Performance of Full Cells Containing Carbonate-Based LiFSI Electrolytes and Silicon-Graphite Negative Electrodes

The energy density of lithium-ion cells can be significantly increased by the use of silicon-containing negative electrodes. However, the long-term performance of these cells is limited by the stability of the silicon electrode-electrolyte interface, which is continually disrupted during electrochemical cycling. Therefore, the development of electrolyte systems that enhance the stability of this interface is a critical need. In this article, we examine the cycling of [?]20 mAh pouch cells with lithium bis(fluorosulfonyl)imide (LiFSI)-containing carbonate-based electrolytes, silicon-graphite negative electrodes, and Li1.03(Ni0.5Co0.2Mn0.3)0.97O2 based positive electrodes. The effect of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) addition on cell performance is also examined and compared to the performance of our baseline LiPF6-containing cells. Our data show that cells containing only LiFSI show rapid loss of capacity, whereas additions of FEC and VC significantly improve cell capacity retention. Furthermore, the performance of LiFSI-FEC and LiPF6-FEC cells are very similar indicating that the electrolyte salts play a much smaller role in performance degradation than the electrolyte solvent. Future efforts to enhance longevity of cells with silicon-graphite negative electrodes will thereby focus on developing alternative solvent systems.