So how might we model degradation?

It turns out that none of the cell degradation mechanisms that you've already

learned about in the fourth course of this specialization are tied directly to cell

terminal voltage.

But instead they're tied directly to internal stress factors to stress

factors that are happening somewhere inside of the battery cell itself.

So, for example, if we have knowledge of local concentrations of

lithium in the electrolyte at some spacial locations internal to the cell.

If we know the concentrations of lithium on the electrode surfaces at different

places in the battery cell,

then it turns out we can predict imminent collapse of power.

And so we can guide the user away from that, guide the load away from that by

restricting power, so that the power isn't constant for a while and then just gone.

So we can do that if we know those concentrations.

Or, if we have knowledge of local potentials

internal to the electoral electrolyte region inside the battery cell.

That helps us to predict the onset of side reactions like SEI growth, cell

electrolyte interphase growth or lithium plating which if also seen introduced

briefly in the fourth course, and we're going to talk more about it this week.

And if we have knowledge of the mechanical stresses at different points of the cell,

we can predict electrode-particle or composite-electrode fractures So

none of this knowledge is available from equivalent series models,

equivalent circuit models.

None of this is available from the kind of model that we studied in

the second course.

If we're going to develop aging models, it turns out we need to develop physics-based

models of looking at my own battery cells.

They can predict these concentrations inside the cell, it can predict

the stresses and strains, it can predict the potentials and so forth.

If we can do that in some kind of a computationally and mathematically

reasonable way, then we might be able to predict aging directly and

then device controls to control aging.