Preparation method of metal oxide and inorganic oxide loaded flexible carbon nanofiber electrode material and zinc-manganese flow battery thereof

Abstract

The invention discloses a metal oxide and inorganic oxide loaded flexible carbon nanofiber electrode material and a zinc-manganese flow battery thereof, and belongs to the technical field of electrochemical energy storage materials. According to the preparation method, a carbon felt is taken as a substrate, an electrostatic spinning-pre-oxidation-carbonization technology is adopted, and a carbon nanofiber membrane loaded with metal oxide and silicon dioxide nanoparticles is compounded on the surface of the carbon felt, so that a carbon electrode with a pore structure from 1 micron to 100 microns is formed. According to the composite electrode, high electrolyte permeability and zinc ion transmission rate can be realized by utilizing the large aperture of the carbon felt, and meanwhile, through the metal oxide and the silicon dioxide nanoparticles which are uniformly distributed in the carbon nanofibers, the zinc affinity is enhanced, the zinc nucleation sites are increased, and the zinc is guided to be uniformly deposited. The zinc-manganese liquid flow battery negative electrode material is applied to a zinc-manganese liquid flow battery negative electrode, zinc dendrite growth can be remarkably inhibited, the coulombic efficiency and energy efficiency of a battery are improved, the service life of the battery is prolonged, the preparation process is simple, the cost is low, the material is suitable for large-scale production, and a reliable solution is provided for application of a zinc-based liquid flow battery in the large-scale energy storage field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical energy storage materials, and particularly relates to preparation of electrospun functional carbon nanofiber and application thereof in zinc-based flow batteries, and especially relates to a preparation method and application of a flexible carbon nanofiber electrode material loaded with metal oxides and inorganic oxides. BACKGROUND

[0002] Under the dual pressures of energy security and environmental sustainability, the proportion of renewable energy (solar energy, wind energy) is increasing year by year. However, the intermittency and volatility of renewable energy generation lead to mismatch and imbalance between supply and demand of energy systems, and green power storage encounters a bottleneck. Among many technical routes, zinc batteries have great potential in large-scale energy storage due to low cost, high theoretical capacity and environmental friendliness, but the practical application of zinc-based batteries is limited by two major problems. Taking zinc-based flow batteries as an example: first, uncontrollable growth of zinc dendrites at the interface between the carbon electrode and the electrolyte causes short circuit and rapid capacity decay of the battery; second, the electrode electrochemical hydrogen evolution and corrosion side reactions lead to unstable voltage and reduced coulombic and energy efficiency of the battery.

[0003] Current solutions mainly include electrode structure optimization, separator modification and interface protection layer construction to improve the influence of the above problems. However, conventional porous carbon electrodes such as carbon felt, carbon paper, carbon cloth and their modifications cannot completely change their inherent properties to improve the performance of the battery. In order to overcome the limitations of the currently used carbon electrodes, the method of using electrospinning technology to prepare carbon nanofiber from polymer precursors is simple, easy to modify, economical and suitable for large-scale production. The electrospun carbon nanofiber membrane has a three-dimensional network structure, so it has high porosity, large specific surface area, controllable fiber size and other characteristics, and by reasonably adjusting the composition of the spinning precursor, functional carbon fibers can be prepared. However, the flexibility and poor zinc affinity of undoped and unsupported carbon nanofiber membranes limit their application in flow battery electrodes. Further functionalization of modified carbon nanofibers based on application purposes can be divided into in-situ preparation and post-treatment methods. Post-treatment often requires complex and harsh methods to introduce active components, which reduces the mechanical properties of the carbon nanofiber membrane, while in-situ introduction of active components or loading during the electrospinning preparation of carbon nanofiber is an effective means to achieve functionalization, but it also faces the major challenge of balancing effective loading and mechanical properties. SUMMARY

[0004] In view of the problems existing in the current carbon electrode, the present application provides a simple, fast and low-cost preparation method of carbon nanofiber electrode and its application in zinc-based flow batteries.

