Construction of Stable Li₂O‐Rich Solid Electrolyte Interphase for Practical PEO‐Based Li‐Metal Batteries

Abstract Polyethylene oxide (PEO)‐based solid polymer electrolytes (SPE) have garnered recognition as highly promising candidates for advanced lithium‐metal batteries. However, the practical application of PEO‐based SPE is hindered by its low critical current density (CCD) resulting from undesired dendrite growth. In this study, a PEO‐based SPE that exhibits an ultra‐high CCD (4 mA cm⁻²) is presented and enhanced lithium ionic conductivity through the incorporation of small amounts of P₂S₅ (PS). The crystalline Li₂O‐rich and P/S‐containing solid electrolyte interphase (SEI) is revealed by cryo‐electron microscope (cryo‐EM) and Time of flight secondary ion mass spectrometry (TOF‐SIMS), which inhibits dendrite growth and adverse reactions between SPE and reductive lithium, thus offering a spherical growth behavior for dendrite‐free lithium metal anode. Consequently, utilizing the PS‐integrated SPE, a Li‐Li symmetric cell demonstrates reduced resistance during operation, enabling stable cycles exceeding 200 hours at 0.5 mA cm⁻² and 0.5 mAh cm⁻², a stringent test condition for PEO‐based electrolytes. Moreover, a Li/SPE/LiFePO₄ (LFP) pouch cell exhibits 80% capacity retention after 100 cycles with 50 µm Li and 30 µm PEO electrolyte, showcasing its potential for practical applications.