Tuning additive functionality via a molecular-by-design strategy: Acyl silanes for stable high-nickel cobalt-lean cathodes in lithium-based batteries

Abstract

Developing multifunctional electrolyte additives is essential for stabilizing high-nickel cobalt-lean cathodes, which are prone to interphase instability and parasitic side reactions, particularly at elevated voltages. Herein, a molecular-by-design strategy is presented that enables systematic tuning of interphase chemistry and hydrofluoric acid (HF) scavenging capability via single-bond (Si–X, X = Me, Me₂N, F) variation within an acyl silane framework. Three structurally analogous yet functionally distinct additives were synthesized: di-tert-butyl methyl adamantoyl silane ((Me)tBu₂SiCOAd; Ad is 1-Ad), (di-methyl amino) di-tert-butyl adamantoyl silane ((Me₂N)tBu₂SiCOAd), and di-tert-butyl fluoro adamantoyl silane ((F)tBu₂SiCOAd). In Li||LiNi_0.9Co_0.05Mn_0.05O₂ (Li||NCM90) cells with carbonate-based electrolyte, (Me₂N)tBu₂SiCOAd, significantly improves cycling stability, delivering 90 % capacity retention after 200 cycles at 1C and 4.3 V (30 % improvement over the blank), and 80 % retention at 4.4 V (42 % improvement). This enhancement is attributed to its multifunctionality: stable interphase formation and effective HF scavenging via the Si-N bond. Conversely, (Me)tBu₂SiCOAd contributes only to interphase formation, while (F)tBu₂SiCOAd is ineffective. These findings are supported by theoretical simulations, which reveal a low activation barrier for HF scavenging by (Me₂N)tBu₂SiCOAd and explain the inert behavior of (F)tBu₂SiCOAd. Overall, this study demonstrates how targeted single-bond modulation enables precise molecular tuning of additive functionality in high-nickel cobalt-lean systems.