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Electrochemical characteristics of the hybrid carbon (HC) graphite-hard carbon and graphite-coke have been investigated for the application of these materials as negative electrodes in lithium secondary batteries with a long cycle life. The graphite-hard carbon HC showed a higher reversible lithium capacity and better cycle performance than did the graphite-coke HC. X-ray photoelectron spectroscopy and nuclear magnetic resonance spectroscopy were used to analyze the deterioration mechanisms of the graphite-HC and graphite-coke HC. The decomposition products after the charge/discharge cycles were considered to be LiF and a carbonate compound, and the increase in inactive lithium in the decomposition products for the graphite-hard carbon HC was smaller than that for the graphite-coke HC. Therefore, it was thought that the graphite-hard carbon HC negative electrode suppressed the decomposition of the electrolyte and showed better cycle performance than did the graphite-coke HC negative electrode. Consequently, graphite-hard carbon HC is a promising negative electrode material for long-life lithium secondary batteries for dispersed-type energy storage systems. © 2002 The Electrochemical Society. All rights reserved.

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