Electrochemical Cycling Behaviour and Shape Changes of Zn Electrodes in Mildly Acidic Aqueous Electrolytes Containing Quaternary Ammonium Salts

Platform of advanced characterization techniques for batteries: We studied Quaternary Ammonium Salt additions to mildly-acidic aqueous battery electrolytes, to improve Zn anode performance. Electrochemical measurements, combined with multi-scale 2D/3D imaging, allowed to rank the additives with respect to interface control by molecule-specific cathodic and anodic inhibition. Synergizing mossy growth and passivation – the most critical factors affecting Zn cyclability – can both be effectively suppressed with TBAB.

Abstract

Secondary Zn–based batteries are a valid alternative to Li for stationary storage, but commercial devices are not yet available, chiefly owing to anode shape-change and passivation issues. Mildly acidic aqueous solutions are actively studied, since they seem to limit unstable growth of Zn, with respect to the alkaline ones, customary for primary batteries. Additives can further improve the performance of mildly acidic electrolytes. In this work we focus on the impact of a series of quaternary ammonium salts (TBAB, CTAB, DMDTDAB, BDMPAC, BPPEI, PDADMAC), selected to represent a comprehensive range of molecular functionalities. Electrochemical measurements (cyclic voltammetry, chronopotentiometry and galvanostatic-cycling in split-cells), combined with 2D and 3D imaging techniques (SEM, stereomicroscopy and in situ tomography) were adopted for the assessment Zn behaviour. This multi-technique approach pinpointed TBAB as the single most effective additive for low-current density operation, while at high current densities the additive-free electrolyte allows better cycling performance, coherently with similar results for alkaline electrolytes.

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