Rapid Screening of Novel Electrolytes for High Calendar Lifetime Lithium-Ion Cells with Silicon-Based Anodes

While cycle-life parity between graphite and silicon (Si) based lithium-ion batteries (LIBs) is being reached, calendar lifetime of Si anodes remains disappointing compared to its graphite counterpart 1 . Silicon anode, owing to its intrinsic high (electro)chemical reactivity, exhibits poorly passivating solid electrolyte interphase (SEI) characteristics in common electrolyte formulations optimized for graphitic systems like LiPF 6 salt in EC:EMC solvents. Rapid electrolyte screening for calendar lifetime optimization is essential for enabling silicon anodes, as standardized calendar lifetime estimation with the USABC open circuit voltage reference performance test (OCV-RPT) requires long-duration experiments (~years) for accuracy 2 . In this work, we perform calendar lifetime screening of novel electrolytes for Si anodes utilizing voltage-hold (V-hold) experiments. The V-hold protocol with shortened runtime (~weeks) affords faster testing as compared to the conventional OCV-RPT protocol. Composite silicon anodes with low (15 wt.% Si) and high contents of silicon (70 wt. %Si) are tested with fluorine-free electrolyte systems (e.g. LiBOB in EC:EMC) and EC free electrolytes (e.g. LiPF 6 in FEC:EMC) respectively. Capacity during the V-hold has reversible anode lithiation and irreversible SEI growth contributions; consequently, a physics-based capacity deconvolution algorithm is devised to accurately split the parasitic currents for quantitative calendar lifetime estimation. The development of this synergistic experiment-modeling testing paradigm aids in the identification of electrolyte compositions that form stable, passivating SEI films on the silicon-based anodes. Figure 1 shows the voltage-hold cycle data for (a) fluorine-free and (b) fluorine-rich (right) electrolytes with 15% Si composite anodes collected in a 3-electrode cell. The corresponding normalized capacity and current profiles for 4.1V hold portion are shown in (c) and (d) respectively. Accurate deconvolution of irreversible capacity from the hold capacity is needed to obtain SEI stability information for calendar lifetime. 1 McBrayer, J.D., Rodrigues, M.T.F., Schulze, M.C., Abraham, D.P., Apblett, C.A., Bloom, I., Carroll, G.M., Colclasure, A.M., Fang, C., Harrison, K.L. and Liu, G., 2021. Calendar aging of silicon-containing batteries. Nature Energy, 6(9), pp.866-872. 2 U.S. Department of Energy Vehicle Technologies Program, United States Advanced Battery Consortium Battery Test Manual For Electric Vehicles , Revision 3.1, October 2020 http://www.uscar.org/guest/article_view.php?articles_id=86 Figure 1