2.4 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: Partner(s): Funding: Duration: G. Mourouga, X. Yang, J. O. Schumacher, T J. Schmidt, C. Iojoiu ETH Zürich, Univ. Grenoble-Alpes, JenaBatteries European Commission, Horizon 2020, Marie Skłodowska-Curie Training Networks 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: Figure 6. TEMPO (up) and Paraquat (down) oxidation and reduction via chloride exchange. tron transfer process, and the absence of precious metal catalysts make this chemistry an interesting A common issue faced by ORFBs, however, is the transfer of both active organic molecules and solseparates the positive and negative electrode. 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

These molecules yield a fast chloride-coupled eleccandidate for green, low-cost energy storage [2]. vent through the ion-exchange membrane, which of transport in concentrated solutions.

Figure 2: Picture of positive (left) and negative (right) reservoirs after cycling. The height was initially equal.

Figure 3: illustration of charge interactions in concentrated solutions and ion-exchange membranes.

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.