Aqueous Stability of Alkali Superionic Conductors from First-Principles Calculations

Abstract

Ceramic alkali superionic conductor solid electrolytes (SICEs) play a prominent role in the development of rechargeable alkali-ion batteries, ranging from replacement of organic electrolytes to being used as separators in aqueous batteries. The aqueous stability of SICEs is an important property in determining their applicability in various roles. In this work, we analyze the aqueous stability of twelve well-known Li-ion and Na-ion SICEs using Pourbaix diagrams constructed from first-principles calculations. We also introduce a quantitative free-energy measure to compare the aqueous stability of SICEs under different environments. Our results show that though oxides are, in general, more stable in aqueous environments than sulfides and halide-containing chemistries, the cations present play a crucial role in determining whether solid phases are formed within the voltage and pH ranges of interest.

Impact of hydration on ion transport in Li2Sn2S5·xH2O

“…That work also reported that Li 2 Sn 2 S 5 shows fast Li + diffusion, 35 which raises questions about the mechanism and about whether the transport properties can be further improved by hydration. One can be optimistic that the material will not decompose, since other lithium tin suldes are reportedly stable under air and moisture [36][37][38][39][40][41][42] (unlike the thiophosphates), [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] while Li 4 SnS 4 and other alkali tin suldes can form stable hydrates. 36,57 Here we show that the water content in Li 2 Sn 2 S 5 $xH 2 O can be varied from x ¼ 0 to 10 by adjusting the humidity.…”

Divalent-doped Na3Zr2Si2PO12 natrium superionic conductor: Improving the ionic conductivity via simultaneously optimizing the phase and chemistry of the primary and secondary phases

“…Originally conceived as a replacement for β-alumina in high-temperature Na-S batteries, NASICON-based compounds have nevertheless garnered significant interest for low/roomtemperature applications as electrodes and solid electrolytes for both Li and Na-ion rechargeable batteries [3][4][5][6]. Unlike sulfide solid electrolytes [7][8][9][10][11], NASICONs are oxides, which are considerably more air and moisture stable [12][13][14][15]. However, the major challenge for NASICONs thus far are their typically moderate-to-low total (bulk plus grain boundary) ionic conductivities at room temperature (~0.1 mS/cm) due to the poorly-conducting ZrO 2 phases formed at grain boundaries [16][17][18][19][20].…”

Data mining of molecular dynamics data reveals Li diffusion characteristics in garnet Li7La3Zr2O12

“…Within the Li-conducting garnet family, Li x La 3 M 2 O 12 (x = 5 for M = Nb, Ta or x = 7 for M = Zr)19 has attracted extensive attention due to its relatively high Li conductivity at RT, high stability with respect to Li metal, compatibility with high voltage cathode materials19, and stability with water20. Among these garnet oxides, Li-stuffed Li 7 La 3 Zr 2 O 12 (LLZO)16 holds great promise but also raises intriguing questions because it has two polymorphs that show vastly different Li conductivity.…”