CN112448008A

CN112448008A - Composite membrane with ultrathin functional layer for flow battery and preparation and application thereof

Info

Publication number: CN112448008A
Application number: CN201910802763.0A
Authority: CN
Inventors: 李先锋; 戴卿; 张华民
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-08-28
Filing date: 2019-08-28
Publication date: 2021-03-05
Anticipated expiration: 2039-08-28
Also published as: CN112448008B

Abstract

The invention relates to a composite membrane with an ultrathin functional layer for a flow battery, and preparation and application thereof. The composite membrane is a porous base membrane prepared by blending hydrophobic polymer resin and hydrophilic polymer resin through an immersion precipitation phase inversion method, the formed porous base membrane consists of a skin layer and a macroporous support layer, and then a functional layer with nano-scale thickness is grown in situ on the surface of the skin layer of the base membrane or the surfaces of two sides of the base membrane through liquid-liquid phase interface polymerization reaction. The prepared composite membrane has an ultrathin and compact functional layer, so that the composite membrane has ultrahigh ionic conductivity and ionic selectivity. The performance of the all-vanadium redox flow battery assembled by the composite film prepared by the method breaks through the bottleneck, and the ultrahigh output power is achieved.

Description

Composite membrane with ultrathin functional layer for flow battery and preparation and application thereof

Technical Field

The present invention relates to an ion-conducting membrane for a flow battery.

Background

The flow battery is a large-scale energy storage technology for realizing the large-scale application of renewable energy sources, and has the advantages of flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety, environmental protection, low maintenance cost and the like. The full-vanadium redox flow battery (VFB) is the most mature technology, and has the advantages of high safety, large output power and energy storage capacity scale, high response speed, good charge-discharge cycle performance, long service life (the service life is more than 15 years), high cost performance and the like. However, the high cost of the all-vanadium redox flow battery limits the further industrialization of the all-vanadium redox flow battery, and in order to reduce the manufacturing cost of the all-vanadium redox flow battery, the material cost of the galvanic pile must be reduced by increasing the output power of the all-vanadium redox flow battery.

The membrane is a key component of the all-vanadium redox flow battery, plays a role in blocking active substances of a positive electrode and a negative electrode and simultaneously transmitting other ions to enable the battery to form a loop, and the commercially used perfluorinated sulfonic acid ion exchange membrane is represented by a Nafion series membrane produced by DuPont, has high chemical stability, but is expensive, poor in ion selectivity and low in ion conductivity, and limits the all-vanadium redox flow battery in cost and performance. The porous ion conduction membrane has a highly-through pore channel structure, is favorable for ion transfer, has flexible structural design, has high stability, and can greatly improve the performance of the all-vanadium redox flow battery.

However, the porous ion-conducting membrane prepared by the conventional phase inversion method still has difficulty in meeting the requirement of high current density, and one of the important reasons is that the functional layer (skin layer) of the porous membrane and the support layer are formed at the same step, and in order to improve the selectivity of the porous membrane, the skin layer must be denser, but this also results in the reduction of the porosity of the support layer and the deterioration of the pore passage connectivity, thereby improving the resistance of the whole membrane, increasing the ohmic polarization of the corresponding VFB, and the battery cannot maintain high efficiency at high output. Due to the above performance bottlenecks of porous membranes prepared by phase inversion methods in the prior art, VFB batteries with both high output power and high efficiency have not been realized.

Disclosure of Invention

The invention aims to provide an ultrahigh-performance composite membrane and a preparation method thereof aiming at the problem of dependency between ion selectivity and conductivity of a VFB ion conductive membrane. The composite membrane takes a polymer porous membrane as a substrate, and a compact and ultrathin functional layer is generated in situ on the surface of the substrate by utilizing an interface polymerization method. The preparation method of the composite membrane is simple, and the ion selectivity and conductivity are excellent.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:

a composite membrane with an ultrathin functional layer for a flow battery is a porous base membrane prepared by blending hydrophobic polymer resin and hydrophilic polymer resin through an immersion precipitation phase inversion method, the formed porous base membrane consists of a skin layer and a macroporous support layer, and then a functional layer with a nano-scale thickness is grown in situ on the surface of the skin layer of the base membrane or the surfaces of two sides of the membrane through liquid-liquid phase interfacial polymerization reaction, wherein the thickness of the functional layer is 50-500nm, and preferably 100-200 nm. The pore diameter of the basement membrane skin layer is 1-100nm, preferably 5-20 nm; the surface porosity of the skin layer is calculated by an SEM image and is 5-40%, preferably 10-20%, and the surface porosity is the ratio of the cross section area of the surface pore canal in the surface area (known by an SEI image); the thickness of the skin layer is 50nm-1 μm, preferably 100nm-500 nm; the pore diameter of the macroporous support layer is 50nm-10 μm, preferably 50nm-200 nm; the surface porosity of the macroporous support layer is 20-80%, preferably 50-80%; the thickness of the macroporous support layer is 80-150 μm, preferably 90-110 μm

