Revision of the Li–Si Phase Diagram: Discovery and Single-Crystal X-ray Structure Determination of the High-Temperature Phase Li_4.11Si

Silicon has been regarded as a promising anode material for future lithium-ion batteries, and Li–Si phases play an important role. A detailed reinvestigation of the Li-rich part of the binary Li–Si phase diagram revealed the existence of a new phase, Li 4.106(2) Si (Li 16.42 Si 4 ). Li 16.42 Si 4 forms through the peritectic decomposition of the Li-richest phase Li 17 Si 4 at 481–486 °C and was characterized by single-crystal X-ray diffraction ( a = 4.5246(2) Å, b = 21.944(1) Å, c = 13.2001(6) Å, space group Cmcm, Z = 16), differential scanning calorimetry, and theoretical calculations. Li 16.42 Si 4 represents a high-temperature phase that is thermodynamically stable above ∼480 °C and decomposes peritectically at 618 ± 2 °C to Li 13 Si 4 and a melt. Li 16.42 Si 4 can be retained at room temperature. The structure consists of 3 and 10 different kinds of Si and Li atoms, respectively. Two Li positions show occupational disorder. Si atoms are well-separated from each other and have only Li atoms as nearest neighbors. This is similar to Li 17 Si 4 and Li 15 Si 4 compositionally embracing Li 16.42 Si 4 . The SiLi n coordination polyhedra in the series Li 15 Si 4, Li 16.42 Si 4, and Li 17 Si 4 are compared. Li 15 Si 4 exclusively features coordination numbers of 12, Li 16.42 Si 4 of 12 and 13, and Li 17 Si 4 reveals 13- and 14-coordinated Si atoms. The band structure and density of states of Li 16.42 Si 4 were calculated on the basis of two ordered model structures with nominal compositions Li 16 Si 4 (a hypothetical Zintl phase) and Li 16.5 Si 4 . Both reveal a metallic character that is analogous to Li 17 Si 4 . In contrast, the electronic structure of Li 15 Si 4 is characteristic of a p-doped semiconductor.