Simultaneous manipulation of electron/Zn2+ ion flux and desolvation effect enabled by in-situ built ultra-thin oxide-based artificial interphase for controlled deposition of zinc metal anodes

https://doi.org/10.1016/j.cej.2022.141015Get rights and content

Highlights

  • New spin-coating approach of Zn2+-rich slurry is developed for stable Zn anodes.

  • Zn anode is modified by ultra-thin ZnO-rich solid electrolyte interphase.

  • The modified Zn induces dendrite-free and preferential Zn growth along Zn(002) plane.

  • Manipulated electron/Zn2+ flux, desolvation effect, and 2D atom diffusion are proved.

  • We achieved excellent long-term cyclability along with ultralow voltage hystersis.

Abstract

Aqueous Zn metal batteries (AZMBs) are promising candidates for large-scale energy storage systems, but metallic Zn anodes persistently suffer from severe dendrite proliferation, causing a steep decline in battery lifetime and limiting practical applications. In this study, an ultrathin, sturdy artificial solid electrolyte interphase (ASEI), mainly composed of interconnected ZnO nanoparticles (ZnO-rich ASEI), is fabricated on the Zn surface by a novel in-situ ZnO nucleation and growth strategy to alleviate this dendrite problem. The uniformly and densely coated ZnO-rich ASEI enabled simultaneous manipulation of electron/Zn2+ flux and the desolvation effect on the Zn surface, which minimized the occurrence of dendrites and side-reactions and improved Zn deposition kinetics. The ZnO-rich ASEI effectively guided preferential Zn growth along the Zn(002) plane with thorough 2D atom diffusion confinement for even Zn plating. Consequently, despite the thin thickness of ZnO-rich ASEI, the symmetric cell achieved an outstanding cyclability (over 550 h) even under harsher condition (20 mA cm−2, 10 mAh cm−2) than a realistic condition (5 mAh cm−2) of practical AZMBs. Moreover, the voltage hysteresis reduction effect stemming from ZnO-rich ASEI is excellent compared to state-of-the-art research related to ASEI@Zn. The superiority of ZnO-rich ASEI@Zn was also verified in a Zn/MnO2 full-cell test, exhibiting superb long-term cyclability. This study provides a new direction for future research on stable Zn anodes using ASEI fabrication.

Introduction

The burgeoning development of electric vehicles and portable consumer electronics, causing global ever-growing energy demand, has motivated research into reliable and high-performance energy storage devices [1]. Despite our increasing reliance on lithium-ion batteries (LIBs) for several years owing to their high energy density and outstanding rechargeability, the insufficient natural availability of lithium, increasing cost of crucial elemental components for manufacture, and potential safety concerns driven by the flammability of toxic organic electrolytes limit grid-scale energy storage applications of LIBs [2], [3]. Moreover, environmental concerns regarding the worldwide goal of carbon neutrality have led mankind to focus on the utilization of renewable but intermittently available energy (such as solar, tide, and wind) and the development of highly stable, safe, and cost-efficient energy storage systems (ESSs) for storing energy generated from clean energy sources [4]. Aqueous multivalent-ion (Zn2+, Mg2+, Ca2+, and Al3+) batteries [5], [6], [7], in this respect, have attracted widespread attention as highly promising candidates for safe large-scale ESSs by virtue of aqueous electrolytes having better intrinsic safety (including non-flammability and non-toxicity), higher ionic conductivity, environmental benignity, and more cost-effectiveness in comparison with organic electrolytes [8]. Excellent results have been obtained in the domain of rechargeable aqueous Zn metal batteries (AZMBs) based on neutral/mild electrolytes (such as ZnSO4 and Zn(CF3SO3)2 solutions) since 2012 [9]; therefore, AZMBs have emerged as the most significant competitor among the alternatives owing to the distinctive advantages of metallic Zn anodes, such as (1) high theoretical gravimetric and volumetric capacities (820 mAh g−1 and 5,855 mAh cm−3), (2) suitable redox potential of Zn2+/Zn (-0.762 V vs standard hydrogen electrode), (3) high overpotential for H2 evolution in aqueous solution, (4) outstanding chemical compatibility in air and water (simplifying battery manufacturing process comparing to Li-based batteries), and (5) rich natural abundance (≈230 million tons) in the Earth’s crust compared with Li [10], [11]. Inspired by these marked merits, various AZMBs, including Zn-MnO2 [12], [13], Zn-V2O5 [14], Zn-I2 [15], [16], Zn-air [17], and Zn-Co [18] battery systems, have been studied in the last decade and achieved inspiring cycling performance.

