Combinatorial Study of the Sn-Cu-C System for Li-Ion Battery Negative Electrode Materials

Thin-film combinatorial sputter-deposited Sn-Cu-C alloys for negative electrodes of Li-ion batteries were characterized using electron microprobe (energy-dispersive spectroscopy), X-ray diffraction, electrochemical methods, and Sn-119 Mossbauer effect spectroscopy. Combinatorial libraries with nominal compositions SnxCuyC1-x-y with x = 0.49, x = 0.39, and x = 0.25 (0 < y < 1 - x) and SnxCuyC1-x-y with y/x = 6/5 (0 < 1 - x - y < 0.45) were investigated. The addition of carbon was responsible for a decrease in grain size and an increase in specific capacity, which approached the calculated value (based on 4.4Li/Sn + 0.5Li/C). Mossbauer effect spectra were compared with differential capacity (dQ/dV vs V) and it was determined that the sample with the best capacity retention most closely resembled nanostructured Cu6Sn5 grains embedded in a C matrix, yielding over 90% capacity retention after 30 cycles. However, changes in dQ/dV vs V suggested that regions of Cu6Sn5 were steadily growing or aggregating as Li was cycled, which may be a limiting factor in later cycles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3476311] All rights reserved.