Spatial Ion-Gradient Solid Polymer Electrolytes for Stable Solid-State Sodium Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid-state sodium batteries (NaSSBs) face challenges balancing ionic conductivity, mechanical strength, and interface stability.
• Achieving these properties simultaneously is crucial for practical NaSSB applications.

Purpose of the Study:

• To develop a polymer electrolyte for NaSSBs that overcomes the trade-offs between ionic conductivity, mechanical robustness, and interface stability.
• To demonstrate a surface-bulk decoupling strategy for enhanced electrolyte performance.

Main Methods:

• A polyvinylidene fluoride-based polymer electrolyte with an ion-concentrated surface layer was synthesized.
• Differential electrochemical mass spectrometry (DEMS) was used to analyze parasitic reactions.
• Operando 23Na NMR spectroscopy characterized sodium deposition.
• Na||Na symmetric cells and Na4Fe3(PO4)2P2O7//Na cells were assembled and tested.

Main Results:

• The ion-concentrated surface layer effectively suppressed parasitic reactions and maintained bulk electrolyte advantages.
• The electrolyte achieved high room-temperature ionic conductivity (4.52 × 10-4 S cm-1).
• Stable cycling of Na||Na symmetric cells for over 360 hours was achieved.
• High capacity retention (90.9% after 5000 cycles) was observed in Na4Fe3(PO4)2P2O7//Na cells.

Conclusions:

• The surface-bulk decoupling strategy provides a practical approach for designing advanced solid-state electrolytes.
• The developed electrolyte enables stable Na metal deposition and long-term cycling performance in NaSSBs.
• This work contributes to the advancement of high-performance and safe solid-state sodium battery technology.