Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present a DFT investigation of lithium adsorption, charge transfer, 
and diffusion on pristine and defective graphene. The work is technically well 
executed and methodologically sound. The paper is clearly structured, logically 
written, and fits within the scope of Coatings. However, the contribution is 
largely incremental, as similar systems and mechanisms have been reported 
previously. The manuscript would benefit from stronger novelty, deeper physical 
interpretation, and clearer connection to practical applications.

In detail, 

(i) The authors need to make clear what news insight is gained in the present study 
compared to the previous publications [11,22].

(ii) The study focuses solely on atomic-scale properties (binding energy, charge transfer, 
diffusion barrier). It would greatly improve the impact to estimate how these 
translate into practical parameters such as Li diffusion coefficients, open-circuit 
potential, or theoretical specific capacity.

(iii) Also, Table 1 contains repetitive structural data and can be replaced with a simple
sentence. 

(iv) The conclusions are rather a summary and mostly restate the results. They would
profit from a few sentences highlighting broader implications for graphene defect design 
in next-generation LIB anodes.

Once these changes are implemented, the paper is probably fit for publication.

Author Response

      We would like to thank you very much for your comments and kind suggestions on our manuscript. We have made a revision to our manuscript based on the comments. And point-by-point responses to the comments have been summarized in the following part, and the corresponding revisions have been highlighted in red color in our paper for reviewers.

Reviewer #1

Comment 1: The authors need to make clear what news insight is gained in the present study compared to the previous publications [11,22].

Response 1: Thank you for your valuable comment. We fully agree that clarifying the novel insights relative to key prior studies [11, 22] is critical to highlighting the scientific contribution of our work. Below, we clarify our novel insights through direct comparisons with [11, 22]:

    For reference [11], Zhou et al. [11] pioneered the study of Li adsorption/diffusion on defective graphene but exclusively focused on divacancy (DV5-8-5) and Stone-Wales (SW55-77) defects, and did not investigate single vacancy (SV) graphene—a widely observed point defect in experimental graphene synthesis. While our study systematically characterizes the SV graphene’s Li storage behavior, which complement and extend the understanding from Zhou et al. [11].

    For reference [22], Datta et al. [22] focused on defect density effects (e.g., 6.25–25% DV density) and reported that higher DV density boosts Li storage capacity (up to 1675 mAh/g). However, they did not investigate the effect of different defect types (e.g., SV vs. DV5-8-5).

Comment 2: The study focuses solely on atomic-scale properties (binding energy, charge transfer, diffusion barrier). It would greatly improve the impact to estimate how these translate into practical parameters such as Li diffusion coefficients, open-circuit potential, or theoretical specific capacity.

Response 2: Thank you very much for your valuable suggestion, we fully agree that linking atomic-scale properties to practical parameters (e.g., Li diffusion coefficients, open-circuit potential, theoretical specific capacity) is of great significance for boosting the application-oriented value of our work. We sincerely appreciate your guidance on this point. While we must acknowledge a key limitation of the current study based on density functional theory (DFT) optimizations and nudged elastic band (NEB) calculations: These analyses are unable to directly derive macroscale practical parameters.

     To address this gap, we have planned follow-up research that will extend the current work: we will conduct ab initio molecular dynamics (AIMD) simulations on defective graphene-silicon composite electrode materials. AIMD method will enable us to capture dynamic Li diffusion behavior over finite time scales, providing the kinetic data needed to estimate diffusion coefficients.

Comment 3: Also, Table 1 contains repetitive structural data and can be replaced with a simple sentence.

Response 3: Thank you for your comment regarding Table 1. We have revised this section as suggested. Specifically, we have removed the original Table 1 and integrated its core information into the main text of Section 3.1. The specific revisions are as follows:

    To further analyze the structural changes of graphene layers before and after Li adsorption, we investigated the variations in C-C bond lengths in the graphene plane near the adsorbed Li ions. Before Li adsorption, the C-C bond lengths of the carbon hexagon ring in the p-Gr lattice beneath the Li₁ ion are approximately 1.413 Å, which is consistent with previous reports [7]. After Li adsorption, the bond lengths increase slightly to around 1.415 Å, with a maximum change of only 0.002 Å. This negligible variation indicates that Li adsorption has little effect on the lattice structure of p-Gr.

