Sustainable silicon anodes facilitated via a double-layer interface engineering: Inner SiOx combined with outer nitrogen and boron co-doped carbon

Abstract

Silicon-based (Si) materials are promising anodes for lithium-ion batteries (LIBs) because of their ultrahigh theoretical capacity of 4200 mA h g−1. However, commercial applications of Si anodes have been hindered by their drastic volume variation (∼300%) and low electrical conductivity. Here, to tackle the drawbacks, a hierarchical Si anode with double-layer coatings of a SiOx inner layer and a nitrogen (N), boron (B) co-doped carbon (C–NB) outer layer is elaborately designed by copyrolysis of Si–OH structures and a H3BO3-doped polyaniline polymer on the Si surface. Compared with the pristine Si anodes (7 mA h g−1 at 0.5 A g−1 after 340 cycles and 340 mA h g−1 at 5 A g−1), the modified Si-based materials (Si@SiOx@C–NB nanospheres) present superior cycling stability (reversible 1301 mA h g−1 at 0.5 A g−1 after 340 cycles) as well as excellent rate capability (690 mA h g−1 at 5 A g−1) when used as anodes in LIBs. The unique double-layer coating structure, in which the inner amorphous SiOx layer acts as a buffer matrix and the outer defect-rich carbon enhances the electron diffusion of the whole anode, makes it possible to deliver excellent electrochemical properties. These results indicate that our double-layer coating strategy is a promising approach not only for the development of sustainable Si anodes but also for the design of multielement-doped carbon nanomaterials.