Designing Strain-Less Electrode Materials: Computational Analysis of Volume Variations in Li-Ion and Na-Ion Batteries

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study analyzes electrochemically-induced volume variations in battery materials, attributing these variations to ionic, electronic, and structural factors. Key findings indicate that ionic changes significantly depend on the alkali type used, while electronic contributions, crucial in isotropic materials like spinels, are less predictive. Structural responses, influenced by material elasticity, dictate the reversibility and efficiency of the intercalation process. The research recommends enhancing battery performance by selecting harder materials to reduce volume variations, though this may limit capacity. Techniques like isotropic hardness tuning, designing compact electrodes, and doping with small ions are proposed to exploit the material's elastic properties, thereby improving durability and reducing volume changes during use.
The paper contains original information that could impact the research community; however, it requires some minor revisions before publication. My comments are as follows:

 1. Page 3 - “We first focus on the volume of intercalated (deintercalated) compounds in Fig. 1 (Fig. 2), respectively, for the considered materials, using different functionals to evaluate our theoretical setup.” This sentence could be clarified for better readability as: "We initially focus on the volume of intercalated compounds shown in Fig. 1 and deintercalated compounds in Fig. 2, for the materials considered, using various functionals to evaluate our theoretical setup."

2. Page 3 - When compared with experimental data (see Supplementary Information 1), a fair agreement is obtained for all functionals, with the PBE+U+D3 functional yielding the best mean errors and deviations. 'See supplementary' should be in parentheses.

3. Page 3 "For the considered values of ionic radii, see Supplementary Information 2. Importantly, as shown in Supplementary Information 3," it should be clarified whether these refer to Figures 2 and 3 in the supplementary information. Please make necessary changes for clarity when referencing supplementary materials.

4. Page 6 - Define all parameters and provide units in Equation 1.

5. Page 7 - "From the different possible contributions, one might expect a contribution, ∂V Ionic/∂nA, from the additional removal of an alkali ion, proportional to its ionic volume in its environment (Oh versus Td). "Please clarify this sentence and define 'Oh' and 'Td'.

6. Page 9 –“Interestingly, a mean difference between trend lines for sodiated and lithiated compounds ∆V Ionic Na→Li = ∂V Ionic/∂nNa − ∂V Ionic/∂nLi ≈ 3.5 ų is found to correspond approximately to the difference between the computed ionic volume and the tabulated ionic radii.”
This sentence is somewhat convoluted and difficult to follow due to the dense use of technical terms and mathematical notations. Please revise to clarify the expression and ensure that the description flows more logically.

7. In conclusion - The author refers to a term called 'quasi-nil effect' which has not been mentioned or discussed in the main text before. Please clarify this further.

8. By decomposing the electrochemically-induced volume variations ∂V/∂nA between ionic contributions. Aren't the electrochemically induced volume variations and ∂V/∂nA the same thing? Please clarify.

Comments on the Quality of English Language

The paper is difficult to read and follow due to its writing style. This is mainly due to missing punctuations and poorly structured sentences.

Author Response

point-by-point response in the attached letter

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors analyzed the volume changes of two electrode materials with different structures during the cycle by theoretical calculation. A large number of calculation results support the proposed conclusions. This study is of great significance to the development of electrode materials. Some minor revision suggestions are as follows.

1. Explain the trends and unusual data in the graph. When discussing volume change, explain in detail the specific effects of different transition metals on volume change and why.

2. It is recommended to verify the calculation results through specific experimental methods, such as using XRD or TEM to observe the microstructural changes of electrode materials.

3. The authors should mention the accuracy limitations of the computational methods used, such as the possible margin of error in predicting material properties.

4. Please provide a detailed description of how the volume change is decomposed into electronic, ionic, and structural contributions, including specific steps and methods for calculating these contributions.

5. It is recommended that the authors discuss in detail the specific principles for designing stress-free electrode materials, such as the specific properties that need to be considered when selecting materials, such as elastic modulus, volume change trend, etc.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

 Point-by-point response in the attached letter.

Author Response File: Author Response.pdf