Surface Passivation of MoO₃ Nanorods by Atomic Layer Deposition toward High Rate Durable Li Ion Battery Anodes

We demonstrate an effective strategy to overcome the degradation of MoO₃ nanorod 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 50 charge/discharge cycles, HfO₂-coated MoO₃ electrodes exhibited specific capacity of 657 mAh/g; on the other hand, bare 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 photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction were carried out to explain the capacity retention mechanism after HfO₂ coating. (Figure Presented).