Negative electrode degradation induced by two-stage zinc plating and its recovery in zinc batteries

Domain: neuroscience
Published: 2026-01-27
Editorial outcome: major_revision

Abstract
Controlling the morphology of Zinc (Zn) deposits is an effective strategy to produce stable Zn-metal batteries. However, the degradation of Zn negative electrodes and changes in their morphology remain poorly understood. Here, we show that the Zn plating process has two distinct stages. The first being the formation of relatively dense, lumpy Zn, while the second involves the formation of porous mossy Zn on its protrusions, which changes into electrochemically inactive dead Zn during stripping. Based on this, we propose a strategy involving a combination of cationic and anionic reagents to revive the dead Zn. The cations create a positively charged inert region on the negative electrode surface for Zn-ion dispersion that inhibits mossy Zn formation, while the anions act as a redox mediator to revive the dead Zn. Consequently, the Zn negative electrode shows a Coulombic efficiency (CE) of 99.7% and stable Zn plating/stripping over 1400 h (10 mA cm−2 and 10 mAh cm−2). An Ah-scale pouch cell retains 96.2% capacity after 800 cycles. This work provides key insights into mossy Zn formation and proposes a promising approach for stable Zn-metal batteries.

Introduction
Rechargeable zinc-metal batteries (ZMBs) are known for their intrinsic safety, low cost, non-toxicity, and compatibility with aqueous electrolytes, and are regarded as a major alternative to lithium batteries1,2. These distinctive advantages position ZMBs as an ideal candidate for safety-critical uses, including smart grids and residential energy storage systems3. Nevertheless, their practical deployment has some major problems, primarily stemming from non-uniform Zn electrodeposition at the negative electrode, which triggers short circuits and rapid capacity decay4,5.

Many efforts have focused on elucidating the fundamental mechanisms governing this Zn nucleation and growth6–10. Current understanding is that the Zn deposition morphology is influenced by many factors, including current density11,12, ionic transport properties of electrolyte13,14, interfacial electrochemical environment15,16, and a lattice mismatch between the substrate and Zn17,18. To solve the problem of irregular Zn plating on planar substrates, various methods have been used, including, but not limited to, surface modification19,20, three-dimensional design of the host structure21,22, and changing the electrolyte formula23–25. Some recent studies have identified a dominant deposition morphology at low current densities, which is high-surface-area porous Zn comprised of tortuous nanowires or nanosheets, and distinct from classical diffusion-limited dendritic growth6,26–28. This prevalent but poorly understood structure, often described as mossy Zn rather than conventional dendrites, warrants particular attention due to its correlation with the formation of electrochemically inactive dead Zn that causes capacity loss during stripping. However, the origin, development, and prevention of the formation of this material remain poorly understood.

We now report the reason for the formation of mossy Zn and a strategy for its suppression and the reactivation of dead Zn. Using optical monitoring, we have revealed a two-stage plating mechanism consisting of the initial formation of compact lumpy Zn, followed by a transition to a mossy structure by the development of surface protrusions. During subsequent stripping of Zn, we have shown that the irreversible conversion of mossy Zn to inactive dead Zn is due to the loss of interfacial contact between the substrate and Zn. To deal with this issue, we report the use of cationic and anionic reagents in which the cationic component forms a positively charged inert region on the negative electrode surface to prevent local Zn2+ accumulation, while the anionic species acts as a redox mediator to revive the dead Zn. This combination allows prolonged Zn plating/stripping over 1400 h in Zn||Zn symmetric cells at 10 mA cm−2 and 10 mAh cm−2 and gives a life of 800 cycles to Ah-scale Zn||I2 pouch cells.

Results
Two-stage plating and stripping of the Zn negative electrode
To in situ monitor the Zn plating and stripping process, we designed a Zn||Ti cell in a customized microdish with openings on three sides, as depicted in Fig. 1a and Supplementary Fig. 1. The working electrode (a Ti wire) and counter electrode (a Zn wire) were aligned with ~1 mm spacing in a 1 M zinc trifluoromethanesulfonate (ZnOTF) aqueous electrolyte, accompanied by a Zn reference electrode. Ti was used as the working electrode because it is one of the most common current collectors for Zn negative electrodes and can prevent hydrogen evolution from affecting the observation of Zn plating. When a constant current density of 1 mA cm−2 was applied, metallic Zn deposits with a characteristic metallic luster nucleated on the Ti surface (Fig. 1c and Supplementary Video 1). The corresponding scanning electron microscopy (SEM) images show that the initial lumpy Zn deposits have a well-defined crystalline structure (Fig. 1d) that matches the thermodynamic Wulff construction of a hexagonal close-packed (hcp) Zn crystal. This smooth Zn surface acts like a mirror, specularly reflecting a large amount of incident light from the microscope’s illumination source directly back into the objective lens, which gives the Zn deposits a luminescent appearance.

After plating for ~60 min, the lumpy Zn progressively fills intergranular voids while exposing distinct edges. At the same time, a secondary mossy Zn morphology—comprised of a one-dimensional filamentary structure—nucleates preferentially at the protrusions on the lumpy Zn (Fig. 1d) and it is this mossy phase which eventually dominates the plating, whereas the lumpy Zn remains unchanged.

The voltage versus time profile showed decreased polarization during mossy Zn formation (Fig. 1b), contrary to classical dendritic behavior where interface depletion typically increases polarization. This fundamental difference suggests distinctly different mechanisms between mossy Zn growth and conventional diffusion-limited dendrite growth.

The morphological change of Zn deposits correlates with the increase in local current density at surface protrusions of lumpy Zn, which is attributed to an electric field concentration effect, commonly referred to as the “tip effect”. To support this mechanism, we performed finite element simulations to visualize the current density and electric field distribution of both two Zn morphologies. In this model, regular hexagons and elongated bars represent lumpy Zn and mossy Zn, respectively. As shown in Fig. 1e, f, the gradient colors denote current intensity and electric field. The maximum current density and electric field are intensely concentrated at the tips and edges of the lumpy Zn, triggering the formation of Zn whiskers. Once a mossy filament forms, the concentrated point shifts to the top of the Zn filament, creating a positive feedback loop that drives the rampant growth of mossy Zn.

Parametric studies showed the universality of this two-stage plating mechanism under different conditions. A prolonged deposition time leads to the proliferation of mossy Zn in the space between electrodes, ultimately causing cell short-circuiting without the production of other structures (Supplementary Fig. 2). Increasing or decreasing the current density produces a similar morphology change during Zn plating (Supplementary Figs. 3 and 4). We found that two-stage Zn deposition and stripping occurred on a planar Ti foil electrode during the cycle, indicating that this phenomenon is independent of the electrode’s geometric form (Supplementary Fig. 5). We also discovered that the simple replacement of the Zn salt in the electrolyte with typical ZnSO4, ZnCl2, and Zn(ClO4)2 electrolytes, did not prevent the initiation and growth of mossy Zn (Supplementary Figs. 6–8). The salt anion might influence the nucleation size and the timing of the transition of Zn morphologies. The use of Zn as the deposition substrate appeared to accelerate the formation of the mossy Zn (Supplementary Fig. 9). In addition, the use of stack pressure compressed the Zn deposits, making it more uniform, but did not change the intrinsic mechanism of the two-stage deposition process (Supplementary Figs. 10 and 11).

During the subsequent stripping process, the mossy Zn rapidly shrank until only black insoluble residues were left on the surface of the lumpy Zn (Fig. 1g), which then to dissolve, accompanied by a small increase in voltage polarization, implying that the lumpy Zn was more electrochemically stable than the mossy Zn. When the cell was charged to a cut-off potential of 0.5 V (vs. Zn/Zn2+), substantial Zn remained on the surface of the Ti electrode due to poor interfacial contact, generating electrochemically isolated dead Zn.

Characterization of lumpy and mossy Zn
During the transition from lumpy Zn to mossy Zn, we have investigated the changes in physical and electrochemical properties of the Zn deposits, such as crystallographic features, electrochemical active area, and resistance to side-reactions. As shown in Fig. 2a, diffraction peaks corresponding to (002)Zn, (101)Zn, and Ti substrate were detected after plating for 10 min. A key finding is that the (101)Zn and (100)Zn peaks intensified as the plating time increased, especially after the formation of the mossy Zn. The corresponding peak intensity ratios I(101)/I(002) and I(100)/I(002) were calculated and are shown in Fig. 2b. The I(101)/I(002) ratio increased dramatically from 1.06 to 1.75 when the deposition time increased from 60 to 120 min, implying (101)Zn-textured growth occurred in the mossy Zn.

The increased electrochemically active surface area induced by mossy Zn formation was corroborated by electric double-layer capacitance (EDLC) measurements (Fig. 2c and Supplementary Fig. 12). Moreover, the changes in impedance were monitored during the Zn plating. The interfacial impedance remained at ~400 Ω for the first 60 min and then markedly decreased to ~100 Ω, suggesting the formation of mossy Zn (Fig. 2d). This finding is consistent with both the optical microscope observations and EDLC results. The high electrochemical activity of the mossy Zn typically led to decreased anti-corrosion ability and increased hydrogen evolution. As expected, Tafel curves showed a sequential increase in corrosion current from 0.21 to 0.72, 1.77, and 4.12 mA cm−2 as the plating time increased from 10 to 60, 90, and 120 min (Fig. 2e). Figure 2f showed the linear sweep voltammetry (LSV) curves of different Zn deposits. The formation of the mossy Zn results in a significant increase in hydrogen evolution current for the Zn deposits at a same potential.

Combining the above results, a schematic, which describes the two-stage process of the Zn plating and stripping, is shown in Fig. 2g. The initial plating produces a lumpy Zn structure with a well-defined shape (Stage 1), whose edge growth gradually disrupts the homogeneity of the Zn-ion flux, inducing localized protrusions that develop into one-dimensional Zn filaments, which swiftly evolve into mossy Zn by tip-enhanced deposition (Stage 2). During stripping, preferential dissolution of the mossy Zn generates electrically isolated dead Zn due to the loss of interfacial contact between the filaments. This degradation underscores the critical need to suppress mossy Zn formation and revive dead Zn for battery longevity.

For this purpose, we have added a two-function reagent with cationic and anionic components to the electrolyte to prevent the formation of mossy Zn and revive the dead Zn (Fig. 2h). The cations migrate to the surface of the negative electrode driven by the electric field, creating a positively charged inert region that homogenizes the Zn-ion distribution, thus deterring the formation of mossy Zn. The anions, with their redox activity, generate oxidative mediators to react with the dead Zn to form electroactive Zn ions that can return for use in the battery cycle. As a proof-of-concept, acetylcholine iodide (ACI), consisting of acetylcholine cations and iodine anions (Supplementary Fig. 13), was introduced into a baseline ZnOTF electrolyte and is subsequently denoted as ZnOTF-ACI. Of note, the combination strategy of cations and anions is not limited to the ACI, as other bi-ionic form analogs exhibit similar effects, which will be discussed later.

Cation-mediated Zn plating without mossy Zn
We first investigated the role of acetylcholine cations in controlling the Zn deposition. To elucidate the adsorption layer of acetylcholine cations at the electrode and electrolyte interface, electrochemical quartz crystal microbalance (EQCM) measurements were performed. The experimental setup is shown in Fig. 3a, where an Au wafer with a quartz crystal sensor serves as the working electrode, and 0.2 M Na2SO4 aqueous solution containing NaI, containing ACI, and containing neither were used as electrolytes. When the potential swept from 0.1 V to −0.4 V (vs. Ag/AgCl), the maximum mass increase was ~7.3 and 3.6 ng in the 0.2 M Na2SO4 and 0.2 M Na2SO4-NaI, respectively (Fig. 3b, c). However, ~60.1 ng was detected when ACI was added. This large increase in mass is mainly attributed to the adsorption of acetylcholine cations rather than Na+, I−, or H2O.

To better elucidate the cation-mediated Zn negative electrode interface, we conducted the density functional theory (DFT) calculations (Supplementary Fig. 14 and Supplementary Data 1). As shown in Fig. 3f, the adsorption energy of the horizontal acetylcholine cations (−3.86 eV) was much higher than that of H2O (−0.32 eV), Zn2+ (−1.46 eV), iodide anions (−2.79 eV), and the vertical acetylcholine cations (−3.23 eV). This confirms the preferential adsorption between the acetylcholine cations and Zn negative electrode, which creates a positively charged inert layer on the Zn negative electrode to disperse Zn2+ ions.

Optical microscopy captured distinct deposition behavior in the ZnOTF-ACI electrolyte (Fig. 4a, Supplementary Fig. 15 and Supplementary Video 2). Specifically, after plating for 10 min, abundant shiny Zn seeds were uniformly distributed on the surface of the Ti electrode. These grew and fused together to produce a uniform coverage of the Ti electrode. Subsequent growth maintained a planar morphology, contrasting sharply with the filamentary growth in the baseline ZnOTF electrolyte. SEM images show a flat, lumpy Zn structure throughout the deposition process, accompanied by the emergence of the (002)Zn texture with typical microscopic changes (Fig. 4b). X-ray diffraction (XRD) also showed that the intensity of the (002)Zn peak increased slightly as the plating time increased (Fig. 4c and Supplementary Fig. 16). Notably, the significant improvement in Zn deposition morphology is attributed to acetylcholine cations rather than iodide anions, as the addition of iodide anions alone does not inhibit the formation of mossy Zn (Supplementary Fig. 17).

In addition, the in situ electrochemical impedance spectra (EIS) showed only a slight change in interfacial impedance during the Zn deposition process, indicating a good interfacial stability of the Zn deposits (Fig. 4d). Compared to its counterpart, the Nyquist plots of half-cells with the ZnOTF-ACI electrolyte had a small semicircle at the high-frequency region, possibly corresponding to the acetylcholine cation adsorption forming an additional interface. The Zn deposits with acetylcholine cations had a low surface area, thus providing strong resistance against corrosion and hydrogen evolution even in the baseline ZnOTF electrolyte (Supplementary Figs. 18 and 19). The initial nucleation behavior of Zn ions was investigated using chronoamperometry (CA). It was found that the current response of the ZnOTF-ACI electrolyte stabilized in a short time (~10 s) at a polarization of −150 mV, whereas the baseline ZnOTF electrolyte has a continuously increasing value over 300 s (Supplementary Fig. 20). This indicates that acetylcholine cations restrain the two-dimensional diffusion of Zn ions and promote uniform and flat Zn deposition. These results show that acetylcholine cations effectively prevent the transition from the deposition of lumpy Zn to mossy Zn. As a result, most Zn deposits can be stripped from the Ti substrate during subsequent charging, leaving behind a few particles of Zn debris (Fig. 4e).

