Layer structured bismuth selenides Bi2Se3 and Bi3Se4 for high energy and flexible all-solid-state micro-supercapacitors

In this work, bismuth selenides (Bi₂Se₃ and Bi₃Se₄), 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), Bi₂Se₃ nanoplates exhibit much better performance as an electrode material than Bi₃Se₄ nanoparticles do, delivering a higher specific capacitance (272.9 F g^-1) than that of Bi₃Se₄ (193.6 F g^-1) at 5 mV s^-1. This result may be attributed to the fact that Bi₂Se₃ nanoplates possess more active electrochemical surfaces for the reversible surface redox reactions owing to their planar quintuple stacked layers (septuple layers for Bi₃Se₄). 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 Bi₂Se₃ AMSC device delivers a much better supercapacitor performance, exhibits a large stack capacitance of 89.5 F cm^-3 at 20 mV s^-1 (Bi₃Se₄: 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 Bi₂Se₃ (Bi₃Se₄:90.3%). Clearly, Bi₂Se₃ nanoplates can be promising electrode materials for flexible annular interdigital AMSCs.