CN106560944B - Porous carbon fiber paper electrode material used for all-vanadium redox flow battery and its preparation and application - Google Patents

Abstract

A porous carbon fiber paper electrode material for an all-vanadium redox flow battery, the thickness of the porous carbon fiber paper electrode is 50-1000 μm, which is composed of carbon fibers with a diameter of 5-20 μm, and the porosity of the porous carbon fiber paper is 60-90%; Porous structure, the specific surface area of carbon fiber is 5‑50m ² /g, and the pore size is 50‑2000nm. The prepared porous carbon fiber paper has significantly improved specific surface area and oxygen-containing functional groups, which can significantly improve the electrocatalytic activity of the carbon fiber material for the redox reaction of vanadium ions. This electrode material is suitable for all-vanadium redox flow batteries, which can reduce the battery electrode spacing, reduce the internal resistance of the battery, and reduce the charge transfer resistance, improve the voltage efficiency and energy efficiency of the all-vanadium redox flow battery, thereby improving its working current density, making The weight, volume and cost of the battery with the same output power are greatly reduced.

Description

Porous carbon fiber paper electrode material for all-vanadium redox flow battery and its preparation and application

technical field

The invention relates to the field of liquid flow energy storage batteries in the chemical energy storage technology, in particular to an electrode of an all-vanadium liquid flow battery.

Background technique

All-vanadium redox flow batteries are flexible in system design due to their independent output power and capacity; high energy efficiency, long life, high operational stability and reliability, and low self-discharge; large degree of freedom in location selection, no pollution, and simple maintenance. It has the advantages of low operating cost and high safety, and has broad development prospects in terms of large-scale energy storage. There is a significant need in power generation and smart grid construction.

At present, the main limitation restricting the commercialization of all-vanadium redox flow batteries is cost. To reduce its cost, there are two main solutions: one is to reduce the cost of key materials, such as ion exchange membranes, electrolytes, and electrode bipolar plates; the other is to increase the power density of the battery. Because the power density of the battery is increased, the same stack can be used to achieve greater power output, and the footprint and space of the energy storage system can also be reduced, its environmental adaptability and the mobility of the system can be improved, and the liquid flow can be expanded. Application fields of energy storage batteries. To improve the power density of the battery, it is necessary to increase its operating current density. However, an increase in operating current density leads to a decrease in voltage efficiency and energy efficiency. In order to improve the working current density of the battery without reducing the energy efficiency, it is necessary to reduce the battery polarization as much as possible, that is, ohmic polarization, electrochemical polarization and concentration polarization, and reduce the voltage loss.

As one of the key components of the all-vanadium flow energy storage battery, the performance of the electrode has a great influence on the flow energy storage battery. The all-vanadium redox flow battery electrode material in the prior art is usually made by pre-oxidizing, carbonizing, and graphitizing polyacrylonitrile needle-punched original felt in air. There are many procedures, resulting in high production cost, and the prepared graphite felt is electrically conductive. Poor catalytic activity. The electrocatalytic activity of the electrode directly determines the intrinsic reaction rate of the electrochemical reaction, which largely affects the working current density and energy efficiency of the battery. Therefore, in order to obtain high working current density and energy efficiency, a suitable activation method should be adopted to improve the electrocatalytic activity of the graphite felt as much as possible. The methods for reducing the electrochemical polarization of flow energy storage batteries in the published patent documents mainly include:

(1) Carry out oxidative modification treatment on electrode materials such as graphite felt, carbon paper, etc., modify oxygen-containing functional groups on the surface of carbon fibers, improve the electrocatalytic activity of the electrode, and reduce the electrochemical polarization of the battery, as in patents CN 101465417A and CN101182678A A method for electrochemical oxidation of graphite felt is disclosed.

(2) Metallizing electrode materials such as graphite felt, carbon paper, etc., that is, modifying metal ions on the surface of carbon fiber, such as Sun et al. (Sun, BT; Skyllas-Kazacos, M. Chemical Modification and Electrochemical Behavior of Graphite Fiber in Acidic VanadiumSolution.Electrochim.Acta 1991, 36, 513-517.) modified Mn ²⁺ , Te ⁴⁺ , In ³⁺ and Ir ³⁺ on the surface of carbon fiber, and found that Ir ³⁺ had the most improvement on the electrocatalytic activity of the electrode material. However, due to the high cost of electrodes due to the use of noble metals, it is not suitable for large-scale applications.

