A mxene-based flexible electrode material and a preparation method thereof

Abstract

The application discloses a kind of MXene-based flexible electrode materials and preparation method thereof, it is related to electrochemical energy storage material technical field.The electrode material includes carbon cloth current collector, active material layer loaded on the surface of carbon cloth current collector and binder polyvinylidene fluoride;Active material layer is composed of ice assisted in-situ polymerization MXene / polystyrene complex.Prepare MXene nanosheet dispersion liquid, freeze treatment after vacuum suction filtration into wet film, make interlayer combined water in-situ iceing gently open interlayer spacing, intercalate during iceing process by adding aniline solution, add oxidizing agent solution and carry out in-situ polymerization, obtain MXene / polystyrene complex, the obtained composite material is mixed with polyvinylidene fluoride, NMP solution is coated on the surface of carbon cloth and dried, and the present application synchronously solves the problem of MXene sheet layer stacking agglomeration, poor interface adaptability and single material capacity limitation, with high specific capacity, excellent rate performance and long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to an MXene-based flexible electrode material and its preparation method. Background Technology

[0002] In recent years, the rapid iteration of wearable electronic products has made flexible energy storage technology a current research hotspot. As a key component of energy storage devices, electrode materials directly determine the energy density, cycle stability, and application adaptability of the devices. Developing electrode materials that combine high specific capacity, high conductivity, excellent flexibility, and long-term cycle stability has become a research hotspot and core technological challenge in the field of electrochemical energy storage.

[0003] Among numerous candidate material systems, MXene, as a novel type of two-dimensional transition metal carbide / nitride, has become one of the preferred flexible energy storage electrode materials due to its metal-like high conductivity, ultra-large specific surface area, tunable layered structure, abundant surface functional groups, and excellent electrochemical activity, with very broad application prospects.

[0004] However, MXene materials still face the following drawbacks in practical applications: First, MXene nanosheets are prone to severe aggregation and stacking, leading to blockage of ion transport channels and obscuring of active sites; second, MXene has poor interfacial compatibility with commonly used current collectors, making it easy for active materials to detach from the current collector surface and resulting in high interfacial charge transfer resistance; third, the energy storage capacity of a single MXene material is limited, making it difficult to meet the practical application requirements of high-performance flexible electrodes. These drawbacks restrict the large-scale application of MXene in flexible energy storage electrodes. Summary of the Invention

[0005] This invention addresses the problems of easy stacking and agglomeration of MXene materials in practical applications, poor adaptability of current collector interfaces, and limited energy storage capacity of single materials, as described in the background art. It provides an MXene-based flexible electrode material and its preparation method.

[0006] An MXene-based flexible electrode material comprises the following components: a carbon cloth current collector, an active material layer loaded on the surface of the carbon cloth current collector, and a binder;

[0007] The active material layer is composed of an I-PM composite material, which is an MXene / polyaniline composite, wherein polyaniline is uniformly intercalated between MXene sheets, and polyaniline and MXene are bonded by hydrogen bonds and coordination bonds; the binder is polyvinylidene fluoride.

[0008] Furthermore, the mass ratio of the I-PM composite material to polyvinylidene fluoride is 8:1.

[0009] A method for preparing MXene-based flexible electrode materials includes the following steps: S1. Preparation of MXene nanosheet dispersion; S2. Vacuum filter the MXene nanosheet dispersion obtained in step S1 into a wet film, and freeze it to make the water bound between the MXene layers freeze in situ; S3. Add aniline solution to the wet film after freezing treatment for reaction, and then add oxidant solution to carry out in-situ polymerization reaction, so that aniline monomers are confined and polymerized in the MXene interlayer to obtain I-PM composite material; S4. The I-PM composite material obtained in step S3 is mixed with polyvinylidene fluoride and solvent and ground into a slurry, which is then coated onto the surface of the carbon cloth current collector and dried to obtain the MXene-based flexible electrode material.

[0010] Furthermore, the preparation of MXene nanosheets in step S1 includes: mixing LiF with HCl solution, adding MAX phase Ti3AlC2 powder under ice bath conditions, stirring and reacting in a 40°C water bath for 48 hours, centrifuging and washing until pH≥6, ultrasonic dispersion, and centrifuging to collect the upper suspension.

[0011] Furthermore, the freezing temperature in step S2 is -18°C to -24°C, and the freezing time is 2 hours; the wet membrane in step S2 is obtained by removing free water and retaining interlayer bound water through vacuum filtration.

[0012] Furthermore, the oxidant solution in step S3 contains HCl, water, and ammonium persulfate, and the in-situ polymerization reaction is carried out at an ambient temperature of 4°C for 8 hours.

[0013] Furthermore, the drying temperature in step S4 is 60°C, and the drying time is 6 hours.

[0014] The technical solution of the present invention has the following beneficial effects: In the field of MXene-based flexible electrodes, those skilled in the art typically focus on the direct impact of single modification methods such as conductive polymer intercalation and the selection of different current collectors on electrode performance. However, the understanding of the intrinsic relationships between these modification methods and the synergistic control of process parameters is still insufficient. This invention selects carbon cloth as the flexible current collector substrate and develops an ice-assisted in-situ polymerization strategy that combines vacuum filtration and freezing, synergistically improving the overall performance of the electrode from two dimensions: current collector adaptation and control of the interlayer structure of the active material.

[0015] Carbon cloth with a three-dimensional interwoven fiber porous structure was selected as the current collector substrate. The high specific surface area and abundant active functional groups of the carbon cloth provide sufficient physical anchoring sites and chemical binding sites for MXene nanosheets, achieving uniform and dense loading of MXene and effectively inhibiting sheet aggregation, while simultaneously constructing stable interfacial bonding and continuous electron / ion transport channels. Polyaniline itself possesses excellent conductivity, good electrochemical activity, and low preparation cost, making it an ideal guest material for MXene intercalation modification. Building upon this foundation, and addressing the issues of incomplete aniline monomer intercalation and easy agglomeration of polyaniline in traditional polymerization processes, this invention counterintuitively utilizes a known drawback of conventional freezing methods—freezing can form large ice crystals that disrupt the lamellar structure. By removing free water from the MXene dispersion through vacuum filtration, retaining only interlayer bound water, the subsequent freezing process ensures that ice crystals nucleate confined within the MXene interlayers. The gentle expansion force generated by the freezing of interlayer bound water uniformly widens the interlayer spacing, providing diffusion channels for aniline monomers to enter the interlayer. Once inside the interlayer, aniline monomers undergo in-situ polymerization within this confined space, naturally limiting the growth of polyaniline to the nanoscale, achieving uniform dispersion without the need for external dispersants. Simultaneously, the -NH2 on the polyaniline molecular chain forms hydrogen bonds with the -OH on the MXene surface, and N atoms form coordination bonds with Ti atoms. This strong interfacial bonding effectively reduces the interfacial charge transfer resistance.

