Polybenzimidazole porous ion conducting membrane as well as preparation method and application thereof

Abstract

The invention discloses a polybenzimidazole porous ion conducting membrane as well as a preparation method and application thereof, and belongs to the technical field of battery diaphragms. The polybenzimidazole porous ion conducting membrane is made of a polybenzimidazole polymer; the polybenzimidazole polymer contains a six-membered cycloalkane structure. Polymer molecules in the polybenzimidazole porous ion conducting membrane contain six-membered cycloalkane structures, protonation and deprotonation capabilities of N-groups on imidazole rings in polybenzimidazole polymers are high, and the polybenzimidazole porous ion conducting membrane has high proton conductivity and ion selectivity. The obtained polybenzimidazole porous ion conduction membrane can realize ion transfer under the condition of not introducing any ion exchange group, and has high selectivity and high stability.

Description

Technical Field

[0001] The present application relates to a polybenzimidazole porous ion conducting membrane and a preparation method and application thereof, belonging to the technical field of battery separators. Background Art

[0002] Liquid flow battery is a new electrochemical energy storage technology. Compared with other energy storage technologies, it has the advantages of flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety and environmental protection, independent design of power and capacity, and low maintenance cost. It can be widely used in wind power, solar energy and other renewable energy power generation and storage, emergency power supply systems, backup power stations and power system peak shaving and valley filling, and has broad application prospects in the field of energy storage.

[0003] The battery separator is an important component of the liquid flow battery. It plays the role of blocking the positive and negative electrolytes and providing a proton transmission channel. The proton conductivity, chemical stability and ion selectivity of the membrane will directly affect the electrochemical performance and service life of the battery. Therefore, the membrane is required to have high ion selectivity and high proton conductivity, as well as good chemical stability and low cost. The membrane materials currently used at home and abroad are mainly Nafion membranes developed by DuPont in the United States. Nafion membranes have excellent performance in proton conductivity and chemical stability, but their high price and poor selectivity limit the industrial application of the membrane. Therefore, it is crucial to develop battery separators with high selectivity, high stability and low cost. However, due to the presence of ion exchange groups, the chemical stability of non-fluorinated ion exchange membranes in liquid flow batteries is not enough to meet the long-term use requirements.

[0004] In order to solve the stability problem caused by the presence of ion exchange groups in non-fluorinated ion exchange membranes, our team developed a porous ion screening conductive membrane, which achieves the selective separation of active substances and carriers through the pore size screening effect, with high selectivity and high conductivity. However, there is a trade-off effect between the selectivity and conductivity of porous ion conductive membranes, which limits the further improvement of flow battery performance. Summary of the invention

[0005] According to one aspect of the present application, a polybenzimidazole porous ion conductive membrane is provided, in which the polymer molecules contain a hexacycloalkane structure, the -N- group on the imidazole ring in the polybenzimidazole polymer has strong protonation and deprotonation capabilities, and has high proton conductivity and ion selectivity. The obtained polybenzimidazole porous ion conductive membrane can realize ion transfer without introducing any ion exchange groups, and has high selectivity and high stability.

[0006] The polybenzimidazole porous ion conducting membrane of the present application is made of polybenzimidazole polymer;

[0007] The polybenzimidazole polymer contains a six-membered cycloalkane structure, and the structure is shown in the following formula I or formula II:

[0008]

[0009] Wherein, n is any integer from 10 to 500;

[0010] The pore size of the polybenzimidazole porous ion conductive membrane is 0.01-100 nm.

[0011] In the present application, n is the degree of polymerization.

[0012] Preferably, n is 300-500.

[0013] Optionally, n is independently selected from any value of 10, 50, 100, 200, 300, 350, 400, 450, 500 or a range between any two of the above values.

[0014] Optionally, the thickness of the polybenzimidazole porous ion conducting membrane is 1-200 μm; preferably, the thickness of the polybenzimidazole porous ion conducting membrane is 3-150 μm.

[0015] Optionally, the thickness of the polybenzimidazole porous ion conductive membrane is independently selected from any value among 1μm, 2μm, 3μm, 10μm, 20μm, 40μm, 50μm, 60μm, 80μm, 100μm, 120μm, 140μm, 150μm, 160μm, 180μm, 200μm or a range between any two of the above.

