Skein-shaped ZnO/N-doped carbon microstructures as a high performance anode material for lithium-ion batteries

Zinc oxide (ZnO) has significant attentions as an alternative anode material for lithium-ion batteries because of its high theoretical capacity (987 mA h g⁻¹), lack of toxicity, abundance, and environmental friendliness. In particular, the theoretical capacity of ZnO is almost three times higher than that of the commercial graphite anode (about 372 mA h g⁻¹) as a result of its alloying and conversion reactions with lithium ions. However, severe capacity fading and poor reaction kinetics are often caused by the low electrical conductivity, slow lithium-ion diffusion, and large volume changes of ZnO during repeated charge/discharge processes. To overcome these drawbacks, N-doped carbon-coated ZnO microstructures are synthesized through a facile hydrothermal reaction and the subsequent calcination process using citric acid and urea as carbon and nitrogen sources, respectively. The ZnO sample has a hierarchical skein-shaped morphology and exhibits a higher discharge capacity of about 1047 mA h g⁻¹ after 100 cycles at a 0.1 C rate in the 0.01–3.0 V voltage range, compared to those of bare ZnO and carbon-coated ZnO samples (about 42 and 341 mA h g⁻¹ after 100 cycles, respectively).