Simultaneously Ion- and Electron-Conducting Block Copolymer Binders for Battery Electrodes*

Lithium-ion batteries provide a portable, on-demand source of electrical energy and are comprised of multiple components for storing and releasing ions, transporting charges, and maintaining mechanical integrity. Polymeric binders, although representing only a fraction of the battery, are an important component for maintaining adhesion between different parts. Polymers that are simultaneously ion- and electron-conducting and redox-active are potentially ideal materials for use in electrodes, and here we show that such polymers can improve both mechanical and electrochemical properties of electrodes. First, flexible, carbon-free hybrid battery cathodes are prepared using poly(3-hexylthiophene)-\textit{block}-poly(ethyleneoxide) (P3HT-$b$-PEO) as a binder. Only 5\textunderscore wt {\%} polymer was required to triple the flexibility of V$_{\mathrm{2}}$O$_{\mathrm{5}}$, and electrodes comprised of 10\textunderscore wt {\%} polymer had unusually high toughness (293\textunderscore kJ/m$^{\mathrm{3}})$ and specific energy (530\textunderscore Wh/kg), both higher than reduced graphene oxide paper electrodes. Next, we present work on self-doped conjugated polymeric binders, which provide stable conductivities and are fully water-processable. These materials are incorporated into V$_{\mathrm{2}}$O$_{\mathrm{5}}$ cathodes and suppress the crystallization of V2O5, even at thermal annealing temperatures above 400 $^{\circ}$ C, maintaining the more favorable aerogel structure. Finally, we discuss the design and development of conjugated and redox-active polymers in Silicon anodes. These results highlight the importance of tradeoffs between mechanical and electrochemical performance in the design of conjugated polymeric binders.