Dual carbon and void space confined SiOx/C@void@Si/C yolk-shell nanospheres with high-rate performances and outstanding cyclability for lithium-ion batteries anodes

Silicon-based anode materials with high theoretical capacity have great challenges of enormous volume expansion and poor electronic conductivity. Herein, a novel dual carbon confined SiOx/C@void@Si/C yolk-shell monodisperse nanosphere with void space have been fabricated through hydrothermal reaction, carbonization, and in-situ low-temperature aluminothermic reduction. Furthermore, the O/Si ratio and void space between SiOx/C core and Si/C shell can be effectively tuned by the length of aluminothermic reduction time. The SiOx/C core plays a role of maintaining the spherical structure and the void space can accommodate the volume expansion of Si. Moreover, the inner and outer carbons not only alleviate volume variation of SiOx and Si but also enhance the electrical conductivity of composites. Benefiting from the synergy of the double carbon and void space, the optimized VSC-14 anode affords prominent cycle stability with reversible capacity of 1094 mAh g-1 after 550 cycles at 200 mA g-1. By pre-lithiation treatment, the VSC-14 achieves an initial Coulombic efficiency of 93.27% at 200 mA g-1 and a reversible capacity of 348 mAh g-1 at 5 A g-1 after 4000 cycles. Furthermore, the pouch cell using VSC-14 anode and LiFePO4 cathode delivers a reversible capacity of 138 mAh g-1 at 0.2C. We hope this strategy can provide a scientific method to synthesis yolk-shell Si-based materials.