CN111446460A

CN111446460A - Multi-diameter electrode and preparation method and application thereof

Info

Publication number: CN111446460A
Application number: CN202010197653.9A
Authority: CN
Inventors: 赵天寿; 孙静; 范新庄
Original assignee: Guangzhou HKUST Fok Ying Tung Research Institute
Current assignee: Guangzhou HKUST Fok Ying Tung Research Institute
Priority date: 2020-03-19
Filing date: 2020-03-19
Publication date: 2020-07-24
Anticipated expiration: 2040-03-19
Also published as: CN111446460B

Abstract

The invention provides a multi-diameter electrode and a preparation method and application thereof, and relates to the technical field of flow batteries. The multi-diameter electrode comprises two or more carbon fiber filament groups with the diameter ranges, the diameters of the carbon fiber filaments are 100nm-20 mu m, and the diameter sizes of two groups of carbon fiber filaments with the adjacent diameter ranges are different by at least 100 nm; wherein the diameter size of the fiber filament group with the minimum diameter is 100-1000nm, and the diameter size of the fiber filament group with the maximum diameter is 10-20 μm. The preparation method comprises the following steps: s1, dissolving polyacrylonitrile in a solvent to prepare spinning solutions with two or more mass concentrations; s2, carrying out multi-needle electrostatic spinning on the spinning solution to obtain a fiber membrane formed by stacking fiber yarns with multiple diameters and sizes; and S3, pre-oxidizing and carbonizing the fiber membrane to obtain the multi-diameter electrode. The multi-diameter electrode has larger specific surface area, can reduce the activation loss of the battery, improve the permeability and reduce the concentration polarization of the battery.

Description

Multi-diameter electrode and preparation method and application thereof

Technical Field

The invention relates to the technical field of flow batteries, in particular to a multi-diameter electrode and a preparation method and application thereof.

Background

In order to deal with the problems of global climate change, environmental pollution, energy shortage and the like, renewable energy sources such as solar energy, wind energy and the like are widely concerned and developed. However, these renewable energy power generation devices have the characteristics of volatility and intermittency, and therefore, it is necessary to utilize a large-scale energy storage system to implement efficient grid connection of the renewable energy power generation devices and implement peak shaving, frequency modulation, and the like of a power grid. In recent years, the flow battery has attracted much attention as an energy storage system because of its advantages of no regional limitation, independent capacity and power, good safety, long cycle life, and the like.

The electrode, one of the main components of the flow battery, not only provides the electrochemical reaction site, but also affects the transport of the electrolyte in the porous electrode, so its geometry and surface properties directly affect the battery performance. In order to reduce electrochemical polarization, ohmic polarization and concentration polarization, the electrode of the flow battery has the characteristics of large specific surface area, high permeability, high conductivity, high electrochemical activity and the like. At present, the electrode material of the flow battery is mainly carbon material, and comprises commercial carbon materials such as graphite felt, carbon paper, carbon cloth and the like. Commercial carbon materials have the characteristics of large pore size and porosity, and thus have high permeability. However, commercial carbon materials have small specific surface areas (typically not more than 1 m)²g^-1) And the redox reaction activity of the flow battery is low, and when the redox reaction is directly used for the flow battery, the output power density of the flow battery is greatly limited.

In recent years, some progress has been made in the preparation of nanoscale carbon fibers using electrospinning techniques and their application to flow batteries. Carbon fibers produced by electrospinning generally have a large specific surface area (10-100 a) thanks to the size of the carbon fibers in the nanometer range0m²g^-1) (ii) a At the same time, however, the permeability of electrospun carbon electrodes is greatly reduced compared to commercial carbon electrodes, and thus direct use of electrospun carbon fiber electrodes in flow batteries results in greater concentration polarization, resulting in batteries that can only operate at lower current densities.

Disclosure of Invention

In view of the above, there is a need to provide a multi-diameter electrode, which has two or more sizes, can realize a large specific surface area while ensuring a high permeability of the electrode, can simultaneously reduce electrochemical polarization and concentration polarization of the battery, and can be adapted to redox flow batteries with different requirements.

