CN110197919B - Ion-conducting porous diaphragm for all-vanadium redox flow battery and preparation method and application thereof - Google Patents
Ion-conducting porous diaphragm for all-vanadium redox flow battery and preparation method and application thereof Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
- H01M8/1018—Polymeric electrolyte materials
- H01M8/1041—Polymer electrolyte composites, mixtures or blends
- H01M8/1046—Mixtures of at least one polymer and at least one additive
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
- H01M8/1018—Polymeric electrolyte materials
- H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
- H01M8/1086—After-treatment of the membrane other than by polymerisation
- H01M8/1088—Chemical modification, e.g. sulfonation
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
- H01M8/184—Regeneration by electrochemical means
- H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2250/00—Fuel cells for particular applications; Specific features of fuel cell system
- H01M2250/10—Fuel cells in stationary systems, e.g. emergency power source in plant
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention discloses an ion-conducting porous diaphragm for an all-vanadium redox flow battery and a preparation method and application thereof; the porous diaphragm is applied to the all-vanadium redox flow battery, is prepared by adopting a casting solution containing high-quality-concentration organic polymer resin, and the exchange rate of a solvent and a non-solvent in the film forming process of the porous diaphragm is changed by adding a surfactant so as to influence the final structure of the porous diaphragm. According to the invention, the size of the prepared porous diaphragm pore channel is controlled by controlling the addition of the surfactant, so that the proton conductivity of the membrane can be effectively increased on the premise of keeping high vanadium ion selectivity, and the balance of the selectivity of the membrane to vanadium ions and high proton conductivity is realized. After the surfactant is introduced into the porous diaphragm, the hydrophilicity of the porous diaphragm is greatly improved, the interface resistance between the porous diaphragm and the electrolyte is effectively reduced, and the polarization effect of the battery is reduced.
Description
Technical Field
The invention relates to the technical field of all-vanadium redox flow batteries, in particular to an ion-conducting porous diaphragm for an all-vanadium redox flow battery and a preparation method and application thereof.
Background
The flow battery is a novel electrochemical energy storage technology, has the advantages of high efficiency, modular design, safety, environmental protection, simple maintenance, low operation cost and the like, and shows outstanding application prospects in the fields of wind power generation, photovoltaic power generation, power grid peak clipping and valley filling, distributed power stations, smart power grids and the like. The full Vanadium Flow Battery (VFB) is the most promising flow battery among the current flow batteries due to the advantages of high charging and discharging efficiency, environmental friendliness, flexible design, high safety, low self-discharge, long life, and the like.
The battery diaphragm is one of key materials of the all-vanadium redox flow battery, and on one hand, the battery diaphragm separates positive and negative electrolytes so as to avoid cross contamination of positive and negative active ions and self-discharge; and on the other hand, conductive ions such as protons are allowed to pass through to form an internal circuit of the battery. VFB battery separators should have the following characteristics: the high ionic conductivity enables the battery to have higher voltage efficiency so as to reduce the polarization phenomenon of the battery; the high vanadium ion selectivity enables the battery to have higher coulombic efficiency and reduces the self-discharge of the battery; has better mechanical property, chemical corrosion resistance and electrochemical oxidation resistance, and ensures longer service life.
The current commercial vanadium battery at home and abroad uses a diaphragm material which is mainly Nafion membrane developed by DuPont. In the flow battery, although the Nafion membrane is expensive and has poor ion selectivity, the Nafion membrane is still incomparable with many commercial membranes at present in terms of ion conductivity, mechanical properties, chemical properties, service life and the like. However, the use of Nafion membranes is limited due to their relatively high cost and poor ion selectivity. In view of the above problems, non-fluorine ion exchange membranes have become a hot point of research, common non-fluorine polymers are materials such as sulfonated polyaryletherketone, polyarylethersulfone, polyimide and the like, however, for most of non-fluorine ion exchange membranes, the structure of the materials is damaged when ion exchange groups are introduced, the oxidation stability of the membranes is greatly reduced, and thus the service life of the membranes in VFB is limited. Therefore, the development of a porous separator with high ionic conductivity, high selectivity, high stability and low cost as a battery separator is crucial to the promotion of the commercialization process of the all-vanadium flow battery.
