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 ∼50ppm) 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.