Abstract
Layered-layered yolk-shell powders with composition 0.6Li(Li1/3Mn2/3)O2· 0.4Li(Ni1/3Co1/3Mn1/3)O2 are 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 Li1.12Ni0.14Co0.14Mn0.59O2. Mean grain sizes of the yolk-shell 0.6Li(Li1/3Mn2/3)O2·0.4Li(Ni1/3Co1/3Mn1/3)O2 powders, post-treated at 700, 750, and 800°C, measured from high resolution TEM images, are 47, 54, and 79nm, 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 239mA 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 183mA h g−1, respectively, and the corresponding capacity retentions are 43, 70, and 77%.
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