Flake Cu-Sn alloys as negative electrode materials for rechargeable lithium batteries

We have prepared the intermetallic compound Cu6Sn5 using mechanical-alloyin g, gas-atomizing, and melt-spinning techniques. The electrochemical perform ance of the compound is critically dependent on its morphology due to diffe rent preparation methods. The Cu6Sn5 alloy created by mechanical alloying, consisting of <1 <mu>m thick flake powder, has the best battery performance of all compounds. It delivers a rechargeable capacity of 200 mAh/g (2000 A h/L) over 50 cycles when the cycled voltage range is restricted to 0.2-1.5 V. The effect of the mechanical-alloying time and Cu/Sn ratio on its batter y performance was further investigated. The presence of excess Cu in alloy, relative to Cu6Sn5, showed improved cyclability at the expense of capacity , whereas an excess of Sn resulted in poor cyclability. A lithium-ion cell based on a flaked Cu-Sn microcomposite alloy negative electrode and a 5 V L iNixMn2-xO4 positive electrode was assembled. The cell showed an average wo rking voltage at 4.0 V and cycled well with a reversible capacity of ca. 20 0 mAh/g based on the pure Cu-Sn alloy when a cell was cycled between 3.5 an d 4.6 V. (C) 2001 The Electrochemical Society.