**5. Conclusions**

In this work, we studied the aging behavior of a Li-ion cell and investigated the ionic conductivity variation of the cell and its relation to the appearance of unwanted lithium deposition on the surface of negative electrode particles from the 116th cycle. We introduced five regions that explained the transport mechanisms of lithium from one electrode to the other, including the Li<sup>+</sup> charge transfer, Li solid diffusion, and Li<sup>+</sup> diffusion through the electrolyte. Simulation data and ionic conductivity calculations showed that both interface and electrolyte conductivity of the anode (*<sup>σ</sup>i*,*<sup>a</sup>* and *<sup>σ</sup>l*,*<sup>a</sup>*) at cycle 116 were four times smaller than the not-aged values. Moreover solid particle conductivity of the anode *<sup>σ</sup>s*,*<sup>a</sup>* showed that the poor distribution of Li in the anode particles along the *x* direction led to local overcharging on the separator side. These effects together caused the cell to plate lithium from the 116th cycle.

**Author Contributions:** Conceptualization, S.M.B. and K.P.B.; methodology, S.M.B. and K.P.B.; software, S.M.B.; formal analysis, S.M.B.; writing–original draft, S.M.B. and K.P.B. ; writing–review and editing, S.M.B.; visualization, S.M.B.; supervision, K.P.B.; funding acquisition, K.P.B.

**Funding:** This research was funded by Robert Bosch GmbH

**Acknowledgments:** The authors thank Robert Bosch GmbH for their financial support through the Bosch Promotionskolleg. The author would also like to thank D. Müller for their constructive criticism of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
