SEI-Component Formation on Nano-Silicon in Rechargeable Lithium-Based Batteries Using Modified Ether-Based Electrolytes
Herein, we studied the interfacial characteristics on a nanostructured silicon electrode cycled in ether-based electrolytes and compared the results to our recent findings with carbonate-based electrolytes. The electrolytes have been modified with well-known additives for Li – S batteries, a fluorinated ether (TTE) and lithium nitrate. The silicon electrodes were exposed to long-term cycling in a half-cell set-up (vs Li/Li+) to demonstrate the importance of such additives (Figure 1). After cycling the post-mortem electrodes were carefully studied by different techniques including XRD, XPS and electron microscopy (SEM/TEM). We used a recently developed silicon-carbon nanocomposite composed of silicon nanoparticles of less than 5 nm embedded into a carbon scaffold. This nanocomposite provides a delithiation capacity of up to 2000 mAh/gSi (five times more than graphite) and an excellent cycle retention of nearly 100 % after 200 cycles in a carbonate-based electrolyte configuration (Figure 1). However, a considerable poorer reversibility is observed in an ether-based electrolyte which is supposed to be caused by a different SEI composition. Since the nanocomposite exhibits a high surface area, a detailed characterization of the interfacial characteristics is possible. The occurrence of diverse SEI-compounds like semi-organic carbonates, LiF, Li2O, phosphorous and sulfur species will be discussed in context of the electrochemical results.
Closing the gap between the basic-research and real application, we studied the effect of polysulfides on the electrochemical performance and on the SEI formation of the silicon electrode in a full-cell set-up. Therefore, a pre-lithiated silicon electrode was assembled with a conventional sulfur electrode and galvanostatically tested for long-term cycling. We will highlight the superior electrochemical performance of the nano-silicon anode instead of metallic lithium. The SEI characteristics of the post-mortem silicon electrode are compared to the silicon electrode cycled in the polysulfide-free ether electrolyte. The results will help to understand degradation mechanism and to design advanced electrolytes for silicon-based electrodes in high-energy lithium-based batteries.
Funded by the German Federal Ministry of Education and Research (BMBF) within the WING Center – Battery Mobility in Saxony (BaMoSa), grant nos. 03X4637A, 03X4637B and 03X4637C.
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