The present invention relates to a method for preparing graphene using a spontaneous process, and particularly, to a method for mass-producing high-quality graphene composed of a single layer or several layers by using lithium intercalation of a graphite electrode occurring during the process of charging a lithium ion battery and a lithium ion capacitor in the preparation of graphene to form a graphite intercalation compound, and performing exfoliation through a reaction with water (or alcohol).