热力学稳定的锂硅化物和锗化物的密度泛函理论计算
Thermodynamically stable lithium silicides and germanides from density-functional theory calculations
摘要：
用密度泛函理论（DFT）对Li-Si和Li-Ge体系进行了计算。锂化硅和锗，包括它们的亚稳相，作为锂离子电池（LIB）阳极发挥着重要的技术作用。计算包括对通过将原子种类从国际晶体结构数据库中的X-Y结构交换为Li-Si和Li-Ge而获得的晶体结构的结构优化，其中X={Li，Na，K，Rb，Cs}并且Y={Si，Ge，Sn，Pb}。为了在各种Li-Si和Li-Ge化学计量下对此进行补充，还进行了从头算随机结构搜索（AIRSS）。在基态化学计量之间，包括最近发现的Li $_{17}$ Si $_{4}$相，计算了平均电压，表明锗可能是LIB中硅阳极的更安全的替代品，因为其具有更高的锂插入电压。计算预测高密度Li $_1$ Si $_1$和Li $_1$ Ge $_1$ $P4/mmm$层状相，其分别在2.5和5 GPa以上变为基态，并揭示硅和锗在Li $_x$ Si，$x=2.33-3.25$化学计量范围内形成哑铃的倾向。DFT预测了Li $_{11}$ Ge $_6$ $Cmmm$、Li $_{12}$ Ge $_7$ $Pnma$和Li $_7$ Ge $_3$ $P32_12$相以及几种新的Li-Ge化合物的稳定性，化学计量为Li $_5$ Ge $_2$、Li $_{13}$ Ge $_5$、Li $_8$ Ge $_3$和Li $_{13}$ Ge $_4$。
英文摘要：
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 Li-ion 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$_3$ $P32_12$ phases and several new Li-Ge compounds, with stoichiometries Li$_5$Ge$_2$, Li$_{13}$Ge$_5$, Li$_8$Ge$_3$ and Li$_{13}$Ge$_4$.
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