Energy storage is a major challenge for modern society, with batteries being the prevalent technology of choice. Within this area, sodium oxygen (Na–O2) batteries have the capability to make a step change, thanks to their high theoretical energy density. In order to facilitate their use, the development of electrolytes is critical to overcome certain limitations that arise because of the technology’s unique chemistry, particularly relating to the stability of superoxide species. In this study, we have demonstrated the importance of selecting a suitable electrolyte to facilitate both a highly homogeneous distribution of the discharge products and to minimize the formation of undesirable reaction products. The combination of pyrrolidinium-based ionic liquid and diglyme can dramatically change the cell performance. The effect of sodium salt concentration as well as the amount of diglyme and N-butyl-N-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide, [C4mpyr]­[TFSI], in Na–O2 batteries has also been comprehensively studied by combination of experimental and simulation techniques.

An operando dual-edge X-ray absorption spectroscopy on both transition-metal ordered and disordered LiNi0.5Mn1.5O4 during electrochemical delithiation and lithiation was carried out. The large data set was analyzed via a chemometric approach to gain reliable insights into the redox activity and the local structural changes of Ni and Mn throughout the electrochemical charge and discharge reaction. Our findings confirm that redox activity relies predominantly on the Ni2+/4+ redox couple involving a transient Ni3+ phase. Interestingly, a reversible minority contribution of Mn3+/4+ is also evinced in both LNMO materials. While the reaction steps and involved reactants of both ordered and disordered LNMO materials generally coincide, we highlight differences in terms of reaction dynamics as well as in local structural evolution induced by the TM ordering.

Triphylite-NaFePO4 attracts considerable attention as a cathode material for sodium-ion batteries due to its theoretical capacity (154 mAh/g), sharing also the excellent properties of the analogous triphylite-LiFePO4 used in commercial lithium-ion batteries. In this work, triphylite-NaFePO4 is synthesized from triphylite-LiFePO4 by a low-cost, eco-friendly method, enabling the recovery and subsequent reuse of lithium. NaFePO4 was evaluated as a cathode material in half-cells, exhibiting an initial discharge capacity of 132 mAh/g and good capacity retention (115 mAh/g and ∼100% of Coulombic efficiency after 50 cycles; 101 mAh/g and ∼100% of Coulombic efficiency after 200 cycles). This research confirms that the triphylite-NaFePO4 cathode material is an attractive candidate for sodium-ion batteries, with potential for future commercialization.

Carbon coated tin phosphide is synthesized by an easily scalable ball milling method. The origin of the different electrochemical performance of tin phosphide electrodes in ether- and carbonate-based electrolytes is discussed.