Development and characterization of aqueous sodium-ion hybrid supercapacitor based on NaTi2(PO4)3//activated carbon

Abstract In this work, for the first time, the sodium ion intercalated compound NaTi 2 (PO 4 ) 3 has been designed to function as the anode in combination with activated carbon as the cathode to develop a novel aqueous sodium-ion hybrid supercapacitor based on the Na 2 SO 4 aqueous electrolyte. Both anode and cathode have been fabricated with a thick (>1 mm) freestanding structure. The as-proposed NaTi 2 (PO 4 ) 3 //activated carbon hybrid supercapacitor exhibits a typical supercapacitor-battery behavior. During the galvanostatic charging and discharging process, a linear sloping voltage range from 0 to 0.8 V corresponding to supercapacitor has been observed and an obvious voltage plateau in the range of 0.8–1.6 V could be related with the battery characterization. The hybrid supercapacitor thus brings a much high energy density over conventional supercapacitor based on activated carbon electrode. The NaTi 2 (PO 4 ) 3 //activated carbon system shows a discharge capacity of 27.5 mAh g −1 with an average working voltage of 1.15 V, corresponding to a high energy density of 31.6 Wh kg −1 at a power density of 23 W kg −1 based on the total weight of active electrode materials. It also exhibits excellent cycling behavior with less than 11.7% capacitance loss after 2000 cycles at current density of 200 mA g −1 . The cell delivers a relatively high power ability of 420 W kg −1 with the energy density of 15.5 Wh kg −1 .