Thin films of Cu2Sb and Cu9Sb2 as anode materials in Li-ion batteries

Thin Cu₂Sb films have been prepared by heat-treating Sb films, electrodeposited on Cu substrates. The influence of the electrodeposition conditions and the heat-treatment period on composition and morphology of the films were investigated (SEM and XRD) and the obtained films were tested as anode materials for Li-ion batteries. The Cu₂Sb material showed a stable capacity of 290 mAh g⁻¹ (close to the theoretical capacity of 323 mAh g⁻¹) during more than 60 cycles. The presence of 9-11% (w/w) Sb₂O₃ in the electrodeposited films resulted in smaller particles but also slowed down formation of Cu₂Sb during the heat-treatment step. The presence of Sb₂O₃ was found to decrease the cycling stability although structural reversibility of Cu₂Sb was obtained both with and without Sb₂O₃. Longer heat-treatments of pure Sb films resulted in the formation of Cu₉Sb₂ which was shown to be reduced at a lower potential than Cu₂Sb. The Cu₉Sb₂ was converted to Cu₂Sb during repeated cycling and the capacity of the latter Cu₂Sb material was found to be 230 mAh g⁻¹. While reduction of the materials was complicated by simultaneous formation of an SEI layer, three plateaus could be identified during the oxidation of Li₃Sb, indicating the presence of three separate one-electron oxidation reactions.