pseudo 1D lithium cell model

Hi,
I'm a student self-learning Comsol for my project and I'm trying to model a 1d lithium cell using the general form PDE as an exercise.

1D lithium cell modeling as mainly 2 part : transport of lithium across the cell there is then insertion inside the active material and we have to model transport inside the particle. Separately the model for each part is pretty simple, but I have difficulty combining the 2 parts together.

I already have geometry 1 as the length of the electrode as a simple interval line. So at every point in the electrode there is insertion of lithium inside a particle with varying flux depending on the position in the electrode. Once inside the particle it's a simple diffusion model with the source as the flux determined in the electrode.

I have successfully implemented transport equations and potential for liquid and solid phase, so I know the flux of lithium at any position of the electrode. So i was wondering how do I model the insertion or to couple both physic together. When i try to make another model with another geometry for the spherical particle, I can't call the flux from my cell model it says it doesn't recognize that variable

Is it the right way or should I draw the particle on the same geometry sheet as my cell or use the model coupling function ?

thank you