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Graphical abstract The NA-LDH-OA-2//AC ASC device deliver a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1, and good cycling performance. Highlights • The NA-LDH-OA ultrathin nanosheets were synthesized by two-phase solvothermal method. • Excellent cycling stability of 94.5% capacitance retention after 5000 cycles. • The asymmetric supercapacitor achieved a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1. Abstract Using sodium oleate as surfactant and intercalating agent, a regulated Ni-Al layered double hydroxide (NA-LDH-OA) nanosheets with a high interlayer space were prepared by two-phase method combined with a short reflux process and mild solvothermal reaction. In the process of electrochemical reaction, the electron transport is accelerated by the higher base spacing of the NA-LDH-OA ultrathin nanosheets. The as-prepared material exhibited a high specific capacity (1.040 C cm−2 at a current density of 1.68 mA cm−2) and good cycling performance (capacity retention of 88.25% after 2000 cycles) in a three-electrode system. Moreover, an aqueous asymmetric supercapacitor (ASC) was assembled using the synthesized NA-LDH-OA nanosheets as the positive electrode and activated carbon (AC) as the negative electrode. The aqueous ASC device (NA-LDH-OA-2//AC) achieved a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1, and a good cycling performance of 94.5% retention after 5000 cycles. These results demonstrated that the NA-LDH-OA nanosheets possess the potential for upcoming energy storage devices. [ABSTRACT FROM AUTHOR]