Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript conducts a systematic investigation of the electrothermal behavior of different cylindrical lithium-ion cells under various discharge cutoff voltages and C-rates, and proposes the Thermal Efficiency Ratio as a metric to optimize cutoff-voltage strategies. The topic has strong engineering relevance, the experimental design is generally systematic, and the conclusions offer useful insights, but there are several issues needed to be clarified.

1) In the Materials and Methods section, the authors provide detailed descriptions of the temperature sensor model, attachment method, and the infrared thermal camera. However, the manuscript does not include any figures of the experimental setup, sensor layout, or test platform. Since temperature rise and TER are the core metrics of this study, the temperature-measurement locations and installation method can significantly affect the results and their interpretation. Therefore, it is recommended that the authors include at least one figure illustrating the experimental setup or sensor arrangement to enhance the reproducibility of the experiments.

2) In Equation (3) of Section 2.1, the symbol  is used in the formula, while the text refers to . Both clearly denote the same physical quantity, so this appears to be a typographical inconsistency. I recommend the authors unify the notation throughout the manuscript to avoid confusion and to maintain clarity in the mathematical expressions.

3) In the latter part of Section 2.1, the authors introduce the Peukert exponent and then provide an extensive theoretical discussion with numerous literature citations. This type of literature review is more appropriate for the Introduction, where it can help explain the limitations of classical models and establish the theoretical background of the study. The Methods section should focus on the computational procedures and formula definitions used in this work. Therefore, I recommend moving this discussion to the Introduction to avoid structural confusion and to improve the manuscript’s logical clarity.

4) In Fig. 1, the normalized capacity at 0.5C exceeds 100%, which may be due to the actual capacity being higher than the rated capacity. However, the manuscript should explicitly clarify the normalization method and explain why values greater than 100% may occur.

5) When describing Fig. 2, the authors state that “a pronounced breakpoint appears around 3.0–3.2 V.” However, the curves in this region are smooth and continuous, showing only a sudden increase in slope rather than a true “breakpoint” in the mathematical or physical sense. I recommend using more accurate terminology such as “slope change,” “knee point,” or “capacity drop-off region.”

Author Response

All responses to the reviewers’ comments are included in the attached Word file that we have uploaded.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The article analyses the influence of the lower discharge cutoff voltage on the thermal behaviour and usable energy of different cylindrical Li-ion cells in 18650 (Samsung ICR18650-26J) and 21700 (EVE40PL) formats. The authors perform a series of discharge tests at several C-rates (0.5C, 1C, 1.5C, 2C), measuring both the output energy and the increase in cell surface temperature under controlled laboratory conditions.

Based on an integrated analysis of energy and temperature rise, the authors introduce the Thermal Efficiency Ratio (TER), defined as the ratio of the usable discharge energy to the temperature increase, including a small stabilising constant in the denominator. TER is used to identify optimal cutoff-voltage ranges in which the extracted energy is maximised while the thermal load remains acceptable. In this way, the authors propose a strategy of adaptive cutoff-voltage control that depends on the load and the cell type, and they present TER as a practical tool for implementation in battery management systems (BMS).

The topic is clearly timely, as it relates to the safety and efficiency of battery operation in electric vehicles and energy storage systems – areas of high practical relevance. Introducing TER as a simple yet physically intuitive metric of “how much energy is obtained per degree of temperature rise” appears to be a useful and original tool for comparing operating configurations and cell types. Combining the analysis of cutoff voltage with nonlinear thermal behaviour and the Peukert effect in Li-ion cells represents a valuable extension of previous studies, especially in the context of practical BMS algorithms.

The article is well written and linguistically sound. The description of the experimental setup is complete: the cell formats, nominal capacities, environmental conditions (25 ± 2 °C), and the measurement equipment used are all specified. The use of several discharge current levels (0.5C–2C) is well justified. The energy data are correctly defined as the time integral of the product U·I and then normalised to the nominal energy, which enables meaningful comparisons between cell formats.

I recommend the article for publication after addressing one minor comment:
the authors mention five cells of each type from the same production batch tested in parallel. It would be beneficial to clarify whether the reported values and curves correspond to averages over this population and whether standard deviations/uncertainties were calculated, as the manuscript does not clearly describe the data scatter.

Author Response

All responses to the reviewers’ comments are included in the attached Word file that we have uploaded.

Author Response File: Author Response.docx