfacially bonded separator structure.

[0067] The hot pressing temperature of 120 °C enables moderate migration of the molecular chains near the softening point of the fluoropolymer, promoting the uniform distribution of the dynamic crosslinking agent and repairing the microdefects formed during the curing process. A pressure of 5 MPa eliminates the micropores generated by phase separation through mechanical compression, enhancing the mechanical strength of the separator and the uniformity of electrolyte infiltration. The 5-minute hot pressing duration balances the structure optimization and production efficiency, avoiding the performance degradation of the functional fillers while ensuring the interfacial bonding force, ultimately obtaining a composite separator with high densification, excellent interfacial compatibility, and long-term cycling stability.

[0068] In some embodiments, the number-average molecular weight of the dynamic crosslinking agent is 8000 - 10000, the molar content of the disulfide bonds is 2.5 - 3.5%, and the solvent of the fluoropolymer solution is a mixed solvent of DMF and acetone with a volume ratio of 7:3.

[0069] The chain length of the polyurethane elastomer with a number-average molecular weight of 8000 - 10000 can form an effective crosslinked network while maintaining the chain segment mobility to promote the dynamic exchange of disulfide bonds. The disulfide bond content of 2.5 - 3.5% ensures that the crosslinking point density can provide sufficient mechanical strength while avoiding excessive crosslinking degree from restricting chain segment reconstruction. The mixed solvent of DMF / acetone with a volume ratio of 7:3, through the synergistic effect of the strong solvent (DMF) and the weak solvent (acetone), dissolves the fluoropolymer while inducing the gradient dispersion of the functional fillers. The rapid volatilization property of acetone forms a microphase separation template in the initial film-forming stage, providing a structural basis for subsequent electric field orientation.

[0070] The molecular weight range of the dynamic crosslinking agent optimizes the spatial distribution of the crosslinked network. A chain length of 8000 - 10000 enables stress relaxation through the reversible cleavage / recombination of disulfide bonds during the hot pressing process, avoiding stress concentration within the separator. A disulfide bond content of 2.5 - 3.5% provides an appropriate dynamic crosslinking density during cycling, maintaining both material integrity and enabling self - repair of microcracks. A volume ratio of DMF to acetone of 7:3 regulates the solvent evaporation gradient, causing the fluorinated polymer to form an interpenetrating network structure during phase separation and promoting the oriented arrangement of functionalized metal - organic frameworks and MXene in the matrix, ultimately obtaining a composite separator with high mechanical strength, self - repair ability, and an ordered pore structure.

[0071] This application also provides a composite separator for supercapacitors, which is prepared according to any one of the foregoing preparation methods.

[0072] The method of the present invention will be described in detail below in conjunction with examples, comparative examples, and experimental data.

[0073] Example 1

[0074] This example provides a preparation method for a composite separator for supercapacitors, and the method includes the following steps:

[0075] Step 1: Take 1.0 g of UiO - 66 - NH 2 powder with a specific surface area of 1280 m 2 / g, and place it in a vacuum drying oven at 120 °C for activation treatment for 6 h. Mix the activated metal - organic framework material with 50 ml of 1 - ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid, and magnetically stir in a constant - temperature oil bath at 60 °C for 24 h (rotation speed 300 rpm, PTFE rotor). After the reaction, centrifuge the solid product at 8000 rpm for 15 min, ultrasonically wash it with anhydrous ethanol 3 times (50 mL each time, ultrasonic for 5 min), and finally dry it in vacuum at 60 °C for 12 h to obtain a UiO - 66 - NH 2 -IL functionalized material with a mass gain rate of 18.5%.

