Facile reduction of pseudo-carbonates: Promoting solid electrolyte interphases with dicyanoketene alkylene acetals in lithium-ion batteries

• Replacement of CO in EC and PC by C(CN)2 was examined as electrolyte additives.
• These additives revealed interesting electrochemical and safety attributes.
• The formation of soluble electrolyte degradation products is hindered.

Dicyanoketene ethylene and propylene acetals, DCKEA and DCKPA respectively, have been investigated as electrolyte additives for Li-ion batteries. The purpose was to assess the changes in reduction behaviour and solid electrolyte interphase (SEI) passivation properties upon replacing the carbonyl group of ethylene carbonate (EC) and propylene carbonate (PC) solvents, respectively, by the slightly more electronegative and highly conjugated C(CN)2 group. The experimental reduction potentials and the IR spectroscopy characterisation efforts were further supported by density functional theory (DFT) computations. The two additives were found to, in relatively small amount (0.5 wt%), provide beneficial effects on the capacity retention of 8 mAh cells cycled at 20 and 45 °C. Moreover, the additives proved to enhance the thermal stability of the lithiated graphite/electrolyte interface, as deduced from DSC measurements.