The overall film thickness is 80 to 150. mu.m, preferably 90 to 110 μm. The overall porosity of the membrane is between 40% and 70%, preferably between 50% and 60%.

Fig. 3 is a schematic diagram of a composite film structure, which is divided into a base film and a functional layer, wherein the functional layer is formed by polymer film folds, and the lower part of the bulge is separated from the base film to form a cavity, which is beneficial to reducing mass transfer resistance at the interface of the functional layer/the base film. The depressions are in contact with the base film to prevent the film from falling off the base film.

The functional layer is a dense polymer film with folds stacked to form a stacked layer, and the polymer film with folds forms a cavity with the surface of the base film in the stacking process.

Along the vertical direction of the surface of the base film, the height from the surface of the base film to the lower part of the wrinkle bulge (the bottom of the concave part of the functional layer wrinkle close to one side of the base film) is the cavity height, and the cavity height is 20-500 nm;

the contact area of the functional layer and the surface of the base film accounts for 50-90% of the total area of the surface of the base film;

the thickness of the polyamide film (i.e. the polymer film) is 5-60 nm.

The hydrophobic polymer resin is one or more of polyether sulfone, polysulfone, polyether ketone, polytetrafluoroethylene, polyvinylidene fluoride or polystyrene; preferably one or two of polyether sulfone and polysulfone; the hydrophilic polymer resin is one or more than two of sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone, sulfonated polybenzimidazole, polyvinylpyrrolidone, polybenzimidazole or polyethylene glycol, and the sulfonation degree of the sulfonated polymer is 20-80%; one or two of sulfonated polyether ketone and polyvinylpyrrolidone are preferred, and the sulfonation degree is preferably 40-60%. The mass ratio of the hydrophobic polymer resin to the hydrophilic polymer resin is 0.5: 1 to 9: 1; preferably, 7: 3 to 9: 1;

the functional layer with the nanometer thickness is grown in situ on the surface of the base film by utilizing liquid-liquid phase interfacial polymerization reaction, two active substances capable of mutually reacting and polymerizing are respectively dissolved in a water phase solvent and an oil phase solvent, the two active substances can be polymerized by the polycondensation reaction of acyl chloride and amino or acyl chloride and hydroxyl to prepare a water phase solution and an oil phase solution, and the base film is sequentially soaked in the two solutions so that the functional layer with the nanometer thickness is generated in situ on the surface of the base film.

The active substances in the water phase and the oil phase are two types of monomers which can mutually react and polymerize;

the water phase active substance is one or more than two of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, resorcinol and triethanolamine;

the oil phase active substance is acyl chloride monomer, and the acyl chloride monomer is one or more than two of 1,3, 5-trimethyl benzoyl chloride, isophthaloyl dichloride and cyclohexane-1, 3, 5-tricarbonyl dichloride; preference is given to 1,3, 5-trimethylbenzenecarbonyl chloride

The oily solvent is one or more selected from n-hexane, n-heptane, n-octane, n-nonane, n-decane, chloroform, benzene, toluene and xylene;

the water phase solvent is selected from one or more of water, DMAc, DMF and acetonitrile.

The composite membrane is prepared by the following steps:

(1) dissolving hydrophobic polymer resin and hydrophilic polymer resin in an organic solvent, and stirring to obtain a uniform solution; the solids content is from 15% by weight to 40% by weight, preferably from 25% by weight to 30% by weight.

(2) And (2) flatly paving the solution prepared in the step (1) on a substrate, and preparing a porous base membrane by using an immersion precipitation phase inversion method.

