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Solid electrolytes (SEs) have gained increased attention for their promise to enable higher volumetric energy density and enhanced safety required for future battery systems. SEs are not only a key constituent in all-solid-state batteries, but also important "protectors" of Li metal anodes in next-generation battery configurations, such as Li–air, Li–S, and redox flow batteries. The impedance at interfaces associated with SEs, e.g., internal grain/phase boundaries and their interfacial stability with electrodes, represents two key factors limiting the performance of SEs, yet analyzing these interfaces experimentally at the nano/atomic scale is generally challenging. A mechanistic understanding of the possible instability at interfaces and propagation of interfacial resistance will pave the way to the design of high-performance SE-based batteries. In this review, we briefly introduce the fundamentals of SEs and challenges associated with their interfaces. Next, we discuss experimental techniques that allow for atomic-to-microscale understanding of ion transport and stability in SEs and at their interfaces, specifically highlighting the applications of state-of-the-art and emerging ex situ and in situ transmission electron microscopy (TEM) and scanning TEM (STEM). Representative examples from the current literature that exemplify recent fundamental insights gained from these S/TEM techniques are highlighted. Applicable strategies to improve ion conduction and interfaces in SE-based batteries are also discussed. This review concludes by highlighting opportunities for future research that will significantly promote the fundamental understanding of SEs, specifically further developments in S/TEM techniques that will bring new insights into the design of high-performance interfaces for future electrical energy storage. [ABSTRACT FROM AUTHOR]

Abstract: Solid electrolytes represent a critical component in future batteries that provide higher energy and power densities than the current lithium‐ion batteries. The potential of using ultrathin films is among the best merits of solid electrolytes for considerably reducing the weight and volume of each battery unit, thereby significantly enhancing the energy density. However, it is challenging to fabricate ultrathin membranes of solid electrolytes using the conventional techniques. Here, a new strategy is reported for fabricating sub‐micrometer‐thick membranes of β‐Li3PS4 solid electrolytes via tiled assembly of shape‐controlled, nanoscale building blocks. This strategy relies on facile, low‐cost, solution‐based chemistry to create membranes with tunable thicknesses. The ultrathin membranes of β‐Li3PS4 show desirable ionic conductivity and necessary compatibility with metallic lithium anodes. The results of this study also highlight a viable strategy for creating ultrathin, dense solid electrolytes with high ionic conductivities for the next‐generation energy storage and conversion systems. [ABSTRACT FROM AUTHOR]

Li-ion-conducting solid electrolytes can simultaneously overcome two grand challenges for Li-ion batteries: the severe safety concerns that limit the large-scale application and the poor electrolyte stability that forbids the use of high-voltage cathodes. Nevertheless, the ionic conductivity of solid electrolytes is typically low, compromising the battery performances. Precisely determining the ionic transport mechanism(s) is a prerequisite for the rational design of highly conductive solid electrolytes. For decades, the research on this subject has primarily focused on the atomic and microscopic scales, where the main features of interest are unit cells and microstructures, respectively. Here, it is shown that the largely overlooked mesoscopic scale lying between these extremes could be the key to fast ionic conduction. In a prototype system, (Li0.33La0.56)TiO3, a mesoscopic framework is revealed for the first time by state-of-the-art scanning transmission electron microscopy. Corroborated by theoretical calculations and impedance measurements, it is demonstrated that such a unique configuration maximizes the number of percolation directions and thus most effectively improves the ionic conductivity. This discovery reconciles the long-standing structure-property inconsistency in (Li0.33La0.56)TiO3 and also identifies mesoscopic ordering as a promising general strategy for optimizing Li+ conduction. [ABSTRACT FROM AUTHOR]

A solid‐state high‐voltage (5 V) lithium battery is demonstrated to deliver a cycle life of 10 000 with 90% capacity retention. The solid electrolyte enables the use of high‐voltage cathodes and Li anodes with minimum side reactions, leading to a high Coulombic efficiency of 99.98+%. [ABSTRACT FROM AUTHOR]

Batteries with an aqueous catholyte and a Li metal anode have attracted interest owing to their exceptional energy density and high charge/discharge rate. The long-term operation of such batteries requires that the solid electrolyte separator between the anode and aqueous solutions must be compatible with Li and stable over a wide pH range. Unfortunately, no such compound has yet been reported. In this study, an excellent stability in neutral and strongly basic solutions was observed when using the cubic Li7La3Zr2O12 garnet as a Li-stable solid electrolyte. The material underwent a Li+/H+ exchange in aqueous solutions. Nevertheless, its structure remained unchanged even under a high exchange rate of 63.6 %. When treated with a 2 M LiOH solution, the Li+/H+ exchange was reversed without any structural change. These observations suggest that cubic Li7La3Zr2O12 is a promising candidate for the separator in aqueous lithium batteries. [ABSTRACT FROM AUTHOR]

High‐voltage (5 volt) lithium‐ion chemistry is realized with Lipon, a glass solid electrolyte. In article number 1401408, Juchuan Li, Nancy J. Dudney, and co‐workers describe the battery, which consists of a LiNi0.5Mn1.5O4 spinel cathode and a lithium metal anode. This solid‐state battery delivers a high coulombic efficiency of >99.98% and stable cycling of >90% retention for 10 000 cycles. [ABSTRACT FROM AUTHOR]

We report novel calcium-substituted perovskite-type solid state electrolyte with nominal composition Li 0.344 Sr 0.433 Ca 0.02 Ta 3/4 Hf 1/4 O 3 , which we compare with Li 3/8 Sr 7/16 Ta 3/4 Hf 1/4 O 3. The compounds were synthesized via solid-state reaction and studied by X-ray and neutron powder diffraction and electrochemical impedance spectroscopy. Neutron powder diffraction allowed the Li position in the structure to be accurately determined. Calcium-substituted phase showed higher Li-ion conductivity than the analogous calcium-free phase obtained with our synthesis method. High total Li-ion conductivities of 3.6 ± 1.0 × 10−4 S cm−1 (E a = 431 meV) at 30 °C were reached for calcium-substituted phase, and both bulk and grain-boundary conductivities increased compared to that of the calcium-free phase. The same experiment was conducted on Li 0.344 Sr 0.433 Ca 0.02 Ta 3/4 Zr 1/4 O 3 and led to the same conclusion compared to Li 3/8 Sr 7/16 Ta 3/4 Zr 1/4 O 3. Elemental analysis by energy-dispersive X-ray (EDX) of Li 0.344 Sr 0.433 Ca 0.02 Ta 3/4 Hf 1/4 O 3 showed the formation of an intermediary phase at grain boundaries, which contained essentially strontium, calcium, and oxygen. To better understand the increased bulk conductivity, neutron diffraction was performed on Li 0.344 Sr 0.433 Ca 0.02 Ta 3/4 Hf 1/4 O 3. The results demonstrate the importance of understanding and controlling the grain boundary composition, as much as the bulk composition, to improve the total ionic conductivity of solid electrolytes. For table of Contents Only: Enhanced conductivities with calcium-substituted Li 3/8 Sr 7/16 Ta 3/4 Hf 1/4 O 3 perovskite. Thorough structural characterization reveals intermediary phase at grain boundaries. [Display omitted] • A new calcium-substituted perovskite-type electrolyte has been synthetized. • Li-ion conductivity is two times higher than the analogous calcium-free phase. • The Li-ion conductivity of both grain and grain boundary is increased. • Neutron powder diffraction was used to determine the Li positions in the structure. • An intermediary phase at grain boundaries containing calcium is revealed. [ABSTRACT FROM AUTHOR]