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.