Membrane For Vanadium Redox Flow Battery Research Articles

Cost estimation and performance evaluation of 3D printed membranes for vanadium redox flow batteries

AbstractThe membrane is a central component in the commercialization of vanadium redox flow batteries (VRFB), with Nafion being the preferred material for those membranes. Nafion suffers however from high vanadium crossover and high cost, thus limiting its wider commercial application in VRFB. To address this, studies have focused on sulfonated polyether ether ketone (SPEEK) as an alternative material. This work presents an economic study on the production costs of 3D printed SPEEK (3D‐SPEEK) membranes for VRFB, with multiple production scenarios evaluated. This analysis relies on the performances of 3D‐SPEEK membranes prepared in our laboratory, which have shown higher Coulombic efficiency and lower vanadium ions diffusion than Nafion membranes. Results from the economic analysis revealed that the cost of the 3D‐SPEEK membrane varies from 567.77 to 79.35 €/m2 depending on the production scheme and scale used. Production costs lower than commercial Nafion membranes are achieved when a large production scheme is used. Further analysis shows that 3D‐SPEEK membranes might even be cheaper than conventional SPEEK membranes if their printing time is reduced.

Development of a Selective Layer Via Ultrasonic Spray Coating for Vanadium Redox Flow Batteries: Analysis of Ink Composition and Component Scale-up

Vanadium Redox Flow Battery (VRFB) is a promising technology for stationary energy storage because of its long cycle life and independent energy to power ratio. However, the competitiveness of the technology is hindered by some technological issues, such as vanadium cross-over. Vanadium cross-over is the undesired transport of vanadium ions trough the ion-exchange membrane, causing capacity loss and electrolyte imbalance. Usually, to mitigate cross-over fluxes between the two half-cells, relatively thick membranes (>50 µm) are employed in the commercial applications, meaning increased ohmic losses, reduced energy efficiency and higher system capital cost: indeed, the membrane can contribute up to 50% the cost of the stack [1]. The state-of-the-art membranes for VRFB are made of NafionTM because of its high conductivity, but its not-ideal selectivity towards vanadium ions prevents the use of thin membranes. Alternative cation exchange membranes like SPEEK or SPI are promising because of their reduced permeability, but the low conductivity limits system power density. Instead, anion exchange membranes are still limited by the poor chemical stability and low conductivity [2].The authors in a recent work [3] successfully demonstrated the possibility of mitigating vanadium cross-over though an innovative additional selective layer directly deposited on the membrane. The selective layer, termed as barrier, is a porous component whose pores size tortuous path, thickness and composition are designed to improve ion/proton selectivity. As reported in Cecchetti et al., the barrier layer, manufactured through Reactive Spray Deposition Technology (RSDT) significantly reduced battery self-discharge without hindering the efficiency of the battery [3].In this work, the possibility of manufacturing the barrier via Ultrasonic Spray Coating (USC) is investigated. USC is a commercial and easily scalable technique that exploits the ultrasonic vibration of the nozzle tip to uniformly atomize and spray an ink on a substrate [4]. In particular, the influence of the process parameters and ink composition on the selectivity of the barrier layer and efficiency of the battery were investigated through both morphological and electrochemical characterization in batteries of 4 cm2 and 25 cm2 active area. The deposited barrier layers were directly deposited on NafionTM 212 to form thin layers of 10 µm thickness (Figure 1). The barriers were composed of commercial silica and Vulcan® XC-72R nanoparticles, that introduce a tortuous path for the vanadium ions through the separators, and NafionTM ionomer, acting as a binder and ensuring proton conductivity.After identifying the combination of process parameters and ink composition that ensures the lowest self-discharge of the battery, the scale-up of the barrier at commercial scale was investigated by directly deposition the barrier on NafionTM 212 to obtain an active area of 100 cm2. The 100 cm2 barrier was tested in a VRFB in cycles of charge-discharge cycles with cut-off voltages of 1.65 V and 1 V showing a capacity decay rate of 0.11 % cycle-1 at 50 mA cm-2: four time lower than the reference value (0.44 % cycle-1) reported by Rodby et al. for VRFB in the same range of current density [5].

