Halogen Bonding‐Sustained Accumulation of Polyiodide in Hierarchically Open Micellar Film for Shuttle‐Free Long‐Duration Zn‐I₂ Battery

ABSTRACT

Polyiodides shuttling normally leads to low coulombic efficiency and rapid capacity fading under extended charging‐discharging durations, thereby limiting the application of Zn‐I₂ batteries in long‐duration energy storage (LDES). In this study, self‐assembled film of polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) spherical micelles on activated carbon (AC) is employed as a host for iodine species. The PS‐b‐P2VP micellar film provides abundant spatially distributed pyridyl groups for massive accumulation of iodine through halogen bonding. Moreover, compared to the dense film of P2VP homopolymer, the brush‐like P2VP corona within the PS‐b‐P2VP micellar film creates a hierarchically open platform that facilitate the deep diffusion and robust encapsulation of iodine species. Such distinct structural feature remarkably suppresses the shuttling effect of polyiodides in prolonged charging‐discharging duration. Thus, the resulting AC/PS‐b‐P2VP@I₂ cathode reveals high coulombic efficiency of 97.3% and high capacity of 191.6 mAh g⁻¹ under a long charging‐discharging duration exceeding 20 h, maintaining 96.8% capacity over 2000 h (100 cycles). Furthermore, the assembled Zn‐I₂ pouch cell demonstrates exceptional performance by powering an LED display screen for over 9.7 h, following a 24‐h rest after fully charged, highlighting its promising potential for LDES applications.

A self‐assembled PS‐b‐P2VP micellar film is constructed as an efficient host for iodine species, where the brush‐like P2VP corona provides abundant pyridyl groups for halogen bonding and forms hierarchically open nanoscale gaps for robust iodine encapsulation. The assembled Zn‐I₂ pouch cell continuously powered an LED display screen for more than 9.7 h.

1. Introduction

Sustained growth in the global economy and population has significantly increased the demand for renewable energy, especially solar and wind energy. Nevertheless, the intermittent property of renewable energy threatens the electric reliability [1]. On the other hand, the utilization of electrical energy by grid users demonstrates a cyclical pattern, wherein electricity are elevated during peak demand periods and reduced during off‐peak times (Figure S1). Long‐duration energy storage (LDES) technology, typically possessing a continuous discharge duration exceeding 4 h, offers a promising solution to these challenges [2, 3]. Such technology requires high coulombic efficiency during a single cycle under prolonged charging‐discharging durations, as well as high capacity retention after long periods of rest and long‐term cycling. Among the various electrochemical energy storage technologies, zinc‐ion batteries (ZIBs) possess distinct advantages such as high safety, environmental friendliness, abundant in raw materials, and ease of fabrication [4, 5]. However, most research has focused on the electrochemical behavior of ZIBs under short charging‐discharging durations (Table S1). One of the major challenges hindering the application of ZIBs in LDES lies in the absence of a cathode with sufficient structural and electrochemical stability. Recently, iodine cathode has drawn significant interest because of its low toxicity, high output voltage (1.29 V vs. Zn/Zn²⁺), high theoretical capacity of 211 mAh g⁻¹, and especially reversible I⁻/I₂ redox reaction [6, 7]. Nevertheless, Zn‐iodine (Zn‐I₂) batteries are typically plagued by the shuttle effect of polyiodides [8], leading to decreased coulombic efficiency and faded capacity, especially in prolonged charging‐discharging processes (Figure 1a).

FIGURE 1.

Cathode design for shuttle‐free Zn‐I₂ Battery. (a) Schematic illustration of the shuttling effect in Zn‐I₂ battery under prolonged charging‐discharging durations. (b) Schematic illustration of typical host materials for confining polyiodide species. (c) PS‐b‐P2VP micellar film developed in this work for robust encapsulation of iodine.

