Method for improving electrochemical performance of sodium ion battery hard carbon negative electrode material
By coating the surface of hard carbon (HC) anode material with ethylenediaminetetraacetic acid (EDTA) to form a solid electrolyte membrane (SEI) rich in inorganic matter, the problem of improving the electrochemical performance of hard carbon anode materials in sodium-ion batteries is solved, achieving a simple and efficient performance improvement effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG UNIV
- Filing Date
- 2026-01-12
- Publication Date
- 2026-04-10
AI Technical Summary
In the existing technology, there are challenges in improving the electrochemical performance of hard carbon (HC) anode materials in sodium-ion batteries, especially due to their polarization sensitivity under high current conditions. Furthermore, existing improvement methods are cumbersome and costly, and a simple and effective improvement solution is needed.
By coating the surface of hard carbon (HC) anode material with ethylenediaminetetraacetic acid (EDTA), and then stirring in water and drying at a specific temperature, the hydroxyl groups on the HC surface and the carboxyl groups of EDTA undergo dehydration condensation to form a solid electrolyte membrane (SEI) rich in inorganic matter, thereby improving electrochemical performance.
It significantly improves the cycle stability and electrochemical performance of hard carbon anode materials. After 200 cycles at a current of 0.2 A g-1, the capacity increases to 233.8 mAh g-1, and the capacity retention rate increases from 31% to 75% after 1000 cycles. It also simplifies the production process and reduces costs.
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Abstract
Description
Technical Field
[0001] This invention relates to a method for improving the electrochemical performance of hard carbon anode materials in sodium-ion batteries, belonging to the field of sodium-ion battery technology. Background Technology
[0002] Sodium-ion batteries (SIBs) are a cost-effective novel rechargeable battery system due to the abundance of sodium resources and their lower cost compared to lithium. The use of aluminum current collectors further reduces production costs. However, the standard potential of sodium is 0.3V higher than that of lithium, which lowers the overall energy density of the battery. Therefore, research is needed on electrode materials with high capacity and excellent performance. Some cathode materials for SIBs, such as polyanionic, layered oxide, and ferricyanide materials, have shown excellent electrochemical performance and great commercial potential. Despite numerous reports on SIB anodes, obtaining high-performance anodes remains challenging. For example, hard carbon (HC) materials are highly sensitive to polarization in the plateau region, especially under high current conditions.
[0003] Currently reported methods for improving the performance of hard carbon (HC) mainly include doping, pore structure design and nanostructure control, and electrolyte design. Heteroatom doping (N, S, P, O, B, etc.) can alter the surface structure of HC, improve conductivity, and increase interlayer spacing. However, the presence of heteroatoms can catalyze electrolyte decomposition and irreversibly trap Na+. + This results in a low first coulombic efficiency (iCE). Doping is accompanied by an increase in plateau voltage, which affects energy density. Mesopores promote Na + Embedded, while micropores hinder Na + Diffusion. Fewer micropores and abundant mesopores result in better kinetic behavior of the HC anode. Although the sodium storage kinetics of micropores are poor, the ultramicropores can act as ion sieves, hindering the solvation of Na. + By allowing nonsolventized Na + This improves sodium storage kinetics. By rationally designing the microstructure of HC, the sodium storage time can be shortened. + The diffusion distance of HC is beneficial for improving rate performance. The sodium storage kinetics of HC in ether-based electrolytes are superior to those in ester-based electrolytes because Na... + Ion migration rates are faster in ether-based electrolytes, and more importantly, this may be related to the easier formation of thin, dense, and predominantly inorganic solid electrolyte membranes (SEIs) in ether-based electrolytes. R in ether-based electrolytes SEI (The impedance of the SEI) is much lower than that of the R in the ester electrolyte. SEI This indicates that Na + It is easier to pass through the SEI generated in the ether-based electrolyte. Furthermore, solvated Na... +It exhibits low desolvation energy at the SEI interface in ether-based electrolytes.
