Advancing Polymer Gel Electrolytes for Flexible Supercapacitors: Toward High Ionic Conductivity and Self-Discharge Mitigation

Poly(vinyl alcohol) (PVA)-based gel/solid-state electrolytes are favored for flexible supercapacitors (FSCs) due to their biodegradability, cost-effectiveness, nontoxicity, hydrophilicity, high dielectric constant, and mechanical strength. However, the low ionic conductivity of these gel electrolytes limits the specific capacitance, energy density, rate performance, and cycle life of the supercapacitors. Also, the supercapacitor’s high self-discharge rate adversely affects the device’s overall electrochemical performance. To overcome these challenges, we demonstrated a straightforward strategy to enhance the ionic conductivity while concurrently reducing the self-discharge rate of FSCs by incorporating poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT–PSS) in the PVA/H2SO4 gel electrolyte, and utilizing B,S-codoped graphene (BSGO) as an electrode. The ionic conductivity of the PVA/H2SO4 gel electrolyte with PEDOT–PSS increased substantially from 2.6 to 14 mS/cm, the energy density experienced a twofold enhancement from 4 to 10 Wh/kg, and the rate capability exhibited a remarkable uplift from 50 to 80%. Notably, the self-discharge characteristics of the FSC were significantly mitigated by incorporating PEDOT–PSS in PVA/H2SO4. The fabricated FSC device with modified electrolyte exhibited an impressive voltage retention of 72% of its maximum working voltage after 2400 s in open-circuit conditions, while it was only 43% for PVA/H2SO4. The observed performance enhancement can be attributed to the reversible redox reactions between the sulfonate ions in PEDOT–PSS and the H+ ions in the electrolyte, thereby facilitating improved ionic transport and electrochemical stability.