As the demand for safe, high-energy-density energy storage continues to grow, sodium-metal batteries (SMBs) have emerged as promising alternatives to lithium-ion systems due to the abundance and low cost of sodium resources. However, conventional approaches face a critical dilemma: uncontrolled dendritic growth at the Na anode and the flammability of liquid electrolytes severely compromise both lifespan and safety. Now, researchers from Harbin Institute of Technology, Zhejiang University, and National University of Singapore, led by Professor Yulin Ma, Professor Liguang Wang, Professor Chuankai Fu, and Professor Wei Chen, have presented a breakthrough interphase engineering strategy that fundamentally redefines Na deposition behavior in quasi-solid-state sodium-metal batteries (QSMBs).
Why This Interphase Matters
Traditional artificial solid electrolyte interphases (ASEIs) are typically designed as ionic-conducting but electronically insulating layers (ICIs) to block unwanted electron transfer. While this "bottom" deposition model suppresses side reactions, the intrinsic rigidity of ICIs—combined with the poor fluidity of gel polymer electrolytes—leads to non-uniform Na plating/stripping, mechanical fracture, and eventual dendrite penetration. The novel ionic/electronic mixed conductor interphase (MCI) overcomes this limitation by enabling a surface-induced "top" Na deposition mechanism, where Na⁺ reduction occurs directly on the MCI surface rather than penetrating through it, ensuring dense, conformal, and dendrite-free Na deposition.
Innovative Design and Mechanism
The MCI is synthesized through a simple chemical soaking method, where SbF₃ reacts in situ with Na metal to form a composite layer primarily composed of NaF and Na 3 Sb alloy. DFT calculations reveal that Na₃Sb exhibits exceptionally strong Na⁺ adsorption energy (1.07 eV on Sb-top sites vs. 0.23 eV on NaF), while its semi-metallic nature (band gap of only 0.339 eV) and high electronic conductivity (0.0022 mS cm -2 ) enable rapid electron transfer. The embedded Na₃Sb phase acts as a sodiophilic nucleation scaffold, while NaF provides chemical stability and blocks electron tunneling. A cross-linked CMC binder network further enhances mechanical integrity and adhesion. This unique combination drives a "top" deposition paradigm: Na deposits uniformly on the MCI surface, forming a smooth and compact layer that preserves interfacial integrity and promotes stable SEI formation.
Outstanding Performance
Symmetric Cells: Na||Na symmetric cells with the optimized SFC-Na anode and DOL-based gel polymer electrolyte deliver an ultra-long cycling lifespan of 1000 h at 0.5 mA cm -2 with a remarkably low overpotential of ~40 mV. The critical current density (CCD) reaches 3.1 mA cm -2 —over 5× higher than pristine Na (0.6 mA cm -2 ). Even at elevated current densities of 1.0 and 2.0 mA cm -2 , stable cycling is maintained for 300 h and 180 h, respectively.
Full Cells: QSMBs pairing the SFC-Na anode with Na 3 V 2 (PO 4 ) 3 cathode demonstrate exceptional metrics: 74.1% capacity retention after 9000 cycles at 2C with an average Coulombic efficiency exceeding 99.95%, and a superior rate capability of 91.7 mAh g -1 at 5C. Under high mass loading conditions (5 mg cm -2 ), the cells maintain 92.3% capacity retention after 550 cycles at 2C. A 200 mAh-class pouch cell with high-loading NVP cathode (20 mg cm -2 ) shows favorable stability over 40 cycles, underscoring practical scalability.
Applications and Future Outlook
This work establishes a new design paradigm for artificial interphase layers in alkali metal batteries, shifting from conventional ionic-insulating strategies to mixed-conductor architectures that harness surface-mediated deposition. By fundamentally regulating Na plating/stripping behavior through ultra-sodiophilic, dual-conductive interphases, this research paves the way for next-generation quasi-solid-state batteries combining high safety, ultra-long cycle life, and high energy density.
Stay tuned for more groundbreaking research from this collaborative team at Harbin Institute of Technology, Zhejiang University, and National University of Singapore!
Nano-Micro Letters
News article
Ultra‑Sodiophilic Mixed Conductor Interphase Enabling Uniform Top Deposition for Quasi‑Solid‑State Sodium‑Metal Batteries
29-Jun-2026