Sb is a promising anode material for lithium-ion batteries, but it suffers from fast capacity fading. Previous works have shown that the combination of Sb with an active S or Se matrix improves the cycle stability of the electrodes, although there was no clear verification of the exact mechanism. In this study, we used ex situ X-ray diffraction, ex situ Raman spectroscopy, and in situ dilatometry to study the interactions of Sb with S and Se and to reveal the reasons for the superior cycle stability of Sb2Se3 electrodes. Our results show that the poor stability of Sb electrodes is due to the crystallization of Li3 Sb, leading to the large volume change, high stress, and mechanical failure of the particles. Addition of S or Se into the matrix can inhibit the formation of crystalline Li3 Sb, thus improving capacity retention. The stabilization effect is stronger for a Se matrix than for a S matrix because it enables the re-formation of Sb-Se bonds upon delithiation and prevents phase segregation. In addition, the Se matrix reduces the volume change of the electrode during the charge and discharge, preventing electrode cracking and resulting in good mechanical reversibility.