Taking the all-vanadium flow battery as an example, since vanadium ions and protons (hydrogen ions) in the electrolyte exist in the form of hydrated ions, and the stokes radius of the former is much larger than that of the latter, the protons can freely pass through and the vanadium ions are trapped by adjusting the pore diameter or charge of the porous membrane, so as to realize the separation of the vanadium ions and the protons. The porous diaphragm is low in price, gets rid of the limitation of introducing ion exchange groups on macromolecules, realizes the separation of ions through a pore size sieving mechanism or a Tangnan exclusion mechanism, greatly improves the stability of the diaphragm, and is a hotspot in current research and development.
The preparation of the porous diaphragm usually adopts an immersion precipitation phase inversion technology, and the aperture and the pore structure of the diaphragm have important influence on the performance of the diaphragm. In the preparation process of the membrane, a plurality of methods for regulating and controlling parameters such as aperture, pore structure and the like are adopted, wherein the methods comprise selection of a solvent/non-solvent, addition of a pore-forming agent in a membrane casting solution, addition of a volatile solvent, control of membrane forming conditions and the like. However, in the process of adjusting the pore size, the resistance of the diaphragm is too large due to too small pore size, which causes serious polarization phenomenon, and the pore size is too large, the selectivity of the membrane is poor, and self-discharge is generated, so that the solution of the contradiction between the ionic conductivity and the selectivity of the porous membrane becomes the key for solving the problem.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to solve the problems of poor ionic conductivity and selectivity and the like of a porous diaphragm, the porous diaphragm prepared by introducing a surfactant into the porous diaphragm and adjusting the structure of the porous diaphragm can effectively improve the wettability of the porous diaphragm on electrolyte and improve the proton conductivity of the porous diaphragm, and the surfactant is adsorbed on the surface of the porous diaphragm and shows good selectivity by electrostatic repulsion or formation of hydrogen bonds and high-valence cations (such as vanadium ions), so that the porous diaphragm for the all-vanadium redox flow battery with low cost and excellent performance is obtained.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of an ion-conducting porous diaphragm for an all-vanadium redox flow battery comprises the following steps:
mixing organic polymer resin serving as a raw material with a pore-foaming agent and a surfactant to prepare a membrane casting solution, and preparing the ion-conducting porous membrane for the all-vanadium redox flow battery by an immersion precipitation phase conversion method.
In a preferred embodiment of the present invention, the preparation method comprises the steps of:
(1) dissolving organic polymer resin, a pore-forming agent and a surfactant in an organic solvent to obtain a mixed solution, namely a membrane casting solution;
(2) and (2) coating the casting solution obtained in the step (1) on the surface of a base material, standing, and then immersing into a coagulating bath for solidification to prepare the ion-conducting porous diaphragm for the all-vanadium redox flow battery.
In a preferable embodiment of the present invention, the mass concentration of the organic polymer resin in the membrane casting solution is 10 to 50 wt%, the mass concentration of the pore-forming agent is 1 to 10 wt%, and the mass concentration of the surfactant is greater than 0 and less than or equal to 40 wt%. Also preferably, the mass concentration of the organic polymer resin in the membrane casting solution is 20-40 wt%, the mass concentration of the pore-forming agent is 1.5-8 wt%, and the mass concentration of the surfactant is 0.5-20 wt%. Further preferably, the mass concentration of the organic polymer resin in the membrane casting solution is 30-35 wt%, the mass concentration of the pore-forming agent is 2-5 wt%, and the mass concentration of the surfactant is 1-10 wt%.
In a preferred embodiment of the present invention, the molecular weight of the organic polymer resin is 70 ten thousand g/mol or more; preferably, the organic polymer resin is at least one selected from polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyetherketoneketone, polytetrafluoroethylene, polybenzimidazole, and polyvinylpyridine.
In a preferred embodiment of the present invention, the porogen is selected from a polymeric porogen or selected from a small molecular porogen; preferably, the polymeric porogen is one or more selected from polyvinylpyrrolidone (PVP), polyethylene glycol or polyvinyl alcohol. Preferably, the small molecule pore-forming agent is selected from one or more than two of lithium chloride, lithium bromide or aluminum chloride.