A multi-diameter size electrode comprising two or more groups of carbon filaments having diameters in the range of 100nm to 20 μm, the diameter sizes of two groups of filaments in adjacent diameter ranges differing by at least 100 nm; wherein the diameter of the fiber filament group with the minimum diameter is 100-1000nm, and the diameter of the fiber filament group with the maximum diameter is 10-20 μm.

The multi-diameter electrode can greatly improve the specific surface area of the electrode on the premise of not improving the flow resistance of electrolyte, reduce the activation loss of the battery and simultaneously reduce the electrochemical polarization and concentration polarization of the battery. When the electrode is used for an all-vanadium redox flow battery, the battery can be enabled to be 300mA cm^-2The energy efficiency under the operating current density is up to more than 80%. The electrode structure and the preparation method provided by the invention have wide adjustable range and are suitable for redox flow batteries with different requirements.

In one embodiment, the fiber has 2 fiber groups with diameters ranging from 100nm to 1000nm, 10-20 μm.

In one embodiment, the fiber filament has 3 groups of fiber filaments with diameters in the range of 100-1000nm, 1-10 μm and 10-20 μm.

In one embodiment, the fiber filament has 4 groups of fiber filaments with diameters in the range of 100-1000nm, 1-5 μm, 5-10 μm and 10-20 μm.

In one embodiment, the fiber has 5 fiber groups with diameters of 1000nm, 1-5 μm, 5-10 μm, 10-15 μm and 15-20 μm.

The invention also provides a preparation method of the multi-diameter electrode, which comprises the following steps:

s1, dissolving Polyacrylonitrile (PAN) in a solvent, and preparing spinning solutions with two or more mass concentrations according to the diameter range of each group of fiber yarns, wherein the mass fraction of the spinning solutions is 2-20%;

s2, carrying out multi-needle electrostatic spinning on the spinning solution to obtain a fiber membrane formed by stacking fiber yarns with multiple diameters;

and S3, pre-oxidizing the fiber membrane in air, and carbonizing the fiber membrane in an inert gas atmosphere to obtain the multi-diameter electrode.

According to the preparation method, the electrostatic spinning precursor solutions with different concentrations are prepared, and the multi-needle is matched for electrostatic spinning, so that two or more carbon fiber electrodes with the diameter sizes can be obtained, the size of the fiber filament is 100nm-20 mu m, and the adjustment and the control can be performed according to the situation. The obtained electrode with multiple diameters can greatly improve the specific surface area of the electrode on the premise of not improving the flow resistance of electrolyte, reduce the activation loss of the battery and simultaneously reduce the electrochemical polarization and concentration polarization of the battery.

In one embodiment, the polyacrylonitrile has an average molecular weight of 25000-200000g mol^-1。

In one embodiment, the solvent is selected from: n, N-dimethylformamide and/or N, N-dimethylacetamide.

In one embodiment, the thickness of the fiber membrane is 100 μm-5 mm.

In one embodiment, the step S1 specifically includes: mixing polyacrylonitrile and a solvent, heating at 40-80 ℃ for 10-20h for dissolving, and preparing into spinning solution with 2-10 mass concentrations, wherein the mass fraction of the spinning solution is 2-20%, and the mass fraction difference between the concentrations is at least 1%.

In one embodiment, the mass fraction of the spinning solution with the lowest concentration is 5-12%, and the mass fraction of the spinning solution with the highest concentration is 12-15%.

In one embodiment, the spinning solution has two mass concentrations, which are 12% and 15%, respectively.

In one embodiment, the spinning solution has two mass concentrations, 10% and 15% respectively.

In one embodiment, the spinning solution has three mass concentrations, which are 5%, 10% and 15%.

In one embodiment, in the step S2, the diameter of the needle is 0.2-2mm, and the advancing speed of the spinning solution is 0.2-2m L h^-1The rotating speed of the rotating wheel at the receiving end is 10-1000rpm, the distance between the needle head and the receiver is 10-50cm, the voltage between the needle head and the receiving end is 10-50kV, the temperature of electrostatic spinning is 20-50 ℃, and the relative humidity is 20-70%.

It is understood that the number of different diameter needle types is equal to the number of different mass concentration spinning solution types. The spinning solutions with different mass concentrations are respectively connected with the needle heads with different diameters.

