Decouple charge transfer reactions in the Li-ion battery

In the development of Li-ion batteries (LIBs) with high energy/power density, long cycle-life, fast charging, and high safety, an insight into charge transfer reactions is required. Although electrochemical impedance spectroscopy (EIS) is regarded as a powerful diagnosis tool, it is not a direct but an indirect measurement. With respect to this, some critical questions need to be answered: (i) why EIS can reflect the kinetics of charge transfer reactions; (ii) what the inherent logical relationship between impedance models under different physical scenes is; (iii) how charge transfer reactions compete with each other at multiple scales. This work aims at answering these questions via developing a theory framework so as to mitigate the blindness and uncertainty in unveiling charge transfer reactions in LIBs. To systematically answer the above questions, this article is organized into a three-in-one (review, tutorial, and research) type and the following contributions are made: (i) a brief review is given for impedance model development of the LIBs over the past half century; (ii) an open source code toolbox is developed based on the unified impedance model; (iii) the competive mechanisms of charge transfer reactions are unveiled based on the developed EIS-Toolbox@LIB. This work not only clarifies theoretical fundamentals, but also provides an easy-to-use open source code for EIS-Toolbox@LIB to optimize fast charge/discharge, mitigate cycle aging, and improve energy/power density.