Case study of N-carboxyanhydrides in silicon-based lithium ion cells as a guideline for systematic electrolyte additive research

Incorporation of silicon into negative electrodes is pursued widely to increase the energy density of lithium ion batteries (LIBs). However, severe volume changes of silicon during (de)lithiation cause consumption of active lithium and electrolyte by continuous solid electrolyte interphase (SEI) formation, resulting in deterioration of cell performance. Electrolyte additives offer an unprecedented way to improve LIB cell performance by effective interphase formation. Here, we report a class of electrolyte additives based on substituted N-carboxyanhydrides (N-CAs) designed to effectively tailor the SEI formed in LiNi0.5Co0.2Mn0.3O2 (NCM523) ∥ SiOx/C full cells, which are evaluated in pouch cells with application-relevant electrolyte per-cell capacity ratios. The working mechanism is elucidated systematically by use of complementary postmortem techniques, correlating cycling and storage performance data, gas formation, SEI composition, and electrolyte degradation. With successful additive functionalization, several N-CAs even outperform the state-of-the-art additive fluoroethylene carbonate in terms of capacity retention.