Modification of cathode with host materials has emerged as a widely adopted strategy to confine polyiodide species (Figure 1b), thus suppressing the shuttling effect [9, 10, 11]. A variety of materials, such as active carbon [12], graphene [13], and MXene [10], were extensively utilized to immobilize iodine species (e.g., I₂ and I₃ ⁻) within the cathode via physical adsorption. Biomass composites with chemical adsorption sites have also been developed to stabilize iodine species through the synergy of nano‐confinement and chemical adsorption. For example, natural starch with a double‐helix structure has been introduced as a host to immobilize iodine species (I₂, I⁻, I₃ ⁻, I₅ ⁻) [14]. Further progress has been achieved through the incorporation of ordered framework materials, including covalent organic frameworks (COFs) [15, 16], covalent organic cages [17], and metal‐organic frameworks (MOFs) [18, 19], which provide abundant heteroatom‐based adsorption sites (e.g., S, N, and O) to restrict polyiodide migration. For instance, N_x‐COFs with adjustable nitrogen content were developed as effective host materials for immobilizing iodine species and the assembled Zn‐I₂ battery delivered stable cycling for over 6000 cycles with high capacity retention of 80% at 2.0 A g⁻¹ [20]. Although the cycling stability of Zn‐I₂ batteries at relatively high current densities (thus short charging‐discharging durations, Table S1) has been extensively studied, it remains a critical challenge to achieve high coulombic efficiency in each cycle under prolonged charging‐discharging durations and maintain excellent capacity retention after long periods of rest and long‐term cycling. This is primarily attributed to the oversized or blocked pores and poorly exposed chemical adsorption sites within the host materials, which are inadequate to effectively retain iodine throughout a long period.

In this study, we employ micellar film of polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) block copolymer as a host layer for iodine species (Figure 1c). The P2VP corona is rich in 3D distributed electron‐donating pyridyl groups, which readily form relatively strong halogen bonds with iodine species. The hierarchically structured brush‐like P2VP corona in the PS‐b‐P2VP micellar film also provides open and interconnected nanoscale gaps, which facilitate the robust and massive encapsulation of iodine. The integrated Zn‐I₂ battery reveals a high coulombic efficiency of 97.3% under ultra‐long charging‐discharging durations (20 h), and maintains a capacity retention of 96.8% after operating for over 2000 h. The PS‐b‐P2VP micellar film efficiently inhibits the diffusion of polyiodides into the electrolyte under prolonged charging‐discharging duration and thus enables the practical utilization of Zn‐I₂ battery in LDES.

2. Results and Discussion

The fabrication process of the iodine cathode was schematically illustrated in Figure 2a. First, activated carbon (AC), Ketjen black (particle size: ∼40 nm), and polyvinylidene fluoride were uniformly suspended in N‐methyl‐2‐pyrrolidone by magnetic stirring to prepare a slurry, which was then coated onto a titanium mesh. After oven drying at 80°C, a spherical micellar film was formed on the surface of the blocky AC by drop‐coating a solution of PS‐b‐P2VP micelles in tetrahydrofuran (THF), followed by rapid evaporation of the solvent. Subsequently, the AC host coated with the micellar film was immersed in an aqueous solution containing 0.5 M ZnI₂ and 0.5 M KI, and subjected to an electrochemical plating process for the deposition of iodine. As control experiments, the cathodes with pristine AC, PS‐decorated AC, and P2VP‐decorated AC were also electrochemically deposited with iodine (Figures S2–S4). Scanning electron microscopy (SEM) images showed that the resulting AC in the AC/PS‐b‐P2VP@I₂ cathode was uniformly covered by a layer of spherical nanoparticles (Figures 2b and S5), corresponding to the morphology of PS‐b‐P2VP micellar film [21]. Elemental mapping confirmed the successful loading of iodine on the AC/PS‐b‐P2VP host. Notably, iodine species were abundantly detected in the internal regions of PS‐b‐P2VP micellar film, as indicated by the cross‐section SEM image and elemental mapping analyses (Figure S6). Transmission electron microscopy (TEM) images of the AC/PS‐b‐P2VP@I₂ cathodes further demonstrated that the AC was surrounded by a layer of PS‐b‐P2VP spherical micelles (Figure S7).

FIGURE 2.

Fabrication and analyses of AC/PS‐b‐P2VP@I₂ cathode. (a) Schematic diagram showing the fabrication process of the AC/PS‐b‐P2VP@I₂ cathode. (b) SEM micrographs of the AC/PS‐b‐P2VP@I₂ cathode. (c) XPS spectra of N 1s for the AC/PS‐b‐P2VP@I₂ cathode with iodine loadings of 2.5, 5.0, and 10.0 mg cm⁻². (d and e) UV‐vis spectra of the mixed electrolyte (after 60× dilution) sampled during the plating process with AC/PS‐b‐P2VP (d) and AC (e) hosts. (f) Plots of absorbance intensity at 287 nm (corresponding to dissolved I₃ ⁻) derived from the UV‐vis spectra.

