Al and Ta co-doped LLZO as active filler with enhanced Li⁺ conductivity for PVDF-HFP composite solid-state electrolyte

Battery safety calls for solid state batteries and how to prepare solid electrolytes with excellent performance are of significant importance. In this study, hybrid solid electrolytes combined with organic PVDF-HFP and inorganic active fillers are studied. The modified active fillers of Li_7−x−3y Al _y La₃Zr_2-x Ta _x O₁₂ are obtained by co-element doping with Al and Ta when LLZO is synthesized by calcination. And an high room temperature ionic conductivity of 5.357 × 10⁻⁴ S cm⁻¹ is exhibited by ATLLZO ceramic sheet. The composite solid electrolyte PVDF-HFP/LiTFSI/ATLLZO (PHL-ATLLZO) is prepared by solution casting method, and its electrochemical properties are investigated. The results show that when the contents of lithium salt LiTFSI and active filler ATLLZO are controlled at 40 wt% and 10%, respectively, the ionic conductivity of the resulting composite solid electrolyte is as high as 2.686 × 10⁻⁴ S cm⁻¹ at room temperature, and a wide electrochemical window of 4.75 V is exhibited. The LiFePO₄/PHL-ATLLZO/Li all-solid-state battery assembled based on the composite solid-state electrolyte exhibits excellent cycling stability at room temperature. The cell assembled by casting the composite solid-state electrolyte on the cathode surface shows a discharge specific capacity of 134.3 mAh g⁻¹ and 96.2% capacity retention after 100 cycles at 0.2 C. The prepared composite solid-state electrolyte demonstrates excellent electrochemical performance.