Sulfonated poly(ether ether ketone) membranes for vanadium redox flow battery enabled by the incorporation of ionic liquid‐covalent organic framework complex

AbstractIn vanadium redox flow battery (VRFB). Sulfonated poly(ether ether ketone) (SPEEK) is viewed as a promising alternative to Nafion as a material for vanadium liquid flow battery membrane, due to its low cost and high proton conductivity. However, SPEEK membranes have a Trade‐Off effect of proton conduction and ion selectivity, which limits the performance of VRFB. Here, we exploited the Donnan effect of imidazole cations in ionic liquids (ILs) to improve the ion selectivity of SPEEK membrane. In addition, used porous covalent organic framework materials (COF) with sulfonic acid functional groups to immobilize ionic liquids, which reduced the loss of ILs. The ion selectivity of the SPEEK membrane was further improved. As a result, the cell performance of the composite membrane is improved. At a constant current density of 40 mA cm−2, SPEEK/IL‐5@TpPa‐SO3H‐3 membrane exhibits high coulombic efficiencies (CE: 98.43%) and energy efficiencies (EE: 91.7%). Furthermore, the energy efficiency of the SPEEK/IL‐5@TpPa‐SO3H‐3 membrane decreases only 2.1% after 60 charge/discharge cycles at 100 mA cm−2. Our work proposed a cost‐effective, high‐performance membrane for VRFB.

Long side-chain quaternary ammonium group functionalized polybenzimidazole based anion exchange membranes and their applications

In the present work, new anion exchange membranes (AEMs) are synthesized by using polybenzimidazole (PBI) as the matrix and (5-bromopentyl)-trimethylammonium bromide (BPTMA-Br) as the grafting reagent. The grafted long side-chain quaternary ammonium group endows the PBI membrane with a high ion exchange capacity (IEC) of 1.8 mmol g−1, and increased hydrophilicity and ionic conductivity. The PBI-48%BPTMA membrane shows a gradual decrease in conductivity when immersing in 1 M KOH at 80 °C, and maintains its 65.3% conductivity after 240 h measurement. Nevertheless, the PBI-48%BPTMA membrane displays a large potential in the vanadium redox flow battery (VRFB). The PBI-48%BPTMA membrane possesses a lower area resistance (0.43 Ω cm2) and vanadium ion permeability (6.9 × 10−7 cm2 min−1) than Nafion115 (0.61 Ω cm2 and 3.2 × 10−6 cm2 min−1). Consequently, the assembled VRFB shows higher energy efficiency of 82.7% at 80 mA cm−2 than Nafion115 (77.4%). Meanwhile, the single cell also exhibits almost unchanged performance within the 400 charge-discharge cycles at 100 mA cm−2, demonstrating superior stability of the PBI-BPTMA membrane in VRFB.

A novel porous polyimide membrane with ultrahigh chemical stability for application in vanadium redox flow battery

The chemical stability of membranes is critical for the application in vanadium redox flow battery (VRFB). In this work, a novel porous cross-linked polyimide membrane (PCrPI) with ultrahigh chemical stability is prepared by using β-cyclodextrin (β-CD) as a template. The unique cross-linking structure and imidazole group with Donnan effect of PCrPI membrane can effectively hinder the migration of vanadium ions. Meanwhile, the imidazole group and porous structure of the PCrPI membrane can also enhance ionic transfer and reduce area resistance. In VRFB tests, the PCrPI membrane exhibits higher coulomb efficiency (CE: 96.3–99.6%) and energy efficiency (EE: 67.9–88.9%) than commercial Nafion 212 membrane (CE: 74.3–94.8%; EE: 67.7–77.5%) at the current density of 40–200 mA cm−2. In addition, the charge–discharge cycles of VRFB with the PCrPI membrane are performed 2250 times, and the running time of PCrPI-10 membrane is among the top level compared with previously reported membranes. Meanwhile, the excellent durability of PCrPI-10 membrane is also explained through theoretical calculation with natural bond orbital charge and binding energy. The results show that the application of PCrPI-10 membrane in VRFB will embrace a bright future.

Polysulfone-Based Membranes for Vanadium Redox-Flow Batteries

Redox flow batteries have been recognized as promising electrochemical energy storage devices, due to independent power and energy scaling, long cycle life, fast response, and no self-discharge during storage. A crucial part of a redox flow cell is the membrane which separates the anolyte and catholyte containers. A membrane for vanadium redox flow battery (VRB) should be stable and exhibit high proton conductivity as well as low vanadium species permeability. Perfluorinated ion-exchange membranes such as Nafion® are currently among the most widely used separators for VRBs. However, the best-performance membranes recognized so far are generally expensive, and the crossover of vanadium species across the membrane is noticeable. Therefore, if a cheaper alternative membrane material is found, the cost efficiency of the battery will be improved. We have evaluated earlier the applicability of membranes based on polyacrylonitrile (PAN) in redox-flow batteries using VBR as a model system. It has been shown that the tuning of PAN material microstructure via phase separation and/or hydrolysis provides the desired balance of proton conductivity and vanadium species permeability. The overall energy efficiency of the VBR cell built using the PAN-based membranes has been found comparable to that determined with Nafion® membranes. In this contribution, we extended this approach to the manufacture of membranes based on polysulfone (PS). The porosity and hydrophilicity of the PS membranes was tuned via phase separation, incorporation of polymeric (poly-N-vinylpyrrolidone) or inorganic (silica) additives, and the procedure of the membrane conditioning. Major physico-chemical properties of the membranes (ion conductivity and water permeability) were systematically measured, and the operation of the model VRB assembled using the PS-based membranes was evaluated in comparison with the PAN and Nafion® membranes. This study was financially supported by Russian Science Foundation (project no. 17-73-30006).