[0016] In summary, the carbon cloth current collector solves the problems of MXene loading uniformity and interface stability. The ice-assisted process fully preserves the two-dimensional conductive framework of MXene. The uniform intercalation of PANI significantly widens the interlayer spacing of MXene, fundamentally suppressing layer aggregation and stacking, and constructing a continuous ion transport channel and conductive network. In addition, the crystalline PANI generated by in-situ polymerization is uniformly dispersed on the surface and between layers of MXene, forming a dual-mechanism synergistic energy storage with MXene through double-layer and pseudocapacitive mechanisms, significantly improving the energy storage capacity. PANI and MXene form a strong interfacial bond through hydrogen bonds and coordination bonds, accelerating interfacial electron transfer and reducing charge transfer impedance, while ensuring the performance stability of the structure under flexible bending, providing a new technical path for performance optimization of MXene-based flexible energy storage electrodes. Attached Figure Description

[0017] Figure 1 SEM images of (a / e)MXene / CC, (b / f)MXene / CP, (c / g)MXene / TW, and (d / h)MXene / TF; EDS image of (il)MXene / CC; Figure 2 TEM spectrum of MXene / CC; Figure 3 XRD patterns of different current collectors based on MXene; Figure 4 FTIR spectra of MXene; Figure 5 XPS spectra of MXene / CC: (a) full spectrum; (b) C1s spectrum; (c) O1s spectrum; (d) Ti2p spectrum; Figure 6 CV curves at different scan rates: (a) MXene / CC; (b) MXene / CP; (c) MXene / TW; (d) MXene / TF; Figure 7 GCD curves at different current densities: (a) MXene / CC; (b) MXene / CP; (c) MXene / TW; (d) MXene / TF; Figure 8 EIS spectra of different current collectors based on MXene; Figure 9 (a) Log-log plot of peak current-sweep rate for MXene / CC; (b) percentage contribution of diffusion and capacitance at different sweep rates; (c) capacitance contribution at 50 mV / s; (d) specific capacitance. Figure 10 Comparison images of different samples before and after bending 180°; Figure 11 Comparison images of different samples after 3 hours of ultrasound; Figure 12 SEM images of (a / e)MXene, (b / f)I-PM, (c / g)PM, and (d / h)i-PM; TEM image of (i / j)I-PM; EDS image of (kp)I- / PM; Figure 13 XRD patterns of different samples; Figure 14 FTIR spectra of different samples; Figure 15 (a) XPS full spectrum of MXene and I-PM; XPS spectrum of MXene; (b) C1s spectrum; (c) O1s spectrum; (d) Ti2p spectrum; Figure 16 XPS spectra of I-PM: (a) C1s spectrum; (b) O1s spectrum; (c) Ti2p spectrum; (d) N1s spectrum; Figure 17 (a) CV curve of pure MXene at 10 mV / s; (b) GCD curve at 1 A / g; (c) CV curves of PM / CC, i-PM / CC and I-PM / CC at 10 mV / s; (d) GCD curve at 1 A / g; Figure 18(a / c) CV curves of PM / CC and i-PM / CC at different scan rates; (b / d) GCD curves at different current densities; Figure 19 (a) EIS curves for MXene, PM / CC, i-PM / CC, and I-PM / CC; (b) Specific capacitance; Figure 20 (a) CV curves of I-PM / CC1, I-PM / CC2, and I-PM / CC3 electrodes at 10 mV / s; (b) GCD curves at 1 A / g; (c) CV curves of I-PM / CC2 at different scan rates; (d) GCD curves at different current densities. Figure 21 (a / c) CV curves of I-PM / CC1 and I-PM / CC3 at different scan rates; (b / d) GCD curves at different current densities; Figure 22 EIS curves for (a) I-PM / CC1, I-PM / CC2 and I-PM / CC3 electrodes; (b) specific capacitance curves at different current densities; Figure 23 (a) Log-log plot of peak current-sweep rate for I-PM / CC2; (b) capacitance contribution at 50 mV / s; (c) percentage contribution of diffusion and capacitance behavior at different sweep rates. Figure 24 Comparison of (a) CV curves of I-PM / CC2 before and after 10,000 CV cycles and (b) capacitance retention rate. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In the embodiments of this application, unless otherwise specified, conventional conditions or conditions recommended by the manufacturer were followed. All raw materials used were commercially available industrial-grade or analytical-grade reagents. The MAX phase (Ti3AlC2) was a commercially available product, and carbon cloth (CC), carbon paper (CP), titanium mesh (TW), and titanium foil (TF) were all commercially available industrial-grade products. Electrochemical testing employed a standard three-electrode system, using a graphite rod as the counter electrode and an Ag / AgCl electrode as the reference electrode. The electrolyte was a 1 mol / L H2SO4 aqueous solution. Cyclic voltammetry (CV) scan rates ranged from 2 to 100 mV / s, galvanostatic charge-discharge (GCD) current densities ranged from 1 to 100 A / g, and electrochemical impedance spectroscopy (EIS) frequencies ranged from 10... -2 ~10 5 Hz.

[0020] Example 1: A method for fabricating an MXene-based flexible electrode includes the preparation of MXene nanosheets, current collector compatibility screening, and the preparation of an MXene / current collector composite electrode. The specific steps are as follows: Preparation of MXene nanosheets: In a polytetrafluoroethylene container, 1 g of LiF was added to 20 mL of 9 mol / L HCl solution. Under magnetic stirring, 1 g of MAX phase (Ti3AlC2) powder was slowly added to the solution. The addition process was carried out under ice bath conditions. After the addition was completed, the reaction was continuously stirred for 48 h under a 40 °C water bath. The resulting product was washed with deionized water and centrifuged several times at 11000 r / min until the pH of the supernatant was close to neutral (pH≥6). The precipitate was dispersed in 100 mL of deionized water and sonicated for 30 min in a closed environment. The sonicated dispersion was centrifuged at 2000 r / min for 30 min, and the upper suspension was taken to obtain the MXene suspension, which was stored in a refrigerator for later use. The prepared MXene suspension was freeze-dried in a freeze dryer to obtain MXene powder.

