The lower raw material price of sodium-ion batteries (SIBs) compared to lithium-ion batteries is partially offset by their lower energy density. Thus, SIBs must also be competitive on performance in order to be attractive in terms of price. Aging, in particular, plays an important role here, as does understanding and reliably predicting it. 

To better understand the aging of commercial sodium-ion batteries with layered oxide cathodes, we investigated aging at the electrode level, focusing on resistance increase and capacity fade. We showed that most of the resistance increase during aging is caused by the anode. Interestingly, however, this does not apply to the capacity loss. While aging in lithium-ion batteries is dominated by loss of charge carrier inventory, we used degradation mode analysis to show that aging can be dominated by loss of cathode active material, and verified these results using a three-electrode setup. Due to the electrode potentials, this leads to only weak and thus hidden aging at the beginning of life, which then suddenly increases at a knee point. Thus, determining the degradation modes of sodium-ion batteries is crucial for a precise estimation of remaining useful life.

Rehm, Mathias; Bahrke, Julius; Natterer, Johannes; Milutinovic, Leon; Roehrer, Franz; Jossen, Andreas: „Aging of commercial sodium-ion batteries with layered oxides: how to measure and analyze it?”, in: EES Batteries (2026) Advance Article, https://doi.org/10.1039/D5EB00221D