Emerging Halide Superionic Conductors for All-Solid-State Batteries: Design, Synthesis, and Practical Applications

Abstract

Recently, halide superionic conductors have emerged as promising solid electrolyte (SE) materials for all-solid-state batteries (ASSBs), owing to their inherent properties combining high Li + conductivity, good chemical and electrochemical oxidation stabilities, and mechanical deformability, compared to sulfide or oxide SEs. In this Review, recent advances in halide Li + -and Na + -conducting SEs are comprehensively summarized. After introducing the ionic diffusion mechanism and related governing factors of the crystal structures, we discuss the design strategies, such as the substitution and synthesis protocols, of the halide materials for further improving their properties. We review theoretical and experimental results on electrochemical stabilities and compatibilities with electrode materials. Moreover, we offer a critical assessment of the challenges and issues associated with the development of practical ASSB applications, such as cost considerations, stabilities in atmospheric air, aqueous solutions, and slurryprocessing, and the wet-slurry or dry fabrication of sheet-type electrodes (or SE membranes) for large-format ASSBs. Based on these discussions, we provide a perspective on the future research directions of halide SEs, emphasizing the need for expanding the materials space.

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

“…This can be achieved using low-cost precursors, substituting precious elements with cheap elements, or developing cost-effective synthesis routes. Eighth, the dry-film method provides an effective way to explore engineering issues in all-solid-state pouch cells ( 30 ). The slurry coating process is compatible with current LIB roll-to-roll manufacturing, which has the advantages of high efficiency and low cost.…”

“…In 2018, Asano et al ( 16 ) revisited the halide SSEs Li 3 YCl 6 and Li 3 YBr 6 , demonstrating high room temperature ionic conductivity (> 1 mS cm −1 ), high voltage stability, excellent deformability, and desirable dry air stability. 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 ).…”

Toward Optimization of the Chemical/Electrochemical Compatibility of Halide Solid Electrolytes in All-Solid-State Batteries

“…; X = Cl, Br, and I). They show high ionic conductivity (∼1 mS/cm) and high oxidative stability (>4 V vs Li + /Li) as predicted by density functional theory (DFT) calculations while offering easy fabrication via either solid-state or solution processes. − This enhanced stability was confirmed experimentally by noting greater ASSB performances, relying on the use of Li 3 YCl 6 rather than sulfides, especially when cycled at high potentials. , A culminant demonstration along that line is the remarkable rate capability, long-term cycling performance, and electrochemical stability up to 4.8 V vs Li + /Li recently achieved with the use of scandium-based ionic conducting phases (Li 2 Sc 2/3 Cl 4 and Li 2 Sc 1/3 In 1/3 Cl 4 ). , However, the main drawbacks pertaining to halides are high cost and density as well as their poor electrochemical stability in reduction, preventing their direct use against Li or Li x In y layers in ASSBs . This requires the design of dual SE separators with halides and sulfides facing the positive and negative electrodes, respectively, with the inconvenience of creating more interfaces .…”

Enabling a Co-Free, High-Voltage LiNi0.5Mn1.5O4 Cathode in All-Solid-State Batteries with a Halide Electrolyte

“…Contrary to sulfide-based SSEs, the halide-based SSEs have been recently popularized in cathode composites because of their higher oxidation stability limit compared to their sulfide counterparts. ,− Asano et al were the first to report that low-crystalline Li 3 YCl 6 (LYC) and Li 3 YBr 6 halide SSEs had ionic conductivities of 0.51 and 0.72 mS cm –1 . Various types of other halide SSEs that contain other transition metal ions such as In, Zr, and Sc have been discovered and found to exhibit suitable ionic conductivities with higher oxidative stability windows, thus enabling stable cycling performance of a >4 V class of cathode materials, including NCM cathodes without the protective coating layers. − However, experimental analysis of their decomposition and its products beyond the oxidation stability window as well as their application and performance limitations when used with higher-voltage (>4.8 V) cathode systems have yet to be explored. In this study, we first introduced LYC as the representative halide SSE in the LNMO cathode composite and compared the chemical compatibility between LNMO and LPSCl/LYC via electrochemical, spectroscopic, and electron microscopy methods.…”