[0004] Currently, although the above methods can improve the performance of HC, they have problems such as complicated steps and high production costs. Furthermore, the electrochemical performance of the HC anode needs to be further improved. Therefore, there is an urgent need for a method to improve the electrochemical performance of hard carbon anode materials for sodium-ion batteries. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a method for improving the electrochemical performance of hard carbon anode materials for sodium-ion batteries. This invention enhances electrochemical performance by coating the surface of commercially available hard carbon (HC) anode material particles with a layer of ethylenediaminetetraacetic acid (EDTA). After stirring HC and EDTA in water, during the drying process, the hydroxyl groups on the HC surface and the carboxyl groups of EDTA undergo dehydration condensation. The C=O groups catalyze the preferential reduction of the salt, forming an inorganic-rich SEI, thereby significantly improving the electrochemical performance of the HC anode material.
[0006] The technical solution of the present invention is as follows:
[0007] A method for improving the electrochemical performance of hard carbon anode materials in sodium-ion batteries is disclosed. The method involves coating the surface of a hard carbon (HC) anode material with ethylenediaminetetraacetic acid (EDTA) to obtain an HC-EDTA anode material. Then, the HC-EDTA anode material, a conductive agent, and a binder are coated onto a current collector to form an anode sheet. The anode sheet, the positive electrode sheet, the separator, and the electrolyte are then assembled into a sodium-ion half-cell or a sodium-ion full-cell.
[0008] According to the present invention, the hard carbon anode material is a common commercially available product, such as commercially produced Kuraray hard carbon.
[0009] According to a preferred embodiment of the present invention, the step of coating the surface of the hard carbon anode material with ethylenediaminetetraacetic acid (EDTA) is as follows:
[0010] Hard carbon (HC) anode material powder was added to an aqueous solution of ethylenediaminetetraacetic acid (EDTA), stirred, and then dried to obtain HC-EDTA anode material.
[0011] More preferably, the concentration of the ethylenediaminetetraacetic acid (EDTA) aqueous solution is 0.15-0.9 mg / mL; the mass of EDTA in the EDTA aqueous solution is 1-5% of the mass of the hard carbon (HC) anode material powder.
[0012] More preferably, the stirring time is 10-15 hours, the stirring speed is 300-500 rpm, and the drying is carried out at 120-180°C for 10-15 hours.
[0013] According to a preferred embodiment of the present invention, the conductive agent in the negative electrode sheet is acetylene black, Ketjen black or Super P, the binder is polyvinylidene fluoride (PVdF) and the current collector is copper foil.
[0014] According to a preferred embodiment of the present invention, the negative electrode sheet is prepared by the following method:
[0015] After mixing HC-EDTA negative electrode material, conductive agent, and binder, N-methylpyrrolidone (NMP) is added, and the mixture is ball-milled to obtain a slurry. The obtained slurry is coated on a current collector, dried, and cut to obtain a negative electrode sheet.
[0016] More preferably, the mass ratio of the HC-EDTA anode material, conductive agent, and binder is 8:1:1; the total mass of the HC-EDTA anode material, conductive agent, and binder to the volume ratio of N-methylpyrrolidone (NMP) is 1g:4-6mL.
[0017] More preferably, the ball mill rotates at a speed of 300-500 rpm and the milling time is 3-5 hours;
[0018] More preferably, the drying is performed under vacuum at 50-70°C for 10-15 hours;
[0019] More preferably, the loading of HC-EDTA anode material on the anode sheet is 1-2 mg / cm³. 2 .
[0020] According to a preferred embodiment of the present invention, the method for preparing the positive electrode sheet is a prior art; preferably, the positive electrode sheet is prepared according to the following method:
[0021] The active material, conductive agent, and binder were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added. The mixture was ball-milled into a slurry, coated onto aluminum foil, and then vacuum-dried at 60°C. After vacuum drying, the slurry was cut into positive electrode sheets. The mass of active material per unit area of the positive electrode sheet was 2.5-5 mg / cm². 2 ;
[0022] More preferably, the conductive agent in the positive electrode is acetylene black, and the binder is polyvinylidene fluoride (PVdF).
