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Sodium has a promising future in electrochemical energy storage: Archer Group paper published in Nature Communications shows why

Tuesday, October 17, 2017

Snehashis Choudhury

Designing solid-liquid interphases for sodium batteries

Current state-of-art lithium-ion batteries fall short in meeting the growing demand for long-lasting and lightweight electrical energy storage. Replacing the graphite anode in Li-ion batteries with earth abundant metallic sodium can result in significant improvements in multiple aspects including volume-specific capacity (battery size & weight) and cost. A persistent challenge with these batteries concerns their propensity to fail by short-circuits produced by dendritic metal deposition at the anode during battery recharge and by parasitic reactions between the anode and electrolyte. Numerous literature studies have considered the benefits of high-modulus, solid electrolytes as a means of prevention of dendrite growth by mechanically blocking the dendrites with a physical barrier. Importantly, these studies show that while the tendency for battery failure by dendrite-induced short-circuits can be reduced, other challenges ranging from increased cell weight, cracking of the barriers during battery operation or manufacturing, and interfacial chemical instability of the most promising solid electrolytes with the metal persist.

Recently, the Archer group has shown through theoretical and experimental approaches that more subtle control of interfacial ion and mass transport processes in the electrolyte provide more powerful pathways for achieving stable electrodeposition of reactive metals. The research reported by Choudhury et al. is takes these ideas several steps further to connect first-principles understanding of interfacial ion transport and stability using analytical tools of computational chemistry (in this case Joint-Density Functional Theoretical (J-DFT) analysis). Combining predictions from JDFT with electroanalytical studies and direct visualization of electrodeposition at interfaces, the study explains why some metals such as Magnesium are prone to form stable electrodeposits, while others including Sodium are as notoriously unstable. Specifically, the source of patchy/uneven nucleation is a high surface diffusion barrier for ion transport in the interphase, which prevents the free (un-throttled) movement of metal ions from a liquid electrolyte to a solid electrode during battery charging. It is further shown that a concrete benefit of such analysis is the ability to predict and design simple coatings chemistries for stabilizing recharge of unstable electrodes for sodium metal batteries. In particular, a Sodium Bromide based interphase was found to lower the activation energy of ion transport by three folds and significantly enhance the reversibility of sodium metal batteries.


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