In a preferred embodiment of the present invention, the surfactant is selected from a cationic surfactant and/or an anionic surfactant; still preferably, the cationic surfactant is selected from one or two quaternary ammonium salts such as cetyltrimethylammonium chloride, dodecyldimethylbenzylammonium bromide and the like; the anionic surfactant is selected from one or two sulfonates such as sodium dodecyl benzene sulfonate and sodium dodecyl sulfonate.
In a preferred embodiment of the present invention, the organic solvent is one or more selected from Dimethylformamide (DMF), Dimethylacetamide (DMAC), Nitrogen Methyl Pyrrolidone (NMP), or Dimethylsulfoxide (DMSO).
In a preferred embodiment of the present invention, in the step (2), the coagulation bath is one or more selected from water, ethanol, propanol, butanol, isopropanol, methanol, acetone, DMF, and DMAC.
In a preferred embodiment of the present invention, in the step (2), the curing time is 1 to 60 min.
The invention provides an ion-conducting porous diaphragm for an all-vanadium redox flow battery, which is prepared by the method.
In a preferred embodiment of the present invention, the thickness of the porous membrane is 50 to 500 μm, and further preferably, the thickness of the porous membrane is 150-300 μm. Preferably, the pore size of the porous separator is 0.5-100nm, and the porosity of the porous separator is 20-80%.
The invention provides application of an ion-conducting porous diaphragm, which is used for an all-vanadium flow battery.
The invention provides an all-vanadium redox flow battery which comprises the porous diaphragm.
The beneficial results are that:
1. the porous diaphragm is applied to the all-vanadium redox flow battery and is prepared by adopting a casting solution containing high-quality-concentration organic polymer resin, the exchange rate of a solvent and a non-solvent in the film forming process of the porous diaphragm is changed by adding a surfactant so as to influence the final structure of the porous diaphragm, and the porous diaphragm with controllable structure and performance is obtained by controlling the content of the added surfactant.
2. According to the invention, the size of the pore channel of the prepared porous diaphragm is controlled by controlling the addition amount of the surfactant, so that the proton conductivity of the porous diaphragm can be effectively increased on the premise of keeping high selectivity on vanadium ions, and the balance of the high selectivity and high proton conductivity of the porous diaphragm on the vanadium ions is realized.
3. After the surfactant is introduced into the porous diaphragm, the hydrophilicity of the diaphragm is greatly improved, the interface resistance between the porous diaphragm and the electrolyte is effectively reduced, and the polarization effect of the battery is reduced.
4. The preparation method of the porous diaphragm is simple, the aperture is adjustable, the addition amount of the surfactant is controllable, and the performance of the porous diaphragm can be adjusted by adjusting the parameters, so that the performance of the battery can be adjusted.
5. The preparation material of the porous diaphragm is low in cost and excellent in chemical stability.
6. The invention expands the method for modifying the wettability of the porous diaphragm to the electrolyte.
7. The invention realizes the controllability of the efficiency of the all-vanadium redox flow battery.
Drawings
Fig. 1 is a charge and discharge curve of the porous separator prepared in example 1 in an all vanadium flow battery.
Fig. 2 is a SEM sectional structure view of the porous separators prepared in comparative example 1 and example 1.
Detailed Description
[ preparation method of ion-conducting porous separator for all-vanadium redox flow battery ]
As described above, the invention provides a preparation method of an ion-conducting porous membrane for an all-vanadium redox flow battery, comprising the following steps:
mixing organic polymer resin serving as a raw material with a pore-foaming agent and a surfactant to prepare a membrane casting solution, and preparing the ion-conducting porous membrane for the all-vanadium redox flow battery by an immersion precipitation phase conversion method.
In a preferred embodiment of the present invention, the preparation method comprises the steps of:
(1) dissolving organic polymer resin, a pore-forming agent and a surfactant in an organic solvent to obtain a mixed solution, namely a membrane casting solution;
(2) and (2) coating the casting solution obtained in the step (1) on the surface of a base material, standing, and then immersing into a coagulating bath for solidification to prepare the ion-conducting porous diaphragm for the all-vanadium redox flow battery.
