(4ct) Charge Transport Properties of Electronic and Ionic Conducting Block Copolymers for Lithium Battery Electrodes

Patel, S. N., University of California, Berkeley

Materials with nanostructured conducting domains are essential for a wide range of applications related to alternative energy.  Active materials in battery and fuel cell electrodes such as LiFePO4, graphite, and platinum, are either electronic or ionic insulators.  Nanoscale electron- and ion-conducting domains are necessary for enabling redox reactions in these materials.  For example, a traditional porous lithium battery electrode consists of a redox-active material, carbon black for electronic conduction, and non-conductive binder that holds the particles in place.  The pores are backfilled filled with organic electrolyte for ionic conduction.  In some cases such as LiFePO4, electronic and ionic conductivities are so low that the active materials must be in nanoparticle form, and addressing such particles requires the transport of both kinds of charges to occur on nanometer length scales.  Materials such as block copolymers can self-assemble and form co-continuous nanoscale domains.  The primary focus of my Ph.D. work at UC Berkeley under the advisement of Prof. Nitash Balsara involved the synthesis and characterization of the poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) as a nanostructured electrode binder where the P3HT-domains conduct electronic charges and PEO-domains conducts ionic charges.  The results of ac impedance spectroscopy and dc measurements provided the first evidence of the simultaneous conduction of electronic and ionic charges in a block copolymer.  In addition, my work was the first attempt to study the relationship between morphology and simultaneous electronic and ionic transport.  The application of this material in a lithium battery with LiFePO4 showed specific capacity reaching the theoretical limit and with minimal capacity fade, thus demonstrating the practical application of P3HT-b-PEO as conductive binder material.    Furthermore, the ability of our conductive binder to switch between electronically conducting and insulating states in the positive electrode provides an unprecedented route for automatic overdischarge protection within the battery.  This is in stark contrast to traditional lithium ion batteries where external electronics is used to provide overdischarge protection.

My current work as a postdoctoral researcher at UC Santa Barbara under the advisement of Michael Chabinyc and Ed Kramer focuses on fundamental charge transport properties of semiconducting polymers related to organic transistors and thermoelectric devices. 

I believe the combination my Ph.D. and postdoctoral research provides a unique background spanning all solid-state batteries, organic electronics (e.g. transistors and photovoltaics), and organic thermoelectrics research fields.   The experience of my Ph.D. and postdoctoral research will be used define the foundation of my research group where conductive polymers will be used a tool for a variety of energy storage and conversion applications.