The critical role of Al2O3, BaTiO3 and ZrO2 nanoceramic fillers in PVDF-HFP based composite polymer electrolytes for high performance lithium-metal batteries

Lithium metal batteries (LMBs) can be the ultimate choice for future battery technologies since they use Lithium metal as anode, which offers high theoretical capacity (3860 mAh.g⁻¹) and lowest electrochemical potential (−3.04 V vs. SHE). However, their commercialization is limited by dendritic growth, interfacial instability, and safety risks associated with liquid electrolytes. In this work, composite solid polymer electrolytes (CSPEs) are developed by incorporating various (Al₂O₃, BaTiO₃, and ZrO₂) ceramic fillers into a PVDF-HFP/LiTFSI matrix via a scalable solution casting method. Among these, optimized 10 wt% ZrO₂-based CSPE (PLZ) delivers the highest room-temperature ionic conductivity (9.26 × 10⁻⁵ S cm⁻¹), excellent Li⁺ transference number (0.55), superior tensile strength (3.23 MPa), wide potential window (5.33 V), and good flame retardancy. Li/Li symmetric cells using PLZ showed stable lithium plating/stripping for more than 480 h at 0.10 mA.cm⁻² with a low overpotential of ∼7 mV. Electrochemical impedance spectroscopy and equivalent circuit fitting confirmed the lowest increase in interfacial resistance after cycling. Time-resolved distribution of relaxation time (DRT) and 2D contour analysis revealed that PLZ maintained stable SEI and charge-transfer resistances, while bare CSPEs showed growing interfacial instability during cycling. These improvements are attributed to Lewis acid-base interactions and surface charge effects that reduce crystallinity and promote Li⁺ mobility. Full-cell evaluations with LiFePO₄ and NMC111 cathodes demonstrated high discharge capacities and good cycling stability. Thus, this study offers a promising pathway for developing robust and safe CSPEs for next-generation solid-state LMBs.