Coordination modulation of hydrated zinc ions to enhance redox reversibility of zinc batteries

The dendrite growth of zinc and the side reactions including hydrogen evolution often degrade performances of zinc-based batteries. These issues are closely related to the desolvation process of hydrated zinc ions. Here we show that the efficient regulation on the solvation structure and chemical properties of hydrated zinc ions can be achieved by adjusting the coordination micro-environment with zinc phenolsulfonate and tetrabutylammonium 4-toluenesulfonate as a family of electrolytes. The theoretical understanding and in-situ spectroscopy analysis revealed that the favorable coordination of conjugated anions involved in hydrogn bond network minimizes the activate water molecules of hydrated zinc ion, thus improving the zinc/electrolyte interface stability to suppress the dendrite growth and side reactions. With the reversibly cycling of zinc electrode over 2000 h with a low overpotential of 17.7 mV, the full battery with polyaniline cathode demonstrated the impressive cycling stability for 10000 cycles. This work provides inspiring fundamental principles to design advanced electrolytes under the dual contributions of solvation modulation and interface regulation for high-performing zinc-based batteries and others.

the activate water molecules, thus leading to the enhanced redox kinetics and impressive cycling stability of zinc electrode. Owing to electrochemical data and theoretical calculations, the chemical interaction of zinc ions with phenolsulfonate anions and TBATS was analyzed to provide the indepth understanding of an improved redox reversibility. Consequently, the zinc-based batteries with redox reactions of polyaniline cathodes demonstrated the impressive cycling stability for energy storage. With the highly promising applications of zinc electrode in various zinc-based batteries, the novel electrolytes to regulate the reversible redox reactions of zinc are very intriguing candidates for next-generation energy storage. Therefore, the reviewer would recommend it to be published after suitable revisions. The comments and suggestions about this work are as follows: 1. As for the corrosion test, oxygen dissolved into the aqueous electrolyte would change the corrosion behaviors. Is oxygen removed from the aqueous electrolyte? The related information should be provided. 2. In the molecule dynamic simulation part, both Zn(PS)2 and water molecules are involved in the system. Although trace amount of TBATS was added in the present electrolyte, please explain why TBATS additive is not involved in the theoretical calculation. 3. The mass loading of polyaniline in the pouch cells including the volume of electrolyte should be given in the work to understand the present electrochemical performance. Especially, the conductivity of such molecular electrolyte with coordination networks is generally not good, how to achieve the redox process with conjugated anions? 4. With the novel electrolyte of Zn(PS)2+TBATS, the full cell by coupling of zinc electrode with polyaniline demonstrated enhanced electrochemical performance. A comparable list can be added to exhibit the advances in comparison with the reported results. 5. In Figure 3d, the desolvation energy calculated for Zn(H2O)62+ is lower than those of Zn(H2O)5(SO4) and Zn(H2O)5(PS)+. Accordingly, would the electrochemical performance of zinc electrodes be enhanced in the dilute solution? 6. The Zn2+ ion transference number calculated ( Supplementary Fig. 25) for 1 M Zn(PS)2 is 0.78, but slightly decreased to 0.76 with the addition of TBATS. However, the ionic conductivity of 1 M Zn(PS)2+0.2 TBATS electrolyte is better than that of the electrolyte without additives. How to correlate the relationship between the ionic conductivity and the transference number? 1

Point-to-Point Responses to Reviewers' Comments
We appreciate the reviewers for their helpful and insightful comments, which have greatly helped us to improve the quality of our work. The manuscript has been carefully revised accordingly and the detailed responses and quotations from the revised manuscript are listed below. All the revised parts are highlighted in blue in the manuscript.

To Reviewer#1
Reviewer #1: Comments This manuscript reports the rational regulation of hydrated zinc ions via the coordination process in the presence of zinc phenolsulfonate (Zn(PS)2) and tetrabutylammonium    Figure 2b should be noted.