Anion-mediated reactivation of dead Zn
In addition to the change in Zn deposition produced by acetylcholine cations, the I− anions of the ACI are believed to revive the dead Zn by generating a certain amount of oxidizing mediator (I3−) during charging. From a thermodynamic viewpoint, the reaction between I3− and Zn is spontaneous according to Gibbs free energy calculations (Supplementary Fig. 21). Experimental validation involved immersing the collected dead Zn in a Zn(I3)2 solution for 5 days (Fig. 5a). The initial orange solution became lighter, indicating that I3− was partially consumed by the oxidation of dead Zn, as evidenced by the reduced adsorption intensity in the ultraviolet-visible spectroscopy (UV/Vis) spectra (Fig. 5b). Inductively coupled plasma optical emission spectrometer (ICP-OES) quantification test showed the Zn-ion concentration increasing from 2.34 to 7.47 mM, which nearly matched the theoretical yield (Fig. 5c). These results confirm the effectiveness of the iodine in converting dead Zn (Zn0) to electroactive Zn2+. Furthermore, Znx(OTf)y(OH)2x−y·nH2O (ZOTH), a typical by-product of the reaction between the Zn metal negative electrode and the ZnOTF electrolyte, is an additional form of active Zn loss. By soaking a polished Zn foil in the ZnOTF electrolyte for 7 days, ZOTH nanosheets were easily generated (Fig. 5d, e and Supplementary Fig. 22), which greatly increased the electrical resistivity of the Zn foil to ~2.1×105 Ω·cm (Supplementary Fig. 23). The ZOTH nanosheets also increased the Zn-ion transport resistance (Supplementary Fig. 24). Fortunately, the nanosheets can be removed by treating with the iodine mediator to recover a smooth Zn surface (Fig. 5f), as verified by energy-dispersive spectroscopy (EDS), XRD and X-ray photoelectron spectroscopy (XPS) (Supplementary Figs. 25 and 26). Considering that the I3− might also corrode fresh Zn, the decomposition rates of the I3− on fresh Zn, dead Zn, and ZOTH were compared. Specifically, we immersed three samples—fresh Zn foil, dead Zn, and pre-synthesized ZOTH—in separate vials containing 50 mL of a 2.5 mM I3− solution. Note that due to the uncertain molecular weight of ZOTH, all three samples are in excess relative to the I3−. At intervals of 1, 3, and 7 days, the upper supernatant was extracted to quantify the dissolved Zn2+ by ICP-OES. The results, presented in the Supplementary Fig. 27, clearly showed that the Zn2+ concentration increased in the order: ZOTH > dead Zn > fresh Zn at every time point. This demonstrated that the decomposition rate followed the same order. These different rates might be attributed to the dramatic difference in specific surface area, where dead Zn and ZOTH exhibit porous morphologies with high specific surface areas, while fresh Zn foil is dense and flat and provides a low specific surface area. This kinetic preference ensures that the I3− mediator will predominantly target the high-surface-area inactive species rather than the bulk Zn electrode. Moreover, dead Zn is more prone to be corroded by the electrolyte to produce ZOTH than fresh Zn (Supplementary Fig. 28).

To further demonstrate the recovery of dead Zn in a Zn||Ti cell configuration where dead Zn forms directly on the Ti electrode, we conducted CE measurements with and without ACI. During the formation cycle, 4 mAh cm−2 Zn was first plated on the Ti substrate and then stripped away with a cut-off voltage of 0.5 V, generating 0.28 and 0.87 mAh cm−2 of dead Zn on the Ti in ZnOTF electrolytes with and without ACI (Fig. 5g and Supplementary Fig. 29). The Zn||Ti cell was then subjected to cycle at a capacity of 1 mAh cm−2 for one cycle, and 1.12 mAh cm−2 of Zn was stripped from the Ti substrate with a corresponding CE of 111.6% (Fig. 5h). The over 100% CE is solid evidence for the ACI-assisted recovery of dead Zn. In contrast, only 0.85 mAh cm−2 was obtained in the ZnOTF electrolyte, corresponding to a CE of 85.3%.

To decouple the contributions of the cations and anions, other types of bi-ionic form analogs have also been evaluated. Firstly, to elucidate the effect of anions, we kept the acetylcholine cations constant and replaced I− anions with other halides such as bromide (Br−) and chloride (Cl−). As shown in the Supplementary Figs. 30 and 31, cells with acetylcholine bromide (ACBr) and acetylcholine chloride (ACCl) generated 0.90 and 1.05 mAh cm−2 of dead Zn in the formation cycle, respectively. In the subsequent cycle, they still produced 0.11 and 0.04 mAh cm−2 of dead Zn, corresponding to CEs of 89.2% and 95.8%. This indicates that Cl− and Br− cannot effectively reactivate dead Zn, which might be attributed to their high oxidation potential required to form oxidizing mediator. Secondly, to elucidate the effect of cations, we kept the I− anions constant and replaced the acetylcholine cations with other structurally related cations, including choline (C+), butyrylcholine (BC+), and acetylthiocholine (ATC+). All I−-based bi-ionic analogs (CI, BCI, ATCI) could reactivate dead Zn to some extent, as evidenced by a CE value exceeding 100% (Supplementary Figs. 32–34). This confirms the primary role of the I− anions in capacity recovery.

Aurbach CE tests29,30, which provide a good assessment of Zn plating/stripping efficiency for Zn negative electrodes, also showed the effectiveness of the ACI addition with a significantly higher average CE (98.5%) than with the baseline ZnOTF electrolyte (78.8%, Supplementary Fig. 35). Post-mortem analysis revealed few residual Zn in the ZnOTF-ACI based cell compared to extensive dead Zn accumulation in the baseline electrolyte (Fig. 5i).

Electrochemical performance of the Zn negative electrode
The stability of Zn negative electrodes was assessed in different electrolytes using Zn||Ti asymmetric cells and Zn||Zn symmetric cells. The CE of the Zn negative electrode was first tested to confirm the plating/stripping reversibility. The baseline ZnOTF electrolyte showed instability in its CE during a long-term cycle at 1 mA cm−2 and 1 mAh cm−2; however, the Zn metal CE vastly improved and maintained a high average value of 99.7% over 1800 cycles when using the ZnOTF-ACI electrolyte (Fig. 6a). The ZnOTF-ACI electrolyte retained a low and stable voltage hysteresis of ~34 mV throughout the entire cycling process, whereas that of the baseline ZnOTF electrolyte increased significantly in less than 100 cycles (Fig. 6b, c). Stable Zn plating/stripping was also achieved at a current density of 5 mA cm−2 and an areal capacity of 1 mAh cm−2, and even at a high current density of 10 mA cm−2 and an areal capacity of 5 mAh cm−2 (Supplementary Fig. 37).

The Zn||Zn symmetric cells showed fundamental stability differences between the two electrolytes. As shown in Fig. 6d, while the voltage profiles became unstable after ~100 h for the ZnOTF electrolyte, the voltage remained steady over 6000 h for the ZnOTF-ACI electrolyte at a current density of 1 mA cm−2 and an areal capacity of 1 mAh cm−2. When the current and capacity increased to 5 mA cm−2 and 5 mAh cm−2, respectively, the cell with the ACI electrolyte, had a much longer lifespan of 2000 h (Supplementary Fig. 38) than the cell without the ACI in which the voltage response suddenly dropped to a low value after ~50 h. Time-dependent EIS tests showed that the failure of the cell with the baseline ZnOTF electrolyte originated from a dendrite-induced “soft short”31, a phenomenon absent in cells with the modified electrolyte (Supplementary Figs. 39, 40). Remarkably, under harsh conditions (10 mA cm−2, 10 mAh cm−2, and 38% depth of discharge), the cell with the ZnOTF-ACI electrolyte achieved stable Zn plating/stripping over 1400 h with a 7 Ah cm−2 cumulative plating capacity (Fig. 6e), values that are comparable to, or better than, previously reported designs for Zn negative electrodes (Fig. 6f and Supplementary Table 1)15,32–46. The increased overpotential observed in the late cycle might be attributed to the gradual decomposition and consumption of the aqueous electrolyte under harsh conditions. The stable Zn plating/stripping obtained using the ZnOTF-ACI electrolyte has also been demonstrated at different current densities (Supplementary Fig. 41).

To ensure reliability, the influence of ACI effects on cell performance was validated using other Zn salts, including ZnSO4, ZnCl2, and Zn(ClO4)2. After the introduction of ACI into the baseline electrolyte, both the CE and lifespan of the cells were substantially enhanced, demonstrating the applicability of ACI in stabilizing Zn negative electrodes (Supplementary Figs. 42–44). In addition, the stability of Zn plating/stripping, reflected in the lifespan of symmetric cells, showing significant improvement after the addition of other bi-ionic form analogs (Supplementary Figs. 30–34).

To validate the practicality of the ZnOTF-ACI electrolyte, we then scaled up Zn||Zn symmetric coin cells to large-format pouch cells (7×7 cm2). As shown in Fig. 6g, a symmetric Zn||Zn pouch cell with the ZnOTF-ACI electrolyte sustainably ran over 1100 h at 245 mA and 245 mAh per cycle, producing a high cumulative plating capacity of 134.75 Ah. In contrast, the baseline ZnOTF electrolyte had a high and unstable overpotential after cycling for ~100 h. The performance of the ZnOTF-ACI verifies the enhanced plating/stripping reversibility of the Zn negative electrode under practical conditions, which is ascribed to the two functions of the ZnOTF-ACI electrolyte in preventing mossy Zn formation and reviving the dead Zn.

We also characterized the morphologies and components of the cycled Zn negative electrodes and separators by SEM, XRD, and a three-dimensional (3D) microscope. As shown in Fig. 6h, i and Supplementary Fig. 45, non-uniform Zn deposits and deep pits were detected after cycling with the ZnOTF electrolyte at 5 mA cm−2 and 5 mAh cm−2; however, the Zn metal negative electrode maintained a smooth and shiny surface when using the ZnOTF-ACI electrolyte. From the corresponding separator with the ZnOTF electrolyte, many black and island-shaped dead Zn particles were attached to its surface and caused a significant loss of active Zn, while that using the ZnOTF-ACI electrolyte had a clean surface (Supplementary Fig. 46). XRD patterns showed that the black residue on the cycled Zn negative electrodes and separators consists of metallic Zn and ZOTH by-products (Supplementary Fig. 47). The height characteristics of the cycled Zn negative electrodes were characterized by a 3D microscope. The Zn negative electrode had a low roughness after cycling in the ZnOTF-ACI electrolyte (Fig. 6j, k). In contrast, a Zn negative electrode cycled in the ZnOTF electrolyte had an uneven surface with a maximum height difference of ~81 μm.

Electrochemical performance of full cells
To explore the practical use of the ZnOTF-ACI electrolyte, we coupled Zn metal negative electrodes with iodine positive electrodes in both coin and pouch cell configurations. Cyclic voltammetry (CV) curves of assembled Zn||I2 cells showed a typical I−/I2 redox pair, regardless of the incorporation of ACI in the electrolyte (Fig. 7a). In addition, a higher peak current density in the ZnOTF-ACI electrolyte indicated that the iodine anions of ACI also participate in the charge-discharge process. Coupled with the contribution of the activated carbon to the capacity, the assembled Zn||I2 cells had a high specific capacity exceeding the theoretical value (211 mAh g−1, Supplementary Fig. 48). Specifically, those using the ZnOTF-ACI electrolyte had a higher specific capacity of 289.5 mAh g−1 at 1 A g−1 (based on a preloaded active I2 mass, ~5.3 mg cm−2) compared to the ZnOTF electrolyte (208.9 mAh g−1, Supplementary Fig. 49). As the current increased to 10 A g−1, a high specific capacity of 211.0 mAh g−1 and a capacity retention of 72.9% were maintained in the ZnOTF-ACI, surpassing the values using the ZnOTF electrolyte (135.7 mAh g−1, 65.0%), indicating its good rate performance and reaction kinetics (Supplementary Fig. 50). Figure 7b showed the cycling stability of the Zn||I2 cells at 2 A g−1. The one with the ZnOTF-ACI electrolyte maintained a high discharge capacity of ~230.6 mAh g−1 after 20,000 cycles. However, the Zn||I2 cell with the ZnOTF electrolyte showed a fast capacity decay after ~1600 cycles.

We fabricated a single-layer Zn||I2 pouch cell (7×7 cm2) consisting of a Zn foil negative electrode (45 µm, 26.3 mAh cm−2) and a high mass loaded I2 positive electrode (~28 mg cm−2, 5.6 mAh cm−2), which corresponds to a capacity ratio of the negative electrode to the positive electrode (N/P) of 4.7 (Fig. 7c). The cell had a high capacity of ~264.4 mAh after 20 cycles which remained at ~245.0 mAh after 2500 cycles. The gradual increase in capacity during the initial cycles represents a progressive wetting and activation process, which has been commonly reported in previous studies47,48. We also scaled up the cell to an Ah level by using a double side-coated positive electrode, increasing both the I2 loading (~42 mg cm−2 per side) and electrode size (7.5×9.5 cm2), as illustrated in Fig. 7d. The critical parameters, including positive electrode areal capacity (~8.6 mAh cm−2 per side), N/P (~3.0), and the ratio of electrolyte amount to cell capacity (E/C, ~10 μL mAh−1), were kept at practical levels. The energy density of this pouch cell was calculated as ~70.0 Wh L−1 (see Supplementary Table 3 for the details). As shown in Fig. 7d and Supplementary Fig. 51, the cell with the ZnOTF-ACI electrolyte had a high discharge capacity of 1230 mAh at ~0.45 C and showed a cycling stability for 800 cycles with a high-capacity retention of 96.2% at 1.8 C. Of note, the C-rate is defined as the reciprocal of the time required for the cell to complete one full cycle. The discharge curves at different numbers of cycles reflect the significantly improved cycling stability. Our Zn||I2 pouch cell is at the advanced level of Ah-scale Zn-metal batteries, as demonstrated by the comparison of its performance to other cells given in Supplementary Table 249–58.

Methods
Materials
Zn(CF3SO3)2 (purity ≥99.5%) was purchased from Duoduo Chem. ZnSO4·7H2O (purity ≥99%), ZnCl2 (purity ≥99.99% metals basis), Zn(ClO4)2·6H2O (purity ≥99.995% metals basis), Na2SO4 (purity ≥99%), NaI (purity ≥99.5%), ZnI2 (purity ≥98%), I2 (purity ≥99.8%), ethanol (purity ≥99.5%), Acetylcholine bromide (purity ≥98%), Acetylcholine chloride (purity ≥99%), and Acetylthiocholine iodide (purity ≥98%) were procured from Aladdin. Choline iodide (purity ≥98%) and Butyrylcholine iodide (purity ≥99%) were bought from Macklin. Acetylcholine iodide (purity >98%) were obtained from TCI. Activated carbon (AC, YP50F) and polytetrafluoroethylene (PTFE, PTFE-770) was purchased from Shenzhen Kejing Star Technology Co., Ltd. Zn foil (purity ≥99.99%), Ti foil (purity ≥99.99%), Zn wire (purity ≥99.99%) and Ti wire (purity ≥99.99%) were purchased from Wuhan Luojia Yanxin Technology Co., Ltd.

Electrolyte preparation
For the 1 M ZnOTF electrolyte, 36.353 g Zinc trifluoromethanesulfonate was completely dissolved in ultrapure water to form a 100 mL solution with a volumetric flask. The ZnOTF-ACI electrolyte was prepared similarly, except that a certain amount of acetylcholine iodide powder was introduced during dissolution. The electrolyte preparation was conducted in an ambient atmosphere at 25±2°C. Our experiments indicate that the optimum concentration of ACI is ~0.5 M (Supplementary Fig. 36).

