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Abstract NiFe 2 O 4 (NFO) with different morphologies were successfully synthesized via a facile hydrothermal method of different precipitants. Results showed that the NFO obtained using urea as precipitant (NFO-U) formed a nanosheet shape, while the powders prepared using CH 3 COONa (NFO-C) exhibited a nanoparticle structure. Both of the two NFO showed a good crystallinity. Conclusion was reached through the results of BET and electrochemical tests that layer structure would improve the properties through a larger specific surface area. Encouragingly, the specific capacitance of NFO-U could arrive 240.9 F/g at the current density of 1 A/g. It was worth noting that the cycle performance of NFO-U was excellent, of which the specific capacitance improved to 128% after 2000 cycles. In addition, an asymmetric supercapacitor (ASC) system was constructed utilizing NFO-U as positive electrode while activated carbon (AC) as negative electrode. The two-electrode system showed a good performance with energy density of 10.15 Wh/kg at a power density of 140 W/kg. Therefore, the construction of sheet-like structures greatly improved the electrochemical performance of NiFe 2 O 4 materials. [ABSTRACT FROM AUTHOR]

• The partial S-doping NiFe 2 O 4 was obtained through a facile hydrothermal method. • The d-spacing of NiFe 2 O 4 was expended caused by partial S-doping. • The impact of partial S-doping to NiFe 2 O 4 is exposed by VASP analysis. • The optimal electrode exhibited the highest specific capacitance of 284 F/g. Nickel ferrite exhibits many advantages as electrode materials in the application of supercapacitor, such as high energy capacity and excellent cycle stability. Whereas, compared with identical-metal sulfides, the specific capacitance of NiFe 2 O 4 is still insufficient. Hence, to combine the superiorities of oxides and sulfides, partial sulfur doping NiFe 2 O 4 is obtained through hydrothermal synthesis method. Analyzed by Vienna Ab-initio Simulation Package (VASP) software and high-resolution transmission electron microscopy, the lattice parameters of NiFe 2 O 4 are confirmed to be expanded by introducing sulfur atoms, which is beneficial to electrochemical performances. At a current density of 1 A/g, the specific capacitance of partial sulfur doping NiFe 2 O 4 is calculated to be 284 F/g, higher than that of the original NiFe 2 O 4 of 182.2 F/g. Moreover, a maximum energy density of 21.14 Wh/kg is achieved at a power density of 375 W/kg. This work shows that partial sulfur doping could improve the electrochemical performance of NiFe 2 O 4. To sum up, this work provides an effective way to enhance the poor electrochemical performance of oxides, greatly encouraging the application of oxides in energy storage field. [Display omitted] [ABSTRACT FROM AUTHOR]