Response:
Thanks. Accordingly, the nucleation potential on Ti substrate is presented in Supplementary Fig. 18, and the related discussion is added in Page 6. "Moreover, lower nucleation potentials of 90 and 73 mV are observed on Ti substrate in 1 M Zn(PS)2 electrolyte with/without TBATS in comparison with the nucleation potential of 101 mV in 1 M ZnSO4 electrolyte ( Supplementary Fig. 18). The results exhibit the unique features of such electrolytes for the favorable deposition of zinc." Supplementary Fig. 18 Enlarged CV curves of Ti-Zn asymmetric cells in different electrolytes (Fig. 2b).
2 Comments 2. The deposition structure is important to exhibit the cycling stability of metal-based batteries. In-situ optical microscopy observations exhibit the cross-section image of the Zn deposition process (Figure 1i, j). However, the real morphology after deposition should be provided to examine the different macro-structures with the possible formation of Zn dendrites.
Response: Thanks for your good suggestion. The related information is added in revised manuscript ( Supplementary Fig. 7), accordingly.
The obvious color difference is observed on the zinc foils in 1 M ZnSO4 owing to the uneven deposition. With the extension of deposition time, the zinc deposited in dark gray color is formed. The gradual growth of zinc protrusion into the obvious zinc dendrites with the prolonging deposition time results in the loose deposition of Zn with porous structure and larger thickness (about 21, 16 μm) (Supplementary Fig. 8a-d). The Zn deposited in 1 M Zn(PS)2 electrolyte is relatively uniform. In contrast, the dense deposition of zinc is observed in 1 M Zn(PS)2+0.2 TBATS electrolyte, exhibiting the light gray color, similar with that of pure Zn. The uniform growth of Zn with the compact layer of 9.6 μm is achieved in 1 M Zn(PS)2+0.2 TBATS electrolyte, which is close to the theoretical thickness (~ 8.5 µm under 5 mAh cm -2 , Supplementary Fig. 8e, f).

Comments 3. Does the TBATS additives change the properties of the bulk electrolyte?
Raman spectra would be helpful in detecting the potential changes of the bulk electrolyte with TBATS additives. Data should be provided to investigate.
Response: Thanks. Raman spectroscopy was employed to examine the potential change of electrolytes with/without TBATS. Notably, the similar profiles of Raman spectra ( Fig R1) are obtained, showing the typical features of sulfonate group and benzene ring groups. It's evident that the TBATS additive does not change basic properties of the bulk electrolyte. Considering the low amount of TBATA (0.2 mg mL -1 ), the additive is more likely to regulate the interface of zinc/electrolyte as the shielding layer, rather than change the solvation properties of bulk electrolyte.    Ip=2.69×10 5 n 3/2 ADZn 1/2 v 1/2 CZn where Ip is the peak current, n is the number of electrons, A is the area of the electrode, DZn is the diffusion coefficient of Zn 2+ ions, v is the scan rate and CZn is the concentrate of Zn 2+ ions. Taking the average value of anodic and cathodic process, the DZn values are calculated to be 9.53×10 -9 , 5.22×10 -7 and 4.69×10 -7 cm 2 s -1 in 1 M ZnSO4, 1 M Zn(PS)2 and 1 M Zn(PS)2+0.2 TBATS, respectively. The enhanced transfer ability of Zn 2+ ions would be responsible for the good rate performance and high specific capacity. Additionally, it has been revealed that the intercalation of counterions including H + is involved in energy storage process in the cathode along with the redox reactions of polyaniline (Angew. Chem. Int. Ed. 57, 16359-16363 (2018); Chem. Eng. J. 448, 137711 (2022)). In the present case, both H + and Zn 2+ as counterions would be involved in the energy storage process of polyaniline due to the electrostatic interaction. Notably, the additional zinc ions with the enhanced transfer ability are available in Zn(PS)2+0.2 TBATS electrolyte due to the easy desolvation, which would improve the energy storage process of polyaniline with counterion intercalation and thus enhance electrochemical performance.