[0023] More preferably, the ratio of the total mass of the active material, conductive agent and binder in the positive electrode sheet to the volume of N-methylpyrrolidone (NMP) is 1g:1-3mL;
[0024] More preferably, the ball mill rotates at a speed of 300-500 rpm and the milling time is 3-5 hours;
[0025] More preferably, when forming a sodium-ion half-cell, the active material on the positive electrode is Na, and when forming a sodium-ion full-cell, the active material on the positive electrode is Na3V2(PO4)3(NVP).
[0026] According to a preferred embodiment of the present invention, the electrolyte is a 1 mol / L NaPF6-ethylene carbonate (EC) / diethyl carbonate (DEC) solution, wherein the electrolyte is obtained by dissolving NaPF6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), wherein the volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) in the mixed solvent is 1:1.
[0027] According to a preferred embodiment of the present invention, the diaphragm is a Whatman GF / F glass fiber membrane.
[0028] According to the present invention, the test voltage of the negative electrode during the half-cell electrochemical performance test is 0.01-2.0V vs. Na / Na. + The test voltage of the negative electrode during the full-cell electrochemical performance test is 2.0-4.0V.
[0029] The technical features and beneficial effects of this invention are as follows:
[0030] 1. This invention uses commercially available anode materials, which are low in cost and easy to mass-produce.
[0031] 2. This invention only requires pre-coating the surface of the negative electrode material particles. After HC and EDTA are stirred in water, they are dried at a specific temperature. During the drying process, the hydroxyl groups on the surface of HC and the carboxyl groups of EDTA undergo dehydration condensation. The C=O catalytic salt is preferentially reduced to form an SEI rich in inorganic substances, thereby greatly improving the electrochemical performance of the hard carbon (HC) negative electrode material. There is no need for complex morphology and structure control, and a small amount of EDTA greatly improves its cycle stability.
[0032] 3. The HC-EDTA anode prepared by this invention has a specific oxidation state of 0.2 A g. -1 After 200 cycles at a current of [current value missing], it showed 233.8 mAh g. -1 The capacity is [missing information], while HC is only 123.2mAh g. -1 A full cell was assembled using HC-EDTA anode material matched with Na3V2(PO4)3 (NVP) cathode. Compared with uncoated HC, the performance of EDTA-coated HC was improved, with a performance of 0.2 A g. -1At the current density, the capacity retention rate increased from 31% to 75% after 1000 cycles. These results indicate that EDTA coating is a simple and universal method to improve the electrochemical performance of hard carbon anode materials; at the same time, only a small amount of EDTA is needed to play a significant role in the stable cycling of the battery. Attached Figure Description
[0033] Figure 1 The XRD patterns (a) and Raman patterns (b) of the HC-EDTA anode material and the hard carbon (HC) anode material prepared in Example 1 are shown.
[0034] Figure 2 XPS spectra of the HC-EDTA anode material and the hard carbon (HC) anode material prepared in Example 1, where (a) is the hard carbon (HC) anode material and (b) is the HC-EDTA anode material.
[0035] Figure 3 SEM images of the HC-EDTA anode material and the hard carbon (HC) anode material prepared in Example 1, where (a) is the hard carbon (HC) anode material and (b) is the HC-EDTA anode material.
[0036] Figure 4 The electrochemical performance test results of half-cells assembled from negative electrode sheets prepared with the HC-EDTA negative electrode material of Example 1 and the hard carbon (HC) negative electrode material of Comparative Example 1 are shown, where (a) is the first charge-discharge curve with a current density of 0.05 A g. -1 (b) is 0.2A g -1 Cyclic performance under current, (c) is the mean and standard deviation of coulombic efficiency in Figure (b), and (d) is the rate performance under different current densities.
