Hierarchical flower-like conductive CoNiO2 microspheres constructed with ultrathin mesoporous nanosheets towards long-cycle-life hybrid supercapacitors

Abstract

Highly conductive transitional metal oxides (TMOs) positive electrodes can well address intrinsic power mismatching issues between negative and positive electrodes for advanced asymmetric supercapacitors. Purposeful exploration and rational design of dynamical TMOs with favorable microstructures and high-rate pseudocapacitances are crucially desired for advanced hybrid devices. Herein, we report efficiently bottom-up synthesis of hierarchical flower-like conductive CoNiO2 microspheres (CNOMS) self-constructed with mesoporous (∼2.4 nm) ultrathin nanosheet subunits of approximately 3.5–4.8 nm in thickness. Our CNOMS appealingly promise a fast electron and ion transport, large electroactive surface and strong structure stability in one. As a virtue of the compositional/structural features, the obtained CNOMS electrode with a high loading of 5 mg cm−2 delivers large specific capacitances of ∼854.9 and ∼414.5 F g−1 at high current rates of 1 and 20 A g−1 in 2 M aqueous KOH electrolyte, much superior to those of monometallic nickel/cobalt oxides counterparts. Encouragingly, the CNOMS-based hybrid device exhibits high energy density of ∼36.2 Wh kg−1 at a power rate of 160.0 W kg−1, as well as ∼100.8% long-duration capacitance retention over 10000 consecutive charge/discharge cycles. More promisingly, our CNOMS specimen is substantially highlighted as competitive electrode for long-cycle-life hybrid supercapacitors.