Comparing the Lithiation and Sodiation of Hard-Carbon Using Online Electrochemical Mass Spectrometry

Abstract

Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries (LIBs), especially for applications in which weight and size play a subordinate role.1 In contrast to LIBs, graphite is not a viable anode active material for SIBs since sodium cannot be inserted into graphite. So-called hard-carbons are promising anode active materials for SIBs because of their easy synthesis, high capacity, and high cycling stability.2 Major challenges are the high irreversible capacity in the first cycle and the stability of the solid electrolyte interphase (SEI).3 - 4 Online electrochemical mass spectrometry (OEMS) is a powerful tool for identifying and quantifying evolved gasses during SEI formation, giving insight into the mechanism of SEI formation. For LIB research, our group had developed a two-compartment OEMS cell design that enables the investigation of evolved gases from one of the electrodes of a battery cell without interference from the gases evolved from the other electrode, which is particularly useful for the mechanistic study of electrolyte additives or impurities without influences of the counter electrode.5–8 In this study, we investigate the gas evolution during the first lithiation/delithiation cycles of a hard-carbon anode active material using our existing two-compartment cell design. This will then be compared to the gas evolution during the first sodiation/desodiation cycles of the same hard-carbon material using a newly developed two-compartment OEMS-cell design for the study of sodium-ion batteries, which is based on a gas impermeable solid electrolyte separator composed of sodium ion conducting β-alumina. We compare the quantities of evolved gasses and look at the onset potentials of gas evolution during the first alkaline metal insertion. On the basis of gassing and impedance data,9,10 the differences in SEI formation and its properties will be discussed.Acknowledgments: We gratefully acknowledge funding by the BMBF (Federal Ministry of Education and Research, Germany) for its financial support under the auspices of the ExZellTUM III project, grant number 03XP0255