GO-modified membranes for vanadium redox flow battery

Graphene oxide (GO) has attracted tremendous attention in membrane-based separation field as it can filter ions and molecules. Recently, GO-based materials have emerged as excellent modifiers for vanadium redox flow battery (VRFB) application. Its high mechanical and chemical stability, nearly frictionless surface, high flexibility, and low cost make GO-based materials as proper materials for the membranes in VRFB. In VRFB, a membrane acts as the key component to determine the performance. Therefore, employing low vanadium ion permeability with excellent stability membrane in vanadium electrolytes is important to ensure high battery performance. Herein, recent progress of GO-modified membranes for VRFB is briefly reviewed. This review begins with current membranes used for VRFB, followed by the challenges faced by the membranes. In addition, the transport mechanism of vanadium ion and the stability properties of GO-modified membranes are also discussed to enlighten the role of GO in the modified membranes.

Pore-Size-Tuned Graphene Oxide Frameworks as Ion-Selective and Protective Layers on Hydrocarbon Membranes for Vanadium Redox-Flow Batteries.

The laminated structure of graphene oxide (GO) membranes provides exceptional ion-separation properties due to the regular interlayer spacing ( d) between laminate layers. However, a larger effective pore size of the laminate immersed in water (∼11.1 Å) than the hydrated diameter of vanadium ions (>6.0 Å) prevents its use in vanadium redox-flow batteries (VRFB). In this work, we report an ion-selective graphene oxide framework (GOF) with a d tuned by cross-linking the GO nanosheets. Its effective pore size (∼5.9 Å) excludes vanadium ions by size but allows proton conduction. The GOF membrane is employed as a protective layer to address the poor chemical stability of sulfonated poly(arylene ether sulfone) (SPAES) membranes against VO2+ in VRFB. By effectively blocking vanadium ions, the GOF/SPAES membrane exhibits vanadium-ion permeability 4.2 times lower and a durability 5 times longer than that of the pristine SPAES membrane. Moreover, the VRFB with the GOF/SPAES membrane achieves an energy efficiency of 89% at 80 mA cm-2 and a capacity retention of 88% even after 400 cycles, far exceeding results for Nafion 115 and demonstrating its practical applicability for VRFB.

Polyacrylonitrile-Based Membranes for Aqueous Redox-Flow Batteries

Due to several advantages (independent power and energy sizing, long cycle life, fast response, and no self-discharge during storage), redox-flow batteries have been recognized as promising electrochemical energy storage devices. A crucial part of the redox flow-cell is the membrane separating the anolyte and catholyte containers (thus providing for charge carriers conductivity and preventing the cross-mixing of the redox-active components). For example, a membrane for vanadium redox-flow battery (VRB) should be stable against oxidation by VO2 + cations as well as to reduction by V2+ cations and exhibit high proton conductivity to provide high voltage efficiency of the battery as well as low vanadium permeability to ensure high Coulombic efficiency. Perfluorinated membranes such as Nafion® are currently the most widely used ion-exchange membranes for VRBs. However, the best-performance membranes recognized so far are generally expensive, and the crossover of vanadium species across the membrane is rather high. Therefore, if a cheaper alternative membrane material is found, the cost efficiency of the battery will be drastically improved. In this contribution, we demonstrate the applicability of membranes based on polyacrylonitrile (PAN) in redox-flow batteries. Using VBR as a model system, we have shown that microporous PAN membranes provide the desired balance of proton conductivity and vanadium species permeability and are chemically resistant under the VBR operation conditions. The proton conductivity of PAN-based membranes is usually lower than that of Nafion® membranes, but the vanadium ions transport is significantly suppressed. This makes the overall energy efficiency of the VBR cell built using the PAN-based membrane comparable to that determined with Nafion® membranes. It is important to mention that porosity and hydrophilicity of PAN membranes can be easily tuned, enabling facile adjustment of its ion-conducting properties. We have studied the influence of the PAN membranes preparation conditions on their characteristics and elaborated the procedures of the membrane modification by introduction of hydrophilic nanoparticles and by heat treatment. This work was financially supported by Russian Foundation for Basic Research (project no. 16-33-60185 mol_a_dk) and by Centre for Electrochemical Energy of Skolkovo Institute of Science and Technology.

