Germanium and Tin Selenide Nanocrystals for High-Capacity
Lithium Ion Batteries: Comparative Phase Conversion of Germanium and
Tin
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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 GeSe<sub><i>x</i></sub> and SnSe<sub><i>x</i></sub> (<i>x</i> = 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 (Li<sub>4.4</sub>Ge or Li<sub>4.4</sub>Sn). Remarkably, SnSe<sub><i>x</i></sub> exhibited higher
rate capabilities than GeSe<sub><i>x</i></sub>. Ex situ
X-ray diffraction and Raman spectroscopy revealed the <i>cubic</i>–<i>tetragonal</i> 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