Bismuth carbon nanowire-based planar electrochemical filter capacitor and preparation method thereof

Abstract

The invention relates to the technical field of electrochemical energy storage, and discloses a preparation method of a bismuth carbon nanowire-based planar electrochemical filter capacitor, which comprises the following steps of: (1) adding 2g of polyacrylonitrile and 1g of bismuth nitrate pentahydrate into 20mL of dimethylformamide, and stirring for 12 hours at room temperature in an argon atmosphere to obtain a white transparent viscous spinning precursor solution; (2) filling the spinning precursor solution into an injector with a 20G needle, and taking a roller wrapped by aluminum foil as a receiving device; according to the bismuth carbon nanowire-based planar electrochemical filter capacitor and the preparation method thereof, bismuth nitrate pentahydrate and polyacrylonitrile are co-dissolved in a spinning precursor solution, and after electrostatic spinning and gradient heat treatment, in-situ generation and uniform embedding of bismuth or oxide nanoparticles thereof in a carbon nanofiber matrix are realized; the problems of particle aggregation and weak interface bonding caused by a traditional post-loading method are effectively avoided, and the integrity and cycling stability of the electrode structure are improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a bismuth-carbon nanowire-based planar electrochemical filter capacitor and its preparation method. Background Technology

[0002] Filter capacitors, as key passive components used in electronic circuits to smooth voltage and suppress ripple, are widely used in power management, signal processing, and high-frequency electronic systems. Although traditional aluminum electrolytic capacitors have a large volumetric capacitance, their equivalent series resistance is high, limiting their high-frequency response capability and making it difficult to meet the needs of modern high-frequency, miniaturized electronic systems. In contrast, carbon-based electrochemical capacitors, due to their excellent conductive network and fast ion response capability, can achieve a phase angle of approximately -72° at a 120Hz power frequency, approaching ideal capacitor behavior (ideal capacitor phase angle is -90°), demonstrating excellent filtering potential.

[0003] In existing technologies, carbon nanofiber membranes are often prepared using electrospinning combined with carbonization processes as electrode materials. However, carbon nanowire electrodes prepared solely with polyacrylonitrile (PAN) as a precursor, while possessing a good conductive network and a certain frequency response capability, generally have low specific capacity, making it difficult to achieve effective energy storage improvement while maintaining high-frequency filtering characteristics. To improve capacity, researchers have attempted to introduce metal or metal oxide active components, but such composite materials often suffer from high-frequency phase angle degradation due to extended ion diffusion paths and increased interfacial impedance, failing to meet the requirements for fast response in power frequency (e.g., 120Hz) filtering.

[0004] In addition, existing composite electrodes mostly rely on physical mixing or post-loading to introduce active materials, which easily leads to particle agglomeration and uneven distribution, and the binding force with the carbon matrix is ​​weak, resulting in poor structural stability during repeated electrochemical cycles. How to achieve in-situ construction of high-density, uniformly dispersed electrochemical active phase while maintaining the continuous network structure of carbon nanofibers has become a key technical bottleneck restricting the performance breakthrough of electrochemical filter capacitors.

[0005] Therefore, there is an urgent need to develop a new type of electrode material and its preparation method that can significantly improve the areal capacitance of electrochemical filter capacitors without sacrificing high-frequency phase response characteristics, and ensure the uniformity and stability of the material structure. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a bismuth-carbon nanowire-based planar electrochemical filter capacitor and its preparation method. It has the advantages of in-situ uniform dispersion of bismuth phase in carbon nanofiber matrix, continuous and dense electrode structure, and controllable thickness and areal density. It solves the problems of low specific capacity of traditional carbon nanowire electrodes, and the tendency of high-frequency phase angle degradation after the introduction of active materials, making it difficult to achieve both high capacity and good filtering performance.

[0008] (II) Technical Solution

[0009] To achieve the aforementioned objectives of "uniform in-situ dispersion of the bismuth phase in a carbon nanofiber matrix, continuous and dense electrode structure, and controllable thickness and areal density," this invention provides the following technical solution: a method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor, comprising the following steps:

[0010] (1) Add 2g of polyacrylonitrile and 1g of bismuth nitrate pentahydrate to 20mL of dimethylformamide and stir at room temperature for 12 hours under argon atmosphere to obtain a white, transparent and viscous spinning precursor solution.

