Study on Li₇P₃S₁₁ material was carried out by ab initio calculation using the Vienna ab initio Simulation Package (VASP)[1]. Li₇P₃S₁₁ was known as a super-ionic conductor (5.4 mS/cm at 25°C) to be a solid-electrolyte of all-solid-state lithium batteries. Two different crystal structure of Li₇P₃S₁₁ were reported by Onodera (2010) and Tatsumisago (2007) with slight difference on atomic positions. Between total energies of VASP calculation on two structures, Tatsumisago’s structure had slightly more stable energy (Etotal –92.573 eV). Among Li₇P₃S₁₁, Li₃PS₄, Li₄P₂S₆ and Li₄P₂S₇, the formation potential of Li₇P₃S₁₁ was the highest value of 2.216 V(Li/Li⁺) to be the most stable material. Chemical reactivity of Li₇P₃S₁₁ material toward moisture to be Li₇P₃O₁₁ had the reaction energy of –0.34 eV. Li⁺ conduction of Li₇P₃S₁₁ take place through vacancy and interstitial diffusion pathways. Xiong (2014) reported on the formation potential of Li_7-1P₃S₁₁. Evaluated result of the formation potential of Li_14-1P₆S₂₂ was also appeared similar to Xiong’s results. Formation potentials of Li₁₄₊₁P₆S₂₂ were also evaluated for four different interstitial sites. Site(III) denoted at Xiong’s report had 0.643 V(Li/Li⁺) to be the most easy accommodation of Li⁺ ion. Patterns of the total density of states (TDOS) of Li_14+xP₆S₂₂ (x=1,0,-1) were not so different and shown ~3.5 eV by the Hyed-Scuseria-Ernzerhof (HSE) hybrid functional and ~2.1 eV by GGA to be electronic insulator.

[1] Kresse,G.; Hafner, J. Phys. Rev. B, 47 (1993) 558; 49 (1994) 14251.