Electrospun carbon nanofiber material prepared from a PILs-PAN hybrid precursor and its application in vanadium batteries

Abstract

This invention relates to the field of battery materials and energy storage technology, specifically to an electrospun carbon nanofiber material prepared from a PILs-PAN mixed precursor and its application in vanadium batteries. The method involves first preparing a binary nanofiber material by electrospinning a PILs-PAN mixed precursor, in which fine fibers of polymeric ionic liquid PILs are uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers. This material is then subjected to pre-oxidation and carbonization treatments to obtain an electrospun carbon nanofiber material with a gradient pore structure. This invention utilizes a simple and controllable electrospinning technique. By simply changing the composition of the precursor solution, i.e., introducing a polymeric ionic liquid with high conductivity, carbon nanofibers of varying diameters can be obtained. Fine fibers with diameters of tens of nanometers attach to the surface of PAN fibers with diameters of hundreds of nanometers, effectively increasing the electrode reaction area and reactivity.

Description

Technical Field

[0001] This invention relates to the field of battery materials and energy storage technology, specifically to an electrospun carbon nanofiber material prepared from a PILs-PAN hybrid precursor and its application in vanadium batteries. Background Technology

[0002] Developing clean and renewable energy is a key approach to solving the crisis of fossil fuels such as oil, and has become a core method for ensuring energy security, improving the ecological environment, and promoting green and sustainable development. With the rapid development of renewable energy, large-scale energy storage technologies have gradually become a research hotspot. Among numerous energy storage technologies, redox flow batteries, with their inherent safety, scalability, long cycle life, fast response speed, and large energy storage capacity, have gradually become the leader in the field of large-scale, long-term energy storage.

[0003] As the site of electrochemical reactions in vanadium batteries, the performance of electrodes directly determines the energy conversion efficiency and stability of the battery. Currently, the electrode materials widely used in the market for flow batteries are mainly based on polyacrylonitrile-based carbon fibers. This material has advantages such as low cost, high conductivity, and good chemical stability, but its poor electrochemical reactivity severely limits its application performance and the industrialization of vanadium batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide an electrospun carbon nanofiber material prepared from a PILs-PAN hybrid precursor, and to apply it to the electrode material of an all-vanadium redox flow battery, which can effectively improve electrode activity and enhance battery performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is: an electrospun carbon nanofiber material prepared from a PILs-PAN mixed precursor, which is prepared by first preparing a binary nanofiber material from the PILs-PAN mixed precursor by electrospinning, and then obtaining an electrospun carbon nanofiber material with a gradient pore structure by pre-oxidation and carbonization treatment; the binary nanofiber material is composed of fine fibers of polymeric ionic liquid PILs uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers.

[0006] Furthermore, the diameter of the polymeric ionic liquid (PILs) fine fibers is 10–30 nm, and the diameter of the polyacrylonitrile (PAN) coarse fibers is 100–300 nm.

[0007] Furthermore, the polymeric ionic liquids (PILs) are polymeric ionic liquids prepared using 1-vinyl-3-methylimidazolium as a monomer.

[0008] Furthermore, the molecular weight of the polyacrylonitrile (PAN) is 90,000 to 150,000.

[0009] A method for preparing electrospun carbon nanofiber materials using PILs-PAN mixed precursors includes the following steps:

[0010] 1) Dissolve polyacrylonitrile (PAN) in N,N,-dimethylformamide (DMF) solution to obtain a PAN / DMF electrospinning precursor solution with a PAN mass percentage concentration of 10-20%;

[0011] 2) Polymer ionic liquids (PILs) were prepared using 1-vinyl-3-methylimidazolium as a monomer.

[0012] 3) Add polymeric ionic liquids (PILs) to the PAN / DMF electrospinning precursor solution obtained in step 1) and mix evenly to obtain a PILs-PAN / DMF mixed precursor solution;

[0013] 4) The PILs-PAN / DMF mixed precursor solution was drawn into an electrospinning syringe, and electrospinning was performed using electrospinning technology to prepare a binary nanofiber material in which fine fibers of polymeric ionic liquid PILs are uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers.

[0014] 5) The binary nanofiber material is flattened with a corundum plate, placed in a tube furnace for pre-oxidation and carbonization, and then cooled to room temperature to obtain an electrospun carbon nanofiber material with a gradient pore structure.

[0015] Further, step 2) specifically involves: adding 1-vinyl-3-methylimidazolium bromide (ViEtIm) + Br - Azobisisobutyronitrile (AIBN) and azobisisobutyronitrile (AIBN) were added to CHCl3 solvent and refluxed in an oil bath at 70 ℃ ~ 80 ℃ for 5 ~ 6 h under a N2 protective atmosphere. After cooling to room temperature, the resulting product was washed with CHCl3 and dried under vacuum to obtain polymeric ionic liquids (PILs).