However, irrespective of the development of advanced cathode materials, the realization of long-life rechargeable AZMBs is still fraught with critical challenges originating from the inferior stability of metallic Zn in aqueous environments. Specifically, uncontrollable Zn dendrite growth and incessant faradaic and non-faradaic side reactions during repetitive cycling are the principal Achilles heels of practical reversible AZMB implementation. Although the intrinsic Zn dendrite issue may be mitigated to some extent in neutral or mildly acidic electrolytes rather than alkaline electrolytes, the formation of detrimental dendritic and/or dead Zn arising from ununiform distribution of electric field and ion flux on the anode surface according to the “tip effect” still exists during long-term cycling of AZMBs [19]; typical Zn dendrites with considerably high Young’s modulus (∼100 GPa) can readily puncture into the routine separator and ultimately cause internal short-circuits, a short battery lifespan, low Coulombic efficiency (CE), and catastrophic safety concerns [20]. A traditional Zn anode is thermodynamically unsettled in routine aqueous electrolytes and has a tendency to dissolve with hydrogen evolution reaction (HER) over the entire pH range on the basis of the Pourbaix diagram, giving rise to undesirable electrochemical Zn corrosion (induced by dissolved O2/free H2O) and the inevitable accumulation of Zn2+-insulating by-products (such as zinc hydroxides and zincates), which passivate the Zn surface [21], [22]. Moreover, these irregular and tortuous by-product layers are likely to accelerate unceasing side reactions (including HER and electrolyte consumption) at the electrode–electrolyte interface and, thus, deteriorate the comprehensive electrochemical performance of AZMBs. Therefore, feasible Zn metallic anodes that cast off these irreversibility issues are becoming increasingly essential for improving the electrochemical durability of anode materials for practical AZMBs.

To date, strenuous endeavors around the entire AZMB system have been undertaken to ameliorate long-standing problems in the development of stabilized Zn metal anodes, which are similar to reported strategies aimed at addressing Li dendrite issues in Li metal batteries [23], [24]. In terms of electrolytes, diverse organic/inorganic additives (such as plant extracts [20], dimethyl sulfoxide [25], Ti3C2Tx MXene [26], anionic tin sulfide nanosheets [27], and polyacrylamide [28]) were developed as an efficient strategy to manipulate Zn dendrite growth and Zn ion solvation. Unfortunately, these adsorption-type additives do not radically reduce interfacial side-reactions, especially under AZMB operating conditions with high current densities and capacities [29]. Furthermore, the utilization of modified electrolyte formulations (including “H2O-mixed deep eutectic solvent” [30] and “water-in-salt” [31] systems), which could serve as a suitable Zn dendrite and H2O-induced Zn corrosion inhibitor due to their lower water content than conventional aqueous electrolytes [32], might result in compromised ion transfer kinetics of AZMBs, ascending toxicity and viscosity of electrolytes, and increased total weight and cost of assembled batteries [33]. Fortunately, multifarious strategies in the realm of geometric Zn anode/host designs (such as 3D Zn host/anode construction [34], [35], [36], Zn alloy anodes [37], [38], and utilization of MXene-based materials [39]) allow reduced Zn protrusion and dendrite growth by furnishing uniform local current density and accelerated surface charge transfer with enlarged electroactive anode surface area [40]. However, though most of these strategies can enhance interfacial contact between electrolyte and electrode which is conducive for flat Zn deposition, persistent side reactions and corrosion rate are inevitably expedited due to an open environment of electrolyte-anode interface and exposed Zn surface area increment [41].

