Amorphous S-doped NixCo3-xO4 for high-performance asymmetric supercapacitors

Amorphous S-doped NixCo3-xO4 materials were successfully synthesized using a facile co-precipitation method through changing additive in a mixed solution. As-prepared amorphous S-doped NixCo3-xO4 exhibit different Ni/Co ratio, O/S ratio, morphology and structure when a mixed solution including sodium dodecyl sulfate, without additive, or containing glycine. S-doped NixCo3-xO4 prepared with a mixed solution excluding additive (denoted as NixCo3-xO4-ySy-2) exhibits remarkable supercapacitive performance due to optimum Ni/Co ratio, minimum O/S ratio, proper morphology and structure. NixCo3-xO4-ySy-2 delivers a specific capacitance of 1335 F g−1 at 0.5 A g−1 and a ultra-high specific capacitance retention of 68.7% even at 16 A g−1, demonstrating high specific capacitance and good rate capability. Moreover, NixCo3-xO4-ySy-2 shows an initial specific capacitance retention of 80.8% after 2000 cycles, implying superior cycling stability. The assembled asymmetric supercapacitor (ASC) based on NixCo3-xO4-ySy-2 as the positive electrode and AC as the negative electrode achieves outstanding energy density of 31.87 Wh kg−1 at a power density of 900 W kg−1. The specific capacitance retention of the ASC is up to 90.2% after 2000 cycles, exhibiting excellent cycling stability. This study shows a promising electrode for supercapacitors device and provides an effective strategy for design of high-performance supercapacitor electrode materials.