The Preparation And Lithiation Properties Of SnO₂/Cu/C Composite Anode Materials

Tin oxide SnO₂ is promising Li-ion anode materials due to its high theoretical specific capacity, lower operating potential and easy process than graphite. However, two main problems limit the applications of SnO₂ anode, one is the low initial coulombic efficiency（ICE）, the other is the huge volume variation during Li-Sn alloying/de-alloying reactions, which results in the pulverization of the electrode and rapid capacity decay. To overcome the above two problems of SnO₂ anode, the SnO₂/Cu and SnO₂/Cu/C composite anode materials were prepared by different preparing techniques, the effect of preparing process and the amount of additives on the microstructure and electrochemical preperties of the composite anodes were investigated. The important conclusions were obtained as following:Firstly, the SnO₂/Cu composites were prepared by the mechanical milling. The results show that the ICE of SnO₂/Cu composite（SnO₂:Cu=1:2 mol ratio） milled for 50 h, with 20:1 ball-to-powder weight ratio is about 76%, which is higher than the theoretical ICE value（52.4%） of pure SnO₂. The microstructure analysis on the SnO₂/Cu-50 h composite shows that nanosized SnO₂ of about 10 nm were uniformly dispersed in the micorsized Cu particles, which is composed of nanocrystal Cu of about 10²0nm. It is believed that this specific nanostructure of SnO₂/Cu composite facialiated the reversibility of Li2 O in the charging reaction, thus explaining the increase of ICE value.To improve the cyclic performance of SnO₂/Cu composite anode, the SnO₂/Cu composite was further milled with graphite by mechanical milling. It is found that the 20h-milled SnO₂/Cu/C composite with addition amount of 30 wt.% graphite shows the best cycling performance, the capacity maintains at about 459.6m Ah g-1at 80 thcycles at current density 100 m A g-1, about 371.6 m Ah g-1at 150 th cycles.This result is much bettern than the SnO₂/Cu composite（250.0 m Ah g-1 at 20 th cycles）.To further refine and disperse the SnO₂/Cu particles inside, the mechanically-milled SnO₂/Cu/C composite was treated by liquor milling, which uses rather small Zr O2 balls in the alcoholic solution and high milling speed. It is found that the SnO₂/Cu composite（20³0 nm） were significantly refined and uniformly embedded into the graphite matrix. It is also found that Cu was partially oxided. The results show that the 4h-liquor-milled SnO₂/Cu/C composite have the best cyclability, its capacity is about 580.5m Ah g-1 at 150 th cycles at the current density of 100 m A g-1. In addition, the impedance spectra and charging-discharging rate testing results show that the conductivity and rate performance of SnO₂/Cu/C composite were greatly improved after the liquor milling.