Electrochemical stability of graphite-coated copper in lithium-ion batteryelectrolytes

The electrochemical stability of graphite-coated battery-grade copper foil was investigated in two Li-ion battery electrolytes consisting of 1 M LiPF6 in ternary mixtures of (I) propylene carbonate (PC)-ethylene carbonate (EC )-dimethyl carbonate (DMC) [1:1:3] and (II) EC-DMC-methyl ethyl carbonate ( MEC) [1:1:1]. Cyclic voltammetry was used to study the oxidation-reduction of the graphite-coated copper in the electrolyte solutions. Bulk electrolys is was used to quantitatively study the dissolution of the graphite-coated copper in dry electrolyte and electrolyte doped with impurities of H2O or H F. The results were compared with those obtained at uncoated copper foil el ectrodes. It was found that the graphite coating greatly influenced the oxi dation-reduction behavior of the copper substrate and provided some protect ion to the copper from oxidation. impurities increased the oxidation tenden cy of graphite-coated copper. It was also found that the integrity of the g raphite-coated copper electrode was greatly influenced in electrolyte (I) d uring the bulk electrolysis whereas the electrode was rather stable in elec trolyte (II). (C) 2000 The Electrochemical Society. S0013-4651(00)05-028-X. All rights reserved.