X‐ray photoelectron spectroscopy (XPS) spectra of N 1s were employed to investigate the interaction between the PS‐b‐P2VP micellar film and iodine species. AC/PS‐b‐P2VP@I₂ cathodes with different iodine loadings were prepared by varying the electrochemical plating time. The loading amount of iodine was quantified by the increased weight of the electrodes after plating and vacuum drying. With a low iodine loading of 1.0 mg cm⁻² (Figure S8a), the XPS spectra displayed a strong peak at 399.3 eV belonging to the free‐state pyridyl nitrogen, and a weaker peak at 400.9 eV corresponding to the coordinated pyridyl nitrogen [22, 23]. The XPS peak area ratio of coordinated pyridyl nitrogen to free pyridyl nitrogen in AC/PS‐b‐P2VP at different iodine loadings was presented in Table S2. When increasing the iodine mass loading (Figure 2c), the peak for the free‐state nitrogen remarkably decreased while the peak for the coordinated nitrogen considerably increased, indicating an electron donation to the adsorbed I₂ species, possibly through halogen bonding [24, 25]. On the other hand, Fourier‐transform infrared (FTIR) spectra of the AC/PS‐b‐P2VP host revealed an obvious peak at 1591 cm⁻¹ (Figure S8b), which can be attributed to the C‐N stretching vibration of the pyridyl groups in PS‐b‐P2VP [26]. This peak was considerably weakened and shifted to a smaller wavenumber after the association with iodine, again confirming the formation of strong halogen bonds between the iodine species and the electron‐donating pyridyl groups within the PS‐b‐P2VP micellar film [27, 28].

Optical images acquired during the iodine plating process showed that the surrounding solution of the AC electrode quickly turned brown and became dark after 40 min (Figure S9), suggesting a weak immobilization of iodine. In contrast, the plated iodine was effectively encapsulated within the AC/PS‐b‐P2VP host as the surrounding solution remained in a relatively light brown color after 40 min. UV‐vis spectra acquired during the iodine plating process clearly illustrated that the I₃ ⁻ in the electrolytes can be effectively restricted upon utilizing the AC/PS‐b‐P2VP host (Figures 2d–f and S10).

The electrochemical performance of the AC/PS‐b‐P2VP@I₂ cathode was evaluated using coin cells assembled with zinc foil as the anode and 2 M ZnSO₄ as the electrolyte. The iodine loading was about 10.5 mg cm⁻². After resting for 48 h since fully charged, the AC/PS‐b‐P2VP@I₂ cathode revealed an appealing capacity retention of 94.0%, significantly higher than those of the AC@I₂ (81.5%) and AC/P2VP@I₂ (88.6%) cathodes (Figure 3a,b). Even when the rest period was extended to 72 h, the AC/PS‐b‐P2VP@I₂ cathode retented 87.2% of original capacity (Figure S11). Under an extended charging‐discharging durations of 20.4 h at an ultralow current (0.02 A g⁻¹) the AC/PS‐b‐P2VP@I₂ cathode achieved a high initial coulombic efficiency of 94.3% (Figure 3c). By contrast, the AC/P2VP@I₂ and AC@I₂ cathodes delivered a charging‐discharging durations of 19.3 h and 18.2 h along with a low initial coulombic efficiency of 90.1% and 87.4%, respectively, under the same current density. Notably, the AC/PS‐b‐P2VP@I₂ cathode still retained long charging‐discharging durations of 19.5 h in the 100th cycles (Figure S12). Furthermore, the resulting cathode exhibited a high capacity of 191.6 mAh g⁻¹ and maintained a coulombic efficiency of 97.3% over 100 cycles (2000 h) (Figure 3d). By comparison, the AC@I₂ (Figure 3e), AC/P2VP@I₂ (Figure 3f), and AC/PS@I₂ (Figure S13) cathodes delivered capacities of only 166.1, 183.1, and 147.1 mAh g⁻¹, respectively, accompanied by low coulombic efficiencies of 87.8%, 90.4%, and 87.5%. To further evaluate the practicality of the AC/PS‐b‐P2VP@I₂ cathode for LDES applications, its electrochemical performance was investigated at an ultralow current (0.01 A g⁻¹). As shown in Figure S14, an ultralong charging‐discharging duration of 42.3 h was achieved, along with a high coulombic efficiency of 94.9%. The AC/PS‐b‐P2VP@I₂ cathode exhibited stable operation over 61 cycles, with a high capacity retention of 94.5% (Figure S15).

