Preparation and electrochemical properties of Si@C/CNTs composites derived from crosslinked chitosan

Silicon possesses high theoretical specific capacity but suffers from huge volume expansion and poor electrical conductivity during cycling, resulting in significantly reduced capacity and poor cycling stability. These issues could greatly be alleviated by the encapsulation of silicon nanoparticles in carbon materials. Therefore, a three-dimensional (3D) network Si@CTS precursor was prepared in this work through in-situ encapsulation of silicon nanoparticles in stable hydrogel formed by crosslinking chitosan with glutaraldehyde as a cross-linking agent. After freeze-drying followed by oxidation stabilization at 280 ºC for 2 h under air and subsequent heat treatment at 800 ºC for 2 h under Ar atmosphere, uniformly distributed 3D Si@C composites were obtained. The effects of added amounts of carbon nanotubes (CNTs) on the structures and electrochemical properties of the as-obtained composites were investigated. The results showed uniformly distributed silicon nanoparticles in the amorphous carbon layer owing to the freeze-drying and oxidation treatments conducive to maintaining the skeleton structure of the material. The amorphous carbon and appropriate CNTs effectively buffered the volume changes, as well as improved the ionic and electronic conductivity. Si@C/CNTs-10% showed better comprehensive electrochemical performances at CNTs added amount of about 10 wt%. The discharge specific capacities at 0.1 A·g −1 after 150 cycles, as well as at 1.0 and 2.0 A·g −1 after 1000 cycles were estimated to 943.1, 461.3, and 123.1 mAh·g −1 , respectively. Chitosan was crosslinked by glutaraldehyde as a crosslinking agent to in-situ encapsulate silicon particles and carbon nanotubes, mainly due to the reaction of amino and aldehyde groups on chitosan to generate schiff bases. After freeze-drying and heat treatments, 3D Si@C/CNTs composites were obtained. • A Si/C anode was made by encapsulating Si nanoparticles with crosslinked chitosan. • The crosslinking reaction was carried out at room temperature by glutaraldehyde. • The materials' 3D skeleton structure can be kept by freeze drying and oxidation. • The materials' unique conductive structure makes good electrochemical properties.