Alloying Reaction Materials for LIB Anode

Abstract

The critical size of the GeO2 nanoparticle for lithium battery anode applications and identity its quantum confinement and its related effects on the electrochemical performance were determined. GeO2 nanoparticles with different sizes of ~ 2 nm, ~6 nm, ~10 nm and ~35 nm were prepared by adjusting the reaction rate, controlling reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO2 nanoparticles, the 6 nm-sized GeO2 showed the best electrochemical performance. Unexpectedly smaller particles of the 2 nm-sized GeO2 showed the inferior electrochemical performances compared to those of the 6 nm-sized one. This was due to the low electrical conductivity of the 2 nm-sized GeO2 caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. The SiGe alloy for anode material of LIB has been also studied frequently. However, the research for concentration control of Si or Ge element in SiGe alloy has been reported rarely. Here, controlling overpotential attributed to Si concentration gradient via surface segregation of Si was successfully achieved, leading to fine-adjustment for electrochemical properties. In the manuscript, we provide details about synthesis and characterizations of SiGe alloy nanowire counting segregation degree of Si and its sophisticated anode performance control for Li ion battery. We believe that our findings will contribute not only for the fundamental understandings about the surface chemistry involved with segregation control, but also for research guide to fine overpotential control and its related effect. And we employ a facile hydrothermal method for deposition of MoS2 on the surface of the hierarchical nano-structure of graphene (H-NG), which exhibite high surface area and high electron conductivity. Since the H-GNs can provide highly efficient electronic pathways and surface area during the charge/discharge cycles of LIBs, the fabricated LIB exhibits high capacity and excellent cycling performance. The Kirkendall effect is the noble method for preparing hollow metallic nanostructure without any template. This effect caused by different diffusivities of atoms in adjacent two phases, that is, the fast atoms in inner layer diffuse via the slow atoms in outer layer. During diffusion process, supersaturation of lattice vacancies develops into interior pore which is inner part of final hollow structure. This strategy has been extensively used for development of hollow metal oxide or sulfide. However, there is little attention of the Kirkendall effect in semiconductor materials. Although a few trials are reported, the diffusion mechanism in semiconductor has remained elusive. Here, we synthesized silicon and germanium hollow structures by semiconductor atom diffusion via its oxide and investigated the diffusion mechanism in semiconductor materials by computational simulation. We could control the depth of diffusion layer that is internal empty space. We also show that application in LIB anodes of these hollow semiconductor nanostructures is fascinating for future anode materials.