Electrode fabrication
AC electrode. The AC electrode was prepared by a dry process. AC powder and PTFE powder were manually mixed at a 9:1 weight ratio until uniform, then transferred to the chamber of a high-speed disperser (MSK-SFM-D300, Shenzhen Kejing Star Technology Co., Ltd). After rotating at 9000 rpm for 4 min and repeating this process three times, the PTFE powder transformed into fibers and created a robust network to bind the AC powder. The mixture was then evenly spread onto a cleaned aluminium foil and converted into a seamless, self-supporting film by a hot calendering machine (MSK-H2150-E, Shenzhen Kejing Star Technology Co., Ltd) at 60±2°C. The thickness of the AC film was controlled by adjusting the gap between the two rolls of the calendering machine. By sandwiching a titanium mesh collector between two AC films and consolidating them using a mechanical press (PC-30, Tianjin Jingtuo Instrument Technology Co., Ltd), the AC electrodes were obtained. They were then resized according to the requirements of the different cells.

I2 positive electrode. The aforementioned AC electrode was used as the host for the I2 to produce a composite electrode. A low-loaded I2 positive electrode (~5.3 mg cm−2, for a coin cell) was prepared by a drop-coating method, which involved dropping an appropriate amount of I2 containing ethanol solution onto a thin AC electrode (~6 mg cm−2). High-loaded I2 positive electrodes (~28 and ~84 mg cm−2) were prepared by electrodepositing. Specifically, thick AC electrodes and Zn foils were used as the positive and negative electrodes, respectively. These electrodes were placed on opposite sides of an acrylic container, with a 0.5 M ZnI2 aqueous electrolyte filling the space between them. During galvanostatic charging, iodine ions in the electrolyte were electroplated onto the AC electrodes to form solid I2. An areal iodine loading of ~28 mg cm−2 was achieved by charging at a current density of 150 mA for 2 h on a 7×7 cm2 AC electrode. A higher loading of ~84 mg cm−2 (for the bi-layer pouch cells) was achieved by charging at 600 mA for 2 h on a 7.5×9.5 cm2 AC electrode. The iodine positive electrode was obtained by washing several times with ultrapure water and drying for 24 h in an oven at 40°C.

Pouch cell assembly
Zn foils were mechanically polished and rinsed in ethanol before use. The Zn||Zn pouch cell was assembled using two polished Zn foils (7×7 cm2) and one Whatman GF/B glass fiber separator (7.2×7.2 cm2), with 5 mL of electrolyte injected. The thickness of the Whatman GF/B separator after compression is ~500 μm, with an average pore size of 1.0 μm. For a single-layer pouch cell, one I2 positive electrode (7×7 cm2) and one Zn negative electrode (7×7 cm2) were placed on either side of the separator. An Ah-scale Zn||I2 pouch cell was produced by a bi-layer structure of two Zn negative electrodes (7.5×9.5 cm2), one I2 positive electrode (7.5×9.5 cm2), and two separators (7.7×9.7 cm2). These assembled stacks were accommodated in Al-plastic bag and filled with electrolyte. The injection of the electrolyte for single-layer Zn-I2 pouch cells and Ah-scale Zn||I2 pouch cells was controlled at approximately 21 and 10 μL mAh−1, respectively. After degassing and heat sealing, these pouch cells rested for 2 h to ensure complete wetting. Galvanostatic cycling stability tests were conducted under a uniform pressure (~2 kPa) to ensure satisfactory component contact for these cells.

Material characterization
The morphologies, microstructure, and corresponding elemental maps were obtained using a scanning electron microscope (SEM, Thermo Scientific Apreo 2S) equipped with energy-dispersive spectroscopy (EDS). The crystallographic phase and chemical composition were analyzed by (XRD, Rigaku MiniFlex), X-ray photoelectron spectroscopy (XPS, PHI 5000 Versa Probe II), and inductively coupled plasma optical emission spectrometer (ICP-OES, Arcos II MV). The surface roughness and 3D morphologies of Zn negative electrodes were examined using the same 3D microscope. The cycled Zn electrode is extracted from the cell and cleaned with ultrapure water and ethanol. Following vacuum drying at 40°C for 2 h, it is subjected to SEM, XRD, and other tests. The UV/Vis absorption spectra of iodine-containing solutions were tested by a UV/Vis spectrometer (LAMBDA 365) after diluting with ultrapure water by a factor of 50.

In situ optical observation
The optical microscopy observations were conducted using a home-made liquid cell, where a Ti wire (30 mm in length and 0.5 mm in diameter), a Zn wire (30 mm in length and 1 mm in diameter), and a Zn wire (10 mm in length and 1 mm in diameter) served as the working, counter, and reference electrodes, respectively. Prior to the assembly of the optical cell, the Ti wire and Zn wire were polished with 10,000 mesh sandpaper to remove surface oxides and thoroughly cleaned with deionized water and ethanol. The cell was sealed with waterproof tape to prevent electrolyte leakage. The optical cell was connected to a battery tester to perform a cycle of Zn plating and stripping. Corresponding voltage response was also recorded. Meanwhile, an ultra-depth three-dimensional microscope (DeltaPix DPXM6000) was used to capture a series of changes in Zn plating/stripping morphology over time during the cycle.

In situ EQCM
In situ EQCM (DyneChem DC-QMC3100) measurements were performed in a three-electrode cell consisting of an Au wafer working electrode, Ti counter electrode, and Ag/AgCl reference electrode. The assembled cell was examined with a LSV test at 5 mV s−1. The change in resonant frequency (Δf) of the quartz crystal during the LSV test was recorded. Therefore, the mass change (Δm) of the quartz crystal electrode can be calculated using the following Sauerbrey equation:
Δm = −(C × A × sqrt(ρμ) × Δf) / (2f0^2) (1)
Where A is the piezoelectrically active crystal area (0.28274 cm2), ρ is the density of quartz (2.648 g cm−3), μ is the shear modulus of quartz (2.947×1011 g cm−1 s−2), f0 is the resonant frequency of the quartz crystal (9 MHz), and Δf is the frequency change.

In situ FT-IR
In situ FT-IR measurements were performed using a ThermoFisher Scientific Nicolet iS50 spectrometer equipped with a liquid nitrogen-cooled Mercury Cadmium Telluride (MCT) detector and a silicon attenuated total reflection (ATR) accessory. Prior to use, the substrate plane of the Si prism was mechanically polished using aluminum oxide suspensions of different particle sizes until a mirror-like finish was achieved, followed by rinsing with deionized water. In the in situ FTIR cell, a Ti mesh served as the working electrode, while Zn foil functioned as both the counter electrode and reference electrode. The incidence angle was set at 60°, with a spectral resolution of 4 cm−1. Each spectral data was collected at an interval of 60 s. The FT-IR spectroscopy combined with the galvanostatic discharge method was used to monitor the Zn deposition process on the electrode surface.

Electrochemical measurements
The Zn||Zn symmetrical coin cells (CR2032) were assembled with two identical polished Zn foils (~45 μm in thickness and 12 mm in diameter), one Whatman GF/B glass fiber separator (16 mm in diameter), and 120 μL of the electrolyte. Galvanostatic Zn plating/stripping was performed in different cycling conditions. For Zn||Ti asymmetrical coin cells, Ti foil (~30 μm in thickness and 12 mm in diameter) was used as the working electrode, and the charge cutoff potential was set at 0.5 V (vs. Zn/Zn2+). A “reservoir” protocol was used to assess the average CE of Zn plating/stripping. First, the assembled asymmetrical Zn-Ti cell was subjected to one cycle at a capacity of 5 mAh cm−2 to remove any impurities on the Ti substrate. Then, a given amount of charge (QT), e.g., 5 mAh cm−2, was deposited on the Ti substrate as a Zn “reservoir”. Afterwards, repeated Zn stripping/plating was conducted (10 cycles) under a areal capacity (QC) of 1 mAh cm−2. Finally, the residual Zn was completely stripped at a cut-off potential of 0.5 V (vs. Zn/Zn2+), providing the final stripping capacity (QS). The average CE was calculated using the following equation:
CEavg = (QS + 10 × QC) / (QT + 10 × QC) (2)
The voltage window for the Zn||I2 cells was 0.3–1.8 V. The hydrogen evolution performance was investigated in a 1 M Na2SO4 aqueous solution with a three-electrode system using Zn deposits as the working electrode, platinum as the counter electrode, and Ag/AgCl as the reference electrode. In situ EIS was conducted every 10 min during Zn plating using an electrochemical workstation (Biologic VSP-3e). The EIS spectra were collected over the frequency range of 105 to 0.05 Hz under open-circuit potential conditions with a potentiostatic mode (10 mV amplitude, 10 points per decade). For resistivity tests, the voltage response was measured at a constant current of 0.5 mA on a sample sandwiched between two stainless steel electrodes. The resistivity (ρ) was calculated using the following equation:
ρ = (U × S) / (I × L) (3)
where U is the average response voltage, S is the contact area (1.13 cm2), I is the applied current (0.5 mA), and L is the thickness of the sample (~45 μm). The electrochemical experiments were conducted in an air-conditioned laboratory environment with an average temperature of 25 ± 2°C.

Finite element simulations
Finite element method simulations were performed using COMSOL Multiphysics. A two-dimensional model was developed to simulate the current density and electric field distribution at the negative electrode/electrolyte interface. In this model, the length of two electrodes was 15 μm and the distance between them was 10 μm. The lumpy Zn was represented by three hexagonal protrusions, each with a side length of 2 μm. Additionally, rectangular Zn with a height of 1 μm and width of 0.1 μm were incorporated on the hexagons to simulate mossy Zn growth. The ionic conductivity of the 1 M ZnOTF electrolyte filling the interelectrode gap was set to 3.2 S m−159. The positive electrode and negative electrode potentials were held at 0.05 and 0 V (vs. Zn/Zn2+), respectively.

DFT calculations
First-principles DFT calculations were performed in the Vienna Ab initio Simulation Package (VASP)60. The exchange-correlation interactions were described by the PBE functional within the generalized gradient approximation, with a plane-wave cutoff energy of 500 eV61. The electronic self-consistency criterion was set to 10−5 eV, and the force on each atom was converged below 0.03 eV Å−1. The Zn substrate was modeled as a four-layer 6×6 supercell and a 25 Å vacuum layer was constructed. The dispersion corrections were included by the DFT-D3 scheme. Geometry optimizations were performed using a Γ-only k-mesh for the Brillouin zone sampling. The geometry relaxation was applied for the top two layers of the Zn slab62. The adsorption energy (Eads) was calculated using the following equation:
Eads = Etotal − Esub − EZn (4)
where Etotal is the total energy of the adsorption system, Esub is the total energy of the adsorbate, EZn is the energy of a free Zn(002)-slab.

