Entropy‐Driven Design of Dual‐Polymer Electrolytes for Structural Energy Storage Applications

Multifunctional electrolytes with efficient ionic transport and mechanical load‐bearing are crucial for next‐generation structural energy storage systems. However, existing structural electrolytes face an intrinsic trade‐off between ionic conductivity and mechanical integrity. This study introduces an entropy‐driven solid polymer electrolyte (SPE) design that simultaneously improves ionic transport and mechanical performance. By blending polylactic acid (PLA) and polymethyl methacrylate (PMMA) at distinct molecular weights with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), we leverage molecular‐weight‐mediated configurational entropy to tune SPE performance. Characterizations including differential scanning calorimetry, X‐ray diffraction, and Fourier‐transform infrared spectroscopy confirm miscible, interpenetrating networks with pervasive Li ⁺ ‐carbonyl coordination and high‐entropy states. Electrochemical impedance spectroscopy demonstrates all dual‐polymer electrolytes outperform single‐polymer counterparts in ionic conductivity. Notably, a high‐entropy formulation achieves ionic conductivity three orders of magnitude higher and activation energy 50%–65% lower than single‐polymer versions. Mechanically, while single‐polymer electrolytes occupy opposite ends of the toughness‐stiffness spectrum, dual‐polymer electrolytes overcome this by combining both attributes for a balanced response. One formulation attains a synergistic balance, delivering high stiffness (≈0.58 GPa) while preserving substantial toughness. These results illustrate that entropy‐driven tuning navigates the conductivity‐mechanics trade‐off, engineering SPEs with balanced properties for structural energy storage applications.