[0037] Figure 5 The electrochemical performance test results of half-cells assembled from the HC-EDTA anode materials prepared in Examples 1-3 and the hard carbon (HC) anode material of Comparative Example 1 are shown, where (a) is 0.2 A g. -1 (a) Cyclic performance under current, and (b) Rate performance under different current densities.
[0038] Figure 6 XPS F 1s spectra of the negative electrode sheets prepared by the HC-EDTA negative electrode material prepared in Example 1 and the hard carbon (HC) negative electrode material of Comparative Example 1 after 3 cycles, where (a) is Comparative Example 1 and (b) is Example 1.
[0039] Figure 7The electrochemical performance test results of the full cell assembled from the HC-EDTA anode material prepared in Example 1 and the hard carbon (HC) anode material in Comparative Example 1 are shown, where (a) is the first charge-discharge curve with a current of 0.05 A g. -1 (b) is 0.2A g -1 Cyclic performance under current. Detailed Implementation
[0040] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments.
[0041] The raw materials used in the examples were all commercially available products, and the hard carbon anode material used was Kuraray hard carbon.
[0042] Example 1
[0043] A method for improving the electrochemical performance of hard carbon anode materials in sodium-ion batteries includes the following steps:
[0044] (1) Preparation of HC-EDTA negative electrode material
[0045] 0.015 g of ethylenediaminetetraacetic acid (EDTA) was dissolved in 30 mL of water to obtain an EDTA aqueous solution. 0.5 g of hard carbon (HC) anode material powder with a particle size of 5 μm was added to the above-obtained EDTA aqueous solution. The mass of EDTA was 3% of the mass of the hard carbon (HC) anode material powder. The mixture was stirred at 350 rpm for 12 h and then dried at 150 °C for 12 h to obtain the HC-EDTA anode material.
[0046] (2) Preparation of negative electrode
[0047] HC-EDTA anode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVdF) were mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was then added, with the total mass ratio of HC-EDTA anode material, conductive agent acetylene black, and binder PVdF to NMP volume being 1 g:5 mL. The mixture was ball-milled at 400 rpm for 4 hours to obtain a slurry. This slurry was coated onto copper foil and vacuum-dried at 60°C for 12 hours. The resulting material was then cut into anode sheets, with a HC-EDTA anode material loading of 1.5 mg / cm² per unit area. 2 .
[0048] (3) Preparation of positive electrode sheet
[0049] The active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVdF) were mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was then added. The total mass ratio of the active material, conductive agent acetylene black, and binder PVdF to the volume ratio of NMP was 1 g:2 mL. The mixture was ball-milled at 400 rpm for 4 hours to obtain a slurry. The slurry was coated onto aluminum foil and vacuum-dried at 60°C for 12 hours. The resulting material was then cut into positive electrode sheets, with an active material loading of 4 mg / cm² per unit area. 2 When forming a sodium-ion half-cell, the active material on the positive electrode is Na; when forming a sodium-ion full-cell, the active material on the positive electrode is Na3V2(PO4)3(NVP).
[0050] (4) Battery assembly
[0051] The battery is assembled into a sodium-ion half-cell or full-cell battery, including a positive electrode (Na electrode and NVP positive electrode), a negative electrode, a Whatman GF / F glass fiber separator, a 1 mol / L NaPF6-ethylene carbonate (EC) / diethyl carbonate (DEC) electrolyte, and a CR2025 battery case. The battery assembly is carried out in a glove box. The NaPF6-ethylene carbonate (EC) / diethyl carbonate (DEC) electrolyte is obtained by dissolving NaPF6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), with a volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) of 1:1 in the mixed solvent.
[0052] Half-cell electrochemical charge-discharge test voltage range: 0.01-2.0V (vs. Na / Na) + The full-cell electrochemical charge-discharge test voltage range is 2.0-4.0V.
[0053] Example 2
[0054] A method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries is described in Example 1, except that: in step (1), the mass of ethylenediaminetetraacetic acid (EDTA) is 0.005 g, and the mass of ethylenediaminetetraacetic acid (EDTA) is 1% of the mass of hard carbon (HC) anode material powder.
[0055] Example 3
[0056] A method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries is described in Example 1, except that: in step (1), the mass of ethylenediaminetetraacetic acid (EDTA) is 0.025 g, and the mass of ethylenediaminetetraacetic acid (EDTA) is 5% of the mass of hard carbon (HC) anode material powder.
[0057] Comparative Example 1
[0058] A method for improving the electrochemical performance of hard carbon anode materials for sodium-ion batteries is described in Example 1, except that: the EDTA coating in step (1) is not performed, and commercial hard carbon (HC) powder is directly used as the anode material to prepare the electrode sheet.
[0059] Experimental Example 1
[0060] Material characterization
[0061] Figure 1-3 The characterization results are shown for the HC-EDTA anode material prepared in Example 1 and the hard carbon (HC) anode material in Comparative Example 1. Figure 1 The XRD patterns showed that EDTA coating had no effect on the (002) peak of the hard carbon (HC) material, and the interlayer spacing remained unchanged. Raman spectroscopy indicated an increase in surface defects after coating. Figure 2 A CN peak was observed in the XPS spectrum, indicating that EDTA is coated on the HC surface; SEM images ( Figure 3 This indicates that the coating process has almost no effect on the morphology of the material.
[0062] Experimental Example 2
[0063] Electrochemical performance of half-cell
[0064] Figure 4 The electrochemical performance test results of half-cells assembled from negative electrode sheets prepared with the HC-EDTA negative electrode material of Example 1 and the hard carbon (HC) negative electrode material of Comparative Example 1 are shown. Figure 4 Figure (a) shows the first-cycle charge-discharge curves of HC||Na and HC-EDTA||Na, with similar iCE values; at 0.05 A g -1 After 3 cycles of electrochemical activation, 0.2 A g -1 The cycling performance of the two materials was evaluated under the given current, such as... Figure 4 As shown in (b), Example 1 retained 233.8 mAh g after 200 cycles. -1 The specific capacity of [the sample] is [higher], while that of Comparative Example 1 is only 123.2 mAh g. -1 ; Figure 4 (c) is Figure 4 (b) Mean and variance of coulombic efficiency. The mean coulombic efficiency of HC after EDTA coating is higher and the variance is smaller, indicating that the SEI formed by HC after EDTA coating is more stable during battery charging and discharging. Figure 4 Figure (d) compares the rate performance of HC and HC-EDTA in half-cells as the current density increases from 0.05 A g to 2.0 A g. -1 The specific capacity of HC-EDTA gradually decreases, and at all current densities, its specific capacity is higher than that of HC.
[0065] Figure 5 The electrochemical performance test results of half-cells assembled from the HC-EDTA anode materials prepared in Examples 1-3 and the hard carbon (HC) anode material of Comparative Example 1 are shown in 0.05 A g. -1 After 3 cycles of electrochemical activation, 0.2 A g -1 The cycling performance of the four materials was evaluated under a current, such as... Figure 5 As shown in Figure (a), Example 1 retained 233.8 mAh g after 200 cycles. -1 The specific capacity is higher than that of the hard carbon coated in Examples 2-3. Figure 5 (b) compares the rate performance of the four materials as the current density increases from 0.05 A to 2.0 A g. -1 In Example 1, the specific capacity gradually decreased, and the specific capacity was the highest at all current densities. Therefore, based on the above results, the performance of HC was best when the EDTA coating ratio was 3%.
[0066] Figure 6 The negative electrode sheets prepared in Example 1 and Comparative Example 1 were subjected to a reaction at 0.05 A g. -1 XPS F1s spectra after 3 cycles under the current were compared, revealing that HC-EDTA had a higher NaF content, which is beneficial for Na + The transport of these components reduces the overpotential and promotes the improvement of the electrochemical performance of HC.
