ZnO nanoneedle arrays directly grown on bulk nickel substrate for li ion battery electrodes with improved performance

In this paper, a low-temperature (T=70degC) solution-phase approach has been developed for the fabrication of vertically-aligned ZnO nanoneedle arrays directly on bulk nickel substrate. The synthetic process involving no seeds, no catalysts, and no surfactants can be readily scaled up. The as-grown ZnO arrays are further used for the first time as anode materials for Li-ion batteries operated in the voltage window 0.05-2.5 V. In the preparation of battery electrode, there is no need to transfer the obtained ZnO arrays to a different surface or align them; in addition, no conducting carbon and other additives such as binder are employed. These offer significant advantages with respect to the cost and practicability. Galvanostatic cycling experiments show that our ZnO nanoneedle arrays exhibit considerably improved performance (especially the cycling stability) as compared to the powder of disordered nano needles. A first discharge capacity of 1219 mAh/g and a reversible discharge capacity of ~495 mAh/g after 10 cycles are observed (current rate: 200 mA/g). In contrast, ZnO film consisting of random nano needles has a smaller first discharge capacity (1090 mAh/g) and its reversible capacity fades rapidly even from the second cycle. The electrochemical performance of ZnO nanoneedle arrays can be further tuned by heat treatment of ZnO active materials at Ar atmosphere, which enhances the adhesion of ZnO to nickel substrate. Our results, combined with the fact that ZnO are cheap, easily prepared, and environmentally compatible, make the ZnO nanoneedle arrays a promising anode material for Li-ion batteries.