Quantum Size Effect Synergizes Space‐Limited Domain Action for Advanced Aqueous Zinc‐Iodine Batteries

Abstract

Rechargeable aqueous zinc‐iodine batteries (AZIBs) demonstrate immense potential for large‐scale energy storage owing to their high theoretical capacity, resource abundance, and low cost. However, their practical deployment is hampered by the notorious polyiodide shuttle effect and sluggish redox kinetics. Herein, an Al‐TCPP(Fe) metal‐organic framework (MOF) is designed and synthesized with specific functional sites as an advanced iodine host. The unique microporous structure of this MOF provides significant spatial confinement, which effectively suppresses the dissolution and migration of polyiodide intermediates, thereby mitigating the shuttle effect. Furthermore, precisely engineered Fe‐N₄ catalytic sites embedded within the MOF framework induce a quantum size effect under nanoscale confinement, which significantly modulates the electronic structure of the Fe sites, dramatically accelerating the iodine redox kinetics. Benefiting from these structural merits, the resulting I₂@Al‐TCPP(Fe) cathode delivers a high specific capacity of 210.95 mAh g⁻¹ at 1C, achieves an ultralong cycling lifespan of over 54 000 cycles at a high rate of 50C, and enables the fabrication of an ampere‐hour‐level pouch cell. This work highlights a synergistic strategy of coupling the quantum size effect with spatial confinement to engineer advanced MOF‐based hosts, paving the way for developing high‐performance, long‐lifespan aqueous zinc‐iodine batteries.

A functionalized MOF, Al‐TCPP(Fe), featuring micropores and Fe‐N₄ sites, acts as a superior iodine host for aqueous zinc‐iodine batteries. This dual‐function design synergistically confines polyiodides and catalyzes iodine redox through quantum‐size‐tuned Fe‐N₄ sites. The resulting battery achieves a remarkable cycling stability of over 54 000 cycles at 50C and is demonstrated in a scalable 1.6 Ah flexible pouch cell, offering a new strategy for long‐life energy storage.

1. Introduction

The escalating global demand for sustainable and secure energy storage solutions has prompted intensive research into alternatives beyond conventional lithium‐ion batteries.^{[ 1 ]} Aqueous zinc‐iodine batteries (AZIBs) have emerged as a particularly promising candidate owing to their inherent safety derived from non‐flammable aqueous electrolytes, environmental benignity, the low cost of abundant zinc and iodine resources, and a high theoretical specific capacity (e.g., ≈211 mAh g⁻¹ for the I₂/I⁻ redox couple).^{[ 2} , ³ , ^{4 ]} However, the practical realization of high‐performance AZIBs is severely hindered by challenges intrinsic to iodine cathode chemistry. The primary obstacle is the notorious “shuttle effect,” wherein soluble polyiodide intermediates (predominantly I₃ ⁻ and I₅ ⁻) readily dissolve and diffuse across the separator to the zinc anode. This phenomenon triggers parasitic side reactions at the anode surface, leading to the continuous loss of active material, low coulombic efficiency, and rapid capacity decay.^{[ 5} , ⁶ , ^{7 ]}

To mitigate the polyiodide shuttle effect and enhance the electrochemical performance of iodine, various porous carbonaceous materials—including activated carbon,^{[ 8 ]} carbon nanotubes,^{[ 9 ]} and graphene derivatives^{[ 10} , ¹¹ , ¹² , ^{13 ]}—have been extensively explored as iodine hosts, owing to their large surface areas and high electrical conductivity. However, their relatively weak physical interactions and often broad pore size distributions limit the efficacy of long‐term polyiodide confinement, particularly at high iodine loadings.^{[ 14 ]} Beyond these cathode‐centric strategies, other research has focused on the electrolyte, precisely reconfiguring solvation and interfacial/interphasial chemistry through molecular‐ and component‐level synergy. This is exemplified by the use of stereoisomeric additives,^{[ 15 ]} the dual cationic‐shielding and anionic‐chemistry effects of KHP,^{[ 16 ]} and MoSx–GO hybrid hydrogels,^{[ 17 ]} which collectively aim to suppress the shuttle effect while accelerating Zn²⁺ migration kinetics. However, merely suppressing the shuttle effect addresses the symptom rather than the root cause. The slow kinetics of the iodine reduction reaction (IRR, I₂ → 2I⁻) lead to the complexation of unreacted iodine with the produced iodide ions, forming a substantial amount of polyiodide intermediates (e.g., I₃ ⁻) that trigger a cascade of detrimental side reactions.^{[ 18 ]} Critically, achieving precise, molecular‐level control over the confinement environment while simultaneously promoting efficient charge transfer at the host‐iodine interface to accelerate the IRR remains a formidable challenge for conventional materials.^{[ 19 ]} There is a pressing need to develop advanced host materials that possess both well‐defined porous structures for effective physical immobilization and tunable chemical environments to boost iodine reduction kinetics.^{[ 20} , ^{21 ]}

Metal‐organic frameworks (MOFs), constructed from metal nodes/clusters coordinated with organic linkers, represent a unique class of crystalline porous materials with unprecedented structural and chemical tunability.^{[ 22 ]} Their exceptionally high specific surface areas, controllable pore sizes and topologies, and potential for functionalization make them highly attractive for addressing the limitations of AZIBs.^{[ 23} , ^{24 ]} Specifically, the well‐ordered pore structure of MOFs provides an ideal platform for implementing a spatial confinement strategy.^{[ 25 ]} By carefully selecting MOFs with an appropriate pore size, soluble polyiodides can be physically trapped within the framework cavities, effectively preventing their dissolution and diffusion, thereby suppressing the shuttle effect and enhancing cycling stability.^{[ 26 ]} Furthermore, the nanometer‐scale dimensions of MOF pores or the use of MOF nanocrystals can introduce quantum‐size effects,^{[ 27} , ^{28 ]} potentially altering the electronic properties and reactivity of the confined iodine species. This nanoconfinement can lower the energy barrier for charge transfer, enhance ion diffusion kinetics within the confined space, increase catalytic activity, heighten affinity for polyiodides, and accelerate the IRR, leading to improved rate performance and active material utilization. Rational design of the MOF structure allows for the optimization of host‐guest interactions and can modulate the electronic environment around the confined iodine, offering a pathway to simultaneously achieve effective immobilization and accelerated electrochemical kinetics.^{[ 29 ]}

