Abstract: High-security and high-energy-density energy storage technologies have become crucial for supporting the integration of renewable energy under the deep implementation of the "dual carbon" strategy. Sodium metal anode, with its advantages of abundant resources, low cost, and high theoretical specific capacity, and solid-state electrolytes, which are non-flammable and leak-free, combine to form sodium metal solid-state batteries that achieve both high capacity and high safety. However, the ionic conductivity, mechanical strength, and interface compatibility of solid-state electrolytes remain core bottlenecks. This study uses alkali lignin as the matrix and introduces polyethylene glycol (PEG) through physical blending (LEPM) and chemical grafting (L-EGPM) methods, and composites with polyvinylidene fluoride (PVDF) , sodium difluorosulfonate (NaFSI) , and MgF₂. It systematically compares the structures and properties of the two composite solid-state electrolytes. LEPM has an amorphous structure, with a uniform and dense membrane layer and molecular-level dispersion of components, while L-EGPM forms a crystalline phase due to chemical grafting and has cracks on the surface. The room-temperature ionic conductivity of LEPM is as high as 9.60×10⁻⁴ S·cm⁻¹ and the electrochemical window is up to 5.31 V, significantly superior to L-EGPM (8.16×10⁻⁴ S·cm⁻¹, 4.4 V) . In sodium symmetric battery cycling tests, LEPM can achieve 500 cycles, but due to insufficient mechanical strength, it eventually short-circuits; while L-EGPM only operates stably for 300 cycles, but the polarization fluctuation is minimal. In the all-cell, LEPM has a higher initial capacity, faster activation, reaches the peak capacity in 30 cycles, and has a sensitive rate response, and can stably cycle more than 100 times at 0.05C, demonstrating excellent low-rate performance and flexible application potential. The physical blending plasticization strategy enables LEPM to have high ionic conductivity, wide electrochemical window, and excellent film-forming properties, suitable for flexible or low-rate scenarios. This research provides a new idea for the application-oriented design of low-cost, high-performance biomass-based solid-state electrolytes.