[0011] (2) The spinning precursor solution is loaded into a syringe with a 20G needle. An aluminum foil-wrapped roller is used as the receiving device. The distance between the needle and the roller is controlled to be 20cm, the injection rate is 0.8mL / h, the needle translation speed is 500mm / min, the roller rotation speed is 120r / min, the voltage applied to the needle is +13kV, the voltage applied to the roller is -2kV, and electrospinning is performed for 5 hours to obtain white nonwoven fabric.

[0012] (3) Place the white non-woven fabric and aluminum foil in a vacuum oven at 60°C and dry for 12 hours. Then peel off the aluminum foil and cut it to the predetermined size.

[0013] (4) The cut nonwoven fabric is heated to 250°C in air at a heating rate of 5°C / min and kept at that temperature for 2 hours to obtain brown-black nonwoven fabric.

[0014] (5) The brown-black nonwoven fabric is heated to 750°C in an argon atmosphere at a heating rate of 5°C / min and kept at that temperature for 2 hours to obtain black bismuth carbon nanowire nonwoven fabric.

[0015] (6) The black bismuth carbon nanowire nonwoven fabric is processed into a planar interdigitated electrode structure, and an electrolyte containing LiTFSI is added to assemble it into a planar electrochemical filter capacitor.

[0016] Preferably, the electrolyte is an organic solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0017] Preferably, in step (6), the planar interdigitated electrode is a symmetrical interdigitated structure formed by laser cutting, with a single electrode width of 200-500μm and an electrode spacing of 100-300μm.

[0018] Preferably, the mass ratio of polyacrylonitrile to bismuth nitrate pentahydrate in the spinning precursor solution is 2:1.

[0019] Preferably, the black bismuth carbon nanowire nonwoven fabric contains a bismuth phase existing in the form of elemental bismuth or bismuth oxide (Bi2O3).

[0020] Preferably, the pyrolysis treatment is carried out under an argon atmosphere with an argon flow rate of 50-100 mL / min.

[0021] Preferably, the black bismuth carbon nanowire nonwoven fabric has a thickness of 10-50 μm and an areal density of 0.5-2.0 mg / cm³. 2 .

[0022] A bismuth carbon nanowire-based planar electrochemical filter capacitor includes a bismuth carbon nanowire nonwoven fabric prepared by the above method as an electrode material, wherein the electrode material comprises a carbon nanofiber matrix and bismuth or bismuth oxide nanoparticles dispersed therein.

[0023] Preferably, the bismuth or bismuth oxide nanoparticles have a particle size of 10-100 nm and are distributed in an embedded form inside or on the surface of carbon nanofibers.

[0024] (III) Beneficial Effects

[0025] Compared with the prior art, the present invention provides a bismuth carbon nanowire-based planar electrochemical filter capacitor and its preparation method, which has the following beneficial effects:

[0026] 1. The bismuth carbon nanowire-based planar electrochemical filter capacitor and its preparation method are described. By co-dissolving bismuth pentahydrate nitrate and polyacrylonitrile in a spinning precursor solution, followed by electrospinning and gradient heat treatment, bismuth or its oxide nanoparticles are generated and uniformly embedded in a carbon nanofiber matrix. This effectively avoids the problems of particle agglomeration and weak interfacial bonding caused by traditional post-loading methods, and improves the integrity of the electrode structure and cycle stability.

[0027] 2. The bismuth-carbon nanowire-based planar electrochemical filter capacitor and its preparation method: The bismuth-carbon nanowire electrode prepared by this method maintains an excellent phase angle (approximately -72°) at 120Hz, which is comparable to that of a pure carbon nanowire electrode (-71.9°), and is significantly better than most composite electrodes. It successfully meets the dual requirements of high-frequency response and high energy storage capacity of electrochemical filter capacitors, and overcomes the technical obstacle of sacrificing filtering performance due to the introduction of active materials in existing composite electrodes. Attached Figure Description

[0028] Figure 1 This is a low-magnification field emission scanning electron microscope (SEM) image of the bismuth carbon nanowire nonwoven fabric of the present invention.

