An approach to application for LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 cathode material at high cutoff voltage by TiO_2 coating

摘要

Nickel-rich LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 cathode material is coated with nano-sized anatase TiO_2 synthesized via hydrolyzation method to improve its electrochemical performance at high cutoff voltage of 4.5 V. Scanning electron microscopy (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) results show that the anatase TiO_2 is successfully coated on the surface of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 with nanoscale and the coating layer thickness is about 25-35 nm. X-ray diffraction (XRD) test results indicate that appropriate amount of TiO_2 coating is beneficial to form a good layered structure with less cation disorder. Charge-discharge test results demonstrate that the TiO_2-coated LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 presents excellent cycling capability, rate capability and thermal stability at cutoff voltage of 4.5 V. The 1.0 wt.% TiO_2-coated LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 exhibits a capacity retention of 88.7% after 50 cycles at 1 C and a discharge capacity of 135.8 mAh g~(-1) after 10 cycles at 5 C, comparing to those of the pristine LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 of only 78.1% and 85.4 mAh g ~(-1). Electrochemical impedance spectroscopy (EIS) and differential scanning calorimeter (DSC) tests results provide evidence that the improved electrochemical properties are mainly attributed to the suppression of the interface reaction between the cathode and electrolyte and the improvement of structural stability of the material by coating.