Comment 4: The conclusions are rather a summary and mostly restate the results. They would profit from a few sentences highlighting broader implications for graphene defect design in next-generation LIB anodes.

Response 4: Thank you for your valuable suggestion. We have revised the Conclusions section by incorporating a few sentences highlighting broader implications for graphene defect design in next-generation LIB anodes. The specific revised conclusions are as follows:

     In this work, we conducted a systematic first-principles investigation to explore the effects of SV and DV5-8-5 defects on the Li adsorption, charge transfer, and diffusion behaviors of graphene anodes for LIBs. The key conclusions are summarized as follows:

1. Pristine graphene (p-Gr) maintains a planar structure after Li adsorption, with Li ions preferentially anchoring at hollow sites. In contrast, SV Gr undergoes significant out-of-plane distortion and notable C-C bond changes due to Li adsorption. DV5-8-5 Gr retains planar geometry but exhibits the largest C-C bond length variation among the three systems. Binding energy results confirm that defects enhance Li adsorption stability, with DV5-8-5 Gr showing the strongest Li-graphene interaction, followed by SV Gr and p-Gr.
2. Bader charge analysis and Δρ plots reveal that defects promote charge transfer from Li ions to graphene. The charge transfer amount follows the order: DV5-8-5 Gr > SV Gr > p-Gr. This enhancement originates from defect-induced local electron density redistribution.
3. The NEB method demonstrates that defects significantly reduce Li diffusion barriers.

     Our results suggest that intentional introduction of point defects particularly DV5-8-5 defects, is recommended when utilizing graphene as an LIB anode material, which simultaneously achieve stronger Li binding and faster Li diffusion compared to SV defects or pristine graphene. 

Reviewer 2 Report

Comments and Suggestions for Authors

Notes attached

Comments for author File: Comments.pdf

Author Response

 Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a density functional theory investigation of lithium adsorption, charge transfer, and diffusion on pristine and defective graphene systems. The topic is scientifically relevant and aligns well with ongoing research on defect-engineered carbon materials for lithium-ion battery anodes. The study is generally well organized; however, the manuscript still exhibits several substantial weaknesses that must be addressed before it can be considered for publication.

1. A primary concern relates to the novelty of the work. Much of the reported behavior—such as the preference of Li for hollow sites on pristine graphene, the enhancement of adsorption strength due to vacancies, and the reduction of diffusion barriers near defects—has already been comprehensively described in well-established prior studies. The manuscript does not sufficiently differentiate its contribution from previous DFT works, such as those https://doi.org/10.1021/jp304861d, https://doi.org/10.1021/am3000962, and others. The authors should articulate clearly what new insights are gained from this particular set of calculations, how their methodology extends or improves upon earlier investigations, and why the community needs this new dataset. Without such clarification, the manuscript risks appearing confirmatory rather than original.
2. Regarding methodology, several important computational details are missing or insufficiently justified. The manuscript presents no convergence tests for the chosen k-point sampling, plane-wave cutoff energy, or vacuum size, all of which are critical to ensure numerical reliability. A 3×3×1 k-mesh may be coarse even for a 6×6 supercell, and the authors need to demonstrate that the selected parameters do not compromise accuracy. Additionally, the treatment of the isolated Li atom used in adsorption energy calculations is not explained; for instance, it is unclear whether spin polarization was applied. The absence of information on dipole correction along the nonperiodic direction is also problematic because such corrections are often required when modeling charged or polarized systems in slab geometries. These omissions reduce the reproducibility and credibility of the computational approach.
3. The interpretation of the Bader charge analysis results is also questionable. The authors argue that defects promote charge transfer from Li to graphene, yet the numerical values reported differ by only a small amount (approximately 0.893 e for pristine graphene versus 0.902–0.907 e for defective systems). Variations of this magnitude are extremely small in the context of Bader analysis and may fall within the sensitivity limits of the grid used. It is therefore inappropriate to use these values as the basis for strong mechanistic claims. The authors should consider either refining the charge analysis with higher grid resolution, complementing the analysis with additional charge-partitioning schemes, or tempering their interpretation to emphasize qualitative tendencies instead of asserting significant quantitative differences.
4. The presentation and clarity of the figures also require improvement. Figures depicting atomic configurations, charge density differences, and NEB pathways lack essential annotations such as isosurface values, scale bars, atom labels, and consistent color schemes. Several images appear low in resolution. For a computational materials study, high-quality graphical communication is essential, especially when structural distortions and charge redistributions form a key part of the argument. Including detailed and consistent figure captions and using vector graphics would significantly improve readability.
5. Another conceptual issue arises in the structural analysis. The authors state that the DV5-8-5 defect remains planar after lithium adsorption, yet double vacancy reconstructions in graphene typically produce slight out-of-plane distortions. This claim should be supported with numerical data describing atomic displacements perpendicular to the plane. Similarly, the large changes in specific C–C bond lengths reported after adsorption should be discussed with reference to actual lattice relaxation patterns rather than only presented as isolated values.
6. The diffusion analysis, although methodologically described, is incomplete. Only a single diffusion pathway is examined for each graphene type. Vacancy-containing graphene structures possess multiple non-equivalent pathways, and the energy landscape can vary substantially depending on the direction of migration relative to the defect reconstruction. To claim that defects universally reduce diffusion barriers, the authors should evaluate at least one additional pathway for both the single vacancy and the double vacancy models. Furthermore, saddle-point geometries should be illustrated directly for transparency.

