The electrochemical reaction mechanisms of the tin oxides, SnO and SnO2, were investigated to obtain a fundamental understanding of their Li insertion/extraction behaviors using ex situ X-ray diffraction, X-ray absorption near edge structure, X-ray absorption fine structure, and high-resolution transmission electron microscopy analyses along with differential capacity plots. The results of the analyses thoroughly demonstrated partial recombination reactions of SnO and SnO2. (C) 2015 The Electrochemical Society. All rights reserved.