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 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.