Microstructural stability of nanocrystalline LiCoO2 in lithium thin-film batteries under high-voltage cycling

The microstructural stability of nanocrystalline LiCoO2 cathodes in rechargeable thin-film batteries after high-voltage cycling was investigated by transmission electron microscopy. It was found that besides the trigonal-LiCoO2 phase, there are two other phases of LixCoO2, spinel and H1-3, that form inside the nanocrystalline cathode after electrochemical cycling (charge cutoff voltages >= 4.5 V). The formation of the aforementioned secondary phases in the cathode material is irreversible and leads to capacity loss in lithium thin-film batteries. (c) 2007 American Institute of Physics.