In its current form, the manuscript requires substantial revision for scientific rigor, methodological completeness, clarity of presentation, and articulation of original contributions. I recommend a major revision.

Author Response

 Please see the attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have sufficiently revised their manuscript. It is now publishable.  

Author Response

We truly appreciate the time and effort you have invested in evaluating our work. Thank you again for your valuable guidance and support.  

Reviewer 3 Report

Comments and Suggestions for Authors

The revised manuscript reflects substantial effort, and several earlier concerns—particularly regarding methodological clarity and structural analysis—have been partially addressed. However, the revision still contains major scientific and methodological deficiencies that must be resolved before the manuscript can be considered for publication. My comments below focus exclusively on the most critical issues requiring your immediate attention.

1. The treatment of spin polarization remains a fundamental problem. Vacancy defects in graphene typically generate localized magnetic moments, and therefore, spin-polarized DFT is required for accurate total energies, adsorption energies, charge transfer, and diffusion barriers. In the response, you acknowledge that preliminary spin-polarized tests produce substantially different binding energies—approximately twice as large as the non-spin-polarized values—yet these corrected calculations were neither completed nor incorporated into the manuscript. This inconsistency undermines the reliability of all quantitative results reported. You must either (i) fully recompute all energies and analyses using spin-polarized DFT or (ii) provide a rigorous and physically defensible justification for using non-spin-polarized calculations. At present, neither requirement is fulfilled.

2. The diffusion analysis remains incomplete. Although you indicate that additional NEB pathways have been identified, their calculations are not yet finished. Because defect-containing graphene exhibits multiple non-equivalent migration directions, a single diffusion path per model is insufficient to support general claims about reduced diffusion barriers. The manuscript must include at least one additional, fully converged NEB path for both the single-vacancy and DV5-8-5 structures, with complete energy profiles and saddle-point geometries. A revision cannot be accepted while essential parts of the analysis are still pending.

3. The figures and visualizations require improvement to ensure scientific clarity. The charge density difference plots should include explicit isosurface values and a consistent color scale. The NEB figures should clearly label the initial, saddle, and final configurations, and the energy axes should be unambiguous. Although you note that figures have been revised, several remain insufficiently annotated or low in informational content.

4. Some of the structural interpretations would benefit from more precise quantitative support. Out-of-plane displacement data for DV5-8-5 graphene, for example, should be summarized clearly—either in a concise table or an expanded paragraph—so that the claim of near-planarity after Li adsorption is fully substantiated.

In summary, the manuscript still requires substantial revision, particularly in the treatment of spin polarization, completion of all NEB pathways, enhancement of figure clarity, and inclusion of quantitative structural metrics. Addressing these issues thoroughly will greatly strengthen the scientific foundation and reproducibility of the study.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf