Janna Maranas

Abstract:

Rechargeable lithium ion batteries are widely used in portable electronic devices. There are several advantages to replacing the organic liquid electrolyte with one based on a polymeric material, most notably the ability to use lithium metal as the anode material. Such "solid polymer electrolytes" or SPEs suffer from low conductivity and dendrite formation on recharge. Dendrites can be prevented if the material is stiff, however, attempts to stiffen the polymer will decrease conductivity because fast conduction requires the polymer to be flexible. To make progress, we must decouple conductivity and mechanical properties. We address this issue by the use of large aspect ratio nanofillers. Spherical nanopolymers have been known to improve conductivity for the past 10 years. Their influence depends on surface chemistry. If the surface is acidic (in the sense that it is an electron acceptor), conductivity is improved more than if it is basic. This talk will demonstrate that high aspect ratio fillers, tunable surface chemistry and whisker alignment lead to significant gains in conductivity. We propose that these fillers serve as nucleation sites for (polyethylene oxide)6(ClO4)1, the crystalline structure with fast conduction. At the eutectic composition, (polyethylene oxide)10(ClO4)1, multiple layers are formed, further enhancing conductivity. There are many demonstrations of nanofillers significantly increasing stiffness in polymers without salt. We expect the same result with Li salts, and thus we decouple conductivity and mechanical properties.