Sodium bis(fluorosulfonyl)imide based aqueous electrolytes exhibit a wide electrochemical stability window of up to 2.6 V when the water-to-salt molar ratio falls below 2:1, enabling the fabrication of high-voltage rechargeable aqueous sodium-ion batteries.

To guide the choice of future synthetic targets for single‐molecule electronics, qualitative design rules are needed, which describe the effect of modifying chemical structure. Here the effect of heteroatom substitution on destructive quantum interference (QI) in single‐molecule junctions is, for the first time experimentally addressed by investigating the conductance change when a “parent” meta‐phenylene ethylene‐type oligomer (m‐OPE) is modified to yield a “daughter” by inserting one nitrogen atom into the m‐OPE core. We find that if the substituted nitrogen is in a meta position relative to both acetylene linkers, the daughter conductance remains as low as the parent. However, if the substituted nitrogen is in an ortho position relative to one acetylene linker and a para position relative to the other, destructive QI is alleviated and the daughter conductance is high. This behavior contrasts with that of a para‐connected parent, whose conductance is unaffected by heteroatom substitution. These experimental findings are rationalized by transport calculations and also agree with recent “magic ratio rules”, which capture the role of connectivity in determining the electrical conductance of such parents and daughters.

The discovery of enhanced electrochemical stability for aqueous electrolytes with very high salt concentration has stimulated the development of high-voltage aqueous batteries. We show that a key factor limiting the applicability of these batteries is the tendency of highly concentrated electrolytes to crystallize near room temperature, leading to cell failure. Here we report the use of asymmetric anions as solution to suppress the crystallization of highly concentrated aqueous electrolytes. We demonstrate this approach with a ternary sodium-ion electrolyte that we employ in a 2 V class aqueous sodium-ion battery based on a NaTi2(PO4)3 anode and a Na3(VOPO4)2F cathode. This cell displays excellent cycling stability at 30 °C with capacity retention of 85% after 100 cycles at C/5 and 77% after 500 cycles at 1C. The cell reaches a specific energy of 64 Wh kg–1 on the basis of the active masses of both electrodes, twice as high as previously reported for this electrode couple. Further, the cell can be operated down to temperatures of at least −10 °C, with capacity retention of 74% after 500 cycles at C/5.