KHCO_3 activated carbon microsphere as excellent electrocatalyst for VO^(2+)/VO_2^+ redox couple for vanadium redox flow battery

In this paper,carbon microsphere prepared by hydrothermal treatment was activated by KHCO_3 at high temperature,and employed as the catalyst for VO^(2+)/VO_2^+redox reaction for vanadium redox flow battery(VRFB).Carbon microsphere can be etched by KHCO_3 due to the reaction between the pyrolysis products of KHCO_3 and carbon atoms.Moreover,KHCO_3 activation can bring many oxygen functional groups on carbon microsphere,further improving the wettability of catalyst and increasing the active sites.The electrocatalytic properties of carbon microsphere from hydrothermal treatment are improved by high temperature carbonization,and can further be enhanced by KHCO_3 activation.Among carbon microsphere samples,the VO^(2+)/VO_2^+redox reaction exhibits the highest electrochemical kinetics on KHCO_3 activated sample.The cell using KHCO_3 activated carbon microsphere as the positive catalyst demonstrates higher energy efficiency and larger discharge capacity,especially at high current density.The results reveal that KHCO_3 activated carbon microsphere is an efficient,low-cost carbon-based catalyst for VO^(2+)/VO_2^+redox reaction for VRFB system.

Towards an all-vanadium redox flow battery with higher theoretical volumetric capacities by utilizing the VO^2＋/V^3＋ couple

An all-vanadium redox flow battery with V（IV） as the sole parent active species is developed by accessing the VO2＋/V3＋ redox couple. These batteries, referred to as V4RBs, possess a higher theoretical volumetric capacity than traditional VRBs. Copper ions were identified as an effective additive to boost the battery performance.

High performance of zinc-ferrum redox flow battery with Ac^-/HAc buffer solution

A green low-cost redox flow battery using Zn/Znredox couple in HAc/NaAc medium and Fe/Feredox couple in HSOmedium was first proposed and investigated for potential stationary energy storage applications. The presence of HAc/NaAc in the negative electrolyte can keep the pH between 2.0 and 6.0even when a large amount of Hions move into negative electrolyte from positive electrolyte through ion exchange membrane. In the pH range of 2.0–6.0, the chemical reaction of Zn species with Hspecies is very insignificant; furthermore, the electroreduction of Hion on the negative electrode is significantly suppressed at this pH range. The zinc-ferrum redox flow battery（Zn/Fe RFB） operated within a voltage window of 0.5–2.0 V with a nearly 90% utilization ratio, and its energy efficiency is around 71.1% at room temperature. These results show that Zn/Fe RFB is a promising option as a stationary energy storage equipment.

A bipolar verdazyl radical for a symmetric all-organic redox flow-type battery

A symmetric all-organic non-aqueous redox flow-type battery was investigated employing the neutral small molecule radical 3-phenyl-1,5-di-p-tolylverdazyl,which can be reversibly oxidized and reduced in one-electron processes,as the sole charge storage material.Cyclic voltammetry of the verdazyl radical in 0.5 M tetrabutylammonium hexa fluoro phosphate(TBAPF6)in acetonitrile revealed redox couples at-0.17 V and-1.15 V vs.Ag+/Ag,leading to a theoretical cell voltage of 0.98 V.From the dependence of peak currents on the square root of the scan rate,diffusion coefficients on the order of 4 x 10 6 cm2 s-1 were demonstrated.Cycling performance was assessed in a static cell employing a Tokoyuma AHA anion exchange membrane,with 0.04 M verdazyl as catholyte and anolyte in 0.5 M TBAPF6 in acetonitrile at a current density of 0.12 mA cm-2.Although coulombic efficiencies were good(94%-97%)throughout the experiment,the capacity faded gradually from high initial values of 93%of the theoretical discharge capacity to 35%by the 50th cycle.Voltage and energy efficiencies were 68%and 65%,respectively.Postcycling analysis by cyclic voltammetry revealed that decomposition of the active material with cycling is a leading cause of cell degradation.

