Neutron diffraction and electrochemical studies on Li1−xAg2Sn

A large sample of single phase, polycrystalline Li1−xAg2Sn has been synthesized by melting the elements in sealed tantalum tubes and subsequent annealing. Li1−xAg2Sn crystallizes with a ternary ordered version of the BiF3 structure. The lithium atoms were clearly localized from a neutron powder diffraction study: λ=109.59 pmλ=109.59 pm, a=659.37(7) pma=659.37(7) pm; space group Fm  3¯m; RP=12.2%RP=12.2% and RF=5.1%RF=5.1%. Time-dependent electrochemical polarisation techniques, i.e., coulometric titration, chronopotentiometry, chronoamperometry and cyclic voltammetry were used to study the kinetics of lithium ion diffusion in this stannide. Prior investigations on the lithium mobility in Li1−xAg2Sn using temperature dependent solid state 7Li NMR showed positive indications of Li1−xAg2Sn being an anode material. Li1−xAg2Sn has been characterized using electrochemical measurements and the chemical diffusion coefficient, DLiDLi has been determined. The chemical diffusion coefficient values of ∼10−6–10−7 cm2s−1 and a nearly reversible insertion/deinsertion in the voltage range between 1.6 and 2.1 V point out that Li1−xAg2Sn is another example of a ternary intermetallic compound with good lithium and electron mobility.

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