[0005] The present application aims to provide a three-dimensional high-conductivity and super-zinc-phil carbon fiber framework structure, in which metal oxide and inorganic oxide nanoparticles are uniformly distributed in the carbon fiber, and the synergistic effect of the metal oxide and amorphous inorganic oxide nanoparticle plasticizer in the carbon fiber framework makes the carbon nanofiber electrode exhibit high strength and high toughness, and the nanoparticles exhibit significant affinity with the negative zinc of the zinc-based flow battery, thereby making the zinc uniformly nucleate and deposit, inhibiting the growth of zinc dendrites, enhancing the efficiency of the flow battery, and improving the service life and safety of the flow battery.

[0006] The technical solution for achieving the purpose of the present application is as follows: In a first aspect, an electrospinning-pre-oxidation-carbonization method is used, in which first, metal salt and tetraethyl orthosilicate are uniformly dissolved in N-N dimethylformamide solution according to a certain proportion, then polyacrylonitrile is added until it is completely dissolved to prepare a spinning solution, then a nanofiber membrane is obtained by electrospinning, and finally a flexible carbon nanofiber membrane uniformly loaded with metal oxide and inorganic oxide nanoparticles is prepared through pre-oxidation and carbonization steps, and the specific steps are as follows: Step 1: Dissolve an appropriate amount of metal salt in 10 ml of N,N-dimethylformamide (DMF), and stir at 60°C to fully mix.

[0007] Step 2: Add a certain amount of plasticizer tetraethyl orthosilicate (TEOS) to the mixed solution obtained in step 1 above, and mix uniformly.

[0008] Step 3: Add a certain amount of polyacrylonitrile (PAN) to the mixed solution obtained in step 2 above, and stir vigorously at 60°C for 8h to obtain a uniform transparent mixed solution as a spinning solution. After stirring is completed, stand still overnight for defoaming treatment.

[0009] Step 4: Inject the spinning solution into a 10 ml syringe, connect the needle to a positive voltage, and collect a layer of aluminum foil on the collector drum. Electrospinning is carried out within a certain voltage range, and a fiber membrane is formed on the aluminum foil after spinning is completed.

[0010] Step 5: Place the spinning fiber membrane in a vacuum drying oven overnight to evaporate the excess DMF solvent.

[0011] Step 6: Place the fiber membrane in a box-type high-temperature sintering furnace for pre-oxidation treatment at 200-300°C for 1-2h; then place the pre-oxidized fiber membrane in an argon-protected tube furnace for carbonization at 700-950°C for 1-2h. The metal salt in the fiber membrane is oxidized to form uniformly dispersed metal nanoparticles, and the plasticizer TEOS is oxidized to form uniformly dispersed silicon dioxide (SiO2) nanoparticles, obtaining a flexible carbon nanofiber membrane loaded with metal oxide and inorganic oxide.

[0012] Further, the metal salt in step 1 is one or more of anhydrous zinc acetate, manganese chloride, etc.

[0013] Further, the ratio of the plasticizer in step 2 to the metal salt in step 1 is 2:1~1.5.

[0014] Further, in the spinning solution of step 3, the mass fraction of polyacrylonitrile is 10-14%.

[0015] Further, the electrospinning parameters in step 4 are: the syringe propelling speed is 0.015-0.020 ml / min, the reciprocating motor speed is 200 mm / min, the collection roller rotation speed is 200-3000 rpm, the spinning voltage is 16-17 kV, the spinning temperature is 28-31℃, and the humidity is 40-45%.

[0016] Further, the drying temperature in step 5 is 60℃, and the time is 12 h.

[0017] Further, in step 6, the pre-oxidation heating rate is 2℃ / min, and the carbonization heating rate is 5℃ / min. The obtained carbon fiber has a diameter of 600-700 nm; the electrospun carbon fiber membrane has a thickness of 40-100 microns, a bending degree of 180° without breaking, and can be repeatedly bent and folded, having super flexibility.