(3) Dissolving the water phase active substance in water to obtain 0.01-10 wt./v.% water phase solution; preferably 0.5-8 wt./v.%; dissolving the oil phase active substance in an oily solvent to obtain 0.01-1 wt./v.% oil phase solution, preferably 0.1-0.8 wt./v.%;

(4) immersing the porous base membrane in the aqueous solution, soaking for 30s-10min, preferably 1-3min, taking out, wiping the surfaces of the two sides of the membrane, or sticking one side of the macroporous supporting layer of the membrane on a glass sheet, and wiping one side of the outward skin layer (the surface of the side far away from the glass sheet) of the membrane by using a sponge stick, filter paper or mirror wiping paper; and (3) putting the film with the surfaces on both sides wiped dry or the film with one side wiped dry and the glass sheet into an oil phase solution, soaking for 5s-30min, preferably 1-3min, taking out to obtain a composite film with a functional layer with nano-scale thickness in-situ grown on the surface of the skin layer of the base film or the surfaces on both sides of the film by using liquid-liquid phase interfacial polymerization reaction, and storing the film in water for later use.

The immersion precipitation phase inversion method comprises the following specific steps:

volatilizing the substrate paved with the film preparation solution in air for 0-2 minutes, and then quickly immersing the substrate into a poor solvent of resin for curing for 1-60 minutes to form a porous base film;

the poor solvent is one or more than two of water, ethanol and isopropanol.

The composite membrane is applied to the all-vanadium redox flow battery.

Through a large amount of researches, the hydrophilic polymer of the base membrane is added too much, so that the surface aperture is too large, and the selectivity of the generated separation layer is reduced. The decrease of the hydrophilic polymer causes the decrease of the conductivity of the base membrane and the increase of the overall resistance of the composite membrane. The hydrophobic porous base membrane causes the affinity of the separation layer and the base membrane to be reduced, the stability of the separation layer to be reduced, and the selectivity to be reduced. Hydrophilic polymers with appropriate surface pore size are most advantageous for forming a separation layer with few defects.

The increased acidity of the base membrane leads to a lower degree of crosslinking of the separation layer and a lower selectivity, but at the same time leads to an increased conductivity, so that there is an optimum value where too low acidity of the base membrane leads to a high selectivity and a low conductivity; too strong acidity results in low selectivity and high conductivity. The acidity of the base film can be achieved by adjusting the sulfonation degree of SPEEK, the ratio of SPEEK.

The surface recombination of the skin layer is best, the selectivity and the conductivity are both greatly improved, and the conductivity is reduced although the selectivity is high in the surface recombination of the two sides; and the selectivity is lower due to the recombination on the surface of the supporting layer.

The invention further provides an application of the composite membrane in an all-vanadium redox flow battery.

The invention has the following beneficial results:

1. compared with the composite membrane prepared by the prior art, the composite membrane prepared by the interfacial polymerization method has the advantages that the thickness of the generated high polymer membrane is very thin because the area of a phase interface is narrow, and the generated thin membrane can inhibit the diffusion of active substances and inhibit the generation of new thin membranes. Further, the active material is preferentially diffused through a path having a small diffusion resistance by using a concentration difference as a driving force, but when there is a defect on the surface of the film, the active material is mainly diffused to the defect, and thus the formed film has few defects. In addition, the ultrathin functional layer generated in situ by an interfacial polymerization method has a compact cross-linking structure, cross-linked molecular chains are stacked to form a channel with the diameter smaller than 1nm, the diameter of the channel is smaller than that of hydrated vanadium ions, the hydrated vanadium ions can be effectively prevented from passing through the channel, accurate screening is realized, and simultaneously, due to the existence of intermolecular channels and the very thin thickness of the functional layer, protons can quickly pass through the functional layer, so that the interface polymerization functional layer brings high ion selectivity, and only very small surface resistance is improved, the prepared composite membrane with the ultrathin functional layer structurally has the characteristics of high ion selectivity and high conductivity, and the problem of contradiction between the ion selectivity and the conductivity of the ion conduction membrane for VFB is fundamentally solved.

2. The functional layer formed by interfacial polymerization has a highly cross-linked structure, so that the functional layer has high chemical stability and brings stable cycle performance to VFB.

3. The functional layer and the base film of the composite film are formed respectively and can be independently regulated and controlled, the functional layer with high selectivity and low surface resistance is combined with the support layer with high conductivity, the performance bottleneck of the porous film prepared by a one-step phase conversion method is hopefully broken, and the VFB battery with both high output power and high energy efficiency is realized.

Drawings

FIG. 1(A) surface SEM picture of PES/SPEEK porous base film; (B) is a surface SEM picture of example 1.

FIG. 2(A) is a cross-sectional SEM photograph of the composite membrane of example 1; (B) example 1 cross-sectional TEM image of composite membrane.

FIG. 3 is a schematic view of a composite membrane structure according to the present invention.

