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 slurry-processing, 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. 

Emerging Halide Superionic Conductors for All-Solid-State Batteries: Design, Synthesis, and Practical Applications

Hindered urea bonds are introduced as self-healing units in a polymer electrolyte for Li-metal batteries. Differently from standard commercial separators, the poly(urea-urethane) system works for hundreds of cycles after several damage/healing steps.

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Self-healable dynamic poly(urea-urethane) gel electrolyte for lithium batteries

The development of high-performance inorganic solid electrolytes is central to achieving high-energy- density solid-state batteries. Whereas these solid-state materials are often prepared via classic solid-state syntheses, recent efforts in the community have shown that mechanochemical reactions, solution syntheses, microwave syntheses, and various post-synthetic heat treatment routines can drastically affect the structure and microstructure, and with it, the transport properties of the materials. On the one hand, these are important considerations for the upscaling of a materials processing route for industrial applications and industrial production. On the other hand, it shows that the influence of the different syntheses on the materials' properties is neither well understood fundamentally nor broadly internalized well. Here we aim to review the recent efforts on understanding the influence of the synthetic procedure on the synthesis – (micro)structure – transport correlations in superionic conductors. Our aim is to provide the field of solid-state research a direction for future efforts to better understand current materials properties based on synthetic routes, rather than having an overly simplistic idea of any given composition having an intrinsic conductivity. We hope this review will shed light on the underestimated influence of synthesis on the transport properties of solid electrolytes toward the design of syntheses of future solid electrolytes and help guide industrial efforts of known materials.

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On the underestimated influence of synthetic conditions in solid ionic conductors.

Nonflammable quasi-solid electrolyte for energy-dense and long-cycling lithium metal batteries with high-voltage Ni-rich layered cathodes

All-solid-state batteries (ASSBs) have gained extensive attention due to their improved safety and high specific energy density compared with conventional liquid lithium-ion batteries. As the key component of ASSBs, several kinds of solid electrolytes have been developed to meet the complicated requirements. Among such solid electrolytes, sulfide electrolytes are considered to be the most promising candidates because of their high ionic conductivity and suitable mechanical properties. However, there are still several unresolved obstacles restricting the development of sulfide-based ASSBs, such as limited ionic conductivity and intrinsic and interfacial instability. As for these issues, herein, recent research advances are reviewed from two typical approaches: element doping and interface modification. The experiment details and gained achievements are introduced. Furthermore, several modalities of sulfide electrolyte layers oriented towards commercialization of ASSBs and their merits and demerits are discussed.

Recent advances in sulfide electrolytes toward high specific energy solid-state lithium batteries

Polymer electrolytes and interfaces in solid-state lithium metal batteries

Dense Sphene-type Solid Electrolyte Through Rapid Sintering for Solid-state Lithium Metal Battery

The invention discloses a method for preparing garnet type solid electrolyte by regulating and controlling lithium vacancy content, and belongs to the field of solid ion materials. The structural expression of the garnet type solid electrolyte is Li7-zLa3-yAyZr2-xBxO12, the La site is partially substituted by using an element A, the Zr site is partially substituted by using an element B, and the lithium vacancy content z is regulated and controlled between 0-1 by changing the numerical values of x and y. According to the preparation method, the phase forming temperature of the cubic phase garnet type solid electrolyte and the densification temperature of the ceramic sheet body can be remarkably reduced, and the obtained garnet type solid electrolyte has relatively high density and ionic conductivity and also has good electrochemical stability on a metal lithium negative electrode. The preparation method is simple, low in cost and easy for industrial production, and the obtained garnettype solid electrolyte can be applied to all-solid-state lithium ion batteries, lithium air batteries, other energy storage devices and the like.

Lingqiao Wu

Papers

Polymer electrolytes and interfaces in solid-state lithium metal batteries

Dense Sphene-type Solid Electrolyte Through Rapid Sintering for Solid-state Lithium Metal Battery

Method for preparing garnet type solid electrolyte by regulating and controlling lithium vacancy content