Multilayered Sn–Zn–Cu alloy thin-film as negative electrodes for advanced lithium-ion batteries

Sn-based alloy compounds have been considered as possible alternatives for carbon in lithium-ion batteries and attract great attentions because of their large electrochemical capacity compared with that of carbon. In this work, a multilayered Sn–Zn/Zn/Cu alloy thin-film electrode has been prepared by electroplating method. The structure and performance of the electrode before and after heat treatment have been investigated. It is found that Cu₆Sn₅ phase and multilayered structure in electrode are formed after heat treatment. This optimized structure of the heat-treated electrode results in enhanced cycle life. The capacity of the electrode is over 320 mA h g^?1 after 100 cycles; though it is 83 mA h g^?1 after 20 cycles for as-plated electrode. The Sn–Cu and Zn–Cu alloy formed a network in the electrode is considered to strengthen the electrode and reduce the effect of volume expansion and phase transition during cycling. Experimental results also reveal that lower cut-off potential (0.05 V) for charging and higher one (1.2 V) for discharging result in long cycle life and high discharge capacity, respectively. The reason of capacity decay of the heat-treatment electrode during cycling has also been investigated. All these results show that the electroplated Sn–Zn-based alloy film on Cu foil would be a promising negative material with high capacity and low cost for Li secondary batteries.