FIG. 4 is a comparison of vanadium ion permeation rates of the composite membrane of example 1, the membrane of comparative example 1, and the base membrane.

FIG. 5 is a comparison of cell efficiencies (current density of 80 mAcm) for the base film, comparative example 1 film, comparative example 2 film and the composite film of example 1^-2)。

Figure 6 is a comparison of the different current density cell efficiencies of the composite membrane of example 1 and the membrane of comparative example 1.

FIG. 7 is a cycle stability test (current density 260 mAcm) for the composite membrane of example 1^-2)。

FIG. 8 is a capacity fade rate test (current density 80 mAcm) for the composite membrane of example 1^-2)。

Fig. 9 shows a film forming mechanism of a functional layer of the composite film prepared according to the present invention.

Detailed Description

The following examples are further illustrative of the present invention and are not intended to limit the scope of the present invention.

Comparative example 1

Assembled using Nafion 115 membrane manufactured by dupontThe vanadium flow battery is used as a comparative example, wherein the catalytic layer is activated carbon felt, the bipolar plate is a graphite plate, and the effective area of the membrane is 48cm²Current density of 80mA cm^-2The concentration of vanadium ions in the electrolyte is 1.50mol L^-1，H₂SO₄The concentration is 3mol L^-1. The coulombic efficiency of the all-vanadium redox flow battery assembled by the commercial Nafion 115 membrane is 93.38%, the voltage efficiency is 88.30%, and the energy efficiency is 82.45%.

Comparative example 2 (PA-PES/SPEEK composite film prepared by spray coating method)

The preparation method of the PES/SPEEK porous base membrane is completely the same as that of the example 1, and a layer of Nafion isopropanol solution is sprayed on the PES/SPEEK porous base membrane by using a spraying method to form an ultrathin functional layer. 4.8008g of sulfonated polyether ether ketone (SPEEK) and 19.1954g of polyether sulfone (PES) were dissolved in 56.1924g of DMAc, stirred at 25 ℃ for 48 hours, left to stand for 24 hours, and stored in water. Formic acid was used to dissolve 1 wt.% Polyamide (PA) and a spray gun was used to spray a 1 wt.% PA solution onto PES/SPEEK. The spraying amount of the PA solution is respectively 0mL, 0.6mL, 1.2mL and 2.4mL, the thickness of the functional layer is respectively 0, 500-nm, 900-nm and 2-mum, and along with the increase of the PA proportion, the coulombic efficiency of the battery equipped with the corresponding composite membrane is sequentially increased and is respectively equal to 79.2%, 88.5%, 98.4% and 98.6%; the voltage efficiency decreases in sequence, equal to 89.2%, 85.7%, 80.6% and 78.6%, respectively; the energy efficiencies are equal to 70.5%, 75.8%, 79.3% and 77.5%, respectively.

Example 1

4.8008g SPEEK (degree of sulfonation 60%) and 19.1954g PES were dissolved in 56.1924g DMAc, stirred at 25 ℃ for 48 hours, left to stand for 24 hours, the polymer solution was spread on a glass plate, the glass plate was quickly immersed in water, cured to a film, and stored in water. 4.2019g of m-phenylenediamine is dissolved in 210mL of deionized water, the mixture is stirred for 10min until the m-phenylenediamine is fully dissolved, 0.1504g of 1,3, 5-trimethylbenzene acyl chloride is dissolved in 100mL of n-hexane, and the mixture is subjected to ultrasonic treatment for 5min to fully dissolve the m-phenylenediamine. Soaking a PES/SPEEK porous membrane in a solution of m-phenylenediamine for 3min, taking out the base membrane, attaching a support layer with one side facing upwards on a glass sheet with the same size as the membrane, wiping the solution on the surface of the membrane by using a piece of mirror wiping paper, pouring a normal hexane solution of 1,3, 5-trimethylbenzene acyl chloride into a culture dish, soaking the membrane and the glass sheet in the solution, keeping for 1min, taking out, and storing in water. Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm.

As shown in fig. 2A, as seen from the cross section of example 1, example 1 has a base film having a bicontinuous structure and an ultra-thin functional layer, and both the pore portion and the polymer portion of the base film having the bicontinuous structure are continuously penetrated, thereby having both excellent ion conductivity and mechanical strength. The ultrathin functional layer has a short mass transfer path and low proton conduction resistance. It can be seen from TEM (fig. 2B) that the functional layer has an uneven morphology, with a maximum thickness of about 180nm and a minimum thickness of about 100nm, corresponding to the surface SEM image, and that the presence of many cavities in the functional layer is beneficial to reducing the mass transfer resistance at the functional layer/base film interface. The height of the cavity is 30-70nm, and the contact area ratio of the functional layer and the surface of the base film is 70%.

