Electrochemical behavior of nanocrystalline tin oxide electrodeposited on a Cu substrate for Li-ion batteries

Abstract

Nanocrystalline (5–10 nm) Cu-doped (∼3–25 at%) tin oxide films have been obtained by electrochemical deposition on a Cu substrate. In the initial stage of electrodeposition, the Cu2+ ions dissolved from the Cu substrate and then co-deposited back with tin oxide on the substrate. The dQ/dV figure for the assembled cell, using the Cu-doped tin oxide as anode, indicated that Li2O possessed electrochemical reversibility in a high voltage range (larger than 1.2 V), and it was maintained for at least 15 charge/discharge cycles. Both the nanometer dimensions of the deposited coating and the Cu doping in the SnO2 lattice activated the Li2O to transform metallic Cu and Sn to metal oxides (CuO and SnO2) and Li+ ions. Thus the capacity of SnO2 coatings can be promoted from the contribution of reactions involving the formation/decomposition of Li2O besides the alloying/dealloying of Sn with Li. The effect of the cutoff voltage range on the capacity and cyclability was also discussed. At voltages lower than 1.0 V, Li2O cannot be activated due to the deficiency of overpotential. The absence of Li2O decomposition during the charging step led to a lower capacity but a stronger bonding between the Li2O and other particles. Thus the cyclability for a low maximum voltage (415 mAh g−1 at the 15th cycle) was better than that for high maximum voltage. The experiment not only provides a novel, fast and low-cost process to fabricate anodes for Li-ion batteries, but also clarifies the electrochemical behavior of the nanocrystalline Cu-doped SnO2 electrode.