In this context, the originality of our work lies in the synergistic integration of crystallographic confinement within the MOF lattice and the quantum size effects at specific Fe‐N₄ sites, all within a single framework. This integrated strategy aims to simultaneously immobilize polyiodides and accelerate I₂/I⁻ kinetics, diverging from conventional approaches that focus on electrolyte/additive engineering or traditional porous carbon hosts. In this study, we synthesized an iron‐coordinated, aluminum‐based porphyrinic framework, Al‐TCPP(Fe), from TCPP organic linkers via a combined solvothermal and hydrothermal method. In this framework, iron atoms coordinated with nitrogen atoms serve as highly efficient active sites for a zinc‐iodine battery cathode host. The strong physicochemical confinement effect enhances reversible iodine conversion. A high affinity for iodine and polyiodides not only facilitates rapid iodine nucleation and accelerates IRR kinetics but also stabilizes the iodine/iodide species, thereby suppressing the shuttle effect (Figure 1 ) and improving the long‐term performance of the Zn‐I₂ battery. Through a combination of physical characterization and theoretical simulations—including Density Functional Theory (DFT), Molecular Dynamics (MD), and Finite Element Method (FEM) analysis—we have validated the ameliorating effect of Al‐TCPP(Fe) on both the polyiodide shuttle and iodine conversion kinetics from multiple perspectives, from macroscopic to microscopic, while also elucidating the electron transfer mechanism during the IRR. The resulting AZIBs demonstrate exceptional long‐term cycling stability (7500 cycles at 2C) and retain a specific capacity of 107.9 mAh g⁻¹ after 54 000 cycles, even at an ultrahigh rate of 50C. Furthermore, the system exhibits outstanding electrochemical performance even at a high iodine loading of 10.96 mg cm⁻², and the fabricated pouch cell achieves an ampere‐hour (Ah)‐level capacity. This research demonstrates the potential of this material for high‐loading and fast‐charging applications, offering new insights for the future design of long‐life zinc‐iodine batteries for large‐scale energy storage.

Figure 1.

Schematic of the working mechanism of the Zn‐I₂ battery, highlighting the synergy between quantum size and spatial confinement effects within the Al‐TCPP(Fe) MOF cathode host.

2. Results and Discussion

The TCPP(Fe) precursor was initially synthesized via a solvothermal method, followed by a hydrothermal process to prepare ultrathin nanosheets of the Al‐TCPP(Fe) MOF. The TCPP(Fe) precursor exhibited a rod‐like morphology (Figure S1a, Supporting Information) with uniform internal elemental distribution (Figure S1b, Supporting Information), indicative of self‐stacking among the organic ligands. Subsequently, coordination of the ligands' carboxylate groups via Al─O bonds established a stable 3D framework in the Al‐TCPP(Fe) MOF, concurrently exposing a greater number of catalytically active sites. During synthesis, the cationic headgroup of the surfactant cetyltrimethylammonium bromide (CTAB) is proposed to coordinate with carboxyl groups exposed at the MOF edges. This interaction, leaving the hydrophobic alkyl chains oriented outward, is thought to hinder vertical stacking and suppress out‐of‐plane growth of the Al‐TCPP(Fe) MOFs.^{[ 30 ]} Consequently, this promotes anisotropic growth, resulting in the formation of an ultrathin nanosheet morphology (Figure 2a). Energy‐dispersive X‐ray spectroscopy (EDS) mapping (Figure S2, Supporting Information) confirmed the uniform distribution of constituent elements throughout the material, further supporting its successful synthesis. Transmission electron microscopy (TEM) provided further insight into the structural details. The TCPP(Fe) precursor consisted of self‐stacked units and lacked distinct lattice fringes (Figure S1c, Supporting Information). In contrast, the Al‐TCPP(Fe) MOFs exhibited a clear nanosheet morphology (Figure 2b) and were highly crystalline, displaying well‐defined lattice fringes with a spacing of 1.6 nm (Figure 2c), corresponding to the (100) crystallographic plane. The powder X‐ray diffraction (PXRD) pattern of the Al‐TCPP(Fe) MOF (Figure 2d) is in excellent agreement with an orthorhombic crystal system belonging to the Cmmm space group. The characteristic diffraction peaks observed at 2θ = 7.68° and 13.78° are assigned to the (201) and (401) crystal planes, respectively, indicating successful coordination between the Al(OH)O₄ metal clusters (nodes) and four TCPP(Fe) organic ligands, which also attests to the high crystallinity of the material. This diffraction signature is characteristic of frameworks built from octahedrally coordinated M³⁺ centers and carboxylate linkers, confirming that the Al(OH)O₄ clusters function as the fundamental building blocks of the 3D Al‐TCPP(Fe) architecture.^{[ 31 ]} Conversely, the PXRD pattern of the TCPP(Fe) precursor (Figure S3, Supporting Information) showed poor crystallinity, consistent with its self‐stacked nature, displaying primarily a broad peak indicative of preferential orientation along the (100) stacking direction.

Figure 2.

Preparation and structural characterization of the Al‐TCPP(Fe) sample. a) Scanning electron microscopy (SEM) image of Al‐TCPP(Fe). b) TEM image of Al‐TCPP(Fe). c) HRTEM image of Al‐TCPP(Fe). d) XRD pattern of Al‐TCPP(Fe). e) XANES spectra of TCPP(Fe), Al‐TCPP(Fe), Fe foil, FeO, and Fe₃O₄. f) Wavelet transform analysis of Al‐TCPP(Fe). g) Raman spectra of TCPP(Fe) and Al‐TCPP(Fe). h) FTIR spectra of TCPP, TCPP(Fe), and Al‐TCPP(Fe). i) Nitrogen adsorption/desorption isotherms and corresponding pore size distribution of Al‐TCPP(Fe).