STABILITY AND PERFORMANCE EVALUATION OF ION-EXCHANGE MEMBRANES FOR VANADIUM REDOX FLOW BATTERY

The performance of vanadium redox flow battery (VRFB) is highly dependent on the efficiency of the membrane. Generally, anion exchange membranes and cation exchange membranes can be applied in the VRFB. In this paperwork, AMI-7001S anion exchange membrane and CMI-7000S cation exchange membranes were tested for their suitability in the VRFB application. Both of the membranes were originally used for electrocoat and water treatment system. In order to study the behavior of the membranes in the VRFB, several tests were performed. This includes VO2+ ion permeability, ionic conductivity, ion selectivity, chemical stability and single cell performance. The results obtained were compared to Nafion 117 which is a proton exchange membrane. This membrane is one of the most established membranes for VRFB. From the experiment, it can be summarized that the membranes are unsuitable to be used in VRFB. This is due to the low ion selectivity, poor chemical stability and high resistance.

In-situ and ex-situ degradation of sulfonated polyimide membrane for vanadium redox flow battery application

In this work the degradation behavior of sulfonated polyimide-hydrogen type (SPI-H) membrane for vanadium redox flow battery (VRFB) usage was investigated through in-situ and ex-situ measurements. Morphological, mechanical and physico-chemical properties, together with structure information of the SPI-H membrane or its oligomer before and after degradation were characterized. Both optical photographs and SEM images show more serious destruction of surface morphology of SPI-H membrane during in-situ degradation than ex-situ one. Decrease in mechanical property and viscosity average molecular weight of SPI-H membrane after degradation in different immersion solutions verifies that both H+ and V(V) play important roles in accelerating the decomposition. FTIR results demonstrate that –SO3H groups of SPI-H membrane in VRFB aren’t destructed. 1H-NMR spectra verify the scission of polymer chain and the hydrolysis of imide ring of SPI-H membrane after degradation. XPS spectra evidence the oxidation of –NH2 groups of one hydrolysis product of SPI-H. According to all the experimental results, the 2-step degradation mechanism including hydrolysis and oxidation of SPI-H membrane in VRFB is proposed.

Performance of the vanadium redox-flow battery (VRB) for Si-PWA/PVA nanocomposite membrane

The performance of Si-PWA/PVA nanocomposite membrane in vanadium redox-flow battery (VRB) is reported. Structurally, the membrane consisted of a dispersion of sub-micron-sized silica immobilized phosphotungstic acid (Si-PWA) inorganic ion-exchanging phase in the continuous phase of cross-linked poly(vinyl alcohol) (PVA). SEM micrographs indicated the defect-free top surface of membrane with similar morphology of Nafion-115. Good ion selectivity and availability of ion-exchangeable sites were observed as indicated by higher transport number (0.89) and ion-exchange capacity (IEC) (1.20 meq g−1), respectively. Oxidative stability of the membrane was good in vanadium ion species (V4+, V3+, and V2+) but its stability in V5+ solution and Fenton’s reagent was slightly lower than Nafion-115. Vanadium ion permeability (0.69 × 10−7 cm min−1) of Si-PWA/PVA membrane was significantly lower than Nafion-115. Suitability for VRB with Si-PWA/PVA membrane was assessed from open-circuit voltage (OCV) decay which was lower compared to Nafion-115. Single-cell VRB with Si-PWA/PVA membrane exhibited lower voltage during charge and higher during discharge with excellent cyclic stability compared to VRB with Nafion-115.

Colloidal silicalite-nafion composite ion exchange membrane for vanadium redox-flow battery

Colloidal silicalite-Nafion composite membranes have been synthesized with a two-layer structure consisting of a top layer of colloidal silicalite in Nafion matrix and a base layer of pure Nafion. The composite membrane with an overall thickness of 120–130μm exhibited higher proton-to-vanadyl ion transport selectivity and lower electrical resistance than the 183μm-thick commercial Nafion-117® membrane. The improved proton selectivity in the composite membrane is due primarily to the ability of the sub-nanometer-sized zeolitic pores to block the hydrated metal ions while permitting the small hydrated protons to enter and diffuse through. The low electrical resistance of the composite membrane is attributed to the reduced thickness of the Nafion base film and the thinness of the layer containing silicalite nanoparticles (<30μm). When being used as ion exchange membrane in the vanadium redox flow battery, the composite membrane with a silicalite content of 5wt% has achieved an energy efficiency of 77% at 60mA/cm2 which is significantly higher than the 65% efficiency obtained by the Nafion-117 membrane. The composite membrane also has shown excellent stability after one month of cyclic operation of the battery.

Chemical and mechanical degradation of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

A sulfonated poly(sulfone) (S-Radel®) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V5+ solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V4+ solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm−1 band corresponding to a loss in the sulfonate SO2 stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V5+ ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.