In addition, the carbon felt or graphite felt electrode currently used is thicker, resulting in a larger electrode spacing, which increases the internal resistance of the battery, that is, ohmic polarization. Therefore, in order to obtain smaller ohmic polarization, it is necessary to use electrode material with smaller thickness.

SUMMARY OF THE INVENTION

In order to solve the problems of large thickness and low electrocatalytic activity of the all-vanadium redox flow battery electrode, the present invention provides a highly active porous carbon fiber paper electrode material for all-vanadium redox flow battery and a preparation method thereof.

To achieve the above object, the technical scheme adopted in the present invention is:

A highly active porous carbon fiber paper electrode material for an all-vanadium redox flow battery has a thickness of 50-1000 μm, is composed of carbon fibers with a diameter of 5-20 μm, and the porosity of the porous carbon fiber paper is 60-90%; the surface of the carbon fiber is a porous structure , the specific surface area of carbon fiber is 5-50m ² /g, and the pore size is 50-2000nm. The electrode material can be prepared by the following methods:

1) After degumming the chopped carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry;

2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process;

3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.;

4) Raise the hot-pressed carbon paper base paper to the specified temperature A under an inert atmosphere, and keep it at a constant temperature for 0.5-3h;

5) Then adjust to the specified temperature B, feed the mixture of activated gas and inert gas at a constant temperature for 2-60min;

6) then cooled to room temperature under the protection of an inert atmosphere to obtain a porous carbon fiber paper electrode material;

in,

The chopped carbon fiber is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber, the length is 5mm-30mm, and the diameter is 5-20μm;

The dispersant is one or more of polyethylene oxide, carboxymethyl cellulose and polyacrylamide;

The concentration of the dispersant in the slurry is 0.01-0.2%;

The concentration of the phenolic resin in the ethanol solution of the phenolic resin is 0.5-15%;

The gas of the inert atmosphere is one or more of nitrogen, argon or helium;

The specified temperature A is greater than or equal to the specified temperature B;

The specified temperature A is 1000～2300℃;

The specified temperature B is 700～1500℃;

The activated gas is one or both of water vapor or CO ₂ , and the volume concentration of water vapor and/or CO ₂ in the mixed gas is 2-50%, preferably 2-20%.

Alternatively, the electrode material of the present invention can also be prepared by the following method:

1) After degumming the chopped carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry;

2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process;

3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.;

4) The carbon paper base paper formed by hot pressing is raised to the specified temperature C under the mixed gas atmosphere of activated gas and inert gas, and the constant temperature is maintained for 2min-2h;

5) then cooled to room temperature under the protection of an inert atmosphere to obtain a porous carbon fiber paper electrode material;

in,

The chopped carbon fiber is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber, the length is 5mm-30mm, and the diameter is 5-20μm;

The dispersant is one or more of polyethylene oxide, carboxymethyl cellulose and polyacrylamide;

The concentration of the dispersant in the slurry is 0.01-0.2%;

The concentration of the phenolic resin in the ethanol solution of the phenolic resin is 0.5-15%;

The gas of the inert atmosphere is one or more of nitrogen, argon or helium;

The activated gas is one or both of water vapor or CO ₂ , and the volume concentration of water vapor and/or CO ₂ in the mixed gas is 2-50%, preferably 2-20%;

The specified temperature C is 800-1800°C.

The present invention has the following advantages:

(1) The electrode material prepared by the preparation method of the present invention has a large number of pores on the surface of the carbon fiber, which increases the specific surface area of the electrode material, and can obtain a large number of surface oxygen-containing functional groups, and the hydrophilicity is obviously improved, which can significantly reduce the liquid flow storage. The electrochemical polarization of the energy battery greatly improves the electrocatalytic activity of the electrode material for the VO ²⁺ /VO ₂ ⁺ and V ²⁺ /V ³⁺ redox reactions, reduces the charge transfer resistance, and improves the all-vanadium solution. The voltage efficiency and energy efficiency of the flow battery are improved, so as to improve its working current density, so that the weight, volume and cost of the battery with the same output power are greatly reduced.

