Electrochemical Performance of Si/C-Argyrodite Solid-State Composites: Limitations of The Effective Ionic Transport

Silicon-graphite composite electrodes have emerged as an alternative to lithium metal or silicon anodes in all solid-state batteries due to their resistance to electro-chemomechanical failure, while maintaining low lithiation potential.¹ While those materials are designed for lithium-ion batteries, their limited intrinsic ionic conductivity hinders application in all-solid-state batteries requiring efficient charge carrier transport in the all-solid electrodes. Therefore, a design of the effective conductivities is imperative to achieve the best electrochemical performance. This can only be achieved by understanding the relations of charge carrier transport in the used materials as well as their composites under careful consideration of their preparation.²<br/>In our study, we focus on understanding the impact of charge carrier transport within a composite of silicon on graphite and argyrodite solid electrolyte on the electrochemical performance. Through a systematic variation of the Si/C to solid electrolyte ratio we show an exponential increase of the effective ionic conductivity in the anode composite with increasing content of solid electrolyte. Simultaneously, the electronic transport remains high (~S/cm) and virtually independent of the volume fraction. This enhanced effective transport in the composites translates to a substantial improvement in the specific capacities achievable when charging and discharging across various C-rates.³ In addition, we investigate the influence of temperature to gain information about the activation energy of the ionic transport in the composites. Our results underscore the importance of tailoring charge carrier transport properties in solid-state composite anodes to achieve optimal electrochemical performance.³<br/><br/>References:<br/>(1) Müller, J.; Abdollahifar, M.; Vinograd, A.; Nöske, M.; Nowak, C.; Chang, S. J.; Placke, T.; Haselrieder, W.; Winter, M.; Kwade, A.; Wu, N. L. Si-on-Graphite Fabricated by Fluidized Bed Process for High-Capacity Anodes of Li-Ion Batteries. Chem. Eng. J. 2021, 407, 126603. https://doi.org/10.1016/j.cej.2020.126603.<br/>(2) Janek, J.; Zeier, W. G. Challenges in Speeding up Solid-State Battery Development. Nat. Energy 2023, 8 (March), 230–240. https://doi.org/10.1038/s41560-023-01208-9.<br/>(3) Rudel, Y.; Rana, M.; Ruhl, J.; Rosenbach, C.; Müller, J.; Michalowski, P.; Kwade, A.; Zeier, W. G. Investigating the Influence of the Effective Ionic Transport on the Electrochemical Performance of Si/C-Argyrodite Solid-State Composites. Batter. Supercaps 2023, 6 (8), 1–6. https://doi.org/10.1002/batt.202300211.