X‐ray absorption near‐edge structure (XANES) analysis of the TCPP(Fe) and Al‐TCPP(Fe) MOFs revealed that their Fe K‐edge positions are intermediate between those of Fe foil and FeO, indicating that the iron species in both materials exist in a valence state between 0 and +2, suggesting a relatively reduced state^{[ 32 ]} (Figure 3e). The pre‐edge peak observed at 7113 eV corresponds to the Fe 1s→3d transition (Figure 3e, inset); the introduction of Al did not significantly alter the valence state of Fe. The Fourier‐transformed extended X‐ray absorption fine structure (EXAFS) spectrum of Al‐TCPP(Fe) exhibits a primary peak at 1.45 Å, corresponding to Fe‐N₄ coordination (Figure S4a, Supporting Information). This observation confirms that Fe‐N coordination is the dominant motif, rather than Fe─Fe bonding (expected ≈ 2.20 Å). Detailed wavelet transform (WT) analysis further supports the assignment of the Fe‐N coordination path in both TCPP(Fe) and Al‐TCPP(Fe), with a maximum intensity around k ≈ 4.1 Å⁻¹ (Figure S4b, Supporting Information; Figure 2f). This is distinctly different from the Fe‐Fe path in Fe foil (k ≈ 8 Å⁻¹) or the Fe‐O path in FeO (k ≈ 6 Å⁻¹) (Figure S4c,d, Supporting Information). The Raman spectrum of the Al‐TCPP(Fe) MOF displays characteristic peaks for the porphyrin ligand at 1246 cm⁻¹ (C‐H_pyrrole), 1501 cm⁻¹ (C_α‐C_m), 1560 cm⁻¹ (C_β‐C_β/C_β‐H), and 1610 cm⁻¹ (C═C). Peaks indicative of Fe─N stretching vibration and Al─O vibration were observed at 1002 and 824 cm⁻¹, respectively (Figure 2g).^{[ 33 ]} Fourier‐transform infrared (FT–IR) spectroscopy (Figure 2h) showed that the characteristic absorption peak at 970 cm⁻¹, attributed to the N─H in‐plane vibration within the porphyrin macrocycle of the free TCPP ligand, disappeared in the spectra of TCPP(Fe) and Al‐TCPP(Fe) MOFs.^{[ 34 ]} Concurrently, a new absorption peak emerged around 1000 cm⁻¹. This new peak is assigned to Fe─N stretching/bending vibrations, confirming the successful chelation of Fe into the porphyrin core and the formation of the Fe‐N₄ structure,^{[ 35 ]} which is potentially capable of leveraging quantum size effects to enhance catalytic performance. Compared to TCPP(Fe), the coordination of carboxylate groups to Al ions in Al‐TCPP(Fe) resulted in a decreased intensity of the C═O stretching peak (≈1700 cm⁻¹) and the appearance of an Al─O vibration peak (≈575 cm⁻¹).^{[ 36 ]} These spectral changes signify the successful formation of Al(OH)O₄ metal nodes and confirm the synthesis of the Al‐TCPP(Fe) MOF.

Figure 3.

Electrochemical performance of Al‐TCPP(Fe). a) Cyclic voltammetry (CV) curves for I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC cathodes. b) Linear sweep voltammetry (LSV) curves for the oxidation process. c) LSV curves for the reduction process and the corresponding Tafel slopes. d) Rate performance of I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC at various current densities (0.5, 1, 2, 3, 4, and 5C). e) Cycling performance of Zn‐I₂ batteries utilizing I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC cathodes. f) Cycling performance of Zn‐I₂ battery with I₂@Al‐TCPP(Fe) at 2C. g) Cycling performance of the I₂@Al‐TCPP(Fe)‐based Zn‐I₂ pouch cell. h) Cycling performance of the Zn‐I₂ battery with the I₂@Al‐TCPP(Fe) cathode at 50C. i) Comparison of the cycling performance with previously reported iodine cathodes.

Nitrogen (N₂) adsorption isotherms measured at 77 K revealed that the Al‐TCPP(Fe) MOFs possess a specific surface area of 761.48 m² g⁻¹ and a pore size distribution centered at 2.4 nm (Figure 2i). Although activated carbon (AC) exhibited a larger specific surface area (1301.56 m² g⁻¹, Figure S5, Supporting Information), its larger average pore diameter (3.97 nm) provides limited confinement for iodine, potentially proving less effective in mitigating iodine loss. Thermogravimetric analysis (TGA, Figure S6, Supporting Information) indicated that both AC and Al‐TCPP(Fe) MOFs, possessing well‐defined porous structures, accommodate a greater amount of the active material (iodine) compared to amorphous TCPP(Fe), highlighting the role of spatial confinement. The main peak in the derivative thermogravimetric (DTG) curve for Al‐TCPP(Fe) MOFs occurred at a higher temperature (197 °C) than that for AC (184 °C), signifying that elevated temperatures are required to release iodine from the Al‐TCPP(Fe) host, indicative of stronger iodine adsorption. Furthermore, the broader and somewhat hierarchical peak shape observed for Al‐TCPP(Fe) MOFs suggests a range of interaction strengths between iodine molecules and potentially diverse pore environments or active sites within the MOF structure. The presence of numerous active sites and excellent thermal stability affirms the suitability of the Al‐TCPP(Fe) MOF as a host material for iodine loading.

Additionally, X‐ray photoelectron spectroscopy (XPS) was employed for in‐depth analysis of the surface elemental composition and chemical states. In the high‐resolution N 1s spectrum of the TCPP organic ligand (Figure S7a–c, Supporting Information), peaks at binding energies of ≈393 and 395 eV were assigned to unprotonated pyridinic‐like (═N─) and protonated pyrrolic‐like (N─H) nitrogen atoms within the porphyrin core,^{[ 37 ]} respectively. The high‐resolution N 1s spectrum of the TCPP(Fe) precursor (Figure S8d–g, Supporting Information) revealed that upon iron incorporation, the peak associated with unprotonated nitrogen intensified due to coordination with iron (Figure S8f, Supporting Information), while a feature at ≈396 eV was attributed to residual uncoordinated porphyrin nitrogen or nitrogen signals from potential axial ligands.^{[ 38 ]} The significant differences between the N 1s spectra of TCPP and TCPP(Fe) confirm the transition from protonated/unprotonated states to a fully coordinated state, indicating the successful formation of the Fe‐N₄ coordination structure. The Fe 2p spectrum exhibited peaks for Fe 2p_3/2 and Fe 2p_1/2 at ≈706.88 and 719.96 eV, respectively, accompanied by satellite peaks arising from spin‐orbit coupling.^{[ 35} , ^{39 ]} The Fe 2p_3/2 main peak position at 706.88 eV suggests an iron valence state intermediate between Fe(0) and Fe(II).

