Titanium Carbide MXene Enabling Temperature-Dependent High Ionic Conductivity in Solid Polymer Electrolytes

Solid polymer electrolytes (SPEs) are promising candidates for next-generation solid-state lithium-ion batteries due to their mechanical flexibility, ease of fabrication, and potential for enhanced safety compared to liquid electrolytes, but their practical applications remain restricted by low ionic conductivity and sensitivity to operating conditions. In this work, high-quality few-layered Ti ₃ C ₂ T _x MXene nanoflakes were synthesized via a mild, Li-ion-assisted etching route, offering a safer alternative to conventional HF-based methods, and incorporated into PVA, PAN, and PVDF polymer matrices to form highly conductive composite SPEs. Temperature- and humidity-dependent in-plane and through-plane ionic conductivity measurements were performed between 20–80°C at 70% relative humidity. All MXene-filled SPEs exhibited enhanced ionic conductivity with increasing temperature, reaching 88–116 mS cm ^− 1 at 60–80°C, surpassing that of conventional electrolytes. Among them, PVA-based SPEs showed exceptional performance, delivering in-plane and through-plane Li-ion conductivities of 116.23 mS cm-1 and 6.76 mS cm ^− 1 at 60°C, attributed to reduced polymer crystallinity, enhanced segmental mobility, and water-mediated Li ⁺ transport along MXene interlayers. PAN-based composites offered a balance of high conductivity and mechanical stability, while PVDF systems showed limited humidity responsiveness, highlighting the role of polymer hydrophilicity in Li ⁺ -H ₂ O-MXene coupled transport. Arrhenius analysis revealed reduced activation energies (0.3–0.8 eV) under humid conditions, confirming humidity-assisted ion migration. These results demonstrate MXenes as multifunctional nanofillers and dynamic ion transport channels, providing valuable insights for designing durable, flexible, and thermally stable SPEs for solid-state batteries and hybrid energy storage devices.