[0029] Figure 2 This is a medium-magnification SEM image of the bismuth carbon nanowires of this invention.

[0030] Figure 3 This is a high-magnification SEM image of the bismuth-carbon nanowires of the present invention;

[0031] Figure 4 The cyclic voltammetry (CV) curves of the planar electrochemical filter capacitor of the present invention at different scan rates are shown.

[0032] Figure 5 This is a comparison diagram of the time-domain filtering effect of the electrochemical filter capacitor of this invention at a 120Hz power frequency;

[0033] Figure 6 This is a Bode phase angle-frequency relationship diagram of the bismuth carbon nanowire and pure carbon nanowire electrodes of the present invention;

[0034] Figure 7 The Nyquist impedance spectra of the bismuth carbon nanowire and pure carbon nanowire electrodes of this invention are shown.

[0035] Figure 8 This is a bar chart comparing the area-to-capacity ratio of the bismuth-carbon nanowire electrode and the pure carbon nanowire electrode of this invention.

[0036] Figure 9 This is a graph showing the ripple suppression test results of the electrochemical filter capacitor of this invention at 120Hz;

[0037] Figure 10 This is a graph showing the ripple suppression test results of the electrochemical filter capacitor of this invention at 1000Hz;

[0038] Figure 11 This is a flowchart of the preparation method of the bismuth-carbon nanowire-based planar electrochemical filter capacitor of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention proposes a method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor. According to embodiments of the invention, refer to the appendix... Figure 1-11 As shown, the above method includes:

[0041] First, an electrospinning precursor solution containing polyacrylonitrile and bismuth nitrate pentahydrate is prepared. In this step, the polymer and metal salt are dissolved together in a polar aprotic solvent to form a uniform, transparent spinning solution with a certain degree of viscoelasticity, which lays the foundation for the subsequent in-situ embedding of the bismuth phase in carbon fibers.

[0042] In the embodiments of the present invention, the polyacrylonitrile (PAN) used has a molecular weight of approximately 150,000, the solvent is dimethylformamide (DMF), and the metal source is bismuth nitrate pentahydrate Bi(NO3)3·5H2O.

[0043] Preferably, the mass ratio of PAN to bismuth salt is 2:1, which balances the spinning formability and the loading density of the active phase.

[0044] Subsequently, an electrospinning process is performed to obtain a continuous nanofiber nonwoven fabric. In this step, a high-voltage electrostatic field is used to stretch the precursor solution into micron / submicron-sized fibers, which are then deposited on a rotating receiving device to form a self-supporting flexible membrane structure.

[0045] In an embodiment of the present invention, a 20G stainless steel needle is used, the injection rate is 0.8 mL / h, the distance between the needle tip and the receiving roller is 20 cm, and the roller surface is wrapped with aluminum foil as a temporary carrier to facilitate subsequent peeling; the roller speed is set to 120 r / min, the needle lateral translation speed is 500 mm / min, the applied voltage is +13 kV for the needle and -2 kV for the roller, and the spinning time is 5 hours; the resulting white nonwoven fabric, together with the aluminum foil, is placed in a vacuum oven at 60°C and dried for 12 hours to completely remove residual solvent.

[0046] Next, the dried fiber membrane is subjected to gradient heat treatment to complete the pre-oxidation and carbonization processes in sequence. In this step, the fiber structure is first stabilized at low temperature in an air atmosphere to prevent melting and collapse during high-temperature carbonization. Then, it is pyrolyzed at high temperature in an inert atmosphere to simultaneously achieve the formation of carbon skeleton and the reduction / conversion of bismuth species.

[0047] Specifically, the temperature was increased to 250°C at 5°C / min and held for 2 hours in an air atmosphere to obtain a brownish-black pre-oxidized fiber membrane; then it was transferred to a tube furnace and heated to 750°C at the same rate under argon protection (flow rate controlled within the range of 50-100 mL / min) and held for 2 hours to finally obtain a black bismuth carbon nanowire nonwoven fabric.

[0048] Measurements showed that the nonwoven fabric was approximately 30 μm thick and had an areal density of 1.2 mg / cm³. 2 .