[0016] Preferably, the pore size of the polybenzimidazole porous ion conductive membrane is 0.5-50 nm.

[0017] Optionally, the pore size of the polybenzimidazole porous ion conductive membrane is independently selected from any value among 0.01nm, 0.02nm, 0.05nm, 0.1nm, 0.5nm, 0.6nm, 1nm, 1.2nm, 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 100nm or a range between any two of the above.

[0018] Optionally, the porosity of the polybenzimidazole porous ion conducting membrane is 5-90%; preferably, the porosity of the polybenzimidazole porous ion conducting membrane is 20-80%.

[0019] Optionally, the porosity of the polybenzimidazole porous ion conductive membrane is independently selected from any value of 5%, 10%, 15%, 20%, 25%, 40%, 50%, 60%, 70%, 80%, 90% or a range between any two of the above.

[0020] Optionally, the polybenzimidazole polymer is a random copolymer.

[0021] Optionally, the average molecular weight of the polybenzimidazole polymer is 4000-1000000.

[0022] Optionally, the polybenzimidazole polymer comprises cis and trans configurations of six-membered cycloalkane.

[0023] On the other hand, the present application provides a method for preparing the polybenzimidazole porous ion conductive membrane, comprising: dissolving the polybenzimidazole polymer in an organic solvent, stirring to obtain a mixture solution, coating it on a glass plate, immersing it in a non-solvent, and curing it into a film to obtain the polybenzimidazole porous ion conductive membrane.

[0024] Optionally, the mass fraction of the polybenzimidazole polymer in the mixture solution is 1-50%; preferably, the mass fraction of the polybenzimidazole polymer in the mixture solution is 5-40%.

[0025] Optionally, the mass fraction of the polybenzimidazole polymer in the mixture solution is independently selected from any value of 1%, 3%, 5%, 10%, 15%, 20%, 30%, 40%, 45%, 50% or a range between any two of the above.

[0026] Optionally, the dissolving temperature is 20-200°C.

[0027] Optionally, the stirring time is 0.5-72h.

[0028] Optionally, the immersion time is 1-120 min; preferably, the immersion time is 30-80 min.

[0029] Specifically, the immersion time is 60 min.

[0030] Optionally, the impregnation temperature is 20-30°C.

[0031] Specifically, the immersion temperature was 25°C.

[0032] Optionally, the organic solvent is selected from any one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO).

[0033] Optionally, the non-solvent is selected from one or more of water, n-heptane, n-hexane, cyclohexane, methanol, ethanol, propanol and butanol.

[0034] In another aspect, the present application provides an application of the polybenzimidazole porous ion conductive membrane in a liquid flow battery.

[0035] The beneficial effects of this application include:

[0036] (1) The polymer molecules in the polybenzimidazole porous ion conductive membrane of the present application contain a six-membered cycloalkane structure. The -N- group on the imidazole ring in the polybenzimidazole polymer has a strong protonation and deprotonation ability, has high proton conductivity and ion selectivity, and shows excellent performance in liquid flow batteries.

[0037] (2) The polybenzimidazole porous ion conducting membrane of the present application can realize ion transfer without introducing any ion exchange groups, and has high selectivity and high stability.

[0038] (3) The polybenzimidazole porous ion conductive membrane of the present application has good mechanical properties.

[0039] (4) The preparation method of the polybenzimidazole porous ion conductive membrane of the present application is simple, the preparation conditions are mild, the pore size is controllable, and mass production is easy to achieve.

[0040] (5) This application broadens the types and application scope of membrane materials for liquid flow batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the structural formula of the polybenzimidazole used in Example 1.

[0042] Figure 2 This is a cross-sectional SEM image of the membrane of Example 1P1, with a size of 20 μm. DETAILED DESCRIPTION

[0043] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0044] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0045] The preparation method of polybenzimidazole in the embodiments and comparative examples is as follows:

[0046] Dissolve 5g of phosphorus pentoxide in 50g of methanesulfonic acid, add to a 500ml three-necked flask, heat and stir to form a clear solution, then add 4.31g of diphenyltetramine and 3.44g of 1,4-trans-cyclohexanedicarboxylic acid. The total mass percentage of dicarboxylic acid and diphenyltetramine in methanesulfonic acid solvent is 15.5%. Stir and heat to 130 degrees. After reacting for 1.5 hours, cool down and pour into a 5wt% sodium hydroxide solution. After standing for 24 hours, wash thoroughly with water until the solution is neutral. Filter and dry.

