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Thds Electrostatics coupled convergance problem

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Hi everyone!

I try to simulate a 3D microstructure of a lithium ion battery (just of the anode). I simulate the electrolyte with ionic transport of 2 ion species c_el, c_elA with c_el as positive and c_elA as negative ions. I do that with transport of diluted species with migration in electric field. The source of the electric field is the voltage V_ES which is from an Electrostatics, defined also in the electrolyte region. In this electrostatics I define a space charge density with the value: (c_el-c_elA)*F (F=Faraday constant). That should create my V_ES.
I also define initial values for the 2 concentrations c_el0 = c_elA0 = 1000 mol/m^3 and for the voltage V_ES = 0V
At the open (not to the electrode bordering) side, I define a constant concentration of the positive ions c_el = c_el0 to simulate the constant inflow of that one species of ions (the Li-Ions), and a constant electric potential 0V.

For the connection to the electrode I define a current density j_ct (charge transfer) after the Butler-Volmer equation, with which the charged ions leave the electrolyte and with which uncharged particles enter the electrode material. Therfore I simulate the Electrode material with a transport of diluted species (only one sort of particles now and without migration in an electric field, so uncharged) and an electric current, which leaves the electrode on the other side with a current density of j_L. So j_L should control the running of the battery.
I start the j_L with a step function from 0.1s to 1s.

The problem now is, that the progam starts but the convergence goes up to a scale of 1E8, when the current j_L starts to rise. And it has something to do with the coupling of the transport of diluted species and the electrostatics in the electrolyte. If I deactivate the electrical migration or the space charge density, the program goes through.

Hope somebody can help me

Cheers,
Chris!

By the way I use 4.2a.

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