2,2,5,5-Tetramethyl-2,5-disila-1-oxacyclopentane as a bifunctional electrolyte additive for Ni-rich (LiNi0.9Co0.05Mn0.05O2) cathode in Li-ion batteries

Abstract

Ni-rich ternary oxides (LiNixCoyMnzO2, x + y + z = 1, x ≥ 0.6) has received growing attention due to its high reversible capacity and high working voltage. However, the practical application of Ni-rich cathodes is still obstructed by the serious interfacial instability and structural degradation during long-term cycling. In this work, we propose a novel cyclic siloxane additive, i.e. 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMDSi). With this additive, the capacity retention of NCM90||Li cells can be improved to 85% after 200 cycles at 1C (1C = 180 mA g−1). The working mechanism of this novel additive has been clearly disclosed with the help of scanning electronic microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and liquid nuclear magnetic resonance (NMR) techniques. The results show that TMDSi can effectively scavenge HF and suppress the dissolution of transition metal ions from the NCM90 cathode. Furthermore, its decomposition products can also form a uniform protective CEI film on the surface of NCM90 particles to maintain the complete morphology and reduce parasitic side reactions at the cathode interface. This bifunctional working mechanism makes TMDSi a promising electrolyte additive for Ni-rich cathode in Li-ion batteries.