In situ encapsulated Fe3O4 nanosheet arrays with graphene layers as an anode for high-performance asymmetric supercapacitors

Abstract

Energy density of asymmetric supercapacitors (ASCs) is greatly limited by the electrochemical performance, especially low specific capacitance and poor cycling stability, of anode materials. To achieve high-performance ASCs, herein, we designed and synthesized a new anode material of Fe₃O₄ nanosheet arrays, which were encapsulated in situ by graphene layers (G@Fe₃O₄) through plasma enhanced chemical vapor deposition. Vertical-standing G@Fe₃O₄ nanosheet arrays directly on the conductive substrates can facilitate electrolyte diffusion and reduce the internal resistance. Furthermore, the highly conductive graphene layers in situ encapsulating the Fe₃O₄ nanosheets not only could provide fast ion and electron transport pathways, but could also maintain a stable structure for G@Fe₃O₄. When used as electrodes, G@Fe₃O₄ exhibited highest capacitance (up to 732 F g⁻¹), better rate capability, and cycling stability as compared to pristine Fe₃O₄. Furthermore, an asymmetric supercapacitor device synthesized using G@Fe₃O₄ as an anode and CuCo₂O₄ as the cathode showed a high energy density of up to 82.8 W h kg⁻¹ at a power density of 2047 W kg⁻¹ and good cycling stability (88.3% capacitance after 10 000 cycles).