Carbonization temperature is an influential parameter in fabricating electrodes for energy devices because it allows better charge/ion storage and transfer. Renewable kraft lignin-based nanofibers were synthesized utilizing a facile electrospinning technique and then converted into carbon nanofibers (CNFs) mats using heat treatment at various temperatures (600, 800, and 1000 °C) in this study. These prepared candidates were characterized and compared using SEM and BET analyses for morphological, surface area, and porosity differences. Additionally, Raman spectroscopy and I-V experiments were used to learn more about the I_D/I_G ratio and electrical conductivity. These samples were also subjected to a detailed functional group analysis using FTIR and XPS. CV, GCD, and EIS experiments were carried out to compare the electrochemical performance of CNFs mats as of the free-standing electrodes. The findings suggest that to achieve desired properties in lignin-PVA blend-based free-standing CNFs mats, the carbonization temperature of 800 °C is optimal. A balanced combination of defects level, functional groups, and mesoporous surface led to better supercapacitor performance of 800 °C (specific capacitance of 196.63 F/g @ 1 A/g) treated CNFs mats. These findings show that high-performance CNFs free-standing electrodes for supercapacitor applications can be designed without pseudocapacitive material using an optimized carbonization parameter.