Alexander Giovannitti1 Davide Moia1 Piers Barnes1 Iain McCulloch1 2 J. Nelson1

1, Imperial College London, London, , United Kingdom
2, King Abdullah University of Science and Technology (KAUST), Thuwal, , Saudi Arabia

Here, we present a strategy for the design of polymers for battery electrodes where we combine separately optimized structures for the backbone and side chains of conjugated polymers to achieve efficient mixed electronic and ionic conduction. We consider conjugated polymers with a low ionization potential or large electron affinity to address specifications for both cathode and anode materials with redox potentials which fit well with the allowed electrochemical window for water. After identifying suitable organic semiconductors which can be reversibly be charged and discharged in aqueous solutions, we studied the role of the side chain on the electrochemical redox reactions. Polar side chains were attached at the backbone to increase ion conduction to allow for a reversible and fast charging and discharging of the materials in pH neutral sodium chloride water based electrolytes. A similar strategy has previously been successfully applied to the design of polymers for organic electrochemical transistors for bioelectronics.1 Here, we show how the specific capacity of these materials, when used as electrodes, can be further improved through side chain engineering. We demonstrate the fabrication of battery devices with a water based electrolyte using p and n-type conjugated polymers as the cathode and the anode. The device shows promising stability, charging rate and can be operated under a nearly unipolar potential window of 1.4 V.

1. A. Giovannitti, C. B. Nielsen, D.-T. Sbircea, S. Inal, M. Donahue, M. R. Niazi, D. A. Hanifi, A. Amassian, G. G. Malliaras, J. Rivnay, and I. McCulloch, Nat. Commun., 2016, 7, 13066.