Solid-State NMR and Electrochemical Dilatometry Study on Li + Uptake/Extraction Mechanism in SiO Electrode

Abstract

This work reports the uptake/extraction mechanism in silicon monoxide as the negative electrode in lithium secondary batteries. A combined study of solid-state - and -nuclear magnetic resonance (NMR), electrochemical dilatometry, and charge-discharge cycling consistently demonstrates that the domain in irreversibly reacts with to produce lithium silicates and in the first discharging period, whereas the elemental Si domain reversibly reacts, delivering the same charge-discharge characteristics to those of conventional amorphous Si electrodes. The volume expansion accompanied by the irreversible reaction is less significant than that caused by the lithiation of Si domain. The postmortem analysis made on cycled electrodes reveals a phase segregation between the lithium silicates/ and lithiated Si phase. It is likely that the lithium silicates/ phase plays a buffering role against the volume change of Si matrix, but the crack formation at the phase boundaries and eventual pulverization are still a problem to be solved.