Lithium-Ion Insertion Properties of Solution-Exfoliated Germanane

Abstract

The high theoretical energy density of alloyed lithium and germanium (LiGe), 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.

Recent Progress on Germanene and Functionalized Germanene: Preparation, Characterizations, Applications, and Challenges

“…A variety of applications for germanene and functionalized germanene in different fields have been reported in recent years . In the following section, we will concentrate on reviewing about the recent applications using the novel materials that we believe will have an important impact on future technology.…”

“…Germanene and functionalized germanene have been used or proposed to be promising for a wide range of energy conversion and storage applications, especially for batteries. Serino et al utilized the 2D GeH nanosheet structure for lithium batteries to moderate stress, which is generated by high volume expansion of Ge‐based materials . As anode for Li‐ion battery, a GeH–carbon composite displayed high energy densities of nearly 1100 mAh g −1 over 100 charge/discharge cycles.…”

“…Meanwhile, from the identical cyclic voltammograms, this group demonstrated that, for Li‐ion batteries, the lithiation and delithiation by GeH and bulk Ge are similar. The lithium insertion and extraction capacities for GeH–carbon anodes were measured by the constant‐current method ( Figure a,b) . Figure a shows charge–discharge profiles of GeH anode cycled between 2.5 and 0.1 V at different charge/discharge rates, and the capacity between C/10 and 2 C is displayed to reflect the performance of the material.…”

“…Besides, the Coulombic efficiencies are represented by blue circles. c) Cycling performance of a GeH anode at 1 C. a–c) Reproduced with permission . Copyright 2017, American Chemical Society.…”

2D Elemental Nanomaterials Beyond Graphene

“…Some calculations have found a bandgap of 3.2 eV for monolayer germanane . Owing to its high carrier mobility, on/off ratio, Li‐ion storage capacity, germanane may find applications in transistors, batteries as well as photocatalysis. Thermal annealing in the temperature range of 180–220 °C can cause dehydrogenation of germanane, forming multilayer germanene.…”