Anodic Oxidation of Conductive Carbon and Ethylene Carbonate in High-Voltage Li-Ion Batteries Quantified by On-Line Electrochemical Mass Spectrometry

The anodic oxidation stability of battery components like the conductive carbon black (Super C65) and the co-solvent ethylene carbonate (EC) is of great relevance, especially with regards to high-voltage cathode materials. In this study, we use On-line Electrochemical Mass Spectrometry (OEMS) to deconvolute the CO and CO₂ evolution from the anodic oxidation of carbon and electrolyte by using a fully ¹³C-isotope labeled electrolyte based on ethylene carbonate with 2 M LiClO₄. We present a newly developed two-compartment cell, which provides a tight seal between anode and cathode compartment via a solid Li⁺-ion conducting separator, and which thus allows us to examine the effect of trace amounts of water on the anodic oxidation of carbon (¹²C) and ethylene carbonate (¹³C) at high potentials (> 4.5 V) and 10 to 60°C. Moreover, we report on the temperature dependence of the water-driven hydrolysis of ethylene carbonate accompanied by CO₂ evolution. Finally, by quantifying the evolution rates of ¹²CO/¹²CO₂ and ¹³CO/¹³CO₂ at 5.0 V, we demonstrate that the anodic oxidation of carbon and electrolyte can be substantial, especially at high temperature and in the presence of trace water, posing significant challenges for the implementation of 5 V cathode materials.