Scientists at Sun Yat-sen University in China have developed a new tin–sodium anode that marks a major step forward for next-generation sodium batteries. The design solves two long-standing issues in sodium-metal systems: the formation of dangerous dendrites (branches of sodium that can pierce parts of the battery) and the gradual loss of sodium during cycling.
The anode has a two-layer structure. A graded tin–sodium alloy sits on top, guiding sodium ions smoothly during charging and preventing the uneven deposition that triggers dendrites. Beneath it, a pure sodium layer acts as a built-in reservoir, feeding sodium back into the alloy to keep it stable over long use. Microscopy confirms this gradient architecture, while a naturally formed sodium ethoxide film helps maintain a smooth, stable surface.
The performance gains are significant. In symmetric cells, the anode operates for more than 12,000 hours at moderate currents and 7,000 hours at higher currents, far outlasting pure sodium. Even under extreme fast-charging conditions, it runs for over 700 hours without forming dendrites. The anode also accelerates sodium-ion movement, cutting the ion-transport barrier by half.
Full cells using a sodium vanadium phosphate (NVP) cathode perform strongly under practical conditions. With standard cathode loadings, they retain over 75% capacity after 1,000 cycles. At industrially relevant loadings, they still deliver nearly 1,000 stable cycles and reach around 200 Wh/kg, one of the highest energy densities reported for sodium-metal coin cells.
This energy density is comparable to lithium iron phosphate (LFP) batteries, which typically provide 150–180 Wh/kg, though still below the 220–280 Wh/kg of high-energy lithium-ion chemistries like NMC. Even so, achieving long cycle life at high loading shows that sodium-metal systems are rapidly progressing. With further optimisation, this approach could offer a cost-effective and sustainable alternative for large-scale energy storage.
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