Electrode–Electrolyte Interphase Stability and Molecular-Volume-Assisted Li ⁺ Solvation Regulation for the LiNi 0.8 Co 0.15 Al 0.05 O ₂ Cathode

Nickel-rich layered cathodes such as LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) offer high specific capacity, yet their cycling durability is often limited by sluggish Li + transport kinetics and continuous electrode–electrolyte interphase degradation. This work employs trimethylsilyl acetate (TMS) as a functional electrolyte additive and reveals its molecular-volume-assisted Li + solvation regulation effect. The large molecular volume of TMS perturbs the original Li + -solvent coordination environment, promoting greater PF 6 – participation in Li + solvation. Furthermore, its preferential oxidative decomposition forms a thin and uniform CEI, enhancing interfacial kinetics, which is also supported by in situ EIS combined with DRT analysis during charging. As a result, an NCA coin cell with 2% TMS achieves capacity retentions of 84.8% at 1 C and 87.8% at 2 C after 200 cycles, versus 65.1% and 68.2% for the baseline electrolyte. The lithium-ion transference number is also improved from 0.28 to 0.50. This work combines additive molecular-volume-assisted Li + solvation regulation with interfacial stabilization, providing a useful reference for the design of organosilicon additives to improve the cycling stability of NCA cathodes.