Analysis of the passivating layer and the electrolyte in the system:: petroleum coke/solution of LiCF3SO3 in mixed organic carbonates

The chemical composition of the passivating layer formed on a petroleum coke surface in LiCF3SO3-PC/EC/DMC electrolyte was explored using FTIR and NMR spectroscopies and gas chromatography. Analyses concerned either the passivating layer on the petroleum coke or the aqueous solution in which it was hydrolyzed. They indicate that RCO3Li and Li2CO3 are the major constituents of the passivating layer. Our experimental data allow us to specify the part of the irreversible faradic capacity which is engaged in the formation of each constituent of the passivating layer. It is shown that the reduction of solvents and of their impurities only corresponds to 50% of the capacity loss. Moreover, electrolyte analyses allow us to detect the presence of soluble species coming from the passivating layer that are probably the cause of self discharge phenomena in batteries. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.