Building Bulk and Interface Dual Fast Li⁺ Conducting Pathway in Composite Solid Polymer Electrolyte Membrane for All–Solid–State Lithium–Metal Batteries

Abstract Solid polymer electrolytes (SPEs) are considered a promising solution to the safety problems of lithium‐ion batteries (LIBs) using liquid electrolytes. However, the high crystallinity and low ionic conductivity hinder the practical application of SPEs. Herein, we design a composite solid polymer electrolyte with a dual fast Li⁺ conducting pathway in bulk and interface by incorporating highly Li⁺ conductive ceramic Li_6.4Ga_0.2La₃Zr₂O₁₂ (LGLZO) in polyethylene oxide (PEO)/Li–bis (trifluoromethanesulfonyl) imide (LiTFSI) system. Compared to Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO), LGLZO provides better Li⁺ conductivity; therefore, a fast Li⁺ conducting pathway will form in the bulk of LGLZO nanofillers. Besides, LGLZO nanofiller accelerates the dissociation of LiTFSI and benefits the transfer of free Li⁺ through the SPEs near the LGLZO surface, forming another interface fast Li⁺ conducting pathway in the SPEs. Benefits from the dual fast Li⁺ pathway design, the composite electrolyte membrane with 15 wt % LGLZO nanoparticles presents a high ionic conductivity of 8.0×10⁻⁴ S cm⁻¹ at 60 °C. The Li−Li symmetric cells with optimized content LGLZO show good cycling stability (no short circuit even after 1000 h), and the all–solid Li/LiFePO₄ batteries exhibit excellent cycling performance (remained 154 mAh g⁻¹ after 500 cycles at 0.2 C under 60 °C).