Data availability
All data generated in this study are provided in the manuscript, Supplementary Information, and Source Data file. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study provides an interesting discovery of two-stage Zn deposition and proposes an effective anion-cation additive (ACI) to suppress mossy Zn formation and revive dead Zn. The Zn anodes exhibited considerable advances in compact deposition and cycling performance. And the practical applications have also been well demonstrated in Ah-scale pouch cells. These results would be of general interest to the relevant research field. Therefore, this manuscript is suitable for publication in Nature Communications after addressing the following concerns.\n1. Regarding the in-situ optical observation of two-stage Zn deposition, I am curious why the authors used a Ti wire electrode as the working electrode. Does this two-stage deposition phenomenon also exist in conventional planar electrodes and batteries? Additional experiments are needed to strengthen the universality of two-stage deposition.\n2. As we all known, the shuttle effect in zinc-iodine batteries involves polyiodide species (e.g., I3−, I5−) migrating to the negative electrode, causing capacity decay and Zn corrosion. Here, the author proposes that the oxidative I3− reacts with dead zinc to increase the reversibility of the Zn anode. Could this process exacerbate Zn corrosion? An explanation is needed for why I₃⁻ does not intensify side reactions.\n3. In Fig. 3a, EQCM data show mass changes but cannot distinguish between cation adsorption and cation-anion co-adsorption. Control experiments testing the anion alone (e.g., iodide salts without acetylcholine) would clarify interfacial interactions.\n4. Could the iodine anion independently affect the morphology of zinc deposits? Please provide more experiments and explanations.\n5. Is ACI’s success specific to the ZnOTF electrolyte? Testing ACI with alternative zinc salts (e.g., ZnSO4) would demonstrate broader applicability.\n6. In Fig.6, an activation process is observed in Zn||I₂ pouch cells with ACI but not in coin cells. Please give an explanation.\n7. In Zn||Zn symmetric cell testing, the overpotential of the ZnOTF-ACI electrolyte gradually increases upon cycling. What causes this?\n8. A thorough revision of the entire manuscript is recommended to correct some typos. For example, “0.2 Na2SO4” → “0.2 M Na2SO4” (Line 161), “whereases” → “whereas” (Line 191).", "reviewer_2": "This work investigates the failure mechanism of the Zn anode during cycling and reveals two distinct Zn deposition morphologies, which are critical to understanding the reversibility and cycling life of zinc-based batteries. Based on insights into the Zn deposition process, the authors design a bifunctional electrolyte additive that not only homogenizes Zn²⁺ flux but also facilitates the rejuvenation of inactive Zn via a spontaneous redox reaction. Benefiting from the engineered electrolyte, the authors demonstrate a significant enhancement in the lifespan of pouch cells. The bi-layer pouch cell shows promising practical performance under harsh testing conditions.\nOverall, this study presents a comprehensive investigation, spanning from fundamental mechanism elucidation to material-level innovations and practical cell demonstrations. The experiments are thorough, and the research logic is generally sound. However, several minor issues remain, such as insufficient experimental details and ambiguous mechanistic explanations. Therefore, I recommend minor revision before the manuscript can be considered for publication in Nature Communications.\nComments and Suggestions:\n1. Please provide a detailed schematic or image of the custom-designed three-electrode cell, preferably with multi-angle views and a magnified image of the central region. Additionally, the authors should explain why the deposited Zn appears luminescent. More experimental details regarding the custom-built optical microscope and EQCM setup are also needed.\n2. There are some writing issues. For example, “0.2 Na₂SO₄” should be corrected to “0.2 M Na₂SO₄” or “0.2 mol L⁻¹ Na₂SO₄.”\n3. The manuscript reports two Zn deposition morphologies: lumpy and mossy. The authors should provide a more in-depth analysis of the mechanisms driving these morphological differences. Is the variation substrate-induced, or does it relate to Zn²⁺ depletion near the electrode–electrolyte interface? The proposed mechanism, wherein edge growth of lumpy Zn disrupts the homogeneous Zn²⁺ flux, requires further clarification and supporting evidence.\n4. In Figure 6a, the authors attribute the increase in capacity at higher current rates to redox activity of ACI. This interpretation is questionable without normalization to electrode mass or active material content. Please clarify.\n5. In Figures 6c and 6d, the definition of C-rate appears inconsistent between the two cells. The authors should ensure consistent and clearly defined electrochemical testing parameters across figures.", "reviewer_3": "This manuscript demonstrated the effect of bi-ionic effect of cation and anion on regulating Zn deposit morphology and reviving dead Zn via in situ optic microscopy. For confirming this effect, the authors showed a practical ampere hour scale pouch cell which has cycle retention of 96.2% for 800 cycles. However, this manuscript is not suitable for publication in Nature Communications due to its lack of novelty and insufficient depth in conveying a significant scientific message. Overall, the novelty and clarity of the proposed ACI mechanism are insufficient. To substantiate the hypothesis, further investigations using complementary analytical techniques or simulations are necessary.\nThe following comments are the reason why this manuscript is not suitable for publications.\n1.The authors claim that the two-stage plating and stripping behavior of the Zn anode occurs only under their optical cell setup. However, in practical systems, Zn metal operates under applied pressure, and similar behaviors should also be examined in pressure-applied configurations, such as coin cells or pouch cells, at defined pressure levels. In addition, the plating and stripping behavior should be investigated using ZnSO₄ and other types of Zn salts to confirm whether the phenomenon is salt-dependent\n2.The authors used Zn(OTf)2, which is significantly more expensive than ZnSO4. Since ZnSO4 is more widely used in practice, it is necessary for the authors to verify whether the two-stage plating and stripping behavior is also observed with other common Zn salts, such as ZnSO4, ZnCl2, and Zn(ClO4)2.\n3.To ensure reliability, the influence of the bionic (ACI) effect on cell performance should be validated using other types of Zn salts\n4.The overall analysis of the effect of ACI is insufficient to clearly elucidate the underlying mechanism. The mechanism of ACI is unclear for stabilizing the Zn metal interface.\n5.There is no guarantee that iodine ions selectively decompose only ZOTH; they may also dissolve fresh Zn. Therefore, it is necessary to compare the decomposition ratio between fresh Zn and ZOTH. Furthermore, the adsorption selectivity of ZOTH to fresh Zn and dead Zn need to be analyzed.\n6.Significantly, the effect of bi-ionic (ACI) should be more deeply studied with the mechanism and other types of bi-ionic form analogues should be compared."}, "author_response": "Point-by-point response to the reviewers’ comments\nDear reviewers,\nWe would like to thank you for your insightful and constructive comments.\nAccording to your comments, we have conducted additional experiments and\ntheoretical calculations, and updated the manuscript and supplementary information\nwith new data. In the following point-by-point response, we aim to clarify all the\nconcerns raised and hope that the revised version is satisfactory. The changes have\nbeen highlighted in yellow in this response and the revised manuscript for your\nconvenience.\nWith best regards,\nSincerely\nHui-Ming Cheng on behalf of all authors\n---------------------------------------------------------------------------\nHui-Ming Cheng, Professor\nInstitute of Technology for Carbon Neutrality, Shenzhen Key Laboratory of Energy\nMaterials for Carbon Neutrality, Shenzhen Institutes of Advanced Technology,\nChinese Academy of Sciences, Shenzhen 518055, China\nE-mail: hm.cheng@siat.ac.cn\nThis study provides an interesting discovery of two-stage Zn deposition and proposes\nan effective anion-cation additive (ACI) to suppress mossy Zn formation and revive\ndead Zn. The Zn anodes exhibited considerable advances in compact deposition and\ncycling performance. And the practical applications have also been well\ndemonstrated in Ah-scale pouch cells. These results would be of general interest to\nthe relevant research field. Therefore, this manuscript is suitable for publication in\nNature Communications after addressing the following concerns.\nGeneral response: We are sincerely grateful to Reviewer #1 for his/her positive and\nencouraging evaluation of our manuscript. We also appreciate Reviewer #1 for the\nconstructive comments and valuable suggestions, which help us improve the clarity,\nrigor, and overall impact of our work. We are trying to solve all the points raised in\nthe comments with additional experiments, data analysis, and textual revisions\nthroughout the manuscript.\nComments 1: Regarding the in-situ optical observation of two-stage Zn deposition, I\nam curious why the authors used a Ti wire electrode as the working electrode. Does\nthis two-stage deposition phenomenon also exist in conventional planar electrodes\nand batteries? Additional experiments are needed to strengthen the universality of\ntwo-stage deposition.\nResponse: We thank the reviewer for the constructive comments. Ti wire was chosen\nas the working electrode for in-situ optical observation based on the following reasons:\ni) Ti is one of the commonly used current collectors in Zn batteries, and is therefore\nrepresentative; ii) Ti has high resistance against hydrogen evolution reaction, which\ncan prevent hydrogen bubble from affecting the observation of Zn plating; iii) the\nwire geometry is ideal for the custom optical cell, allowing for precise alignment and\na clear view of the Zn plating process.\nWe fully agree with the reviewer that demonstrating this two-stage plating\nphenomenon on conventional electrodes is crucial. Following the suggestion, we have\n2\nconducted additional experiments in the revised manuscript. As shown in the new\nSupplementary Fig. 5, planar Ti foil was used as the substrate for Zn deposition. We\nfound that two-stage Zn plating and stripping also occurred on the Ti foil electrode\nduring the cycle, indicating that this phenomenon is independent of the electrode’s\ngeometric form.\nTo further verify its occurrence in practical battery configurations, we disassembled\nZn||Ti coin cells after different plating/stripping times. Corresponding optical photos\nof the planar Zn anodes (new Supplementary Fig. 10) revealed a same progression,\ni.e., initial lumpy Zn plating followed by the formation of porous mossy Zn. These\nresults provide definitive evidence that the two-stage deposition is a general intrinsic\nbehavior of Zn electrodeposition, observable under pressure and in realistic battery\nenvironments.\nSupplementary Fig. 5 Two-stage plating and stripping of the Zn anode on a Ti\nfoil. (a) The optical cell setup. (b) Typical voltage-time profile of Zn plating and\nstripping at 1 mA cm−2. Optical microscope photos of the two-stage Zn (c) plating and\n(d) stripping. Scale bar, 500 μm.\nZnOTF electrolyte at 1 mA cm−2. (a) Typical voltage-time profile of Zn plating and\nstripping. (b) Optical microscope photos of the two-stage Zn plating and stripping.\nScale bar, 500 μm.\nSome descriptions have been added in the revised manuscript as follows:\n“Ti was used as the working electrode because it is one of the most common current\ncollectors for Zn anodes and can prevent hydrogen evolution from affecting the\nobservation of Zn plating.”\n“We found that two-stage Zn deposition and stripping occurred on a planar Ti foil\nelectrode during the cycle, indicating that this phenomenon is independent of the\nelectrode’s geometric form (Supplementary Fig. 5).”\n“In addition, the application of stack pressure compressed the Zn deposition, making\nit more uniform, but did not change the intrinsic mechanism of the two-stage\ndeposition process (Supplementary Figs. 10, 11).”\n4\n2. As we all known, the shuttle effect in zinc-iodine batteries involves polyiodide\nspecies (e.g., I −, I −) migrating to the negative electrode, causing capacity decay and\n3 5\nZn corrosion. Here, the author proposes that the oxidative I − reacts with dead zinc to\n3\nincrease the reversibility of the Zn anode. Could this process exacerbate Zn corrosion?\nAn explanation is needed for why I₃⁻ does not intensify side reactions.\nResponse: We thank the reviewer for the insightful comments. We agree that the\nuncontrolled shuttle of polyiodides can lead to Zn corrosion. The concern for the\nreviewer is: would I ⁻ corrode the bulk Zn anode? To clarify this concern, we\n3\nperformed a comparative kinetics study by immersing an equal mass of fresh Zn foil\nand dead Zn in I₃⁻ solutions. As shown in the new Supplementary Fig. 27, the\nconcentration of Zn2⁺ released from the dead Zn sample is significantly higher than\nthat from the fresh Zn sample over the same period (1, 3, and 7 days), as quantified by\nICP-OES. This proves that I ⁻ preferentially reacts with dead Zn. We attribute this\n3\nselectivity to the larger specific surface area and higher reactivity of the porous,\nmossy dead Zn than the dense, flat fresh Zn foil. In addition, the amount of ACI\nadded into the electrolyte (~0.5 M) has been carefully optimized to provide moderate\nI ⁻ for reactivation while keeping its concentration below the threshold that would\n3\ncause severe corrosion of bulk Zn. The cycled Zn anode with the ZnOTF-ACI\nelectrolyte showed no obvious ZOTH by-products (Supplementary Fig. 47), which\nfurther demonstrated that the ACI does not intensify side reactions. Therefore, in our\ndesign, the I ⁻ species function as a controlled redox mediator specifically targeted to\n3\nreact with electrochemically inactive species, thereby enhancing reversibility without\nexacerbating corrosion of the active Zn anode.\nSome descriptions have been added in the revised manuscript as follows:\n“Considering that the I − might also corrode fresh Zn, the decomposition rates of the\n3\nsamples—fresh Zn foil, dead Zn, and pre-synthesized ZOTH—in separate vials\ncontaining 50 mL of a 2.5 mM I ⁻ solution. Note that due to the uncertain molecular\n3\nweight of ZOTH, all three samples are in excess relative to the I ⁻. At intervals of 1, 3,\n3\nand 7 days, the upper supernatant was extracted to quantify the dissolved Zn2⁺\nconcentration by ICP-OES. The results, presented in the Supplementary Fig. 27,\nclearly showed that the Zn2⁺ concentration increased in the order: ZOTH > dead Zn >\nfresh Zn at every time point. This demonstrated that the decomposition rate followed\nthe same order. These different rates might be attributed to the dramatic difference in\nspecific surface area, where dead Zn and ZOTH exhibit highly porous morphologies\nwith high specific surface areas, while fresh Zn foil is dense and flat and provides a\nlow specific surface area. This kinetic preference ensures that the I ⁻ mediator will\n3\npredominantly target the high-surface-area inactive species rather than the bulk Zn\nanode.”\n6\n3. In Fig. 3a, EQCM data show mass changes but cannot distinguish between cation adsorption and cation-anion co-adsorption. Control experiments testing the anion alone (e.g., iodide salts without acetylcholine) would clarify interfacial interactions.