Transport and Charge Carrier Chemistry in Lithium Sulfide

Abstract

Lithium sulfide is a functional material of great importance for battery research, since it is the discharge product in Li–S cathodes and a frequent component of anode passivation layers. In both cases, transport of charge carriers in Li2S is critical for performance. The exploration of charge carrier chemistry in such a simple binary compound is also of fundamental scientific interest. For that purpose, impedance spectroscopy and electromotive force measurements are performed over a broad range of temperatures and doping conditions. The results indicate predominant ion conduction and can be quantitatively explained by a defect chemical model based on Frenkel disorder and vacancy‐dopant association. Mobilities and migration barriers for both vacancy and interstitial defects are deduced. The thermodynamic and kinetic parameters derived for Li+ transport in antifluorite Li2S show remarkable agreement with the analogous parameters for F− transport in fluorite compounds such as BaF2, thereby improving the structural understanding of charge carrier chemistry in such compounds. An application of these results to passivation layers in solid state batteries is also discussed.

Li2S‐Based Li‐Ion Sulfur Batteries: Progress and Prospects

“…[42] The nanostructure rendered good contact between the Li 2 S and the carbon matrix as well as an adequate Reproduced with permission. [27] Copyright 2019, Wiley-VCH. density of reaction sites.…”

Dual effect of MgS addition on li2s ionic conductivity and all-solid-state Li–S cell performance

“…Therefore, the effect of a MgS particle should be noted in this case as the effect of nanoionics was expected to contribute to an improvement of both the ionic conductivities and activation energy for the samples with x = 0.15 and 0.2. Upon doping with 4% mol of MgS, a slight increase of the ionic conductivity of Li 2 S was observed by Lorger et al [12]. Recently, nanocomposites of Li 2 S and transition metals were prepared by heating mixtures of Li metal and transition metal sulfides at 600 °C [20].…”

“…This observation may suggest that Mg 2+ was successfully dissolved into the Li 2 S structure to form a Li 2−2x Mg x S solid solution with the limitation at x of nearly 0.1. In fact, the effect of Mg 2+ doping on Li 2 S ionic conductivity was also investigated by Lorger et al, but only a slight improvement of the ionic conductivity was observed [12]. Takeuchi et al prepared Li 2 S-FeS nanocomposites with different molar ratios and applied them to all-solid-state batteries [18].…”

“…T. Hakari et al observed an increase of the Li + conductivity in Li 2 S-LiX (X = I − , Br − , Cl − ) and reported the superior performance of batteries that employed these as active materials even though the electrode ionic and electronic conductivities were further enhanced by the addition of both a solid electrolyte and vapor-grown carbon fiber [11]. A systematic study of Li + transport in Li 2 S, conducted by S. Lorger et al, led to the conclusion that the ion conduction is governed by Frenkel disorder and vacancy-dopant association [12]. Density functional theory calculations were employed to stimulate the effect of transition metal doping on the Li 2 S properties, and it was found that Fe doping resulted in a reduction of the Li vacancy formation energy and the induction of a gap state, which then resulted in the accommodation of an electron during extraction / insertion of a Li ion [13].…”

Environmentally Friendly Binders for Lithium‐Sulfur Batteries

“…Third, the electronic and ionic conductivity of sulfur and Li 2 S/Li 2 S 2 are poor, thus uncontrolled deposition of solid active materials during charging‐discharging process would easily generate “dead sulfur”, which cannot participate in the following redox reaction . Fourth, thick SEI layer and Li dendrite growing on the lithium surface, as well as other problems such as liquid electrolyte exhausting would further exacerbate the cycle life or even lead to considerable security risks …”