Wildcat Discovery Technologies is developing novel electrolyte additives and noncarbonate solvent formulations that yield improved solid electrolyte interphase (SEI) layers on silicon alloy anodes. The large volumetric changes in silicon during charge/discharge cycles result in mechanical disruption of conventional SEI's leading to rapid capacity fade as the cell cycles. Novel additives are demonstrated to improve cycle life of silicon based materials by forming less brittle, more mechanically robust SEI passivation layers. Since propylene carbonate (PC) is not expected to form an effective SEI layer, the additives are tested with PC to determine their efficacy. Wildcat's high throughput electrolyte formulation, cell assembly, and test capabilities enable the evaluation of hundreds of additives in a very short timeframe.

Once effective SEI additives are identified in a PC-based formulation, other non-SEI forming solvents can be evaluated. Since the additives are effective without solvent participation in SEI formation, solvents can be considered that may not be reductively stable on the anode - and also opens the possibility to more oxidatively stable or less flammable solvents. Wildcat has evaluated hundreds of combinations of noncarbonate solvents with its initial silicon anode SEI additives. This presentation will focus on the results of the additive improvement to cycle life in NMC//Si full cells, and illustrate the opportunities for novel solvent combinations.