[0016] Furthermore, in step 3), the mass ratio of polymeric ionic liquids (PILs) to PAN is 1:50 to 1:200.

[0017] Furthermore, in step 4), the process conditions for the electrospinning technology are as follows: the stainless steel nozzle is of model G15 to G22; the take-up device is a stainless steel roller with a rotation speed of 50 to 150 r / min; the voltage between the nozzle and the roller is 18 to 22 kV; the distance between the nozzle and the roller is 10 to 15 cm; the spinning temperature is 25 to 30 ℃; the spinning humidity is 30 to 50 %RH; and the pushing speed is 10 to 50 µL / min.

[0018] Further, in step 5), the pre-oxidation treatment conditions are: under an air atmosphere, the temperature is increased to 180–200 °C at a heating rate of 2–5 °C / min, held for 10–20 min, and then increased to 290–300 °C at a heating rate of 1–2 °C / min, held for 60–70 min; the carbonization treatment conditions are: under a nitrogen or argon atmosphere, the temperature is increased to 1000–1100 °C at a heating rate of 5–10 °C / min, held for 120–130 min.

[0019] This invention provides the application of an electrospun carbon nanofiber material prepared from a PILs-PAN hybrid precursor as an electrode material in an all-vanadium redox flow battery.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention utilizes a simple and controllable electrospinning technique to obtain binary nanofibers of varying diameters by simply changing the composition of the precursor solution, i.e., introducing a polymeric ionic liquid with high conductivity. Fine PILs fibers with diameters of tens of nanometers are attached to the surface of PAN fibers with diameters of hundreds of nanometers, effectively improving the electrode reaction area and reaction activity.

[0022] 2. The present invention is simple and highly controllable, and can significantly improve the wettability of the electrode, thereby improving the electrolyte utilization rate and energy conversion efficiency during battery charging and discharging. Attached Figure Description

[0023] Figure 1 Scanning electron microscope images of PAN-ECNFs (a) and PILs-PAN-ECNFs (b) prepared for Example 1.

[0024] Figure 2 Cyclic voltammetry curves of PAN-ECNFs and PILs-PAN-ECNFs prepared in Example 1 in 0.1 M VOSO4 + 2 M H2SO4 (scan rate: 5 mV·s) -1 ). Detailed Implementation

[0025] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0026] In a first aspect, this invention provides an electrospun carbon nanofiber material prepared from a PILs-PAN mixed precursor. The PILs-PAN mixed precursor is first prepared into a binary nanofiber material by electrospinning, and then subjected to pre-oxidation and carbonization treatments to obtain an electrospun carbon nanofiber material with a gradient pore structure. The binary nanofiber material is composed of fine fibers of polymeric ionic liquid PILs uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers.

[0027] This invention introduces highly conductive polymeric ionic liquids (PILs) into a traditional PAN / DMF precursor solution by controlling the composition of the electrospinning precursor solution. Through electrospinning, the fine fibers of the PILs are uniformly distributed on the surface of coarse polyacrylonitrile (PAN) fibers, forming a binary nanofiber material. Subsequent pre-oxidation and carbonization treatments yield electrospun carbon nanofibers with a gradient pore structure, thereby effectively increasing the active reaction area of ​​the electrode. The surface activity and hydrophilicity of the electrode are significantly improved, effectively promoting the electrode reaction process of the positive and negative electrodes of vanadium batteries and enhancing the energy conversion efficiency of the battery.

[0028] In some feasible embodiments, the polymeric ionic liquid (PILs) fine fibers have a diameter of 10–30 nm, and the polyacrylonitrile (PAN) coarse fibers have a diameter of 100–300 nm.

[0029] The polymeric ionic liquid (PILs) fine fibers and polyacrylonitrile (PAN) coarse fibers provided by this invention are carbon nanofibers of varying diameters. The fine PILs fibers with a diameter of tens of nanometers are attached to the surface of PAN fibers with a diameter of hundreds of nanometers, forming a gradient pore structure. The small diameter fibers provide a larger active area, which is beneficial to reducing electrochemical polarization. The large diameter fibers provide a larger pore structure, which is beneficial to reducing concentration polarization. The reduction of polarization overpotential further helps to improve the electrolyte utilization rate and energy conversion efficiency of the battery, effectively improving the electrode reaction area and reaction activity.

