Thermodynamically stable lithium silicides and germanides from density functional theory calculations

Abstract

High-throughput density-functional-theory (DFT) calculations have been performed on the Li-Si and Li-Ge systems. Lithiated Si and Ge, including their metastable phases, play an important technological rôle as Liion battery (LIB) anodes. The calculations comprise structural optimisations on crystal structures obtained by swapping atomic species to Li-Si and Li-Ge from the X-Y structures in the International Crystal Structure Database, where X={Li,Na,K,Rb,Cs} and Y={Si,Ge,Sn,Pb}. To complement this at various Li-Si and Li-Ge stoichiometries, ab initio random structure searching (AIRSS) was also performed. Between the ground-state stoichiometries, including the recently found Li 17 Si 4 phase, the average voltages were calculated, indicating that germanium may be a safer alternative to silicon anodes in LIB, due to its higher lithium insertion voltage. Calculations predict high-density Li 1 Si 1 and Li 1 Ge 1 P4/mmm layered phases which become the ground state above 2.5 and 5 GPa respectively and reveal silicon and germanium's propensity to form dumbbells in the Li x Si, x = 2.33 − 3.25 stoichiometry range. DFT predicts the stability of the Li 11 Ge 6 Cmmm, Li 12 Ge 7 Pnma and Li 7 Ge 3 P32 1 2 phases and several new Li-Ge compounds, with stoichiometries

Structural Evolution of Electrochemically Lithiated MoS2 Nanosheets and the Role of Carbon Additive in Li-Ion Batteries

“…47,48 AIRSS has successfully predicted the structures of phases of Li-ion batteries (LIBs) containing sulfur, 49 phosphorus, 50 silicon, and germanium. 51 Not limited to ground-state crystal structures, AIRSS has been used to understand point defects 52 and continuous phase transitions in LIBs. 53 AIRSS searches were carried out on stoichiometries of Li x Mo y S 2 y at ratios of less than of 8:1 of Li:MoS 2 which corresponds to a theoretical capacity of up to 1688 mAh/g.…”

Is zeroth order crystal structure prediction (CSP_0) coming to maturity? What should we aim for in an ideal crystal structure prediction code?

“…66 CSP on varying stoichiometries has also impacted energy materials research, with Li 7 Ge 3 being predicted 67 and then found in research on germanium anodes in lithium batteries.…”

Enhanced Li-storage performances of dually-protected CoGeO3 nanocomposites as anode materials for lithium ion batteries

“…In general, the emergence of amorphous of Li-Ge alloys has played a crucial role to provide Li-storage capability during discharge/charge [49][50][51] [52]. The conversion between crystalline and amorphous Ge was believed to occur by virtue of amorphous Li 9 Ge 4 [49] or Li 15 Ge 4 [53] during Li-cycling.…”

“…(3)-(6). Because of the formation of electrochemically amorphous active materials (Curve 1 inFigure 6c) in the charge stage[49][50][51]57], it is very difficult to discriminate the exact crystal phases of the charged materials with conventional XRD technique. As a beneficial reference, we have annealed the active materials at N 2 atmosphere for 30 minutes in the hope of crystallizing the amorphous substances (Curve 2, 3 inFigure 6cand ESI).…”