Ultralight Flexible Electrodes of Nitrogen-Doped Carbon Macrotube Sponges for High-Performance Supercapacitors.

Light-weight and flexible supercapacitors with outstanding electrochemical performances are strongly desired in portable and wearable electronics. Here, ultralight nitrogen-doped carbon macrotube (N-CMT) sponges with 3D interconnected macroporous structures are fabricated and used as substrate to grow nickel ferrite (NiFe2 O4 ) nanoparticles by vapor diffusion-precipitation and in situ growth. This process effectively suppresses the agglomeration of NiFe2 O4 , enabling good interfacial contact between N-CMT sponges and NiFe2 O4 . More remarkably, the as-synthesized NiFe2 O4 /N-CMT composite sponges can be directly used as electrodes without additional processing that could cause agglomeration and reduction of active sites. Benefiting from the tubular structure and the synergetic effect of NiFe2 O4 and N-CMT, the NiFe2 O4 /N-CMT-2 exhibits a high specific capacitance of 715.4 F g-1 at a current density of 1 A g-1 , and 508.3 F g-1 at 10 A g-1 , with 90.9% of capacitance retention after 50 000 cycles at 1 A g-1 in an alkaline electrolyte. Furthermore, flexible supercapacitors are fabricated, yielding areal specific capacitances of 1397.4 and 1041.2 mF cm-2 at 0.5 and 8 mA cm-2 , respectively. They also exhibit exceptional cycling performance with capacitance retention of 92.9% at 1 mA cm-2 after 10 000 cycles under bending. This work paves a new way to develop flexible, light-weight, and high-performance energy storage devices.