Upon incorporation of Al, the O 1s spectrum of Al‐TCPP(Fe) (Figure S9b, Supporting Information) showed significant changes. The peak around 533.5 eV, characteristic of hydroxyl oxygen (O─H) in the carboxylic acid group, diminished or disappeared. Concurrently, a dominant peak emerged at lower binding energies (≈531–532 eV), attributed to the carboxylate oxygen (COO⁻) coordinated to aluminum (Al─O).^{[ 40 ]} This shift indicates that the chemical environments of the two oxygen atoms become equivalent or similar upon deprotonation and coordination. Coordinated water molecules potentially bound to the Al nodes could also contribute a signal in this range. Compared to pristine TCPP, the transformation of the O 1s spectrum in Al‐TCPP(Fe) from a structure representing both C═O and O─H in ─COOH to predominantly a single peak characteristic of carboxylate oxygen confirms the coordination of carboxyl groups to Al, reflecting deprotonation and Al─O bond formation.^{[ 41 ]} Analysis of the high‐resolution Al 2p spectrum (Figure S9e, Supporting Information) revealed a binding energy slightly lower than that typically observed for Al₂O₃ (around 77 eV).^{[ 42 ]} This negative shift is attributed to electron donation from the coordinating organic ligands, slightly increasing the electron density around the aluminum centers. The Fe 2p high‐resolution spectrum of Al‐TCPP(Fe) showed no significant changes compared to that of TCPP(Fe), indicating that Al introduction did not substantially alter the local chemical environment of the Fe centers. Finally, a comparison of the high‐resolution C 1s spectra (not explicitly shown but implied) for TCPP, TCPP(Fe), and Al‐TCPP(Fe) demonstrated that the introduction of either Fe or Al did not cause significant alterations to the carbon backbone, confirming the structural integrity of the organic linker.

The results indicate that the Al‐TCPP(Fe) MOFs exhibit a 3D structure. Furthermore, their substantial specific surface area and porosity facilitate high iodine loading capacity and minimize the loss of the active species, fully leveraging the material's inherent spatial confinement effect. Additionally, the Fe‐N₄ active centers within the material serve as catalysts for rapid iodine redox reactions, potentially via the quantum size effect. This catalytic function effectively accelerates I₂ nucleation and enhances reaction kinetics, consequently mitigating the shuttle effect.

The electrochemical performance of Zn‐I₂ batteries utilizing I₂@AC, I₂@TCPP(Fe), and I₂@Al‐TCPP(Fe) as cathode materials was investigated. The cyclic voltammetry (CV) curve for the Zn‐I₂ battery employing the I₂@Al‐TCPP(Fe) cathode exhibited a pair of redox peaks (Figure 4a). Specifically, the oxidation and reduction peaks were observed at 1.242 and 1.16 V, respectively, resulting in a potential difference (ΔEp) between these peaks of ≈82 mV. In comparison, the ΔEp values for I₂@TCPP(Fe) and I₂@AC were 70 and 93 mV, respectively. This indicates that both I₂@Al‐TCPP(Fe) and I₂@TCPP(Fe) possess favorable reaction kinetics, facilitating rapid electron transfer within the material.^{[ 43 ]} As depicted in Figure 3b, the Tafel slope determined from the oxidation peak was 78 mV dec⁻¹ for I₂@Al‐TCPP(Fe) and 77 mV dec⁻¹ for I₂@TCPP(Fe), whereas it was 95 mV dec⁻¹ for I₂@AC. For the reduction process (Figure 3c), the Tafel slopes for the Zn‐I₂ battery configured with I₂@AC, I₂@TCPP(Fe), and I₂@Al‐TCPP(Fe) cathodes were 196, 183, and 178 mV dec⁻¹, respectively. These results suggest that for both oxidation and reduction, I₂@Al‐TCPP(Fe) exhibits lower reaction resistance, thereby promoting expedited catalysis. Consequently, the two materials featuring Fe‐N₄ catalytic centers exhibit high electrocatalytic activity toward the I₂/I⁻ conversion, effectively alleviating the issue of sluggish kinetics commonly observed in zinc‐iodine (Zn‐I₂) batteries. Notably, the I₂@Al‐TCPP(Fe) material demonstrated stable and efficient electrocatalytic activity during cycling, as evidenced by the largely unchanged peak profiles over three consecutive charge‐discharge cycles (Figure S10, Supporting Information). Furthermore, the electrochemical performance of the three materials was compared under varying rate conditions (Figure 3d). It was observed that even upon returning to a 0.5 C rate after cycling at higher rates, the Zn‐I₂ battery with the I₂@Al‐TCPP(Fe) cathode retained a high discharge specific capacity of 211.75 mAh g⁻¹, demonstrating excellent rate capability and cyclic reversibility. Conversely, while I₂@TCPP(Fe) initially exhibited a comparable discharge specific capacity, its performance degraded with increasing cycle number. This degradation is attributed to the structural collapse of the amorphous TCPP(Fe) material, leading to a loss of active catalytic sites and reduced catalytic conversion efficiency for I₂/I⁻. The Zn‐I₂ battery utilizing the I₂@AC cathode exhibited more rapid capacity decay as the rate increased, indicating that materials lacking catalytic centers suffer from sluggish electrode reaction kinetics and consequently deliver lower discharge specific capacity at higher current densities. Additionally, compared to the I₂@AC cathode (41 mV polarization), the galvanostatic discharge‐charge (GDC) curves (Figure S11, Supporting Information) revealed smaller voltage polarization for cathodes based on I₂@Al‐TCPP(Fe) (31 mV) and I₂@TCPP(Fe) (35 mV). These disparities are likely attributable to the catalytic capability of the Fe‐N₄ structure, which significantly promotes polyiodide conversion.

Figure 4.

Electrochemical kinetics and in situ spectroscopic analysis of I₂@Al‐TCPP(Fe) and I₂@AC cathodes. a) CV curves of I₂@Al‐TCPP(Fe) recorded at scan rates ranging from 0.2 to 1.0 mV s⁻¹. b) Corresponding linear fits of log(i) versus log(v). c) Contribution ratios of capacitive and diffusion‐controlled processes for the I₂@Al‐TCPP(Fe) electrode at various scan rates. d) LSV curves of Al‐TCPP(Fe) for the iodine reduction reaction (IRR) at various rotation rates, measured in an electrolyte containing 5 m KI and 0.5 mm I₂. e) LSV curves of AC for the IRR at various rotation rates, measured in the same electrolyte. f) Koutecký–Levich plots derived from the LSV data, along with the calculated electron transfer number (n) for both catalysts. g) In situ Raman spectra of the I₂@Al‐TCPP(Fe) cathode at different discharge/charge states. h) In situ UV spectra of I₂@Al‐TCPP(Fe) cathode at different discharge/charge states.