In a preferred embodiment of the present invention, in step (1), the mixing temperature of the mixed solution, i.e., the preparation temperature of the membrane casting solution, is not specifically limited, and those skilled in the art can understand that it is required to completely mix the organic polymer resin, the porogen and the surfactant, and ensure that the mixing time is not too long, so as to improve the preparation efficiency of the porous membrane; preferably, the temperature for mixing the mixed solution is 50-100 ℃, and at the temperature, after 6-10 hours, the organic polymer resin, the pore-forming agent and the surfactant can be completely dissolved in the organic solvent, and a uniform and stable mixed solution can be formed; it will be understood by those skilled in the art that the manner of mixing is not particularly limited, and may be ultrasonic mixing, magnetic stirring mixing, mechanical stirring mixing, etc., as long as the mixed solution can be prepared.
In a preferred embodiment of the present invention, in step (1), the mixing ratio of the organic polymer resin, the pore-forming agent and the surfactant in the membrane casting solution is not specifically limited, and it satisfies that the prepared mixed solution, that is, the ion-conducting porous membrane for the all-vanadium redox flow battery of the present invention can be prepared and obtained after the membrane casting solution is solidified by a coagulation bath. Preferably, the mass concentration of the organic polymer resin in the membrane casting solution is 10-50 wt%, the mass concentration of the pore-forming agent is 1-10 wt%, and the mass concentration of the surfactant is greater than 0 and less than or equal to 40 wt%. Also preferably, the mass concentration of the organic polymer resin in the membrane casting solution is 20-40 wt%, the mass concentration of the pore-forming agent is 1.5-8 wt%, and the mass concentration of the surfactant is 0.5-20 wt%. Further preferably, the mass concentration of the organic polymer resin in the membrane casting solution is 30-35 wt%, the mass concentration of the pore-forming agent is 2-5 wt%, and the mass concentration of the surfactant is 1-10 wt%. The organic polymer resin, the pore-forming agent and the surfactant with the mass concentration are selected on one hand because the casting solution containing the polymer with the high mass concentration can be used for preparing the porous diaphragm with high selectivity and can also ensure high mechanical performance; on the other hand, the fine adjustment of the pores is realized by controlling the dosage of the surfactant, so that the porous membrane reaches the balance of ion selectivity and proton conduction.
In a preferred embodiment of the present invention, in the step (1), the molecular weight and the polymerization degree of the organic polymer resin are not particularly limited, and may be any molecular weight and polymerization degree which are known to those skilled in the art to be soluble in the organic solvent. The selection of the organic polymer resin is not particularly limited, and any organic polymer resin can be used for preparing the porous diaphragm, and the purpose of using the porous diaphragm for the all-vanadium redox flow battery can be achieved. Preferably, the molecular weight of the organic polymer resin is greater than or equal to 70 ten thousand g/mol; the organic polymer resin in the range is selected because the organic polymer resin has better mechanical property, and can meet the use requirement of the porous diaphragm for the all-vanadium liquid flow; preferably, the organic polymer resin is at least one selected from polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyetherketoneketone, polytetrafluoroethylene, polybenzimidazole, and polyvinylpyridine.
In a preferred embodiment of the present invention, in step (1), the porogen is not specifically limited, and can be used in combination with an organic polymer resin to achieve a porogen effect. Preferably, the porogenic agent is selected from a high molecular porogenic agent or a small molecular porogenic agent; the macromolecule pore-foaming agent is selected from any macromolecule pore-foaming agent which can be matched with organic macromolecule resin and used by persons skilled in the art. Preferably, the polymeric porogen is one or more selected from polyvinylpyrrolidone (PVP), polyethylene glycol or polyvinyl alcohol. The small molecular pore-forming agent is selected from any small molecular pore-forming agent which can be matched with organic polymer resin and is known by the technical personnel in the field. Preferably, the small molecule pore-forming agent is selected from one or more than two of lithium chloride, lithium bromide or aluminum chloride.
In a preferred embodiment of the present invention, in step (1), the surfactant is not specifically limited, and can be used in combination with an organic polymer resin, and can be adsorbed on the surface of the prepared porous membrane, so as to achieve that a high-valence cation (such as vanadium ion) is well selected by electrostatic repulsion, and moreover, the surfactant can change the exchange rate of a solvent and a non-solvent of the porous membrane during a membrane forming process, so as to influence the final structure of the porous membrane; preferably, the surfactant is selected from cationic surfactants and/or anionic surfactants; still preferably, the cationic surfactant is selected from one or two quaternary ammonium salts such as cetyltrimethylammonium chloride, dodecyldimethylbenzylammonium bromide and the like; the anionic surfactant is selected from one or two sulfonates such as sodium dodecyl benzene sulfonate and sodium dodecyl sulfonate.
