In the present work, we report a convenient method for preparing non-stoichiometric cobalt sulfide with one-pot solvothermal method. Different Co x S y  nanomaterials are synthesized for supercapacitor application. This experiment explores the influence of ethanol and N , N -dimethylformamide (DMF) on the microstructure and properties of Co x S y . X-ray diffraction (XRD), scanning electron microscopy, and Brunner–Emmet–Teller (BET) measurements demonstrated that Co x S y (ethanol) and Co x S y (DMF) have different structures and morphologies. Electrochemical supercapacitor performance of Co x S y (ethanol) and Co x S y (DMF) is characterized via cyclic voltammetry, galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. These results show that Co x S y (DMF) has better electrochemical performance than Co x S y (ethanol), and its capacitance can reach 347.4 F/g at the current density of 0.5 A/g. Moreover, Co x S y (DMF) also delivers a better cycling stability of about 70.8% capacity retention after 3000 cycles at a current density of 4 A/g. In addition, the assembled asymmetric supercapacitor of Co x S y (DMF)//active carbon shows an excellent energy density of 66.4 Wh/kg at a power density of 483.1 W/kg. These results indicate that Co x S y (DMF) has a good application prospect in the field of supercapacitor.