Highly Flexible Self-Assembled V$_{\mathrm{2}}$O$_{\mathrm{5}}$~Cathodes Enabled by Conducting Diblock Copolymers

Structural energy storage materials combining load-bearing mechanical properties and high energy storage performance are desired for applications in wearable devices or flexible displays. Vanadium pentoxide (V$_{\mathrm{2}}$O$_{\mathrm{5}})$ is a promising cathode material for possible use in flexible battery electrodes, but it remains limited by low Li$^{\mathrm{+}}$ diffusion coefficient and electronic conductivity, severe volumetric changes upon cycling, and limited mechanical flexibility. Here, we demonstrate a route to address these challenges by blending a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-\textit{block}-poly(ethyleneoxide) (P3HT-$b$-PEO), with V$_{\mathrm{2}}$O$_{\mathrm{5}}$ to form a mechanically flexible, electro-mechanically stable hybrid electrode. V$_{\mathrm{2}}$O$_{\mathrm{5}}$ layers were arranged parallel in brick-and-mortar-like fashion held together by the P3HT-$b$-PEO binder. This unique structure significantly enhances mechanical flexibility, toughness and cyclability without sacrificing capacity. Electrodes comprised of 10 wt{\%} polymer have unusually high toughness (293 kJ/m$^{\mathrm{3}})$ and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes.