Sn-Doped Beta Zeolite with Rich Lewis Acidic Sites Enhances Lithium-Ion Dissociation and Transport in PEO-Based Solid Polymer Electrolytes

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) demonstrate strong electrode adhesion and facile processability, making them promising candidates in all-solid-state lithium metal batteries (ASSLMBs). However, poor ionic conductivity, low Li⁺ transference number, and insufficient mechanical strength greatly limit their practical application. Zeolite, a porous ceramic material rich in active sites, shows significant potential as a filler in the PEO-based SPEs. In this study, we prepared heteroatomic Sn-Beta zeolite with high Lewis acid activity through a simple two-step postsynthesis process and explored the mechanism of action of metal acidic sites on Li⁺ dissociation and transport. The Lewis acidic metal sites in the Sn-Beta zeolite effectively weaken the coordination environment of Li⁺ by binding the O atoms in PEO via metal-oxygen bonds, facilitating the transfer of Li⁺ along the PEO polymer chains. Moreover, it can promote the dissociation of the lithium salt by anchoring TFSI^- anions, resulting in the release of free Li⁺. The obtained SPE (PL-Sn-Beta) exhibits a high ionic conductivity of 1.40 × 10^-3 S cm^-1 at 60 °C and a Li⁺ transference number of up to 0.51. Furthermore, the ordered pore channels of the Sn-Beta zeolite provide uniform Li-ion transport pathways, facilitating homogeneous Li⁺ deposition. As a result, the lithium symmetric cell with PL-Sn-Beta demonstrates a stable lithium plating/stripping cycle performance for over 2200 h at 60 °C and 0.1 mA cm^-2. Meanwhile, the initial discharge capacity of the Li/PL-Sn-Beta/LiFePO₄ full cell reaches 145.6 mAh g^-1 at 1 C and 60 °C, and the capacity retention rate is 81.5% after 500 cycles. This work provides theoretical insights into the mechanism of zeolite fillers in SPEs as well as new design concepts.