[0030] In some feasible embodiments, the polymeric ionic liquids (PILs) are further prepared using 1-vinyl-3-methylimidazolium as a monomer. The preparation of polymeric ionic liquids (PILs) using 1-vinyl-3-methylimidazolium as a monomer has the advantages of low cost, simple method, and high yield.

[0031] In some feasible embodiments, the molecular weight of the polyacrylonitrile (PAN) is further 90,000 to 150,000 in order to obtain a PAN / DMF precursor solution with suitable concentration and viscosity, which is beneficial for subsequent electrospinning.

[0032] A second aspect of this invention provides a method for preparing electrospun carbon nanofiber materials using PILs-PAN mixed precursors, comprising the following steps:

[0033] 1) Dissolve polyacrylonitrile (PAN) in N,N,-dimethylformamide (DMF) solution to obtain a PAN / DMF electrospinning precursor solution with a PAN mass percentage concentration of 10-20%;

[0034] 2) Polymer ionic liquids (PILs) were prepared using 1-vinyl-3-methylimidazolium as a monomer.

[0035] 3) Add polymeric ionic liquids (PILs) to the PAN / DMF electrospinning precursor solution obtained in step 1) and mix evenly to obtain a PILs-PAN / DMF mixed precursor solution;

[0036] 4) The PILs-PAN / DMF mixed precursor solution was drawn into an electrospinning syringe, and electrospinning was performed using electrospinning technology to prepare a binary nanofiber material in which fine fibers of polymeric ionic liquid PILs are uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers.

[0037] 5) The binary nanofiber material is flattened with a corundum plate, placed in a tube furnace for pre-oxidation and carbonization, and then cooled to room temperature to obtain an electrospun carbon nanofiber material with a gradient pore structure.

[0038] This invention utilizes a simple and controllable electrospinning technique. By simply altering the composition of the precursor solution—specifically by introducing a polymeric ionic liquid with high conductivity—two binary nanofiber materials with different fiber diameters can be obtained through a single electrospinning process. Tiny fibers with diameters of tens of nanometers are attached to the surface of PAN fibers with diameters of hundreds of nanometers. The binary nanofiber materials undergo subsequent pre-oxidation and carbonization processes to ultimately obtain porous carbon nanofiber electrode materials. This effectively increases the electrode reaction area and significantly enhances the electrode's surface activity and hydrophilicity, thereby effectively promoting the electrode reaction process at the positive and negative electrodes of vanadium batteries and improving the battery's energy conversion efficiency.

[0039] In some feasible implementations, further, step 2) specifically involves: adding 1-vinyl-3-methylimidazolium bromide (ViEtIm + Br - Azobisisobutyronitrile (AIBN) and azobisisobutyronitrile (AIBN) were added to CHCl3 solvent and refluxed in an oil bath at 70 ℃ ~ 80 ℃ for 5 ~ 6 h under N2 protective atmosphere. After cooling to room temperature, the resulting product was washed with CHCl3 and dried under vacuum to obtain polymeric ionic liquids (PILs).

[0040] In some feasible implementations, further, in step 3), the mass ratio of polymeric ionic liquid (PILs):PAN is 1:50 to 1:200. A suitable mass ratio of PILs to PAN can produce a binary nanofiber material in which the fine fibers of polymeric ionic liquid PILs are uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers. If the amount of PILs is too small and the fine fibers are too few, the activity improvement effect of the electrode material will not be obvious. If the amount of PILs is too large and the fine fibers are too many, the porosity of the carbon fiber three-dimensional network structure will be reduced, which is not conducive to the flow of electrolyte inside the electrode.

[0041] In some feasible implementations, further, in step 4), the process conditions for the electrospinning technology are as follows: the stainless steel nozzle is model G15 to G22; the take-up device is a stainless steel roller with a rotation speed of 50 to 150 r / min; the voltage between the nozzle and the roller is 18 to 22 kV; the distance between the nozzle and the roller is 10 to 15 cm; the spinning temperature is 25 to 30 ℃; the spinning humidity is 30 to 50 %RH; and the pushing speed is 10 to 50 µL / min. Electrospinning under these process parameters can obtain binary nanofiber materials with good uniformity and continuity.

[0042] In some feasible embodiments, further, in step 5), the pre-oxidation treatment conditions are: under an air atmosphere, heating to 180–200 °C at a heating rate of 2–5 °C / min, holding for 10–20 min, then heating to 290–300 °C at a heating rate of 1–2 °C / min, holding for 60–70 min; the pre-oxidation treatment allows the structure of the PAN nanofibers to be maintained during the subsequent high-temperature carbonization process; the carbonization treatment conditions are: under a nitrogen or argon atmosphere, heating to 1000–1100 °C at a heating rate of 5–10 °C / min, holding for 120–130 min; a suitable carbonization process generates graphite microcrystals in the fiber, giving it higher conductivity.