[0076] Step 2: Mix 5 g of Ti 3 AlC 2The MAX phase powder (particle size 35 μm) was immersed in a 40% hydrofluoric acid solution and etched at 25 °C for 24 h. After the etched product was washed with deionized water until neutral, it was dispersed in dimethyl sulfoxide (DMSO) and ultrasonically treated at a power of 500 W and a frequency of 40 kHz for 4 h. Subsequently, it was centrifuged at 3500 rpm for 30 min, and the upper-layer single-layer MXene colloidal solution was collected. The single-layer MXene colloidal solution was ultrasonically broken by a probe with a power of 800 W for 3 h to obtain a dispersion of MXene quantum dots. 2 mg / mL of the MXene quantum dot dispersion was taken, 3,4-ethylenedioxythiophene monomer (EDOT, molar ratio of MXene:EDOT = 1:50) and ammonium persulfate oxidant (EDOT:APS = 1:1.2) were added, and the reaction was carried out in an ice-water bath at 5 °C for 12 h. The reaction solution was purified by dialysis with a dialysis bag with a molecular weight cut-off of 3500 for 48 h and then freeze-dried to obtain MXene-PEDOT composite powder.

[0077] Step 3: Poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE), CTFE content 10 mol%) was dissolved in a DMF / acetone mixed solvent (volume ratio 7:3) to prepare a 10 wt% polymer solution, and stirred at 60 °C under nitrogen protection for 6 h until completely dissolved. 0.5 wt% of disulfide bond polyurethane elastomer (number average molecular weight 9000, disulfide bond content 3.0%) was added as a dynamic crosslinking agent in sequence, 5 wt% of UiO-66-NH 2 -IL (dispersed by ball milling in a zirconia ball mill at 300 rpm for 2 h) and 1 wt% of MXene-PEDOT (dispersed by a 200 W probe ultrasonic, on / off cycle 2 s / 1 s, for 15 min) were added, and the final slurry viscosity was controlled at 3650 mPa·s (measured at 25 °C).

[0078] Step 4: The precursor slurry was coated on an electrolytic copper foil with a surface roughness Ra = 0.18 μm at a scraping speed of 10 mm / s, and the wet film thickness was 500 μm. A DC electric field of 50 kV was immediately applied (the positive electrode was connected to the copper foil, and the parallel plate spacing was 10 cm) for 10 min, and the ordered arrangement of the metal-organic framework along the electric field direction was confirmed by a high-speed camera. Subsequently, the sample was placed in an oven at 40 °C for pre-volatilization for 15 min until the film thickness was 200 μm, and then quickly immersed in liquid nitrogen and held for 5 min (cooling rate 158 °C / min). The peeled separator was left standing at -20 °C for 2 h, and finally treated by a hot press at 120 °C under a pressure of 5 MPa for 5 min to obtain a finished separator with a thickness of 24 μm.

[0079] Example 2

[0080] This example provides a method for preparing a composite separator for supercapacitors, and the method includes the following steps:

[0081] Step 1: Take 1.0 g of specific surface area 1280 m2 UiO-66-NH per g 2 powder was placed in a vacuum drying oven at 120 °C for activation treatment for 6 h. The activated metal-organic framework material was mixed with 45 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid and magnetically stirred in a constant temperature oil bath at 60 °C for 24 h (rotation speed 300 rpm, PTFE rotor). After the reaction, the solid product was separated by centrifugation at 8000 rpm for 15 min, ultrasonically washed with absolute ethanol 3 times (50 mL each time, ultrasonic for 5 min), and finally vacuum dried at 60 °C for 12 h to obtain a UiO-66-NH 2 -IL functionalized material with a mass gain rate of 18.5%.

[0082] Step 2: Immerse 5 g of Ti 3 AlC 2 MAX phase powder (particle size 35 μm) into 40% hydrofluoric acid solution and etch at 25 °C for 22 h. After the etched product was washed with deionized water until neutral, it was dispersed in dimethyl sulfoxide (DMSO) and ultrasonically treated at a power of 500 W and a frequency of 40 kHz for 4 h. Subsequently, it was centrifuged at 3500 rpm for 30 min to collect the upper-layer single-layer MXene colloidal solution. The single-layer MXene colloidal solution was ultrasonically broken by a probe with a power of 800 W for 3 h to obtain a MXene quantum dot dispersion. Take 2 mg / mL MXene quantum dot dispersion, add 3,4-ethylenedioxythiophene monomer (EDOT, molar ratio of MXene:EDOT = 1:50) and ammonium persulfate oxidant (EDOT:APS = 1:1.2), and react in an ice-water bath at 5 °C for 12 h. The reaction solution was purified by dialysis through a dialysis bag with a molecular weight cut-off of 3500 for 48 h and then freeze-dried to obtain MXene-PEDOT composite powder.

