The growing demand for portable and flexible electronics, such as roll-up displays, electronic papers, and wearable sensing devices, has stimulated the development of flexible energy storage devices. Herein, we demonstrate the fabrication of a high-voltage solid-state flexible free-standing supercapacitor with an ionogel separator. The negative electrode, titanium niobate, was hydrothermally grown onto a carbon cloth to ensure intimate contact. And the ionogel separator is based on EMIMBF4/P(VDF-HFP)/LiTFSI to ensure safety and high voltage. Our study shows that this device could exhibit reasonable area specific capacitance, relatively wide working potential (0-4 V), and outstanding high-temperature performances. And with that, it could deliver a super-high energy density of 397.3 mu Wh cm(-2), and almost no decay was observed after 1000 cycles. This strategy, combining high area specific capacitance electrodes (0.26 mAh cm(-2)) and ionogel separators, will pave a new road for the development of solid-state flexible lithium-ion supercapacitors with a high energy density.