Hydrolysis of Ethylene Carbonate with Water and Hydroxide under Battery Operating Conditions

This study deals with the decomposition of ethylene carbonate (EC) by H 2 O in the absence and presence of catalytically active hydroxide ions (OH − ) at reaction conditions close to lithium-ion battery operation. We use On-line Electrochemical Mass Spectrometry (OEMS) to quantify the CO 2 evolved by these reactions, referred to as H 2 O-driven and OH − -driven EC hydrolysis. By examining both reactions at various temperatures (10 – 80°C) and water concentrations (<20 ppm or 200, 1000, and 5000 ppm H 2 O) with or without catalytically active OH − ions in EC with 1.5 M LiClO 4 , we determine an Arrhenius relationship between the CO 2 evolution rate and the cell temperature. While the apparent activation energy for the base electrolyte (<20 ppm H 2 O) is very large (app. E a ≈153 kJ/mol), substantially lower values are obtained in the presence of H 2 O (app. E a ≈99 ± 3 kJ/mol), which are even further decreased in the presence of catalytically active OH − (app. E a ≈43 ± 5 kJ/mol). Our data show that OH − -driven EC hydrolysis is relevant already at room temperature, whereas H 2 O-driven EC hydrolysis (i.e., without catalytically active OH − ) is only relevant at elevated temperature (≥40°C), as is the case for the base electrolyte. Thus, catalytic quantities of OH − , e.g., from hydroxide contaminants on the surface of transition metal oxide based active materials, would be expected to lead to considerable CO 2 gassing in lithium-ion cells.