Stabling Zinc Metal Anode with Polydopamine Regulation through Dual Effects of Fast Desolvation and Ion Confinement

Abstract

and suitable redox potential (−0.76 V vs standard hydrogen electrode). [2] However, corrosion, passivation, and dendrites on the Zn anode, as well as parasitic side reactions severely hinder the application of AZIBs in energy-storage systems. [3] In addition, the limited specific area of commercial Zn foil results in inadequate contact between electrolyte and anode, thus preventing Zn ion transport at the electrolyte-anode interface. The inherent rough surface results in the continuous deposition of Zn 2+ on the tips with an enhanced electric field, which gradually evolves into the formation of Zn dendrites. [4] Interface modification, structural design, and Zn alloying are typical strategies for improving the performance of Zn anodes. [5] However, the 3D structure and eutectic alloy design of Zn anodes weaken the inherent strengths of AZIBs, that is, their low cost and environmental benignity. [6] Similar to the optimization strategy for lithium metal, the protective layer coated on the surface of zinc acts as a continuous solid-electrolyte interface (SEI) between the metal zinc anode and electrolyte. [7] Hence, interface modification is an effective method for improving the stability of zinc electrode interface and for alleviating the disordered deposition of Zn 2+ and dendrite growth. [8] However, many coating strategies Metal zinc is recognized as a promising anode candidate for aqueous zinc-ion batteries (AZIBs), however, dendrites and byproducts formation severe deteriorate its reversibility and practical lifespan. Herein, a polydopamine (PDA) layer, which offers the dual effects of fast desolvation and ion confinement, is constructed on the surface of a Zn anode for efficient AZIBs. The abundant polar functional groups in PDA significantly enhance interfacial contact in aqueous media, which reduces the number of water molecules reaching the zinc surface through fast desolvation, thus lowering the energy barrier for Zn 2+ migration. Furthermore, the porous PDA coating controls the ion flux via the ion-confinement effect, thereby accelerating Zn 2+ kinetics on the zinc surface. Consequently, Zn@PDA exhibits significantly improved Zn 2+ deposition kinetics (nucleation potential of only 32.6 mV vs 50.2 mV of bare Zn) compared with bare Zn at 2.0 mA cm −2 , with a dendrite-free surface and negligible byproduct formation. When paired with a MnO 2 cathode, the Zn@PDA// MnO 2 cell delivers high discharge capacity and long cycle stability without significant performance deterioration over 1000 cycles at 1.0 A g −1 . Additionally, the cell demonstrates excellent shelving-restoring performance.

Electrolyte‐Wettability Issues and Challenges of Electrode Materials in Electrochemical Energy Storage, Energy Conversion, and Beyond

“…Reproduced with permission. [32] Copyright 2022, Wiley-VCH. c) Long-term cycling stability of MnO 2 /Zn and MnO 2 /PVB@Zn batteries at 5 C with the corresponding CEs.…”

“…[78,174,175] Some polymer films with rich polar functional groups such as poly(vinyl butyral) (PVB), PDA, poly(vinylidene difluoride) (PVDF) generally exhibit significant electrolyte-wettability, because the polarity of those polar functional groups is close to the polarity of water and has more negative binding energy with Zn 2+ (-OH, -NH 2 , and, -COH are −235.45, −241.30, and −295.74 kcal mol −1 ). [32,79,80] Thus, electrolyte-wettability of Zn metal anode toward aqueous electrolytes could be enhanced by coating the electrolyte-wettable polymer films on surface of the Zn anode using facile spin-coating [78] and/or scrape-coating (Figure 17a,b). [32] The PVB-coated Zn (PVB@Zn) anode delivers an extended deposition and stripping cycling life of 2200 h in symmetric batteries at the current density of 0.5 mA cm −2 .…”

“…According to the reported literature, the recent research progresses of wettability control of electrode materials in electrochemical energy storage, energy conversion, and capacitive deionization could be summarized as follows: i) for supercapacitors and metal ion batteries, the better electrolyte-wettable electrode materials generally facilitates electrolyte ion diffusion in electrode and increase ion-accessible surface area, thereby increasing specific capacity, enhancing rate performance, and reducing interface impedance for the electrode, as well as improves energy density, power density, and cycle stability of the devices; [24][25][26][27][28][29] ii) in metal-based batteries, the excellent electrolytewettability of anodes could reduce nucleation overpotential, increase nucleation sites, homogenize the interfacial cation distribution, and promote the formation of thin and stable solid electrolyte interface (SEI) films, leading to the formation and growth of metal dendrites being inhibited and improving cycle stability and safety of the metal-based batteries; [30][31][32][33] iii) the increased electrolyte-wettability is helpful for the initial adsorption of water (reactants) on the electrode material surface and the detachment of the evolved H 2 or O 2 bubbles from the electrode material surface, which increases the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) catalytic kinetics of the electrode in electrochemical water splitting systems; [34,35] iv) similar to supercapacitors, the electrode materials used in capacitive deionization often use modification strategies of increasing electrolytewettability to improve the salt adsorption capacity (SAC) and salt adsorption rate (SAR) of the electrode; [36] and, v) unlike supercapacitors, metal-ion batteries, electrochemical water splitting systems, capacitive deionization, and anodes of metal-based batteries, the electrolyte-philicity of electrodes are demanded moderation in gas cathodes (such as O 2 , CO 2 , and air electrodes) for metal-based batteries and fuel cells, owing to a certain hydration state of the electrodes could ensure an adequate proton conductivity, but excessive water results in the blocked gas pathways and increases mass transport losses. [37,38] In view of the electrolyte-wettability of electrodes has a remarkably impact on its electrochemical energy storage and conversion performance, the study of electrolyte-wettability of elec-trode materials has spawned extensive attention across the globe.…”

Dielectric–Metallic Double-Gradient Composition Design for Stable Zn Metal Anodes

“…The rate performance measurement shows that Zn-GZH can possess a lower and more stable voltage hysteresis at currents ranging from 0.5 to 20 mA cm –2 (Figure S19e). The electrochemical performance of Zn-GZH is superior to the recently reported Zn protective layers under mildly acidic conditions (Figure g). ,,,,− According to the previous analyses, the improvement of electrode stability by the dielectric–metallic ultrathin film can be attributed to the intrinsic high permittivity, high breakdown voltage, and good interfacial compatibility, which can effectively block the electron pathways, reduce side reactions, and further ensure electrochemical reversibility …”

Dendrite-Free and Highly Stable Zn Metal Anode with BaTiO3/P(VDF-TrFE) Coating

“…), − polymers (polyamide, polydopamine, 502 glue, etc. ), − or carbonaceous materials (carbon nanotubes, graphene, etc. ), , is a more direct method to prevent direct reactions between the Zn electrode and aqueous electrolyte to restrain Zn dendrite growth and side effects.…”