Facile Synthesis of Amorphous Ge Supported by Ni Nanopyramid Arrays as an Anode Material for Sodium‐Ion Batteries

Abstract

In this work, we introduce Ni nanopyramid arrays (NPAs) supported amorphous Ge anode architecture and demonstrate its effective improvement in sodium storage properties. The Ni−Ge NPAs are prepared by facile electrodeposition and sputtering method, which eliminates the need for any binder or conductive additive when used as a Na‐ion battery anode. The electrodes display stable cycling performance and enhanced rate capabilities in contrast with planar Ge electrodes, which can be owing to the rational design of the architectured electrodes and firm bonding between current collector and active material (i. e. Ni and Ge, respectively). To validate improvement of nanostructures on electrochemical performance, sodium insertion behavior of crystalline Ge derived from Mg 2 Ge precursor has been investigated, in which limited but effective enhancement of sodium storage properties are realized by introducing porous nanostructure in crystalline Ge. These results show that elaborately designed configuration of Ge electrodes may be a promising anode for Na‐ion battery applications.

Towards Germanium Layered Materials as Superior Negative Electrodes for Li‐, Na‐, and K‐Ion Batteries

“…Note that the conductive additive contributes to the capacity with ∼270 mAh/g for Li, ∼120 mAh/g for Na and ∼150 mAh/g for K (Figure S3). Surprisingly, the sodiation of germanane delivered a capacity that exceeds the theoretical capacity for NaGe (396 mAh/g), according to the literature more than one Na can be inserted in the Ge matrix . For potassium, the optimal cycling conditions must be established before assuming an improved cyclability.…”

Si and Ge‐Based Anode Materials for Li‐, Na‐, and K‐Ion Batteries: A Perspective from Structure to Electrochemical Mechanism

“…In analogy with Si, the insertion of sodium in c‐Ge is almost negligible. The major obstacle lies in the high diffusion barrier for Na in Ge lattice, due to its larger size the activation energy for migration between the interstitial sites in the lattice is higher (1.5 eV for Na compared to 0.51 eV for Li) . Still, c‐Ge can be amorphized after the first discharge/charge cycle while the sodiation continues in the amorphous phase .…”

“…The major obstacle lies in the high diffusion barrier for Na in Ge lattice, due to its larger size the activation energy for migration between the interstitial sites in the lattice is higher (1.5 eV for Na compared to 0.51 eV for Li) . Still, c‐Ge can be amorphized after the first discharge/charge cycle while the sodiation continues in the amorphous phase . Amorphous Ge is active toward sodiation, the phase diagram indicates NaGe as the most sodiated phase, but recent reports have shown the insertion of more than one sodium in the Ge lattice, corresponding to Na 1.6 Ge .…”

“…Still, c‐Ge can be amorphized after the first discharge/charge cycle while the sodiation continues in the amorphous phase . Amorphous Ge is active toward sodiation, the phase diagram indicates NaGe as the most sodiated phase, but recent reports have shown the insertion of more than one sodium in the Ge lattice, corresponding to Na 1.6 Ge . In addition, GeO x has shown some activity versus Na, with the formation of Na 2 O that serves as a buffer to accommodate the volume changes during cycling …”

“…Ge nanocolumns improve Na kinetics due to their short diffusion length and 430 mAh g −1 are obtained with a capacity retention of 88% after 100 cycles . a‐Ge NP supported in Ni nanopyramids with enhanced cycling stability and rate capability, due to enough space between each pyramid to buffer the volume changes and the intimate contact between Ni and Ge that shorten the diffusion paths . The use of a‐Ge thin film or porous c‐Ge NP in which all the sodiation products are amorphous .…”