[0049] Finally, the obtained bismuth carbon nanowire nonwoven fabric was processed into a planar interdigitated electrode structure, and an electrolyte was added to assemble it into an electrochemical filter capacitor. In this step, a symmetrical interdigitated configuration was constructed using laser precision cutting technology. The width of a single electrode was 300 μm, the electrode spacing was 200 μm, and the electrolyte was a 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) organic mixed solvent, which has a wide electrochemical window and good ionic conductivity.

[0050] In a second aspect, the present invention provides a bismuth carbon nanowire-based planar electrochemical filter capacitor, the electrode material of which is prepared by the above method and comprises a continuous carbon nanofiber network and bismuth or bismuth oxide (Bi2O3) nanoparticles uniformly dispersed therein; the bismuth phase mainly exists in the form of elemental bismuth (Bi), as verified by XRD; a small amount of bismuth oxide (Bi2O3) may form on the surface due to contact with air, but this does not affect the main electrochemical performance; the particle size is distributed between 10-100 nm, mainly embedded in the fiber or attached to the surface, effectively avoiding agglomeration and improving interface stability.

[0051] In a third aspect of the present invention, the electrochemical filter capacitor proposed in this invention has both high area specific capacitance and excellent high frequency response characteristics, making it particularly suitable for 120Hz power frequency filtering scenarios. It also has advantages such as flexibility, thinness, and integrability, which are in line with the trend of miniaturization of modern electronic devices.

[0052] The embodiments of the present invention are described in detail below. It should be noted that the following embodiments are merely illustrative examples, and all reagents used are commercially available analytical grade reagents. Unless otherwise specified, all process parameters are performed within the aforementioned range.

[0053] Example 1

[0054] As attached Figure 10 As shown in the figure, this embodiment provides a method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor, including the following steps:

[0055] (1) Weigh 2.0g of polyacrylonitrile and 1.0g of bismuth nitrate pentahydrate Bi(NO3)3·5H2O, add them to 20mL of dimethylformamide, and stir magnetically at room temperature for 12 hours under argon protection to obtain a white, transparent, viscous spinning precursor solution.

[0056] (2) Draw the above solution into a 5mL syringe, equip it with a 20G needle, use a metal roller wrapped with aluminum foil as the receiver, set the needle tip distance to the roller to 20cm, the injection rate to 0.8mL / h, the needle translation speed to 500mm / min, the roller rotation speed to 120r / min, apply a needle voltage of +13kV and a roller voltage of -2kV, electrospin for 5 hours to obtain white nonwoven fabric;

[0057] (3) Place the obtained nonwoven fabric and aluminum foil in a vacuum oven at 60°C for 12 hours to dry. After cooling, carefully peel off the aluminum foil and cut it into 2cm×2cm square pieces.

[0058] (4) The sample was placed in a muffle furnace and heated to 250°C at 5°C / min in air atmosphere and kept at that temperature for 2 hours to obtain brown-black pre-oxidized nonwoven fabric.

[0059] (5) Transfer to a tube furnace, and heat to 750℃ at 5℃ / min under argon gas flow (80mL / min) protection and hold for 2 hours. After natural cooling, black bismuth carbon nanowire nonwoven fabric is obtained.

[0060] (6) The non-woven fabric is processed into symmetrical interdigitated electrodes (electrode width 300μm, spacing 200μm) using a CO2 laser cutting system. 1mol / L LiTFSI / acetonitrile-propylene carbonate (1:1v / v) electrolyte is added to the electrode area and then encapsulated to obtain a planar electrochemical filter capacitor.

[0061] (7) Performance testing:

[0062] (7-1) Characterization of the microstructure of bismuth carbon nanowire nonwoven fabric

[0063] The morphology of the black bismuth carbon nanowire nonwoven fabric obtained in step (5) was observed using field emission scanning electron microscopy; as shown in the attached figure. Figure 1 As shown, the prepared nanofibers exhibit a continuous, unbroken network structure, with a dense overall arrangement and good flexibility; Figure 2 Further examination revealed that the fiber diameter distribution was uniform, averaging approximately 300 nm, with a smooth surface and no obvious pores or defects; Figure 3 A large number of bright white nanoparticles were clearly observed to be uniformly distributed inside and on the surface of the carbon fiber, with the particle size concentrated in the range of 10–100 nm. This result confirms that the bismuth phase has been successfully embedded in the carbon matrix in situ without obvious agglomeration.

