Oxygen-Deficient Nb ₂ O ₅ -Filled PEO Polymer Electrolyte Enabling High Li-Ion Transference Number and Uniform Lithium Deposition for Lithium Metal Solid-State Batteries

PEO-derived polymer electrolytes hold promise for economical, deformable lithium metal batteries with elevated energy density. Nevertheless, their deployment is constrained by insufficient Li + transport, restricted electrochemical stability, uncontrolled Li dendrite proliferation, and inferior anode cyclability. Herein, we introduce oxygen-deficient Nb 2 O 5 (Ov-Nb 2 O 5 ) into a polyethylene oxide host to fabricate an innovative solid-state electrolyte. The Ov-Nb 2 O 5 particles anchor PEO chains via Lewis acid−base interaction, forming a robust oxide−polymer interface. This interaction effectively prevents filler aggregation and reduces PEO crystallinity, yielding a homogeneous electrolyte membrane with enhanced mechanical strength. The resulting architecture accelerates Li + migration across the polymer, thereby elevating ionic transport and restraining dendrite advancement. The PEO/LiTFSI/10%Ov-Nb 2 O 5 electrolyte demonstrates a conductivity of 2.5 × 10 −4 S cm −1 alongside a Li + transference number of 0.63 at 60 °C. Furthermore, Li-metal symmetric cells sustain steady deposition/dissolution exceeding 1500 h under 0.2 mA cm −2 . When paired with a LiFePO 4 cathode, the full cell achieves a reversible capacity of 121.4 mAh g −1 at 0.5 C and retains 91.7% of its capacity after 400 cycles. This investigation underscores an effective approach for engineering multifunctional fillers toward advanced solid electrolytes featuring rapid ion conduction and exceptional interfacial durability.