Measurement of Volume Changes and Associated Stresses in Ge Electrodes Due to Na/Na⁺ Redox Reactions

Abstract

In situ electrochemical cells were assembled with an amorphous germanium (a-Ge) film as working electrode and sodium foil as reference and counter electrode. The stresses generated in a-Ge electrodes due to electrochemical reaction with sodium were measured in real-time during the galvanostatic cycling. A specially designed patterned a-Ge electrode was cycled against sodium and the corresponding volume changes were measured using an AFM; it was observed that sodiation/desodiation of a-Ge results in more than 300% volume change, consistent with literature. The potential and stress response showed that the a-Ge film undergoes irreversible changes during the first sodiation process, but the subsequent desodiation/sodiation cycles are reversible. The stress response of the film reached steady-state after the initial sodiation and is qualitatively similar to the response of Ge during lithiation, i.e., initial linear elastic response followed by extensive plastic deformation of the film to accommodate large volume changes. However, despite being bigger ion, sodiation of Ge generated lower stress levels compared to lithiation. Consequently, the mechanical dissipation losses associated with plastic deformation are lower during sodiation process than it is for lithiation.

Insights into the Sodiation Kinetics of Si and Ge Anodes for Sodium-Ion Batteries

“…Subhajit et al reported that the amorphous Ge thin film undergoes ∼240% volume change after the full sodiation, which corresponds to roughly Na 1.4 Ge. 56 Also, the amorphous Ge nanowires are observed to suffer from a ∼300% volume expansion upon sodiation, in which the reaction terminates at Na 1.6 Ge. 34 Hence, it is anticipated that the formation of the Na 3 Ge phase would induce a larger volume expansion (more Na is stored), thereby possibly more susceptible to mechanical failures.…”

“…Quantitatively, compressive stress of 0.56 GPa is observed when a Ge film is sodiated at room temperature, above which a higher compression is expected. 56 On the other hand, the electrical resistivities of Ge and its sodiated phases should also play a role. Although no direct evidence can be found on how Na inclusion affects the electrical conductivity of the sodiated Ge, the sodiated Sn (the element below Ge in the periodic table) is reported to be more electrically resistive as the Na content increases, not uncommon for intermetallic phases.…”

Multiscale Investigation of Sodium‐Ion Battery Anodes: Analytical Techniques and Applications

“…So far, the focus was clearly based on lithium‐ion batteries and only limited data exists on post‐lithium systems. [ 111,112 ] Thoroughly investigated lithium‐based anode materials include lithium titanate (LTO), [ 106 ] silicon, [ 113 ] germanium, [ 114 ] and aluminum. [ 115 ] Research on cathodes includes layered oxides for lithium‐ion batteries [ 116 ] and the olivine FePO 4 .…”