Two electron utilization of methyl viologen anolyte in nonaqueous organic redox flow battery

Methyl viologen （MV） as a bench-mark anolyte material has been frequently applied in aqueous organic redox flow batteries （AORFBs） towards large-scale renewable energy storage. However, only the first re- duction of MV was utilized in aqueous electrolytes because of the insoluble MV0generated from the second reduction of MV. Herein, we report that methyl viologen with bis（trifluoromethane）sulfonamide counter anion, MVTFSI, can achieve two reversible reductions in a nonaqueous supporting elec- trolyte. Paired with （Ferrocenylmethyl）trimethylammonium bis（trifluoromethanesulfonyl）imide, FcNFFSI, as catholyte, the MVTFS/FcNTFSI nonaqueous organic redox flow battery （NOARFB） can take advantage of either one electron or two electron storage of the methyl viologen moiety and provide theoretical energy density of 24.9Wh/L and a cell voltage of up to 1.5V. Using a highly conductive LiTFSI/CH_3CN supporting electrolyte and a porous Daramic separator, the NOARFB displayed excellent cycling performance, includ- ing up to a 68.3g energy efficiency at 40 mA/cm2, and more than 88g total capacity retention after 100 cycles.

Performance of redox flow battery systems in Japan

Renewable energies, such as solar and wind power, are increasingly being introduced as alternative energy sources on a glosbal scale toward a low-carbon society. For the next generation power network, which uses a large number of these distributed power generation sources, energy storage technologies will be indispensable. Among these technologies, battery energy storage technology is considered to be most viable. Sumitomo Electric Industries, Ltd. has developed a redox flow battery system suitable for large scale energy storage, and carried out several demonstration projects on the stabilization of renewable energy output using the redox flow battery system. This paper describes the advantages of the redox flow battery and reviews the demonstration projects.

Soft Template-Induced Porous Polyvinylidene Fluoride Membrane for Vanadium Flow Batteries

Vanadium flow batteries(VFBs)are considered ideal for grid-sc ale,long-duration energy storage applications owing to their decoupled output power and storage capacity,high safety,efficiency,and long cycle life.However,the widespread adoption of VFB s is hindered by the use of expensive Nafion membranes.Herein,we report a soft template-induced method to develop a porous polyvinylidene fluoride(PVDF)membrane for VFB applications.By incorporating water-soluble and flexible polyethylene glycol(PEG 400)as a soft template,we induced the aggregation of hydrophilic sulfonated poly(ether ether ketone),resulting in phase separation from the hydrophobic PVDF polymer during membrane formation.This process led to the creation of a porous PVDF membrane with controllable morphologies determined by the polyethylene glycol content in the cast solution.The optimized porous PVDF membrane enabled a stable VFB performance for 200 cycles at a current density of 80 mA/cm^(2),and the VFB exhibited a Coulombic efficiency of 95.2%and a voltage efficiency of 87.8%.These findings provide valuable insights for the development of highly stable membranes for VFB applications.

System Energy and Efficiency Analysis of 12.5 W VRFB with Different Flow Rates

Vanadium redox flow battery(VRFB)is considered one of the most potential large-scale energy storage technolo-gies in the future,and its electrolyte flow rate is an important factor affecting the performance of VRFB.To study the effect of electrolyte flow rate on the performance of VRFB,the hydrodynamic model is established and a VRFB system is developed.The results show that under constant current density,with the increase of electrolyte flow rate,not only the coulombic efficiency,energy efficiency,and voltage efficiency will increase,but also the capacity and energy discharged by VRFB will also increase.But on the other hand,as the flow rate increases,the power of the pump also increases,resulting in a decrease in system efficiency.The energy discharged by the system does not increase with the increase in flow rate.Considering the balance between efficiency and pump power loss,it is experimentally proved that 120 mL·min-1 is the optimal working flow rate of the VRFB system,which can maximize the battery performance and discharge more energy.

Swelling-induced morpholine functionalized adamantane-containing poly(aryl ether ketone)membranes for vanadium flow batteries

Swelling-induced morpholine functionalized adamantane-containing poly(aryl ether ketone) (MAPEK) membranes were prepared for vanadium flow batteries. MAPEK membranes were prepared from chloromethylated polymer and morpholine and further swelling-induced with hot phosphoric acid to obtain membranes with enhanced ionic conductivity. The swelling, selectivity, and ionic conductivity of MAPEK membranes were regulated by varying the swelling temperature. Selective swelling-induced microphase separation in MAPEK membranes, forming wider ion transport pathways and resulting in low area resistance. The unique rigid adamantane-containing backbone limited the swelling of membranes. Consequently, MAPEK membranes showed excellent selectivity and conductivity (vanadium ion permeability coefficient of MAPEK membranes was lower than 3.82 × 0−7 cm2min−1) (Nafion212 membrane, 42.5 × 0−7 cm2min−1), and MAPEK-150 membrane exhibited low area resistance (0.17 Ωcm2). The vanadium flow batteries (VFB) with MAPEK-150 membrane exhibited high energy efficiency (91.1% at 80 mAcm−2, 81.4% at 200 mAcm−2). Furthermore, MAPEK membranes showed good stability in VFB and oxidative electrolytes. The swelling-induced method utilized in this work is a versatile and facile method to enhance the conductivity of ion-exchange membranes.

