Cyclic P₃O₉ ^3- Trimer: A Network Former for Amorphous Superionic Conductors in Sodium Solid-State Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• All-solid-state sodium-ion batteries (ASSNIBs) require solid-state electrolytes (SSEs) with fast ion conduction, high voltage stability, and mechanical flexibility.
• Current SSEs face challenges in simultaneously achieving these critical properties.

Purpose of the Study:

• To introduce a novel class of amorphous oxyhalide SSEs based on cyclic trimetaphosphate anions.
• To investigate the structure-property relationships governing ionic conductivity and electrochemical stability.
• To demonstrate the performance of these SSEs in ASSNIBs.

Main Methods:

• Facile mechanochemical synthesis of amorphous oxyhalide SSEs incorporating cyclic trimetaphosphate (P3O9^3-) anions.
• Structural characterization to understand the 3D coordination network and anion arrangement.
• Electrochemical testing to measure ionic conductivity, electrochemical window, and battery cycling performance.

Main Results:

• A new family of amorphous oxyhalide SSEs was synthesized using P3O9^3- as a network-forming unit.
• The electrolytes exhibit an ultralow activation energy (0.33 eV) due to a dynamic anion-assisted transport mechanism.
• Optimized SSEs achieved high ionic conductivity (0.80 mS·cm^-1) and a wide electrochemical window (1.4–4.2 V).
• ASSNIBs demonstrated stable cycling at 4.2 V with 92% capacity retention after 300 cycles.

Conclusions:

• Cyclic trimetaphosphate anions are effective in constructing amorphous SSEs with desirable properties for ASSNIBs.
• The dynamic anion-assisted transport mechanism significantly enhances Na+ conduction.
• This work establishes a new design strategy for high-performance solid-state electrolytes.