Morphological Evolution of Zn-Sponge Electrodes Monitored by In Situ X-ray Computed Microtomography

Abstract

Use of Zn sponges has been recently proposed as an effective means of limiting the shape change and dendrite formation issues, affecting the anodes of electrically rechargeable Zn-based batteries. This paper contributes to this field of research with in situ X-ray computed microtomography (XCMT) monitoring of the morphological and chemical changes undergone by Zn-sponge anodes during electrochemical cycling. Starting from a pristine anode, fabricated in the discharged state, this was first charged and then subjected to a representative series of charge–discharge sequences and, in correspondence, it was studied by XCMT in order to determine (i) the volume fractions of Zn and ZnO, porosity, and their space arrangement and (ii) the degree of connectivity of the elemental Zn framework. Good stability of the metal framework, reversibility of the Zn and ZnO phases, and their space distribution, with a limited alteration of the pore structure, were observed over more than 60 charge–discharge cycles.

In situ x-ray computed tomography of zinc–air primary cells during discharge: correlating discharge rate to anode morphology

“…Nonetheless, the presence of a pore phase could potentially be utilised in the future design of rechargeable zinc-air cells; for example, such pores could act like a scaffold, or as nucleation points, into which ZnO could form. Such scaffolds have been suggested in the form of sponges [23,31], and it is clear to see here that they could play a significant role in increasing the lifetime of rechargeable zinc-air batteries.…”

“…Some of the earlier studies include work by Arlt et al to investigate the state-of-charge (SoC) in primary commercial cells and model some of the mechanisms for shape change and particle shrinking [19], and work by Schröder et al to monitor the air electrode during discharge [20]. More recent work has included the study of shape change of zinc during discharge/charge cycles [21], deposition of zincate onto the cathode [22], and morphology changes in zinc sponges during cycling [23]. Degradation mechanisms like dendrite growth have also been studied using operando x-ray CT [13] and imaging data has been used to validate models for zinc particle shape change [24].…”

“…Degradation mechanisms like dendrite growth have also been studied using operando x-ray CT [13] and imaging data has been used to validate models for zinc particle shape change [24]. Limitations of some of the works mentioned here are that they were carried out at synchrotron x-ray sources [13,23]. While synchrotron sources are unmatched in terms of x-ray flux, which allows for higher temporal resolution, access to beamlines is limited and experiment durations are often short, with limited scope for replicate experiments.…”

3D Architectures for Batteries and Electrodes

“…Advanced operando analytical methods for battery characterization, for example, the X-ray computed microtomography studies previously noted, [27,28] can provide exquisite detail about battery electrode chemistry and structure, as well as the structure of buried interfaces during cell operation. These methods, including advanced in situ electron microscopy studies of battery electrodes, [38] have rapidly developed during the past decades.…”

“…[ 24 ] The core–shell structure of the alkaline discharge product ZnO at Zn sponge anodes [ 25,26 ] has been further substantiated by an operando X‐ray microcomputed tomography (XMCT) study, which confirms the uniformity of dendrite‐free charge–discharge in the aperiodic 3D morphology. [ 27 ] A recent operando X‐ray absorption near edge structure XMCT analysis of a composite solid‐state Li‐ion battery electrode demonstrated the opposite— inhomogeneity in 3D arising from slow ion transport in the composite structure. [ 28 ] An opportunity awaits operando characterization of the greater uniformity of reaction in 3D battery architectures.…”