[0021] Fabrication of MXene / different current collector composite electrodes: Carbon cloth (CC), carbon paper (CP), titanium mesh (TW), and titanium foil (TF) were used as current collector substrates. 2 mg of MXene powder and 0.25 mg of PVDF powder were mixed evenly in an agate mortar at a mass ratio of 8:1. One drop of NMP solvent was added, and the mixture was ground into a uniform slurry. The slurry was then evenly coated onto the clean surfaces of the carbon cloth, carbon paper, titanium mesh, and titanium foil, respectively. The coated electrodes were placed in a vacuum oven and dried at 60°C for 6 hours to obtain MXene / CC, MXene / CP, MXene / TW, and MXene / TF composite electrodes, respectively.

[0022] The microstructure and electrochemical performance of the prepared MXene and four sets of composite electrodes were characterized.

[0023] SEM characterization results are shown below. Figure 1 MXene nanosheets were uniformly loaded onto the surface of carbon cloth fibers in a continuous and dense manner. The fibrous porous structure of the carbon cloth was completely covered by the MXene nanosheets, and the interfiber gaps were fully filled with MXene. No uneven loading, local exposure, or pore blockage was observed. The MXene nanosheets were arranged in a layered and orderly manner, with uniform spacing between the layers, and no obvious stacking, aggregation, or agglomeration growth. EDS elemental mapping ( Figure 1 The IL (indicating a high concentration of ions) shows that Ti, F, O, and C are all uniformly distributed on the sample surface. In contrast, MXene / CP (indicating a lower concentration of ions) Figure 1 The particulate matter adhering to the surfaces of b and f is uneven in size and irregular in shape; MXene / TW ( Figure 1 In the titanium mesh of C and G), there are a large number of MXene aggregates in the gaps, and the MXene on the mesh surface is unevenly dispersed, with local stacking; MXene / TF ( Figure 1 In the middle (d) and (h) sections, the MXene agglomeration phenomenon on the smooth surface of the titanium foil is most obvious. The formed granular agglomerates tightly cover the surface of the titanium foil, with almost no dispersed MXene nanosheets.

[0024] TEM characterization results are shown in Figure 2 MXene nanosheets exhibit a typical two-dimensional layered morphology, with thin sheets, clear outlines, and no obvious agglomeration or adhesion between layers. In high-resolution imaging mode, lattice fringes can be clearly observed, and the characteristic interplanar spacing d = 0.257 nm is highly matched with the standard interplanar spacing of MXene (002) crystal planes, indicating that the prepared MXene has good crystallization properties.

[0025] XRD characterization results are shown below. Figure 3 All four composite electrodes exhibited sharp and clear characteristic diffraction peaks at 2θ = 6.57°, corresponding to the (002) crystal plane of MXene. The MXene / CC and MXene / CP samples showed characteristic crystal plane peaks of carbon materials at 2θ = 25.9°; the MXene / TW and MXene / TF samples showed characteristic double peaks of titanium metal at 2θ = 38.3° and 40.1°, respectively.

[0026] FTIR characterization results are shown in Figure 4 3436cm -1 The absorption peak at 1464 cm⁻¹ corresponds to the stretching vibration of -OH groups on the MXene surface; -1 and 1392cm -1 The absorption peak at 1060 cm⁻¹ is attributed to the bending vibration of the oxygen (-O) group on the MXene surface; -1The strong absorption peak at corresponds to the stretching vibration of -F.

[0027] The XPS characterization results are shown in Figure 5 . The full spectrum of the MXene / CC sample can clearly detect four characteristic elemental signal peaks of C1s, F1s, O1s and Ti2p. The C1s fine spectrum ( Figure 5 b) can be deconvoluted into three characteristic peaks with binding energies of 284.8 eV (C-C), 286.4 eV (C-O) and 289.5 eV (C=O), respectively. The O1s fine spectrum ( Figure 5 c) can be deconvoluted into two characteristic peaks with binding energies of 532.6 eV (C-Ti-O) and 533.9 eV (C-Ti-OH), respectively. The Ti2p fine spectrum ( Figure 5 d) exhibits the characteristic double peaks of Ti2p3 / 2 (460.7 eV) and Ti2p1 / 2 (466.5 eV).

[0028] The CV test results are shown in Figure 6 . The four groups of composite electrodes all exhibit typical electrochemical response characteristics within the scanning rate range of 5~100 mV / s. Among them, MXene / CC has the largest enclosed area of CV curves at all scanning rates, and presents the clearest and symmetric redox peaks in the potential range of -0.2~0.5 V. The enclosed areas of CV curves of MXene / CP, MXene / TW and MXene / TF are all much smaller than that of MXene / CC, the redox peaks are obviously broadened, and the peak shape has low recognizability.

[0029] The GCD test results are shown in Figure 7 . The GCD curve of MXene / CC presents an ideal symmetrical triangle, the slopes of the charge and discharge platforms are consistent, with no obvious voltage polarization, voltage drop and curve distortion; under the same current density, the charge and discharge time of MXene / CC is significantly longer than that of the other three groups. The GCD curve of MXene / CP still maintains a triangular outline, but the linearity of the charge and discharge platform decreases, and the charge and discharge time is shorter than that of MXene / CC. The GCD curve of MXene / TW is a triangle with rounded corners, with no clear charge and discharge platform, and the charge and discharge time is significantly shorter than that of the two carbon-based electrodes. The charge and discharge time of MXene / TF is the shortest among the four groups.

[0030] The EIS test results are shown in Figure 8 . The Nyquist plots of the four groups of composite electrodes are all composed of a capacitance resistance semicircle in the high-frequency region and an inclined straight line in the low-frequency region. The order of charge transfer resistance (Rct) of the four groups of electrodes is: MXene / CC < MXene / CP < MXene / TW < MXene / TF. Among them, the diameter of the high-frequency capacitance resistance semicircle of MXene / CC is the narrowest among the four groups, indicating that its Rct is the smallest.

[0031] The test results of specific capacitance and rate performance are shown in Figure 9 At a current density of 1 A / g, the specific capacitance of MXene / CC is 199.29 F / g; when the current density is increased to 20 A / g, the specific capacitance can still be maintained at 178.54 F / g, with a rate retention rate of 89.58%. The specific capacitance of MXene / CP, MXene / TW, and MXene / TF at a current density of 1 A / g is much lower than that of MXene / CC, and the specific capacitance decreases significantly after the current density is increased to 5 A / g.

[0032] The results of the charge storage kinetics analysis are shown in Figure 9 The anode peak b-value of MXene / CC is 0.804, and the cathode peak b-value is 0.898. At a scan rate of 5 mV / s, the diffusion capacitance contribution is 37.66%, at a scan rate of 100 mV / s, the fast capacitance contribution reaches 88.23%, and at a scan rate of 50 mV / s, the capacitance contribution accounts for 78.18% of the total charge storage, indicating that the charge storage process is mainly controlled by capacitance, supplemented by diffusion control.

[0033] The bending test results are shown below. Figure 10 Carbon cloth, after being fully bent 180°, exhibits no wrinkles, cracks, or deformation on its surface. Upon removal of external force, it instantly springs back 180°, restoring its original three-dimensional mesh-like flat shape. Carbon paper, after being bent 180°, only recovers to approximately 50° after the external force is removed, exhibiting significant irreversible deformation. Titanium mesh and titanium foil both undergo severe permanent plastic deformation after being bent 180°, showing virtually no tendency to self-recover after the external force is removed.

[0034] The results of the ultrasonic adhesion stability test are shown below. Figure 11 After continuous ultrasonic treatment in 1 mol / L H2SO4 electrolyte for 3 hours, the MXene / CC composite electrode showed only a very small amount of MXene detachment, and the supported layer remained intact. The MXene / CP, MXene / TW, and MXene / TF electrodes all showed significant MXene detachment, with severe damage to the supported layer.

[0035] The results show that carbon cloth, with its three-dimensional interwoven fiber porous structure and abundant active functional groups on the surface, can achieve uniform and dense loading of MXene nanosheets, construct stable interfacial bonding and continuous electron / ion transport channels, making carbon cloth an ideal substrate material for MXene-based flexible electrodes.

[0036] Example 2: Carbon cloth solves the substrate load problem of flexible electrodes, but it cannot solve the defects of MXene layer stacking and insufficient capacity of single components. It is necessary to introduce high-capacity guest materials for modification. Based on Example 1, polyaniline (PANI) is introduced as a guest material to modify MXene through interlayer intercalation, prepare PM (MXene / PANI) composite material and fabricate PM / CC electrode. The specific steps are as follows: Preparation of MXene nanosheets: Prepared according to the method described in Example 1.

[0037] Preparation of PM(MXene / PANI) composite materials: Dissolve 20 mg MXene in 50 mL of water, sonicate for 30 min, and then vacuum filter to obtain a wet film, which is then placed in a petri dish for later use. Place 150 μL aniline and 20 mL of water in a clean beaker, sonicate for 1 h, and then pour the mixture into a petri dish; react for 2 h. Place 0.833 mL HCl, 19.167 mL water, and 0.55 g ammonium persulfate in a clean beaker and sonicate for 1 h. After the 2 h reaction in the petri dish is complete, pour the oxidant solution into the petri dish and place it in the refrigerator's cold storage compartment for in-situ polymerization for 8 h. Wash the product four times with ethanol by centrifugation, dry it in a vacuum oven at 60 °C for 6 h, grind it evenly, and store it to obtain the PM composite material.

[0038] Fabrication of PM / CC composite electrode Take 2 mg of PM powder and 0.25 mg of PVDF powder, mix them evenly in an agate mortar at a mass ratio of 8:1, add 1 drop of NMP solvent, and grind until a uniform mud-like slurry is formed. Coat the slurry evenly on the surface of a clean carbon cloth, and dry it in a vacuum oven at 60°C for 6 hours to obtain a PM / CC composite electrode.

[0039] The microstructure of the prepared PM composite material and the PM / CC electrode were characterized and their electrochemical performance was tested.

[0040] SEM characterization results are shown below. Figure 12 In samples c and g, localized fractures of the MXene sheets were observed in PM samples, along with significant PANI aggregation.

[0041] XRD characterization results are shown below. Figure 13 The pure MXene sample exhibited a sharp (002) characteristic diffraction peak at 2θ = 7.52°. The (002) characteristic peak of the PM sample shifted to 2θ = 6.34°, indicating that PANI molecules had been inserted between the MXene layers, achieving effective control of the interlayer spacing. In addition, the PM sample showed characteristic diffraction peaks of PANI at 2θ = 9.30°, 14.55°, 19.92°, and 25.04°, corresponding to its (001), (011), (020), and (200) crystal planes, respectively, confirming that the aniline monomers intercalated between the MXene layers had successfully polymerized to form PANI with a regular crystal structure.

[0042] FTIR characterization results are shown in Figure 14 Pure MXene at 3436cm -1 1464cm -1 1392cm -1 and 1060cm-1 Absorption peaks appear at [values], corresponding to the surface -OH, -O, and -F functional groups, respectively. Several new absorption peaks appear in the FTIR spectrum of PM: 1491 cm⁻¹. -1 and 1578cm -1 The absorption peaks at 1301 cm⁻¹ are attributed to the stretching vibrations of the C=N bonds in the PANI molecular chain and the C=C bonds in the benzene ring skeleton, respectively; -1 and 1146cm -1 The absorption peaks at these locations correspond to the stretching vibrations of the CN bond and the in-plane stretching vibrations of the CH bond in the PANI molecule, respectively. Meanwhile, MXene's original 3436 cm⁻¹... -1 1464cm -1 Characteristic peaks are still present, but their intensity has slightly decreased.

[0043] CV test results are shown below Figure 17 The CV curve of the c-PM / CC electrode at a scan rate of 10 mV / s shows obvious redox peaks, but its integrated area is significantly lower than that of the electrode prepared by the subsequent ice-assisted process. GCD test results are shown in […]. Figure 17 The GCD curves of the PM / CC electrodes exhibit approximately symmetrical nonlinear characteristics, indicating an energy storage mechanism based on the synergistic effect of double-layer capacitance and pseudocapacitance.

