Second-Life Batteries Modeling for Performance Tracking in a Mobile Charging Station

Round 1

Reviewer 1 Report

Before publication, the following issues must be addressed:

1. In Line 102, authors stated that the battery used in this study is 94 Ah battery "cell". However, 94 Ah capacity sounds very large for a battery "cell". Please double-check if it is a battery "cell" or a battery "module". Also, in experimental setup section, detailed battery cell parameters should be summarized in a table, such as battery size (length, width, and thickness), weight, cathode/anode material, nominal voltage, and maximum charging/minimum discharging voltage. 

2. The battery models are developed based on the battery cell from a BMW i3, but the simulation results are compared with the battery behaviors of the battery in the Golf-GTE PHEV. These two batteries have different material, different chemistry, different capacity, and more importantly, at different aging level. The model validation should be conducted using the experimental data from a same battery. 

3. Some information are missing in Figure 15. Red and blue lines are not presented. 

4. Authors stated this paper is the first paper which provides "Experimental assessment of the second life battery performance" in Section 1.1. However, this assessment is only some regular measurements of an aged battery, which has no novelty. Indeed, there are many available battery aging articles which provide detailed battery performance degradation process from when the battery was new to when the battery is at EOL (end-of-life).

5. Similarly, authors stated that "this is the first article to model a second life battery cell extracted from an electric vehicle". Actually, the battery aging models presented in most battery aging articles can be applied to a "second life battery cell extracted from an electric vehicle". 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The topic of characterization and modeling of high power battery cells for second life applications is highly relevant. I would like to congratulate the authors, as this work represents a very interesting pilot study of a possible new application for batteries beyond their first life: mobile charging stations. 

In order to improve the overall quality of the manuscript, I have a few observations:

1. In general, the document needs an english grammar revision.

2. Check if all the captions match their corresponding figure or table, as I found a few mismatches, for example: the caption for figure 15 doesn't correspond to the figure itself.

3. Some figures are difficult to read. When colors are used to  differentiate multiple curves, the selected colors are too dark, making it difficult to distinguish them (for example Figures 8 and 13), maybe adding markers would make reading those figures easier. Something similar could be argued about figure 11, where is quite difficult to differentiate between the results for both models.

4. Even if the application proposed in this work is new, it may be worth to add a paragraph in the introduction that works as a review of typical applications for second life batteries in order to add a bit of context to your work.

5. Even if there is not an universally accepted definition for SoH, for the resistance it may be worth to adopt adefinition that takes decreasing values with ageing, for example SoH_R = 100*(1 - (R(t)-R_BOL)/R_BOL), instead of the definition presented in eq A5.

6. One of the points the authors highlight in the conslusions is the usage of open software, namely DATTES and VEHLIB. It may be worth to expand the explanation of how these two applications were used during the characterization and modelling process.

7. At two points in the manuscript, last paragraph of section 2 and in the conclusions, the authors present the argument that the end of first life threshold (currently defined at 20 or 30 % capacity fade) should be reconsidered. I don't understand the reasoning behind this claim, as I believe that the characterization results from a single cell are not enough to back such conclusion. This battery cell could be an outlier, as highlighted by the authors when they hypothesized that the cell could came from a crashed vehicle. 

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors provided very detailed response to the review report. All the issues/questions have been addressed in the revised manuscript.