The novel structure of few-layer carbon@bulk carbon is synthesized via controlling diffusion depth from liquid phase (KOH aqueous) to solid phase (carbon precursor) for using tamarisk-tree as carbon precursor. Few-layer carbon@bulk carbon shows the highest specific capacitance of 413.0 F g −1 with specific surface area of 1964.2 m2 g −1. The symmetric supercapacitor assembled with few-layer carbon@bulk carbon delivers a maximum specific energy of 20.2 and 9.83 Wh kg−1 in Li2SO4 and KOH electrolyte, respectively. Specific capacitance of the device maintains 93.5% of the initial value at 4 A g −1 in KOH electrolyte after 10, 000 cycles. The high electrochemical performance and good cycle stability exhibits the potential application of this kind of biomass based carbon materials in energy storage. © 2020 Elsevier Ltd