Newsletter 12/21

Word from the coordinators

Dear readers,

the second year of SONAR is coming to an end and we can look back on a mixed time. On the one hand, we have achieved many minor and major successes; on the other, everything is still overshadowed by the COVID-19 pandemic. SONAR started in January 2020 with the onset of the ongoing pandemic. Face-to-face meetings have been impossible this year, and anti-COVID measures have presented a particular challenge to the two institutes working experimentally (CNRS and Fraunhofer ICT), although so far no long-term delays have resulted.

Work on the modelling has proceeded as planned and, at the beginning of 2021, the partners UNSW and Fraunhofer ICT started work in the areas of stack and system modelling and simulation, and cost analysis. A doctoral student was found for each of these topics; both are now firmly integrated into the project team and have achieved very interesting initial results.

One of the most important events for us was the evaluation of SONAR by the European Innovation and Networks Executive Agency (INEA) on behalf of the European Commission. Through reports and presentations, we were able to communicate the results of our work to the evaluators, who then approved the second stage of the project.

In order to better disseminate the results of SONAR and to raise the profile of flow battery research in general, SONAR is coordinating a network of EU-funded projects on the topic of flow batteries: “FLORES”. This year the network has worked hard to raise political awareness, through the creation of a policy brief on the status of flow battery research and future requirements. This document has attracted wide interest, including among national and EU policy makers. Within the EU there is a comparatively high number of commercial and academic representatives in the field of flow batteries. However, these players need further support to meet the future demand for stationary storage for renewable energies.

A particular highlight of the year's developments in SONAR is the first working version of the high-throughput screening for new organic active materials for redox flow batteries. As reported in the last newsletter, the first step has been taken and the system provides automated redox potentials for the organic class of quinones in hydrogenation and de-hydrogenation reactions. A first version of the software will be presented as a demonstrator at the Smart Energy Conference and Exhibition in Sydney in May 2022, and at a joint workshop between the SONAR and COMPBAT projects in mid-2022. As work progresses, the system will be able to calculate the properties of other substance classes, and a kinetics and cell module will be integrated to calculate the properties of batteries on the basis of individual cells.

A public workshop on modelling and simulation is planned for mid-2022 together with the COMPBAT project. According to current plans, the workshop will take place during the week and at the location of the International Flow Battery Forum. More details will be announced later.

In 2022 there will also be a number of conferences on modelling and simulation. We have submitted papers and posters and will work to increase our dissemination activities as more results are achieved. So there is definitely the opportunity to come into direct contact with a representative of the project if you attend conferences on this topic.

In this newsletter, you will find some articles by SONAR staff on a variety of topics. We hope this will give you a better overview of SONAR's work. While the first newsletter described the basic modelling activities, this newsletter focusses on the 3D cell, stack and system, and cost analysis.

We would also like to take this opportunity to thank our Industrial Exploitation Board (Jena Batteries, SGL Carbon, Volterion, Enerox, Schmalz, SCM) for their generous support.

We wish you a healthy and relaxing Christmas holiday, and a good start to the new year 2022!

Carolyn Fisher & Jens Noack

(Project manager & Project coordinator)

Pore scale resolved continuum model for cell performance

Amadeus Wolf, KIT, Germany

Figure 1: Exemplary pore and fibre size distribution of graphite felt material
Figure 2: Color-coded thickness mesh of an exemplary graphite felt

SONAR includes the development of a pore scale resolved continuum model to investigate the cell performance in order to identify and visualize cell limitations such as structure-dependent transport limitations or fluctuating local overpotentials. The latest research on different RFB systems shows that the electrode pore structure and the materials used influence the battery performance and its efficiency. The planned work also includes the examination of computer-generated 3D porous electrodes, to gain further knowledge on how structural properties, e.g. the porosity, specific surface area, fiber and pore size, affect the battery behavior. Moreover, a method for the reconstruction of real porous media by X-ray tomography is being developed to utilize the structure as a finite-volume mesh within the simulations.

Different commercially available carbon-based electrode materials, like graphite felts or reticulated vitreous carbons, were chosen for study within the early stage of the project. The results will give an overview of potential candidates for application in novel redox systems. Carbon materials are perfectly suited to RFB applications due to their high electrical conductivity, good electrochemical stability and their low cost.

The structure on the micrometre scale was obtained through the reconstruction of 3D X-ray micro-computed tomography scans with a voxel size in the one-digit micrometre range. After image visualization, processing and segmentation, a digital twin was created. This serves as the electrode domain in the 3D resolved continuum simulation and could be successfully applied. In the course of the project, it will be shown whether the digital twin is suitable for finite-volume simulations. In Figure 1, pore and fibre size distributions of the different samples can be seen.

To visualize the electrode structure and dimensions, color-coded thickness meshes were used, showing the referential values of the local thickness between boundary points. The colour purple refers to the minimum thickness, whereas green-yellow refers to the maximum value.

Moreover, a detailed list of different electro-conducting material properties like the electrical conductivity, porosity, density or fibre precursors are gathered. These parameters serve as a basis data input for the different modelling approaches within SONAR.

