Loss of active material (LAM) is one of the physical causes of Cell degradation.
Main mechanisms of anode active material loss are particle cracking and loss of contact, between particles or to the current collector. Anode is cracking due to change in volume due to Lithium intercalation (10% volume change for graphite). Anode cracking leads to solvent cointercalation into the graphite (alongside lithium), gas evolution, and graphite exfoliation.
Main mechanisms of cathode active material loss are structural disordering and metal dissolution. On overcharge, LCO or NMC layers can collapse, eliminating a lot of slots for Lithium intercalation at once.
Thus, usually, lithiated anode and delithiated cathode materials are lost. The effects of such losses on the Cell open-circuit voltage curve are illustrated in [1]:
The effect of the loss of lithiated anode is very similar to the effect of the simple Loss of lithium inventory: OCV decreases more abruptly towards 0% SoC than in a pristine cell, but the curve is almost identical to that of a pristine cell for SoC > 50%.
The effect of the loss of delithiated cathode is that the OCV curve looks generally compressed compared to the OCV curve of a pristine cell, without significant change in the shape.
Note that the charts above illustrating as if the cycleable range ends at 20-30% SoC are misleading: in practice, SoC is itself estimated from the Cell terminal voltage and thus ranges between 0% and 100% even in degraded cells. See Electrode voltage curves are steeper when the electrode has little lithium for more discussion of this.
Estimated loss of active material in a cell is one of the Cell parameters.
See also Positive feedback loops of cell degradation associated with loss of active material.
We can discern between the physical causes of cell degradation by looking at the OCV function.