FIGURE 3.

Electrochemical performance of the AC/PS‐b‐P2VP@I₂ cathode under extended charging‐discharging durations. (a) Voltage–time curves of different cathodes during charging, a 48‐h rest period, and discharging. (b) Capacity retention of different cathodes after a 48‐h rest following full charge. (c) Charging‐discharging duration of different cathodes recorded at an ultra‐low current of 0.02 A g⁻¹ in the 20th cycle. (d–f) Cycling performance of the AC/PS‐b‐P2VP@I₂ (d), AC@I₂ (e) and AC/P2VP@I₂ (f) cathodes under extended charging‐discharging durations at a current density of 0.02 A g⁻¹. Inset: the corresponding voltage‐time curves of different cathodes at the current density of 0.02 A g‐1. (g and h) Schematic representations of the iodine‐stabilizing mechanisms in PS‐b‐P2VP (g) and P2VP (h).

The outstanding electrochemical performance of the AC/PS‐b‐P2VP@I₂ cathode could be majorly attributed to the effective suppression of the polyiodide shuttling effect. The PS‐b‐P2VP micellar film provided abundant, readily accessible, and spatially distributed pyridyl groups that interact strongly with the iodine species via halogen bonding. On the other hand, the brush‐like P2VP corona within the micellar film forms a hierarchically open architecture, enabling deep penetration and robust encapsulation of iodine species. Moreover, the interconnected channels between adjacent P2VP coronas further immobilize iodine species through a pronounced nanoconfinement effect (Figure 3g). In contrast, the P2VP homopolymer in the AC/P2VP@I₂ cathode formed a relatively dense film with occluded pores and inaccessible coordination sites (Figure 3h), which led to low coulombic efficiency and rapid capacity fading under prolonged charging‐discharging duration.

The AC/PS‐b‐P2VP@I₂ cathode exhibited a high capacity of 187.4 mAh g⁻¹ and an average coulombic efficiency of 99.2% at 0.2 A g⁻¹ (Figure S16a). Moreover, the cathode retained 91.8% of its initial capacity after 1500 cycles (2950 h). By contrast, the AC@I₂ cathode showed rapid capacity fading to 143.4 mAh g⁻¹ after only 147 cycles. The AC/P2VP@I₂ and AC/PS@I₂ cathodes delivered relatively lower capacities of 163.7 mAh g⁻¹ after 500 cycles and 144.1 mAh g⁻¹ after 92 cycles (Figure S16b), respectively, under the same current density, primarily due to the migration of iodine species. SEM images of the AC/PS‐b‐P2VP@I₂ cathode after 30 cycles showed that the PS‐b‐P2VP spherical micelles were still uniformly distributed on the AC surface (Figure S17), highlighting the excellent structural stability within the cathode. The cycling stability of the AC/PS‐b‐P2VP@I₂ cathode was compared with that reported in previous studies, taking into account both charging‐discharging duration and current density (Figure S18). The lifespan of the AC/PS‐b‐P2VP@I₂ cathode significantly outperformed that of other reported aqueous zinc‐based batteries (V₂O₅‐D [29], PEO‐LiVO [30], Mg_0.9Mn₃O₇·2.7H₂O [31], NS‐MnO₂ [32], NiVO [33], Pb₂[IBr]₆ [34], MgX‐AB@I₂ [35], TMAI‐I₂ [36], Zn@Sn‐ZnF₂||I₂ [37]). Such remarkable performance highlights the unique advantages of the AC/PS‐b‐P2VP@I₂ cathode and underscores its strong potential for LDES applications.

