Sodium battery life improves significantly with a COF-polymer electrolyte designed for fast charging and long cycling. In a 2026 Nature Communications study, researchers engineered a sulfonate-functionalized covalent organic framework, or COF, inside a fluorinated polymer electrolyte. As a result, the material delivered faster sodium-ion transport, stronger interfaces, and stable performance in solid-state sodium batteries.
The team focused on a COF called TpPa-SO3Na. They built it from TpPa-SO3H through sodium-ion exchange with sodium acetate. This structure formed ordered hexagonal pores and dense −SO3-Na+ groups. These features created directional pathways for sodium ions. In turn, the polymer matrix reinforced the structure and improved ion dissociation.
How the COF-polymer electrolyte improves sodium battery life
The composite combined TpPa-SO3Na with a fluorinated PNSE polymer matrix. Because the polymer contains polar C–F and C–Cl groups, it supports ion transport and strengthens the electrolyte film. Moreover, the interpenetrating network linked mechanical durability with efficient ionic pathways.
The researchers confirmed the material structure with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and elemental mapping. These tests showed high crystallinity, uniform chemistry, and well-defined ionic channels. Next, molecular dynamics simulations revealed how sodium ions moved through the material. The ions gathered near the −SO3 groups inside the COF pores. Therefore, the electrolyte created continuous and directional transport paths instead of random ion movement.
COF-polymer electrolyte delivers strong conductivity and stability
The electrochemical results were impressive. The COF-polymer electrolyte reached an ionic conductivity of 1.2 mS cm-¹ at 30 °C. That value greatly exceeded the conductivity of the polymer alone. In addition, the composite improved the mechanical strength of the electrolyte. This combination supported both fast charging and long-term cycling.
The material also formed stable interphases at both electrodes. At the sodium metal anode, it created a gradient solid electrolyte interphase rich in NaF and Na2O. This layer guided uniform sodium deposition and limited dendrite growth. At the cathode, it formed a fluorine-rich cathode electrolyte interphase with NaF and Na2O nanocrystals. Consequently, the cathode interface resisted degradation and maintained performance at higher voltage.
COF-polymer electrolyte performance in sodium cells
Symmetric sodium cells using the composite electrolyte ran stably for 6,750 hours at 0.1 mA cm-² and 0.2 mAh cm-². They also showed low polarization of about 85 mV. Furthermore, the electrolyte achieved a critical current density of 1.9 mA cm-², which indicates robust rate capability.
In Na||NNM coin cells, the system delivered 82.5 mAh g-¹ at 1 A g-¹. It retained 77.2% of capacity after 1,000 cycles. Then it retained 83.5% after 2,000 cycles in another test condition. The cells also cycled up to 4.2 V and kept 92.7% capacity after 180 cycles. These figures show that the electrolyte supports both high-rate operation and long service life.
Operando impedance testing and distribution-of-relaxation-times analysis further supported the results. Both methods showed lower interfacial resistance and faster ion transport during cycling. Thus, the electrolyte improved battery kinetics in real operating conditions.
COF-polymer electrolyte shows scale-up potential
The researchers also tested the design in a larger 1 Ah hard-carbon||O3-NFM pouch cell. This step matters because scale-up often determines real-world value. Encouragingly, the pouch cell retained 87.3% of its capacity after 488 cycles. Therefore, the electrolyte design appears suitable for larger sodium solid-state batteries, not just small laboratory cells.
This study shows a clear materials strategy for stronger sodium battery performance. First, the COF offers ordered nanopores and fixed sulfonate groups. Next, the fluorinated polymer adds dielectric strength, flexibility, and interface support. Together, these features improve sodium-ion migration and protect both electrodes during repeated fast charging.
Why this COF-polymer electrolyte matters in 2026
Solid-state sodium batteries continue to attract attention in 2026 because they pair abundant raw materials with safer battery designs. In that context, this COF-polymer electrolyte stands out for its balanced performance. It improves conductivity, supports stable interfaces, and maintains capacity over hundreds to thousands of cycles. Just as importantly, it works in both coin cells and a 1 Ah pouch cell.
Overall, the findings suggest that sulfonate-functionalized COFs can play a central role in next-generation sodium battery electrolytes. By guiding ion transport and stabilizing interfaces, this composite electrolyte extends sodium battery life under fast charging while preserving strong electrochemical performance.
Source: Mu, Y., Li, C., et al. (2026). Engineering ion migration and interface chemistry via covalent organic framework-enhanced polymer electrolytes for fast-charging sodium solid-state batteries. Nature Communications. DOI: 10.1038/s41467-026-75417-7.
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