| Lithium ion batteries (LIBs) with the advantages of high working voltage, high energy densityand environmental friendliness, has become the main research direction of new energy materials. In LIBs anode materials, the theoretical capacity of commercial carbon is only 372 mAh g-1, which has not been able to meet the increasing needs of business. The calculation results show that the metal tin is considered one of the most promising materials in lithium ion battery replacement, because it has a maximum theoretical specific capacity of 993 mAh g-1, which twice more than that of commercial carbon. However, the large volume change of the tin anode materilas causes a drastic pulverization during the cycling performance, which lead to the deterioration of the electrode materials, limiting its commercial application. The electrochemical properties of metal tin materials will be improved by the nanometer stucture and the reasonable modification. This paper aims to systematically study the structure and characterization of metal tin, alloy and carbon-coated nanocomposite, to improve the electrochemical performances of intercalation/deintercalation lithium, to discuss scientific questions on the preparation and properties of materials, to make the foundation for research and application of new tin-based nanostructure anode materials for lithium ion batteries. In this paper, DC arc discharge method as the mainly for fabrication of nanomaterials method, combined with specific process and modification technology, effectively improves the properties of tin based materials. The main results are as follows:(1) Preparation and properties of elemental tin and tin alloy nanoparticles.Elemental metal tin nanoparticles (NPs) were in situ synthesized by DC arc plasma method in a mixture of hydrogen and argon atmosphere, the average size are 50～80 nm, the electrode shows a initial specific capacity of 935 mAh g-1, and it shows a large volume change of the tin anode materilas causes a drastic pulverization during the cycling performance, which lead to the deterioration of the electrode material, and the reversible capacity just reduces to 7 mAh g-1 after 4 cycles. In order to alleviate the volume expansion during cyclings, the first measure is introducing inert elements (Fe, Cu) to form intermetallic compouds; The second is forming tin oxide.The average size of Sn-Fe NPs are 30～100 nm, and the electrode shows the initial charge/discharge specific capacity of 221/449 mAh g-1, but the reversible capacity is reduced to 11 mAh g-1 after 50 cycles. For the system of Sn-Cu NPs electrode, the average size are 100～150 nm, the initial discharge capacity is 416.50 mAh g-1, and the second one is reduced to 90 mAh g-1. The capacity fading is more serious. However, the effect is limited to using alloy nanoparticles for relieving the volume expansion.The initial charge/discarge specific capacity of tin oxide nanoparticles are 315.90/907.50 mAh g-1, and the reversible capacity is reduced to 47 mAh g-1 after 3 cycles. Compared with the tin nanoparticles, its stability has improved, but still cannot meet the requirements.(2) Preparation and properties of carbon coated tin-based nanoparticles.Carbon coated tin-based nanocomposites (NCs) with a typical core/shell structure were in situ synthesized by DC arc discharge method in methane atmosphere. The Sn/C NCs present a uniform structure of carbon nanotubes (CNTs). Tin is partially-filled into multi-wall CNTs (MWCNTs), average size of which is about 40 nm in diameter,200-300 nm in length and 5-7 nm in thickness. Te electrochemical results show a relatively low initial discharge specific capacity of 850 mAh g-1. It maintained at 380 mAh g-1 after 15 cycles, which shows a better cycle performance. Arc discharge method is firstly used to in-situ fabricate Sn/C NCs in the carbon rich condition, and it creats a new path for the preparation of non-catalytic activity metal components in the nanometer of Sn/C composite.The catalytic active component of Sn-Fe/C NCs with a core/shell structure were in-situ synthesized by DC arc discharge method in the methane atmosphere. For the electrochemical properties of Sn-Fe/C NCs, the initial charge/discharge specific capacity are 520/818 mAh g-1, which with a stable cyclic performance, the reversible specific capacity is maintained at 373 mAh g-1 after 50 cycles. Sn-Ni/C NCs were synthesized with the same method, the initial charge/discharge specific capacity are 193/362 mAh g-1, the reversible specific capacity is maintained at about 150 mAh g-1 after 500 cycles. Dual activity of Sn-Al/C NCs were fabricated with the same method, the initial charge/discharge specific capacity are 212/476 mAh g-1, and the reversible capacity is 125 mAh g-1 after 100 cycles. SnOx/C NCs electrode shows the initial discharge specific capacity of 882 mAh g-1, the coulombic efficiency is as high as 98% after 20 cycles. Compared with the cycling performance of carbon-free tin based materials, carbon-coated tin based materials has a high stable properties.(3) The interface structure of Sn/C and Sn-Fe/C NCs electrode were in-depth studied by the electrochemical impedance spectroscopy (EIS) method. By the fittings, the exchange current density on the surface of Sn/C NCs is three times than that of Sn NPs. The Li+ diffusion rate of Sn-Fe/C NCs electrode is five times than that of Sn-Fe NPs, the results further reflect that addictive carbon can provid good electrical conductivity, benefit to electron exchange and Li+ diffusion rate during lithiation/delithiation, confirming that carbon composite nanostructure is an effective way to improve the performance of the electrode. |
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