A hierarchical porous hard carbon@Si@soft carbon material for advanced lithium-ion batteries.

Silicon (Si) is considered as one of the most potential commercial materials for the next-generation lithium-ion batteries (LIBs) owing to its high theoretical capacity and low voltage platform. However, the severe volume expansion and poor electric conductivity of Si anodes limit the practical application. Herein, a hierarchical porous hard carbon@Si@soft carbon (PHC@Si@SC) material was prepared by a chemical vapor deposition (CVD) and following calcination process. The differences in capacities and initial Coulombic efficiencies (ICEs) resulting from variations in silane deposition are demonstrated using PHC@Si as a model. To improve the cycling performance, a cheap pitch-derived soft carbon was introduced to protect the nano-Si to suppress the volume expansion. The formed PHC@Si@SC anode delivers a high capacity of 1625 mAh g and a high ICE of 86.8%, attributed to the excellent cooperation of hard and soft carbon. The capacity retention is 55% after 100 cycles with a harsh N/P ratio of 1.1 in a PHC@Si@SC||NCM811 full cell. This work provides a strategy, which is easy to scale up for practical application.