The electrochemical kinetics of the AC/PS‐b‐P2VP@I₂ cathode was evaluated using a Zn‐I₂ coin cell. The AC/PS‐b‐P2VP@I₂ cathode exhibited a smaller voltage gap and higher current density between the characteristic redox peaks in the cyclic voltammetry (CV) curves than the AC@I₂ cathode at a scan rate of 0.5 mV s⁻¹ (Figure 4a), indicating enhanced ion transport and a correspondingly higher capacity [38]. The CV curves of the AC/PS‐b‐P2VP@I₂ cathode revealed a high degree of overlap after the initial three cycles, demonstrating an excellent electrochemical reversibility (Figure S19). As shown in the Nyquist plots in Figure 4b, the charge‐transfer resistance (R _ct) was significantly reduced from 154.3 Ω for the AC@I₂ cathode to 53.1 Ω for the AC/PS‐b‐P2VP@I₂ cathode, as indicated by the smaller semicircle, indicative of accelerated ion diffusion and enhanced electrochemical reaction kinetics [39]. This can be attributed to the open and interconnected nanoscale channels and spatially distributed coordination sites provided by the unique spherical structure of the PS‐b‐P2VP micellar films. The ion diffusion coefficient was measured by galvanostatic intermittent titration technic (GITT) (Figure S20). As presented in Figure 4c,d, the AC/PS‐b‐P2VP@I₂ cathode exhibited a higher ions diffusion coefficient (3.11 × 10⁻⁹ cm² s⁻¹) than the AC@I₂ cathode (2.35 × 10⁻⁹ cm² s⁻¹) and the AC/P2VP@I₂ cathode (2.80 × 10⁻⁹ cm² s⁻¹, Figure S21), further confirming the enhanced ion transport kinetics.

FIGURE 4.

Electrochemical kinetics and stability of the AC/PS‐b‐P2VP@I₂ cathode. (a) CV curves of different cathodes under 0.5 mV s⁻¹. (b) Nyquist plots of the batteries with different cathodes. Inset: the equivalent circuit corresponding to the EIS data. (c and d) Calculated ion diffusion coefficient in the AC/PS‐b‐P2VP@I₂ (c) and AC@I₂ (d) cathodes at different charge/discharge stages. (e) Rate performance of different cathodes with various current densities. (f) Ultra‐long cycling performance of different cathodes under a current density of 3 A g⁻¹.

The AC/PS‐b‐P2VP@I₂ cathode showed high specific capacities of 199.2, 182.4, 170.7, 156.7, and 145.7 mAh g⁻¹ at various current densities (Figure 4e), indicating an excellent rate capability. Such appealing rate performance can be attributed to the rapid electrochemical kinetics enabled by the PS‐b‐P2VP spherical micellar films. In contrast, the AC@I₂ cathode exhibited lower capacities of 184.8, 174.8, 158.3, 137.9, and 125.0 mAh g⁻¹ under the same conditions. Notably, when the current density was returned to 0.2 A g⁻¹, the capacity of the AC/PS‐b‐P2VP@I₂ cathode recovered to 199.6 mAh g⁻¹, significantly surpassing that of the AC@I₂ cathode (178.8 mAh g⁻¹). Owing to the effective suppression of the polyiodide shuttling effect, the AC/PS‐b‐P2VP@I₂ cathode exhibited high capacity of 153.9 mAh g⁻¹ and operated stably for over 20,900 cycles (2080 h) at 3.0 A g⁻¹, achieving a capacity retention of 95.5% (Figure 4f). By comparison, the AC@I₂ cathode suffered from severe capacity degradation, dropping to 95.4 mAh g⁻¹ after just 441 cycles. The capacity of the AC/P2VP@I₂ cathode decreased to 117.4 mAh g⁻¹ after 2150 cycles, corresponding to 85.7% retention of its initial capacity (Figure S22).

To evaluate the practical applicability of the AC/PS‐b‐P2VP@I₂ cathode, a Zn‐I₂ pouch cell was assembled using a cathode with dimensions of 6.5 cm × 8.0 cm and an iodine loading of 17.3 mg cm⁻² (Figure 5a). The resulting pouch cell revealed a long discharge duration of 5.6 h at 0.035 A g⁻¹, delivering a high capacity of 186.2 mAh and a coulombic efficiency of 99.8% (Figure 5b). Generally, the iodine content and areal capacity of the AC/PS‐b‐P2VP@I₂ cathode is superior to those of most previously reported iodine cathodes (Table S3). Furthermore, it retained 99.1% of its initial capacity over 118 cycles (1360 h) at 0.035 A g⁻¹ (Figure 5c), indicating that the iodine species were robustly immobilized by the PS‐b‐P2VP micellar films. Upon employing 20 µm Zn foil, the Zn‐I₂ battery assembled with the AC/PS‐b‐P2VP@I₂ cathode also maintained stable operation for 62 cycles at a low N/P ratio of 3.2, corresponding to 31.3% Zn utilization (Figure S23). Due to the effective suppression of polyiodide shuttling, the pouch cell with the AC/PS‐b‐P2VP@I₂ cathode demonstrated exceptional performance, successfully powering an LED display screen for over 9.7 h during the daytime, after 24 h of rest after fully charged at night (Figure 5d, the detailed process was documented in Figure S24), underscoring its promising potential for LDES applications to store energy during off‐peak times and provide energy during peak‐demand periods.

