Li12Si7, eine Verbindung mit trigonal-planarem Si4-Cluster und planaren Si5-Ringen

Structural and dynamic characterization of Li12Si7 and Li12Ge7 using solid state NMR

“…All prepared samples are crystalline and pure within the detection limit of x-ray diffraction and have an orthorhombic unit cell (space group Pnma). The refined lattice parameters for Li 12 Si 7 (a ¼860.0(1), b ¼1976.7(3), c ¼1434.0(3) pm) and Li 12 Ge 7 (a ¼871.8(3), b ¼2005.1 (8), c ¼1454.0(6) pm), are in good agreement with the data reported in the literature.…”

“…The crystalline lithium silicides available through thermal synthesis routes are Li 12 Si 7 , Li 7 Si 3 , Li 13 Si 4 , and Li 21 Si 5 [1][2][3][4][5][6][7][8]. Electrochemical lithiation of silicon so far has only resulted in amorphous Li x Si material [9], and solid state NMR studies have been interpreted in terms of local lithium environments comparable to those present in crystalline silicides, their quantitative distribution depending on the extent of the electrochemical charge transfer executed [10][11][12].…”

“…A major step in the understanding of silicon based anodes was achieved through the in-situ NMR study of the lithiation of silicon [10]. The 7 Li resonances of the known crystalline lithium silicides have distinguishable NMR shifts and can thus be utilized to determine the composition of the anode material by post mortem as well as in situ characterization. While these previous works provided a detailed understanding of the electrochemical lithiation process, both the static and magic-angle spinning NMR spectra measured at room temperature are strongly influenced by the lithium ion dynamics, resulting in partial or complete motional averaging of the NMR signals of crystallographically distinguishable lithium sites.…”

“…While these previous works provided a detailed understanding of the electrochemical lithiation process, both the static and magic-angle spinning NMR spectra measured at room temperature are strongly influenced by the lithium ion dynamics, resulting in partial or complete motional averaging of the NMR signals of crystallographically distinguishable lithium sites. In the lowest-lithium containing binary phase, Li 12 Si 7 , the detailed motional dynamics have been recently characterized by 7 Li relaxometry, leading to the identification and quantitative characterization of a very fast one-dimensional diffusion process and two additional three-dimensional diffusion processes, which are somewhat slower [15]. These motional processes need yet to be related to crystallographic information.…”

“…In order to gain deeper insights into the structure and bonding in Li 12 Si 7 , the present study reports a comprehensive solid state NMR characterization of the silicide framework using 29 Si MAS-NMR, aided by 2-D J-resolved, radio frequency driven recoupling (RFDR) and { 7 Li} 29 Si cross-polarization-heteronuclear correlation experiments. Furthermore, the bonding states of the various lithium ions and their differential dynamics in Li 12 Si 7 and its analogous germanide phase are investigated by temperature dependent 6 Li MAS-NMR and 7 Li wideline NMR spectra.…”