\nResponse: We thank the reviewer for the very useful comment. Following the\nreviewer’s suggestion, we performed a control EQCM experiment using a 0.2 M\nNa SO aqueous solution with NaI. As shown in Figs. 3a-3c, when the potential swept\n2 4\nfrom 0.1 V to −0.4 V (vs. Ag/AgCl), the maximum mass increase was ~3.6 ng, which\nwas comparable to that of the Na SO solution (~7.3 ng), but significantly lower than\n2 4\nthat of the Na SO -ACI solution (~60.1 ng). This indicates that iodide anions do not\n2 4\nadsorb or accumulate on the electrode surface under an applied electric field. The\nmass increase observed in the Na SO -ACI solution is mainly attributable to the\n2 4\nadsorption and accumulation of acetylcholine cations.\nFigs. 3a-3c (a) Schematic of the EQCM measurement setup. (b) Linear sweep\nvoltammetry curves in an EQCM test at 5 mV s−1. (c) Mass change curves of different\nNa SO solutions.\n2 4\nSome descriptions have been added in the revised manuscript as follows:\n“… and 0.2 M Na SO aqueous solutions containing NaI, containing ACI, and\n2 4\ncontaining neither were used as electrolytes. When the potential swept from 0.1 V to\n−0.4 V (vs. Ag/AgCl), the maximum mass increase was ~7.3 and 3.6 ng in the 0.2 M\nNa SO and 0.2 M Na SO -NaI, respectively (Figs. 3b, 3c). However, ~60.1 ng was\n2 4 2 4\ndetected when ACI was added. This large increase in mass is mainly attributed to the\nadsorption of acetylcholine cations rather than Na+, I−, or H O.”\n2\n7\n4. Could the iodine anion independently affect the morphology of zinc deposits?\nPlease provide more experiments and explanations.\nResponse: We appreciate the reviewer for this important question. To directly\ndecouple the effect of the iodine anion from the bi-ionic components, we\nsystematically compared the Zn deposition morphology in three electrolytes,\nincluding 1 M ZnOTF, 1 M ZnOTF + 0.5 M KI (providing I⁻ anions without\nacetylcholine cations), and 1 M ZnOTF + 0.5 M ACI (providing both I⁻ anions and\nacetylcholine cations). As shown in the Fig. 1c, Fig. 4a and new Supplementary Fig.\n17, the Zn deposits from both the baseline ZnOTF and the ZnOTF-KI electrolyte are\nloose and porous. In contrast, only the ACI-added electrolyte produces compact and\nuniform Zn deposits. In addition, the assembled Zn//Ti cell and Zn//Zn cell with the\nZnOTF-KI electrolyte short-circuited after ~142 and ~116 h of cycling, respectively\n(Response Fig. 1), indicating that mossy Zn still formed within the cells despite the\naddition of KI. These results provide clear evidence that the iodide anions alone\ncannot control the Zn deposition morphology. The dramatic improvement in Zn\ndeposition morphology is achieved when the acetylcholine cation is present.\ncm−2. (a) Typical voltage-time profile of Zn plating. (b) Optical microscope photos of\nthe two-stage Zn plating. Scale bar, 500 μm.\nResponse Fig. 1 Galvanostatic Zn plating/stripping in Zn//Ti and Zn//Zn cells with\nthe ZnOTF-KI electrolyte.\nSome descriptions have been added in the revised manuscript as follows:\n“Notably, the significant improvement in Zn deposition morphology is attributed to\nacetylcholine cations rather than iodide anions, as the addition of iodide anions alone\ndoes not inhibit the formation of mossy Zn (Supplementary Fig. 17).”\n5. Is ACI’s success specific to the ZnOTF electrolyte? Testing ACI with alternative\nzinc salts (e.g., ZnSO ) would demonstrate broader applicability.\nreviewer’s suggestion, we have evaluated the electrochemical performance of the ACI\nin a 1 M ZnSO electrolyte (denoted as ZnSO -ACI). As illustrated in new\n4 4\n4\nachieved a high average CE of 99.6% for 400 cycles at 10 mA cm−2 and 5 mAh cm−2,\nwhich is much higher than that of the ZnSO electrolyte (98.1% for 130 cycles). In\n4\naddition, the Zn//Zn symmetrical cells with the ZnSO -ACI electrolyte produced\n4\nstable cycling over ~1,100 h at 5 mA cm−2 and 5 mAh cm−2. In contrast, the cell with\nthe ZnSO electrolyte failed due to short-circuiting after only ~120 h. Of note,\n4\nregardless of whether the ZnOTF or ZnSO salt was used, the electrochemical\n4\nperformance was significantly improved after the ACI was added. These results show\nthat ACI is compatible with common Zn salts and can endow Zn anodes with\nexcellent cycling stability.\nSupplementary Fig. 42 Galvanostatic Zn plating/stripping in Zn//Ti and Zn//Zn\ncells with the ZnSO and ZnSO -ACI electrolyte.\n4 4\nSome descriptions have been added in the revised manuscript as follows:\n“To ensure reliability, the influence of ACI effects on cell performance was validated\nusing other Zn salts, including ZnSO , ZnCl , and Zn(ClO ) . Following the\n4 2 4 2\nintroduction of ACI into the baseline electrolyte, both the CE and cycling life of the\n10\ncells were substantially enhanced, demonstrating the excellent applicability of ACI in\nstabilizing Zn anodes (Supplementary Figs. 42-44).”\n6. In Fig.6, an activation process is observed in Zn||I₂ pouch cells with ACI but not in\ncoin cells. Please give an explanation.\nResponse: We thank the reviewer for the valuable question. The observed activation\nprocess (gradual capacity increase in the initial cycles) in the pouch cells is a common\ncharacteristic of thick, high-loading electrodes and is not typically seen in thin-\nelectrode coin cells. This difference arises from the distinct electrode thickness and\nmass loading used in the two cell configurations. Specifically, for coin cell tests, we\nused thin electrodes with a moderate iodine loading of ~5 mg cm⁻² and a thickness of\n~120 μm. At this scale, the electrode was readily wetted by the electrolyte. Therefore,\nthe cell achieved its maximum capacity almost immediately, with no significant\nactivation process. In contrast, practical pouch cells were assembled with thick, high-\nloading electrodes (single-sided loading of ~28 mg cm⁻², thickness ~500 μm). This\ndense, thick structure requires several cycles for the electrolyte to fully wet the\nelectrode and for the active material to be completely utilized. The gradual increase in\ncapacity during the initial cycles represents this progressive wetting and activation\nprocess, which has been commonly reported in previous studies using similarly\ndesigned thick electrodes (Angew. Chem. Int. Ed., 2024, 63: e202407909; Nat.\nCommun., 2025, 16: 71).\nSome descriptions have been added in the revised manuscript as follows:\n“The gradual increase in capacity during the initial cycles represents a progressive\nwetting and activation process, which has been commonly reported in previous\nstudies47,48.”\n“47. Xu P, et al. In‐Situ Solid Electrolyte Interface via Dual Reaction Strategy for\nHighly Reversible Zinc Anode. Angew. Chem. Int. Ed. 63, e202407909 (2024).\n48. Zhang B, et al. Electrolyte design for reversible zinc metal chemistry. Nat.\nCommun. 16, 71 (2025).”\n11\n7. In Zn||Zn symmetric cell testing, the overpotential of the ZnOTF-ACI electrolyte\ngradually increases upon cycling. What causes this?\nResponse: We thank the reviewer for the insightful question. While the observed\ngradual increase in overpotential during the cycling is indeed, this phenomenon\noccurs more frequently in the later stages of cycling. For example, the overpotential\nof the Zn//Zn symmetric cell increased from 77.3 mV at the start of cycling to 84.6\nmV after 1000 h at high current density/capacity of 10 mAcm−2/10 mAh cm−2 (Fig. 6e\nand Response Fig. 2). Only after cycling exceeds 1300 h does the overpotential\ngradually increase to 119.4 mV and continue until the cell fails. The increased\noverpotential observed in the late cycle might be attributed to the gradual\ndecomposition and consumption of the aqueous electrolyte under harsh conditions\n(high current density, high capacity, and prolonged cycling). This is a common\nchallenge observed in many long-cycle studies of aqueous Zn batteries (Nat.\nCommun., 2025, 16: 5565; Nat. Commun., 2023, 14: 4981), as water molecules and\nsalt anions can participate in unavoidable parasitic reactions over time.\nResponse Fig. 2 Overpotential of Zn//Zn coin cells with the ZnOTF-ACI\nelectrolyte at 10 mAcm−2/10 mAh cm−2.\nSome descriptions have been added in the revised manuscript as follows:\n“The increased overpotential observed in the late cycle might be attributed to the\ngradual decomposition and consumption of the aqueous electrolyte under harsh\nconditions.”\n12\n8. A thorough revision of the entire manuscript is recommended to correct some typos.\nFor example, “0.2 Na SO ” → “0.2 M Na SO ” (Line 161), “whereases” →\n2 4 2 4\n“whereas” (Line 191).\nResponse: We sincerely apologize for the typos and have corrected them in the\nrevised manuscript. The revised manuscript has been carefully reviewed.\nSome descriptions have been added in the revised manuscript as follows:\n“… and 0.2 M Na SO aqueous solutions containing NaI, containing ACI, and\n2 4\ncontaining neither were used as electrolytes. When the potential swept from 0.1 V to\n−0.4 V (vs. Ag/AgCl), the maximum mass increase was ~7.3 and 3.6 ng in the 0.2 M\nNa SO and 0.2 M Na SO -NaI, respectively (Figs. 3b, 3c).”\n2 4 2 4\n“… whereas the baseline ZnOTF electrolyte has a continuously increasing value over\n300 s (Supplementary Fig. 20).”\nThis work investigates the failure mechanism of the Zn anode during cycling and\nreveals two distinct Zn deposition morphologies, which are critical to understanding\nthe reversibility and cycling life of zinc-based batteries. Based on insights into the Zn\ndeposition process, the authors design a bifunctional electrolyte additive that not only\nhomogenizes Zn²⁺ flux but also facilitates the rejuvenation of inactive Zn via a\nspontaneous redox reaction. Benefiting from the engineered electrolyte, the authors\ndemonstrate a significant enhancement in the lifespan of pouch cells. The bi-layer\npouch cell shows promising practical performance under harsh testing conditions.\nOverall, this study presents a comprehensive investigation, spanning from\nfundamental mechanism elucidation to material-level innovations and practical cell\ndemonstrations. The experiments are thorough, and the research logic is generally\nsound. However, several minor issues remain, such as insufficient experimental\ndetails and ambiguous mechanistic explanations. Therefore, I recommend minor\nrevision before the manuscript can be considered for publication in Nature\nCommunications.\nGeneral response: We sincerely thank Reviewer #2 for his/her thorough review and\npositive evaluation of our work. We also appreciate the reviewer’s constructive\ncomments regarding the need for more detailed experimental descriptions and clearer\nmechanistic explanations. We are trying to solve each of the points raised in the\ncomments with additional experiments, theoretical simulation, and mechanistic\nexplanations in the revised manuscript.\nComments 1: Please provide a detailed schematic or image of the custom-designed\nthree-electrode cell, preferably with multi-angle views and a magnified image of the\ncentral region. Additionally, the authors should explain why the deposited Zn appears\nluminescent. More experimental details regarding the custom-built optical\nmicroscope and EQCM setup are also needed.\nsuggestions, we have added a detailed schematic of the custom-designed three-\nelectrode cell, as shown in the new Fig. 1a. Ti wire, Zn wire, and Zn wire serve as the\nworking electrode, counter electrode, and reference electrode, respectively. Photos of\nthe optical cell from different angles is shown in the new Supplementary Fig. 1. The\ncustomized micro dish features openings on three sides to allow the placement of the\nthree electrodes. The working electrode (a Ti wire) and counter electrode (a Zn wire)\nare aligned with ~1 mm spacing in an aqueous Zn-ion electrolyte. The cell is sealed\nwith waterproof tape to prevent electrolyte leakage. Finally, it is connected to a\nbattery tester and placed under an ultra-depth optical microscope for in-situ optical\nobservation.\nRegarding to reviewer’s concern on the apparent luminescence of Zn deposits, this\nphenomenon is primarily related to optical effects associated with surface topography\nand light reflection. Specifically, the initially plated lumpy Zn are relatively dense and\ncompact with well-defined crystalline facets (as seen in Fig. 1d). This smooth Zn\nsurface acts like a mirror, specularly reflecting a large amount of incident light from\nthe microscope’s illumination source directly back into the objective lens. This high\ndegree of reflection is perceived by the observer as a bright or luminescent\nappearance. In contrast, the mossy Zn consists of a porous, high-surface-area network\nof Zn filaments. This rough structure scatters and absorbs incident light much more\neffectively. Rather than being reflected directly back to the lens, the light is diffused\nin many directions. Consequently, much less light reaches the detector, resulting in a\ndark appearance.\nWe sincerely apologize for not providing relevant experimental details for in-situ\noptical observation and EQCM measurements in the original manuscript. Following\nthe suggestions, we have added detailed descriptions of the testing setup and methods\nin the revised version. For optical observations, multi-angle photos of the optical cell\nand the microscope were provided as shown in the new Supplementary Fig. 1.\nFurthermore, experimental details have been supplemented in the Methods section as\n15\nfollows. The optical microscopy observations were conducted using a homemade\nliquid cell, where a Ti wire (30 mm in length and 0.5 mm in diameter), a Zn wire (30\nmm in length and 1 mm in diameter), and a Zn wire (10 mm in length and 1 mm in\ndiameter) served as the working, counter, and reference electrodes, respectively. Prior\nto the assembly of the optical cell, the Ti wire and Zn wire were polished with 10,000\nmesh sandpaper to remove surface oxides and thoroughly cleaned with deionized\nwater and ethanol. The cell was sealed with waterproof tape to prevent electrolyte\nleakage. The optical cell was connected to a battery tester to perform a cycle of Zn\nplating and stripping. Corresponding voltage response was also recorded. Meanwhile,\nan ultra-depth three-dimensional microscope (DeltaPix DPX M6000) was used to\ncapture a series of changes in Zn plating/stripping morphology over time during the\ncycle.\nFor in-situ EQCM measurement, experimental details have been added in the\nMethods section as follows. The in-situ electrochemical quartz crystal microbalance\n(DyneChem DC-QMC3100) measurements were performed in a three-electrode cell\nconsisting of an Au wafer working electrode, Ti counter electrode, and Ag/AgCl\nreference electrode. The assembled cell was examined with a linear sweep\nvoltammetry (LSV) test at 5 mV s−1. The change in resonant frequency (∆f) of the\nquartz crystal during the LSV test was recorded. Therefore, the mass change (∆m) of\nthe quartz crystal electrode can be calculated using the following Sauerbrey equation:\n𝐴𝐴𝜌𝜌𝜌𝜌\n∆𝑚𝑚 = − 2 ∆𝑓𝑓\nWhere A is the piezoelectrically active crys2ta𝑓𝑓l0 area (0.28274 cm2), ρ is the density of\nquartz (2.648 g cm−3), μ is the shear modulus of quartz (2.947 × 1011 g cm−1s−2), f is\n0\nthe resonant frequency of the quartz crystal (9 MHz), and ∆f is the frequency change.\nSupplementary Fig. 1 Photos of the custom-designed three-electrode cell and\nthree-dimensional microscope.\nSome descriptions have been added in the revised manuscript as follows:\n“…as depicted in Fig. 1a and Supplementary Fig. 1.”\n“This smooth Zn surface acts like a mirror, specularly reflecting a large amount of\nincident light from the microscope’s illumination source directly back into the\nobjective lens, which gives the Zn deposits a luminescent appearance.”\nIn-situ optical observation\nThe optical microscopy observations were conducted using a homemade liquid cell,\nwhere a Ti wire (30 mm in length and 0.5 mm in diameter), a Zn wire (30 mm in\nlength and 1 mm in diameter), and a Zn wire (10 mm in length and 1 mm in diameter)\n17\nserved as the working, counter, and reference electrodes, respectively. Prior to the\nassembly of the optical cell, the Ti wire and Zn wire were polished with 10,000 mesh\nsandpaper to remove surface oxides and thoroughly cleaned with deionized water and\nethanol. The cell was sealed with waterproof tape to prevent electrolyte leakage. The\noptical cell was connected to a battery tester to perform a cycle of Zn plating and\nstripping. Corresponding voltage response was also recorded. Meanwhile, an ultra-\ndepth three-dimensional microscope (DeltaPix DPX M6000) was used to capture a\nseries of changes in Zn plating/stripping morphology over time during the cycle.