Examining Concentration-Reliant Zn Deposition/Stripping Behavior in Organic Alcohol/Sulfones-Modified Aqueous Electrolytes

Revealing the Limitation Induced by Hydroxyl in Regulating Solvation Structure of Zn2+ and Overcoming Challenges with Hybrid Additives towards Highly Stable Zinc Anodes

In the field of electrolyte design for aqueous zinc-ion batteries (AZIBs), additives containing hydroxyl have been demonstrated to effectively modulate the solvation structure of Zn2+. However, reported studies typically focus solely on the effectiveness of hydroxyl while neglecting the issues that emerge during solvation structure regulation. The strong electron-attracting capability of Zn2+ attracts electrons from the oxygen in hydroxyl, thereby weakening the strength of hydroxyl, the hydrogen evolution reaction (HER) is also pronounced. This work innovatively reveals the limitation of hydroxyl-containing additives and proposes a synergistic regulation strategy based on hybrid additives. Arginine with a high isoelectric point is introduced into the electrolyte system containing hydroxyl additives. The protonation effect and electrostatic attraction of arginine enable it to absorb protons at the anode released by the weakened hydroxyl, thereby compensating for the limitation of hydroxyl additives. Under the synergistic action of hybrid additives, the Zn|Zn battery achieved stable deposition/stripping for over 1200 hours under 10 mA cm-2 and 10 mAh cm-2. Moreover, the Zn|Cu battery cycled for over 570 hours with a high Coulombic efficiency of 99.82 %. This study presents a pioneering perspective for the further application of AZIBs.

Correlating Buffering Agents' Premier pH with Interface Stability Toward Long-Term Zn Metal Anodes

Aqueous solvents in Zn metal batteries inevitably induces hydrogen evolution reactions (HER) due to fluctuating pH levels in electrolytes, leading to severe side reactions and dendrite growth. To address these challenges, buffering agents have been recently proposed as a solution to maintain constant electrolyte pH values upon cycling. Nonetheless, the critical role of buffering additives' premier pH in determining interface stability is largely overlooked. Herein, two types of buffering agents, single amphoteric and conjugate acid-base pairs, are employed to correlate their initial pHs with the interface stability. Based on the observations, the lifetime of Zn metal anodes initially increases and then decreases as the initial pH level goes up from 2.0 to 5.0, with an optimal lifetime at pH 3.3 for both buffering agent categories. This phenomenon lies in ample H+ in low pH and rich OH- in high pH, leading to either severe HER or by-products passivation layer. The optimized pH allows cells to deliver a high average Coulombic efficiency of 99.61% over 1500 cycles at a large current density of 5 mA cm-2, which is significantly superior to 345 cycles achieved in the pristine electrolyte. Furthermore, this enhanced interface enables stable Zn/activated carbon full batteries over 15 000 cycles.

Overcoming challenges of protonation effects induced by high isoelectric point amino acids through a synergistic strategy towards highly stable and reversible zinc electrode-electrolyte interface

Amino acids are among the most commercially promising additive solutions for achieving stable zinc anodes. However, greater attention should be given to the limitation arising from the protonation effects induced by high isoelectric point amino acids in the weakly acidic electrolytes of aqueous zinc-ion batteries (AZIBs). In this study, we introduce histidine (HIS) and ethylenediaminetetraacetic acid (EDTA) as hybrid additives into the aqueous electrolyte. Protonated HIS is adsorbed onto the anode interface, inducing uniform deposition and excluding H2O from the inner Helmholtz plane (IHP). Furthermore, the addition of EDTA compensates for the limitation of protonated HIS in excluding solvated H2O. EDTA reconstructs the solvation structure of Zn2+, resulting in a denser zinc deposition morphology. The results demonstrate that the Zn||Zn battery achieved a cycling lifespan exceeding 1480 h at 5 mA cm-2 and 5 mAh cm-2. It also reached over 900 h of cycling at a zinc utilization rate of 70 %. This study provides an innovative perspective for advancing the further development of AZIBs.

Highly Potent and Low-Volume Concentration Additives for Durable Aqueous Zinc Batteries: Machine Learning-Enabled Performance Rationalization

The essential virtues of aqueous zinc battery chemistry stem from the energy-dense zinc metal anode and mild aqueous electrolytes. Yet, their incompatibility - as exposed by zinc's corrosion and associated dendrite problem - poses a challenge to achieving improved cycle life under practically relevant parameters. While electrolyte additives are a scalable strategy, additives that can function at low volume concentrations remain elusive. Here, through screening alkanol and alkanediol chemistries, 1,2-butanediol and pentanediol are unveiled as highly potent additives, which operate at a practical 1 volume% concentration owing to their ability to furnish dynamic solid-electrolyte interphase through pronounced interfacial filming. This unique mechanistic action renders effective corrosion and dendrite mitigation, resulting in up to five to twenty-fold zinc cyclability enhancement with a high Coulombic efficiency (up to 99.9%) and improved full-cell performance under demanding conditions, including at elevated temperatures. A machine learning-based analysis is presented to rationalize the additive performance relative to critical physicochemical descriptors, which can pave the way for a rational approach to efficient additive discoveries.

Weak-Water-Coordination Electrolyte to Stabilize Zinc Anode Interface for Aqueous Zinc Ion Batteries

The performance of zinc-ion batteries is severely hindered by the uncontrolled growth of dendrites and the severe side reactions on the zinc anode interface. To address these challenges, a weak-water-coordination electrolyte is realized in a peptone-ZnSO4 -based electrolyte to simultaneously regulate the solvation structure and the interfacial environment. The peptone molecules have stronger interaction with Zn2+ ions than with water molecules, making them more prone to coordinate with Zn2+ ions and then reducing the active water in the solvated sheath. Meantime, the peptone molecules selectively adsorb on the Zn metal surface, and then are reduced to form a stable solid-electrolyte interface layer that can facilitate uniform and dense Zn deposition to inhabit the dendritic growth. Consequently, the Zn||Zn symmetric cell can exhibit exceptional cycling performance over 3200 h at 1.0 mA cm-2 /1.0 mAh cm-2 in the peptone-ZnSO4 -based electrolyte. Moreover, when coupled with a Na2 V6 O16 ·3H2 O cathode, the cell exhibits a long lifespan of 3000 cycles and maintains a high capacity retention rate of 84.3% at 5.0 A g-1 . This study presents an effective approach for enabling simultaneous regulation of the solvation structure and interfacial environment to design a highly reversible Zn anode.