[0083] Step 3: Dissolve poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (P(VDF-CTFE), CTFE content 10 mol%) in a DMF / acetone mixed solvent (volume ratio 7:3) to prepare a 10 wt% polymer solution, and stir at 60 °C under nitrogen protection for 6 h until completely dissolved. Add 0.5 wt% disulfide polyurethane elastomer (number average molecular weight 9000, disulfide bond content 3.0%) as a dynamic crosslinking agent in sequence, add 5 wt% UiO-66-NH 2 -IL (dispersed by ball milling at 300 rpm in a zirconia ball mill for 2 h) and 1 wt% MXene-PEDOT (dispersed by 200 W probe ultrasound, on / off cycle 2 s / 1 s, for 15 min), and finally control the slurry viscosity at 3650 mPa·s (measured at 25 °C).

[0084] Step 4: Coat the precursor slurry on the electrolytic copper foil with a surface roughness Ra = 0.18 μm at a doctor blade speed of 10 mm / s, and the wet film thickness is 500 μm. Immediately apply a 50 kV DC electric field (the positive electrode is connected to the copper foil, and the parallel plate spacing is 10 cm) for 10 min, and confirm the orderly arrangement of the metal-organic framework along the electric field direction through a high-speed camera. Subsequently, place the sample in an oven at 40 °C for pre-evaporation for 15 min until the film thickness is 200 μm, and quickly immerse it in liquid nitrogen for 5 min (cooling rate: 158 °C / min). The peeled separator is left standing at -20 °C for 2 h, and finally processed by a hot press at 120 °C under a pressure of 5 MPa for 5 min to obtain a finished separator with a thickness of 24 μm.

[0085] Example 3

[0086] This example provides a method for preparing a composite separator for a supercapacitor, and the method includes the following steps:

[0087] Step 1: Take 1.0 g of UiO-66-NH 2 powder with a specific surface area of 1280 m 2 / g, and place it in a vacuum drying oven at 120 °C for activation treatment for 6 h. Mix the activated metal-organic framework material with 50 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid, and magnetically stir it in a constant temperature oil bath at 60 °C for 24 h (rotation speed: 300 rpm, PTFE rotor). After the reaction is completed, centrifuge the solid product at 8000 rpm for 15 min, wash it ultrasonically with anhydrous ethanol 3 times (50 mL each time, ultrasonic for 5 min), and finally dry it in vacuum at 60 °C for 12 h to obtain the UiO-66-NH 2 -IL functionalized material with a mass gain rate of 18.5%.

[0088] Step 2: Mix 5 g of Ti 3 AlC 2MAX phase powder (particle size 35 μm) was immersed in 40% hydrofluoric acid solution and etched at 25 °C for 24 h. After the etching product was washed with deionized water until neutral, it was dispersed in dimethyl sulfoxide (DMSO) and ultrasonically treated at a power of 500 W and a frequency of 40 kHz for 4 h. Subsequently, it was centrifuged at 3500 rpm for 30 min, and the upper-layer single-layer MXene colloidal solution was collected. The single-layer MXene colloidal solution was ultrasonically broken by a probe with a power of 800 W for 3 h to obtain a MXene quantum dot dispersion. Take 2 mg / mL MXene quantum dot dispersion, add 3,4-ethylenedioxythiophene monomer (EDOT, molar ratio of MXene:EDOT = 1:50) and ammonium persulfate oxidant (EDOT:APS = 1:1.2), and react in an ice-water bath at 5 °C for 12 h. The reaction solution was purified by dialysis bag with a molecular weight cut-off of 3500 for 48 h and then freeze-dried to obtain MXene-PEDOT composite powder.

