Lithium consuming parasitic reactions which induce active lithium loss (ALL) are a major reason for capacity fading in lithium ion batteries (LIBs).^{[1, 2]} As a consequence of capacity fading, the usable energy density is reduced. Typically, the ALL is set equal to the accumulated irreversible capacity (sum of the differences between charge and discharge capacity in each cycle, AIC). However, regarding the AIC it is known that it includes all parasitic reactions which generate a parasitic current. Hence, the AIC cannot be directly equated with ALL. Due to this, we proposed a novel approach in the following named as IRLC method, which is based on the remaining active lithium content of the cell, in order to determine the ALL with a higher accuracy. Therefore, a cell with a three electrode set-up is cycled and afterwards the positive electrode is de-lithiated with help of the former reference electrode in order to obtain the remaining active lithium content. Finally, the ALL can be calculated by using the remaining and the initial active lithium content. In order to evaluate the IRLC method we investigated different anode materials. It can be shown that within the first cycles the ALL can be described moderately well with help of AIC. However, with increasing cycle number the difference between ALL and AIC increases, most likely attributed to the fact that the impact of SEI formation and repair becomes smaller in comparison to other parasitic reactions which do not consume lithium. Furthermore, one additional advantage of the IRLC method is that it allows a statement whether the reduction of lithium content is crucial for capacity fading or whether the fading is related to host material losses or other degradation mechanisms e.g. a higher charge transfer resistances due to a growing SEI film.

1. Krueger, S., et al., How Do Reactions at the Anode/Electrolyte Interface Determine the Cathode Performance in Lithium-Ion Batteries? Journal of the Electrochemical Society, 2013. 160(4): p. A542-A548.

2. Vetter, J., et al., Ageing mechanisms in lithium-ion batteries. Journal of Power Sources, 2005. 147(1-2): p. 269-281.