Graphene nanoribbon wrapped cobalt manganite nanocubes for high performance all-solid-state flexible supercapacitors

Abstract

Nanocubes of cobalt manganite, CoMn₂O₄, were grown in situ over graphene nanoribbons (GNRs) to form a CoMn₂O₄/GNR composite during hydrothermal processing. The proposed all-solid-state supercapacitor (SC), CoMn₂O₄/GNR//CoMn₂O₄/GNR, with a polymer gel electrolyte showed an excellent electrochemical performance. It can be reversibly cycled over a large potential range of 3 V, resulting from the synergism of the pseudocapacitive and electrical double layer capacitor (EDLC) materials. The pseudocapacitance arises from the binary redox couple of the different cations in CoMn₂O₄, which, in combination with the GNRs, endows a high performance and long term stability. The SC demonstrates a high energy density of 44.6 W h kg⁻¹ and a power density of 11.3 kW kg⁻¹ with a short diffusion coefficient (D_a) of 1.02 × 10⁻⁷ cm² s⁻¹ and a relaxation time constant (τ) of 5.6 μs. It demonstrates ∼95% capacitive retention with a steady coulombic efficiency even after 12 000 charge/discharge cycles. Moreover, a steady performance of the cell with good capacitive behaviour, even in the harsh environment of different bending states, encourages its commercial use in portable electronics.