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Vanadium Redox Flow Batteries: a Review Oriented to Fluid-Dynamic Optimization

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Vanadium Redox Flow Batteries: a Review Oriented to Fluid-Dynamic Optimization energies Review Vanadium Redox Flow Batteries: A Review Oriented to Fluid-Dynamic Optimization Iñigo Aramendia 1,* , Unai Fernandez-Gamiz 1 , Adrian Martinez-San-Vicente 1, Ekaitz Zulueta 2 and Jose Manuel Lopez-Guede 2 1 Nuclear Engineering and Fluid Mechanics Department, University of the Basque Country UPV/EHU, Nieves Cano 12, 01006 Vitoria-Gasteiz, Spain; [email protected] (U.F.-G.); [email protected] (A.M.-S.-V.) 2 Automatic Control and System Engineering Department, University of the Basque Country UPV/EHU, Nieves Cano 12, 01006 Vitoria-Gasteiz, Spain; [email protected] (E.Z.); [email protected] (J.M.L.-G.) * Correspondence: [email protected]; Tel.: +34-945-014-066 Abstract: Large-scale energy storage systems (ESS) are nowadays growing in popularity due to the increase in the energy production by renewable energy sources, which in general have a random intermittent nature. Currently, several redox flow batteries have been presented as an alternative of the classical ESS; the scalability, design flexibility and long life cycle of the vanadium redox flow battery (VRFB) have made it to stand out. In a VRFB cell, which consists of two electrodes and an ion exchange membrane, the electrolyte flows through the electrodes where the electrochemical reactions take place. Computational Fluid Dynamics (CFD) simulations are a very powerful tool to develop feasible numerical models to enhance the performance and lifetime of VRFBs. This review aims to present and discuss the numerical models developed in this field and, particularly, to analyze different types of flow fields and patterns that can be found in the literature. The numerical studies presented in this review are a helpful tool to evaluate several key parameters important to optimize the energy systems based on redox flow technologies. Citation: Aramendia, I.; Fernandez-Gamiz, U.; Keywords: energy storage; vanadium redox flow battery; VRFB; flow battery; vanadium; flow field; Martinez-San-Vicente, A.; Zulueta, E.; CFD; numerical model Lopez-Guede, J.M. Vanadium Redox Flow Batteries: A Review Oriented to Fluid-Dynamic Optimization. Energies 2021, 14, 176. https://doi. 1. Introduction org/10.3390/en14010176 The growing consumption of fossil fuel reserves [1], the constant increase in power Received: 4 November 2020 demand [2] and the environmental concerning has served to focus the attention on the Accepted: 25 December 2020 development of sustainable energy alternatives, particularly wind and solar, for electricity Published: 31 December 2020 generation and, therefore, to reduce greenhouse gas emissions [3]. Nowadays we are involved in a daily global development, which is constantly increasing our requirement of Publisher’s Note: MDPI stays neu- energy across the world, while the Earth in its own form and its natural resources cannot tral with regard to jurisdictional clai- follow this development anymore. With all of this in mind, we are all compelled to study ms in published maps and institutio- the different forms of energy sources in terms of security, access, sustainability, climate nal affiliations. change mitigation and reduction of environmental and health impacts [4]. Renewable energies like wind and solar have experienced an exponential enhancement and spreading during the last 20 years, however, the random and intermittent nature of this kind of energies makes difficult to fully take advantage of them. For that reason, large-scale Copyright: © 2020 by the authors. Li- energy storage systems (ESS) are growing in popularity to guarantee the suitable and censee MDPI, Basel, Switzerland. appropriate utilization of these power sources [5]. To that end, battery technology emerged This article is an open access article as a practical application due to the large-scale storage power and volume [6]. In fact, the distributed under the terms and con- ditions of the Creative Commons At- European Commission in its 2016 Integrated SET-Plan reported that to ensure European tribution (CC BY) license (https:// Union competitiveness in the global battery sector, potential uses for batteries beyond creativecommons.org/licenses/by/ e-mobility need to be exploited [7]. Figure1 shows the installed capacity from energy 4.0/). Energies 2021, 14, 176. https://doi.org/10.3390/en14010176 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 20 Energies 2021, 14, 176 2 of 20 energy storage technologies in 2019, according to the International Energy Agency (IEA), with only 5% of the total capacity provided by batteries. storage technologies in 2019, according to the International Energy Agency (IEA), with only 5% of the total capacity provided by batteries. Figure 1. Installed capacity from energy storage technologies, 2019. Source: IEA. Figure 1. Installed capacity from energy storage technologies, 2019. Source: IEA. To date, many types of redox flow batteries have been proposed depending on the redoxTo date, couples many used. types