Thinner-than-paper and broad-temperature-adaptive zinc-iodine batteries enabled by nanophase separated deep-eutectic hydrogel electrolytes

Domain: biology
Published: 2026-04-03
Editorial outcome: major_revision

Abstract
Hydrogel electrolyte based secondary batteries are promising for wearable electronics, yet face challenges including limited mechanical resilience, and narrow temperature range. Herein, we report a robust deep-eutectic hydrogel electrolyte fabricated via synergistic interplay of dual nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks. The interwoven nanophase separation architecture, integrating hydrophilic polyvinyl alcohol phases and hydrophobic polyacrylonitrile phases, realizes high fracture-strength (4.1 MPa) and toughness (13.66 MJ m−3). Meanwhile, deep-eutectic chemistry modulates Zn2+ solvation structures and leverages cyano-coordination channels of polyacrylonitrile to achieve high Zn2+ ionic conductivity (28.2 mS cm−1) and transference number (0.65) at 20 °C. Concurrently, abundant hydrogen bonds induced by multiple donor sites of hydrophilic phases, urethane, and Zn(ClO4)2 immobilize active H2O to ensure broad-temperature durability. This tripartite synergy directs planar Zn deposition along (002) planes and suppresses dendrite growth, enabling Zn||I2 batteries with a thinner-than-paper thickness (42 μm) and high flexibility. The assembled Zn||I2 batteries demonstrate high specific energy (108.99 Wh kg−1) and cycling stability (over 36,000 cycles under −40 to 80 °C). In this work, the convergence of molecule design, phase modulation, and process engineering establishes a feasible methodological framework for developing advanced flexible batteries that integrate high energy density and harsh environment tolerance.

Introduction
Aqueous zinc-metal batteries have emerged as promising candidates for next-generation energy storage, owing to their inherent safety, cost-effectiveness, and environmental compatibility.[1-9] However, conventional liquid electrolytes (LE) suffer from critical limitations, including leakage susceptibility, narrow temperature range, and uncontrolled zinc dendrite growth, which severely restrict their practical deployment.[10-14] Hydrogel electrolytes (HE), particularly polyvinyl alcohol (PVA)-derived HEs, can somewhat lock up water molecules by hydrogen bonds and inhibit dendrite growth, but still remain plagued by intrinsic trade-offs.[15-21] Specifically, HE systems often restricted by the reconcile mechanical robustness with electrochemical performance, the excessive free water content that compromises temperature adaptability, and the thickness usually exceeding 100 μm that diminish energy density.[22-29] Although phase-separated HE, as demonstrated in our prior work, have shown enhanced modulus and dendrite suppression, it remains a significant challenge to achieve simultaneous advances in thin geometries, broad-temperature resilience, and electrochemical stability.[30]

Herein, we present the fabrication of a robust deep-eutectic HE (deep-eutectic-HE) via synergistic integration of nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks. The interwoven nanophase separation architecture, engineered through solvent-exchange, establishes a dual-domain structure comprising hydrophilic PVA phases and hydrophobic polyacrylonitrile (PAN) phases, endowing the hydrogel with good mechanical properties (4.1 MPa fracture strength and 13.66 MJ m−3 toughness). Concurrently, hydrogen-bond interactions between hydrophilic phases, urethane (UR) moieties, water molecules, and ClO4− ions immobilize active water, enabling stable operation across a broad temperature range (−40 to 80 °C). Deep-eutectic chemistry and cyano-coordination pathways of PAN collaboratively reconfigure Zn2+ solvation structures, achieving high ionic conductivity (28.2 mS cm−1) and Zn2+ transference numbers (0.65), while suppressing polyiodide shuttling. This tripartite synergy directs planar Zn deposition on (002) crystallographic planes and mitigates dendrite formation, enabling Zn||I2 full batteries with a thinner-than-paper thickness (42 μm) and high flexibility that deliver stable power under mechanical deformation (180° bending). The as-assembled Zn||I2 pouch battery achieves high specific energy and volumetric energy density (108.99 Wh kg−1 and 189.41 Wh L−1), rate capability, and long lifespan under broad temperatures (with 92.31%, 75.28%, and 81.00% capacity retention after 36,000 cycles at −40, 20, and 80 °C, respectively). By synergistically optimizing molecular compositions, phase structures, and fabrication processes, a practical systematic approach is built to engineer advanced flexible batteries that simultaneously achieve good energy storage capacity and resistance to harsh environments.

Results
Design, preparation, and characterizations of deep-eutectic-HE

In this work, we propose a synergistic architectural strategy to construct a robust deep-eutectic-HE capable of reconciling thin geometries with good mechanical properties, electrochemical performances, and temperature adaptability. The stepwise fabrication strategy is realized by integrated manipulation of nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks in the HE matrix, as presented in Fig. 1a. Typically, the fabrication paradigm commences with dimethyl sulfoxide (DMSO) mediated dissolution of polyvinyl alcohol (PVA) and acrylonitrile (AN). The strong hydrogen-bond disrupting capability of DMSO enables nearly complete dissociation of intra- and inter-chain interactions, yielding a homogeneous polymeric precursor.[31] Subsequent heating initiates the polymerization of AN, driving the in-situ formation of a dual-network PAN-PVA composite through progressive crosslinking and chain entanglement. Finally, the DMSO removal and Zn2+ electrolyte exchange step establishes uniform polymer-electrolyte integration, and also optimizes zinc ion solvation structure via competitive coordination between unsaturated cyano groups and water molecules.[30] During this phase evolution process, hydrophilic phases (rooted in the hydrophilic hydroxyl groups on PVA chains) and hydrophobic phases (formed via dipole-dipole interactions of PAN segments) spontaneously organize into a dual-nanophase separated architecture. This architecture, in synergy with the crystalline domains formed by a part of PVA segments, significantly enhances the mechanical strength of deep-eutectic-HE. Simultaneously, the hydrophilic hydroxyl groups of PVA contribute to expanding the polymer network, increasing the content of hydrated eutectic solvent in the hydrogel and forming abundant hydrogen bonds with H2O to reduce the activity of H2O. Moreover, the hydrophobic cyano groups on PAN chains construct a rapid transfer channel for Zn2+, thereby improving the electrochemical kinetics of deep-eutectic-HE.[30, 32]

To benchmark the advantages of deep-eutectic-HE across mechanical and electrochemical properties, we chose the non-gelated deep-eutectic liquid electrolytes (H2O/Zn(ClO4)2/UR, namely deep-eutectic-LE), the non-eutectic liquid electrolytes (H2O/Zn(ClO4)2, namely non-eutectic-LE), and gelated non-eutectic-LE (namely non-eutectic-HE) as the control groups. The attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra (Fig. 1b) revealed critical molecular interactions among UR, Zn(ClO4)2, and trace H2O. Compared with non-eutectic-HE and non-eutectic-LE, the N–H asymmetric stretching vibrations (3325 and 3415 cm−1) of deep-eutectic-HE and deep-eutectic-LE underwent a 54–66 cm−1 blue shift accompanied by peak broadening upon eutectic formation, indicating hydrogen-bond reorganization between UR molecules, water clusters, and ClO4− anions due to the addition of UR. Simultaneously, the C=O stretching vibration of deep-eutectic-HE and deep-eutectic-LE red-shifted by 6 cm−1 (1687 → 1681 cm−1), confirming Zn2+ coordination to carbonyl oxygen atoms within UR.[32] Complementary Raman analyses (Fig. 1c) demonstrated vibrational mode modifications consistent with this interaction. The C–N and N–H stretching frequencies of UR in deep-eutectic-HE and deep-eutectic-LE shifted by +17 and +10 cm−1 respectively, reinforcing evidence for three-dimensional hydrogen-bond network formation.[32]

Scanning electron microscopy (SEM) image of deep-eutectic-HE (Fig. 1d) revealed a well-defined nanophase-separated structure with phase dimensions of 10–30 nm, substantially below the wavelengths of visible light (400–700 nm). This contrasts sharply with non-eutectic-HE (Supplementary Fig. 1), where the salting-in effect induced by excess ions suppresses phase separation, resulting in a porous morphology with limited hierarchical structure.[33] Specifically, the poorly hydrated chaotropes anions (ClO4−) will induce hydrophilic effects of the polymer chain segments, while weakening the hydrogen bonds between polymer chain segments, causing the polymer to dissolve (i.e., salting in). Consequently, the compaction degree of the PVA network is significantly reduced, making it difficult to form a nanoscale phase separation structure with PAN.[34] The atomic force microscopy (AFM) mapping (Fig. 1e and Supplementary Fig. 2-3) further validated the nanophase-separated structure of deep-eutectic-HE, revealing its phase size of 20 nm approximately.[33] The small-scale nanophase separation structure not only significantly enhanced the toughness of deep-eutectic-HE, but also improved its transparency. The optical implications of this nano-structuring become apparent in Supplementary Fig. 4, where both deep-eutectic-HE and non-eutectic-HE exhibit >90% visible-light transmittance – a direct consequence of subwavelength phase-separation dimensions.[30] X-ray diffraction (XRD) patterns (Fig. 1f) provided crystallographic evidence for enhanced structural order, with deep-eutectic-HE displaying intensified (101) and (200) diffraction peaks of PVA at 18.0° and 21.3°, respectively. This improved crystallinity established a structural foundation for good mechanical performance through optimized polymer chain packing.[35] Given the complexity of structural domains of deep-eutectic-HE, small-angle X-ray scattering (SAXS) profiles (Fig. 1g) further quantitatively resolved the nanophase-separated structure, revealing two characteristic distances at 25.7 nm and 10.9 nm corresponding to hydrophobic and crystalline domain spacing, respectively.[36] These dimensions, which aligned with SEM-observed phase separation, also explained the enhanced optical clarity and mechanical robustness of deep-eutectic-HE through nanoconfined polymer dynamics.

Mechanical Properties and Temperature Tolerance of deep-eutectic-HE

The mechanical properties of deep-eutectic-HE were systematically evaluated to elucidate the synergistic effects of nanophase-separated architecture, hydrated eutectic solvation, and hydrogen-bond network optimization. Tensile testing (Fig. 2a-b) demonstrated good mechanical properties in deep-eutectic-HE relative to non-eutectic-HE, with enhancements in fracture strain (752%), fracture strength (4.09 MPa), elastic modulus (1.84 MPa), and toughness (13.66 MJ m−3). These good mechanical properties of deep-eutectic-HE stem from two complementary mechanisms. First, ClO4−, as chaotropic ions positioned on the right side of the Hofmeister series, typically induce polymer dissolution through salting-in effects.[37-38] In deep-eutectic-HE, however, UR-mediated hydrogen bonds with ClO4− mitigates this destabilizing interaction while reinforcing the hydrogel network. Second, replacing DMSO (a good solvent) with deep-eutectic-LE (a poor solvent) in deep-eutectic-HE shifts thermodynamic equilibria toward polymer chain association, promoting crystalline domain formation as evidenced by XRD analysis (Fig. 1f).[39] This nanophase separation engineering strategy enabled fabrication of thin deep-eutectic-HE membranes down to 6 μm thickness (Fig. 2c), which maintain strong load-bearing capacity by sustaining 2.2 kg weights without fracture (Fig. 2d) – a 44-fold improvement over non-eutectic-HE.

Differential scanning calorimetry (DSC) profiles in Fig. 2e also revealed distinct phase-transition behaviors among the four electrolyte samples. Deep-eutectic-HE and non-eutectic-HE demonstrated glass transition temperatures of −85.7 °C and −80.5 °C, whereas deep-eutectic-LE and non-eutectic-LE exhibited exothermic crystallization peaks at −43 and −81.8 °C, respectively. Benefiting from the high concentration of Zn(ClO4)2, non-eutectic-LE and non-eutectic-HE exhibit similar low freezing points.[40] For deep-eutectic-LE, the addition of UR increases hydrogen bonds with H2O, restricting movements such as vibration or rotation of the H2O molecules, resulting in an elevation in the glass transition temperature.[41] For deep-eutectic-HE, the dense network structure effectively confines H2O molecules within nanoscale pores, thereby inhibiting the nucleation and growth of ice crystals.[42] Compared to non-eutectic-HE, the additional 5.2 °C glass transition temperature reduction in deep-eutectic-HE underscored the critical role of eutectic chemistry in optimizing low-temperature adaptability.

