Nanocolumnar Germanium Thin Films as a High-Rate Sodium-Ion Battery Anode Material

Abstract

Both nanocolumnar and dense germanium thin films, synthesized by evaporative deposition, were tested as a potential anode material for sodium-ion batteries. The reversible capacity of the nanocolumnar films was found to be 430 mAh/g, which is higher than the theoretical capacity of 369 mAh/g. The nanocolumnar films retained 88% of their initial capacity after 100 cycles at C/5, whereas the dense films began to deteriorate after ∼15 cycles. Additionally, the nanocolumnar films were stable at charge/discharge rates up to 27C (10 A/g). The diffusion coefficient for sodium in germanium was estimated, from impedance analysis of the dense films, to be ∼10 −13 cm 2 s −1 . Modeling of diffusion in the sodium-germanium system predicts that sodium diffusion in the near-surface layers of the material is significantly faster than in the bulk. These results show that small feature sizes are critical for rapid, reversible electrochemical sodiation of germanium.

Recent Progress in Electrode Materials for Sodium‐Ion Batteries

“…[ 445 ] Ge is also theoretically predicted not to be capable of storing Na in its crystalline structure; [ 419 ] therefore, most works have focused on amorphous Ge in thin fi lm and nanowire form. [ 419,[446][447][448] The fi rst report of Ge as a NIB anode material indicated that the amorphous Ge thin fi lm delivered a reversible capacity of 350 mA h g −1 for 15 cycles. [ 448 ] A recent work by Kohandehghan et al also experimentally revealed that crystalline Ge exhibits a capacity of less than 20 mA h g −1 (Figure 18 d, top), whereas amorphorized Ge nanowires exhibited a capacity 370 mA h g −1 (Figure 18 d, bottom).…”

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…As a result, the anodes retained up to $80% of their original capacity after 300 cycles [453]. These authors have also explored the use of silicon-germanium alloys [446] and pure germanium [454] as anode materials. Germanium is expected to be a suitable material for battery anodes as its high electronic and ionic conductivity should allow for a very high charge/discharge rate.…”

“…Thus, by systematically changing the composition of Si (1Àx) Ge x alloy, it was found that the anode's specific capacity decreased and its electronic conductivity and high-rate performance increased with germanium content. Meanwhile, an outstanding result found when using pure germanium OAD thin films in sodium-ion batteries was a high rate of operation at room temperature with this anode material [454]. For an overall view of this work on ion batteries, readers are redirected to a recent review of this group [231], where in addition to summarizing their advances in the fabrication of anodes, they also comment on the use of amorphous OAD TiO 2 films as cathodes (see Ref.…”

Core–Shell Ge@Graphene@TiO2 Nanofibers as a High‐Capacity and Cycle‐Stable Anode for Lithium and Sodium Ion Battery

“…[ 25,64,65 ] Thankfully, the theoretical calculations predicted that the sodium could alloy with germanium (Ge) to form NaGe (Ge + Na + + e − ↔ NaGe), [ 10 ] giving a theoretical capacity of 369 mA h g −1 . Abel et al [ 20 ] synthesized Ge nanocolumnar fi lms by evaporative deposition with a reversible capacity of 430 mA h g −1 . And a 3D Si/Ge nanorods was reported by Yue et al [ 25 ] exhibited excellent electrochemical performance.…”