Nanostructured Si_(1-x)Ge_x for Tunable Thin Film Lithium-Ion Battery Anodes

Abstract

Both silicon and germanium are leading candidates to replace the carbon anode of lithium ions batteries. Silicon is attractive because of its high lithium storage capacity while germanium, a superior electronic and ionic conductor, can support much higher charge/discharge rates. Here we investigate the electronic, electrochemical and optical properties of Si(1-x)Gex thin films with x = 0, 0.25, 0.5, 0.75, and 1. Glancing angle deposition provided amorphous films of reproducible nanostructure and porosity. The film's composition and physical properties were investigated by X-ray photoelectron spectroscopy, four-point probe conductivity, Raman, and UV-vis absorption spectroscopy. The films were assembled into coin cells to test their electrochemical properties as a lithium-ion battery anode material. The cells were cycled at various C-rates to determine the upper limits for high rate performance. Adjusting the composition in the Si(1-x)Gex system demonstrates a trade-off between rate capability and specific capacity. We show that high-capacity silicon anodes and high-rate germanium anodes are merely the two extremes; the composition of Si(1-x)Gex alloys provides a new parameter to use in electrode optimization.

Nanostructured Anode Materials for Lithium Ion Batteries: Progress, Challenge and Perspective

“…[90,91] Therefore, the volumetric energy densities of such electrode materials should be calculated at their fully lithiated state, but unfortunately it is often calculated prior to lithiation. [92] It is assumed that the use of any new anode material will increase the energy density of LIBs by improved capacity but in fact energy density strongly depends on several parameters (cell CE, irreversible capacity loss, anode porosity, inactive volume, anode average voltage, volumetric capacity and cathode standard voltage etc.). The effect of various factors on the cell performance is explained as follows.…”

High Energy Density Germanium Anodes for Next Generation Lithium Ion Batteries

“…The Si-Ge anodes can be in the form of layered Si-Ge, Si-Ge alloys, physical mixture of Si-Ge, and alloys in combination with other metals like copper (Cu), nickel (Ni), and molybdenum (Mo) [95][96][97][98][99][100][101][102]. Si and Ge are miscible over the entire range of composition and terminal phases in lithiation have similar Li contents (Li15Si4 and Li15Ge4), structures, and lattice constants [100,103,104].…”

“…Si and Ge are miscible over the entire range of composition and terminal phases in lithiation have similar Li contents (Li15Si4 and Li15Ge4), structures, and lattice constants [100,103,104]. Si-Ge and Si-Ge-Mo multilayer anodes, prepared by magnetron sputtering, were reported lately [95][96][97]. For instance, Mo dispersed homogeneously in the Si and Ge matrix prevented the active material from aggregating, resulting on the enhancement of the capacity and cycling performance, with the Si0.41 Ge0.34Mo0.25 composite film showing long cycleability of 870 mAh g -1 over 100 cycles [96].…”

“…For instance, Mo dispersed homogeneously in the Si and Ge matrix prevented the active material from aggregating, resulting on the enhancement of the capacity and cycling performance, with the Si0.41 Ge0.34Mo0.25 composite film showing long cycleability of 870 mAh g -1 over 100 cycles [96]. Meanwhile, Si-Ge multilayered anodes onto Cu current collector exhibited a stable reversible capacity of 1559 mAh g -1 after 100 cycles [97]. Nanostructured Si1-xGex thin films, with x = 0, 0.25, 0.5, 0.75, 1, were recently tested for their electronic, electrochemical, and optical properties [100].…”

Improved Electrochemical Performance of a GexSi1−xAlloy Negative Electrode for Lithium-Ion Batteries

“…5 A galvanostatic chargedischarge test was carried out with a 2032-type coin cell and an electrochemical measurement system (HJ-1001SM8A Hokuto Denko Co., Ltd. or BS2506 KEISOKUKI) in the potential range between 0.005 and 2.000 V vs. Li + /Li at 303 K under a constant current density of 1 C. 1 C for Ge 0.1 Si 0.9 and Ge 0.1 Si 0.9 /LaSi 2 (50:50 wt %) was calculated to be 3360 and 1680 mA g ¹1 , respectively, based on a theoretical value of 3580 mA h g ¹1 for Li 15 Si 4 and 1384 mA h g ¹1 for Li 15 Ge 4 . 8,10 The capacity of LaSi 2 is vanishingly small. 5 Both the counter and reference electrodes consisted of Li metal sheets (Rare Metallic, 99.9% thickness; 1 mm).…”