Single-Ion QSE for Fast Sodium Metal Batteries

Single-ion QSE for fast sodium metal batteries is moving sodium-based energy storage closer to practical, high-power use. Researchers from Southeast University, working with HiNa Battery Technology Co., Ltd. and Yangzhou University, developed a dual interlocked mediator strategy for quasi-solid-state electrolytes. As a result, the system combines fast Na+ transport, stable electrode interfaces, and long cycling performance in one design. The study shows how the Sn-FB quasi-solid-state electrolyte supports ultrafast charging, long life, and strong mechanical stability in sodium metal batteries.

Single-Ion QSE for Fast Sodium Metal Batteries: Why It Stands Out

Quasi-solid-state electrolytes can improve safety and flexibility in battery systems. However, this new electrolyte also delivers strong ion transport. The Sn-FB QSE reaches a near-unity Na+ transference number of 0.94. In addition, it achieves high ionic conductivity of 1.3 mS cm-1. Together, these values show that Na+ ions carry most of the current. Therefore, the electrolyte supports fast and efficient charge transport during battery operation.

The design avoids complex polymer modification routes. Instead, the team used a dual-mediator architecture that regulates both bulk transport and interfacial chemistry. This balanced approach helps the electrolyte deliver speed, durability, and stability at the same time.

Single-Ion QSE for Fast Sodium Metal Batteries: How the Electrolyte Works

The researchers built the electrolyte with two linked mediators: a cationic Sn2+-containing salt and the anion difluoro(oxalato)borate, or DFOB-. First, Sn2+ initiates in situ cationic polymerization of 1,3-dioxolane to form PDOL. Meanwhile, DFOB- slows the polymerization rate. As a result, the process creates a more uniform amorphous network.

This control improves material quality. For example, the polydispersity index falls to 1.6, compared with 4.5 in the Sn-only QSE. In addition, the puncture strength reaches 8.5 kPa. These numbers indicate a tougher and more consistent electrolyte framework.

Molecular dynamics simulations further explain the transport gains. DFOB- coordinates with Na+ and weakens Na+-O(PDOL) interactions. Consequently, the Na+ coordination number drops from 4.87 to 2.81. This change frees more sodium ions for transport. The diffusion coefficient rises to 16.8 Å2 ns-1, which is six times faster than conventional liquid electrolytes.

Interphase Design Improves Both Electrodes

The same dual-mediator system also improves battery interfaces during operation. At the sodium metal anode, Sn2+ reduces first because it has the lowest LUMO energy level at -4.87 eV. It then forms a hybrid NaSn alloy and inorganic-rich solid-electrolyte interphase. This layer smooths electric fields and supports more uniform sodium deposition. As a result, the nucleation overpotential drops to just 50 mV.

At the cathode, DFOB- oxidizes because of its high HOMO energy level of -8.12 eV. It forms a thin but robust cathode-electrolyte interphase only 14 nm thick. That thickness is less than half that of conventional systems. Moreover, the layer reaches an average Young’s modulus of 8.9 GPa, which is about ten times higher than the Sn-only QSE. Therefore, the cathode interface remains strong while still allowing rapid ion movement.

Single-Ion QSE for Fast Sodium Metal Batteries: Performance Results

The electrochemical results are impressive across several measures. In Na||Na symmetric cells, the Sn-FB QSE delivers 6000 hours of stable cycling without dendrite formation at 0.1 mA cm-2. It also keeps polarization near 0.1 V during long operation. In addition, the critical current density reaches 3.0 mA cm-2, while the exchange current density reaches 10 μA cm-2.

Full-cell testing also shows strong rate capability and long cycle life. When paired with Na3V2(PO4)3 cathodes, the cells retain 80.1 mAh g-1 at an ultrafast 15C rate. They also keep 90% of capacity after 2000 cycles at 3C. Even at 5C, the system still delivers 53.4 mAh g-1 after 800 cycles. Furthermore, the electrolyte provides an electrochemical stability window up to 4.7 V versus Na+/Na.

Single-Ion QSE for Fast Sodium Metal Batteries in Practical Formats

The team also tested the electrolyte in formats that matter for practical use. High-mass-loading full cells with 5 mg cm-2 NVP cathodes retain 75% capacity after 500 cycles at 1C. In pressure-free pouch cells sized 4 × 5 cm2, the system delivers 93.3 mAh g-1 and keeps 84% capacity retention after 19 cycles. The pouch cell also continues to operate under repeated full folding, which highlights its flexibility and mechanical resilience.

The electrolyte also works with high-loading NaNi1/3Fe1/3Mn1/3O2 cathodes at 17.54 mg cm-2. In that setup, the battery delivers 129.9 mAh g-1 initially and 108.9 mAh g-1 after 17 cycles. This result shows strong compatibility with more than one cathode chemistry.

Single-Ion QSE for Fast Sodium Metal Batteries: What It Means

This research presents a clear path for better sodium metal batteries. The dual interlocked mediator strategy unites fast ion conduction, robust mechanics, and adaptive bilateral interphases in one electrolyte. Moreover, the in situ polymerization route supports scalable processing. Because of that, the design could fit existing battery manufacturing methods.

Overall, the Sn-FB quasi-solid-state electrolyte delivers a compelling combination of tNa+ 0.94, conductivity of 1.3 mS cm-1, 6000-hour symmetric-cell stability, and 90% retention after 2000 cycles at 3C. These results make single-ion QSE design an important advance for fast-charging, long-life sodium metal batteries in 2026.

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