[0047] Taking the all-vanadium liquid flow battery as an example, the test instrument is the BT 2000 ArBin charge and discharge instrument. The performance test conditions of the all-vanadium liquid flow battery are as follows: the end plate is stainless steel, the bipolar plate is a graphite plate, the positive and negative electrodes are both made of carbon felt as electrodes, and the effective area of ​​the electrode is 48cm 2 The vanadium ion concentration in the positive and negative electrolytes is 1.5 mol L -1 , H 2 SO 4 The concentration is 3 mol L -1 The volume of the positive and negative electrolytes is 60 mL each; the battery adopts constant current charge and discharge mode, and the current density is 80 mA cm -2 The charge and discharge cut-off voltages are 1.55 and 1V respectively.

[0048] The thickness test instrument is a micrometer.

[0049] The test conditions for porosity are as follows: wipe the water off the membrane surface with filter paper and weigh it immediately. Then dry the weighed membrane at room temperature and pressure, and finally weigh the completely dried membrane. The membrane porosity is calculated as shown in the following formula.

[0050]

[0051] Among them, M w and M d are the weights of wet film and dry film respectively; ρ represents the density of water at room temperature; S is the surface area of ​​the dry film; l is the thickness of the dry film.

[0052] The pore size distribution is tested by positron annihilation lifetime spectroscopy.

[0053] The morphology characterization was performed by scanning electron microscopy under the following conditions: 10KV; to obtain cross-sectional samples, the film was placed in liquid nitrogen for freeze-quenching. Before observation, all samples were gold-sprayed (using a magnetron ion sputtering instrument, MSP-2S).

[0054] The mechanical properties were tested using a Shimadzu AG-2004 universal testing machine. The film was cut into samples of 1 cm × 7 cm in size, and the film thickness was measured and recorded using a micrometer. The sample was then fixed on a universal testing machine with a clamp width of 1 cm for tensile testing.

[0055] The surface resistance test instrument uses electrochemical impedance spectroscopy (EIS, Solartron 1260+1287) to test the surface resistance of the membrane, and the test frequency range is 1kHz to 1MHz. The sample to be tested (effective area 1cm×1cm) is fixed in the middle of the homemade conductivity cell, and the cavities on both sides are filled with 3mol L -1 Sulfuric acid solution. Before testing, the sample to be tested was heated to 3 mol L -1 Soak in sulfuric acid solution for more than 10 hours to fill the pores with sulfuric acid solution. The surface resistance of the membrane is calculated by the resistance difference of the conductivity cell with and without the membrane;

[0056] The vanadium permeability test instrument is a TU-1901 model UV spectrophotometer. The test conditions are as follows: the test pool includes two chambers, and the effective area between the two chambers is 3×3cm 2 84 mL of 1.5 mol / L was added to the left chamber. -1 VOSO 4 +3.0mol L -1 H 2 SO 4 solution, add the same volume of 1.5 mol L -1 MgSO 4 +3.0mol L -1 H 2 SO 4 solution. MgSO 4 Used to balance the ionic strength of the left and right chambers to reduce water migration caused by osmotic pressure. During the test, the solutions in the left and right chambers are stirred simultaneously to reduce concentration polarization. During the test, 3 mL of sample solution is taken out from the right chamber at regular intervals, and 3 mL of the original solution is added to keep the bath volume constant. VO in the sample 2+ The concentration was measured by UV-visible spectrophotometer (TU-1901).

[0057] Example 1

[0058] (1) 2 g of polybenzimidazole was dissolved in 18 g of N,N-dimethylacetamide (DMAc) to obtain a uniform solution with a mass fraction of 10%. The structure of the polybenzimidazole (polymerization degree 400) used was as follows: Figure 1 shown.

[0059] (2) The polybenzimidazole solution prepared in step (1) is poured onto a clean and flat glass plate, and is scraped using a 500 μm thick scraper, and then the entire glass plate is immersed in a non-solvent (water) at 25° C. for 0.5 h to obtain a polybenzimidazole porous ion conductive membrane, denoted as P1 membrane, having a thickness of 50 μm, a porosity of 50%, and a pore size distribution range of 0.6-10 nm.

