Scientists exploited NMR to study sodium structures and dynamics for next generation batteries
|Sodium-ion batteries represent a safer, more ecological and efficient alternative to conventional ones. However, to improve their performance stability and solid electrolyte interphase formation, it is important to choose the right anode material. In this context, hard carbons are promising candidates: therefore, it is important to characterise sodium storage in terms of both structures and dynamics in these materials.
To do so, CERIC PhD candidate Matej Gabrijelčič, supervisor Alen Vižintin and colleagues of the Slovenian NMR (Nuclear Magnetic Resonance) Centre exploited different, complementary techniques, including operando, in situ and ex situ solid-state spectroscopy techniques available at the CERIC Slovenian Partner Facility at the National Institute of Chemistry, in Ljubljana. Using 600MHz MAGIC and 400MHz NIKA NMR spectrometers. Scentistis found out that at higher temperatures, larger pores facilitate the formation of quasi-metallic sodium clusters, improving sodium storage capacity. Moreover, they discovered that solid electrolyte interphase originates from sodium fluoride (NaF) forming on the hard carbon surface, with sodium carbonate (Na₂CO₃) embedded within the layer. Researchers could then derive a possible explanation of Na+ ions behavior in hard carbon during sodiation: actually, ions are adsorbed on the hard carbon surface and inserted between graphene layers and then fill the pore walls. Here, if the pores are large enough (i.e. if carbonization temperature is high enough), quasi-metallic Na clusters are formed at the end. Underpotential sodiation leads to Na metal plating, with distinct NMR chemical shifts reflecting the different properties of plated Na and dendrites.
This in depth understanding of structures and dynamics can help to enhance the permomance of sodium-ion anodes, allowing to develop more efficient and long-lasting batteries.
With this highlight and the related paper we would like to remember Prof. Dr. Gregor Mali, distinguished researcher at CERIC’s Slovenian Partner Facility and one of the most renowned scientists worldwide in the field of NMR research on porous materials.
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