(2) Compared with the existing activated carbon fiber, the electrode material prepared by the preparation method of the present invention has a smaller specific surface area, only 5-50 m ² /g, and the pores are all distributed on the surface of the carbon fiber, which will not greatly increase the carbon fiber. The body resistance of the paper electrode, and because the thickness of the electrode is small, only less than 1mm, greatly reduces the electrode spacing, reduces the internal resistance of the battery, and improves the working current density of the battery.

(3) The electrode material of the present invention has a simple preparation method, no special requirements for equipment, convenient operation, low cost, high practical value, and easy mass production.

Description of drawings

Fig. 1 is the scanning electron microscope photograph of the porous carbon fiber paper prepared in the embodiment of the present invention 1;

Fig. 2 is the cyclic voltammogram of the porous carbon fiber paper prepared in Example 1 of the present invention and the carbon paper in Comparative Example 1 to V(IV)/V(V) pairs, scanning rate: 10mV/s;

Figure 3 is a cyclic voltammetry diagram of the porous carbon fiber paper prepared in Example 1 of the present invention and the carbon paper in Comparative Example 1 to V(II)/V(III) pairs, scanning rate: 10mV/s;

Detailed ways

The present invention will be described in detail below through specific embodiments.

Example 1

Prepare a polyacrylonitrile-based chopped carbon fiber with a length of 10 mm, degumming it in an acetone solution, and put it into an aqueous solution containing 0.1% polyethylene oxide dispersant for beating to form a polyacrylonitrile-based carbon fiber slurry. Then, it was made into a carbon paper precursor with a unit area weight of 40 g/m ² by wet molding equipment; after that, it was immersed in an ethanol solution with a concentration of phenolic resin of 1% for 30 minutes, and then dried at 200 ° C. The carbon paper base paper was prepared by hot pressing under the pressure of 6MPa; the carbon paper base paper was placed in an electric furnace, and heated to 1600°C at a heating rate of 10°C/min under _N2 atmosphere, and kept at a constant temperature for 1 h; then cooled to 1300°C, A mixture of CO ₂ and N ₂ was introduced, and the flow rates of CO ₂ and N ₂ were 40 ml/min and 200 ml/min, respectively, and the reaction was performed at a constant temperature for 30 min; and then cooled to room temperature to obtain porous carbon fiber paper.

In order to test the electrochemical activity of vanadium ion redox couple on the surface of porous carbon fiber paper, the porous carbon fiber paper prepared in Example 1 was tested by cyclic voltammetry. The porous carbon fiber paper was used as the working electrode, the non-porous graphite plate was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode. Prepare electrolytes with concentrations of 0.05MV(Ⅱ)+0.05MV(Ⅲ)+3M H ₂ SO ₄ and 0.05MV(Ⅳ)+0.05MV(Ⅴ)+3M H ₂ SO ₄ , for V(Ⅳ)/V( The electrochemical activity of V) and V(II)/V(III) pairs on the surface of porous carbon fiber paper were studied, respectively. The SEM photo of the porous carbon fiber paper in this example is shown in Figure 1, and it can be observed that a large number of nanopores are distributed on the surface of the carbon fiber. The cyclic voltammetry curves of this material are shown in Figures 2 and 3, comparing the electrochemical performance of V(IV)/V(V) and V(II)/V(III) on the porous carbon fiber paper and the carbon paper in Comparative Example 1 The positions of the oxidation and reduction peaks and the magnitudes of the peak currents show that the porous carbon fiber paper prepared in this example has significantly improved electrocatalytic activity and electrochemical reversibility.

A carbon paper with a size of 4 cm × 3 cm was cut from the porous carbon fiber paper prepared in Example 1 as an electrode, assembled into a single cell, and tested for charge and discharge performance. The positive electrolyte is 1.5M VO ²⁺ in 3M H ₂ SO ₄ solution 40ml, and the negative electrolyte is 1.5MV ³⁺ 3M H ₂ SO ₄ solution 40ml. The current efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of the porous carbon fiber paper single cells at different current densities are summarized in Table 1. Compared with the carbon paper in Comparative Example 1, the voltage efficiency of the porous carbon fiber paper single cell in this example increased from 75.6% to 90.0% at a current density of 80mA/cm ² , and the energy efficiency could reach 84.3%; Under the high current density of ² , the voltage efficiency is increased from 70.7% to 84.9%, and the energy efficiency is increased to 80.1%. The higher the current density, the more significant the improvement effect is.