In one embodiment, 5 to 12 wt% of the dope is connected to a needle having an inner diameter of 0.40 to 1.07mm, and 12 to 15 wt% of the dope is connected to a needle having an inner diameter of 1.07 to 1.40 mm.

In one example, 12 wt% dope was attached to a 17G needle (1.07 mm ID) and 15 wt% dope was attached to a 15G needle (1.40 mm ID).

In one example, 10 wt% dope was attached to a 20G needle (internal diameter 0.60mm) and 15 wt% dope was attached to a 15G needle (internal diameter 1.40 mm).

In one example, 5 wt% dope was attached to a 22G needle (inner diameter 0.40mm), 10 wt% dope was attached to a 20G needle (inner diameter 0.60mm), and 15 wt% dope was attached to a 15G needle (inner diameter 1.40 mm).

In one embodiment, in the step S3, the pre-oxidation temperature is 220-^-1And the pre-oxidation time is 1-3 h.

In one embodiment, the inert gas is selected from: one or more of nitrogen, argon and hydrogen.

In one embodiment, the mass fraction of hydrogen in the inert gas is less than or equal to 10%.

In one embodiment, the carbonization temperature in step S3 is 800-^-1The carbonization time is 0.5-5 h.

The invention also provides an application of the multi-diameter electrode in the preparation of a flow battery. When the electrode is used for the all-vanadium redox flow battery, the battery can be ensured to be 300mA cm^-2The energy efficiency under the operating current density reaches more than 80 percent.

Compared with the prior art, the invention has the following beneficial effects:

According to the preparation method, the electrostatic spinning precursor solutions with different concentrations are prepared, and the multi-needle is matched for electrostatic spinning, so that two or more carbon fiber electrodes with the diameter sizes can be obtained, the size of the fiber filament is 100nm-20 mu m, and the adjustment and the control can be performed according to the situation.

Drawings

FIG. 1 is a microscopic structure view of a dual-diameter electrode in an example;

FIG. 2 shows the total vanadium flow battery at 100-400mA cm in the example^-2A constant current charging and discharging curve chart under different operating current densities;

FIG. 3 shows the total vanadium flow battery at 100-400mA cm in the example^-2And (3) efficiency graphs of constant current charging and discharging under different operating current densities.

Detailed Description

To facilitate an understanding of the invention, a more complete description of the invention will be given below in terms of preferred embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Example 1

A dual diameter electrode prepared by the following method:

s1, weighing 2.4g of polyacrylonitrile and 17.6g N, N-dimethylformamide, mixing, and heating in a water bath at 70 ℃ for 12 hours to prepare a spinning precursor solution (namely spinning solution) with the concentration of 12 wt%; weighing 3g of polyacrylonitrile and 17g N, N-dimethylformamide, mixing, heating and dissolving in 70 ℃ water bath to prepare 15 wt% spinning precursor solution;

s2, putting 10m L12 wt% spinning precursor solution into a syringe, connecting with a 17G needle (inner diameter 1.07mm), and setting the solution advancing speed to be 1m L h^-1In addition, 15m L15 wt% spinning precursor solution was connected to a 15G needle (inner diameter 1.40mm) and the solution advancing speed was set to 1.5m L h^-1. The voltage of electrospinning is set to be 17kV, the distance from the needle head to the receiving end is 20cm, and the rotating speed of the receiving rotating wheel is 200 rpm. The environment temperature of electrospinning is 25 ℃, the relative humidity is 55%, and the fiber membrane is taken down after spinning for 10 hours;

s3, placing the fiber membrane in a muffle furnace to be pre-oxidized for 2h at 250 ℃, wherein the heating rate is 1 ℃ for min^-1(ii) a Carbonizing the preoxidized fiber filaments at 1100 deg.C for 1h under nitrogen protection atmosphere at a heating rate of 5 deg.C for min^-1And finally, obtaining the product after carbonization is finished.

