Engineering the Core–Shell-Structured NCNTs-Ni2Si@Porous Si Composite with Robust Ni–Si Interfacial Bonding for High-Performance Li-Ion Batteries

A new strategy has been innovatively proposed for wrapping the Ni-incorporated and N-doped carbon nanotube arrays (Ni-NCNTs) on porous Si with robust Ni-Si interfacial bonding to form the core-shell-structured NCNTs-Ni₂Si@Si. The hierarchical porous silicon core was first fabricated via a novel self-templating synthesis route based on two crucial strategies: in situ thermal evaporation of crystal water from the perlite for producing porous SiO₂ and subsequent magnesiothermic reduction of porous SiO₂ into porous Si. Ni-NCNTs were subsequently constructed based on the Ni-catalyzed tip-growth mechanism and were further engineered to fully wrap the porous Si microparticles by forming the Ni₂Si alloy at the heterojunction interface. When the prepared NCNTs-Ni₂Si@Si was evaluated as the anode material for Li-ion batteries, the hierarchical porous system in the Si core and the rich void spaces in carbon nanotube arrays contributed to the remarkable accommodation of volume expansion of Si as well as the significant increase of Li⁺ diffusion and Si utilization. Moreover, the Ni₂Si alloy, which chemically linked the Ni-NCNTs and porous Si, not only provided good electronic contact between the Si core and carbon shell but also effectively prevented the CNTs' detachment from the Si core during cycling. The multifunctional structural design rendered the whole electrode highly stable and active in Li storage, and the electrochemically active NCNTs-Ni₂Si@Si electrode delivered a high reversible capacity of 1547 mAh g^-1 and excellent cycling stability (85% capacity retention after 600 discharge-charge cycles) at a current density of 358 mA g^-1 (0.1 C) as well as good rate performance (778 mAh g^-1 at 2 C), showing great potential as an efficient and stable anode for high energy density Li-ion batteries.