Supplementary Fig. 30
Linear fitting between the peak current and the square root of the scan rates of the CV curves for PANI-Zn batteries.
Minor issues, Comments 1. Figure  Comments 2. Figure 2d, "strong" and "weak" cannot be used to describe binding energy, "high" and "low" will be more appropriate, or "strong binding", "weak binding".
Response: Thank you for your good suggestion. The Fig. 2d is revised, accordingly.
Comments 3. Figure 5d, it is not appropriate to use a red CE axis, as the red color is actually for a cycling stability curve.
Response: Thanks. The Fig. 5d is corrected.

To Reviewer#2
Reviewer #2: The submitted work is another effort among many in recent couple of years aimed to mitigate Zn anode corrosion as well as HER issues by electrolyte engineering. This time, the authors reported an aqueous Zn(PS)2 along with TBATS surface modifier as a better electrolyte than ZnSO4. Note that electrolyte engineering by additives is all old tricks used by Zn-plating industry. While it makes sense to use newly designed Zn salt and additives for mitigating Zn corrosion issue (as well as HER) for Zn-plating process, it is equally important to consider its potential impact on cathodic reactions for Zn-ion batteries. Unfortunately, there is no discussion on that aspect in this paper. As many early studies have demonstrated that H + intercalation in cathodes accounts for a significant portion of the capacity. The source of H + is the H2O solvating Zn 2+ . If they are replaced by PSas stated by the authors, would H + storage in the cathode be inhibited and the capacity of the battery be significantly lowered? These are important questions that the authors should have addressed.
Response: Thanks for the reviewer's positive comments and good question.
We agree with the reviewer that the electrolyte additives have been used in the metal plating industry and to inhibit the metal corrosion. Indeed, the related research works would provide useful principles for rationally designing new electrolytes to regulate the deposition of metals. The development of electrolyte as an important component of a battery is also crucial to achieve the high-performance (Nat. Energy 6, 763-763 (2021)).
We really appreciate the reviewer's deep insight with the specific focus on the energy storage process of polyaniline in the cathode. We agree with the reviewer that counterions (e.g., H + ) are involved in the energy storage process of polyaniline due to the electrostatic interaction along with the redox reactions (Angew. Chem. Int. Ed. 57, 16359-16363 (2018); Chem. Eng. J. 448, 137711 (2022)). The related discussion is added in Page 14 and Supplementary information (Pages 37-38).
According to the plausible energy storage process ( Supplementary Fig. 36), both H + ion and Zn 2+ ions from the bulk electrolyte are possibly involved into the polyaniline chains along with the redox reactions during the discharge process. During the charging process, the counterions, such as SO4 2-, PSanions are also adsorbed into the polyaniline chains to balance the charge. The adsorption of counterions on the random polyaniline chains is highly dependent on the electrostatic interaction. To examine the potential impact on cathodic reactions for Zn-ion batteries, the similar profiles of Raman spectra (Fig. R1) in 1 M Zn(PS)2+0.2 TBATS and 1 M ZnSO4 show the gradual changes of characteristic groups corresponding to the benzene ring and the quinone ring during the charge and discharge process. Upon the charging process, the new peaks for the evolution of PANI structure at 416, 525 and 580 cm -1 are assigned to the out-of-plane deformation of aromatic ring. The red-shift of peak at 1168 cm -1 (C-H bending vibrations of quinone ring) and the typical peaks of quinonoid structure at 1417 (C-C stretching vibrations of quinoid ring), 1492 (C=N stretching vibration), 1567 cm -1 (C=C stretching vibrations) suggest the oxidation of PANI with the extraction process of Zn 2+ and H + ions. Upon the discharging process, the absence of the quinonoid structure with the gradual presence of the benzenoid ring suggests the good reversibility (Fig. 5e, Supplementary Fig. 34 a,b and Table 7). The results revealed that the energy storage mechanism is not changed obviously in the different electrolytes.
