Atomic absorption spectroscopy (AAS) was shown to be an effective method to quantitatively evaluate the stability of battery-grade copper foils in lithium-ion battery electrolytes at open-circuit. The results showed that copper stability was different between "fresh" electrolyte and electrolytes that had been "aged" for 6 months. In the "fresh" electrolyte, the copper foils showed a small amount of dissolution (up to similar to50 ppm) during their storage for up to 20 weeks. In the "aged" electrolyte, a large amount of copper dissolution (up to several hundred ppm) was found. The study showed that the condition of the electrolytes was critical to the stability of the copper foils. (C) 2003 Elsevier Ltd. All rights reserved.