Fabrication and understanding of CuSi-Si@carbon@graphene nanocomposites as high-performance anodes for lithium-ion batteries.

Besides silicon's low electronic conductivity, another critical issue for using silicon as the anode for lithium-ion batteries (LIBs) is the dramatic volume variation (>300%) during lithiation/delithiation processes, which can lead to rapid capacity fading and poor rate capability, thereby hampering silicon's practical applications in batteries. To mitigate these issues, herein, we report our findings on the design and understanding of a self-supported CuSi-Si@carbon@graphene (CuSi-SCG) nanocomposite anode. The nanocomposite is composed of CuSi-Si core and carbon shell with core/shell particles uniformly encapsulated by graphene nanosheets anchored directly on a Cu foil. In this design, the carbon shell, the highly elastic graphene nanosheet, and the formed conductive and inactive CuSi phase in Si serve as buffer media to suppress volume variation of Si during lithiation/delithiation processes and to facilitate the formation of a stable solid electrolyte interface (SEI) layer as well as to enable good transport kinetics. Chemomechanical simulation results quantitatively coincide with the in situ TEM observations of volume expansion and provide process details not seen in experiments. The optimized CuSi-SCG nanocomposite anode exhibits good rate performance and delivers reversible capacity of 483 mA h g (based on the total weight of CuSi-SCG) after 500 cycles with capacity retention of about 80% at high current density of 4 A g, rendering the nanocomposite a desirable anode candidate for high-performance LIBs.