Plating and stripping of zinc is a central component in a variety of aqueous batteries, metal-air chemistries, and flow/semiflow systems. While zinc is a divalent charge carrier and highly abundant, zinc-based chemistries need to operate well outside the water stability window to compete with the energy density of higher voltage lithium ion batteries. Recent theoretical and electrochemical studies have suggested that Zn(TFSI)2 in organic solvents provide high anodic stability, but with varying degrees of conductivity and reversibility during electrodeposition. To better understand the connections between electrochemical performance and structural changes during plating and stripping requires a multimodal approach to characterize zinc species in the electrolyte, the electric double layer, and bulk metal deposits. Using multiple synchrotron X-ray methods with spatial resolution ranging from atomic length scales to microns, we have studied the coordination of zinc in solution, its adsorption and reduction at a charged interface, and the kinetics of bulk deposition. X-ray absorption spectroscopy was used to study a wide range of nonaqueous zinc electrolytes with varying concentration. In agreement with molecular dynamics simulations, we find that Zn in acetonitrile begins to form ion pairs above ~0.1 M, which correlates with its improved anodic stability and ionic conductivity compared to other organic solvents. X-ray diffraction and fluorescence was used to compare the kinetics and reversibility of zinc electrodeposition with cyclic voltammetry. Intriguingly, electrochemical alloying with the underlying Pt current collector was found to influence zinc’s overpotential for deposition and ultimately influenced the morphology of the zinc deposits. Finally, the structure of Zn2+ and analogous multivalent ions was measure using a combination of surface diffraction and resonant scattering during initial sorption and subsequent desolvation.

Solvation and desolvation in nonaqueous zinc batteries

254th National Meeting (2017)

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