Evaluating the High-Voltage Stability of Conductive Carbon and Ethylene Carbonate with Various Lithium Salts

The anodic stability of conductive carbon and alkyl carbonate-based electrolyte solvents is a crucial requirement for the success of high-voltage lithium-ion cells, particularly at elevated temperatures. In order to quantify the oxidative stability of ethylene carbonate (EC), a critical component of lithium-ion battery electrolytes, and conductive carbons, we have evaluated the stability of a 13C-labeled conductive carbon and an EC-based electrolyte up to 5.5 V vs Li+/Li. We examined the behavior between 25 °C and 60 °C for four different lithium salts (LiClO4, LiPF6, LiTFSI, and LiBF4). This is done by means of On-line Electrochemical Mass Spectrometry (OEMS), whereby the isotopically labeled carbon is used to differentiate between the CO and CO2 evolution from the oxidation of the conductive carbon (13CO/13CO2) and of the electrolyte (12CO/12CO2). Our analysis reveals that conductive carbon is stable with LiPF6, however, pronounced electrolyte oxidation and gaseous byproducts like HF, PF5 and POF3 are observed. LiBF4 provides an excellent carbon and electrolyte stability even at 50 °C, rendering it as a better salt than LiPF6 for the cathode side in high-voltage lithium-ion cells.