[0060] The morphology of the P1 film was characterized, such as Figure 2 As shown, the membrane exhibits a porous structure.

[0061] The mechanical properties of the P1 membrane were tested. The tensile strength of the membrane was 40 MPa and the elastic modulus was 1.5 GPa, showing good mechanical properties, as shown in Table 1.

[0062] Assemble the permeation cell using P1 membrane, with 1.5M VOSO on the left 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120mL, and both sides are magnetically stirred. 3mL of sample is taken from the right side at regular intervals, and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of P1 membrane is 1.11×10 -7 cm 2 h -1 , which is smaller than the commercial Nafion 115 membrane (4.39×10 -5 cm 2 h -1 ), showing higher selectivity. In addition, as shown in Table 1, the surface resistance of the P1 membrane is 0.014Ωcm 2 , which is less than the surface resistance of commercial Nafion 115 membrane (0.04Ωcm 2 ), proving that the P1 membrane has a higher proton conductivity.

[0063] As shown in Table 2, the all-vanadium liquid flow battery assembled with the P1 membrane has a coulombic efficiency of 99.58%, a voltage efficiency of 90.04%, and an energy efficiency of 89.66%, which are higher than the efficiency of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), showing excellent performance. Within 100 cycles, the capacity retention rate of the all-vanadium liquid flow battery assembled with the P1 membrane is 88%, which is higher than the capacity retention rate of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium liquid flow battery assembled with the P1 membrane can operate continuously and stably for more than 2000 cycles, and the performance has not been significantly attenuated, proving that the membrane has excellent chemical stability.

[0064] Example 2

[0065] A polybenzimidazole porous ion conducting membrane was prepared according to the method (process and conditions) described in Example 1, except that the thickness of the membrane was 2 μm. The prepared membrane was denoted as P2 membrane.

[0066] The mechanical properties of the P2 membrane were tested, and the tensile strength of the membrane was 32 MPa and the elastic modulus was 2.0 GPa, showing relatively good mechanical properties, as shown in Table 1.

[0067] The permeation cell device is assembled using the P2 membrane. The left one is 1.5M VOSO 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of P2 membrane is 1.99×10 -7 cm 2 h -1 , which is greater than that of P1 membrane but lower than that of commercial Nafion 115 membrane. This is because the decrease in thickness reduces the membrane's resistance to vanadium ion migration, causing its selectivity to decrease. At the same time, its tensile strength decreases.

[0068] In addition, as shown in Table 1, the surface resistance of the P2 film is 0.009 Ωcm 2 , which is less than the surface resistance of P1 membrane and commercial Nafion 115 membrane (0.04Ωcm 2 ), proving that the P2 membrane has a higher proton conductivity. This is because the decrease in membrane thickness reduces the migration impedance of protons, which increases the proton conductivity of the membrane.

[0069] As shown in Table 2, the all-vanadium liquid flow battery assembled with the P2 membrane has a coulombic efficiency of 99.36%, a voltage efficiency of 90.15%, and an energy efficiency of 89.57%, which are higher than the efficiency of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), showing excellent performance. Within 100 cycles, the capacity retention rate of the all-vanadium liquid flow battery assembled with the P2 membrane is 86%, which is higher than the capacity retention rate of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium liquid flow battery assembled with the P2 membrane can operate continuously and stably for more than 2000 cycles, and the performance has not been significantly attenuated, proving that the membrane has excellent chemical stability.

[0070] Example 3

[0071] A polybenzimidazole porous ion conducting membrane was prepared according to the method (process and conditions) described in Example 1, except that the thickness of the membrane was 180 μm. The prepared membrane was denoted as P3 membrane.

[0072] The mechanical properties of the P3 membrane were tested, and the tensile strength of the membrane was 49 MPa and the elastic modulus was 0.9 GPa, showing good mechanical properties, as shown in Table 1.

