Reinforced Anti‐Oxidative Degradation and Interface Stabilization in Bimetal Oxide Filler‐Based PEO Electrolytes for Lithium Metal Batteries

Abstract Polyethylene oxide (PEO) electrolytes hold significant potential for the next‐generation all‐solid‐state lithium metal batteries. However, their practical application is limited by low ionic conductivity, unstable solid electrolyte interphase (SEI) and, especially, poor oxidative stability under high voltages. Herein, a filler‐modified PEO is proposed to address these challenges. The filler, TIO (SnO ₂ doped with In ₂ O ₃ ), is rich in oxygen vacancies, acting as Lewis acids to interact with TFSI ⁻ , which releases more Li ⁺ and achieves a higher ionic conductivity and Li ⁺ transference number. Moreover, Sn ⁴⁺ /In ³⁺ in the TIO can form alloy phases with lithium metal to facilitate Li ⁺ deposition and transport across the SEI. Consequently, Li//LiFePO ₄ cells using the filler‐modified PEO exhibit a reversible capacity of ∼140 mAh g ⁻¹ and excellent capacity retention of 92% over 800 cycles at 0.2 C. Importantly, the TIO interacts with hydroxy groups and H atom on α‐C in PEO, reducing PEO's reactivity and extending its decomposition potential to 4.75 V. Owing to the inhibited oxidative decomposition upon high‐voltage cycling, the filler‐modified PEO enables Li//LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cells to achieve an outstanding initial capacity of 170 mAh g ⁻¹ and maintain 70% capacity retention over 200 cycles at 0.5 C at a high cut‐off voltage of 4.3 V.