NMC Charge Transfer Symmetry Breaks during Cycle Aging of Lithium-Ion Cells
Authors: Ji Yuefan , Schwartz Daniel T. 
Published: August 2024

Second harmonic nonlinear electrochemical impedance spectroscopy (2nd-NLIES) is a uniquely capable method for probing the symmetry of charge transfer in an electrochemical cell. [1,2] Kirk et al. are the first to try and quantify this symmetry-breaking using 2nd-NLEIS, but the single particle model (SPM) was not ideally matched to the thick porous electrodes under study. [3] Recently, we have introduced a systematic development of a porous electrodes model to describe the 2nd-NLEIS response along with the equivalent circuit presentation to bridge the gap between analytical solutions and well-accepted equivalent circuit models. [4] We have also demonstrated the performance of this model in analyzing 2nd-NLEIS data using the previously published experiments. [5] A data analysis pipeline and Python toolbox have been built to facilitate the simultaneous analysis of EIS and 2nd-NLEIS data. [5,6]
In this work, we take advantage of the previously published data analysis pipeline and use it to analyze a much larger dataset of EIS and 2nd-NLEIS that is composed of 48 commercial 1.5 Ah LiNMC ∣ C LIBs (INR 18650–15 M). These batteries are cycled under four different aging conditions (Current: 3A or 4 A; Temperature: 5 oC or 25 oC) for up to 1500 charge-discharge cycles. These data were obtained at 10%, 30%, and 50% state of charge (SoC) of the designed stopping cycles. Simultaneous parameter estimation of linear EIS and 2nd-NLEIS is used to extract physical parameters that quantify battery aging under different operating conditions. In addition to the well-known increase of charge transfer resistance, [7] the breaking of charge transfer symmetry over aging for the cathode is elaborated with these extensive cycling data, confirming the growth in charge transfer asymmetry upon extended aging. Our results also reveal that low temperature operations can accelerate battery degradation, resulting in a substantial increase in charge transfer asymmetry than the room-temperature operation. Consequently, the degree of charge transfer asymmetry emerges as a crucial battery diagnostics characteristic that has never been measured before.

References

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