In a preferred embodiment of the present invention, in step (1), the organic solvent is not specifically limited, and may be any organic solvent known to those skilled in the art that can dissolve the organic polymer resin, the porogen and the surfactant and can prepare a uniform and stable mixed solution, and preferably, the organic solvent is selected from one or more of Dimethylformamide (DMF), Dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) and Dimethylsulfoxide (DMSO).
In a preferred embodiment of the present invention, in the step (2), the substrate may be any substrate with a flat or uneven surface, which is known to those skilled in the art to be able to prepare the separator, and the size and shape of the substrate are not particularly limited, and may be reasonably selected according to the size and shape of the separator to be prepared, and the substrate with a suitable size and shape may be selected by those skilled in the art. Preferably, the substrate is a glass plate, a stainless steel plate or a nonwoven fabric.
In a preferred embodiment of the present invention, in the step (2), the coating manner is not particularly limited, and any coating manner known to those skilled in the art may be used to prepare the porous separator, and preferably, the coating manner may be at least one of roll coating, knife coating, spray coating, dipping, and the like. As an example, the casting solution is coated on a substrate having a flat surface by using a coating blade having a thickness of 50 to 500 μm.
In a preferred embodiment of the present invention, in step (2), the substrate coated with the casting solution is left standing in an air atmosphere at a suitable temperature (i.e., a temperature lower than the boiling point of each component in the casting solution, preferably lower than the boiling point of the organic solvent in the casting solution, for example, the temperature may be 0 to 100 ℃) in order to completely volatilize the organic solvent in the casting solution as much as possible so as to facilitate the curing thereof in the coagulation bath. It will be understood by those skilled in the art that the time for the standing is not particularly limited, and is related to the coating thickness of the casting solution on the surface of the substrate and the ambient temperature for the standing, and the time for the standing is prolonged when the coating thickness of the casting solution on the surface of the substrate is thicker and the ambient temperature for the standing is lower, and the time for the standing is shortened when the coating thickness of the casting solution on the surface of the substrate is thinner and the ambient temperature for the standing is higher; preferably, the standing time is 1-30 min.
In a preferred embodiment of the present invention, in step (2), the thickness of the casting solution on the surface of the substrate is not specifically limited, and it can be understood by those skilled in the art that the thickness of the casting solution is related to the thickness of the porous membrane to be prepared, and if the thickness of the porous membrane to be prepared is thick, the thickness of the casting solution on the surface of the substrate is also thick, and similarly, if the thickness of the porous membrane to be prepared is thin, the thickness of the casting solution on the surface of the substrate is also thin; as will be appreciated by those skilled in the art, the casting solution will vary in thickness upon standing and curing on the surface of the substrate. Preferably, the thickness of the membrane casting solution on the surface of the substrate is 50-500 μm, and more preferably 150-300 μm.
In a preferred embodiment of the present invention, in step (2), the selection of the coagulation bath is not particularly limited, and any liquid known to those skilled in the art in which the solidification of the casting solution may occur may be used. Preferably, the coagulation bath is selected from one or more of water, ethanol, propanol, butanol, isopropanol, methanol, acetone, DMF or DMAC. Illustratively, the coagulation bath is a mixed solution of water and DMF; or a mixed solution of water and DMAC, or ethanol, or water, etc.
In a preferred embodiment of the present invention, in step (2), the curing temperature and time in the coagulation bath are not particularly limited, and those skilled in the art can know the temperature and time for curing the casting solution, and the prepared porous membrane for the all-vanadium flow battery is ensured to achieve the purpose of use. Preferably, the curing time is 1-60 min.
[ ion-conductive porous separator for all-vanadium redox flow battery ]
As described above, the present invention provides an ion-conducting porous separator for an all-vanadium redox flow battery, which is prepared by the above method.
In a preferred embodiment of the present invention, the porous membrane is obtained by controlling a low proton conductive porous membrane prepared from a casting solution containing a polymer with high quality concentration by adding a surfactant, and has both high ion conductivity and good ion selectivity, and exhibits excellent electrochemical performance. Meanwhile, the electrochemical performance of the porous diaphragm can be controllably adjusted by adjusting the dosage of the surfactant.