[0018] In a second aspect, the application provides a preparation method of a composite electrode of a zinc-based flow battery, the composite electrode serving as a negative electrode of the zinc-based flow battery; the negative electrode being a carbon fiber membrane loaded with metal oxide and silicon dioxide nanoparticles and a carbon felt, obtained by the preparation method of any one of the first aspect.

[0019] Compared with the prior art, the application has the following advantages and positive effects: The application adopts a flexible carbon nanofiber membrane composite electrode loaded with metal oxide and inorganic oxide prepared in situ, fully utilizes the large pore size of the carbon felt to achieve excellent electrolyte permeability and zinc ion transmission rate, utilizes the metal oxide and silicon dioxide nanoparticles to improve the zincophilic active site and adsorption rate, and improves the zinc deposition uniformity and inhibits the growth of zinc dendrites.

[0020] The technical scheme of the application adopts the electrospinning technology, has low process difficulty, simple operation, and cheap raw materials, can be used for large-scale production, and has high commercial value after transformation. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 (a) flexible carbon nanofiber electrospinning membrane and (b) original carbon felt electron microscope image; Figure 2 (a) flexible carbon nanofiber electrospinning membrane and (b) original carbon felt electron microscope image; Figure 3 Three folding bending figures for the spunlaced membrane; Figure 4 (a) Coulomb efficiency and (b) energy efficiency using the spunlaced membrane and pristine carbon felt as electrodes; Figure 5 Time-voltage curve using the spunlaced membrane and pristine carbon felt as electrodes. Figure 6 TEM and elemental distribution images of the electrospun membrane. DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with embodiments. The specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0023] The present application provides a metal oxide and inorganic oxide nanoparticle loaded carbon nanofiber composite electrode, which is formed by using a commercialized pristine carbon felt as a substrate and combining a nanoparticle loaded carbon nanofiber membrane to form a three-dimensional composite electrode with a size of 1 micrometer to 100 micrometers.

[0024] Embodiment 1 As a preferred embodiment of the present application, the electrospun carbon fiber membrane is prepared by pre-oxidizing and carbonizing an electrospun fiber membrane, and the zinc oxide and silicon dioxide nanoparticles are uniformly loaded in the fiber, and the fiber diameter is 600-700 nm. The electrospun carbon fiber has super-high flexibility, and does not break when folded by 180°, and restores the shape after unfolding.

[0025] The present application provides a carbon nanofiber membrane loaded with zinc oxide and silicon dioxide nanoparticles, which is specifically as follows: After the anhydrous zinc acetate and tetraethyl orthosilicate are sequentially dissolved uniformly in the DMF solvent, the polyacrylonitrile is dissolved uniformly to form a spinning precursor solution. The spinning is collected on a drum receiver covered with aluminum foil by using the electrospinning technology. After the aluminum foil and the spinning membrane are removed after the spinning is completed, vacuum drying is performed, and then pre-oxidation and carbonization treatment are performed to obtain the carbon fiber membrane loaded with zinc oxide and silicon dioxide.

[0026] As a preferred embodiment of the present application, the mass fraction of the polyacrylonitrile in the spinning precursor solution is 10-14% (preferably 14%), the mass fraction of the anhydrous zinc acetate is 4%, and the mass fraction of the tetraethyl orthosilicate is 8%.

[0027] Preferably, the electrospinning parameters are as follows: the syringe propelling speed is 0.015 ml / min, the reciprocating width is 15 cm, the reciprocating speed is 200 mm / min, the collector rotating speed is 200 rpm, the spinning voltage is 17 kV, the spinning ambient temperature is 30°C, the ambient humidity is 40%, and the spinning time is 8 h.

[0028] Preferably, the pre-oxidation of the electrospun fiber membrane refers to oxidation at 260°C for 1-2 h in a muffle furnace or box furnace, with a temperature rising rate of 2°C / min.

[0029] Preferably, the further carbonization of the pre-oxidized membrane refers to carbonization at a temperature of 700-950°C for 1 h in a tube furnace under an argon atmosphere, with a temperature rising rate of 5°C / min.

