High-Voltage Cycling Behavior of Thin-Film LiCoO[sub 2] Cathodes

Abstract
Thin-film LiCoO2LiCoO2 cathodes having grains of 0.3 μm diam combined with the Lipon electrolyte exhibit excellent capacity retention when cycled up to 4.4 V. High capacity (170±10(170±10 mAh/g) and energy density (690±60(690±60 mWh/g) were obtained between 3.0 and 4.4 V at 0.1 mA/cm2,mA/cm2, with the capacity fade rate 4.4 V, there is a more rapid increase in cell resistance and reduced capacity at high current densities. This is attributed to the onset of a phase transition at >4.4 V accompanied by an abrupt change in the c parameter. When a LiCoO2LiCoO2 cathode is completely delithiated by charging to 5.0 V, cycling ability is still retained, but Li reinsertion into CoO2CoO2 is not a fully reversible reaction of the Li extraction from LiCoO2.LiCoO2. © 2002 The Electrochemical Society. All rights reserved.