In a preferred embodiment of the present invention, the thickness, pore size and porosity of the porous separator are not particularly limited, and may be selected from the use environment thereof and meet the use purpose thereof as a porous separator for an all-vanadium flow battery. Preferably, the thickness of the porous membrane is 50-500 μm, and further preferably, the thickness of the porous membrane is 150-300 μm. Preferably, the pore size of the porous separator is 0.5-100nm, and the porosity of the porous separator is 20-80%.
[ use of ion-conductive porous separator for all-vanadium flow battery ]
As previously mentioned, the present invention provides the use of an ion-conducting porous separator for an all vanadium flow battery.
[ all vanadium redox flow battery ]
As previously described, the present invention provides an all vanadium flow battery comprising the above porous separator.
In a preferable scheme of the invention, the coulombic efficiency of the all-vanadium redox flow battery is more than 89%, the voltage efficiency is more than 80%, and the energy efficiency is more than 75%.
In a preferred embodiment of the invention, the charging voltage of the all-vanadium redox flow battery is lower than 1.4V, and the discharging voltage is higher than 1.3V.
The voltage efficiency refers to a ratio of an average voltage of a discharge voltage to an average voltage of a charge voltage.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that various changes or modifications can be made by those skilled in the art after reading the disclosure of the present invention, and such equivalents also fall within the scope of the invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
Ultrasonically dispersing 0.5g of PVP and 0.4g of hexadecyltrimethylammonium chloride in 16mL of dimethylacetamide to form a uniform solution, then adding 8.4g of polyvinylidene fluoride, heating and stirring at 80 ℃ to prepare a uniform polymer solution, namely a casting solution, adopting a mixed solution of ethanol and water (the volume ratio is 1:1) as a coagulating bath, adopting a manual scraper, controlling the thickness of a membrane formed by the casting solution on a glass plate to be 250 mu m, evaporating the membrane formed by the casting solution in air for 10min, then immersing the membrane in the coagulating bath for curing for 30min, and placing the prepared PVDF porous membrane in water for storage.
The mass concentration of the organic polymer resin in the mixed solution is 34.6 wt%, the mass concentration of the pore-forming agent in the mixed solution is 2.05 wt%, and the mass concentration of the cationic surfactant in the mixed solution is 1.6 wt%.
The PVDF porous membrane prepared by the method is assembled into the all-vanadium redox flow battery, wherein the catalyst layer is an activated carbon felt, and the bipolar plateIs a graphite plate, and the effective area of the PVDF porous diaphragm is 4cm-2Current density of 80mA cm-2The concentration of vanadium ions in the electrolyte is 1.5 mol.L-1The concentration of sulfuric acid is 3 mol.L-1。
Fig. 1 is a charge and discharge curve of the porous separator prepared in example 1 in an all vanadium flow battery. As can be seen from fig. 1, the initial charge voltage of the cell assembled with the porous separator is lower than 1.38V and the initial discharge voltage is higher than 1.4V, indicating that the porous separator has good proton conductivity, so that the assembled cell has a weak polarization phenomenon.
The coulombic efficiency of the all-vanadium redox flow battery assembled by the PVDF porous diaphragm is 94%, the voltage efficiency is 80.2%, and the energy efficiency is 75.4%.
Example 2
The other conditions were the same as in example 1 except that the mass of cetyltrimethylammonium chloride was 0.6 g.
The mass concentration of the organic polymer resin in the mixed solution is 34.3 wt%, the mass concentration of the pore-forming agent in the mixed solution is 2.04 wt%, and the mass concentration of the cationic surfactant in the mixed solution is 2.45 wt%.
The test conditions were the same as in example 1, and the results were: the coulombic efficiency was 93.8%, the voltage efficiency was 85.2%, and the energy efficiency was 80%.
Example 3
The other conditions were the same as in example 1 except that the mass of cetyltrimethylammonium chloride was 0.8 g.
The mass concentration of the organic polymer resin in the mixed solution is 34 wt%, the mass concentration of the pore-forming agent in the mixed solution is 2.02 wt%, and the mass concentration of the cationic surfactant in the mixed solution is 3.23 wt%.
The test conditions were the same as in example 1, and the results were: the coulombic efficiency was 89.6%, the voltage efficiency was 83.7%, and the energy efficiency was 75%.
