TY - JOUR
T1 - Untangling the Structure and Dynamics of Lithium-Rich Anti-Perovskites Envisaged as Solid Electrolytes for Batteries
AU - Hanghofer, Isabel
AU - Redhammer, Günther
AU - Rhode, Sebastian
AU - Hanzu, Ilie
AU - Senyshyn, Anatoliy
AU - Wilkening, Martin
AU - Rettenwander, Daniel
PY - 2018
Y1 - 2018
N2 - Lithium-rich anti-perovskites (LiRAPs) have attracted
a great deal of attention as they have been praised as
another superior group of solid electrolytes that can be used to
realize all-solid-state batteries free of flammable liquids. Despite
several studies that have reported on the properties of LiRAPs,
many questions remain unanswered. In particular, these include
fundamental ones concerning the structure, stability, and Li-ion
conductivity and diffusivity. Moreover, it is not clear whether
some of the previously reported compounds do really exist. To
untangle the current picture of LiRAPs, we synthesized “Li3OCl”
and Li2OHCl polymorphs and applied a wide spectrum of
methods, such as powder X-ray diffraction (PXRD), powder
neutron diffraction (PND), nuclear magnetic resonance spectroscopy, and impedance spectroscopy to carefully shed some light
on LiRAPs. Here we self-critically conclude that the cubic polymorph of the two compounds cannot be easily distinguished by
PXRD alone as the lattice metrics and the lattice parameters are very similar. Furthermore, PXRD suffers from the difficulty of
detecting H and Li. Even Rietveld refinement of our PND data turned out to be complicated and not easily interpreted in a
straightforward way. Nevertheless, here we report the first structural models for the cubic and a new orthorhombic polymorph
containing also structural information about the H atoms. In situ PXRD of “Li3OCl”, intentionally exposed to air, revealed rapid
degradation into Li2CO3 and amorphous LiCl·xH2O. Most likely, the instability of “Li3OCl” explains earlier findings about the
unusually high ion conductivities as the decomposition product LiCl·xH2O offers an electrical conductivity that is good enough
for some applications, excluding, of course, those that need aprotic conditions or electrolytes free of any moisture. Considering
“H-free Li3OCl” as well as Li5(OH)3Cl2, Li5
(OH)2Cl3, Li3
(OH)2Cl, and Li3(OH)Cl2, we are confident that Li4(OH)3Cl and
variants of Li3−x(OHx)Cl, where x > 0, are, from a practical point of view, so far the only stable lithium-rich anti-perovskites.
AB - Lithium-rich anti-perovskites (LiRAPs) have attracted
a great deal of attention as they have been praised as
another superior group of solid electrolytes that can be used to
realize all-solid-state batteries free of flammable liquids. Despite
several studies that have reported on the properties of LiRAPs,
many questions remain unanswered. In particular, these include
fundamental ones concerning the structure, stability, and Li-ion
conductivity and diffusivity. Moreover, it is not clear whether
some of the previously reported compounds do really exist. To
untangle the current picture of LiRAPs, we synthesized “Li3OCl”
and Li2OHCl polymorphs and applied a wide spectrum of
methods, such as powder X-ray diffraction (PXRD), powder
neutron diffraction (PND), nuclear magnetic resonance spectroscopy, and impedance spectroscopy to carefully shed some light
on LiRAPs. Here we self-critically conclude that the cubic polymorph of the two compounds cannot be easily distinguished by
PXRD alone as the lattice metrics and the lattice parameters are very similar. Furthermore, PXRD suffers from the difficulty of
detecting H and Li. Even Rietveld refinement of our PND data turned out to be complicated and not easily interpreted in a
straightforward way. Nevertheless, here we report the first structural models for the cubic and a new orthorhombic polymorph
containing also structural information about the H atoms. In situ PXRD of “Li3OCl”, intentionally exposed to air, revealed rapid
degradation into Li2CO3 and amorphous LiCl·xH2O. Most likely, the instability of “Li3OCl” explains earlier findings about the
unusually high ion conductivities as the decomposition product LiCl·xH2O offers an electrical conductivity that is good enough
for some applications, excluding, of course, those that need aprotic conditions or electrolytes free of any moisture. Considering
“H-free Li3OCl” as well as Li5(OH)3Cl2, Li5
(OH)2Cl3, Li3
(OH)2Cl, and Li3(OH)Cl2, we are confident that Li4(OH)3Cl and
variants of Li3−x(OHx)Cl, where x > 0, are, from a practical point of view, so far the only stable lithium-rich anti-perovskites.
U2 - 10.1021/acs.chemmater.8b02568
DO - 10.1021/acs.chemmater.8b02568
M3 - Article
SN - 0897-4756
VL - 30
SP - 8134
EP - 8144
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 22
ER -