Table 1 Cell efficiencies of single cells using _CO2 -activated carbon felt as electrodes in each example and single cells in comparative examples at different current densities

Comparative example

The carbon paper produced by SGL company in Germany was used as a comparative example, and the carbon paper with a size of 4 cm × 3 cm was cut out as an electrode to assemble a single cell, and the charge and discharge performance was tested. The positive electrolyte is 1.5M VO ²⁺ in 3M H ₂ SO ₄ solution 40ml, and the negative electrolyte is 1.5MV ³⁺ 3M H ₂ SO ₄ solution 40ml. Its cell efficiencies at different current densities are shown in Table 1, which cannot perform effective charge ^- discharge cycles at a high current density of 140 mA/cm.

Example 2

Prepare pitch-based chopped carbon fibers with a length of 15 mm, degumming them in acetone solution, and put them into an aqueous solution containing 0.05% polyacrylamide dispersant for beating to form a pitch-based carbon fiber slurry, which is then wet-processed. The carbon paper precursor with a unit area weight of 50 g/m ² was prepared by the molding equipment; after that, it was immersed in an ethanol solution with a concentration of phenolic resin of 1% for 30 min, and then dried and then hot-pressed at 180 ° C. The carbon paper base paper was prepared with a pressure of 5MPa; the carbon paper base paper was placed in an electric furnace, heated to 1400°C at a heating rate of 5°C/min under _N2 atmosphere, and kept at a constant temperature for 1 h; then cooled to 800°C, and water vapor and The mixed gas of N ₂ , the flow rates of water vapor and N ₂ were 10 ml/min and 200 ml/min, respectively, and the reaction was performed at a constant temperature for 30 min; and then the porous carbon fiber paper was prepared by cooling to room temperature.

The single cell assembly evaluation conditions are the same as those in Example 1, and the difference from Example 1 is that: the all-vanadium redox flow battery using the porous carbon fiber paper of this example as the electrode, when the current density is 80 mA/cm ² , the voltage efficiency and energy efficiency are respectively When the current density is increased to 120mA/cm ² , the voltage efficiency and energy efficiency are still maintained at 76.6% and 73%. Compared with Comparative Example 1, the battery performance is greatly improved.

Example 3

Prepare viscose-based chopped carbon fiber with a length of 10mm, degumming it in acetone solution, and put it into an aqueous solution containing 0.05% polyacrylamide dispersant for beating to form viscose-based carbon fiber slurry. A carbon paper precursor with a unit area weight of 50 g/m ² was prepared by wet molding equipment; after that, it was immersed in an ethanol solution with a concentration of phenolic resin of 0.5% for 30 min, and then dried at 180 ° C and heated at 180 °C. The carbon paper base paper was obtained by compression molding, and the pressure was 5MPa; the carbon paper base paper was placed in an electric furnace, and heated to 1300°C at a heating rate of 5°C/min under _N2 atmosphere, and the temperature was kept constant for 1 h; A mixture of CO ₂ and N ₂ , the flow rates of CO ₂ and N ₂ were 20ml/min and 200ml/min, respectively, and the reaction was performed at a constant temperature for 30min; then cooled to room temperature to obtain porous carbon fiber paper.

The single cell assembly evaluation conditions are the same as those of Example 1, and the difference from Example 1 is that: using the activated carbon felt of this example as the electrode of the all-vanadium redox flow battery, when the current density is 80mA/cm ² , the voltage efficiency and energy efficiency are respectively 80.7% and 75.8%; when the current density was increased to 120 mA/cm ² , the voltage efficiency and energy efficiency remained at 75.8% and 71.8%.

