Counterion condensation and ionic conductivity in microphase separated block copolymer electrolytes*

Ion-conducting polymer electrolytes are central components to many types of electrochemical cells spanning batteries, fuel cells, and water purification units. Ionic conductivity is an important property of these materials as it controls the thermodynamic efficiency of electrochemical systems. Many studies correlate micro-structure attributes of polymer electrolytes to ionic conductivity. However, the impact of counterion condensation, a proxy for the extent and strength of ion-pairing, on ionic conductivity has received less attention and its impact on ionic conductivity is not clearly known. This talk highlights our effort to study counterion condensation in thin film ion-conducting block copolymer electrolytes with precisely defined microstructures. Ionic conductivity and 2D AFM force mapping, combined with all-atomistic molecular simulations, substantiate that microphase separated block copolymer electrolytes are less prone to counterion condensation resulting in lower resistances to ionic charge transport. These findings motivate future studies to probe counterion condensation in precisely defined block copolymer electrolyte microstructures as function of solvation and charge density.