Encapsulating micro-nano Si/SiO_x into conjugated nitrogen-doped carbon as binder-free monolithic anodes for advanced lithium ion batteries

Silicon monoxide, a promising silicon-based anode candidate for lithium-ion batteries, has recently attracted much attention for its high theoretical capacity, good cycle stability, low cost, and environmental benignity. Currently, the most critical challenge is to improve its low initial coulombic efficiency and significant volume changes during the charge-discharge processes. Herein, we report a binder-free monolithic electrode structure based on directly encapsulating micro-nano Si/SiO_x particles into conjugated nitrogen-doped carbon frameworks to form monolithic, multi-core, cross-linking composite matrices. We utilize micro-nano Si/SiO_x reduced by high-energy ball-milling SiO as active materials, and conjugated nitrogen-doped carbon formed by the pyrolysis of polyacrylonitrile both as binders and conductive agents. Owing to the high electrochemical activity of Si/SiO_x and the good mechanical resiliency of conjugated nitrogen-doped carbon backbones, this specific composite structure enhances the utilization efficiency of SiO and accommodates its large volume expansion, as well as its good ionic and electronic conductivity. The annealed Si/SiO_x/polyacrylonitrile composite electrode exhibits excellent electrochemical properties, including a high initial reversible capacity (2734 mA h g^-1 with 75% coulombic efficiency), stable cycle performance (988 mA h g^-1 after 100 cycles), and good rate capability (800 mA h g^-1 at 1 A g^-1 rate). Because the composite is naturally abundant and shows such excellent electrochemical performance, it is a promising anode candidate material for lithium-ion batteries. The binder-free monolithic architectural design also provides an effective way to prepare other monolithic electrode materials for advanced lithium-ion batteries.