Figure 3e illustrates the cycling performance of the three distinct cathode materials. In contrast to I₂@TCPP(Fe), which lacks a defined 3D spatial structure, and I₂@AC, devoid of catalytically active centers, the I₂@Al‐TCPP(Fe) cathode maintained a specific capacity of 172.11 mAh g⁻¹ and a capacity retention of 85.55% after 2750 cycles at a C‐rate of 1C. The rapid performance degradation observed for I₂@TCPP(Fe) is attributed to the structural collapse of the amorphous TCPP(Fe) material during cycling, hindering effective catalytic conversion of iodine species. Consequently, Zn‐I₂ batteries utilizing the I₂@TCPP(Fe) cathode experienced substantial capacity decay after ≈400 cycles, primarily due to the pronounced shuttle effect of generated polyiodides, leading ultimately to cell failure. While the I₂@AC cathode exhibited commendable cycling stability, its lack of catalytic centers prevented the full utilization of the theoretical specific capacity of iodine, resulting in a comparatively lower overall discharge capacity. This comparative analysis underscores the synergistic advantages conferred by the combination of highly efficient catalysis, potentially enhanced by quantum size effects, and effective spatial confinement within the I₂@Al‐TCPP(Fe) structure. Owing to these merits, the I₂@Al‐TCPP(Fe) cathode maintains robust catalytic performance even at an ultralow rate(Figure S12a, Supporting Information)—a condition that typically exacerbates the shuttle effect—or with a high iodine loading of up to 10.96 mg cm⁻². Consequently, the corresponding high‐loading Zn‐I₂ cell achieves 1370 stable cycles (Figure S12b, Supporting Information) with an initial specific capacity of 206.5 mAh g⁻¹. During extended cycling tests conducted at 2C (Figure 3f), the I₂@Al‐TCPP(Fe) cathode retained a specific capacity of 163.16 mAh g⁻¹ after 7500 cycles, corresponding to a capacity retention of 82.26%. The pouch cell constructed with an I₂@Al‐TCPP(Fe) cathode delivers a practical ampere‐hour‐scale capacity (Figure 3g) with well‐defined charge‐discharge characteristics (Figure S13, Supporting Information). As a proof‐of‐concept demonstration, the cell successfully powers a small electrical device (Figure S14, Supporting Information), highlighting its potential for real‐world applications. Remarkably, under demanding high‐rate testing conditions at 50C (Figure 3h), the cell endured over 54 000 cycles with minimal capacity decay per cycle, highlighting the exceptional potential of this Zn‐I₂ battery configuration for fast‐charging applications. The performance metrics achieved with the I₂@Al‐TCPP(Fe) cathode are comparable to, and in several aspects surpass, those of various previously reported iodine‐based cathodes (Figure 3i; Table S2, Support Information).

To elucidate the underlying charge storage mechanisms, the redox chemistry of the cathodes was investigated. Cyclic voltammetry (CV) curves were recorded for the I₂@AC, I₂@TCPP(Fe), and I₂@Al‐TCPP(Fe) cathodes at scan rates ranging from 0.2 to 1.0 mV s⁻¹ (Figure 4a; Figures S15–S17, Supporting Information). Corresponding b‐values and the proportions of capacitive contribution were determined from these data. For the I₂@Al‐TCPP(Fe) cathode, the peak potentials exhibited minimal shifts with increasing scan rate, indicating the high electrochemical reversibility of the iodine redox reactions within this electrode. The calculated b‐values for the redox peaks (denoted as peak 1 and peak 2) of I₂@Al‐TCPP(Fe) were 0.84 and 0.95, respectively. These values, approaching 1.0, suggest that the I₂/I⁻ redox kinetics are predominantly governed by surface‐controlled capacitive processes rather than diffusion‐limited processes.^{[ 44 ]} Moreover, the capacitive contribution to the total charge storage for I₂@Al‐TCPP(Fe) increased from 57.54% at 0.2 mV s⁻¹ to 75.83% at 1.0 mV s⁻¹, notably exceeding the contributions observed for the I₂@AC and I₂@TCPP(Fe) cathodes under similar conditions (Figures S13 and S14, Supporting Information). This predominantly capacitive behavior is advantageous, correlating with enhanced specific capacity and superior rate performance. Concurrently, the lower charge transfer resistance associated with such processes contributes to improved cyclic stability.^{[ 45} , ^{46 ]} These electrochemical advantages are plausibly attributed to the efficient electrocatalytic activity originating from quantum size effects associated with the Fe‐N₄ centers within the metal‐organic framework (MOF) structure.

In Zn‐I₂ batteries, the number of transferred electrons is intimately linked to the reaction mechanism.^{[ 47} , ^{48 ]} The iodine cathode can undergo various conversion pathways, such as the I⁻/I₂ redox couple^{[ 49} , ^{50 ]} and reactions involving polyiodides,^{[ 51 ]} IO₃ ⁻,^{[ 52} , ^{53 ]} or I⁺.^{[ 54 ]} To systematically determine the electron transfer number for the iodine reduction reaction (IRR), we performed rotating disk electrode (RDE) measurements at various rotation speeds of 400, 900, 1600, and 2500 rpm (Figure S18a, Supporting Information). Subsequently, the relationship between rotation speed and current was derived from the data in Figure 4d,e, and Figure S18b (Supporting Information), as plotted in Figure 4f. According to the Koutecký‐Levich (K‐L) equation, the electron transfer number for I₂ in the presence of the Al‐TCPP(Fe) catalyst was calculated to be 1.98, which corroborates a nearly ideal two‐electron conversion between I₂ and I⁻. Furthermore, the Al‐TCPP(Fe) MOF facilitates the IRR by forming charge‐transfer complexes with molecular iodine, leading to accelerated kinetics and a catalytic performance that surpasses that of conventional activated carbon (AC).

