Sulfonated poly(tetramethydiphenyl ether ether ketone) membranes for vanadium redox flow battery application

Sulfonated poly(tetramethydiphenyl ether ether ketone) (SPEEK) with various degree of sulfonation is prepared and first used as ion exchange membrane for vanadium redox flow battery (VRB) application. The vanadium ion permeability of SPEEK40 membrane is one order of magnitude lower than that of Nafion 115 membrane. The low cost SPEEK membranes exhibit a better performance than Nafion at the same operating condition. VRB single cells with SPEEK membranes show very high energy efficiency (>84%), comparable to that of the Nafion, but at much higher columbic efficiency (>97%). In the self-discharge test, the duration of the cell with the SPEEK membrane is two times longer than that with Nafion 115. The membrane keeps a stable performance after 80-cycles charge-discharge test.     

Preparation and properties of sulfonated poly(fluorenyl ether ketone) membrane for vanadium redox flow battery application

In order to develop novel membranes for vanadium redox flow battery (VRB) with low self-discharge rate and low cost, sulfonated poly(fluorenyl ether ketone) (SPFEK) was synthesized directly via aromatic nucleophilic polycondensation of bisphenol fluorene with 60% sulfonated difluorobenzophenone and 40% difluorobenzophenone. The SPFEK membrane shows the lower permeability of vanadium ions. The open circuit voltage evaluation demonstrates that the SPFEK membrane is superior to Nafion 117 membrane in self-discharge test. Both energy efficiencies (EE) and power densities of the VRB single cell based on the SPFEK membrane are higher than those of the VRB with Nafion 117 membrane at the same current densities. The highest coulombic efficiency (CE) of VRB with SPFEK membrane is 80.3% while the highest CE of the VRB with Nafion 117 membrane is 77.0%. The SPFEK membrane shows the comparative stability to Nafion 117 membrane in VO₂⁺ electrolyte. The experimental results suggest that SPFEK membrane is a promising ion exchange membrane for VRB.     

SPEEK/ SGO proton exchange membranes with superior proton selectivity for vanadium redox battery

质子交换膜作为钒液流电池的关键材料之一,其质子选择性决定钒电池的最终性能。本文对氧化石墨烯（GO）进行磺化改性得到其衍生物GO-SO3H（SGO）,以SPEEK为基质,通过掺杂方式制备一系列质子交换膜（SPEEK/SGO,简写为S/SGO）,对膜的含水率、离子交换容量、面电阻、质子电导率、钒离子渗透率、力学性能以及耐氧化性进行表征,并研究不同SGO含量共混膜的相关电池性能。SEM显示SGO在SPEEK基质中可较好分散,并且,SGO的加入提高了吸水率和质子电导率,S/SGO-1膜的质子选择性[14.14×104 (S·min)/cm3]比SPEEK膜[8.49×104 (S·min)/cm3]提高了66.5%。在50 mA/cm2电流密度下电池性能测试中,S/SGO-1膜的能量效率达到87.8%,自放电时间可达78 h,是Nafion115膜（30 h）的2.6倍。     

Pre-irradiation grafting of styrene and maleic anhydride onto PVDF membrane and subsequent sulfonation for application in vanadium redox batteries

A poly(vinylidene difluoride) (PVDF) membrane was grafted with styrene (St) and maleic anhydride (MAn) using an electron-beam-induced pre-irradiation grafting technique. The grafted membrane (PVDF-g-PS-co-PMAn) was then sulfonated and hydrolyzed to give an ion exchange membrane (denoted as PVDF-g-PSSA-co-PMAc) for vanadium redox flow batteries (VRB) use. Micro-FTIR analysis indicated that PVDF was successfully grafted and sulfonated at the above condition, and the membrane with a high grafting yield (GY) can be easily prepared in a St/MAn binary system at low dose due to a synergistic effect. The water uptake and ion exchange capacity (IEC) of the PVDF-g-PSSA-co-PMAc membrane increased with GY, so too did the conductivity. At a GY of 33.6%, the resulting PVDF-g-PSSA-co-PMAc membrane showed a much higher IEC and conductivity than a conventional Nafion117 membrane, and a much lower permeability of vanadium ions: ca. 1/11 to 1/16 of that through Nafion117. Open circuit voltage measurements showed that the VRB assembled with the PVDF-g-PSSA-co-PMAc membrane maintained values above 1.3 V after a period of 33 h, which was much longer than that with the Nafion117 membrane. It is expected that this work provides a new approach for the fabrication of ion exchange membranes for VRB.     

