Demonstrating U-shaped zinc deposition with 2D metal-organic framework nanoarrays for dendrite-free zinc batteries

Abstract

Aqueous zinc (Zn) battery has shown its great promise as intrinsically safe battery technology. However, Zn batteries are still far from practical use, mainly due to Zn dendrite growth and side reactions. We propose a U-shaped deposition configuration to address the dendrite issue of Zn anode, which is achieved within a nanoarray of 2D metal-organic framework (MOF) flakes grown on the Zn anode. Rich zincophilic sites of the flakes enable uniform pre-seeding of Zn ions, followed by lateral deposition of Zn metal onto the MOF flakes and bottom-up plating from the anode surface, finally achieving a U-shaped deposition. The U-shaped deposition configuration is well demonstrated by simulation results in which the ion concentration and current distribution are regulated by the MOF arrays. This procedure combining pre-seeding and bottom-up deposition naturally eliminates the “tip effect” and inhibits Zn dendrite. Together with the ideal suppression of the hydrogen evolution reaction, the Zn metal anode features long cycling stability up to 1880 h at a current density of 5 mA cm⁻² and extends the long lifespan to full cells. This study demonstrates a renewed understanding of controlling Zn deposition in practical batteries and paves a new avenue toward dendrite-free metal anodes.

Introduction

Aqueous Zn batteries have attracted wide attention due to their high theoretical volumetric capacity (5855 mAh cm⁻³), low redox potential (−0.762 V vs standard hydrogen electrode), and environmental friendliness [[1], [2], [3], [4]–5] .However, challenges such as Zn dendrite growth, interface corrosion, and side reactions (e.g., hydrogen evolution reaction, HER) at the anode-electrolyte interface have hindered the application of Zn batteries [[6], [7], [8]–9]. Due to the low Zn/Zn²⁺ redox potential, HER inevitably occurs on the Zn-electrolyte interface during Zn deposition [9], which results in the fast accumulation of byproducts, thus decreasing the Coulombic efficiency (CE) and cycling stability of the batteries [[10], [11], [12], [13], [14], [15]–16]. Moreover, due to a “tip effect” and a high lattice mismatch between deposited Zn and bare Zn substrate, Zn is likely deposited as perpendicular dendrites during plating [17]. The dendrite growth causes dead Zn, side reactions and possible separator penetration, resulting in a short circuit during the charge/discharge process [[18], [19]–20]. It is therefore necessary to develop stable Zn anodes with uniform Zn deposition/dissolution and a suppressed HER to endow batteries with a long lifespan.

Recently, interfacial modification through various coating layers, such as organic polymers [21,22], inorganic compounds [23], and organic-inorganic hybrids [24], has been widely utilized to regulate the diffusion, nucleation, and deposition of Zn ions for reversible plating/stripping. The large volume change of the Zn anode during the plating/stripping process would inevitably cause the detachment or crack of the coating layers. Building 3D matrixes with open channels for Zn metal anode is proven effective to alleviate the volume change [[25], [26], [27], [28], [29], [30], [31]–32], while in most cases, Zn metal is still deposited in a mode of uncontrolled morphology and a large surface area, in which more side reactions may occur between the deposited Zn and the aqueous electrolyte. A zincophilic matrix that attracts Zn ions is expected to reasonably guide the Zn deposition within the matrix, alleviating the “tip effect” during the plating and mitigating the uncontrolled Zn deposition [33]. However, it remains unclear what the ideal Zn deposition mode is for a practical (dense) and effective (free from dendrites) Zn anode. As for the approach of coating, what is the desired structure for realizing such an ideal deposition?

Herein, we propose a U-shaped Zn deposition configuration to address the dendrite issues, which is achieved within the nanoarray of 2D MOF flakes grown on the Zn anode (Fig. 1). This novel configuration well eliminates the “tip effect” and realizes uniform Zn deposition for long-life Zn anodes. Using a self-template method, we fabricated a nanoarray structure composed of zincophilic MOF flakes anchored on the Zn foil. N- and O-containing sites yield zincophilicity of the MOF flakes, enabling uniform pre-seeding of Zn ions that is followed by the lateral Zn deposition onto these flakes during the bottom-up plating starting from the anode surface, finally achieving a spatially controlled U-shaped deposition along the nanoarray. As a result, the 2D MOF nanoarray coated Zn anode following the U-shaped deposition configuration realizes greatly improved plating/stripping reversibility, cycling stability, and lifespan, achieving long durability of 1880 h with a low overpotential (50 mV) at 5 mA cm⁻². When the coated anode is coupled with a Zn_xV₂O₅•H₂O (ZVO) cathode, the full cell exhibits excellent cycling stability and good capacity retention of 83% after 1000 cycles. This study provides not only an effective method to build long-life Zn metal anodes, but also implies a fundamental understanding of metal deposition, not limited to Zn, in the desired manner to produce dendrite-free metal anodes.