FIGURE 5.

Pouch cell derived from the AC/PS‐b‐P2VP@I₂ cathode for LDES. (a) Optical image of the pouch cell assembled with the AC/PS‐b‐P2VP@I₂ cathode. (b) Galvanostatic charging‐discharging curves of the pouch cell with the AC/PS‐b‐P2VP@I₂ cathode at 0.035 A g⁻¹. (c) Cycling stability of the pouch cell with the AC/PS‐b‐P2VP@I₂ cathode at 0.035 A g⁻¹. (d) Demonstration of LDES by the Zn‐I₂ pouch cell with the AC/PS‐b‐P2VP@I₂ cathode.

Adsorption energies of iodine species on PS‐b‐P2VP were calculated to elucidate the role of the PS‐b‐P2VP micellar film in suppressing polyiodide shuttling. 2‐Ethylpyridine and graphene were used to represent the P2VP corona of PS‐b‐P2VP and AC for simplicity. The independent gradient model based on Hirshfeld partition (IGMH) analysis revealed a pronounced interaction between 2‐ethylpyridine (particularly the pyridyl nitrogen) and I₂ (Figure 6a). Compared with graphene (Figure S26), 2‐ethylpyridine showed a stronger interaction with I₂ (‐0.44 eV vs. ‐0.21 eV) and I₃ ⁻ (‐0.16 eV vs. ‐0.09 eV), as illustrated in Figure 6c. Considering the partial protonation of the pyridyl nitrogen in a mildly acidic 2 M ZnSO₄ electrolyte (Figure S25), the adsorption energy of I₂ and I₃ ⁻ on protonated 2‐ethylpyridine were also calculated (Figure 6b). The adsorption energies of protonated 2‐ethylpyridine toward I₂ and I₃ ⁻ were ‐0.05 and ‐0.58 eV, respectively. Therefore, iodine preferentially interacted with 2‐ethylpyridine, whereas I₃ ⁻ preferentially interacted with protonated 2‐ethylpyridine. These results further indicated a stronger affinity of the P2VP corona for iodine species, thereby effectively encapsulating them within the PS‐b‐P2VP micellar film.

FIGURE 6.

Mechanism investigation on the mitigation of polyiodide shuttling by the PS‐b‐P2VP micellar film. (a and b) IGMH analysis between 2‐ethylpyridine and iodine (a) and triiodide (b) (blue, red, and green colors indicate attraction, repulsion, and van der Waals interactions, respectively). (c) Calculated adsorption energies of iodine and triiodide with PS‐b‐P2VP and PS‐b‐P2VP_H (represented by 2‐ethylpyridine and protonated 2‐ethylpyridine, respectively) and AC (represented by graphene), respectively. (d and e) In situ UV‐vis spectra of the ZnSO₄ electrolytes during the charging‐discharging process while soaking with the AC@I₂ (d) and AC/PS‐b‐P2VP@I₂ (e) cathodes. (f) Corresponding absorbance intensity at 287 nm derived from the UV‐vis spectra during the discharging process. (g) High‐resolution N 1s XPS spectra of the AC/PS‐b‐P2VP@I₂ cathode at fully charged and discharged states (current density for charge and discharge: 0.02 A g⁻¹). (h) Raman spectra of the AC/PS‐b‐P2VP@I₂ cathode obtained during the charging‐discharging process at 0.02 A g⁻¹.

