The Impact of Vinylene Carbonate, Fluoroethylene Carbonate and Vinyl Ethylene Carbonate Electrolyte Additives on Electrode/Electrolyte Reactivity Studied Using Accelerating Rate Calorimetry

Abstract

The effects of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and vinyl ethylene carbonate (VEC) electrolyte additives on electrode/electrolyte reactivity at elevated temperatures were investigated using accelerating rate calorimetry (ARC). Li(Ni_1/3Mn_1/3Co_1/3)O₂ (NMC) and graphite (mesocarbon microbeads (MCMB)) were utilized as the electrodes and 1.0 M LiPF₆ in ethylene carbonate (EC):diethyl carbonate (DEC) (1:2 by volume) was chosen as control electrolyte. Adding 10 wt% VC, FEC or VEC to the electrolyte does not significantly impact the reactivity of delithiated NMC compared to the control electrolyte. However, the three additives affected the reactivity between lithiated graphite and electrolyte at elevated temperatures in different ways. Adding VC (up to 10%) reduces the reactivity between lithiated graphite and electrolyte below about 200°C, adding VEC does not affect the reactivity at all, while adding over 5 wt% FEC causes a small exotherm beginning as low as 50°C. After this small exotherm completes, electrolytes with 10 wt% FEC show more reactivity with lithiated graphite than control electrolyte above 130°C. These results give a head to head comparison of the reactivity of electrolytes containing VC, VEC or FEC with charged electrode materials at elevated temperatures and show that the use of VC and VC at levels of 10 wt% or less should not compromise the safety of Li-ion batteries.