Thermal endurance characterization via DSC (Fig. 2f) also highlighted contrasting high-temperature responses. Neither deep-eutectic-HE nor deep-eutectic-LE displayed endothermic transitions between 20–120 °C, confirming their structural integrity under relatively high temperatures.[43] This stability arises from the capacity of deep-eutectic system to minimize free water content through UR-mediated hydrogen-bond networks and nanoconfined water states. In contrast, non-eutectic-HE and non-eutectic-LE underwent a phase transition at 72.3 and 74.0 °C due to unbound water evaporation, as evidenced by its larger number of hydrogen bonds among H2O. Rheological profiling (Fig. 2g) corroborated this thermal endurance, showing stable storage modulus (G′) and loss modulus(G″) for deep-eutectic-HE during heating cycles versus progressive stiffening in non-eutectic-HE due to free water evaporation. Water retention studies (Supplementary Fig. 5) quantified the hydration dynamics underpinning this thermal stability: deep-eutectic-HE retained 88.4% water content after 48 h at 25 °C/15% RH, higher than non-eutectic-HE (78.5%) through UR-mediated water immobilization.

Molecular dynamics (MD) simulations (Fig. 2h and Supplementary Fig. 6) quantitatively resolved water confinement states in these electrolyte systems. Fig. 2j demonstrated that non-eutectic-HE and non-eutectic-LE contain the most hydration bonds between H2O molecules, rendering them susceptible to both ice crystallization at low temperatures and dehydration-induced structural collapse at elevated temperatures. Conversely, deep-eutectic-HE and deep-eutectic-LE exhibited reduced number of hydrogen bonds, confirming effective water activity suppression through the combined effects of hydrogen-bond networks and eutectic solvent interactions. Moreover, deep-eutectic-HE exhibited an even lower number of hydrogen bonds compared to deep-eutectic-LE, attributed to the hydrogen-bond adsorption of H2O by the polymer network of hydrophilic PVA phases. These MD results aligned well with DSC-observed thermal behaviors, indicating the restricted water mobility directly correlates with enhanced cryogenic performance and evaporation resistance.

MD simulation simultaneously unveiled alterations of Zn2+ solvation structures (Fig. 2i and Supplementary Fig. 6, with source data provided as Supplementary Data 1-8). For non-eutectic-LE, radial distribution function (RDF, g(r)) analysis confirmed a first solvation shell coordination number of 6 for H2O around Zn2+ (Fig. 2k). Post-gelation, the emergence of coordination interactions between Zn2+ and cyano in PAN chains led to their incorporation into the first solvation shell, thereby diminishing the hydration number to 5.37. Strikingly, the introduction of UR induced a pronounced reduction in the hydration number within the first solvation shell of Zn2+, dropping below 3 in both deep-eutectic-HE and deep-eutectic-LE systems. This substantial perturbation of the Zn2+ solvation structure correlated with an enhancement in the diffusion coefficient of Zn2+, exhibiting a 9-fold increase in deep-eutectic-HE relative to the non-eutectic LE (Fig. 2l), thereby enabling its higher ionic conductivity.

Electrochemical performances of deep-eutectic-HE

The electrochemical performances of deep-eutectic-HE were systematically investigated through Zn||Zn and SS (stainless steel)||SS symmetric batteries. Temperature-dependent ionic conductivity profiling (Supplementary Fig. 7 and Table 1) demonstrated efficient charge transport capabilities of deep-eutectic-HE across −40 to 80 °C. The deep-eutectic-HE maintained 28.2 mS cm−1 ionic conductivity at 20 °C and retained 1.7 mS cm−1 at −40 °C. This is a direct consequence of hydrogen-bond-mediated water confinement that suppresses ice nucleation while preserving ion mobility. Comparative analyses (Fig. 3a, Supplementary Fig. 8 and Table 2-4) showed deep-eutectic-LE, non-eutectic-HE and non-eutectic-LE exhibited inferior room-temperature conductivities (11.0, 8.0, and 6.2 mS cm−1, respectively), with deep-eutectic-LE becoming non-conductive below −40 °C due to crystalline phase formation. The structure of non-eutectic-HE collapsed at 80 °C (Supplementary Fig. 8c), further highlighting the critical role of UR-enhanced hydrogen-bond networks in stabilizing hydrated eutectic architectures.

Zn2+ transference number (tZn2+) analyses (Fig. 3b and Supplementary Fig. 9) quantified Zn2+ transport kinetics of deep-eutectic-HE (tZn2+ = 0.62–0.68 across −40 to 80 °C), higher than deep-eutectic-LE (tZn2+ = 0.36–0.38), non-eutectic-HE (tZn2+ = 0.43–0.46) and non-eutectic-LE (tZn2+ = 0.41–0.46). This enhancement arises from synergistic effects: cyano groups on PAN chains coordinate with Zn2+ ions to establish rapid ionic migration channels while hydrogen-bond UR-ClO4− complexes restrict anion mobility, collectively restructuring the Zn2+ solvation structure (Fig. 2i).[44-47] Electrochemical impedance spectroscopy (EIS) measurements (Fig. 3c and Supplementary Table 5) revealed interfacial resistance values of 238.22 Ω for Zn|deep-eutectic-HE|Zn battery, significantly lower than those of deep-eutectic-LE (465.98 Ω), non-eutectic-HE (663.73 Ω) and non-eutectic-LE (599.18 Ω) counterparts, attributable to optimized electrode-electrolyte adhesion.

Rate performance evaluations (Fig. 3d and Supplementary Fig. 10) revealed that deep-eutectic-HE maintains a voltage polarization below 200 mV across a broad current density range (0.2–5.0 mA cm−2), contrasting sharply with non-eutectic-HE, which exhibited large polarization (>5.0 V) at 5.0 mA cm−2. This improved electrochemical performance of deep-eutectic-HE primarily stems from its optimized Zn2+ ion transport kinetics and reduced interfacial impedance.[48] Tafel analyses (Fig. 3e) corroborated these findings, showing its low corrosion current (0.06 μA cm−2) and suppressed polarization behavior, again verifying its ability to achieve stable Zn2+ ion plating/stripping behavior.

Long-term cycling testing (Fig. 3f) demonstrated the improved electrochemical stability of deep-eutectic-HE, sustaining operation for 4200 h with minimal polarization (<100 mV at 0.5 mA cm−2 and 0.5 mAh cm−2). This starkly contrasts with the rapid failures in deep-eutectic-LE (100 h), non-eutectic-HE (200 h), and non-eutectic-LE (230 h) where Zn dendrite penetration caused the short circuits of batteries. The Zn|deep-eutectic-HE|Zn symmetric battery exhibited highly reversible Zn plating/stripping behavior, unequivocally validating the synergistic advantages of deep-eutectic-HE: rapid Zn2+ ion transport kinetics, robust dendrite suppression capability, and prolonged cyclability.

Broad-temperature evaluations (Fig. 3g-3h) validated the broad temperature adaptability of deep-eutectic-HE. The critical working temperature tests of Zn||Zn symmetric batteries assembled with different electrolytes revealed that the Zn|deep-eutectic-HE|Zn symmetric battery could maintain stable electrochemical performance up to ~80 °C, which is better than those of deep-eutectic-LE (~70 °C), non-eutectic-HE (~50 °C), and non-eutectic-LE (~60 °C) counterparts (Supplementary Fig. 11). When the operation temperature was raised higher than the critical working temperature, significant ionic insulation would occur due to the precipitation of salts from solvent evaporation for LE samples or the collapse of gel structure for HE samples. The Zn|deep-eutectic-HE|Zn symmetric battery maintained stable cycling for more than 800 h with polarizations of 153.4 mV (at −40 °C) and 56.6 mV (at 80 °C), enabled by UR-H2O hydrogen bonds that suppress H2O-H2O network formation. In contrast, non-eutectic-HE exhibited large voltage polarization (>1.0 V) at −40 °C, and failed at 80 °C due to structural collapse. Meanwhile, deep-eutectic-LE and non-eutectic-LE suffered rapid short-circuiting under high temperatures. In conclusion, deep-eutectic-HE displayed the ability to optimize ion transport kinetics, inhibit Zn dendrite growth, and maintain structural stability under demanding conditions.

The electrochemical stability window of deep-eutectic-HE was also investigated via linear sweep voltammetry. Supplementary Fig. 12 demonstrated that deep-eutectic-HE achieved an expanded electrochemical stability window (2.69 V), surpassing deep-eutectic-LE (2.57 V), non-eutectic-HE (2.49 V), and non-eutectic-LE (2.44 V). This enhancement arises from restricted water molecule mobility within the hydrogen-bond eutectic network, which suppresses parasitic reactions at elevated potentials. To contextualize these results, Fig. 3i and Supplementary Table 6-7 compared deep-eutectic-HE against other recent reported HEs across several critical performance parameters: fracture strength (4.09 MPa), ionic conductivity (28.2 mS cm−1), electrochemical stability window (2.69 V), low-temperature tolerance (−40 °C), high-temperature tolerance (80 °C), film thickness (6 μm), coordination number of Zn-H2O (2.71), Zn2+ transference number (0.65), cycling stability, and battery lifespan.[16, 30, 49-59] Overall, the as-proposed deep-eutectic-HE combines these attributes, establishing it as a multifunctional electrolyte platform.

Zinc electro-plating/stripping behaviors guided by deep-eutectic-HE

To comprehensively investigate the capacity of deep-eutectic-HE to regulate zinc deposition behavior, multi-scale analyses of Zn||Cu half batteries were conducted. Due to the inferior electrochemical performances of non-eutectic-HE and non-eutectic-LE, deep-eutectic-LE was chosen as a control group for subsequent tests. The average Coulombic efficiency, a critical metric for evaluating zinc utilization reversibility, was measured over 20 electro-plating/stripping cycles using the Aurbach method (Fig. 4a).[60] The deep-eutectic-HE achieved an average Coulombic efficiency of 98.47%, higher than deep-eutectic-LE (96.99%) by 1.48%. Voltage-time profiles (Fig. 4b) further revealed the reduced polarization of deep-eutectic-HE, with a 33% reduction in hysteresis compared to deep-eutectic-LE during the initial deposition phase.

Detailed overpotential analyses (Fig. 4c and Supplementary Fig. 13) quantified the kinetic advantages of deep-eutectic-HE. The nucleation overpotential (42.6 mV vs. 66.5 mV) and mass-transfer overpotential (22.0 mV vs. 46.4 mV) of deep-eutectic-HE relative to deep-eutectic-LE were reduced by 35.9% and 52.6%, respectively. These improvements stem from synergistic effects between molecular-scale coordination chemistry and macro-scale mechanical properties. At the atomic level, cyano groups along the polymer backbone in PAN form transient coordination complexes with Zn2+, creating low-energy migration pathways that lower activation barriers for Zn2+ transport.[30] Macroscopically, the high elastic modulus of deep-eutectic-HE generates substantial mechanical resistance against the growth of zinc dendrites during zinc deposition, physically constraining vertical growth while promoting lateral spreading of Zn across the electrode surface.[30, 61, 62]

Cyclic voltammetry (CV) provided additional evidences on optimized reaction kinetics (Fig. 4d). The deep-eutectic-HE exhibited a peak response current density of 15.9 mA cm−2 with minimal polarization (33 mV) compared to deep-eutectic-LE (9.2 mA cm−2 and 68 mV). The 72.8% current density enhancement directly results from the coordinated action of accelerated Zn2+ mobility and spatially confined deposition geometry. This dual mechanism ensures rapid ion replenishment at the electrode-electrolyte interface while maintaining planar deposition morphology through stress distribution.

Crystallographic orientation analyses via XRD revealed fundamental differences in zinc deposition patterns (Fig. 4e). After 50 cycles (100 h), deep-eutectic-HE enhanced the (002) plane diffraction intensity by 40.97% relative to pristine zinc foil, indicating preferential horizontal growth along this low-surface-energy crystallographic orientation.[63-65] In sharp contrast, deep-eutectic-LE increased (101) plane dominance, promoting vertically zinc dendrite formation, ultimately leading to severe Zn dendrite growth. SEM analyses of cycled zinc negative electrodes in deep-eutectic-HE and deep-eutectic-LE revealed stark morphological contrasts. Fig. 4f demonstrates that deep-eutectic-HE enables horizontally aligned, layered zinc deposition, maintaining negative electrode surface uniformity over prolonged cycling. This planar growth mode ensures stable ion flux and interfacial integrity. In contrast, deep-eutectic-LE promotes vertical dendrite formation within 50 cycles, with progressive sharpening leading to severe surface roughness (Fig. 4g). After 200 cycles in deep-eutectic-LE, interconnected protrusions were observed on the Zn electrode, heightening the risks of separator penetration. XRD data (Fig. 4e) corroborate these findings, showing preferential horizontal (002) plane deposition in deep-eutectic-HE versus longitudinal crystallographic growth in deep-eutectic-LE. The zinc deposition behavior in different electrolytes was observed by in-situ optical microscopy (Supplementary Fig. 14). In deep-eutectic-HE, the Zn surface is flat and smooth, without obvious protrusions throughout the whole deposition process. In contrast, in deep-eutectic-LE, Zn protrusions emerge on Zn surface after consecutive deposition for 20 min, and obvious Zn dendrites are observed after 40 min. These results are consistent well with the SEM observations (Fig. 4f-g), indicating that the deep-eutectic-HE is effective in inhibiting the growth of Zn dendrites. The combined XRD, SEM and in-situ optical microscopy evidences conclusively established the dual functionality of deep-eutectic-HE in sustaining electrochemical stability and enforcing dendrite-suppressive deposition, critical for long-term battery reliability.