The pH of ~4.1 for 1 M Zn(PS)2, 1 M Zn(PS)2+0.2 TBATS is comparable with that for 1 M ZnSO4 (~4.4). For the different electrolytes with similar hydrogen ion concentration, the possible H + intercalation is not changed during the energy storage process of polyaniline in cathode, although the introduction of large anion decreases the coordination number of water molecules that would dissociate into the hydrogen ion at the close interface of zinc. Especially, the enhanced battery performance with larger specific capacity (Fig. 5b) suggests that the presence of PSdoes not result in the lack of H + for capacity fade. In the presence case, both H + and Zn 2+ as counterions would be involved in the energy storage process along with the redox of polyaniline chains. Notably, the low binding energy of the Zn-PS bond (-420.7 kcal mol -1 ) in 1 M Zn(PS)2+0.2 TBATS suggests the easy desolvation into the free Zn 2+ ions for the energy storage process. The diffusion coefficient of Zn 2+ ions (DZn) are calculated to be 9.53×10 -9 and 4.69×10 -7 cm 2 s -1 in 1 M ZnSO4 and 1 M Zn(PS)2+0.2 TBATS, respectively ( Supplementary Fig. 30). The enhanced Zn 2+ ions migration ability would also contribute to the energy storage process of polyaniline with cation intercalation.
From the calculation results of Zn 2+ ion transference number ( , Supplementary  Fig. 28), the for 1 M Zn(PS)2+0.2 TBATS is 0.76, which is much higher than 0.25 in 1 M ZnSO4, indicating that more Zn 2+ ions can be migrated to supplement the consumption at the electrode-electrolyte interface. The XPS spectra were performed to examine the component changes during the PANI redox process. As shown in Supplementary Fig. 35a, C, N and Cl elements were detected in the initial PANI, suggesting the successful preparation of PANI. With the absence of Cldopants after the first discharge cycle ( Supplementary Fig. 35b), the peaks ( Supplementary Fig. 35c, d), corresponding to Zn and S elements respectively are observed, suggesting Zn 2+ , PSions are involved in the energy staroge process. H + /Zn 2+ as counterions, are adsorbed onto the reduced polyaniline chains to neutralize the charges on the polyaniline chains. Typically, the oxidized groups on the polyaniline chains, such as -NH + -and -NH + =, are stabilized by the PSanion via the electrostatic interaction. The N 1s can be fitted with four components, i.e., -N= (~398.6 eV), -NH-(~399.5 eV), -NH + -(~400.6 eV) and -NH + = (~402 eV). The -NH-component is corresponding to the reduced state and the others are in the oxided status. The amount of the oxidized and reduced components are almost equal in accord with the emeraldine state of the polymer at the initial state ( Supplementary Fig. 35e, f). Upon the discharge process, the reduced -NH-component increases to 70.5% with the H + /Zn 2+ adsorption. Upon the charge process, polyaniline is oxidized, H + /Zn 2+ is desorbed from the polyaniline chains with the desreasing of the reduced -NH-component (22.7%). Meanwhile, the oxidized components, -NH + -and -NH + = increase to 49.5 and 19.1%, respectively, accompanied by the adsorption of dopant PSto balance charge.
On the basis of the above discussion, the H + intercalation in cathode would not be changed in the present electrolytes with similar pH values. The intercalation of both ions including H + and Zn 2+ is coupled with the redox reactions of polyaniline. The calculated desolvation energy of Zn(H2O)5(PS) + and Zn(H2O)5(SO4) are -492.2 kcal mol -1 and -719.4 kcal mol -1 , respectively (Fig. 3d), which is favorable to the desolvation process of Zn 2+ ions. Notably, the additional zinc ions are available, which would be involved in the energy storage process of polyaniline with counterion intercalation, thus leading to the improved specific capacity ( Supplementary Fig. 36).
For the anode, the theoretical understanding and in-situ spectroscopy analysis revealed that the favorable coordination of hydrated zinc ions with the conjugated PSanions are able to minimize the activate water molecules, thus improving the zinc/electrolyte interface stability (Fig. R2). Therefore, the present electrolyte does not result in the lack of H + for capacity fade, but enhance the battery performance with the favorable regulation on the coordination of hydrated zinc ions.

