Discussion Forum

Hi,

I am currently working on an End-of-Life (EOL) battery model and trying to model transition metal dissolution from the electrodes as one of the degradation mechanisms. The reaction association with this mechanism is given in the attached "Mn_Dissolution.png" discussed in the paper (Lee, Yoonkoo et al. “A Comprehensive Experimental and Modeling Study on Dissolution in Li-Ion Batteries.” Journal of The Electrochemical Society (2019): n. pag.).

The rate of Mn dissolution is modeled with the help of above reaction as,

where is the rate constant and is the concentration of hydrogen ions obtained by solving the species balance given in the atttached "Species_Balance.png".

As seen in the "Mn_Dissolution.png", Li+ ions are generated during this reaction which needs to be coupled back to the Li+ species balance which is solved internally in the Lithium-Ion Battery Interface. So, to do this, I used the Non-Faradaic Reactions Node under Porous Electrode Node where we can add this source as , which is coupled back to the Li+ species balance as given in the COMSOL equations "COMSOL_Eqs.png" of the Porous Electrode Node.

Some concerns arose while implementing the above mechanism:

1. Given that the term in "COMSOL_Eqs.png" is with a '+' sign, signifying that, a positive value (R_Mndiss * a_pos * 2/y_Mn * t_factor) entered in the tab in "NonFaradaic_Rxn.png" should result in the increasing concentration of Li+, however a decreasing trend was observed. In another run, a negative value (-R_Mndiss * a_pos * 2/y_Mn * t_factor) was entered which gave an increasing trend for Li+ concentration. What could be the possible reason behind this behaviour?
2. Secondly, what is the role of "Reaction rate (mol/(m^3s))" value under the "Reaction rate for dissolving-depositing species" (See "NonFaradaic_Rxn.png"). Should it be kept zero or equal to the magnitude of term. One of the COMSOL examples employing the Non-Faradaic Reactions node Adsorption-Desorption Voltammetry used the "Reaction rate (mol/(m^2s))" value as equal to entered for the source term (See "NonFaradaic_Rxn2.png"). Please clarify regarding the term's magnitude as well as sign.