A dendrite-free anode for stable aqueous rechargeable zinc-ion batteries

Highlights

• Aqueous rechargeable Zinc-ion batteries for large-scale energy storage.

• Electrospun PAN nanofiber layer for zinc dendrite inhibition.

• A facile, robust, and cost-effective approach for improved battery performance.

Abstract

Due to its low cost, high specific co, and environmental friendliness, zinc is considered a potential anode material for aqueous rechargeable Zn-ion batteries. However, practical applications remain a challenge due to uncontrolled dendrite formation. Herein, we have utilized a strategy where a microporous nanofiber layer of polyacrylonitrile (PAN) is electrospun onto Cu foil and used as the current collector for the anode to inhibit dendrite generation. The polar nitrile groups on the nanofibers expedite the uniform transport of Zn²⁺ and allow homogenous Zn deposition, which ultimately inhibits dendrite growth. The symmetrical cell equipped with this new fabricated electrode shows over 270 stable cycles without a short circuit. The full cell formed with MnO₂ as the cathode exhibits improved cycle stability up to 300 cycles at a current density of 0.5 A g⁻¹.

Introduction

The global demand for energy storage is ever-increasing in both developed and developing countries due to massive industrial activities. Therefore, the economy is focusing more on clean, renewable energy and becoming less dependent on fossil fuels, which is why we need a way to store the intermittent renewable energy that is generated by ocean tides, wind, and solar radiation [1], [2], [3], [4], [5]. Since the successful commercialization of lithium-ion batteries (LIBs) in the early1990s, it has been employed in numerous applications, from portable electronic devices to hybrid electric vehicles/electric vehicles (HEVs/EVs), due to their compact size, lightweight, long cycle life, and high power/energy density [6], [7], [8], [9], [10]. Nevertheless, the development of the LIB technology has been hindered owing to its high cost, aging issues, and use of flammable organic electrolytes, which can trigger fires in the battery during overcharge and discharge, limiting the application in large scale electrochemical energy storage (EES) system [11], [12], [13].

Zinc-ion aqueous-based rechargeable (ZIB) batteries have great potential as reliable alternatives for large-scale energy applications owing to their low cost, high safety, and both large theoretical (820 mAh g⁻¹) and high volumetric capacity (5850 mAh cm⁻³) [2], [14], [15], [16], [17], [18], [19], [20], [21]. ZIBs exhibit low electric potential (−0.762 V) vs. SHEs, are easy to scale up, have significantly high ionic conductivity, and utilize abundant and easily obtainable materials [20], [21], [22]. These features make ZIBs very attractive for commercial and residential energy storage. Nevertheless, issues such as dendrite formation, poor coulombic efficiency, quick capacity fading, and parasitic side reactions impede their further development for commercial applications [22], [23], [24], [25], [26], [27], [28], [29], [30]. Over the past few years, extensive efforts have been devoted to mitigating or even completely eliminating these issues by suitable coping approaches, such as electrolyte concentrating [25], [31], nonaqueous electrolytes [26], [32], [33], [34], electrolyte additives [35], [36], [37], solid-state electrolytes [38], [39], structured electrodes [26], [40], [41], [42], and surface modifications [26], [27], [28], [43], [44], [45], [46], [47], [48]. In addition to these strategies, it has also been documented that uncontrollable Zn dendrites primarily originate from the spatial heterogeneity of Zn²⁺ and an uneven electric field distribution on the electrode surface, also called the “tip effect” [25], [27], [49], [50], [51], [52], [53].

Zhao et al. utilized a “brightener-inspired” polyamide layer that limits Zn²⁺ ion diffusion and attenuates the nucleation barrier to regulate Zn deposition efficiently [50]. Using a similar approach, Zhang et al. developed a stable 3D anode structure and used polyacrylamide as an electrolyte that shows dendrite-free stripping/plating behavior using a Cu-Zn solid solution interface on a copper mesh, which helps promote uniform nucleation of zinc [54]. Interfacial stability and Zn²⁺ ion-transfer kinetics have been effectively regulated, and side reactions are prevented by a new kind of Zn anode modified by the porous and 3D ZnO architectures [52]. More recently, Lu et al. described that Ag-coated Zn shows a small zinc deposition overpotential, fast kinetics for zinc dissolution/deposition, and improved electrolyte wettability with repeated plating/stripping behavior up to 1450 h [55]. Moreover, hierarchical current collectors (CCs), such as aluminum or copper, with a high electroactive surface area and steady electric field, could impede dendrite growth [56], [57]. Thus, the deposition of Zn onto these CCs demonstrates a viable strategy to attenuate dendrite growth and produce durable ZIBs with a high rate capacity [57], [58]. In another interesting article, Zheng et al. claimed that reversible epitaxial electrodeposition at the Zn anodes could be attained by electrically conductive coatings such as graphene and metals, which have a low lattice mismatch for Zn and are capable of regulating nucleation, growth, and reversibility over thousands of cycles with coulombic efficiency (CE) ˃ 99.7% [58]. We can conclude that uniform zinc nucleation and the Zn²⁺ distribution is therefore a critical prerequisite to suppress Zn dendrite formation.

Herein, we demonstrate a straightforward and effective strategy to realize high-efficiency and stable Zn stripping/plating. In our design, a polyacrylonitrile (PAN) porous nanofiber network is first electrospun uniformly onto a Cu foil, which is used as a CC for the zinc anode. The pendant polar nitrile groups of the PAN nanofibers coordinate with the Zn²⁺ present in the electrolyte, which facilitates the regular diffusion and even deposition of Zn through the porous nanofiber frameworks. Benefiting from this methodology, dense, flat, and dendrite-free Zn plating in a symmetric cell with 270 stable cycles at a current density of 2 mA cm⁻² is realized by suppressing the irregular deposition of Zn.