To Reviewer#3 Reviewer #3: In this manuscript, the authors induced the rational modulation of the coordination micro-environment with zinc phenolsulfonate (Zn(PS)2) and tetrabutylammonium 4-toluenesulfonate (TBATS) as a new family of electrolytes. Such electrolytes endow the favorable coordination of zinc ions with conjugated phenolsulfonate anions that involved in hydrogen bond network to minimize the activate water molecules, thus leading to the enhanced redox kinetics and impressive cycling stability of zinc electrode. Owing to electrochemical data and theoretical calculations, the chemical interaction of zinc ions with phenolsulfonate anions and TBATS was analyzed to provide the in-depth understanding of an improved redox reversibility. Consequently, the zinc-based batteries with redox reactions of polyaniline cathodes demonstrated the impressive cycling stability for energy storage. With the highly promising applications of zinc electrode in various zinc-based batteries, the novel electrolytes to regulate the reversible redox reactions of zinc are very intriguing candidates for next-generation energy storage. Therefore, the reviewer would recommend it to be published after suitable revisions. The comments and suggestions about this work are as follows:
We really appreciate the reviewer's positive comments.

Comments 1. As for the corrosion test, oxygen dissolved into the aqueous electrolyte would change the corrosion behaviors. Is oxygen removed from the aqueous electrolyte?
The related information should be provided.

Response:
Thanks for your good question. In order to eliminate the influence of dissolved oxygen in the electrolyte, nitrogen is bubbled continuously into the electrolyte for 30 min before the corrosion test. Then, zinc foil was put into the electrolyte and sealed in the glass vial for one week. Supplementary Fig. 12 Optical image of glass vial for the corrosion test.

Comments 2. In the molecule dynamic simulation part, both Zn(PS)2 and water molecules are involved in the system. Although trace amount of TBATS was added in
14 the present electrolyte, please explain why TBATS additive is not involved in the theoretical calculation.
Response: Thanks for your good question. The solvation structure of Zn 2+ ions was simulated theoretically to obtain the bond information with large cations in electrolyte on the basis of the present computing ability available. Such information is helpful to understand the coordination of Zn 2+ ions with water molecules. In this work, the optimum electrolyte composition is 1 M Zn(PS)2 with 0.2 mg mL -1 TBATS. The calculated molar ratio of zinc salt over additive is about 2068: 1. Therefore, the theoretical calculation with the trace additives involved was established in order to optimize the calculation model and calculation resources.

Comments 3. The mass loading of polyaniline in the pouch cells including the volume of electrolyte should be given in the work to understand the present electrochemical performance. Especially, the conductivity of such molecular electrolyte with coordination networks is generally not good, how to achieve the redox process with conjugated anions?
Response: Thanks. The related information is added in the revised manuscript (Page 17).
"The pouch cell was assembled with PANI cathode, glass fiber separator and Zn foil anode. The PANI cathode was prepared by pressing the mixture of PANI, acetylene black and polytetrafluoroethylene (PTFE) at a weight ratio of 7:2:1 on Ti foil. The mass loading of PANI was about 70 mg and the electrolyte was 700 μL (10 μL mg -1 )." The ion conductivity of 1 M Zn(PS)2 calculated is 38.97 mS cm -1 which is close to the reported value of 1 M ZnSO4 (43.7 mS cm -1 , Angew. Chem. Int. Ed. 60, 18247-18255 (2021)). When 0.2 mg mL -1 TBATS is added, the conductivity further increases to 41.94 mS cm -1 . The results exhibit that the ion conductivity of the new electrolyte is even better than that of 1 M ZnSO4. Especially, the calculated desolvation energy of Zn(H2O)5(PS) + is -492.2 kcal mol -1 (Fig. 3d), which is lower than that of Zn(H2O)5(SO4) (-719.4 kcal mol -1 ). The easily available of zinc ions with good transfer ability would contribute to the charge storage process, as demonstrated in Supplementary Fig. 36.   Figure 3d, the desolvation energy calculated for Zn(H2O)6 2+ is lower than those of Zn(H2O)5(SO4) and Zn(H2O)5(PS) + . Accordingly, would the electrochemical performance of zinc electrodes be enhanced in the dilute solution?