[0067] Experimental Example 3
[0068] Electrochemical performance of full cells
[0069] The electrochemical performance of HC-EDTA in a full cell was further investigated using NVP as the cathode material. Figure 7 (a) shows that the iCE of the two materials is not significantly different; Figure 7 Figure (b) shows that at 0.2A g -1 At current, after 1000 cycles, HC-EDTA||NVP showed 259.0 mAh g. -1 The specific capacity of the HC||NVP full cell decreased to 110.8 mAh g under the same conditions. -1 The capacity retention rate increased from 31% to 75% after the coating treatment.
Claims
1. A method for improving the electrochemical performance of hard carbon anode materials in sodium-ion batteries, characterized in that, This method involves coating the surface of a hard carbon anode material with ethylenediaminetetraacetic acid (EDTA) to obtain an HC-EDTA anode material. Then, the HC-EDTA anode material, a conductive agent, and a binder are coated onto a current collector to prepare an anode sheet. The anode sheet, the positive electrode sheet, the separator, and the electrolyte are then assembled into a sodium-ion half-cell or a sodium-ion full-cell.
2. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The steps for coating the surface of hard carbon anode material with ethylenediaminetetraacetic acid are as follows: Hard carbon anode material powder was added to an aqueous solution of ethylenediaminetetraacetic acid, stirred, and then dried to obtain HC-EDTA anode material.
3. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 2, characterized in that, The concentration of the ethylenediaminetetraacetic acid aqueous solution is 0.15-0.9 mg / mL; the mass of ethylenediaminetetraacetic acid in the ethylenediaminetetraacetic acid aqueous solution is 1-5% of the mass of the hard carbon anode material powder.
4. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 2, characterized in that, The stirring time is 10-15 hours, and the stirring speed is 300-500 rpm; the drying is carried out at 120-180℃ for 10-15 hours.
5. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The conductive agent in the negative electrode is acetylene black, Ketjen black or Super P, the binder is polyvinylidene fluoride, and the current collector is copper foil.
6. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The negative electrode sheet is prepared according to the following method: After mixing HC-EDTA negative electrode material, conductive agent, and binder, N-methylpyrrolidone is added and ball milled to obtain a slurry. The obtained slurry is coated on a current collector, dried, and cut to obtain a negative electrode sheet.
7. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The mass ratio of the HC-EDTA anode material, conductive agent, and binder is 8:1:1; the total mass of the HC-EDTA anode material, conductive agent, and binder to the volume ratio of N-methylpyrrolidone is 1g:4-6mL; the ball milling speed is 300-500rpm, and the ball milling time is 3-5h; the drying is performed under vacuum at 50-70℃ for 10-15h; the loading of the HC-EDTA anode material on the anode sheet is 1-2mg / cm³. 2 .
8. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The positive electrode sheet is prepared according to the following method: The active material, conductive agent, and binder were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone was added. The mixture was ball-milled into a slurry, which was then coated onto aluminum foil. After coating, the slurry was vacuum-dried at 60°C. Following vacuum drying, the slurry was cut into positive electrode sheets. The mass of active material per unit area of the positive electrode sheet was 2.5-5 mg / cm². 2 .
9. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 8, characterized in that, The conductive agent in the positive electrode is acetylene black, and the binder is polyvinylidene fluoride; the total mass ratio of the active material, conductive agent, and binder in the positive electrode to the volume ratio of N-methylpyrrolidone is 1g:1-3mL; the ball milling speed is 300-500rpm, and the ball milling time is 3-5h; when forming a sodium-ion half-cell, the active material on the positive electrode is Na, and when forming a sodium-ion full-cell, the active material on the positive electrode is Na3V2(PO4)3.
10. The method for improving the electrochemical performance of hard carbon anode material in sodium-ion batteries according to claim 1, characterized in that, The electrolyte is a 1 mol / L NaPF6-ethylene carbonate / diethyl carbonate solution, which is obtained by dissolving NaPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate, wherein the volume ratio of ethylene carbonate to diethyl carbonate in the mixed solvent is 1:1; the membrane is a Whatman GF / F glass fiber membrane.