Redox flow batteries-Concepts and chemistries for cost-effective energy storage

Electrochemical energy storage is one of the few options to store the energy from intermittent renewable energy sources like wind and solar. Redox flow batteries （RFBs） are such an energy storage system, which has favorable features over other battery technologies, e.g. solid state batteries, due to their inherent safety and the independent scaling of energy and power content. However, because of their low energy-density, low powerdensity, and the cost of components such as redox species and membranes, commercialised RFB systems like the all- vanadium chemistry cannot make full use of the inherent advantages over other systems. In principle, there are three pathways to improve RFBs and to make them viable for large scale application： First, to employ electrolytes with higher energy density. This goal can be achieved by increasing the concentration of redox species, employing redox species that store more than one electron or by increasing the cell voltage. Second, to enhance the power output of the battery cells by using high kinetic redox species, increasing the cell voltage, implementing novel cell designs or membranes with lower resistance. The first two means reduce the electrode surface area needed to supply a certain power output, thereby bringing down costs for expensive components such as membranes. Third, to reduce the costs of single or multiple components such as redox species or membranes. To achieve these objectives it is necessary to develop new battery chemistries and cell configurations. In this review, a comparison of promising cell chemistries is focused on, be they all-liquid, slurries or hybrids combining liquid, gas and solid phases. The aim is to elucidate which redox-system is most favorable in terms of energy-density, power-density and capital cost. Besides, the choice of solvent and the selection of an inorganic or organic redox couples with the entailing consequences are discussed.

全产业链贯通布局下钒液流电池长时储能发展思考

清洁能源的发展和“双碳”目标的实施推动了能源结构调整和电网系统升级,这必将催生巨大的万亿长时储能需求,麦肯锡预测2030年全球可再生能源占比将升至60%~70%,长时储能比2025年增加5~10倍(预计2025年30~40 GW)。全钒液流电池相比其他电化学储能具有安全长寿、灵活可靠、资源丰富等优点,2018~2023年国家和地方发布了多项清洁能源储能配置标准的政策性文件,在此背景下钒储能电池行业企业持续高速增长,行业集中度提升,宏观领域表现为我国钒储能产业正处在加速发展期。目前,钒储能电池总体成本较高,主要原因是钒原料价格高,降低成本的核心环节是钒资源提取成本和电解液生产制造成本。中国恩菲研发的短流程制备钒电解液技术相对于传统钒电解液制备技术具有流程短、钒利用率高的特点,制造成本降低了30%~50%,后期随着钒资源开发和新工艺的研发成功,钒储能产业降本优势将愈发突出。在国家政策支持下,钒液流电池储能系统有望在短期内实现规模化、商业化应用,成为储能领域的重要选择。未来,钒液流电池储能系统仍需从多方面进行优化,如重视技术创新和研发、健全回收利用体系等,以实现钒液流电池长时储能产业的可持续发展。

新型储能金属钒资源需求预测与供应分析

随着全球太阳能、风能等新能源的快速发展,储能作为解决其发电间歇性等问题的必备设施,未来也将迎来爆发式增长。钒液流电池具有本征安全、全生命周期经济性好及环境友好等特点,且已具备产业化应用条件,在储能领域的重要性不断凸显。本文分析了未来钒液流电池的发展趋势,设置了高速发展、参考和低速发展3种情景,结合钒液流电池单位钒用量,预测了未来不同情景下储能领域钒资源需求趋势。研究发现,未来钒资源需求将快速增长,尤其是在高增长情景下,全球2040年钒资源需求将较2021年增长276~338倍;分析全球钒资源的供应情况,认为随着钒液流电池的迅速发展,未来钒资源将供不应求。针对以上情况,研究提出:一是提高钒液流电池的技术研发力度;二是加大钒矿的地质勘查力度,积极探索新的钒矿资源;三是创新钒钛磁铁矿的提钒方法和技术,提高钒资源利用效率;四是加大钒资源的回收利用;五是重视境外钒钛磁铁矿的布局与开发。

