, 0.7Li(CB 9 H 10)−0.3Li(CB 11 H 12), 6.7 mS cm −1), [11,12] and halides (e.g., Li 3 YX 6 [X = Cl, Br], 0.51-1.7 mS cm −1). [13,14] Thus far, oxide and sulfide SEs have been the most commonly investigated candidates. However, their pros and cons counteract each other. Oxide SEs possess high intrinsic electrochemical oxidation stabilities and relatively acceptable chemical stabilities; however, owing to their brittle nature, it is difficult to integrate them in devices. [3,10,15-17] On the other hand, the most important advantage of sulfide SEs, that is, mechanical deformability, which enables scalable cold-pressing-based fabrication protocols, is offset by their poor (electro)chemical stabilities. [3,16,18-20] On exposing sulfide SEs to humid air, the evolution of toxic H 2 S gases occurs. [21-26] Moreover, sulfide SEs exhibit oxidative decomposition at <3 V (vs Li/Li +) and are also incompatible with conventional layered LiMO 2 (M = Ni, Co, Mn, and Al) cathodes. [16,19,27] This issue can be alleviated by using protective coatings, such as LiNbO 3 and Li 3−x B 1−x C x O 3 ; [7,27] however, this constitutes additional processing costs. Furthermore, the oxidative decomposition of sulfide SEs at the surface of conductive carbon additives is unavoidable. [28-31] Recently, through reinvestigations on halide SEs, several compounds exhibiting Li + conductivities exceeding 10 −4 S cm −1 have been identified. [13,32−36] Asano and coworkers reported that trigonal Li 3 YCl 6 and monoclinic Li 3 YBr 6 showed high Li + Owing to the combined advantages of sulfide and oxide solid electrolytes (SEs), that is, mechanical sinterability and excellent (electro)chemical stability, recently emerging halide SEs such as Li 3 YCl 6 are considered to be a game changer for the development of all-solid-state batteries. However, the use of expensive central metals hinders their practical applicability. Herein, a new halide superionic conductors are reported that are free of rare-earth metals: hexagonal close-packed (hcp) Li 2 ZrCl 6 and Fe 3+-substituted Li 2 ZrCl 6 , derived via a mechanochemical method. Conventional heat treatment yields cubic close-packed monoclinic Li 2 ZrCl 6 with a low Li + conductivity of 5.7 × 10 −6 S cm −1 at 30 °C. In contrast, hcp Li 2 ZrCl 6 with a high Li + conductivity of 4.0 × 10 −4 S cm −1 is derived via ball-milling. More importantly, the aliovalent substitution of Li 2 ZrCl 6 with Fe 3+ , which is probed by complementary analyses using X-ray diffraction, pair distribution function, X-ray absorption spectroscopy, and Raman spectroscopy measurements, drastically enhances the Li + conductivity up to ≈1 mS cm −1 for Li 2.25 Zr 0.75 Fe 0.25 Cl 6. The superior interfacial stability when using Li 2+x Zr 1−x Fe x Cl 6 , as compared to that when using conventional Li 6 PS 5 Cl, is proved. Furthermore, an excellent electrochemical performance of the all-solid-state batteries is achieved via the combination of Li 2 ZrCl 6 and single-crystalline LiNi 0.88 Co 0.11 Al 0.01 O 2 .

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.