Electrochemical performances of zinc-metal batteries

For practical validation, we constructed full batteries using zinc foil negative electrodes and iodine positive electrodes. To ensure compatibility with the thin deep-eutectic-HE (6 μm), I2/carbon nanotubes (CNTs) composite positive electrode was developed by a convenient filtration and adsorption method (Supplementary Fig. 15). Zn||I2 full batteries were then assembled with thin I2/CNTs positive electrode (20 μm thick). The robust nanoarchitecture enables fabrication of 6-μm-thick deep-eutectic-HE membranes while resisting dendrite penetration (Supplementary Fig. 16-17). By integrating Zn foil negative electrode (10 μm), deep-eutectic-HE (6 μm), I2/CNTs positive electrode (20 μm), and polyimide (PI) package (3 μm × 2), the Zn||I2 full battery achieved high compactness (42 μm total thickness, Fig. 5a, g), representing 55% reduction compared to standard A4 paper (104 μm, ISO 216). The achieved thickness is competitive compared to some recent relevant reports.[16, 30, 49-56]

During the discharging process of Zn||I2 batteries, I2 in the positive electrode undergoes a reduction reaction and converts into I−, which combines with Zn2+ in the electrolyte to form ZnI2 and adsorbs in the positive electrode. Oppositely, a reverse pathway occurs during the charge process. Notably, the tailored eutectic chemical environment induces a paradigm shift in iodide ion chemistry through multi-scale confinement effects (Fig. 5a). The I− solubility undergoes a three-order-of-magnitude reduction from 9.22 M in conventional aqueous systems to merely 0.79 M in deep-eutectic-LE (Supplementary Fig. 18), fundamentally inhibiting the loss of active substances and altering the iodine redox equilibrium (I2 + I− ⇌ I3−).[66] This dramatic solubility suppression originates from synergistic steric hindrance and electronic modulation. The hydrogen-bond network between UR, H2O and ClO4− creates molecular-scale barriers that physically restrict I− accommodation.[66] Density functional theory (DFT) simulations quantitatively verified this dual confinement mechanism. As illustrated in Supplementary Fig. 19a (with source data provided as Supplementary Data 9-12), the diffusion energy barrier for I− migration increases exponentially from 1.98 eV in non-eutectic system to 3.69 eV in the deep-eutectic system. This is an 86% enhancement that effectively mitigates I2 shuttling at the molecular level. Concurrently, the formation energy of I3− complexes rises by 32% (0.280 eV in deep-eutectic system vs. 0.173 eV in non-eutectic system, Supplementary Fig. 19b), indicating thermodynamic disfavoring of polyiodide generation. Moreover, the coordinated evolution of deep-eutectic-HE simultaneously locks activity water molecules via hydrogen bonds with UR and ClO4− ions while reducing Zn2+ hydration number, collectively conferring resistance to both low and high temperatures without sacrificing ionic transport efficiency.[43]

Rate capability tests in Fig. 5b revealed that the Zn|deep-eutectic-HE|I2 battery maintains a specific discharge capacity of 198.39 mAh g−1 when returning to 0.5 A g−1 after high-rate cycling at 10 A g−1, demonstrating 99.80% capacity retention relative to initial low-rate value. This improved reversibility contrasts sharply with the deep-eutectic-LE system, which exhibits rapid capacity degradation, delivering only 97.86 mAh g−1 at 10 A g−1 with 79.25% capacity recovery upon rate reduction (Fig. 5b and Supplementary Fig. 20). The enhanced rate performance of deep-eutectic-HE benefits from its faster Zn2+ transfer kinetics and higher zinc electro-deposition/stripping homogeneity.[20, 67-68] In contrast, the inferior rate performance of deep-eutectic-LE control sample originates from three synergistic limitations. Firstly, sluggish Zn2+ transport kinetics of deep-eutectic-LE arise from the unoptimized Zn2+ solvation structure, causing insufficient dissociation and reduced ionic conductivity under rapid ion flux demands at high rates. Secondly, the absence of a robust hydrogen-bond network in deep-eutectic-LE induces elevated interfacial impedance and uncontrolled Zn dendrite, both of which consuming active Zn and electrolyte, resulting in irreversible capacity loss. Thirdly, the low Zn2+ transference number of deep-eutectic-LE exacerbates a concentration polarization across electrodes at high rates, further limiting positive electrode capacity utilization. These factors collectively result in the poor rate performance of deep-eutectic-LE control sample.

Long-term cycling stability of Zn|deep-eutectic-HE|I2 battery was assessed subsequently (Fig. 5c), maintaining a Coulombic efficiency of >99.5% over 36,000 cycles at 5 A g−1, an initial specific capacity of 146.15 mAh g−1, and a capacity retention of 75.28% (average decay: 0.0007% per cycle). When cycled at 2 A g−1, the Zn|deep-eutectic-HE|I2 battery also displayed an initial specific capacity of 170.28 mAh g−1 and a capacity retention of 65.77% (average decay: 0.0034% per cycle) after 10,000 cycles (Supplementary Fig. 21). Thermogravimetric analysis offered a clear explanation for the capacity degradation during long-term cycling (Supplementary Fig. 22).[59] After 10,000 cycles at 2.0 A g−1, it was discovered that the I2 content retained in the positive electrode had diminished to 71.39% of its initial level, which could be ascribed to tardive I− dissolution and polyiodide shuttling behaviors. Comparatively, deep-eutectic-LE battery exhibited rapid capacity decay at 5.0 and 2.0 A g−1, attributed to its lower Zn2+ transport kinetics, uncontrolled dendrite growth, and electrolyte decomposition. Long-term cycling tests were also conducted at a high I2 loading of 4.0–5.0 mg cm−2 (Supplementary Fig. 23). The Zn|deep-eutectic-HE|I2 battery similarly demonstrated better electrochemical performances, boasting an initial specific capacity of 144.32 mAh g−1 and a capacity retention of 88.35% (average decay: 0.0011% per cycle), which markedly surpasses those of Zn|deep-eutectic-LE|I2 battery.

The comprehensive rate capability and cycling assessments validate that deep-eutectic-HE delivers high cycling stability and good rate performance in Zn||I2 full batteries, surpassing conventional HEs. Self-discharge tests were also performed to evaluate the suppression of I− dissolution and polyiodide shuttling effects in deep-eutectic-HE (Supplementary Fig. 24). After standing for 24 h, the capacity retention of Zn|deep-eutectic-HE|I2 battery is 93.50%, much higher than that of Zn|deep-eutectic-LE|I2 battery (80.37%), indicating the improved capability of deep-eutectic-HE to inhibit I− dissolution and polyiodide shuttling.

Temperature resilience tests (Fig. 5d-e) further highlighted the broad temperature adaptability of deep-eutectic-HE. Under −40 °C conditions, the Zn|deep-eutectic-HE|I2 battery enabled 36,000 cycles with a capacity retention of 92.31% (initial: 97.05 mAh g−1; decay rate: 0.0002%/cycle). At 80 °C, the Zn|deep-eutectic-HE|I2 battery delivered an initial specific capacity of 146.15 mAh g−1 and a capacity retention of 81.00% after 36,000 cycles (decay rate: 0.0002%/cycle). In sharp contrast, deep-eutectic-LE counterparts failed catastrophically within 10 cycles under high temperatures due to frozen electrolyte channels (upon low temperature) and accelerated corrosion (upon high temperature). The broad temperature resilience demonstrated by deep-eutectic-HE under varied temperature conditions (−40 °C to 80 °C) confirms its robust thermomechanical stability and preserves ionic transport characteristics across a wide temperature range. This temperature-adaptive behavior, arising from its synergistic interplay of nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks, established its viability for deployment in geographically diverse environments spanning arctic to desert climates.

Soft-packaged pouch Zn|deep-eutectic-HE|I2 batteries demonstrated high specific energy of 108.99 Wh kg−1 and high volumetric energy density of 189.41 Wh L−1 when paired with thicker electrodes, a performance competitive compared to some recent reported zinc-metal batteries (Fig. 5f, Supplementary Fig. 25 and Supplementary Table 8).[69-76] To validate the extensive and universal applicability of deep-eutectic-HE, we also fabricated and tested full battery based on V2O5 positive electrode material. The assembled Zn|deep-eutectic-HE|V2O5 full battery achieved good energy storage performance, delivering a specific energy of 76.89 Wh kg−1 and a volume energy density of 236.62 Wh L−1, both metrics significantly surpassing recent reported zinc-metal batteries. Furthermore, the practical feasibility was validated by three series-connected thinner-than-paper Zn||I2 batteries that successfully powered a 5×10 light emitting diode (LED) array (3.0 V operational threshold) under demanding conditions, including: (1) severe mechanical deformation (e.g., repeated 180° folding into paper-airplane like origami structures), (2) complete fragmentation via scissor dissection, and (3) cycling under low and high temperatures (−40 °C to 80 °C), as visualized in Supplementary Fig. 26-27. Even under 90° and 180° bending states, the capacity retention trends of the thinner-than-paper Zn||I2 pouch batteries during 3,000 cycles are almost identical to the normal unbent state (Supplementary Fig. 28), confirming that the batteries maintain stable electrochemical performances even under significant mechanical deformation, highlighting its potential for practical flexible applications. Moreover, to better demonstrate practical viability, we have integrated three series-connected thinner-than-paper batteries into a watch band for powering a wristwatch, as well as charging a smartphone (Supplementary Fig. 29 and Movie 1-2). These demonstrations highlight the integrability and processability of our electrolyte in more complex and demanding flexible electronic devices.

Methods
Chemicals and materials
Zn(ClO4)2.6H2O, urethane (UR), dimethyl sulfoxide (DMSO, 99%), acrylonitrile (AN, 99%), N, N’-methylenebis(acrylamide) (MBA, 99%), ammonium persulfate (APS, 98%), activated carbon (AC, phosphotungstic acid modified), iodine (I2, 99.99%), vanadium oxide (V2O5, 99.99%), N-Methylpyrrolidone (NMP, 99.9%), and lithium iodide (LiI, 99%) were purchased from Aladdin. Polyvinyl alcohol (PVA, M.W. 89,000–98,000, 99% hydrolyzed) was purchased from Sigma Aldrich. Ethanol and acetone were purchased from Wuxi Yasheng Chemical Co., Ltd. Triton X-100 surfactant (10%, Sterile) was purchased from Shanghai Biyun Tian Biotechnology Co., Ltd. Ketjen black (KB, ECP600JD) was purchased from Suzhou Sinero Co., Ltd. Polyvinylidene difluoride (PVDF, 99%) was purchased from Macklin (Shanghai, China). Zinc foils (99.999%, 10–20 μm) were purchased from Shanghai Wenheng Metal Materials Co., Ltd. Cu foils (99.99%, 16 μm) and stainless steel (SS, 316L, 10 μm) foils were purchased from Hefei Kejing Material Co., Ltd. Glass fiber separators (aperture of 2.7 μm) were purchased from Hangzhou Situofan Biotechnology Co., Ltd. Aqueous microporous filtration membranes (0.22 μm) were purchased from Tianjin Jinteng Technology Co., Ltd. All materials were directly used without further purification. Amino-functionalized carbon nanotubes (amino-CNTs, 98%) were purchased from Shenzhen Suiheng Technology Co., Ltd. All metal ingots are used directly without any rolling, surface cleaning, or storing in inert environments treatments.

Preparation of deep-eutectic liquid electrolyte (deep-eutectic-LE) and non-eutectic liquid electrolyte (non-eutectic-LE)
The deep-eutectic-LE sample is prepared by mixing Zn(ClO4)2, deionized water, and UR in a molar ratio of 1:8:4.5 and stirring at 75 °C for 30 min. The non-eutectic-LE sample is prepared by mixing Zn(ClO4)2 and deionized water in a 1:8 molar ratio and stirring at 20 °C for 30 min.

