Evaluation of Alternative Lithium Salts in Li Ion Batteries with SiOx-based Anodes: Characteristic Failure Mechanisms and Different Impacts of the Fluoroethylene Carbonate Additive

Arifiadi, A. Anindityo, Minar, Jaroslav, Das, Ankita, Voigt, Dominik, Vahnstiege, Marc, Buchmann, Julius, Demelash, Feleke, Yan, Peng, Nowak, Sascha, Frank Glorius, Winter, Martin, Kasnatscheew, Johannes

Abstract

Incorporating silicon-based active materials, e.g., SiO x , into the negative electrodes can increase the gravimetric/volumetric energy of Li ion batteries. Nevertheless, SiO x shortens cycle life due to the large volume expansion during charge/discharge cycling. The mechanical stress on the solid electrolyte interphase (SEI) necessitates continuous SEI repair, which accelerates active lithium loss (ALL) over cycling. In this work, the impact of common lithium salts is investigated in electrolytes for LiNi0.5Co0.2Mn0.3O2 (NCM 523) || 10%SiO x -graphite Li ion pouch cells. The end-of-life (EOL) with LiPF6 can be enhanced by anode passivation via fluoroethylene carbonate (FEC), which not only decreases ALL but also suppresses failure cascades (e.g., electrode crosstalk) initiated by HF over the course of SiO x reactions with LiPF6. Though ALL remains similar when adding FEC to lithium bis(oxalato)borate (LiBOB), it enhances the generation of active Li through oxidation reactions at the cathode, likely due to the inverse crosstalk of partly soluble SEI species. This "self-healing" or "recovery" mechanism reactivates the apparently "wasted SEI" and formerly lost capacity, thereby enhancing cycle life. This positive effect is even more pronounced with LiDFOB. However, the accompanying gassing of the oxalato-based salts remains an obstacle to practical applicability.