Synthesis Of Sulphide Composites And Lithium (Sodium) Storage Properies

"Energy crisis" and "environmental pollution" is the two serious problems, which have received considerable attention since2000s. The development of electric vehicles (could be decrease dependence on fossil fuels and reduced carbon emissions) and large-scale green energy storage system (deployment of renewable energy resources) is the main way to solve this problem. Lithium (sodium) ion battery and supercapacitor et al, with the many advantages, such as:high energy density, high power density, long life, cheaper and environmental protection, have become the most promising electrical energy storage. Now, the commercialized graphite and other carbon for lithium (sodium) ion batteries are very difficult to break through performance it only from the battery assembly technological. Especially, the lithium ion battery and sodium ion battery has important significance for the development of electric vehicle and large-scale green energy storage. Therefore, the development high performance lithium ion battery and sodium ion battery electrode material is more and more importance. Recent progress has demonstrated that sulphide composites are very promising candidates of electrode material for lithium (sodium) ion battery based on their unique physical and chemical properties, such as conductivity, mechanical and thermal stability and cyclability. In this paper, we have fabricated SnS2-Graphene composite, ternary Cu2SnS3and CuFeS2, which were researched their lithium (sodium) storage properties. The main results and new findings in this work are summarized as follows:(1) In chapter2, we design a novel2D layer SnS2/graphene nanosheet composite with highly reversible lithium ion storage. The high lithium storage performance exhibit in three aspects:first, the specific capacity of this composite is high and good cycle life (it could deliver a charge capacity of1063mAh g-1for at least100cycles at0.2A g-1and918mAh g-1even after500cycles at1A g-1); second, the first cycle columbic is as high as89.7%; third, this composite electrode still could deliver a reversible capacity of712mAh g-1at5A g-1. The outstanding electrochemical performance of this composite is due to the unique2D layer structure of this composite.(2) The idea of sodium-ion batteries as a substitute of lithium-ion batteries for grid-scale energy storage was initially driven by cost considerations. Hence there is a strong current interest in research high-performance sodium-ion batteries electrode marterials. In chapter3, we have firstly developed a SnS2-RGO composite with excellent electrochemical performance as the anode of sodium-ion batteries. The SnS2-RGO electrode demonstrated a high charge specific capacity (630mAh g-1at0.2A g-1), good rate performance (544mAh g-1at2A g-1) and long cycle-life (500mAh g-1at1A g-1for400cycles). The performance surpasses any other NIB anode reported in the literature to date. The excellent electrochemical performance could be attributed to the SnS2layered structure where the increased interlayer spacing could better accommodate the volume change in Na-Sn insertion and de-insertions; and fast collection and conduction of electrons through a highly conductive RGO network.(3) In chapter4, ternary Cu2SnS3mesoporous nanospheres and cabbage-like nanostructures are synthesized by a simple solvothermal route. A different structures formation mechanism was controled by the reactant and surfactant. Besides, a possible electrochemical reaction mechanism was proposed based on cyclic voltammetry testing results and confirmed by subsequent ex situ XRD studies. By comparison, the Cu2SnS3nanostructures electrodes deliver a better lithium storage and cycle life performance, which is the first reversible capacity as high as842mAh g"1and remain at621mAh g"1after50cycles (only436mAh g-1after50cycles of mesoporous nanospheres).(4) In chapter5, we report a novel ternary CuFeS2microstructure by a simple solvothermal route. The CuFeS2microstructures have been shown an admirable lithium storage property. The first discharge and charge specific capacity of767and614mAh g-1at0.2A g-1, respectively. The first coulombic efficiency is80%. A good rate performance up to4A g"1, the discharge specific capacity is-400mAh g-1. The electrode was also very stable to cycling; providing a nearly unvarying capacity of-600mAh g-1at0.5A g-1even after400charge-discharge cycles. We have also studied the sodium storage property of the CuFeS2microstructures. The first discharge specific capacity628mAh g-1is and charge specific capacity of511mAh g-1, which is the the initial irreversible capacity loss of18.6%. The ternary CuFeS2microstructure is showing excellent lithium storage performance, and the synthesis approach is very simple and inexpensive. This is providing valuable experience for studing other sulphide materials as lithium (sodium) ion battery.