One-Step Low-Temperature Molten Salt Synthesis of Two-Dimensional Si@SiO_x@C Hybrids for High-Performance Lithium-Ion Batteries

Various strategies have been developed to mitigate the huge volume expansion of a silicon-based anode during the process of (de)lithiation and accelerate the transport rate of the ions/electrons for lithium-ion batteries (LIBs). Here, we report a one-step synthetic route through a low-temperature eutectic molten salt (LiCl–KCl, 352 °C) to fabricate two-dimensional (2D) silicon–carbon hybrids (Si@SiOx@MpC), in which the silicon nanoparticles (SiNPs) with an ultrathin SiOx layer are fully encapsulated by graphene-like carbon nanosheets derived from a low-cost mesophase pitch. The combination of an amorphous graphene-like carbon conductive matrix and a SiOx protective layer strongly promotes the electrical conductivity, structure stability, and reaction kinetics of the SiNPs. Consequently, the optimized Si@SiOx@MpC-2 anode delivers large reversible capacity (1239 mAh g–1 at 1.0 A g–1), superior rate performance (762 mAh g–1 at 8 A g–1), and long cycle life over 600 cycles (degradation rate of only 0.063% every cycle). When coupled with a homemade nano-LiFePO4 cathode in a full cell, it exhibits a promising energy density of 193.5 Wh kg–1 and decent cycling stability for 200 cycles at 1C. The methodology driven by salt melt synthesis paves a low-cost way toward simple fabrication and manipulation of silicon–carbon materials in liquid media.