The Overlooked Role of Battery Cell Relaxation: How Reversible Effects Manipulate Accelerated Aging Characterization^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Interesting paper, however scientifically limited in my opinion due to the lack of statistically relevant data. As far as I understand, each testing profile was only applied to one cell, and each cell has an unknown history. How can you make conclusions about degradation modes and projections based on this limited information? 

Other comments: 

1. Line 119 -> 123: you mention simulations by the authors but these are not elaborated, referenced or shown. Please adapt
2. Your previous publication [34] is referenced quite a bit, but I cannot find it, so I find it difficult to understand the novelty of this work compared to your previous one. 
3. You make assumptions about the electrochemical behavior (l355 -> l357 for example) that you cannot prove. Can you find supporting literature (or perform post-mortem testing) for this? 
4. The limitation of your test data becomes very clear in your statement made on line 436, about the unexpected long lifetime of a specific test condition. 
5. The analysis of the effect of the DOD on relaxation time is unfortunately limited by your decision to perform CU's on test-cycle basis, not on Full-equivalent cycle basis, which would have make sure that you have a fair comparison. However you do acknowledge that.
6. You state that the increase of Ueodc increases in the first cycling sequence is due to the temperature influences: can you explain/prove?
7. Section 3.3.2 on C-rate influence: Degradation seems to be extremely fast, even for relatively mild conditions, do you agree? The 1C/0.37C condition does not last even 600 cycles, do you know why?
8.  Line 638 -> 640: that claim is unsupported  and I don't understand why you claim that the behavior is consistent with "all analysis techniques applied in this work". It does not make sense to me at all why a storage SOC of 6% would be better than one at 23%. I have a suspicion that this is caused by the lack of statistical variation due to limited cell numbers and an outlier in your dataset. 
9. The work contains multiple times the word "LIBLIB", should be fixed. 
10. General question: can you elaborate on how your work can be used to still accelerate degradation tests but reduce the effect of the reversible capacity loss becoming irreversible? Is it possible to have faster degradation testing while still being "realistic", and what would the impact be on the test design? 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study systematically examines the effects of operational protocols on  the formation and rehomogenization of cell inhomogeneities. They find the increasing cell inhomogenization lead to growing reversible capacity losses, particularly under conditions with shorter cycling interruptions. They point out the importance of considering cell relaxation in cycle aging studies to  ensure reliable and accurate lifetime predictions. The experimental design is scientifically reasonable and the data is comprehensive.  I suggest accepting the article. 

Some minor mistakes:

1. In Figure 6 "Progression of UEODC over cycles; the asterisk markers indicate  voltage relaxation due to unintended rest phases caused by a power outage (b) "  There is no asterisk markers in Figure 6b.
2. Line 737, " In this study, we assessed the aging characteristics of LIBLIBs, "

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

See attached

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper focuses on the role of battery relaxation in the accelerated aging process of lithium-ion batteries, and systematically discusses the effects of test procedures, stress factors (DOD, C-rate) and recovery methods on the non-uniformity and life of batteries. The research design is reasonable and the data are detailed. The conclusion is of great value to optimize the battery aging test method and improve the reliability of life prediction. However, some conclusions are not supported enough, and the experimental repeatability and theoretical interpretation need to be further improved.

Specific Response Suggestions to Reviewer Comments

1. Conduct replicate experiments (e.g., 3 cells per test case) for critical conditions (e.g., Substudy 1’s "orange curve" anomaly) to confirm robustness.
2. Although the constant temperature of 25°C is mentioned, it is not stated whether internal temperature fluctuations (such as the effect of spontaneous heat on relaxation) are monitored. It is recommended to supplement the temperature data or analyze it for potential interference with the results. Discuss how self-heating impacts inhomogeneity.
3. Incorporate a discussion on silicon-graphite volume changes at low DOD (<40%) vs. high DOD (>40%) to explain the lack of inhomogeneity below the threshold.
4. Add a schematic (supplementary material) illustrating the EMSI effect’s dependence on DOD-driven electrolyte motion.
5. Perform post-mortem SEM/EDS on electrodes from static vs. dynamic recovery cases to validate lithium redistribution (e.g., silicon-graphite lithiation homogeneity).
6. Figure 8 shows no significant change in volume difference at DOD<40%, but does not explain the mechanism in depth (such as critical effects of electrolyte movement or electrode volume change). It is recommended to supplement theoretical analysis with microscopic models (e.g. SEI growth, lithium deposition).
7. Lithium coating detection: The 2C/2C test case in Figure 10(d) does not show lithium stripping characteristics, but it is presumed that a coating is still present. It is recommended that non-destructive tests (such as neutron diffraction or acoustic sensing) be supplemented to verify the hypothesis.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf