Constructing effective TiO2 nano-coating for high-voltage Ni-rich cathode materials for lithium ion batteries by precise kinetic control

In order to improve the performance of Ni-rich cathode materials for lithium-ion batteries at high cut-off voltage, a highly effective TiO2 nano-coating is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by precisely controlling the hydrolytic dynamics of Ti4+, and the effect of this coating layer is systematically studied, especially at high upper cut-off voltage. The continuous TiO2 nano-coating layer provides a complete protection for LiNi0.8Co0.1Mn0.1O2 particles and enhances the reversibility of the phase transition between hexagonal and hexagonal (H2 -> H3) during cycling, which guarantees an excellent cycling stability under high upper cut-off voltage up to 4.5 V. Electrochemical impedance spectroscopy results confirm a stable interface between electrolyte and electrode and the fast kinetics at the surface of the modified sample. High Resolution Transmission Electron Microscopy (HR-TEM) measurement for the cycled electrodes further verifies the slight structure decay of the coated sample comparing with the pristine one. Thus, the modified sample presents excellent cycling stability with capacity retention of 72.2% after 500 cycles and 63.4% after 1000 cycles with the upper cut-off voltage of 4.5 V and 4.3 V, respectively. This work provides a universal method to prepare conformal TiO2 nano-coating and also offer guidance to properly evaluate the function of a coating.