The effects of radio frequency sputtering of TiO₂ on Li[Li_0.07Ni_0.38Co_0.15Mn_0.4]O₂ Cathode for Lithium Ion Batteries

A radio frequency (RF) sputtering system is used to coat nano-thick TiO₂ layer on the overlithiated layered metal oxide (OLO) electrode. The X-ray diffraction (XRD) and the field emission-scanning electron microscope (FE-SEM) images indicate amorphous TiO₂ is coated on the top surface of the electrode with a thickness of ∼20 nm for the 40 min sputtered sample. The sample sputtered for 40 minutes cycled at 90 mA g?1 between 2 and 4.8 V versus Li+/Li has 15 mA h g?1 more specific capacity at 100th cycle than that of the uncoated sample. In the voltage profiles, additional overpotential is unobservable upon sputtering TiO2 in comparison to that of the reference sample. Further analyses by the electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) demonstrate the sputtered sample has less electrolyte decomposition products on the surface than that of the reference sample. Moreover, in the case of sputtering, reduced amount of transition metal and Li2O are deposited on the surface of the counter electrode, Li. In summary, the sputtered TiO₂ acts as nano-sized artificial solid electrolyte interface (SEI) layer, which protects the surface of the electrode and improves kinetic properties, leading to improved performance.