Effect of Short-Chain Polymer Binders on the Mechanical and Electrochemical Performance of Silicon Anodes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Recommendation: Minor Revision In this study, the authors modified the chemical structure of PVDF by grafting carboxyl end groups and shortening its molecular chains. In addition, various binders with different molecular chain lengths were blended to investigate their functional roles in silicon-anode batteries. These two strategies were demonstrated to effectively mitigate the severe volume changes of silicon anodes during the charge-discharge process. However, several specific concerns should be addressed: 1. The chemical structure of PVDF presented in Table 1 should be carefully checked and revised. 2. The data lines in the figures should be replaced with data points to enhance reader comprehension. 3. Figures 7 and 9 show that the PVDF-PAA binder exhibits significantly lower peel strength and capacity than the conventional LiOH-PAA binder. Furthermore, chemical modification of PVDF-PAA is likely to increase the production cost. A reasonable explanation should be provided to justify the proposed use of the PVDF-PAA binder in this work.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The work is devoted to increasing the mechanical strength and electrochemical stability of silicon anodes of lithium-ion batteries by optimizing polymer binders. Silicon has a theoretical capacity almost tenfold compared to graphite, but its use is complicated by significant volumetric expansion, causing destruction of the electrode structure. Three approaches are studied: chemical modification of PVDF with shortening of chains and introduction of carboxyl groups, selection of low-molecular and alternative binders, and the design of multilayer anodes with an adhesive layer. It is shown that excessive shortening of chains worsens adhesion to the current collector, reducing the service life of the cell, while a combination of short- and long-chain PAA with the correct architecture increases the capacity and strength. The greatest effect is achieved with the use of a PVDF adhesive layer, which prevents mixing of layers and ensures stability during cycling. The results demonstrate the importance of combining binder flexibility and strong adhesion to create durable next-generation silicon anodes.
However, a number of improvements and clarifications should be made in the article:
1. The introduction clearly identifies the problem of silicon volume expansion up to 275% and indicates that this leads to electrode destruction. However, the authors did not sufficiently support this information with quantitative comparative data on various strategies for solving it in existing studies. This could strengthen the rationale for the relevance of the work. For example, it would be useful to provide statistics on the service life of elements with silicon anodes using standard PAA or PVDF binders to clearly show the scale of the problem and the place of the proposed solution.
2. In the Materials and Methods section (lines 157–164), the electrode composition is fixed at 60% silicon, 30% binder, and 10% carbon black. This is a relatively high binder percentage compared to industrial standards (usually 5–15%), which can significantly affect the specific capacity and mechanical properties. The authors should have justified why this composition was chosen and compared it with more “production” proportions.
3. The cell assembly methodology is described in sufficient detail, but the formation and testing modes (lines 170–174) could have been expanded with an additional explanation of why this particular order of C-rate changes was chosen. This is important, since testing in a certain sequence can affect electrode degradation and mask the weaknesses of individual samples.
4. In mechanical tests (lines 364–370), the authors record that PVDF modification reduces the adhesion strength. However, they do not evaluate elasticity or elastic modulus, which could have more fully characterized the trade-off between flexibility and strength. Without this data, it is difficult to conclude which parameter is most critical for the durability of the anodes. 5. The nanoindentation results section (lines 374–389) shows that the shortened chain samples have increased indentation depth. However, the authors should have further assessed the distribution of residual strain over the surface and possible localized brittleness zones, as structural inhomogeneity may have a significant impact on cycling degradation.
6. The correlation between peel force and capacity (lines 421–425) confirms the importance of adhesion, but is only based on six data points. A more reliable conclusion would require a larger sample or at least a statistical analysis (R², p-value) to quantitatively confirm the strength of the relationship.
7. The results for multilayer anodes (lines 480–486) show that the use of PVDF in the adhesion layer improves performance. However, there are no long-term cycling data (100+ cycles) to confirm the stability of this effect. It is possible that the benefits only manifest themselves in the early stages of cell operation. 8. In the conclusion section (lines 520–533), the authors state that excessive shortening of chains leads to fragmentation and reduced adhesion. This conclusion is consistent with the experimental data on strength and capacity, but is somewhat generalized - it is not stated what are the acceptable limits of chain length to maintain a balance of properties.
9. In mechanical tests of adhesive layers (lines 505–517), the authors demonstrate a sharp drop in strength when using the same solvent in both layers. This is a valuable result, but it would be worthwhile to further test intermediate cases, for example, with partial compatibility of solvents, in order to more accurately determine the threshold of adhesion failure.

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The cars checked my locking. Before this part, you should start planning your own work. In the middle of the statue it was worth paying attention to. The authors should prepare the status according to the MDPI standard.