Preparation of deep-eutectic hydrogel electrolyte (deep-eutectic-HE) and non-eutectic hydrogel electrolyte (non-eutectic-HE)
The deep-eutectic-HE and non-eutectic-HE samples are prepared through a convenient solvent-exchange process. Briefly, a certain amount of PVA powder is dissolved in DMSO under vigorous stirring at 95 °C for about 30 min to obtain a uniform 5 wt.% PVA solution. Subsequently, AN (3 M), MBA (3 mM), and APS (2 mM) are added to the PVA solution under an ice-water bath. Then, the above solution is transferred to a customized mold and copolymerized at 70 °C for 2 h in air isolation, leading to the pristine organogel. Finally, deep-eutectic-HE or non-eutectic-HE sample is prepared by immersing the organogel in deep-eutectic-LE or non-eutectic-LE respectively for 48 h to complete the solvent-exchange between DMSO and deep-eutectic-LE or non-eutectic-LE.

Preparation of positive electrode
The I2/CNTs positive electrode is prepared by a filtration and adsorption method. Briefly, amino-CNTs (108 mg), AC (12 mg), KB (6 mg), and Triton X-100 surfactant (1 mL) are dissolved in deionized water. Then, the above solution is subjected to ultrasonic dispersion treatment in an ice-water bath for 200 min using an ultrasonic cell disruptor to obtain a uniform mixture solution. Next, the above solution is vacuum filtered via an aqueous microporous filtration membrane. Afterwards, the filtration membrane is dissolved and washed by acetone, and the resulting CNTs film with a thickness of 20–200 μm is dried in a vacuum oven at 80 ºC for 24 h. The obtained self-supporting CNTs film is stamped into circular electrode plates with a diameter of 10 mm. Subsequently, the CNTs film electrode is immersed in an ethanol solution of 0.1 M I2 for 24 h to fully adsorb I2 into the CNTs film electrode (I2/CNTs). Finally, the I2/CNTs electrode is transferred to a vacuum oven and dried at 80 ºC for 24 h to obtain the I2/CNTs positive electrode. The loading amount of I2 active material is varied to be about 0.5–1.5 mg cm−2 (unless otherwise noted), 4.0–5.0 mg cm−2 (for high I2 loading tests), or 18–22 mg cm−2 (for the assembly of soft-packed batteries), which is determined by the thickness of CNTs film. All I2/CNTs positive electrodes are used directly without any rolling, surface cleaning, or storing in inert environments treatments.
The V2O5 positive electrode is prepared using a scratch coating method. Briefly, 140 mg of V2O5, 40 mg of KB, and 20 mg of PVDF (with a mass ratio of 7:2:1) were evenly ground with a agate mortar, and mixed with NMP, and stirred for 24 h to form a uniform slurry. The slurry is coated on a SS foil (thickness of 10 μm) with a stainless-steel scraper and dried in a vacuum oven at 60 ºC for 24 h. After drying, the V2O5 positive electrode is rolled by a roller machine with a pressure of 10 MPa. The active mass loading is 19–22 mg cm−2. All V2O5 positive electrodes are used directly without any surface cleaning or storing in inert environments treatments.

Material characterizations
Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra are collected using a Thermo Fisher Scientific Nicolet iS10. Raman spectra were collected using a Horiba JY Raman spectrometer equipped with a 473 nm laser light source. Scanning electron microscopy (SEM) images are obtained using FEI Nova NanoSEM-450 field emission scanning electron microscopy. The 2D and 3D topographies of the samples are observed with a Bruker Dimension Icon atomic force microscopy (AFM) instrument. The optical transmittance measurements are measured via a Shimadzu UV-2700 UV-vis-NIR spectrophotometer. X-ray diffraction (XRD) data is obtained using a Bruker D8 ADVANCE powder X-ray diffractometer. Small angle X-ray scattering (SAXS) data are measured on the Xeuss 2.0 SAXS system. The mechanical properties are measured using an Instron 3343 instrument. Differential scanning calorimetry (DSC) tests are conducted using a PerkinElmer Pyris 1 analyzer. The rheological tests are performed on a TA DHR-2 rheometer. The temperature-dependent sweeps are conducted ranging from 10 to 100 °C at 0.1% strain and 5 rad s−1. The moisture retention rate is tested by drying method. Specifically, a standard cylindrical sample is exposed to an environment of 25 °C and 15% relative humidity (RH). During this process, the weight of the sample is regularly measured, and the water retention of the sample over time is calculated using Equation (1), as provided below. The percentage content of I2 in the electrode is evaluated via thermogravimetric (TG) analysis on a Netzsch STA 449C thermal analyzer with a heating rate of 10 °C min−1 from 30 to 500 °C under a dry air atmosphere. Some electrodes and electrolytes are directly characterized after preparation, while others are obtained from aqueous batteries after specific electrochemical tests. In the air environment, stainless-steel pliers are used for disassembling CR2032 batteries, and stainless-steel tweezers are used to transfer electrodes and electrolytes. After transferring from the battery, the negative electrodes are rinsed with deionized water and dried at 60 °C before further characterization, while positive electrodes and electrolytes are dried without rinsed. The inert atmosphere has never been used.

Fabrication of the batteries
The electrochemical performances of LE and HE samples are evaluated using CR2032 batteries or soft-packaged pouch batteries. The SS||SS symmetrical batteries are composed of two SS foils (diameter of 12 mm, thickness of 10 μm) and a specific electrolyte. The Zn||Zn symmetrical batteries are composed of two Zn foils (diameter of 12 mm, thickness of 10 μm) and a specific electrolyte. The Zn||Cu half batteries are composed of a Zn foil negative electrode (diameter of 12 mm, thickness of 10 μm), a Cu foil positive electrode (diameter of 12 mm, thickness of 16 μm), and a specific electrolyte. The Zn||SS half batteries are composed of a Zn foil negative electrode (diameter of 12 mm, thickness of 10 μm), a SS foil positive electrode (diameter of 12 mm, thickness of 10 μm), and a specific electrolyte. The Zn||I2 CR2032 batteries are composed of a Zn foil negative electrode (diameter of 12 mm, thickness of 10 μm), a I2 positive electrode (diameter of 12 mm, thickness of 20 μm), and a specific electrolyte. The single layer Zn||I2 soft-packaged pouch batteries are composed of a layer of Zn foil negative electrode (5.0 cm × 4.0 cm, thickness of 10 μm), a layer of I2 positive electrode (5.0 cm × 4.0 cm, thickness of 20 μm, active mass loading of 1.0–1.5 mg cm−2 or 4.0–5.0 mg cm−2), and a layer of deep-eutectic-HE (6.0 cm × 5.0 cm, thickness of 10 μm). The multi-layer Zn||I2 soft-packaged pouch batteries are composed of 11 layers of Zn foil negative electrodes (5.0 cm × 4.0 cm, thickness of 10 μm), 10 layers of I2 positive electrodes (5.0 cm × 4.0 cm, thickness of 190±10 μm, active mass loading of 18–22 mg cm−2), and 20 layers of deep-eutectic-HEs (6.0 cm × 5.0 cm, thickness of 10 μm). The multi-layer Zn||V2O5 soft-packaged pouch batteries are composed of 11 layers of Zn foil negative electrodes (5.0 cm × 4.0 cm, thickness of 15 μm), 10 layers of V2O5 positive electrodes (double-side coated, 5.0 cm × 4.0 cm, thickness of 100±10 μm, active mass loading of 19–22 mg cm−2), and 20 layers of deep-eutectic-HEs (6.0 cm × 5.0 cm, thickness of 10 μm).
The diameter, thickness and shell material of the above-mentioned CR2032 battery are 20 mm, 3.2 mm, and stainless steel, respectively. The above-mentioned soft-packaged pouch batteries are packaged with polyimide films (thickness of 3 μm) under a vacuum condition, without applying external pressure during the charging/discharging cycling process. The above-mentioned electrolytes refer to deep-eutectic-HE (without any separator), deep-eutectic-LE (with glass fiber separators), non-eutectic-HE (without any separator), or non-eutectic-LE (with glass fiber separators). The thickness of deep-eutectic-HE, non-eutectic-HE and glass fiber separator are 10 μm, 100 μm and 250 μm, respectively. The size of deep-eutectic-HE, non-eutectic-HE and glass fiber separator used in CR2032 batteries are 16 mm in diameters. The size of deep-eutectic-HEs used in soft-packaged pouch batteries are 5.5 cm × 4.5 cm. All electrolytes are used within 7 days after preparation, storing in glass bottles (LEs) and cling films (HEs) under air atmosphere (20±2 °C). LEs and HEs are transferred with a pipettor (polypropylene pipette tip) and a stainless-steel tweezer under air atmosphere (20±2 °C), respectively. The glass fiber separators are cut with a stainless-steel circular slicer and are directly wetted by dripping electrolyte during battery assembly instead of prewetting. The negative/positive ratio (N/P) of the above-mentioned Zn||I2 coin batteries, Zn||I2 soft-packaged pouch batteries and Zn||V2O5 soft-packaged pouch batteries are calculated to be 18.50–55.50 or 5.55–6.94, 1.26–1.54 and 1.35–1.57 (based on the active mass loading of positive electrodes).

Electrochemical measurements
The cyclic voltammetry (CV), linear sweep voltammetry (LSV), alternating-current electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and Tafel curves are collected on RST-5200F and CHI-760 electrochemical workstations at 20±2 °C. The CV and LSV tests are performed at a scan rate of 1.0 mV s−1, with a potential range of −0.2–0.4 V and 1.0–3.0 V (vs. Zn/Zn2+), respectively. The EIS tests are performed with an amplitude of 5 mV in the frequency range between 100 kHz and 0.01 Hz at 20±2 °C. The measurement is conducted after holding the batteries at the specified temperature for 1 h during open-circuit potential. Nyquist plots obtained from EIS tests are fitted using ZView software. The CA tests are conducted after EIS tests immediately with a polarization voltage of 10 mV and a discharging time of 600 seconds. The Tafel curves are collected at the scanning rate of 1 mV s−1 across a voltage range of ±180 mV relative to the open-circuit voltage.
Galvanostatic charge/discharge cycling tests and rate performance measurements are conducted on a NEWARE CT-4008Tn battery analyzer using constant current techniques in a incubator (−40±2 °C, 20±2 °C or 80±2 °C). The Zn||Zn symmetrical batteries are tested at the current density ranging from 0.5–5.0 mA cm−2 with an area capacity of 0.5 mAh cm−2. The average Coulomb efficiency is measured with the Zn||Cu half batteries using the following procedure: a discharging process is first performed at a current density of 0.5 mA cm-2 for 1 hour. Then, 20 charging/discharging cycles are performed at 0.5 mA cm-2 with an area capacity of 0.5 mAh cm−2. Finally, the battery is charged to 0.5 V (vs. Zn/Zn2+) at a current density of 0.5 mA cm-2. The average Coulombic efficiency is then calculated via Equation 4. The Zn||I2 batteries are tested at the current density ranging from 0.5–10.0 A g−1 with a discharging cut-off potential of 0.7 V (vs. Zn/Zn2+) and a charging cut-off potential of 1.5 V (vs. Zn/Zn2+). The Zn||V2O5 batteries are tested at the current density of 0.5 A g−1 (based on the mass of V2O5 positive electrode active materials) with a discharging cut-off potential of 0.2 V (vs. Zn/Zn2+) and a charging cut-off potential of 1.6 V (vs. Zn/Zn2+). All electrochemical tests are conducted in a gas environment of air. No local temperature measurements are carried out. The specific capacities and current density of Zn||I2 and Zn||V2O5 batteries are calculated according to the mass of positive electrode active materials.
All electrochemical measurements are repeated at least 3 times to ensure statistical reliability and reproducibility. The values of ionic conductivity (5 repetitions) and Zn2+ transference number (5 repetitions) reflect statistical analysis of all tested batteries in parallel experiments, as these tests allow high-throughput measurement under identical conditions, and enable rigorous error quantification critical for characterization. Conversely, the CV (3 repetitions), LSV (3 repetitions), Tafel (3 repetitions) and long-cycling performance (3-5 repetitions) data presented in the figures represent measurements from a specific representative battery selected from multiple identical experiments (exhibited median performance in several repetitions). This approach is adopted because a single battery can display its detailed electrochemical performance in a complete curve, while the statistical analysis inevitably loses some critical information, especially the large amount of data of galvanostatic charge/discharge cycling tests (over 1000 cycles).

Calculation equations
The water retention (𝑊) is calculated according to the following equation:
𝑊 = 𝑊𝑠 / 𝑊0 × 100% Equation (1)
where 𝑊0 and 𝑊𝑠 are the mass of the sample after exposure for 0 and s h, respectively.
The ionic conductivity (σ) is calculated according to the following equation:
𝜎 = 𝑙 / (𝑅∙𝑆) Equation (2)
where 𝑙 and 𝑆 represent the thickness and area of the electrolyte, respectively. 𝑅 is the bulk resistance of the electrolyte.
The Zn-ion transference number (𝑡𝑍𝑛2+) is calculated according to the following equation:
𝑡𝑍𝑛2+ = 𝐼𝑠(Δ𝑉−𝐼0𝑅𝑒𝑙0) / 𝐼0(Δ𝑉−𝐼𝑠𝑅𝑒𝑙𝑠) Equation (3)
where Δ𝑉 is the polarization voltage (30 mV), 𝐼0 and 𝐼𝑠 are the initial current and steady current, respectively. 𝑅𝑒𝑙0 and 𝑅𝑒𝑙𝑠 are the initial interfacial resistance and steady interfacial resistance, respectively.
The average Coulombic efficiency (𝐶𝐸𝑎𝑣𝑔) during the Zn plating/stripping process in Zn||Cu half batteries is calculated according to the following equation:
𝐶𝐸𝑎𝑣𝑔 = 1− (𝑄1−𝑄𝑟) / (𝑄𝑐𝑁) Equation (4)
where 𝑄1 is the initial Zn plating capacity (5.0 mAh cm−2), 𝑄𝑟 is the capacity retention measured by the final Zn stripping process, 𝑄𝑐 is the fixed plating or striping capacity (0.5 mAh cm−2) involved in a single plating or stripping process (half cycle), and 𝑁 is the cycling number of plating/stripping process.
The percentage content of I2 in the electrode (𝑀𝐼2) is calculated according to the following equation:
𝑀𝐼2 = (𝑀𝐼2+C+H2O−𝑀C+H2O) / (1−𝑀C+H2O) Equation (5)
where 𝑀𝐼2+C+H2O and 𝑀C+H2O are the weight loss of electrodes containing I2 and electrodes without I2 in TG tests, respectively.
The percentage content of I2 retained in the positive electrode (I2 remained) is calculated according to the following equation:
I2 remained = 𝑀After (1−𝑀Before) / 𝑀Before (1−𝑀After) Equation (6)
where 𝑀Before and 𝑀After are the percentage content of I2 in the positive electrode before and after charging/discharging cycling tests, respectively.
The standard deviation (SD) of the samples is calculated according to the following equation:
SD = √ (∑ni=1 (xi−x̅)2) / (n−1) Equation (7)
where xi, x̅, and n are the i-th sample data, sample mean, and sample size, respectively. All error bars mentioned in the text represent SD.
The specific capacity of the batteries is calculated according to the following equation:
Specific capacity = 𝐶 / 𝑀𝑝 Equation (8)
where 𝐶 and 𝑀𝑝 are the capacity (mAh) and mass (g) of the positive electrode active materials, respectively.
The specific energy of the batteries is calculated according to the following equation:
Specific energy = 𝐸 / 𝑀 Equation (9)
where 𝐸 and 𝑀 are the total energy (Wh) and total mass (kg) of the battery, respectively.
The volumetric energy density of the batteries is calculated according to the following equation:
Volumetric energy density = 𝐸 / 𝑉 Equation (10)
where 𝐸 and 𝑉 are the total energy (Wh) and total volume (L) of the battery, respectively.