Comments 5. In
Response: Thanks for your good question. According to the desolvation energy, Zn(H2O)6 2+ would be more favorable for the ion transfer in the dilute solution. However, more active water molecules would be released in the Zn 2+ ion desolvation process, resulting in the corrosion of zinc electrode along with the hydrogen evolution reaction. Therefore, additional electrolyte is added to regulate the solvation structure for improving the cycling stability. In the present case, the dilute solution 0.2 M Zn(PS)2 exhibits the lower ions conductivity of 17.15 mS cm -1 (vs. 38.97 mS cm -1 for 1 M Zn(PS)2), which is not able to meet the ion consumption in the redox reaction process, resulting in the concentration polarization in the dilute solution ( Supplementary Fig. 2). Therefore, the electrochemical performance of zinc electrodes is not enhanced in the dilute solution. Supplementary Fig. 2 a) Voltage-time curves of Zn-Zn symmetric cells in Zn(PS)2 electrolytes with various concentrations at 1 mA cm -2 , 1 mAh cm -2 and b) the enlarged detail. Fig. 25 Response: Thanks for your good question. The ion transference number is the ratio of the charge transferred by the given ion to the total charge (J. Electrochem. Soc. 162, A2720-A2722 (2015)). With the addition of TBATS, the ionized ions are increased in the solution due to the presence of TBA + and TS -, which are involved in the charge transfer process. Hence, the ion transference number of Zn 2+ ion slightly decreases to 0.76. Ionic conductivity refers to the conduction phenomenon caused by ion migration in the electric field. The ionic conductivity of strong electrolyte solution increases with increasing concentration (the number of conductive particles) (J. Phys. Chem. B 105, 4603-4610 (2001)). The number of ions that could migrate in the electric field increases because of the ionization of TBATS. Hence, the ionic conductivity of 1 M Zn(PS)2 electrolyte increases to 41.9 mS cm -1 from 39.0 mS cm -1 in the presence of TBATS.

Comments 6. The Zn 2+ ion transference number calculated (Supplementary
For the Zn(PS)2 electrolyte, the Zn 2+ ion transference number is related to the diffusion of Zn 2+ ion and its counterion according to the following equation: 2 2 where is the Zn 2+ transference number, is the Zn 2+ ions conductivity, and is the PSions conductivity. The transference number can be considered as simply the fraction of the total ionic conductivity that is carried by Zn 2+ .

REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): The paper has been well revised and improved. Now it can be accepted as it is.
Reviewer #2 (Remarks to the Author): The responses from the authors to this reviewer's early comments are not satisfactory. Therefore, it prompted this reviewer to read the paper for the second time. The authors' responses provided new XPS data showing the oxidation state of H+ of PANI during discharge (reduction) and charge (oxidation), suggesting PANI is redox reversible. But it doesn't support that there is co-insertion of H+ from the electrolyte, which could be a reason why PANI is a low capacity cathode. The authors could cite literature data or perform additional tests with polar aprotic solvents to prove the lack of H+ insertion in PANI. The second read through also finds more issues.
• The experimental section lacks details. For example, the authors presented the data of surface zeta-potential and differential capacitance in Fig. 4, but there is virtually no description on how these data were collected. • The overpotential of 22.6 mV of Zn/Zn symmetrical cell at 1 mA/cm2 should not be considered low as the authors claimed. The author can easily compare literature data with their own data.
• The dissolution issue of PANI in aqueous solutions needs to be discussed. • It is unclear why the authors selected PANI as the cathode since this is a low-capacity cathode. Have the authors tried high-capacity layered oxides such as V-oxides based materials? • Fig. S5, y-axis, should the unit be mV? • There are many other typos that should be double checked and corrected.
Reviewer #3 (Remarks to the Author): The authors have addressed all comments very well, the paper is ready to be accepted.
We appreciate the reviewers for their helpful and insightful comments, which have greatly helped us to improve the quality of our work. The manuscript has been carefully revised accordingly and the detailed responses and quotations from the revised manuscript are listed below. All the revised parts are highlighted in blue in the manuscript.