[0044] The results of the multi-scan CV test are shown below. Figure 18 In the CV curves of the PM / CC electrode within the scan rate range of 2–100 mV / s, obvious redox peaks are observed. However, at high scan rates, the peak positions shift significantly, and the peak symmetry is poor. The results of multi-current-density GCD tests are shown below. Figure 18 In the case of electrode b, under gradient current densities of 1, 2, 6, 10, and 20 A / g, the charge-discharge time of PM / CC is significantly shorter than that of the electrode prepared by the subsequent ice-assisted process.

[0045] EIS test results are shown below. Figure 19 In the middle a., the semi-circular diameter of the high-frequency region of the PM / CC electrode is significantly larger than that of the electrode prepared by the subsequent ice-assisted process, indicating that it has a higher charge transfer resistance.

[0046] The results of the specific capacitance and rate performance tests are shown below. Figure 19 b. At a current density of 1 A / g, the specific capacitance of PM / CC is 494.94 F / g, which is 2.48 times that of pure MXene / CC (199.29 F / g); at an ultra-high current density of 100 A / g, the capacitance retention is 65.59%.

[0047] Voltage window test results show that the CV test of pure MXene was conducted within a voltage window of -0.4 to 0.3V, while the voltage window of the PM / CC composite electrode shifted upward to 0 to 0.7V. This indicates that the introduction of PANI brought about a redox reaction at a higher potential, effectively widening the working voltage window.

[0048] The results show that the introduction of PANI intercalation modification can effectively improve the specific capacitance and operating voltage window of the MXene-based composite electrode, and the double-layer capacitance of PANI and MXene forms a complementary and synergistic effect. However, in the polymerization process, the intercalation process of aniline monomers between MXene layers is difficult to control precisely. Incomplete intercalation directly leads to the aggregation of PANI on the MXene surface and outside the layer, which masks a large number of active sites and significantly hinders ion transport pathways. Therefore, the overall energy storage performance of the electrode still has considerable room for improvement.

[0049] Example 3: To address the issues of incomplete PANI intercalation and agglomeration in the polymerization process of Example 2, this paper proposes a reverse approach to the defect of freeze-assisted polymerization—"during the freezing process, a large amount of free water forms large-sized ice crystals, causing the MXene sheets to be squeezed and broken, and the two-dimensional structure to collapse." The approach involves strictly confining the growth of ice crystals within the MXene interlayers and using the expansion force of the ice crystals as an interlayer support. An I-PM composite material is prepared using a vacuum filtration-freezing synergistic process, with the specific steps as follows: Preparation of MXene nanosheets: Prepared according to the method described in Example 1.

[0050] Preparation of I-PM (ice-assisted in-situ polymerization of MXene / PANI) composite materials: Dissolve 20 mg MXene in 50 mL of water, sonicate for 30 min, filter to form a wet membrane, place in a clean petri dish, and freeze for 2 h. During freezing, add 150 μL aniline and 20 mL of water to a clean beaker and sonicate for 1 h. After freezing, pour the aniline solution into the petri dish and react for 2 h. Add 0.833 mL HCl, 19.167 mL water, and 0.55 g ammonium persulfate to a clean beaker and sonicate for 1 h. After the reaction in the petri dish is complete, pour the oxidant solution into the petri dish and polymerize in situ in the refrigerator for 8 h. Wash the product four times with ethanol by centrifugation, dry in a vacuum oven at 60 °C for 7 h, grind evenly, and store to obtain the I-PM composite material.

[0051] Preparation of I-PM / CC composite electrode: Take 2 mg of I-PM powder and 0.25 mg of PVDF powder, put them into an agate mortar at a mass ratio of 8:1 and mix them evenly. Add 1 drop of NMP solvent and grind until a uniform mud-like slurry is formed. Coat the slurry evenly on the surface of a clean carbon cloth and dry it in a vacuum oven at 60°C for 6 hours to obtain an I-PM / CC composite electrode.

[0052] As a comparison, the following control group samples were also prepared: Control group 1: The PM (non-in-situ polymerized MXene / PANI) composite material was prepared according to the method described in Example 2.

[0053] Control group 2: Preparation of i-PM (direct cryo-assisted MXene / PANI) composite material: Dissolve 20 mg of MXene in 50 mL of water, sonicate for 30 min, and then freeze the beaker in the freezer for 2 h. During freezing, add 150 μL of aniline and 20 mL of water to a clean beaker, sonicate for 1 h, and then pour the mixture into the frozen beaker. React for 2 h. Add 0.833 mL of HCl, 19.167 mL of water, and 0.55 g of ammonium persulfate to a clean beaker and sonicate for 1 h. After the reaction in the frozen beaker is complete, pour the oxidant solution into the frozen beaker and place it in the refrigerator for in-situ polymerization for 8 h. Wash the product four times with ethanol by centrifugation, dry it in a vacuum oven at 60 °C for 7 h, grind it evenly, and store it to obtain the i-PM composite material.

[0054] Fabrication of i-PM / CC composite electrode: Take 2 mg of i-PM powder and 0.25 mg of PVDF powder, mix them evenly in an agate mortar at a mass ratio of 8:1, add 1 drop of NMP solvent, and grind until a uniform mud-like slurry is formed. Coat the slurry evenly on the surface of a clean carbon cloth, and dry it in a vacuum oven at 60°C for 6 hours to obtain an i-PM / CC composite electrode.

[0055] Control group 3: Pure MXene, MXene powder and MXene / CC electrode were prepared according to the method described in Example 1.

[0056] The prepared I-PM composite material and each control group sample were characterized at multiple scales.

[0057] SEM characterization results are shown below. Figure 12 Original MXene ( Figure 12 Samples a and e exhibit a typical two-dimensional layered structure, with uniform sheet size, regular and orderly arrangement, almost no obvious defects on the surface, and no significant stacking or aggregation. I-PM samples ( Figure 12 In samples b and f, the MXene two-dimensional sheets are intact, without sheet breakage or stacking, and PANI is uniformly dispersed between the layers and on the surface, without aggregation. PM samples ( Figure 12 In samples c and g), localized fractures of MXene sheets were observed, along with significant PANI aggregation. (i-PM sample) Figure 12 Irreversible and severe fragmentation of the MXene sheets in d and h) resulted in the complete loss of the integrity of the two-dimensional structure.

