Functionalized Phosphonium Cations Enable Zn Metal Reversibility in Aqueous Electrolytes

a. Schematic illustration of different phosphonium cation chemistries in aqueous electrolytes; b. Interphase morphology on Zn anode; c. Voltage profile during Zn plating/stripping testing in a Cu│Zn (10 mm) cell with 20% Zn utilization per cycle and d. corresponding CE. b-d. for aqueous 4m Zn(TFSI)2 + 4m P444(2O1)-TFSI electrolyte.

Scientific Achievement

The presence of P444(2O1)+ cation in aqueous electrolyte enhances Zn reversibility dramatically by enabling a high Coulombic efficiency (CE, > 99%) at high utilization (20% Zn per cycle) for Zn plating/stripping, suppressing hydrogen evolution, and allowing a remarkable dendrite-free cycling even under aggressive conditions (2.5 mA/cm2, 2.5 mAh/cm2).

Significance and Impact

We correlate the enhanced Zn reversibility with interfacial structure and interphasial chemistries modification. This presents a promising new direction to address the irreversible issues of a Zn metal anode in mild acidic aqueous electrolytes with the addition of reactive supporting cations

Research Details

  • The effect of these supporting salts on bulk electrolyte structure was also investigated using small angle neutron scattering (SANS), infrared spectroscopy (FTIR), and Raman spectroscopy.
  • Combining sputtering XPS, TEM and DFT calculation, we revealed the different electrochemical behaviors and interphasial chemistries induced by the chemical functionalities on phosphonium cations P4441+ and P444(2O1)+

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 DOI: 10.1002/anie.202017020

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