Halide‐based solid electrolytes: The history, progress, and challenges

Abstract

Lithium metal solid‐state batteries (LMSBs) have attracted extensive attention over the past decades, due to their fascinating advantages of safety and potential for high energy density. Solid‐state electrolytes (SEs) with fast ionic transport and excellent stability are indispensable components in LMSBs. Heretofore, a series of inorganic SEs have been extensively explored, such as sulfide‐ and oxide‐based electrolytes. Unfortunately, they both have difficulty in achieving a satisfactory balance of conductivity and stability, and oxides suffer from a high impedance of grain boundaries, while sulfides encounter poor stability. Halide‐based solid electrolytes are gradually emerging as one of the most promising candidates for LMSBs due to their advantages of decent room temperature ionic conductivity (>10−3 S cm−1), good compatibility with oxide cathode materials, good chemical stability, and scalability. Herein, research and development of the widely studied metal halide SEs including fluorides, chlorides, bromides, and iodides are reviewed, mainly focusing on the structures and ionic conductivities as well as preparation methods and electrochemical/chemical stabilities. And then, based on typical metal halide solid electrolytes, we emphasize the interface issues (grain boundaries, cathode−electrolyte and electrolyte–anode interfaces) that exist in the corresponding LMSBs and summarize the related work on understanding and engineering these interfaces. Furthermore, the typical (or in situ) characterization tools widely used for solid‐state interfaces are reviewed. Finally, a perspective on the future direction for developing high‐performance LMSBs based on the halide electrolyte family is put out.

On the Influence of Li3InCl6−PEDOT:PSS Hybrids in Solid‐State Batteries Prepared via an Aqueous One‐Pot Approach

“…The superionic halides have recently received much attention because they show high electrochemical stability towards high-potential cathode active materials, and they can be synthesized via solution-based approaches. [21,[27][28][29][30][31][32] Additionally, the degree of decomposition for halides was reported as much lower than for the sulfides cell with conductive additives, making halide-based systems even more attractive for an indepth investigation to mitigate the problem mentioned above. [18,[22][23][24][25][26] Since the majority of the exploited polymer binders used in the halide-based systems necessitated the use of organic solvents, the interest in the development of the processes with the use of other 'greener' solvents is high.…”

Ultrathin All‐Inorganic Halide Solid‐State Electrolyte Membranes for All‐Solid‐State Li‐Ion Batteries

“…The use of flammable organic electrolytes poses an increasing safety concern on conventional Li-ion batteries, especially for large-scale applications such as electric vehicles and energy storage systems. [1,2] Replacing flammable liquid electrolytes with nonflammable inorganic solid-state electrolytes (ISSEs) has been regarded as the most promising way to radically improve the battery safety for future development. [3][4][5][6][7] However, it is noticed that the solid electrolyte layer in current solid cells is usually over 500 μm in thickness, in some cases even to 1 mm, 30-60 times that of conventional polyolefin separators (≈15 μm) in commercial lithium-ion batteries (LIBs).…”

“…[29][30][31][32][33][34][35][36][37] Compared with oxide SSEs, halide SSEs do not require high-temperature sintering and exhibit better mechanical flexibility, which can be cold-pressed. [2,38] In addition, halide SSEs are relatively light (e.g., 2.69 g cm −3 for Li 3 InCl 6 vs 5.11 g cm −3 for Li 7 La 3 Zr 2 O 12 ), which makes them a promising candidate for practical all-solid-state Li batteries (Figure 1b). [39,40] Compared with sulfide SSEs, halide SSEs are environmentally friendly (no toxic gases are produced when exposed to air).…”

Liquid Metal Mediated Heterostructure Fluoride Solid Electrolytes of High Conductivity and Air Stability for Sustainable Na Metal Batteries

“…In recent years, halide SEs have emerged as promising alternatives due to their wide ESW, deformability, and high ionic conductivity similar to that of sulfide SEs. − However, the current research on halide SEs mainly focuses on lithium halides for LMBs (e.g., Li 3 MX 6 ; M = In, Y, and Sc; X = F, Cl, and Br). The studies conducted on sodium halides for SMBs are still limited. , It has been reported that the ionic conductivities of NaAlCl 4 and NaZrCl 4 are 3.9 × 10 –6 and 1.8 × 10 –5 S/cm at 30 °C, respectively.…”