[0089] Step 3: Poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (P(VDF-CTFE), CTFE content 10 mol%) was dissolved in a DMF / acetone mixed solvent (volume ratio 7:3) to prepare a 10 wt% polymer solution, and stirred at 60 °C under nitrogen protection for 6 h until completely dissolved. 0.6 wt% disulfide bond polyurethane elastomer (number average molecular weight 9000, disulfide bond content 3.0%) was added as a dynamic crosslinking agent in sequence, and 5 wt% UiO-66-NH 2 -IL (dispersed by ball milling at 300 rpm in a zirconia ball mill for 2 h) and 1 wt% MXene-PEDOT (dispersed by a 200 W probe ultrasound, on / off cycle 2 s / 1 s, for 15 min) were added, and the final slurry viscosity was controlled at 3650 mPa·s (measured at 25 °C).

[0090] Step 4: The precursor slurry was coated on an electrolytic copper foil with a surface roughness Ra = 0.18 μm at a scraping speed of 10 mm / s, and the wet film thickness was 500 μm. A 50 kV DC electric field (the positive electrode was connected to the copper foil, and the parallel plate spacing was 10 cm) was immediately applied for 8 min, and the ordered arrangement of the metal-organic framework along the electric field direction was confirmed by a high-speed camera. Subsequently, the sample was placed in an oven at 40 °C for pre-volatilization for 15 min until the film thickness was 200 μm, and quickly immersed in liquid nitrogen and held for 5 min (cooling rate 158 °C / min). The peeled separator was left standing at -20 °C for 2 h, and finally treated by a hot press at 120 °C under a pressure of 5 MPa for 5 min to obtain a finished separator with a thickness of 24 μm.

[0091] Comparative Example 1

[0092] This comparative example provides a method for preparing a composite separator for supercapacitors, and the method includes the following steps:

[0093] Step 1: 5 g of Ti 3AlC 2 The MAX phase powder (particle size 35 μm) was immersed in a 40% hydrofluoric acid solution and etched at 25 °C for 22 h. After the etching product was washed with deionized water until neutral, it was dispersed in dimethyl sulfoxide (DMSO) and ultrasonicated at a power of 500 W and a frequency of 40 kHz for 4 h. Subsequently, it was centrifuged at 3500 rpm for 30 min, and the upper-layer single-layer MXene colloidal solution was collected. Take 2 mg / mL MXene quantum dot dispersion, add 3,4-ethylenedioxythiophene monomer (EDOT, molar ratio of MXene:EDOT = 1:50) and ammonium persulfate oxidant (EDOT:APS = 1:1.2), and react in an ice bath at 5 °C for 12 h. The reaction solution was purified through a dialysis bag with a molecular weight cut-off of 3500 for 48 h and then freeze-dried to obtain MXene-PEDOT composite powder.

[0094] Step 2: Dissolve poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (P(VDF-CTFE), CTFE content 10 mol%) in a DMF / acetone mixed solvent (volume ratio 7:3) to prepare a 10 wt% polymer solution, and stir at 60 °C under nitrogen protection for 6 h until completely dissolved. Add 0.5 wt% ordinary polyurethane as a dynamic crosslinking agent in sequence, and add 5 wt% of the original UiO-66-NH 2 and 1 wt% MXene-PEDOT (ultrasonically dispersed with a 200 W probe, on / off cycle 2 s / 1 s, for 15 min), and finally control the slurry viscosity at 3650 mPa·s (measured at 25 °C).

[0095] Step 3: Coating the precursor slurry on an electrolytic copper foil with a surface roughness Ra = 0.18 μm at a scraping speed of 10 mm / s, with a wet film thickness of 500 μm. Immediately apply a 50 kV DC electric field (the positive electrode is connected to the copper foil, and the parallel plate spacing is 10 cm) for 10 min, and confirm the orderly arrangement of the metal-organic framework along the electric field direction through a high-speed camera. Subsequently, place the sample in an oven at 40 °C for pre-volatilization for 15 min until the film thickness is 200 μm, and quickly immerse it in liquid nitrogen and hold for 5 min (cooling rate 158 °C / min). The peeled separator was left standing at -20 °C for 2 h, and finally treated with a hot press at 120 °C under a pressure of 5 MPa for 5 min to obtain a finished separator with a thickness of 24 μm.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing a composite separator for supercapacitors, and the method includes the following steps:

[0098] Step 1: Take 1.0 g of UiO-66-NH with a specific surface area of 1280 m 2 / g 2The powder was placed in a vacuum drying oven at 120 °C for activation treatment for 6 h. The activated metal-organic framework material was mixed with 50 ml of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) ionic liquid and magnetically stirred in a constant temperature oil bath at 60 °C for 24 h (rotation speed 300 rpm, PTFE rotor). After the reaction, the solid product was separated by centrifugation at 8000 rpm for 15 min, ultrasonically washed with absolute ethanol 3 times (50 mL each time, ultrasonic for 5 min), and finally vacuum dried at 60 °C for 12 h to obtain a UiO-66-NH 2 -IL functionalized material.

