We report on a new family of argyrodite lithium superionic conductors, as solid solutions Li 6+x M x Sb 1−x S 5 I (M = Si, Ge, Sn), that exhibit superionic conductivity. These represent the first antimony argyrodites to date. Exploration of the series using a combination of single crystal X-ray and synchrotron/neutron powder diffraction, combined with impedance spectroscopy, reveals that an optimal degree of substitution (x), and substituent induces slight S 2− /I − anion site disorderbut more importantly drives Li + cation site disorder. The additional, delocalized Li-ion density is located in new high energy lattice sites that provide intermediate interstitial positions (local minima) for Li + diffusion and activate concerted ion migration, leading to a low activation energy of 0.25 eV. Excellent room temperature ionic conductivity of 14.8 mS•cm −1 is exhibited for cold-pressed pelletsup to 24 mS•cm −1 for sintered pelletsamong the highest values reported to date. This enables all-solid-state battery prototypes that exhibit promising properties. Furthermore, even at −78 °C, suitable bulk ionic conductivity of the electrolyte is retained (0.25 mS•cm −1 ). Selected thioantimonate iodides demonstrate good compatibility with Li metal, sustaining over 1000 h of Li stripping/plating at current densities up to 0.6 mA•cm −2 . The significantly enhanced Li ion conduction and lowered activation energy barrier with increasing site disorder reveals an important strategy toward the development of superionic conductors.

Argyrodites, Li6PS5X (X = Cl, Br), are considered to be one of the most promising solid-state electrolytes for solid-state batteries. However, while traditional ball-mill approaches to prepare these materials do not promote scale-up, solution-based preparative methods have resulted in poor ionic conductivity. Herein, we report a solution-engineered, scalable approach to these materials, including the new argyrodite solid solution phase Li6–y PS5–y Cl1+y (y = 0–0.5), that shows very high ionic conductivities (up to 3.9 mS·cm–1) and negligible electronic conductivities. These properties are almost the same as their analogues prepared by solid-state methods, owing to a lack of amorphous contributions and low impurity contents ranging from 3 to 10%. Electrochemical performance is demonstrated for Li6PS5Cl in a prototype solid-state battery and compared to that of the same solid electrolyte derived from classic ball-milling processing.

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A new disordered chlorospinel superionic conductor, Li2Sc2/3Cl4, enables high-voltage all solid state batteries up to 4.6 V vs. Li+/Li.

Metrics & MoreArticle Recommendations CONSPECTUS: As the world transitions away from fossil energy to green and renewable energy, electrochemical energy storage increasingly becomes a vital component of the mix to conduct this transition.The central goal in developing next-generation batteries is to maximize the gravimetric and volumetric energy density and battery cycle life and improve safety. All solid-state batteries using a solid electrolyte and a lithium metal anode represent one of the most promising technologies that can achieve this goal. Highly conductive solid electrolytes (>10 mS•cm −1 ) are the key component to remove the safety concerns inherent with flammable organic liquid electrolytes and achieve high energy density by enabling high active material loading. Considering a range of inorganic solid electrolytes that have been developed to date, sulfide solid electrolytes exhibit the highest ionic conductivities, which even surpass those of conventional organic liquid electrolytes. Argyrodite-structured sulfide solid electrolytes are among the most promising materials in this class and are currently the dominantly used solid electrolytes for all-solid-state battery fabrication. Argyrodite solid electrolytes are particularly appealing because of their ultrahigh Li-ion conductivity, quasi-stable solid−electrolyte interphase (SEI) formed with Li metal, and ability to be prepared via scalable solution-assisted synthesis approaches. These factors are all vital for commercial applications.In this Account, we afford an overview of our recent development of several argyrodite superionic conductors, including Li 6.6 Si 0.6 Sb 0.5 S 5 I (24 mS•cm −1 ), Li 6.6 Ge 0.6 P 0.4 S 5 I (18 mS•cm −1 ), and Li 5.5 PS 4.5 Cl 1.5 (12 mS•cm −1 ), and a comprehensive understanding of the origin of the underlying high conductivity, namely, sulfide/halide anion site disorder and Li cation site disorder. A high degree of sulfide/halide anion site disorder (changes in anion distribution) modifies the anionic charge, which in turn strongly influences the lithium distribution. A more inhomogeneous charge distribution in anion-disordered systems generates a spatially diffuse and delocalized lithium density, resulting in faster ionic transport. Lithium cation site disorder generated by increasing Li carrier concentration through aliovalent substitution creates high-energy interstitial sites for Li ion diffusion, which activate concerted ion migration and flatten the energy landscape for Li ion diffusion. This enables high conductivity in Li-rich argyrodite superionic conductors. These concepts are also expected to promote the design of rational new solid electrolytes and fundamental understanding of the structure−ion transport relationships in inorganic ionic conductors.Collectively, a comprehensive and deep understanding of the interphase formation between argyrodite solid electrolytes and cathode active materials/Li metal and the failure mechanism of all-solid-state batteries with argyrodite solid electrolytes will lead to the bo...

All-solid-state Li-ion batteries that utilize nonflammable solid electrolytes are considered potential candidates for sustainable energy storage systems. Although sulfide solid electrolytes have been widely explored, their lack of electrochemical stability above 2.7 V requires the application of protective coating layer on 4 V-class cathode materials, whereas the superior oxidative stability of chloride solid electrolytes enables their direct use with such high voltage cathodes. Here, we report a metastable trigonal phase of Li3YbCl6 with an ionic conductivity of 1.0 × 10–4 S·cm–1 and mixed-metal halide solid electrolytes, Li3–x Yb1–x Zr x Cl6, with conductivities up to 1.1 mS·cm–1 at room temperature. Combined neutron, single-crystal, and powder X-ray diffraction methods reveal that Zr-substitution for Yb in Li3YbCl6 triggers a trigonal-to-orthorhombic phase transition and forms new, lower energy pathways for Li-ion migration. All-solid-state cell cycling with uncoated >4 V-class cathodes is enabled by the high electrochemical oxidation stability of the mixed-metal halide solid electrolyte.

A combination of the maximum entropy method and AIMD simulations demonstrates that polyanion [PS 4 ] 3À rotation is facile in the fast ion conductors b-Li 3 PS 4 and its Si-substituted analog, Li 3.25 Si 0.25 P 0.75 S 4 , but absent in the nonconductive phase, g-Li 3 PS 4 . The increased entropy upon the substitution of Si for P stabilizes the high-temperature rotor phase (b-Li 3 PS 4 ) at room temperature. Jointtime correlation analysis and AIMD simulations show that [PS 4 ]/[SiS 4 ] anion rotational dynamics are coupled to and greatly enhance cation diffusion by widening the bottleneck for Li + -ion transport.

An in situ variable-temperature neutron diffraction study of Li3PS4 reveals the structure and Li-ion diffusion pathways (via MEM and BVEL calculations) of the high temperature fast-ion conductor, α-Li3PS4, (Ea = 0.22 eV), and compares them to those of other polymorphs and the Si-substituted phase.