Showing papers by "Penghao Xiao published in 2013"
TL;DR: In this article, a layered sulfide, Na0.5NbS2 (space group: P63/mmc), was synthesized by a conventional solid-state reaction as an electrode material for a Na-ion battery.
Abstract: A layered sulfide, Na0.5NbS2 (space group: P63/mmc), was synthesized by a conventional solid-state reaction as an electrode material for a Na-ion battery. Galvanostatic Na insertion/extraction was performed to characterize the system NaxNbS2 (0 ≤ x ≤ 1.0) operating on the Nb(IV)/Nb(III) redox couple. Although the system shows a high specific capacity of 143.6 mAh g–1, the voltage profile is not suitable with a signature of Na/vacancy ordering at x = 0.5. First-principles calculation was applied to reveal possible structures of NaxNbS2 and describe the corresponding electrochemical properties. The calculated Na binding energies and voltages are in good agreement with experimental charge/discharge voltages. We also found a possible atomic arrangement of Na/vacancy ordering in Na0.5NbS2. Although layered NaMS2 systems allow full sodium intercalation, the strong Na+–Na+ intralayer interaction induces layer gliding and Na+-ion ordering that create undesirable steps in the voltage profile.
57 citations
TL;DR: In this paper, the calculated Raman spectrum of α-Li3V2(PO4)3 provided by density functional theory is presented along with symmetry assignments for all of the calculated and observed modes through Raman microscopy.
Abstract: Monoclinic α-Li3V2(PO4)3 has a complex 3-D metal phosphate framework that provides mobility for all three lithium ions, giving it the highest gravimetric capacity (197 mAh/g) of all the transition-metal phosphates. Along with its high gravimetric capacity, its thermal and electrochemical stability make it of great interest as a cathode material for lithium-ion energy storage devices. Raman spectroscopy has proven to be a unique analytical tool for studying electrode materials of lithium-ion batteries due to its ability to probe structural changes at the level of chemical bonds. In this work, the calculated Raman spectrum of α-Li3V2(PO4)3 provided by density functional theory is presented along with symmetry assignments for all of the calculated and observed modes through Raman microscopy. Furthermore, the phase stability of microcrystalline α-Li3V2(PO4)3 was studied as a function of irradiation power density. Follow-up thermal studies confirm that two structural phase transitions, β and γ, occur at elevat...
37 citations
TL;DR: In this paper, the minimum energy pathway of the phase transition with density functional theory under different pressure conditions with the generalized solid-statenudgedelasticband method was calculated.
Abstract: Recent experiments have shown that the perovskite to post-perovskite phase transformation in CaIrO3 occurs more readily at room temperature when a shear stress is applied as compared to isotropic pressure. To understand this mechanistically, we have calculated the minimum-energy pathway of the phase transition with density functionaltheoryunderdifferentpressureconditionswiththegeneralizedsolid-statenudgedelasticbandmethod. Our results reveal that shear stress significantly lowers the barrier and stabilizes the product state while isotropic pressure initially raises the barrier and only reduces the barrier at pressures above 90 GPa. The nonmonotonic change in barrier with isotropic pressure is explained in terms of an increase in the activation volume under low pressure and a decrease under high pressure.
13 citations