[0064] (7-2) Characterization of the electrochemical behavior of electrode materials

[0065] The assembled planar electrochemical filter capacitor was tested using cyclic voltammetry (CV) within a voltage window of 0-2V, with scan rates set at 100V / s, 300V / s, 500V / s, and 1000V / s, respectively; see attached. Figure 4 As shown, all CV curves exhibit an approximately rectangular profile and maintain a good shape even at an ultra-high scan rate of 1000V / s, indicating that the electrode has excellent double-layer capacitance characteristics and fast ion response capability, making it suitable for high-frequency operating conditions.

[0066] (7-3) Time-domain verification of the filtering function

[0067] Construct a full-wave rectification-filtering test circuit with a 120Hz pulsating DC voltage as the input signal; see attached. Figure 5 As shown, after the original rectified waveform (top) is filtered by the device of this invention (bottom), the output voltage is significantly smoothed and the fluctuation amplitude is greatly reduced, which intuitively demonstrates its excellent filtering effect.

[0068] (7-4) Evaluation of high-frequency phase response characteristics

[0069] Electrochemical impedance spectroscopy (EIS) was used in the frequency range of 10 4 The impedance characteristics of the device were tested under conditions of Hz to 1Hz and excitation amplitude of 5mV; see attached. Figure 6 As shown, at 120 Hz, the phase angle of the bismuth carbon nanowire electrode is -71.7°, while that of the control group pure carbon nanowire electrode is -71.9°. The two are almost identical, indicating that the introduction of the bismuth active phase did not degrade the high-frequency capacitance response behavior, and successfully met the dual requirements of high capacity and fast response.

[0070] (7-5) Analysis of the Nyquist plot of the impedance spectrum

[0071] As attached Figure 7 As shown, the Nyquist plots of both bismuth-carbon nanowires and pure carbon nanowires exhibit nearly vertical straight lines, especially in the low-frequency region where the slope is close to 90°, reflecting ideal capacitance behavior. At the 120Hz data point, the real part of the impedance of bismuth-carbon nanowires is slightly higher than that of the pure carbon sample, but the overall difference is small, further confirming that its high-frequency performance is not significantly affected.

[0072] (7-6) Quantitative comparison of area specific capacity

[0073] As attached Figure 8 As shown, under the same test conditions, the areal capacity of the bismuth carbon nanowire electrode is significantly higher than that of the pure carbon nanowire electrode, indicating that the introduction of the bismuth phase effectively improves the charge storage capacity without sacrificing the frequency response characteristics.

[0074] (7-7) Circuit testing of actual filtering performance

[0075] A rectifier-filter circuit with a load resistor of 2kΩ was constructed, and its ripple suppression effect was tested at input frequencies of 120Hz and 1000Hz, respectively; see attached. Figure 9 As shown, at 120Hz, the peak-to-peak value of the input ripple voltage is approximately 1.0V, which is reduced to approximately 0.2V after filtering by the capacitor of this invention; as shown in the attached figure. Figure 10 As shown, at 1000Hz, the peak-to-peak value of the input ripple voltage is approximately 1.0V, which drops to approximately 0.1V after filtering. The ripple rejection ratio exceeded 80% in both tests, and the output waveform was stable, fully demonstrating that the electrochemical filter capacitor has excellent filtering capability over a wide frequency range and can meet the requirements of modern power supply systems for low ripple and high stability.

[0076] In summary, combined with the appendix Figures 1 to 10 All experimental data show that the bismuth-carbon nanowire-based electrode prepared in Example 1 of this invention not only achieves in-situ, uniform, and embedded distribution of bismuth nanoparticles in carbon fibers, but also significantly improves the areal capacitance and actual filtering efficiency while maintaining an excellent phase angle (≈-72°) at 120Hz. Its structural integrity, electrochemical stability, and high-frequency applicability are all superior to traditional carbon-based electrodes, providing a reliable technical path for the development of high-performance micro electrochemical filter capacitors.

