Three-dimensional graphene encapsulated hollow CoSe₂-SnSe₂ nanoboxes for high performance asymmetric supercapacitors

Abstract

Construction of metal selenides with a large specific surface area and a hollow structure is one of the effective methods to improve the electrochemical performance of supercapacitors. However, the nano-material easily agglomerates due to the lack of support, resulting in the loss of electrochemical performance. Herein, we successfully design a three-dimensional graphene (3DG) encapsulation-protected hollow nanoboxes (CoSe2-SnSe2) composite aerogel (3DG/CoSe2-SnSe2) via a co-precipitation method coupled with self-assembly route, followed by a high temperature selenidation strategy. The obtained aerogel possesses porous 3DG conductive network, large specific surface area and plenty of reactive active sites. It could be used as a flexible and binder-free electrode after a facile mechanical compression process, which provided a high specific capacitance of 460 F g-1 at 0.5 A g-1, good rate capability of 212.7 F g-1 at 10 A g-1, and excellent cycle stability due to the fast electron/ion transfer and electrolyte diffusion. With the as-prepared 3DG/CoSe2-SnSe2 as positive electrodes and the AC (activated carbon) as negative electrodes, an asymmetric supercapacitor (3DG/CoSe2-SnSe2//AC) was fabricated, which delivered a high specific capacity of 38 F g-1 at 1A g-1 and an energy density of 11.89 W h kg-1 at 749.9 W kg-1, as well as a capacitance retention of 91.1% after 3000 cycles. This work provides a new method for preparing electrode material.

Three-Dimensional Graphene-Wrapped CoSe2 Nanowires for High-Performance Asymmetric Supercapacitors

“…Compared to conventionally closed structures, the unique 3D hierarchical structure of 3DG/CoSe 2 NWs presents numerous advantages. The 3D interconnected porous network with large openings enhances the mechanical strength and long-term performance of electrode materials in ion intercalation reactions. − The 1D porous nanowires encapsulated in the 3DG network consist of multiple active CoSe 2 nanoparticles, providing abundant active sites. − The porous structure of nanowires efficiently prevents the aggregation of CoSe 2 nanoparticles, accommodates their volume expansion during charging and discharging, and prevents the collapse of traditional electrode materials. − As a result, 3DG/CoSe 2 NWs exhibited high reversible capacity and excellent performance. Electrochemical tests show that the flexible electrode 3DG/CoSe 2 NWs has a high reversible capacity of 1272 F g –1 at 1 A g –1 .…”