Recently, the use of surface manipulation strategies analogous to those of metallic Li anodes[42], [43], the grafting of artificial solid electrolyte interphases (SEI) on Zn anodes (such as nano-CaCO3 [44], montmorillonite [45], metal seeds [19], metal–organic frameworks [46], carbon-based materials [47], and polymers [48]) has also been considered one of the most promising approaches to simultaneously minimize dendrite proliferation and irreversible side reactions by providing physical shielding and current/ion flux redistribution in the vicinity of the Zn anode surface. In general, ASEIs can be classified as ex-situ physical preprocessing coating techniques and in-situ direct growth on a Zn anode [49]. Although most ASEIs built using either methodologic approach have been verified to be effective, ex-situ SEIs are prone to uncompacted interfacial adhesion and local inhomogeneity, resulting in a gradual loss of anode protection, accompanied by cracking, degradation, and detachment of the SEIs owing to dramatic volume changes during long-term dynamic cycling [50]. Therefore, rather than temporarily postponing dendritic/dead Zn generation, alternative strategies have been proposed to fabricate durable artificial in-situ SEIs in recent years. In-situ SEIs are usually constructed by chemical or electrochemical methods, which can facilitate the improvement of interfacial Zn-SEI contact and SEI surface uniformity and stability owing to the self-termination effect. Although it is very challenging to develop ideal in-situ SEIs in mild electrolytes, some successful attempts (such as ZnS [51], MXene-integrated Zn [52], quasi-solid electrolyte by using CaSO4·2H2O [53], ZnF2-rich organic/inorganic hybrid SEI [54], and Bi-based energizer consisting of metallic Bi and ZnBi alloy [55]) have been reported to date. Furthermore, most reported SEIs were prepared with a relatively high thickness, which would unavoidably sacrifice the gravimetric and volumetric specific capacities of the AZMBs. Additionally, given the high Young’s modulus of Zn dendrites, fabricating robust protective SEIs to induce stable Zn deposition beneath the SEIs is also a highly challenging task. Therefore, despite the progress toward stable Zn anodes, there is still a substantial gap between laboratory-scale and industrially applicable AZMBs.

From analyses of the aforementioned research, “guiding Zn plating on in-situ ultra-thin ASEI without dendrite” has been hypothesized as a potential strategy to stabilize a Zn anode [56]. In this study, a novel in-situ ASEI formation strategy to directly assemble ultra-thin (∼115 nm) and compact ASEIs was developed primarily composed of uniform agglomeration of numerous ZnO nanoparticles (denoted as ZnO-rich ASEI) on the Zn anode surface. Owing to the favorable interfacial electron/Zn2+ ion flux redistribution and remarkably reduced desolvation activation energy of ZnO-rich ASEI@Zn, the deposited Zn was evenly plated on the ZnO-rich ASEI@Zn. More importantly, by employing ZnO-rich ASEI, significant 2D atom diffusion confinement during the Zn nucleation process and preferential Zn growth along the Zn(002) plane during repeated Zn stripping/plating were observed using electrochemical/ X-ray diffraction (XRD) analysis and in-situ/ex-situ morphological observations; this phenomenon can effectively restrain side reactions and bulk dendrite formation. Consequently, the Zn/Zn symmetric cells using ZnO-rich ASEI@Zn delivered outstanding rate capabilities (at 0.5–10 mA cm−2 with a fixed capacity of 1 mAh cm−2) and superior cycling stability over 1500 h with obviously reduced overpotentials (at 1 mA cm−2, 1 mAh cm−2). Even under harsh stripping/plating conditions (10 or 20 mA cm−2, 10 mAh cm−2), the ZnO-rich ASEI@Zn cell exhibited better cyclability with low polarization compared to a bare Zn cell. Moreover, the ZnO-rich ASEI@Zn/MnO2 batteries delivered enhanced electrochemical performance. Our findings may offer new insights into the development of thin ASEIs that minimize the impact on the gravimetric/volumetric specific capacities of AZMBs.

Section snippets

Results and discussion

In contrast to LIBs, where compact SEIs can block fatal side reactions between the anode and organic electrolytes [3], loose SEIs naturally formed on bare Zn anodes easily fail to isolate aqueous electrolytes and thus worsen typical side reactions (including HER, corrosion, and insulating by-product formation) and notorious dendrite problems in AZMBs. Considering this situation, we designed a multifunctional ZnO-rich ASEI that can be obtained through a sequential two-step method, as

Conclusion

In summary, we prepared a new type of in-situ built ASEI created by the uniform agglomeration of numerous ZnO NPs (ZnO-rich ASEI@Zn) via simple spin-coating approach of Zn2+-rich slurry on the Zn surface, combined with a subsequent low-temperature annealing process. Clearly, despite the ultrathin (∼115 nm) thickness of ZnO-rich ASEI, it can manipulate the electron/Zn2+ ion flux and desolvation effect in the vicinity of the Zn surface enabled by its beneficial merits: (1) improved wettability by

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (2022R1A2C3003319), South Korea, the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2018M3D1A1058744), South Korea. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, South Korea

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