Graphene Monoxide Bilayer As a High-Performance on/off Switching Media for Nanoelectronics

The geometries and electronic characteristics of the graphene monoxide (GMO) bilayer are predicted via density functional theory (DFT) calculations. All the possible sequences of the GMO bilayer show the typical interlayer bonding characteristics of two-dimensional bilayer systems with a weak van der Waals interaction. The band gap energies of the GMO bilayers are predicted to be adequate for electronic device application, indicating slightly smaller energy gaps (0.418–0.448 eV) compared to the energy gap of the monolayer (0.536 eV). Above all, in light of the band gap engineering, the band gap of the GMO bilayer responds to the external electric field sensitively. As a result, a semiconductor-metal transition occurs at a small critical electric field (<i>E</i>_C = 0.22–0.30 V/Å). It is therefore confirmed that the GMO bilayer is a strong candidate for nanoelectronics

Dominant Factors Governing the Rate Capability of a TiO₂ Nanotube Anode for High Power Lithium Ion Batteries

Titanium dioxide (TiO₂) is one of the most promising anode materials for lithium ion batteries due to low cost and structural stability during Li insertion/extraction. However, its poor rate capability limits its practical use. Although various approaches have been explored to overcome this problem, previous reports have mainly focused on the enhancement of both the electronic conductivity and the kinetic associated with lithium in the composite film of active material/conducting agent/binder. Here, we systematically explore the effect of the contact resistance between a current collector and a composite film of active material/conducting agent/binder on the rate capability of a TiO₂-based electrode. The vertically aligned TiO₂ nanotubes arrays, directly grown on the current collector, with sealed cap and unsealed cap, and conventional randomly oriented TiO₂ nanotubes electrodes were prepared for this study. The vertically aligned TiO₂ nanotubes array electrode with unsealed cap showed superior performance with six times higher capacity at 10 C rate compared to conventional randomly oriented TiO₂ nanotubes electrode with 10 wt % conducting agent. On the basis of the detailed experimental results and associated theoretical analysis, we demonstrate that the reduction of the contact resistance between electrode and current collector plays an important role in improving the electronic conductivity of the overall electrode system

Si/Ge Double-Layered Nanotube Array as a Lithium Ion Battery Anode

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3<i>C</i> rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries