Chemical and Structural Instabilities of LiCoO_2 Cathodes at Deep Lithium Extraction

摘要

Presently, lithium-ion cells use the layered LiCoO_2 cathodes, but only 50% of the theoretical capacity of LiCoO_2 could be practically utilized (140 mAh/g). The reason for the limited capacity of LiCoO_2 cathodes is not fully established in the literature. We showed recently by characterizing the Li_(1-x)CoO_2 samples obtained by chemically extracting lithium from LiCoO_2 that the limited capacity could be due to the chemical instability occurring at deep charge. We present here a systematic investigation of the structural and chemical stabilities of Li_(1-x)CoO_2 by monitoring both the oxygen content and the crystal chemistry as a function of lithium content and the reaction time of chemical lithium extraction.