Formation of Uniform SnO2 Coating Layer on Carbon Nanofiber by Pretreatment in Atomic Layer Deposition

Abstract

<p>Carbon nanofibers (CNF) are widely used as active agents for electrodes in Li-ion secondary battery cells, supercapacitors, and fuel cells. Nanoscale coatings on CNF electrodes can increase the output and lifespan of battery devices. Atomic layer deposition (ALD) can control the coating thickness at the nanoscale regardless of the shape, suitable for coating CNFs. However, because the CNF surface comprises stable C–C bonds, initiating homogeneous nuclear formation is difficult because of the lack of initial nucleation sites. This study introduces uniform nucleation site formation on CNF surfaces to promote a uniform SnO<sub>2</sub> layer. We pretreat the CNF surface by introducing H<sub>2</sub>O or Al<sub>2</sub>O<sub>3</sub> (trimethylaluminum + H<sub>2</sub>O) before the SnO<sub>2</sub> ALD process to form active sites on the CNF surface. Transmission electron microscopy and energy-dispersive spectroscopy both identify the SnO<sub>2</sub> layer morphology on the CNF. The Al<sub>2</sub>O<sub>3</sub>-pretreated sample shows a uniform SnO<sub>2</sub> layer, while island-type SnOx layers grow sparsely on the H<sub>2</sub>Opretreated or untreated CNF.</p>