Oxygen-deficient BiFeO3-NC nanoflake anodes for flexible battery-supercapacitor hybrid devices with high voltage and long-term stability

Perovskite bismuth ferrite (BiFeO3) has been extensively regarded as a high-capacity battery-type electrode material for battery-supercapacitor hybrid (BSH) devices, due to the reversible redox reactions of Bi3+ and Fe3+ to greatly suppress the hydrogen evolution reaction for the extension of operating voltage windows, but usually suffers from irreversible phase decomposition in the charge/discharge process. We report a novel Li-ion BSH device based on oxygen-deficient BiFeO3 nanoflakes stabilized by N-doped carbon (BiFeO3-NC) and N/S/P-codoped carbon nanosheet foams (N/S/P-CNSFs) as anodes and cathodes respectively. The oxygen-deficient BiFeO3 nanoflake electrode exhibits a high charge storage capacity and excellent cycling stability in LiCl electrolyte, attributed to the fast Li+ intercalation/de-intercalation accompanied with the reversible lattice distortion of crystalline BiFeO3 in the charge/discharge process. The N-doped carbon shell as an outer layer of the BiFeO3-NC nanoflakes, has been manifested to play an important role in the improvement of specific capacity, rate capability and cycling stability. The assembled flexible BSH device with the stable operating voltage of 1.9 V, can deliver a high specific capacity (up to 155 mAh g−1 at 1 A g−1) and ultra-long stability (92.6% after 10,000 cycles), opening up new avenues for developing high-voltage long-life energy storage devices.