[0077] Example 2

[0078] This embodiment provides a method for preparing a bismuth carbon nanowire-based planar electrochemical filter capacitor. The only difference between this embodiment and Embodiment 1 is that:

[0079] In step (1), bismuth nitrate pentahydrate is replaced with an equimolar amount of silver nitrate (AgNO3), and the remaining process parameters are completely consistent with those in Example 1.

[0080] Performance testing revealed that while the obtained silver-carbon nanowire electrode possesses a certain degree of conductivity, its phase angle at 120 Hz is only -65.3°, and its areal capacitance is 3.82 mF / cm². -2 The voltage was significantly lower than that in Example 1; meanwhile, the 120Hz ripple voltage was 58mV in the filtering test, indicating poor suppression.

[0081] The results indicate that while the silver phase can improve conductivity, it lacks effective pseudocapacitance contribution and is prone to migration and aggregation at high temperatures, making it difficult to balance high capacitance and high frequency response. In contrast, the bismuth phase combines moderate redox activity with structural stability, making it more suitable for electrochemical filter capacitors.

[0082] Example 3

[0083] This embodiment provides a method for preparing a bismuth carbon nanowire-based planar electrochemical filter capacitor. The only difference between this embodiment and Embodiment 1 is that:

[0084] In step (5), the carbonization temperature is adjusted from 750℃ to 600℃, while the other conditions remain unchanged.

[0085] Testing revealed that the bismuth species in the obtained material were not completely reduced. XRD patterns showed that Bi₂O₃ was the main phase, and the content of elemental Bi was significantly reduced. SEM observation showed that the fiber structure partially collapsed, and the flexibility decreased. EIS testing showed a phase angle of -68.4° at 120Hz and an areal specific capacity of 4.15 mF / cm². -2The filtered 120Hz ripple voltage was 49mV. The results show that although a lower carbonization temperature can retain more oxygen-containing functional groups, it is not conducive to the full reduction of the bismuth phase and the graphitization of the carbon skeleton, resulting in insufficient conductivity and structural stability, and the overall performance is inferior to that of Example 1.

[0086] Example 4

[0087] This embodiment provides a method for preparing a bismuth carbon nanowire-based planar electrochemical filter capacitor. The only difference between this embodiment and Embodiment 1 is that:

[0088] In step (6), the electrode width of the interdigitated electrode was adjusted to 500 μm and the electrode spacing was adjusted to 100 μm to investigate the effect of the geometric configuration on the device performance.

[0089] Test results show that although reducing the electrode spacing is beneficial for lowering the ion transport path, the excessive electrode width leads to a decrease in the effective specific surface area; EIS results show a phase angle of -70.1° at 120Hz and an areal specific capacity of 4.63 mF / cm². -2 The voltage was slightly lower than that in Example 1; the ripple voltage at 120Hz was 41mV in the filtering test; this result indicates that the electrode geometry needs to achieve a balance between ion diffusion distance and effective area, and the 300μm / 200μm configuration used in Example 1 is the optimal design.

[0090] Comparative Example 1

[0091] This comparative example provides a method for preparing a planar electrochemical filter capacitor based on pure carbon nanowires, which differs from Example 1 only in that:

[0092] In step (1), bismuth nitrate pentahydrate is not added; instead, 2.0 g of PAN is dissolved in 20 mL of LDMF to prepare the spinning solution, and the subsequent processes are exactly the same.

[0093] As attached Figure 6 , 7 As shown in Figure 8, the obtained pure carbon nanowire electrode exhibits excellent high-frequency response with a phase angle of -71.9° at 120 Hz, but its areal capacitance is only 3.48 mF / cm². -2 (Appendix) Figure 8 The concentration was significantly lower than the 5.21 mFcm in Example 1. -2 The 120Hz ripple voltage during the filter test was 52mV (see attached image). Figure 9 This result confirms that the introduction of the bismuth phase effectively improves the charge storage capacity without sacrificing the frequency response, thus verifying the superiority of the technical solution of this invention.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a bismuth-doped fiber film capacitor without gradient heat treatment, the only difference from Example 1 being:

[0096] The pre-oxidation process in step (4) is omitted, and the dried fiber membrane is directly carbonized in argon at 750°C for 2 hours.

