The Studies On Stability Of Nanostructured Sn-Co Alloy Anodes For Lithium Ion Batteries

Due to the high theoretical specific capacity, Sn has been one of the promising anodes for new generation of lithium ion batteries. However, the volume expansion of Sn-based anodes during cycling leads to the poor cyclic stability, and limits their commercial applications. To accommodate the volume expansion effectively, Sn-Co@PMMA nanomaterials with core-shell structure have been synthesized, including nanoparticles and 3-D nanowire array.In galvanic replacement reaction, hollow Sn-Co nanoparticles with different thicknesses can be obtained by tuning the diameters of Co nanoparticles. The SnCo-20 hollow nanoparticles exhibit high reversible capacity, because the thinner thickness and larger hollow volume rate of hollow SnCo-20 nanoparticles could alleviate the volume expansion. Hollow Sn-Co@PMMA nanoparticles possess uniform PMMA layer, with the thickness of 25-35 nm. From the results, hollow Sn-Co@PMMA nanomaterials have superior cyclic stability. After 100 cycles, the capacity of hollow Sn-Co nanoparticles decays to 480 mAh/g, but the capacity of hollow Sn-Co@PMMA nanoparticles prepared by in situ polymerization retains 585 mAh/g with the coulomb efficiency of 99.8 %.In the process of electrodeposition, Sn-Co nanowire array with different lengths and diameters can be obtained by adjusting electrodeposition time and apertures of AAO templates. The results show that the shorter nanowire array has superior cyclic stability, because the structural advantage of 3D nanowire array can be maintained by shorter nanowires. Sn-Co@PMMA nanowire array prepared by perfusion method possesses uniform PMMA layer, with the thickness of 35 nm. The results show that the electrochemical performance of Sn-Co@PMMA nanowire array has been improved significantly. After 100 cycles, the capacity of Sn-Co nanowire array falls to 0.55 mAh/cm2, but the capacity of Sn-Co@PMMA nanowire array maintains 0.71 mAh/cm2 with the coulomb efficiency of 99.1 %.