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As a promising alternative to current commercial lithium-ion batteries, all-solid-state sodium-ion battery (ASS-SIB) requires solid electrolytes (SEs) with high Na ionic conductivity and good stability. Recently, lithium halide SEs have...

The energy band structures and electron (hole) effective masses of perfect crystalline silicon and silicon with various vacancy defects are investigated by using the plane-wave pseudopotential method based on density functional theory. Our results show that the effect of monovacancy and divacancy on the energy band structure of crystalline silicon is primarily reflected in producing the gap states and the local states in valence band maximum. It also causes breaking the symmetry of energy bands resulting from the Jahn-Teller effect, while only producing the gap states for the crystalline silicon with hexavacancy ring. However, vacancy point defects could not essentially affect the effective masses that are derived from the native energy bands of crystalline silicon, except for the production of defect states. Simultaneously, the Jahn-Teller distortions only affect the gap states and the local states in valence band maximum, but do not change the symmetry of conduction band minimum and the nonlocal states in valence band maximum, thus the symmetry of the effective masses. In addition, we study the electron (hole) effective masses for the gap states and the local states in valence band maximum.

Formation energies of nitrogen (N)/vacancy (v) monomers, N–N and N–v dimers and N–v complexions in an ideal face-centered cubic (fcc) lattice of iron are obtained via DFT calculations. Based on a thermodynamic model, the occupancies of various complexions and the vacancy concentration as a function of the chemical potential of N and temperature T are predicted. We found that increasing the chemical potential or content of N can increase the vacancy concentration considerably, e.g. compared with the case without nitrogen, increasing the N content to 10 at% at 750 K can increase the vacancy concentration by about eight orders of magnitude when a saturated concentration is reached.

The enabling of all-solid-state lithium-ion batteries with high energy density requires the development of superionic solid electrolytes (SEs) with good chemical and electrochemical stability. Recently, Li₃YCl₆ and Li₃YBr₆ with high Li ion conductivity and good oxidation stability have attracted extensive attention. However, the effect of Li-ion concentration regulation on the performance of the materials is not clear so far. In this work, we study the structural, electronic and ionic diffusion properties of a series of Li_xYCl_3+x (x=2.14, 3, 4.2) and Li_xYBr_3+x (x=1.8, 3, 5) by using first-principles calculation based on density functional theory. The calculated results show that the Li-ion concentration has a significant effect on the properties of the materials, and with increasing of x value, higher Li-ion, more stable structure, larger band gap, and lower migration barrier, enabling the ability to tune the performance of the materials. In addition, the calculated results further show that Li₃YCl₆ and Li₃YBr₆ with the best balance of Li-ion carrier concentration and vacancy concentration exhibit the highest structural stabilities, the largest band gaps, and the lowest migration barriers among all similar structures. Our dindings provide a new strategy and idea for designing better-performance halide SEs.