Origin of Superionic Li₃Y_1–xIn_xCl₆ Halide Solid Electrolytes with High Humidity Tolerance

Abstract

The high ionic conductivity, air/humidity tolerance, and related chemistry of Li3MX6 solid-state electrolytes (SSEs, M is a metal element, and X is a halogen) has recently gained significant interest. However, most of the halide SSEs suffer from irreversible chemical degradation when exposed to a humid atmosphere, which originates from hydrolysis. Herein, the function of the M atom in Li3MX6 was clarified by a series of Li3Y1–x In x Cl6 (0 ≤ x < 1). When the ratio of In3+ was increased, a gradual structural conversion from the hexagonal-closed-packed (hcp) anion arrangement to cubic-closed-packed (ccp) anion arrangement has been traced. Compared to hcp anion sublattice, the Li3MX6 with ccp anion sublattice reveals faster Li+ migration. The tolerance of Li3Y1–x In x Cl6 towards humidity is highly improved when the In3+ content is high enough due to the formation of hydrated intermediates. The correlations among composition, structure, Li+ migration, and humidity stability presented in this work provide insights for designing new halide-based SSEs.

Interplay between Li3YX6 (X = Cl or Br) solid electrolytes and the Li metal anode

“…More importantly, this was achieved without any extra coating that is typically needed for sulfide solid electrolytes. Following the above report on Li 3 YCl 6 and Li 3 YBr 6 in 2018 [8], researchers discovered similar superior performance in many other halide solid electrolytes, including Li 3 InCl 6 [7,[9][10][11], Li 3 ScCl 6 [12], and Li 3 ErCl 6 [13][14][15]. Li 3 MX 6 -type (M = non-Li element, X = Cl or Br) halides have thus rapidly become a popular family of high-performance solid electrolytes [5].…”

Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li3-xIn1-xZrxCl6 (0 ≤ X ≤ 0.5)

“…35 Interestingly and advantageously, Li3InCl6 is fully recoverable after humidity exposure and synthesizable via a water-mediated route resulting in a conductivity of ~2 mS•cm -1 at 25 °C. 25,35,36 Common hightemperature or mechanochemical synthesis of Li3InCl6 results in comparable room-temperature conductivities of ~1.5 mS•cm -1 . 24,35 Li3InCl6 adapts a monoclinic structure (space group: C2/m) and was initially solved from single crystal X-ray diffraction by Schmidt et al 37 It crystallizes in a layered structure consisting of edge-sharing (InCl6) 3-and (LiCl6) 5-octahedra.…”

Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li3-xIn1-xZrxCl6 (0 ≤ X ≤ 0.5)

“…However, reported conductivities of Li3InCl6 are higher and range between 1.5 mS•cm -1 -2 mS•cm -1 . 24,25,35 The differences in conductivity may stem from the varying synthesis parameters and 16 annealing times that were applied, since it is known for the halide materials that synthesis conditions have a severe influence on structure and properties. 29,31,32,50 In addition, the small conductivity discrepancy may also be due to the known interlaboratory deviations in the ionic conductivity of these mechanically soft materials.…”

“…In contrast to the aliovalent substitutions, phase transitions were observed for the isovalent substitution series Li3Y1-xInxCl6 changing from an orthorhombic to the trigonal phase for Li3YCl6 when exceeding a substitution degree of x(In) = 0.1 and then, adapting the monoclinic structure of Li3InCl6 for x(In) ≥ 0.3. 35 Interestingly and advantageously, Li3InCl6 is fully recoverable after humidity exposure and synthesizable via a water-mediated route resulting in a conductivity of ~2 mS•cm -1 at 25 °C. 25,35,36 Common hightemperature or mechanochemical synthesis of Li3InCl6 results in comparable room-temperature conductivities of ~1.5 mS•cm -1 .…”

“…25,35,36 Common hightemperature or mechanochemical synthesis of Li3InCl6 results in comparable room-temperature conductivities of ~1.5 mS•cm -1 . 24,35 Li3InCl6 adapts a monoclinic structure (space group: C2/m) and was initially solved from single crystal X-ray diffraction by Schmidt et al 37 It crystallizes in a layered structure consisting of edge-sharing (InCl6) 3-and (LiCl6) 5-octahedra. The (InCl6) 3-octahedra are exclusively located within the (001) lattice plane, whereas (LiCl6) 5octahedra can be found within the (002) lattice plane (Figure 1a).…”