To Reviewer#1
Reviewer #1 (Remarks to the Author): The paper has been well revised and improved. Now it can be accepted as it is.
We really appreciate the reviewer's support and recommendation of our work for publication in Nature Communications.

To Reviewer#2
Reviewer #2: (Remarks to the Author): The responses from the authors to this reviewer's early comments are not satisfactory. Therefore, it prompted this reviewer to read the paper for the second time. The authors' responses provided new XPS data showing the oxidation state of H + of PANI during discharge (reduction) and charge (oxidation), suggesting PANI is redox reversible. But it doesn't support that there is co-insertion of H + from the electrolyte, which could be a reason why PANI is a low capacity cathode. The authors could cite literature data or perform additional tests with polar aprotic solvents to prove the lack of H + insertion in PANI.

Response:
We would like to thank the reviewer for his/her reading and insightful feedback. Following the valuable comments, we have revised our manuscript carefully and made substantial revisions as per the comments.
Following your valuable comments, the Zn(PS)2 salt and TBATS additive were dissolved in an aprotic solvent, N, N-dimethylformamide (DMF) to eliminate the H + insertion contribution. In the aprotic electrolyte, the CV curves exhibit a pair of redox peaks situated at 1.29 and 0.95 V, corresponding to the redox reactions of PANI ( Supplementary Fig. 36a). The low ionic conductivity results in the large potential polarization ( Supplementary Fig. 36b, c). In contrast, the smaller polarization in aqueous electrolyte would be contributed to the favorable redox process of PANI. The assembled PANI-Zn battery delivers the similar specific capacity at different current density ( Supplementary Fig. 36d). Specifically, the specific capacity is 185 mAh g -1 at the current density of 0.1 A g -1 which is comparable to that in aqueous electrolyte (194 mAh g -1 ) (Supplementary Fig. 36d).
We thanks the reviewer for proposing the valuable method to prove the possible H + insertion by using an aprotic solvent. Obviously, the H + insertion is not dominant to the energy storge process of PANI in the present case. It has been revealed that the counterions including H + but not limited to, are involved in the energy storage process suspensions." "Differential capacitance-potential curves were obtained by impedance methods 35 with assembled Ti-Zn asymmetric cells. The capacitance can be calculated from the equation: C=(2πfZim) -1 . where C is the capacitance, Zim is the imaginary component of the impedance, and f is the frequency of the ac perturbation." Comments 2. The overpotential of 22.6 mV of Zn/Zn symmetrical cell at 1 mA/cm 2 should not be considered low as the authors claimed. The author can easily compare literature data with their own data.
Response: Thanks for your good suggestion. A complete table is added for overpotential comparison. It can be seen that the low overpotential in the present case is comparable and even better than those results reported recently.

Comments 3. The dissolution issue of PANI in aqueous solutions needs to be discussed.
Response: Thanks. The related discussion is presented based on the collected data.
The color change of separator into brown is observed possibly due to the decomposition of PANI in ZnSO4 electrolyte. In comparison with the initial status of PANI ( Supplementary Fig. 38a), the nanoflakes corresponding to Zn4SO4(OH)6⸱H2O (JCPDS: 39-0690, Supplementary Fig. 39) are formed on the electrode in 1 M ZnSO4 electrolyte ( Supplementary Fig. 38b). The formation of these Zn4SO4(OH)6⸱H2O would induce the volume stress, and subsequently result in the structure changes as well as the dissolution of PANI during the cycling stablity test. In contrast, no by-product is formed for the electrode in Zn(PS)2 electrolyte, which would be contributed to the favorable