[0073] The permeation cell device is assembled using P3 membrane, with 1.5M VOSO on the left. 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of P3 membrane is 1.03×10 -7 cm 2 h -1 , which is lower than that of P1-P2 membranes and commercial Nafion 115 membranes. This is because the increase in thickness increases the membrane's resistance to vanadium ion migration, increasing its selectivity. At the same time, it also increases its tensile strength. In addition, as shown in Table 1, the surface resistance of the P3 membrane is 0.026Ωcm 2 , which is higher than the surface resistance of P1-P2 membranes but lower than the commercial Nafion 115 membrane (0.04Ωcm 2), indicating that although the proton conductivity of the P3 membrane has decreased, it is still better than the commercial Nafion115 membrane. This is because the increase in membrane thickness increases the migration impedance of protons, which reduces the proton conductivity of the membrane.

[0074] As shown in Table 2, the all-vanadium liquid flow battery assembled with the P3 membrane has a coulombic efficiency of 99.77%, a voltage efficiency of 89.41%, and an energy efficiency of 89.20%, which are higher than the efficiency of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), showing excellent performance. Within 100 cycles, the capacity retention rate of the all-vanadium liquid flow battery assembled with the P3 membrane is 90%, which is higher than the capacity retention rate of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium liquid flow battery assembled with the P3 membrane can operate continuously and stably for more than 2000 cycles, and the performance has not been significantly attenuated, proving that the membrane has excellent chemical stability.

[0075] It can be seen from the test results of Examples 2-3 and Example 1 that the decrease in thickness reduces the impedance of the membrane to the migration of vanadium ions, reduces its selectivity, and reduces its tensile strength. When the membrane thickness decreases, the migration impedance of protons is reduced, and the proton conductivity of the membrane is increased. Conversely, the increase in thickness increases the impedance of the membrane to the migration of vanadium ions, increases its selectivity, and increases its tensile strength. When the membrane thickness increases, the migration impedance of protons is also increased, and the proton conductivity of the membrane is reduced.

[0076] Example 4

[0077] A polybenzimidazole porous ion conductive membrane was prepared according to the method (process and conditions) described in Example 1, except that the mass fraction of the polybenzimidazole solution was 45%. The prepared membrane was denoted as P4 membrane, and its porosity was 10% and the pore size distribution range was 0.02-0.5 nm.

[0078] The mechanical properties of the P4 membrane were tested, and the tensile strength of the membrane was 54 MPa and the elastic modulus was 0.7 GPa, showing good mechanical properties, as shown in Table 1.

[0079] The permeation cell device is assembled using P4 membrane, with 1.5M VOSO on the left. 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of P4 membrane is 0.84×10 -7 cm 2 h -1 , which is lower than that of P1-P3 membranes and commercial Nafion 115 membranes. This is because the increase in the content of polybenzimidazole in the casting solution reduces the porosity of the membrane and reduces the pore size, which increases the impedance of the membrane to the migration of vanadium ions and increases its selectivity. At the same time, it increases its tensile strength. In addition, as shown in Table 1, the surface resistance of the P4 membrane is 0.035Ωcm 2 , which is higher than the surface resistance of P1-P3 membranes but lower than the commercial Nafion 115 membrane (0.04Ωcm 2 ), indicating that although the proton conductivity of the P4 membrane has decreased, it is still better than the commercial Nafion115 membrane. This is because the increase in the polybenzimidazole content in the casting solution reduces the porosity of the membrane and the pore size, which increases the migration impedance of the proton and reduces the proton conductivity of the membrane.

[0080] As shown in Table 2, the all-vanadium liquid flow battery assembled with the P4 membrane has a coulombic efficiency of 99.80%, a voltage efficiency of 89.32%, and an energy efficiency of 89.14%, which is higher than the efficiency of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), showing excellent performance. Within 100 cycles, the capacity retention rate of the all-vanadium liquid flow battery assembled with the P4 membrane is 91%, which is higher than the capacity retention rate of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium liquid flow battery assembled with the P4 membrane can operate continuously and stably for more than 2000 cycles, and the performance has not been significantly attenuated, proving that the membrane has excellent chemical stability.

[0081] Example 5

[0082] A polybenzimidazole porous ion conductive membrane was prepared according to the method (process and conditions) described in Example 1, except that the mass fraction of the polybenzimidazole solution was 3%. The prepared membrane was denoted as P5 membrane, and its porosity was 85%, and the pore size distribution range was 1.2-70 nm;

[0083] The mechanical properties of the P5 membrane were tested. The tensile strength of the membrane was 30 MPa and the elastic modulus was 2.6 GPa, showing good mechanical properties, as shown in Table 1.