[0058] TEM characterization results are shown in Figure 12 In the i and j of the I-PM, MXene maintains a complete and continuous two-dimensional layered substrate structure. A large number of low-contrast nanoparticles are scattered on the surface and between the MXene sheets, with uniform size and distribution, which are PANI nanoparticles generated by in-situ polymerization. High-resolution lattice images can identify two sets of characteristic lattice fringes: one set has a crystal plane spacing of about 0.257 nm, corresponding to the (002) characteristic crystal plane of MXene, confirming that the intrinsic crystal structure of MXene remains stable and there is no lattice distortion, sheet peeling or structural collapse; the other set has a crystal plane spacing of 0.251 nm, corresponding to the (200) crystal plane of PANI, confirming that the PANI generated by in-situ polymerization is crystalline.

[0059] The EDS element mapping results are shown below. Figure 12 In the test area, the five elements Ti, F, N, O, and C were uniformly distributed throughout the entire test area, without segregation or local enrichment; the distribution of N element highly overlapped with that of Ti element, confirming the uniform recombination of PANI on the MXene substrate.

[0060] XRD characterization results are shown below. Figure 13 The pure MXene sample exhibits a sharp (002) characteristic diffraction peak at 2θ = 7.52°. The (002) characteristic peak of the I-PM sample shifts to 2θ = 5.97°, a shift significantly greater than that of the PM sample (2θ = 6.34°) and the i-PM sample (2θ = 6.29°), indicating that the interlayer spacing of the I-PM sample is maximized. The PM, i-PM, and I-PM samples all show characteristic diffraction peaks of PANI at 2θ = 9.30°, 14.55°, 19.92°, and 25.04°, corresponding to the (001), (011), (020), and (200) crystal planes, respectively, confirming the formation of crystalline PANI.

[0061] FTIR characterization results are shown in Figure 14 Pure MXene at 3436cm -1 1464cm -1 1392cm -1 and 1060cm -1 Absorption peaks appear at [values], corresponding to the surface -OH, -O, and -F functional groups, respectively. A new PANI characteristic peak is added to the FTIR spectra of PM, i-PM, and I-PM: 1491 cm⁻¹. -1 and 1578cm-1 The absorption peaks at 1301 cm⁻¹ are attributed to the stretching vibrations of the C=N bonds in the PANI molecular chain and the C=C bonds in the benzene ring skeleton, respectively; -1 and 1146cm -1 The absorption peaks at these locations correspond to the stretching vibrations of the CN bond and the in-plane stretching vibrations of the CH bond in the PANI molecule, respectively. The original characteristic peaks of MXene in I-PM are still retained, but their intensities are slightly weakened, indicating that there is a good interfacial binding between MXene and PANI, rather than a simple physical mixing.

[0062] The XPS full spectrum results are shown below. Figure 15 Pure MXene exhibits four characteristic peaks: C1s, F1s, O1s, and Ti2p. The I-PM composite material not only retains all the characteristic elemental signals of MXene, but also adds a new N1s characteristic peak. This signal originates from the characteristic amine (-NH-) and imine (-N=) structures on the PANI molecular chain generated by in-situ polymerization.

[0063] High-resolution peak-splitting results of pure MXene C1s spectrum are shown in [reference needed]. Figure 15 In the middle b, the strong characteristic peak at 281.7 eV corresponds to the C-Ti covalent bond; the C / C peak at 284.8 eV corresponds to adsorbed carbon on the surface; and the CO peak at 288.1 eV corresponds to oxygen-containing functional groups generated by slight oxidation. The high-resolution peaking results for O1s are shown in [reference needed]. Figure 15 The C-Ti-O peak at 530.4 eV corresponds to the intrinsic terminal oxygen coordination structure of MXene; the C-Ti-OH peak at 531.9 eV confirms the presence of numerous hydroxyl terminal groups on the MXene surface. High-resolution Ti2p peak separation results are shown below. Figure 15 The Ti2p3 / 2 orbital has two fitted peaks at 455.5 eV and 459.3 eV, a Ti-C bond characteristic peak at 461.9 eV, and a Ti2p1 / 2 characteristic peak at 464.7 eV.

[0064] The high-resolution peak-splitting results of the C1s spectrum of I-PM are shown in the figure. Figure 16 In the a. I-PM, only a single C-Ti bond characteristic peak appears at 284.8 eV. Compared with pure MXene, the C-Ti bond signal completely disappears, which is due to the uniform coating effect of PANI induced by the ice-assisted process—the PANI molecular chains are completely and uniformly coated on the surface of the MXene sheets, completely obscuring the C-Ti bond signal of the MXene bulk phase.

[0065] The high-resolution peak-splitting results of the O1s spectrum of I-PM are shown below. Figure 16 In the middle b, the C-Ti-O peak is located at 531.6 eV, and the C-Ti-OH peak is located at 532.5 eV. Both show a significant positive shift compared to pure MXene. (High-resolution Ti2p spectrum of I-PM) Figure 16 In c), all characteristic peaks are shifted positively overall. The positive shift of the O1s and Ti2p peaks indicates that PANI and the oxygen-containing functional groups on the MXene surface have formed a synergistic effect of hydrogen bonds and coordination bonds. The electron clouds of O and Ti atoms shift towards the N atoms in PANI, resulting in an increase in their binding energy, which directly confirms the strong interaction and electron transfer effect at the two-phase interface.

[0066] The peak-splitting results of the N1s high-resolution spectrum of I-PM are shown in the figure. Figure 16 The characteristic peaks of the quinone imine group (-N=) at 399.5 eV and the benzene amino group (-NH-) at 401.1 eV perfectly match the typical chemical state characteristics of conductive PANI, confirming that PANI generated by ice-assisted in-situ polymerization has good electrochemical activity.

