Electrochemical stability of graphite-coated copper in lithium-ion battery electrolytes

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 electrolysis was used to quantitatively study the dissolution of the graphite-coated copper in dry electrolyte and electrolyte doped with impurities of H2O or HF. The results were compared with those obtained at uncoated copper foil electrodes. It was found that the graphite coating greatly influenced the oxidation-reduction behavior of the copper substrate and provided some protection to the copper from oxidation. impurities increased the oxidation tendency of graphite-coated copper. It was also found that the integrity of the graphite-coated copper electrode was greatly influenced in electrolyte (I) during the bulk electrolysis whereas the electrode was rather stable in electrolyte (II). (C) 2000 The Electrochemical Society. S0013-4651(00)05-028-X. All rights reserved.