[0030] Subsequently, a carbon felt was used as a positive electrode, and the electrospun fiber obtained in the present embodiment and the carbon felt were used as a composite electrode as a negative electrode, to prepare an alkaline zinc-manganese flow battery. The electrode size was 3 cm 3 cm; the positive electrolyte was a sodium permanganate and sodium hydroxide solution, the sodium permanganate concentration was 0.1 mol / L, and the sodium hydroxide concentration was 6 mol / L; the negative electrolyte was a zinc oxide and sodium hydroxide solution, the zinc oxide concentration was 0.1 mol / L, and the sodium hydroxide concentration was 6 mol / L; and the separator was a Nafion 212 ion exchange membrane.

[0031] Battery test: the electrolyte flow rate was 40 ml / min; the charge and discharge current density was 60 mA / cm2; the charge cutoff voltage was 2.2 V, and the discharge cutoff voltage was 1.7 V.

[0032] Comparative Example In the present comparative example, a carbon felt was used as a positive electrode, and an original carbon felt (CF) without any treatment was used as a negative electrode, to prepare an alkaline zinc-manganese flow battery. The electrode size was 3 cm 3 cm; the positive electrolyte was a sodium permanganate and sodium hydroxide solution, the sodium permanganate concentration was 0.1 mol / L, and the sodium hydroxide concentration was 6 mol / L; the negative electrolyte was a zinc oxide and sodium hydroxide solution, the zinc oxide concentration was 0.1 mol / L, and the sodium hydroxide concentration was 6 mol / L; and the separator was a Nafion 212 ion exchange membrane.

[0033] The results of the examples and the comparative example are as follows: Figure 1The SEM images of the electrospun carbon fiber film side and the commercial raw carbon felt side of the embodiment are shown. It can be seen that the diameter of the electrospun carbon fiber is finer than that of the carbon felt, being about several hundred nanometers, while the diameter of the carbon felt fiber is about several tens of microns, so the specific surface area of the electrode is obviously increased on the electrospun carbon fiber side; in the electrospun carbon fiber film, a gap of 1 micron is formed between the fibers, while on the carbon felt side, a pore of tens of microns or even nearly 100 microns is formed between the thicker fibers.

[0034] Figure 2 The pore size distribution graphs measured by mercury intrusion method of the electrospun film and the commercial carbon felt are shown. The electrospun film has a pore size of 1 micron to 10 microns, and the carbon felt has a pore size distribution of about 100 microns. This is consistent with the pore size distribution observed by scanning electron microscopy.

[0035] Figure 3 The electrospun carbon fiber film made by the patent has good flexibility, and it can be seen that after three different folds or bends, the electrospun film has no signs of fragmentation.

[0036] Figure 4 The Coulomb efficiency and energy efficiency graphs of the composite electrode composed of the electrospun carbon fiber film and the commercial carbon felt electrode are shown. It can be clearly seen that the Coulomb efficiency of the composite electrode using the electrospun carbon fiber film is maintained at about 98.6%, and the energy efficiency is stable at about 86%, which is obviously more stable than the raw carbon felt.

[0037] Figure 5 The time-voltage graph of the composite electrode composed of the electrospun film and the electrode composed of ordinary carbon felt is shown. It can be seen that the battery composed of raw carbon felt has an irreversible increase in voltage after about 48 h of cycling, and eventually breaks through the protection voltage, forcing the battery to stop running. This may be caused by two phenomena. First, zinc dendrites are generated inside the battery, increasing the internal resistance of the battery and causing the voltage to rise. This phenomenon is irreversible, causing the voltage to rise. Second, the zinc dendrites pierce the separator, causing the battery to short circuit. The battery voltage of the composite electrode composed of the electrospun film is stable for 300 h.

Claims

1. A flexible carbon nanofiber electrode material supported on metal oxides and inorganic oxides, characterized in that, It is composed of carbon felt as a substrate and carbon nanofiber membrane loaded with metal oxide and silica nanoparticles.

