Electrospinning and subsequent carbonization of ternary polymer blends led to many interesting and important composition-dependent characteristics. Ternary blends consisting of polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), and poly(N-vinyl-2-pyrrolidone) (PVP) exhibited unique phase separation behaviors, which were attributed to the disparities in intermolecular interactions among the constituent polymer pairs. In addition to this phase behavior, combination of the individual characteristics of each polymer as a carbon precursor led to unique morphologies and microstructural properties of the carbonized nanofiber products (CNPs). Representatively, use of PMMA as a continuous phase in the blend generated a bundle-like morphology, while the combination of PAN and PMMA/PVP as a continuous phase and dispersed phases, respectively, led to the development of open, effective porosity. These morphological and microstructural properties were correlated with the electrochemical properties of the CNPs. High specific discharge capacitances were achieved from the CNPs with open, effective porosity, even in highly viscous ionic liquid electrolytes of relatively large molecules. It is anticipated that precise control of the composition of ternary-blend precursors will result in further optimized properties for specific applications.