Swelling-Controlled\nDouble-Layered SiO_<i>x</i>/Mg₂SiO₄/SiO_<i>x</i> Composite with Enhanced\nInitial Coulombic Efficiency for Lithium-Ion\nBattery

Abstract

Si-based\nanode materials are considered as potential materials\nfor high-energy lithium-ion batteries (LIBs) with the advantages of\nhigh specific capacities and low operating voltages. However, significant\ninitial capacity loss and large volume variations during cycles are\nthe primary restrictions for the practical application of Si-based\nanodes. Herein, we propose an affordable and scalable synthesis of\ndouble-layered SiO_<i>x</i>/Mg₂SiO₄/SiO_<i>x</i> composites through the magnesiothermic\nreduction of micro-sized SiO with Mg metal powder at 750 °C for\n2 h. The distinctive morphology and microstructure of the double-layered\nSiO_<i>x</i>/Mg₂SiO₄/SiO_<i>x</i> composite are beneficial as they remarkably\nimprove the reversibility in the first cycle and completely suppress\nthe volume variations during cycling. In our material design, the\noutermost layer with a highly porous SiO_<i>x</i> structure provides abundant active sites by securing a pathway for\nefficient access to electrons and electrolytes. The inner layer of\nMg₂SiO₄ can constrain the large volume expansion\nto increase the initial Coulombic efficiency (ICE). Owing to these\npromising structural features, the composite prepared with a 2:1 molar\nratio of SiO to Mg exhibited initial charge and discharge capacities\nof 1826 and 1381 mA h g^–1, respectively, with an\nICE of 75.6%. Moreover, it showed a stable cycle performance, maintaining\nhigh capacity retention of up to >86.0% even after 300 cycles.\nThe\nproposed approach provides practical insight into the mass production\nof advanced anode materials for high-energy LIBs.