Effect of moisture on the phase transition of β-PbSnF4 at ambient temperature as the fast fluoride ion conductor.

The solid-state electrolyte β -PbSnF 4 has been reported to have the highest fluorine-ion conductivity at room temperature among four different structures of the monoclinic (α), orthorhombic (o), cubic (γ), and tetragonal (β) at steady state. Therefore, finding an effective way to prepare β -PbSnF 4 or to transform β -PbSnF 4 from other phases is a research hotspot in FIBs. In particular, the transition mechanisms between γ -PbSnF 4 and β -PbSnF 4 are still unclear in the reported literature because the influence of trace moisture is ignored in previous research, which always leads to controversial conclusions about the phase transition mechanism. Previous articles have reported that γ -PbSnF 4 can only be transformed into β -PbSnF 4 by aging at a high temperature above 100 °C. However, this work shows that the transition from γ -PbSnF 4 to β -PbSnF 4 can occur at room temperature. Moisture is the critical factor in inducing the phase transition from γ to β -PbSnF 4. The resulting β -PbSnF 4 has a high fluoride-ion conductivity of 8.1 × 10−4 S cm−1, while the solid electrolyte for an all-solid-state FIB with BiF 3 as the cathode and Sn as the anode has a maximum discharge capacity of 55.8 mAh g−1 at 120 °C. [Display omitted] • γ -PbSnF 4 can be converted into β -PbSnF 4 at room temperature. • The moisture can induce the phase translation. • A high fluoride ion conductivity of 8.1*10−4 S cm−1 is achieved. • The protons in the H 2 O can trigger the rearrangement of the F atoms. [ABSTRACT FROM AUTHOR]