Surface Overpotential as a Key Metric for the Discharge-Charge Reversibility of Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are receiving increasingattentionfor power-grid energy storage systems. Nevertheless, warranting long-termreversible operation is not trivial owing to uncontrolled interfacialphenomena related to zinc dendritic growth and parasitic reactions.Herein, the addition of hexamethylphosphoramide (HMPA) to the electrolyterevealed the surface overpotential (|& eta;(s)|) to be akey metric of the reversibility. HMPA adsorbs onto active sites onthe zinc metal surface, raising the surface overpotential toward loweringthe nucleation energy barrier and decreasing the critical size (r (crit)) of nuclei. We also correlated the observedinterface-to-bulk properties by the Wagner (Wa) dimensionless number.The controlled interface enables a Zn|V6O13 fullcell to retain 75.97% capacity for 2000 cycles, with a capacity lossof only 1.5% after 72 h resting. Our study not only delivers AZIBswith unparalleled cycling and storage performance but also proposessurface overpotential as a key descriptor regarding the sustainabilityof AZIB cycling and storage.N

Corrosion as the origin of limited lifetime of vanadium oxide-based aqueous zinc ion batteries

Aqueous zinc ion batteries are receiving increasing attention for large-scale energy storage systems owing to their attractive features with respect to safety, cost, and scalability. Although vanadium oxides with various compositions have been demonstrated to store zinc ions reversibly, their limited cyclability especially at low current densities and their poor calendar life impede their widespread practical adoption. Herein, we reveal that the electrochemically inactive zinc pyrovanadate (ZVO) phase formed on the cathode surface is the main cause of the limited sustainability. Moreover, the formation of ZVO is closely related to the corrosion of the zinc metal counter electrode by perturbing the pH of the electrolyte. Thus, the dissolution of VO2(OH)(2)(-), the source of the vanadium in the ZVO, is no longer prevented. The proposed amalgamated Zn anode improves the cyclability drastically by blocking the corrosion at the anode, verifying the importance of pH control and the interplay between both electrodes. Aqueous zinc ion batteries are good systems for large-scale energy storage. Here, the authors report that the corrosion of zinc metal anode is the origin of limited lifetime of vanadium oxide-based aqueous zinc ion batteries, and supressing corrosion improves the calendar and cycle lifetime markedly.N

Highly Reversible, Grain-Directed Zinc Deposition in Aqueous Zinc Ion Batteries

Achieving highly reversible Zn metal anodes is a crucial step in advancing the performance of aqueous zinc ion batteries. However, despite the relative stability of Zn metal in aqueous environments, Zn metal is plagued by deterrents such as dendritic growth, H-2 evolution, and corrosion. This mainly stems from the absence of a stable solid-electrolyte interphase (SEI), an inevitable consequence of moderate concentration aqueous electrolytes. In response to such issues, herein, an artificial SEI formed from cross-linked gelatin is introduced by coating the surface of Zn metal. The presence of the gelatin layer significantly changes the deposition morphology of Zn, where its plated surface is much more uniform and dense compared to bare Zn metal. Interestingly, grain-directed electrodeposition can be observed in which the crystallographic orientation of the underlying Zn metal substrate determines the directionality of electrochemically plated Zn. This mode of growth results in a highly uniform and dense surface, translating to enhanced electrochemical stability.

Cationic Additive with a Rigid Solvation Shell for High-Performance Zinc Ion Batteries

Despite substantial progresses, in aqueous zinc ion batteries (AZIBs), developing zinc metal anodes with long-term reliable cycling capabilities is nontrivial because of dendritic growth and related parasitic reactions on the zinc surface. Here, we exploit the tip-blocking effect of a scandium (Sc3+) additive in the electrolyte to induce uniform zinc deposition. Additional to the tri-valency of Sc3+, the rigidity of its hydration shell effectively prevents zinc ions from concentrating at the surface tips, enabling highly stable cycling under challenging conditions. The shell rigidity, quantified by the rate constant of the exchange reaction (k(ex)), is established as a key descriptor for evaluating the tip-blocking effect of redox-inactive cations, explaining inconsistent results when only the valence state is considered. Moreover, the tip-blocking effect of Sc3+ is maintained in blends with organic solvents, allowing the zinc anode to cycle reliably even at -40 degrees C without corrosion.N