Flexible sandwich-structured LLZTO/P(VDF-TrFE) composite electrolyte membrane for enhanced cycling stability in lithium metal batteries

Composite polymer electrolytes (CPEs) used in solid-state lithium metal batteries (SSLBs) continue to face challenges, including a gradual rise in interfacial resistance and unchecked growth of lithium dendrites. Herein, a flexible and mechanically robust sandwich-structured CSE membrane is constructed, features poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) containing 4 wt% Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) used on the top and bottom, with a central layer compose of 70 wt% LLZTO with P(VDF-TrFE), refers to PTL4. The flexible outer layers enriched in polymer, provide excellent electrode contact, while the rigid middle layer characterized by a high content of LLZTO, effectively impedes lithium dendrite penetration and enhances Li + conductivity. The as prepared PTL4 exhibits high ionic conductivity of 1.02 × 10 −4  S cm −1 at 30 °C, a wide electrochemical window up to 4.9 V, and outstanding mechanical properties (tensile strength of 8.9 MPa and 150 % strain). The symmetric Li|PTL4|Li cells demonstrate stable cycling performance for over 1500 h at 30 °C. Moreover, Li|PTL4|LiFePO 4 cells maintain exceptional capacity of 98 % after 250 cycles at a high rate of 0.5C, accompanied by an average Coulombic efficiency exceeding 99.5 %. Furthermore, the fabricated pouch cells are characterized by their foldability, cutability, and puncture resistance, underscoring their potential to enhance battery safety.