Sulfonated‐ TiO ₂ Nanorod–Reinforced PEO Composite Solid Electrolytes f

Solid‐state lithium batteries (SSBs) represent a promising next‐generation energy storage technology, yet the practical application of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs) is hindered by limited ionic conductivity and poor oxidative stability at high voltages. In this work, we present a novel composite solid electrolyte (CSE) that overcomes these limitations by coupling the extended 1D morphology of titanium dioxide nanorods with active surface sulfonation (STiO ₂ ). Unlike conventional pristine fillers that act merely as passive structural disruptors, the STiO ₂ nanorods actively participate in the local ionic coordination. The highly electronegative sulfonic groups act as localized Lewis base sites that promote LiTFSI dissociation, facilitating the formation of continuous Li ⁺ transport pathways. Raman spectroscopy indicates that this active functionalization enhances salt dissociation, increasing the fraction of free Li ⁺ ions from 55.27% to 61.27%. Consequently, the optimized CSE (5 wt.% STiO ₂ ) delivers an enhanced ionic conductivity of 1.5 × 10 ⁻⁴  S cm ⁻¹ at 30 °C and an improved Li ⁺ transference number. Furthermore, rigorous evaluation using carbon‐coated electrodes and chronoamperometric floating tests demonstrates an electrochemical stability window beyond 5 V vs Li ⁺ /Li, indicating excellent kinetic stability against continuous parasitic oxidation. Ex situ SEM and EIS analyses support that the robust composite architecture successfully mitigates dendrite penetration, maintaining a stable lithium interface for nearly 1000 h. Finally, the CSE 5% demonstrates proof‐of‐concept feasibility for cycling various cathodes (LFP, NMC111, and LNMO), establishing the synergistic coupling of 1D morphology and active surface chemistry as a highly effective strategy for advancing high‐energy‐density SSBs.