\nIn-situ EQCM\nThe in-situ EQCM (DyneChem DC-QMC3100) measurements were performed in a\nthree-electrode cell consisting of an Au wafer working electrode, Ti counter electrode,\nand Ag/AgCl reference electrode. The assembled cell was examined with a linear\nsweep voltammetry (LSV) test at 5 mV s−1. The change in resonant frequency (∆f) of\nthe quartz crystal during the LSV test was recorded. Therefore, the mass change (∆m)\nof the quartz crystal electrode can be calculated using the following Sauerbrey\nequation:\n𝐴𝐴𝜌𝜌𝜌𝜌\n∆𝑚𝑚 = − 2 ∆𝑓𝑓 (1)\nWhere A is the piezoelectrically active crys2ta𝑓𝑓l0 area (0.28274 cm2), ρ is the density of\nquartz (2.648 g cm−3), μ is the shear modulus of quartz (2.947 × 1011 g cm−1s−2), f is\n0\nthe resonant frequency of the quartz crystal (9 MHz), and ∆f is the frequency change.\nComments 2: There are some writing issues. For example, “0.2 Na₂SO₄” should be\ncorrected to “0.2 M Na₂SO₄” or “0.2 mol L⁻¹ Na₂SO₄.”\nResponse: We sincerely thank the reviewer for his/her meticulous reading and for\npointing out these typos. We have conducted a thorough proofreading of the entire\nmanuscript to identify and correct all potential typos.\n“… and 0.2 M Na SO aqueous solutions containing NaI, containing ACI, and\n2 4\ncontaining neither were used as electrolytes. When the potential swept from 0.1 V to\n−0.4 V (vs. Ag/AgCl), the maximum mass increase was ~7.3 and 3.6 ng in the 0.2 M\nNa SO and 0.2 M Na SO -NaI, respectively (Fig. 3b, 3c).”\n2 4 2 4\nComments 3: The manuscript reports two Zn deposition morphologies: lumpy and\nmossy. The authors should provide a more in-depth analysis of the mechanisms\ndriving these morphological differences. Is the variation substrate-induced, or does it\nrelate to Zn²⁺ depletion near the electrode–electrolyte interface? The proposed\nmechanism, wherein edge growth of lumpy Zn disrupts the homogeneous Zn²⁺ flux,\nrequires further clarification and supporting evidence.\nResponse: We sincerely thank the reviewer for this critical comment, which allows us\nto elaborate on the mechanistic insights into the two-stage deposition phenomenon.\nComprehensive investigations lead us to conclude that this morphology transition is\nprimarily driven by crystallographic evolution and subsequent local electric field\nconcentration, rather than being substrate-induced or caused by interfacial Zn²⁺\ndepletion. Our rationale is supported by the following evidence:\nFirstly, the two-stage deposition (initial lumpy Zn followed by mossy Zn) is\nconsistently observed on different substrates such as Ti and Zn, as shown in Figs. 1c,\n1g and Supplementary Fig. 9. This substrate-independent Zn plating behavior rules\nout a substrate-induced origin.\nSecondly, according to the classical space charge model, interfacial Zn-ion depletion\nis mainly associated with two core parameters, including limiting current density (J )\nlim\nand Sand’s time. When the applied current exceeds the J , ion depletion occurs after\nlim\na certain period of time (i.e., Sand’s time), accompanied by a sharp increase in\npolarization (Phys. Soc. London, 1901, 1: 45-79). The J can be calculated by the\nlim\nfollowing equation:\n19\n4𝑍𝑍𝑐𝑐𝐶𝐶0𝐹𝐹𝐹𝐹\n𝐽𝐽𝑙𝑙𝑙𝑙𝑙𝑙 =\nWhere Z\nc\nis the charge number of Zn ions, C𝐿𝐿0 is the bulk salt concentration, F is the\nFaraday’s constant, D is the Zn-ion diffusion coefficient (7.03×10−6 cm2/s, Small,\n2024, 20: e2307388), and L (1 mm in this work) is the distance between two\nelectrodes. In our system, the calculated J is ~54.3 mA cm−2, significantly higher\nlim\nthan the current density applied in our work. Therefore, Zn ion depletion does not\noccur. Moreover, the transition to mossy Zn is accompanied by a distinct decrease in\npolarization (Fig. 1b). Therefore, interfacial Zn²⁺ depletion is not the trigger for the\nmossy Zn formation.\nThirdly, we have also investigated the Zn plating behavior in other common Zn salts,\nincluding ZnSO , ZnCl , and Zn(ClO ) . The results unequivocally demonstrate that\n4 2 4 2\nthe two-stage plating and stripping behavior is a universal phenomenon across\ncommon Zn salt types (new Supplementary Figs. 6-8).\nFinally, after ruling out these potential reasons, the two-stage plating may be\nattributed to an intrinsic characteristic of Zn deposition. As a typical hexagonal close-\npacked metallic material, the initial Zn nucleation favors the formation of\nthermodynamically stable crystallites with well-defined shapes, which matches the\nthermodynamic Wulff construction. This aligns with our observation that Zn deposits\ninitially appear in a lumpy morphology. As the plating capacity increases, the lumpy\nZn gradually grows, exposing the highly active Zn(100) and Zn(101) crystal facets\n(Figs. 2a, b). As is widely accepted, Zn(100) and Zn(101) facets have a more uneven\nequipotential surface along the horizontal direction than that of the Zn(002) facets\n(Adv. Mater., 2021, 33: 2100187), which leads to the formation of surface protrusions.\nThese protrusions typically exhibit concentrated electric fields and high current\ndensities, serving as deposition hotspots that trigger Zn whisker formation. Once\nformed, these whiskers further exacerbate the unevenness of the electric field on the\nzinc anode surface, which further results in the rapid growth of mossy Zn. This aligns\nwell with in-situ optical observations, SEM, and XRD results.\nto visualize the current density and electric field distribution of two Zn morphologies.\nIn this model, regular hexagons and rectangles represent lumpy Zn and mossy Zn,\nrespectively. The detailed simulation parameters and methods are described in the\nMethods section in the revised manuscript. As shown in the new Figs. 1e, f, the\ngradient colors denote current intensity and electric field. The maximum current\ndensity and electric field are intensely concentrated at the tips and edges of the lumpy\nZn, triggering the formation of Zn whiskers. Once a filament forms, the concentrated\npoint shifts to the top of the Zn filament, creating a positive feedback loop that drives\nthe rampant growth of mossy Zn. Based on these experiments and theoretical\nsimulations, we conclude that the two-stage plating is an inherent characteristic of Zn\ndeposition. It begins with the thermodynamically favorable crystallization of lumpy\nZn, whose subsequent growth creates protrusions that concentrate the electric field\nand Zn-ion flux, promoting the formation of mossy Zn.\nFigs. 1e, f COMSOL simulation of current density distribution and electric field\ndistribution near Zn anode surface at different plating stages.\nSome descriptions have been added in the revised manuscript as follows:\n“The morphological change of Zn deposits correlates with the increase in local current\ndensity at surface protrusions of lumpy Zn, which is attributed to an electric field\nconcentration effect, commonly referred to as the “tip effect”. To support this\nmechanism, we performed finite element simulations to visualize the current density\nand electric field distribution of both two Zn morphologies. In this model, regular\nhexagons and elongated bars represent lumpy Zn and mossy Zn, respectively. As\nshown in Figs. 1e, f, the gradient colors denote current intensity and electric field. The\nmaximum current density and electric field are intensely concentrated at the tips and\n21\nedges of the lumpy Zn, triggering the formation of Zn whisker. Once a mossy\nfilament forms, the concentrated point shifts to the top of the Zn filament, creating a\npositive feedback loop that drives the rampant growth of mossy Zn.”\n“Finite element simulations\nFinite element method (FEM) simulations were performed using COMSOL\nMultiphysics. A two-dimensional model was developed to simulate the current\ndensity and electric field distribution at the anode/electrolyte interface. In this model,\nthe length of two electrodes was 15 μm and the distance between them was 10 μm.\nThe lumpy Zn was represented by three hexagonal protrusions, each with a side\nlength of 2 μm. Additionally, rectangular Zn with a height of 1 μm and width of 0.1\nμm were incorporated on the hexagons to simulate mossy Zn growth. The ionic\nconductivity of the 1 M ZnOTF electrolyte filling the interelectrode gap was set to 3.2\nS m⁻1 59. The cathode and anode potentials were held at 0.05 V and 0 V, respectively.”\n“59. Shi X, Zeng J, Yi A, Wang F, Liu X, Lu X. Unveiling the Failure Mechanism of\nZn Anodes in Zinc Trifluorosulfonate Electrolyte: The Role of Micelle-like Structures.\nJ. Am. Chem. Soc. 146, 20508-20517 (2024).”\nComments 4: In Figure 6a, the authors attribute the increase in capacity at higher\ncurrent rates to redox activity of ACI. This interpretation is questionable without\nnormalization to electrode mass or active material content. Please clarify.\nResponse: We thank the reviewer for raising this point. We apologize for this\noversight. Following the suggestion, the current in the cyclic voltammetry (CV) are\npresented as current density (A g⁻1) in the revised manuscript. The original Figure 6a\nhas changed to Figure 7a due to the addition of data during the revision process. As\nshown in Fig. 7a, the cell with the ZnOTF-ACI electrolyte exhibits higher peak\ncurrent densities than those with the baseline ZnOTF electrolyte, which are attributed\nto the participation of the I⁻/I redox couple from the ACI. We have revised the main\n2\n22\ntext accordingly and appreciate the reviewer’s comment which helped us improve the\nclarity of our data presentation.\nFig. 7a CV of Zn||I coin cells using different electrolytes.\nIn addition, a higher peak current density in the ZnOTF-ACI electrolyte indicated that\nthe iodine anions of ACI also participate in the charge-discharge process.\nComments 5: In Figures 6c and 6d, the definition of C-rate appears inconsistent\nbetween the two cells. The authors should ensure consistent and clearly defined\nelectrochemical testing parameters across figures.\nResponse: We sincerely appreciate the reviewer’s meticulous comment. In the\nmanuscript, the C-rate is defined as the reciprocal of the time required for the cell to\ncomplete one full cycle. In Figs. 6c and 6d, due to differences in size and capacity\nbetween the two pouch cells, different currents were used to perform the long-cycling\ntests. Consequently, the time required to complete one full cycle also varied, resulting\nin differences in the C-rate. In the revised version, we have clarified the definition of\nthe C-rate to prevent any misunderstanding.\nSome descriptions have been added in the revised manuscript as follows:\n23\n“Of note, the C-rate is defined as the reciprocal of the time required for the cell to\ncomplete one full cycle.”\nThis manuscript demonstrated the effect of bi-ionic effect of cation and anion on\nregulating Zn deposit morphology and reviving dead Zn via in situ optic microscopy.\nFor confirming this effect, the authors showed a practical ampere hour scale pouch\ncell which has cycle retention of 96.2% for 800 cycles. However, this manuscript is\nnot suitable for publication in Nature Communications due to its lack of novelty and\ninsufficient depth in conveying a significant scientific message. Overall, the novelty\nand clarity of the proposed ACI mechanism are insufficient. To substantiate the\nhypothesis, further investigations using complementary analytical techniques or\nsimulations are necessary.\nThe following comments are the reason why this manuscript is not suitable for\npublications.\nGeneral response: We sincerely thank Reviewer #3 for taking his/her time to review\nour work. We understand the reviewer’s concerns regarding the novelty of our study\nand would like to take this opportunity to clarify the key advancements and unique\ncontributions of our work as follows.\nFirstly, the formation of electrochemically inactive “dead Zn” is a well-known yet\npoorly understood failure mode in Zn batteries. Prior research often attributed it to\npassive layer formation or simple dendritic growth. Our work provides clear and\ndirect evidence that dead Zn originates from a universal two-stage Zn planting and\nstripping process. Stage 1 (Lumpy Zn): Initial deposition forms relatively dense,\ncrystalline Zn deposits, which are often electrochemically reversible. Stage 2 (Mossy\nZn): Subsequent growth occurs preferentially on the protrusions of the lumpy Zn,\nforming a porous mossy structure. It is this mossy Zn that, during stripping, loses\nelectrical contact with the substrate and becomes permanently inactivated as dead Zn.\nThe discovery of a universal two-stage plating/stripping mechanism that\nfundamentally explains the origin of dead Zn formation, a long-standing capacity loss\nmechanism in Zn batteries that was previously insufficiently understood.\ncombination of cationic and anionic reagents to revive the dead Zn. The cations form\na dynamic, positively charged inert region at the Zn/electrolyte interface to disperse\nthe Zn-ion flux, thereby proactively suppressing the initiation of mossy Zn at the\nedges of lumpy Zn deposits. The iodide anions function as a redox mediator. During\ncharging, it is partly oxidized to I ⁻, which then spontaneously and selectively reacts\n3\nwith the already-formed dead Zn, recycling lost capacity and converting it back to\nelectroactive Zn2+ for use in the subsequent cycle. As a result, a single-layer Zn//I\n2\npouch cell remained a high capacity of ~245.0 mAh after 2500 cycles. In addition, a\npractical Ah-scale Zn//I pouch cell showed an outstanding cycling stability for 800\n2\ncycles with a high-capacity retention of 96.2%, which is at the advanced level of Zn-\nmetal batteries.\nMoreover, we have carefully considered each of concerns and have conducted\nextensive new experiments, calculations, and analyses, which were detailed in the\nfollowing point by point response. We hope that these revisions resolve all the\nconcerns raised and improve the overall quality of the manuscript.\nFinally, given the novel insights and record-breaking performance metrics, we\nrespectfully request the reviewer to reconsider the significance and novelty of our\nwork. We believe this study not only expands the fundamental understanding of Zn\ndeposition and dead Zn formation, but also provides an effective strategy for practical\naqueous Zn-based batteries, well aligning with the high standards and broad scope of\nNature Communications.\nComments 1: The authors claim that the two-stage plating and stripping behavior of\nthe Zn anode occurs only under their optical cell setup. However, in practical systems,\nZn metal operates under applied pressure, and similar behaviors should also be\nexamined in pressure-applied configurations, such as coin cells or pouch cells, at\ndefined pressure levels. In addition, the plating and stripping behavior should be\n26\ninvestigated using ZnSO and other types of Zn salts to confirm whether the\n4\nphenomenon is salt-dependent.\nResponse: We thank the reviewer for these critical questions regarding the\nuniversality of the two-stage plating and stripping of the Zn anode. We apologize for\nany misunderstanding arising from our original manuscript; it was not our intention to\nimply that this behavior is exclusive to the optical cell. On the contrary, our\ncomprehensive investigations confirm that the two-stage deposition is a general and\nintrinsic characteristic of Zn electrodeposition, which is retained under certain applied\npressure and across different common Zn salts. Please see our detailed responses\nbelow, and the new data has been added to the revised manuscript.\nWe fully agree with the reviewer that practical battery systems operate under pressure.\nFollowing the suggestion, we conducted dedicated experiments to investigate the Zn\ndeposition behavior in coin cells under typical assembly pressures. We disassembled\ncoin cells after different plating and stripping times at 1 mA cm⁻² and examined the\nanode surfaces by optical microscope. As shown in the new Supplementary Fig. 10,\nafter 10 min of plating, a metallic-luster Zn deposit, i.e., lumpy Zn, appeared on the Ti\nsurface. As the plating time was increased to 30 min, some black Zn deposits\nnucleated on the surface of the lumpy Zn, indicating that mossy Zn began to nucleate\nat this stage. When the plating time reached 60 min, the Ti surface was basically\ncovered by mossy Zn, indicating that mossy Zn would dominate the plating process.