[0084] The permeation cell device is assembled using P5 membrane, with 1.5M VOSO on the left. 4Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of P5 membrane is 3.05×10 -7 cm 2 h -1 , which is higher than that of P1-P4 membranes and commercial Nafion 115 membranes. This is because the decrease in the content of polybenzimidazole in the casting solution increases the porosity of the membrane and increases the pore size, which reduces the impedance of the membrane to the migration of vanadium ions and reduces its selectivity. At the same time, its tensile strength decreases. In addition, as shown in Table 1, the surface resistance of the P5 membrane is 0.007Ωcm 2 , which is lower than the surface resistance of P1-P4 membranes and commercial Nafion 115 membranes (0.04Ωcm 2 ), indicating that the P5 membrane has a higher proton conductivity. This is because the decrease in the polybenzimidazole content in the casting solution increases the porosity of the membrane and increases the pore size, which reduces the migration impedance of protons and increases the proton conductivity of the membrane.

[0085] As shown in Table 2, the all-vanadium liquid flow battery assembled with the P5 membrane has a coulombic efficiency of 99.17%, a voltage efficiency of 92.56%, and an energy efficiency of 91.79%, which are higher than the efficiency of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), showing excellent performance. Within 100 cycles, the capacity retention rate of the all-vanadium liquid flow battery assembled with the P5 membrane is 84%, which is higher than the capacity retention rate of the all-vanadium liquid flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium liquid flow battery assembled with the P5 membrane can operate continuously and stably for more than 2000 cycles, and the performance has not been significantly attenuated, proving that the membrane has excellent chemical stability.

[0086] As can be known from the test results of embodiment 4-5 and embodiment 1, the rising of polybenzimidazole content in the casting solution makes the porosity of the film decline, and the pore size decreases, which increases the impedance of the film to the migration of vanadium ions, increases its selectivity, and simultaneously increases its tensile strength. In addition, the porosity of the film declines, and the pore size decreases, which also increases the migration impedance of protons, and the proton conductivity of the film declines. On the contrary, the decline of polybenzimidazole content in the casting solution makes the porosity of the film rise, and the pore size becomes larger, which reduces the impedance of the film to the migration of vanadium ions, reduces its selectivity, and simultaneously decreases its tensile strength. In addition, the porosity of the film increases, and the pore size decreases, which also reduces the migration impedance of protons, and the proton conductivity of the film increases.

[0087] Comparative Example 1

[0088] A polybenzimidazole porous ion conductive membrane was prepared according to the method (process and conditions) described in Example 1, except that the mass fraction of the polybenzimidazole solution was 0.05%. The prepared membrane was denoted as p1 membrane, and its porosity was 96%, and the pore size distribution range was 50-200 nm.

[0089] The mechanical properties of the p1 membrane were tested. The tensile strength of the membrane was 10 MPa, the elastic modulus was 3.5 GPa, and the mechanical properties were very poor, as shown in Table 1.

[0090] The permeation cell device is assembled using the p1 membrane. The left side is 1.5M VOSO 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of the p1 membrane is 927×10 -7 cm 2 h -1 , higher than P1-P5 membranes and commercial Nafion 115 membranes. This is because the polybenzimidazole content in the casting solution is too low, the membrane porosity is too high, and the pore size is too small, which greatly reduces the membrane's impedance to vanadium ion migration and significantly reduces its selectivity. At the same time, its tensile strength decreases. In addition, as shown in Table 1, the surface resistance of the p1 membrane is 0.001Ωcm 2 , which is lower than the surface resistance of P1-P5 membranes and commercial Nafion 115 membranes (0.04Ωcm 2), indicating that the p1 membrane has a higher proton conductivity. This is because the further decrease in the polybenzimidazole content in the casting solution increases the porosity of the membrane and reduces the pore size, which reduces the migration impedance of protons and increases the proton conductivity of the membrane.