[0067] The results show that the vacuum filtration-freezing synergistic ice-assisted in-situ polymerization strategy precisely removes free water through vacuum filtration, retaining only the interlayer bound water of MXene. This allows ice crystals to nucleate and grow in situ only at the interlayer bound water sites during freezing, gently expanding and widening the interlayer spacing, thus avoiding mechanical damage to the MXene sheets caused by large-sized ice crystals formed by free water. In contrast, the comparative i-PM sample, which did not undergo filtration, contained a large amount of free water. During low-temperature freezing, this free water underwent heterogeneous nucleation and formed large-sized ice crystals. The mechanical compressive stress generated by the directional growth of these ice crystals led to irreversible breakage of the MXene sheets and collapse of the layered structure. The ice crystals, acting as a microscopic support, provided favorable conditions for the diffusion of aniline monomers into the interlayer. Aniline completed in-situ polymerization within a confined space, and PANI was uniformly dispersed and formed a strong interfacial bond with MXene through hydrogen bonds and coordination bonds. This strategy simultaneously solved three technical challenges: incomplete intercalation, PANI agglomeration, and weak interfacial bonding.

[0068] Example 4: Electrochemical performance optimization and application verification of an I-PM / CC flexible electrode: Based on Example 3, the differences in electrochemical performance of electrodes prepared by different process routes were systematically evaluated, and the active material loading was optimized and long-term cycling stability was verified. The specific steps are as follows: Performance comparison of electrodes made using different processes: The electrochemical performance of the MXene / CC electrode prepared in Example 1, the PM / CC electrode prepared in Example 2, the I-PM / CC electrode prepared in Example 3, and the i-PM / CC electrode prepared in Control Group 2 of Example 3 were compared and tested in a three-electrode system with 1 mol / L H2SO4 electrolyte.

[0069] CV test results are shown below Figure 17. Pure MXene exhibits typical pseudocapacitive characteristics within the voltage window of -0.4~0.3 V; the voltage windows of PM / CC, i-PM / CC and I-PM / CC composite electrodes are shifted upward to 0~0.7 V. At a scan rate of 10 mV / s, the I-PM / CC electrode has the largest CV integration area, corresponding to the highest charge storage capacity; the integration areas of CV curves of both PM / CC and i-PM / CC electrodes are significantly lower than that of the I-PM / CC electrode. The GCD test results are shown in Figure 17 , the GCD curves of all samples present good symmetry and nonlinear characteristics, and the I-PM / CC electrode exhibits the longest discharge duration.

[0070] The multi-scan rate CV test results are shown in Figure 18 as a and c. Both PM / CC and i-PM / CC electrodes have obvious redox peaks in their CV curves within the scan rate range of 2~100 mV / s, but the integration area of the CV curve of i-PM / CC is larger than that of PM / CC, the symmetry of the redox peaks is better than that of PM / CC, and the peak potential difference is smaller than that of PM / CC, indicating that the polarization degree of the i-PM / CC electrode is lower than that of PM / CC; with the increase of scan rate, the shift of redox peak positions of i-PM / CC is smaller than that of PM / CC, indicating that its charge transfer resistance is lower. The multi-current density GCD test results are shown in Figure 18 as b and d. Under the gradient current densities of 1, 2, 6, 10 and 20 A / g, the charge and discharge durations of i-PM / CC are all significantly longer than those of PM / CC, indicating that its specific capacitance is higher and the rate performance is better.

[0071] The EIS test results are shown in Figure 19 as a. The order of the semicircle diameters in the high-frequency region of the Nyquist plots of the four groups of electrodes is: I-PM / CC < i-PM / CC < PM / CC < MXene / CC, wherein the I-PM / CC electrode has the smallest semicircle diameter in the high-frequency region, indicating that it has the lowest charge transfer resistance (Rct) and the fastest interfacial ion / electron transfer rate.

[0072] The comparison results of specific capacitance and rate performance are shown in Figure 19 as b. At a current density of 1 A / g, the specific capacitances of MXene / CC, PM / CC, i-PM / CC and I-PM / CC are 199.29 F / g, 494.94 F / g, 519.31 F / g and 631.71 F / g, respectively; the specific capacitance of I-PM / CC is 3.17 times that of pure MXene / CC, which is 27.6% higher than that of PM / CC and 21.6% higher than that of i-PM / CC. At an ultra-high current density of 100 A / g, the capacitance retention rates of the four groups of electrodes are 64.58%, 65.59%, 65.99% and 79.35% respectively, and the rate stability of I-PM / CC is significantly better than that of the other three groups.

[0073] Load optimization: Take 1 mg, 2 mg, and 3 mg of I-PM powder, and mix them with 0.125 mg, 0.25 mg, and 0.375 mg of PVDF powder (mass ratio of 8:1) in an agate mortar. Add 1 drop of NMP solvent to each mixture and grind until a uniform mud-like slurry is formed. Coat the slurry evenly on the surface of a clean carbon cloth and dry it in a vacuum oven at 60°C for 6 hours to obtain I-PM / CC1, I-PM / CC2, and I-PM / CC3 composite electrodes, respectively.

[0074] CV test results are shown below Figure 20 a and Figure 21 In Figures a and c, the CV curves of all three electrode loadings showed obvious redox peaks, corresponding to the reversible transition of the PANI benzo-quinone structure and the valence state changes of Ti atoms and oxygen-containing functional groups on the MXene surface. I-PM / CC2 had the largest CV integration area; the CV curve integration area of ​​I-PM / CC1 was significantly larger than that of I-PM / CC3. Within a wide scan rate range of 2–100 mV / s, the CV curve of I-PM / CC2 did not show significant shape distortion or peak shift. Figure 20 (c); The peak shapes of the CV curves for I-PM / CC1 and I-PM / CC3 remained basically intact as the scan rate increased. Figure 21 (a, c)

[0075] The GCD test results are shown below. Figure 20 b, d and Figure 21 In sections b and d, I-PM / CC2 exhibits the longest charge-discharge duration. At current densities of 1, 2, 5, and 10 A / g, the charge-discharge duration of I-PM / CC1 is significantly longer than that of I-PM / CC3. The GCD curves of each electrode maintain excellent symmetry and consistency at different current densities, exhibiting an approximately symmetrical triangular morphology.

[0076] EIS test results are shown below. Figure 22 In Figure a, the Nyquist plots of the three electrodes, I-PM / CC1, I-PM / CC2, and I-PM / CC3, all show regular semicircles in the high-frequency region, and the solution resistance of all electrodes is below 0.5 Ω. The slope of the curve for the I-PM / CC2 electrode in the low-frequency region is significantly higher than that of the other two groups, indicating that its ion diffusion kinetics are optimal.

