Lesson Learned from NMR: Characterization and Ionic Conductivity of LGPS-like Li₇SiPS₈

Abstract

We report on the facile solid-state synthesis and characterization of Li7SiPS8, a new member of the tetragonal Li10GeP2S12 (LGPS)-type family of ultrafast Li+ solid electrolytes. We analyze the structure, phase stability, and Li+ conductivity of tetragonal and orthorhombic LSiPS by pulsed field gradient NMR and impedance spectroscopy, which show conductivities at room temperature of up to 2 mS cm–1. Although ranking tetragonal LiSiPS as an ultrafast solid electrolyte, the observed conductivity is unexpectedly low compared to other members of this solid-solution system. Utilizing solid-state NMR, quantitative phase analysis, and impedance spectroscopy, we identify an amorphous thiophosphate side phase with low Si content, which limits the intergrain conductivity and, hence, a potentially higher total conductivity. This case study thus highlights the need for comprehensive structural analysis of LGPS-type materials beyond the crystalline fractions to fully characterize the structure–property relationships in these glass-ceramic compounds.

How Certain Are the Reported Ionic Conductivities of Thiophosphate-Based Solid Electrolytes? an Interlaboratory Study

“…up to 4.5 mScm -1 range for sample (1), we were not able to detect any outliers in any of the samples with the IQR method. In the case of samples (1) and 2, the median shows a skewness to lower and higher conductivity values, respectively, whereas for the lower conducting samples (3), (4) and (5) we observe that the mean and the median are closer to one another. Moreover, the calculated median for the lower conducting samples is close to the center of the IQR box, which suggests that the spread in the conductivity can be viewed as following a normal distribution.…”

“…Fast ionic conductors such as lithium and sodium thiophosphates are currently being investigated for their possible application in all-solid-state batteries. 1,2 Recent research efforts have found a variety of Li + and Na + based materials such as the thiophosphates Li11-xM1-xP2+xS12 (M = Si, Ge, Sn), [3][4][5][6][7][8] Li2S-P2S5 glasses, [9][10][11][12][13][14][15] Li6PS5X (X = Cl, Br, I), [16][17][18][19][20][21][22] Na3PS4 [23][24][25][26][27] and Na11Sn2PS12. 11,28,29 These materials can exhibit ionic conductivities > 1 mScm -1 , making them viable for solid-state battery applications.…”

Finding the Right Blend: Interplay Between Structure and Sodium Ion Conductivity in the System Na5AlS4–Na4SiS4

“…In addition to isovalent substitution, aliovalent substitution can be used to not only alter the polarizability of the lattice and influence the size of diffusion pathways, but also to tune the charge carrier concentration. Similar to the LGPS system (Kamaya et al, 2011;Bron et al, 2013Bron et al, , 2016Kuhn et al, 2013aKuhn et al, ,b, 2014Kato et al, 2014Kato et al, , 2016Hori et al, 2015a,b;Harm et al, 2019), tetrel elements were employed in the Na 3+x T x P 1-x S 4 (T = Si, Sn) system to increase the charge carrier density and increase the overall ionic conductivity. The Sn-containing compounds are structurally very similar to the LGPS-like Li 10 SnP 2 S 12 and show conductivities of 4 · 10 −5 S cm −1 for Na 10 SnP 2 S 12 and the highest measured sodium ionic conductivity at room temperature for sulfides of 4 · 10 −3 S cm −1 for Na 11 Sn 2 PS 12 (Bron et al, 2013;Richards et al, 2016;Duchardt et al, 2018).…”

How Certain Are the Reported Ionic Conductivities of Thiophosphate-Based Solid Electrolytes? an Interlaboratory Study

“…Dataset C -Reported values Table S6. Dataset D -Reported values 1 density determined based on the geometric dimensions of the pelletized powders; 2 density measured experimentally using a gas pycnometer; 3 ratio of the reported densities; 4 calculated ratio between density 1 and the crystallographic density, 5 activation energies reported and obtained using "#$ = ' exp +− -. 31 2, 6 activtion energies converted to eV by organizing group, which are the values used for the statistics.…”