Self-assembly of hierarchical microsized hard carbon-supported Si encapsulated in nitrogen-doped carbon as anode for lithium-ion batteries

Dramatic volumetric variation and poor cyclic stability are great challenges for the practical application of Si anode in lithium-ion batteries. In this work, hierarchical microsized hard carbon-supported Si encapsulated in nitrogen-doped carbon (HC/Si@NC) composites is successfully synthesized via electrostatic self-assembly between an intrinsic negatively charged hard carbon precursor and positively charged Si nanoparticles for the first time. Resorcinol formaldehyde resin sphere synthesized through a low-cost extended Stöber method is used as the carbon core precursor to support Si nanoparticles, followed by carbon coating and carbonization process to further fix Si on the carbon core and enhance the conductivity. The hierarchical structure where Si nanoparticles are tightly anchored onto the carbon core can significantly alleviate the volumetric expansion of Si, and the carbon can enhance the conductivity of the composites. As a result, the as-achieved HC/Si@NC composites exhibit outstanding cycling stability and good structural integrity maintenance. The composites deliver a reversible capacity of 541 mAh g −1 with a capacity retention of 92.1% after 100 cycles at a current density of 0.2 A g −1 and a capacity of 350 mAh g −1 after 300 cycles at a higher current density of 1 A g −1 .