Xiao Zhang

Layered-structure nanoribbons with efficient electron transport and short lithium ion insertion lengths are promising candidates for Li battery applications. Here we studied at the single nanostructure level the chemical, structural, and electrical transformations of V2O5 nanoribbons. We found that transformation of V2O5 into the omega-Li3V2O5 phase depends not only on the width but also the thickness of the nanoribbons. Transformation can take place within 10 s in thin nanoribbons, suggesting a Li diffusion constant 3 orders of magnitude faster than in bulk materials, resulting in a significant increase in battery power density (360 C power rate). For the first time, complete delithiation of omega-Li3V2O5 back to the single-crystalline, pristine V2O5 nanoribbon was observed, indicating a 30% higher energy density. These new observations are attributed to the ability of facile strain relaxation and phase transformation at the nanoscale. In addition, efficient electronic transport can be maintained to charge a Li3V2O5 nanoribbon within less than 5 s. These exciting nanosize effects can be exploited to fabricate high-performance Li batteries for applications in electric and hybrid electric vehicles.

Air sensitivity remains a substantial barrier to the commercialization of sodium (Na)-layered oxides (NLOs). This problem has puzzled the community for decades because of the complexity of interactions between air components and their impact on both bulk and surfaces of NLOs. We show here that water vapor plays a pivotal role in initiating destructive acid and oxidative degradations of NLOs only when coupled with carbon dioxide or oxygen, respectively. Quantification analysis revealed that reducing the defined cation competition coefficient (η), which integrates the effects of ionic potential and sodium content, and increasing the particle size can enhance the resistance to acid attack, whereas using high-potential redox couples can eliminate oxidative degradation. These findings elucidate the underlying air deterioration mechanisms and rationalize the design of air-stable NLOs.

III−VI and I−III−VI semiconductors with anomalous grain boundaries have been actively studied for high efficiency photovoltaic applications. Nanowire morphology can provide a well-defined nanodomain for studying grain boundary and p−n junction physics for improving solar cell efficiency. We report the synthesis of In2Se3 and CuInSe2 single crystalline nanowires via a Au-catalyzed vapor−liquid−solid growth. Superlattice forms in In2Se3 nanowires at room temperature and a reversible superlattice transformation takes place at 200 °C. Cu concentration in CuInSe2 nanowires can be controlled, and nanowires show a dependence of crystal structure on Cu concentration.