Epitaxial Metal–Organic Framework for Stabilizing the Formation of a Solid Electrolyte Interphase on the Si Anode of a Lithium-Ion Battery

Si, used to make high-capacity anodes for Li-ion batteries, undergoes unstable electrolyte decomposition that limits its wider commercial use. The decomposed electrolyte deposits on the Si surface as an insulating solid electrolyte interphase (SEI). The Si electrode is known to grow a porous and thick SEI that hinders e– and Li+ diffusion, resulting in rapid capacity fade. Fluoroethylene carbonate (FEC), an electrolyte additive, is known to alleviate the SEI issue by promoting polymerization and cross-linking, leading to a denser and thinner SEI. Nonetheless, current commercial anodes incorporate limited amounts of Si due to the unsatisfactory capacity retention of Si. To improve the ability of FEC to polymerize and cross-link the SEI further, inorganic coatings have been employed and have been shown to be beneficial with regard to the cycling performance. However, previous works utilized expensive techniques, such as atomic or molecular layer deposition processes. Here, we demonstrate for the first time a low-cost atomic layer inorganic/organic hybrid coating of an epitaxial metal–organic framework, HKUST-1, via a wet-chemical method on a Si electrode. To realize this, we studied the working mechanism of the HKUST-1 coating. Owing to its affinity to FEC, the coating allows more efficient polymerization and cross-linking of the Si SEI. This results in the formation of a denser and thinner SEI, which reduces the impedance and enhances the electrochemical cycling performance.