Structural Optimization of Al-Doped Li[Ni0.90Co0.05Mn0.05]O-2 Cathode for Li-Ion Batteries

Aluminum is a well-known dopant element as it is used in Li[Ni0.80Co0.15Al0.05]O-2 but its optimized usage in Li[Ni x Co y Mn z ]O-2 cathodes with x >= 0.90 has not been explored in depth. Here, we survey various Al-dopant concentrations (0.5, 1, 2, 3, and 5 mol%) to investigate the effect of Al-doping of highly Ni-rich layered Li[Ni0.90Co0.05Mn0.05]O-2 cathode with respect to the electrochemical and structural properties. It is shown that Al is effective in enhancing the electrochemical performance of the Li[Ni0.90Co0.05Mn0.05]O-2 cathode at higher than 1 mol% concentrations but becomes detrimental at 3 mol% or greater concentrations. In particular, Li[Ni0.90Co0.05Mn0.05]O-2 with 2 mol% Al-doping delivers the most optimal electrochemical performance with 93% capacity retention over 100 cycles at 0.5 C within the 2.7-4.3 V voltage range as compared to the 85% retention of Li[Ni0.90Co0.05Mn0.05]O-2 under the same conditions vs Li-0/Li+ in half cells. Analyses of the ex situ and in situ X-ray diffraction patterns, cell impedances over 100 cycles, and cross-sectional electrode images reveal that appropriate amounts of Al in the layered structure alleviate the extent of unit cell volume changes during charge, but excessive Al-dopant addition leads to the formation of gamma-LiAlO2 byproducts that consume available Li to significantly impair the efficacy of the cathode.