[0043] A third aspect of the present invention provides the application of electrospun carbon nanofiber materials prepared from PILs-PAN hybrid precursors as electrode materials in all-vanadium redox flow batteries.

[0044] In summary, this invention utilizes a simple and controllable electrospinning technique to prepare porous carbon nanofibers by simply changing the composition of the precursor solution. This effectively increases the electrode reaction area and reactivity, significantly improves electrode wettability, and enhances electrolyte utilization and energy conversion efficiency during battery charging and discharging.

[0045] Example 1

[0046] (a) Comparative example – Polyacrylonitrile carbon nanofiber electrode material (PAN-ECNFs)

[0047] The preparation method includes the following steps:

[0048] 1) Dissolve dried polyacrylonitrile (PAN) powder with a molecular weight of 150,000 in N,N,-dimethylformamide (DMF) solution and stir magnetically at 80 °C for 6 h until completely dissolved to obtain a PAN / DMF electrospinning precursor solution with a mass percentage concentration of 14% polyacrylonitrile (PAN).

[0049] 2) The PAN / DMF electrospinning precursor solution was drawn into the syringe of the electrospinning equipment, and polyacrylonitrile nanofibers were obtained using electrospinning technology. Electrospinning conditions: stainless steel nozzle model G20, stainless steel roller take-up device, roller speed 100 r / min; voltage between nozzle and roller 20 kV; distance between nozzle and roller 12 cm; spinning temperature 25 ℃; spinning humidity 30 %RH; feed speed 30 µL / min; 24 mL precursor solution spun.

[0050] 3) The obtained polyacrylonitrile nanofiber material was flattened using a corundum plate and placed in a tube furnace for pre-oxidation treatment. Specifically, under an air atmosphere, the temperature was increased to 180℃ at a rate of 2℃ / min and held for 10 min, followed by increasing the temperature to 290℃ at a rate of 1℃ / min and holding for 60 min. Then, a carbonization treatment was performed: under a N2 atmosphere, the temperature was increased to 1000℃ at a rate of 5℃ / min and held for 120 min, followed by cooling to room temperature to obtain polyacrylonitrile carbon nanofiber electrode material, labeled PAN-ECNFs.

[0051] The obtained SEM images of PAN-ECNFs are as follows Figure 1 As shown in (a), the diameter of the coarse PAN fibers is approximately 150–300 nm, and the surface is smooth.

[0052] (II) Electrospun carbon nanofiber materials prepared from PILs-PAN hybrid precursors

[0053] The preparation method includes the following steps:

[0054] 1) Dissolve dried polyacrylonitrile (PAN) powder with a molecular weight of 150,000 in N,N,-dimethylformamide (DMF) solution and stir magnetically at 80 °C for 6 h until completely dissolved to obtain a PAN / DMF electrospinning precursor solution with a mass percentage concentration of 14% polyacrylonitrile (PAN).

[0055] 2) Add 5.0 g ViEtIm+ Br - 0.1 g of AIBN was added to 50 mL of CHCl3 solvent, and the mixture was refluxed in an oil bath at 70 °C for 5 h under a N2 protective atmosphere. After cooling to room temperature, the product was washed 3 to 5 times with CHCl3 and dried under vacuum to obtain a pale yellow solid polymeric ionic liquid (PILs).

[0056] 3) Add polymeric ionic liquids (PILs) to the above 14% PAN / DMF electrospinning precursor solution, wherein the mass ratio of PILs to PAN is 1:100, and ultrasonically stir to mix them evenly to obtain a PILs-PAN mixed precursor solution.

[0057] 4) 10 mL of the PILs-PAN mixed precursor solution was drawn into the syringe of the electrospinning equipment. Continuous electrospinning was then performed to obtain binary nanofiber materials. Electrospinning conditions: G20 stainless steel nozzle; stainless steel roller take-up unit; roller speed 100 r / min; voltage between nozzle and roller 20 kV; distance between nozzle and roller 12 cm; spinning temperature 25 ℃; spinning humidity 30 %RH; push speed 30 µL / min.

[0058] 5) The obtained binary nanofiber material was flattened using a corundum plate and placed in a tube furnace for pre-oxidation treatment. Specifically, under an air atmosphere, the temperature was increased to 180°C at a rate of 2°C / min and held for 10 min, followed by increasing the temperature to 290°C at a rate of 1°C / min and holding for 60 min. Then, carbonization treatment was performed: under a N2 atmosphere, the temperature was increased to 1000°C at a rate of 5°C / min and held for 120 min, followed by cooling to room temperature to obtain electrospun carbon nanofibers, labeled PILs-PAN-ECNFs.

