  We report a neutral salt water based battery which uses p-type and n-type
solution processed polymer films as the cathode and the anode of the cell. The
specific capacity of the electrodes (approximately 30 mAh cm-3) is achieved via
formation of bipolarons in both the p-type and n-type polymers. By engineering
ethylene glycol and zwitterion based side chains attached to the polymer
backbone we facilitate rapid ion transport through the non-porous polymer
films. This, combined with efficient transport of electronic charge via the
conjugated polymer backbones, allowed the films to maintain constant capacity
at high charge and discharge rates (>1000 C-rate). The electrodes also show
good stability during electrochemical cycling (less than 30% decrease in
capacity over >1000 cycles) and an output voltage up to 1.4 V. The performance
of these semiconducting polymers with polar side-chains demonstrates the
potential of this material class for fast-charging, water based electrochemical
energy storage devices.
