Toward high performance all solid-state Na batteries: Investigation of electrolytes comprising NaPF₆, poly(ethylene oxide) and TiO₂

Solid electrolytes based on polyethylene oxide (PEO) have been studied for decades, owing to their facile and low-cost processing, good electrochemical stability, and excellent complexation with alkali metal salts. Complexes of PEO with appropriate sodium salts are well known for ionic conduction. Here, pristine NaPF₆:P(EO)₁₆ and a composite solid electrolyte containing TiO₂ nanowires were investigated as candidates for rechargeable solid-state sodium batteries. Comprehensive electrochemical characterizations were carried out, including ionic conductivity, transference number, and structural stability. At elevated temperatures, the specific capacity of an all-solid-state Na₃Ti₂(PO₄)₃ (Na/NTP) sodium battery was 110 mAh g^-1, higher than room-temperature cells with liquid electrolyte solutions. We attribute this behavior to increased conductivity of the polymer electrolyte, induced by the ceramic nanofiller, combined with enhanced electronic conductivity of the NTP cathode.