Built-In Electric Field in Si/Ge Heterojunction Suppressing Li+ Trapping Boosts High Initial Coulombic Efficiency of Silicon Anodes

Silicon (Si) anodes are promising candidates for surpassing the energy density limits of current lithium‑ion batteries, owing to the ultra‑high theoretical capacity (4200 mAh g −1 ). However, their practical implementation is hindered by irreversible lithium (Li) loss, which originates from the continuous formation of the solid electrolyte interphase (SEI) and the irreversible trapping of Li + within the silicon matrix due to sluggish Li + diffusion kinetics. To address these issues, a Si/Ge@C heterojunction anode has been designed. In this configuration, a conformal carbon coating effectively mitigates volume expansion and suppresses parasitic reactions on the Si surface, thereby reducing excessive SEI formation. Moreover, the Si/Ge heterojunction establishes a built‑in electric field oriented from Si to Ge, which reduces Li + trapping. This built‑in electric field not only facilitates Li + migration toward Ge during lithiation but also provides an additional driving force to extract trapped Li + from Si during delithiation. Consequently, the optimized Si/Ge@C anode delivers a high initial Coulombic efficiency (ICE) of 92.47% and maintains a high capacity of 539.77 mAh g −1 over 500 cycles at 200 mA g −1 .