Stack and system modelling for numerical simulation: the hydraulic stack model

Jack Xinjie Guan, UNSW, Australia

At this stage, the work focuses on developing a hydraulic stack model and an electrochemical stack model. The initial model is based on the well-established vanadium redox flow battery chemistry and, through variable inputs, can be further extended to organic redox flow couples of SONAR's interest. With the model, the redox flow batteries can be simulated for their stoichiometric or applied flow rates (either constant or variable), the pressure losses of components, the pump energy required for the stack, concentrations of species, cell voltages and currents (including shunt currents). Thermal factors are also under investigation, with the final model to include hydraulic, electrochemical and thermal stack and system models to optimise system efficiency.  

Cost-analysis and techno-economical modelling

Daniel Gerlach, Fraunhofer ICT, Germany

The success of a technology depends primarily on economic factors. For this reason, it is important to compare the costs of different technologies. All important influencing factors for the different technologies must be taken into account and related to the technical properties such as performance and efficiency. Almost no results are available for a cost assessment of organic FBs, but the wide range of organic active species makes them increasingly worth investigating.

As a basis for this techno-economic consideration, an existing model of a 10 kW / 120 kWh vanadium flow battery (VFB) was optimized and a lab-scale FB was developed for further investigation. This lab-scale FB is first used to study a VFB with electrolytes of different molarities in 3 test cycles, which are also standardized and include behavior at different electrical currents as well as aging tests. The same tests are then performed with aqueous organic FBs (AOFB), where MV / 4-HO-TEMPO and AQS / BQDS in different molarities were selected as redox pairs. These AOFBs are analyzed and compared with the laboratory scale VFB results. In addition to the most commonly studied parameters such as energy density and power density, temperature and cell resistance are also investigated. This is intended to provide the best possible techno-economic conclusions on a component-by-component basis.

Regarding the socio-economic factors, a system for evaluating the toxicity of electrolytes was developed in order to be able to include an initial assessment of the social acceptance of such a FB in the evaluation.

In further studies, broadly validated models will be developed, which should enable statements on CAPEX and LCOS, but also on application-related acceptance estimates.

With a later investigation of scaling factors, it may be possible to make reliable predictions of this kind, at least for individual components, e.g. also for (small) industrial applications on the basis of the laboratory results. 

Figure 3: left) Comparison of an inorganic (vanadium) and an organic (MV/4OH-TEMPO) FB concerning power and energy density (including standard deviation) on the base of several laboratory scale FBs and right) holistic economic model (considering the classification of all components to different order hierarchies) of these flow batteries as a sunburst diagram.

Latest News

November 2021

Flow battery test cell at Fraunhofer ICT for validation of simulation results

SONAR successfully completes phase I of the project

After a project duration of 18 months, the SONAR project was evaluated by INEA, the project executive agency of the European Commission (EC), as planned. Within the framework of a report and a special review meeting, the EC project officers and an external reviewer were presented with the results of the project so far. The main focus was on the status of the development of the high-throughput screening method to search for new organic active materials, as well as the sub-aspects based on atomistic, Kinetic Monte Carlo (meso-scale) and continuum modelling and simulation. SONAR successfully passed the peer review and secured funding for the next phase, which will also focus on the stack, system, costs and behavior in the network.

Screenshot of GUI for interactive manipulation

ZHAW publishes open source 0D cell model and program to calculate flow battery characteristics

November 11, 2021

As part of SONAR, the University of Applied Sciences Zurich, Switzerland, has published an open-source program for calculating the characteristics of organic redox flow batteries. The program is based on the popular mathematical application "Mathematica" and allows the evaluation of polarization curves as predicted by the 0D-U-I-SoC model for user-specified model parameters. Especially for small and medium current densities, which are not in the range of mass transport limitations, the results of the software are very accurate and can be adapted to the specific battery chemistry by adjusting the input parameters. This allows statements to be made about the expected voltages and currents, as well as capacities and energy densities at different states of charge for an almost infinite number of battery chemistries.

In the SONAR project, ZHAW is responsible for the development of optimized cell models for automated high-throughput screening of organic active materials for future, novel redox-flow batteries to store renewable energy.

The open source simulation software and a user discussion forum are available on GitHub.

Upcoming Events

Meet SONAR members in 2022 at:

May 4-5, ICC Sydney, Australia
Smart Energy Conference and Exhibition
together with CENELEST
May 15-19, Aachen, Germany 31st Topical Meeting of the International Society of Electrochemistry
Theory and Computation in Electrochemistry: Seeking Synergies in Methods. Materials and Systems
May 29-June 2, Vancouver, Canada 241st Meeting of The Electrochemical Society
June 20-22, Stockholm, Sweden 32nd Topical Meeting of the International Society of Electrochemistry
Experimental and Modelling tools for Electrochemical Energy Devices
Date not fixed yet International Flow Battery Forum 2022
Date not fixed yet Joint COMPBAT/SONAR workshop on modelling and simulation on Monday in the week of the IFBF
September 12-16, Online 73rd Annual Meeting of the International Society of Electrochemistry
Electrochemistry - Powering a Healthier Planet
November 27-30, Santiago, Chile 33rd Topical Meeting of the International Society of Electrochemistry
Challenges in Molecular Electrochemistry and Surface Reactivity