Fig. 3 is a schematic view of a composite film structure, which is divided into a base film and a functional layer, wherein the functional layer is formed by polymer film folds, the lower part of a protrusion is separated from the base film to form a cavity, and a recess is in contact with the base film to prevent the film from falling off the base film.

As shown in fig. 4, the vanadium ion permeation rate of example 1 is greatly reduced compared to the base film and comparative example 1, which indicates that example 1 has good vanadium resistance, and compared to the base film, example 1 only polymerizes a functional layer of 100-180nm on the surface of the base film, and the result shows that the vanadium resistance of example 1 is greatly improved, which indicates that the 100-180nm functional layer has excellent vanadium resistance.

As shown in fig. 5, compared to the base films (coulombic efficiency (CE) ═ 61.8%, and Voltage Efficiency (VE) ═ 92.8%), CE of example 1 increased greatly to 99.2%, while VE did not decrease to 92.8%, indicating that the ultra-thin functional layer can bring ultra-high vanadium-blocking ability to the film without significantly increasing the sheet resistance of the film, and the energy efficiency (EE ═ 92.1%) of example 1 is much higher than that of the commercial Nafion 115 film (comparative example 1) (EE ═ 82.5%) and the composite film prepared by spray coating (comparative example 2) (EE ═ 86.5%) in combination of high vanadium-blocking performance and low sheet resistance.

As shown in fig. 6, as the current density was gradually increased, the polarization of the battery was gradually increased, resulting in a decrease in voltage efficiency, and since the film of example 1 had a lower sheet resistance, the internal resistance of the battery was smaller than that of comparative example 1, the polarization of the battery of example 1 was smaller than that of comparative example 1, and the current density of example 1 could reach 260mAcm cm on the premise that the energy efficiency was more than 80%^-2。

As shown in FIG. 7, the battery of example 1 was able to operate at 260mAcm^-2The current density is stably cycled for 1000 times, which shows that the stability is excellent.

As shown in fig. 8, the capacity retention ratio of example 1 is significantly improved compared to that of comparative example 1, because the composite film of example 1 has excellent vanadium resistance, and can efficiently prevent vanadium ions of the positive and negative electrodes from being connected with each other.

Example 2

The concentration of 1,3, 5-trimethylbenzoyl chloride was changed to 0.8 wt./v.% as in example 1, and 0.8012g of 1,3, 5-trimethylbenzoyl chloride was dissolved in 100mL of n-hexane, and the other conditions were the same as in example 1. The functional layer is about 120 (thinnest) to 340 (thickest) nm thick. 80mA cm of assembled all-vanadium flow battery^-2The cell efficiency was 97.6% CE, 92.8% VE, and 90.6% EE.

Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm.

The height of the cavity is 50-170nm, and the contact area ratio of the functional layer and the surface of the base film is 50%.

Example 3

In the same manner as in example 1, the organic polymer resin was changed to polybenzimidazole, and the casting solution had a solid content of 15%, and the other conditions were the same as in example 1. The thickness of the functional layer is 130 (thinnest part) to 200 (thickest part) nm. 80mA cm^-2The cell efficiency was 98.1% CE, 92.2% VE, and 90.4% EE. Parameters of a basement membrane: the pore diameter of the cortex is 10-30nm, the surface porosity of the cortex is 20%, and the thickness of the cortex is 150nmThe aperture of the macroporous support layer is 5-10 mu m, the surface porosity of the macroporous support layer is 60 percent, and the thickness of the macroporous support layer is 80 mu m. The height of the cavity is 30-70nm, and the contact area ratio of the functional layer and the surface of the base film is 80%.

Example 4 (oil phase monomer is isophthaloyl chloride)

The same procedure as in example 1 was repeated except that the oil phase active material was changed to isophthaloyl dichloride and the conditions were the same as in example 1. The thickness of the functional layer is 60-230nm and 80mA cm^-2The battery efficiency was CE 96.0%, VE 92.5%, EE 88.8%, and the capacity retention rate was 70% for 100 cycles. Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm. The thickness of the functional layer is 300nm-450nm, and the contact area ratio of the functional layer and the surface of the base film is 50% when the cavity height is 100 and 380 nm.