[0097] The results showed that the obtained material was severely melted and adhered, losing its fibrous morphology (SEM images showed large areas of dense blocky structure), and could not form a continuous conductive network; the electrode mechanical strength was extremely poor, making it difficult to laser cut; even if it was barely assembled, the device had extremely high internal resistance, with a phase angle of only -52.6° at 120Hz, and almost no filtering function; these results fully demonstrate that the pre-oxidation step is crucial for stabilizing the PAN molecular chain and preventing high-temperature melting, and is a key process step for achieving high-quality bismuth carbon nanowire structures.

[0098] In summary, this bismuth-carbon nanowire-based planar electrochemical filter capacitor and its fabrication method, through in-situ bismuth phase embedding, optimized heat treatment process, and interdigitated electrode structure, significantly improve the areal capacitance (reaching 5.21 mF / cm²) while maintaining excellent high-frequency response (120 Hz phase angle ≈ -72°). -2 With a ripple suppression rate of over 94%, it combines the advantages of flexibility, thinness, and integrability, providing a high-performance filtering solution for miniaturized electronic devices.

[0099] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor, characterized in that, Includes the following steps: (1) Add 2g of polyacrylonitrile and 1g of bismuth nitrate pentahydrate to 20mL of dimethylformamide and stir at room temperature for 12 hours under argon atmosphere to obtain a white, transparent and viscous spinning precursor solution. (2) The spinning precursor solution is loaded into a syringe with a 20G needle. An aluminum foil-wrapped roller is used as the receiving device. The distance between the needle and the roller is controlled to be 20cm, the injection rate is 0.8mL / h, the needle translation speed is 500mm / min, the roller rotation speed is 120r / min, the voltage applied to the needle is +13kV, the voltage applied to the roller is -2kV, and electrospinning is performed for 5 hours to obtain white nonwoven fabric. (3) Place the white non-woven fabric and aluminum foil in a vacuum oven at 60°C and dry for 12 hours. Then peel off the aluminum foil and cut it to the predetermined size. (4) The cut nonwoven fabric is heated to 250°C in air at a heating rate of 5°C / min and kept at that temperature for 2 hours to obtain brown-black nonwoven fabric. (5) The brown-black nonwoven fabric is heated to 750°C in an argon atmosphere at a heating rate of 5°C / min and kept at that temperature for 2 hours to obtain black bismuth carbon nanowire nonwoven fabric. (6) The black bismuth carbon nanowire nonwoven fabric is processed into a planar interdigitated electrode structure, and an electrolyte containing LiTFSI is added to assemble it into a planar electrochemical filter capacitor.

2. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: The electrolyte is an organic solution of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

3. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: In step (6), the planar interdigitated electrode is a symmetrical interdigitated structure formed by laser cutting, with a single electrode width of 200-500μm and an electrode spacing of 100-300μm.

4. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: The mass ratio of polyacrylonitrile to bismuth nitrate pentahydrate in the spinning precursor solution is 2:

1.

5. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: The black bismuth carbon nanowire nonwoven fabric contains a bismuth phase existing in the form of elemental bismuth or bismuth oxide (Bi2O3).

6. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: The pyrolysis process is carried out under an argon atmosphere with an argon flow rate of 50-100 mL / min.

7. The method for preparing a bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 1, characterized in that: The black bismuth carbon nanowire nonwoven fabric has a thickness of 10-50 μm and an areal density of 0.5-2.0 mg / cm³. 2 .

8. A bismuth-carbon nanowire-based planar electrochemical filter capacitor, characterized in that: The electrode material includes bismuth carbon nanowire nonwoven fabric prepared by any one of claims 1-7, wherein the electrode material comprises a carbon nanofiber matrix and bismuth or bismuth oxide nanoparticles dispersed therein.

9. A bismuth-carbon nanowire-based planar electrochemical filter capacitor according to claim 8, characterized in that: The bismuth or bismuth oxide nanoparticles have a particle size of 10-100 nm and are distributed in an embedded form inside or on the surface of carbon nanofibers.

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