The microstructure of the dual-diameter electrode obtained in this example is shown in FIG. 1, in which the filament diameter of the fine filament group is 800nm and the coarse fiber isThe diameter of the fiber filament of the filament group is 10 μm, and the specific surface area of the electrode can reach 5.4m²g^-1。

Battery tests performed on the dual diameter electrode of this example:

taking a double-diameter electrode with the thickness of 700 mu M and the area of 2cm × 2cm as an all-vanadium redox flow battery electrode, and assembling the electrode, a polytetrafluoroethylene pad, a Nafion @ NR-212 diaphragm, a graphite plate with an interdigital flow field, a gold-plated copper current collecting plate, an aluminum end plate and a bakelite plate into a single cell by fastening bolts, wherein the positive electrolyte is 20M L1M VO (vanadium oxide) 20M²⁺+3M H₂SO₄The solution of the negative electrode electrolyte is 20m L1M V³⁺+3M H₂SO₄The solution and electrolyte are pumped by a double-channel peristaltic pump for 76m L min^-1The pump speed is cycled.

The vanadium redox flow battery based on the double-diameter electrode of the embodiment is at 100-400mA cm^-2The constant current charge and discharge curves at different operating current densities within the range are shown in fig. 2. The vanadium redox flow battery based on the double-diameter electrode of the embodiment is at 100-400mA cm^-2The constant current charge and discharge efficiency at different operating current densities within the range is shown in fig. 3. Wherein, at 300mA cm^-2At current density, the voltage efficiency of the cell was 81.39%, and the energy efficiency was 81.25%.

Example 2

A double diameter electrode was prepared substantially as in example 1, except that:

the concentrations of the two electrostatic spinning precursor solutions are respectively 10 wt% and 15 wt%, the needles in the electrospinning process are respectively 20G (inner diameter of 0.60mm) and 15G (inner diameter of 1.40mm), and the advancing speed of the needle is 1.0m L h^-1And 1.5m L h^-1. The double diameter size electrode was obtained through the same pre-oxidation and carbonization processes as in example 1.

The diameters of the filaments of the filament group of the double-diameter electrode obtained in this example were 500nm and 10 μm, respectively. The battery test shows that the current density is 300mA cm^-2At current density, the voltage efficiency of the cell was 79.25% and the energy efficiency was 78.67%.

Example 3

A three-diameter electrode was prepared in substantially the same manner as in example 1, except that:

three different concentrations of electrostatic spinning precursor solutions are used, the concentrations are respectively 5 wt%, 10 wt% and 15 wt%, the needles corresponding to electrospinning are respectively 22G (inner diameter is 0.40mm), 20G (inner diameter is 0.60mm) and 15G (inner diameter is 1.40mm), and the advancing speed of the needle is 0.5m L h^-1，1.0mL h^-1And 1.5m L h^-1. Three-diameter electrodes were obtained by the same pre-oxidation and carbonization as in example 1.

The filament diameters of the filament groups of the three-diameter electrode obtained in this example were 200nm, 500nm and 10 μm, respectively. The battery test shows that the current density is 300mA cm^-2At current density, the voltage efficiency of the cell was 75.48% and the energy efficiency was 74.82%.

Comparative example 1

A nanoscale diameter electrode is prepared by the following method:

s1, weighing 2g of polyacrylonitrile and 18g N, N-dimethylformamide, mixing, and heating in a water bath at 70 ℃ for 12 hours to prepare a 10 wt% spinning precursor solution;

s2, putting 10m L10 wt% spinning precursor solution into an injector, connecting a 20G (inner diameter 0.6mm) needle, and setting the solution advancing speed to be 1m L h^-1The voltage of electrospinning is set to be 20kV, the distance from the needle head to the receiving end is 20cm, and the rotating speed of the receiving rotating wheel is 200 rpm. The environment temperature of electrospinning is 25 ℃, the relative humidity is 45%, and the fiber membrane is taken down after spinning for 10 hours;

s3, placing the taken fiber membrane in a muffle furnace to be pre-oxidized for 2h at 250 ℃, wherein the heating rate is 1 ℃ for min^-1Carbonizing the preoxidized fiber yarn at 1100 deg.C for 1h under nitrogen atmosphere at a heating rate of 5 deg.C for min^-1And finally, obtaining the product after carbonization is finished.

The filament diameter of the single-diameter electrode obtained in this comparative example was about 500nm and the specific surface area was 50m²g^-1But the permeability is poor.

The single-diameter electrode prepared in the comparative example was assembled into an all-vanadium redox flow battery according to the battery assembly method of example 1 and subjected to a constant current charge-discharge test. In that300mA cm^-2At current density, the cell energy efficiency was 70.6%.