Amphoteric ion exchange membrane synthesized by direct polymerization for vanadium redox flow battery application

Novel sulfonated poly (fluorenyl ether ketone) with pendant quaternary ammonium groups (SPFEKA) was successfully synthesized by one-pot copolymerization of bis(4-fluoro-3-sulfophenyl)sulfone disodium salt, 4,4′-difluorobenzophenone, bisphenol fluorene and 2,2′-dimethylaminemethylene-9,9′-bis(4-hydroxyphenyl) fluorene (DABPF). The chemical structures were confirmed by FT-IR, and ¹H NMR. The thermal properties were fully investigated by TGA. The synthesized copolymers SPFEKAs are soluble in aprotic solvents, and can be cast into membranes on a glass plate from their N,N′-dimethylacetamide (DMAc) solution. A new kind of amphoteric ion exchange membrane (AIEM) was obtained by immersed SPFEKA into 1 M sulfuric acid. The proton conductivities of these membranes are comparable to the most reported sulfonated polymers under the same conditions. The permeability of vanadium ions in vanadium redox flow battery (VRB) was effectively suppressed by introducing quaternary ammonium groups for Donnan exclusion effect. AIEM-20% possess a only 4.4% vanadium ion permeability of Nafion 115. Cell performance tests showed that the VRB assembled with AIEM-20% shows the highest coulombic efficiency (CE) at the current density of 50 mA/cm², because of its lowest VO²⁺ permeability. In conclusion, these ionomers could be promising candidates for ion-exchange membranes for VRB applications.     

Nafion/polyvinylidene fluoride blend membranes with improved ion selectivity for vanadium redox flow battery application

Nafion/PVDF blends are employed to prepare the ion exchange membranes for vanadium redox flow battery (VRB) application for the first time. The addition of the highly crystalline and hydrophobic PVDF effectively confines the swelling behavior of Nafion. In VRB single cell test, the Nafion/PVDF binary membranes exhibit higher columbic efficiency than recast Nafion at various current densities. The blend membrane with 20 wt% of PVDF (N_0.8P_0.2) shows energy efficiency of 85% at 80 mA cm⁻², which is superior to that of recast Nafion. N_0.8P_0.2 membrane also possesses twice longer duration in OCV decay test and much lower permeation of VO²⁺ compared with recast Nafion. These results indicate that the addition of PVDF is a simple and efficient way to improve the ion selectivity of Nafion, and the polymer blends with optimized mass fraction of PVDF show good potential for VRB application.     

Research progress of vanadium redox flow battery for energy storage in China

Principle and characteristics of vanadium redox flow battery (VRB), a novel energy storage system, was introduced. A research and development united laboratory of VRB was founded in Central South University in 2002 with the financial support of Panzhihua Steel Corporation. The laboratory focused their research mainly on the selection and preparation of electrode materials, membrane material and modification, stable concentrated electrolyte producing approach, test cell configuration design and optimization. Some relevant foundation problems, such as state of vanadium in sulfurous acid with various additives, the difference of electrochemical reaction rate in anode and in cathode, the crossover of vanadium ions and so on, have been emphasized. The details of these studies have been given and discussed. A 5 kW VRB stack was fabricated in the laboratory and its performances, especially electrochemical performance such as voltage efficiencies, energy efficiencies, and durability, were fully tested. The results will be shown in the talk.The key technologies of developing VRB, such as to improve the activity of its electrode materials, the stability of electrolyte and selectivity of separator, were also discussed. In addition, the research progresses in other laboratories in China were briefly introduced.     

Nafion/SiO2 hybrid membrane for vanadium redox flow battery

Sol–gel derived Nafion/SiO₂ hybrid membrane is prepared and employed as the separator for vanadium redox flow battery (VRB) to evaluate the vanadium ions permeability and cell performance. Nafion/SiO₂ hybrid membrane shows nearly the same ion exchange capacity (IEC) and proton conductivity as pristine Nafion 117 membrane. ICP-AES analysis reveals that Nafion/SiO₂ hybrid membrane exhibits dramatically lower vanadium ions permeability compared with Nafion membrane. The VRB with Nafion/SiO₂ hybrid membrane presents a higher coulombic and energy efficiencies over the entire range of current densities (10–80 mA cm⁻²), especially at relative lower current densities (<30 mA cm⁻²), and a lower self-discharge rate compared with the Nafion system. The performance of VRB with Nafion/SiO₂ hybrid membrane can be maintained after more than 100 cycles at a charge–discharge current density of 60 mA cm⁻². The experimental results suggest that the Nafion/SiO₂ hybrid membrane approach is a promising strategy to overcome the vanadium ions crossover in VRB.     

Recent progress on vanadium flow battery technologies

全钒液流电池因其安全可靠,使用寿命长,环境友好,电池均匀性好,可实时直接监测其充放电状态等特点,已成为规模储能技术领域的重要设备.本文详细分析了全钒液流电池的产业化挑战,从而提出主要技术发展方向.另外,重点对中国科学院大连化学物理研究所和大连融科储能技术发展有限公司合作团队在电堆,电池系统和应用示范方面的最新进展进行了总结.     

