, 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 .

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as Li and Ni will be intensively used in large batteries for electric vehicles (EVs). These elements may be fully consumed for EV applications, so it will be impossible to have enough of them for batteries designed for large energy storage. These concerns have produced increasing interest in alternative technologies, with sodium-based storage chemistry among the leading modalities. [2] Reversible sodium intercalation received attention as one of the leading post-lithium battery technologies, as it combines several very attractive properties. Various merits are attributed to Nabased cells, in particular safety, low cost, Earth abundance, and environmental friendliness. [2c,3] As a consequence, many cathode compounds that can be utilized in sodium batteries were recently reported, including organic compounds, [4] polyanionic compounds, [5] and transition metal oxides. [6] Among them, manganese-based cathode materials have attracted much attention due to their low cost and significant Earth abundance.The tunnel-type sodium manganese oxide Na 0.44 MnO 2 is particularly attractive owing to its unique large tunnels suitable for sodium intercalation. [7] The crystal structure of Na 0.44 MnO 2 is shown in Figure 1a. There are five distinct crystallographic manganese sites and three sodium sites, where Mn(1) and Mn(2) are occupied by Mn 3+ , and Mn(3), Mn(4), and Mn (5) are occupied Mn 4+ . [8] The structural frame is built up of double and triple linear chains with edge-shared MnO 6 octahedra and single chains of edge-shared MnO 5 square-pyramids. Each chain is aligned parallel to the c-axis and connected to neighboring chains via a corner-sharing of the polyhedra, resulting in two types of tunnels: the 1D tunnels occupied by Na(1) atoms ( Figure 1b) and the 2D tunnels occupied by Na(2) and Na(3) atoms, which are positioned in large zig-zag shaped cavities (Figure 1c). Interestingly, unlike common layered oxides, such a structure is very stable in aqueous solutions, even upon electrochemical sodium intercalation/deintercalation. [7f,9] Thus, recently many publications focused on Na 0.44 MnO 2 as a particularly promising cathode material for both aqueous and nonaqueous sodium-ion batteries. [10] However, to our knowledge, their sodium storage mechanisms were not determined experimentally due to the complex multifold oxidation/reduction steps, while ab initio calculations were reported. [8] Besides that, Tunnel-type sodium manganese oxide is a promising cathode material for aqueous/nonaqueous sodium-ion batteries, however its storage mechanism is not fully understood, in part due to the complicated sodium intercalation process. In addition, low cyclability due to manganese dissolution has limited its practical application in rechargeable batteries. Here, the intricate sodium intercalation mechanism of Na 0.44 MnO 2 is revealed by combination of electrochemical characterization, structure determination from powder X-ray diffraction data, 3D bond valence difference maps, and barrier-energy calculations of the sodium ...

with storage chemistry based on nature abundant elements among the leading modalities. [2] Among the various candidates, sodiumbased chemistry received attention as one of the leading post-LIB technologies. [2d,3] Rechargeable sodium-based batteries exhibit various merits such as safety, low price, natural abundance, and environmental friendliness. [4] Various types of host materials were reported for sodium-ion batteries including polyanionic compounds, [5] transition metal oxides, [6] and organic compounds. [7] Among the transition metal oxides, tunnel structured Na 0.44 MnO 2 has received special interest owing to its unique crystal structure and earth abundance of its raw materials. Many recent publications focused on this oxide as a particularly promising cathode material for both aqueous and nonaqueous sodium-ion batteries. [8] A survey of the literature reveals that the observed reversible capacity is always limited by the inherent phase change from sodium-poor Na 0.22 MnO 2 to sodium-rich Na 0.66 MnO 2. As a result, nearly all previously obtained Na 0.44 MnO 2 materials delivered reversible capacity of only ≈120 mAh g −1 in nonaqueous electrolyte solution. [8c] Doping by various cations including titanium, [9] iron, [10] and cobalt [11] and anions such as fluorine [12] was performed to enhance the structural stability and diffusion kinetics. Inspired by these attempts, we focus here on fluorine and aluminum as doping elements due to their interesting and potential properties; the former can change the binding energy of oxygen and promote the sodium diffusion rate, [12,13] while the latter showed enhanced structural stability in cathode materials. [14] Substitution of Mn/O in a Na 0.44 MnO 2 by Al/F results in a new crystal structure with a chemical formula of Na 0.46 Mn 0.93 Al 0.07 O 1.79 F 0.21 , which departs from the tunneltype manganese oxide structure. The substitution drastically improves these materials as high-capacity sodium-ion cathodes. The new phase shows 2D diffusion pathways with a lower diffusion energy barrier than the 1D Na 0.44 MnO 2 structure. Furthermore, we clearly uncover the sodium storage behavior by structural analyses and the effect of Al/F-doping by 3D bond valence energy landscape calculations. Na 0.44 MnO 2 (also named NMO) has an orthorhombic crystal structure with Pbam symmetry. It consists of double and triple Various types of sodium manganese oxides are promising cathode materials for sodium storage systems. One of the most considerable advantages of this family of materials is their widespread natural abundance. So far, only a few host candidates have been reported and there is a need to develop new materials with improved practical electrochemical performance. Here, P2-type Al/F-doped sodium manganese oxide as well as its unique sodium storage mechanism is demonstrated by a combination of electrochemical characterization, structural analyses from powder X-ray diffraction (XRD) data, and 3D bond valence energy level calculations for the sodium diffusion pathways. The mat...

Sulfide inorganic materials have the potential to be used as solid electrolytes (SEs) in Li-ion all-solid-state batteries (ASSBs) owing to their high ionic conductivity and mechanical softness. However, H2S gas release in ambient air is a critical issue for realizing scalable production of these materials. In the present study, we designed aliovalent substitutions of Sb5+ for Ge4+ in Li4GeS4 to produce a series of materials with a general nominal composition of Li4–x Ge1–x Sb x S4. With increasing Sb substitution up to the solubility limit (x = 0.4), the unit cell expands, the ionic conductivity increases, and the activation energy decreases. Among the series, the material with x = 0.4 displays the highest ionic conductivity, ∼10–4 S cm–1 at 303 K, 2 orders of magnitude higher than that of the unsubstituted Li4GeS4, and the main phase of the material is determined to be Li3.68Ge0.69Sb0.31S4 by the X-ray Rietveld refinement. It also shows high air stability: 70% of the initial ionic conductivity is retained without any structural degradation after exposure to air with a relative humidity of 15% for 70 min at 303 K, in contrast to a control sample of Li3PS4 retaining only 10% of the initial conductivity. A press cell composed of a TiS2 composite cathode, an In–Li alloy anode, and a Li3.68Ge0.69Sb0.31S4 electrolyte showed excellent cycle performance, demonstrating the electrolyte as a dry-air-stable SE candidate for ASSBs. These results provide insights into the synthesis design of air-stable SEs with appropriate compositions and improved performance.