Novel Battery Chemistries Using Electrically Conducting Polymers Synthesised from Deep Eutectic Solvents and Aqueous Solutions

Here we describe the fabrication and testing of novel cells using a conducting polymer membrane, Zn metal anode and a deep eutectic solvent electrolyte. Several different polyaniline-modified electrodes have been formed in various deep eutectic solvents (DESs) and aqueous media using cyclic voltammetry, and subsequently characterised using the electrochemical quartz crystal microbalance (EQCM). The morphologies of the obtained polymers have also been characterised using scanning electron microscopy (SEM), atomic force microscopy (AFM) and 3D optical microscopy. The more compact and dense polyaniline (PANI) films were achieved in DESs, while the films produced from aqueous media exhibited open structures of increased porosities. EQCM showed that the motion of mobile species between films and electrolyte during redox cycling, via the related change in mass, is different in DESs compared to aqueous media; a contributory factor is the higher viscosity and ionic nature of the latter. The electrochemical stabilities and capacitances of these polymers were studied after incorporation of graphite (GR) particles or metal oxides. Graphite particles improved the power and energy densities, as well as the stability of polymers, compared with their ‘pure’ counterparts. The capacity retention of the ternary nanocomposites (PANI/MoO2/GR electrode grown from Oxaline) was 87 %, whereas the lowest retention was found for pure PANI was 13 % after 300 charge–discharge cycles. The PANI composite has been successfully used as a cathode, with Zn metal as anode, in wet batteries (aqueous salt/DES electrolyte). The battery suffered from a low coulombic efficiency of only 51 % in DES at room temperature, whereas at 50oC the efficiency was 97 %. At 50oC and a current density of 0.0625 mA cm-2, the battery showed an energy density of 104 Wh kg-1 at a power density of 75 W kg-1, and a capacity of 344 mA hg-1 for discharge at 0.09 mC cm-2.This suggests the polymer/graphite systems would be more suitable for a power source and battery applications than those using only the pure polymer.