Layer structured bismuth selenides Bi 2 Se 3 and Bi 3 Se 4 for high energy and flexible all-solid-state micro-supercapacitors.

In this work, bismuth selenides (Bi2 Se3 and Bi3 Se4 ), both of which have a layered rhombohedral crystal structure, have been found to be useful as electrode materials for supercapacitor applications. In a liquid electrolyte system (6M KOH), Bi2 Se3 nanoplates exhibit much better performance as an electrode material than Bi3 Se4 nanoparticles do, delivering a higher specific capacitance (272.9 F g-1 ) than that of Bi3 Se4 (193.6 F g-1 ) at 5 mV s-1 . This result may be attributed to the fact that Bi2 Se3 nanoplates possess more active electrochemical surfaces for the reversible surface redox reactions owing to their planar quintuple stacked layers (septuple layers for Bi3 Se4 ). To meet the demands of electronic skin, we used a novel flexible annular interdigital structure electrode to support the all-solid-state micro-supercapacitors (AMSCs). The Bi2 Se3 AMSC device delivers a much better supercapacitor performance, exhibits a large stack capacitance of 89.5 F cm-3 at 20 mV s-1 (Bi3 Se4 : 79.1 F cm-3 ), a high energy density of 17.9 mWh cm-3 and a high power density of 18.9 W cm-3 . The bismuth selenides also exhibit good cycle stability, with 95.5% retention after 1000 c for Bi2 Se3 (Bi3 Se4 :90.3%). Clearly, Bi2 Se3 nanoplates can be promising electrode materials for flexible annular interdigital AMSCs.