A Series of Ternary Metal Chloride Superionic Conductors for High‐Performance All‐Solid‐State Lithium Batteries

Abstract

Understanding the relationship between structure, ionic conductivity, and synthesis is the key to the development of superionic conductors. Here, a series of Li3‐3xM1+xCl6 (−0.14 < x ≤ 0.5, M = Tb, Dy, Ho, Y, Er, Tm) solid electrolytes with orthorhombic and trigonal structures are reported. The orthorhombic phase of Li–M–Cl shows an approximately one order of magnitude increase in ionic conductivities when compared to their trigonal phase. Using the Li–Ho–Cl components as an example, their structures, phase transition, ionic conductivity, and electrochemical stability are studied. Molecular dynamics simulations reveal the facile diffusion in the z‐direction in the orthorhombic structure, rationalizing the improved ionic conductivities. All‐solid‐state batteries of NMC811/Li2.73Ho1.09Cl6/In demonstrate excellent electrochemical performance at both 25 and −10 °C. As relevant to the vast number of isostructural halide electrolytes, the present structure control strategy guides the design of halide superionic conductors.

Investigation of Structure, Ionic Conductivity, and Electrochemical Stability of Halogen Substitution in Solid-State Ion Conductor Li3YBrxCl6–x

“…Experimentally measuring the solid electrolyte stability window is challenging. Previous reports have often determined the electrochemical stability window using cyclic voltammetry (CV), which shows a pair of peaks to reflect the reduction and oxidation reactions. ,, However, the short exposure time of a CV scan makes it challenging to probe the electrochemical stability window of solid electrolytes, in which the kinetics of decomposition are sluggish due to the limited contact area, poor electronic conductivity, and charge transfer . To circumvent these problems, the electrochemical stability was measured as reported in Schwietert et al Electrochemical cells were assembled using a simultaneous reference and counter electrode (in this case a Li intercalation (Li 4 Ti 5 O 12 (LTO-C)) and alloying compound (Li–In) with constant potential for the Li concentrations measured) and a composite of the solid electrolyte mixed with carbon black as a working electrode (see schematic Figure a).…”

Prospects of halide-based all-solid-state batteries: From material design to practical application

“…All the previous results demonstrate that structural tuning can substantially influence the ionic conductivity of halide SSEs ( 68 , 71 , 72 ). On the basis of our understanding, halide SSEs with an hcp anion sublattice have an anisotropic ion transport network, in which ion transport in the z -direction is likely the rate-determining step ( 39 ). Therefore, any strategy facilitating ion transport along the z -direction can increase the ionic conductivity of halide SSEs.…”

“…This groundbreaking work has sparked global research interest in halide SSEs ( 13 – 16 , 18 – 21 , 24 – 30 ). Until now, various halide SSEs have been synthesized, spanning from fluorides to iodines, such as Li 3 AlF 6 ( 31 , 32 ), Li 3 GaF 6 ( 33 ), Li 3 InCl 6 ( 24 , 25 ), Li 3 ScCl 6 ( 34 ), spinel LiSc 2/3 Cl 4 ( 35 ), Li 3 ErCl 6 ( 36 ), Li 3 YCl 6 ( 37 , 38 ), Li 3 HoCl 6 ( 39 ), Li 3 YBr 6 ( 40 – 42 ), Li 3 HoBr 6 ( 43 ), Li 3 InBr 6 ( 44 ), Li 2 ZrCl 6 ( 45 ), Li 3− x M 1− x Zr x Cl 6 (M = Y, Er, Yb, and Fe) ( 29 , 45 – 49 ), Li 3 LaI 6 ( 50 ), and Li 3 ErI 6 ( 51 ). In parallel, halide Na-ion counterparts have also been developed ( 52 , 53 ), some of which include Na 2 ZrCl 6 ( 54 ), Na 3− x Er 1− x Zr x Cl 6 ( 55 ), and Na 3− x Y 1− x Zr x Cl 6 ( 56 ).…”

Re-investigating the structure–property relationship of the solid electrolytes Li 3−xIn1−xZrxCl6 and the impact of In–Zr(iv) substitution

“…33 The Pnma phase can also be synthesized without Zr-substitution, by synthesizing the material by co-melting of the reagents with small LiCl deciency. 30 For Li 3 M(III)Cl 6 with smaller M(III), such as In (0.80 Å) and Sc (0.75 Å), the structure crystallizes in monoclinic C2/m. 25,34 The end member Li 2 ZrCl 6 also crystallizes in monoclinic C2/m 25,34 (isostructural to Li 3 InCl 6 ) when synthesized with conventional ampoule synthesis, as well as in trigonal P 3m1 when synthesized mechanochemically.…”

“…29 This still holds under the same synthesis conditions, but different synthesis methods have shown to be able to disturb this trend. [30][31][32] For the materials with M(III) = Y (ref. 20), Er (ref.…”