Abstract
Impedance growth of electrodes cycled with an upper cutoff potential of 4.5 V is caused by side reactions involving species on the surface of and -based electrolyte. These detrimental chemical species can apparently be removed by a heat-treatment to 550°C because electrodes made with heat-treated materials show excellent capacity retention even when cycled to 4.5 V. The detrimental surface species can be subsequently reformed on heat-treated materials by exposure of to water, suggesting prolonged air exposure is responsible for their formation on commercial samples. © 2003 The Electrochemical Society. All rights reserved.