Mechano-Electrochemical Synergy of Lignin Cross-Linked PVA Gel Polymer Electrolytes for Wide-Temperature Flexible Supercapacitors

The rapid development of flexible electronics has intensified the demand for high-performance energy storage solutions. This research aims to enhance the performance of flexible supercapacitors under extreme temperatures through a lignin cross-linked poly(vinyl alcohol) (PVA) gel electrolyte. By incorporating lignin with PVA and using polyethylene glycol diglycidyl ether as a cross-linker, a hydrogel (PL<i>x</i>, <i>x</i> represents the mass ratio of lignin to PVA) with an enhanced three-dimensional network structure was constructed. Furthermore, the electrolyte's wide-temperature electrochemical behavior was optimized by incorporating <i>N,N</i>-dimethylformamide (DMF) and lithium nitrate (LiNO₃). Results show that the PL0.3 hydrogel exhibits exceptional mechanical properties, with a tensile strength of 4.04 ± 0.16 MPa, an elongation at break of 520.08 ± 67.72%, and a compressive strength of up to 25 MPa. Notably, the PL0.3-D5H5Li2 (lignin at 0.3x PVA mass, DMF/H₂O = 5:5, and 2 mol/L LiNO₃) gel electrolyte exhibits superior temperature resilience, achieving a tensile strength of 1.24 MPa and elongation at break of 60.42% at -20 °C, and a tensile strength exceeding 1.41 MPa at 80 °C. Electrochemical tests reveal that at 2.0 V, the supercapacitor retains 95% Coulombic efficiency and nearly 100% capacitance retention after 8000 charge-discharge cycles. At -20 °C, it retains 83.5% of its room-temperature specific capacitance (64.58 F g^-1), and after 2000 cycles at 80 °C, capacitance retention is 83%. These findings strongly support the application of flexible supercapacitors in wide-temperature conditions and suggest a promising future in high-performance energy storage systems.