Anodic materials for rechargeable Li-batteries

Six sub-micro-crystalline alloy powders (Sn–Sb, Sn–Ag, Sb–Ag, and Sn–Sb–Ag alloys), where all constituents are able to alloy reversibly with Li and which are therefore characterized by large theoretical Li storage capacities, have been synthesized by chemical precipitation with NaBH4, and their composite electrodes have been electrochemically tested by constant current cycling and cyclic voltammetry. Sn/SnSb and SnSb showed the best performance, with stable capacities of 600 and 500 mAh g−1, respectively, for more than 30 cycles. All of the materials exhibit large irreversible capacities in the first cycle, which are also often found for other metallic–intermetallic systems. Since, however, first cycle efficiencies of 89–95% can be achieved with electroplated thin Sn films, this is not an intrinsic problem of Sn or Sn-containing compounds, and it is not the trapping of Li in any of the many lithiated Sn phases that should be the main reason for the large irreversible capacities of the composite electrodes, but rather other factors, such as oxide impurities and especially contact problems in the composite electrode.