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

Abstract

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 13 C-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 (LiClO 4 , LiPF 6 , LiTFSI, and LiBF 4 ). 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 CO 2 evolution from the oxidation of the conductive carbon ( 13 CO/ 13 CO 2 ) and of the electrolyte ( 12 CO/ 12 CO 2 ). Our analysis reveals that conductive carbon is stable with LiPF 6 , however, pronounced electrolyte oxidation and gaseous byproducts like HF, PF 5 and POF 3 are observed. LiBF 4 provides an excellent carbon and electrolyte stability even at 50 °C, rendering it as a better salt than LiPF 6 for the cathode side in high-voltage lithium-ion cells.