When the oil phase active substance is 1,3, 5-trimethylbenzene acyl chloride, compared with isophthaloyl dichloride, the prepared composite membrane has higher selectivity and higher coulombic efficiency, because the ultrathin functional layer generated in situ by an interfacial polymerization method has a compact cross-linked structure when the oil phase active substance is 1,3, 5-trimethylbenzene acyl chloride, cross-linked molecular chains are stacked to form a channel with the diameter less than 1nm, and the diameter of the channel is less than that of hydrated vanadium ions, so that water and vanadium ions can be more effectively blocked from passing through, and accurate screening is realized.

Example 5

In the same manner as in example 1, the active material in the water phase was changed to 9, 9-bis (4-aminophenyl) fluorene, 2.1052g of 9, 9-bis (4-aminophenyl) fluorene was dissolved in 210mL of deionized water, the soaking time in the water phase was changed to 10min, and the soaking time in the oil phase was changed to 10min, and the other conditions were the same as in example 1. The thickness of the functional layer is 40-100 nm. 80mA cm^-2The cell efficiency was CE 96.8%, VE 84.9%, and EE 82.2%. Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm. The thickness of the functional layer is 50-100nm, and the contact area ratio of the functional layer with the surface of the base film is 90% when the cavity height is 20-50 nm.

Example 6 (both sides composite functional layer)

As in example 1, the two side surfaces of the membrane were wiped dry without using a glass plate to shield either side surface, and a solution of 1,3, 5-trimethylbenzoyl chloride in hexane was poured into a petri dish, the membrane and the glass plate were immersed therein for 1min, and then taken out and stored in water to obtain a membrane having functional layers on both sides, the functional layer having a thickness of 100-180 nm. 80mA cm^-2The cell efficiency was 99.2% CE, 91.9% VE, and 91.2% EE. Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm. The thickness of the functional layer on one side of the base film skin layer is 100-180nm, and the contact area ratio of the functional layer and the base film surface is 70% when the cavity height is 20-80 nm; the thickness of the functional layer at one side of the support layer is 130-300nm, the height of the cavity is 50-120n m, and the contact area ratio of the functional layer and the surface of the base film is 60%.

Comparative example 3 (support layer side composite functional layer)

In the same manner as in example 1, the supporting layer side of the base film was faced upward, and the skin layer was faced downward and adhered to a glass sheet having the same size as the film, the solution on the surface of the film was wiped with a piece of mirror wiping paper, the n-hexane solution of 1,3, 5-trimethylbenzoyl chloride was poured into a petri dish, the film and the glass sheet were immersed together, and the solution was kept for 1min, and then taken out and stored in water to obtain a composite functional layer having a thickness of 100-. 80mA cm^-2The cell efficiency was 96.5% CE, 92.9% VE, and 89.6% EE. Parameters of a basement membrane: the aperture of the cortex is 5-20nm, the porosity of the surface of the cortex is 14%, the thickness of the cortex is 300nm, the aperture of the macroporous support layer is 50-200nm, the porosity of the surface of the macroporous support layer is 50%, and the thickness of the macroporous support layer is 105 μm. The thickness of the functional layer is 130-300nm, the height of the cavity is 50-120nm, and the contact area ratio of the functional layer and the surface of the base film is 60%.

The performance comparison of the examples 1 and 6 and the comparative example shows that after the functional layer is compounded on the surface of the skin layer of the porous base membrane, the selectivity and the conductivity of the membrane are greatly improved, the coulombic efficiency and the voltage efficiency of the battery are obviously improved, and although the selectivity is high, the conductivity is reduced in the compounding of the surfaces on two sides; and the selectivity is low due to the fact that the surface aperture of the supporting layer is too large (>50nm), which is not beneficial to forming a stable and compact functional layer, compared with example 1, the selectivity of the relatively loose functional layer is low, the CE is low, although the conductivity is improved, and VE is slightly improved, the overall efficiency is not as good as that of example 1, and EE is lower than that of example 1.

Comparative example 4 (vapor phase reforming method)

In comparison with example 1, the preparation method of the porous base film was replaced with vapor (humidity) phase inversion, and the glass plate was rapidly placed in an environment of 50 ℃ and 95% humidity and left to stand for 10min, otherwise the same as example 1, 80mA cm^-2The cell efficiency was 99.5% CE, 88.2% VE, and 87.8% EE. Parameters of a basement membrane: the spongy pore symmetrical membrane is only divided into a non-skin layer and a supporting layer, and the aperture of the spongy pore is 500 nm. The thickness of the functional layer is 140-200nm, the height of the cavity is 70-150nm, and the contact area ratio of the functional layer and the surface of the base film is 60%.

