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 Li_1+x(Ni_xCo_zMn_z)_wO₂, 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 °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 LiNi_0.8Co_0.1Mn_0.1O₂ (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 °C under oxygen that results in Zr doping. It is established that some ZrO₂ remains even after annealing at ≥800 °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.