储能电池建模与状态估计研究进展

储能电池具有能够平滑可再生能源输出,提高电力系统灵活性和应对电力需求峰谷等优势,有助于推动可再生能源发展,从而应对环境污染和能源紧缺的双重压力。目前市场主流的储能电池为锂离子电池,具有高比能特性,同时新型储能电池也在蓬勃发展,其中全钒液流电池具有高安全性的优势,液态金属电池具有超长循环寿命,在电力储能领域具有重要应用前景。储能电池的建模和状态估计对提高储能电池系统性能,确保其安全性以及优化维护效率至关重要,因此文中对锂离子电池、全钒液流电池和液态金属电池的建模和状态估计进行综述。首先,介绍了储能电池状态估计的整体框架,对基于实验的方法、基于模型的方法和基于数据驱动的方法进行整体介绍,并对荷电状态(state of charge,SOC)、健康状态(state of health,SOH)和剩余使用寿命(remaining useful life,RUL)进行概括;然后,从原理出发,分别总结了不同储能电池体系的内部工作过程、模型构建、状态估计与电池管理过程;最后,对不同储能电池体系的主要工作特性进行横向对比和总结,旨在为储能电池选择和发展提供启示。

全钒液流电池用磺化聚芴醚酮质子交换膜的制备及性能

首先,将9,9-二(3,5-二甲基-4-羟基苯基)芴(DMBHF)、9,9-双(4-羟苯基)芴(BHF)和4,4’-二氟二苯甲酮(DFB)在高温下缩聚,得到聚芴醚酮(PFEK-x)(x=30、40、50,x为DMBHF含量,以DFB的物质的量计,下同);接着,利用溴代反应将PFEK-x的甲基功能化为溴甲基;然后,通过4-羟基苯磺酸钠的SN2亲核取代制得具有不同离子交换容量的磺化聚芴醚酮(SPFEK-x);最后,通过溶液浇铸法成膜并酸化,制得新型低成本质子交换膜(PEMs)。采用^(1)HNMR、FTIR、TGA对其进行了表征,并对其性能进行了测试。结果表明,SPFEK-40膜具有较高的质子传导率及离子选择性、较低的钒离子渗透率及面电阻,综合性能优异。以SPFEK-40膜组装的全钒液流电池(VRFB)在电流密度为80 m A/cm^(2)时的能量效率为88.2%,高于以Nafion 212膜组装的VRFB的84.8%。此外,以SPFEK-40膜组装的VRFB在30次循环后放电容量保持率为84.3%,远高于以Nafion 212膜组装的VRFB(66.1%)。该合成路线的原料来源广泛,价格低廉,不涉及危险的磺化反应,易于工业放大。制得的SPFEK-x均具有良好的机械性能和氧化稳定性。

Highly stable side-chain-type cardo poly(aryl ether ketone)s membranes for vanadium flow battery

Vanadium flow batteries(VFBs)have drawn considerable attention as an emerging technology for largescale energy storage systems(ESSs).One of the pivotal challenges is the availability of eligible ion exchange membranes(ICMs)that provide high ion selectivity,proton conductivity,and stability under rigorous condition.Herein,a‘side-chain-type’strategy has been employed to fabricate highly stable phenolphthalein-based cardo poly(arylene ether ketone)s(PAEKs)membrane with low area resistance(0.058Ωcm^(2)),in which flexible alkyl spacers effectively alleviated inductive withdrawing effect from terminal ion exchange groups thus enabling a stable backbone.The assembled VFBs based on PAEKs bearing pendent alkyl chain terminated with quaternary ammonium(Q-PPhEK)demonstrated an energy efficiency above 80%over 700 cycles at 160 mA/cm^(2).Such a remarkable results revealed that the side-chain-type strategy contributed to enhancing the ICMs stability in strong oxidizing environment,meanwhile,more interesting backbones would be woken with this design engaging in stable ICMs for VFBs.