Theoretical simulations
All theoretical calculations are performed using Materials Studio. The geometric structures and binding energies between PAN, PVA, UR, H2O, and Zn(ClO4)2 are optimized using the DMol3 module. The gradient approximation (GGA) of the Perdew-Burke-Ernzerh (PBE) functional is used to describe electron exchange and associated energy. Density functional theory (DFT) - D3 method is used in the calculation to consider van der Waals forces. The plane wave cutoff energy is set to 520 eV, and the energy convergence value between two consecutive steps is less than 10−5 eV. The maximum allowable force is less than 0.002 eV/Å, and the maximum allowable displacement is less than 0.005 Å.
Four electrolyte models are constructed to simulate four as-prepared electrolytes: deep-eutectic-HE, deep-eutectic-LE, non-eutectic-HE, and non-eutectic-LE, respectively. Molecular dynamics (MD) simulations are performed on four electrolyte models using the Forcite module. The Condensed Phase Optimized Molecular Potential (COMPASS III) force field is selected for atomic simulation studies for all MD simulations. For each system, the isothermal isobaric ensemble (NPT) is first used to pre-equilibrate the system for 1 ns. Then, a 5 ns MD run is performed in the canonical ensemble (NVT) to achieve equilibrium, followed by a 5 ns NVT simulation to obtain the final electrolyte model. The time step of the MD simulation process mentioned above is set to 1 fs.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript addresses critical challenges in aqueous zinc-metal batteries by proposing and constructing a deep-eutectic hydrogel electrolyte that simultaneously achieves ultrathin configuration, high mechanical strength, and broad temperature tolerance. By leveraging a nanophase-separated PVA/PAN dual-phase structure, a hydrated deep eutectic solvent system, and an interpenetrating hydrogen-bonding network, the authors successfully achieve multiple objectives including water activity regulation, Zn2+ solvation structure optimization, and effective dendrite suppression. The resulting electrolyte demonstrates excellent ionic conductivity (28.2 mS cm-1) and mechanical performance (4.1 MPa fracture strength). Notably, the Zn-I2 flexible batteries assembled with this electrolyte deliver long-term cycling stability across an extreme temperature range (−40 to 80 °C), showcasing strong application potential. However, major revision is recommended before acceptance. Specific comments are as follows:\n1. The manuscript would benefit from a more detailed quantitative comparison of the Zn2+ solvation structure and electrochemical behavior between the proposed electrolyte and conventional thin hydrogel electrolytes (e.g., PVA-based systems), to better highlight the unique advantages of the presented system.\n2. Although the manuscript emphasizes the “yin-yang” dual-phase structure formed by PVA and PAN, the individual functional roles of these phases are described too briefly. A more thorough explanation is encouraged.\n3. According to the Supporting Information (SI), the preparation method of the iodine cathode is the same for both coin and pouch cells. However, the electrodes display significantly different iodine loadings. Please clarify how this discrepancy arises under the same preparation conditions.\n4. The equation used for calculating Zn2+ transference number in the SI contains an error in the oxidation state of Zn2+. Please correct this.\n5. The manuscript presents only ex-situ zinc plating/stripping results. For a more comprehensive understanding of zinc deposition behavior under different electrolytes, in-situ optical microscopy observations are recommended.\n6. The reported hydrogel thickness of 6 μm is based on measurements using a micrometer screw gauge. However, such instruments are generally unreliable for measurements below 10 μm. It is strongly recommended to supplement this with alternative, more accurate thickness measurement methods.\n7. The solubility values of iodine species in different electrolytes are listed without any information on the testing method. To enhance data credibility, please provide detailed procedures for how solubility was determined.\n8. Due to polyiodide shuttling, Zn-I2 batteries are prone to self-discharge. While the manuscript discusses this issue via theoretical calculations, experimental validation (e.g., open-circuit voltage decay tests) is necessary to confirm whether self-discharge occurs in practice.\n9. The manuscript provides the thickness of the pouch cell but lacks details on its length and width. Additionally, despite employing a high-loading iodine cathode (18–22 mg cm-2), the device is only used to power an LED display—an application that requires minimal current and could be handled by a coin cell. To better demonstrate practical viability, the authors should discuss the integrability and processability of this electrolyte in more complex or demanding flexible electronic devices.\n10. It is suggested to supplement electrochemical performance tests under different mechanical deformation conditions.", "reviewer_2": "This study presents an ultra-robust deep-eutectic hydrogel electrolyte fabricated via synergistic interplay of dual nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks. The unique yin-yang nanophases separation and deep-eutectic chemistry endows this hydrogel with excellent mechanical properties, electrochemical properties and temperature adaptability. The as-assembled zinc-iodine battery is thinner than paper (42 μm), which is impressive. The article features prominent innovation, systematic experimental design, detailed data, and reliable conclusions, holding significant academic value and application potential. It is recommended for acceptance, while there are some problems which shall be solved before its publication.\n1. It is mentioned that “hydrophilic PVA “yang” segments and hydrophobic PAN “yin” segments spontaneously organize into a yin-yang dual-nanophase separated architecture”. In addition, the author claims that the crystalline hydrogen-bond “yang” networks and dipole-stabilized hydrophobic “yin” zones cooperatively enhance mechanical strength of deep-eutectic-HE. The meanings of \"yang\" and \"yin\" seem to be ambiguous. Please provide a more specific description of \"yang\" and \"yin\".\n2. It is mentioned that “the salting-in effect induced by excess ions suppresses phase separation, resulting in a porous morphology with limited hierarchical structure”. Please provide a specific explanation for this phenomenon.\n3. The calculation method for the average Coulomb efficiency in Figure 4a should be provided.\n4. As shown in Figure 5b, Zn||deep-eutectic-LE||I2 battery exhibited a significant capacity decrease at high-rates. Why does deep-eutectic-LE exhibit poor performance at high rates? A more detailed discussion is necessary.\n5. Some experimental data in the paper did not provide error ranges. In some key performance tests, including elastic modulus, toughness, ionic conductivities and Zn2+ transference numbers, multiple repeated experiments should be conducted, and the error bar of the data should be provided.", "reviewer_3": "This work explored the fabrication of ultrathin Zinc iodide batteries using a robust deep-eutectic hydrogel electrolyte (HE) for flexible batteries with high energy density. The authors developed an ultra-robust hydrogel electrolyte with good ionic conductivity and mechanical resilience for Zinc-Iodine batteries with enhanced cycling durability. The presented research provides new insights into the design of ultrathin electrolytes for flexible batteries and holds significant scientific value. Therefore, this work can be considered for publication after the following points have been addressed carefully,\n1. The changes (or decrease) in glass transition temperature(Tg) with and without the addition of UR for the hydrogel electrode (HE) are 5.2 °C, whereas the change in Tg for the liquid electrolyte (LE) with UR is observed as ¬38 °C. The author should provide a reason why LE shows a greater Tg difference with UR.\n2. The Yin-Yang phase separation in HE can be seen clearly from the AFM phase image. The author should provide a AFM phase image of the film in addition to a height image.\n3. The authors provide a brief discussion on the mechanism of the Zinc-I2 battery, which should decipher what happens during charge and discharge, and how Zn ions are stored.\n4. It's impressive to see the cell with HE works well at extreme conditions of 80 °C. It would be more advantageous to explore the critical temperature at which the cell fails. ie., Up to what is the maximum temperature (harsh condition), the cell performs well.\n5. The author should provide a comparison of this work with similar work in the literature to highlight the advantages of this work.\n6. The mass loading for the electrochemical test is too low. The performance of the cell should be tested with a mass loading higher than 3 mg cm-2.\n7. At 2Ag-1, the capacity retention is 65.77% after 10k cycles. Here, what is the cause of the capacity degradation (other than dendrite formation) in the charge and discharge curve? The author should compare the structure change (using XRD or XPS) of the electrode after degradation with that of a fresh electrode to illustrate the degradation."}, "author_response": "Manuscript ID: NCOMMS-25-57311-T\nManuscript title: Thinner-Than-Paper and Extreme-Temperature-Adaptive Znic-Iodine Batteries Enabled by Nanophase Separated Deep-Eutectic Hydrogel Electrolytes\nWe sincerely appreciate the reviewers’ valuable suggestions on this manuscript. We have carefully revised the manuscript according to the reviewers’ valuable and helpful suggestions. The revised sections are highlighted in yellow. The point-by-point responses to the reviewers’ comments are listed as below:\nReviewer #1:\nThis manuscript addresses critical challenges in aqueous zinc-metal batteries by proposing and constructing a deep-eutectic hydrogel electrolyte that simultaneously achieves ultrathin configuration, high mechanical strength, and broad temperature tolerance. By leveraging a nanophase-separated PVA/PAN dual-phase structure, a hydrated deep eutectic solvent system, and an interpenetrating hydrogen-bonding network, the authors successfully achieve multiple objectives including water activity regulation, Zn2+ solvation structure optimization, and effective dendrite suppression. The resulting electrolyte demonstrates excellent ionic conductivity (28.2 mS cm−1) and mechanical performance (4.1 MPa fracture strength). Notably, the Zn-I flexible batteries assembled with this electrolyte deliver long-term cycling stability across an extreme temperature range (−40 to 80 °C), showcasing strong application potential. However, major revision is recommended before acceptance. Specific comments are as follows:\nResponse: Thank you very much for taking your valuable time to review our manuscript and offer positive comments and thoughtful suggestions, which enables us to improve our manuscript. We have carefully addressed your concerns point-by-point, as detailed below.\nQ1. The manuscript would benefit from a more detailed quantitative comparison of the Zn2+ solvation structure and electrochemical behavior between the proposed electrolyte and conventional thin hydrogel electrolytes (e.g., PVA-based systems), to better highlight the unique advantages of the presented system.\nResponse: Thank you for your constructive suggestion. As per your recommendation, we have supplemented detailed quantitative comparisons of the Zn2+ solvation structures and the electrochemical behaviors between the proposed electrolyte and conventional thin hydrogel electrolytes in the revised Manuscript and Supplementary Information (SI), as follows:\nTo contextualize these results, Fig. 3i and Supplementary Table 5-6 compared deep-eutectic-HE against other state-of-the-art HEs across several critical performance parameters: fracture strength (4.09 MPa), ionic conductivity (28.2 mS cm−1), electrochemical stability window (2.69 V), low-temperature tolerance (−40 °C), high-temperature tolerance (80 °C), film thickness (6 μm), coordination number of Zn-H O (2.71), Zn2+ transference number (0.65), cycling stability, and battery lifespan.[16, 30, 49-59]\nOverall, the as-proposed deep-eutectic-HE uniquely combines these attributes, establishing it as a promising multifunctional electrolyte platform.\nFig. 3 Electrochemical performances. i, Performance comparisons between the deep-eutectic-HE and other recently reported HEs in terms of fracture strength, ionic conductivity, electrochemical stability window, and low-/high-temperature tolerance.\nSupplementary Table 5. Parameter comparisons of the fracture strength, low-/high-temperature tolerance, film thickness, and Zn2+ solvation structures between the deep-eutectic-HE in this work with other representative hydrogel or eutectic electrolytes reported in previous literature.\nHigh- Zn2+ Solvation\nFracture /Low- Film structure\nReference Electrolyte strength temperatur thickness (Coordination\n(MPa) e tolerance (μm) number of Zn-\n(°C) H O)\n4.10 80/−40 6.0 2.71\nwork (hydrogel/eutectic)\nPAM-Hbimcp-Zn\n[16] 0.10 25/−45 1000.0 4.33\n(hydrogel)\nPVA-PAM-PAN\n[30] 24.80 25/−10 500.0 5.00\n(hydrogel)\nBD/Zn(ClO ) /LiCl\n4 2\n[49] 0.06 70/−20 200.0 2.00\n(hydrogel/eutectic)\nPAM-1,2-PG\n[50] 0.04 25/−30 700.0 5.76\n(hydrogel)\nSAu-PAA/PVP\n[51] 3.50 60/−25 2000.0 N/A\n(hydrogel/eutectic)\nChCl/EG-PVA\n[52] 0.51 50/−40 1000.0 5.00\n(hydrogel/eutectic)\nUrea/ZnAc /LiAc\n2\n[53] 0.06 60/−20 N/A 2.00\n(eutectic)\nChCl/EG-PTFE\n[54] 3.50 80/−20 750.0 N/A\n(hydrogel/eutectic)\nZn(OTf) -Cellulose\n2\n[55] 0.82 60/20 10.0 6.00\n(hydrogel/eutectic)\nC-PVA/PAN\n[56] 24.70 60/30 20.0 N/A\n(hydrogel)\nSupplementary Table 6. Performance comparisons of the electrochemical performances between the deep-eutectic-HE in this work with other representative hydrogel or eutectic electrolytes reported in previous literature at room temperature, including ionic conductivity, Zn2+ transference number (t 2+), electrochemical stability window (ESW),\nZn\ncycling stability, and battery lifespan.\nCycling\nIonic Battery lifespan\nESW stability\nReference Electrolyte conductivity t\nZn\n2+ (Cathode\n(V) (mA\n(mS cm−1) /A g−1/cycles)\ncm−2/h)\nThis Deep-eutectic-HE\n28.16 0.65 2.69 0.5/4200 I /5.0/36000\n2\nwork (hydrogel/eutectic)\nPAM-Hbimcp-Zn\n[16] 38.20 0.77 2.49 1.0/500 V\n5\n/2.0/1000\n(hydrogel)\nPVA-PAM-PAN\n[30] 28.90 0.52 2.51 0.5/2000 V\n5\n/1.0/800\n(hydrogel)\nBD/Zn(ClO ) /LiCl\n4 2\n[49] 5.62 0.30 2.60 1.0/5000 PANI/3.0/1000\n(hydrogel/eutectic)\nPAM-1,2-PG\n[50] 29.60 N/A 2.55 1.0/3600 VOH/1.0/500\n(hydrogel)\nUrea/ZnAc /LiAc\n2\n[53] 2.34 N/A 2.20 0.5/1130 LMO/0.6/920\n(eutectic)\nZn(OTf) -Cellulose\n2\n[55] 29.50 N/A 1.90 4.0/4100 V\n5\n/1.0/1000\n(hydrogel/eutectic)\nC-PVA/PAN NH 4 V 4 O 10\n[56] 17.40 0.64 2.48 1.0/3500\n(hydrogel) /20.0/3000\nPEGDA/1173/Zn\n[57] 17.51 0.56 2.60 1.0/2100 I\n2\n/2.0/10000\n(hydrogel)\nIC-ZnSO\n4\n[58] 42.95 0.51 2.72 1.0/1000 I\n2\n/1.0/5000\n(hydrogel)\nPVA-urea-ZnSO\n4\n[59] 31.20 N/A 2.54 0.1/2300 I /1.0/8500\n2\n(hydrogel)\nThese parameter and performance comparisons clearly underscore the unique advantages of the as-proposed deep-eutectic-HE system in terms of fracture strength, low-/high-temperature tolerance, film thickness, Zn2+ solvation structure, and electrochemical performances. We hope this response addresses your concern adequately.\nQ2. Although the manuscript emphasizes the \"yin-yang\" dual-phase structure formed by PVA and PAN, the individual functional roles of these phases are described too briefly. A more thorough explanation is encouraged.\nResponse: Thank you for your valuable feedback. We have carefully revised the manuscript to provide a more thorough explanation of the individual functional roles of PVA and PAN phases within the \"yin-yang\" dual-phase structure as follows:\nDuring this phase evolution process, hydrophilic phases (rooted in the hydrophilic hydroxyl groups on PVA chains) and hydrophobic phases (formed via dipole-dipole interactions of PAN segments) spontaneously organize into a dual-nanophase separated architecture. This architecture, in synergy with the crystalline domains formed by a part of PVA segments, significantly enhances the mechanical strength of deep-eutectic-HE. Simultaneously, the hydrophilic hydroxyl groups of PVA contribute to expanding the polymer network, increasing the content of hydrated eutectic solvent in the hydrogel and forming abundant hydrogen bonds with H O to reduce the activity of H O. Moreover, the\n2 2\nhydrophobic cyano groups on PAN chains construct a rapid transfer channel for Zn2+, thereby improving the electrochemical kinetics of deep-eutectic-HE.