Cobalt-carbon framework encapsulation as solid electrolyte interphase ensures stable SiO_x anodes for lithium storage

Non-stoichiometric silicon oxide (SiO_x, 0<x<2) is a promising anode material for lithium batteries. However, it suffers from low intrinsic conductivity and large volume expansion. In particular, reaching a stable solid electrolyte interphase (SEI) is difficult due to continuous electrolyte consumption. In this work, hollow silicon oxide (h-SiO_x) spheres were encapsulated in cobalt–carbon (Co–C) frameworks and their derived nitrogen-doped carbon nanotube networks (N-CNTs). This design solved the problems of electrolyte depletion and repetitive formation of SEI layers and enabled fast kinetics. In addition, the flexible carbon nanotubes and metal–carbon solid frameworks of the prepared materials provide mechanical supports, which can adapt to the volume change of SiO_x. The h-SiO_x@Co@N-CNTs exhibit superior cycling stability and high-rate capability as anode materials for lithium-ion batteries. It delivered a capacity of 701 mAh g⁻¹ and a capacity retention of 100% over 370 cycles at a current density of 0.2 A g⁻¹. In addition, the capacity did not fade after 500 cycles at a current density of 1.0 A g⁻¹. The result demonstrates the advantage of the synthesized structure for lithium-ion batteries, which can also give some inspiration for this material optimization.