Germanium–tin alloy nanocrystals for high-performance lithium ion batteries

Abstract

Germanium–tin (Ge_1−xSn_x) alloy nanocrystals were synthesized using a gas-phase laser photolysis reaction of tetramethyl germanium and tetramethyl tin. A composition tuning was achieved using the partial pressure of precursors in a closed reactor. For x < 0.1, cubic phase alloy nanocrystals were exclusively produced without separation of the tetragonal phase Sn metal. In the range of x = 0.1–0.4, unique Ge_1−xSn_x–Sn alloy–metal hetero-junction nanocrystals were synthesized, where the Sn metal domain becomes dominant with x. Thin graphitic carbon layers usually sheathed the nanocrystals. We investigated the composition-dependent electrochemical properties of these nanocrystals as anode materials of lithium ion batteries. Incorporation of Sn (x = 0.05) significantly increased the capacities (1010 mA h g⁻¹ after 50 cycles) and rate capabilities, which promises excellent electrode materials for the development of high-performance lithium batteries.