High-Entropy Tailored UCl₃-Type Halides With Enhanced Ionic Conduction and Stability for All-Solid-State Sodium...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Developing advanced solid electrolytes (SEs) is critical for high-performance all-solid-state sodium-ion batteries (ASSNIBs).
• Existing sodium-based halide SEs often suffer from low ionic conductivity and insufficient electrochemical stability, limiting their application in high-voltage ASSNIBs.
• Blocked ion diffusion pathways and anionic oxidation bottlenecks hinder conductivity and stability in conventional halide systems.

Purpose of the Study:

• To design and synthesize a novel halide-based solid electrolyte with enhanced ionic conductivity and electrochemical stability for ASSNIBs.
• To investigate the structural and electrochemical properties of a high-entropy cerium chloride (HE-CeCl3) composition.
• To evaluate the performance of the developed electrolyte in a complete ASSNIB device.

Main Methods:

• Synthesis of a high-entropy CeCl3-based composition: NaLa0.472Ce0.472Ta0.155Nb0.155Zr0.155Cl6 (HE-CeCl3).
• Characterization of ionic conductivity and electrochemical stability using electrochemical impedance spectroscopy and cyclic voltammetry.
• Assembly and testing of ASSNIBs using the HE-CeCl3 electrolyte and a Na3(VOPO4)2F cathode in mold-type and pouch-type cells.

Main Results:

• The synthesized HE-CeCl3 exhibits an ionic conductivity exceeding 10^-3 S cm^-1.
• Local structural distortions in HE-CeCl3 promote Na-ion diffusion through one-dimensional pathways with reduced energy barriers.
• HE-CeCl3 demonstrates robust high-voltage stability (4.46 V vs. Na+/Na), good solvent tolerance, and suppressed anion oxidation kinetics.
• ASSNIBs utilizing HE-CeCl3 show long-term cycling stability (88.3% capacity retention after 600 cycles) and high areal capacity (1.7 mAh cm^-2).

Conclusions:

• The high-entropy design strategy effectively enhances both ionic conduction and electrochemical stability in sodium-ion conductors.
• HE-CeCl3 presents a promising candidate for practical, wet-processed ultrathin electrolyte films in ASSNIBs.
• This work accelerates the development of advanced ASSNIBs by providing a versatile material design approach.