All-vanadium of redox [ 8flow,9], zinc-bromine batteries have [10,11 been], all-iron proposed [12], semi-solid depending on the redoxlithium couples [13] and used. hydrogen-bromine All-vanadium [14 [8,9],] are somezinc-bromine of the most [10,11], common all-iron types of redox[12], flowsemi-solid lith- batteries (RFB) that can be found in the literature. Since Skyllas-Kazacos et al. [15,16] sug- iumgested [13] aand Vanadium hydrogen-bromine Redox Flow Battery [14] (VRFB) are some in 1985, of this the electrochemical most common energy types storage of redox flow batteriesdevice (RFB) has experimented that can be a majorfound development, in the literature. making Since it one Skyllas-Kazacos of the most popular et flow al. [15,16] sug- gestedbatteries a Vanadium these days Redox [17]. Flow Flow batteries Battery are a (VRFB) remarkable in option1985, this for the electrochemical large-scale energy energy stor- agestorage device issue has due experimented to their scalability, a major design development, flexibility, long life making cycle, low it maintenanceone of the andmost popular good safety systems [18,19]. Table1 summarizes the main characteristics of flow batteries flow batteries these days [17]. Flow batteries are a remarkable option for the large-scale as well as other type of energy storage systems. It is important also to highlight the main energyadvantages storage that issue flow due batteries to their offer scalability, [18,20,21]: design flexibility, long life cycle, low mainte- nance• andIndependence good safety between systems peak power [18,19]. and Table the energy 1 summarizes capacity: as the the former main depends characteristics of flow batterieson the dimension as well as of other the stack, type the of latter energy is related storage to the systems. dimension It ofis theimportant tanks and also to high- light thehence main the advantages quantity of electrolyte that flow stored. batteries In some offer conventional [18,20,21]: technologies, such as • the lithium-ion batteries, the two parameters cannot be divided. • IndependencePossibility of changing between the peak electrolyte power of theand storage the energy tanks while capacity: working. as the former depends • on Thethe securitydimension of the of process the stack, and its the long latter life cycle is related make the to LCOS the dimension (Levelized Cost of the of tanks and henceStorage) the onequantity of the mostof electrolyte important parameters stored. In of some the battery conventional [22]. technologies, such as • theUsing lithium-ion vanadium batteries, in both anolyte the tw ando parameters catholyte. The cannot cross-mixing be divided. species due to the non-ideal ion exchange membrane occurs, but since vanadium is used in both sides, • Possibilitythe loss of of capacity changing is not definitive:the electrolyte the solutions of the could storage be shuffled tanks andwhile go backworking. to the • Theinitial security state. Theof the battery process could and also beits leftlong unused life cycle for a long make period the ofLCOS time with(Levelized low Cost of Storage)loss of charge,one of because the most of the important fact that both parameters electrolytes of are the stored battery separately. [22]. • • UsingShort vanadium response time: in both thanks anolyte to the fastand electrochemical catholyte. The kinetics, cross-mixing the response species time due to the non-idealis brief if ion the electrodesexchange are membrane kept full of occurs, electrolyte bu andt since the pumpsvanadium are ready is used to start in both sides, working. • theSolution loss of properties: capacity theis not acid definitive: vanadium solution the solutions is inflammable, could and be even shuffled if it is toxicand go back to thein initial solid state state. (especially The battery V2O5 .),could this form also is be not left present unused in the for normal a long condition period of of time with lowworking loss of but charge, when thebecause solutions of arethe made. fact that both electrolytes are stored separately. • • ShortOn theresponse other hand, time: the thanks technology to the of VRFBfast elec is nowadaystrochemical in an kinetics, “early commercial” the response time is state [23] and is still facing some issues as [20]: • briefLow if specificthe electrodes energy and are power: kept this full is relatedof electrolyte mainly to theand low the cell pumps voltage andare theready to start working.low solubility of the vanadium species (i.e., low number of ions reacting) within a • Solutionlimiting properties: temperature the range acid from va 5nadium◦C to 40 ◦ solutionC. is inflammable, and even if it is toxic in solid state (especially V2O5.), this form is not present in the normal condition of working but when the solutions are made. • On the other hand, the technology of VRFB is nowadays in an “early commercial” state [23] and is still facing some issues as [20]: • Low specific energy and power: this is related mainly to the low cell voltage and the low solubility of the vanadium species (i.e., low number of ions reacting) within a limiting temperature range from 5 °C to 40 °C.
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