No abstract

No abstract

No abstract

Although high-voltage-stable halide solid electrolytes (SEs) have emerged, only a few Na + halide SEs have been developed thus far. Moreover, the use of expensive elements reduces the suitability of all-solid-state Na-ion batteries (ASNBs). Herein, the new mechanochemically prepared orthorhombic NaAlCl 4 is demonstrated to exhibit a 10-fold enhancement in Na + conductivity (3.9 × 10 −6 S cm −1 at 30 °C) compared to annealed samples. The feasibility of NaAlCl 4 for ASNBs is also validated for the first time. X-ray Rietveld refinement with bond valence energy landscape calculations reveals 1D-preferable 2D Na + conduction pathways. High-voltage stability up to ∼4.0 V (vs Na/Na + ) is confirmed by electrochemical measurements and theoretical calculations. Furthermore, the outstanding electrochemical performance of NaCrO 2 /Na 3 Sn ASNBs at 30 and 60 °C is demonstrated (e.g., 82.9% capacity retention at the 500th cycle at 60 °C and 1C), shedding light on the potential of the cost-effective and safe energy storage systems.L i-ion batteries (LIBs) have expanded into application areas such as large-scale energy storage systems (ESSs) that could stabilize the power grid. 1,2 However, the price of Li rose more than 10-fold over the past decade (from 6.06 USD kg −1 in 2012 to 75 USD kg −1 in 2022 for Li 2 CO 3 ). 3 In addition, the uneven distribution of Li mines has caused political and economic issues. 4−7 Moreover, there are safety concerns about LIBs, as seen from frequent fire accidents associated with the use of flammable organic liquid electrolytes. 8−10 These factors have impeded the widespread use of LIBs for ESSs. 8,9,11 Solidifying electrolytes with nonflammable inorganic Na + superionic conductors could improve safety and reduce cost, making all-solid-state Na-ion or Na batteries (ASNBs) promising for use as ESSs. 4,12−26 Sulfide SEs have been extensively investigated due to their high ionic conductivity and mechanical deformability which allows for the cold-pressing-based fabrication of all-solid-state batteries. 12−19,24,27−32 The first sulfide Na + superionic conductor, cubic Na 3 PS 4 , had a Na + conductivity of 0.2 mS cm −1 . 13 Since then, various aliovalent and/or isovalent substitutions for Na 3 PS 4 have been investigated, which produced compounds with improved Na + conductivity, [15][16][17][18][19]24,30,33 including Na 3 SbS 4 (1 mS cm −1 ), Na 1−2x Ca x PS 4 (1 mS cm −1 ), Na 3−x PS 4−x Cl x (1 mS cm −1 ), and Na 3-x Sb 1−x W x S 4 (maximum ∼40 mS cm −1 ). However, the electrochemical oxidation stability of sulfide SEs is as low as ∼2 V (vs Na/Na + ). 25,28 Recently, halide SEs have emerged as a game changer because they are mechanically sinterable, similarly to sulfide SEs, and exhibit excellent electrochemical oxidation stability and interfacial compatibility with LiMO x (M = Ni, Co, Mn, and Al mixture) cathode active materials (CAMs). 31,34,35 Since the seminal report on Li 3 YCl 6 (0.5 mS cm −1 ) that demonstrated stable cycling of LiCoO 2 with a high initial Coulombic efficiency (ICE) of ...

Designing highly conductive and (electro)chemical stable inorganic solid electrolytes using cost-effective materials is crucial for developing all-solid-state batteries. Here, we report halide nanocomposite solid electrolytes (HNSEs) ZrO2(-ACl)-A2ZrCl6 (A = Li or Na) that demonstrate improved ionic conductivities at 30 °C, from 0.40 to 1.3 mS cm−1 and from 0.011 to 0.11 mS cm−1 for Li+ and Na+, respectively, compared to A2ZrCl6, and improved compatibility with sulfide solid electrolytes. The mechanochemical method employing Li2O for the HNSEs synthesis enables the formation of nanostructured networks that promote interfacial superionic conduction. Via density functional theory calculations combined with synchrotron X-ray and 6Li nuclear magnetic resonance measurements and analyses, we demonstrate that interfacial oxygen-substituted compounds are responsible for the boosted interfacial conduction mechanism. Compared to state-of-the-art Li2ZrCl6, the fluorinated ZrO2−2Li2ZrCl5F HNSE shows improved high-voltage stability and interfacial compatibility with Li6PS5Cl and layered lithium transition metal oxide-based positive electrodes without detrimentally affecting Li+ conductivity. We also report the assembly and testing of a Li-In||LiNi0.88Co0.11Mn0.01O2 all-solid-state lab-scale cell operating at 30 °C and 70 MPa and capable of delivering a specific discharge of 115 mAh g−1 after almost 2000 cycles at 400 mA g−1.

In article number 2003190, Kyung‐Wan Nam, Yoon Seok Jung and co‐workers develop a new halide solid electrolyte, Fe3+‐substituted Li2ZrCl6, that is mechanically sinterable, (electro)chemical‐oxidation tolerant, and free of rare‐earth metals. The outstanding performance of the all‐solid‐state batteries using LiCoO2 and LiNi0.88Co0.11Al0.01O2 is enabled by the use of the newly developed halide superionic conductors.