As can be seen from the comparison, the porous base membrane prepared by the immersion precipitation phase conversion method has larger difference in the microstructure of the functional layer compounded on the porous base membrane due to the difference in the structure of the base membrane compared with the base membrane prepared by the steam phase conversion method, and the steam phase conversion membrane has a honeycomb structure, and the pore channels in the membrane are not communicated, so that the mass transfer is not facilitated. The immersion precipitation phase conversion method is relatively compact in skin layer, but is very thin and small in pore size, the stability of an interface polymerization layer generated in situ on the surface of the interface polymerization layer is higher, the penetrating pore structure of the support layer is more favorable for proton transmission, and the coulomb efficiency is improved.

As shown in FIG. 1A, the PES/SPEEK porous basement membrane has a groove-shaped porous skin layer, and the surface is favorable for the diffusion of active substances in the basement membrane, so that the reaction at the interface is more uniform. As shown in FIG. 1B, the polyamide membrane grown on the surface of the porous base membrane by interfacial polymerization has a rough morphology with a high specific surface area, which is beneficial to mass transfer.

Since the region of the phase interface is narrow and the formed thin film suppresses diffusion of the active material and generation of a new thin film, the thickness of the formed polymer film is very thin. Further, since the active material is preferentially diffused through a path having a small diffusion resistance by using the concentration difference as a driving force, the active material is preferentially diffused to a defect having a small resistance, and thus the formed thin film has few defects.

The prepared composite membrane is applied to a flow battery, and in order to obtain an ion conduction membrane with high ion selectivity and conductivity, the relationship between various influencing factors and the composite membrane structure needs to be comprehensively considered.

In all the examples in the following table, a preferred porous base membrane material is adopted, hydrophobic polymer resin is polyether sulfone (PES), hydrophilic polymer resin is sulfonated polyether ether ketone (SPEEK), the proportion and the sulfonation degree of the PES and the SPEEK are changed, other conditions are the same as those in example 1 and fig. 9, the film forming mechanism of the prepared ultrathin functional layer is taken, active substances are m-phenylenediamine and 1,3, 5-trimethylbenzene chloride, the m-phenylenediamine is dissolved in water (water phase), the 1,3, 5-trimethylbenzene chloride is dissolved in n-hexane (oil phase), after the hydrophilic porous base membrane is soaked in an aqueous phase solution, the m-phenylenediamine is soaked in membrane pores, water beads on the surface of the membrane are wiped, after the membrane is soaked in the oil phase, the m-phenylenediamine in the water phase is diffused to the oil phase, and the m-phenylenediamine in the water phase rapidly reacts with the 1,3, 5-trimethylbenzene chloride at a water/oil phase interface.

TABLE 1 Effect of other parameters of porous base membranes on Performance (80mA cm)^-2)

The table is only provided with partial experimental data, and can be used for explaining a preferred selection rule of the battery performance.

From the results in the table, it is found by analysis that the surface pore diameter is too large due to the addition of too much hydrophilic polymer to the base film, and the selectivity of the formed separation layer is lowered. The decrease of the hydrophilic polymer causes the decrease of the conductivity of the base membrane and the increase of the overall resistance of the composite membrane. The hydrophobic porous base membrane causes the affinity of the separation layer and the base membrane to be reduced, the stability of the separation layer to be reduced, and the selectivity to be reduced. Hydrophilic polymers with appropriate surface pore size are most advantageous for forming a separation layer with few defects.

Meanwhile, a great deal of research shows that the acidity of the base film is enhanced to reduce the crosslinking degree of the formed interfacial polymerization layer and reduce the selectivity, but the conductivity is increased at the same time, so that the base film has the optimal quality, and the base film has too low acidity to cause high selectivity and low conductivity; too strong acidity results in low selectivity and high conductivity. The acidity of the base film can be adjusted by the proportion of the sulfonated polymer and the degree of sulfonation.

Claims

1. A composite membrane for a flow battery with an ultrathin functional layer is characterized in that: the composite membrane is a porous base membrane prepared by blending hydrophobic polymer resin and hydrophilic polymer resin through an immersion precipitation phase inversion method, the formed porous base membrane is formed by laminating a skin layer and a macroporous support layer, and then a compact functional layer with nano-scale thickness is grown in situ on the surface of the skin layer of the base membrane or the surfaces of two sides of the base membrane by using liquid-liquid phase interfacial polymerization reaction, wherein the thickness of the functional layer is 50-500nm, preferably 100-200 nm.