[0091] As shown in Table 2, the all-vanadium flow battery assembled with the p1 membrane has a coulombic efficiency of 74.14%, a voltage efficiency of 93.72%, and an energy efficiency of 69.48%. Except for the voltage efficiency, the coulombic efficiency and energy efficiency are lower than the efficiency of the all-vanadium flow battery assembled with the Nafion 115 membrane (coulombic efficiency of 94.51%, voltage efficiency of 87.88%, and energy efficiency of 83.06%), and the performance is poor. Within 100 cycles, the capacity retention rate of the all-vanadium flow battery assembled with the p1 membrane is 67%, which is lower than the capacity retention rate of the all-vanadium flow battery assembled with the Nafion 115 membrane (78%) (Table 2). In addition, the all-vanadium flow battery assembled with the p1 membrane can only operate continuously and stably for more than 50 cycles, and the chemical stability is poor.

[0092] Comparative Example 2

[0093] A polybenzimidazole porous ion conductive membrane was prepared according to the method (process and conditions) described in Example 1, except that the mass fraction of the polybenzimidazole solution was 60%. The prepared membrane was denoted as p2 membrane, and its porosity was 2% and the pore size distribution range was 0.001-0.01 nm.

[0094] The mechanical properties of the p2 membrane were tested. The tensile strength of the membrane was 60 MPa, the elastic modulus was 0.2 GPa, and the mechanical properties were very poor, as shown in Table 1.

[0095] The permeation cell device is assembled using the p2 membrane. The left one is 1.5M VOSO 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120mL and both sides are magnetically stirred. 3mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of the p2 membrane is 0.09×10 -7 cm 2 h -1, which is lower than that of P1-P5 membranes and commercial Nafion 115 membranes. This is because the polybenzimidazole content in the casting solution is too high, the porosity of the membrane is too low, and the pore size is too small, which greatly increases the membrane's impedance to vanadium ion migration and increases its selectivity. At the same time, it increases its tensile strength. In addition, as shown in Table 1, the surface resistance of the p2 membrane is 10.40Ωcm 2 , which is higher than the surface resistance of P1-P5 membranes and commercial Nafion 115 membranes (0.04Ωcm 2 ), indicating that the p2 membrane has a lower proton conductivity. This is because the polybenzimidazole content in the casting solution is too high, the porosity of the membrane is too low, and the pore size is too small, which greatly increases the migration impedance of protons and reduces the proton conductivity of the membrane.

[0096] When assembling an all-vanadium liquid flow battery using a p2 membrane, the battery could not operate due to the large membrane impedance.

[0097] It can be seen from the test results of Comparative Examples 1-2 and Example 1 that the polybenzimidazole content in the casting solution is too low, the porosity of the membrane is too high, and the pore size is too small, which greatly reduces the impedance of the membrane to the migration of vanadium ions, greatly reduces its selectivity, and simultaneously reduces its tensile strength. In addition, the porosity of the membrane increases and the pore size decreases, which reduces the migration impedance of protons and increases the proton conductivity of the membrane. On the contrary, when the polybenzimidazole content in the casting solution is too high, the porosity of the membrane is too low, and the pore size is too small, the impedance of the membrane to the migration of vanadium ions and the tensile strength are greatly increased, while the migration impedance of protons is greatly increased, which greatly reduces the proton conductivity of the membrane.

[0098] Comparative Example 3

[0099] A polybenzimidazole porous ion conducting membrane was prepared according to the method (process and conditions) described in Example 1, except that the thickness of the membrane was 250 μm. The prepared membrane was denoted as p3 membrane.

[0100] The mechanical properties of the p3 membrane were tested. The tensile strength of the membrane was 58 MPa, the elastic modulus was 0.2 GPa, and the mechanical properties were very poor, as shown in Table 1.

[0101] The permeation cell device is assembled using the p3 membrane. The left one is 1.5M VOSO 4 Dissolved in 3M HO 2 SO 4 In the middle, on the right is 1.5M MgSO 4 Dissolved in 3M HO 2 SO 4 The volume of both sides is 120 mL and both sides are magnetically stirred. 3 mL of sample is taken from the right side at regular intervals and the same volume of original solution is added at the same time. The concentration of the sample is measured by UV spectrophotometer as a function of time. As can be seen from Table 1, the vanadium permeability coefficient of the p3 membrane is 0.10×10-7 cm 2 h -1 , which is lower than that of P1-P5 membranes and commercial Nafion 115 membranes. This is because the increase in thickness increases the membrane's resistance to vanadium ion migration, increasing its selectivity. At the same time, it increases its tensile strength. In addition, as shown in Table 1, the surface resistance of the p3 membrane is 10.26Ωcm 2 , which is higher than the surface resistance of P1-P5 membranes and commercial Nafion 115 membranes (0.04Ωcm 2 ), indicating that the p3 membrane has a lower proton conductivity. This is because the membrane thickness is too high, which greatly increases the migration impedance of protons and reduces the proton conductivity of the membrane.

