Microphase separated block copolymers consisting of an amorphous poly͑ethylene oxide͒ ͑PEO͒-based polymer covalently bound to a second polymer offer a highly attractive avenue to achieving both dimensional stability and high ionic conductivity in polymer electrolytes for solid-state rechargeable lithium batteries. However, due to the strong thermodynamic incompatibility typically found for most polymer pairs, the disordered, liquid state of the copolymer can rarely be achieved without the incorporation of a solvent, which complicates processing. Herein, we report the design of new block copolymer electrolytes based on poly͑methyl methacrylate͒, PMMA, and poly͑oligo oxyethylene methacrylate͒, POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a microphase separated ͑ordered͒ morphology at ambient temperature. Although pure PMMA-b-POEM is segmentally mixed at all temperatures, it is shown that microphase separation in these materials can be induced in a controlled manner by the incorporation of even limited amounts of lithium trifluoromethane sulfonate (LiCF 3 SO 3 ), a salt commonly employed to render PEO ionically conductive. Such ''salt-induced'' microphase separation suggests a simple method for designing new solid polymer electrolytes combining high ionic conductivities with excellent dimensional stability and improved processing flexibility.

For nearly 20 years, poly(ethylene oxide)-based materials have been researched for use as electrolytes in solid-state rechargeable lithium batteries. Technical obstacles to commercialization derive from the inability to satisfy simultaneously the electrical and mechanical performance requirements: high ionic conductivity along with resistance to flow. Herein, the synthesis and characterization of a series of poly(lauryl methacrylate)-b-poly[oligo(oxyethylene) methacrylate]-based block copolymer electrolytes (BCEs) are reported. With both blocks in the rubbery state (i.e., having glass transition temperatures well below room temperature) these materials exhibit improved conductivities over those of glassy-rubbery block copolymer systems. Dynamic rheological testing verifies that these materials are dimensionally stable, whereas cyclic voltammetry shows them to be electrochemically stable over a wide potential window, i.e., up to 5 V at 55ЊC. A solid-state rechargeable lithium battery was constructed by laminating lithium metal, BCE, and a composite cathode composed of particles of LiAl 0.25 Mn 0.75 O 2 (monoclinic), carbon black, and graphite in a BCE binder. Cycle testing showed the Li/BCE/LiAl 0.25 Mn 0.75 O 2 battery to have a high reversible capacity and good capacity retention. Li/BCE/Al cells have been cycled at temperatures as low as Ϫ20ЊC.

Thin film miscible blends of poly(methyl methacrylate) (PMMA) and a branched random copolymer of methyl methacrylate and methoxy poly(ethylene glycol) monomethacrylate, P(MMA-r-MnG), were investigated by neutron reflectivity. The branched copolymer, which has a higher surface tension than PMMA, was nevertheless found to segregate to and completely cover both the surface and silicon substrate following annealing in 2000 Å thick films with ≥2 wt % P(MMA-r-MnG). This is in contrast to linear polyethylene oxide, which was depleted at both film interfaces when blended with PMMA and annealed. The reflectivity results were confirmed by contact angle studies, which indicate that the surfaces of P(MMA-r-MnG)/PMMA blends behave like that of pure P(MMA-r-MnG), resulting in a hydrophilic surface that is stable against dissolution in water-based environments. The branched hydrophilic additive is further shown to render PMMA resistant to protein adsorption and cell adhesion.

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A self-organizing, nanocomposite electrode ͑SONE͒ system was developed as a model lithium alloy-based anode for rechargeable lithium batteries. In situ X-ray adsorption spectroscopy, galvanostatic testing, cyclic voltammetry, X-ray diffraction, and transmission electron microscopy were used to analyze the electrode, which was fabricated from a polyethylene oxide-based block copolymer, single-walled carbon nanotubes, and gold salt. Processing involved a single mixing step without need of a reducing agent. It was found that thermodynamic self-assembly of the block copolymer could provide a template for incorporation of both the gold salt and nanotubes. Electrochemical testing and subsequent analysis showed that owing to the small particle size and the surrounding block copolymer matrix, the SONE system could cycle over 600 cycles with rates varying between C/1.8 and 8.8C with little evidence of decrepitation or coarsening.

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