Research Report 2020
2.4
Institute of Computational Physics
Modelling Capacity Fade in Organic Redox-Flow Batteries: Thermodynamics of Transport in Concentrated Solutions
Organic redox flow batteries (ORFB) show great promise as a low-cost, sustainable energy storage device, with longer expected lifetime compared to competing storage technologies [1]. The aim of this work is to provide a better understanding of the transport processes in ion-exchange membranes, a key component of the batteries regarding lifetime. The ICP collaborates in this regard with the FlowCamp consortium, a research and training project funded by the European Union’s MarieSklodowska-Curie programme. FlowCamp involves 11 partner organisations from 8 different countries. Research in FlowCamp aims to improve materials for high-performance, low-cost next-generation redox-flow batteries. Contributors: G. Mourouga, X. Yang, J. O. Schumacher, T J. Schmidt, C. Iojoiu Partner(s): ETH Zürich, Univ. Grenoble-Alpes, JenaBatteries Funding: European Commission, Horizon 2020, Marie Skłodowska-Curie Training Networks Duration: 2018–2021 One of the organic systems studied within the FlowCamp project is the TEMPO/Paraquat all-organic redox couple [2] developed by the German startup JenaBatteries:
Understanding the transport processes that lead to active molecule crossover and solvent transfer is an important step towards improving battery lifetime and requires a careful thermodynamic formulation of transport in concentrated solutions.
Figure 6. TEMPO (up) and Paraquat (down) oxidation and reduction via chloride exchange. Figure 3: illustration of charge interactions in concentrated solutions and ion-exchange membranes.
These molecules yield a fast chloride-coupled electron transfer process, and the absence of precious metal catalysts make this chemistry an interesting candidate for green, low-cost energy storage [2]. A common issue faced by ORFBs, however, is the transfer of both active organic molecules and solvent through the ion-exchange membrane, which separates the positive and negative electrode.
The aim of our work in the FlowCamp project is to provide a thermodynamically consistent approach to the simulation of transport in concentrated solutions, including modelling of chemical activity and osmotic processes. This approach, applied to ion-exchange membranes in flow batteries, is aimed at understanding and predicting capacity fade, an important advance towards further improvement of membrane design and battery lifetime. [1] X. Wei et al., “Materials and Systems for Organic Redox Flow Batteries: Status and Challenges,” ACS Energy Lett., vol. 2, no. 9, pp. 2187–2204, Sep. 2017. [2] T. Janoschka et al., “An aqueous, polymer-based redox-flow battery using non-corrosive, safe, and low-cost materials,” Nature, vol. 527, no. 7576, pp. 78–81, Oct. 2015.
Figure 2: Picture of positive (left) and negative (right) reservoirs after cycling. The height was initially equal.
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