[0102] When assembling an all-vanadium liquid flow battery using a p3 membrane, the battery could not operate due to the large membrane impedance.

[0103] It can be seen from the test results of Comparative Example 3 and Example 1 that when the thickness of the membrane is too high, the selectivity and mechanical strength are greatly improved, while the membrane impedance increases sharply and the proton conductivity decreases significantly.

[0104] Comparative Example 4

[0105] A polybenzimidazole porous ion conducting membrane was prepared according to the method (process and conditions) described in Example 1, except that the thickness of the membrane was 0.5 μm. The prepared membrane was denoted as p4 membrane.

[0106] The mechanical properties of the p4 membrane were tested, but since the membrane was too thin, its performance could not be tested and it could not be used to assemble an all-vanadium liquid flow battery.

[0107] From the test results of Comparative Example 4 and Example 1, it can be seen that the thickness of the membrane is too low and the mechanical properties are too poor to characterize the physical and chemical properties and battery performance.

[0108] Table 1 Preparation conditions and physicochemical parameters of membranes in different embodiments and comparative examples

[0109]

[0110]

[0111] Table 2 Performance of membrane-assembled all-vanadium flow batteries in different embodiments and comparative examples

[0112]

[0113] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A polybenzimidazole porous ion conducting membrane, It is characterized in that The material is polybenzimidazole polymer; The polybenzimidazole polymer contains a six-membered cycloalkane structure, and the structure is shown in the following formula I or formula II: Wherein, n is any integer from 10 to 500; The pore size of the polybenzimidazole porous ion conductive membrane is 0.01-100 nm.

2. The polybenzimidazole porous ion conducting membrane according to claim 1, It is characterized in that The thickness of the polybenzimidazole porous ion conductive membrane is 1-200 μm; Preferably, the polybenzimidazole porous ion conductive membrane has a thickness of 3-150 μm.

3. The polybenzimidazole porous ion conducting membrane according to claim 1, It is characterized in that The pore size of the polybenzimidazole porous ion conductive membrane is 0.5-50 nm.

4. The polybenzimidazole porous ion conducting membrane according to claim 1, It is characterized in that The porosity of the polybenzimidazole porous ion conductive membrane is 5-90%; Preferably, the porosity of the polybenzimidazole porous ion conductive membrane is 20-80%.

5. The polybenzimidazole porous ion conducting membrane according to claim 1, It is characterized in that The average molecular weight of the polybenzimidazole polymer is 4000-1000000; Preferably, the polybenzimidazole polymer comprises cis and trans configurations of six-membered cycloalkanes; Preferably, the polybenzimidazole polymer is a random copolymer; Preferably, n is 300-500.

6. A method for preparing the polybenzimidazole porous ion conducting membrane according to any one of claims 1 to 5, It is characterized in that include: The polybenzimidazole polymer is dissolved in an organic solvent, stirred to obtain a mixture solution, coated on a glass plate, immersed in a non-solvent, and cured to form a film to obtain the polybenzimidazole porous ion conductive membrane.

7. The method for preparing the polybenzimidazole porous ion conducting membrane according to claim 6, It is characterized in that The mass fraction of the polybenzimidazole polymer in the mixture solution is 1-50%; Preferably, the mass fraction of the polybenzimidazole polymer in the mixture solution is 5-40%.

8. The polybenzimidazole porous ion conducting membrane according to claim 6, It is characterized in that The organic solvent is selected from any one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; The non-solvent is selected from any one or more of water, n-heptane, n-hexane, cyclohexane, methanol, ethanol, propanol, and butanol.

9. The method for preparing the polybenzimidazole porous ion conducting membrane according to claim 6, It is characterized in that The dissolving temperature is 20-200°C; Preferably, the stirring time is 0.5-72h; Preferably, the immersion time is 1-120 min.

10. Use of the polybenzimidazole porous ion conductive membrane according to any one of claims 1 to 5 in a liquid flow battery.

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