Electrochemical and electron microscopic characterization of thin-film LiCoO2 cathodes under high-voltage cycling conditions

Thin-film LiCoO2 batteries using the Lipon electrolyte exhibit excellent cycleability up to 4.4 V. With the enhanced voltage limit for repeatable cycling, the thin-film cathode delivers a specific capacity of 170 mAh/g, which is 22% higher than that for previous LiCoO2 cathodes cycled to 4.2 V No evidence of grain fracture was detected by transmission electron microscopy (TEM) in the cathode layer after cycling to 4.4 V. When cycled to >4.4 V, capacity fades and cell resistance increases more rapidly, attributed to the onset of a phase transition at >4.4 V. Fracture of grains was observed by TEM in the cathode layer after cycling to 5 V Nanocrystalline films show better cycleability to 5 V than films with a larger grain size. (C) 2003 Elsevier Science B.V. All rights reserved.