Abstract
We demonstrate an effective strategy to overcome the degradation of MoO3 nanotod anodes in lithium (Li) ion batteries at high-rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO3 nanorods by HfO2 using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific Capacity of HfO2-coated MoO3 electrodes is 68% higher than that of bare MoO3 electrodes after 50 charge/discharge cycles. After 550 charge/discharge cycles, HfO2-coated MoO3 electrodes exhibited specific capacity of 657 mAh/g; on the other hand, hare MoO3 showed only 460 mAh/g. Furthermore, we observed that HfO2-coated MoO3 electrodes tend, to,stabilize faster than bare MoO3 electrodes because nanoscale HfO2 layer prevents structural degradation of MoO3 nanorods. Additionally; the growth temperature of MoO3 nanorods, and the effect of HfO2 layer thickness was studied and found to be important parameters for optimum battery performance the growth temperature defines the microstructural features and HfO2 layer thickness defines the diffusion coefficient of Li-ions through the passivation layer to. the active material. Furthermore, ex situ high resolution transmission electron microscopy, X-ray phothelectron spectroscopy, Raman spectroscopy, and X-ray diffraction were carried out to explain the capacity retention mechanism after HfO2 coating.