Silicon Nanosheets Confined into Nitrogen-Doped Porous Carbon Microcage Enabling Efficient Lithium Storage

Abstract

Silicon (Si) is regarded as the promising next-generation commercial anode in high energy lithium-ion batteries (LIBs), attributed to its natural abundance, high theoretical capacity (4200 mAh g-1) and low voltage profile (<0.5 V). However, the huge volume change and tremendous capacity fading of silicon during lithiation/delithiation have been hindering its practical application. Herein, a facile and scalable method was proposed to prepare the Si nanosheets limited in 3D porous N-doped carbon microcages (Si@NCM) particles with ternary oxygen-bridged covalent chemical bond, i.e., Si-O-C bonding. As a kind of anode materials, the Si@NCM rendered an extremely surprising reversible capacity of 930.2 mAh g-1 after 2000 cycles at a current density of 5 A g-1 at ambient temperature. More interestingly, it afforded an overwhelming capacity of 950.7 mAh g-1 after 3000 cycles at 20 A g-1 at 80°C, with 89.8% capacity retention, and an excellent rate capability of 594.8 mAh g-1 at 50 A g-1. The impressive electrochemical performance was ascribed to its multi-scaled network structure and moderate covalent bonding, which enhanced Li+ diffusion kinetics and accommodated the volume expansion of the silicon. This simple fabrication approach holds great commercial possibility in practical application of next-generation advanced LIBs.

Keywords: Silicon nanosheets, Si@NCM anode, Porous microsphere, Lithium ion batteries