Photoelectron Spectroscopic Evidence for Overlapping Redox Reactions for SnO2 Electrodes in Lithium-Ion Batteries

Abstract

In-house and synchrotron-based photoelectron spectroscopy (XPS and HAXPES) evidence is presented for an overlap between the conversion and alloying reaction during the cycling of SnO2 electrodes in lithium-ion batteries (LIBs). This overlap resulted in an incomplete initial reduction of the SnO2 as well as the inability to regenerate the reduced SnO2 on the subsequent oxidative scan. The XPS and HAXPES results clearly show that the SnO2 conversion reaction overlaps with the formation of the lithium tin alloy and that the conversion reaction gives rise to the formation of a passivating Sn layer on the SnO2 particles. The latter layer renders the conversion reaction incomplete and enables lithium tin alloy to form on the surface of the particles still containing a core of SnO2. The results also show that the reoxidation of the lithium tin alloy is incomplete when the formation of tin oxide starts. It is proposed that the rates of the electrochemical reactions and hence the capacity of SnO2-based electrodes ...