Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility.

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode-electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH--reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries.

Development of Fluoride-Ion Primary Batteries: The Electrochemical Defluorination of CF x.

The lithium-carbon monofluoride (Li-CF x ) couple has the highest specific energy of any practical battery chemistry. However, the large polarization associated with the CF x electrode (>1.5 V loss) limits it from achieving its full discharge energy, motivating the search for new CF x reaction mechanisms with reduced overpotential. Here, using a liquid fluoride (F)-ion conducting electrolyte at room temperature, we demonstrate for the first time the electrochemical defluorination of CF x cathodes, where metal fluorides form at a metal anode instead of the CF x cathode. F-ion primary cells were developed by pairing CF x cathodes with either lead (Pb) or tin (Sn) metal anodes, which achieved specific capacities of over 700 mAh g-1 and over 400 mAh g-1, respectively. Solid-state 19F and 119Sn{19F} nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman, inductively coupled plasma (ICP), and X-ray fluorescence (XRF) measurements establish that upon discharge, the CF x cathode defluorinates while Pb forms PbF2 and Sn forms both SnF4 and SnF2. Technological development of F-ion metal-CF x cells based on this concept represents a promising avenue for realizing primary batteries with high specific energy.