[0077] The results of the capacitance comparison are shown below. Figure 22In section b, at a current density of 1 A / g, the specific capacitances of I-PM / CC1, I-PM / CC2, and I-PM / CC3 are 613.25 F / g, 631.71 F / g, and 553.64 F / g, respectively, with I-PM / CC2 exhibiting the highest specific capacitance. At an ultra-high current density of 100 A / g, the capacitance retention rates of I-PM / CC1 and I-PM / CC2 are 77.64% and 79.35%, respectively, while the rate performance of I-PM / CC3 shows a sharp decline.

[0078] Kinetic analysis (I-PM / CC2): Plot a double logarithmic relationship between the anode peak current, cathode peak current, and the corresponding scan rate. The results are shown in [the table below]. Figure 23 In the middle, a. The formula i=av is used. b Fitting the data, the anode peak b-value of the I-PM / CC2 electrode is 0.90, and the cathode peak b-value is 0.85. Both characteristic b-values ​​are highly close to 1, indicating that the charge storage process of this electrode is mainly dominated by fast capacitive behavior.

[0079] Using formula The capacitance contribution and diffusion contribution were calculated separately, and the results are shown in [the table below]. Figure 23 In Figures b and c, at a scan rate of 50 mV / s, capacitive contribution accounts for 80.93% of the total capacitance. As the scan rate increases from 2 mV / s to 50 mV / s, the proportion of capacitive contribution in the total capacitance increases from 60.38% to 92.08%, indicating that the charge storage process of the I-PM / CC2 electrode is dominated by surface Faraday pseudocapacitance rather than diffusion capacitance.

[0080] Cyclic stability test: The I-PM / CC2 electrode was subjected to 10,000 consecutive CV tests at a scan rate of 100 mV / s. The results are shown in [Figure number missing]. Figure 24 After 10,000 CV cycles, the CV curve profile and peak characteristics of the electrode remained basically consistent with those before cycling, with no obvious peak distortion or characteristic peak intensity attenuation. Based on the integral area calculation of the CV curves before and after cycling, the capacitance retention rate of the I-PM / CC2 electrode after 10,000 deep cycles was 95.61%, indicating that the electrode has excellent long-term cycling stability.

[0081] The results show that I-PM / CC2 is the optimal ratio, with a specific capacitance of 631.71 F / g at a current density of 1 A / g, which is 3.17 times that of the pure MXene / CC electrode; the capacitance retention rate is 79.35% at an ultra-high current density of 100 A / g; and the capacitance retention rate is 95.61% after 10,000 CV cycles. The ice-assisted in-situ polymerization strategy precisely controls the water content of the MXene film through vacuum filtration, so that ice crystals nucleate only in the interlayer confinement during freezing, and gently expand to open the interlayer spacing. After the aniline monomer fully enters the interlayer, it completes in-situ polymerization in the confined space, which completely preserves the two-dimensional conductive framework of MXene. PANI is uniformly intercalated and forms an electric double layer with MXene to form a pseudocapacitive synergistic energy storage. Strong interfacial bonding is constructed through hydrogen bonds and coordination bonds, forming a continuous ion transport channel and a continuous conductive network, realizing a leapfrog improvement in the electrochemical performance of MXene-based flexible electrodes.

[0082] In summary, this application successfully constructed an I-PM / CC flexible composite electrode by selecting carbon cloth as the optimal flexible current collector substrate and developing a vacuum filtration-freezing synergistic ice-assisted in-situ polymerization strategy. This strategy transforms ice crystals from potential structural disruptors into interlayer intercalation aids. The electrode simultaneously solves three core challenges: easy stacking and agglomeration of MXene sheets, poor interface compatibility with the current collector, and limited energy storage capacity of a single material. It possesses high specific capacitance, excellent rate performance, and long cycle life, showing broad application prospects in wearable electronic devices and flexible energy storage devices.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An MXene-based flexible electrode material, characterized in that, It comprises the following components: a carbon cloth current collector, an active material layer loaded on the surface of the carbon cloth current collector, and a binder; The active material layer is composed of an I-PM composite material, which is an MXene / polyaniline composite, wherein polyaniline is uniformly intercalated between MXene sheets, and polyaniline and MXene are bonded by hydrogen bonds and coordination bonds; the binder is polyvinylidene fluoride.

2. The MXene-based flexible electrode material according to claim 1, characterized in that, The mass ratio of the I-PM composite material to polyvinylidene fluoride is 8:

1.

3. A method for preparing the MXene-based flexible electrode material as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of MXene nanosheet dispersion; S2. Vacuum filter the MXene nanosheet dispersion obtained in step S1 into a wet film, and freeze it to make the water bound between the MXene layers freeze in situ; S3. Add aniline solution to the wet film after freezing treatment for reaction, and then add oxidant solution to carry out in-situ polymerization reaction, so that aniline monomers are confined and polymerized in the MXene interlayer to obtain I-PM composite material; S4. The I-PM composite material obtained in step S3 is mixed with polyvinylidene fluoride and solvent and ground into a slurry, which is then coated onto the surface of the carbon cloth current collector and dried to obtain the MXene-based flexible electrode material.

4. The preparation method according to claim 3, characterized in that, The preparation of MXene nanosheets in step S1 includes: mixing LiF with HCl solution, adding MAX phase Ti3AlC2 powder under ice bath conditions, stirring and reacting in a 40℃ water bath for 48h, centrifuging and washing until pH≥6, ultrasonic dispersion, and centrifuging to collect the upper suspension.

5. The preparation method according to claim 3, characterized in that, The freezing temperature in step S2 is -18℃ to -24℃, and the freezing time is 2h; the wet membrane in step S2 is obtained by removing free water and retaining interlayer bound water through vacuum filtration.

6. The preparation method according to claim 3, characterized in that, The oxidant solution in step S3 contains HCl, water and ammonium persulfate, and the in-situ polymerization reaction is carried out at an ambient temperature of 4°C for 8 hours.

7. The preparation method according to claim 3, characterized in that, The drying temperature in step S4 is 60°C and the drying time is 6 hours.

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