To better understand the role of the PS‐b‐P2VP micellar film in suppressing the polyiodide shuttling, in‐situ UV‐vis spectroscopy of the electrolyte was conducted. The custom‐designed quartz cell used for these measurements is shown in Figure S27a. The electrolyte was 2 M ZnSO₄, with Zn foil as the anode and either AC@I₂ or AC/PS‐b‐P2VP@I₂ as the cathode. The polyiodide‐containing electrolyte was replaced with fresh 2 M ZnSO₄ upon full discharge, followed by continuous charging. During both discharge and charge processes (Figure 6d,e), the AC/PS‐b‐P2VP@I₂ cathode showed markedly weaker absorption bands at 287 and 349 nm (characteristic of I₃ ⁻ species [40]) compared to the AC@I₂ cathode (Figures 6f and S27b). It strongly indicated that the PS‐b‐P2VP micellar film effectively suppresses the diffusion of iodine species into the electrolyte, thereby delivering high coulombic efficiency and excellent capacity retention during prolonged charge‐discharge cycling, thereby promoting its potential for LDES applications.

XPS of the AC/PS‐b‐P2VP@I₂ cathode revealed that the intensity of the peak corresponding to the coordinated pyridyl nitrogen (400.7 eV) markedly decreased in the fully discharged state (Figure 6g), which could be attributed to the reduction of I₂ to I⁻, leading to the dissociation of halogen bonds with the pyridyl groups in the PS‐b‐P2VP micellar film. The XPS peak area ratio of coordinated pyridyl nitrogen to free pyridyl nitrogen at various charge/discharge states during different cycles was also presented in Table S4. Upon fully re‐charged, the peak restored the original intensity, confirming the re‐establishment of coordination between the pyridyl groups and reformed iodine. Moreover, the recovery of the peak intensity at the fully charged state in the 10th cycle (Figure S28) further suggested the reversibility of the coordination and dissociation between the pyridyl groups and iodine, reflecting the excellent reaction reversibility of the accumulated iodine species in the hierarchically open PS‐b‐P2VP micellar film. Raman spectroscopy of the AC/PS‐b‐P2VP@I₂ cathode revealed the peaks associated with I₃ ⁻ (110 and 140 cm⁻¹), I₅ ⁻ (165 cm⁻¹) and I₂ (215 cm⁻¹) during the charging process (Figure 6 h) [41]. The decreased intensity during the substantial discharge process demonstrated that the encapsulated polyiodide species (I₂, I₃ ⁻, I₅ ⁻) in the brush‐like P2VP corona can be fully utilized during discharge, leading to improved coulombic efficiency and extended long‐term cycling life‐span under prolonged charge‐discharge conditions.

3. Conclusion

In conclusion, micellar film of PS‐b‐P2VP block copolymer has been developed as a host layer for iodine species. The P2VP corona in the micellar film, featuring a 3D distribution of electron‐donating pyridyl groups, readily binds iodine via halogen bonding, thus minimizing its diffusion under extended charging‐discharging duration. In addition, the hierarchically organized brush‐like corona forms open, interconnected nanoscale channels that ensure robust and high‐capacity iodine encapsulation. Owing to the unique micellar structure, the polyiodide shuttling effect was significantly suppressed during long‐duration charging‐discharging cycling. Notably, the AC/PS‐b‐P2VP@I₂ cathode achieved a high coulombic efficiency of 97.3% and a specific capacity of 191.6 mAh g⁻¹ under prolonged charge‐discharge durations exceeding 20.0 h, while retaining 96.8% of its initial capacity after 2000 h (100 cycles). This cathode could also operate stably for over 20,900 cycles (2080 h) at 3.0 A g⁻¹, achieving a high‐capacity retention of 95.5%. Leveraging the PS‐b‐P2VP micellar film, the Zn‐I₂ pouch cell exhibited stable operation for over 1360 h with an iodine loading of 17.3 mg cm⁻², effectively powering an LED display screen for more than 9.7 h during the daytime, after 24 h of rest in a fully charged state overnight. Overall, this work has demonstrated an effective physicochemical adsorption strategy based on halogen bonding within the PS‐b‐P2VP micellar film for immobilizing iodine species, thereby advancing the development of Zn‐I₂ batteries for LDES applications.

Author Contributions

Zhenglin Li: writing – original draft, formal analysis, data curation. Jingchun Wang: data curation, writing – review and editing. Na Yang: software, methodology, validation. Ruijia Chen: data curation, formal analysis. Zhenfeng Feng: data curation, formal analysis. Yan Sun: investigation, supervision, writing – review and editing. Chengshuo Shen: software, methodology, validation. Huibin Qiu: writing – review and editing, supervision, resources, funding acquisition, project administration.

Conflicts of Interest

There are no conflicts of interest to declare.

Supporting information

Supporting File: anie72760‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.