2. The flexible carbon nanofiber electrode material supported on metal oxides and inorganic oxides according to claim 1, characterized in that, The carbon felt has micron-sized pores with a pore size ranging from tens of micrometers to 100 micrometers; the carbon nanofiber membrane loaded with metal oxides and silica nanoparticles has a carbon nanofiber diameter of 600-700 nanometers, a membrane thickness of 40-100 micrometers, can bend at an angle of up to 180° without breaking, and contains pores ranging from 1 micrometer to 10 micrometers.

3. The flexible carbon nanofiber electrode material supported on metal oxides and inorganic oxides according to claim 1, characterized in that, The metal oxide is formed by the oxidation of a metal salt, wherein the metal salt is one or more of anhydrous zinc acetate and manganese chloride; the silica nanoparticles are formed by the oxidation of tetraethyl silicate.

4. A method for preparing a flexible carbon nanofiber electrode material supported on metal oxides and inorganic oxides as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve the metal salt in N,N-dimethylformamide and stir at 60°C until fully mixed; (2) Add tetraethyl silicate to the mixed solution obtained in step (1) and stir until the mixture is homogeneous; (3) Add polyacrylonitrile to the mixed solution obtained in step (2), stir vigorously at 60°C for 8 hours, let stand overnight to defoam, and obtain spinning solution; (4) Inject the spinning solution into the syringe and perform electrospinning to form a fiber film on the collector roller covered with aluminum foil; (5) Place the fiber membrane in a vacuum drying oven and dry it at 60°C for 12 hours to evaporate excess solvent; (6) The dried fiber membrane was placed in a box-type high-temperature sintering furnace and pre-oxidized at 200-300℃ for 1-2 hours with a pre-oxidation heating rate of 2℃ / min. Then the pre-oxidized fiber membrane was placed in a tube furnace under argon protection and carbonized at 700-950℃ for 1-2 hours with a carbonization heating rate of 5℃ / min to obtain a carbon nanofiber membrane loaded with metal oxides and silica nanoparticles. (7) The carbon nanofiber membrane obtained in step (6) is combined with carbon felt to obtain a flexible carbon nanofiber electrode material supported by metal oxides and inorganic oxides.

5. The preparation method according to claim 4, characterized in that, The ratio of the metal salt in step (1) to the tetraethyl silicate in step (2) is 1:(1.5-2); the mass fraction of polyacrylonitrile in the spinning solution in step (3) is 10-14%.

6. The preparation method according to claim 4, characterized in that, The electrospinning parameters in step (4) are as follows: syringe advance speed 0.015 - 0.020 ml / min, reciprocating motor speed 200 mm / min, collecting roller speed 200 - 3000 rpm, spinning voltage 16 - 17 kV, spinning temperature 28 - 31℃, and humidity 40 - 45%.

7. The preparation method according to claim 4, characterized in that, In step (1), the metal salt is one or more of anhydrous zinc acetate and manganese chloride.

8. A zinc-manganese redox flow battery, characterized in that, It includes a negative electrode and a positive electrode; the negative electrode is a flexible carbon nanofiber electrode material supported on metal oxides and inorganic oxides as described in any one of claims 1-3.

9. The zinc-manganese redox flow battery according to claim 8, characterized in that, The negative electrode electrolyte of the zinc-manganese flow battery is a mixed solution of zinc oxide and sodium hydroxide, wherein the concentration of zinc oxide is 0.1 mol / L and the concentration of sodium hydroxide is 6 mol / L; the positive electrode electrolyte is a mixed solution of sodium permanganate and sodium hydroxide, wherein the concentration of sodium permanganate is 0.1 mol / L and the concentration of sodium hydroxide is 6 mol / L.

10. The zinc-manganese redox flow battery according to claim 8, characterized in that, The zinc-manganese redox flow battery uses a Nafion 212 ion exchange membrane as the separator; the electrolyte flow rate is 40 ml / min, the charge / discharge current density is 60 mA / cm², the charging cutoff voltage is 2.2 V, and the discharging cutoff voltage is 1.7 V.

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