Electrochemical properties of yolk-shell structured layered-layered composite cathode powders prepared by spray pyrolysis

Layered-layered yolk-shell powders with composition 0.6Li(Li_1/3Mn_2/3)O₂· 0.4Li(Ni_1/3Co_1/3Mn_1/3)O₂are prepared by spray pyrolysis. Metal oxides-carbon composite powders are first formed as an intermediate product near the reactor entrance by drying and decomposition of droplets. Combustion, contraction, and recombustion processes of intermediate product produce yolk-shell-structured powders. The yolk-shell structure of the powders prepared directly by spray pyrolysis is maintained even after post-treatment at 800 °C; this treatment temperature yields the best electrochemical performance. The composition of the powders post-treated at 800 °C is Li_1.12Ni_0.14Co_0.14Mn_0.59O₂. Mean grain sizes of the yolk-shell 0.6Li(Li_1/3Mn_2/3)O₂·0.4Li(Ni_1/3Co_1/3Mn_1/3)O₂powders, post-treated at 700, 750, and 800 °C, measured from high resolution TEM images, are 47, 54, and 79 nm, respectively, and their BET surface areas are 14, 9, and 7 m²g^-1. The initial discharge capacities of the powders, post-treated at the above temperatures, are 188, 280, and 239 mA h g^-1, respectively, and their initial Coulombic efficiencies are 87, 80, and 78%. Discharge capacities after 50 cycles of the post-treated powders are 81, 194, and 183 mA h g^-1, respectively, and the corresponding capacity retentions are 43, 70, and 77%.