Morpho-electrochemical behavior of particulate Zn electrodes revealed by X-ray and neutron tomography.

Aqueous rechargeable Zn-based batteries are gaining attention for their sustainability, safety, and cost-effectiveness; however, no industrially viable solutions are yet available, due to the synergistic issues of passivation and shape change. In particular, flow batteries with particulate Zn anodes are attractive for long-term stationary storage, at the cost of additional morpho-chemical processes involving the Zn particle bed and the interparticle space (IPS). Thus, the understanding of this system requires space-dependent information about the arrangement, dimensions, and chemical states of Zn and its discharge products. To this aim, we employ dual-probe chemically sensitive X-ray and thermal neutron tomography and radiography. Specifically, we analyzed an in situ anode in both pristine and discharged states, and we followed its self-discharge process in operando. In situ X-ray tomography reveals the advancement of Zn particle consumption and IPS development. In situ neutron tomography shows the formation and distribution of hydroxides. In operando, neutron radiography gives access to hydrogen bubble formation and dynamics. This first-of-its-kind analysis provides crucial insights, directly informing anode design strategies. Our findings contribute to paving the way for next-generation Zn flow batteries with improved efficiency and longevity.