Anchoring silicon on the basal plane of graphite via a three-phase heterostructure for highly reversible lithium storage

Abstract

Interfacial stability is crucial to electrochemical performance, especially the cycle life and Coulombic efficiency (CE), of anodes for lithium-ion batteries (LIBs). However, stabilization of silicon (Si) nanoparticles on the basal plane of graphite nanosheets (GNs) and their effect on both cycling performance and CE have been lacking. Herein, deposition of Si nanoparticles on the basal plane of GNs is achieved by magnesiothermic reduction of mixture of silica (SiO2) nanoparticles and GNs. When the molar ratio of SiO2 to GNs in the reactant is above 0.33, Si nanoparticle and GN form an interfacial 3C-SiC layer. Both Si and interfacial 3C-SiC are oriented in their [111] crystallographic direction in parallel with [002] direction of GNs. The energetics of this three-phase heterostructure, (111) [11¯0]Si//(111) [11¯0]3C-SiC//(002) [110]GNs, is calculated using density functional theory (DFT), which indicates strong bonding at two interfaces of Si(111)/3C-SiC(111) and 3C-SiC(111)/GNs(001). The composite anode with a three-phase heterostructure demonstrates a high initial CE of 97.8% and a rapid increase of the CE to 99.4% after only five cycles with a capacity retention of 82.9% after 100 cycles, owing to the strong bonding between Si and GNs via the interfacial 3C-SiC layer, which maintains electrical connection despite the volume changes of Si during cycling.