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.