Crucially, in situ Raman spectroscopy was employed to investigate the I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC cathodes in a 2 m ZnSO₄ electrolyte. This analysis elucidated the I₂/I⁻ conversion mechanism in Zn‐I₂ batteries, thereby providing further insight into how the synergistic effect of quantum size effects and spatial confinement enhances the electrochemical performance of these batteries. The in situ Raman spectra clearly revealed the formation of intermediates I₃ ⁻ (104 cm⁻¹) and I₅ ⁻ (165 cm⁻¹) during the charge/discharge cycles of the Zn‐I₂ battery.^{[ 55} , ^{56 ]} For the battery utilizing the I₂@Al‐TCPP(Fe) cathode, the signals corresponding to both I₃ ⁻ and I₅ ⁻ were consistently weak throughout cycling (Figure 4g). This demonstrates that the microporous Al‐TCPP(Fe) MOF material, featuring Fe‐N₄ sites, effectively catalyzes the reversible conversion of iodine species (I₂ ↔ I₅ ⁻ ↔ I₃ ⁻). Furthermore, the confinement effect within the micropores also effectively suppressed polyiodide shuttling. In contrast, for the battery with the I₂@TCPP(Fe) cathode, although it also possessed Fe‐N₄ catalytic centers, structural collapse during cycling led to the deactivation of these centers and a gradual decrease in catalytic performance. Consequently, partial polyiodide shuttling occurred, resulting in slightly higher polyiodide signals compared to the Al‐TCPP(Fe) cathode (Figure S19a, Supporting Information). Conversely, with the I₂@AC cathode material, the polyiodide signals increased rapidly during charging, reaching high intensities. Moreover, the I₅ ⁻ signal persisted even after discharge to the cutoff voltage (Figure S20a, Supporting Information). These excessive peak intensities suggest poor reversibility in the conversion of iodine intermediates and limited beneficial chemical interactions with the host, indicating that the polyiodide shuttle effect was not effectively suppressed. In situ UV–vis spectroscopy was employed to further elucidate the conversion behavior of iodine species during the charge‐discharge processes (Figure S21, Supporting Information). Compared with the I₂@Al‐TCPP(Fe) cathode (Figure 4h), the I₂@TCPP(Fe) cathode exhibited a considerably lower absorbance in its UV–vis spectrum (Figure S19b, Supporting Information). This is attributed to the highly efficient catalytic centers within its structure, which facilitate rapid kinetics for the iodine reduction reaction (IRR) during the initial charge‐discharge cycle. Consequently, the generation of excess polyiodide ions is suppressed. This observation is consistent with the comparable electrochemical performance of I₂@TCPP(Fe) and I₂@Al‐TCPP(Fe) during the early stages of long‐term cycling. In contrast, the I₂@AC cathode demonstrated significant absorption peaks at 288.3 and 351.5 nm during the discharge process^{[ 57} , ^{58 ]} (Figure S20b, Supporting Information), which are ascribed to the formation of I₃ ⁻ polyiodide ions, likely generated through parasitic reactions and/or the shuttle effect.

DFT calculations were employed to gain detailed insights into the interactions between three distinct materials and various iodine species. For the AC material (Figure S22a,b, Supporting Information), the adsorption of iodine is predominantly characterized by physisorption, lacking significant charge transfer or distinct adsorption sites.^{[ 59 ]} In contrast, the TCPP(Fe) material's (Figure S23a,b, Supporting Information) porphyrin core exhibited pronounced electron accumulation/depletion regions, indicating a stronger polarization effect toward iodine species, which led to charge redistribution around the central Fe atom. Concurrently, corresponding regions within the porphyrin ring demonstrated a degree of positive charge accumulation, suggesting the formation of π‐iodine charge‐transfer interactions that facilitate the effective adsorption of iodine species. Following iodine adsorption, the Al‐TCPP(Fe) material (Figure S24a,b, Supporting Information) displayed electron density rearrangement over a broader range and with greater intensity compared to the TCPP(Fe) material, indicative of multi‐site, multi‐center interactions. As depicted in Figure S25a (Supporting Information), the Electron Localization Function (ELF) analysis for I⁻ adsorption on AC also confirmed the physisorptive nature of their interaction, revealing no significant charge transfer or covalent bond formation. Conversely, the interactions between the Fe atoms in both Al‐TCPP(Fe) and TCPP(Fe) materials and the iodide ion (I⁻) (Figure S25b, Supporting Information; Figure 5d) exhibited a strong propensity for chemisorption, particularly involving covalent interactions with the Fe atoms.^{[ 47 ]} Bader charge analysis corroborated this (Figure 5a–c), demonstrating significant charge transfer involving the Fe atoms in the Al‐TCPP(Fe) material, signifying a stronger interaction between Al‐TCPP(Fe) and the iodide ion.

Figure 5.

Computational analysis of the interaction between Al‐TCPP(Fe) and iodine species. a) Bader charge analysis of Al‐TCPP(Fe) before interaction with elemental iodine (I₂). b,c) Bader charge analysis of Al‐TCPP(Fe) after interaction with I₂. d) Electron Localization Function (ELF) map for I⁻ adsorbed on Al‐TCPP(Fe). e) Spin density map of Al‐TCPP(Fe). f) Projected Density of States (PDOS) and corresponding d‐band centers of Al‐TCPP(Fe) before and after interaction with I₂. g) PDOS and corresponding p‐band centers of isolated I₂ compared to I₂ interacting with Al‐TCPP(Fe), TCPP(Fe), and AC. h) Calculated adsorption energies of iodine species on the three materials (Al‐TCPP(Fe), TCPP(Fe), and AC). i) Gibbs free energy diagrams illustrating the reduction pathway of I₂ on Al‐TCPP(Fe), TCPP(Fe), and AC.

Spin density calculations reveal a high localization of spin density near the Fe atoms within the Al‐TCPP(Fe) material, indicating a greater contribution of unpaired spin electrons to the material's reactivity^{[ 60 ]} (Figure 5e). This increased spin density near the Fe atoms in Al‐TCPP(Fe) suggests enhanced reactivity, particularly for catalytic processes involving redox reactions with iodine species. This phenomenon is attributed to the quantum size effect associated with the Fe sites; as the effective particle size diminishes, the electronic energy levels near the Fermi level transition from quasi‐continuous to discrete (Figure S26, Supporting Information; Figure 5f). This transition is accompanied by an upward shift of the d‐band center, which is known to correlate with enhanced catalytic performance. Upon interaction between molecular iodine (I₂) and the Fe atoms in Al‐TCPP(Fe), the d‐band center shifts upward from −1.544 to −1.087 eV. This shift signifies enhanced charge transfer between iodine and iron, thereby facilitating the I⁻/I₂ redox reaction. To further evaluate the interaction between I₂ and the different materials, the Partial Density of States (PDOS) of I₂ and the corresponding p‐band centers were calculated (Figure 5g). Compared to the relatively isolated electronic states of pure I₂, the continuous PDOS patterns for I₂ adsorbed on the three materials exhibit significant distribution around the Fermi level, indicating substantial orbital hybridization between iodine and the substrates.^{[ 14 ]} The p‐band center for I₂ adsorbed on Al‐TCPP(Fe) (I₂@Al‐TCPP(Fe)) is located at −1.779 eV. This value is closer to the Fermi level compared to those for I₂@TCPP(Fe) and I₂@AC, suggesting that I₂ on Al‐TCPP(Fe) is more readily activated for reaction.