[0059] The resulting PILs-PAN-ECNFs had a thickness of approximately 50 μm, as shown in the SEM images. Figure 1 As shown in (b), the material contains two types of fibers with different diameters: PAN forms coarse fibers with a diameter of approximately 100–300 nm, and PILs form fine fibers with a diameter of approximately 10–30 nm. The fine PILs fibers are evenly distributed on the surface of the coarse PAN fibers.

[0060] Example 2 Electrochemical performance testing of electrospun carbon nanofiber electrode materials prepared from PILs-PAN mixed precursors

[0061] 1) Cyclic Voltmeter-Ammeter Test

[0062] Methods: A three-electrode system was used, with 1 cm prepared in Example 1 as an example. 2 PAN-ECNFs and PILs-PAN-ECNFs electrode materials were used as working electrodes, saturated glycerol co-electrode as reference electrode, platinum sheet as counter electrode, and 0.1 MVOSO4 + 2.0 M H2SO4 as electrolyte. The electrochemical performance of the electrodes was investigated by cyclic voltammetry at a scan rate of 5 mV / s.

[0063] like Figure 2 As shown, V is displayed on both electrodes. 2+ / V 3+ and VO 2+ / VO2 + The redox peaks of the redox couple. However, compared to the blank PAN-ECNFs, the CV curves measured on the PILs-PAN-ECNFs electrode have larger peak currents and smaller peak potential differences. This is attributed to the larger specific surface area and better electrolyte permeability of the PILs-PAN-ECNFs electrode material, which increases the effective reaction area and improves the electrochemical reaction activity.

[0064] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing electrospun carbon nanofiber materials from a PILs-PAN mixed precursor, characterized in that, The preparation method includes the following steps: 1) Dissolve polyacrylonitrile (PAN) in N,N,-dimethylformamide (DMF) solution to obtain a PAN / DMF electrospinning precursor solution with a PAN mass percentage concentration of 10-20%; 2) Polymer ionic liquids (PILs) were prepared using 1-vinyl-3-methylimidazolium as a monomer; 3) Add the polymeric ionic liquid PILs to the PAN / DMF electrospinning precursor solution obtained in step 1), mix well, and obtain a PILs-PAN / DMF mixed precursor solution; the mass ratio of polymeric ionic liquid PILs:PAN is 1:50 to 1:

200. 4) The PILs-PAN / DMF mixed precursor solution was drawn into an electrospinning syringe, and electrospinning was performed using electrospinning technology to prepare a binary nanofiber material in which fine fibers of polymeric ionic liquid PILs are uniformly distributed on the surface of coarse polyacrylonitrile PAN fibers. 5) The binary nanofiber material is flattened with a corundum plate, placed in a tube furnace for pre-oxidation and carbonization, and then cooled to room temperature to obtain an electrospun carbon nanofiber material with a gradient pore structure.

2. The preparation method according to claim 1, characterized in that, Step 2) Specifically, 1-vinyl-3-methylimidazolium bromide and azobisisobutyronitrile are added to CHCl3 solvent, and refluxed in an oil bath at 70 ℃ ~ 80 ℃ for 5 ~ 6 h under a N2 protective atmosphere. After cooling to room temperature, the resulting product is washed with CHCl3 and dried under vacuum to obtain polymeric ionic liquids (PILs).

3. The preparation method according to claim 1, characterized in that, In step 4), the process conditions for the electrospinning technology are as follows: the stainless steel nozzle is model G15 to G22; the take-up device is a stainless steel roller with a rotation speed of 50 to 150 r / min; the voltage between the nozzle and the roller is 18 to 22 kV; the distance between the nozzle and the roller is 10 to 15 cm; the spinning temperature is 25 to 30 ℃; the spinning humidity is 30 to 50 %RH; and the pushing speed is 10 to 50 µL / min.

4. The preparation method according to claim 1, characterized in that, In step 5), the pre-oxidation treatment conditions are as follows: under an air atmosphere, the temperature is increased to 180–200 °C at a heating rate of 2–5 °C / min, held for 10–20 min, and then increased to 290–300 °C at a heating rate of 1–2 °C / min, held for 60–70 min; the carbonization treatment conditions are as follows: under a nitrogen or argon atmosphere, the temperature is increased to 1000–1100 °C at a heating rate of 5–10 °C / min, held for 120–130 min.

5. Electrospun carbon nanofiber material prepared according to any one of claims 1-4.

6. The application of electrospun carbon nanofiber materials prepared according to any one of claims 1-4 as electrode materials in vanadium redox flow batteries.

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