Construction of a core–double-shell structured Si@graphene@Al 2 O 3 composite for a high-performance lithium-ion battery anode

The vast volume expansion of the Si anode during the charging process leads to rapid cycling performance fading and limits its applications in lithium-ion batteries. In this study, a unique core–double-shell structured porous Si@graphene@glycerin-Al 2 O 3 (p-Si@G@g-Al 2 O 3 ) composite is successfully prepared by using a porous Si (p-Si) microsphere as the core and graphene(G)/Al 2 O 3 as the double shell layer via an electrostatic self-assembly strategy and a glycerin-involved sol–gel process. The addition of glycerin can reduce the nucleation growth rate of Al(OH) 3 during the sol–gel process and enable more uniform deposition of an ultrathin Al 2 O 3 layer on p-Si@G microspheres. Owing to the crucial role of the lithiated Al 2 O 3 (LiAlO 2 )/G double shell layer in shielding the inner p-Si microsphere from the electrolyte and consolidating the mechanical structure of the p-Si microsphere, the synthesized p-Si@G@g-Al 2 O 3 shows good cycling stability with a high reversible capacity of 1804.5 mA h g −1 at 0.2 A g −1 and excellent rate capacity with a capacity of 439 mA h g −1 at 8 A g −1 , superior to those of p-Si@G and p-Si electrodes. Moreover, the electrochemical performance of p-Si@G@g-Al 2 O 3 can also be further improved by ∼10% by only adding 5 wt% of carbon nanotubes (CNTs) in a slurry, due to the good capability of CNTs in building the interconnecting network between p-Si@G@g-Al 2 O 3 microspheres.