A significantly improved membrane for vanadium redox flow battery

A novel sandwich-type sulfonated poly(ether ether ketone) (SPEEK)/tungstophosphoric acid (TPA)/polypropylene (PP) composite membrane for a vanadium redox flow battery (VRB) has been developed with improved properties: the permeability of vanadium ions is greatly reduced and the performance of the VRB cell is greatly increased. The membrane is based on a traditional SPEEK membrane embedded with TPA but PP is used to enhance the membrane for the first time. Although its voltage efficiency (VE) is a little lower than that of a Nafion 212 membrane, it is expected to have good prospects for VRB systems because of its low cost and good performance.     

Vanadium redox battery: Positive half-cell electrolyte studies

The vanadium redox battery (VRB) employs two “electrolyte tanks” that store energy in the form of the two vanadium redox couples and a cell “stack” where the charge/discharge reactions occur. To date, 2 M vanadium electrolyte have been successfully used in large demonstration projects for stationary applications. For mobile applications however, higher vanadium concentrations are required to reduce the size and weight of the battery. The main limitation for the vanadium electrolyte concentration and subsequently its energy density in the VRB is the thermal precipitation of the V(V) ion at elevated temperatures. In this paper optimization study of vanadium V(V) supersaturated solutions in terms of concentrations, temperature, and precipitation behavior are reported along with properties such as density and viscosity. It appears that 3.0–3.5 M V(V) solutions in 6 M total sulfate are sufficiently stable at temperatures up to 30 °C, although 2 M solutions are still required for operation at higher temperatures of about 40 °C.     

Analysis of a model for the operation of a vanadium redox battery

Although the vanadium redox battery (VRB) has recently attracted considerable interest as an energy storage technology, it has a relatively poor energy-to-volume ratio and a system complexity compared with other technologies; however, modelling can assist in optimizing cell and stack design. This paper analyzes a 2D time-dependent single-phase isothermal model for the operation of a single cell in a VRB. Unlike in all previous work, asymptotic methods are used to determine the characteristic current density scale in terms of operating conditions and cell component properties. Also, the analysis reveals that the fluid mechanics decouples from the electrochemistry, at leading order; an asymptotically reduced model is then proposed which preserves the original geometrical resolution. This approach is recommended for accurate and computationally efficient VRB stack models, as has been achieved for polymer electrolyte fuel cells; this will be a prerequisite for the use of modelling in stack design and thence large-scale commercialization of the VRB. Finite-element methods are used to compute results for the 1D steady state high-stoichiometry limit; although an idealized case, it is recommended for the in-situ experimental acquisition of VRB electrokinetic data that can then be used for the model when applied under more general operating conditions.     

Preparation and characterization of a novel layer-by-layer porous composite membrane for vanadium redox flow battery (VRB) applications

By the solution casting method, a novel porous membrane has been prepared for VRB by doping sulfonated poly(fluorenyl ether ketone) (SPFEK) with imidazole, and then imidazole was washed out by extraction with solution. The proton conductivity of porous membrane increased with increasing the content of imidazole, but proton/vanadium ion (H/V) selectivity decreased. Layer-by-layer (LbL) technique was used to improve the porous membrane with high selectivity. Moreover, the performance of VRB using SPFEK-20.7imidazole-(PDDA/PSS)₈ membrane which is doped with 20.7 wt.% content of imidazole and then removed imidazole, and then deposited with eight LbL bilayers exhibits the highest columbic efficiency (CE) of 92.5% at 30 mA cm⁻².     

Operation modes for partially failed vanadium redox battery (VRB) energy storage systems

围绕全钒电池系统在部分失效条件下如何保持正常运行全面展开实验验证与理论分析.从电池系统结构组成角度分析了导致全钒电池系统失效的若干情况,并借助实验模拟和实验数据统计分析,总结归纳出全钒电池系统在部分失效条件下的运行特性,从而提出采用降额定功率与倍额定功率两种部分失效运行模式.研究证实该两种运行模式对系统运行效率无显著影响,是实现全钒电池储能系统在部分失效紧急情况下仍能保持正常运转的合理操作.     

全钒液流电池电气模型建模与验证

为准确把握全钒液流电池的实际应用特性,基于全钒液流电池原理,采用建模与仿真软件建立了全钒液流电池的电气模型,并结合5kW全钒液流电池样机系统将仿真与试验充放电电压结果进行比较。结果表明,该模型能较好地模拟线性情况下全钒液流电池的充放电电压特性和暂态特性,验证了模型的准确性和适用范围。     

Robust proton exchange membrane for vanadium redox flow batteries reinforced by silica-encapsulated nanocellulose

High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm⁻² are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm⁻², which is stable during 200 charge-discharge cycles.     

