Year

2015

Degree Name

Master of Engineering - Research

Department

Institute for Superconducting and Electronic Materials

Abstract

Lithium (Li)-ion batteries have attracted wide attention for grid-scale energy storage application in the last several years. The price of lithium-ion batteries is dramatically constrained, however, by the extent of lithium sources. Therefore, sodium-ion batteries are regarded as a substitute for lithium-ion batteries because of both the low cost associated with the high natural abundance of sodium and the decent energy densities, which is similar to those for Li. This Master's work on sodium-ion batteries can be mainly divided into two parts: 1) synthesis of antimony-tin alloy materials for anode materials in sodium-ion batteries; 2) synthesis and characterization of carbon-coated Graphene-SnO2 (i.e., Gr-SnO2-C), carbon-coated Graphene-SnS (Gr-SnS-C) as anode materials for rechargeable sodium-ion batteries.

Alloy-based materials were prepared by a simple and low-cost technique with the addition of a reducing reagent. Firstly, polyacrylonitrile (PAN) was first dissolved into N,N-dimethylformamide(DMF). Then, antimony chloride and tin chloride dihydrate were added to the solution, followed by a simple electrospinning method. After carbonization, SnSb alloy could be obtained. By this method, nanofibers with a diameter of 100nm nanofiber could be obtained, which creates pathways for ion conduction. At the same time, numerous factors that have an impact on performance and many comparisons were investigated, for example, the selection of different binders, different electrolytes, etc. SnSb alloy shows a relatively higher electrochemical performance than pure Sb and pure Sn. In terms of the selection of binders, carboxymethyl cellulose (CMC) binders have higher performance than PVDF. What is more, the composites which contain PAN also provide higher capacity and better rate capability. After several comparisons, SnSb nanofiber which uses CMC as binder and PAN in its solution was found to have the best electrochemical performance (480mAh g-1 after 100cycles) with the current density of 270mA g-1. The excellent electrochemical performance indicates that the SnSb alloy nanofiber could be a very promising candidate as anode material for sodium-ion batteries.

For carbon coated Graphene-SnS (Gr-SnS), firstly, Graphene-SnO2 (Gr-SnO2) material was prepared by an environmentally friendly and simple hydrothermal technique. Then, carbon-coated SnO2/graphene nanosheets (Gr-SnO2-C) were also synthesized on the gram scale via a similar hydrothermal method, followed by carbonization. In this method, the obtained SnO2 particles are uniformly distributed on the surface of the graphene and the carbon coating layer, which can work together to effectively maintain the stability of the structural arrangement, serve as good electronic conductors, and allows Na+ access. In addition, the surface carbon coating layer can effectively separate the SnO2/graphene sheets, preventing aggregation during the charge/discharge processes. After sulfidation, the Gr-SnO2-C was transformed to carbon-coated Graphene-SnS (Gr-SnS-C). The composite provides quite good electrochemical performance, 680mAh g-1 at the current density of 90mAg-1. This work reveals a new method to prepare carbon-coated metal oxide on graphene, which could be used to prepare electrode materials with excellent electrochemical performance for sodium-ion batteries.

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