Gram-Scale Synthesis of Nanosized Li3 HoBr6 Solid Electrolyte for All-Solid-State Li-Se Battery

Halide solid-state electrolytes for all-solid-state batteries: structural design, synthesis, environmental stability, interface optimization and challenges

Since the huge breakthrough in 2018, research on halide solid-state electrolytes (SSEs) has set off a new craze. In comparison with oxide and sulfide SSEs, halide SSEs have more balanced properties in various aspects, including ionic conductivity, electrochemical stability window, and moisture resistance. Herein, the overall knowledge and deep understanding of halide SSEs and their practical applications in all-solid-state batteries (ASSBs) are introduced. Firstly, the principle of screening halide SSE components is proposed. Among F, Cl, Br and I anions, the Cl anion is excellent owing to its suitable ionic conductivity and electrochemical stability window. The Sc, Y, and lanthanide elements are also more compatible with Cl anions in terms of electronegativity. Secondly, the structural design theory of halide SSEs with high ionic conductivity and the mechanism of Li ion migration are described. A monoclinic structure is more conducive to Li ion migration, compared with trigonal and orthorhombic structures. Additionally, substitution strategies for halide SSEs are discussed, mainly including dual-halogen, isovalent cation substitution, and aliovalent cation substitution. Furthermore, the mechanism of moisture resistance and synthesis method of halide SSEs are analyzed. Compared with the solid-state reaction and mechanochemistry method, wet chemical synthesis is more likely to achieve scale-up production of halide SSEs. Finally, the application prospects and challenges of halide SSEs in ASSBs are outlined.

Cryo-EM Revealing the Origin of Excessive Capacity of the Se Cathode in Sulfide-Based All-Solid-State Li-Se Batteries

Selenium (Se), whose electronic conductivity is nearly 25 orders higher than that of sulfur (S) and whose theoretical volumetric capacity is 3254 mAh cm^-3, is considered as a potential alternative to S to overcome the poor electronic conductivity issue of the S cathode in the lithium (Li)-S battery. However, the study of the Li-Se battery, particularly a Li-Se all-solid-state battery (ASSB), is still in its infancy. Herein, we report the performance of Li-Se ASSBs at both room temperature (RT) and high temperature (HT, 50 °C), using a Li₁₀Si_0.3PS_6.9Cl_1.8 (LSPSCl) solid-state electrolyte and Li-In anode. With a Se loading of 7.6 mg cm^-2, the Li-Se battery displayed a record high reversible capacity of 6.8 mAh cm^-2 after 50 cycles at HT, which exceeds the theoretical areal capacity of 5.2 mAh cm^-2 for Se. Moreover, the RT Li-Se ASSB delivered an initial areal capacity of about 2 mAh cm^-2 at a current density of 1 A g^-1 for 1200 cycles with a capacity retention of 67%. Cryo-electron microscopy revealed that the excessive capacity of Se at HT can be attributed to the formation of a previously unknown S₅Se₄ phase during charging, which participated reversibly in a subsequent redox reaction. The formation of the S₅Se₄ phase originated from the reaction of Se with S, which was generated by the decomposition of LSPSCl at HT. These results unlock the electrochemistry of a Li-Se ASSB, suggesting that a Li-Se ASSB is a viable alternative to a Li-S battery for energy storage applications.

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

The safety of lithium-ion batteries has caused notable concerns about their widespread adoption in electric vehicles. A nascent but promising approach to enhancing battery safety is using solid-state electrolytes (SSEs) to develop all-solid-state batteries, which exhibit unrivaled safety and superior energy density. A new family of SSEs based on halogen chemistry has recently gained renewed interest because of their high ionic conductivity, high-voltage stability, good deformability, and cost-effective and scalable synthesis routes. Here, we provide a comprehensive review of halide SSEs concerning their crystal structures, ion transport kinetics, and viability for mass production. Furthermore, their moisture sensitivity and interfacial challenges are summarized with corresponding effective strategies. Last, halide-based all-solid-state Li-ion and Li-S pouch cells with energy density targets of 400 and 500 Wh kg^-1 are projected to guide future endeavors. This work serves as a comprehensive guideline for developing halide SSEs from material design to practical application.

A Novel Ethanol-Mediated Synthesis of Superionic Halide Electrolytes for High-Voltage All-Solid-State Lithium-Metal Batteries

Halide electrolytes are rising stars among inorganic solid-state electrolytes due to their high ionic conductivity and good compatibility with high-voltage electrodes. However, their traditional synthesis methods including ball-milling annealing are usually energy-intensive and time-consuming compared with liquid-mediated routes. What's more, the only method in aqueous solution is not perfect considering detrimental effect of trace water for battery performances. Here, we propose a novel ethanol-mediated synthesis route for superionic Li₃InCl₆ electrolyte via energy-friendly dissolution and post-treatment. The organics in ethanol-mediated precursor disappear in form of light gas during post-treatment. And Li₃InCl₆ with best thermal stability and ionic conductivity (0.79 mS cm^-1, 20 °C) can be successfully prepared after postheating for 3 h at 200 °C. Besides, it is also found that the ionic conductivity of Li₃InCl₆ is positively correlated with peak intensity ratio of (131) plane/(001) plane since crystal plane and preferred orientation can directly affect polyhedrons through which lithium ions migrate in crystalline conductors. The assembled LiNi_0.8Co_0.1Mn_0.1O₂/Li₃InCl₆/Li₁₀GeP₂S₁₂/Li-In cell presents high initial charge capacity of 174.8 mAh g^-1 at 0.05 C and a good rate performance of 122.9 mAh g^-1 at 1 C. Especially, the retention rate of charge capacity can reach 94.8% after 200 cycles. The ethanol-mediated synthesized Li₃InCl₆ is a novel promising electrolyte which can be coupled with high-voltage cathode for the application of all-solid-state lithium-metal batteries.