N-Enriched Porous Carbon/SiO2 Composites Derived from Biomass Rice Husks for Boosting Li-Ion Storage: Insight into the Effect of N-Doping.

Abstract

A N-enriched porous carbon/SiO2 (SiO2 /NC) composite from rice husks was prepared by ball milling and tested as a stable anode for lithium ion batteries (LIBs), in which the homogeneous dispersion of SiO2 nanoparticles and carbon matrix, and high level of N-doping can be realized simultaneously. The influence of N-doping on a series of SiO2 /NCs was systematically studied; this proved that the porosity, N-doping content, and electronic conductivity of SiO2 /NC can be controlled by adjusting common nitrogen sources (urea and melamine) and doping routes, including dry and wet milling, to reach a desirable balance of high capacity, long-term cyclability, and rate property. The optimized SiO2 /NC composite delivers a stably reversible capacity of 581 mA h g-1 at the high current load of 1.0 A g-1 at the 1000th cycle. The novel Li-storage mechanism of active silica in a composite was first proposed after observation of the N-doping effect that the redox reaction between SiO2 and Li+ is accelerated to transform into an alloying reaction of generated Si and Li+ , thus enhancing the reversible capacity. Moreover, kinetics analysis confirms that there is a combined Li-storage mechanism of battery-capacitive pattern in composite that contributes to fast charge transfer and ion diffusion during cycle.