The Redox Potential and Chemical Stability of Li7P3S11 Using VASP Calculation

Study on Li 7 P 3 S 11 material was carried out by ab initio calculation using the Vienna ab initio Simulation Package (VASP)[1]. Li 7 P 3 S 11 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 Li 7 P 3 S 11 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 Li 7 P 3 S 11 , Li 3 PS 4 , Li 4 P 2 S 6 and Li 4 P 2 S 7 , the formation potential of Li 7 P 3 S 11 was the highest value of 2.216 V(Li/Li + ) to be the most stable material. Chemical reactivity of Li 7 P 3 S 11 material toward moisture to be Li 7 P 3 O 11 had the reaction energy of –0.34 eV. Li + conduction of Li 7 P 3 S 11 take place through vacancy and interstitial diffusion pathways. Xiong (2014) reported on the formation potential of Li 7-1 P 3 S 11 . Evaluated result of the formation potential of Li 14-1 P 6 S 22 was also appeared similar to Xiong’s results. Formation potentials of Li 14+1 P 6 S 22 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+x P 6 S 22 (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. Figure 1