Synthesis And Characterisation Of Sn/C-based 1D Nanomaterials And Their Application In Lithium-ion Batteries

Tin based materials have become one of the most promising candidates in electrode materials for commercial lithium-ion battery mainly due to their high theoretical capacity. However, there are many fatal shortcomings such as poor conductivity, high volume change brought about during charge and discharge, the pulverization of electrode materials and so on, which lead to the poor cycling performance.In this paper, one dimensional Sn/C hybrid nanomaterials have been prepared by hydrothermal method and further their electrochemical performances have been investigated. Carbon nanotubes (CNTs), potassium stannate (K2SnO3), glucose and cotton fibers etc. have been used as starting materials to synthesize the Sn/C composite with various morphologies and structures, respectively. The as-prepared samples have been characterized with different types of instruments including scanning electron microscope (SEM), X-ray diffraction (XRD), thermo gravimetric analyzer (TGA) and transmission electron microscope (TEM), and further their lithium ion storage performance have been investigated by cyclic voltammetry (CV), galvanostatic charge/discharge experiments, as well as Electrochemical Impedance Spectroscopy (EIS) method.CNTs/SnO2 composite materials with core-shell structures were synthesized from the aqueous solution with CNTs and K2SnO3 by hydrothermal method. The results showed that the CNTs/SnO2 composite materials could be obtained in a wide temperature range of 120-200℃. The acid treatment process and the addition amount of urea in the precursor solution could exerted great effect both on the SnO2 content and the morphology of products. Using acid-treated CNTs as starting materials, the products synthesized below 180℃ by hydrothermal methods when adding 8g urea into 30ml precursor solution, followed by 500℃ heat treatment,, showed a better electrochemical performance with a specific discharge capacity of 340 mAh/g after 50 cycles.In order to improve the cycling performance of CNTs/SnO2 composite nanomaterial, the CNTs/SnO2@C composites materials with core-shell structure were further prepared. Firstly, CNTs/SnO2@C composite were further obtained by carbon-coating process, in which the CNTs/SnO2 composite synthesized in advance by hybrothermal method and the glucose were used as raw material and as the carbon source, respectively.. The composite prepared by hydrothermal method under 180℃ for 4h, followed by the carbonization process under 500 ℃ was uniformly covered by 3nm-thick disordered carbon and delivered a capacity of more than 430 mAh/g when cycled after 50 cycles. Furthermore, CNTs/SnO2@C composites materials were also synthesized by one-pot hydrothermal method using CNTs, K2SnO3 and glucose as starting materials. In the one pot hydrothermal method, alternating temperature might be the critical factor to obatin the novel CNTs/SnO2@C composites.In order to save cost, as well as to favor mass production, one dimensional CTs/SnO2 and CTs/SnO2@C composite materials with different morphologies and structures were prepared from cotton fibers. The one-dimensional CTs/SnO2 nanomaterials have been prepared from cotton fibers and K2SnO3 aqueous solution by hydrothermal method while the one dimensional CTs/SnO2@C nanomaterials were obtained by soaking the CTs/SnO2 composite in PVP solution, followed by heat treatment. The pre-heat treatment of primitive cotton fibers and the heat treatment of product before carbon coating process would be in favor of increasing the content of SnO2 in the composite and further of improving electrochemical performance. There remains 70 percent of SnO2 in the composites experiencing 4-hours heat-treatment of cotton and 1.5-hours heat-treatments of the precursor of CTs/SnO2, which exhibited a specific discharge capacity of 390mAh/g when cycled after 50 cycles.