\nDuring the subsequent stripping process, the mossy Zn rapidly shrank until only black\ninsoluble residues were left on the surface of the lumpy Zn which then to dissolve.\nThe voltage versus time profile is consistent with that of the optical cell. Therefore, it\ncan be concluded that the Zn plating-stripping behavior still exhibits a two-stage\ncharacteristic even in a pressure-applied coin cell system. It is noteworthy that\npressure does have an obvious effect on the stacked morphology of Zn deposits, as\nhas been reported in many reports (Adv. Energy Mater., 2023, 14: 2303047; Small,\n2025, 21: e2501242). We compared the surface roughness of Zn deposits formed in\ncoin cells with and without applied stack pressure. As shown in Response Fig. 3, the\n27\nmaximum height difference was reduced from ~242.9 μm (no applied pressure) to\n~58.8 μm (under pressure). This indicates that pressure macroscopically compresses\nthe Zn deposit, making it relatively denser. Critically, however, this macroscopic\ncompaction did not alter the fundamental two-stage plating mechanism.\nTo quantify pressure’s impact on Zn deposition, we investigated Zn morphologies\nunder 0, 0.5, 2.0, and 5.0 MPa by a pressure setup equipped with a pressure sensor\n(new Supplementary Fig. 11). At 0 MPa, typical two-stage plating was detected in\nthis cell. When a stack pressure of 0.5 MPa was applied, the growth of mossy Zn was\nslightly suppressed. When the stack pressure was increased to 2.0 MPa, mossy Zn was\nstill observed after plating for 30 mins. Even at a high stack pressure of 5.0 MPa, two-\nstage plating was maintained and the deposited Zn was relatively uniform. Therefore,\nwhile a higher pressure can somewhat compact the Zn deposits, it does not prevent\nthe inherent drivers that lead to the initial lumpy growth and the subsequent mossy\ntransition. It is worth noting that glass fiber separators will be crushed when subjected\nto pressures exceeding 5.0 MPa. Through these experiments, it can be concluded that\ntwo-stage plating exists in practical systems and warrants attention.\nTo address the reviewer’s concern on salt-dependency, we performed in-situ optical\nobservations in three of the most common aqueous Zn-ion electrolytes, including 1 M\nZnSO , ZnCl , and Zn(ClO ) . As presented in the new Supplementary Figs. 6-8, the\n4 2 4 2\nmorphological transition from lumpy Zn to mossy Zn is unequivocally captured in all\nthree electrolytes. The salt anion might influence the nucleation size and the timing of\nthe transition but did not change the fundamental two-stage plating and stripping\npattern.\nIt is well worth mentioning that the two-stage deposition (initial lumpy Zn followed\nby mossy Zn) is consistently observed on different substrates such as Ti and Zn, as\nshown in Figs. 1c, 1g and Supplementary Fig. 9. This substrate-independent Zn\nplating behavior rules out a substrate-induced origin.\nZnOTF electrolyte at 1 mA cm−2. (a) Typical voltage-time profile of Zn plating and\nstripping. (b) Optical microscope photos of the two-stage Zn plating and stripping.\nScale bar, 500 μm.\nResponse Fig. 3 3D reconstruction images of Zn deposits (a) with and (b) without\npressure in a coin cell.\nmorphologies of Zn deposits. (a) Photos of the pressure setup and Zn//Ti cell. (b)\nOptical microscope photos of the two-stage Zn plating under different pressures.\nScale bar, 500 μm.\n4\nat 1 mA cm−2. (a) Typical voltage-time profile of Zn plating and stripping. (b) Optical\nmicroscope photos of the two-stage Zn plating and stripping. Scale bar, 500 μm.\nSupplementary Fig. 7 Two-stage Zn plating and stripping in a ZnCl electrolyte\n2\nat 1 mA cm−2. (a) Typical voltage-time profile of Zn plating and stripping. (b) Optical\nmicroscope photos of the two-stage Zn plating and stripping. Scale bar, 500 μm.\n4 2\nelectrolyte at 1 mA cm−2. (a) Typical voltage-time profile of Zn plating and stripping.\n(b) Optical microscope photos of the two-stage Zn plating and stripping. Scale bar,\n500 μm.\nSome descriptions have been added in the revised manuscript as follows:\n“We also discovered that the simple replacement of the Zn salt in the electrolyte with\ntypical ZnSO , ZnCl , and Zn(ClO ) electrolytes, did not prevent the initiation and\n4 2 4 2\ngrowth of mossy Zn (Supplementary Figs. 6-8). The salt anion might influence the\nnucleation size and the timing of the transition of Zn morphologies. The use of Zn as\nthe deposition substrate appeared to accelerate the formation of the mossy Zn\n(Supplementary Fig. 9). In addition, the use of stack pressure compressed the Zn\ndeposits, making it more uniform, but did not change the intrinsic mechanism of the\ntwo-stage deposition process (Supplementary Figs. 10, 11).”\nComments 2: The authors used Zn(OTf) , which is significantly more expensive than\n4 4\n32\nverify whether the two-stage plating and stripping behavior is also observed with\nother common Zn salts, such as ZnSO , ZnCl , and Zn(ClO ) .\n4 2 4 2\nResponse: We thank the reviewer for this practical comment. We agree that Zn(OTf)\n2\nis more expensive than ZnSO and may not be widely used in practice. Our choice of\nwidespread adoption in fundamental Zn battery research. In addition, following the\nreview’s suggestion, we have conducted in-situ optical observations in three\nadditional common electrolytes, including 1 M ZnSO , ZnCl , and Zn(ClO ) , as\n4 2 4 2\nshown in our response to your Comment 1 and in the new Supplementary Figs. 6-8.\nThese results unequivocally demonstrate that the two-stage plating and stripping\nbehavior is a universal phenomenon, observed across common Zn salts. The anions of\nZn salts may influence the kinetics and particle size of the initial nucleation, but it\ndoes not change the fundamental morphological transition. Therefore, while Zn(OTf)\n2\nwas used as a model electrolyte for our detailed investigation, the key finding of this\nwork—the two-stage deposition mechanism—is not specific to Zn(OTf) and is\n2\napplicable to the broader field of aqueous Zn batteries.\nComments 3: To ensure reliability, the influence of the bionic (ACI) effect on cell\nperformance should be validated using other types of Zn salts\nResponse: We thank the reviewer for the useful suggestion, which is crucial for\ndemonstrating the general applicability of our strategy. Following the reviewer’s\nadvice, we have comprehensively evaluated the electrochemical performance of the\nACI in three other common and cost-effective Zn-salt electrolytes, i.e., ZnSO , ZnCl ,\n4 2\nand Zn(ClO ) . As shown in the new Supplementary Fig. 42, the Zn||Ti asymmetric\n4 2\ncells with the ZnSO -ACI electrolyte achieved an average CE of 99.6% and a\n4\nsignificantly prolonged cycling life of over 400 cycles at 10 mA cm⁻2 and 5 mAh\ncm⁻2. This is a substantial improvement over the baseline ZnSO electrolyte, which\n4\nshowed a lower average CE (~98.1%) and rapid failure after ~130 cycles. The Zn//Zn\n33\nsymmetrical cells with the ZnSO -ACI electrolyte retained stable cycling over ~1,100\n4\nh at 5 mA cm−2 and 5 mAh cm−2. In contrast, the cell with the ZnSO electrolyte\n4\nfailed due to short-circuiting after only ~120 h. In ZnCl based electrolytes, the\n2\naverage CE of asymmetric cells and the cycling stability of symmetric cells was\nimproved to 99.9% from 97.8% and ~1,830 h from 74 h after the introduction of ACI\n(new Supplementary Fig. 43). In Zn(ClO ) based electrolytes, the addition of ACI\n4 2\nled to a dramatic enhancement in both the average CE (~99.9% vs. 95.9%) of\nasymmetric cells and the cycling stability (~1,960 h vs. 38 h) of symmetric cells (new\nSupplementary Fig. 44). These results confirm that the beneficial effects of ACI are\nnot limited to the ZnOTF electrolyte. The dual functions of the cationic and anionic\ncomponents in suppressing mossy Zn formation and reactivating dead Zn prove to be\nuniversally effective across different Zn-salt chemistries. This greatly strengthens the\nreliability and practical potential of our proposed approach.\nSupplementary Fig. 42 Galvanostatic Zn plating/stripping in Zn//Ti and Zn//Zn cells\nwith the ZnSO and ZnSO -ACI electrolyte.\n4 4\nwith the ZnCl and ZnCl -ACI electrolyte.\n2 2\nSupplementary Fig. 44 Galvanostatic Zn plating/stripping in Zn//Ti and Zn//Zn cells\nwith the Zn(ClO ) and Zn(ClO ) -ACI electrolyte.\n4 2 4 2\nTo ensure reliability, the influence of ACI effects on cell performance was validated\nusing other Zn salts, including ZnSO , ZnCl , and Zn(ClO ) . After the introduction of\n4 2 4 2\nACI into the baseline electrolyte, both the CE and cycling life of the cells were\nsubstantially enhanced, demonstrating the excellent applicability of ACI in stabilizing\nZn anodes (Supplementary Figs. 42-44).\nComments 4: The overall analysis of the effect of ACI is insufficient to clearly\nelucidate the underlying mechanism. The mechanism of ACI is unclear for stabilizing\nthe Zn metal interface.\nResponse: We thank the reviewer for this critical comment, which provides us with\nthe opportunity to elaborate more clearly on the underlying mechanism of the ACI.\nBased on our existing data and the new experimental and theoretical evidence added\nduring revision, we propose a dual-function mechanism for ACI with combined\ncationic and anionic components to revive dead Zn and stabilize the Zn interface.\nFirstly, to directly decouple the effect of the bi-ionic components, we systematically\ncompared the Zn deposition morphology in three electrolytes, including 1 M ZnOTF,\nZnOTF + 0.5 M ACI (providing both I⁻ anions and acetylcholine cations). As shown\nin the Fig. 1c, Fig. 4a and new Supplementary Fig. 17, the Zn deposits from both the\nbaseline ZnOTF and the ZnOTF-KI electrolyte are loose and porous. In contrast, only\nthe ACI-added electrolyte produces compact and uniform Zn deposits. In addition, the\nassembled Zn//Ti cell and Zn//Zn cell with the ZnOTF-KI electrolyte short-circuited\nafter ~142 and ~116 h of cycling, respectively (Response Fig. 1), indicating that\nmossy Zn still formed within the cells despite the addition of KI. These results\nprovide clear evidence that the iodide anions alone cannot control the Zn deposition\n36\nmorphology. The dramatic improvement in Zn deposition morphology is achieved\nwhen the acetylcholine cation is present.\nSpecially, the cationic component primarily acts to prevent the formation of mossy Zn\nby creating a positively charged inert region on the anode surface for Zn-ion\ndispersion. As demonstrated by the in-situ EQCM data (new Figs. 3a-3c), when the\npotential swept from 0.1 V to −0.4 V (vs. Ag/AgCl), the maximum mass increase was\n~7.3 and 3.6 ng in the 0.2 M Na SO and 0.2 M Na SO -NaI, respectively. However,\n2 4 2 4\n~60.1 ng was detected when the ACI was added. This large increase in mass is mainly\nattributed to the adsorption of acetylcholine cations rather than Na+, I−, or H O, which\n2\nindicates that cations can migrate to and adsorb onto the Zn electrode surface under an\nelectric field.\nTo better elucidate the cations mediated Zn anode interface, we supplemented the in-\nsitu electrochemical Fourier transform infrared spectroscopy (in-situ FT-IR) to\nmonitor the dynamic interfacial evolution at the Zn anode. As shown in the new Fig.\n3d, in-situ FT-IR were conducted in a spectra-electrochemical cell, which consisted of\na Zn counter/reference electrode, a Ti mesh working electrode, and a ZnOTF-ACI\nelectrolyte. Galvanostatic discharge tests were performed, and changes in the\ninterfacial infrared spectra during the discharge were detected. The collected spectrum\nat open-circuit potential was used as the background. As shown in the new Fig. 3e,\nthe absorption band at ~2,980 cm⁻1 is attributed to the C-H stretching band of the\nmethyl group in the acetylcholine cations. The intensity of the C-H stretching band\nprogressively increases during Zn plating, indicating a progressive adsorption process\nof cations onto the electrode surface. This is also consistent with the results from the\nelectrochemical EQCM measurements.\nTo better illustrate the interfacial interactions between the Zn anode and ACI, we have\nsupplemented the revised manuscript with DFT calculations (new Supplementary\nFig. 14 and Supplementary Date1). The corresponding computational details have\nbeen added to the Methods section of the revised manuscript. As shown in the new\nFig. 3f, the adsorption energy of the horizontal acetylcholine cations (−3.86 eV) was\n37\nmuch higher than that of H O (−0.32 eV), Zn2+ (−1.46 eV), iodide anions (−2.79 eV),\n2\nand the vertical acetylcholine cations (−3.23 eV). This confirms the preferential and\nstrong adsorption between the acetylcholine cations and Zn anode, which creates a\npositively charged inert layer on the Zn anode to disperse Zn2⁺ ions.\nRegarding anions for reviving dead Zn, iodide anions can form a certain amount of\noxidative mediator (I −) during charging. These I − preferentially react with dead Zn to\n3 3\nform electroactive Zn ions that can return for use in the battery cycle. The preferential\nreaction of I − with dead Zn was elaborated and experimentally verified in our\n3\nresponse to your next Comment 5. Experimental evidence for iodine’s reactivation of\ndead Zn was validated through multiple experiments in the original manuscript,\nincluding immersion tests, XRD analysis, and electrochemical measurements.\nIn summary, based on the original data supplemented by additional experiments and\ntheoretical calculations, we now have reason to believe that the underlying\nmechanism stabilizing Zn anodes by the ACI has been properly elucidated.\nSupplementary Fig. 17 Two-stage Zn plating in a ZnOTF-KI electrolyte at 1 mA\ncm−2. (a) Typical voltage-time profile of Zn plating. (b) Optical microscope photos of\nthe two-stage Zn plating. Scale bar, 500 μm.\nthe ZnOTF-KI electrolyte.\nFigure 3. Cation mediated Zn anode interface. a Schematic of the EQCM\nmeasurement setup. b Linear sweep voltammetry curves in an EQCM test at 5 mV s−1.\nc Mass change curves of different Na SO based solutions. d Schematic of the in-situ\n2 4\nZnOTF-ACI electrolyte. f Adsorption energy of the acetylcholine cation, I− anion, Zn\nion, and H O on the Zn substrate. The corresponding structural formula are shown in\n2\nthe insets.\nSome descriptions have been added in the revised manuscript as follows:\n“To better elucidate the cation mediated Zn anode interface, we supplemented the in-\nsitu electrochemical Fourier transform infrared spectroscopy (in-situ FT-IR) to\nmonitor the dynamic interfacial evolution at the Zn anode. As shown in Fig. 3d, in-\nsitu FT-IR were conducted in a spectra-electrochemical cell, which consisted of a Zn\ncounter/reference electrode, a Ti mesh working electrode, and a ZnOTF-ACI\nelectrolyte. Galvanostatic discharge tests were performed, and changes in the\ninterfacial infrared spectra during the discharge were detected. The collected spectrum\nat open-circuit potential was used as the background. As shown in Fig. 3e, the\nabsorption band at ~2,980 cm⁻1 is attributed to the C-H stretching band of the\nmethyl group in acetylcholine cations. The intensity of the C-H stretching band\nprogressively increases during Zn plating, indicating a progressive adsorption process\nof cations onto the electrode surface. This is also consistent with the results from the\nelectrochemical EQCM measurements.”\n“To better illustrate the interfacial interactions between the Zn anode and ACI,\nwe have conducted the DFT calculations (Supplementary Fig. 14 and Supplementary\nDate1). As shown in Fig. 3f, the adsorption energy of the horizontal acetylcholine\ncations (−3.86 eV) was much higher than that of H O (−0.32 eV), Zn2+ (−1.46 eV),\n2\niodide anions (−2.79 eV), and the vertical acetylcholine cations (−3.23 eV). This\nconfirms the preferential adsorption between the acetylcholine cations and Zn anode,\nwhich creates a positively charged inert layer on the Zn anode to disperse Zn2⁺ ions.”