Claims (11)

1. Porous carbon fiber paper electrode material for an all-vanadium redox flow battery, characterized in that: the thickness of the porous carbon fiber paper electrode is 50-1000 μm, which is composed of carbon fibers with a diameter of 5-20 μm, and the porosity of the porous carbon fiber paper is 60-90% ; The surface of carbon fiber is porous structure, the specific surface area of carbon fiber is 5-50m ² /g, and the pore size is 50-2000nm; The electrode material is prepared by the following method, 1) After degumming the carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry; 2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process; 3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.; 4) Raise the hot-pressed carbon paper base paper to a specified temperature A of 1000-2300°C under an inert atmosphere, and keep it at a constant temperature for 0.5-3h; 5) Then adjust to the specified temperature B 700～1500℃, feed the mixture of activated gas and inert gas and keep it constant for 2-60min; 6) then cooled to room temperature under the protection of an inert atmosphere to obtain a porous carbon fiber paper electrode material; Or, prepared by the following method, 1) After degumming the chopped carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry; 2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process; 3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.; 4) Raise the hot-pressed carbon paper base paper to a specified temperature of C800-1800°C under a mixed gas atmosphere of activated gas and inert gas, and keep it at a constant temperature for 2min-2h; 5) and then cooled to room temperature under the protection of an inert atmosphere to prepare a porous carbon fiber paper electrode material. 2. The preparation method of the porous carbon fiber paper electrode material according to claim 1, wherein the electrode material is prepared by the following method, 1) After degumming the carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry; 2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process; 3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.; 4) Raise the hot-pressed carbon paper base paper to a specified temperature A of 1000-2300°C under an inert atmosphere, and keep it at a constant temperature for 0.5-3h; 5) Then adjust to the specified temperature B 700～1500℃, feed the mixture of activated gas and inert gas and keep it constant for 2-60min; 6) and then cooled to room temperature under the protection of an inert atmosphere to prepare a porous carbon fiber paper electrode material. 3. according to the described preparation method of claim 2, it is characterized in that: The carbon fiber is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber, the length is 5mm-30mm, and the diameter is 5-20μm. 4. preparation method according to claim 2 is characterized in that: described dispersant is one or more in polyoxyethylene, carboxymethyl cellulose and polyacrylamide; The concentration of the dispersant in the slurry is 0.01-0.2%; The concentration of the phenolic resin in the ethanol solution of the phenolic resin is 0.5-15%. 5. according to the described preparation method of claim 2, it is characterized in that: The gas of the inert atmosphere is one or more of nitrogen, argon or helium; The activated gas is one or both of water vapor or CO ₂ , and the volume concentration of water vapor and/or CO ₂ in the mixed gas is 2-50%; The specified temperature A is greater than or equal to the specified temperature B. 6 . The preparation method according to claim 5 , wherein the volume concentration of water vapor and/or CO ₂ in the mixed gas is 2-20%. 7 . 7. The preparation method according to claim 2 or 5, characterized in that: the specified temperature A is 1400-2300°C; the specified temperature B is 800-1400°C. 8. The preparation method of the porous carbon fiber paper electrode material according to claim 1, wherein the electrode material is prepared by the following method, 1) After degumming the chopped carbon fiber in an acetone solution, put it into an aqueous solution dissolved with a dispersant for beating to form a carbon fiber slurry; 2) The carbon fiber slurry described in step 1) is made into a carbon paper precursor by a wet forming papermaking process; 3) dipping the carbon paper precursor in an ethanol solution of phenolic resin, drying it, and then hot pressing at 150-280° C.; 4) Raise the hot-pressed carbon paper base paper to a specified temperature of C800-1800°C under a mixed gas atmosphere of activated gas and inert gas, and keep it at a constant temperature for 2min-2h; 5) and then cooled to room temperature under the protection of an inert atmosphere to prepare a porous carbon fiber paper electrode material. 9. preparation method according to claim 8 is characterized in that: described chopped carbon fiber is a kind of in polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber, length is 5mm-30mm, diameter is 5mm -20μm; The dispersant is one or more of polyethylene oxide, carboxymethyl cellulose and polyacrylamide; The concentration of the dispersant in the slurry is 0.01-0.2%; The concentration of the phenolic resin in the ethanol solution of the phenolic resin is 0.5-15%; The gas of the inert atmosphere is one or more of nitrogen, argon or helium; The activated gas is one or both of water vapor and CO _{2 , and the volume concentration of water vapor and/or CO 2 in} the mixed gas is 2-50%. 10 . The preparation method according to claim 9 , wherein the volume concentration of water vapor and/or CO ₂ in the mixed gas is 2-20%. 11 . 11. The application of the porous carbon fiber paper electrode material according to claim 1, wherein the porous carbon fiber paper electrode material can be used in an all-vanadium redox flow battery.