Facile synthesis of carbon-coated silicon nanocomposite with tremella-like porous structure for superior lithium-ion storage.

Abstract

Silicon/carbon (Si/C) composites have been envisaged as one of the most promising anode materials for the next-generation lithium-ion batteries (LIBs) with high energy density, and constructing reasonable and cross-scale structures is crucial adjective for high-performance Si/C electrodes. Herein, a facile synthesis strategy was developed by combining gel coating, carbonization, and molten salt-assisted magnesiothermic reduction (MSA-MR), and a unique tremella-like Si/C composite with internal void structure (IV-Si/C) was successfully prepared. The working mechanisms of both sodium alginate (SA) and molten salt (NaCl) on the successful preparation of the target IV-Si/C nanocomposite were also investigated in detail. It was demonstrated that, α-L-guluronic (G) blocks in SA can be cross-linked with cations to promote the interactions with silicon dioxide (SiO2) particles, boosting uniform distribution of nanosized Si particles in the SA-derived carbon matrix. Meanwhile, NaCl generated from SA not only effectively boosted the crystallization of SiO2 during the high-temperature carbonization process but also can effectively inhibit the formation of inert SiC and strengthen reduction of carbon during the MSA-MR treatment, resulting in successful preparation of the tremella-like Si/C composite with abundant internal voids. Benefitting from its unique structure, when used as an alternative anode material for electrochemical lithium storage, the as-obtained IV-Si/C nanocomposite delivered a high reversible specific capacity of 1899.6 mAh g-1 with an initial Coulomb efficiency of 75.96% and superior rate capability and long-term cycling stability. This facile and low-cost synthesis strategy may shed light on the controllable preparation of functional nanomaterials with unique structures, especially high-performance Si/C anode materials for their large-scale application in LIBs.