The Influence of the Electrolyte Composition on the Electrochemical Behaviour of Organic Radical Polymers
Authors: Gerlach Patrick , Burges Rene , Lex-Balducci Alexandra , Schubert Ulrich Sigmar , Balducci Andrea 
Published: February 2020

Organic radical polymers (ORPs) combine a favourable redox chemistry with favourable kinetics [1]. Due to these properties, and thanks to their affordable price, the interest on the use of these polymers for the realization of metal-free batteries constantly increased in the last years [2]. Several types of polymers have been proposed and, among them, the poly(2,2,6,6-tetramethylpiperidinyl-N-oxymethacrylate) (PTMA), which bears a TEMPO group in every repeating unit, has been one of the most investigated [2]. PTMA, which was firstly reported by Nakahara et al., feature a theoretical capacity of 111 mAh/g, displays high rate capabilities and good cycling stability when used in combination with conventional lithium-ion battery (LIBs) electrolytes such as 1 M LiPF6 EC/DEC [1,3,4]. These latter electrolytes have been considered because they are a state-of-the-art in LIBs, which is an established technology. Nevertheless, the use of lithium salts in not needed for the realization of ORP-based batteries, and electrolytes not containing metal salts could be used. These “alternative” electrolytes would contribute to the realization of (completely) metal-free systems. Furthermore, it is important to notice that in the last years only few studies have dedicated to the influence of the electrolyte´s nature and concentration on the electrochemical behaviour of ORPs-based systems.

In this work, we investigated the electrochemical behaviour of PTMA-based electrodes in the electrolytes 1M tetraethylammoniumbis(trifluoromethylsulfonyl)imide (Et4NTFSI) in Propylene Carbonate (PC), 1M 1-butyl-1-methylpyrrolidiuniumbis(trifluoromethylsulfonyl)imide (Pyr14TFSI) in PC and in the neat Pyr14TFSI (this is possible because this salt is an ionic liquid) [5]. Furthermore we investigated the performance of PTMA in combination with 1-Butyl-1-methylpyrrolidinium-tetrafluoroborate (Pyr14BF4) in PC using different concentrations of 1M, 2M and 3M These electrolytes have been verified as feasible candidates for high power storage devices before [6]. We showed that the nature of the electrolyte as well as the electrolyte concentration has a strong influence on the capacity, capacity retention and especially self-discharge of PTMA-based electrodes. Furthermore, we also utilize the PTMA-based electrodes for the realization of asymmetric high power hybrid devices containing neat Pyr14TFSI as the electrolyte, and we showed that these devices display high stability over 10.000 cycles carried out at 10C.

References

[1] S. Muench, A. Wild, C. Friebe, B. Haupler, T. Janoschka, U.S. Schubert, Chemical reviews 116 (2016) 9438–9484.

[2] T. Janoschka, M.D. Hager, U.S. Schubert, Advanced materials (Deerfield Beach, Fla.) 24 (2012) 6397–6409.

[3] K. Nakahara, J. Iriyama, S. Iwasa, M. Suguro, M. Satoh, E.J. Cairns, Journal of Power Sources 165 (2007) 398–402.

[4] K. Nakahara, J. Iriyama, S. Iwasa, M. Suguro, M. Satoh, E.J. Cairns, Journal of Power Sources 165 (2007) 870–873.

[5] P. Gerlach, R. Burges, A. Lex-Balducci, U.S. Schubert, A. Balducci, Journal of Power Sources 405 (2018) 142–149.

[6] S. Pohlmann, C. Ramirez-Castro, A. Balducci, Journal of the Electrochemical Society 162 (2015) A5020-A5030.