Crystalline CoSn2 powders prepared by a ceramic route under an Ar/H2 controlled atmosphere are
examined as a negative electrode for lithium-ion batteries. Ex situ X-ray diffraction measurements show
that an electrochemically driven solid-state transformation of CoSn2 occurs during the first reaction period.
The complete reaction mechanism of CoSn2 is investigated by in situ 119Sn Mössbauer spectroscopy
using a Li-ion plastic cell. The conversion reaction proceeds through a biphasic system, with CoSn2
direct transformation into both a lithium-rich Li
y
Sn (where y ≈ 3.5) compound and metallic Co
nanoparticles. On charge, the electrochemical process is more complex and it includes the conversion
of the Li
y
Sn compound into a modified CoSn2 nanocompound with a variable composition, i.e., a
Li
y
Co
z
Sn2 matrix, which is the active species for the following cycles.
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