Strategies to Stabilize Zinc Metal Anode Interfaces for Long-Cycle Zinc Ion Batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) have garnered significant interest and exhibit substantial potential for next-generation large-scale energy storage applications, attributed to their superior safety, environmental sustainability, and economic viability. Nonetheless, the Zn anode faces several critical challenges, such as uncontrolled dendritic growth, sluggish deposition kinetics, and intrinsic chemical corrosion coupled with hydrogen evolution reactions (HER), which severely impede the cycling performance of zinc anodes. Consequently, it is imperative to devise highly reversible Zn anodes through diverse strategies to effectively extend the cycling lifespan and enhance the capacity retention of AZIBs.

Constructing a protective layer on the zinc anode can directly modulate the dynamic process within the electrode/electrolyte interphase, which has been considered as a particularly effective strategy. However, the reported coatings with conductive nature serve as the undesired nucleation seeds for zinc ions deposition, resulting in the inevitable trapping of zinc atoms within the coating layer. The repeated insertion and extraction can cause volumetric expansion and pulverization, which eventually cause coating failure as the conventional electrode materials. Herein, a hydroxyl-rich Boehmite coating (HR-BC) strategy is developed that combines excellent electrical insulation and high zinc ion conductivity. The hydrophilic hydroxyl groups facilitate hydrogen bond formation with the hydrated zinc ions, accelerating the de-solvation process and suppressing the HER. Additionally, the electrically insulative nature of Boehmite prevents the reduction of zinc ions within HR-BC and results in preferential Zn deposition underneath it, leading to a dendrite-free “sandwich structure” of HR-BC//Zn deposition//Zn foil. Symmetric cells using HR-BC-Zn electrodes obtain an ultralong and stable cycling lifetime of 1700 h at 5 mA cm^-2, along with a high cumulative plating capacity of 4250 mAh cm^-2. When paired with a V₂O₅ cathode, the HR-BC-Zn anode demonstrates a high capacitance retention of 90% and an average Coulombic efficiency (CE) of 99.8% after 4000 cycles. Furthermore, when combined with a heteroatoms-doped carbon (HDC) cathode, the HR-BC-Zn//HDC pouch-type cell exhibits superior lifetime performance with nearly 100% average CE after 15000 cycles at 3.0 A g^-1.

Recent studies also highlighted the potentials of electrolyte additives in regulating the Zn crystallographic orientation and improving Zn deposition reversibility. Nevertheless, these electrolyte additives of small molecules continuously decompose and deplete during the formation of the insoluble SEI layers over long-term cycling, which ultimately impairs the modulation of Zn (002) plane and leads to battery failure. In this study, we present a dynamic regulation strategy to promote (002)-texture growth during Zn deposition. Single-atomic iron-decorated nitrogen-carbon (Fe-N-C) nanoparticles, which can preferentially adsorb on Zn (100) and (101) planes during Zn deposition, are synthesized and incorporated into the electrolyte as an additive. Taking advantage of the reversible adsorption-desorption behavior of Fe-N-C agents, only the planar (002) plane of Zn remain exposed during battery cycling, effectively suppressing hydrogen evolution and dendrite formation. Consequently, Zn//Zn symmetry batteries with Fe-N-C electrolyte additive demonstrate an impressive cycling lifespan of 4,300 h with a cumulative plating capacity of 10.75 Ah cm^-2. Notably, even at a high depth of discharge of 61.5%, the batteries maintain remarkable cycling stability of 120 h. When paired with vanadium-based oxide cathodes, full cells show outstanding durability, sustaining over 4,000 cycles with a capacitance retention of 91.7%.

Currently, the widely used commercial glass fiber (GF) separator suffers from poor mechanical fragility and inhomogeneous pore structure, synthetically making it vulnerable to Zn dendrite-penetrating risks and short-circuit of ZIBs. Herein, we present a self-expedited “Zn²⁺ ion pump” strategy, using a single-atomic cobalt-decorated nitrogen-doped carbon nanoparticle layer integrated into a natural cellulose separator (Co-N-C@CLS), to dynamically regulate the Zn²⁺ interface. The natural cellulose framework provides abundant hydroxyl groups that coordinate hydrated Zn²⁺ via hydrogen bonding, thereby suppressing the activity of water molecules. Concurrently, the single-atomic Co-N-C nanoparticle layer, featuring a low Zn²⁺ migration energy barrier, enables rapid and homogeneous replenishment of interfacial Zn²⁺, eliminating uneven ion distribution and adverse concentration gradients. This synergistic design ensures a uniform Zn²⁺ flux and promotes dendrite-free deposition. As a result, Zn//Zn symmetric cells achieve exceptional stability for over 1200 h at 1 mA cm^-2. Zn//Cu asymmetric cells demonstrate an extended cycling life of 1800 h and a high Coulombic efficiency (CE) of 99.6 %. When paired with V₂O₅ cathodes, full cells deliver superior durability, retaining of 79.3% of their capacitance after 3000 cycles. Furthermore, in zinc-ion supercapacitors, an outstanding capacitance retention of 69.8% with a CE of 99.6% is demonstrated after nearly 200000 cycles.

In conclusion, strategies for stabilizing Zn anodes have been explored through the development of artificial coatings, electrolyte additive engineering and separator decoration. The underlying mechanisms of these approaches have been thoroughly investigated and substantiated. The research presented in this thesis offers valuable insights into the design of highly stable Zn anodes and the development of long-lasting aqueous zinc-ion batteries (AZIBs).

Date of Award	17 Aug 2026
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Wenjun ZHANG (Supervisor)