Boosting Li ⁺ transport in ultra-stable all-solid-state lithium metal batteries via bimetal oxide enhanced PrBaCoFeO _{5+ <i>δ</i>} perovskite nanofillers

Composite solid-state electrolytes (CSEs) have garnered significant attention for next-generation energy storage owing to their inherent safety features compared with those of their liquid counterparts. However, their practical deployment remains hindered by sluggish lithium-ion transport kinetics and interfacial instability. Herein, we introduced a bimetal oxide enhanced strategy for oxygen-vacancy-engineered double perovskite nanofillers (PrBaCoFeO_5+δ, PBCF) to address these challenges in polyethylene oxide (PEO)-based CSEs. The strong Lewis acid-base coordination between Co³⁺/Fe³⁺ sites on PBCF and ether oxygen groups in PEO effectively suppresses polymer-chain crystallization while creating continuous Li⁺ conduction pathways. Importantly, the abundant oxygen vacancies serve as catalytic centers to decompose LiTFSI, thereby forming a robust organic-inorganic hybrid solid electrolyte interphase (SEI). Consequently, the prepared PEO-LiTFSI-PBCF CSE achieves an improved Li⁺ ionic conductivity of 2.76 × 10^–4 S cm^–1 (30°C) and an elevated Li⁺ transference number (0.54). The Li||Li symmetric cell exhibits impressive lithium plating/stripping ability (&gt;6000 h at 0.1 mA cm⁻²) and practical viability in Li||LiFePO₄ full cells with 90.1% capacity retention after 500 cycles at 30°C (0.3C). This defect engineering strategy provides new insights into the construction of fast and stable Li⁺ transport channels in polymer solid-state electrolytes, paving the way for high-energy-density all-solid-state lithium metal batteries.