New design specifications for sodium-ion batteries

U.S. scientists used density functional theory to reveal how sodium ions are stored in nanoporous carbon anodes for sodium-ion batteries, identifying dual ionic and metallic storage mechanisms within the pores. Their findings provide practical design guidelines to improve battery voltage, safety, and commercial viability for stationary energy storage.

January 21, 2026 Emiliano Bellini

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From pv magazine Global

Researchers from Brown University in the United States have investigated the behavior of sodium storage in carbon materials used in sodium-ion batteries, with the aim of improving their commercial viability for stationary renewable energy storage applications.

“Our work provides guidelines for synthesizing anode materials that maximize overall battery performance,” said lead author Lincoln Mtemeri. “Our findings offer some of the first concrete design specifications for producing hard carbon anodes — or other carbon materials with similar porous structures — in the laboratory. This could help pave the way for the future commercial use of sodium-ion batteries.”

The researchers explained that hard carbon is widely regarded as a promising anode material for sodium-ion batteries because of its unique combination of structure, chemistry, and transport properties. Its disordered, porous, and conductive nature enables efficient ion storage, rapid charge transport, and long-term electrochemical stability. However, the team noted that the sodiation mechanism in hard carbon remains poorly understood, due to the complexity of its structure. This lack of understanding has also limited the development of theoretical models capable of accurately quantifying the material’s open-circuit voltage.

In the study “Structural descriptors controlling pore-filling mechanism in hard carbon electrode during sodiation,” published in ESS Batteries, the researchers examined zeolite-templated carbon (ZTC). ZTC is a nanoporous carbon material synthesized using zeolites as hard templates, enabling precise control over pore size and well-defined ion diffusion pathways.

The team employed density functional theory (DFT), a quantum-mechanical computational method used to calculate the electronic structure of atoms, molecules, and solids, to analyze sodium behavior within the nanopores. The simulations showed that when sodium atoms enter the pores, they initially bind to the pore walls through ionic interactions. Once the pore surfaces are fully occupied, additional sodium accumulates in the pore centers, forming metallic clusters.

The researchers found that two sodium storage mechanisms — ionic adsorption along the pore walls and metallic aggregation in the pore centers — play a critical role in battery performance. The coexistence of ionic and metallic sodium helps maintain a low anode potential, which increases the overall battery voltage, since the cell voltage is defined as the cathode potential minus the anode potential. At the same time, ionic sodium suppresses sodium metal plating, which could otherwise cause short circuits between adjacent pores.

“This helps us determine the optimal pore size,” Mtemeri said. “We show that a pore size of around one nanometer maintains the desired balance between ionicity and metallicity.”

Looking ahead, the researchers said the descriptors developed in the research work, including pore size, specific volume, and carbon topology, could serve as practical design guidelines for optimizing carbon-based electrodes in sodium-ion batteries.

“Sodium is 1,000 times more abundant than lithium, which makes it a more sustainable option,” co-author Yue Qi said. “Now we understand exactly which pore features are important and that enables us to design anode materials accordingly.”

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