Direct Evidence of Reversible SnO2-Li Reactions in Carbon Nanospaces

We present herein that carbon nanospaces are the keyreaction spaceto improve the reversibility of the reaction of SnO2 withLi-ions for lithium-ion batteries, demonstrated by both ex situ andin situ observations using high-resolution scanning transmission electronmicroscopy with electron energy loss spectroscopy. Conversion-typeelectrode materials, such as SnO2, undergo large volumechanges and phase separation during the charge-discharge process,which lead to degradation in the battery performance. By confiningthe SnO2-Li reaction within carbon nanopores, thebattery performance is improved. However, the exact phase changesof SnO2 in the nanospaces are unclear. By directly observingthe electrodes during the charge-discharge process, the carbonwalls are capable of preventing the expansion of SnO2 particlesand minimizing the conversion-induced phase separation of Sn and Li2O on the sub-nanometer scale. Thus, nanoconfinement structurescan effectively improve the reversibility performance of conversion-typeelectrode materials.

Automated summary

This study demonstrates that carbon nanospaces serve as the key reaction space to enhance the reversibility of SnO2-Li reaction in lithium-ion batteries. By confining the reaction within carbon nanopores, the expansion of SnO2 particles and the phase separation of Sn and Li2O can be prevented. These nanoconfinement structures effectively improve the reversibility performance of conversion-type electrode materials.