A new transition-metal-based antimony fluoride sulfate compound, Ni 0.779 SbF 3 (SO 4 ), has been studied, which appears to be a promising candidate for an electrode material in supercapacitor devices. The hydrothermal synthetic technique has been employed for growing single crystals. The single-crystal X-ray diffraction study reveals that it crystallizes in the orthorhombic space group Cmce with unit cell parameters a = 15.1710 ( 3) Å, b = 7.1843 (11) Å, and c = 11.070 (17) Å and Z = 8. The crystal structure consists of a [SbF 3 O 2 ] polyhedron and a [SO 4 ] tetrahedron along with cis-and trans-[NiO 4 F 2 ] octahedrons of two different Ni atoms that result in negatively charged [NiSbF 3 • SO 4 ] n layers in the crystal structure, where each layer is made up of chains of [Ni(1)O 6 F 2 ] n , [Ni(2)O 8 F 2 ] n , and [(SbF 3 ) 2 (SO 4 ) 2 ] n4− . The partial occupancy on Ni sites resulted in the compound being nonstoichiometric. The morphological analysis by both scanning electron microscopy (SEM) and tunneling electron microscopy (TEM) reveals a multilayer dense nanoflake-like morphology. Thermogravimetric analysis (TG-DTA) shows that the compound has a high thermal stability with a decomposition temperature above 450 °C. The density functional theory (DFT) and density of states (DOS) are found to be commensurate with the experimental results. The material shows good electrochemical performance with a capacitance of 245 F g −1 at a specific current density of 1 A g −1 . Further, the electrochemical impedance spectroscopy (EIS) study confirms the capacitive nature of the electrode.