While the theoretical capacity of Si is high (3579 mAh g^-1 for Li₁₅Si₄) and has a relatively low discharge potential (370 mV vs Li/Li⁺), impediments need to be overcome before fully commercializing Si-based batteries. One key challenge is compensating for irreversible losses of Li due to its consumption to form a solid electrolyte interface (SEI) during the first cycle. Prelithiation of Si anodes is a method that has been studied to overcome challenges associated with these losses, with a variety of approaches a studied over the past 15 years. Electrochemical prelithiation is one of the most common and well-established techniques; however, there are significant challenges are associated with implementing electrochemical prelithiation at scale. Disassembly of the cell is required to reassemble full cells with the prelithiated anode, which is cumbersome and could damage the structural integrity of the electrode, ultimately increasing manufacturing costs. Additionally, controlling the amount prelithiated electrochemically can be difficult and lead to Li plating. Herein, we report a protocol for prelithiation of true Si-based composite electrodes (70% Si by wt. %) using an alternative thermal evaporation approach and will be compared to the aforementioned electrochemical prelithiation approach. Upon thermal evaporation, amorphous Li_xSi alloying is favorable through the electrode bulk where the stoichiometry can be reproducibly controlled using a QCM to quantify deposition rate. Complete elemental and electrochemical characterization is provided for prelithiated electrodes by thermal evaporation. This approach resulted in full cells which cycled with an improvement in initial coulombic efficiency by 15.8% and a 47.8% reduction in total capacity loss by the end of SEI formation cycling. Subsequent C/3 cycling showed up to a 62.9% increase in specific capacity in prelithiated cells. Changes in surface composition of the SEI were also observed for chemical vs electrochemical formation routes, confirmed by EIS and XPS, which could play a role in overall cycling performance. Furthermore, thermal evaporation is a viable approach toward advancing efforts to further improve Si-based Li-ion battery performance.

Amanda Musgrove

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