Investigating the Compatibility of TTMSP and FEC Electrolyte Additives for LiNi0.5Mn0.3Co0.2O2 (NMC)–Silicon Lithium-Ion Batteries

This study examines the compatibility of multielectrolyte additives for NMC-silicon lithium-ion batteries. Research studies with Si-based anodes have shown stable reversible cycling using electrolytes containing fluoroethylene carbonate (FEC). At the same time, the electrolyte additive, tris(trimethylsilyl) phosphite (TTMSP), has shown to improve the electrochemical performance of nickel-rich layered cathodes, such as LiNi_0.5Mn_0.3Co_0.2O₂ (NMC). However, the combination of these electrolyte additives for the realization of a full-cell NMC-Si lithium-ion battery has not been previously explored. Changes in the electrochemical performance (capacity retention, internal cell resistance, and electrochemical impedance) in half-cells are studied as the ratio of TTMSP and FEC is tuned. At the optimal TTMSP/FEC ratio of 0.33 (T1F3), the NMC-Si full-cells achieve a 2× longer cycle life when compared to the FEC-rich (T0F4) electrolyte. Moreover, T1F3 full-cells demonstrate 1.5 mAh/cm² areal capacities and high-capacity retention (25% more than T0F4). A detailed investigation of the electrode-electrolyte interfaces is conducted by using time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The chemical species depth profiles and elemental analysis illustrate adequate hydrogen fluoride (HF) scavenging. These results demonstrate the synergistic effects of electrolyte additives in minimizing the capacity degradation in NMC-Si full-cells by effectively stabilizing the electrode-electrolyte interfaces.