Sodium batteries without anodes hold 80% capacity for 1,400 cycles thanks to a solvent trick

Anode-free sodium batteries promise low-cost, high-energy-density storage, but they have been held back by a stubborn problem: every charge–discharge cycle irreversibly consumes some of the sodium, so the cell fades and dies. Now a team led by Weijiang Xue reports in Nature Energy that a molecular-level redesign of the electrolyte, built around the cyclic ether 1,3-dioxane, dramatically slows that sodium loss. In 300-milliampere-hour pouch cells with a commercially relevant cathode loading of about 20 milligrams per square centimetre, the anode-free cells retained roughly 80% of their capacity after 1,400 cycles at a 1 C rate.

The strategy attacks sodium loss from two directions at once. First, 1,3-dioxane coordinates only weakly with sodium ions, which makes it easier for those ions to shed their solvent shell and deposit as reversible sodium metal. Second, the solvent undergoes controlled oligomerization — a partial linking of molecules into short chains — that builds a thin, robust solid–electrolyte interphase on the sodium surface. That protective film suppresses continuous decomposition of the electrolyte and stabilizes the repeated plating and stripping of sodium, the two processes that normally bleed capacity away cycle after cycle.

Anode-free designs are attractive because the cell is assembled without a sodium metal anode; sodium is supplied entirely by the cathode and plates onto a bare current collector during the first charge. Removing the anode slashes cost and weight, but it also leaves the cell with no sodium reserve, so any sodium that is permanently trapped in side reactions or in a fragile, resistive interface is lost forever. The durability of the sodium plating and stripping process therefore sets the lifetime of the whole battery.

The performance figures reported for the pouch cells extend well beyond long cycle life. The cells operated at rates up to 3 C, meaning they could charge or discharge in as little as 20 minutes. They maintained 88% of their capacity at −40 °C, a temperature at which most electrolytes become sluggish and sodium deposition turns uneven. The cells also achieved a round-trip energy efficiency of up to about 98%, indicating that very little energy is wasted in parasitic reactions during cycling.

The study characterizes the interphasial chemistry behind these results. Analyses of the solid–electrolyte interphase formed in the dioxane-based electrolyte show the thin, robust film that the controlled oligomerization produces, and liquid chromatography coupled with high-resolution mass spectrometry of extracts from cycled pouch cells identifies the oligomerized components that make up the protective layer. The coordination interaction between sodium ions and the solvent molecules was examined directly, supporting the link between weak solvation and reversible sodium deposition.

Temperature behaviour was tested explicitly. Sodium plating and stripping were evaluated both at 25 °C and at low temperatures with different electrolytes, and the anode-free pouch cells — built with a carbon-coated aluminium current collector paired with a sodium-containing layered oxide cathode — were cycled at low temperature as well. The 88% capacity retention at −40 °C stands out because low-temperature operation is a known weak point for sodium and lithium metal chemistries alike, where slow ion transport typically degrades deposition uniformity.

The cathode used in the pouch cells, referred to in the study as NFPP, is paired with a carbon-coated aluminium anode current collector, the configuration that defines the anode-free architecture. With a cathode loading of about 20 milligrams per square centimetre, the cells approach the areal loadings needed for practical cells rather than small coin-cell demonstrations, and the 300-milliampere-hour pouch format moves the result closer to the scale at which real batteries are judged.

The work is presented as a demonstration of a molecular electrolyte design strategy for extending anode-free battery lifetime rather than as a commercialization announcement. The reported results come from laboratory pouch cells under the stated test conditions, and the electrolyte’s performance in larger formats, over longer durations, or under fast-charge protocols beyond those tested remains to be established. Even so, the combination of 1,400-cycle retention, 3 C rate capability, −40 °C operation and near-98% energy efficiency in a single anode-free sodium system is, by the authors’ account, a substantial advance for a chemistry whose economics depend on squeezing out every irreversibly lost sodium ion.

Subject of Research: Electrolyte design for long-lived anode-free sodium batteries

Article Title: Stable anode-free sodium batteries enabled by controlled oligomerization

Article References: Ding, S., Chen, X., Yao, Z., Hao, M., Tian, C., Wang, X., Zhang, N., Zhang, H., Han, X., Li, R., Xu, L., Chen, Z., Wang, J., Hu, Y.-S., & Xue, W. (2026). Stable anode-free sodium batteries enabled by controlled oligomerization. Nature Energy. https://doi.org/10.1038/s41560-026-02154-y

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02154-y

Keywords: anode-free batteries, sodium batteries, electrolyte design, 1,3-dioxane, solid–electrolyte interphase, oligomerization, sodium plating and stripping, low-temperature operation, pouch cells, energy storage, Stable, anode-free