Zinc Anodes Modified by One‐Molecular‐Thick Self‐Assembled Monolayers for Simultaneous Suppression of Side‐Reactions and Dendrite‐Formation in Aqueous Zinc‐Ion Batteries

Abstract

Repeated charge/discharge in aqueous zinc‐ion batteries (ZIBs) commonly results in surface corrosion/passivation and dendrite formation on zinc anodes, which is a major challenge for the commercialization of zinc‐based batteries. In this work, metallic Zn modified by self‐assembled monolayers is described as a viable anode for ZIBs. ω‐mercaptoundecanoic acid that is spontaneously adsorbed on Zn (MUDA/Zn) contributes to the simultaneous suppression of side reactions and dendrite formation in ZIBs. Though one‐molecular‐thick, densely packed alkyl chains prohibit H2O and H+ from making direct contact with the underlying Zn, and surface carboxylate moieties (–COO‐) effectively repel anionic species (OH‐) in a solution, which renders a Zn anode inert against zincate formation within a wide range of pH. In contrast, the electrostatic attraction between surface‐carboxylates and cations increases the concentration of Zn2+ on the surface of MUDA/Zn to facilitate Zn plating/stripping with less overpotentials. The high concentration of Zn2+ also results in an increased number of nucleation sites, which enhances the lateral growth of Zn with no formation of dendrites. As a result, MUDA/Zn shows excellent stability during prolonged Zn plating/stripping within a wide range of pH. The advantageous properties of MUDA/Zn are also retained in full‐cells coupled with δ‐MnO2 cathodes.

Challenges and Strategies in the Development of Zinc‐Ion Batteries

“…where the electrons obtained from the oxidation of Zn in (1) are used to reduce hydrogen ions in (4) shown in Figure 6d. [75,137] On the contrary, Mwemezi et al and others proffered that the HER involves water reduction proceeding in the following fashion at the electrodes [102,135,141,149,156] 2H…”

“…[137][138][139][140] While it may be expected that Zn 2+ /Zn redox processes would be the only electrochemical processes occurring, the small electrochemical stability window of the aqueous electrolyte (1.23 V) and the low standard electrode potential of Zn 2+ /Zn (−0.76 V) causes interfacial side reactions based on the Pourbaix diagram (Figure 6a). [6,137,[141][142][143][144][145][146][147][148][149] This can result in the excessive consumption of the electrode and electrolyte, [137,150,151] affecting the Zn 2+ /Zn redox processes important to energy storage.…”

“…[143,156] Furthermore, the evolution of hydrogen would hinder the uniform Zn deposition, worsening dendrite formation. [112] The increase in the local regional pH would favor byproduct formation reactions [141,148,149,152] Zn…”

“…forming a passivation layer of ZnO on the anode when the solubility limit of Zn(OH) 4 2− has been reached through the following [141,[153][154][155]158] Zn (OH…”

Recent advances of organic polymers for zinc-ion batteries

“…They are facing safety concerns that hinder their development in the eld of largescale electrochemical energy storage. [10][11][12] Compared to organic electrolyte batteries, rechargeable aqueous batteries are good alternatives, especially for large-scale energy storage systems. 13 Owing to their inherent low cost, high safety, and environmentally-friendly features, ZIBs are considered to be one of the most promising candidates for next-generation energy storage.…”