Controlling the shape change and dendritic growth in Zn negative electrodes for application in Zn/Ni batteries

Abstract

Abstract Porous zinc electrodes are elaborated, assembled in Zn/Ni 3–4 Ah prismatic batteries and monitored upon charge/discharge cycling (150 cycles at C/3 rate followed by 150 cycles at 1C rate). Migration of zinc within the thickness of the zinc electrodes is revealed by X-Ray radiography, scanning electron microscopy, and X-EDS elemental cartography. Electrodes using either zinc oxide plus calcium hydroxide or directly calcium zincate as active material show similar behavior: neither dendrite formation nor morphological shape changes are observed after 300 charge/discharge cycles. Upon cycling, zinc accumulates at the core of the porous electrode, in the vicinity of the primary current collector and not at the surface, therefore avoiding any risk of dendrite formation. This suggest that the electrode operation is controlled by a core-shell mechanism, with a core of active zinc in the vicinity of the primary current collector, trapped in an electrode shell which is created by the outer portion of the electrode (active material, conductive additives, binder …). However, changing from C/3 to 1C rate after 150 cycles significantly improves the capacity of batteries using calcium zincate; this is correlated to its initial atomic homogeneity associated with higher porosity and an optimal electronic percolation.