From Surface ZrO2 Coating to Bulk Zr Doping by High Temperature Annealing of Nickel-Rich Lithiated Oxides and Their Enhanced Electrochemical Performance in Lithium Ion Batteries
One of the major hurdles of Ni-rich cathode materials Li1+x(NixCozMnz)(w)O-2, y > 0.5 for lithium-ion batteries is their low cycling stability especially for compositions with Ni >= 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 degrees C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO2) or (2) lattice doping by cations like Zr4+, Al3+, Mg2+, etc. This paper demonstrates the enhanced electrochemical behavior of Ni-rich material LiNi0.8Co0.1Mn0.1O2 (NCM811) coated with a thin ZrO2 layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at >= 700 degrees C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at 800 degrees C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO2 coating in combination with a zirconium doping.