Solid solutions with fluorite-type structure in the PbF2-SrF2-KF system were prepared by mechanochemical synthesis. The structure and morphology of the synthesized materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Thermal analysis of samples confirmed the absence of phase transitions which are characteristic of PbF2. Temperature dependence of the ionic conductivity of the solid electrolytes in the PbF2-SrF2-KF system was investigated by impedance spectroscopy. The high ionic conductivity of the Pb0.75Sr0.20K0.05F1.95 sample (3.05 × 10−4 S/cm at 20 °C) made it possible to create a fluoride-ion battery model on its basis. The cell operation demonstrates the possibility of using the Pb0.75Sr0.2K0.05F1.95 solid electrolyte in solid-state fluoride-ion batteries (FIBs).