Combining ferrocene and iodine results in enhanced thermoelectrochemical (or thermogalvanic) waste heat harvesting abilities, for both the Seebeck coefficient and the overall power output. All systems displayed a mixture of ferrocene, ferrocenium, iodine and triiodide. The observed enhancement correlates with lower electron-density on the ferrocene; the synergistic improvement observed for mixtures of substituted ferrocenes and iodine is attributed to the formation of charge-transfer complexes. Combining dibutanoylferrocene and iodine resulted in the highest Seebeck coefficient of 1.67 mV K(-1).

Water-in-salt and water-in-bisalt electrolytes have recently attracted much attention due to their expanded electrochemical stability windows. The concentration limit of such electrolytes is constrained by the solubility of the lithium salts employed, ca. 21 m (mol kg–1) for LiTFSI (lithium bis­(trifluoromethanesulfonyl)­imide). By adding a second lithium salt, the total salt concentration can be increased, but the hydrogen evolution keeps limiting the application of such systems in batteries with low potential anodes. Herein we report a water-in-bisalt electrolyte with a record salt concentration (31.4 m LiTFSI + 7.9 m Li­[N­(CH3)2((CH2)3SO3)­((CH2)4SO3)]) in which the bulky anion completely prevents the crystallization, even at such low water contents. Although the hydrogen evolution reaction is not completely suppressed, the expanded electrochemical stability window allows for low potential reactions such as aluminum–lithium alloying. The high salt concentration favors the formation of a suitable passivation layer that can be further engineered by modifying the anion structure.

Novel fluorine-free salts for aqueous lithium-ion and sodium-ion battery electrolytes.

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Synthesis and characterisation of super-cooled solvent-free liquid electrolytes for Li and Na batteries.