Nafion/organically modified silicate hybrids membrane for vanadium redox flow battery

In our previous work, Nafion/SiO₂ hybrid membrane was prepared via in situ sol–gel method and used for the vanadium redox flow battery (VRB) system. The VRB with modified Nafion membrane has shown great advantages over that of the VRB with Nafion membrane. In this work, a novel Nafion/organically modified silicate (ORMOSIL) hybrids membrane was prepared via in situ sol–gel reactions for mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS). The primary properties of Nafion/ORMOSIL hybrids membrane were measured and compared with Nafion and Nafion/SiO₂ hybrid membrane. The permeability of vanadium ions through the Nafion/ORMOSIL hybrids membrane was measured using an UV–vis spectrophotometer. The results indicate that the hybrids membrane has a dramatic reduction in crossover of vanadium ions compared with Nafion membrane. Fourier transform infrared spectra (FT-IR) analysis of the hybrids membrane reveals that the ORMOSIL phase is well formed within hybrids membrane. Cell tests identify that the VRB with Nafion/ORMOSIL hybrids membrane presents a higher coulombic efficiency (CE) and energy efficiency (EE) compared with that of the VRB with Nafion and Nafion/SiO₂ hybrid membrane. The highest EE of the VRB with Nafion/ORMOSIL hybrids membrane is 87.4% at 20 mA cm⁻², while the EE of VRB with Nafion and the EE of VRB with Nafion/SiO₂ hybrid membrane are only 73.8% and 79.9% at the same current density. The CE and EE of VRB with Nafion/ORMOSIL hybrids membrane is nearly no decay after cycling more than 100 times (60 mA cm⁻²), which proves the Nafion/ORMOSIL hybrids membrane possesses high chemical stability during long charge–discharge process under strong acid solutions. The self-discharge rate of the VRB with Nafion/ORMOSIL hybrids membrane is the slowest among the VRB with Nafion, Nafion/SiO₂ and Nafion/ORMOSIL membrane, which further proves the excellent vanadium ions blocking characteristic of the prepared hybrids membrane.     

Modeling of a Vanadium Redox Flow Battery for power system dynamic studies

Vanadium Redox Flow Battery (VRB) is an electrochemical energy storage system based on a reversible chemical reaction within a sealed electrolyte. Several models have been developed which now offer a good understanding of the VRB operating principles; this knowledge is important to evaluate its performance when applied in power systems. However, these models depend on parameters that are difficult to obtain experimentally or in data sheets. In this regard, this article presents a new VRB model based on the stack efficiency curves, usually determined by the manufacturer. This model is especially useful for computing intensive applications, such as power system dynamic studies, in order to maintain a low run-time. Finally, the simulation results obtained through the proposed model are compared with laboratory results of an experimental VRB system, showing a striking resemblance with only a little relative error arising from them.     

Graphene based polymer electrolyte membranes for electro-chemical energy applications

Graphene, a material with exceptional properties, has dragged an attention worldwide due to its applicability in wide range of applications particularly in energy sector. With the growing human population, an intense need has aroused to explore alternate ways to meet upsurge demand of energy, where the sources of non-renewable energy are limited. Energy conversion and storage devices e.g. fuel cell, electrolyzer, batteries use polymer electrolyte membranes (PEM) as electrolyte/separator, as an important component. PEM plays a vital role in such devices, which can be prepared by functional polymers. Various PEMs consisting of various fillers have been developed to fulfill the needs of energy devices. Graphene oxide (GO), a fascinating material, has stimulated interest among researchers due to its various applications including energy based devices. This review mainly deals with graphene oxide (GO) based polymer electrolyte membranes and their applications in energy devices. Advancements in the development of GO membranes, interaction with polymer matrix and their electrochemical properties has been summarized. This review provides a profound insight about graphene based polymer electrolyte membranes for energy related applications including polymer electrolyte membranes fuel cell (PEMFC), vanadium redox flow battery (VRB) and Li-ion battery.     

氢能发电技术的研究（Ⅲ）—离子交换膜对离子膜颜料电池放电性能的影响

测试分析了3种不同离子交换膜材料的水存留量,溶涨率和离子导电率,结果表明水存留量的膜材料溶涨率和离子导电离也相应较大,对不同离子交换膜的耐热和耐压稳定性测试结果发现3种离子交换膜在200℃以下范围内都没有发生相变或其它结构性变化,失重率都低于5％,因此3种膜材料在200℃以下温度范围内使用是安全可靠的,不同膜材料的耐压机械强度均随着热压处理温度升高而逐渐下降,在相同热压温度条件下的耐压强度的,SH117B膜大于或等于Nafion117膜,Nafion117膜大于或等于SH117A膜,离子交换膜也是影响燃料电池放电性能的一个重要因素,Nafion117组装的燃料电池最大放电功率密度分别是SH117A膜和SH117B膜组装的燃料电池最大放电功率密度的1．28倍和2．4倍。