Facile assembly of cobalt-nickel double hydroxide nanoflakes on nitrogen-doped hollow carbon spheres for high performance asymmetric supercapacitors

Cobalt-nickel double hydroxide has high theoretical specific capacity and electrochemical activity but undergoes poor rate performance and cycle stability. Herein, cobalt-nickel double hydroxide/nitrogen-doped hollow carbon spheres (CoNi-DH/NHCS) hybrids with a hollow structure were fabricated via a simple deposition method at room temperature. Structural analysis confirmed that ultrathin CoNi-DH nanosheets with hydrotalcite structure were grown on the surface of NHCS. The presence of NHCS can adapt to volume changes during repeated charge-discharge procedures and improve stability. In addition, owing to the accelerated ions diffusion in the ultrathin nanosheets and improved conductivity, the electrode with a cobalt content of 15% presents the highest specific capacity (578 C g−1 at 1 A g−1) as well as brilliant rate capacity (76.54%, 1–20 A g−1). The all-solid-state asymmetric supercapacitor 15CoNi-DH/NHCS‖NHCS depicts a superior energy density of 27.51 Wh kg−1 at 800 W kg−1 as well as distinguished cycle stability of 91.65% reservation after 10000 cycles.