Running out of lithium? A route to differentiate between capacity losses and active lithium losses in lithium-ion batteries

rises with increasing cycle number. With this approach, a differentiation between "simple" irreversible capacities and truly detrimental "active Li losses" is possible and, thus, Coulombic efficiency can be directly related to the remaining useable cell capacity for the first time. Overall, the exact determination of the remaining active lithium content of the cell is of great importance, because it allows a statement on whether the reduction in lithium content is crucial for capacity fading or whether the fading is related to other degradation mechanisms such as material or electrode failure.