Flexible solid-state supercapacitors (SSCs) as a candidate for energy storage source, have been attracting intensive attention. Graphene-based materials for SSCs have been widely studied. However, most reported preparation methods for graphene-based materials are energy-consuming, time-consuming and environmentally hazardous, what's more, the assembling of SSCs need additives, such as current collectors, flexible substrates. So, it is necessary to develop simpler and greener attempts to achieve highperformance, cost-effective, substrates/additives-free and flexible electrodes for SSC devices. Herein, we reported a green and facile one-step process of electrochemical oxidation and expansion in salt solution to activate graphite foil (GF) for fabricating expanded graphite foil (EGF). The EGF electrode with unique structure and high conductivity showed high supercapacitor performance of 65 mF cm(-2), remarkable rate-capability maintaining at a level of 80% even at a current density of 20 mA cm(-2) and excellent cycling stability with 95% capacitance remaining after 10000 cycles at a current density of 20 mA cm(-2). Moreover, a symmetric flexible all-solid supercapacitor (SSC) device was integrated using EGFs without any current collectors and additives. The flexible EGF-based device showed a high capacitance capacity of 30.5 mF cm(-2), excellent rate performance and good cycle stability which make it holds promise for applications in flexible, portable and wearable electronic devices. (C) 2017 Elsevier Ltd. All rights reserved.