Interfacial processes at charge-storing materials have a great impact on such critical operational characteristics as rate capabilities, cycle and calendar life, and safety. For example, solid-electrolyte interfaces that form spontaneously at Li-ion electrodes under operation serve to control surface reactivity, yet may not yield optimized electrode and battery performance. Recent advancements in nanoscale coatings protocols open new opportunities to apply deliberately designed surface coatings at practical electrode structures and materials. Initiated chemical vapor deposition (iCVD) has emerged as one such tool, providing the capability to generate ultrathin polymer coatings with thickness control at the nanoscale , even on complex three-dimensional (3D) substrates . The siloxane-based polymers most commonly generated by iCVD contain ether-like functionalities that support the solvation and transport of Li+ salts, such that they are readily transformed into Li-ion conductors . We are evaluating iCVD as a means to coat the surfaces of conventional powder-composite electrodes, graphite-based anodes and metal oxide/phosphate-containing cathodes, with ultrathin (5–50 nm) polysiloxanes. The resulting polymer-modified electrodes are assembled into Li-ion coin cells containing liquid electrolytes, in which we examine such properties as specific power, coulombic efficiency, cycle life, and tolerance to overcharge/overdischarge conditions. In pursuit of advanced 3D battery designs, we also continue to explore iCVD-based polymers as nanoscale solid-state Li-ion conductors.
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