[30, 32]\nThese detailed descriptions aim to better clarify the synergistic effects and unique advantages of this dual-phase design. We hope this response addresses your concern adequately.\nQ3. According to the Supporting Information (SI), the preparation method of the iodine cathode is the same for both coin and pouch cells. However, the electrodes display significantly different iodine loadings. Please clarify how this discrepancy arises under the same preparation conditions.\nResponse: Thank you for your insightful comment. We have carefully addressed this concern in the revised Supplementary Information (SI). The detailed preparation processes of different iodine cathodes have been included in SI as follows:\nAfterwards, the filtration membrane was dissolved and washed by acetone, and the resulting CNTs film with a thickness of 20–200 μm was dried in a vacuum oven at 80 ºC for 24 h.\nThe loading amount of I active material is varied to be about 0.5–1.5 mg cm−2 (unless\n2\notherwise noted), 4.0–5.0 mg cm−2 (for high I loading tests), or 18–22 mg cm−2 (for the\n2\nassembly of soft-packed batteries), which is determined by the thickness of CNTs film.\nSpecifically, the iodine loadings were mainly determined based on the thickness of the CNTs film, a parameter that can be precisely controlled during the vacuum filtration process. We hope these added experimental details resolve your query.\nQ4. The equation used for calculating Zn2+ transference number in the SI contains an error in the oxidation state of Zn2+. Please correct this.\nResponse: Thank you for pointing out this crucial error. We have thoroughly checked and corrected the equation for calculating the Zn2+ transference number in the Supplementary Information (SI). The oxidation state of Zn2+ has now been accurately represented in the revised equation as follows:\nThe Zn-ion transference number (𝑡 ) was calculated according to the following\n𝑍𝑛2+\nequation:\nt = \n𝐼𝑆(Δ𝑉−𝐼0𝑅\ne\n0\nl\n)\n(Equation 3)\n𝑍𝑛2+ 𝐼0(Δ𝑉−𝐼𝑠𝑅\ne\ns\nl\n)\nwhere Δ𝑉 is the polarization voltage (30 mV), 𝐼 and 𝐼 are the initial current and\n0 𝑠\nsteady current, respectively. 𝑅0 and 𝑅𝑠 are the initial interfacial resistance and steady\ne𝑙 𝑒𝑙\ninterfacial resistance, respectively.\nAdditionally, we have double-checked all other equations and relevant calculations in the SI to ensure there are no further mistakes. We appreciate your attention to detail, which has helped us improve the accuracy of our work.\nQ5. The manuscript presents only ex-situ zinc plating/stripping results. For a more comprehensive understanding of zinc deposition behavior under different electrolytes, in-situ optical microscopy observations are recommended.\nResponse: Thank you for your insightful suggestion. To provide a more comprehensive understanding of zinc deposition behavior under different electrolytes, we have incorporated in-situ optical microscopy observations in the revised Manuscript and Supplementary Information (SI) as follows:\nSupplementary Fig. 14 a-b, In-situ optical microscopy images of the Zn plating processes in (a) deep-eutectic-HE and (b) deep-eutectic-LE, respectively.\nThe zinc deposition behavior in different electrolytes was observed by in-situ optical microscopy (Supplementary Fig. 14). In deep-eutectic-HE, the Zn surface is flat and smooth, without obvious protrusions throughout the whole deposition process. In contrast, in deep-eutectic-LE, Zn protrusions emerge on Zn surface after consecutive deposition for 20 min, and obvious Zn dendrites are observed after 40 min. These results are consistent well with the SEM observations (Fig. 4f-g), indicating that the deep-eutectic-HE is effective in inhibiting the growth of Zn dendrites.\nThese in-situ optical microscopy observations complement our ex-situ results and offer deeper insights into the deposition mechanisms. We hope the addition of these data meets your expectations.\nQ6. The reported hydrogel thickness of 6 μm is based on measurements using a micrometer screw gauge. However, such instruments are generally unreliable for measurements below 10 μm. It is strongly recommended to supplement this with alternative, more accurate thickness measurement methods.\nResponse: Thank you for your constructive advice. To address the concern regarding the accuracy of hydrogel thickness measurement, we have supplemented our study with side-view SEM measurements. The SEM images, now included in both the revised Manuscript and Supplementary Information (SI), provide more precise and reliable measurement results of the gel thickness, in line with our initial measurement data.\nSupplementary Fig. 17 a-b, Side-view SEM images of deep-eutectic-HE, indicating that it has a film thickness of 5.84 μm.\nImpressively, the ultra-robust nanoarchitecture enables fabrication of 6-μm-thick deep-eutectic-HE membranes while resisting dendrite penetration (Supplementary Fig. 16-17).\nWe hope this additional evidence could address your concern.\nQ7. The solubility values of iodine species in different electrolytes are listed without any information on the testing method. To enhance data credibility, please provide detailed procedures for how solubility was determined.\nResponse: Thank you for your valuable feedback regarding the solubility testing methods of iodine species in different electrolytes. To enhance the credibility of the solubility data for iodine species in different electrolytes, we have described the detailed experimental procedures for the solubility tests in Supplementary Information (SI) as follows:\nThe solubility tests of I− species in deep-eutectic-LE, non-eutectic-LE, and 2 M ZnSO\n4\naqueous solution were conducted as follows: First, a saturated solution of LiI was prepared in each electrolyte by stirring excess LiI at 25 °C for 24 h until reaching a dissolution equilibrium. The mixture was then filtered through a 0.22 μm syringe filter to remove undissolved LiI, and the weight of which was obtained via weighing the syringe filter after drying. Then, the concentration of iodine species in the filtrate can be calculated based on the weight variation of LiI.\nWe hope these supplemented experimental details provide the necessary transparency and strengthen the reliability of our findings.\nQ8. Due to polyiodide shuttling, Zn-I batteries are prone to self-discharge. While the\n2\nmanuscript discusses this issue via theoretical calculations, experimental validation (e.g., open-circuit voltage decay tests) is necessary to confirm whether self-discharge occurs in practice.\nResponse: Thank you for your insightful suggestion. To experimentally validate the self-discharge behavior of Zn-I batteries, we have conducted self-discharge tests. The results\n2\nare now presented in the revised Supplementary Information (SI), as follows.\nSupplementary Fig. 24 Self-discharge tests of Zn||I batteries assembled with deep-\n2\neutectic-HE or deep-eutectic-LE at the current density of 0.5 A g−1, respectively.\nSelf-discharge tests were also performed to evaluate the suppression of I− dissolution and polyiodide shuttling effects in deep-eutectic-HE (Supplementary Fig. 24). After standing for 24 h, the capacity retention of Zn||deep-eutectic-HE||I battery is 93.50%,\n2\nmuch higher than that of Zn||deep-eutectic-LE||I battery (80.37%), indicating the\n2\nexcellent capability of deep-eutectic-HE to inhibit I− dissolution and polyiodide shuttling.\nThese experimental results favorably complement our theoretical calculations and strengthen the reliability of our findings. We hope this addition adequately addresses your concern.\nQ9. The manuscript provides the thickness of the pouch cell but lacks details on its length and width. Additionally, despite employing a high-loading iodine cathode (18–22 mg\ncm−2), the device is only used to power an LED display—an application that requires minimal current and could be handled by a coin cell. To better demonstrate practical viability, the authors should discuss the integrability and processability of this electrolyte in more complex or demanding flexible electronic devices.\nResponse: Thank you for your valuable feedback. We have now supplemented the length and width parameters for all pouch batteries in the manuscript and Supplementary Information (SI). Meanwhile, we have also discussed the integrability and processability of the thinner-than-paper batteries in more complex or demanding flexible electronic devices. The related contents have been added in the revised Manuscript and SI, as follows:\nFig. 5 Electrochemical performances of zinc-metal batteries. g, Optical photographs of thinner-than-paper Zn||deep-eutectic-HE||I battery and its ability to power a LED\n2\npanel after folded into a paper airplane and cut off different parts by scissors (The size of each Zn||deep-eutectic-HE||I battery is 6.0 cm × 4.8 cm × 42 μm).\n2\nof −40 °C and (b) a high temperature of 80 °C. The size of each Zn||deep-eutectic-HE||I\n2\nbattery is 6.0 cm × 4.8 cm × 42 μm.\nSupplementary Fig. 28 a-b, Optical photographs of three series-connected thinner-than-paper Zn||deep-eutectic-HE||I batteries (a) integrated into a wristwatch band and its\n2\nability to power a wristwatch and (b) its ability to charge a smartphone. The size of each Zn||deep-eutectic-HE||I battery is 5.0 cm × 2.5 cm × 42 μm.\nWe hope these additions adequately address your concerns.\nQ10. It is suggested to supplement electrochemical performance tests under different mechanical deformation conditions.\nResponse: Thank you for your constructive suggestion. To better demonstrate the mechanical robustness of the flexible batteries, we have supplemented electrochemical performance tests under different bending conditions in the revised Manuscript and Supplementary Information (SI) as follows:\nSupplementary Fig. 27 Long-term cycling stability of thinner-than-paper Zn||deep-eutectic-HE||I pouch batteries tested under different bending states: unbent, bent to 90°,\n2\nbent to 180°, respectively, and then recovered to unbent state.\nEven under 90° and 180° bending states, the capacity retention trends of the thinner-than-paper Zn||I pouch batteries during 3,000 cycles are almost identical to the normal\n2\nunbent state (Supplementary Fig. 27), confirming that the batteries maintain stable electrochemical performances even under significant mechanical deformation, highlighting its potential for practical flexible applications.\nWe hope these supplemented experimental data could adequately addresses your concern.\nReviewer #2:\nThis study presents an ultra-robust deep-eutectic hydrogel electrolyte fabricated via synergistic interplay of dual nanophase separation, hydrated eutectic solvation, and hydrogen-bond networks. The unique yin-yang nanophases separation and deep-eutectic chemistry endows this hydrogel with excellent mechanical properties, electrochemical properties and temperature adaptability. The as-assembled zinc-iodine battery is thinner than paper (42 μm), which is impressive. The article features prominent innovation, systematic experimental design, detailed data, and reliable conclusions, holding significant academic value and application potential. It is recommended for acceptance, while there are some problems which shall be solved before its publication.\nResponse: We sincerely thank you for your review of our manuscript and providing very helpful comments to improve it. We have carefully addressed your concerns point-by-point, as detailed below.\nQ1. It is mentioned that \"hydrophilic PVA \"yang\" segments and hydrophobic PAN \"yin\" segments spontaneously organize into a yin-yang dual-nanophase separated architecture\". In addition, the author claims that the crystalline hydrogen-bond \"yang\" networks and dipole-stabilized hydrophobic \"yin\" zones cooperatively enhance mechanical strength of deep-eutectic-HE. The meanings of \"yang\" and \"yin\" seem to be ambiguous. Please provide a more specific description of \"yang\" and \"yin\".\nResponse: Thanks for your valuable suggestion! In the context of our research, the \"Yang\" phase refers to the hydrophilic segments composed of polyvinyl alcohol (PVA), while the \"yin\" phase is composed of hydrophobic polyacrylonitrile (PAN). As the terms \"yang\" and \"yin\" are metaphorical, they can easily mislead readers. Therefore, the use of the expression \"yin-yang resemblance\" has been avoided throughout the revised Manuscript. The content related to \"yang\" and \"yin\" has been modified as follows:\nDuring this phase evolution process, hydrophilic phases (rooted in the hydrophilic hydroxyl groups on PVA chains) and hydrophobic phases (formed via dipole-dipole interactions of PAN segments) spontaneously organize into a dual-nanophase separated architecture. This architecture, in synergy with the crystalline domains formed by a part of PVA segments, significantly enhances the mechanical strength of deep-eutectic-HE. Simultaneously, the hydrophilic hydroxyl groups of PVA contribute to expanding the polymer network, increasing the content of hydrated eutectic solvent in the hydrogel and forming abundant hydrogen bonds with H O to reduce the activity of H O. Moreover, the\n2 2\nhydrophobic cyano groups on PAN chains construct a rapid transfer channel for Zn2+, thereby improving the electrochemical kinetics of deep-eutectic-HE.[30, 32]\nQ2. It is mentioned that \"the salting-in effect induced by excess ions suppresses phase separation, resulting in a porous morphology with limited hierarchical structure\". Please provide a specific explanation for this phenomenon.\nResponse: Thank you for your insightful comment regarding the statement, \"the salting-in effect induced by excess ions suppresses phase separation, resulting in a porous morphology with limited hierarchical structure.\" We appreciate the opportunity to provide a more detailed explanation of this phenomenon in the revised Manuscript as follows:\nSpecifically, the poorly hydrated chaotropes anions ClO −) will induce hydrophilic\n4\neffects of the polymer chain segments, while weakening the hydrogen bonds between polymer chain segments, causing the polymer to dissolve (i.e., salting in). Consequently, the compaction degree of the PVA network is significantly reduced, making it difficult to form a nanoscale phase separation structure with PAN.[34]\nWe hope this supplemented discussion can adequately address your concern.\nQ3. The calculation method for the average Coulomb efficiency in Figure 4a should be provided.\nResponse: Thank you for your constructive feedback on our manuscript. We have now included a detailed description of the calculation method for the average Coulomb efficiency presented in Fig. 4a as follows:\nThe average Coulombic efficiency (𝐶𝐸 ) during the Zn plating/stripping process in\n𝑎𝑣𝑔\nZn||Cu half batteries was calculated according to the following equation:\n𝐶𝐸 = 1−\n𝑄1−𝑄𝑟\n(Equation 4)\n𝑎𝑣𝑔\n𝑄𝑐𝑁\nwhere 𝑄 is the initial Zn plating capacity (5.0 mAh cm−2), 𝑄 is the capacity retention\n1 𝑟\nmeasured by the final Zn stripping process, 𝑄 is the fixed plating or striping capacity\n𝑐\n(0.5 mAh cm−2) involved in a single plating or stripping process (half cycle), and 𝑁 is the cycling number of plating/stripping process.\nThis addition enhances the reproducibility and clarity of our results. We appreciate your guidance in improving the manuscript.\nQ4. As shown in Figure 5b, Zn||deep-eutectic-LE||I battery exhibited a significant\n2\ncapacity decrease at high-rates. Why does deep-eutectic-LE exhibit poor performance at high rates? A more detailed discussion is necessary.\nResponse:\nThank you for your insightful comment regarding the capacity reduction of the Zn||deep-eutectic-LE||I battery at high rates, and we have supplemented relevant descriptions in\n2\nthe manuscript:\nIn contrast, the inferior rate performance of deep-eutectic-LE control sample originates from three synergistic limitations. Firstly, sluggish Zn2+ transport kinetics of deep-eutectic-LE arise from the unoptimized Zn2+ solvation structure, causing insufficient dissociation and reduced ionic conductivity under rapid ion flux demands at high rates. Secondly, the absence of a robust hydrogen-bond network in deep-eutectic-LE induces elevated interfacial impedance and uncontrolled Zn dendrite, both of which consuming active Zn and electrolyte, resulting in irreversible capacity loss. Thirdly, the low Zn2+ transference number of deep-eutectic-LE exacerbates a concentration polarization across electrodes at high rates, further limiting cathode capacity utilization. These factors collectively result in the poor rate performance of deep-eutectic-LE control sample.\nWe hope this explanation could clarify the capacity reduction of Zn||deep-eutectic-LE||I battery at high rates.\nResponse: Thank you very much for your critical feedback regarding data reproducibility and statistical rigor. To address these concerns, we have presented error ranges of all key experimental data (including elastic modulus, toughness, ionic conductivities and Zn2+ transference numbers) in the revised Manuscript and Supplementary Information (SI), calculated from ≥ 3 independent repetitions. The updated data sets have been supplemented in the revised Manuscript and SI, as follows:\nFig. 2 Mechanical Properties and Temperature Tolerance. a-b, (a) Tensile-strain curves, (b) elastic modulus, and toughness of deep-eutectic-HE and non-eutectic-HE.\nFig. 3 Electrochemical performances. a-c, (a) Ionic conductivities, (b) Zn2+ transference numbers, and (c) interfacial impedances of deep-eutectic-HE, deep-eutectic-LE, non-eutectic-HE, and non-eutectic-LE at different temperatures, respectively.\nSupplementary Fig. 7 (a) Nyquist plots of Zn||deep-eutectic-HE||Zn symmetric batteries and (b) ionic conductivities of deep-eutectic-HE in a temperature range from −40 to 80 °C.\nReviewer #3:\nThis work explored the fabrication of ultrathin Zinc iodide batteries using a robust deep-eutectic hydrogel electrolyte (HE) for flexible batteries with high energy density. The authors developed an ultra-robust hydrogel electrolyte with good ionic conductivity and mechanical resilience for Zinc-Iodine batteries with enhanced cycling durability. The presented research provides new insights into the design of ultrathin electrolytes for flexible batteries and holds significant scientific value. Therefore, this work can be considered for publication after the following points have been addressed carefully,\nResponse: Thank you for your review of our manuscript and the positive comments. We have carefully addressed your concerns point-by-point, as detailed below.\nQ1: The changes (or decrease) in glass transition temperature(Tg) with and without the addition of UR for the hydrogel electrode (HE) are 5.2 °C, whereas the change in Tg for the liquid electrolyte (LE) with UR is observed as −38 °C. The author should provide a reason why LE shows a greater Tg difference with UR.\nResponse: Thank you for your insightful comments highlighting the distinct Tg responses of HE and LE to UR addition. The +5.2 °C Tg increase in HE contrasts sharply with the −38 °C decrease in LE, reflecting divergent structural interactions.\nIn LE, UR forms extensive hydrogen bonds with H O, restricting vibrational/rotational\n2\nmobility of H O molecules, resulting in a relatively higher increase of 38 °C in Tg.[41] In\n2\ncontrast, pre-existing polymer network of HE confines H O within nanoscale pores,\n2\nthereby inhibiting the nucleation and growth of ice crystals.[42] The topological constraints of the polymer network already dominate, resulting in a modest Tg change. We have revised the manuscript to provide deeper insights into these mechanisms as follows:\nBenefiting from the high concentration of Zn(ClO ) , non-eutectic-LE and non-\n4 2\neutectic-HE exhibit similar ultra-low freezing points.[40] For deep-eutectic-LE, the addition of UR increases hydrogen bonds with H O, restricting movements such as\n2\nvibration or rotation of the H O molecules, resulting in an elevation in the glass transition\n2\ntemperature.[41] For deep-eutectic-HE, the dense network structure effectively confines\nH O molecules within nanoscale pores, thereby inhibiting the nucleation and growth of\n2\nice crystals.[42]\nThank you again for your valuable feedback, which has helped us improve the clarity and depth of our discussion.\nQ2: The Yin-Yang phase separation in HE can be seen clearly from the AFM phase image. The author should provide a AFM phase image of the film in addition to a height image.\nResponse: Thank you for your insightful comments and constructive suggestions regarding our AFM data. We understand that providing a more comprehensive set of AFM images is crucial for accurately elucidating the properties of materials. In our original study, the AFM tests were conducted using the \"auto-scan\" mode. Under this mode, we were only able to export the in-phase images. These in-phase images represent the surface topography when the phase difference between the probe vibration and the driving signal is close to 0, and they are mainly used to characterize the elastic interactions of the object.\nTo enhance the scientific rigor of our data, we have supplemented both the in-phase image and the amplitude error map in the revised Supplementary Information (SI).\nFurthermore, to fully address your concern, we have also included the AFM measurement results obtained in the tapping mode for the deep-eutectic-HE in the revised SI, as supplemented below. The tapping-mode AFM characterization is advantageous as it can provide phase images. As you correctly pointed out, the phase separation in deep-eutectic-HE can be clearly observed from the AFM phase image. This additional data set allows for a more in-depth and accurate analysis of the characteristics of deep-eutectic-HE. We believe that these supplementary experimental data could significantly strengthen the scientific foundation of our work.\nSupplementary Fig. 2 a-b, (a) 3D height and (b) corresponding 2D height AFM images collected on the surface of deep-eutectic-HE. c-d, Height distributions measured along the selected scan lines in (b). e-f, (e) In-phase image and (f) amplitude error image collected on the surface of deep-eutectic-HE.\nSupplementary Fig. 3 a-b, (a) AFM height image, (b) corresponding phase image and (c) corresponding amplitude error image collected on the surface of deep-eutectic-HE in the tapping mode.\nThank you again for your valuable input, which has helped us improve the quality and comprehensiveness of our research.\nQ3: The authors provide a brief discussion on the mechanism of the Zinc-I battery, which\n2\nshould decipher what happens during charge and discharge, and how Zn ions are stored.\nResponse: Thank you for your insightful feedback. In response to your suggestion, we have enriched the discussion on the mechanism of zinc-I battery in the revised\nDuring the discharging process of Zn-I batteries, I in the cathode undergoes a\n2 2\nreduction reaction and converts into I−, which combines with Zn2+ in the electrolyte to form ZnI and adsorbs in the cathode. Oppositely, a reverse pathway occurs during the\n2\ncharge process.\nSpecifically, the following chemical reactions occur during the charge-discharge processes of zinc-I batteries:\n2\nscientific value of our work.\nQ4: It's impressive to see the cell with HE works well at extreme conditions of 80 °C. It would be more advantageous to explore the critical temperature at which the cell fails. ie., Up to what is the maximum temperature (harsh condition), the cell performs well.\nResponse: Thanks for your insightful comment. We fully agree that exploring the critical failure temperature of the cell is crucial. Following your suggestion, we have conducted additional critical temperature tests, and the experimental results are presented in Supplementary Fig. 11 in the Supplementary Information, as follows:\nSupplementary Fig. 11 The critical working temperature tests of Zn||Zn symmetric batteries assembled with of deep-eutectic-HE, deep-eutectic-LE, non-eutectic-HE, and non-eutectic-LE, respectively.\nThe critical working temperature tests of Zn||Zn symmetric batteries assembled with different electrolytes revealed that the Zn||deep-eutectic-HE||Zn symmetric battery could maintain stable electrochemical performance up to ~80 °C, which is much superior to those of deep-eutectic-LE (~70 °C), non-eutectic-HE (~50 °C), and non-eutectic-LE (~60 °C) counterparts (Supplementary Fig. 11). When the operation temperature was raised higher than the critical working temperature, significant ionic insulation would occur due to the precipitation of salts from solvent evaporation for LE samples or the collapse of gel structure for HE samples.\nThese supplemented experimental data further underscore the robustness of our battery design under harsh conditions and provides valuable insights for its practical applications.\nQ5: The author should provide a comparison of this work with similar work in the literature to highlight the advantages of this work.\nResponse: Thank you for your constructive suggestion. We have addressed this concern by supplementing detailed comparisons between the proposed electrolyte in this work with previous studies in the literature. Specifically, we have provided a thorough analysis comparing these electrolytes in terms of fracture strength, low-/high-temperature tolerance, film thickness, Zn2+ solvation structure, and electrochemical performances in the revised Manuscript and Supplementary Information (SI), as follows:\nTo contextualize these results, Fig. 3i and Supplementary Table 5-6 compared deep-eutectic-HE against other state-of-the-art HEs across several critical performance parameters: fracture strength (4.09 MPa), ionic conductivity (28.2 mS cm−1), electrochemical stability window (2.69 V), low-temperature tolerance (−40 °C), high-temperature tolerance (80 °C), film thickness (6 μm), coordination number of Zn-H O (2.71), Zn2+ transference number (0.65), cycling stability, and battery lifespan.[16, 30, 49-59]\nOverall, the as-proposed deep-eutectic-HE uniquely combines these attributes, establishing it as a promising multifunctional electrolyte platform.\nFig. 3 Electrochemical performances. i, Performance comparisons between the deep-eutectic-HE and other recently reported HEs in terms of fracture strength, ionic conductivity, electrochemical stability window, and low-/high-temperature tolerance.\nSupplementary Table 5. Parameter comparisons of the fracture strength, low-/high-temperature tolerance, film thickness, and Zn2+ solvation structures between the deep-eutectic-HE in this work with other representative hydrogel or eutectic electrolytes reported in previous literature.\nHigh-/Low- Zn2+ Solvation\nFracture Film\ntemperature structure\nReference Electrolyte strength thickness\ntolerance (Coordination\n(MPa) (μm)\n(°C) number of Zn-H O)\nThis work 4.10 80/−40 6.0 2.71\n(hydrogel/eutectic)\nPAM-Hbimcp-Zn\n[16] 0.10 25/−45 1000.0 4.33\n(hydrogel)\nPVA-PAM-PAN\n[30] 24.80 25/−10 500.0 5.00\n(hydrogel)\nBD/Zn(ClO ) /LiCl\n4 2\n[49] 0.06 70/−20 200.0 2.00\n(hydrogel/eutectic)\nPAM-1,2-PG\n[50] 0.04 25/−30 700.0 5.76\n(hydrogel)\nSAu-PAA/PVP\n[51] 3.50 60/−25 2000.0 N/A\n(hydrogel/eutectic)\nChCl/EG-PVA\n[52] 0.51 50/−40 1000.0 5.00\n(hydrogel/eutectic)\nUrea/ZnAc /LiAc\n2\n[53] 0.06 60/−20 N/A 2.00\n(eutectic)\nChCl/EG-PTFE\n[54] 3.50 80/−20 750.0 N/A\n(hydrogel/eutectic)\nZn(OTf) -Cellulose\n2\n[55] 0.82 60/20 10.0 6.00\n(hydrogel/eutectic)\nC-PVA/PAN\n[56] 24.70 60/30 20.0 N/A\n(hydrogel)\nSupplementary Table 6. Performance comparisons of the electrochemical performances between the deep-eutectic-HE in this work with other representative hydrogel or eutectic electrolytes reported in previous literature at room temperature, including ionic conductivity, Zn2+ transference number (t 2+), electrochemical stability window (ESW),\nZn\ncycling stability, and battery lifespan.\nCycling\nIonic Battery lifespan\nESW stability\nReference Electrolyte conductivity t\nZn\n2+ (Cathode\n(V) (mA\n(mS cm−1) /A g−1/cycles)\ncm−2/h)\nDeep-eutectic-HE\nThis work 28.16 0.65 2.69 0.5/4200 I\n2\n/5.0/36000\n(hydrogel/eutectic)\nPAM-Hbimcp-Zn\n[16] 38.20 0.77 2.49 1.0/500 V\n5\n/2.0/1000\n(hydrogel)\nPVA-PAM-PAN\n[30] 28.90 0.52 2.51 0.5/2000 V\n5\n/1.0/800\n(hydrogel)\nBD/Zn(ClO ) /LiCl\n4 2\n[49] 5.62 0.30 2.60 1.0/5000 PANI/3.0/1000\n(hydrogel/eutectic)\nPAM-1,2-PG\n[50] 29.60 N/A 2.55 1.0/3600 VOH/1.0/500\n(hydrogel)\nUrea/ZnAc /LiAc\n2\n[53] 2.34 N/A 2.20 0.5/1130 LMO/0.6/920\n(eutectic)\nZn(OTf) -Cellulose\n2\n[55] 29.50 N/A 1.90 4.0/4100 V\n5\n/1.0/1000\n(hydrogel/eutectic)\nC-PVA/PAN NH 4 V 4 O 10\n[56] 17.40 0.64 2.48 1.0/3500\n(hydrogel) /20.0/3000\nPEGDA/1173/Zn\n[57] 17.51 0.56 2.60 1.0/2100 I\n2\n/2.0/10000\n(hydrogel)\nIC-ZnSO\n4\n[58] 42.95 0.51 2.72 1.0/1000 I\n2\n/1.0/5000\n(hydrogel)\nPVA-urea-ZnSO\n4\n[59] 31.20 N/A 2.54 0.1/2300 I /1.0/8500\n2\n(hydrogel)\nThese parameter and performance comparisons clearly demonstrate the distinct advantages of the deep-eutectic-HE proposed in this work in terms of fracture strength, low-/high-temperature tolerance, film thickness, Zn2+ solvation structure, and electrochemical performances. We hope these supplemented comparisons can adequately address your concern.\nQ6: The mass loading for the electrochemical test is too low. The performance of the cell should be tested with a mass loading higher than 3 mg cm−2.\nResponse: Thank you for your insightful suggestion. To address this concern, we have now conducted additional high mass loading tests with a loading higher than 3 mg cm−2. The detailed results and corresponding analysis have been thoroughly supplemented in the revised Manuscript and Supplementary Information (SI) as follows:\nSupplementary Fig. 23 Long-term cycling stabilities of Zn||deep-eutectic-HE||I and\n2 2\na high current density of 5.0 A g−1.\nLong-term cycling tests were also conducted at a high I loading of 4.0–5.0 mg cm-2\n2\n(Supplementary Fig. 23). The Zn||deep-eutectic-HE||I battery similarly demonstrated\n2\nbetter electrochemical performances, boasting an initial capacity of 144.32 mAh g−1 and a capacity retention of 88.35% (average decay: 0.0011% per cycle), which markedly surpasses those of Zn||deep-eutectic-LE||I battery.\nQ7: At 2 Ag−1, the capacity retention is 65.77% after 10k cycles. Here, what is the cause of the capacity degradation (other than dendrite formation) in the charge and discharge curve? The author should compare the structure change (using XRD or XPS) of the electrode after degradation with that of a fresh electrode to illustrate the degradation.\nResponse: Thank you for your valuable comments that can significantly improve the quality of our work. To address the issue of identifying the root cause of capacity degradation (excluding dendrite formation), we have employed thermogravimetric (TG) analysis in the revised Manuscript and Supplementary Information (SI) as follows:\nSupplementary Fig. 22 Thermogravimetric analysis of I /CNTs cathodes before and\n2\nafter 10,000 cycles at 2.0 A g−1. The percentage content of I in the cathodes before and\n2\nafter long-term cycling tests were calculated to be 34.71% and 27.51% via Equation 5, respectively.[59] The percentage content of I retained in the cathode after long-term\n2\ncycling test was calculated to be 71.39% via Equation 6.\nThermogravimetric analysis offered a clear explanation for the capacity degradation during long-term cycling (Supplementary Fig. 22).[59] After 10,000 cycles at 2.0 A g−1, it was discovered that the I content retained in the cathode had diminished to 71.39% of\n2\nits initial level, which could be ascribed to tardive I− dissolution and polyiodide shuttling behaviors.\nMeanwhile, it should be noted that iodine participates in conversion-type reactions (Zn + I ⇋ ZnI ) in Zn-I batteries. During the charging/discharging processes, the I\n2 2 2 2\ncontent retained in the cathode would be varied, but the cathodic host material (CNTs) does not undergo any structural changes. Consequently, it is not feasible to explore the causes of capacity degradation by XRD or XPS, as these techniques rely on detecting structural or chemical state alterations. This is clearly demonstrated in Fig. R1 and Fig. R2 as follows:\nFig. R1 XRD spectra of (black curve) pristine CNTs as cathodic host material, (green curve) I /CNTs cathode before cycling, and (blue curve) I /CNTs cathode after 10,000\n2 2\ncycles at 2.0 A g-l, respectively.\nFig. R2 XPS spectra at I 3d level of I /CNTs cathode (green curve) before and (blue curve) after 10,000 cycles at 2.0 A g-l, respectively.\nWe hope these additions can comprehensively address your concern about understanding the capacity degradation mechanism."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Based on the revisions provided, the manuscript has been appropriately revised, and this version can be accepted.", "reviewer_2": "ALl my concerns have been addressed properly, I have no more comments on this work."}, "author_response": ""}]

Decision letter