Direct Evidence of Reversible SnO<sub>2</sub>–Li Reactions in Carbon Nanospaces
Hiroo Notohara, Koki Urita, Isamu Moriguchi
Abstract
We present herein that carbon nanospaces are the key reaction space to improve the reversibility of the reaction of SnO 2 with Li-ions for lithium-ion batteries, demonstrated by both ex situ and in situ observations using high-resolution scanning transmission electron microscopy with electron energy loss spectroscopy. Conversion-type electrode materials, such as SnO 2, undergo large volume changes and phase separation during the charge–discharge process, which lead to degradation in the battery performance. By confining the SnO 2 –Li reaction within carbon nanopores, the battery performance is improved. However, the exact phase changes of SnO 2 in the nanospaces are unclear. By directly observing the electrodes during the charge–discharge process, the carbon walls are capable of preventing the expansion of SnO 2 particles and minimizing the conversion-induced phase separation of Sn and Li 2 O on the sub-nanometer scale. Thus, nanoconfinement structures can effectively improve the reversibility performance of conversion-type electrode materials.