An Electrochemical and XRD Study of Lithium Insertion into Mechanically Alloyed Magnesium Stannide

The intermetallic Mg₂Sn is a promising negative electrode material for rechargeable lithium cells. Preliminary cycling tests have demonstrated stable capacities at 400 mAh/g for 20 cycles. Magnesium stannide was produced by mechanically alloying magnesium and tin powders. Mechanical alloying can convert the equilibrium Mg₂Sn phase to a metastable phase by the introduction of defects with extended milling times. In situ X-ray diffraction has shown that the cubic Li₂MgSn phase, which is similar in size and structure to cubic Mg₂Sn, is produced by lithium insertion into the equilibrium and metastable phases. The conversion from the metastable phase is irreversible, so subsequent lithium removal from Li₂MgSn produces the equilibrium Mg₂Sn phase.