\n“In-situ FT-IR\nThe in-situ FT-IR measurements were performed using a Thermo Fisher\nCadmium Telluride (MCT) detector and a silicon attenuated total reflection (ATR)\naccessory. Prior to use, the substrate plane of the Si prism was mechanically polished\nusing aluminum oxide suspensions of different particle sizes until a mirror-like finish\nwas achieved, followed by rinsing with deionized water. In the in-situ FTIR cell, a Ti\nmesh served as the working electrode, while Zn foil functioned as both the counter\nelectrode and reference electrode. The incidence angle was set at 60°, with a spectral\nresolution of 4 cm⁻1. Each spectral data was collected at an interval of 60 s. The in-\nsitu FT-IR spectroscopy combined with the galvanostatic discharge method was used\nto monitor the Zn deposition process on the electrode surface.”\n“DFT calculations\nFirst-principles DFT calculations were performed in the Vienna Ab initio Simulation\nPackage (VASP)60. The exchange-correlation interactions were described by the PBE\nfunctional within the generalized gradient approximation, with a plane-wave cutoff\nenergy of 500 eV61. The electronic self-consistency criterion was set to 10−5 eV, and\nthe force on each atom was converged below 0.03 eV Å−1. The Zn substrate was\nmodeled as a four-layer 6×6 supercell and a 25 Å vacuum layer was constucted. The\ndispersion corrections were included by the DFT-D3 scheme. Geometry optimizations\nwere performed using a Γ-only k-mesh for the Brillouin zone sampling. The geometry\nrelaxation was applied for the top two layers of the Zn slab62. The adsorption energy\n(E ) was calculated using the following equation:\nads\nwhere E\ntotal\nis the total ener𝐸𝐸g𝑎𝑎y𝑎𝑎 𝑎𝑎of= th𝐸𝐸e𝑡𝑡𝑡𝑡 𝑡𝑡a𝑎𝑎d𝑙𝑙s−orp𝐸𝐸t𝑎𝑎i𝑠𝑠o𝑠𝑠n −sy𝐸𝐸s𝑍𝑍te𝑍𝑍m, E\nsub\nis the energy of (t4he)\nadsorbate, E is the energy of a free Zn(002)-slab.”\nZn\n“60. Kresse G, Furthmüller J. Efficient iterative schemes for ab initio total-energy\ncalculations using a plane-wave basis set. Physical Review B 54, 11169-11186\n(1996).\n61. Perdew JP, Burke K, Ernzerhof M. Generalized Gradient Approximation Made\nSimple. Phys. Rev. Lett. 77, 3865-3868 (1996).\n41\n62. Wang V, Xu N, Liu J-C, Tang G, Geng W-T. VASPKIT: A user-friendly\ninterface facilitating high-throughput computing and analysis using VASP code.\nComput. Phys. Commun. 267, 108033 (2021).”\nComments 5: There is no guarantee that iodine ions selectively decompose only\nZOTH; they may also dissolve fresh Zn. Therefore, it is necessary to compare the\ndecomposition ratio between fresh Zn and ZOTH. Furthermore, the adsorption\nselectivity of ZOTH to fresh Zn and dead Zn need to be analyzed.\nResponse: We thank the reviewer for raising this point regarding the selectivity of I ⁻\n3\nmediated reactions. To directly compare the decomposition ratios, we immersed three\nsamples—fresh Zn foil, collected dead Zn, and pre-synthesized ZOTH—in separate\nvials containing 50 mL of a 2.5 mM I ⁻ solution. Note that due to the uncertain\n3\nmolecular weight of ZOTH, all three samples were in excess relative to the I ⁻.\nintervals of 1, 3, and 7 days, the upper supernatant was extracted to quantify the\ndissolved Zn2+ concentration by ICP-OES. The results, presented in the new\nSupplementary Fig. 27, clearly showed that the Zn2+ concentration increased in the\norder: ZOTH > dead Zn > fresh Zn at every time point. This demonstrated that the\ndecomposition rate followed the same order. These different rates might be attributed\nto the dramatic difference in specific surface area, where dead Zn and ZOTH exhibit\nporous morphologies with high specific surface areas, while fresh Zn foil is dense and\nflat and provides a low specific surface area. This kinetic preference ensures that the\nI ⁻ mediator will predominantly target the high-surface-area inactive species rather\n3\nthan the bulk Zn anode.\nRegarding the reviewer’s comment on the adsorption selectivity of ZOTH to fresh Zn\nand dead Zn, it is believed that ZOTH can form on both of them. This is because\ndead Zn consists of chemically zero-valent metallic Zn and divalent Zn-ion species\n(e.g., ZOTH, ZnO), while fresh Zn is zero-valent metallic Zn. ZOTH might form\nmore easily on dead Zn compared to fresh Zn. We conducted XRD and XPS tests on\ndead Zn and fresh Zn after immersing them in the ZnOTF electrolyte for 5 days (new\nboth the immersed dead Zn and fresh Zn. The intensity of the ZOTH was slightly\nhigher on the dead Zn than on the fresh Zn. Furthermore, XPS analysis detected a\nhigher S and F element content on the surface of the immersed dead Zn, suggesting\nthat dead Zn is more prone to forming the ZOTH byproduct. Consequently, it can be\nconcluded that ZOTH by-products form more easily on dead Zn than on fresh Zn.\nIn summary, the I ⁻-mediated rejuvenation process exhibits a beneficial kinetic\n3\nselectivity towards inactive species, safeguarding the structural integrity of the bulk\nZn anode while effectively recovering lost capacity.\nSupplementary Fig. 27 ICP-OES of the KI solution after treatment with fresh\nSupplementary Fig. 28 (a) XRD and (b) XPS of dead Zn and fresh Zn after\nsoaking in the ZnOTF electrolyte for 5 days.\n“Considering that the I − might also corrode fresh Zn, the decomposition rates of the\n3\nsamples—fresh Zn foil, dead Zn, and pre-synthesized ZOTH—in separate vials\ncontaining 50 mL of a 2.5 mM I ⁻ solution. Note that due to the uncertain molecular\n3\nweight of ZOTH, all three samples are in excess relative to the I ⁻. At intervals of 1, 3,\n3\nand 5 days, the upper supernatant was extracted to quantify the dissolved Zn2⁺\nconcentration by ICP-OES. The results, presented in the Supplementary Fig. 27,\nclearly showed that the Zn2⁺ concentration increased in the order: ZOTH > dead Zn >\nfresh Zn at every time point. This demonstrated that the decomposition rate followed\nthe same order. These different rates might be attributed to the dramatic difference in\nspecific surface area, where dead Zn and ZOTH exhibit porous morphologies with\nhigh specific surface areas, while fresh Zn foil is dense and flat and provides a low\nspecific surface area. This kinetic preference ensures that the I ⁻ mediator will\n3\npredominantly target the high-surface-area inactive species rather than the bulk Zn\nanode.”\n“Moreover, dead Zn is more prone to be corroded by the electrolyte to produce ZOTH\nthan fresh Zn (Supplementary Fig. 28).”\nComments 6: Significantly, the effect of bi-ionic (ACI) should be more deeply studied\nwith the mechanism and other types of bi-ionic form analogues should be compared.\nResponse: We appreciate the reviewer’s valuable question. Regarding the mechanism\nof ACI, we have supplemented new experiments, calculations, and analysis, as\ndetailed in our response to your comment 4. Following the reviewer’s suggestion that\nACI should be compared with other types of bi-ionic form analogues, we have\nevaluated a series of bi-ionic analogues to decouple the contributions of the cations\nand anions.\nreplaced I⁻ anions with other halides such as bromide (Br⁻) and chloride (Cl⁻). As\nshown in the new Supplementary Figs. 30, 31, cells with acetylcholine bromide\n(ACBr) and acetylcholine chloride (ACCl) generated 0.90 and 1.05 mAh cm⁻2 of dead\nZn in the formation cycle, respectively. In the subsequent cycle, they still produced\n0.11 and 0.04 mAh cm⁻2 of dead Zn, corresponding to CEs of 89.2% and 95.8%.\nThis indicates that Cl⁻ and Br⁻ cannot effectively reactivate dead Zn, which might be\nattributed to their high oxidation potential required to form oxidizing mediator. In\naddition, the long-term cycling stability of Zn anodes was assessed in ZnOTF-ACCl\nand ZnOTF-ACBr electrolytes using Zn//Zn symmetric cells (new Supplementary\nFigs. 30, 31). While ACBr and ACCl achieved some improvement in Zn||Zn\nsymmetric cell cycling over the ZnOTF baseline electrolyte (~1130 h and ~1060 h at\n5 mA cm⁻2/5 mAh cm⁻2), they were inferior to that of ACI (>2000 h). This\ndemonstrates that the cations can suppress the formation of mossy Zn to prevent the\ncell from short-circuiting in a short time, and the anions are crucial for achieving\nultra-long life via dead Zn recovery.\nSecondly, to elucidate the effect of cations, we kept the I⁻ anions constant and\nreplaced the acetylcholine cations with other structurally related cations, including\ncholine (C⁺), butyrylcholine (BC⁺), and acetylthiocholine iodide (ATC+). All I⁻-based\nbi-ionic analogues (CI, BCI, ATCI) could reactivate dead Zn to some extent, as\nevidenced by a CE value exceeding 100% (new Supplementary Figs. 32-34). This\nconfirms the primary role of the I⁻ anions in capacity recovery. The stability of Zn\nplating/stripping, reflected in the symmetric cell cycling, shows significant\nimprovement after the addition of I⁻-based bi-ionic analogues (new Supplementary\nFigs. 32-34). The cycling life decreased in the order: ACI (~2,000 h) > BCI (~1,860\nh) > ATCI (~1,270 h) > ChI (~850 h). This ranking might correlate with the\nadsorption energy and spatial configuration of the cations on the Zn surface, which\ndetermines their efficacy in suppressing mossy Zn.\nZn anode. The cation governs the interfacial Zn-ion distribution for inhibiting mossy\nZn formation, while the anion provides a redox-mediated recovery of dead Zn. We\nbelieve these systematic comparisons provide a deeper mechanistic insight requested\nby the reviewer and firmly establish the rationale behind our selection of ACI.\nSupplementary Fig. 30 Tests of dead Zn and electrochemical performances using\nthe bi-ionic form analogue of ACBr. (a)Typical voltage profiles of the formation of\ndead Zn at 1 mA cm⁻2. Inset in (a) is the corresponding simplified structural formula.\n(b) Voltage profiles of Zn//Ti cells with the ZnOTF-ACBr electrolyte at 5 mA cm⁻2\nafter the formation cycle. (c) Galvanostatic Zn plating/stripping in Zn//Zn cells with\nthe ZnOTF-ACBr electrolyte.\nusing the bi-ionic form analogue of ACCl. (a) Typical voltage profiles of the\nformation of dead Zn at 1 mA cm⁻2. Inset in (a) is the corresponding simplified\nstructural formula. (b) Voltage profiles of Zn//Ti cells with the ZnOTF-ACCl\nelectrolyte at 5 mA cm⁻2 after the formation cycle. (c) Galvanostatic Zn\nplating/stripping in Zn//Zn cells with the ZnOTF-ACCl electrolyte.\nSupplementary Fig. 32 Tests of dead zinc and electrochemical performances\nusing the bi-ionic form analogue of Cl. (a) Typical voltage profiles of the formation\n47\nof dead Zn at 1 mA cm⁻2. Inset in (a) is the corresponding simplified structural\nformula. (b) Voltage profiles of Zn//Ti cells with the ZnOTF-CI electrolyte at 5 mA\ncm⁻2 after the formation cycle. (c) Galvanostatic Zn plating/stripping in Zn//Zn cells\nwith the ZnOTF-CI electrolyte.\nSupplementary Fig. 33 Tests of dead zinc and electrochemical performances\nusing the bi-ionic form analogue of BCl. (a) Typical voltage profiles of the\nformation of dead Zn at 1 mA cm⁻2. Inset in (a) is the corresponding simplified\nstructural formula. (b) Voltage profiles of Zn//Ti cells with the ZnOTF-BCI\nelectrolyte at 5 mA cm⁻2 after the formation cycle. (c) Galvanostatic Zn\nplating/stripping in Zn//Zn cells with the ZnOTF-BCI electrolyte.\nusing the bi-ionic form analogue of ATCl. (a) Typical voltage profiles of the\nformation of dead Zn at 1 mA cm⁻2. Inset in (a) is the corresponding simplified\nstructural formula. (b) Voltage profiles of Zn//Ti cells with the ZnOTF-ATCI\nelectrolyte at 5 mA cm⁻2 after the formation cycle. (c) Galvanostatic Zn\nplating/stripping in Zn//Zn cells with the ZnOTF-ATCI electrolyte.\nSome descriptions have been added in the revised manuscript as follows:\n“Of note, the combination strategy of cations and anions is not limited to the ACI,\nas other bi-ionic form analogues exhibit similar effects, which will be discussed later.”\n“To decouple the contributions of the cations and anions, other types of bi-ionic form\nanalogues have also been evaluated. Firstly, to elucidate the effect of anions, we kept\nthe acetylcholine cations constant and replaced I⁻ anions with other halides such as\nbromide (Br⁻) and chloride (Cl⁻). As shown in the Supplementary Figs. 30, 31, cells\nwith acetylcholine bromide (ACBr) and acetylcholine chloride (ACCl) generated 0.90\nand 1.05 mAh cm⁻2 of dead Zn in the formation cycle, respectively. In the subsequent\ncycle, they still produced 0.11 and 0.04 mAh cm⁻2 of dead Zn, corresponding to CEs\nof 89.2% and 95.8%. This indicates that Cl⁻ and Br⁻ cannot effectively reactivate dead\noxidizing mediator. Secondly, to elucidate the effect of cations, we kept the I⁻ anions\nconstant and replaced the acetylcholine cations with other structurally related cations,\nincluding choline (C⁺), butyrylcholine (BC⁺), and acetylthiocholine iodide (ATC+).\nAll I⁻-based bi-ionic analogues (CI, BCI, ATCI) could reactivate dead Zn to some\nextent, as evidenced by a CE value exceeding 100% (Supplementary Figs. 32-34).\nThis confirms the primary role of the I⁻ anions in capacity recovery.”\n“In addition, the stability of Zn plating/stripping, reflected in the symmetric cell\ncycling, showing significant improvement after the addition of other bi-ionic form\nanalogues (Supplementary Figs. 30-34).”\nDear reviewers,\nThank you for your constructive comments about our manuscript. The comments have\nbeen addressed point-by-point below.\nReviewer #1: Authors have carefully addressed my concerns, now it merits for\npublication.\nResponse: We are sincerely grateful to Reviewer #1 for his/her recognition of our\nwork.\nReviewer #2: All of my concerns have been clarified well, and I recommend this\nmanuscript to be published without further adjustment.\nResponse: We are very grateful to Reviewer #2 for recommending our work for\npublication without further adjustments.\nReviewer #3: The authors have thoroughly revised the manuscript, resulting in\nsignificant improvements. Therefore, it is now suitable for publication.\nResponse: We are deeply grateful to Reviewer #3 for his/her recommendation of our\nwork for publication.\nWith best regards,\nSincerely\nHui-Ming Cheng on behalf of all authors\n---------------------------------------------------------------------------\nHui-Ming Cheng, Professor\nInstitute of Technology for Carbon Neutrality, Shenzhen Key Laboratory of Energy\nMaterials for Carbon Neutrality, Shenzhen Institutes of Advanced Technology,\nChinese Academy of Sciences, Shenzhen 518055, China\nE-mail: hm.cheng@siat.ac.cn\n1"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Authors have carefully addressed my concerns, now it merits for publication.", "reviewer_2": "All of my concerns have been clarified well, and I recommend this manuscript to be published without further adjustment.", "reviewer_3": "The authors have thoroughly revised the manuscript, resulting in significant improvements. Therefore, it is now suitable for publication."}, "author_response": "Point-by-point response to the reviewers’ comments\nDear reviewers,\nThank you for your constructive comments about our manuscript. The comments have\nbeen addressed point-by-point below.\nReviewer #1: Authors have carefully addressed my concerns, now it merits for\npublication.\nResponse: We are sincerely grateful to Reviewer #1 for his/her recognition of our\nwork.\nReviewer #2: All of my concerns have been clarified well, and I recommend this\nmanuscript to be published without further adjustment.\nResponse: We are very grateful to Reviewer #2 for recommending our work for\npublication without further adjustments.\nReviewer #3: The authors have thoroughly revised the manuscript, resulting in\nsignificant improvements. Therefore, it is now suitable for publication.\nResponse: We are deeply grateful to Reviewer #3 for his/her recommendation of our\nwork for publication.\nWith best regards,\nSincerely\nHui-Ming Cheng on behalf of all authors\n---------------------------------------------------------------------------\nHui-Ming Cheng, Professor\nInstitute of Technology for Carbon Neutrality, Shenzhen Key Laboratory of Energy\nMaterials for Carbon Neutrality, Shenzhen Institutes of Advanced Technology,\nChinese Academy of Sciences, Shenzhen 518055, China\nE-mail: hm.cheng@siat.ac.cn\n1"}]

Decision letter