A Fluoride-Ion-Conducting Solid Electrolyte with Both High Conductivity and Excellent Electrochemical Stability

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• Solid-state fluoride-ion batteries (FIBs) offer potential advantages over lithium-ion batteries but are limited by solid electrolyte performance.
• Existing solid electrolytes for FIBs suffer from low ionic conductivity at room temperature or narrow electrochemical stability windows (ESW).
• These limitations hinder the development of high-performance, room-temperature operable FIBs.

Purpose of the Study:

• To design and synthesize a novel solid electrolyte for FIBs that overcomes the limitations of existing materials.
• To achieve simultaneously high ionic conductivity and a broad electrochemical stability window (ESW) at room temperature.
• To demonstrate the performance of the new solid electrolyte in a functional solid-state FIB.

Main Methods:

• Design and synthesis of a novel solid electrolyte: CsPb_0.9 K_0.1 F_2.9.
• Characterization of ionic conductivity at room temperature.
• Evaluation of the electrochemical stability window (ESW).
• Fabrication and testing of a solid-state FIB cell using the developed electrolyte.

Main Results:

• The synthesized CsPb_0.9 K_0.1 F_2.9 solid electrolyte exhibits a room-temperature conductivity of 1.23 × 10^-3 S cm^-1.
• This conductivity is comparable to state-of-the-art conductive solid electrolytes for FIBs.
• The solid electrolyte demonstrates a significantly broader ESW compared to previously reported materials.
• A solid-state FIB cell utilizing CsPb_0.9 K_0.1 F_2.9 was successfully cycled at 25 °C for 4581 hours with minimal capacity fade, operating at higher voltages than other room-temperature FIBs.

Conclusions:

• The novel CsPb_0.9 K_0.1 F_2.9 solid electrolyte simultaneously achieves high room-temperature ionic conductivity and a broad electrochemical stability window.
• These properties enable the construction of high-voltage, stable solid-state fluoride-ion batteries operable at room temperature.
• This development represents a significant advancement towards practical solid-state FIB technology.