全钒液流电池储能系统最新研究进展

阐述了全钒液流电池结构、工作原理和优缺点,综述了学术圈及产业界针对全钒液流电池的电堆、电解液和电池管理系统等关键系统所开展的技术研究最新进展,指出通过提高电堆电密和电解液短流程制备技术,可有效降低液流电池成本。电解液制备流程的改进和降本将是下一步重点研究方向。

Large scale preparation of 20 cm×20 cm graphene modified carbon felt for high performance vanadium redox flow battery

Vanadium redox flow batteries(VRFBs)are widely applied in energy storage systems(e.g.,wind energy,solar energy),while the poor activity of commonly used carbon-based electrode limits their large-scale application.In this study,the graphene modified carbon felt(G/CF)with a large area of 20 cm×20 cm has been successfully prepared by a chemical vapor deposition(CVD)strategy,achieving outstanding electrocatalytic redox reversibility of the VRFBs.The decorating graphene can provide abundant active sites for the vanadium redox reactions.Compared with the pristine carbon felt(CF)electrode,the G/CF composite electrode possesses more defective sites on surface,which enhances activity toward VO^(2+)/VO^(2+)couple and electrochemical performances.For instance,such G/CF electrode delivered remarkable voltage efficiency(VE)of 88.4%and energy efficiency(EE)of 86.4%at 100 mA·cm^(-2),much higher than CF electrode by 2.1%and 3.78%,respectively.The long-term cycling stability of G/CF electrode was further investigated and a high retention value of 47.6%can be achieved over 600 cycles.It is demonstrated that this work develops a promising and effective strategy to synthesize the large size of carbon electrode with high performances for the next-generation VRFBs.

Recent advances in metals and metal oxides as catalysts for vanadium redox flow battery:Properties,structures,and perspectives

Vanadium redox flow battery(VRFB)is a kind of battery with wide application prospect.Electrode material is one of the key components of VRFB,and its stability directly affects the performance of battery.Among all kinds of electrode materials,carbon-based material has the best comprehensive properties.However,carbon-based electrodes still have disadvantages such as poor hydrophilicity and low electrochemical activity which need to be improved.One of the effective ways to improve the performance of electrode is to modify carbon-based material with metals and metal oxides.The metal catalysts have excellent electrical conductivity and high catalytic activity.The metal oxide catalysts have the advantages of low cost,wide variety and strong oxidizing properties.This work introduced the application of metal and metal oxide modified electrodes in VRFB in recent years,classified the catalysts,studied their catalytic performance and mechanism.The metal catalysts were reviewed from precious metals and base metals.The metal oxide catalysts were classified and discussed according to the similar properties of the same group elements.This work compared different modification methods,summarized the research progress of metal and metal oxide modification,and proposes the future development direction of electrodes and catalysts.

3.5价全钒液流电池用电解液研究现状与展望

全钒液流电池因其固有的安全性、长达十年以上的服役寿命、适应大规模应用及易于回收利用等优势,作为最具应用前景的大规模储能技术得到空前发展,预计到2030年国内全钒液流电池新增装机规模将达到93 GWh。钒电池主要由电解液、电堆和输送系统构成,电解液成本占电池总成本40%以上,其低成本高效制备技术是钒电池大规模商业化发展的关键。钒电解液的主要制备方法包括化学还原法、电解法、溶剂萃取法和离子交换法等。化学还原法是以V_(2)O_(5)和钒酸铵为原料经化学还原制备获得电解液的,工艺成熟,但存在还原剂残留和原料成本较高的问题;电解法工艺流程短,但整体能耗高,电解效率低;离子交换法和溶剂萃取法通常以含钒浸出液为原料,无需经过钒产品制备环节,但流程仍较为繁琐,且难以直接获得3.5价钒电解液。总结归纳了近年来3.5价钒电解液的制备方法,概括了各种方法的原理、工艺流程以及优缺点,以期为3.5价钒电解液制备新技术的开发提供参考。

全钒液流电池在储能领域的应用与展望

随着可再生能源发电量的迅速提高,快速增长的储能需求使全钒氧化还原液流电池逐渐成为行业的热点之一。虽然全钒液流电池存在能量效率低、成本高等问题,但是在储能领域应用前景广阔。从全钒液流电池的主要运行特点出发,分析和综述全钒液流电池运行中主要性能损失、经济性和环保性的研究现状,介绍全钒液流电池的应用现状及未来展望,为后续的工程应用研究决策提供参考。