Sodium-ion batteries (NIBs) are a promising drop-in technology in the battery sector due to the abundance of the required elements and correspondingly low costs. However, the anode and cathode materials as well as the electrolyte are not yet as optimized as their Lithium-ion counterpart. This leads to a comparatively shorter cycle life. In order to improve the technology, ageing mechanisms must be identified and minimized. A detailed analysis can provide approaches to improve both service life and performance.
For the experimental work, aging cycles are performed with Hard Carbon | Sodium Vanadium Phosphate cells with an EC:PC electrolyte and with the addition of the additive FEC. Every 100 cycles, impedance measurements and post-mortem analyses shed light on the state of aging.
The measurements are supplemented by analyses using a Doyle-Fuller-Newman model with an integrated SEI [1]. The model can be used to quantify rate limitations and ageing mechanisms. By integrating a multi-step multi-reaction (MSMR) mechanism, additional insights into the electrode materials can be found.
With these techniques, ageing and performance are placed in the context of cell chemistry and electrode design. Both the changing composition of the SEI and the material fatigue are illuminated. The analysis is carried out in the interaction of experiment and model in order to show the contribution of the individual ageing mechanisms to the loss of performance. Through modeling and post mortem analysis, the aging mechanisms are additionally assigned to the individual electrodes or the electrolyte.
Losses in the operation of high-energy cells at relatively high rates are strongly related to the structural cohesion of the electrodes and the electrolyte chemistry. In principle, the development and optimization of all cell components can therefore increase the service life of the cells. This work analyzes which aging processes lead to the greatest limitations. Particular attention is paid to electrolyte decomposition.

Literature:
[1] D. Witt, F. Röder, U. Krewer, Batteries & Supercaps, 5, 7 (2022).