Atomic and electronic structure of superionic solid electrolyte Li 10 GeP 2 S 12
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Atomic and electronic structure of superionic solid electrolyte Li10GeP2S12 Ka Xionga*, Roberto Longo Pazosa and Kyeongjae Choa,b,† a
Materials Science & Engineering Dept, The University of Texas at Dallas, Richardson, TX 75080, USA b Physics Dept, The University of Texas at Dallas, Richardson, TX 75080, USA
*[email protected] † kjcho @utdallas.edu
ABSTRACT We investigate the electronic structure of interstitial Li and Li vacancy in Li10GeP2S12 by first principles calculations. We find that the Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li10GeP2S12. The energy barrier for Li interstitial diffusion in Li10GeP2S12 is estimated to be 1.4 eV, which is much larger than that of the Li vacancy in Li10GeP2S12. This fact suggests that the ion conductivity arises from the migration of Li vacancy. INTRODUCTION Lithium batteries have great potential to be used to store electrical energy for future electrical vehicles due to their high energy and power densities [1]. However, to develop a Li battery to meet the desired requirements remains challenging, which requires exploring new electrochemistry and materials. Inorganic solid electrolytes have attracted much attention for being used in lithium batteries to replace conventional liquid electrolytes to achieve better safety and reliability [2-3]. This has led to intensive research during the last three decades and many electrolyte candidates have been proposed such as lithium phosphate oxynitride (LiPON) and Li2S-P2S5-based glasses such as lithium thiophosphate. LiPON has been used as commercial solid electrolyte in thin-film batteries [4-7]. However, its ionic conductivity is rather low (10-6 S cm-1). To improve the performance of the battery cell, the electrolyte material should have high ionic conductivity. Moreover, a good electrolyte should also satisfy two other requirements: it should have low electric conductivity (good insulator) and it should be stable in contact with both cathode and anode electrodes. It has been recently reported that a new super ionic conductor Li10GeP2S12 possesses an ionic conductivity up to 12 mS cm-1, which is so far the highest achieved among all the solid electrolytes and is comparable to the conductivity of liquid electrolyte [8]. To date, there are few studies have been dedicated to understand the properties of this material [8,9,10]. Clearly, a practical use of solid electrolytes will require significant research efforts for fundamental understanding of the material properties at atomic scales. In this work, we use first principles calculations to investigate the atomic and electronic structures of Li defects (interstitial Li and Li vacancy) in Li10GeP2S12. COMPUTATIONAL METHODS The calculations were performed by the total energy plane-wave basis code VASP [11]. The pseudopotential is generated using the projected augmented wave (PAW) method. An energy cutoff of 400 eV and a 4x4x4 k-point Monkhorst-Pack grid are used. For defect calculations, w
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