2. The composite film of claim 1, wherein: the pore diameter of the basement membrane skin layer is 1-100nm, preferably 5-20 nm; the surface porosity of the skin layer is 5-40%, preferably 10-20%, and the surface porosity is the ratio of the cross section area of the surface pore canal in the surface area; the thickness of the skin layer is 50nm-1 μm, preferably 100nm-500 nm; the pore diameter of the macroporous support layer is 50nm-10 μm, preferably 50nm-200 nm; the surface porosity of the macroporous support layer is 20-80%, preferably 50-80%; the thickness of the macroporous support layer is 80-150 μm, preferably 90-110 μm.

3. The composite film of claim 2, wherein: the mass ratio of the hydrophobic polymer resin to the hydrophilic polymer resin is 0.5: 1 to 9: 1; preferably, 7: 3 to 9: 1; the hydrophobic polymer resin is one or more of polyether sulfone, polysulfone, polyether ketone, polytetrafluoroethylene, polyvinylidene fluoride or polystyrene; preferably one or two of polyether sulfone and polysulfone; the hydrophilic polymer resin is one or more than two of sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone, sulfonated polybenzimidazole, polyvinylpyrrolidone, polybenzimidazole or polyethylene glycol, and the sulfonation degree of the sulfonated polymer (sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone or sulfonated polybenzimidazole) is 20-80 percent respectively; one or two of sulfonated polyether ketone and polyvinylpyrrolidone are preferred, and the sulfonation degrees of the sulfonated polyether ketone and the polyvinylpyrrolidone are respectively preferably 40% -60%.

4. The composite film of claim 1, wherein: the functional layer with nano-scale thickness is formed by in-situ growth of two active substances capable of mutually reacting and polymerizing on the surface of the base film through liquid-liquid phase interfacial polymerization reaction, wherein the two active substances are respectively dissolved in a water phase solvent and an oil phase solvent to prepare a water phase solution and an oil phase solution, and the base film is sequentially soaked in the two solutions to form the functional layer with nano-scale thickness on the surface of the base film in situ.

5. The composite film of claim 4, wherein:

the oil phase active substance is acyl chloride monomer, and the acyl chloride monomer is one or more than two of 1,3, 5-trimethyl benzoyl chloride, isophthaloyl dichloride and cyclohexane-1, 3, 5-tricarbonyl dichloride; 1,3, 5-Tribenzoyl chloride is preferred.

6. The composite film according to claim 5 or 6, wherein:

7. A method of making a composite membrane according to any one of claims 1 to 6, wherein: the composite membrane is prepared by the following steps:

(1) dissolving hydrophobic polymer resin and hydrophilic polymer resin in an organic solvent, and stirring to obtain a uniform solution; solids content of 15% to 40% by weight, preferably 25% to 30% by weight;

(2) flatly paving the solution prepared in the step (1) on a substrate, and preparing a porous base membrane by using an immersion precipitation phase inversion method;

(3) dissolving the aqueous phase active substance in water to obtain 0.01-10 wt./v.% (g/ml) aqueous phase solution; preferably 0.5-8 wt./v.%; dissolving the oil phase active substance in an oily solvent to form an oil phase solution with a concentration of 0.01-1 wt./v.% (g/ml), preferably 0.1-0.8 wt./v.%;

(4) immersing the porous base membrane in the aqueous solution, soaking for 30s-10min, preferably 1-3min, taking out, wiping the surfaces of the two sides of the membrane, or sticking one side of the macroporous supporting layer of the membrane on a glass sheet, and wiping one side of the outward skin layer (the surface of the side far away from the glass sheet) of the membrane by using a sponge stick, filter paper or mirror wiping paper; and (3) putting the film with the surfaces on both sides wiped dry or the film with one side wiped dry and the glass sheet into an oil phase solution, soaking for 5s-30min, preferably 1-3min, taking out to obtain a composite film with a functional layer with nano-scale thickness grown in situ on the surface of the skin layer of the base film or the surfaces on both sides of the film by using liquid-liquid phase interfacial polymerization reaction, and storing the film in water for later use.

8. The method of claim 7, wherein: the immersion precipitation phase inversion method comprises the following specific steps:

the poor solvent is one or more than two of water, ethanol and isopropanol.

9. Use of a composite film according to any of claims 1 to 6, wherein: the composite membrane is applied to the all-vanadium redox flow battery.