Homogenizing Stress Distribution to Construct a Stable LiF-rich Solid Electrolyte Interphase in Silicon/Carbon Anodes

Inducing homogeneous stress distribution is essential for enhancing the structural stability of silicon/carbon (Si/C) anodes. To this end, a liquid-phase synthesis approach combined with an electrochemical technique is proposed to in situ construct a robust LiF-rich interphase on the Si/C surface. Both the functional interphase and pre-designed void within the carbon layer induce a stable LiF-rich solid electrolyte interface (SEI) through their synergistic management of anisotropic stress evolution, significantly increasing interfacial mechanical strength, suppressing electrode polarization and electron leakage into the electrolyte, and achieving superior interface stability. Fatigue resistance, theoretical simulations, and electrode surface analyses reveal that stress concentration and catastrophic strain localization are effectively restrained, causing an intact interface and reduced energy barriers for Li⁺ de-solvation and diffusion. The dQ/dV curves and voltage drop analysis disclose a more reversible phase transition process for Li₁₅Si₄ in the optimal electrode upon cycling. These factors are collectively attributed to the homogeneous stress distribution. Therefore, the optimized electrode delivers outstanding electrochemical robustness, achieving 96.5% capacity retention after 1000 cycles at 4 A g^-1 and a rate capacity of 589.5 mAh g^-1 at 6 A g^-1. The proposed strategy, homogenizing stress distribution, offers a novel paradigm for constructing a stable SEI on electrodes undergoing severe volume fluctuations.