Improved Electrochemical Properties of Nickel-Rich, Low-Cobalt Layered Oxide Cathodes Using Dual-Functional Di-tert-butylmethyl Adamantoyl Silane Additives

With an increasing demand for high-energy-density lithium-ion batteries (LIBs), nickel-rich cathodes such as LiNi_0.9Mn_0.05Co_0.05O₂ (NMC90) have gained significant interest due to their relatively low cobalt and high specific energy. However, cycling stability is compromised due to parasitic reactions at the electrode-electrolyte interfaces of NMC90. Herein, we demonstrate improved electrochemical properties of NMC90 using di-tert-butylmethyl adamantoyl silane (RSiCOAd: R is tBu(CH₃)₂ and Ad is 1-Ad) as an additive in a commercial electrolyte. Upon detailed electrochemical and spectroscopic analysis, we demonstrate that the RSiCOAd additive undergoes in situ decomposition to form a fluorinated organosiloxane passivation layer on the NMC90 surface and enhanced fluorination on the lithium anode surface. This phenomenon could significantly mitigate the parasitic reactions at the cathode-electrolyte interface while improving the electrochemical performances. Furthermore, the practical viability of the RSiCOAd additive is evaluated by full-cell studies with the graphite anode. After prolonged 200 cycles, full cells containing RSiCOAd with the incorporation of just 1% additive demonstrate an impressive ∼10% higher capacity retention, outperforming pristine NMC90 full cells.