Microstructures of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode in a 10 Ah lithium ion battery (LIB) after 700 charging-discharging cycles at 60°C are investigated by X-ray diffraction (XRD), Rietveld refinement, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HR-TEM). The phase transition of H1 (initial hexagonal phase) to H2 (second hexagonal phase) is irreversible, and after that the phase of H2 is an active material during cycling. There are two consecutive layered phases H2 (H2-1 and H2-2) in charged state (4.2V) cathode while three H2 phases (H2-2’, H2-3, H2-4) in discharged state (3.0 V) one, respectively. And 2.5 wt% H2 phase is electrochemically inactive. The crystallite size decreases while strain increases, the degree of Li/Ni cation disordering also increases as well as many pulverized particles with a large number of cracks and voids appear in the cycled cathode compared to the pristine material. Besides, “active” lithium is severely irreversible consumed in the full cell system. The primary reasons for capacity fade of the positive electrode in commercial LIB are summed up as follows: i) formation of the defects in the bulk material, ii) existence of inactive H2 phase, iii) high degree of Li/Ni cation disordering and iv) the reduction of the “active” lithium in cathode.

Pb plays an important role in determining the morphologies and mechanical properties of the Mg₂Si phase in Mg-2.5Si-xPb alloys. As the amount of Pb increases from 0.4 wt.% to 1 wt.%, the primary Mg₂Si phase is refined during solidification. Its morphologies transform from equiaxed-dendrite to polygonal and finally to roughly circular. The key reason for morphology evolution is the preferential adsorption of Pb atoms on Mg₂Si {100} surfaces to suppress the growth rate along the ⟨100⟩ directions, which is demonstrated by the adsorption model based on first principles. In addition, the hardness of the Mg₂Si phase decreases with the increasing solution content of Pb according to the results of the nanoindentation. With the addition of Pb at 1 wt.%, Pb content in the primary Mg₂Si phase reaches a maximum of 0.4 wt.%, and the hardness of the primary Mg₂Si phase reaches a minimum of 3.64 GPa. This reduction in hardness is attributed to the augmented ionic bond ratio resulting from the solution of Pb, which concurrently enhances the toughness of the Mg₂Si phase.