Uniform Li-ion diffusion and robust solid electrolyte interface construction for kilogram-scale Si@ZIF powder as the anode in Li-ion batteries

The zeolitic imidazolate framework (ZIF) is characterized by a highly ordered structure, large cavities, and thermal/chemical stabilities and has been widely researched for energy storage. In this study, using commercial Si powder with a diameter of 50-200 nm at a kilogram scale, Si@ZIF core-shell particles with dispersed ZIF-8 rhombic dodecahedrons were fabricated by a one-pot method and achieved excellent electrochemical perfor-mance. With the specific pore diameter and ordered network formed by membered rings, experimental results demonstrated that the ZIF-8 shell realized a uniform and accelerated Li+ diffusion route, alleviated volumetric expansion of the Si core, and constructed a LiF-concentrated robust solid electrolyte interface film with less unnecessary consumption of electrolyte and Li+. Density functional theory calculations verified the higher adsorption energy for Li-solvated clusters and the de-solvation effect on the surface of ZIF-8, which can increase Li+ concentration along the one-dimensional channels of 4-membered ring with a diameter similar to that of Li+ for high-speed and uniform Li+ intercalation. Furthermore, the large and elastic rhombic dodecahedrons formed by pure ZIF-8 buffered the volume change and maintained the integrity of the Si electrode during cycling. As a result, the Si@8Z anode achieved a reversible capacity of 818.5 mAh g-1 after 650 cycles at 1 A g-1 with a high initial coulombic efficiency of 88.2 % and outstanding rater performance even at 8 A g-1. Nevertheless, the capacity of the Si anode decreased to 0 mAh g-1 after 200 cycles. The present work clarifies the effect of ZIF on the performance of Si anodes and provides a simple method to modify commercial Si powder.