Core-shell SiO@F-doped C composites with interspaces and voids as anodes for high-performance lithium-ion batteries

Core-shell F-doped carbon coated SiO composites with interspaces and some small voids (SiO@F-doped C) are successfully fabricated using bulk SiO as starting material. With the assistance of polytetrafluoroethylene (PTFE), both etching and carbon coating of SiO are firstly performed in a single step, which largely lowers the production cost of materials. The SiO@F-doped C composite obtained by annealing the mixture of SiO and PTFE with a mass ratio of 5:3 at 650 °C shows the highest stable discharge capacity with excellent cycling stability. It delivers a stable discharge capacity of about 975 mAh g −1 at a current density of 100 mA g −1 . Even after the current density increases to 1600 mA g −1 , a stable discharge capacity of about 553 mAh g −1 can be achieved. At a current density of 400 mA g −1 , the composite maintains a discharge capacity of 752 mAh g −1 after 350 cycles, the retention of which is 99.2% versus that in the second cycle. Compared with the annealed SiO, in addition to higher conductivity, the ions diffusion rate of the SiO@F-doped C composite increases 2.94 times while the volume expansion falls by more than half, which should be responsible for its significantly enhanced electrochemical performance.