2D ultrathin nanomaterials have attracted a significant interest for their application in flexible and lightweight energy storage devices. In this work, we report the fabrication, by electrophoretic deposition (EPD), of flexible all-solid-state symmetric high cell potential supercapacitors, comprised of holey reduced graphene oxide - manganese dioxide nanosheets (HGM). HGM films were electrophoretically deposited in a layer-by-layer fashion onto targeted substrates, with net thicknesses ranging from 0.2 to 2.5 mm. The assembled HGM films were highly compact with the density of similar to 2.2 g cm(-3). The resulting symmetric HGM supercapacitors, using PVA-LiClO4 gel as an electrolyte, exhibited excellent electrochemical capacitive performance over a wide cell potential window of 0.0-1.6 V. Operating at ultra-high charge-discharge rates, up to 5000 mV s(-1), the HGM supercapacitors delivered excellent areal specific capacitances of 12-46 mF cm(-2), corresponding to volumetric specific capacitances of 557-182 F cm(-3) at thickness of 0.2-2.5 mm, respectively. Furthermore, the HGM supercapacitors exhibited long-term cycling stability with a retention over 80% of its initial capacitance after 2000 cycles. Considering the facile scale-up capability of the EPD process, our approach paves a promising route for the manufacture of next-generation flexible all-solid-state supercapacitors with high energy and high power density. Published by Elsevier Ltd.