RESUMO
The high theoretical energy density of alloyed lithium and germanium (Li15Ge4), 1384 mAh/g, makes germanium a promising anode material for lithium-ion batteries. However, common alloy anode architectures suffer from long-term instability upon repetitive charge-discharge cycles that arise from stress-induced degradation upon lithiation (volume expansion >300%). Here, we explore the use of the two-dimensional nanosheet structure of germanane to mitigate stress from high volume expansion and present a facile method for producing stable single-to-multisheet dispersions of pure germanane. Purity and degree of exfoliation were assessed with scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. We measured representative germanane battery electrodes to have a reversible Li-ion capacity of 1108 mAh/g when cycled between 0.1 and 2 V vs Li/Li+. These results indicate germanane anodes are capable of near-theoretical-maximum energy storage, perform well at high cycling rates, and can maintain capacity over 100 cycles.
RESUMO
This paper describes the process of making ordered mesoporous silicon (Si) thin films. The process begins with mesoporous silica (SiO 2) thin films that are produced via evaporation induced self-assembly (EISA) using sol-gel silica precursors with a diblock copolymer template. This results in a film with a cubic lattice of 15 nm diameter pores and 10 nm thick walls. The silicon is produced through reduction of the silica thin films in a magnesium (Mg) vapor at 675 degrees C. Magnesium reduction preserves the ordered pore-solid architecture but replaces the dense silica walls with 10-17 nm silicon crystallites. The resulting porous silicon films are characterized by a combination of low and high angle X-ray diffraction, combined with direct SEM imaging. The result is a straightforward route to the production of ordered nanoporous silicon.
