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Organic additives with high-reduction potentials are generally applied in aqueous electrolytes to stabilize the Zn anode, while compromise safety and environmental compatibility. Highly concentrated water-in-salt electrolytes have been proposed to realize the high reversibility of Zn plating/stripping; however, their high cost and viscosity hinder their practical applications. Therefore, exploring low-concentration Zn salts, that can be used directly to stabilize Zn anodes, is of primary importance. Herein, we developed an asymmetric anion group, bi (difluoromethanesulfonyl) (trifluoromethanesulfonyl) imide (DFTFSI-) -based novel zinc salt, Zn (DFTFSI) 2, to obtain a high ionic conductivity and a highly stable dendrite-free Zn anode. Experimental tests and theoretical calculations verified that DFTFSI- in the Zn2+ solvation sheath and inner Helmholtz plane would be preferentially reduced to construct layer-structured SEI films, inhibiting hydrogen evolution and side reactions. Consequently, the Zn | | || Zn symmetric cell with 1M Zn (DFTFSI) 2 aqueous electrolyte delivers an ultralong cycle life for >2500 h outperforming many other conventional Zn salt electrolytes. The Zn | | || Br2 battery also exhibits a long lifespan over 1200 cycles at ~99. 8 % Coulombic efficiency with a high capacity retention of 92. 5 %. Furthermore, this outstanding performance translates well to a high-areal-capacity Zn | | || Br2 battery (~5. 6 mAh ⋅ cm-2), cycling over 320 cycles with 95. 3 % initial capacity retained.
Chen et al. (Mon,) studied this question.