Unveiling the mechanisms into Li-trapping induced (ir)reversible capacity loss for silicon anode

Commercialization of silicon (Si) anodes has been tremendously hampered by its low Coulombic efficiency and poor cycling stability in lithium-ion batteries (LIBs). As it is often the case, huge volume change of Si material, and the consequent unstable solid electrolyte interphase (SEI) formation, manifest two major attributes to a hastened electrode failure. However, this recognition is not comprehensive. In this work, we find that Li-trapping represents to be a major factor determining initial Coulombic efficiency and cycling stability for Si anodes. Moreover, through titration gas chromatography (TGC) and high-resolution transmission electron microscopy (HRTEM), we identify two existing forms of the trapped Li, which are: (1) trapped active Li due to sluggish Li+ lithiation/delithiation kinetics; (2) trapped inactive Li resulted from the pulverization of Si particles. First-off, during initial charge-discharge, trapped active Li accounts for ca. 40% of the first irreversible capacity. By further exploring the evolution of Li-trapping, it is observed that the accumulation of trapped inactive Li turns a dominant factor for the capacity decline, accounting for ∼75% of the total capacity loss after 20 cycles. We expect that the significance and fundamentals of Li-trapping elucidated herein will trigger new strategies in modifying Si anodes towards high-performance Si-based LIBs.