Templated Nanocomposite Electrodes for Rechargeable Lithium Batteries

Nanostructured composite materials for use in battery technologies have received increased attention as these materials enable improved performance. Polymer systems that locally phase separate into nanometer-scale domains present a valuable template for inorganic materials leading to organic-inorganic hybrid structures. In this work, we investigate the fabrication of high energy density electrode materials for solid-state rechargeable batteries by incorporating continuous, nanoscale phases within one component of self-organizing amphiphilic copolymer systems. The in situ growth of cathodic components in ion-conducting copolymer domains allows for control of morphology and increases the interface-tovolume ratio, thereby increasing the specific electrode area over which faradaic reactions can occur and decreasing ion diffusion distances within the electrode. We begin with templates of microphaseseparating rubbery block and graft copolymers that our research group has previously developed as solid-state electrolytes. The template systems include atom transfer radical polymerized poly((oxyethylene)9 methacrylate)-block-poly(butyl methacrylate), POEM-bPBMA, with a domain periodicity of ~32nm, and freeradically synthesized poly((oxyethylene)9 methacrylate)graft-poly(dimethyl siloxane), POEM-g-PDMS, with a domain periodicity of ~25nm. The resulting microphaseseparated polymer is a structure of alternating hydrophilic (Li-ion conducting) and hydrophobic regions. Sol-gel chemistry involving vanadium alkoxide precursors enables in situ growth of active vanadium oxide phases within the continuous ion conducting domains of the microphase-separated copolymer. Small angle x-ray scattering (SAXS) and scanning transmission electron microscopy (STEM) reveal the morphology of the nanocomposite and confirm the spatially-selective incorporation of the inorganic component. Upon addition of vanadium oxide, the domain spacing (as shown in SAXS) increases. STEM chemical maps of POEM-bPBMA containing vanadium oxide, shown in Figure 1 and 2, depict the continuous structure of the amorphous vanadium oxide throughout the POEM domains of the polymer. To provide contrast between POEM and PBMA domains, the specimen was stained with ruthenium tetraoxide, which infuses preferentially into POEM. Figures 1 and 2 chemically map ruthenium and vanadium across the sample. The two figures represent similar distribution patterns confirming the co-location of vanadium oxide and POEM. The selective interaction of the active components with POEM was further verified by differential scanning calorimetry (DSC) and FT-IR spectroscopy. Through the use of different alkoxide precursors of vanadium and prehydrolyzing the precursor prior to incorporation, up to 30wt% (13v%) inorganic in varying morphologies can be obtained. The nanoscale, structure-directing property of the microphase separating copolymer system can also be used to incorporate electronically conductive components needed for wiring of the lithium-active vanadium oxide domains. Results of continuing efforts in this regard will be discussed.