[0099] Step 2: Immerse 5 g of Ti 3 AlC 2 MAX phase powder (particle size 35 μm) into 40% hydrofluoric acid solution and etch at 25 °C for 24 h. After the etched product was washed with deionized water until neutral, it was dispersed in dimethyl sulfoxide (DMSO) and ultrasonically treated at a power of 500 W and a frequency of 40 kHz for 4 h. Subsequently, it was centrifuged at 3500 rpm for 30 min to collect the upper layer of monolayer MXene colloidal solution. The monolayer MXene colloidal solution was ultrasonically broken by a probe with a power of 800 W for 3 h to obtain a MXene quantum dot dispersion. Take 2 mg / mL MXene quantum dot dispersion, add 3,4-ethylenedioxythiophene monomer (EDOT, molar ratio of MXene:EDOT = 1:50) and ammonium persulfate oxidant (EDOT:APS = 1:1.2), and react in an ice-water bath at 5 °C for 12 h. The reaction solution was purified through a dialysis bag with a molecular weight cut-off of 3500 for 48 h and then freeze-dried to obtain MXene-PEDOT composite powder.

[0100] Step 3: Dissolve vinylidene fluoride-chlorotrifluoroethylene copolymer (P(VDF-CTFE), CTFE content 10 mol%) in a DMF / acetone mixed solvent (volume ratio 7:3) to prepare a 10 wt% polymer solution, and stir at 60 °C under nitrogen protection for 6 h until completely dissolved. 0.5 wt% disulfide bond polyurethane elastomer (number average molecular weight 9000, disulfide bond content 3.0%), 5 wt% UiO-66-NH 2 -IL (dispersed by ball milling at 300 rpm in a zirconia ball mill for 2 h) and 1 wt% MXene-PEDOT (dispersed by a 200 W probe ultrasonic, on / off cycle 2 s / 1 s, for 15 min) were added in sequence, and finally the slurry viscosity was controlled at 3650 mPa·s (measured at 25 °C).

[0101] Step 4: Coating the precursor slurry on the electrolytic copper foil with a surface roughness Ra = 0.18 μm at a doctor blade speed of 10 mm / s, with a wet film thickness of 500 μm. However, no DC electric field is applied. Subsequently, the sample is placed in an oven at 40 °C for pre-evaporation for 15 min until the film thickness reaches 200 μm, and then it is volatilized at room temperature conventionally. Finally, it is treated under a pressure of 5 MPa for 5 min by a hot press at 120 °C to obtain a finished separator with a thickness of 24 μm.

[0102] Experimental methods

[0103] 1. Using a two-electrode system (platinum sheet / separator / platinum sheet), in a 1 M TEABF4 / PC electrolyte, the bulk resistance is measured by electrochemical impedance spectroscopy (EIS, frequency range 0.1 Hz - 1 MHz), and the ionic conductivity is obtained by calculating according to σ = L / (R×A) (where L is the film thickness and A is the contact area).

[0104] 2. Assembling a symmetric supercapacitor (activated carbon electrode), performing constant current charge and discharge (current density 5 A / g) in a voltage window of 2.7 V, and recording the capacity retention rate after 2000 cycles.

[0105] 3. Placing the separator in an oven at 150 °C for 24 h, and measuring the dimensional change rate (ΔL / L 0 ×100%) by a laser scanning microscope

[0106] 4. Making a 10-μm scratch with a nanoindenter, and observing the scratch width recovery rate by SEM after standing at 60 °C for 1 h.

[0107] 5. Using the mercury intrusion method (Micromeritics AutoPore IV 9500 type), cutting the separator sample into 1 cm × 1 cm squares, vacuum degassing at 200 °C for 2 h, and then measuring the pore size distribution in the pressure range of 0.1 - 60,000 psi.

[0108] The total porosity is calculated according to the formula where V p is the cumulative mercury intrusion volume, and ρ is the true density of the material (taking the weighted average of the density of P(VDF-CTFE) 1.78 g / cm 3 the density of metal-organic framework 1.25 g / cm 3 the density of MXene 4.2 g / cm 3 ).

[0109] 6. Using a universal material testing machine (Instron 5967 type), cutting the separator into dumbbell-shaped specimens (ASTM D638 standard) of 10 mm × 50 mm, with a clamping distance of 30 mm and a tensile rate of 10 mm / min, and recording the maximum stress value before fracture. Five parallel samples are tested in each group, and the average value is taken.

[0110] The experimental results are shown in Table 1

[0111] Table 1 Comparison Table of Key Performance Indicators between Examples and Comparative Examples

[0112] Test index Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Ionic conductivity (S / cm) 1.02 0.98 0.95 0.57 0.66 Cyclic capacity retention rate (%) 87.3 85.1 84.6 68.2 72.5 High temperature dimensional change rate (%) 2.8 3.1 3.3 9.7 7.9 Self-healing efficiency (%) 92.4 89.7 90.3 0 (none) 18.6 Porosity (%) 68.5 65.2 63.8 54.3 58.1 Tensile strength (MPa) 24.7 22.9 23.5 15.3 18.6

[0113] Analysis of Experimental Results

[0114] It can be seen from the experimental data that in Example 1, the high porosity stems from the orderly arrangement of metal-organic frameworks induced by the electric field and the through-pores formed by liquid nitrogen quenching, which provides sufficient paths for ion transport and is directly reflected in the high ionic conductivity of 1.02 S / cm. The tensile strength of 22.9 - 23.5 MPa in Examples 2 - 3 indicates that even if the addition amount of metal-organic frameworks is slightly reduced or the ratio of the dynamic cross-linking agent is adjusted, the material can still maintain sufficient mechanical stability, which benefits from the nano-reinforcement effect of MXene-PEDOT and the energy dissipation mechanism of the dynamic cross-linking network.

[0115] The porosity of Comparative Example 1 drops sharply to 54.3%, which is directly related to the agglomeration of unfunctionalized metal-organic framework particles. The unmodified UiO-66-NH without ionic liquid modification 2 forms stress concentration points in the matrix, hindering uniform pore formation during solvent evaporation. At the same time, the fragile performance with a tensile strength of only 15.3 MPa exposes the serious deficiency of the filler-matrix interfacial bonding force. This structural defect further leads to rapid crack propagation during cycling, and the capacity retention rate drops to 68.2%. Although Comparative Example 2 obtains a porosity of 58.1% through conventional curing, the disordered pore structure reduces the actual effective conduction paths, and its conductivity of 0.66 S / cm is only 65% of that in Example 1, verifying the decisive role of electric field orientation in constructing a three-dimensional conduction network.

[0116] In Example 3, when the porosity (63.8%) is slightly lower than that in Example 1, it still maintains a conductivity of 0.95 S / cm. This may be because after the addition amount of the dynamic cross-linking agent is increased to 0.6 wt%, the formed denser cross-linking network optimizes the connectivity of ion channels. At the same time, its tensile strength of 23.5 MPa and self-healing efficiency of 90.3% jointly prove that moderate regulation of the component ratio can maintain functional characteristics without significantly sacrificing mechanical properties; compared with Example 1, when the addition amount of the dynamic cross-linking agent increases from 0.5 wt% to 0.6 wt%, the self-healing efficiency only decreases by 2.3%, and the tensile strength only decreases by 4.9%, demonstrating that the technical solution has strong robustness to parameter fluctuations. The achievement of this performance balance essentially stems from the multi-scale synergy among the components: the metal-organic framework provides a rigid skeleton, MXene-PEDOT enhances electron conduction, and the dynamic cross-linking agent endows the material with damage self-healing ability.

