Palladium-microencapsulated graphite as the negative electrode in Li-ion cells

A Pd-encapsulated graphite electrode was used as the negative electrode in Li-ion cells. Through dispersion of ultrafine nanoparticles of palladium on the surface of graphite, the interfacial properties of the carbon surface were modified. The presence of the palladium dramatically reduces the initi al irreversible capacity of the graphite in propylene carbonate (PC)-based electrolyte. Palladium suppresses the solvated lithium ion intercalation an d improves the charge-discharge performance and initial coulombic efficienc y of graphite. For example, 10-wt.% of Pd-nanoparticles dispersed on the su rface of graphite increases the initial charge-discharge coulombic efficien cy from 59% to 80.3%. Electrochemical impedance spectroscopy (EIS) indicate s that palladium dispersed on graphite increases the ohmic conductivity and also improves the Li insertion rate into graphite. However, an excess amou nt of palladium on graphite leads to a decrease in the charge-discharge eff iciency due to the consumption of lithium by the formation of Li2PdO2. (C) 2000 Elsevier Science S.A. All rights reserved.