Comparative example 1
Ultrasonically dispersing 0.5g of PVP in 16mL of dimethylacetamide to form a uniform solution, then adding 8.4g of polyvinylidene fluoride, heating and stirring at 80 ℃ to prepare a uniform polymer solution, namely a casting solution, adopting a mixed solution of ethanol and water (the volume ratio is 1:1) as a coagulating bath, adopting a manual scraper, controlling the thickness of a film formed by the casting solution on a glass plate to be 250 mu m, evaporating the film formed by the casting solution in air for 10min, then immersing the film in the coagulating bath for curing for 30min, and storing the prepared PVDF porous diaphragm in water for later use.
The mass concentration of the organic polymer resin in the mixed solution is 35 wt%, the mass concentration of the pore-forming agent in the mixed solution is 2.09 wt%, and the mass concentration of the surfactant in the mixed solution is 0 wt%.
The PVDF porous membrane prepared by the method is assembled into an all-vanadium redox flow battery, wherein a catalyst layer is an activated carbon felt, a bipolar plate is a graphite plate, and the effective area of the PVDF porous membrane is 4cm-2Current density of 80mA cm-2The concentration of vanadium ions in the electrolyte is 1.5 mol.L-1The concentration of sulfuric acid is 3 mol.L-1。
The assembled all-vanadium redox flow battery cannot be subjected to charge and discharge tests due to large resistance.
Fig. 2 is a SEM sectional structure view of the porous separators prepared in comparative example 1 and example 1. As can be seen from fig. 2, the porous separator prepared in example 1 has an increased pore size (as shown in fig. 2 b) after the addition of the surfactant, compared to the pore size (as shown in fig. 2 a) of the porous separator prepared in comparative example 1, and thus facilitates the proton transport of the porous separator.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for preparing an ion-conducting porous separator, comprising the steps of:
(1) dissolving organic polymer resin, a pore-forming agent and a surfactant in an organic solvent to obtain a mixed solution, namely a membrane casting solution; the mass concentration of the organic polymer resin in the membrane casting solution is 30-35 wt%, the mass concentration of the pore-forming agent is 2-5 wt%, and the mass concentration of the surfactant is 1-10 wt%;
(2) coating the casting solution obtained in the step (1) on the surface of a base material, standing, and then immersing into a coagulating bath for curing to obtain the ion-conducting porous diaphragm;
the pore-foaming agent is selected from a high molecular pore-foaming agent or a small molecular pore-foaming agent; the macromolecule pore-foaming agent is selected from one or more than two of polyethylene glycol or polyvinyl alcohol, and the micromolecule pore-foaming agent is selected from one or more than two of lithium chloride, lithium bromide or aluminum chloride.
2. The production method according to claim 1, wherein the molecular weight of the organic polymer resin is 70 ten thousand g/mol or more; the organic polymer resin is at least one selected from polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyether ketone, polytetrafluoroethylene, polybenzimidazole or polyvinyl pyridine.
3. The method according to claim 1, wherein the surfactant is selected from a cationic surfactant and/or an anionic surfactant; the cationic surfactant is selected from one or two of hexadecyl trimethyl ammonium chloride and dodecyl dimethyl benzyl ammonium bromide; the anionic surfactant is selected from one or two of sodium dodecyl benzene sulfonate and sodium dodecyl sulfonate.
4. The method according to claim 1, wherein the organic solvent is one or more selected from Dimethylformamide (DMF), Dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and Dimethylsulfoxide (DMSO).
5. The method according to claim 1, wherein in the step (2), the coagulation bath is one or more selected from water, ethanol, propanol, butanol, isopropanol, methanol, acetone, DMF, and DMAC.
6. The production method according to any one of claims 1 to 5, wherein in the step (2), the curing time is 1 to 60 min.
7. An ion-conducting porous separator, characterized in that it is prepared by the process according to any one of claims 1 to 6.
8. The porous separator according to claim 7, wherein the thickness of the porous separator is 50 to 500 μm, the pore size of the porous separator is 0.5 to 100nm, and the porosity of the porous separator is 20 to 80%.
9. Use of the porous separator of claim 7 or 8 in an all vanadium flow battery.
10. An all vanadium flow battery comprising the porous separator of claim 7 or 8.
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