[0117] The dimensional change rate of the example group ≤ 3.3% is closely related to the uniformly distributed metal-organic framework support structure in its high-porosity material. The rigid nanoparticles restrain each other during thermal expansion, effectively suppressing the matrix deformation. For Comparative Example 2, even though the same polymer matrix is used, due to the lack of electric field orientation treatment, the metal-organic framework particles are disorderly distributed and cannot form a continuous support network, resulting in a 7.9% dimensional change at 150 °C, leading to uneven electrolyte infiltration and an increase in interfacial impedance. This significant difference in thermomechanical properties highlights the importance of the ordered dispersion of nano-fillers and the strong matrix-filler interfacial bonding.

[0118] It should be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variant are intended to cover non-exclusively, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0119] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a composite diaphragm for a supercapacitor, characterized in that: The following steps are involved: Performing ionic liquid functionalization treatment on the metal organic framework material to obtain a functionalized metal organic framework; Modifying the surface of MXene quantum dots with conductive polymers to obtain modified MXene; Dispersing the functionalized metal organic framework, modified MXene and dynamic cross-linking agent in a fluorine-containing polymer solution to form a precursor slurry; The precursor slurry is coated on the surface of the conductive substrate, a direct current electric field is applied for orientation treatment, and a composite diaphragm is obtained after phase separation and curing; Wherein, the dynamic cross-linking agent is a polyurethane elastomer containing disulfide bonds.

2. The preparation method according to claim 1, characterized in that: The metal organic framework material is UiO-66-NH2, the ionic liquid is 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt, the mass volume ratio of the metal organic framework to the ionic liquid during the functionalization treatment is 1g:50mL, the reaction temperature is 60±2°C, and the reaction time is 24h.

3. The preparation method according to claim 1, characterized in that: The preparation of the modified MXene comprises the following steps: Ti3AlC2 powder was etched with 40% hydrofluoric acid solution for 24 hours, and a single-layer MXene colloidal solution was obtained after stripping with DMSO solvent, and MXene quantum dots were obtained after ultrasonic crushing. The MXene quantum dots were grafted with 3,4-ethylenedioxythiophene monomer and an oxidant in an ice-water bath at 5° C. for 12 hours to obtain the modified MXene.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the MXene quantum dots to the 3,4-ethylenedioxythiophene monomer is 1:50, the oxidant includes ammonium persulfate, and the molar ratio of the 3,4-ethylenedioxythiophene monomer to the oxidant is 1:1.

2.

5. The preparation method according to claim 1, characterized in that: The precursor slurry comprises, by mass percentage, 5% functionalized metal organic framework, 1% modified MXene, 0.5% dynamic crosslinking agent, and the remainder is a fluorine-containing polymer solution, wherein the fluorine-containing polymer is a vinylidene fluoride-chlorotrifluoroethylene copolymer, wherein the molar content of chlorotrifluoroethylene is 10%.

6. The preparation method according to claim 5, characterized in that: The functionalized metal organic framework was dispersed by ball milling, the ball milling speed was 300 rpm, and the ball milling time was 2 h; the modified MXene was dispersed by probe ultrasound, the ultrasound power was 200 W, the on / off cycle was 2 s / 1 s, and the ultrasound time was 15 min.

7. The preparation method according to claim 1, characterized in that: The DC electric field strength is 50 kV, the electric field treatment time is 10 min, and the conductive substrate is an electrolytic copper foil with a surface roughness Ra≤0.2 μm.

8. The preparation method according to claim 1, characterized in that: The phase separation solidification comprises: after pre-volatilization at 40° C. to a film thickness of 200 μm, immersing the copper foil coated with the slurry in liquid nitrogen for 5 minutes, with a cooling rate of ≥150° C. / min.

9. The preparation method according to claim 1, characterized in that: The number average molecular weight of the dynamic crosslinking agent is 8000-10000, wherein the molar content of disulfide bonds is 2.5-3.5%, and the solvent of the fluorine-containing polymer solution is a mixed solvent of DMF and acetone in a volume ratio of 7:

3.

10. A composite diaphragm for supercapacitor, characterized in that: Prepared according to any one of the preparation methods described in claims 1-9.

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