Comparative example 2

A micron-sized diameter electrode is prepared by the following method:

s1, weighing 3g of polyacrylonitrile and 17g N, N-dimethylformamide, mixing, and heating in a water bath at 70 ℃ for 12 hours to prepare a 15 wt% spinning precursor solution;

s2, putting 10m L15 wt% PAN spinning precursor solution into a syringe, connecting a 15G (inner diameter of 1.40mm) needle, and setting the solution advancing speed to be 1m L h^-1Setting the electrospinning voltage to be 20kV, setting the distance from a needle head to a receiving end to be 20cm, setting the rotating speed of a receiving rotating wheel to be 200rpm, setting the electrospinning environmental temperature to be 25 ℃, setting the relative humidity to be 55%, and taking down the fiber membrane after 10h of spinning;

The filament diameter of the single-diameter electrode obtained in this comparative example was about 10 μm, and the specific surface area was 2.2m²g^-1The permeability is greatly improved.

The single-diameter electrode prepared in the comparative example was assembled into an all-vanadium redox flow battery according to the battery assembly method of example 1 and subjected to a constant current charge-discharge test. At 300mA cm^-2At current density, the energy efficiency of the cell was 72.8%.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The electrode is characterized by comprising two or more carbon fiber filament groups with the diameter ranges of 100nm-20 mu m, and the diameter sizes of two groups of fiber filaments with the adjacent diameter ranges are different by at least 100 nm; wherein the diameter of the fiber filament group with the minimum diameter is 100-1000nm, and the diameter of the fiber filament group with the maximum diameter is 10-20 μm.

2. The multi-diameter electrode as claimed in claim 1, wherein the fiber filaments have 3 sets of fiber filaments with diameters ranging from 100nm to 1000nm, 1 to 10 μm, and 10 to 20 μm.

3. The multi-diameter electrode as claimed in claim 1, wherein the fiber filaments have 4 sets of fiber filaments with diameters in the range of 100nm, 1-5 μm, 5-10 μm, 10-20 μm.

4. The multi-diameter-size electrode as claimed in claim 1, wherein the fiber filaments have 5 sets of fiber filaments with diameters in the range of 100nm, 1-5 μm, 5-10 μm, 10-15 μm, and 15-20 μm, respectively.

5. A method of manufacturing a multi-diameter size electrode according to any of claims 1 to 4, comprising the steps of:

s1, dissolving polyacrylonitrile in a solvent, and preparing spinning solutions with two or more mass concentrations according to the diameter range of each group of fiber yarns, wherein the mass fraction of the spinning solution is 2-20%;

6. The method as claimed in claim 5, wherein the polyacrylonitrile has an average molecular weight of 25000-200000g mol^-1(ii) a The solvent is selected from: n, N-dimethylformamide and/or N, N-dimethylacetamide; the thickness of the fiber membrane is 100 mu m-5 mm.

7. The preparation method according to claim 5 or 6, wherein the step S1 specifically comprises: mixing polyacrylonitrile and a solvent, heating at 40-80 ℃ for 10-20h for dissolving, and preparing a spinning solution with 2-10 mass concentrations, wherein the mass fraction of the spinning solution is 2-20%, and the mass fraction difference between the concentrations is at least 1%;

in the step S2, the diameter of the needle is 0.2-2mm, and the advancing speed of the spinning solution is 0.2-2m L h^-1The rotating speed of the rotating wheel at the receiving end is 10-1000rpm, the distance between the needle head and the receiver is 10-50cm, the voltage between the needle head and the receiving end is 10-50kV, the temperature of electrostatic spinning is 20-50 ℃, and the relative humidity is 20-70%.

8. The method as claimed in claim 5, wherein in step S3, the pre-oxidation temperature is 220-300 ℃, and the temperature-raising rate is 1-10 ℃ for min^-1And the pre-oxidation time is 1-3 h.

9. The method according to claim 5, wherein in step S3, the inert gas is selected from the group consisting of: one or more of nitrogen, argon and hydrogen; the carbonization temperature is 800-3000 ℃, and the heating rate is 2-10 ℃ for min^-1The carbonization time is 0.5-5 h.

10. Use of a multi-diameter electrode according to any one of claims 1 to 4 in the manufacture of a flow battery.