Owing to pronounced charge transfer and electron orbital hybridization, the Al‐TCPP(Fe) material demonstrates significantly stronger calculated adsorption affinity for iodine species compared to the other two materials investigated^{[ 61 ]} (Figure 5h). RDE measurements indicate a 2‐electron transfer pathway for the IRR, a finding that is corroborated by our theoretical calculations (detailed in the Supporting Information). Analysis of the Gibbs free energy profile for the reduction of iodine to iodide ions further corroborated the superior catalytic activity of TCPP(Fe) and Al‐TCPP(Fe) relative to AC (Figure 5i). In the rate‐determining step (RDS) of the I₃ ⁻ ↔ I⁻ reaction, the calculated Gibbs free energy barrier (ΔG) for I₂@Al‐TCPP(Fe) was 0.99 eV, which is substantially lower than the barriers calculated for I₂@AC (1.27 eV) and I₂@TCPP(Fe) (1.46 eV). This finding indicates that the Fe‐N₄ sites within the I₂@Al‐TCPP(Fe) cathode host material effectively accelerate polyiodide conversion, thereby mitigating the detrimental I₃ ⁻ shuttle effect. Considering the overall reaction energy barriers, the values for I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC were determined to be 2.11, 2.12, and 2.29 eV, respectively. The lower overall barrier for I₂@Al‐TCPP(Fe) suggests a more favorable thermodynamic pathway and faster kinetics for the reversible electrochemical reaction, underscoring its superior catalytic performance.

Classical MD) simulations were employed to evaluate the ability of three materials to confine the diffusion of iodine (I₂) under pristine, charged, and discharged conditions. Representative snapshots are presented to visualize the states of the various components before and after the simulation.^{[ 62} , ^{63 ]} Under pristine conditions, diffusion coefficients calculated from Mean Squared Displacement (MSD) analysis indicated that I₂ diffusion was lowest in Al‐TCPP(Fe), signifying substantial restriction of iodine mobility (Figure 6a). Furthermore, during simulated charging and discharging processes, the diffusion coefficient within Al‐TCPP(Fe) remained consistently lower than those observed for the other two materials (Figure S27a,b, Supporting Information). Radial Distribution Function (RDF) analysis for Al‐TCPP(Fe) revealed the emergence of a new peak at 3.24 Å during charge/discharge cycles (Figure S28a, Supporting Information), suggesting that iron atoms consistently maintain an optimal distance for efficient catalytic adsorption of iodine species throughout battery operation (Figure S24a, Supporting Information). In contrast, TCPP(Fe) exhibited structural instability, resulting in larger average distances between the catalytic sites and iodine species throughout the simulation compared to Al‐TCPP(Fe) (Figure S28b, Supporting Information). Snapshots from the MD simulations further illustrated the structural instability of TCPP(Fe) (Figure S27c, Supporting Information), showing its propensity to collapse. This structural degradation likely leads to the deactivation of catalytic centers, thereby reducing catalytic efficiency and negatively impacting the electrochemical performance and cycling stability of the corresponding zinc‐iodine battery. Conversely, Al‐TCPP(Fe) maintained its structural integrity and stable 3D framework throughout extended simulation times (Figure 6b). This stability facilitates both the efficient catalysis by the Fe‐N₄ moieties and the suppression of polysulfide species via spatial confinement. Complementary COMSOL Multiphysics simulations corroborated the superior ability of Al‐TCPP(Fe) to mitigate the polyiodide shuttle effect.^{[ 64 ]} The Al‐TCPP(Fe) model, characterized by smaller pore apertures (Figure 6c), effectively confines iodine within its channels, preventing dissolution into the electrolyte and minimizing active material loss. Conversely, the I₂@TCPP(Fe) model demonstrated that adsorption alone is insufficient to restrict iodine diffusion effectively (Figure S29, Supporting Information). Moreover, the potential dissolution of TCPP(Fe) itself in the electrolyte could exacerbate the diffusion of iodine species within the electrode material. Similarly, the large pore structure of the I₂@AC model exhibited poor iodine containment, leading to gradual dissolution into the electrolyte and consequent loss of active material. Collectively, these theoretical calculations indicate that the unique 3D spatial configuration of the Al‐TCPP(Fe) MOF material imparts both outstanding catalytic performance and effective spatial confinement, thereby enhancing reaction kinetics and significantly suppressing the detrimental polyiodide shuttle effect.

Figure 6.

Analysis of iodine confinement dynamics and electrode characterization in Zn‐I₂ batteries. a) MSD plots of I₂ molecules within Al‐TCPP(Fe), TCPP(Fe), and AC under ambient conditions. b) Snapshots of the Al‐TCPP(Fe) system at the start (top) and after 100 ns (bottom) of MD simulation. c) COMSOL Multiphysics simulation results showing the I₂ concentration distribution within I₂@Al‐TCPP(Fe) and I₂@AC models during the discharge process. d) Depth‐profiled I 3d X‐ray photoelectron spectroscopy (XPS) spectra of the I₂@Al‐TCPP(Fe) cathode after cycling in a Zn‐I₂ battery. e) Depth‐profiled I 3d XPS spectra of the I₂@AC cathode after cycling in a Zn‐I₂ battery. f) FIB‐SEM image of the zinc anode after cycling in a Zn‐I₂ battery utilizing the I₂@Al‐TCPP(Fe) cathode. g) 3D reconstructed TOF‐SIMS images of the zinc anode after cycling in Zn‐I₂ batteries employing (top) I₂@Al‐TCPP(Fe) and (bottom) I₂@TCPP(Fe) cathodes. h) XRD pattern of the zinc anode after 100 cycles.

