Germanium and Tin Selenide Nanocrystals for High-Capacity Lithium Ion Batteries: Comparative Phase Conversion of Germanium and Tin

Abstract

Germanium and tin sulfide nanostructures are considered the most promising candidates for useful alternative materials in commercial Li-graphite anodes of lithium ion batteries. Selenides have received less attention, but the electrochemical reaction mechanism is still being debated. We report the novel synthesis of GeSex and SnSex (x = 1 and 2) nanocrystals by a gas-phase laser photolysis reaction and their 0.8 excellent reversible capacity for lithium ion batteries. The capacity was 400-800 (mA h)/g after 70 cycles, which is close to the theoretical capacity (Li4.4Ge or Li4.4Sn). Remarkably, SnSex exhibited higher rate capabilities than GeSex. Ex situ X-ray diffraction and Raman spectroscopy revealed the cubic-tetragonal phase conversion of Ge and Sn upon lithiation/delithiation to support their distinctive lithium ion battery capacities. First-principles calculations of the Li intercalation volume change indicate that the smallest volume expansion in the cubic Sn phase can guarantee the enhanced cycling capability of the Sn compounds.