Dual-polymer composite solid-state electrolyte with enhanced Li+ conduction and interfacial compatibility for lithium metal batteries

It is a persistent goal for solid-state electrolytes to enhance their ionic conductivity while maintaining good mechanical strength to potentially inhibit lithium dendrites. In this work, we introduce garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) fillers and polyacrylonitrile (PAN) into thermoplastic polyurethane (TPU) to fabricate a composite solid-state electrolyte. The TPU matrix contains hard segments (−NH−COO−) that provide efficient mechanical support and soft segments (−O−) responsible for good flexibility and elasticity. When blended with PAN, hydrogen bonds form between the functional groups of PAN and TPU, establishing strong intermolecular connections that further enhance the structural/electrochemical stability of the electrolyte. A stable polymer/filler interface can be constructed through the ion-dipole coordination interaction between the metal ions at the LLZTO surface and the −CN groups of PAN. Benefiting from the intricate interactions among the PAN/TPU dual polymers and the LLZTO filler, the composite electrolyte exhibits not only exceptional flexibility (a tensile strain of 208%) and tensile strength (40 MPa), but also a good ionic conductivity of 2.33 × 10 −4 S cm⁻¹ at room temperature, a high oxidation potential of 4.48 V, and an excellent Li + transference number of 0.79. The Li||LiFePO 4 battery employing this composite solid-state electrolyte exhibits remarkable electrochemical stability, delivering an initial discharge capacity of 127.4 mAh g −1 at 0.3C and room temperature, and maintains a capacity retention of 91.9% after 600 cycles. This work provides a new electrolyte modification strategy for next-generation solid-state lithium metal batteries.