Preparation And Lithium Storage Properties Of Sn-based Compound Nanoparticles

Li-ion batteries have been widely used in many fields for its outstanding energy storage and electrochemical properties. Eletrode materials, as a key factor to the development of Li-ion batteries, have been the focus since the concept of Li-ion batteries is proposed. Li-ion rechargeable batteries have used LiCoO₂ for the anode and carbon for the cathode. Though the development research on application of lithium ion batteries has made their capacity improve largely in recent years, energy density of the batteries with current electrode materials is reaching the theoretical limit. The only way to meet demand for even more power is to find a new electrode material. Sn-based materials have been studied extensively for their high theoretical Lithium insertion capacity. However, these materials have a serious drawback when used as the anode, which is the poor cycle performance caused by its volume expansion/shrinkage during the charge/discharge of lithium ion batteries. It is expected that materials possess high capacity retention and stable microstructure by decreasing the size of electrode materials. It is an effective method to modificate the electrochemical properties by nanotechnology.In this paper, Fe-Sn, Ni-Sn and Mg-Sn nanoparticles were prepared by an arc discharge method. The phases, morphology, and thermal properties of nanoparticles were investigated by means of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and differential scanning calorimeters (DSC). As for Fe-Sn system, the synthesized nanoparticles have a shell-core structure with a SnO₂ shell of 5-10 nm in thickness and a core of polycrystalline intermetallic compounds. It was found that the intermetallic compounds FeSn₂ and Fe₃Sn₂ were generated and coexist with the Sn phase as a single nanoparticle. The DSC analysis showed that Fe-Sn nanoparticles have high oxidation resistance in air. Additionally, a mechanism of the nanoparticle formation was also interpreted on the basis of experimental results and thermodynamic principles. As for Ni-Sn system, XRD results indicate that Ni₃Sn₄ coexist with Ni and Sn in nanoparticles. Compositions of compressed bulk mixture are different from those of corresponding nanoparticles, which attribute to larger evaporating rate of Ni compared to that of Sn. In view of non-equilibrium reaction and very short reaction time, Ni₃Sn₄ coexists with other phases in nanoparticles. In comparison with Sn nanoparticles with low melting point, intermetallic Ni-Sn nanoparticles exhibit high thermal stability, and mild oxidation reaction can be observed at temperatures around 725 K. As for Mg-Sn system, XRD results indicate that multi-phases (Mg, Sn, and Mg₂Sn) coexist in nanoparticles and Mg₂Sn is the main phase for all samples under a condition of this work. TG-DTA results indicate that nanoparticles exhibit good oxidation resistance, and obvious oxidation reaction can not be observed under the temperatures of 700 K.In addition, Mg-Sn nanoparticles have been evaluated as an anode in lithium cells. Charge and discharge capacities approaching 193 mAh/g and 150 mAh/g in the first cycle, respectively. After 30 cycles, the charge capacity is 61 mAh/g. As a potential anode material for Lithium ion batteries, Mg₂Sn have many drawbacks and must be modificated in order to satisfy practical applications.