Abstract
the capacity of Li-rich layered cathode powder was strongly affected by its particle size. By using sol-gel process, particle size of Li1.2Mn0.54Ni0.13Co0.13O2 powder obtained is around 200 nm. On the other hand, Li1.2Mn0.54Ni0.13Co0.13O2 powder synthesized by solid-state reaction method gives particle size as coarse as 1.0μm. The initial discharge capacity of sol-gel processed Li-rich cathode was 250 mAh/g. After 40 cycles, the discharge capacity from the same cathode still shows a capacity as high as 205 mAh/g. However, for cathode powder from solid-state reaction, its initial capacity was 190 mAh/g that is 24% lower than that of sol-gel processed cathode. After 40 cycles, the capacity degraded to 137 mAh/g. The enhanced capacity of sol-gel processed Li-rich cathode is attributed to its enormous surface area and short Li diffusion distance provided for electrochemical reaction to take place.
Furthermore, the TEM diffraction analysis of cycled Li[Li0.2Mn0.54Ni0.13Co0.13]O2 shows the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may also induce a large lattice distortion resulting in lattice breakdown and capacity fading. In additions, the phase transition may be caused by the redox reaction of transition metal ions through charging/discharging tests.