Unraveling the mechanism of methyl acetate additive for reinforcing the solid electrolyte interface on graphite anodes

Abstract

The addition of electrolyte additives shows significant effect on the low temperature performance of lithium-ion batteries (LIBs), but the underlying mechanism remains to be further elucidated and understood. Here, we take methyl acetate (MA) as an example to explore the mechanism of low-temperature additives on the graphite interface. The effects of the MA additive, demonstrated by scanning electrochemical microscopy (SECM) and atomic force microscopy, optimize the electron insulating properties and mechanical properties of the graphite anode. This optimized electrolyte improves the graphite performance with a capacity of 343.8 mA h g⁻¹ after 300 cycles at room temperature and 302.9 mA h g⁻¹ at low temperature (−10 °C), while the capacity decreases sharply without MA, and at the same time improves the rate performance which increases the capacity retention at 4C from 18% to 55%. The reinforced electronic insulation SEI is observed in the first discharge process with MA addition in SECM feedback mode and remains stable in the next cycles. The results show that a stable ultrathin SEI with an inorganic/organic bilayer structure rapidly forms in the first cycle with MA addition, the outer organic layer provides mechanical suppression and the inner inorganic layer promotes the interface mechanical strength with excellent ion transport, which suppresses the continuous decomposition of electrolytes and improves the mechanical properties of the SEI.