To evaluate the structural stability of Al‐TCPP(Fe) MOFs as an iodine host material, a suite of physical characterizations was performed. SEM was employed to examine the morphology of cathode materials comprising I₂@Al‐TCPP(Fe), I₂@TCPP(Fe), and I₂@AC after 100 cycles in Zn‐I₂ batteries. The SEM images revealed that the I₂@Al‐TCPP(Fe) cathode maintained a smooth surface morphology without significant evidence of structural collapse (Figure S30a, Supporting Information). In contrast, both the I₂@TCPP(Fe) and I₂@AC cathodes exhibited noticeable morphological degradation (Figure S30b,c, Supporting Information). Furthermore, XPS confirmed the integrity of the MOF structure post‐cycling. The high‐resolution N 1s spectrum (Figure S31a, Supporting Information) indicated the persistent presence of Fe─N coordination bonds, confirming that the coordination interaction between Fe and N was preserved after cycling. Depth profile analysis via Ar⁺ sputtering demonstrated a progressive increase in the signal intensities of both the Fe─N bonds (Figure S31b, Supporting Information) and the Al‐O components associated with the Al(OH)O₄ metal nodes (Figure S31c, Supporting Information) with increasing etching depth. This finding confirms the stability of the fundamental Fe‐N₄ structural units and Al(OH)O₄ metal nodes within the bulk of the Al‐TCPP(Fe) MOF material integrated into the cathode. The consistent detection of these characteristic XPS signals, representing the basic building blocks of the MOF, underscores the high structural stability of the material. Reflecting the enhanced structural stability of the Al‐TCPP(Fe) MOF host during cycling, XPS analysis of the corresponding zinc anode surface revealed a higher iodine signal intensity when paired with the I₂@Al‐TCPP(Fe) cathode compared to systems using I₂@TCPP(Fe) or I₂@AC cathodes (Figure S32, Supporting Information). Moreover, Ar⁺ depth profiling of the cycled I₂@Al‐TCPP(Fe) cathode itself showed a gradually increasing iodine signal with etching depth, suggesting that the Al‐TCPP(Fe) material effectively confines the iodine active species within its structure, thereby mitigating active material loss(Figure 6d). Conversely, the cycled I₂@AC and I₂@TCPP(Fe) cathodes exhibited a much weaker overall iodine signal, which showed no significant intensification upon Ar⁺ sputtering, indicating poor retention of the iodine active species(Figure 6e; Figure S33, Supporting Information).

Owing to the robust confinement of iodine and iodide species by Al‐TCPP(Fe), polyiodide anions are effectively anchored within the cathode during cycling. This strategy effectively mitigates the shuttle effect and prevents polyiodide‐induced corrosion of the zinc anode, thereby enhancing the battery's cycling stability. Under the same test conditions, SEM images (Figure S34, Supporting Information) reveal that the zinc anode in the Zn‐I₂ cell employing the I₂@AC cathode exhibits significant polyiodide‐induced corrosion after cycling, indicative of a severe shuttle effect. In contrast, the zinc anode surface in the cell utilizing the I₂@Al‐TCPP(Fe) cathode remains smooth and free from corrosion marks after cycling. Focused ion beam scanning electron microscopy (FIB‐SEM) cross‐sectional imaging of the zinc anode cycled with the I₂@Al‐TCPP(Fe) cathode reveals a smooth and intact surface(Figure 6f). This condition facilitates efficient Zn deposition while minimizing the formation of byproducts and Zn dendrites. Conversely, anodes cycled with cathodes based on the other two materials displayed severe corrosion (Figure S35, Supporting Information). 3D reconstructed Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS) imaging of the zinc anode, after cycling against the I₂@Al‐TCPP(Fe) cathode, reveals a negligible distribution of I₃ ⁻ species (Figure 6g; Figure S36, Supporting Information). Moreover, the major constituents of the solid electrolyte interphase (SEI) layer on the electrode surface remain well‐preserved, facilitating subsequent Zn²⁺ plating and stripping (Figure S37, Supporting Information). Complementary XPS analyses indicate minimal iodine signals both on the surface and within the bulk of this anode (Figure S38, Supporting Information), underscoring the superior ability of the Al‐TCPP(Fe) material to inhibit polyiodide shuttling. XRD was employed to identify the byproducts formed on the zinc anode during cycling (Figure 6h). Apart from a peak at 2θ = 12.23°, the other high‐intensity diffraction peaks are assigned to metallic zinc. The peak at 2θ = 12.23° corresponds to the (001) plane of basic zinc sulfate hydrate (Zn₄SO₄(OH)₆·4H₂O), identified as a common byproduct formed on the zinc anode during cycling, the excessive accumulation of which is detrimental to long‐term cell performance. Notably, under identical testing conditions, the diffraction peak intensity corresponding to this byproduct was minimal for the anode cycled with the I₂@Al‐TCPP(Fe) cathode, indicating a significant suppression of parasitic side reactions. These findings collectively demonstrate that Al‐TCPP(Fe) effectively suppresses the polyiodide shuttle effect, preventing both the corrosion of the zinc anode and associated parasitic reactions, thereby enabling the realization of high‐performance, stable Zn‐I₂ batteries with minimized shuttle phenomena.

3. Conclusion

In this study, by integrating the quantum size effect with spatial confinement, we fabricated 3D spatially coordinated Al‐TCPP(Fe) MOFs featuring highly efficient Fe‐N₄ catalytic centers to serve as an iodine host material for Zn‐I₂ batteries. This design effectively confines iodine redox reactions within a suitable porous architecture, thereby significantly mitigating the polyiodide shuttle effect. Enhanced adsorption affinity between the constituent iron atoms and iodine species arises through charge transfer and orbital hybridization, which also effectively lowers the energy barrier for polyiodide conversion. Furthermore, the intricate 3D spatial structure physically hinders the shuttle behavior of iodine species. Consequently, the resulting I₂@Al‐TCPP(Fe) cathode exhibits a high reversible capacity (172.11 mAh g⁻¹ at 1C after 2750 cycles) and excellent cycling stability (107.9 mAh g⁻¹ at 50C after 54 000 cycles). Moreover, even under a high iodine loading of 10.96 mg cm^{− 2}, the cathode maintains 78.9% of its initial capacity after 1370 cycles, demonstrating significant potential for practical applications. This synergistic strategy, combining the quantum size effect and spatial confinement, offers valuable insights for the rational design of advanced Zn‐I₂ batteries.

Conflict of Interest

The authors declare no conflict of interest.

Supporting information

Supporting Information

Li S., Nie Y., Wang Y., et al. “Quantum Size Effect Synergizes Space‐Limited Domain Action for Advanced Aqueous Zinc‐Iodine Batteries.” Adv. Mater. 38, no. 4 (2026): e14577. 10.1002/adma.202514577

Data Availability Statement

Research data are not shared.