The choice of the electrode binder strongly affects the environmental friendliness of electrochemical energy storage devices as reviewed herein.

The Raman shifts of the TFSI − expansion-contraction mode in N-butyl-Nmethylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL) electrolytes were analyzed to compare the ionic coordination of magnesium with lithium and sodium. In the Mg 2+ -IL electrolytes, the TFSI − anions are found in three different potential energy environments, while only two populations of TFSI − are evident in the Na + -and Li + -IL electrolytes. For Mg 2+ , the high frequency peak component is associated with a TFSI − that is in a bidentate coordination with a single metal cation and can therefore be considered a contact ion pair (CIP) solvate. The mid frequency component is attributed primarily to bridging aggregate (AGG) TFSI − solvate or a weakly bound monodentate CIP TFSI − . The low frequency peak is well-known to be associated with "free" TFSI − anions. The average number of TFSI − per Mg 2+ cation (n) is 3 to 4. In comparison, the value of n is 4 at very low concentrations and decreases with increasing salt mole fraction to 2 for Li + and Na + , where n of Na + is larger than that of Li + at any given concentration. The results imply the existence of anionic magnesium solvates of varying sizes. The identity of the Mg 2+ charge-carrying species is complex due to the presence of bridging AGG solvates in solution. It is likely that there is a combination of single Mg 2+ solvate species and larger complexes containing two or more cations. In comparison, the primary Li + and Na + charge-carrying species are likely [Li(TFSI) 2 ] − and [Na(TFSI) 3 ] 2− in the concentration range successfully implemented in IL-based electrolyte batteries. These solvates result in Mg 2+ cations that are mobile in the IL-based electrolytes as demonstrated by the reversible magnesiation/ demagnesiation in V 2 O 5 aerogel electrodes.

The rapid growth of the worldwide demand of lithium for batteries (LIBs) can possibly lead to a shortage of its reserves. Sodium batteries represent a promising alternative because they enable much higher energy densities than other battery systems, with the exception of LIBs, and are not limited by sodium availability. Herein, we present a novel, Na + ion intercalation material, Na 0.45 Ni 0.22 Co 0.11 Mn 0.66 O 2 (space group P6 3 /mmc) synthesized in air by a coprecipitation method followed by a thermal treatment and a water-rinsing step. This material performs a specific capacity of 135 mA h g −1 with a Coulombic efficiency exceeding 99.7%. Upon long-term cycling tests the material shows excellent capacity retention after more than 250 cycles. Such an overall performance, superior to that of presently known sodium-ion cathodes, represents a step further toward the realization of sustainable batteries for efficient stationary energy storage.